Context : Massive Ultracompact Galaxies ( MUGs ) are common at z = 2-3 , but very rare in the nearby Universe .
Simulations predict that the few surviving MUGs should reside in galaxy clusters , whose large relative velocities prevent them from merging , thus maintaining their original properties ( namely stellar populations , masses , sizes and dynamical state ) .

Aims : Our goal is to obtain a complete census of the MUG population at 0.02 < z < 0.3 , determining the number density , population properties and environment .

Methods : We take advantage of the high-completeness , large-area spectroscopic GAMA survey , complementing it with deeper imaging from the KiDS and VIKING surveys .
We find a set of 22 bona-fide MUGs , defined as having high stellar mass ( > 8 \times 10 ^ { 10 } M _ { \odot } ) and compact size ( R _ { e } < 2 kpc ) .
An additional set of 7 lower-mass objects ( 6 \times 10 ^ { 10 } < M _ { \star } /M _ { \odot } < 8 \times 10 ^ { 10 } ) are also potential candidates according to typical mass uncertainties .

Results : The comoving number density of MUGs at low redshift ( z < 0.3 ) is constrained at ( 1.0 \pm 0.4 ) \times 10 ^ { -6 } Mpc ^ { -3 } , consistent with galaxy evolution models .
However , we find a mixed distribution of old and young galaxies , with a quarter of the sample representing ( old ) relics .
MUGs have a predominantly early/swollen disk morphology ( Sérsic index 1 < n < 2.5 ) with high stellar surface densities ( \langle \Sigma _ { e } \rangle \sim 10 ^ { 10 } M _ { \odot } Kpc ^ { -2 } ) .
Interestingly , a large fraction feature close companions – at least in projection – suggesting that many ( but not all ) reside in the central regions of groups .
Halo masses show these galaxies inhabit average-mass groups .

Conclusions : As MUGs are found to be almost equally distributed among environments of different masses , their relative fraction is higher in more massive overdensities , matching the expectations that some of these galaxies fell in these regions at early times .
However , there must be another channel leading some of these galaxies to an abnormally low merger history because our sample shows a number of objects that do not inhabit particularly dense environments .