Star Cluster Candidates in M81

We present a catalog of extended objects in the vicinity of M81 based a set of 24 Hubble Space Telescope Advanced Camera for Surveys (ACS) Wide Field Camera (WFC) F814W (I-band) images. We have found 233 good globular cluster candidates; 92 candidate HII regions, OB associations, or diffuse open clusters; 489 probable background galaxies; and 1719 unclassified objects. We have color data from ground-based g- and r-band MMT Megacam images for 79 galaxies, 125 globular cluster candidates, 7 HII regions, and 184 unclassified objects. The color-color diagram of globular cluster candidates shows that most fall into the range 0.25 < g-r < 1.25 and 0.5 < r-I < 1.25, similar to the color range of Milky Way globular clusters. Unclassified objects are often blue, suggesting that many of them are likely to be HII regions and open clusters, although a few galaxies and globular clusters may be among them.Comment: 35 pages, 11 figures, submitted to A

Edge States and Entanglement Entropy

It is known that gauge fields defined on manifolds with spatial boundaries support states localized at the boundaries. In this paper, we demonstrate how coarse-graining over these states can lead to an entanglement entropy. In particular, we show that the entanglement entropy of the ground state for the quantum Hall effect on a disk exhibits an approximate ``area " law.Comment: 16 pages, minor corrections and futher details adde

Edge States in Gauge Theories: Theory, Interpretations and Predictions

Gauge theories on manifolds with spatial boundaries are studied. It is shown that observables localized at the boundaries (edge observables) can occur in such models irrespective of the dimensionality of spacetime. The intimate connection of these observables to charge fractionation, vertex operators and topological field theories is described. The edge observables, however, may or may not exist as well-defined operators in a fully quantized theory depending on the boundary conditions imposed on the fields and their momenta. The latter are obtained by requiring the Hamiltonian of the theory to be self-adjoint and positive definite. We show that these boundary conditions can also have nice physical interpretations in terms of certain experimental parameters such as the penetration depth of the electromagnetic field in a surrounding superconducting medium. The dependence of the spectrum on one such parameter is explicitly exhibited for the Higgs model on a spatial disc in its London limit. It should be possible to test such dependences experimentally, the above Higgs model for example being a model for a superconductor. Boundary conditions for the 3+1 dimensional $BF$ system confined to a spatial ball are studied. Their physical meaning is clarified and their influence on the edge states of this system (known to exist under certain conditions) is discussed. It is pointed out that edge states occur for topological solitons of gauge theories such as the 't Hooft-Polyakov monopoles.Comment: 36 pages, LATEX File (revised because figures had problems

A Genuine Intermediate-Age Globular Cluster in M33

We present deep integrated-light spectroscopy of nine M33 globular clusters taken with the Hectospec instrument at the MMT Observatory. Based on our spectroscopy and previous deep color-magnitude diagrams obtained with HST/WFPC2, we present evidence for the presence of a genuine intermediate-age globular cluster in M33. The analysis of Lick line indices indicates that all globular clusters are metal-poor ([Z/H] <~ -1.0) and that cluster M33-C38 is about 5-8 Gyr younger than the rest of the sample M33 star clusters. We find no evidence for a population of blue horizontal branch stars in the CMD of M33-C38, which rules out the possibility of an artificially young spectroscopic age due to the presence of hot stars. We infer a total mass of 5-9 x 10^4 M_sol for M33-C38, which implies that M33-C38 has survived ~2-3 times longer than some dynamical evolution model predictions for star clusters in M33, although it is not yet clear to which dynamical component of M33 - thin disk, thick disk, halo - the cluster is associated.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letter

Towards a calibration of SSP models from the optical to the mid-infrared

Our knowledge about unresolved stellar systems comes from comparing integrated-light properties to SSP models. Therefore it is crucial to calibrate the latter as well as possible by integrated-light colors of clusters that have reliable ages and metallicities (deep CMDs and/or spectroscopy of individual giants). This is especially true for the NIR and MIR, which contain important population synthesis diagnostics and are often used to derive masses of stellar systems at hight redshifts. Here we present integrated colors of MC clusters using new VRI photometry and 2MASS data. In the imminent future we will include MIR data from Spitzer/IRAC. We compare our new colors with popular SSP models to illustrate their strengths and weaknesses.Comment: 2 pages, 1 figure, to appear in the proceedings of IAU Symposium No241 "Stellar Populations as building blocks of galaxies", A. Vazdekis & R. Peletier, ed