arXiv subjects

T. Contini

Publications and source records attributed to T. Contini.

At least 199 records · Page 11Linked to original sources

arXiv2006

The VIMOS-VLT Deep Survey - The evolution of galaxy clustering per spectral type to z~1.5

We measure the evolution of clustering for galaxies with different spectral types from 6495 galaxies with 17.5<=I_AB<=24 and measured spectroscopic redshift in the first epoch VIMOS-VLT Deep Survey. We classify our sample into 4 classes, based on the fit of well-defined galaxy spectral energy distributions on observed multi-color data. We measure the projected function wp(rp) and estimate the best-fit parameters for a power-law real-space correlation function. We find the clustering of early-spectral-type galaxies to be markedly stronger than that of late-type galaxies at all redshifts up to z<=1.2. At z~0.8, early-type galaxies display a correlation length r_0=4.8+/-0.9h^{-1}Mpc, while late types have r_0=2.5+/-0.4h^{-1}Mpc. The clustering of these objects increases up to r_0=3.42+/-0.7h^{-1}Mpc for z~1.4. The relative bias between early- and late-type galaxies within our magnitude-limited survey remains approximately constant with b~1.7-1.8 from z~=0.2 up to z~=1, with indications for a decrease at z>1.2, due to the growth in clustering of the star-forming population. We find similar results when splitting the sample into `red' and `blue' galaxies using the observed color bi-modality. When compared to the expected linear growth of mass fluctuations, a natural interpretation of these observations is that: (a) the assembly of massive early type galaxies is already mostly complete in the densest dark matter halos at z~=1; (b) luminous late-type galaxies are located in higher-density, more clustered regions of the Universe at z~=1.5 than at present, indicating that star formation activity is progressively increasing, going back in time, in the higher-density peaks that today are mostly dominated by old galaxies.

astro-ph↗

arXiv2006

Evidence for environment-dependent galaxy Luminosity Function up to z=1.5 in the VIMOS-VLT Deep Survey

We measure the evolution of the galaxy Luminosity Function as a function of large-scale environment up to z=1.5 from the VIMOS-VLT Deep Survey (VVDS) first epoch data. The 3D galaxy density field is reconstructed using a sample of 6582 galaxies with 17.5 < I_{AB} < 24 and measured spectroscopic redshifts. We split the sample in four redshift bins up to z=1.5 and in under-dense and over-dense environments according to the average density contrast δ=0. There is a strong dependence of the Luminosity Function (LF) with large-scale environment up to z=1.2: the LF shape is observed to have a steeper slope in under-dense environments. We find a continuous brightening of ΔM* ~0.6 mag from z=0.25 to z=1.5 both in under-dense and over-dense environments. The rest-frame B-band luminosity density continuously increases in under-dense environments from z=0.25 to z=1.5 whereas its evolution in over-dense environments presents a peak at z~0.9. We interpret the peak by a complex interplay between the decrease of the star formation rate and the increasing fraction of galaxies at δ>0 due to hierarchical growth of structures. As the environmental dependency of the LF shape is already present at least up to z=1.2, we therefore conclude that either the shape of the LF is imprinted very early on in the life of the Universe, a `nature' process, or that `nurture' physical processes shaping up environment relation have already been efficient earlier than a look-back time corresponding to 30% of the current age of the Universe.

astro-ph↗

arXiv2005

The [OII]/Halpha ratio of emission line galaxies in the 2dF redshift survey

We investigate the systematic variation of the [OII]3727/Halpha flux line ratio as a function of various galaxy properties, i.e., luminosity, metallicity, reddening, and excitation state, for a sample of 1124 emission-line galaxies, with a mean redshift z ~ 0.06, drawn from the Two Degree Field Galaxy Redshift Survey. The mean observed and extinction-corrected emission-line flux ratios agree well with the values derived from the $B$-band selected Nearby Field Galaxy Survey galaxy sample, but are significantly different from the values obtained from the Halpha-selected Universidad Complutense de Madrid Survey galaxy sample. This is because the different selection criteria applied in these surveys lead to a significant difference in the mean extinction and metallicity of different samples. We use the R_{23} parameter to estimate the gas-phase oxygen abundance and find that the extinction-corrected [OII]3727/Halpha ratio depends on the oxygen abundance. For 12+log(O/H)>8.4, we confirm that the emission-line ratio decreases with increasing metallicity. We have extended the relationship further to the metal-poor regime, 12+log(O/H)< 8.4, and find that the correlation between the extinction-corrected [OII]3727/Halpha ratio and the metallicity reverses in comparison to the relationship for metal-rich galaxies. For metal-poor galaxies, in contrast with metal-rich ones, the variation of extinction-corrected [OII]3727/Halpha ratio is correlated with the ionization states of the interstellar gas.

astro-ph↗

arXiv2005

The VIMOS Integral Field Unit: data reduction methods and quality assessment

With new generation spectrographs integral field spectroscopy is becoming a widely used observational technique. The Integral Field Unit of the VIsible Multi-Object Spectrograph on the ESO-VLT allows to sample a field as large as 54" x 54" covered by 6400 fibers coupled with micro-lenses. We are presenting here the methods of the data processing software developed to extract the astrophysical signal of faint sources from the VIMOS IFU observations. We focus on the treatment of the fiber-to-fiber relative transmission and the sky subtraction, and the dedicated tasks we have built to address the peculiarities and unprecedented complexity of the dataset. We review the automated process we have developed under the VIPGI data organization and reduction environment (Scodeggio et al. 2005), along with the quality control performed to validate the process. The VIPGI-IFU data processing environment is available to the scientific community to process VIMOS-IFU data since November 2003.

astro-ph↗

arXiv2005

The VIRMOS deep imaging survey IV: Near-infrared observations

In this paper we present a new deep, wide-field near-infrared imaging survey. Our J- and K-band observations in four separate fields complement optical BVRI, ultraviolet and spectroscopic observations undertaken as part of the VIMOS-VLT deep survey (VVDS). In total, our survey spans ~400arcmis^2. Our catalogues are reliable in all fields to at least Kvega~20.75 and Jvega~21.50 (defined as the magnitude where object contamination is less than 10% and completeness greater than 90%). Taken together these four fields represents a unique combination of depth, wavelength coverage and area. We describe the complete data reduction process and outline a comprehensive series of tests carried out to characterise the reliability of the final catalogues. We compare the statistical properties of our catalogues with literature compilations. We find that our J- and K-selected galaxy counts are in good agreement with previously published works, as are our (J-K) versus K colour-magnitude diagrams. Stellar number counts extracted from our fields are consistent with a synthetic model of our galaxy. Using the location of the stellar locus in colour-magnitude space and the measured field-to-field variation in galaxy number counts we demonstrate that the absolute accuracy of our photometric calibration is at the 5% level or better. Finally, an investigation of the angular clustering of K- selected extended sources in our survey displays the expected scaling behaviour with limiting magnitude, with amplitudes in each magnitude bin in broad agreement with literature values.

astro-ph↗

arXiv2005

The VIMOS VLT Deep Survey - First epoch VVDS-Deep survey: 11564 spectra with 17.5<=IAB<=24, and the redshift distribution over 0< z <=5

This paper presents the ``First Epoch'' sample from the VIMOS VLT Deep Survey (VVDS). The VVDS goals, observations, data reduction with VIPGI, and redshift measurement with KBRED are discussed. Data have been obtained with the VIsible Multi Object Spectrograph (VIMOS) on the ESO-VLT UT3, allowing to observe ~600 slits simultaneously at R~230. A total of 11564 objects have been observed in the VVDS-02h and VVDS-CDFS Deep fields over a total area of 0.61deg^2, selected solely on the basis of apparent magnitude 17.5 <=I_{AB} <=24. The VVDS covers the redshift range 0 < z <= 5. It is successfully going through the ``redshift desert'' 1.5 1.4. The survey reaches a redshift measurement completeness of 78% overall (93% including less reliable objects), with a spatial sampling of the population of galaxies of 25% and ~30% in the VVDS-02h and VVDS-CDFS. The redshift accuracy measured from repeated observations with VIMOS and comparison to other surveys is ~276km/s. From this sample we present for the first time the redshift distribution of a magnitude limited spectroscopic sample down to IAB=24. The redshift distribution has a median of z=0.62, z=0.65, z=0.70, and z=0.76, for magnitude limited samples with IAB<=22.5, 23, 23.5, and 24. A high redshift tail above redshift 2 and up to redshift 5 becomes readily apparent for IAB>23.5, probing the bright star forming population of galaxies. This sample provides an unprecedented dataset to study galaxy evolution over 90% of the life of the universe

astro-ph↗

arXiv2005

The VIMOS-VLT Deep Survey: Evolution of the galaxy luminosity function up to z=2 in first epoch data

We investigate the evolution of the galaxy luminosity function from the VIMOS-VLT Deep Survey (VVDS) from the present to z=2 in five (U, B, V, R and I) rest-frame band-passes. We use the first epoch VVDS deep sample of 11,034 spectra selected at 17.5 <= I_{AB} <= 24.0, on which we apply the Algorithm for Luminosity Function (ALF), described in this paper. We observe a substantial evolution with redshift of the global luminosity functions in all bands. From z=0.05 to z=2, we measure a brightening of the characteristic magnitude M* included in the magnitude range 1.8-2.5, 1.7-2.4, 1.2-1.9, 1.1-1.8 and 1.0-1.6 in the U, B, V, R and I rest-frame bands, respectively. We confirm this differential evolution of the luminosity function with rest-frame wavelength, from the measurement of the comoving density of bright galaxies (M < M*(z=0.1)). This density increases by a factor of around 2.6, 2.2, 1.8, 1.5, 1.5 between z=0.05 and z=1 in the U, B, V, R, I bands, respectively. We also measure a possible steepening of the faint-end slope of the luminosity functions, with Δα~ -0.3 between z=0.05 and z=1, similar in all bands.

astro-ph↗

arXiv2005

The VIMOS VLT Deep Survey - The evolution of galaxy clustering to z=2 from first epoch observations

This paper presents the evolution of the clustering of the main population of galaxies from z=2.1 to z=0.2, from the first epoch VIMOS VLT Deep Survey (VVDS), a magnitude limited sample with 17.5<=I_{AB}<=24. We have computed the correlation functions ξ(r_p,π) and w_p(r_p), and the correlation length r_0(z), for the VVDS-02h and VVDS-CDFS fields, for a total of 7155 galaxies in a 0.61deg^2 area. We find that the correlation length in this sample stays roughly constant from z=0.5 to z=1.1, with r_0(z)=2.5-2.8 h^{-1} Mpc (comoving), for galaxies comparable in luminosity to the local 2dFGRS and SDSS samples, indicating that the amplitude of the correlation function was ~2.5x lower at z~1 than observed locally. The correlation length in our lowest redshift bin z=[0.2,0.5] is r_0=2.4 h^{-1} Mpc, lower than for any other population at the same redshift, indicating the low clustering of very low luminosity galaxies, 1.5 magnitudes fainter than in the 2dFGRS or SDSS. The correlation length is increasing to r_0~3.0 h^{-1} Mpc at higher redshifts z=[1.3,2.1], as we are observing increasingly brighter galaxies, comparable to galaxies with MB_AB=-20.5 locally. We compare our measurement to the DEEP2 measurements in the range z=[0.7,1.35] \citep{coil} on the population selected applying the same magnitude and color selection criteria as in their survey, and find comparable results. The slowly varying clustering of VVDS galaxies as redshift increases is markedly different from the predicted evolution of the clustering of dark matter, indicating that bright galaxies are already tracing the large scale structures emerging from the dark matter distribution 9-10 billion years ago, a supporting evidence for a strong evolution of the galaxy vs. dark matter bias.

astro-ph↗

arXiv2005

The VIMOS VLT Deep Survey: Computing the two point correlation statistics and associated uncertainties

We are presenting in this paper a detailed account of the methods used to compute the three-dimensional two-point galaxy correlation function in the VIMOS-VLT deep survey (VVDS). We investigate how instrumental selection effects and observational biases affect the measurements and identify the methods to correct them. We quantify the accuracy of our correction method using an ensemble of fifty mock galaxy surveys generated with the GalICS semi-analytic model of galaxy formation which incorporate the same selection biases and tiling strategy as the real data does. We demonstrate that we are able to recover the real-space two-point correlation function xi(s) to an accuracy better than 10% on scales larger than 1 h^{-1} Mpc, and of about 30% on scales below 1 h^{-1} Mpc, with the sampling strategy used for the first epoch VVDS data. The projected correlation function w_p(r_p) is recovered with an accuracy better than 10% on all scales 0.1 <= r <= 10 h^{-1} Mpc. There is a tendency for a small but systematic under-estimate of the correlation length derived from w_p(r_p) of 6% on average, remaining after our correction process. The large number of simulated surveys allows us to provide a reliable estimate of the cosmic error on the measurements of the correlation length r_0, of about 15-20% for the first epoch VVDS observation (Le Fevre et al.2004, astro-ph/0409133). The error estimation and measurement techniques outlined in this paper are being used in several studies which investigate in detail the clustering properties of galaxies in the VVDS data.

astro-ph↗

arXiv2005

The VVDS-VLA Deep Field II. Optical and near infrared identifications of VLA S(1.4GHz)>80 microJy sources in the VIMOS VLT Deep Survey VVDS-02h field

In this paper we present the optical and near-infrared identifications of the 1054 radio sources detected in the 20cm deep radio survey down to a 5sigma flux limit of about 80 microJy obtained with the VLA in the VIMOS VLT Deep Survey VVDS-02h deep field. Using U,B,V,R,I and K data, we identified 718 radio sources (~74% of the whole sample). The photometric redshift analysis shows that, in each magnitude bin, the radio sample has a higher median photometric redshift than the whole optical sample, while the median (V-I) color of the radio sources is redder than the median color of the whole optical sample. These results suggest that radio detection is preferentially selecting galaxies with higher intrinsic optical luminosity. From the analysis of the optical properties of the radio sources as function of the radio flux, we found that while about 35% of the radio sources are optically unidentified in the higher radio flux bin (S> 1.0 mJy), the percentage of unidentified sources decreases to about 25% in the faintest bins (S< 0.5 mJy). The median I magnitude for the total sample of radio sources,i.e. including also the unidentified ones, is brighter in the faintest radio bins than in the bin with higher radio flux. This suggests that most of the faintest radio sources are likely to be associated to relatively lower radio luminosity objects at relatively modest redshift, rather than radio-powerful, AGN type objects at high redshift.

astro-ph↗

arXiv2005

The VIMOS VLT Deep Survey: Evolution of the non-linear galaxy bias up to z=1.5

We present the first measurements of the Probability Distribution Function (PDF) of galaxy fluctuations in the VIMOS-VLT Deep Survey (VVDS) cone, covering 0.4x0.4 deg between 0.4 0.8; ii) the formation of bright galaxies is inhibited below a characteristic mass-overdensity threshold whose amplitude increases with redshift and luminosity; iii) the biasing function is non linear in all the redshift bins investigated with non-linear effects of the order of a few to 10% on scales >5Mpc.

astro-ph↗

arXiv2004

The VLT-VIMOS Mask Preparation Software

VIMOS (VIsible Multi-Object Spectrograph) is a multi-object imaging spectrograph installed at the VLT (Very large Telescope) at the ESO (European Southern Observatory) Paranal Observatory, especially suited for survey work. VIMOS is characterized by its very high multiplexing factor: it is possible to take up to 800 spectra with 10 arcsec long slits in a single exposure. To fully exploit its multiplexing potential, we designed and implemented a dedicated software tool: the VIMOS Mask Preparation Software (VMMPS), which allows the astronomer to select the objects to be spectroscopically observed, and provides for automatic slit positioning and slit number maximization within the instrumental constraints. The output of VMMPS is used to manufacture the slit masks to be mounted in the instrument for spectroscopic observations.

astro-ph↗

arXiv2004

The VVDS data reduction pipeline: introducing VIPGI, the VIMOS Interactive Pipeline and Graphical Interface

The VIMOS VLT Deep Survey (VVDS), designed to measure 150,000 galaxy redshifts, requires a dedicated data reduction and analysis pipeline to process in a timely fashion the large amount of spectroscopic data being produced. This requirement has lead to the development of the VIMOS Interactive Pipeline and Graphical Interface (VIPGI), a new software package designed to simplify to a very high degree the task of reducing astronomical data obtained with VIMOS, the imaging spectrograph built by the VIRMOS Consortium for the European Southern Observatory, and mounted on Unit 3 (Melipal) of the Very Large Telescope (VLT) at Paranal Observatory (Chile). VIPGI provides the astronomer with specially designed VIMOS data reduction functions, a VIMOS-centric data organizer, and dedicated data browsing and plotting tools, that can be used to verify the quality and accuracy of the various stages of the data reduction process. The quality and accuracy of the data reduction pipeline are comparable to those obtained using well known IRAF tasks, but the speed of the data reduction process is significantly increased, thanks to the large set of dedicated features. In this paper we discuss the details of the MOS data reduction pipeline implemented in VIPGI, as applied to the reduction of some 20,000 VVDS spectra, assessing quantitatively the accuracy of the various reduction steps. We also provide a more general overview of VIPGI capabilities, a tool that can be used for the reduction of any kind of VIMOS data.

astro-ph↗

arXiv2004

Massive Star Populations in Wolf-Rayet Galaxies

We analyze longslit spectral observations of fourteen Wolf-Rayet galaxies from the sample of Schaerer, Contini & Pindao (1999). All 14 galaxies show broad Wolf-Rayet emission in the blue region of the spectrum, consisting of a blend of NIII4640, CIII4650, CIV4658, and HeII4686 emission lines, which is a spectral characteristic of WN stars. Broad CIV5808 emission, termed the red bump, is detected in 9 galaxies and CIII5996 is detected in 6 galaxies. These emission features are due to WC stars. We derive the numbers of late WN and early WC stars from the luminosity of the blue and red bumps, respectively. The number of O stars is estimated from the luminosity of the Hbeta emission line, after subtracting the contribution of WR stars. The Schaerer & Vacca 1998 (hereafter SV98) models predict that the number of WR stars relative to O stars, N_WR/N_O, increases with metallicity. For low metallicity galaxies, the results agree with predictions of evolutionary synthesis models for galaxies with a burst of star formation, and indicates an IMF slope -2 < Gamma < -2.35 in the low metallicity regime. For high metallicity galaxies our observations suggest a Salpeter IMF (Gamma = -2.35) and an extended short burst. The main possible sources of error are the adopted luminosities for single WCE and WNL stars. We also report, for the first time, NGC 450 as a galaxy with WR characteristics.

astro-ph↗

arXiv2004

Oxygen and nitrogen abundances in nearby galaxies. Correlations between oxygen abundance and macroscopic properties

We performed a compilation of more than 1000 published spectra of HII regions in spiral galaxies. The oxygen and nitrogen abundances in each HII region were recomputed in a homogeneous way, using the P-method. The radial distributions of oxygen and nitrogen abundances were derived. The correlations between oxygen abundance and macroscopic properties are examined. There is a significant difference between the L-Z relationship obtained here and that based on the oxygen abundances determined through the R_23-calibrations. The oxygen abundance of NGC 5457 recently determined using direct measurements of Te (Kennicutt, Bresolin & Garnett 2003) agrees with the L-Z relationship derived here, but is in conflict with the L-Z relationship derived with the R_23-based oxygen abundances. The obtained L-Z relation for spirals is compared to that for irregulars. Our sample of galaxies shows evidence that the slope of the O/H-M_B relationship for spirals is slightly more shallow than that for irregulars. The effective oxygen yields were estimated for spiral and irregular galaxies. The effective oxygen yield increases with increasing luminosity from M_B=-11 to M_B=-18 (or with increasing rotation velocity from Vrot=10 km/s to Vrot=100 km/s) and then remains approximately constant. Irregular galaxies from our sample have effective oxygen yields lowered by a factor of 3 at maximum, i.e. irregular galaxies usually keep at least 1/3 of the oxygen they manufactured during their evolution.

astro-ph↗

arXiv2004

Chemical abundances in spiral and irregular galaxies. O and N abundances derived from global emission--line spectra

The validity of oxygen and nitrogen abundances derived from the global emission-line spectra of galaxies via the P-method has been investigated using a collection of published spectra of individual HII regions in irregular and spiral galaxies. The conclusions of Kobulnicky, Kennicutt & Pizagno (1999) that global emission-line spectra can reliably indicate the chemical properties of galaxies has been confirmed. It has been shown that the comparison of the global spectrum of a galaxy with a collection of spectra of individual HII regions can be used to distinguish high and low metallicity objects and to estimate accurate chemical abundances in a galaxy. The oxygen and nitrogen abundances in samples of UV-selected and normal nearby galaxies have been determined. It has been found that the UV-selected galaxies occupy the same area in the N/O -- O/H diagram as individual HII regions in nearby galaxies. Finally, we show that intermediate-redshift galaxies systematically deviate from the metallicity -- luminosity trend of local galaxies.

astro-ph↗

arXiv2004

Star-forming galaxies at z ~ 2: a major science case for the EMIR/GOYA survey on GTC

We present the first results of a project aiming to derive the physical properties of high-redshift lensed galaxies, intrinsically fainter than the Lyman break galaxies currently observed in the field. From FORS and ISAAC spectroscopy on the VLT, we use the full rest-frame UV-to-optical range to derive the physical properties (SFR, extinction, chemical abundances, dynamics, mass, etc) of low-luminosity z ~ 2 star-forming galaxies. Although the sample is still too small for statistical studies, these results give an insight into the nature and evolutionary status of distant star-forming objects and their link with present-day galaxies. Such a project will serve as a basis for the scientific analysis of the EMIR/GOYA survey on the GTC.

astro-ph↗

arXiv2004

The Luminosity-Metallicity relation in the local universe from the 2dF Galaxy Redshift Survey

We investigate the Luminosity-Metallicity (L-Z) relation in the local universe (z < 0.15) using spectra of 6387 star-forming galaxies extracted from the 2dF Galaxy Redshift Survey. This sample is by far the largest to date used to perform such a study. We distinguish star-forming galaxies from AGNs using "standard" diagnostic diagrams to build a homogeneous sample of starburst galaxies for the L-Z study. We propose new diagnostic diagrams using "blue" emission lines ([OII]3727, [OIII]5007 and Hbeta) only to discriminate starbursts from AGNs in intermediate-redshift (z > 0.3) galaxies. Oxygen-to-hydrogen (O/H) abundance ratios are estimated using the "strong-line" method, which relates the strength of bright emission lines (parameters R23 and O32) to O/H. We confirm the existence of the luminosity-metallicity relation over a large range of abundances (~ 2 dex) and luminosities (~ 9 magnitudes). We find a linear relation between the gas-phase oxygen abundance and both the "raw" and extinction-corrected absolute B-band magnitude with a rms of 0.27. A similar relation, with nearly the same scatter, is found in the R band. This relation is in good agreement with the one derived by Melbourne & Salzer (2002) using the KISS data. However, our L-Z relation is much steeper than previous determinations using samples of "normal" irregular and spiral galaxies. This difference seems to be primarily due to the choice of the galaxy sample used to investigate the L-Z relation rather than any systematic error affecting the O/H determination. We anticipate that this luminosity-metallicity relation will be used as the local "reference" for future studies of the evolution with cosmic time of fundamental galaxy scaling relations. (Abridged version).

astro-ph↗