| Abstract
| - We present new and archival Chandra snapshot (≈10 ks each) observations of 15 optically identified [from the Sloan Digital Sky Survey (SDSS)] Type 2 quasars at z= 0.40-0.73. When combined with existing X-ray data, this work provides complete X-ray coverage for all 25 radio-quiet Type 2 quasars with log L[O III]> 9.28 L⊙ from Zakamska et al. Two targets out of 15 were not detected by Chandra and most of the remaining sources are X-ray weak, with nine having less than 10 counts in the 0.5-8 keV band. Low- to moderate-quality spectral analysis was limited to three sources, whose properties are consistent with the presence of column densities in the range NH≈ 1022-1023 cm−2 in the source rest frame. If the [O iii] luminosity is a reliable proxy for the intrinsic X-ray luminosity, the current X-ray data indicate that Compton-thick quasars may hide among ≈65 per cent of the SDSS Type 2 quasar population (LX,meas/LX,[O III]< 0.01); however, since the Type 2 quasar sample is selected on [O iii] luminosity, the estimated Compton-thick quasar fraction may be overestimated. Using archival Spitzer observations, we find that ≈50 per cent of SDSS Type 2 quasars appear to be obscured by Compton-thick material based on both the LX,meas/LX,mid-IR (where mid-IR corresponds to rest frame 12.3 μm) and LX,meas/LX,[O III] ratios. We use this information to provide an estimate of the Compton-thick quasar number density at z≈ 0.3-0.8, which we find is in broad agreement with the expectations from X-ray background models.
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