Extended Coronal Emission Lines in Active Galactic Nuclei

VLT and NTT spectra are used to examine the nuclear and extended coronal line emission in a sample of well-known Seyfert 1 and 2 galaxies. The excellent spatial resolution obtained with VLT allowed us to map [SiVI] 1.963 $\mu$m and [SiVII] 2.48 $\mu$m on scales of up to 20 pc. Coronal line emission, extended to distances of $\sim$100 pc, is detected in some of the lines analyzed, particularly in [FeX] 6374\AA, [FeXI] 7891\AA, and [SiVII] 2.48$\mu$m. Most coronal lines are strongly asymmetric towards the blue and broader than low-ionization lines. This result is particularly important for Circinus, where previous observations had failed at detecting larger widths for high-ionization lines. Photoionization models are used to investigate the physical conditions and continuum luminosities necessary to produced the observed coronal emission. We found that an ionization parameter U> 0.10 is necessary to reproduce the observations, although the clouds should be located at distances < 30 pc.Comment: 4 pages, 6 figures, to appear in proceedings of IAU Symposium No. 222, The Interplay Among Black Holes, Stars and ISM in Galacti Nucle

The central parsecs of active galactic nuclei: challenges to the torus

Type 2 AGN are by definition nuclei in which the broad-line region and continuum light are hidden at optical/UV wavelengths by dust. Via accurate registration of infrared (IR) Very Large Telescope adaptive optics images with optical \textit{Hubble Space Telescope} images we unambiguously identify the precise location of the nucleus of a sample of nearby, type 2 AGN. Dust extinction maps of the central few kpc of these galaxies are constructed from optical-IR colour images, which allow tracing the dust morphology at scales of few pc. In almost all cases, the IR nucleus is shifted by several tens of pc from the optical peak and its location is behind a dust filament, prompting to this being a major, if not the only, cause of the nucleus obscuration. These nuclear dust lanes have extinctions $A_V \geq 3-6$ mag, sufficient to at least hide the low-luminosity AGN class, and in some cases are observed to connect with kpc-scale dust structures, suggesting that these are the nuclear fueling channels. A precise location of the ionised gas H$\alpha$ and [\textsc{Si\,vii}] 2.48 $\mu$m coronal emission lines relative to those of the IR nucleus and dust is determined. The H$\alpha$ peak emission is often shifted from the nucleus location and its sometimes conical morphology appears not to be caused by a nuclear --torus-- collimation but to be strictly defined by the morphology of the nuclear dust lanes. Conversely, [\textsc{Si\,vii}] 2.48 $\mu$m emission, less subjected to dust extinction, reflects the truly, rather isotropic, distribution of the ionised gas. All together, the precise location of the dust, ionised gas and nucleus is found compelling enough to cast doubts on the universality of the pc-scale torus and supports its vanishing in low-luminosity AGN. Finally, we provide the most accurate position of the NGC 1068 nucleus, located at the South vertex of cloud B.Comment: 23 pages, 10 figures, accepted for publication in MNRA

Optical Surface Photometry of a Sample of Disk Galaxies. II Structural Components

This work presents the structural decomposition of a sample of 11 disk galaxies, which span a range of different morphological types. The U, B, V, R, and I photometric information given in Paper I (color and color-index images and luminosity, ellipticity, and position-angle profiles) has been used to decide what types of components form the galaxies before carrying out the decomposition. We find and model such components as bulges, disks, bars, lenses and rings.Comment: 14 figures. Accepted for publication in A&

Time-resolved infrared emission from radiation-driven central obscuring structures in Active Galactic Nuclei

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 physical model of the central obscurer. Temporal changes are mostly visible at shorter wavelengths, close to the combined peak of the dust opacity as well as the central source spectrum and are caused by variations in the column densities of the generated outflow. Due to the three-component morphology of the hydrodynamical models -- a thin disc with high density filaments, a surrounding fluffy component (the obscurer) and a low density outflow along the rotation axis -- we find dramatic differences depending on wavelength: whereas the mid-infrared images are dominated by the elongated appearance of the outflow cone, the long wavelength emission is mainly given by the cold and dense disc component. Overall, we find good agreement with observed characteristics, especially for those models, which show clear outflow cones in combination with a geometrically thick distribution of gas and dust, as well as a geometrically thin, but high column density disc in the equatorial plane.Comment: 16 pages, 12 figures, accepted for publication in MNRA

The central molecular gas structure in LINERs with low luminosity AGN: evidence for gradual disappearance of the torus

We present observations of the molecular gas in the nuclear environment of three prototypical low luminosity AGN (LLAGN), based on VLT/SINFONI AO-assisted integral-field spectroscopy of H2 1-0 S(1) emission at angular resolutions of ~0.17". On scales of 50-150 pc the spatial distribution and kinematics of the molecular gas are consistent with a rotating thin disk, where the ratio of rotation (V) to dispersion (sigma) exceeds unity. However, in the central 50 pc, the observations reveal a geometrically and optically thick structure of molecular gas (V/sigma10^{23} cm^{-2}) that is likely to be associated with the outer extent of any smaller scale obscuring structure. In contrast to Seyfert galaxies, the molecular gas in LLAGN has a V/sigma<1 over an area that is ~9 times smaller and column densities that are in average ~3 times smaller. We interpret these results as evidence for a gradual disappearance of the nuclear obscuring structure. While a disk wind may not be able to maintain a thick rotating structure at these luminosities, inflow of material into the nuclear region could provide sufficient energy to sustain it. In this context, LLAGN may represent the final phase of accretion in current theories of torus evolution. While the inflow rate is considerable during the Seyfert phase, it is slowly decreasing, and the collisional disk is gradually transitioning to become geometrically thin. Furthermore, the nuclear region of these LLAGN is dominated by intermediate-age/old stellar populations (with little or no on-going star formation), consistent with a late stage of evolution.Comment: 15 pages, including 4 figures and 1 table, Accepted for publication in ApJ Letter

Low optical polarisation at the core of the optically-thin jet of M87

We study the optical linear and circular polarisation in the optically-thin regime of the core and jet of M87. Observations were acquired two days before the Event Horizon Telescope (EHT) campaign in early April 2017. A high degree ($\sim 20$ per cent) of linear polarisation (P$_{\rm lin}$) is detected in the bright jet knots resolved at $\sim 10\, \rm{arcsec}$ to $23\, \rm{arcsec}$ ($0.8$-$1.8\, \rm{kpc}$) from the centre, whereas the nucleus and inner jet show P$_{\rm lin} \lesssim 5$ per cent. The position angle of the linear polarisation shifts by $\sim 90$ degrees from each knot to the adjacent ones, with the core angle perpendicular to the first knot. The nucleus was in a low level of activity (P$_{\rm lin} \sim 2$-$3$ per cent), and no emission was detected from HST-1. No circular polarisation was detected either in the nucleus or the jet above a $3\sigma$ level of P$_{\rm circ} \leq 1.5$ per cent, discarding the conversion of P$_{\rm lin}$ into P$_{\rm circ}$. A disordered magnetic field configuration or a mix of unresolved knots polarised along axes with different orientations could explain the low P$_{\rm lin}$. The latter implies a smaller size of the core knots, in line with current interferometric observations. Polarimetry with EHT can probe this scenario in the future. A steep increase of both P$_{\rm lin}$ and P$_{\rm circ}$ with increasing frequency is expected for the optically-thin domain, above the turnover point. This work describes the methodology to recover the four Stokes parameters using a $\lambda/4$ wave-plate polarimeter.Comment: Accepted for publication in MNRAS. 10 pages, 8 figure