Environments of high and low excitation radio galaxies

¹ Instituto de Ciencias Astronómicas, de la Tierra y del Espacio (ICATE) Av. Nazario Benavidez 8175 Oeste Chimbas San Juan, Argentina
² Universidad Nacional de San Juan San Juan, Argentina
³ Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) Buenos Aires, Argentina
⁴ Facultad de Ciencias Exactas, Físicas y Naturales (FCEFYN-UNSJ), Universidad Nacional de San Juan Av. José Ignacio de la Roza Oeste 590 San Juan, Argentina

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 3 March 2025
Accepted: 24 October 2025

Abstract

Aims. Active galactic nuclei (AGNs) play a crucial role in shaping galaxy evolution through their feedback mechanisms. Low-excitation radio galaxies (LERGs) and high-excitation radio galaxies (HERGs) are thought to exhibit distinct feedback modes, and might potentially influence their surrounding environment in different ways.

Methods. This study aims to investigate the clustering properties and environmental differences of LERG and HERG. We analyse properties of galaxies in the vicinity of both AGN types to identify environmental trends.

Results. We utilized extensive datasets from the Sloan Digital Sky Survey (SDSS), the NRAO VLA Sky Survey (NVSS), and Faint Images of the Radio Sky at Twenty-Centimeters (FIRST). Clustering analyses were performed using the projected cross-correlation function between AGNs and inactive galaxies and then compared against matched control samples. The galaxy populations around each AGN class are statistically compared on the basis of their stellar mass, colour, and luminosity.

Conclusions. The LERGs and HERGs inhabit distinctly different environments. The LERGs are preferentially found in denser regions and are surrounded by redder, more massive, and brighter galaxies compared to the HERGs, even after matching host properties and radio power. Except at low masses, LERGs are commonly found residing in more clustered environments than inactive galaxies with matched physical properties of their hosts, while the opposite effect is observed in HERGs. We also identify trends in the colours of neighbouring galaxies, suggesting environmental influences beyond the host galaxy. These results highlight the strong interplay between the environment and radio AGN activity and support previous findings that link these effects to different fuelling mechanisms and gas supply.