Black Hole Mass Estimation of a Background Quasar in the Vicinity of the cD Galaxy Holm 15A

This study analyzes spectra from the central region of the galaxy cluster Abell 85 observed with GTC/OSIRIS, focusing on the cD galaxy Holm 15A and the point-like X-ray source SDSS J004150.75-091824.3, projected 13.74\arcsec from Holm 15A. For the latter, we found it is a background quasar with a redshift of $1.56386 \pm 0.00397$, ruling out the possibility of it being a rogue BH gravitationally bound to Holm 15A. In addition, using single-epoch spectroscopy, we report that the quasar J004150 hosts a Supermassive Black Hole (SMBH) with a mass of $\log(M_{\text{BH}}/\mathrm{M_{\odot}}) = 8.72 \pm 0.26$.