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

V. Motta, E. Ibar, T. Verdugo, J. Molina, T. M. Hughes, M. Birkinshaw, O. López-Cruz, J. H. Black, D. Gunawan, C. Horellou, J. Magana

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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 μm (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) × 1010 M o 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, , 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 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 o yr-1), implying a molecular gas depletion time of 0.25 ± 0.08 Gyr.

Original languageEnglish
Article numberL16
Number of pages5
JournalAstrophysical Journal Letters
Issue number2
Early online date13 Aug 2018
Publication statusPublished - 20 Aug 2018


  • galaxies: clusters: individual (1ES0657-558)
  • galaxies: evolution
  • galaxies: ISM
  • gravitational lensing: strong
  • submillimeter: galaxies


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