Letter to the Editor

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

¹ School of Mathematical and Physical Sciences, Macquarie University, NSW, 2109 Australia
e-mail: tamal.mukherjee@hdr.mq.edu.au
² Macquarie University Astrophysics and Space Technologies Research Centre, Sydney, NSW, 2109 Australia
³ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, PO Box 218 Hawthorn, 3122 VIC, Australia
⁴ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT, 2611 Australia
⁵ International Centre for Radio Astronomy Research (ICRAR), Curtin University, Bentley, WA, Australia
⁶ International Centre for Radio Astronomy Research (ICRAR), The University of Western Australia, Crawley, WA, 6009 Australia
⁷ School of Physics, University of New South Wales, Sydney, NSW, 2052 Australia
⁸ Sydney Institute for Astronomy, School of Physics, University of Sydney, NSW, 2006 Australia
⁹ ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO-3D), Australia

Received: 9 October 2023
Accepted: 9 November 2023

Abstract

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 Δ_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.