- ID:
- ivo://CDS.VizieR/J/A+A/658/A8
- Title:
- Resolved jet of 3C 273 at 150 MHz
- Short Name:
- J/A+A/658/A8
- Date:
- 02 Feb 2022 13:25:19
- Publisher:
- CDS
- Description:
- Since its discovery in 1963, 3C 273 has become one of the most widely studied quasars with investigations spanning the electromagnetic spectrum. While much has therefore been discovered about this historically notable source, its low-frequency emission is far less well understood. Observations in the MHz regime have traditionally lacked the resolution required to explore small-scale structures, such as knots and diffuse jet emission, that are key to understanding the processes that result in the observed emission. Advances in the processing of LOFAR international baseline data have now removed this limitation, providing the opportunity to explore this key area for the first time. In this paper we use the first sub-arcsecond images of 3C 273 at MHz frequencies to investigate the morphology of the compact jet structures and the processes that result in the observed spectrum. We will determine the jet's kinetic power, place constraints on the bulk speed and inclination angle of the jets, and look for evidence of the elusive counterjet at 150MHz. Using the full complement of LOFAR's international stations (German, Poland, France, UK, Sweden), we produce 0.31x0.21 arcsec images of 3C 273 at 150MHz. Using ancillary data at GHz frequencies, we fit free-free absorption (FFA) and synchrotron self-absorption (SSA) models to each region in order to determine their validity in explaining the observed spectra. The images presented display for the first time that robust, high-fidelity imaging of low-declination complex sources is now possible with the LOFAR international baselines. We show that the main small-scale structures of 3C 273 match those seen at higher frequencies, with a tenuous detection of an extension to the outer lobe. We find that FFA and SSA models are able to describe the spectrum of the knots and, while differentiating between model types requires further observations, conclude that absorption is present in the observed emission. We determine the kinetic power of the jet to be in the range of 3.5x10^43^-1.5x10^44^erg/s which agrees with estimates made using higher frequency observations. We derive lower limits for the bulk speed and Lorentz factor of beta>0.55 and Gamma>1.2 respectively. The counter-jet remains undetected at 150MHz, placing a limit on the peak brightness of S_cj_150<40mJy/beam.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+AS/128/153
- Title:
- Revised GB/GB2 sample of radio sources
- Short Name:
- J/A+AS/128/153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The revised sample of 373 extragalactic radio sources brighter than 0.2 Jy at 1.4GHz is presented. These sources, selected from the finding Green Bank surveys, were mapped at 1465 MHz using the VLA at different configurations. The biases introduced into the original GB (Maslowski, 1972AcA....22..227M) and GB2 (Machalski, 1978AcA....28..367M) catalogues by confusion as well as partial resolution by the VLA at its A-configuration, are eliminated. In effect, a number of sources have been excluded, and a few other are included into the revised sample. Now the sample is about 99, 97 and 95 per cent complete for sources with S_1.4_>=0.55Jy, 0.25Jy<=S_1.4_<0.55Jy, and 0.2Jy<=S_1.4_<0.25Jy, respectively. Table 3 gives the compilation of the radio, optical, and X-ray data available for the sample sources.
- ID:
- ivo://CDS.VizieR/VIII/31
- Title:
- Revised source list for the Rees 38-MHz survey
- Short Name:
- VIII/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a revised machine-readable source list for the Rees 38-MHz (or '8C') survey with improved positions and no redundancy. The Rees 38-MHz survey covers an area of about 1 sr north of declination +60 degrees. The angular resolution is 4.5 x 4.5cosec(Dec) arcmin**2 and the limiting flux density over much of the survey area is about 1 Jy. Both of these figures are an improvement by nearly an order of magnitude on previous surveys at this frequency. Users of these data should consult and cite the original survey paper by Rees as primary reference (1990MNRAS.244..233R) with the present publication (1995MNRAS.274..447H) as a supplementary revision. The recommended style of reference is thus : "The revised Rees 38-MHz survey (Rees 1990, catalogue revised Hales et. al 1995)." Note that for interest the source list includes data on some sources at declinations lower than +60 degrees, but that the right ascension coverage is not complete below +60 degrees.
724. RMS survey
- ID:
- ivo://CDS.VizieR/J/MNRAS/452/4029
- Title:
- RMS survey
- Short Name:
- J/MNRAS/452/4029
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of ammonia observations towards 66 massive star forming regions identified by the Red Midcourse Space Experiment Source survey. We have used the Green Bank Telescope and the K-Band Focal Plane Array to map the ammonia (NH_3_) (1,1) and (2,2) inversion emission at a resolution of 30 arcsec in 8 arcmin regions towards the positions of embedded massive star formation. We have identified a total of 115 distinct clumps, approximately two-thirds of which are associated with an embedded massive young stellar object or compact HII region, while the others are classified as quiescent. There is a strong spatial correlation between the peak NH3 emission and the presence of embedded objects. We derive the spatial distribution of the kinetic gas temperatures, line widths, and NH3 column densities from these maps, and by combining these data with dust emission maps we estimate clump masses, H_2_ column densities and ammonia abundances. The clumps have typical masses of ~1000M_{sun}_ and radii ~0.5pc, line widths of ~2km/s and kinetic temperatures of ~16-20K. We find no significant difference between the sizes and masses of the star-forming and quiescent subsamples; however, the distribution maps reveal the presence of temperature and line width gradients peaking towards the centre for the star-forming clumps while the quiescent clumps show relatively uniform temperatures and line widths throughout. Virial analysis suggests that the vast majority of clumps are gravitationally bound and are likely to be in a state of global free fall in the absence of strong magnetic fields. The similarities between the properties of the two subsamples suggest that the quiescent clumps are also likely to form massive stars in the future, and therefore provide an excellent opportunity to study the initial conditions of massive pre-stellar and protostellar clumps.
- ID:
- ivo://CDS.VizieR/J/A+A/501/539
- Title:
- RMS survey. 6cm observations of YSOs
- Short Name:
- J/A+A/501/539
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Red MSX Source (RMS) survey is an ongoing multi-wavelength observational programme designed to return a large, well-selected sample of massive young stellar objects (MYSOs). We have identified ~2000 MYSO candidates located throughout the Galaxy by comparing the colours of MSX and 2MASS point sources to those of known MYSOs. The aim of these follow-up observations is to identify other objects with similar colours such as ultra compact (UC) HII regions, evolved stars and planetary nebulae (PNe) and distinguish between genuine MYSOs and nearby low-mass YSOs. To identify the populations of UCHII regions and PNe within the sample and examine their Galactic distribution. We have conducted high resolution radio continuum observations at 6cm towards 659 MYSO candidates in the northern hemisphere (10{deg}<l<250{deg}) using the Very Large Array (VLA). These observations have a spatial resolution of ~1-2" and typical image rms noise values of ~0.22mJy - sensitive enough to detect a HII region powered by B0.5 star at the far side of the Galaxy. In addition to these targeted observations we present archival data towards a further 315 RMS sources extracted from a previous VLA survey of the inner Galaxy.
- ID:
- ivo://CDS.VizieR/J/A+A/559/A27
- Title:
- RM Synthesis of 33 sources around M31
- Short Name:
- J/A+A/559/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Low-frequency radio continuum observations are best suited to search for radio halos of inclined galaxies. Polarization measurements at low frequencies allow the detection of small Faraday rotation measures caused by regular magnetic fields in galaxies and in the foreground of the Milky Way. The detection of low-frequency polarized emission from a spiral galaxy such as M31 allows us to assess the degree of Faraday depolarization, which can be compared with models of the magnetized interstellar medium.
- ID:
- ivo://CDS.VizieR/J/ApJS/247/53
- Title:
- ROGUE. I. SDSS galaxies with FIRST
- Short Name:
- J/ApJS/247/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the catalog of Radio sources associated with Optical Galaxies and having Unresolved or Extended morphologies I (ROGUE I), consisting of 32616 spectroscopically selected galaxies. It is the largest handmade catalog of this kind, obtained by cross-matching galaxies from the Sloan Digital Sky Survey (SDSS) Data Release 7 and radio sources from both the First Images of Radio Sky at Twenty Centimetre (FIRST) survey and the NRAO Very Large Array Sky Survey, without imposing a limit on the radio flux densities. The catalog provides a visual classification of radio and optical morphologies of galaxies presenting a FIRST core within 3" of the optical position. The radio morphological classification is performed by examining the radio-optical overlays of linear sizes equal to 1Mpc at the source distance, while the 120" image snapshots from the SDSS database are used for optical classification. The results of our search are as follows: (i) single-component unresolved and elongated radio sources constitute the major group in the ROGUE I catalog (~90%), and ~8% exhibit extended morphologies; (ii) samples of 269, 730, and 115 Fanaroff-Riley (FR) type I, II, and hybrid galaxies, respectively, are presented; (iii) we report 55 newly discovered giant/possible giant, 16 double-double, 9 X-shaped, and 25 Z-shaped radio sources; (iv) on the optical front, most galaxies have elliptical morphologies (~62%) while spirals form the second major category (~17%) followed by distorted (~12%) and lenticular (~7%) morphologies; and (v) division between the FR I and the FR II sources in the radio-optical luminosity plane is blurred, in tune with recent studies.
- ID:
- ivo://CDS.VizieR/J/A+AS/122/235
- Title:
- ROSAT active galaxies identifications
- Short Name:
- J/A+AS/122/235
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table 2 gives the 5 GHz high resolution radio source properties for the 1861 Rosat-GreenBank (RGB) sources for which subarcsecond positions and core radio flux densities were obtained. After submission of this paper, we discovered a possible systematic position error in a very small subset of sources. In particular, the sources RGB J0131+005, RGB J0139+178, RGB J0143+129, RGB J0157+235A, RGB J0232+202, RGB J0233+024A, RGB J0243+171, RGB J0256+035, RGB J0303+059, RGB J0308+104, RGB J0312+243A, RGB J0312+242C, and RGB J0314+063 were all observed in our "c" epoch VLA runs and show large systematic offsets with respect to sources found in the NVSS survey. We re-examined these sources and found the position reported in the tables is accurate given our data, but that the noise on these fields before any CLEANing is abnormally high. We thank Dr. Alastair Edge for pointing out this discrepancy. Table 3 gives the 5 GHz radio source properties for the 436 Rosat-Green Bank (RGB) sources for which only low resolution data were obtained. Table 4 gives the 83 Rosat-Green Bank (RGB) sources for which no radio source greater than 5 sigma was observed in the follow-up VLA observations. These catalogs consist of radio- and X-ray-loud AGN selected from a correlation of the 1987 Green Bank radio catalog and the Rosat All-Sky Survey.
- ID:
- ivo://CDS.VizieR/J/A+A/356/445
- Title:
- ROSAT-FIRST AGN correlation
- Short Name:
- J/A+A/356/445
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a correlation of the ROSAT All-Sky Survey with the April 1997 release of the VLA 20cm FIRST (Cat. <VIII/59>) catalogue. We focus our analysis on the 843 X-ray sources which have unique radio counterparts. The majority of these objects (84%) have optical counterparts on the POSS 1 plates. Approximately 30% have been previously classified and we obtain new spectroscopic classifications for 85 sources by comparison with the ongoing FIRST Bright Quasar Survey and 106 additional sources from our own new spectroscopic data. Approximately 51% of the sources are presently classified, and the majority of the unclassified objects are optically faint. The newly classified sources are generally radio weak, exhibiting properties intermediate with previous samples of radio- and X-ray-selected AGN. This also holds for the subsample of 71 BL Lacs which includes many intermediate objects. The 146 quasars show no evidence for a bimodal distribution in their radio-loudness parameter, indicating that the supposed division between radio-quiet and radio-loud AGN may not be real. The X-ray and radio luminosities are correlated over two decades in radio luminosity, spanning the radio-loud and radio-quiet regimes, with radio-quiet quasars showing a linear correlation between the two luminosities. Many of the sources show peculiar or unusual properties which call for more detailed follow-up observations. We also give the X-ray and radio data for the 518 X-ray sources for which more than one radio object is found. Because of the difficulties inherent in identifying optical counterparts to these complex sources, we do not consider these data in the current analysis.
- ID:
- ivo://CDS.VizieR/J/A+AS/122/201
- Title:
- ROSAT Galactic Plane Survey observations
- Short Name:
- J/A+AS/122/201
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The analysis of the part of the ROSAT all-sky survey covering the galactic plane is the scope of a dedicated project called the ROSAT Galactic Plane Survey. In order to statistically understand the nature of the =~14000 sources discovered by ROSAT at |b|<=20{deg}, a number of sample areas have been chosen for follow-up optical identification. In this paper we present the X-ray and optical material gathered in a region located in the Cygnus constellation, centered at l=90{deg}, b=0{deg} and covering an area of 64.5deg^2^. A total of 95 and 128 sources are detected with a maximum likelihood larger than 10 and 8 respectively. With a typical survey exposure time of the order of 700 to 900 s the flux completeness level is =~0.02cts/s corresponding to =~2x10^-13^erg/cm^2^/s. The position of the sample area allows to investigate the soft X-ray content of a rather typical region of the galactic plane. In this paper we describe the details of the observational procedures and data reduction. For each ROSAT source we list the main X-ray characteristics together with those of the proposed optical identification. When appropriate, we also show optical spectra and finding charts. The full analysis and discussion of these data are presented in a companion paper (Motch et al. 1997, Cat. <J/A+A/318/111>).
