NGC5846-UDG1: A galaxy formed mostly by star formation in massive, extremely dense clumps of gas

TL;DR

This study reveals that the ultra-diffuse galaxy NGC5846-UDG1 has an exceptionally high number of globular clusters, suggesting most stars formed in dense, massive gas clumps during early galaxy formation, contrasting with typical dispersed star formation.

Contribution

It provides detailed analysis of NGC5846-UDG1's globular cluster system, showing most stars likely formed in dense clusters, highlighting a different galaxy formation process.

Findings

NGC5846-UDG1 hosts 54 globular clusters, more than similar luminosity galaxies.

Globular clusters comprise about 13% of the galaxy's total light.

Most stars in the galaxy likely formed in dense globular clusters.

Abstract

It has been shown that ultra-diffuse galaxies (UDGs) have higher specific frequencies of globular clusters on average than other dwarf galaxies with similar luminosities. The UDG NGC5846-UDG1 is among the most extreme examples of globular cluster-rich galaxies found so far. Here we present new Hubble Space Telescope (HST) observations and analysis of this galaxy and its globular cluster system. We find that NGC5846-UDG1 hosts $54 \pm 9$ globular clusters, three to four times more than any previously known galaxy with a similar luminosity, and higher than reported in previous studies. With a galaxy luminosity of $L_{V,\mathrm{gal}} \approx 6 \times 10^7\,{\rm L}_{\odot}$ ($M_\star \approx 1.2 \times 10^8\,{\rm M}_\odot$) and a total globular cluster luminosity of $L_{V,\mathrm{GCs}} \approx 7.6 \times 10^6\,{\rm L}_{\odot}$, we find that the clusters currently comprise $\sim 13 \%$ of the total light. Taking into account the effects of mass loss from clusters during their formation and throughout their lifetime, we infer that most of the stars in the galaxy likely formed in globular clusters, and very little to no "normal" low-density star formation occurred. This result implies that the most extreme conditions during early galaxy formation promoted star formation in massive and dense clumps, in contrast to the dispersed star formation observed in galaxies today.