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Abstract
The assembly history of massive galaxies remains a major unsolved problem for galaxy evolution. In the hierarchical galaxy formation paradigm, mergers are expected to play a vital role during the evolution of massive galaxies. As galaxy-galaxy interactions are more frequent for galaxies in groups as compared to isolated galaxies, a relationship between large-scale environment and galaxy properties is expected. However, many of the studies to date have found no significant dependence on environment once the known dependence on stellar mass is considered.
Integral field spectroscopy enables the mapping of stellar populations and kinematics across individual galaxies. This is important since evidence of the accretion history of passive galaxies is predicted to be preserved in the stellar population radial profiles (when and how the stars were formed) and in the 2D kinematics (which contain clues about how these stars entered the halo) of low-redshift galaxies.
In this project we determine how the physical properties of galaxies vary with galactocentric radius to help us constrain the evolution process of early-type galaxies, and to shed light on how their properties depend on environment. We draw a sample of passive galaxies from the SAMI Galaxy Survey, which is one of only two surveys that allow us to study a statistically significant number of galaxies in a range of environments.
We first focus on stellar population gradients, which contain information on how important interactions were during the formation of the galaxy. We do not observe a significant difference between the stellar population gradients of central and satellite galaxies at fixed stellar mass and as a function of halo mass. This evidence suggests that the inner regions (within 2Re) of central passive galaxies form in a similar fashion to those of passive satellites.
We also build triaxial Schwarzschild orbit-superposition models to examine the different dynamical components of galaxies. We find that the changes of internal structures within 1Re are correlated with the total stellar mass of the individual galaxies. By dividing the stellar orbital distribution into cold, warm, hot, and counter-rotating components, we find an increasing fraction of hot orbits with increasing stellar mass, while warm and cold orbits show a decreasing trend with mass. We also find that, although these intrinsic properties correlate strongly with stellar mass, environment does play a secondary role.
