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Ly-alpha/H-alpha Ratio of Singly Ionized Helium in Quasars | | Wei Zheng
; Li-Zhi Fang
; | | Date: |
29 Apr 1998 | | Subject: | astro-ph | | Affiliation: | Johns Hopkins University) and Li-Zhi Fang (University of Arizona | | Abstract: | He II Ly-alpha 304/H-alpha 1640 emission lines are mainly produced by recombination, and their canonical ratio of about 10 may be a sensitive reddening indicator. We obtain the high S/N optical spectra of two quasars and combine them with the far-UV spectra that show the He II 304 emission. For HS 1700+64, the He II 1640 emission is not detected, and an upper limit to it sets the ratio greater than 20. For Q0302-003, the ratio is very low, on the order of unity. The most plausible cause for such a low ratio is extinction in the EUV band by very fine grains of dust. Q0302-003 has a prominent narrow component of FWHM ~ 2000 km/s in its major emission lines, and it appears that reddening is associated only with the line-emitting region. We suggest that the geometry of the line-emitting region in high-z quasars resembles that in the low-luminosity active galaxies, with the presence of dust mostly in the outer part. | | Source: | arXiv, astro-ph/9804323 | | Services: | Forum | Review | PDF | Favorites | |
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