Spectral synthesis in the ultraviolet. II - Stellar populations and star formation in blue compact galaxies

Abstract

view Abstract Citations (192) References (86) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectral Synthesis in the Ultraviolet. II. Stellar Populations and Star Formation in Blue Compact Galaxies Fanelli, Michael N. ; O'Connell, Robert W. ; Thuan, Trinh X. Abstract Far-UV spectra of seven blue compact galaxies have been obtained with the IUE satellite. These objects span a range in luminosity of -21 <= M_B_ <= -13. We have investigated their stellar content and star formation history by applying the technique of optimizing population synthesis utilizing the library of far-UV stellar spectra developed by Fanelli, O'Connell, and Thuan. The far-UV absorption-line spectra of these galaxies are clearly composite, with the signatures of main-sequence types between O3 and mid-A. Most of the low-ionization absorption lines have a stellar origin. The Si IV and C IV features in several objects have P Cygni profiles. In Haro 1 the strength of Si IV indicates a significant blue supergiant population. The metal-poor blue compact dwarf Mrk 209 displays weak absorption lines, evidence that the stellar component has the same low metallicity as observed in the ionized gas (Z ~ 0.1 Z_sun_). Good fits to the data are obtained with the synthesis technique. We find that the solutions yield stellar luminosity functions which display large discontinuities, indicative of discrete star formation episodes or bursts. Continuous star formation cannot account for the observations. The current burst of star formation appears to have lasted for less than 10 Myr. In all cases except Mrk 209 there is evidence of earlier star formation episodes. For Haro 2 there were at least two earlier bursts, the most recent of which ended not more than ~20 Myr ago. The A star populations in our models point to significant star formation activity 500 Myr or more ago. In the cases other than that of Haro 2, we cannot distinguish between a few isolated bursts and a continuing series of short bursts separated by ~20-30 Myr. The amount of UV extinction is found to be low, 0.0 <~ E(B- V) <~ 0.35, significantly smaller than values derived from the Balmer decrement for the same object. The UV light preferentially emerges through windows of low optical depth. We find evidence for a positive correlation between the amount of UV extinction and the metallicity of the galaxy. UV synthesis provides an independent estimate of the current ionizing star content which appears to be in agreement with estimates based on observations in the visible, radio, and infrared. Star formation rates can also be estimated for the hot stars detected directly in the UV, and these rates highlight the intensity of the starbursts. In the more luminous galaxies Haro 1 and Haro 15, ~3 M_sun_ yr^-1^ of gas is being converted into massive (m >~ 10 M_sun_) stars, a value independent of the nature of the initial mass function. Publication: The Astrophysical Journal Pub Date: November 1988 DOI: 10.1086/166869 Bibcode: 1988ApJ...334..665F Keywords: Compact Galaxies; Star Distribution; Star Formation; Stellar Spectra; Ultraviolet Spectra; Absorption Spectra; Dwarf Galaxies; Main Sequence Stars; Stellar Luminosity; Supergiant Stars; Astrophysics; GALAXIES: STELLAR CONTENT; STARS: FORMATION; ULTRAVIOLET: SPECTRA full text sources ADS | data products NED (8) SIMBAD (7) MAST (1) INES (1) Related Materials (3) Part 1: 1987ApJ...321..768F Part 3: 1990ApJ...364..272F Part 4: 1992ApJS...82..197F