Aims.We have computed the evolution of the rest-frame B-band luminosity function (LF) for bulge and disk-dominated galaxies since z=1.2. Methods: .We use a sample of 605 spectroscopic redshifts with ...IAB? 24 in the Chandra Deep Field South from the VIMOS-VLT Deep Survey, 3555 galaxies with photometric redshifts from the COMBO-17 multi-color data, coupled with multi-color HST/ACS images from the Great Observatories Origin Deep Survey. We split the sample in bulge- and disk-dominated populations on the basis of asymmetry and concentration parameters measured in the rest-frame B-band. Results: .We find that at z=0.4-0.8, the LF slope is significantly steeper for the disk-dominated population (?=-1.19 ± 0.07) compared to the bulge-dominated population (?=-0.53 ± 0.13). The LF of the bulge-dominated population is composed of two distinct populations separated in rest-frame color: 68% of red (B-I)AB>0.9 and bright galaxies showing a strongly decreasing LF slope ?=+0.55 ± 0.21, and 32% of blue (B-I)AB<0.9 and more compact galaxies which populate the LF faint-end. We observe that red bulge-dominated galaxies are already well in place at z?1, but the volume density of this population is increasing by a factor 2.7 between z? 1 and z? 0.6. It may be related to the building-up of massive elliptical galaxies in the hierarchical scenario. In addition, we observe that the blue bulge-dominated population is dimming by 0.7 mag between z? 1 and z? 0.6. Galaxies in this faint and more compact population could possibly be the progenitors of the local dwarf spheroidal galaxies.
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.
This paper presents the evolution of the clustering of the main population of galaxies from z 2 to z = 0.2, from the first epoch VIMOS VLT Deep Survey (VVDS), a magnitude limited sample with 17.5 ...less than or equal to I sub(AB) less than or equal to 24. The sample allows a direct estimate of evolution from within the same survey over the time base sampled. We have computed the correlation functions xi (r sub(p), pi ) and w sub(p)(r sub(p)), and the correlation length r sub(0)(z), for the VVDS-02h and VVDS-CDFS fields, for a total of 7155 galaxies in a 0.61 deg super(2) area. We find that the correlation length in this sample slightly increases from z = 0.5 to z = 1.1, with r sub(0)(z) = 2.2-2.9 h super(-1) Mpc (comoving), for galaxies comparable in luminosity to the local 2dFGRS and SDSS samples, indicating that the amplitude of the correlation function was 2.5 times lower at z 1 than observed locally. The correlation length in our lowest redshift bin z = 0.2, 0.5 is r sub(0) = 2.2 h super(-1) Mpc, lower than for any other population at the same redshift, indicating the low clustering of very low luminosity galaxies, 1.5 mag fainter than in the 2dFGRS or SDSS. The correlation length increases to r sub(0) similar to 3.6 h super(-1) Mpc at higher redshifts z = 1.3, 2.1, as we are observing increasingly brighter galaxies, comparable to galaxies with M sub(BsubAB) = -20.5 locally. We compare our measurement to the DEEP2 measurements in the range z = 0.7, 1.35 and find comparable results when applying the same magnitude and color selection criteria as in their survey. The slowly varying clustering of VVDS galaxies as redshift increases is markedly different from the predicted evolution of the clustering of dark matter, indicating that bright galaxies traced higher density peaks when the large scale structures were emerging from the dark matter distribution 9-10 billion years ago, being supporting evidence for a strong evolution of the galaxy vs. dark matter bias.
Aims. This paper presents a detailed comparison between high-redshift observations from the VIMOS-VLT Deep Survey (VVDS) and predictions from the Munich semi-analytical model of galaxy formation. In ...particular, we focus this analysis on the magnitude, redshift, and colour distributions of galaxies, as well as their clustering properties. Methods. We constructed 100 quasi-independent mock catalogues, using the output of the semi-analytical model presented in De Lucia & Blaizot (2007, MNRAS, 375, 2). We then applied the same observational selection function of the VVDS-Deep survey, so as to carry out a fair comparison between models and observations. Results. We find that the semi-analytical model reproduces well the magnitude counts in the optical bands. It tends, however, to overpredict the abundance of faint red galaxies, in particular in the i' and z' bands. Model galaxies exhibit a colour bimodality that is only in qualitative agreement with the data. In particular, we find that the model tends to overpredict the number of red galaxies at low redshift and of blue galaxies at all redshifts probed by VVDS-Deep observations, although a large fraction of the bluest observed galaxies is absent from the model. In addition, the model overpredicts by about 14 per cent the number of galaxies observed at 0.2 < z < 1 with I sub(AB) < 24. When comparing the galaxy clustering properties, we find that model galaxies are more strongly clustered than observed ones at all redshift from z = 0.2 to z = 2, with the difference being less significant above z 1. When splitting the samples into red and blue galaxies, we find that the observed clustering of blue galaxies is well reproduced by the model, while red model galaxies are much more clustered than observed ones, being principally responsible for the strong global clustering found in the model. Conclusions. Our results show that the discrepancies between Munich semi-analytical model predictions and VVDS-Deep observations, particularly in the galaxy colour distribution and clustering, can be explained to a large extend by an overabundance of satellite galaxies, mostly located in the red peak of the colour bimodality predicted by the model.
We investigate the dependence of galaxy clustering on the galaxy intrinsic luminosity at high redshift, using the data from the First Epoch VIMOS-VLT Deep Survey (VVDS). The size (6530 galaxies) and ...depth (I sub(AB) < 24) of the survey allows us to measure the projected two-point correlation function of galaxies, omega sub(p)(r sub(p)), for a set of volume-limited samples up to an effective redshift < z > = 0.9 and median absolute magnitude -19.6 < M sub(B) < -21.3. Fitting omega sub(p)(r sub(p)) with a single power-law model for the real-space correlation function xi (r) = (r/r sub(0)) super(- gamma ), we measure the relationship of the correlation length r sub(0) and the slope gamma with the sample median luminosity for the first time at such high redshift. Values from our lower-redshift samples (0.1 < z < 0.5) are fully consistent with the trend observed by larger local surveys. In our high redshift sample (0.5 < z < 1.2), we find that the clustering strength suddenly rises around M* sub(B), apparently with a sharper inflection than at low redshifts. Galaxies in the faintest sample (< M sub(B) > = -19.6) have a correlation length r sub(0) = 2.7 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(3) sub(3) h super(-1) Mpc, compared to r sub(0) = 5.0 super(+) sub(-) super(1) sub(1) super(.) sub(.) super(5) sub(6) h super(-1) Mpc at < M sub(B) > = -21.3. The slope of the correlation function is observed to correspondingly steepen significantly from gamma = 1.6 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(1) sub(1) to gamma = 2.4 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(4) sub(2). This is not observed either by large local surveys or in our lower-redshift samples and seems to imply a significant change in the way luminous galaxies trace dark-matter halos at z similar to 1 with respect to z similar to 0. At our effective median redshift z 0.9 this corresponds to a strong difference of the relative bias, from b/b* < 0.7 for galaxies with L < L* to b/b* 1.4 for galaxies with L > L*.
We measure the real-space galaxy power spectrum on large scales at redshifts 0.5-1.2 using optical colour selected samples from the Canada-France-Hawaii Telescope Legacy Survey. With the redshift ...distributions measured with a preliminary similar to 14000 spectroscopic redshifts from the VIMOS Public Extragalactic Redshift Survey (VIPERS), we deproject the angular distribution and directly estimate the three-dimensional power spectrum. We use a maximum likelihood estimator that is optimal for a Gaussian random field giving well-defined window functions and error estimates. This measurement presents an initial look at the large-scale structure field probed by the VIPERS. We measure the galaxy bias of the VIPERS-like sample to be bg= 1.38 +/- 0.05 ( sigma 8= 0.8) on scales k < 0.2hMpc-1 averaged over 0.5 < z < 1.2. We further investigate three photometric redshift slices, and marginalizing over the bias factors while keeping other Lambda cold dark matter parameters fixed, we find the matter density Omega m= 0.30 +/- 0.06.
Aims. This paper presents a detailed comparison between high-redshift observations from the VIMOS-VLT Deep Survey (VVDS) and predictions from the Munich semi-analytical model of galaxy formation. In ...particular, we focus this analysis on the magnitude, redshift, and colour distributions of galaxies, as well as their clustering properties. Methods. We constructed 100 quasi-independent mock catalogues, using the output of the semi-analytical model presented in De Lucia & Blaizot (2007, MNRAS, 375, 2). We then applied the same observational selection function of the VVDS-Deep survey, so as to carry out a fair comparison between models and observations. Results. We find that the semi-analytical model reproduces well the magnitude counts in the optical bands. It tends, however, to overpredict the abundance of faint red galaxies, in particular in the i′ and z′ bands. Model galaxies exhibit a colour bimodality that is only in qualitative agreement with the data. In particular, we find that the model tends to overpredict the number of red galaxies at low redshift and of blue galaxies at all redshifts probed by VVDS-Deep observations, although a large fraction of the bluest observed galaxies is absent from the model. In addition, the model overpredicts by about 14 per cent the number of galaxies observed at 0.2 < z < 1 with IAB < 24. When comparing the galaxy clustering properties, we find that model galaxies are more strongly clustered than observed ones at all redshift from z = 0.2 to z = 2, with the difference being less significant above z ≃ 1. When splitting the samples into red and blue galaxies, we find that the observed clustering of blue galaxies is well reproduced by the model, while red model galaxies are much more clustered than observed ones, being principally responsible for the strong global clustering found in the model. Conclusions. Our results show that the discrepancies between Munich semi-analytical model predictions and VVDS-Deep observations, particularly in the galaxy colour distribution and clustering, can be explained to a large extend by an overabundance of satellite galaxies, mostly located in the red peak of the colour bimodality predicted by the model.
We use the overdensity field reconstructed in the volume of the COSMOS area to study the nonlinear biasing of the zCOSMOS galaxies. The galaxy overdensity field is reconstructed using the current ...sample of ~8500 accurate zCOSMOS redshifts at I(AB)<22.5 out to z~1 on scales R from 8 to 12 Mpc/h. By comparing the probability distribution function (PDF) of galaxy density contrast delta_g to the lognormal approximation of the PDF of the mass density contrast delta, we obtain the mean biasing function b(delta,z,R) between the galaxy and matter overdensity field and its second moments b(hat) and b(tilde) up to z~1. Over the redshift interval 0.4<z<1 the conditional mean function <delta_g|delta> = b(delta,z,R) delta is of the following characteristic shape. The function vanishes in the most underdense regions and then sharply rises in a nonlinear way towards the mean densities. <delta_g|delta> is almost a linear tracer of the matter in the overdense regions, up to the most overdense regions in which it is nonlinear again and the local effective slope of <delta_g|delta> vs. delta is smaller than unity. The <delta_g|delta> function is evolving only slightly over the redshift interval 0.4<z<1. The linear biasing parameter increases from b(hat)=1.24+/-0.11 at z=0.4 to b(hat)=1.64+/-0.15 at z=1 for the M_B<-20-z sample of galaxies. b(hat) does not show any dependence on the smoothing scale from 8 to 12 Mpc/h, but increases with luminosity. The measured nonlinearity parameter b(tilde)/b(hat) is of the order of a few percent (but it can be consistent with 0) and it does not change with redshift, the smoothing scale or the luminosity. By matching the linear bias of galaxies to the halo bias, we infer that the M_B<-20-z galaxies reside in dark matter haloes with a characteristic mass of about 3-6 x 10^12 Msol, depending on the halo bias fit.
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