- ID:
- ivo://CDS.VizieR/J/ApJS/241/18
- Title:
- A 6.7GHz methanol maser survey. II. |b|<2{deg}
- Short Name:
- J/ApJS/241/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of our systematic survey for Galactic 6.7GHz Class II CH_3_OH maser emission toward a sample of young stellar objects. The survey was conducted with the Shanghai Tianma Radio Telescope (TMRT). The sample consists of 3348 sources selected from the all-sky Wide-field Infrared Survey Explorer (WISE) point-source catalog. We discussed the selection criteria in detail and the detection results of those at high Galactic latitudes (i.e., |b|>2{deg}) in a previous paper (Paper I; Yang+ 2017, J/ApJ/846/160). Here, we present the results from the survey of those at low Galactic latitudes, i.e., |b|<2{deg}. Of 1875 selected WISE point sources, 291 positions that were actually associated with 224 sources that were detected with CH_3_OH maser emission. Among them, 32 are newly detected. A majority of the newly detected sources are associated with bright WISE sources. The majority of the detected sources (209/224=93.3%) are quite close to the Galactic Plane (|b|<1{deg}) and lie on the inner spiral arms with positive local standard of rest velocities. The detection rate and the color-color distribution of our detection are all matched with our anticipation. Combining with detections from previous surveys, we compile a catalog of 1085 sources with 6.7GHz CH_3_OH maser emission in our Galaxy.
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- ID:
- ivo://CDS.VizieR/J/AZh/72/22
- Title:
- A 95 GHz Survey of Methanol Masers
- Short Name:
- J/AZh/72/22
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A 95GHz survey of methanol emission in the 8_0_-7_1_A^+^ transition was conducted with the 20-m radio telescope at Onsala. Twenty-six new sources were detected in the emission line. At least nine out of the 35 studied sources are masers.
- ID:
- ivo://CDS.VizieR/J/ApJ/832/187
- Title:
- ALMA and VLA radio continuum obs. of NGC 6334I
- Short Name:
- J/ApJ/832/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Very Large Array and Atacama Large Millimeter/submillimeter Array imaging of the deeply embedded protostellar cluster NGC 6334I from 5cm to 1.3mm at angular resolutions as fine as 0.17" (220au). The dominant hot core MM1 is resolved into seven components at 1.3mm, clustered within a radius of 1000au. Four of the components have brightness temperatures >200K, radii ~300au, minimum luminosities ~10^4^L_{sun}_, and must be centrally heated. We term this new phenomenon a "hot multi-core." Two of these objects also exhibit compact free-free emission at longer wavelengths, consistent with a hypercompact HII region (MM1B) and a jet (MM1D). The spatial kinematics of the water maser emission centered on MM1D are consistent with it being the origin of the high-velocity bipolar molecular outflow seen in CO. The close proximity of MM1B and MM1D (440au) suggests a proto-binary or a transient bound system. Several components of MM1 exhibit steep millimeter spectral energy distributions indicative of either unusual dust spectral properties or time variability. In addition to resolving MM1 and the other hot core (MM2) into multiple components, we detect five new millimeter and two new centimeter sources. Water masers are detected for the first time toward MM4A, confirming its membership in the protocluster. With a 1.3mm brightness temperature of 97K coupled with a lack of thermal molecular line emission, MM4A appears to be a highly optically thick 240L_{sun}_ dust core, possibly tracing a transient stage of massive protostellar evolution. The nature of the strongest water maser source CM2 remains unclear due to its combination of non-thermal radio continuum and lack of dust emission.
- ID:
- ivo://CDS.VizieR/J/A+A/641/A97
- Title:
- ALMA Magellanic Bridge A molecular clouds
- Short Name:
- J/A+A/641/A97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Magellanic Bridge is a tidal feature located between both Magellanic Clouds, containing young stars formed in situ. Its proximity allows high-resolution studies of molecular gas, dust and star formation in a tidal, low metallicity environment. Our goal is to characterize gas and dust emission in Magellanic Bridge A, the source with the highest 870um excess of emission found in single dish surveys. Using the ALMA telescope including the Morita Array, we mapped with sub-parsec resolution a 3arcmin, field of view centered on the Magellanic Bridge A molecular cloud, in 1.3mm continuum emission and ^12^CO(2-1 line emission. This region was also mapped in continuum at 870um and in ^12^CO(2-1) line emission at ~6pc resolution with the APEX telescope. To study its dust properties, we also use archival Herschel and Spitzer data. We combine the ALMA and APEX ^12^CO(2-1) line cubes to study the molecular gas emission. Magallanic Bridge A breaks up into two distinct molecular clouds in dust and ^12^CO(2-1) emission, which we call North and South. Dust emission in the North source, according to our best parameters from fitting the far-infrared fluxes, is ~3K colder than in the South source in correspondence to its less developed star formation. Both dust sources present large submillimeter excesses in LABOCA data: according to our best fits the excess over the modified blackbody (MBB) fit to the Spitzer/Herschel continuum is E(870um)~7 and E(870um)~3 for the North and South sources respectively. Nonetheless, we do not detect the corresponding 1.3mm continuum with ALMA. Our limits are compatible with the extrapolation of the MBB fits and therefore we cannot independently confirm the excess at this longer wavelength. The ^12^CO(2-1) emission is concentrated in two parsec-sized clouds with virial masses around 400 and 700M_{sun}_ each. Their bulk volume densities are n(H_2_)~0.7-2.6x10^3^cm^-3^, larger than typical bulk densities of Galactic molecular clouds. The ^12^CO luminosity to H_2_ mass conversion factor {alpha}_CO_ is 6.5 and 15.3M_{sun}_/(K.(km/s)pc^2^) for the North and South clouds, calculated using their respective virial masses and ^12^CO(2-1) luminosities. Gas mass estimates from our MBB fits to dust emission yields masses M~1.3x10^3^M_{sun}_ and 2.9x10^3^M_{sun}_ for North and South respectively, a factor of ~4 larger than the virial masses we infer from ^12^CO.
- ID:
- ivo://CDS.VizieR/J/ApJ/871/251
- Title:
- ALMA obs. of ethyl formate toward Orion KL
- Short Name:
- J/ApJ/871/251
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Orion KL is one of the prime templates of astrochemical and prebiotic chemical studies. We wish to explore more organic molecules with increasing complexity in this region. In particular, we have searched for one of the most complex organic molecules detected in space so far, ethyl formate (C_2_H_5_OCHO). This species is the next step in chemical complexity after the simplest member of esters (methyl formate, CH_3_OCHO). The mechanisms leading to its formation are still poorly known. We have used high angular resolution (~1.5") ALMA observations covering a large bandwidth from 214 to 247GHz. We have detected 82 unblended lines of C_2_H_5_OCHO (49 and 33 of the trans- and gauche- conformers, respectively). The line images showed that C2H5OCHO arises mainly from the compact ridge and the hot core-southwest regions. The derived rotational temperatures and column densities are 122+/-34K, (0.9+/-0.3)x10^16^cm^-2^ for the hot core-SW, and 103+/-13K, (0.6+/-0.3)x10^16^cm^-2^ for the compact ridge. The comparison of spatial distribution and abundance ratios with chemically related molecules (methyl formate, ethanol, and formic acid) indicates that C_2_H_5_OCHO is likely formed on the surface of dust grains by addition of CH_3_ to functional-group radicals (CH_2_OCHO) derived from methyl formate (CH_3_OCHO).
- ID:
- ivo://CDS.VizieR/J/ApJ/883/129
- Title:
- ALMA obs. of star-forming regions toward NGC6334I
- Short Name:
- J/ApJ/883/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The relative column densities of the structural isomers methyl formate, glycolaldehyde, and acetic acid are derived for a dozen positions toward the massive star-forming regions MM1 and MM2 in the NGC 6334I complex, which are separated by ~4000au. Relative column densities of these molecules are also gathered from the literature for 13 other star-forming regions. In this combined data set, a clear bimodal distribution is observed in the relative column densities of glycolaldehyde and methyl formate. No such distribution is evident with acetic acid. The two trends are comprised of star-forming regions with a variety of masses, suggesting that there must be some other common parameter that is heavily impacting the formation of glycolaldehyde. This is indicative of some demonstrable differentiation in these cores; studying the abundances of these isomers may provide a clue as to the integral chemical processes ongoing in a variety of protostellar environments.
- ID:
- ivo://CDS.VizieR/J/MNRAS/410/2662
- Title:
- AMI 1.8cm observations in c2d small clouds
- Short Name:
- J/MNRAS/410/2662
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform deep 1.8-cm radio continuum imaging towards 13 protostellar regions selected from the Spitzer c2d small clouds and cores programme at high resolution (25-arcsec) in order to detect and quantify the cm-wave emission from deeply embedded young protostars. Within these regions we detect 15 compact radio sources which we identify as radio protostars including two probable new detections. The sample is in general of low bolometric luminosity and contains several of the newly detected VeLLO sources. We determine the 1.8cm radio luminosity to bolometric luminosity correlation, L_rad_-L_bol_, for the sample and discuss the nature of the radio emission in terms of the available sources of ionized gas. We also investigate the Lrad-LIR correlation and suggest that radio flux density may be used as a proxy for the internal luminosity of low-luminosity protostars.
- ID:
- ivo://CDS.VizieR/J/MNRAS/415/893
- Title:
- AMI-LA 16 GHz sources in Perseus region
- Short Name:
- J/MNRAS/415/893
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep radio continuum observations of the cores identified as deeply embedded young stellar objects in the Perseus molecular cloud by the Spitzer c2d programme at a wavelength of 1.8cm with the Arcminute Microkelvin Imager Large Array (AMI-LA). We detect 72% of Class 0 objects from this sample and 31% of Class I objects. No starless cores are detected. We use the flux densities measured from these data to improve constraints on the correlations between radio luminosity and bolometric luminosity, infrared luminosity and, where measured, outflow force. We discuss the differing behaviour of these objects as a function of protostellar class and investigate the differences in radio emission as a function of core mass. Two of four possible very low luminosity objects (VeLLOs) are detected at 1.8cm.
- ID:
- ivo://CDS.VizieR/J/AJ/152/92
- Title:
- Ammonia and CO outflow around 6.7GHz methanol masers
- Short Name:
- J/AJ/152/92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Single point observations are presented in NH_3_ (1, 1) and (2, 2) inversion transitions using the Effelsberg 100m telescope for a sample of 100 6.7GHz methanol masers and mapping observations in the ^12^CO and ^13^CO (1-0) transitions using the Purple Mountain Observatory Delingha 13.7m telescope for 82 sample sources with detected ammonia. A further 62 sources were selected for either ^12^CO or ^13^CO line outflow identification, producing 45 outflow candidates, 29 using ^12^CO and 16 using ^13^CO data. Twenty-two of the outflow candidates were newly identified, and 23 had trigonometric parallax distances. Physical properties were derived from ammonia lines and CO outflow parameters were calculated. Histograms and statistical correlations for ammonia, CO outflow parameters, and 6.7GHz methanol maser luminosities are also presented. No significant correlation was found between ammonia and maser luminosity. However, weak correlations were found between outflow properties and maser luminosities, which may indicate that outflows are physically associated with 6.7GHz masers.
- ID:
- ivo://CDS.VizieR/J/ApJS/175/509
- Title:
- Ammonia spectral atlas in Perseus
- Short Name:
- J/ApJS/175/509
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present ammonia observations of 193 dense cores and core candidates in the Perseus molecular cloud made using the Robert F. Byrd Green Bank Telescope. We simultaneously observed the NH_3_(1,1), NH_3_(2,2), C_2_S (2_1_=>1_0_), and C^34^_2_S(2_1_=>1_0_) transitions near {nu}=23GHz for each of the targets with a spectral resolution of {delta}v~0.024km/s. We find ammonia emission associated with nearly all of the (sub)millimeter sources, as well as at several positions with no associated continuum emission. For each detection, we have measured physical properties by fitting a simple model to every spectral line simultaneously. Where appropriate, we have refined the model by accounting for low optical depths, multiple components along the line of sight, and imperfect coupling to the GBT beam. For the cores in Perseus, we find a typical kinetic temperature of T_k_=11K, a typical column density of N_NH3_~10^14.5^/cm2, and velocity dispersions ranging from {sigma}v=0.07 to 0.7km/s. However, many cores with {sigma}v>0.2km/s show evidence for multiple velocity components along the line of sight.
