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Centro de Astrofísica da Universidade do Porto

VVDS-SWIRE Clustering evolution from a spectroscopic sample of galaxies with redshift 0.2 < z < 2.1 selected from Spitzer IRAC 3.6 μm and 4.5 μm photometry

S. de la Torre, O. Le Fèvre, S. Arnouts, L. Guzzo, D. Farrah, C. Lonsdale, B. Meneux, S. Oliver, A. Pollo, I. Waddington, D. Bottini, F. Fang, B. Garilli, V. Le Brun, D. Maccagni, J.-P. Picat, R. Scaramella, M. Scodeggio, D. Shupe, J. A. Surace, L. Tresse, G. Vettolani, A. Zanichelli, C. Adami, S. Bardelli, M. Bolzonella, A. Cappi, S. Charlot, P. Ciliegi, T. Contini, S. Foucaud, P. Franzetti, I. Gavignaud, O. Ilbert, H. J. McCracken, B. Marano, C. Marinoni, A. Mazure, R. Merighi, S. Paltani, R. Pellò, L. Pozzetti, M. Radovich, G. Zamorani, E. Zucca, M. Bondi, A. Bongiorno, J. Brinchmann, O. Cucciati, F. Lamareille, Y. Mellier, P. Merluzzi, S. Temporin, D. Vergani, C. J. Walcher


Aims. By combining the VIMOS VLTDeep Survey (VVDS)with the SpitzerWide-area InfraRed Extragalactic survey (SWIRE) data, we have built the currently largest spectroscopic sample of galaxies selected in the rest-frame near-infrared. In particular, we have obtained 2040 spectroscopic redshifts for a sample of galaxies with a magnitude measured at 3.6μm (m3.6)AB < 21.5, and 1255 spectroscopic redshifts for a sample of galaxies with (m4.5)AB < 21. These allow us to investigate, for the first time using spectroscopic redshifts, the clustering evolution of galaxies selected from their rest-frame near-infrared luminosity, in the redshift range 0.2 < z < 2.1.
Methods. We use the projected two-point correlation function wp(rp) to study the thre dimensional clustering properties of galaxies detected at 3.6μm and 4.5μm with the InfraRed Array Camera (IRAC) in the SWIRE survey with measured spectroscopic redshifts from the first epoch VVDS. In addition, we measure the clustering properties of a larger sample of 16672 SWIRE galaxies for which we have accurate photometric redshifts on the same field by computing the angular correlation function, and we compare these measurements.
Results. We find that in the flux limited samples at 3.6μm and 4.5μm, the clustering length does not change from redshift ∼ 2 to the present. In addition, we find that the clustering lengths are systematically higher when galaxy samples are selected from increasingly redder wavelengths. The measured clustering lengths have a mean value around r0 ≃ 3.9 h−1 Mpc for the galaxies selected at 3.6μm and a mean value of r0 ≃ 4.4 h−1 Mpc for the galaxies selected at 4.5μm, all across the redshift range explored. These values are larger than the typical values found for I-band selected galaxies in the same redshift range, but we find that the difference in clustering length between I-band and 3.6 − 4.5μm selected samples is decreasing with increasing redshift to become comparable at z ≃ 1.5. We interpret this as evidence that galaxies with older stellar populations and galaxies actively forming stars reside in comparably overdense environments at epochs earlier than z ≃ 1.5, supporting the recently reported flattening of the color-density relation at high redshift. The increasing difference in clustering length observed between rest-frame UV-optical and infrared selected samples could then be an indication that star formation is gradually shifting to lower density regions as cosmic time increases, while the older passively evolving galaxies trace the location of the highest primordial peaks.

Astronomy and Astrophysics
Volume 475, Page 443
November 2007

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