EDP Sciences
Free access
Volume 415, Number 3, March I 2004
Page(s) 931 - 940
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20031717

A&A 415, 931-940 (2004)
DOI: 10.1051/0004-6361:20031717

The radio galaxy K-z relation: The $\mathsf{10^{12}}~$M $\mathsf{_\odot}$ mass limit

Masses of galaxies from the L $\mathsf{_{K}}$ luminosity, up to z $\mathsf{> 4}$
B. Rocca-Volmerange1, 2, D. Le Borgne1, C. De Breuck1, M. Fioc1, 3 and E. Moy4

1  Institut d'Astrophysique de Paris, 98bis, Bd Arago, 75014 Paris, France
2  Université de Paris-Sud XI, Bât. 333, 91405 Orsay Cedex, France
3  Université Paris VI, 4, place Jussieu, 75252 Paris Cedex 05, France
4  DSM/DAPNIA, Service d'Astrophysique, CEA-Saclay, Bât. 709, 91191 Gif-sur-Yvette, France

(Received 28 April 2003 / Accepted 7 November 2003 )

The narrow K- z relation of powerful radio galaxies in the Hubble K-band diagram is often attributed to the stellar populations of massive elliptical galaxies. Because it extends over a large range of redshifts ( 0 < z < 4), it is difficult to estimate masses at high redshifts by taking into account galaxy evolution. In the present paper, we propose to estimate the stellar masses of galaxies using the galaxy evolution model PÉGASE. We use star formation scenarios that successfully fit faint galaxy counts as well as z = 0 galaxy templates. These scenarios also predict spectra at higher  z, used to estimate valid photometric redshifts. The baryonic mass of the initial gas cloud $M_{{\rm bar}}$ is then derived. The K- z relation is remarkably reproduced by our evolutionary scenario for elliptical galaxies of baryonic mass $M_{{\rm bar,max}} \simeq
10^{12}~M_\odot$ , at all z up to z = 4. $M_{{\rm bar,max}}$ is also the maximum mass limit of all types of galaxies. Using another initial mass function (IMF), even a top-heavy one, does not alter our conclusions. The high value of $M_{{\rm bar,max}}$ observed at z > 4 implies that massive clouds were already formed at early epochs. We also find that the $M_{{\rm bar,max}}$ limit is similar to the critical mass $M_{{\rm crit}}$ of a self-gravitating cloud regulated by cooling (Rees & Ostriker 1977; Silk 1977). Moreover, the critical size $r_{{\rm crit}}\simeq 75~{\rm kpc}$ is remarkably close to the typical diameter of Ly $\alpha$ haloes surrounding distant radio galaxies. This confirms the validity of the method of baryonic mass determination based on the K-band luminosity. A puzzling question that remains to be answered is the short time-scale of mass-accumulation required to form such massive galaxies at z = 4. We discuss the dispersion of the K- z relation in terms of uncertainties on the mass limit. The link between the presence of the active nucleus and a large stellar mass is also discussed.

Key words: galaxies: evolution -- galaxies: fundamental parameters -- galaxies: distances and redshifts -- cosmology: observations

Offprint request: B. Rocca-Volmerange, brigitte.rocca@iap.fr

© ESO 2004