Far Ultraviolet Spectroscopic ExplorerObservations of the Blue Compact Dwarf Galaxy Markarian 59

Abstract

New Far Ultraviolet Spectroscopic Explorer (FUSE) far-UV spectroscopy of the nearby metal-deficient (Z☉/8) cometary blue compact dwarf (BCD) galaxy Markarian (Mrk) 59 is discussed. The data are used to investigate element abundances in its interstellar medium. The H I absorption lines are characterized by narrow cores that are interstellar in origin and by broad wings that are stellar in origin. The mean interstellar H I column density is ~7 × 1020 cm-2 in Mrk 59. No H2 lines are seen and N(H2) is 1015 cm-2 at the 10 σ level. The lack of diffuse H2 is due to the combined effect of a strong UV radiation field that destroys the H2 molecules and a low metallicity that leads to a scarcity of dust grains necessary for H2 formation. P Cygni profiles of the S VI λλ933.4, 944.5 and O VI λλ1031.9, 1037.6 lines are seen, indicating the presence of very hot O stars and a stellar wind terminal velocity of ~1000 km s-1. By fitting the line profiles with multiple components having each a velocity dispersion b = 7 km s-1 and spanning a radial velocity range of 100 km s-1, some of which can be saturated, we derive heavy element abundances in the neutral gas. We find log N(O I)/N(H I) = -5.0 ± 0.3 or [O I/H I] = -1.5 for the neutral gas, about a factor of 10 below the oxygen abundance of the supergiant H II region, implying self-enrichment of the latter.