A Warped Accretion Disk and Wide‐Angle Outflow in the Inner Parsec of the Circinus Galaxy

Abstract

We present the first VLBI maps of H 2 O maser emission (1.3 cm) 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 AE 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 / r À0:5 ), the maximum detected rotation speed is 260 km s À1 , and the inferred central mass is ð1:7 AE 0:3Þ Â 10 6 M . The outflowing masers are irregularly distributed above and below the disk, with relative outflow velocities up to $AE160 km s À1 , 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, although 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 less than 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 active galactic nuclei. 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 active galactic nuclei.

Mapping the circumnuclear dust in nearby AGN with MIDI

“…We find a small hot component with a FWHM of 22 mas (∼ 0.4 pc at the distance of Circinus), which is highly ellipsoidal and has a temperature of 390 K. This component has the same size and position angle as the rotating maser disc found by Greenhill et al (2003) (see figure 2). The second component is significantly larger, reflecting the fact that a large part of the flux (∼ 90%) is resolved with our interferometric setup.…”

“…A highly elongated hot emission region (yellow) is surrounded by an extended, almost round and cooler emission region (brown). At the centre, the locus of H2O maser emitters in a disk from Greenhill et al (2003) is over-plotted. The parameters fitted are: F W HM -full width at half maximum (in mas), a/b -axis ratio, T -temperature (in K) and f -filling factor for each of the two components; τSiO -optical depth of the silicate absorption and α -position angle for both components.…”

Water vapour at high redshift: Arecibo monitoring of the megamaser in MG J0414+0534

“…UGC3789; Reid et al 2009), the inner parts of relativistic jets ("jet-masers", e.g. Mrk 348; Peck et al 2003) or nuclear outflows (Circinus; Greenhill et al 2003), which are associated with active galactic nuclei (AGN). In contrast to optical and ultraviolet radiation, the radio photons can penetrate the enormous column densities of gas and dust that often obscure the line of sight to the nucleus.…”

Masers in AGN environments

“…See review by Greenhill (2002a). References: (1) Churchwell et al (1977), (2) Dos Santos & Lépine (1979), (3) Gardner & Whiteoak (1982), (4) Claussen & Lo (1986), (5) Claussen et al (1988), (6) Nakai, Inoue, & Miyoshi (1993), (7) Braatz et al (1996), (8) Greenhill et al (2002b), (9) Greenhill et al (1995), (10) Miyoshi et al (1995), (11) Gallimore et al (1996), (12) Claussen et al (1998) Greenhill et al (2003a), (14) Greenhill et al (2003b), (15) Kondratko et al (2006a), Braatz et al (2004), (17) Macri et al (2006), (18) Barvainis & Antonucci (2005), (19) Humphreys et al (2005), and (20) Braatz et al (this volume).…”