The XMM-Newton wide field survey in the COSMOS field: Clustering dependence of X-ray selected AGN on host galaxy properties

Abstract

Aims: We study the spatial clustering of 632 (1130) XMM-COSMOS active galactic nuclei (AGNs) with known spectroscopic or photometric redshifts in the range z = [0.1-2.5] in order to measure the AGN bias and estimate the typical mass of the hosting dark matter (DM) halo as a function of AGN host galaxy properties. <BR /> Methods: We created AGN subsamples in terms of stellar mass, M<SUB>*</SUB>, and specific black hole accretion rate, L<SUB>X</SUB>/M<SUB>*</SUB>, to study how AGN environment depends on these quantities. Further, we derived the M<SUB>*</SUB>-M<SUB>halo</SUB> relation for our sample of XMM-COSMOS AGNs and compared it to results in literature for normal non-active galaxies. We measured the projected two-point correlation function w<SUB>p</SUB>(r<SUB>p</SUB>) using both the classic and the generalized clustering estimator, based on photometric redshifts, as probability distribution functions in addition to any available spectroscopic redshifts. We measured the large-scale (r<SUB>p</SUB> ≳ 1 h<SUP>-1</SUP> Mpc) linear bias b by comparing the clustering signal to that expected of the underlying DM distribution. The bias was then related to the typical mass of the hosting halo M<SUB>halo</SUB> of our AGN subsamples. Since M<SUB>*</SUB> and L<SUB>X</SUB>/M<SUB>*</SUB> are correlated, we matched the distribution in terms of one quantity and we split the distribution in the other. <BR /> Results: For the full spectroscopic AGN sample, we measured a typical DM halo mass of log (M<SUB>halo</SUB>/h<SUP>-1</SUP> M<SUB>☉</SUB>) = 12.79<SUB>-0.43</SUB><SUP>+0.26</SUP>, similar to galaxy group environments and in line with previous studies for moderate-luminosity X-ray selected AGN. We find no significant dependence on specific accretion rate L<SUB>X</SUB>/M<SUB>*</SUB>, with log (M<SUB>halo</SUB>/h<SUP>-1</SUP> M<SUB>☉</SUB>) = 13.06<SUB>-0.38</SUB><SUP>+0.23</SUP> and log (M<SUB>halo</SUB>/h<SUP>-1</SUP> M<SUB>☉</SUB>) = 12.97<SUB>-1.26</SUB><SUP>+0.39</SUP> for low and high L<SUB>X</SUB>/M<SUB>*</SUB> subsamples, respectively. We also find no difference in the hosting halos in terms of M<SUB>*</SUB> with log (M<SUB>halo</SUB>/h<SUP>-1</SUP> M<SUB>☉</SUB>) = 12.93<SUB>-0.62</SUB><SUP>+0.31</SUP> (low) and log (M<SUB>halo</SUB>/h<SUP>-1</SUP> M<SUB>☉</SUB>) = 12.90<SUB>-0.62</SUB><SUP>+0.30</SUP> (high). By comparing the M<SUB>*</SUB>-M<SUB>halo</SUB> relation derived for XMM-COSMOS AGN subsamples with what is expected for normal non-active galaxies by abundance matching and clustering results, we find that the typical DM halo mass of our high M<SUB>*</SUB> AGN subsample is similar to that of non-active galaxies. However, AGNs in our low M<SUB>*</SUB> subsample are found in more massive halos than non-active galaxies. By excluding AGNs in galaxy groups from the clustering analysis, we find evidence that the result for low M<SUB>*</SUB> may be due to larger fraction of AGNs as satellites in massive halos.