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A SEARCH FOR H I LYMAN α COUNTERPARTS TO ULTRA-FAST X-RAY OUTFLOWS

Prompted by the H I Lyα absorption associated with the X-ray ultra-fast outflow at −17 300 km s in the quasar PG 1211+143, we have searched archival UV spectra at the expected locations of H I Lyα absorption for a large sample of ultra-fast outflows identified in XMM-Newton and Suzaku observations. Sixteen of the X-ray outflows have predicted H I Lyα wavelengths falling within the bandpass of spectra from either the Far Ultraviolet Spectroscopic Explorer or the Hubble Space Telescope, although none of the archival observations were simultaneous with the X-ray observations in which UFOs were detected. In our spectra broad features with full-width at half-maximum of 1000 km s have 2-σ upper limits on the H I column density of generally < ∼ 2× 10 13 cm. Using grids of photoionization models covering a broad range of spectral energy distributions, we find that producing Fe XXVI Lyα X-ray absorption with equivalent widths > 30 eV and associated H I Lyα absorption with NHI < 2 × 10 13 cm requires total absorbing column densities NH > 5 × 10 22 cm and ionization parameters log ξ > ∼ 3.7. Nevertheless, a wide range of SEDs would predict observable H I Lyα absorption if ionization parameters are only slightly below peak ionization fractions for Fe XXV and Fe XXVI. The lack of Lyα features in the archival UV spectra indicates that either the UFOs have very high ionization parameters, very hard UV-ionizing spectra, or that they were not present at the time of the UV spectral observations due to variability.