Central mass and luminosity of Milky Way satellites in the LCDM model

TL;DR

This paper uses simulations and semi-analytic models within the LCDM framework to explain the observed uniform mass scale of Milky Way satellites and their wide luminosity range, linking it to galaxy formation physics.

Contribution

It demonstrates that the common mass scale of satellites can be explained by the physics of galaxy formation in the LCDM model, considering accretion and photo-ionization effects.

Findings

The narrow mass range results from similar circular velocities at accretion (~20 km/s).

Wide luminosity range arises from different accretion times and baryonic suppression.

The common mass scale reflects a specific star formation threshold velocity.

Abstract

It has been pointed out that the Galactic satellites all have a common mass around 1e7 Msun within 300 pc (M03), while they span almost four order of magnitudes in luminosity (Mateo et al. 1993, Strigari et al. 2008). It is argued that this may reflect a specific scale for galaxy formation or a scale for dark matter clustering. Here we use numerical simulations coupled with a semi-analytic model for galaxy formation, to predict the central mass and luminosity of galactic satellites in the LCDM model. We show that this common mass scale can be explained within the Cold Dark Matter scenario when the physics of galaxy formation is taken into account. The narrow range of M03 comes from the narrow distribution of circular velocities at time of accretion (peaking around 20 km/s) for satellites able to form stars and the not tight correlation between halo concentration and circular velocity. The wide range of satellite luminosities is due to a combination of the mass at time of accretion and the broad distribution of accretion redshifts for a given mass. This causes the satellites baryonic content to be suppressed by photo-ionization to very different extents. Our results favor the argument that the common mass M03 reflects a specific scale (circular velocity ~ 20 km/s) for star formation.