Three quasars from a survey of strong 25-μm emitters

Abstract

We have carried out a spectroscopic survey of 750 sources that are strong 25-μm emitters from the IRAS Faint Source data base. Many of these sources are previously unknown active galactic nuclei including new IRAS quasars, three of which we describe here: F21382-2659, Z06367-6845 and Z05558-5008. They are all radio and X-ray quiet, and compared to the known IRAS quasars they have similar 25-μm luminosities, L(25 μm), but lower values of L(25 μm)/L(B). Their F(25 μm)/F(60 μm) IRAS colours lie in the range 0.33 to 1.08, indicating the presence of relatively warm dust, presumably in a dusty torus surrounding the central source, and with temperatures similar to those of the known IRAS quasars. The quasar with the warmest dust, F21382-2659, exhibits broad (full width at half-maximum ∼4000 km s-1) asymmetric Balmer lines with Hγ having an opposite asymmetry to the other broad lines; also Hβ (only) is double-peaked. Fe II is very weak in F21382-2659 but strong in the other two quasars, and the anticorrelation between Fe II and [O III] holds as anticipated. Two of the quasars are unpolarized: although F21382-2659 is optically polarized (2.1 per cent at 4950 Å), we argue that this provides little insight into the orientation of its dust torus relative to the line of sight.