An ACA Survey of [C I] ³P₁-³P₀, CO J = 4 - 3, and Dust Continuum in Nearby U/LIRGs

Abstract

We present the results of surveying [C I] ³P₁-³P₀, ¹²CO J = 4 - 3, and 630 μm dust continuum emission for 36 nearby ultra/luminous infrared galaxies (U/LIRGs) using the Band 8 receiver mounted on the Atacama Compact Array of the Atacama Large Millimeter/submillimeter Array. We describe the survey, observations, data reduction, and results; the main results are as follows. (i) We confirmed that [C I] ³P₁-³P₀ has a linear relationship with both the ¹²CO J = 4 - 3 and 630 μm continuum. (ii) In NGC 6052 and NGC 7679, ¹²CO J = 4 - 3 was detected but [C I] ³P₁-³P₀ was not detected with a [C I] ³P₁-³P₀/¹²CO J = 4 - 3 ratio of ≲0.08. Two possible scenarios of weak [C I] ³P₁-³P₀ emission are C⁰-poor/CO-rich environments and an environment with an extremely large [C I] ³P₁-³P₀ missing flux. (iii) There is no clear evidence showing that galaxy mergers, AGNs, and dust temperatures control the ratios of [C I] ³P₁-³P₀/¹²CO J = 4 - 3 and ${L}_{[{\rm{C}}\,{\rm\small{I}}](1-0)}^{{\prime} }/{L}_{630\mu {\rm{m}}}$ . (iv) We compare our nearby U/LIRGs with high-z galaxies, such as galaxies on the star formation main sequence (MS) at z ~ 1 and submillimeter galaxies (SMGs) at z = 2-4. We found that the mean value for the [C I] ³P₁-³P₀/¹²CO J = 4 - 3 ratio of U/LIRGs is similar to that of SMGs but smaller than that of galaxies on the MS.