The rest ultraviolet to infrared spectral energy distributions of heavily reddened quasars are "V-shaped" and hot-dust poor

TL;DR

This study analyzes the spectral energy distributions of heavily reddened quasars, revealing common UV-excess features, hot dust deficits, and implications for AGN feedback and dust ejection phases.

Contribution

It provides the first detailed SED analysis of heavily reddened quasars across UV to infrared, highlighting their hot dust deficiency and scattering properties, and linking them to the LRD population.

Findings

Most HRQs show UV-excess relative to reddened continuum.

HRQs exhibit a deficit of hot dust compared to blue quasars.

Weak correlation between UV scattering fraction and hot dust emission.

Abstract

We present a rest-ultraviolet to infrared spectral energy distribution (SED) analysis of 63 heavily reddened quasars (HRQs) at redshifts z=0.7-2.7 and with dust extinctions E(B-V)=0.4-1.8. Our analysis demonstrates that SEDs with red optical and blue UV continua are very common in HRQs, with more than 82 per cent of the sample showing a UV-excess relative to the reddened quasar continuum. We model the SEDs by combining a reddened quasar and an unobscured scattered light component, though contributions from a star-forming host galaxy cannot be ruled out. The average scattering fraction is small (0.3 per cent). Higher scattering fractions are ruled out by the (i-K)=2.5 colour-cut used to select HRQs which pre-dates the discovery of the JWST "Little Red Dot" (LRD) population. Hence, LRDs generally have bluer UV continua. Nevertheless, four HRQs satisfy the LRD UV/optical continuum slope selections and are therefore massive, cosmic noon analogues of LRDs. Analysis of the near-infrared SEDs of HRQs reveals a deficit of hot dust relative to blue quasars, similar to what is observed in LRDs. This suggests HRQs trace a phase where strong AGN feedback processes eject dust from the inner torus. The UV scattering fraction of HRQs is weakly correlated with the amount of hot dust emission and anti-correlated with the line-of-sight extinction, E(B-V). This is consistent with the hot dust acting as the scattering medium, and the line-of-sight extinction being dominated by dust on interstellar medium scales in the host galaxy.