Issue |
A&A
Volume 699, July 2025
|
|
---|---|---|
Article Number | A320 | |
Number of page(s) | 17 | |
Section | Galactic structure, stellar clusters and populations | |
DOI | https://doi.org/10.1051/0004-6361/202451292 | |
Published online | 16 July 2025 |
The diverse physical origins of stars in the dynamically hot bulge: CALIFA versus IllustrisTNG
1
Shanghai Astronomical Observatory, Chinese Academy of Sciences,
80 Nandan Road,
Shanghai
200030,
China
2
School of Astronomy and Space Sciences, University of Chinese Academy of Sciences,
No. 19A Yuquan Road,
Beijing
100049,
PR
China
3
Max-Planck-Institut für Astronomie,
Königstuhl 17,
69117
Heidelberg,
Germany
4
Department of Astronomy, Xiamen University, Xiamen,
Fujian
361005,
China
5
Kavli Institute for Astronomy and Astrophysics, Peking University,
Beijing
100871,
China
6
Instituto de Astrofísica de Canarias, Calle Via Láctea s/n,
38200
La Laguna, Tenerife,
Spain
7
Depto. Astrofísica, Universidad de La Laguna, Calle Astrofísico Francisco Sánchez s/n,
38206
La Laguna, Tenerife,
Spain
★ Corresponding authors: zhangle@shao.ac.cn; lzhu@shao.ac.cn
Received:
28
June
2024
Accepted:
9
December
2024
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 (fhot ~ 0.18) of the dynamically hot component in galaxies with stellar masses of M* ~ 1–2 × 1010 M⊙, and the morphology of each orbital component in the TNG50 and TNG100 galaxies closely resembles that found in the CALIFA galaxies. We therefore used 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 (M* ≲ 1010 M⊙) 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 z = 0 are predominantly born hot. (2) In higher-mass galaxies (M* ≳ 1010 M⊙) 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 Re 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. 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.
Key words: methods: numerical / galaxies: evolution / galaxies: general / galaxies: kinematics and dynamics
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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