Abundances in the H I envelope of the extremely low metallicity blue compact dwarf galaxy SBS 0335-052 from far ultraviolet spectroscopic explorer observations

We present Far Ultraviolet Spectroscopic Explorer spectroscopy of SBS 0335-052, the second most metal-deficient blue compact dwarf (BCD) galaxy known [log (O/H) = -4.70]. In addition to the H I Lyman series, we detect C II, N I, N II, O I, Si II, Ar I, and Fe II absorption lines, mainly arising from the extended H I envelope in which SBS 0335-052 is embedded. No H₂ absorption lines are seen. The absence of diffuse H₂ implies that the warm H₂ detected through infrared emission must be very clumpy and associated with the star-forming regions. The clumps should be denser than ∼1000 cm^-3 and hotter than ∼1000 K and account for ≥5% of the total H I mass. Although SBS 0335-052 is a probable young galaxy, its neutral gas is not pristine. The metallicity of its neutral gas is similar to that of its ionized gas and is equal to log (O/H) ∼ -5. This metallicity is comparable to that found in the H I envelopes of four other BCDs with ionized gas metallicities spanning the wide range from log (O/H) = -4.8 to -3.8, and in Lyα absorbers, fueling the speculation that there may have been previous enrichment of the primordial neutral gas to a common metallicity level of log (O/H) ∼ -5, possibly by Population III stars.