Environmental Effects on Properties of Type 2 QSOs

Type 2 QSOs (QSO2s) are intrinsically luminous QSOs embedded in dusty environments. In this work, we study the radio, optical, and soft X-ray properties of 887 optically selected [O III]-based QSO2s (Reyes et al. 2008) at z<0.83 to investigate the connection between QSO2s and their environments. We use SDSS data to measure the luminosity-limited galaxy counts in a volume centered on each QSO2 and defined by Δ z<0.1 (based on photometric redshifts) and within a projected distance of 1.5 Mpc of the QSO2 (δ_1.5Mpc). We used ROSAT All Sky Survey (RASS) data to estimate the X-ray excess. Hsu & Chen (2010), after correcting for Galactic absorption, obtain a lower limit for the intrinsic neutral hydrogen column density (N_H) toward each of the QSO2s. About 50% of these sources have N_H > 10²² cm^-2. We take this value as a threshold to subdivide QSO2s into high- and low-N_H groups, and compare their environments. The distributions δ_1.5Mpc of the two populations show that, in regions of higher galaxy density, QSO2s are dominated by the high-N_H population (Figure 1), suggesting a closer connection between more obscured QSO2s and surrounding galaxies.