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

Abstract

Abstract. 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 bar is then derived. The K-z relation is remarkably reproduced by our evolutionary scenario for elliptical galaxies of baryonic mass M bar,max 1012 M , at all z up to z = 4. M 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 bar,max observed at z > 4 implies that massive clouds were already formed at early epochs. We also find that the M bar,max limit is similar to the critical mass M crit of a self-gravitating cloud regulated by cooling (Rees & Ostriker 1977;Silk 1977). Moreover, the critical size r crit 75 kpc is remarkably close to the typical diameter of Lyα 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.

Deep low-frequency radio observations of the NOAO Boötes field

“…This links together two known correlations, namely the correlation between spectral index and redshift (Tielens et al 1979;Blumenthal & Miley 1979) and the correlation between K-band magnitude and redshift (K − z correlation; e.g., Willott et al 2003;Rocca-Volmerange et al 2004). We remark that the correlation between spectral index and redshift is not a tight correlation; for a given spectral index there is a range of possible redshifts for a radio source (e.g., Miley & De Breuck 2008).…”

STELLAR MASSES OF LYMAN BREAK GALAXIES, Lyα EMITTERS, AND RADIO GALAXIES IN OVERDENSE REGIONS ATz= 4-6

“…One technique is based on the hypothesis that at very early times the most massive galaxies trace the highest density regions and can thus be used as "lighthouses" to pinpoint possible "protoclusters." Radio galaxies (RGs) are among the largest and most massive galaxies at z = 2-5 (M * ∼ 10 10−12 M , e.g., Pentericci et al 1997;Rocca-Volmerange et al 2004;Seymour et al 2007;Hatch et al 2009, this paper), while the most luminous high-redshift quasars (QSOs) have some of the largest black hole masses inferred (M BH ∼ 10 8−10 M , e.g. Jiang et al 2007;Kurk et al 2007).…”

Disentangling star formation and AGN activity in powerful infrared luminous radio galaxies at 1 <z< 4

“…Previous studies have shown that the most powerful radio galaxies present exceptionally high masses (e.g. De Breuck et al 2002;Rocca-Volmerange et al 2004;Seymour et al 2007). This places powerful radio galaxies at the top of the galaxy mass distribution seen in large field galaxy samples (e.g., Marchesini et al 2009;Ilbert et al 2013).…”