THE SPECTRAL ENERGY DISTRIBUTION OF THE z = 3 QUASAR: HS 1946 + 7658

摘要

For the bright z = 3.02 radio-quiet quasar, HS 1946 + 7658, we have obtained radio to X-ray data within the past year: 5 GHz and 1415 MHz data from the VLA; IR photometry at J, H, K, L′ (3.4 μm) and N; IR spectroscopy; UBVRI photometry; optical spectrophotometry and high-resolution spectra; and an X-ray spectrum from the ROSAT PSPC. The spectral energy distribution (SED) constructed from these data is compared to the mean SED for a set of low-redshift quasars, and while they appear generally similar, there are several differences. In relation to the low-redshift mean, the SED of HS 1946 + 7658 shows (1) only an upper limit at 10 μm (a rest wavelength of 2.5 μm), indicating that HS 1946 + 7658 does not have a strong near-IR excess such as hot dust would produce; (2) relatively weak Fe Ⅱ and Balmer continuum emission at ～3000 A; and (3) a steeper turndown shortward of Lyα, even after correction for the Lyα forest absorption lines.