- 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.
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Search Results
- 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/A+AS/90/327
- Title:
- 1612MHz OH survey of IRAS point sources
- Short Name:
- J/A+AS/90/327
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 2703 sources have been observed at the 1612MHz transition of OH, and 783 OH/IR stars were detected; 597 of these detections are new discoveries. The IRAS sources were detected on the basis of their IRAS fluxes at 12, 25 and 60um. The survey is 70% complete for IRAS sources in the Southern hemisphere (Dec<-10{deg}) with F(12um)>3Jy, with IR colors log(F25/F12)>-0.2 and log(F60/F12)<0.6 Note that the file catalog.dat contains all observed sources, with a flag indicating the detection or non-detection; the detected sources only are listed in the printed version of Table2, while sources without detectable 1612MHz emission are listed in Table3 (on microfiche)
- ID:
- ivo://CDS.VizieR/J/A+A/470/191
- Title:
- Mid-IR and radio interferometry of S Ori
- Short Name:
- J/A+A/470/191
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first multi-epoch study that includes concurrent mid-infrared and radio interferometry of an oxygen-rich Mira star. We obtained mid-infrared interferometry of S Ori with VLTI/MIDI at four epochs in December 2004, February/March 2005, November 2005, and December 2005. We concurrently observed v=1, J=1-0 (43.1GHz) and v=2, J=1-0 (42.8GHz) SiO maser emission toward S Ori with the VLBA in January, February, and November 2005. The MIDI data are analyzed using self-excited dynamic model atmospheres including molecular layers, complemented by a radiative transfer model of the circumstellar dust shell. The VLBA data are reduced to the spatial structure and kinematics of the maser spots. The modeling of our MIDI data results in phase-dependent continuum photospheric angular diameters of 9.0+/-0.3mas (phase 0.42), 7.9+/-0.1mas (0.55), 9.7+/-0.1mas (1.16), and 9.5+/-0.4mas (1.27). The dust shell can best be modeled with Al2O3 grains alone using phase-dependent inner boundary radii between 1.8 and 2.4 photospheric radii. The dust shell appears to be more compact with larger optical depth near visual minimum (tau_V_~2.5), and more extended with lower optical depth after visual maximum (tau_V_~1.5). The ratios of the 43.1GHz/42.8GHz SiO maser ring radii to the photospheric radii are 2.2+/-0.3/2.1+/-0.2 (phase 0.44), 2.4+/-0.3/2.3+/-0.4 (0.55), and 2.1+/-0.3/1.9+/-0.2 (1.15). The maser spots mark the region of the molecular atmospheric layers shortly outward of the steepest decrease of the mid-infrared model intensity profile. Their velocity structure indicates a radial gas expansion. S Ori shows significant phase-dependences of photospheric radii and dust shell parameters. Al2O3 dust grains and SiO maser spots form at relatively small radii of ~1.8-2.4 photospheric radii. Our results suggest increased mass-loss and dust formation close to the surface near minimum visual phase, when Al2O3 dust grains are co-located with the molecular gas and the SiO maser shells, and a more expanded dust shell after visual maximum. Silicon does not appear to be bound in dust, as our data shows no sign of silicate grains.
- ID:
- ivo://CDS.VizieR/J/A+A/570/A110
- Title:
- Mid-IR properties of OH maser galaxies
- Short Name:
- J/A+A/570/A110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compiled all 119 OH maser galaxies (110 out of them are megamasers, i.e., L_OH_>10L_{sun}_) published so far and cross-identified these OH masers with the Wide-Field Infrared Survey Explorer (WISE) catalog, to investigate the middle infrared (MIR) properties of OH maser galaxies. The WISE magnitude data at the 3.4, 4.6, 12 and 22{mu}m (W1 to W4) are collected for the OH maser sample and one control sample, which are non-detection sources. The color-color diagrams show that both OH megamaser (OHM) and non-OHM (ultra)luminous infrared galaxies ((U)LIRGs) are far away from the single blackbody model line and many of them can follow the path described by the power-law model. The active galaxy nuclei (AGN) fraction is about ~40% for both OHM and non-OHM (U)LIRGs, according to the AGN criteria W1-W2>=0.8. Among the Arecibo survey sample, OHM sources tend to have a lower luminosity at short MIR wavelengths (e.g., 3.4{mu}m and 4.6{mu}m) than that of non-OHM sources, which should come from the low OHM fraction among the survey sample with large 3.4{mu}m and 4.6{mu}m luminosity. The OHM fraction tends to increase with cooler MIR colors (larger F_22{mu}m_/F_3.4{mu}m_). These may be good for sample selection when searching OH megamasers, such as excluding extreme luminous sources at short MIR wavelengths, choosing sources with cooler MIR colors. In the case of the power-law model, we derived the spectral indices for our samples. For the Arecibo survey sample, OHM (U)LIRGs tend to have larger spectral index {alpha}_22-12_ than non-OHM sources, which agrees with previous results. One significant correlation exists between the WISE infrared luminosity at 22{mu}m and the color [W1]-[W4] for the Arecibo OHM hosts. These clues should provide suitable constraints on the sample selection for OH megamaser surveys by future advanced telescopes (e.g., FAST). In addition, the correlation of maser luminosity and the MIR luminosity of maser hosts tends to be non-significant, which may indirectly support the pumping of OHM emission that is dominated by the far infrared radiation, instead of the MIR radiation.
