arXiv subjects

Yuya Nakatani

Publications and source records attributed to Yuya Nakatani.

8 recordsLinked to original sources

arXiv2026

XRISM Resolves the Circum-nuclear Environment of NGC 4945

Compton-thick Active Galactic Nuclei (AGN) represent one of the most elusive phases of massive black hole growth, yet are expected to contribute substantially to the Cosmic X-ray Background and the integrated growth of massive black holes. NGC 4945 is the closest Compton-thick AGN and amongst the brightest AGN in the hard X-ray sky, making it an important benchmark for more distant Compton-thick AGN. We present the first high-resolution X-ray spectral analysis of NGC 4945 using XRISM/Resolve. The entire 4-15 keV Resolve spectrum, including a strong Fe K$α$ doublet and weak Compton Shoulder, is well described by a de-coupled dual-obscurer model. The model features a low-covering-factor Compton-thick primary obscurer intersecting the line-of-sight that permits the rapidly variable, direct transmitted coronal continuum to dominate above 10 keV. A Compton-thin secondary reprocessor with a high covering factor dominates the reprocessed emission between $\sim$4-10 keV. Assuming that virial motion accounts for line broadening, the secondary reprocessor can exist at $\sim$0.12 pc, and could help explain the weak high-ionisation optical and infrared emission lines observed in NGC 4945. If such obscuration geometries are common among more distant and/or fainter Compton-thick AGN, our results suggest that simpler coupled X-ray spectral modelling could substantially over-estimate Compton-thick covering factors and under-estimate intrinsic X-ray luminosities.

astro-ph.GA↗

arXiv2026

Decoupled Kinematics and Excitation in the Compton-thick AGN NGC 6552: Spatially Resolved KOOLS-IFU Observations

Hard X-ray selected Compton-thick AGNs provide a relatively obscuration-resistant census of accretion, but optical line diagnostics can be strongly shaped by extinction and geometry. Spatially resolved integral-field spectroscopy can mitigate these effects and provides direct constraints on outflow kinematics and ionization state on kiloparsec scales. We present KOOLS-IFU optical integral-field spectroscopy of NGC 6552 obtained on the 3.8 m Seimei Telescope. Using spatially resolved emission-line ratios and non-parametric [O III]5007 kinematics over the central ~2 kpc, we test whether ionized-gas kinematics are locally coupled to excitation. The [O III]5007 width W80 is broadly elevated across the inner region (~530-830 km/s) and declines monotonically with projected galactocentric distance, consistent with a centrally concentrated outflow that decelerates at larger radii. Despite this clear kinematic structure, neither W80 nor the velocity asymmetry parameter dv shows a statistically significant correlation with [O III]5007/Hbeta. Order-of-magnitude outflow energetics yield Edot_K/L_bol ~ 0.01%-0.28% (for assumed n_e = 50-1000 cm^-3), consistent with [O III]-based estimates tracing only the ionized phase of a multi-phase outflow. We conclude that in NGC 6552 both the total line broadening traced by W80 and dv are consistent with being governed primarily by spatial dynamical structure and line-of-sight superposition of multiple kinematic components, with no statistically significant coupling to excitation-driven processes detected at our sensitivity level. A positive W80-[O III]5007/Hbeta coupling does emerge in the small subset of bins for which the two-component fit is most strongly favored statistically, which deeper observations will be needed to confirm.

astro-ph.GA↗

arXiv2026

Complex Nuclear Structure in Seyfert 2 Galaxy NGC 4388 Revealed by XRISM Observation

We report results from the simultaneous XRISM (183 ks) and NuSTAR (62 ks) observations of the Seyfert-2 galaxy NGC 4388. This AGN has the brightest Fe K$α$ line among Compton-thin, obscured sources. To model the reflection continuum and fluorescent lines, we employ an updated version of XCLUMPY and a broad line region model with a disk-like geometry. The profile of the neutral Fe-K fluorescent line is well described as the sum of three components convolved with Gaussians with FWHM values of $\sim 290\ \mathrm{km\ s^{-1}}$, $\sim 1470\ \mathrm{km\ s^{-1}}$, and $\sim 11100\ \mathrm{km\ s^{-1}}$. These line widths correspond to radii of 1.5 pc, 0.060 pc, and $1.0\times10^{-3}$ pc by assuming Keplerian motion, which we interpret as the dusty torus, its inner edge region, and the BLR, respectively. The data suggest that the Fe K$α$ BLR component is larger than that of H$α$ (FWHM of 4500 $\mathrm{km\ s^{-1}}$) in the polarized optical spectrum, implying that the velocity field of the BLR is dominated by that parallel to the equatorial plane. In addition, Fe XXVI Ly$α$ and Fe XXV absorption lines are detected, characterized by $\logξ \sim 3.50~\mathrm{erg\ cm\ s^{-1}}$, $\log{N_{\mathrm{H}}} \sim 22.1~\mathrm{cm^{-2}}$, $v_{\mathrm{out}} \sim 40\ \mathrm{km\ s^{-1}}$, and $σ_v \sim 160\ \mathrm{km\ s^{-1}}$. We infer that the absorber is gravitationally bound and is possibly associated with a failed wind, consistent with a radiation-driven fountain flow.

astro-ph.HE↗

arXiv2026

XRISM Discovery of Multiple Ionized Fe-K Emission and Absorption Components in Centaurus A

We present the first clear detection of ionized Fe-K emission and absorption components in the nearby radio galaxy Centaurus A, revealed by the high-resolution XRISM/Resolve detector. In the 6.5-6.9 keV band, XRISM reveals multiple Fe XXV and Fe XXVI emission components. One is a broad (with a width of sigma = 3000 km/s) and redshifted (+3400 km/s) component, originating at D = 0.02 pc from the central black hole. The other two components are narrow (with a width of sigma = 500 km/s) and exhibit redshifted and blueshifted velocities (+2600 km/s and -1500 km/s), originating from more distant regions (D = 0.1 pc). The photo-ionized model explains the broader component, while the two narrower components can be explained by either photo-ionization or collisional ionization. One interpretation is that the broader component is an outflow at ~10^2 R_S (R_S; Schwarzschild radius) and the narrow component is a shock-heated plasma close to the torus, with a possible connection to the JWST-discovered outflow outside the torus. Two blueshifted absorption lines are detected at ~7.1 keV (~10^4 km/s) and ~10.6 keV (~10^5 km/s). The line significance of the 10.6 keV line is above 98%. The absorption line components might be attributed to the broad emission component. These results demonstrate the high potential of XRISM/Resolve to characterize ionized emission and absorption features in the Fe-K band. Our findings establish a new benchmark in the study of circumnuclear environments in low-luminosity radio galaxies, thereby contributing to a broader understanding of AGN unification.

astro-ph.HE↗

arXiv2025

IMPACTX: An X-ray Spectral Model for Polar Dust and Clumpy Torus

We construct a generic X-ray spectral model for the reflection component from the clumpy torus and dusty gas in the polar region (polar dusty gas) in an active galactic nucleus (AGN), designated as Inclusive spectral energy distribution Model of Polar dust And Clumpy Torus for X-ray (IMPACTX). To calculate the spectra, we utilize the Monte-Carlo based, 3-dimensional radiative transfer code SKIRT. The adopted geometry is the same as that of the IMPACT model (Ogawa et al. in prep.), consisting of a clumpy torus defined by Nenkova et al. (2008) and paraboloid-shell polar dusty gas launched at the inner radius of the torus. We discuss the dependence of the X-ray spectrum on geometrical parameters in comparison with the conventional torus-only model (XCLUMPY). As an example, we have simultaneously applied the IMPACTX and IMPACT models to the X-ray and infrared spectra of the nearby Seyfert 2 galaxy NGC 4388, and have found a solution that can well reproduce both spectra. This demonstrates the importance of using both X-ray and infrared data to constrain the nuclear structure of an AGN.

astro-ph.HE↗

arXiv2025

XRISM analysis of the complex Fe K$α$ line in Centaurus A

We analyze the high-resolution XRISM/Resolve spectrum of the Fe K$α$ emission line of the nearest active galactic nucleus, in Centaurus A. The line features two narrow and resolved peaks of Fe K$α_1$, and Fe K$α_2$ with a FWHM of $(4.8\pm0.2)\times10^2$ km/s each. A broad line with a FWHM of $(4.3\pm0.3)\times10^3$ km/s, and with a flux similar to the two narrow line cores, is also required. This broad component is not observed in the optical or IR spectra of Cen A. The line shape requires the existence of an emission region that extends from $\sim10^{-3}$ pc to $\sim10^1$ pc. Assuming that the emissivity follows a radial power-law profile of $r^{-q}$, we find $q\approx2$. This may indicate an extended corona, an emitting region that bends towards the corona, or a non-uniform density. When assuming $q=3$, the line shape can only be reproduced by including three emitting components in the model. The measured best-fit inclination is $24^{+13}_{-7}$ degrees, but higher inclinations are only slightly disfavored. A single blurred MYTorusL line profile can describe the line shape, but requires a large relative normalization. This could be due to past variability, modified abundances, or differing geometries. The line shape can be reproduced from the radii measured by reverberation mapping, but only if an additional extended emitting region at small radii is included.

astro-ph.HE↗

arXiv2025

AGN outflows and their properties in Mrk 766 as revealed by KOOLS-IFU on the Seimei Telescope

We present the emission-line flux distributions and their ratios, as well as the gas outflow features, of the innermost 2 kpc region of the type 1 Seyfert galaxy Mrk 766, using the Kyoto Okayama Optical Low-dispersion Spectrograph with an optical-fiber integral field unit on the Seimei Telescope. We find that the central region of Mrk 766 is kinematically disturbed, exhibiting asymmetric and radially distributed AGN-driven ionized gas outflows traced by \OIII\ with velocities exceeding 500 \kms. The mass of the ionized gas outflow is estimated to be $10^{4.65-5.95} M_{\odot}$, and the mass outflow rate is $0.14-2.73$ M${\odot}$ yr$^{-1}$. This corresponds to a kinetic power, $\dot{E}_{\rm K}$, of $4.31 \times 10^{40} \ {\rm erg} \ {\rm s^{-1}}< \dot{E}_{\rm K} < 8.62 \times 10^{41} \ {\rm erg} \ {\rm s^{-1}}$, which is equivalent to $0.08\%-1.53\%$ of the bolometric luminosity, $L_{\rm bol}$. This result is consistent with other observed properties of ionized gas outflows, although it is lower than the theoretical predictions in AGN feedback models ($\sim5\%$), implying that ionized gas outflows traced by \OIII\ represent only a minor fraction of the total outflows ejected from the host galaxy. Given the asymmetric and radially distributed outflow signatures observed across the host galaxy within the limited field of view, the maximum distance the outflowing gas has traveled remains an open question.

astro-ph.GA↗

arXiv2023

Broadband X-ray Spectral Study of Nuclear Structure in Local Obscured Radio Galaxies

Radio galaxies are a key population to understand the importance of relativistic jets in AGN feedback. We present the results of a systematic, broadband X-ray spectral analysis of hard X-ray selected radio galaxies to investigate their nuclear structures. In this study, we focus on the seven most radio-loud, X-ray obscured narrow line radio galaxies in the \textit{Swift}/BAT 70 month AGN catalog. The spectra from 0.5 keV up to 66 keV obtained with \textit{Suzaku} and \textit{NuSTAR} of six objects are newly analyzed here by utilizing the X-ray clumpy torus model (XCLUMPY), whereas we refer to Ogawa et al. (2021) for the results of Centaurus A. We find that these radio galaxies have similar torus covering fractions compared with radio quiet AGNs at the same Eddington ratios ($-3 < \log λ_{\rm Edd} < -1$). This result implies that (1) the torus structure is not an important factor that determines the presence of jets and (2) AGN jets have physically little effect on the torus.

astro-ph.HE↗