The optical properties of IR-selected and MG II broad absorption line quasars

Abstract

Spectra covering the rest frame region λλ5000-6800 are presented for 19 IR-selected AGNs. This sample is of particular interest because it contains four low-ionization broad absorption line QSOs (BALQSOs) out of 38 objects. Measurements of emission lines in the observed region, including Hα, [O III] λ5007, the Fe II emission, He I λ5876, and the Na I D doublet are tabulated, together with a four-parameter description of the Hα line profile. A variety of statistical tests show no strong differences in emission- line properties between these IR-selected AGNs and a well-studied sample of optically selected QSOs. Within the IR-selected sample, however, a number of properties show significant differences between the four BALQSOs and the remaining objects. 1. The low-ionization BALQSOs have no or very weak [O III] emission compared to other objects. It is argued that this is an indication that these BALQSOs are not seen along a preferred line of sight but are drawn from a class of objects in which the covering factor of the absorbing material is in excess of 10% and may approach unity. 2. He I λ5876 is systematically weaker (and Na I λλ 5889, 5995 may be stronger) in the BALQSOs than in the non-BALQSOs. This suggests an intrinsic difference in the emission-line regions of the two different classes. 3. The BALQSOs all have Hα lines with large blue asymmetries. This excess emission on the blue side of the line profile could be from the BAL material itself. 4. Three of the four BALQSOs show Na I D absorption, ranging from a single weak doublet in 14026+4341 at an outflow velocity of 1000 km s^-1^ to a 11,000 km s^-1^ wide trough in 0759+6508. The individual doublets seen are all optically thin. 5. Unlike the other IR-selected objects, the (Fe II-subtracted) continuum of the BALQSOs show broad features which we cannot easily explain. Possible explanations include molecular band emission and absorption by an expanding BAL shell of a continuum scattered from dust within the shell.