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We compare the spatial clustering and physical properties of the activegalactic nuclei (AGN) and star-forming galaxies (SFG) at fixed stellar massusing a volume limited sample from the Sloan Digital Sky Survey (SDSS). Theanalysis of the two-point correlation function shows that the AGN are morestrongly clustered than the SFG. The closer proximity to the $5^{th}$ nearestneighbour for the AGN than that for the SFG indicates that AGN prefer thedenser regions. We compare the distributions of the $(u-r)$ colour, starformation rate (SFR), D$4000$ and concentration index of the AGN and SFG aftermatching their stellar mass distributions. The null hypothesis can be rejectedat $>99.99\%$ confidence level in each case. The comparisons are also carriedout at different densities. The differences persist at the same significancelevel in both the high and low density regions, implying that such differencesdo not originate from the variations in the density. Alternatively stated, theAGN activity can be triggered in both the high and low density regions. Ananalysis of the correlations between the different physical properties at fixedstellar mass reveals that the anticorrelations of SFR with morphology, colourand recent star formation history are $2-3$ times stronger for the AGN than forthe SFG. It suggests that the presence of a bulge and the availability of gasare the two most crucial requirements for AGN activity. We propose a picturewhere the galaxies at fixed stellar mass may have widely different assemblyhistories, leading to significant variations in bulge properties and cold gascontent. Whether a galaxy of a given stellar mass can acquire the suitableconditions for AGN activity remains uncertain due to a broad diversity ofassembly history. We conclude that AGN are stochastic phenomena owing to anunderlying role of the assembly bias.

Clustering and physical properties of the star-forming galaxies and AGN: does assembly bias have a role in AGN activity?