JWST Spectroscopic View of a Rapidly Growing Dust-obscured Quasar at $z \sim 4$: Effect of Dust Extinction Correction on Black Hole Mass and Eddington Ratio Estimation

Abstract

In the merger-driven galaxy evolution scenario, the central supermassive black holes (SMBHs) in dust obscured galaxies grow rapidly. Interestingly, a recent work \citep{suh24} on a dust-obscured galaxy, LID-568 at $z=3.965$, has shown that its SMBH is growing extremely fast at about 40 times of the Eddington-limited accretion rate (i.e., super-Eddington accretion). However, the heavy dust extinction of the host galaxy could affect the result if not corrected properly. Here, we analyze James Webb Space Telescope (JWST) NIRSpec/IFU and MIRI spectra of LID-568. By measuring its bolometric luminosity ($L_{\rm bol}$) and BH mass ($M_{\rm BH}$) using an extinction-free estimator based on mid-infrared spectra, we obtain $L_{\rm bol} = 10^{46.83\pm0.07}\,{\rm erg\,s^{-1}}$ and $M_{\rm BH} = 10^{8.43\pm0.15}\,M_{\odot}$. The measured Eddington ratio ($\lambda_{\rm Edd}$) is 1.97$\pm$0.88, consistent with the accretion rate at the Eddington limit; in other words, not in super-Eddington in a significant manner. This result underscores challenges and the importance of carefully considering dust extinction when analyzing the BH growth in dust-obscured quasars.