Post on 05-Jan-2016
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