A sample of giant radio sources from the NVGRC catalog

TL;DR

This study identifies and characterizes giant radio sources from the NVGRC catalog using visual inspection and compares their properties across redshifts, revealing insights into their morphology, environment, and evolutionary phases.

Contribution

The paper presents a new sample of 125 previously unidentified giant radio sources and analyzes their morphological and environmental properties in detail.

Findings

48% of inspected sources are giant radio sources

33% of sources show fading features

25% exhibit signs of restarted activity

Abstract

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.