Seyfert Galaxies and Their Environment

The role played by environment on nuclear activity in galaxies is not clear and largely debated (see e.g. Barnes & Hernquist 1992, Kelm 1996). To overcome statistical uncertainties, environment properties of two large samples of Seyfert galaxies (Sy 1 and Sy 2 have been kept separated) have been computed and compared with equivalent size “normal galaxy” sample ones. Seyfert samples have been extracted from the Veron & Veron catalogue (Veron & Veron 1996), whilst “normal galaxies” have been randomly extracted from ZCAT (Huchra 1993). The samples are limited in cz ([1500–9500] km/sec) and contain 149 Sy 1, 173 Sy 2 and 160 “normal galaxies” (hundreds of random extractions from ZCAT). For each galaxy neighbors have been computed (from ZCAT) within two variables radii, R (isolation radius) and r (pair separation), which span [0.2 - 2] h100 Mpc. and [20–90]h100 kpc. respectively. Neighbors must lie also within 700 km/sec from the galaxy. In this way, for each value of R and r, environment of each galaxy has been “quantified”.