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The dynamical friction timescale for globular clusters to sink to the center of a dwarf elliptical galaxy (dE) is significantly less than a Hubble time if the halos have isothermal profiles and the globular clusters formed with the same radial density profile as the underlying stellar population. We examine the summed radial distribution of the entire globular cluster systems and the bright globular cluster candidates in 65 Virgo and Fornax Cluster dEs for evidence of dynamical friction processes. We find that the bright dE nuclei could have been formed from the merger of orbitally decayed massive clusters, but the faint nuclei are several magnitudes fainter than expected. These faint nuclei are found primarily in MV > −14 dEs which have high globular cluster specific frequencies and extended globular cluster systems. In these galaxies, the formation of new star clusters, high central dark matter densities, extended dark matter halos, or tidal interactions may act to prevent dynamical friction from collapsing the entire globular cluster population into a bright nucleus.
We present preliminary results on the shape of the globular cluster luminosity function and the colors and inferred metallicities of the clusters in dwarf elliptical galaxies imaged with HST. The luminosity function (LF) of the GC candidates is consistent with a Gaussian-shaped LF similar to that in giant ellipticals. Also, with a mean color of (V - I) = 0.94, most of the GCs appear to be old and metal-poor ([Fe/H] = −1.4) like GCs in the Galaxy and in nearby giant ellipticals. This suggests that the bulk of the clusters were formed more than 10 Gyr ago.
We combine specific globular cluster frequencies (SN) with newly measured surface brightness profiles to identify dEs that may be stripped dIs. Luminous dEs generally have higher surface brightnesses and steep central light profiles. Conversely, fainter dEs have low surface brightnesses and flatter central light profiles. The most likely candidates for stripped dIs have low SN and low central surface brightnesses.
Of all blood cultures positive for coagulase-negative staphylococci collected in 1 year at an academic hospital, 100 were selected randomly for review and designated true positives or contaminated. For the 85 patients whose cultures were determined to be contaminated, chart abstractions revealed substantial unnecessary antibiotic administration, additional laboratory tests and procedures, and hospital readmissions.
The influence of the specimen temperature during MeV Kr irradiation on the extent of compositional disordering in GaAs-AlAs superlattices (SLs) has been determined. We have investigated whether radiation-enhanced diffusion (RED) could be employed to reduce the dose required to completely disorder a SL by ion implanation. Metalorganic chemical vapor deposition grown GaAs-AlAs SLs were implanted with 0.75 MeV Kr to a dose of 2×1016 cm−2 at various sample temperatures ranging from 133 K to 523 K. The extent of disordering induced by the irradiations was determined by Rutherford backscattering spectrometry and secondary ion mass spectrometry. For low temperature irradiations (133 K to 233 K), complete intermixing of the SL is observed. However, the extent of intermixing of the SL decreases with increasing specimen temperature between room temperature and 523 K. We propose two possible explanations to interpret these results: (i) that the amount of ion beam mixing decreases with increasing temperature; and (ii) that the RED coefficient is negative which suggests the existence of a miscibility gap in the GaAs-AlAs SL system.
We present a Gemini/GMOS program to measure spectroscopic metallicities and ages of globular clusters (GCs) and nuclei in dwarf elliptical galaxies in the Virgo and Fornax Clusters. Preliminary results indicate that the globular clusters are old and metal-poor, very similar to the GCs in the Milky Way halo. The nuclei tend to be more metal-rich than the globular clusters but more metal-poor and older, on average, than the stars in the bodies of the galaxies. The [α/Fe] ratio appears to be solar for the GCs, nuclei, and dEs, but the uncertainties do not exclude some globular clusters from being enhanced in alpha elements.
We present the 2D kinematics of the nuclear region of the double-nucleated low-luminosity elliptical galaxy IC 225. Observations with the GMOS-N IFU at Gemini Observatory show a large amount of metal-rich gas coincident with the off-center nucleus. However, preliminary kinematics analysis indicates that the velocity of the stars in the off-center nucleus is distinct from that of the gas at the same position. Therefore, this is an intriguing example of how the formation of a nucleus or bulge may be occurring in a low-luminosity elliptical galaxy.
Globular clusters (GCs) and nuclei in dEs are important probes for for studying cosmology and galaxy evolution. GCs and nuclei are usually formed in the high pressures of starbursts, therefore resolved stellar color-magnitude diagrams and integrated colors, magnitudes, or spectra yield ages and metallicities which are snapshots of the conditions during the most violent and important star forming episodes of the galaxies. Most are older, more metal-poor, and more enriched in $\alpha$-elements than the underlying dE field stars. About 25% have formed within the last $\sim$6~Gyr from enriched gas. Many nuclei have the properties of brights GCs but some can be distinguished by large sizes and composite stellar populations. The relatively large numbers of GCs in dEs shows that they are an important source of GCs to galaxies that accrete them.
Integral Field Spectroscopy provides a powerful new tool for disentangling the complex structure of Active Galactic Nuclei—allowing 2D mapping of the distribution, kinematics and excitation of ionized gas and of stellar velocity profiles and populations. Such comprehensive datasets are likely to reveal important clues about the physics of the narrow line region, interactions with the host galaxy and central dynamical forces. Here we present observations of the central regions of NGC1068, obtained using the visible-wavelength GMOS-IFU at Gemini North and NGC4151, taken with a prototype near-infrared fibre IFU at the UK Infrared Telescope.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html
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