Investigating the Young Stellar Populations and Hierarchies in Nearby Galaxies with the UVIT. III. Evidence for a Largest Scale of Correlated Stellar Structures and a Non-universal Fractal Dimension
Abstract
Scale-free turbulent motions, gravitational collapse and galactic dynamics govern galactic-scale, hierarchical organization of star formation (SF) within galaxies. Past studies suggest that properties of SF hierarchies depend upon host galaxy properties and interstellar medium (ISM) conditions. To characterize SF hierarchies, we performed two-point correlation function analysis on ~25000 UV-selected star-forming clumps (SFCs) identified in a morphologically diverse sample of 8 classic spirals, 6 flocculent spirals and 3 dwarf irregulars. We found that SF hierarchies in galaxies exhibit a maximum spatial scale -- the correlation length (lcorr) -- largest scale up to which SF is spatially correlated, presumably owing to ISM turbulence. The lcorr values range from ~100 pc to 3.4 kpc and exhibit strong dependence on the galaxy's stellar mass, morphology and nature of spiral arms. This suggests that a galaxy's gravitational potential and spiral structure place an upper limit on the sizes of the largest, hierarchically structured SF complexes. Connecting lcorr with turbulence injection sources suggests that stellar feedback in dwarf irregulars, whereas disk instabilities and spiral structure in classic/flocculent spirals dominate towards sustaining their SF hierarchies up to the lcorr scale. These hierarchies disperse to near-random distributions on timescales (Tdis) ranging from 20-160 Myr. The broad range of derived lcorr, projected fractal dimension (D2 ∈ 0.71−1.73), and Tdis indicates a non-universal, galaxy-specific nature of SF hierarchies. In this work, full coverage of each galaxy's star-forming extent with the AstroSat-UltraViolet Imaging Telescope uniquely enabled us to connect global parameters of SF hierarchies with large-scale galaxy properties.
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BibTeX
@misc{shashank2026investigating,
title = {{Investigating the Young Stellar Populations and Hierarchies in Nearby Galaxies with the UVIT. III. Evidence for a Largest Scale of Correlated Stellar Structures and a Non-universal Fractal Dimension}},
author = {Gairola Shashank and Smitha Subramanian and Shyam H. Menon and Chayan Mondal and Kathryn Grasha and Richard de Grijs and Prasun Dutta and Annapurni Subramaniam},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.01065},
eprint = {2609.01065},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.01065},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Investigating the Young Stellar Populations and Hierarchies in Nearby Galaxies with the UVIT. III. Evidence for a Largest Scale of Correlated Stellar Structures and a Non-universal Fractal Dimension
AU - Gairola Shashank
AU - Smitha Subramanian
AU - Shyam H. Menon
AU - Chayan Mondal
AU - Kathryn Grasha
AU - Richard de Grijs
AU - Prasun Dutta
AU - Annapurni Subramaniam
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2609.01065
UR - https://arxiv.org/abs/2609.01065
AB - Scale-free turbulent motions, gravitational collapse and galactic dynamics govern galactic-scale, hierarchical organization of star formation (SF) within galaxies. Past studies suggest that properties of SF hierarchies depend upon host galaxy properties and interstellar medium (ISM) conditions. To characterize SF hierarchies, we performed two-point correlation function analysis on ~25000 UV-selected star-forming clumps (SFCs) identified in a morphologically diverse sample of 8 classic spirals, 6 flocculent spirals and 3 dwarf irregulars. We found that SF hierarchies in galaxies exhibit a maximum spatial scale -- the correlation length (l_corr) -- largest scale up to which SF is spatially correlated, presumably owing to ISM turbulence. The l_corr values range from ~100 pc to 3.4 kpc and exhibit strong dependence on the galaxy's stellar mass, morphology and nature of spiral arms. This suggests that a galaxy's gravitational potential and spiral structure place an upper limit on the sizes of the largest, hierarchically structured SF complexes. Connecting l_corr with turbulence injection sources suggests that stellar feedback in dwarf irregulars, whereas disk instabilities and spiral structure in classic/flocculent spirals dominate towards sustaining their SF hierarchies up to the l_corr scale. These hierarchies disperse to near-random distributions on timescales (T_dis) ranging from 20-160 Myr. The broad range of derived l_corr, projected fractal dimension (D_2 ∈ 0.71−1.73), and T_dis indicates a non-universal, galaxy-specific nature of SF hierarchies. In this work, full coverage of each galaxy's star-forming extent with the AstroSat-UltraViolet Imaging Telescope uniquely enabled us to connect global parameters of SF hierarchies with large-scale galaxy properties.
ER -