On the lack of correlation between Mg II 2796, 2803 Angstrom and Lyman alpha emission in lensed star-forming galaxies

TL;DR

This study investigates the emission properties of Mg II and Lyman alpha lines in gravitationally lensed star-forming galaxies, revealing no correlation and suggesting different origins for Mg II emission compared to nebular lines.

Contribution

It provides new insights into the origins of Mg II emission, showing it likely arises from reprocessed stellar continuum rather than nebular emission in high-redshift galaxies.

Findings

Mg II emission and Lyman alpha show no correlation in equivalent widths.

Mg II emission is broader and more redshifted than nebular lines.

Mg II emission may originate from reprocessed stellar continuum, not nebular emission.

Abstract

We examine the Mg II 2796, 2803 Angstrom, Lyman alpha, and nebular line emission in five bright star-forming galaxies at 1.66<z<1.91 that have been gravitationally lensed by foreground galaxy clusters. All five galaxies show prominent Mg II emission and absorption in a P Cygni profile. We find no correlation between the equivalent widths of Mg II and Lyman alpha emission. The Mg II emission has a broader range of velocities than do the nebular emission line profiles; the Mg II emission is redshifted with respect to systemic by 100 to 200 km/s. When present, Lyman alpha is even more redshifted. The reddest components of Mg II and Lyman alpha emission have tails to 500-600 km/s, implying a strong outflow. The lack of correlation in the Mg II and Lyman alpha equivalent widths, the differing velocity profiles, and the high ratios of Mg II to nebular line fluxes together suggest that the bulk of Mg II emission does not ultimately arise as nebular line emission, but may instead be reprocessed stellar continuum emission.