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We study the Local Group (LG) dwarf galaxy population predicted by the apostle $Lambda$CDM cosmological hydrodynamics simulations. These indicate that: (i)~the total mass within $3$ Mpc of the Milky Way-Andromeda midpoint ($M_{rm 3Mpc}$) typically exceeds $sim 3$ times the sum of the virial masses ($M_{rm 200crit}$) of the two primaries and (ii)~the dwarf galaxy formation efficiency per unit mass is uniform throughout the volume. This suggests that the satellite population within the virial radii of the Milky Way and Andromeda should make up fewer than one third of all LG dwarfs within $3$ Mpc. This is consistent with the fraction of observed LG galaxies with stellar mass $M_*>10^7,M_{odot}$ that are satellites ($12$ out of $42$; i.e., $28$ per cent). For the apostle galaxy mass-halo mass relation, the total number of such galaxies further suggests a LG mass of $M_{rm 3 Mpc}sim 10^{13} , M_{odot}$. At lower galaxy masses, however, the observed satellite fraction is substantially higher ($42$ per cent for $M_*>10^5,M_{odot}$). If this is due to incompleteness in the field sample, then $sim 50$ dwarf galaxies at least as massive as the Draco dwarf spheroidal must be missing from the current LG {it field} dwarf inventory. The incompleteness interpretation is supported by the pronounced flattening of the LG luminosity function below $M_*sim 10^7, M_{odot}$, and by the scarcity of low-surface brightness LG field galaxies compared to satellites. The simulations indicate that most missing dwarfs should lie near the virial boundaries of the two LG primaries, and predict a trove of nearby dwarfs that await discovery by upcoming wide-field imaging surveys.
Recent observational and theoretical studies of the Local Group (LG) dwarf galaxies have highlighted their unique star formation history, stellar metallicity, gas content, and kinematics. We investigate the commonality of these tantalizing features b
The gas content of the complete compilation of Local Group dwarf galaxies (119 within 2 Mpc) is presented using HI survey data. Within the virial radius of the Milky Way (224 kpc here), 53 of 55 dwarf galaxies are devoid of gas to limits of M$_{rm HI
XMM-Newton and Chandra have ushered in a new era for the study of dwarf galaxies in the Local Group. We provide an overview of the opportunities, challenges, and some early results. The large number of background sources relative to galaxy sources is
The shallow faint-end slope of the galaxy mass function is usually reproduced in $Lambda$CDM galaxy formation models by assuming that the fraction of baryons that turns into stars drops steeply with decreasing halo mass and essentially vanishes in ha
Motivated by the stellar fossil record of Local Group (LG) dwarf galaxies, we show that the star-forming ancestors of the faintest ultra-faint dwarf galaxies (UFDs; ${rm M}_{rm V}$ $sim -2$ or ${rm M}_{star}$ $sim 10^{2}$ at $z=0$) had ultra-violet (