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Register a new userX-ray Constraint on Location of AGN Torus in Circinus Galaxy
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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 originated from the torus, particularly Fe K$alpha$, carry key information on the radii of line emitting regions. Utilizing XCLUMPY (Tanimoto et al. 2019), 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 (NuSTAR), 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 $N_mathrm{H}^mathrm{Equ}=2.16^{+0.24}_{-0.16}times 10^{25} mathrm{cm}^{-2}$), geometrically thin (torus angular width $sigma=10.3^{+0.7}_{-0.3} mathrm{degrees}$), viewed edge-on (inclination $i=78.3^{+0.4}_{-0.9} mathrm{degrees}$), and has super-solar abundance ($1.52^{+0.04}_{-0.06}$ times solar). Simultaneously analyzing the Chandra/HETG first, second, and third order spectra with consideration of the spatial extent of the Fe K$alpha$ line emitting region, we constrain the inner radius of the torus to be $1.9^{+3.1}_{-0.8}times 10^5$ times the gravitational radius, or $1.6^{+1.5}_{-0.9}times 10^{-2} mathrm{pc}$ for a black hole mass of $(1.7pm 0.3)times 10^6 M_{odot}$. This is about 3 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.
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We construct an X-ray spectral model from the clumpy torus in an active galactic nucleus (AGN), designated as XCLUMPY, utilizing the Monte Carlo simulation for Astrophysics and Cosmology framework (MONACO: Odaka et al. 2011, 2016). The adopted geometry of the torus is the same as that in Nenkova et al. (2008), who assume a power law distribution of clumps in the radial direction and a normal distribution in the elevation direction. We investigate the dependence of the X-ray continuum and Fe K$alpha$ fluorescence line profile on the torus parameters. Our model is compared with other torus models: MYTorus model (Murphy & Yaqoob 2009), Ikeda model (Ikeda et al. 2009), and CTorus model (Liu & Li 2014). As an example, we also present the results applied to the broadband X-ray spectra of the Circinus galaxy observed with XMM-Newton, Suzaku, and NuSTAR. Our model can well reproduce the data, yielding a hydrogen column density along the equatorial plane $N_{mathrm{H}}^{mathrm{Equ}} = 9.08_{-0.08}^{+0.14} times 10^{24}$ cm$^{-2}$, a torus angular width $sigma = 14.7_{-0.39}^{+0.44}$ degree, and a 2--10 keV luminosity $log L_{2-10}/mathrm{erg s^{-1}} = 42.8$. These results are discussed in comparison with the observations in other wavelengths.
(Abridged) With infrared interferometry it is possible to resolve the nuclear dust distributions that are commonly associated with the dusty torus in active galactic nuclei (AGN). The Circinus galaxy hosts the closest Seyfert 2 nucleus and previous interferometric observations have shown that its nuclear dust emission is well resolved. To better constrain the dust morphology in this active nucleus, extensive new observations were carried out with MIDI at the Very Large Telescope Interferometer. The emission is distributed in two distinct components: a disk-like emission component with a size of ~ 0.2 $times$ 1.1 pc and an extended component with a size of ~ 0.8 $times$ 1.9 pc. The disk-like component is elongated along PA ~ 46{deg} and oriented perpendicular to the ionisation cone and outflow. The extended component is elongated along PA ~ 107{deg}, roughly perpendicular to the disk component and thus in polar direction. It is interpreted as emission from the inner funnel of an extended dust distribution and shows a strong increase in the extinction towards the south-east. We find no evidence of an increase in the temperature of the dust towards the centre. From this we infer that most of the near-infrared emission probably comes from parsec scales as well. We further argue that the disk component alone is not sufficient to provide the necessary obscuration and collimation of the ionising radiation and outflow. The material responsible for this must instead be located on scales of ~ 1 pc, surrounding the disk. The clear separation of the dust emission into a disk-like emitter and a polar elongated source will require an adaptation of our current understanding of the dust emission in AGN. The lack of any evidence of an increase in the dust temperature towards the centre poses a challenge for the picture of a centrally heated dust distribution.
We describe a complete volume limited sample of nearby active galaxies selected by their 14-195keV luminosity, and outline its rationale for studying the mechanisms regulating gas inflow and outflow. We describe also a complementary sample of inactive galaxies, selected to match the AGN host galaxy properties. The active sample appears to have no bias in terms of AGN type, the only difference being the neutral absorbing column which is two orders of magnitude greater for the Seyfert 2s. In the luminosity range spanned by the sample, log L_{14-195keV} [erg/s] = 42.4-43.7, the optically obscured and X-ray absorbed fractions are 50-65%. The similarity of these fractions to more distant spectroscopic AGN samples, although over a limited luminosity range, suggests that the torus does not strongly evolve with redshift. Our sample confirms that X-ray unabsorbed Seyfert 2s are rare, comprising not more than a few percent of the Seyfert 2 population. At higher luminosities, the optically obscured fraction decreases (as expected for the increasing dust sublimation radius), but the X-ray absorbed fraction changes little. We argue that the cold X-ray absorption in these Seyfert 1s can be accounted for by neutral gas in clouds that also contribute to the broad line region (BLR) emission; and suggest that a geometrically thick neutral gas torus co-exists with the BLR and bridges the gap to the dusty torus.
CIGALE is a powerful multiwavelength spectral energy distribution (SED) fitting code for extragalactic studies. However, the current version of CIGALE is not able to fit X-ray data, which often provide unique insights into AGN intrinsic power. We develop a new X-ray module for CIGALE, allowing it to fit SEDs from the X-ray to infrared (IR). We also improve the AGN fitting of CIGALE from UV-to-IR wavelengths. We implement a modern clumpy two-phase torus model, SKIRTOR. To account for moderately extincted type 1 AGNs, we implement polar-dust extinction. We publicly release the source code (named X-CIGALE). We test X-CIGALE with X-ray detected AGNs in SDSS, COSMOS, and AKARI-NEP. The fitting quality (as indicated by reduced $chi^2$) is good in general, indicating that X-CIGALE is capable of modelling the observed SED from X-ray to IR. We discuss constrainability and degeneracy of model parameters in the fitting of AKARI-NEP, for which excellent mid-IR photometric coverage is available. We also test fitting a sample of AKARI-NEP galaxies for which only X-ray upper limits are available from Chandra observations, and find that the upper limit can effectively constrain the AGN SED contribution for some systems. Finally, using X-CIGALE, we assess the ability of Athena to constrain the AGN activity in future extragalactic studies.
In some AGN, nuclear dust lanes connected to kpc-scale dust structures provide all the extinction required to obscure the nucleus, challenging the role of the dusty torus proposed by the Unified Model. In this letter we show the pc-scale dust and ionized gas maps of Circinus constructed using sub-arcsec-accuracy registration of infrared VLT AO images with optical textit{Hubble Space Telescope} images. We find that the collimation of the ionized gas does not require a torus but is caused by the distribution of dust lanes of the host galaxy on $sim$10 pc scales. This finding questions the presumed torus morphology and its role at parsec scales, as one of its main attributes is to collimate the nuclear radiation, and is in line with interferometric observations which show that most of the pc-scale dust is in the polar direction. We estimate that the nuclear dust lane in Circinus provides $1/3$ of the extinction required to obscure the nucleus. This constitutes a conservative lower limit to the obscuration at the central parsecs, where the dust filaments might get optically thicker if they are the channels that transport material from $sim$100 pc scales to the centre.
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