The CIViL* Survey: The Discovery of a C iv Dichotomy in the Circumgalactic Medium of L* Galaxies

Abstract

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 ^⋆ galaxies survey (PID # 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 ( s SFR > 10 ^−11 yr ^−1 ) and passive galaxies (sSFR ≤ 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 J. Tumlinson et al., 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 ≳3.03 × 10 ^6 M _⊙ 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.

Keywords

• Galaxy evolution
• Circumgalactic medium
• Quasar absorption line spectroscopy