^ abcdefgGordon, M. A.; Sorochenko, R.L. (2008). Radio recombination lines: their physics and astronomical applications. New York: Springer. ISBN978-0-387-09604-9.
^ abcdefghBendo, G. J.; Beswick, R. J.; D'Cruze, M. J.; Dickinson, C.; Fuller, G. A.; Muxlow, T. W. B. (1 May 2015). "ALMA observations of 99 GHz free-free and H40 line emission from star formation in the centre of NGC 253". Monthly Notices of the Royal Astronomical Society: Letters. 450 (1): L80–L84. doi:10.1093/mnrasl/slv053. ((cite journal)): no-break space character in |title= at position 46 (help)
^Alves, Marta I. R.; Davies, Rodney D.; Dickinson, Clive; Davis, Richard J.; Auld, Robbie R.; Calabretta, Mark; Staveley-Smith, Lister (April 2010). "Diffuse radio recombination line emission on the Galactic plane between l=36° and 44°". Monthly Notices of the Royal Astronomical Society. doi:10.1111/j.1365-2966.2010.16595.x.
^ abcdRoy, A. L.; Goss, W. M.; Anantharamaiah, K. R. (May 2008). "Detection of the H92α recombination line from the starbursts in the Circinus galaxy and NGC 1808". Astronomy and Astrophysics. 483 (1): 79–88. doi:10.1051/0004-6361:20077405. ((cite journal)): no-break space character in |title= at position 65 (help)
^ abAraya, Esteban; Baan, Willem A.; Hofner, Peter (October 2004). "Studies of Extragalactic Formaldehyde and Radio Recombination Lines". The Astrophysical Journal Supplement Series. 154 (2): 541–552. doi:10.1086/423246.
^ abcdSeaquist, E. R.; Carlstrom, J. E.; Bryant, P. M.; Bell, M. B. (July 1996). "Millimeter Recombination Line Emission in the Starburst Galaxy M82". The Astrophysical Journal. 465: 691. doi:10.1086/177454.
^Seaquist, E. R.; Kerton, C. R.; Bell, M. B. (July 1994). "Millimeter recombination lines and the state of ionized gas in M82". The Astrophysical Journal. 429: 612. doi:10.1086/174348.
^ abRodriguez‐Rico, C. A.; Viallefond, F.; Zhao, J.‐H.; Goss, W. M.; Anantharamaiah, K. R. (December 2004). "Very Large Array H92α and H53α Radio Recombination Line Observations of M82". The Astrophysical Journal. 616 (2): 783–803. doi:10.1086/425109.
Gordon, M. A.; Sorochenko, R.L. (2008). Radio recombination lines: their physics and astronomical applications. New York: Springer. ISBN978-0-387-09604-9.