arXiv subjects

C. J. Phillips

Publications and source records attributed to C. J. Phillips.

39 records · Page 3Linked to original sources

arXiv1997

A comprehensive search for extragalactic 6.7-GHz methanol masers

We have used the Australia Telescope Compact Array (ATCA) to search for 6.7-GHz methanol maser emission towards 87 galaxies. We chose the target sources using several criteria, including far-IR luminosities and the presence of known OH megamasers. In addition, we searched for methanol masers in the nearby starburst galaxy NGC 253, making a full spectral-line synthesis image. No emission was detected in any galaxies, with detection limits ranging from 25 mJy to 75 mJy. This is surprising, given the close association of OH and methanol masers in Galactic star-formation regions, and significantly constrains models of OH megamaser emission. This absence of maser emission may be a result of low methanol abundances in molecular clouds in starburst galaxies.

astro-ph↗

arXiv1996

PKS 1830-211: A Possible Compound Gravitational Lens

Measurements of the properties of gravitational lenses have the power to tell us what sort of universe we live in. The brightest known radio Einstein ring/gravitational lens PKS 1830-211 (Jauncey et al., 1991), whilst obscured by our Galaxy at optical wavelengths, has recently been shown to contain absorption at the millimetre waveband at a redshift of 0.89 (Wiklind and Combes, 1996a). We report the detection of a new absorption feature, most likely due to neutral hydrogen in a second redshift system at z = 0.19. Follow-up VLBI observations have spatially resolved the absorption and reveal it to cover the NE compact component and part of the lower surface brightness ring. This new information, together with existing evidence of the unusual VLBI radio structure and difficulties in modeling the lensing system, points to the existence of a second lensing galaxy along our line of sight and implies that PKS 1830-211 may be a compound gravitational lens.

astro-ph↗

arXiv1996

A Survey of the Galactic Plane for 6.7-GHz Methanol Masers I: l = 325.0 - 335.0 ; b = -0.53 - 0.53

We report the results of the first complete survey of an area of the Galactic Plane for maser emission from the 6.7-GHz transition of methanol. The survey covers a 10.6-square-degree region of the Galactic Plane in the longitude range 325-335 degrees and latitude range -0.53-0.53 degrees. The survey is sensitive to masers with a peak flux density greater than approximately 2.6 Jy. The weakest maser detected has a peak flux density of 2.3 Jy and the strongest a peak flux density of 425 Jy. We detected a total of 50 distinct masers, 26 of which are new detections. We show that many 6.7-GHz methanol masers are not associated with IRAS sources, and that some are associated with sources that have colours differing from those of a typical ultra-compact HII region (UCHII). We estimate that the number of UCHII regions in the Galaxy is significantly more than suggested by IRAS-based estimates, possibly by more than a factor of two.

astro-ph↗