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

The properties of gas in the haloes 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 Ha observations of the edge-on dwarf galaxy UGC 1281 in order to determine the existence of extraplanar 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 Ha integral field spectroscopy using PPAK at Calar Alto and deep HI observations with the Westerbork Synthesis Radio Telescope (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 Ha emission up to 25 arcsec (655 pc) in projection above the plane and in general a low Ha flux. Compared to other dwarf galaxies UGC 1281 is a normal dwarf galaxy with a slowly rising rotation curve that flattens off at 60 kms(-1) and a central depression in its H I distribution. Its H I extends 70 arcsec (1.8 kpc) in projection from the plane. This gas can be explained by either a warp partially in the line-of-sight or a purely edge-on warp with rotational velocities that decline with a vertical gradient of 10.6 +/- 3.7 kms(-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.