A sample of giant radio sources from the NVGRC catalog

TL;DR

This work systematically re-evaluates giant radio sources in the NVGRC catalog by visually inspecting 370 candidates and their surroundings, using multiwavelength data to confirm radio morphology and identify host galaxies. It derives redshift estimates via empirical $m_r$–$z$ relations, quantifies radio loudness and rest-frame 1.4 GHz luminosities, and classifies host types, finding FRII domination and substantial environmental influence on GRSs. The study identifies 197 GRSs (including 125 new identifications), reveals 20 additional GRSs outside the NVGRC catalog, and shows that about 70% of GRS hosts reside in relatively dense environments, with a detection efficiency of around 30% for the catalog's original algorithm. These results illuminate selection effects, host demographics, and environmental interactions shaping the observed GRS population, contributing to understanding giant radio source evolution and IGM conditions.

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.

Figures (3)

• Figure 1: Scatter plots illustrating the correlation between de-reddened apparent $r$-band magnitudes and spectroscopic redshifts: (a) shows the distribution for 71 GRGs with known spectroscopic redshifts, along with the linear regression fit (dotted line). (b) displays the same correlation for 23 GRQs with spectroscopic redshifts. In both panels, the X-axis (redshift) is plotted on a logarithmic scale.
• Figure 2: Histograms and their Gaussian fits illustrating the distributions of two key parameters: (a) distribution of radio loudness indices; (b) distribution of radio luminosities at 1.4 GHz, expressed in W Hz$^{-1}$. In both panels, the data are separated by host type: galaxies are shown in grey; quasars and IR-excess galaxies are shown in red.
• Figure 3: The histograms and their Gaussian fits illustrate the distributions of de-reddened $r$-band magnitudes (panel a) and logarithmic redshifts (panel b) for host galaxies of 140 GRSs with neighbors (gray) and 57 GRSs without neighbors (red).