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 to 2000Å) 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 (∼ 10 7 to 4 × 10 11 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 one 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 multi-dimensional 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, 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 better interpret the rest-frame UV spectra of star-forming galaxies at high-redshift, and stress that the degree of similarity between local starbursts and high-redshift galaxies in this multi-dimensional parameter space can already be tested empirically. The results on local starbursts suggest that the high-redshift 'Lyman Drop-Out' galaxies are typically highly reddened and extinguished by dust (average factor of 5 to 10 in the UV), may have moderately high metallicities (0.1 to 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 -3gas that can 'pollute' the inter-galactic medium.the vacuum-UV contains a wealth of spectral features, including the resonance transitions of most cosmically-abundant ionic species (cf. Morton 1991). These give UV spectroscopy a unique capability for diagnosing the (hot) stellar population and the physical, chemical, and dynamical state of gas in starbursts.Since ground-based optical observations of galaxies at high-redshifts sample the vacuum-UV portion of their rest-frame spectrum, we cannot understand how galaxies evolved without documenting the vacuum-UV properties of galaxies in the present epoch.In particular, a thorough understanding of how to exploit the diagnostic power of the rest-frame UV spectral properties of local starbursts will give astronomers powerful tools with which to study star-formation and galaxy-evolution in the early universe. Accordingly, we have undertaken an analysis of the vacuum-UV spectroscopic properties of a sample of 45 starburst and related galaxies in the local universe using the IUE archives. In section 2, we describe our analysis of these data. In section 3 we use the data to docum...

Rest‐Frame Ultraviolet Spectra of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \De

“…This systematic study is in some ways a high-redshift analog to the work of Heckman et al (1998), which characterized the region of UV spectroscopic parameter space inhabited by local starburst galaxies. In particular, we would like to gain more detailed information about the properties of the largescale outflows of interstellar material that are inferred in LBGs from blueshifted interstellar absorption and redshifted Ly emission, relative to the systemic stellar redshift Franx et al 1997;Lowenthal et al 1997).…”

Submillimetre-wavelength detection of dusty star-forming galaxies at high redshift

“…5,6 Furthermore, the effects of dust can cause the SFRs in the detected UV-bright objects to be grossly underestimated (see, e.g., ref. 7), and many rapid star forming galaxies may even be omitted from the optical samples.…”

Metals in Star-Forming Galaxies at High Redshift

“…More metal-rich galaxies are thought to host more powerful starbursts with correspondingly larger mechanical energy release by stellar winds and supernovae. The energy input leads to increased macroscopic turbulence and higher gas velocities at higher O/H (Heckman et al 1998). If the same applies to star-forming galaxies in the high-redshift universe, their measured equivalent widths again indicate an oxygen abundance of about 1/3 the solar value.…”

“…Heckman et al (1998) pointed out the close correlation of the Si IV λ1400 and C IV λ1550 equivalent widths with O/H in a sample of local star-forming galaxies. This correlation seems surprising, as these stellar-wind lines are deeply saturated.…”