Dissecting the Red Sequence: Star Formation Histories & Mass to Light Ratios
description
Transcript of Dissecting the Red Sequence: Star Formation Histories & Mass to Light Ratios
Dissecting the Red Sequence:
Star Formation Histories & Mass to Light Ratios
Dissecting the Red Sequence:
Star Formation Histories & Mass to Light Ratios
Genevieve J. GravesUniversity of California, Santa Cruz
with Sandra Faber & Ricardo Schiavon
binning: and Mdyn/Lbinning: and Mdyn/L
Mdyn 2 Re 2
L Ie Re2 IeRe
at fixed , Re :
variations in Ie variations in Mdyn/L
bin by and Mdyn/L
low
high
high Mdyn /L
low Mdyn /L
Metallicity Hyperplane (MHP)Trager et al. (2000)
the metallicity hyperplanethe metallicity hyperplane
Mdyn /L
Md
yn
/L
M
dy
n /L
MHP maps onto FP X-sectionMHP maps onto FP X-section
(Age, [Fe/H]) (, Mdyn /L)
variations in Mdyn /L within Revariations in Mdyn /L within Re
stellar population(age, Z)
Mdyn
L
Mdyn
Mtot
Mtot
M,real
M,real
M,IMF
M,IMF
L= x x x
dynamical mass
estimator
DM fraction IMF
dynamical mass estimatordynamical mass estimator
UW: May 27, 2008
Cappellari et al. (2006) - IFU data, dynamical models Bolton et al. (2007) - strong lensing
SAURON Survey: SLACS Survey:
variations in Mdyn /L within Revariations in Mdyn /L within Re
stellar population(age, Z)
Mdyn
L
Mdyn
Mtot
Mtot
M,real
M,real
M,IMF
M,IMF
L= x x x
dynamical mass
estimator
DM fraction IMF
SLACS, SAURON
the metallicity hyperplanethe metallicity hyperplane
constant M /LBruzual & Charlot (2003)*
M/L vs. Mdyn /LM/L vs. Mdyn /L
M / L*
Mdyn / L
log
M* /
L
log
Md
yn /
L
(SSP)
variations in Mdyn /L within Revariations in Mdyn /L within Re
stellar population(age, Z)
Mdyn
L
Mdyn
Mtot
Mtot
M,real
M,real
M,IMF
M,IMF
L= x x x
dynamical mass
estimator
DM fraction IMF
not enoughSLACS, SAURON
two tilts of the FPtwo tilts of the FP
Stellar Population:M/L
M/L
log
log
Re
log
Re
Dark Matter, IMF: Mdyn / M 2 Re
Mdyn
residual tilt: Mdyn / M
FP midplane
M/L vs. Mdyn /LM/L vs. Mdyn /L
M / L*
Mdyn / L
log
M* /
L
log
Md
yn /
L
observational conclusionsobservational conclusions
• ETG star formation histories = 2-D parameter space(variations with and with Mdyn/L)
• 2-D family of star formation histories = X-section of FP
• Stellar population effects cannot account for observed tiltof the FP, or the observed thickness of the FP
variations in the IMF or central DM fraction requiredhigh Mdyn/M correlated with short duration star formation
• The two tilts of the FP:Stellar population effects (M/L) and variable IMF or DM
fraction (Mdyn/M) tilts rotate the FP around different axes
variations in the IMF?variations in the IMF?
log M (M)
M lo
g (d
N /
d lo
g M
)
0.1 1 10 100
M*/L from Chabrier IMF
need some galaxieswith higher M/L
more at low end
more at high end
high end more attractive to match
[Mg/Fe]
variation in DM fraction?variation in DM fraction?
• genuine lack of stellar mass for given halo mass (low star formation efficiency)
- early truncation of star formation through quenching?(by AGN or massive halo)
• redistribution of stellar and dark matter inside/outside Re
- gas-rich vs. dry mergers?
Mdyn /L is measured within Re
low sf efficiency: halo quenching?low sf efficiency: halo quenching?
0 2 4 6 8z
Cattaneo et al. (2008)
late quenching:high Ie, low Mdyn/L
early quenching:low Ie, high Mdyn/L
naturally produces correlationbetween Mdyn /L , short duration star formation @ fixed
low sf efficiency: AGN feedback?low sf efficiency: AGN feedback?
Nesvadba et al. (2008)
-600
600
0 km/s
Galaxy w/ Powerful Radio Jets @ z=2.4
[OIII]5007 emission:
* aligned w/ radio lobes
* large outflow velocities
* outflow mass-loadingand lifetime can carryout ~ few x 1010 M
SF truncated in high Mdyn/L objects
redistribution of stars?redistribution of stars?
gas fraction
R / Re
log
Md
yn /
M
Robertson et al. (2006)
1%
40%fgas varies w/ mass
contributes to FP tilt
gas fraction of major-merger changes
Mdyn / M
could also have fgas variations @ fixed
FP thickness
~0.2 dex
long-duration SF gas-rich mergers
future workfuture work
• test variable IMF vs. variable DM fraction- look at galaxy cores where DM should be unimportant- look for central starburst contribution from gas-rich merger
(2-component galaxy light profiles)
• chemical evolution models - what forms of variable IMFs match both Mdyn/M and [Mg/Fe]?
• the role of environment: - both merger and massive halo explanations imply environment plays a role - relations for central galaxies vs. satellites
M/L vs. Mdyn /LM/L vs. Mdyn /L
M / L*
Mdyn / L
log
M* /
L
log
Md
yn /
L
(SSP)
M / L*(constant SFR)
M/L from Age, [Fe/H]M/L from Age, [Fe/H]