The Ultraviolet Spectroscopic Properties of Local Starbursts: Implications at High Redshift

Abstract

We report the results of a systematic study of the vacuum ultraviolet (λ ~= 1150-2000 Å) spectra of a sample of 45 starburst and related galaxies observed with the IUE satellite. These span broad ranges in metallicity (from 0.02 to 3 times solar), bolometric luminosity (~10⁷-4 × 10¹¹ L_⊙), and galaxy properties (e.g., including low-mass dwarf galaxies, normal disk galaxies, and massive galactic mergers). The projected size of the IUE spectroscopic aperture is typically 1 to several kpc and therefore usually encompasses the entire starburst and is similar to the aperture sizes used for spectroscopy of high-redshift galaxies. Our principal conclusion is that local starbursts occupy a very small fractional volume in the multidimensional manifold defined by such fundamental parameters as the extinction, metallicity, and vacuum-UV line strengths (both stellar and interstellar) of the starburst and the rotation speed (mass) and absolute magnitude of the starburst's ``host'' galaxy. More metal-rich starbursts are redder and more heavily extinguished in the UV, are more luminous, have stronger vacuum-UV lines, and occur in more massive and optically brighter host galaxies. We advocate using these local starbursts as a ``training set'' to learn how to interpret the rest frame UV spectra of star-forming galaxies at high redshift better, and we stress that the degree of similarity between local starbursts and high-redshift galaxies in this multidimensional parameter space can already be tested empirically. The results on local starbursts suggest that the high- redshift ``Lyman Dropout'' galaxies are typically highly reddened and extinguished by dust (by an average factor of 5-10 in the UV), may have moderately high metallicities (0.1-1 times solar?), are probably building galaxies with stellar surface-mass densities similar to present-day ellipticals, and may be suffering substantial losses of metal-enriched gas that can ``pollute'' the intergalactic medium.