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The object 4C 71.07 is a high-redshift blazar whose spectral energy distribution shows a prominent big blue bump and a strong Compton dominance. We present the results of a 2-yr multiwavelength campaign led by the Whole Earth Blazar Telescope (WEBT) to study both the quasar core and the beamed jet of this source. The WEBT data are complemented by ultraviolet and X-ray data from Swift , and by γ-ray data by Fermi. The big blue bump is modelled by using optical and near-infrared mean spectra obtained during the campaign, together with optical and ultraviolet quasar templates. We give prescriptions to correct the source photometry in the various bands for the thermal contribution, in order to derive the non-thermal jet flux. The role of the intergalactic medium absorption is analysed in both the ultraviolet and X-ray bands. We provide opacity values to deabsorb ultraviolet data, and derive a best-guess value for the hydrogen column density of |$N_{\rm H}^{\rm best}=6.3 \times 10^{20} \rm \, cm^{-2}$| through the analysis of X-ray spectra. We estimate the disc and jet bolometric luminosities, accretion rate, and black hole mass. Light curves do not show persistent correlations among flux changes at different frequencies. We study the polarimetric behaviour and find no correlation between polarization degree and flux, even when correcting for the dilution effect of the big blue bump. Similarly, wide rotations of the electric vector polarization angle do not seem to be connected with the source activity. [ABSTRACT FROM AUTHOR]

We present the 1–100 GeV spectral energy distribution (SED) for a population of 148 high-synchrotron-peaked (HSP) blazars recently detected with Fermi -LAT as part of the First Brazil-ICRANet Gamma-ray Blazar (1BIGB) catalogue. Most of the 1BIGB sources have their γ-ray spectral properties presented here for the first time, representing a significant new extension of the γ-ray blazar population. Since our sample was originally selected from an excess signal in the 0.3–500 GeV band, the sources stand out as promising TeV blazar candidates, potentially in reach of the forthcoming very high energy (VHE) γ-ray observatory, Cherenkov Telescope Array (CTA). The flux estimates presented here are derived considering PASS8 data, integrating over more than 9 yr of Fermi -LAT observations. We also review the full broad-band fit between 0.3 and 500 GeV presented in the original 1BIGB paper for all sources, updating the power-law parameters with currently available Fermi -LAT data set. The importance of these sources in the context of VHE population studies with both current instruments and the future CTA is evaluated. To do so, we select a subsample of 1BIGB sources and extrapolate their γ-ray SEDs to the highest energies, properly accounting for absorption due to the extragalactic background light. We compare those extrapolations to the published CTA sensitivity curves and estimate their detectability by CTA. Two notable sources from our sample, namely 1BIGB J224910.6 − 130002 and 1BIGB J194356.2+211821, are discussed in greater detail. All γ-ray SEDs are made publicly available via the Brazilian Science Data Center (BSDC) service, maintained at CBPF, in Rio de Janeiro. [ABSTRACT FROM AUTHOR]

Blazar PKS 2155–304 is one of the sources that has been well monitored under the SMARTS (Small Moderate Aperture Research Telescope System) project. SMARTS light curves in the BVRJK bands and spectral indices connecting the B with the J band of PKS 2155–304 from 2008 to 2015 are presented at near-nightly cadence, and divided into a number of segments without long observational gaps for comparison investigations on shorter time-scales. The optical and near-infrared (NIR) variations are simultaneous, with time lags of no longer than a couple of days, which suggests a temporal coherence of the corresponding jet-emitting regions. Long- and short-term optical–NIR variability shows that optical bands are fainter and vary less than the IR bands, while fractional variability amplitudes show no clear trend on long-term time-scales and in segments of light curves, probably owing to effects from stochastic processes. The prominent flares presented in the optical–NIR light curves tend to show an asymmetric feature with different rise and decay time-scales. The spectral indices varied on diverse time-scales, and the source showed no clear trend on long-term time-scales, an occasional appearance of tendencies of flatter-when-brighter on short-term time-scales, and an independent clockwise evolving loop pattern, suggesting a complex spectral evolution with the flux. [ABSTRACT FROM AUTHOR]

We present quasar bolometric corrections using the [OIII]λ5007 narrow emission line luminosity based on the detailed spectral energy distributions of 53 bright quasars at low to moderate redshift (0.0345 < z < 1.0002). We adopted two functional forms to calculate Liso, the bolometric luminosity determined under the assumption of isotropy: Liso=AL[OIII] for comparison with the literature and log(Liso)=B+Clog(L[OIII]), which better characterizes the data. We also explored whether 'Eigenvector 1 (EV1)', which describes the range of quasar spectral properties and quantifies their diversity, introduces scatter into the L[OIII] -Liso relationship. We found that the [OIII] bolometric correction can be significantly improved by adding a term including the equivalent width ratio RFeII ≡EWFeII/EWHβ, which is an EV1 indicator. Inclusion of RFeII in predicting Liso is significant at nearly the 3σ level and reduces the scatter and systematic offset of the luminosity residuals. Typically, [OIII] bolometric corrections are adopted for Type 2 sources where the quasar continuum is not observed and in these cases, RFeII cannot be measured. We searched for an alternative measure of EV1 that could be measured in the optical spectra of Type 2 sources but were unable to identify one. Thus, the main contribution of this work is to present an improved [OIII] bolometric correction based on measured bolometric luminosities and highlight the EV1 dependence of the correction in Type 1 sources. [ABSTRACT FROM AUTHOR]

In an effort to understand the cause of the apparent depletion in the number density of radio-loud active galactic nuclei (AGNs) at z > 3, this work investigates the viability of the so-called cosmic microwave background (CMB) quenching mechanism of intrinsically jetted, high-z AGNs, whereby inverse Compton scattering of CMB photons off electrons within the extended lobes results in a substantial dimming of the lobe synchrotron emission at GHz frequencies, while simultaneously boosting their diffuse X-ray signal. We focus on five z > 3.5 radio galaxies that have sufficiently deep Chandra exposure (>50 ks) to warrant a meaningful investigation of any extended X-ray emission. For those objects with evidence for statistically significant extended X-ray lobes (4C 41.17 and 4C 03.24), we combine the Chandra measurements with literature data at lower frequencies to assemble the systems' spectral energy distributions (SEDs), and utilize state-of-the-art SED modelling - including emission from the disc, torus, jet, hotspots and lobes - to infer their physical parameters. For both radio galaxies, the magnetic energy density in the hotspots is found to exceed the energy density in CMB photons, whereas the opposite is true for the lobes. This implies that any extended synchrotron emission likely originates from the hotspots themselves, rather than the lobes. Conversely, inverse Compton scattering of CMB photons dominates the extended X-ray emission from the lobes, which are effectively 'radio-quenched'. As a result, CMB quenching is effective in these systems in spite of the fact that the observed X-ray to radio luminosity ratio does not bear the signature (1 + z)4 dependence of the CMB energy density. [ABSTRACT FROM AUTHOR]

We derive constraints on feedback by active galactic nuclei (AGN) by setting limits on their thermal Sunyaev-Zel'dovich (SZ) imprint on the cosmic microwave background. The amplitude of any SZ signature is small and degenerate with the poorly known sub-mm spectral energy distribution of theAGNhost galaxy and other unresolved dusty sources along the line of sight. Here we break this degeneracy by combining microwave and sub-mm data from Planck with all-sky far-infraredmaps from the AKARI satellite. We first test our measurement pipeline using the Sloan Digital Sky Survey (SDSS) redMaPPer catalogue of galaxy clusters, finding a highly significant detection (>20σ) of the SZ effect together with correlated dust emission. We then constrain the SZ signal associated with spectroscopically confirmed quasi-stellar objects (QSOs) from SDSS data release 7 (DR7) and the Baryon Oscillation Spectroscopic Survey (BOSS) DR12. We obtain a low-significance (1.6σ) hint of an SZ signal, pointing towards a mean thermal energy of≃5 × 1060 erg, lower than reported in some previous studies. A comparison of our results with high-resolution hydrodynamical simulations including AGN feedback suggests QSO host masses ofM200c ∼ 4 × 1012 h-1M☉, but with a large uncertainty. Our analysis provides no conclusive evidence for an SZ signal specifically associated with AGN feedback. [ABSTRACT FROM AUTHOR]

The XXL survey currently covers two 25 deg2 patches with XMM observations of ~10 ks. We summarize the scientific results associated with the first release of the XXL dataset, which occurred in mid-2016.We review several arguments for increasing the survey depth to 40 ks during the next decade of XMM operations. X-ray (z<2) cluster, (z<4) active galactic nuclei (AGN), and cosmic background survey science will then benefit from an extraordinary data reservoir. This, combined with deep multi-observations, will lead to solid standalone cosmological constraints and provide a wealth of information on the formation and evolution of AGN, clusters, and the X-ray background. In particular, it will offer a unique opportunity to pinpoint the z>1 cluster density. It will eventually constitute a reference study and an ideal calibration field for the upcoming eROSITA and Euclid missions. [ABSTRACT FROM AUTHOR]

We present high-angular (0.17-0.35 arcsec) resolution imaging polarimetric observations of Mrk 231 in the 3.1 μm filter using MMT-Pol on the 6.5-m MMT, and in the 8.7, 10.3, and 11.6 μm filters using CanariCam on the 10.4-m Gran Telescopio CANARIAS. In combination with already published observations, we compile the 1-12 μm total and polarized nuclear spectral energy distribution (SED). The total flux SED in the central 400 pc is explained as the combination of (1) a hot (731 ± 4 K) dusty structure, directly irradiated by the central engine, which is at 1.6 ± 0.1 pc away and attributed to be in the pc-scale polar region, (2) an optically-thick, smooth and disc-like dusty structure ('torus') with an inclination of 48° ± 23° surrounding the central engine, and (3) an extinguished (AV = 36 ± 5 mag) starburst component. The polarized SED decreases from 0.77 ± 0.14 per cent at 1.2 μm to 0.31 ± 0.15 per cent at 11.6 μm and follows a power-law function, λ ~0.57. The polarization angle remains constant (~108°) in the 1-12 μm wavelength range. The dominant polarization mechanism is explained as scattering-off hot dust grains in the pc-scale polar regions. [ABSTRACT FROM AUTHOR]

A multi-epoch, multi-instrument analysis of the Seyfert 1 galaxy HE 0436-4717 is conducted using optical to X-ray data from XMM-Newton and Swift (including the Burst Alert Telescope). Fitting of the UV-to-X-ray spectral energy distribution shows little evidence of extinction and the X-ray spectral analysis does not confirm previous reports of deep absorption edges from O VIII. HE 0436-4717 is a 'bare' Seyfert with negligible line-of-sight absorption making it ideal to study the central X-ray emitting region. Three scenarios were considered to describe the X-ray data: partial covering absorption, blurred reflection, and soft Comptonization. All three interpretations describe the 0.5-10.0 keV spectra well. Extrapolating the models to 100 keV results in poorer fits for the partial covering model. When also considering the rapid variability during one of the XMM-Newton observations, the blurred reflection model appears to describe all the observations in the most self-consistent manner. If adopted, the blurred reflection model requires a very low iron abundance in HE 0436-4717. We consider the possibilities that this is an artefact of the fitting process, but it appears possible that it is intrinsic to the object. [ABSTRACT FROM AUTHOR]

We report multiple epoch VLA/JVLA observations of 89 northern hemisphere sources, most with 37 GHz flux density >1 Jy, observed at 4.8, 8.5, 33.5, and 43.3GHz. The high frequency selection leads to a predominantly flat spectrum sample, with 85% of our sources being in the Planck Early Release Compact Source Catalog (ERCSC). These observations allow us to: 1) validate Planck's 30 and 44 GHz flux density scale; 2) extend the radio spectral energy distributions of Planck sources to lower frequencies allowing for the full 5—857 GHz regime to be studied; and 3) characterize the variability of these sources. At 30 GHz and 44 GHz, the JVLA and Planck flux densities agree to within ∼3%. On timescales of less than two months the median variability of our sources is 2%. On timescales of about a year the median variability increases to 14%. Using the WMAP 7-year data, the 30 GHz median variability on a 1—6 years timescale is 16%. [ABSTRACT FROM AUTHOR]

ABSTRACT Many blazars detected by the Fermi satellite, observed spectroscopically in the optical, are line-less, and have been classified as BL Lac objects. Optical-ultraviolet (UV) photometry of nearly 100 of them allowed us to determine the redshift for a handful of objects and redshift upper limits in the great majority. A few of these are candidates to be 'blue quasars', namely flat spectrum radio quasars whose broad emission lines are hidden by an overwhelming synchrotron emission peaking in the UV. This implies that the emitting electrons have high energies. In turn, this requires relatively weak radiative cooling, a condition that can be met if the main radiative dissipation of the jet power occurs outside the broad-line region. We confirm this hypothesis by studying and modelling the spectral energy distributions of the four 'blue quasars' recently discovered. Furthermore, we discuss the distribution of Fermi blazars in the γ-ray spectral index-γ-ray luminosity plane, and argue that 'blue quasars' objects are a minority within the blazar populations. [ABSTRACT FROM AUTHOR]

Most of the extragalactic sources detected at TeV energies are BL Lac objects. They belong to the subclass of high-frequency-peaked BL Lac objects (HBLs) exhibiting spectral energy distributions with a lower energy peak in the X-ray band; this is widely interpreted as synchrotron emission from relativistic electrons. The X-ray spectra are generally curved and well described in terms of a log-parabolic shape. In a previous investigation of TeV HBLs (TBLs) we found two correlations between their spectral parameters. (1) The synchrotron peak luminosity Lp increases with its peak energy Ep and (2) the curvature parameter b decreases as Ep increases. The first is consistent with the synchrotron scenario, while the second is expected from statistical/stochastic acceleration mechanisms for the emitting electrons. Here, we present an extensive X-ray analysis of a sample of HBLs observed with XMM-Newton and Swift but undetected at TeV energies (UBLs), to compare their spectral behavior with that of TBLs. Investigating the distributions of their spectral parameters and comparing the TBL X-ray spectra with that of UBLs, we develop a criterion to select the best HBL candidates for future TeV observations. [ABSTRACT FROM AUTHOR]

To exploit synergies between the Herschel Space Observatory and next generation radio facilities, we have extended the semi-empirical extragalactic radio continuum simulation of Wilman et al. to the mid- and far-infrared. Here, we describe the assignment of infrared spectral energy distributions (SEDs) to the star-forming galaxies and active galactic nuclei, using Spitzer 24, 70 and 160 μm and SCUBA 850 μm survey results as the main constraints. Star-forming galaxies dominate the source counts, and a model in which their far-infrared–radio correlation and infrared SED assignment procedure are invariant with redshift underpredicts the observed 24 and 70 μm source counts. The 70 μm deficit can be eliminated if the star-forming galaxies undergo stronger luminosity evolution than originally assumed for the radio simulation, a requirement which may be partially ascribed to known non-linearity in the far-infrared–radio correlation at low luminosity if it evolves with redshift. At 24 μm, the shortfall is reduced if the star-forming galaxies develop SEDs with cooler dust and correspondingly stronger polycyclic aromatic hydrocarbon emission features with increasing redshift at a given far-infrared luminosity, but this trend may reverse at in order not to overproduce the submillimetre source counts. The resulting model compares favourably with recent Balloon-borne Large Aperture Submillimetre Telescope ( BLAST) results, and we have extended the simulation data base to aid the interpretation of Herschel surveys. Such comparisons may also facilitate further model refinement and revised predictions for the Square Kilometre Array and its precursors. [ABSTRACT FROM AUTHOR]

We report the analysis of near-infrared (near-IR) imaging, polarimetric and spectroscopic observations of the powerful radio galaxy 3C 433 , obtained with the Hubble Space Telescope ( HST) and the United Kingdom Infrared Telescope. The high spatial resolution of HST allows us to study the near-nuclear regions of the galaxy (<1 kpc). In line with previous observations, we find that 3C 433 has an unresolved core source that is detected in all near-IR bands, but dominates over the host galaxy emission at m. Our analysis reveals (1) the presence of a dust lane aligned close to the perpendicular [position angle ] to the inner radio jet axis , (2) a steep slope to the near-IR spectral energy distribution (SED; ), (3) an apparent lack of broad permitted emission lines at near-IR wavelengths, in particular the absence of a broad Paα emission line and (4) high intrinsic polarization for the unresolved core nuclear source , with an E-vector perpendicular to the inner radio jet. Using five independent techniques, we determine an extinction to the compact core source in the range mag. An analysis of the long wavelength SED rules out a synchrotron origin for the high near-IR polarization of the compact core source. Therefore, scattering and dichroic extinction are plausible polarizing mechanisms, although in both of these cases the broad permitted lines from the active galactic nuclei are required to have a width (full width at half-maximum) to escape detection in our near-IR spectrum. Dichroic extinction is the most likely polarization mechanism because it is consistent with the various available extinction estimates. In this case, a highly ordered, coherent toroidal magnetic field must be present in the obscuring structure close to the nucleus. [ABSTRACT FROM AUTHOR]

This paper is the second part of a work investigating the properties of dusty tori in active galactic nuclei (AGN) by means of multicomponent spectral energy distribution (SED) fitting. It focuses on low-luminosity, low-redshift AGN selected among emission line galaxies in the overlapping regions between Spitzer Wide-area Infrared Extragalactic Survey (SWIRE) and Sloan Digital Sky Survey Data Release 4 as well as X-ray, radio and mid-infrared selected type 2 AGN samples from the literature. The available multiband photometry covers the spectral range from the u band up to 160 μm. Using a standard minimization, the observed SED of each object is fit to a set of multicomponent models comprising a stellar component, a high optical depth torus and cold emission from a starburst (SB). The torus components assigned to the majority of the objects were those of the highest optical depth of our grid of models . The contribution of the various components (stars, torus, SB) is reflected in the position of the objects on the Infrared Array Camera (IRAC) colour diagram, with star-, torus- and SB-dominated objects occupying specific areas of the diagrams and composite objects lying in between. The comparison of type 1 (as derived from Hatziminaoglou et al.) and type 2 AGN properties is broadly consistent with the unified scheme. The estimated ratio between type 2 and 1 objects is about 2–2.5:1. The AGN accretion-to-infrared luminosity ratio is an indicator of the obscuration of the AGN since it scales down with the covering factor. We find evidence supporting the receding torus paradigm, with the estimated fraction of obscured AGN, derived from the distribution of the covering factor, decreasing with increasing optical luminosity over four orders of magnitude. The average star formation rates (SFRs) are of for the low- z sample, for the other type 2 AGN and for the quasars; this result however, might simply reflect observational biases, as the quasars under study were one to two orders of magnitude more luminous than the various type 2 AGN. For the large majority of objects with 70 and/or 160 μm detections, an SB component was needed in order to reproduce the data points, implying that the far-infrared emission in AGN arises mostly from star formation; moreover, the SB-to-AGN luminosity ratio shows a slight trend with increasing luminosity. [ABSTRACT FROM AUTHOR]

The broad-band spectral energy distributions (SEDs) of blazars exhibit two broad spectral components which in leptonic emission models are attributed to synchrotron radiation and synchrotron self-Compton (SSC) radiation of relativistic electrons. During high-state phases, the high-frequency SSC component dominates over the low-frequency synchrotron component implying that the inverse Compton SSC losses of electrons are at least equal or greater than the synchrotron losses of electrons. The linear synchrotron cooling, included routinely in radiation models of blazars, then has to be replaced by the SSC cooling. It is shown that the SSC energy-loss rate of electrons calculated in the Thomson limit (SST cooling) depends on an energy integral of the actual electron spectrum, reflecting the dependence of the energy density of the target synchrotron photons on the differential electron energy spectrum. The dependence of the SST loss rate on the initial kinetic energy of injected electrons is a collective effect completely different from the linear synchrotron cooling case. For the illustrative case of instantaneous injection of monoenergetic particles, we solve the non-linear kinetic equation for the intrinsic temporal evolution of the relativistic particles under SST cooling and compare the solution with the standard linear synchrotron cooling solution. For standard blazar emission region parameters, we find that under SST cooling electrons cool much more rapidly than in linear synchrotron cooling. The different cooling behaviour of electrons implies differences for the optically thin synchrotron and SSC radiation intensity and fluence energy spectra. The first difference concerns the duration of the SSC flare at different scattered photon energies. At large SSC photon energies, the SST cooled duration time is much smaller than the synchrotron cooled duration time, whereas at small SSC photon energies the SST cooled flare lasts much longer than the synchrotron cooled flare. Secondly, strong differences in the spectral behaviour of the total SSC fluence occur. At low scattered photon energies, the synchrotron cooled total SSC fluence exhibits a flatter power-law behaviour than the SST cooled total SSC fluence . Thirdly, the SST cooled total synchrotron fluence exhibits a steeper (by ) power-law behaviour [ ] than the synchrotron cooled total synchrotron fluence [ ] below the same exponential cut-off energy. These predictions of spectral behaviour with time and frequency provide conclusive tests for the presence or absence of linear synchrotron cooling or non-linear SST cooling in flaring non-thermal sources. [ABSTRACT FROM AUTHOR]

We present a new time-dependent inhomogeneous jet model of non-thermal blazar emission, which reproduces the entire spectral energy distribution together with the rapid gamma-ray variability. Ultrarelativistic leptons are injected at the base of a jet and propagate along the jet structure. We assume continuous reacceleration and cooling, producing a relativistic quasi-maxwellian (or ‘pile-up’) particle energy distribution. The synchrotron and synchrotron self-Compton jet emissivity are computed at each altitude. Klein–Nishina effects as well as intrinsic gamma–gamma absorption are included in the computation. Due to the pair production optical depth, considerable particle density enhancement can occur, particularly during flaring states. Time-dependent jet emission can be computed by varying the particle injection, but due to the sensitivity of pair production process, only small variations of the injected density are required during the flares. The stratification of the jet emission, together with a pile-up distribution, allows significantly lower bulk Lorentz factors, compared to one-zone models. Applying this model to the case of PKS and its big TeV flare observed in 2006, we can reproduce simultaneously the average broad-band spectrum of this source as well as the TeV spectra and TeV light curve of the flare with bulk Lorentz factor lower than 15. [ABSTRACT FROM AUTHOR]

We estimate the power of relativistic, extragalactic jets by modelling the spectral energy distribution of a large number of blazars. We adopt a simple one-zone, homogeneous, leptonic synchrotron and inverse Compton model, taking into account seed photons originating both locally in the jet and externally. The blazars under study have an often dominant high-energy component which, if interpreted as due to inverse Compton radiation, limits the value of the magnetic field within the emission region. As a consequence, the corresponding Poynting flux cannot be energetically dominant. Also the bulk kinetic power in relativistic leptons is often smaller than the dissipated luminosity. This suggests that the typical jet should comprise an energetically dominant proton component. If there is one proton per relativistic electrons, jets radiate around 2–10 per cent of their power in high-power blazars and 3–30 per cent in less powerful BL Lacs. [ABSTRACT FROM AUTHOR]

Starting from a sample of Sloan Digital Sky Survey quasars appearing also in the Two-Micron All-Sky Survey, we study the continuum properties of ∼1000 objects observed in eight bands, from near-infrared to ultraviolet. We construct the mean spectral energy distribution (SED) and compare and contrast the continua of radio-loud and radio-quiet quasar (RLQ and RQQ, respectively) objects. The SEDs of the two populations are significantly different, in the sense that RLQs are redder with power-law spectral indices and in the spectral range between 1014.5 and 1015.35 Hz. This difference is discussed in terms of different extinctions, different disc temperatures, or slopes of the non-thermal component. [ABSTRACT FROM AUTHOR]

This is the third in a series of papers that present observations and results for a sample of 76 ultrasteep-spectrum radio sources designed to find galaxies at high redshift. Here we present multifrequency radio observations, from the Australia Telescope Compact Array, for a subset of 37 galaxies from the sample. Matched resolution observations at 2.3, 4.8 and 6.2 GHz are presented for all galaxies, with the galaxies additionally observed at 8.6 and 18 GHz. New angular size constraints are reported for 19 sources based on high-resolution 4.8- and 6.2-GHz observations. Functional forms for the rest-frame spectral energy distributions are derived: 89 per cent of the sample is well characterized by a single power law, whilst the remaining 11 per cent show some flattening towards higher frequencies: not one source shows any evidence for high-frequency steepening. We discuss the implications of this result in light of the empirical correlation between redshift and spectral index seen in flux-limited samples of radio galaxies. Finally, a new physical mechanism to explain the redshift – spectral index correlation is posited: extremely steep-spectrum radio galaxies in the local universe usually reside at the centres of rich galaxy clusters. We argue that if a higher fractions of radio galaxies, as a function of redshift, are located in environments with densities similar to nearby rich clusters, then this could be a natural interpretation for the correlation. We briefly outline our plans to pursue this line of investigation. [ABSTRACT FROM AUTHOR]

We discuss the panchromatic properties of 99 088 galaxies selected from the Sloan Digital Sky Survey (SDSS) Data Release 1 ‘main’ spectroscopic sample (a flux-limited sample for 1360 deg2). These galaxies are positionally matched to sources detected by ROSAT, Galaxy Evolution Explorer (GALEX), two-Micron All-Sky Survey (2MASS), Infrared Astronomical Satellite ( IRAS), Green Bank GB6 survey (GB6), Faint Images of the Radio Sky at Twenty-centimetres (FIRST), NRAO VLA Sky Survey (NVSS) and Westerbork Northern Sky Survey (WENSS). The matching fraction varies from <1 per cent for ROSAT and GB6 to ∼40 per cent for GALEX and 2MASS. In addition to its size, the advantages of this sample are well-controlled selection effects, faint flux limits and the wealth of measured parameters, including accurate X-ray to radio photometry, angular sizes and optical spectra. We find strong correlations between the detection fraction at other wavelengths and optical properties such as flux, colours and emission-line strengths. For example, ∼2/3 of SDSS ‘main’ galaxies classified as active galactic nucleus (AGN) using emission-line strengths are detected by 2MASS, while the corresponding fraction for star-forming galaxies (SFs) is only ∼1/10. Similarly, over 90 per cent of galaxies detected by IRAS display strong emission lines in their optical spectra, compared to ∼50 per cent for the whole SDSS sample. Using GALEX, SDSS and 2MASS data, we construct the ultraviolet–infrared (UV–IR) broad-band spectral energy distributions for various types of galaxies, and find that they form a nearly one-parameter family. For example, the SDSS u- and r-band data, supplemented with redshift, can be used to ‘predict’ K-band magnitudes measured by 2MASS with an rms scatter of only 0.2 mag. When a dust content estimate determined from SDSS spectra with the aid of models is also utilized, this scatter decreases to 0.1 mag and can be fully accounted for by measurement uncertainties. We demonstrate that this interstellar dust content, inferred from optical SDSS spectra by Kauffmann et al., is indeed higher for galaxies detected by IRAS and that it can be used to ‘predict’ measured IRAS 60 μm flux density within a factor of 2 using only SDSS data. We also show that the position of a galaxy in the emission-line-based Baldwin–Phillips–Terlevich diagram is correlated with the optical light concentration index and u− r colour determined from the SDSS broad-band imaging data, and discuss changes in the morphology of this diagram induced by requiring detections at other wavelengths. Notably, we find that SDSS ‘main’ galaxies detected by GALEX include a non-negligible fraction (10–30 per cent) of AGNs, and hence do not represent a clean sample of starburst galaxies. We study the IR–radio correlation and find evidence that its slope may be different for AGN and SFs and related to the Hα/Hβ line-strength ratio. [ABSTRACT FROM AUTHOR]

We describe improved modelling of the emission by dust in a toroidal-like structure heated by a central illuminating source within active galactic nuclei (AGNs). We have chosen a simple but realistic torus geometry, a flared disc, and a dust grain distribution function including a full range of grain sizes. The optical depth within the torus is computed in detail taking into account the different sublimation temperatures of the silicate and graphite grains, which solves previously reported inconsistencies in the silicate emission feature in type 1 AGNs. We exploit this model to study the spectral energy distributions (SEDs) of 58 extragalactic (both type 1 and type 2) sources using archival optical and infrared data. We find that both AGN and starburst contributions are often required to reproduce the observed SEDs, although in a few cases they are very well fitted by a pure AGN component. The AGN contribution to the far-infrared luminosity is found to be higher in type 1 sources, with all the type 2 requiring a substantial contribution from a circumnuclear starburst. Our results appear in agreement with the AGN unified scheme, because the distributions of key parameters of the torus models turn out to be compatible for type 1 and type 2 AGNs. Further support to the unification concept comes from comparison with medium-resolution infrared spectra of type 1 AGNs by the Spitzer observatory, showing evidence for a moderate silicate emission around 10 μm, which our code reproduces. From our analysis we infer accretion flows in the inner nucleus of local AGNs characterized by high equatorial optical depths , moderate sizes and very high covering factors ( per cent) on average. [ABSTRACT FROM AUTHOR]

We present two XMM–Newton observations of the luminous , radio-quiet quasar PG 1407+265, separated by 11 months. The data indicate two distinct states: a highly variable, bright state (first epoch); and a quiescent, low-flux one (second epoch). During the low-flux state the spectrum is consistent with a single, unabsorbed power law. However, during the brighter state a highly variable, steep component is statistically required. Contemporaneous ultraviolet data from the Optical Monitor allow an estimate of the optical-to-X-ray spectral index , which appears typical of radio-quiet quasars during the low-flux state, but extremely flat during the high-flux state. The XMM–Newton data can be described as originating from a combination of jet and accretion disc processes, in which the (relativistic) X-ray jet only works intermittently. The scenario could help to describe some of the complexities seen in the broad-band spectral energy distribution of PG 1407+265, such as weak high-ionization emission lines, strong Fe ii, unbeamed continuum and the weak radio emission relative to the optical. [ABSTRACT FROM AUTHOR]

We address the question of why low-luminosity radio sources with similar flat radio spectra show a range of optical activity. The investigation is based on the spectral energy distributions (SEDs) of objects from the 200-mJy sample. We gathered new data from the VLA at 43 GHz, from SCUBA in the JCMT at 2000, 1350 and 850 μm, and from the ISOPHOT instrument on ISO at 170, 90, 60 and 25 μm. There is considerable diversity amongst the SEDs of the objects: there are objects with steep broad-band spectra between centimetre and millimetre bands (14 per cent of the sample); there are those with flat broad-band spectra over most of the spectral range (48 per cent of the sample); and there are those which show pronounced submillimetre/infrared excesses (27 per cent of the sample). Some objects of the first group have two-sided radio morphology, indicating that their parsec-scale emission is not dominated by beamed jet emission. Amongst the objects that have smooth broad-band spectra from the radio to the infrared, there are passive elliptical galaxies as well as the expected BL Lacertae objects. The most pronounced submillimetre/infrared excesses are shown by the broad-emission-line objects. [ABSTRACT FROM AUTHOR]

We present the analysis and results from a series of XMM–Newton observations of the distant blazar PMN J0525−3343 at a redshift of 4.4. The X-ray spectrum shows a spectral flattening below ∼1 keV, confirming earlier results from ASCA and BeppoSAX . The spectrum is well fitted by a power-law continuum with either a spectral break or absorption; no sharp features are apparent in the spectrum. No variability is seen in the individual light curves, although there is evidence of small longer-term variations (∼ months in the blazar frame) in both flux and (0.1–2.4)/(2–10) keV flux ratio. Very low levels of optical–UV extinction and the lack of any evidence of a Lyman-limit system at the quasar redshift rule out neutral absorption and we argue that the most plausible explanation is the presence of a warm, ionized absorber. Very strong C iv absorption in the optical spectrum already implies the presence of highly ionized material along the line of sight. Warm absorber models using the photoionization code cloudy are consistent with both the X-ray and C iv data, yielding a column density and ionization parameter . [ABSTRACT FROM AUTHOR]

ABSTRACT We use long-slit spectroscopic optical data to derive the properties of the extended emitting gas and the nuclear luminosity of a sample of 18 Seyfert 2 galaxies. From the emission-line luminosities and ratios we derive the density, reddening and mass of the ionized gas as a function of distance up to 2–4 kpc from the nucleus. Taking into account the geometric dilution of the nuclear radiation, we derive the radial distribution of covering factors and the minimum rate of ionizing photons emitted by the nuclear source. This number is an order of magnitude larger than that obtained from the rate of ionizing photons ‘intercepted’ by the gas and measured from the Hα luminosity. A calibration is proposed to recover this number from the observed luminosity. The He iiλ4686/Hβ line ratio was used to calculate the slope of the ionizing spectral energy distribution (SED), which in combination with the number of ionizing photons allows the calculation of the hard X-ray luminosities. These luminosities are consistent with those derived from X-ray spectra in the eight cases for which such data are available and recover the intrinsic X-ray emission in Compton-thick cases. Our method can thus provide reliable estimates of the X-ray fluxes in Seyfert 2 galaxies for the cases where it is not readily available. We also use the ionizing SED and luminosity to predict the infrared luminosity under the assumption that it is dominated by reprocessed radiation from a dusty torus, and find a good agreement with the observed IRAS luminosities. [ABSTRACT FROM AUTHOR]

ABSTRACT An analysis is presented of the power spectrum of X-ray variability of the bright Seyfert 1 galaxy Mrk 766 as observed by XMM–Newton. Over the 0.2–10 keV energy range the power spectral density (PSD) is well-represented by a power-law with a slope of α[sub low]≈ 1 at low frequencies, breaking to a slope of α[sub hi]= 2.8[sup +0.2][sub -0.4] at a frequency f[sub br]≈ 5 × 10[sup -4] Hz . As has been noted before, this broken power-law PSD shape is similar to that observed in the Galactic black hole candidate Cygnus X-1. If it is assumed that Mrk 766 shows a power spectrum similar in form to that of Cyg X-1, and that the break time-scale scales linearly with black hole mass, then the mass of the black hole in Mrk 766 is inferred to be &lsim; 5 × 10[sup 5] M[sub ⊙] . This rather low mass would mean Mrk 766 radiates above the Eddington limit. The coherence between different energy bands is significantly below unity implying that variations in the different energy bands are rather poorly correlated. The low coherence can be explained in the framework of standard Comptonization models if the properties of the Comptonizing medium are rapidly variable or if there are several distinct emission sites. [ABSTRACT FROM AUTHOR]