FEAST: Probing Hierarchical Star Formation with the Spatial Distributions of Young Star Clusters

TL;DR

This study uses the angular two-point correlation function to analyze the hierarchical spatial distribution of young star clusters in four nearby galaxies, revealing their structuring and evolution over time with data from JWST and HST.

Contribution

It introduces a comprehensive analysis of YSC spatial distributions across multiple galaxies using TPCF, highlighting the evolution of hierarchical structuring with age and providing new insights into star formation processes.

Findings

Hierarchical structuring is evident in young star clusters, especially those younger than 10 Myr.

Clusters aged 10-300 Myr become increasingly randomly distributed, reaching randomness around 100 Myr.

Young YSCs have fractal indices consistent with a universal star formation process.

Abstract

We apply the angular two-point correlation function (TPCF) to the spatial distribution of young star clusters (YSCs) in four nearby star forming galaxies (NGC 628, NGC 4449, M51, and M83) in order to investigate their underlying hierarchical structuring. Using newly constructed catalogs of YSCs in the emerging phase (eYSCs), identified in the infrared with JWST, and optical YSCs detected in archival HST data, we compute TPCFs for various cluster samples and age bins across the four galaxies as part of the FEAST (Feedback in Emerging extrAgalactic Star ClusTers) program. We find clear evidence of hierarchical structuring, especially in eYSCs and YSCs with ages < 10 Myr (referred to as oYSCs), which show similar TPCFs within each galaxy. NGC 628 exhibits a clear distinction between the TPCFs of eYSCs and oYSCs, implying a shorter randomization timescale. In contrast, clusters aged 10 to 300 Myr exhibit progressively more random spatial distributions, becoming effectively random after $\sim$ 100 Myr, consistent with earlier studies. The two-dimensional fractal index $D_2$ of the YSCs underlying distribution is calculated from model fits to TPCFs. Our values of $D_2$ derived from the youngest YSC populations align better with the expected value of $D_2 \sim $1.3 for a universal star formation process compared to previous findings.