VLA HI Line Observations of the Extremely Metal-Poor Blue Compact Dwarf   Galaxy SBS 0335-052
  We present the results of HI mapping with the NRAO VLA of one of the most metal-deficient blue compact dwarf (BCD) galaxies known, SBS 0335-052, with an oxygen abundance of only 1/40 that of the Sun. We study the structure and dynamics of the neutral gas in this chemically young object with a spatial resolution of 20.5"x15" (~ 5.4 x 3.9 kpc at an assumed distance of 54.3 Mpc), a sensitivity at the 2sigma detection level of ~2.0K or 7.5x10^19 cm^-2 and a velocity resolution of 21.2 km s^-1. We detected a large HI complex associated with this object with an overall size of about 66 by 22 kpc and elongated in the East-West direction. There are two prominent, slightly resolved peaks visible in the integrated HI map, separated in the East-West direction by 22 kpc (84"). The eastern peak is nearly coincident with the position of the optical galaxy SBS 0335-052. The western peak is about a factor of 1.3 brighter in the HI line and is identified with a faint blue compact dwarf galaxy, SBS 0335-052W, with m_B = 19.4, and a metallicity close to the lowest values known for BCDs, about 1/50 that of the Sun. The radial velocities of both systems are similar, suggesting that the two BCDs SBS 0335-052 and SBS 0335-052W constitute a pair of dwarf galaxies embedded in a common HI envelope. Alternatively, the BCDs can be the nuclei of two distinct interacting primordial HI clouds. The estimated total dynamical mass, assuming the BCDs form a bound system, is larger than 6x10^9 Msun. This is to be compared to a total gaseous mass M_gas = 2.1x10^9 Msun, and a total stellar mass Mstar < 10^8 Msun. Hence, the mass of the SBS 0335-052 system is dominated by dark matter (abridged). 
S. A. Pustilnik (1), E. Brinks (2), T. X. Thuan (3), V. A. Lipovetsky   (1), Y. I. Izotov (4) ((1) Special Astrophysical Obs...