THE RARE 23.1 GHz METHANOL MASERS IN NGC 7538 IRS 1 (original) (raw)
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The Astrophysical Journal
We report the first sub-arcsecond VLA imaging of 6 GHz continuum, methanol maser, and excitedstate hydroxyl maser emission toward the massive protostellar cluster NGC6334I following the recent 2015 outburst in (sub)millimeter continuum toward MM1, the strongest (sub)millimeter source in the protocluster. In addition to detections toward the previously known 6.7 GHz Class II methanol maser sites in the hot core MM2 and the UCHII region MM3 (NGC6334F), we find new maser features toward several components of MM1, along with weaker features ∼ 1 ′′ north, west, and southwest of MM1, and toward the non-thermal radio continuum source CM2. None of these areas have heretofore exhibited Class II methanol maser emission in three decades of observations. The strongest MM1 masers trace a dust cavity, while no masers are seen toward the strongest dust sources MM1A, 1B and 1D. The locations of the masers are consistent with a combination of increased radiative pumping due to elevated dust grain temperature following the outburst, the presence of infrared photon propagation cavities, and the presence of high methanol column densities as indicated by ALMA images of thermal transitions. The non-thermal radio emission source CM2 (2 ′′ north of MM1) also exhibits new maser emission from the excited 6.035 and 6.030 GHz OH lines. Using the Zeeman effect, we measure a line-of-sight magnetic field of +0.5 to +3.7 mG toward CM2. In agreement with previous studies, we also detect numerous methanol and excited OH maser spots toward the UCHII region MM3, with predominantly negative line-of-sight magnetic field strengths of −2 to −5 mG and an intriguing south-north field reversal.
DETECTION OF 36 GHz CLASS I METHANOL MASER EMISSION TOWARD NGC 253
The Astrophysical Journal, 2014
We have used the Australia Telescope Compact Array (ATCA) to search for emission from the 4 −1 → 3 0 E transition of methanol (36.2 GHz) towards the center of the nearby starburst galaxy NGC 253. Two regions of emission were detected, offset from the nucleus along the same position angle as the inner spiral arms. The emission is largely unresolved on a scale of 5 ′′ , has a full-width half maximum (FWHM) line width of < 30 km s −1 , and an isotropic luminosity orders of magnitude larger than that observed in any Galactic star formation regions. These characteristics suggest that the 36.2 GHz methanol emission is most likely a maser, although observations with higher angular and spectral resolution are required to confirm this. If it is a maser this represents the first detection of a class I methanol maser outside the Milky Way. The 36.2 GHz methanol emission in NGC 253 has more than an order of magnitude higher isotropic luminosity than the widespread emission recently detected towards the center of the Milky Way. If emission from this transition scales with nuclear star formation rate then it may be detectable in the central regions of many starburst galaxies. Detection of methanol emission in ultra-luminous infra-red galaxies (ULIRGs) would open up a new tool for testing for variations in fundamental constants (in particular the proton-to-electron mass ratio) on cosmological scales.
A masing event in NGC 6334I: contemporaneous flaring of hydroxyl, methanol, and water masers
Monthly Notices of the Royal Astronomical Society
As a product of the maser monitoring program with the 26 m telescope of the Hartebeesthoek Radio Astronomy Observatory (HartRAO), we present an unprecedented, contemporaneous flaring event of 10 maser transitions in hydroxyl, methanol, and water that began in 2015 January in the massive star-forming region NGC 6334I in the velocity range −10 to −2 km s −1 . The 6.7 GHz methanol and 22.2 GHz water masers began flaring within 22 days of each other, while the 12.2 GHz methanol and 1665 MHz hydroxyl masers flared 80 and 113 days later respectively. The 1665 MHz, 6.7 GHz, and 22.2 GHz masers have all remained in their flared state for nearly 3 years. The brightest flaring components increased by factors of 66, 21, 26, and 20 in the 12.2 and 6.7 GHz methanol, 1665 MHz hydroxyl and 22.2 GHz water maser transitions respectively; some weaker components increased by up to a factor of 145. We also report new maser emission in the 1720, 6031, and 6035 MHz OH lines and the 23.1 GHz methanol line, along with the detection of only the fifth 4660 MHz OH maser. We note the correlation of this event with the extraordinary (sub)millimeter continuum outburst from the massive protostellar system NGC 6334I-MM1 and discuss the implications of the observed time lags between different maser velocity components on the nature of the outburst. Finally, we identify two earlier epoch maser flaring events likely associated with this object, which suggest a recurring accretive phenomenon that generates powerful radiative outbursts.
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.
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
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.
A Catalog of CH3OH 70-61 A+ Maser Sources in Massive Star-forming Regions
Astrophysical Journal Supplement Series, 2004
We present Very Large Array observations of the 7 0 − 6 1 A + methanol maser transition at 44 GHz towards NGC 6334F, G8.67−0.36, and M17. These arcsecond resolution observations complete a previous, larger VLA survey of this maser transition in high-mass star-forming regions reported by Kurtz et al. We confirm the presence of 44 GHz methanol maser emission in all three sources, detecting eight distinct maser components in NGC 6334F, twelve components in G8.67−0.36 and one in M17.
Observations of methanol masers in star-forming regions
New Astronomy Reviews, 1999
We present VLBI observations of 6.7 and 12.2 GHz methanol masers in three star-forming regions, NGC7538, W75N and S252. Our results reveal linear structures in the VLBI maps and monotonic velocity gradients in the three sources. All these results are consistent with Keplerian disks of diameter of | 1000-2000 AU around young stars of mass | (10-30) M .
Proceedings of the International Astronomical Union
Our 2015-2016 ALMA 1.3 to 0.87 mm observations (resolution ~200 au) of the massive protocluster NGC6334I revealed that an extraordinary outburst had occurred in the dominant millimeter dust core MM1 (luminosity increase of 70×) when compared with earlier SMA data. The outburst was accompanied by the flaring of ten maser transitions of three species. We present new results from our recent JVLA observations of Class II 6.7 GHz methanol masers and 6 GHz excited OH masers in this region. Class II masers had not previously been detected toward MM1 in any interferometric observations recorded over the past 30 years that targeted the bright masers toward other members of the protocluster (MM2 and MM3=NGC6334F). Methanol masers now appear both toward and adjacent to MM1 with the strongest spots located in a dust cavity ~1 arcsec (1300 au) north of the MM1B hypercompact HII region. In addition, new excited OH masers appear on the non-thermal source CM2. These data reveal the dramatic effects...
The properties and polarization of the H 2 O and CH 3 OH maser environment of NGC 7538-IRS 1
Astronomy & Astrophysics, 2011
Context. NGC7538 is a complex massive star-forming region. The region is composed of several radio continuum sources, one of which is IRS 1, a high-mass protostar, from which a 0.3 pc molecular bipolar outflow was detected. Several maser species have been detected around IRS 1. The CH 3 OH masers have been suggested to trace a Keplerian-disk, while the H 2 O masers are almost aligned to the outflow. More recent results suggested that the region hosts a torus and potentially a disk, but with a different inclination than the Keplerian-disk that is supposed to be traced by the CH 3 OH masers. Aims. Tracing the magnetic field close to protostars is fundamental for determining the orientation of the disk/torus. Recent studies showed that during the protostellar phase of high-mass star formation the magnetic field is oriented along the outflows and around or on the surfaces of the disk/torus. The observations of polarized maser emissions at milliarcsecond resolution can make a crucial contribution to understanding the orientation of the magnetic field and, consequently, the orientation of the disk/torus in NGC7538-IRS 1. Methods. The NRAO Very Long Baseline Array was used to measure the linear polarization and the Zeeman-splitting of the 22 GHz H 2 O masers toward NGC7538-IRS 1. The European VLBI Network and the MERLIN telescopes were used to measure the linear polarization and the Zeeman-splitting of the 6.7 GHz CH 3 OH masers toward the same region. Results. We detected 17 H 2 O masers and 49 CH 3 OH masers at high angular resolution. We detected linear polarization emission toward two H 2 O masers and toward twenty CH 3 OH masers. The CH 3 OH masers, most of which only show a core structure, seem to trace rotating and potentially infalling gas in the inner part of a torus. Significant Zeeman-splitting was measured in three CH 3 OH masers. No significant (3σ) magnetic field strength was measured using the H 2 O masers. We also propose a new description of the structure of the NGC7538-IRS 1 maser region.