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Blazars optical emission is generally dominated by relativistic jets, although the host galaxy, accretion disc, and broad-line region (BLR) may also contribute significantly. Disentangling their contributions has been challenging for years due to the dominance of the jet. To quantify the contributions to the spectral variability, we use the statistical technique for dimensionality reduction non-negative matrix factorization on a spectroscopic data set of 26 γ -ray blazars. This technique allows to model large numbers of spectra in terms of a reduced number of components. We use a priori knowledge to obtain components associated with meaningful physical processes. The sources are classified according to their optical spectrum as host-galaxy dominated BL Lac objects (BL Lacs), BL Lacs, or flat spectrum radio quasars (FSRQs). Host-galaxy sources show less variability, as expected, and bluer-when-brighter (BWB) trends, as the other BL Lacs. For FSRQs, more complicated colour-flux behaviours are observed: redder-when-brighter for low states saturating above a certain level and, in some cases, turning to BWB. We are able to reproduce the variability observed during 10 yr using only two to four components, depending on the type. The simplest scenario corresponds to host-galaxy blazars, whose spectra are reconstructed using the stellar population and a power law (PL) for the jet. BL Lac spectra are reproduced using from two to four PLs. Different components can be associated with acceleration/cooling processes taking place in the jet. The reconstruction of FSRQs also incorporates a QSO-like component to account for the BLR, plus a very steep PL, associated with the accretion disc. [ABSTRACT FROM AUTHOR]

According to theory, the torus of active galactic nuclei (AGN) is sustained from a wind coming off the accretion disc, and for low efficient AGN, it has been proposed that such structure disappears. However, the exact conditions for its disappearance remain unclear. This can be studied throughout the reflection component at X-rays, which is associated with distant and neutral material at the inner walls of the torus in obscured AGN. We select a sample of 81 AGNs observed with NuSTAR with a distance limit of D< 200 Mpc and Eddington rate |$\rm {\lambda _{Edd} \equiv L_{bol}/L_{Edd}\lt 10^{-3}}$|⁠. We fit the 3–70 keV spectra using a model accounting for a partial-covering absorber plus a reflection component from neutral material. We find that the existence of the reflection component spans in a wide range of black hole mass and bolometric luminosities, with only ∼13 per cent of our sample (11 sources) lacking of any reflection signatures. These sources fall in the region in which the torus may be lacking in the L-MBH diagram. For the sources with a detected reflection component, we find that the vast majority of them are highly obscured (⁠|$\rm {\log \ N_H \gt 23}$|⁠), with |$\rm {\sim 20{{\ \rm per\ cent}}}$| being Compton-thick. We also find an increase in the number of unobscured sources and a tentative increase on the ratio between |$\rm {FeK\alpha }$| emission line and Compton-hump luminosities toward |$\rm {\lambda _{Edd}=10^{-5}}$|⁠ , suggesting that the contribution of the |$\rm {FeK\alpha }$| line changes with Eddington ratio. [ABSTRACT FROM AUTHOR]

In this paper, we present a multi-epoch analysis of NGC 1052, a prototypical low-luminisity active galactic nucleus, using XMM –Newton, Suzaku and NuSTAR observations taken from 2001 to 2017. This is the first time that results from NuSTAR observations have been reported for NGC 1052. Regarding technical aspects, we found a wavelength-dependent calibration issue between simultaneous XMM –Newton and NuSTAR spectra, characterized by a change in the photon index of |$\rm { \Gamma _{NuSTAR}- \Gamma _{XMM-Newton}=0.17\pm 0.04}$|⁠. We use ancillary Chandra data to decontaminate the nuclear spectrum from circumnuclear contributors. We find that two baseline models can fit the broad (0.5–50 keV) X-ray spectrum of the source. One consists of a power-law-like continuum that is absorbed by a uniform absorber, and is reflected by neutral material, and a separate power-law component in the soft band. The second model consists of a clumpy absorber. The reflection component is still present, but not the soft-band power law. Instead, absorption by a warm absorber is necessary to fit the spectra. This is the first time that a reflection component has been established in this object, thanks to high-energy data from NuSTAR. This component is constant in flux and shape, supporting the idea that it is produced away from the central source (probably in the torus). We find flux, spectral slope and absorption variations on time-scales of months to years. We also find that a patchy absorber can explain the behaviour of this source better, as it is ∼200 times more likely than the uniform absorber and yields smaller intrinsic variations. [ABSTRACT FROM AUTHOR]

The Balmer emission originated in the broad-line region (BLR) of active galactic nuclei (AGNs) could be either weak and difficult to detect, or even absent, for low-luminosity AGNs, as low-ionization nuclear emission-line regions (LINERs). Our goals in this paper are threefold. First, we want to explore the AGN nature of nearby type-1 LINERs. Secondly, we aim at deriving a reliable interpretation for the different components of emission lines by studying their kinematics and ionization mechanism. Thirdly, we intend to probe the neutral gas in the nuclei of these LINERs. We study the 22 local ($$z$$  < 0.025) type-1 LINERs from the Palomar survey, on the basis of optical ground- and space-based long-slit spectroscopic observations taken with the TWIN spectrograph at Calar Alto Observatory (CAHA) and ALFOSC/NOT (Andalucia Faint Object Spectrograph and Camera/2.6 m North Optical Telescope). Kinematics and fluxes of a set of emission lines, from H $$\beta \, \lambda$$ 4861 to [S  ii ] λλ6716, 6731, and the NaD λλ5890, 5896 doublet in absorption have been modelled and measured, after the subtraction of the underlying starlight. We also use ancillary spectroscopic data from HST /STIS (Hubble Space Telescope /Space Telescope Imaging Spectrograph). We found that the broad H α component is sometimes elusive in our ground-based spectroscopy, whereas it is ubiquitous for space-based data. By combining optical diagnostic diagrams, theoretical models [for AGNs, post-asymptotic giant branch (pAGB) stars, and shocks] and the weak/strong-[O  i ] classification, we exclude the pAGB star scenario in favour of the AGN as the dominant mechanism of ionization in these LINERs, being shocks however relevant. The kinematical properties of the emission lines may indicate the presence of ionized outflows, preferentially seen in [O  i ]. However, the neutral gas outflows, diagnosed by NaD, would appear to be less frequent. [ABSTRACT FROM AUTHOR]

We present mid-infrared (MIR; 7.5-13.5 μm) imaging and spectroscopy observations obtained with the CanariCam (CC) instrument on the 10.4-m Gran Telescopio CANARIAS for a sample of 20 nearby,MIR bright and X-ray luminous quasi-stellar objects (QSOs).We find that for the majority of QSOs the MIR emission is unresolved at angular scales∼0.3 arcsec, corresponding to physical scales ≲600 pc. We find that the higher-spatial resolution CC spectra have similar shapes to those obtained with Spitzer/IRS, and hence we can assume that the spectra are not heavily contaminated by extended emission in the host galaxy. We thus take advantage of the higher signal-to-noise ratio Spitzer/IRS spectra, as a fair representation of the nuclear emission, to decompose it into a combination of active galactic nuclei (AGN), polycyclic aromatic hydrocarbon (PAH) and stellar components. In most cases, the AGN is the dominant component, with a median contribution of 85 per cent of the continuum light at MIR (5-15 μm) within the IRS slit. This IR AGN emission is well reproduced by CLUMPY torus models. We find evidence for significant differences in the parameters that describe the dusty tori of QSOs when compared with the same parameters of Seyfert 1 and 2 nuclei. In particular, we find a lower number of clouds (N0 ≲ 12), steeper radial distribution of clouds (q ∼ 1.5-3.0) and clouds that are less optically thick (τV ≲ 100) than in Seyfert 1, which could be attributed to dusty structures that have been partially evaporated and piled up by the higher radiation field in QSOs. We find that the combination of the angular width σtorus, viewing angle i, and number of clouds along the equatorial line, N0, produces large escape probabilities (Pesc > 2 per cent) and low geometrical covering factors (f2 ≲ 0.6), as expected for AGN with broad lines in their optical spectra. [ABSTRACT FROM AUTHOR]

Context. Seyfert 1.8/1.9 are sources showing weak broad Hα components in their optical spectra. According to unification schemes, they are seen with an edge-on inclination, similar to type 2 Seyfert galaxies, but with slightly lower inclination angles. Aims. We aim to test whether Seyfert 1.8/1.9 have similar properties at UV and X-ray wavelengths. Methods. We used the 15 Seyfert 1.8/1.9 in the Véron Cetty and Véron catalog with public data available from the Chandra and/or XMM-Newton archives at different dates, with timescales between observations ranging from days to years. All the spectra of the same source were simultaneously fit with the same model and different parameters were left free to vary in order to select the variable parameter(s). Whenever possible, short-term variations from the analysis of the X-ray light curves and long-term UV variations from the optical monitor onboard XMM-Newton were studied. Our results are homogeneously compared with a previous work using the same methodology applied to a sample of Seyfert 2. Results. X-ray variability is found in all 15 nuclei over the aforementioned ranges of timescales. The main variability pattern is related to intrinsic changes in the sources, which are observed in ten nuclei. Changes in the column density are also frequent, as they are observed in six nuclei, and variations at soft energies, possibly related to scattered nuclear emission, are detected in six sources. X-ray intra-day variations are detected in six out of the eight studied sources. Variations at UV frequencies are detected in seven out of nine sources. Conclusions. A comparison between the samples of Seyfert 1.8/1.9 and 2 shows that, even if the main variability pattern is due to intrinsic changes of the sources in the two families, these nuclei exhibit different variability properties in the UV and X-ray domains. In particular, variations in the broad X-ray band on short timescales (days to weeks), and variations in the soft X-rays and UV on long timescales (months to years) are detected in Seyfert 1.8/1.9 but not in Seyfert 2. Overall, we suggest that optically classified Seyfert 1.8/1.9 should be kept separated from Seyfert 2 galaxies in UV/X-ray studies of the obscured AGN population because their intrinsic properties might be different. [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]

We present subarcsecond resolution mid-infrared (MIR) images obtained with 8-10 m-class ground-based telescopes of a complete volume-limited (DL < 40 Mpc) sample of 24 Seyfert galaxies selected from the Swift/Burst Alert Telescope nine month catalogue. We use those MIR images to study the nuclear and circumnuclear emission of the galaxies. Using different methods to classify the MIR morphologies on scales of ~400 pc, we find that the majority of the galaxies (75-83 per cent) are extended or possibly extended and 17-25 per cent are pointlike. This extended emission is compact and it has low surface brightness compared with the nuclear emission, and it represents, on average, ~30 per cent of the total MIR emission of the galaxies in the sample. We find that the galaxies whose circumnuclear MIR emission is dominated by star formation (SF) show more extended emission (650 ± 700 pc) than active galactic nuclei (AGN)-dominated systems (300 ± 100 pc). In general, the galaxies with pointlike MIR morphologies are face-on or moderately inclined (b/a ~ 0.4-1.0), and we do not find significant differences between the morphologies of Sy1 and Sy2. We used the nuclear and circumnuclear fluxes to investigate their correlation with different AGN and SF activity indicators. We find that the nuclear MIR emission (the inner ~70 pc) is strongly correlated with the X-ray emission (the harder the X-rays the better the correlation) and with the [O IV] ?25.89 µm emission line, indicating that it is AGN-dominated. We find the same results, although with more scatter, for the circumnuclear emission, which indicates that the AGN dominates the MIR emission in the inner ~400 pc of the galaxies, with some contribution from SF. [ABSTRACT FROM AUTHOR]

We investigate the evolutionary connection between local IR-bright galaxies (log LIR ≥ 11.4 L⊙) and quasars. We use high angular resolution (∼ 0.3-0.4 arcsec∼ few hundred parsecs) 8 − 13 μm ground-based spectroscopy to disentangle the AGN mid-IR properties from those of star formation. The comparison between the nuclear 11.3 μm PAH feature emission and that measured with Spitzer/IRS indicates that the star formation is extended over a few kpc in the IR-bright galaxies. The AGN contribution to the total IR luminosity of IR-bright galaxies is lower than in quasars. Although the dust distribution is predicted to change as IR-bright galaxies evolve to IR-bright quasars and then to optical quasars, we show that the AGN mid-IR emission of all the quasars in our sample is not significantly different. In contrast, the nuclear emission of IR-bright galaxies with low AGN contributions appears more heavily embedded in dust although there is no clear trend with the interaction stage or projected nuclear separation. This suggests that the changes in the distribution of the nuclear obscuring material may be taking place rapidly and at different interaction stages washing out the evidence of an evolutionary path. When compared to normal AGN, the nuclear star formation activity of quasars appears to be dimming whereas it is enhanced in some IR-bright nuclei, suggesting that the latter are in an earlier star-formation dominated phase. [ABSTRACT FROM AUTHOR]

We present 31.5 µm imaging photometry of 11 nearby Seyfert galaxies observed from the Stratospheric Observatory For Infrared Astronomy (SOFIA) using the Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST). We tentatively detect extended 31 µm emission for the first time in our sample. In combination with this new data set, subarcsecond resolution 1-18 µm imaging and 7.5-13 µm spectroscopic observations were used to compute the nuclear spectral energy distribution (SED) of each galaxy.We found that the turnover of the torus emission does not occur at wavelengths ≤31.5 µm, which we interpret as a lower-limit for the wavelength of peak emission. We used CLUMPY torus models to fit the nuclear infrared (IR) SED and infer trends in the physical parameters of the AGN torus for the galaxies in the sample. Including the 31.5 µm nuclear flux in the SED (1) reduces the number of clumpy torus models compatible with the data, and (2) modifies the model output for the outer radial extent of the torus for 10 of the 11 objects. Specifically, six (60 per cent) objects show a decrease in radial extent while four (40 per cent) show an increase.We find torus outer radii ranging from <1 to 8.4 pc. [ABSTRACT FROM AUTHOR]

The origin of the unification model for Active Galactic Nuclei (AGN) was the detection of broad hydrogen recombination lines in the optical polarized spectrum of the Seyfert 2 galaxy (Sy2) NGC 1068. Since then, a search for the hidden broad-line region (HBLR) of nearby Sy2s started, but polarized broad lines have only been detected in ~30-40% of the nearby Sy2s observed to date. Here we present new VLT/FORS2 optical spectropolarimetry of a sample of 15 Sy2s, including Compton-thin and Compton-thick sources. The sample includes six galaxies without previously published spectropolarimetry, some of them normally treated as non-hidden BLR (NHBLR) objects in the literature, four classified as NHBLR, and five as HBLR based on previous data. We report ≥4σ detections of a HBLR in 11 of these galaxies (73% of the sample) and a tentative detection in NGC 5793, which is Compton-thick according to the analysis of X-ray data performed here. Our results confirm that at least some NHBLRs are misclassified, bringing previous publications reporting differences between HBLR and NHBLR objects into question. We detect broad Ha and Hβ components in polarized light for 10 targets, and just broad Hα for NGC 5793 and NGC 6300, with line widths ranging between 2100 and 9600 km s-1. High bolometric luminosities and low column densities are associated with higher polarization degrees, but not necessarily with the detection of the scattered broad components. [ABSTRACT FROM AUTHOR]

We present far-infrared (FIR) 70-500?μm imaging observations obtained with Herschel/Photodetector Array Camera (PACS) and Spectral and Photometric Imaging REceiver (SPIRE) of 33 nearby (median distance of 30 Mpc) Seyfert galaxies from the Revised Shapley-Ames (RSA) catalogue. We obtain the FIR nuclear (r = 1?kpc and r = 2?kpc) and integrated spectral energy distributions (SEDs). We estimate the unresolved nuclear emission at 70?μm and we fit the nuclear and integrated FIR SEDs with a grey body model. We find that the integrated FIR emission of the RSA Seyferts in our sample is dominated by emission from the host galaxy, with dust properties similar to those of normal galaxies (non-AGN). We use four criteria to select galaxies whose nuclear 70?μm emission has a significant AGN contribution: (1) elevated 70/160?μm flux ratios, (2) spatially resolved, high dust temperature gradient, (3) 70?μm excess emission with respect to the fit of the FIR SEDs with a grey body, and (4) excess of nuclear SFR obtained from 70?μm over SFR from mid-infrared indicators. 16 galaxies (48 per cent of the initial sample) satisfy at least one of these conditions, whereas 10 satisfy half or more. After careful examination of these, we select six bona fide candidates (18 per cent of the initial sample) and estimate that ~40-70 per cent of their nuclear (r = 1-2?kpc) 70?μm emission is contributed by dust heated by the AGN. [ABSTRACT FROM AUTHOR]

Context. Obscured active galactic nuclei (AGNs) are thought to be very common in the Universe. Observations and surveys have shown that the number of sources increases for near galaxies and at the low-luminosity regime (the so-called LLAGNs). Furthermore, many AGNs show changes in their obscuration properties at X-rays that may suggest a configuration of clouds very close to the accretion disk. However, these variations could also be due to changes in the intrinsic continuum of the source. It is therefore important to study nearby AGN to better understand the locus and distribution of clouds in the neighbourhood of the nucleus. Aims. We aim to study the nuclear obscuration of LLAGN NGC835 and its extended emission using mid-infrared observations. Methods. We present sub-arcsecond-resolution mid-infrared 11.5 µm imaging of the LLAGN galaxy NGC835 obtained with the instrument CanariCam in the Gran Telescopio CANARIAS (GTC), archival Spitzer/IRS spectroscopy, and archival Chandra data observed in 2000, 2008, and 2013. Results. The GTC/CanariCam 11.5 µm image reveals faint extended emission out to ~6 arcsec. We obtained a nuclear flux of F(11:5 µm) ~ 18 mJy; whereas the extended emission accounts for 90% of the total flux within the 6 arcsec. This means that the low angular resolution (~4 arcsec) IRS spectrum is dominated by this extended emission and not by the AGN. This is clearly seen in the Spitzer/IRS spectrum, which resembles that of star-forming galaxies. Although the extended soft X-ray emission shows some resemblance with that of the mid-infrared, the knots seen at X-rays are mostly located in the inner side of this mid-infrared emission. The nuclear X-ray spectrum of the source has undergone a spectral change between 2000/2008 and 2013. We argue that this variation is most probably due to changes in the hydrogen column density from ~8 × 1023 cm–2 to ~3 × 1023 cm–2. NGC835 therefore is one of the few LLAGN, together with NGC1052, in which changes in the absorber can be claimed. [ABSTRACT FROM AUTHOR]

We present an atlas of mid-infrared (mid-IR) ~7.5-13 μm spectra of 45 local active galactic nuclei (AGN) obtained with CanariCam on the 10.4 m Gran Telescopio CANARIAS (GTC) as part of an ESO/GTC large programme. The sample includes Seyferts and other lowluminosity AGN (LLAGN) at a median distance of 35 Mpc and luminous AGN, namely PG quasars, (U)LIRGs, and radio galaxies (RG) at a median distance of 254 Mpc. To date, this is the largest mid-IR spectroscopic catalogue of local AGN at sub-arcsecond resolution (median 0.3 arcsec). The goal of this work is to give an overview of the spectroscopic properties of the sample. The nuclear 12 μm luminosities of the AGN span more than four orders of magnitude, vL12μm ~ 3 × 1041-1046 erg s-1. In a simple mid-IR spectral index versus strength of the 9.7 μm silicate feature diagram most LLAGN, Seyfert nuclei, PG quasars, and RGs lie in the region occupied by clumpy torus model tracks. However, the mid-IR spectra of some might include contributions from other mechanisms. Most (U)LIRG nuclei in our sample have deeper silicate features and flatter spectral indices than predicted by these models suggesting deeply embedded dust heating sources and/or contribution from star formation. The 11.3 μm polycyclic aromatic hydrocarbon (PAH) feature is clearly detected in approximately half of the Seyfert nuclei, LLAGN, and (U)LIRGs. While the RG, PG quasars, and (U)LIRGs in our sample have similar nuclear vL12μm, we do not detect nuclear PAH emission in the RGs and PG quasars. [ABSTRACT FROM AUTHOR]

We present an analysis of the nuclear infrared (IR, 1.6-18 µm) emission of the ultraluminous IR galaxy UGC 5101 to derive the properties of its active galactic nucleus (AGN) and its obscuring material. We use new mid-IR high angular resolution (0.3-0.5 arcsec) imaging using the Si-2 filter (λC = 8.7µm) and 7.5-13 µm spectroscopy taken with CanariCam (CC) on the 10.4 m Gran Telescopio CANARIAS. We also use archival Hubble Space Telescope/NICMOS and Subaru/COMICS imaging and Spitzer/IRS spectroscopy. We estimate the near- and mid-IR unresolved nuclear emission by modelling the imaging data with galfit. We decompose the Spitzer/IRS and CC spectra using a power-law component, which represents the emission due to dust heated by the AGN, and a starburst component, both affected by foreground extinction. We model the resulting unresolved near- and mid-IR, and the starburst subtracted CC spectrum with the CLUMPY torus models of Nenkova et al. The derived geometrical properties of the torus, including the large covering factor and the high foreground extinction needed to reproduce the deep 9.7µm silicate feature, are consistent with the lack of strong AGN signatures in the optical. We derive an AGN bolometric luminosity Lbol ~ 1.9 × 1045 erg s-1 that is in good agreement with other estimates in the literature. [ABSTRACT FROM AUTHOR]

Context. Variability across the electromagnetic spectrum is a property of active galactic nuclei (AGN) that can help constrain the physical properties of these galaxies. Nonetheless, the way in which the changes happen and whether they occur in the same way in every AGN are still open questions. Aims. This is the third in a series of papers with the aim of studying the X-ray variability of different families of AGN. The main purpose of this work is to investigate the variability pattern(s) in a sample of optically selected Seyfert 2 galaxies. Methods. We use the 26 Seyfert 2s in the Véron-Cetty and Véron catalog with data available from Chandra and/or XMM-Newton public archives at different epochs, with timescales ranging from a few hours to years. All the spectra of the same source were simultaneously fitted, and we let different parameters vary in the model. Whenever possible, short-term variations from the analysis of the light curves and/or long-term UV flux variations were studied. We divided the sample into Compton-thick and Compton-thin candidates to account for the degree of obscuration. When transitions between Compton-thick and thin were obtained for different observations of the same source, we classified it as a changing-look candidate. Results. Short-term variability at X-rays was studied in ten cases, but variations are not found. From the 25 analyzed sources, 11 show long-term variations. Eight (out of 11) are Compton-thin, one (out of 12) is Compton-thick, and the two changing-look candidates are also variable. The main driver for the X-ray changes is related to the nuclear power (nine cases), while variations at soft energies or related to absorbers at hard X-rays are less common, and in many cases these variations are accompanied by variations in the nuclear continuum. At UV frequencies, only NGC5194 (out of six sources) is variable, but the changes are not related to the nucleus. We report two changing-look candidates, MARK273 and NGC7319. Conclusions. A constant reflection component located far away from the nucleus plus a variable nuclear continuum are able to explain most of our results. Within this scenario, the Compton-thick candidates are dominated by reflection, which suppresses their continuum, making them seem fainter, and they do not show variations (except MARK3), while the Compton-thin and changing-look candidates do. [ABSTRACT FROM AUTHOR]

Context. Most of the optically classified low-ionisation, narrow emission-line regions (LINERs) nuclei host an active galactic nucleus (AGN). However, how they fit into the unified model (UM) of AGN is still an open question. Aims. The aims of this work are to study at mid-infrared (mid-IR) (1) the Compton-thick nature of LINERs (i.e. hydrogen column densities of NH> 1.5 × 1024 cm-2) and (2) the disappearance of the dusty torus in LINERs predicted from theoretical arguments. Methods. We have compiled all the available low spectral-resolution, mid-IR spectra of LINERs from the InfraRed Spectrograph (IRS) onboard Spitzer. The sample contains 40 LINERs. We have complemented the LINER sample with Spitzer/IRS spectra of PGQSOs, Type-1 Seyferts (S1s), Type-2 Seyferts (S2s), and StarBurst (SB) nuclei. We studied the AGN compared to the starburst content in our sample using different indicators: the equivalent width of the polycyclic aromatic hydrocarbon at 6.2 µm, the strength of the silicate feature at 9.7 µm, and the steepness of the mid-IR spectra. We classified the spectra as SB-dominated and AGN-dominated, according to these diagnostics and compared the average mid-IR spectra of the various classes. Moreover, we studied the correlation between the 12 µm luminosity, vLv(12 µm), and the 2-10 keV energy band X-ray luminosity, LX(2-10 keV). Results. In 25 out of the 40 LINERs (i.e. 62.5%), the mid-IR spectra are not SB-dominated, similar to the comparison S2 sample (67.7%). The average spectra of both SB-dominated LINERs and S2s are very similar to the average spectrum of the SB class. The average spectrum of AGN-dominated LINERs is different from the average spectra of the other optical classes, showing a rather flat spectrum at 6-28 µm. We find that the average spectrum of AGN-dominated LINERs with X-ray luminosities LX(2-10 keV) > 1041 erg/s is similar to the average mid-IR spectrum of AGN-dominated S2s. However, faint LINERs (i.e. LX(2-10 keV) < 1041 erg/s) show flat spectra different from any of the other optical classes. The correlation between vLv(12 µm) and LX(2-10 keV) for AGN nicely extends towards low luminosities only if SB-dominated LINERs are excluded and if the 2-10 keV band X-ray luminosity is corrected in Compton-thick LINER candidates. Conclusions. We find that LINERs proposed as Compton-thick candidates at X-ray wavelengths may be confirmed according to the X-ray to mid-IR luminosity relation. We show evidence that the dusty-torus disappear when their bolometric luminosity is below Lbol ≃ 1042 erg/s. We suggest that the dominant emission at mid-IR of faint LINERs might be a combination of an elliptical galaxy host (characterised by the lack of gas), a starburst, a jet, and/or ADAF emission. Alternatively, the mid-IR emission of some of these faint LINERs could be a combination of elliptical galaxy plus carbon-rich planetary nebulae. To reconcile the Compton-thick nature of a large number of LINERs without dusty-torus signatures, we suggest that the material producing the Compton-thick X-ray obscuration is free of dust. [ABSTRACT FROM AUTHOR]

We present mid-infrared (MIR) imaging and spectroscopic data of the Seyfert 2 galaxy Mrk 1066 obtained with CanariCam (CC) on the 10.4-m Gran Telescopio CANARIAS (GTC). The galaxy was observed in imaging mode with an angular resolution of 0.24 arcsec (54 pc) in the Si-2 filter (8.7 μm). The image reveals a series of star-forming knots within the central ∼400 pc, after subtracting the dominant active galactic nucleus (AGN) component. We also subtracted this AGN unresolved component from the 8-13 μm spectra of the knots and the nucleus, and measured equivalent widths (EWs) of the 11.3 μm polycyclic aromatic hydrocarbon (PAH) feature which are typical of pure starburst galaxies. This EW is larger in the nucleus than in the knots, confirming that, at least in the case of Mrk 1066, the AGN dilutes, rather than destroys, the molecules responsible for the 11.3 μm PAH emission. By comparing the nuclear GTC/CC spectrum with the Spitzer/Infrared Spectrograph (IRS) spectrum of the galaxy, we find that the AGN component that dominates the continuum emission at λ < 15 μm on scales of ∼60 pc (90-100 per cent) decreases to 35-50 per cent when the emission of the central ∼830 pc is considered. On the other hand, the AGN contribution dominates the 15-25 μm emission (75 per cent) on the scales probed by Spitzer/IRS. We reproduced the nuclear infrared emission of the galaxy with clumpy torus models, and derived a torus gas mass of 2 × 105 M⊙, contained in a clumpy structure of ∼2 pc radius and with a column density compatible with Mrk 1066 being a Compton-thick candidate, in agreement with X-ray observations. We find a good match between the MIR morphology of Mrk 1066 and the extended Paβ, Brγ and [O III] λ5007 emission. This coincidence implies that the 8.7 μm emission is probing star formation, dust in the narrow-line region and the oval structure previously detected in the near-infrared. On the other hand, the Chandra soft X-ray morphology does not match any of the previous, contrary to what it is generally assumed for Seyfert galaxies. A thermal origin for the soft X-ray emission, rather than AGN photoionization, is suggested by the different data analysed here. [ABSTRACT FROM AUTHOR]

We present Gran Telescopio CANARIAS CanariCam 8.7 μm imaging and 7.5–13 μm spectroscopy of six local systems known to host an active galactic nucleus (AGN) and have nuclear star formation. Our main goal is to investigate whether the molecules responsible for the 11.3 μm polycyclic aromatic hydrocarbon (PAH) feature are destroyed in the close vicinity of an AGN. We detect 11.3 μm PAH feature emission in the nuclear regions of the galaxies as well as extended PAH emission over a few hundred parsecs. The equivalent width (EW) of the feature shows a minimum at the nucleus but increases with increasing radial distances, reaching typical star-forming values a few hundred parsecs away from the nucleus. The reduced nuclear EWs are interpreted as due to increased dilution from the AGN continuum rather than destruction of the PAH molecules. We conclude that at least those molecules responsible for the 11.3 μm PAH feature survive in the nuclear environments as close as 10 pc from the AGN and for Seyfert-like AGN luminosities. We propose that material in the dusty tori, nuclear gas discs, and/or host galaxies of AGN is likely to provide the column densities necessary to protect the PAH molecules from the AGN radiation field. [ABSTRACT FROM PUBLISHER]

Aims. This programme is aimed at obtaining one of the largest X-ray selected samples of identified active galactic nuclei to date in order to characterise such a population at intermediate fluxes, where most of the Universe's accretion power originates.We present the XMM-NewtonWide Angle Survey (XWAS), a new catalogue of almost a thousand X-ray sources spectroscopically identified through optical observations. Methods. A sample of X-ray sources detected in 68 XMM-Newton pointed observations was selected for optical multi-fibre spectroscopy. Optical counterparts and corresponding photometry of the X-ray sources were obtained from the SuperCOSMOS Sky Survey. Candidates for spectroscopy were initially selected with magnitudes down to R ~ 21, with preference for X-ray sources having a flux F0.5-4.5keV ⩾ 10-14 erg s-1 cm-2. Optical spectroscopic observations were made using the Two Degree Field of the Anglo Australian Telescope, and the resulting spectra were classified based on optical emission lines. Results. We have identified through optical spectroscopy 940 X-ray sources over Ω ~ 11.8 deg2 of the sky. Source populations in our sample can be summarised as 65% broad line active galactic nuclei (BLAGN), 16% narrow emission line galaxies (NELGs), 6% absorption line galaxies (ALGs) and 13% stars. An active nucleus is also likely to be present in the large majority of the X-ray sources spectroscopically classified as NELGs or ALGs. Sources lie in high-galactic latitude (∣b∣ > 20 deg) XMM-Newton fields mainly in the southern hemisphere. Owing to the large parameter space in redshift (0 ⩽ z ⩽ 4.25) and flux (10-15 ⩽ F0.5-4.5keV ⩽ 10-12 erg s-1 cm-2) covered by the XWAS this work provides an excellent resource for the further study of subsamples and particular cases. The overall properties of the extragalactic objects are presented in this paper. These include the redshift and luminosity distributions, optical and X-ray colours and X-ray-to-optical flux ratios. [ABSTRACT FROM AUTHOR]

Context. One of the most distinctive features in active galactic nuclei (AGN) is the variability of their emission. Variability has been discovered at X-ray, UV, and radio frequencies on timescales from hours to years. Among the AGN family and according to theoretical studies, low-ionization nuclear emission line region (LINER) nuclei would be objects variable on long timescales. Aims. Our purpose is to investigate spectral X-ray variability in LINERs and to understand the nature of these types of objects, as well as their accretion mechanism. Methods. Chandra and XMM-Newton public archives were used to compile X-ray spectra of seven LINER nuclei at different epochs with timescales of years. To search for variability we fit all spectra from the same object with a set of models to identify the parameters responsible for the variability pattern. We also analyzed the light curves to search for short timescale (from hours to days) variability. Whenever possible, UV variability was also studied. Results. We found spectral variability in four objects (NGC1052, NGC3226, NGC4278, and NGC4552), with variations mostly related to hard energies (2-10 keV). These variations are generated by several possible changes that act either alone or in combination: changes in the soft excess or in the absorber. Added to this can be intrinsic variations of the source, which may also be responsible by themselves for the spectral variability. These variations occurred within years, the shortest timescale being found for NGC4278 (two months). Another two galaxies (NGC4261 and NGC 5846) apparently do not vary. No short timescale variations during individual observations were found. Our analysis confirms the previously reported anticorrelation between the X-ray spectral index, Γ, and the Eddington ratio, Lbol/LEdd, and also the correlation between the X-ray to UV flux ratio, αox, and the Eddington ratio, Lbol/LEdd. These results support an advection dominated accretion flow as the accretion mechanism in LINERs. [ABSTRACT FROM AUTHOR]

Context. Active galactic nuclei (AGN), powered by accretion onto supermassive black holes (SMBHs), are thought to be scaled up versions of Galactic black hole X-ray binaries (BH-XRBs). In the past few years evidence of such correspondence include similarities in the broadband shape of the X-ray variability power spectra, with characteristic bend times-scales scaling with mass. Aims. The aim of this project is to characterize the X-ray temporal properties of a sample of AGN to study the connection among different classes of AGN and their connection with BH-XRBs. Methods. We have performed a uniform analysis of the power spectrum densities (PSDs) of 104 nearby (z < 0.4) AGN using 209 XMM-Newton/pn observations. These PSDs span ≃ 3 decades in temporal frequencies, ranging from minutes to days. The PSDs have been estimated in three energy bands: 0.2-10 (total), 0.2-2 (soft), and 2-10 keV (hard). The sample comprises 61 Type-1 AGN, 21 Type-2 AGN, 15 NLSy1, and 7 BLLACS. We have fitted each PSD to two models: (1) a single power-law model and (2) a bending power-law model. Results. Among the entire sample, 72% show significant variability in at least one of the three bands tested. A high percentage of low-luminosity AGN do not show any significant variability (86% of LINERs). The PSD of the majority of the variable AGN was well described by a simple power-law with a mean index of α = 2.01 ?± 0.01. In 15 sources we found that the bending power law model was preferred with a mean slope of α = 3.08 ± 0.04 and a mean bend frequency of ? ?b ? ≃ 2 × 10-4 Hz. Only KUG?1031+398 (RE?J1034+396) shows evidence for quasi-periodic oscillations. The "fundamental plane" relating variability timescale, black hole mass, and luminosity is demonstrated using the new X-ray timing results presented here together with a compilation of the previously detected timescales from the literature. Conclusions. Both quantitative (i.e. scaling with BH mass) and qualitative (overall PSD shapes) found in this sample of AGN are in agreement with the expectations for the SMBHs and BH-XRBs being the same phenomenon scaled-up with the size of the BH. The steep PSD slopes above the high frequency bend bear a closer resemblance to those of the "soft/thermal dominated" BH-XRB states than other states. [ABSTRACT FROM AUTHOR]