Gravitationally lensed quasars: light curves, observational constraints, modeling and the Hubble constant.

audience: researcherThe central topic of this thesis is gravitational lensing, a phenomenon that occurs when light rays from a background source pass near a massive object located on the line of sight and are deflected. It is one of the most wonderful observational fact in favour of the General Theory of Relativity (Einstein, 1916). This phenomenon constitutes a powerful tool to probe different areas in astrophysics, including cosmology, which is our main interest. In particular we study gravitationally lensed quasars. Refsdal (1964) was the first to state that time delays between different lensed images of the same object, if this one is intrisically variable, can lead to the measurement of the Hubble constant H0, which is related the actual expansion rate of the Universe. Up to now, only a few lensed quasars have led to H0 and the precision on it has never reached the one obtained with other methods as the ones based on the Cosmic Distance Ladder. That is why some scientists from around the globe decided to unite their force to measure H0 from about thirty lensed quasars. To reach that goal, these objects are being monitored with some mid-sized ground-based telescopes located in both hemispheres. This thesis is realised in the framework of this collaboration called COSMOGRAIL for COSmological MOnitoring of GRAvItational Lenses. This work focuses on image processing and on several steps mandatory to obtain a measurement of H0 from lensed quasars: the acquisiton of the light curves from which it is possible to extract the time delays and the acquisition of the observational constraints necessary to model the gravitational potential responsible for the observed configura- tion. The central technique of this work is the image deconvolution with the MCS algorithm (Magain, Courbin & Sohy, 1998). The main principle of this algorithm is the non-violation of the sampling theorem in trying to obtain a better resolution in the deconvolved frame instead of an infinite one. The final resolution in the deconvolved frame is chosen by the user and as it is known, every image is decomposed in a contri- bution from the point sources and another one from all the extended structures such as arcs, rings and galaxies. To obtain good light curves from data coming from several telescopes, good reduction procedures are needed. That is why Vuissoz (2008) developed a semi-automated reduc- tion pipeline including deconvolution with the MCS algorithm. In the framework of the i ii Abstract present thesis, we adapt it to one of the telescopes used by the collaboration whose data were never used before, i.e. the Mercator telescope. We also bring some modifications to this pipeline, e.g. concerning the estimation of the error on the magnitudes of the light curves. We apply this revised version of the reduction pipeline to HE 0435-1223, a quadruply imaged quasar with already measured time delays (Kochanek et al., 2006). Another object, the quad WFI J2026-4536, is then investigated: we obtain light curves for each of the four lensed images. Thanks to the CASTLES project (Cfa-Arizona Space Telescope LEns Survey1), many lensed quasars have been observed with the camera 2 of NICMOS (Near Infrared Camera and Multi-Object Spectrometer ) on board the Hubble Space Telescope. With these high resolution images, we can obtain very accurate constraints on the geometry of the lensed systems. But most of the time no star is available in the field of view to obtain a good Point Spread Function (PSF). That is why we develop an iterative strategy combined with the MCS algorithm: we call it ISMCS. This technique allows to use the lensed images themselves to improve the PSFs step by step while simultaneously deconvolving the frame to obtain better estimations of the extended structures in the image. We first test this strategy on a quadruply imaged quasar, the Cloverleaf gravitational lens (H1413+117), and obtain relative positions precise to 1 milliarcsecond (mas). We then apply ISMCS to the quadruply imaged quasar WFI J2033-4723 in order to con- tribute to the estimate of the Hubble constant, as this object was monitored by our team. We then study a sample of seven lensed systems currently monitored by COSMOGRAIL and for which time delays have never been obtained. Here again, we obtain positional constraints with an accuracy of around 1 to 2 mas thanks to the application of ISMCS. We then model these systems with simple mass profiles for the main lens galaxy and obtain an estimation of the values of the time delays. Finally we apply ISMCS to a sample of eleven lensed quasars which already have measured time delays. When the delays have been remeasured by our team, in four cases until now, we also model the potential of the lens with simple mass profiles to estimate H0. 1http://www.cfa.harvard.edu/castle

High precision photometry in crowded stellar fields

peer reviewedA deconvolution-based method which allows to derive high-precision photometry of stars in crowded fields, proves very useful for a variety of astronomical projects, including transit searches for extrasolar planets

The QSO HE0450-2958: Scantily dressed or heavily robed? A normal quasar as part of an unusual ULIRG

(Abridged) The luminous z=0.286 quasar HE0450-2958 is interacting with a companion galaxy at 6.5 kpc distance and the whole system is a ULIRG. A so far undetected host galaxy triggered the hypothesis of a mostly "naked" black hole (BH) ejected from the companion by three-body interaction. We present new HST/NICMOS 1.6micron imaging data at 0.1" resolution and VLT/VISIR 11.3micron images at 0.35" resolution that for the first time resolve the system in the near- and mid-infrared. We combine these with existing optical HST and CO maps. (i) At 1.6micron we find an extension N-E of the quasar nucleus that is likely a part of the host galaxy, though not its main body. If true, this places HE0450-2958 directly onto the M_BH-M_bulge-relation for nearby galaxies. (ii) HE0450-2958 is consistent with lying at the high-luminosity end of Narrow-Line Seyfert 1 Galaxies, and more exotic explanations like a "naked quasar" are unlikely. (iii) All 11.3micron radiation in the system is emitted by the quasar nucleus, which is radiating at super-Eddington rate, L/L_Edd=6.2+3.8-1.8, or 12 M_sun/yr. (iv) The companion galaxy is covered in optically thick dust and is not a collisional ring galaxy. It emits in the far infrared at ULIRG strength, powered by Arp220-like star formation (strong starburst-like). An M82-like SED is ruled out. (v) With its black hole accretion rate HE0450-2958 produces not enough new stars to maintain its position on the M_BH-M_bulge-relation, and star formation and black hole accretion are spatially disjoint; the bulge has to grow by redistribution of preexisting stars. (vi) Systems similar to HE0450-2958 with spatially disjoint ULIRG-strength star formation and quasar activity are rare. At z<0.43 we only find <4% (3/77) candidates for a similar configuration.Comment: 12 pages, 6 figures, accepted for publication in Ap

Gravitationall lensing evidence against extended dark matter halos

It is generally thought that galaxies are embedded in dark matter halos extending well beyond their luminous matter. The existence of these galactic halos is mainly derived from the larger than expected velocities of stars and gas in the outskirts of spiral galaxies. Much less is known about dark matter around early-type (elliptical or lenticular) galaxies. We use gravitational lensing to derive the masses of early-type galaxies deflecting light of background quasars. This provides a robust measurement of the total mass within the Einstein ring, a circle whose diameter is comparable to the separation of the different quasar images. We find that the mass-to-light ratio of the lensing galaxies does not depend on radius, from inner galactic regions out to several half-light radii. Moreover, its value does not exceed the value predicted by stellar population models by more than a factor two, which may be explained by baryonic dark matter alone, without any need for exotic matter. Our results thus suggest that, if dark matter is present in early-type galaxies, its amount does not exceed the amount of luminous matter and its density follows that of luminous matter, in sharp contrast to what is found from rotation curves of spiral galaxies

Analysis of luminosity distributions and shape parameters of strong gravitational lensing elliptical galaxies

Context. The luminosity profiles of galaxies acting as strong gravitational lenses can be tricky to study. Indeed, strong gravitational lensing images display several lensed components, both point-like and diffuse, around the lensing galaxy. Those objects restrain the study of the galaxy luminosity to its inner parts. Therefore, the usual fitting methods perform rather badly on such images. Previous studies of strong lenses luminosity profiles using such codes and various PSF-determining methods have resulted in somewhat discrepant results. Aims. The present work aims at investigating the causes of those discrepancies, as well as at designing more robust techniques to study the morphology of early-type lensing galaxies, with the ability to subtract lensed signal from their luminosity profiles. Methods. Each shape parameter, namely, the position angle, ellipticity and half-light radius of the galaxy, are determined as independently from each other as possible. The half-light radius measurement method is based on the computation of isophotes. Its robustness regarding various specific aspects of gravitational lensing image processing is analysed and tested versus that of a widely used fitting code, GALFIT. Those techniques are then applied on a sample of systems from the CASTLES database. Results. Simulations show that, when restricted to small, inner parts of the lensing galaxy, the technique presented here is more robust than GALFIT. It gives unbiased results, while GALFIT leads to an overestimation of the half-light radius that can reach about 10%, depending, among others, on the SNR. It is therefore better-suited than GALFIT for gravitational lensing images. It is also able to study lensing galaxies that are not much larger than the PSF, as opposed to GALFIT. New values for the half-light radius of the objects in our sample are presented and compared to previous works

Etude d'un dispositif experimental pour mesurer l'effet faible dans l'interaction neutron-proton

SIGLEAvailable from CEN Saclay, Service de Documentation, 91191 Gif-sur-Yvette Cedex (France) / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc