We present a new, high resolution HST/GHRS spectrum of quasar Q0302003, and use the He Lyman-α absorption, together with a high resolution Keck spectrum of the HI Lyman-α forest, to probe the distribution and ionization state of the protogalactic foreground gas at z ≈ 3.3. Within ≈ 4000 km/sec of the quasar redshift the spectrum shows a substantial flux (τ ≈ 1) with “He Lyman-α forest” absorpti...

We have conducted observations of the environment around the z=2.15 radio loud quasar 1550-269 in search of distant galaxies associated either with it or the z=2.09 CIV absorber along its line of sight. Such objects will be distinguished by their red colours, R-K>4.5. We find five such objects in a 1.5 arcmin field around the quasar, with typical K’ magnitudes of ∼20.4 and no detected R band em...

We use semi-analytic modeling on top of the Millennium simulation to study the joint formation of galaxies and their embedded supermassive black holes. Our goal is to test scenarios in which black hole accretion and quasar activity are triggered by galaxy mergers, and to constrain different models for the lightcurves associated with individual quasar events. In the present work we focus on stud...

We provide a simple theoretical model for the quasar luminosity function at high redshifts that naturally reproduces the statistical properties of the luminous SDSS quasar sample at redshifts z ∼ 4.3 and z & 5.7. Our model is based on the assumptions that quasar emission is triggered by galaxy mergers, and that the black hole mass is proportional to a power-law in the circular velocity of the h...

Context. For the first time spectroscopic galaxy redshift surveys are reaching the scales where galaxies can be studied together with the nearest quasars. This gives an opportunity to study the dependence between the activity of a quasar and its environment in a more extensive way than before. Aims. We study the spatial distribution of galaxies and groups of galaxies in the environments of low ...

We have conducted ultra-deep optical and deep near-infrared observations of a field around the z = 1.226 radio-quiet quasar 104420.8+055739 from the ClowesCampusano LQG of 18 quasars at z ∼ 1.3 in search of associated galaxy clustering. Galaxies at these redshifts are distinguished by their extremely-red colours, with I − K > 3.75, and we find a factor ∼11 overdensity of such galaxies in a 2.25...

We present the analysis of a representative sample of 20 bright low-redshift quasars (MB < −23 and z < 0.35) observed spectroscopically with the VLT. The FORS1 spectra, obtained in Multi Object Spectroscopy (MOS) mode, allow to observe simultaneously the quasars and several reference stars used to spatially deconvolve the data. Applying the MCS deconvolution method, we are able to separate the ...

The detection of large quantities of dust in z ∼ 6 quasars by infrared and radio surveys presents puzzles for the formation and evolution of dust in these early systems. Previously (Li et al. 2007), we showed that luminous quasars at z & 6 can form through hierarchical mergers of gas-rich galaxies, and that these systems are expected to evolve from starburst through quasar phases. Here, we calc...

We present imaging and spectroscopic observations for six quasars at z ≥ 5.9 discovered by the CanadaFrance High-z Quasar Survey (CFHQS). The CFHQS contains sub-surveys with a range of flux and area combinations to sample a wide range of quasar luminosities at z ∼ 6. The new quasars have luminosities 10 to 75 times lower than the most luminous SDSS quasars at this redshift. The least luminous q...

We report the discovery of a new gravitationally lensed quasar, SDSS J131339.98+515128.3, at a redshift of 1.875 with an image separation of 1. 24. The lensing galaxy is clearly detected in visible-light follow-up observations. We also identify three absorption-line doublets in the spectra of the lensed quasar images, from which we measure the lens redshift to be 0.194. Like several other known...