We present computations of the metals photoionization structures of pressure supported gas clouds in gravitationally dominant dark-matter mini-halos in the extended Galactic halo or Local Group environment .
We consider low-metallicity ( 0.1 - 0.3 solar ) clouds that are photoionized by the present-day metagalactic radiation field , and which are also pressure-confined by a hot external medium .
We study the properties of \Lambda CDM Burkert ( and also NFW ) mini-halos with characteristic circular velocities from 12 to 30 km s ^ { -1 } ( 10 ^ { 8 } – 2 \times 10 ^ { 9 } M _ { \odot } ) .
We present results for the volume densities and projected column densities of low-ionization metal atoms and ions , C ii , N i , O i , Si ii , and S ii , produced in the neutral cloud cores , and high-ions , C iv , N v , O vi , Si iii , Si iv , and S iii produced in the ionized shielding envelopes .
We examine the possible relationships between the compact H i high-velocity clouds ( CHVCs ) , dwarf galaxies , and high-velocity ionized C iv absorbers , within the context of photoionized mini-halo models for such objects .
In pressure-confined ( P / k \sim 50 cm ^ { -3 } K ) mini-halo models for the CHVCs the photoionization states are much lower than in the C iv absorbers .
However , for lower bounding pressures \lesssim 1 cm ^ { -3 } K , in more massive \sim 2 \times 10 ^ { 9 } M _ { \odot } dwarf galaxy scale halos , the photoionization states in the outer envelopes resemble those observed in the C iv HVCs .
An important exception is O vi for which our photoionization models underpredict the relative abundances by about an order-of-magnitude , suggesting that additional processes are at play as concluded by Sembach et al .
( 2000 ; 2003 ) .
For the cloud size-scales expected in median \Lambda CDM Burkert halos , a gas metallicity of 0.3 solar is required to produce absorption-line strengths comparable to those in the C iv HVCs .
We argue that fully ionized and starless “ dark galaxies ” could be detectable in the local universe as UV metal line absorbers with ionization states similar to the C iv absorbers .