Abstract:
Measurement of black hole mass for low-z (z≤ 0.8) Active Galactic Nuclei (AGNs) is difficult due to the strong contribution
from host galaxy stellar light necessitating detailed spectral decomposition to estimate the AGN luminosity. Here, we present
an empirical relation to estimate host galaxy stellar luminosity from the optical spectra of AGNs at z ≤ 0.8. The spectral
data were selected from the fourteenth data release of the Sloan Digital Sky Survey (SDSS-DR14) quasar catalogue having a
signal-to-noise ratio at 5100 Å (SNR5100) >10 containing 11 415 quasars. The median total luminosity (log (Ltotal/[erg s−1])),
stellar luminosity (log (Lstar/[erg s−1])), and AGN continuum luminosity ((log Lcont/[erg s−1])) in our sample are 44.52, 44.06,
and 44.30, respectively. We fit the AGN power-law continuum, host galaxy, and iron blend contribution, simultaneously over
the entire available spectrum. We found the host galaxy fraction to anticorrelate with continuum luminosity and can be well represented by a polynomial function, which can be used to correct the stellar light contribution from AGN spectra. We also
found anticorrelation between host galaxy fraction and iron strength, Eddington ratio, and redshift. The empirical relation gives
comparable results of host-fraction with the image decomposition method.
