The relation between the size and luminosity for both bright and faint early-type galaxies has been repeatedly discussed as a crucial proxy for understanding evolutionary scenarios , as galaxies grow and lose their stellar mass in different physical processes .
The class of compact early-type galaxies ( cEs ) are , however , distinct outliers from this relation and mainly found around massive galaxies in the centres of groups and clusters .
The recent discovery of a cE in isolation provided a new opportunity to understand their formation scenario in a different environment .
Here , we report the discovery of an isolated cE , CGCG 036-042 , using imagery from the Sloan Digital Sky Survey ( SDSS ) .
The CGCG 036-042 has an r -band absolute magnitude ( M _ { r } ) of - 18.21 mag and a half-light radius ( R _ { e } ) of 559 pc .
Interestingly , it possesses a faint outer stellar component , which extends up to 10 kpc from its centre and has a nearly constant r -band surface brightness of \sim 26 mag/arcsec ^ { 2 } .
ESO-VLT long-slit spectroscopic data reveal that the simple stellar population ( SSP ) properties are fairly similar to those of previously identified cEs , with an intermediate-age of 7.15 \pm 1.17 Gyr , a metallicity of –0.18 \pm 0.07 dex and a supersolar alpha-element abundance of 0.2 \pm 0.05 dex .
The SSP metallicity also shows a significant decline outward from the center , by 0.5 dex over one half light radius .
We discuss the possible origin of this galaxy and suggest that it might have originated from a merger of even smaller objects – a well established scenario for the formation of massive early-type galaxies .