An ACA Survey of [C i] 3 P 1 − 3 P 0 , CO J = 4 − 3, and Dust Continuum in Nearby U/LIRGs

Abstract

We present the results of surveying [C i ] 3 P 1 – 3 P 0 , 12 CO J = 4 − 3, and 630 μ m 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 ] 3 P 1 – 3 P 0 has a linear relationship with both the 12 CO J = 4 − 3 and 630 μ m continuum. (ii) In NGC 6052 and NGC 7679, 12 CO J = 4 − 3 was detected but [C i ] 3 P 1 – 3 P 0 was not detected with a [C i ] 3 P 1 – 3 P 0 / 12 CO J = 4 − 3 ratio of ≲0.08. Two possible scenarios of weak [C i ] 3 P 1 – 3 P 0 emission are C 0 -poor/CO-rich environments and an environment with an extremely large [C i ] 3 P 1 – 3 P 0 missing flux. (iii) There is no clear evidence showing that galaxy mergers, AGNs, and dust temperatures control the ratios of [C i ] 3 P 1 – 3 P 0 / 12 CO J = 4 − 3 and L [ C I ] ( 1 − 0 ) ′ / L 630 μ 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 ] 3 P 1 – 3 P 0 / 12 CO J = 4 − 3 ratio of U/LIRGs is similar to that of SMGs but smaller than that of galaxies on the MS.