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- ID:
- ivo://CDS.VizieR/J/ApJ/835/3
- Title:
- 218GHz obs. of embedded protostars in Ophiuchus
- Short Name:
- J/ApJ/835/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present APEX 218GHz observations of molecular emission in a complete sample of embedded protostars in the Ophiuchus star-forming region. To study the physical properties of the cores, we calculate H_2_CO and c-C_3_H_2_ rotational temperatures, both of which are good tracers of the kinetic temperature of the molecular gas. We find that the H_2_CO temperatures range between 16K and 124K, with the highest H_2_CO temperatures toward the hot corino source IRAS 16293-2422 (69-124K) and the sources in the {rho} Oph A cloud (23-49K) located close to the luminous Herbig Be star S1, which externally irradiates the {rho} Oph A cores. On the other hand, the c-C_3_H_2_ rotational temperature is consistently low (7-17K) in all sources. Our results indicate that the c-C_3_H_2_ emission is primarily tracing more shielded parts of the envelope whereas the H_2_CO emission (at the angular scale of the APEX beam; 3600 au in Ophiuchus) mainly traces the outer irradiated envelopes, apart from in IRAS 16293-2422, where the hot corino emission dominates. In some sources, a secondary velocity component is also seen, possibly tracing the molecular outflow.
- ID:
- ivo://CDS.VizieR/J/ApJ/777/157
- Title:
- 90GHz obs. of high-mass star-forming regions
- Short Name:
- J/ApJ/777/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical changes of high-mass star-forming regions provide a potential method for classifying their evolutionary stages and, ultimately, ages. In this study, we search for correlations between molecular abundances and the evolutionary stages of dense molecular clumps associated with high-mass star formation. We use the molecular line maps from Year 1 of the Millimetre Astronomy Legacy Team 90GHz (MALT90) Survey. The survey mapped several hundred individual star-forming clumps chosen from the ATLASGAL survey to span the complete range of evolution, from prestellar to protostellar to H II regions. The evolutionary stage of each clump is classified using the Spitzer GLIMPSE/MIPSGAL mid-IR surveys. Where possible, we determine the dust temperatures and H_2_ column densities for each clump from Herschel/Hi-GAL continuum data. From MALT90 data, we measure the integrated intensities of the N_2_H^+^, HCO^+^, HCN and HNC(1-0) lines, and derive the column densities and abundances of N_2_H^+^ and HCO^+^. The Herschel dust temperatures increase as a function of the IR-based Spitzer evolutionary classification scheme, with the youngest clumps being the coldest, which gives confidence that this classification method provides a reliable way to assign evolutionary stages to clumps. Both N_2_H^+^ and HCO^+^ abundances increase as a function of evolutionary stage, whereas the N_2_H^+^(1-0) to HCO^+^(1-0) integrated intensity ratios show no discernable trend. The HCN(1-0) to HNC(1-0) integrated intensity ratios show marginal evidence of an increase as the clumps evolve.
- ID:
- ivo://CDS.VizieR/J/ApJ/614/607
- Title:
- 8.4GHz obs. of scintillating sources
- Short Name:
- J/ApJ/614/607
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compare the milliarcsecond-scale morphology of scintillating and nonscintillating sources. The scintillating sources are drawn from those flat-spectrum extragalactic radio sources discovered, by the Micro-Arcsecond Scintillation-Induced Variability Survey (MASIV, Lovell et al, 2003AJ....126.1699L), to have flux density variability at 5GHz on timescales from hours to days. Intrinsic source structure information is obtained from previously published and/or publicly available 8.4GHz Very Long Baseline Array images. A sample of low flux density (S_{nu}=5GHz_<0.3Jy) scintillating sources was compared with a sample of high flux density (S_{nu}=5GHz_~1Jy) scintillators, as well as a sample of high flux density nonscintillators.
- ID:
- ivo://CDS.VizieR/J/ApJ/750/170
- Title:
- 6.035GHz OH observations of two IRAS
- Short Name:
- J/ApJ/750/170
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of 6.035GHz hydroxyl (OH) maser flares toward the massive star-forming region IRAS 18566+0408 (G37.55+0.20), which is the only region known to show periodic formaldehyde (4.8GHz H_2_CO) and methanol (6.7GHz CH_3_OH) maser flares. The observations were conducted between 2008 October and 2010 January with the 305m Arecibo Telescope in Puerto Rico. We detected two flare events, one in 2009 March and one in 2009 September to November. The OH maser flares are not simultaneous with the H_2_ CO flares, but may be correlated with CH_3_ OH flares from a component at corresponding velocities. A possible correlated variability of OH and CH_3_ OH masers in IRAS 18566+0408 is consistent with a common excitation mechanism (IR pumping) as predicted by theory.
- ID:
- ivo://CDS.VizieR/J/A+A/482/483
- Title:
- GHz-peaked spectrum (GPS) sources
- Short Name:
- J/A+A/482/483
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gigahertz-peaked spectrum (GPS) sources and high frequency peakers (HFPs) are among the smallest of active galactic nuclei currently believed to represent the earliest phases in the evolution of extragalactic radio sources. Recently there has been evidence of contamination by other types of radio sources among the GPS and HFP samples, but the confirmed GPS sources or HFPs also seem to form a very heterogeneous population. We study the statistical clustering of the GPS sources and the HFPs by taking as many source parameters as possible to find homogeneous groups among the sources. We expect the clustering to give us insight into the physical parameters that play a role in different source populations. We have collected a sample of 206 GPS sources and HFPs from the literature and gathered a massive database of various source properties, such as the redshift, the size, the polarization, the magnitudes, and the properties of the radio continuum. To visualize and to cluster these multidimensional data we used self-organising maps (SOM), which are neural networks trained by an unsupervised algorithm. We have classified the sources with an auxiliary classification to trace the locations of different types of radio continuum spectra on the map.
- ID:
- ivo://CDS.VizieR/J/A+AS/131/303
- Title:
- GHz-Peaked-Spectrum radio sources
- Short Name:
- J/A+AS/131/303
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We define a complete sample of thirty-three GHz-Peaked-Spectrum (GPS) radio sources based on their spectral properties. We present measurements of the radio spectra and polarization of the complete sample and a list of additional GPS sources which fail one or more criteria to be included in the complete sample. The majority of the data have been obtained from quasi-simultaneous multi-frequency observations at the Very Large Array (VLA) during 3 observing sessions. Low frequency data from the Westerbork Synthesis Radio Telescope (WSRT) and from the literature have been combined with the VLA data in order to better define the spectral shape. The objects presented here show a rather wide range of spectral indices at high and low frequencies, including a few cases where the spectral index below the turnover is close to the theoretical value of 2.5 typical of self-absorbed incoherent synchrotron emission. Faint and diffuse extended emission is found in about 10% of the sources. In the majority of the GPS sources, the fractional polarization is found to be very low, consistent with the residual instrumental polarization of 0.3%.
- ID:
- ivo://CDS.VizieR/J/other/AstBu/74.348
- Title:
- 164 GHz-peaked spectrum sources
- Short Name:
- J/other/AstBu/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gigahertz-Peaked spectrum (GPS) sources are compact active galactic nuclei, presumably young precursors of bright radio sources. The study of GPS radio properties provides information about the features of synchrotron radiation in extragalactic sources. Also in applied research, GPS sources are useful as compact stationary radio sources in the sky for astrometric purposes. This paper presents the results of a multifrequency GPS study based on quasi-simultaneous measurements with the RATAN-600 radio telescope during the 2006-2017 period. A catalog of GPS spectral flux densities at six frequencies - 1.1, 2.3, 4.8, 7.7/8.2, 11.2, and 21.7GHz - is obtained. In addition, for the analysis of radio spectra, data from low-frequency surveysGLEAM(GaLactic and Extragalactic AllskyMurchisonwidefield array survey) and TGSS (Tata institute for fundamental research GMRT Sky Survey) and high-frequency measurements from Planck survey are used. A total number of 164 GPS and candidates have been identified (17 of them are new discoveries), which makes up a small fraction of GPS in the initial sample of bright AGNs - about 2%. The physical properties and formation conditions of synchrotron radiation is found to be quite different in GPS of different AGNs types. The deficit of distant GPS (z>2) with low maximum frequencies (less than 1GHz) has been confirmed. The existing "size-peak frequency" anticorrelation is continuous. The continuum radio spectra are found to become statistically steeper with increasing redshift.
- ID:
- ivo://CDS.VizieR/J/MNRAS/380/1449
- Title:
- 1.4GHz radio sources in Lynx and Hercules fields
- Short Name:
- J/MNRAS/380/1449
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With the goal of identifying high-redshift radio galaxies with Fanaroff-Riley class I (FR I) classification, here are presented high-resolution, wide-field radio observations, near-infrared and optical imaging and multi-object spectroscopy of two fields of the Leiden-Berkeley Deep Survey. These fields, Hercules.1 and Lynx.2, contain a complete sample of 81 radio sources with S(1.4GHz)>0.5mJy within 0.6deg^2^. This sample will form the basis for a study of the population and cosmic evolution of high-redshift, low-power, FR I radio sources which will be presented in Paper II. Currently, the host galaxy identification fraction is 86 per cent with 11 sources remaining unidentified at a level of r'>=25.2mag (Hercules; 4 sources) or r'>=24.4mag (Lynx; 7 sources) or K>=20mag. Spectroscopic redshifts have been determined for 49 per cent of the sample and photometric redshift estimates are presented for the remainder of the sample.
- ID:
- ivo://CDS.VizieR/J/ApJ/769/125
- Title:
- 1.4GHz radio variability in FIRST & SDSS Stripe 82
- Short Name:
- J/ApJ/769/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on a blind survey for extragalactic radio variability that was carried out by comparing two epochs of data from the Faint Images of the Radio Sky at Twenty centimeters survey with a third epoch from a new 1.4GHz survey of SDSS Stripe 82. The three epochs are spaced seven years apart and have an overlapping area of 60deg^2^. We uncover 89 variable sources down to the millijansky level, 75 of which are newly identified, and we find no evidence for transient phenomena. This new sample of variable sources allows us to infer an upper limit to the mean characteristic timescale of active galactic nucleus radio variability of 14yr. We find that only 1% of extragalactic sources have fractional variability f_var_>3, while 44% of Galactic sources vary by this much. The variable sample contains a larger fraction of quasars than a comparable non-variable control sample, though the majority of the variable sources appear to be extended galaxies in the optical. This implies that either quasars are not the dominant contributor to the variability of the sample, or that the deep optical data allow us to detect the host galaxies of some low-z quasars. We use the new, higher resolution data to report on the morphology of the variable sources. Finally, we show that the fraction of sources that are variable remains constant or increases at low flux densities. This may imply that next generation radio surveys with telescopes like Australian Square Kilometer Array Pathfinder and MeerKAT will see a constant or even increasing fraction of variable sources down into the sub-millijansky regime.