The variability of UV/optical Fe ii emission lines in a QSO: SDSS J142052.43+525622.4

Abstract

The variability of the UV and optical Fe ii emission is investigated for a QSO, SDSS J142052.43+525622.4 ($z = 0.676$), with 50 spectroscopic observations covering 1047 d in the observed frame. This QSO is selected from the Sloan Digital Sky Survey-Reverberation Mapping (SDSS-RM) project. Using multiple components to model the pseudo-continuum and emission lines (Mg ii, H$\beta $, [O iii], Fe ii), some results are outlined as follows: (i) Based on the distribution of the [O iii] 5007 A luminosity, the flux-calibration uncertainty is about 7.8%. For the UV continuum, this QSO appears bluer when it gets brighter, while we cannot find this trend for the optical continuum. It is possible that there is a contamination from the hosts in the optical continuum. (ii) There is a strong correlation between the UV and optical Fe ii equivalent width, which shows an intimate connection between them. However, the full width at half-maximum (FWHM) of the UV Fe ii is generally larger than FWHM of the optical Fe ii. The redshift of the UV Fe ii is generally larger than for the optical Fe ii. These results show that the region emitting the UV Fe ii is located inside and has a larger inflow than the optical Fe ii. (iii) Based on the collisionally ionized model, the hydrogen column density is ${\sim}10^{23}\mbox{ cm}^{-2}$ calculated from the intensity ratio of the optical to UV Fe ii. This Fe ii intensity ratio has a strong relation with the UV/optical continuum spectral index. (iv) The intrinsic Baldwin effect for the UV/optical Fe ii is significant and the EW of the UV Fe ii decreases more quickly than the optical Fe ii when this QSO becomes bright.