- ID:
- ivo://CDS.VizieR/J/A+A/610/A27
- Title:
- Compact radio sources in NGC 6334D to F
- Short Name:
- J/A+A/610/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence and properties of compact radio sources embedded in massive star forming regions can reveal important physical properties about these regions and the processes occurring within them. The NGC 6334 complex, a massive star forming region, has been studied extensively. Nevertheless, none of these studies has focused in its content in compact radio sources. Aims. Our goal here is to report on a systematic census of the compact radio sources toward NGC 6334, and their characteristics. This will be used to attempt to define their very nature. We used the VLA C band (4-8GHz) archive data with 0.36" (500AU) of spatial resolution and noise level of 50Jy/bm to carry out a systematic search for compact radio sources within NGC 6334. We also searched for infrared counterparts to provide some constraints on the nature of the detected radio sources. A total of 83 compact sources and three slightly resolved sources were detected. Most of them are here reported for the first time. We found that 29 of these 86 sources have infrared counterparts and three are highly variable. Region D contains 18 of these sources. The compact source toward the center, in projection, of region E is also detected. From statistical analyses, we suggest that the 83 reported compact sources are real and most of them are related to NGC 6334 itself. A stellar nature for 27 of them is confirmed by their IR emission. Compared with Orion, region D suffers a deficit of compact radio sources. The infrared nebulosities around two of the slightly resolved sources are suggested to be warm dust, and we argue that the associated radio sources trace free-free emission from ionized material. We confirm the thermal radio emission of the compact source in region E. However, its detection at infrared wavelengths implies that it is located in the foreground of the molecular cloud. Finally, three strongly variable sources are suggested to be magnetically active young stars.
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- ID:
- ivo://CDS.VizieR/J/AJ/133/2559
- Title:
- Compact radio sources in spiral galaxies. II.
- Short Name:
- J/AJ/133/2559
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the analysis of deep radio observations of the interacting galaxy system M51 from the Very Large Array, with the goal of understanding the nature of the population of compact radio sources in nearby spiral galaxies. We detect 107 compact radio sources, 64% of which have optical counterparts in a deep H{alpha} Hubble Space Telescope image. Thirteen of the radio sources have X-ray counterparts from a Chandra observation of M51. We find that six of the associated H{alpha} sources are young supernova remnants (SNRs) with resolved shells. Most of the SNRs exhibit steep radio continuum spectral indices consistent with synchrotron emission. We detect emission from the Type Ic SN 1994I nearly a decade after explosion: the emission (160+/-22uJy/beam at 20cm, 46+/-11uJy/beam at 6cm, {alpha}=-1.02+/-0.28) is consistent with light-curve models for Type Ib/Ic supernovae. We detect X-ray emission from the supernova; however, no optical counterpart is present. We report on the analysis of the Seyfert 2 nucleus in this galaxy, including the evidence for bipolar outflows from the central black hole.
- ID:
- ivo://CDS.VizieR/J/AJ/130/586
- Title:
- Compact radio sources in the galactic plane
- Short Name:
- J/AJ/130/586
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Archival data have been combined with recent observations of the Galactic plane using the Very Large Array to create new catalogs of compact centimetric radio sources. The 20cm source catalog covers a longitude range of -20{deg}<l<120{deg} the latitude coverage varies from +/-0.8{deg} to +/-2.7{deg}. The total survey area is about 331{deg}^2^; coverage is 90% complete at a flux density threshold of about 14mJy, and over 5000 sources are recorded. The 6cm catalog covers 43{deg}^2^ in the region -10{deg}<l<42{deg}, |b|<0.4{deg} to a 90% completeness threshold of 2.9mJy; over 2700 sources are found. Both surveys have an angular resolution of about 6". These catalogs provide a 30% (at 20cm) to 50% (at 6cm) increase in the number of high-reliability compact sources in the Galactic plane, as well as greatly improved astrometry, uniformity, and reliability; they should prove useful for comparison with new mid- and far-infrared surveys of the Milky Way.
- ID:
- ivo://CDS.VizieR/J/AZh/91/503
- Title:
- Compact radio sources near Galactic center
- Short Name:
- J/AZh/91/503
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using literature data on approximately 400 compact radio sources detected with the Very Large Array and located in the direction of the Galactic center within 2{deg} of the compact source Sgr A*, 69 sources whose angular sizes are determined by scattering on electron density inhomogeneities were distinguished. Fifty-five of these are extragalactic, two are supercompact HII regions, ten are sources of maser emission, and two are variable Galactic sources. The excess of the apparent angular sizes of maser sources within 2{deg} of the Galactic center above the mean size of objects of this class in other parts of the Galaxy found in many studies cannot be explained purely by the effect of scattering of their radio emission on interstellar plasma inhomogeneities. The angular sizes of these objects are increased due to scattering only within Galactic longitudes of about 0.4{deg} and Galactic latitudes less than 0.1{deg}. The turbulent medium responsible for scattering of radio emission of compact sources in the immediate vicinity of the Galactic center is strongly concentrated toward the compact source Sgr A* at the Galactic center. No extragalactic sources are observed within 0.4{deg} in longitude and 0.2{deg} in latitude of the Galactic center, because of their low brightness due to the superstrong scattering in this region. Data on scatter broadening can be used to study the distribution of turbulent plasma near the Galactic center.
- ID:
- ivo://CDS.VizieR/J/ApJ/773/67
- Title:
- Compact radio sources near the Galactic center
- Short Name:
- J/ApJ/773/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed the Galactic center (GC) region at 0.154 and 0.255GHz with the Giant Metrewave Radio Telescope. A total of 62 compact likely extragalactic (EG) sources are detected. Their scattering sizes decrease linearly with increasing angular distance from the GC up to about 1{deg}. The apparent scattering sizes of the sources are more than an order of magnitude less than predicted earlier by the NE2001 model of Galactic electron distribution within 359.5{deg}<l<0.5{deg} and -0.5{deg}<b<0.5{deg} (Hyperstrong Scattering Region) of the Galaxy. High free-free optical depths ({tau}) are observed toward most of the extended non-thermal sources within 0.6{deg} from the GC. Significant variation of {tau} indicates that the absorbing medium is patchy at an angular scale of ~10' and n_e_ is ~10/cm3, which matches the NE2001 model. This model predicts the EG sources to be resolved out from 1.4GHz interferometric surveys. However, out of 10 EG sources expected in the region, 8 likely EG are present in the 1.4GHz catalog. Ionized interfaces of dense molecular clouds to the ambient medium are most likely responsible for strong scattering and low radio frequency absorption. However, dense GC clouds traced by CS J=1-0 emission are found to have a narrow distribution of ~0.2{deg} across the Galactic plane. Angular distribution of most EG sources seen through the so-called Hyperstrong Scattering Region are random in b, and typically ~7 out of 10 sources will not be seen through the dense molecular clouds, which explains why most of them are not scatter broadened at 1.4GHz.
- ID:
- ivo://CDS.VizieR/J/ApJS/80/211
- Title:
- Compact Radio Sources Near the Galactic Plane
- Short Name:
- J/ApJS/80/211
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of the extension of the 20-cm Galactic-plane survey reported by Zoonematkermani to Galactic latitudes of +/-1.8{deg} over the central region of the Milky Way are reported. A total of 1457 discrete radio sources down to flux densities of less than about 5mJy, and 95% completion is achieved at 20mJy. A detailed comparison of all radio sources from the survey in this longitude range with the IRAS Point Source Catalog provides classification for 13% of the objects, including 159 compact H II regions, and nearly 100 planetary nebulae, over 70 of which are identified. The identity of the remaining radio sources is discussed.
- ID:
- ivo://CDS.VizieR/J/ApJ/809/10
- Title:
- Compact radio sources within 30" of Sgr A*
- Short Name:
- J/ApJ/809/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent broadband 34 and 44GHz radio continuum observations of the Galactic center have revealed 41 massive stars identified with near-IR (NIR) counterparts, as well as 44 proplyd candidates within 30" of SgrA*. Radio observations obtained in 2011 and 2014 have been used to derive proper motions of eight young stars near Sgr A*. The accuracy of proper motion estimates based on NIR observations by Lu et al. (2009ApJ...690.1463L) and Paumard et al. (2006, J/ApJ/643/1011) have been investigated by using their proper motions to predict the 2014 epoch positions of NIR stars and comparing the predicted positions with those of radio counterparts in the 2014 radio observations. Predicted positions from Lu et al. show an rms scatter of 6mas relative to the radio positions, while those from Paumard et al. show rms residuals of 20mas. We also determine the mass-loss rates of 11 radio stars, finding rates that are on average ~2 times smaller than those determined from model atmosphere calculations and NIR data. Clumpiness of ionized winds would reduce the mass loss rate of WR and O stars by additional factors of 3 and 10, respectively. One important implication of this is a reduction in the expected mass accretion rate onto Sgr A* from stellar winds by nearly an order of magnitude to a value of a few x10^-7^m_{sun}_/yr. Finally, we present the positions of 318 compact radio sources within 30" of Sgr A*, 45 of which have stellar counterparts in the NIR K_s_ (2.18{mu}m) and L' (3.8{mu}m) bands.
- ID:
- ivo://CDS.VizieR/J/MNRAS/408/2261
- Title:
- Compact steep spectrum new sample
- Short Name:
- J/MNRAS/408/2261
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new sample of compact steep spectrum (CSS) sources with radio luminosity below 10^26^W/Hz at 1.4GHz; these are called low-luminosity compact (LLC) objects. The sources have been selected from the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey and observed with the multi-element radio linked interferometer network (MERLIN) at the L and C bands. The main criterion used for selection was the luminosity of the objects, and approximately one-third of the CSS sources from the new sample have a value of radio luminosity comparable to Fanaroff-Riley type 1 sources (FR Is). About 80 per cent of the sources have been resolved and about 30 per cent have weak extended emission and disturbed structures when compared with the observations of higher-luminosity CSS sources. We have studied the correlation between radio power and linear size, and the redshift with a larger sample that also included published samples of compact objects and large-scale FR IIs and FR Is.
- ID:
- ivo://CDS.VizieR/J/MNRAS/315/839
- Title:
- Compact variable radio sources at 151MHz. I.
- Short Name:
- J/MNRAS/315/839
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Cambridge Low-Frequency Synthesis Telescope has been used to produce a representative sample of low-frequency variable sources. 20 fields, each covering an area of approximately 9{deg}x9{deg}cosecDE, have been observed at 151MHz at between 2 and 10 epochs over the period from 1984 to 1996. At each epoch, maps were made with rms noise levels of typically 10^-15^mJy/beam. From a total of ~6000 sources detected on these maps, 207 are found for which the flux density variations between at least two epochs appear significant at greater than the 3{sigma} level. A numerical model is used to assess the true significance of the variability, given the analysis method adopted. This shows that for about half of the sources which appear to vary by >3{sigma} the variability is genuine. For the other half it is caused by random statistical fluctuations; most of the spurious variables vary by <=3.5{sigma} between a single pair of epochs. A catalogue of the variable sources is presented, which includes an estimate of the probability that a given source is a genuine variable. Fractional flux density variations of between 5 and 100% (typically 15-25%) have been detected on a range of time-scales from 1 to 12 years.
- ID:
- ivo://CDS.VizieR/J/ApJ/511/612
- Title:
- Comparison of Radio-loud and Quiet Quasars
- Short Name:
- J/ApJ/511/612
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have made radio observations of 87 optically selected quasars at 5 GHz with the VLA in order to measure the radio power for these objects and hence determine how the fraction of radio-loud quasars varies with redshift and optical luminosity. The sample has been selected from the recently completed Edinburgh Quasar Survey and covers a redshift range of 0.3{<=}z{<=}1.5 and an optical absolute magnitude range of (-26.5){<=}M_B_{<=}(-23.5) (h=1/2, q_o_=1/2). We have also matched other existing surveys with the Faint Images of the Radio Sky at Twenty Centimeters and NRAO VLA Sky Survey radio catalogs and combined these data so that the optical luminosity-redshift plane is now far better sampled than before. We have fitted a model to the probability of a quasar being radio-loud as a function of absolute magnitude and redshift, and from this model we infer the radio-loud and radio-quiet optical luminosity functions. The radio-loud optical luminosity function is featureless and flatter than the radio-quiet one. It evolves at a marginally slower rate if quasars evolve by density evolution, but the difference in the rate of evolutions of the two different classes is much less than was previously thought.
