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

Dwarf spheroidal galaxies are the smallest known stellar systems where underNewtonian interpretations, a significant amount of dark matter is required toexplain observed kinematics. In fact, they are in this sense the most heavilydark matter dominated objects known. That, plus the increasingly small sizes ofthe newly discovered ultra faint dwarfs, puts these systems in the regime wheredynamical friction on individual stars starts to become relevant. We calculatethe dynamical friction timescales for pressure supported isotropic sphericaldark matter dominated stellar systems, yielding $\tau_{DF} =0.93 (r_{h}/10pc)^{2} (\sigma/ kms^{-1}) Gyr$, { where $r_{h}$ is the half-light radius}. Fora stellar velocity dispersion value of $3 km/s$, as typical for the smallest ofthe recently detected ultra faint dwarf spheroidals, dynamical frictiontimescales becomes smaller than the $10 Gyr$ typical of the stellar ages forthese systems, for $r_{h}<19 pc$. Thus, this becomes a theoretical lower limitbelow which dark matter dominated stellar systems become unstable to dynamicalfriction. We present a comparison with structural parameters of the smallestultra faint dwarf spheroidals known, showing that these are already close tothe stability limit derived, any future detection of yet smaller such systemswould be inconsistent with a particle dark matter hypothesis.

Theoretical lower limits on sizes of ultra faint dwarf galaxies from dynamical friction