The Faint Stellar Object SDSS J1257+3419 is a Dark Matter Dominated System

TL;DR

This paper argues that SDSS J1257+3419 is a dark matter dominated dwarf spheroidal galaxy, based on derived mass-size relations and high mass-to-light ratio consistent with known dSphs.

Contribution

The study introduces a method to estimate the mass of faint stellar objects assuming they are dark matter dominated, supporting SDSS J1257+3419 as a dwarf spheroidal galaxy.

Findings

Mass of SDSS J1257+3419 is approximately 7 million solar masses.

Mass-to-light ratio of SDSS J1257+3419 is about 1000.

Supports classification of SDSS J1257+3419 as a dark matter dominated dSph.

Abstract

A recent study has revealed SDSS J1257+3419 is either a faint and small dwarf galaxy or a faint and widely extended globular cluster. In this Letter, the author suggests this stellar system is a dwarf spheroidal (dSph). Adopting an observational relation between binding energy and mass of old stellar systems, we derive a relation between mass and size of dSphs by assuming that they are dark matter dominated and virialized objects. Letting half-light radius represent size of SDSS J1257+3419, we find that its mass is $\sim 7\times 10^6$ solar mass. This indicates mass-to-light ratio ($M/L$) of SDSS J1257+3419 is about 1000 in the solar unit. This large $M/L$ is expected from a Mateo plot of dSphs. Thus, we insist SDSS J1257+3419 is a dSph.