UV FeII emission model of HE 0413−4031 and its relation to broad-line time delays

Context. FeII emission is a well-known contributor to the UV spectra of active galactic nuclei and the modeling of this part may affect the results obtained for the MgII λ2800 emission, which is one of the lines used for black hole mass measurements and cosmological applications.
Aims: We tested different FeII emission models when modeling the UV emission of the intermediate-redshift quasar HE 0413−4031 to see how the use of a specific template affects the MgII λ2800 line properties and the measurement of the MgII λ2800 and UV FeII time delays with respect to the continuum.
Methods: We used the 11-year monitoring of the selected quasar HE 0413−4031 with the South African Large Telescope (SALT), and we supplemented this monitoring with the near-IR spectrum taken with the SOAR telescope, which gave access to the Hβλ4861 and [OIII] λλ4959, 5007 emission lines at the rest frame and allowed for a precise measurement of the redshift.
Results: A new redshift determination (z = 1.39117 ± 0.00017) using [OIII] λλ4959, 5007 gave a very different value than the previous determination based only on the UV FeII pseudocontinuum (z = 1.3764). It favors a different decomposition of the spectrum into MgII and UV FeII emissions. The line characteristics and the time delay of the MgII emission (224₋₂₃⁺²¹ days) are not significantly affected. However, in comparison with the previous analysis, the rest-frame UV FeII time delay (251₋₇⁺⁹ days) is consistent with the inferred UV FeII line full width at half maximum (FWHM) of 4200 km s⁻¹ that is only slightly smaller than the MgII line FWHM. Hence the FeII-emitting material is more distant than the MgII-emitting gas in HE 0413−4031 by ∼0.023 pc (4700 AU). The inferred velocity shift of both MgII and UV FeII lines with respect to the systemic redshift is now rather low, below 300 km s⁻¹. In addition, we constructed an updated MgII radius-luminosity (R − L) relation from 194 sources, which is more than double the previous sample. The MgII R − L relation is flatter than the UV FeII, optical FeII, and HβR − L relations. While the new decomposition of the spectrum is satisfactory, we see a need to create better FeII templates using the newest version of the code CLOUDY.

Based on observations made with the Southern African Large Telescope (SALT).