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19th of July 2021
The edge-on Fourcade-Figueroa galaxy
by Saponara et al.
Studies of the stellar and HI (neutral hydrogen) gas kinematics in dwarf and Low Surface Brightness (LSB) galaxies are essential for deriving constraints on their dark matter distribution. Saponara et al. have combined new Giant Metrewave Radio Telescope (GMRT) data with archival Australia Telescope Compact Array (ATCA) data for a sensitive high-resolution study of the prototypical superthin Fourcade-Figueroa (FF) galaxy. Also known as ESO 270−G017, the galaxy was discovered optically in 1970 as an elongated and diffuse object. Located 2.5 degrees southeast of the core of Centaurus A, the galaxy was initially thought to be part of the Centaurus A group, however, recent distance estimates place it just beyond Centaurus A, at a distance of 7 Mpc.

The ATCA 21-cm observations were carried out in January 1993, June and July 1993 and November 2008 using the 750, 6A and EW367 array configurations respectively, with a total time on-source of 27 h 40 min. The GMRT observations were made over ∼14 h during June-July 2015 and January 2016. The resulting combined dataset reveals an HI diameter of 20 arcmin with HI emission was detected over the velocity range from ∼720 to 920 km/s. At a distance of 6.95 Mpc, this corresponds to a total HI mass of 2.2 billion solar masses. The image above shows the HI velocity field of the galaxy, with contour levels of 768, 788, 808, 828, 848, 868, 888 km/s. The systemic velocity of galaxy is 828 km/s so lower velocities correspond to the side of the galaxy rotating towards us, and higher velocities to the side of the galaxy rotating away from us. More details are given in the preprint of the paper.

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