Constraining young massive cluster properties with radio-continuum observations: The Arches cluster
0004-6361
Abstract
Context. The Arches cluster, located in the Galactic Centre (GC) is one of the best astrophysical laboratories to study the properties of massive stars and young massive clusters (YMCs). However, despite having been observed for decades at different wavelengths, several fundamental parameters of the Arches cluster remain uncertain. Aims. Our goal is to constrain key cluster parameters – i.e. cluster age, mass, and initial mass function (IMF) – by comparing the observed stellar radio flux density distribution of the Arches cluster to those derived from a set of synthetic clusters. Methods. We used the deep X-band (10 GHz) Very Large Array data from our previous radio continuum study of the Arches cluster. We modelled each simulated cluster with three parameters: age, mass, and IMF slope. We used three different stellar evolutionary models, GENEC, PARSEC, and MIST, at two different metallicities, solar (Z = 0.014) and super-solar (Z = 0.020). We ran Markov chain Monte Carlo simulations for each model-metallicity combination to explore parameter space. Results. All models and metallicities return preferred ages in the 2 ≲ tage/Myr ≲ 3 range. Using radio data alone, we obtained an IMF slope of αIMF = −1.85+0.28−0.20, averaged over all models, where uncertainties are dominated by the degeneracy between cluster mass and IMF slope. If we use the IMF slope from previous infrared studies as model prior, the cluster mass distributions peak at ∼2.7×104 M⊙, and we can establish a lower limit at ≳2×104 M⊙ for the Arches cluster mass. Conclusions. Radio continuum observations of their most massive stars can be used to constrain YMC parameters. In the case of the Arches cluster, age can be determined regardless of prior spectroscopic information, which can be useful to characterise newly discovered YMCs in the GC. Furthermore, our results support the idea that a top-heavy IMF may be preferred in the GC or in YMCs in general.