Mean Transmitted Flux in the Ly$α$ Forest From a Sample of 2QZ Quasars

Abstract: The power spectrum of transmitted flux in the Ly$\alpha$ forest in spectra of distant quasars gives us an information about matter power spectrum on the smallest spatial scales which is very important for testing of different models of dark matter. Only a few independent samples of spectra obtained on diferent instruments have been used for this purpose, thus using of additional independent sample is useful for verification an existing results. We used the data from the 2dF (Two-degree Field) QSO Redshift Survey (2QZ) to obtain the mean transmitted flux for three different redshift bins. After visual inspection and rejection of spectra with broad absorption lines, damped Ly$\alpha$ systems and low signal-to-noise ratio spectra our final sample contains 655 quasars with redshift range 2.3 $<z<$ 2.9. We present the results on composite spectra, determination of continuum level for different redshift ranges and the mean transmission in the Ly$\alpha$ forest as a function of redshift within the range 2.1 $<z_{forest}<$ 2.5. The obtained redshift-dependence of the mean transmission agrees well with the results of other authors. These results can be used for calculation of the flux power spectrum of Ly$\alpha$ forest.