Star formation histories of Coma cluster galaxies matched to simulated orbits hint at quenching around first pericenter

We study the relation between star formation history of galaxies falling into a high-density cluster environment and their likely orbital histories using both observational and simulation data. We use high-resolution spectra of 12 galaxies of the Coma Cluster around NGC 4874 (the X-ray center of the Coma Cluster). The stellar and kinematic properties of the galaxies are modeled using STECKMAP. We extract the probability distribution of two orbital parameters - infall and pericenter times - of these galaxies from N-body dark matter only simulations extending up to z = -1/2 ( ~10 Gyr in the future). The probability distribution of orbital parameters is compensated for the interloper probabilities of the satellites. We carry out a probability-based study to compare the cumulative (probability) distribution of the two orbital parameters with the star formation rates and the fraction of stellar mass formed. We find that massive galaxies (M_* > 10^10 M_sun) are quenched even before falling into the cluster environment. This may be due to internal quenching mechanisms or group pre-processing, although it is hard to ascertain the individual contribution of various processes. Lower mass galaxies form stars between infall and first pericenter passage and all the galaxies in our sample are quenched by the time of their first pericentric passage. Ram pressure and tidal stripping are likely to be the dominant processes as they peak with proximity to the cluster center.