$K$-band integral field spectroscopy and optical spectroscopy of massive
  young stellar objects in the Small Magellanic Cloud
  We present $K$-band integral field spectroscopic observations towards 17
massive young stellar objects (YSOs) in the low metallicity Small Magellanic
Cloud (SMC) and two YSO candidates in the compact H ii regions N81 and N88 A
(also in the SMC). These sources, originally identified using $Spitzer$
photometry and/or spectroscopy, have been resolved into 29 $K$-band continuum
sources. By comparing Br$\gamma$ emission luminosities with those presented for
a Galactic sample of massive YSOs, we find tentative evidence for increased
accretion rates in the SMC. Around half of our targets exhibit emission line
(Br$\gamma$, He i and H$_2$) morphologies which extend significantly beyond the
continuum source and we have mapped both the emission morphologies and the
radial velocity fields. This analysis also reveals evidence for the existence
of ionized low density regions in the centre outflows from massive YSOs.
Additionally we present an analysis of optical spectra towards a similar sample
of massive YSOs in the SMC, revealing that the optical emission is
photo-excited and originates near the outer edges of molecular clouds, and is
therefore consistent with a high mean-free path of UV photons in the
interstellar medium (ISM) of the SMC. Finally, we discuss the sample of YSOs in
an evolutionary context incorporating the results of previous infrared and
radio observations, as well as the near-infrared and optical observations
presented in this work. Our spectroscopic analysis in both the $K$-band and the
optical regimes, combined with previously obtained infrared and radio data,
exposes differences between properties of massive YSOs in our own Galaxy and
the SMC, including tracers of accretion, discs and YSO--ISM interactions.
