We compare a new R = 120 , 000 spectrum of PG 1634 + 706 ( z _ { QSO } = 1.337 ,m _ { V } = 14.9 ) obtained with the HDS instrument on Subaru to a R = 45 , 000 spectrum obtained previously with HIRES/Keck .
In the strong Mg ii system at z = 0.9902 and the multiple cloud , weak Mg ii system at z = 1.0414 , we find that at the higher resolution , additional components are resolved in a blended profile .
We find that two single-cloud weak Mg ii absorbers were already resolved at R = 45 , 000 , to have b = 2 - 4 km s ^ { -1 } .
The narrowest line that we measure in the R = 120 , 000 spectrum is a component of the Galactic Na i absorption , with b = 0.90 \pm 0.20 km s ^ { -1 } .
We discuss expectations of similarly narrow lines in various applications , including studies of DLAs , the Mg i phases of strong Mg ii absorbers , and high velocity clouds .
By applying Voigt profile fitting to synthetic lines , we compare the consistency with which line profile parameters can be accurately recovered at R = 45 , 000 and R = 120 , 000 .
We estimate the improvement gained from superhigh resolution in resolving narrowly separated velocity components in absorption profiles .
We also explore the influence of isotope line shifts and hyperfine splitting in measurements of line profile parameters , and the spectral resolution needed to identify these effects .
Super high resolution spectra of quasars , which will be routinely possible with 20-meter class telescopes , will lead to greater sensitivity for absorption line surveys , and to determination of more accurate physical conditions for cold phases of gas in various environments .