It has been widely remarked that compact , massive , elliptical-like galaxies are abundant at high redshifts but exceedingly rare in the Universe today , implying significant evolution such that their sizes at z \sim 2 \pm 0.6 have increased by factors of 3 to 6 to become today ’ s massive elliptical galaxies .
These claims have been based on studies which measured the half-light radii of galaxies as though they are all single component systems .
Here we identify 21 spheroidal stellar systems within 90 Mpc that have half-light , major-axis radii R _ { e } \lesssim 2 kpc , stellar masses 0.7 \times 10 ^ { 11 } < M _ { * } / M _ { \odot } < 1.4 \times 10 ^ { 11 } , and Sérsic indices typically around a value of n = 2 to 3 .
This abundance of compact , massive spheroids in our own backyard — with a number density of 6.9 \times 10 ^ { -6 } Mpc ^ { -3 } ( or 3.5 \times 10 ^ { -5 } Mpc ^ { -3 } per unit dex in stellar mass ) — and with the same physical properties as the high-redshift galaxies , had been over-looked because they are encased in stellar disks which usually result in galaxy sizes notably larger than 2 kpc .
Moreover , this number density is a lower limit because it has not come from a volume-limited sample .
The actual density may be closer to 10 ^ { -4 } , although further work is required to confirm this .
We therefore conclude that not all massive ‘ spheroids ’ have undergone dramatic structural and size evolution since z \sim 2 \pm 0.6 .
Given that the bulges of local early-type disk galaxies are known to consist of predominantly old stars which existed at z \sim 2 , it seems likely that some of the observed high redshift spheroids did not increase in size by building ( 3D ) triaxial envelopes as commonly advocated , and that the growth of ( 2D ) disks has also been important over the past 9–11 billion years .