We present FUSE 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 H _ { 2 } absorption lines are seen .
The absence of diffuse H _ { 2 } implies that the warm H _ { 2 } detected through infrared emission must be very clumpy and associated with the star-forming regions .
The clumps should be denser than \sim 1000 cm ^ { -3 } and hotter than \sim 1000 K and account for \geq 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 log O/H \sim –5 .
This metallicity is comparable to those 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 log O/H = –3.8 , and in Ly \alpha 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 \sim –5 , possibly by Population III stars .