Gravitational instability of Einstein-Gauss-Bonnet black holes under tensor mode perturbations

We analyze the tensor mode perturbations of static, spherically symmetric solutions of the Einstein equations with a quadratic Gauss-Bonnet term in dimension $D > 4$. We show that the evolution equations for this type of perturbations can be cast in a Regge-Wheeler-Zerilli form, and obtain the exact potential for the corresponding Schr\"odinger-like stability equation. As an immediate application we prove that for $D \neq 6$ and $\alpha >0$, the sign choice for the Gauss-Bonnet coefficient suggested by string theory, all positive mass black holes of this type are stable. In the exceptional case $D =6$, we find a range of parameters where positive mass asymptotically flat black holes, with regular horizon, are unstable. This feature is found also in general for $\alpha < 0$.Comment: 7 pages, 1 figure, minor corrections, references adde

Quantum Particles Constrained on Cylindrical Surfaces with Non-constant Diameter

We present a theoretical formulation of the one-electron problem constrained on the surface of a cylindrical tubule with varying diameter. Because of the cylindrical symmetry, we may reduce the problem to a one-dimensional equation for each angular momentum quantum number $m$ along the cylindrical axis. The geometrical properties of the surface determine the electronic structures through the geometry dependent term in the equation. Magnetic fields parallel to the axis can readily be incorporated. Our formulation is applied to simple examples such as the catenoid and the sinusoidal tubules. The existence of bound states as well as the band structures, which are induced geometrically, for these surfaces are shown. To show that the electronic structures can be altered significantly by applying a magnetic field, Aharonov-Bohm effects in these examples are demonstrated.Comment: 7 pages, 7 figures, submitted to J. Phys. Soc. Jp

A UV to Mid-IR Study of AGN Selection

We classify the spectral energy distributions (SEDs) of 431,038 sources in the 9 sq. deg Bootes field of the NOAO Deep Wide-Field Survey (NDWFS). There are up to 17 bands of data available per source, including ultraviolet (GALEX), optical (NDWFS), near-IR (NEWFIRM), and mid-infrared (IRAC/MIPS) data, as well as spectroscopic redshifts for ~20,000 objects, primarily from the AGN and Galaxy Evolution Survey (AGES). We fit galaxy, AGN, stellar, and brown dwarf templates to the observed SEDs, which yield spectral classes for the Galactic sources and photometric redshifts and galaxy/AGN luminosities for the extragalactic sources. The photometric redshift precision of the galaxy and AGN samples are sigma/(1+z)=0.040 and sigma/(1+z)=0.169, respectively, with the worst 5% outliers excluded. Based on the reduced chi-squared of the SED fit for each SED model, we are able to distinguish between Galactic and extragalactic sources for sources brighter than I=23.5. We compare the SED fits for a galaxy-only model and a galaxy+AGN model. Using known X-ray and spectroscopic AGN samples, we confirm that SED fitting can be successfully used as a method to identify large populations of AGN, including spatially resolved AGN with significant contributions from the host galaxy and objects with the emission line ratios of "composite" spectra. We also use our results to compare to the X-ray, mid-IR, optical color and emission line ratio selection techniques. For an F-ratio threshold of F>10 we find 16,266 AGN candidates brighter than I=23.5 and a surface density of ~1900 AGN per deg^2.Comment: Submitted to ApJ, 35 pages, 17 figures, 2 table

Presentation and Outcomes After Medical and Surgical Treatment Versus Medical Treatment Alone of Spontaneous Infectious Spondylodiscitis: A Systematic Literature Review and Meta-Analysis.

Study Design: Systematic literature review. Objectives: The aims of this study were to (1) describe the clinical features, disabilities, and incidence of neurologic deficits of pyogenic spondylodiscitis prior to treatment and (2) compare the functional outcomes between patients who underwent medical treatment alone or in combination with surgery for pyogenic spondylodiscitis. Methods: A systematic literature review was performed using PubMed according to PRISMA guidelines. No year restriction was put in place. Statistical analysis of pooled data, when documented in the original report (ie, number of patients with desired variable and number of patients evaluated), was conducted to determine the most common presenting symptoms, incidence of pre- and postoperative neurologic deficits, associated comorbidities, infectious pathogens, approach for surgery when performed, and duration of hospitalization. Outcomes data, including return to work status, resolution of back pain, and functional recovery were also pooled among all studies and surgery-specific studies alone. Meta-analysis of studies with subgroup analysis of pain-free outcome in surgical and medical patients was performed. Results: Fifty of 1286 studies were included, comprising 4173 patients undergoing either medical treatment alone or in combination with surgery. Back pain was the most common presenting symptom, reported in 91% of patients. Neurologic deficit was noted in 31% of patients. Conclusion: Medical management remains first-line treatment of infectious pyogenic spondylodiscitis. Surgery may be indicated for progressive pain, persistent infection on imaging, deformity or neurologic deficits. If surgery is required, reported literature shows potential for significant pain reduction, improved neurologic function and a high number of patients returning to a normal functional/work status

Detection of Extended Polarized Ultraviolet Radiation from the z = 1.82 Radio Galaxy 3C 256

We have detected spatially extended linear polarized UV emission from the high-redshift radio galaxy 3C~256 ($z=1.82$). A spatially integrated ($7.8''$ diameter aperture) measurement of the degree of polarization of the $V-$band (rest frame 0.19 $\mu$m) emission yields a value of 16.4\% ($\pm 2.2$\%) with a position angle of $42{}\rlap{\rm .}^\circ 4$ ($\pm 3{}\rlap{\rm .}^\circ 9$), orthogonal to the position angle on the sky of the major axis of the extended emission. The peak emission measured with a $3.6''$ diameter circular aperture is 11.7\% ($\pm 1.5$\%) polarized with a position angle of $42{}\rlap{\rm .}^\circ 4$ ($\pm 3{}\rlap{\rm .}^\circ 6$). An image of the polarized flux is presented, clearly displaying that the polarized flux is extended and present over the entire extent of the object. While it has been suggested that the UV continuum of 3C~256 might be due to star formation (Elston 1988) or a protogalaxy (Eisenhardt \& Dickinson 1993) based on its extremely blue spectral energy distribution and similar morphology at UV and visible wavelengths, we are unable to reconcile the observed high degree of polarization with such a model. While the detection of polarized emission from HZRGs has been shown to be a common phenomena, 3C~256 is only the third object for which a measurement of the extended polarized UV emission has been presented. These data lend additional support to the suggestion first made by di Serego Alighieri and collaborators that the ``alignment effect'', the tendency for the extended UV continuum radiation and line emission from HZRGs to be aligned with the major axis of the extended radio emission, is in large part due to scattering of anisotropic nuclear emission.Comment: 11 pages, LaTeX (aaspp style) file. Figure available by request to [email protected]

Chandra Observations of the QSO Pair Q2345+007: Binary Quasar or Massive Dark Lens?

The components of the wide (7.3") separation quasar pair Q2345+007A,B (z=2.15) have the most strikingly similar optical spectra seen to date (Steidel & Sargent 1991) yet no detected lensing mass, making this system the best candidate known for a massive (1e14 Msun) dark matter lens system. Here we present results from a 65ksec Chandra observation designed to investigate whether it is a binary quasar or a gravitational lens. We find no X-ray evidence for a lensing cluster to a (0.5-2keV) flux limit of 2e-15 cgs, which is consistent with lensing only for a reduced baryon fraction. Using the Chandra X-ray observations of the quasars themselves, together with new and published optical measurements, we use the observed emission properties of the quasars for further tests between the lens and binary hypotheses. Assuming similar line-of-sight absorption to the images, we find that their X-ray continuum slopes are inconsistent (Gamma_A=2.30 and Gamma_B=0.83) as are their X-ray to optical flux ratios. The probability that B suffers absorption sufficient to account for these spectral differences is negligible. We present new optical evidence that the flux ratio of the pair is variable, so the time-delay in a lens scenario could cause some of the discrepancies. However, adequately large variations in overall spectral energy distribution are rare in individual QSOs. All new evidence here weighs strongly toward the binary interpretation. Q2345+007 thus may represent the highest redshift example known of interaction-triggered but as-yet unmerged luminous AGN.Comment: 15 pages, Latex, emulateapj style, including 3 tables and 5 figures. Accepted Feb 1, 2002 for publication in ApJ Main Journal. See also http://hea-www.harvard.edu/~pgreen/Papers.htm

The Spitzer Space Telescope First-Look Survey: KPNO MOSAIC-1 R-band Images and Source Catalogs

(Abridged) We present R-band images covering more than 11 square degrees of sky obtained with the KPNO 4-m telescope in preparation for the Spitzer Space Telescope First Look Survey. The FLS was designed to characterize the mid-infrared sky at depths 2 orders of magnitude deeper than previous surveys. The extragalactic component is the first cosmological survey done with Spitzer. Two relatively large regions of the sky were observed: the main FLS extra galactic field (17h18m+59d30m) and ELAIS-N1 field (16h10m+54d30m). The overall quality of the images is high. The relative astrometric accuracy is better than 0.1'' and the typical seeing is 1.1''. Images are relatively deep since they reach a median 5-sigma depth limiting magnitude of R=25.5 (Vega). Catalogs have been extracted using SExtractor using thresholds in area and flux for which the number of false detections is below 1% at R=25. Only sources with S/N greater than 3 have been retained in the final catalogs. Comparing the galaxy number counts from our images with those of deeper R-band surveys, we estimate that our observations are 50% complete at R=24.5. These limits in depth are sufficient to identify a substantial fraction of the infrared sources which will be detected by Spitzer.Comment: 21 pages, 15 Postscript figures, uses aastex, AJ accepted. Images and catalogs at http://ssc.spitzer.caltech.edu/fls/extragal/noaor_data.htm

The Chandra XBootes Survey - III: Optical and Near-IR Counterparts

The XBootes Survey is a 5-ks Chandra survey of the Bootes Field of the NOAO Deep Wide-Field Survey (NDWFS). This survey is unique in that it is the largest (9.3 deg^2), contiguous region imaged in X-ray with complementary deep optical and near-IR observations. We present a catalog of the optical counterparts to the 3,213 X-ray point sources detected in the XBootes survey. Using a Bayesian identification scheme, we successfully identified optical counterparts for 98% of the X-ray point sources. The optical colors suggest that the optically detected galaxies are a combination of z<1 massive early-type galaxies and bluer star-forming galaxies whose optical AGN emission is faint or obscured, whereas the majority of the optically detected point sources are likely quasars over a large redshift range. Our large area, X-ray bright, optically deep survey enables us to select a large sub-sample of sources (773) with high X-ray to optical flux ratios (f_x/f_o>10). These objects are likely high redshift and/or dust obscured AGN. These sources have generally harder X-ray spectra than sources with 0.1<f_x/f_o<10. Of the 73 X-ray sources with no optical counterpart in the NDWFS catalog, 47 are truly optically blank down to R~25.5 (the average 50% completeness limit of the NDWFS R-band catalogs). These sources are also likely to be high redshift and/or dust obscured AGN.Comment: 19 pages, 13 figures, ApJ accepted. Catalog can be found at: http://www.noao.edu/noao/noaodeep or ftp://archive.noao.edu/pub/catalogs/xbootes

Mean flow and spiral defect chaos in Rayleigh-Benard convection

We describe a numerical procedure to construct a modified velocity field that does not have any mean flow. Using this procedure, we present two results. Firstly, we show that, in the absence of mean flow, spiral defect chaos collapses to a stationary pattern comprising textures of stripes with angular bends. The quenched patterns are characterized by mean wavenumbers that approach those uniquely selected by focus-type singularities, which, in the absence of mean flow, lie at the zig-zag instability boundary. The quenched patterns also have larger correlation lengths and are comprised of rolls with less curvature. Secondly, we describe how mean flow can contribute to the commonly observed phenomenon of rolls terminating perpendicularly into lateral walls. We show that, in the absence of mean flow, rolls begin to terminate into lateral walls at an oblique angle. This obliqueness increases with Rayleigh number.Comment: 14 pages, 19 figure