The PAndAS view of the Andromeda satellite system - I. A Bayesian search for dwarf galaxies using spatial and color-magnitude information

TL;DR

This paper introduces a Bayesian algorithm that effectively detects dwarf galaxies in photometric surveys by utilizing spatial and color-magnitude data, successfully recovering known objects and discovering new candidates in the Andromeda system.

Contribution

The paper presents a novel Bayesian method that combines spatial and color-magnitude information for dwarf galaxy detection, improving sensitivity and accuracy over previous techniques.

Findings

Successfully recovered all known dwarf galaxies in PAndAS

Discovered one new globular cluster candidate

Identified 143 significant detections, with some likely being faint dwarf galaxies

Abstract

We present a generic algorithm to search for dwarf galaxies in photometric catalogs and apply it to the Pan-Andromeda Archaeological Survey (PAndAS). The algorithm is developed in a Bayesian framework and, contrary to most dwarf-galaxy-search codes, makes use of both the spatial and color-magnitude information of sources in a probabilistic approach. Accounting for the significant contamination from the Milky Way foreground and from the structured stellar halo of the Andromeda galaxy, we recover all known dwarf galaxies in the PAndAS footprint with high significance, even for the least luminous ones. Some Andromeda globular clusters are also recovered and, in one case, discovered. We publish a list of the 143 most significant detections yielded by the algorithm. The combined properties of the 39 most significant isolated detections show hints that at least some of these trace genuine dwarf galaxies, too faint to be individually detected. Follow-up observations by the community are mandatory to establish which are real members of the Andromeda satellite system. The search technique presented here will be used in an upcoming contribution to determine the PAndAS completeness limits for dwarf galaxies. Although here tuned to the search of dwarf galaxies in the PAndAS data, the algorithm can easily be adapted to the search for any localised overdensity whose properties can be modeled reliably in the parameter space of any catalog.