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Frédéric Courbin

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Publications associées (229)

Spectroscopy of extended Ly alpha envelopes around z=4.5 quasars

Pierre North, Alexander Patrick Eigenbrod, Frédéric Courbin

What are the frequency, shape, kinematics, and luminosity of Ly alpha envelopes surrounding radio-quiet quasars at high redshift, and is the luminosity of these envelopes related to that of the quasar or not? As a first step towards answering these questio ...

2012

Image analysis for cosmology: results from the GREAT10 Galaxy Challenge

Nicolas Cantale, Malte Tewes, Frédéric Courbin, Marc Gentile, Guldariya Nurbaeva, Richard Massey

In this paper, we present results from the weak-lensing shape measurement GRavitational lEnsing Accuracy Testing 2010 (GREAT10) Galaxy Challenge. This marks an order of magnitude step change in the level of scrutiny employed in weak-lensing shape measureme ...

Blackwell Publishing Ltd, Oxford2012

Further Evidence That Quasar X-Ray Emitting Regions Are Compact: X-Ray And Optical Microlensing In The Lensed Quasar Q J0158-4325

Malte Tewes, Georges Meylan, Frédéric Courbin

We present four new seasons of optical monitoring data and six epochs of X-ray photometry for the doubly imaged lensed quasar Q J0158-4325. The high-amplitude, short-period microlensing variability for which this system is known has historically precluded ...

Iop Publishing Ltd2012

A fast empirical method for galaxy shape measurements in weak lensing surveys

Nicolas Cantale, Malte Tewes, Georges Meylan, Frédéric Courbin

We describe a simple and fast method to correct ellipticity measurements of galaxies from the distortion by the instrumental and atmospheric point spread function (PSF), in view of weak lensing shear measurements. The method performs a classification of ga ...

Edp Sciences S A2012

Three quasi-stellar objects acting as strong gravitational lenses

Malte Tewes, Georges Meylan, Frédéric Courbin, François Henri Ambroise Rérat

We report the discovery of three new cases of quasi-stellar objects (QSOs) acting as strong gravitational lenses on background emission line galaxies: SDSS J0827+5224 (z(QSO) = 0.293, z(s) = 0.412), SDSS J0919+2720 (z(QSO) = 0.209, z(s) = 0.558), SDSS J100 ...

2012

Evolution of the observed Ly alpha luminosity function from z=6.5 to z=7.7: evidence for the epoch of reionization?

Frédéric Courbin, Jean-Paul Richard Kneib, Benjamin Yvan Alexandre Clement

Aims. Ly alpha emitters (LAEs) can be detected out to very high redshifts during the epoch of reionization. The evolution of the LAE luminosity function with redshift is a direct probe of the Ly alpha transmission of the intergalactic medium (IGM), and the ...

2012

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses X. Modeling based on high-precision astrometry of a sample of 25 lensed quasars: consequences for ellipticity, shear, and astrometric anomalies

Georges Meylan, Frédéric Courbin

Gravitationally lensed quasars can be used as powerful cosmological and astrophysical probes. We can (i) infer the Hubble constant H-0 based on the so-called time-delay technique, (ii) unveil substructures along the line-of-sight toward distant galaxies, a ...

2012

COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses

Yves Revaz, Malte Tewes, Georges Meylan, Frédéric Courbin

We present accurate time delays for the quadruply imaged quasar HE 0435-1223. The delays were measured from 575 independent photometric points obtained in the R-band between January 2004 and March 2010. With seven years of data, we clearly show that quasar ...

2011

VLT adaptive optics search for luminous substructures in the lens galaxy towards SDSS J0924+0219

Nicolas Cantale, Malte Tewes, Georges Meylan, Frédéric Courbin

The anomalous flux ratios between quasar images are suspected of being caused by substructures in lens galaxies. We present new deep and high-resolution H and Ks imaging of the strongly lensed quasar SDSS J0924+0219 obtained using the ESO VLT with adaptive ...

2011

Zooming into the broad line region of the gravitationally lensed quasar QSO 2237+0305 equivalent to the Einstein Cross III. Determination of the size and structure of the C-IV and C-III] emitting regions using microlensing

Georges Meylan, Alexander Patrick Eigenbrod, Frédéric Courbin, Rudiger Schmidt

Aims. We aim to use microlensing taking place in the lensed quasar QSO 2237+0305 to study the structure of the broad line region (BLR) and measure the size of the region emitting the C-IV and C-III] lines. ...

2011

Gravitational Lensing Accuracy Testing 2010 (Great10) Challenge Handbook

Frédéric Courbin, Marc Gentile, Guldariya Nurbaeva, Anaïs Marie Rassat, Richard Massey, Michael Hirsch, Matthias Bethge

GRavitational lEnsing Accuracy Testing 2010 (GREAT10) is a public image analysis challenge aimed at the development of algorithms to analyze astronomical images. Specifically, the challenge is to measure varying image distortions in the presence of a varia ...

2011

On the effect of image denoising on galaxy shape measurements

Georges Meylan, Frédéric Courbin, Marc Gentile, Guldariya Nurbaeva

Weak gravitational lensing is a very sensitive way of measuring cosmological parameters, including dark energy, and of testing current theories of gravitation. In practice, this requires exquisite measurement of the shapes of billions of galaxies over larg ...

2011

Direct detection of galaxy stellar halos: NGC 3957 as a test case

Frédéric Courbin, Martin Tafelmeyer, Pascale Jablonka

We present a direct detection of the stellar halo of the edge-on S0 galaxy NGC 3957, using ultra-deep VLT/VIMOS V and R images. This is achieved with a sky subtraction strategy based on infrared techniques. These observations allow us to reach unprecedente ...

2010

Constraining the low-mass end of the initial mass function with gravitational lensing

Frédéric Courbin

The low-mass end of the stellar initial mass function (IMF) is constrained by focusing on the baryon-dominated central regions of strong lensing galaxies. We study in this Letter the Einstein Cross (Q2237+0305), a z = 0.04 barred galaxy whose bulge acts as ...

2010

Results of the GREAT08 Challenge: an image analysis competition for cosmological lensing

Frédéric Courbin, Marc Gentile, Anaïs Marie Rassat, Richard Massey, Michael Hirsch, Matthias Bethge

We present the results of the Gravitational LEnsing Accuracy Testing 2008 (GREAT08) Challenge, a blind analysis challenge to infer weak gravitational lensing shear distortions from images. The primary goal was to stimulate new ideas by presenting the probl ...

Blackwell Publishing Ltd, Oxford2010

First case of strong gravitational lensing by a QSO: SDSS J0013+1523 at z=0.120

Malte Tewes, Georges Meylan, Frédéric Courbin, François Henri Ambroise Rérat

We present the first case of strong gravitational lensing by a QSO: SDSS J0013 + 1523 at z = 0.120. The discovery is the result of a systematic search for emission lines redshifted behind QSOs, among 22 298 spectra of the SDSS data release 7. Apart from th ...

2010

Deep optical spectroscopy of extended Ly alpha emission around three radio-quiet z=4.5 quasars

Pierre North, Alexander Patrick Eigenbrod, Frédéric Courbin

We report the first results of a spectroscopic search for Ly alpha envelopes around three z similar to 4.5 radio-quiet quasars. Our observational strategy adopts the FORS2 spectrograph mounted to the UT1 of the Very Large Telescope (VLT) in the multi-slit ...

2008

Microlensing variability in the gravitationally lensed quasar QSO 2237+0305 equivalent to the Einstein Cross - I. Spectrophotometric monitoring with the VLT

Georges Meylan, Alexander Patrick Eigenbrod, Frédéric Courbin

We present the results of the first long-term (2.2 years) spectroscopic monitoring of a gravitationally lensed quasar, namely the Einstein Cross QSO 2237+0305. The goal of this paper is to present the observational facts to be compared in follow-up papers ...

2008

Microlensing variability in the gravitationally lensed quasar QSO 2237+0305 equivalent to the Einstein Cross II. Energy profile of the accretion disk

Georges Meylan, Alexander Patrick Eigenbrod, Frédéric Courbin

We present the continuation of our long-term spectroscopic monitoring of the gravitationally lensed quasar QSO 2237 + 0305. We investigate the chromatic variations observed in the UV/optical continuum of both quasar images A and B, and compare them with nu ...

2008

Simultaneous estimation of time delays and quasar structure

Georges Meylan, Christel Vuissoz, Frédéric Courbin

We expand our Bayesian Monte Carlo method for analyzing the light curves of gravitationally lensed quasars to simultaneously estimate time delays and the sizes of quasar continuum emission regions including their mutual uncertainties. We apply the method t ...

2008

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