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Scaling Relations in HI Selected Star-Forming Galaxies

Scaling Relations in HI Selected Star-Forming Galaxies. 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. 2007

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Scaling Relations in HI Selected Star-Forming Galaxies

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

  2. 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. 2007 • Ivy Wong: PhD U. Melbourne 2007

  3. 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

  4. Star 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

  5. Selection • 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)

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

  7. Measurements • 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

  8. SFR 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

  9. EW correlations • Weaker correlations with EW • Note narrow range of EW rxy = 0.48 rxy = -0.18

  10. Relation 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 ~ HI1.06 , rxy = 0.59,  = 0.45 SFR ~ R0.91 , rxy = 0.75,  = 0.29 tgas ~ HI-0.64 , rxy = -0.77,  = 0.26

  11. Orbital 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 • Find log(torb) = 8.92,  = 0.17 • torb = 840 Myr to factor 1.5 Disk size set by time since collapse?

  12. R versusLR • 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)

  13. 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

  14. SFR(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

  15. 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

  16. 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

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