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

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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 heracles Fabian Walter Erik Rosolowsky MPIA UBC Frank Bigiel Eva Schinnerer UC Berkeley THINGS plus… MPIA Elias Brinks Antonio Usero Gaelle Dumas U Hertfordshire OAN, Madrid MPIA Erwin de Blok Andreas Schruba Helmut Wiesemeyer U Cape Town IRAM … MPIA Rob Kennicutt Axel Weiss Karl Schuster Cambridge MPIfR IRAM Barry Madore Carsten Kramer Karin Sandstrom Carnegie IRAM MPIA Michele Thornley Daniela Calzetti Kelly Foyle Bucknell UMass MPIA Collaborators 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 -2 • Very wide-field (~ r25) and sensitive (σ ~ 1-2 Msun pc ) NGS The HI Nearby Galaxy Survey HI Walter et al. (2008), AJ Special Issue (2008) • VLA HI maps of 34 galaxies: Sa - Irr and T • Resolution ~ 6-10” (100-500 pc) by 5 km s-1 • Sensitivity ~ 5 x1019 cm-2 per channel map HERACLES • Publicly available www.mpia.de/THINGS M51 / NGC 5194 M82 / NGC 3034 M104 / NGC 4594 M74 / NGC 628 M66 / NGC 3627 M63 / NGC 5055 Messier Galaxies M95 / NGC 3351 M94 / NGC 4736 M99 / NGC 4254 NGC 2146 NGC 2841 NGC 3198 NGC 4536 NGC 2903 NGC 4579 M100 / NGC 4321 NGC 3521 NGC 3938 NGC 4725 NGC 4569 Big Spiral Galaxies NGC 4631 NGC 5713 NGC 6946 NGC 3184 More Big Spiral Galaxies NGC 7331 NGC 337 NGC 925 NGC 4625 NGC 3049 Lower Mass Galaxies NGC 4214 NGC 2976 NGC 2403 NGC 3077 NGC 4559 NGC 3190 NGC 2798 DDO 053 DDO 154 DDO 165 Holmberg I Holmberg II IC 2574 NGC 2366 M81 Dwarf A M81 Dwarf B NGC 5457 NGC 4236 Really Little Guys Only H2 Only HI 2 What’s in a gray point? , and H I - 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 Star Formation, H see F. Bigiel talk Only H2 Only HI 2 , and H I Star Formation Rate Per Area Star Formation Rate Per Area H2 Gas (from CO) Per Area HI Gas Per Area Star Formation, H Wong & Blitz ’02, Kennicutt+ ’07, Bigiel+ ‘08 Star Formation and H2 : comparison with Literature 2 Kennicutt ‘98 spirals and bursts; Murgia+ ‘02, Young+ ‘95; Schuster+ ‘07 Kennicutt+ ‘07; Crosthwaite & Turner ‘07; Leroy+ ‘05; circle-stars: LG dwarfs SFR vs. H Gas Depletion Time vs. H2/HI SFR/gas andH -1 Star Formation Rate Per Unit Total (HI+H2) Gas [yr ] 2 /H I H 2 [fromCO]-to-H I Ratio Gas Depletion Time vs. H2/HI SFR/gas andH -1 Star Formation Rate Per Unit Total (HI+H2) Gas [yr ] 2 /H I H 2 [fromCO]-to-H I Ratio So What Sets H2-to-HI? H 2 /H I andRadius H2 [from CO]-to-HI Ratio Galactocentric Radius[r Young+ ‘95, Wong &Blitz ‘02,Heyer+ ‘04 ‘95,Wong Young+ 25 ] H2/HI and Radius I [from CO] or H 2 stacked HI stacked CO “Mass” Surface Density of H Galactocentric Radius [r25] Why We Made Wide Maps Why We Andreas Schruba et al. in prep. H2/HI and Total Gas Surface Density Ratio I ? I [from CO]-to-H -to-H 2 2 H -2 Total (HI + H2) Gas Surface Density [M pc ] So What Sets H Krumholz+ ‘09ab H2/HI vs. Dust to Gas Ratio H 2 /H I andDust-to-GasRatio Draine & Li‘07,Robertson &Kravtsov‘08; Krumholz+‘09ab; Gnedin+ ‘09 H2 [from CO]-to-HI Ratio Dust-to-Gas Ratio [IR+Draine&Li‘07/gasmaps] H2/HI vs. Pressure H 2 /H I andPressure H [from CO]-to-HI Ratio Elmegreen & Parravano ‘94, Wong & Blitz‘02,& Rosolowsky‘04, ‘06 &Parravano ‘94,Wong Elmegreen Midplane Hydrostatic Pressure[cm 2 -3 K]~volumedensity see E.Ostrikertalk H2/HI vs. Qgas H 2 /H I andInstability Martin & Kennicutt ‘01, Wong &Blitz‘02, Kim &Ostriker‘01, ‘07,Boissier+ ‘03 Martin & Kennicutt‘01, Wong H2 [from CO]-to-HI Ratio Toomre’s QParameter [gasonly] H2/HI vs. Qstars+gas H 2 /H I andInstability H2 [from CO]-to-HI Ratio Wang & Silk ‘94, Rafikov ‘01, Boissier+ ‘03, Li+ ‘05,’06, Yang+ ‘07 &Silk ‘94,Rafikov‘01, Boissier+‘03, Li+‘05,’06,Yang+ Wang Toomre’s QParameter [gasandstars] H2/HI vs. Qstars+gas H 2 /H I andInstabilityNowForaFlaringStellarDisk H2 [from CO]-to-HI Ratio Wang & Silk ‘94, Rafikov ‘01, Boissier+ ‘03, Li+ ‘05,’06, Yang+ ‘07 &Silk ‘94,Rafikov‘01, Boissier+‘03, Li+‘05,’06,Yang+ Wang Toomre’s QParameter [gasandstars] see M.MacLowtalk H2/HI vs. Stars H 2 /H I andStars H2 [from CO]-to-HI Ratio Stellar SurfaceDensity [M pc -2 ] H2/HI vs. “Arms” H 2 /H I andAzimuthalStructure Gas DensityEnhancement overAzimuthalAverage [fractional] H2 [from CO]-to-HI Ratio Rank Correlation between X and H2 [from CO]-to-HI Quantity Rcorr with CO/HI Control for Total Gas Total (H2+HI) Gas 0.75 … Radius -0.43 -0.23 Dust-to-Gas Ratio 0.48 0.35 Pressure 0.78 0.29 Stars 0.62 0.34 Q … gas only -0.23 0.29* … gas and stars -0.36 0.33* … gas and stars (flared) -0.50 0.27* Azimuthal Enhancement 0.38 -0.17* * Wrong sense (expect anti-correlation) Numbers! 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 XCO from Dust in the Local Group CO-to-H2 Conversion Factor Local GroupGalaxy (HightoLowMetallicity) see K. Sandstrom andA.Bolattotalks see K.Sandstrom.
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