Galactic Winds across the Gas-rich Merger Sequence. II. Lyα Emission and Highly Ionized O vi and N v Outflows in Ultraluminous Infrared Galaxies

Abstract

This paper is the second in a series aimed at examining the gaseous environments of z ≤ 0.3 quasars and ultraluminous infrared galaxies (ULIRGs) as a function of AGN/host galaxy properties across the merger sequence. This second paper focuses on the Lyα emission and O vi 1032, 1038 and N v 1238, 1243 absorption features, tracers of highly ionized gas outflows, in ULIRGs observed with HST/COS. Lyα emission is detected in 15 out of 19 ULIRGs, and 12 of the 14 clear Lyα detections show emission with blueshifted velocity centroids and/or wings. The equivalent widths of the Lyα emission increase with increasing AGN luminosities and AGN bolometric fractions. The blueshifts of the Lyα emission correlate positively with those of the [O iii] λ5007 emission, where the latter traces the ionized gas outflows. The Lyα escape fractions tend to be slightly larger in objects with stronger AGN and larger outflow velocities, but they do not correlate with nebular line reddening. Among the 12 ULIRGs with good continuum signal-to-noise ratios, O vi and/or N v absorption features are robustly detected in six of them, all of which are blueshifted, indicative of outflows. In the combined ULIRG + quasar sample, the outflows are more frequently detected in the X-ray weak or absorbed sources. The absorption equivalent widths, velocities, and velocity dispersions of the outflows are also higher in the X-ray weak sources. No other strong correlations are visible between the properties of the outflows and those of the AGN or host galaxies.