Large-scale H I structure of the Circinus galaxy

HI observations with the Australia Telescope Compact Array (ATCA) are used to study the neutral gas distribution and kinematics of the Circinus galaxy. One of the most outstanding features of Circinus is its enormous size (at least 80 arcmin or nearly 100 kpc, assuming a distance of 4 Mpc) revealing a beautiful large-scale spiral pattern. The fit of a tilted-ring model to the velocity field reveals a strong kinematic warp of the outer spiral arms. The inner region (radius 250 arcsec or 5 kpc) contains a highly elongated structure with non-circular motions, suggesting that Circinus is a barred spiral galaxy. At the centre of Circinus there is a 50-arcsec or 1-kpc-radius H I ring or disc rotating with a speed of at least 200 km s(-1).