HALOGAS: HI Observations and Modeling of the Nearby Edge-on Spiral Galaxy NGC 4244

TL;DR

This study uses 21-cm observations and modeling to analyze the HI distribution and kinematics of the edge-on galaxy NGC 4244, revealing a velocity lag, a warp component, and features like a star formation-driven shell.

Contribution

It provides the first detailed modeling of HI kinematics in NGC 4244, showing a velocity lag and ruling out a significant extended halo, emphasizing the role of a warp in disk thickening.

Findings

Detected a velocity lag of approximately -9 km/s/kpc in both galaxy halves.

Found no evidence for a significantly extended HI halo.

Identified a star formation-driven shell feature.

Abstract

We present 21-cm observations and models of the HI kinematics and distribution of NGC 4244, a nearby edge-on Scd galaxy observed as part of the Westerbork Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) survey. Our models give insight into the HI kinematics and distribution with an emphasis on the potential existence of extra-planar gas as well as a negative gradient in rotational velocity with height above the plane of the disk (a lag). Our models yield strong evidence against a significantly extended halo and instead favor a warp component along the line of sight as an explanation for some of the observed thickening of the disk. Based on these models, we detect a lag of -9 +3/-2 km s-1 kpc-1 in the approaching half and -9 +/-2 km s-1 kpc-1 in the receding half. This lag decreases in magnitude to -5+/-2 km s-1 kpc-1 and -4+/-2 km s-1 kpc-1 near a radius of 10 kpc in the approaching and receding halves respectively. Additionally, we detect several distinct morphological and kinematic features including a shell that is probably driven by star formation within the disk.