Extending the baseline: Spitzer Mid-Infrared Photometry of Globular Cluster Systems in the Centaurus A and Sombrero Galaxies

Spitzer IRAC mid-infrared photometry is presented for the globular cluster (GC) systems of the NGC 5128 ("Centaurus A") and NGC 4594 ("Sombrero") galaxies. Existing optical photometric and spectroscopic are combined with this new data in a comprehensive optical to mid-IR colour catalogue of 260 GCs. Empirical colour-metallicity relationships are derived for all optical to mid-IR colour combinations. These colours prove to be very effective quantities to test the photometric predictions of simple stellar population (SSP) models. In general, four SSP models show larger discrepancies between each other and the data at bluer wavelengths, especially at high metallicities. Such differences become very important when attempting to use colour-colour model predictions to constrain the ages of stellar populations. Furthermore, the age-substructure determined from colour-colour diagrams and 91 NGC 5128 GCs with spectroscopic ages from Beasley et al. (2008) are inconsistent, suggesting any apparent GC system age-substructure implied by a colour-colour analysis must be verified independently. Unlike blue wavebands, certain optical to mid-IR colours are insensitive to the flux from hot horizontal branch stars and thus provide an excellent metallicity proxy. The NGC 5128 GC system shows strong bimodality in the optical R-band to mid-IR colour distributions, hence proving it is bimodal in metallicity. In this new colour space, a colour-magnitude trend, a "blue tilt", is found in the NGC 5128 metal-poor GC data. The NGC 5128 young GCs do not contribute to this trend. [abridged]Comment: 16 pages, 12 colour figures. To be published in MNRAS. Catalogue available from the first author. Full resolution copy available here http://lee.spitler.googlepages.com/spitzer_spitler.pd

A Spatial Text Analysis of J. R. R. Tolkien\u27s Middle-Earth

Using a technique called “distant reading”, which aggregates and analyzes large amounts of data with computational models that can be used to understand literature and find insights or patterns that may otherwise be undetectable, this paper seeks to understand the system of J. R. R. Tolkien’s fictional world of Middle-earth through a statistical approach. In an attempt to provide an entirely different view on his work, this paper examines semantic aspects of Tolkien’s corpus and how they complement the narrative structure, with particular emphasis on the topographic landscape and the journeys of specific characters through the space of Middle-earth itself

Globular clusters as probes of galaxy formation

Observations and analysis of globular cluster systems associated with three galaxy types are presented. Spectroscopy of globular cluster (GC) candidates in the Sculptor spirals NGC 253 and NGC 55 has identified 15 GCs in these galaxies. This spectroscopic sample, combined with plate scans, indicates total GC populations consistent with that expected for their luminosity and morphological type. From these data, we define new GC samples for spectroscopy. Radial velocities of 87 GCs in the Virgo elliptical NGC 4472 have been obtained, yielding data for 144 GCs when combined with previous studies. We find the blue GCs have significantly higher velocity dispersion than the red GCs, with little rotation in either population. The GCs dispersion profile declines slowly, yielding mass profiles consistent with X-ray data. We find a steeply rising M/L ratio, indicative of a massive dark halo surrounding this galaxy. From line-strengths of the GCs, we derive ages and metallicities for the GCs using simple stellar population (SSP) models. We find that the GCs are old and coeval and the bimodality seen in then- colours reflects metallicity rather than age differences. The GCs exhibit solar abundance ratios and both subpopulations show evidence for radial metallicity gradients. We have obtained high S/N spectra for 64 star clusters in the Large Magellanic Cloud. We measure their Lick indices to test the age and metallicity calibration of SSP models by comparison with literature values. We find our metallicities are consistent, although the values from our integrated spectra are slightly higher. The agreement of the ages for the old GCs is good, but is somewhat poorer for the youngest clusters. We obtain an age-metallicity relation for the clusters consistent with the galaxy's field stars. We show first results of a project to investigate the age and metallicity distributions of globular cluster systems using semi-analytic models of galaxy formation

Asymmetric synthesis of 2-substituted oxetan-3-ones via metalated SAMP/RAMP hydrazones

2-Substituted oxetan-3-ones can be prepared in good yields and enantioselectivities (up to 84% ee) by the metalation of the SAMP/RAMP hydrazones of oxetan-3-one, followed by reaction with a range of electrophiles that include alkyl, allyl, and benzyl halides. Additionally, both chiral 2,2- and 2,4-disubstituted oxetan-3-ones can be made in high ee (86–90%) by repetition of this lithiation/alkylation sequence under appropriately controlled conditions. Hydrolysis of the resultant hydrazones with aqueous oxalic acid provides the 2-substituted oxetan-3-ones without detectable racemization

Galaxy Disruption in a Halo of Dark Matter

The relics of disrupted satellite galaxies around the Milky Way and Andromeda have been found, but direct evidence of a satellite galaxy in the early stages of being disrupted has remained elusive. We have discovered a dwarf satellite galaxy in the process of being torn apart by gravitational tidal forces as it merges with a larger galaxy's dark matter halo. Our results illustrate the morphological transformation of dwarf galaxies by tidal interaction and the continued build-up of galaxy halos.Comment: 7 pages, Latex, 4 figures, to appear in Science v301 p563

Evidence for the disky origin of luminous Virgo dwarf ellipticals from the kinematics of their globular cluster systems

We report evidence for dynamically significant rotation in the globular cluster systems of two luminous Virgo dwarf ellipticals, VCC1261 and VCC1528. Including previous results for VCC1087, the globular cluster systems of all three Virgo dwarf ellipticals studied in detail to date exhibit v_rot/sigma > 1. Taking the rotation seen in the globular clusters as maximal disk rotation, we find all three dEs lie on the r-band Tully-Fisher relation. We argue that these data support the hypothesis that luminous dEs are the remnants of transformed disk galaxies. We also obtained deep, longslit data for the stars in VCC1261 and VCC1528. Both these galaxies show rapid rotation in their inner regions, with spatial scales of ~0.5 kpc. These rotation velocities are similar to those seen in the GC systems. Since our longslit data for Virgo dEs extend out to 1-2 effective radii (typical of deep observations), whereas the globular clusters extend out to 4--7 effective radii, we conclude that non-detections of rotation in many luminous dEs may simply be due to a lack of radial coverage in the stellar data, and that globular clusters represent singularly sensitive probes of the dynamics of dEs. Based on these data, we suggest that gas disks are significant sites of globular cluster formation in the early universe.Comment: To appear in the AJ, corrected typographical errors in Table 1, added a referenc