Jean-François Claeskens

Future supernovae data and quintessence models

The possibility of unambiguously determining the equation of state of the cosmic dark energy with existing and future supernovae data is investigated. We consider four evolution laws for this equation of state corresponding to four quintessential models, i.e. (i) a cosmological constant, (ii) a general barotropic fluid, (iii) a perfect fluid with a linear equation of state and (iv) a more physical model based on a pseudo-Nambu-Goldstone boson field. We explicitly show the degeneracies present not only within each model but also between the different models: they are caused by the multi-integral relation between the equation of state of dark energy and the luminosity distance. Present supernova observations are analysed using a standard Χ 2 method and the minimal Χ 2 values obtained for each model are compared. We confirm the difficulty in discriminating between these models using present type Ia supernovae data only. By means of simulations, we then show that future SNAP observations will not remove all the degeneracies. For example, wrong estimations of Ω m with a good value of Χ 2 m i n could be found if the right cosmological model is not used to fit the data. Finally, we give some probabilities for obtaining unambiguous results, free from degeneracies. In particular, the probability of confusing a cosmological constant with a true barotropic fluid with an equation of state different from -1 is shown to be 95 per cent at a 2σ level.

Multi-wavelength study of the gravitational lens system RXS J1131-1231. III. Long slit spectroscopy: Micro-lensing probes the QSO structure

Aims. We discuss and characterize micro-lensing among the 3 brightest lensed images (A-B-C) of the gravitational lens system RXS J1131-1231 (a quadruply imaged AGN) by means of long slit optical and NIR spectroscopy. Qualitative constraints on the size of different emission regions are derived. We also perform a spectroscopic study of two field galaxies located within 1.6 arcmin radiu s from the lens. Methods. We decompose the spectra into their individual emission components using a multi-component fitting approach. A complem entary decomposition of the spectra enables us to isolate the macro-lensed fraction of the spectra independently of any spectr al modelling. Results. 1. The data support micro-lensing de-amplification of image s A & C. Not only is the continuum emission microlensed in those images but also a fraction of the Broad Line emitting Region (BLR). 2. Micro-lensing of a very broad component of Mg II emission line suggests that the corresponding emission occurs in a region more compact than the other components of the emission line. 3. We find evidence that a large fraction of the Fe II emission arises in the outer parts of the BLR. We also find a ver y compact emitting region in the ranges 3080-3540 A and 4630-4800 A that is likely associated with Fe II. 4. The [O III] narrow emission line regions are partly spatially resolve d. This enables us to put a lower limit of∼ 110h −1 pc on their intrinsic size. 5. Analysis of Mg II absorption found in the spectra indicates that the absorbin g medium is intrinsic to the quasar, has a covering factor of 20%, and is constituted of small clouds homogeneously distributed in front of the continuum and BLRs. 6. Two neighbour galaxies are detected at redshifts z = 0.10 and z = 0.289. These galaxies are possible members of galaxy groups reported at those redshifts.

An XMM-Newton look at the Wolf-Rayet star WR 40 - The star itself, its nebula and its neighbours

We present the results of an XMM-Newton observation of the field of the Wolf-Rayet star WR 40. Despite a nominal exposure of 20 ks and the high sensitivity of the satellite, the star itself is not detected: we thus derive an upper limit on its X-ray flux and luminosity. Joining this result to recent reports of a non-detection of some WC stars, we suggest that the X-ray emission from single normal Wolf-Rayet stars could often be insignificant despite remarkable instabilities in the wind. On the basis of a simple modelling of the opacity of the Wolf-Rayet wind of WR 40, we show that any X-ray emission generated in the particular zone where the shocks are supposed to be numerous will indeed have little chance to emerge from the dense wind of the Wolf-Rayet star. We also report the non-detection of the ejecta nebula RCW 58 surrounding WR 40. Concerning the field around these objects, we detected 33 X-ray sources, most of them previously unknown: we establish a catalog of these sources and cross-correlate it with catalogs of optical/infrared sources.

Multi wavelength study of the gravitational lens system RXS J1131-1231. II. Lens model and source reconstruction

Aims. High angular resolution images of the complex gravitational lens system RXS J1131-1231 (a quadruply imaged AGN with a bright Einstein ring) obtained with the Advanced Camera for Surveys and NICMOS instruments onboard the Hubble Space Telescope are analysed to determine the lens model and to reconstruct the host galaxy. Methods. The lens model is constrained by the relative astrometric positions of the lens and point-like images, and by the extended lensed structures. The non-parametric light distribution is recovered in the source plane by means of back ray-tracing. Results. 1- Precise astrometry and photometry of the four QSO lensed images (A-D) and of the lensing galaxy (G) are obtained. They are found in agreement with an independent study presented in a companion paper. The position and colours of the X object seen in projection close to the lens are found to be only compatible with a satellite galaxy associated with the lens. 
2- The Singular Isothermal Ellipsoid plus external shear provides a good fit of the astrometry of images A-D. The positions of extended substructures are also well reproduced. However an octupole (

Gravitational lensing by damped Ly-alpha absorbers

m=4

The design and performance of the Gaia photometric system

) must be added to the lens potential in order to reproduce the observed lens position, as well as the

Detection of the lensing galaxy for the double QSO HE 1104-1805

I_{\rm B}/I_{\rm C}

Multi-wavelength study of the gravitational lens system RXS J113155.4-123155. I. Multi-epoch optical and near infrared imaging

point-like image flux ratio. The ellipticity and orientation of the mass quadrupole are found similar to those of the light distribution, fitted by a Sersic profile. The lens (

HST and ground-based observations of the gravitational lens system Q1009-0252 A & B

z=0.295

HST Observations of Gravitationally Lensed QSOs

) is found to be a massive elliptical in a rich environment and showing possible evolution with respect to