An isolated, compact early-type galaxy with a diffuse stellar component:
  merger origin?
  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.
