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 eta=0.44pc1 - 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.