Bulletin of the American Physical Society
APS April Meeting 2010
Volume 55, Number 1
Saturday–Tuesday, February 13–16, 2010; Washington, DC
Session G13: Astrophysical Searches for Dark Matter and New Physics |
Hide Abstracts |
Sponsoring Units: DAP DPF Chair: Simona Murgia, SLAC KIPAC Room: Washington 6 |
Sunday, February 14, 2010 8:30AM - 8:42AM |
G13.00001: Untangling Galactic History in Action Space Robyn Sanderson, John Bochanski, Andrew West, Adam Burgasser, James Binney Action-angle variables provide an instructive alternative viewpoint for studying the dynamical properties of objects in our Galaxy. Using a numerical method that constructs actions in an axisymmetric potential fit to the rotation curve of the Milky Way, we determine the locations in action space of two samples of stars from the SDSS survey for which complete six-dimensional phase space information is available: a small sample of ultra-cool dwarfs thought to include a large proportion of halo stars, and a large sample of M dwarfs that includes both disk and halo stars. We use this technique to examine the orbits of halo stars, compare the dynamical properties of the Milky Way thin and thick disks, and search for moving groups. We also demonstrate how observational errors and selection functions may be projected into action space, and forecast the performance of our method for next-generation astrometric surveys. [Preview Abstract] |
Sunday, February 14, 2010 8:42AM - 8:54AM |
G13.00002: Gravitational Rotation Curves for the THINGS Survey James O'Brien The use of Galactic Rotation Curves has long been thought to provide evidence for the existence of Dark Matter. Although dark matter is currently the commonly accepted solution to the discrepancies found in galactic rotation curves between observation and theory, numerous dark matter alternative theories are beginning to emerge as possible solutions as well, in part because the galactic halos used in dark matter fits involve one or two extra external free parameters per galaxy. Among these alternative theories, the Conformal Gravity theory first presented by Weyl and recently advanced by Mannheim and Kazanas presents a renormalizable, fourth order theory, which does not assume the existence of dark matter, nor is inferred as an ad hoc addition to standard gravity. Moreover, Conformal Gravity can serve to define the rotation curves of spiral and dwarf galaxies with no external free parameters, thus eliminating the ambiguity of the current dark matter halo mass models. The THINGS survey is a recent sample of 18 galaxies, consisting of both dwarf and spiral galaxies, at distances between 2 and 15 Mpc. We thus apply the conformal theory to the THINGS data to produce rotation curves that fit the data with very high accuracy without the need for dark matter. The results yield rotation curves, which being parameter free, are strikingly more convincing than those of the standard gravity with dark matter. [Preview Abstract] |
Sunday, February 14, 2010 8:54AM - 9:06AM |
G13.00003: A Generalized Secondary Infall Model Phillip Zukin, Edmund Bertschinger The inner slope of a dark matter halo's density profile affects our understanding of galaxy formation and evolution and has implications for dark matter indirect detection. While simulations seem to predict a cuspy steep inner slope, observations suggest flat core-like profiles. This discrepancy is known as the Cusp Core problem. We attempt to shed light on the problem, through analytic means, by generalizing the self-similar secondary infall model to include angular momentum. In our model, each halo is represented by a two parameter family of solutions. One parameter describes the initial mass perturbation and the other defines how a given shell is torqued through evolution. We show how the inner slope varies with parameters. [Preview Abstract] |
Sunday, February 14, 2010 9:06AM - 9:18AM |
G13.00004: Using anisotropy to identify a dark matter signal in diffuse gamma-ray emission with Fermi Jennifer Siegal-Gaskins, Vasiliki Pavlidou, Brandon Hensley Dark matter annihilation in Galactic substructure will produce diffuse gamma-ray emission of remarkably constant intensity across the sky, making it difficult to disentangle this Galactic dark matter signal from the extragalactic gamma-ray background. Recent studies have considered the angular power spectrum of the diffuse emission from various extragalactic source classes and from Galactic dark matter. I'll discuss these results and show how the energy dependence of anisotropies in the total measured diffuse emission could be used to confidently identify a signal from dark matter in Fermi data. Finally, I'll present new results demonstrating how anisotropy analysis could extend the capabilities of current indirect dark matter searches. [Preview Abstract] |
Sunday, February 14, 2010 9:18AM - 9:30AM |
G13.00005: Probing the Dark Matter-Galaxy Formation Connection with Lyman Alpha Emitting Galaxies Eric Gawiser I will describe how our understanding of cosmological structure formation is used to probe the dark matter properties of high-redshift galaxies and to identify their present-day descendants. Samples of 261 and 162 Lyman Alpha Emitting (LAE) galaxies at redshifts $z=2.1$ and $z=3.1$, respectively, were discovered in deep narrow-band imaging of the MUSYC survey. The LAEs exhibit a moderate clustering bias of $b=1.8+-0.3$, which implies median dark matter halo masses of $10^{11}$ M$_\odot$. The evolution of dark matter halo mass with redshift predicts that these LAEs evolve into typical present-day galaxies like the Milky Way, whereas other high-redshift galaxy populations, including Lyman Break Galaxies and Active Galactic Nuclei, typically evolve into more massive galaxies. Hence these Lyman Alpha Emitting galaxies represent our first direct knowledge of the progenitors of galaxies like the Milky Way seen when the universe was only 2-3 Gyr in age. I will also describe how these galaxies will be used by HETDEX and LSST to probe cosmological parameters including the dark energy equation-of-state and neutrino masses.\\ References: Gawiser et al. 2007 (Astrophysical Journal 671, 278), Guaita et al. 2009 (ArXiv:0910.2244) [Preview Abstract] |
Sunday, February 14, 2010 9:30AM - 9:42AM |
G13.00006: Morphological Tests of the Pulsar and Dark Matter Interpretations of the WMAP Haze J. Patrick Harding The WMAP Haze is an excess in microwave emission coming from the center of the Milky Way galaxy. In the case of synchrotron emission models of the Haze, we present tests for the source of radiating high-energy electrons/positrons. We explore several models in the case of a pulsar population or dark matter coannihilation as the source. These morphological signatures of these models are small behind the WMAP Galactic mask, but are testable and constrain the source models. In particular, a zero central density Galactic pulsar population model is in tension with the observed WMAP Haze. The Planck observatory's greater sensitivity and expected smaller Galactic mask should potentially provide a robust signature of the WMAP Haze as either a pulsar population or the dark matter. [Preview Abstract] |
Sunday, February 14, 2010 9:42AM - 9:54AM |
G13.00007: Verification of Indirect Indications of the Nature of Dark Matter Kevork Abazajian Several observations have drawn considerable interest as potential indications for indirect signatures of the nature of dark matter. Radio synchrotron towards the galactic center, the ``WMAP haze,'' high-energy cosmic ray electron/positron observations, as well as the behavior of dark matter in small scale structure, are potential signals for properties of the dark matter. I will discuss how current and future observations will test the dark matter interpretation of these signals. [Preview Abstract] |
Sunday, February 14, 2010 9:54AM - 10:06AM |
G13.00008: Luke-warm dark matter: Bose-condensation of ultra-light particles Mihai Bondarescu, Andrew Lundgren, Ruxandra Bondarescu, Jayashree Balakrishna We discuss the thermal evolution and Bose condensation of ultra-light dark matter particles with Compton wavelength of galactic scales. Agglomerations of these particles form stable halo structures and naturally exhibit no small scale structure. They are supported against gravitational collapse by Heisenberg's uncertainty principle similar to boson stars. We find that these ultra-light scalars Bose condense at high temperatures. The condensate has a very high critical temperature allowing us to treat the ground state and excited states separately. The particles in excited states are ultra-relativistic and act like radiation, while the bosons in the ground state have the same effect on the universe as presureless matter. We then solve the Friedman-Klein Gordon equations and study the cosmological evolution of this scalar field. [Preview Abstract] |
Sunday, February 14, 2010 10:06AM - 10:18AM |
G13.00009: Particle Production and Big Rip Singularities Jason Bates In 1929, Edwin Hubble found that objects in our Universe generally recede from us at a rate proportional to their distance, suggesting that the Universe as a whole is expanding. More recently, astronomers have observed that this expansion is accelerating. According to Einstein's theory of gravity, all normal matter in the Universe should act to slow the rate of expansion, so there must be something new which is causing this acceleration. Cosmologists call this ``Dark Energy.'' One of the possibilities for dark energy leads to a Universe which expands to an infinite size in a finite amount of time. This scenario is called a ``Big Rip,'' because near the end of time this expansion overcomes all other forces in the Universe - even atoms are ripped apart. However, Quantum Mechanics predicts that as the Universe expands particles will be created. If enough particles are created, this process could slow or even halt the expansion, and the ``Big Rip'' might be avoided. Using numerical methods, we considered the quantum effects for massive and massless scalar fields, and found that while at late times quantum effects do grow large, they do not become comparable to the dark energy until very near the singularity when the curvature of the Universe approaches the Planck scale. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700