The feeble giant. Discovery of a large and diffuse Milky Way dwarf galaxy in the constellation of Crater

TL;DR

The paper reports the discovery of Crater 2, a large, diffuse, low-surface-brightness dwarf galaxy in the Milky Way, providing new insights into its size, luminosity, and possible group accretion history.

Contribution

This is the first identification of Crater 2, a large and faint dwarf galaxy, expanding knowledge of the Milky Way's satellite population and their spatial arrangements.

Findings

Crater 2 is the fourth largest Milky Way dwarf galaxy.

Crater 2 has a very low surface brightness, comparable to ultra-faint dwarfs.

Crater 2 may be part of an accreted group with other satellites.

Abstract

We announce the discovery of the Crater 2 dwarf galaxy, identified in imaging data of the VST ATLAS survey. Given its half-light radius of ~1100 pc, Crater 2 is the fourth largest dwarf in the Milky Way, surpassed only by the LMC, SMC and the Sgr dwarf. With a total luminosity of $M_V\approx-8$, this satellite galaxy is also one of the lowest surface brightness dwarfs. Falling under the nominal detection boundary of 30 mag arcsec$^{-2}$, it compares in nebulosity to the recently discovered Tuc 2 and Tuc IV and UMa II. Crater 2 is located ~120 kpc from the Sun and appears to be aligned in 3-D with the enigmatic globular cluster Crater, the pair of ultra-faint dwarfs Leo IV and Leo V and the classical dwarf Leo II. We argue that such arrangement is probably not accidental and, in fact, can be viewed as the evidence for the accretion of the Crater-Leo group.