Christopher P. O'Dea

The Compact Steep-Spectrum and Gigahertz Peaked-Spectrum Radio Sources

I review the radio to X-ray properties of gigahertz peaked-spectrum (GPS) and compact steep- spectrum (CSS) sources, the current hypotheses for their origin, and their use to constrain the evolution of powerful radio galaxies. The GPS and CSS sources are compact, powerful radio sources with well-defined peaks in their radio spectra (near 1 GHz in the GPS and near 100 MHz in the CSS). The GPS sources are entirely contained within the extent of the narrow-line region (&1 kpc), while the CSS sources are contained entirely within the host galaxy (&15 kpc). The peaks in the spectra are probably due to synchrotron self-absorption, though free-free absorption through an inhomogeneous screen may also play a role. The turnover frequency varies with linear size l as , suggesting a simple physical relationship between these parameters. The radio 20.65 n / l m morphologies are strikingly like those of the large-scale classical doubles, though some sources can have very distorted morphologies suggestive of interactions. Radio polarization tends to be low, and in some cases the Faraday rotation measures can be extremely large. The IR properties are consistent with stellar populations and active galactic nucleus (AGN) bolometric luminosity similar to that of the 3CR classical doubles. The optical host galaxy properties (absolute magnitude, Hubble diagram, evidence for interaction) are consistent with those of the 3CR classical doubles. CSS sources at all redshifts exhibit high surface brightness optical light (most likely emission-line gas) that is aligned with the radio axis. The optical emission-line properties suggest (1) interaction of the radio source with the emission-line gas and (2) the presence of dust toward the emission-line regions. X- ray observations of high-redshift GPS quasars and a couple of GPS galaxies suggest the presence of significant columns of gas toward the nuclei. Searches for cold gas in the host galaxies have revealed large amounts of molecular gas and smaller amounts of atomic gas in several sources, though probably not enough to confine the radio sources. The main competing models for the GPS and CSS sources are that (1) they are frustrated by interaction with dense gas in their environments and (2) they are young and evolving radio sources that will become large-scale sources. Combining the bright GPS and CSS samples with the 3CR results in a sample spanning a range in source size of 10 5 that can be used to study source evolution. The number density versus linear size relation is consistent with a picture in which the sources expand with constant velocity and the radio power drops with linear size l according to . This strong evolution suggests that at least some of the 20.5 P / l GPS and CSS sources evolve to become lower luminosity FR 1 radio sources. The GPS and CSS sources are important probes of their host galaxies and will provide critical clues to the origin and evolution of powerful radio sources.

Quasars, their host galaxies and their central black holes

We present the final results from our deep Hubble Space Telescope (HST) imaging study of the host galaxies of radio-quiet quasars (RQQs), radio-loud quasars (RLQs) and radio galaxies (RGs). We describe and analyse new Wide Field & Planetary Camera 2 (WFPC2) R-band observations for 14 objects, which when combined with the first tranche of HST imaging reported in McLure et al., provide a complete and consistent set of deep, red, line-free images for statistically matched 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 that has yielded a 5-GHz detection of all but one of the 33 active galactic nuclei (AGN) in our sample. Careful modelling of our images, aided by a high dynamic-range point spread function, has allowed us to determine accurately the morphology, luminosity, scalelength and axial ratio of every host galaxy in our sample. Armed with this information we have undertaken a detailed comparison of the properties of the hosts of these three types of powerful AGN, both internally and with the galaxy population in general. We find that spheroidal hosts become more prevalent with increasing nuclear luminosity such that, for nuclear luminosities MV < −23.5, the hosts of both radio-loud and radio-quiet AGN are virtually all massive ellipticals. Moreover, we demonstrate that the basic properties of these hosts are indistinguishable from those of quiescent, evolved, low-redshift ellipticals of comparable mass. This result rules out the possibility that radio-loudness is determined by host-galaxy morphology, and also sets severe constraints on evolutionary schemes that attempt to link low-z ultraluminous infrared galaxies with RQQs. Instead, we show that our results are as expected given the relationship between black hole and spheroid mass established for nearby galaxies, and apply this relation to estimate the mass of the black hole in each object. The results agree remarkably well with completely independent estimates based on nuclear emission-line widths; all the quasars in our sample have Mbh > 5 × 108 M⊙, while the radio-loud objects are confined to Mbh > 109 M⊙. This apparent mass-threshold difference, which provides a natural explanation for why RQQs outnumber RLQs by a factor of 10, appears to reflect the existence of a minimum and a maximum level of black hole radio output, which is a strong function of black hole mass (∝M2−2.5bh). Finally, we use our results to estimate the fraction of massive spheroids/black holes that produce quasar-level activity. This fraction is ≃0.1 per cent at the present day, rising to >10 per cent at z≃ 2–3.

UNIFICATION OF THE RADIO AND OPTICAL PROPERTIES OF GIGAHERTZ PEAK SPECTRUM AND COMPACT STEEP-SPECTRUM RADIO SOURCES

We adopt the view that the classes of active galactic nuclei (AGN) known variously as gigahertz peak spectrum (GPS) sources, compact steep-spectrum (CSS) sources, and compact symmetric objects (CSO) generally represent the same sort of object and show that both their radio spectra and optical emission can be explained by a single model which incorporates the e†ects produced by the interaction of a jet- driven nonthermal lobe with a dense interstellar medium. Following Begelman, we assume that these sources are young AGNs yr) in which the jets are propagating through an interstellar (ages ( 106 medium in which the hydrogen number density, decreases as a power law with radius, with the index n H dB 1 E2 and cm~3 at 1 kpc. The bow shock preceding the radio lobe is radiative at early n H D 10E100 times in such a dense environment, and the optical line emission produced by the shocked ISM and the associated photoionized precursor is proportional to the monochromatic radio power, consistent with the observational data of Gelderman & Whittle. The ionized gas surrounding the lobes has a signi-cant emission measure and a correspondingly high free-free opacity which is responsible for the 0.1E1 GHz peaks in the radio spectra. For jet energy Nuxes D1045E1046 ergs s~1, consistent with the observed radio powers of these objects, the crucial observed anticorrelation between peak frequency and size is readily recovered. The form of the radio spectra (power laws at high and low frequencies) indicate that the absorption is due to a cloudy/-lamentary medium with an approximately uniform distribution of opa- cities resulting from a combination of a two-phase interstellar medium, shock shredding of clouds impacted by the bow shock and thermal instabilities in the shocked ISM. The ionized medium envelop- ing the radio source also forms a Faraday screen which produces high rotation measure and substantial depolarization, readily accounting for another key property of this class of AGNs. Subject headings: radio continuum: galaxies

What are the gigahertz peaked-spectrum radio sources?

The astrophysical implications of recent radio and optical observations of the powerful compact gigahertz peaked-spectrum (GPS) radio sources are discussed. Some tentative conclusions are presented and a scenario based on the existing data is suggested. It is argued that the spectrum is due to synchrotron self-absorption, which is assumed as the basis for the present inferences from the radio spectral shape. The finding that some GPS sources have a very narrow spectral shape is consistent with the hypothesis that there is a narrow range of size scales which dominate the radio luminosity. The highly inverted LF radio spectrum is consistent with the hypothesis that the radio source is tightly confined. The conclusion that the radio polarization of these sources is systematically low is consistent either with a very tangled magnetic field or very large Faraday rotation measures. It is suggested that GPS radio sources are formed when the radio plasma is confined on the scale of the narrow-line region by an unusually dense and clumpy ISM. The existing optical spectroscopic results are also consistent with the existence of a dense and dusty nuclear ISM.

A complete sample of GHz-peaked-spectrum radio sources and its radio properties

We dene a complete sample of thirty-three GHz-Peaked-Spectrum (GPS) radio sources based on their spectral properties. We present measurements of the radio spectra and polarization of the complete sample and a list of additional GPS sources which fail one or more criteria to be included in the complete sample. The majority of the data have been obtained from quasi-simultaneous multi-frequency observations at the Very Large Array (VLA) during 3 observing sessions. Low frequency data from the Westerbork Synthesis Radio Telescope (WSRT) and from the literature have been com- bined with the VLA data in order to better dene the spectral shape. The objects presented here show a rather wide range of spectral indices at high and low frequencies, including a few cases where the spectral index below the turnover is close to the theoretical value of 2.5 typical of self-absorbed incoherent synchrotron emission. Faint and diuse ex- tended emission is found in about 10% of the sources. In the majority of the GPS sources, the fractional po- larization is found to be very low, consistent with the residual instrumental polarization of 0.3% 1 .

The host galaxies of luminous quasars

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 ≥ M V ≥ - 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 M V < -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 M BH ≃ 3 x 10 9 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/L Edd < 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 M V = -27 should be found in massive elliptical hosts, which at the present day would have M V ≃ -24.5.

A NICMOS imaging study of high-z quasar host galaxies

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 radio- loud and radio-quiet quasars, selected to lie within the same narrow range of optical absolute magnitude (−24 ≥ MV ≥ −25). Filter and target selection were designed to ensure that at each redshift the images sample the same part of the objects rest- frame spectrum, longwards of 4000u where starlight from the host galaxy is relatively prominent, but avoiding potential contamination by (Oiii)�5007 and Hemission lines. At z ≃ 1 we have been able to establish host-galaxy luminosities and scalelengths with sufficient accuracy to demonstrate that the hosts of bothradio-loud and radio- quiet quasars lie on the same Kormendy relation described by 3CR radio galaxies at comparable redshift (McLure & Dunlop 2000). Taken at face value the gap between the host luminosities of radio-loud and radio-quiet objects appears to have widened from only ≃ 0.4 mag. at z ≃ 0.2 (Dunlop et al. 2001) to ≃ 1 mag. at z ≃ 1, 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 hosts have proved harder to characterise accurately, and for only two of the nine z ≃ 2 quasars observed has it proved possible to properly constrain the scalelength of the host galaxy. However, the data are of sufficient quality to yield host- galaxy luminosities accurate to within a factor ≃ 2. At this redshift the luminosity gap between radio-loud and radio-quiet quasars 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 z ≃ 0.2. If the relationship between black-hole and spheroid mass is unchanged out to redshift z ≃ 2, then our results rule out any model of quasar evolution which involves a substantial component of luminosity evolution (e.g. Kauffmann & Haehnelt 2000). Rather, this study indicates that at z ≃ 2 there is a substantial increase in the number density of active black holes, along with a moderate increase in the fueling efficiency of a typical observed quasar. The fact that this latter effect is not displayed by the radio-loud objects in our sample might be explained by a selection effect arising from the fact that powerful radio sources are only produced by the most massive black holes (Dunlop et al. 2001; McLure & Dunlop 2000b).

Observations of H i absorbing gas in compact radio sources at cosmological redshifts

We present an overview of the occurrence and properties of atomic gas associated with compact radio sources at redshifts up to z = 0.85. Searches for H i 21cm absorption were made with the Westerbork Synthesis Radio Telescope at UHF-high frequencies (725-1200 MHz). Detections were obtained for 19 of the 57 sources with usable spectra (33%). We have found a large range in line depths, from � = 0.16 to � � 0.001. There is a substantial variety of line profiles, including Gaussians of less than 10kms 1 , to more typically 150kms 1 , as well as irregular and multi-peaked absorption profiles, sometimes spanning several hundred kms 1 . Assuming uniform coverage of the entire radio source, we obtain column depths of atomic gas between 1×10 19 and 3.3×10 21 (Tsp/100 K)(1/f) cm 2 . There is evidence for significant gas motions, but in contrast to earlier results at low redshift, there are many sources in which the H i velocity is substantially negative (up to v = 1420kms 1 ) with respect to the optical redshift, suggesting that in these sources the atomic gas, rather than falling into the centre, may be be flowing out, interacting with the jets, or rotating around the nucleus.

H 2O and OH Masers as Probes of the Obscuring Torus in NGC 1068

Original article can be found at: http://adsabs.harvard.edu/abs/ Copyright American Astronomical Society. DOI: 10.1086/177187 [Full text of this article is not available in the UHRA]

Kiloparsec-scale radio emission in Seyfert galaxies : evidence for starburst-driven superwinds ?

We report the results of a pilot program to search for kiloparsec-scale radio emission in 13 Seyfert galaxies, using the Westerbork Synthesis Radio Telescope. While it has been known for some time now that Seyfert galaxies generally contain nuclear, subkiloparsec-scale radio sources, this is the first systematic attempt to image larger scale radio emission in Seyfert galaxies. These observations reveal the presence of kiloparsecscale, diffuse, sometimes bubble-like radio emission in 12 of these sources. This large-scale, extra-nuclear radio emission is randomly oriented with respect to the small-scale nuclear radio source axis but tends to align with the minor axis of the host galaxy disk