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

TL;DR

This study uses KAT-7 radio telescope observations to analyze the HI distribution and kinematics of NGC 253, revealing extended halo gas, a declining rotation curve, and evidence of starburst-driven outflows, demonstrating KAT-7's capabilities.

Contribution

First detailed HI study of NGC 253 with KAT-7, showing extended halo gas and novel profile fitting technique, advancing understanding of starburst galaxy kinematics.

Findings

Detected 33% more HI flux than previous observations.

HI extends up to 14 kpc from the disk.

Kinematic evidence supports starburst-driven outflows.

Abstract

We present HI observations of the Sculptor Group starburst spiral galaxy NGC 253, obtained with the Karoo Array Telescope (KAT-7). KAT-7 is a pathfinder for the SKA 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% more flux than previous VLA observations, mainly in the outer parts and in the halo for a total HI mass of $2.1 \pm 0.1$ $\times 10^{9}$ M$_{\odot}$. 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 disk. A novel technique, based on interactive profile fitting, was used to separate the main disk gas from the anomalous (halo) gas. The rotation curve (RC) derived for the HI disk 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 disk, kinematically lagging by ~100 km/sec. 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 (SFR) is compatible with the starburst nature of NGC 253.