Description of source "G305.21+0.21" from Voronkov et al. (2014)

This is a well-studied region of high-mass star formation (see Walsh et al. 2007 and references therein). There are two 6.7-GHz masers in the region, the stronger 305.208+0.206 and the weaker 305.202+0.208 (Green et al. 2012a), which were referred to as G305A and G305B, respectively, by Walsh et al. (2007). The latter site (G305B) is associated with a strong infrared source (see Fig. 1) but no detected radio-continuum emission, while the former (G305A) is a deeply embedded hot core detected in a number of molecular tracers which has either no associated infrared source or a very weak one (e.g. Walsh et al. 2007). The source has two prominent H II regions, one located approximately 30 arcsec to the south-east of G305A just outside the region shown in Fig. 1 (referred to as G305HII(SE) by Walsh et al. 2007) and the other located 15 arcsec to the west of G305B (referred to as G305HII by Walsh et al. 2007). None of the 6.7-GHz masers appear to be directly associated with any of these H II regions (Phillips et al. 1998). The contours in Fig. 1 represent reprocessed ATCA archival data at 6 cm (project code C865, 6A array configuration). The emission at 36 and 44 GHz is scattered around the large area exceeding the FWHM of the primary beam. Locations A–E, G and L seem to be associated with G305A and, except for A and B which are situated in the vicinity of the 6.7-GHz maser, are arranged in an elliptic arc approximately 10 × 7 arcsec2 across possibly tracing an outflow cavity. The strongest masers at both 36 and 44 GHz are at location F, approximately 3 arcsec to the east of the 6.7-GHz maser position at G305B. This region is active in a number of rare class I methanol maser transitions which require higher-than-average temperatures and densities to form (see the discussion of this source by Voronkov et al. 2010a). It is worth noting that in addition to the 25-GHz methanol masers at F (Voronkov et al. 2005a, 2010a), Walsh et al. (2007) found 25-GHz maser emission at D as well as the broad and possibly quasi-thermal emission at B which may be a counterpart to the broad 36- and 44-GHz features seen in the spectrum (see Fig. 1).

Detected at 44 GHz only, the maser emission at J is seen projected on to the continuum source G305HII and may, therefore, be associated with the interface between this H II region and the molecular gas in the cold cloud identified by Walsh & Burton (2006) in the area to the south-west of G305B and G305HII. The maser emission at K, H and I may also originate from this cloud or its interface.

However, given the angular separation of at least 10 arcsec, it seems unlikely that the emission at K and H is caused by interaction with G305HII.