Abundances in the H I Envelope of the Extremely Low Metallicity Blue Compact Dwarf Galaxy SBS?0335–052 from Far Ultraviolet Spectroscopic Explorer Observations*

摘要

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.