Dissecting the Red Sequence:

Stellar Population Properties in Fundamental Plane Space

Dissecting the Red Sequence:

Stellar Population Properties in Fundamental Plane Space

Genevieve J. Graves, S. M. FaberUniversity of California, Santa Cruz

with Ricardo Schiavon

zoo of ETG scaling lawszoo of ETG scaling laws

Early Type Galaxy (ETG) scaling laws:

Fundamental PlaneColor - Magnitude Mg - Metallicity - LuminosityM* /L - Letc…

structurevs.

stellar populations

ETG structure:the fundamental plane

ETG structure:the fundamental plane

Virial Thm:

GM / Re 2

M 2 Re

Definition:

Ie L / Re2

L Re2 Ie

If M / L = const.:

M L

Jorgensen et al. (1996)

2 Re Re2 Ie

Re 2 Ie-1

Observed FP is “tilted” from the virial plane

Age-metallicity hyperplaneAge-metallicity hyperplane

Trager et al., AJ, 120, 165, 2001: 50 local ellipticals

* High-S/N spectra from Gonzalez (1993)

* Age and Z from H, Mg b, Fe5270, and F5335

Older >>

Me

tal-r

ich

>>

Lines of constant

Color-mag- hyperplaneColor-mag- hyperplane

Color-magnitude relation

Color- relation

-magnitude relation

Graves, Faber & Schiavon (2008c, ApJ, in press)

zoo of ETG scaling lawszoo of ETG scaling laws

Early Type Galaxy (ETG) scaling laws:

Fundamental PlaneColor - Magnitude Mg - Metallicity - LuminosityM* /L - Letc…

structurevs.

stellar populations

different projectionsof underlying relation

explore full parameter space

ETG sample selectionETG sample selection

* 0.04 < z < 0.08

* no emission! ( < 2 in H and [OII] )

* concentrated light profile ( R90 / R50 > 2.5)

* no color selection

Our sample: ~16,000 SDSS early type galaxy spectra

spectra: S / N ~ 20 Å-1

red

blue

faint bright

binning galaxies in FP spacebinning galaxies in FP space

bright med

faint

faint med bright

* sort galaxies into bins* stack spectra of galaxies in each bin* determine age, [Fe/H], [Mg/H], [Mg/Fe]

Graves, Faber & Schiavon (2008a,submitted to ApJ)

log

I e

stellar pops along the FPstellar pops along the FP

faint mid bright

Graves, Faber & Schiavon (2008a)

Age (Gyr)

4 13

log

log

Re

log

Re

view of fp approx face-on

faint medium brtight

star formation history is independent of Re

H, <Fe>, Mg b

Age, [Fe/H], [Mg/Fe]

Age (Gyr)

4 13

[Fe/H]

-0.5 0.1

[Mg/Fe]

0.0 0.4

log

faint mid bright

log

Re

log

Re

log

Re

Graves, Faber & Schiavon (2008a)

stellar pops along the FPstellar pops along the FP

stellar populations along the fpstellar populations along the fp

UW: May 27, 2008log

Nelan et al. 2005

[Mg/Fe] [Mg/Fe]

0.31

0.31 [Z/H]

[Mg/H]

0.53

0.68

[Fe/H]

0.37

Graves, Faber & Schiavon (2008a)

log Age

log Age

0.59

0.57

interpretation interpretation

[/Fe] ~ [Mg/Fe]

log

[Z/H] ~ [Mg/H]

log AgeHigher- galaxies are:

Nelan et al. (2005)

* older (“downsizing”)

* more metal-rich (deeper potential wells)

* enhanced in -elements relative to solar (shorter star formation timescale)

stellar populations along the fpstellar populations along the fp

UW: May 27, 2008log

Nelan et al. 2005

Graves, Faber & Schiavon (2008a)

stellar pops thru the FPstellar pops thru the FP

@ fixed , galaxies with higher Ie have:

• younger ages

• higher [Fe/H]

• lower [Mg/Fe]

longer duration

star formation

lo

g I e

log

I e

Graves, Faber & Schiavon (2008a)

log Ie is local residual above

or below plane at fixed Re and

low

high

low Ie

high Ie

Age-Metallicity Hyperplane (MHP) Trager et al. (2000)

age-metallicity hyperplaneage-metallicity hyperplane

Graves, Faber & Schiavon (2008b)

logIe

MHP maps onto FP X-sectionMHP maps onto FP X-section

(Age, [Fe/H]) (, logIe)

MHP maps onto FP X-sectionMHP maps onto FP X-section

(Age, [Fe/H]) (, logIe)

log

I e

lo

g I e

toy star-formation modeltoy star-formation model

Trend along the planewith : * Higher- galaxies

formed stars earlier and faster.

Trend perpendicular to theplane: * Higher-SB galaxies made

stars longer. * Consistent with a range of

quenching times and late arrivals onto the FP.

conclusionsconclusions

We have mapped stellar population properties in 3-D FP space

Stellar pops can be inferred (on average) from easily measured structural parameters

Stellar populations vary with but not Re along the FP

2-D family of star formation histories maps to X-section of FP - Younger, brighter stellar pops above; older, dimmer pops below

The two underlying population parameters may be the mean epoch of SFR and the duration of SFR

four questionsfour questions

1) Why are stellar populations independent of R? This is not true of spiral galaxies today. It is also not predicted by current

SAMs.

2) Why is the transition smooth between the E-dominated red sequence and the S0-dominated red sequence?

3) Will the picture change when LINERS and Transition galaxies are added?

4) How much do galaxies scatter inside each bin?