UNSATURATED LOW-IONIZATION BROAD ABSORPTION LINES IN THE QUASAR SDSS J144842.45+042403.1

摘要

We present a detailed analysis of the exceptional low-ionization broad absorption line (LoBAL) quasar SDSS J144842.45+042403.1. The C Ⅳ absorption trough, which is likely saturated, has a box-shaped bottom at a flux level of 2%-5% of the unabsorbed flux. A large fraction of at least 80% of the C Ⅳ and Fe Ⅱ emission-line fluxes are obliterated by the CⅣ broad absorption lines (BALs), spanning 3000 km s~~(-1) in velocity. This indicates that the outflow intercepts most of the lines of sight to the continuum source and the broad emission line region (BELR). Therefore, the BAL region (BALR) should be located outside the BELR, and its size is no less than that of the BELR. The Al Ⅲ and Mg Ⅱ BAL troughs, which are well resolved, are found to be unsaturated and to show the same velocity structures. Meanwhile, their velocities largely overlap that of the C Ⅳ BAL, indicating that the LoBALs and the HiBALs (high-ionization BALs) are closely associated and most likely produced from the same outflow. The column densities of the Mg~+ and Al~(2+) ions in the outflow are measured. Results from an X-ray observation performed with Chandra suggest the presence of intrinsic X-ray absorption with a hydrogen column density of 10~(22)-10~(23) cm~(-2). The measured Mg~+ and Al~(2+) column densities can be well reproduced in models with a dimensionless ionization parameter of log U > -1.5 and a total hydrogen column density of N_H = 2.8 × 10~(22)U cm~(-2). A comparison of models with the observed properties also suggests that the outflow is either very highly ionized (with a high column density) or clumpy.