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

Abstract

The properties of gas in the halos of galaxies tell us something about the properties of the interstellar medium. Here we report on deep HI and Hα observations of UGC 1281 in order to determine the existence of extra planar gas and its kinematics. This is the first time the halo characteristics of a dwarf galaxy have been investigated. These observations are compared to 3D models in order to determine the distribution of HI in the galaxy. We find that UGC 1281 has Hα emission up to 25″(655 pc,∼ 0.6 Hα hR) in projection above the plane and in general a low Hα flux. Its HI extends 70″ (1.8 kpc, ∼ 1.5 HI hR) in projection from the plane. This neutral extra-planar gas can be explained by either a line-of-sight warp or a thick disk with rotational velocities that decline with a vertical gradient of 10.6 ± 3.7 km s-1 kpc-1. 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. © Springer-Verlag Berlin Heidelberg 2012.