Discovery of Hydrogen Radio Recombination Lines at z = 0.89 toward PKS 1830-211 oleh Kimberly L. Emig, Neeraj Gupta, Pedro Salas, Sébastien Muller, Sergei A. Balashev, Françoise Combes, Emmanuel Momjian, Yiqing Song, Preshanth Jagannathan, Partha P. Deka, Gyula I. G. Józsa, Hans-Rainer Klöckner, Abhisek Mohapatra, Pasquier Noterdaeme, Patrick Petitjean, Raghunathan Srianand, Jonah D. Wagenveld