A New ATCA HI Absorption Survey Katie Jameson · A New ATCA HI Absorption Survey of the Small...

A New ATCA HI Absorption Survey of the Small Magellanic Cloud:

Katie JamesonAustralian National UniversityN. McClure-Griffiths, B. Liu, L. Staveley-Smith, J. Dickey, A. Bolatto, J. Dawson, H. Dénes, D. Li, S. Stanimirovic, M. Wolfire, T. Wong

credit: Alex Cherney

credit: ESO

Australia Telescope Compact Array (ATCA)

Atacama Large Millimeter Array (ALMA)

credit:V. Belokurov, D. Erkal

Large Magellanic Cloud (LMC)

Small Magellanic Cloud (SMC)

Cold Neutral Gas Everywhere, CO not so much

The Larger Galaxy Evolution Puzzle

2. Cold Neutral Gas to Molecular Gas

3. Molecular Gas to Stars

1. Warm Neutral Gas to Cold Neutral Gas

Star Formation

Galactic

Magnetic Fields

Feedback

Pieces of the Star Formation Puzzle

2. Cold Neutral Gas to Molecular Gas

3. Molecular Gas to Stars

1. Warm Neutral Gas to Cold Neutral Gas

Bigiel+ 2008

Atomic-dominated

The Magellanic Clouds: Nearby Laboratories to Study Star Formation

at Low Metallicity

SAGE+HERITAGE

SMCZ’ ~ 1/5

D ~ 60 kpcM* ~ 108 M⦿

LMCZ’ ~ 1/2D ~ 50 kpcM* ~ 109 M⦿

Measuring HI properties using emission and absorption line measurements

Emission spectrum

ATCA

CNM

CNM

CNM

CNM

CNM

WNM

Absorption spectrum

Significant improvement on existing measurements

Dickey+ 2000

στ ∼ 0.05 − 0.2

Nsource = 28

Nabs = 13

Δvch = 0.8 km s−1

This Work

στ ∼ 0.01 − 1

Nsource = 55

Nabs = 37

Δvch = 0.2 km s−1

x3

x4

x2

x5

Our new view of HI absorption in the SMC

Grey scale flux range= -5.0 120.0 JY/BEAM

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758 DICKEY ET AL. Vol. 536

TABLE 2

SOURCES WITH NO ABSORPTION DETECTED

R.A. Decl. S N1 N2 EW1 EW2 Ts1

Ts2

Name (J2000) (J2000) (mJy) pq (K km s~1) (K km s~1) (km s~1) (km s~1) (K) (K)(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)

J003412[733316 . . . . . . 00 34 12.2 [73 33 16 28 0.186 739 651 [6.9 ^ 2.3 [2.9 ^ 1.0 [106 [249J003424[721144 . . . . . . 00 34 24.5 [72 11 44 119 0.062 200 174 1.0 ^ 0.8 [0.1 ^ 0.5 [85 [132J003754[725157 . . . . . . 00 37 54.7 [72 51 57 80 0.092 841 806 [1.8 ^ 1.1 1.0 ^ 0.6 [244 [462J003801[725211 . . . . . . 00 38 01.0 [72 52 11 36 0.203 863 809 [2.7 ^ 2.5 [2.2 ^ 1.2 [113 [232J003939[714142 . . . . . . 00 39 39.6 [71 41 42 59 0.165 310 238 0.3 ^ 2.0 0.9 ^ 1.3 [49 [81J003947[713736 . . . . . . 00 39 47.5 [71 37 36 40 0.123 222 132 [0.8 ^ 1.5 [0.9 ^ 1.0 [47 [72J004047[714600 . . . . . . 00 40 47.9 [71 46 00 365 0.019 223 277 [0.5 ^ 0.2 [0.1 ^ 0.1 [317 [541J004327[704136 . . . . . . 00 43 27.1 [70 41 36 133 0.049 187 96 [1.4 ^ 0.6 [0.8 ^ 0.4 [101 [159J004330[704148 . . . . . . 00 43 30.7 [70 41 48 134 0.056 181 101 0.9 ^ 0.7 0.6 ^ 0.5 [86 [129J004808[741206 . . . . . . 00 48 08.4 [74 12 06 99 0.119 1034 1043 1.0 ^ 1.5 1.4 ^ 0.6 [233 [580J005608[703846 . . . . . . 00 56 08.0 [70 38 46 40 0.182 295 232 [1.2 ^ 2.3 [0.3 ^ 1.4 [43 [70J005652[712301 . . . . . . 00 56 52.7 [71 23 01 30 0.177 820 779 [1.0 ^ 2.2 [1.8 ^ 1.4 [123 [193J010930[713456 . . . . . . 01 09 30.8 [71 34 56 86 0.088 1091 1042 1.3 ^ 1.1 0.7 ^ 0.5 [331 [667J011035[722808 . . . . . . 01 10 35.6 [72 28 08 27 0.189 2077 2058 [2.6 ^ 2.3 [3.6 ^ 1.1 [294 [636J011056[731405 . . . . . . 01 10 56.5 [73 14 05 61 0.147 2855 2832 8.9 ^ 1.8 7.5 ^ 1.0 322 378

NOTE.ÈUnits of right ascension are hours, minutes, and seconds, and units of declination are degrees, arcminutes, and arcseconds.

position (J2000) in columns (2) and (3). The continuum Ñuxdensity is in column (4) ; this is uncorrected for the primarybeam attenuation, and it includes only the compact Ñux, i.e.,that portion unresolved by the interferometer, so thesevalues should not be compared with continuum Ñux den-sities measured at other frequencies. The rms noise in theoptical depth spectrum is in column (5). This noise dependson the total integration time that we were able to allocate tothe source and its (primary beam attenuated) Ñux density.The absorption spectra were taken with spectrometer chan-nels spaced by 3.91 kHz \ 0.825 km s~1 and total band-width 845 km s~1. Figure 1 shows the location of thesources superposed on the map of the total 21 cm emissionfrom the SMC from Stanimirovic et al. (1999).

The calibration of the data was done using the AIPSpackage. We observed reference sources 0252[712 forphase and gain calibration every 30 minutes or less and1934[038 at least once per day for Ñux and bandpass cali-bration. The data were then transferred to the MIRIADpackage for correction to heliocentric velocities and theappropriate vector averaging with phase shifts to create thespectrum toward each continuum source position. In thisPOSSM or UVSPEC step, we include only data from base-lines longer than 3 kj, which corresponds to fringe separa-tion of about 70A, since variations in the emission in the Ðeldcause serious confusion on larger scales, which pollutes theabsorption spectra on shorter baselines.

The emission spectra are taken from the spectral linecube constructed by Stanimirovic et al. (1999). This is acombination of data from a mosaicked survey using acompact conÐguration of the ATCA (Staveley-Smith et al.1997) and a single-dish survey taken with the Parkes 64 mtelescope. The steps involved in this combination aredescribed fully by Stanimirovic (1999). The most importantcharacteristic of this data for our application is that itincludes all short spacings up to 375 m so that it is equiva-lent to a map made by a single dish with beam size about100A, i.e., gain of 63.1 K (Jy per beam)~1. We compute theemission spectra by averaging over a 3 ] 3 pixel area cen-tered on the background source positions. The pixels are30A, so this is a square roughly 1 beamwidth on a side.

Figures 2È14 show the absorption and emission spectratoward all sources that show detected or marginallydetected absorption lines. The absorption spectra areabove, the emission below. Heliocentric (in fact, solarsystem barycentric) velocities are scaled at the bottom. Thedetection threshold (3p) in the absorption spectrum is indi-cated by the error bar on the left side. The Gaussian Ðts tothe absorption lines are indicated, as is the sum of theGaussians (this is described in ° 3.2 below). The zero line of

FIG. 1.ÈBackground source positions superposed on a map of thecolumn density of H I from the 21 cm emission study of Stanimirovic et al.(1999). The crosses indicate background sources ; if the sources showabsorption, then a circle is drawn around the cross, with the radius of thecircle proportional to the equivalent width, EW.

0h30m45m1h00m15m30m

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0 1 2 3 4 5 6 7 8tpeak

Emergence of narrow+deep and shallow+wide absorption features

Jameson, Liu, McClure-Griffiths+ in prep

Dickey+ 2000No. 2, 2000 COLD ATOMIC GAS IN SMC 759

FIG. 2.ÈEmission and absorption spectra in the direction ofJ003824[742212. The absorption spectrum is above, the emission spec-trum below. The Gaussian Ðts to the line components are indicated. The 3pthreshold for detection of absorption is shown on the left side of the upperspectrum. In emission, the wider line indicates the centered spectrum, fromthe inner 90@@ ] 90@@ square ; the Ðner line is the spectrum from the boxaround this square, out to 210@@ ] 210@@. The two horizontal lines at thebottom of the emission spectrum indicate the zero level and the 3 Kthreshold for the restricted integrals of the emission and absorption inTable 1.

FIG. 3.ÈEmission and absorption spectra in the direction ofJ004956[723555, as in Fig. 2.


the emission spectrum is shown, as is a threshold of 3 Kwhich is used to set ranges of velocity integration in ° 3.1.

In general, the emission spectra do not show any obviouse†ects of absorption toward our background continuumsources. This is because a typical continuum Ñux of 100 mJycontributes only about 6 K of total brightness temperatureto the emission cube. Few of our sources show absorption(e~q) of more than 50% (q \ 0.7), so we expect dips in the


Lower by ~2.5x compared to Dickey+00

The absorbing HI gas is cold


0 200 400 600 800<Ts > (K)

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SMC (Ntotal = 36)Mean <Ts >= 118 KMass-weighted Mean <Ts >= 179 K

CNM

CNM

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The absorbing HI gas is cold everywhere


CNM

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Identifying absorption features


75 100 125 150 175 200 225 250

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Cold gas temperatures of individual features


0 20 40 60 80Tc (K)

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SMC (Ntotal = 29)q = 0.25q = 0.75q = 0.50

21 K 28 K 38 K

Tc ~ 30 K

Tc = m + (1 − q)Tew

Tc shows no regional dependence


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110 <vlsrk < 120 km/s 120 <vlsrk < 130 km/s 130 <vlsrk < 140 km/s

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140 <vlsrk < 150 km/s 150 <vlsrk < 160 km/s 160 <vlsrk < 170 km/s

0h30m45m1h00m15m30m

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180 <vlsrk < 190 km/s

0h30m45m1h00m15m30m

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Probing the HI-to-H2 transition: ALMA ACA CO Follow-up Observations

1 Scientific Justification

The Large and Small Magellanic Clouds (LMC and SMC, respectively) provide the best laboratoryto study the low metallicity ISM at high resolution and provide detailed insight into the physics ofstar formation and galaxy evolution in high redshift galaxies at high resolution. One of the majorrate-limiting steps in star formation is the ability to form molecular gas. In the Milky Way, there is agap in our ability to trace the gas as it makes the transition from cool atomic hydrogen to molecularhydrogen, as neither 21-cm emission nor CO emission are bright for environments with a range ofdensity, temperature, and radiation field that is typical of the outer layers of a molecular cloud. This“dark” gas may be even more common in the Magellanic Clouds, where the lower dust-to-gas ratiomeans the photo-dissociation rate of molecules is higher than in the Milky Way, and the cool atomicmedium may penetrate much deeper into the dense interstellar clouds (Jameson et al. 2016). This“dark” gas may not be completely dark as Jameson et al. (2017) have shown that there is faint COemission out to the estimated H i-to-H2 transition in the outskirts of molecular clouds in star-formingregions in the SMC using ALMA ACA+TP 12CO (2� 1) observations. In this project we will probeeven more deeply to search for traces of CO emission in regions where we can fully understand theconditions of the cold neutral gas from H i absorption studies.We have partially completed a large project (⇠ 500/800 total hours completed) with the Australian

Telescope Compact Array (ATCA) to observe H i (and OH) absorption towards ⇠ 50 cm-wavelengthcontinuum sources in the LMC and ⇠ 30 in the SMC (PI: McClure-Gri�ths). Figure 1 shows thepositions of all the targeted continuum sources on top of the integrated intensity H i maps withthe subset of sources we will target with the proposed observations. This project will allow us tomeasure the variations in the fraction of cold-to-warm H i gas with galactic environment, understandthe relationship between pressure and cold gas temperature, and better understand the nature of“CO-dark” gas in the Magellanic Clouds. We propose to search for CO emission using theACA in standalone mode towards the same continuum sources with measurements ofH i absorption from the ATCA large project in order to study the H i-to-H2 transitionand the nature of the “CO-dark” or “CO-faint” gas at low metallicity.

Figure 1: Integrated H I of LMC (left) and SMC (right) overlaid with target sources. The box size is proportional tothe source flux. The blue circle shows the size of the ATCA primary beam to 80% response.

plus 1 hour per day for very accurate bandpass calibration on 1934-638. From the sensitivity calculator, and ourobserving experience, we achieve �s � 3 mJy Bm�1 per 0.8 km s�1 channel (binning 8 CABB narrow-bandchannels), giving at least �� = 0.05 on all sources of Sbkg > 60 mJy. Accounting for additional time required toobserve close pairs and the 12hr SMC continuum survey, the total project requires 804 hours to observe our 59fields, giving 77 sources.

Progress and future plansWe commenced observations in the 16APRS semester and continued through the 16OCTS semester for a total of

514 hours. Given our progress we expect to complete the project in the 17APRS semester. As of writing, we haveobserved 31 sources in the LMC and 8 sources in the SMC. By the end of the 16OCTS we expect to have observedan additional 7 fields (covering 10 sources) in the SMC. Assuming all of the observations go as planned for theremainder of the current semester, we will have 14 remaining LMC fields (15 sources) and 8 remaining SMC fields(10 sources) to observe during the 17APRS semester.

All of the data for 16APRS have been calibrated, imaged and spectra extracted. A few sources have required re-processing and self-calibration to ensure the best quality spectra, that is an on-going process. Data from our recentNovember observing are currently being reduced. We have performed automated Gaussian decomposition (Lindneret al., 2015) on approximately 1/3 of the spectra observed so far. Source lists, observing logs and progress of datareduction is all captured on our website: http://sites.google.com/site/atcamcs/home. Two exam-ple sources, one from the LMC and one from the SMC, are shown in Figure 2. These demonstrate the outstandingquality of our spectra and the multiple cold components detected. The LMC source, 0517-718, was observed byDickey et al. (1994). The new, sensitive data have resolved what had appeared as one component of FWHM ⇠ 6km s�1 into three distinct narrow components, changing the estimates of spin temperature.

HI emission spectra, which are essential for calculations of Ts and NH , are currently being extracted from thehigh resolution ATCA+Parkes surveys of the LMC & SMC (Kim et al., 2003; Stanimirovic et al., 1999) and willultimately be updated with GASKAP for improved parameter determination.

This project is currently well resourced in people-power. In addition to the senior researchers providing guidanceand advice, we have one PhD student (B. Liu at ICRAR/UWA) and one postdoc (K. Jameson at ANU) whose primaryprojects involve on this survey. Liu has been responsible for source selection, planning and conducting most of theobservations. K. Jameson has very recently joined ANU and will be working extensively on the comparison withmolecular gas in the SMC. Jameson and Liu are working together on the spectral fitting. Jameson will also managethe OH spectra.

To complete our original observational request for C3086 we require a total of 288 hours (24 blocks of12hrs) in the 2017APRS semester. This includes 23.5 days to cover the remaining fields plus 0.5 day to completea partially observed field. Fifteen of the requested days are LMC days; we strongly request that these be scheduledstarting no later than 0h LST so that we can reach the earlier sources that we had to skip in the current semesterbecause of late scheduling.

4

SWDarkPK









4

Fig. 1. — Integrated intensity H i images of the LMC (left) and SMC (right) with the backgroundcontinuum sources with targeted with the ATCA survey shown with red crosses, the black boxesshow the relative strengths of the sources, and the yellow circles indicate the sources we plan totarget with our proposed observations. The green box shows the location of the ACA+TP 12CO(2�1) map of the SWDarkPK region (Jameson et al. 2017). The blue circles show the ⇠ 400 ATCAprimary beam FWHM, which translate to ⇠ 600 pc and ⇠ 750 pc for the LMC and SMC.

1

No 12CO (2-1) detections! (7” resolution)

Probing the HI-to-H2 transition: ALMA ACA 12CO Observations

1 Scientific Justification

The Large and Small Magellanic Clouds (LMC and SMC, respectively) provide the best laboratoryto study the low metallicity ISM at high resolution and provide detailed insight into the physics ofstar formation and galaxy evolution in high redshift galaxies at high resolution. One of the majorrate-limiting steps in star formation is the ability to form molecular gas. In the Milky Way, there is agap in our ability to trace the gas as it makes the transition from cool atomic hydrogen to molecularhydrogen, as neither 21-cm emission nor CO emission are bright for environments with a range ofdensity, temperature, and radiation field that is typical of the outer layers of a molecular cloud. This“dark” gas may be even more common in the Magellanic Clouds, where the lower dust-to-gas ratiomeans the photo-dissociation rate of molecules is higher than in the Milky Way, and the cool atomicmedium may penetrate much deeper into the dense interstellar clouds (Jameson et al. 2016). This“dark” gas may not be completely dark as Jameson et al. (2017) have shown that there is faint COemission out to the estimated H i-to-H2 transition in the outskirts of molecular clouds in star-formingregions in the SMC using ALMA ACA+TP 12CO (2� 1) observations. In this project we will probeeven more deeply to search for traces of CO emission in regions where we can fully understand theconditions of the cold neutral gas from H i absorption studies.We have partially completed a large project (⇠ 500/800 total hours completed) with the Australian

Telescope Compact Array (ATCA) to observe H i (and OH) absorption towards ⇠ 50 cm-wavelengthcontinuum sources in the LMC and ⇠ 30 in the SMC (PI: McClure-Gri�ths). Figure 1 shows thepositions of all the targeted continuum sources on top of the integrated intensity H i maps withthe subset of sources we will target with the proposed observations. This project will allow us tomeasure the variations in the fraction of cold-to-warm H i gas with galactic environment, understandthe relationship between pressure and cold gas temperature, and better understand the nature of“CO-dark” gas in the Magellanic Clouds. We propose to search for CO emission using theACA in standalone mode towards the same continuum sources with measurements ofH i absorption from the ATCA large project in order to study the H i-to-H2 transitionand the nature of the “CO-dark” or “CO-faint” gas at low metallicity.









4

SWDarkPK









4

Fig. 1. — Integrated intensity H i images of the LMC (left) and SMC (right) with the backgroundcontinuum sources with targeted with the ATCA survey shown with red crosses, the black boxesshow the relative strengths of the sources, and the yellow circles indicate the sources we plan totarget with our proposed observations. The green box shows the location of the ACA+TP 12CO(2�1) map of the SWDarkPK region (Jameson et al. 2017). The blue circles show the ⇠ 400 ATCAprimary beam FWHM, which translate to ⇠ 600 pc and ⇠ 750 pc for the LMC and SMC.

1

map of the SMC (Mizuno et al. 2001). The region is also quiescent with no active star formationnearby. As most of the radio continuum sources with H i absorption line measurements are foundaway from star forming regions, the SWDarkPK region provides a similar environment that allowsus to better estimate the properties of the CO emission in regions with cold neutral gas and likelymolecular gas. In Fig. 3. we see that the 12CO (2 � 1) emission is clumpy and the structures aregenerally < 3000, which is the maximum recoverable size scale of the ACA. While the small, faintstructures may be unresolved, we are mainly interested in the strength of the 12CO emission, notthe small-scale structure along these lines-of-sight. This makes ACA-only observations ideal for ourproposed project.

Fig. 4. — Peak temperature 12CO (2 � 1)ACA+TP map (⇠ 700 resolution) for the qui-escent SWDarkPK region in the SMC fromJameson et al. (2017) with contours show-ing the 1, 2, 4, 6, 8, 10 K levels. The re-gion shows faint, clumpy emission in a re-gion away from active star formation, whichwe expect to be similar to the regions wherewe have H i absorption line measurements.Due to the clumpy nature of the CO emis-sion, ACA-only data should be su�cient asthe structures are smaller than the maxi-mum recoverable size-scale of ⇠ 3000.

In the SWDarkPK, the peak temperature of the faint emission is ⇠ 1 K. The H i column densityin the SWDarkPK is on the higher end of those probed by the ATCA survey (NHi ⇠ 1⇥ 1021 cm�2),with a more representative column density being ⇠ 4⇥ lower. We scale the faintest emission inSWDarkPK lower by a factor of 4 and adopt Tpeak ⇠ 0.025 K as our representative estimate of thepeak 12CO emission. To detect 0.25 K at the high resolution of the correlator mode (⇠ 0.3 km s�1)at S/N = 10 will require a sensitivity of 0.025 K, which can be achieved in ⇠ 1.7 hours on-sourceobservation time for each source. We will also be able to further average the data to at least 1 kms�1 channels, which will allow us to detect down to Tpeak ⇠ 0.07 K at S/N ⇠ 5 given that narrowlines will likely still be ⇠ 3 km s�1 wide. These single-pointing maps will be ⇠ 7⇥ more sensitivethan the existing map of SWDarkPK. While it is unlikely that we will detect 13CO in these di↵useregions, if there is detected 13CO it will inform us about the conditions of the molecular gas andindicate the presence of dense molecular gas.Finally, our continuum observations will reveal whether any of the cm-continuum sources also have

detectable continuum emission in the mm-wavelengths. We have included all sources detected in theAustralia Telescope 20 GHz (AT20G) Survey (Murphy et al. 2010) in our subset of targets. If wefind mm-continuum sources, this will be highly useful to be able to target them for future molecularabsorption line observations, in particular to look for HCO+ absorption as another indicator ofmolecular gas.

References

Bolatto et al. 2011, ApJ, 741, 12Israel 1997, A&A, 328, 471Jameson et al. 2017, ApJ, submittedJameson et al. 2016, ApJ, 825, 12Mizuno et al. 2010, PASJ, 53, 971

Murphy et al. 2010, MNRAWS, 402, 2403Pineda et al. 2017, arXiv:1704.00739Requena-Torres et al. 2016, A&A, 589, A28Wolfire et al. 2010, ApJ, 716, 1191

4

Jameson+ (2018)

Probing the HI-to-H2 transition: ALMA ACA CO Observations

map of the SMC (Mizuno et al. 2001). The region is also quiescent with no active star formationnearby. As most of the radio continuum sources with H i absorption line measurements are foundaway from star forming regions, the SWDarkPK region provides a similar environment that allowsus to better estimate the properties of the CO emission in regions with cold neutral gas and likelymolecular gas. In Fig. 3. we see that the 12CO (2 � 1) emission is clumpy and the structures aregenerally < 3000, which is the maximum recoverable size scale of the ACA. While the small, faintstructures may be unresolved, we are mainly interested in the strength of the 12CO emission, notthe small-scale structure along these lines-of-sight. This makes ACA-only observations ideal for ourproposed project.

Fig. 4. — Peak temperature 12CO (2 � 1)ACA+TP map (⇠ 700 resolution) for the qui-escent SWDarkPK region in the SMC fromJameson et al. (2017) with contours show-ing the 1, 2, 4, 6, 8, 10 K levels. The re-gion shows faint, clumpy emission in a re-gion away from active star formation, whichwe expect to be similar to the regions wherewe have H i absorption line measurements.Due to the clumpy nature of the CO emis-sion, ACA-only data should be su�cient asthe structures are smaller than the maxi-mum recoverable size-scale of ⇠ 3000.

In the SWDarkPK, the peak temperature of the faint emission is ⇠ 1 K. The H i column densityin the SWDarkPK is on the higher end of those probed by the ATCA survey (NHi ⇠ 1⇥ 1021 cm�2),with a more representative column density being ⇠ 4⇥ lower. We scale the faintest emission inSWDarkPK lower by a factor of 4 and adopt Tpeak ⇠ 0.025 K as our representative estimate of thepeak 12CO emission. To detect 0.25 K at the high resolution of the correlator mode (⇠ 0.3 km s�1)at S/N = 10 will require a sensitivity of 0.025 K, which can be achieved in ⇠ 1.7 hours on-sourceobservation time for each source. We will also be able to further average the data to at least 1 kms�1 channels, which will allow us to detect down to Tpeak ⇠ 0.07 K at S/N ⇠ 5 given that narrowlines will likely still be ⇠ 3 km s�1 wide. These single-pointing maps will be ⇠ 7⇥ more sensitivethan the existing map of SWDarkPK. While it is unlikely that we will detect 13CO in these di↵useregions, if there is detected 13CO it will inform us about the conditions of the molecular gas andindicate the presence of dense molecular gas.Finally, our continuum observations will reveal whether any of the cm-continuum sources also have

detectable continuum emission in the mm-wavelengths. We have included all sources detected in theAustralia Telescope 20 GHz (AT20G) Survey (Murphy et al. 2010) in our subset of targets. If wefind mm-continuum sources, this will be highly useful to be able to target them for future molecularabsorption line observations, in particular to look for HCO+ absorption as another indicator ofmolecular gas.

References

Bolatto et al. 2011, ApJ, 741, 12Israel 1997, A&A, 328, 471Jameson et al. 2017, ApJ, submittedJameson et al. 2016, ApJ, 825, 12Mizuno et al. 2010, PASJ, 53, 971

Murphy et al. 2010, MNRAWS, 402, 2403Pineda et al. 2017, arXiv:1704.00739Requena-Torres et al. 2016, A&A, 589, A28Wolfire et al. 2010, ApJ, 716, 1191

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Pouch-sized Talk: Cold HI gas is everywhere, CO not so much

New HI absorption line survey in SMC- >2x more sources- up to 5x greater sensitivity- 4x higher spectral resolution

Preliminary Results• Resolving narrow and shallow+wide absorption features• <Ts> significantly lower than previous work• Low cloud temps. from individual absorption features• No clear environmental dependence of cold gas properties• CO only detected near one source

Future ALMA CO data of all sources

A New ATCA HI Absorption Survey Katie Jameson · A New ATCA HI Absorption Survey of the Small...

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