arXiv subjects

Yoshihiro Ueda

Publications and source records attributed to Yoshihiro Ueda.

At least 127 records · Page 7Linked to original sources

arXiv2018

Study of Nature of Corona in Narrow Line Seyfert 1 Galaxies

We study X-ray spectra of four Narrow Line Seyfert 1 galaxies (NLS1s), Mrk 110, SWIFT J2127.4+5654, IGR J16185-5928, and WKK 4438, using Suzaku and NuSTAR data. The spectra of the four sources are reproduced with a model consisting of a cutoff power law component, a reflection component, and a soft excess component. The photon indices of all the sources are found to be ~ 2. The cutoff energies are constrained to be ~ 40 keV for Mrk 110, SWIFT J2127.4+5654, and WKK 4438, whereas a lower limit of 155 keV is obtained for IGR J16185-5928. We find that the NLS1s in our sample have systematically softer spectra and lower cutoff energies than Broad Line Seyfert 1 galaxies reported in the literature. We also perform spectral fittings with a model in which the cutoff power law is replaced with the thermal Comptonization model in order to directly obtain the electron temperature of the corona (kTe). The fits give kTe ~ 10-20 keV for Mrk 110 and SWIFT J2127.4+5654, and lower limits of kTe > 18 keV for IGR J16185-5928 and kTe > 5 keV for WKK 4438. We divide the NuSTAR data of SWIFT J2127.4+5654 into three periods according to the flux. The spectral fits in the three periods hint that kTe is the lower in the higher flux period. The results of the four sources suggest a possible anti-correlation between kTe and the ratio of the luminosity of Compton up-scattered photons to the Eddington luminosity. The anti-correlation can be explained by a simple model in which electrons in the corona are cooled and heated through inverse Compton scattering and Coulomb collisions with protons, respectively.

astro-ph.HE↗

arXiv2018

ALMA 26 Arcmin$^{2}$ Survey of GOODS-S at One-millimeter (ASAGAO): Average Morphology of High-$z$ Dusty Star-Forming Galaxies is an Exponential-Disk ($n \simeq 1$)

We present morphological properties of dusty star-forming galaxies at z=1-3 determined with high-resolution (FWHM~0"19) Atacama Large Milllimeter/submilimeter Array (ALMA) 1-mm band maps of our ASAGAO survey covering a 26-arcmin^2 area in GOODS-S. In conjunction with the ALMA archival data, the present sample consists of 42 ALMA sources with a wide rest-frame far-infrared (FIR) luminosity L_FIR range of ~10^11-10^13 Lo. To obtain an average rest-frame FIR profile, we perform individual measurements and careful stacking of the ALMA sources using the uv-visibility method that includes positional-uncertainty and smoothing-effect evaluations through Monte-Carlo simulations. We find that the dusty star-forming galaxies have the average FIR-wavelength Sersic index and effective radius of n_FIR=1.2+/-0.2 and R_e,FIR=1.0-1.3 kpc, respectively, additionally with a point source at the center, indicative of the existence of AGN. The average FIR profile agrees with a morphology of an exponential-disk clearly distinguished from a spheroidal profile (Sersic index of 4). We also examine the rest-frame optical Sersic index n_opt and effective radius R_e,opt with the deep Hubble Space Telescope (HST) images. Interestingly, we obtain n_opt=0.9+/-0.3 (~n_FIR) and R_e,opt=3.2+/-0.6 kpc (>R_e,FIR), suggesting that the FIR-emitting disk is embedded within a larger stellar disk. The rest-frame UV and FIR data of HST and ALMA provide us a radial surface density profile of the total star-formation rate (SFR), where the FIR SFR dominates over the UV SFR at the center. Under the simple assumption of a constant SFR, a compact stellar distribution found in z~1-2 compact quiescent galaxies (cQGs) is well reproduced, while a spheroidal stellar morphology of cQGs (n_opt=4) cannot, suggestive of other important mechanisms such as dynamical dissipation.

astro-ph.GA↗

arXiv2018

Broadband X-ray Spectral Analysis of the Double-Nucleus Luminous Infrared Galaxy Mrk 463

We present a broadband (0.4-70 keV) X-ray spectral analysis of the luminous infrared galaxy (LIRG) system Mrk 463 observed with Nuclear Spectroscopic Telescope Array (NuSTAR), Chandra, and XMM-Newton, which contains double active galactic nuclei (AGNs) (Mrk 463E and Mrk 463W) with a separation of $\sim$ 3.8 kpc. Detecting their transmitted hard X-ray $>10$ keV continua with NuSTAR, we confirm that Mrk 463E and Mrk 463W have AGNs with intrinsic luminosities of (1.6-2.2) $\times 10^{43}$ and (0.5-0.6) $\times 10^{43}$ erg s$^{-1}$ (2-10 keV) obscured by hydrogen column densities of 8 $\times 10^{23}$ and 3 $\times 10^{23}$ cm$^{-2}$, respectively. Both nuclei show strong reflection components from cold matter. The luminosity ratio between X-ray (2-10 keV) and [O IV] 25.89 $μ$m of Mrk 463E is $\sim$5 times smaller than those of normal Seyfert galaxies, suggesting that the intrinsic SED is X-ray weak relative to the UV luminosity. In fact, the bolometric AGN luminosity of Mrk 463E estimated from $L^{\prime}$-band (3.8 $μ$m), [O IV] 25.89 $μ$m, and [Ne V] 14.32 $μ$m lines indicate a large bolometric-to-X-ray luminosity ratio, $κ_{\rm 2-10 keV} \approx$ 110-410, and a high Eddington ratio, $λ_{\rm Edd} \sim$ 0.4-0.8. We suggest that the merger triggered a rapid growth of the black hole in Mrk 463E, which is not yet deeply "buried" by circumnuclear dust. By contrast, the $L^{\prime}$-band luminosity of Mrk 463W is unusually small relative to the X-ray luminosity, suggesting that the Eddington ratio is low ($<10^{-3}$) and it might be still in an early phase of merger-driven AGN activity.

astro-ph.HE↗

arXiv2018

Hard X-ray View of HCG 16 (Arp 318)

We report the hard X-ray (3-50 keV) view of the compact group HCG 16 (Arp 318) observed with Nuclear Spectroscopic Telescope Array (NuSTAR). NGC 838 and NGC 839 are undetected at energies above 8 keV, showing no evidence of heavily obscured active galactic nuclei (AGNs). This confirms that these are starburst-dominant galaxies as previously suggested. We perform a comprehensive broadband (0.3-50 keV) X-ray spectral analysis of the interacting galaxies NGC 833 and NGC 835, using data of NuSTAR, Chandra, and XMM-Newton observed on multiple epochs from 2000 to 2015. NuSTAR detects the transmitted continua of low-luminosity active galactic nuclei (LLAGNs) in NGC 833 and NGC 835 with line-of-sight column densities of $\approx 3 \times10^{23}$ cm$^{-2}$ and intrinsic 2-10 keV luminosities of $\approx 3\times10^{41}$ erg s$^{-1}$. The iron-K$α$ to hard X-ray luminosity ratios of NGC 833 and NGC 835 suggest that their tori are moderately developed, which may have been triggered by the galaxy interactions. We find that NGC 835 underwent long-term variability in both intrinsic luminosity (by a factor of 5) and absorption (by $ΔN_{\rm H} \approx 2\times10^{23}$ cm$^{-2}$). We discuss the relation between the X-ray and total infrared luminosities in local LLAGNs hosted by spiral galaxies. The large diversity in their ratios is consistent with the the general idea that the mass accretion process in the nucleus and the star forming activity in the disk are not strongly coupled, regardless of the galaxy environment.

astro-ph.GA↗

arXiv2018

Suzaku Observations of Heavily Obscured (Compton-thick) Active Galactic Nuclei selected by Swift/BAT Hard X-ray Survey

We present a uniform broadband X-ray (0.5-100.0 keV) spectral analysis of 12 Swift/Burst Alert Telescope (BAT) selected Compton-thick ($\log N_{\mathrm{H}}/\mathrm{cm}^{-2} \geq 24$) Active Galactic Nuclei (CTAGNs) observed with Suzaku. The Suzaku data of 3 objects are published here for the first time. We fit the Suzaku and Swift spectra with models utilizing an analytic reflection code and those utilizing the Monte Carlo based model from an AGN torus by Ikeda et al. 2009. The main results are as follows. (1) The estimated intrinsic luminosity of a CTAGN strongly depends on the model; applying Compton scattering to the transmitted component in an analytic model may largely overestimates the intrinsic luminosity at large column densities. (2) Unabsorbed reflection components are commonly observed, suggesting that the tori are clumpy. (3) Most of CTAGNs show small scattering fractions (<0.5%) implying a buried AGN nature. (4) Comparison with the results obtained for Compton-thin AGNs (Kawamuro et al. 2016) suggests that the properties of these CTAGNs can be understood as a smooth extension from Compton-thin AGNs with heavier obscuration; we find no evidence that the bulk of the population of hard X-ray selected CTAGN is different from less obscured objects.

astro-ph.HE↗

arXiv2017

Asymptotic stability of traveling wave solutions for nonlocal viscous conservation laws with explicit decay rates

We consider scalar conservation laws with nonlocal diffusion of Riesz-Feller type such as the fractal Burgers equation. The existence of traveling wave solutions with monotone decreasing profile has been established recently (in special cases). We show the local asymptotic stability of these traveling wave solutions in a Sobolev space setting by constructing a Lyapunov functional. Most importantly, we derive the algebraic-in-time decay of the norm of such perturbations with explicit algebraic-in-time decay rates.

math.AP↗

arXiv2017

BAT AGN Spectroscopic Survey - V. X-ray properties of the Swift/BAT 70-month AGN catalog

Hard X-ray ($\geq 10$ keV) observations of Active Galactic Nuclei (AGN) can shed light on some of the most obscured episodes of accretion onto supermassive black holes. The 70-month Swift/BAT all-sky survey, which probes the 14-195 keV energy range, has currently detected 838 AGN. We report here on the broad-band X-ray (0.3-150 keV) characteristics of these AGN, obtained by combining XMM-Newton, Swift/XRT, ASCA, Chandra, and Suzaku observations in the soft X-ray band ($\leq 10$ keV) with 70-month averaged Swift/BAT data. The non-blazar AGN of our sample are almost equally divided into unobscured ($N_{\rm H}< 10^{22}\rm cm^{-2}$) and obscured ($N_{\rm H}\geq 10^{22}\rm cm^{-2}$) AGN, and their Swift/BAT continuum is systematically steeper than the 0.3-10 keV emission, which suggests that the presence of a high-energy cutoff is almost ubiquitous. We discuss the main X-ray spectral parameters obtained, such as the photon index, the reflection parameter, the energy of the cutoff, neutral and ionized absorbers, and the soft excess for both obscured and unobscured AGN.

astro-ph.HE↗

arXiv2017

Discovery of the new X-ray transient MAXI J1807+132: a Candidate of a Neutron Star Low-mass X-ray binary

We report on the detection and follow-up multi-wavelength observations of the new X-ray transient MAXI J1807+132 with the MAXI/GSC, Swift, and ground-based optical telescopes. The source was first recognized with the MAXI/GSC on 2017 March 13. About a week later, it reached the maximum intensity ($\sim$10 mCrab in 2-10 keV), and then gradually faded in $\sim$10 days by more than one order of magnitude. Time-averaged Swift/XRT spectra in the decaying phase can be described by a blackbody with a relatively low temperature (0.1-0.5 keV), plus a hard power-law component with a photon index of $\sim$2. These spectral properties are similar to those of neutron star low-mass X-ray binaries (LMXBs) in their dim periods. The blackbody temperature and the radius of the emission region varied in a complex manner as the source became dimmer. The source was detected in the optical wavelength on March 27-31 as well. The optical flux decreased monotonically as the X-ray flux decayed. The correlation between the X-ray and optical fluxes is found to be consistent with those of known neutron star LMXBs, supporting the idea that the source is likely to be a transient neutron star LMXB.

astro-ph.HE↗

arXiv2017

The close environments of accreting massive black holes are shaped by radiative feedback

The large majority of the accreting supermassive black holes in the Universe are obscured by large columns of gas and dust. The location and evolution of this obscuring material have been the subject of intense research in the past decades, and are still highly debated. A decrease in the covering factor of the circumnuclear material with increasing accretion rates has been found by studies carried out across the electromagnetic spectrum. The origin of this trend has been suggested to be driven either by the increase in the inner radius of the obscuring material with incident luminosity due to the sublimation of dust; by the gravitational potential of the black hole; by radiative feedback; or by the interplay between outflows and inflows. However, the lack of a large, unbiased and complete sample of accreting black holes, with reliable information on gas column density, luminosity and mass, has left the main physical mechanism regulating obscuration unclear. Using a systematic multi-wavelength survey of hard X-ray-selected black holes, here we show that radiation pressure on dusty gas is indeed the main physical mechanism regulating the distribution of the circumnuclear material. Our results imply that the bulk of the obscuring dust and gas in these objects is located within the sphere of influence of the black hole (i.e., a few to tens of parsecs), and that it can be swept away even at low radiative output rates. The main physical driver of the differences between obscured and unobscured accreting black holes is therefore their mass-normalized accretion rate.

astro-ph.HE↗

arXiv2017

X-Ray bright optically faint active galactic nuclei in the Subaru Hyper Suprime-Cam wide survey

We construct a sample of X-ray bright optically faint active galactic nuclei by combining Subaru Hyper Suprime-Cam, XMM-Newton, and infrared source catalogs. 53 X-ray sources satisfying i band magnitude fainter than 23.5 mag and X-ray counts with EPIC-PN detector larger than 70 are selected from 9.1 deg^2, and their spectral energy distributions (SEDs) and X-ray spectra are analyzed. 44 objects with an X-ray to i-band flux ratio F_X/F_i>10 are classified as extreme X-ray-to-optical flux sources. SEDs of 48 among 53 are represented by templates of type 2 AGNs or starforming galaxies and show signature of stellar emission from host galaxies in the optical in the source rest frame. Infrared/optical SEDs indicate significant contribution of emission from dust to infrared fluxes and that the central AGN is dust obscured. Photometric redshifts determined from the SEDs are in the range of 0.6-2.5. X-ray spectra are fitted by an absorbed power law model, and the intrinsic absorption column densities are modest (best-fit log N_H = 20.5-23.5 cm^-2 in most cases). The absorption corrected X-ray luminosities are in the range of 6x10^42 - 2x10^45 erg s^-1. 20 objects are classified as type 2 quasars based on X-ray luminsosity and N_H. The optical faintness is explained by a combination of redshifts (mostly z>1.0), strong dust extinction, and in part a large ratio of dust/gas.

astro-ph.GA↗

arXiv2017

BAT AGN Spectroscopic Survey I: Spectral Measurements, Derived Quantities, and AGN Demographics

We present the first catalog and data release of the Swift-BAT AGN Spectroscopic Survey (BASS). We analyze optical spectra of the majority of AGN (77%, 641/836) detected based on their 14-195 keV emission in the 70-month Swift BAT all-sky catalog. This includes redshift determination, absorption and emission line measurements, and black hole mass and accretion rate estimates for the majority of obscured and un-obscured AGN (74%, 473/641) with 340 measured for the first time. With ~90% of sources at z<0.2, the survey represents a significant census of hard-X-ray selected AGN in the local universe. In this first catalog paper, we describe the spectroscopic observations and datasets, and our initial spectral analysis. The FWHM of the emission lines show broad agreement with the X-ray obscuration (~94%), such that Sy 1-1.8 have NH<10^21.9 cm^-2, and Seyfert 2, have NH>10^21.9 cm^-2. Seyfert 1.9 show a range of column densities. Compared to narrow line AGN in the SDSS, the X-ray selected AGN have a larger fraction of dusty host galaxies suggesting these types of AGN are missed in optical surveys. Using the most sensitive [OIII]/Hbeta and [NII]/Halpha emission line diagnostic, about half of the sources are classified as Seyferts, ~15% reside in dusty galaxies that lack an Hbeta detection, but for which the line upper limits imply either a Seyfert or LINER, ~15% are in galaxies with weak or no emission lines despite high quality spectra, and a few percent each are LINERS, composite galaxies, HII regions, or in known beamed AGN.

astro-ph.HE↗

arXiv2017

Nature of hard X-ray (3-24 keV) detected luminous infrared galaxies in the COSMOS field

We investigate the nature of far-infrared (70 um) and hard X-ray (3-24 keV) selected galaxies in the COSMOS field detected with both Spitzer and Nuclear Spectroscopic Telescope Array (NuSTAR). By matching the Spitzer-COSMOS catalog against the NuSTAR-COSMOS catalog, we obtain a sample consisting of a hyperluminous infrared galaxy with log(L_IR/L_sun) > 13, 12 ultraluminous infrared galaxies with 12 < log(L_IR/L_sun) < 13, and 10 luminous infrared galaxies with 11 < log(L_IR/L_sun) < 12, i.e., 23 Hy/U/LIRGs in total. Using their X-ray hardness ratios, we find that 12 sources are obscured active galactic nuclei (AGNs) with absorption column densities of N_H > 10^22 cm^-2, including several Compton-thick (N_H ~ 10^24 cm^-2) AGN candidates. On the basis of the infrared (60 um) and intrinsic X-ray luminosities, we examine the relation between star-formation (SF) and AGN luminosities of the 23 Hy/U/LIRGs. We find that the correlation is similar to that of optically-selected AGNs reported by Netzer (2009), whereas local, far-infrared selected U/LIRGs show higher SF-to-AGN luminosity ratios than the average of our sample. This result suggests that our Hy/U/LIRGs detected both with Spitzer and NuSTAR are likely situated in a transition epoch between AGN-rising and cold-gas diminishing phases in SF-AGN evolutional sequences. The nature of a Compton-thick AGN candidate newly detected above 8 keV with NuSTAR (ID 245 in Civano et al. 2015) is briefly discussed.

astro-ph.GA↗

arXiv2017

The Swift/BAT AGN Spectroscopic Survey (BASS) -- VI. The Gamma_X - L/L_Edd relation

We study the observed relation between accretion rate (in terms of L/L_Edd) and shape of the hard X-ray spectral energy distribution (namely the photon index Gamma_X) for a large sample of 228 hard X-ray selected, low-redshift active galactic nuclei (AGN), drawn from the Swift/BAT AGN Spectroscopic Survey (BASS). This includes 30 AGN for which black hole mass (and therefore L/L_Edd) is measured directly through masers, spatially resolved gas or stellar dynamics, or reverberation mapping. The high quality and broad energy coverage of the data provided through BASS allow us to examine several alternative determinations of both Gamma_X and L/L_Edd. For the BASS sample as a whole, we find a statistically significant, albeit very weak correlation between Gamma_X and L/L_Edd. The best-fitting relations we find, Gamma_X=0.15 log(L/L_Edd)+const., are considerably shallower than those reported in previous studies. Moreover, we find no corresponding correlations among the subsets of AGN with different M_BH determination methodology. In particular, we find no robust evidence for a correlation when considering only those AGN with direct or single-epoch M_BH estimates. This latter finding is in contrast to several previous studies which focused on z>0.5 broad-line AGN. We discuss this tension and conclude that it can be partially accounted for if one adopts a simplified, power-law X-ray spectral model, combined with L/L_Edd estimates that are based on the continuum emission and on single-epoch broad line spectroscopy in the optical regime. We finally highlight the limitations on using Gamma_X as a probe of supermassive black hole evolution in deep extragalactic X-ray surveys.

astro-ph.GA↗

arXiv2017

The Quasar Luminosity Function at Redshift 4 with Hyper Suprime-Cam Wide Survey

We present the luminosity function of z=4 quasars based on the Hyper Suprime-Cam Subaru Strategic Program Wide layer imaging data in the g, r, i, z, and y bands covering 339.8 deg^2. From stellar objects, 1666 z~4 quasar candidates are selected by the g-dropout selection down to i=24.0 mag. Their photometric redshifts cover the redshift range between 3.6 and 4.3 with an average of 3.9. In combination with the quasar sample from the Sloan Digital Sky Survey in the same redshift range, the quasar luminosity function covering the wide luminosity range of M1450=-22 to -29 mag is constructed. It is well described by a double power-law model with a knee at M1450=-25.36+-0.13 mag and a flat faint-end slope with a power-law index of -1.30+-0.05. The knee and faint-end slope show no clear evidence of redshift evolution from those at z~2. The flat slope implies that the UV luminosity density of the quasar population is dominated by the quasars around the knee, and does not support the steeper faint-end slope at higher redshifts reported at z>5. If we convert the M1450 luminosity function to the hard X-ray 2-10keV luminosity function using the relation between UV and X-ray luminosity of quasars and its scatter, the number density of UV-selected quasars matches well with that of the X-ray-selected AGNs above the knee of the luminosity function. Below the knee, the UV-selected quasars show a deficiency compared to the hard X-ray luminosity function. The deficiency can be explained by the lack of obscured AGNs among the UV-selected quasars.

astro-ph.GA↗

arXiv2017

NuSTAR and Swift observations of the ultraluminous X-ray source IC 342 X-1 in 2016: witnessing spectral evolution

We report on an X-ray observing campaign of the ultraluminous X-ray source IC 342 X-1 with NuSTAR and Swift in 2016 October, in which we captured the very moment when the source showed spectral variation. The Swift/XRT spectrum obtained in October 9--11 has a power-law shape and is consistent with those observed in the coordinated XMM-Newton and NuSTAR observations in 2012. In October 16--17, when the 3--10 keV flux became $\approx$4 times higher, we performed simultaneous NuSTAR and Swift observations. In this epoch, the source showed a more round-shaped spectrum like that seen with ASCA 23 years ago. Thanks to the wide energy coverage and high sensitivity of NuSTAR, we obtained hard X-ray data covering up to $\sim$30 keV for the first time during the high luminosity state of IC 342 X-1. The observed spectrum has a broader profile than the multi-color disk blackbody model. The X-ray flux decreased again in the last several hours of the NuSTAR observation, when the spectral shape approached those seen in 2012 and 2016 October 9--11. The spectra obtained in our observations and in 2012 can be commonly described with disk emission and its Comptonization in cool ($T_{\rm e} \approx 4$ keV), optically-thick ($τ\approx 5$) plasma. The spectral turnover seen at around 5--10 keV shifts to higher energies as the X-ray luminosity decreases. This behavior is consistent with that predicted from recent numerical simulations of super-Eddington accretion flows with Compton-thick outflows. We suggest that the spectral evolution observed in IC 342 X-1 can be explained by a smooth change in mass accretion rate.

astro-ph.HE↗

arXiv2017

The dust covering factor in active galactic nuclei

The primary source of emission of active galactic nuclei (AGN), the accretion disk, is surrounded by an optically and geometrically thick dusty structure ("the so-called dusty torus"). The infrared radiation emitted by the dust is nothing but a reprocessed fraction of the accretion disk emission, so the ratio of the torus to the AGN luminosity ($L_{\text{torus}}/L_{\text{AGN}}$) should correspond to the fraction of the sky obscured by dust, i.e. the covering factor. We undertook a critical investigation of the $L_{\text{torus}}/L_{\text{AGN}}$ as the dust covering factor proxy. Using state-of-the-art 3D Monte Carlo radiative transfer code, we calculated a grid of spectral energy distributions (SEDs) emitted by the clumpy two-phase dusty structure. With this grid of SEDs, we studied the relation between $L_{\text{torus}}/L_{\text{AGN}}$ and the dust covering factor for different parameters of the torus. We found that in the case of type 1 AGNs the torus anisotropy makes $L_{\text{torus}}/L_{\text{AGN}}$ underestimate low covering factors and overestimate high covering factors. In type 2 AGNs $L_{\text{torus}}/L_{\text{AGN}}$ always underestimates covering factors. Our results provide a novel easy-to-use method to account for anisotropy and obtain correct covering factors. Using two samples from the literature, we demonstrated the importance of our result for inferring the obscured AGN fraction. We found that after the anisotropy is properly accounted for, the dust covering factors show very weak dependence on $L_{\text{AGN}}$, with values in the range of $\approx0.6-0.7$. Our results also suggest a higher fraction of obscured AGNs at high luminosities than those found by X-ray surveys, in part owing to the presence of a Compton-thick AGN population predicted by population synthesis models.

astro-ph.GA↗

arXiv2017

BAT AGN Spectroscopic Survey - IV: Near-Infrared Coronal Lines, Hidden Broad Lines, and Correlation with Hard X-ray Emission

We provide a comprehensive census of the near-Infrared (NIR, 0.8-2.4 $μ$m) spectroscopic properties of 102 nearby (z < 0.075) active galactic nuclei (AGN), selected in the hard X-ray band (14-195 keV) from the Swift-Burst Alert Telescope (BAT) survey. With the launch of the James Webb Space Telescope this regime is of increasing importance for dusty and obscured AGN surveys. We measure black hole masses in 68% (69/102) of the sample using broad emission lines (34/102) and/or the velocity dispersion of the Ca II triplet or the CO band-heads (46/102). We find that emission line diagnostics in the NIR are ineffective at identifying bright, nearby AGN galaxies because ([Fe II] 1.257$μ$m/Pa$β$ and H$_2$ 2.12$μ$m/Br$γ$) identify only 25% (25/102) as AGN with significant overlap with star forming galaxies and only 20% of Seyfert 2 have detected coronal lines (6/30). We measure the coronal line emission in Seyfert 2 to be weaker than in Seyfert 1 of the same bolometric luminosity suggesting obscuration by the nuclear torus. We find that the correlation between the hard X-ray and the [Si VI] coronal line luminosity is significantly better than with the [O III] luminosity. Finally, we find 3/29 galaxies (10%) that are optically classified as Seyfert 2 show broad emission lines in the NIR. These AGN have the lowest levels of obscuration among the Seyfert 2s in our sample ($\log N_{\rm H} < 22.43$ cm$^{-2}$), and all show signs of galaxy-scale interactions or mergers suggesting that the optical broad emission lines are obscured by host galaxy dust.

astro-ph.GA↗

arXiv2016

Shedding Light on the Compton-thick Active Galactic Nucleus in the Ultra-luminous Infrared Galaxy UGC 5101 with Broadband X-ray Spectroscopy

We report the broadband X-ray spectra of the ultra-luminous infrared galaxy (ULIRG) UGC 5101 in the 0.25-100 keV band observed with Swift/Burst Alert Telescope (BAT), NuSTAR, Suzaku, XMM-Newton, and Chandra. A Compton-thick AGN obscured with a hydrogen column density of $\approx 1.3\times10^{24}$ cm$^{-2}$ is detected above 10 keV. A spectral fit with a numerical torus model favors a large half opening angle of the torus, $>41$ degrees, suggesting that the covering fraction of material heavily obscuring the X-ray source is moderate. The intrinsic 2-10 keV luminosity is determined to be $\approx 1.4\times 10^{43}$ erg s$^{-1}$, which is $\approx$2.5 times larger than the previous estimate using only data below 10 keV with a simple spectral model. We find that UGC 5101 shows the ratio between the [O IV] 26 $μ$m line and 2-10 keV luminosities similar to those of normal Seyfert galaxies, along with other ULIRGs observed with NuSTAR, indicating that a significant portion of local ULIRGs are not really "X-ray faint" with respect to the flux of forbidden lines originating from the narrow line region (NLR). We propose a possible scenario that (1) the AGN in UGC 5101 is surrounded not only by Compton-thick matter located close to the equatorial plane but also by Compton-thin ($N_\mathrm{H} \sim 10^{21}$ cm$^{-2}$) matter in the torus-hole region and (2) it is accreting at a high Eddington rate with a steep UV to X-ray spectral energy distribution. Nevertheless, we argue that AGNs in many ULIRGs do not look extraordinary (i.e., extremely X-ray faint), as suggested by recent works, compared with normal Seyferts.

astro-ph.GA↗