In this second paper of the series we study, with new Keck/DEIMOS spectra, the stellar populations of seven spectroscopically confirmed ultra-diffuse galaxies (UDGs) in the Coma cluster. We find intermediate to old ages (∼ 7 Gyr), low metallicities ([Z/H]∼ -0.7 dex) and mostly super-solar abundance patterns ([Mg/Fe] ∼ 0.13 dex). These properties are similar to those of low-luminosity (dwarf) galaxies inhabiting the same area in the cluster and are mostly consistent with being the continuity of the stellar mass scaling relations of more massive galaxies. These UDGs' star formation histories imply a relatively recent infall into the Coma cluster, consistent with the theoretical predictions for a dwarf-like origin. However, considering the scatter in the resulting properties and including other UDGs in Coma, together with the results from the velocity phase-space study of the Paper I in this series, a mixed-bag of origins is needed to explain the nature of all UDGs. Our results thus reinforce a scenario in which many UDGs are field dwarfs that become quenched through their later infall onto cluster environments, whereas some UDGs could be be genuine primordial galaxies that failed to develop due to an early quenching phase. The unknown proportion of dwarf-like to primordial-like UDGs leaves the enigma of the nature of UDGs still open.

We present spatially-resolved stellar kinematics of the well-studied ultra diffuse galaxy (UDG) Dragonfly 44, as determined from 25.3 hrs of observations with the Keck Cosmic Web Imager. The luminosity-weighted dispersion within the half-light radius is σ 1/2 = 33 +3 −3 km s −1 , lower than what we had inferred before from a DEIMOS spectrum in the Hα region. There is no evidence for rotation, with V max / σ < 0.12 (90 % confidence) along the major axis, in possible conflict with models where UDGs are the high-spin tail of the normal dwarf galaxy distribution. The spatially-averaged line profile is more peaked than a Gaussian, with Gauss-Hermite coefficient h 4 = 0.13 ± 0.05. The mass-to-light ratio within the effective radius is (M dyn /L I )(< R e ) = 26 +7 −6 M /L , similar to other UDGs and higher by a factor of six than smaller galaxies of the same luminosity. 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 rising velocity dispersion profile, from σ = 26 +4 −4 km s −1 at R = 0.2 kpc to σ = 41 +8 −8 km s −1 at R = 5.1 kpc. The profile can only be fit with a cuspy NFW profile if the orbital distribution has strong tangential anisotropy, with β = −0.8 +0.4 −0.5 . An alternative explanation is that the dark matter profile has a core: a Di Cintio et al. (2014) density profile with a mass-dependent core provides a very good fit to the kinematics for a halo mass of log(M 200 /M ) = 11.2 +0.6 −0.6 and β = −0.1 +0.2 −0.3 , i.e. isotropic orbits. This model predicts a slight positive kurtosis, in qualitative agreement with the measured h 4 parameter. UDGs such as Dragonfly 44 are dark matter dominated even in their centers, and can constrain the properties of dark matter in a regime where baryons usually dominate the kinematics: small spatial scales in massive halos. In a companion paper (Wasserman et al. 2019) we provide constraints on the axion mass in the context of "fuzzy" dark matter models.

We use Keck/DEIMOS spectroscopy to confirm the cluster membership of 16 ultra-diffuse galaxies (UDGs) in the Coma cluster, bringing the total number of spectroscopically confirmed UDGs to 24. We also identify a new cluster background UDG. In this pilot study of Coma UDGs in velocity phase-space, we find evidence that most present-day Coma UDGs have a recent infall epoch while a few may be ancient infalls. These recent infall UDGs have higher absolute relative line-of-sight velocities, bluer optical colors, and are smaller in size, unlike the ancient infalls. The kinematics of the spectroscopically confirmed Coma UDG sample is similar to that of the cluster late-type galaxy population. Our velocity phase-space analysis suggests that present-day cluster UDGs have a predominantly accretion origin from the field, acquire velocities corresponding to the mass of the cluster at accretion as they are accelerated towards the cluster center, and become redder and bigger as they experience the various physical processes at work within the cluster.

We apply the Jeans Anisotropic MGE (JAM) dynamical modelling method to SAGES Legacy Unifying Globulars and GalaxieS (SLUGGS) survey data of earlytype galaxies in the stellar mass range 10 10 < M * /M < 10 11.6 that cover a large radial range of 0.1 − 4.0 effective radii. We combine SLUGGS and ATLAS 3D datasets to model the total-mass profiles of a sample of 21 fast-rotator galaxies, utilising a hyperparameter method to combine the two independent datasets. The total-mass density profile slope values derived for these galaxies are consistent with those measured in the inner regions of galaxies by other studies. Furthermore, the total-mass density slopes (γ tot ) appear to be universal over this broad stellar mass range, with an average value of γ tot = −2.12 ± 0.05 , i.e. slightly steeper than isothermal. We compare our results to model galaxies from the Magneticum and EAGLE cosmological hydrodynamic simulations, in order to probe the mechanisms that are responsible for varying total-mass density profile slopes. The simulated-galaxy slopes are shallower than the observed values by ∼ 0.1 − 0.3, indicating that the physical processes shaping the mass distributions of galaxies in cosmological simulations are still incomplete. For galaxies with M * > 10 10.7 M in the Magneticum simulations, we identify a significant anticorrelation between total-mass density profile slopes and the fraction of stellar mass formed ex situ (i.e. accreted), whereas this anticorrelation is weaker for lower stellar masses, implying that the measured total mass density slopes for low-mass galaxies are less likely to be determined by merger activity.

The discovery of the ultra-diffuse galaxy NGC 1052-DF2 and its peculiar population of star clusters has raised new questions about the connections between galaxies and dark matter halos at the extremes of galaxy formation. In light of debates over the measured velocity dispersion of its star clusters and the associated mass estimate, we constrain mass models of DF2 using its observed kinematics with a range of priors on the halo mass. Models in which the galaxy obeys a standard stellar-halo mass relation are in tension with the data and also require a large central density core. Better fits are obtained when the halo mass is left free, even after accounting for increased model complexity. The dynamical mass-to-light ratio for our model with a weak prior on the halo mass is 1.7 +0.7 −0.5 M /L ,V , consistent with the stellar population estimate for DF2. We use tidal analysis to find that the low-mass models are consistent with the undisturbed isophotes of DF2. Finally we compare with Local Group dwarf galaxies and demonstrate that DF2 is an outlier in both its spatial extent and its relative dark matter deficit.

We present Hubble Space Telescope/Advanced Camera for Surveys (ACS) imaging of 23 very low surface brightness (μ e,V ∼25-27.5) galaxies detected in the fields of four nearby galaxy groups. These objects were selected from deep optical imaging obtained with the Dragonfly Telephoto Array. Seven are newly identified, while most of the others had been seen previously in visual surveys of deep photographic plates and more recent surveys. Few have previously been studied in detail. From the ACS images, we measure distances to the galaxies using both the tip of the red giant branch method and the surface brightness fluctuations method. We demonstrate that the two methods are consistent with each other in the regime where both can be applied. The distances to 15 out of 20 galaxies with stable measurements are consistent with that of the targeted group within errors. This suggests that assuming group membership based solely on projected proximity is ∼75% successful in this regime. The galaxies are nearly round, with a median axis ratio of 0.85, and visually resemble dwarf spheroidal galaxies. The objects have a range of sizes, from R e =0.4 kpc to R e =1.8 kpc, with a median á ñ = R 1.0 kpc e . They range in luminosity from M V =−11.4 to M V =−15.6, with a median á ñ = -M 12.4 V . Galaxies with R e ∼1 kpc and M V ∼−12 are fairly rare in the Local Group, but we find many of them in this relatively small sample. Four of the objects fall in the class of ultra-diffuse galaxies, with R e >1.5 kpc and μ 0,V >24 mag arcsec −2 , including the recently identified dark matter deficient galaxy NGC 1052-DF2.

Given the absence of directly detected dark matter (DM) as weakly interacting massive particles, there is strong interest in the possibility that DM is an ultra-light scalar field, here denoted as "fuzzy" DM. Ultra-diffuse galaxies, with the sizes of giant galaxies and the luminosities of dwarf galaxies, have a wide range of DM halo masses, thus providing new opportunities for exploring the connections between galaxies and their DM halos. Following up on new integral field unit spectroscopic observations and dynamics modeling of the DM-dominated ultra-diffuse galaxy Dragonfly 44 in the outskirts of the Coma Cluster, we present models of fuzzy DM constrained by the stellar dynamics of this galaxy. We infer a scalar field mass of ∼ 3 × 10 −22 eV, consistent with other constraints from galaxy dynamics but in tension with constraints from Lyα forest power spectrum modeling. While we are unable to statistically distinguish between fuzzy DM and "normal" cold DM models, we find that the inferred properties of the fuzzy DM halo satisfy a number of predictions for halos in a fuzzy DM cosmology. In particular, we find good agreement with the predicted core size-halo mass relation and the predicted transition radius between the quantum pressure-dominated inner region and the outer halo region.

Context. Globular clusters (GCs) are emerging as powerful tracers of the chemical composition of extragalactic stellar populations. Aims. We present new abundance measurements for eleven GCs in the Local Group galaxies NGC 147, NGC 6822, and Messier 33. These are combined with previously published observations of four GCs in the Fornax and WLM galaxies. Methods. The abundances were determined from analysis of integrated-light spectra, obtained with the HIRES spectrograph on the Keck I telescope and with UVES on the VLT. We used our analysis technique that has been developed for this purpose and tested on Milky Way GCs. Results. We find that the clusters with [Fe/H] < −1.5 are all α-enhanced at about the same level as Milky Way GCs. Their Na abundances are also generally enhanced relative to Milky Way halo stars, suggesting that these extragalactic GCs resemble their Milky Way counterparts in containing significant fractions of Na-rich stars. For [Fe/H] > −1.5, the GCs in M33 are also α-enhanced, while the GCs that belong to dwarfs (NGC 6822 SC7 and Fornax 4) have closer to Solar-scaled α-element abundances. The abundance patterns in SC7 are remarkably similar to those in the Galactic GC Ruprecht 106, including significantly sub-solar [Na/Fe] and [Ni/Fe] ratios. In NGC 147, the GCs with [Fe/H] < −2.0 account for about 6% of the total luminosity of stars in the same metallicity range, a lower fraction than those previously found in the Fornax and WLM galaxies, but substantially higher than in the Milky Way halo. Conclusions. At low metallicities, the abundance patterns suggest that GCs in the Milky Way, dwarf galaxies, and M33 experienced similar enrichment histories and/or processes. At higher metallicities, the lower levels of α-enhancement in the GCs found in dwarf galaxies resemble the abundance patterns observed in field stars in nearby dwarfs. Constraining the presence of multiple populations in the GCs is complicated by the lack of information about detailed abundances in field stars of the corresponding metallicities. We suggest that correlations such as [Na/Fe] vs. [Ni/Fe] may prove useful for this purpose if an accuracy of ∼ 0.1 dex or better can be reached for the integrated-light measurements.