Faint fuzzies are metal-rich apparently-old star clusters with unusually large radii (7−15 pc), found mostly in S0 galaxies, whose source remain obscure. To identify their origins, we compare planetary nebulae and neutral hydrogen with faint fuzzy positions and line-of-sight velocities in NGC 1023. In this way, we rule out scenarios in which these objects are associated with an on-going merger or with a spheroid population in NGC 1023. Their kinematics are indistinguishable from the stellar disk population in this galaxy, and we conclude that faint fuzzies are most likely just remnant open clusters. Their observed association with S0s then simply reflects the difficulty of identifying such objects in later-type disk galaxies.

Various laboratory‐based experiments are underway attempting to detect dark matter directly. The event rates and detailed signals expected in these experiments depend on the dark matter phase‐space distribution on submilliparsec scales. These scales are many orders of magnitude smaller than those that can be resolved by conventional N‐body simulations, so one cannot hope to use such tools to investigate the effect of mergers in the history of the Milky Way on the detailed phase‐space structure probed by the current experiments. In this paper, we present an alternative approach to investigate the results of such mergers, by studying a simplified model for a merger of a subhalo with a larger parent halo. With an appropriate choice of parent halo potential, the evolution of material from the subhalo can be expressed analytically in action‐angle variables, so it is possible to obtain its entire orbit history very rapidly without numerical integration. Furthermore by evolving backwards in time, we can obtain arbitrarily high spatial resolution for the current velocity distribution at a fixed point. Although this model cannot provide a detailed quantitative comparison with the Milky Way, its properties are sufficiently generic that it offers qualitative insight into the expected structure arising from a merger at a resolution that cannot be approached with full numerical simulations. Preliminary results indicate that the velocity‐space distribution of dark matter particles remains characterized by discrete and well‐defined peaks over an extended period of time, both for single and multimerging systems, in contrast to the simple smooth velocity distributions sometimes assumed in predicting laboratory experiment detection rates. In principle, this structure contains a wealth of information about the formation history of the Milky Way's dark halo.

Direct detection of dark matter on the Earth depends crucially on its density and its velocity distribution on a milliparsec scale. Conventional N‐body simulations are unable to access this scale, making the development of other approaches necessary. In this paper, we apply the method developed by Fantin, Merrifield and Green in 2008 to a cosmologically based merger tree, transforming it into a useful instrument to reproduce and analyse the merger history of a Milky Way‐like system. The aim of the model is to investigate the implications of any ultrafine structure for the current and next generation of directional dark matter detectors. We find that the velocity distribution of a Milky Way‐like galaxy is almost smooth, due to the overlap of many streams of particles generated by multiple mergers. Only the merger of a 1010 M⊙ subhalo can generate significant features in the ultralocal velocity distribution, detectable at the resolution attainable by current experiments.

Various laboratory-based experiments are underway attempting to detect dark matter directly. The event rates and detailed signals expected in these experiments depend on the dark matter phase space distribution on sub-milliparsec scales. These scales are many orders of magnitude smaller than those that can be resolved by conventional N-body simulations, so one cannot hope to use such tools to investigate the effect of mergers in the history of the Milky Way on the detailed phase-space structure probed by the current experiments. In this paper we present an alternative approach to investigating the results of such mergers, by studying a simplified model for a merger of a sub-halo with a larger parent halo. With an appropriate choice of parent halo potential, the evolution of material from the sub-halo can be expressed analytically in action-angle variables, so it is possible to obtain its entire orbit history very rapidly without numerical integration. Furthermore by evolving backwards in time, we can obtain arbitrarily-high spatial resolution for the current velocity distribution at a fixed point. Although this model cannot provide a detailed quantitative comparison with the Milky Way, its properties are sufficiently generic that it offers qualitative insight into the expected structure arising from a merger at a resolution that cannot be approached with full numerical simulations. Preliminary results indicate that the velocity-space distribution of dark matter particles remains characterized by discrete and well-defined peaks over an extended period of time, both for single and multi-merging systems, in contrast to the simple smooth velocity distributions sometimes assumed in predicting laboratory experiment detection rates. In principle, this structure contains a wealth of information about the formation history of the Milky Way's dark halo.

During the past 20 years, numerous stellar streams have been discovered in both the Milky Way and the Local Group. These streams have been tidally torn from orbiting systems, which suggests that most should roughly trace the orbit of their progenitors around the Galaxy. As a consequence, they play a fundamental role in understanding the formation and evolution of our Galaxy. This project is based on the possibility of applying a technique developed by Binney to various tidal streams and overdensities in the Galaxy. The aim is to develop an efficient method to constrain the Galactic gravitational potential, to determine its mass distribution, and to test distance measurements. Here we apply the technique to the Grillmair & Dionatos GD-1 cold stellar stream. In the unrealistic case of noise-free data, the results show that the technique provides excellent discrimination against incorrect potentials and that it is possible to predict the heliocentric distance very accurately. This changes dramatically when errors are taken into account, which wash out most of the results. Nevertheless, it is still possible to rule out spherical potentials and set constraints on the distance of a given stream.