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Changing-look active galactic nuclei (CLAGNs) show the appearance and disappearance of broad emission lines in their UV/optical spectra on timescales of months to decades. Here, we investigate how CL transitions depend on several AGN parameters such as accretion rate, obscuration properties and black hole mass. We study a sample of 20 nearby optically-identified CLAGNs from the BAT AGN Spectroscopic Survey (BASS), using quasi-simultaneous optical and X-ray observations taken in the last $\sim 40$ years. We find that for all CLAGNs, the transition is accompanied by a change in Eddington ratio. The CL transitions are not associated with changes in the obscuration properties of the AGN. CLAGNs are found to have a median Eddington ratio lower than the AGNs in the BASS sample in which CL transitions were not detected. The median of the transition Eddington ratio (Eddington ratio at which AGN changes its state) is found to be $\sim 0.01$ for type 1 $\leftrightarrow$ 1.8/1.9/2 transition, which is consistent with the hard $\leftrightarrow$ soft state transition in black hole X-ray binaries. Most CL events are constrained to occur within 3-4 years, which is considerably shorter than the expected viscous timescale in AGN accretion disk. The transitions of the optical CLAGNs studied here are likely associated to state changes in the accretion flow, possibly driven by disk-instability., Comment: Accepted for publication in Astronomy & Astrophysics

We analyze the Spitzer spectra of 140 active galactic nuclei (AGN) detected in the hard X-rays (14-195 keV) by the Burst Alert Telescope (BAT) on board Swift. This sample allows us to probe several orders of magnitude in black hole masses ($10^6-10^9 M_{\odot}$), Eddington ratios ($10^{-3}-1$), X-ray luminosities ($10^{42}-10^{45}\rm\,erg\,s^{-1}$), and X-ray column densities ($10^{20}-10^{24}\rm\,cm^{-2}$). The AGN emission is expected to be the dominant source of ionizing photons with energies $\gtrsim50$ eV, and therefore high-ionization mid-infrared (MIR) emission lines such as [Ne V] 14.32, 24.32 $\mu$m and [O IV] 25.89 $\mu$m are predicted to be good proxies of AGN activity, and robust against obscuration effects. We find high detection rates ($\gtrsim85-90$ per cent) for the mid-infrared coronal emission lines in our AGN sample. The luminosities of these lines are correlated with the 14-150 keV luminosity (with a typical scatter of $\sigma \sim 0.4-0.5$ dex), strongly indicating that the mid-infrared coronal line emission is driven by AGN activity. Interestingly, we find that the coronal lines are more tightly correlated to the bolometric luminosity ($\sigma \sim 0.2-0.3$ dex), calculated from careful analysis of the spectral energy distribution, than to the X-ray luminosity. We find that the relationship between the coronal line strengths and $L_{14-150\rm\,keV}$ is independent of black hole mass, Eddington ratio and X-ray column density. This confirms that the mid-infrared coronal lines can be used as unbiased tracers of the AGN power for X-ray luminosities in the $10^{42}-10^{45}\rm\,erg\,s^{-1}$ range., Comment: ApJ in press

The origin of a compact millimeter (mm, 100-250 GHz) emission in radio-quiet active galactic nuclei (RQ AGN) remains debated. Recent studies propose a connection with self-absorbed synchrotron emission from the accretion disk X-ray corona. We present the first joint ALMA ($\sim$100 GHz) and X-ray (NICER/XMM-Newton/Swift; 2-10 keV) observations of the unobscured RQ AGN, IC 4329A ($z = 0.016$). The time-averaged mm-to-X-ray flux ratio aligns with recently established trends for larger samples (Kawamuro et al. 2022, Ricci et al. 2023), but with a tighter scatter ($\sim$0.1 dex) compared to previous studies. However, there is no significant correlation on timescales of less than 20 days. The compact mm emission exhibits a spectral index of $-0.23 \pm 0.18$, remains unresolved with a 13 pc upper limit, and shows no jet signatures. Notably, the mm flux density varies significantly (factor of 3) within 4 days, exceeding the contemporaneous X-ray variability (37% vs. 18%) and showing the largest mm variations ever detected in RQ AGN over daily timescales. The high amplitude variability rules out scenarios of heated dust and thermal free-free emission, pointing toward a synchrotron origin for the mm radiation in a source of $\sim$1 light day size. While the exact source is not yet certain, an X-ray corona scenario emerges as the most plausible compared to a scaled-down jet or outflow-driven shocks.}, Comment: Submitted to A&A

We present the results of a joint {\it XMM-Newton} and {\it NuSTAR} campaign on the active galactic nucleus (AGN) IC 4329A, consisting of 9 $\times$ 20 ks {\it XMM-Newton} observations, and 5 $\times$ 20 ks {\it NuSTAR} observations within nine days, performed in August 2021. Within each observation, the AGN is not very variable, with the fractional variability never exceeding 5%. Flux variations are observed between the different observations, on timescales of days, with a 30% ratio between the minimum and the maximum 2-10 keV flux. These variations follow the softer-when-brighter behavior typically observed in AGN. In all observations, a soft excess is clearly present. Consistently with previous observations, the X-ray spectra of the source exhibit a cut-off energy between 140 and 250 keV, constant within the error in the different observations. We detected a prominent component of the $6.4$\,keV Fe~K$\alpha$ line consistent with being constant during the monitoring, consisting of an unresolved narrow core and a broader component likely originating in the inner accredion disc. We find that the reflection component is weak ($R_{\rm max}=0.009\pm0.002$) and most likely originating in distant neutral medium. We also found the presence of a warm absorber component together with an ultra-fast outflow. Looking at their energetic, these outflows have enough mechanical power to exercise a significant feedback impact on the AGN surrounding environment., Comment: Accepted for publication in Astronomy & Astrophysics

Stellar and black hole feedback heat and disperse surrounding cold gas clouds, launching gas flows off circumnuclear and galactic disks and producing a dynamic interstellar medium. On large scales bordering the cosmic web, feedback drives enriched gas out of galaxies and groups, seeding the intergalactic medium with heavy elements. In this way, feedback shapes galaxy evolution by shutting down star formation and ultimately curtailing the growth of structure after the peak at redshift 2-3. To understand the complex interplay between gravity and feedback, we must resolve both the key physics within galaxies and map the impact of these processes over large scales, out into the cosmic web. The Advanced X-ray Imaging Satellite (AXIS) is a proposed X-ray probe mission for the 2030s with arcsecond spatial resolution, large effective area, and low background. AXIS will untangle the interactions of winds, radiation, jets, and supernovae with the surrounding ISM across the wide range of mass scales and large volumes driving galaxy evolution and trace the establishment of feedback back to the main event at cosmic noon., Comment: 29 pages, 18 figures; this white paper is part of a series commissioned for the AXIS Probe mission concept

Accreting supermassive black holes (SMBHs) located at the center of galaxies are typically surrounded by large quantities of gas and dust. The structure and evolution of this circumnuclear material can be studied at different wavelengths, from the submillimeter to the X-rays. Recent X-ray studies have shown that the covering factor of the obscuring material tends to decrease with increasing Eddington ratio, likely due to radiative feedback on dusty gas. Here we study a sample of 549 nearby (z<0.1) hard X-ray (14-195 keV) selected non-blazar active galactic nuclei (AGN), and use the ratio between the AGN infrared and bolometric luminosity as a proxy of the covering factor. We find that, in agreement with what has been found by X-ray studies of the same sample, the covering factor decreases with increasing Eddington ratio. We also confirm previous findings which showed that obscured AGN typically have larger covering factors than unobscured sources. Finally, we find that the median covering factors of AGN located in different regions of the column density-Eddington ratio diagram are in good agreement with what would be expected from a radiation-regulated growth of SMBHs., Comment: ApJ in press

An interesting feature in active galactic nuclei (AGN) accreting at low rate is the weakness of the reflection features in their X-ray spectra, which can result from the gradual disappearance of the torus with decreasing accretion rates. It has been suggested that low luminosity AGN (LLAGN) would have a different reflector configuration compared with high luminosity AGN, either covering a smaller fraction of the sky or simply having less material. Additionally, we note that the determination of the spectral index ($\Gamma$) and the cut-off energy of the primary power-law emission is affected by the inclusion of reflection models, showing the importance of using them to study the accretion mechanism, especially in the case of the LLAGN that have previously shown a high dispersion on the relation between $\Gamma$ and the accretion rate. Our purpose is to constrain the geometry and column density of the reflector in a sample of LLAGN covering a broad X-ray range of energy combining data from XMM-Newton + NuSTAR + Swift of a hard X-ray-flux limited sample of 17 LLAGN from BASS/DR2 with accretion rates $\lambda_{Edd}$=L$_{\rm Bol}$/L$_{\rm Edd}$<10$^{-3}$. We fit all spectra using the reflection model for torus (borus02) and accretion disk (Xillver) reflectors. We found a tentative correlation between the torus column density and the accretion rate, LLAGN shows a lower column density compared with the high-luminosity objects. We also confirm the relation between $\Gamma$ and $\lambda_{Edd}$, with a smaller scatter than previously reported, thanks to the inclusion of high-energy data and the reflection models. Our results are consistent with a break at $\lambda_{Edd}\sim10^{-3}$, suggestive of a different accretion mechanism compared with higher accretion AGN., Comment: Accepted for publication in Astronomy & Astrophysics

We derive the most up-to-date Swift-Burst Alert Telescope (BAT) blazar luminosity function in the 14-195 keV range, making use of a clean sample of 118 blazars detected in the BAT 105-month survey catalog, with newly obtained redshifts from the BAT AGN Spectroscopic Survey (BASS). We determine the best-fit X-ray luminosity function for the whole blazar population, as well as for Flat Spectrum Radio Quasars (FSRQs) alone. The main results are: (1) at any redshift, BAT detects the most luminous blazars, above any possible break in their luminosity distribution, which means we cannot differentiate between density and luminosity evolution; (2) the whole blazar population, dominated by FSRQs, evolves positively up to redshift z~4.3, confirming earlier results and implying lower number densities of blazars at higher redshifts than previously estimated. The contribution of this source class to the Cosmic X-ray Background at 14-195 keV can range from 5-18%, while possibly accounting for 100% of the MeV background. We also derived the average 14 keV-10 GeV SED for BAT blazars, which allows us to predict the number counts of sources in the MeV range, as well as the expected number of high-energy (>100 TeV) neutrinos. A mission like COSI, will detect 40 MeV blazars and 2 coincident neutrinos. Finally, taking into account beaming selection effects, the distribution and properties of the parent population of these extragalactic jets are derived. We find that the distribution of viewing angles is quite narrow, with most sources aligned within < 5{\deg} of the line of sight. Moreover, the average Lorentz factor, <$\Gamma$>= 8-12, is lower than previously suggested for these powerful sources., Comment: Accepted for publication in the Astrophysical Journal; 33 pages; 8 Tables; 16 Figures

We investigate the connection between supermassive black holes (SMBHs) and their host dark matter halos in the local universe using the clustering statistics and luminosity function of AGN from the Swift/BAT AGN Spectroscopic survey (BASS DR2). By forward-modeling AGN activity into snapshot halo catalogs from N-body simulations, we test a scenario in which SMBH mass correlates with dark matter (sub)halo mass for fixed stellar mass. We compare this to a model absent of this correlation, where stellar mass alone determines the SMBH mass. We find that while both simple models are able to largely reproduce the abundance and overall clustering of AGN, the model in which black hole mass is tightly correlated with halo mass is preferred by the data by $1.8\sigma$. When including an independent measurement on the black hole mass-halo mass correlation, this model is preferred by $4.6\sigma$. We show that the clustering trends with black hole mass can further break the degeneracies between the two scenarios, and that our preferred model reproduces the measured clustering differences on 1-halo scales between large and small black hole masses. These results indicate that the halo binding energy is fundamentally connected to the growth of supermassive black holes., Comment: Accepted for publication in ApJ

We study the relation between obscuration and supermassive black hole (SMBH) growth using a large sample of hard X-ray selected Active Galactic Nuclei (AGN). We find a strong decrease in the fraction of obscured sources above the Eddington limit for dusty gas ($\log \lambda_{\rm Edd}\gtrsim -2$) confirming earlier results, and consistent with the radiation-regulated unification model. This also explains the difference in the Eddington ratio distribution functions (ERDFs) of type 1 and type 2 AGN obtained by a recent study. The break in the ERDF of nearby AGN is at $\log \lambda_{\rm Edd}^{*}=-1.34\pm0.07$. This corresponds to the $\lambda_{\rm Edd}$ where AGN transition from having most of their sky covered by obscuring material to being mostly devoid of absorbing material. A similar trend is observed for the luminosity function, which implies that most of the SMBH growth in the local Universe happens when the AGN is covered by a large reservoir of gas and dust. These results could be explained with a radiation-regulated growth model, in which AGN move in the $N_{\rm H}-\lambda_{\rm Edd}$ plane during their life cycle. The growth episode starts with the AGN mostly unobscured and accreting at low $\lambda_{\rm Edd}$. As the SMBH is further fueled, $\lambda_{\rm Edd}$, $N_{\rm H}$ and covering factor increase, leading AGN to be preferentially observed as obscured. Once $\lambda_{\rm Edd}$ reaches the Eddington limit for dusty gas, the covering factor and $N_{\rm H}$ rapidly decrease, leading the AGN to be typically observed as unobscured. As the remaining fuel is depleted, the SMBH goes back into a quiescent phase., Comment: Accepted for publication in ApJ

We present integral field spectroscopic observations of NGC 5972 obtained with the Multi Unit Spectroscopic Explorer (MUSE) at VLT. NGC 5972 is a nearby galaxy containing both an active galactic nucleus (AGN), and an extended emission line region (EELR) reaching out to $\sim 17$ kpc from the nucleus. We analyze the physical conditions of the EELR using spatially-resolved spectra, focusing on the radial dependence of ionization state together with the light travel time distance to probe the variability of the AGN on $\gtrsim 10^{4}$ yr timescales. The kinematic analysis suggests multiple components: (a) a faint component following the rotation of the large scale disk; (b) a component associated with the EELR suggestive of extraplanar gas connected to tidal tails; (c) a kinematically decoupled nuclear disk. Both the kinematics and the observed tidal tails suggest a major past interaction event. Emission line diagnostics along the EELR arms typically evidence Seyfert-like emission, implying that the EELR was primarily ionized by the AGN. We generate a set of photoionization models and fit these to different regions along the EELR. This allows us to estimate the bolometric luminosity required at different radii to excite the gas to the observed state. Our results suggests that NGC 5972 is a fading quasar, showing a steady gradual decrease in intrinsic AGN luminosity, and hence the accretion rate onto the SMBH, by a factor $\sim 100$ over the past $5 \times 10^{4}$ yr., Comment: To be published in The Astrophysical Journal

Ionised gas kinematics provide crucial evidence of the impact that active galactic nuclei (AGN) have in regulating star formation in their host galaxies. Although the presence of outflows in AGN host galaxies has been firmly established, the calculation of outflow properties such as mass outflow rates and kinetic energy remains challenging. We present the [OIII]5007 ionised gas outflow properties of 22 z$<$0.1 X-ray AGN, derived from the BAT AGN Spectroscopic Survey using MUSE/VLT. With an average spatial resolution of 1" (0.1-1.2 kpc), the observations resolve the ionised gas clouds down to sub-kiloparsec scales. Resolved maps show that the [OIII] velocity dispersion is, on average, higher in regions ionised by the AGN, compared to star formation. We calculate the instantaneous outflow rates in individual MUSE spaxels by constructing resolved mass outflow rate maps, incorporating variable outflow density and velocity. We compare the instantaneous values with time-averaged outflow rates by placing mock fibres and slits on the MUSE field-of-view, a method often used in the literature. The instantaneous outflow rates (0.2-275 $M_{\odot}$ yr$^{-1}$) tend to be 2 orders of magnitude higher than the time-averaged outflow rates (0.001-40 $M_{\odot}$ yr$^{-1}$). The outflow rates correlate with the AGN bolometric luminosity ($L_{\rm bol}\sim$ 10$^{42.71}$-10$^{45.62}$ erg/s) but we find no correlations with black hole mass (10$^{6.1}$-10$^{8.9}$ M$_{\odot}$), Eddington ratio (0.002-1.1) and radio luminosity (10$^{21}$-10$^{26}$ W/Hz). We find the median coupling between the kinetic energy and $L_{\rm bol}$ to be 1%, consistent with the theoretical predictions for an AGN-driven outflow., Comment: Main paper: 20 pages, 15 figures, 3 tables. Accepted for publication in MNRAS

The merger of two or more galaxies can enhance the inflow of material from galactic scales into the close environments of Active Galactic Nuclei (AGN), obscuring and feeding the supermassive black hole (SMBH). Both recent simulations and observations of AGN in mergers have confirmed that mergers are related to strong nuclear obscuration. However, it is still unclear how AGN obscuration evolves in the last phases of the merger process. We study a sample of 60 Luminous and Ultra-luminous IR galaxies (U/LIRGs) from the GOALS sample observed by NuSTAR. We find that the fraction of AGN that are Compton-thick (CT; $N_{\rm H}\geq 10^{24}\rm\,cm^{-2}$) peaks at $74_{-19}^{+14}\%$ at a late merger stage, prior to coalescence, when the nuclei have projected separations of $d_{\rm sep}\sim 0.4-6$ kpc. A similar peak is also observed in the median $N_{\rm H}$ [$(1.6\pm0.5)\times10^{24}\rm\,cm^{-2}$]. The vast majority ($85^{+7}_{-9}\%$) of the AGN in the final merger stages ($d_{\rm sep}\lesssim 10$ kpc) are heavily obscured ($N_{\rm H}\geq 10^{23}\rm\,cm^{-2}$), and the median $N_{\rm H}$ of the accreting SMBHs in our sample is systematically higher than that of local hard X-ray selected AGN, regardless of the merger stage. This implies that these objects have very obscured nuclear environments, with the $N_{\rm H}\geq 10^{23}\rm\,cm^{-2}$ gas almost completely covering the AGN in late mergers. CT AGN tend to have systematically higher absorption-corrected X-ray luminosities than less obscured sources. This could either be due to an evolutionary effect, with more obscured sources accreting more rapidly because they have more gas available in their surroundings, or to a selection bias. The latter scenario would imply that we are still missing a large fraction of heavily obscured, lower luminosity ($L_{2-10}\lesssim 10^{43}\rm\,erg\,s^{-1}$) AGN in U/LIRGs.

We present the first high signal-to-noise broadband X-ray spectrum of the radio-quiet type-2 Seyfert ESO 033-G002, combining data from $XMM$-$Newton$ and $NuSTAR$. The nuclear X-ray spectrum is complex, showing evidence for both neutral and ionised absorption, as well as reflection from both the accretion disc and more distant material, but our broadband coverage allows us to disentangle all of these different components. The total neutral column during this epoch is $N_{\rm{H}} \sim 5-6 \times 10^{22}$ cm$^{-2}$, consistent with the optical classification of ESO 033-G002 as a type-2 Seyfert but not so large as to prevent us from robustly determining the properties of the innermost accretion flow. The ionised absorption - dominated by lines from Fe XXV and Fe XXVI - reveals a moderately rapid outflow ($v_{\rm{out}} \sim 5400$ km s$^{-1}$) which has a column comparable to the neutral absorption. We find the disc reflection from the innermost regions to be extreme, with a reflection fraction of $R_{\rm{frac}} \sim 5$. This requires strong gravitational lightbending and, in turn, both an extremely compact corona (within $\sim$2 $R_{\rm{G}}$ of the black hole) and a rapidly rotating black hole ($a^* > 0.96$). Despite this tight size constraint, with a temperature of $kT_{\rm{e}} = 40-70$ keV the X-ray corona in ESO 033-G002 appears similar to other AGN in terms of its placement in the compactness-temperature plane, consistent with sitting close to the limit determined by runaway pair production. Finally, combining X-ray spectroscopy, timing and updated optical spectroscopy, we also estimate the mass of the black hole to be $\log[M_{\rm{BH}} / M_{\odot}] \sim 7.0 - 7.5$., Comment: 15 pages, 8 figures; published in MNRAS

Accreting supermassive black holes (SMBHs), also known as active galactic nuclei (AGN), are generally surrounded by large amounts of gas and dust. This surrounding material reprocesses the primary X-ray emission produced close to the SMBH and gives rise to several components in the broadband X-ray spectra of AGN, including a power-law possibly associated with Thomson-scattered radiation. In this work, we study the properties of this scattered component for a sample of 386 hard-X-ray-selected, nearby ($z \sim 0.03$) obscured AGN from the 70-month Swift/BAT catalog. We investigate how the fraction of Thomson-scattered radiation correlates with different physical properties of AGN, such as line-of-sight column density, X-ray luminosity, black hole mass, and Eddington ratio. We find a significant negative correlation between the scattering fraction and the column density. Based on a large number of spectral simulations, we exclude the possibility that this anti-correlation is due to degeneracies between the parameters. The negative correlation also persists when considering different ranges of luminosity, black hole mass, and Eddington ratio. We discuss how this correlation might be either due to the angle dependence of the Thomson cross-section or to more obscured sources having a higher covering factor of the torus. We also find a positive correlation between the scattering fraction and the ratio of [OIII] $\lambda$5007 to X-ray luminosity. This result is consistent with previous studies and suggests that the Thomson-scattered component is associated with the narrow-line region., Comment: Accepted for publication in MNRAS, 18 pages, 9 figures, 2 tables, 1 equation

Accretion disks and coronae around massive black holes have been studied extensively, and they are known to be coupled. Over a period of 30 years, however, the X-ray (coronal) flux of Mrk 817 increased by a factor of 40 while its UV (disk) flux remained relatively steady. Recent high-cadence monitoring finds that the X-ray and UV continua in Mrk 817 are also decoupled on time scales of weeks and months. These findings could require mechanical beaming of the innermost accretion flow, and/or an absorber that shields the disk and/or broad line region (BLR) from the X-ray corona. Herein, we report on a 135 ks observation of Mrk 817 obtained with NuSTAR, complemented by simultaneous X-ray coverage via the Neil Gehrels Swift Observatory. The X-ray data strongly prefer a standard relativistic disk reflection model over plausible alternatives. Comparable fits with related models constrain the spin to lie in the range 0.5 < a < 1, and the viewing angle to lie between 10 deg. < theta < 22 deg. (including 1-sigma statistical errors and small systematic errors related to differences between the models). The spectra also reveal strong evidence of moderately ionized absorption, similar to but likely less extreme than obscuring events in NGC 5548 and NGC 3783. Archival Swift data suggest that the absorption may be variable. Particularly if the column density of this absorber is higher along the plane of the disk, it may intermittently mask or prevent coupling between the central engine, disk, and BLR in Mrk 817., Comment: Accepted for publication in ApJ Letters

Broadband X-ray spectroscopy of the X-ray emission produced in the coronae of active galactic nuclei (AGN) can provide important insights into the physical conditions very close to their central supermassive black holes. The temperature of the Comptonizing plasma that forms the corona is manifested through a high-energy cutoff that has been difficult to directly constrain even in the brightest AGN because it requires high-quality data at energies above 10 keV. In this paper we present a large collection of coronal cutoff constraints for obscured AGN based on a sample of 130 AGN selected in the hard X-ray band with Swift/BAT and observed nearly simultaneously with NuSTAR and Swift/XRT. We find that under a reasonable set of assumptions regarding partial constraints the median cutoff is well constrained to 290$\pm$20 keV, where the uncertainty is statistical and given at the 68% confidence level. We investigate the sensitivity of this result to our assumptions and find that consideration of various known systematic uncertainties robustly places the median cutoff between 240 keV and 340 keV. The central 68% of the intrinsic cutoff distribution is found to be between about 140 keV and 500 keV, with estimated uncertainties of 20 keV and 100 keV, respectively. In comparison with the literature, we find no clear evidence that the cutoffs in obscured and unobscured AGN are substantially different. Our analysis highlights the importance of carefully considering partial and potentially degenerate constraints on the coronal high-energy cutoff in AGN., Comment: Accepted for publication in ApJ; 21 pages, 7 figures

We study the X-ray spectra of a sample of 19 obscured, optically-selected Seyfert galaxies (Sy 1.8, 1.9 and 2) in the local universe ($d \leq 175$~Mpc), drawn from the CfA Seyfert sample. Our analysis is driven by the high sensitivity of NuSTAR in the hard X-rays, coupled with soft X-ray spectra using XMM-Newton, Chandra, Suzaku, and Swift/XRT. We also analyze the optical spectra of these sources in order to obtain accurate mass estimates and Eddington fractions. We employ four different models to analyze the X-ray spectra of these sources, which all result in consistent results. We find that 79-90 % of the sources are heavily obscured with line-of-sight column density $N_{\rm H} > 10^{23}~\rm cm^{-2}$. We also find a Compton-thick ($N_{\rm H} > 10^{24}~\rm cm^{-2}$) fraction of $37-53$ %. These results are consistent with previous estimates based on multi-wavelength analyses. We find that the fraction of reprocessed to intrinsic emission is positively correlated with $N_{\rm H}$ and negatively correlated with the intrinsic, unabsorbed, X-ray luminosity (in agreement with the Iwasawa-Taniguchi effect). Our results support the hypothesis that radiation pressure regulates the distribution of the circumnuclear material., Comment: Accepted for publication in ApJ

We present $NuSTAR$ observations of four active galactic nuclei (AGN) located within 15 Mpc. These AGN, namely ESO 121-G6, NGC 660, NGC 3486 and NGC 5195, have observed X-ray luminosities of $L_{\rm 2-10\ keV, obs} \lesssim$ 10$^{39}$ erg s$^{-1}$, classifying them as low luminosity AGN (LLAGN). We perform broadband X-ray spectral analysis for the AGN by combining our $NuSTAR$ data with $Chandra$ or $XMM-Newton$ observations to directly measure their column densities ($N_{\rm H}$) and infer their intrinsic power. We complement our X-ray data with archival and new high angular resolution mid-infrared (mid-IR) data for all objects, except NGC 5195. Based on our X-ray spectral analysis, we found that both ESO 121-G6 and NGC 660 are heavily obscured ($N_{\rm H}$ > 10$^{23}$ cm$^{-2}$; $L_{\rm 2-10\ keV,\ int} \sim$ 10$^{41}$ erg s$^{-1}$), and NGC 660 may be Compton-thick. We also note that the X-ray flux and spectral slope for ESO 121-G6 have significantly changed over the last decade, indicating significant changes in the obscuration and potentially accretion rate. On the other hand, NGC 3486 and NGC 5195 appear to be unobscured and just mildly obscured, respectively, with $L_{\rm 2-10\ keV,\ int} <$ 10$^{39}$ erg s$^{-1}$; i.e., genuine LLAGN. Both of the heavily obscured AGN have $L_{\rm bol} >$ 10$^{41}$ erg s$^{-1}$ and $\lambda_{\rm Edd} \gtrsim$ 10$^{-3}$, and are detected in high angular resolution mid-IR imaging, indicating the presence of obscuring dust on nuclear scale. NGC 3486 however, is undetected in high-resolution mid-IR imaging, and the current data do not provide stringent constraints on the presence or absence of obscuring nuclear dust in the AGN., Comment: 18 pages, 11 figures, 3 tables, accepted for publication in MNRAS

We report on the determination of electron densities, and their impact on the outflow masses and rates, measured in the central few hundred parsecs of 11 local luminous active galaxies. We show that the peak of the integrated line emission in the AGN is significantly offset from the systemic velocity as traced by the stellar absorption features, indicating that the profiles are dominated by outflow. In contrast, matched inactive galaxies are characterised by a systemic peak and weaker outflow wing. We present three independent estimates of the electron density in these AGN, discussing the merits of the different methods. The electron density derived from the [SII] doublet is significantly lower than than that found with a method developed in the last decade using auroral and transauroral lines, as well as a recently introduced method based on the ionization parameter. The reason is that, for gas photoionized by an AGN, much of the [SII] emission arises in an extended partially ionized zone where the implicit assumption that the electron density traces the hydrogen density is invalid. We propose ways to deal with this situation and we derive the associated outflow rates for ionized gas, which are in the range 0.001--0.5 M$_{\odot}$yr$^{-1}$ for our AGN sample. We compare these outflow rates to the relation between $\dot{M}_{out}$ and $L_{AGN}$ in the literature, and argue that it may need to be modified and rescaled towards lower mass outflow rates., Comment: accepted by MNRAS; 30 pages (the last 8 of which are extra figures in an appendix). This is an update of the original version posted

We present the highest resolution --- 15 pc (0.03'') --- ALMA $^{12}$CO(2-1) line emission and 1.3mm continuum maps, tracers of the molecular gas and dust, respectively, in the nearby merging galaxy system NGC 6240, that hosts two supermassive black holes growing simultaneously. These observations provide an excellent spatial match to existing Hubble optical and near-infrared observations of this system. A significant molecular gas mass, $\sim$9$\times$10$^9$M$_\odot$, is located in between the two nuclei, forming a clumpy stream kinematically dominated by turbulence, rather than a smooth rotating disk as previously assumed from lower resolution data. Evidence for rotation is seen in the gas surrounding the southern nucleus, but not in the northern one. Dynamical shells can be seen, likely associated with nuclear supernovae remnants. We further detect the presence of significant high velocity outflows, some of them reaching velocities $>$500 km/s, affecting a significant fraction, $\sim$11\% of the molecular gas in the nuclear region. Inside the spheres of influence of the northern and southern supermassive black holes we find molecular masses of 7.4$\times$10$^8$M$_\odot$ and 3.3$\times$10$^9$M$_\odot$, respectively. We are thus directly imaging the reservoir of gas that can accrete onto each supermassive black hole. These new ALMA maps highlight the critical need for high resolution observations of molecular gas in order to understand the feeding of supermassive black holes and its connection to galaxy evolution in the context of a major galaxy merger., Comment: 27 pages, 13 figures, accepted for publication by The Astrophysical Journal

We present a detailed study of ionized outflows in a large sample of ~650 hard X-ray detected AGN. Using optical spectroscopy from the BAT AGN Spectroscopic Survey (BASS) we are able to reveal the faint wings of the [OIII] emission lines associated with outflows covering, for the first time, an unexplored range of low AGN bolometric luminosity at low redshift (z~0.05). We test if and how the incidence and velocity of ionized outflow is related to AGN physical parameters: black hole mass, gas column density, Eddington Ratio, [OIII], X-ray, and bolometric luminosities. We find a higher occurrence of ionized outflows in type 1.9 (55%) and type 1 AGN (46%) with respect to type 2 AGN (24%). While outflows in type 2 AGN are evenly balanced between blue and red velocity offsets with respect to the [OIII] narrow component, they are almost exclusively blueshifted in type 1 and type 1.9 AGN. We observe a significant dependence between the outflow occurrence and accretion rate, which becomes relevant at high Eddington ratios (> -1.7). We interpret such behaviour in the framework of covering factor-Eddington ratio dependence. We don't find strong trends of the outflow maximum velocity with AGN physical parameters, as an increase with bolometric luminosity can be only identified when including samples of AGN at high luminosity and high redshift taken from literature., Comment: Accepted for publication in MNRAS, 15 pages, 19 figures, 1 table

We present a flux-resolved X-ray analysis of the dwarf Seyfert 1.8 galaxy NGC 4395, based on three archival $XMM-Newton$ and one archival $NuSTAR$ observations. The source is known to harbor a low mass black hole ($\sim 10^4- {\rm a~ few~}\times 10^{5}~\rm M_\odot$) and shows strong variability in the full X-ray range during these observations. We model the flux-resolved spectra of the source assuming three absorbing layers: neutral, mildly ionized, and highly ionized ($N_{\rm H} \sim 1.6\times 10^{22}-3.4 \times 10^{23}~\rm cm^{-2}$, $\sim 0.8-7.8 \times 10^{22}~\rm cm^{-2}$, and $ 3.8 \times 10^{22}~\rm cm^{-2}$, respectively. The source also shows intrinsic variability by a factor of $\sim 3$, on short timescales, due to changes in the nuclear flux, assumed to be a power law ($\Gamma = 1.6-1.67$). Our results show a positive correlation between the intrinsic flux and the absorbers' ionization parameter. The covering fraction of the neutral absorber varies during the first $XMM-Newton$ observation, which could explain the pronounced soft X-ray variability. However, the source remains fully covered by this layer during the other two observations, largely suppressing the soft X-ray variability. This suggests an inhomogeneous and layered structure in the broad line region. We also find a difference in the characteristic timescale of the power spectra between different energy ranges and observations. We finally show simulated spectra with $XRISM$, $Athena$, and $eXTP$, which will allow us to characterize the different absorbers, study their dynamics, and will help us identify their locations and sizes., Comment: Accepted for publication in ApJ

We report on our combined analysis of HST, VLT/MUSE, VLT/SINFONI, and ALMA observations of the local Seyfert 2 galaxy, NGC 5728 to investigate in detail the feeding and feedback of the AGN. The datasets simultaneously probe the morphology, excitation, and kinematics of the stars, ionized gas, and molecular gas over a large range of spatial scales (10 pc--10 kpc). NGC 5728 contains a large stellar bar which is driving gas along prominent dust lanes to the inner 1 kpc where the gas settles into a circumnuclear ring. The ring is strongly star forming and contains a substantial population of young stars as indicated by the lowered stellar velocity dispersion and gas excitation consistent with HII regions. We model the kinematics of the ring using the velocity field of the CO (2--1) emission and stars and find it is consistent with a rotating disk. The outer regions of the disk, where the dust lanes meet the ring, show signatures of inflow at a rate of 1 M$_{\sun}$ yr$^{-1}$. Inside the ring, we observe three molecular gas components corresponding to the circular rotation of the outer ring, a warped disk, and the nuclear stellar bar. The AGN is driving an ionized gas outflow that reaches a radius of 250 pc with a mass outflow rate of 0.08 M$_{\sun}$ yr$^{-1}$ consistent with its luminosity and scaling relations from previous studies. While we observe distinct holes in CO emission which could be signs of molecular gas removal, we find that largely the AGN is not disrupting the structure of the circumnuclear region., Comment: accepted for publication in MNRAS; 22 pages + Appendix, 16 figures

The recently released 105-month {\it Swift}-Burst Alert Telescope (BAT) all-sky hard X-ray survey catalog presents an opportunity to study astrophysical objects detected in the deepest look at the entire hard X-ray (14$-$195 keV) sky. Here we report the results of a multifrequency study of 146 blazars from this catalog, quadrupling the number compared to past studies, by utilizing recent data from the {\it Fermi}-Large Area Telescope (LAT), Swift-BAT, and archival measurements. In our $\gamma$-ray analysis of $\sim$10 years of the LAT data, 101 are found as $\gamma$-ray emitters, whereas, 45 remains LAT undetected. We model the broadband spectral energy distributions with a synchrotron-inverse Compton radiative model. On average, BAT detected sources host massive black holes ($M_{\rm bh}\sim10^9$ M$_{\odot}$) and luminous accretion disks ($L_{\rm d}\sim10^{46}$ erg s$^{-1}$). At high-redshifts ($z>2$), BAT blazars host more powerful jets with luminous accretion disks compared to those detected only with the {\it Fermi}-LAT. We find good agreement in the black hole masses derived from the single-epoch optical spectroscopic measurements and standard accretion disk modeling approaches. Other physical properties of BAT blazars are similar to those known for {\it Fermi}-LAT detected objects., Comment: 16 pages, 7 figures, 6 tables, to appear in the Astrophysical Journal. Full data tables and SED plots are included in the arXiv uploaded files

Current measurements show that the observed fraction of Compton-thick (CT) AGN is smaller than the expected values needed to explain the cosmic X-ray background. Prior fits to the X-ray spectrum of the nearby Seyfert-2 galaxy NGC 5347 ($z=0.00792,\, D =35.5 \rm ~Mpc $) have alternately suggested a CT and Compton-thin source. Combining archival data from $Suzaku$, $Chandra$, and - most importantly - new data from $NuSTAR$, and using three distinct families of models, we show that NGC 5347 is an obscured CTAGN ($N_{\rm H} > 2.23\times 10^{24}~\rm cm^{-2}$). Its 2-30~keV spectrum is dominated by reprocessed emission from distant material, characterized by a strong Fe K$\alpha$ line and a Compton hump. We found a large equivalent width of the Fe K$\alpha$ line ($\rm EW = 2.3 \pm 0.3$ keV) and a high intrinsic-to-observed flux ratio ($\sim 100$). All of these observations are typical for bona fide CTAGN. We estimate a bolometric luminosity of $L_{\rm bol} \simeq 0.014 \pm 0.005~L_{\rm Edd.}$. The $Chandra$ image of NGC 5347 reveals the presence of extended emission dominating the soft X-ray spectrum ($E < 2\,\rm keV$), which coincides with the [O III] emission detected in the $Hubble ~Space~ Telescope$ images. Comparison to other CTAGN suggests that NGC 5347 is broadly consistent with the average properties of this source class. We simulated $XRISM$ and $Athena$/X-IFU spectra of the source, showing the potential of these future missions in identifying CTAGN in the soft X-rays., Comment: Accepted for publication in ApJ

[Abridged] In our previous work on Ark 120, we found that its 2014 X-ray spectrum is dominated by Comptonisation, while the relativistic reflection emission only originates at tens of $R_{\rm g}$ from the SMBH. As a result, we could not constrain the SMBH spin from disc reflection alone. Our aim is to determine its SMBH spin from an alternative technique based on the global energetics of the disc-corona system. The spectral analysis uses simultaneous XMM-Newton (OM and pn) and NuSTAR observations on 2014 March 22 and 2013 February 18. We applied the optxconv model (based on optxagnf) to self consistently reproduce the emission from the inner corona (warm and hot thermal Comptonisation) and the outer disc (colour temperature corrected black body), taking into account both the disc inclination angle and relativistic effects. We modelled the mild relativistic reflection of the incident Comptonisation components using the xilconv model. We infer a SMBH spin of 0.83$^{+0.05}_{-0.03}$, adopting the SMBH reverberation mass of 1.50$\times$10$^{8}$ M$_{\odot}$. In addition, we find that the coronal radius decreases with increasing flux (by about a factor of two), from 85$^{+13}_{-10}$ $R_{\rm g}$ in 2013 to 14$\pm$3 $R_{\rm g}$ in 2014. This is the first time that such a constraint is obtained for a SMBH spin from this technique, thanks to the bare properties of Ark 120, its well determined SMBH mass, and the presence of a mild relativistic reflection component in 2014 which allows us to constrain the disc inclination angle. We caution that these results depend on the detailed disc-corona structure, which is not yet fully established. However, the realistic parameter values found suggest that this is a promising method to determine spin in moderate accretion rate AGN., Comment: 15 pages, 7 figures. Accepted for publication in A&A

The bulk of the X-ray emission in Active Galactic Nuclei (AGN) is produced very close to the accreting supermassive black hole (SMBH), in a corona of hot electrons which up scatters optical and ultraviolet photons from the accretion flow. The cutoff energy ($E_{\rm C}$) of the primary X-ray continuum emission carries important information on the physical characteristics of the X-ray emitting plasma, but little is currently known about its potential relation with the properties of accreting SMBHs. Using the largest broad-band (0.3-150 keV) X-ray spectroscopic study available to date, we investigate how the corona is related to the AGN luminosity, black hole mass and Eddington ratio ($\lambda_{\rm Edd}$). Assuming a slab corona the median values of the temperature and optical depth of the Comptonizing plasma are $kT_{\rm e}=105 \pm 18$ keV and $\tau=0.25\pm0.06$, respectively. When we properly account for the large number of $E_{\rm C}$ lower limits, we find a statistically significant dependence of the cutoff energy on the Eddington ratio. In particular, objects with $ \lambda_{\rm Edd}>0.1$ have a significantly lower median cutoff energy ($E_{\rm C}=160\pm41$ keV) than those with $\lambda_{\rm Edd}\leq 0.1$ ($E_{\rm C}=370\pm51$ keV). This is consistent with the idea that radiatively compact coronae are also cooler, because they tend to avoid the region in the temperature-compactness parameter space where runaway pair production would dominate. We show that this behaviour could also straightforwardly explain the suggested positive correlation between the photon index ($\Gamma$) and the Eddington ratio, being able to reproduce the observed slope of the $\Gamma-\lambda_{\rm Edd}$ trend., Comment: Accepted for publication in MNRAS

We present a broadband X-ray spectral analysis of the M51 system, including the dual active galactic nuclei (AGN) and several off-nuclear point sources. Using a deep observation by NuSTAR, new high-resolution coverage of M51b by Chandra, and the latest X-ray torus models, we measure the intrinsic X-ray luminosities of the AGN in these galaxies. The AGN of M51a is found to be Compton thick, and both AGN have very low accretion rates ($\lambda_{\rm Edd} <10^{-4}$). The latter is surprising considering that the galaxies of M51 are in the process of merging, which is generally predicted to enhance nuclear activity. We find that the covering factor of the obscuring material in M51a is $0.26 \pm 0.03$, consistent with the local AGN obscured fraction at $L_{\rm X}\sim 10^{40}$ erg s$^{-1}$. The substantial obscuring column does not support theories that the torus, presumed responsible for the obscuration, disappears at these low accretion luminosities. However, the obscuration may have resulted from the gas infall driven by the merger rather than the accretion process. We report on several extra-nuclear sources with $L_{\rm X}>10^{39}$ erg s$^{-1}$ and find that a spectral turnover is present below 10 keV in most such sources, in line with recent results on ultraluminous X-ray sources., Comment: Accepted for publication in ApJ

We characterize the environments of local accreting supermassive black holes by measuring the clustering of AGN in the Swift/BAT Spectroscopic Survey (BASS). With 548 AGN in the redshift range 0.01

We present optical and near-IR Integral Field Unit (IFU) and ALMA band 6 observations of the nearby dual Active Galactic Nuclei (AGN) Mrk 463. At a distance of 210 Mpc, and a nuclear separation of $\sim$4 kpc, Mrk 463 is an excellent laboratory to study the gas dynamics, star formation processes and supermassive black hole (SMBH) accretion in a late-stage gas-rich major galaxy merger. The IFU observations reveal a complex morphology, including tidal tails, star-forming clumps, and emission line regions. The optical data, which map the full extent of the merger, show evidence for a biconical outflow and material outflowing at $>$600 km s$^{-1}$, both associated with the Mrk 463E nucleus, together with large scale gradients likely related to the ongoing galaxy merger. We further find an emission line region $\sim$11 kpc south of Mrk 463E that is consistent with being photoionized by an AGN. Compared to the current AGN luminosity, the energy budget of the cloud implies a luminosity drop in Mrk 463E by a factor 3-20 over the last 40,000 years. The ALMA observations of $^{12}$CO(2-1) and adjacent 1mm continuum reveal the presence of $\sim$10$^{9}$M$_\odot$ in molecular gas in the system. The molecular gas shows velocity gradients of $\sim$800 km/s and $\sim$400 km/s around the Mrk 463E and 463W nuclei, respectively. We conclude that in this system the infall of $\sim$100s $M_\odot$/yr of molecular gas is in rough balance with the removal of ionized gas by a biconical outflow being fueled by a relatively small, $<$0.01% of accretion onto each SMBH., Comment: Accepted by The Astrophysical Journal, 23 pages, 19 figures

Using new APEX and JCMT spectroscopy of the CO 2-1 line, we undertake a controlled study of cold molecular gas in moderately luminous Active Galactic Nuclei (AGN) and inactive galaxies from the Luminous Local AGN with Matched Analogs (LLAMA) survey. We use spatially resolved infrared photometry of the LLAMA galaxies from 2MASS, WISE, IRAS & Herschel, corrected for nuclear emission using multi-component spectral energy distribution (SED) fits, to examine the dust-reprocessed star-formation rates (SFRs), molecular gas fractions and star formation efficiencies (SFEs) over their central 1 - 3 kpc. We find that the gas fractions and central SFEs of both active and inactive galaxies are similar when controlling for host stellar mass and morphology (Hubble type). The equivalent central molecular gas depletion times are consistent with the discs of normal spiral galaxies in the local Universe. Despite energetic arguments that the AGN in LLAMA should be capable of disrupting the observable cold molecular gas in their central environments, our results indicate that nuclear radiation only couples weakly with this phase. We find a mild preference for obscured AGN to contain higher amounts of central molecular gas, which suggests a connection between AGN obscuration and the gaseous environment of the nucleus. Systems with depressed SFEs are not found among the LLAMA AGN. We speculate that the processes that sustain the collapse of molecular gas into dense pre-stellar cores may also be a prerequisite for the inflow of material on to AGN accretion disks., Comment: 24 pages, 18 figures, 2 part Appendix; accepted for publication in MNRAS

In a complete sample of local 14-195 keV selected AGNs and inactive galaxies, matched by their host galaxy properties, we study the spatially resolved stellar kinematics and luminosity distributions at near-infrared wavelengths on scales of 10-150 pc, using SINFONI on the VLT. In this paper, we present the first half of the sample, which comprises 13 galaxies, 8 AGNs and 5 inactive galaxies. The stellar velocity fields show a disk-like rotating pattern, for which the kinematic position angle is in agreement with the photometric position angle obtained from large scale images. For this set of galaxies, the stellar surface brightness of the inactive galaxy sample is generally comparable to the matched sample of AGN but extends to lower surface brightness. After removal of the bulge contribution, we find a nuclear stellar light excess with an extended nuclear disk structure, and which exhibits a size-luminosity relation. While we expect the excess luminosity to be associated with a dynamically cooler young stellar population, we do not typically see a matching drop in dispersion. This may be because these galaxies have pseudo-bulges in which the intrinsic dispersion increases towards the centre. And although the young stars may have an impact in the observed kinematics, their fraction is too small to dominate over the bulge and compensate the increase in dispersion at small radii, so no dispersion drop is seen. Finally, we find no evidence for a difference in the stellar kinematics and nuclear stellar luminosity excess between these active and inactive galaxies., Comment: 34 pages, 25 figures. Accepted for publication in MNRAS

We analyze the evolution of the dual AGN in ESO 509-IG066, a galaxy pair located at z=0.034 whose nuclei are separated by 11 kpc. Previous observations with XMM-Newton on this dual AGN found evidence for two moderately obscured ($N_H\sim10^{22}$ cm$^{-2}$) X-ray luminous ($L_X\sim10^{43}$ erg/s) nuclear sources. We present an analysis of subsequent Chandra, NuSTAR and Swift/XRT observations that show one source has dropped in flux by a factor of 10 between 2004 and 2011, which could be explained by either an increase in the absorbing column or an intrinsic fading of the central engine possibly due to a decrease in mass accretion. Both of these scenarios are predicted by galaxy merger simulations. The source which has dropped in flux is not detected by NuSTAR, which argues against absorption, unless it is extreme. However, new Keck/LRIS optical spectroscopy reveals a previously unreported broad H-alpha line which is highly unlikely to be visible under the extreme absorption scenario. We therefore conclude that the black hole in this nucleus has undergone a dramatic drop in accretion rate. From AO-assisted near-infrared integral-field spectroscopy of the other nucleus, we find evidence that the galaxy merger is having a direct effect on the kinematics of the gas close to the nucleus of the galaxy, providing a direct observational link between the galaxy merger and the mass accretion rate on to the black hole., Comment: Accepted for publication in ApJ

We identify sources with extremely hard X-ray spectra (i.e., with photon indices of Gamma<0.6 in the 13 sq. deg. NuSTAR serendipitous survey, to search for the most highly obscured AGNs detected at >10 keV. Eight extreme NuSTAR sources are identified, and we use the NuSTAR data in combination with lower energy X-ray observations (from Chandra, Swift XRT, and XMM-Newton) to characterize the broad-band (0.5-24 keV) X-ray spectra. We find that all of the extreme sources are highly obscured AGNs, including three robust Compton-thick (CT; N_H > 1.5e24 cm^-2) AGNs at low redshift (z<0.1), and a likely-CT AGN at higher redshift (z=0.16). Most of the extreme sources would not have been identified as highly obscured based on the low energy (<10 keV) X-ray coverage alone. The multiwavelength properties (e.g., optical spectra and X-ray/MIR luminosity ratios) provide further support for the eight sources being significantly obscured. Correcting for absorption, the intrinsic rest-frame 10-40 keV luminosities of the extreme sources cover a broad range, from ~ 5 x 10^42 to 10^45 erg s^-1. The estimated number counts of CT AGNs in the NuSTAR serendipitous survey are in broad agreement with model expectations based on previous X-ray surveys, except for the lowest redshifts (z<0.07) where we measure a high CT fraction of f_CT^obs = 30 (+16 -12) %. For the small sample of CT AGNs, we find a high fraction of galaxy major mergers (50 +/- 33%) compared to control samples of "normal" AGNs., Comment: 19 pages, 15 figures, 5 tables; Accepted for publication in ApJ; Author list updated

To fully understand cosmic black hole growth we need to constrain the population of heavily obscured active galactic nuclei (AGN) at the peak of cosmic black hole growth ($z\sim$1-3). Sources with obscuring column densities higher than $\mathrm{10^{24}}$ atoms $\mathrm{cm^{-2}}$, called Compton-thick (CT) AGN, can be identified by excess X-ray emission at $\sim$20-30 keV, called the "Compton hump". We apply the recently developed Spectral Curvature (SC) method to high-redshift AGN (25\times 10^{43}}$ erg $\mathrm{s^{-1}}$. In the Cosmological evolution survey (COSMOS), we find an observed CT fraction of $\mathrm{15^{+4}_{-3}\%}$ (40/272) or $\mathrm{32\pm11 \%}$ when corrected for the survey sensitivity. When comparing to low redshift AGN with similar X-ray luminosities, our results imply the CT AGN fraction is consistent with having no redshift evolution. Finally, we provide SC equations that can be used to find high-redshift CT AGN (z>1) for current (XMM-Newton) and future (eROSITA and ATHENA) X-ray missions., Comment: 10 pages, 8 figures

We present X-ray bolometric correction factors, $\kappa_{Bol}$ ($\equiv L_{Bol}/L_X$), for Compton-thick (CT) active galactic nuclei (AGN) with the aim of testing AGN torus models, probing orientation effects, and estimating the bolometric output of the most obscured AGN. We adopt bolometric luminosities, $L_{Bol}$, from literature infrared (IR) torus modeling and compile published intrinsic 2--10 keV X-ray luminosities, $L_{X}$, from X-ray torus modeling of NuSTAR data. Our sample consists of 10 local CT AGN where both of these estimates are available. We test for systematic differences in $\kappa_{Bol}$ values produced when using two widely used IR torus models and two widely used X-ray torus models, finding consistency within the uncertainties. We find that the mean $\kappa_{Bol}$ of our sample in the range $L_{Bol}\approx10^{42}-10^{45}$ erg/s is log$_{10}\kappa_{Bol}=1.44\pm0.12$ with an intrinsic scatter of $\sim0.2$ dex, and that our derived $\kappa_{Bol}$ values are consistent with previously established relationships between $\kappa_{Bol}$ and $L_{Bol}$ and $\kappa_{Bol}$ and Eddington ratio. We investigate if $\kappa_{Bol}$ is dependent on $N_H$ by comparing our results on CT AGN to published results on less-obscured AGN, finding no significant dependence. Since many of our sample are megamaser AGN, known to be viewed edge-on, and furthermore under the assumptions of AGN unification whereby unobscured AGN are viewed face-on, our result implies that the X-ray emitting corona is not strongly anisotropic. Finally, we present $\kappa_{Bol}$ values for CT AGN identified in X-ray surveys as a function of their observed $L_X$, where an estimate of their intrinsic $L_{X}$ is not available, and redshift, useful for estimating the bolometric output of the most obscured AGN across cosmic time., Comment: Accepted for publication in ApJ

We present a sample of 10 low-mass active galactic nuclei (AGNs) selected from the 40-month NuSTAR serendipitous survey. The sample is selected to have robust NuSTAR detections at $3 - 24$~keV, to be at $z < 0.3$, and to have optical r-band magnitudes at least 0.5~mag fainter than an $L_\star$ galaxy at its redshift. The median values of absolute magnitude, stellar mass and 2--10 X-ray luminosity of our sample are $\langle M_r\rangle = -20.03$, $\langle M_\star\rangle = 4.6\times10^{9}M_\odot$, and $\langle L_{2-10\mathrm{keV}}\rangle = 3.1\times10^{42}$ erg s$^{-1}$, respectively. Five objects have detectable broad H$\alpha$ emission in their optical spectra, indicating black-hole masses of $(1.1-10.4)\times 10^6 M_\odot$. We find that $30^{+17}_{-10}\%$ of the galaxies in our sample do not show AGN-like optical narrow emission lines, and one of the ten galaxies in our sample, J115851+4243.2, shows evidence for heavy X-ray absorption. This result implies that a non-negligible fraction of low-mass galaxies might harbor accreting massive black holes that are missed by optical spectroscopic surveys and $<10$ keV X-ray surveys. The mid-IR colors of our sample also indicate these optically normal low-mass AGNs cannot be efficiently identified with typical AGN selection criteria based on WISE colors. While the hard ($>10$ keV) X-ray selected low-mass AGN sample size is still limited, our results show that sensitive NuSTAR observations are capable of probing faint hard X-ray emission originating from the nuclei of low-mass galaxies out to moderate redshift ($z<0.3$), thus providing a critical step in understanding AGN demographics in low-mass galaxies., Comment: Accepted for publication in ApJ. 27 pages, 6 tables, 10 figures, including one online figure set available at https://ctjchen.github.io/ctc_nustardwarf_figset.pdf (v2: updated acknowledgement.)

MCG-5-23-16 was targeted in early 2015 with a half mega-seconds observing campaign using NuSTAR. Here we present the spectral analysis of these datasets along with an earlier observation and study the relativistic reflection and the primary coronal source. The data show strong reflection features in the form of both narrow and broad iron lines plus a Compton reflection hump. A cutoff energy is significantly detected in all exposures. The shape of the reflection spectrum does not change in the two years spanned by the observations, suggesting a stable geometry. A strong positive correlation is found between the cutoff energy and both the hard X-ray flux and spectral index. The measurements imply that the coronal plasma is not at the runaway electron-positron pair limit, and instead contains mostly electrons. The observed variability in the coronal properties is driven by a variable optical depth. A constant heating to cooling ratio is measured implying that there is a feedback mechanism in which a significant fraction of the photons cooling the corona are due to reprocessed hard X-rays., Comment: Accepted for publication in ApJ

NGC 1448 is one of the nearest luminous galaxies ($L_{8-1000\mu m} >$ 10$^{9} L_{\odot}$) to ours ($z$ $=$ 0.00390), and yet the active galactic nucleus (AGN) it hosts was only recently discovered, in 2009. In this paper, we present an analysis of the nuclear source across three wavebands: mid-infrared (MIR) continuum, optical, and X-rays. We observed the source with the Nuclear Spectroscopic Telescope Array (NuSTAR), and combined this data with archival Chandra data to perform broadband X-ray spectral fitting ($\approx$0.5-40 keV) of the AGN for the first time. Our X-ray spectral analysis reveals that the AGN is buried under a Compton-thick (CT) column of obscuring gas along our line-of-sight, with a column density of $N_{\rm H}$(los) $\gtrsim$ 2.5 $\times$ 10$^{24}$ cm$^{-2}$. The best-fitting torus models measured an intrinsic 2-10 keV luminosity of $L_{2-10\rm{,int}}$ $=$ (3.5-7.6) $\times$ 10$^{40}$ erg s$^{-1}$, making NGC 1448 one of the lowest luminosity CTAGNs known. In addition to the NuSTAR observation, we also performed optical spectroscopy for the nucleus in this edge-on galaxy using the European Southern Observatory New Technology Telescope. We re-classify the optical nuclear spectrum as a Seyfert on the basis of the Baldwin-Philips-Terlevich diagnostic diagrams, thus identifying the AGN at optical wavelengths for the first time. We also present high spatial resolution MIR observations of NGC 1448 with Gemini/T-ReCS, in which a compact nucleus is clearly detected. The absorption-corrected 2-10 keV luminosity measured from our X-ray spectral analysis agrees with that predicted from the optical [OIII]$\lambda$5007\AA\ emission line and the MIR 12$\mu$m continuum, further supporting the CT nature of the AGN., Comment: Accepted for publication in ApJ on Dec. 27th, 2016; 14 pages; 9 figures and 2 tables

We present the first full catalog and science results for the NuSTAR serendipitous survey. The catalog incorporates data taken during the first 40 months of NuSTAR operation, which provide ~20Ms of effective exposure time over 331 fields, with an areal coverage of 13 sq deg, and 497 sources detected in total over the 3-24 keV energy range. There are 276 sources with spectroscopic redshifts and classifications, largely resulting from our extensive campaign of ground-based spectroscopic followup. We characterize the overall sample in terms of the X-ray, optical, and infrared source properties. The sample is primarily comprised of active galactic nuclei (AGNs), detected over a large range in redshift from z = 0.002 - 3.4 (median of = 0.56), but also includes 16 spectroscopically confirmed Galactic sources. There is a large range in X-ray flux, from log( f_3-24keV / erg s^-1 cm^-2 ) ~ -14 to -11, and in rest-frame 10-40 keV luminosity, from log( L_10-40keV / erg s^-1 ) ~ 39 to 46, with a median of 44.1. Approximately 79% of the NuSTAR sources have lower energy (<10 keV) X-ray counterparts from XMM-Newton, Chandra, and Swift/XRT. The mid-infrared (MIR) analysis, using WISE all-sky survey data, shows that MIR AGN color selections miss a large fraction of the NuSTAR-selected AGN population, from ~15% at the highest luminosities (Lx > 10^44 erg s^-1) to ~80% at the lowest luminosities (Lx < 10^43 erg s^-1). Our optical spectroscopic analysis finds that the observed fraction of optically obscured AGNs (i.e., the Type 2 fraction) is F_Type2 = 53(+14-15)%, for a well-defined subset of the 8-24 keV selected sample. This is higher, albeit at a low significance level, than the Type 2 fraction measured for redshift- and luminosity-matched AGNs selected by <10 keV X-ray missions., Comment: 49 pages, 23 figures, 8 tables. Accepted for publication in ApJ

We discuss the broadband X-ray spectrum of GRS 1734-292 obtained from non-simultaneous XMM-Newton and NuSTAR observations, performed in 2009 and 2014, respectively. GRS1734-292 is a Seyfert 1 galaxy, located near the Galactic plane at $z=0.0214$. The NuSTAR spectrum ($3-80$ keV) is dominated by a primary power-law continuum with $\Gamma=1.65 \pm 0.05$ and a high-energy cutoff $E_c=53^{+11}_{-8}$ keV, one of the lowest measured by NuSTAR in a Seyfert galaxy. Comptonization models show a temperature of the coronal plasma of $kT_e=11.9^{+1.2}_{-0.9}$ keV and an optical depth, assuming a slab geometry, $\tau=2.98^{+0.16}_{-0.19}$ or a similar temperature and $\tau=6.7^{+0.3}_{-0.4}$ assuming a spherical geometry. The 2009 XMM-Newton spectrum is well described by a flatter intrinsic continuum ($\Gamma=1.47^{+0.07}_{-0.03}$) and one absorption line due to Fe\textsc{XXV} K$\alpha$ produced by a warm absorber. Both data sets show a modest iron K$\alpha$ emission line at $6.4$ keV and the associated Compton reflection, due to reprocessing from neutral circumnuclear material.

We discuss the environment of local hard X-ray selected active galaxies, with reference to two independent group catalogues. We find that the fraction of these AGN in S0 host galaxies decreases strongly as a function of galaxy group size (halo mass) - which contrasts with the increasing fraction of galaxies of S0 type in denser environments. However, there is no evidence for an environmental dependence of AGN in spiral galaxies. Because most AGN are found in spiral galaxies, this dilutes the signature of environmental dependence for the population as a whole. We argue that the differing results for AGN in disk-dominated and bulge-dominated galaxies is related to the source of the gas fuelling the AGN, and so may also impact the luminosity function, duty cycle, and obscuration. We find that there is a significant difference in the luminosity function for AGN in spiral and S0 galaxies, and tentative evidence for some difference in the fraction of obscured AGN., Comment: accepted for publication in MNRAS. 12 pages with 10 figures

We analyse high-quality NuSTAR observations of the local (z = 0.011) Seyfert 2 active galactic nucleus (AGN) IC 3639, in conjunction with archival Suzaku and Chandra data. This provides the first broadband X-ray spectral analysis of the source, spanning nearly two decades in energy (0.5-30 keV). Previous X-ray observations of the source below 10 keV indicated strong reflection/obscuration on the basis of a pronounced iron fluorescence line at 6.4 keV. The hard X-ray energy coverage of NuSTAR, together with self-consistent toroidal reprocessing models, enables direct broadband constraints on the obscuring column density of the source. We find the source to be heavily Compton-thick (CTK) with an obscuring column in excess of $3.6\times10^{24}$ cm$^{-2}$, unconstrained at the upper end. We further find an intrinsic 2-10 keV luminosity of $\textrm{log}_{10}(L_{\textrm{2-10 keV}} \textrm{[erg s}^{-1}]) = 43.4^{+0.6}_{-1.1}$ to 90% confidence, almost 400 times the observed flux, and consistent with various multi-wavelength diagnostics. Such a high intrinsic to observed flux ratio in addition to an Fe-K$\alpha$ fluorescence line equivalent width exceeding 2 keV is extreme amongst known bona fide CTK AGN, which we suggest are both due to the high level of obscuration present around IC 3639. Our study demonstrates that broadband spectroscopic modelling with NuSTAR enables large corrections for obscuration to be carried out robustly, and emphasises the need for improved modelling of AGN tori showing intense iron fluorescence., Comment: Accepted for publication in the The Astrophysical Journal, 26/10/2016

Hot, Dust-Obscured Galaxies (Hot DOGs), selected from the WISE all sky infrared survey, host some of the most powerful Active Galactic Nuclei (AGN) known, and might represent an important stage in the evolution of galaxies. Most known Hot DOGs are at $z> 1.5$, due in part to a strong bias against identifying them at lower redshift related to the selection criteria. We present a new selection method that identifies 153 Hot DOG candidates at $z\sim 1$, where they are significantly brighter and easier to study. We validate this approach by measuring a redshift $z=1.009$, and an SED similar to higher redshift Hot DOGs for one of these objects, WISE J1036+0449 ($L_{\rm\,Bol}\simeq 8\times 10^{46}\rm\,erg\,s^{-1}$), using data from Keck/LRIS and NIRSPEC, SDSS, and CSO. We find evidence of a broadened component in MgII, which, if due to the gravitational potential of the supermassive black hole, would imply a black hole mass of $M_{\rm\,BH}\simeq 2 \times 10^8 M_{\odot}$, and an Eddington ratio of $\lambda_{\rm\,Edd}\simeq 2.7$. WISE J1036+0449 is the first Hot DOG detected by NuSTAR, and the observations show that the source is heavily obscured, with a column density of $N_{\rm\,H}\simeq(2-15)\times10^{23}\rm\,cm^{-2}$. The source has an intrinsic 2-10 keV luminosity of $\sim 6\times 10^{44}\rm\,erg\,s^{-1}$, a value significantly lower than that expected from the mid-infrared/X-ray correlation. We also find that the other Hot DOGs observed by X-ray facilities show a similar deficiency of X-ray flux. We discuss the origin of the X-ray weakness and the absorption properties of Hot DOGs. Hot DOGs at $z\lesssim1$ could be excellent laboratories to probe the characteristics of the accretion flow and of the X-ray emitting plasma at extreme values of the Eddington ratio., Comment: Accepted for publication in ApJ, 16 pages

Aims. We study the long-term variability of the well-known Seyfert 2 galaxy Mrk 1210 (a.k.a. UGC 4203, or the Phoenix galaxy). Methods. The source was observed by many X-ray facilities in the last 20 years. Here we present a NuSTAR observation and put the results in context of previously published observations. Results. NuSTAR observed Mrk 1210 in 2012 for 15.4 ks. The source showed Compton-thin obscuration similar to that observed by Chandra, Suzaku, BeppoSAX and XMM-Newton over the past two decades, but different from the first observation by ASCA in 1995, in which the active nucleus was caught in a low flux state - or obscured by Compton-thick matter, with a reflection-dominated spectrum. Thanks to the high-quality hard X-ray spectrum obtained with NuSTAR and exploiting the long-term spectral coverage spanning 16.9 years, we can precisely disentangle the transmission and reflection components and put constraints on both the intrinsic long-term variability and hidden nucleus scenarios. In the former case, the distance between the reflector and the source must be at least ~ 2 pc, while in the latter one the eclipsing cloud may be identified with a water maser-emitting clump., Comment: 10 pages, 11 figures, accepted for publication in A&A

We use high spectral resolution (R > 8000) data covering 3800-13000\r{A} to study the physical conditions of the broad line region (BLR) of nine nearby Seyfert 1 galaxies. Up to six broad HI lines are present in each spectrum. A comparison - for the first time using simultaneous optical to near-infrared observations - to photoionisation calculations with our devised simple scheme yields the extinction to the BLR at the same time as determining the density and photon flux, and hence distance from the nucleus, of the emitting gas. This points to a typical density for the HI emitting gas of 10$^{11}$cm$^{-3}$ and shows that a significant amount of this gas lies at regions near the dust sublimation radius, consistent with theoretical predictions. We also confirm that in many objects the line ratios are far from case B, the best-fit intrinsic broad-line H$\alpha$/H$\beta$ ratios being in the range 2.5-6.6 as derived with our photoionization modeling scheme. The extinction to the BLR, based on independent estimates from HI and HeII lines, is A$_V$ $\le$ 3 for Seyfert 1-1.5s, while Seyfert 1.8-1.9s have A$_V$ in the range 4-8. A comparison of the extinction towards the BLR and narrow line region (NLR) indicates that the structure obscuring the BLR exists on scales smaller than the NLR. This could be the dusty torus, but dusty nuclear spirals or filaments could also be responsible. The ratios between the X-ray absorbing column N$_H$ and the extinction to the BLR are consistent with the Galactic gas-to-dust ratio if N$_H$ variations are considered., Comment: 19 pages, 14 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society

We present $NuSTAR$ X-ray observations of the active galactic nucleus (AGN) in NGC 7674. The source shows a flat X-ray spectrum, suggesting that it is obscured by Compton-thick gas columns. Based upon long-term flux dimming, previous work suggested the alternate possibility that the source is a recently switched-off AGN with the observed X-rays being the lagged echo from the torus. Our high-quality data show the source to be reflection-dominated in hard X-rays, but with a relatively weak neutral Fe K$\alpha$ emission line (equivalent width [EW] of $\approx$ 0.4 keV) and a strong Fe XXVI ionised line (EW $\approx$ 0.2 keV). We construct an updated long-term X-ray light curve of NGC 7674 and find that the observed 2-10 keV flux has remained constant for the past $\approx$ 20 years, following a high flux state probed by $Ginga$. Light travel time arguments constrain the minimum radius of the reflector to be $\sim$ 3.2 pc under the switched-off AGN scenario, $\approx$ 30 times larger than the expected dust sublimation radius, rendering this possibility unlikely. A patchy Compton-thick AGN (CTAGN) solution is plausible, requiring a minimum line-of-sight column density ($N_{\rm H}$) of 3 $\times$ 10$^{24}$ cm$^{-2}$ at present, and yields an intrinsic 2-10 keV luminosity of (3-5) $\times$ 10$^{43}$ erg s$^{-1}$. Realistic uncertainties span the range of $\approx$ (1-13) $\times$ 10$^{43}$ erg s$^{-1}$. The source has one of the weakest fluorescence lines amongst {\em bona fide} CTAGN, and is potentially a local analogue of bolometrically luminous systems showing complex neutral and ionised Fe emission. It exemplifies the difficulty of identification and proper characterisation of distant CTAGN based on the strength of the neutral Fe K$\alpha$ line., Comment: MNRAS accepted version

In this paper we report the results of an X-ray monitoring campaign on the heavily obscured Seyfert galaxy Markarian 3 carried out between the fall of 2014 and the spring of 2015 with NuSTAR, Suzaku and XMM-Newton. The hard X-ray spectrum of Markarian 3 is variable on all the time scales probed by our campaign, down to a few days. The observed continuum variability is due to an intrinsically variable primary continuum seen in transmission through a large, but still Compton-thin column density (N_H~0.8-1.1$\times$10$^{24}$ cm$^{-2}$). If arranged in a spherical-toroidal geometry, the Compton scattering matter has an opening angle ~66 degrees and is seen at a grazing angle through its upper rim (inclination angle ~70 degrees). We report a possible occultation event during the 2014 campaign. If the torus is constituted by a system of clouds sharing the same column density, this event allows us to constrain their number (17$\pm$5) and individual column density, [~(4.9$\pm$1.5)$\times$10$^{22}$ cm$^{-2}$]. The comparison of IR and X-ray spectroscopic results with state-of-the art "torus" models suggests that at least two thirds of the X-ray obscuring gas volume might be located within the dust sublimation radius. We report also the discovery of an ionized absorber, characterised by variable resonant absorption lines due to He- and H-like iron. This discovery lends support to the idea that moderate column density absorbers could be due to clouds evaporated at the outer surface of the torus, possibly accelerated by the radiation pressure due to the central AGN emission leaking through the patchy absorber., Comment: Accepted for publication in MNRAS, 17 pages, 11 figures, 5 tables

We investigate the 1.4 GHz radio properties of 92 nearby (z<0.05) ultra hard X-ray selected Active Galactic Nuclei (AGN) from the Swift Burst Alert Telescope (BAT) sample. Through the ultra hard X-ray selection we minimise the biases against obscured or Compton-thick AGN as well as confusion with emission derived from star formation that typically affect AGN samples selected from the UV, optical and infrared wavelengths. We find that all the objects in our sample of nearby, ultra-hard X-ray selected AGN are radio quiet; 83\% of the objects are classed as high-excitation galaxies (HEGs) and 17\% as low-excitation galaxies (LEGs). While these low-z BAT sources follow the radio--far-infrared correlation in a similar fashion to star forming galaxies, our analysis finds that there is still significant AGN contribution in the observed radio emission from these radio quiet AGN. In fact, the majority of our BAT sample occupy the same X-ray--radio fundamental plane as have been observed in other samples, which include radio loud AGN --- evidence that the observed radio emission (albeit weak) is connected to the AGN accretion mechanism, rather than star formation., Comment: (11 pages, 5 figures, accepted for publication in MNRAS)