arXiv subjects

S. Arnouts

Publications and source records attributed to S. Arnouts.

161 records · Page 9Linked to original sources

arXiv2002

ESO Imaging Survey. Exploring the optical/infrared imaging data of CDF-S: Point Sources

This paper describes the methodology currently being implemented in the EIS pipeline for analysing optical/infrared multi-colour data. The aim is to identify different classes of objects as well as possible undesirable features associated with the construction of colour catalogues. The classification method used is based on the xi^2-fitting of template spectra to the observed SEDs, as measured through broad-band filters. Its main advantage is the simultaneous use of all colours, properly weighted by the photometric errors. In addition, it provides basic information on the properties of the classified objects (eg redshift, effective temperature). These characteristics make the xi^2-technique ideal for handling large multi-band datasets. The results are compared to the more traditional colour-colour selection and, whenever possible, to model predictions. In order to identify objects with odd colours, either associated with rare populations or to possible problems in the catalogue, outliers are searched for in the multi-dimensional colour space using a nearest-neighbour criterion. Outliers with large xi^2-values are individually inspected to further investigate their nature. The tools developed are used for a preliminary analysis of the multi-colour point source catalogue constructed from the optical/infrared imaging data obtained for the Chandra Deep Field South (CDF-S). These data are publicly available, representing the first installment of the ongoing EIS Deep Public Survey.

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arXiv2001

On the Nature of the EIS Candidate Clusters: Confirmation of z<0.6 candidates

We use public V-band imaging data from the wide-angle surveys conducted by the ESO Imaging Survey project (EIS) to further investigate the nature of the EIS galaxy cluster candidates. These were originally identified by applying a matched-filter algorithm which used positional and photometric data of the galaxy sample extracted from the I-band survey images. In this paper, we apply the same technique to the galaxy sample extracted from V-band data and compare the new cluster detections with the original ones. We find that ~75% of the low-redshift cluster candidates (z<0.6) are detected in both passbands and their estimated redshifts show good agreement with the scatter in the redshift differences being consistent with the estimated errors of the method. For the ``robust'' I-band detections the matching frequency approaches ~85%. We also use the available (V-I) color to search for the red sequence of early-type galaxies observed in rich clusters over a broad range of redshifts. This is done by searching for a simultaneous overdensity in the three-dimensional color-projected distance space. We find significant overdensities for ~75% of the ``robust'' candidates with z_I<0.6. We find good agreement between the characteristic color associated to the detected "red sequence" and that predicted by passive evolution galaxy models for ellipticals at the redshift estimated by the matched-filter. The results presented in this paper show the usefulness of color data, even of two-band data, to both tentatively confirm cluster candidates and to select possible cluster members for spectroscopic observations. Based on the present results, we estimate that ~150 EIS clusters with z_I<0.6 are real, making it one of the largest samples of galaxy clusters in this redshift range currently available in the southern hemisphere.

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arXiv2001

Pre-FLAMES Survey: Observations of Selected Stellar Fields

This paper presents the first set of fully calibrated images and associated stellar catalogs of the Pre-FLAMES survey being carried out by the ESO Imaging Survey (EIS) project. The primary goal of this survey is to provide the ESO community with data sets from which suitable target lists can be extracted for follow-up observations with the new VLT facility FLAMES. For this purpose 160 stellar fields have been selected for observations in B, V and I using the 8kx8k Wide Field Imager (WFI) at the MPG/ESO 2.2 m telescope at La Silla. These data have been used to assess the observing strategy adopted and to define suitable reduction techniques and procedures for the preparation of input catalogs for FLAMES. The images and catalogs presented here are publicly available and can be requested from the URL address ``http://www.eso.org/eis''.

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arXiv2001

ESO Imaging Survey. Deep Public Survey: Multi-Color Optical Data for the Chandra Deep Field South

This paper presents multi-passband optical data obtained from observations of the Chandra Deep Field South (CDF-S), located at alpha ~ 3h 32m, delta ~ -27d 48m. The observations were conducted at the ESO/MPG 2.2m telescope at La Silla using the 8kx8k Wide-Field Imager (WFI). This data set, taken over a period of one year, represents the first field to be completed by the ongoing Deep Public Survey (DPS) being carried out by the ESO Imaging Survey (EIS) project. This paper describes the optical observations, the techniques employed for un-supervised pipeline processing and the general characteristics of the final data set. The paper includes data taken in six different filters U'UBVRI. The data cover an area of about 0.25 square degrees reaching 5 sigma limiting magnitudes of U'_AB=26.0, U_AB=25.7, B_AB=26.4$, V_AB=25.4, R_AB=25.5 and I_AB= 24.7 mag, as measured within a 2xFWHM aperture. The optical data covers the area of ~ 0.1

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arXiv2001

Measuring the Redshift Evolution of Clustering: the Hubble Deep Field South

We present an analysis of the evolution of galaxy clustering in the redshift interval 0<z<4.5 in the HDF-S. The HST optical data are combined with infrared ISAAC/VLT observations, and photometric redshifts are used for all the galaxies brighter than I_AB<27.5. The clustering signal is obtained in different redshift bins using two different approaches: a standard one, which uses the best redshift estimate of each object, and a second one, which takes into account the redshift probability function of each object. This second method makes it possible to improve the information in the redshift intervals where contamination from objects with insecure redshifts is important. With both methods, we find that the clustering strength up to z~3.5 in the HDF-S is consistent with the previous results in the HDF-N. While at redshift lower than z~1 the HDF galaxy population is un/anti-biased (b<1) with respect to the underlying dark matter, at high redshift the bias increases up to b~2-3, depending on the cosmological model. These results support previous claims that, at high redshift, galaxies are preferentially located in massive haloes, as predicted by the biased galaxy formation scenario. The impact of cosmic errors on our analyses has been quantified, showing that errors in the clustering measurements in the HDF surveys are indeed dominated by shot-noise in most regimes. Future observations with instruments like the ACS on HST will improve the S/N by at least a factor of two and more detailed analyses of the errors will be required. In fact, pure shot-noise will give a smaller contribution with respect to other sources of errors, such as finite volume effects or non-Poissonian discreteness effects.

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arXiv2001

Multicolor observations of the Hubble Deep Field South

We present a deep multicolor (UBVIJsHKs) catalog of galaxies in the HDF-S, based on observations obtained with the HST WFPC2 in 1998 and VLT-ISAAC in 1999. The photometric procedures were tuned to derive a catalog optimized for the estimation of photometric redshifts. In particular we adopted a ``conservative'' detection threshold which resulted in a list of 1611 objects. The behavior of the observed source counts is in general agreement with the result of Casertano et al. (2000) in the HDF-S and Williams et al. (1996) in the HDF-N, while the corresponding counts in the HDF-N provided by Fernandez-Soto et al. (1999) are systematically lower by a factor 1.5 beyond I_AB=26. After correcting for the incompleteness of the source counts, the object surface density at I_AB<27.5 is estimated to be 220 per square arcmin, providing an estimate of the Extragalactic Background Light in the I band consistent with the work of Madau & Pozzetti(2000). The comparison between the median V-I color in the HDF-North and South shows a significant difference around I_AB~26, possibly due to the presence of large scale structure at z~1 in the HDF-N. High-z galaxy candidates (90 U dropout and 17 B dropout) were selected by means of color diagrams, down to a magnitude I_AB=27, with a surface density of (21+-1) and (3.9+-0.9) per square arcmin, respectively. 11 EROs (with (I-K)_AB>2.7) were selected down to K_AB=24, plus 3 objects whose upper limit to the Ks flux is still compatible with the selection criterion. The corresponding surface density of EROs is (2.5+-0.8) per sq.arcmin ((3.2+-0.9) per sq.arcmin if we include the three Ks upper limits). They show a remarkably non-uniform spatial distribution and are classified with roughly equal fractions in the categories of elliptical and starburst galaxies.

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arXiv2001

Parasitic Light in NGST instruments: the accuracy of photometric redshifts and the effect of filter leaks in the visible and near IR camera

A detailed analysis of NGST multiband photometry applied to the reference case of the study of high-redshift galaxies has been carried out with simulations based on galaxy SEDs derived from the currently available empirical and model templates and on plausible standard filter-sets. In order to correctly identify star forming galaxies in the redshift range 5 2 and avoid confusion with other SEDs it is mandatory to have photometric information in optical bands, besides a standard IR filter-set like F110 F160 K L M. In particular by adding the V606, I814 and z-Gunn filters a good discrimination is obtained above z>5 for star forming galaxies and z>1 for early-types. The case for an extension of the NGST wavelength domain to the optical range is therefore strongly supported by this analysis. The effects of leaks in the filter blocking have also been investigated. In spite of rather pessimistic assumptions (a constant leak at a level of 10^{-4} of the peak transmission over the whole spectral range or a leak of Gaussian shape placed at 1.5 times the effective wavelength of the filter with an amplitude of 10^{-3} of the peak transmission and a width of 5% of the central wavelength) the effects are not dramatic: the accuracy of the determination of photometric redshifts with a standard V606 I814 z-Gunn F110 F160 K L M filter set does not significantly deteriorate for a sample limited to M_AB~30. In the range 5.5<z<12.5 a rather high accuracy with a typical error |z_sim-z_phot|<=0.2 is achieved. With the filter blocking achieved by the present standard technology, extended and continuous spectral coverage appears to be the driving factor to maximize the scientific output.

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arXiv2001

ESO Imaging Survey. Deep Public Survey: Infrared Data for the Chandra Deep Field South

This paper presents new J and Ks near-infrared data obtained from observations of the Chandra Deep Field South (CDF-S) conducted at the ESO 3.5m New Technology Telescope (NTT). These data were taken as part of the ongoing Deep Public Survey (DPS) being carried out by the ESO Imaging Survey (EIS) program, extending the EIS-DEEP survey. Combined these surveys now provide a contiguous coverage over an area of 400 square arcmin in the near-infrared, nearly matching that covered by the deep X-ray observations of Chandra, four times the area of the original EIS-DEEP survey. The paper briefly describes the observations and the new techniques being employed for pipeline processing jittered infrared observations, which include unbiased de-fringing and sky-background subtraction, pixel-based astrometry and stacking and pixel registration based on a multi-resolution decomposition of the images. The astrometric solution is based on a pre-release of the GSC-II catalog and has an accuracy of < 0.15 arcsec. The final images for 12 pointings presented here reach median 5 sigma limiting magnitudes of J_AB~23.4 and K_AB~22.6 as measured within an aperture 2xFWHM. The frame to frame variation of the photometric zero-point is estimated to be <0.09 mag. The data are publicly available in the form of fully calibrated J and Ks pixel maps and source lists extracted for each pointing. These data can be requested through the URL ``http://www.eso.org/eis''.

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arXiv2000

Optical/Infrared Survey of Galaxy Clusters

In this contribution the ongoing effort to build a statistical sample of clusters of galaxies over a wide range of redshifts to study the evolution of clusters and member galaxies is reviewed. The starting point for this project has been the list of candidate clusters identified from the I-band EIS-WIDE survey data. Since the completion of this survey, new optical/infrared observations have become available and have been used to confirm some of these candidates using the photometric data alone or in combination with the results of follow-up spectroscopic observations. Our preliminary results show that the yield of real physical associations from the original catalog is conservatively >60% and that a large sample of clusters in the southern hemisphere, extending to high-redshifts, is within reach.

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arXiv2000

Photometric redshifts and selection of high redshift galaxies in the NTT and Hubble Deep Fields

We present and compare in this paper new photometric redshift catalogs of the galaxies in three public fields: the NTT Deep Field, the HDF-N and the HDF-S. Photometric redshifts have been obtained for thewhole sample, by adopting a $χ^2$ minimization technique on a spectral library drawn from the Bruzual and Charlot synthesis models, with the addition of dust and intergalactic absorption. The accuracy, determined from 125 galaxies with known spectroscopic redshifts, is $σ_z\sim 0.08 (0.3)$ in the redshift intervals $z=0-1.5 (1.5-3.5)$. The global redshift distribution of I-selected galaxies shows a distinct peak at intermediate redshifts, z~0.6 at I_{AB}<26 and z~0.8 at I_{AB}<27.5 followed by a tail extending to z~6. We also present for the first time the redshift distribution of the total IR-selected sample to faint limits ($Ks \leq 21$ and $J\leq22$). It is found that the number density of galaxies at 1.25 5 candidates in the HDF filter set and that the 4 brightest candidates at $z>5$ in the HDF-S are indeed most likely M stars. (ABRIDGED)

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arXiv2000

The First VLT FORS1 spectra of Lyman-break candidates in the HDF-S and AXAF Deep Field

We report on low-resolution multi-object spectroscopy of 30 faint targets (R \~ 24-25) in the HDF-S and AXAF deep field obtained with the VLT Focal Reducer/low dispersion Spectrograph (FORS1). Eight high-redshift galaxies with 2.75< z < 4 have been identified. The spectroscopic redshifts are in good agreement with the photometric ones with a dispersion $σ_z = 0.07$ at z<2 and $σ_z = 0.16$ at z>2. The inferred star formation rates of the individual objects are moderate, ranging from a few to a few tens solar masses per year. Five out of the eight high-z objects do not show prominent emission lines. One object has a spectrum typical of an AGN. In the AXAF field two relatively close pairs of galaxies have been identified, with separations of 8.7 and 3.1 proper Mpc and mean redshifts of 3.11 and 3.93, respectively.

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arXiv1999

ESO Imaging Survey: Past Activities and Future Prospects

The ESO Imaging Survey (EIS) is an ongoing project to carry out public imaging surveys to support programs on the ESO Very Large Telescope (VLT). The first phase of the project started in July 1997 and consisted of a moderately deep, large-area survey (EIS-WIDE) and a deep optical/infrared survey (EIS-DEEP) using the ESO New Technology Telescope (NTT). EIS has recently reached another milestone with the completion of a Pilot Survey using the Wide-Field Image (WFI), an 8k by 8k mosaic CCD camera mounted on the MPG/ESO 2.2m telescope at La Silla. This paper briefly reviews the results of the original EIS and gives an update of the results obtained from the observations carried out as part of the Pilot Survey. Work in progress on the development of an advanced pipeline for handling data from large CCD mosaics and facilities to make the access to data products easier for external users are also discussed.

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arXiv1998

The NTT Susi Deep Field

We present a deep BVrI multicolor catalog of galaxies in a 5.62 sq.arcmin field 80 arcsec south of the high redshift (z=4.7) quasar BR 1202-0725, derived from observations with the direct CCD camera SUSI at the ESO NTT. The formal 5$σ$ magnitude limits (in 2 x FWHM apertures) are 26.9, 26.5, 25.9 and 25.3 in B, V, r and I respectively. Counts, colors for the star and galaxy samples are discussed and a comparison with a deep HST image in the I band is presented. The percentage of merged or blended galaxies in the SUSI data to this magnitude limit is estimated to be not higher than 1%. At the same galactic latitude of the HDF but pointing toward the galactic center, the star density in this field is found to be ~3 times higher, with ~20% of the objects with V-I > 3.0. Reliable colors have been measured for galaxies selected down to r = 26. The choice of the optical filters has been optimized to define a robust multicolor selection of galaxies at 3.8 <= z <= 4.4. Within this interval the surface density of galaxy candidates with r < 26 in this field is 2.7 +/- 0.4 arcmin^-2 corresponding to a comoving density of Star Formation Rate at 3.8 <= z <= 4.4 of 10^{-2.00} - 10^{-1.82} h^3 Mo /yr/ Mpc^3.

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arXiv1998

Early-Type Galaxies in the Hubble Deep Field: The Star Formation History

We have investigated the properties of a complete K-band selected sample of 35 elliptical and S0 galaxies brighter than K=20.15 in the Hubble Deep Field, as representative of the field galaxy population. This sample has been derived from deep K-band image by the KPNO-IRIM camera, by applying a rigorous morphological classification scheme based on quantitative analyses of the surface brightness profiles. The broad-band spectra of the sample galaxies allow us to date their dominant stellar populations. The majority of bright early-types in this field are found at redshifts z<1.3 to display colors indicative of a fairly wide range of ages (typically 1.5 to 3 Gyrs). We find that the major episodes of star-formation building up typical M_star galaxies have taken place during a wide redshift interval 1 1.3, which should be detectable during the luminous star-formation phase expected to happen at these redshifts. Obvious solutions are a) that the merging events imply perturbed morphologies which prevent selecting them by our morphological classification filter, or b) that a dust-polluted ISM obscures the (either continuous or episodic) events of star-formation. We conclude that the likely solution is a combination thereof, i.e. a set of dust-enshrouded merging-driven starbursts occurring during the first few Gyrs of the galaxy's lifetime.

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arXiv1998

Early-type Galaxies in the Hubble Deep Field. The -r_e relation and the lack of large galaxies at high redshift

We present the results of the detailed surface photometry of a sample of early-type galaxies in the Hubble Deep Field. Effective radii, surface brightnesses and total V_606 magnitudes have been obtained, as well as U_300, B_450, I_814, J, H and K colors, which are compared with the predictions of chemical-spectrophotometric models of population synthesis. Spectroscopic redshifts are available for 23 objects. For other 25 photometric redshifts are given. In the -r_e plane the early-type galaxies of the HDF, once the appropriate K+E corrections are applied, turn out to follow the `rest frame' Kormendy relation. This evidence, linked to the dynamical information gathered by Steidel et al.(1996), indicates that these galaxies, even at z~2-3, lie in the Fundamental Plane, in a virial equilibrium condition. At the same redshifts a statistically significant lack of large galaxies [i.e. with Log r_e(kpc) > 0.2] is observed.

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arXiv1997

The ESO-Sculptor Faint Galaxy Survey: Large-Scale Structure and Galaxy Populations at 0.1 < z < 0.5

We describe the current status of the ESO-Sculptor Survey. The observational goal has been to produce a new multi-color photometric catalogue of galaxies in a region located near the southern galactic pole, complemented by a spectroscopic survey. The primary scientific objectives are (1) to map the spatial distribution of galaxies at 0.1 < z < 0.5 and (2) to provide a database for studying the variations in the spectro-photometric properties of distant galaxies as a function of redshift and local environment. The photometric survey provides total magnitudes in the bands B, V (Johnson) and R (Cousins) to limiting magnitudes of 24.5, 24.0, 23.5 respectively. To these limits, the catalog contains about 9500, 12150, 13000 galaxies in B, V, R bands respectively and is the first large digital multi-colour photometric catalog at this depth. This photometric survey provides the entry catalog for a fully-sampled redshift survey of ~ 700 galaxies with R < 20.5. Here, we describe the characteristics of the photometric and spectroscopic samples of the ESO-Sculptor, and report the results obtained so far on the large-scale structure, the spectral classification, and the luminosity function.

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arXiv1997

The ESO-Sculptor Faint Galaxy Redshift Survey: The Photometric Sample

We present the photometric sample of a faint galaxy survey carried out in the southern hemisphere, using CCDs on the 3.60m and NTT-3.5m telescopes at La Silla (ESO). The survey area is a continuous strip of 0.2 deg x 1.53 deg located at high galactic latitude (-83 deg) in the Sculptor constellation. The photometric survey provides total magnitudes in the bands B, V (Johnson) and R (Cousins) to limiting magnitudes of 24.5, 24.0, 23.5 respectively. To these limits, the catalog contains about 9500, 12150, 13000 galaxies in B, V, R bands respectively and is the first large digital multi-colour photometric catalog at this depth. This photometric survey also provides the entry catalog for a fully-sampled redshift survey of ~ 700 galaxies with R < 20.5 (Bellanger et al. 1995). In this paper, we describe the photometric observations and the steps used in the data reduction. The analysis of objects and the star-galaxy separation with a neural network are performed using SExtractor, a new photometric software developed by E. Bertin (1996). The photometric accuracy of the resulting catalog is ~ 0.05 mag for R < 22. The differential galaxy number counts in B, V, R are in good agreement with previously published CCD studies and confirm the evidence for significant evolution at faint magnitudes as compared to a standard non evolving model (by factors 3.6, 2.6, 2.1). The galaxy colour distributions B-R, B-V of our sample show a blueing trend of ~ 0.5 mag between 21 < R < 23.5 in contrast to the V-R colour distribution where no significant evolution is observed.

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