Beyond the Brim of the Hat: Kinematics of Globular Clusters out to Large Radius in the Sombrero Galaxy

We have obtained radial velocity measurements for 51 new globular clusters around the Sombrero galaxy. These measurements were obtained using spectroscopic observations from the AAOmega spectrograph on the Anglo-Australian Telescope and the Hydra spectrograph at WIYN. Combined with our own past measurements and velocity measurements obtained from the literature we have constructed a large database of radial velocities that contains a total of 360 confirmed globular clusters. Previous studies' analyses of the kinematics and mass profile of the Sombrero globular cluster system have been constrained to the inner ~9' (~24 kpc or ~5 effective radii), but our new measurements have increased the radial coverage of the data, allowing us to determine the kinematic properties of M104 out to ~15' (~41 kpc or ~9 effective radii). We use our set of radial velocities to study the GC system kinematics and to determine the mass profile and V-band mass-to-light profile of the galaxy. We find that the V-band mass-to-light ratio increases from 4.5 at the center to a value of 20.9 at 41 kpc (~9 effective radii or 15'), which implies that the dark matter halo extends to the edge of our available data set. We compare our mass profile at 20 kpc (~4 effective radii or ~7.4') to the mass computed from x-ray data and find good agreement. We also use our data to look for rotation in the globular cluster system as a whole, as well as in the red and blue subpopulations. We find no evidence for significant rotation in any of these samples.Comment: Accepted for publication in the Astronomical Journal; 23 pages, 14 figures, and 2 table

Alignments of the Dominant Galaxies in Poor Clusters

We have examined the orientations of brightest cluster galaxies (BCGs) in poor MKW and AWM clusters and find that, like their counterparts in richer Abell clusters, poor cluster BCGs exhibit a strong propensity to be aligned with the principal axes of their host clusters as well as the surrounding distribution of nearby (< 20/h Mpc) Abell clusters. The processes responsible for dominant galaxy alignments are therefore independent of cluster richness. We argue that these alignments most likely arise from anisotropic infall of material into clusters along large-scale filaments.Comment: 8 pages, 5 figure

Modelling of the Complex CASSOWARY/SLUGS Gravitational Lenses

We present the first high-resolution images of CSWA 31, a gravitational lens system observed as part of the SLUGS (Sloan Lenses Unravelled by Gemini Studies) program. These systems exhibit complex image structure with the potential to strongly constrain the mass distribution of the massive lens galaxies, as well as the complex morphology of the sources. In this paper, we describe the strategy used to reconstruct the unlensed source profile and the lens galaxy mass profiles. We introduce a prior distribution over multi-wavelength sources that is realistic as a representation of our knowledge about the surface brightness profiles of galaxies and groups of galaxies. To carry out the inference computationally, we use Diffusive Nested Sampling, an efficient variant of Nested Sampling that uses Markov Chain Monte Carlo (MCMC) to sample the complex posterior distributions and compute the normalising constant. We demonstrate the efficacy of this approach with the reconstruction of the group-group gravitational lens system CSWA 31, finding the source to be composed of five merging spiral galaxies magnified by a factor of 13.Comment: Accepted for publication in MNRA

Spectroscopy of Globular Clusters out to Large Radius in the Sombrero Galaxy

We present new velocities for 62 globular clusters in M104 (NGC 4594, the Sombrero Galaxy), 56 from 2dF on the AAT and 6 from Hydra on WIYN. Combined with previous data, we have a total sample of 108 M104 globular cluster velocities, extending to 20 arcmin radius (~60 kpc), along with BVR photometry for each of these. We use this wide-field dataset to study the globular cluster kinematics and dark matter content of M104 out to 10 arcmin radius (30 kpc). We find no rotation in the globular cluster system. The edge-on nature of M104 makes it unlikely that there is strong rotation which is face-on and hence unobserved; thus, the absence of rotation over our large radial range appears to be an intrinsic feature of the globular cluster system in M104. We discuss ways to explain this low rotation, including the possibility that angular momentum has been transferred to even larger radii through galaxy mergers. The cluster velocity dispersion is ~230 km/s within several arcmin of the galaxy center, and drops to ~150 km/s at ~10 arcmin radius. We derive the mass profile of M104 using our velocity dispersion profile, together with the Jeans equation under the assumptions of spherical symmetry and isotropy, and find excellent agreement with the mass inferred from the stellar and gas rotation curve within 3 arcmin radius. The M/L_V increases from ~4 near the galaxy center to ~17 at 7 arcmin radius (~20 kpc, or 4 R_e), thus giving strong support for the presence of a dark matter halo in M104. More globular cluster velocities at larger radii are needed to further study the low rotation in the globular cluster system, and to see if the dark matter halo in M104 extends beyond a radius of 30 kpc.Comment: 40 pages, 7 figures, accepted for publication in Ap