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We present a study of the environments of extended radio sources in theAustralia Telescope Low Brightness Survey (ATLBS). The radio sources wereselected from the Extended Source Sample (ATLBS-ESS), which is a well definedsample containing the most extended of radio sources in the ATLBS sky surveyregions. The environments were analyzed using 4-m CTIO Blanco telescopeobservations carried out for ATLBS fields in the SDSS ${\rm r}^{\prime}$ band.We have estimated the properties of the environments using smoothed densitymaps derived from galaxy catalogs constructed using these optical imaging data.The angular distribution of galaxy density relative to the axes of the radiosources has been quantified by defining anisotropy parameters that areestimated using a new method presented here. Examining the anisotropyparameters for a sub-sample of extended double radio sources that includes allsources with pronounced asymmetry in lobe extents, we find good evidence forenvironmental anisotropy being the dominant cause for lobe asymmetry in thathigher galaxy density occurs almost always on the side of the shorter lobe, andthis validates the usefulness of the method proposed and adopted here. Theenvironmental anisotropy parameters have been used to examine and compare theenvironments of FRI and FRII radio sources in two redshift regimes ($z<0.5$ and$z>0.5$). Wide-angle tail sources and Head-tail sources lie in the mostoverdense environments. The Head-tail source environments (for the HT sourcesin our sample) display dipolar anisotropy in that higher galaxy density appearsto lie in the direction of the tails. Excluding the Head-tail and Wide-angletail sources, subsamples of FRI and FRII sources from the ATLBS survey appearto lie in similar moderately overdense environments, with no evidence forredshift evolution in the regimes studied herein.

Environments of Extended Radio Sources in the ATLBS Survey