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

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 Frank Bigiel (Univ. of Heidelberg)

There Is Not One Magic Scale/Process Extragalactic (Ionized) Gas Young Stars Gas Accretion Star Formation Diffuse (Atomic) Dense Gas (Molecular) Gas Cloud Structure Cloud Bound Formation (Molecular) Gas

A Molecular Bathtub Extragalactic (Ionized) Gas Young “Cloud (H 2 ) Formation” Stars 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. Diffuse (Atomic) Dense This is basically the classic “star Gas (Molecular) formation threshold.” Gas Bound (Molecular) Gas

From Cold (Bound?) Gas to Stars Extragalactic (Ionized) Gas Young “Molecular SF ‘Law’” Stars In high z galaxies, inner parts of disks, starbursts, galaxy centers, most gas is H 2 already (we think) and “H 2 ” and SF are the most straightforward observables. Diffuse (Atomic) Dense This is the current most commonly Gas (Molecular) studied link at galaxy scales. Gas Bound (Molecular) Gas

But Only Dense Gas Forms Stars Extragalactic (Ionized) Gas Young “Dense Gas Threshold” Stars In the Milky Way stars form overwhelmingly inside the high density parts of a cloud. Linking star formation to the dense structures is a huge part of Galactic star formation. Diffuse (Atomic) Dense This is, e.g., the topic probed by HCN- Gas (Molecular) star formation comparisons. Gas Bound (Molecular) Gas

Understanding These Processes Via Observations H 2 (CO) HI (21-cm) SFR (IR, H α , UV) Dust (IR) Metallicity (spec) UV field (IR) Stars (optical/NIR) Rotation (HI/CO) Dynamics (HI/CO) Cloud Properties

An Incomplete Look at (Some) Gas Scaling Relations Context H 2 – Star Formation H 2 - HI Balance Dense(r) Gas Tracers

Star Formation Occurs in Molecular Gas Azimuthal averages in 30 galaxies SFR Surface Density (UV+IR) [M sun yr -1 kpc -2 ] Atomic Gas (21-cm) Molecular Gas (CO 2-1) Gas Surface Density [M sun pc -2 ] Wong+ ‘02, Kennicutt+ ‘07, S CHRUBA + ’11 , CF . Leroy+ ‘08, Bigiel+ ‘08

Local Disks – Most Apparent Behavior 1-to-1 C OMPILATION FROM L EROY + ‘13

Local Disks – Important Variations 0 log 10 SFR Surface Density (M � yr -1 kpc -2 ) -1 30 galaxies, 1 kpc resolution -2 -3 -1 0 +1 +2 +3 log 10 H 2 Surface Density (M � pc -2 ) L EROY + ’13, S CHRUBA + ‘11, B IGIEL + ‘08

COLD GASS: Clear SFR/CO Correlation with M * S AINTONGE + ’11, ‘12, ’13; L RTOU + ‘13

Early Type Galaxies: Same Qualitative M * Trend D AVIS ET A TLAS -3D ’13; C . F . A LATALO , Y OUNG

Deviations for Low-Mass Galaxies Stellar Mass H 2 Depletion Time (Fixed CO-to-H 2 ) Dust-to-Gas Ratio Each Point: S AINTONGE + ’12, Y OUNG + ’95, L EROY + ’13 Whole-galaxy average

Metallicity/DGR and CO B OLATTO + ’13; CF . S ANDSTROM + ’13

Conversion Factor Across Local Disk Galaxies S ANDSTROM + ‘13

Conversion Factor On Galaxy Scales A CCURSO + ‘17

Application to SF-CO Scaling Relations A CCURSO + ’17 , CF . S AINTONGE + ‘11, S CHRUBA + ’12, B OSELLI + ‘14

Application to SF-CO Scaling Relations A CCURSO + ’17, CF . S CHRUBA + ’12, B OSELLI + ‘14 T HOUGH SEE G ARDAN +’07 B RAINE + ‘11, B OTHWELL + ’14 , H UNT + ’15

SFR-H 2 Variations about a “Normal” Relation

Local Depletion Time and Dynamical Pressure M EIDT ET PAWS ’13 ( PLOT FROM ‘15) , SUBM . D EPENDENCE ON D YNAMICS , CF . E . G . W ANG + ‘13, E LLISON + ’11, R ENAUD + ‘12

Cloud-Scale Structure and Environment K ODA + ’09, C OLOMBO + ‘14 , H UGHES + ‘13, S CHINNERER + ‘13, P ETY + ‘13; M EIDT + ‘13,‘15

P HYSICS AT H IGH A NGULAR R ESOLUTION IN N EARBY G ALAXIES T EAM : 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) O NGOING 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 H α Imaging: Blanc, Groves, Ho T ALK BY I-T ING H O , T UESDAY NOEMA’s biggest mosaic: IC 342 in CO (Schruba, Kruijssen)

Summary: SF-CO Scaling Relations 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)

An Incomplete Look at (Some) Gas Scaling Relations Context H 2 – Star Formation H 2 - HI Balance Dense(r) Gas Tracers

H 2 – HI Balance on Galaxy Scales S AINTONGE + ‘16

H 2 – HI Balance on Galaxy Scales S AINTONGE + ‘16

H 2 – HI Balance Across Local Galaxies Column density predicts H 2 fraction, with HI showing a narrow distribution Molecular to Atomic Gas Ratio HI H 2 S CHRUBA + ‘11; L EROY + ’08; B IGIEL + ’08; L EROY + IN PREP .

H 2 – HI Balance Across Local Galaxies Residuals in H 2 /HI vs. column correlate with dust-to-gas ratio. Divided by Avg. Ratio at that Surface Density Molecular to Atomic Gas Ratio Molecular to Atomic Gas Ratio Down Leroy+ in prep. Physics of HI shielding layer: Krumholz+ ‘09ab, Wolfire+ ’10

H 2 – HI Balance Across Local Galaxies W ONG + ’13 T HEORETICAL P REDICTIONS CF . K RUMHOLZ + ‘09, M C K EE & K RUMHOLZ ‘10

Summary: H 2 -HI Balance 1. H 2 /HI increases strongly with M * for main sequence galaxies 2. Highest sSFR galaxies do not have highest H 2 /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.

An Incomplete Look at (Some) Gas Scaling Relations Context H 2 – Star Formation H 2 - HI Balance Dense(r) Gas Tracers

Dense Gas Tracers in Normal Disk Galaxies Different molecular transitions at λ =3-4mm emit effectively at different densities. Comparing them gives a handle on the density distribution within a beam. R ADEX ( VAN DER TAK ‘07) CALCULATIONS FROM L EROY ET AL . (2017)

Why This is Hard 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. Mean CO CO / 40 Mean HCN Mean HCN D ATA : B IGIEL ET AL . (2016), M APS INTEGRATED FROM P ETY ET AL . (2013)

Surveying Dense Gas Tracers in Normal Disk Galaxies 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. IRAM 30-m 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.). ALMA Ÿ Focal plane array ARGUS now working. Dense gas in other galaxies a key science case (“DEGAS” Large Program PI: Kepley). GBT

Whole Galaxy Maps of Dense Gas Tracers 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, 13 CO, C 18 O in 9 disk galaxies spanning range of properties • Resolution ~ 1 – 2 kpc • Wide suite of ancillary data (radio-UV) • First results 2016. B IGIEL ET AL . 2016, J IMENEZ -D ONAIRE ET AL . 2017 A , B P H D THESIS , C ORMIER + TO BE SUBM ., L EROY + ‘2017, GALLAGHER + SUBM .

Whole Galaxy Maps of Dense Gas Tracers HCN, HCO+, HNC (1-0) mapping of 9 nearby disk galaxies 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. B IGIEL ET AL . 2016, J IMENEZ -D ONAIRE ET AL . 2017 A , B P H D THESIS , C ORMIER + TO BE SUBM ., L EROY + ‘2017, GALLAGHER + SUBM .