The cos-dwarfs survey: The carbon reservoir around sub-l∗ galaxies

We report new observations of circumgalactic gas from the COS-Dwarfs survey, a systematic investigation of the gaseous halos around 43 low-mass z ≤ 0.1 galaxies using background QSOs observed with the Cosmic Origins Spectrograph. From the projected one-dimensional and two-dimensional distribution of C IV absorption, we find that C IV is detected out to ≈100 kpc (corresponding roughly to ≈0.5 R _vir) of the host galaxies. The C IV absorption strength falls off radially as a power law, and beyond ≈0.5 R _vir, no C IV absorption is detected above our sensitivity limit of ≈50-100 mÅ. We find a tentative correlation between detected C IV absorption strength and star formation, paralleling the strong correlation seen in highly ionized oxygen for L ∼ L∗ galaxies by the COS-Halos survey. The data imply a large carbon reservoir in the circumgalactic medium (CGM) of these galaxies, corresponding to a minimum carbon mass of ≳ 1.2 × 10⁶ M_⊙ out to ∼110 kpc. This mass is comparable to the carbon mass in the interstellar medium and exceeds the carbon mass currently in the stars of these galaxies. The C IV absorption seen around these sub-L∗ galaxies can account for almost two-thirds of all W_r ≥ 100 mÅ C IV absorption detected at low z. Comparing the C IV covering fraction with hydrodynamical simulations, we find that an energy-driven wind model is consistent with the observations whereas a wind model of constant velocity fails to reproduce the CGM or the galaxy properties.