Mopra observations of G305.2+0.2: massive star formation at different evolutionary stages?

Abstract

We have successfully used a new on-the-fly mapping technique with the Mopra radio telescope to image G305.2+0.2 in transitions of (CO)-C-13, HCO+, N2H+, CH3CN and CH3OH. All these species appear to be concentrated towards the infrared-quiet methanol maser site G305A (G305.21+0.21). We suggest that this region contains an extremely deeply embedded site of massive star formation, with comparable qualities to the low-mass Class 0 stage. The infrared-bright methanol maser site G305B (G305.21+0.20) also exhibits emission in all the mapped transitions, but always at a lower level. We suggest this is because it harbours a site of massive star formation older and more developed than G305.21+0.21. All transitions appear to be extended beyond the size of the Mopra beam (30 arcsec). (CO)-C-13 and HCO+ line wings are suggestive of an outflow in the region, but the spatial resolution of these data is insufficient to identify the powering source. A narrow-lined (1.6 km s(-1) compared to a typical line FWHM of 6.4 km s(-1)) N2H+ source (G305SW) is found 90 arcsec to the south-west of the main star-forming centres, which does not correspond to any CH3CN or CH3OH source, nor does it correspond well to (CO)-C-13 or HCO+ emission in the vicinity. We suggest this may be a massive, cold, quiescent and possibly pre-stellar core.