Mg⁺ absorptions on the radial and transverse directions of quasars

Two quasars close in the celestial sphere but with evidently distinct systemic redshifts constitute a quasar pair. Using the quasar spectra gathered by the Sloan Digital Sky Survey, this research obtained 22 quasar pairs, where the associated Mg II lambda lambda 2796, 2803 absorption lines at a close systemic redshift are identified along the transverse direction toward the background quasar and the radial direction toward the foreground quasar for each of the pairs. In the transverse direction, we observe that the Mg IIAA2796, 2803 detected would be dominated by the halos of foreground quasars, while the Mg II lambda lambda 2796, 2803 detected in the radial direction can be originated in quasar outflows, host galaxies, and halos. If the absorption lines originated in quasar host galaxies or halos, the relative velocities along the sightline and the strengths and widths of the absorption lines detected in the radial direction are consistent with those detected in the transverse direction. However, all the relative velocities along the sightline and the strengths and widths of the outflow absorption lines detected in the radial directions are likely different from those detected in the transverse directions.