SDSS J2125-0813: the evidence for the origination of optical Fe II emission lines from an accretion disc near a central black hole

We report on the radio-quiet quasar SDSS J2125-0813 which obviously emits optical Fe II emission lines and double-peaked broad Balmer emission lines. Using the accretion disc model for double-peaked, broad, low-ionization emission lines, we reproduce the composite line spectra at the optical band between 4100 and 5600 angstrom. Broad Fe II emission lines can be fitted simultaneously with the broad H beta and Mg I lines, such that all broad lines have an elliptical disc profile with the same disc parameters. This result indicates that the optical Fe II emission lines originate from the accretion disc near the central black hole which produces the double-peaked broad Balmer emission lines. Furthermore, we find that the object has a dimensionless accretion rate (m) over dot similar to 0.4-0.6, which is much larger than the accretion rate for the advection-dominated accretion flow (ADAF) mode, and that the energy budget of the accretion disc is enough to power the double-peaked broad Balmer emission lines.