FR II Quasars: Infrared Properties, Star Formation Rates, and Extended Ionized Gas

TL;DR

This study analyzes infrared properties and star formation in FR II quasars, finding low star formation rates and suggesting EELRs result from jet-related gas ejection rather than starburst activity.

Contribution

It provides the first infrared spectral analysis of FR II quasars with and without EELRs, revealing low star formation rates and their implications for galaxy evolution.

Findings

Mid-infrared spectra show no significant star formation features.

EELRs are likely caused by jet-driven gas ejection, not starburst winds.

FR II quasars deviate from typical star formation and black hole growth correlation.

Abstract

We present Spitzer IRS spectra and MIPS photometry of 12 radio-loud QSOs with FR II morphologies at z ~ 0.3. Six of the sources are surrounded by luminous extended emission-line regions (EELRs), while the other six do not have such extended nebulae. The two subsamples are indistinguishable in their mid-infrared spectra and overall infrared spectral energy distributions (SEDs). For both subsamples, the mid-infrared aromatic features are undetected in either individual sources or their stacked spectra, and the SEDs are consistent with pure quasar emission without significant star formation. The upper limits to the star formation rate are sufficiently low that starburst-driven superwinds can be ruled out as a mechanism for producing the EELRs, which are instead likely the result of the ejection of most of the gas from the system by blast waves accompanying the launching of the radio jets. The FR II quasars deviate systematically from the correlation between host galaxy star formation rate and black hole accretion rate apparently followed by radio-quiet QSOs, implying little or no bulge growth coeval with the current intensive black hole growth. We also present a new Spitzer estimate of the star formation rate for the starburst in the host galaxy of the compact steep-spectrum radio quasar 3C 48.