The HERACLES View of the H -To-HI Ratio in Galaxies

The HERACLES View of the H2-to-HI Ratio in Galaxies Adam Leroy (NRAO, Hubble Fellow) Fabian Walter, Frank Bigiel, the HERACLES and THINGS teams The Saturday Morning Summary •ꢀStar formation rate vs. gas relation on ~kpc scales breaks apart into: ꢀA relatively universal CO-SFR relation in nearby disks ꢀSystematic environmental scalings in the CO-to-HI ratio •ꢀThe CO-to-HI ratio is ꢀa strong function of radius, total gas, and stellar surface density ꢀcorrelated with ISM properties: dust-to-gas ratio, pressure ꢀharder to link to dynamics: gravitational instability, arms •ꢀInterpretation: ꢀthe CO-to-HI ratio traces the efficiency of GMC formation ꢀDensity and dust can explain much of the observed behavior heraclesꢀ Fabian Walter Erik Rosolowsky MPIA UBC Frank Bigiel Eva Schinnerer UC Berkeley THINGS plus… MPIA Elias Brinks Gaelle Dumas Antonio Usero U Hertfordshire MPIA OAN, Madrid Erwin de Blok Helmut Wiesemeyer Andreas Schruba U Cape Town IRAM MPIA Rob Kennicutt Karl Schuster Axel Weiss Cambridge IRAM MPIfR Barry Madore Karin Sandstrom Carsten Kramer Carnegie MPIA IRAM Michele Thornley Kelly Foyle Daniela Calzetti Bucknell MPIA UMass The HERA CO-Line Extragalactic Survey First maps Leroy et al. (2009) •ꢀIRAM 30m Large Program to map CO J = 2→1 line •ꢀInstrument: HERA receiver array operating at 230 GHz •ꢀ47 galaxies: dwarfs to starbursts and massive spirals •ꢀVery wide-field (~ r25) and sensitive (σ ~ 1-2 Msun pc-2) The HI Nearby Galaxy Survey Walter et al. (2008), AJ Special Issue (2008) •ꢀVLA HI maps of 34 galaxies: Sa - Irr •ꢀResolution ~ 6-10” (100-500 pc) by 5 km s-1 •ꢀSensitivity ~ 5 x1019 cm-2 per channel map •ꢀPublicly available www.mpia.de/THINGS M51 / NGC 5194 M82 / NGC 3034 M104 / NGC 4594 M66 / NGC 3627 <ul style="display: flex;"><li style="flex:1">M74 / NGC 628 </li><li style="flex:1">M63 / NGC 5055 </li></ul>M99 / NGC 4254 <ul style="display: flex;"><li style="flex:1">M95 / NGC 3351 </li><li style="flex:1">M94 / NGC 4736 </li></ul>NGC 2146 <ul style="display: flex;"><li style="flex:1">NGC 2841 </li><li style="flex:1">NGC 3198 </li><li style="flex:1">NGC 4536 </li></ul><ul style="display: flex;"><li style="flex:1">NGC 2903 </li><li style="flex:1">NGC 4579 </li><li style="flex:1">M100 / NGC 4321 </li></ul><ul style="display: flex;"><li style="flex:1">NGC 3521 </li><li style="flex:1">NGC 3938 </li><li style="flex:1">NGC 4725 </li><li style="flex:1">NGC 4569 </li></ul><ul style="display: flex;"><li style="flex:1">NGC 4631 </li><li style="flex:1">NGC 5713 </li></ul><ul style="display: flex;"><li style="flex:1">NGC 6946 </li><li style="flex:1">NGC 3184 </li></ul>More Big Spiral Galaxies NGC 7331 <ul style="display: flex;"><li style="flex:1">NGC 337 </li><li style="flex:1">NGC 4625 </li></ul><ul style="display: flex;"><li style="flex:1">NGC 925 </li><li style="flex:1">NGC 3049 </li></ul>Lower Mass Galaxies <ul style="display: flex;"><li style="flex:1">NGC 4214 </li><li style="flex:1">NGC 2976 </li><li style="flex:1">NGC 2403 </li></ul>NGC 2798 <ul style="display: flex;"><li style="flex:1">NGC 3077 </li><li style="flex:1">NGC 4559 </li><li style="flex:1">NGC 3190 </li></ul><ul style="display: flex;"><li style="flex:1">DDO 165 </li><li style="flex:1">DDO 053 </li><li style="flex:1">DDO 154 </li><li style="flex:1">Holmberg I </li></ul>Holmberg II <ul style="display: flex;"><li style="flex:1">IC 2574 </li><li style="flex:1">NGC 2366 </li></ul><ul style="display: flex;"><li style="flex:1">M81 Dwarf A </li><li style="flex:1">M81 Dwarf B </li><li style="flex:1">NGC 5457 </li><li style="flex:1">NGC 4236 </li></ul><ul style="display: flex;"><li style="flex:1">Only H2 </li><li style="flex:1">Only HI </li></ul>What’s in a gray point? -ꢀIndividual data from 23 galaxies. -ꢀPicked to have HI and metals -ꢀ13” resolution ~ Nyquist sampled. -ꢀc. 30k independent measurements. -ꢀRed points: median and 1σ scatter see F. Bigiel talk <ul style="display: flex;"><li style="flex:1">Only H2 </li><li style="flex:1">Only HI </li></ul><ul style="display: flex;"><li style="flex:1">H2 Gas (from CO) Per Area </li><li style="flex:1">HI Gas Per Area </li></ul>Wong & Blitz ’02, Kennicutt+ ’07, Bigiel+ ‘08 Star Formation and H2 Kennicutt ‘98 spirals and bursts; Murgia+ ‘02, Young+ ‘95; Schuster+ ‘07 Kennicutt+ ‘07; Crosthwaite & Turner ‘07; Leroy+ ‘05; circle-stars: LG dwarfs SFR/gas and H2/HI H2 [from CO]-to-HI Ratio SFR/gas and H2/HI H2 [from CO]-to-HI Ratio H2/HI and Radius Galactocentric Radius [r25] Young+ ‘95, Wong & Blitz ‘02, Heyer+ ‘04 H2/HI and Radius stacked HI stacked CO Galactocentric Radius [r25] Andreas Schruba et al. in prep. H2/HI and Total Gas Surface Density Total (HI + H2) Gas Surface Density [M pc-2] Krumholz+ ‘09ab H2/HI and Dust-to-Gas Ratio Dust-to-Gas Ratio [IR + Draine & Li ‘07 / gas maps] Draine & Li ‘07, Robertson & Kravtsov ‘08; Krumholz+ ‘09ab; Gnedin+ ‘09 see E. Ostriker talk H2/HI and Pressure Midplane Hydrostatic Pressure [cm-3 K] ~ volume density Elmegreen & Parravano ‘94, Wong & Blitz ‘02, Blitz & Rosolowsky ‘04, ‘06 H2/HI and Instability Toomre’s Q Parameter [gas only] Martin & Kennicutt ‘01, Wong & Blitz ‘02, Kim & Ostriker ‘01, ‘07, Boissier+ ‘03 H2/HI and Instability Toomre’s Q Parameter [gas and stars] Wang & Silk ‘94, Rafikov ‘01, Boissier+ ‘03, Li+ ‘05,’06, Yang+ ‘07 see M. Mac Low talk H2/HI and Instability Now For a Flaring Stellar Disk Toomre’s Q Parameter [gas and stars] Wang & Silk ‘94, Rafikov ‘01, Boissier+ ‘03, Li+ ‘05,’06, Yang+ ‘07 H2/HI and Stars Stellar Surface Density [M pc-2] H2/HI and Azimuthal Structure Gas Density Enhancement over Azimuthal Average [fractional] Rank Correlation between X and H2 [from CO]-to-HI <ul style="display: flex;"><li style="flex:1">Quantity </li><li style="flex:1">Rcorr with CO/HI </li><li style="flex:1">Control for Total Gas </li></ul>Total (H2+HI) Gas Radius 0.75 -0.43 0.48 0.78 0.62 … -0.23 0.35 0.29 0.34 Dust-to-Gas Ratio Pressure Stars Q<ul style="display: flex;"><li style="flex:1">… gas only </li><li style="flex:1">-0.23 </li></ul>-0.36 -0.50 0.38 0.29* 0.33* 0.27* -0.17* … gas and stars … gas and stars (flared) Azimuthal Enhancement * Wrong sense (expect anti-correlation) Summary •ꢀStar formation rate vs. gas relation on ~kpc scales breaks apart into: ꢀA relatively universal CO-SFR relation in nearby disks ꢀSystematic environmental scalings in the CO-to-HI ratio •ꢀThe CO-to-HI ratio is ꢀa strong function of radius, total gas, and stellar surface density ꢀclearly correlated with ISM properties: dust-to-gas ratio, pressure ꢀhard to link to dynamics: gravitational instability, arms •ꢀInterpretation: ꢀthe CO-to-HI ratio traces the efficiency of GMC formation ꢀDensity and dust can explain much of the observed behavior see K. Sandstrom and A. Bolatto talks Local Group Galaxy (High to Low Metallicity)

The HERACLES View of the H -To-HI Ratio in Galaxies

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