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

Jiménez-Andrade, E.F.; Magnelli, B.; Karim, A.; Jones, G.C.; Carilli, C.L.; Romano-Díaz, E.; Gómez-Guijarro, C.; Toft, S.; Bertoldi, F.; Riechers, D.A.; Schinnerer, E.; Sargent, M.; Michałowski, M.J.; Fraternali, F.; Staguhn, J.G.; Smolčić, V.; Aravena, M.; Harrington, K.C.; Sheth, K.; Capak, P.L.; Koekemoer, A.M.; van Kampen, E.; Swinbank, M.; Zirm, A.; Magdis, G.E.; Navarrete, F.

Abstract

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 12CO 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 12CO 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 12CO(2 →1) emission line, we derived L′CO=(3.4±0.6)×1010 K km s−1 pc2, which yields a molecular gas mass of MH2(αCO/4.3)=(1.5±0.3)×1011 M⊙ and unveils a gas-rich system with μgas(αCO/4.3)≡MH2/M⋆=3.3±0.7. The extreme star formation efficiency of AzTEC/C159, parametrized by the ratio LIR/L′CO=(216±80) L⊙ (K km s−1 pc2)−1, is comparable to merger-driven starbursts such as local ultra-luminous infrared galaxies and SMGs. Likewise, the 12CO(5 →4)/CO(2 →1) line brightness temperature ratio of r52 = 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 – H2 mass conversion factor in AzTEC/C159, that is, αCO=3.9−1.3+2.7 M⊙ K−1 km−1 s pc−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.

Citation

Jiménez-Andrade, E., Magnelli, B., Karim, A., Jones, G., Carilli, C., Romano-Díaz, E., Gómez-Guijarro, C., Toft, S., Bertoldi, F., Riechers, D., Schinnerer, E., Sargent, M., Michałowski, M., Fraternali, F., Staguhn, J., Smolčić, V., Aravena, M., Harrington, K., Sheth, K., Capak, P., …Navarrete, F. (2018). Molecular gas in AzTEC/C159: a star-forming disk galaxy 1.3 Gyr after the Big Bang. Astronomy & Astrophysics, 615, Article A25. https://doi.org/10.1051/0004-6361/201732186

• Journal Article Type: Article
• Acceptance Date: Feb 9, 2018
• Online Publication Date: Jul 5, 2018
• Publication Date: Jul 5, 2018
• Deposit Date: Jul 20, 2018
• Publicly Available Date: Jul 20, 2018
• Journal: Astronomy and astrophysics.
• Print ISSN: 0004-6361
• Electronic ISSN: 1432-0746
• Publisher: EDP Sciences
• Peer Reviewed: Peer Reviewed
• Volume: 615
• Article Number: A25
• DOI: https://doi.org/10.1051/0004-6361/201732186
• Public URL: https://durham-repository.worktribe.com/output/1325666