Spectra of quasar narrow-line regions

To isolate these two components, we construct a library of high S/N optical composite spectra created from the Sloan Digital Sky Survey (SDSS-DR7). We divide the sample into bins of continuum luminosity and H{beta} FWHM that are used to construct median composites at different redshift steps up to 0.75.

We measure the luminosities of the narrow-emission lines [NeV]{lambda}3427, [NeIII]{lambda}3870, [OIII]{lambda}5007, and [OII]{lambda}3728 with ionization potentials (IPs) of 97, 40, 35, and 13.6eV respectively. The high IP lines' luminosities show no evidence of increase with redshift consistent with no evolution in the AGN SED or the host galaxy ISM illuminated by the continuum. In contrast, we find that the [OII] line becomes stronger at higher redshifts, and we interpret this as a consequence of enhanced star formation contributing to the [OII] emission in host galaxies at higher redshifts.