- ID:
- ivo://CDS.VizieR/J/ApJ/854/170
- Title:
- Methanol (CH_3_OH) and OH masers in NGC 6334I
- Short Name:
- J/ApJ/854/170
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the first sub-arcsecond VLA imaging of 6GHz continuum, methanol maser, and excited-state hydroxyl maser emission toward the massive protostellar cluster NGC 6334I 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 6.7GHz Class II methanol maser sites in the hot core MM2 and the UCHII region MM3 (NGC 6334F), we find new maser features toward several components of MM1, along with weaker features ~1" north, west, and southwest of MM1, and toward the nonthermal 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 nonthermal radio emission source CM2 (2" north of MM1) also exhibits new maser emission from the excited 6.035 and 6.030GHz OH lines. Using the Zeeman effect, we measure a line-of-sight magnetic field of +0.5 to +3.7mG 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 -5mG and an intriguing south-north field reversal.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/764/L19
- Title:
- Methanol emission from the Galactic Center
- Short Name:
- J/ApJ/764/L19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of a widespread population of collisionally excited methanol J=4_-1_ to 3_0_E sources at 36.2GHz from the inner 66'x18' (160x43pc) of the Galactic center. This spectral feature was imaged with a spectral resolution of 16.6km/s taken from 41 channels of a Very Large Array continuum survey of the Galactic center region. The revelation of 356 methanol sources, most of which are maser candidates, suggests a large abundance of methanol in the gas phase in the Galactic center region. There is also spatial and kinematic correlation between SiO (2-1) and CH_3_OH emission from four Galactic center clouds: the +50 and +20km/s clouds and G0.13-0.13 and G0.25+0.01. The enhanced abundance of methanol is accounted for in terms of induced photodesorption by cosmic rays as they travel through a molecular core, collide, dissociate, ionize, and excite Lyman Werner transitions of H_2_. A time-dependent chemical model in which cosmic rays drive the chemistry of the gas predicts CH_3_OH abundance of 10^-8^ to 10^-7^ on a chemical timescale of 5x10^4^ to 5x10^5^ years. The average methanol abundance produced by the release of methanol from grain surfaces is consistent with the available data.
- ID:
- ivo://CDS.VizieR/J/AZh/84/839
- Title:
- Methanol emission of isolated maser condensations
- Short Name:
- J/AZh/84/839
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distribution of the radial velocities of class I methanol masers relative to the velocities of their parent molecular clouds is analyzed. This analysis is based on catalog data for methanol masers detected up to the present time in both the northern and southern hemispheres, together with catalog data for the CS(2-1) line, which traces dense, quiescent gas. Results for a large sample of sources show that, in contrast to class II methanol masers, which undergo Keplerian motions in protoplanetary disks, class I methanol masers retain their velocities in the local system of rest of the surrounding medium, and do not participate in the ejection of matter in bipolar out flows. They can be adequately described using a model in which matter ejected from active parts of the associated star-forming regions flows around isolated maser condensations. This compresses the maser clumps, enhancing the concentration of methanol and facilitating collisional pumping of the masers.
- ID:
- ivo://CDS.VizieR/J/MNRAS/444/566
- Title:
- Methanol maser associated outflows
- Short Name:
- J/MNRAS/444/566
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have selected the positions of 54 6.7GHz methanol masers from the Methanol Multibeam Survey catalogue, covering a range of longitudes between 20{deg} and 34{deg} of the Galactic plane. These positions were mapped in the J=3-2 transition of both the ^13^CO and C^18^O lines. A total of 58 ^13^CO emission peaks are found in the vicinity of these maser positions. We search for outflows around all ^13^CO peaks, and find evidence for high-velocity gas in all cases, spatially resolving the red and blue outflow lobes in 55 cases. Of these sources, 44 have resolved kinematic distances, and are closely associated with the 6.7GHz masers, a subset referred to as Methanol Maser Associated Outflows (MMAOs). We calculate the masses of the clumps associated with each peak using 870{mu}m continuum emission from the ATLASGAL survey. A strong correlation is seen between the clump mass and both outflow mass and mechanical force, lending support to models in which accretion is strongly linked to outflow. We find that the scaling law between outflow activity and clump masses observed for low-mass objects, is also followed by the MMAOs in this study, indicating a commonality in the formation processes of low-mass and high-mass stars.
- ID:
- ivo://CDS.VizieR/J/AZh/79/328
- Title:
- Methanol maser condensations in W 48
- Short Name:
- J/AZh/79/328
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The methanol-line spectra in two maser condensations at velocities ~41 and ~45km/s in the star-forming region W 48 have been studied.
- ID:
- ivo://CDS.VizieR/J/MNRAS/291/261
- Title:
- Methanol maser of IRAS-selected sources
- Short Name:
- J/MNRAS/291/261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A survey of ultracompact (UC) HII regions has been carried out by searching for 6.669-GHz methanol maser emission from a sample of 535 IRAS-selected candidates. A total of 201 candidates exhibit methanol emission. These sources have been used, in conjunction with previously identified UC HII regions, to provide a base for further studies of such regions. Estimates of distances have indicated that the identified UC HII regions tend to have some Galactic structure but it is not clear whether they lie in or between the spiral arms of the Galaxy. The regions are tightly constrained to the plane of the Galaxy. Comparison of identified regions and IRAS sources selected by Wood & Churchwell indicates that there there is some degree of contamination, which could be due to an older phase in the life on an UC HII region where methanol maser emission is not apparent. Luminosities and spectral types have been derived for many of the regions. The maximum number of maser spots observed seems to increase with increasing peak maser luminosity, which indicates that the maser emission is more dependent on the abundance of methanol than the availability of far-infrared radiation.
- ID:
- ivo://CDS.VizieR/J/other/IJAA/4.571
- Title:
- Methanol masers in HII regions
- Short Name:
- J/other/IJAA/4.5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As the recent publication by Breen et al. (2013MNRAS.435..524B) found, Class II methanol masers are exclusively associated with high mass star forming regions. Based on the positions of the Class I and II methanol and H_2_O masers, UC HII regions and 4.5um infrared sources, and the center velocities (vLSR) of the Class I methanol and H_2_O masers, compared to the vLSR of the Class II methanol masers, we propose three disk-outflow models that may be traced by methanol masers. In all three models, we have located the Class II methanol maser near the protostar, and the Class I methanol maser in the outflow, as is known from observations during the last twenty years. In our first model, the H_2_O masers trace the linear extent of the outflow. In our second model, the H_2_O masers are located in a circumstellar disk. In our third model, the H_2_O masers are located in one or more outflows near the terminating shock where the outflow impacts the ambient interstellar medium. Together, these models reiterate the utility of coordinated high angular resolution observations of high mass star forming regions in maser lines and associated star formation tracers.
- ID:
- ivo://CDS.VizieR/J/A+AS/110/81
- Title:
- Methanol masers towards IRAS sources
- Short Name:
- J/A+AS/110/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our second search for 6.7-GHz methanol masers towards colour-selected IRAS sources. Five hundred and twenty IRAS sources that meet the far-infrared colour criteria set by Wood & Churchwell (1989ApJ...340..265W) for ultra-compact HII regions were searched for 6.7-GHz methanol maser emission, to a sensitivity limit of 5Jy. Thirty one new maser sources were detected. We also compare the FIR colours of the newly detected maser sources with those detected by Schutte et al. (1993MNRAS.261..783S) and the IRAS counterparts of sources that have both methanol and hydroxyl maser emission. It was found that the average flux distribution of the newly detected sources differs significantly from that of all other known 6.7-GHz methanol maser sources. It is argued that the differences may be due either to intrinsic differences between the three groups of sources or to interstellar extinction. An analysis of the relation between the 6.7-GHz maser and IRAS flux densities shows that the maser flux density is always less than the 100{mu}m flux density while only three sources have a maser flux density greater than the 60{mu}m flux density. Far-infrared pumping of the 6.7-GHz methanol masers is therefore in principle viable although it was found that the apparent maser efficiency will exceed 10 per cent for a significant number of sources in the case of FIR pumping by photons between 50 and 100{mu}m. The overall detection rates on the IRAS [25-12] vs [60-12] two-colour diagram are also presented. Possible new search strategies for masers in colour-selected IRAS sources are discussed.
- ID:
- ivo://CDS.VizieR/J/AZh/79/610
- Title:
- Methyl acetylene observations of warm clouds
- Short Name:
- J/AZh/79/610
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of a survey of 63 galactic star-forming region in the 6k-5k and 5k-4k methyl acetylene lines at 102.5 and 85.5GHz are presented. Fourty-three sources were detected at 102.5GHz, and twenty-five at 85.5GHz
- ID:
- ivo://CDS.VizieR/J/MNRAS/235/1313
- Title:
- Metrewave Extragalactic Variability
- Short Name:
- J/MNRAS/235/1313
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report a detailed statistical study of the intensity variations in 412 extragalactic radio sources randomly selected from the ~2000 sources which have been observed with the Culgoora circular array at 80 and 160 MHz during the interval 1970-84. Our results are: (i) About 47 per cent of the sample displays significant variability on time scales of months or years. (ii) A similar degree of variability is shown by QSOs, radio galaxies and sources in blank optical fields. (iii) Sources with flatter radio spectra are more variable. (iv) There is a weak increase in variability for the lower-galactic-latitude sources. (v) There is a correlation between month-to-month variability and year-to year variability in the same sources. (vi) The degree of variability at 80MHz is related to that at 160MHz. (vii) Most of the sources in both the variable and non-variable categories have a component with angular diameter <1arcsec. Our results are partly consistent with an origin in refractive scintillation by large-scale electron density turbulence in the intervening medium. There are, however, serious difficulties in explaining, from the existing theory of slow galactic scintillation, the short time-scale of the scintillation. Our results are probably more in accord with the focusing and occulting effects of compact interstellar ionized structures recently identified at microwave frequencies.