Galaxy cosmological mass function

¹ Observatório do Valongo, Universidade Federal do Rio de Janeiro, Brazil
e-mail: amanda05@astro.ufrj.br
² Instituto de Física, Universidade Federal do Rio de Janeiro, Brazil
³ Vatican Observatory Research Group, Steward Observatory, University of Arizona, USA

Received: 16 January 2014
Accepted: 17 September 2014

Abstract

Aims. This paper studies the galaxy cosmological mass function (GCMF) in a semi-empirical relativistic approach that uses observational data provided by recent galaxy redshift surveys.

Methods. Starting from a previously presented relation between the mass-to-light ratio, the selection function obtained from the luminosity function (LF) data and the luminosity density, the average luminosity L, and the average galactic mass ℳ_g were computed in terms of the redshift. ℳ_g was also alternatively estimated by means of a method that uses the galaxy stellar mass function (GSMF). Comparison of these two forms of deriving the average galactic mass allowed us to infer a possible bias introduced by the selection criteria of the survey. We used the FORS Deep Field galaxy survey sample of 5558 galaxies in the redshift range 0.5 <z< 5.0 and its LF Schechter parameters in the B-band, as well as this sample’s stellar mass-to-light ratio and its GSMF data.

Results. Assuming ℳ_g0 ≈ 10¹¹ℳ_⊙ as the local value of the average galactic mass, the LF approach results in L_B ∝ (1 + z)^{(2.40 ± 0.03)} and ℳ_g ∝ (1 + z)^{(1.1 ± 0.2)}. However, using the GSMF results to calculate the average galactic mass produces ℳ_g ∝ (1 + z)^{(− 0.58 ± 0.22)}. We chose the latter result because it is less biased. We then obtained the theoretical quantities of interest, such as the differential number counts, to finally calculate the GCMF, which can be fitted by a Schechter function, but whose fitted parameter values are different from the values found in the literature for the GSMF.

Conclusions. This GCMF behavior follows the theoretical predictions from the cold dark matter models in which the less massive objects form first, followed later by more massive ones. In the range 0.5 <z< 2.0 the GCMF has a strong variation that can be interpreted as a higher rate of galaxy mergers or as a strong evolution in the star formation history of these galaxies.