Kinematics of Interstellar Gas in Nearby UV-Selected Galaxies Measured with HST/STIS Spectroscopy

摘要

We measure Doppler shifts of interstellar absorption lines in HST/STISspectra of individual star clusters in nearby UV-selected galaxies. Values forsystemic velocities, which are needed to quantify outflow speeds, are takenfrom the literature, and verified with stellar lines. We detect outflowing gasin eight of 17 galaxies via low-ionization lines (e.g., CII, SiII, AlII), whichtrace cold and/or warm gas. The starbursts in our sample are intermediate inluminosity (and mass) to dwarf galaxies and luminous infrared galaxies (LIRGs),and we confirm that their outflow speeds (ranging from -100 km/s to nearly -520km/s with an accuracy of ~80 km/s) are intermediate to those previouslymeasured in dwarf starbursts and LIRGs. We do not detect the outflow inhigh-ionization lines (such as CIV or SiIV); higher quality data will be neededto empirically establish how velocities vary with the ionization state of theoutflow. We do verify that the low-ionization UV lines and optical NaI doubletgive roughly consistent outflow velocities solidifying an important linkbetween studies of galactic winds at low and high redshift. To obtain highersignal-to-noise, we create a local average composite spectrum, and compare itto the high-z Lyman Break composite spectrum. Surprisingly, the low-ionizationlines show similar outflow velocities in the two samples. We attribute this toa combination of weighting towards higher luminosities in the local composite,as well as both samples being on average brighter than the ``turnover''luminosity in the v-SFR relation.