Galaxy morphology classification: are stellar circularities enough?
We present a preliminary study exploring whether the stellar orbital circularity of simulated galaxies, available from precomputed catalogs in the IllustrisTNG project, can be used as a proxy for a broad morphological classification. We focus on the publicly available "Stellar Circular...
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| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Astronomical Observatory, Department of Astronomy, Belgrade
2025-01-01
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| Series: | Serbian Astronomical Journal |
| Subjects: | |
| Online Access: | https://doiserbia.nb.rs/img/doi/1450-698X/2025/1450-698X2510061B.pdf |
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| Summary: | We present a preliminary study exploring whether the stellar orbital
circularity of simulated galaxies, available from precomputed catalogs in
the IllustrisTNG project, can be used as a proxy for a broad morphological
classification. We focus on the publicly available "Stellar Circularities,
Angular Momenta, Axis Ratios" catalog, which enables a simple kinematic
decomposition of the stellar component into disk and spheroid subsystems. By
validating this approach against the more detailed five-component kinematic
decomposition in TNG50, we confirm that the circularity-based disk fraction
correlates most strongly with the thin disk, while the bulge fraction
broadly represents the combined contribution of classical bulges and stellar
halos. We then apply this decomposition to galaxies in the TNG100 simulation
at redshift z = 0 and identify a data-motivated threshold of Fdisk = 0:25 to
distinguish early- and late-type galaxies. This threshold, being lower
than the commonly adopted value of 0:4, better captures the diversity of
disk-dominated systems and avoids excluding galaxies with moderately
prominent disks. Additionally, we identify irregular or morphologically
complex systems based on galaxies with low total disk and spheroid mass
fractions. Using this classification, we recover a morphology-density
relation that is broadly consistent with observations: the late-type
galaxies dominate in the field, while the early-type galaxies are the most
prevalent morphological type in clusters. Our results demonstrate that
stellar circularity alone can serve as an accessible and computationally
efficient morphological proxy. We also discuss the potential for this
classification to support machine learning efforts as a baseline or training
set for future morphological studies. |
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| ISSN: | 1450-698X 1820-9289 |