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 &gt; 10 −11 yr −1 ) and passive galaxies (sSFR ≤ 10 −11 yr −1 ) to be 72 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow/> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>18</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>14</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> % [21/29] and 23 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow/> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>15</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>27</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> % [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.