Emission Lines from Companion Galaxies of QSOs

Anticipating new spectroscopic studies of quasar companions, we calculate expected emission line spectra for the companion galaxies. Under the assumption of isotropic photoionizing radiation, we predict equivalent widths for Hα, Hβ, [O iii] λ5007, [O ii] λ3727, [Ne iii] λ3869, and Mg ii λ2798 lines. We consider 6 quasars, two of which (PKS 213514 and PKS 2349-014) have very close companions with projected separation < 4h kpc. For these companions the calculated emission lines should be easily observable, with Wλ ∼> 20 Å for the [O iii], [O ii], and Hα lines. Presence of strong emission lines from the companions occupying only a tiny solid angle would suggest that 1) quasar radiation is isotropic; 2) companion galaxies have measurable amount of gas, which can be assessed using the photoionization models; 3) host galaxies, if present, have been depleted of gas or do not interact with the companions. Subject headings: quasars: emission lines — quasars: general — quasars: individual (PKS 2135-14, PKS 2349-014, PHL 909, NAB 0205+02, HE 1029-1401, PKS 0405-123)