MUSE Analysis of Gas around Galaxies (MAGG)

VII. Emission line galaxies near strong blended Lyα absorption systems at z  ≳  3

¹ Dipartimento di Fisica “G. Occhialini”, Università degli Studi di Milano-Bicocca, Piazza della Scienza 3, I-20126 Milano, Italy
² INAF – Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, I-34143 Trieste, Italy
³ INAF – Osservatorio Astronomico di Brera, Via Brera 28, I-21021 Milano, Italy
⁴ Aix Marseille Université, CNRS, CNES, LAM, Marseille, France

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 18 December 2025
Accepted: 9 April 2026

Abstract

We investigate the connection between strong, blended Lyα absorption systems (SBLAs) and ≈1000 Lyα-emitting galaxies (LAEs) at z ≳ 3 in 28 quasar fields from the MUSE Analysis of Gas around Galaxies (MAGG) survey. Selecting SBLAs as spectral regions with transmitted flux −0.05 < F < 0.25 over ≈ 138 km s⁻¹ bins, we find a strong correlation with LAEs within a projected distance of R ≤ 300 kpc and line-of-sight velocity separation of |Δv| ≤ 300 km s⁻¹. The association rate increases significantly with decreasing flux, a trend that persists also at smaller separations (R < 100 kpc). A two-dimensional cross-correlation analysis confirms significant clustering of LAEs around SBLAs, while no such clustering is seen for spectral regions with F > 0.25. The correlation appears to also depend on the width of the spectral window used to identify SBLAs, with a larger window yielding a stronger signal. Our analysis confirms that SBLAs serve as probes of the circumgalactic medium (CGM) at the interface between the Lyα forest and the optically thick Lyman limit systems. The significant dependence of the LAE-SBLA cross-correlation on the spectral binning used to select these absorbers motivates future tests of the current SBLA framework as a tracer of halos.