Ly-alpha/H-alpha Ratio of Singly Ionized Helium in Quasars
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.
Keywords
Cite
@article{arxiv.astro-ph/9804323,
title = {Ly-alpha/H-alpha Ratio of Singly Ionized Helium in Quasars},
author = {Wei Zheng and Li-Zhi Fang},
journal= {arXiv preprint arXiv:astro-ph/9804323},
year = {2009}
}
Comments
18 pages, including 2 figures To appear in Astrophysical Journal