G. Ivashchenko, O. Sergijenko, O. Torbaniuk
We present a new more accurate approach to the composite spectra construction
based on stacking spectra with similar slopes \alpha_\lambda\ within the
wavelength range redward of Ly\alpha\ emission line, which allows to reduce a
noise. With the help of this technique a detailed study of the HI
Ly\alpha-forest region (\lambda_rest~1050-1200 \AA) of the own sample of 3,439
medium-resolution quasar spectra from SDSS DR7 was performed. More than 14
lines were found within it, three of which were found in previous studies of
quasar composite spectra from SDSS and some others were found in composite
spectra from space-based telescopes or high-resolution spectra of individual
quasars from ground-based telescopes. The parameters of these lines were
calculated. It was shown that the continuum level within the Ly\alpha-forest
region cannot be considered as a power-low with the same slope as in the region
redward of Ly\alpha\ emission line. Any dependence of the slope \alpha_\lambda\
on luminosity in SDSS u, g, r and i bands as far as on luminosity in 1450-1470
\AA\ band was not found. The proposed approach can be applied for generation of
new templates for more precise quasar redshift measurements, theoretical
determination of K-correction and color-indexes, as far as for determination of
continuum and mean transmission in Ly\alpha-forest studies. It was shown that
the uncertainties in the mean transmission caused by using the composite
spectra made with common approach can constitute about 20%.
View original:
http://arxiv.org/abs/1112.6083
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