Expanding Ionized Shells around Star Forming Regions in the Most Metal-Poor Blue Compact Galaxies

Abstract

While the importance of large-scale motions in dwarf galaxies, generated during the periods of enhanced SF is widely recognized, little is known on the parameters of expanding shells in the extremely metal-deficient BCGs. We show the first results from the 6-m Russian and 4-m KPNO telescopes demonstrating the presence of expanding ionized shells around the regions with current SF burst in 6 new BCG/Hii galaxies with the oxygen abundance in the range of log(O/H)+l 2 = 7.35 to ~ 7.6, and MB in the range −11.^m5 to −15.^m7. Their Ha velocity curves, sampled with the accuracy of 3–5 km s⁻¹ show invariably significant deviations correlated with the positions of bright HII regions. The shape of these deviations in the plane ‘V vs R’ imply radial expansions with the amplitudes of ten to a hundred km s⁻¹. The diameters of corresponding shells are in the range 0.1–1 kpc. Since the efficiency of stellar winds for very low metallicities is significantly reduced, the main energetics of the shells discovered in extremely metal-poor galaxies should be powered by the cumulative effect of SN explosions. These shells represent the wide range of ages and thus can be in principle used to confront the results of model simulations on shell dynamics.

Partially supported by the LOC and RFBR grant No. 00-02-26667.

Partially supported by the LOC and INTAS grant No. 97-0033.