arXiv subjects

J. P. Kneib

Publications and source records attributed to J. P. Kneib.

59 records · Page 4Linked to original sources

arXiv1998

An ultra-deep ISOCAM observation through a cluster-lens

We present results of ultra-deep ISOCAM observations through a cluster-lens at 7 and 15 micron with the Infrared Space Observatory (ISO) satellite. These observations reveal a large number of luminous Mid-Infrared (MIR) sources. Cross-identification in the optical and Near-Infrared (NIR) wavebands shows that about half of the 7 micron sources are cluster galaxies. The other 7 micron and almost all 15 micron sources are identified as lensed distant galaxies. Thanks to the gravitational amplification they constitute the faintest MIR detected sources, allowing us to extend the number counts in both the 7 and 15 micron bands. In particular, we find that the 15 micron counts have a steep slope alpha_15 = -1.5 +/- 0.3 and are large, with N_15 (>30 microJy}) = 13 +/- 5 per square arcmin. These numbers rule out non-evolutionary models and favour very strong evolution. Down to our counts limit, we found that the resolved 7 and 15 microns background radiation intensity is respectively (2 +/-0.5) 10^(-9) and (5 +/-1) 10^(-9) W m^(-2) sr^(-1).

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arXiv1998

Detection and Study of High-Redshift Galaxies Through Cluster-Lenses

We discuss a method to build up and study a sample of distant galaxies, with 2<z<5, using the gravitational amplification effect in cluster-lenses for which the mass distribution is well known. The candidates are selected close to the critical lines at high-z, through photometric redshift estimates on a large wavelength range. With respect to other methods, this procedure allows to reduce the selection biases in luminosity, thanks to the cluster magnification of ~1 magnitude, and towards active SFRs when the near-IR domain is included. Some new results obtained with this technique are presented and discussed.

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arXiv1995

X-ray analysis and matter distribution in the lens-cluster Abell 2390

We present a deep X-ray ROSAT/HRI observation of the rich cluster-lens Abell 2390 and the analysis of the gas and matter distribution in the cluster. The X-ray centroid coincides with the location of the central cD galaxy, and the core appears to be dominated by a massive cooling flow, one of the strongest ones ever studied. On larger scales, the X-ray distribution is elliptical and locally distorted by a significant ``sub-structure" located some 100 $h^{-1}$ kpc from the center. The mass of this sub-structureis estimated to be $\sim$ 1/20 of the total cluster mass and appears tobe associated with an enhancement in the galaxy distribution, in the region where the giant ``straight arc" and several arclets are observed. A simple lens model basedon the geometrical properties of the X-ray gas shows that this sub-structure allows to explain in a simple manner the peculiar shape of the arc and puts strong constraints on the total mass distribution in the central part of this cluster. The derived M/L in the central part of the cluster is found to be around 250 in solar units, a rather common value compared with other cluster-lenses. Moreover, the link between the matter distribution derived from the lens model and the density profile issued from the X-ray map analysis is used to infer the temperature profile in the cluster. This profile shows a significant decrease near the center, in agreement with the existence of the cooling flow. Both X-ray and lensing constraints are tied together to give a consistent picture of the dynamics of the central part of A2390.

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arXiv1995

A combined X-ray and gravitational lensing study of the massive cooling-flow cluster PKS0745-191

We present spatially-resolved X-ray spectroscopy of the X-ray luminous cluster of galaxies, PKS0745-191, using observations made with the ASCA and ROSAT satellites. The X-ray data measure the density, temperature, and metallicity profiles of the cluster gas and constrain the distribution of mass in the cluster to a radius of \sim 1.5 Mpc. We report the discovery of a bright gravitationally-lensed arc at a redshift, z_{\rm arc} = 0.433, in the cluster. This result identifies PKS0745 as the lowest-redshift cluster (z_{\rm clus} = 0.1028) known to exhibit gravitational lensing. The properties of the lensed source are consistent with an S_{\rm ab} galaxy with ongoing star formation. The projected cluster mass determined from lensing arguments is in excellent agreement with the value measured from a multiphase analysis of the X-ray data. This contrasts with previously-reported results for the clusters Abell 1689 and Abell 2218, for which discrepancies of \sim a factor 2 in the lensing and X-ray masses are observed. At both X-ray and optical wavelengths PKS0745 appears regular and dynamically relaxed. Abell 1689 and Abell 2218 exhibit more complex dynamical states, indicative of ongoing merger events. We suggest that merging activity has lead to line-of-sight mass enhancements in these systems. The X-ray spectra and images presented here confirm that PKS0745 contains one of the largest known cooling flows, with a mass deposition rate of \sim 1000 \Msunpyr.

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arXiv1994

Spectroscopic Studies of the Two Eros Candidate Microlensed Stars

Low resolution spectroscopy, and UBVRI photometry, have been obtained for the two EROS microlensing candidates. Radial velocities indicate that both stars are members of the Large Magellanic Cloud. The spectrum and the colours of EROS1, the first candidate, reveal that it is a moderately reddened main-sequence B star with H emission lines. The presence of H absorption lines seems to be more the signature of a normal star than that of a cataclysmic variable. As to EROS2, the second candidate, its spectrum and photometry are those of an unreddened normal main-sequence A star, but it cannot be totally excluded that they represent those of a nova in the pre-outburst phase. Although it is not yet possible to exclude intrinsic stellar variations, the interpretation in terms of microlensing effects remain the most natural one.

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