| The thesis mainly utilized quasar spectra of the Sloan Digital Sky Survey(SDSS)to systematically search for Mg Ⅱ>l2796,2803 and CⅣ λλ1548,1551 absorption line systems and statistically analyze their properties.In the first chapter,we summarized the basic properties and uniform model of the quasar;the classifications,origins and statistical characteristics of absorption lines;and the survey programs of the SDSS.In the second chapter,using the Data Release 9 Quasar spectra from the Baryonic Oscillation Spectroscopic Survey(BOSS),we systematically searched for narrow Mg Ⅱand CⅣ absorption systems in the spectral data redward of the Ly a emission line until the red wing of the Mg Ⅱ emission line.We have detected a total numbers of 18 598 Mg Ⅱ systems with 0.2933≤ z≤ 2.6529,and 41 479 C Ⅳ systems with 1.4544 ≤ z ≤4.9224.Most of these systems(>95%)are located between the completely saturated absorption and completely unsaturated absorption.About 75%Mg Ⅱ systems have Wrλ2796 ≥ 1 A,and about 29%of C Ⅳ systems have Wrλ1548 ≥ 1 A.We found that the redshift number density of absorbers is similar to the evolution of the cosmic star formation rate density,which likely indicated that the formation of the metal absorption lines is related to the star formation rate within galaxies.For Mg Ⅱ and C Ⅳ systems imprinted on the same quasar spectra and located at the same redshifts,Mg Ⅱ systems are more likely to be saturated absorptions when compared with C Ⅳ systems,and the associated absorbing gas shows higher ionization relative to the intervening one.We found that the strength and relative velocity(β)of associated absorbers are not related to the radio detection of quasar,but depend on the continual luminosity of quasar.Theβof absorbers show complex distributions which probably consists of three classes of absorbers:(1)cosmologically intervening absorbers;(2)environmental absorbers that reside within the quasar host galaxies or galaxy clusters;(3)quasar outflow absorbers.The C Ⅳ environmental absorbers have a wider β distribution relative to the Mg Ⅱenvironmental absorbers.As the ancillary program,BOSS repeatedly observed some quasars that have been confirmed by the SDSS-Ⅰ/Ⅱ.In the third chapter,we used the quasars from the SDSS with repeated observations to analyze the variations of narrow Mg Ⅱ and C Ⅳ absorp-tion systems,which have time-scales of about 150-2643 days in the quasar rest frame.We found that 52 C Ⅳ systems show obvious variations in absorption strength and 5 variable systems have values of β>0.06.The changes in absorption strengths are re-lated neither to time-scales of the two SDSS observations nor to absorber velocities in quasar rest frame.For Mg Ⅱ systems,we did not find a system with confident levels of>4σ for λ2796 lines and>3σ for.λ2803 lines.In the fourth chapter,based on quasar catalogs of the SDSS DR7 and DR12,we assembled quasar pairs with proper project distance less than 1 Mpc to investigate the surrounding gas of foreground quasars and the properties of intervening absorbers that intersected sightlines of both foreground and background quasars.We found that strengths of transverse absorptions inversely correlate with project distance at dp<300 kpc,while this anticorrelation is disappeared when it is extended to larger project dis-tance.The anticorrelation between incidence of transverse absorption and project dis-tance is extended to 350 kpc for Mg Ⅱ absorptions and 250 kpc for C Ⅳ ones.We found that the incidence of Mg Ⅱ associated absorbers is much smaller than that of transverse ones with dp<350 kpc,and they are agreement with each other for trans-verse absorbers beyond dp>350 kpc.Turning to C Ⅳ absorptions,the incidence of transverse absorbers is larger than that of associated ones at dp<100 kpc,while it is in turn beyond dp>100.In addition,we found that the incidences of absorber pairs significantly decline with increasing project distance before 300 kpc while it is in turn beyond 600 kpc.The fifth chapter present some programs that are expected to do in the future. |
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