Browsing by Author "Courbin, F"
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- ItemA method for spatial deconvolution of spectra(2000) Courbin, F; Magain, P; Kirkove, M; Sohy, SA method for spatial deconvolution of spectra is presented. It follows the same fundamental principles as the "MCS image deconvolution algorithm" recently developed by Magain, Courbin, & Sohy and uses information contained in the spectrum of a reference point-spread function to spatially deconvolve spectra of very blended sources. An improved resolution rather than an infinite one is aimed at, overcoming the well-known problem of "deconvolution artifacts." As in the MCS algorithm, the data are decomposed into a sum of analytical point sources and a numerically deconvolved background so that the spectrum of extended sources in the immediate vicinity of bright point sources may be accurately extracted and sharpened. The algorithm has been tested on simulated data including seeing variation as a function of wavelength and atmospheric refraction. It is shown that the spectra of severely blended point sources can be resolved while fully preserving the spectrophotometric properties of the data. Extended objects "hidden" by bright point sources (up to 4-5 mag brighter) can be accurately recovered as well, provided the data have a sufficiently high total signal-to-noise ratio (200-300 per spectral resolution element). Such spectra are relatively easy to obtain, even down to faint magnitudes, within a few hours of integration time with 10 m class telescopes.
- ItemA search for clusters and groups of galaxies on the line of sight towards 8 lensed quasars(2004) Faure, C; Alloin, D; Kneib, JP; Courbin, FIn this paper we present new ESO/VLT FORS1 and ISAAC images of the fields around eight gravitationally lensed quasars: CTQ 414, HE 0230-2130, LBQS 1009-0252, B 1030+074, HE 1104-1805, B 1359+154, H 1413+117 and HE 2149-2745. When available and deep enough, HST/WFPC2 data were also used to infer the photometric redshifts of the galaxies around the quasars. The search of galaxy overdensities in space and redshift, as well as a weak-shear analysis and a mass reconstruction are presented in this paper. We find that there are most probably galaxy groups towards CTQ 414, HE 0230-2130, B 1359+154, H 1413+117 and HE 2149-2745, with masses <4x10(14) M-circle dot h(-1). Considering its photometric redshift, the galaxy group discovered in the field around HE 1104-1805 is associated with the quasar rather than with the lensing potential.
- ItemAbout 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, FPhotometric 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).
- ItemAn 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, GWe 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.
- ItemCosmic alignment toward the radio Einstein ring PKS 1830-211?(2002) Courbin, F; Meylan, G; Kneib, JPOptical and near-IR Hubble Space Telescope and Gemini North adaptive optics images, further improved through deconvolution, are used to explore the gravitationally lensed radio source PKS 1830-211. The line of sight to the quasar at z = 2.507 appears to be very busy, with the presence, within 0."5 from the source, of (1) a possible galactic main-sequence star, (2) a faint red lensing galaxy visible only in H band, and (3) a new object whose colors and morphology match those of an almost face-on spiral. The V-I color and faint I magnitude of the latter suggest that it is associated with the molecular absorber seen toward PKS 1830-211, at z = 0.89 rather than with the z = 0.19 H I absorber previously reported in the spectrum of PKS 1830-211. While this discovery might ease the interpretation of the observed absorption lines, it also complicates the modeling of the lensing potential well, hence decreasing the interest in using this system as a means to measure H-0 through the time delay between the lensed images. This is the first case of a quasar lensed by an almost face-on spiral galaxy.
- ItemDeep imaging of AX J2019+112(1999) Benítez, N; Broadhurst, T; Rosati, P; Courbin, F; Squires, G; Lidman, C; Magain, PWe detect a distant cluster of galaxies centered on the QSO lens and luminous X-ray source AX J2019 + 112, a.k.a. the "Dark Cluster." Using deep V and I Keck images and wide-held K-s imaging from the New Technology Telescope (NTT), a tight red sequence of galaxies is identified within a radius of 0.2 h(-1) Mpc of the known z = 1.01 elliptical lensing galaxy. The sequence, which includes the central elliptical galaxy, has a slope in good agreement with the model predictions of Kodama et al. for z similar to 1. We estimate the integrated rest-frame luminosity of the cluster to be L-V greater than or equal to 3.2 x 10(11) h(-2) L. (after accounting for significant extinction at the low latitude of this field), more than an order of magnitude higher than previous estimates. The central region of the cluster is deconvolved using the technique of Magain, Courbin, & Sohy, revealing a thick central are coincident with an extended radio source. All the observed lensing features are readily explained by differential magnification of a radio-loud active galactic nucleus by a shallow elliptical potential. The QSO must lie just outside the diamond caustic, producing two images; the are is a highly magnified image formed from a region close to the center of the host galaxy, projecting inside the caustic. The mass-to-light ratio within an aperture of 0.4 h(-1) Mpc is M-X/L-V = 224(-78)(+112)h(M/L-V)., using the X-ray temperature. The strong lens model yields a compatible value, M/L-V = 372(-94)(+94)h(M/L-V)., whereas an independent weak-lensing analysis sets an upper limit of M/L-V < 520h(M/L-V)., typical of massive clusters.
- ItemExploring the gravitationally lensed system HE 1104-1805: near-IR spectroscopy(2000) Courbin, F; Lidman, C; Meylan, G; Kneib, JP; Magain, PA new technique for the spatial deconvolution of spectra is applied to near-IR (0.95-2.50 mu m) NTT/SOFI spec tra of the lensed, radio-quiet quasar HE 1104-1805. The continuum of the lensing galaxy is revealed between 1.5 mu m and 2.5 mu m Although the spectrum does not show strong emission features, it is used in combination with previous optical and IR photometry to infer a plausible redshift in the range 0.8 < z < 1.2. Modeling of the system shows that the lens is complex, probably composed of the red galaxy seen between the quasar images and a more extended component associated with a galaxy cluster with fairly low velocity dispersion (575 km s(-1)). Unless more constrains can be put on the mass distribution of the cluster, e.g. from deep X-ray observations, HE 1104-1805 will not be a good system to determine H-0. We stress that multiply imaged quasars with known time delays may prove more useful as tools for detecting dark mass in distant lenses than for determining cosmological parameters.
- ItemExploring the gravitationally lensed system HE 1104-1805: VLT spectroscopy of the lens at z=0.729(2000) Lidman, C; Courbin, F; Kneib, JP; Golse, G; Castander, F; Soucail, GUsing FORS2, mounted on Kueyen CUT2 of the VLT), we have obtained the redshift of the lensing galaxy in the gravitational lens system HE 1104-1805. We measure z = 0.729 +/- 0.001, in good agreement with previous estimates based on the time delay and the position of the lens on the fundamental plane. It also coincides with one of the metal line absorption systems that are seen in high resolution spectra of HE 1104-1805.
- ItemOn-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, IWe 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.
- ItemResolved stellar populations of super-metal-rich star clusters in the bulge of M 31(2000) Jablonka, P; Courbin, F; Meylan, G; Sarajedini, A; Bridges, TJ; Magain, PWe have applied the MCS image deconvolution algorithm (Magain et al. 1998) to HST/WFPC2 V, I data of three M 31 bulge globular clusters (G170, G177, and G198) and control fields near each cluster. All three clusters are clearly detected, with an increase in stellar density with decreasing radius from the cluster centers: this is the first time that stars have been resolved in bulge clusters in the inner regions of another galaxy. From the RGB slopes of the clusters and the difference in I magnitude between the HE and the top of the RGB, we conclude that these three clusters all have roughly solar metallicity, in agreement with earlier integrated-light spectroscopic measurements. Our data support a picture whereby the M 31 bulge clusters and field stars were born from the same metal-rich, gas, early in the galaxy formation.
- ItemThe late afterglow and host galaxy of GRB 990712(2000) Hjorth, J; Holland, S; Courbin, F; Dar, A; Olsen, LF; Scodeggio, MWe present deep Hubble Space Telescope (HST) imaging, as well as ground-based imaging and spectroscopy, of the optical afterglow associated with the long-duration gamma-ray burst GRB 990712 and its host galaxy. The data were obtained 48-123 days after the burst occurred. The magnitudes of the host (R = 21.9, V = 22.5) and optical afterglow (R = 25.4, V= 25.8, 47.7 days after the burst) favor a scenario in which the optical light follows a pure power-law decay with an index of alpha similar to -1.0. We find no evidence for a contribution from a supernova like SN 1998bw. This suggests that either there are multiple classes of long-duration gamma-ray bursts or that the peak luminosity of the supernova was more than 1.5 mag fainter than SN 1998bw. The HST images and EFOSC2 spectra indicate that the gamma-ray burst was located in a bright, extended feature (possibly a star-forming region) 1.4 kpe from the nucleus of a 0.2L*(B) galaxy at z = 0.434, possibly a Seyfert 2 galaxy. The late-time afterglow and host galaxy of GRB 990712 bear some resemblance to those of GRB 970508.
- ItemThe lensing system towards the doubly imaged quasar SBS 1520+530(2002) Faure, C; Courbin, F; Kneib, JP; Alloin, D; Bolzonella, M; Burud, IThe 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.
- ItemTime 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, GWe 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).