Investigating Disk-Halo Flows and Accretion: A Kinematic and Morphological Analysis of Extraplanar HI in NGC 3044 and NGC 4302

TL;DR

This study analyzes the kinematics and morphology of extraplanar HI in NGC 3044 and NGC 4302, revealing lagging gas, disturbances, and environmental effects, advancing understanding of disk-halo flows and gas accretion in spiral galaxies.

Contribution

It provides detailed kinematic models of extraplanar HI in two edge-on galaxies, highlighting the presence of lagging gas and environmental influences, and compares observations with theoretical expectations.

Findings

Detection of lagging extraplanar HI with radial shallowing.

Identification of disturbed kinematics and morphology in both galaxies.

Evidence that lag properties are influenced by internal processes and environment.

Abstract

To further understand the origins of and physical processes operating in extra-planar gas, we present observations and kinematic models of HI in the two nearby, edge-on spiral galaxies NGC 3044 and NGC 4302. We model NGC 3044 as a single, thick disk. Substantial amounts of extra-planar HI are also detected. We detect a decrease in rotation speed with height (a lag) that shallows radially, reaching zero at approximately R25. The large-scale kinematic asymmetry of the approaching and receding halves suggests a recent disturbance. The kinematics and morphology of NGC 4302, a Virgo Cluster member, are greatly disturbed. We model NGC 4302 as a combination of a thin disk and a second, thicker disk, the latter having a hole near the center. We detect lagging extra-planar gas, with indications of shallowing in the receding half, although its characteristics are difficult to constrain. A bridge is detected between NGC 4302 and its companion, NGC 4298. We explore trends involving the extra-planar HI kinematics of these galaxies, as well as galaxies throughout the literature, as well as possible connections between lag properties with star formation and environment. Measured lags are found to be significantly steeper than those modeled by purely ballistic effects, indicating additional factors. Radial shallowing of extra-planar lags is typical and occurs between 0.5R25 and R25, suggesting internal processes are important in dictating extra-planar kinematics.