Discovery of an Ultra-Faint Dwarf Galaxy in the Intracluster Field of the Virgo Center : A fossil of the First Galaxies?

TL;DR

A newly discovered ultra-faint dwarf galaxy in the Virgo cluster's intracluster field exhibits properties similar to primordial galaxies, potentially serving as a fossil remnant of the first galaxies, expanding understanding beyond the Local Group.

Contribution

First detection of an ultra-faint dwarf galaxy in the Virgo cluster's intracluster space, suggesting it may be a relic of the earliest galaxies.

Findings

Located at 16.4 Mpc distance, confirming Virgo membership.

Properties similar to Local Group ultra-faint dwarfs.

Likely a fossil remnant of the first galaxies.

Abstract

Ultra-faint dwarf galaxies (UFDs) are newcomers among galaxies, and are the faintest galaxies in the observed universe. To date, they have only been found around the Milky Way Galaxy and M31 in the Local Group. We present the discovery of an UFD in the intracluster field in the core of the Virgo cluster (Virgo UFD1), which is far from any massive galaxies. The color-magnitude diagram of the resolved stars in this galaxy shows a narrow red giant branch, similar to those of metal-poor globular clusters in the Milky Way. We estimate its distance by comparing the red giant branch with isochrones, and we obtain a value 16.4 +/- 0.4 Mpc. This shows that it is indeed a member of the Virgo cluster. From the color of the red giants we estimate its mean metallicity to be very low, [Fe/H]= -2.4 +/- 0.4. Its absolute V-band magnitude and effective radius are derived to be M_V = -6.5 +/- 0.2 and r_eff = 81 +/- 7 pc, much fainter and smaller than the classical dwarf spheroidal galaxies. Its central surface brightness is estimated to be as low as u_V,0 = 26.37 +/- 0.05 mag arcsec^-2. Its properties are similar to those of the Local Group analogs. No evidence of tidal features are found in this galaxy. Considering its narrow red giant branch with no asymptotic giant branch stars, low metallicity, and location, it may be a fossil remnant of the first galaxies.