Testing Drivers for Star Formation in Galaxies

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Testing Drivers for Star Formation in Galaxies
Adam Leroy (MPIA?NRAO, Hubble Fellow) Fabian
Walter (MPIA) Frank Bigiel (UC Berkeley) The
THINGS and HERACLES teams
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The HERA CO-Line Extragalactic Survey
HERACLES
Leads A. Leroy F. Walter Team F. Bigiel, E.
Brinks, W.J.G. de Blok, G. Dumas, D. Calzetti, R.
C. Kennicutt, C. Kramer, H-W Rix, E. Schinnerer,
A. Schruba, K.-F. Schuster, A. Usero, A. Weiss,
H. Wiesemeyer
HERACLES

• IRAM 30m maps of CO J 2?1 line (500h)
• Targets heavily overlap THINGS, SINGS, KINGFISH
• 44 galaxies from dwarfs to starbursts and
  massive spirals
• Very wide-field ( r25) and sensitive (? 2
  Msun pc-2)
• Public release end of 2010

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Current Status of Heracles
NGC 0925
NGC 2146
NGC 0337
NGC 0628
NGC 2403
NGC 2841
NGC 2903
NGC 2798
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Current Status of Heracles
NGC 3184
NGC 3198
NGC 2976
NGC 3049
NGC 3938
NGC 4214
NGC 3351
NGC 3521
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Current Status of Heracles
NGC 4321
NGC 4536
NGC 4579
NGC 4254
NGC 7331
NGC 5194
NGC 6946
Schuster 07
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Current Status of Heracles
NGC 4736
NGC 5055
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Current Status of Heracles
DDO 053
DDO 154
DDO 165
M81 Dwarf A
M81 Dwarf B
NGC 2366
Holmberg I
Holmberg II
IC 2574
NGC 4236
NGC 4625
NGC 5474
Low mass, low metallicity nondections (actually
super interesting, but a story for another talk)
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Data Sets
SINGS Kennicutt 03
HERACLES Leroy 09
GALEX NGS Gil de Paz 07
THINGS Walter 08
ISM and Star Formation
Interpretation
Zibetti 09 Bottema 93 Kregel 05 Bell 03
de Blok 08 Tamburro 09
Draine Li 07 Draine 07
Calzetti 07 Salim 07 Kennicut 98
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Where is the ISM Good At Forming Stars?

• Three easy answers
• phase (HI vs. H2)
• radius
• gas surface density
• A deeper look
• dust-to-gas ratio (metallicity)
• hydrostatic pressure
• gravitational instability
• spiral structure

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Star Formation and H2 traced by CO
SFR vs. H2 in HERACLES
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Star Formation and H2 traced by CO

• Individual data from 23 galaxies.
• 13 resolution Nyquist sampled.
• c. 30k independent measurements.

SFR vs. H2 in HERACLES
Whats in a gray point?
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Star Formation and H2 traced by CO
SFR vs. H2 in HERACLES
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Star Formation and HI
SFR vs. HI
Hunter Elmegreen 98, Wong Blitz 02,
Kennicutt 07, Bigiel 08
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SFR/gas and H2/HI
Star Formation Efficiency vs. H2/HI
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H2/HI and Radius
Rmol vs. Radius
Young 95, Wong Blitz 02, Heyer 04
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H2/HI and Gas Surface Density
Rmol vs. Gas
Krumholz 09ab
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Where is the ISM Good At Forming Stars?

• Three easy answers
• phase (HI vs. H2)
• radius
• gas surface density
• A deeper look
• dust-to-gas ratio (metallicity)
• hydrostatic pressure
• gravitational instability
• spiral structure

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H2/HI and Gas Surface Density
H2/HI vs. Gas
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H2/HI and Gas Surface Density
Where the Action is
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H2/HI and Dust-to-Gas Ratio (over a narrow range
of ?gas)
H2/HI vs. DGR over 8 - 20 Msun pc-2
Draine Li 07 (dust), Robertson Kravtsov 08
Krumholz 09ab Gnedin 09
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H2/HI and Pressure (over a narrow range of ?gas)
H2/HI vs. Pressure over 8 - 20 Msun pc-2
Elmegreen Parravano 94, Wong Blitz 02,
Blitz Rosolowsky 04, 06
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H2/HI and Instability (over a narrow range of
?gas)
H2/HI vs. Qgas over 8 - 20 Msun pc-2
Martin Kennicutt 01, Wong Blitz 02, Kim
Ostriker 01, 07, Boissier 03
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H2/HI and Instability (over a narrow range of
?gas)
H2/HI vs. Qstarsgas over 8 - 20 Msun pc-2
Wang Silk 94, Rafikov 01, Boissier 03, Li
05,06, Yang 07
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H2/HI and Radius (for Arm and Interarm Regions)
Spiral Shocks?
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H2/HI and Gas Surface Density (for Arm and
Interarm Regions)
Spiral Shocks?
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Where is the ISM Good At Forming Stars?

• The ISM is good at forming stars where gas is
  molecular.
• Gas is molecular
• where the total gas surface density is high.
• in the inner parts of galaxies.
• For gas surface densities near Rmol H2/HI 1
  
• dust-to-gas ratio and pressure correlate with
  Rmol.
• disks marginally stable, Q shows weak/anti
  correlation with Rmol.
• spiral arms enhanced Rmol just a result of
  higher ?gas ?
• H2 formation driven by ISM physics, only
  indirectly by large-scale processes

Leroy, Walter, Brinks, Bigiel, de Blok, Madore,
Thornley, 2008, AJ, 136, 278 ( new stuff)