Class I methanol masers in the outflow of IRAS 16 547-4247

Abstract

The Australia Telescope Compact Array (ATCA) has been used to image class I methanol masers at 9.9, 25 (a series from J = 2 to 9), 84, 95 and 104 GHz located in the vicinity of IRAS 16 547−4247 (G343.12−0.06), a luminous young stellar object known to harbour a radio jet. The detected maser emission consists of a cluster of six spots spread over an area of 30 arcsec. Five spots were detected in only the 84-and 95-GHz transitions (for two spots the 84-GHz detection is marginal), while the sixth spot shows activity in all 12 observed transitions. We report the first interferometric observations of the rare 9.9-and 104-GHz masers. It is shown that the spectra contain a very narrow spike (< 0.03 km s −1 ) and the brightness temperature in these two transitions exceeds 5.3 × 10 7 and 2.0 × 10 4 K, respectively. The three most southern maser spots show a clear association with the shocked gas traced by the H 2 2.12-µm emission associated with the radio jet and their velocities are close to that of the molecular core within which the jet is embedded. This fact supports the idea that the class I masers reside in the interface regions of outflows. Comparison with OH masers and infrared data reveals a potential discrepancy in the expected evolutionary state. The presence of the OH masers usually means that the source is evolved, but the infrared data suggest otherwise. The lack of any class II methanol maser emission at 6.7 GHz in the source raises an additional question, Is this source too young or too old to have a 6.7-GHz maser? We argue that both cases are possible and suggest that the evolutionary stage where the class I masers are active, may last longer and start earlier than when the class II masers are active. However, it is currently not possible to reveal the exact evolutionary status of IRAS 16 547−4247.

A search for water masers associated with class II methanol masers – II. Longitude range 341° to 6°

“…Class I methanol masers appear spread around a star forming region, distributed over linear scales of up to 1 pc (e.g. Kurtz et al 2004;Voronkov et al 2006;Cyganowski et al 2009;Voronkov et al 2014;Jordan et al 2015), whereas, class II methanol masers reside close to their parent YSO (e.g. Caswell 1997).…”

New class I methanol masers

“…The reported interferometric observations are scarce and confined to single source papers only (e.g. Voronkov et al 2006;Voronkov et al 2010;Sjouwerman et al 2010;Fish et al 2011). The typical spread of maser spots is comparable to or exceeds the beam size of a 20-m class single dish at the frequencies of these transitions (Kurtz et al 2004;Voronkov et al 2006).…”

“…Voronkov et al 2006;Voronkov et al 2010;Sjouwerman et al 2010;Fish et al 2011). The typical spread of maser spots is comparable to or exceeds the beam size of a 20-m class single dish at the frequencies of these transitions (Kurtz et al 2004;Voronkov et al 2006). Therefore, interferometric observations, which allow us to measure positions of each maser sport accurately, are crucial even to get meaningful detection statistics.…”

“…at 36 and 44 GHz), which are the subject of this paper, are usually found offset from the presumed origin of excitation (e.g. Kurtz et al 2004;Voronkov et al 2006), and are found in regions of both high-and low-mass star formation (Kalenskii et al 2010 and their paper in this volume).…”

“…Therefore, the majority of candidate maser transitions searchable with the Atacama Large Millimetre Array (ALMA) in the millimetre and sub-millimetre bands belong to class I. In the following sections we review observational properties of all known and 44 GHz (pluses) maser spots on top of the outflow image traced by 2.12µm H2 emission in G343.12-0.06, contours show the 12mm continuum emission (see also Voronkov et al 2006) New class I methanol masers 435 class I methanol maser series before summarising predictions for ALMA in bands 6 and 7. For simplicity, we refer to the maser series by the lowest frequency transition.…”