The NGC 5253 star cluster system. I. Standard modelling and infrared-excess sources

TL;DR

This study uses high-resolution Hubble data to analyze the properties of star clusters in NGC 5253, revealing insights into their ages, masses, and infrared excess, and highlighting the galaxy's complex star formation history.

Contribution

It provides a detailed reexamination of cluster properties with improved resolution and wavelength coverage, and explores the origins of IR excess in young clusters using spectral synthesis models.

Findings

Most clusters are low-mass and young, consistent with the galaxy's starburst activity.

IR excess in young clusters likely caused by stochastic effects and stellar color variations.

Presence of intermediate-age and old globular clusters indicates multiple star formation episodes.

Abstract

Using high-resolution Hubble Space Telescope data, we reexamine the fundamental properties (ages, masses and extinction values) of the rich star cluster population in the dwarf starburst galaxy NGC 5253. The gain in resolution compared to previous studies is of order a factor of two in both spatial dimensions, while our accessible wavelength range transcends previous studies by incorporation of both near-ultraviolet and near-infrared (IR) passbands. We apply spectral synthesis treatments based on two different simple stellar population model suites to our set of medium-, broad-band and H-alpha images to gain an improved physical understanding of the IR-excess flux found for a subset of young clusters (30 of 149). With the caveat that our models are based on fully sampled stellar mass functions, the NGC 5253 cluster population is dominated by a significant number of relatively low-mass (M_cl <= a few 10^4 Msun) objects with ages ranging from a few x 10^6 to a few x 10^7 yr, which is in excellent agreement with the starburst age of the host galaxy. The IR-excess clusters are almost all found in this young age range and have masses of up to a few x 10^4 Msun. The IR excess in the relatively low-mass NGC 5253 clusters is most likely caused by a combination of stochastic sampling effects and colour variations due to the presence of either luminous red or pre-main-sequence stars. We also find a small number of intermediate-age (~ 1 Gyr-old), ~10^5 Msun clusters, as well as up to a dozen massive, ~10 Gyr-old globular clusters. Their presence supports the notion that NGC 5253 is a very active galaxy that has undergone multiple episodes of star cluster formation.