Measuring the black hole masses of high-redshift quasars

A new technique is presented for determining the black hole masses of high-redshift quasars from optical spectroscopy. The new method utilizes the full-width at half-maximum (FWHM) of the low-ionization Mg  ii emission line and the correlation between the broad-line region (BLR) radius and the continuum luminosity at 3000 Å. Using archival ultraviolet (UV) spectra it is found that the correlation between BLR radius and 3000-Å luminosity is tighter than the established correlation with 5100-Å luminosity. Furthermore, it is found that the correlation between BLR radius and 3000-Å continuum luminosity is consistent with a relation of the form   R _BLR∝λ L ^1/2_λ  , as expected for a constant ionization parameter. Using a sample of objects with broad-line radii determined from reverberation mapping it is shown that the FWHM of Mg  ii and Hβ are consistent with following an exact one-to-one relation, as expected if both Hβ and Mg  ii are emitted at the same radius from the central ionizing source. The resulting virial black hole mass estimator based on rest-frame UV observables is shown to reproduce black hole mass measurements based on reverberation mapping to within a factor of 2.5 (1σ). Finally, the new UV black hole mass estimator is shown to produce identical results to the established optical (Hβ) estimator when applied to 128 intermediate-redshift  (0.3 < z < 0.9)  quasars drawn from the Large Bright Quasar Survey and the radio-selected Molonglo quasar sample. We therefore conclude that the new UV virial black hole mass estimator can be reliably used to estimate the black hole masses of quasars from   z ∼ 0.25  through to the peak epoch of quasar activity at   z ∼ 2.5  via optical spectroscopy alone.     

The relation between extended radio and line emission for radio-loud quasars

We explore the relationship between the extended radio and line emission for a radio-loud quasar sample including both core-dominated and lobe-dominated quasars. A strong correlation is present between the extended radio and broad-line emission. The core emission is also correlated with the broad-line emission for core-dominated quasars in the sample. The statistical behaviour of the core emission of lobe-dominated quasars is rather different from that of core-dominated quasars. The extended radio luminosity is a good tracer for jet power, while the core luminosity can only be a jet power tracer for core-dominated quasars.     

Multiwavelength XMM–Newton observations of the Laor et al. sample of PG quasars

We present XMM–Newton /EPIC spectra for the Laor et al. sample of Palomar Green (PG) quasars. We find that a power law provides a reasonable fit to the 2–5 keV region of the spectra. Excess soft X-ray emission below 2 keV is present for all objects, with the exception of those known to contain a warm absorber. However, a single power law is a poor fit to the 0.3–10.0 keV spectrum and instead we find that a simple model, consisting of a broken power law (plus an iron line), provides a reasonable fit in most cases. The equivalent width of the emission line is constrained in just 12 objects but with low (<2σ) significance in most cases. For the sources whose spectra are well fitted by the broken-power-law model, we find that various optical and X-ray line and continuum parameters are well correlated; in particular, the power-law photon index is well correlated with the FWHM of the Hβ line and the photon indices of the low- and high-energy components of the broken power law are well correlated with each other. These results suggest that the 0.3–10 keV X-ray emission shares a common (presumably non-thermal) origin, as opposed to suggestions that the soft excess is directly produced by thermal disc emission or via an additional spectral component. We present XMM–Newton Optical Monitor (OM) data, which we combine with the X-ray spectra so as to produce broad-band spectral energy distributions (SEDs), free from uncertainties due to long-term variability in non-simultaneous data. Fitting these optical–UV spectra with a Comptonized disc model indicates that the soft X-ray excess is independent of the accretion disc, confirming our interpretation of the tight correlation between the hard and soft X-ray spectra.     

New insights on the QSO radio-loud/radio-quiet dichotomy: SDSS spectra in the context of the 4D eigenvector1 parameter space

We search for a dichotomy/bimodality between radio-loud (RL) and radio-quiet (RQ) type 1 active galactic nuclei (AGN). We examine several samples of Slogan Digital Sky Survey (SDSS) quasi-stellar objects (QSOs) with high signal-to-noise ratio optical spectra and matching Faint Images of the Radio Sky at Twenty-cm/NRAO VLA Sky Survey (FIRST/NVSS) radio observations. We use the radio data to identify the weakest RL sources with a Fanaroff–Riley type II (FR II) structure to define a RL/RQ boundary which corresponds to log   L _1.4 GHz= 31.6  erg s⁻¹ Hz⁻¹. We measure the properties of broad-line Hβ and Fe  ii emission to define the optical plane of a 4DE1 spectroscopic diagnostic space. The RL quasars occupy a much more restricted domain in this optical plane compared to the RQ sources, which a 2D Kolmogorov–Smirnov test finds to be highly significant. This tells us that the range of broad-line region kinematics and structure for RL sources is more restricted than for the RQ QSOs, which supports the notion of dichotomy. FR II and CD RL sources also show significant 4DE1 domain differences that likely reflect differences in line-of-sight orientation (inclined versus face-on, respectively) for these two classes. The possibility of a distinct radio-intermediate (RI) population between RQ and RL source is disfavoured because a 4DE1 diagnostic space comparison shows no difference between RI and RQ sources. We show that searches for dichotomy in radio versus bolometric luminosity diagrams will yield ambiguous results mainly because in a reasonably complete sample, the radio brightest RQ sources will be numerous enough to blur the gap between RQ and RL sources. Within resolution constraints of NVSS and FIRST, we find no FR I sources among the broad-line quasar population.     

Broad-line Balmer decrements in blue active galactic nuclei

We have investigated the broad-line Balmer decrements (Hα/Hβ) for a large, homogeneous sample of Seyfert 1 galaxies and quasi-stellar objects (QSOs) using spectroscopic data obtained in the Sloan Digital Sky Survey. The sample, drawn from the Fourth Data Release, comprises 446 low-redshift ( z ≲ 0.35) active galactic nuclei (AGN) that have blue optical continua as indicated by the spectral slopes in order to minimize the effect of dust extinction. We find that (i) the distribution of the intrinsic broad-line Hα/Hβ ratio can be well described by log-Gaussian, with a peak at  Hα/Hβ= 3.06  and a standard deviation of about 0.03 dex only; (ii) the Balmer decrement does not correlate with AGN properties such as luminosity, accretion rate and continuum slope, etc.; (iii) on average, the Balmer decrements are found to be only slightly larger in radio-loud sources (3.37) and sources having double-peaked emission-line profiles (3.27) compared to the rest of the sample. We therefore suggest that the broad-line Hα/Hβ ratio can be used as a good indicator for dust extinction in the AGN broad-line region; this is especially true for radio-quiet AGN with regular emission-line profiles, which constitute the vast majority of the AGN population.     

Hubble Space Telescope ultraviolet spectroscopy of blazars: emission-line properties and black hole masses

The ultraviolet (UV) spectra of 16 blazars  (〈 z 〉≃ 1)  from the archives of the Hubble Space Telescope Faint Object Spectrograph have been analysed in order to study in a systematic way the properties of their broad UV emission lines. We find that the luminosities of the most prominent and intense lines, Lyα and C  iv λ1549, are similar to those of normal radio-loud quasars at comparable redshifts. However, the equivalent widths of blazar lines are significantly smaller than those of radio-loud quasars. Therefore, while the intrinsic broad-line region luminosity of blazars appears to be indistinguishable from that of radio-loud quasars, their continuum must be comparatively higher, most probably due to relativistic beaming. We have combined the UV luminosities of the debeamed continuum with the emitting gas velocity to derive estimates of the masses of the central supermassive black holes. The size of the broad-line region was computed in two ways: (1) via an empirical relationship between UV continuum luminosity and broad-line region size, and (2) through the external photon density required by blazar models to reproduce the inverse Compton components observed at γ-rays. The second method yields significantly different results from the first method, suggesting that it provides only a very rough estimate or a lower limit on the size of the broad-line region. We find that the average mass of the central black holes in blazars is  ∼2.8 × 10⁸ M_⊙  , with a large dispersion, comparable to those computed for other radio-loud active galactic nuclei.     

Evolutionary unification in composite active galactic nuclei

In this paper, we present an evolutionary unification scenario, involving supermassive black holes (SMBHs) and starbursts (SBs) with outflow (OF), that seems capable of explaining most of the observational properties (of at least part) of active galactic nuclei (AGN).
The scenario includes a nuclear/circumnuclear SB closely associated with the AGN where the narrow-line region (NLR), broad-line region (BLR) and broad absorption line (BAL) region are produced in part by the OF process with shells and in compact supernova remnants (cSNRs).
The OF process in BAL quasi-stellar objects (QSOs) with extreme infrared (IR) and Fe  ii emission is studied. In addition, the Fe  ii problem regarding the BLR of AGN is analysed. The correlations between the BAL, IR emission, Fe  ii intensity and the intrinsic properties of the AGN are not clearly understood. We suggest here that the behaviour of the BAL, IR and Fe  ii emission in AGN can be understood within an evolutionary and composite model for AGN.
In our model, strong BAL systems and Fe  ii emission are present (and intense) in young IR objects. Parameters like the BALs, IR emission, Fe  ii /Hβ intensity ratio, Fe  ii equivalent width (EW), broad-line width, [O  iii ]λ5007-Å intensity and width, NLR size, X-ray spectral slope in radio quiet (RQ) AGN plus lobe separation, and lobe to core intensity ratio in radio loud (RL) AGN are proposed to be fundamentally time-dependent variables inside time-scales of the order of 10⁸ yr. Orientation/obscuration effects take the role of a second parameter providing the segregation between Seyfert 1/Seyfert 2 galaxies (Sy1/Sy2) and broad-/narrow-line radio galaxies (BLRG/NLRG).     

Equatorial scattering and the structure of the broad-line region in Seyfert nuclei: evidence for a rotating disc

We present detailed scattering models confirming that distinctive variations in polarization across the broad Hα line, which are observed in a significant fraction of type 1 Seyfert galaxies, can be understood in terms of a rotating line-emitting disc surrounded by a coplanar scattering region (the equatorial scattering region). The predicted polarization properties are: (i) averaged over wavelength, the position angle (PA) of polarization is aligned with the projected disc rotation axis and hence also with the radio source axis; (ii) the polarization PA rotates across the line profile, reaching equal but opposite (relative to the continuum PA) rotations in the blue and red wings; and (iii) the degree of polarization peaks in the line wings and passes through a minimum in the line core. We identify 11 objects that exhibit these features to different degrees. In order to reproduce the large-amplitude PA rotations observed in some cases, the scattering region must closely surround the emission disc and the latter must itself be a relatively narrow annulus – presumably the Hα-emitting zone of a larger accretion disc. Asymmetries in the polarization spectra may be attributable to several possible causes, including bulk radial infall in the equatorial scattering region, or contamination by polar scattered light. The broad Hα lines do not, in general, exhibit double-peaked profiles, suggesting that a second Hα-emitting component of the broad-line region is present, in addition to the disc.     

The profiles of polarized broad Hα lines in radio galaxies

We present spectropolarimetric observations of seven broad-line radio galaxies. We find significantly polarized broad Hα emission in four objects including two, Arp 102B and 3C 390.3, which have double-peaked line profiles. In these objects the prominent redshifted and blueshifted peaks of the broad Hα line have no clear counterparts in polarized flux. This conflicts with theoretical predictions for a relativistic line-emitting disc with an electron scattering atmosphere, one of the leading models advanced to account for the double-peaked lines. The shapes and widths of the polarized line profiles can be explained if, as expected in unified schemes, the scattering occurs near the poles of an obscuring torus. However, the observed polarization position angles favour geometries in which the scattering plane is perpendicular to the radio jet. A configuration in which Hα photons emitted by a biconical flow are scattered off the inner wall of the torus has this property, and would also produce a single-peaked scattered line profile. With the exception of 3C 227, the sample as a whole conforms to the general trend in powerful radio galaxies for the optical polarization to be aligned with the radio source axis, favouring toroidal rather than polar scattering.     

Late-type galaxies observed with SAURON: two-dimensional stellar and emission-line kinematics of 18 spirals

We present the stellar and gas kinematics of a sample of 18 nearby late-type spiral galaxies (Hubble types ranging from Sb to Sd), observed with the integral-field spectrograph SAURON at the 4.2-m William Herschel Telescope. SAURON covers the spectral range 4800–5380 Å, allowing us to measure the Hβ, Fe, Mg b absorption features and the emission in the Hβ line and the  [O  iii ]λλ4959, 5007 Å  and  [N  i ]λλ5198, 5200 Å  doublets over a  33 × 41-arcsec²  field of view. The maps cover the nuclear region of these late-type galaxies and in all cases include the entire bulge. In many cases the stellar kinematics suggests the presence of a cold inner region, as visible from a central drop in the stellar velocity dispersion. The ionized gas is almost ubiquitous and behaves in a complicated fashion: the gas velocity fields often display more features than the stellar ones, including wiggles in the zero-velocity lines, irregular distributions, ring-like structures. The line ratio [O  iii ]/Hβ often takes on low values over most of the field, probably indicating a wide-spread star formation.     

Three quasars from a survey of strong 25-μm emitters

We have carried out a spectroscopic survey of 750 sources that are strong 25-μm emitters from the IRAS Faint Source data base. Many of these sources are previously unknown active galactic nuclei including new IRAS quasars, three of which we describe here: F21382−2659, Z06367−6845 and Z05558−5008. They are all radio and X-ray quiet, and compared to the known IRAS quasars they have similar 25-μm luminosities, L (25 μm), but lower values of L (25 μm)/ L ( B ). Their F (25 μm)/ F (60 μm) IRAS colours lie in the range 0.33 to 1.08, indicating the presence of relatively warm dust, presumably in a dusty torus surrounding the central source, and with temperatures similar to those of the known IRAS quasars. The quasar with the warmest dust, F21382−2659, exhibits broad (full width at half-maximum ∼4000 km s⁻¹) asymmetric Balmer lines with H γ having an opposite asymmetry to the other broad lines; also H β (only) is double-peaked. Fe  ii is very weak in F21382−2659 but strong in the other two quasars, and the anticorrelation between Fe  ii and [O  iii ] holds as anticipated. Two of the quasars are unpolarized: although F21382−2659 is optically polarized (2.1 per cent at 4950 Å), we argue that this provides little insight into the orientation of its dust torus relative to the line of sight.     

Correlation between radio and broad-line emission in radio-loud quasars

We present a correlation between radio and broad-line emission for a sample of radio-loud quasars that supports a close link between accretion processes and relativistic jets. BL Lac objects seem to follow the statistical behaviour of quasars, but with fainter broad-line emission.     

Infrared photometric study of type II quasars

For this paper, we collected almost all of the type II quasars so far discovered. Among them, 485 sources have photometric data at JHK bands, mainly from Two-Micron All-Sky Survey observations, 65 sources have IRAS photometric data in at least one of the three IRAS bands at 25, 60 and 100 μm and 15 sources have IRAS photometric data in all three IRAS bands. We find that in nearly half of all type II quasars, both the near- and far-infrared radiations are dominated by starlight or thermal reprocessing of starlight by dust in the underlying galaxy. The infrared radiation of the other group (slightly over half) is dominated by a non-thermal radiation in the near-infrared, and mostly in the far-infrared also (although there is a mixture particularly for the longer wavelengths). It is proposed that for the later group, hidden broad lines may exist in the infrared. On the basis of our and previous results, we also discuss the possibility that there are two distinct classes of type II quasars: 'true' type II quasars without a broad-line region and heavily obscured type I quasars, in full analogy with the case for type II Seyfert galaxies. No relationships can be found for either the near-infrared or the far-infrared colours and the redshift. Correlations between absolute magnitude in the near- and far-infrared with redshift are found, but could be due to a flux limit (Malmquist bias).     

The nature of the intranight variability of radio-quiet quasars

We select a sample of 10 radio-quiet quasars with confirmed intranight optical variability and with available X-ray data. We compare the variability properties and the broad-band spectral constraints to the predictions of intranight variability by three models: (i) irradiation of an accretion disc by a variable X-ray flux, (ii) an accretion disc instability, (iii) the presence of a weak blazar component. We concluded that the third model, e.g. the blazar component model, is the most promising if we adopt a cannonball model for the jet variable emission. In this case, the probability of detecting the intranight variability is within 20–80 per cent, depending on the ratio of the disc to the jet optical luminosity. Variable X-ray irradiation mechanism is also possible but only under additional requirement: either the source should have a very narrow Hβ line or occasional extremely strong flares should appear at very large disc radii.     

HST Planetary Camera images of quasar host galaxies

We present Hubble Space Telescope ( HST ) images of seven low-redshift quasars (six taken with the Planetary Camera, one with the Wide Field Camera). These complete the sample of 14 quasars observed by the Faint Object Camera Investigation Definition Team (FOC IDT). Following subtraction of the quasar nuclear light, host galaxies can be seen in all seven cases. A combination of the optical morphology and luminosity profiles of the residual host galaxies and the results of 2D cross-correlation model fitting implies that five of the objects have elliptical host galaxies and two have disc host galaxies. The luminosities vary from slightly fainter than L ^* to about 1.3 mag brighter than L ^*.   We discuss the properties of the complete sample of 14 quasars. Nine of the objects appear to have elliptical host galaxies (all six of the radio-loud quasars in the sample as well as three radio-quiet quasars). Two further radio-quiet quasars appear to lie in disc galaxies. The other three objects (radio-quiet, ultraluminous infrared quasars) all lie in violently interacting systems. The sample as a whole has an average luminosity about 0.8 mag brighter than L ^*, although the radio-loud objects have hosts on average 0.7 mag brighter than the radio-quiet objects.   We compare our results with those from HST imaging of quasars by other authors. Taken together, our observations are in broad agreement with those of Bahcall et al. Radio-loud quasars appear to lie in luminous elliptical galaxies whereas radio-quiet quasars are found to lie in either elliptical or spiral hosts. Host galaxy luminosities (of radio-quiet and radio-loud quasars) are much brighter than would be expected if they followed a Schechter luminosity function.     

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 C  iv 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 Hβ measurements are available. Combining with the results from the previously studied Mg  ii 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.     

Emission-line outflows in PKS1549−79: the effects of the early stages of radio-source evolution?

We present new spectroscopic observations of the southern radio galaxy         . Despite the flat-spectrum character of the radio emission from this source, our optical spectra show no sign of the broad permitted lines and non-stellar continuum characteristic of quasar nuclei and broad-line radio galaxies. However, the high-ionization forbidden lines, including [O  iii ] λλ 5007, 4959, are unusually broad for a narrow-line radio galaxy     , and are blueshifted by 600 km s⁻¹ relative to the low-ionization lines such as [O  ii ] λλ 3726,3729. The [O  ii ] lines are also considerably narrower     than the [O  iii ] lines, and have a redshift consistent with that of the recently detected H  i 21-cm absorption-line system. Whereas the kinematics of the [O  iii ] emission lines are consistent with outflow in an inner narrow-line region, the properties of the [O  ii ] emission lines suggest that they are emitted by a more extended and quiescent gaseous component. We argue that, given the radio properties of the source, our line of sight is likely to be lying close to the direction of bulk outflow of the radio jets. In this case it is probable that the quasar nucleus is entirely obscured at optical wavelengths by the material responsible for the H  i absorption-line system. The unusually broad [O  iii ] emission lines suggest that the radio source is intrinsically compact. Overall, our data are consistent the idea that     is a radio source in an early stage of evolution.     

Ultraviolet Fe ii emission in z∼ 2 quasars

We present spectra of six luminous quasars at   z ∼ 2  , covering rest wavelengths 1600−3200 Å. The fluxes of the UV Fe  ii emission lines and Mg  ii λ2798 doublet, the line widths of Mg  ii and the 3000 Å luminosity were obtained from the spectra. These quantities were compared with those of low-redshift quasars at   z = 0.06–0.55  studied by Tsuzuki et al. In a plot of the Fe  ii (UV)/Mg  ii flux ratio as a function of the central black hole mass, Fe  ii (UV)/Mg  ii in our   z ∼ 2  quasars is systematically greater than in the low-redshift quasars. We confirmed that luminosity is not responsible for this excess. It is unclear whether this excess is caused by rich Fe abundance at   z ∼ 2  over low-redshift or by non-abundance effects such as high gas density, strong radiation field and high microturbulent velocity.     

The CLASS blazar survey – II. Optical properties

This paper presents the optical properties of the objects selected in the CLASS blazar survey. Because an optical spectrum is now available for 70 per cent of the 325 sources present in the sample, a spectral classification, based on the appearance of the emission/absorption lines, is possible. A wide variety of optical spectral types is found. Besides 'classical' BL Lacs (42), BL Lac candidates (5) and high-power     flat spectrum radio quasars (67), a significant number of 'passive' elliptical galaxies (41) is also found. Moreover, 33 broad emission line objects with a low radio power     are discovered, suggesting that at least a fraction (∼     per cent) of low-power blazars have a broad line region. Finally, 34 objects showing only narrow emission lines, either as a result of some starburst activity in the host galaxy or as a result of the presence of an active galactic nucleus, appear in the sample.     

ASCA observations of two steep soft X-ray quasars

Steep soft X-ray (0.1–2 keV) quasars share several unusual properties: narrow Balmer lines, strong Fe  II emission, large and fast X-ray variability, and a rather steep 2–10 keV spectrum. These intriguing objects have been suggested to be the analogues of Galactic black hole candidates in the high, soft state. We present here results from ASCA observations for two of these quasars: NAB 0205 + 024 and PG 1244 + 026.   Both objects show similar variations (factor of ∼ 2 in 10 ks), despite a factor of ∼ 10 difference in the 0.5–10 keV luminosity (7.3 × 10⁴³ erg s⁻¹ for PG 1244 + 026 and 6.4 × 10⁴⁴ erg s⁻¹ for NAB 0205 + 024, assuming isotropic emission, H ₀ = 50.0 and q ₀ = 0.0).   The X-ray continuum of the two quasars flattens by 0.5–1 going from the 0.1–2 keV band towards higher energies, strengthening recent results on another half-dozen steep soft X-ray active galactic nuclei.   PG 1244 + 026 shows a significant feature in the '1-keV' region, which can be described either as a broad emission line centred at 0.95 keV (quasar frame) or as edge or line absorption at 1.17 (1.22) keV. The line emission could be a result of reflection from a highly ionized accretion disc, in line with the view that steep soft X-ray quasars are emitting close to the Eddington luminosity. Photoelectric edge absorption or resonant line absorption could be produced by gas outflowing at a large velocity (0.3–0.6 c ).