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30 August 2010

Evolution of Galaxy Stellar Mass Functions, Mass Densities, and Mass to Light ratio from z~7 to z~4

Authors: Gonzalez, Labbé, Bouwens, Illingworth, Franx, Kriek
Link to article: arXiv:1008.3901v1

This paper address a very important question about the built-up and evolution of galaxies at high redshift, by deriving stellar masses from SED fitting for ~400 LBG observed with Hubble-WFC3/IR and Spitzer-IRAC in the GOODS South field. Using Bruzual & Charlot models with a Salpeter IMf, masses are obtained assuming a constant Star Formation History for galaxies. 

By fitting the Mass vs Luminosity relation at z~4 - with a slope that makes the M/L ratio increase with luminosity - and finding no clear evidence for evolution with redshift, this work use the UV Luminosity Functions of Bouwens et al. (2007-2010) and Monte-Carlo simulations to derive Mass Functions (MF) at z~4,5,6,7. The results show a significant difference with theoretical expectations from numerical simulations, and especially a much more flatter faint end slope. 

The last part of this paper show a comparison of the stellar mass growth computed by 2 different approaches: a quite large disagreement is found between the integration of the SFR density over time [SFRD ~ (1+z)^-6.3] compared with the integration of MF for the 4 bins of redshift [SMD ~ (1+z)^-2.8]. The authors propose that dust extinction overestimates, low duty cycle for SF or shortcomings in the modeling of faint galaxies may explain this noticeable difference.

1 comment:

  1. This is indeed a very interesting paper. One point that I am not sure about is: why is the assumption in the SED modelling in general that star formation histories are declining or constant. There is ample evidence from simulations and models that star formation histories should be increasing up to z ~4-5. It would be very interesting to see how well the actual SED fits for such star formation histories are. Another slightly confusing point is that the SED modelling is done assuming dust, but the star formation rates are shown without dust correction.