COMPOSITION AND COOLING IN EXTRAGALACTIC H II REGIONS

> in this proposal, more time is being requested for dgarnett.sws_nes this is a joint proposal for programs dgarnett.sws_nes and medmunds.propiso. we request supplemental iso observing time to recover science lost because of the reduced sensitivity of the sws. we will make deep full grating scans with sws and lws of one very metalrich h ii region in the spiral galaxy m51 (twice solar z) and the very metalpoor h ii galaxy sbs 0335052 (2% solar z). the data will be used to measure a variety of nebular ir emission lines which are important coolants and abundance diagnostics in the ionized gas. because of their weak sensitivity to electron temperature, the ir finestructure lines can be used to measure heavy element abundances with greater reliability than highexcitation optical forbidden lines, especially in metalrich nebulae where electron temperature measurements are not available. we will confront two very pressing problems of h ii region physics: (1) the relation between optical emission line strengths and abundances for lowexcitation h ii regions in the inner parts of spiral galaxies; this is poorly known because electron temperatures can not be measured in such objects, and unique photoionization models for such nebulae are sensitive to competing influences of dust, density and abundance variations; and (2) are there large systematic uncertainties in the abundance scale due to electron temperature fluctuations within ionized nebulae. measurement of the ir emission lines in these nebulae will allow us to (i) determine, for the first time, accurate chemical abundances in the gas at metallicities above solar; (ii) greatly improve the calibration of strong line abundance indicators for giant hvirgulii regions at high metallicities, with considerable benefit to the truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]