HI observations of the nearest starburst galaxy NGC 253 with the SKA precursor KAT-7

Abstract

We present HI observations of the Sculptor group starburst spiral galaxy NGC 253, obtained with theKaroo Array Telescope (KAT-7).KAT-7 is a pathfinder for the SquareKilometreArray precursor MeerKAT, under construction. The short baselines and low system temperature of the telescope make it very sensitive to large-scale, low-surface-brightness emission. The KAT-7 observations detected 33 per cent more flux than previous Very Large Array observations, mainly in the outer parts and in the halo for a total HI mass of 2.1 ± 0.1 × 109 M⊙. HI can be found at large distances perpendicular to the plane out to projected distances of-9-10 kpc away from the nucleus and-13-14 kpc at the edge of the disc. A novel technique, based on interactive profile fitting, was used to separate the main disc gas from the anomalous (halo) gas. The rotation curve (RC) derived for the HI disc confirms that it is declining in the outer parts, as seen in previous optical Fabry-Perot measurements. As for the anomalous component, its RC has a very shallow gradient in the inner parts and turns over at the same radius as the disc, kinematically lagging by 100 km s-1. The kinematics of the observed extra-planar gas is compatible with an outflow due to the central starburst and galactic fountains in the outer parts. However, the gas kinematics shows no evidence for inflow. Analysis of the near-IR WISE data, shows clearly that the star formation rate is compatible with the starburst nature of NGC 253.