Evidence of Gas Depletion in Quasars with Moderate Radio Emission

TL;DR

This paper investigates how AGN feedback interacts with the cold gas content of host galaxies across a range of radio activity. By building a Herschel-detected quasar sample at $z\sim1.5$ and cross-matching with radio catalogs, the authors classify objects into radio loud, radio-detected radio quiet, and radio-undetected groups, then model their spectral energy distributions with CIGALE, incorporating a radio component and the SKIRTOR AGN torus. The key finding is that radio-detected radio-quiet quasars exhibit about $0.3$ dex lower dust and gas masses than the other groups, and show higher fractions and velocities of ionized outflows, suggesting more efficient AGN feedback at moderate radio activity. These results imply a nuanced role for radio emission in quenching gas reservoirs and star formation, motivating high-resolution follow-up to directly probe ISM–radio interactions.

Abstract

The energy released by active galactic nuclei (AGNs) is considered to have a profound impact on the cold gas properties of their host galaxies, potentially heating or removing the gas and further suppressing star formation. To understand the feedback from AGN radio activity, we investigate its impacts on the cold gas reservoirs in AGNs with different radio activity levels. We construct a quasar sample with a mean $z\sim1.5$ and a mean $L_{\rm bol}\sim10^{45.8}\ \rm erg\ s^{-1}$, all with Herschel detections to enable estimates of the total gas mass through the galactic dust continuum emission. The sample is then cross-matched with radio catalogs and divided into radio loud (RL) quasars, radio-detected radio quiet (RQ) quasars and radio-undetected quasars based on their radio loudness. Through spectral energy distribution (SED) fitting, we find the radio-detected RQ quasars exhibit evidence of gas deficiency with host galaxies possessing $\sim 0.3$ dex lower dust and gas masses compared to the other two groups, despite being matched in $M_{\rm BH}$, $L_{\rm bol}$, $M_{*}$ and SFR. Furthermore, evidence from optical spectra shows that both the fraction and velocity of outflows are higher in the radio-detected RQ group, suggesting a connection between the ionized gas outflows and the moderate radio activity. These results suggest that the AGN feedback could be more efficient in AGNs with weak/moderate radio emission than in those without radio detection or those with strong radio emission. Further high-resolution observations are needed to understand the interaction between the interstellar medium and the weak/moderate AGN radio activity.

Figures (3)

• Figure 1: The distribution of the redshift and $L_{\rm bol}$ of our sample SDSSDR16Q_pro. The upper panel and the right panel show the distributions of the redshift and $L_{\rm bol}$ respectively.
• Figure 2: (a)-(c) Distributions of the relative flux difference $f_b\equiv (F_{b,\rm cModel}-F_{b,\rm PSF})/{F_{b,\rm cModel}}$ in $r$, $i$ and $z$ bands for the total sample (orange) and the symmetric distribution (gray) obtained by mirroring the negative-$f_b$ part to the positive side.
• Figure 3: The comparisons between different magnitudes of UKIDSS. The blue points in top panels refer to the magnitudes of extended sources. The green points in bottom panels refer to the magnitudes of point sources. The red dashed line in each plot is the one-to-one line.