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Abstract We present an analysis of 10 ks snapshot Chandra observations of 12 shocked post-starburst galaxies, which provide a window into the unresolved question of active galactic nuclei (AGN) activity in post-starburst galaxies and its role in the transition of galaxies from active star formation to quiescence. While seven of the 12 galaxies have statistically significant detections (with two more marginal detections), the brightest only obtained 10 photons. Given the wide variety of hardness ratios in this sample, we chose to pursue a forward-modeling approach to constrain the intrinsic luminosity and obscuration of these galaxies, rather than stacking. We constrain the intrinsic luminosity of obscured power laws based on the total number of counts and spectral shape, itself mostly set by the obscuration, with hardness ratios consistent with the data. We also tested thermal models. While all the galaxies have power-law models consistent with their observations, a third of the galaxies are better fit as an obscured power law and another third are better fit as thermal emission. If these post-starburst galaxies, early in their transition, contain AGNs, then these are mostly confined to lower obscuration ( N H ≤ 10 23 cm −2 ) and lower luminosity ( L 2−10 keV ≤ 10 42 erg s −1 ). Two galaxies, however, are clearly best fit as significantly obscured AGNs. At least half of this sample shows evidence of at least low-luminosity AGN activity, though none could radiatively drive out the remaining molecular gas reservoirs. Therefore, these AGNs are more likely along for the ride, having been fed gas by the same processes driving the transition. 

We present a multiwavelength study of IC 860, a nearby post-starburst galaxy at the early stage of transitioning from blue and star forming to red and quiescent. Optical images reveal a galaxy-wide, dusty outflow originating from a compact core. We find evidence for a multiphase outflow in the molecular and neutral gas phase from the CO position–velocity diagram and NaD absorption features. We constrain the neutral mass outflow rate to be ∼0.5M_⊙yr⁻¹, and the total hydrogen mass outflow rate to be ∼12M_⊙yr⁻¹. Neither outflow component seems able to escape the galaxy. We also find evidence for a recent merger in the optical images, CO spatial distribution, and kinematics, and evidence for a buried active galactic nucleus in the optical emission line ratios, mid-IR properties, and radio spectral shape. The depletion time of the molecular gas reservoir under the current star formation rate is ∼7 Gyr, indicating that the galaxy could stay at the intermediate stage between the blue and red sequence for a long time. Thus the timescales for a significant decline in star formation rate (quenching) and gas depletion are not necessarily the same. Our analysis supports the quenching picture where outflows help suppress star formation by disturbing rather than expelling the gas and shed light on possible ongoing activities in similar quenching galaxies.