Relations between the Fractional Variation of the Ionizing Continuum and C iv Broad Absorption Lines with Different Ionization Levels

Abstract

This paper explores the correlation between the fractional variation of the ionizing continuum and C iv broad absorption lines (BALs) with different ionization levels. Our results reveal anti-correlations between fractional variation of the continuum and fractional equivalency width (EW) variation of the C iv BALs without Al iii BAL/mini-BALs at corresponding velocities, providing evidence for the widespread influence of the ionizing continuum variability on the variation of HiBALs. Conversely, for C iv BALs accompanied by Al iii BAL/mini-BALs (LoBAL groups), no significant correction is detected. The absence of such a correlation does not rule out the possibility that variations in these low-ionization lines are caused by ionizing continuum variability, but rather suggests the influence of BAL saturation to some extent. This saturation effect is reflected in the distribution of the fractional EW variation, where the C iv BAL group accompanied by Al iii BAL has a smaller standard deviation for the best-fitting Gaussian component than the two BAL groups without Al iii BAL. However, the distribution of fractional variation of their continuum does not show any significant difference. Besides the saturation influence, another potential explanation for the lack of correlations in the LoBAL groups may be the effects of other variability mechanisms besides the ionization change, such as clouds transiting across the line of sight.