Scaling Relations in HI Selected Star-Forming Galaxies

Scaling Relations in HI Selected Star-Forming Galaxies

Gerhardt R. MeurerThe Johns Hopkins University

Gerhardt R. MeurerThe Johns Hopkins University

TeamsTeams

SINGG: Survey of Ionization in Neutral Gas Galaxies

SUNGG: Survey of Ultraviolet emission in Neutral Gas Galaxies

The primary workers: Dan Hanish: PhD Johns Hopkins U. 2007 Ivy Wong: PhD U. Melbourne 2007

SINGG: Survey of Ionization in Neutral Gas Galaxies

SUNGG: Survey of Ultraviolet emission in Neutral Gas Galaxies

The primary workers: Dan Hanish: PhD Johns Hopkins U. 2007 Ivy Wong: PhD U. Melbourne 2007

MotivationMotivation

Study SF properties in a sample not biased by optical selection

Determine how SF relates to observed HI and stellar content

Compare to well known sequences Probe the SF law Use multiple SF tracers to probe the IMF

Study SF properties in a sample not biased by optical selection

Determine how SF relates to observed HI and stellar content

Compare to well known sequences Probe the SF law Use multiple SF tracers to probe the IMF

Star Formation TracersStar Formation Tracers

H traces O stars M* > 15 Msun

Secondary emission IMF sensitive

Vacuum UV traces O and B stars Dominates emitted

SED of SF pops very sensitive to dust

H traces O stars M* > 15 Msun

Secondary emission IMF sensitive

Vacuum UV traces O and B stars Dominates emitted

SED of SF pops very sensitive to dust

SelectionSelection

Blind to optical properties Even sampling of log(MHI) HI Peak flux > 0.05 Jy Pick nearest galaxies in bins

|b| > 30º; dLMC > 10º; dSMC > 6º Use HIMF to normalize total

SFR. SINGG: 468 selected SUNGG is sub-sample of

SINGG (~1/3 sample)

Blind to optical properties Even sampling of log(MHI) HI Peak flux > 0.05 Jy Pick nearest galaxies in bins

|b| > 30º; dLMC > 10º; dSMC > 6º Use HIMF to normalize total

SFR. SINGG: 468 selected SUNGG is sub-sample of

SINGG (~1/3 sample)

ObservationsObservations

Ha : CTIO 1.5m, 0.9m (also CTIO Schmidt, ANU 2.3m) UV : Galex FIR : IRAS HI : Parkes 64m (single dish)

Ha : CTIO 1.5m, 0.9m (also CTIO Schmidt, ANU 2.3m) UV : Galex FIR : IRAS HI : Parkes 64m (single dish)

MeasurementsMeasurements

Fluxes from curves of growth (mostly)

Rough corrections for dust absorption

MR based correction to H fluxes

UV color based correction for Galex fluxes

Distance independent SF indicators

SFR - star formation intensity (measured within re)

EW(H) - SF rate w.r.t. past average (measured within re)

tgas - gas cycling time

Fluxes from curves of growth (mostly)

Rough corrections for dust absorption

MR based correction to H fluxes

UV color based correction for Galex fluxes

Distance independent SF indicators

SFR - star formation intensity (measured within re)

EW(H) - SF rate w.r.t. past average (measured within re)

tgas - gas cycling time

SFR vs. tgasSFR vs. tgas

Only single sources shown

tgas ~ SFR-0.77

rxy = -0.75 , = 0.25 dex

H observations -> HI mass to factor of 1.8

Only single sources shown

tgas ~ SFR-0.77

rxy = -0.75 , = 0.25 dex

H observations -> HI mass to factor of 1.8

EW correlationsEW correlations

Weaker correlations with EW Note narrow range of EW

Weaker correlations with EW Note narrow range of EW

rxy = 0.48 rxy = -0.18

Relation to the SF lawRelation to the SF law

SFR correlates with pseudo gas density It correlates better with R (cf. Dopita et al. 1994)

tgas correlates even better with R

SFR correlates with pseudo gas density It correlates better with R (cf. Dopita et al. 1994)

tgas correlates even better with R

SFR ~ HI1.06 , rxy = 0.59, = 0.45

SFR ~ R0.91 , rxy = 0.75, = 0.29

tgas ~ HI-0.64 , rxy = -0.77, = 0.26

Orbital time scaleOrbital time scale

Alternate SF Law - 10% ISM consumption in torb (Kennicutt 1998)

Get torb from HI line width: assume Vrot ~ 0.5W50(HI) at rmax

require a/b > 1.4

Alternate SF Law - 10% ISM consumption in torb (Kennicutt 1998)

Get torb from HI line width: assume Vrot ~ 0.5W50(HI) at rmax

require a/b > 1.4

Find log(torb) = 8.92, = 0.17

torb = 840 Myr to factor 1.5

Find log(torb) = 8.92, = 0.17

torb = 840 Myr to factor 1.5

Disk size set by time since collapse?

R versus LRR versus LR

Luminosity - surface brightness relation confirmed

Extends to fainter levels than probed by SDSS (Kauffmann et al, 2003, MNRAS, 341, 54)

Slope, R dispersion: 0.54 , 0.39 (OLS bissector)

0.40 , 0.36 (OLS Y|X)

Luminosity - surface brightness relation confirmed

Extends to fainter levels than probed by SDSS (Kauffmann et al, 2003, MNRAS, 341, 54)

Slope, R dispersion: 0.54 , 0.39 (OLS bissector)

0.40 , 0.36 (OLS Y|X)

SFR(H) versus LR SFR(H) versus LR

SF intensity from H has shallower relation with LR.

Low luminosity galaxies “building-up” wrt high luminosity ones

Evidence for Downsizing

SF intensity from H has shallower relation with LR.

Low luminosity galaxies “building-up” wrt high luminosity ones

Evidence for Downsizing

SFR(UV) versus LRSFR(UV) versus LR

Surface brightness correlation with LR is weaker and more shallow in the UV

Galaxies tend to bigger in the UV

Downsizing more prominent in UV

Surface brightness correlation with LR is weaker and more shallow in the UV

Galaxies tend to bigger in the UV

Downsizing more prominent in UV

H / UV ratioH / UV ratio

The H/UV ratio ranges by a factor of ~10

Correlates with H surface brightness

Fractional content of O stars highest at high SF intensity

Implies that the IMF is not constant

The H/UV ratio ranges by a factor of ~10

Correlates with H surface brightness

Fractional content of O stars highest at high SF intensity

Implies that the IMF is not constant

SummarySummary SF properties tightly correlated with HI and stellar content

Both ISM and stars important for SF law Galaxies rotate in synchronicity

Outer disk size set by time since collapse SF intensity has shallower correlation with luminosity than

does stellar surface brightness lower luminosity galaxies less evolved (downsizing)

The H/UV ratio depends on SF intensity The IMF is not constant

SF properties tightly correlated with HI and stellar content Both ISM and stars important for SF law

Galaxies rotate in synchronicity Outer disk size set by time since collapse

SF intensity has shallower correlation with luminosity than does stellar surface brightness lower luminosity galaxies less evolved (downsizing)

The H/UV ratio depends on SF intensity The IMF is not constant