Abstract

The spectrum lines of different quasars (QSOs) have been investigated, emphasis on the weak emission lines existent in the Lyα forest region using principal component analysis method (PCA) in the wavelength range from 1020 to 1600Å. The first, the second and the third principal component spectra (PCS) involve 63.4, 14.5 and 6.2% of the variance respectively, as the first seven PCS involve 96.1% of the total variance. The first PCS contain peak from high ionization emission lines namely the emission lines of Lyα and Lyβ (OVI, NV, SiIV, and CIV), these peaks are sharp and strong and the second PCS has peaks from low ionization emission lines (FeII, FeIII, SiII, and CII) that these emission lines are wide and almost rounded. By using the PCS, can be produced the QSO spectra artificially that are useful for investigation of how to discover QSOs and their continuum spectrum classification. By using the weights of the first two PCS can be defined five classes: class Zero and classes from ItoIV, these classifications will help to discover the continuum spectrum in the Lyα forest. 21 continuum (Listed in Table 1) have been used upon spectrum of bright QSOs from SDSS with z~3 and a signal to noise ratio more than 20 (S/N>20) and apparent magnitude less than 18 (m_g<18). Initially, by investigating the spectrum of each one of these QSOs, the QSOs were classified and the peak of emission line of Lyα belonging to each one of classes was investigated. In the rest, the result mean spectrum of 21 QSOs were compared with mean spectrum of 50 QSOs with redshift 0.14<z<1.04 in Suzuki et al. (2007).

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