Nuclear Activity in UZC Compact Groups

Compact Groups are ideal places to investigate the role of environment on galaxy formation and evolution. Their high galaxy density coupled with their low velocity dispersion makes them the most suitable systems to study galaxy-galaxy interaction and the AGN-environment relation. UZC Compact Groups sample (UZC-CG, Focardi & Kelm 2002) contains 986 galaxies belonging to 291 groups. We have taken 642 low resolution UZC spectra from the Z-Machine Archive and 221 medium resolution spectra from the Sloan Data Archive (Release Four). As 131 are in common with the first ones, we have a total of 732 spectra. The main goal of this study is to measure and classify the nuclear activity found in galaxies belonging to compact groups, with this aim we have measured the equivalent width of emission lines (Hβ, [OIII], Hα, [NII], [SII]...) and their ratio. Diagnostic diagrams, like log([OIII]/Hβ) vs log([NII]/Hα) and log ([OIII]/Hβ) vs log([SII](6717+6731Å)/Hα) have been used to do the spectral classification. As a whole, from the 732 galaxies with available spectra, 65% show emission lines. We present a detailed analysis of the 159 UZC-CGs with spectra for all member. We show that 65 % of these galaxies have nuclear activity (HII nuclear regions, LINERs or Syefert2). Finally we will show how galaxy and CG properties relate to the presence and kind of nuclear activity.