On the streaming motions of haloes and galaxies

Little is known about the statistics of gravitationally lensed quasars at large (7–30 arcsec) image separations, which probe masses on the scale of galaxy clusters. We have carried out a survey for gravitationally lensed objects, among sources in the FIRST 20-cm radio survey that have unresolved optical counterparts in the digitizations of the Palomar Observatory Sky Survey. From the statistics of ongoing surveys that search for quasars among FIRST sources, we estimate that there are about 9100 quasars in this source sample, making this one of the largest lensing surveys to date. Using broad-band imaging, we have isolated all objects with double radio components separated by 5–30 arcsec that have unresolved optical counterparts with similar BVI colours. Our criteria for similar colours conservatively allow for observational error and for colour variations due to time delays between lensed images. Spectroscopy of these candidates shows that none of the pairs are lensed quasars. This sets an upper limit (95 per cent confidence) on the lensing fraction in this survey of 3.3×10⁻⁴, assuming 9100 quasars. Although the source redshift distribution is poorly known, a rough calculation of the expected lensing frequency and the detection efficiencies and biases suggests that simple theoretical expectations are of the same order of magnitude as our observational upper limit. Our procedure is novel in that our exhaustive search for lensed objects does not require prior identification of the quasars in the sample as such. Characterization of the FIRST-selected quasar population will enable use of our result to constrain quantitatively the mass properties of clusters.     

The quasar epoch and the stellar ages of early-type galaxies

We investigate the hypothesis that quasars formed together with the stellar populations of early-type galaxies. This hypothesis – in conjunction with the stellar ages of early-type galaxies from population synthesis models, the relation of black hole mass to bulge velocity dispersion, and the velocity dispersion distribution of spheroids from the Sloan Digital Sky Survey – completely determines the cosmic accretion history of supermassive black holes and the redshift evolution of the characteristic luminosity. On the other hand, the precise shape of the luminosity function of quasars depends on the light curve of quasars and – in the optical, but not so much in X-rays – on the covering factor of the dust surrounding the active nucleus. We find a plausible set of assumptions for which the coeval formation of supermassive black holes and elliptical galaxies is in good agreement with the observed B -band and X-ray luminosity functions of quasars.     

Measurement of dwarf galaxies in the rich clusters Abell 665 and 963 at z=0.2

We show that the luminosity functions of the distant rich clusters Abell 665 ( z =0.182) and Abell 963 ( z =0.206) are flat or gradually rising down to M_R =−14, with α≈−1.2±0.4 [here α is the logarithmic slope of the luminosity function: φ( L )∝ L ^α at the faint end]. We do not confirm the steep luminosity functions (α≤−1.8) that have been recently proposed for these two clusters.
Several technical points are discussed in detail. In particular, we compute the corrections to the background contamination caused by gravitational lensing from the cluster dark matter, and show that the corrections are small unless we wish to determine variations in the luminosity function on small scales.
Recent observations have also shown that the field galaxy luminosity function at z ≈0.2 is also shallow between M_B =−19 and M_B =−13. Abell 665 and 963 are two of the richest clusters known at that redshift. We therefore propose that the galaxy luminosity function might be universal in this magnitude range at z =0.2.
The dwarf galaxies that we see in Abell 665 have a colour distribution that is strongly peaked at B − R =1.9. We compute K -corrections based on the spectral energy distributions of local galaxies, and show that these are probably dwarf spheroidal galaxies. This might suggest that the dwarf spheroidal population observed in Virgo already existed at z =0.2.     

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.     

Gravitational lensing by stars in a galaxy halo: Theory of combined weak and strong scattering

The theory of gravitational lensing of background quasars by stars in the halo of a galaxy is considered. In the limiting case of small ‘optical depth’, only one star is close enough to the beam to cause strong scattering, and the effect of all the other stars is treated as a perturbation with both systematic and random components. The perturbation coming from weak scattering can increase the number of images and the amplification in those cases where the amplification is already high; such events are preferentially selected in flux limited observations. The theory is applicable to the apparent association of background quasars with foreground galaxies. A comparison with earlier work on the same problem is given. The relevance of these results to gravitational lensing by galaxies as perturbed by random inhomogeneities surrounding the ray path is also briefly discussed.     

The host galaxies of luminous radio-quiet quasars

We present the results of a deep K -band imaging study which reveals the host galaxies around a sample of luminous radio-quiet quasars. The K -band images, obtained at UKIRT, are of sufficient quality to allow accurate modelling of the underlying host galaxy. Initially, the basic structure of the hosts is revealed using a modified clean deconvolution routine optimized for this analysis. Two of the 14 quasars are shown to have host galaxies with violently disturbed morphologies which cannot be modelled by smooth elliptical profiles. For the remainder of our sample, 2D models of the host and nuclear component are fitted to the images using the χ ² statistic to determine goodness of fit. Host galaxies are detected around all of the quasars. The reliability of the modelling is extensively tested, and we find the host luminosity to be well constrained for nine quasars. The derived average K -band absolute K -corrected host galaxy magnitude for these luminous radio-quiet quasars is 〈 M _K 〉=25.15±0.04, slightly more luminous than an L * galaxy. The spread of derived host galaxy luminosities is small, although the spread of nuclear-to-host ratios is not. These host luminosities are shown to be comparable to those derived from samples of quasars of lower total luminosity, and we conclude that there is no correlation between host and nuclear luminosity for these quasars. Nuclear-to-host ratios break the lower limit previously suggested from studies of lower nuclear luminosity quasars and Seyfert galaxies. Morphologies are less certain but, on the scales probed by these images, some hosts appear to be dominated by spheroids while others appear to have disc-dominated profiles.     

1–5 μm imaging of 3CRR galaxies: the K–z relation and the geometry of the torus

It has been claimed by Taylor et al. that the low-redshift end of the K – z relation for radio galaxies is too bright by about half a magnitude owing to contributions from the obscured quasar nuclei. Such a result has major implications for the use of the K -band Hubble diagram in understanding the cosmological evolution of radio galaxies. In this paper we present 1–5-μm imaging data of a nearly complete sample of low-redshift radio galaxies; this approach allows us to determine accurately the strengths of any unresolved nuclear components in the galaxies. We detect nuclear sources in five targets, whose broad-band colours are consistent with reddened quasar spectra. In all the five cases the ratio of the inferred intrinsic near-infrared luminosity to the narrow-line luminosity is typical of quasars. We find a correlation between the inferred nuclear extinction and core-to-lobe ratio, which places constraints on the geometry of the torus. We find evidence for a shift of the K – z relation to fainter magnitudes, but by a much smaller amount (∼0.1 mag) than determined by Taylor et al. Under the assumption that the nuclear sources in radio galaxies have the same intrinsic near-infrared spectra as quasars, our multiwavelength images allow us to limit any possible shift to less than 0.3 mag.     

Distribution of quasars on the sky

It is shown that high-redshift quasars of bright apparent magnitude are concentrated in the direction of the centre of the Local Group of galaxies. A number of them are distributed along a line originating from the Local Group companion galaxy, M 33. A similar, but shorter and fainter line of quasars is seen emanating from the spiral galaxy NGC 300 in the next nearest, Sculptor Group of galaxies. The concentration of bright quasars in the Local Group direction is supported by bright radio sources catalogued in high-frequency surveys. One of the consequences of this large-scale inhomogeneity is to explain the different gradient of radio source counts in the direction of the Local Supercluster, a result discovered in 1978 but never investigated further. Previously reported homogeneity and isotropy of radio-source counts over the sky would seem to be an effect of integrating nearby, large-scale groupings with more distant, smaller-scale groupings over different directions in the sky. More careful analyses as a function of flux strength and spectral index on various scales over the sky are now required. Previous conclusions about radio source and quasar luminosity and number evolution drawn from logN- logS counts would then need to be re-evaluated.     

Evolution of Quasar Host Galaxies

Near-IR images, obtained at the ESO-VLT during excellent seeing conditions, of a sample of 17 radio-loud and radio-quiet quasars in the redshift range 1 < z < 2 are presented. The host galaxies of both types of quasars appear to follow the expected trend in luminosity of massive ellipticals undergoing simple passive evolution. We find a systematic difference by a factor ∼2 in the host luminosity between RLQs and RQQs that does not change significantly from z = 2 to the present epoch. Quasar hosts appear thus to be already well formed at z ∼ 2 and similar to massive inactive spheroids. These findings are in disagreement with the predictions of models for the joint formation and evolution of galaxies and active nuclei based on the hierarchical structure formation scenario.     

Quasars lensed by globular clusters of spiral and elliptical galaxies

Based on the SDSS catalog, we have found new close quasar—galaxy pairs. We analyze the radial distribution of quasars from pairs around galaxies of different types. We show that the quasars from pairs follow the density profile of halo globular clusters. This is new observational evidence that the quasars projected onto the halos of galaxies are magnified by gravitational lensing by halo globular clusters.     

Quasars in Regions of Rich Clusters of Galaxies

Certain characteristics of quasars observed in the regions of three rich clusters of galaxies are investigated. It is shown that the luminosity functions constructed for samples of quasars from the regions of the Virgo and Fornax clusters are similar to each other and show a very sharp maximum at a stellar magnitude of 18^m.0-18^m.3. The maximum of the luminosity function for quasars from the region of the Coma cluster (A 1656) is shifted toward fainter magnitudes and lies at 21^m. This effect is explained by the affiliation of the majority of the quasars to the respective clusters. It is shown that the absolute stellar magnitude of these quasars is –13^m, which corresponds to the luminosity of dwarf galaxies of low luminosity. It is suggested that the local quasars are formed in two ways: by ejection from galactic nuclei and in quasar associations without a parent galaxy, directly from protostellar matter.     

A comparative HST imaging study of the host galaxies of radio-quiet quasars, radio-loud quasars and radio galaxies – I

We present the first results from a major HST WFPC2 imaging study aimed at providing the first statistically meaningful comparison of the morphologies, luminosities, scalelengths and colours of the host galaxies of radio-quiet quasars, radio-loud quasars and radio galaxies. We describe the design of this study and present the images that have been obtained for the first half of our 33-source sample. We find that the hosts of all three classes of luminous AGN are massive elliptical galaxies, with scalelengths ≃10 kpc, and R − K colours consistent with mature stellar populations. Most importantly, this is first unambiguous evidence that, just like radio-loud quasars, essentially all radio-quiet quasars brighter than M _R =−24 reside in massive ellipticals. This result removes the possibility that radio 'loudness' is directly linked to host galaxy morphology, but is however in excellent accord with the black hole/spheroid mass correlation recently highlighted by Magorrian et al. We apply the relations given by Magorrian et al. to infer the expected Eddington luminosity of the putative black hole at the centre of each of the spheroidal host galaxies we have uncovered. Comparison with the actual nuclear R -band luminosities suggests that the black holes in most of these galaxies are radiating at a few per cent of the Eddington luminosity; the brightest host galaxies in our low- z sample are capable of hosting quasars with M _R ≃− 28, comparable to the most luminous quasars at z ≃3. Finally, we discuss our host-derived black hole masses in the context of the radio luminosity:black hole mass correlation recently uncovered for nearby galaxies by Franceschini et al., and consider the resulting implications for the physical origin of radio loudness.     

Implications for unified schemes from submillimetre and far-infrared follow-up of radio-selected samples

We extend our previous analysis which used generalized luminosity functions (GLFs) to predict the number of quasars and galaxies in low-radio-frequency-selected samples as a function of redshift, radio luminosity, narrow-emission-line luminosity and type of unified scheme. Our extended analysis incorporates the observed submillimetre (850-μm) flux densities of radio sources, employs a new method which allows us to deal with non-detections, and focuses on the high-luminosity population. First, we conclude that the submillimetre luminosity L ₈₅₀ of low-frequency-selected radio sources is correlated with the bolometric luminosity L _bol of their quasar nuclei via an approximate scaling relation   L ₈₅₀∝ L ^0.7±0.2_bol  . Secondly, we conclude that there is quantitative evidence for a receding-torus-like physical process for the high-luminosity population within a two-population unified scheme for radio sources; this evidence comes from the fact that radio quasars are brighter in both narrow emission lines and submillimetre luminosity than radio galaxies matched in radio luminosity and redshift. Thirdly, we note that the combination of a receding-torus-like scheme and the assumption that the observed submillimetre emission is dominated by quasar-heated dust yields a scaling relation   L ₈₅₀∝ L ^1/2_bol  which is within the errors of that determined here for radio-selected quasars, and consistent with that inferred for radio-quiet quasars.     

Far-infrared-loud quasars – I. Disturbed and quiescent quasars in the PG survey

We use host galaxy imaging studies of the PG quasar survey to compare the far-infrared (FIR) properties of quasars with disturbed and undisturbed host galaxies. By using survival analysis, we show that the quasars with disturbed host galaxies, with morphologies classified from a homogeneous data set, have a 60-μm luminosity distribution that is different from that of those with undisturbed hosts with >97 per cent confidence. For morphological classifications using an inhomogeneous data set, including HST data for some objects, this confidence rises to >99 per cent confidence. The mean 60-μm luminosity of the disturbed-host quasars is several times greater than that of the undisturbed-host quasars. However, possible biases in the PG survey might affect these conclusions. Our results are interpreted as supporting the idea that quasars are related to at least some ultraluminous infrared galaxies. We discuss the implications of this result for studies of quasar and galaxy evolution.     

Globular clusters as candidates for gravitational lenses to explain quasar-galaxy associations

We argue that globular clusters (GCs) are good candidates for gravitational lenses in explaining quasar-galaxy associations. The catalog of associations (Bukhmastova 2001) compiled from the LEDA catalog of galaxies (Paturel 1997) and from the catalog of quasars (Veron-Cetty and Veron 1998) is used. Based on the new catalog, we show that one might expect an increased number of GCs around irregular galaxies of types 9 and 10 from the hypothesis that distant compact sources are gravitationally lensed by GCs in the halos of foreground galaxies. The King model is used to determine the central surface densities of 135 GCs in the Milky Way. The distribution of GCs in central surface density was found to be lognormal.     

Observational manifestations and intrinsic properties of the RCR sources in terms of a unified model

We present a summary results of the study of radio sources showing significant variations of integral flux density using the data from the RATAN-600 surveys of 1980–1994 at a frequency of 7.6 cm. The majority of the detected variable sources have flat radio spectra, although there are also all other spectrum types found. Point and compact sources predominate, although all known morphological structures are found in the sample. Variability is detected both in quasars and galaxies. Using the catalog data, we found brightness variations in the optical and/or infrared ranges for a half of host objects of radio sources. We analyzed the properties of nonvariable and variable RCR sources. We compared the ratio of absolute magnitude to radio luminosity for sources with the active nucleus types determined from the optical data. It is found that this parameter is approximately the same for quasars with different radio luminosity. It isminimum for the strongest radio galaxies and grows up to the level characteristic of quasars with the decrease of radio luminosity. Considering that the ratio depends on obscuring properties of a dust torus, such behavior can be explained if we assume that the torus geometry and its optical depth depend on the source long. This parameter is slightly higher among variable sources than among nonvariable ones which counts in favor of the nucleus more open to an observer.     

Rest-frame optical and far-infrared observations of extremely bright Lyman-break galaxy candidates at z∼ 2.5

We have investigated the rest-frame optical and far-infrared properties of a sample of extremely bright candidate Lyman-break galaxies (LBGs) identified in the Sloan Digital Sky Survey. Their high ultraviolet luminosities and lack of strong ultraviolet emission lines are suggestive of massive starbursts, although it is possible that they are more typical luminosity LBGs which have been highly magnified by strong gravitational lensing. Alternatively, they may be an unusual class of weak-lined quasars. If the ultraviolet and submillimetre (submm) properties of these objects mirror those of less luminous, starburst LBGs, then they should have detectable rest-frame far-infrared emission. However, our submm photometry fails to detect such emission, indicating that these systems are not merely scaled-up (either intrinsically or as a result of lensing) examples of typical LBGs. In addition we have searched for the morphological signatures of strong lensing, using high-resolution, near-infrared imaging, but we find none. Instead, near-infrared spectroscopy reveals that these systems are, in fact, a rare class of broad absorption line quasars.     

Investigation of galaxy and quasar luminosity evolution in the model of standard cosmology

It is shown that the Hubble curvem(z) for galaxies and quasars averaged over a large volume of data forms in the first approximation a single continuous curve in the interval of red shifts 10^–2.5z4.5, which is satisfactorily described by the dependence .A large deviation of the observed mean dependence from the theoretical one predicted by the standard cosmology is explained by the evolution of the galaxy and especially quasar luminosity. The corresponding mid-statistical function of the absolute luminosity variation for the last 4/5 times of existence in the Universe is equal toM(z)–M(z ₀)=logz/z ₀+2z–0.4z ².The luminosity of the most far distant from the observed quasars on the average by 5–6 stellar magnitudes high than the luminosity of near galaxies and quasars. It is obtained that even the most far distant quasars atz5 are in the maximum of luminosity, or their extinction has just began, thus the quasar formation should be expected forz>(5–6). The relative rate of the luminosity decrease of galaxies and near quasars is rather accurately amounts in the recent epoch 7% per 10⁹ years. The obtained average Hubble curve of galaxies and quasars is evidently the main cause of their evolution in the Universe.     

Galaxy populations in the Fornax and Virgo clusters

In these first results from a photographic survey of nearby clusters and groups of galaxies, we compare the luminosity functions of galaxies of various Hubble types in the core of the Formax cluster to luminosity functions in the core of the Virgo cluster from Sandageet al. (1985). The galaxy classifications for the two clusters are based on identical plate material, and are hence directly comparable. The properties (galaxy density, velocity dispersion, X-ray luminosity) of the two clusters are quite different, yet we find few significant differences in the luminosity functions, or in the morphological mix of galaxies between the two clusters. In particular, while there is some indication that the ratios of giants to dwarfs and early to late-type galaxies in the two clusters differ, we cannot exclude the possibility that the ratios are identical. We discuss the selection limits of our survey and the completeness corrections that must be applied to the faint end of the luminosity function. The effective surface brightness of early-type galaxies in our sample decreases with decreasing luminosity. We show that this correlation is not an artifact of our selection criteria for dwarf spheroidal galaxies and use it to determine the relative distances to the Fornax and Virgo clusters. We also present evidence for a radial variation in the luminosity function of dwarf ellipticals within the two clusters in the sense that the faint end of the luminosity distribution is enhanced at the centre of each cluster.