HALOGAS observations of NGC 4414: fountains, interaction, and ram pressure

TL;DR

Deep HI imaging of NGC 4414 reveals a stable inner disk, a disturbed outer disk with a warp, and signs of past minor interaction, illustrating environmental effects on seemingly undisturbed galaxies.

Contribution

First detailed deep HI imaging of NGC 4414 showing its kinematic structure, warp, and interaction signatures, enhancing understanding of galaxy-environment interactions.

Findings

Inner HI disk is regularly rotating

Outer disk exhibits a U-shaped warp

Presence of a stellar shell indicating past interaction

Abstract

We present deep HI imaging of the nearby spiral galaxy NGC 4414, taken as part of the Westerbork HALOGAS (Hydrogen Accretion in LOcal GAlaxieS) survey. The observations show that NGC 4414 can be characterized by a regularly rotating inner HI disk, and a more disturbed outer disk. Modeling of the kinematics shows that the outer disk is best described by a U-shaped warp. Deep optical imaging also reveals the presence of a low surface brightness stellar shell, indicating a minor interaction with a dwarf galaxy at some stage in the past. Modeling of the inner disk suggests that about 4 percent of the inner HI is in the form of extra-planar gas. Because of the the disturbed nature of the outer disk, this number is difficult to constrain for the galaxy as a whole. These new, deep observations of NGC 4414 presented here show that even apparently undisturbed galaxies are interacting with their environment.