A candidate of a type 2 quasi-stellar object at z=0.9:: Large X-ray absorption with a strong broad Hα emission line

Deep hard X-ray and near-infrared observations of a type 2 radio-quiet quasi-stellar object (QSO) candidate at z = 0.9, AX J08494+4454, are reported. The 0.5-10 keV Chandra X-Ray Observatory spectrum of AX J08494+4454 is hard and is explained well with a power-law continuum absorbed by a hydrogen column density of (2.3 +/- 1.1) x 10(23) cm(-2). The 2-10 keV luminosity of the object is estimated to be 7.2(-2.0)(+3.6) x 10(44) ergs s(-1), after correcting the absorption, and reaches hard X-ray luminosities of QSOs. The large X-ray absorption and the large intrinsic luminosity support the original identification of AX J08494+4454 as a type 2 radio-quiet QSO. Nevertheless, the deep Subaru/IRCS J-band spectroscopic observation suggests the presence of a strong broad Halpha emission line from AX J08494+4454. If real, the broad Halpha emission line has a velocity width of 9400+/-1000 km s(-1), which corresponds to a typical broad Balmer line velocity width of a luminous QSO. The existence of the strong broad Halpha line means that the object is not a type 2 QSO but a luminous cousin of a Seyfert 1.9 galaxy in the source-frame optical spectrum. The Balmer decrement of broad lines and the broad Halpha emission to the hard X-ray luminosity ratio suggest that the nucleus is affected by dust extinction with an A(V) of 1-3 mag in the optical wavelength. Optical colors and faint optical magnitudes of AX J08494+4454 are consistent with the model. The estimated amount of dust extinction is much smaller than that expected from the X-ray column density (A(V) = 130+/-60 mag).