The "Cosmic Seagull": A Highly Magnified Disk-Like Galaxy At Z Similar Or Equal To 2.8 Behind The Bullet Cluster

Abstract We present Atacama Large Millimeter/submillimeter Array measurements of the “Cosmic Seagull,” a strongly magnified galaxy at z = 2.7779 behind the Bullet Cluster. We report CO(3–2) and continuum 344 μ m (rest-frame) data at one of the highest differential magnifications ever recorded at submillimeter wavelengths ( μ up to ∼50), facilitating a characterization of the kinematics of a rotational curve in great detail (at ∼620 pc resolution in the source plane). We find no evidence for a decreasing rotation curve, from which we derive a dynamical mass of (6.3 ± 0.7) × 10 10 M ⊙ within r = 2.6 ± 0.1 kpc. The discovery of a third, unpredicted, image provides key information for a future improvement of the lensing modeling of the Bullet Cluster and allows a measure of the stellar mass, <?CDATA ${1.6}_{-0.86}^{+1.9}\times {10}^{10}\,{M}_{\odot }$?> , unaffected by strong differential magnification. The baryonic mass is expected to be dominated by the molecular gas content ( f gas ≤ 80 ± 20%) based on an <?CDATA ${M}_{{{\rm{H}}}_{2}}$?> mass estimated from the difference between dynamical and stellar masses. The star formation rate (SFR) is estimated via the spectral energy distribution (SFR = 190 ± 10 M ⊙ yr −1 ), implying a molecular gas depletion time of 0.25 ± 0.08 Gyr.