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Published January 15, 1981 | Published
Journal Article Open

Infrared and optical observations of the hydrogen lines in quasars


Infrared and optical spectrophotometric observations of the hydrogen lines in a sample of 16 quasars are reported. Combining these observations with previously published observations of hydrogen lines in quasars brings to 12 the number of quasars for which the Pɑ/Hɑ/Hβ line ratios have been measured and brings to nine the number of quasars for which the Lɑ/Hɑ line ratio has been measured. The Pɑ/Hɑ ratios in low-redshift quasars are distributed around the case B value with a tendency toward values lower than that predicted by case B. The Hɑ/Hβ values in these same quasars are generally greater than the case B value. The trend in the Pɑ/Hɑ/Hβ ratios is for the Pɑ/Hɑ ratio to decrease as Hɑ/Hβ increases. The decrease of the Pɑ/Hɑ ratio with increasing Hɑ/Hβ ratio is the most significant correlation found from the present data that any valid model of the line-emitting regions must explain. The low values of the Lɑ/Hɑ compared to the case B value are confirmed for a large sample of high-redshift quasars. Lɑ is apparently destroyed rather than Hɑ being enhanced. We conclude that reddening external to the einission-line regions cannot satisfactorily explain all the observed hydrogen line ratios. The current observations do not support the model of internal dust destroying resonantly scattered Lɑ, but such a model cannot be ruled out on the basis of the present data. Models of the emission-line regions that apply radiative transfer and collisional excitation effects in the lines appear to be necessary to explain the current observations.

Additional Information

© 1981 American Astronomical Society. Received 1980 May 19; accepted 1980 July 22. We thank our observing assistants Gary Tuton, Juan Carrasco, Bruce Cuney, and Howard Laming, and S. Beckwith, I. Gatley, A. Hyland, J. Mould, D. Nadeau, and K. Sellgren for assistance in obtaining these observations, R. Green for providing positions of quasars in advance of publication, R. Puetter and H. E. Smith for discussing their unpublished data with us, J. Krolik and R. Puetter for discussing the theoretical implications of the observations, and J. Krolik and K. Davidson for a careful reading of the manuscript. This work was supported by NASA and NSF grants.

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Published - 1981ApJ___243__369S.pdf


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