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

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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 [Mpc-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 [Mpc-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)

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