MUSE Analysis of Gas around Galaxies (MAGG) - VI. The cool and enriched gas environment of z≳3 Lyα emitters

We present a novel dataset that extends our view of the cosmic gas around z ≈ 3−4 Lyα emitters (LAEs) in the Muse Analysis of Gas around Galaxies (MAGG) survey by tracing a cool and enriched gas phase through 47 Mg ii absorbers identified in newly obtained VLT/X-shooter near-infrared quasar spectra. Jointly with the more ionized gas traced by C iv systems and the neutral H i from previous work, we find that LAEs are distributed inside cosmic structures that contain multiphase gas in composition and temperature. All gas phases are a strong function of the large-scale galaxy environment: the Mg ii and the C iv strength and kinematics positively correlate with the number of associated galaxies, and it is ≈3−4 times more likely to detect metal absorbers around groups of LAEs than isolated ones. Exploring the redshift evolution, the covering factor of Mg ii around groups of LAEs and isolated ones remains approximately constant from z ≈ 3−4 to z . 2, but the one of C iv around group galaxies drops by z . 2. Adding the cool enriched gas traced by the Mg ii absorbers to the results that we obtained for the H i and C iv gas, we put forward a picture in which LAEs lie along gas filaments that contain high column-density H i systems and are enriched by strong C iv and Mg ii absorbers. While the Mg ii gas appears to be more centrally concentrated near LAEs, weaker C iv systems instead trace a more diffuse gas phase extended up to larger distances around the galaxies.