In a sample of local active galactic nuclei studied at a spatial resolution on the order of 10 pc we show that the interstellar medium traced by the molecular hydrogen v=1-0 S(1) 2.1um line forms a geometrically thick, clumpy disk. The kinematics of the molecular gas reveals general rotation, although an additional significant component of random bulk motion is required by the high local velocity dispersion. The size scale of the typical gas disk is found to have a radius of ~30 pc with a comparable vertical height. Within this radius the average gas mass is estimated to be ~10^7 Msun based on a typical gas mass fraction of 10%, which suggests column densities of Nh ~ 5x10^23 cm^-2. Extinction of the stellar continuum within this same region suggest lower column densities of Nh ~ 2x10^22 cm^-2, indicating that the gas distribution on these scales is dominated by dense clumps. In half of the observed Seyfert galaxies this lower column density is still great enough to obscure the AGN at optical/infrared wavelengths. We conclude, based on the spatial distribution, kinematics, and column densities that the molecular gas observed is spatially mixed with the nuclear stellar population and is likely to be associated with the outer extent of any smaller scale nuclear obscuring structure. Furthermore, we find that the velocity dispersion of the molecular gas is correlated with the star formation rate per unit area, suggesting a link between the two phenomena, and that the gas surface density follows known "Schmidt-Kennicutt" relations. The molecular/dusty structure on these scales may be dynamic since it is possible that the velocity dispersion of the gas, and hence the vertical disk height, is maintained by a short, massive inflow of material into the nuclear region and/or by intense, short-lived nuclear star formation.
We present new mid-infrared (MIR) imaging data for three Type-1 Seyfert galaxies obtained with T-ReCS on the Gemini-South Telescope at subarcsecond resolution. Our aim is to enlarge the sample studied in a previous work to compare the properties of Type-1 and Type-2 Seyfert tori using clumpy torus models and a Bayesian approach to fit the infrared nuclear spectral energy distributions (SEDs). Thus, the sample considered here comprises 7 Type-1, 11 Type-2, and 3 intermediate-type Seyferts. The unresolved IR emission of the Seyfert 1 galaxies can be reproduced by a combination of dust heated by …
We present a detailed study of the X-ray and optical spectra of the luminous Seyfert galaxy Mrk 1393, which revealed variable partial obscuration of the active nucleus. The X-ray spectra obtained by XMM-Newton and Swift show moderate absorption with a column density around 3x10^21 cm^-2, consistent with a dust-reddening interpretation of the steep Balmer decrement seen in recent optical spectra. The X-ray flux in the 0.5 to 2 keV band during the XMM-Newton observation in 2005 and Swift observation in 2006 was a factor 6 brighter than that of the ROSAT All Sky Survey in 1991. In the past 4 year…
The Seyfert Galaxy Mrk 335 is known for its frequent changes of flux and spectral shape in the X-ray band occurred during recent years. These variations may be explained by the onset of a wind that previous, non-contemporaneous high-resolution spectroscopy in X-ray and UV bands located at accretion disc scale. A simultaneous new campaign by XMM-Newton and HST caught the source at an historical low flux in the X-ray band. The soft X-ray spectrum is dominated by prominent emission features, and by the effect of a strong ionized absorber with an outflow velocity of 5-6X10$^3$~km~s$^{-1}$. The bro…
We present ALMA Band 6 $^{12}$CO(2--1) line and rest-frame 232GHz continuum observations of the nearby Compton-thick Seyfert galaxy NGC5643 with angular resolutions 0.11-0.26arcsec (9-21pc). The CO(2--1) integrated line map reveals emission from the nuclear and circumnuclear region with a two-arm nuclear spiral extending 10arcsec on each side. The circumnuclear CO(2--1) kinematics can be fitted with a rotating disk, although there are regions with large residual velocities and/or velocity dispersions. The CO(2--1) line profiles of these regions show two different velocity components. One is as…
We study the obscuring structure of circumnuclear disks (CNDs) by considering supernova (SN) feedbacks from nuclear starburst and the effect of anisotropic radiative pressure from AGNs. We suppose that the mass accretion onto a central supermassive black hole (SMBH) is triggered by SN-driven turbulence within CNDs, and we explore how the structures of CNDs depend on the BH mass ($M_{\rm BH}$) and AGN luminosity ($L_{\rm AGN}$). We find that the obscuring fraction ($f_{\rm obs}$) peaks at $\sim10\%$ of the Eddington luminosity ($L_{\rm Edd}$), and its maximal value is $f_\mathrm{obs} \sim 0.6$ …
Active galactic nuclei (AGNs) are believed to be obscured by an optical thick "torus" that covers a large fraction of solid angles for the nuclei. However, the physical origin of the tori and the differences in the tori among AGNs are not clear. In a previous paper based on three-dimensional radiation-hydorodynamic calculations, we proposed a physics-based mechanism for the obscuration, called "radiation-driven fountains," in which the circulation of the gas driven by central radiation naturally forms a thick disk that partially obscures the nuclear emission. Here, we expand this mechanism and…
We present new central stellar velocity dispersion measurements for 428 galaxies in the Palomar spectroscopic survey of bright, northern galaxies. Of these, 142 have no previously published measurements, most being relatively late-type systems with low velocity dispersions (< 100 km/s). We provide updates to a number of literature dispersions with large uncertainties. Our measurements are based on a direct pixel-fitting technique that can accommodate composite stellar populations by calculating an optimal linear combination of input stellar templates. The original Palomar survey data were take…
We obtained new quantitative determinations of the nitrogen abundance and a consistent relation between nitrogen and oxygen abundances for a sample of Seyfert 2 galaxies located at redshift $z < 0.1$. We carried out this analysis using the Cloudy code to build detailed photoionization models. We were able to reproduce observed optical narrow emission line intensities for 44 sources compiled from the literature. Our results show that Seyfert 2 nuclei have nitrogen abundances ranging from $\sim0.3$ to $\sim 7.5$ times the solar value. We derived the relation $\rm \log(N/H)=1.05 (\pm0.09) \times …
We performed a systematic analysis of the 4.67 $μ$m CO ro-vibrational absorption band toward nearby active galactic nuclei (AGNs) and analyzed the absorption profiles of ten nearby galaxies collected from the AKARI and Spitzer spectroscopic observations that show the CO absorption feature by fitting a plane-parallel local thermal equilibrium gas model. We found that CO gas is warm (200--500 K) and has a large column density ($N_\mathrm{H}\gtrsim10^{23}~\mathrm{cm^{-2}}$). The heating of the gas is not explicable by either UV heating or shock heating because these processes cannot represent the…
Observationally established correlations between black hole mass and host galaxy structural/dynamical properties (like the M_BH - sigma relation) give support to the idea of an intimate link between the growth of black holes (BHs) and their host galaxies. Active galactic nuclei represent a poorly understood phase (or phases) in the life of a galaxy, during which the BH growth is directly observable. With the advent of wide-field surveys and high angular resolution instruments, it is now possible to observe the source of energy in Seyfert galaxies and QSOs, and conduct both statistical and deta…
Molecular gas is believed to be the fuel for star formation and nuclear activity in Seyfert galaxies. To explore the role of magnetic fields in funneling molecular gas into the nuclear region, measurements of the magnetic fields embedded in molecular gas are needed. By applying the new velocity gradient technique (VGT) to ALMA and PAWS's CO isotopolog data, we obtain the first detection of CO-associated magnetic fields in several nearby Seyfert galaxies and their unprecedented high-resolution magnetic field maps. The VGT-measured magnetic fields in molecular gas globally agree with those infer…
We present results on a systematic study of flux variability on hourly time-scales in a large sample of active galactic nuclei (AGN) in the 3-79 keV band using data from Nuclear Spectroscopic Telescope Array. Our sample consists of 4 BL Lac objects (BL Lacs), 3 flat spectrum radio quasars (FSRQs) 24 Seyfert 1, 42 Seyfert 2 and 8 narrow line Seyfert 1 (NLSy1) galaxies. We find that in the 3-79 keV band, about 65% of the sources in our sample show significant variations on hourly time scales. Using Mann-Whitney U-test and Kolmogorov-Smirnov test, we find no difference in the variability behaviou…
The central engines of Seyfert galaxies are thought to be enshrouded by geometrically thick gas and dust structures. In this article, we derive observable properties for a self-consistent model of such toroidal gas and dust distributions, where the geometrical thickness is achieved and maintained with the help of X-ray heating and radiation pressure due to the central engine. Spectral energy distributions (SEDs) and images are obtained with the help of dust continuum radiative transfer calculations with RADMC-3D. For the first time, we are able to present time-resolved SEDs and images for a ph…
Seyfert 1.8/1.9 are sources showing weak broad H-alpha components in their optical spectra. We aim at testing whether Seyfert 1.8/1.9 have similar properties at UV and X-ray wavelengths to Seyfert 2. We use the 15 Seyfert 1.8/1.9 in the Veron Cetty and Veron catalogue with public data available from the Chandra and/or XMM-Newton archives at different dates, with timescales between observations ranging from days to years. Our results are homogeneously compared with a previous work using the same methodology applied to a sample of Seyfert 2 (Hernandez-Garcia et al. 2015). X-ray variability is fo…
Several studies of nearby active galactic nuclei (AGN) have shown that the soft X-ray emission presents a size and morphology that resembles that of the narrow-line region (NLR) traced by [O III]. Since the NLR is mainly constituted by gas photoionised by the AGN, it seems logical to assume that this is also the primary source of the soft X-ray emission. However, these results are based on individual sources or small samples, particularly focused on type-2 Seyfert galaxies. Very little has been said concerning other types of AGN. The purpose of this work is to compare the circumnuclear morphol…
We studied the physical parameters of a sample comprising of all Spitzer/IRS public spectra of Seyfert galaxies in the mid-infrared (5.2-38$μ$m range) under the active galactic nuclei (AGN) unified model. We compare the observed spectra with $\sim10^6$ CLUMPY model spectral energy distributions, which consider a torus composed of dusty clouds. We find a slight difference in the distribution of line-of-sight inclination angle, $i$, requiring larger angles for Seyfert 2 (Sy2) and a broader distribution for Seyfert 1 (Sy1). We found small differences in the torus angular width, $σ$, indicating th…
We present the results of our ALMA observations of three AGN-dominated nuclei in optical Seyfert 1 galaxies (NGC 7469, I Zw 1, and IC 4329 A) and eleven luminous infrared galaxies (LIRGs) with various levels of infrared estimated energetic contributions by AGNs at the HCN and HCO+ J=3-2 emission lines. The HCN and HCO+ J=3-2 emission lines are clearly detected at the main nuclei of all sources, except for IC 4329 A. The vibrationally excited (v2=1f) HCN J=3-2 and HCO+ J=3-2 emission lines are simultaneously covered, and HCN v2=1f J=3-2 emission line signatures are seen in the main nuclei of tw…
We have obtained high-resolution mid-infrared (MIR) imaging, nuclear spectral energy distributions (SEDs) and archival Spitzer spectra for 22 low-luminosity active galactic nuclei (LLAGN; L_bol < 5 x 10^42 erg/s). Infrared (IR) observations may advance our understanding of the accretion flows in LLAGN, the fate of the obscuring torus at low accretion rates, and, perhaps, the star formation histories of these objects. However, while comprehensively studied in higher-luminosity Seyferts and quasars, the nuclear IR properties of LLAGN have not yet been well-determined. In these proceedings we sum…
Dedicated searches generally find a decreasing fraction of obscured Active Galactic Nuclei (AGN) with increasing AGN luminosity. This has often been interpreted as evidence for a decrease of the covering factor of the AGN torus with increasing luminosity, the so-called receding torus models. Using a complete flux-limited X-ray selected sample of 199 AGN, from the Bright Ultra-hard XMM-Newton Survey, we determine the intrinsic fraction of optical type-2 AGN at 0.05$\leq$z$\leq$1 as a function of rest-frame 2-10 keV X-ray luminosity from 10$^{42}$ to 10$^{45}$ erg/s. We use the distributions of …
A decade ago the archetypal Seyfert-1 galaxy NGC 5548 was discovered to have undergone major spectral changes. The soft X-ray flux had dropped by a factor of 30 while new broad and blueshifted UV absorption lines appeared. This was explained by the emergence of a new obscuring wind from the accretion disk. Here we report on the striking long-term variability of the obscuring disk wind in NGC 5548 including new observations taken in 2021-2022 with the Swift Observatory and the Hubble Space Telescope's (HST) Cosmic Origins Spectrograph (COS). The X-ray spectral hardening as a result of obscurati…
We investigate the discrepancy between oxygen abundance estimations for narrow-line regions (NLRs) of Active Galactic Nuclei (AGNs) type Seyfert 2 derived by using direct estimations of the electron temperature (Te-method) and those derived by using photoionization models. In view of this, observational emission-line ratios in the optical range (3000 < λ(Å) < 7000) of Seyfert 2 nuclei compiled from the literature were reproduced by detailed photoionization models built with the Cloudy code. We find that the derived discrepancies are mainly due to the inappropriate use of the relations between …
For the first time, the helium abundance relative to hydrogen (He/H), which relied on direct measurements of the electron temperature, has been derived in the narrow line regions (NLRs) from a local sample of Seyfert 2 nuclei. In view of this, optical emission line intensities [$3000 \: < λ\: < \: 7000$] of 65 local Seyfert 2 nuclei ($z \: < \: 0.2$), taken from Sloan Digital Sky Survey Data Release 15 and additional compilation from the literature, were considered. We used photoionization model grid to derive an Ionization Correction Factor (ICF) for the neutral helium. The application of thi…
The narrow-line region (NLR) consists of gas clouds ionized by the strong radiation from the active galactic nucleus (AGN), distributed in the spatial scale of AGN host galaxies. The strong emission lines from the NLR are useful to diagnose physical and chemical properties of the interstellar medium in AGN host galaxies. However, the origin of the NLR is unclear; the gas clouds in NLRs may be originally in the host and photoionized by the AGN radiation, or they may be transferred from the nucleus with AGN-driven outflows. For studying the origin of the NLR, we systematically investigate the ga…
Are "Changing-Look" Active Galactic Nuclei Special in the Coevolution of Supermassive Black Holes and their Hosts? II. The Case of Changing-Look Narrow-Line Seyfert 1 Galaxies
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；Guangxi Key Laboratory for Relativistic Astrophysics, School of Physical Science and Technology, Guangxi University（广西大学物理科学与技术学院相对论天体物理广西重点实验室）；School of Astronomy and Space Science, University of Chinese Academy of Sciences（中国科学院大学天文与空间科学学院）；Department of Astronomy, University of California, Berkeley（加州大学伯克利分校天文学系）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）
Active galactic nuclei (AGN) are powered by accreting supermassive black holes, surrounded by a torus of obscuring material. Recent studies have shown how the torus structure, formerly thought to be homogeneous, appears to be 'patchy': the detection of variability in the line-of-sight hydrogen column density, in fact, matches the description of an obscurer with a complex structure made of clouds with different column density. In this work, we perform a multi-epoch analysis of the X-ray spectra of the Seyfert 2 galaxy NGC 7479 in order to estimate its torus properties, such as the average colum…
The origin of the unification model for Active Galactic Nuclei (AGN) was the detection of broad hydrogen recombination lines in the optical polarized spectrum of the Seyfert 2 galaxy (Sy2) NGC 1068. Since then, a search for the hidden broad-line region (HBLR) of nearby Sy2s started, but polarized broad lines have only been detected in 30-40% of the nearby Sy2s observed to date. Here we present new VLT/FORS2 optical spectropolarimetry of a sample of 15 Sy2s, including Compton-thin and Compton-thick sources. The sample includes six galaxies without previously published spectropolarimetry, some o…
For the first time, the argon abundance relative to hydrogen abundance (Ar/H) in the narrow line region of a sample of Seyfert 2 nuclei has been derived. In view of this, optical narrow emission line intensities of a sample of 64 local Seyfert 2 nuclei (z < 0.25) taken from Sloan Digital Sky Survey DR7 and measured by the MPA/JHU group were considered. We adopted the Te-method for AGNs, which is based on direct determination of the electron temperature, together with a grid of photoionization model results, built with the Cloudy code, to obtain a method for the derivation of the Ar/H abundance…
We discuss the dense molecular gas in central regions of nearby Seyfert galaxies, and report new arcsec resolution observations of HCN(1-0) and HCO$^+$(1-0) for 3 objects. In NGC 3079 the lines show complex profiles as a result of self-absorption and saturated continuum absorption. H$^{13}$CN reveals the continuum absorption profile, with a peak close to the galaxy's systemic velocity that traces disk rotation, and a second feature with a blue wing extending to $-350$km s$^{-1}$ that most likely traces a nuclear outflow. The morphological and spectral properties of the emission lines allow us …
Far-Infrared (FIR) photometry from the the Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory is presented for 313 nearby, hard X-ray selected galaxies from the 58-month Swift Burst Alert Telescope (BAT) Active Galactic catalog. The present data do not distinguish between the FIR luminosity distributions at 70 and 160um for Seyfert 1 and Seyfert 2 galaxies. This result suggests that if the FIR emission is from the nuclear obscuring material surrounding the accretion disk, then it emits isotropically, independent of orientation. Alternatively, a significant fra…
