期刊
ASTROPHYSICAL JOURNAL
卷 686, 期 1, 页码 195-200出版社
UNIV CHICAGO PRESS
DOI: 10.1086/590384
关键词
dark matter; intergalactic medium; quasars : individual (SDSS J1711+6052, SDSS J2346-0016); surveys; ultraviolet : general
资金
- NASA [GO-9759, 9806, 10231, NAS 5-26555]
We present the UV spectra of two quasars obtained with the Hubble Space Telescope Advanced Camera for Surveys (HST ACS) prism ( R similar to 100). One quasar, at redshift = 3: 5, shows an absorption edge consistent either with nearly fully ionized helium with an intergalactic He II Ly alpha optical depth at 304 angstrom of tau(304) > 3.1 (90% confidence), or a He III region with edge 5.4 Mpc from the QSO. The spectrum of the second quasar, at z = 3.8, has a broad absorption profile extending across the He II emission line of the quasar consistent with a damped absorption profile from an intervening He II system at z similar or equal to 3.7 with a column density of approximately 10(22) cm(-2). In this case, the extremely high He II column density and absence of strong H I absorption suggests that the radiation field is quite weak at 4 ryd. The combined He II and H I signatures are consistent with photoionization by a compact (1-100 pc) star-forming region located approximately 10 Mpc from the quasar.
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