The Low-Redshift Quasar-Quasar Correlation Function from an Extragalactic Hα Emission-Line Survey to z = 0.4

We study the large-scale spatial distribution of low-redshift quasars and Seyfert 1 galaxies using a sample of 106 luminous emission-line objects (_B ≈ -23) selected by their Hα emission lines in a far-red objective prism survey (0.2 < z < 0.37). Of the 106 objects, 25 were previously known active galactic nuclei (AGNs), and follow-up spectroscopy for an additional 53 objects (including all object pairs with separation r < 20 h^-1 Mpc) confirmed 48 AGNs and 5 narrow emission line galaxies (NELGs). The calculated amplitude of the spatial two-point correlation function for the emission-line sample is A = 0.4(r < 20 h^-1 Mpc) × 20^1.8 = 142 ± 53. Eliminating the confirmed NELGs from the sample, we obtain the AGN clustering amplitude A = 98 ± 54. Using Monte Carlo simulations, we reject the hypothesis that the observed pair counts were drawn from a random distribution at the 99.97% and 98.6% confidence levels for the entire sample and the AGN subset, respectively. We measure a decrease in the quasar clustering amplitude by a factor of 3.7 ± 2.0 between z = 0.26 and z ≈ 1.5, and present the coordinates, redshifts, and follow-up spectroscopy for the 15 previously unknown AGNs and four luminous NELGs that contribute to the clustering signal.