There Is Not One Magic Scale/Process Extragalactic (Ionized) Gas - - PowerPoint PPT Presentation

Frank Bigiel (Univ. of Heidelberg)

Gas Scaling Relations in Galaxies*

*with a focus on molecular gas and local galaxies

Optical: HST (PI: Chandar)

• Mol. Gas: ALMA (PI: Schinnerer/PHANGS)

Image credit: K. Sliwa/PHANGS

There Is Not One Magic Scale/Process

Diffuse (Atomic) Gas Dense (Molecular) Gas Young Stars Bound (Molecular) Gas Extragalactic (Ionized) Gas

Gas Accretion Cloud Formation Cloud Structure Star Formation

Dense (Molecular) Gas

“Cloud (H2) Formation” In dwarfs and outer disks, the ISM is mostly diffuse, warm gas and the key to get stars is just to get cold, bound clouds. SF is fast after this. This is basically the classic “star formation threshold.”

Extragalactic (Ionized) Gas Bound (Molecular) Gas Diffuse (Atomic) Gas Young Stars

A Molecular Bathtub

Young Stars Dense (Molecular) Gas Extragalactic (Ionized) Gas Bound (Molecular) Gas Diffuse (Atomic) Gas

“Molecular SF ‘Law’” In high z galaxies, inner parts of disks, starbursts, galaxy centers, most gas is H2 already (we think) and “H2” and SF are the most straightforward

• bservables.

This is the current most commonly studied link at galaxy scales.

From Cold (Bound?) Gas to Stars

Young Stars Extragalactic (Ionized) Gas Diffuse (Atomic) Gas Dense (Molecular) Gas Bound (Molecular) Gas

“Dense Gas Threshold” In the Milky Way stars form

• verwhelmingly inside the high

density parts of a cloud. Linking star formation to the dense structures is a huge part of Galactic star formation. This is, e.g., the topic probed by HCN- star formation comparisons.

But Only Dense Gas Forms Stars

H2 (CO) HI (21-cm) SFR (IR, Hα, UV) Dust (IR) Metallicity (spec) UV field (IR) Stars (optical/NIR) Rotation (HI/CO) Dynamics (HI/CO) Cloud Properties

Understanding These Processes Via Observations

Context H2 - HI Balance Dense(r) Gas Tracers H2 – Star Formation

An Incomplete Look at (Some) Gas Scaling Relations

Molecular Gas (CO 2-1)

SFR Surface Density (UV+IR) [Msun yr-1 kpc-2] Gas Surface Density [Msun pc-2]

Wong+ ‘02, Kennicutt+ ‘07, SCHRUBA+ ’11, CF. Leroy+ ‘08, Bigiel+ ‘08 Atomic Gas (21-cm) Azimuthal averages in 30 galaxies

Star Formation Occurs in Molecular Gas

COMPILATION FROM LEROY+ ‘13

Local Disks – Most Apparent Behavior 1-to-1

30 galaxies, 1 kpc resolution log10 SFR Surface Density (M yr-1 kpc-2) log10 H2 Surface Density (M pc-2)

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+1 +2 +3

• 1
• 2
• 3

LEROY+ ’13, SCHRUBA+ ‘11, BIGIEL+ ‘08

Local Disks – Important Variations

SAINTONGE+ ’11, ‘12, ’13; LRTOU+ ‘13

COLD GASS: Clear SFR/CO Correlation with M*

DAVIS ET ATLAS-3D ’13; C.F. ALATALO, YOUNG

Early Type Galaxies: Same Qualitative M* Trend

Each Point: Whole-galaxy average

Stellar Mass Dust-to-Gas Ratio

SAINTONGE+ ’12, YOUNG+ ’95, LEROY+ ’13

H2 Depletion Time (Fixed CO-to-H2)

Deviations for Low-Mass Galaxies

BOLATTO+ ’13; CF. SANDSTROM+ ’13

Metallicity/DGR and CO

SANDSTROM+ ‘13

Conversion Factor Across Local Disk Galaxies

ACCURSO+ ‘17

Conversion Factor On Galaxy Scales

ACCURSO+ ’17, CF. SAINTONGE+ ‘11, SCHRUBA+ ’12, BOSELLI+ ‘14

Application to SF-CO Scaling Relations

ACCURSO+ ’17, CF. SCHRUBA+ ’12, BOSELLI+ ‘14 THOUGH SEE GARDAN+’07 BRAINE+ ‘11, BOTHWELL+ ’14, HUNT+ ’15

Application to SF-CO Scaling Relations

SFR-H2 Variations about a “Normal” Relation

MEIDT ET PAWS ’13 (PLOT FROM ‘15), SUBM. DEPENDENCE ON DYNAMICS, CF. E.G. WANG+ ‘13, ELLISON+ ’11, RENAUD+ ‘12

Local Depletion Time and Dynamical Pressure

KODA+ ’09, COLOMBO+ ‘14, HUGHES+ ‘13, SCHINNERER+ ‘13, PETY+ ‘13; MEIDT+ ‘13,‘15

Cloud-Scale Structure and Environment

TEAM: Frank Bigiel (ZAH/ITA), Guillermo Blanc (Carnegie) Eric Emsellem (ESO), Andres Escala (U. Chile), Brent Groves (ANU), Annie Hughes (IRAP/OMP), Kathryn Kreckel (MPIA), Diederik Kruijssen (ZAH/ARI), Adam Leroy (OSU), Sharon Meidt (MPIA), Jerome Pety (IRAM), Laura Perez (U. Chile), Erik Rosolowsky (Alberta), Patricia Sanchez-Blazquez (PUC), Karin Sandstrom (UCSD), Eva Schinnerer (MPIA), Andreas Schruba (MPE), Antonio Usero (OAN) Affiliated members making huge contributions: Melanie Chevance (ITA/ZAH), Cinthya Herrera (IRAM), I Ting Ho (MPIA), Kazimir Sliwa (MPIA), Jiayi Sun (OSU) ONGOING PROGRAMS: ALMA High Resolution CO 2-1 Imaging: PIs Leroy and Blanc (“12× PAWS”) Dense gas spectroscopy: Bigiel IRAM/EMPIRE, Leroy ALMA MUSE mapping (1 galaxy so far, future: 20): Kreckel, Blanc, Schinnerer Narrow band Hα Imaging: Blanc, Groves, Ho NOEMA’s biggest mosaic: IC 342 in CO (Schruba, Kruijssen) PHYSICS AT HIGH ANGULAR RESOLUTION IN NEARBY GALAXIES TALK BY I-TING HO, TUESDAY

• 1. SFR traces H2 more directly than HI.
• 2. In the disks of big galaxies, the implied depletion time is 1 to a

few Gyr.

• 3. Trends with galaxy properties:
• depletion time increases with stellar mass
• early type galaxies show the same trend
• apparent depletion time shorter at low metallicity
• 4. Within galaxies, centers show wide range of SFR/H2.
• 5. Even a “normal” scaling hides systematic variations.

(e.g., dynamical suppression in M51 inner arms)

Summary: SF-CO Scaling Relations

Context H2 - HI Balance Dense(r) Gas Tracers H2 – Star Formation

An Incomplete Look at (Some) Gas Scaling Relations

SAINTONGE+ ‘16

H2 – HI Balance on Galaxy Scales

SAINTONGE+ ‘16

H2 – HI Balance on Galaxy Scales

Molecular to Atomic Gas Ratio SCHRUBA+ ‘11; LEROY+ ’08; BIGIEL+ ’08; LEROY+ IN PREP. Column density predicts H2 fraction, with HI showing a narrow distribution HI H2

H2 – HI Balance Across Local Galaxies

Molecular to Atomic Gas Ratio

Down Molecular to Atomic Gas Ratio Divided by Avg. Ratio at that Surface Density

Residuals in H2/HI vs. column correlate with dust-to-gas ratio.

Leroy+ in prep. Physics of HI shielding layer: Krumholz+ ‘09ab, Wolfire+ ’10

H2 – HI Balance Across Local Galaxies

WONG+ ’13 THEORETICAL PREDICTIONS CF. KRUMHOLZ+ ‘09, MCKEE & KRUMHOLZ ‘10

H2 – HI Balance Across Local Galaxies

• 1. H2/HI increases strongly with M* for main sequence galaxies
• 2. Highest sSFR galaxies do not have highest H2/HI fractions
• 3. Across disk galaxies: strong systematic changes in H2/HI
• 4. Dependences on gas column, stellar surface density, pressure.
• 5. Second order dependences on dust-to-gas ratio.

Summary: H2-HI Balance

Context H2 - HI Balance Dense(r) Gas Tracers H2 – Star Formation

An Incomplete Look at (Some) Gas Scaling Relations

Different molecular transitions at λ=3-4mm emit effectively at different densities. Comparing them gives a handle on the density distribution within a beam.

RADEX (VAN DER TAK ‘07) CALCULATIONS FROM LEROY ET AL. (2017)

Dense Gas Tracers in Normal Disk Galaxies

Mean CO Mean HCN CO / 40 Mean HCN Dense gas tracers are faint – here is the disk-integrated mean spectrum of M51. CO is on average 30-40 times fainter. This means ~1000 times longer for a matched quality map.

DATA: BIGIEL ET AL. (2016), MAPS INTEGRATED FROM PETY ET AL. (2013)

Why This is Hard

Ÿ First large pointed survey of galaxy disks (Usero+ ’15). Ÿ First whole-disk mapping survey (“EMPIRE”, Bigiel+ ’16). 9 galaxies, CO/HCN/HCO+/more, Jimenez-Donaire thesis. Ÿ Unmatched machine to resolve density-sensitive line ratios as a function of environment (e.g., center vs. disk, bar vs. arm). Ÿ First sample of full maps of inner 3-6 kpc in dense gas tracers and CO isotopologues (Gallagher, Leroy, Bigiel et al. ApJ subm.). Ÿ Focal plane array ARGUS now working. Dense gas in other galaxies a key science case (“DEGAS” Large Program PI: Kepley).

IRAM 30-m ALMA GBT

Surveying Dense Gas Tracers in Normal Disk Galaxies

BIGIEL ET AL. 2016, JIMENEZ-DONAIRE ET AL. 2017A,B PHD THESIS, CORMIER+ TO BE SUBM., LEROY+ ‘2017,

GALLAGHER+ SUBM.

HCN, HCO+, HNC (1-0) mapping of 9 nearby disk galaxies EMIR Multi-line Probe of the ISM Regulating Galaxy Evolution PI: F. Bigiel, ~500 hr IRAM Large Program 2015-2017

• Full galaxy maps of HCN, HCO+, CS,

CO, 13CO, C18O in 9 disk galaxies spanning range of properties

• Resolution ~ 1 – 2 kpc
• Wide suite of ancillary data (radio-UV)
• First results 2016.

Whole Galaxy Maps of Dense Gas Tracers

EMPIRE TEAM

• M. Jimenez-Donaire, D. Cormier,
• A. Leroy, A. Usero, F. Walter, K. Schuster,
• S. García-Burillo, C. Kramer, J. Pety,
• K. Sandstrom, E. Schinnerer, A.

Hughes, A. Kepley, A. D. Bolatto,

• A. Schruba, L. Zschaechner.

HCN, HCO+, HNC (1-0) mapping of 9 nearby disk galaxies

BIGIEL ET AL. 2016, JIMENEZ-DONAIRE ET AL. 2017A,B PHD THESIS, CORMIER+ TO BE SUBM., LEROY+ ‘2017,

GALLAGHER+ SUBM.

Whole Galaxy Maps of Dense Gas Tracers

Whole Galaxy Maps of Dense Gas Tracers

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2 4 6 8 10 12 log HCN [K km s-1 pc2] ∝ Dense gas 2 4 6 8 10 12 14 log IR Luminosity [LO

• ] ∝ Star Formation Rate

Gao & Solomon 2004 Gao el al. 2007 Krips et al. 2008 Gracia-Carpio et al. 2008 Juneau et al. 2009 Garcia-Burillo et al. 2012 Privon et al. 2015 Gao & Solomon 2004 Gao el al. 2007 Krips et al. 2008 Gracia-Carpio et al. 2008 Juneau et al. 2009 Garcia-Burillo et al. 2012 Privon et al. 2015 Chen et al. 2017 Braine et al. 2016 Stephens et al. 2016 Buchbender et al. 2013 Wu et al. 2010 Brouillet et al. 2005 Chin et al. 1997/98 Chen et al. 2017 Braine et al. 2016 Stephens et al. 2016 Buchbender et al. 2013 Wu et al. 2010 Brouillet et al. 2005 Chin et al. 1997/98 Kepley et al. 2014 Bigiel et al. 2015 Usero et al. 2015 EMPIRE galaxies Gallagher et al. 2017 EMPIRE centers Jones et al. 2012 - CMZ Kepley et al. 2014 Bigiel et al. 2015 Usero et al. 2015 EMPIRE galaxies Gallagher et al. 2017 EMPIRE centers Jones et al. 2012 - CMZ

JIMENEZ-DONAIRE ET EMPIRE IN PREP., GALLAGHER+ SUBM, BIGIEL+ ’16, CF. CHEN+ ‘15

• 1. Spectroscopic tracers of cloud structure (e.g., HCN/CO) also

show systematic variations.

• 2. Perhaps surprisingly (or not) SFR per dense gas also shows

substantial variation.

Summary: Dense Gas Tracers

TALKS BY M.ALLAGHER, Y. GAO, TUESDAY