Improved composite spectra of quasars within the HI Lyα-forest region

Details Improved composite spectra of quasars within the HI Lyα-forest region Improved composite spectra of quasars within the HI Lyα-forest region

2011-12-28

arxiv.org/abs/1112.6083v1

Astronomy and Astrophysics

Astrophysics

Cosmology and Extragalactic Astrophysics

15 pages, 10 figures, 20 tables

Scientific paper

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%.

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