Speaker
Description
We determine the total stellar mass fraction (stellar mass/total mass) in
clusters of galaxies using data from the Dark Energy Survey for ∼ 300 clusters
in the redshift range 0.2-0.3 (Zhang et al. 2019). We use the total observed
luminosity of the clusters, including their Brightest Cluster Galaxy (BCG),
satellite galaxies, and Intracluster Light (ICL). Previous studies claimed that
clusters are inefficient in star formation when investigating the stellar light in
the BCG relative to the total cluster mass; the stellar mass of the BCG relative
to the total cluster mass drops sharply with increasing cluster mass. Here we
find that when the total stellar mass in clusters is included, as obtained from
the total cluster luminosity, clusters are not inefficient in star formation. In
fact, we find that clusters are as efficient in star formation as expected from the
sum of their individual cluster members. We find the total stellar mass fraction
in rich clusters to be ~1.5% ± 0.6%, exactly as expected from the sum of the
luminosity function of cluster members, which have stellar mass fractions that
range from ~3% for bright L* galaxies to very low stellar mass fractions for
fainter galaxies. The BGCs simply do not grow their stellar light as fast as
clusters grow their mass. This is indeed expected since merging clusters grow
their mass continuously, while BCGs merge and grow only occasionally. Finally,
we find that the total stellar mass traces the total mass of clusters well. This
can potentially offer a new tracer of total cluster mass.
