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A possible trigger of the multiple population phenomenon in star clusters

Andrés E. Piatti

TL;DR

The paper addresses what triggers the multiple populations (MPs) phenomenon in star clusters. It proposes that MPs arise when clusters form during periods of intense host-galaxy star formation and supports this with an observational synthesis across the Milky Way, Sagittarius, Helmi streams, and the Magellanic Clouds. A lower mass limit for MP hosting is identified, given by $\log_{10}(M/M_{sun}) = (-0.036 \pm 0.005) \times (t/\mathrm{Gyr}) + 4.916 \pm 0.100$, with MPs preferentially present in more massive clusters formed during SFR peaks; a multivariate logistic regression yields coefficients $6.60 \pm 3.10$ (SFR) and $5.93 \pm 2.14$ (mass) with $p$-values $0.03$ and $0.00$, respectively, and $R^2=0.83$, accuracy $94\%$. This supports an environmental trigger scenario where galaxy-scale star formation episodes set conditions that enable MP formation inside clusters.

Abstract

Multiple populations (MPs) is a intra-star cluster phenomenon consisting in star-to-star variation of the abundance of some light chemical elements. They have been observed in many star clusters, most of them old globular clusters, populating the Milky Way and other satellite galaxies. Since the study of MPs became more systematic, different astrophysical parameters have been claimed to be the main responsible for its occurrence. However, at the present time, no attempt would seem to have solved this conundrum. This work deals with a potential trigger of the MPs phenomenon, based on the gathered observational evidence of the existence of MPs in some star clusters and the absence of its in others. We found that star clusters with MPs mostly formed during time intervals of intense star formation activity in a galaxy, for instance during the galaxy formation epoch, a close galaxy encounter, etc. At those time intervals where relative peaks in the galaxy star formation rate occur, star clusters with masses above a lower mass limit harbour MPs. This lower star cluster mass limit would marginally depend on the star cluster age.

A possible trigger of the multiple population phenomenon in star clusters

TL;DR

The paper addresses what triggers the multiple populations (MPs) phenomenon in star clusters. It proposes that MPs arise when clusters form during periods of intense host-galaxy star formation and supports this with an observational synthesis across the Milky Way, Sagittarius, Helmi streams, and the Magellanic Clouds. A lower mass limit for MP hosting is identified, given by , with MPs preferentially present in more massive clusters formed during SFR peaks; a multivariate logistic regression yields coefficients (SFR) and (mass) with -values and , respectively, and , accuracy . This supports an environmental trigger scenario where galaxy-scale star formation episodes set conditions that enable MP formation inside clusters.

Abstract

Multiple populations (MPs) is a intra-star cluster phenomenon consisting in star-to-star variation of the abundance of some light chemical elements. They have been observed in many star clusters, most of them old globular clusters, populating the Milky Way and other satellite galaxies. Since the study of MPs became more systematic, different astrophysical parameters have been claimed to be the main responsible for its occurrence. However, at the present time, no attempt would seem to have solved this conundrum. This work deals with a potential trigger of the MPs phenomenon, based on the gathered observational evidence of the existence of MPs in some star clusters and the absence of its in others. We found that star clusters with MPs mostly formed during time intervals of intense star formation activity in a galaxy, for instance during the galaxy formation epoch, a close galaxy encounter, etc. At those time intervals where relative peaks in the galaxy star formation rate occur, star clusters with masses above a lower mass limit harbour MPs. This lower star cluster mass limit would marginally depend on the star cluster age.

Paper Structure

This paper contains 5 sections, 1 equation, 2 figures, 1 table.

Table of Contents

  1. Introduction
  2. Analysis and discussion
  3. Conclusions
  4. Data availability
  5. Properties of star clusters with studies about MPs.

Figures (2)

  • Figure 1: SFRs of the MW ruizlaraetal2020spitonietal2024; Sagittarius deboeretal2015; Helmi streams ruizlaraetal2022; LMC and SMC massanaetal2022 are shown, respectively. Open and filled circles are star clusters without and with MPs, respectively, drawn on the SFRs at their corresponding ages.
  • Figure 2: Normalized SFR versus star cluster mass. The symbols are as in Figure \ref{['fig1']} with sizes proportional to the star cluster ages. Typical error bars are also shown.