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

Abstract

We have conducted a Galactic plane survey of methanol masers at 6668 MHz using a seven‐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° through the Galactic Centre to 6°. Within 6° of the Galactic 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 disc population; there is no high‐latitude population that might be ascribed to the Galactic bulge. Within 2° of the Galactic Centre the maser velocities all lie between −60 and +77 km s−1, a range much smaller than the 540 km s−1 range observed in CO. Elsewhere, the maser with highest positive velocity (+107 km s−1) occurs, surprisingly, near longitude 355° and is probably attributable to the Galactic bar. The maser with the most negative velocity (−127 km s−1) is near longitude 346°, 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 Galactic 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.

Discovery of Two New Class Ii Methanol Maser Transitions in G 345.01+1.79

“…In contrast, when it was first observed in the early 1990s, the peak velocity of the 6.7 GHz methanol maser was at −17 km s −1 (Caswell et al 1995b). The intensity of that spectral feature has declined over the intervening 20 years (see, e.g., Ellingsen et al 2004;Caswell et al 2010), and the peak of the 6.7 GHz maser emission is now at ∼−21 km s −1 . The 19.9 GHz methanol maser is now the only transition which peaks at −17 km s −1 , and in contrast to the other rare/weak methanol maser transitions no emission is observed at velocities less than −19 km s −1 .…”

H2O Southern Galactic Plane Survey (HOPS): Paper III – properties of dense molecular gas across the inner Milky Way

“…By definition, the stellar mass of YMCs is 10 4 M . Our first criteria is therefore to select HOPS sources (Caswell et al 2010(Caswell et al , 2011 and plus symbols are HOPS water masers (Walsh et al 2011(Walsh et al , 2014. White contours show the NH 3 (1,1) integrated intensity emission.…”

“…The NH 3 (1,1) data cubes show there is almost no change in velocity across the main ridge of source which contains most of the mass. Unless there are convergent gas motions of >10 km s −1 purely in the plane of the sky, which seems unlikely, (Caswell et al 2010(Caswell et al , 2011 and plus symbols are HOPS water masers (Walsh et al 2011(Walsh et al , 2014. White contours show the NH 3 (1,1) integrated intensity emission.…”

EARLY-STAGE MASSIVE STAR FORMATION NEAR THE GALACTIC CENTER: Sgr C

“…High-resolution data to search for dense star-forming gas toward the G359.44−0.102 EGO (Stolovy et al 2006, blue), Hi-GAL (Molinari et al 2010, green) and ATLASGAL surveys (Schuller et al 2009, red), respectively. Very Large Array 1.4 GHz continuum data from Lang et al (2010) (Caswell et al 2010 were obtained in 2009 June with the compact-north configuration of SMA at 280 GHz (PI: Kauffmann). These data consist of a mosaic of five ∼45 fields covering the EGO and its surrounding clump with spectral resolution of 0.44 km s −1 .…”