Molecular gas in AzTEC/C159: a star-forming disk galaxy 1.3 Gyr after the Big Bang

Jiménez-Andrade, E. F. and Magnelli, B. and Karim, A. and Jones, G. C. and Carilli, C. L. and Romano-Díaz, E. and Gómez-Guijarro, C. and Toft, S. and Bertoldi, F. and Riechers, D. A. and Schinnerer, E. and Sargent, M. and Michałowski, M. J. and Fraternali, F. and Staguhn, J. G. and Smolčić, Vernesa and Aravena, M. and Harrington, K. C. and Sheth, K. and Capak, P. L. and Koekemoer, A. M. and van Kampen, E. and Swinbank, M. and Zirm, A. and Magdis, G. E. and Navarrete, F. (2018) Molecular gas in AzTEC/C159: a star-forming disk galaxy 1.3 Gyr after the Big Bang. Astronomy and Astrophysics, 615. A25. ISSN 0004-6361

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We studied the molecular gas properties of AzTEC/C159, a star-forming disk galaxy at z = 4:567, in order to better constrain the nature of the high-redshift end of the submillimeter-selected galaxy (SMG) population. We secured 12^CO molecular line detections for the J = 2→1 and J = 5→4 transitions using the Karl G. Jansky Very Large Array (VLA) and the NOrthern Extended Millimeter Array (NOEMA) interferometer. The broad (FWHM ~ 750 km s^-1) and tentative double-peaked profiles of the two 12^CO lines are consistent with an extended molecular gas reservoir, which is distributed in a rotating disk, as previously revealed from [CII] 158 μm line observations. Based on the 12^CO(2→1) emission line, we derived L'_CO = (3.4 ± 0.6)x10^10 Kkm s^-1 pc^2, which yields a molecular gas mass of M_H2 (α_CO/4.3) = (1.5 ± 0.3)x10^11 M_⊙ and unveils a gas-rich system with μ_gas(α_CO/=4.3)≡ M_H2/M_⋆ = 3.3 ± 0.7. The extreme star formation efficiency of AzTEC/C159, parametrized by the ratio L_IR/L'_CO = (216 ± 80) L_⊙ (K km s^-1 pc^2)^-1, is comparable to merger-driven starbursts such as local ultra-luminous infrared galaxies and SMGs. Likewise, the 12^CO(5→4)/CO(2→1) line brightness temperature ratio of r_52 = 0.55 ± 0.15 is consistent with high-excitation conditions as observed in SMGs. Based on mass budget considerations, we constrained the value for the L'_CO – H_2 mass conversion factor in AzTEC/C159, that is, α_CO = 3.9 ^+2.7 _-1.3 M_⊙ K^-1 km^-1 spc^-2, which is consistent with a self-gravitating molecular gas distribution as observed in local star-forming disk galaxies. Cold gas streams from cosmological filaments might be fueling a gravitationally unstable gas-rich disk in AzTEC/C159, which breaks into giant clumps and forms stars as efficiently as in merger-driven systems and generates high gas excitation. These results support the evolutionary connection between AzTEC/C159-like systems and massive quiescent disk galaxies at z ~ 2.

Item Type: Article
Keywords: galaxies: high-redshift, galaxies: formation, galaxies: ISM, ISM: molecules
Date: 2018
Subjects: NATURAL SCIENCES > Physics > Astronomy and Astrophysics
Additional Information: © ESO 2018. Received: 27 October 2017; Accepted: 9 February 2018; Published online: 05 July 2018.
Divisions: Faculty of Science > Department of Physics
Publisher: EDP Sciences
Depositing User: Vernesa Smolčić
Date Deposited: 14 Apr 2019 18:05
Last Modified: 14 Apr 2019 18:29

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