A study of class II methanol maser condensations in the star-forming region W48 (original) (raw)
Related papers
Class I Methanol Masers: Signposts of Star Formation?
The Astronomical Journal, 2008
Class I methanol masers appear to probe very early stages of star formation. An observational survey of the 44 and 36 GHz methanol lines toward several star-forming regions was conducted using the Haystack Observatory 37 m telescope. Examining the intensities of the 36 GHz Class I maser line as compared to the 44 GHz maser line, it is seen that the 36 GHz line is enhanced toward sources where there is no apparent sign of star formation. Sources where the 36 GHz emission is absent, but the 44 GHz emission is strong, appear to be those where ultracompact H ii regions and millimeter continuum sources are present. Existing models for the excitation of Class I methanol masers show strong temperature and density dependences for the presence or lack of certain methanol transitions. The 36 GHz masers appear in regimes where the temperatures are low-below 100 K. The 44 GHz masers are excited in a wider range of gas temperatures (80-200 K), supporting the hypothesis that these transitions are still masing even when the 36 GHz masers are quenched.
Distribution and excitation of thermal methanol in 6.7 GHz maser bearing star-forming regions
Astronomy & Astrophysics, 2011
Context. Candidate high mass star forming regions can be identified through the occurrence of 6.7 GHz methanol masers. In these sources the methanol abundance of the gas must be enhanced, as the masers require a considerable methanol path length. The place and time of origin of this enhancement is not well known. Similarly, it is debated in which of the physical components of the high mass star forming region the masers are located. Aims. The aim of this study is to investigate the distribution and excitation of the methanol gas around Cep A and to describe the physical conditions of the region. In addition the large scale abundance distribution is determined in order to understand the morphology and kinematics of star forming regions in which methanol masers occur. Methods. The spatial distribution of the methanol is studied by mapping line emission, as well as the column density and excitation temperature, which are estimated using rotation diagrams. For a limited number of positions the parameters are checked with non-LTE models. Furthermore, the distribution of the methanol abundance is derived in comparison with archival dust continuum maps. Results. Methanol is detected over a 0.3 × 0.15 pc area centred on the Cep A HW2 source, showing an outflow signature. Most of the gas can be characterized by a moderately warm rotation temperature (30−60 K). At the central position two velocity components are detected with different excitation characteristics, the first related to the large-scale outflow. The second component, uniquely detected at the central location, is probably associated with the maser emission on much smaller scales of 2 ′′ . Detailed analysis reveals that the highest densities and temperatures occur for these inner components. In the inner region the dust and gas are shown to have different physical parameters. Conclusions. Abundances of methanol in the range 10 −9 -10 −7 are inferred, with the abundance peaking at the maser position. The geometry of the large-scale methanol is in accordance with previous determinations of the Cep A geometry, in particular those from methanol masers. The dynamical and chemical time-scales are consistent with the methanol originating from a single driving source associated with the HW2 object and the masers in its equatorial region.
A methanol line survey toward high-mass star-forming regions
Astronomy & Astrophysics, 2002
We present the results of a search for methanol maser and thermal lines in 11 transitions in the range 85-112 GHz toward 23 star-forming regions exhibiting class I and class II methanol masers. The selected frequencies are 85.5, 86.6, 94.5, 95.1, 96.7 (quartet line series), 107.0, 108.8 and 111.2 GHz. Five masers were confirmed at 107.0 GHz while new masers were found at 85.5, 86.6 and 108.8 GHz. Many detected emission lines have a quasi-thermal origin. The detection rates of methanol emission are high at 95.1 GHz (87%) and 96.7 GHz (96%), satisfactory at 107.0 and 108.9 GHz (∼50%) while the detection rates at 85.5, 94.5 and 111.3 GHz are low (∼20%). Most reported 95.1 GHz emission is masing.
2011
The aim of this study is to investigate the distribution and excitation of the methanol gas around Cep A and to describe the physical conditions of the region. In addition the large scale abundance distribution is determined in order to understand the morphology and kinematics of star forming regions in which methanol masers occur. The spatial distribution of the methanol is studied by mapping line emission, as well as the column density and excitation temperature, which are estimated using rotation diagrams. For a limited number of positions the parameters are checked with non-LTE models. Furthermore, the distribution of the methanol abundance is derived in comparison with archival dust continuum maps. Methanol is detected over a 0.3x0.15 pc area centred on the Cep A HW2 source, showing an outflow signature. Most of the gas can be characterized by a moderately warm rotation temperature (30-60K). At the central position two velocity components are detected with different excitation characteristics, the first related to the large-scale outflow. The second component, uniquely detected at the central location, is probably associated with the maser emission on much smaller scales of 2". Detailed analysis reveals that the highest densities and temperatures occur for these inner components. In the inner region the dust and gas are shown to have different physical parameters. Abundances of methanol in the range 10E-9 - 10E-7 are inferred, with the abundance peaking at the maser position. The geometry of the large-scale methanol is in accordance with previous determinations of the Cep A geometry, in particular those from methanol masers. The dynamical and chemical time-scales are consistent with the methanol originating from a single driving source associated with the HW2 object and the masers in its equatorial region.
Maser and thermal methanol emission in the millimeter wave range: new masers at 1.3mm and 2.8 mm
Proceedings of the International Astronomical Union
Results of a survey of Galactic star-forming regions in the lines of methanol 8 −1 − 7 0 E at 229.8 GHz, 3 −2 − 4 −1 E at 230.0 GHz, 0 0 − 1 −1 E at 108.9 GHz, and a series of methanol lines J 1 − J 0 E near 165 GHz are presented. Two masers, DR 21(OH) and DR 21 West, and two maser candidates, L 379 IRS3 and NGC 6334I(N), as well as 16 thermal sources are found at 229.8 GHz. This is the first detection of methanol masers at a wavelength as short as 1 mm. At 108.9 GHz, masers were found towards G345.01+1.79 and probably, towards M 8E. Thermal emission is found towards 28 objects. Only thermal emission was found at 165 and 230.0 GHz (20 and 7 sources, respectively). The masers at 229.8 GHz belong to class I, whereas those at 108.9 GHz belong to class II, according to the classification by Menten (1991). The masers in DR 21(OH) and DR 21 West can be roughly fitted by models with the gas kinetic temperature of the order of 50 K. The detection of the 108.9 GHz masers towards G345.01+1.79 and M 8E may indicate on a specific geometry of these objects. The combination of the existence of the class II J 0 − J −1 E masers towards W 3(OH), G345.01+1.79, W 48, and Cep A and our non-detection of the 3 −2 − 4 −1 E and J 1 − J 0 E lines is an evidence that the class II masers in these objects are pumped by the radiation of hot dust rather than by that of UC HII-regions.
The Astrophysical Journal Supplement Series, 2019
We report a systematic survey of a 6.7 GHz Class II methanol maser toward a sample of 448 sources selected from the Red Midcourse Space Experiment Source catalog. These sample sources are composed of high-mass starforming region (HMSFR) candidates and have been studied as tracers of HMSFRs, such as water masers or radio continuum emission of ultracompact H II region. The survey was conducted using the Shanghai Tianma Radio Telescope. Through the observations, we simultaneously studied the 4.7 and 6.0 GHz excited-state interstellar hydroxyl (OH) maser lines and 10 hydrogen radio recombination lines (RRLs) in the C band. In total, we detected 6.7 GHz methanol masers and RRLs from 102 and 116 sources, respectively. In addition, 4, 3, and 10 sources exhibit OH masers at 4765.56, 6030.75, and 6035.09 MHz transitions, respectively. Through the survey, we identified four new 6.7 GHz methanol maser sources and three new excited-state OH maser sources (one at 4750 MHz and two at 6035 MHz). The statistical analysis demonstrated that there is a positive correlation of luminosity between 6.7 GHz methanol masers and RRLs. A good correlation of integrated luminosity between radio continuum emission and the 6.7 GHz methanol masers is presented with respect to the RRL emission sources. The average of the integrated luminosities of the RRLs in the sources with 6.7 GHz masers is greater than those without the 6.7 GHz masers; similarly, the average of integrated luminosities of the 6.7 GHz methanol masers in the sources with RRLs is greater than those without the RRLs. Moreover, we found that the averages of the emission measure and electron temperature of H II regions associated with 6.7 GHz methanol masers are larger than those without the 6.7 GHz methanol masers. This suggests that the masers are most likely produced in high gas density and luminous regions with brighter RRLs and higher radio continuum emission.
44 GHZ Class I Methanol (CH3OH) Maser Survey in the Galactic Center
The Astrophysical Journal
We report on a large 44 GHz (7 0 − 6 1 A +) methanol (CH 3 OH) maser survey of the Galactic Center (GC). The Karl G. Jansky Very Large Array was used to search for CH 3 OH maser emission covering a large fraction of the region around Sgr A. In 25 pointings, over 300 CH 3 OH maser sources (> 10σ) were detected. The majority of the maser sources have a single peak emission spectrum with line of sight velocities that range from about −13 km s −1 to 72 km s −1. Most maser sources were found to have velocities around 35−55 km s −1 , closely following velocities of neighboring interacting molecular clouds. The full width half maximum of each individual spectral feature is very narrow (∼0.85 km s −1 on average). In the north, where Sgr A East is known to be interacting with the 50 km s −1 molecular cloud, more than 100 44 GHz CH 3 OH masers were detected. In addition, three other distinct concentrations of masers were found, which appear to be located closer to the interior of the interacting molecular clouds. Possibly a subset of masers are associated with star formation, although conclusive evidence is lacking. Subject headings: masers − ISM: supernova remnants − ISM: individual objects (Sgr A East) − masers − radio lines: ISM
Variability of Class II methanol masers in massive star forming regions
Proceedings of the International Astronomical Union, 2012
Class II methanol masers are known to be tracers of an early phase of massive star formation. The 6.7- and 12.2-GHz methanol maser transitions can show a significant amount of variability, including periodic variations. Studying maser variability can lead to important insights into conditions in the maser environment but first the maser time-series need to be characterised. The results of long-term monitoring of 8 regularly-varying sources will be presented and methods of period-search discussed.
Interferometric and single-dish observations of 44, 84 and 95 GHz Class I methanol masers
Proceedings of the International Astronomical Union, 2017
We present observations of massive star-forming regions selected from the IRAS Point Source Catalog. The observations were made with the Very Large Array and the Large Millimeter Telescope to search for Class I methanol masers. We made interferometric observations of 125 massive star-forming regions in the 44 GHz methanol maser transition; 53 of the 125 fields showed emission. The data allow us to demonstrate associations, at arcsecond precision, of the Class I maser emission with outflows, HII regions and shocks traced by 4.5 μm emission. We made single-dish observations toward 38 of the 53 regions with 44 GHz masers detected to search for the methanol transitions at 84.5, 95.1, 96.7, 107.0, and 108.8 GHz. We find detection rates of 74, 55, 100, 3, and 45%, respectively. We used a wide-band receiver which revealed many other spectral lines that are common in star-forming regions.
Search for class II methanol masers at 23.1 GHz
Monthly Notices of the Royal Astronomical Society, 2004
In the early days of methanol maser discoveries, the 9 2 -10 1 A + transition at 23.1 GHz was found to exhibit maser characteristics in the northern star-forming region W3(OH) and probable maser emission in two other sources. Attention subsequently turned to the 6.6-GHz 5 1 -6 0 A + methanol maser transition, which has proved a valuable tracer of early high-mass star formation. We have undertaken a new search for 23.1-GHz methanol masers in 50 southern star formation regions using the Parkes radio telescope. The target sources all exhibit class II methanol maser emission at 6.6 GHz, with 20 sources also displaying maser features in the 107.0-GHz 3 1 -4 0 A + methanol line. Strong emission at 23.1 GHz in NGC 6334F was confirmed, but no emission was detected in the remaining sources. Thus the 23.1-GHz methanol masers are rare.