How Quasar Feedback May Shape the Co-evolutionary Paths

Wako Ishibashi

doi:10.3389/fspas.2017.00026

Abstract

Observations point towards some form of co-evolutionary sequence, from dust-enshrouded starbursts to luminous unobscured quasars. Active galactic nucleus (AGN) feedback is generally invoked to expel the obscuring dusty gas in a blow-out event, eventually revealing the hidden central quasar. However, the physical mechanism driving AGN feedback, either due to winds or radiation, remains uncertain and is still a source of much debate. We consider quasar feedback, based on radiation pressure on dust, which directly acts on the obscuring dusty gas. We show that AGN radiative feedback is capable of efficiently removing the obscuring cocoon, and driving powerful outflows on galactic scales, consistent with recent observations. I will discuss how such quasar feedback may provide a natural physical interpretation of the observed evolutionary path, and the physical implications in the broader context of black hole-host galaxy co-evolution.

Highlights

Active galactic nuclei (AGN) and nuclear starbursts are observed to be intimately coupled, both fueled by the rapid infall of matter, possibly triggered by galaxy mergers (e.g., Alexander and Hickox, 2012, and references therein)
The physical mechanism for AGN feedback is not specified, and in particular no explicit connection is made with the dust component
The first point implies that even dense material can potentially be disrupted; while the second point implies that the more dusty gas is more ejected (Ishibashi and Fabian, 2016b)

Summary

INTRODUCTION

Active galactic nuclei (AGN) and nuclear starbursts are observed to be intimately coupled, both fueled by the rapid infall of matter, possibly triggered by galaxy mergers (e.g., Alexander and Hickox, 2012, and references therein). A “co-evolutionary sequence,” starting from dust-obscured starbursts (e.g., ultraluminous infrared galaxies or ULIRG) leading to unobscured optical quasars, has been widely discussed since Sanders et al (1988). Some form of AGN feedback is required to expel the obscuring gas and dust in a short-lived “blow-out” event. There has been renewed interest in the topic, following the discovery of new populations of dust-reddened quasars at high redshifts (close to the peak epoch of both AGN and starburst activities), likely caught in the short-lived blow-out phase (e.g., Banerji et al, 2012, 2015). We propose a physical mechanism that directly makes use of the dust in order to drive AGN feedback, and we briefly discuss how such AGN radiative feedback may naturally explain the observed co-evolutionary path (Ishibashi and Fabian, 2016b)

AGN RADIATIVE FEEDBACK

DUST OBSCURATION AND BLOW-OUT

THE DUAL ROLE OF DUST