Constraining Galaxy Overdensities around Three z ∼ 6.5 Quasars with ALMA and MUSE
R. A. Meyer, Roberto Decarli, Fabian Walter, Qiong Li, Ran Wang, Chiara Mazzucchelli, Eduardo Bañados, Emanuele Paolo Farina, Bram Venemans
Abstract
Abstract We quantify galaxy overdensities around three high-redshift quasars with known [C ii ] 158 μ m companions: PJ231–20 ( z = 6.59), PJ308–21 ( z = 6.24), and J0305–3150 ( z = 6.61). Recent SCUBA2 imaging revealed the presence of 17 submillimeter galaxies (SMGs) with sky separations 0.′7 < θ < 2.′4 from these three quasars. We present ALMA Band 6 follow-up observations of these SCUBA2-selected SMGs to confirm their nature and redshift. We also search for continuum-undetected [C ii ] 158 μ m emitters in the ALMA pointings and make use of archival MUSE observations to search for Ly α emitters (LAEs) associated with the quasars. While most of the SCUBA2-selected sources are detected with ALMA in the continuum, no [C ii ] 158 μ m line emission could be detected, indicating that they are not at the quasar redshifts. Based on the serendipitous detection of CO 7–6 and [C i ] 809 μ m emission lines, we find that four SMGs in the field of PJ231–20 are at z ∼ 2.4, which is coincident with the redshift of an Mg ii absorber in the quasar rest-frame UV spectrum. We report the discovery of two LAEs within <0.6 cMpc of PJ231–20 at the same redshift, indicating an LAE overdensity around this quasar. Taken together, these observations provide new constraints on the large-scale excess of Ly α - and [C ii ] 158 μ m -emitting galaxies around z > 6 quasars and suggest that only wide-field observations, such as MUSE, ALMA, or JWST mosaics, can reveal a comprehensive picture of large-scale structure around quasars in the first billion years of the universe.