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Register a new userA Warped Accretion Disk and Wide Angle Outflow in the Inner Parsec of the Circinus Galaxy
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We present the first VLBI maps of H2O maser emission (lambda 1.3cm) in the nucleus of the Circinus Galaxy, constructed from data obtained with the Australia Telescope Long Baseline Array. The maser emission traces a warped, edge-on accretion disk between radii of 0.11+/-0.02 and ~0.40 pc, as well as a wide-angle outflow that extends up to ~1 pc from the estimated disk center. The disk rotation is close to Keplerian (v varies as 1/sqrt(r)), the maximum detected rotation speed is 260 km/s, and the inferred central mass is 1.7+/-0.3 x 10^6 solar masses. The outflowing masers are irregularly distributed above and below the disk, with relative outflow velocities up to ~+/-160 km/s, projected along the line of sight. The flow probably originates closer than 0.1 pc to the central engine, possibly in an inward extension of the accretion disk, though there is only weak evidence of rotation in the outward moving material. We observe that the warp of the disk appears to collimate the outflow and to fix the extent of the ionization cone observed on larger angular scales. This study provides the first direct evidence (i.e., through imaging) of dusty, high-density, molecular material in a nuclear outflow <1 pc from the central engine of a Seyfert galaxy, as well as the first graphic evidence that warped accretion disks can channel outflows and illumination patterns in AGN. We speculate that the same arrangement, which in some ways obviates the need for a geometrically thick, dusty torus, may apply to other type-2 AGN.
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We employ MUSE/VLT data to study the ionised and highly ionised gas phases of the feedback in Circinus, the closest Seyfert 2 galaxy to us. The analysis of the nebular emission allowed us to detect a remarkable high-ionisation gas outflow beyond the galaxy plane traced by the coronal lines [Fe VII] $lambda$6089 and [Fe X] $lambda$6374, extending up to 700 pc and 350 pc NW from the nucleus, respectively. This is the first time that the [Fe X] emission is observed at such distances from the central engine in an AGN. The gas kinematics reveals expanding gas shells with velocities of a few hundred km s$^{-1}$, spatially coincident with prominent hard X-ray emission detected by Chandra. Density and temperature sensitive line ratios show that the extended high-ionisation gas is characterized by a temperature reaching 25000 K and an electron density > 10$^2$ cm$^{-3}$. We found that local gas excitation by shocks produced by the passage of a radio jet leads to the spectacular high-ionisation emission in this object. This hypothesis is fully supported by photoionisation models that accounts for the combined effects of the central engine and shocks. They reproduce the observed emission line spectrum at different locations inside and outside of the NW ionisation cone. The energetic outflow produced by the radio jet is spatially located close to an extended molecular outflow recently reported using ALMA which suggests that they both represent different phases of the same feedback process acting on the AGN.
Recent observations which resolved the mid-infrared (MIR) emission of nearby active galactic nuclei (AGN), surprisingly revealed that their dust emission appears prominently extended in the polar direction, at odds with the expectations from the canonical dusty torus. This polar dust, tentatively associated with dusty winds driven by radiation pressure, is found to have a major contribution to the MIR flux from scales of a few to hundreds of parsecs. When facing a potential change of paradigm, case studies of objects with the best intrinsic resolution are essential. One such source with a clear detection of polar dust is a nearby, well-known AGN in the Circinus galaxy. In the first paper, we successfully explained the peculiar MIR morphology of Circinus observed on large, tens of parsec scales with a model consisting of a compact dusty disc and an extended hollow dusty cone. In this work, we further refine the model on smaller, parsecs scales to test whether it can also explain the MIR interferometric data. We find that a model composed of a thin dusty disc seen almost edge-on and a polar outflow in the form of a hyperboloid shell can reproduce well the VLTI/MIDI observations at all wavelengths, baselines and position angles. In contrast, while providing a good fit to the integrated MIR spectrum, the dusty torus model fails to reproduce the spatially resolved interferometric data. We put forth the disc$+$hyperboloid wind model of Circinus AGN as a prototype for the dust structure in the AGN population with polar dust.
(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.
Powerful winds driven by active galactic nuclei (AGN) are often invoked to play a fundamental role in the evolution of both supermassive black holes (SMBHs) and their host galaxies, quenching star formation and explaining the tight SMBH-galaxy relations. Recent observations of large-scale molecular outflows in ultra-luminous infrared galaxies (ULIRGs) have provided the evidence to support these studies, as they directly trace the gas out of which stars form. Theoretical models suggest an origin of these outflows as energy-conserving flows driven by fast AGN accretion disk winds. Previous claims of a connection between large-scale molecular outflows and AGN activity in ULIRGs were incomplete because they were lacking the detection of the putative inner wind. Conversely, studies of powerful AGN accretion disk winds to date have focused only on X-ray observations of local Seyferts and a few higher redshift quasars. Here we show the clear detection of a powerful AGN accretion disk wind with a mildly relativistic velocity of 0.25c in the X-ray spectrum of IRAS F11119+3257, a nearby (z = 0.189) optically classified type 1 ULIRG hosting a powerful molecular outflow. The AGN is responsible for ~80% of the emission, with a quasar-like luminosity of L_AGN = 1.5x10^46 erg/s. The energetics of these winds are consistent with the energy-conserving mechanism, which is the basis of the quasar mode feedback in AGN lacking powerful radio jets.
GW170817 is the first gravitational wave detection of a binary neutron star merger. It was accompanied by radiation across the electromagnetic spectrum and localized to the galaxy NGC 4993 at a distance of 40 Mpc. It has been proposed that the observed gamma-ray, X-ray and radio emission is due to an ultra-relativistic jet launched during the merger, directed away from our line of sight. The presence of such a jet is predicted from models positing neutron star mergers as the central engines driving short-hard gamma-ray bursts (SGRBs). Here we show that the radio light curve of GW170817 has no direct signature of an off-axis jet afterglow. While we cannot rule out the existence of a jet pointing elsewhere, the observed gamma-rays could not have originated from such a jet. Instead, the radio data requires a mildly relativistic wide-angle outflow moving towards us. This outflow could be the high velocity tail of the neutron-rich material dynamically ejected during the merger or a cocoon of material that breaks out when a jet transfers its energy to the dynamical ejecta. The cocoon scenario can explain the radio light curve of GW170817 as well as the gamma-rays and X-rays (possibly also ultraviolet and optical emission), and hence is the model most consistent with the observational data. Cocoons may be a ubiquitous phenomenon produced in neutron star mergers, giving rise to a heretofore unidentified population of radio, ultraviolet, X-ray and gamma-ray transients in the local universe.
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