High-resolution spectroscopy of flat-spectrum quasars. I. Redshifted emission and absorption in PKS 2145+067

Abstract

We report Very Large Telescope (VLT) observations of the quasar PKS 2145+067. We obtained high-resolution (R≈100 000 or 3 km s^-1) optical spectra with the UV-Visual Echelle Spectrograph (UVES) at the VLT UT2 telescope. The emission redshift measured from \ion{[O}{iii]} is z_em =1.0003. In our spectra, the well-known intervening metal-rich absorption system at z_abs =0.79089 shows Mg II absorption lines resolved into 15 velocity components with a total spread of about 206 km s^-1. This absorption is consistent with a line of sight passing through the extended gaseous halo of a disk galaxy. The derived Doppler line broadening parameters are in the range b=2 to 5 km s^-1. We also detected absorption lines of Mg I, Fe II, and Ca II in the same system. The ionization state of the absorbing gas is analyzed and compared with previous studies of PKS 2145+067. Finally, we discuss the implications of high-resolution data for proposed cosmological variations of the fine-structure constant.

Based on observations collected at the European Southern Observatory, Paranal, Chile (ESO Programmes 67.C-0157 and 70.C-0239).