The CIViL* Survey: The Discovery of a C IV Dichotomy in the CGM of L* Galaxies

This paper investigates C IV absorption in the circumgalactic medium (CGM) of L* galaxies and its relationship with galaxy star formation rates. We present new observations from the C IV in L* survey (CIViL*; PID$\mathrm{\#}$17076) using the Hubble Space Telescope/Cosmic Origins Spectrograph. By combining these measurements with archival C IV data (46 observations total), we estimate detection fractions for star-forming (sSFR $>$ 10${}^{-11}$ yr${}^{-1}$) and passive galaxies (sSFR $\le$ 10${}^{-11}$ yr${}^{-1}$) to be 72${}_{-18}^{+14}$% [21/29] and 23${}_{-15}^{+27}$% [3/13], respectively. This indicates a significant dichotomy in C IV presence between L* star-forming and passive galaxies, with over 99% confidence. This finding aligns with Tumlinson et al. (2011), which noted a similar dichotomy in O VI absorption. Our results imply a substantial carbon reservoir in the CGM of L* galaxies, suggesting a minimum carbon mass of $\gtrsim$ 3.03 $\times$ 10${}^6$ M${}_{\odot }$ out to 120 kpc. Together, these findings highlight a strong connection between star formation in galaxies and the state of their CGM, providing insight into the mechanisms governing galaxy evolution.