Far-Ultraviolet Spectrum of Fairall 9 with the Hopkins Ultraviolet Telescope

Abstract

We observed the Seyfert 1 galaxy Fairall 9 with the Hopkins Ultraviolet Telescope (HUT) for ~3500 s during the Astro-2 mission. The spectrum covers 820--1840 A with a resolution of ~3 A. The intrinsic far-UV continuum is unattenuated to wavelengths as short as 920 A (~880 A in the galaxy's rest frame) and can be fitted with a power law with f nu ~ nu -1.0 after a reddening correction corresponding to E_{B - V} = 0.03 mag. The power-law fit to the far-UV continuum of Fairall 9 may be extrapolated to connect to the soft X-ray component measured with ROSAT, forming a weak UV bump. Photoionization by such an energy distribution would produce relatively weak high-ionization lines. The intensity ratio of O VI lambda 1034 + Ly beta emission to that of C IV lambda 1549 is ~0.36. While this is typical for high-redshift quasars, it is one of the lowest among the low-luminosity, low-redshift AGNs observed by HUT. A correlation between the strength of O VI emission and the soft X-ray excess is supported by the observations of Fairall 9 and other AGNs.