A lot of absorption lines are in the bluewards of Lyα emission line of quasar which is well-known as Lyαforest. Most of absorption lines in this forest belong to the Lyα absorption of the neutral hydrogen in the inter-galactic medium (IGM). For high redshift quasars and in the continuum with low and medium resolution, there are no many regions without absorption, so that, the quasar continuum i...

We investigate the luminosity dependence of quasar clustering, inspired by numerical simulations of galaxy mergers that incorporate black hole growth. These simulations have motivated a new interpretation of the quasar luminosity function. In this picture, the bright end of the quasar luminosity function consists of quasars radiating nearly at their peak luminosities, while the faint end consis...

Quasar-galaxy associations, if they result from the effect of gravitational lensing by foreground galaxies, depend sensitively on the shape of the quasar number counts. Two kinds of quasar number-magnitude relations are predicted to produce quite different properties in quasar-galaxy associations: the counts of Boyle, Shanks and Peterson (1988; BSP) provide both positive and “negative” associat...

We compare the observed clustering of quasars and galaxies as a function of redshift, mass, luminosity, and color/morphology, to constrain models of quasar fueling and the co-evolution of spheroids and supermassive black holes (BHs). High redshift (z . 3) quasars are shown to be drawn from the progenitors of local z = 0 early-type galaxies, with the characteristic quasar luminosity L∗ at a give...

The quasar HE0450-2958 was recently discovered to reside ∼ 7 kpc away from a galaxy that was likely disturbed by a recent merger. The lack of a massive spheroid of stars around the quasar raised the unlikely suggestion that it may have formed in a dark galaxy. Here we explain this discovery as a natural consequence of a dynamical kick imparted to the quasar as it interacted with a binary black ...

Using∼300,000 photometrically classified quasars, by far the largest quasar sample ever used for such analyses, we study the redshift and luminosity evolution of quasar clustering on scales of ∼50 h kpc to ∼20 h Mpc from redshifts of z̄ ∼0.75 to z̄ ∼2.28. We parameterize our clustering amplitudes using realistic dark matter models, and find that a ΛCDM power spectrum provides a superb fit to our ...

We report the results from an ASCA observation of the high-luminosity, radio-loud quasar PKS 2149-306 (redshift 2.345), covering the approximately 1.7-30 keV band in the quasar frame. We find the source to have a luminosity approximately 6x1047 ergs s-1 in the 2-10 keV band (quasar frame). We detect an emission line centered at approximately 17 keV in the quasar frame. Line emission at this ene...

The observed number counts of quasars may be explained either by long-lived activity within rare massive hosts, or by short-lived activity within smaller, more common hosts. It has been argued that quasar lifetimes may therefore be inferred from their clustering length, which determines the typical mass of the quasar host. Here we point out that the relationship between the mass of the black-ho...

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 foreground gas just below the quasar redshift z ≈ 3.3. Within ≈ 4000 km/sec of the quasar redshift the spectrum shows a substantial flux (τ ≈ 1) with “He Lyman-α forest...

This review attempts to describe developments in the fields of quasar and quasar host galaxies in the past five. In this time period, the Sloan and 2dF quasar surveys have added several tens of thousands of quasars, with Sloan quasars being found to z > 6. Obscured, or partially obscured quasars have begun to be found in significant numbers. Black hole mass estimates for quasars, and our confid...