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
- M74 / NGC 628
- M63 / NGC 5055
M99 / NGC 4254
- M95 / NGC 3351
- M94 / NGC 4736
NGC 2146
- NGC 2841
- NGC 3198
- NGC 4536
- NGC 2903
- NGC 4579
- M100 / NGC 4321
- NGC 3521
- NGC 3938
- NGC 4725
- NGC 4569
- NGC 4631
- NGC 5713
- NGC 6946
- NGC 3184
More Big Spiral Galaxies
NGC 7331
- NGC 337
- NGC 4625
- NGC 925
- NGC 3049
Lower Mass
Galaxies
- NGC 4214
- NGC 2976
- NGC 2403
NGC 2798
- NGC 3077
- NGC 4559
- NGC 3190
- DDO 165
- DDO 053
- DDO 154
- Holmberg I
Holmberg II
- IC 2574
- NGC 2366
- M81 Dwarf A
- M81 Dwarf B
- NGC 5457
- NGC 4236
- Only H2
- Only HI
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
- Only H2
- Only HI
- H2 Gas (from CO) Per Area
- HI Gas Per Area
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
- Quantity
- Rcorr with CO/HI
- Control for Total Gas
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
- … gas only
- -0.23
-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)