Formation and Evolution of Early-Type Galaxies in clusters

Yara Jaffé1,2

Alfonso AragÓn-Salamanca1

1. The University of Nottingham

2. European Southern Observatory

MAGPOP08

Paris, 12 Nov. 2008

OUTLINE

- Introduction

- Scatter-age test

- The data

- Some results

- Conclusions

The CMD of galaxies in clusters

Universality of the CMR

z = 0: Visvanathan & Sandage

1977 z = 0: Bower, Lucey & Ellis

1992

z > 0: Mei et. al. 2006

z > 0: De Lucia et. al. 2007

Slope (m) Mass-metallicity relation

Scatter (δ) due to small changes in tF

Evolution of m and b E’s evolved

passively since formation at high z:

SF history: THE PARAMETER

tAvailable time

tF(look-back time since

last episode of SF)

tH(total age of the Universe)

= Δt / (tH - tF)

ΔtSpread in

formation time

t=0

THE SCATTER-AGE TEST

1. Measure the observed scatter (σ) from the CMR

2. Compute δint by subtracting the errors introduced from the photometry

3. Colour evolution for different values of β using:

4. Comparison with population synthesis models

THE DATA

ESO Distant Clusters Survey (EDisCS)

Detailed follow-up of 20 clusters from LCDCS (Gonzalez et al. 2001) at 0.4 < z < 1

Each field containing a main cluster and some other secondary clusters and groups

EDisCS Deep optical photometry from VLT (14 nights) White et al. 2005

Near-IR photometry from NTT (20 nights) Aragon-Salamanca et al., in preparation

Multi-object spectroscopy with FORS2/VLT (25 nights) Halliday et al. 2004; Milvang-Jensen et al. 2008 HST imaging for the of the highest-z clusters (80 orbits) Desai et al. 2007

Narrow band Hα (3 clusters) and XMM data (3 clusters) Finn et al. 2005 and Johnson et al. 2006 respectively

Sub-set of 137 early type galaxies (selected by morphology) in 10 clusters

AIM:

To probe if the scatter or tF, for a fixed value of β, depend on:

The morphological sample (E´s vs. S0´s) The cut in Luminosity (mass) The colour chosen in the CMDs Properties of the clusters ?

SOME RESULTS...

1. Individual analysis (cluster by cluster)

2. Overall analysis (all the clusters together)

CMDs of the clustersCL 1216.8-1201z = 0.79Age at z = 6.87 Gyrs----------------------------

No. galaxies = 31δint = 0.065 ±

0.009

residuals

MODEL COMPARISON

Bruzual & Charlot 2003

- SSP

- 3 different metallicities

- Chabrier's IMF

- Low res. libraries

- 0.1 Gyr of constant SF and then passive evol.

- No dust attenuation

CL 1216.9-1201

d(R-I) / dtF

Zsub-solar

Zsolar

Zover-solar

R -

I

tF (Gyr)

d(R

-I)/

dt F

DIFFERENT COLOURS (in CMDs)

All the early-type galaxies In CL 1216.8 1201 (z~0.8)

R-I I-J R-J V-I I-K V-J

U V

DIFFERENT COLOURS

β=1.0

β=0.3

β=0.1

...

tH(z)

SCATTER ANALYSIS

1. Individual analysis (cluster by cluster)

2. Overall analysis (all the clusters)

SUB-SAMPLES

All the galaxiesin all the clusters

Low σv High σvLow z High z

Es S0s Lum Faint

RESIDUAL DISTRIBUTION

δint=0.076-0.004+0.005

( δint=0.063 )

All the sample:

β=1.0 Δt(rf U-V) ~ 1.7

Gyr

β=0.3 Δt(rf U-V)~ 1.0

Gyr

β=0.1 Δt(rf U-V) ~

0.5 Gyr

.… tH(<z>)

= Δt / (tH - tF)

δint(rf U-V) δint(rf U-V)

t F (

Gyr)

t F (

Gyr)

PRELIMINARY CONCLUSIONS:

• For CL 1216.8 1201 all the colours seem to give consistent tF (for β=0.3 and β=1.0) scatter about the CMR is due to age differences

• The estimated tF doesn’t seem to change much (within errors) with galaxy luminosity (mass), morphology or cluster propperties (vel. disp and z) but some trends are found