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We combine the Herschel Space Observatory PACS (Photoconductor Array Camera and Spectrometer) and SPIRE (Spectral and Photometric Imaging Receiver) photometry with archival WISE (Wide-field Infrared Survey Explorer) photometry to construct the spectral energy distributions (SEDs) for over 300 local (z < 0.05), ultrahard X-ray (14-195 keV) selected active galactic nuclei (AGN) from the Swift Burst Alert Telescope (BAT) 58-month catalogue. Using a simple analytical model that combines an exponentially cutoff power law with a single temperature modified blackbody, we decompose the SEDs into a host galaxy and AGN component. We calculate dust masses, dust temperatures, and star formation rates (SFRs) for our entire sample and compare them to a stellar mass-matched sample of local non-AGN galaxies. We find AGN host galaxies have systematically higher dust masses, dust temperatures, and SFRs due to the higher prevalence of late-type galaxies to host an AGN, in agreement with previous studies of the Swift/BAT AGN. We provide a scaling to convert X-ray luminosities into 8-1000 μmAGN luminosities, as well as determine the bestmid-to-far IR colours for identifying AGN-dominated galaxies in the IR regime. We find that for nearly 30 per cent of our sample, the 70 μm emission contains a significant contribution from theAGN (>0.5), especially at higher luminosities (L14-195 keV > 1042.5 erg s-1). Finally, we measure the local SFR-AGN luminosity relationship, finding a slope of 0.18, large scatter (0.37 dex), and no evidence for an upturn at high AGN luminosity. We conclude with a discussion on the implications of our results within the context of galaxy evolution with and without AGN feedback. [ABSTRACT FROM AUTHOR]

We test the consistency of active galactic nuclei (AGN) optical flux variability with the damped random walk (DRW) model. Our sample consists of 20 multiquarter Kepler AGN light curves including both Type 1 and 2 Seyferts, radio-loud and -quiet AGN, quasars, and blazars. Kepler observations of AGN light curves offer a unique insight into the variability properties of AGN light curves because of the very rapid (11.6-28.6 min) and highly uniform rest-frame sampling combined with a photometric precision of 1 part in 105 over a period of 3.5 yr. We categorize the light curves of all 20 objects based on visual similarities and find that the light curves fall into five broad categories. We measure the first-order structure function of these light curves and model the observed light curve with a general broken power-law power spectral density (PSD) characterized by a short-time-scale power-law index γ and turnover time-scale τ. We find that less than half the objects are consistent with a DRW and observe variability on short time-scales (~2 h). The turnover time-scale τ ranges from ~10-135 d. Interesting structure function features include pronounced dips on rest-frame time-scales ranging from 10-100 d and varying slopes on different time-scales. The range of observed short-time-scale PSD slopes and the presence of dip and varying slope features suggests that the DRW model may not be appropriate for all AGN. We conclude that AGN variability is a complex phenomenon that requires a more sophisticated statistical treatment. [ABSTRACT FROM AUTHOR]

We present the first of a series of studies of the evolution of galaxies in compact groups over the past 3 Gyr. This article focuses on the evolution of nuclear activity and how it has been affected by the dense environment of the groups. Our analysis is based on the largest multiwavelength compact-group sample to date, containing complete ultraviolet-infrared (UV-IR) photometry for 1770 isolated groups (7417 galaxies). We classified the nuclear activity of the galaxies based on optical emission-line and mid-infrared (mid-IR) diagnostic methods, as well as using spectral energy distribution fitting. We observe a 15 per cent increase in the number of active galactic nucleus (AGN)-hosting late-type galaxies found in dynamically old groups over the past 3 Gyr, accompanied by a corresponding decrease in their circumnuclear star formation. Comparing our compact group results with those for local isolated field and interacting pair galaxies, we find no differences in the AGNs at the same redshift range. Based on both optical and mid-IR colour classifications, we report the absence of Seyfert 1 nuclei and attribute this to the low accretion rates caused by depletion of gas. We propose that the observed increase in low-ionization nuclear emission-line regions (LINERs) and Seyfert 2 nuclei (at low z) in early-type galaxies of dynamically young groups is due to the morphological transformation of lenticular galaxies into elliptical ones. Finally, we show that, at any given stellar mass, galaxies found in dynamically old groups are more likely to host an AGN. Our findings suggest that depletion of gas due to past star formation and tidal stripping is the major mechanism driving the evolution of nuclear activity in compact groups of galaxies. [ABSTRACT FROM AUTHOR]

Obscured active galactic nuclei (AGNs) provide an opportunity to study the material surrounding the central engine. Geometric and physical constraints on the absorber can be deduced from the reprocessed AGN emission. In particular, the obscuring gas may reprocess the nuclear X-ray emission producing a narrow Fe Kα line and a Compton reflection hump. In recent years, models of the X-ray reflection from an obscuring torus have been computed; however, although the reflecting gas may be dusty, the models do not yet take into account the effects of dust on the predicted spectrum. We study this problem by analysing two sets of models, with and without the presence of dust, using the one-dimensional photoionization code CLOUDY. The calculations are performed for a range of column densities (22 < log[NH(cm-2)] < 24.5) and hydrogen densities (6 < log[nH(cm-3)] < 8). The calculations show the presence of dust can enhance the Fe Kα equivalent width (EW) in the reflected spectrum by factors up to ≈8 for Compton thick (CT) gas and a typical interstellar medium grain size distribution. The enhancement in EW with respect to the reflection continuum is due to the reduction in the reflected continuum intensity caused by the anisotropic scattering behaviour of dust grains. This effect will be most relevant for reflection from distant, predominately neutral gas, and is a possible explanation for AGNs which show a strong Fe Kα EW and a relatively weak reflection continuum. Our results show it is an important to take into account dust while modelling the X-ray reflection spectrum, and that inferring a CT column density from an observed Fe Kα EW may not always be valid. Multidimensional models are needed to fully explore the magnitude of the effect. [ABSTRACT FROM AUTHOR]

Hawkins reported on a class of ‘naked’ active galactic nuclei (AGN) characterized by strong amplitude optical brightness variability and the complete absence of broad emission lines in the optical spectrum. The variability suggests that the nucleus is seen directly, however the absence of broad lines contradicts the simple formulation of Unified Models for AGN. We present the results of quasi-simultaneous spectroscopic observations with XMM–Newton and New Technology Telescope (NTT) (La Silla) of two ‘naked’ AGN. We confirm the ‘naked’ nature of Q2131−427 for which no broad emission line components have been detected in the optical spectrum and its X-ray spectrum shows no signs of intrinsic absorption. The optical and X-ray mismatch in this source cannot be ascribed to a high nuclear dust-to-gas ratio and a Compton-thick nature is ruled out on the basis of the high ratio. The broad-line region (BLR) may be completely absent in this source, possibly as a consequence of its low Eddington ratio. On the other hand, the optical spectrum of Q2130−431 shows Hα and Hβ broad emission line components, revealing the presence of a BLR. A mild X-ray absorption is expected in intermediate type 1.8 Seyfert galaxies like Q2130−431, however we put a very low upper limit on the column density , also the low Balmer decrement suggests that the BLR itself does not suffer from reddening. We propose that in this object the BLR is intrinsically weak, making a case of ‘true’ intermediate Seyfert galaxy. We also report on the X-ray detection of the Abell 3783 galaxy cluster in the XMM–Newton field of view of the Q2131−427 observation. [ABSTRACT FROM AUTHOR]

We present the results of H- and K-band very large telescope/Spectrograph for INtegral Field Observations in the Near Infrared (VLT/SINFONI) integral field spectroscopy of the Ultraluminous Infrared Galaxy (ULIRG) IRAS 19 254–7245 (the Super-antennae), an interacting double galaxy system containing an embedded active galactic nuclei. Deep K-band spectroscopy reveals Paα arising in a warped disc with position angle of 330° and an inclination . The kinemetric parameters derived for H2 are similar to Paα. Two high-ionization emission lines, [Si vi] and [Al ix], are detected and we identify as [Ni ii] the line observed at 1.94 μm. Diluting non-stellar continuum, which was previously detected, has decayed, and the H-band continuum emission is consistent with pure stellar emission. Based on H2 emission-line ratios, it is likely that at the central 1-kpc region H2 is excited by ultraviolet fluorescence in dense clouds while shock excitation is dominant further out. This scenario is supported by very low Paα to H2 line ratio detected outside the nuclear region and non-thermal ortho/para ratios (∼2.0–2.5) close to the nucleus. [ABSTRACT FROM AUTHOR]

Low-luminosity active galactic nuclei (AGNs) are perceived to be radio loud and devoid of a ‘big blue bump’, indicating a transition from a radiatively efficient, geometrically thin, accretion disc in high-luminosity AGNs, to a geometrically thick, radiatively inefficient accretion flow at low luminosities and accretion rates. I revisit the issue of the spectral energy distributions (SEDs) of low-luminosity AGNs using recently published, high angular resolution data at radio, ultraviolet (UV) and X-ray wavelengths, for a sample of 13 nearby galaxies with low-ionization nuclear emission-line region (LINER) nuclei. I show that, contrary to common wisdom, low-luminosity LINERs have significant non-stellar UV flux, and UV/X-ray luminosity ratios similar, on average, to those of Seyfert 1 nuclei ∼104 times more luminous. The index that quantifies this ratio is in the range between −0.8 and −1.4, and is below the extrapolation to low luminosities of the relation between and UV luminosity observed at higher luminosities. In terms of radio loudness, most of the LINERs are indeed radio loud (or sometimes even ‘super radio loud’) based on their radio/UV luminosity ratios, when compared to the most luminous quasars. However, the entire distribution of radio loudness has been shown to shift to higher radio/UV ratios at low AGN luminosities. In the context of this global shift, some LINERs (the majority) can be considered radio quiet, and some (from among those with black hole masses ) are radio loud. The SEDs of these low-luminosity AGNs are thus quite similar to those of Seyferts up to luminosities of , and there is no evidence for a sharp change in the SED at the lowest luminosities. Thin AGN accretion discs may therefore persist at low accretion rates, in analogy to some recent findings for Galactic stellar-mass accreting black holes. [ABSTRACT FROM AUTHOR]

We present a study of the spectral variability of the Seyfert I galaxy MCG–6-30-15 based on the two long XMM–Newton observations from 2000 and 2001. The X–ray spectrum and variability properties of the 2001 data have previously been well described with a two-component model consisting of a variable power-law and a much less variable reflection component, containing a broad relativistic iron line from the accretion disc around a rapidly rotating Kerr black hole. The lack of variability of the reflection component has been interpreted as an effect of strong gravitational light bending very close to the central black hole. Using an improved reflection model, we fit the two-component model to time-resolved spectra of both observations. Assuming that the photon index of the power law is constant, we reconfirm the old result and show that this does not depend on the time-scale of the analysis. [ABSTRACT FROM AUTHOR]

This is the third paper of a series devoted to the study of the global properties of Joguet's sample of 79 nearby galaxies observable from the southern hemisphere, of which 65 are Seyfert 2 galaxies. We use the population synthesis models of Paper II to derive ‘pure’ emission-line spectra for the Seyfert 2 galaxies in the sample, and thus explore the statistical properties of the nuclear nebular components and their relation to the stellar populations. We find that the emission-line clouds suffer substantially more extinction than the starlight, and we confirm the correlations between stellar and nebular velocity dispersions and between emission-line luminosity and velocity dispersions, although with substantial scatter. Nuclear luminosities correlate with stellar velocity dispersions, but Seyferts with conspicuous star-forming activity deviate systematically towards higher luminosities. Removing the contribution of young stars to the optical continuum produces a tighter and steeper relation, , consistent with the Faber–Jackson law. Emission-line ratios indicative of the gas excitation such as [O iii]/Hβ and [O iii]/[O ii] are statistically smaller for Seyferts with significant star formation, implying that ionization by massive stars is responsible for a substantial and sometimes even a dominant fraction of the Hβ and [O ii] fluxes. We use our models to constrain the maximum fraction of the ionizing power that can be generated by a hidden active galactic nucleus (AGN). We correlate this fraction with classical indicators of AGN photoionization (i.e. X-ray luminosity and nebular excitation), but find no significant correlations. Thus, while there is a strong contribution of starbursts to the excitation of the nuclear nebular emission in low-luminosity Seyferts, the contribution of the hidden AGN remains elusive even in hard X-rays. [ABSTRACT FROM AUTHOR]

We present XMM–Newton observations of the Seyfert 1 active galactic nucleus (AGN) . We have conducted a study into the warm absorber present in this source, and using high-resolution Reflection Grating Spectrometer (RGS) data we find that the absorption can be characterized by two phases: a phase with log ionization parameter ξ of 0.50 (where ξ is in units of erg cm s−1) and a column of , and a phase with log ξ of 1.62 and a column of . An iron Kα line is detected. Neutral absorption is also present in the source, and we discuss possible origins for this. On the assumption that the ionized absorbers originate as an outflow from the inner edge of the torus, we use a new method for finding the volume filling factor. Both phases of have small volume filling factors (≤1 per cent). We also derive the volume filling factors for a sample of 23 AGN using this assumption and for the absorbers with , we find reasonable agreement with the filling factors obtained through the alternative method of equating the momentum flow of the absorbers to the momentum loss of the radiation field. By comparing the filling factors obtained by the two methods, we infer that some absorbers with occur at significantly larger distances from the nucleus than the inner edge of the torus. [ABSTRACT FROM AUTHOR]

We have investigated optical properties of 4248 infrared galaxies (IRGs) by positionally matching data from theInfrared Astronomical Satellite(IRAS) and the Sloan Digital Sky Survey Data Release 3 (SDSS DR3). As a result of the large sky area coverage of both surveys, we have obtained an opportunity to study an unprecedentedly large number of 4248 infrared galaxies spanning four orders of infrared luminosity range. Our sample includes three hyperluminous infrared galaxiesand the large number of 178 ultraluminous infrared galaxies. In addition, it is important to have a statistical number of lower-luminosity infrared galaxiesin order to link the well-studied ultraluminous infrared galaxies to normal star-forming galaxies. Our findings are as follows. (i) We found that more infrared luminous galaxies tend to have a smaller local galaxy density, being consistent with the picture where luminous IRGs are created by the merger–interaction of galaxies that happens more often in lower-density regions. (ii) The fractions of active galactic nuclei (AGNs) increase as a function ofLir. (iii) There is a good correlation betweenLir andfor AGNs, suggesting that both of the parameters can be a good estimator of the total power of AGNs. (iv) A good correlation is found betweenLir and the optically estimated star formation rate (SFR) for star-forming galaxies, suggestingLir is a good indicator of galaxy SFR. However, caution is needed when SFR is estimated usingLir, i.e. high SFR galaxies selected byLir are frequently as a result of merger/interaction, whereas high SFR galaxies selected by optical emission are often normal spiral or Magellanic-cloud-like irregular galaxies. (v) More IR luminous galaxies have a slightly larger Hα/Hβ ratio. (vi) More IR luminous galaxies have a more centrally concentrated morphology, being consistent with the morphological appearance of galaxy–galaxy merger remnants. The optical images of ultra-/very luminous infrared galaxies also show frequent signs of merger/interaction. (vii) Comparison with the spectral energy distribution synthesis models indicates that the majority of luminous infrared galaxiesmay be in a post-starburst phase, sharing a similar (but not the same) merger/interaction origin with E+A galaxies. [ABSTRACT FROM AUTHOR]

We present detailed scattering models confirming that distinctive variations in polarization across the broad Hα line, which are observed in a significant fraction of type 1 Seyfert galaxies, can be understood in terms of a rotating line-emitting disc surrounded by a coplanar scattering region (the equatorial scattering region). The predicted polarization properties are: (i) averaged over wavelength, the position angle (PA) of polarization is aligned with the projected disc rotation axis and hence also with the radio source axis; (ii) the polarization PA rotates across the line profile, reaching equal but opposite (relative to the continuum PA) rotations in the blue and red wings; and (iii) the degree of polarization peaks in the line wings and passes through a minimum in the line core. We identify 11 objects that exhibit these features to different degrees. In order to reproduce the large-amplitude PA rotations observed in some cases, the scattering region must closely surround the emission disc and the latter must itself be a relatively narrow annulus– presumably the Hα-emitting zone of a larger accretion disc. Asymmetries in the polarization spectra may be attributable to several possible causes, including bulk radial infall in the equatorial scattering region, or contamination by polar scattered light. The broad Hα lines do not, in general, exhibit double-peaked profiles, suggesting that a second Hα-emitting component of the broad-line region is present, in addition to the disc. [ABSTRACT FROM AUTHOR]