Fundamental differences in the X-ray accretion properties of low and high-excitation radio galaxies
Abstract
We characterise the accretion rate properties of radio-detected AGN by combining deep radio and X-ray observations of the Boötes field. We used deep international LOFAR telescope observations to identify 2840 radio-AGN across 0.3 < z ≤ 2, divided into samples that are complete in radio luminosity. We further split this sample into four different classes: radio-quiet AGN (RQ-AGN), high-excitation radio galaxies (HERGs), and low-excitation radio galaxies (LERGs) hosted by star-forming (SF-LERGs) and quiescent galaxies (Q-LERGs). Through performing X-ray stacking, we determined the average X-ray luminosities, LX, 2−10 keV and average specific X-ray luminosities, λsLX (X-ray luminosity scaled by the stellar mass; a proxy for the accretion rate). We studied how these X-ray properties depend on radio luminosity, stellar mass, and redshift for each of the four AGN classes. We found that the LERGs, regardless of their star-formation activity, show significantly lower LX, 2−10 keV and λsLX than both HERGs and RQ-AGN across all redshifts. The average X-ray luminosities for the HERGs, RQ-AGN, and SF-LERGs typically increase with redshift, which may be associated with the increased cold gas fractions at earlier times, resulting in more enhanced black hole accretion. The average X-ray luminosities show weak-to-no correlation with radio luminosity at a given redshift, suggesting that the physical processes producing the X-ray and radio emission may not be coupled on spatial and/or temporal scales.
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BibTeX
@misc{kondapally2026fundamental,
title = {{Fundamental differences in the X-ray accretion properties of low and high-excitation radio galaxies}},
author = {R. Kondapally and T. Holc and J. Aird and K. J. Duncan and P. N. Best and D. M. Alexander and S. Das and L. K. Morabito and S. Shenoy and D. J. B. Smith},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.04130},
eprint = {2609.04130},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.04130},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Fundamental differences in the X-ray accretion properties of low and high-excitation radio galaxies
AU - R. Kondapally
AU - T. Holc
AU - J. Aird
AU - K. J. Duncan
AU - P. N. Best
AU - D. M. Alexander
AU - S. Das
AU - L. K. Morabito
AU - S. Shenoy
AU - D. J. B. Smith
PY - 2026
DA - 2026/09/27
PB - arXiv
DO - 10.48550/arxiv.2609.04130
UR - https://arxiv.org/abs/2609.04130
AB - We characterise the accretion rate properties of radio-detected AGN by combining deep radio and X-ray observations of the Boötes field. We used deep international LOFAR telescope observations to identify 2840 radio-AGN across 0.3 < z ≤ 2, divided into samples that are complete in radio luminosity. We further split this sample into four different classes: radio-quiet AGN (RQ-AGN), high-excitation radio galaxies (HERGs), and low-excitation radio galaxies (LERGs) hosted by star-forming (SF-LERGs) and quiescent galaxies (Q-LERGs). Through performing X-ray stacking, we determined the average X-ray luminosities, L_X, 2−10 keV and average specific X-ray luminosities, λ_sL_X (X-ray luminosity scaled by the stellar mass; a proxy for the accretion rate). We studied how these X-ray properties depend on radio luminosity, stellar mass, and redshift for each of the four AGN classes. We found that the LERGs, regardless of their star-formation activity, show significantly lower L_X, 2−10 keV and λ_sL_X than both HERGs and RQ-AGN across all redshifts. The average X-ray luminosities for the HERGs, RQ-AGN, and SF-LERGs typically increase with redshift, which may be associated with the increased cold gas fractions at earlier times, resulting in more enhanced black hole accretion. The average X-ray luminosities show weak-to-no correlation with radio luminosity at a given redshift, suggesting that the physical processes producing the X-ray and radio emission may not be coupled on spatial and/or temporal scales.
ER -