Browsing by Author "Meylan, G"
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- 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.
- 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.
- 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.
- ItemToward an understanding of the globular cluster overabundance around the central giant elliptical galaxy NGC 1399(1999) Kissler-Patig, M; Grillmair, CJ; Meylan, G; Brodie, JP; Minniti, D; Goudfrooij, PWe investigate the kinematics of a combined sample of 74 globular clusters around NGC 1399. Their high velocity dispersion, increasing with radius, indicates their association with the gravitational potential of the galaxy cluster rather than with that of NGC 1399 itself. We find no evidence for rotation in the full sample, although there is some indication of rotation in the outer regions. The data do not allow us to detect differences between the kinematics of the blue and red subpopulations of globular clusters. A comparison of the globular cluster systems of NGC 1399 and those of NGC 1404 and NGC 1380 indicates that the globular clusters in all three galaxies are likely to have formed via similar mechanisms and at similar epochs. The only property that distinguishes the NGC 1399 globular cluster system from these others is that it is 10 times more abundant. We summarize the evidence for associating these excess globular clusters with the galaxy cluster rather than with NGC 1399 itself and suggest that the overabundance can be explained by tidal stripping, at an early epoch, of neighboring galaxies and subsequent accumulation of globular clusters in the gravitational potential of the galaxy cluster.