Quasar Host Environments: The view from Planck

TL;DR

This study uses Planck data to analyze the far-infrared emission of nearly 300,000 quasars across a wide redshift range, revealing dust dominance, synchrotron activity in radio-loud QSOs, and thermal SZ signals at high redshifts, shedding light on quasar environments.

Contribution

First large-scale measurement of QSO far-infrared emission across redshifts using Planck, combining multi-component filtering and stacking techniques.

Findings

Dust emission peaks at z~2, aligning with cosmic star formation.

Radio-loud QSOs show increasing synchrotron luminosity with redshift.

Thermal SZ detected at z=2.5-4, indicating hot halo gas presence.

Abstract

We measure the far-infrared emission of the general quasar (QSO) population using Planck observations of the Baryon Oscillation Spectroscopic Survey QSO sample. By applying multi-component matched multi-filters to the seven highest Planck frequencies, we extract the amplitudes of dust, synchrotron and thermal Sunyaev-Zeldovich (SZ) signals for nearly 300,000 QSOs over the redshift range $0.1<z<5$. We bin these individually low signal-to-noise measurements to obtain the mean emission properties of the QSO population as a function of redshift. The emission is dominated by dust at all redshifts, with a peak at $z \sim 2$, the same location as the peak in the general cosmic star formation rate. Restricting analysis to radio-loud QSOs, we find synchrotron emission with a monochromatic luminosity at $100\,\rm{GHz}$ (rest-frame) rising from $\overline{L_{\rm synch}}=0$ to $0.2 \, {\rm L_\odot} {\rm Hz}^{-1}$ between $z=0$ and 3. The radio-quiet subsample does not show any synchrotron emission, but we detect thermal SZ between $z=2.5$ and 4; no significant SZ emission is seen at lower redshifts. Depending on the supposed mass for the halos hosting the QSOs, this may or may not leave room for heating of the halo gas by feedback from the QSO.