Easylife: the data reduction and survey handling system for VIPERS

We present Easylife, the software environment developed within the framework of the VIPERS project for automatic data reduction and survey handling. Easylife is a comprehensive system to automatically reduce spectroscopic data, to monitor the survey advancement at all stages, to distribute data within the collaboration and to release data to the whole community. It is based on the OPTICON founded project FASE, and inherits the FASE capabilities of modularity and scalability. After describing the software architecture, the main reduction and quality control features and the main services made available, we show its performance in terms of reliability of results. We also show how it can be ported to other projects having different characteristics.Comment: pre-print, 17 pages, 4 figures, accepted for publication in Publications of the Astronomical Society of the Pacifi

EZ: A Tool for Automatic Redshift Measurement

We present EZ (Easy redshift), a tool we have developed within the VVDS project to help in redshift measurement from otpical spectra. EZ has been designed with large spectroscopic surveys in mind, and in its development particular care has been given to the reliability of the results obtained in an automatic and unsupervised mode. Nevertheless, the possibility of running it interactively has been preserved, and a graphical user interface for results inspection has been designed. EZ has been successfully used within the VVDS project, as well as the zCosmos one. In this paper we describe its architecture and the algorithms used, and evaluate its performances both on simulated and real data. EZ is an open source program, freely downloadable from http://cosmos.iasf-milano.inaf.it/pandora.Comment: accepted for publication in Publications of the Astronomical Society of the Pacifi

Scaling relations of cluster elliptical galaxies at z~1.3. Distinguishing luminosity and structural evolution

[Abridged] We studied the size-surface brightness and the size-mass relations of a sample of 16 cluster elliptical galaxies in the mass range 10^{10}-2x10^{11} M_sun which were morphologically selected in the cluster RDCS J0848+4453 at z=1.27. Our aim is to assess whether they have completed their mass growth at their redshift or significant mass and/or size growth can or must take place until z=0 in order to understand whether elliptical galaxies of clusters follow the observed size evolution of passive galaxies. To compare our data with the local universe we considered the Kormendy relation derived from the early-type galaxies of a local Coma Cluster reference sample and the WINGS survey sample. The comparison with the local Kormendy relation shows that the luminosity evolution due to the aging of the stellar content already assembled at z=1.27 brings them on the local relation. Moreover, this stellar content places them on the size-mass relation of the local cluster ellipticals. These results imply that for a given mass, the stellar mass at z~1.3 is distributed within these ellipticals according to the same stellar mass profile of local ellipticals. We find that a pure size evolution, even mild, is ruled out for our galaxies since it would lead them away from both the Kormendy and the size-mass relation. If an evolution of the effective radius takes place, this must be compensated by an increase in the luminosity, hence of the stellar mass of the galaxies, to keep them on the local relations. We show that to follow the Kormendy relation, the stellar mass must increase as the effective radius. However, this mass growth is not sufficient to keep the galaxies on the size-mass relation for the same variation in effective radius. Thus, if we want to preserve the Kormendy relation, we fail to satisfy the size-mass relation and vice versa.Comment: Accepted for publication in A&A, updated to match final journal versio

LBT/MODS spectroscopy of globular clusters in the irregular galaxy NGC 4449

We present intermediate-resolution (R$\sim$1000) spectra in the $\sim$3500-10,000 A range of 14 globular clusters in the magellanic irregular galaxy NGC 4449 acquired with the Multi Object Double Spectrograph on the Large Binocular Telescope. We derived Lick indices in the optical and the CaII-triplet index in the near-infrared in order to infer the clusters' stellar population properties. The inferred cluster ages are typically older than $\sim$9 Gyr, although ages are derived with large uncertainties. The clusters exhibit intermediate metallicities, in the range $-1.2\lesssim$[Fe/H]$\lesssim-0.7$, and typically sub-solar [$\alpha/Fe$] ratios, with a peak at $\sim-0.4$. These properties suggest that i) during the first few Gyrs NGC 4449 formed stars slowly and inefficiently, with galactic winds having possibly contributed to the expulsion of the $\alpha$-elements, and ii) globular clusters in NGC 4449 formed relatively "late", from a medium already enriched in the products of type Ia supernovae. The majority of clusters appear also under-abundant in CN compared to Milky Way halo globular clusters, perhaps because of the lack of a conspicuous N-enriched, second-generation of stars like that observed in Galactic globular clusters. Using the cluster velocities, we infer the dynamical mass of NGC 4449 inside 2.88 kpc to be M($<$2.88 kpc)=$3.15^{+3.16}_{-0.75} \times 10^9~M_\odot$. We also report the serendipitous discovery of a planetary nebula within one of the targeted clusters, a rather rare event.Comment: Accepted for publication in MNRAS; corrected typo in author lis

EXTraS discovery of an X-ray superflare from an L dwarf

We present the first detection of an X-ray flare from an ultracool dwarf of spectral class L. The event was identified in the EXTraS database of XMM-Newton variable sources, and its optical counterpart, J0331-27, was found through a cross-match with the Dark Energy Survey Year 3 release. Next to an earlier four-photon detection of Kelu-1, J0331-27 is only the second L dwarf detected in X-rays, and much more distant than other ultracool dwarfs with X-ray detections (photometric distance of 240 pc). From an optical spectrum with the VIMOS instrument at the VLT, we determine the spectral type of J0331-27 to be L1. The X-ray flare has an energy of EX,F 3c 2 7 1033 erg, placing it in the regime of superflares. No quiescent emission is detected, and from 2.5 Ms of XMM-Newton data we derive an upper limit of LX, qui &lt; 1027 erg s-1. The flare peak luminosity (LX, peak = 6.3 7 1029 erg s-1), flare duration (\u3c4decay 48 2400 s), and plasma temperature ( 4816 MK) are similar to values observed in X-ray flares of M dwarfs. This shows that strong magnetic reconnection events and the ensuing plasma heating are still present even in objects with photospheres as cool as 3c2100 K. However, the absence of any other flares above the detection threshold of EX, F 3c 2.5 7 1032 erg in a total of 3c2.5 Ms of X-ray data yields a flare energy number distribution inconsistent with the canonical power law dN/dE 3c E-2, suggesting that magnetic energy release in J0331-27 - and possibly in all L dwarfs - takes place predominantly in the form of giant flares

The VIMOS Public Extragalactic Redshift Survey (VIPERS). Never mind the gaps: comparing techniques to restore homogeneous sky coverage

[Abridged] Non-uniform sampling and gaps in sky coverage are common in galaxy redshift surveys, but these effects can degrade galaxy counts-in-cells and density estimates. We carry out a comparison of methods that aim to fill the gaps to correct for the systematic effects. Our study is motivated by the analysis of the VIMOS Extragalactic Redshift Survey (VIPERS), a flux-limited survey (i<22.5) based on one-pass observations with VIMOS, with gaps covering 25% of the surveyed area and a mean sampling rate of 35%. Our findings are applicable to other surveys with similar observing strategies. We compare 1) two algorithms based on photometric redshift, that assign redshifts to galaxies based on the spectroscopic redshifts of the nearest neighbours, 2) two Bayesian methods, the Wiener filter and the Poisson-Lognormal filter. Using galaxy mock catalogues we quantify the accuracy of the counts-in-cells measurements on scales of R=5 and 8 Mpc/h after applying each of these methods. We also study how they perform to account for spectroscopic redshift error and inhomogeneous and sparse sampling rate. We find that in VIPERS the errors in counts-in-cells measurements on R<10 Mpc/h scales are dominated by the sparseness of the sample. All methods underpredict by 20-35% the counts at high densities. This systematic bias is of the same order as random errors. No method outperforms the others. Random and systematic errors decrease for larger cells. We show that it is possible to separate the lowest and highest densities on scales of 5 Mpc/h at redshifts 0.5<z<1.1, over a large volume such as in VIPERS survey. This is vital for the characterisation of cosmic variance and rare populations (e.g, brightest galaxies) in environmental studies at these redshifts.Comment: 17 pages, 13 figures, accepted for publication in A&A (revised version after minor revision and language editing

The zCOSMOS redshift survey : Influence of luminosity, mass and environment on the galaxy merger rate

The contribution of major mergers to galaxy mass assembly along cosmic time is an important ingredient to the galaxy evolution scenario. We aim to measure the evolution of the merger rate for both luminosity/mass selected galaxy samples and investigate its dependence with the local environment. We use a sample of 10644 spectroscopically observed galaxies from the zCOSMOS redshift survey to identify pairs of galaxies destined to merge, using only pairs for which the velocity difference and projected separation of both components with a confirmed spectroscopic redshift indicate a high probability of merging. We have identified 263 spectroscopically confirmed pairs with r_p^{max} = 100 h^{-1} kpc. We find that the density of mergers depends on luminosity/mass, being higher for fainter/less massive galaxies, while the number of mergers a galaxy will experience does not depends significantly on its intrinsic luminosity but rather on its stellar mass. We find that the pair fraction and merger rate increase with local galaxy density, a property observed up to redshift z=1. We find that the dependence of the merger rate on the luminosity or mass of galaxies is already present up to redshifts z=1, and that the evolution of the volumetric merger rate of bright (massive) galaxies is relatively flat with redshift with a mean value of 3*10^{-4} (8*10^{-5} respectively) mergers h^3 Mpc^{-3} Gyr^{-1}. The dependence of the merger rate with environment indicates that dense environments favors major merger events as can be expected from the hierarchical scenario. The environment therefore has a direct impact in shapping-up the mass function and its evolution therefore plays an important role on the mass growth of galaxies along cosmic time.Comment: submitted to A&A, 17 pages, 12 figure

The optical spectra of 24 μm galaxies in the COSMOS field. I. Spitzer MIPS bright sources in the zCOSMOS-bright 10k catalog

We study zCOSMOS-bright optical spectra for 609 Spitzer MIPS 24 μm-selected galaxies with S_(24) μ m > 0.30 mJy and I 10^(11) Lסּ galaxies at 0.6 < z < 0.7 are ~0.6 dex higher than the average ratio of all zCOSMOS galaxies at similar redshifts. Massive star formation and AGNs could simultaneously be present in those galaxies with the highest ionizing fluxes. (5) Roughly 1/3 of the galaxies with metallicity measurements at 0.5 < z < 0.7 lie below the general mass-metallicity relation at the corresponding redshifts. The strengths of the 4000 Å break and the Hδ EW of our galaxies show that secondary bursts of star formation are needed to explain the spectral properties of most IR sources. The LIRG and ULIRG phases occur, on average, between 10^7 and 10^8 yr after the onset of a starburst on top of underlying older stellar populations. These results are valid for galaxies of different IR luminosities at 0.6 < z < 1.0 and seem independent of the mechanisms triggering star formation

The VIMOS Public Extragalactic Redshift Survey (VIPERS). Exploring the dependence of the three-point correlation function on stellar mass and luminosity at 0.5<z<1.1

The three-point correlation function (3PCF) is a powerful probe to investigate the clustering of matter in the Universe in a complementary way with respect to lower-order statistics, providing additional information with respect to the two-point correlation function and allowing us to shed light on biasing, nonlinear processes, and deviations from Gaussian statistics. In this paper, we analyse the first data release of the VIMOS Public Extragalactic Redshift Survey (VIPERS), determining the dependence of the three-point correlation function on luminosity and stellar mass at $z=[0.5,1.1]$. We exploit the VIPERS Public Data Release 1, consisting of more than 50,000 galaxies with B-band magnitudes in the range $-21.6\lesssim M_{\rm B}-5\log(h)\lesssim-19.9$ and stellar masses in the range $9.8\lesssim\log(M_\star[h^{-2}\,M_\odot])\lesssim 10.7$. We measure both the connected 3PCF and the reduced 3PCF in redshift space, probing different configurations and scales, in the range $2.5<r\,$[Mpc/h]$<20$. We find a significant dependence of the reduced 3PCF on scales and triangle shapes, with stronger anisotropy at larger scales ($r\sim10$ Mpc/h) and an almost flat trend at smaller scales, $r\sim2.5$ Mpc/h. Massive and luminous galaxies present a larger connected 3PCF, while the reduced 3PCF is remarkably insensitive to magnitude and stellar masses in the range we explored. These trends, already observed at low redshifts, are confirmed for the first time to be still valid up to $z=1.1$, providing support to the hierarchical scenario for which massive and bright systems are expected to be more clustered. The possibility of using the measured 3PCF to provide independent constraints on the linear galaxy bias $b$ has also been explored, showing promising results in agreement with other probes.Comment: 12 pages, 11 figures, 2 tables, accepted for publication in A&