The Cosmic Seagull: A Highly Magnified Disk-like Galaxy at z ≃ 2.8 behind the Bullet Cluster

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 mu m (rest-frame) data at one of the highest differential magnifications ever recorded at submillimeter wavelengths (mu up to similar to 50), facilitating a characterization of the kinematics of a rotational curve in great detail (at similar to 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). x. 10(10) M-circle dot 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, 1.6(-0.86)(+1.9) x 10(10) M-circle dot,. 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 M-H2 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-circle dot yr(-1)), implying a molecular gas depletion time of 0.25 +/- 0.08 Gyr.