The VIMOS VLT Deep Survey

Evolution of the non-linear galaxy bias up to z = 1.5

¹ INAF - Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italia
² Laboratoire d'Astrophysique de Marseille, UMR 6110 CNRS-Université de Provence, Traverse du Siphon-Les trois Lucs, 13012 Marseille, France e-mail: christian.marinoni@cpt.univ-mrs.fr
³ INAF - Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate, Italia
⁴ INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italia
⁵ INAF - Osservatorio Astronomico di Roma, via Osservatorio 2, 00040 Monteporzio Catone (Roma), Italia
⁶ Institut d'Astrophysique de Paris, UMR 7095, 98 bis Bd Arago, 75014 Paris, France
⁷ INAF - IASF, Via Bassini 15, 20133 Milano, Italia
⁸ Laboratoire d'Astrophysique - Observatoire Midi-Pyrénées, Toulouse, France
⁹ INAF - Istituto di Radio-Astronomia, Via Gobetti 101, 40129 Bologna, Italia
¹⁰ Università di Bologna, Dipartimento di Astronomia, via Ranzani 1, 40127 Bologna, Italia
¹¹ Max Planck Institut fur Astrophysik, 85741 Garching, Germany
¹² INAF - Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italia
¹³ Università di Milano-Bicocca, Dipartimento di Fisica, Piazza della scienza 3, 20126 Milano, Italia

Received: 2 March 2005
Accepted: 17 June 2005

Abstract

We present the first measurements of the Probability Distribution Function (PDF) of galaxy fluctuations in the four-passes, first-epoch VIMOS-VLT Deep Survey (VVDS) cone, covering deg between . We show that the PDF of density contrasts of the VVDS galaxies is an unbiased tracer of the underlying parent distribution up to redshift z=1.5, on scales R=8 and 10 h^-1Mpc. The second moment of the PDF, i.e. the rms fluctuations of the galaxy density field, is to a good approximation constant over the full redshift baseline investigated: we find that, in redshift space, for galaxies brighter than has a mean value of in the redshift interval . The third moment, i.e. the skewness, increases with cosmic time: we find that the probability of having underdense regions is greater at than it was at . By comparing the PDF of galaxy density contrasts with the theoretically predicted PDF of mass fluctuations we infer the redshift-, density- and scale-dependence of the biasing function between galaxy and matter overdensities up to redshift z=1.5. Our results can be summarized as follows: i) the galaxy bias is an increasing function of redshift: evolution is marginal up to and more pronounced for ; ii) the formation of bright galaxies is inhibited below a characteristic mass-overdensity threshold whose amplitude increases with redshift and luminosity; iii) the biasing function is non linear in all the redshift bins investigated with non-linear effects of the order of a few to ~10 % on scales >5 h^-1Mpc. By subdividing the sample according to galaxy luminosity and colors, we also show that: iv) brighter galaxies are more strongly biased than less luminous ones at every redshift and the dependence of biasing on luminosity at is in good agreement with what is observed in the local Universe; v) red objects are systematically more biased than blue objects at all cosmic epochs investigated, but the relative bias between red and blue objects is constant as a function of redshift in the interval , and its value () is similar to what is found at .