Isolated galaxies in hierarchical galaxy formation models - present-day properties and environmental histories

In this study, we have carried out a detailed, statistical analysis of isolated model galaxies, taking advantage of publicly available hierarchical galaxy formation models. To select isolated galaxies, we employ 2D methods widely used in the observational literature, as well as a more stringent 3D isolation criterion that uses the full 3D-real space information. In qualitative agreement with observational results, isolated model galaxies have larger fractions of late-type, star forming galaxies with respect to randomly selected samples of galaxies with the same mass distribution. We also find that the samples of isolated model galaxies typically contain a fraction of less than 15 per cent of satellite galaxies, that reside at the outskirts of their parent haloes where the galaxy number density is low. Projection effects cause a contamination of 2D samples of about 18 per cent, while we estimate a typical completeness of 65 per cent. Our model isolated samples also include a very small (few per cent) fraction of bulge dominated galaxies (B/T > 0.8) whose bulges have been built mainly by minor mergers. Our study demonstrates that about 65-70 per cent of 2D isolated galaxies that are classified as isolated at z = 0 have indeed been completely isolated since z = 1 and only 7 per cent have had more than 3 neighbours within a comoving radius of 1 Mpc. Irrespectively of the isolation criteria, roughly 45 per cent of isolated galaxies have experienced at least one merger event in the past (most of the mergers are minor, with mass ratios between 1:4 and 1:10). The latter point validates the approximation that isolated galaxies have been mainly influenced by internal processes.Comment: 15 pages, 13 figures, minor changes in the text, accepted for publication by MNRA

Reconstructing the galaxy density field with photometric redshifts: II. Environment-dependent galaxy evolution since z≃3z \simeq 3

Although extensively investigated, the role of the environment in galaxy formation is still not well understood. In this context, the Galaxy Stellar Mass Function (GSMF) is a powerful tool to understand how environment relates to galaxy mass assembly and the quenching of star-formation. In this work, we make use of the high-precision photometric redshifts of the UltraVISTA Survey to study the GSMF in different environments up to $z \sim 3$, on physical scales from 0.3 to 2 Mpc, down to masses of $M \sim 10^{10} M_{\odot}$. We witness the appearance of environmental signatures for both quiescent and star-forming galaxies. We find that the shape of the GSMF of quiescent galaxies is different in high- and low-density environments up to $z \sim 2$ with the high-mass end ($M \gtrsim 10^{11} M_{\odot}$) being enhanced in high-density environments. On the contrary, for star-forming galaxies a difference between the GSMF in high- and low density environments is present for masses $M \lesssim 10^{11} M_{\odot}$. Star-forming galaxies in this mass range appear to be more frequent in low-density environments up to $z < 1.5$. Differences in the shape of the GSMF are not visible anymore at $z > 2$. Our results, in terms of general trends in the shape of the GSMF, are in agreement with a scenario in which galaxies are quenched when they enter hot gas-dominated massive haloes which are preferentially in high-density environments.Comment: 18 pages, 10 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Societ

An Optical/NIR Exploration of Forming Cluster Environments at High Redshift with VLT, Keck, and HST

The past decade has been witness to immense progress in the understanding of the early stages of cluster formation both from a theoretical and observational perspective. During this time, samples of forming clusters at higher redshift, termed "protoclusters", once comprised of heterogeneous mix of serendipitous detections or detections arising from dedicated searches around rare galaxy populations, have begun to compete with lower-redshift samples both in terms of numbers and in the homogeneity of the detection methods. Much of this progress has come from optical/near-infrared (NIR) imaging and spectroscopic campaigns designed to target large numbers of typical galaxies to exquisite depth. In this poster talk I will focus on observations from VIMOS on VLT, MOSFIRE/DEIMOS on Keck, and a 50-orbit cycle 29 HST WFC3/G141 grism campaign taken as part of the Charting Cluster Construction with VUDS and ORELSE (C3VO) survey. These observations, combined with novel mapping and search techniques, have uncovered a large number of "protostructures" at 2 < z < 5 that appear to resemble clusters and groups forming in the early universe. I will discuss the development of the methods for finding, confirming, and characterizing proto-clusters and proto-groups in our sample, as well as groups and clusters at intermediate redshifts. Several case studies of spectroscopically-confirmed massive proto-clusters with a diverse set of properties will be presented. I will finally discuss constraints on the relationship between star formation rate, stellar mass, and galaxy density at these redshift

LBT-MODS spectroscopy of high-redshift candidates in the Chandra J1030 field. A newly discovered z∼\sim2.8 large scale structure

We present the results of a spectroscopic campaign with the Multi-Object Double Spectrograph (MODS) instrument mounted on the Large Binocular Telescope (LBT), aimed at obtaining a spectroscopic redshift for seven Chandra J1030 sources with a photometric redshift >=2.7 and optical magnitude r_AB=[24.5-26.5]. We obtained a spectroscopic redshift for five out of seven targets: all of them have z_spec>=2.5, thus probing the reliability of the Chandra J1030 photometric redshifts. The spectroscopic campaign led to the serendipitous discovery of a z~2.78 large scale structure (LSS) in the J1030 field: the structure contains four X-ray sources (three of which were targeted in the LBT-MODS campaign) and two non-X-ray detected galaxies for which a VLT-MUSE spectrum was already available. The X-ray members of the LSS are hosted in galaxies that are significantly more massive (log(M_*/M_sun)=[10.0-11.1]) than those hosting the two MUSE-detected sources (log(M_*/M_sun)<10). Both observations and simulations show that massive galaxies, and particularly objects having log(M_*/M_sun)>10, are among the best tracers of large scale structures and filaments in the cosmic web. Consequently, our result can explain why X-ray-detected AGN have also been shown to be efficient tracers of large scale structures.Comment: 16 pages, 9 Figures. Accepted for publication in Astronomy and Astrophysic

Spectroscopic confirmation of a Coma Cluster progenitor at z~2.2

We report the spectroscopic confirmation of a new protocluster in the COSMOS field at z ∼ 2.2, originally identified as an overdensity of narrow-band selected Hα emitting candidates. With only two masks of Keck/MOSFIRE near-IR spectroscopy in both H (∼ 1.47-1.81 μm) and K (∼ 1.92- 2.40 μm) bands (∼ 1.5 hour each), we confirm 35 unique protocluster members with at least two emission lines detected with S/N > 3. Combined with 12 extra members from the zCOSMOS-deep spectroscopic survey (47 in total), we estimate a mean redshift, line-of-sight velocity dispersion, and total mass of zmean=2.23224 ± 0.00101, σlos=645 ± 69 km s−1, and Mvir ∼ (1 − 2)×10^14 M⊙ for this protocluster, respectively. We estimate a number density enhancement of δg ∼ 7 for this system and we argue that the structure is likely not virialized at z ∼ 2.2. However, in a spherical collapse model, δg is expected to grow to a linear matter enhancement of ∼ 1.9 by z=0, exceeding the collapse threshold of 1.69, and leading to a fully collapsed and virialized Coma-type structure with a total mass of Mdyn(z=0) ∼ 9.2×10^14 M⊙ by now. This observationally efficient confirmation suggests that large narrow-band emission-line galaxy surveys, when combined with ancillary photometric data, can be used to effectively trace the large-scale structure and protoclusters at a time when they are mostly dominated by star-forming galaxies

The zCOSMOS 10k-Bright Spectroscopic Sample

We present spectroscopic redshifts of a large sample of galaxies with I_(AB) < 22.5 in the COSMOS field, measured from spectra of 10,644 objects that have been obtained in the first two years of observations in the zCOSMOS-bright redshift survey. These include a statistically complete subset of 10,109 objects. The average accuracy of individual redshifts is 110 km s^(–1), independent of redshift. The reliability of individual redshifts is described by a Confidence Class that has been empirically calibrated through repeat spectroscopic observations of over 600 galaxies. There is very good agreement between spectroscopic and photometric redshifts for the most secure Confidence Classes. For the less secure Confidence Classes, there is a good correspondence between the fraction of objects with a consistent photometric redshift and the spectroscopic repeatability, suggesting that the photometric redshifts can be used to indicate which of the less secure spectroscopic redshifts are likely right and which are probably wrong, and to give an indication of the nature of objects for which we failed to determine a redshift. Using this approach, we can construct a spectroscopic sample that is 99% reliable and which is 88% complete in the sample as a whole, and 95% complete in the redshift range 0.5 < z < 0.8. The luminosity and mass completeness levels of the zCOSMOS-bright sample of galaxies is also discussed

Mass and environment as drivers of galaxy evolution in SDSS and zCOSMOS and the origin of the Schechter function

We explore the inter-relationships between mass, star-formation rate and environment in the SDSS, zCOSMOS and other surveys. The differential effects of mass and environment are completely separable to z ~ 1, indicating that two distinct processes are operating, "mass-quenching" and "environment-quenching". Environment-quenching, at fixed over-density, evidently does not change with epoch to z ~ 1, suggesting that it occurs as large-scale structure develops in the Universe. The observed constancy of the mass-function shape for star-forming galaxies, demands that the mass-quenching of galaxies around and above M*, must be proportional to their star-formation rates at all z < 2. We postulate that this simple mass-quenching law also holds over a much broader range of stellar mass and epoch. These two simple quenching processes, plus some additional quenching due to merging, then naturally produce (a) a quasi-static Schechter mass function for star-forming galaxies with a value of M* that is set by the proportionality between the star-formation and mass-quenching rates, (b) a double Schechter function for passive galaxies with two components: the dominant one is produced by mass-quenching and has exactly the same M* as the star-forming galaxies but an alpha shallower by +1, while the other is produced by environment effects and has the same M* and alpha as the star-forming galaxies, and is larger in high density environments. Subsequent merging of quenched galaxies modifies these predictions somewhat in the denser environments, slightly increasing M* and making alpha more negative. All of these detailed quantitative relationships between the Schechter parameters are indeed seen in the SDSS, lending strong support to our simple empirically-based model. The model naturally produces for passive galaxies the "anti-hierarchical" run of mean ages and alpha-element abundances with mass.Comment: 66 pages, 19 figures, 1 movie, accepted for publication in ApJ. The movie is also available at http://www.exp-astro.phys.ethz.ch/zCOSMOS/MF_simulation_d1_d4.mo

VizieR Online Data Catalog: EELGs out to z~1 in zCOSMOS (Amorin+, 2015)

Star formation rates have been computed from Hα or Hβ luminosity (IMF from Chabrier et al. (2003PASP..115..763C) and assuming a theoretical ratio Hα/Hβ=2.82) following Kennicutt (1998ApJ...498..541K). Uncertainties in SFR account for the propagation of errors in line fluxes and reddening. Gas-phase metallicity has been derived using four methods: (1) the direct method (Hagele et al., 2008MNRAS.383..209H); (2) the Te-Z correlation (This work); (3) the N2 calibration (Perez-Montero & Contini, 2009MNRAS.398..949P); and (4) the R23 calibration (McGaugh, 1991ApJ...380..140M) scaled to the direct method using the linear relation presented by Lamareille et al. (2006, Cat. J/A+A/448/893 and 2006A&A...448..907L, see also Perez-Montero et al., 2013A&A...549A..25P). In all cases, 1σ uncertainties in metallicity account for the propagated errors in line fluxes and reddening. (2 data files)

Bose-Einstein correlations of charged hadrons in proton-proton collisions at s\sqrt s = 13 TeV

Bose-Einstein correlations of charged hadrons are measured over a broad multiplicity range, from a few particles up to about 250 reconstructed charged hadrons in proton-proton collisions at $\sqrt{s}$ = 13 TeV. The results are based on data collected using the CMS detector at the LHC during runs with a special low-pileup configuration. Three analysis techniques with different degrees of dependence on simulations are used to remove the non-Bose-Einstein background from the correlation functions. All three methods give consistent results. The measured lengths of homogeneity are studied as functions of particle multiplicity as well as average pair transverse momentum and mass. The results are compared with data from both CMS and ATLAS at $\sqrt{s}$ = 7 TeV, as well as with theoretical predictions.[graphic not available: see fulltext]Bose-Einstein correlations of charged hadrons are measured over a broad multiplicity range, from a few particles up to about 250 reconstructed charged hadrons in proton-proton collisions at $\sqrt{s} =$ 13 TeV. The results are based on data collected using the CMS detector at the LHC during runs with a special low-pileup configuration. Three analysis techniques with different degrees of dependence on simulations are used to remove the non-Bose-Einstein background from the correlation functions. All three methods give consistent results. The measured lengths of homogeneity are studied as functions of particle multiplicity as well as average pair transverse momentum and mass. The results are compared with data from both CMS and ATLAS at $\sqrt{s} =$ 7 TeV, as well as with theoretical predictions