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de la Torre S.,Laboratoire Dastrophysique Of Marseille | de la Torre S.,National institute for astrophysics | de la Torre S.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Le Fevre O.,Laboratoire Dastrophysique Of Marseille | And 54 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2011

We measure the spatial clustering of galaxies as a function of their morphological type at z≃ 0.8, for the first time in a deep redshift survey with full morphological information. This is obtained by combining high-resolution Hubble Space Telescope imaging and Very Large Telescope spectroscopy for about 8500 galaxies to with accurate spectroscopic redshifts from the zCOSMOS-Bright redshift survey. At this epoch, early-type galaxies already show a significantly stronger clustering than late-type galaxies on all probed scales. A comparison to the Sloan Digital Sky Survey Data at z≃ 0.1 shows that the relative clustering strength between early and late morphological classes tends to increase with cosmic time at small separations, while on large scales it shows no significant evolution since z≃ 0.8. This suggests that most early-type galaxies had already formed in intermediate and dense environments at this epoch. Our results are consistent with a picture in which the relative clustering of different morphological types between z≃ 1 and 0 reflects the evolving role of environment in the morphological transformation of galaxies, on top of a global evolution driven by mass. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

De La Torre S.,National institute for astrophysics | De La Torre S.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Guzzo L.,National institute for astrophysics | Kovac K.,ETH Zurich | And 59 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We investigate how the shape of the galaxy two-point correlation function as measured in the zCOSMOS survey depends on local environment, quantified in terms of the density contrast on scales of 5 h-1-Mpc. We show that the flat shape previously observed at redshifts between z= 0.6 and 1 can be explained by this volume being simply 10 per cent overabundant in high-density environments, with respect to a universal density probability distribution function. When galaxies corresponding to the top 10 per cent tail of the distribution are excluded, the measured wp(rp) steepens and becomes indistinguishable from Lambda cold dark matter (ΛCDM) predictions on all scales. This is the same effect recognized by Abbas & Sheth in the Sloan Digital Sky Survey (SDSS) data at z≃ 0 and explained as a natural consequence of halo-environment correlations in a hierarchical scenario. Galaxies living in high-density regions trace dark matter haloes with typically higher masses, which are more correlated. If the density probability distribution function of the sample is particularly rich in high-density regions because of the variance introduced by its finite size, this produces a distorted two-point correlation function. We argue that this is the dominant effect responsible for the observed 'peculiar' clustering in the COSMOS field. © 2010 The Authors. Journal compilation © 2010 RAS.

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