ALMA Observations for CO Emission from Luminous Lyman-break Galaxies at z=6.0293-6.2037

Yoshiaki Ono, Seiji Fujimoto, Yuichi Harikane, Masami Ouchi, Livia Vallini, Andrea Ferrara, Takatoshi Shibuya, Andrea Pallottini, Akio K. Inoue, Masatoshi Imanishi, Kazuhiro Shimasaku, Takuya Hashimoto, Chien-Hsiu Lee, Yuma Sugahara, Yoichi Tamura, Kotaro Kohno, Malte Schramm

Submitted on 1 November 2022


We present our new Atacama Large Millimeter/submillimeter Array (ALMA) observations targeting CO(6-5) emission from three luminous Lyman break galaxies (LBGs) at zspec=6.0293-6.2037 found in the Subaru/Hyper Suprime-Cam survey, whose [OIII]88μm and [CII]158μm emission have been detected with ALMA. We find a marginal detection of the CO(6-5) line from one of our LBGs, J0235-0532, at the 4σ significance level and obtain upper limits for the other two LBGs, J1211-0118 and J0217-0208. Our z=6 luminous LBGs are consistent with the previously found correlation between the CO luminosity and the infrared luminosity. The unique ensemble of the multiple far-infrared emission lines and underlying continuum fed to a photodissociation region model reveal that J0235-0532 has a relatively high hydrogen nucleus density that is comparable to those of low-z (U)LIRGs, quasars, and Galactic star-forming regions with high nH values, while the other two LBGs have lower nH consistent with local star-forming galaxies. By carefully taking account of various uncertainties, we obtain total gas mass and gas surface density constraints from their CO luminosity measurements. We find that J0235-0532 locates below the Kennicutt-Schmidt (KS) relation, comparable to the previously CO(2-1) detected z=5.7 LBG, HZ10. Combined with previous results for dusty starbursts at similar redshifts, the KS relation at z=5-6 is on average consistent with the local one.


Comment: 33 pages, 12 figures, accepted for publication in ApJ

Subject: Astrophysics - Astrophysics of Galaxies