The Next Generation Virgo Cluster Survey (NGVS). XXXV. First Kinematical Clues of Overly Massive Dark Matter Halos in Several Ultradiffuse Galaxies in the Virgo Cluster

Abstract

We present Keck/DEIMOS spectroscopy of the first complete sample of ultradiffuse galaxies (UDGs) in the Virgo cluster. We select all UDGs in Virgo that contain at least 10 globular cluster (GC) candidates and are more than 2.5σ outliers in scaling relations of size, surface brightness, and luminosity (a total of 10 UDGs). We use the radial velocity of their GC satellites to measure the velocity dispersion of each UDG. We find a mixed bag of galaxies, from one UDG that shows no signs of dark matter, to UDGs that follow the luminosity–dispersion relation of early-type galaxies, to the most extreme examples of heavily dark matter–dominated galaxies that break well-known scaling relations such as the luminosity–dispersion or U-shaped total mass-to-light ratio relations. This is indicative of a number of mechanisms at play forming these peculiar galaxies. Some of them may be the most extended version of dwarf galaxies, while others are so extreme that they seem to populate dark matter halos consistent with that of the Milky Way or even larger. Even though Milky Way stars and other GC interlopers contaminating our sample of GCs cannot be fully ruled out, our assessment of this potential problem and simulations indicate that the probability is low and, if present, unlikely to be enough to explain the extreme dispersions measured. Further confirmation from stellar kinematics studies in these UDGs would be desirable. The lack of such extreme objects in any of the state-of-the-art simulations opens an exciting avenue of new physics shaping these galaxies.

Confirmation of an Anomalously Low Dark Matter Content for the Galaxy NGC 1052-DF4 from Deep, High-resolution Continuum Spectroscopy

“…The only previous velocity dispersion measurement of DF4 came from seven GCs (van Dokkum et al 2019a). Analyzing such a small number of dynamical tracers with regular MCMC could lead to a biased dispersion (Laporte et al 2019), and recent papers have proposed modifying MCMC priors for an unbiased estimate (Doppel et al 2021;Toloba et al 2023). For the velocity dispersion of DF4, van Dokkum et al (2019a) used approximate Bayesian computation, which does not rely on explicit likelihood or prior functions and does not suffer from the small sample bias.…”

The Disturbed and Globular-cluster-rich Ultradiffuse Galaxy UGC 9050-Dw1

“…Additionally, GC abundance has been found to be strongly correlated with the total system mass-particularly DM halo mass (e.g., Harris et al 2013;Prole et al 2019;Zaritsky 2022) -which is also true for the UDG regime (Harris et al 2017), allowing for DM halo mass constraints of UDGs to be photometrically obtained. Spectroscopic studies of GCs in UDGs can determine velocity gradients to constrain the evolutionary histories of UDGs further via signals of tidal disruption (Beasley & Trujillo 2016;Toloba et al 2018Toloba et al , 2023. Consequently GC abundance has often been used as a means for discriminating between potential formation scenarios when comparing subpopulations of UDGs that otherwise are quite similar in luminosity and stellar mass.…”