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Register a new userChandra Observations and the Mass Distribution of EMSS1358+6245: Toward Constraints on Properties of Dark Matter
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Chandra observations of lensing galaxy clusters have now provided accurate dark matter profiles for several objects in which the intracluster medium is likely to be in hydrostatic equilibrium. We discuss Chandra observations of the mass profile of one such cluster, EMSS1358+6245. We find no evidence for flattening of the mass density profile at radii greater than 50/h_50 kpc . This result, and similar findings from Chandra observations of other clusters, appear to rule out models in of dark matter self-interaction proposed to explain the flat cores of low-surface brightness galaxies.
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We present Chandra observations of EMSS 1358+6245, a relaxed cooling flow cluster of galaxies at z = 0.328. We employ a new deprojection technique to construct temperature, gas, and dark matter profiles. We confirm the presence of cool gas in the cluster core, and our deprojected temperature profile for the hot component is isothermal over 30 kpc < r < 0.8 Mpc. Fitting the mass profile to an NFW model yields r_s = 153 [+161,-83] kpc and c = 8.4 [+3.4,-2.3]. We find good agreement between our dark matter profile and weak gravitational lensing measurements. We place an upper limit of 42 kpc (90% confidence limit) on the size of any constant density core. We compare this result to recent simulations and place a conservative upper limit on the dark matter particle scattering cross section of 0.1 cm^2/g. This limit implies that the cross-section must be velocity dependent if the relatively shallow core mass profiles of dwarf galaxies are a direct result of dark matter self-interaction.
Quark nuggets are a candidate for dark matter consistent with the Standard Model. Previous models of quark nuggets have investigated properties arising from their being composed of strange, up, and down quarks and have not included any effects caused by their self-magnetic field. However, Tatsumi found that the core of a magnetar star may be a quark nugget in a ferromagnetic state with core magnetic field B between $10^{ 11}$ T and $10^{ 13}$ T. We apply Tatsumi$$s result to quark-nugget dark-matter and report results on aggregation of magnetized quark nuggets (MQNs) after formation from the quark-gluon plasma until expansion of the universe freezes out the mass distribution to include $10^{ -24}$ kg to $10^{ 14}$ kg. Aggregation overcomes weak-interaction decay. Computed mass distributions show MQNs are consistent with requirements for dark matter and indicate that geologic detectors (craters in peat bogs) and space-based detectors (satellites measuring radio-frequency emissions after passage through normal matter) should be able to detect MQN dark matter. Null and positive observations narrow the range of a key parameter B to between $10^{ 11}$ T and 3 $10^{ 13}$ T.
We used radio observations of the neighbour galaxy M31 in order to put constraints on dark matter particle mass and annihilation cross section. Dark matter annihilation in M31 halo produces highly energetic leptons, which emit synchrotron radiation on radio frequencies in the galactic magnetic field. We predicted expected radio fluxes for the two annihilation channels: chichi -> bb* and chichi -> tau^+tau^-. We then compared them with available data on the central radio emission of M31 as observed by four radio surveys: VLSS (74 MHz), WENSS (325 MHz), NVSS (1400 MHz) and GB6 (4850 MHz). Assuming a standard NFW dark matter density profile and a conservative magnetic field distribution inside the Andromeda galaxy, we find that the thermal relic annihilation cross section <sigma v> = 3*10^{-26} cm^3/s or higher are only allowed for WIMP masses greater than 100 GeV and 55 GeV for annihilation into bb* and tau^+tau^- respectively. Taking into account potential uncertainties in the distributions of DM density and magnetic field, the mentioned WIMP limiting masses can be as low as 23 GeV for both channels, and as high as 280 and 130 GeV for annihilation into bb* and tau^+tau^- respectively. These mass values exceed the best up-to-day known constraints from Fermi gamma observations: 40 GeV and 19 GeV respectively [A.Geringer-Sameth and S.M.Koushiappas, Phys. Rev. Lett. 107, 241303 (2011)]. Precise measurements of the magnetic field in the relevant region and better reconstruction of the DM density profile of M31 will be able to reduce the uncertainties of our exclusion limits.
We use large-scale cosmological observations to place constraints on the dark-matter pressure, sound speed and viscosity, and infer a limit on the mass of warm-dark-matter particles. Measurements of the cosmic microwave background (CMB) anisotropies constrain the equation of state and sound speed of the dark matter at last scattering at the per mille level. Since the redshifting of collisionless particles universally implies that these quantities scale like $a^{-2}$ absent shell crossing, we infer that today $w_{rm (DM)}< 10^{-10.0}$, $c_{rm s,(DM)}^2 < 10^{-10.7}$ and $c_{rm vis, (DM)}^{2} < 10^{-10.3}$ at the $99%$ confidence level. This very general bound can be translated to model-dependent constraints on dark-matter models: for warm dark matter these constraints imply $m> 70$ eV, assuming it decoupled while relativistic around the same time as the neutrinos; for a cold relic, we show that $m>100$ eV. We separately constrain the properties of the DM fluid on linear scales at late times, and find upper bounds $c_{rm s, (DM)}^2<10^{-5.9}$, $c_{rm vis, (DM)}^{2} < 10^{-5.7}$, with no detection of non-dust properties for the DM.
We perform a comprehensive study of Milky Way (MW) satellite galaxies to constrain the fundamental properties of dark matter (DM). This analysis fully incorporates inhomogeneities in the spatial distribution and detectability of MW satellites and marginalizes over uncertainties in the mapping between galaxies and DM halos, the properties of the MW system, and the disruption of subhalos by the MW disk. Our results are consistent with the cold, collisionless DM paradigm and yield the strongest cosmological constraints to date on particle models of warm, interacting, and fuzzy dark matter. At $95%$ confidence, we report limits on (i) the mass of thermal relic warm DM, $m_{rm WDM} > 6.5 mathrm{keV}$ (free-streaming length, $lambda_{rm{fs}} lesssim 10,h^{-1} mathrm{kpc}$), (ii) the velocity-independent DM-proton scattering cross section, $sigma_{0} < 8.8times 10^{-29} mathrm{cm}^{2}$ for a $100 mathrm{MeV}$ DM particle mass (DM-proton coupling, $c_p lesssim (0.3 mathrm{GeV})^{-2}$), and (iii) the mass of fuzzy DM, $m_{phi}> 2.9 times 10^{-21} mathrm{eV}$ (de Broglie wavelength, $lambda_{rm{dB}} lesssim 0.5 mathrm{kpc}$). These constraints are complementary to other observational and laboratory constraints on DM properties.
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