Global Far‐Ultraviolet (912–1800 A) Properties of Star‐forming Galaxies

Abstract

We present the results of an archival study of the Hopkins Ultraviolet Telescope (HUT) Astro-2 database. Nineteen spectra of star-forming regions and starburst galaxies were retrieved, reprocessed, and analyzed. The spectra cover the wavelength region 912-1800 A, providing access to the domain of peak luminosity from a young stellar population. We created an atlas of galaxy spectra documenting the continuum and line properties with an emphasis on the relatively unexplored spectral region below 1200 A. The dust obscuration law was derived from a comparison of the HUT spectra with synthetic population models. The law is similar to the commonly adopted starburst reddening curve at longer wavelengths and approaches the Milky Way law near the Lyman break. A simple power-law parameterization is given, which allows users to express the reddening law in terms of the stellar or nebular color excess at ultraviolet or optical wavelengths. The star formation histories were derived from the reddening-corrected continua and the ultraviolet line profiles. We find typical ages of tens of Myr and star formation densities ranging from less than 0.1 to more than 10 M⊙ yr-1 kpc-2. The absorbed ultraviolet luminosity correlates very well with the far-infrared luminosity, as expected if the dominant dust absorption occurs in a foreground screen. This correlation holds even for the most luminous galaxies in our sample, whose IRAS luminosity is in excess of 1011 L⊙.