Publications (60)9.8 Total impact
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Article: Hubble Space Telescope imaging of the CFRS and LDSS redshift surveys II: Structural parameter and the evolution of disk galaxies to z=1
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ABSTRACT: (Abridged) Several aspects of the evolution of star-forming galaxies are studied using measures of the 2-dimensional surface brightness profile of a sample of 341 faint objects selected from the CFRS and LDSS redshift surveys that have been observed with the Hubble Space Telescope. The size function of disk scale lengths in disk-dominated galaxies is found to stay roughly constant to z=1. This result, which is strengthened by inclusion of the local de Jong et al (1996) size function, suggests that the scale lengths of typical disks can not have grown substantially with cosmic epoch since z=1, unless a corresponding number of large disks have been destroyed through merging. In addition to a roughly constant number density, the galaxies with large disks have, as a set, properties consistent with the idea that they are similar galaxies observed at different cosmic epochs. However, on average, they show higher B-band disk surface brightnesses, bluer overall (U-V) colors, higher [OII] 3727 equivalent widths and less regular morphologies at high redshift than at low redshift, suggesting an increase in the star-formation rate by a factor of about 3 to z=0.7. This is consistent with the expectations of recent models for the evolution of the disk of the Milky Way and similar galaxies. The evolution of the large disk galaxies is probably not sufficient to account for the evolution of the overall luminosity function of galaxies over the interval 0<z<1, especially if Omega=1. Analysis of the half-light radii of all the galaxies in the sample and construction of the bivariate size-luminosity function suggests that larger changes in the galaxy population are due to smaller galaxies, those with half-light radii around 5 h_{50}^{-1} kpc Comment: 43 pages, 15 figures, 3 plates12/1997; -
Article: Spectrophotometric properties of galaxies at intermediate redshifts (z ~ 0.2–1.0)
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ABSTRACT: We present the gas-phase oxygen abundance (O/H) for a sample of 131 star-forming galaxies at intermediate redshifts ($0.2<z<1.0$). The sample selection, the spectroscopic observations (mainly with VLT/FORS) and associated data reduction, the photometric properties, the emission-line measurements, and the spectral classification are fully described in a companion paper (Paper I). We use two methods to estimate the O/H abundance ratio: the “standard” $R_{\mathrm{23}}$ method which is based on empirical calibrations, and the CL01 method which is based on grids of photo-ionization models and on the fitting of emission lines. For most galaxies, we have been able to solve the problem of the metallicity degeneracy between the high- and low-metallicity branches of the O/H vs. $R_{\mathrm{23}}$ relationship using various secondary indicators. The luminosity – metallicity ($L-Z$) relation has been derived in the $B$- and $R$-bands, with metallicities derived with the two methods ($R_{\mathrm{23}}$ and CL01). In the analysis, we first consider our sample alone and then a larger one which includes other samples of intermediate-redshift galaxies drawn from the literature. The derived $L-Z$ relations at intermediate redshifts are very similar (same slope) to the $L-Z$ relation obtained for the local universe. Our sample alone only shows a small, not significant, evolution of the $L-Z$ relation with redshift up to $z\sim1.0$. We only find statistical variations consistent with the uncertainty in the derived parameters. Including other samples of intermediate-redshift galaxies, we find however that galaxies at $z\sim1$ appear to be metal-deficient by a factor of ${\sim}3$ compared with galaxies in the local universe. For a given luminosity, they contain on average about one third of the metals locked in local galaxies.http://dx.doi.org/10.1051/0004-6361:20053602. -
Article: Spectrophotometric properties of galaxies at intermediate redshifts (z ~ 0.2–1.0)
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ABSTRACT: We present the spectrophotometric properties of a sample of 141 emission-line galaxies at redshifts in the range $0.2<z<1.0$ with a peak around $z\in[0.2,0.4]$. The analysis is based on medium resolution ($R_{{\rm s}}=500{-}600$), optical spectra obtained at VLT and Keck. The targets are mostly “Canada-France Redshift Survey” emission-line galaxies, with the addition of field galaxies randomly selected behind lensing clusters. We complement this sample with galaxy spectra from the “Gemini Deep Deep Survey” public data release. We have computed absolute magnitudes of the galaxies and measured the line fluxes and equivalent widths of the main emission/absorption lines. The last two have been measured after careful subtraction of the fitted stellar continuum using the platefit software originally developed for the SDSS and adapted to our data. We present a careful comparison of this software with the results of manual measurements. The pipeline has also been tested on lower resolution spectra, typical of the “VIMOS/VLT Deep Survey” ($R_{{\rm s}}=250$), by resampling our medium resolution spectra. We show that we can successfully deblend the most important strong emission lines. These data are primarily used to perform a spectral classification of the galaxies in order to distinguish star-forming galaxies from AGNs. Among the initial sample of 141 emission-line galaxies, we find 7 Seyfert 2 (narrow-line AGN), 115 star-forming galaxies and 16 “candidate” star-forming galaxies. Scientific analysis of these data, in terms of chemical abundances, stellar populations, etc., will be presented in subsequent papers of this serie.http://dx.doi.org/10.1051/0004-6361:20053601. -
Article: A census of the physical parameters of nearby galaxies
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ABSTRACT: Not AvailableVazdekis, A.;Peletier, R. F.: Stellar Populations as Building Blocks of Galaxies, Cambridge Univ. Press, 556-560 (2007). -
Article: The rest-frame optical colours of 99 000 sloan digital sky survey galaxies
Monthly Notices of the Royal Astronomical Society, v.371, 121-137 (2006). -
Article: Panchromatic properties of 99 000 galaxies detected by SDSS, and (some by) ROSAT, GALEX, 2MASS, IRAS, GB6, FIRST, NVSS and WENSS surveys
Monthly Notices of the Royal Astronomical Society, v.370, 1677-1698 (2006). -
Article: VVDS-SWIRE - Clustering evolution from a spectroscopic sample of galaxies with redshift 0.2 < z < 2.1 selected from Spitzer IRAC 3.6 μ m and 4.5 μ m photometry
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ABSTRACT: Aims. By combining data from the VIMOS VLT Deep Survey (VVDS) with the Spitzer Wide-area InfraRed Extragalactic survey (SWIRE), we have built the currently largest spectroscopic sample of high redshift galaxies selected in the rest-frame near-infrared. We have obtained 2040 spectroscopic redshifts of galaxies with (m_(3.6))_(AB) < 21.5 at 3.6 μm, and 1255 spectroscopic redshifts of galaxies with (m_(4.5))_(AB) < 21. These allow us to investigate the clustering evolution of galaxies selected via their rest-frame near-infrared luminosity in the redshift range 0.2 < z < 2.1. Methods. We use the projected two-point correlation function w_p(r_p) to study the three dimensional clustering properties of galaxies detected at 3.6 μm and 4.5 μm with the InfraRed Array Camera (IRAC) in the SWIRE survey with measured spectroscopic redshifts from the first epoch VVDS. We compare these properties to those of a larger sample of 16672 SWIRE galaxies for which we have accurate photometric redshifts in the same field. Results. We find that in the 3.6 μm and 4.5 μmm flux limited samples, the apparent correlation length does not change from redshift ~2 to the present. The measured correlation lengths have a mean value of r_0 ≃ 3.9 ± 0.5 h^(-1) Mpc for the galaxies selected at 3.6 μm and a mean value of r_0 ≃ 4.4 ± 0.5 h^(-1) Mpc for the galaxies selected at 4.5 μm, across the whole redshift range explored. These values are larger than those typicaly found for I-band selected galaxies at I_(AB) < 24, for which r_0 varies from 2.69 h^(-1) Mpc to 3.63 h^(-1) Mpc between z = 0.5 to z = 2.1. We find that the difference in correlation length between I-band and 3.6-4.5 μm selected samples decreases with increasing redshift, becoming comparable at z ≃ 1.5. We interpret this as evidence that galaxies with older stellar populations and galaxies actively forming stars reside in comparably over-dense 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 correlation length with cosmic time observed between rest-frame UV-optical and near-infrared selected samples could then be an indication that star formation is gradually shifting to lower density regions with decreasing redshift, while the older, passively evolving galaxies remain in the most over-dense peaks. -
Article: The VIMOS VLT Deep Survey
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ABSTRACT: We present a detailed analysis of the Galaxy Stellar Mass Function (GSMF) of galaxies up to $z=2.5$ as obtained from the VIMOS VLT Deep Survey (VVDS). Our survey offers the possibility to investigate the GSMF using two different samples: (1) an optical ($I$-selected $17.5 <I_{\rm AB}<24$) main spectroscopic sample of about 6500 galaxies over 1750 arcmin$^2$ and (2) a near-IR ($K$-selected $K_{\rm AB}<22.34~{\rm and}~K_{\rm AB}<22.84$) sample of about 10 200 galaxies, with photometric redshifts accurately calibrated on the VVDS spectroscopic sample, over 610 arcmin$^2$. We apply and compare two different methods to estimate the stellar mass ${\cal M}_{\rm stars}$ from broad-band photometry based on different assumptions about the galaxy star-formation history. We find that the accuracy of the photometric stellar mass is satisfactory overall, and show that the addition of secondary bursts to a continuous star formation history produces systematically higher (up to 40%) stellar masses. We derive the cosmic evolution of the GSMF, the galaxy number density and the stellar mass density in different mass ranges. At low redshift ($z\simeq0.2$) we find a substantial population of low-mass galaxies ($<$10$^9~M_\odot$) composed of faint blue galaxies ($M_I-M_K \simeq 0.3$). In general the stellar mass function evolves slowly up to $z\sim0.9$ and more rapidly above this redshift, in particular for low mass systems. Conversely, a massive population is present up to $z=2.5$ and has extremely red colours ($M_I-M_K\simeq 0.7$–$0.8$). We find a decline with redshift of the overall number density of galaxies for all masses ($59\pm5$% for ${\cal M}_{\rm stars} > 10^8~M_\odot$ at $z=1$), and a mild mass-dependent average evolution (“mass-downsizing”). In particular our data are consistent with mild/negligible (${<}30$%) evolution up to $z\sim0.7$ for massive galaxies (${>}6\times10^{10}~M_\odot$). For less massive systems the no-evolution scenario is excluded. Specifically, a large fraction (${\ge}50\%$) of massive galaxies have been assembled and converted most of their gas into stars at $z\sim1$, ruling out “dry mergers” as the major mechanism of their assembly history below $z\simeq1$. This fraction decreases to ${\sim}33\%$ at $z\sim2$. Low-mass systems have decreased continuously in number density (by a factor of up to $4.1\pm0.9$) from the present age to $z=2$, consistent with a prolonged mass assembly also at $z<1$. The evolution of the stellar mass density is relatively slow with redshift, with a decrease of a factor of $2.3\pm0.1$ at $z=1$ and about $4.5\pm0.3$ at $z=2.5$.http://dx.doi.org/10.1051/0004-6361:20077609. -
Article: Physical properties of galaxies and their evolution in the VIMOS VLT Deep Survey
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ABSTRACT: Aims. We present a continuation of our study about the relation between stellar mass and gas-phase metallicity in the VIMOS VLT Deep Survey (VVDS). In this work we extend the determination of metallicities up to redshift $\approx$1.24 for a sample of 42 star-forming galaxies with a mean redshift value of 0.99.Methods. For a selected sample of emission-line galaxies, we use both diagnostic diagrams and empirical calibrations based on [Oii] emission lines along with the empirical relation between the intensities of the [Oiii] and [Neiii] emission lines and the theoretical ratios between Balmer recombination emission lines to identify star-forming galaxies and to derive their metallicities. We derive stellar masses by fitting the whole spectral energy distribution with a set of stellar population synthesis models.Results. These new methods allow us to extend the mass-metallicity relation to higher redshift. We show that the metallicity determinations are consistent with more established strong-line methods. Taken together this allows us to study the evolution of the mass-metallicity relation up to $z$ $\approx$ 1.24 with good control of systematic uncertainties. We find an evolution with redshift of the average metallicity of galaxies very similar to those reported in the literature: for a given stellar mass, galaxies at $z$ ~ 1 have, on average, a metallicity ~ 0.3 dex lower than galaxies in the local universe. However we do not see any significant metallicity evolution between redshifts $z$ ~ 0.7 (Paper I) and $z$ ~ 1.0 (this paper). We find also the same flattening of the mass-metallicity relation for the most massive galaxies as reported in Paper I at lower redshifts, but again no apparent evolution of the slope is seen between $z$ ~ 0.7 and $z$ ~ 1.0.http://dx.doi.org/10.1051/0004-6361:200810558. -
Article: Physical properties of galaxies and their evolution in the VIMOS VLT Deep Survey
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ABSTRACT: Aims. We want to derive the mass-metallicity relation of star-forming galaxies up to $z$ ~ 0.9, using data from the VIMOS VLT Deep Survey. The mass-metallicity relation is commonly understood as the relation between the stellar mass and the gas-phase oxygen abundance.Methods. Automatic measurement of emission-line fluxes and equivalent widths have been performed on the full spectroscopic sample of the VIMOS VLT Deep Survey. This sample is divided into two sub-samples depending on the apparent magnitude selection: wide ($I_{\mathrm{AB}}$ < 22.5) and deep ($I_{\mathrm{AB}}$ < 24). These two samples span two different ranges of stellar masses. Emission-line galaxies have been separated into star-forming galaxies and active galactic nuclei using emission line ratios. For the star-forming galaxies the emission line ratios have also been used to estimate gas-phase oxygen abundance, using empirical calibrations renormalized in order to give consistent results at low and high redshifts. The stellar masses have been estimated by fitting the whole spectral energy distributions with a set of stellar population synthesis models.Results. We assume at first order that the shape of the mass-metallicity relation remains constant with redshift. Then we find a stronger metallicity evolution in the wide sample as compared to the deep sample. We thus conclude that the mass-metallicity relation is flatter at higher redshift. At $z$ ~ 0.77, galaxies at $10^{9.4}$ solar masses have $-0.18$ dex lower metallicities than galaxies of similar masses in the local universe, while galaxies at $10^{10.2}$ solar masses have $-0.28$ dex lower metallicities. By comparing the mass-metallicity and luminosity-metallicity relations, we also find an evolution in mass-to-light ratio: galaxies at higher redshifts being more active. The observed flattening of the mass-metallicity relation at high redshift is analyzed as evidence in favor of the open-closed model.http://dx.doi.org/10.1051/0004-6361:200810397. -
Article: The VVDS-VLA deep field
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ABSTRACT: Aims. The availability of wide angle and deep surveys, both in the optical and the radio band, allows us to explore the evolution of radio sources with optical counterparts up to redshift $z\sim 1.1$ in an unbiased way using large numbers of radio sources and well defined control samples of radio-quiet objects.Methods. We use the 1.4 GHz VIMOS-VLA Deep Survey, the optical VIMOS-VLT Deep Survey and the CFHT Legacy Survey to compare the properties of radio-loud galaxies with respect to the whole population of optical galaxies. The availability of multiband photometry and high quality photometric redshifts allows us to derive rest-frame colors and radio luminosity functions to a limit of a $B$ rest-frame magnitude of $M_B=-20$. We derive spectrophotometric types, following the classification of Zucca et al. (2006, A&A, 455, 879), in order to have a priori knowledge of the optical evolution of different galaxy classes.Results. Galaxy properties and luminosity functions are estimated up to $z\sim 1$ for radio-loud and radio-quiet early and late type galaxies. Radio-loud late type galaxies show significantly redder colors than radio-quiet objects of the same class and this is related to the presence of more dust in stronger star forming galaxies. We estimate the optical luminosity functions, stellar masses and star formation rate distributions for radio sources and compare them with those derived for a well defined control sample, finding that the probability of a galaxy to be a radio emitter significantly increases at high values of these parameters. Radio-loud early type galaxies exhibit luminosity evolution in their bivariate radio-optical luminosity function, due to evolution in the radio-optical ratio. The lack of evolution of the mass function of radio-loud early type galaxies means that no new AGN are formed at redshift $z<1$. In contrast, radio-loud late type objects exhibit a strong evolution, both in luminosity and density, of the radio luminosity function for $z>0.7$. This evolution is a direct effect of the strong optical evolution of this class and no significant change with redshift in the radio-optical ratio is required. With the knowledge of the radio-optical ratio and the optical and radio luminosity functions for late type galaxies, we show that it is possible to estimate the star formation history of the Universe up to redshift $z\sim 1.5$, using optical galaxies as tracers of the global radio emission.http://dx.doi.org/10.1051/0004-6361:200810567. -
Article: The VIMOS VLT deep survey
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ABSTRACT: Aims. We present a new $K_{\rm s}$-band survey that represents a significant extension to the previous wide-field $K_{\rm s}$-band imaging survey within the 0226-04 field of the VIMOS-VLT deep survey (VVDS). The new data add ~458 arcmin$^2$ to the previous imaging program, thus allowing us to cover a total contiguous area of ~600 arcmin$^2$ within this field.Methods. Sources were identified both directly on the final $K$-band mosaic image and on the corresponding, deep $\chi^2-g^{\prime}r^{\prime}i^{\prime}$ image from the CFHT Legacy Survey in order to reduce contamination, while ensuring compilation of a truly $K$-selected catalogue down to the completeness limit of the $K_{\rm s}$-band. The newly determined $K_{\rm s}$-band magnitudes are used in combination with the ancillary multiwavelength data for determining accurate photometric redshifts.Results. The final catalogue totals ~52 000 sources, out of which ~4400 have a spectroscopic redshift from the VVDS first epoch survey. The catalogue is 90% complete down to $K_{{\rm Vega}}$ = 20.5 mag. We present $K_{\rm s}$-band galaxy counts and angular correlation function measurements down to this magnitude limit. Our results are in good agreement with previously published work. We show that using $K$ magnitudes to determine photometric redshifts significantly lowers the incidence of catastrophic errors. The data presented in this paper are publicly available through the CENCOS database.http://dx.doi.org/10.1051/0004-6361:20078526. -
Article: The VIMOS-VLT deep survey
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ABSTRACT: Aims. In this paper we discuss the mix of star-forming and passive galaxies up to $z$ ~ 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 $D_n$(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.http://dx.doi.org/10.1051/0004-6361:20065942. -
Article: VVDS-SWIRE
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ABSTRACT: Aims.By combining data from the VIMOS VLT Deep Survey (VVDS) with the Spitzer Wide-area InfraRed Extragalactic survey (SWIRE), we have built the currently largest spectroscopic sample of high redshift galaxies selected in the rest-frame near-infrared. We have obtained 2040 spectroscopic redshifts of galaxies with $(m_{3.6})_{\rm AB}$ < 21.5 at 3.6 $\mu $m, and 1255 spectroscopic redshifts of galaxies with $(m_{4.5})_{\rm AB}$ < 21. These allow us to investigate the clustering evolution of galaxies selected via their rest-frame near-infrared luminosity in the redshift range 0.2 < $z$ < 2.1.Methods.We use the projected two-point correlation function $w_{\rm p}(r_{\rm p})$ to study the three dimensional clustering properties of galaxies detected at 3.6 $\mu $m and 4.5 $\mu $m with the InfraRed Array Camera (IRAC) in the SWIRE survey with measured spectroscopic redshifts from the first epoch VVDS. We compare these properties to those of a larger sample of 16672 SWIRE galaxies for which we have accurate photometric redshifts in the same field.Results.We find that in the 3.6 $\mu $m and 4.5 $\mu $m flux limited samples, the apparent correlation length does not change from redshift ~2 to the present. The measured correlation lengths have a mean value of $r_0$ $\simeq$ 3.9$\pm$0.5 h$^{-1}$ Mpc for the galaxies selected at 3.6 $\mu $m and a mean value of $r_0$ $\simeq$ 4.4$\pm$0.5 h$^{-1}$ Mpc for the galaxies selected at 4.5 $\mu $m, across the whole redshift range explored. These values are larger than those typicaly found for $I$-band selected galaxies at $I_{\rm AB}$ < 24, for which $r_0$ varies from 2.69 h$^{-1}$ Mpc to 3.63 h$^{-1}$ Mpc between $z$ = 0.5 to $z = 2.1$. We find that the difference in correlation length between $I$-band and 3.6-4.5 $\mu$m selected samples decreases with increasing redshift, becoming comparable at $z$ $\simeq$ 1.5. We interpret this as evidence that galaxies with older stellar populations and galaxies actively forming stars reside in comparably over-dense environments at epochs earlier than $z$ $\simeq$ 1.5, supporting the recently reported flattening of the color-density relation at high redshift. The increasing difference in correlation length with cosmic time observed between rest-frame UV-optical and near-infrared selected samples could then be an indication that star formation is gradually shifting to lower density regions with decreasing redshift, while the older, passively evolving galaxies remain in the most over-dense peaks.http://dx.doi.org/10.1051/0004-6361:20077161. -
Article: The VIMOS VLT Deep Survey
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ABSTRACT: Context. The rate at which galaxies grow via successive mergers is a key element in understanding the main phases of galaxy evolution.Aims. We measure the evolution of the fraction of galaxies in pairs and the merging rate since redshift z ~ 1 assuming a ($H_0$ = 70 km s$^{-1}$ Mpc$^{-1}$, $\Omega_{\rm M}$ = 0.3 and $\Omega_{\Lambda}$ = 0.7) cosmology.Methods. From the VIMOS VLT Deep Survey we use a sample of 6464 galaxies with $I_{\rm AB}$$ \leq$ 24 to identify 314 pairs of galaxies, each member with a secure spectroscopic redshift, which are close in both projected separation and in velocity.Results. We estimate that at z ~ 0.9, 10.9 $\pm$ 3.2% of galaxies with $M_{B}(z)$$ \leq$ -18-Qz ($Q$ = 1.11) are in pairs with separations $\Delta r_{\rm p}$$ \leq$ 20 h$^{-1}$ kpc, $\Delta v$$\leq$ 500 km s$^{-1}$, and with $\Delta M_{B}$$ \leq$ 1.5, significantly larger than 3.8 $\pm$ 1.7% at $z$ ~ 0.5; thus, the pair fraction evolves as (1 + $z$)$^m$ with $m$ = 4.73 $\pm$ 2.01. For bright galaxies with $M_{B}(z = 0)$ $\leq$ -18.77, the pair fraction is higher and its evolution with redshift is flatter with $m$ = 1.50 $\pm$ 0.76, a property also observed for galaxies with increasing stellar masses. Early-type pairs (dry mergers) increase their relative fraction from 3% at $z$ ~ 0.9 to 12% at $z$ ~ 0.5. The star formation rate traced by the rest-frame [OII] $EW$ increases by $26$ $\pm$ 4% for pairs with the smallest separation $r_{\rm p}$$ \leq$ 20 h$^{-1}$ kpc. Following published prescriptions to derive merger timescales, we find that the merger rate of $M_{B}(z)$$ \leq $-18-Qz galaxies evolves as $N_{\rm mg}$ = (4.96 $\pm$ 2.07)$\times$10$^{-4}$$\times(1 + z)^{2.20 \pm 0.77}$ mergers Mpc$^{-3}$ Gyr$^{-1}$.Conclusions. The merger rate of galaxies with $M_{B}(z)$$ \leq$ -18-Qz has significantly evolved since $z$ ~ 1 and is strongly dependent on the luminosity or stellar mass of galaxies. The major merger rate increases more rapidly with redshift for galaxies with fainter luminosities or stellar mass, while the evolution of the merger rate for bright or massive galaxies is slower, indicating that the slow evolution reported for the brightest galaxies is not universal. The merger rate is also strongly dependent on the spectral type of galaxies involved. Late-type mergers were more frequent in the past, while early-type mergers are more frequent today, contributing to the rise in the local density of early-type galaxies. About 20% of the stellar mass in present day galaxies with $\log(M/M_{{\odot}}) $$\geq$ 9.5 has been accreted through major merging events since $z$ = 1. This indicates that major mergers have contributed significantly to the growth in stellar mass density of bright galaxies over the last half of the life of the Universe.http://dx.doi.org/10.1051/0004-6361/200810569. -
Article: The Vimos VLT Deep Survey
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ABSTRACT: 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 $0.2<z<1.4$.Results. We observe a significant mass and optical color segregation over the whole redshift interval covered by our sample, such that the median value of the mass distribution is larger and the rest-frame optical color is redder in regions of high galaxy density. The amplitude of the mass segregation changes little with redshift, at least in the high stellar mass regime that we can uniformly sample over the $0.2 < z < 1.4$ redshift interval. The color segregation, instead, decreases significantly for $z > 0.7$. However, when we consider only galaxies in narrow bins of stellar mass, in order to exclude the effects of stellar mass segregation on galaxy properties, we no longer observe any significant color segregation.http://dx.doi.org/10.1051/0004-6361/200810511. -
Article: The VIMOS VLT Deep Survey
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ABSTRACT: Aims. Our aim is to investigate the history of mass assembly for galaxies of different stellar masses and types.Methods. We selected a mass-limited sample of 4048 objects from the VIMOS VLT Deep Survey (VVDS) in the redshift interval 0.5 $\le$ $z$ $\le$ 1.3. We then used an empirical criterion, based on the amplitude of the 4000 ÅBalmer break ($D_{\rm n}$4000), to separate the galaxy population into spectroscopically early- and late-type systems. The equivalent width of the [OII]3727 line is used as proxy for the star formation activity. We also derived a type-dependent stellar mass function in three redshift bins.Results. We discuss to what extent stellar mass drives galaxy evolution, showing for the first time the interplay between stellar ages and stellar masses over the past 8 Gyr. Low-mass galaxies have small $D_{\rm n}$4000 and at increasing stellar mass, the galaxy distribution moves to higher $D_{\rm n}$4000 values as observed in the local Universe. As cosmic time goes by, we witness an increasing abundance of massive spectroscopically early-type systems at the expense of the late-type systems. This spectral transformation of late-type systems into old massive galaxies at lower redshift is a process started at early epochs ($z$ > 1.3) and continuing efficiently down to the local Universe. This is also confirmed by the evolution of our type-dependent stellar mass function. The underlying stellar ages of late-type galaxies apparently do not show evolution, most likely as a result of a continuous and efficient formation of new stars. All star formation activity indicators consistently point towards a star formation history peaked in the past for massive galaxies, with little or no residual star formation taking place in the most recent epochs. In contrast, most of the low-mass systems show just the opposite characteristics, with significant star formation present at all epochs. The activity and efficiency of forming stars are mechanisms that depend on galaxy stellar mass, and the stellar mass assembly becomes progressively less efficient in massive systems as time elapses. The concepts of star formation downsizing and mass assembly downsizing describe a single scenario that has a top-down evolutionary pattern in how the star formation is quenched, as well as how the stellar mass is grown. The role of (dry) merging events seems to be only marginal at $z$ < 1.3, as our estimated efficiency in stellar mass assembly can possibly account for the progressive accumulation of observed passively evolving galaxies.http://dx.doi.org/10.1051/0004-6361:20077910. -
Article: The VIMOS VLT Deep Survey
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ABSTRACT: We have reconstructed the three-dimensional density fluctuation maps to $z\sim 1.5$ using the distribution of galaxies observed in the VVDS-Deep survey. We use this overdensity field to measure the evolution of the probability distribution function and its lower-order moments over the redshift interval $0.7< z <1.5$. We apply a self-consistent reconstruction scheme which includes a complete non-linear description of galaxy biasing and which has been thoroughly tested on realistic mock samples. We find that the variance and skewness of the galaxy distribution evolve over this redshift interval in a way that is remarkably consistent with predictions of first- and second-order perturbation theory. This finding confirms the standard gravitational instability paradigm over nearly 9 Gyr of cosmic time and demonstrates the importance of accounting for the non-linear component of galaxy biasing to consistently reproduce the higher-order moments of the galaxy distribution and their evolution.http://dx.doi.org/10.1051/0004-6361:20078891. -
Article: The rest-frame optical colours of 99000 Sloan Digital Sky Survey galaxies
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ABSTRACT: We discuss the colours of 99088 galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 1 `main' spectroscopic sample (a flux-limited sample, rPet < 17.77, for 1360 deg2) in the rest-frame Strömgren system (uz, vz, bz, yz). This narrow-band (~200 Å) photometric system, first designed for the determination of effective temperature, metallicity and gravity of stars, measures the continuum spectral slope of galaxies in the rest-frame 3200-5800 Å wavelength range. We synthesize rest-frame Strömgren magnitudes from SDSS spectra, and find that galaxies form a remarkably narrow locus (~0.03 mag) in the resulting colour-colour diagram. Using the Bruzual & Charlot population-synthesis models, we demonstrate that the position of a galaxy along this locus is controlled by metallicity and age of the dominant stellar population. The distribution of galaxies along the locus is bimodal, with the local minimum corresponding to an ~1-Gyr-old single stellar population. The position of a galaxy perpendicular to the locus is independent of metallicity and age, and reflects the galaxy's dust content, as implied by both the models and the statistics of IRAS detections. Comparison of the galaxy locus in the rest-frame Strömgren colour-colour diagram with the galaxy locus in the HdeltaA-Dn(4000) diagram, utilized by Kauffmann et al. to estimate stellar masses, reveals a tight correlation, although the two analysed spectral ranges barely overlap. Furthermore, the rest-frame r - i colour (5500-8500 Å wavelength range) can be `predicted' with an rms of 0.05 mag using the rest-frame Strömgren colours. Overall, the galaxy spectral energy distribution in the entire ultraviolet to near-infrared range can be described as a single-parameter family with an accuracy of 0.1 mag, or better. This nearly one-dimensional distribution of galaxies in the multidimensional space of measured parameters strongly supports the conclusion of Yip et al., based on a principal component analysis, that SDSS galaxy spectra can be described by a small number of eigenspectra. Furthermore, the rest-frame Strömgren colours correlate tightly with the classification scheme proposed by Yip et al. based on the first three eigenspectra. Apparently, the contributions of stellar populations that dominate the optical emission from galaxies are combined in a simple and well-defined way. We also find a remarkably tight correlation between the rest-frame Strömgren colours of emission-line galaxies and their position in the Baldwin-Phillips-Terlevich diagram. These correlations between colours and various spectroscopic diagnostic parameters support earlier suggestions that rest-frame Strömgren photometry offers an efficient tool to study faint cluster galaxies and low surface brightness objects without performing time-consuming spectral observations. -
Article: The host galaxies of active galactic nuclei
Monthly Notices of the Royal Astronomical Society, v.346, 1055-1077 (2003).
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Institutions
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2006
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Max-Planck-Institut für Astrophysik
Garching bei München, Bavaria, Germany -
University of Connecticut
- Department of Physics
Storrs, CT, USA
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2005–2006
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University of Porto
Porto, Distrito do Porto, Portugal -
French National Centre for Scientific Research
- Institut d'astrophysique spatiale (IAS)
Paris, Ile-de-France, France
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