Testing massive star evolution, star-formation history, and feedback at
  low metallicity: Photometric analysis of OB stars in the SMC Wing
  The supergiant ionized shell SMC-SGS 1 (DEM 167), located in the outer Wing
of the Small Magellanic Cloud (SMC), resembles structures that originate from
an energetic star-formation event and later stimulate star formation as they
expand into the ambient medium. However, stellar populations within and
surrounding SMC-SGS 1 tell a different story. We present a photometric study of
the stellar population encompassed by SMC-SGS 1 in order to trace the history
of this structure and its potential influence on star formation within the
low-density, low-metallicity SMC Wing. For a stellar population that is
physically associated with SMC-SGS 1, we combined near-ultraviolet (NUV)
photometry from the Galaxy Evolution Explorer (GALEX) with archival optical
(V-band) photometry from the ESO Danish 1.54m Telescope. Given their colors and
luminosities, we estimated stellar ages and masses by matching observed
photometry to theoretical stellar isochrone models. We find that the
investigated region supports an active, extended star-formation event spanning
$\sim$ 25 - 40 Myr ago, as well as continued star formation into the present.
Using a standard initial mass function (IMF), we infer a lower bound on the
stellar mass from this period of $\sim 3 \times 10^4 M_{\odot}$, corresponding
to a star-formation intensity of $\sim$ 6 $\times$ 10$^{-3}$ M$_{\odot}$
kpc$^{-2}$ yr$^{-1}$. The spatial and temporal distributions of young stars
encompassed by SMC-SGS 1 imply a slow, consistent progression of star formation
over millions of years. Ongoing star formation along the edge of and interior
to SMC-SGS 1 suggests a combined stimulated and stochastic mode of star
formation within the SMC Wing. A slow expansion of the shell within this
low-density environment may preserve molecular clouds within the volume of the
shell, leaving them to form stars even after nearby stellar feedback expels
local gas and dust.
