Improved technique for quasar composite spectra generation

Abstract

We present a new approach to the composite spectra construction based on stacking spectra with similar slopes α λ within the wavelength range redward of Lyα emission line, which allows to reduce the typical noise. With the help of this technique a detailed study of the HI Lyα-forest region (λ rest ≈ 1050 − 1200 Å) of the own sample of 3439 medium-resolution quasar spectra from SDSS DR7 was performed. More than 14 lines were found within this wavelength range, three of which were known from previous studies of quasar composite spectra from SDSS and some others were known in composite spectra from space-based telescopes or high-resolution spectra of individual quasars from ground-based telescopes.

Some spectral properties of the quasar ultraviolet bump

“…For our study we used 16 composite spectra of quasars compiled by us [Ivashchenko et al, 2012]. Each of these spectra was generated of 200 individual ones with similar spectral indices α λ within the range 1270 − 1480 Å namely from those that have the values of α λ close to −0.6 − k • 0.1, where k = 1..16 is the composite number.…”