A first GLIMPSE into star clusters populations across cosmic time

TL;DR

This study presents the first sample of high-redshift star clusters observed with JWST, revealing their properties, formation epochs, and the star cluster mass function at z>1, providing insights into early stellar structure formation.

Contribution

First detection and analysis of high-redshift star clusters with JWST, including their physical properties, formation history, and the star cluster mass function at z>1.

Findings

Most star clusters formed during cosmic noon (z=1-4) and are young (<100 Myr).

Star clusters have high stellar densities, similar to local nuclear star clusters.

The star cluster mass function follows a power-law with slope -1.89.

Abstract

We present the first sample of 222 high-redshift (z>0.5) star clusters, detected with JWST/NIRCam in 78 magnified galaxies from different galaxy cluster fields. The majority of the systems (~60%) is observed in the very deep NIRCam observations of the cluster AbellS1063 (GLIMPSE program), showing the power that deep observations, combined with lensing, has to reveal these primordial stellar structures. We perform simultaneous size-flux estimates in all available NIRCam filters and spectral energy distribution (SED) fitting analysis to recover star cluster physical properties. All star cluster candidates have very high magnification. Star clusters and clumps show similar ages and redshift distributions, although noticeable differences are seen in their masses, sizes and stellar surface densities inherent to the lack of resolution in the latter group. We reconstruct the formation redshift of star clusters and find that the large majority of the observed star clusters show young ages (<100 Myr) and seems to form at cosmic noon (CN,1<z<4). A small sample of CN star clusters is about 1 Gyr old, these potential globular clusters have formed well within cosmic reionization. Star clusters have stellar densities in the range 10^2 to 10^6 M/pc^2, with median values around 10^4 pc2. Their sizes and densities better overlap with those of nuclear star clusters in the local Universe. These intrinsic properties make high-z star clusters a viable channel to grow intermediate mass black holes. We use Bayesian inference to make first direct measurement of the star cluster mass function at z>1, based on a subsample of 60 star clusters younger than 100 Myr and with masses above 2e6 Msun. The star cluster mass function is well described by a power-law with slope beta = -1.89 suggesting that a power-law -2 function might already be in place in the distant Universe.