The CO-dark molecular gas in the cold H I arc Gan Luo, Di Li, Zhi-Yu Zhang, Thomas G. Bisbas, Ningyu Tang, Lingrui Lin, Yichen Sun, Pei Zuo and Jing Zhou A&A, 685 (2024) L12 Published online: 20 May 2024 DOI: 10.1051/0004-6361/202450067