Andromeda XXXV: The Faintest Dwarf Satellite of the Andromeda Galaxy

TL;DR

Andromeda XXXV is the faintest satellite galaxy of Andromeda discovered, exhibiting properties similar to other dwarf galaxies but with unique age-metallicity characteristics compared to Milky Way satellites.

Contribution

This paper reports the discovery and detailed characterization of Andromeda XXXV, the faintest known Andromeda satellite, highlighting its structural and stellar population properties.

Findings

Andromeda XXXV is the least luminous Andromeda satellite discovered.

Its stellar population shows a spread in age and metallicity, unlike similar Milky Way satellites.

Properties align with known dwarf galaxies in the Local Group.

Abstract

We present the discovery of Andromeda XXXV, the faintest Andromeda satellite galaxy discovered to date, identified as an overdensity of stars in the Pan-Andromeda Archaeological Survey and confirmed via Hubble Space Telescope imaging. Located at a heliocentric distance of $927^{+76}_{-63}$ kpc and $158^{+57}_{-45}$ kpc from Andromeda, Andromeda XXXV is an extended ($r_h = 53\,^{+13}_{-11}$ pc), elliptical ($\epsilon = 0.4\, \pm 0.2$), metal-poor ($[\text{Fe}/\text{H}]\sim-1.9$) system, and the least luminous ($M_V=-5.2 \pm 0.3$) of Andromeda's dwarf satellites discovered so far. Andromeda XXXV's properties are consistent with the known population of dwarf galaxies around the Local Group, bearing close structural resemblance to the Canes Venatici II and Hydra II Milky Way (MW) dwarf satellite galaxies. Its stellar population, characterized by a red horizontal branch or a red clump feature, mirrors that of other Andromeda satellite galaxies in showing evidence for a spread in age and metallicity, with no signs of younger stellar generations. This age-metallicity spread is not observed in MW satellites of comparable stellar mass, and highlights the persistent differences between the satellite systems of Andromeda and the MW, extending even into the ultrafaint regime.