Description
The Sloan Digital Sky Survey (SDSS) has repeatedly observed the eROSITA Final Equatorial Survey (eFEDS), providing optical spectroscopy for ~12,000 X-ray sources. Motivated by studies linking AGN obscuration to the optical-to-MIR color, r−W2 (Hickox et al. 2007; Andonie et al. 2025, submitted), I have used SDSS spectra to examine how AGN optical properties vary with r−W2 (i.e., obscuration) as a function of redshift. To do this, I stack optical spectra in bins of r−W2 and redshift and fit them using PyQSOfit, incorporating components for the host galaxy, AGN, and absorption and emission lines.
We find that r−W2 is strongly correlated with dust reddening. As expected, broad emission lines (e.g., broad Ha, Hβ, Hγ, Mg II, C III]) systematically decrease in flux with increasing r−W2, indicating growing dust extinction toward the quasar. Interestingly, the same trend is observed in narrow lines (e.g., [O III], [O II], narrow Hβ, [Ne III]), suggesting that the narrow-line region is more compact and closer to the SMBH than previously thought. We also find that the velocity of the [OIII] wing systematically increases with r-W2, also indicating a correlation between outflow rate and dust reddening. I will also present the variation of the X-ray spectra and optical photometric properties of the sample with r-W2. Finally, I will discuss how color selections are useful to identify different AGN populations, which will be crucial for analyzing the hundreds of thousands of optical spectra being observed by current and future facilities such as SDSS, DESI, and 4MOST.
