English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Ultrafaint dwarf galaxies ($M_\star\lesssim10^{5-6}\,{\rm M}_\odot$) arerelics of an early phase of galaxy formation. They contain some of the oldestand most metal-poor stars in the Universe which likely formed before the epochof hydrogen reionisation. These galaxies are so faint that they can only bedetected as satellites of the Milky Way. They are so small that they are justbarely resolved in current cosmological hydrodynamics simulations. Here wecombine very high resolution cosmological $N$-body simulations with asemi-analytic model of galaxy formation to study the demographics and spatialdistribution of ultrafaint satellites in Milky Way-mass haloes. We show thatthe abundance of these galaxies is correlated with the assembly history of thehost halo: at fixed mass, haloes assembled earlier contain, on average, moreultrafaint satellites today than haloes assembled later. We identify simulatedgalactic haloes that experience an ancient Gaia-Enceladus-Sausage-like and arecent LMC-like accretion event and find that the former occurs in 33% of thesample and the latter in 9%. Only 3% experience both events and these areespecially rich in ultrafaint satellites, most acquired during the ancientaccretion event. Our models predict that the radial distribution of satellitesis more centrally concentrated in early-forming haloes. Accounting for thedepletion of satellites by tidal interactions with the central disc, we find avery good match to the observed radial distribution of satellites in the MilkyWay over the entire radial range. This agreement is mainly due to the abilityof our model to track 'orphan' galaxies after their subhaloes fall below theresolution limit of the simulation.

The little things matter: relating the abundance of ultrafaint satellites to the hosts' assembly history