The VLA-VIRMOS Deep Field Bondi, M.; Ciliegi, P.; Zamorani, G. ...
Astronomy and astrophysics (Berlin),
06/2003, Letnik:
403, Številka:
3
Journal Article
Aims. We present a measurement of the dependence of galaxy clustering on galaxy stellar mass at redshift z\sim0.9, 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, w_{\rm p}(r_{\rm p}), within mass-selected sub-samples covering the range similar to 10 super(9) and similar to 10 similar to M_\odot. 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_\odot) =9.5, with about two thirds of the galaxies in the range 9<\log\,(M/M_\odot) <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/M_\odot) =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\sim0.85. We quantify this by fitting the projected function w_{\rm p}(r_{\rm p}) with a power-law model. The clustering length increases from r sub(0) =2.76 sub(-0.15) super(+0.17) h super(-1) Mpc for galaxies with mass 10 {9} similar to M_\odot$--> M>10 {9} similar to M_\odot to r sub(0) =4.28 sub(-0.45) super(+0.43) h super(-1) Mpc when only the most massive (10 similar to M_\odot$--> M>10 similar to M_\odot) are considered. At the same time, we observe a significant increase in the slope, which over the same range of masses, changes from gamma=1.67_to gamma=2.28_. Comparison to the SDSS measurements at z\sim0.15 shows that the evolution of w_{\rm p}(r_{\rm p}) is significant for samples of galaxies with M<10 similar to M_\odot, while it is negligible for more massive objects. Considering the growth of structure, this implies that the linear bias b_{\rm L} of the most massive galaxies evolves more rapidly between these two cosmic epochs. We quantify this effect by computing the value of b_{\rm L} from the SDSS and VVDS clustering amplitudes and find that b_{\rm L} decreases from 1.5\pm0.2 at z\sim0.85 to 1.33\pm0.03 at z\sim0.15, for the most massive galaxies, while it remains virtually constant (b_{\rm L}\sim1.3) 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.
Measuring the build-up of stellar mass is one of the main objectives of studies of galaxy evolution. Traditionally, the mass in stars and the star formation rates have been measured by different ...indicators, such as photometric colours, emission lines, and the UV and IR emission. We intend to show that it is possible to derive the physical parameters of galaxies from their broad-band spectral energy distribution out to a redshift of 1.2. This method has the potential to yield the physical parameters of all galaxies in a single field in a homogeneous way, thus overcoming problems with the sample size that particularly plague methods relying on spectroscopy. We use an extensive dataset, assembled in the context of the VVDS survey, which reaches from the UV to the IR and covers a sample of 84 073 galaxies over an area of 0.89 deg2. We also use a library of 100 000 model galaxies with a wide variety of star formation histories (in particular including late bursts of star formation). We find that we can determine the physical parameters stellar mass, age, and star formation rate with good confidence. We validate the star formation rate determination in particular by comparing it to a sample of spectroscopically observed galaxies with an emission-line measurement. While the attenuation in the galaxies shows more scatter, the mean over the sample is unbiased. Metallicity, however, cannot be measured from rest-frame optical photometry alone. As a first application we use our sample to build the number density function of galaxies as a function of stellar mass, specific star formation rate, and redshift. We are then able to study whether the stellar mass function at a later time can be predicted from the stellar mass function and star formation rate distribution at an earlier time. We find that, between redshifts of 1.02 and 0.47, the predicted growth in stellar mass from star formation agrees with the observed one. However, the predicted stellar mass density for massive galaxies is lower than observed, while the mass density of intermediate mass galaxies is overpredicted. This apparent discrepancy can be explained by major and minor mergers. Indeed, when comparing with a direct measurement of the major merger rate from the VVDS survey, we find that major mergers can account for about half of the mass build-up at the massive end. Minor mergers are very likely to contribute the missing fraction.
We measure the evolution of clustering for galaxies with different spectral types from 6495 galaxies with 17.5 less than or equal to I sub(AB) less than or equal to 24 and measured spectroscopic ...redshifts in the first epoch VIMOS-VLT Deep Survey (VVDS). We divide our sample into four classes, based on the fit of well-defined galaxy spectral energy distributions on observed multi-color data. We measure the projected correlation function w sub(p)(r sub(p)) and estimate the best-fit parameters for a power-law real-space correlation function xi (r) = (r/r sub(o)) super(- gamma ). We find the clustering of early-spectral-type galaxies to be markedly stronger than that of late-type galaxies at all redshifts up to z 1.2. At z similar to 0.8, early-type galaxies display a correlation length r sub(0) = 4.8 plus or minus 0.9 h super(-1) Mpc, while late types have r sub(0) = 2.5 plus or minus 0.4 h super(-1) Mpc. For the latest class of star-forming blue galaxies, we are able to push our clustering measurement to an effective redshift z similar to 1.4, for luminous galaxies (M sub(B)(AB) -21). The clustering of these objects increases up to r sub(0) = 3.42 plus or minus 0.7 h super(-1) Mpc for z = 1.2,2.0. The relative bias between early- and late-type galaxies within our magnitude-limited survey remains approximately constant with b = 1.6 plus or minus 0.3 from z = 0 to z = 1.2. This result is in agrement with the local findings and fairly robust against different way of classifying red and blue galaxies. When compared to the expected linear growth of mass fluctuations, a natural interpretation of these observations is that: (a) the assembly of massive early type galaxies is already mostly complete in the densest dark matter halos at z 1; (b) luminous late-type galaxies are located in higher-density, more clustered regions of the Universe at z 1.5 than their local low luminous counterpart, indicating that star formation activity is progressively increasing, going back in time, in the higher-density peaks that today are mostly dominated by old galaxies.
The spectroscopic analysis of 117 serendipitous sources in the HELLAS2XMM 1df (1 degree field) survey is described. Of these, 106 sources, of which 86% have a spectroscopic redshift, are used to ...evaluate the fraction of X-ray absorbed (log N sub(H) > 22) Active Galactic Nuclei (AGN) in the 2-10 keV flux range 0.8-20 x 10 super(-14) erg cm super(-2) s super(-1). This fraction turns out lower than what is predicted by two well known Cosmic X-Ray Background synthesis models, and the discrepancy is significant at the 99.999% level. This result consolidates the findings recently obtained by other authors. In the flux interval explored, the data are consistent with an intrinsic distribution of the absorbing columns (flat per decade above log N sub(H) > 21) independent of luminosity and redshift, together with an AGN luminosity function evolving purely in luminosity. It is shown that, on the other hand, extrapolation to lower fluxes fails to reproduce the results inferred from the Chandra Deep Field North survey. It is found that about 40% of the high luminosity sources in our sample have best fit log N sub(H) > 22, and the surface density of these X-ray obscured QSOs can then be estimated at about 48 per square degree, at the flux limit of similar to 10 super(-14) erg cm super(-2) s super(-1) of the HELLAS2XMM 1df survey. As a side issue, 5 or 6 out of 60 sources, that is about 10%, identified with broad line AGN, turn out to be affected by log N sub(H) > 22 absorption.
Aims. In this paper we discuss the mix of star-forming and passive galaxies up to z similar to 2, based on the first epoch VIMOS-VLT Deep Survey (VVDS) data. Methods. We compute rest-frame magnitudes ...and colors and analyse the color-magnitude relation and the color distributions. We also use the multi-band VVDS photometric data and spectral templates fitting to derive multi-color galaxy types. Using our spectroscopic dataset we separate galaxies based on a star-formation activity indicator derived combining the equivalent width of the OII emission line and the strength of the D sub( )n(4000) continuum break. Results. In agreement with previous works we find that the global galaxy rest-frame color distribution follows a bimodal distribution at z \le 1, and we establish that this bimodality holds up to at least z =1.5. The details of the rest-frame color distribution depend however on redshift and on galaxy luminosity, with faint galaxies being bluer than the luminous ones over the whole redshift range covered by our data, and with galaxies becoming bluer as redshift increases. This latter blueing trend does not depend, to a first approximation, on galaxy luminosity. The comparison between the spectral classification and the rest-frame colors shows that about 35-40% of the red objects are in fact star forming galaxies. Hence we conclude that the red sequence cannot be used to effectively isolate a sample of purely passively evolving objects within a cosmological survey. We show how multi-color galaxy types have a slightly higher efficiency than rest-frame color in isolating the passive, non star- forming galaxies within the VVDS sample. Connected to these results is also the finding that the color-magnitude relations derived for the color and for the spectroscopically selected early-type galaxies have remarkably similar properties, with the contaminating star-forming galaxies within the red sequence objects introducing no significant offset in the rest frame colors. Therefore the average color of the red objects does not appear to be a very sensitive indicator for measuring the evolution of the early-type galaxy population.
Context: Hierarchical models of galaxy formation predict that the properties of a dark matter halo depend on the large-scale environment surrounding the halo. As a result of this correlation, we ...expect massive haloes to be present in larger number in overdense regions than in underdense ones. Given that a correlation exists between a galaxy stellar mass and the hosting dark matter halo mass, the segregation in dark matter halo mass should then result in a segregation in the distribution of stellar mass in the galaxy population. Aims: In this work we study the distribution of galaxy stellar mass and rest-frame optical color as a function of the large-scale galaxy distribution using the VLT VIMOS Deep Survey sample, in order to verify the presence of segregation in the properties of the galaxy population. Methods: We use VVDS redshift measurements and multi-band photometric data to derive estimates of the stellar mass, rest-frame optical color, and of the large-scale galaxy density, on a scale of approximately 8 Mpc, for a sample of 5619 galaxies in the redshift range 0.2
We model the evolution of the mean galaxy occupation of dark matter haloes over the range 0.1 < z < 1.3, using the data from the VIMOS-VLT Deep Survey. The galaxy projected correlation function wp(r ...sub(p)) was computed for a set of luminosity-limited subsamples and fits to its shape were obtained using two variants of halo occupation distribution (HOD) models. These provide us with a set of best-fitting parameters, from which we obtain the average mass of a halo and average number of galaxies per halo. We find that after accounting for the evolution in luminosity and assuming that we are largely following the same population, the underlying dark matter halo shows a growth in mass with decreasing redshift as expected in a hierarchical structure formation scenario. Using two different HOD models, we see that the halo mass grows by 90 per cent over the redshift interval z = 0.5, 1.0. This is the first time the evolution in halo mass at high redshifts has been obtained from a single data survey and it follows the simple form seen in N-body simulations with M(z) = M sub(0) e super(- beta z), and beta = 1.3 plus or minus 0.30. This provides evidence for a rapid accretion phase of massive haloes having a present-day mass M sub(0) similar to 10 super(13.5) h super(-1) M sub( Phi ) with a m > 0.1 M sub(0) merger event occurring between redshifts of 0.5 and 1.0. Furthermore, we find that more luminous galaxies are found to occupy more massive haloes irrespective of the redshift. Finally, the average number of galaxies per halo shows little increase from redshift z similar to 1.0 to similar to 0.5, with a sharp increase by a factor of similar to 3 from z similar to 0.5 to similar to 0.1, likely due to the dynamical friction of subhaloes within their host haloes.
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