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]