Benedetta Vulcani

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

We present the galaxy stellar mass function 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 ≤ z ≤ 0.07), and the ESO Distant Cluster Survey (EDisCS) (0.4 ≤ z ≤ 0.8). We investi- gate the total mass function and find that it evolves noticeably with redshift. The shape at M∗ > 10 11 Mdoes not evolve, but below M∗ ∼ 10 10.8 Mthe mass function at high red- shift is flat, while in the local Universe it flattens out at lower masses. The population of M∗ = 10 10.2 -10 10.8 Mgalaxies must have grown significantly between z = 0.8 and 0. We analyse the mass functions of different morphological types (ellipticals, S0s and late types), and also find that 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 per cent of the stellar mass is in elliptical galaxies. Another ∼43 per cent of the mass is in S0 galaxies in local clusters, while it is in late types in distant clusters. To explain the observed trends, we discuss the importance of those mechanisms that could shape the mass function. 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 on to 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 mass function of late-type galaxies in clusters and, indirectly, that of early-type galaxies through subsequent morphological transformations.

The grism lens-amplified survey from space (glass). i. survey overview and first data release

We give an overview of the Grism Lens Amplified Survey from Space (GLASS), a large Hubble Space Telescope program aimed at obtaining grism spectroscopy of the fields of ten massive clusters of galaxies at redshift z=0.308-0.686, including the Hubble Frontier Fields (HFF). The Wide Field Camera 3 yields near infrared spectra of the cluster cores, covering the wavelength range 0.81-1.69mum through grisms G102 and G141, while the Advanced Camera for Surveys in parallel mode provides G800L spectra of the infall regions of the clusters. The WFC3 spectra are taken at two almost orthogonal position angles in order to minimize the effects of confusion. After summarizing the scientific drivers of GLASS, we describe the sample selection as well as the observing strategy and data processing pipeline. We then utilize MACSJ0717.5+3745, a HFF cluster and the first one observed by GLASS, to illustrate the data quality and the high-level data products. Each spectrum brighter than H_AB=23 is visually inspected by at least two co-authors and a redshift is measured when sufficient information is present in the spectra. Furthermore, we conducted a thorough search for emission lines through all the GLASS WFC3 spectra with the aim of measuring redshifts for sources with continuum fainter than H_AB=23. We provide a catalog of 139 emission-line based spectroscopic redshifts for extragalactic sources, including three new redshifts of multiple image systems (one probable, two tentative). In addition to the data itself we also release software tools that are helpful to navigate the data.

Through the Looking GLASS: HST Spectroscopy of Faint Galaxies Lensed by the Frontier Fields Cluster MACSJ0717.5+3745

The Grism Lens-Amplified Survey from Space (GLASS) is a Hubble Space Telescope (HST) Large Program, which will obtain 140 orbits of grism spectroscopy of the core and infall regions of 10 galaxy clusters, selected to be among the very best cosmic telescopes. Extensive HST imaging is available from many sources including the CLASH and Frontier Fields programs. We introduce the survey by analyzing spectra of faint multiply-imaged galaxies and z ≳ 6 galaxy candidates obtained from the first 7 orbits out of 14 targeting the core of the Frontier Fields cluster MACSJ0717.5+3745. Using the G102 and G141 grisms to cover the wavelength range 0.8-1.7 μm, we confirm four strongly lensed systems by detecting emission lines in each of the images. For the 9 z ≳ 6 galaxy candidates clear from contamination, we do not detect any emission lines down to a 7 orbit 1σ noise level of ∼5 × 10 -18 erg s-1 cm-2. Taking lensing magnification into account, our flux sensitivity reaches ∼0.2-5 × 10-18 erg s-1cm-2. These limits over an uninterrupted wavelength range rule out the possibility that the high-z galaxy candidates are instead strong line emitters at lower redshift. These results show that by means of careful modeling of the background - and with the assistance of lensing magnification - interesting flux limits can be reached for large numbers of objects, avoiding pre-selection and the wavelength restrictions inherent to ground-based multi-slit spectroscopy. These observations confirm the power of slitless HST spectroscopy even in fields as crowded as a cluster core.

Superdense massive galaxies in the ESO Distant Cluster Survey (EDisCS)

We find a significant number of massive and compact galaxies in clusters from the ESO Distant Clusters Survey (EDisCS) at 0.4 < z < 1. They have similar stellar masses, ages, sizes and axial ra tios to local z � 0.04 compact galaxies in WINGS clusters, and to z = 1.4 - 2 massive and passive galaxies found in the general field. If non-BCG cluster galaxies of all densities, morphol ogies and spectral types are considered, the median size of EDisCS galaxies is only a factor 1.18 smaller than in WINGS. We show that for morphologically selected samples, the morphological evolution taking place in a significant fraction of galaxies during the last Gyrs may introduce an apparent, spurious evolution of size with redshift, which is actually due to intrinsic differences in the selected samples. We conclude that the median mass-size relation of cluster galaxies does not evolve significantly from z � 0.7 to z � 0.04. In contrast, the masses and sizes of BCGs and galaxies with

COMPARING THE RELATION BETWEEN STAR FORMATION AND GALAXY MASS IN DIFFERENT ENVIRONMENTS

Analyzing 24 μm 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, 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 these with results from 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 galaxies, to avoid possible active galactic nucleus 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. Separately comparing 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 ~two times lower than the field. We conclude that the average SFR in star-forming galaxies varies with galaxy environment at a fixed galaxy mass.

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 thanMB =− 18.7 taken from the Millennium Galaxy Catalogue (MGC, Liske et al.), a 38 deg 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 10 members, and 63 per cent have fewer than five members. Non-group galaxies were subdivided into ‘binary’ systems of two bright close companions, and ‘single’ galaxies with no companion, in order to identify different environments useful for future scientific analyses. 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 the World Wide Web.

Suppressing star formation in quiescent galaxies with supermassive black hole winds

Quiescent galaxies with little or no ongoing star formation dominate the population of galaxies with masses above 2 × 1010 times that of the Sun; the number of quiescent galaxies has increased by a factor of about 25 over the past ten billion years (refs 1, 2, 3, 4). Once star formation has been shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat the gas that is subsequently accreted from either stellar mass loss or mergers and that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centres of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized-gas velocity gradients from which we infer the presence of centrally driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as ten per cent of the quiescent population with masses around 2 × 1010 times that of the Sun. In a prototypical example, we calculate that the energy input from the galaxy’s low-level active supermassive black hole is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.

THE IMACS CLUSTER BUILDING SURVEY. IV. THE LOG-NORMAL STAR FORMATION HISTORY OF GALAXIES

We present here a simple model for the star formation history (SFH) of galaxies that is successful in describing both the star formation rate density (SFRD) over cosmic time, as well as the distribution of specific star formation rates (sSFRs) of galaxies at the current epoch, and the evolution of this quantity in galaxy populations to a redshift of z = 1. We show first that the cosmic SFRD is remarkably well described by a simple log-normal in time. We next postulate that this functional form for the ensemble is also a reasonable description for the SFHs of individual galaxies. Using the measured sSFRs for galaxies at z ~ 0 from Paper III in this series, we then construct a realization of a universe populated by such galaxies in which the parameters of the log-normal SFH of each galaxy are adjusted to match the sSFRs at z ~ 0 as well as fitting, in ensemble, the cosmic SFRD from z = 0 to z = 8. This model predicts, with striking fidelity, the distribution of sSFRs in mass-limited galaxy samples to z = 1; this match is not achieved by other models with a different functional form for the SFHs of individual galaxies, but with the same number of degrees of freedom, suggesting that the log-normal form is well matched to the likely actual histories of individual galaxies. We also impose the sSFR versus mass distributions at higher redshifts from Paper III as constraints on the model, and show that, as previously suggested, some galaxies in the field, particularly low mass galaxies, are quite young at intermediate redshifts. As emphasized in Paper III, starbursts are insufficient to explain the enhanced sSFRs in intermediate redshift galaxies; we show here that a model using only smoothly varying log-normal SFHs for galaxies, which allows for some fraction of the population to have peak star formation at late times, does however fully explain the observations. Finally, we show that this model, constrained in detail only at redshifts z < 1, also produces the main sequence of star-formation observed at 1.5 < z < 2.5, again suggesting that the log-normal SFHs are a close approximation to the actual histories of typical galaxies.

Galaxy And Mass Assembly (GAMA): the wavelength-dependent sizes and profiles of galaxies revealed by MegaMorph

We investigate the relationship between colour and structure within galaxies using a large, volume-limited sample of bright, low-redshift galaxies with optical–near-infrared imaging from the Galaxy And Mass Assembly survey. We fit single-component, wavelength-dependent, elliptical Sersic models to all passbands simultaneously, using software developed by the MegaMorph project. Dividing our sample by n and colour, the recovered wavelength variations in effective radius (Re) and Sersic index (n) reveal the internal structure, and hence formation history, of different types of galaxies. All these trends depend on n; some have an additional dependence on galaxy colour. Late-type galaxies (nr 2.5), even though they maintain constant n with wavelength, revealing that ellipticals are a superimposition of different stellar populations associated with multiple collapse and merging events. Processes leading to structures with larger Re must be associated with lower metallicity or younger stellar populations. This appears to rule out the formation of young cores through dissipative gas accretion as an important mechanism in the recent lives of luminous elliptical galaxies.

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.