Le Zhang, Ling Zhu, Annalisa Pillepich, Min Du, Fangzhou Jiang

| Summary:

[[{“value”:”We compare the internal stellar structures of central galaxies in the TNG50
and TNG100 simulations and field galaxies in the CALIFA survey. The luminosity
fractions of the dynamically cold, warm, and hot components in both TNG50 and
TNG100 galaxies exhibit general consistency with those observed in CALIFA
galaxies. For example, they all exhibit a minimum luminosity fraction of the
dynamically hot component in galaxies with intermediate stellar masses, and the
morphology of each orbital component in the TNG50 and TNG100 galaxies closely
resembles that found in the CALIFA galaxies. We therefore use the simulations
to quantify the physical origins of the different components, focusing on the
dynamically hot component in TNG50. We identify three primary regimes and thus
physical processes: (1) in low mass galaxies that have not experienced major
mergers, stars are born with a wide range of circularity distributions and have
remained relatively unchanged until the present day. Consequently, hot stars in
such galaxies at redshift 0 are predominantly born hot. (2) In higher mass
galaxies lacking major mergers, most stars are initially born cold but are
subsequently heated through secular evolution. (3) In galaxies across the
entire mass range, mergers, if they occurred, significantly increased the hot
orbital fraction. As a result, the dynamically hot bulge within $R_e$ of
present-day galaxies does not indicate their past merger histories; instead,
the hot stars in the outer regions are mostly heated or accreted by mergers,
thus indicating galaxy merger history. The massive galaxies are initially born
with cold, rotationally supported structures, consistent with recent
observations from the James Webb Space Telescope (JWST) regarding high-redshift
galaxies.”}]] 

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