- 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.
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Search Results
- 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/ApJS/215/25
- Title:
- Methyl formate (HCOOCH_3_) observations
- Short Name:
- J/ApJS/215/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have surveyed a sample of massive star-forming regions located over a range of distances from the Galactic center for methyl formate, HCOOCH_3_, and its isotopologues H^13^COOCH_3_ and HCOO^13^CH_3_. The observations were carried out with the APEX telescope in the frequency range 283.4-287.4GHz. Based on the APEX observations, we report tentative detections of the ^13^C-methyl formate isotopologue HCOO^13^CH_3_toward the following four massive star-forming regions: Sgr B2(N-LMH), NGC 6334 IRS 1, W51 e2, and G19.61-0.23. In addition, we have used the 1mm ALMA science verification observations of Orion-KL and confirm the detection of the ^13^C-methyl formate species in Orion-KL and image its spatial distribution. Our analysis shows that the ^12^C/^13^C isotope ratio in methyl formate toward the Orion-KL Compact Ridge and Hot Core-SW components (68.4+/-10.1 and 71.4+/-7.8, respectively) are, for both the ^13^C-methyl formate isotopologues, commensurate with the average ^12^C/^13^C ratio of CO derived toward Orion-KL. Likewise, regarding the other sources, our results are consistent with the ^12^C/^13^C in CO. We also report the spectroscopic characterization, which includes a complete partition function, of the complex H^13^COOCH_3_ and HCOO^13^CH_3_species. New spectroscopic data for both isotopomers H^13^COOCH_3_and HCOO^13^CH_3_, presented in this study, have made it possible to measure this fundamentally important isotope ratio in a large organic molecule for the first time.
- ID:
- ivo://CDS.VizieR/J/A+A/587/L4
- Title:
- Methyl isocyanate in Orion
- Short Name:
- J/A+A/587/L4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The recent analysis of the composition of the frozen surface of comet 67P/Churyumov-Gerasimenko has revealed a significant number of complex organic molecules. Methyl isocyanate (CH_3_NCO) is one of the more abundant species detected on the comet surface. In this work we report extensive characterization of its rotational spectrum resulting in a list of 1269 confidently assigned laboratory lines and its detection in space towards the Orion clouds where 399 lines of the molecule have been unambiguously identified. We find that the limited mm-wave laboratory data reported prior to our work require some revision. The abundance of CH_3_NCO in Orion is only a factor of ten below those of HNCO and CH_3_CN. Unlike the molecular abundances in the coma of comets, which correlate with those of warm molecular clouds, molecular abundances in the gas phase in Orion are only weakly correlated with those measured on the comet surface. We also compare our abundances wit those derived recently for this molecule towards Sgr B2 (Halfen et al., 2015ApJ...812L...5H). A more accurate abundance of CH_3_NCO is provided for this cloud based on our extensive laboratory work.
- 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.
- ID:
- ivo://CDS.VizieR/J/A+A/630/A108
- Title:
- MG B2016+112 radio images
- Short Name:
- J/A+A/630/A108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we exploit the gravitational lensing effect to detect proper motion in the highly magnified gravitationally lensed source MG B2016+112. We find positional shifts up to 6mas in the lensed images by comparing two very long baseline interferometric (VLBI) radio observations at 1.7GHz that are separated by 14.359 years, and provide an astrometric accuracy of the order of tens of as. From lens modelling, we exclude a shift in the lensing galaxy as the cause of the positional change of the lensed images, and we assign it to the background source. The source consists of four sub-components, separated by 175 pc, with proper motion of the order of tens {mu}as/yr for the two components at highest magnification ({mu}~350) and of the order of a few mas/yr for the two components at lower magnification ({mu}~2). We propose single Active Galactic Nuclei (AGN) and dual AGN scenarios to explain the source plane. Although, the latter interpretation is supported by the archival multi-wavelength properties of the object. In this case, MG B2016+112 would represent the highest redshift dual radio-loud AGN system discovered thus far, and would support the merger interpretation for such systems. Also, given the low probability (~10^-5^) of detecting a dual AGN system that is also gravitationally lensed, if confirmed, this would suggest that such dual AGN systems must be more abundant in the early Universe than currently thought.
- ID:
- ivo://CDS.VizieR/J/ApJ/754/38
- Title:
- MgII absorption systems for Flat-Spectrum Radio QSOs
- Short Name:
- J/ApJ/754/38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The conventional wisdom that the rate of incidence of MgII absorption systems, dN/dz (excluding "associated systems" having a velocity {beta}c relative to the active galactic nucleus (AGN) of less than ~5000km/s), is totally independent of the background AGNs has been challenged by a recent finding that dN/dz for strong MgII absorption systems toward distant blazars is 2.2+/-^0.8^_0.6_ times the value known for normal optically selected quasars (QSOs). This has led to the suggestion that a significant fraction of even the absorption systems with {beta} as high as ~0.1 may have been ejected by the relativistic jets in the blazars, which are expected to be pointed close to our direction. Here, we investigate this scenario using a large sample of 115 flat-spectrum radio-loud quasars (FSRQs) that also possess powerful jets, but are only weakly polarized. We show, for the first time, that dN/dz toward FSRQs is, on the whole, quite similar to that known for QSOs and that the comparative excess of strong MgII absorption systems seen toward blazars is mainly confined to {beta}<0.15. The excess relative to FSRQs probably results from a likely closer alignment of blazar jets with our direction; hence, any gas clouds accelerated by them are more likely to be on the line of sight to the active quasar nucleus.
- ID:
- ivo://CDS.VizieR/J/ApJS/75/801
- Title:
- MGIV (Fourth MIT-Green Bank) 5GHz Survey
- Short Name:
- J/ApJS/75/801
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The MIT-Green Bank IV (MG IV) 5 GHz survey covers 0.504 sr of sky in the right ascension range 15.5 to 2.5 hours, between +37.00 and +50.98 degrees declination (B1950). The final MG IV catalog contains 3427 sources detected with a signal-to-noise ratio greater than 5. The catalog was produced from two separate north and south surveys with the National Radio Astronomy Observatory (NRAO) 91m transit telescope. The north survey was produced from data collected while scanning the telescope north from +39.0 to +50.98 degrees declination and the south survey from data collected from scans from +48.98 to +37.00 degrees declination. The completeness and reliability of the final source list is checked by examination of north and south source lists in a twice observed comparison region, lying between +39.15 and +48.83 degrees declination and excluding the area between +/-10 degrees Galactic latitude. The comparison region covers 0.270 sr of sky and contains 1094 sources. In this region, the MG IV catalog contains 423 sources brighter than 90 mJy and is shown to be 99.1 +/- 1.2% complete at this flux density level. Spectral indices are computed for sources identified in the NRAO 1400 MHz Survey (published by Condon and Broderick in 1985). A comparison of the spectral index distributions between +/- 10 and outside of +/- 10 degrees Galactic latitude is presented.
