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Abstract: We present the results of an analysis of a well-selected sample of galaxieswith active and inactive galactic nuclei from the Sloan Digital Sky Survey, inthe range 0.01 < z < 0.16. The SDSS galaxy catalogue was split into two classesof active galaxies, Type~2 AGN and composites, and one set of inactive,star-forming-passive galaxies. For each active galaxy, two inactive controlgalaxies were selected by matching redshift, absolute magnitude, inclination,and radius. The sample of inactive galaxies naturally divides into a red and ablue sequence, while the vast majority of AGN hosts occur along the redsequence. In terms of H-alpha equivalent width, the population of compositegalaxies peaks in the valley between the two modes, suggesting a transitionpopulation. However, this effect is not observed in other properties such ascolour-magnitude space, or colour-concentration plane. Active galaxies are seento be generally bulge-dominated systems, but with enhanced H-alpha emissioncompared to inactive red-sequence galaxies. AGN and composites also occur inless dense environments than inactive red-sequence galaxies, implying that thefuelling of AGN is more restricted in high-density environments. These resultsare therefore inconsistent with theories in which AGN host galaxies are a`transition- population. We also introduce a systematic 3D spectroscopicimaging survey, to quantify and compare the gaseous and stellar kinematics of awell-selected, distance-limited sample of up to 20 nearby Seyfert galaxies, and20 inactive control galaxies with well-matched optical properties. The surveyaims to search for dynamical triggers of nuclear activity and addressoutstanding controversies in optical-IR imaging surveys.

Author: P. B. Westoby, C. G. Mundell, I. K. Baldry



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