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Дата изменения: Tue Nov 24 21:32:27 1998
Дата индексирования: Sat Sep 11 22:12:35 2010
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Introduction

Since its discovery as an extremely low-metallicity galaxy, the blue compact galaxy (BCG) SBS 0335-052 (SBS - Second Byurakan Survey) has been proposed to be good candidate for a nearby, young dwarf galaxy (Izotov et al. 1990). This chemically-unevolved galaxy with oxygen abundance 1/40 of solar value (Terlevich et al. 1992; Melnick, Heydary-Malayeri & Leisy 1992; Izotov et al. 1997) is the second most metal-deficient BCG known, after I Zw 18, with oxygen abundance 1/50 (O/H)$_\odot$ (Skillman & Kennicutt 1993, hereafter SK93). New evidence in favor of the evolutionary youth of SBS 0335-052 has been found in subsequent studies. Hubble Space Telescope (HST) V, I imaging of this galaxy (Thuan, Izotov & Lipovetsky 1997, hereafter TIL97) has shown blue (V-I) colors not only in the region of current star formation, but also in the extended, low-intensity envelope 4 kpc⁵ in diameter. The emission from the underlying component, with color (V-I) = 0.0-0.2, resembles the combined effect of ionized gas emission and emission from young ($\leq$10⁸ yr) stars (Izotov et al. 1997). Another piece of evidence in favor of small age of SBS 0335-052 has been found by Thuan & Izotov (1997) from HST UV spectrophotometry. They have shown that this galaxy is a damped Ly$\alpha$ system with extremely high neutral hydrogen column density N(H I) = 7$\times$10²¹cm^-2 suggesting a large amount of unprocessed neutral gas around the galaxy. The heavy element abundances in neutral gas are several orders of magnitude lower than those in the ionized gas (Thuan & Izotov 1997). The Very Large Array (VLA) map of SBS 0335-052 shows the presence of a large extended H I cloud, 64 kpc in size, at the same redshift with mass two orders of magnitude larger than the observed mass of stars (Pustilnik et al. 1998). Two prominent, slightly-resolved H I peaks have been detected, separated by 22 kpc. The eastern peak coincides approximately with SBS 0335-052. Pustilnik et al. (1997) made an identification of the western H I peak using the Digital Sky Survey (DSS) and found an optical counterpart designated as SBS 0335-052W. The redshift of this faint, slightly elongated compact galaxy, derived from the 6m telescope optical spectrum is close to that of SBS 0335-052, suggesting that these two galaxies and H I cloud form a unique system. Pustilnik et al. (1997) did not detect either [N II] or [S II] lines in SBS 0335-052W due to their weakness and concluded that this object may be a low-metallicity young galaxy. However, this conclusion is based on a low S/N spectrum in the $\lambda$$\lambda$4800-7200Å spectral range, so that the oxygen abundance was not derived. In this paper we present new MMT and Keck II telescope spectrophotometric observations and 3.5m Calar Alto telescope CCD R, I photometry, derive for the first time the element abundances and obtain R, I and (R-I) profiles in SBS 0335-052W.