What are the frequency, shape, kinematics, and luminosity of Ly alpha envelopes surrounding radio-quiet quasars at high redshift, and is the luminosity of these envelopes related to that of the quasar or not? As a first step towards answering these questions, we have searched for Ly alpha envelopes around six radio-quiet quasars at z similar to 4.5, using deep spectra taken with the FORS2 spectrograph attached to the UT1 of the Very Large Telescope (VLT). Using the multi-slit mode allows us to observe several point spread function stars simultaneously with the quasar, and to remove the point-like emission from the quasar, unveiling the faint underlying Ly alpha envelope with unprecedented depth. An envelope is detected around four of the six quasars, which suggests that these envelopes are very frequent. Their diameter varies in the range 26 less than or similar to d less than or similar to 64 kpc, their surface brightness in the range 3 x 10(-19) less than or similar to mu less than or similar to 2 x 10(-17) erg s(-1) cm(-2) arcsec(-2), and their luminosity in the range 10(42) less than or similar to L(Ly alpha) less than or similar to 1044 erg s(-1). Their shape may be strongly asymmetric. The Ly alpha emission line full width at half maximum (FWHM) is 900 < FWHM < 2200 km s-1 and its luminosity correlates with that of the broad line region (BLR) of the quasar, with the notable exception of BR2237-0607, the brightest object in our sample. The same holds for the relation between the envelope Ly alpha luminosity and the ionizing luminosity of the quasar. While the deep slit spectroscopy presented in this paper is very efficient at detecting very faint Ly alpha envelopes, narrow-band imaging is now needed to measure accurately their spatial extent, radial luminosity profile, and total luminosity. These observables are crucial to help us discriminate between the three possible radiation processes responsible for the envelope emission: (i) cold accretion, (ii) fluorescence induced by the quasar, and (iii) scattering of the BLR photons by cool gas.

Aims. We aim to use microlensing taking place in the lensed quasar QSO 2237 + 0305 to study the structure of the broad line region (BLR) and measure the size of the region emitting the C iv and C iii] lines.

Aims. We report on the redshift of the lensing galaxy and of the quasar QJ 0158-4325 and on the lens model of the system.Methods. A deep VLT/FORS2 spectrum and HST/NICMOS-F160W images are deconvolved. From the images we derive the light profile of the lensing galaxy and an accurate relative astrometry for the system. In addition we measure the flux ratio between the quasar images in the Mg II emission line to constrain the mass model.Results. From the spectrum we measure the redshift of the lensing galaxy (z = 0.317 +/- 0.001) and of the quasar (z = 1.294 +/- 0.008). Using the flux ratio in the lens model allows us to discard the SIE as a suitable approximation of the lens potential. On the contrary the truncated-PIEMD gives a good fit to the lens and leads to a time delay of Delta t(A-B) = -14.5 +/- 0.1 days, with H(0) = 73 km s(-1) Mpc(-1).Conclusions. Using the flux ratio to constrain the mass model favors the truncated-PIEMD over the SIE, while ignoring this constraint leaves the choice open.

We conducted an exploratory search for quasars at z ∼ 6–8, using the Early Data Release (EDR) from the United Kingdom Infrared Deep Sky Survey (UKIDSS) cross-matched to panoramic optical imagery. High-redshift quasar candidates are chosen using multi-color selection in i, z, Y, J, H, and K bands. After removal of apparent instrumental artifacts, our candidate list consisted of 34 objects. We further refined this list with deeper imaging in the optical for ten of our candidates. Twenty-five candidates were followed up spectroscopically in the near-infrared and in the optical. We confirmed 25 of our spectra as very low-mass main-sequence stars or brown dwarfs, which were indeed expected as the main contaminants of this exploratory search. The lack of quasar detection is not surprising: the estimated probability of finding a single z > 6 quasar down to the limit of UKIDSS in 27.3 deg2 of the EDR is <5%. We find that the most important limiting factor in this work is the depth of the available optical data. Experience gained in this pilot project can help refine high-redshift quasar selection criteria for subsequent UKIDSS data releases.

We present the results of the first long-term (2.2 years) spectroscopic monitoring of a gravitationally lensed quasar, namely the Einstein Cross Q2237+0305. The goal of this paper is to present the observational facts to be compared in follow-up papers with theoretical models to constrain the inner structure of the source quasar. We spatially deconvolve deep VLT/FORS1 spectra to accurately separate the spectrum of the lensing galaxy from the spectra of the quasar images. Accurate cross-calibration of the 58 observations at 31-epoch from October 2004 to December 2006 is carried out with non-variable foreground stars observed simultaneously with the quasar. The quasar spectra are further decomposed into a continuum component and several broad emission lines to infer the variations of these spectral components. We find prominent microlensing events in the quasar images A and B, while images C and D are almost quiescent on a timescale of a few months. The strongest variations are observed in the continuum of image A. Their amplitude is larger in the blue (0.7 mag) than in the red (0.5 mag), consistent with microlensing of an accretion disk. Variations in the intensity and profile of the broad emission lines are also reported, most prominently in the wings of the CIII] and center of the CIV emission lines. During a strong microlensing episode observed in June 2006 in quasar image A, the broad component of the CIII] is more highly magnified than the narrow component. In addition, the emission lines with higher ionization potentials are more magnified than the lines with lower ionization potentials, consistent with the results obtained with reverberation mapping. Finally, we find that the V-band differential extinction by the lens, between the quasar images, is in the range 0.1-0.3 mag.

D. Sluse †a, A. Eigenbrod a, F. Courbin a, D. Hutsemékers b‡, J.-F. Claeskens b, G. Meylan a, E. Agol c, J. Surdej b§ a Laboratoire d’Astrophysique, Ecole Polytechnique Fédéra le de Lausanne (EPFL) Observatoire de Sauverny, 1290 Versoix, Switzerland b Institut d’Astrophysique et de Géophysique, Université de Liège, Allée du 6 Août 17, B5C, B-4000 Sart Tilman, Belgium c Astronomy Department, University of Washington, Box 35158 0, Seattle, WA 98195, USA E-mail: dominique.sluse@epfl.ch

We present the first VLT near-IR observations of a gravitationally lensed quasar, using adaptive optics and laser guide star. These observations can be considered as a test bench for future systematic observations of lensed quasars with adaptive optics, even when bright natural guide stars are not available in the nearby field. With only 14 min of observing time, we derived very accurate astrometry of the quasar images and of the lensing galaxy, with 0.05 '' spatial resolution, comparable to the Hubble Space Telescope (HST). In combination with deep VLT optical spectra of the quasar images, we use our adaptive optics images to constrain simple models for the mass distribution of the lensing galaxy. The latter is almost circular and does not need any strong external shear to fit the data. The time delay predicted for SDSS J0806+2006, assuming a singular isothermal ellipsoid model and the concordance cosmology, is Delta t similar or equal to 50 days. Our optical spectra indicate a flux ratio between the quasar images of A/B = 1.3 in the continuum and A/B = 2.2 in both the Mg II and in the C III] broad emission lines. This suggests that microlensing affects the continuum emission. However, the constant ratio between the two emission lines indicates that the broad emission line region is not microlensed. Finally, we see no evidence of reddening by dust in the lensing galaxy.

We report the first results of a spectroscopic search for Ly alpha envelopes around three z similar to 4.5 radio-quiet quasars. Our observational strategy adopts the FORS2 spectrograph mounted to the UT1 of the Very Large Telescope (VLT) in the multi-slit mode. This allows us to observe simultaneously the quasars and several PSF stars. The spectra of the latter are used to remove the point-like quasar from the data, and to unveil the faint underlying Lya envelopes associated with the quasars to unprecedented depth. We clearly detect an envelope around two of the three quasars. The sizes of these envelopes are 10 '' and 13 '' (i. e. 67 kpc and 87 kpc). This is 5 to 10 times larger than predicted by the models of Haiman & Rees (2001, ApJ, 556, 87) and up to 100 times fainter. Our observations are in more robust agreement with models involving a clumpy envelope such as Alam & Miralda-Escuda (2002, ApJ, 568, 576) or Chelouche et al. (2007, ApJ, submitted). We find that the brighter quasars also have the brighter envelopes but that the extent of the envelopes does not depend on the quasar luminosity. Although our results are based on only two objects with a detected Lya envelope, the quality of the spatial deblending of the spectra lends considerable for hope to estimating the luminosity function and surface brightness profiles of high redshift Ly alpha envelopes down to F similar to 2-3 x 10(-21) erg s(-1) cm(-2) angstrom(-1). We conclude that the most efficient strategy for studying high redshift Lya quasar envelopes is to acquire both narrow-band images and deep slit-spectra.

We present the main results of the first long-term spectrophotometric monitoring of the “Einstein cross” Q2237+0305 and of the single-epoch spectra of the lensed quasar J1131-1231. From October 2004 to December 2006, we find that two prominent microlensing events affect images A B in Q2237+0305 while images C D remain grossly unaffected by microlensing on a time scale of a few months. Microlensing in A B goes with chromatic variations of the quasar continuum. We observe stronger micro-amplification in the blue than in the red part of the spectrum, as expected for continuum emission arising from a standard accretion disk. Microlensing induced variations of the CIII] emission are observed both in the integrated line intensity and profile. Finally, we also find that images C D are about 0.1-0.3 mag redder than images A B. The spectra of images A-B-C in J1131-1231 reveal that, in April 2003, microlensing was at work in images A and C. We find that microlensing de-amplifies the continuum emission and the Broad Line Region (BLR) in these images. Contrary to the case of Q2237+0305, we do not find evidence for chromatic microlensing of the continuum emission. On the other hand, we observe that the Balmer and MgII broad line profiles are deformed by microlensing. These deformations imply an anti-correlation between the width of the emission line and the size of the corresponding emitting region. Finally, the differential microlensing of the FeII emission suggests that the bulk of FeII is emitted in the outer parts of the BLR while another fraction of FeII is produced in a compact region.

We present the results of the first long-term (2.2 years) spectroscopic monitoring of a gravitationally lensed quasar, namely the Einstein Cross Q2237+0305. We spatially deconvolve deep VLT/FORS1 spectra to accurately separate the spectrum of the lensing galaxy from the spectra of the quasar images. Accurate cross-calibration of the observations at 31 epochs from October 2004 to December 2006 is carried out using foreground stars observed simultaneously with the quasar. The quasar spectra are further decomposed into a continuum component and several broad emission lines. We find prominent microlensing events in the quasar images A and B, while images C and D are almost quiescent on a timescale of a few months. The strongest variations are observed in the continuum, and their amplitude is larger in the blue than in the red, consistent with microlensing of an accretion disk. Variations in the intensity and profile of the broad emission lines are also reported, most prominently in the wings of the CIII] and in the center of the CIV emission lines. During a strong microlensing episode observed in quasar image A, the broad component of the CIII] is more magnified than the narrow component. In addition, the emission lines with higher ionization potentials are more magnified than the lines with lower ionization potentials, consistent with the stratification of the broad line region (BLR) infered from reverberation mapping observations.

Aims: The knowledge of the redshift of a lensing galaxy that produces multiple images of a background quasar is essential to any subsequent modeling, whether related to the determination of the Hubble constant H_0 or to the mass profile of the lensing galaxy. We present the results of our ongoing spectroscopic observations of gravitationally lensed quasars in order to measure the redshift of their lensing galaxies. We report on the determination of the lens redshift in seven gravitationally lensed systems. Methods: Our deep VLT/FORS1 spectra are spatially deconvolved in order to separate the spectrum of the lensing galaxies from the glare of the much brighter quasar images. Our observing strategy involves observations in Multi-Object-Spectroscopy (MOS) mode which allows the simultaneous observation of the target and of several crucial PSF and flux calibration stars. The advantage of this method over traditional long-slit observations is that it allows a much more reliable extraction and flux calibration of the spectra. Results: We obtain the first reliable spectra of the lensing galaxies in six lensed quasars: FBQ 0951+2635 (z=0.260), BRI 0952-0115 (z=0.632), HE 2149-2745 (z=0.603), Q 0142-100 (z=0.491), SDSS J0246-0825 (z=0.723), and SDSS J0806+2006 (z=0.573). The last 3 redshifts also correspond to the MgII doublet seen in absorption in the quasar spectra at the lens redshift. Our spectroscopic redshifts of HE 2149-2745 and FBQ 0951+2635 are higher than previously reported, which means that H_0 estimates from these two systems must be revised to higher values. Finally, we reanalyse our spectra of Q 1355-2257 and find MgII in absorption at z=0.702, confirming our previous redshift estimate. The spectra of all lenses are typical of early-type galaxies.

Our aim is to measure the time delay between the two gravitationally lensed images of the z(qso) = 1.547 quasar SDSS J1650+ 4251, in order to estimate the Hubble constant H-0.Methods. Our measurement is based on R- band light curves with 57 epochs obtained at Maidanak Observatory, in Uzbekistan, from May 2004 to September 2005. The photometry is performed using simultaneous deconvolution of the data, which provides the individual light curves of the otherwise blended quasar images. The time delay is determined from the light curves using two very different numerical techniques, i. e., polynomial fitting and direct cross- correlation. The time delay is converted into H-0 following analytical modeling of the potential well.Results. Our best estimate of the time delay is Delta t = 49.5 +/- 1.9 days, i. e., we reach a 3.8% accuracy. The R- band flux ratio between the quasar images, corrected for the time delay and for slow microlensing, is F-A/ F-B = 6.2 +/- 5%.Conclusions. The accuracy reached on the time delay allows us to discriminate well between families of lens models. As for most other multiply imaged quasars, only models of the lensing galaxy that have a de Vaucouleurs mass profile plus external shear give a Hubble constant compatible with the current most popular value ( H-0 = 72 +/- 8 kms(-1) Mpc(-1)). A more realistic singular isothermal sphere model plus external shear gives H-0 = 51.7(-3.0)(+4.0) km s(-1) Mpc(-1)

Aims. We present the results of the first long-term spectroscopic monitoring of a gravitationally lensed quasar, for QSO 2237+0305: the Einstein Cross. We show that chromatic microlensing-induced variations constantly affect the spectra of all four images of the lensed quasar. The goal of the present paper is to present the observational facts to later be compared with theoretical models in order to constrain the inner structure of the source quasar. Methods. We spatially deconvolve deep VLT/FORS1 spectra in order to accurately separate the spectrum of the lensing galaxy from the spectra of the quasar images. Accurate cross-calibration of the 31-epoch observations is carried out using non-variable foreground stars observed simultaneously to the quasar. The quasar spectra are further decomposed into several components in order to infer the variations in the continuum, and in the broad emission lines. Results. We find the most prominent microlensing events in quasar images A and B, while C and D are almost quiescent on a time scale of a few months. The strongest variations are observed in the continuum. Their amplitude is larger in the blue than in the red, consistent with microlensing of an accretion disk. Variations in the intensity and profile of the broad emission lines are also reported, most prominently in the wings of the C III] and center of the C IV emission lines. During a strong microlensing episode in quasar image A, the broad component of the C III] is more highly magnified than the narrow component. In addition, the emission lines with higher ionization potentials are more magnified than the lines with lower ionization potentials, consistent with the results obtained with reverberation-mapping. Finally, we find that the V-band differential extinction by the lens, between the quasar images is in the range 0.1-0.3.