Accretion Properties of High- and Low-Excitation Young Radio Galaxies

TL;DR

This study examines the connection between accretion rates, emission-line properties, and radio features in young radio galaxies, revealing that high-excitation galaxies have significantly higher accretion rates than low-excitation ones.

Contribution

It provides new insights into the accretion properties of young radio galaxies by comparing high- and low-excitation types using emission-line and radio data.

Findings

HEGs have ~1 dex higher Eddington ratios than LEGs.

Emission line luminosities correlate with radio core luminosity.

Accretion and radio activity are fundamentally connected.

Abstract

Young radio galaxies (YRGs) provide an ideal laboratory to explore the connection between accretion disk and radio jet thanks to their recent jet formation. We investigate the relationship between the emission-line properties, the black hole accretion rate, and the radio properties using a sample of 34 low-redshift (z < 0.4) YRGs. We classify YRGs as high-excitation galaxies (HEGs) and low-excitation galaxies (LEGs) based on the flux ratio of high-ionization to low-ionization emission lines. Using the H{\alpha} luminosities as a proxy of accretion rate, we find that HEGs in YRGs have \sim1 dex higher Eddington ratios than LEGs in YRGs, suggesting that HEGs have higher mass accretion rate or higher radiative efficiency than LEGs. In agreement with previous studies, we find that the luminosities of emission lines, in particular H{\alpha}, are correlated with radio core luminosity, suggesting that accretion and young radio activities are fundamentally connected.