The HI Kinematics of NGC 4013: a Steep and Radially Shallowing Extra-planar Rotational Lag

TL;DR

This study uses deep HI observations to analyze the warped galaxy NGC 4013, revealing a thin, flaring disk with a radially shallowing vertical rotational lag, contributing to understanding disk-halo dynamics.

Contribution

It provides detailed measurements of the HI disk structure and the radial variation of the rotational lag in NGC 4013, offering insights into disk-halo interactions and lag behavior.

Findings

HI disk is thin with flaring structure

Vertical rotational lag decreases with radius, reaching zero near R_25

Lag steepness and radial shallowing are consistent with recent edge-on galaxy studies

Abstract

NGC 4013 is a distinctly warped galaxy with evidence of disk-halo activity. Through deep HI observations and modeling we confirm that the HI disk is thin (central exponential scale height of with an upper limit of 4" or 280 pc), but flaring. We detect a vertical gradient in rotation velocity (lag), which shallows radially from a value of -35 +7/-28 km/s/kpc at 1.4' (5.8 kpc), to a value of zero near R_25 (11.2 kpc). Over much of this radial range, the lag is relatively steep. Both the steepness and the radial shallowing are consistent with recent determinations for a number of edge-ons, which have been difficult to explain. We briefly consider the lag measured in NGC 4013 in the context of this larger sample and theoretical models, further illuminating disk-halo flows.