1106.2023
Non Aci-symmetric anisotropy of solar wind turbulence
Turner, Gogoberidze, Chapman, Hnat, Mueller
* Cluster: a space mission of ESA with NASA participation, to study the Earth's magnetosphere over the course of an entire solar cycle. Composed of four identical spacecraft flying in a tetrahedral formation. The 4 spacecrafts were successfully launched in 2000. Collect 3d information on how the solar wind interacts with the magnetosphere. 4 clusters named Rumba, Salsa, Samba, and Tango (!), or C1, C2, C3, and C4. Have highly elliptical orbits (4R_E to almost 30 R_E).
* Taylor's hypothesis: no wiki entry
Symmetry in turbulence theory: essentially frame-invariance; in MHD turbulence, axisymmetry of fluctuations with respect to the background magnetic field. Paradoxically, the power in fluctuations in the turbulent solar wind are observed to be ordered wrt the bulk macroscopic flow, as well as the bg magnetic field. Quantify non-axisymmetry across intertial and dissipations rages using in-situ observations from Cluster. The observed "inertial range" non-axisymmetry is reproduced by a Direct Numerical Simulation of MHD turbulence. A linear superposition of transverse waves with axisymmetric fluctuations generates the trend in non-axisymmetry in 'fly-by' sampling. The observed non-axisymmetric anisotropy may simly arise as a sampling effect related to Taylor's hypothesis, and not related to the plasma dynamics itself.
1108.1195
The extreme small scales: do satellite galaxies trace dark matter?
Watson, Berlind, McBride, Hogg, Jiang
Model small-scale clustering in SDSS to investigate radial distribution of galaxies within their host DM halo. Correlation function down to 10<r<400 kpc/h with luminosity thresholds from Mr=-18 to -23. Use HOD framework with free paremeters that specify both number and spatial distribution of galaxies within their DM halos. Assume first galaxy lives in the center of the halo; additional satellite galaxies follow radial density profile similar to NFW; except concentration and inner slope are allowed to vary. In low luminosity samples, satellite galaxies (I'm assuming their distribution within the host halo) have radial profiles consistent with NFW. Mr<-20 and brighter satellite galaxies have radial profiles with significantly steeper inner slopes than NFW (more like -2 than -1) that are enclosed within one tenth of the virial radius of a halo. Define M_(1/10), a useful metric of concentration, which is the fraction of satellite galaxies (or mass) that are enclosed within one tenth of the virial radius of a halo. M_(1/10) for low luminosity satellite galaxies agrees with NFW, but for luminous galaxies it's 2.5-4 times higher. The luminous galaxies are more centrally concentrated within their DM haloes than the DM itself. Our results suggest that the processes that govern the spatial distribution of galaxies, once they have merged into larger haloes, must be luminosity dependent, such that luminous galaxies become poor tracers of the underlying DM.
* why would more luminous galaxies be more centrally concentrated in the halo? What physical processes would make it do that? Is it the merger history?
1108.1198
Measuring BAO and non-Gaussianity via QSO clustering
Sawangwit, ... Ross, et al
Goals: (i) search for BAO and LSS in current QSO survey data, and (ii) use these and simulate/forecast results to assess the science case for a new, >10x larger, QSO survey. Combine SDSS, 2QZ and 2SLAQ surveys for a ~60k sample of quasars. Find hint of peak in correlation function at 105 Mpc/h, but at low statistical significance. Compare with mock catalog by Hoyle+ (2002) and the statistical error estimates are consistent at 100 Mpc/h scales. Determine necessary survey size to obtain 3-4 sigma significance on this peak: need ~250k z<2.2 QSOs over 3000 deg^2. This can test discontinuity of DE between 1<z<2.2. A survey with 50% higher QSO sky density and 50% larger are can give ~6 sigma BAO detection, leading to a 60% error of the size of BOSS in the DE evolution parameter, w_a. Another important aim for QSO survey is to place new limits on primordial non-Gaussianity at large scales, testing tentative evidence for the evolution of the linear form of the combined QSO xi(s) at z~1.6. Such QSO survey will also determine the gravitational growth rate at z~1.6 via z-space distortions, allow lensing tomography via QSO magnification bias, while also measuring the exact luminosity dependence of small-scale QSO clustering.
* BigBOSS lists 630k LyA QSO's.
1108.1307
Gravitational waves from compact binaries
van der Sluys
Summary of history of understanding of gravitational waves, and how compact binaries were used to transform the GW status. Describe types of compact (stellar) binaries that LISA will observe. Status and near future of LIGO, Virgo and GEO discussed; expected detection rates for the Advanced detectors and the accuracies with which binary parameters can be determined when BH/NS inspirals are detected.
* Ooooh, I want to read this one, about the history of the science of GWs.
1108.1407
Dark matter detection with hard X-ray telescopes
Jeltema, Profumo
Impact of future hard X-ray observations on the search for indirect signatures of particle DM in nearby clusters or groups of galaxies. The hard X-ray energy band (will likely) fall squarely at the peak of the inverse Compton emission from electrons and positrons produced by DM annihilation. Most promising are the low-mass models with hard e-p+ annihilation final state spectrum, and intermediate-mass models with a soft electron-positron spectrum. Constraints on DM models similar to the current constraints from the Fermi Gamma-Ray space telesope will be close to the limit of the sensitivity of the near-tuerm hard X-ray telescopes NuSTAR and ASTRO-H for relatively long observations, but an instrument similar to the Wide Field imager on the International X-ray Observatory will allow significant gains to be made. In the future, the ability to probe low to intermediate DM particle masses with hard X-ray observations may provide a good complement to next-generation gamma-ray instruments like the CTA (Cherenkov telescope array) with will be sensitive to high-energy gamma-rays, thus only to relatively large particle masses.
1108.1195
The extreme small scales: do satellite galaxies trace dark matter?
Watson, Berlind, McBride, Hogg, Jiang
Model small-scale clustering in SDSS to investigate radial distribution of galaxies within their host DM halo. Correlation function down to 10<r<400 kpc/h with luminosity thresholds from Mr=-18 to -23. Use HOD framework with free paremeters that specify both number and spatial distribution of galaxies within their DM halos. Assume first galaxy lives in the center of the halo; additional satellite galaxies follow radial density profile similar to NFW; except concentration and inner slope are allowed to vary. In low luminosity samples, satellite galaxies (I'm assuming their distribution within the host halo) have radial profiles consistent with NFW. Mr<-20 and brighter satellite galaxies have radial profiles with significantly steeper inner slopes than NFW (more like -2 than -1) that are enclosed within one tenth of the virial radius of a halo. Define M_(1/10), a useful metric of concentration, which is the fraction of satellite galaxies (or mass) that are enclosed within one tenth of the virial radius of a halo. M_(1/10) for low luminosity satellite galaxies agrees with NFW, but for luminous galaxies it's 2.5-4 times higher. The luminous galaxies are more centrally concentrated within their DM haloes than the DM itself. Our results suggest that the processes that govern the spatial distribution of galaxies, once they have merged into larger haloes, must be luminosity dependent, such that luminous galaxies become poor tracers of the underlying DM.
* why would more luminous galaxies be more centrally concentrated in the halo? What physical processes would make it do that? Is it the merger history?
1108.1198
Measuring BAO and non-Gaussianity via QSO clustering
Sawangwit, ... Ross, et al
Goals: (i) search for BAO and LSS in current QSO survey data, and (ii) use these and simulate/forecast results to assess the science case for a new, >10x larger, QSO survey. Combine SDSS, 2QZ and 2SLAQ surveys for a ~60k sample of quasars. Find hint of peak in correlation function at 105 Mpc/h, but at low statistical significance. Compare with mock catalog by Hoyle+ (2002) and the statistical error estimates are consistent at 100 Mpc/h scales. Determine necessary survey size to obtain 3-4 sigma significance on this peak: need ~250k z<2.2 QSOs over 3000 deg^2. This can test discontinuity of DE between 1<z<2.2. A survey with 50% higher QSO sky density and 50% larger are can give ~6 sigma BAO detection, leading to a 60% error of the size of BOSS in the DE evolution parameter, w_a. Another important aim for QSO survey is to place new limits on primordial non-Gaussianity at large scales, testing tentative evidence for the evolution of the linear form of the combined QSO xi(s) at z~1.6. Such QSO survey will also determine the gravitational growth rate at z~1.6 via z-space distortions, allow lensing tomography via QSO magnification bias, while also measuring the exact luminosity dependence of small-scale QSO clustering.
* BigBOSS lists 630k LyA QSO's.
1108.1307
Gravitational waves from compact binaries
van der Sluys
Summary of history of understanding of gravitational waves, and how compact binaries were used to transform the GW status. Describe types of compact (stellar) binaries that LISA will observe. Status and near future of LIGO, Virgo and GEO discussed; expected detection rates for the Advanced detectors and the accuracies with which binary parameters can be determined when BH/NS inspirals are detected.
* Ooooh, I want to read this one, about the history of the science of GWs.
1108.1407
Dark matter detection with hard X-ray telescopes
Jeltema, Profumo
Impact of future hard X-ray observations on the search for indirect signatures of particle DM in nearby clusters or groups of galaxies. The hard X-ray energy band (will likely) fall squarely at the peak of the inverse Compton emission from electrons and positrons produced by DM annihilation. Most promising are the low-mass models with hard e-p+ annihilation final state spectrum, and intermediate-mass models with a soft electron-positron spectrum. Constraints on DM models similar to the current constraints from the Fermi Gamma-Ray space telesope will be close to the limit of the sensitivity of the near-tuerm hard X-ray telescopes NuSTAR and ASTRO-H for relatively long observations, but an instrument similar to the Wide Field imager on the International X-ray Observatory will allow significant gains to be made. In the future, the ability to probe low to intermediate DM particle masses with hard X-ray observations may provide a good complement to next-generation gamma-ray instruments like the CTA (Cherenkov telescope array) with will be sensitive to high-energy gamma-rays, thus only to relatively large particle masses.
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