Galaxies of 10¹² M_⊙ at z ≥ 4 Along the K-z Sequence

Abstract

Stellar masses of galaxies are derived from the K-band (2.2 μm) photometry by taking into account evolution and cosmological effects with the code PÉGASE. The evolution scenarios are robust: they give reference spectra for valid photometric redshifts and fit the deepest galaxy counts with the standard cosmological model. Baryonic masses of the progenitor gaseous clouds are then derived. The baryonic maximum value M_bar,max = 10¹² M_⊙ fits the radio galaxy K-z sequence from z = 0 to 4. Since this cut value is observed at all z in the Hubble diagram, it favors a physical origin: i.e., the fragmentation limit of 10¹² M_⊙ predicted by Rees & Ostriker, 1977. One consequence is the discovery of high mass (≃ 10¹² M_⊙) galaxies at z ≥ 4, constraining the mass accumulation time-scales (Rocca-Volmerange et al. 2003).