We study the dependence of the M BH -M host relation on the redshift up to z = 3 for a sample of 96 quasars, the host galaxy luminosities of which are known. Black hole masses were estimated assuming virial equilibrium in the broad-line regions, while the host galaxy masses were inferred from their luminosities. With these data, we are able to pin down the redshift dependence of the M BH -M host relation along 85 per cent of the Universe age. We show that, in the sampled redshift range, the M BH -L host relation remains nearly unchanged. Once we take into account the ageing of the stellar population, we find that the M BH /M host ratio ( ) increases by a factor of ∼7 from z = 0 to z = 3. We show that evolves with z regardless of the radio loudness and of the quasar luminosity. We propose that the most massive black holes, living their quasar phase at high redshift, become extremely rare objects in host galaxies of similar mass in the Local Universe.

We study the geometry of the Hbeta broad emission region by comparing the M_BH values derived from Hbeta through the virial relation with those obtained from the host galaxy luminosity in a sample of 36 low redshift (z around 0.3) quasars. This comparison lets us infer the geometrical factor f needed to de-project the line-of-sight velocity component of the emitting gas. The wide range of f values we found, together with the strong dependence of f on the observed line width, suggests that a disc-like model for the broad line region is preferable to an isotropic model, both for radio loud and radio quiet quasars. We examined similar observations of the CIV line and found no correlation in the width of the two lines. Our results indicate that an inflated disc broad line region, in which the Carbon line is emitted in a flat disc while Hbeta is produced in a geometrically thick region, can account for the observed differences in the width and shape of the two emission lines.Comment: Accepted for publication in MNRA

We present near-infrared imaging of the host galaxies of low-luminosity quasars at 1 < z < 2, aimed at investigating the relationship between the nuclear and host-galaxy luminosities at high redshift. This work complements our previous study to trace the cosmological evolution of the host galaxies of high-luminosity quasars. The sample consists of nine radio-loud (RLQ) and six radio-quiet (RQQ) low-luminosity quasars. They have similar redshift and optical luminosity distributions, and together with the high-luminosity quasars, cover a large range of the quasar luminosity function. For all but two of the quasars, we have been able to derive the global properties of the surrounding nebulosity. The host galaxies of both types of quasars are massive inactive ellipticals between L Ã and 10L Ã , with RLQ hosts being significantly more luminous than RQQ hosts. This luminosity gap is independent of the rest-frame U-band luminosity but correlated with the rest-frame R-band luminosity. The color difference between the RQQs and the RLQs is likely a combination of an intrinsic difference in the strength of the thermal and nonthermal components in their SEDs, and a selection effect due to internal dust extinction. For the combined set of quasars, we find a reasonable correlation between the nuclear and the host luminosities. This correlation is less apparent for RQQs than for RLQs. If the R-band luminosity represents the bolometric luminosity, and the host luminosity is proportional to the black hole mass, as in nearby massive spheroids, quasars emit in a relatively narrow range with respect to their Eddington luminosity and with the same distribution for RLQs and RQQs.

We present the analysis of the photometric and spectroscopic properties of a sample of 29 low redshift (z < 0.6) QSOs for which both HST WFPC2 optical images and ultraviolet HST FOS spectra are available. For each object we measure the R band absolute magnitude of the host galaxy, the C IV (1550 Å) line width and the 1350 Å continuum luminosity. From these quantities we can estimate the black hole (BH) mass through the M BH − L bulge relation for inactive galaxies, and from the virial method based on the kinematics of the regions emitting the broad lines. The comparison of the masses derived from the two methods yields information on the geometry of the gas emitting regions bound to the massive BH.

We study the M BH -M host relation as a function of cosmic time in a sample of 96 quasars from z = 3 to the present epoch. In this paper, we describe the sample, the data sources and the new spectroscopic observations. We then illustrate how we derive M BH from single-epoch spectra, pointing out the uncertainties in the procedure. In a companion paper, we address the dependence of the ratio between the black hole mass and the host-galaxy luminosity and mass on cosmic time.