2025/10/13 by Lucas Wang, Jian Ge, Wang, Lucas +3
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena
paper · pdf · doi:10.48550/arxiv.2510.13863
openalex publication_date 2025/10/13 · openalex created_date 2025/10/18 · openalex updated_date 2026/07/28
Ca II absorbers, characterized by dusty and metal-rich environments, provide unique insights into the interstellar medium of galaxies. However, their rarity and weak absorption features have hindered comprehensive studies. In this work, we present a novel dual CNN approach to detect Ca II absorption systems, analyzing over 100,000 quasar spectra from the Sloan Digital Sky Survey (SDSS) Data Release 16. Our primary CNN identifies Ca II features, while a secondary CNN cross-verifies these detections using five Fe II absorption lines. This approach yielded 1,646 Ca II absorption systems, including 525 previously known absorbers and 1,121 new discoveries, nearly tripling the size of any previously reported catalog. Among our Ca II absorbers, 95 are found to show the 2175Å dust feature (2DA), corresponding to 22% of strong absorbers, 7% of weak absorbers, and ∼12% of the overall Ca II population at 0.8 < zabs < 1.4. Across the full redshift range of 0.36 < zabs < 1.4, ∼1.5% of Mg II absorbers host Ca II.