arXiv subjects

Olga Zhelenkova

Publications and source records attributed to Olga Zhelenkova.

4 recordsLinked to original sources

arXiv2025

New Radio Data on Sources of the Big Trio Program for Searching for Distant Radio Galaxies

Radio sources with steep and ultra-steep spectra, identified through a series of surveys of the Cold experiment using the RATAN-600 radio telescope, formed the basis of the Big Trio program aimed at discovering distant radio galaxies. With the advent of new radio, optical, and infrared sky surveys, it became possible to carry out additional studies of the 113 radio sources observed within this program using the 6-meter BTA telescope. Morphological features indicative of the evolutionary state of radio sources revealed that 9 objects exhibit signs of restarted activity, 12 can be classified as young, and 2 as dying. Based on their WAT/NAT and WRS morphologies, 24 sources are likely located within galaxy groups or clusters, or show evidence of jet reorientation. Additionally, four objects in the sample represent pairs of radio sources whose host galaxies are separated by only a few tens of kiloparsecs. Continuum spectra were constructed, and variability indices were calculated. A high proportion of sources with a variability index ($V>3$) is attributed to significant differences in angular resolution between the TXS and VCSS surveys, as well as to underestimated flux densities for certain double-lobed sources. A comparison of spectral indices derived from older and newer data indicates a decrease in the number of steep-spectrum sources in the sample. This reduction is most likely due to improved characterization of the low-frequency portion of the continuum spectra following the incorporation of GLEAM data. However, for some radio sources, the observed spectral changes may reflect internal evolution, that observed in a shift of the spectral peak or a roll-off in the radio spectrum towards lower frequencies, as evidenced by flux density measurements from various catalogues covering a period of up to forty years.

astro-ph.CO↗

arXiv2025

A sample of giant radio sources from the NVGRC catalog

We present the results of a search for megaparsec-scale sources in the NVGRC catalog of candidates of giant radio source (GRS) based on the NVSS sky survey. We visually inspected 370 NVGRC sources, as well as radio sources falling within a neighborhood of about one square degree around the target object. In the studied sample, 48% of objects were classified as giant radio sources, 14% as sources with a projected linear size of less than 0.72 Mpc, and 38\% as physically unrelated objects combined by the recognition algorithm into one radio source. We identified 197 gaints, of which 72 radio sources are known GRGs or GRQs, and 125 sources were identified by us as GRS for the first time. Comparing the proportion of FRI giants in four redshift bins, we found that for z<0.05, the proportions of FRI and FRII sources were approximately equal, but already at z>0.15 the proportion of FRI giants decreases sharply. The predominance of FRII giants in the GRS lists is most likely due to observational selection due to the sensitivity limit of existing radio surveys. Comparing the NVSS and VLASS cutouts, we found that 33% of sources can be classified as fadded. 25% of the sources show a restart of the radio source phase. 38% of the sources have deformed radio lobes. Our GRS sample includes 74% of galaxies, 15% of IR-excess galaxies, which, according to the WISE photometric data, can be attributed to quasars, and 11% of quasars. When visually examining the optical survey cutouts, we noted the presence of close neighbors for the hosts and/or their belonging to known groups or clusters of galaxies. Close neighbors at a distance of less than 50 kpc were found for 39% of radio sources, and 28% of sources are part of groups or clusters of galaxies. Thus, about 70% of gaints are in a fairly dense environment, and this proportion may be higher.

astro-ph.GA↗

arXiv2025

High Frequency Peak Radio Sources from the AT20G Catalogue and Their Radio Spectra

A sample of high-frequency peaker (HFP) candidates was formed from the AT20G catalog radio sources with spectral indices of the optically thick emission region $α_{below}$ exceeding +0.5. A study of the spectral properties of the sources in the sample, which included 269 radio sources, was performed. The spectra of the sources were constructed and the spectral indices below $α_{below}$ and above the peak $α_{above}$, the peak frequency $ν_{obs}$, the flux density at the peak frequency $S_{peak}$, and the peak half-width in the radio spectrum were determined. Analysis of the spectra showed that the sample is fairly homogeneous and consists of HFPs with $ν_{obs}>5$ GHz. Most sources (67%) do not have data at frequencies below 0.8 GHz. 187 sources have ultra-inverted spectra ($α_{below}>$+0.7), which is 3.2% of all sources in the AT20G catalog and 70% of radio sources in our sample. Optical identification of radio sources in the sample showed that 70% of the hosts are quasars. The sample consists of compact objects with radio luminosity at 20 GHz in the range of $10^{23}$-$10^{30}$ W/Hz, angular sizes of emitting regions of radio sources are 0.002-0.25 mas, projected linear sizes are from 0.2 to 30 pc. The dependence of the peak frequencies of radio sources on their angular sizes is in good agreement with that previously discovered for CSS and GPS sources.

astro-ph.CO↗

arXiv2018

Study of RCR Catalogue Radio Source Integral Spectra

We present the characteristics of the sources found on the averaged scans of the "Cold" experiment 1980--1999 surveys in the right-ascension interval $2^h$< RA <$7^h$. Thereby, a refinement of the parameters of the RC catalog sources (RATAN Cold) for this interval is complete. To date, the RCR catalog (RATAN Cold Refined) covers the right-ascension interval $2^h$< RA <$17^h$ and includes 830 sources. The spectra are built for them with the use of new data in the range of 70--230 MHz. The dependence between the spectral indices $α_{0.5}$, $α_{3.94}$ and integral flux density at the frequencies of 74 and 150 MHz, at 1.4, 3.94 and 4.85 GHz is discussed. We found that at 150 MHz in most sources the spectral index $α_{0.5}$ gets steeper with increasing flux density. In general, the sources with flat spectra are weaker in terms of flux density than the sources with steep spectra, which especially differs at 150 MHz. We believe that this is due to the brightness of their extended components, which can be determined by the type of accretion and the neighborhood of the source.

astro-ph.GA↗