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Classification of gamma-ray targets for velocity-dependent and subhalo-boosted dark-matter annihilation
Thomas Lacroix, Gaetán Facchinetti, Judit Pérez-Romero, Martin Stref, Julien Lavalle, David Maurin, Miguel Sánchez-Conde, izvirni znanstveni članek

Opis: Gamma-ray observations have long been used to constrain the properties of dark matter (DM), with a strong focus on weakly interacting massive particles annihilating through velocity-independent processes. However, in the absence of clear-cut observational evidence for the simplest candidates, the interest of the community in more complex DM scenarios involving a velocity-dependent cross-section has been growing steadily over the past few years. We present the first systematic study of velocity-dependent DM annihilation (in particular p-wave annihilation and Sommerfeld enhancement) in a variety of astrophysical objects, not only including the well-studied Milky Way dwarf satellite galaxies, but nearby dwarf irregular galaxies and local galaxy clusters as well. Particular attention is given to the interplay between velocity dependence and DM halo substructure. Uncertainties related to halo mass, phase-space and substructure modelling are also discussed in this velocity-dependent context. We show that, for s-wave annihilation, extremely large subhalo boost factors are to be expected, up to 10^11 in clusters and up to 10^6–10^7 in dwarf galaxies where subhalos are usually assumed not to play an important role. Boost factors for p-wave annihilation are smaller but can still reach 10^3 in clusters. The angular extension of the DM signal is also significantly impacted, with e.g. the cluster typical emission radius increasing by a factor of order 10 in the s-wave case. We also compute the signal contrast of the objects in our sample with respect to annihilation happening in the Milky Way halo. Overall, we find that the hierarchy between the brightest considered targets depends on the specific details of the assumed particle-physics model.
Ključne besede: dark matter theory, dwarf galaxies, galaxy clusters, gamma-ray theory
Objavljeno v RUNG: 27.01.2023; Ogledov: 347; Prenosov: 0
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Dark matter search in dwarf irregular galaxies with the Fermi Large Area Telescope
Viviana Gammaldi, Judit Pérez-Romero, Javier Coronado-Blázquez, Mattia di Mauro, Ekaterina Karukes, Miguel Sánchez-Conde, Paolo Salucci, 2021, izvirni znanstveni članek

Opis: We analyze 11 years of Fermi-Large Area Telescope (LAT) data corresponding to the sky regions of seven dwarf irregular (dIrr) galaxies. DIrrs are dark matter (DM)-dominated systems, proposed as interesting targets for the indirect search of DM with gamma rays. The galaxies represent interesting cases with a strong disagreement between the density profiles (core versus cusp) inferred from observations and numerical simulations. In this work, we addressed the problem by considering two different DM profiles, based on both the fit to the rotation curve (in this case, a Burkert cored profile) and results from N-body cosmological simulations (i.e., Navarro-Frenk-White cuspy profile). We also include halo substructure in our analysis, which is expected to boost the DM signal by a factor of 10 in halos such as those of dIrrs. For each DM model and dIrr, we create a spatial template of the expected DM-induced gamma-ray signal to be used in the analysis of Fermi-LAT data. No significant emission is detected from any of the targets in our sample. Thus, we compute upper limits on the DM annihilation cross section versus mass parameter space. Among the seven dIrrs, we find IC10 and NGC6822 to yield the most stringent individual constraints, independently of the adopted DM profile. We also produce combined DM limits for all objects in the sample, which turn out to be dominated by IC10 for all DM models and annihilation channels, i.e., b¯b, τ+τ−, and W+W−. The strongest constraints are obtained for b¯b and are at the level of <σv>∼7×10−26 cm3 s−1 at mχ ∼ 6 GeV. Though these limits are a factor of ∼3 higher than the thermal relic cross section at low weakly interacting massive particles masses, they are independent from and complementary to those obtained by means of other targets.
Ključne besede: Dark matter, gamma-ray astronomy, galaxies, astronomical masses and mass distributions
Objavljeno v RUNG: 26.01.2023; Ogledov: 304; Prenosov: 0
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Tiara Hung, Suvi Gezari, Tanja Petrushevska, 2018, izvirni znanstveni članek

Opis: We present results from a systematic selection of tidal disruption events (TDEs) in a wide area (4800 deg2 ) g + R band experiment by the Intermediate Palomar Transient Factory (iPTF) with a rolling cadence of 1 and 3 days. We use photometric selection criteria to down select from a total of 493 nuclear transients detected during the experiment to a sample of 26 blue (g − r < 0 mag) nuclear transients in red host galaxies. Using Swift follow-up UV and X-ray imaging, and ground-based optical spectroscopy, we classify 14 Type Ia supernovae (SNe Ia), 9 highly variable active galactic nuclei (AGNs), 2 confirmed TDEs, and 1 potential core-collapse supernova. From our study, we measure a TDE per galaxy rate of 1.7 +2.85 −1.27 ×10−4 gal−1 yr−1 (90% CL in Poisson statistics) using a galaxy number density estimated from the SDSS luminosity function. We find that it is possible to filter out AGNs by employing a more stringent transient color cut (g − r < −0.2 mag). The UV is an important discriminator for filtering out SN contamination, since in the optical, SNe Ia can appear as blue as TDEs in their early phases. However, the contamination from SN Ia drops significantly with a more stringent spatial offset cut, suggesting higher precision in astrometry is essential for separating TDEs from SNe Ia in the optical. Our most stringent optical photometric selection criteria yields a contamination rate of 4.5:1, allowing for a manageable number of TDE candidates for complete spectroscopic follow-up and real-time classification in the ZTF era.
Ključne besede: accretion, accretion disks – black hole physics – galaxies: nuclei – ultraviolet: general
Objavljeno v RUNG: 02.03.2022; Ogledov: 884; Prenosov: 54
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Testing the predictions of axisymmetric distribution functions of galactic dark matter with hydrodynamical simulations
Mihael Petač, Julien Lavalle, Arturo Núñez-Castiñeyra, Emmanuel Nezri, 2021, izvirni znanstveni članek

Opis: Signal predictions for galactic dark matter (DM) searches often rely on assumptions regarding the DM phase-space distribution function (DF) in halos. This applies to both particle (e.g. p-wave suppressed or Sommerfeld-enhanced annihilation, scattering off atoms, etc.) and macroscopic DM candidates (e.g. microlensing of primordial black holes). As experiments and observations improve in precision, better assessing theoretical uncertainties becomes pressing in the prospect of deriving reliable constraints on DM candidates or trustworthy hints for detection. Most reliable predictions of DFs in halos are based on solving the steady-state collisionless Boltzmann equation (e.g. Eddington-like inversions, action-angle methods, etc.) consistently with observational constraints. One can do so starting from maximal symmetries and a minimal set of degrees of freedom, and then increasing complexity. Key issues are then whether adding complexity, which is computationally costy, improves predictions, and if so where to stop. Clues can be obtained by making predictions for zoomed-in hydrodynamical cosmological simulations in which one can access the true (coarse-grained) phase-space information. Here, we test an axisymmetric extension of the Eddington inversion to predict the full DM DF from its density profile and the total gravitational potential of the system. This permits to go beyond spherical symmetry, and is a priori well suited for spiral galaxies. We show that axisymmetry does not necessarily improve over spherical symmetry because the (observationally unconstrained) angular momentum of the DM halo is not generically aligned with the baryonic one. Theoretical errors are similar to those of the Eddington inversion though, at the 10-20% level for velocity-dependent predictions related to particle DM searches in spiral galaxies. We extensively describe the approach and comment on the results.
Ključne besede: galaxy dynamics, dark matter experiments, dark matter simulations, dark matter theory, cosmology, nongalactic astrophysics, astrophysics of galaxies, high energy physics
Objavljeno v RUNG: 01.10.2021; Ogledov: 1174; Prenosov: 61
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Two-integral distribution functions in axisymmetric galaxies: Implications for dark matter searches
Mihael Petač, Piero Ullio, 2019, izvirni znanstveni članek

Opis: We address the problem of reconstructing the phase-space distribution function for an extended collisionless system, with known density profile and in equilibrium within an axisymmetric gravitational potential. Assuming that it depends on only two integrals of motion, namely the energy and the component of the angular momentum along the axis of symmetry Lz , there is a one-to-one correspondence between the density profile and the component of the distribution function that is even in Lz, as well as between the weighted azimuthal velocity profile and the odd component. This inversion procedure was originally proposed by Lynden-Bell and later refined in its numerical implementation by Hunter and Qian; after overcoming a technical difficulty, we apply it here for the first time in presence of a strongly flattened component, as a novel approach of extracting the phase-space distribution function for dark matter particles in the halo of spiral galaxies. We compare results obtained for realistic axisymmetric models to those in the spherical symmetric limit as assumed in previous analyses, showing the rather severe shortcomings in the latter. We then apply the scheme to the Milky Way and discuss the implications for the direct dark matter searches. In particular, we reinterpret the null results of the Xenon1T experiment for spin-(in)dependent interactions and make predictions for the annual modulation of the signal for a set of axisymmetric models, including a self-consistently defined corotating halo.
Ključne besede: dark matter, astrophysics of galaxies, high energy physics, phenomenology
Objavljeno v RUNG: 01.10.2021; Ogledov: 1166; Prenosov: 0
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Equilibrium axisymmetric halo model for the Milky Way and its implications for direct and indirect dark matter searches
Mihael Petač, 2020, izvirni znanstveni članek

Opis: We for the first time provide self-consistent axisymmetric phase-space distribution models for the Milky Way's dark matter (DM) halo which are carefully matched against the latest kinematic measurements through Bayesian analysis. By using broad priors on the individual galactic components, we derive conservative estimates for the astrophysical factors entering the interpretation of direct and indirect DM searches. While the resulting DM density profiles are in good agreement with previous studies, implying ρ⊙≈10-2 M⊙/pc3, the presence of baryonic disc leads to significant differences in the local DM velocity distribution in comparison with the standard halo model. For direct detection, this implies roughly 30% stronger cross section limits at DM masses near detectors maximum sensitivity and up to an order of magnitude weaker limits at the lower end of the mass range. Furthermore, by performing Monte Carlo simulations for the upcoming DARWIN and DarkSide-20k experiments, we demonstrate that upon successful detection of heavy DM with coupling just below the current limits, the carefully constructed axisymmetric models can eliminate bias and reduce uncertainties by more then 50% in the reconstructed DM coupling and mass, but also help in a more reliable determination of the scattering operator. Furthermore, the velocity anisotropies induced by the baryonic disc can lead to significantly larger annual modulation amplitude and sizable differences in the directional distribution of the expected DM-induced events. For indirect searches, we provide the differential J factors and compute several moments of the relative velocity distribution that are needed for predicting the rate of velocity-dependent annihilations. However, we find that accurate predictions are still hindered by large uncertainties regarding the DM distribution near the galactic center.
Ključne besede: dark matter, astrophysics, galaxies, high energy physics, experiments, phenomenology
Objavljeno v RUNG: 01.10.2021; Ogledov: 1061; Prenosov: 38
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