Active galactic nuclei in void regions

We present a comprehensive study of accretion activity in the most underdense environments in the universe, the voids, based on the SDSS DR2 data. Based on investigations of multiple void regions, we show that active galactic nuclei ( AGNs) are definitely common in voids, but that their occurrence rate and properties differ from those in walls. AGNs are more common in voids than in walls, but only among moderately luminous and massive galaxies (M-r < -20, log M-*/M-circle dot < 10.5), and this enhancement is more pronounced for the relatively weak accreting systems (i.e., L-[O III] < 10(39) erg s(-1)). Void AGNs hosted by moderately massive and luminous galaxies are accreting at equal or lower rates than their wall counterparts, show lower levels of obscuration than in walls, and have similarly aged stellar populations. The very few void AGNs in massive bright hosts accrete more strongly, are more obscured, and are associated with younger stellar emission than wall AGNs. These trends suggest that the accretion strength is connected to the availability of fuel supply, and that accretion and star formation coevolve and rely on the same source of fuel. Nearest neighbor statistics indicate that the weak accretion activity (LINER-like) usually detected in massive systems is not influenced by the local environment. However, H II galaxies, Seyferts, and transition objects are preferentially found among more grouped small-scale structures, indicating that their activity is influenced by the rate at which galaxies interact with each other. These trends support a potential H II -> Seyfert/transition object -> LINER evolutionary sequence that we show is apparent in many properties of actively line-emitting galaxies, in both voids and walls. The subtle differences between void and wall AGNs might be explained by a longer, less disturbed duty cycle of these systems in voids.