M. J. Hardcastle

The Herschel ATLAS

The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 570 deg2 of the extragalactic sky, 4 times larger than all the other Herschel extragalactic surveys combined, in five far-infrared and submillimeter bands. We describe the survey, the complementary multiwavelength data sets that will be combined with the Herschel data, and the six major science programs we are undertaking. Using new models based on a previous submillimeter survey of galaxies, we present predictions of the properties of the ATLAS sources in other wave bands.

Hot and cold gas accretion and feedback in radio-loud active galaxies

We have recently shown that X-ray observations of the population of ‘low-excitation’ radio galaxies, which includes most low-power, Fanaroff‐Riley class I sources as well as some more powerful Fanaroff‐Riley class II objects, are consistent with a model in which the active nuclei of these objects are not radiatively efficient at any waveband. In another recent paper, Allen et al. have shown that Bondi accretion of the hot, X-ray emitting phase of the intergalactic medium (IGM) is sufficient to power the jets of several nearby, low-power radio galaxies at the centres of clusters. In this paper, we combine these ideas and suggest that accretion of the hot phase of the IGM is sufficient to power all low-excitation radio sources, while high-excitation sources are powered by accretion of cold gas that is in general unrelated to the hot IGM. This model explains a number of properties of the radio-loud active galaxy population, and has important implications for the energy input of radio-loud active galactic nuclei into the hot phase of the IGM: the energy supply of powerful high-excitation sources does not have a direct connection to the hot phase.

An X-Ray Study of Magnetic Field Strengths and Particle Content in the Lobes of FR II Radio Sources

We present a Chandra and XMM-Newton study of X-ray emission from the lobes of 33 classical double radio galaxies and quasars. We report new detections of lobe-related X-ray emission in 11 sources. Together with previous detections, we find that X-ray emission is detected from at least one radio lobe in � 75% of the sample. For all of the lobe detections, we find that the measured X-ray flux can be attributed to inverse Compton scattering of the cosmic microwave background radiation, with magnetic field strengths in the lobes between 0.3Beq and 1.3Beq, where the value Beq corresponds to equipartition between the electrons and magnetic field, assuming a filling factor of unity. ThereisastrongpeakinthemagneticfieldstrengthdistributionatB � 0:7Beq.Wefindthatmorethan70%oftheradio lobes are either at equipartition or electron dominated by a small factor. The distribution of measured magnetic field strengthsdiffersfornarrow-andbroad-lineobjects,inthesensethatbroad-lineradiogalaxiesandquasarsappeartobe further from equipartition; however,thisislikelytobeduetoacombinationofprojectioneffectsandworsesystematic uncertainty in the X-ray analysis for those objects. Our results suggest that the lobes of classical double radio sources do not contain an energetically dominant proton population, because this would require the magnetic field energy density to be similar to the electron energy density rather than the overall energy density in relativistic particles. Subject headings: galaxies: active — quasars: general — radiation mechanisms: nonthermal — X-rays: galaxies Online material: color figure

Chandra and Xmm-Newton observations of a sample of low-redshift FR I and FR II radio galaxy nuclei

We present spectral results from Chandra and XMM-Newton observations of a sample of 22 low-redshift (z < 0.1) radio galaxies and consider whether the core emission originates from the base of a relativistic jet, or an accretion flow, or contains contributions from both. We find correlations between the unabsorbed X-ray, radio, and optical fluxes and luminosities of FR I-type radio-galaxy cores, implying a common origin in the form of a jet. On the other hand, we find that the X-ray spectra of FR II-type radio galaxy cores are dominated by absorbed emission, with NH 1023 atoms cm-2, which is likely to originate in an accretion flow. We discuss several models that may account for the different nuclear properties of FR I- and FR II-type cores and also demonstrate that both heavily obscured, accretion-related and unobscured, jet-related components may be present in all radio galaxy nuclei. Any absorbed, accretion-related components in FR I-type galaxies have low radiative efficiencies.

The X-ray nuclei of intermediate-redshift radio sources

We present a Chandra and XMM-Newtonspectral analysis of the nuclei of the radio galaxies and radio-loud quasars from the 3CRR sample in the redshift range 0.1 < z < 0.5. In the range of radio luminosity sampled by these objects, mostly FRIIs, it has been clear for some time that a population of radio galaxies (‘low-excitation radio galaxies’) cannot easily participate in models that unify narrow-line radio galaxie s and broad-line objects. We show that low-excitation and narrow-line radio galaxies have systematically different nuclear Xray properties: while narrow-line radio galaxies universa lly show a heavily absorbed nuclear X-ray component, such a heavily absorbed component is rarely found in sources classed as low-excitation objects. Combining our data with the results of our earlier work on the z < 0.1 3CRR sources, we discuss the implications of this result for unified models, for the origins of mid-infrared emission from radio sources, and for the nature of the apparent FRI/FRII dichotomy in the X-ray. The lack of direct evidence for accretion-related X-ray emission in FRII LERGs leads us to argue that there is a strong possibility that some, or most, FRII LERGs accrete in a radiatively inefficient mode. However, our result s are also consistent with a model in which the accretion mode is the same for low- and high-excitation FRIIs, with the lower accretion luminosities in FRII LERGs attributed instead to more efficient radio luminosity production in those objects.

Radio and X-Ray Observations of the Jet in Centaurus A

We present new, high dynamic range VLA images of the inner jet of the closest radio galaxy, Centaurus A. Over a 10 yr baseline we detect apparent subluminal motions (v � 0:5c) in the jet on scales of hundreds of parsecs. The inferred speeds are larger than those previously determined using VLBI on smaller scales and provide new constraints on the angle made by the jet to the line of sight if we assume jet-counterjet symmetry. The new images also allow us to detect faint radio counterparts to a number of previously unidentified X-ray knots in the inner part of the jet and counterjet, showing conclusively that these X-ray features are genuinely associated with the outflow. However, we find that the knots with the highest X-ray/radio flux density ratios do not have detectable proper motions, suggesting that they may be related to standing shocks in the jet; we consider some possible internal obstacles that the jet may encounter. Using new, high-resolution Chandra data, we discuss the radio to X-ray spectra of the jet and the discrete features that it contains, and we argue that the compact radio and X-ray knots are privileged sites for the in situ particle acceleration that must be taking place throughout the jet. We show that the offsets observed between the peaks of the radio and X-ray emission at several places in the Cen A jet are not compatible with the simplest possible models involving particle acceleration and downstream advection together with synchrotron and expansion losses. Subject headings: galaxies: active — galaxies: individual (Centaurus A, NGC 5128) — galaxies: nuclei — radio continuum: galaxies — X-rays: galaxies

The active nuclei of z < 1.0 3CRR radio sources

We combine Chandraand XMM-NewtonX-ray data from our previous papers with new X-ray observations and with Spitzer mid-infrared data in order to study the nature of the nuclei o f radio galaxies and radio-loud quasars with z < 1.0 from the 3CRR sample. The significant increase in sample size over our previous work, the reduction of bias in the sample as a result of new observations, and the availability of more mid-infrared data allow us to show conclusively that almost all objects classed as low-excitation ra dio galaxies in optical spectroscopic studies lack a radiatively efficient active nucleus. We show that the distribution of absorbing columns in the narrow-line radio galaxies differs from the population of X-ray-selected radioquiet type-2 quasars and from that in local Seyfert 2s. We comment on the current evidence for the nature of the soft X-ray component in radio-galaxy nuclear spectra, concluding that a jet origin for this component is very hard to evade. Finally, we discuss the recently discovered ‘fundamental plane’ of black hole activity, showing th at care must be taken when placing radio-loud AGN on such diagnostic diagrams.

X-RAY EMISSION FROM THE HOT INTERSTELLAR MEDIUM AND SOUTHWEST RADIO LOBE OF THE NEARBY RADIO GALAXY CENTAURUS A

We present results from two Chandra/ACIS-I observations and one XMM-Newton observation of X-ray emission from the interstellar medium (ISM) and the inner radio lobes of the nearby radio galaxy Centaurus A. The ISM has an average radial surface brightness profile that is well described by a � -model profile with index � ¼ 0:40 � 0:04 and a temperature of kBTISM � 0:29 keV beyond 2 kpc from the nucleus. We find that diffuse X-ray emission is coincident with the outer half of the southwest radio lobe, and a bright X-ray enhancement is detected along the edge of the lobe. On the basis of energetic and lifetime arguments, we reject a nonthermal explanation for this emission. We model this emission as a thin, hot shell or cap of X-ray– emitting plasma surrounding the radio lobe that was created by the supersonic inflation of the lobe. This plasma shell is both hotter than (kBTSH � 2:9 keV) and greatly overpressurized relative to the ambient ISM, indicating supersonic expansion. We estimate that the lobe is expanding into the ISM at approximately Mach 8.5, or 2400 km s � 1 . We are not directly observing the bow shock, but rather the cooler, denser material that is accumulating ahead of the contact discontinuity. The thermal energy in the shell is a significant fraction of the thermal energy of the hot ISM, demonstrating the possibility that the hot ISM of early galaxies can be reenergized by outflows from nuclear activity. Interestingly, no similarly bright X-ray emission is detected in or along the edge of the northeast lobe, implying that there are differences in the dynamics and evolution of the kiloparsec-scale radio components. Subject headings: galaxies: active — galaxies: individual (Centaurus A, NGC 5128) — galaxies: ISM — galaxies: jets — radio continuum: galaxies — X-rays: galaxies On-line material: color figures

A Chandra observation of the X-ray environment and jet of 3C 31

We have observed the twin-jet radio galaxy 3C 296 with Chandra. X-ray emission is detected from the nucleus, from the inner parts of the radio jet and from a small-scale thermal environment around the jet deceleration region. As we have found in previous observations of other twin-jet radio galaxies, the X-ray jet and a steep pressure gradient in the external thermal environment are associated with the region where strong bulk deceleration of the jet material is suggested by radio observations. Our observations provide additional evidence that the inner jets of twin-jet objects are always associated with a relatively cool, dense central X-ray emitting component with a short cooling time.

ROSAT X-ray observations of 3CRR radio sources

Over half the 3CRR sample of radio galaxies and quasars has been observed in X-rays with ROSAT pointed observations, and we present results from these observations, discussing many of the sources in detail. The improved spatial resolution of ROSAT over earlier missions allows a better separation of the nuclear and extended components of the X-ray emission. We investigate the relationship between nuclear X-ray and core radio luminosity and show that our results support a model in which every radio galaxy and quasar has a beamed nuclear soft X-ray component directly related to the radio core. We report evidence for rich cluster environments around several powerful quasars. These X-ray environments are comparable to those of high-redshift radio galaxies.