A global view on star formation: The GLOSTAR Galactic plane survey IV.
  Radio continuum detections of young stellar objects in the Galactic Centre
  region
  The Central Molecular Zone (CMZ), a $\sim$200 pc sized region around the
Galactic Centre, is peculiar in that it shows a star formation rate (SFR) that
is suppressed with respect to the available dense gas. To study the SFR in the
CMZ, young stellar objects (YSOs) can be investigated. Here we present radio
observations of 334 2.2 $\mu$m infrared sources that have been identified as
YSO candidates. Our goal is to investigate the presence of centimetre
wavelength radio continuum counterparts to this sample of YSO candidates which
we use to constrain the current SFR in the CMZ. As part of the GLOSTAR survey,
D-configuration VLA data was obtained for the Galactic Centre, covering
-2$^{\circ}<l<$2$^{\circ}$ and -1$^{\circ}<b<$1$^{\circ}$, with a frequency
coverage of 4-8 GHz. We matched YSOs with radio continuum sources based on
selection criteria and classified these radio sources as potential HII regions
and determined their physical properties. Of the 334 YSO candidates, we found
35 with radio continuum counterparts. We find that 94 YSOs are associated with
dense dust condensations identified in the 870 $\mu$m ATLASGAL survey, of which
14 have a GLOSTAR counterpart. Of the 35 YSOs with radio counterparts, 11 are
confirmed as HII regions, based on their spectral indices and the literature.
We estimated their Lyman continuum photon flux in order to estimate the mass of
the ionising star. Combining these with known sources, the present-day SFR in
the CMZ is calculated to be $\sim$0.068 M$_{\odot}$ yr$^{-1}$, which is
$\sim$6.8$\%$ of the Galactic SFR. Candidate YSOs that lack radio counterparts
may not have yet evolved to the stage of exhibiting an HII region or,
conversely, are older and have dispersed their natal clouds. Since many lack
dust emission, the latter is more likely. Our SFR estimate in the CMZ is in
agreement with previous estimates in the literature.
