SALT long-slit spectroscopy of HE 0435-4312: fast change in the Mg II emission line shape
The MgII emission line is visible in the optical band for intermediate redshift quasars (0.4<z<1.6) and it is thus an extremely important tool to measure the black hole mass and to understand the structure of the Broad Line Region. We aim to determine the substructure and the variability of the MgII line with the aim to identify which part of the line comes from a medium in Keplerian motion. Using SALT telescope we performed ten spectroscopic observation of a quasar HE 0435-4312 (z=1.2231) over the period of 3 years (Dec 23/24, 2012 to Dec 7/8, 2015). We find that the line is well modeled by two Lorentzian components, and the relative strength of these components vary with time. The line maximum is shifted in a time-dependent way from the position of the Fe II pseudo-continuum, although the effect is not very strong, and the line asymmetry varies in time. We also note very different local conditions in the formation region of Mg II and FeII. The timescale for the line shape variability is of the order of the light travel time to the emitting region, therefore the changes are most likely due to the varying irradiation patterns and the presence of the two components does not imply two distinct emission regions.