An Emerging Wolf-Rayet Massive Star Cluster in NGC 4449
  We present a panchromatic investigation of the partially-embedded, emerging
massive cluster Source 26 (= S26) in NGC 4449 with optical spectra obtained at
Apache Point Observatory and archival Hubble, Spitzer, and Herschel Space
Telescope images. First identified as a radio continuum source with a thermal
component due to ionized material, the massive cluster S26 also exhibits
optical Wolf-Rayet (WR) emission lines that reveal a large evolved massive star
population. We find that S26 is host to $\sim$240 massive stars, of which
$\sim$18 are Wolf-Rayet stars; the relative populations are roughly consistent
with other observed massive star forming clusters and galaxies. We construct
SEDs over two spatial scales (roughly 100 pc and 300 pc) that clearly exhibit
warm dust and polycyclic aromatic hydrocarbon (PAH) emission. The best fit dust
and grain models reveal that both the intensity of the exciting radiation and
PAH grain destruction increase toward the cluster center. Given that the
timescale of evacuation is important for the future dynamical evolution of the
cluster, it is important to determine whether O- and WR stars can evacuate the
material gradually before supernova do so on a much faster timescale. With a
minimum age of $\approx$ 3 Myr, it is clear that S26 has not yet fully
evacuated its natal material, which indicates that unevolved O-type stars alone
do not provide sufficient feedback to remove the gas and dust. We hypothesize
that the feedback of WR stars in this cluster may be necessary for clearing the
material from the gravitational potential of the cluster. We find S26 is
similar to Emission Line Clusters observed in the Antennae Galaxies and may be
considered a younger analog to 30 Doradus in the LMC.
