A study of the optical and radio absorption-line systems in AO 0235+164

We investigate physical conditions in the two absorption systems present in AO 0235+164. A scan of the optical spectrum is presented. We confirm the redshift system at z=0.852, and give accurate equivalent widths for lines in the system at z=0.524. A study of the optical and 21 cm absorption spectra of the lower redshift gas shows that both types of absorption do not arise in the same line-producing region. Whereas the 21 cm features are formed in a few clouds with velocity widths ..delta..vapprox.6 km s/sup -1/, the optical lines are produced in a ''turbulent'' region with ..delta..vapprox.100 km s/sup -1/. We suggest three observational test to detect the proposed ''turbulent'' region. An analysis of the optical spectrum of the gas at z=0.852 shows that the absorbing region is characterized by ..delta nu..