1. Dissecting the Red Sequence: Star Formation Histories & Mass to Light Ratios
Genevieve J. Graves
University of California, Santa Cruz
with Sandra Faber & Ricardo Schiavon

2. variations in Ie  variations in Mdyn/L
binning:  and Mdyn/L
at fixed , Re :
variations in Ie  variations in Mdyn/L
Mdyn 2 Re 2
L Ie Re IeRe 
bin by  and Mdyn/L

3. the metallicity hyperplane
Metallicity Hyperplane (MHP)
Trager et al. (2000)
high Mdyn /L
low Mdyn /L
low 
high 

4. MHP maps onto FP X-section
 Mdyn /L
  Mdyn /L
(Age, [Fe/H]) (, Mdyn /L) 
Mdyn /L

5. variations in Mdyn /L within Re
Mtot
M,real
M,IMF = x
dynamical
mass
estimator
DM fraction
IMF
stellar population
(age, Z)

6. dynamical mass estimator
SAURON Survey:
SLACS Survey:
Cappellari et al. (2006) - IFU data, dynamical models
Bolton et al. (2007) - strong lensing
UW: May 27, 2008

7. variations in Mdyn /L within Re
SLACS, SAURON
Mdyn L
Mtot
M,real
M,IMF = x
dynamical
mass
estimator
DM fraction
IMF
stellar population
(age, Z)

8. the metallicity hyperplane
constant M /L
Bruzual & Charlot (2003) *

9. M/L vs. Mdyn /L
M / L *
Mdyn / L
(SSP)
log Mdyn / L
log M* / L

10. variations in Mdyn /L within Re
SLACS, SAURON
not enough
Mdyn L
Mtot
M,real
M,IMF = x
dynamical
mass
estimator
DM fraction
IMF
stellar population
(age, Z)

11. two tilts of the FP FP midplane Stellar Population: M/L   M/L
log Re
Stellar Population:
M/L
M/L  
residual tilt: Mdyn / M
log Re
Dark Matter, IMF:
Mdyn / M  2 Re
 Mdyn
log 

12. M/L vs. Mdyn /L
M / L *
Mdyn / L
log Mdyn / L
log M* / L

13. observational 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 tilt
of the FP, or the observed thickness of the FP
variations in the IMF or central DM fraction required
high 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

14. variations in the IMF? M log (dN / d log M) log M (M) more at low end
M*/L from Chabrier IMF
need some galaxies
with higher M/L
M log (dN / d log M)
more at high end
high end more
attractive to match
[Mg/Fe]
log M (M)

15. variation in DM fraction?
 Mdyn /L is measured within Re
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?

16. low sf efficiency: halo quenching?
early quenching:
low Ie, high Mdyn/L
Cattaneo et al. (2008)
late quenching:
high Ie, low Mdyn/L
naturally produces correlation
between Mdyn /L , short duration
star fixed  z

17. low sf efficiency: AGN feedback?
Galaxy w/ Powerful Radio
z=2.4
[OIII]5007 emission:
* aligned w/ radio lobes
* large outflow velocities
* outflow mass-loading
and lifetime can carry
out ~ few x 1010 M
Nesvadba et al. (2008)
-600
600
0 km/s
SF truncated in
high Mdyn/L objects

18. redistribution of stars?
gas fraction of
major-merger changes
Mdyn / M
gas fraction 1%
~0.2 dex
fgas varies w/ mass
 contributes to FP tilt
40%
log Mdyn / M
could also have fgas fixed 
 FP thickness
long-duration SF  gas-rich mergers
R / Re
Robertson et al. (2006)

19. future 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

20. M/L vs. Mdyn /L * * M / L (constant SFR) M / L Mdyn / L (SSP)
log Mdyn / L
log M* / L

21. M/L from Age, [Fe/H]