October
2025
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2025ApJ...991..197X
Authors
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Xu, C. K.
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Cheng, C.
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Yun, M. S.
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Appleton, P. N.
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Emonts, B. H. C.
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Braine, J.
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Gallagher, S. C.
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Guillard, P.
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Lisenfeld, U.
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O'Sullivan, E.
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Renaud, F.
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Aromal, P.
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Duc, P.-A.
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Labiano, A.
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Togi, A.
Abstract
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We present new observational evidence supporting the hypothesis that SQ-A, a starburst in the intragroup medium (IGrM) of Stephan's Quintet (SQ), is triggered by a high-speed collision between two gas systems, one associated with the IGrM (v ∼ 6900 km s−1) and another with the intruder galaxy NGC 7318b (v ∼ 6000 km s−1). The new CO(2─1) data set from the Atacama Large Millimeter/submillimeter Array has angular resolutions between 0.″2 and 7.″0 and the new Very Large Array H I data cube has an angular resolution of 6.″6×7.″9 . The CO maps show that the two gas systems are bridged by another system with an intermediate velocity of ∼6600 km s−1, whereas the H I data show that the component of v ∼ 6600 km s−1 fits well into a gap in the more extended v ∼ 6000 km s−1 component, albeit with a displacement of ∼5 kpc. Both the bridge and the complementary distributions between different gas systems are common features of starbursts triggered by cloud─cloud collision. An analysis of clumps (sizes of 100─200 pc) reveals very diversified star formation (SF) activity in clumps belonging to different kinematic systems, with the molecular gas depletion time of the v ∼ 6900 km s−1 clumps being more than 10 times longer than that of the v ∼ 6600 km s−1 clumps. The results are consistent with a scenario in which the enhanced SF activity (and the starburst) in the system of v ∼ 6600 km s−1 is due to gas compression generated in cloud─cloud collisions, whereas the suppression of SF in the v ∼ 6900 km s−1 system is due to vortices (i.e. gas rotation) generated in more complex collisions involving dense clouds and diffuse intercloud gas associated with high-speed shocks.
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