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Session 69 - Starburst Galaxies.
Display session, Thursday, June 11
Atlas Ballroom,

[69.06] Kinematics of I Zwicky 18 and Companion Galaxy

R. J. Dufour (Rice U.), P. L. Shopbell (Caltech)

We present preliminary results of deep Fabry-Perot imaging of ionized gas in the most metal-poor starburst galaxy known, I Zwicky 18, and of an emission ring in the possible companion Im galaxy to the NW. The observations were made in 1997 February using the Maryland-Caltech Fabry-Perot interferometer on the Palomar 200-inch telescope. Using an etalon kindly lent us by J. Bland-Hawthorn of the AAO, we were able to obtain \sim14 km s^-1 velocity resolution imagery of the H\alpha emission in I Zw 18 over a \pm250 km s^-1 velocity range around its mean radial velocity (+750 km s^-1). This velocity resolution is higher than in recent optical studies of the kinematics of this galaxy. We present maps of the spatial velocity structure at roughly 0.8'' seeing-limited resolution and compare the kinematics with the morphology of the ionized gas and young stars evident from HST WFPC2 images in H\alpha, [O \sc iii], and BVR bandpasses. We interpret the complex velocity components resolved in terms of the interplay between starbursts, local stellar winds, large superbubbles, and the possible tidal effects from a nearby companion Im galaxy of comparable mass. We also compare and contrast our results to those of two other recent investigations. Ultimately, our goal is to construct a model relating the observed ionized gas kinematics to the recent star formation history of I Zw 18 evident from analysis of the HST imagery.

In addition, we present medium resolution optical spectra of the faint ring nebula in the companion galaxy obtained in 1998 March with the Keck II telescope. We confirm previous reports that the emission lines appear only to be Balmer H \sc i lines with no [O \sc ii] or [O \sc iii] detected. The likelyhood that it is a non-radiative SNR is suggested.

This study was supported in part by AURA/STScI grants GO-5434, GO-5915, and GO-6826 to Rice University and/or Caltech.

Program listing for Thursday