Primordial environment of supermassive black holes

II. Deep Y- and J-band images around the z ~ 6.3 quasar SDSS J1030+0524

¹ INAF–Osservatorio Astronomico di Bologna, via Piero Gobetti 93/3, 40129 Bologna, Italy
e-mail: barbara.balmaverde@oabo.inaf.it
² Dipartimento di Fisica e Astronomia, Alma Mater Studiorum, Universitá degli Studi di Bologna, via Piero Gobetti, 93/2, 40129 Bologna, Italy
³ Department of Physics, Yale University, PO Box 208121, New Haven, CT 06520, USA
⁴ Yale Center for Astronomy & Astrophysics, Physics Department, PO Box 208120, New Haven, CT 06520, USA
⁵ European Southern Observatory, Alonso de Cordova 3107, Casilla 19, 19001 Santiago, Chile
⁶ Department of Astronomy and Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802, USA
⁷ Institute for Gravitation and the Cosmos, The Pennsylvania state University, University Park, PA 16802, USA
⁸ Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy

Received: 23 February 2017
Accepted: 6 June 2017

Abstract

Many cosmological studies predict that early supermassive black holes (SMBHs) can only form in the most massive dark matter halos embedded within large-scale structures marked by galaxy overdensities that may extend up to ~10 physical Mpc. This scenario, however, has not been confirmed observationally, as the search for galaxy overdensities around high-z quasars has returned conflicting results. The field around the z = 6.31 quasar SDSSJ1030+0524 (J1030) is unique for multi-band coverage and represents an excellent data legacy for studying the environment around a primordial SMBH. In this paper we present wide-area (~25′ × 25′) Y- and J-band imaging of the J1030 field obtained with the near infrared camera WIRCam at the Canada-France-Hawaii Telescope (CFHT). We built source catalogs in the Y- and J-band, and matched those with our photometric catalog in the r, z, and i bands presented in our previous paper and based on sources with z_AB< 25.2 detected using z-band images from the the Large Binocular Cameras (LBC) at the Large Binocular Telescope (LBT) over the same field of view. We used these new infrared data together with H and K photometric measurements from the MUlti-wavelength Survey by Yale-Chile (MUSYC) and with the Spitzer Infrared Array Camera (IRAC) data to refine our selection of Lyman break galaxies (LBGs), extending our selection criteria to galaxies in the range 25.2 <z_AB< 25.7. We selected 21 robust high redshift candidates in the J1030 field with photometric redshift z ~ 6 and colors i−z ≥ 1.3. We found a significant asymmetry in the distribution of the high redshift galaxies in J1030, supporting the existence of a coherent large-scale structure around the quasar. We estimated an overdensity of z ~ 6 galaxies in the field of δ = 2.4, which is significant at >4σ. The overdensity value and its significance are higher than those found in our previous paper and we interpret this as evidence of an improved LBG selection.