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Georges Meylan

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Publications associées (182)

Microlensing of the broad line region in 17 lensed quasars

Georges Meylan, Frédéric Courbin

When an image of a strongly lensed quasar is microlensed, the different components of its spectrum are expected to be differentially magnified owing to the different sizes of the corresponding emitting region. Chromatic changes are expected to be observed ...

Edp Sciences S A2012

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

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

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

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

The Low-Mass Initial Mass Function In The 30 Doradus Starburst Cluster

Marilyne Andersen, Georges Meylan

We present deep Hubble Space Telescope NICMOS 2 F160W band observations of the central 56 '' x 57 '' (14 pc x 14.25 pc) region around R136 in the starburst cluster 30Dor (NGC 2070) located in the Large Magellanic Cloud. Our aim is to derive the stellar ini ...

2009

The Environments Of High-Redshift Quasi-Stellar Objects

Georges Meylan

We present a sample of i(775)-dropout candidates identified in five Hubble Advanced Camera for Surveys (ACS) fields centered on Sloan Digital Sky Survey quasi-stellar objects (QSOs) at redshift z similar to 6. Our fields are as deep as the GOODS ACS images ...

American Astronomical Society2009

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

Evidence for metallicity spreads in three massive M31 globular clusters

Georges Meylan, Pascale Jablonka

Aims. We quantify the intrinsic width of the red giant branches of three massive globular clusters in M31 in a search for metallicity spreads within these objects. ...

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

COSMOGRAIL: the COSmological MOnitoring of GRAvItational lenses - VII. Time delays and the Hubble constant from WFI J2033-4723

Georges Meylan, Christel Vuissoz, Frédéric Courbin

Gravitationally lensed quasars can be used to map the mass distribution in lensing galaxies and to estimate the Hubble constant H-0 by measuring the time delays between the quasar images. Here we report the measurement of two independent time delays in the ...

2008

An exploratory search for z greater than or similar to 6 quasars in the ukidss early data release

Georges Meylan, Alexander Patrick Eigenbrod, Frédéric Courbin

We conducted an exploratory search for quasars at z similar to 6-8, using the Early Data Release (EDR) from the United Kingdom Infrared Deep Sky Survey (UKIDSS) cross-matched to panoramic optical imagery. High-redshift quasar candidates are chosen using mu ...

2008

A sharp look at the gravitationally lensed quasar SDSS J0806+2006 with laser guide star adaptive optics at the VLT

Georges Meylan, Alexander Patrick Eigenbrod, Frédéric Courbin

We present the first VLT near-IR observations of a gravitationally lensed quasar, using adaptive optics and laser guide star. These observations can be considered as a test bench for future systematic observations of lensed quasars with adaptive optics, ev ...

2008

Observations Of The Gas Reservoir Around A Star-Forming Galaxy In The Early Universe

Georges Meylan

We present a high signal-to-noise spectrum of a bright galaxy at z = 4.9 in 14 hr of integration on VLT FORS2. This galaxy is extremely bright, i(850) = 23.10 +/- 0.01, and is strongly lensed by the foreground massive galaxy cluster A1689 (z = 0.18). Stell ...

2008

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