Active galactic nuclei (AGNs) can be divided into two major classes, namely radio-loud and radio-quiet AGNs. A small subset of the radio-loud AGNs is called blazars, which are believed to be unified with Fanaroff-Riley type I and type II (FRI&II) radio galaxies. Following our previous work, we present a latest sample of 966 sources with measured radio flux densities of the core and extended components. The sample includes 83 BL Lacs, 473 flat spectrum radio quasars, 101 Seyferts, 245 galaxies, 52 FRIs&IIs and 12 unidentified sources. We then calculate the radio core-dominance parameters and spectral indices and study their relationship. Our analysis shows that the core-dominance parameters and spectral indices are quite different for different types of sources. We also confirm that the correlation between core-dominance parameter and radio spectral index extends over all the sources in a large sample presented.
We study the synchrotron component of the spectral energy distribution on the sample of 877 blazars using ASDC SED Builder Tool with available broadband data from the literature. Our sample includes 423 flat-spectrum radio sources (FSRQs), 361 BL Lac objects and candidates, and 93 blazars of uncertain type. We have made an estimation of the synchrotron peak frequency for the 875 objects and further classified them as high, intermediate and low synchrotron peaked sources (HSPs/ISPs/LSPs). For each source NVSS name (RA (HHMMSS) and DEC (DDMMSS) for the J2000.0 epoch), alias, redshift, R band magnitude, synchrotron peak frequency, correlation coefficient, flux density at 4.8GHz, SED class, blazar type and selection method are presented.
We present a large sample of 501 radio-selected BL Lac candidates from a combination of Sloan Digital Sky Survey (SDSS) Data Release 5 optical spectroscopy and the Faint Images of the Radio Sky at 20cm (FIRST) radio survey; this is one of the largest BL Lac samples yet assembled, and each object emerges with homogeneous data coverage. Each candidate is detected in the radio from FIRST and confirmed in SDSS optical spectroscopy to have (1) no emission feature with measured rest-equivalent width larger than 5{AA} and (2) no measured CaII H/K depression larger than 40%. We subdivide our sample into 426 higher-confidence candidates and 75 lower-confidence candidates.
We present the radio properties of optically selected quasars with z>=3. The complete sample consists of 102 quasars with a flux density level S_1.4_>=100mJy in a declination range -35{deg}<=Dec.<=+49{deg}. The observations were obtained in 2017-2020 using the radio telescope RATAN-600. We measured flux densities at six frequencies 1.2, 2.3, 4.7, 8.2, 11.2, and 22GHz quasi-simultaneously with uncertainties of 9-31 per cent. The detection rate is 100, 89, and 46 per cent at 4.7, 11.2, and 22GHz, respectively. We have analysed the averaged radio spectra of the quasars based on the RATAN and literature data. We classify 46 per cent of radio spectra as peaked-spectrum, 24 per cent as flat, and none as ultra-steep spectra ({alpha}<=-1.1). The multifrequency data reveal that a peaked spectral shape (PS) is a common feature for bright high-redshift quasars. This indicates the dominance of bright compact core emission and the insignificant contribution of extended optically thin kpc-scale components in observed radio spectra. Using these new radio data, the radio loudness log R was estimated for 71 objects with a median value of 3.5, showing that the majority of the quasars are highly radio-loud with log R>2.5. We have not found any significant correlation between z and {alpha}. Several new megahertz- peaked spectrum (MPS) and gigahertz- peaked spectrum (GPS) candidates are suggested. Further studies of their variability and additional low-frequency observations are needed to classify them precisely.
The results of a comprehensive analysis of continuous radio spectra of a sample of Gigahertz-Peaked Spectrum (GPS) sources are reported. The sources are selected from a flux-density-complete sample (S more or equal 200mJy at 4.8 or 5GHz) using multifrequency measurements of the RATAN-600 radio telescope and data from the CATS astrophysical catalogs support system. The analysis revealed a very small number (1-2%) of "classical" GPS objects, which is significantly less than the expected fraction of 10%. GPS galaxies are found to have narrower and steeper radio spectra than quasars. The low-frequency part of the spectrum is seen to become steeper with increasing redshift. Galaxies and quasars at the same z have comparable angular sizes, whereas their luminosities may differ by one order of magnitude. At large redshifts there is a deficit of objects with low (several GHz) peak frequencies. The number of GPS galaxies decreases sharply with redshift, and most of them are found at z between 0.01 and 1.81. GPS quasars are found at large redshifts, from 0.11 to 3.99. A quarter of the sample consists of blazars whose spectra may temporarily have a convex shape when the object is in active state.
We started a follow-up investigation of the "Deep X-ray Radio Blazar Survey" objects with declination >-10{deg} to better understand the blazar phenomenon. We undertook a survey with the European Very Long Baseline Interferometry Network at 5GHz to make the first images of a complete sample of weak blazars, aiming at a follow-up comparison between high- and low-power samples of blazars. We observed 87 sources with the EVN at 5GHz during the period October 2009 to May 2013. The observations were correlated at the Max-Planck-Institut fuer Radioastronomie and at the Joint Institute for VLBI in Europe. The correlator output was analysed using both the AIPS and DIFMAP software packages. All of the sources observed were detected. Point-like sources are found in 39 cases on a milli-arcsecond scale, and 48 show core-jet structure. The total flux density distribution at 5GHz has a median value <S>=44^+23^_-10_mJy. A total flux density <=150mJy is observed in 68 out of 87 sources. Their brightness temperature T_b_ ranges between 10^7^K and 10^12^K. According to the spectral indices previously obtained with multi-frequency observations, 58 sources show a flat spectral index, and 29 sources show a steep spectrum or a spectrum peaking at a frequency around 1-2GHz. Adding to the DXRBS objects we observed those already observed with ATCA in the Southern sky, we found that 14 blazars and a Steep Spectrum Radio Quasars, are associated to {gamma}-ray emitters. We found that 56 sources can be considered blazars. We also detected 2 flat spectrum narrow line radio galaxies. About 50% of the blazars associated to a {gamma}-ray object are BLLacs, confirming that they are more likely detected among blazars {gamma}-emitters. We confirm the correlation found between the source core flux density and the {gamma}-ray photon fluxes down to fainter flux densities. We also found that weak blazars are also weaker {gamma}-ray emitters compared to bright blazars. Twenty-two sources are SSRQs or Compact Steep-spectrum Sources, and 7 are GigaHz Peaked Sources. The available X-ray ROSAT observations allow us to suggest that CSS and GPS quasars are not obscured by large column of cold gas surrounding the nuclei. We did not find any significant difference in X-ray luminosity between CSS and GPS quasars.
The paper analyzes a lightning storm on Saturn that raged for 7.5 months at a planetocentric latitude of 35 deg. south from 27 November 2007 until 15 July 2008. The storm system produced about 277000 lightning events termed SEDs (for Saturn Electrostatic Discharges) that were detected by the Cassini RPWS (Radio and Plasma Wave Science) instrument. The SEDs are organized in episodes, lasting typically for half a Saturn rotation. SEDs can be detected when the observer Cassini is within the radio horizon (usually when the storm and Cassini are on the same side of the planet), and they are not detected when Cassini is beyond the radio horizon (Cassini and the storm on opposite sides). Saturn's atmospheric storm features have a much higher angular velocity than Cassini around Saturn, so that one SED episode is typically related to one Saturn rotation. The SEDs from this storm, lasting from the end of Nov. 2007 until mid-July 2008 (termed storm F), occurred in 439 SED episodes.
A compilation of 21 cm line spectral parameters specifically designed for application of the Tully-Fisher (TF) distance method is presented for 1201 spiral galaxies, primarily field Sc galaxies, for which optical I-band photometric imaging is also available. New H I line spectra have been obtained for 881 galaxies. For an additional 320 galaxies, spectra available in a digital archive have been reexamined to allow application of a single algorithm for the derivation of the TF velocity width parameter. A velocity width algorithm is used that provides a robust measurement of rotational velocity and permits an estimate of the error on that width taking into account the effects of instrumental broadening and signal-to-noise. The digital data are used to establish regression relations between measurements of velocity widths using other common prescriptions so that comparable widths can be derived through conversion of values published in the literature. The uniform H I line widths presented here provide the rotational velocity measurement to be used in deriving peculiar velocities via the TF method.
The fraction of compact active galactic nuclei (AGNs) that exhibit interstellar scintillation (ISS) at radio wavelengths, as well as their scintillation amplitudes, have been found to decrease significantly for sources at redshifts z>~2. This can be attributed to an increase in the angular sizes of the {mu}as-scale cores or a decrease in the flux densities of the compact {mu}as cores relative to that of the mas-scale components with increasing redshift, possibly arising from (1) the space-time curvature of an expanding universe, (2) AGN evolution, (3) source selection biases, (4) scatter broadening in the ionized intergalactic medium (IGM) and intervening galaxies, or (5) gravitational lensing. We examine the frequency scaling of this redshift dependence of ISS to determine its origin, using data from a dual-frequency survey of ISS of 128 sources at 0<~z<~4. We present a novel method of analysis which accounts for selection effects in the source sample.
We present multiwavelength identifications for the counterparts of 1088 submillimeter sources detected at 850{mu}m in the SCUBA-2 Cosmology Legacy Survey (S2CLS) study of the UKIRT Infrared Deep Sky Survey-Ultra-Deep Survey (UDS) field. By utilizing an Atacama Large Millimeter Array (ALMA) pilot study on a subset of our bright SCUBA-2 sample as a training set, along with the deep optical-near-infrared (OIR) data available in this field, we develop a novel technique, Optical-IR Triple Color (OIRTC), using z-K, K-[3.6], [3.6]-[4.5] colors to select the candidate submillimeter galaxy (SMG) counterparts. By combining radio identification and the OIRTC technique, we find counterpart candidates for 80% of the Class = 1 >=4{sigma} SCUBA-2 sample, defined as those that are covered by both radio and OIR imaging and the base sample for our scientific analyses. Based on the ALMA training set, we expect the accuracy of these identifications to be 82%+/-20%, with a completeness of 69%+/-16%, essentially as accurate as the traditional p-value technique but with higher completeness. We find that the fraction of SCUBA-2 sources having candidate counterparts is lower for fainter 850{mu}m sources, and we argue that for follow-up observations sensitive to SMGs with S_850_>~1mJy across the whole ALMA beam, the fraction with multiple counterparts is likely to be >40% for SCUBA-2 sources at S_850_>~4mJy. We find that the photometric redshift distribution for the SMGs is well fit by a lognormal distribution, with a median redshift of z=2.3+/-0.1. After accounting for the sources without any radio and/or OIRTC counterpart, we estimate the median redshift to be z=2.6+/-0.1 for SMGs with S_850_>1mJy. We also use this new large sample to study the clustering of SMGs and the far-infrared properties of the unidentified submillimeter sources by stacking their Herschel SPIRE far-infrared emission.
