The host galaxies of low luminosity quasars at high redshift

Advances in Space Research, 1999

We describe the results from a series of ground-based and HST programs aimed at investigating the host galaxies of both radio-loud and radio-quiet quasars (RLQs & RQQs) and FRII radio galaxies (RGs) at low redshifts (0.1 < z < 0.3). Our results are in good agreement with those of other recent studies of host galaxies. In general the hosts of powerful AGN are large, luminous (> 2L') galaxies, with underlying stellar populations which are predominantly old and red. The host galaxies of RLQs are massive ellipticals, indistinguishable from the FRII radio galaxies, consistent with unification of these sources by viewing angle. Although we find disc-like hosts around two low-luminosity (A4R > -23.5) R&&s, our R-band imaging campaign with HST, though currently incomplete, indicates that all quasars with MR < -23.5, occur in massive elliptical galaxies regardless of their radio luminosity.

Astronomy and …, 1998

We present the results of a high resolution (0.27 px −1) near-infrared H band (1.65 µm) imaging survey of a complete sample of 20 flat spectrum radio quasars (FSRQ) extracted from the 2Jy catalogue of radio sources (Wall & Peacock 1985). The observed objects are intrinsically luminous with median M(B) =-25.5. The median redshift of the objects in the sample is z = 0.65. At this redshift, the H band observations probe the old stellar population of the hosts at rest frame wavelength of ∼1 µm. We are able to detect the host galaxy clearly for six (30 %) FSRQs and marginally for six (30 %) other FSRQs, while the object remains unresolved for eight (40 %) cases. We find the galaxies hosting FSRQs to be very luminous (M(H)∼-27). Compared with the typical galaxy luminosity L* (M*(H)∼-25) they appear ∼2 mag brighter, although the undetected hosts may reduce this difference. They are also at least as bright as, and probably by ∼1 mag brighter than, the brightest cluster galaxies (M(H)∼-26). The luminosities of the FSRQ hosts are intermediate between host galaxies of low redshift radio-loud quasars and BL Lac objects (M(H)∼-26), and the hosts of high redshift radio-loud quasars (M(H)∼-29), in good agreement with current unified models for radio-loud AGN, taking into account stellar evolution in the elliptical host galaxies. Finally, we find an indicative trend between the host and nuclear luminosity for the most luminous FSRQs, supporting the suggestion based on studies of lower redshift AGN, that there is a minimum host galaxy luminosity which increases linearly with the quasar luminosity.

The Astrophysical Journal, 2001

We present high spatial resolution near-infrared H-band (1.65 µm) images, taken with ISAAC on UT1 of ESO VLT, of three radio-loud quasars at z∼1.5, as a pilot study for imaging of a larger sample of radio-loud and radio-quiet quasars in the redshift range 1 < z < 2. We are able to clearly detect the host galaxy in two quasars (PKS 0000-177 and PKS 0348-120) and marginally in the third (PKS 0402-362). The host galaxies appear compact (average bulge scale-length R(e) ∼ 4 kpc) and luminous (average M(H) =-27.6±0.1). They are ∼2.5 mag more luminous than the typical galaxy luminosity (M*(H) =-25.0±0.2), and are comparable to the hosts of low redshift radio-loud quasars (M(H) ∼-26), taking into account passive stellar evolution. Their luminosities are also similar to those of high redshift radio galaxies. All three quasars have at least one close companion galaxy at a projected distance < 50 kpc from the quasar, assuming they are at the same redshift.

The Astrophysical Journal, 2008

The properties of high-redshift quasar host galaxies are studied in order to investigate the connection between galaxy evolution, nuclear activity, and the formation of supermassive black holes. We combine new near-IR observations of three high-redshift quasars (2 < z < 3), obtained at the ESO Very Large Telescope equipped with adaptive optics, with selected data from the literature. For the three new objects we were able to detect and characterize the properties of the host galaxy, found to be consistent with those of massive elliptical galaxies of M R $ À24:7 for the one radio-loud quasar, and M R $ À23:8 for the two radio-quiet quasars. When combined with existing data at lower redshift, these new observations depict a scenario where the host galaxies of radio-loud quasars are seen to follow the expected trend of luminous ($5L Ã) elliptical galaxies undergoing passive evolution. This trend is remarkably similar to that followed by radio galaxies at z > 1:5. Radio-quiet quasar hosts also follow a similar trend but at a lower average luminosity ($0.5 mag dimmer). The data indicate that quasar host galaxies are already fully formed at epochs as early as $2 Gyr after the big bang and then passively fade in luminosity to the present epoch.

Monthly Notices of the Royal Astronomical Society, 2004

We present the results of a deep Hubble Space Telescope (HST)/Wide Field and Planetary Camera 2 imaging study of 17 quasars at z≃ 0.4, designed to determine the properties of their host galaxies. The sample consists of quasars with absolute magnitudes in the range −24 ≥MV≥− 28, allowing us to investigate host galaxy properties across a decade in quasar luminosity, but at a single redshift. Our previous imaging studies of active galactic nuclei hosts have focused primarily on quasars of moderate luminosity, but the most powerful objects in the current sample have powers comparable to the most luminous quasars found at high redshifts. We find that the host galaxies of all the radio-loud quasars, and all the radio-quiet quasars in our sample with nuclear luminosities MV < −24, are massive bulge-dominated galaxies, confirming and extending the trends deduced from our previous studies. From the best-fitting model host galaxies we have estimated spheroid and hence black hole (BH) masses, and the efficiency (with respect to the Eddington luminosity) with which each quasar emits radiation. The largest inferred black hole mass in our sample is MBH≃; 3 × 109 M⊙, comparable to the mass of the black holes at the centres of M87 and Cygnus A. We find no evidence for super-Eddington accretion rates in even the most luminous objects (0.05 < L/LEdd < 1.0). We investigate the role of scatter in the black hole–spheroid mass relation in determining the ratio of quasar to host-galaxy luminosity, by generating simulated populations of quasars lying in hosts with a Schechter mass function. Within the subsample of the highest-luminosity quasars, the observed variation in nuclear-host luminosity ratio is consistent with being the result of the scatter in the black hole–spheroid relation. Quasars with high nuclear-host luminosity ratios can be explained in terms of sub-Eddington accretion rates on to black holes in the high-mass tail of the black hole–spheroid relation. Our results imply that, owing to the Schechter function cut-off, host mass should not continue to increase linearly with quasar luminosity, at the very highest luminosities. Any quasars more luminous than MV=−27 should be found in massive elliptical hosts, which at the present day would have MV≃−24.5.

1997

A sample of 16 quasars selected from the Large Bright Quasar Survey in the redshift range 0.4 &lt; z &lt; 0.5 has been imaged in the R band with the Planetary Camera on the WFPC2 instrument of the Hubble Space Telescope. The host galaxy magnitudes are mostly similar to or brighter than L∗, and the host luminosity is positively correlated with the luminosity of the quasar nuclear component. There is no distinction in host galaxy magnitude between radio-loud and radio-quiet quasars, assuming they are all of the same galaxy type. Many of the host galaxies in the sample have small axial ratios, which may indicate that they are inclined disk systems. Alternatively, this elongated appearance may be due to bars or other distinctive morphological features which are visible while the bulk of the underlying lower surface brightness components of the host galaxy are not. Subject headings: galaxies:active – quasars:general 1 Accepted for publication in the Astrophysical Journal Letters. This wo...

Monthly Notices of the Royal Astronomical Society, 2001

We present the first results from a major Hubble Space Telescope programme designed to investigate the cosmological evolution of quasar host galaxies from z ≃ 2 to the present day. Here we describe J and H-band NICMOS imaging of two quasar samples at redshifts of 0.9 and 1.9 respectively. Each sample contains equal numbers of radioloud and radio-quiet quasars, selected to lie within the same narrow range of optical absolute magnitude (−24 ≥ M V ≥ −25). Filter and target selection were designed to ensure that at each redshift the images sample the same part of the object's restframe spectrum, longwards of 4000Å where starlight from the host galaxy is relatively prominent, but avoiding potential contamination by [Oiii]λ5007 and Hα emission lines.

New Astronomy Reviews, 2006

We report on ESO-VLT adaptive optics imaging of one radio-loud quasar at z ∼ 3. In spite of the large distance of the object we are able to detect its surrounding extended nebulosity the properties of which are consistent with an underlying massive galaxy of M K ∼ -27 and effective radius R e = 7 kpc. As far as we know this is the clearest detection of a radio loud quasar host at high redshift. The host luminosity is indicative of the existence of massive spheroids even at this early cosmic epoch. The host luminosity is about 1 magnitude fainter than the expected value based on the average trend of the host galaxies of RLQ at lower redshift. The result, which however is based on a single object, suggests that at z ∼ 3 there is a deviation from a luminosity-redshift dependence regulated only by passive evolution.

Monthly Notices of the Royal Astronomical Society, 2003

We present the final results from our deep HST imaging study of the host galaxies of radio-quiet quasars (RQQs), radio-loud quasars (RLQs) and radio galaxies (RGs). We describe and analyze new WFPC2 R-band observations for 14 objects which, when combined with the first tranche of HST imaging reported in , provide a complete and consistent set of deep, red, line-free images for statisticallymatched samples of 13 RQQs, 10 RLQs and 10 RGs in the redshift band 0.1 < z < 0.25. We also report the results of new deep VLA imaging which has yielded a 5 GHz detection of all but one of the 33 AGN in our sample.

Astron J, 2001

Deep optical images have been gathered for a nearly complete sample of radio galaxies from the Revised 3rd Cambridge (3CR) Catalog in the redshift range 0.15 < z < 0.65. Total and nuclear magnitudes and colors have been extracted. The richness of the galaxy clustering environment has also been quantified by calculating the amplitude of the galaxy-galaxy spatial covariance function (B gg), showing overdensities ranging up to Abell class 0-1 clusters. These optical data are compared to similar data from an existing sample of radio-loud quasars in the same redshift range for the purpose of determining the relationship between radio galaxies and quasars. In the range 0.15 < z < 0.4, we find that quasars and radio galaxies have significantly different environments in that only radio galaxies are found in rich cluster environments. This comparison appears to rule out the hypothesis that all quasars are radio galaxies viewed from a particular angle at the 97% confidence level (99.6% confidence level if N-galaxies are considered quasars). The existence of quasars in clusters at z > 0.4 supports the hypothesis that some radio-loud quasars may dim with time and evolve into radio galaxies with an efolding time of ∼ 0.9 Gyr. A compatible scenario is presented for this evolution in which the quasar dims due to the absence of low velocity interactions between the quasar host and companion galaxies which trigger quasar activity and/or a diminishing fuel supply caused by the more effective gas "sweeping" of a growing intracluster medium.