1. Dissecting the Red Sequence: Stellar Population Properties in Fundamental Plane Space Genevieve J. Graves, S. M. Faber University of California, Santa Cruz with Ricardo Schiavon

2. early type galaxy evolution  CDM: hierarchical formation (small things form first) “Downsizing”: massive galaxies are old, star formation moves to smaller galaxies How are these processes related? mass assemblystar formation history present-day structurecurrent stellar population

3. zoo of ETG scaling laws Early Type Galaxy (ETG) scaling laws: Fundamental Plane Color - Magnitude Mg -  Metallicity - Luminosity M * /L - L etc… structure vs. stellar populations

4. ETG structure: the fundamental plane Virial Th m : GM / R e   2 M   2 R e Definition: I e  L /  R e 2 L  R e 2 I e If M / L = const.: M  L Jorgensen et al. (1996)  2 R e  R e 2 I e R e   2 I e -1 Observed FP is “tilted” from the virial plane

5. Age-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 >> Metal-rich >> Lines of constant 

6. Color-mag- hyperplane Color-magnitude relation Color-  relation  -magnitude relation Graves, Faber & Schiavon (2008c, ApJ, in press)

7. zoo of ETG scaling laws Early Type Galaxy (ETG) scaling laws: Fundamental Plane Color - Magnitude Mg -  Metallicity - Luminosity M * /L - L etc… structure vs. stellar populations different projections of underlying relation explore full parameter space

8. ETG sample selection * 0.04 < z < 0.08 * no emission! ( < 2  in H  and [OII] ) * concentrated light profile ( R 90 / R 50 > 2.5) * no color selection Our sample: ~16,000 SDSS early type galaxy spectra spectra: S / N ~ 20 Å -1 red blue faint bright

9. binning galaxies in FP space bright med faint medbright * 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

10. stellar pops along the FP faintmidbright Graves, Faber & Schiavon (2008a) Age (Gyr) 4 13 log  log R e view of fp approx face-on

11. faint medium brtight star formation history is independent of R e H ,, Mg b Age, [Fe/H], [Mg/Fe] Age (Gyr) 4 13 [Fe/H] -0.50.1 [Mg/Fe] 0.0 0.4 log  faintmidbright log R e Graves, Faber & Schiavon (2008a) stellar pops along the FP

12. stellar populations along the fp UW: May 27, 2008 log  Nelan et al. 2005 [Mg/Fe] 0.31 [Z/H] [Mg/H] 0.53 0.68 [Fe/H] 0.37 Graves, Faber & Schiavon (2008a) log Age 0.59 0.57

13. stellar populations along the fp UW: May 27, 2008 log  Nelan et al. 2005 [Mg/Fe] 0.31 [Z/H] [Mg/H] 0.53 0.68 [Fe/H] 0.37 Graves, Faber & Schiavon (2008a) log Age 0.59 0.57

14. interpretation [  /Fe] ~ [Mg/Fe] log  [ Z/H] ~ [Mg/H] log Age Higher-  galaxies are: Nelan et al. (2005) * older (“downsizing”) * more metal-rich (deeper potential wells) * enhanced in  -elements relative to solar (shorter star formation timescale)

15. stellar populations along the fp UW: May 27, 2008 log  Nelan et al. 2005 Graves, Faber & Schiavon (2008a)

16. stellar pops thru the FP @ fixed , galaxies with higher I e have: younger ages higher [Fe/H] lower [Mg/Fe] longer duration star formation  log I e Graves, Faber & Schiavon (2008a)  log I e is local residual above or below plane at fixed R e and 

17. stellar populations across the fp GG, Faber & Schiavon (2008a) @ fixed , galaxies with lower M dyn /L have: younger ages higher [Fe/H] lower [Mg/Fe] longer duration star formation log I e  log M dyn / L

18. low  high  low I e high I e Age-Metallicity Hyperplane (MHP) Trager et al. (2000) age-metallicity hyperplane Graves, Faber & Schiavon (2008b)

19.   logI e MHP maps onto FP X-section (Age, [Fe/H]) ( ,  logI e )

20.   logI e MHP maps onto FP X-section (Age, [Fe/H]) ( ,  logI e )

21.  MHP maps onto FP X-section (Age, [Fe/H]) ( ,  logI e )  logI e

22. MHP maps onto FP X-section (Age, [Fe/H]) ( ,  logI e )  log I e

23. toy star-formation model Trend along the plane with  : * Higher-  galaxies formed stars earlier and faster. Trend perpendicular to the plane: * Higher-SB galaxies made stars longer. * Consistent with a range of quenching times and late arrivals onto the FP.

24. conclusions  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 R e 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

25. four 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?

26. 2-D family of star formation Age  [Fe/H]  [Mg/Fe]  Age  [Fe/H]  [Mg/Fe]    Ie Ie More massive galaxies (higher  ): * form stars at earlier times * retain metals (Fe, Mg) * form stars rapidly at fixed , lower I e galaxies: * have shorter star formation timescales