Scaling Relations in HI Selected Star-Forming Galaxies Gerhardt R. Meurer The Johns Hopkins University Gerhardt R. Meurer The Johns Hopkins University

Teams 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 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 Ivy Wong: PhD U. Melbourne 2007

Motivation 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 Tracers H  traces O stars M * > 15 M sun 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 M sun Secondary emission IMF sensitive Vacuum UV traces O and B stars Dominates emitted SED of SF pops very sensitive to dust

Selection Blind to optical properties Even sampling of log(M H I ) H I Peak flux > 0.05 Jy Pick nearest galaxies in bins |b| > 30 º ; d LMC > 10 º ; d SMC > 6 º Use H I MF to normalize total SFR. SINGG: 468 selected SUNGG is sub-sample of SINGG (~1/3 sample)

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

Measurements Fluxes from curves of growth (mostly) Rough corrections for dust absorption M R based correction to H  fluxes UV color based correction for Galex fluxes Distance independent SF indicators  SFR - star formation intensity (measured within r e ) EW(H  ) - SF rate w.r.t. past average (measured within r e ) t gas - gas cycling time Fluxes from curves of growth (mostly) Rough corrections for dust absorption M R based correction to H  fluxes UV color based correction for Galex fluxes Distance independent SF indicators  SFR - star formation intensity (measured within r e ) EW(H  ) - SF rate w.r.t. past average (measured within r e ) t gas - gas cycling time

 SFR vs. t gas Only single sources shown t gas ~  SFR r xy = -0.75,  = 0.25 dex H  observations -> HI mass to factor of 1.8

EW correlations Weaker correlations with EW Note narrow range of EW r xy = 0.48r xy = -0.18

Relation to the SF law  SFR correlates with pseudo gas density It correlates better with  R (cf. Dopita et al. 1994) t gas correlates even better with  R  SFR ~  HI 1.06, r xy = 0.59,  = 0.45  SFR ~  R 0.91, r xy = 0.75,  = 0.29 t gas ~  HI -0.64, r xy = -0.77,  = 0.26

Orbital time scale Alternate SF Law - 10% ISM consumption in t orb (Kennicutt 1998) Get t orb from HI line width: assume V rot ~ 0.5W 50 (HI) at r max require a/b > 1.4 Find log(t orb ) = 8.92,  = 0.17 t orb = 840 Myr to factor 1.5 Find log(t orb ) = 8.92,  = 0.17 t orb = 840 Myr to factor 1.5 Disk size set by time since collapse?

 R versus L R 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 L R SF intensity from H  has shallower relation with L R. Low luminosity galaxies “building-up” wrt high luminosity ones Evidence for Downsizing

 SFR (UV) versus L R Surface brightness correlation with L R is weaker and more shallow in the UV Galaxies tend to bigger in the UV Downsizing more prominent in UV Surface brightness correlation with L R is weaker and more shallow in the UV Galaxies tend to bigger in the UV Downsizing more prominent in UV

H  / 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

Summary 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