T. S. Jackson

An SDSS Survey For Resolved Milky Way Satellite Galaxies. I. Detection Limits

We present the detection limits of a new survey for resolved low surface brightness satellite galaxies to the Milky Way, based on the Sloan Digital Sky Survey (SDSS). Our survey exploits SDSSs major strengths (multicolor photometry, depth, large-scale, and uniformity) by combining filter smoothing with limits in both magnitude and color space to search for low surface brightness galaxies and stellar counterparts to the compact high-velocity clouds out to the Milky Ways virial radius (~350 kpc). Our calculated detection limits for a purely old stellar population vary with galaxy size and distance between μV,0 = 26.7 and 30.1 mag arcsec-2. These limits will allow us to detect systems whose surface brightnesses are 0.5–3.9 mag arcsec-2 fainter than Sextans, the lowest surface brightness Local Group member known. Our survey not only is sensitive to lower surface brightness stellar populations than possible with previous Local Group surveys, but will also allow us to make an unbiased and well-defined assessment of the completeness of the observed Local Group galaxy luminosity function, so that we may compare the results with the predictions of various structure formation scenarios.

Model characterization of gapless edge modes of topological insulators using intermediate Brillouin-zone functions.

We characterize gapless edge modes in translation invariant topological insulators. We show that the edge mode spectrum is a continuous deformation of the spectrum of a certain gluing function defining the occupied state bundle over the Brillouin zone (BZ). Topologically non-trivial gluing functions, corresponding to non-trivial bundles, then yield edge modes exhibiting spectral flow. We illustrate our results for the case of chiral edge states in two dimensional Chern insulators, as well as helical edges in quantum spin Hall states.

The Galactic distribution of asymptotic giant branch stars

We study the Galactic distribution of ∼10 000 candidate asymptotic giant branch (AGB) stars selected by IRAS colours and variability index. The distance to each star is estimated by assuming a narrow luminosity function and a model-derived bolometric correction. The characteristic AGB star luminosity, L AGB, is determined from the condition that the highest number density must coincide with the Galactic bulge. Assuming a bulge distance of 8 kpc, we determine L AGB ∼ 3500 L⊙, in close agreement with values obtained for nearby AGB stars using the Hipparcos data, and those obtained by other methods. We find that there are no statistically significant differences in the Galactic distribution of AGB stars with different IRAS colours, implying a universal density distribution. The direct determination of this distribution shows that it is separable in the radial, R, and vertical, z, directions. Perpendicular to the Galactic plane, the number density of AGB stars is well described by an exponential function with a vertical scaleheight of 300 pc. In the radial direction the number density of AGB stars is constant up to R ∼ 5 kpc, and then it decreases exponentially with a scalelength of ∼1.6 kpc. This fall-off extends to at least 12 kpc, where the sample becomes too small. The overall normalization implies that there are ∼200 000 AGB stars in the Galaxy. We estimate the [25]‐[12] colour distribution of AGB stars for an unbiased volume-limited sample. By using a model-dependent transformation between the colour and mass-loss rate, ˙ M, we constrain the time dependence of ˙ M. The results suggest that for 10 −6 < ˙ M < 10 −5 M⊙ yr −1 the mass-loss rate increases exponentially with time. We find only marginal evidence that

Theory of minimum spanning trees. II. Exact graphical methods and perturbation expansion at the percolation threshold.

Continuing the program begun by the authors in a previous paper, we develop an exact low-density expansion for the random minimum spanning tree (MST) on a finite graph and use it to develop a continuum perturbation expansion for the MST on critical percolation clusters in space dimension d . The perturbation expansion is proved to be renormalizable in d=6 dimensions. We consider the fractal dimension D(p) of paths on the latter MST; our previous results lead us to predict that D(p)=2 for d>d(c)=6 . Using a renormalization-group approach, we confirm the result for d>6 and calculate D(p) to first order in epsilon=6-d for d<6 using the connection with critical percolation, with the result D(p)=2-epsilon/7+O(epsilon(2)) .

Geometric stability of topological lattice phases.

The fractional quantum Hall (FQH) effect illustrates the range of novel phenomena which can arise in a topologically ordered state in the presence of strong interactions. The possibility of realizing FQH-like phases in models with strong lattice effects has attracted intense interest as a more experimentally accessible venue for FQH phenomena which calls for more theoretical attention. Here we investigate the physical relevance of previously derived geometric conditions which quantify deviations from the Landau level physics of the FQHE. We conduct extensive numerical many-body simulations on several lattice models, obtaining new theoretical results in the process, and find remarkable correlation between these conditions and the many-body gap. These results indicate which physical factors are most relevant for the stability of FQH-like phases, a paradigm we refer to as the geometric stability hypothesis, and provide easily implementable guidelines for obtaining robust FQH-like phases in numerical or real-world experiments.

A CATALOG OF BRIGHT FILAMENTARY STRUCTURES IN THE INTERSTELLAR MEDIUM

We present a listing of prominent filamentary structures in the interstellar cirrus, selected with an eye toward current and planned far-infrared and submillimeter polarimetry facilities. The filaments were identified on the 100 μm plates of the IRAS Sky Survey Atlas (ISSA), using a computer vision algorithm that is unbiased with respect to source intensity. Our catalog is two-tiered: the selection criteria in the Galactic plane are based on the sensitivity limits of airborne polarimeters such as the proposed HALE instrument for SOFIA, and away from the plane the limits are dictated by the sensitivities of balloon-borne cosmic microwave background experiments, such as BOOMERanG and MAXIMA. Infrared detector technology is currently at the point where detecting the polarization of the interstellar cirrus is feasible, and we hope this catalog will assist any experimenter undertaking this task.