Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985aj.....90....1k&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 90, Jan. 1985, p. 1-4.
Astronomy and Astrophysics
Astronomy
17
Balmer Series, Galactic Nuclei, H Alpha Line, Lyman Alpha Radiation, Quasars, Seyfert Galaxies, X Ray Sources, Active Galactic Nuclei, Hydrogen Clouds, Iue, Luminosity, Ultraviolet Astronomy
Scientific paper
New observations of the Ly-alpha/H-alpha ratio in a set of X-ray-selected active galactic nuclei and an archival study of International Ultraviolet Explorer (IUE) observations of Ly-alpha in low-redshift quasars and Seyfert galaxies have been used to form a large sample (49 objects) for studying the influence of soft X-rays on the enhancement of Balmer emission in the broad-line region. In common models of broad-line clouds, the Balmer lines are formed deep in the interior, largely by collisional excitation. Heating within the clouds is provided by soft X-ray radiation, while Ly-alpha is formed mainly by recombination after photoionization. The ratio Ly-alpha/H-alpha is expected to depend weakly on the ratio of ionizing ultraviolet luminosity to X-ray luminosity, L(UV)/L(x). If the Ly-alpha luminosity is used as a measure of L(UV), a weak dependence of Ly-alpha/H-alpha on the X-ray luminosity is found (valid at the 94 percent confidence level), similar to previous results. Future definitive studies depend more critically on contemporaneous observations and better internal reddening estimates rather than a larger sample size.
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