arXiv subjects

G. Zamorani

Publications and source records attributed to G. Zamorani.

At least 451 records · Page 25Linked to original sources

arXiv2005

A large population of galaxies 9 to 12 billion years back in the history of the Universe

To understand the evolution of galaxies, we need to know as accurately as possible how many galaxies were present in the Universe at different epochs. Galaxies in the young Universe have hitherto mainly been identified using their expected optical colours, but this leaves open the possibility that a significant population remains undetected because their colours are the result of a complex mix of stars, gas, dust or active galactic nuclei. Here we report the results of a flux-limited I-band survey of galaxies at look-back times of 9 to 12 billion years. We find 970 galaxies with spectroscopic redshifts between 1.4 and 5. This population is 1.6 to 6.2 times larger than previous estimates, with the difference increasing towards brighter magnitudes. Strong ultraviolet continua (in the rest frame of the galaxies) indicate vigorous star formation rates of more than 10 to 100 solar masses per year. As a consequence, the cosmic star formation rate is higher than previously measured at redshifts of 3 to 4.

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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.

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arXiv2005

The evolution of early-type galaxies at z~1 from the K20 survey

We have performed VLT spectroscopy of an almost complete sample of 18 early-type galaxies with 0.88 < z < 1.3 plus two at z=0.67, selected from the K20 survey, and derived the velocity dispersion for 15+2 of them. By combining these data with HST and VLT images, we study the Fundamental Plane (FP), the Faber-Jackson and the Kormendy relations at z~1, and compare them with the local ones. The FP at z~1 keeps a remarkably small scatter, and shows both an offset and a rotation, which we interpret in terms of evolution of the mass-to-light ratio, and possibly of the size. We show evidence that the evolution rate depends on galaxy mass, being faster for less massive galaxies. We discuss the possible factors driving the evolution of spheroids and compare our results with the predictions of the hierachical models of galaxy formation.

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arXiv2005

The K20 survey. VII. The spectroscopic catalogue: spectral properties and evolution of the galaxy population

The K20 survey is a near infrared-selected, deep (Ks < 20) redshift survey targeting galaxies in two independent regions of the sky, the CDFS and the q0055-2659 field. The total Ks-selected sample includes 545 objects. Optical spectra for 525 of them have been obtained, providing 501 spectroscopic identifications (including 12 type-1 AGN and 45 stars). This paper describes the final K20 spectroscopic catalogue, along with the technique used to determine redshifts, measure the spectral features and characterize the spectra. The classification of the galaxy spectra has been performed according to a simple parametric recipe that uses the equivalent widths of the two main emission lines (O[II] and Halpha+[N II]) and two continuum indices (the 4000A break index, and a near-UV color index, C(28-39)). We defined three main spectroscopic classes: red early-type galaxies, blue emission-line galaxies and the intermediate galaxies, which show emission lines but a red continuum. More than 95% of the examined galaxies is included in one of these spectral types and a composite spectrum is built for each of the three galaxy classes. The blue emission-line and the early-type galaxies have been divided in redshift bins, and the corresponding composite spectra have been built, in order to investigate the evolution of the spectral properties of the K20 galaxies with redshift.

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arXiv2004

The B-Band Luminosity Function of Red and Blue Galaxies up to z=3.5

We have explored the redshift evolution of the luminosity function of red and blue galaxies up to $z=3.5$. This was possible joining a deep I band composite galaxy sample, which includes the spectroscopic K20 sample and the HDFs samples, with the deep $H_{AB}=26$ and $K_{AB}=25$ samples derived from the deep NIR images of the Hubble Deep Fields North and South, respectively. About 30% of the sample has spectroscopic redshifts and the remaining fraction well-calibrated photometric redshifts. This allowed to select and measure galaxies in the rest-frame blue magnitude up to $z\sim 3$ and to derive the redshift evolution of the B-band luminosity function of galaxies separated by their rest-frame $U-V$ color or specific (i.e. per unit mass) star-formation rate. The class separation was derived from passive evolutionary tracks or from their observed bimodal distributions. Both distributions appear bimodal at least up to $z\sim 2$ and the locus of red/early galaxies is clearly identified up to these high redshifts. Both luminosity and density evolutions are needed to describe the cosmological behaviour of the red/early and blue/late populations. The density evolution is greater for the early population with a decrease by one order of magnitude at $z\sim 2-3$ with respect to the value at $z\sim 0.4$. The luminosity densities of the early and late type galaxies with $M_B<-20.6$ appear to have a bifurcation at $z>1$. Indeed while star-forming galaxies slightly increase or keep constant their luminosity density, "early" galaxies decrease in their luminosity density by a factor $\sim 5-6$ from $z\sim 0.4$ to $z\sim 2.5-3$. A comparison with one of the latest versions of the hierarchical CDM models shows a broad agreement with the observed number and luminosity density evolutions of both populations.

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arXiv2004

The GALEX-VVDS Measurement of the Evolution of the Far-Ultraviolet Luminosity Density and the Cosmic Star Formation Rate

In a companion paper (Arnouts et al. 2004) we presented new measurements of the galaxy luminosity function at 1500 Angstroms out to z~1 using GALEX-VVDS observations (1039 galaxies with NUV<24.5 and z>0.2) and at higher z using existing data sets. In this paper we use the same sample to study evolution of the FUV luminosity density. We detect evolution consistent with a (1+z)^{2.5+/-0.7} rise to z~1 and (1+z)^{0.5+/-0.4} for z>1. The luminosity density from the most UV-luminous galaxies (UVLG) is undergoing dramatic evolution (x30) between 0 25%) of the total FUV luminosity density at z<1. We measure dust attenuation and star formation rates of our sample galaxies and determine the star formation rate density as a function of redshift, both uncorrected and corrected for dust. We find good agreement with other measures of the SFR density in the rest ultraviolet and Halpha given the still significant uncertainties in the attenuation correction.

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arXiv2004

The spatial clustering of X-ray selected AGN and galaxies in the Chandra Deep Field South and North

We investigate the spatial clustering of X-ray selected sources in the two deepest X-ray fields to date, namely the 2Msec Chandra Deep Field North (CDFN) and the 1Msec Chandra Deep Field South (CDFS). The projected correlation function w(r_p), measured on scales ~0.2-10 h^-1 Mpc for a sample of 240 sources with spectroscopic redshift in the CDFN and 124 sources in the CDFS at a median redshift of z~0.8, is used to constrain the amplitude and slope of the real space correlation function xi(r)=(r/r0)^-gamma. The clustering signal is detected at high confidence (>~ 7 sigma) in both fields. The amplitude of the correlation is found to be significantly different in the two fields, the correlation length r0 being 8.6 +- 1.2 h^-1 Mpc in the CDFS and 4.2 +- 0.4 h^-1 Mpc in the CDFN, while the correlation slope gamma is found to be flat in both fields: gamma=1.33 +- 0.11 in the CDFS and gamma=1.42 +- 0.07 in the CDFN (a flat Universe with Omega_m=0.3 and Omega_L=0.7 is assumed; 1 sigma Poisson error estimates are considered). The correlation function has been also measured separately for sources classified as AGN or galaxies. In both fields AGN have a median redshift of z~0.9 and a median 0.5-10 keV luminosity of L_x~10^43 erg s^-1, i.e. they are generally in the Seyfert luminosity regime. As in the case of the total samples, we found a significant difference in the AGN clustering amplitude between the two fields, the best fit correlation parameters being r0=10.3 +- 1.7 h^-1 Mpc, gamma=1.33 +- 0.14 in the CDFS, and r0=5.5 +- 0.6 h^-1 Mpc, gamma=1.50 +- 0.12 in the CDFN. Within each field no statistically significant difference is found between soft and hard X-ray selected sources or between type 1 and type 2 AGN. (abridged)

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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.

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arXiv2004

XMM-Newton observations of Extremely Red Objects and the link with luminous, X-ray obscured Quasars

We present the results of a deep (about 80 ks) XMM-Newton survey of the largest sample of near-infrared selected Extremely Red Objects (R-K>5) available to date to K_S< 19.2. At the relatively bright X-ray fluxes (F_{2-10 keV}> 4x10^{-15} cgs) and near-infrared magnitude probed by the present observations, the fraction of AGN (i.e., X-ray detected) among the ERO population is small (~3.5%); conversely, the fraction of EROs among hard X-ray selected sources is much higher (~20%). The X-ray properties of EROs detected in our XMM-Newton observation indicate absorption in excess of 10^{22} cm^{-2} in a large fraction of them. We have also considered additional samples of X-ray detected EROs available in the literature. X-ray spectral analysis of the highest S/N sources unambiguously indicates that large columns of cold gas (even >10^{23} cm^{-2}) are the rule rather than the exception. The X-ray, optical, and near-infrared properties of those X-ray selected EROs with a spectroscopic or photometric redshift nicely match those expected for quasars 2, the high-luminosity, high-redshift obscured AGNs predicted in baseline XRB synthesis models. A close correlation is detected between X- and K-band fluxes. For the AGN EROs this is consistent, under reasonable assumptions, with the relation established locally between the host galaxies and their central black holes. This suggest that the majority of EROs are powered by massive black holes accreting, on average, at about 0.03-0.1 of the Eddington limit.

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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.

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arXiv2004

A new photometric technique for the joint selection of star-forming and passive galaxies at 1.4<z<2.5

A simple two color selection based on B-, z-, and K- band photometry is proposed for culling galaxies at 1.4 -0.2 (AB) allows to select actively star-forming galaxies at z>1.4, independently on their dust reddening. Instead, objects with BzK<-0.2 and (z-K)>2.5 (AB) colors include passively evolving galaxies at z>1.4, often with spheroidal morphologies. Simple recipes to estimate the reddening, SFRs and masses of BzK-selected galaxies are derived, and calibrated on K<20 galaxies. Based on their UV (reddening-corrected), X-ray and radio luminosities, the BzK-selected star-forming galaxies with K<20 turn out to have average SFR ~ 200 Msun yr^-1, and median reddening E(B-V)~0.4. Besides missing the passively evolving galaxies, the UV selection appears to miss some relevant fraction of the z~2 star-forming galaxies with K<20, and hence of the (obscured) star-formation rate density at this redshift. The high SFRs and masses add to other existing evidence that these z=2 star-forming galaxies may be among the precursors of z=0 early-type galaxies. Theoretical models cannot reproduce simultaneously the space density of both passively evolving and highly star-forming galaxies at z=2. In view of Spitzer Space Telescope observations, an analogous technique based on the RJL photometry is proposed to complement the BzK selection and to identify massive galaxies at 2.5<z<4.0. These color criteria should help in completing the census of the stellar mass and of the star-formation rate density at high redshift (abridged).

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