Bulletin of the American Physical Society
APS April Meeting 2017
Volume 62, Number 1
Saturday–Tuesday, January 28–31, 2017; Washington, DC
Session M5: Simulating Dark Matter and Galaxies |
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Sponsoring Units: DAP Chair: Priya Natarajan, Yale University Room: Virginia B |
Sunday, January 29, 2017 3:30PM - 3:42PM |
M5.00001: An Improved Signal Model for Axion Dark Matter Searches Erik Lentz To date, most direct detection searches for axion dark matter, such as those by the Axion Dark Matter eXperiment (ADMX) microwave cavity search, have assumed a signal shape based on an isothermal spherical model of the Milky Way halo. Such a model is not capable of capturing contributions from realistic infall, nor from a baryonic disk. Modern N-Body simulations of structure formation can produce realistic Milky Way-like halos which include the influences of baryons, infall, and environmental influences. This talk presents an analysis of the Romulus25 N-Body simulation in the context of direct dark matter axion searches. An improved signal shape and an account of the relevant halo dynamics are given. [Preview Abstract] |
Sunday, January 29, 2017 3:42PM - 3:54PM |
M5.00002: Concentrations of Simulated Dark Matter Halos Hillary Child We present the concentration-mass (c-M) relation of dark matter halos in two new high-volume high-resolution cosmological N-body simulations, Q Continuum and Outer Rim. Concentration describes the density of the central regions of halos; it is highest for low-mass halos at low redshift, decreasing at high mass and redshift. The shape of the c-M relation is an important probe of cosmology. We discuss the redshift dependence of the c-M relation, several different methods to determine concentrations of simulated halos, and potential sources of bias in concentration measurements. To connect to lensing observations, we stack halos, which also allows us to assess the suitability of the Navarro-Frenk-White profile and other profiles, such as Einasto, with an additional shape parameter. [Preview Abstract] |
Sunday, January 29, 2017 3:54PM - 4:06PM |
M5.00003: Topology and geometry of the dark matter web Nesar Ramachandra, Sergei Shandarin Topological connections in the single-streaming voids and multi-streaming filaments and walls reveal a cosmic web structure different from traditional mass density fields. A single void structure not only percolates the multi-stream field in all the directions, but also occupies over 99 per cent of all the single-streaming regions. Sub-grid analyses on scales smaller than simulation resolution reveal tiny pockets of voids that are isolated by membranes of the structure. For the multi-streaming excursion sets, the percolating structure is much thinner than the filaments in over-density excursion approach. We also introduce, for the first time, a framework to detect dark matter haloes in multi-stream fields. Closed compact regions hosting local maxima of the multi-stream field are detected using local geometrical conditions and properties of the Lagrangian sub-manifold. All the halo particles are guaranteed to be completely outside void regions of the Universe. Majority of the halo candidates are embedded in the largest structure that percolates the entire volume. [Preview Abstract] |
Sunday, January 29, 2017 4:06PM - 4:18PM |
M5.00004: Halo Core Tracking for Galaxy Placement in Cosmological Simulations Danila Korytov Synthetic galaxy catalogs are an important product of cosmological simulations. Upcoming surveys, such as LSST, require high volume and high resolution simulations for generating large object catalogs. These catalogs have many uses including testing and improving analysis pipelines, predictions for different cosmologies and investigations of systematic errors. Dark matter (DM) only simulations are able to reach the required volume and resolution but need an accurate prescription for galaxy placement within DM halos. We present a method for galaxy placement. For halos above a characteristic mass, central DM simulation particles are taken as tracer particles for a galaxy. These halo "cores" are tracked through the simulation and may merge with other "cores" or be ripped apart by halo tidal forces. We examine how accurately we can reproduce galaxy cluster profiles, two point correlation functions and other galaxy statistics. [Preview Abstract] |
Sunday, January 29, 2017 4:18PM - 4:30PM |
M5.00005: Dark-Matter-only simulations of the 2cDM model with $\sigma(v)$ as a solution to the CDM small-scale problems Keita Todoroki, Mikhail V. Medvedev The standard CDM model is believed to have problems on small -- galactic and sub-galactic -- scales, namely the substructure problem (SSP), too-big-to-fail (TBTF) problem and core-cusp problem (CCP). Recently, we've shown that a two-component (e.g., flavor-mixed) dark matter (2cDM) model can resolve all these problems altogether via particle elastic collisions ({\it a l\'a} SIDM) and particle mass conversions. 2cDM does not have the early-universe problem faced by some alternative multicomponent models, yet it resolves the SSP and TBTF that SIDM cannot do. In the new suite of simulations reported here, we explored the velocity dependence of cross-sections of scattering and conversion, $\sigma(v)=\sigma_0 v^a$, where $\sigma_0$ and $a$ are constants. We found that (i) 2cDM predictions are robust; (ii) many specific 2cDM models are consistent with available observed velocity functions in a wide range of $\sigma_0$, i.e., between 1-0.1 cm$^2$/g, and even down to 0.01 cm$^2$/g for some; (iii) core sizes in dwarfs and clusters further constrain viable models. These models are to be explored in simulations with baryons, star formation and baryonic feedback. [Preview Abstract] |
Sunday, January 29, 2017 4:30PM - 4:42PM |
M5.00006: The Dynamical Response of Dark Matter to Galaxy Evolution Affects Direct-Detection Experiments Michael Petersen, Neal Katz, Martin Weinberg Over a handful of rotation periods, dynamical processes in barred galaxies induce non-axisymmetric structure in dark matter halos. Using n-body simulations of a Milky Way-like barred galaxy, we identify both a trapped dark-matter component, a shadow bar, and a strong response wake in the dark-matter distribution that affects the predicted dark-matter detection rates for current and future experiments. We find that the magnitude of the combined stellar and shadow bar evolution makes a 30\% increase in disk-plane density. This is significantly larger that of previously claimed deviations from the standard halo model. The dark-matter density and kinematic wakes driven by the Milky Way bar increase the detectability of dark matter overall, especially for the experiments with higher minimum velocities. These astrophysical features increase the detection rate by more than a factor of two when compared to the standard halo model and by a factor of ten for experiments with high minimum recoil energy thresholds. These same features increase (decrease) the annual modulation for low (high) minimum recoil energy experiments. We present physical arguments for why these dynamics are generic for barred galaxies such as the Milky Way rather than contingent on a specific galaxy model. [Preview Abstract] |
Sunday, January 29, 2017 4:42PM - 4:54PM |
M5.00007: Effects of an expanding caustic ring on a distribution of stars Sankha Subhra Chakrabarty, Pierre Sikivie In self-similar axially symmetric model of galactic halo, caustic rings lie on the galactic disk and expand on cosmological time scale. We study the motion of a distribution of stars under the gravitational field of an expanding caustic ring. We investigate how the bulk velocities of the stars are affected by the caustic. [Preview Abstract] |
Sunday, January 29, 2017 4:54PM - 5:06PM |
M5.00008: Strong Evidence for the Density-Wave Theory of Spiral Structure in Disk Galaxies: Pitch Angle Measurements in Different Wavelengths of Light. Hamed Pour-Imani, Daniel Kennefick, Julia Kennefick, Benjamin Davis, Douglas Shields, Mohamed Shameer Abdeen The density-wave theory of galactic spiral-arm structure makes a striking prediction that the pitch angle of spiral arms should vary with the wavelength of the galaxy's image. The reason is that stars are born in the density wave but move out of it as they age. They move ahead of the density wave inside the co-rotation radius, and fall behind outside of it, resulting in a tighter pitch angle at wavelengths that image stars (optical and near infrared) than those that are associated with star formation (far infrared and ultraviolet). In this study we combined large sample size with wide range of wavelengths, from the ultraviolet to the infrared to investigate this issue. For each galaxy we used an optical wavelength image (B-band: 445 nm) and images from the Spitzer Space Telescope at two infrared wavelengths (infrared: 3.6 and 8.0 $\mu $m) and we measured the pitch angle with the 2DFFT and Spirality codes (Davis et al. 2012; Shields et al. 2015). We find that the B-band and 3.6 $\mu $m images have smaller pitch angles than the infrared 8.0 $\mu $m image in all cases, in agreement with the prediction of density-wave theory. We also used images in the ultraviolet from Galaxy Evolution Explorer, whose pitch angles agreed with the measurements made at 8.0 $\mu $m. Because stars imaged at those wavelengths have not had time during their short lives to move out of the star-forming region. [Preview Abstract] |
Sunday, January 29, 2017 5:06PM - 5:18PM |
M5.00009: A description of the Cosinusoidal Potential and Cosmology John Cumalat, David Bartlett A replacement for Newtonian gravity will be discussed, namely : m $\phi$(r) = (GmM/r) cos[2$\pi$r/$\lambda_o$]. (This replacement is motivated by a paper which shows that only very few central point potentials have an associated uniqueness theorem.) The value of $\lambda_o$ is selected to be 400 pc. With this constant, the Newtonian gravitation potential differs from the Cosinusoidal potential by 1 part in 10$^{14}$ within our solar system - essentially indistinguishable. The cosinusoidal potential is consistent with the flat rotation curves and the Tully-Fisher law for disk galaxies. It also explains other features of our Galaxy in the halo. Another consequence of this potential is that the bending of light by gravitational lenses can probably be explained without dark matter. [Preview Abstract] |
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