EZ: A Tool For Automatic Redshift Measurement Garilli, B.; Fumana, M.; Franzetti, P. ...
Publications of the Astronomical Society of the Pacific,
07/2010, Letnik:
122, Številka:
893
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We present EZ (Easy redshift), a tool we have developed within the VVDS project to help in redshift measurement from optical 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 article 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 the Pandora Web Site.1
Context. Processes driving mass assembly are expected to evolve on different timescales along cosmic time. A transition might happen around z similar to 1 as the cosmic star formation rate starts its ...decrease. Aims. We aim to identify the dynamical nature of galaxies in a representative sample to be able to infer and compare the mass assembly mechanisms across cosmic time. Methods. We present an analysis of the kinematics properties of 50 galaxies with redshifts 0.9 \textless z \textless 1.6 from the MASSIV sample observed with SINFONI/VLT with a mass range from 4.5 x 10(9) M-circle dot to 1.7 x 10(11) M-circle dot and a star formation rate from 6 M-circle dot yr(-1) to 300 M-circle dot yr(-1). This is the largest sample with 2D kinematics in this redshift range. We provide a classification based on kinematics as well as on close galaxy environment. Results. We find that a significant fraction of galaxies in our sample (29%) experience merging or have close companions that may be gravitationally linked. This places a lower limit on the fraction of interacting galaxies because ongoing mergers are probably also present but harder to identify. We find that at least 44% of the galaxies in our sample display ordered rotation, whereas at least 35% are non-rotating objects. All rotators except one are compatible with rotation-dominated (V-max/sigma \textgreater 1) systems. Non-rotating objects are mainly small objects (R-e \textless 4 kpc). They show an anti-correlation of their velocity dispersion and their effective radius. These low-mass objects (log M-star \textless 10.5) may be ongoing mergers in a transient state, galaxies with only one unresolved star-forming region, galaxies with an unstable gaseous phase or, less probably, spheroids. Combining our sample with other 3D-spectroscopy samples, we find that the local velocity dispersion of the ionized gas component decreases continuously from z similar to 3 to z = 0. The proportion of disks also seems to be increasing in star-forming galaxies when the redshift decreases. The number of interacting galaxies seems to be at a maximum at z similar to 1.2. Conclusions. These results draw a picture in which cold gas accretion may still be efficient at z similar to 1.2 but in which mergers may play a much more significant role at z similar to 1.2 than at higher redshift. From a dynamical point of view, the redshift range 1 \textless z \textless 2 therefore appears as a transition period in the galaxy mass assembly process(star star star star).
ABSTRACT 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 with different characteristics.
The estimate of radial abundance gradients in high-redshift galaxies allows to constrain their star formation history and their interplay with the surrounding intergalactic medium. The authors ...present VLT/SINFONI integral-field spectroscopy of a first sample of 50 galaxies at z similar to 1.2 in the MASSIV survey. Using the N2 ratio between the NII 6584 and H alpha rest-frame optical emission lines as a proxy for oxygen abundance in the interstellar medium, they measured the metallicity of the sample galaxies. Seven galaxies display a positive gradient at a high confidence level. Four out of these are interacting, and one is a chain galaxy. They suggest that interactions might be responsible for shallowing and even inverting the abundance gradient. They also identify two interesting correlations in their sample: galaxies with higher gas velocity dispersion have shallower/positive gradients; and metal-poor galaxies tend to show a positive gradient, whereas metal-rich ones tend to show a negative one.
The contribution of the merging process to the early phase of galaxy assembly at z > 1 and, in particular, to the build-up of the red sequence, still needs to be accurately assessed. We aim to ...measure the major merger rate of star-forming galaxies at 0.9 < z < 1.8, using close pairs identified from integral field spectroscopy (IFS). Merging of star-forming galaxies is frequent at around the peak in star formation activity. Our results show that gasrich mergers make an important contribution to the growth of massive galaxies since z ~1.5, particularly on the build-up of the red sequence.
We present the final release of the multiwavelength XMM-Large Scale Structure (LSS) data set, covering the full survey area of 11.1 deg2, with X-ray data processed with the latest XMM-LSS pipeline ...version. The present publication supersedes the catalogue from the first paper in this series, pertaining to the initial 5 deg2. We provide X-ray source lists in the customary energy bands (0.5-2 and 2-10 keV) for a total of 6721 objects in the deep full-exposure catalogue and 5572 in the catalogue limited to 10 ks, above a detection likelihood of 15 in at least one band. We also provide a multiwavelength catalogue, cross-correlating our list with infrared, near-infrared, optical and ultraviolet catalogues. Customary data products, such as X-ray fits images and thumbnail images from the Canada-France-Hawaii Telescope Legacy Survey and the Spitzer Wide-Area Infrared Extragalactic Survey, are made available, together with our data base in Milan, which can be queried interactively. Also, a static snapshot of the catalogues has been supplied to the Centre de Données astronomiques de Strasbourg (CDS).
We develop a Principal Component Analysis aimed at classifying a subset of 27 350 spectra of galaxies in the range 0.4 < z < 1.0 collected by the VIMOS Public Extragalactic Redshift Survey (VIPERS). ...We apply an iterative algorithm to simultaneously repair parts of spectra affected by noise and/or sky residuals, and reconstruct gaps due to rest-frame transformation, and obtain a set of orthogonal spectral templates that span the diversity of galaxy types. By taking the three most significant components, we find that we can describe the whole sample without contamination from noise. We produce a catalogue of eigencoefficients and template spectra that will be part of future VIPERS data releases. Our templates effectively condense the spectral information into two coefficients that can be related to the age and star formation rate of the galaxies. We examine the spectrophotometric types in this space and identify early, intermediate, late and starburst galaxies.
The Vimos VLT deep survey Garilli, B.; Le Fèvre, O.; Guzzo, L. ...
Astronomy and astrophysics (Berlin),
08/2008, Letnik:
486, Številka:
3
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Context. The VVDS-Wide survey has been designed to trace the large-scale distribution of galaxies at z similar to 1 on comoving scales reaching similar to 100 h super(-1) Mpc, while providing a good ...control of cosmic variance over areas as large as a few square degrees. This is achieved by measuring redshifts with VIMOS at the ESO VLT to a limiting magnitude I AB = 22.5, targeting four independent fields with sizes of up to 4 deg super(2) each. Aims. We discuss the survey strategy which covers 8.6 deg super(2) and present the general properties of the current redshift sample. This includes 32 734 spectra in the four regions, covering a total area of 6.1 deg super(2) with a sampling rate of 22 to 24%. This paper accompanies the public release of the first 18 143 redshifts of the VVDS-Wide survey from the 4 deg super(2) contiguous area of the F22 field at RA = 22\rm phi . Methods. We have devised and tested an objective method to assess the quality of each spectrum, providing a compact figure-of-merit. This is particularly effective in the case of long-lasting spectroscopic surveys with varying observing conditions. Our figure of merit is a measure of the robustness of the redshift measurement and, most importantly, can be used to select galaxies with uniform high-quality spectra to carry out reliable measurements of spectral features. We also use the data available over the four independent regions to directly measure the variance in galaxy counts. We compare it with general predictions from the observed galaxy two-point correlation function at different redshifts and with that measured in mock galaxy surveys built from the Millennium simulation. Results. The purely magnitude-limited VVDS Wide sample includes 19 977 galaxies, 304 type I AGNs, and 9913 stars. The redshift success rate is above 90% independent of magnitude. A cone diagram of the galaxy spatial distribution provides us with the current largest overview of large-scale structure up to z similar to 1, showing a rich texture of over- and under-dense regions. We give the mean N (z) distribution averaged over 6.1 deg super(2) for a sample limited in magnitude to I AB = 22.5. Comparing galaxy densities from the four fields shows that in a redshift bin Delta z = 0.1 at z similar to 1 one still has factor-of-two variations over areas as large as similar to 0.25 deg super(2). This level of cosmic variance agrees with that obtained by integrating the galaxy two-point correlation function estimated from the F22 field alone. It is also in fairly good statistical agreement with that predicted by the Millennium simulations. Conclusions. The VVDS WIDE survey currently provides the largest area coverage among redshift surveys reaching z similar to 1. The variance estimated over the survey fields shows explicitly how clustering results from deep surveys of even 1 deg super(2) size should be interpreted with caution. The survey data represent a rich data base to select complete sub-samples of high-quality spectra and to study galaxy ensemble properties and galaxy clustering over unprecedented scales at these redshifts. The redshift catalog of the 4 deg super(2) F22 field is publicly available at http://cencosw.oamp.fr.
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