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SQ-A is a starburst in the intra-group medium (IGrM) of the famous compact group Stephan's Quintet (SQ). There has been a long controversy on whether SQ-A is triggered by a collision of two gas systems, one is associated with the IGrM (v~6900 km/s) and another with the intruder galaxy NGC 7318b (v~6000 km/s). The counter argument against the collisional scenario is based on the fact that in a large scale shock ridge (~40 kpc) in the middle of SQ, which is also due to the collision between the IGrM and the intruder, the star formation (SF) is suppressed rather than enhanced. In this paper, using new ALMA CO(2-1) observations and new VLA high resolution HI data, together with JWST 15um image, we aim to solve this controversy. Our results indicate that the collisional effect on the SF is very complex: while collisions between dense clouds (cloud-cloud collision) can lead to starburst (as in SQ-A), collisions between dense clouds and diffuse inter-cloud gas can cause SF suppression (as in the shock ridge region). Our results may have far-reaching implications in studies of interacting galaxy systems (mergers, groups, clusters) since the triggered SF plays an important role in these systems.

BIO

Prof. Cong Xu graduated with a B.S. in 1980 from Nankai University and a PhD in Astrophysics in 1988 from SISSA in Trieste, Italy. As a post-doctoral researcher, he worked at ICTP in Trieste, as Humboldt Fellow in Bonn, at Max-Planck Institute for Nuclear Physics in Heidelberg, and at Infrared Processing and Analysis Center, Caltech. He was a Staff Scientist at Caltech from 1999-2016. Since 2016, he has been a Professor at CASSACA (CAS South America Center for Astronomy), NAOC. Cong's research interest covers a wide range of topics, including infrared/sub-mm emission of galaxies, starburst galaxies, and galaxy mergers; star formation process, ISM, and their interplay with galaxies; the large-scale distribution of galaxies in local universe; distant galaxies and galaxy evolution.

Host: Cheng Li