Unraveling the Spectral Energy Distributions of Clustered YSOs

Abstract

Stars form in clustered environments, but how they form when the available resources are shared is still not well understood. A related question is whether the IMF is in fact universal across galactic environments, a galactic initial mass function (IGIMF), or whether it is an average of local IMFs. One of the long-standing problems in resolving this question and in the study of young clusters is observational: the emission from multiple sources is frequently seen as blended because at different wavelengths or with different telescopes the beam sizes are different. The confusion hinders our ability to fully characterize clustered star formation. Here we present a new method that uses a genetic algorithm and Bayesian inference to fit the blended SEDs and images of individual YSOs in confused clusters. We apply this method to the infrared photometry of a sample comprising 70 Spitzer-selected, low-mass ($M_{\rm{cl}}<100~\rm{M}_{\odot}$) young clusters in the galactic plane, and use the derived physical parameters to investigate the distributions of masses and evolutionary stages of clustered YSOs, and the implications of those distributions for studies of the IMF and the different models of star formation. We find that for low-mass clusters composed of class I and class II YSOs, there exists a non-trivial relationship between the total stellar mass of the cluster ($M_{\rm{cl}}$) and the mass of its most massive member ($m_{\rm{max}}$). The properties of the derived correlation are most compatible with the random sampling of a Kroupa IMF, with a fundamental high-mass limit of $150~\rm{M}_{\odot}$. Our results are also compatible with SPH models that predict a dynamical termination of the accretion in protostars, with massive stars undergoing this stopping at later times in their evolution.