On the origin of the red excess in very young super star clusters: the case of SBS 0335-052E

TL;DR

This paper models the impact of nebular emission on the spectral energy distribution of very young super star clusters, explaining the red flux excess observed in SBS 0335-052E by including nebular contributions.

Contribution

It introduces a self-consistent model incorporating nebular emission to better explain the red excess in young star clusters, especially in low-metallicity environments.

Findings

Nebular emission significantly contributes to NIR flux at around 10 Myr.

The model explains the red flux excess in SBS 0335-052E clusters.

Nebular phase lasts longer in low-metallicity environments.

Abstract

The spectral energy distribution analysis of very young unresolved star clusters challenges our understanding of the cluster formation process. Studies of resolved massive clusters in the Milky Way and in the nearby Magellanic Clouds show us that the contribution from photoionized gas is very important during the first Myr of cluster evolution. We present our models which include both a self-consistent treatment of the photoionized gas and the stellar continuum and quantify the impact of such nebular component on the total flux of young unresolved star clusters. A comparison with other available models is considered. The very young star clusters in the SBS 0335-052E dwarf starburst galaxy are used as a test for our models. Due to the low metallicity of the galactic medium our models predict a longer lasted nebular phase which contributes between 10-40% of the total near infrared (NIR) fluxes at around 10 Myr. We propose thus a possible solution for the observed flux excess in the 6 bright super star clusters of SBS 0335-052E. Reines et al. showed that the observed cluster fluxes, in the red-optical and NIR range, sit irreconcilably above the provided stellar continuum models. We find that in the age range estimated from the H_alpha emission we can explain the red excess in all the 6 super star clusters as due to nebular emission, which at cluster ages around 10 Myr still affects the NIR wavebands substantially.