arXiv subjects

R. J. McLure

Publications and source records attributed to R. J. McLure.

158 records · Page 9Linked to original sources

arXiv2002

Coupled spheroid and black-hole formation, and the multifrequency detectability of active galactic nuclei and submillimetre sources

We use a simple model of spheroid formation to explore the relationship between the creation of stars and dust in a massive proto galaxy and the growth of its central black hole. This model predicts that sub-mm luminosity peaks after only ~ 0.2 Gyr. However, without a very massive seed black hole, Eddington-limited growth means that a black hole mass of 10^9 solar masses, and hence very luminous AGN activity, cannot be produced until > 0.5 Gyr after the formation of the first massive stars in the halo. The model thus predicts a time-lag between the peak of sub-mm luminosity and AGN luminosity in a massive proto-elliptical of a few times 10^8 years. For a formation redshift z = 5, this means that powerful AGN activity is delayed until z = 3.5, by which time star formation in the host is 90% complete, and sub-mm luminosity has declined to ~ 25% of its peak value. This provides a natural explanation for why successful sub-mm detections of luminous radio galaxies are largely confined to z > 2.5. Conversely the model also predicts that while all high-redshift luminous sub-mm-selected sources should contain an active (and growing) black hole, the typical luminosity of the AGN in such objects is ~1000 times smaller than that of the most powerful AGN. This is consistent with the almost complete failure to detect sub-mm selected galaxies with existing X-ray surveys. Finally the model yields a black-hole:spheroid mass ratio which evolves rapidly in the first Gyr, but asymptotes to ~ 0.001-0.003 in agreement with results at low redshift. This ratio arises not because the AGN terminates star formation, but because fueling of the massive black hole is linked to the total mass of gas available for star formation in the host.

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arXiv2002

Old elliptical galaxies at z=1.5 and the Kormendy relation

Deep spectroscopy of the two mJy radio galaxies LBDS 53W069 and 53W091 has previously shown them to have old (>3 Gyr) stellar populations at z=1.5. Here we present the results of HST observations of these galaxies. 53W069 has an r^1/4 profile in both the F814W & F110W data with an effective radius of 0.30 arcsec (2.7 kpc). The restframe U-B colour gradient requires a stellar population of super-solar (3Z_sun) metallicity that formed on a very short timescale at high redshift (z>5). 53W091 has a regular r^1/4 profile in F110W with an effective radius of 0.32 arcsec (2.9 kpc). The F814W profile is more extended and is consistent with a blue exponential disk that contributes 20% of the flux within r_e. The restframe U-B colour gradient is significantly larger than that observed in field ellipticals at z<1, implying a stellar population of mixed metallicity (1-3Z_sun) that formed in a high-redshift rapid burst. We have compared these two LBDS radio galaxies with the Kormendy relation of ten 3CR radio galaxies at z=0.8. The LBDS galaxies follow the same relation as the more radio-luminous 3CR galaxies, assuming passive evolution of their stellar populations, although they are smaller than the 3CR galaxies whose mean effective radius is 12 kpc. Their sizes and radio luminosities are consistent with scaling relations applied to the 3CR galaxies, in which both radio power and effective radius scale with galaxy mass. Compared with a sample of z=0.4 cluster ellipticals, 53W069 & 53W091 lie well within the scatter of the Kormendy relation. We conclude that the hosts of these mJy radio sources at z=1.5 are passively-evolving elliptical galaxies that will evolve into ordinary L* ellipticals by the present day. (Abridged)

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arXiv2002

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 half maximum (FWHM) of the low-ionization MgII emission line and the correlation between broad-line region (BLR) radius and continuum luminosity at 3000 Angstroms. Using archival UV spectra it is found that the correlation between BLR radius and 3000 Angstrom luminosity is tighter than the established correlation with 5100 Angstrom luminosity. Furthermore, it is found that the correlation between BLR radius and 3000 Ang luminosity is consistent with a relation of the form $R_{BLR} \propto lambda L_{lambda}^{0.5}$, 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 MgII and H beta are consistent with following an exact one-to-one relation, as expected if both H beta and MgII 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 (1 sigma). Finally, the new UV black-hole mass estimator is shown to produce identical results to the established optical (H beta) 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.

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arXiv2002

Discovery of the host galaxy of HDF850.1, the brightest sub-mm source in the Hubble Deep Field

Despite extensive observational efforts, the brightest sub--mm source in the Hubble Deep Field, HDF850.1, has failed to yield a convincing optical/infrared identification almost 4 years after its discovery. This failure is all the more notable given the availability of supporting multi-frequency data of unparalleled depth, and sub-arcsec positional accuracy for the sub-mm/mm source. Consequently, HDF850.1 has become a test case of the possibility that the most violently star-forming objects in the universe are too red and/or distant to be seen in the deepest optical images. Here we report the discovery of the host galaxy of HDF850.1. This object has been revealed by careful analysis of a new, deep K-prime image of the HDF obtained with the Subaru 8.2-m telescope. Its reality is confirmed by a similar analysis of the HST NICMOS F160W image of the same region. This object is extremely faint (K=23.5), clumpy (on sub-arcsec scales) and very red (I-K > 5.2; H-K = 1.4 +- 0.35). The likelihood that it is the correct identification is strongly reinforced by a reanalysis of the combined MERLIN+VLA 1.4-GHz map of the field which yields a new radio detection of HDF850.1 only 0.1 arcsec from the new near-ir counterpart, and with sufficient positional accuracy to exclude all previously considered alternative optical candidates. We have calculated new confidence limits on the estimated redshift of HDF850.1 and find z = 4.1 +- 0.5. We also calculate that the flux density of HDF850.1 has been boosted by a factor of ~3 through lensing by the intervening elliptical 3-586.0, consistent with predictions that a small but significant fraction of blank-field sub-mm sources are lensed by foreground galaxies. We discuss the wider implications of these results for the sub-mm population and cosmic star-formation history.

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arXiv2002

The black hole - bulge mass relation in active and inactive galaxies

New virial black-hole mass estimates are presented for a sample of 72 AGN covering three decades in optical luminosity. Using a model in which the AGN broad-line region (BLR) has a flattened geometry, we investigate the M_{bh)-L_{bulge} relation for a combined 90-object sample, consisting of the AGN plus a sample of 18 nearby inactive elliptical galaxies with dynamical black-hole mass measurements. It is found that, for all reasonable mass-to-light ratios, the M_{bh}-L_{bulge} relation is equivalent to a linear scaling between bulge and black-hole mass. The best-fitting normalization of the M_{bh}-M_{bulge} relation is found to be M_{bh}=0.0012M_{bulge}, in agreement with recent black-hole mass studies based on stellar velocity dispersions. Furthermore, the scatter around the M_{bh}-L_{bulge} relation for the full sample is found to be significantly smaller than has been previously reported (Δ\log M_{bh}=0.39 dex). Finally, using the nearby inactive elliptical galaxy sample alone, it is shown that the scatter in the M_{bh}-L_{bulge} relation is only 0.33 dex, comparable to that of the M_{bh}-sigma relation. These results indicate that reliable black-hole mass estimates can be obtained for high redshift galaxies.

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arXiv2001

On the black hole - bulge mass relation in active and inactive galaxies

New black-hole mass estimates are presented for a sample of 72 AGN covering three decades in optical luminosity. Using a sub-sample of Seyfert galaxies, which have black-hole mass estimates from both reverberation mapping and stellar velocity dispersions, we investigate the geometry of the AGN broad-line region (BLR). It is demonstrated that a model in which the orbits of the line-emitting material have a flattened geometry is favoured over randomly orientated orbits. Using this model we investigate the M_{bh}-L_{bulge} relation for a combined 90-object sample, consisting of the AGN plus a sample of 18 nearby inactive elliptical galaxies with dynamical black-hole mass measurements. It is found that, for all reasonable mass-to-light ratios, the M_{bh}-L_{bulge} relation is equivalent to a linear scaling between bulge and black-hole mass. The best-fitting normalization of the M_{bh}-M_{bulge} relation is found to be M_{bh}=0.0012M_{bulge}, in agreement with recent black-hole mass studies based on stellar velocity dispersions. Furthermore, the scatter around the M_{bh}-L_{bulge} relation for the full sample is found to be significantly smaller than has been previously reported (Delta \log M_{bh}=0.39 dex). Finally, using the nearby inactive elliptical galaxy sample alone, it is shown that the scatter in the M_{bh}-L_{bulge} relation is only 0.33 dex, comparable to that of the M_{bh}-sigma relation. These results indicate that reliable black-hole mass estimates can be obtained for high redshift galaxies.

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arXiv2001

The black-hole masses of Seyfert galaxies and quasars

The central black-hole masses of a sample of 30 luminous quasars are estimated using H-beta FWHM measurements from a combination of new and previously-published nuclear spectra. The quasar black-hole mass estimates are combined with reverberation-mapping measurements for a sample of Seyfert galaxies (Wandel 1999) in order to study AGN black-hole masses over a wide range in nuclear luminosity. It is found that black-hole mass and bulge luminosity are well correlated and follow a relation consistent with that expected if black-hole and bulge mass are directly proportional. Contrary to the results of Wandel (1999) no evidence is found that Seyfert galaxies follow a different Mblack-Mbulge relation to quasars. However, the black-hole mass distributions of the radio-loud and radio-quiet quasar sub-samples are found to be significantly different, with the median black-hole mass of the radio-loud quasars a factor of three larger than their radio-quiet counterparts. Finally, utilizing the elliptical galaxy fundamental plane to provide stellar velocity dispersion estimates, a comparison is performed between the virial H-beta black-hole mass estimates and those of the Mblack-sigma correlations of Gebhardt et al. (2000a) and Merritt & Ferrarese (2000). With the disc-like geometry of the broad-line region adopted in this paper, the virial H-beta black-hole masses indicate that the correct normalization of the black-hole vs. bulge mass relation is Mblack=0.0025Mbulge, while the standard assumption of purely random broad-line velocities leads to Mblack=0.0008Mbulge. The normalization of Mblack=0.0025Mbulge provided by the disc model is in remarkably good agreement with that inferred for our quasar sample using the (completely independent) Mblack-sigma correlations.

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arXiv2001

A NICMOS imaging study of high-z quasar host galaxies

We present the first results from a major Hubble Space Telescope program 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 radio-loud 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 rest-frame spectrum, avoiding potential contamination by [OIII]lambda5007 and H-alpha emission lines. At z=1 the hosts of both radio-loud and radio-quiet quasars lie on the same Kormendy relation described by 3CR radio galaxies at comparable redshift. There is some evidence for a gap of ~1 mag between the host luminosities of RLQs and RQQs, a difference that cannot be due to emission-line contamination given the design of our study. However, within current uncertainties, simple passive stellar evolution is sufficient to link these galaxies with the elliptical hosts of low-redshift quasars of comparable nuclear output, implying that the hosts are virtually fully assembled by z=1. At z=2 the luminosity gap appears to have widened further to ~1.5 mag. Thus while the hosts of radio-loud quasars remain consistent with a formation epoch of z>3, allowing for passive evolution implies that the hosts of radio-quiet quasars are ~2-4 times less massive at z=2 than at low z.

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arXiv2001

The radio-loudness dichotomy: environment or black-hole mass?

The results of a comprehensive study of the cluster environments and black-hole masses of an optically matched sample of radio-loud and radio-quiet quasars are presented. No evidence is found for a difference in large-scale environments, with both quasar classes found to be located in clusters of Abell class $\sim0$ . Conversely, virial black-hole mass estimates based on H$_β$ line-widths show a clear difference in the quasar black-hole mass distributions. Our results suggest that a black-hole mass of $\sim10^{9}\Msolar$ is required to produce a powerful radio-loud quasar, and that it is black-hole mass and accretion rate which hold the key to the radio-loudness dichotomy.

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arXiv2000

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 optimised for this analysis. 2 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 chi-squared 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 9 quasars. The derived average K-band absolute K-corrected host galaxy magnitude for these luminous radio-quiet quasars is =-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 but others appear to have disk-dominated profiles.

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arXiv2000

Two-Dimensional Modelling of Optical HST and Infrared Tip-Tilt Images of Quasar Host Galaxies

A description is given of the method used to extract quasar host-galaxy parameters from the deep Hubble Space Telescope quasar images presented by McLure et al. (1999) and Dunlop et al. (2000). We then give the results of extensive testing of this technique on a wide range of simulated quasar+host combinations spanning the redshift range of our HST study (0.1 < z < 0.3). These simulations demonstrate that, when applied to our deep HST images, our method of analysis can easily distinguish the morphological type of a given host galaxy, as well as determining its scalelength, luminosity, axial ratio and position angle to within an accuracy of a few percent. We also present new infrared tip-tilt images of 4 of the most luminous quasars in our {\sc hst} sample, along with the outcome of modelling these data in a similar manner. The results provide further confidence in the accuracy of the derived host-galaxy scalelengths, and allow accurate determination of $R-K$ colours for this subset of sources. All 4 of these quasar host galaxies have very similar red colours, $R-K = 2.9 \pm 0.2$, indicative of a well-evolved stellar population.

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arXiv2000

The cluster environments of powerful radio-loud and radio-quiet AGN

The spatial clustering amplitude (B_{gq}) is determined for a sample of 44 powerful AGN at z~0.2. No significant difference is detected in the richness of the cluster environments of the radio-loud and radio-quiet sub-samples, both of which typically inhabit environments as rich as Abell Class ~0. Comparison with radio luminosity-matched samples from Hill & Lilly (1991) and Wold et al. (2000a) suggests that there is no epoch-dependent change in environment richness out to at least z>=0.5 for either radio galaxies or radio quasars. Comparison with the APM cluster survey shows that, contrary to current folklore, powerful AGN do not avoid rich clusters, but rather display a spread in cluster environment which is perfectly consistent with being drawn at random from the massive elliptical population. Finally, we argue that virtually all Abell class ~0 clusters contained an active galaxy during the epoch of peak quasar activity at z~2.5.

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arXiv2000

The Evolution of 3CR Radio Galaxies from z=1

We present the results of a comprehensive re-analysis of the images of a virtually complete sample of 28 powerful 3CR radio galaxies with redshifts 0.6<z<1.8 from the HST archive. Using a two-dimensional modelling technique we have derived scalelengths and absolute magnitudes for a total of 16 3CR galaxies with a median redshift of z=0.8. Our results confirm the basic conclusions of Best, Longair & Röttgering (1997, 1998) in that we also find z=1 3CR galaxies to be massive, well-evolved ellipticals, whose infrared emission is dominated by starlight. However, we in fact find that the scalelength distribution of 3CR galaxies at z \simeq 1 is completely indistinguishable from that derived for their low-redshift counterparts from our own recently-completed HST study of AGN hosts at z \simeq 0.2. There is thus no evidence that 3CR radio galaxies at z \simeq 1 are dynamically different from 3CR galaxies at low redshift. Moreover, for a 10-object sub-sample we have determined the galaxy parameters with sufficient accuracy to demonstrate, for the first time, that the z \simeq 1 3CR galaxies follow a Kormendy relation which is indistinguishable from that displayed by low-redshift ellipticals if one allows for purely passive evolution. The implied rather modest level of passive evolution since z \simeq 1 is consistent with that predicted from spectrophotometric models provided one assumes a high formation redshift (z \ge 4) within a low-density Universe. We conclude that there is no convincing evidence for significant dynamical evolution among 3CR galaxies in the redshift interval 0<z<1, and that simple passive evolution remains an acceptable interpretation of the K-z relation for powerful radio galaxies.

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arXiv1998

A comparative HST imaging study of the host galaxies of radio-quiet quasars, radio-loud quasars and radio galaxies: Paper 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 which 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 the the 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. (1998). 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 percent 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. (1998), and the resulting implications for the physical origin of radio loudness.

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