The effect of radiation pressure compression (RPC) on ionized gas in Active Galactic Nuclei (AGN) likely sets the photoionized gas density structure. The photoionized gas free-free absorption and emission are therefore uniquely set by the incident ionizing flux. We use the photoionization code Cloudy RPC model results to derive the expected relations between the free-free emission and absorption properties and the distance from the AGN centre, for a given AGN luminosity. The free-free absorption frequency of RPC gas is predicted to increases from $\sim$100 MHz on the kpc scale, to $\sim$100 GHz on the sub-pc scale, consistent with observations of spatially resolved free-free absorption. The free-free emission at 5 GHz is predicted to yield a radio loudness of $R\sim 0.03$, below the typical observed values of $R\sim 0.1-1$ in radio-quiet AGN. However, the flat free-free radio continuum may become dominant above 100 GHz. The suggested detection of optically thin free-free emission in NGC 1068, on the sub pc torus scale, is excluded as the brightness temperature is too high for optically thin free-free emission. However, excess emission observed with ALMA above 150 GHz in NGC 1068, is consistent with the predicted free-free emission from gas just outside the broad line region, a region which overlaps the hot dust disc resolved with GRAVITY. Extended $\sim$100 pc scale free-free emission is also likely present in NGC 1068. Future sub mm observation of radio quiet AGN with ALMA may allow to image the free-free emission of warm photoionized gas in AGN down to the 30 mas scale, including highly absorbed AGN.
A fraction of quasars present broad absorption lines, produced by outflowing gas with typical velocities of 3000 - 10,000 km/s. If the outflowing gas fills a significant fraction of the volume where it resides, then it will be highly ionized by the quasar due to its low density, and will not produce the observed UV absorption. The suggestion that the outflow is shielded from the ionizing radiation was excluded by recent observations. The remaining solution is a dense outflow with a filling factor $f<10^{-3}$. What produces such a small $f$? Here we point out that radiation pressure confinement…
We present the line observations in our ALMA imaging spectral scan toward three deeply buried nuclei in NGC 4418 and Arp 220. We cover 67 GHz in $f_{\rm rest}$=215-697 GHz at about 0.2$"$ (30, 80 pc) resolution. All the nuclei show dense line forests; we report our initial line identification using 55 species. The line velocities generally indicate gas rotation around each nucleus, tracing nuclear disks of $\sim$100 pc sizes. We confirmed the counter-rotation of the nuclear disks in Arp 220 and that of the nuclear disk and the galactic disk in NGC 4418. While the brightest lines exceed 100 K, …
We present results of H I absorption experiment done using the Giant Metrewave Radio Telescope (GMRT) towards 27 low- and intermediate-luminosity ($P_{\rm 1.4 GHz}$ $\sim$10$^{23}$-10$^{26}$ W Hz$^{-1}$) radio active galactic nuclei (AGN), classified as either low excitation radio galaxies (LERGs) or high excitation radio galaxies (HERGs) and with WISE colour W2[4.6 $μ$m]$-$W3[12 $μ$m]$>$ 2. We report H I absorption detection towards seven radio AGNs, six of which are new. Combined with other sources from literature classified as LERGs or HERGs, we confirm our earlier result that compact radio…
We have selected a sample of 80 candidates for obscured radio-loud active galactic nuclei and presented their basic optical/near-infrared (NIR) properties in Paper 1. In this paper, we present both high-resolution radio continuum images for all of these sources and HI 21cm absorption spectroscopy for a few selected sources in this sample. A-configuration 4.9 and 8.5 GHz VLA continuum observations find that 52 sources are compact or have substantial compact components with size <0.5" and flux density >0.1 Jy at 4.9 GHz. The most compact 36 sources were then observed with the VLBA at 1.4 GHz. On…
We present a search for associated HI 21 cm absorption in a sample of 29 radio-loud active galactic nuclei (AGNs) at $0.7 < z < 1$, carried out with the upgraded Giant Metrewave Radio Telescope. We detect HI 21 cm absorption against none of our target AGNs, obtaining $3σ$ upper limits to the optical depth of $\lesssim$ 1% per 50 km s$^{-1}$ channel. The radio luminosity of our sources is lower than that of most AGNs searched for HI 21 cm absorption at similar redshifts in the literature, and, for all targets except two, the UV luminosity is below the threshold $10^{23}$ W Hz$^{-1}$, above whic…
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…
This review summarises what we have learnt in the last two decades based on HI 21-cm absorption observations about the cold interstellar medium (ISM) in the central regions of active galaxies and the interplay between this gas and the active nucleus (AGN). HI absorption is a powerful tracer on all scales, from the pc scales to many tens of kpc. Given the strong radio continuum often associated with the central activity, HI absorption can be used to study the HI near an AGN out to much higher redshifts than is possible using HI emission. HI absorption has been used to characterise the general I…
X-ray spectroscopy offers an opportunity to study the complex mixture of emitting and absorbing components in the circumnuclear regions of active galactic nuclei, and to learn about the accretion process that fuels AGN and the feedback of material to their host galaxies. We describe the spectral signatures that may be studied and review the X-ray spectra and spectral variability of active galaxies, concentrating on progress from recent Chandra, XMM-Newton and Suzaku data for local type 1 AGN. We describe the evidence for absorption covering a wide range of column densities, ionization and dyna…
The relations observed between supermassive black holes and their host galaxies suggest a fundamental link in the processes that cause these two objects to evolve. A more comprehensive understanding of these relations could be gained by increasing the number of supermassive black hole mass (M) measurements. This can be achieved, in part, by continuing to model the stellar dynamics at the centers of galactic bulges using data of the highest possible spatial resolution. Consequently, we present here an atlas of galaxies in the Space Telescope Imaging Spectrograph (STIS) data archive that may hav…
We report the first detections of associated H{\sc i} 21\,cm absorption in Gigahertz-peaked-spectrum (GPS) sources at high redshifts, $z > 1$, using the Giant Metrewave Radio Telescope (GMRT). Our GMRT search for associated H{\sc i} 21\,cm absorption in a sample of 12 GPS sources yielded two new detections of absorption, towards TXS~1200+045 at $z = 1.226$ and TXS~1245$-$197 at $z = 1.275$, and five non-detections. These are only the sixth and seventh detections of associated H{\sc i} 21\,cm absorption in active galactic nuclei (AGNs) at $z > 1$. Both H{\sc i} 21\,cm absorption profiles are wi…
We performed a detailed study of the extended cool gas, traced by MgII absorption [$W_r(2796)\geq0.3$~Å], surrounding 14 narrow-line active galactic nuclei (AGNs) at 0.12<z<0.22 using background quasar sight-lines. The background quasars probe the AGNs at projected distances of $60\leq D\leq265$~kpc. We find that, between $100\leq D\leq200$~kpc, AGNs appear to have lower MgII gas covering fractions (0.09$^{+0.18}_{-0.08}$) than quasars (0.47$^{+0.16}_{-0.15}$) and possibly lower than in active field galaxies (0.25$^{+0.11}_{-0.09}$). We do not find a statistically significant azimuthal angle d…
Highly ionized, z=0 metal absorption lines detected in the X-ray spectra of background active galactic nuclei (AGNs) provide an effective method to probe the hot ($T\sim10^6$ K) gas and its metal content in and around the Milky Way. We present an all-sky survey of the $K_α$ transition of the local O VII absorption lines obtained by Voigt-profile fitting archival XMM-Newton observations. A total of 43 AGNs were selected, among which 12 are BL Lac-type AGNs, and the rest are Seyfert 1 galaxies. At above the $3σ$ level the local O VII absorption lines were detected in 21 AGNs, among which 7 were …
Both long and short gamma-ray bursts (GRBs) are expected to occur in the dense environments of active galactic nuclei (AGN) accretion disks. As these bursts propagate through the disks they live in, they photoionize the medium causing time-dependent opacity that results in transients with unique spectral evolution. In this paper we use a line-of-sight radiation transfer code coupling metal and dust evolution to simulate the time-dependent absorption that occurs in the case of both long and short GRBs. Through these simulations, we investigate the parameter space in which dense environments lea…
In this paper we further explore the implications that this has for the currently popular consensus that it is the orientation of the circumnuclear obscuring torus which determines whether absorption is present along our sight-line. The fact that at logL > 23 W/Hz, both type-1 and type-2 objects exhibit a 50% probability of detection, suggests that this is not the case and that the bias against detection of HI absorption in type-1 objects is due purely to the inclusion of the logL > 23 W/Hz sources. Similarly, the ultra-violet luminosities can also explain why the presence of 21-cm absorption …
Whether aimed for the study of the planetary systems, the distribution of the stars in the galaxies or the formation of the large-scale structures in the Universe, the sizes of numerical simulations are becoming increasingly important in terms of their virtual volumes and computer memories. The visualization of the data becomes more complicated with the requirement of the exposition of the large number of data points. In order to lighten such burden, Virtual Observatories (VO) have been developed and are now essential tools in astronomy to share existing data, for visualization and for data an…
We present the most up-to-date X-ray luminosity function (XLF) and absorption function of Active Galactic Nuclei (AGNs) over the redshift range from 0 to 5, utilizing the largest, highly complete sample ever available obtained from surveys performed with Swift/BAT, MAXI, ASCA, XMM-Newton, Chandra, and ROSAT. The combined sample, including that of the Subaru/XMM-Newton Deep Survey, consists of 4039 detections in the soft (0.5--2 keV) and/or hard ($>2$ keV) band. We utilize a maximum likelihood method to reproduce the count-rate versus redshift distribution for each survey, by taking into accoun…
The warm absorbers observed in more than half of all nearby active galactic nuclei (AGN) are tracers of ionized outflows located at parsec scale distances from the central engine. If the smallest inferred ionization parameters correspond to plasma at a few $10^4$~K, then the gas undergoes a transition from being bound to unbound provided it is further heated to $\sim 10^6$~K at larger radii. Dannen et al. recently discovered that under these circumstances, thermally driven wind solutions are unsteady and even show very dense clumps due to thermal instability. To explore the observational conse…
In our Galaxy, light antinuclei composed of antiprotons and antineutrons can be produced through high-energy cosmic-ray collisions with the interstellar medium or could also originate from the annihilation of dark-matter particles that have not yet been discovered. On Earth, the only way to produce and study antinuclei with high precision is to create them at high-energy particle accelerators. Although the properties of elementary antiparticles have been studied in detail, the knowledge of the interaction of light antinuclei with matter is limited. We determine the disappearance probability of…
Using archival data from the HI Parkes All Sky Survey (HIPASS) we have searched for 21 cm line absorption in 204 nearby radio and star-forming galaxies with continuum flux densities greater than $S_{1.4} \approx 250$ mJy within the redshift range $0 < cz < 12000$ km s$^{-1}$. By applying a detection method based on Bayesian model comparison, we successfully detect and model absorption against the radio-loud nuclei of four galaxies, of which the Seyfert 2 galaxy 2MASX J130804201-2422581 was previously unknown. All four detections were achieved against compact radio sources, which include three …
X-ray Absorption Variability in NGC 1142: Another Constraint on the Nature of the Torus/Broad-Line Region in Active Galactic Nuclei
Clemson University（克莱姆森大学）；University of Virginia（弗吉尼亚大学）；Università degli Studi di Bologna（博洛尼亚大学）；INAF-Osservatorio Astronomico di Bologna（意大利国家天体物理研究所博洛尼亚天文台）；INAF-Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）；University of Illinois at Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校）；European Southern Observatory（欧洲南方天文台）
