Paul van derder Werf

Leiden Observatory

Dense gas in ULIRGsDense gas in ULIRGs

CreteCreteSeptember 15, September 15,

20082008

Dense gas in ULIRGsDense gas in ULIRGs 2

CreditsCredits

Padeli Papadopoulos (Bonn University)Kate Isaak (Cardiff University)

Dense gas in ULIRGsDense gas in ULIRGs 3

““Simple people who think that they can learn astronomy bySimple people who think that they can learn astronomy byonly looking at the stars, without knowledge of mathematics,only looking at the stars, without knowledge of mathematics,will in a future life become birds."will in a future life become birds." (Plato, T(Plato, T) )

Dense gas in ULIRGsDense gas in ULIRGs 4

OutlineOutline

ULIRGs and their integrated molecular gas properties

molecular gas tracers in ULIRGs star formation laws thermal balance in molecular gas in ULIRGs

case study: Mrk 231 outlook: the HerCULES project

Dense gas in ULIRGsDense gas in ULIRGs 5

GEHRsGEHRsSSCsSSCsHII galaxiesHII galaxiesELGsELGsCNELGsCNELGsW-R galaxiesW-R galaxiesBCGsBCGsBCDsBCDsLIGs, LIRGsLIGs, LIRGsULIGs, ULIRGsULIGs, ULIRGsLUVGs, UVLGsLUVGs, UVLGs

nuclear starbursts circumnuclear starburstsclumpy irregular galaxies Ly galaxiesE+A galaxies K+A galaxiesLBGsDRGsEROsSCUBA galaxiesSMGs

The starburst bestiaryThe starburst bestiary

(Kennicutt 2005)(Kennicutt 2005)

SFR 1SFR

b

Dense gas in ULIRGsDense gas in ULIRGs 6

Simple-minded estimate of Simple-minded estimate of ""maximum star formation ratemaximum star formation rate""

gasmax gas

ff

22 3

4selfgravitating sphere:

MM M G

t

RG

In the absence of external pressure, the maximum star formation rate occurs In the absence of external pressure, the maximum star formation rate occurs when a gas mass is turned into stars on the free-fall timescale.when a gas mass is turned into stars on the free-fall timescale.

31

max 0100 yr100 km/s

M M

Dense gas in ULIRGsDense gas in ULIRGs 7

Starformation efficiencyStarformation efficiency Starbursts cannotStarbursts cannot be simply scaled be simply scaled up.up. More intense More intense starbursts starbursts are also more are also more efficientefficient with their fuel.with their fuel. (Gao & Solomon 2001)

LLIRIR SFR SFR

LLIRIR//LLCOCO

SFR/SFR/MMHH22

SFESFE2

1FIR0 0

H

10 0

10 0

10 0

10 0

ULIRGs: 100

Milky Way: 1.5

Galactic GMCs: 1.8

OMC-1: 54

Orion BN-KL: 400

L L MM

L M

L M

L M

L M

Dense gas in ULIRGsDense gas in ULIRGs 8

Role of dense gasRole of dense gas

More dense gas means more efficient star formation.More dense gas means more efficient star formation.

(Gao & Solomon 2001)

LLHCNHCN//LLCOCO mass fraction of mass fraction of densedense gas gas

LLIRIR//LLCOCO

SFR/SFR/MMHH22

SFESFE

Dense gas in ULIRGsDense gas in ULIRGs 9

ULIRGs are morphologically ULIRGs are morphologically messymessy

(Evans (Evans et al.et al.))

Dense gas in ULIRGsDense gas in ULIRGs 10

……but normally have well-but normally have well-ordered nuclear gas ordered nuclear gas kinematicskinematics

(Downes & Solomon 1998)(Downes & Solomon 1998)

Dense gas in ULIRGsDense gas in ULIRGs 11

Molecular gas in ULIRGsMolecular gas in ULIRGs CO 1—0 reveals large gas masses, concentrated in compact

structures (disks or rings), typically < 1 kpc in radius (Downes, Solomon, Radford, Scoville,…)

X-factor converting CO luminosity into H2 mass is subject of endless debate, since

In ULIRGs a factor of 4 below “normal” is often adopted (Downes, Solomon, et al). Uncertain!

Higher CO lines trace gas that is both warm and dense. Resulting H2 masses (e.g., for high-z galaxies) are then even more uncertain.

b

nXT

Dense gas in ULIRGsDense gas in ULIRGs 12

Density or chemistry?Density or chemistry? Influence of AGN on

abundances of HCN, HCO+ under debate (Gracia-Carpio et al 2006, Papadopoulos 2007, Krips et al 2008).

PDR/XDR models disagree: Maloney et al 1996: HCN/HCO+

ratio enhanced in XDRs Meijerink & Spaans 2006, 2007:

HCN/HCO+ ratio suppressed in XDRs

Dense gas in ULIRGsDense gas in ULIRGs 13

SCUBASCUBA850 850 mm

Dense Dense vsvs. diffuse gas: the . diffuse gas: the AntennaeAntennae

SPIFI/JCMTSPIFI/JCMT(Isaak, Nikola, Stacey, & Van der Werf, (Isaak, Nikola, Stacey, & Van der Werf, in prep.in prep.))

[C[CII] widespread, CO ] widespread, CO JJ=7=76 isolated!6 isolated!

[CI]

CO J=76

Dense gas in ULIRGsDense gas in ULIRGs 14

A fundamental tracer of star A fundamental tracer of star forming gas?forming gas?

(Wu (Wu et al.et al.))

starbursts,starbursts,(U)LIRGs(U)LIRGs

GalacticGalacticstarformingstarformingcorescores

One relation!One relation!

Dense gas in ULIRGsDense gas in ULIRGs 15

Star formation laws:Star formation laws: Using CO 1—0, we get ~ 0.8 Using HCN 1—0 or CO 3—2, we get ~ 1.0

What do higher density tracers show?

IR lineL L

Dense gas in ULIRGsDense gas in ULIRGs 16

HCOHCO++ 4—3 in Mrk 231 (10hrs 4—3 in Mrk 231 (10hrs JCMT)JCMT)

Dense gas in ULIRGsDense gas in ULIRGs 17

HCN 4HCN 4——3 in UGC 5101 (12hrs 3 in UGC 5101 (12hrs JCMT)JCMT)

(Papadopoulos, Isaak, & Van der Werf, (Papadopoulos, Isaak, & Van der Werf, in prep.in prep.))

Dense gas in ULIRGsDense gas in ULIRGs 18

Star formation laws:Star formation laws: Using CO 1—0, we get ~ 0.8 Using HCN 1—0 or CO 3—2, we get ~ 1.0

What do higher density tracers show?

Using HCN 3—2, we get ~ 0.7 (Bussman et al., astro-ph)

Using HCN 4—3, we get ~ 0.6 (Papadopoulos, Isaak, & Van der Werf, in prep.)

IR lineL L

Dense gas in ULIRGsDense gas in ULIRGs 19

ImplicationsImplications Inconsistent with simple picture of a density threshold of a few 104 for tracing star forming gas.

However, a model of star formation in molecular clouds with: lognormal density distribution (e.g., from supersonic turbulence) Kennicutt-Schmidt star formation law with exponent ~ 1.5:

can account for this (Krumholz & Thompson 2007, Narayanan et al., 2008)

Explanation of the resulting star formation laws: Low-LIR galaxies have a large contribution from sub-thermally excited line

emission High-LIR galaxies have large amounts of gas with n>ncrit

1.5SFR g

Dense gas in ULIRGsDense gas in ULIRGs 20

Probing dense molecular gasProbing dense molecular gas

LineLine TTexex

[K][K]nncritcrit

[cm[cm—3—3]]

CO 1CO 100 5.55.5 1.7∙101.7∙1033

CO 4CO 433 5555 8.0∙108.0∙1044

CO 6CO 655 116116 2.5∙102.5∙1055

HCN 1HCN 100 4.34.3 1.4∙101.4∙1055

HCN 4HCN 433 4242 5.5∙105.5∙1066

molecular gasmolecular gas

densedense molecular gas molecular gastemperaturetemperature of dense gas of dense gas

Dense gas in ULIRGsDense gas in ULIRGs 21

Mid-Mid-JJ CO lines in Mrk231 CO lines in Mrk231

RxW/JCMT(Papadopoulos, Isaak & Van der Werf 2007)

Mrk231 CO 65 and 43model based only onCO 1—0, 2—1 & 3—2

model based onCO 1—0 to 4—3 and 6—5

Dense gas in ULIRGsDense gas in ULIRGs 22

diffuse phase: T 50—85 K, n 300—103 cm—3 – up to CO 3—2

dense phase: T 50—65 K, n 104 cm—3— CO 4—3 and higher

Total gas mass is dominated by the dense component: M 1.5—3.5∙1010 M.

Mid-Mid-JJ CO lines probe dense gas CO lines probe dense gas

Dense gas in ULIRGsDense gas in ULIRGs 23

(Fischer et al., 1997, 1999; Luhman et al., 1998; Malhotra et al., 1997, 2000;Helou et al., 2000)

Thermal balance of the dense gasThermal balance of the dense gasArp220: L[CII] / LFIR 1.3·10—4

(cf. normal galaxies: 10—2-3)

what cools the dense gas ? NB: [CI] 609 mm not suppressed (Gérin & Phillips 1999)

Dense gas in ULIRGsDense gas in ULIRGs 24

Cooling budget in Mrk231Cooling budget in Mrk231

CO cooling from the dense phase approaches [C II] cooling

Consistent with dense PDRs Solution to the [C II] problem Full understanding crucial in

ALMA era

Line Lline

[L][C II] 158 m

3.6∙108

[C I] 3.4∙106

CO diffuse 5.8∙106

CO dense >1.5∙108

Dense gas in ULIRGsDense gas in ULIRGs 25

Summary and outlookSummary and outlook Although optically messy, molecular gas in ULIRGs normally show ordered

motion.

Hence they can be analysed using the “normal” tools such as Kennicutt-Schmidt type star formation laws.

The observed CO/HCN line vs. IR correlations are consistent with a KS-law in a turbulent ISM with lognormal density distribution.

Beware of PDR/XDR chemistry affecting abundances of HCN, HCO+ and others

Mid-J CO lines are excellent probes of warm, dense gas, which forms the dominant mass component in objects studied in detail.

Integrated CO emission comparable to [CII] in ULIRGs. Thermal budget suggests dense PDRs are dominant.

Explore the low-z universe in mid-J CO lines: HerCULES

Dense gas in ULIRGsDense gas in ULIRGs 26

Who is HerCULES?Who is HerCULES?Paul van der Werf (Leiden; PI)Susanne Aalto (Onsala)Peter Ade (Cardiff)Lee Armus (Spitzer SC)Vassilis Charmandaris (Crete)Aaron Evans (Stony Brook)Jackie Fischer (NRL)Yu Gao (Purple Mountain)Eduardo Gonzalez-Alfonso (Henares)Thomas Greve (MPIA)Rolf Güsten (MPIfR)Andy Harris (U Maryland)Chris Henkel (MPIfR)Kate Isaak (Cardiff)Frank Israel (Leiden)Carsten Kramer (Cologne)Steve Lord (NASA Herschel SC)

Jesus Martín-Pintado (Madrid)Joe Mazzarella (IPAC)Rowin Meijerink (Berkeley)Padelis Papadopoulos (Bonn)Sabine Philipp (DLR)Adam Rykala (Cardiff)Dave Sanders (U Hawaii)Giorgio Savini (Cardiff)Howard Smith (CfA)Marco Spaans (Groningen)Luigi Spinoglio (Rome)Gordon Stacey (Cornell)Sylvain Veilleux (U Maryland)Cat Vlahakis (Leiden)Fabian Walter (MPIA)Axel Weiß (MPIfR)Martina Wiedner (Cologne)Manolis Xilouris (Athens)

Dense gas in ULIRGsDense gas in ULIRGs 27

What is HerCULES?What is HerCULES? Herschel Comprehensive (U)LIRG Emission Survey HerCULES is an approved Herschel Open Time Key

Program to uniformly and statistically measure the neutral gas cooling lines in a flux-limited sample of (U)LIRGs.

Sample: all IRAS RBGS ULIRGs with S60 > 12.19 Jy (6 sources) all IRAS RBGS LIRGs with S60 > 16.8 Jy (23 sources)

Observations: SPIRE/FTS full high-resolution scans: 200 to 670 m at R ≈ 600, covering

CO 5—4 to 13—12 and [CI] (+ other lines?) PACS line scans of [CII] and both [OI] lines All targets observed to same (expected) S/N Extended sources observed at several positions

Dense gas in ULIRGsDense gas in ULIRGs 28

Why HerCULES?Why HerCULES? develop use of the CO rotational ladder as a

diagnostic

inventory of neutral gas cooling

statistically robust approach

low-z benchmark for future ALMA observations

Dense gas in ULIRGsDense gas in ULIRGs 29

PDRs PDRs vs.vs. XDRs XDRs Identical incident energy

densities give very different CO spectra

Very high J CO lines are unique XDR tracers

Need full coverage of CO ladder in real galaxies

(Spaans & Meijerink 2008)

Dense gas in ULIRGsDense gas in ULIRGs 30

A local benchmark for high-A local benchmark for high-zz galaxiesgalaxies

Even in ALMA era, often limited spatial resolution on very high z galaxies, but many lines available

HerCULES will provide an empirical framework for interpreting these data.

(Walter, Weiß et al.)

Dense gas in ULIRGsDense gas in ULIRGs 31

HerCULES sampleHerCULES sampleTargetTarget log(log(LLFIRFIR//LL))Mrk 231Mrk 231 12.5112.51IRAS F17207—IRAS F17207—00140014

12.3912.39

IRAS 13120—IRAS 13120—54535453

12.2612.26

Mrk 273Mrk 273 12.1412.14IRAS F05189—IRAS F05189—25242524

12.2012.20

Arp 299Arp 299 11.8811.88NGC 6240NGC 6240 11.8511.85IRAS F18293—IRAS F18293—34133413

11.8111.81

Arp 193Arp 193 11.6711.67IC 1623IC 1623 11.6511.65NGC 1614NGC 1614 11.6011.60NGC 7469NGC 7469 11.5911.59NGC 3256NGC 3256 11.5611.56

+Arp 220, NGC 1068, NGC4418 from GTO+Arp 220, NGC 1068, NGC4418 from GTO

TargetTarget log(log(LLFIRFIR//LL))IC 4687/4686IC 4687/4686 11.5511.55NGC 2623NGC 2623 11.5411.54NGC 34NGC 34 11.4411.44MCGMCG++12—02—12—02—001001

11.4411.44

Mrk 331Mrk 331 11.4111.41IRAS 13242—IRAS 13242—57135713

11.3411.34

NGC 7771NGC 7771 11.3411.34Zw 049.057Zw 049.057 11.2711.27NGC 5135NGC 5135 11.1711.17IRAS F11506—IRAS F11506—38513851

11.1011.10

NGC 2146NGC 2146 11.0711.07NGC 7552NGC 7552 11.0311.03NGC 1365NGC 1365 11.0011.00