The Extent of Chemically Enriched Gas around Star-forming Dwarf Galaxies

Supernova driven winds are often invoked to remove chemically enriched gas from dwarf galaxies to match their low observed metallicities. In such shallow potential wells, outflows may produce massive amounts of enriched halo gas (circumgalactic medium, CGM) and pollute the intergalactic medium (IGM). Here, we present a survey of the CGM and IGM around 18 star-forming field dwarfs with stellar masses of log M-*/M-circle dot approximate to 8-9 at z approximate to 0.2. Eight of these have CGM probed by quasar absorption spectra at projected distances, d, less than that of the host virial radius, R-h. Ten are probed in the surrounding IGM at d/R-h = 1-3. The absorption measurements include neutral hydrogen, the dominant silicon ions for diffuse cool gas (T similar to 10(4) K; Si II, Si III, and Si IV), moderately ionized carbon (C IV), and highly ionized oxygen (O VI). Metal absorption from the CGM of the dwarfs is less common and approximate to 4 x weaker compared to massive star-forming galaxies, though O VI absorption is still common. None of the dwarfs probed at d/R-h = 1-3 have definitive metal-line detections. Combining the available silicon ions, we estimate that the cool CGM of the dwarfs accounts for only 2%-6% of the expected silicon budget from the yields of supernovae associated with past star formation. The highly ionized O VI accounts for approximate to 8% of the oxygen budget. As O VI traces an ion with expected equilibrium ion fractions of less than or similar to 0.2, the highly ionized CGM may represent a significant metal reservoir even for dwarfs not expected to maintain gravitationally shock heated hot halos.