  Using numerical hydrodynamic simulations, we study the gravitational
fragmentation of an unstable protostellar disc formed during the collapse of a
pre-stellar core with a mass of 1.2 M_sun. The forming fragments span a mass
range from about a Jupiter mass to very-low-mass protostars and are located at
distances from a few tens to a thousand AU, with a dearth of objects at < 100
AU. We explore the possibility of observational detection of the fragments in
discs viewed through the outflow cavity at a distance of 250 pc. We demonstrate
that one hour of integration time with the Atacama Large
Millimeter/sub-millimeter Array (ALMA) is sufficient to detect the fragments
with masses as low as 1.5 M_Jup at orbital distances up to 800 AU from the
protostar. The ALMA resolution sets the limit on the minimum orbital distance
of detectable fragments. For the adopted resolution of our simulated ALMA
images of 0.1", the fragments can be detected at distances down to 50 AU. At
smaller distances, the fragments usually merge with the central density peak.
The likelihood for detecting the fragments reduces significantly for a lower
resolution of 0.5". Some of the most massive fragments, regardless of their
orbital distance, can produce characteristic peaks at approximately 5 micron
and hence their presence can be indirectly inferred from the observed spectral
energy distributions of protostars.
