| 1. |
- Galli, Silvia, et al.
(författare)
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Systematic uncertainties in constraining dark matter annihilation from the cosmic microwave background
- 2013
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 88:6, s. 063502-
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Tidskriftsartikel (refereegranskat)abstract
- Anisotropies of the cosmic microwave background (CMB) have proven to be a very powerful tool to constrain dark matter annihilation at the epoch of recombination. However, CMB constraints are currently derived using a number of reasonable but yet untested assumptions that could potentially lead to a misestimation of the true bounds (or any reconstructed signal). In this paper we examine the potential impact of these systematic effects. In particular, we separately study the propagation of the secondary particles produced by annihilation in two energy regimes: first following the shower from the initial particle energy to the keV scale, and then tracking the resulting secondary particles from this scale to the absorption of their energy as heat, ionization, or excitation of the medium. We improve both the high- and low-energy parts of the calculation, in particular finding that our more accurate treatment of losses to sub-10.2 eV photons produced by scattering of high-energy electrons weakens the constraints on particular dark matter annihilation models by up to a factor of 2. On the other hand, we find that the uncertainties we examine for the low-energy propagation do not significantly affect the results for current and upcoming CMB data. We include the evaluation of the precise amount of excitation energy, in the form of Lyman-alpha photons, produced by the propagation of the shower, and examine the effects of varying the helium fraction and helium ionization fraction. In the recent literature, simple approximations for the fraction of energy absorbed in different channels have often been used to derive CMB constraints: we assess the impact of using accurate vs approximate energy fractions. Finally we check that the choice of recombination code (between RECFAST V1.5 and COSMOREC), to calculate the evolution of the free electron fraction in the presence of dark matter annihilation, introduces negligible differences.
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| 2. |
- Iocco, Fabio, et al.
(författare)
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Evidence for dark matter in the inner Milky Way
- 2015
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Ingår i: Nature Physics. - 1745-2473 .- 1745-2481. ; 11:3, s. 245-248
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Tidskriftsartikel (refereegranskat)abstract
- The ubiquitous presence of dark matter in the Universe is today a central tenet in modern cosmology and astrophysics(1). Throughout the Universe, the evidence for dark matter is compelling in dwarfs, spiral galaxies, galaxy clusters as well as at cosmological scales. However, it has been historically difficult to pin down the dark matter contribution to the total mass density in the Milky Way, particularly in the innermost regions of the Galaxy and in the solar neighbourhood(2). Here we present an up-to-date compilation of Milky Way rotation curve measurements(3-13), and compare it with state-of-the-art baryonic mass distribution models(14-26). We show that current data strongly disfavour baryons as the sole contribution to the Galactic mass budget, even inside the solar circle. Our findings demonstrate the existence of dark matter in the inner Galaxy without making any assumptions about its distribution. We anticipate that this result will compel new model-independent constraints on the dark matter local density and profile, thus reducing uncertainties on direct and indirect dark matter searches, and will help reveal the structure and evolution of the Galaxy.
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| 3. |
- Iocco, Fabio, et al.
(författare)
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Lithium Synthesis in Microquasar Accretion
- 2012
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 109:2, s. 021102-
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Tidskriftsartikel (refereegranskat)abstract
- We study the synthesis of lithium isotopes in the hot tori formed around stellar mass black holes by accretion of the companion star. We find that sizable amounts of both stable isotopes Li-6 and Li-7 can be produced, the exact figures varying with the characteristics of the torus and reaching as much as 10(-2) M-circle dot for each isotope. This mass output is enough to contaminate the entire Galaxy at a level comparable with the original, pregalactic amount of lithium and to overcome other sources such as cosmic-ray spallation or stellar nucleosynthesis.
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| 4. |
- Iocco, Fabio, et al.
(författare)
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Testing modified Newtonian dynamics in the Milky Way
- 2015
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 92:8
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Tidskriftsartikel (refereegranskat)abstract
- Modified Newtonian dynamics (MOND) is an empirical theory originally proposed to explain the rotation curves of spiral galaxies by modifying the gravitational acceleration, rather than by invoking dark matter. Here, we set constraints on MOND using an up-to-date compilation of kinematic tracers of the Milky Way and a comprehensive collection of morphologies of the baryonic component in the Galaxy. In particular, we find that the so-called standard interpolating function cannot explain at the same time the rotation curve of the Milky Way and that of external galaxies for any of the baryonic models studied, while the so-called simple interpolating function can for a subset of models. Upcoming astronomical observations will refine our knowledge on the morphology of baryons and will ultimately confirm or rule out the validity of MOND in the Milky Way. We also present constraints on MOND-like theories without making any assumptions on the interpolating function.
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| 5. |
- Mellema, Garrelt, et al.
(författare)
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Reionization and the Cosmic Dawn with the Square Kilometre Array
- 2013
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 36:1-2, s. 235-318
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Tidskriftsartikel (refereegranskat)abstract
- The Square Kilometre Array (SKA) will have a low frequency component (SKA-low) which has as one of its main science goals the study of the redshifted 21 cm line from the earliest phases of star and galaxy formation in the Universe. This 21 cm signal provides a new and unique window both on the time of the formation of the first stars and accreting black holes and the subsequent period of substantial ionization of the intergalactic medium. The signal will teach us fundamental new things about the earliest phases of structure formation, cosmology and even has the potential to lead to the discovery of new physical phenomena. Here we present a white paper with an overview of the science questions that SKA-low can address, how we plan to tackle these questions and what this implies for the basic design of the telescope.
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| 6. |
- Pato, Miguel, et al.
(författare)
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Dynamical constraints on the dark matter distribution in the Milky Way
- 2015
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :12
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Tidskriftsartikel (refereegranskat)abstract
- An accurate knowledge of the dark matter distribution in the Milky Way is of crucial importance for galaxy formation studies and current searches for particle dark matter. In this paper we set new dynamical constraints on the Galactic dark matter profile by comparing the observed rotation curve, updated with a comprehensive compilation of kinematic tracers, with that inferred from a wide range of observation-based morphologies of the bulge, disc and gas. The generalised Navarro-Frenk-White (NFW) and Einasto dark matter profiles are fitted to the data in order to determine the favoured ranges of local density, slope and scale radius. For a representative baryonic model, a typical local circular velocity v(0) = 230 km/s and a distance of the Sun to the Galactic centre R-0 = 8 kpc, we find a local dark matter density rho(0) = 0.420(-0.018)(+0.021) (2 sigma) +/- 0.025 GeV/cm(3) (rho(0) = 0.420(-0.021)(+0.019) (2 sigma) +/- 0.026 GeV/cm(3)) for NFW (Einasto), where the second error is an estimate of the systematic due to baryonic modelling. Apart from the Galactic parameters, the main sources of uncertainty inside and outside the solar circle are baryonic modelling and rotation curve measurements, respectively. Upcoming astronomical observations are expected to reduce all these uncertainties substantially over the coming years.
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| 7. |
- Pato, Miguel, et al.
(författare)
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THE DARK MATTER PROFILE OF THE MILKY WAY : A NON-PARAMETRIC RECONSTRUCTION
- 2015
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 803:1
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Tidskriftsartikel (refereegranskat)abstract
- We present the results of a new, non-parametric method to reconstruct the Galactic dark matter profile directly from observations. Using the latest kinematic data to track the total gravitational potential and the observed distribution of stars and gas to set the baryonic component, we infer the dark matter contribution to the circular velocity across the Galaxy. The radial derivative of this dynamical contribution is then estimated to extract the dark matter profile. The innovative feature of our approach is that it makes no assumption on the functional form or shape of the profile, thus allowing for a clean determination with no theoretical bias. We illustrate the power of the method by constraining the spherical dark matter profile between 2.5 and 25 kpc away from the Galactic center. The results show that the proposed method, free of widely used assumptions, can already be applied to pinpoint the dark matter distribution in the Milky Way with competitive accuracy, and paves the way for future developments.
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| 8. |
- Smith, Rowan J., et al.
(författare)
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Weakly interacting massive particle dark matter and first stars : suppression of fragmentation in primordial star formation
- 2012
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 761:2, s. 154-
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Tidskriftsartikel (refereegranskat)abstract
- We present the first three-dimensional simulations to include the effects of dark matter annihilation feedback during the collapse of primordial minihalos. We begin our simulations from cosmological initial conditions and account for dark matter annihilation in our treatment of the chemical and thermal evolution of the gas. The dark matter is modeled using an analytical density profile that responds to changes in the peak gas density. We find that the gas can collapse to high densities despite the additional energy input from the dark matter. No objects supported purely by dark matter annihilation heating are formed in our simulations. However, we find that dark matter annihilation heating has a large effect on the evolution of the gas following the formation of the first protostar. Previous simulations without dark matter annihilation found that protostellar disks around Population III stars rapidly fragmented, forming multiple protostars that underwent mergers or ejections. When dark matter annihilation is included, however, these disks become stable to radii of 1000 AU or more. In the cases where fragmentation does occur, it is a wide binary that is formed.
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| 9. |
- Weniger, Christoph, et al.
(författare)
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CMB bounds on dark matter annihilation : Nucleon energy losses after recombination
- 2013
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 87:12, s. 123008-
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Tidskriftsartikel (refereegranskat)abstract
- We consider the propagation and energy losses of protons and antiprotons produced by dark matter annihilation at redshifts 100 < z less than or similar to 2000. In the case of dark matter annihilations into quarks, gluons and weak gauge bosons, protons and antiprotons carry about 20% of the energy injected into e(+/-) and gamma's, but their interactions are normally neglected when deriving cosmic microwave background bounds from altered recombination histories. Here, we follow numerically the energy-loss history of typical protons/antiprotons in the cosmological medium. We show that about half of their energy is channeled into photons and e(+/-), and we present a simple prescription to estimate the corresponding strengthening of the cosmic microwave background bounds on the dark matter annihilation cross section.
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| 10. |
- Zackrisson, Erik, et al.
(författare)
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Finding high-redshift dark stars with the James Webb Space Telescope
- 2010
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Ingår i: Astrophysical Journal. - : The American Astronomical Society. - 0004-637X .- 1538-4357. ; 717:1, s. 257-267
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Tidskriftsartikel (refereegranskat)abstract
- The first stars in the history of the universe are likely to form in the dense central regions of similar to 10(5)-10(6) M-circle dot cold dark matter halos at z approximate to 10-50. The annihilation of dark matter particles in these environments may lead to the formation of so-called dark stars, which are predicted to be cooler, larger, more massive, and potentially more long-lived than conventional population III stars. Here, we investigate the prospects of detecting high-redshift dark stars with the upcoming James Webb Space Telescope (JWST). We find that all dark stars with masses up to 10(3) M-circle dot are intrinsically too faint to be detected by JWST at z > 6. However, by exploiting foreground galaxy clusters as gravitational telescopes do, certain varieties of cool (T-eff <= 30,000 K) dark stars should be within reach at redshifts up to z approximate to 10. If the lifetimes of dark stars are sufficiently long, many such objects may also congregate inside the first galaxies. We demonstrate that this could give rise to peculiar features in the integrated spectra of galaxies at high redshifts, provided that dark stars make up at least similar to 1% of the total stellar mass in such objects.
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