Origin of long-wavelength emission in radio-quiet quasars

Determine the physical origin of the long-wavelength (millimeter to radio) emission in radio-quiet quasars, distinguishing among proposed mechanisms such as coronal synchrotron emission, dust emission from the torus, star-formation-related processes, and low-power jets, to resolve the long-standing uncertainty about the dominant contributor.

Background

Understanding the source of long-wavelength emission in radio-quiet quasars is central to modeling active galactic nuclei (AGN) and their environments. Competing hypotheses include compact coronal synchrotron emission, thermal dust from the torus, star-formation-related free-free/synchrotron, and weak jets. Direct spatial resolution at the required sub-0.01 pc scales is beyond current facilities, motivating indirect probes such as microlensing.

This paper reports evidence favoring coronal emission in RXJ1131-1231 via microlensing-based size constraints and a mm–X-ray luminosity relation consistent with coronal expectations, but the broader population-level question remains open.

References

One of the key open questions is the origin of long-wavelength emission from radio-quiet quasars.

— Detection of millimeter-wave coronal emission in a quasar at cosmological distance using microlensing  (2503.13313 - Rybak et al., 17 Mar 2025) in Abstract (page 1)

While the correlation holds across a wide range of galaxy properties, its evolution with redshift remains uncertain.

— An ALMA Band 7 survey of SDSS/Herschel quasars in Stripe 82: II. The nature of FIR-bright quasars  (2609.16951 - Hatziminaoglou et al., 15 Sep 2026) in Section 1, Introduction

LRDs, usually detected in the near-IR in the early universe, so far have been radio-undetected for unknown reasons, possibly influenced by their large distances and the limitations in our observational capabilities.

— A Radio-Bright Local Little Red Dot Analog  (2608.16200 - Rodriguez et al., 17 Aug 2026) in Section 1, Introduction