Galaxies Properties in the SDSS Evolution Environment and

Galaxies Properties in the SDSS: Evolution, Environment and Mass Mariangela Bernardi UPitt/UPenn

Outline The SDSS sample n Early-type galaxies: formation and evolution models n Environment and Evolution (Bernardi et al. 2004 a) n Color-L-s : Age and Metallicity (Bernardi et al 2004 b) n The Most Massive Galaxies: Double Trouble? (Bernardi et al. 2004 c) n

Galaxies

Late-type Galaxy Early-type Galaxy

PCA Spectral Classification Early-type Galaxies

Why study early-types? n Very homogeneous, old stellar population ¨ Bulge n stars plausibly oldest in Universe Tight correlations between observables: R-L, s-L, color-L, R-m, etc. ¨ Strong constraints on models ¨ Stars formed in single-burst—easier to build models n Cosmology ¨ Time(z) relation; also gravitational lensing ¨ Homogeneity useful for peculiar velocity studies n Joint formation of spheroids and Black Holes?

Early-type Galaxy Sample Selection Criteria From a sample of ~250, 000 SDSS galaxies Photometric parameter frac. Dev > 0. 8 n PCA spectral type (eclass < 0) n Magnitude limit (14. 5 < mr < 17. 6) n Velocity dispersion available (S/N > 10) n ~ 40, 000 early-type galaxies

Outline The SDSS sample n Early-type galaxies: formation and evolution models n Environment and Evolution (Bernardi et al. 2004 a) n Color-L-s : Age and Metallicity (Bernardi et al 2004 b) n The Most Massive Galaxies: Double Trouble? (Bernardi et al. 2004 c) n

CDM: hierarchical gravitational clustering The formation time of “Elliptical galaxies” is the BIG problem!! The most massive galaxies are the last to form … … even though their stars could be the first to form

Galaxy formation models predict… n n n Early-type galaxies in the field should be younger than those in clusters Metallicity should not depend on environment The stars in more massive galaxies are coeval or younger than those in less massive galaxies Kauffmann & Charlot 1998 see also De Lucia et al. 2003 The key: measure Age & Metallicity

The optical portion of the galaxy spectrum is due to the light of stellar photospheres K giant star Typical elliptical galaxy

Galaxies composed of stars 1) Stellar Library 2) Star Formation History 3) Initial Mass Function reproduce fluxes, colors, and spectra of galaxies e. g. Worthey 1994, Vazdekis 1999, Trager et al. 2000, Bruzual & Charlot 2003, Thomas, Maraston & Bender 2003

Problem: Age-Metallicity degeneracy Stars weak in heavy elements are bluer than metal-rich stars (line blanketing effects and higher opacities) Galaxy models must account for metallicity changes increase of heavy elements due to SN explosions

Different Age – Same Metallicity Easy to separate young and old populations of the same metallicity

Same Age – Different Metallicity Easy to separate coeval populations of different metallicity

Age – Metallicity degeneracy Hard to separate populations which have a combination of age and metallicity

How to disentangle age from metallicity? n n Absorption lines (e. g. Lick indices) Stellar population models metallicity age Hb EW = Mgb Fe l 2 (1 -FIl/FCl) dl Additional complication l 1 [a/Fe] enhancement

The [a/Fe] enhancement problem SN, which produce most of the metals, are of two types:

--- z < 0. 07 --- 0. 07 < z < 0. 09 --- 0. 09 < z < 0. 12 --- 0. 12 < z < 0. 15 Large s are a-enhanced

Stellar Population Synthesis Models Age Thomas, Maraston & Bender 2003 Metallicity Corrected for a-enhancement ☺ [a/Fe] > [a/Fe] Calibrated to the Lick system --- lower resolution --- no flux calibration!!

Problems with models Can we learn something just from the absorption lines?

Testing predictions of galaxy formation models … n n n Early-type galaxies in the field should be younger than those in clusters Metallicity should not depend on environment The stars in more massive galaxies are coeval or younger than those in less massive galaxies

Outline The SDSS sample n Early-type galaxies: formation and evolution models n Environment and Evolution (Bernardi et al. 2004 a) n Color-L-s : Age and Metallicity (Bernardi et al 2004 b) n The Most Massive Galaxies: Double Trouble? (Bernardi et al. 2004 c) n

Environment …. From ~ 25, 000 early-types at z < 0. 14 3500 in high density regions 4500 in low density regions L > 3 L* C 4 Cluster Catalog (Miller et al. 2004) Lcl > 1. 75 x 1011 h-2 L ~ 10 L* Bernardi et al. (2004 a)

The Fundamental Plane The virial theorem: young old n n n Three observables + M/L ~ L 0. 14 FP is combination with minimum scatter Cluster galaxies 0. 1 mag fainter than field galaxies --- Cluster --- Field --- BCG Cluster galaxies older than field by ~ 1 Gyr BCGs more homogeneous

Z ~ 0. 05 …. . Evolution Z~ 0. 17 Dt ~ 1. 3 Gyr D 4000 increases with time; Hd, Hg decreases

Evolution as a clock

Some implications: n early-type galaxies in the field should be younger than those in clusters Observed differences cluster-field small (~ 1 Gyr)

Outline The SDSS sample n Early-type galaxies: formation and evolution models n Environment and Evolution (Bernardi et al. 2004 a) n Color-L-s : Age and Metallicity (Bernardi et al 2004 b) n The Most Massive Galaxies: Double Trouble? (Bernardi et al. 2004 c) n

Color-Magnitude

Color-Magnitude is a consequence of Color-s & L-s

Age – Metallicity from Color-Magnitude [Z/H]=0. 6 9 Age 1 [Z/H]=0. 6 12 Bernardi et al. (2004 b) Age 2 [Z/H]=0 L ↑ Age↑ [Z/H] ↓ [Z/H]=0. 6 Age 9 L ↑ Age↑ [Z/H] ↑ 12 Age 4 [Z/H]=0 1 Models from Bruzual & Charlot (2003)

Slope of C-M independent of redshift out to z~1 C-M due to Mass-[Z/H] not Mass-Age Kodama et al. (1998)

C-M due to Mass-[Z/H] residuals from C-M due to Age of stellar population increases with galaxy mass: Massive galaxies are older In contrast to published semianalytic galaxy formation models Bernardi et al. (2004 b)

At fixed L/Mass: 1) more massive galaxies are older 2) fainter galaxies are older 3) galaxies with smaller R are older 4) higher s galaxies are older

Some implications: n early-type galaxies in the field should be younger than those in clusters Observed differences cluster-field small (~ 1 Gyr) n More massive galaxies are coeval or younger than the less massive ones SDSS indicates opposite: smaller galaxies are younger

Outline The SDSS sample n Early-type galaxies: formation and evolution models n Environment and Evolution (Bernardi et al. 2004 a) n Color-L-s : Age and Metallicity (Bernardi et al 2004 b) n The Most Massive Galaxies: Double Trouble? (Bernardi et al. 2004 c) n

The Most Massive Galaxies: Double Trouble? 105 objects with (s > 350 km/s) n Single/Massive? n formation models assume s < 250 km/s ¨ BHs (2 x 109 M ) ¨ Galaxy n Superposition? ¨ interaction rates ¨ dust content ¨ binary lenses

● Single/Massive ڤ Double ◊ BCG Sheth et al. 2003 Bernardi et al. 2004 c Expect 1/300 objects to be a superposition

‘Double’ from spectrum and image

‘Double’ from spectrum, not image

‘Single’ ?

● Single/Massive ڤ Double ◊ BCGs are bluer than main sample at fixed s Doubles are outliers

Dry Mergers?

HST images: with ACS-HRC SDSS J 151741. 7 -004217. 6 1’ 3” SDSS s = 407 ± 27 km/s HST

SDSS J 204712. 0 -054336. 7 1’ 3’ SDSS s = 404 ± 32 km/s HST

s = 369 ± 22 s = 383 ± 27 s = 385 ± 34 s = 385 ± 24 Single galaxies with s ~ 400 km/s Semi-analytics models s = 407 ± 27 s = 395 ± 27 s = 402 ± 35 = 404 ± 32 use a cut at Vc = 350 km/s (i. e. s = 350/√ 2 ~ 250 km/s) s = 408 ± 39 Cut should be at higher Vc? ? s = 413 ± 35 HST: ACS-HRC 6 single 4 multiple

Conclusions n Problems with galaxy formation models ¨ Dependence on environment weak ¨ Low s galaxies are younger (future work: quantify differential evolution) C-M C-s & M-s n Follow-up Most Massive Galaxies n ¨ Analysis of HST images underway ¨ Increase the sample ¨ Submitting follow-up proposals with 8 m