Ultra-compact massive galaxies ucmg s , i.e .
galaxies with stellar masses \mbox { $M _ { \star } $ } > 8 \times 10 ^ { 10 } M _ { \odot } and effective radii \mbox { $R _ { e } $ } < 1.5 kpc , are very rare systems , in particular at low and intermediate redshifts .
Their origin as well as their number density across cosmic time are still under scrutiny , especially because of the paucity of spectroscopically confirmed samples .
We have started a systematic census of ucmg candidates within the ESO Kilo Degree Survey , together with a large spectroscopic follow-up campaign to build the largest possible sample of confirmed ucmg s. This is the third paper of the series and the second based on the spectroscopic follow-up program .
Here , we present photometrical and structural parameters of 33 new candidates at redshifts 0.15 \lesssim z \lesssim 0.5 and confirm 19 of them as ucmg s , based on their nominal spectroscopically inferred M _ { \star } and R _ { e } .
This corresponds to a success rate of \sim 58 \% , nicely consistent with our previous findings .
The addition of these 19 newly confirmed objects , allows us to fully assess the systematics on the system selection , and finally reduce the number density uncertainties .
Moreover , putting together the results from our current and past observational campaigns and some literature data , we build the largest sample of ucmg s ever collected , comprising 92 spectroscopically confirmed objects at 0.1 \lesssim z \lesssim 0.5 .

This number raises to 116 , allowing for a 3 \sigma tolerance on the M _ { \star } and R _ { e } thresholds for the ucmg definition .
For all these galaxies we have estimated the velocity dispersion values at the effective radii which have been used to derive a preliminary mass–velocity dispersion correlation .