Class I Methanol Masers: Signposts of Star Formation? (original) (raw)
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The Astrophysical Journal Supplement Series, 2017
We present a survey of 56 massive star-forming regions in the 44 GHz methanol maser transition made with the Karl G. Jansky Very Large Array (VLA); 24 of the 56 fields showed maser 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 micron emission. We find a total of 83 maser components with linewidths ranging from 0.17 to 3.3 km s −1 with a nearly flat distribution and a median value of 1.1 km s −1. The relative velocities of the masers with respect to the systemic velocity of the host clouds range from −2.5 to 3.1 km s −1 with a distribution peaking near zero. We also study the correlation between the masers and the so-called extended green objects (EGOs) from the GLIMPSE survey. Multiple sources in each field are revealed from IR images as well as from centimeter continuum emission from VLA archival data; in the majority of cases the 44 GHz masers are positionally correlated with EGOs which seem to trace the younger sources in the fields. We report a possible instance of a 44 GHz maser associated with a low-mass protostar. If confirmed, this region will be the fifth known star-forming region that hosts Class I masers associated with low-mass protostars. We discuss three plausible cases of maser variability.
Search for Class I methanol masers in low-mass star formation regions
Monthly Notices of the Royal Astronomical Society, 2010
A survey of young bipolar outflows in regions of low-to-intermediate-mass star formation has been carried out in two class I methanol maser transitions: 7 0 − 6 1 A + at 44 GHz and 4 −1 −3 0 E at 36 GHz. We detected narrow features towards NGC 1333I2A, NGC 1333I4A, HH25MMS, and L1157 at 44 GHz, and towards NGC 2023 at 36 GHz. Flux densities of the lines detected at 44 GHz are no higher than 11 Jy and the relevant source luminosities are about 10 22 erg s −1 , which is much lower than those of strong masers in high-mass star formation regions. No emission was found towards 39 outflows. All masers detected at 44 GHz are located in clouds with methanol column densities of the order of or larger than a few ×10 14 cm −2 . The upper limits for the non-detections are typically of the order of 3-5 Jy. Observations in 2004, 2006, and 2008 did not reveal any significant variability of the 44 GHz masers in NGC 1333I4A, HH25MMS, and L1157.
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.
Search for class I methanol maser emission in various types of objects in the interstellar medium
Astronomy Reports, 2011
Observations of various types of objects in the northern sky were obtained at 44 GHz in the 7 0 −6 1 A + methanol line on the 20-m Onsala radio telescope (Sweden), in order to search for Class I methanol maser emission in the interstellar medium: regions of formation of high-mass stars, dust rings around HII regions, and protostellar candidates associated with powerful molecular outflows and Galactic HII regions. Seven new Class I methanol masers have been discovered toward regions of formation of highmass stars, and the existence of two previously observed masers confirmed. The following conclusions are drawn: (1) neither the association of a bipolar outflow manifest in the wings of CO lines with a highmass protostellar object (HMPO) nor the presence of thermal emission in lines of complex molecules are sufficient conditions for the detection of Class I methanol emission; no association with HMPOs radiating at 44 GHz was found for EGOs (a new class of object tracing bipolar outflows); (2) the existence of H 2 O masers and Class II methanol masers in the region of a HMPO enhances the probability of detecting Class I methanol emission toward the HMPO; Class II methanol masers with stronger line fluxes are associated with Class I methanol masers.
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.
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.
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
A study of class II methanol maser condensations in the star-forming region W48
Astronomy Reports, 2002
In the star forming region W48 the spectrum of methanol lines is studied. It is found that the intensity of the 2 0-3-1E (12.2 GHz) line anti-correlates with the intensity of the 51-60A + (6.7 GHz). All other class II methanol lines in the spectrum of W48 (2 1-3 0A+(157 GHz), 3}-4 0 A + (107 GHz) (possibly) and Jo-J_ 1E (157 GHz)) demonstrate the same behaviour as 2 0-3-1E (12.2 GHz) line. This fact contradicts to the current models of the class II methanol maser emission. The effect is confirmed in the sample of 67 sources. For the explanation of this fact some possibilities are considered.