We present a sample of 115 very low optical surface brightness, highly extended, H i-rich galaxies carefully selected from the ALFALFA survey that have similar optical absolute magnitudes, surface brightnesses, and radii to recently discovered "ultra-diffuse" galaxies (UDGs). However, these systems are bluer and have more irregular morphologies than other UDGs, are isolated, and contain significant reservoirs of H i. We find that while these sources have normal star formation rates for H i selected galaxies of similar stellar mass, they have very low star formation efficiencies. We further present deep optical and H i synthesis follow up imaging of three of these H i-bearing ultra-diffuse sources. We measure H i diameters extending to ∼40 kpc, but note that while all three sources have large H i diameters for their stellar mass, they are consistent with the H i mass -H i radius relation. We further analyze the H i velocity widths and rotation velocities for the unresolved and resolved sources respectively, and find that the sources appear to inhabit halos of dwarf galaxies. We estimate spin parameters, and suggest that these sources may exist in high spin parameter halos, and as such may be potential H i-rich progenitors to the ultra-diffuse galaxies observed in cluster environments.

We present a spectro-photometric survey of 2522 extragalactic globular clusters (GCs) around twelve early-type galaxies, nine of which have not been published previously. Combining space-based and multi-colour wide field ground-based imaging, with spectra from the Keck DEIMOS instrument, we obtain an average of 160 GC radial velocities per galaxy, with a high velocity precision of ∼ 15 km s −1 per GC. After studying the photometric properties of the GC systems, such as their spatial and colour distributions, we focus on the kinematics of metal-poor (blue) and metal-rich (red) GC subpopulations to an average distance of ∼ 8 effective radii from the galaxy centre.Our results show that for some systems the bimodality in GC colour is also present in GC kinematics. The kinematics of the red GC subpopulations are strongly coupled with the host galaxy stellar kinematics. The blue GC subpopulations are more dominated by random motions, especially in the outer regions, and decoupled from the red GCs. Peculiar GC kinematic profiles are seen in some galaxies: the blue GCs in NGC 821 rotate along the galaxy minor axis, whereas the GC system of the lenticular galaxy NGC 7457 appears to be strongly rotation supported in the outer region.We supplement our galaxy sample with data from the literature and carry out a number of tests to study the kinematic differences between the two GC subpopulations. We confirm that the GC kinematics are coupled with the host galaxy properties and find that the velocity kurtosis and the slope of their velocity dispersion profiles is different between the two GC subpopulations in more massive galaxies.

Globular star clusters contain thousands to millions of old stars packed within a region only tens of light years across. Their high stellar densities make it very probable that their member stars will interact or collide. There has accordingly been considerable debate about whether black holes should exist in these star clusters. Some theoretical work suggests that dynamical processes in the densest inner regions of globular clusters may lead to the formation of black holes of approximately 1,000 solar masses. Other numerical simulations instead predict that stellar interactions will eject most or all of the black holes that form in globular clusters. Here we report the X-ray signature of an accreting black hole in a globular cluster associated with the giant elliptical galaxy NGC 4472 (in the Virgo cluster). This object has an X-ray luminosity of about 4 x 10(39) erg s(-1), which rules out any object other than a black hole in such an old stellar population. The X-ray luminosity varies by a factor of seven in a few hours, which excludes the possibility that the object is several neutron stars superposed.

We have investigated the global properties of the globular cluster (GC) systems of three early-type galaxies: the Virgo cluster elliptical NGC 4406, the field elliptical NGC 3379, and the field S0 galaxy NGC 4594. These galaxies were observed as part of a wide-field CCD survey of the GC populations of a large sample of normal galaxies beyond the Local Group. Images obtained with the Mosaic detector on the Kitt Peak 4-m telescope provide radial coverage to at least 24 ′ , or ∼70−100 kpc. We use BV R photometry and image classification to select GC candidates and thereby reduce contamination from non-GCs, and HST WFPC2 data to help quantify the contamination that remains. The GC systems of all three galaxies have color distributions with at least two peaks and show modest negative color gradients. The proportions of blue GCs range from 60−70% of the total populations. The GC specific frequency (S N ) of NGC 4406 is 3.5±0.5, ∼20% lower than past estimates and nearly identical to S N for the other Virgo cluster elliptical included in our survey, NGC 4472. S N for NGC 3379 and NGC 4594 are 1.2±0.3 and 2.1±0.3, respectively; these are similar to past values but the errors have been reduced by a factor of 2−3. We compare our results for the early-type sample (including NGC 4472) to models for the formation of massive galaxies and their GC systems. Of the scenarios we consider, a hierarchical merging picture -in which metal-poor GCs form at high redshift in protogalactic building blocks and metal-rich GC populations are built up over time during subsequent gas-rich mergers -appears most consistent with the data.the GC systems, such as overall mean colors, total numbers, and specific frequencies, making these values subject to considerable uncertainties. Well-constrained global values are what is needed to test the model predictions as well as to improve our overall understanding of GC systems and their relationship to galaxy formation. Accordingly, we have observed the GC systems of a large sample of both early-type and spiral galaxies. The survey employs wide-field CCD imaging to observe the full extent of the galaxy GC systems, good resolution to help eliminate background galaxies from the GC candidate lists, and three-color photometry to isolate bona fide GCs from contaminating stars and galaxies. In addition, archival Hubble Space Telescope (HST) images are available for most of the targets; these data are used to help quantify the level of contamination in the GC lists.