Extended Emission-Line Regions: Remnants of Quasar Superwinds?

TL;DR

This study uses integral-field-unit spectroscopy to analyze luminous extended emission-line regions around low-redshift quasars, revealing their kinematic properties, ionization sources, metallicities, and possible origins linked to quasar activity and galaxy mergers.

Contribution

It provides new observational data confirming that EELRs are photoionized by quasars, often associated with radio jets, and suggests their origin as gas expelled during galaxy mergers and quasar activity.

Findings

EELRs often show velocities exceeding 500 km/s, up to 1100 km/s.

EELRs are photoionized by quasars with low metallicities.

Most EELRs are likely formed from gas swept out by radio jet-driven blast waves.

Abstract

We give an overview of our recent integral-field-unit spectroscopy of luminous extended emission-line regions (EELRs) around low-redshift quasars, including new observations of 5 fields. Previous work has shown that the most luminous EELRs are found almost exclusively around steep-spectrum radio-loud quasars, with apparently disordered global velocity fields, and little, if any, morphological correlation with either the host-galaxy or the radio structure. Our new observations confirm and expand these results. The EELRs often show some clouds with velocities exceeding 500 km/s, ranging up to 1100 km/s, but the velocity dispersions, with few exceptions, are in the 30-100 km/s range. Emission-line ratios show that the EELRs are clearly photoionized by the quasars. Masses of the EELRs range up to >10^10 Msun. Essentially all of the EELRs show relatively low metallicities, and they are associated with quasars that, in contrast to most, show similarly low metallicities in their broad-line regions. The two objects in our sample that do not have classical double-lobed radio morphologies (3C48, with a compact-steep-spectrum source; Mrk1014, radio-quiet, but with a weak compact-steep-spectrum source) are the only ones that appear to have recent star formation. While some of the less-luminous EELRs may have other origins, the most likely explanation for the ones in our sample is that they are examples of gas swept out of the host galaxy by a large-solid-angle blast wave accompanying the production of the radio jets. The triggering of the quasar activity is almost certainly the result of the merger of a gas-rich galaxy with a massive, gas-poor galaxy hosting the supermassive black hole.