Parameterisation of Galaxy Spectra in the 2dF Galaxy Redshift Survey

The 2dF Galaxy Redshift Survey has already yielded over 130,000 galaxy spectra (out of the planned 250,000). We present a method for the parameterisation of galaxy spectra in the 2dF and other large redshift surveys using a new continuous parameter η = 0.44 pc₁−pc₂, based on a Principal Components Analysis (where pc₁ and pc₂ are the projections onto the first and second principal components respectively). This parameter is designed to be robust to instrumental uncertainties and it represents the absorption/emission strength of a galaxy.