Astronomy & Astrophysics

Free access article

A&A 442, 801-825 (2005)
DOI: 10.1051/0004-6361:20052966

The VIMOS VLT Deep Survey

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

C. Marinoni^{1, 2}, O. Le Fèvre², B. Meneux², A. Iovino¹, A. Pollo³, O. Ilbert^{2, 4}, G. Zamorani⁴, L. Guzzo³, A. Mazure², R. Scaramella⁵, A. Cappi⁴, H. J. McCracken⁶, D. Bottini⁷, B. Garilli⁷, V. Le Brun², D. Maccagni⁷, J. P. Picat⁸, M. Scodeggio⁷, L. Tresse², G. Vettolani⁹, A. Zanichelli⁹, C. Adami², S. Arnouts², S. Bardelli⁴, J. Blaizot², M. Bolzonella¹⁰, S. Charlot^{6, 11}, P. Ciliegi⁹, T. Contini⁸, S. Foucaud⁷, P. Franzetti⁷, I. Gavignaud⁸, B. Marano¹⁰, G. Mathez⁸, R. Merighi⁴, S. Paltani², R. Pellò⁸, L. Pozzetti⁴, M. Radovich¹², E. Zucca⁴, M. Bondi⁹, A. Bongiorno¹⁰, G. Busarello¹², S. Colombi⁶, O. Cucciati^{1, 13}, F. Lamareille⁸, Y. Mellier⁶, P. Merluzzi¹², V. Ripepi¹² and D. Rizzo⁸

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 $0.4\times0.4$ deg between 0.4<z<1.5. 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, $\sigma_8$ for galaxies brighter than $\mathcal=-20+5\log h$ has a mean value of $0.94 \pm 0.07$ in the redshift interval 0.7 < z < 1.5. The third moment, i.e. the skewness, increases with cosmic time: we find that the probability of having underdense regions is greater at $z \sim 0.7$ than it was at $z \sim 1.5$ . 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 $b(z, \delta, R)$ 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 $z \sim 0.8$ and more pronounced for $z \gtrsim 0.8$ ; 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 $z \sim 0.8$ 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 0.7 < z < 1.5, and its value ( $b^{\rm rel}\sim 1.4$ ) is similar to what is found at $z \sim 0$ .

Key words: cosmology: large-scale structure of Universe -- galaxies: distances and redshifts -- galaxies: evolution -- galaxies: statistics

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