Variable Stars in the Giant Satellite Galaxy Antlia 2

We report 350 pulsating variable stars found in four DECam fields (similar to 12 deg(2)) covering the Antlia 2 satellite galaxy. The sample of variables includes 318 RR Lyrae stars and eight anomalous Cepheids in the galaxy. Reclassification of several objects designated previously to be RR Lyrae as anomalous Cepheids get rid of the satellite's stars intervening along the line of sight. This in turn removes the need for prolific tidal disruption of the dwarf, in agreement with the recently updated proper motion and pericenter measurements based on Gaia EDR3. There are also several bright foreground RR Lyrae stars in the field, and two distant background variables located similar to 45 kpc behind Antlia 2. We found RR Lyrae stars over the full search area, suggesting that the galaxy is very large and likely extends beyond our observed area. The mean period of the RRab in Antlia 2 is 0.599 days, while the RRc have a mean period of 0.368 days, indicating the galaxy is an Oosterhoff-intermediate system. The distance to Antlia 2 based on the RR Lyrae stars is 124.1 kpc (mu (0) = 20.47) with a dispersion of 5.4 kpc. We measured a clear distance gradient along the semimajor axis of the galaxy, with the southeast side of Antlia 2 being similar to 13 kpc farther away from the northwest side. This elongation along the line of sight is likely due to the ongoing tidal disruption of Ant 2.

Automated summary

We report the discovery of 350 pulsating variable stars in four DECam fields covering the Antlia 2 satellite galaxy, including 318 RR Lyrae stars and eight anomalous Cepheids. Reclassification of some previously designated RR Lyrae objects as anomalous Cepheids supports the updated proper motion and pericenter measurements, indicating a lack of tidal disruption in the dwarf galaxy. The presence of bright foreground RR Lyrae stars and distant background variables suggests that Antlia 2 is a large galaxy extending beyond the observed area.