| Abstract: We present new results on the distribution and evolution of triply ionized carbon (C IV) absorption systems over the past ~4 billion years. We developed an automated matched-kernel convolution technique combined with an adaptive signal-to-noise framework to robustly identify C IV absorbers in quasar spectra. Applying this method ~300,000 quasars from the DESI Year 3 sample, we detect more than 100,000 C IV systems spanning the redshift range 1.4 < z < 4.8, constituting the largest C IV absorber catalog to date. We quantify the catalog completeness using Monte Carlo simulations, achieving over 95% completeness at rest-frame equivalent widths EW ≥ 1.5 Å. The underlying detection pipeline is generic and extensible to other metal-line doublets, enabling uniform searches for multiple ionic species in low-resolution spectroscopic data and joint constraints on metal enrichment using several tracers.
We study the redshift evolution of C IV absorbers by measuring their incidence and comoving number density. Both quantities increase by factors of about 2–5 from z ≈ 4.5 to z ≈ 1.4. Using the column densities measurements, we derive the cosmic mass density of C IV, which increases by a factor ~3.6 over this range, indicating a significant build-up of carbon in the Universe. Treating C IV as a reliable tracer of metal enrichment, we further constrain the mean IGM metallicity and provide a tight lower limit of log(Z_IGM/Z_sun) ≳ −3.5, with a smooth decline toward earlier cosmic times.
Finally, we discuss how these trends link to the evolution of the cosmic star-formation rate and He II photoheating and metal enrichment and the evolving ionizing background. Our publicly released catalog provides a valuable resource for connecting metal absorbers to the circumgalactic medium and the cosmic web, enabling key science for upcoming facilities such as Roman, LSST, and future Stage-V spectroscopic surveys. |
