Speaker
Description
The removal/strangulating of gas in cluster environments cause the stop of star formation, especially on extended cold disks, while tidal shocking/stripping might destroy or heat the cold disks in galaxies formed before fell into the cluster. The cold disk fraction and stellar population provide fossil records on how the cluster environments impact on the galaxy structure formation.
In the context of the Fornax3D project, we analyzed 21 galaxies in the Fornax cluster observed with MUSE/VLT by applying a novel population-orbit superposition method.
By fitting the luminosity distribution, stellar kinematics, age and metallicity maps simultaneously, we obtained the internal stellar orbit distribution and stellar population distributions.
Based on the model, we decompose the dynamically cold disk (orbital circularity λz > 0.8) for each galaxy, and obtain its luminosity fraction, age and metallicity radial profiles. For galaxies in the Fornax cluster, we find that the luminosity fraction of cold disk in recent infallers are consistent with field galaxies from CALIFA, while the cold disk fractions in ancient infallers with tinfall > 8 Gyr are a factor of ∼ 4 lower, with control of stellar mass. Moreover, the stellar age of cold disk is highly correlated with galaxy infall time into the cluster, and we find positive age gradients in cold disks, with stars in the inner disk being younger than those in the outer disk, contrary to the expectation of inside-out growth.
We then directly compare our results with galaxies in Fornax-like clusters in TNG50 simulations, and find that they agree with each other remarkably well on cold disk fractions, stellar age, age gradients, and their dependence on galaxy’s infall time to the cluster. In the simulations, we find gas in the outer disk was partly removed and partly compacted into the inner regions when falling into the cluster, which leads to quick stop of star formation in the outer disk, but a long tail of star formation in the inner regions. The turnover of star formation radius from out to inner regions is highly correlated with the galaxy’s infall time. This process explains most of the above results. At the same time, tidal shocking partially heats the cold disk formed before infall, which further reduces the cold disk fraction in ancient infallers which bear the strongest tidal effects.
