CIV absorption in BAL QSOs

We quantify this diversity by exploring the distribution of the CIV BAL properties, full width at half-maximum (FWHM), maximum depth of absorption and its velocity shift (v_md_), using the Sloan Digital Sky Survey DR7 quasar catalogue. We find the following: (i) Although the median CIV BAL profile in the quasar rest-frame becomes broader and shallower as the UV continuum slope ({alpha}UV at 1700-3000{AA}) gets bluer, the median individual profile in the absorber rest-frame remains identical, and is narrow (FWHM=3500km/s) and deep.

Only 4 percent of BALs have FWHM>10000km/s. (ii) As the HeII emission equivalent width (EW) decreases, the distributions of FWHM and v_md_ extend to larger values, and the median maximum depth increases. These trends are consistent with theoretical models in which softer ionizing continua reduce overionization, and allow radiative acceleration of faster BAL outflows.