\u3cem\u3eN\u3c/em\u3e-Body Simulations of Alternative Gravity Models

Theories in which gravity is weaker on cosmological scales have been proposed to explain the observed acceleration of the universe. The nonlinear regime in such theories is not well studied, though it is likely that observational tests of structure formation will lie in this regime. A class of alternative gravity theories may be approximated by modifying Poisson’s equation. We have run N-body simulations of a set of such models to study the nonlinear clustering of matter on 1–100 Mpc scales. We find that nonlinear gravity enhances the deviations of the power spectrum of these models from standard gravity. This occurs due to mode coupling, so that models with an excess or deficit of large-scale power (at k \u3c 0.2 Mpc-1) lead to deviations in the power spectrum at smaller scales as well (up to k ~ 1 Mpc-1), even though the linear spectra match very closely on the smaller scales. This makes it easier to distinguish such models from general relativity using the three-dimensional power spectrum probed by galaxy surveys and the weak lensing power spectrum. If the potential for light deflection is modified in the same way as the potential that affects the dark matter, then weak lensing constrains deviations from gravity even more strongly. Our simulations show that, even with a modified potential, gravitational evolution is approximately universal. Based on this, the Peacock-Dodds approach can be adapted to get an analytical fit for the nonlinear power spectra of alternative gravity models, though the recent Smith et al. formula is less successful. Our conclusions extend to models with modifications of gravity on scales of 1–20 Mpc. We also use a way of measuring projected power spectra from simulations that lowers the sample variance, so that fewer realizations are needed to reach a desired level of accuracy

N-Body Simulations of Alternate Gravity Models

Theories in which gravity is weaker on cosmological scales have been proposed to explain the observed acceleration of the universe. The nonlinear regime in such theories is not well studied, though it is likely that observational tests of structure formation will lie in this regime. A class of alternate gravity theories may be approximated by modifying Poisson's equation. We have run N-body simulations of a set of such models to study the nonlinear clustering of matter on 1-100 Mpc scales. We find that nonlinear gravity enhances the deviations of the power spectrum of these models from standard gravity. This occurs due to mode-coupling, so that models with an excess or deficit of large-scale power (at k < 0.2/Mpc) lead to deviations in the power spectrum at smaller scales as well (up to k ~ 1/Mpc), even though the linear spectra match very closely on the smaller scales. This makes it easier to distinguish such models from general relativity using the three-dimensional power spectrum probed by galaxy surveys and the weak lensing power spectrum. If the potential for light deflection is modified in the same way as the potential that affects the dark matter, then weak lensing constrains deviations from gravity even more strongly. Our simulations show that even with a modified potential, gravitational evolution is approximately universal. Based on this, the Peacock-Dodds approach can be adapted to get an analytical fit for the nonlinear power spectra of alternate gravity models, though the recent Smith et al formula is less successful. Our conclusions extend to models with modifications of gravity on scales of 1-20 Mpc. We also use a way of measuring projected power spectra from simulations that lowers the sample variance, so that fewer realizations are needed to reach a desired level of accuracy.Comment: 26 pages, 10 figures, matches published versio

Spherical Collapse and Cluster Counts in Modified Gravity Models

Modifications to the gravitational potential affect the nonlinear gravitational evolution of large scale structures in the Universe. To illustrate some generic features of such changes, we study the evolution of spherically symmetric perturbations when the modification is of Yukawa type; this is non-trivial, because we should not and do not assume that Birkhoff's theorem applies. We then show how to estimate the abundance of virialized objects in such models. Comparison with numerical simulations shows reasonable agreement: When normalized to have the same fluctuations at early times, weaker large scale gravity produces fewer massive halos. However, the opposite can be true for models that are normalized to have the same linear theory power spectrum today, so the abundance of rich clusters potentially places interesting constraints on such models. Our analysis also indicates that the formation histories and abundances of sufficiently low mass objects are unchanged from standard gravity. This explains why simulations have found that the nonlinear power-spectrum at large k is unaffected by such modifications to the gravitational potential. In addition, the most massive objects in CMB-normalized models with weaker gravity are expected to be similar to the high-redshift progenitors of the most massive objects in models with stronger gravity. Thus, the difference between the cluster and field galaxy populations is expected to be larger in models with stronger large-scale gravity.Comment: 9 pages, 8 figures Accepted by Phys. Rev.

Photometric Redshifts with Surface Brightness Priors

We use galaxy surface brightness as prior information to improve photometric redshift (photo-z) estimation. We apply our template-based photo-z method to imaging data from the ground-based VVDS survey and the space-based GOODS field from HST, and use spectroscopic redshifts to test our photometric redshifts for different galaxy types and redshifts. We find that the surface brightness prior eliminates a large fraction of outliers by lifting the degeneracy between the Lyman and 4000 Angstrom breaks. Bias and scatter are improved by about a factor of 2 with the prior for both the ground and space data. Ongoing and planned surveys from the ground and space will benefit, provided that care is taken in measurements of galaxy sizes and in the application of the prior. We discuss the image quality and signal-to-noise requirements that enable the surface brightness prior to be successfully applied.Comment: 15 pages, 13 figures, matches published versio

BLAST Observations of the South Ecliptic Pole field: Number Counts and Source Catalogs

We present results from a survey carried out by the Balloon-borne Large Aperture Submillimeter Telescope (BLAST) on a 9 deg^2 field near the South Ecliptic Pole at 250, 350 and 500 {\mu}m. The median 1{\sigma} depths of the maps are 36.0, 26.4 and 18.4 mJy, respectively. We apply a statistical method to estimate submillimeter galaxy number counts and find that they are in agreement with other measurements made with the same instrument and with the more recent results from Herschel/SPIRE. Thanks to the large field observed, the new measurements give additional constraints on the bright end of the counts. We identify 132, 89 and 61 sources with S/N>4 at 250, 350, 500 {\mu}m, respectively and provide a multi-wavelength combined catalog of 232 sources with a significance >4{\sigma} in at least one BLAST band. The new BLAST maps and catalogs are available publicly at http://blastexperiment.info.Comment: 25 pages, 6 figures, 4 tables, Accepted by ApJS. Maps and catalogs available at http://blastexperiment.info

Spitzer MIPS 24 and 70 micron Imaging near the South Ecliptic Pole: Maps and Source Catalogs

We have imaged an 11.5 sq. deg. region of sky towards the South Ecliptic Pole (RA = 04h43m, Dec = -53d40m, J2000) at 24 and 70 microns with MIPS, the Multiband Imaging Photometer for Spitzer. This region is coincident with a field mapped at longer wavelengths by AKARI and the Balloon-borne Large Aperture Submillimeter Telescope. We discuss our data reduction and source extraction procedures. The median depths of the maps are 47 microJy/beam at 24 micron and 4.3 mJy/beam at 70 micron. At 24 micron, we identify 93098 point sources with signal-to-noise ratio (SNR) >5, and an additional 63 resolved galaxies; at 70 micron, we identify 891 point sources with SNR >6. From simulations, we determine a false detection rate of 1.8% (1.1%) for the 24 micron (70 micron) catalog. The 24 and 70 micron point-source catalogs are 80% complete at 230 microJy and 11 mJy, respectively. These mosaic images and source catalogs will be available to the public through the NASA/IPAC Infrared Science Archive.Comment: 30 pages, 9 figures, 4 tables. Submitted to ApJS. Maps and catalogs can be downloaded from http://blastexperiment.info/release/SEP_MIPS/sep-mips.php, and will be soon be available through IRS

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

N-body simulations, weak lensing, and photo-z\u27s: Numerical projects in cosmology

General Relativity is an extremely well-tested theory over 15 orders of magnitude, on laboratory to solar system scales. However, recent measurements, including evidence from Type Ia supernovae, show that the expansion of the universe is accelerating. This means that GR, cannot unproblematically be extrapolated to fit the properties of our universe on horizon scales. With recourse to either a strange form of energy density ( dark energy ), or a modification of GR, the acceleration can be explained; distinguishing which is the correct model requires detailed observations of large-scale structure formation. In this thesis, I address three issues that are important to these observations: generating predictions by N-body simulation of alternate gravity models, efficiently obtaining accurate redshifts for galaxies using photometric redshifts with surface brightness priors, and finally modeling PSF effects for a proposed weak lensing survey

N-body simulations, weak lensing, and photo-z\u27s: Numerical projects in cosmology

General Relativity is an extremely well-tested theory over 15 orders of magnitude, on laboratory to solar system scales. However, recent measurements, including evidence from Type Ia supernovae, show that the expansion of the universe is accelerating. This means that GR, cannot unproblematically be extrapolated to fit the properties of our universe on horizon scales. With recourse to either a strange form of energy density ( dark energy ), or a modification of GR, the acceleration can be explained; distinguishing which is the correct model requires detailed observations of large-scale structure formation. In this thesis, I address three issues that are important to these observations: generating predictions by N-body simulation of alternate gravity models, efficiently obtaining accurate redshifts for galaxies using photometric redshifts with surface brightness priors, and finally modeling PSF effects for a proposed weak lensing survey

A Focus on the Right Atrium

We report a case of a 70-year-old woman who presented for a cavotricuspid isthmus atrial flutter ablation that was aborted prematurely. On subsequent imaging, she was discovered to have a right atrial diverticulum, which was present on prior imaging but not reported, likely due to unfamiliarity with the entity. (Level of Difficulty: Intermediate.