Sp1149. I. Constraints on the Balmer L–σ Relation for H ii Regions in a Spiral Galaxy at Redshift z = 1.49 Strongly Lensed by the MACS J1149 Cluster

Abstract The luminosities ( L ) and velocity dispersions ( σ ) of the extinction-corrected Balmer emission lines of giant H ii regions in nearby galaxies exhibit a tight correlation (∼0.35 dex scatter). There are few constraints, however, on whether giant H ii regions at significant look-back times follow an L – σ relation, given the angular resolution and sensitivity required to study them individually. We measure the luminosities and velocity dispersions of H α and H β emission from 11 H ii regions in Sp1149, a spiral galaxy at redshift ( z ) 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 α luminosities of the H ii regions at z = 1.49 are a factor of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>6.4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.9</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> brighter than predicted by the low-redshift L – σ relation we measure from Very Large Telescope MUSE spectroscopy. If the lens model is accurate, then the H ii regions in Sp1149 differ from their low-redshift counterparts. We identify an H ii region in Sp1149 that is dramatically brighter (by 2.03 ± 0.44 dex) than our low-redshift L – σ relation predicts given its low velocity dispersion. Finally, the H ii regions in Sp1149 are consistent, perhaps surprisingly, with the z ≈ 0 star-forming locus on the Baldwin–Phillips–Terlevich diagram.