Milky Way-like Gas Excitation in an Ultrabright Submillimeter Galaxy at z = 1.6

Author(s): Nikolaus Sulzenauer, Helmut Dannerbauer, A. Díaz-Sánchez, Bodo Ziegler, S. Iglesias-Groth, R. Rebolo Lopez
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 μL_IR=1.66^+0.04_−0.04×10¹³ L_⊙ and apparent star formation rate μSFR_IR = 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.
Organisation(s): Department of Astrophysics
External organisation(s): Institute of Astrophysics of the Canary Islands, University of La Laguna, Max-Planck-Institut für Radioastronomie, Universidad Politécnica de Cartagena
Journal: The Astrophysical journal Letters
Volume: 923
No. of pages: 9
ISSN: 2041-8205
DOI: https://doi.org/10.3847/2041-8213/ac2eba
Publication date: 12-2021
Peer reviewed: Yes
Austrian Fields of Science 2012: 103003 Astronomy, 103004 Astrophysics, 103044 Cosmology
Keywords
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Portal url: https://ucrisportal.univie.ac.at/en/publications/7321920d-060c-413a-9277-483bd05fb4f7

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