The Parkes survey of methanol masers at 44.07 GHz

Furuya

2010

A&A

102

Context. Among the tracers of the earliest phases in the massive star formation process, methanol masers have gained increasing importance. The phenomenological distinction between Class I and II methanol masers is based on their spatial association with objects such as jets, cores, and ultracompact Hii regions, but is also believed to correspond to different pumping mechanisms: radiation for Class II masers, collisions for Class I masers. Aims. We surveyed a large sample of massive star-forming regions in Class I and II methanol masers. The sample consists of 296 sources, divided into two groups named high and low according to their and [60-12] IRAS colours. Previous studies indicate that the two groups may contain similar sources in different evolutionary stages, with the high sources representing the more evolved stages. Therefore, the sample can be used to assess a sequence for the occurrence of Class I and II methanol masers during the evolution of a massive star-forming region. Methods. We observed the 6 GHz (Class II) CH 3 OH maser with the Effelsberg 100-m telescope, and the 44 GHz and 95 GHz (Class I) CH 3 OH masers with the Nobeyama 45-m telescope. Results. We detected 55 sources in the Class II line (39 high and 16 low, 12 new detections); 27 sources in the 44 GHz Class I line (19 high and 8 low, 17 new detections); 11 sources in the 95 GHz Class I line (eight high and three low, all except one are new detections). The detection rate of Class II masers decreases with the distance of the source (as expected), whereas that of Class I masers peaks at ∼5 kpc. This could be due to the Class I maser spots being spread over a region < ∼ 1 pc, comparable to the telescope beam diameter at a distance of ∼5 kpc. We also find that the two Class I lines have similar spectral shapes at 44 GHz and 95 GHz, which confirms that they have the same origin.Conclusions. Our statistical analysis shows that the ratio between the detection rates of Class II and Class I methanol masers is basically the same in high and low sources. Therefore, both maser types seem to be equally associated with each evolutionary phase. In contrast, all maser species (including H 2 O) have about three times higher detection rates in high than in low sources. This could indicate that the phenomena from which all masers originate become progressively more active with time during the earliest evolutionary phases of a high-mass star-forming region.

Section: Introductionmentioning

confidence: 81%

Class I and Class II methanol masers in high-mass star-forming regions

Fontani¹,

Furuya

2010

A&A

102

“…OH masers were reported in the main 1.665 and 1.667 GHz, and the satellite 1.720 GHz lines (Caswell & Haynes 1983;Edris et al 2007), whereas the 1.612 GHz OH satellite was observed in absorption. CH 3 OH thermal lines were observed at 25, 96.7, 157, 241.7, and 255 GHz by Leurini et al (2007), and maser emission was reported for the Class II 6.7 GHz (Menten 1991;Caswell et al 1995b;Szymczak et al 2000) and 12.2 GHz (Caswell et al 1995a), and the Class I 44.1 GHz (Slysh et al 1994) and95.2 GHz (Val'tts et al 2000) transitions. High-resolution (≥ 1 ), interferometric observations towards G16.59-0.05 of the 22.2 GHz H 2 O (Forster & Caswell 1999;Beuther et al 2002c), 1.665 GHz OH (Forster & Caswell 1999), and 6.7 GHz CH 3 OH (Walsh et al 1998) maser lines, associate the maser activity with the sources "a" and "b".…”

Section: The Hmsfr G1659-005mentioning

confidence: 95%

VLBI study of maser kinematics in high-mass star-forming regions

Sanna

Moscadelli

et al. 2010

A&A

Aims. To study the high-mass star-forming process, we started a large project to unveil the gas kinematics close to young stellar objects (YSOs) through the Very Long Baseline Interferometry (VLBI) of maser associations. By comparing the high spatial resolution maser data that traces the inner kinematics of the (proto)stellar cocoon with interferometric thermal data that traces the large-scale environment of the hot molecular core (HMC) harboring the (proto)stars, we can investigate the nature and identify the sources of large-scale motions. The present paper focuses on the high-mass star-forming region G16.59-0.05. Methods. Using the VLBA and the EVN arrays, we conducted phase-referenced observations of the three most powerful maser species in G16.59-0.05: H 2 O at 22.2 GHz (4 epochs), CH 3 OH at 6.7 GHz (3 epochs), and OH at 1.665 GHz (1 epoch). In addition, we performed high-resolution (≥0. 1), high-sensitivity (<0.1 mJy) VLA observations of the radio continuum emission from the starforming region at 1.3 and 3.6 cm.Results. This is the first work to report accurate measurements of the relative proper motions of the 6.7 GHz CH 3 OH masers. The different spatial and 3-D velocity distributions clearly indicate that the 22 GHz water and 6.7 GHz methanol masers trace different kinematic environments. The bipolar distribution of 6.7 GHz maser line-of-sight velocities and the regular pattern of observed proper motions suggest that these masers are tracing rotation around a central mass of about 35 M . The flattened spatial distribution of the 6.7 GHz masers, oriented NW−SE, suggests that they can originate in a disk/toroid rotating around the massive YSO that drives the 12 CO (2−1) outflow, oriented NE−SW, observed on an arcsec scale. The extended, radio continuum source observed close to the 6.7 GHz masers could be excited by a wide-angle wind emitted from the YSO associated with the methanol masers, and such a wind has proven to be energetic enough to drive the NE−SW 12 CO (2−1) outflow. The H 2 O masers are distributed across a region offset about 0. 5 to the NW of the CH 3 OH masers, in the same area as where the emission of high-density molecular tracers, typical of HMCs, was detected. We postulate that a distinct YSO, possibly in an earlier evolutionary phase than what excites the methanol masers, is responsible for the excitation of the water masers and the HMC molecular lines.

“…Caswell et al (2000) detected thermal CH 3 OH emission from the 156.6 GHz (see also Slysh et al 1999) and 107.0 GHz transitions, this latter superimposed on a maser component. Methanol maser emission was also reported at 6.7 GHz (e.g., Menten 1991;Goedhart et al 2004), 12.2 GHz (e.g., Caswell et al 1993;Błaszkiewicz & Kus 2004), 44.1 GHz (Slysh et al 1994), and 95.2 GHz (Val'tts et al 2000). First attempts to measure Zeeman splitting of the 6.7 GHz maser components suggest a magnetic field strength of a few tens of mG (Vlemmings 2008).…”

Section: The Hmsfr G2301-041mentioning

confidence: 96%

VLBI study of maser kinematics in high-mass star-forming regions

Sanna

Moscadelli

et al. 2010

A&A

Aims. We performed a detailed study of maser and radio continuum emission toward the high-mass star-forming region G23.01−0.41. This study aims at improving our knowledge of the high-mass star-forming process by comparing the gas kinematics near a newly born young stellar object (YSO), analyzed through high spatial resolution maser data, with the large-scale environment of its native hot molecular core (HMC), identified in previous interferometric observations of thermal continuum and molecular lines. Methods. Using the VLBA and the EVN arrays, we conducted phase-referenced observations of the three most powerful maser species in G23.01−0.41: H 2 O at 22.2 GHz (4 epochs), CH 3 OH at 6.7 GHz (3 epochs), and OH at 1.665 GHz (1 epoch). In addition, we performed high-resolution (≥0. 1), high-sensitivity (<0.1 mJy) VLA observations of the radio continuum emission from the HMC at 1.3 and 3.6 cm. Results. We have detected H 2 O, CH 3 OH, and OH maser emission clustered within 2000 AU from the center of a flattened HMC, oriented SE-NW, from which emerges a massive 12 CO outflow, elongated NE-SW, extended up to the pc-scale. Although the three maser species show a clearly different spatial and velocity distribution and sample distinct environments around the massive YSO, the spatial symmetry and velocity field of each maser specie can be explained in terms of expansion from a common center, which possibly denotes the position of the YSO driving the maser motion. Water masers trace both a fast shock (up to 50 km s −1 ) closer to the YSO, powered by a wide-angle wind, and a slower (20 km s −1 ) bipolar jet, at the base of the large-scale outflow. Because the compact free-free emission is found offset from the putative location of the YSO along a direction consistent with that of the maser jet axis, we interpret the radio continuum in terms of a thermal jet. The velocity field of methanol masers can be explained in terms of a composition of slow (4 km s −1 in amplitude) motions of radial expansion and rotation about an axis approximately parallel to the maser jet. Finally, the distribution of line-of-sight velocities of the hydroxyl masers suggests that they can trace gas less dense (n H 2 ≤ 10 6 cm −3 ) and more distant from the YSO than that traced by the water and methanol masers, which is expanding toward the observer. A few pairs of OH masers, with different circular polarization, are well aligned in position on the sky and we interpret them as Zeeman pairs. From Zeeman splitting, the derived typical values of the magnetic field are of a few mG.