Warp or lag? The ionized and neutral hydrogen gas in the edge-on dwarf galaxy UGC 1281

TL;DR

This study investigates the gaseous halo and kinematics of the edge-on dwarf galaxy UGC 1281 using deep HI and Hα observations, revealing a warp in the gas distribution and providing new insights into dwarf galaxy halo properties.

Contribution

First detailed analysis of gaseous halo characteristics and kinematics in a dwarf galaxy, using combined HI and Hα data and 3D modeling.

Findings

UGC 1281 has Hα emission up to 655 pc above the plane.

HI extends 1.8 kpc from the plane with a warped distribution.

A line-of-sight warp with declining rotational velocities best explains the data.

Abstract

The properties of gas in the halos of galaxies constrain global models of the interstellar medium. Kinematical information is of particular interest since it is a clue to the origin of the gas. Until now mostly massive galaxies have been investigated for their halo properties. Here we report on deep HI and H{\alpha} observations of the edge-on dwarf galaxy UGC 1281 in order to determine the existence of extra-planar gas and the kinematics of this galaxy. This is the first time a dwarf galaxy is investigated for its gaseous halo characteristics. We have obtained H{\alpha} integral field spectroscopy using PPAK at Calar Alto and deep HI observations with the WSRT of this edge-on dwarf galaxy. These observations are compared to 3D models in order to determine the distribution of HI in the galaxy. We find that UGC 1281 has H{\alpha} emission up to 25"(655 pc) in projection above the plane and in general a low H{\alpha} flux. Compared to other dwarf galaxies UGC 1281 is a normal dwarf galaxy with a slowly rising rotation curve that flattens off at 60 km/s and a central depression in its HI distribution. Its HI extends 70" (1.8 kpc) in projection from the plane. This gas can be explained by either a warp partially in the line-of-sight warp or a purely edge-on warp with rotational velocities that decline with a vertical gradient of 10.6 \pm 3.7 km/s/kpc. The line-of-sight warp model is the preferred model as it is conceptually simpler. In either model the warp starts well within the optical radius.