Draft version October 30, 2018Preprint typeset using LATEX style emulateapj v. 12/16/11

MID-INFRARED PROPERTIES OF NEARBY LUMINOUS INFRARED GALAXIES I: SPITZER IRS SPECTRAFOR THE GOALS SAMPLE

S. Stierwalt1,2, L. Armus1, J.A. Surace1, H. Inami1,3, A.O. Petric1,4, T. Diaz-Santos1, S. Haan1,5, V.Charmandaris6,7, J. Howell1, D.C. Kim8, J. Marshall1, J.M. Mazzarella9, H.W.W. Spoon10, S. Veilleux11, A.Evans2,8, D. B. Sanders12, P. Appleton13, G. Bothun14, C.R. Bridge4, B. Chan9, D. Frayer15, K. Iwasawa16, L.J.Kewley12, S. Lord9, B.F. Madore17, J.E. Melbourne4, E.J. Murphy17, J.A. Rich12, B. Schulz13, E. Sturm18, V.

U12, T. Vavilkin19, K. Xu9

Draft version October 30, 2018

ABSTRACT

The Great Observatories All-Sky LIRG Survey (GOALS) is a comprehensive, multiwavelength studyof luminous infrared galaxies (LIRGs) in the local universe. Here we present low resolution SpitzerIRS spectra covering 5-38µm and provide a basic analysis of the mid-IR spectral properties observedfor nearby LIRGs. In a companion paper, we discuss detailed fits to the spectra and compare theLIRGs to other classes of galaxies. The GOALS sample of 244 nuclei in 180 luminous (1011 ≤LIR/L� < 1012) and 22 ultraluminous (LIR/L� ≥ 1012) IR galaxies represents a complete subsetof the IRAS Revised Bright Galaxy Sample and covers a range of merger stages, morphologies andspectral types. The majority (>60%) of the GOALS LIRGs have high 6.2µm PAH equivalent widths(EQW6.2µm > 0.4µm) and low levels of silicate absorption (s9.7µm > -1.0). There is a general trendamong the U/LIRGs for both silicate depth and mid-infrared (MIR) slope to increase with increasingLIR. U/LIRGs in the late to final stages of a merger also have, on average, steeper MIR slopes andhigher levels of dust obscuration. Together, these trends suggest that as gas & dust is funneled towardsthe center of a coalescing merger, the nuclei become more compact and more obscured. As a result,the dust temperature increases leading also to a steeper MIR slope. The sources that depart fromthese correlations have very low PAH equivalent width (EQW6.2µm < 0.1µm) consistent with theiremission being dominated by an AGN in the MIR. These extremely low PAH equivalent width sourcesseparate into two distinct types: relatively unobscured sources with a very hot dust component (andthus very shallow MIR slopes) and heavily dust obscured nuclei with a steep temperature gradient.The most heavily dust obscured sources are also the most compact in their MIR emission, suggestingthat the obscuring (cool) dust is associated with the outer regions of the starburst and not simply ameasure of the dust along the line of sight through a large, dusty disk. A marked decline is seen forthe fraction of high EQW (star formation dominated) sources as the merger progresses. The decline isaccompanied by an increase in the fraction of composite sources while the fraction of sources where anAGN dominates the MIR emission remains low. When compared to the MIR spectra of submillimetergalaxies (SMGs) at z∼2, both the average GOALS LIRG and ULIRG spectra are more absorbed at9.7µm and the average GOALS LIRG has more PAH emission. However, when the AGN contributionsto both the local GOALS LIRGs and the high-z SMGs are removed, the average local starburstingLIRG closely resembles the starburst-dominated SMGs.

1 Spitzer Science Center, California Institute of Technology,1200 E. California Blvd., Pasadena, CA 91125. e-mail: sabri-nas@virginia.edu

2 Department of Astronomy, University of Virginia, P.O. Box400325, Charlottesville, VA 22904.

3 National Optical Astronomy Observatory, 950 N. CherryAve, Tucson, AZ 85719.

4 Department of Astronomy, California Institute of Technol-ogy, 1200 E. California Blvd., Pasadena, CA 91125.

5 CSIRO Astronomy & Space Science, Marsfield NSW 2122,Australia.

6 Department of Physics and ITCP, University of Crete, GR-71003 Heraklion, Greece.

7 IESL/Foundation for Research and Technology - Hellas, GR-71110, Heraklion, Greece and Chercheur Associe, Observatoirede Paris, F-75014, Paris, France.

8 National Radio Astronomy Observatory, 520 EdgemontRoad, Charlottesville, VA 22903.

9 Infrared Processing & Analysis Center, MS 100-22, Califor-nia Institute of Technology, Pasadena, CA 91125.

10 Department of Astronomy, Cornell University, Ithaca, NY,14853.

11 Astronomy Department, University of Maryland, CollegePark, MD 20742.

12 Institute for Astronomy, University of Hawaii, 2680 Wood-lawn Drive, Honolulu, HI 96825.

13 NASA Herschel Science Center, 770 S. Wilson Ave.,Pasadena, CA 91125.

14 Physics Department, University of Oregon, Eugene, OR97402.

15 National Radio Astronomy Observatory, P.O. Box 2, GreenBank, WV 24944.

16 INAF-Observatorio Astronomico di Bologna, Via Ranzani1, Bologna, Italy.

17 The Observatories, Carnegie Institute of Washington, 813Santa Barbara Street, Pasadena, CA 91101.

18 MPE, Postfach 1312, 85741 Garching Germany.19 Department of Physics and Astronomy, SUNY Stony Brook,

Stony Brook, NY, 11794.

arX

iv:1

302.

4477

v1 [

astr

o-ph

.CO

] 1

8 Fe

b 20

13

2 Stierwalt et al.

1. INTRODUCTION

A principal achievement of the Infrared AstronomicalSatellite (IRAS) was the discovery of a large popula-tion of galaxies whose bolometric luminosities were dom-inated by emission in the infrared. At the highest lumi-nosities, local ultraluminous infrared galaxies (ULIRGs;LIR ≥ 1012L�) have been heavily studied (Armus et al.2007; Sanders et al. 1988; Murphy et al. 1996; Spoonet al. 2006; Desai et al. 2007; Rigopoulou et al. 1999;Genzel et al. 1998), and a clear formation picture hasbeen pieced together to explain their extreme emissionin the infrared: more than 90% of local ULIRGs are theproducts of major mergers between molecular gas-richgalaxies. The large amounts of gas that are funneledinto the centers of these mergers lead to intense star for-mation, the feeding of a central AGN, extremely compactreservoirs of molecular gas, and infrared luminosities onthe order of ten times their optical luminosities.

While ULIRGs constitute only 3% of the IRAS RevisedBright Galaxy Sample (RBGS; Sanders et al. 2003), atjust slightly lower luminosities, luminous infrared galax-ies (LIRGs; 1011M� ≤ LIR < 1012M�) make up almost1/3 of the IR sources and have formation histories thatare far less straightforward. In the local universe, thereis evidence that galaxy-galaxy interactions and mergersdrive the large IR luminosities in some LIRGs (Sanders& Mirabel 1996) and many high-z submillimeter galaxies(SMGs) show hints of disturbed optical and radio mor-phologies (Blain et al. 2002; Dasyra et al. 2008). How-ever, at least 20% and as many as 40% of local LIRGsmay have no history of major tidal interactions (How-ell et al., in prep). LIRGs are also represented acrossthe full range of merger stages, unlike ULIRGs which arealmost always at the very end stages of coalescing.

Although LIRGs are relatively rare in the local uni-verse, their comoving number density increases by morethan 100 times from the current epoch to z∼1, (Le Floc’het al. 2005; Magnelli et al. 2009) until LIRGs dominatethe total IR energy density at redshifts of z∼1-2 whenstar formation in the universe was at its peak (Caputiet al. 2007). Piecing together the formation mechanismsand subsequent evolution of these LIRG systems is thusvital to understanding the processes governing star for-mation and black hole accretion, the main sources ofemitting power in the IR.

The Great Observatories All-sky LIRG Survey(GOALS; Armus et al. 2009) represents a complete sub-set of the RBGS comprising 180 LIRGs and 22 ULIRGsand aims to provide a multiwavelength understanding ofthe formation and evolution of local LIRGs as a class ofgalaxy. As part of the Spitzer Legacy survey, a completeset of IR imaging (Infrared Array Camera (IRAC) at3.6, 4.5, 5, and 8µm, and Multiband Imaging Photome-ter (MIPS) at 24, 70, and 160µm) and IR spectroscopyat both high and low resolution (Infrared Spectrograph(IRS) from 5-38µm) is available for the entire sample. Inaddition, imaging in the near-IR/optical (Hubble SpaceTelescope NICMOS and ACS; Haan et al. 2011, Kim etal., in prep), the UV (Galaxy Evolution Explorer near-and far-UV; Howell et al. 2010), and the X-Ray (Chan-dra; Iwasawa et al. 2011) are available for large subsetsof the sample.

In this paper, we present the mid-infrared (MIR) spec-

tra for 244 galaxy nuclei in the 202 nearby GOALSU/LIRG systems taken with the low resolution moduleon the Spitzer Infrared Spectrograph (IRS; Houck et al.2004). The MIR properties derived directly from sucha large, complete sample of LIRG spectra will allow usto place these intermediate-luminosity systems into thecontext of both the extensive previous local ULIRG stud-ies as well as those for lower luminosity, star-forming orstarbursting systems (Brandl et al. 2006; Smith et al.2007b; O’Dowd et al. 2009; Wu et al. 2010).

Full spectral decompositions, including fits to the gasand dust features as well as the SEDs covered by the IRSdata, for the entire sample along with the comparisonof MIR galaxy properties to those at other wavelengthswill be presented in Stierwalt et al. (2013b). The analy-sis presented here focuses on properties derived directlyfrom the MIR spectra. In Section 2, we present the lowresolution MIR spectra observed with the Spitzer IRSShort-Low and Long-Low modules and describe our datareduction methods. In Section 3 we give the distribu-tions of the MIR properties and investigate correlationswith LIR and compactness. In Section 4, we follow eachMIR property through the merging process, and we placeour results into a high redshift context through compar-isons to MIR spectra of submillimeter galaxies at z∼2in Section 5. Finally, our summary and conclusions arepresented in Section 6.

2. OBSERVATIONS & DATA REDUCTION

2.1. The Sample

The GOALS sample consists of 244 galaxy nuclei in180 luminous and 22 ultraluminous nearby IR galaxies.New spectra were obtained using the staring mode for theIRS Short-Low (SL: 5.5-14.5µm) and Long-Low (LL: 14-38µm) modules for 157 galaxies (PID 30323; PI L. Ar-mus). Integration times were determined from nuclearflux densities measured from IRAC and MIPS imagesand range from 45-120 seconds in SL and 30-120 sec-onds in LL. Secondary nuclei were targeted when theMIPS 24µm flux ratio of primary to secondary was ≤5. Archival spectroscopic observations were used for theremaining 45 systems and borrowed most heavily fromstaring program PIDs 105, 3247, & 20549 and mappingprogram PIDs 73, 3269, & 30577.

All 202 systems are nearby but cover a range of dis-tances (15 Mpc < D < 400 Mpc) and so the resultingprojected IRS slit size varies from source to source. Atthe median galaxy distance of 100 Mpc, the nuclear spec-trum covers the central 1.8 kpc in SL and the central 5.2kpc in LL.

2.2. Data Reduction

Staring mode spectroscopic data were reduced usingthe S17 and S18.7 IRS pipelines from the Spitzer ScienceCenter20. For most sources, off-source nods were usedto perform background sky subtraction. In the cases ofmore extended objects, dedicated background pointingswere used to determine the sky surface brightness. Onedimensional spectra were extracted using the standardextraction aperture and point source calibration modesin SPICE21 which employs a tapered extraction aperture

20 http://ssc.spitzer.caltech.edu/irs/features.html21 http://ssc.spitzer.caltech.edu/postbcd/doc/spice.pdf

MIR Properties of Nearby LIRGs 3

that averages roughly to a size of 10.′′6× 36.′′6 in LL and3.′′7× 9.′′5 in SL. After masking bad pixels, multiple nodswere averaged to produce the final spectrum.

Of the archival data, 27 spectra were taken in staringmode and were reduced as described above. For the re-maining 18 systems, spectra were extracted from low res-olution mapping mode data using CUBISM (Smith et al.2007a). Two-dimensional BCDs were assembled, obvi-ous bad pixels were removed and nuclear spectra wereextracted. In two cases (CGCG011-076 and IC1623B),smaller apertures were necessary to avoid other sourcesin the Long-Low maps, but for most sources 2×5 pixelextraction apertures centered on the galaxy’s nucleuswere used to resemble as closely as possible the resultsthat would have been achieved with staring mode ob-servations. However, since the tapered aperture used bySPICE cannot be completely reproduced by the squareapertures in CUBISM, a further mapping-to-staring-mode correction was applied to all spectra derived fromlow resolution archival maps. The correction, a mul-tiplicative factor that is a function of wavelength, wasderived from NGC6240, a star-forming merger remnanttypical of the GOALS sample for which both staring andmapping data were obtained. The correction functionvaries from 1.3 to 2.7 over SL wavelengths and from 1.7to 2.3 over LL wavelengths.

The IRAC 8µm (Channel 4) images for six exam-ple GOALS galaxy nuclei are shown in Figure 1 withthe SL and LL extraction aperture projections overlaid(in the case of staring mode data) or with the CU-BISM extraction windows overlaid (in the case of map-ping mode data). The low resolution IRS spectrum foreach source is also presented along with each MIR image.Spectra for the remainder of the galaxy nuclei, orderedby right ascension, are available as online material andcan also be found at http://goals.ipac.caltech.edu/. Forfive galaxies (IIIZw035, IRASF03359+1523, MCG+08-18-013, IRASF17132+5313, and MCG-01-60-022), thearchival SL staring mode observations were not cen-tered on the galaxy nucleus, so the SL slit overlaysare not shown and the extracted spectra were not usedin our analysis. Complete IRS observations were notavailable for an additional 6 galaxies (no LL spec-tra: NGC2388, NGC4922, and VV705; no SL spectra:IRASF08339+6517; no IRS data: ESO550-IG025 andIC4518). One galaxy (NGC1068; Howell et al. 2007) sat-urates the spectrograph and so is also not shown.

2.3. Scale Factors

For each spectrum a break occurs between the SL andLL modules near 14µm due to the larger LL slit, whichcovers nine times the area covered by the SL slit. Thescale factors required to match the SL flux to the LL fluxare not applied to the spectra in Figures 1 and A1 but arecalculated from the overlap in the SL1 and LL2 modulesand presented in Table 1. Scale factors are not given forany source missing either SL or LL data. For a small mi-nority of cases (CGCG448-020, ESO077-IG014, ESO173-G015, ESO255-IG007, ESO343-IG013, ESO440-IG058(northern nuclei only), IRAS03582+6012, IRASF06076-2139, NGC5653, NGC6090, NGC3690 (western nucleionly), and NGC5256), the scale factor is not given be-cause the placement of the LL slit covered multiple nucleiwhile the smaller SL slit covered only one.

The median scale factors are 1.22 and 1.70 for the star-ing and mapping mode data respectively. The larger me-dian scale factor for mapping data most likely reflects aselection bias toward mapping more extended sources.Twelve scale factors are < 1 (i.e. more flux is recov-ered from SL than from LL), but for all twelve, the scalefactors are also >0.9 and thus represent normal statisti-cal scatter for sources with scale factors near unity. Noclear correlation is observed between the scale factorsand galaxy distance, but at distances > 300 Mpc, a cut-off that includes 6 sources, the scale factors are all <1.2. Similarly, at distances closer than 30 Mpc, there arethree GOALS sources that all have scale factors > 1.6.

The scale factors are applied as a uniform multiplica-tive factor across the entirety of the SL spectra and thusboost equally the PAH fluxes, the continuum, and theabsorption features. Since calculations of the equivalentwidth of the 6.2µm PAH and the depth of the silicatefeature at 9.7µm (EQW6.2µm and s9.7µm; see next sec-tion) both use measurements of feature flux relative tothe continuum, neither are affected by the scaling of theSL spectrum at these low redshifts. The MIR slopes(Fν [30µm]/Fν [15µm]) are also unaffected as they onlyrely on data from the (unscaled) LL portion of the spec-trum.

2.4. s9.7µm, MIR Slope, & EQW6.2µm

Silicate depths at 9.7µm (s9.7µm) were measured di-rectly from the MIR spectra via: sλ = log(fλ/Cλ) wherefλ is the measured flux at the central wavelength of theabsorption feature and Cλ is where the level of the con-tinuum flux would be in the absence of the absorptionfeature, based on an extrapolation to the surroundingcontinuum. Thus, a positive value, sλ > 0, suggestsemission at that wavelength and the deeper the absorp-tion, the lower the s9.7µm value.

The fluxes Fν at 15µm and at 30µm were determinedfrom the average of eight data points surrounding eachwavelength and were then used to calculate the MIRslope. The wavelength regions used fell within ∼14.7-15.4µm for Fν [15µm] and ∼29.5-30.8µm for Fν [30µm].

Equivalent widths for the 6.2µm PAH feature(EQW6.2µm) were measured for each spectrum using themethod outlined in Brandl et al. (2006). Briefly, a splinefit was used to estimate the continuum surrounding the6.2µm PAH feature, and the continuum fit was sub-tracted from the spectrum. In most cases, anchor pointsin determining the continuum were set at 5.15µm <λ <5.31µm, 5.8µm < λ < 5.9µm, 6.5µm < λ < 6.8µm,and 7.1µm< λ < 7.2µm, but each spectrum was visuallyinspected to make sure no features or bad points occurredin these ranges. The PAH flux was then measured usingdirect integration. The 6.2µm feature was selected forthe EQW calculation because, of the five brightest PAHfeatures, it is the least affected by silicate absorption at9.7µm and 18.5µm, and it is not blended with other PAHfeatures. However, in some cases the 6.2µm PAH featurepartially overlaps with the absorption feature due to wa-ter ice at 6.0µm. For those sources found by the spec-tral fitting to have τice >0 (see Stierwalt et al. 2013b),the ice absorption was assumed to affect the underly-ing continuum but not the PAH emission, and the EQWwas calculated accordingly. Four galaxies have only up-per limits placed on their EQW6.2µm: IRAS05223+1908,

4 Stierwalt et al.

0.1

1.0

NG

C0023

0.1

1.0

NG

C0232_E

0.1

1.0

10.0

NG

C0034

0.1

1.0

MC

G+

12−

02−

001

0.1

1.0

Arp256

0.1

1.0

NG

C0317B

0.1

1.0

ES

O350−

IG

038

0.1

1.0

10.0

IC

1623B

10

λ (

µ m

)

0.1

1.0

NG

C0232_W

10

λ (

µ m

)

0.1

1.0

MC

G−

03−

04−

014

Fig.1.—

IRA

C8µ

m(C

han

nel

4)

images

wit

hS

pit

zer

IRS

Sh

ort

-Low

(wh

ite)

an

dL

on

g-L

ow

(bla

ck)

extr

act

ion

ap

ertu

rep

roje

ctio

ns

an

dlo

wre

solu

tion

spec

tra

for

six

GO

AL

Sgala

xy

nu

clei

.E

ach

image

is45′′

by

45′′

.S

pec

tral

flu

xd

ensi

ties

are

giv

enin

[Jy].

Sim

ilar

images

for

the

rem

ain

der

of

the

sam

ple

are

availab

leas

on

lin

em

ate

rial

an

dca

nals

ob

efo

un

dathttp://goals.ipa

c.caltech.edu.

MIR Properties of Nearby LIRGs 5

MCG-03-34-064, NGC4418, and IRAS08572+3015.

2.5. Merger Stages

Merger stages for the entire sample were determinedvia visual inspection of the IRAC 3.6µm (Channel 1) im-ages. Each galaxy was assigned one of the following fivedesignations: ‘N’ for nonmergers (no sign of merger ac-tivity or massive neighbors), ‘a’ for pre-mergers (galaxypairs prior to a first encounter), ‘b’ for early-stage merg-ers (post-first encounter with galaxy disks still symmetricand in tact but with signs of tidal tails), ‘c’ for mid-stage mergers (showing amorphous disks, tidal tails, andother signs of merger activity), or ‘d’ for late-stage merg-ers (two nuclei in a common envelope). Given the res-olution of the IRAC images (∼2′′), late stage mergerscan be easily mistaken for nonmergers in the 3.6-µm im-ages. To alleviate this problem, any galaxies classified asnonmergers or early stage mergers in the IRAC imageswith available higher resolution imaging in the literaturethat clearly showed signs of a late stage major mergerwere changed accordingly. We also use the literature toidentify spectroscopic pairs which resulted in reclassify-ing some nonmergers as pre-mergers.

For a subset of 78 GOALS galaxies (all withlog(LIR/L�) >11.4), we have additional merger classifi-cations based on available HST B, I, and H-band images.The higher resolution of this imaging enables a more de-tailed classification system with more finely tuned mergerstage designations (stages 0 through 6). These mergerstages were already described and presented in Haanet al. (2011), but we reproduce and discuss them here toaid with cross-referencing the two classification schemes.

3. MID-INFRARED PROPERTIES OF NEARBY LIRGS

3.1. LIRG vs ULIRG Distributions

Silicate depths, MIR slopes, PAH equivalent widths,and all associated uncertainties for the GOALS sample,in addition to the SL-to-LL scale factors and mergerstages, are presented in Table 1, and the distributionsof EQW6.2µm,s9.7µm, and MIR slope are shown in Fig-ure 2. The EQW6.2µm and s9.7µm parameters are notgiven for the five sources with off-centered SL spectra,and MIR slopes are not presented for the four sourceswithout available either SL or LL spectra or for the 12sources for which multiple nuclei are observed within theLL slit.

As shown in Figure 2, the majority of LIRGs (63%)are dominated by PAH emission (EQW6.2µm >0.4µm),show little to no silicate absorption (s9.7µm > -1),and have MIR slopes of 4 < Fν [30µm]/Fν [15µm] <10. Only six LIRGs have deep silicate absorptionwith s9.7µm < -1.75 (NGC4418, IRAS03582+6012 E,ESO203-IG001, IRASF10038-3338, IRASF12224-0624,and ESO60-IG016). The remainder of the LIRGs showweak to no silicate absorption with a significant fraction(23%) of LIRGs showing silicates in emission at 9.7µm,including 11% with s9.7µm > 0.15. A few of the LIRGswith s9.7µm > 0 are likely AGN-dominated (EQW6.2µm

< 0.27µm) and thus any absorption at 9.7µm is filledin by an excess of hot dust. However, most are lowerluminosity galaxies with 90% having log(LIR/L�) <11.25. These LIRGs are likely analagous to the unob-scured starburst NGC 7714, a galaxy whose IR emis-

0

20

40

60

80

100

0

20

40

60

80

100

N

−4 −3 −2 −1 0 1Silicate Strength (s9.7µ m)

02468

N

0

20

40

60

80

100

120

0

20

40

60

80

100

120

N

0.5 1.0 1.5log (F

ν[30µm]/F

ν[15µm])

0 4 8

N

0

20

40

60

80

0

20

40

60

80

N

0.0 0.2 0.4 0.6 0.8

6.2µm PAH EQW (µm)

02468

N

Fig. 2.— Distributions of MIR spectral parameters (upper pan-els). Top: silicate strength at 9.7µm, Middle: logarithm of MIRslope, and Bottom: equivalent width of the 6.2µm PAH feature.On average, GOALS ULIRGs (filled red histograms) have deepersilicate absorption depths, steeper MIR slopes, andlower equivalentwidths than the GOALS sample as a whole (white histograms).The lower panel on each plot shows the same GOALS ULIRG dis-tributions with a smaller y-scale. The filled solid black portionof the lowest bin of the EQW6.2µm histogram represents the foursources for which only upper limits are measured.

sion is fueled almost entirely by star formation (Mar-shall et al. 2007). The silicate strengths in the LIRGshave a median of s9.7µm = -0.25 ± 0.58 and rangefrom the heavily obscured NGC4418 at s9.7µm = -3.51± 0.09 to NGC5395, the southern component of theLIRG system Arp84, which shows silicates in emission

6 Stierwalt et al.

(s9.7µm = 0.52 ± 0.07). Five LIRGs are continuum dom-inated and show at most only weak PAH or line fea-tures (EQW6.2µm < 0.04µm and s9.7µm > -0.2; MCG-03-34-064, IRAS05223+1908, NGC1275, NGC7674, andAM0702-601 N).

While the majority of LIRGs favor the high endof the distribution in both EQW6.2µm and s9.7µm,they are found clustered in an intermediate range ofMIR slopes with a median of Fν [30µm]/Fν [15µm] =7.11±4.74. The MIR slopes measured for the LIRGsrange from Fν [30µm]/Fν [15µm] = 2.00 ± 0.01 inIRAS05223+1908 which shows a near power-law spec-trum in the MIR to Fν [30µm]/Fν [15µm] = 35.40 ± 1.38in IRAS10173+0828.

For those LIRGs with measurable 6.2µm PAH EQWs,the values range from EQW6.2µm = 0.005µm ±0.003µm for the northeastern component of the LIRGpair IRAS03582+6012 to EQW6.2µm = 0.78µm ±0.01µm for the most southeastern of the three galax-ies composing the LIRG system IRAS17578-0400. Thedistribution for all of the GOALS LIRGs has a medianof EQW6.2µm = 0.55µm ±0.18µm. The same medianvalue was found for a sample of lower luminosity star-bursting galaxies (Brandl et al. 2006). Tight limits areplaced on the EQW for the three LIRGs and one ULIRGwithout a 6.2µm PAH detection: IRAS05223+1908 at<0.043µm, MCG-03-34-064 at <0.044µm, NGC4418 at<0.066µm, and IRAS08572+3915 at <0.081µm.

The GOALS ULIRGs, represented by the solid red his-tograms in Figure 2, show a clear offset from the LIRGsin their distributions for all three fundamental proper-ties. The ULIRGs have a higher median flux density ra-tio (Fν [30µm]/Fν [15µm] = 12.54±5.41), a lower medianPAH equivalent width (EQW6.2µm = 0.30µm±0.17µm),and deeper median silicate absorption (s9.7µm = -1.05 ±0.85). The GOALS ULIRGs span nearly the full rangeof MIR slopes covered by LIRGs but are not found withEQW6.2µm >0.52µm or with s9.7µm >-0.15. Comparingthe derived values for the 22 ULIRGs in GOALS with thelarger samples from Spoon et al. (2007) (104 ULIRGs)and Veilleux et al. (2009) (QUEST; 50 ULIRGs), we findthat the larger numbers of ULIRGs in these samples re-sult in a larger spread in MIR properties (i.e. 6.2µmPAH EQWs up to 0.8µm and silicate depths up to 0.2;Spoon et al. (2007)). However, the median values areconsistent with ULIRGs having lower EQW6.2µm, deepers9.7µm, and steeper MIR slope than LIRGs: medianEQW6.2µm = 0.15µm & s9.7µm = -1.47 (Spoon et al.2007) and median Fν [30µm]/Fν [15µm] = 11.6 (Veilleuxet al. 2009).

The results of a Kolmogorov-Smirnov (KS) test giveprobabilities of <0.01% that the chance deviations be-tween the distributions of EQW6.2µm, s9.7µm, and MIRslope for GOALS LIRGs vs ULIRGs are expected to belarger assuming they are derived from the same parentsample. In other words, the two samples are significantlydifferent. These probabilities decrease by several ordersof magnitude when the QUEST and Spoon et al. (2007)ULIRGs are included. When the GOALS ULIRGs arecompared to the larger ULIRG samples, the KS testsuggests the chance deviations in their distributions inMIR slope, EQW6.2µm, and s9.7µm are expected to belarger with probabilities of 80%, 40%, and 30%, i.e. it islikely the GOALS ULIRGs and the Spoon et al. (2007) &

Veilleux et al. (2009) samples are derived from the sameparent sample.

3.2. Correlations with LIR

Figure 3 shows the distributions of s9.7µm, MIR slope,and EQW6.2µm as a function of IR luminosity, LIR. TheIR luminosities for all 202 U/LIRG systems were pre-sented in Armus et al. (2009) and derived using the defi-nitions of Sanders & Mirabel (1996)22. In cases of multi-ple nuclei, the total LIR for the system is divided accord-ing to the ratio of the fluxes at 70µm for each nuclei. Ina small number of cases, 70µm images are not availableand so 24µm flux ratios are used instead.

There is a general trend among the U/LIRGs for bothsilicate depth and MIR slope to increase with increas-ing LIR. The sources that depart from these correla-tions at deep levels of silicate obscuration (top panel) orshallow MIR slopes (middle panel) have, in both cases,very low PAH equivalent width (EQW6.2µm < 0.27µm)and are thus likely dominated by emission from an AGN.Increasingly luminous systems become increasingly dustobscured until a turnover occurs at s9.7µm∼ -1.5, abovewhich the buried AGN candidates show no further cor-relation between s9.7µm and LIR. As LIR decreases, theMIR slopes flatten until Fν [30µm]/Fν [15µm]. 0.5, be-low which the relatively unobscured AGN have high LIRgiven their slopes. ULIRGs have an average EQW6.2µm

that is lower than that for LIRGs, but sources with alarge range of luminosities are found at each equivalentwidth (lower panel) so there is not a tight correlationbetween LIR and EQW6.2µm.

3.3. Disentangling s9.7µm, MIR Slope, & EQW6.2µm

To further disentangle the relationship between the3 main MIR parameters, we examine the s9.7µm andEQW6.2µm versus MIR slope parameter spaces in Figure4. The distribution of s9.7µm with MIR slope is color-coded by EQW6.2µm (panel a) while the distributionof EQW6.2µm with MIR slope is color-coded by s9.7µm(panel b).

In the majority of LIRGs, star formation dominatesthe intense MIR emission and the similar conditions inthe photodissociation regions resulting in this (PAH-dominated) emission lead to similar MIR propertiesamong the bulk of the GOALS sample. In Figure 4a,the majority of GOALS galaxies, those with EQW6.2µm

> 0.27µm (green squares and blue stars), show a roughcorrelation between increasing MIR slope and increasingsilicate depth (lower s9.7µm). The starburst galaxies ofBrandl et al. (2006) which span mostly luminosities be-low 1011L� exhibit a similar relationship between τ9.7µmand Fν [30µm]/Fν [15µm] with the same slope. The trendin Figure 4a suggests that the average dust temperaturerises as a consequence of the nuclei becoming more ob-scured and compact. As the dust temperature increases,the rising portion of the blackbody emission spectrumshifts to shorter wavelengths, and warmer sources haveincreasingly more flux at 30µm as seen for the GOALSU/LIRGs with s9.7µm >-1.5.

22 LIR/L� = 4π(DL[m])2(FIR[Wm−2])/3.826 × 1026[Wm−2]and FIR = 1.8 × 10−14(13.48f12µm + 5.16f25µm + 2.58f60µm +f100µm[Wm−2])

MIR Properties of Nearby LIRGs 7

−4 −3 −2 −1 0 1Silicate Strength (s9.7µ m)

10.0

10.5

11.0

11.5

12.0

12.5

13.0lo

g(L

IR/L

sun)

EQW< 0.27µm

0.27µm<EQW< 0.54µm

EQW >0.54µm

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6log (F

ν[30µm]/F

ν[15µm])

10.0

10.5

11.0

11.5

12.0

12.5

13.0

log

(LIR

/Lsu

n)

EQW< 0.27µm

0.27µm<EQW< 0.54µm

EQW >0.54µm

0.0 0.2 0.4 0.6 0.86.2µm PAH EW (µm)

10.0

10.5

11.0

11.5

12.0

12.5

13.0

log(L

IR/L

sun)

EQW< 0.27µm

0.27µm<EQW< 0.54µm

EQW >0.54µm

Fig. 3.— Distribution of MIR spectral parameters with LIRcolor-coded by EQW6.2µm. Top: silicate strength at 9.7µm, Mid-dle: logarithm of MIR slope, and Bottom: equivalent width ofthe 6.2µm PAH feature. There is a loose trend among LIRGs forincreasing silicate depth and MIR slope with increasing LIR. How-ever, LIRGs span nearly the full range of EQW6.2µm at any givenluminosity.

Most of the sources with low PAH equivalent width,however, do not follow these simple trends in MIR prop-erties. In Figure 4a, these low-EQW sources (red cir-cles) are split roughly into two populations: those thatare relatively unobscured with shallow MIR slopes and

those heavily obscured sources (s9.7µm<-1.5) with steepMIR slopes. A similar split is observed in Figure 4b:for EQW6.2µm <0.27µm, the heavily obscured sources(purple circles) are found at steeper MIR slopes whilethe relatively unobscured sources (magenta circles) arefound at the shallowest flux density ratios.

An increasingly significant hot dust component froman AGN leads both to a decrease in EQW6.2µm andto a flatter MIR slope. For the GOALS sources withthe strongest, relatively unobscured AGN (s9.7µm&-0.6;EQW6.2µm.0.05µm), an upper limit to the MIR slopecan be set at Fν [30µm]/Fν [15µm]<4 from both panelsin Figure 4. These galaxies (including IRAS05223+1908and UGC08058) are represented by the red circles in thelower right corner of panel a and the magenta circles inthe lower left corner of panel b. No other sources arefound with flatter MIR slopes. This limit agrees withthat observed for the starbursts of Brandl et al. (2006)and for the QUEST ULIRGs of Veilleux et al. (2009).Relatively unobscured AGN can thus be identified basedon their low MIR flux density ratio alone.

In the most heavily obscured, low EQW galaxies, how-ever, the MIR continuum slopes are steeper due to theburied, hot source. These galaxies (red circles in theleft half of Figure 4a and purple circles in Figure 4b)have steep MIR slopes for the same reason sources withs9.7µm∼-1.5 in Figure 4a have steep MIR slopes: most ofthe warm dust emission is hidden behind a large amountof cooler dust. A comparison to the 5 mJy UnbiasedSpitzer Extragalactic Survey (5MUSES; Wu et al. 2010)highlights the difference between the low and high s9.7µmsources at low EQW6.2µm. The 5MUSES sample is 24-µm selected (indicating the presence of hot dust) butlacks the heavily obscured sources found in GOALS. Thedistributions for the two samples in Figure 4b are roughlythe same (5MUSES is represented by the dashed line al-though there is significant scatter about this line; see Wuet al. (2010)) - both show the lowest EQW6.2µm sourceshave the shallowest MIR slopes - except 5MUSES lacksthe obscured low EQW6.2µm galaxies (purple circles inFigure 4b).

The apparent strength of the 9.7µm silicate feature(i.e. the depth of the absorption feature that does notaccount for any silicate emission, s9.7µm) is shown versusEQW6.2µm in Figure 5 for GOALS LIRGs (open circles)and ULIRGs (red triangles). No galaxies are observedwith both high equivalent widths and large levels of sili-cate absorption. However, at low equivalent widths, twodistinct branches, similar to those seen by Spoon et al.(2007), emerge that clearly distinguish the lower equiva-lent width (EQW6.2µm < 0.1µm) sources with minimalto no silicate absorption (s9.7µm > -0.5) from those dom-inated by silicate absorption (heavily obscured sources;s9.7µm <-1.75). Sources with intermediate levels of sili-cate absorption are not found at low equivalent widths.

As shown in Figure 5, the highly absorbed sources arenot limited to ULIRGs. At values of s9.7µm < -1.75, theGOALS sample includes five ULIRGs (labeled in Fig-ure 5) as well as the dense, compact nascent starburstLIRG NGC4418 (Spoon et al. 2001; Roussel et al. 2003;Evans et al. 2006) and five additional LIRGs that spana large range of LIRG luminosities: IRASF12224-0624(log(LIR/L�) = 11.36), IRAS03582+6012 (log(LIR/L�)= 11.42), IRASF10038-3338 (log(LIR/L�) = 11.78),

8 Stierwalt et al.

−4 −3 −2 −1 0 Silicate Strength (s9.7µ m)

1

10

100F

ν[3

0µ

m]/

Fν[1

5µ

m]

a)

EQW< 0.27µm0.27µm< EQW< 0.54µmEQW >0.54µm

0.0 0.2 0.4 0.6 0.86.2µm PAH EW (µm)

s9.7µm < −1.5

−0.6 < s9.7µm

−1.5 < s9.7µm < −0.6

b)

Fig. 4.— Distribution of MIR slope (Fν [30µm]/Fν [15µm]) versus a) silicate absorption at 9.7µm color-coded by EQW6.2µm and b)EQW6.2µm color-coded by s9.7µm. GOALS sources with EQW6.2µm >0.27µm (green squares + blue stars in panel a, right side of panelb) show a rough correlation between increasing silicate depth and increasing MIR slope (a) and follow the correlation between EQW6.2µmand MIR slope observed in the 24-µm selected 5MUSES sample (dashed line, b; Wu et al. (2010)). At low EQW (EQW6.2µm <0.27µm;red circles in panel a, left side of panel b), relatively unobscured AGN-dominated sources all have MIR slopes below ∼4. However, atthe deepest levels of silicate absorption (left side of panel a, purple circles in panel b), the MIR slope is no longer a clear indicator oftemperature and so the heavily obscured sources do not follow the trend in panel a, and the location of the 15-µm continuum between the9.7µm and 18.5µm absorption features lead to elevated MIR slopes in panel b. Although far less numerous (only 18% of GOALS nucleihave EQW6.2µm < 0.27µm), the lowest equivalent width sources cover a wider range of LIR, MIR slope, and s9.7µm than those sources ofhigher EQW6.2µm that make up the majority of the sample.

0.01 0.10 1.006.2µm PAH EW (µm)

1

0

−1

−2

−3

−4

Sil

icate

Str

en

gth

(s 9

.7µ

m)

IRAS03582+6012

IRAS08572+3915NGC4418

Mrk231

NGC1275

Arp220

LIRG

ULIRG

Fig. 5.— Equivalent width of the 6.2µm PAH versus silicate strength for the LIRGs (open circles) and ULIRGs (red triangles) of theGOALS sample. The majority (>60%) of the LIRGs are found at EQW6.2µm > 0.4µm and s9.7µm > -1.0, while nearly all ULIRGshave EQW6.2µm < 0.5µm and s9.7µm < -0.5. Sources at low EQW are divided into two distinct branches (silicate-dominated versuscontinuum-dominated).

MIR Properties of Nearby LIRGs 9

ESO60-IG016 (log(LIR/L�) = 11.82), and ESO203-IG001 (log(LIR/L�) = 11.86).

3.4. Compactness

The most heavily obscured nuclei among the GOALSgalaxies are also the most compact: they all show little-to-no MIR emission extending outside of the IRS slit.In Figure 6, the silicate strength is plotted against η, aparameter that represents the fraction of the emission at24µm intercepted by the IRS slit:

η = log(FMIPStot [24µm]/F IRSslit [24µm]) (1)

where FMIPStot [24µm] is the total flux of a source as mea-

sured from its MIPS 24µm image (Mazzarella et al.,in prep) and F IRSslit [24µm] is the flux within the IRS slitderived by convolving the MIPS-24µm filter with thelow resolution IRS spectrum. The most obscured sources(s9.7µm < -1.75) all have η ∼ 0 (i.e. all of the flux mea-sured by the larger MIPS field of view at 24µm is alsorecovered within the much smaller IRS slit).

Although distance effects could act to disguise an ex-tended component in comparisons of total versus intra-slit fluxes if all of the obscured sources were the most dis-tant, the median distance for the heavily obscured, lowη nuclei is only 60% larger than the median distance forthe less obscured sources (190 Mpc vs 115 Mpc) suggest-ing distance alone cannot be driving the difference in η.Even more importantly, the heavily obscured, low η tailof the distribution in Figure 6 includes the two closest,obscured LIRGs, NGC4418 at 36.5 Mpc and s9.7µm =-3.51 ± 0.09 and NGC3690 at 50.7 Mpc and s9.7µm =-1.65± 0.02. Both of these LIRGs would have been easilyresolved had they shown any extended MIR emission.Additionally, the existence of galaxies with high η andlow s9.7µm with distances well above 100 Mpc indicatethat extended sources can still be resolved even at largerdistances.

The fraction of resolved emission within the IRS slit isalso much lower for the obscured sources. The fraction ofextended emission (FEE13.2µm) is defined by Dıaz-Santoset al. (2010) as the fraction of emission within the IRSslit originating outside of the unresolved component (i.e.a point source at that distance). For the most obscuredGOALS nuclei, the average 〈FEE13.2µm〉 = 0.07 com-pared to 〈FEE13.2µm〉 = 0.39 for the remaining (weaklyobscured or unobscured) LIRGs. As discussed in detailin Dıaz-Santos et al. (2010), such a dramatic differencein FEE between obscured and unobscured nuclei cannotbe the result of distance effects alone.

Together the low η, the low FEE13.2µm, and their in-clusion of nearby sources suggest the nuclei in these heav-ily obscured sources dominate the 24-µm emission fromtheir parent galaxies, and so the most heavily obscuredLIRGs and ULIRGs also have the most compact MIRcontinuum emission. Given their low EQW6.2µm, if ex-treme levels of obscuration are not simply masking thePAH emission, the higher densities in these nuclei maycreate an environment where PAH dust grains are notpresent or the conditions are not appropriate for excitingthem (i.e. lacking in photodissociation regions). Alter-natively, the low EQW6.2µm may indicate an increase inthe continuum flux at 6µm due to a rise in dust temper-ature. None of the low η, high s9.7µm nuclei are observed

to be [NeV] emitters (Petric et al. 2011), most likely be-cause their large optical depths obscure any line emissionthat would be present at 14.3µm.

−4 −3 −2 −1 0 1Silicate Strength (s9.7µ m)

0.0

0.5

1.0

1.5

η =

lo

g(F

tot[

24

µm

]/F

sli

t[2

4µ

m])

EQW6.2µm < 0.27µm

0.27µm < EQW6.2µm < 0.54µm

EQW6.2µm > 0.54µm

Fig. 6.— Silicate strength versus η, a measure of the total-to-slitflux ratio at 24µm. GOALS LIRGs and ULIRGs are color codedby 6.2µm PAH equivalent width with low equivalent width (AGN-dominated) sources (EQW6.2µm < 0.27µm) represented by redcircles and high equivalent width (starburst-dominated) sources(EQW6.2µm > 0.54µm) represented by blue stars. Intermedi-ate EQW (composite) sources are shown by orange (0.27µm <EQW6.2µm < 0.41µm) and green (0.41µm < EQW6.2µm <0.54µm) squares. Heavily obscures sources have no extended com-ponent to their 24µm emission (η ∼0).

4. TRACING MIR PROPERTIES THROUGH MERGERSTAGE

In Figure 7, silicate strength, MIR slope, and PAHequivalent width are traced through merger stage forGOALS galaxies. To look for subtle differences in MIRproperties throughout the merging process, we focus ononly those sources that have HST classifications (column11 in Table 1). Since this subset contains only six galax-ies with no indication of a merger (stage 0), we includeall of the nonmergers (Stage N) from the IRAC-basedclassifications (column 10 in Table 1) to derive a moresecure median for each spectral property. Although theHST data samples only LIRGs with log(LIR/L�)>11.4,the dense sampling of merger stages made possible bythe deep, high spatial resolution optical and NIR imagesprovides a much finer look at the spectral changes alongthe merger sequence. Mean values for each merger stageclipped at 3σ are shown in red with their associated stan-dard deviations.

As the mergers progress and gas & dust is funneledtowards the center, galaxies become on average moreobscured with steeper MIR slopes. Silicate depths ofs9.7µm. -1 are only reached at merger stages of 3and later. No LIRG systems in merger stage 1 haveFν [30µm]/Fν [15µm]> 1, while the average MIR slope is>1 for the later stages 4-6. These two results agree withseveral studies finding higher LIR at later merger stagessince, as shown in Figure 3, increasing MIR slope andsilicate depth are also linked to higher LIR in LIRGs.As merging galaxies coalesce, the nuclei become more

10 Stierwalt et al.

compact and more obscured, and, as a result, the dusttemperature increases leading to a steeper MIR slope asdiscussed in Section 3.

N 1 2 3 4 5+6Merger Stage

−3

−2

−1

0

1

Sil

icat

e S

tren

gth

−3

−2

−1

0

1

Sil

icat

e S

tren

gth

N 1 2 3 4 5+6Merger Stage

0.2

0.4

0.6

0.8

1.0

1.2

1.4

log(F

30µ

m/F

15µ

m)

0.2

0.4

0.6

0.8

1.0

1.2

1.4

log(F

30µ

m/F

15µ

m)

N 1 2 3 4 5+6Merger Stage

0.0

0.2

0.4

0.6

0.8

6.2

µm

PA

H E

QW

[µ

m]

0.0

0.2

0.4

0.6

0.8

6.2

µm

PA

H E

QW

[µ

m]

Fig. 7.— MIR properties of GOALS galaxies traced throughmerger stage. Top: silicate strength (s9.7µm), Middle: MIR slope(log(Fν [30µm]/Fν [15µm]), and Bottom: EQW6.2µm. Mergers(Stages 1-6) are represented by the 78 GOALS galaxies for whichhigh resolution HST imaging is available (Haan et al. 2011, ; seeColumn (11) in Table 1). Nonmergers (StageN) are classified usingIRAC 3.6µm images and the literature (see Section 2.5 for details).Mean values for each merger stage clipped at 3σ are shown in redwith their associated standard deviations.

There is some indication that lower PAH equiva-lent widths are favored at later merger stages but thisis mostly dominated by the fact that only starburst-dominated galaxies (EQW6.2µm>0.54µm) are observedin stage 1. (The one exception is southern componentof the LIRG system AM0702-601.) For all other mergerstages, the full range of EQW6.2µm is observed.

A clearer link between PAH equivalent width andmerger stage is observed when galaxies are binned bytheir EQW6.2µm(and thus the likely AGN contributionto the MIR). In Figure 8 the LIRGs are divided intothree EQW6.2µm bins indicating AGN dominated sources(red circles), composite sources (green squares), and star-bursts (blue stars). Starbursts clearly play a dominantrole at early merger stages as was also shown by Pet-ric et al. (2011) and Haan et al. (2011), but the de-cline in the starburst contribution is not balanced by anincrease in AGN-dominated sources. The contributionfrom LIRGs with an AGN dominating in the MIR staysat a roughly constant fraction throughout the mergerprocess, but composite sources (i.e. the weaker AGNthat are not yet entirely dominant over star formation inthe MIR) show a marked increase at later merger stages.This may indicate that the timescales for the AGN tobegin to dominate the MIR emission are longer than themerger timescale (a few hundred million years). In bothFigures 7 and 8, the nonmerging LIRGs cover nearly thefull range of every MIR property investigated.

N 1 2 3 4 5+6Merger Stage

0.0

0.2

0.4

0.6

0.8

1.0

Nu

mb

er F

ract

ion

N 1 2 3 4 5+6

0.0

0.2

0.4

0.6

0.8

1.0EQW < 0.27µm0.27µm < EQW < 0.54µmEQW > 0.54µm

Fig. 8.— Overall AGN fraction (as determined by EQW of the6.2µm PAH) traced through merger stage for the GOALS sample.Merger stages are classified as described in Figure 7. A markeddecline is seen for the fraction of high EQW (star formation domi-nated; blue stars) sources as the merger progresses. This decline isaccompanied by an increased contribution not from the strongestAGN (red circles) which remain low but from the composite sources(i.e. weaker AGN that are not yet entirely dominant over star for-mation in the MIR; green squares).

5. COMPARISONS TO SUBMILLIMETER GALAXIES

The dust-enshrouded, strongly starbursting nature ofLIRGs makes them obvious candidates for possible lo-cal analogs to the dusty submillimeter galaxies (SMGs)that make a significant contribution to the global starformation rate density at higher redshifts. In Figure 9,we compare different subsets of the GOALS MIR spectrawith the average SMG spectra from Menendez-Delmestreet al. (2009) (hereafter M09) derived from a sample of 24SMGs at redshifts of 0.65 < z <3.2. All average spec-tra for both the LIRGs and the SMGs are normalized at6.8µm. In agreement with the conclusions of Desai et al.(2007) and M09, the average local ULIRG spectrum (redline in Figure 9a) is more absorbed than the average SMGspectrum (black line) but has weaker PAH emission. Al-though GOALS LIRGs are less obscured than ULIRGson average, the average LIRG spectrum (dashed line)

MIR Properties of Nearby LIRGs 11

is still more absorbed than the average SMG while alsoshowing stronger PAH emission at 6.2µm, 7.7µm, and11.3µm. Even when the nuclear emission of galaxies isremoved, the spectrum of the extended component ofLIRGs does not resemble that of the total SMG com-posite (Dıaz-Santos et al. 2011). The average local star-burst (blue line; Brandl et al. 2006) shows a similar levelof silicate absorption but much stronger PAH emissioncompared to the average SMG.

0

2

4

6

8

Fν/F

ν[6

.8µ

m]

(Norm

ali

zed) ULIRGs

Starbursts (Brandl+06)

LIRGsSMGs (M09)

a)

6 8 10 12 14λ (µm)

0.51.01.5

Fν/F

ν[S

MG

]

0

2

4

6

8

Fν/F

ν[6

.8µ

m]

(Norm

ali

zed)

AGN LIRGsStarburst LIRGsStarburst SMG (M09)

b)

6 8 10 12 14λ (µm)

0.51.01.5

Fν/F

ν[S

MG

]

Fig. 9.— Comparison of GOALS average LIRG and ULIRGspectra to average submillimeter galaxy spectra from Menendez-Delmestre et al. (2009): a) the composite SMG spectrum (black)is less obscured than the average ULIRG (red) and the averageLIRG (dashed) but has weaker PAH emission than local starbursts(blue). b) after removing the AGN-dominated systems from boththe average SMG and the average LIRG, the average starburstSMG spectrum (black) is well-represented by the starburst LIRGs(EQW6.2µm >0.54µm; blue) but not the AGN-dominated LIRGs(EQW6.2µm <0.27µm; red) with the exception of a feature at∼10.5µm. All average spectra are normalized at λ = 6.8µm andthe shaded gray area represents the 1-σ standard deviation to theaveraged SMG spectrum. Residuals are shown in the bottom pan-els.

The fraction of MIR emission attributed to AGN over-all for the GOALS LIRGs is only 12% (Petric et al. 2011),and M09 observed a contribution of <32% from AGN tothe total bolometric luminosity in SMGs. However, asseen in Figures 1 and A1, those sources dominated byAGN have MIR spectra that are vastly different from

those with strong PAH emission. The low equivalentwidth sources (i.e. those with MIR emission that is mostlikely AGN-dominated) also show a larger scatter in theirMIR properties, as discussed in Section 3. To reduce pos-sible confusion caused by this AGN contribution, we alsocompare the average SMG spectrum for only those SMGswithout AGN indicators in the MIR (i.e starburst SMGswith EQW7.7µm >1µm & αMIR <0.5; M09) to averageLIRG spectra with and without an AGN contribution inFigure 9b.

The average AGN-dominated LIRG spectrum (LIRGswith EQW6.2µm <0.27µm; red line) clearly does notresemble the average starburst SMG (solid black line).However the average starburst-dominated LIRG spectra(EQW6.2µm >0.54µm; blue line) is a better match to theaverage starburst SMG. All three average spectra agreewithin 15% below 10µm (see the residuals in the lowerpanel).

Between 10-11µm, all three average LIRG spectra inFigure 9b agree closely, but no subset of the GOALSLIRGs or ULIRGs reproduces the emission feature ob-served in the average starburst SMG spectrum near10.5µm. Although the feature is also not detected inthe average (low resolution) local starburst spectrum (seeFigure 9a), both the [SIV] emission line at 10.51µm anda PAH feature at 10.60µm are clearly seen in the aver-age of the high resolution IRS spectra of the same star-burst sample (see Figure 4 of Bernard-Salas et al. 2009).The feature detected in the low resolution SMG spec-tra is likely a blend of these two features (Sturm et al.2000; Bernard-Salas et al. 2009; Smith et al. 2007b),but may be dominated by the PAH feature emissionsince it remains faint and unresolved at low resolution.Bernard-Salas et al. (2009) also detect a third feature at10.75µm that they associate with PAH emission due toits close correlation with the 11.3µm PAH which maycontribute to the emission in the SMGs.

6. SUMMARY & CONCLUSIONS

We presented low resolution IRS spectra for 244 galaxynuclei in the GOALS sample of 180 LIRGs and 22ULIRGs. The GOALS galaxies cover a range of spec-tral types, silicate strengths, and merger stages, and rep-resent a complete subset of the IRAS Revised BrightGalaxy Sample. We investigated the MIR propertiesdirectly measured from the spectra and discovered thefollowing:1) Local LIRGs cover a large range of MIR properties andany single LIRG cannot represent the class as a whole.LIRGs span 0.005µm < EQW6.2µm <0.78µm (withnondetections of the 6.2µm PAH reachingEQW6.2µm <0.043µm), -3.51 < s9.7µm < 0.052(with 23% of LIRGs showing silicate emission), and 2.00< Fν [30µm]/Fν [15µm] < 35.40. However, the majority(63%) of LIRGs have EQW6.2µm > 0.4, s9.7µm > -1.0,and MIR slopes in the range of 4 < Fν [30µm]/Fν [15µm]< 10.2) The GOALS ULIRGs span a narrower range of MIRproperties than those covered by the LIRGs. When com-pared to LIRGs, the ULIRGs (LIR > 1012L�) havea steeper median slope (Fν [30µm]/Fν [15µm] = 12.54for the ULIRGs compared to Fν [30µm]/Fν [15µm] =7.11 for the LIRGs), a lower mean equivalent width(EQW6.2µm = 0.30µm versus EQW6.2µm = 0.55µm),

12 Stierwalt et al.

and deeper average silicate absorption (s9.7µm = -1.05versus s9.7µm = -0.25).3) There is a general trend among the U/LIRGs for bothsilicate depth and MIR slope to increase with increasingLIR. As LIR increases, the temperature may rise as aconsequence of the nuclei becoming more obscured andcompact. As the dust temperature increases, the ris-ing portion of the blackbody emission spectrum shifts toshorter wavelengths, and warmer sources have increas-ingly more flux at 30µm, and thus steeper MIR slopes.The sources that depart from these correlations, in bothcases, have very low PAH equivalent width (EQW6.2µm

< 0.1µm) consistent with their MIR emission being dom-inated by an AGN.4) Although less numerous (only 18% of the sample),LIRGs with the largest contributions from AGN (thosewith EQW6.2µm < 0.27µm) cover a wider range of MIRslopes and silicate strengths than those sources of higherequivalent width that make up the majority of the sam-ple. The sources with extremely low PAH equivalentwidths (EQW6.2µm<0.1µm) separate into two distincttypes: relatively unobscured sources with a very hot dustcomponent (and thus very shallow MIR slopes) and heav-ily dust obscured nuclei with a steep temperature gradi-ent. For the AGN-dominated LIRGs with low apparentobscuration, an upper limit to the MIR slope can be setat Fν [30µm]/Fν [15µm]∼4. The most obscured nuclei,however, have steeper MIR slopes due to most of theirwarm dust emission being hidden behind a large amountof cooler dust.

suggesting 5) The LIRGs most likely harboring buriedAGN (the obscured nuclei with s9.7µm<-1.75) all haveEQW6.2µm <0.2µm and lack any extended componentto their MIR emission at 24µm. Extreme levels of dustobscuration may simply be blocking PAH emission, orthe higher densities in these nuclei may create an environ-ment where PAH dust grains are not present or the con-ditions are not appropriate for exciting them (i.e. lackingin photodissociation regions). Their compact nature sug-gests that their obscuring (cool) dust is associated withthe outer regions of the starburst and not simply a mea-

sure of the dust along the line of sight through a large,dusty disk.6) U/LIRGs in the late to final stages of a merger have,on average, steeper MIR slopes and higher levels of dustobscuration. As merging galaxies coalesce and gas & dustis funneled towards the center, the nuclei become morecompact and more obscured. As a result, the dust tem-perature increases leading also to a steeper MIR slope. Amarked decline is seen for the fraction of high EQW (starformation dominated) sources as the merger progresses.The decline is accompanied by an increase in the fractionof composite sources while the fraction of sources wherean AGN dominates the MIR emission remains low.7) Despite their dusty and starbursty nature, the aver-age nearby LIRG spectrum does not resemble the averagecomposite (starburst + AGN) MIR spectrum from sub-millimeter galaxies at z∼2. Both the average LIRG andULIRG spectra are more absorbed at 9.7µm and the av-erage LIRG has more PAH emission. However, once theAGN contributions are removed from the average LIRGand from the average SMG spectra, the PAH emissionand level of silicate absorption of the average spectrumfor starburst-dominated SMGs (i.e. those without AGNspectral signatures; Menendez-Delmestre et al. 2009) arefit well by the average starburst-dominated local LIRG.

The Spitzer Space Telescope is operated by the JetPropulsion Laboratory, California Institute of Technol-ogy, under NASA contract 1407. This research has madeuse of the NASA/IPAC Extragalactic Database (NED)which is operated by the Jet Propulsion Laboratory,California Institute of Technology, under contract withthe National Aeronautics and Space Administration.This research has made use of the NASA/IPAC InfraredScience Archive, which is operated by the Jet Propul-sion Laboratory, California Institute of Technology,under contract with the National Aeronautics SpaceAdministration. We would like to thank M. Cluver formany helpful discussions and K. Menendez-Delmestrefor sharing her average SMG spectra.

REFERENCES

Armus, L., Charmandaris, V., Bernard-Salas, J., et al. 2007, ApJ,656, 148

Armus, L., Mazzarella, J. M., Evans, A. S., et al. 2009, PASP,121, 559

Bernard-Salas, J., Spoon, H. W. W., Charmandaris, V., et al.2009, ApJS, 184, 230

Blain, A. W., Smail, I., Ivison, R. J., Kneib, J.-P., & Frayer,D. T. 2002, Phys. Rep., 369, 111

Brandl, B. R., Bernard-Salas, J., Spoon, H. W. W., et al. 2006,ApJ, 653, 1129

Caputi, K. I., Lagache, G., Yan, L., et al. 2007, ApJ, 660, 97Dasyra, K. M., Yan, L., Helou, G., et al. 2008, ApJ, 680, 232Desai, V., Armus, L., Spoon, H. W. W., et al. 2007, ApJ, 669, 810Dıaz-Santos, T., Charmandaris, V., Armus, L., et al. 2010, ApJ,

723, 993—. 2011, ApJ, 741, 32Evans, A. S., Solomon, P. M., Tacconi, L. J., Vavilkin, T., &

Downes, D. 2006, AJ, 132, 2398Genzel, R., Lutz, D., Sturm, E., et al. 1998, ApJ, 498, 579Haan, S., Surace, J. A., Armus, L., et al. 2011, AJ, 141, 100Houck, J. R., Roellig, T. L., van Cleve, J., et al. 2004, ApJS, 154,

18Howell, J. H., Mazzarella, J. M., Chan, B. H. P., et al. 2007, AJ,

134, 2086

Howell, J. H., Armus, L., Mazzarella, J. M., et al. 2010, ApJ, 715,572

Iwasawa, K., Sanders, D. B., Teng, S. H., et al. 2011, A&A, 529,A106

Le Floc’h, E., Papovich, C., Dole, H., et al. 2005, ApJ, 632, 169Magnelli, B., Elbaz, D., Chary, R. R., et al. 2009, A&A, 496, 57Marshall, J. A., Herter, T. L., Armus, L., et al. 2007, ApJ, 670,

129Menendez-Delmestre, K., Blain, A. W., Smail, I., et al. 2009,

ApJ, 699, 667Murphy, Jr., T. W., Armus, L., Matthews, K., et al. 1996, AJ,

111, 1025O’Dowd, M. J., Schiminovich, D., Johnson, B. D., et al. 2009,

ApJ, 705, 885Petric, A. O., Armus, L., Howell, J., et al. 2011, ApJ, 730, 28Rigopoulou, D., Spoon, H. W. W., Genzel, R., et al. 1999, AJ,

118, 2625Roussel, H., Helou, G., Beck, R., et al. 2003, ApJ, 593, 733Sanders, D. B., Mazzarella, J. M., Kim, D.-C., Surace, J. A., &

Soifer, B. T. 2003, AJ, 126, 1607Sanders, D. B., & Mirabel, I. F. 1996, ARA&A, 34, 749Sanders, D. B., Soifer, B. T., Elias, J. H., et al. 1988, ApJ, 325, 74Smith, J. D. T., Armus, L., Dale, D. A., et al. 2007a, PASP, 119,

1133

MIR Properties of Nearby LIRGs 13

Smith, J. D. T., Draine, B. T., Dale, D. A., et al. 2007b, ApJ,656, 770

Spoon, H. W. W., Keane, J. V., Tielens, A. G. G. M., Lutz, D., &Moorwood, A. F. M. 2001, A&A, 365, L353

Spoon, H. W. W., Marshall, J. A., Houck, J. R., et al. 2007, ApJ,654, L49

Spoon, H. W. W., Tielens, A. G. G. M., Armus, L., et al. 2006,ApJ, 638, 759

Stierwalt, S., et al. 2013b, ApJ, in prepSturm, E., Lutz, D., Tran, D., et al. 2000, A&A, 358, 481Veilleux, S., Rupke, D. S. N., Kim, D.-C., et al. 2009, ApJS, 182,

628Wu, Y., Helou, G., Armus, L., et al. 2010, ApJ, 723, 895

14 Stierwalt et al.

TABLE

1Mid-IR

SpectralParametersfortheGOALSSample

Sou

rceS

hort-L

ow

RA

/D

EC

(PA

)L

on

g-L

ow

RA

/D

EC

(PA

)6.2µm

EQ

W(σ

)s9.7µm

(σ)

Fν[3

0µm

]/Fν[1

5µm

](σ)

Sca

leM

erger

MS

Nam

e[J

2000]

[ ◦]

[J2000]

[ ◦]

[µm

]F

acto

rS

tage

(HS

T)

NG

C0023

00h

09m

53.4

s+

25d

55m

26.3

s(-3

2.8

)00h

09m

53.4

s+

25d

55m

26.3

s(-1

16.6

)0.5

8(0

.01)

0.1

8(0

.04)

6.8

1(0

.04)

1.4

9b

NG

C0034

00h

11m

06.4

s-1

2d

06m

28.7

s(3

5.3

)∗00h

11m

06.5

s-1

2d

06m

29.2

s(1

17.7

)∗0.4

5(0

.02)

-0.7

9(0

.03)

9.9

4(0

.09)

1.7

0d

5A

rp256

00h

18m

50.9

s-1

0d

22m

36.6

s(-3

6.1

)00h

18m

50.9

s-1

0d

22m

36.6

s(-1

19.8

)0.7

2(0

.01)

-0.2

6(0

.03)

6.7

3(0

.07)

1.2

2b

3E

SO

350-IG

038

00h

36m

52.5

s-3

3d

33m

17.1

s(1

63.1

)00h

36m

52.5

s-3

3d

33m

17.0

s(7

9.4

)0.1

5(0

.004)

-0.3

4(0

.02)

4.7

3(0

.01)

1.1

5c

NG

C0232

W00h

42m

45.8

s-2

3d

33m

40.7

s(-4

4.6

)00h

42m

45.8

s-2

3d

33m

40.7

s(-1

28.3

)0.5

5(0

.01)

-0.3

8(0

.03)

7.3

3(0

.03)

1.2

1b

NG

C0232

E00h

42m

52.8

s-2

3d

32m

27.5

s(-4

4.6

)00h

42m

52.8

s-2

3d

32m

27.5

s(-1

28.3

)0.1

6(0

.005)

-0.2

6(0

.03)

3.6

3(0

.03)

1.1

6b

MC

G+

12-0

2-0

01

00h

54m

03.9

s+

73d

05m

06.0

s(7

1.1

)00h

54m

03.9

s+

73d

05m

05.9

s(-1

2.7

)0.6

5(0

.01)

-0.2

4(0

.02)

7.1

9(0

.04)

1.0

8c

3N

GC

0317B

00h

57m

40.4

s+

43d

47m

32.1

s(-2

9.6

)00h

57m

40.4

s+

43d

47m

32.1

s(-1

13.4

)0.5

7(0

.01)

-0.8

6(0

.05)

8.2

3(0

.09)

1.1

5a

IC1623B

01h

07m

47.6

s-1

7d

30m

25.4

s(2

5.4

)∗01h

07m

47.3

s-1

7d

30m

28.4

s(1

9.1

)∗0.3

0(0

.004)

-0.9

8(0

.02)

7.7

1(0

.01)

1.7

3c

3M

CG

-03-0

4-0

14

01h

10m

09.0

s-1

6d

51m

09.6

s(1

50.7

)01h

10m

08.9

s-1

6d

51m

10.6

s(-1

26.8

)0.6

7(0

.01)

-0.0

4(0

.02)

6.9

8(0

.09)

1.1

6N

0E

SO

244-G

012

01h

18m

08.3

s-4

4d

27m

43.5

s(-7

9.0

)01h

18m

08.3

s-4

4d

27m

43.6

s(-1

62.7

)0.6

6(0

.01)

-0.3

2(0

.13)

7.3

9(0

.06)

1.1

9b

CG

CG

436-0

30

01h

20m

02.6

s+

14d

21m

42.7

s(-2

7.1

)01h

20m

02.6

s+

14d

21m

42.7

s(-1

10.9

)0.3

5(0

.01)

-1.1

0(0

.10)

8.9

4(0

.09)

1.1

0b

2E

SO

353-G

020

01h

34m

51.2

s-3

6d

08m

14.5

s(-5

8.4

)01h

34m

51.2

s-3

6d

08m

14.5

s(-1

42.1

)0.5

4(0

.01)

-0.5

8(0

.04)

7.2

6(0

.10)

1.4

2N

RR

032

N01h

36m

23.4

s-3

7d

19m

18.0

s(-5

9.0

)01h

36m

23.4

s-3

7d

19m

18.1

s(-1

42.7

)0.5

2(0

.01)

0.0

9(0

.03)

6.1

9(0

.10)

1.2

8a

RR

032

S01h

36m

24.1

s-3

7d

20m

25.9

s(-5

8.9

)01h

36m

24.1

s-3

7d

20m

25.9

s(-1

42.7

)0.7

0(0

.01)

-0.3

8(0

.04)

6.7

4(0

.09)

1.1

4a

IRA

SF

01364-1

042

01h

38m

52.9

s-1

0d

27m

11.2

s(1

49.2

)01h

38m

52.8

s-1

0d

27m

12.0

s(-1

10.8

)0.3

9(0

.01)

-1.2

7(0

.08)

32.7

2(1

.04)

1.4

1d

5IIIZ

w035

—01h

44m

30.5

s+

17d

06m

08.7

s(-1

09.1

)—

—23.5

2(0

.24)

—a

3N

GC

0695

01h

51m

14.2

s+

22d

34m

56.4

s(-2

3.5

)01h

51m

14.3

s+

22d

34m

55.4

s(-1

07.3

)0.6

5(0

.01)

0.3

1(0

.02)

6.1

7(0

.09)

1.8

6N

UG

C01385

01h

54m

53.8

s+

36d

55m

04.0

s(-2

2.0

)01h

54m

53.8

s+

36d

55m

04.1

s(-1

05.7

)0.6

4(0

.01)

-0.0

0(0

.11)

6.7

3(0

.08)

1.1

2a

NG

C0838

W02h

09m

24.7

s-1

0d

08m

09.6

s(1

62.7

)02h

09m

24.7

s-1

0d

08m

09.5

s(7

8.9

)0.4

5(0

.01)

0.2

7(0

.03)

4.7

6(0

.10)

1.6

3a

NG

C0838

E02h

09m

38.7

s-1

0d

08m

47.5

s(1

62.6

)02h

09m

38.7

s-1

0d

08m

47.5

s(7

8.9

)0.7

4(0

.01)

0.2

3(0

.03)

7.5

9(0

.06)

2.0

0a

NG

C0838

S02h

09m

42.8

s-1

0d

11m

02.3

s(1

62.6

)02h

09m

42.8

s-1

0d

11m

02.3

s(7

8.9

)0.5

0(0

.01)

-0.8

3(0

.03)

6.7

2(0

.04)

1.1

8a

NG

C0828

02h

10m

09.5

s+

39d

11m

24.6

s(-1

9.3

)02h

10m

09.5

s+

39d

11m

24.7

s(-1

03.0

)0.6

1(0

.01)

-0.0

9(0

.03)

5.0

4(0

.05)

1.6

4d

IC0214

02h

14m

05.5

s+

05d

10m

25.4

s(-2

6.2

)02h

14m

05.4

s+

05d

10m

25.4

s(-1

10.0

)0.6

4(0

.01)

-0.0

5(0

.02)

6.5

1(0

.10)

1.3

4d

NG

C0877

S02h

17m

53.2

s+

14d

31m

18.1

s(-2

4.5

)02h

17m

53.2

s+

14d

31m

18.2

s(-1

08.3

)0.4

6(0

.01)

-1.1

6(0

.10)

7.1

1(0

.17)

1.3

6a

NG

C0877

N02h17m

59.7

s+

14d

32m

38.0

s(-2

4.5

)02h

17m

59.6

s+

14d

32m

38.0

s(-1

08.3

)0.3

5(0

.03)

0.1

6(0

.03)

6.1

4(0

.14)

2.1

0a

MC

G+

05-0

6-0

36

S02h

23m

19.0

s+

32d

11m

18.1

s(1

55.4

)02h

23m

19.0

s+

32d

11m

18.2

s(7

1.7

)0.5

4(0

.01)

0.1

9(0

.03)

6.1

2(0

.22)

1.4

6a

2M

CG

+05-0

6-0

36

N02h

23m

22.0

s+

32d

11m

48.4

s(1

55.4

)02h

23m

22.0

s+

32d

11m

48.5

s(7

1.7

)0.4

8(0

.01)

-0.2

5(0

.02)

6.2

3(0

.07)

1.2

9a

2U

GC

01845

02h

24m

08.0

s+

47d

58m

11.8

s(-3

1.2

)02h

24m

08.0

s+

47d

58m

11.9

s(-1

15.0

)0.5

8(0

.01)

-0.4

0(0

.03)

7.7

1(0

.09)

1.1

8N

NG

C0958

02h

30m

42.9

s-0

2d

56m

20.4

s(-2

7.6

)02h

30m

42.9

s-0

2d

56m

20.4

s(-1

11.3

)0.2

9(0

.01)

0.0

0(0

.08)

4.9

6(0

.15)

1.7

7N

MIR Properties of Nearby LIRGs 15

Sou

rce

Sh

ort

-Low

RA

/D

EC

(PA

)L

on

g-L

ow

RA

/D

EC

(PA

)6.2µm

EQ

W(σ

)s 9.7µm

(σ)

Fν[3

0µm

]/Fν[1

5µm

](σ

)S

cale

Mer

ger

MS

Nam

e[J

2000]

[◦]

[J2000]

[◦]

[µm

]F

act

or

Sta

ge

(HS

T)

NG

C0992

02h

37m

25.5

s+

21d

06m

04.4

s(-

21.8

)02h

37m

25.5

s+

21d

06m

04.4

s(-

105.5

)0.7

2(0

.01)

0.0

5(0

.04)

6.4

1(0

.09)

1.2

8c

UG

C02238

02h

46m

17.5

s+

13d

05m

44.3

s(-

24.7

)02h

46m

17.5

s+

13d

05m

44.9

s(-

108.2

)0.6

3(0

.01)

-0.3

7(0

.04)

5.6

6(0

.07)

1.1

4d

IRA

SF

02437+

2122

02h

46m

39.1

s+

21d

35m

10.1

s(-

22.3

)02h

46m

39.1

s+

21d

35m

10.3

s(-

104.0

)0.1

6(0

.01)

-1.2

5(0

.06)

8.8

1(0

.16)

1.0

6c

UG

C02369

02h

54m

01.8

s+

14d

58m

15.4

s(-

22.9

)02h

54m

01.8

s+

14d

58m

15.5

s(-

106.7

)0.5

7(0

.01)

-0.1

1(0

.07)

6.4

8(0

.03)

1.3

0b

3U

GC

02608

N03h

15m

01.5

s+

42d

02m

08.5

s(-

21.8

)03h

15m

01.5

s+

42d

02m

08.6

s(-

105.6

)0.2

0(0

.003)

-0.2

2(0

.02)

5.0

4(0

.02)

1.1

5N

UG

C02608

S03h

15m

14.6

s+

41d

58m

49.9

s(-

21.8

)03h15m

14.6

s+

41d

58m

49.9

s(-

105.5

)0.2

5(0

.14)

0.5

2(0

.32)

4.5

9(1

.60)

1.7

2N

NG

C1275

03h

19m

48.2

s+

41d

30m

41.9

s(1

57.6

)03h

19m

48.2

s+

41d

30m

41.7

s(7

3.8

)0.0

2(0

.003)

0.2

6(0

.02)

2.7

3(0

.01)

1.0

1N

IRA

SF

03217+

4022

03h

25m

05.4

s+

40d

33m

32.3

s(-

22.2

)03h

25m

05.4

s+

40d

33m

32.3

s(-

105.9

)0.5

5(0

.01)

-0.4

7(0

.03)

8.3

4(0

.07)

1.1

7d

NG

C1365

03h

33m

36.4

s-3

6d

08m

26.0

s(-

51.0

)03h

33m

36.4

s-3

6d

08m

25.5

s(7

4.4

)0.1

3(0

.002)

0.1

0(0

.05)

5.6

5(0

.03)

1.6

7N

IRA

SF

03359+

1523

—03h

38m

47.1

s+

15d

32m

53.2

s(-

102.3

)—

—12.4

5(0

.16)

—d

CG

CG

465-0

12

N03h

54m

07.8

s+

15d

59m

24.1

s(-

17.6

)03h

54m

07.8

s+

15d59m

24.2

s(-

101.3

)0.6

7(0

.02)

0.4

3(0

.03)

4.3

3(0

.16)

1.8

3a

CG

CG

465-0

12

S03h

54m

16.1

s+

15d

55m

43.2

s(-

17.6

)03h

54m

16.1

s+

15d

55m

43.3

s(-

101.3

)0.6

0(0

.01)

-0.0

2(0

.03)

6.6

4(0

.66)

1.6

5c

IRA

S03582+

6012

W04h

02m

32.0

s+

60d

20m

38.3

s(-

12.6

)04h

02m

32.0

s+

60d

20m

38.3

s(-

96.3

)0.6

4(0

.01)

0.0

8(0

.04)

8.8

0(0

.08)

—c

IRA

S03582+

6012

E04h

02m

33.0

s+

60d

20m

41.8

s(-

12.6

)04h

02m

33.0

s+

60d

20m

41.8

s(-

96.3

)0.0

1(0

.003)

-3.0

4(0

.03)

6.3

9(0

.02)

—c

UG

C02982

04h

12m

22.6

s+

05d

32m

50.5

s(-

15.8

)04h

12m

22.6

s+

05d

32m

50.5

s(-

99.6

)0.6

8(0

.01)

0.1

8(0

.03)

5.1

1(0

.06)

2.0

2d

ES

O420-G

013

04h

13m

49.7

s-3

2d

00m

25.5

s(-

49.4

)04h

13m

49.7

s-3

2d

00m

25.5

s(-

133.2

)0.3

0(0

.003)

-0.2

7(0

.03)

5.4

3(0

.04)

1.2

1N

NG

C1572

04h

22m

42.8

s-4

0d

36m

03.6

s(-

131.6

)04h

22m

42.8

s-4

0d

36m

03.6

s(1

44.7

)0.4

6(0

.01)

-0.1

6(0

.03)

6.7

6(0

.08)

1.2

0N

IRA

S04271+

3849

04h

30m

33.1

s+

38d

55m

48.0

s(-

10.8

)04h

30m

33.1

s+

38d

55m

48.0

s(-

94.5

)0.6

1(0

.01)

-0.2

9(0

.04)

7.8

5(0

.12)

1.2

5d

NG

C1614

04h

33m

59.8

s-0

8d

34m

43.1

s(-

26.7

)04h

33m

59.8

s-0

8d

34m

40.8

s(-

110.4

)0.6

1(0

.01)

-0.4

1(0

.02)

4.8

1(0

.01)

1.4

0d

5U

GC

03094

04h

35m

33.9

s+

19d

10m

18.3

s(1

67.0

)04h

35m

33.8

s+

19d

10m

17.5

s(-

97.5

)0.4

3(0

.005)

-0.3

2(0

.02)

5.0

5(0

.06)

1.1

6N

ES

O203-I

G001

04h

46m

49.5

s-4

8d

33m

30.1

s(-

106.3

)04h

46m

49.5

s-4

8d

33m

30.1

s(1

70.0

)0.0

3(0

.01)

-3.2

0(0

.17)

15.0

5(0

.33)

0.9

8d

3M

CG

-05-1

2-0

06

04h

52m

05.0

s-3

2d

59m

27.1

s(-

141.0

)04h

52m

05.0

s-3

2d

59m

27.0

s(1

35.3

)0.5

3(0

.01)

-0.0

2(0

.03)

7.2

5(0

.07)

1.1

1N

NG

C1797

05h

07m

44.8

s-0

8d

01m

08.7

s(-

18.8

)05h

07m

44.8

s-0

8d

01m

08.7

s(-

102.5

)0.6

2(0

.01)

-0.2

0(0

.03)

7.7

2(0

.08)

1.3

0a

CG

CG

468-0

02

W05h08m

19.7

s+

17d

21m

47.5

s(1

73.1

)05h

08m

19.7

s+

17d

21m

47.5

s(8

9.3

)0.1

2(0

.005)

-0.0

1(0

.03)

3.7

5(0

.05)

1.0

4b

CG

CG

468-0

02

E05h

08m

21.2

s+

17d

22m

07.7

s(1

73.1

)05h

08m

21.2

s+

17d

22m

07.7

s(8

9.3

)0.5

4(0

.01)

-0.9

5(0

.04)

10.3

8(0

.19)

1.0

3b

IRA

S05083+

2441

S05h

11m

25.9

s+

24d

45m

18.0

s(1

70.4

)05h

11m

25.9

s+

24d

45m

18.0

s(8

6.6

)0.7

2(0

.01)

-0.1

6(0

.04)

7.9

9(0

.11)

1.1

7N

VII

Zw

031

05h

16m

46.4

s+

79d

40m

12.7

s(1

55.0

)05h

16m

46.3

s+

79d

40m

12.7

s(7

1.3

)0.6

4(0

.01)

-0.2

2(0

.04)

7.3

7(0

.11)

1.2

7N

0IR

AS

05129+

5128

05h

16m

56.0

s+

51d

31m

57.3

s(2

.3)

05h

16m

56.0

s+

51d

31m

57.3

s(-

81.5

)0.5

4(0

.01)

-0.6

1(0

.04)

8.7

5(0

.11)

1.2

7d

IRA

SF

05189-2

524

05h

21m

01.3

s-2

5d

21m

45.6

s(-

2.5

)05h

21m

01.4

s-2

5d

21m

46.1

s(-

86.2

)0.0

3(0

.002)

-0.2

9(0

.02)

5.0

4(0

.01)

0.9

8d

IRA

SF

05187-1

017

05h

21m

06.5

s-1

0d

14m

46.8

s(-

13.7

)05h

21m

06.5

s-1

0d

14m

46.2

s(-

108.7

)0.5

3(0

.03)

-0.6

4(0

.14)

14.9

0(0

.51)

1.0

6N

16 Stierwalt et al.

Sou

rceS

hort-L

ow

RA

/D

EC

(PA

)L

on

g-L

ow

RA

/D

EC

(PA

)6.2µm

EQ

W(σ

)s9.7µm

(σ)

Fν[3

0µm

]/Fν[1

5µm

](σ)

Sca

leM

erger

MS

Nam

e[J

2000]

[ ◦]

[J2000]

[ ◦]

[µm

]F

acto

rS

tage

(HS

T)

IRA

S05223+

1908

05h

25m

16.7

s+

19d

10m

48.0

s(-1

0.1

)05h

25m

16.7

s+

19d

10m

48.0

s(-9

3.8

)<

0.0

1(—

)0.1

2(0

.02)

2.0

0(0

.01)

0.9

9N

MC

G+

08-1

1-0

02

05h

40m

43.7

s+

49d

41m

41.3

s(1

69.6

)05h

40m

43.7

s+

49d

41m

41.3

s(8

5.9

)0.5

6(0

.01)

-0.8

9(0

.03)

9.4

7(0

.08)

1.2

2d

NG

C1961

05h

42m

04.7

s+

69d

22m

43.1

s(1

62.9

)05h

42m

04.7

s+

69d

22m

43.2

s(7

9.2

)0.2

4(0

.01)

0.0

3(0

.09)

4.1

8(0

.05)

1.9

3d

UG

C03351

05h

45m

48.2

s+

58d

42m

03.1

s(1

55.1

)05h

45m

48.1

s+

58d

42m

03.2

s(7

1.4

)0.5

3(0

.01)

-0.6

8(0

.04)

6.8

8(0

.10)

1.0

7a

IRA

S05442+

1732

05h

47m

11.2

s+

17d

33m

46.5

s(-9

.3)

05h

47m

11.2

s+

17d

33m

46.6

s(-9

3.0

)0.6

6(0

.01)

-0.3

8(0

.02)

7.5

2(0

.03)

1.1

6a

IRA

SF

06076-2

139

06h

09m

45.8

s-2

1d

40m

23.9

s(1

66.3

)06h

09m

45.8

s-2

1d

40m

23.8

s(1

10.0

)0.3

3(0

.02)

-1.3

9(0

.09)

7.9

8(0

.10)

—c

UG

C03410

W06h

13m

58.8

s+

80d

28m

35.2

s(1

54.7

)06h

13m

58.8

s+

80d

28m

35.2

s(7

0.8

)0.6

2(0

.01)

0.1

5(0

.04)

3.3

8(0

.06)

1.6

0a

UG

C03410

E06h

14m

30.5

s+

80d

26m

59.9

s(1

54.6

)06h

14m

30.5

s+

80d

26m

59.9

s(7

1.0

)0.6

3(0

.01)

0.1

4(0

.05)

5.1

9(0

.03)

1.7

9a

NG

C2146

06h

18m

37.5

s+

78d

21m

24.3

s(1

7.7

)06h

18m

37.7

s+

78d

21m

25.8

s(-6

2.4

)0.6

7(0

.01)

-0.4

3(0

.02)

9.9

6(0

.01)

2.4

3d

ES

O255-IG

007

W06h

27m

21.7

s-4

7d

10m

36.5

s(-1

28.8

)06h

27m

21.7

s-4

7d

10m

36.4

s(1

47.4

)0.6

2(0

.01)

-0.2

6(0

.02)

8.3

1(0

.03)

—b

3E

SO

255-IG

007

E06h

27m

22.5

s-4

7d

10m

47.6

s(-1

28.8

)06h

27m

22.5

s-4

7d

10m

47.5

s(1

47.4

)0.6

5(0

.02)

0.2

6(0

.02)

8.0

5(0

.04)

—b

3E

SO

255-IG

007

S06h

27m

23.1

s-4

7d

11m

02.9

s(-1

28.8

)06h

27m

23.1

s-4

7d

11m

02.9

s(1

47.4

)0.6

9(0

.02)

-0.1

0(0

.02)

7.2

7(0

.04)

—b

3E

SO

557-G

002

S06h

31m

45.7

s-1

7d

38m

44.8

s(-1

67.6

)06h

31m

45.7

s-1

7d

38m

44.7

s(1

08.7

)0.7

0(0

.07)

0.3

4(0

.06)

6.4

2(0

.64)

1.0

9a

ES

O557-G

002

N06h

31m

47.2

s-1

7d

37m

16.5

s(-1

67.6

)06h

31m

47.2

s-1

7d

37m

16.4

s(1

08.7

)0.6

0(0

.01)

-0.7

3(0

.04)

12.1

8(0

.09)

1.0

4a

UG

C03608

06h

57m

34.4

s+

46d

24m

10.7

s(1

74.4

)06h

57m

34.4

s+

46d

24m

10.7

s(9

0.6

)0.5

3(0

.01)

-0.3

2(0

.03)

7.4

0(0

.07)

1.1

3b

IRA

SF

06592-6

313

06h

59m

40.3

s-6

3d

17m

52.5

s(-1

64.8

)06h

59m

40.3

s-6

3d

17m

52.5

s(1

11.5

)0.4

8(0

.01)

-0.3

1(0

.04)

6.9

8(0

.08)

1.1

0N

AM

0702-6

01

N07h

03m

24.1

s-6

0d

15m

21.8

s(-1

63.8

)07h03m

24.1

s-6

0d

15m

21.8

s(1

12.4

)0.0

4(0

.002)

-0.1

0(0

.02)

3.1

1(0

.01)

1.2

4a

1A

M0702-6

01

S07h

03m

28.5

s-6

0d

16m

43.6

s(-1

63.8

)07h

03m

28.5

s-6

0d

16m

43.6

s(1

12.4

)0.6

8(0

.01)

-0.0

5(0

.03)

7.2

1(0

.72)

1.3

7a

1N

GC

2342

07h

09m

18.1

s+

20d

38m

09.5

s(2

.6)

07h

09m

18.1

s+

20d

38m

09.9

s(9

9.4

)0.6

7(0

.01)

-0.0

6(0

.03)

8.0

7(0

.11)

1.2

8a

NG

C2369

07h

16m

37.9

s-6

2d

20m

36.4

s(5

0.9

)∗07h

16m

37.8

s-6

2d

20m

34.2

s(4

3.2

)∗0.4

8(0

.01)

-0.6

0(0

.02)

5.8

8(0

.02)

1.6

5N

IRA

S07251-0

248

07h

27m

37.6

s-0

2d

54m

54.2

s(-1

70.4

)07h

27m

37.6

s-0

2d

54m

54.2

s(1

05.9

)0.0

9(0

.01)

-2.3

5(0

.14)

13.3

8(0

.12)

1.1

0d

NG

C2388

07h

28m

53.4

s+

33d

49m

08.9

s—

0.5

3(0

.005)

0.0

7(0

.06)

——

aM

CG

+02-2

0-0

03

S07h

35m

41.5

s+

11d

36m

42.0

s(-1

73.9

)07h

35m

41.5

s+

11d

36m

42.0

s(1

02.3

)0.5

8(0

.05)

0.4

7(0

.18)

4.6

2(0

.66)

1.7

4a

MC

G+

02-2

0-0

03

N07h

35m

43.5

s+

11d

42m

34.7

s(-1

73.9

)07h

35m

43.4

s+

11d

42m

34.7

s(1

02.3

)0.1

7(0

.003)

-0.4

9(0

.04)

10.0

8(0

.14)

1.2

6a

IRA

S08355-4

944

08h

37m

01.8

s-4

9d

54m

30.3

s(-1

55.8

)08h

37m

01.8

s-4

9d

54m

30.2

s(1

20.5

)0.1

9(0

.003)

-0.3

2(0

.02)

6.5

9(0

.04)

1.1

6d

3IR

AS

F08339+

6517

—08h

38m

23.2

s+

65d

07m

14.5

s(1

09.0

)—

—7.3

7(0

.05)

—N

NG

C2623

08h

38m

24.1

s+

25d

45m

17.4

s(1

1.9

)08h

38m

24.1

s+

25d

45m

17.2

s(-7

1.8

)0.2

7(0

.01)

-1.1

2(0

.05)

14.6

6(0

.13)

1.0

5d

5E

SO

432-IG

006

W08h

44m

27.2

s-3

1d

41m

50.9

s(-1

55.6

)08h

44m

27.2

s-3

1d

41m

50.8

s(1

20.7

)0.6

4(0

.01)

0.0

2(0

.04)

6.2

3(0

.11)

1.2

9b

ES

O432-IG

006

E08h

44m

28.9

s-3

1d

41m

30.4

s(-1

55.6

)08h

44m

28.9

s-3

1d

41m

30.3

s(1

20.7

)0.4

1(0

.01)

-0.0

1(0

.07)

6.9

1(0

.14)

1.0

5b

ES

O60-IG

016

08h

52m

31.8

s-6

9d

01m

55.8

s(-8

4.5

)08h

52m

31.8

s-6

9d

01m

55.7

s(-1

68.2

)0.1

1(0

.004)

-1.7

6(0

.04)

7.7

1(0

.04)

1.0

9b

3

MIR Properties of Nearby LIRGs 17

Sou

rce

Sh

ort

-Low

RA

/D

EC

(PA

)L

on

g-L

ow

RA

/D

EC

(PA

)6.2µm

EQ

W(σ

)s 9.7µm

(σ)

Fν[3

0µm

]/Fν[1

5µm

](σ

)S

cale

Mer

ger

MS

Nam

e[J

2000]

[◦]

[J2000]

[◦]

[µm

]F

act

or

Sta

ge

(HS

T)

IRA

SF

08572+

3915

09h

00m

25.4

s+

39d

03m

54.6

s(1

9.0

)09h

00m

25.4

s+

39d

03m

55.1

s(-

64.7

)<

0.0

3(—

)-3

.58

(0.0

4)

5.2

4(0

.01)

1.0

1d

3IR

AS

09022-3

615

09h

04m

12.7

s-3

6d

27m

01.6

s(2

3.2

)09h

04m

12.7

s-3

6d

27m

01.7

s(-

60.5

)0.1

4(0

.004)

-0.8

8(0

.03)

7.9

7(0

.05)

1.0

5d

IRA

SF

09111-1

007

W09h

13m

36.5

s-1

0d

19m

30.0

s(-

160.9

)09h

13m

36.5

s-1

0d

19m

29.9

s(1

15.4

)0.4

7(0

.02)

-0.7

3(0

.10)

12.5

4(0

.39)

1.1

3b

IRA

SF

09111-1

007

E09h

13m

38.9

s-1

0d

19m

19.9

s(-

160.9

)09h

13m

38.9

s-1

0d

19m

19.9

s(1

15.4

)0.5

2(0

.03)

-0.1

5(0

.07)

5.9

1(0

.26)

1.3

0b

UG

C04881

W09h

15m

54.7

s+

44d

19m

50.7

s(-

161.0

)09h

15m

54.7

s+

44d

19m

50.7

s(1

15.3

)0.6

1(0

.01)

-0.2

7(0

.04)

9.1

7(0

.31)

1.1

0c

UG

C04881

E09h

15m

55.5

s+

44d

19m

57.2

s(-

161.0

)09h

15m

55.5

s+

44d

19m

57.3

s(1

15.3

)0.4

0(0

.01)

-0.8

1(0

.04)

10.2

2(0

.17)

1.0

1c

UG

C05101

09h

35m

51.6

s+

61d

21m

11.7

s(4

7.4

)09h

35m

51.7

s+

61d

21m

12.0

s(-

36.4

)0.1

3(0

.005)

-0.7

8(0

.05)

7.6

9(0

.05)

0.9

9d

MC

G+

08-1

8-0

13

—09h

36m

37.2

s+

48d

28m

27.9

s(1

19.2

)—

—7.4

8(0

.05)

—a

Arp

303

S09h

46m

20.3

s+

03d02m

44.3

s(-

163.3

)09h

46m

20.3

s+

03d

02m

44.4

s(1

12.9

)0.6

0(0

.02)

0.0

6(0

.04)

6.0

6(0

.11)

2.5

5a

Arp

303

N09h

46m

21.1

s+

03d

04m

15.9

s(-

163.3

)09h

46m

21.1

s+

03d

04m

16.0

s(1

12.9

)0.5

7(0

.06)

0.0

8(0

.09)

4.5

6(0

.10)

1.5

8a

NG

C3110

10h

04m

02.0

s-0

6d

28m

29.5

s(1

61.6

)∗10h

04m

02.2

s-0

6d

28m

31.9

s(6

5.7

)∗0.6

4(0

.01)

0.1

9(0

.03)

5.9

1(0

.04)

2.1

0a

ES

O374-I

G032

10h

06m

04.7

s-3

3d

53m

06.3

s(-

128.3

)10h

06m

04.7

s-3

3d

53m

06.2

s(1

48.0

)0.0

3(0

.002)

-2.7

4(0

.04)

9.3

6(0

.03)

1.1

3d

IRA

SF

10173+

0828

10h

20m

00.2

s+

08d

13m

33.8

s(-

162.9

)10h

20m

00.2

s+

08d

13m

33.6

s(1

13.3

)0.3

5(0

.04)

-1.2

0(0

.12)

35.4

0(1

.38)

1.0

7a

NG

C3221

10h

22m

20.3

s+

21d

34m

22.1

s(-

162.9

)10h

22m

20.3

s+

21d

34m

22.1

s(1

13.3

)0.7

5(0

.01)

-0.1

2(0

.04)

5.9

4(0

.05)

1.4

4N

NG

C3256

10h

27m

51.2

s-4

3d

54m

13.8

s(-

5.5

)10h

27m

51.3

s-4

3d

54m

13.9

s(-

57.4

)0.6

1(0

.01)

-0.2

8(0

.02)

8.1

6(0

.04)

1.3

3d

5E

SO

264-G

036

10h

43m

07.5

s-4

6d

12m

44.3

s(-

111.2

)10h

43m

07.5

s-4

6d

12m

44.3

s(1

65.0

)0.4

4(0

.01)

-0.0

4(0

.02)

5.4

9(0

.03)

1.8

7N

ES

O264-G

057

10h

59m

01.8

s-4

3d

26m

25.8

s(-

137.5

)10h

59m

01.8

s-4

3d

26m

25.8

s(1

38.8

)0.6

0(0

.01)

-0.1

9(0

.04)

7.4

6(0

.10)

1.3

4d

IRA

SF

10565+

2448

10h

59m

18.1

s+

24d

32m

34.9

s(2

5.3

)10h

59m

18.1

s+

24d

32m

35.4

s(-

58.4

)0.5

1(0

.01)

-0.7

5(0

.04)

9.5

1(0

.07)

1.0

8d

2M

CG

+07-2

3-0

19

11h

03m

54.0

s+

40d

51m

00.7

s(-

159.7

)11h

03m

54.0

s+

40d

51m

00.7

s(1

16.6

)0.6

4(0

.01)

-0.5

5(0

.03)

12.4

0(1

.24)

1.1

4d

CG

CG

011-0

76

11h

21m

12.2

s-0

2d

59m

02.4

s(1

64.4

)∗11h

21m

12.3

s-0

2d

59m

03.0

s(1

57.9

)∗0.3

2(0

.02)

-0.4

2(0

.03)

4.3

5(0

.05)

1.3

0a

IRA

SF

11231+

1456

11h

25m

45.1

s+

14d

40m

35.8

s(-

166.8

)11h

25m

45.1

s+

14d

40m

36.4

s(1

17.0

)0.6

0(0

.01)

-0.2

2(0

.03)

8.9

0(0

.20)

0.9

3a

1E

SO

319-G

022

11h

27m

54.1

s-4

1d

36m

52.4

s(-

126.3

)11h

27m

54.1

s-4

1d

36m

52.4

s(1

50.0

)0.4

2(0

.02)

-0.3

0(0

.05)

10.8

1(0

.17)

1.1

1d

NG

C3690

W11h

28m

31.1

s+

58d

33m

41.6

s(1

08.8

)∗11h

28m

31.1

s+

58d

33m

43.6

s(4

4.3

)∗0.1

2(0

.002)

-0.7

7(0

.02)

4.4

8(0

.00)

—c

3N

GC

3690

E11h

28m

33.8

s+

58d

33m

47.0

s(5

1.5

)∗11h

28m

33.7

s+

58d

33m

48.3

s(4

4.3

)∗0.3

8(0

.003)

-1.6

5(0

.02)

12.1

2(0

.01)

1.4

4c

3E

SO

320-G

030

11h

53m

11.6

s-3

9d

07m

47.3

s(1

66.3

)∗11h

53m

11.6

s-3

9d

07m

45.6

s(1

58.2

)∗0.5

8(0

.01)

-0.2

2(0

.02)

13.2

4(0

.05)

1.4

4N

ES

O440-I

G058

N12h

06m

51.7

s-3

1d

56m

46.4

s(-

152.0

)12h

06m

51.7

s-3

1d

56m

46.3

s(1

24.3

)0.5

6(0

.02)

0.3

7(0

.04)

9.8

0(0

.98)

—b

ES

O440-I

G058

S12h

06m

51.9

s-3

1d

56m

59.2

s(-

152.0

)12h

06m

51.9

s-3

1d

56m

59.1

s(1

24.3

)0.6

6(0

.01)

-0.4

5(0

.03)

7.5

6(0

.06)

1.2

1b

IRA

SF

12112+

0305

12h

13m

46.0

s+

02d

48m

40.8

s(-

161.5

)12h

13m

46.0

s+

02d

48m

40.6

s(1

14.8

)0.3

0(0

.03)

-1.2

4(0

.14)

16.6

5(0

.34)

1.1

3d

4E

SO

267-G

030

W12h

13m

52.3

s-4

7d

16m

25.9

s(-

132.3

)12h

13m

52.3

s-4

7d

16m

25.8

s(1

44.0

)0.6

8(0

.01)

-0.0

8(0

.04)

7.3

9(0

.10)

1.1

5a

NG

C4194

12h

14m

09.6

s+

54d

31m

34.3

s(1

79.7

)12h

14m

09.5

s+

54d

31m

33.8

s(9

6.0

)0.5

5(0

.005)

-0.2

9(0

.02)

7.6

5(0

.05)

1.3

7d

18 Stierwalt et al.

Sou

rceS

hort-L

ow

RA

/D

EC

(PA

)L

on

g-L

ow

RA

/D

EC

(PA

)6.2µm

EQ

W(σ

)s9.7µm

(σ)

Fν[3

0µm

]/Fν[1

5µm

](σ)

Sca

leM

erger

MS

Nam

e[J

2000]

[ ◦]

[J2000]

[ ◦]

[µm

]F

acto

rS

tage

(HS

T)

ES

O267-G

030

E12h

14m

12.8

s-4

7d

13m

43.0

s(-1

32.4

)12h

14m

12.8

s-4

7d

13m

42.9

s(1

43.9

)0.5

0(0

.01)

-0.0

1(0

.03)

4.8

6(0

.06)

1.6

1a

IRA

S12116-5

615

12h

14m

22.1

s-5

6d

32m

32.9

s(-1

32.4

)12h

14m

22.1

s-5

6d

32m

32.8

s(1

43.9

)0.3

6(0

.01)

-0.8

5(0

.03)

7.9

3(0

.07)

1.1

1N

0IR

AS

F12224-0

624

12h

25m

03.9

s-0

6d

40m

52.2

s(1

7.5

)12h25m

03.9

s-0

6d

40m

52.1

s(-6

6.3

)0.0

7(0

.02)

-2.1

2(0

.15)

28.3

4(1

.46)

0.9

5N

NG

C4418

12h

26m

54.6

s-0

0d

52m

40.0

s(1

8.9

)12h

26m

54.6

s-0

0d

52m

40.1

s(-6

4.8

)<

0.0

2(—

)-3

.51

(0.0

9)

7.8

3(0

.01)

1.0

4N

UG

C08058

12h

56m

14.3

s+

56d

52m

25.4

s(8

0.3

)12h

56m

14.4

s+

56d

52m

24.7

s(-3

.4)

0.0

1(0

.001)

-0.4

8(0

.02)

3.6

7(0

.01)

1.0

2d

NG

C4922

13h

01m

25.3

s+

29d

18m

50.0

s—

0.1

6(0

.003)

-0.6

0(0

.24)

——

cC

GC

G043-0

99

13h

01m

50.3

s+

04d

20m

00.1

s(-1

64.9

)13h

01m

50.3

s+

04d

20m

00.2

s(1

11.4

)0.5

5(0

.01)

-0.8

1(0

.03)

9.1

2(0

.17)

1.1

4d

MC

G-0

2-3

3-0

98

W13h

02m

19.7

s-1

5d

46m

04.0

s(-1

60.9

)13h

02m

19.7

s-1

5d

46m

03.9

s(1

15.3

)0.5

5(0

.01)

-0.0

4(0

.03)

5.7

7(0

.07)

1.1

5b

MC

G-0

2-3

3-0

98

E13h

02m

20.4

s-1

5d

45m

59.4

s(-1

60.9

)13h

02m

20.4

s-1

5d

45m

59.3

s(1

15.3

)0.7

0(0

.02)

0.0

4(0

.05)

8.4

7(0

.21)

1.2

9b

ES

O507-G

070

13h

02m

52.4

s-2

3d

55m

18.3

s(-1

53.1

)13h02m

52.4

s-2

3d

55m

18.2

s(1

23.2

)0.5

6(0

.01)

-1.2

4(0

.10)

13.5

8(0

.19)

1.1

0d

IRA

S13052-5

711

13h

08m

18.7

s-5

7d

27m

29.9

s(-1

44.6

)13h

08m

18.7

s-5

7d

27m

29.9

s(1

31.7

)0.6

1(0

.01)

-0.5

1(0

.03)

12.0

9(0

.21)

1.1

2a

IC0860

13h

15m

03.5

s+

24d

37m

08.0

s(-1

77.8

)13h

15m

03.5

s+

24d

37m

08.1

s(9

8.4

)0.4

3(0

.01)

-0.9

8(0

.11)

33.1

5(0

.29)

1.1

4N

IRA

S13120-5

453

13h

15m

06.5

s-5

5d

09m

23.6

s(-1

37.2

)13h

15m

06.5

s-5

5d

09m

23.8

s(1

39.1

)0.4

5(0

.01)

-0.9

1(0

.03)

12.5

4(0

.07)

1.2

6d

5V

V250a

W13h

15m

30.7

s+

62d

07m

45.7

s(-1

37.5

)13h

15m

30.7

s+

62d

07m

45.7

s(1

38.8

)0.7

6(0

.03)

-0.2

3(0

.11)

8.0

9(0

.33)

1.3

5b

2V

V250a

E13h

15m

35.0

s+

62d

07m

29.1

s(-1

37.5

)13h

15m

35.0

s+

62d

07m

29.1

s(1

38.8

)0.6

3(0

.01)

-0.6

7(0

.03)

7.6

5(0

.05)

1.0

3b

2U

GC

08387

13h

20m

35.4

s+

34d

08m

22.1

s(-1

69.5

)13h

20m

35.4

s+

34d

08m

22.2

s(1

05.6

)0.6

2(0

.01)

-1.0

1(0

.03)

10.8

0(0

.10)

1.0

7d

4N

GC

5104

13h

21m

23.1

s+

00d

20m

32.6

s(-1

67.4

)13h

21m

23.2

s+

00d

20m

33.2

s(1

13.7

)0.5

1(0

.01)

-0.4

7(0

.04)

6.6

7(0

.11)

1.2

1N

MC

G-0

3-3

4-0

64

13h

22m

24.5

s-1

6d

43m

42.7

s(-1

59.5

)13h

22m

24.5

s-1

6d

43m

42.6

s(1

16.8

)<

0.0

1(—

)-0

.18

(0.0

2)

2.1

3(0

.00)

0.9

6a

NG

C5135

13h

25m

44.1

s-2

9d

50m

00.7

s(1

5.0

)13h

25m

44.2

s-2

9d

50m

00.4

s(-6

8.7

)0.4

9(0

.01)

-0.2

4(0

.02)

5.7

8(0

.03)

1.5

3N

ES

O173-G

015

13h

27m

23.8

s-5

7d

29m

21.7

s(-1

48.7

)13h27m

23.8

s-5

7d

29m

21.6

s(1

27.5

)0.5

3(0

.01)

-1.3

1(0

.08)

15.0

4(0

.07)

—N

IC4280

13h

32m

53.4

s-2

4d

12m

25.3

s(-1

57.6

)13h

32m

53.4

s-2

4d

12m

25.2

s(1

18.6

)0.5

9(0

.01)

0.1

3(0

.04)

5.2

4(0

.09)

1.5

6N

NG

C5256

13h

38m

17.7

s+

48d

16m

32.9

s(-1

62.4

)13h

38m

17.6

s+

48d

16m

33.9

s(1

13.9

)0.4

4(0

.02)

-0.4

7(0

.03)

6.4

1(0

.03)

—b

3A

rp240

W13h

39m

53.0

s+

00d

50m

25.3

s(1

9.1

)13h

39m

53.0

s+

00d

50m

25.3

s(-6

4.6

)0.6

3(0

.01)

-0.0

1(0

.03)

7.1

8(0

.19)

1.6

6b

2A

rp240

E13h

39m

57.7

s+

00d

49m

51.0

s(1

9.1

)13h

39m

57.7

s+

00d

49m

51.0

s(-6

4.6

)0.5

4(0

.01)

0.1

2(0

.03)

6.3

1(0

.19)

1.6

9b

UG

C08696

13h

44m

42.2

s+

55d

53m

13.2

s(9

3.5

)13h

44m

42.3

s+

55d

53m

12.6

s(9

.8)

0.1

2(0

.01)

-1.3

7(0

.05)

12.3

6(0

.07)

1.0

6d

4U

GC

08739

13h

49m

13.9

s+

35d

15m

26.6

s(-1

69.7

)13h

49m

13.9

s+

35d

15m

26.6

s(1

06.5

)0.5

1(0

.01)

-0.5

9(0

.03)

6.7

4(0

.12)

2.1

4N

ES

O221-IG

010

13h

50m

56.9

s-4

9d

03m

19.2

s(-1

53.3

)13h

50m

56.9

s-4

9d

03m

19.1

s(1

23.0

)0.6

9(0

.01)

0.0

3(0

.03)

7.2

6(0

.08)

1.4

8N

NG

C5331

S13h

52m

16.2

s+

02d

06m

05.5

s(-1

71.0

)13h

52m

16.2

s+

02d

06m

05.5

s(1

05.2

)0.6

1(0

.01)

-0.4

3(0

.03)

7.0

6(0

.10)

1.1

9c

3N

GC

5331

N13h

52m

16.5

s+

02d

06m

31.3

s(-1

71.0

)13h

52m

16.4

s+

02d

06m

31.3

s(1

05.2

)0.6

0(0

.01)

0.1

3(0

.03)

5.2

4(0

.24)

1.1

1c

3A

rp84

N13h

58m

33.6

s+

37d

27m

13.2

s(-1

78.0

)13h

58m

33.6

s+

37d

27m

13.2

s(9

8.2

)0.6

2(0

.01)

-0.0

8(0

.03)

6.8

4(0

.03)

1.0

9c

MIR Properties of Nearby LIRGs 19

Sou

rce

Sh

ort

-Low

RA

/D

EC

(PA

)L

on

g-L

ow

RA

/D

EC

(PA

)6.2µm

EQ

W(σ

)s 9.7µm

(σ)

Fν[3

0µm

]/Fν[1

5µm

](σ

)S

cale

Mer

ger

MS

Nam

e[J

2000]

[◦]

[J2000]

[◦]

[µm

]F

act

or

Sta

ge

(HS

T)

Arp

84

S13h

58m

37.9

s+

37d

25m

28.2

s(-

178.0

)13h

58m

37.9

s+

37d

25m

28.2

s(9

8.2

)0.1

7(0

.02)

0.5

2(0

.07)

3.8

2(0

.24)

2.1

0c

CG

CG

247-0

20

14h

19m

43.3

s+

49d

14m

11.5

s(-

152.2

)14h

19m

43.3

s+

49d

14m

11.6

s(1

15.2

)0.5

6(0

.01)

-0.2

0(0

.03)

7.6

4(0

.10)

1.1

3N

NG

C5653

14h

30m

10.4

s+

31d

12m

56.1

s(1

72.7

)14h

30m

10.4

s+

31d

12m

56.1

s(8

9.0

)0.5

4(0

.01)

0.2

5(0

.03)

7.3

5(0

.04)

—N

IRA

SF

14348-1

447

14h

37m

38.4

s-1

5d

00m

24.0

s(-

167.2

)14h

37m

38.3

s-1

5d

00m

24.6

s(1

09.1

)0.2

5(0

.01)

-1.3

6(0

.16)

16.7

6(0

.36)

1.1

4d

4IR

AS

F14378-3

651

14h

40m

59.0

s-3

7d

04m

33.1

s(-

160.3

)14h

40m

58.9

s-3

7d

04m

33.0

s(1

16.0

)0.3

9(0

.03)

-1.1

4(0

.16)

15.7

1(0

.30)

1.0

8d

6N

GC

5734

N14h

45m

09.0

s-2

0d

52m

13.2

s(-

167.1

)14h

45m

09.0

s-2

0d

52m

13.2

s(1

09.1

)0.4

7(0

.01)

0.1

2(0

.03)

5.0

1(0

.14)

1.6

6a

NG

C5734

S14h

45m

11.0

s-2

0d

54m

48.7

s(-

167.1

)14h

45m

11.0

s-2

0d

54m

48.5

s(1

09.1

)0.4

9(0

.01)

-0.0

4(0

.04)

5.0

7(0

.08)

2.1

5a

VV

340a

S14h

57m

00.3

s+

24d

36m

24.2

s(1

77.8

)14h

57m

00.3

s+

24d

36m

24.3

s(9

4.1

)0.5

8(0

.02)

0.3

3(0

.04)

4.8

2(0

.31)

1.3

7b

1V

V340a

N14h

57m

00.7

s+

24d

37m

05.4

s(1

77.8

)14h

57m

00.7

s+

24d

37m

05.5

s(9

4.1

)0.5

8(0

.01)

-0.6

3(0

.03)

6.2

1(0

.10)

0.8

2b

1C

GC

G049-0

57

15h

13m

13.1

s+

07d

13m

33.1

s(1

55.9

)∗15h

13m

13.0

s+

07d

13m

35.2

s(5

9.8

)∗0.5

1(0

.04)

-0.8

3(0

.03)

31.4

0(0

.39)

1.0

5N

VV

705

15h

18m

06.4

s+

42d

44m

36.6

s(-

145.5

)—

0.7

5(0

.06)

0.3

2(0

.06)

——

bE

SO

099-G

004

15h

24m

58.0

s-6

3d

07m

29.2

s(-

169.3

)15h

24m

58.0

s-6

3d

07m

29.1

s(1

06.9

)0.5

3(0

.01)

-0.7

8(0

.04)

7.7

4(0

.06)

1.0

4d

3IR

AS

F15250+

3608

15h

26m

59.4

s+

35d

58m

37.7

s(1

70.1

)15h

26m

59.4

s+

35d

58m

37.2

s(8

6.3

)0.0

3(0

.01)

-2.6

9(0

.07)

10.5

2(0

.03)

0.9

7d

5N

GC

5936

15h

30m

00.8

s+

12d

59m

22.3

s(-

172.2

)15h

30m

00.8

s+

12d

59m

22.4

s(1

04.0

)0.6

2(0

.01)

-0.1

3(0

.03)

6.4

1(0

.07)

1.2

5N

Arp

220

15h

34m

57.3

s+

23d

30m

11.7

s(1

78.0

)15h

34m

57.2

s+

23d

30m

11.1

s(9

4.2

)0.1

7(0

.004)

-2.2

6(0

.06)

20.3

8(1

.67)

1.0

8d

4N

GC

5990

15h

46m

16.4

s+

02d

24m

55.7

s(-

171.3

)15h

46m

16.4

s+

02d

24m

55.8

s(1

04.9

)0.1

5(0

.002)

-0.1

1(0

.03)

4.7

4(0

.02)

1.2

2a

NG

C6052

16h

05m

13.1

s+

20d

32m

35.6

s(5

9.0

)∗16h

05m

12.9

s+

20d

32m

35.5

s(5

1.7

)∗0.6

9(0

.03)

-0.0

6(0

.03)

6.6

3(0

.04)

3.0

8c

NG

C6090

16h

11m

40.2

s+

52d

27m

24.9

s(2

6.8

)16h

11m

40.3

s+

52d

27m

24.7

s(-

57.0

)0.7

3(0

.02)

-0.0

4(0

.03)

7.5

4(0

.03)

—c

4IR

AS

F16164-0

746

16h

19m

11.8

s-0

7d

54m

02.7

s(-

177.8

)16h

19m

11.8

s-0

7d

54m

02.7

s(1

02.1

)0.6

1(0

.01)

-1.1

8(0

.07)

11.5

8(0

.20)

1.0

3d

5C

GC

G052-0

37

16h

30m

56.5

s+

04d

04m

58.5

s(1

6.1

)16h

30m

56.5

s+

04d

04m

58.8

s(1

01.2

)0.6

2(0

.01)

-0.2

1(0

.02)

7.0

7(0

.09)

1.1

6N

NG

C6156

16h

34m

52.5

s-6

0d

37m

07.5

s(-

179.8

)16h

34m

52.5

s-6

0d

37m

07.5

s(9

6.4

)0.3

7(0

.01)

0.4

7(0

.02)

5.8

9(0

.02)

1.2

3N

ES

O069-I

G006

16h

38m

11.8

s-6

8d

26m

08.0

s(1

78.6

)16h

38m

11.8

s-6

8d

26m

07.9

s(9

4.8

)0.6

4(0

.01)

-0.4

0(0

.04)

7.9

1(0

.10)

1.1

7b

2IR

AS

F16399-0

937

16h

42m

40.1

s-0

9d

43m

13.5

s(-

176.4

)16h

42m

40.1

s-0

9d

43m

13.4

s(9

9.9

)0.4

3(0

.01)

-1.1

2(0

.04)

9.0

9(0

.09)

1.1

4d

3E

SO

453-G

005

N16h

47m

29.4

s-2

9d

19m

06.8

s(-

175.6

)16h

47m

29.4

s-2

9d

19m

06.7

s(1

00.7

)0.7

4(0

.07)

0.4

7(0

.05)

5.2

1(0

.14)

1.5

1N

ES

O453-G

005

S16h

47m

31.1

s-2

9d

21m

21.6

s(-

175.6

)16h

47m

31.1

s-2

9d

21m

21.5

s(1

00.6

)0.4

2(0

.01)

-0.4

7(0

.09)

27.1

1(2

.71)

1.2

2N

NG

C6240

16h

52m

58.9

s+

02d

24m

03.7

s(-

177.4

)16h

52m

58.9

s+

02d

24m

03.0

s(9

8.9

)0.3

5(0

.01)

-0.9

2(0

.07)

7.7

2(0

.04)

1.0

5d

4IR

AS

F16516-0

948

16h

54m

23.9

s-0

9d

53m

20.6

s(-

177.9

)16h

54m

23.9

s-0

9d

53m

20.5

s(9

8.4

)0.6

9(0

.01)

0.1

8(0

.03)

7.0

2(0

.15)

1.6

7d

NG

C6286

N16h

58m

24.0

s+

58d

57m

21.4

s(-

117.4

)16h

58m

24.0

s+

58d

57m

21.9

s(1

16.3

)0.6

6(0

.02)

0.0

8(0

.03)

6.8

1(0

.07)

1.1

4b

NG

C6286

S16h

58m

31.3

s+

58d

56m

10.7

s(2

7.8

)16h

58m

31.7

s+

58d

56m

13.5

s(1

16.3

)0.5

9(0

.01)

-0.4

0(0

.03)

5.9

7(0

.04)

0.9

1b

IRA

SF

17132+

5313

—17h

14m

20.2

s+

53d

10m

30.4

s(-

102.2

)—

—9.6

7(0

.97)

—b

20 Stierwalt et al.

Sou

rceS

hort-L

ow

RA

/D

EC

(PA

)L

on

g-L

ow

RA

/D

EC

(PA

)6.2µm

EQ

W(σ

)s9.7µm

(σ)

Fν[3

0µm

]/Fν[1

5µm

](σ)

Sca

leM

erger

MS

Nam

e[J

2000]

[ ◦]

[J2000]

[ ◦]

[µm

]F

acto

rS

tage

(HS

T)

IRA

SF

17138-1

017

17h

16m

35.6

s-1

0d

20m

37.9

s(1

73.8

)17h

16m

36.0

s-1

0d

20m

41.2

s(1

.2)∗

0.6

8(0

.01)

-0.3

7(0

.04)

7.1

7(1

.51)

4.1

2d

6IR

AS

F17207-0

014

17h

23m

22.0

s-0

0d

17m

00.8

s(1

73.2

)17h

23m

22.0

s-0

0d

17m

01.0

s(8

9.5

)0.3

1(0

.01)

-1.2

6(0

.07)

26.3

9(0

.24)

1.2

2d

5E

SO

138-G

027

17h

26m

43.4

s-5

9d

55m

54.8

s(-1

77.1

)17h

26m

43.3

s-5

9d

55m

54.7

s(9

9.1

)0.5

2(0

.01)

-0.3

5(0

.06)

8.1

3(0

.03)

1.1

4N

UG

C11041

17h

54m

51.9

s+

34d

46m

34.0

s(-1

4.4

)17h

54m

51.9

s+

34d

46m

34.0

s(-9

8.2

)0.5

8(0

.01)

0.0

7(0

.03)

5.2

7(0

.04)

2.2

6N

CG

CG

141-0

34

17h

56m

56.6

s+

24d

01m

01.8

s(-1

1.9

)17h

56m

56.6

s+

24d

01m

01.8

s(-9

5.6

)0.4

8(0

.01)

-0.6

4(0

.06)

9.3

5(0

.16)

1.1

8N

IRA

S17578-0

400

W18h

00m

24.3

s-0

4d

01m

04.2

s(1

71.6

)18h

00m

24.3

s-0

4d

01m

04.1

s(8

7.9

)0.6

2(0

.02)

0.1

6(0

.09)

8.5

6(0

.25)

2.2

8b

IRA

S17578-0

400

N18h

00m

31.8

s-0

4d

00m

53.8

s(1

71.6

)18h

00m

31.8

s-0

4d

00m

53.7

s(8

7.9

)0.6

8(0

.01)

-0.6

7(0

.05)

21.1

8(0

.24)

1.4

5b

IRA

S17578-0

400

S18h

00m

34.1

s-0

4d

01m

44.3

s(1

71.6

)18h

00m

34.1

s-0

4d

01m

44.2

s(8

7.9

)0.7

8(0

.01)

0.1

5(0

.07)

6.3

8(0

.21)

1.8

3a

IRA

S18090+

0130

W18h

11m

33.4

s+

01d

31m

42.3

s(1

69.3

)18h

11m

33.4

s+

01d

31m

42.4

s(8

5.5

)0.5

2(0

.03)

-0.7

2(0

.10)

8.0

4(0

.26)

1.1

9b

IRA

S18090+

0130

E18h

11m

38.4

s+

01d

31m

40.2

s(1

69.3

)18h

11m

38.4

s+

01d

31m

40.3

s(8

5.5

)0.6

1(0

.01)

-0.2

8(0

.04)

7.1

6(0

.06)

1.2

2b

2N

GC

6621

18h

12m

55.2

s+

68d

21m

48.4

s(2

1.6

)∗18h

12m

54.8

s+

68d

21m

48.7

s(5

.2)∗

0.5

6(0

.01)

-0.1

6(0

.02)

5.8

3(0

.01)

1.2

6b

IC4687

18h

13m

39.7

s-5

7d

43m

30.5

s(1

3.6

)∗18h

13m

40.2

s-5

7d

43m

33.5

s(2

.1)∗

0.7

3(0

.02)

0.1

2(0

.02)

6.5

0(0

.02)

1.5

6b

CG

CG

142-0

34

W18h16m

33.8

s+

22d

06m

38.9

s(1

72.9

)18h

16m

33.8

s+

22d

06m

39.0

s(8

9.1

)0.4

8(0

.01)

-0.2

4(0

.03)

5.6

2(0

.21)

1.0

3a

CG

CG

142-0

34

E18h

16m

40.7

s+

22d

06m

46.4

s(1

72.9

)18h

16m

40.7

s+

22d

06m

46.5

s(8

9.1

)0.5

1(0

.01)

-0.4

8(0

.03)

7.3

4(0

.11)

1.9

5a

IRA

SF

18293-3

413

18h

32m

41.1

s-3

4d

11m

27.1

s(-8

.8)

18h

32m

41.1

s-3

4d

11m

27.1

s(-9

2.5

)0.6

3(0

.01)

-0.5

1(0

.02)

7.6

6(0

.05)

1.3

8c

1N

GC

6670

W18h

33m

34.3

s+

59d

53m

17.9

s(-7

.3)

18h33m

34.3

s+

59d

53m

17.9

s(-9

1.0

)0.6

3(0

.01)

-0.2

2(0

.03)

8.8

2(0

.11)

1.8

5b

2N

GC

6670

E18h

33m

37.8

s+

59d

53m

22.8

s(-7

.3)

18h

33m

37.8

s+

59d

53m

22.8

s(-9

1.0

)0.6

1(0

.01)

-0.3

4(0

.03)

8.7

8(0

.10)

1.2

6b

2IC

4734

18h

38m

25.8

s-5

7d

29m

25.4

s(1

67.4

)18h

38m

25.8

s-5

7d

29m

25.3

s(8

3.7

)0.5

1(0

.01)

-0.6

0(0

.04)

8.2

6(0

.09)

1.3

5N

NG

C6701

18h

43m

12.5

s+

60d

39m

11.9

s(-6

.0)

18h

43m

12.5

s+

60d

39m

11.9

s(-8

9.8

)0.5

5(0

.01)

-0.1

5(0

.09)

7.1

0(0

.07)

1.2

7N

VV

414

W19h

10m

53.9

s+

73d

24m

36.1

s(0

.6)

19h

10m

53.9

s+

73d

24m

36.1

s(-8

3.2

)0.6

4(0

.01)

0.1

0(0

.03)

7.2

4(0

.06)

1.4

1c

2V

V414

E19h

11m

04.3

s+

73d

25m

32.6

s(0

.6)

19h

11m

04.3

s+

73d

25m

32.6

s(-8

3.1

)0.2

9(0

.01)

-0.0

8(0

.02)

5.4

6(0

.02)

1.0

8c

2E

SO

593-IG

008

19h

14m

31.2

s-2

1d

19m

06.4

s(-1

3.2

)19h

14m

31.2

s-2

1d

19m

06.3

s(-9

6.9

)0.5

6(0

.01)

-0.5

9(0

.03)

8.9

2(0

.12)

1.3

8d

4IR

AS

F19297-0

406

19h

32m

22.3

s-0

4d

00m

00.2

s(1

56.3

)19h

32m

22.3

s-0

4d

00m

00.2

s(7

2.6

)0.3

0(0

.02)

-1.0

5(0

.13)

15.0

7(0

.25)

1.1

6d

4IR

AS

19542+

1110

19h

56m

35.8

s+

11d

19m

05.4

s(-6

.4)

19h

56m

35.8

s+

11d

19m

05.4

s(-9

0.1

)0.2

9(0

.02)

-0.7

4(0

.08)

14.5

3(0

.31)

1.0

7N

0E

SO

339-G

011

19h

57m

37.6

s-3

7d

56m

08.4

s(-2

2.0

)19h

57m

37.6

s-3

7d

56m

08.4

s(-1

05.8

)0.2

7(0

.01)

-0.3

1(0

.03)

4.6

4(0

.04)

1.2

2N

NG

C6907

20h

25m

06.5

s-2

4d

48m

32.6

s(-2

2.2

)20h

25m

06.5

s-2

4d

48m

32.5

s(-1

05.9

)0.5

7(0

.01)

0.1

0(0

.03)

6.6

7(0

.04)

1.6

2N

MC

G+

04-4

8-0

02

20h

28m

35.1

s+

25d

44m

00.2

s(2

.8)

20h

28m

35.1

s+

25d

44m

00.2

s(-8

0.9

)0.5

7(0

.01)

-0.4

7(0

.03)

5.2

2(0

.05)

1.7

3a

NG

C6926

20h

33m

06.1

s-0

2d

01m

38.8

s(-1

2.0

)20h

33m

06.1

s-0

2d

01m

38.7

s(-9

5.7

)0.3

7(0

.01)

-0.4

9(0

.03)

5.0

7(0

.05)

1.4

5d

IRA

S20351+

2521

20h

37m

17.7

s+

25d

31m

39.1

s(3

.8)

20h

37m

17.7

s+

25d

31m

39.1

s(-7

9.9

)0.5

7(0

.01)

-0.2

4(0

.04)

7.5

0(0

.10)

1.6

8N

0C

GC

G448-0

20

W20h57m

24.0

s+

17d

07m

35.1

s(-1

1.9

)20h

57m

24.0

s+

17d

07m

35.2

s(-9

5.6

)0.4

8(0

.01)

-0.4

2(0

.02)

9.1

4(0

.04)

—c

3

MIR Properties of Nearby LIRGs 21

Sou

rce

Sh

ort

-Low

RA

/D

EC

(PA

)L

on

g-L

ow

RA

/D

EC

(PA

)6.2µm

EQ

W(σ

)s 9.7µm

(σ)

Fν[3

0µm

]/Fν[1

5µm

](σ

)S

cale

Mer

ger

MS

Nam

e[J

2000]

[◦]

[J2000]

[◦]

[µm

]F

act

or

Sta

ge

(HS

T)

CG

CG

448-0

20

E20h

57m

24.3

s+

17d

07m

39.1

s(-

11.9

)20h

57m

24.3

s+

17d

07m

39.2

s(-

95.6

)0.2

7(0

.01)

-0.9

2(0

.03)

9.8

2(0

.04)

—c

3IR

AS

20551-4

250

20h

58m

26.8

s-4

2d

39m

01.7

s(1

62.1

)20h

58m

26.7

s-4

2d

39m

02.8

s(7

8.4

)0.1

0(0

.01)

-2.5

2(0

.10)

7.5

9(0

.02)

1.0

4d

5E

SO

286-G

035

21h

04m

11.1

s-4

3d

35m

34.4

s(-

27.5

)21h

04m

11.1

s-4

3d

35m

34.4

s(-

111.2

)0.6

9(0

.01)

-0.2

4(0

.03)

7.0

2(0

.09)

1.4

3a

IRA

S21101+

5810

21h

11m

29.3

s+

58d

23m

07.6

s(1

0.5

)21h

11m

29.3

s+

58d

23m

07.6

s(-

73.2

)0.5

5(0

.02)

-0.8

7(0

.07)

11.0

6(0

.15)

1.0

4c

2E

SO

343-I

G013

S21h

36m

10.5

s-3

8d

32m

42.4

s(-

31.9

)21h

36m

10.5

s-3

8d

32m

42.4

s(-

115.6

)0.6

1(0

.01)

-0.0

9(0

.03)

9.2

1(0

.18)

—c

ES

O343-I

G013

N21h

36m

10.9

s-3

8d

32m

32.6

s(-

1.9

)21h

36m

10.9

s-3

8d

32m

32.6

s(-

115.6

)0.4

7(0

.01)

-0.4

8(0

.02)

6.7

1(0

.07)

—c

NG

C7130

21h

48m

19.6

s-3

4d

57m

01.9

s(1

54.1

)21h

48m

19.5

s-3

4d

57m

02.1

s(7

0.4

)0.3

0(0

.01)

-0.2

7(0

.03)

5.6

7(0

.03)

1.4

2N

ES

O467-G

027

22h

14m

39.9

s-2

7d

27m

51.4

s(-

36.7

)22h

14m

39.9

s-2

7d

27m

51.3

s(-

120.4

)0.6

2(0

.01)

0.2

9(0

.02)

5.4

8(0

.09)

2.2

4N

IC5179

22h

16m

09.0

s-3

6d

50m

38.1

s(1

21.5

)∗22h

16m

09.3

s-3

6d

50m

33.8

s(1

15.9

)∗0.6

3(0

.01)

0.0

7(0

.02)

5.4

2(0

.02)

2.4

3N

ES

O602-G

025

22h

31m

25.5

s-1

9d

02m

04.0

s(-

31.4

)22h

31m

25.4

s-1

9d

02m

04.0

s(-

117.1

)0.4

5(0

.01)

-0.6

6(0

.04)

6.2

3(0

.08)

1.1

7N

UG

C12150

22h

41m

12.2

s+

34d

14m

56.9

s(-

20.1

)22h

41m

12.2

s+

34d

14m

56.8

s(-

98.7

)0.5

3(0

.01)

-0.4

2(0

.02)

8.1

4(0

.09)

1.2

7N

ES

O239-I

G002

22h

49m

39.8

s-4

8d

50m

58.4

s(-

48.3

)22h

49m

39.8

s-4

8d

50m

58.4

s(-

132.0

)0.4

5(0

.02)

-0.4

9(0

.04)

10.3

5(0

.12)

1.0

8d

5IR

AS

F22491-1

808

22h

51m

49.4

s-1

7d

52m

24.5

s(1

55.2

)22h

51m

49.2

s-1

7d

52m

24.8

s(7

1.5

)0.4

8(0

.02)

-1.0

4(0

.13)

17.6

3(0

.33)

1.1

4d

4N

GC

7469

23h

03m

15.6

s+

08d

52m

26.2

s(-

29.7

)23h

03m

15.6

s+

08d

52m

27.3

s(-

113.4

)0.2

3(0

.002)

0.0

6(0

.02)

4.8

1(0

.03)

1.1

2a

2C

GC

G453-0

62

23h

04m

56.5

s+

19d

33m

07.6

s(-

24.9

)23h

04m

56.6

s+

19d33m

07.8

s(-

103.6

)0.5

8(0

.02)

-0.4

6(0

.04)

12.8

3(0

.10)

1.5

0N

ES

O148-I

G002

23h

15m

47.0

s-5

9d

03m

17.0

s(1

36.3

)23h

15m

47.0

s-5

9d

03m

18.4

s(5

2.6

)0.3

1(0

.01)

-0.6

6(0

.03)

6.4

9(0

.05)

1.0

3c

4IC

5298

23h

16m

00.7

s+

25d

33m

24.4

s(-

19.5

)23h

16m

00.7

s+

25d

33m

24.5

s(-

103.3

)0.1

2(0

.004)

-0.3

7(0

.02)

7.4

1(0

.02)

1.0

1N

0N

GC

7552

23h

16m

10.6

s-4

2d

35m

03.8

s(1

12.9

)∗23h

16m

10.6

s-4

2d

35m

05.8

s(1

07.8

)∗0.5

6(0

.01)

-0.2

1(0

.02)

6.6

2(0

.01)

1.7

2N

NG

C7591

23h

18m

16.3

s+

06d

35m

08.7

s(-

27.4

)23h

18m

16.2

s+

06d

35m

09.2

s(-

109.7

)0.4

8(0

.01)

-0.3

7(0

.05)

7.9

6(0

.13)

1.2

1N

NG

C7592

W23h

18m

21.7

s-0

4d

24m

57.6

s(1

19.1

)∗23h

18m

21.5

s-0

4d

24m

54.2

s(1

12.9

)∗0.3

0(0

.01)

-1.0

8(0

.03)

5.1

3(0

.02)

1.1

0b

NG

C7592

E23h

18m

22.7

s-0

4d

24m

57.8

s(1

19.1

)∗23h

18m

22.8

s-0

4d

25m

02.3

s(1

12.9

)∗0.6

9(0

.01)

0.1

1(0

.02)

8.3

8(0

.07)

1.2

0b

ES

O077-I

G014

W23h

21m

03.7

s-6

9d

13m

00.9

s(-

55.8

)23h

21m

03.7

s-6

9d

13m

00.9

s(-

139.5

)0.6

3(0

.01)

-0.5

9(0

.04)

11.8

4(0

.17)

—b

2E

SO

077-I

G014

E23h

21m

05.4

s-6

9d

12m

47.2

s(-

55.8

)23h

21m

05.4

s-6

9d

12m

47.2

s(-

139.5

)0.4

9(0

.01)

-0.6

1(0

.03)

12.5

4(0

.12)

—b

2N

GC

7674

23h

27m

56.7

s+

08d

46m

44.5

s(1

16.5

)∗23h

27m

56.6

s+

08d

46m

41.8

s(2

0.5

)∗0.0

2(0

.01)

-0.1

3(0

.02)

2.5

2(0

.02)

1.1

3a

2N

GC

7679

23h

28m

46.6

s+

03d

30m

41.7

s(-

27.4

)23h

28m

46.6

s+

03d

30m

41.7

s(-

111.1

)0.6

4(0

.01)

0.3

4(0

.02)

5.7

8(0

.06)

1.4

1a

IRA

SF

23365+

3604

23h

39m

01.3

s+

36d

21m

10.2

s(-

35.5

)23h

39m

01.4

s+

36d

21m

11.3

s(-

119.2

)0.4

1(0

.02)

-1.4

1(0

.17)

10.0

4(0

.11)

1.8

9d

5M

CG

-01-6

0-0

22

—23h

42m

00.7

s-0

3d

36m

54.7

s(-

114.0

)—

—7.2

4(0

.13)

—a

IRA

S23436+

5257

23h

46m

05.4

s+

53d

14m

01.3

s(-

3.9

)23h

46m

05.4

s+

53d

14m

01.3

s(-

87.7

)0.3

7(0

.01)

-0.2

2(0

.03)

7.0

0(0

.06)

1.2

4c

4A

rp86

S23h

46m

58.5

s+

29d

27m

31.6

s(-

19.8

)23h

46m

58.5

s+

29d

27m

31.8

s(-

103.5

)0.7

2(0

.01)

0.1

2(0

.02)

6.1

4(0

.11)

1.6

1b

Arp

86

N23h

47m

04.8

s+

29d

28m

59.6

s(-

19.7

)23h

47m

04.8

s+

29d

28m

59.8

s(-

103.5

)0.3

2(0

.01)

0.1

4(0

.04)

6.7

2(0

.18)

1.5

3b

22 Stierwalt et al.

Sou

rceS

hort-L

ow

RA

/D

EC

(PA

)L

on

g-L

ow

RA

/D

EC

(PA

)6.2µm

EQ

W(σ

)s9.7µm

(σ)

Fν[3

0µm

]/Fν[1

5µm

](σ)

Sca

leM

erger

MS

Nam

e[J

2000]

[ ◦]

[J2000]

[ ◦]

[µm

]F

acto

rS

tage

(HS

T)

NG

C7771

W23h

51m

04.0

s+

20d

09m

02.0

s(-1

9.8

)23h

51m

04.0

s+

20d

09m

02.0

s(-1

03.6

)0.3

9(0

.01)

0.2

7(0

.06)

6.2

6(0

.11)

1.3

4N

NG

C7771

S23h

51m

22.5

s+

20d

05m

47.0

s(-1

9.8

)23h

51m

22.5

s+

20d

05m

47.0

s(-1

03.6

)0.3

6(0

.01)

-0.2

0(0

.04)

4.4

2(0

.05)

2.1

1c

NG

C7771

N23h

51m

24.9

s+

20d

06m

43.0

s(-1

9.8

)23h

51m

24.9

s+

20d

06m

43.1

s(-1

03.6

)0.5

2(0

.01)

-0.2

4(0

.03)

8.4

3(0

.04)

1.9

5a

MR

K0331

23h

51m

26.7

s+

20d

35m

10.1

s(-1

9.6

)23h

51m

26.7

s+

20d

35m

10.3

s(-1

03.3

)0.6

3(0

.01)

-0.3

5(0

.03)

9.4

0(0

.05)

1.1

9a

1M

IRS

pectra

lP

ara

meters

of

the

GO

AL

SS

am

ple.

Colu

mn

(1):

Sou

rceN

am

e,C

olu

mn

s(2

)-(5):

the

centra

lrig

ht

ascen

sion

,d

eclinatio

n,

an

dp

ositio

nan

gle

of

the

field

of

view

for

the

SL

an

dL

Lob

servatio

ns

(for

starin

gm

od

ed

ata

:R

AF

OV

,D

EC

FO

V,

&P

AF

OV

from

the

hea

ders

with

ap

oin

ting

accu

racy

with

in1′′;

for

map

pin

gm

od

ed

ata

:ca

lcula

tedfro

mth

efo

ur

corn

ersof

the

extra

ction

ap

erture

used

inC

UB

ISM

),C

olu

mn

(6):

the

equ

ivalen

tw

idth

of

the

6.2µ

mP

AH

featu

rein

µm

,C

olu

mn

(7):

the

ap

paren

td

epth

of

the

9.7µ

msilica

teab

sorp

tion

featu

re,C

olu

mn

(8):

the

MIR

slop

eca

lcula

tedu

sing

Fν

at

15

an

d30µ

m,

Colu

mn

(9):

the

SL

-to-L

Lsca

lefa

ctor,

Colu

mn

(10):

the

merg

ersta

ge

(N=

non

merg

er,a

=p

re-merg

er,b

=ea

rlysta

ge

merg

er,c

=m

id-sta

ge

merg

er,an

dd

=la

testa

ge

merg

er,see

Sectio

n2.5

for

deta

ils),an

dC

olu

mn

(11):

merg

ersta

ge

as

deriv

edfro

mth

eh

igh

resolu

tion

HS

Td

ata

(0=

non

merg

er,1

=p

re-merg

er,2

=on

goin

gm

erger

with

separa

ble

pro

gen

itor

gala

xies,

3=

on

goin

gm

erger

with

pro

gen

itors

sharin

ga

com

mon

envelo

pe,

4=

on

goin

gm

erger

with

dou

ble

nu

cleip

lus

tidal

tail,

5=

post-m

erger

with

single

nu

cleus

plu

sp

rom

inen

tta

il,an

d6

=p

ost-m

erger

with

single

nu

cleus

with

distu

rbed

morp

holo

gy,

as

describ

edin

Haan

etal.

(2011)).

∗D

ata

was

taken

inm

ap

pin

gm

od

e,an

dso

the

PA

was

user-selected

.