A Survey of a Complete Sample of HII Galaxies to Detect HI Companions

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Session 33 -- Galaxies II
Oral presentation, Wednesday, January 12, 2:15-3:45, Crystal Forum Room (Crystal City Marriott)

[33.02] A Survey of a Complete Sample of HII Galaxies to Detect HI Companions

C.L.Taylor (University of Minnesota)

\font\bigtenrm = cmr10 scaled\magstep2 \def\arcsec{$^{\prime \prime}$} \def\kms{km\thinspace s$^{-1}$} \def\cm2{cm$^{-2}$} \font \sc = cmr10 \def\HI{H{\sc I}} \def\HII{H{\sc {II}}}

Title: A Complete Survey of \HII\ Galaxies to Detect \HI\ Companions

C.L. Taylor (U.Minnesota), E. Brinks (NRAO), E.D. Skillman (U.Minnesota)

\HII\ Galaxies are \HI\ rich galaxies which contain one or a few high surface brightness optical knots whose spectra resemble those of \HII\ regions. These knots are areas of intense star formation. The current star formation rates are too high to last a Hubble time, leading to the hypothesis that \HII\ galaxies undergo star formation in discrete bursts. (Searle \& Sargent, 1972, ApJ 173, p. 25) One possible explanation for this phenomenon is that a gravitational interaction triggers the burst of star formation in an otherwise quiescent galaxy.

Taylor, Brinks, \& Skillman (1993, AJ 105, p. 128) mapped in \HI\ 9 isolated \HII\ galaxies with the VLA in its most compact configuration. Five \HI\ companions were discovered near four of the \HII\ galaxies. These \HI\ companions were within a radius of 30 arcmin and within 240 \kms. The companions were typically one order of magnitude smaller than their parent galaxies in both neutral hydrogen and total mass.

Motivated by this success, we have obtained 21-cm VLA observations of a complete, volume limited sample of \HII\ galaxies without obvious interaction partners. The current sample consists of nineteen members with velocities less than 2500 \kms. From our observations we have positively identified 10 companions around 8 galaxies, plus a further four sample members which are gravitationaly interacting with nearby sample members, for a total of at least 12 interacting systems. A preliminary analysis of these objects and the statistical significance of the detection rate will be discussed.

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