CIV BAL disappearance in SDSS QSOs

We detect 73 disappearing BALs in the spectra of 67 unique sources. This corresponds to 3.9% of BALs disappearing within 4.9yr (rest frame), and 5.1% of our BAL QSOs exhibit at least one disappearing BAL within 4.9yr (rest frame). We estimate the average lifetime of a BAL along our line of sight (~=80-100yr), which appears consistent with the accretion disk orbital time at distances where winds are thought to originate.

We inspect various properties of the disappearing BAL sample and compare them to the corresponding properties of our main sample. We also investigate the existence of a correlation in the variability of multiple troughs in the same spectrum, and find it persistent at large velocity offsets between BAL pairs, suggesting that a mechanism extending on a global scale is necessary to explain the phenomenon. We select a more reliable sample of disappearing BALs on the basis of some criteria adopted in a previous publication, where a subset of our current sample was analyzed, and compare the findings from the two works, obtaining generally consistent results.