Browsing by Author "Burud, I"

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    About the origin of extinction in the gravitational lens system MG J0414+0534
    (1999) Angonin-Willaime, MC; Vanderriest, C; Courbin, F; Burud, I; Magain, P; Rigaut, F
    Photometric measurements of the highly reddened gravitational mirage MG J0414+0534 have been carried out either by PSF subtraction or by applying accurate deconvolution algorithms to optical (R, I) and near-infrared (K) images obtained at CFHT and NOT under sub-arcsecond seeing conditions. It is confirmed that the close pair of images A1-A2 suffers a larger extinction than B and C. While the colours of image A2 obtained from ground-based data seem inconsistent with a simple reddening law, higher resolution images available from HST archives reveal an additional extended component (arc) which introduces significant errors in the photometric decomposition. When the are component is properly taken into account, the colours of the 4 nucleus images do agree with a classical reddening law, with A2 being by far the most obscured component. Such a differential extinction (maximum difference Delta E(R-I) similar or equal to 0.6) is likely due to the tensing galaxy. This does not mean that all the extinction occurs into the lens. Indeed, the fact that the are is much less red than the images of the nucleus suggests that an important part of the reddening is intrinsic to the source. Finally, no significant variability is observed within this data set, i.e. between 1994 and 1997, while a discrepancy from earlier data is noticed for (A1 + A2).
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    An optical time-delay for the lensed BAL quasar HE 2149-2745
    (2002) Burud, I; Courbin, F; Magain, P; Lidman, C; Hutsemékers, D; Kneib, JP; Hjorth, J; Brewer, J; Pompei, E; Germany, L; Pritchard, J; Jaunsen, AO; Letawe, G; Meylan, G
    We present optical V and i-band light curves of the gravitationally lensed BAL quasar HE 2149-2745. The data, obtained with the 1.5 m Danish Telescope (ESO-La Silla) between October 1998 and December 2000, are the first from a long-term project aimed at monitoring selected lensed quasars in the Southern Hemisphere. A time delay of 103+/-12 days is determined from the light curves. In addition, VLT/FORS1 spectra of HE 2149 2745 are deconvolved in order to obtain the spectrum of the faint lensing galaxy, free of any contamination by the bright nearby two quasar images. By cross-correlating the spectrum with galaxy-templates we obtain a tentative redshift estimate of z = 0.495+/-0:01. Adopting this redshift, a Omega = 0.3, Lambda = 0.7 cosmology, and a chosen analytical lens model, our time-delay measurement yields a Hubble constant of H-0 = 66+/-8 km s(-1) Mpc(-1) (1sigma error) with an estimated systematic error of +/-3 km s(-1) Mpc(-1). Using non-parametric models yields H-0 = 65+/-8 km s(-1) Mpc(-1) (1sigma error) and confirms that the lens exhibits a very dense/concentrated mass profile. Finally, we note, as in other cases, that the flux ratio between the two quasar components is wavelength dependent. While the flux ratio in the broad emission lines-equal to 3.7-remains constant with wavelength, the continuum of the brighter component is bluer. Although the data do not rule out extinction of one quasar image relative to the other as a possible explanation, the effect could also be produced by differential microlensing by stars in the lensing galaxy.
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    On-axis spatially resolved spectroscopy of low redshift quasar host galaxies
    (2002) Courbin, F; Letawe, G; Magain, P; Wisotzki, L; Jablonka, P; Jahnke, DK; Kuhlbrodt, B; Alloin, D; Meylan, G; Minniti, D; Burud, I
    We present the first result of a comprehensive spectroscopic study of quasar host galaxies. On-axis, spatially resolved spectra of low redshift quasars have been obtained with FORS1, mounted on the 8.2 m ESO Very Large Telescope, Antu. The spectra are spatially deconvolved using a spectroscopic version of the "MCS deconvolution algorithm". The algorithm decomposes two dimensional spectra into the individual spectra of the central point-like nucleus and of its host galaxy. Applied to HE 1503+0228 at z = 0.135 (M-B = -23.0), it provides us with the spectrum of the host galaxy between 3600 Angstrom and 8500 Angstrom (rest-frame), at a mean resolving power of 700. The data allow us to measure several of the important Lick indices. The stellar populations and gas ionization state of the host galaxy of HE 1503+0228 are very similar to the ones measured for normal non-AGN galaxies. Dynamical information is also available for the gas and stellar components of the galaxy. Using deconvolution and a deprojection algorithm, velocity curves are derived for emission lines, from the center up to 400 away from the nucleus of the galaxy. Fitting a simple three-components mass model (point mass, spherical halo of dark matter, disk) to the position-velocity diagram, we infer a mass of M(r < 1 kpc) = (2.0 +/- 0.3) x 10(10) M-. within the central kiloparsec of the galaxy, and a mass integrated over 10 kpc of M(r < 10 kpc) = (1.9 +/- 0.3) x 10(11) M-., with an additional 10% error due to the uncertainty on the inclination of the galaxy. This, in combination with the analysis of the stellar populations indicates that the host galaxy of HE 1503+0228 is a normal spiral galaxy.
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    The lensing system towards the doubly imaged quasar SBS 1520+530
    (2002) Faure, C; Courbin, F; Kneib, JP; Alloin, D; Bolzonella, M; Burud, I
    The gravitational potential responsible for the lensing effect in SBS 1520+530 is studied over length scales from a few arc-seconds to a few arc-minutes. For this purpose, we use sharply deconvolved Hubble Space Telescope images in the optical and near-IR, in combination with ground based optical data obtained over a wider field-of-view. In particular, we have carried out a multi-color analysis in order to identify groups or clusters of galaxies along the line of sight. Photometric redshifts are measured for 139 galaxies unveiling significant excesses of galaxies 1.0' NW and 1.7' SW of the main lensing galaxy. The photometric redshift inferred both for the main lensing galaxy and for the galaxy concentrations is z = 0.9(-0.25)(+0.10). This is in rough agreement with the measured spectroscopic redshift of the main lensing galaxy, z = 0.71 (Burud et al. 2002), suggesting that it is part of a larger group or cluster. We investigate the impact of including the galaxy cluster, first on the modelling of the lensing system, and second on the expected time-delay between the two quasar images.
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    Time delay and lens redshift for the doubly imaged BAL quasar SBS 1520+530
    (2002) Burud, I; Hjorth, J; Courbin, F; Cohen, JG; Magain, P; Jaunsen, AO; Kaas, AA; Faure, C; Letawe, G
    We present optical R-band light curves of the gravitationally lensed quasar SBS 1520+530 derived from data obtained at the Nordic Optical Telescope. A time delay of 130 +/- 3 days (1sigma) is determined from the light curves. In addition, spectra of SBS 1520+530 obtained at the Keck Observatory are spatially deconvolved in order to extract the spectrum of the faint lensing galaxy, free of any contamination by the light from the bright quasar images. This spectrum indicates a lens redshift z = 0.717, in agreement with one of the absorption systems found in the quasar spectra. The best mass model of the system includes a second nearby galaxy and a cluster of galaxies in addition to the main lensing galaxy. Adopting this model and an Omega = 0.3, Lambda = 0.7 cosmology, our time-delay measurement yields a Hubble constant of H-0 = 51 +/- 9 km s(-1) Mpc(-1) (1sigma error).