Bulge Oscillation Driven by Outflows of Active Galactic Nuclei. I. Fast Outflow Case

TL;DR

This paper explores how fast outflows from active galactic nuclei can induce oscillations in galactic bulges through potential perturbations and star injection, with observable velocities of a few tens of km/s.

Contribution

It introduces a model showing that AGN outflows can cause bulge oscillations and radial velocities, providing a new understanding of bulge dynamics influenced by AGN activity.

Findings

Bulge oscillations driven by AGN outflows are possible.

Radial velocities of bulges can reach a few 10 km/s during outflows.

Bulge velocities tend to zero after AGN activity ceases.

Abstract

There is growing evidence for star formation inside outflows of active galactic nuclei (AGNs). The formed stars are injected into bulges and give rise to perturbation of bulges. In this paper, we investigate the issues of non-rotating, spherically symmetric bulges under the perturbation of fast, massive outflows with stars formed inside. We show that the potential perturbation of outflows together with injection and dynamical friction of these stars could drive bulge oscillations. Still, we find non-zero radial velocity of bulges will be driven by the episodic outflows of AGNs and after the AGN quenched, the radial velocity will tend to zero within a timescale $\sim\tau_{\rm AGN}$, which is the AGN's lifetime. For some typical values of bulges and AGNs, we find the expansion and contraction velocities are of a few $10\,\rm km\,s^{-1}$ for $10^{10}\,M_\odot$ bulges and mass outflowing rate $500\,M_\odot/\rm yr$, which would give observational signatures.