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 Collaborators… Erwin deBlok U Hertfordshire Elias Brinks UC Berkeley Frank Bigiel MPIA Fabian Walter Bucknell Michele Thornley Carnegie Barry Madore Cambridge Rob Kennicutt U CapeTown
UMass Daniela Calzetti IRAM Carsten Kramer MPIfR Axel Weiss MPIA Andreas Schruba OAN, Madrid Antonio Usero THINGS plus…
hera
cles
MPIA Kelly Foyle MPIA Karin Sandstrom IRAM Karl Schuster IRAM Helmut Wiesemeyer MPIA Gaelle Dumas MPIA Eva Schinnerer UBC Erik Rosolowsky
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 M51 /NGC M95 / NGC 3351 M95 /NGC M74 / NGC 628 M74 /NGC M82 / NGC 3034 /NGC M82 M66 / NGC 3627 M66 /NGC M94 / NGC 4736 M94 /NGC M63 / NGC 5055 M63 /NGC M104 4594 /NGC M99 / NGC 4254 M99 /NGC
Messier Galaxies NGC 3521 NGC NGC 2903 NGC NGC 2146 NGC NGC 3938 NGC NGC 2841 NGC NGC 4579 NGC NGC 4725 NGC NGC 3198 NGC M100 4321 /NGC NGC 4569 NGC NGC 4536 NGC
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 M81 Dwarf A Dwarf M81 DDO 053 DDO Holmberg II II Holmberg M81 Dwarf B Dwarf M81 DDO 154 DDO IC 2574 IC NGC 5457 NGC DDO 165 DDO NGC 2366 NGC NGC 4236 NGC Holmberg I Holmberg
Really Little Guys Star Formation, HI, and H2 Only H - - - - - PickedtohaveHIandmetals Individualdatafrom 23galaxies. c.30kindependentmeasurements. 13”resolution ~Nyquistsampled. Red points 2
What’s inagraypoint? : medianand1 σ scatter Only H I
Star Formation, HI, and H2
Star Formation Rate Per Area H Only H 2 Gas(fromCO)PerArea 2
Wong &Blitz’02,Kennicutt+ ’07,Bigiel+ ‘08
Star Formation Rate Per Area H I GasPerArea see F. Bigieltalk Only H I
SFR vs. H2 : comparison with Literature Star FormationandH Kennicutt+ ‘07 Kennicutt ‘98spirals 2
; Crosthwaite &Turner‘07 and bursts; Murgia+ ‘02,Young+ ‘95 ; Leroy+ ‘05 ; circle-stars: LGdwarfs ; Schuster+ ‘07
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 SFR/gas and H2/HI ] -1 ) Gas [yr 2 +H I I /H 2 Star Formation Rate Per Unit Total (H
H2 [from CO]-to-HI Ratio Gas Depletion Time vs. H 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 25 ]
Why We Made Wide Maps H 2 /H I andRadius
“Mass” Surface Density of H2 [from CO] or HI Galactocentric Radius[r Andreas Schruba etal.inprep. 25 ] stacked CO stacked HI
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,Blitz&Rosolowsky ‘04,‘06 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
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 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 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 Numbers! Rank CorrelationbetweenXandH Dust-to-Gas Ratio Radius Total (H Quantity Azimuthal … gasandstars(flared) … gasandstars … gasonly Q Stars Pressure 2 +H Enhancement I ) Gas R corr withCO/H -0.50 -0.36 -0.23 -0.43 0.38 0.62 0.78 0.48 0.75 2 [fromCO]-to-HI I (expect anti-correlation) * Wrong sense Control forTotal Gas -0.17* 0.27* 0.33* 0.29* -0.23 0.34 0.29 0.35 … 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 Conversion Factor 2 CO-to-H from Dust in the Local Group Dust in the Local Group from
CO Local Group Galaxy (High to Low Metallicity) X