2024MNRAS.531..387G

C I absorbers play an important role as indicators for exploring the presence of cold gas in the interstellar medium of galaxies. However, the current data base of C I absorbers is very limited due to their weak absorption feature and rarity. Here, we report results from a search of C I λλ1560, 1656 absorption lines using Mg II absorbers as signposts with modified deep learning algorithms, which provides a very quick way to search for weak C I absorber candidates. A total of 107 C I absorbers were detected, which nearly doubles the size of previously known samples. In addition, we found 17 C I absorbers to be associated with 2175 Å dust absorbers (2DAs), i.e. about 16 per cent C I absorbers are associated with 2DAs. Comparing the average dust depletion patterns of C I absorbers with those of damped Lyman α absorbers (DLAs), Mg II absorbers, Ca II absorbers, and 2175 Å dust absorbers (2DAs) shows that C I absorbers generally have environments with more dust than DLAs, Mg II, and Ca II absorbers, but similar to dust in 2DAs. Similarity between the dust depletion pattern of C I absorbers to that of the warm disc in the Milky Way indicates that C I absorption clouds are possibly associated with disc components in distant galaxies. Therefore, C I absorbers are confirmed to be excellent probes to trace cold gas and dust in the Universe.