Ionization Mechanisms in Quasar Outflows

TL;DR

This study uses integral field spectroscopy to analyze ionization mechanisms in the host galaxy and outflows of four nearby quasars, revealing dominant AGN photoionization and contributions from shocks and star formation.

Contribution

It provides the first detailed comparison of ionization mechanisms in both host and outflow components in nearby quasars using spatially resolved spectroscopy.

Findings

AGN photoionization often dominates both components.

Outflowing gas can be more highly ionized than host gas.

Shocks and star formation also contribute to ionization.

Abstract

The various ionization mechanisms at play in active galactic nuclei (AGN) and quasars have been well studied, but relatively little has been done to separately investigate the contributions of these ionization mechanisms within the host galaxy and outflowing components. Using Gemini integral field spectroscopy (IFS) data, we study the ionization properties of these two components in four nearby ($z \lesssim$ 0.2) radio-quiet Type 1 quasars. Emission line ratios and widths are employed to identify the dominant ionization mechanisms for the host and outflow components in each object. We find that photoionization by the AGN often dominates the ionization of both gaseous components in these systems. In three cases, the outflowing gas is more highly ionized than the gas in the host, indicating that it is more strongly exposed to the ionizing radiation field of the AGN. In two objects, a positive correlation between the line widths and line ratios in the outflowing gas component indicates that shocks with velocities of order 100 $-$ 500 km s$^{-1}$ may also be contributing to the ionization and heating of the outflowing gas component. The line ratios in the outflowing gas of one of these two objects also suggest a significant contribution from photoionization by hot, young stars in the portion of the outflow that is closest to star-forming regions in the host galaxy component. The data thus favor photoionization by hot stars in the host galaxy rather than stars formed in the outflow itself.

Full text

An example of a Research Note of the American Astronomical Society (RNAAS)

Ethan Vishniac

Editor-in-Chief

Johns Hopkins University

Chris Lintott

RNAAS Editor

Oxford University

Greg J. Schwarz

American Astronomical Society

2000 Florida Ave., NW, Suite 300

Washington, DC 20009-1231, USA

August Muench

American Astronomical Society

2000 Florida Ave., NW, Suite 300

Washington, DC 20009-1231, USA

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