Characteristics of Kiso Ultra-Violet Excess Galaxies

Abstract

We examined the general characteristics of the Kiso Ultra-violet Excess Galaxies (KUGs). We present for the first time the quantitative expressions for the criteria of the KUGs; the boundary color separating the KUGs from the non-KUGs is (B-V)_{T} = 0.74 and the KUG degrees of UV strength are found to correlate with the mean (B-V)_{T} colors. We investigate the nature of the KUGs, a sample of blue galaxy population, and show that (1) about a half of the KUGs are spiral galaxies with Sb to Scd, (2) the KUGs are biased to late-type galaxies and include early-type galaxies with young star populations, and (3) the KUGs are preferably found among less luminous galaxies with log L(B) < 10. The KUGs also contain the post-starburst galaxies, many of which are found among the blue galaxy population at intermediate redshifts. The analysis of the far-infrared data shows that a typical present-to-past star formation rate for a KUG is 0.4.Comment: Revised version of astro-ph/9706088, accepted manuscript for AJ; uuencoded gzip'ed tar'ed file containing 25 files; a manuscript (aasms4), 7 tables (aj_pt4), 17 PS figures; To be appeared in The Astronomical Journal, Vol. 114, No. 5 (1997 November issue