Milky Way-like Gas Excitation in an Ultrabright Submillimeter Galaxy at z = 1.6
Abstract
Based on observations with the IRAM 30 m and Yebes 40 m telescopes, we report evidence of the detection of Milky Way-like, low-excitation molecular gas, up to the transition CO(J = 5-4), in a distant, dusty star-forming galaxy at z CO = 1.60454. WISE J122651.0+214958.8 (alias SDSS J1226, the Cosmic Seahorse), is strongly lensed by a foreground galaxy cluster at z = 0.44 with a source magnification of μ = 9.5 ± 0.7. This galaxy was selected by cross-correlating near-to-mid-infrared colors within the full-sky AllWISE survey, originally aiming to discover rare analogs of the archetypical strongly lensed submillimeter galaxy SMM J2135-0102, the Cosmic Eyelash. We derive an apparent (i.e., not corrected for lensing magnification) rest-frame 8-1000 μm infrared luminosity of $\mu {\text{}}{L}_{\mathrm{IR}}={1.66}_{-0.04}^{+0.04}\times {10}^{13}$ μLIR=1.66-0.04+0.04×1013 L ⊙ and apparent star formation rate μSFRIR = 2960 ± 70 M ⊙ yr-1. SDSS J1226 is ultrabright at S 350μm ≃ 170 mJy and shows similarly bright low-J CO line intensities as SMM J2135-0102, however, with exceptionally small CO(J = 5-4) intensity. We consider different scenarios to reconcile our observations with typical findings of high-z starbursts, and speculate about the presence of a previously unseen star formation mechanism in cosmic noon submillimeter galaxies. In conclusion, the remarkable low line luminosity ratio r 5,2 = 0.11 ± 0.02 is best explained by an extended, main-sequence star formation mode-representing a missing link between starbursts to low-luminosity systems during the epoch of peak star formation history.
- Publication:
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The Astrophysical Journal
- Pub Date:
- December 2021
- DOI:
- 10.3847/2041-8213/ac2eba
- arXiv:
- arXiv:2110.05537
- Bibcode:
- 2021ApJ...923L..27S
- Keywords:
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- 594;
- 1061;
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- 790;
- 670;
- 262;
- 1569;
- 734;
- 847;
- 1073;
- 595;
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- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 12 pages incl. one appendix, 5 figures, 2 tables. Accepted for publication in The Astrophysical Journal Letters