arXiv subjects

S. L. Breen

Publications and source records attributed to S. L. Breen.

45 records · Page 3Linked to original sources

arXiv2010

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

We present the second portion of an unbiased survey of the Galactic plane for 6668-MHz methanol masers. This section of the survey spans the longitude range 6 degrees to 20 degrees. We report the detection of 119 maser sources, of which 42 are new discoveries. The masers are tightly constrained to the Galactic plane, with only four outside a latitude range of +/- 1 degree. This longitude region includes the brightest known 6668-MHz methanol maser, 9.621+0.196, as well as the two brightest newly discovered sources in the southern survey as a whole. We list all the sources associated with the 3-kpc arms within +/- 15 degrees longitude and consider further candidates beyond 15 degrees longitude. We identify three new sources associated with the Galactic bar and comment on the density of masers in relation to the bar orientation.

astro-ph.GA↗

arXiv2010

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

We have conducted a Galactic plane survey of methanol masers at 6668 MHz using a 7-beam receiver on the Parkes telescope. Here we present results from the first part, which provides sensitive unbiased coverage of a large region around the Galactic Centre. Details are given for 183 methanol maser sites in the longitude range 345$^{\circ}$ through the Galactic Centre to 6$^{\circ}$. Within 6$^{\circ}$ of the Centre, we found 88 maser sites, of which more than half (48) are new discoveries. The masers are confined to a narrow Galactic latitude range, indicative of many sources at the Galactic Centre distance and beyond, and confined to a thin disk population; there is no high latitude population that might be ascribed to the Galactic Bulge. Within 2$^{\circ}$ of the Galactic Centre the maser velocities all lie between -60 and +77 \kms, a range much smaller than the 540 \kms range observed in CO. Elsewhere, the maser with highest positive velocity (+107 \kms) occurs, surprisingly, near longitude 355$^{\circ}$ and is probably attributable to the Galactic bar. The maser with the most negative velocity (-127 \kms) is near longitude 346$^{\circ}$, within the longitude-velocity locus of the near side of the `3-kpc arm'. It has the most extreme velocity of a clear population of masers associated with the near and far sides of the 3-kpc arm. Closer to the Galactic Centre the maser space density is generally low, except within 0.25 kpc of the Centre itself, the `Galactic Centre Zone', where it is 50 times higher, which is hinted at by the longitude distribution, and confirmed by the unusual velocities.

astro-ph.GA↗

arXiv2010

Masers associated with high-mass star formation regions in the Large Magellanic Cloud

We report the results of a sensitive search for 12.2 GHz methanol maser emission towards a sample of eight high-mass star formation regions in the Large Magellanic Clouds which have been detected in other maser transitions. We detected one source towards the star formation region N105a. This is the first detection of a 12.2 GHz methanol maser outside our Galaxy. We also made near-contemporaneous observations of the 6.7 GHz methanol and 22 GHz water masers towards these sources, resulting in the detection of water maser emission in six new sources, including one associated with the strongest 6.7 GHz maser in the Magellanic Clouds IRAS 05011-6815. The majority of the maser sources are closely associated with objects identified as likely Young Stellar Objects (YSO) on the basis of Spitzer Space Telescope observations. We find that the YSOs associated with masers tend to be more luminous and have redder infrared colours than the sample as a whole. SED modeling of the YSOs shows that the masers are associated with sources of higher central mass, total luminosity and ambient density than the majority of YSOs in the LMC. This is consistent with the well-established relationship between luminous methanol and water masers and young, high-mass objects observed in the Galaxy.

astro-ph.GA↗

arXiv2009

12.2-GHz methanol masers associated with 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 5-sigma 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; suggesting that 12.2-GHz methanol masers are associated with a later evolutionary phase of massive star formation. We present an evolutionary sequence for masers in high-mass star formation regions, placing quantitative estimates on the relative lifetimes for the first time.

astro-ph.SR↗

arXiv2008

High velocity water maser emission from the Post-AGB star OH 009.1-0.4

Observations of H$_2$O masers towards the post-AGB star and water fountain source OH 009.1--0.4 were made as part of HOPS (The H$_2$O southern galactic Plane Survey), with the Mopra radiotelescope. Together with followup observations using the Australia Telescope Compact Array (ATCA), we have identified H$_2$O maser emission over a velocity spread of nearly 400km/s (--109 to +289km/s). This velocity spread appears to be the largest of any known maser source in our Galaxy. High resolution observations with the ATCA indicate the maser emission is confined to a region $0\farcs3 \times 0\farcs3$ and shows weak evidence for a separation of the red- and blueshifted maser spots. We are unable to determine if the water fountain is projected along the line of sight, or is inclined, but either way OH 009.1--0.4 is an interesting source, worthy of followup observations.

astro-ph↗

arXiv2008

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 ~0.17 Jy.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 observations with 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.

astro-ph↗

arXiv2008

Multibeam Maser Survey of methanol and excited OH in the Magellanic Clouds: new detections and maser abundance estimates

We present the results of the first complete survey of the Large and Small Magellanic Clouds for 6668-MHz methanol and 6035-MHz excited-state hydroxyl masers. In addition to the survey, higher-sensitivity targeted searches towards known star-formation regions were conducted. The observations yielded the discovery of a fourth 6668-MHz methanol maser in the Large Magellanic Cloud (LMC), found towards the star-forming region N160a, and a second 6035-MHz excited-state hydroxyl maser, found towards N157a. We have also re-observed the three previously known 6668-MHz methanol masers and the single 6035-MHz hydroxyl maser. We failed to detect emission from either transition in the Small Magellanic Cloud. All observations were initially made using the Methanol Multibeam (MMB) survey receiver on the 64-m Parkes telescope as part of the MMB project and accurate positions have been measured with the Australia Telescope Compact Array (ATCA). We compare the maser populations in the Magellanic Clouds with those of our Galaxy and discuss their implications for the relative rates of massive star-formation, heavy metal abundance, and the abundance of complex molecules. The LMC maser populations are demonstrated to be smaller than their Milky Way counterparts. Methanol masers are under-abundant by a factor of ~45, whilst hydroxyl and water masers are a factor of ~10 less abundant than our Galaxy.

astro-ph↗

arXiv2007

Investigating high-mass star formation through maser surveys

Interstellar masers are unique probes of the environments in which they arise. In studies of high-mass star formation their primary function has been as signposts of these regions and they have been used as probes of the kinematics and physical conditions in only a few sources. With a few notable exceptions, we know relatively little about the evolutionary phase the different maser species trace, nor their location with respect to other star formation tracers. While detailed studies of a small number of maser regions can reveal much about them, other information can only be obtained through large, systematic searches. In particular, such surveys are vital in efforts to determine an evolutionary sequence for the common maser species, and there is growing evidence that methanol masers may trace an earlier phase than the other common maser species of OH and water.

astro-ph↗

arXiv2007

A search for 22-GHz water masers within the giant molecular cloud associated with RCW106

We report the results of a blind search for 22-GHz water masers in two regions, covering approximately half a square degree, within the giant molecular cloud associated with RCW 106. The complete search of the two regions was carried out with the 26-m Mount Pleasant radio telescope and resulted in the detection of nine water masers, five of which are new detections. Australia Telescope Compact Array (ATCA) observations of these detections have allowed us to obtain positions with arcsecond accuracy, allowing meaningful comparison with infrared and molecular data for the region. We find that for the regions surveyed there are more water masers than either 6.7-GHz methanol, or main-line OH masers. The water masers are concentrated towards the central axis of the star formation region, in contrast to the 6.7-GHz methanol masers which tend to be located near the periphery. The colours of the GLIMPSE point sources associated with the water masers are similar to those of 6.7-GHz methanol masers, but slightly less red. We have made a statistical investigation of the properties of the 13CO and 1.2-mm dust clumps with and without associated water masers. We find that the water masers are associated with the more massive, denser and brighter 13CO and 1.2-mm dust clumps. We present statistical models that are able to predict those 13CO and 1.2-mm dust clumps that are likely to have associated water masers, with a low misclassification rate.

astro-ph↗