Australia Telescope National Facility

About: Australia Telescope National Facility is a facility organization based out in Sydney, New South Wales, Australia. It is known for research contribution in the topics: Galaxy & Pulsar. The organization has 699 authors who have published 2774 publications receiving 151507 citations. The organization is also known as: ATNF.

An Extragalactic H I Cloud with No Optical Counterpart

Abstract: We report the discovery, from the H I Parkes All-Sky Survey (HIPASS), of an isolated cloud of neutral hydrogen, which we believe to be extragalactic. The H I mass of the cloud (HIPASS J1712-64) is very low, 1.7 x 10(7) M-circle dot, using an estimated distance of similar to 3.2 Mpc. Most significantly, we have found no optical companion to this object to very faint limits [mu(B) similar to 27 mag arcsec(-2)]. HIPASS J1712-64 appears to be a binary system similar to, but much less massive than, H I 1225 + 01 (the Virgo H. I cloud) and has a size of at least 15 kpc. The mean velocity dispersion measured with the Australia Telescope Compact Array (ATCA) is only 4 km s(-1) for the main component and, because of the weak or nonexistent star formation, possibly reflects the thermal line width (T < 2000 K) rather than bulk motion or turbulence. The peak column density for HIPASS J1712-64, from the combined Parkes and ATCA data, is only 3.5 x 1019 cm(-2), which is estimated to be a factor of 2 below the critical threshold for star formation. Apart from its significantly higher velocity, the properties of HIPASS J1712-64 are similar to the recently recognized class of compact high-velocity clouds. We therefore consider the evidence for a Local Group or Galactic origin, although a more plausible alternative is that HIPASS J1712-64 was ejected from the interacting Magellanic Cloud-Galaxy system at perigalacticon similar to 2 x 10(8) yr ago.

Loops, Drips, and Walls in the Galactic Chimney GSH 277+00+36

Abstract: We present new high-resolution H I images of the Galactic chimney GSH 277+00+36. The chimney is at a distance of ~6.5 kpc, is more than 600 pc in diameter, and extends at least 1 kpc above and below the Galactic midplane. Using the Australia Telescope Compact Array and the Parkes Radiotelescope as part of the Southern Galactic Plane Survey, we have imaged the H I associated with this chimney, with a spatial resolution of ~6 pc. These are among the highest spatial resolution images of an H I chimney. We find very narrow well-defined shell walls, a remarkably empty interior, and complex small-scale structures. The shell walls show a very steep reduction in emission at the interior edge and a more gradual decline toward the exterior. We suggest that this structure is characteristic of compression and may be used to distinguish stellar by-product shells from shell-like structures resulting from random turbulent motions. The shell and chimney walls also exhibit a great deal of small-scale structure, which we discuss in the context of hydrodynamic instabilities. We find that these structures are primarily cold gas with narrow line widths in the range 1.5-2.5 km s-1.

Supernova Remnants in the Magellanic Clouds. V. The Complex Interior Structure of the N206 Supernova Remnant

Abstract: The N206 supernova remnant (SNR) in the Large Magellanic Cloud has long been considered a prototypical "mixed morphology" SNR. Recent observations, however, have added a new twist to this familiar plot: an elongated, radially oriented radio feature seen in projection against the SNR face. Utilizing the high resolution and sensitivity available with the Hubble Space Telescope, Chandra, and XMM-Newton, we have obtained optical emission line images and spatially resolved X-ray spectral maps for this intriguing SNR. Our findings present the SNR itself as a remnant in the middle to late stages of its evolution. X-ray emission associated with the radio linear feature strongly suggests it to be a pulsar wind nebula (PWN). A small X-ray knot is discovered at the outer tip of this feature. The feature's elongated morphology and the surrounding wedge-shaped X-ray enhancement strongly suggest a bow shock PWN structure.

PSR B1745–20 and Young Pulsars in Globular Clusters

Abstract: Recent searches for radio pulsars in globular clusters have targeted the millisecond pulsars (MSPs) that are expected to result from the spin-up of old neutron stars in low-mass X-ray binary systems. These surveys have been very successful, discovering 34 pulsars, most of which are old and probably recycled by accretion-powered spin-up in a binary system. However, three objects have properties that are more like those of the normal population of Galactic pulsars. Timing measurements of one such pulsar, PSR B1745-20, show that it is clearly associated with the cluster NGC 6440 and that it is solitary and young, with a large magnetic field. This pulsar, together with PSR B1820-30B in NGC 6624, establishes long-period pulsars associated with globular clusters as a distinct group that seems to have a completely different genesis to the MSP population in globular clusters. Produced at a comparable rate to the MSPs, the origin of such apparently young objects in very old stellar systems is not understood.

MAGMO: coherent magnetic fields in the star‐forming regions of the Carina‐Sagittarius spiral arm tangent

Abstract: We present the pilot results of the ‘MAGMO’ project, targeted observations of ground-state hydroxyl masers towards sites of 6.7-GHz methanol maser emission in the Carina-Sagittarius spiral arm tangent, Galactic longitudes 280° to 295°. The ‘MAGMO’ project aims to determine if Galactic magnetic fields can be traced with Zeeman splitting of masers associated with star formation. Pilot observations of 23 sites of methanol maser emission were made, with the detection of ground-state hydroxyl masers towards 11 of these and six additional offset sites. Of these 17 sites, nine are new detections of sites of 1665-MHz maser emission, three of them accompanied by 1667-MHz emission. More than 70 per cent of the maser features have significant circular polarization, whilst only ∼10 per cent have significant linear polarization (although some features with up to 100 per cent linear polarization are found). We find 11 Zeeman pairs across six sites of high-mass star formation with implied magnetic field strengths between –1.5 and +3.8 mG and a median field strength of +1.6 mG. Our measurements of Zeeman splitting imply that a coherent field orientation is experienced by the maser sites across a distance of 5.3 ± 2.0 kpc within the Carina-Sagittarius spiral arm tangent.