The Cosmic Evolution of CIV Absorbers at $1.4<z<4.5$: Insights from $100,000$ Systems in DESI Quasars

Abhijeet Anand, J. Aguilar, S. Ahlen, D. Bianchi, A. Brodzeller, D. Brooks, R. Canning, T. Claybaugh, A. Cuceu, A. de la Macorra, P. Doel, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, G. Gutierrez, J. Guy, H. K. Herrera-Alcantar, M. Ishak, S. Juneau, R. Kehoe, A. Kremin, M. Landriau, L. Le Guillou, M. E. Levi, M. Manera, A. Meisner, R. Miquel, J. Moustakas, A. Muñoz-Gutiérrez, L. Napolitano, I. Pérez-Ràfols, G. Rossi, E. Sanchez, D. Schlegel, M. Schubnell, D. Sprayberry, G. Tarlé, M. J. Temple, B. A. Weaver, R. Zhou

First listed 2025-04-28 | Last updated 2025-09-04

Abstract

We present the largest catalog to date of triply ionized carbon (CIV) absorbers detected in quasar spectra from the Dark Energy Spectroscopic Instrument. Using an automated matched-kernel convolution method with adaptive signal-to-noise thresholds, we identify $101,487$ CIV systems in the redshift range $1.4 < z < 4.5$ from $300,637$ quasar spectra. Completeness is estimated via Monte Carlo simulations and catalog is $50\%$ complete at $\mathrm{EW}_{\mathrm{CIV}} \geq 0.4$ Angstroms. The differential equivalent width frequency distribution declines exponentially and shows weak redshift evolution. The absorber incidence per unit comoving path increases by a factor of $2-5$ from $z \approx 4.5$ to $z \approx 1.4$, with stronger redshift evolution for strong systems. Using column densities derived from the apparent optical depth method, we constrain the cosmic mass density of CIV, $Ω_{\mathrm{CIV}}$, which increases by a factor of $\sim 3.8$ from $(0.82 \pm 0.05) \times 10^{-8}$ at $z \approx 4.5$ to $(3.16 \pm 0.2) \times 10^{-8}$ at $z \approx 1.4$. From $Ω_{\rm CIV}$, we estimate a lower limit on intergalactic medium metallicity $\log(Z_{\rm IGM}/Z_{\odot}) \gtrsim -3.25$ at $z \sim 2.3$, with a smooth decline at higher redshifts. These trends trace the cosmic star formation history and HeII photoheating rate, suggesting a link between CIV enrichment, star formation, and UV background over $\sim 3$ Gyr. The catalog also provides a critical resource for future studies connecting circumgalactic metals to galaxy evolution, especially near cosmic noon.

Short digest

From 300,637 DESI quasar spectra, the team assembles the largest C IV absorber catalog to date—101,487 systems across 1.4<z<4.5—via an automated matched‑kernel finder with adaptive S/N thresholds. After Monte Carlo completeness corrections (50% complete at EW_CIV ≥ 0.4 Å), the EW frequency distribution declines exponentially with weak redshift evolution, while the incidence per comoving path rises by a factor of 2–5 toward z≈1.4, most strongly for the strongest systems. Apparent‑optical‑depth column densities yield Ω_CIV increasing by ~3.8×, from (0.82±0.05)×10^-8 at z≈4.5 to (3.16±0.2)×10^-8 at z≈1.4. Interpreting Ω_CIV as enrichment, they infer a lower limit log(Z_IGM/Z⊙) ≳ −3.25 at z≈2.3, tracking cosmic SFR and He II photoheating and providing a foundation to link CGM metals to galaxy growth near cosmic noon.

Key figures to inspect

• Figure 1: Use the S/N–redshift map (with percentile contours) to gauge selection and completeness versus z; note the Lyα‑forest repeat‑observation bump and how it modulates C IV detectability.
• Figure 2: Inspect the example spectrum to see continuum placement and the double‑Gaussian fit to the λ1548/1550 pair; the flat residuals validate normalization and the matched‑kernel detection on real DESI data.
• Figure 3: Compare DR1 vs DR2 absorber redshift histograms to see how DR2 extends path length and shifts the mean z, informing incidence and Ω_CIV leverage.
• Figure 4: Track how completeness‑corrected EW distributions remove the spurious turnover near 0.4 Å, check doublet‑ratio saturation trends, and read off AOD‑based N_CIV versus redshift (mean and scatter) that underpin Ω_CIV.‍