Early Science Result from the Japanese Virtual Observatory: AGN and Galaxy Clustering at z = 0.3 to 3.0

Abstract

Abstract We present the result of a projected cross-correlation analysis of AGNs and galaxies at redshifts from 0.3 to 3.0. The Japanese Virtual Observatory (JVO) was used to obtain Subaru Suprime-Cam images and UKIDSS catalog data around AGNs. We investigated 1809 AGNs, which is about a ten-times larger sample than that used in previous studies on AGN–galaxy clustering at redshifts larger than 0.6; 90% of the AGN samples were optically-selected AGN from the SDSS and 2dF catalogs. The galaxy samples at low redshift include many redder objects from the UKIDSS survey, while at higher redshift they are mainly blue galaxies from Suprime-Cam. We found a significant excess of galaxies around the AGNs at redshifts from 0.3 to 1.8. For the low-redshift samples (z$\lt$ 0.9), we obtained a correlation length of $r_{0}$$=$ 5–6$\ h^{-1}$ Mpc ($\gamma$$=$ 1.8), which indicates that the AGNs at this redshift range reside in a similar environment around typical local galaxies. We also found that AGNs at higher redshift ranges reside in a denser environment than lower redshift AGNs. For z$=$ 1.3–1.8 AGNs, the cross-correlation length was measured as 11$^{+6}_{-3}\ h^{-1}$ Mpc ($\gamma$$=$ 1.8). Considering that our sample of galaxies is based on optical observations with Suprime-Cam at the redshift range, it is expected that blue star-forming galaxies comprise the majority of objects that are observed to be clustered around the AGNs. It has been successfully demonstrated that using the archive through the Virtual Observatory system can provide a powerful tool for investigating the small-scale environment of intermediate redshift AGNs.