Compact to extended Lyman-α emitters in MAGPI: Strong blue-peak emission at z ≳ 3

We report the discovery of three double-peaked Lyman-α emitters (LAEs) exhibiting strong blue-peak emission at 2.9 ≲ z ≲ 4.8 in the VLT/MUSE data obtained as part of the Middle Ages Galaxy Properties with Integral Field Spectroscopy (MAGPI) survey. These strong blue-peak systems provide a unique window into the scattering of Lyα photons by neutral hydrogen (H i), suggesting gas inflows along the line of sight and low H i column density. Two of them at z = 2.9 and z = 3.6, are spatially extended halos with their core regions clearly exhibiting stronger emission at the blue peak than at the red peak. However, spatial variations in the peak ratio and peak separation are evident over 25 × 26 kpc (z = 2.9) and 19 × 28 kpc (z = 3.6) regions in these extended halos. Notably, these systems do not fall in the regime of Lyα blobs or nebulae. To the best of our knowledge, such a Lyα halo with a dominant blue core has not been observed previously. In contrast, the LAE at z ∼ 4.8 is a compact system spanning a 9 × 9 kpc region and stands as the highest-redshift strong blue-peak emitter ever detected. The peak separation of the bright cores in these three systems ranges from ∆_peak ∼ 370 to 660 km s⁻¹. The observed overall trend of decreasing peak separation with increasing radius is supposed to be controlled by H i column density and gas covering fraction. Based on various estimations, in contrast to the compact LAE, our halos are found to be good candidates for Lyman-continuum (LyC) leakers. These findings shed light on the complex interplay between Lyα emission, gas kinematics, and ionizing radiation properties, offering valuable insights into the evolution and nature of high-redshift galaxies.