1. THE FIRST GALAXY FORMATION MODEL WITH THE TP-AGB:
BASIC REVISION OF THE
MASS-LUMINOSITY RELATION
Kingston, June 15th 2009
Chiara Tonini
Red galaxies at high redshift are one of the most important tests of our understanding of galaxy formation.
The red colours of these galaxies and the high near-IR luminosities have led to the interpretation of these objects
as massive and passively evolving. The models struggle to reproduce these objects, because at high redshift
the merger rates are high and the mass assembly is rapid, so objects in models tend to be too blue.
Marie Curie Excellent Grant “UniMass” (PI: Claudia Maraston)
in collaboration with
Claudia Maraston, Daniel Thomas (ICG)
Julien Devriendt, Joe Silk (University of Oxford)

2. THE GALAXY FORMATION MODEL
GALICS:
Hatton et al MNRAS 343, 75
GALaxies In Cosmological Simulations
Hybrid model: N-body + SAM
Box size: 150 Mpc
Number of particles:
from z=35.59
Galactic mass:
Semi-analytics
baryonic cooling onto disks
merger-driven morphology+secular evolution
star formation
feedback from Sne
metallicity evolution
AGN feedback
quenching of SF in satellites
dynamical friction, tidal stripping
dust
stellar populations spectra

3. GalICS + M05
TP-AGB
We tackled the problem with a semi-analytic model (galics) in which we introduce a new recipe for the stellar
populations, the M05 models that include the TP-AGB phase of stellar evolution.
The model originally was equipped with the PEGASE models, which in this respect are equivalent to the BC03 models
widely used in the literature.
Maraston 2005 MNRAS 362, 799 (M05)

4. Results Theoretical colour-magnitude relation: very red!
The predicted colour magnitude relation as a function of redshift
There is a residual star formation in the model, which leads to the effect visible at low z:
The SF dilutes the red colours if the TP-AGB is not present, but with the M05 run the red colours are still
dominated by the TP-AGB, so that virtually disks are undistinguishable from spheroids in these colours
This also tells us that the model produces very red objects that are not dead at all!!!
CT, Maraston, Devriendt, Thomas & Silk, 2009 MNRAS 396L 36T

5. Results Theoretical mass-luminosity relation at same stellar mass
The mass-luminosity relation reflects the different IR emission if we include the TP-AGB
For a given galaxy mass, the corresponding luminosity can be almost one magnitude brighter even at z=1
And expecially at the high mass end!!!!
This affects the data comparison: Conselice at the high mass end finds a discrepancy
But they mass-model with BC03, so they overestimate the mass
So this helps relieving the problem
at same stellar mass
CT, Maraston, Devriendt, Thomas & Silk, 2009 MNRAS 396L 36T

6. Results Theoretical K-band luminosity function TP-AGB AGN FEEDBACK
PEGASE
De Lucia & Blaizot 2007
Bower et al. 2006
Monaco et al. 2007
Menci et al. 2006
Cole et al. 2000
Baugh et al. 2005
TP-AGB
AGN FEEDBACK
The gap between the M05 (TP-AGB) and the PEGASE (no TP-AGB) runs is comparable to the spread induced by different recipes of AGN feedback
CT, Maraston, Thomas, Devriendt & Silk, in preparation

7. Comparison with data: samples
Excellent quality of photometry:
7 nearly-passively evolving galaxies at 1.4<z<2.7 (sp)
HUDF, singled out by BzK criterion
Early-type morphology, not star-forming, not much dust, star age ~ Gyr
Maraston et al ApJ
95 star-forming galaxies at 1.7<z<2.3 (sp)
GOODS-S, singled out by BzK criterion
Dickinson et al., in preparation
CT, Maraston, Thomas, Devriendt & Silk, in preparation

8. Comparison with data at z=2
Colour-magnitude relation --> mass, age and luminosity
Nearly-passive galaxies, ages ~0.2-2 Gyr
24 micron --> measured dust signal is low
Dust: proportional to SFR as from SED fitting, and Bell&Kennicutt 2001
Calzetti
Stellar masses:
Model:
extinction curve: Calzetti
CT, Maraston, Thomas, Devriendt & Silk, in preparation

9. Comparison with data at z=2
Star-forming galaxies
Colour-magnitude relation
Highlight that pegase never reaches the luminosity, not only the colours!!!!!
The slope is right, so we’re also checking that the SFR is right
Pegase does not get the amplitude nor the luminosity
extinction curve: Calzetti
CT, Maraston, Thomas, Devriendt & Silk, in preparation

10. Comparison with data at z=2
Star-forming galaxies
Colour-colour relation --> stellar populations
Balance between stellar populations
Notice that there are galaxies with high J-H, so they’re blue and star forming, but they are also
red in H-Irac3
So we’re able to produce galaxies blue in the UV and red in the nearIR….
These galaxies are red and alive!!!
CT, Maraston, Thomas, Devriendt & Silk, in preparation

11. Conclusions “Red & Dead” galaxies are alive!!!
The model reproduces high redshift galaxy data
Red colours and high near-IR luminosities can be reached in the models without invoking high ages, large masses or large dust reddening
both in nearly-passive and star-forming galaxies
Happy with this result, we proceeded to analyze galaxies at higher redshift….
… and everything breaks down
CT, Maraston, Thomas, Devriendt & Silk, in preparation