arXiv subjects

Bianca M. Poggianti

Publications and source records attributed to Bianca M. Poggianti.

At least 91 records · Page 5Linked to original sources

arXiv2013

The IMACS Cluster Building Survey. I. Description of the Survey and Analysis Methods

The IMACS Cluster Building Survey uses the wide field spectroscopic capabilities of the IMACS spectrograph on the 6.5m Baade Telescope to survey the large-scale environment surrounding rich intermediate-redshift clusters of galaxies. The goal is to understand the processes which may be transforming star-forming field galaxies into quiescent cluster members as groups and individual galaxies fall into the cluster from the surrounding supercluster. This first paper describes the survey: the data taking and reduction methods. We provide new calibrations of star formation rates derived from optical and infrared spectroscopy and photometry. We demonstrate that there is a tight relation between the observed star formation rate per unit B luminosity, and the ratio of the extinctions of the stellar continuum and the optical emission lines. With this, we can obtain accurate extinction-corrected colors of galaxies. Using these colors as well as other spectral measures, we determine new criteria for the existence of ongoing and recent starbursts in galaxies.

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arXiv2013

The IMACS Cluster Building Survey. III. The Star Formation Histories of Field Galaxies

Using data from the IMACS Cluster Building Survey and from nearby galaxy surveys, we examine the evolution of the rate of star formation in field galaxies from $ z = 0.60$ to the present. Fitting the luminosity function to a standard Schechter form, we find a rapid evolution of $M_B^*$ consistent with that found in other deep surveys; at the present epoch $M_B^*$ is evolving at the rate of $0.38 Gyr^{-1}$, several times faster than the predictions of simple models for the evolution of old, coeval galaxies. The evolution of the distribution of specific star formation rates (SSFR) is also too rapid to explain by such models. We demonstrate that starbursts cannot, even in principle, explain the evolution of the SSFR distribution. However, the rapid evolution of both $M_B^*$ and the SSFR distribution can be explained if some fraction of galaxies have star formation rates characterized by both short rise and fall times and by an epoch of peak star formation more recent than the majority of galaxies. Although galaxies of every stellar mass up to $1.4\times10^{11}\Msun$ show a range of epochs of peak star formation, the fraction of "younger" galaxies falls from about 40% at a mass of $4\times10^{10}\Msun$ to zero at a mass of $1.4\times10^{11}\Msun$. The incidence of younger galaxies appears to be insensitive to the density of the local environment; but does depend on group membership: relatively isolated galaxies are much more likely to be young than are group members.

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arXiv2013

The galaxy stellar mass function and its evolution with time show no dependence on global environment

We present the analysis of the galaxy stellar mass function in different environments at intermediate redshift (0.3 10^(10.5) M_sun, to study cluster, group, and field galaxies at z=0.3-0.45, and the ESO Distant Cluster Survey (EDisCS), at masses M_ast > 10^(10.2) M_sun, to investigate cluster and group galaxies at z=0.4-0.8. Therefore, in our analysis we include galaxies that are slightly less massive than the Milky Way. Having excluded the brightest cluster galaxies, we show thatthe shape of the mass distribution does not seem to depend on global environment. Our two main results are: (1) Galaxies in the virialized regions of clusters, in groups, and in the field follow a similar mass distribution. (2) Comparing both ICBS and EDisCS mass functions to mass functions in the local Universe, we find evolution from z~0.4-0.6 to z~0.07. The population of low-mass galaxies has proportionally grown with time with respect to that of massive galaxies. This evolution is independent of environment -- the same for clusters and the field. Furthermore, considering only clusters, we find that no differences can be detected neither within the virialized regions, nor when we compare galaxies within and outside the virial radius. Subdividing galaxies in terms of color, in clusters, groups, and field red and blue galaxies are regulated by different mass functions, but comparing separately the blue and red mass functions in different environments, no differences are detected in their shape.

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arXiv2012

The evolution of galaxy sizes

We present a study of galaxy sizes in the local Universe as a function of galaxy environment, comparing clusters and the general field. Galaxies with radii and masses comparable to high-z massive and compact galaxies represent 4.4% of all galaxies more massive than 3 X 10^{10} M_sun in the field. Such galaxies are 3 times more frequent in clusters than in the field. Most of them are early-type galaxies with intermediate to old stellar populations. There is a trend of smaller radii for older luminosity-weighted ages at fixed galaxy mass. We show the relation between size and luminosity-weighted age for galaxies of different stellar masses and in different environments. We compare with high-z data to quantify the evolution of galaxy sizes. We find that, once the progenitor bias due to the relation between galaxy size and stellar age is removed, the average amount of size evolution of individual galaxies between high- and low-z is mild, of the order of a factor 1.6.

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arXiv2012

Gas reservoirs and star formation in a forming galaxy cluster at z=0.2

We present first results from the Blind Ultra Deep HI Environmental Survey (BUDHIES) of the Westerbork Synthesis Radio Telescope (WSRT). Our survey is the first direct imaging study of neutral atomic hydrogen gas in galaxies at a redshift where evolutionary processes begin to show. In this letter we investigate star formation, HI-content, and galaxy morphology, as a function of environment in Abell 2192 (at z=0.1876). Using a 3-dimensional visualization technique, we find that Abell 2192 is a cluster in the process of forming, with significant substructure in it. We distinguish 4 structures that are separated in redshift and/or space. The richest structure is the baby cluster itself, with a core of elliptical galaxies that coincides with (weak) X-ray emission, almost no HI-detections, and suppressed star formation. Surrounding the cluster, we find a compact group where galaxies pre-process before falling into the cluster, and a scattered population of "field-like" galaxies showing more star formation and HI-detections. This cluster proves to be an excellent laboratory to understand the fate of the HI gas in the framework of galaxy evolution. We clearly see that the HI gas and the star formation correlate with morphology and environment at z=0.2. In particular, the fraction of HI-detections is significantly affected by the environment. The effect starts to kick in in low mass groups that pre-process the galaxies before they enter the cluster. Our results suggest that by the time the group galaxies fall into the cluster, they are already devoid of HI.

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arXiv2012

Cl 1103.7-1245 at z=0.96: the highest redshift galaxy cluster in the EDisCS survey

We present new spectroscopic observations in a field containing the highest redshift cluster of the ESO Distant Cluster Survey (EDisCS). We measure galaxy redshifts and determine the velocity dispersions of the galaxy structures located in this field. Together with the main cluster Cl1103.7$-$1245 (z=0.9580; sigma_{clus} = 522 +/- 111 km/s) we find a secondary structure at z=0.9830, Cl1103.7-1245c. We then characterize the galaxy properties in both systems, and find that they contain very different galaxy populations. The cluster Cl1103.7-1245 hosts a mixture of passive elliptical galaxies and star-forming spirals and irregulars. In the secondary structure Cl1103.7-1245c all galaxies are lower-mass star-forming irregulars and peculiars. In addition, we compare the galaxy populations in the Cl1103.7-1245 z=0.9580 cluster with those in lower redshift EDisCS clusters with similar velocity dispersions. We find that the properties of the galaxies in Cl1103.7-1245 follow the evolutionary trends found at lower redshifts: the number of cluster members increases with time in line with the expected growth in cluster mass, and the fraction of passive early-type galaxies increases with time while star-forming late types become less dominant. Finally, we find that the mean stellar masses are similar in all clusters, suggesting that massive cluster galaxies were already present at z~1.

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arXiv2011

The importance of the local density in shaping the galaxy stellar mass functions

Exploiting the capabilities of four different surveys --- the Padova-Millennium Galaxy and Group Catalogue (PM2GC), the WIde-field Nearby Galaxy-cluster Survey (WINGS), the IMACS Cluster Building Survey (ICBS) and the ESO Distant Cluster Survey (EDisCS) --- we analyze the galaxy stellar mass distribution as a function of local density in mass-limited samples, in the field and in clusters from low (z>0.04) to high (z<0.8) redshift. We find that at all redshifts and in all environments, local density plays a role in shaping the mass distribution. In the field, it regulates the shape of the mass function at any mass above the mass limits. In clusters, it seems to be important only at low masses (log M_ast/M_sun <10.1 in WINGS and log M_ast/M_sun < 10.4 in EDisCS), otherwise it seems not to influence the mass distribution. Putting together our results with those of Calvi et al. and Vulcani et al. for the global environment, we argue that at least at $z\leq 0.8$ local density is more important than global environment in determining the galaxy stellar mass distribution, suggesting that galaxy properties are not much dependent of halo mass, but do depend on local scale processes.

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arXiv2011

The distribution of galaxy morphological types and the morphology-mass relation in different environments at low redshift

We use \sim 2000 galaxies belonging to different environments to show how the fractions of different galaxy morphological types vary with global environment and as function of galaxy stellar mass at low redshift. Considering mass limited galaxy samples with log10 M\star/M\bigodot>= 10.25, we find a smooth increase/decline in the fraction of Es-S0s/late type galaxies going from single galaxies, to binaries, to groups. Considering all environments, the fractional variation is more conspicuous for S0s and late-types than for ellipticals solely due to a sharp enhancement/dearth of S0s/late-types in clusters compared to other environments. The morphological distribution of galaxies in the mass range 10.25 < log10 M\star/M\bigodot < 11 is rather independent both of galaxy stellar mass and global environment, except in clusters. The morphologies of galaxies more massive than log10 M\star/M\bigodot = 11 are instead a function of both galaxy mass and global environment. The morphology-mass relation therefore changes with global environment, showing that galaxy stellar mass cannot be the only parameter driving the morphological distribution of galaxies. The morphology-mass relations for S0 and late-type galaxies in clusters are peculiar compared to other environments, and this strongly suggests that cluster-specific effects act on these two types of galaxies, and that a significant number of S0s in clusters has a different origin with respect to S0s in other environments.

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arXiv2011

The Padova-Millennium Galaxy and Group Catalogue (PM2GC): the group-finding method and the PM2GC catalogues of group, binary and single field galaxies

We present the construction and describe the properties of the Padova-Millennium Galaxy and Group Catalogue (PM2GC), a galaxy catalogue representative of the general field population in the local Universe. We characterize galaxy environments by identifying galaxy groups at 0.04<=z<=0.1 with a Friends-of-Friends (FoF) algorithm using a complete sample of 3210 galaxies brighter than MB = -18.7 taken from the Millennium Galaxy Catalogue (MGC, Liske et al. (2003)), a 38deg^2 photometric and spectroscopic equatorial survey. We identified 176 groups with at least three members, comprising in total 1057 galaxies and representing ~43 per cent of the general field population in that redshift range. The median redshift and velocity dispersion of our groups are 0.0823 and 192 km s^-1, respectively. 88 per cent of the groups have fewer than ten members, and 63 per cent have fewer than five members. Nongroup galaxies were subdivided into "inary" systems of two bright close companions, and "single" galaxies with no companion, in order to identify different environments useful for future scientific analysis. We performed a detailed comparison with the 2PIGG catalogue to validate the effectiveness of our method and the robustness of our results. Galaxy stellar masses are computed for all PM2GC galaxies, and found to be in good agreement with Sloan Digital Survey Data Release 7 (SDSS-DR7) mass estimates. The catalogues of PM2GC groups, group properties and galaxy properties in all environments are publicly available on theWorld Wide Web.

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arXiv2010

The evolution of early-type galaxies in clusters from z~ 0.8 to z~ 0: the ellipticity distribution and the morphological mix

We present the ellipticity distribution and its evolution for early-type galaxies in clusters from z~0.8 to z~0, based on the WIde-field Nearby Galaxy-cluster Survey (WINGS)(0.04 M_B+1.208z>-21. Analyzing this sample, we do not recover exactly the same results of the mass-limited sample. Hence the selection criteria are crucial to characterize the galaxy properties: the choice of the magnitude-delimited sample implies the loss of many less massive galaxies and so it biases the final results. Moreover, although we are adopting the same selection criteria, our results in the magnitude-delimited sample are also not in agreement with those of Holden et al.(2009). This is due to the fact that our and their low-z samples have a different magnitude distribution because the Holden et al.(2009) sample suffers from incompleteness at faint magnitudes.

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arXiv2010

Galaxy stellar mass functions of different morphological types in clusters, and their evolution between z=0.8 and z=0

We present the galaxy stellar mass function (MF) and its evolution in clusters from z~0.8 to the current epoch, based on the WIde-field Nearby Galaxy-cluster Survey (WINGS) (0.04 10^11 M' does not evolve, but below M*~10^10.8 M' the MF at high redshift is flat, while in the Local Universe it flattens out at lower masses. The population of M* = 10^10.2 - 10^10.8 M' galaxies must have grown significantly between z=0.8 and z=0. We analyze the MF of different morphological types (ellipticals, S0s and late-types), and find that also each of them evolves with redshift. All types have proportionally more massive galaxies at high- than at low-z, and the strongest evolution occurs among S0 galaxies. Examining the morphology-mass relation (the way the proportion of galaxies of different morphological types changes with galaxy mass), we find it strongly depends on redshift. At both redshifts, ~40% of the stellar mass is in elliptical galaxies. Another ~43% of the mass is in S0 galaxies in local clusters, while it is in spirals in distant clusters. To explain the observed trends, we discuss the importance of those mechanisms that could shape the MF. We conclude that mass growth due to star formation plays a crucial role in driving the evolution. It has to be accompanied by infall of galaxies onto clusters, and the mass distribution of infalling galaxies might be different from that of cluster galaxies. However, comparing with high-z field samples, we do not find conclusive evidence for such an environmental mass segregation. Our results suggest that star formation and infall change directly the MF of late-type galaxies in clusters and, indirectly, that of early-type galaxies through subsequent morphological transformations.

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arXiv2010

The HST/ACS Coma Cluster Survey. II. Data Description and Source Catalogs

The Coma cluster was the target of a HST-ACS Treasury program designed for deep imaging in the F475W and F814W passbands. Although our survey was interrupted by the ACS instrument failure in 2007, the partially completed survey still covers ~50% of the core high-density region in Coma. Observations were performed for 25 fields that extend over a wide range of cluster-centric radii (~1.75 Mpc) with a total coverage area of 274 arcmin^2. The majority of the fields are located near the core region of Coma (19/25 pointings) with six additional fields in the south-west region of the cluster. In this paper we present reprocessed images and SExtractor source catalogs for our survey fields, including a detailed description of the methodology used for object detection and photometry, the subtraction of bright galaxies to measure faint underlying objects, and the use of simulations to assess the photometric accuracy and completeness of our catalogs. We also use simulations to perform aperture corrections for the SExtractor Kron magnitudes based only on the measured source flux and half-light radius. We have performed photometry for ~73,000 unique objects; one-half of our detections are brighter than the 10-sigma point-source detection limit at F814W=25.8 mag (AB). The slight majority of objects (60%) are unresolved or only marginally resolved by ACS. We estimate that Coma members are 5-10% of all source detections, which consist of a large population of unresolved objects (primarily GCs but also UCDs) and a wide variety of extended galaxies from a cD galaxy to dwarf LSB galaxies. The red sequence of Coma member galaxies has a constant slope and dispersion across 9 magnitudes (-21<M_F814W<-13). The initial data release for the HST-ACS Coma Treasury program was made available to the public in 2008 August. The images and catalogs described in this study relate to our second data release.

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arXiv2010

The evolution of the density of galaxy clusters and groups: denser environments at higher redshifts

We show that, observationally, the projected local density distribution in high-z clusters is shifted towards higher values compared to clusters at lower redshift. To search for the origin of this evolution, we analyze a sample of haloes selected from the Millennium Simulation and populated using semi-analytic models, investigating the relation between observed projected density and physical 3D density, using densities computed from the 10 and 3 closest neighbours. Both observationally and in the simulations, we study the relation between number of cluster members and cluster mass, and number of members per unit of cluster mass. We find that the observed evolution of projected densities reflects a shift to higher values of the physical 3D density distribution. In turn, this must be related with the globally higher number of galaxies per unit of cluster volume N/V in the past. We show that the evolution of N/V is due to a combination of two effects: a) distant clusters were denser in dark matter (DM) simply because the DM density within R_{200} (~the cluster virial radius) is defined to be a fixed multiple of the critical density of the Universe, and b) the number of galaxies per unit of cluster DM mass is remarkably constant both with redshift and cluster mass if counting galaxies brighter than a passively evolving magnitude limit. Our results highlight that distant clusters were much denser environments than today's clusters, both in galaxy number and mass, and that the density conditions felt by galaxies in virialized systems do not depend on the system mass.

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arXiv2009

Comparing the relation between star formation and galaxy mass in different environments

Analyzing 24 mu m MIPS/Spitzer data and the [O II]3727 line of a sample of galaxies at 0.4 < z < 0.8 from the ESO Distant Cluster Survey (EDisCS), we investigate the ongoing star formation rate (SFR) and the specific star formation rate (SSFR) as a function of stellar mass in galaxy clusters and groups, and compare with field studies. As for the field, we find a decline in SFR with time, indicating that star formation (SF) was more active in the past, and a decline in SSFR as galaxy stellar mass increases, showing that the current SF contributes more to the fractional growth of low-mass galaxies than high-mass galaxies. However, we find a lower median SFR (by a factor of ~1.5) in cluster star-forming galaxies than in the field. The difference is highly significant when all Spitzer and emission-line galaxies are considered, regardless of color. It remains significant at z>0.6 after removing red emission-line (REL) galaxies, to avoid possible AGN contamination. While there is overlap between the cluster and field SFR-Mass relations, we find a population of cluster galaxies (10-25%) with reduced SFR for their mass. These are likely to be in transition from star-forming to passive. Comparing separately clusters and groups at z>0.6, only cluster trends are significantly different from the field, and the average cluster SFR at a given mass is ~2 times lower than the field. We conclude that the average SFR in star-forming galaxies varies with galaxy environment at a fixed galaxy mass.

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arXiv2009

Evolution of the Early-Type Galaxy Fraction in Clusters since z = 0.8

We study the morphological content of a large sample of high-redshift clusters to determine its dependence on cluster mass and redshift. Quantitative morphologies are based on bulge+disk decompositions of cluster and field galaxies on deep VLT/FORS2 images of 18 optically-selected clusters at 0.45 < z < 0.80 from the ESO Distant Cluster Survey (EDisCS). Morphological content is given by the early-type galaxy fraction f_et, and early-type galaxies are selected based on their bulge fraction and image smoothness. A set of 158 SDSS clusters is analyzed exactly as the EDisCS sample to provide a robust local comparison. Our main results are: (1) f_et values for the SDSS and EDisCS clusters exhibit no clear trend as a function of sigma. (2) Mid-z EDisCS clusters around sigma = 500 km/s have f_et ~= 0.5 whereas high-z EDisCS clusters have f_et ~= 0.4 (~25% increase over 2 Gyrs). (3) There is a marked difference in the morphological content of EDisCS and SDSS clusters. None of the EDisCS clusters have f_et greater than 0.6 whereas half of the SDSS clusters lie above this value. This difference is seen in clusters of all velocity dispersions. (4) There is a strong correlation between morphology and star formation in SDSS and EDisCS clusters. This correlation holds independent of sigma and z even though the fraction of [OII] emitters decreases from z~0.8 to z~0.06 in all environments. Our results pose an interesting challenge to structural transformation and star formation quenching processes that strongly depend on the global cluster environment and suggest that cluster membership may be of lesser importance than other variables in determining galaxy properties. (ABRIDGED)

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arXiv2009

On the role of the post-starburst phase in the build-up of the red-sequence of intermediate redshift clusters

We present new deep spectroscopic observations of 0.05--0.5 L_* galaxies in one cluster (cl1232.5-1250) drawn from the ESO Distant Cluster Survey (EDisCS) sample, at z = 0.54. The new data extend the spectroscopy already available for this cluster by about 1 magnitude. The cluster has a large fraction of passive galaxies and exhibits a well defined and relatively tight colour-magnitude relation. Among spectroscopic members, only six galaxies are classified as `post-starburst' (k+a). For another EDisCS cluster at similar redshift and with as deep spectroscopy, no member is found to have a k+a spectrum. The low measured numbers of post-starburst systems appear to be inadequate to explain the observed increase of faint red galaxies at lower redshift, even when accounting for the infall of new galaxies onto the cluster. Post-starburst galaxies represent a possible channel to move galaxies from the blue star-forming cloud to the red-sequence, but the available data suggest this is not the dominant channel in galaxy clusters. If the galaxies at the faint end of the red-sequence in nearby clusters originate from the blue galaxies observed in distant galaxy clusters, the transformation must have occurred primarily through physical processes that do not lead to a post-starburst phase. In addition, our data exclude a large population of k+a galaxies at faint magnitudes, as found in the Coma cluster.

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arXiv2009

Evolution of the Rate and Mode of Star Formation in Galaxies since z=0.7

We present the star formation rate (SFR) and starburst fraction (SBF) for a sample of field galaxies from the ICBS intermediate-redshift cluster survey. We use [O II] and Spitzer 24 micron fluxes to measure SFRs, and 24 micron fluxes and H-delta absorption to measure of SBFs, for both our sample and a present-epoch field sample from the Sloan Digital Sky Survey (SDSS) and Spitzer Wide-area Infrared Extragalactic (SWIRE) survey. We find a precipitous decline in the SFR since z=1, in agreement with other studies, as well as a corresponding rapid decline in the fraction of galaxies undergoing long-duration moderate-amplitude starbursts. We suggest that the change in both the rate and mode of star formation could result from the strong decrease since z=1 of gas available for star formation.

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arXiv2009

The ESO Distant Cluster Sample: galaxy evolution and environment out to z=1

The ESO Distant Cluster Survey (EDisCS, P.I. Simon D.M. White, LP 166.A-0162) is an ESO large programme aimed at studying clusters and cluster galaxies at z=0.4-1. How different is the evolution of the star formation activity in clusters, in groups and in the field? Does it depend on cluster mass and/or the local galaxy density? How relevant are starburst and post-starburst galaxies in the different environments? Is there an evolution in the galaxies' structures, and if so, is this related to the changes in their star formation activity? These are some of the main questions that have been investigated using the EDisCS dataset.

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