arXiv subjects

Roser Pello

Publications and source records attributed to Roser Pello.

41 records · Page 3Linked to original sources

arXiv2001

Observing the first galaxies - a case for an intermediate resolution multi-object IR spectrograph

We present a special science case for an intermediate resolution multi-object IR spectrograph for the VLT. We have constructed new models for massive Population III stars and metal-free stellar populations (see Schaerer 2001). The properties of individual stars and integrated populations, including their ionising fluxes and SEDs are discussed. We also study their dependence on the poorly known IMF and the star formation history. The synthetic spectra are used to simulate spectroscopic observations of the expected emission lines of Pop III galaxies. We show that such an instrument should allow the detection and efficient observations of the first galaxies with the VLT.

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arXiv1999

Photometric Redshifts in lensing clusters: Identification and Calibration of faint high-z galaxies

We discuss a method aiming to use photometric redshifts in lensing clusters to access the population of distant background sources. The amplification provided by gravitational lensing allows to calibrate photometric redshifts 1 to 3 magnitudes deeper with respect to field studies. We present and discuss some results obtained with this procedure on extensively studied clusters, as well as the future issues of this project.

astro-ph↗

arXiv1999

Probing distant galaxies with lensing clusters

Clusters of galaxies as gravitational lenses allow to study the stellar content and properties of high-z galaxies much fainter than the usual spectroscopic field surveys. We review the recent results obtained on the identification and study of very distant galaxies seen through lensing clusters. Using the gravitational amplification effect in lenses with well known mass distributions, it is possible to build up and study a sample of galaxies with 1 < z < 7. Source candidates are selected close to the critical lines at high-z, through photometric redshifts computed on a large wavelength interval, as well as lens-inversion criteria. This procedure allows to reduce the selection biases in luminosity, and towards active star-forming objects, provided that selection criteria include IR photometry. This is the method presently used in our large collaborative program, aimimg to perform the spectroscopic follow up with the VLT of high-z candidates selected from suitable photometric campaigns.

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arXiv1997

Spectroscopic Confirmation of Redshifts Predicted by Gravitational Lensing

We present deep spectroscopic measurements of 18 distant field galaxies identified as gravitationally-lensed arcs in a Hubble Space Telescope image of the cluster Abell 2218. Redshifts of these objects were predicted by Kneib et al. (1996) using a lensing analysis constrained by the properties of two bright arcs of known redshift and other multiply-imaged sources. The new spectroscopic identifications were obtained using long exposures with the LDSS-2 spectrograph on the William Herschel Telescope and demonstrate the capability of that instrument to new limits, $R\simeq$24; the lensing magnification implies true source magnitudes as faint as $R\simeq$25. Statistically, our measured redshifts are in excellent agreement with those predicted from Kneib et al.'s lensing analysis which gives considerable support to the redshift distribution derived by the lensing inversion method for the more numerous and fainter arclets extending to $R\simeq 25.5$. We explore the remaining uncertainties arising from both the mass distribution in the central regions of Abell 2218 and the inversion method itself, and conclude that the mean redshift of the faint field population at $R\simeq$25.5 ($B\sim 26$-27) is low, $ $=0.8-1. We discuss this result in the context of redshift distributions estimated from multi-colour photometry. Although such comparisons are not straightforward, we suggest that photometric techniques may achieve a reasonable level of agreement particularly when they include near-infrared photometry with discriminatory capabilities in the $1<z<$2 range.

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arXiv1996

The population of galaxies in the distant clusters Cl 1613+3104 and Cl 1600+4109

We study the photometric properties and content of the distant clusters of galaxies Cl 1613+3104 (z = 0.415) and Cl 1600+4109 (z = 0.540). The former is a rich, concentrated cluster which shows a strong evidence for segregation in luminosity and color. Its population of galaxies separates into two different kinds of objects: a red population compatible with the colors expected for E/S0 galaxies located preferentially in the central part of the cluster, and a sparse blue population explained in part by the presence of normal S/Im galaxies, which is much less concentrated. In the case of Cl 1600+4109, there is a lack of E/S0 galaxies and the population is mainly made up of S/Im galaxies, without any evidence of segregation in magnitude or in color. Both clusters exhibit an important fraction of blue objects, increasing with magnitude. This result is due in part to the presence of normal S/Im galaxies, and also to extremely blue objects probably undergoing an episode of intense star-formation.

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