Primordial environment of super massive black holes: large-scale galaxy overdensities aroundz ~ 6 quasars with LBT

L. Morselli, M. Mignoli, R. Gilli, C. Vignali, A. Comastri, E. Sani, N. Cappelluti, G. Zamorani, M. Brusa, S. Gallozzi, E. Vanzella
2014 Astronomy and Astrophysics  
We investigated the presence of galaxy overdensities around four z∼6 QSOs, namely SDSS J1030+0524 (z = 6.28), SDSS J1148+5251 (z = 6.41), SDSS J1048+4637 (z = 6.20) and SDSS J1411+1217 (z = 5.95), through deep r-, i- and z- band imaging obtained with the wide-field (∼23'×25') Large Binocular Camera (LBC) at the Large Binocular Telescope (LBT). We adopted color-color selections within the i-z vs r-z plane to identify samples of i-band dropouts at the QSO redshift and measure their relative
more » ... heir relative abundance and spatial distribution in the four LBC fields, each covering ∼8×8 physical Mpc at z∼6. The same selection criteria were then applied to z-band selected sources in the ∼1 deg^2 Subaru-XMM Newton Deep Survey to derive the expected number of dropouts over a blank LBC-sized field (∼0.14 deg^2). The four observed QSO fields host a number of candidates larger than what is expected in a blank field. By defining as i-band dropouts objects with z_AB<25, i-z>1.4 and undetected in the r-band, we found 16, 10, 9, 12 dropouts in SDSS J1030+0524, SDSS J1148+5251, SDSS J1048+4637, and SDSS J1411+1217, respectively, whereas only 4.3 such objects are expected over a 0.14 deg^2 blank field. This corresponds to overdensity significances of 3.3, 1.9, 1.7, 2.5σ, respectively. By considering the total number of dropouts in the four LBC fields and comparing it with what is expected in four blank fields of 0.14 deg^2 each, we find that high-z QSOs reside in overdense environments at the 3.7σ level. This is the first direct and unambiguous measurement of the large scale structures around z∼6 QSOs. [shortened]
doi:10.1051/0004-6361/201423853 fatcat:h56rbselczbzbf34gjzyiqg4we