| Abstract : | Ultra-diffuse galaxies (UDGs) are remarkable for their very low stellar surface brightness and relatively large stellar disks given their small dynamical masses. They are found in field to cluster environments, comprising a significant fraction of galaxies in the local universe, and are hence ideal test-beds to understand the formation and evolution of galaxies. The physical mechanism that primarily regulates their structure and kinematics continues to be a puzzle. We carry out the dynamical modeling of a sample of 7 atomic hydrogen-rich field UDGs, employing the distribution function-based galaxy modeling framework AGAMA (Action-based Galaxy Modelling Architecture); the mass models of these galaxies constructed from stellar photometry and HI 21cm radio-synthesis observations were already available in the literature. Similarly, for comparison, we model a sample of 7 low surface brightness galaxies (LSBs) and 8 dwarf irregular galaxies (dIrrs) as well. For each of the 3 samples, we next carry out Principal Component Analysis (PCA) of the structural and kinematical parameters thus obtained to identify the crucial physical mechanisms regulating the dynamics of the galaxies in each of these samples. The first two principal components explain more than ~ 80% of the variation in the data for all the three cases. Interestingly, we note that in case of UDGs and LSBs, their unique structural features are regulated by the asymptotic velocity followed and the specific angular momentum of the stellar disc. However, the dIrrs seem to be dominated by the compactness of its mass distribution and the stellar velocity dispersion. Our results thus indicate that the structure and kinematics of UDGs and LSBs, are possibly governed by the same dynamical mechanisms, which are different from those of the dIrrs. We therefore conclude that the total dynamical mass and the stellar specific angular momentum primarily govern the distinctive structural characteristics of the UDGs. |
