Sp1149 I: Constraints on the Balmer L-sigma Relation for HII Regions in a Spiral Galaxy at Redshift z=1.49 Strongly Lensed by the MACS J1149 Cluster

TL;DR

This study investigates whether giant HII regions at high redshift follow the same luminosity-velocity dispersion relation as nearby galaxies, using gravitational lensing to analyze a galaxy at z=1.49 and comparing results to low-redshift relations.

Contribution

First measurement of the L-sigma relation for HII regions at z=1.49 using gravitational lensing and multiple spectroscopic data sources, revealing differences from local universe relations.

Findings

HII regions at z=1.49 are brighter than local L-sigma predictions.

One HII region is significantly more luminous than expected for its velocity dispersion.

HII regions in Sp1149 align with the local star-forming locus on the BPT diagram.

Abstract

The luminosities and velocity dispersions of the extinction-corrected Balmer emission lines of giant HII regions in nearby galaxies exhibit a tight correlation (~0.35 dex scatter). There are few constraints, however, on whether giant HII regions at significant lookback times follow an L-sigma relation, given the angular resolution and sensitivity required to study them individually. We measure the luminosities and velocity dispersions of H-alpha and H-beta emission from 11 HII regions in Sp1149, a spiral galaxy at redshift z=1.49 multiply imaged by the MACS J1149 galaxy cluster. Sp1149 is also the host galaxy of the first-known strongly lensed supernova with resolved images, SN Refsdal. We employ archival Keck-I OSIRIS observations, and newly acquired Keck-I MOSFIRE and Large Binocular Telescope LUCI long-slit spectra of Sp1149. When we use the GLAFIC simply parameterized lens model, we find that the H-alpha luminosities of the HII regions at z=1.49 are a factor of 6.4+2.9-2.0 brighter than predicted by the low-redshift L-sigma relation we measure from Very Large Telescope MUSE spectroscopy. If the lens model is accurate, then the HII regions in Sp1149 differ from their low-redshift counterparts. We identify an HII region in Sp1149 that is dramatically brighter (by 2.03+-0.44 dex) than our low-redshift L-sigma relation predicts given its low velocity dispersion. Finally, the HII regions in Sp1149 are consistent, perhaps surprisingly, with the z=0 star-forming locus on the Baldwin-Phillips-Terlevich diagram.