Active Galactic Nuclei Torus Research Articles

Observational hints on the torus obscuring gas behaviour through X-rays with NuSTAR data

ABSTRACT 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.

A new look at local ultraluminous infrared galaxies: the atlas and radiative transfer models of their complex physics

ABSTRACT We present the ultraviolet to submillimetre spectral energy distributions (SEDs) of the HERschel Ultra Luminous Infrared Galaxy Survey (HERUS) sample of 42 local ultraluminous infrared galaxies (ULIRGs) and fit them with a Markov chain Monte Carlo code using the CYprus models for Galaxies and their NUclear Spectra (CYGNUS) radiative transfer models for starbursts, active galactic nucleus (AGN) tori, and host galaxy. The Spitzer IRS spectroscopy data are included in the fitting. Our Bayesian SED fitting method takes comparable time to popular energy balance methods but it is more physically motivated and versatile. All HERUS galaxies harbour high rates of star formation but we also find bolometrically significant AGN in all of the galaxies of the sample. We estimate the correction of the luminosities of the AGN in the ULIRGs due to the anisotropic emission of the torus and find that it could be up to a factor of ∼10 for nearly edge-on tori. We present a comparison of our results with the smooth torus model of Fritz et al. and the two-phase models of Siebenmorgen et al. and SKIRTOR. We find that the CYGNUS AGN torus models fit significantly better the SEDs of our sample compared to all other models. We find no evidence that strong AGN appear either at the beginning or end of a starburst episode or that starbursts and AGN affect each other. IRAS 01003−2238 and Mrk 1014 show evidence of dual AGNs in their SED fits, suggesting a minimum dual AGN fraction in the sample of 5 per cent.

Inferring the morphology of AGN torus using X-ray spectra: a reliability study

ABSTRACT Numerous X-ray spectral models have been developed to model emission reprocessed by the torus of an active galactic nucleus (AGN), e.g. UXCLUMPY, CTORUS, and MYTORUS. They span a range of assumed torus geometries and morphologies – some posit smooth gas distributions, and others posit distributions of clouds. It is suspected that given the quality of currently available data, certain model parameters, such as coronal power-law photon index and parameters determining the morphology of the AGN torus, may be poorly constrained due to model degeneracies. In this work, we test the reliability of these models in terms of recovery of parameters and the ability to discern the morphology of the torus using XMM–Newton and NuSTAR spectral data. We perform extensive simulations of X-ray spectra of Compton-thick AGNs under six X-ray spectral models of the torus. We use Bayesian methods to investigate degeneracy between model parameters, distinguish models and determine the dependence of the parameter constraints on the instruments used. For typical exposure times and fluxes for nearby Compton-thick AGN, we find that several parameters across the models used here cannot be well constrained, e.g. the distribution of clouds, the number of clouds in the radial direction, even when the applied model is correct. We also find that Bayesian evidence values can robustly distinguish between a correct and a wrong model only if there is sufficient energy coverage and only if the intrinsic flux of the object is above a particular value determined by the instrument combination and the model considered.

Hypercubes of AGN Tori (HYPERCAT). I. Models and Image Morphology

Abstract Near- and mid-infrared interferometers have resolved the dusty parsec-scale obscurer (torus) around nearby active galactic nuclei (AGNs). With the arrival of extremely large single-aperture telescopes, the emission morphology will soon be resolvable unambiguously, without modeling directly the underlying brightness distribution probed by interferometers today. Simulations must instead deliver the projected 2D brightness distribution as a result of radiative transfer through a 3D distribution of dusty matter around the AGN. We employ such physically motivated 3D dust distributions in tori around AGNs to compute 2D images of the emergent thermal emission, using Clumpy, a dust radiative transfer code for clumpy media. We demonstrate that Clumpy models can exhibit morphologies with significant polar elongation in the mid-infrared (i.e., the emission extends perpendicular to the dust distribution) on scales of several parsecs, in line with observations in several nearby AGNs. We characterize the emission and cloud distribution morphologies. The observed emission from near- to mid-infrared wavelengths generally does not trace the bulk of the cloud distribution. The elongation of the emission is sensitive to the torus opening angle or scale height. For cloud distributions with a flat radial profile, polar extended emission is realized only at wavelengths shorter than ∼18 μm, and shorter than ∼5 μm for steep profiles. We make the full results available through Hypercat, a large hypercube of resolved AGN torus brightness maps computed with Clumpy. Hypercat also comprises software to process and analyze such large data cubes and provides tools to simulate observations with various current and future telescopes.

Transient obscuration event captured in NGC 3227

From Swift monitoring of a sample of active galactic nuclei (AGN) we found a transient X-ray obscuration event in Seyfert-1 galaxy NGC 3227, and thus triggered our joint XMM-Newton, NuSTAR, and Hubble Space Telescope (HST) observations to study this event. Here in the first paper of our series we present the broadband continuum modelling of the spectral energy distribution for NGC 3227, extending from near infrared (NIR) to hard X-rays. We use our new spectra taken with XMM-Newton, NuSTAR, and the HST Cosmic Origins Spectrograph in 2019, together with archival unobscured XMM-Newton, NuSTAR, and HST Space Telescope Imaging Spectrograph data, in order to disentangle various spectral components of NGC 3227 and recover the underlying continuum. We find the observed NIR-optical-UV continuum is explained well by an accretion disk blackbody component (Tmax = 10 eV), which is internally reddened by E(B − V) = 0.45 with a Small Magellanic Cloud extinction law. We derive the inner radius (12 Rg) and the accretion rate (0.1 M⊙ yr−1) of the disk by modelling the thermal disk emission. The internal reddening in NGC 3227 is most likely associated with outflows from the dusty AGN torus. In addition, an unreddened continuum component is also evident, which likely arises from scattered radiation, associated with the extended narrow-line region of NGC 3227. The extreme ultraviolet continuum, and the ‘soft X-ray excess’, can be explained with a ‘warm Comptonisation’ component. The hard X-rays are consistent with a power-law and a neutral reflection component. The intrinsic bolometric luminosity of the AGN in NGC 3227 is about 2.2 × 1043 erg s−1 in 2019, corresponding to 3% Eddington luminosity. Our continuum modelling of the new triggered data of NGC 3227 requires the presence of a new obscuring gas with column density NH = 5 × 1022 cm−2, partially covering the X-ray source (Cf = 0.6).

The dust-gas AGN torus as constrained from X-ray and mid-infrared observations

Context. In recent decades, several multiwavelength studies have been dedicated to exploring the properties of the obscuring material in active galactic nuclei (AGN). Various models have been developed to describe the structure and distribution of this material and constrain its physical and geometrical parameters through spectral fitting techniques. However, questions around the way in which torus mid-infrared (mid-IR) and X-ray emission are related remain unanswered. Aims. In this work, we aim to study whether the dust continuum at mid-IR and gas reflection at X-rays have the same distribution in a sample of AGN. Methods. We carefully selected a sample of 36 nearby AGN with NuSTAR and Spitzer spectra available that satisfy the following criteria: (1) the AGN component dominates the mid-IR spectra (i.e., the stellar and interstellar medium components contribute less than 50% to the spectrum), and (2) the reflection component contributes significantly to the X-ray spectrum. Furthermore, we discarded the sources whose reflection component could be produced by ionized material in the disk. We derived the properties of the nuclear dust and gas through a spectral fitting, using models developed for mid-IR and X-ray wavelengths assuming smooth and clumpy distributions for this structure. Results. We find that a combination of smooth and clumpy distributions of gas and dust, respectively, is preferred for ∼80% of sources with good spectral fits according to the Akaike criterion. However, considering extra information about each individual source, such as the absorption variability, we find that ∼50% of our sources are best described by a clumpy distribution of both dust and gas. The remaining ∼50% of our sources can still be explained with a smooth distribution of gas and a clumpy distribution of dust. Furthermore, we explored the torus dust-to-gas ratio, finding that it is [0.01–1] times that of the interstellar medium. Conclusions. The results presented in this paper suggest that the distribution of the gas and dust in AGN is complex. We find at least six scenarios to explain the observed properties of our sample. In these scenarios, three gas–dust distribution combinations are possible: clumpy–clumpy, smooth–smooth, and smooth–clumpy. Most of them are in agreement with the notion that gas could also be located in the dust-free region, which is consistent with the dust-to-gas ratio found.

The properties of the AGN torus as revealed from a set of unbiased NuSTAR observations

The obscuration observed in active galactic nuclei (AGNs) is mainly caused by dust and gas distributed in a torus-like structure surrounding the supermassive black hole. However, the properties of the obscuring torus of an AGN in X-ray have not yet been fully investigated because of a lack of high-quality data and proper models. In this work, we perform a broadband X-ray spectral analysis of a large, unbiased sample of obscured AGNs (with line-of-sight column density 23 ≤ log(NH) ≤ 24) in the nearby Universe for which high-quality archival NuSTAR data are available. We analyzed the source spectra using the recently developed borus02 model, which enables us to accurately characterize the physical and geometrical properties of AGN-obscuring tori. We compare our results obtained from the unbiased Compton-thin AGNs with those of Compton-thick AGNs. We find that Compton-thin and Compton-thick AGNs may possess similar tori, whose average column density is Compton thick (NH, tor, ave ≈ 1.4 × 1024 cm−2), but they are observed through different (under-dense or over-dense) regions of the tori. We also find that the obscuring torus medium is significantly inhomogeneous, with the torus average column densities being significantly different from their line-of-sight column densities (for most of the sources in the sample). The average torus covering factor of sources in our unbiased sample is cf = 0.67, suggesting that the fraction of unobscured AGNs is ∼33%. We developed a new method to measure the intrinsic line-of-sight column density distribution of AGNs in the nearby Universe, and find the results to be in good agreement with constraints from recent population synthesis models.

X-Ray Constraint on the Location of the AGN Torus in the Circinus Galaxy

Abstract The location of the obscuring “torus” in an active galactic nucleus (AGN) is still an unresolved issue. The line widths of X-ray fluorescence lines originating from the torus, particularly Fe Kα, carry key information on the radii of line-emitting regions. Utilizing XCLUMPY, an X-ray clumpy torus model, we develop a realistic model of emission line profiles from an AGN torus where we take into account line broadening due to the Keplerian motion around the black hole. Then, we apply the updated model to the best available broadband spectra (3–100 keV) of the Circinus galaxy observed with Suzaku, XMM-Newton, Nuclear Spectroscopic Telescope Array, and Chandra, including 0.62 Ms Chandra/HETG data. We confirm that the torus is Compton-thick (hydrogen column density along the equatorial plane is ), geometrically thin (torus angular width ), viewed edge-on (inclination ), and has supersolar abundance ( times solar). Simultaneously analyzing the Chandra/HETG first-, second-, and third-order spectra with consideration of the spatial extent of the Fe Kα line-emitting region, we constrain the inner radius of the torus to be times the gravitational radius, or for a black hole mass of (1.7 ± 0.3) × 106 M ⊙. This is about three times smaller than that estimated from the dust sublimation radius, suggesting that the inner side of the dusty region of the torus is composed of dust-free gas.

Infrared Echoes of Optical Tidal Disruption Events: ∼1% Dust-covering Factor or Less at Subparsec Scale

Abstract The past decade has experienced an explosive increase of optically discovered tidal disruption events (TDEs) with the advent of modern time-domain surveys. However, we still lack a comprehensive observational view of their infrared (IR) echoes in spite of individual detections. To this end, we have conducted a statistical study of the IR variability of the 23 optical TDEs discovered between 2009 and 2018 using the full public data set of the Wide-field Infrared Survey Explorer. The detection of variability is performed on the difference images, yielding 11 objects with significant (>3σ) variability in at least one band, while dust emission can be only fit in 8 objects. Their peak dust luminosity is around 1041–1042 erg s−1, corresponding to a dust-covering factor f c ∼ 0.01 at a subparsec scale. The only exception is the disputed source ASASSN-15lh, which shows an ultra-high dust luminosity (∼1043.5 erg s−1), and this makes its nature even more elusive. Other nondetected objects show even lower f c , which could be lower by one more order of magnitude. The derived f c is generally much lower than those of dusty tori in active galactic nuclei, suggesting either a dearth of dust or a geometrically thin and flat disk in the vicinity of supermassive black holes. Our results also indicate that the optical TDE sample (post-starburst galaxies overrepresented) is seriously biased to events with little dust at subparsec scale, while TDEs in dusty star-forming systems could be more efficiently unveiled by IR echoes.

Evidence for obscured broad [O iii] components in Type-2 AGN

ABSTRACT In the manuscript, we report evidence on broad [O iii] components apparently obscured in Type-2 active galactic nuclei (AGN) under the framework of the unified model, after checking properties of broad [O iii] emissions in large samples of Type-1 and Type-2 AGN in Sloan Digital Sky Survey DR12. We can well confirm the statistically lower flux ratios of the broad to the core [O iii] components in Type-2 AGN than in Type-1 AGN, which can be naturally explained by stronger obscured broad [O iii] components by central dust torus in Type-2 AGN, unless the unified model for AGN was not appropriate to the narrow emission lines. The results provide further evidence to support broad [O iii] components coming from emission regions nearer to central BHs, and also indicate the core [O iii] component as the better indicator for central activities in Type-2 AGN, due to few effects of obscuration on the core [O iii] component. Considering the broad [O iii] components as signs of central outflows, the results provide evidence for strong central outflows being preferentially obscured in Type-2 AGN. Furthermore, the obscured broad [O iii] component can be applied to explain the different flux ratios of [O iii]λ5007Å/H β between Type-1 and Type-2 AGN in the BPT diagram.

Dust Reverberation Mapping in Distant Quasars from Optical and Mid-infrared Imaging Surveys

Abstract The size of the dust torus in active galactic nuclei (AGNs) and their high-luminosity counterparts, quasars, can be inferred from the time delay between UV/optical accretion disk continuum variability and the response in the mid-infrared (MIR) torus emission. This dust reverberation mapping (RM) technique has been successfully applied to ∼70 z ≲ 0.3 AGNs and quasars. Here we present first results of our dust RM program for distant quasars covered in the Sloan Digital Sky Survey Stripe 82 region combining ∼20 yr ground-based optical light curves with 10 yr MIR light curves from the WISE satellite. We measure a high-fidelity lag between W1 band (3.4 μm) and g band for 587 quasars over 0.3 ≲ z ≲ 2 ( ) and two orders of magnitude in quasar luminosity. They tightly follow (intrinsic scatter ∼0.17 dex in lag) the IR lag–luminosity relation observed for z < 0.3 AGNs, revealing a remarkable size–luminosity relation for the dust torus over more than four decades in AGN luminosity, with little dependence on additional quasar properties such as Eddington ratio and variability amplitude. This study motivates further investigations in the utility of dust RM for cosmology and strongly endorses a compelling science case for the combined 10 yr Vera C. Rubin Observatory Legacy Survey of Space and Time (optical) and 5 yr Nancy Grace Roman Space Telescope 2 μm light curves in a deep survey for low-redshift AGN dust RM with much lower luminosities and shorter, measurable IR lags. The compiled optical and MIR light curves for 7384 quasars in our parent sample are made public with this work.

Is Extended Hard X-Ray Emission Ubiquitous in Compton-thick AGN?

Abstract The recent Chandra discovery of extended ∼kiloparsec-scale hard (>3 keV) X-ray emission in nearby Compton-thick (CT) active galactic nuclei (AGN) opens a new window to improving AGN torus modeling and investigating how the central supermassive black hole interacts with and impacts the host galaxy. Since there are only a handful of detections so far, we need to establish a statistical sample to determine the ubiquity of the extended hard X-ray emission in CT AGN and quantify the amount and extent of this component. In this paper, we present the spatial analysis results of a pilot Chandra imaging survey of seven nearby ( 0.006 < z < 0.013 ) CT AGN selected from the Swift-BAT spectroscopic AGN survey. We find that five out of the seven CT AGN show extended emission in the 3–7 keV band detected at >3σ above the Chandra point-spread function (PSF), with ∼12%–22% of the total emission in the extended components. ESO 137-G034 and NGC 3281 display biconical ionization structures with extended hard X-ray emission reaching kiloparsec scales (∼1.9 and 3.5 kpc in diameter). The other three show extended hard X-ray emission above the PSF out to at least ∼360 pc in radius. We find a trend that a minimum 3–7 keV count rate of 0.01 counts s−1 and total excess fraction >20% are required to detect a prominent extended hard X-ray component. Given that this extended hard X-ray component appears to be relatively common in this uniformly selected CT AGN sample, we further discuss the implications for torus modeling and AGN feedback.

X-ray absorption and 9.7 μm silicate feature as a probe of AGN torus structure

The dusty torus plays a vital role in unifying active galactic nuclei (AGNs). However, the physical structure of the torus remains largely unclear. Here we present a systematical investigation of the torus mid-infrared (MIR) spectroscopic feature, i.e., the 9.7μm silicate line, of 175 AGNs selected from the Swift/BAT Spectroscopic Survey (BASS). Our sample is constructed to ensure that each of the 175 AGNs has Spizter/IRS MIR, optical, and X-ray spectroscopic coverage. Therefore, we can simultaneously measure the silicate strength, optical emission lines, and X-ray properties (e.g., the column density and the intrinsic X-ray luminosity). We show that, consistent with previous works, the silicate strength is weakly correlated with the hydrogen column density (), albeit with large scatters. For X-ray unobscured AGNs, the silicate-strength-derived V-band extinction and the broad-Hα-inferred one are both small; however, for X-ray obscured AGNs, the former is much larger than the latter. In addition, we find that the optical type 1 AGNs with strong X-ray absorption on average show significant silicate absorption, indicating that their X-ray absorption might not be caused by dust-free gas in the broad-line region. Our results suggest that the distribution and structure of the obscuring dusty torus are likely to be very complex. We test our results against the smooth and clumpy torus models and find evidence in favor of the clumpy torus model.

Radiation Hydrodynamics Models of Active Galactic Nuclei: Beyond the Central Parsec

Abstract We produce radiation hydrodynamics models of an active galactic nucleus torus plus outflow on 1–100 pc scales. This large scale permits direct comparison with observations, provides justification for configurations used in radiation transfer models, and tests the sensitivity of results of smaller scale dynamical models. We find that anisotropic radiation from an active galactic nucleus accretion disk can cause an outflow to evolve to become more polar, agreeing with the ubiquity of polar extended mid-infrared emission, and the general geometry predicted by radiative transfer models. We also find that the velocity maps can reproduce many features of observations, including apparent counterrotation.

Dust reverberation mapping of type 2 AGN NGC 2110 realized with X-ray and 3–5 μm IR monitoring

ABSTRACT The dust reverberation mapping is one of powerful methods to investigate the structure of the dusty tori in active galactic nuclei (AGNs), and it has been performed on more than a hundred type 1 AGNs. However, no clear results have been reported on type 2 AGNs because their strong optical/UV extinction completely hides their accretion disc emission. Here, we focus on an X-ray-bright type 2 AGN, NGC 2110, and utilize 2–20 keV X-ray variation monitored by MAXI to trace disc emission, instead of optical/UV variation. Comparing it with light curves in the WISE infrared (IR) W1 band ($\lambda =3.4~\mu$m) and W2 band ($\lambda =4.6~\mu$m) with cross-correlation analyses, we found candidates of the dust reverberation time lag at ∼60, ∼130, and ∼1250 d between the X-ray flux variation and those of the IR bands. By examining the best-fitting X-ray and IR light curves with the derived time lags, we found that the time lag of ∼130 d is most favoured. With this time lag, the relation between the time lag and luminosity of NGC 2110 is consistent with those in type 1 AGNs, suggesting that the dust reverberation in NGC 2110 mainly originates in hot dust in the torus innermost region, the same as in type 1 AGNs. As demonstrated by the present study, X-ray and IR simultaneous monitoring can be a promising tool to perform the dust reverberation mapping on type 2 AGNs.

ProSpect: generating spectral energy distributions with complex star formation and metallicity histories

ABSTRACT We introduce ProSpect, a generative galaxy spectral energy distribution (SED) package that encapsulates the best practices for SED methodologies in a number of astrophysical domains. ProSpect comes with two popular families of stellar population libraries (BC03 and EMILES), and a large variety of methods to construct star formation and metallicity histories. It models dust through the use of a Charlot & Fall attenuation model, with re-emission using Dale far-infrared templates. It also has the ability to model active galactic nucleus (AGN) through the inclusion of a simple AGN and hot torus model. Finally, it makes use of MAPPINGS-III photoionization tables to produce line emission features. We test the generative and inversion utility of ProSpect through application to the Shark galaxy formation semi-analytic code, and informed by these results produce fits to the final ultraviolet to far-infrared photometric catalogues produces by the Galaxy and Mass Assembly Survey. As part of the testing of ProSpect, we also produce a range of simple photometric stellar mass approximations covering a range of filters for both observed frame and rest-frame photometry.

Modeling the Infrared Reverberation Response of the Circumnuclear Dusty Torus in AGNs: An Investigation of Torus Response Functions

Abstract The size and structure of the dusty circumnuclear torus in active galactic nuclei (AGNs) can be investigated by analyzing the temporal response of the torus’s infrared (IR) dust emission to variations in the AGN ultraviolet/optical luminosity. This method, reverberation mapping, is applicable over a wide redshift range, but the IR response is sensitive to several poorly constrained variables relating to the dust distribution and its illumination, complicating the interpretation of measured reverberation lags. We have used an enhanced version of our torus reverberation mapping code (TORMAC) to conduct a comprehensive exploration of the torus response functions at selected wavelengths, for the standard interstellar medium grain composition. The shapes of the response functions vary widely over the parameter range covered by our models, with the largest variations occurring at shorter wavelengths (≤4.5 μm). The reverberation lag, quantified as the response-weighted delay (RWD), is most affected by the radial depth of the torus, the steepness of the radial cloud distribution, the degree of anisotropy of the AGN radiation field, and the volume filling factor. Nevertheless, we find that the RWD provides a reasonably robust estimate, to within a factor of ∼3, of the luminosity-weighted torus radius, confirming the basic assumption underlying reverberation mapping. However, overall, the models predict radii at 2.2 μm that are typically a factor of ∼2 larger than those derived from K-band reverberation mapping. This is likely an indication that the innermost region of the torus is populated by clouds dominated by large graphite grains.

New Tools for Self-consistent Modeling of the AGN Torus and Corona

The continuum emission typically observed in the X-ray spectra of active galactic nuclei (AGNs) is thought to arise from inverse-Compton scattering of blackbody photons from the accretion disk by mildly relativistic thermal electrons in a rarefied and relatively hotter corona. By fitting theoretical spectral models (e.g., Poutanen & Svensson 1996; Coppi 1999) to the observed shape of an AGN coronal continuum it is possible to constrain some of its physical parameters, such as the electron temperature and optical depth (e.g., Fabian et al. 2015; Middei et al. 2019).

A NuSTAR and XMM-Newton Study of the Two Most Actively Star-forming Green Pea Galaxies (SDSS J0749+3337 and SDSS J0822+2241)

Abstract We explore X-ray evidence for the presence of active galactic nuclei (AGNs) in the two most actively star-forming Green Pea galaxies (GPs), SDSS J0749+3337 and SDSS J0822+2241, which have star formation rates (SFRs) of 123 M ⊙ yr−1 and 78 M ⊙ yr−1, respectively. The GPs have red mid-infrared (MIR) spectral energy distributions and higher 22 μm luminosities than expected from a proxy of the SFR (Hα luminosity), consistent with hosting AGNs with 2–10 keV luminosities of ∼1044 erg s−1. We thus obtain and analyze the first hard (>10 keV) X-ray data observed with NuSTAR and archival XMM-Newton data below 10 keV. From the NuSTAR ≈20 ks data, however, we find no significant hard X-ray emission. By contrast, soft X-ray emission with 0.5–8 keV luminosities of ≈1042 erg s−1 is significantly detected in both targets, which can be explained only by star formation (SF). A possible reason for the lack of clear evidence is that a putative AGN torus absorbs most of the X-ray emission. Applying a smooth-density AGN torus model, we determine minimum hydrogen column densities along the equatorial plane ( ) consistent with the nondetection. The results indicate cm−2 for SDSS J0749+3337 and cm−2 for SDSS J0822+2241. Therefore, the GPs may host such heavily obscured AGNs. Otherwise, no AGN exists and the MIR emission is ascribed to SF. Active SF in low-mass galaxies is indeed suggested to reproduce red MIR colors. This would imply that diagnostics based on MIR photometry data alone may misidentify such galaxies as AGNs.

The mid-infrared and CO gas properties of an extreme star-forming FeLoBAL quasar

We present a detailed study of a high-redshift iron low-ionization broad absorption line (FeLoBAL) quasar (SDSS1214 at $z = 1.046$), including new interferometric $^{12}$CO $J$=2-1 observations, optical through far-infrared photometry, and mid-infrared spectroscopy. The CO line is well-fit by a single Gaussian centered 40 kms$^{-1}$ away from the systemic velocity and implies a total molecular gas mass of $M_\textrm{gas} = 7.3 \times 10^{10} \textrm{M}_\odot$. The infrared SED requires three components: an active galactic nucleus (AGN) torus, an AGN polar dust component, and a starburst. The starburst dominates the infrared emission with a luminosity of log($L_\textrm{SB}[\textrm{L}_\odot]) = 12.91^{+0.02}_{-0.02}$, implying a star formation rate of about 2000 $\textrm{M}_{\odot}$yr$^{-1}$, the highest known among FeLoBAL quasars. The AGN torus and polar dust components are less luminous, at log($L_\textrm{AGN}[\textrm{L}_\odot]) = 12.36^{+0.14}_{-0.15}$ and log($L_\textrm{dust}[\textrm{L}_\odot]) = 11.75^{+0.26}_{-0.46}$, respectively. If all of the molecular gas is used to fuel the ongoing star formation, then the lower limit on the subsequent duration of the starburst is 40 Myr. We do not find conclusive evidence that the AGN is affecting the CO gas reservoir. The properties of SDSS1214 are consistent with it representing the endpoint of an obscured starburst transitioning through a LoBAL phase to that of a classical quasar.