Double, double, toil, and trouble. The tails, bubbles, and knots of the local compact obscured nucleus galaxy NGC4418

Abstract

Compact obscured nuclei (CONs) are an extremely obscured (N$_ H2 >$1025 cm$^ $) class of galaxy nuclei thought to exist in 20-40 per cent of nearby (ultra-)luminous infrared galaxies While they have been proposed to represent a key phase of the active galactic nucleus (AGN) feedback cycle, the nature of these CONs -- what powers them, their dynamics, and their impact on the host galaxy -- remains unknown. This work analyses the galaxy-scale optical properties of the local CON NGC\,4418 ($z$=0.00727). The key aims of the study are to understand the impact of nuclear outflows on the host galaxy and infer the power source of its CON. Through the mapping of the galaxy spectra and kinematics, we seek to identify new structures in NGC\,4418 to ultimately reveal more about the CON's history, its impact on the host, and, more generally, the role CONs play in galaxy evolution. We present new, targeted integral field unit observations of the galaxy with the Multi-Unit Spectroscopic Explorer (MUSE). For the first time, we mapped the ionised and neutral gas components of the galaxy, along with their dynamical structure, to reveal several previously unknown features of the galaxy. We confirm the presence of a previously postulated, blueshifted outflow along the minor axis of NGC\,4418. We find this outflow to be decelerating and, for the first time, show it to extend in both directions from the nucleus. We report the discovery of two further outflow structures: a redshifted southern outflow connected to a tail of ionised gas surrounding the galaxy and a blueshifted bubble to the north. In addition to these features, we find the iii emission reveals the presence of knots across the galaxy, which are consistent with regions of the galaxy that have been photoionised by an AGN. We identify several new features in NGC\,4418, including a bubble structure, a reddened outflow, and iii knot structures throughout the galaxy. We additionally confirm the presence of a bilateral blueshifted outflow along the minor axis. Based on the properties of these features, we conclude that the CON in NGC\,4418 is most likely powered by AGN activity.