Aims: We present a measurement of the dependence of galaxy clustering on galaxy stellar mass at redshift z ∼ 0.9, based on the first-epoch data from the VVDS-Deep survey. Methods: Concentrating on the redshift interval 0.5 < z < 1.2, we measured the projected correlation function, wp(r p), within mass-selected subsamples covering the range ∼10 9 and ∼1011 M⊙. We explored and quantify in detail the observational selection biases due to the flux-limited nature of the survey, both from the data themselves and with a suite of realistic mock samples constructed by coupling the Millennium Simulation to semi-analytic models. We identify the range of masses within which our main conclusions are robust against these effects. Serious incompleteness in mass is present below log (M/M⊙) = 9.5, with about two thirds of the galaxies in the range 9 < log (M/M⊙) < 9.5 that are lost due to their low luminosity and high mass-to-light ratio. However, the sample is expected to be 100% complete in mass above log (M/Ṁ) = 10. Results: We present the first direct evidence for a dependence of clustering on the galaxy stellar mass at a redshift as high as z ∼ 0.85. We quantify this by fitting the projected function wp(rp) with a power-law model. The clustering length increases from r0 = 2.76 +0.17-0.15 ∼-1 Mpc for galaxies with mass M > 109 M⊙ to r0 = 4.28 +0.43-0.45 h-1 Mpc when only the most massive (M < 1010.5 M⊙) are considered. At the same time, we observe a significant increase in the slope, which over the same range of masses, changes from γ = 1.67+0.08-0.07 to γ = 2.28+0.28-0.27. Comparison to the SDSS measurements at z ∼ 0.15 shows that the evolution of wp(rp) is significant for samples of galaxies with M < 1010.5 M ⊙, while it is negligible for more massive objects. Considering the growth of structure, this implies that the linear bias bl of the most massive galaxies evolves more rapidly between these two cosmic epochs. We quantify this effect by computing the value of bL from the SDSS and VVDS clustering amplitudes and find that bL decreases from 1.5 ± 0.2 at z ∼ 0.85 to 1.33 ± 0.03 at z ∼ 0.15, for the most massive galaxies, while it remains virtually constant (bL ∼ 1.3) for the remaining population. Qualitatively, this is the kind of scenario expected for the clustering of dark-matter halos as a function of their total mass and redshift. Our result therefore seems to indicate that galaxies with the highest stellar mass today were originally central objects of the most massive dark-matter halos at earlier times, whose distribution was strongly biased with respect to the overall mass density field.
Áreas temáticas de ASJC Scopus
- Astronomía y astrofísica
- Ciencias planetarias y espacial