Searching for GC-like abundance patterns in young massive clusters II. -
  Results from the Antennae galaxies
  The presence of multiple populations (MPs) with distinctive light element
abundances is a widespread phenomenon in clusters older than 6 Gyr. Clusters
with masses, luminosities, and sizes comparable to those of ancient globulars
are still forming today. Nonetheless, the presence of light element variations
has been poorly investigated in such young systems, even if the knowledge of
the age at which this phenomenon develops is crucial for theoretical models on
MPs. We use J-band integrated spectra of three young (7-40 Myr) clusters in NGC
4038 to look for Al variations indicative of MPs. Assuming that the large
majority (>70%) of stars are characterised by high Al content - as observed in
Galactic clusters with comparable mass; we find that none of the studied
clusters show significant Al variations. Small Al spreads have been measured in
all the six young clusters observed in the near-infrared. While it is unlikely
that young clusters only show low Al whereas old ones display different levels
of Al variations; this suggests the possibility that MPs are not present at
such young ages at least among the high-mass stellar component. Alternatively,
the fraction of stars with field-like chemistry could be extremely large,
mimicking low Al abundances in the integrated spectrum. Finally, since the
near-infrared stellar continuum of young clusters is almost entirely due to
luminous red supergiants, we can also speculate that MPs only manifest
themselves in low mass stars due to some evolutionary mechanism.
