Hubble Space Telescope observations of He 2-10: Outflows and young super-star clusters

We use Hubble Space Telescope (HST) WFPC2 optical images and GHRS ultraviolet spectroscopy to examine the recent star formation history and properties of the Wolf-Rayet galaxy He 2-10. The high spatial resolution afforded by HST has allowed the identification of a number of starburst knots, or "super-star clusters" (SSCs). The spatial morphology newly revealed by these HST images exhibits a prominent dust lane between the starburst regions known as A and B and a spur of material to the northwest of the nuclear region. Broadband photometry of the SSCs confirms that these objects have ages as young as a few Myr and masses up to 10(5) M-circle dot. Narrowband Ha photometry of the SSCs indicates large equivalent widths for nearly half of them, consistent with ages less than 10 Myr. Since an appreciable fraction of SSCs are this young, the star formation history necessarily must be strongly peaked and not continuous. GHRS UV spectra were obtained for sections of the two starburst regions and were used to determine the parameters of the starburst regions. For a stellar population produced in a single burst with stellar masses between 1 and 100 M-circle dot, the UV luminosities indicate regions A and B have masses between 1.6-2.6 x 10(6) M-circle dot and 2.6-6.6 x 10(4) M-circle dot, respectively. The total starburst mass was between 1 and 100 M-circle dot consistent with the UV luminosity ranges between 1.6 and 2.6 x 10(6) M-circle dot and 2.6 and 6.6 x 10(4) M-circle dot for regions A and B, respectively. The observed integrated H alpha flux is similar to that predicted by the models, implying that the leakage and/or dust absorption of Lyman continuum photons from the starburst regions is small. The integrated Ha equivalent widths of the two regions are substantially smaller than predicted, We attribute this to contamination by the continuum in the starburst regions (the starburst knots do not uniformly fill the GHRS apertures). The UV spectroscopy of starburst region A indicates a large-scale outflow of the interstellar medium of He 2-10 with speeds of at least 360 km s(-1) and a total mass of at least 106 Mo. We estimate that the mass in metals which He 2-10 will expel is enough to raise primordial abundances in approximate to 1 Mpc(3) to 10(-3) to 10(-2) solar.