Claudia MarastonOxford University

The AGB phase and

the ages and masses of high-z galaxies

Galaxy Evolution through Cosmic Times- Venezia, 2006

Claudia Maraston Venice 2006

Constraining Galaxy Formation/Evolution

Needs a stellar population model

Results rely fully on the adopted evolutionary population synthesis code

Ages, star formation histories, stellar masses M*, photo-z, etc. of galaxies from integrated light

Stars: stellar evolution independent of cosmological models

Claudia Maraston Venice 2006

Evolutionary Population Synthesis

Stellar Population model adding up the energetics of all stellar phases following stellar evolution i.e. stellar tracks and isochrones + empiricalrecipes

Isochrone SynthesisBruzual & Charlot93;03Worthey94Vazdekis+96Pegase97Starburst99 Jimenez+04

Fuel ConsumptionBuzzoni89 - only old agesMaraston98;05

Claudia Maraston Venice 2006

Energetics of Stellar Populations:Three Regimes

AGB stars dominate the light of intermediate-age stellar populations

Main Sequence +

He-burning stars dominate the light of young stellar populations

RGB stars dominate the light of old stellar populations

Claudia Maraston Venice 2006

The (Curable) Uncertainties

• Treatment of AGB (mass-loss): tracks uncertain imp at 0.2 < t/Gyr < 2, wav. > 5000 AA• Onset of RGB and MS lifetime (overshooting): • imp at 0.2 < t/Gyr < 3, all lambdas• All critical at high-z, in particular (but not

only) when near-IR sampled

Claudia Maraston Venice 2006

Two Classes of Population Synthesis Models

• Stellar tracks w overshooting- Padova

+ theoretical TP-AGB (BC03,Pegase, Starburst99, etc.)

• Stellar tracks w/o overshooting -Frascati- + TP-AGB semi-empirical (Maraston)

Claudia Maraston Venice 2006

Results: Model SEDs

Maraston 2005, MNRAS, 362, 799 www.astro-physics.ox.ac.uk/~maraston

Claudia Maraston Venice 2006From Ferraro et al. 2004, ApJ

Girardi et al. 00 Padova tracks

Frascati tracks

RGB phase-transition: Frascati tracks are well-calibrated

Calibration with GCs1.Overshooting and RGB onset

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Calibration with LMC globularclusters

Maraston 2005, MNRAS, 362, 799

2. AGB

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Calibration of synthetic optical colours - cf. van der Wel’s talk -

othercolour-colourdiagramsin Maraston05

MC GCs3<SWB<6

Claudia Maraston Venice 2006

Ages & Masses of high-z galaxies

Depend on the adopted evolutionary population synthesis

Claudia Maraston Venice 2006

Effect of spectral synthesis models on high-z galaxies. 1. HUDF

Maraston, Daddi + 06, ApJ

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HUDF galaxies.2.

Claudia Maraston Venice 2006

OLDER THAN UNIVERSE

Maraston, Daddi + 06

HUDF galaxies.3.

Undetected in MIPS!

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Stellar Masses of HUDF Galaxies

Maraston et al.06

Massesget lower

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Photo-z

Claudia Maraston Venice 2006

Near-IR selected z ~ 3 galaxies (sp. redshifts)

Maraston et al. in prep

data from Rigoupolou et al.05

Claudia Maraston Venice 2006

Summary

• Galaxy properties depend on spectral synthesis models

• Recipes for red giants - AGB and RGB - are crucial• Effects of models with empirical AGB

(Maraston98;05) include:• Ages are lower, always smaller than the age of

the Universe • Lower formation redshifts Impact on galaxy• Lower stellar masses formation models• Lower reddening• Effect on photometric redshifts (details in Maraston et al. 06)

Claudia Maraston Venice 2006

Formation redshifts

in prep. with Laura Perry, D. Thomas - Oxford