MNRAS 000, 16 (2023)
Preprint 13th December 2022
Compiled using MNRAS ITpX style file v3.0
The undiscovered ultra-diffuse galaxies of the Local Group
1 Univ. Lyon, Univ. Claude Bernard Lyon I, CNRS, IP2I Lyon/IN2P3, IMR 5822, F-69622, Villeurbanne, France 2 Center for Theoretical Physics, Polish Academy of Sciences, al. Lotnikow 32/46 Warsaw, Poland 3Universidad de La Laguna. Avda. Astrofisico Fco. Sanchez. La Laguna, Tenerife, Spain 4Instituto de Astrofisica de Canarias, Calle Via Lactea s/n, E-38206 La Lag una, Tenerife, Spain 5Leibniz-Institut fir Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany, Racah Institute of Physics, Hebrew University, Jerusalem, 91904 Israel 'Departamento de Fisica Teorica, Modulo 15, Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Madrid, Spain 8Centro de Investigacion Avanzada en Fisica Fundamental (CIAFF), Facultad de Ciencias, Universidad Autonoma de Madrid, 28049 Madrid, Spain 9 International Centre for Radio Astror omy Research, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia 10Univ. Lille, CNRS, Centrale Lille, UMR 9189 CRIStAL, F-59000 Lille, France 11Universite Paris-Saclay, CNRS, Institut d'Astrophysique Spatiale, 91405, Orsay, France 12Tartu Observatory, University of Tartu, Observatooriumi 1, 61602 Toravere, Estonia 13Estonian Academy of Sciences, 10130 Kohtu 6, Tallinn, Estonia
Accepted XXXX . Received XXXX; in original form XXXX
ABSTRACT Ultra-diffuse galaxies (UDGs) are attractive candidates to probe cosmological models and test theories of galaxy formation at
UDGs have been found to date, most of which are satellites of the Milky Way and M31, and only two are isolated galaxies. It is unclear whether so few UDGs are expected. We address this by studying the population of UDGs formed in hydrodynamic constrained simulations of the LG from the HESTIA suite. For a LG with mass ML(<2.5 Mpc) = 8 1012 Mo, we predict that there are 12 3 UDGs (68 per cent confidence) with stellar masses 106 M* / Mo < 109, and effective radii Re 1.5 kpc, in the field of the LG, of which 2_2 (68 per cent confidence) are detectable in the footprint of the Sloan Digital Sky Survey (SDSS). Accounting for survey incompleteness, we find that up to 82, 90, and 100 per cent of all UDGs in the LG field would be
and Time, respectively. Our results suggest that there is a population of UDGs in the LG awaiting discovery. Key words: galaxies: formation -- Local Group -- galaxies: dwarf -- galaxies: luminosity function - galaxies: interactions
1 INTRODUCTION
e = 24 and 28 mag arcsec-2, earning them the sobriquet 'Ultra- Diffuse Galaxies' (UDGs). Hierarchical models of galaxy formation predict the emergence of The circumstances leading to the emergence of such diffuse galax- a large population of low-mass galaxies. Typically, they are dom- inated by sizable dark matter components that make them useful ies are not understood fully and several scenarios have been proposed to explain their formation. These are divided broadly into two main as discerning probes of cosmological models. The most valuable galaxies for this purpose are those that contain little baryonic ma- categories: (i) internal processes that drive s