arXiv subjects

J. F. Le Borgne

Publications and source records attributed to J. F. Le Borgne.

24 records · Page 2Linked to original sources

arXiv2005

Looking for z>7 galaxies with the Gravitational Telescope

We summarize the main results obtained recently by our group on the identification and study of very high-z galaxies (z>7) using lensing clusters as natural gravitational telescopes. A description of our pilot survey with ISAAC/VLT is presented, aimed at the spectroscopic confirmation of z>7 candidate galaxies photometrically selected from deep near-IR, HST and optical ground-based imaging. The first results issued from this survey are discussed, in particular the global photometric properties of our high-z candidates, and the implications for the global star formation rate at very high-z.

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arXiv2003

Properties of Faint Distant Galaxies as seen through Gravitational Telescopes

This paper reviews the most recent developments related to the use of lensing clusters of galaxies as Gravitational Telescopes in deep Universe studies. We summarize the state of the art and the most recent results aiming at studying the physical properties of distant galaxies beyond the limits of conventional spectroscopy. The application of photometric redshift techniques in the context of gravitational lensing is emphasized for the study of both lensing structures and the background population of lensed galaxies. A presently ongoing search for the first building blocks of galaxies behind lensing clusters is presented and discussed.

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arXiv2000

Spectroscopic follow up of arclets in AC114 with the VLT

We present the first results on the VLT/FORS-1 spectroscopic survey of amplified sources and multiple images in the lensing cluster AC114. Background sources were selected in the cluster core, close to the critical lines, using photometric redshifts combined with lensing inversion criteria. Spectroscopic results are given, together with a brief summary of the properties of some of these high-z galaxies.

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arXiv2000

Photometric Redshifts and Gravitational Telescopes

We review the use of photometric redshifts in the particular context of Gravitational Telescopes. We discuss on the possible application of such a technique to the study of both the faint population of distant sources and the properties of cluster lenses. Photometric reshifts could be used to derive the redshift distribution and properties of a very faint subsample of high-z lensed galaxies, otherwise out of reach. Concerning the mass distribution in lensing clusters, photometric reshifts are strongly needed to scale the mass in weak lensing analysis, and to characterize the lensing structure.

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arXiv1999

A ring galaxy at z=1 lensed by the cluster Abell 370

We present a study of a very peculiar object found in the field of the cluster-lens Abell 370. This object displays, in HST imaging, a spectacular morphology comparable to nearby ring-galaxies. From spectroscopic observations at the CFHT, we measured a redshift of $z=1.062$ based on the identification of [O ii] 3727 Åand [Ne v] 3426 Åemission lines. These emission lines are typical of starburst galaxies hosting a central active nucleus and are in good agreement with the assumption that this object is a ring-galaxy. This object is also detected with ISO in the LW2 and LW3 filters, and the mid Infra-Red (MIR) flux ratio favors a Seyfert 1 type. The shape of the ring is gravitationally distorted by the cluster-lens, and most particularly by a nearby cluster elliptical galaxy. Using the cluster mass model, we can compute its intrinsic shape. Requiring that the outer ring follows an ellipse we put constraints on the M/L ratio of the nearby galaxy and derive a magnification factor of 2.5 $\pm$ 0.2. The absolute luminosities of the source are then $L_B = 1.3 \ 10^{12} L_{B \odot}$ and $ν$ L$_ν\simeq 4. 10^{10}$ L$_\odot$ in the mid-IR.

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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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