NOEMA Observations of CO Emission in Arp 142 and Arp 238 Xu, C. K. Lisenfeld, Ute Galaxies: interactions Galaxies: evolution Galaxies: starbust Galaxies: general This work is supported by the National Key R&D Program of China No. 2017YFA0402704 and National Natural Science Foundation of China (NSFC) No. 11873055 and sponsored (in part) by the Chinese Academy of Sciences (CAS) through a grant to the CAS South America Center for Astronomy (CASSACA). C.K.X. acknowledges NSFC grant No. 11733006. U.L. acknowledges support by the research project AYA2017-84897-P from the Spanish Ministerio de Economia y Competitividad, the European Regional Development Funds (FEDER), and the Junta de Andalucia (Spain) grant FQM108. Y.G. acknowledges NSFC grant Nos. 11861131007, 12033004, and 11420101002 and the Chinese Academy of Sciences Key Research Program of Frontier Sciences (grant No. QYZDJ-SSW-SLH008). F.R. acknowledges support from the Knut and Alice Wallenberg Foundation. This work is based on observations carried out under project No. W19BL with the IRAM NOEMA Interferometer. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). We thank the IRAM support astronomer, Ka Tat Wong, for valuable help and advice with the reduction of the data. Previous studies have shown significant differences in the enhancement of the star formation rate (SFR) and star formation efficiency (SFE = SFR/M (mol)) between spiral-spiral and spiral-elliptical mergers. In order to shed light on the physical mechanism of these differences, we present NOEMA observations of the molecular gas distribution and kinematics (linear resolutions of similar to 2 kpc) in two representative close major-merger star-forming pairs: the spiral-elliptical pair Arp 142 and the spiral-spiral pair Arp 238. The CO in Arp 142 is widely distributed over a highly distorted disk without any nuclear concentration, and an off-center ringlike structure is discovered in channel maps. The SFE varies significantly within Arp 142, with a starburst region (region 1) near the eastern tip of the distorted disk showing an SFE similar to 0.3 dex above the mean of the control sample of isolated galaxies and the SFE of the main disk (region 4) 0.43 dex lower than the mean of the control sample. In contrast, the CO emission in Arp 238 is detected only in two compact sources at the galactic centers. Compared to the control sample, Arp 238-E shows an SFE enhancement of more than 1 dex, whereas Arp 238-W has an enhancement of similar to 0.7 dex. We suggest that the extended CO distribution and large SFE variation in Arp 142 are due to an expanding large-scale ring triggered by a recent high-speed head-on collision between the spiral galaxy and the elliptical galaxy, and the compact CO sources with high SFEs in Arp 238 are associated with nuclear starbursts induced by gravitational tidal torques in a low-speed coplanar interaction. 2021-11-15T12:49:13Z 2021-11-15T12:49:13Z 2021-06-29 info:eu-repo/semantics/article Published version: C. K. Xu... [et al.]. 2021 ApJ 918 55. [10.3847/1538-4357/ac0f77] http://hdl.handle.net/10481/71521 eng http://creativecommons.org/licenses/by-nc-nd/3.0/es/ info:eu-repo/semantics/openAccess Atribución-NoComercial-SinDerivadas 3.0 España Institute of Physics Publishing