[en] We report the first broadband X-ray spectra of the low-luminosity active galactic nuclei (LLAGNs), NGC 1566 (type 1.5) and NGC 4941 (type 2), observed with Suzaku and Swift/BAT covering the 0.5-195 keV band. Both targets have hard X-ray luminosities of ∼10^41-42 erg s^–1 in the 15-55 keV band. The spectra of the nucleus are well reproduced by a sum of partially or fully covered transmitted emission and its reflection from the accretion disk, reprocessed emission from the torus accompanied by a strong narrow iron-Kα line, and a scattered component (for NGC 4941). We do not significantly detect a broad iron-Kα line from the inner accretion disk in both targets, and obtain an upper limit on the corresponding solid angle of Ω/2π < 0.3 in NGC 1566. The reflection strength from the torus is moderate, Ω/2π=0.45^+0.13_-0.10 in NGC 1566 and Ω/2π=0.64^+0.69_-0.27 in NGC 4941. Comparison of the equivalent width of the narrow iron-Kα line with a model prediction based on a simple torus geometry constrains its half-opening angle to be θ_oa ≅ 60°-70° in NGC 4941. These results agree with the obscured AGN fraction obtained from hard X-ray and mid-infrared selected samples at similar luminosities. Our results support the implication that the averaged covering fraction of AGN tori is peaked at L ∼ 10^42-43 erg s^–1 but decreases toward lower luminosities.

[en] We present infrared K′-band (2.1 μm) and L′-band (3.8 μm) high-spatial-resolution (<0.″3) imaging observations of 17 nearby (z < 0.17) ultraluminous infrared galaxies (ULIRGs) assisted with the adaptive optics of the Subaru Telescope. We search for compact red K′ − L′ color emission as the indicator of luminous active galactic nuclei (AGNs) due to AGN-heated hot dust emission. Two luminous dual AGN candidates are revealed. Combining these results with those of our previous study, we can state that the detected fraction of luminous dual AGNs in nearby ULIRGs is much less than unity (<20%), even when infrared wavelengths >2 μm are used that should be sensitive to buried AGNs due to small dust extinction effects. For ULIRGs with resolved multiple nuclear K′-band emission, we estimate the activation of supermassive black holes (SMBHs) in individual galaxy nuclei in the form of AGN luminosity normalized by SMBH mass inferred from the stellar luminosity of the host galaxy. We confirm a trend that more massive SMBHs in K′-band brighter primary galaxy nuclei are generally more active, with higher SMBH-mass-normalized AGN luminosity, than less massive SMBHs in K′-band fainter secondary galaxy nuclei, as predicted by numerical simulations of gas-rich major galaxy mergers. In two sources, the presence of even infrared-elusive extremely deeply buried AGNs is indicated by comparisons with available (sub)millimeter data. Non-synchronous SMBH activation (i.e., less activation of less massive SMBHs) and the possible presence of such infrared-elusive AGNs may be responsible for the small fraction of infrared-detected luminous dual AGNs in nearby merging ULIRGs.

[en] We report spatial distributions of the Fe–Kα line at 6.4 keV and the CO(J = 2–1) line at 230.538 GHz in NGC 2110, which are, respectively, revealed by Chandra and Atacama Large Millimeter/submillimeter Array (ALMA) at ≈0.″5. A Chandra 6.2–6.5 keV to 3.0–6.0 keV image suggests that the Fe–Kα emission extends preferentially in a northwest to southeast direction out to ≈3″, or ∼500 pc, on each side. Spatially resolved spectral analyses support this by finding significant Fe–Kα emission lines only in the northwest and southeast regions. Moreover, their equivalent widths are found to be ∼1.5 keV, indicative for the fluorescence by nuclear X-ray irradiation as the physical origin. By contrast, CO(J = 2–1) emission is weak therein. For quantitative discussion, we derive ionization parameters by following an X-ray dominated region (XDR) model. We then find them high enough to interpret the weakness as the result of X-ray dissociation of CO and/or H₂. Another possibility also remains that CO molecules follow a superthermal distribution, resulting in brighter emission in higher-J lines. Further follow-up observations are encouraged to draw a conclusion on what predominantly changes the interstellar matter properties and whether the X-ray irradiation eventually affects the surrounding star formation as active galactic nucleus (AGN) feedback.

[en] 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 $N_{\mathrm{H}}^{\mathrm{E}\mathrm{q}\mathrm{u}}={2.16}_{-<!--\; ???\; -->0.16}^{+0.24}\times <!--\; ??\; -->{10}^{25}{\mathrm{c}\mathrm{m}}^{-<!--\; ???\; -->2}$), geometrically thin (torus angular width $\mathrm{\sigma <!--\; ??\; -->}={10.3}_{-<!--\; ???\; -->0.3}^{+0.7}\mathrm{d}\mathrm{e}\mathrm{g}$), viewed edge-on (inclination $i={78.3}_{-<!--\; ???\; -->0.9}^{+0.4}\mathrm{d}\mathrm{e}\mathrm{g}$), and has supersolar abundance (${1.52}_{-<!--\; ???\; -->0.06}^{+0.04}$ 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 ${1.9}_{-<!--\; ???\; -->0.8}^{+3.1}\times <!--\; ??\; -->{10}^5$ times the gravitational radius, or ${1.6}_{-<!--\; ???\; -->0.9}^{+1.5}\times <!--\; ??\; -->{10}^{-<!--\; ???\; -->2}\mathrm{p}\mathrm{c}$ 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.

[en] We report the results obtained by a systematic, broadband (0.5–150 keV) X-ray spectral analysis of moderately obscured (Compton-thin, $22⩽<!--\; ???\; -->\mathrm{l}\mathrm{o}\mathrm{g}{N}_{\mathrm{H}}<<!--\; <\; -->24$) active galactic nuclei (AGNs) observed with Suzaku and Swift/Burst Alert Telescope (BAT). Our sample consists of 45 local AGNs at $z<<!--\; <\; -->0.1$ with $\mathrm{l}\mathrm{o}\mathrm{g}{L}_{14-<!--\; ???\; -->195\mathrm{k}\mathrm{e}\mathrm{V}}><!--\; >\; -->42$ detected in the Swift/BAT 70-month survey, whose Suzaku archival data are available as of 2015 December. All spectra are uniformly fit with a baseline model composed of an absorbed cutoff power-law component, reflected emission accompanied by a narrow fluorescent iron-Kα line from cold matter (torus), and scattered emission. The main results based on the above analysis are as follows. (1) The photon index is correlated with Eddington ratio, but not with luminosity or black hole mass. (2) The ratio of the luminosity of the iron-Kα line to the X-ray luminosity an indicator of the covering fraction of the torus, shows significant anticorrelation with luminosity. (3) The averaged reflection strength derived from stacked spectra above 14 keV is larger in less luminous ($\mathrm{l}\mathrm{o}\mathrm{g}{L}_{10-<!--\; ???\; -->50\mathrm{k}\mathrm{e}\mathrm{V}}⩽<!--\; ???\; -->43.3$, $R={1.04}_{-<!--\; ???\; -->0.19}^{+0.17}$) or highly obscured ($\mathrm{l}\mathrm{o}\mathrm{g}{N}_{\mathrm{H}}><!--\; >\; -->23$, $R={1.03}_{-<!--\; ???\; -->0.17}^{+0.15}$) AGNs than in more luminous ($\mathrm{l}\mathrm{o}\mathrm{g}{L}_{10-<!--\; ???\; -->50\mathrm{k}\mathrm{e}\mathrm{V}}><!--\; >\; -->43.3$, $R={0.46}_{-<!--\; ???\; -->0.09}^{+0.08}$) or lightly obscured ($\mathrm{l}\mathrm{o}\mathrm{g}{N}_{\mathrm{H}}⩽<!--\; ???\; -->23$, $R={0.59}_{-<!--\; ???\; -->0.10}^{+0.09}$) objects. (4) The ratio of the luminosity of the $[\mathrm{O}\mathrm{I}\mathrm{V}]$ 25.89 μm line to the X-ray luminosity is significantly smaller in AGNs with lower soft X-ray scattering fractions, suggesting that the former luminosity underestimates the intrinsic power of an AGN buried in a torus of small opening angle.

[en] We systematically analyze the broadband (0.5–200 keV) X-ray spectra of hard X-ray (>10 keV) selected local low-luminosity active galactic nuclei (LLAGNs) observed with Suzaku and Swift/BAT. The sample consists of 10 LLAGNs detected with Swift/BAT with intrinsic 14–195 keV luminosities smaller than 10⁴² erg s⁻¹ available in the Suzaku archive, covering a wide range of the Eddington ratio from 10⁻⁵ to 10⁻². The overall spectra can be reproduced with an absorbed cut-off power law, often accompanied by reflection components from distant cold matter, and/or optically thin thermal emission from the host galaxy. In all of the objects, relativistic reflection components from the innermost disk are not required. Eight objects show a significant narrow iron-Kα emission line. Comparing their observed equivalent widths with the predictions from the Monte-Carlo-based torus model by Ikeda et al. (2009), we constrain the column density in the equatorial plane to be $\mathrm{l}\mathrm{o}\mathrm{g}{N}_{\mathrm{H}}^{\mathrm{e}\mathrm{q}}><!--\; >\; -->22.7$, or the torus half-opening angle θ _oa < 70°. We infer that the Eddington ratio (λ _Edd) is a key parameter that determines the torus structure of LLAGNs: the torus becomes large at λ _Edd ≳ 2 × 10⁻⁴, whereas at lower accretion rates it is little developed. The luminosity correlation between the hard X-ray and mid-infrared (MIR) bands of the LLAGNs follows the same correlation as for more luminous AGNs. This implies that mechanisms other than AGN-heated dust are responsible for the MIR emission in low Eddington ratio LLAGNs.

[en] We have shown that Lyα blobs (LABs) may still exist even at $z\sim <!--\; ???\; -->0.3$, about seven billion years later than most other LABs known (Shirmer et al.). Their luminous Lyα and [O iii] emitters at $z\sim <!--\; ???\; -->0.3$ offer new insights into the ionization mechanism. This paper focuses on the two X-ray brightest LABs at $z\sim <!--\; ???\; -->0.3$, SDSS J0113+0106 (J0113) and SDSS J1155−0147 (J1155), comparable in size and luminosity to “B1,” one of the best-studied LABs at $z\gtrsim <!--\; ???\; -->2$. Our NuSTAR hard X-ray (3–30 keV) observations reveal powerful active galactic nuclei (AGN) with $L_{2\text{--}10\mathrm{k}\mathrm{e}\mathrm{V}}=(0.5\text{--}3)\times <!--\; ??\; -->{10}^{44}$ erg s⁻¹. J0113 also faded by a factor of ∼5 between 2014 and 2016, emphasizing that variable AGN may cause apparent ionization deficits in LABs. Joint spectral analyses including Chandra data constrain column densities of $N_{\mathrm{H}}={5.1}_{-<!--\; ???\; -->3.3}^{+3.1}\times <!--\; ??\; -->{10}^{23}$ cm⁻² (J0113) and $N_{\mathrm{H}}={6.0}_{-<!--\; ???\; -->1.1}^{+1.4}\times <!--\; ??\; -->{10}^{22}$ cm⁻² (J1155). J0113 is likely buried in a torus with a narrow ionization cone, but ionizing radiation is also leaking in other directions, as revealed by our Gemini/GMOS 3D spectroscopy. The latter shows a bipolar outflow over 10 kpc, with a peculiar velocity profile that is best explained by AGN flickering. X-ray analysis of J1155 reveals a weakly absorbed AGN that may ionize over a wide solid angle, consistent with our 3D spectra. Extinction-corrected [O iii] log-luminosities are high, ∼43.6. The velocity dispersions are low, ∼100–150 km s⁻¹, even at the AGN positions. We argue that this is a combination of high extinction hiding the turbulent gas and previous outflows that have cleared the escape paths for their successors.

[en] We systematically investigate the near- to far-infrared (FIR) photometric properties of a nearly complete sample of local active galactic nuclei (AGNs) detected in the Swift/Burst Alert Telescope (BAT) all-sky ultra-hard X-ray (14–195 keV) survey. Out of 606 non-blazar AGNs in the Swift/BAT 70 month catalog at high galactic latitudes of $|b|><!--\; >\; -->{10}^{\circ <!--\; ???\; -->}$, we obtain IR photometric data of 604 objects by cross-matching the AGN positions with catalogs from the WISE, AKARI, IRAS, and Herschel infrared observatories. We find a good correlation between the ultra-hard X-ray and mid-IR luminosities over five orders of magnitude ($41<<!--\; <\; -->\mathrm{l}\mathrm{o}\mathrm{g}{L}_{14\text{--}195}<<!--\; <\; -->46$). Informed by previous measurements of the intrinsic spectral energy distribution of AGNs, we find FIR pure-AGN candidates whose FIR emission is thought to be AGN-dominated with low star-formation activity. We demonstrate that the dust covering factor decreases with the bolometric AGN luminosity, confirming the luminosity-dependent unified scheme. We also show that the completeness of the WISE color–color cut in selecting Swift/BAT AGNs increases strongly with 14–195 keV luminosity.

[en] Large-scale outflows are generally considered to be possible evidence that active galactic nuclei (AGNs) can severely affect their host galaxies. Recently, an ultraluminous infrared galaxy (ULIRG) at z = 0.49, AKARI J0916248+073034, was found to have a galaxy-scale [O iii] λ 5007 outflow with one of the highest energy-ejection rates at z < 1.6. However, the central AGN activity estimated from its torus mid-infrared (MIR) radiation is weak relative to the luminous [O iii] emission. In this work we report the first NuSTAR hard X-ray follow-up of this ULIRG to constrain its current AGN luminosity. The intrinsic 2–10 keV luminosity shows a 90% upper limit of 3.0 × 10⁴³ erg s⁻¹ assuming Compton-thick obscuration (N _H = 1.5 × 10²⁴ cm⁻²), which is only 3.6% of the luminosity expected from the extinction-corrected [O iii] luminosity. Using the NuSTAR observation, we successfully identify that this ULIRG has a very extreme case of X-ray deficit among local ULIRGs. A possible scenario to explain the drastic decline in both the corona (X-ray) and torus (MIR) is that the primary radiation from the AGN accretion disk is currently in a fading status, as a consequence of a powerful nuclear wind suggested by powerful ionized outflow in a galaxy scale.

[en] We report the discovery of a Compton-thick (CT), dust-obscured galaxy at z = 0.89, WISE J082501.48+300257.2 (WISE 0825+3002), observed by the Nuclear Spectroscopic Telescope Array. X-ray analysis with the XCLUMPY model revealed that hard X-ray luminosity in the rest-frame 2–10 keV band of WISE 0825+3002 is L _X (2–10 keV) = ${4.2}_{-<!--\; ???\; -->1.6}^{+2.8}\times <!--\; ??\; -->{10}^{44}$ erg s⁻¹ while its hydrogen column density is N _H = ${1.0}_{-<!--\; ???\; -->0.4}^{+0.8}\times <!--\; ??\; -->{10}^{24}$ cm⁻², indicating that WISE 0825+3002 is a mildly CT active galactic nucleus (AGN). We performed spectral energy distribution (SED) fitting with CIGALE to derive its stellar mass, star formation rate, and infrared luminosity. The estimated Eddington ratio based on stellar mass and integration of the best-fit SED of the AGN component is λ _Edd = 0.70, which suggests that WISE 0825+3002 harbors an actively growing black hole behind a large amount of gas and dust. We found that the relationship between the luminosity ratio of X-ray and 6 μm, and Eddington ratio, follows an empirical relation for AGNs reported by Toba et al.