26 research outputs found
Downsizing of supermassive black holes from the SDSS quasar survey (II). Extension to z~4
Starting from the quasar sample of the Sloan Digital Sky Survey (SDSS) for
which the CIV line is observed, we use an analysis scheme to derive the
z-dependence of the maximum mass of active black holes, which overcomes the
problems related to the Malmquist bias. The same procedure is applied to the
low redshift sample of SDSS quasars for which Hbeta measurements are available.
Combining with the results from the previously studied MgII sample, we find
that the maximum mass of the quasar population increases as (1+z)^(1.64+/-0.04)
in the redshift range 0.1<z<4, which includes the epoch of maximum quasar
activity.Comment: 9 pages, 8 figures. To appear in MNRA
On the geometry of broad emission region in quasars
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
The quasar M_bh - M_host relation through Cosmic Time II - Evidence for evolution from z=3 to the present age
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 (Paper I), while the host galaxy masses were inferred from their
luminosities. With this 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 aging of the stellar population, we
find that the M_bh / M_host ratio (Gamma) increases by a factor ~7 from z=0 to
z=3. We show that Gamma evolves with z regardless of the radio loudness and of
the quasar luminosity. We propose that 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.Comment: 10 pages, 8 figures, 2 tables. Accepted for publication in MNRA
The NIR to UV continuum of radio loud vs. radio quiet quasars
Starting from a sample of SDSS quasars appearing also in the 2MASS survey, we
study the continuum properties of about 1000 objects observed in 8 bands, from
NIR to UV. We construct the mean spectral energy distribution (SED) and compare
and contrast the continua of radio loud (RLQ) and radio quiet (RQQ) objects.
The SEDs of the two populations are significantly different in the sense that
RLQs are redder, with power law spectral indices =-0.55+/-0.04 and
=-0.31+/-0.01 in the spectral range between 10^14.5 and 10^15.35
Hz. This difference is discussed in terms of different extinctions, different
disc temperatures, or slopes of the non-thermal component.Comment: 7 pages, 6 figures. To appear in MNRA
The quasar M_bh - M_host relation through Cosmic Time I - Dataset and black hole masses
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.Comment: 16 pages, 6 figures, 5 tables. Accepted for publication in MNRA
Re-classification of the alleged quasar Q0045-3337
We present a medium-resolution optical spectrum of the alleged high-redshift
quasar Q0045-3337, taken at the ESO/3.6m telescope. Our observations show that
the object is not a quasar but a star of spectral type B. We suggest that the
object is either a white dwarf or a halo population Blue Horizontal Branch
star.Comment: Accepted for publication in the Bentham Open Astronomy Journa
The quasar MBH-Mhost relation through cosmic time - II. Evidence for evolution from z = 3 to the present age
The quasar M-BH-M-host relation through cosmic time - I. Data set and black hole masses
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
The quasar M-BH-M-host relation through cosmic time - II. Evidence for evolution from z=3 to the present age
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 (Gamma) increases by a factor of similar to 7 from z = 0 to z = 3. We show that Gamma 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