Probing the He <scp>ii</scp> Reionization ERA via Absorbing C <scp>iv</scp> Historical Yield (HIERACHY). III. The C <scp>iv</scp> Absorber Catalog and Initial Results on Cosmic Abundance Evolution at <i>z</i> ≈ 3–5

Abstract As part of the HIERACHY program, we collect the high signal-to-noise ratio and high-spectral resolution optical spectra of 25 quasars at z ≈ 4–5 to constrain the C iv evolution at z ≈ 3–5. In this paper, we report a catalog of 626 (1263) C iv absorption systems (components) at z ≈ 3–5 with a 50% completeness column density of log( N C iv /cm −2 ) ≈ 12.3. The HIERACHY/MIKE C iv sample is one of the best C iv absorber samples optimized to study the intergalactic medium during the He ii reionization epoch. Using 557 (1090) intervening absorption systems (components), we found the column density distribution function of C iv absorption systems with log( N C iv /cm −2 ) ≳ 12.3 has a broken power-law shape, with the turnover column density log <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mi>N</mml:mi> <mml:mi>crit</mml:mi> </mml:msub> <mml:mo>/</mml:mo> <mml:msup> <mml:mi>cm</mml:mi> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mn>13.3</mml:mn> <mml:msubsup> <mml:mn>5</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.19</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.20</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , which is close to or smaller than the detection limit of most literature samples. We also found that both comoving path length number density dn / dX and cosmic abundance Ω for C iv absorption systems with log( N C iv /cm −2 ) &gt; 13.2 show an increase (at the 2.2 σ and 1.4 σ levels, respectively) from redshift z ≈ 5–3, while absorption systems with log( N C iv /cm −2 ) = 12.3–13.2 exhibit a constant dn / dX and Ω C iv .