Another excellent blog on this paper by the AMIGA group, enjoy!
|The Hickson Compact groups observed in this CARMA study, 3-color g-r-i images are from PanSTARRS.|
|The CO(1-0) image of HCG 40c taken by CARMA, overlaid upon the PanSTARRS g-r-i image, plus the average velocity map from CARMA. Adapted from Alatalo et al. 2015|
|The Schmidt-Kennicutt relation with the HCG galaxies plotted in red.|
The HCGs fall below the relation. Adapted from Alatalo et al. 2015
|The star formation suppression versus the colors of each HCG galaxy. The redder the molecular gas rich HCG galaxy, the higher the suppression in the gas. Adapted from Alatalo et al. 2015|
This has bigger implications for galaxy evolution in general too. Studies have been popping up showing that "dead" galaxies still contain molecular gas (including our own!), and some great work on post-starburst galaxies are showing that they also contain significant reservoirs of molecular gas, despite having quenched their star formation. This challenges the "standard model" for quenching galaxies - that gas must be expelled first and star formation ceases later. Inklings that this is not the only path popped up circumstantially, but this paper shows some of the first evidence that rendering molecular gas infertile could indeed be a way to quench star formation and transition a galaxy, without requiring its molecular reservoir to be rapidly expelled. This also means that "AGN feedback" is not strictly necessary, as the AGN was plugged in to remove the gas rapidly.
It stands to question whether this mode - that is, suppressing the star formation in the molecular gas - is one that is universalizable, or whether it is only going to be seen in the unusual environments like in shocked HCG systems, where the gravitational torques and chaotic motions of the group members provide a constant supply of new turbulence. But it is encouraging to see that we no longer always require an explosive feedback step to explain why galaxies transition and quench their star formation so rapidly.
The official published version can be found on NASA ADS.
To get a PDF version made by me, you can download it here.