The Gas Properties of Galaxies

on and off of a Star-Forming Sequence

David Schiminovich + GALEX Science TeamColumbia University

Simple questions…

What determines: - the star formation rate (SFR) of galaxies?- the rate of change of the SFR?

Must be something about the gas…

Measuring Gas in Galaxies:Direct: HI, CO, etc.

Indirect: Star Formation

Schmidt-Kennicutt Law, “Photometric gas fractions” (e.g. Bell et al. 2003, Knappanan 2004, Reddy et al.

2006)

Indirect: Dust Attenuation

(e.g. Wang & Heckman 1996, Bell 2003,GALEX: Johnson et al. 2007, Martin et al. 2007)

Galaxy Distribution in SFR and Stellar Mass:UV-Optical Color Magnitude DistributionWyder et al (2007)

Bivariate Luminosity Function (z~0.1)

GALEX Medium ImagingSurvey + SDSS(sp)

Wyder, Salim, Martin, Schiminovich

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Interpreting the Color-Magnitude Distribution

Faber et al. (2007) DEEP2

Bell et al.(2007)Combo17

UV-Optical Color Magnitude Distribution:Converting to Physical Properties

Schiminovich et al. (2007) submitted

ObservedDistribution- 1/Vmax

- k-corrected

Intrinsic“Dust-corrected”Distribution

UV,cor->SFRMr,cor-> M*

SFR/M* vs. M* Distribution

‘Red locus’: Upper limit to SFR/M*

Star-formingsequence

Schiminovich et al. (2007) submitted

SFR/M* vs. M* distribution derived frommodel star formation histories

Salim et al. (2007)

IdenticalGALEX+SDSS(sp)Data set

SFR/M* vs. M* Distribution:Star-Forming Sequence

Salim et al. (2007)Noeske et al. (2007)

see also Brinchmann et al. (2004), Feulner et al. (2006)

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Noeske et al (2007) AEGIS team

to z~1

SFR zero-pointincreases vs. z

SFR/M* vs. M* Distribution:Star-Forming Sequence Evolution

Properties of galaxies along blue/red sequence: Stellar Mass Surface Density

Properties of galaxies along SF sequence:Half-light radius: r50,i

Properties of galaxies along SF sequence:SFR Surface Density: SFR

see also Hoopes et al. (2007)

Star-forming galaxies distributed around locus of constant SFR vs. M*

Evolves slowly to z~1 (e.g. Somerville et al. 2007)

Same at z~1(e.g. Noeske et al. 2007)

Same at z~1with increasedintensity

See also Hoopes et al. (2007)

May suggest gas ~ const vs. M*

SB ‘intensity limit’ at least x100 higher

SFR/M* vs. M* Distribution:“Disk-dominated” vs. “Bulge-dominated”

galaxies

“Bulge-dominated” (n > 2.4)

“Disk-dominated” (n < 2.4)

Extends to SF sequenceSchiminovich et al. (2007) submitted

SFR/M* Distribution in M* bins: Disk-dominated vs. Bulge Dominated

Will high SFR bulge-dominated galaxies soon transition to the redsequence?

SFR/M* vs. M* Distribution: Flow

Evolution off of the SF sequence

“Green Valley” evolution

Gas may provideinformation about `potential’ for accretion/quenching(direction)

Schiminovich et al. (2007) submitted Martin et al. (2007)

E4NUV-K=4.8

S0NUV-K=4.2

SaNUV-K=3.9

SbNUV-K=2.8

ScNUV-K=0.9

SdNUV-K=0.4

ImNUV-K=-1

GALEX Nearby Galaxy AtlasGil de Paz et al. (2007)

1037 galaxies (900 both FUV+NUV)

mAB ~ 27.5 mag / arcsec sq.SFR/Area ~ 0.001 Msun/kpc2

Combined with M(HI) from literature (+LEDA)- Heterogeneous selection!

SFR/M* and Gas Fraction vs M* SF Sequence and Residual SF

Galaxies

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SF Sequence:Scatter to low gas fraction

NGC 7252

Quenching?

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SFR/M* and Gas Fraction vs M* SF Sequence and Residual SF

Galaxies

Residual SF:Scatter to high gas fraction

Accretion?

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SFR/M* and Gas Fraction vs M* NGC 5701: Residual SF, elev. gas

fractionAccretion?

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SFR/M* and Gas Fraction vs M* NGC 1023: Residual SF, elev. gas

fractionAccretion?

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SFR/M* and Gas Fraction vs M* NGC 1291: Residual SF, elev. gas

fractionAccretion?See e.g.Kauffmannet al. (2007)

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Massive Galaxy Sample (log M*>10) from

SDSS (z<0.05) + GALEX

Green: Morganti et al. (2006)- SauronRed: Oosterloo et al. (2007) - HIPASS

ALFALFA - mostly lower M* SF sequence galaxies from SDSS

Summary and Conclusions UV-optical CMD displays widely separated blue and red sequences and “green valley”. New aspects are:

• Improved measurements of physical quantities

• Identification of ‘locus’ of SF sequence galaxies and associated scaling relations

• New understanding of the volume-weighted distribution and implications for evolutionary scenarios

In Nearby Galaxy sample HI gas fractions correlate with SFR/M*, but with interesting scatter

Gas properties of galaxies near ‘transition mass’ (log M* ~ 10.5) to moderate gas fractions (1-10%)

worth investigating