S. P. Ellingsen

A warped accretion disk and wide angle outflow in the inner parsec of the Circinus Galaxy

We present the first VLBI maps of H2O maser emission (λ1.3 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 ± 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-0.5), the maximum detected rotation speed is 260 km s-1, and the inferred central mass is (1.7 ± 0.3) × 106 M☉. The outflowing masers are irregularly distributed above and below the disk, with relative outflow velocities up to ~±160 km s-1, 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.

The 6-GHz methanol multibeam maser catalogue - I. Galactic Centre region, longitudes 345° to 6°

Original article can be found at: http://www3.interscience.wiley.com/journal/ Copyright Royal Astronomical Society

The protostellar mass limit for 6.7 GHz methanol masers - I. A low-mass YSO survey

We report the results of a search for 6.7 GHz methanol masers toward low-mass young stellar objects (YSOs) and (pre)protostellar condensations with the Australia Telescope Compact Array (ATCA). Our sample consisted of 13 class 0 proto- stars and 44 class I YSOs as well as 66 (pre)protostellar condensations. A single detection was obtained toward NGC 2024: FIR4 in the Orion B region. This is the first detection of a 6.7 GHz methanol maser in Orion. The nature of FIR4 has been a subject of debate with some evidence suggesting that it is a very cold high-mass (pre)protostellar condensation and others arguing that it is a low-mass YSO. The discovery of a methanol maser associated with this source is inconsistent with both of these hypotheses and we suggest that FIR4 probably harbours an intermediate- or high-mass YSO. The less massive objects in our sample do not exhibit any methanol maser stronger than 400 mJy (4). Based on the nil detection rate toward the low-mass YSOs we can place an upper limit of 3 10 6 K on the brightness temperature of any methanol maser associated with class 0, I or II sources. These results support the hypothesis that no strong methanol masers are associated with low-mass star formation (<3 M).

Science with the Australian Square Kilometre Array Pathfinder

The future of cm and m-wave astronomy lies with the Square Kilometre Array (SKA), a telescope under development by a consortium of 17 countries that will be 50 times more sensitive than any existing radio facility. Most of the key science for the SKA will be addressed through large-area imaging of the Universe at frequencies from a few hundred MHz to a few GHz. The Australian SKA Pathfinder (ASKAP) is a technology demonstrator aimed in the mid-frequency range, and achieves instantaneous wide-area imaging through the development and deployment of phased-array feed systems on parabolic reflectors. The large field-of-view makes ASKAP an unprecedented synoptic telescope that will make substantial advances in SKA key science. ASKAP will be located at the Murchison Radio Observatory in inland Western Australia, one of the most radio-quiet locations on the Earth and one of two sites selected by the international community as a potential location for the SKA. In this paper, we outline the ASKAP project and summarise its headline science goals as defined by the community at large.

Methanol Masers: Reliable Tracers of the Early Stages of High-Mass Star Formation

The GLIMPSE and MSX surveys have been used to examine the mid-infrared properties of a statistically complete sample of 6.7 GHz methanol masers. The GLIMPSE point sources associated with methanol masers are clearly distinguished from the majority, typically having extremely red mid-infrared colors, similar to those expected of low-mass class 0 young stellar objects. The intensity of the GLIMPSE sources associated with methanol masers is typically 4 magnitudes brighter at 8.0 micron than at 3.6 micron. Targeted searches towards GLIMPSE point sources with [3.6]-[4.5] > 1.3 and an 8.0 micron magnitude less than 10 will detect more than 80% of class II methanol masers. Many of the methanol masers are associated with sources within infrared dark clouds (IRDC) which are believed to mark regions where high-mass star formation is in its very early stages. The presence of class II methanol masers in a significant fraction of IRDC suggests that high-mass star formation is common in these regions. Different maser species are thought to trace different evolutionary phases of the high-mass star formation process. Comparison of the properties of the GLIMPSE sources associated with class II methanol masers and other maser species shows interesting trends, consistent with class I methanol masers tracing a generally earlier evolutionary phase and OH masers tracing a later evolutionary phase.

The 6-GHz multibeam maser survey – I. Techniques

A new 7-beam 6 7 GHz receiver has been built to survey the Galaxy and the Magellanic Clouds for newly forming high-mass stars that are pinpointed by strong methanol maser emission at 6668 MHz. The receiver was jointly constructed by Jodrell Bank Observatory (JBO) and the Australia Telescope National Facility (ATNF) and allows simultaneous coverage at 6668 and 6035 MHz. It was successfully commissioned at Parkes in January 2006 and is now being used to conduct the Parkes-Jodrell multibeam maser survey of the Milky Way. This will be the first systematic survey of the entire Galactic plane for masers of not only 6668-MHz methanol, but also 6035-MHz excited-state hydroxyl. The survey is two orders of magnitude faster than most previous systematic surveys and has an rms noise level of �0.17Jy. This paper describes the observational strategy, techniques and reduction procedures of the Galactic and Magellanic Cloud surveys, together with deeper, pointed, follow-up observations and complementary observations with other instruments. It also includes an estimate of the survey detection efficiency. The 111 days of observationswith the Parkes telescope have so far yielded >800 methanol sources, of which �350 are new discoveries. The whole project will provide the first comprehensive Galaxy-wide catalogue of 6668-MHz and 6035-MHz masers.

The Subparsec-Scale Structure and Evolution of Centaurus A: The Nearest Active Radio Galaxy

?????The subparsec-scale structure of Cen A is complex, consisting of a bright jet and a fainter counterjet. The bright jet contains components that have subluminal speeds of approximately 0.1c and undergo irregular episodes of rapid internal evolution. The rapid evolution sometimes observed could be interpreted as evidence for an underlying jet flow much faster (>0.45c) than observed from the proper motion of components (~0.1c). Considering the large-scale morphology of the source, the motions and temporal variations in the jet, and the detection of a counterjet, we conclude that the axis of the Cen A jet lies between ~50? and ~80? to our line of sight. We find that the estimated times of component ejection from the compact core are reasonably coincident with enhancements in hard X-ray intensity and 22 GHz flux density. In the context of the radio galaxy population, Cen A is a low-luminosity FR I?type source and in general has the properties observed in other FR I radio galaxies. Overall, the observations of Cen A presented here, and from other investigations, are consistent with the idea that sources with an FR I appearance are not aligned with our line of sight and have relativistic flow on the subparsec scale. The apparently subluminal subparsec-scale jet components are interpreted as being slow patterns on the relativistic flow.

12.2-GHz methanol masers towards 1.2-mm dust clumps: quantifying high-mass star formation evolutionary schemes

We report the results of a search for 12.2-GHz methanol maser emission, targeted towards 113 known 6.7-GHz methanol masers associated with 1.2-mm dust continuum emission. Observations were carried out with the Australia Telescope National Facility (ATNF) Parkes 64-m radio telescope in the period 2008 June 20–25. We detect 68 12.2-GHz methanol masers with flux densities in excess of our 5σ detection limit of 0.55 Jy, 30 of which are new discoveries. This equates to a detection rate of 60 per cent, similar to previous searches of comparable sensitivity. We have made a statistical investigation of the properties of the 1.2-mm dust clumps with and without associated 6.7-GHz methanol maser and find that 6.7-GHz methanol masers are associated with 1.2-mm dust clumps with high-flux densities, masses and radii. We additionally find that 6.7-GHz methanol masers with higher peak luminosities are associated with less dense 1.2-mm dust clumps than those 6.7-GHz methanol masers with lower luminosities. We suggest that this indicates that more luminous 6.7-GHz methanol masers are generally associated with a later evolutionary phase of massive star formation than less luminous 6.7-GHz methanol maser sources. Analysis of the 6.7-GHz associated 1.2-mm dust clumps with and without associated 12.2-GHz methanol maser emission shows that clumps associated with both class II methanol maser transitions are less dense than those with no associated 12.2-GHz methanol maser emission. Furthermore, 12.2-GHz methanol masers are preferentially detected towards 6.7-GHz methanol masers with associated OH masers, suggesting that 12.2-GHz methanol masers are associated with a later evolutionary phase of massive star formation. We have compared the colours of the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) point sources associated with the maser sources in the following two subgroups: 6.7-GHz methanol masers with and without associated 12.2-GHz methanol masers; and 6.7-GHz methanol masers with high- and those with low-peak luminosities. There is little difference in the nature of the associated GLIMPSE point sources in any of these subgroups, and we propose that the masers themselves are probably much more sensitive than mid-infrared data to evolutionary changes in the massive star formation regions that they are associated with. We present an evolutionary sequence for masers in high-mass star formation regions, placing quantitative estimates on the relative lifetimes for the first time.

The 6-GHz methanol multibeam maser catalogue - II. Galactic longitudes 6° to 20 °

The definitive version is available at: http://onlinelibrary.wiley.com Copyright Royal Astronomical Society.

Methanol Masers as Tracers of Circumstellar Disks

We show that in many methanol maser sources the masers are located in lines, with a velocity gradient along them which suggests that the masers are situated in edge-on circumstellar, or protoplanetary, disks. We present VLBI observations of the methanol maser source G309.92 + 0.48, in the 12.2 GHz (2 0-3 -1 E) transition, which confirm previous observations that the masers in this source lie along a line. We show that such sources are not only linear in space but, in many cases, also have a linear velocity gradient. We then model these and other data in both the 6.7 GHz (5 1-6 0 A +) and the 12.2 GHz (2 0-3 -1 E) transition from a number of star formation regions and show that the observed spatial and velocity distribution of methanol masers, and the derived Keplerian masses, are consistent with a circumstellar disk rotating around an OB star. We consider this and other hypotheses and conclude that about half of these methanol masers are probably located in edge-on circumstellar disks around young stars. This is of particular significance for studies of circumstellar disks because of the detailed velocity information available from the masers.