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Tracing hierarchical star formation out to kiloparsec scales in nearby spiral galaxies with UVIT

Jan 17, 2025 | SHASHANK GAIROLA

RESEARCH HIGHLIGHTS | IIA

Tracing hierarchical star formation out to kiloparsec scales in nearby spiral galaxies with UVIT

SHASHANK GAIROLA | Jan 17, 2025

Molecular clouds fragment under the action of supersonic turbulence and gravity, which results in a scale-free hierarchical distribution of star formation within galaxies. Recent studies suggest that the hierarchical distribution of star formation in nearby galaxies shows a dependence on host galaxy properties. In this context, we study the hierarchical distribution of star formation from a few tens of parsecs up to several kiloparsecs in four nearby spiral galaxies: NGC 1566, NGC 5194, NGC 5457, and NGC 7793, by leveraging large-field-of-view and high-resolution far-ultraviolet (FUV) and near-ultraviolet (NUV) observations from the UltraViolet Imaging Telescope (UVIT). Using the two-point correlation function, we infer that the young star-forming clumps (SFCs) in the galaxies are arranged in a fractal-like hierarchical distribution, but only up to a maximum scale. This largest scale of hierarchy (lcorr) is ubiquitous in all four galaxies and ranges from 0.5 kpc to 3.1 kpc. The flocculent spiral NGC 7793 has roughly five times smaller lcorr than the other three grand design spirals, possibly due to its lower mass, lower pressure environment, and a lack of strong spiral arms. lcorr being much smaller than the galaxy size suggests that the star formation hierarchy does not extend to the full galaxy size and it is likely an effect set by multiple physical mechanisms in the galaxy. The hierarchical distribution of SFCs dissipates almost completely within 10−50 Myr in our galaxy sample, signifying the migration of SFCs away from their birthplaces with increasing age. The fractal dimension of the hierarchy for our galaxies is found to be between 1.05 and 1.50. We also find that depending upon the star formation environment, significant variations can exist in the local and global hierarchy parameters of a galaxy. Overall, our results suggest that the global hierarchical properties of star formation in galaxies are not universal. This study also demonstrates the capabilities of UVIT in characterising the star formation hierarchy in nearby galaxies. In the future, a bigger sample can be employed to better understand the role of large-scale galaxy properties such as morphology and environment as well as physical processes like feedback, turbulence, shear, and interstellar medium conditions in determining the non-universal hierarchical properties of star formation in galaxies.

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Unveiling the kinematics of a central region in the triple-AGN host NGC 7733-7734 interacting group

Mar 01, 2025 | SAILI KESHRI

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Bar formation and destruction in the FIRE-2 simulations

Jan 01, 2025 | SIOREE ANSAR

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IIA offers a vigorous programme of graduate studies that forms a vital component of research & training. The programme is overseen by the board of graduate studies. The Institute is also a major partner in the Joint Astronomy Programme (JAP), organized by the Indian Institute of Science.

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