Discovery of an isolated compact elliptical galaxy in the field

TL;DR

This paper reports the discovery of the first confirmed isolated compact elliptical galaxy in the field, challenging existing formation theories and providing new insights into galaxy evolution.

Contribution

It presents the identification and detailed analysis of an isolated cE galaxy, offering evidence for alternative formation pathways beyond stripping.

Findings

The galaxy is ~900 kpc from its nearest neighbor.

It has an effective radius of ~500 pc and high surface brightness.

Deep imaging shows no underlying disk, confirming its elliptical nature.

Abstract

We present the discovery of an isolated compact elliptical (cE) galaxy, found during a search of SDSS DR7 for cEs, and for which we obtained WHT/ACAM imaging. It is ~900 kpc distant from its nearest neighbour, has an effective r-band radius of ~500 pc and a B-band mean surface brightness within its effective radius of 19.75 mag/arcsec. Serendipitous deep SuprimeCam imaging shows that there is no underlying disk. Its isolated position suggests that there is an alternative channel to the stripping scenario for the formation of compact ellipticals. We also report analysis of recent deeper imaging of the previous candidate free-flying cE, which shows that it is, in fact, a normal dwarf elliptical (dE). Hence the new cE reported here is the first confirmed isolated compact elliptical to be found in the field.