Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new user30 GHz flux density measurements of the Caltech-Jodrell flat-spectrum sources with OCRA-p
145
0
0.0
(
0
)
Authors
S. R. Lowe
Ask ChatGPT about the research
No Arabic abstract
To measure the 30-GHz flux densities of the 293 sources in the Caltech-Jodrell Bank flat-spectrum (CJF) sample. The measurements are part of an ongoing programme to measure the spectral energy distributions of flat spectrum radio sources and to correlate them with the milliarcsecond structures from VLBI and other measured astrophysical properties. The 30-GHz data were obtained with a twin-beam differencing radiometer system mounted on the Torun 32-m telescope. The system has an angular resolution of 1.2 arcmin. Together with radio spectral data obtained from the literature, the 30-GHz data have enabled us to identify 42 of the CJF sources as Giga-hertz Peaked Spectrum (GPS) sources. Seventeen percent of the sources have rising spectra (alpha > 0) between 5 and 30 GHz.
rate research
Read More
We present VLBA observations and a statistical analysis of 5 GHz VLBI polarimetry data from 177 sources in the Caltech-Jodrell Bank flat-spectrum (CJF) survey. The CJF survey, a complete, flux-density-limited sample of 293 extragalactic radio sources, gives us the unique opportunity to compare a broad range of source properties for quasars, galaxies and BL Lacertae objects. We focus primarily on jet properties, specifically the correlation between the jet axis angle and the polarization angle in the core and jet. A strong correlation is found for the electric vector polarization angle in the cores of quasars to be perpendicular to the jet axis. Contrary to previous claims, no correlation is found between the jet polarization angle and the jet axis in either quasars or BL Lac objects. With this large, homogeneous sample we are also able to investigate cosmological issues and AGN evolution.
We report the results of a survey of 442 planetary nebulae at 30 GHz. The purpose of the survey is to develop a list of planetary nebulae as calibration sources which could be used for high frequency calibration in future. For 41 PNe with sufficient data, we test the emission mechanisms in order to evaluate whether or not spinning dust plays an important role in their spectra at 30 GHz. The 30-GHz data were obtained with a twin-beam differencing radiometer, OCRA-p, which is in operation on the Torun 32-m telescope. Sources were scanned both in right ascension and declination. We estimated flux densities at 30 GHz using a free-free emission model and compared it with our data. The primary result is a catalogue containing the flux densities of 93 planetary nebulae at 30 GHz. Sources with sufficient data were compared with a spectral model of free-free emission. The model shows that free-free emission can generally explain the observed flux densities at 30 GHz thus no other emission mechanism is needed to account for the high frequency spectra.
Context: This is the second of a series of papers presenting VLBI observations of the 293 Caltech-Jodrell Bank Flat-Spectrum (hereafter CJF) sources and their analysis. Aims: To obtain a consistent motion dataset large enough to allow the systematic properties of the population to be studied. Methods: We present the detailed kinematic analysis of the complete flux-density limited CJF survey. We computed 2-D kinematic models based on the optimal model-fitting parameters of multi-epoch VLBA observations. This allows us to calculate not only radial, but also orthogonal motions, and thus to study curvature and acceleration. Statistical tests of the motions measured and their reliability have been performed. A correlation analysis between the derived apparent motions, luminosities, spectral indices, and core dominance and the resulting consequences is described. Results: With at least one velocity in each of 237 sources, this sample is much larger than any available before and allows a meaningful statistical investigation of apparent motions and any possible correlations with other parameters in AGN jets. Conclusions: This AGN survey provides the basis for any statistical analysis of jet and jet-component properties.
The Caltech-Jodrell Bank VLBI surveys of bright extragalactic radio sources north of declination 35 deg were carried out between 1990 and 1995 using the Mark-II system, achieving images with a resolution of about 1 mas at 5 GHz. The CJ1 survey (together with the older `PR survey) includes 200 objects with 5 GHz flux density greater than 0.7 Jy; the CJ2 survey includes 193 flat-spectrum sources with 5 GHz flux density greater than 0.35 Jy; and we have defined a complete flux-density limited sample, CJF, of 293 flat-spectrum sources stronger than 0.35 Jy. We summarize the definition of the samples and the VLBI, VLA, MERLIN, and optical observations, and present some highlights of the astrophysical results. These include: (1) superluminal motion and cosmology; (2) morphology and evolution of the `compact symmetric objects (CSOs); (3) two-sided motion in some CSOs; (4) the angular-size - redshift diagram; (5) misalignment of parsec-scale and kiloparsec-scale jets.
We report a Giant Metrewave Radio Telescope (GMRT) survey for associated HI 21-cm absorption from 50 active galactic nuclei (AGNs), at $z approx 0.04 - 3.01$, selected from the Caltech-Jodrell Bank Flat-spectrum (CJF) sample. Clean spectra were obtained towards 40 sources, yielding two new absorption detections, at $z = 0.229$ towards TXS 0003+380 and $z = 0.333$ towards TXS 1456+375, besides confirming an earlier detection, at $z = 1.277$ towards TXS 1543+480. There are 92 CJF sources, at $0.01 lesssim z lesssim 3.6$, with searches for associated HI 21-cm absorption, by far the largest uniformly-selected AGN sample with searches for such absorption. We find weak ($approx 2sigma$) evidence for a lower detection rate of HI 21-cm absorption at high redshifts, with detection rates of $28^{+10}_{-8}$% and $7^{+6}_{-4}$% in the low-$z$ ($z < z_{rm med}$) and high-$z$ ($z > z_{rm med}$) sub-samples, respectively. We use two-sample tests to find that the strength of the HI 21-cm absorption in the AGNs of our sample depends on both redshift and AGN luminosity, with a lower detection rate and weaker absorption at high redshifts and high ultraviolet/radio AGN luminosities. Unfortunately, the luminosity bias in our sample, with high-luminosity AGNs arising at high redshifts, implies that it is not currently possible to identify whether redshift evolution or AGN luminosity is the primary cause of the weaker absorption in high-$z$, high-luminosity AGNs. We find that the strength of HI 21-cm absorption does not depend on AGN colour, suggesting that dust extinction is not the main cause of reddening in the CJF sample.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
