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

Mariangela Bernardi UPitt/UPenn

Galaxies Properties in the SDSS:Galaxies Properties in the SDSS: Evolution, Environment and Evolution, Environment and MassMass

Outline The SDSS sample Early-type galaxies:

formation and evolution models Environment and Evolution (Bernardi et al. 2004a) Color-L-Age and Metallicity (Bernardi et al

2004b) The Most Massive Galaxies: Double Trouble?

(Bernardi et al. 2004c)

Galaxies

Late-type Galaxy

Early-type Galaxy

PCA Spectral Classification

Early-type Galaxies

Why study early-types? Very homogeneous, old stellar population

Bulge stars plausibly oldest in Universe

Tight correlations between observables: R-L, -L, color-L, R-, etc. Strong constraints on models Stars formed in single-burst—easier to build models

Cosmology Time(z) relation; also gravitational lensing Homogeneity useful for peculiar velocity studies

Joint formation of spheroids and Black Holes?

Early-type Galaxy Sample Selection Criteria

Photometric parameter fracDev > 0.8

PCA spectral type (eclass < 0) Magnitude limit (14.5 < mr < 17.6) Velocity dispersion available (S/N > 10)

From a sample of ~250,000 SDSS galaxies

~ 40,000 early-type galaxies

Outline The SDSS sample Early-type galaxies:

formation and evolution models Environment and Evolution (Bernardi et al. 2004a) Color-L-Age and Metallicity (Bernardi et al

2004b) The Most Massive Galaxies: Double Trouble?

(Bernardi et al. 2004c)

CDM: hierarchical gravitational clusteringThe 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…

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 1998see 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

metallicity changes increase of heavy elements due to SN explosions

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

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 degeneracyHard to separate populations which have a combination of age and metallicity

How to disentangle age from metallicity?

Stellar population models

Absorption lines (e.g. Lick indices)

H Mgb Fe

EW =

1FIFCd1

age

metallicity

Additional complication [/Fe] enhancement

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

Large are-enhanced

--- z < 0.07 --- 0.07 < z < 0.09 --- 0.09 < z < 0.12 --- 0.12 < z < 0.15

Stellar Population Synthesis Models

Thomas, Maraston & Bender 2003

Calibrated to the Lick system --- lower resolution --- no flux calibration!!

Corrected for -enhancement ☺[/Fe] > [/Fe]

Age

Metallicity

Problems with models

Can we learn something just from the absorption lines?

Testing predictions of galaxy formation models …

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 Early-type galaxies:

formation and evolution models Environment and Evolution (Bernardi et al. 2004a) Color-L-Age and Metallicity (Bernardi et al

2004b) The Most Massive Galaxies: Double Trouble?

(Bernardi et al. 2004c)

Environment ….

C4 Cluster Catalog (Miller et al. 2004)

L > 3L*

Lcl > 1.75 x 1011 h-2 L ~ 10L*

From ~ 25,000 early-types at z < 0.14

3500 in high density regions4500 in low density regions

Bernardi et al. (2004a)

Cluster galaxies 0.1 mag fainterthan field galaxies

Cluster galaxies older than field by ~ 1Gyr

BCGs more homogeneous

--- Cluster--- Field --- BCG

The Fundamental PlaneThe virial theorem:

Three observables + M/L M/L ~ L0.14

FP is combination with minimum scatter

oldyoung

….. Evolution Z ~ 0.05

Z~ 0.17 t ~ 1.3Gyr

D4000 increases with time; H, H decreases

Evolution as a clock

Some implications:

early-type galaxies in the field should be younger

than those in clusters

Observed differences cluster-field small (~ 1 Gyr)

Outline The SDSS sample Early-type galaxies:

formation and evolution models Environment and Evolution (Bernardi et al. 2004a) Color-L-Age and Metallicity (Bernardi et al

2004b) The Most Massive Galaxies: Double Trouble?

(Bernardi et al. 2004c)

Color-Magnitude

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

Age – Metallicity from Color-Magnitude

Models from Bruzual & Charlot (2003)

12

4

Age

[Z/H]=0.6

[Z/H]=0

9

1

[Z/H]=0.6

[Z/H]=0

12

2

Age

[Z/H]=0

[Z/H]=0.6

1

9 Age

Age

Bernardi et al. (2004b)

L ↑ Age↑ [Z/H] ↑

L ↑ Age↑ [Z/H] ↓

Kodama et al. (1998)

Slope of C-Mindependent of redshift out to z~1

C-M due toMass-[Z/H] not Mass-Age

C-M due to Mass-[Z/H] residuals from C-M due to Age

In contrast to published semi-analytic galaxy formation models

Bernardi et al. (2004b)

Age

Age of stellar population increases with galaxy mass: Massive galaxies are older

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

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

More massive galaxies are coeval or younger than the less massive ones SDSS indicates opposite: smaller galaxies are younger

Outline The SDSS sample Early-type galaxies:

formation and evolution models Environment and Evolution (Bernardi et al. 2004a) Color-L-Age and Metallicity (Bernardi et al

2004b) The Most Massive Galaxies: Double Trouble?

(Bernardi et al. 2004c)

The Most Massive Galaxies: Double Trouble? 105 objects with ( > 350 km/s) Single/Massive?

Galaxy formation models assume < 250 km/s BHs (2 x 109 M)

Superposition? interaction ratesdust contentbinary lenses

● Single/Massive Double ڤ◊ BCG

Sheth et al. 2003

Expect 1/300 objects to be a superposition

Bernardi et al. 2004c

‘Double’ from spectrum and image

‘Double’ from spectrum, not image

‘Single’ ?

● Single/Massive Double ڤ◊ BCG

Doubles are outliers

BCGs are bluer thanmain sample at fixed

Dry Mergers?

HST images: with ACS-HRC

SDSS

HST = 407 ± 27 km/s

SDSS J151741.7-004217.6

3”

1’

SDSS J204712.0-054336.7

= 404 ± 32 km/sHST

SDSS

1’

3’

HST: ACS-HRC

6 single 4 multiple

= 369 ± 22 = 383 ± 27 = 385 ± 34 = 385 ± 24

= 395 ± 27 = 402 ± 35 = 404 ± 32 = 407 ± 27

= 408 ± 39 = 413 ± 35

Single galaxies with ~ 400 km/s

Semi-analytic modelsuse a cut at Vc = 350 km/s

(i.e. = 350/√2 ~ 250 km/s)

Cut should be at higher Vc??

Conclusions Problems with galaxy formation models

Dependence on environment weak Low galaxies are younger (future work: quantify differential evolution)

C-M C- & M- Follow-up Most Massive Galaxies

Analysis of HST images underway Increase the sampleSubmitting follow-up proposals with 8m