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