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

We present spatially-resolved stellar kinematics of the well-studied ultradiffuse galaxy (UDG) Dragonfly 44, as determined from 25.3 hrs of observationswith the Keck Cosmic Web Imager. The luminosity-weighted dispersion within thehalf-light radius is $\sigma_{1/2}=33^{+3}_{-3}$ km/s. There is no evidence forrotation, with $V/\sigma<0.12$ (90% confidence) along the major axis, inapparent conflict with models where UDGs are the high-spin tail of the normaldwarf galaxy distribution. The spatially-averaged line profile is more peakedthan a Gaussian, with Gauss-Hermite coefficient $h_4=0.13\pm 0.05$. Themass-to-light ratio within the effective radius is $M/L=26^{+7}_{-6}$, similarto other UDGs and higher by a factor of six than normal galaxies of the sameluminosity. This difference between UDGs and other galaxies is, however,sensitive to the aperture that is used, and is much reduced when the $M/L$ratios are measured within a fixed radius of 10 kpc. Dragonfly 44 has a risingvelocity dispersion profile, from $\sigma=26^{+4}_{-4}$ km/s at R=0.2 kpc to$\sigma=41^{+8}_{-8}$ km/s at R=5.1 kpc. The profile can only be fit with acuspy NFW profile if the orbital distribution has strong tangential anisotropy,with $\beta=-0.8^{+0.4}_{-0.5}$. An alternative explanation is that the darkmatter profile has a core: a Di Cintio et al. (2014) density profile with amass-dependent core provides a very good fit to the kinematics for a halo massof $\log (M_{200}/{\rm M}_{\odot})=11.2^{+0.6}_{-0.6}$ and$\beta=-0.1^{+0.2}_{-0.3}$, i.e., isotropic orbits. This model predicts aslight positive kurtosis, in qualitative agreement with the measured $h_4$parameter. UDGs such as Dragonfly 44 are dark matter dominated even in theircenters, and can constrain the properties of dark matter in a regime wherebaryons usually dominate the kinematics: small spatial scales in massive halos.

Spatially-resolved stellar kinematics of the ultra diffuse galaxy Dragonfly 44. I. Observations, kinematics, and cold dark matter halo fits