Accretion indicators for the 37 brightest radio sources in the Subaru/XMM-Newton Deep Field

TL;DR

This study investigates the accretion activity of the brightest radio sources in the SXDF using mid-IR data, revealing a correlation between radio luminosity and mid-IR excess indicative of nuclear activity.

Contribution

It provides new insights into the relationship between radio luminosity, mid-IR emission, and accretion states in bright radio sources, especially across the FRI/FRII break.

Findings

Most sources above the FRI/FRII break show mid-IR excess linked to accretion.

Mid-IR excess fraction drops below the FRI/FRII break.

Correlation between mid-IR and blue excess supports the torus scattering model.

Abstract

We study the 37 brightest radio sources in the Subaru/XMM-Newton Deep Field (SXDF). Using mid-IR (Spitzer MIPS 24 micron) data we expect to trace nuclear accretion activity, even if it is obscured at optical wavelengths, unless the obscuring column is extreme. Our results suggest that above the `FRI/FRII' radio luminosity break most of the radio sources are associated with objects that have excess mid-IR emission, only some of which are broad-line objects, although there is one clear low-accretion-rate FRI. The fraction of objects with mid-IR excess drops dramatically below the FRI/FRII break, although there exists at least one high-accretion-rate QSO. Investigation of mid-IR and blue excesses shows that they are correlated as predicted by a model in which a torus of dust absorbs ~30% of the light, and the dust above and below the torus scatters >~1% of the light.