Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session R15: Cosmological Parameters and Halo Structure |
Hide Abstracts |
Sponsoring Units: DAP Chair: Annika Peter, Ohio State University Room: B230-231 |
Monday, April 16, 2018 10:45AM - 10:57AM |
R15.00001: The Viability of Phantom Dark Energy as a Quantum Field in 1st-Order FLRW Space Kevin Ludwick In the standard cosmological framework of the 0th-order FLRW metric and the use of perfect fluids in the stress-energy tensor, dark energy with an equation-of-state parameter $w < -1$ (known as phantom dark energy) implies negative kinetic energy and vacuum instability when modeled as a scalar field. However, the accepted values for present-day $w$ from Planck and WMAP9 include a significant range of values less than $-1$. We consider a more accurate description of the universe through the 1st-order perturbing of the isotropic and homogeneous FLRW metric and the components of the stress-energy tensor and investigate whether a field with an apparent $w<-1$ may still have positive kinetic energy. Treating dark energy as a classical scalar field in this metric, we find that it is not as obvious as one might think that phantom dark energy has negative kinetic energy categorically. Analogously, we find that field models of quintessence dark energy ($w>-1$) do not necessarily have positive kinetic energy categorically. We then investigate the same question treating dark energy as a quantum field in 1st-order FLRW space-time and examining the expectation value of the stress-energy tensor for $w<-1$ using adiabatic expansion. [Preview Abstract] |
Monday, April 16, 2018 10:57AM - 11:09AM |
R15.00002: The dynamics of cosmological models using \texttt{CosmoEJS} Jacob Moldenhauer, Andrew Chang From results we obtain on comparing dark energy and modified gravity cosmological models to some of the latest observational data sets, we present dynamical plots of the model's evolutionary history simulated with \texttt{CosmoEJS}. The \texttt{CosmoEJS} packages allow for interactive simultaneous plotting and comparing of different cosmological models to actual observational data sets. We use the dynamical plots to investigate why some cosmological models do not fit well to low or high redshift data points, depending on the precision. We use various combinations of data sets including supernovae type Ia, baryon acoustic oscillations, strong lensing, cosmic chronometers, redshift space distortions, and the Hubble Constant. While some modified gravity models are excluded by these data sets, others including dark energy models are competitive to the popular flat-$\Lambda$CDM model, especially when attempting to relieve certain tensions. [Preview Abstract] |
Monday, April 16, 2018 11:09AM - 11:21AM |
R15.00003: Sample variance in the local measurements of the Hubble constant Hao-Yi Wu, Dragan Huterer The current $>3\sigma$ tension of the Hubble constant $H_0$ is one of the most highly debated issues in cosmology. While local distance ladder indicates $H_0^{\rm loc}\approx$ 73 $\rm km\ s^{-1}Mpc^{-1}$, cosmic microwave background points to $H_0^{\rm CMB}\approx$ 67 $\rm km\ s^{-1}Mpc^{-1}$. We explore to which extent this tension can be alleviated by the sample variance in the local measurements. Using large-volume cosmological simulations and taking into account the inhomogeneous selection of type Ia supernovae, we find $\sigma(H_0^{\rm loc})$ = 0.31 $\rm km\ s^{-1}Mpc^{-1}$, which is too small to account for the current tension of 6 $\rm km\ s^{-1}Mpc^{-1}$. To explain the current tension would require an underdense region of 150 Mpc with $\delta\approx-0.8$, which is highly unlikely in a $\Lambda$CDM universe and also violates existing observational constraints. [Preview Abstract] |
Monday, April 16, 2018 11:21AM - 11:33AM |
R15.00004: Simulating Cosmic Reionization and its Observable Consequences with Fully-Coupled Radiation-Hydrodynamics Paul Shapiro I will summarize recent progress in modelling the EOR by large- scale simulations of cosmic structure formation, radiative transfer and their interplay. I will describe the first fully-coupled radiation-hydro simulations of reionization and galaxy formation in the Local Universe, in a volume large enough to model global reionization and with enough resolving power to follow the formation and evolution of all the atomic-cooling galactic halos in that volume. A box 91 cMpc on a side was simulated from a constrained realization of primordial fluctuations, chosen to reproduce present-day features of the Local Group, including the Milky Way and M31, and the local universe beyond, including the Fornax and Virgo clusters. These simulations are called CoDa, for "Cosmic Dawn". CoDa I and II, by hybrid CPU-GPU code RAMSES-CUDATON, used 4096-cubed N-body particles for dark matter and 4096-cubed cells for gas and ionizing radiation. CoDa I-AMR, by hybrid CPU-GPU code EMMA, used 2048-cubed particles and 2048-cubed initial cells which refined. All simulations were on the Titan supercomputer at Oak Ridge. [Preview Abstract] |
Monday, April 16, 2018 11:33AM - 11:45AM |
R15.00005: Plasma Constraints on the Cosmological Abundance of Magnetic Monopoles and the Origin of Cosmic Magnetic Fields Mikhail V. Medvedev, Abraham Loeb Existing theoretical and observational constraints on the abundance of magnetic monopoles are limited. Here we demonstrate that an ensemble of monopoles forms a plasma whose properties are well determined and whose collective effects place new tight constraints on the cosmological abundance of monopoles. In particular, the existence of micro-Gauss magnetic fields in galaxy clusters and radio relics implies that the scales of these structures are below the Debye screening length, thus setting an upper limit on the cosmological density parameter of monopoles, $\Omega_M\le 3\times10^{-4}$, which precludes them from being the dark matter. Future detection of Gpc-scale coherent magnetic fields could improve this limit by a few orders of magnitude. In addition, we predict the existence of magnetic Langmuir waves and turbulence which may appear on the sky as ``zebra patterns'' of an alternating magnetic field with ${\bf k\cdot B}\not=0$. We also show that magnetic monopole Langmuir turbulence excited near the accretion shock of galaxy clusters may be an efficient mechanism for generating the observed intracluster magnetic fields. [Preview Abstract] |
Monday, April 16, 2018 11:45AM - 11:57AM |
R15.00006: The ellipticity of galaxy cluster halos from satellite galaxies and weak lensing Tae-hyeon Shin, Joseph Clampitt, Bhuvnesh Jain, Gary Bernstein, Andrew Neil, Eduardo Rozo, Eli Rykoff We study the ellipticity of galaxy cluster halos as characterized by the distribution of cluster galaxies and as measured with weak lensing. We use monte-carlo simulations of elliptical cluster density profiles to estimate and correct for Poisson noise bias, edge bias and projection effects. We apply our methodology to 10,428 SDSS clusters identified by the redMaPPer algorithm with richness above 20. We find a mean axis ratio $= 0.573 \pm 0.002$ (stat) $\pm 0.039$ (sys). We compare this ellipticity of the satellites to the halo shape, through a stacked lensing measurement using optimal estimators of the lensing quadrupole. We find a best-fit axis ratio of $0.56 \pm 0.09$ (stat) $\pm 0.03$ (sys), consistent with the ellipticity of the satellite distribution. Thus cluster galaxies trace the shape of the dark matter halo to within our estimated uncertainties. Finally, we restack the ellipticity measurements along the major axis of the cluster central galaxy's light distribution. From the lensing measurements we infer a misalignment angle with an RMS of ${30^\circ \pm 10}^\circ$ when stacking on the central galaxy. We discuss applications of halo shape measurements to test the effects of the baryonic gas and AGN feedback, as well as dark matter and gravity. [Preview Abstract] |
Monday, April 16, 2018 11:57AM - 12:09PM |
R15.00007: Ultra-diffuse galaxy evolution in simulations Louis Penafiel, Laura Sales We present the study of the evolution of ultra-diffuse galaxy (UDG) properties in the Illustris cosmological simulation. UDGs have stellar masses and appearances similar to dwarf galaxies, but have sizes comparable to Milky Way galaxies, making them have extremely low surface brightnesses. We explore a scenario where the evolution can be attributed to tidal disruption, where most of their mass was stripped as they infall to a central galaxy cluster. We study the evolution of their masses, half-mass radii, and surface brightnesses. We make predictions on the infall times and present day distribution and kinematics that can be compared to future observations. [Preview Abstract] |
Monday, April 16, 2018 12:09PM - 12:21PM |
R15.00008: Stellar Streams Discovered in the Dark Energy Survey Nora Shipp, Alex Drlica-Wagner We perform a search for stellar streams around the Milky Way using the first three years of multi-band optical imaging data from the Dark Energy Survey (DES). We use DES data covering $\sim 5000$ sq. deg. to a depth of $g > 23.5$ with a relative photometric calibration uncertainty of $< 1 \%$. This data set yields unprecedented sensitivity to the stellar density field in the southern celestial hemisphere, enabling the detection of faint stellar streams to a heliocentric distance of $\sim 50$ kpc. We search for stellar streams using a matched-filter in color-magnitude space derived from a synthetic isochrone of an old, metal-poor stellar population. We report the discovery of eleven new stellar streams. In general, these streams are fainter, more distant, and lower surface brightness than streams detected by similar techniques in previous photometric surveys. As a by-product of our stellar stream search, we find evidence for extra-tidal stellar structure associated with four globular clusters: NGC 288, NGC 1261, NGC 1851, and NGC 1904. The ever-growing sample of stellar streams will provide insight into the formation of the Galactic stellar halo, the Milky Way gravitational potential, as well as the large- and small-scale distribution of dark matter around the Milky Way. [Preview Abstract] |
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