CH₃OH and H₂O masers in high-mass star-forming regions

Abstract

Abstract. We present a comparison of Class  CH 3 OH (6.7 GHz) and H 2 O (22.2 GHz) masers at high spatial resolution in a sample of 29 massive star-forming regions. Absolute positions of both maser types are compared with mm dust continuum, cm continuum and mid-infrared sources. All maser features -regardless of the species -are associated with massive mm cores, but only 3 out of 18 CH 3 OH masers and 6 out of 22 H 2 O masers are associated with cm emission likely indicating the presence of a recently ignited massive star. These observations of a homogenous sample of massive, young star-forming regions confirm earlier results, obtained for each maser species separately, that both maser types are signposts of high-mass star formation in very early evolutionary stages. The data are consistent with models that explain CH 3 OH maser emission by radiative pumping in moderately hot cores, requiring the absence, or only weak, free-free cm continuum radiation due to recently ignited stars. Mid-infrared sources are associated with both maser types in approximately 60% of the observed fields. Thus, mid-infrared objects may power maser sites, but the detection of strong mid-infrared emission is not strictly necessary because it might be heavily extincted. A comparison of the spatial separations between the di fferent observed quantities and other properties of the star-forming regions does not reveal any correlation. Our data suggest that CH 3 OH and H 2 O masers need a similar environment (dense and warm molecular gas), but that, due to the different excitation processes (radiative pumping for CH 3 OH and collisional pumping for H 2 O), no spatial correlations exist. Spatial associations are probably coincidences due to insufficient angular resolution and projection effects. The kinematic structures we find in the different maser species show no recognizable pattern, and we cannot draw firm conclusions as to whether the features are produced in disks, outflows or expanding shock waves.

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

“…We know that source evolution and variability play a major role in the detection statistics, however, neither of these are well enough understood at present to be able to account for them explicitly. Our results are also consistent with previous searches for water masers by Beuther et al (2002); Szymczak et al (2005); Xu et al (2008);Breen et al (2010a).…”

Fragmentation in the massive star-forming region IRAS 19410+2336

“…We confirmed their estimation, finding that the visual extinction for 13-s is A v ∼ 2700 (see Table 2). Source 13-s is in an early stage of evolution, according to its NIR excess and the presence of H 2 O and Class ii CH 3 OH masers (Beuther et al 2002d), although the detection of a VLA 3.6 cm source at its position (Sridharan et al 2002), suggests that there is a recently ignited protostar that has already formed an ultracompact or hypercompact Hii region, the detected radio emission being consistent with an ionizing B2 V star (Martín-Hernández et al 2008;Qiu et al 2008;Panagia 1973).…”

“…It is a very active star-forming site, with sources detected from X-rays down to radio wavelengths. It has H 2 O and CH 3 OH maser emission (Sridharan et al 2002;Beuther et al 2002d) and X-ray sources (Beuther et al 2002a), indicating that there is ongoing formation of intermediate-to-high mass stars. The region is embedded within a cluster of over 800 components detected at NIR wavelengths (Martín-Hernández et al 2008;Qiu et al 2008), and it has a rich and energetic outflow component with multiple outflows detected in CO (Beuther et al 2002c(Beuther et al , 2003.…”

ATLASGAL – The APEX telescope large area survey of the galaxy at 870 $\mathsf{\mu}$m

“…Much effort has focused on follow-up studies of bright IR sources detected by the Infrared Astronomy Satellite (IRAS) and showing far-infrared (FIR) colors typical of ultra-compact H ii regions (Wood & Churchwell 1989), e.g., in high-density molecular tracers (Bronfman et al 1996;Molinari et al 1996), dust continuum emission , or maser emission (e.g., Palla et al 1993;Beuther et al 2002). While some studies have revealed a few massive cold cores in the neighborhood of the central compact H ii region (e.g., Garay et al 2004), they were mostly biased against the earliest, possibly coldest phases of massive star formation.…”