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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