STRONG Ca Ⅱ ABSORPTION LINES IN THE REDDENED QUASAR SDSS J2339-0912: EVIDENCE OF THE COLLISION/MERGER IN THE HOST GALAXY?

摘要

We report the detection of strong Ca Ⅱ/Mg Ⅱ absorption lines at the quasar redshift in the narrow-line quasar SDSS J2339 — 0912 (z — 0.6604). The quasar exhibits strong Fe Ⅱ, a small Balmer emission line width, and a very red B - K_s color. Both the optical continuum and broad emission lines are reddened by SMC-like dust of E(B — V) approx= 1.0 mag, while its near-infrared color (J — K_s = 1.60) shows little reddening. The Ca Ⅱ absorption lines are saturated and resolved with an FWHM of 362 km s~(-1) and an equivalent width of W_(Cank) = 4.2 A (in the source rest frame). Mg Ⅱ absorption lines are also saturated and have a similar line width. The line profile and the fact that there is no evidence of starlight from the host galaxy suggest that these absorption lines are not of a stellar origin. The ratio of column density of Ca Ⅱ to that of dust is consistent with that of the interstellar medium (ISM) in our Galaxy. We suggest that both the heavy reddening and the large absorption line width are due to the highly disturbed ISM on the line of sight toward the quasar and that the disturbance is caused by a galaxy collision or even merger in the quasar host galaxy.