OpticalBVIimaging and H I synthesis observations of the dwarf irregular Galaxy ESO 364-G029

Abstract

As part of an effort to enlarge the number of well-studied Magellanic-type galaxies, we obtained broadband optical imaging and neutral hydrogen radio synthesis observations of the dwarf irregular galaxy ESO 364-G 029. The optical morphology characteristically shows a bar-like main body with a one-sided spiral arm, an approximately exponential light distribution, and offset photometric and kinematic centers. The HI distribution is mildly asymmetric and, although slightly offset from the photometric center, roughly follows the optical brightness distribution, extending to over 1.2 Holmberg radii (where mu_B = 26.5 mag/arcsec^2). In particular, the highest HI column densities closely follow the bar, one-arm spiral, and a third optical extension. The rotation is solid-body in the inner parts but flattens outside of the optical extent. The total HI flux F_HI = 23.1 pm 1.2 Jy km/s, yielding a total HI mass M_HI= (6.4 pm 1.7) x 10^8 Msun (for a distance D = 10.8 pm 1.4 Mpc) and a total HI mass-to-blue-luminosity ratio M_HI/L_B = (0.96 pm 0.14) Msun / Lsun,B (distance independent). The HI data suggest a very complex small-scale HI structure, with evidence of large shells and/or holes, but deeper observations are required for a detailed study. Follow-up observations are also desirable for a proper comparison with the Large Magellanic Cloud, where despite an optical morphology very similar to ESO 364-G 029 the HI bears little resemblance to the optical.