Star formation in quasar and active galaxy environments

We use the 2dF public 100 K data release of galaxies and samples of quasars and active galaxies taken from the Veron-Cetty and Veron catalogue to study the nature of galaxies in the surroundings of active objects with redshifts in the range 0.1 < z < 0.2. We explore the distribution of neighbour 2dF galaxy spectral types, eta, at different projected distances from the quasars and active galaxies with radial velocity difference DeltaV = 500 km s(-1). For comparison, we perform a similar analysis on the environment of typical galaxies in the 2dF catalogue, a sample of bright early-type galaxies, i.e. eta < 1.4 and M-bJ < -21, and also on a sample of 2dF galaxy groups. We find a higher relative fraction of emission-line galaxies, i.e. with 2dF spectral type indices eta > 3.5, in the vicinity of quasars and active galaxies compared to that in the neighbourhood of typical galaxies, bright early types and groups. This effect extends up to projected distance r(p) similar to 1 h(-1) Mpc for active galaxies and r(p) similar to 3 h(-1) Mpc for quasars. We also find a tendency for companion galaxies of quasars to be brighter than the neighbours of active galaxies within r(p) similar to 3 h(-1) Mpc. We estimate average star-formation rates for objects at different distances from quasars, active galaxies, galaxies and groups. We find a significantly higher star-formation activity within similar to2.0 h(-1) Mpc from quasars with respect to typical galaxies, which reinforces the idea that star formation is enhanced in the neighbourhood of quasars. Our tests with the group environment provide evidence against quasars being associated with groups. Also, our analysis of the neighbours of bright early types shows that although these galaxies are typical hosts of quasars, their companion galaxies are significantly different in terms of the star-formation activity.