Abstract
The proximity profile in the spectra of z≈ 3 quasars, where fluxes
extend blueward of the He ii Lyα wavelength 304 (1+z) Å, is
one of the most important spectral features in the study of the
intergalactic medium (IGM). Based on the Hubble Space Telescope spectra
of 24 He ii quasars, we find that the majority of them display a
proximity profile, corresponding to an ionization radius as large as 20
Mpc in the source's rest frame. In comparison with those in the H i
spectra of the quasars at z ≈ 6, the He ii proximity effect is more
prominent and is observed over a considerably longer period of
reionization. The He ii proximity zone sizes decrease at higher
redshifts, particularly at z\gt 3.3. This trend is similar to that for H
i, signaling an onset of He ii reionization at z≳ 4. For quasar
SDSS1253+6817 (z = 3.48), the He ii absorption trough displays a gradual
decline and serves as a good case for modeling the He ii reionization.
To model such a broad profile requires a quasar radiation field whose
energy distribution between 4 and 1 Rydberg is considerably harder than
normally assumed. The UV continuum of this quasar is indeed
exceptionally steep, and the He ii ionization level in the quasar
vicinity is higher than the average level in the IGM. These results are
evidence that a very hard EUV continuum from this quasar produces a
large ionized zone around it. Distinct exceptions are the two brightest
He ii quasars at z ≈ 2.8, for which no significant proximity profile
is present, probably implying that they are very young.
Original language | English |
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Article number | 142 |
Pages (from-to) | 142 |
Number of pages | 13 |
Journal | Astrophysical Journal |
Volume | 806 |
Issue number | 1 |
DOIs | |
Publication status | Published - 10 Jun 2015 |
Keywords
- intergalactic medium
- quasars: general
- ultraviolet: general
- HUBBLE-SPACE-TELESCOPE
- DIGITAL-SKY-SURVEY
- LY-ALPHA FOREST
- GALAXY-EVOLUTION-EXPLORER
- GUNN-PETERSON ABSORPTION
- COMPOSITE QUASAR SPECTRA
- LYMAN-LIMIT ABSORPTION
- INTERGALACTIC MEDIUM
- HIGH-REDSHIFT
- HST/COS OBSERVATIONS