The dynamical evolution of the stellar clumps in the Sparkler galaxy

TL;DR

This study uses N-body simulations to investigate whether stellar clumps observed around the Sparkler galaxy at z=1.4 can evolve into globular clusters by analyzing their dynamical evolution over 9.23 billion years.

Contribution

It provides the first detailed dynamical modeling of high-redshift stellar clumps to assess their potential evolution into present-day globular clusters.

Findings

Dynamical friction causes massive clumps to migrate inward, possibly forming bulges.

Tidal stripping reduces clump masses, aligning them with typical globular cluster masses.

Most surviving clumps remain too large to become globular clusters.

Abstract

Recent JWST observations detected stellar clumps around the z=1.4 gravitationally lensed Sparkler galaxy (of stellar mass $M_*\sim 10^9\,\mathrm{M_\odot}$), with ages and metallicities compatible with globular clusters (GCs). However, most of their masses ($>10^6\,\mathrm{M_\odot}$) and sizes (>30 pc) are about 10 times those of GCs in the local Universe. To assess whether these clumps can evolve into GCs, we performed N-body simulations of their dynamical evolution from z=1.4 to z=0 (9.23 Gyr), under the effect of dynamical friction and tidal stripping. Dynamical friction is studied performing multiple runs of a clump system in a Sparkler-like spherical halo of mass $M_{200}\simeq 5\times 10^{11}\,\mathrm{M_\odot}$ (from the stellar-to-halo mass relation). For the tidal stripping, we simulated resolved clumps, orbiting in an external, static gravitational potential including the same halo as in the dynamical friction simulations and also a Sparkler-like stellar disk. Dynamical friction causes the clumps with mass $>10^7\,\mathrm{M_\odot}$ to sink into the galaxy central regions, possibly contributing to the bulge growth. In absence of tidal stripping, the mass distribution of the surviving clumps (40%) peaks at $5\times 10^6\,\mathrm{M_\odot}$, implying the presence of uncommonly over-massive clumps at z=0. Tidal shocks by the stellar disk strip considerable mass from low-mass clumps, even though their sizes remain larger than those of present-day GCs. When the surviving clumps are corrected for tidal stripping, their mass distribution peak shifts to $2\times 10^6\,\mathrm{M_\odot}$, compatible with massive GCs. Our simulations suggest that a fraction of the Sparkler clumps is expected to fall into the central regions, where they might become bulge fossil fragments or contribute to form a nuclear star cluster. The remaining clumps are too large in size to be progenitors of GCs.