G. Busarello

The VIMOS VLT deep survey. The evolution of galaxy clustering to z 2 from first epoch observations

This paper presents the evolution of the clustering of the main population of galaxies from z=2.1 to z=0.2, from the first epoch VIMOS VLT Deep Survey (VVDS), a magnitude limited sample with 17.5<=I_{AB}<=24. We have computed the correlation functions \\xi(r_p,\\pi) and w_p(r_p), and the correlation length r_0(z), for the VVDS-02h and VVDS-CDFS fields, for a total of 7155 galaxies in a 0.61deg^2 area. We find that the correlation length in this sample stays roughly constant from z=0.5 to z=1.1, with r_0(z)=2.5-2.8 h^{-1} Mpc (comoving), for galaxies comparable in luminosity to the local 2dFGRS and SDSS samples, indicating that the amplitude of the correlation function was ~2.5x lower at z~1 than observed locally. The correlation length in our lowest redshift bin z=[0.2,0.5] is r_0=2.4 h^{-1} Mpc, lower than for any other population at the same redshift, indicating the low clustering of very low luminosity galaxies, 1.5 magnitudes fainter than in the 2dFGRS or SDSS. The correlation length is increasing to r_0~3.0 h^{-1} Mpc at higher redshifts z=[1.3,2.1], as we are observing increasingly brighter galaxies, comparable to galaxies with MB_AB=-20.5 locally. We compare our measurement to the DEEP2 measurements in the range z=[0.7,1.35] \\citep{coil} on the population selected applying the same magnitude and color selection criteria as in their survey, and find comparable results. 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 are already tracing the large scale structures emerging from the dark matter distribution 9-10 billion years ago, a supporting evidence for a strong evolution of the galaxy vs. dark matter bias.

ACCESS- V. dissecting ram-pressure stripping through integral-field spectroscopy and multiband imaging

We study the case of a bright (L>L*) barred spiral galaxy from the rich cluster A3558 in the Shapley supercluster core (z=0.05) undergoing ram-pressure stripping. Integral-field spectroscopy, complemented by multi-band imaging, allows us to reveal the impact of ram pressure on the interstellar medium. We study in detail the kinematics and the physical conditions of the ionized gas and the properties of the stellar populations. We observe one-sided extraplanar ionized gas along the full extent of the galaxy disc. Narrow-band Halpha imaging resolves this outflow into a complex of knots and filaments. The gas velocity field is complex with the extraplanar gas showing signature of rotation. In all parts of the galaxy, we find a significant contribution from shock excitation, as well as emission powered by star formation. Shock-ionized gas is associated with the turbulent gas outflow and highly attenuated by dust. All these findings cover the whole phenomenology of early-stage ram-pressure stripping. Intense, highly obscured star formation is taking place in the nucleus, probably related to the bar, and in a region 12 kpc South-West from the centre. In the SW region we identify a starburst characterized by a 5x increase in the star-formation rate over the last ~100 Myr, possibly related to the compression of the interstellar gas by the ram pressure. The scenario suggested by the observations is supported and refined by ad hoc N-body/hydrodynamical simulations which identify a rather narrow temporal range for the onset of ram-pressure stripping around t~60 Myr ago, and an angle between the galaxy rotation axis and the intra-cluster medium wind of ~45 deg. Taking into account that the galaxy is found ~1 Mpc from the cluster centre in a relatively low-density region, this study shows that ram-pressure stripping still acts efficiently on massive galaxies well outside the cluster cores.

On the Invariant Distribution of Galaxies in the re--mie plane out to z = 0.64

We study the evolution of the relation between half-light (effective) radius, re, and mean surface brightness, μe, known as the Kormendy relation, out to redshift z = 0.64 in the V-band rest frame on the basis of a large sample of spheroidal galaxies (N = 228) belonging to three clusters of galaxies. The present sample constitutes the largest data set for which the Kormendy relation is investigated up to a look-back time of ~6 Gyr (H0 = 70 km s-1 Mpc-1, Ωm = 0.3, ΩΛ = 0.7). A new fitting procedure, which suitably accounts for selection criteria effects, makes it possible for the first time to study the trend of the slope (β) and of the intrinsic dispersion (σ) of the Kormendy relation, and the properties of the whole distribution in the re-μe plane as a function of look-back time. The slope β of the relation does not change from z = 0.64 to the present epoch: β = 2.92 ± 0.08, implying a tight constraint of 18%-28% on the variation of the stellar formation epoch along the sequence of spheroidal galaxies per decade of radius. The intrinsic dispersion of the relation, σ = 0.40 ± 0.03, does not vary with redshift, and the distribution of galaxy sizes, as well as the distribution in the plane of the effective parameters, does not vary among the clusters, as proven by the Kolmogorov-Smirnov tests. We conclude that whatever the mechanism driving galaxy evolution is, it does not significantly affect the properties of bright galaxies in the log re-μe plane at least since z = 0.64. The evolution of the zero point of the Kormendy relation is fully explained by the cosmological dimming in an expanding universe plus the passive luminosity evolution of stellar populations with high formation redshift (zf > 2).

The VVDS-VLA Deep Field II. Optical and near infrared identifications of VLA S(1.4GHz)>80 microJy sources in the VIMOS VLT Deep Survey VVDS-02h field

In this paper we present the optical and near-infrared identifications of the 1054 radio sources detected in the 20cm deep radio survey down to a 5sigma flux limit of about 80 microJy obtained with the VLA in the VIMOS VLT Deep Survey VVDS-02h deep field. Using U,B,V,R,I and K data, we identified 718 radio sources (~74% of the whole sample). The photometric redshift analysis shows that, in each magnitude bin, the radio sample has a higher median photometric redshift than the whole optical sample, while the median (V-I) color of the radio sources is redder than the median color of the whole optical sample. These results suggest that radio detection is preferentially selecting galaxies with higher intrinsic optical luminosity. From the analysis of the optical properties of the radio sources as function of the radio flux, we found that while about 35% of the radio sources are optically unidentified in the higher radio flux bin (S> 1.0 mJy), the percentage of unidentified sources decreases to about 25% in the faintest bins (S< 0.5 mJy). The median I magnitude for the total sample of radio sources,i.e. including also the unidentified ones, is brighter in the faintest radio bins than in the bin with higher radio flux. This suggests that most of the faintest radio sources are likely to be associated to relatively lower radio luminosity objects at relatively modest redshift, rather than radio-powerful, AGN type objects at high redshift.

The VIMOS-VLT deep survey : Luminosity dependence of clustering at z ≃ 1

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_{AB}<24) of the survey allows us to measure the projected two-point correlation function of galaxies, w_p(r_p) for a set of volume-limited samples up to an effective redshift =0.9 and median absolute magnitude -19.6< M_B < -21.3. Fitting w_p(r_p) with a single power-law model for the real-space correlation function xi(r)=(r/r_0)^{-gamma}, we measure the relationship of the correlation length r_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

Probing galaxy evolution through the internal colour gradients, the Kormendy relations and the Photometric Plane of cluster galaxies at z ~ 0.2

We present a detailed analysis of the photometric properties of galaxies in the cluster A 2163B at redshift z ∼ 0.2. R-, I -a ndK-band structural parameters, (half light radius Re, mean surface brightness � µ� e within Re and Sersic index n )a re derived for N ∼ 60 galaxies, and are used to study their internal colour gradients. For the first time, we use the slopes of optical- NIR Kormendy relations to study colour gradients as a function of galaxy size, and we derive the Photometric Plane at z ∼ 0.2 in the K band. Colour gradients are negligible at optical wavelengths, and are negative in the optical-NIR, amounting on average to −0.48 ± 0.06. This result is in agreement with our previous measurements of colour gradients at intermediate redshifts, and imply a metallicity gradient in galaxies of ∼0.2 dex per radial decade. The analysis of the Kormendy relation suggests that its slope increases from the optical to the NIR, implying that colour gradients do not vary or even do become less steep in more massive galaxies. Such a result is not simply accomodated within a monolithic collapse scenario, while it can be well understood within a hierarchical merging framework. Finally, we derive the first NIR Photometric Plane at z ∼ 0.2, accounting for both the correlations on the measurement uncertainties and the selection effects. The Photometric Plane at z ∼ 0.2 is consistent with that at z ∼ 0, with an intrinsic scatter significantly smaller than the Kormendy relation but larger than the Fundamental Plane.

ACCESS - II. A complete census of star formation in the Shapley supercluster - UV and IR luminosity functions

We present panoramic Spitzer/MIPS mid- and far-infrared (MIR/FIR) and GALEX ultraviolet imaging of the most massive and dynamically active system in the local Universe, the Shapley supercluster at z = 0.048, covering the five clusters that make up the supercluster core. We combine these data with existing spectroscopic data from 814 confirmed supercluster mem- bers to produce the first study of a local rich cluster including both ultraviolet and infrared luminosity functions (LFs). This joint analysis allows us to produce a complete census of star formation (both obscured and unobscured), extending down to star formation rates (SFRs) ∼0.02-0.05 Myr −1 , and quantify the level of obscuration of star formation among cluster galaxies, providing a local benchmark for comparison to ongoing and future studies of cluster galaxies at higher redshifts with Spitzer and Herschel .T heGALEX near-ultraviolet (NUV) and far-ultraviolet (FUV) luminosity functions (LFs) obtained have steeper faint-end slopes than the local field population, due largely to the contribution of massive, quiescent galaxies at MFUV −16. The 24- and 70-µm galaxy LFs for the Shapley supercluster instead have shapes fully consistent with those obtained for the Coma cluster and for the local field galaxy pop- ulation. This apparent lack of environmental dependence for the shape of the FIR luminosity function suggests that the bulk of the star-forming galaxies that make up the observed cluster infrared LF have been recently accreted from the field and have yet to have their star forma- tion activity significantly affected by the cluster environment. We estimate a global SFR of 327 Myr −1 over the whole supercluster core, of which just ∼20 per cent is visible directly in the ultraviolet continuum and ∼80 per cent is reprocessed by dust and emitted in the infrared. The level of obscuration (LIR/LFUV) in star-forming galaxies is seen to increase linearly with LK over 2 orders of magnitude in stellar mass.

Structure and Evolution of Galaxy Clusters: Internal Dynamics of ABCG 209 at z

We report the results about the internal dynamics of the rich galaxy cluster ABGC 209 on the basis of new spectroscopic and photometric data. ABCG209 is a peak of 112 detected member galaxies at z= 0.209, characterised by a high value of the line–of–sight velocity dispersion, σv ∼ 1400 km s−1. The cluster shows evidence of relevant substructure and dynamical segregation, and is characterised by a preferential SE–NW direction. The observational scenario suggests that ABCG209 is a strongly evolving cluster, possibly in an advanced phase of merging.We study the internal dynamics of the rich galaxy cluster ABGC209 on the basis of new spectroscopic and pho- tometric data. The distribution in redshift shows that ABCG209 is a well isolated peak of 112 detected member galaxies at z = 0.209, characterised by a high value of the line-of-sight velocity dispersion, σv = 1250-1400 km s −1 , on the whole ob- served area (1 h −1 Mpc from the cluster center), that leads to a virial mass of M = 1.6-2.2 ×10 15 h −1 Mwithin the virial radius, assuming the dynamical equilibrium. The presence of a velocity gradient in the velocity field, the elongation in the spatial distribution of the colour-selected likely cluster members, the elongation of the X-ray contour levels in the Chandra image, and the elongation of cD galaxy show that ABCG209 is characterised by a preferential NW-SE direction. We also find a significant deviation of the velocity distribution from a Gaussian, and relevant evidence of substructure and dynamical segregation. All these facts show that ABCG209 is a strongly evolving cluster, possibly in an advanced phase of merging.

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We present new photometric V-, R- and I-band data for the rich galaxy cluster AC 118 at z = 0.31. The new photometry covers an area of 8.6 x 8.6 arcmin 2 , corresponding to 2.9 x 2.9 Mpc 2 (H 0 = 50 km s - 1 Mpc - 1 , qo = 0.5 and A = 0). The data have been collected for a project aimed at studying galaxy evolution through the color-magnitude relation and the fundamental plane. We provide a catalogue including all the sources (N = 1206) detected in the cluster field. The galaxy sample is complete to V = 22.8 mag (N g a l = 574), R = 22.3 mag (N g a l = 649) and I = 20.8 mag (N g a l = 419). We give aperture magnitudes within a fixed aperture of 4.4 arcsec and Kron magnitudes. We also give photometric redshifts for 459 sources for which additional U- and K-band photometry is available. We derive and discuss the V- and R-band luminosity functions. The catalogue, which is distributed in electronic form, is intended as a tool for studies in galaxy evolution.

0.21

We present an analysis of the mid-infrared (MIR) colours of 165 70-μm-detected galaxies in the Shapley supercluster core (SSC) at z= 0.048 using panoramic Spitzer/MIPS 24- and 70-μm imaging. While the bulk of galaxies show f70/f24 colours typical of local star-forming galaxies, we identify a significant subpopulation of 23 70-μm-excess galaxies, whose MIR colours (f70/f24 > 25) are much redder and cannot be reproduced by any of the standard model IR spectral energy distributions (SEDs). These galaxies are found to be strongly concentrated towards the cores of the five clusters that make up the SSC, and also appear rare among local field galaxies, confirming them as a cluster-specific phenomenon. Their optical spectra and lack of significant ultraviolet emission imply little or no ongoing star formation, while fits to their panchromatic SEDs require the far-IR emission to come mostly from a diffuse dust component heated by the general interstellar radiation field rather than ongoing star formation. Most of these 70-μm-excess galaxies are identified as ∼L* S0s with smooth profiles. We find that almost every cluster galaxy in the process of star formation quenching is already either an S0 or Sa, while we find no passive galaxies of class Sb or later. Hence the formation of passive early-type galaxies in cluster cores must involve the prior morphological transformation of late-type spirals into Sa/S0s, perhaps via pre-processing or the impact of cluster tidal fields, before a subsequent quenching of star formation once the lenticular encounters the dense environment of the cluster core. In the cases of many cluster S0s, this phase of star formation quenching is characterized by an excess of 70-μm emission, indicating that the cold dust content is declining at a slower rate than star formation. We suggest that the excess 70-μm emission during quenching is due to either (i) a reduction of the star formation efficiency as proposed within the morphological quenching scenario or (ii) a 2–3 times increase in the dust-to-gas ratio or metallicity of the remaining interstellar medium, as predicted by chemical evolutionary models of galaxies undergoing ram-pressure stripping or starvation.