LBT-MODS spectroscopy of high-redshift candidates in the Chandra J1030 field

A newly discovered z ∼ 2.8 large-scale structure

¹ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Piero Gobetti, 93/3, 40129 Bologna, Italy
e-mail: stefano.marchesi@inaf.it
² Department of Physics and Astronomy, Clemson University, Kinard Laboratory of Physics, 140 Delta Epsilon Ct., Clemson, SC 29634, USA
³ Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, via Gobetti 93/2, 40129 Bologna, Italy
⁴ Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, via G. Sansone 1, 50019 Sesto Fiorentino, Firenze, Italy
⁵ Istituto Nazionale di Astrofisica (INAF) – Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 50125 Firenze, Italy
⁶ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, Via A. Corti 12, 20133 Milano, Italy
⁷ Scuola Internazionale Superiore di Studi Avanzati (SISSA), Via Bonomea 265, 34136 Trieste, Italy
⁸ Department of Physics, University of Miami, 1320 S Dixie Highway, Coral Gables, FL 33146, USA
⁹ INAF – Istituto di Radioastronomia, via P. Gobetti 101, 40129 Bologna, Italy

Received: 20 November 2022
Accepted: 21 March 2023

Abstract

We present the results of a spectroscopic campaign with the Multi-Object Double Spectrograph (MODS) instrument mounted on the Large Binocular Telescope (LBT), aimed at obtaining a spectroscopic redshift for seven Chandra J1030 sources with a photometric redshift ≥2.7 and optical magnitude r_AB = [24.5 − 26.5]. We obtained a spectroscopic redshift for five out of seven targets: all of them have z_spec ≥ 2.5, thus probing the reliability of the Chandra J1030 photometric redshifts. The spectroscopic campaign led to the serendipitous discovery of a z ∼ 2.78 large-scale structure (LSS) in the J1030 field: the structure contains four X-ray sources (three of which were targeted in the LBT-MODS campaign) and two non-X-ray-detected galaxies for which a VLT-MUSE spectrum was already available. We also find 26 galaxies with a photometric redshift in the range z_phot = [2.68 − 2.88], which we consider candidate LSS members. The X-ray members of the LSS are hosted in galaxies that are significantly more massive (log(M_*/M_⊙) = [10.0 − 11.1]) than both those hosting the two MUSE-detected sources (log(M_*/M_⊙) < 10) and those belonging to the photometric sample (median stellar mass log(M_*/M_⊙) = 10.0). Both observations and simulations show that massive galaxies, and particularly objects with log(M_*/M_⊙) > 10, are among the best tracers of LSSs and filaments in the cosmic web. Consequently, our result can explain why X-ray-detected active galactic nuclei have also been shown to be efficient tracers of LSS.