While apparently supplying tremendous power to their extended radio-emitting regions, the nuclei of most radio galaxies emit little detectable radiation. It is proposed that at the centre of each is a spinning black hole surrounded by a torus of gas too hot and tenuous to radiate efficiently. The torus anchors magnetic fields which extract rotational energy from the hole in the form of two collimated beams of relativistic particles and fields. These in turn drive the observed radio jets and hot spots. A large supply of accreting gas is thus unnecessary and radio galaxies may be interpreted as starved quasars.

Ion-supported tori and the origin of radio jets

Observations with the Wide-Field Camera of the Hubble Space Telescope (HST) are presented for a representative sample of 20 intrinsically luminous quasars with redshifts smaller than 0.30. These observations show that luminous quasars occur in diverse environments that include ellipticals as bright as the brightest cluster galaxies (two), apparently normal ellipticals (10), apparently normal spirals with H II regions (three), complex systems of gravitationally interacting components (three), and faint surrounding nebulosity (two). The quasar host galaxies are centered on the quasar to the accuracy of our measurements, 400 pc. There are more radio-quiet quasars in galaxies that appear to be ellipticals (seven) than in spiral hosts (three), contrary to expectations. However, three, and possibly five, of the six radio-loud quasars have detectable elliptical hosts, in agreement with expectations. The luminous quasars studied in this paper occur preferentially in luminous galaxies. The average absolute magnitude of the hosts is 2.2 mag brighter than expected for a field galaxy luminosity function. The superb optical characteristics of the repaired HST make possible the detection of close galactic companions; we detect eight companion galaxies within projected distances of 10 kpc from quasar nuclei. The presence of very close companions, the images of current gravitational interactions, and the higher density of galaxies around the quasars suggest that gravitational interactions play an important role in triggering the quasar phenomenon.

/pdf/hubble-space-telescope-images-of-a-sample-of-20-nearby-d15vlmuta0.pdf

Hubble Space Telescope Images of a Sample of 20 Nearby Luminous Quasars

In the present-day universe, supermassive black hole masses (MBH) appear to be strongly correlated with their galaxy’s bulge luminosity, among other properties. In this study, we explore the analogous relationship between MBH, derived using the virial method, and the stellar R-band bulge luminosity (LR) or stellar bulge mass (M∗) at epochs of 1 . z . 4.5 using a sample of 31 gravitationally lensed AGNs and 20 non-lensed AGNs. At redshifts z > 1.7 (10–12 Gyrs ago), we find that the observed MBH–LR relation is nearly the same (to within ∼ 0.3 mag) as it is today. When the observed LR are corrected for luminosity evolution, this means that the black holes grew in mass faster than their hosts, with the MBH/M∗ mass ratio being a factor of & 4 +21 times larger at z > 1.7 than it is today. By the redshift range 1 . z . 1.7 (8–10 Gyrs ago), the MBH/M∗ ratio is at most two times higher than today, but it may be consistent with no evolution. Combining the results, we conclude that the ratio MBH/M∗ rises with look-back time, although it may saturate at ≈ 6 times the local value. Scenarios in which moderately luminous quasar hosts at z & 1.7 were fully formed bulges that passively faded to the present epoch are ruled out. Subject headings: galaxies: evolution — galaxies: quasars — galaxies: fundamental parameters — galaxies: structure — galaxies: bulges

Probing the Coevolution of Supermassive Black Holes and Galaxies Using Gravitationally Lensed Quasar Hosts

What is the relevance of major mergers and interactions as triggering mechanisms for active galactic nuclei (AGNs)
activity? To answer this long-standing question, we analyze 140 XMM-Newton-selected AGN host galaxies and
a matched control sample of 1264 inactive galaxies over z ~ 0.3–1.0 and M_∗ < 10^(11.7) M_⊙ with high-resolution
Hubble Space Telescope/Advanced Camera for Surveys imaging from the COSMOS field. The visual analysis of
their morphologies by 10 independent human classifiers yields a measure of the fraction of distorted morphologies
in the AGN and control samples, i.e., quantifying the signature of recent mergers which might potentially be
responsible for fueling/triggering the AGN. We find that (1) the vast majority (>85%) of the AGN host galaxies
do not show strong distortions and (2) there is no significant difference in the distortion fractions between active
and inactive galaxies. Our findings provide the best direct evidence that, since z ~ 1, the bulk of black hole (BH)
accretion has not been triggered by major galaxy mergers, therefore arguing that the alternative mechanisms, i.e.,
internal secular processes and minor interactions, are the leading triggers for the episodes of major BH growth.We
also exclude an alternative interpretation of our results: a substantial time lag between merging and the observability
of the AGN phase could wash out the most significant merging signatures, explaining the lack of enhancement
of strong distortions on the AGN hosts. We show that this alternative scenario is unlikely due to (1) recent major
mergers being ruled out for the majority of sources due to the high fraction of disk-hosted AGNs, (2) the lack of
a significant X-ray signal in merging inactive galaxies as a signature of a potential buried AGN, and (3) the low
levels of soft X-ray obscuration for AGNs hosted by interacting galaxies, in contrast to model predictions.

/pdf/the-bulk-of-the-black-hole-growth-since-z-1-occurs-in-a-855jleezob.pdf

The Bulk of the Black Hole Growth Since z ~ 1 Occurs in a Secular Universe: No Major Merger-AGN Connection

We test the hypothesis that QSOs are formed via strong tidal interactions or mergers, initially going through an ultraluminous infrared phase Our approach is to look for traces of this phase in the host galaxies of QSOs We select a sample of low-redshift bona fide QSOs that may be in a transitionary stage between ultraluminous infrared galaxies (ULIGs) and QSOs These objects, which we call transition QSOs, have an intermediate position in the far-infrared color-color diagram between the regions occupied by the two classes of objects We carry out a systematic spectroscopic and imaging study of these objects in order to determine their interaction and star-forming histories By modeling the spectra, we obtain ages for the recent starburst events in the host galaxies and interacting companions We have discussed the first five objects in the sample in detail in previous publications; here we present results for the remaining four objects, and discuss the sample as a whole We find that all nine transition QSOs are undergoing tidal interactions and that eight are major mergers Every object also shows strong recent star-forming activity, and in at least eight cases this activity is directly related to the tidal interaction The ages we derive for the starburst populations range from currently active star formation in some objects to poststarburst ages 300 Myr in others There is also a clear connection between interactions, starbursts, and QSO activity Seven of the QSOs in the sample are also ULIGs; statistical considerations show that the two phenomena are necessarily physically related in these objects Our results imply one of two scenarios: (1) at least some ULIGs evolve to become classical QSOs, and the transition stage lasts 300 Myr; or (2) at least some QSOs are born under the same conditions as ULIGs, and their lifetime as QSOs lasts 300 Myr We discuss other properties and trends found in the sample, and propose a model that accounts for all of them, as well as the youth of these systems

Quasi-Stellar Objects, Ultraluminous Infrared Galaxies, and Mergers*

Host galaxies of quasars and their association with galaxy clusters.

Resolution of quasar images.

The image (excluding the jet) of 3C 273 has been resolved with structure extending approx.15'' from the quasar to a surface brightness level, m/sub R/roughly-equal25 mag arcsec/sup -2/. The integrated magnitude of the underlaying nebulosity, Rroughly-equal16, corresponds to M/sub R/roughly-equal-25, and the isophotal angular diameter to Droughly-equal90 kpc.

T. Gehren

Papers

Host galaxies of quasars and their association with galaxy clusters.

Resolution of quasar images.

Discovery of nebulosity associated with the quasar 3C 273