Discovery of strongly blue shifted mid-infrared [NeIII] and [NeV] emission in ULIRGs

TL;DR

This study discovers significant blue shifted mid-infrared neon emission lines in ULIRGs, indicating AGN-driven outflows and interactions with radio jets, revealing complex ionized gas kinematics.

Contribution

It reports the first large-scale detection of blue shifted neon lines in ULIRGs and links these features to AGN activity and radio jet interactions.

Findings

30% of ULIRGs show blue shifted neon emission lines.

Higher incidence of blue shifted [NeV] in AGN-dominated sources.

Correlation between line width and radio luminosity suggests jet-ISM interactions.

Abstract

We report the discovery of blue shifted (delta(V) > 200 km/s) mid-infrared [NeIII] and/or [NeV] emission in 25 out of 82 ULIRGs (30% of our sample). The incidence of blue shifted [NeV] emission is even higher (59%) among the sources with a [NeV] detection -- the tell-tale signature of an active galactic nucleus (AGN). Sixteen ULIRGs in our sample, eleven of which are optically classified as AGN, have [NeIII] blue shifts above 200 km/s. A comparison of the line profiles of their 12.81um [NeII], 15.56um [NeIII] and 14.32um [NeV] lines reveals the ionization of the blue shifted gas to increase with blue shift, implying decelerating outflows in a stratified medium, photo-ionized by the AGN. The strong correlation of the line width of the [NeIII] line with the radio luminosity indicates that interaction of expanding radio jets with the dense ISM surrounding the AGN may explain the observed neon line kinematics for the strongest radio sources in this sample.