Astronomy and Astrophysics – Astrophysics
Scientific paper
1997-06-23
Astronomy and Astrophysics
Astrophysics
43 pages including figures; uses aaspp and psfig; 5 tables use apjpt4; Accepted (11 June 1997) for publication in the Astrophy
Scientific paper
We present a longslit optical spectrophotometric survey in the irregular "post-starburst" galaxy NGC 1569 to search for chemical gradients and inhomogeneities in the interstellar medium. Despite the presence of two massive evolved starclusters and numerous HII regions, we find no evidence for chemical gradients or inhomogeneities that may be attributed to enrichment from the recent star formation activity. The chemical properties are consistent with 12+log(O/H)=8.19+/-0.04 and log(N/O)=-1.40+/-0.05 at all locations. No localized chemical self-enrichment ("pollution") from massive star evolution is found, even though the data are sensitive to the chemical yields from as few as two or three massive stars. Flat chemical abundance profiles appear to be the rule rather than the exception in low-mass galaxies. Strong chemical signatures in the surrounding interstellar material should be detected unless one or more of the following are true: 1) Different star forming regions throughout the studied galaxies ``conspire'' to keep star formation rates and global abundances uniform at all times, 2) ejecta from stellar winds and supernovae are transported to all corners of the galaxy on timescales of <10^7 yr, and are mixed instantaneously and uniformly, or 3) freshly synthesized elements remain unmixed with the surrounding interstellar medium and reside in a hard-to-observe hot 10^6 K phase or a cold, dusty, molecular phase. We advance the third scenario as the most plausible, and we suggest ways to locate the chemical products of massive star formation in starburst galaxies.
Kobulnicky Henry A.
Skillman Evan D.
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