Dense Gas and Star Formation in Nearby Galaxies EMIR Multi-line Probe of the ISM Regulating Galaxy Evolution (EMPIRE)

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1 Dense Gas and Star Formation in Nearby Galaxies EMIR Multi-line Probe of the ISM Regulating Galaxy Evolution (EMPIRE) Henrik Beuther on behalf of: Frank Bigiel (ZAH, Univ. of Heidelberg) A. Leroy, A. Usero, F. Walter, D. Cormier, M. Jiminez, K. Schuster, S. Garcia- Burillo, C. Kramer, J. Pety, K. Sandstrom, E. Schinnerer, A. Hughes, A. Kepley, A. BolaDo, A. Schruba, G. Dumas, L. Zschaechner

2 Dense Gas and Star Formation Gao & Solomon (2004): Linear correlation of HCN and IR across a wide range of systems (in contrast to CO) argues for a universal dense gas precondition for star formation.

3 Dense Gas in Milky Way Cores Wu et al. (2005): The scaling in Galactic cores resembles that in whole bright systems.

4 Dense Gas, Filaments, and Galaxies Lada et al. (2012, 2014): HCN-IR correlation invoked along with local clouds to again argue for a universal dense gas efficiency based on similarities to local clouds. See also Heiderman et al. (2010), Evans et al. (2014)

5 Differences Among Galaxy Populations Garcia-Burillo et al. 2012: HCN and HCO+ vs. IR relations for disk-averaged starbursts (LIRG) and normal star forming galaxies appear different, especially accounting for conversion factors.

6 EMPIRE Pilot Study M51 HCN, HCO+, HNC (1-0) mapping of the entire M51 disk EMIR Multi-line Probe of the ISM Regulating Galaxy Evolution PI: F. Bigiel, IRAM Large Program ~ , ~440 hr Full galaxy maps of HCN, HCO+, CS, 13 CO, C 18 O in 9 disk galaxies Additional lines accessible via stacking (e.g. C 2 H, N 2 H +, etc.) Status: 3 galaxies completed First results 2015 work in progress Bigiel et EMPIRE (in prep.)

7 EMPIRE Pilot Study M51 Wide suite of ancillary data, incl. HI, all lower-j CO lines, IR, optical, UV Many quantities known across these galaxies from previous work (gas and stellar surface densities, gas kinematics, dust-to-gas ratios, etc.) CO(2-1) HI Kinematics Near-IR UV, Hα, 24µm M51

8 Case Study: Dense Gas in the Antennae Galaxies Provide context for the EMPIRE disks: dense gas and star formation in a major merger CARMA observations of 12 CO(1-0) and HCN(1-0), HCO + (1-0), HNC(1-0), CS(2-1) Dense gas tracers detected in 5 regions CO(2-1) HI Kinematics Near-IR UV, Hα, 24µm M51 HCN(1-0) contours 12 CO(1-0) contours PACS 70µm HST, Whitmore+ '10 Bigiel+ subm.

9 Filling in the Luminosity Gap Points fill in luminosity range between whole galaxies and clouds big parts of disks. New data: Disk pointings (Usero et al.) EMPIRE pilot: M51 pixels Antenna pointings

10 All Just Dense Gas? HCN in Normal Disk Galaxies Apparent dense gas fraction predicts apparent bulk mol. gas depletion time but with huge scatter. Disk pointings M51 pixels M82 regions Antenna pointings

11 Dense Gas Fraction in M51 Apparent dense gas fraction function of local conditions, here: stellar surface density (~galactocentric radius) Disk pointings M51 pixels Usero et al. accepted + Bigiel et al. (in prep.)

12 Dense Gas Star Formation Efficiency in M51 But! The IR-to-HCN ratio varies systematically as a function of local disk structure (stellar surface density, radius, etc. here stellar surface density). Dense gas is less good at forming stars in overall denser regions. Disk Survey M51 bins M51 points IR-to-HCN vs Stellar Surface Density Gray points: 1 kpc, Red points: binned data Usero et al. accepted; M51: Bigiel et al. (in prep.)

13 Summary & Discussion Points Large program EMPIRE underway new survey of dense gas tracers and optically thin CO lines across 9 galaxy disks First results from pilot programs (disk pointings: Usero+ accep., M51 map: Bigiel+ subm.& in prep., see also Kepley+ 2014): Observe systematic trends in IR-to-HCN ( dense gas efficiency ) and HCN-to-CO ( dense gas fraction ) as a function of surface density, molecular fraction. Consistent with Garcia-Burillo et al. (2012), Longmore et al. (2013). May weaken the extragalactic component of the simple density threshold model for star formation popular in the Galactic community. Very specific behavior of the HCN-to-dense gas conversion factor needed to save a universal density threshold (see Usero et al. accepted, on astroph shortly) Will be explored further in EMPIRE, along with drivers for IR-to-HCN and HCN-to-CO across disks and along with more detailed modeling of the physical conditions in the bulk molecular gas (CO lines)