Synthetic observations of H$_2$D$^+$ towards high-mass starless cores
  Young massive stars are usually found embedded in dense and massive molecular
clumps and are known for being highly obscured and distant. During their
formation process, deuteration is regarded as a potentially good indicator of
the formation stage. Therefore, proper observations of such deuterated
molecules are crucial, but still, hard to perform. In this work, we test the
observability of the transition o-H$_2$D$^+(1_{10}$-$1_{11})$, using a
synthetic source, to understand how the physical characteristics are reflected
in observations through interferometers and single-dish telescopes. In order to
perform such tests, we post-processed a magneto-hydrodynamic simulation of a
collapsing magnetized core using the radiative transfer code POLARIS.
  Using the resulting intensity distributions as input, we performed
single-dish (APEX) and interferometric (ALMA) synthetic observations at
different evolutionary times, always mimicking realistic configurations.
Finally, column densities were derived to compare our simulations with real
observations previously performed. Our derivations for o-H$_2$D$^+$ are in
agreement with values reported in the literature, in the range of
10$^{\!10-11}$cm$^{\!-2}$ and 10$^{\!12-13}$cm$^{\!-2}$ for single-dish and
interferometric measurements, respectively.
