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.     

On the geometry of broad emission region in quasars

We study the geometry of the Hβ broad emission region by comparing the M _BH values derived from Hβ through the virial relation with those obtained from the host galaxy luminosity in a sample of 36 low-redshift  ( z ∼ 0.3)  quasars. This comparison lets us infer the geometrical factor f needed to deproject 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 linewidth, 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 C  iv 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 Hβ is produced in a geometrically thick region, can account for the observed differences in the width and shape of the two emission lines.     

On reverberation and cross-correlation estimates of the size of the broad-line region in active galactic nuclei

It is known that the dependence of the emission-line luminosity of a typical cloud in the active galactic nuclei (AGN) broad-line regions (BLRs) upon the incident flux of ionizing continuum can be non-linear. We study how this non-linearity can be taken into account in estimating the size of the BLR by means of the 'reverberation' methods. We show that the BLR size estimates obtained by cross-correlation of emission-line and continuum light curves can be much (up to an order of magnitude) less than the values obtained by reverberation modelling. This is demonstrated by means of numerical cross-correlation and reverberation experiments with model continuum flares and emission-line transfer functions and by means of practical reverberation modelling of the observed optical spectral variability of NGC 4151. The time behaviour of NGC 4151 in the Hα and Hβ lines is modelled on the basis of the observational data by Kaspi et al. and the theoretical BLR model by Shevchenko. The values of the BLR parameters are estimated that allow to judge on the size and physical characteristics of the BLR. The small size of the BLR, as determined by the cross-correlation method from the data of Kaspi et al., is shown to be an artefact of this method. So, the hypothesis that the BLR size varies in time is not necessitated by the observational data.     

Emission-line properties of Seyfert 2 nuclei

This is the third paper of a series devoted to the study of the global properties of Joguet's sample of 79 nearby galaxies observable from the southern hemisphere, of which 65 are Seyfert 2 galaxies. We use the population synthesis models of Paper II to derive 'pure' emission-line spectra for the Seyfert 2 galaxies in the sample, and thus explore the statistical properties of the nuclear nebular components and their relation to the stellar populations. We find that the emission-line clouds suffer substantially more extinction than the starlight, and we confirm the correlations between stellar and nebular velocity dispersions and between emission-line luminosity and velocity dispersions, although with substantial scatter. Nuclear luminosities correlate with stellar velocity dispersions, but Seyferts with conspicuous star-forming activity deviate systematically towards higher luminosities. Removing the contribution of young stars to the optical continuum produces a tighter and steeper relation,   L ∝σ⁴_★  , consistent with the Faber–Jackson law.
Emission-line ratios indicative of the gas excitation such as [O  iii ]/Hβ and [O  iii ]/[O  ii ] are statistically smaller for Seyferts with significant star formation, implying that ionization by massive stars is responsible for a substantial and sometimes even a dominant fraction of the Hβ and [O  ii ] fluxes. We use our models to constrain the maximum fraction of the ionizing power that can be generated by a hidden active galactic nucleus (AGN). We correlate this fraction with classical indicators of AGN photoionization (i.e. X-ray luminosity and nebular excitation), but find no significant correlations. Thus, while there is a strong contribution of starbursts to the excitation of the nuclear nebular emission in low-luminosity Seyferts, the contribution of the hidden AGN remains elusive even in hard X-rays.     

The Hα luminosity function and star formation rate up to z ∼ 1

We describe ISAAC/ESO-VLT observations of the Hαλ6563 Balmer line of 33 field galaxies from the Canada–France Redshift Survey (CFRS) with redshifts selected between 0.5 and 1.1. We detect Hα in emission in 30 galaxies and compare the properties of this sample with the low-redshift sample of CFRS galaxies at   z ∼ 0.2  . We find that the Hα luminosity,   L (Hα)  , is tightly correlated to   M ( B _AB)  in the same way for both the low- and high-redshift samples.   L (Hα)  is also correlated to L ([O  ii ]λ3727), and again the relation appears to be similar at low and high redshifts. The ratio L (lsqb;O  ii ])/   L (Hα)  decreases for brighter galaxies by as much as a factor of 2 on average. Derived from the Hα luminosity function, the comoving Hα luminosity density increases by a factor 12 from  〈 z 〉= 0.2  to  〈 z 〉= 1.3  . Our results confirm a strong rise of the star formation rate (SFR) at   z < 1.3  , proportional to  (1 + z )^4.1±0.3  (with   H ₀= 50 km s⁻¹ Mpc⁻¹, q ₀= 0.5  ). We find an average  SFR(2800 Å)/SFR (Hα)  ratio of 3.2 using the Kennicutt SFR transformations. This corresponds to the dust correction that is required to make the near-ultraviolet data consistent with the reddening-corrected Hα data within the self-contained, I -selected CFRS sample.     

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.     

XMM–Newton and Chandra observations of SHEEP sources

We present Chandra and XMM–Newton observations of 12 bright  [ f (2–10 keV) > 10⁻¹³ erg cm⁻² s⁻¹]  sources from the ASCA search for the High Energy Extragalactic Population (SHEEP) survey. Most of these have been either not observed or not detected previously with the ROSAT mission, and therefore they constitute a sample biased towards hard sources. The Chandra observations are important in locating the optical counterpart of the X-ray sources with accuracy. Optical spectroscopic observations show that our sample is associated with both narrow-line (NL) (six objects) and broad-line (BL) active galactic nuclei (AGN) (five objects), with one source remaining unidentified. Our sources cover the redshift range 0.04–1.29, spanning luminosities from 10⁴² to  10⁴⁵ erg s⁻¹  (2–10 keV). The NL sources have preferentially lower redshift (and luminosity) compared to the BL ones. This can be most easily explained in a model where the NL AGN are intrinsically less luminous than the BL ones in line with the results of Steffen et al. The X-ray spectral fittings show a roughly equal number of obscured  ( N _H > 10²² cm⁻²)  and unobscured  ( N _H < 10²² cm⁻²)  sources. There is a clear tendency for obscured sources to be associated with NL AGN and unobscured sources with BL ones. However, there is a marked exception with the highest obscuring column observed at a BL AGN at a redshift of z = 0.5.     

An optimized Hβ index for disentangling stellar population ages

We have defined a new Hβ absorption index definition,  Hβ_o  , which has been optimized as an age indicator for old and intermediate age stellar populations. Rather than using stellar spectra, we employed for this purpose a library of stellar population spectral energy distributions of different ages and metallicities at moderately high resolution.  Hβ_o  provides us with improved abilities for lifting the age–metallicity degeneracy affecting the standard Hβ Lick index definition. The new index, which has also been optimized against photon noise and velocity dispersion, is fully characterized with wavelength shift, spectrum shape, dust extinction and [α/Fe] abundance ratio effects.  Hβ_o  requires spectra of similar qualities as those commonly used for measuring the standard Hβ Lick index definition. Aiming at illustrating the use and capabilities of  Hβ_o  as an age indicator we apply it to Milky Way globular clusters and to a well selected sample of early-type galaxies covering a wide range in mass. The results shown here are particularly useful for applying this index and understand the involved uncertainties.     

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).     

On the polarization of Hα scattered by neutral hydrogen in active galactic nuclei

Raman scattering by atomic hydrogen converts the UV continuum around Lyβ into optical continuum around Hα, and the basic atomic physics has been discussed in several works on symbiotic stars. We propose that the same process may operate in active galactic nuclei (AGN) and calculate the linear polarization of the broad emission lines Raman-scattered by high-column neutral hydrogen component. The conversion efficiency of the Raman scattering process is discussed and the expected scattered flux is computed using the spectral energy distribution of an AGN given by a typical power law. The high-column H  i component in AGN is suggested by many observations, encompassing the radio through UV and X-ray ranges.   When neutral hydrogen component with a column density ∼10²² cm⁻² is present around the active nucleus, it is found that the scattered Hα is characterized by a very broad width ∼20 000 km s⁻¹ and that the strength of the polarized flux is comparable to that of the electron-scattered flux expected from a conventional unified model of narrow-line AGN. The width of the scattered flux is mainly determined by the column density of the neutral scatterers where the total scattering optical depth becomes of order unity. The asymmetry in the Raman scattering cross-section around Lyβ introduces red asymmetric polarized profiles around Hα. The effects of the blended Lyβ and O  vi 1034 doublet are also investigated.   We briefly discuss the spectropolarimetric observations performed on the Seyfert galaxy IRAS 110548-1131 and the narrow line radio galaxy Cyg A. Several predictions regarding the scattering by the high-column neutral hydrogen component in AGN are discussed.     

Active galactic nuclei dust tori at low and high luminosities

A cornerstone of active galactic nuclei (AGN) unification schemes is the presence of an optically and a geometrically thick dust torus. It provides the obscuration to explain the difference between type 1 and type 2 AGN. We investigate the influence of the dust distribution on the Eddington limit of the torus. For smooth dust distributions, the Eddingtion limit on the dust alone is five orders of magnitudes below the limit for electron scattering in a fully ionized plasma, while a clumpy dust torus has an Eddington limit slightly larger than the classical one. We study the behaviour of a clumpy torus at low and high AGN luminosities. For low luminosities of the order of  ∼10⁴² erg s⁻¹  , the torus changes its characteristics and obscuration becomes insufficient. In the high-luminosity regime, the clumpy torus can show a behaviour which is consistent with the 'receding torus' picture. The derived luminosity-dependent fraction of type 2 objects agrees with recent observational results. Moreover, the luminosity-dependent covering factor in a clumpy torus may explain the presence of broad-line AGN with high column densities in X-rays.     

Cygnus A: stars, dust and cones

We present new Hubble Space Telescope ( HST  ) continuum and spectral line images of the radio galaxy Cygnus A. The images show much complex structure in the central kpc². Continuum images show the central dust lane in detail, allowing detailed maps of E ( B  −  V ) to be constructed; the dust appears to follow a roughly Galactic extinction law. The emission-line components are resolved in the line images and investigated in detail. A clear 'opening cone' morphology is found, especially in the lines of Hα and [O  i ]. Blue condensations are seen in the south-eastern emission component and surrounding the central region. These are almost certainly due to star formation, which began <1 Gyr ago as deduced from the colour of the regions. More extended blue continuum is also seen and corresponds to the blue polarized component detected by other recent spectropolarimetric observations.     

An 80-kpc Lyα halo around a high-redshift type-2 quasi-stellar object

We announce the discovery of an extended emission-line region associated with a high-redshift type-2 quasi-stellar object (QSO). The halo, which was discovered in our new wide-field narrow-band survey, resides at   z = 2.85  in the Spitzer First Look Survey region and is extended over ∼80 kpc. Deep very long baseline interferometry (VLBI) observations imply that approximately 50 per cent of the radio emission is extended on scales >200 pc. The inferred active galactic nuclei (AGN) luminosity is sufficient to ionize the extended halo, and the optical emission is consistent with being triggered coevally with the radio source. The Lyα halo is as luminous as those found around high-redshift radio galaxies; however, the active nucleus is several orders of magnitude less luminous at radio wavelengths than those Fanarof–Riley type II (FRIIs) more commonly associated with extended emission-line regions. AMS05 appears to be a high-redshift analogue to the radio-quiet quasar E1821+643 which is core dominated, but which also exhibits extended Fanarof–Riley type I (FRI)-like structure and contains an optically powerful AGN. We also find evidence for more quiescent kinematics in the Lyα emission line in the outer regions of the halo, reminiscent of the haloes around the more powerful FRIIs. The optical to mid-infrared spectral energy distribution is well described by a combination of an obscured QSO  ( L _bol∼ 3.4 ± 0.2 × 10¹³ L_⊙)  and a 1.4 Gyr old simple stellar population with mass  ∼3.9 ± 0.3 × 10¹¹ M_⊙  .     

X-ray-selected active galactic nuclei with red optical continua

We discuss the properties of X-ray-selected 'red' active galactic nuclei (AGN) from the RIXOS sample. These are Seyfert 1 galaxies and quasars whose optical continua are relatively soft, i.e. with an energy index, α_opt > 2. There are 14 objects in the RIXOS sample that satisfy this criterion and they cover a range in redshift from z  = 0.08 to 1.27. Of these, two have characteristics that suggest that the continuum is intrinsically red, i.e. an optical continuum which does not appear to have been significantly reddened by dust or to have contaminating light from the host galaxy. A further three objects show evidence of being absorbed by cold gas and dust with columns of up to ∼ 10²² cm⁻². The data are inconclusive on the remaining AGN.     

A quantitative determination of the AGN content in local ULIRGs through L-band spectroscopy

We present a quantitative estimate of the relative active galactic nucleus (AGN)/starburst content in a sample of 59 nearby  ( z < 0.15)  infrared bright ultraluminous infrared galaxies (ULIRGs) taken from the 1-Jy sample, based on infrared L -band (3–4 μm) spectra. By using diagnostic diagrams and a simple deconvolution model, we show that at least 60 per cent of local ULIRGs contain an active nucleus, but the AGN contribution to the bolometric luminosity is relevant only in  ∼15–20  per cent of the sources. Overall, ULIRGs appear to be powered by the starburst process, responsible for >85 per cent of the observed infrared luminosity. The subsample of sources optically classified as low-ionization nuclear emission-line regions (LINERs; 31 objects) shows a similar AGN/starburst distribution as the whole sample, indicating a composite nature for this class of objects. We also show that a few ULIRGs, optically classified as starbursts, have L -band spectral features suggesting the presence of a buried AGN.     

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.     

Optical and infrared diagnostics of SDSS galaxies in the SWIRE survey

We present the rest-frame optical and infrared colours of a complete sample of  1114 z < 0.3  galaxies from the Spitzer Wide-Area Infrared Extragalactic (SWIRE) Legacy Survey and the Sloan Digital Sky Survey (SDSS). We discuss the optical and infrared colours of our sample and analyse in detail the contribution of dusty star-forming galaxies and active galactic nuclei (AGN) to optically selected red sequence galaxies.
We propose that the optical  ( g − r )  colour and infrared  log( L ₂₄/ L _3.6)  colour of galaxies in our sample are determined primarily by a bulge-to-disc ratio. The  ( g − r )  colour is found to be sensitive to the bulge-to-disc ratio for disc-dominated galaxies, whereas the  log( L ₂₄/ L _3.6)  colour is more sensitive for bulge-dominated systems.
We identify ∼18 per cent (195 sources) of our sample as having red optical colours and infrared excess. Typically, the infrared luminosities of these galaxies are found to be at the high end of star-forming galaxies with blue optical colours. Using emission-line diagnostic diagrams, 78 are found to have an AGN contribution and 117 are identified as star-forming systems. The red  ( g − r )  colour of the star-forming galaxies could be explained by extinction. However, their high optical luminosities cannot. We conclude that they have a significant bulge component.
The number densities of optically red star-forming galaxies are found to correspond to ∼13 per cent of the total number density of our sample. In addition, these systems contribute ∼13 per cent of the total optical luminosity density, and 28 per cent of the total infrared luminosity density of our SWIRE/SDSS sample. These objects may reduce the need for 'dry mergers'.     

The properties of cataclysmic variables in photometric Hα surveys

We report on the properties of 71 known cataclysmic variables (CVs) in photometric Hα emission-line surveys. Our study is motivated by the fact that the Isaac Newton Telescope (INT) Photometric Hα Survey of the northern galactic plane (IPHAS) will soon provide r ',  i ' and narrow-band Hα measurements down to   r '≃ 20  for all northern objects between  − 5° < b < +5°  . IPHAS thus provides a unique resource, both for studying the emission-line properties of known CVs and for constructing a new CV sample selected solely on the basis of Hα excess. Our goal here is to carry out the first task and prepare the way for the second. In order to achieve this, we analyse data on 19 CVs already contained in the IPHAS data base and supplement this with identical observations of 52 CVs outside the galactic plane.
Our key results are as follows: (i) the recovery rate of known CVs as Hα emitters in a survey like IPHAS is ≃70 per cent; (ii) of the ≃30 per cent of CVs which were not recovered ≃75 per cent were clearly detected but did not exhibit a significant Hα excess at the time of our observations; (iii) the recovery rate depends only weakly on CV type; (iv) the recovery rate depends only weakly on orbital period; (v) short-period dwarf novae tend to have the strongest Hα lines. These results imply that photometric emission-line searches provide an efficient way of constructing CV samples that are not biased against detection of intrinsically faint, short-period systems.     

Narrow-band CCD photometry of giant H ii regions

We have obtained accurate CCD narrow-band Hβ and Hα photometry of giant H  ii regions (GEHRs) in M33, NGC 6822 and M101. Comparison with previous determinations of emission-line fluxes shows large discrepancies; their probable origins are discussed. Combining our new photometric data with global velocity dispersion ( σ ) derived from emission linewidths, we review the     relation. A re-analysis of the properties of the GEHRs included in our sample shows that age spread and the superposition of components in multiple regions introduce a considerable spread in the regression. Combining the information available in the literature regarding ages of the associated clusters, evolutionary footprints on the interstellar medium, and kinematical properties of the knots that build up the multiple GEHRs, we find that a subsample – which we refer to as young and single GEHRs – do follow a tight relation in the     plane.