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14 pages, 901 KiB

Open AccessArticle

Constraints to Dark Matter Annihilation from High-Latitude HAWC Unidentified Sources

by Javier Coronado-Blázquez and Miguel A. Sánchez-Conde

Galaxies 2020, 8(1), 5; https://doi.org/10.3390/galaxies8010005 - 30 Dec 2019

Cited by 9 | Viewed by 3521

Abstract

The

Λ

CDM cosmological framework predicts the existence of thousands of subhalos in our own Galaxy not massive enough to retain baryons and become visible. Yet, some of them may outshine in gamma rays provided that the dark matter is made of weakly [...] Read more.

The

Λ

CDM cosmological framework predicts the existence of thousands of subhalos in our own Galaxy not massive enough to retain baryons and become visible. Yet, some of them may outshine in gamma rays provided that the dark matter is made of weakly interacting massive particles (WIMPs), which would self-annihilate and would appear as unidentified gamma-ray sources (unIDs) in gamma-ray catalogs. Indeed, unIDs have proven to be competitive targets for dark matter searches with gamma rays. In this work, we focus on the three high-latitude (

| b | \geq 10

) sources present in the 2HWC catalog of the High Altitude Water Cherenkov (HAWC) observatory with no clear associations at other wavelengths. Indeed, only one of these sources, 2HWC J1040+308, is found to be above the HAWC detection threshold when considering 760 days of data, i.e., a factor 1.5 more exposure time than in the original 2HWC catalog. Other gamma-ray instruments, such as Fermi-LAT or VERITAS at lower energies, do not detect the source. Also, this unID is reported as spatially extended, making it even more interesting in a dark matter search context. While waiting for more data that may shed further light on the nature of this source, we set competitive upper limits on the annihilation cross section by comparing this HAWC unID to expectations based on state-of-the-art N-body cosmological simulations of the Galactic subhalo population. We find these constraints to be particularly competitive for heavy WIMPs, i.e., masses above ∼25 (40) TeV in the case of the

b \bar{b}

(

τ^{+} τ^{-}

) annihilation channel, reaching velocity-averaged cross section values of

2 \times 10^{- 25}

(

5 \times 10^{- 25}

) cm

^{3}

·s

^{- 1}

. Although far from testing the thermal relic cross section value, the obtained limits are independent and nicely complementary to those from radically different DM analyses and targets, demonstrating once again the high potential of this DM search approach. Full article

(This article belongs to the Special Issue The Role of Halo Substructure in Gamma-Ray Dark Matter Searches)

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14 pages, 2468 KiB

Open AccessArticle

Gamma-Ray Sensitivity to Dark Matter Subhalo Modelling at High Latitudes

by Francesca Calore, Moritz Hütten and Martin Stref

Galaxies 2019, 7(4), 90; https://doi.org/10.3390/galaxies7040090 - 26 Nov 2019

Cited by 13 | Viewed by 2543

Abstract

Searches for “dark” subhaloes in gamma-ray point-like source catalogues are among promising strategies for indirect dark matter detection. Such a search is nevertheless affected by uncertainties related, on the one hand, to the modelling of the dark matter subhalo distribution in Milky-Way-like galaxies, [...] Read more.

Searches for “dark” subhaloes in gamma-ray point-like source catalogues are among promising strategies for indirect dark matter detection. Such a search is nevertheless affected by uncertainties related, on the one hand, to the modelling of the dark matter subhalo distribution in Milky-Way-like galaxies, and, on the other hand, to the sensitivity of gamma-ray instruments to the dark matter subhalo signals. In the present work, we assess the detectability of dark matter subhaloes in Fermi-LAT catalogues, taking into accounts uncertainties associated with the modelling of the galactic subhalo population. We use four different halo models bracketing a large set of uncertainties. For each model, adopting an accurate detection threshold of the LAT to dark matter subhalo signals and comparing model predictions with the number of unassociated point-sources in Fermi-LAT catalogues, we derive upper limits on the annihilation cross section as a function of dark matter mass. Our results show that, even in the best-case scenario (i.e., DMonly subhalo model), which does not include tidal disruption from baryons, the limits on the dark matter parameter space are less stringent than current gamma-ray limits from dwarf spheroidal galaxies. Comparing the results obtained with the different subhalo models, we find that baryonic effects on the subhalo population are significant and lead to dark matter constraints that are less stringent by a factor of ∼2 to ∼5. This uncertainty comes from the unknown resilience of dark matter subhaloes to tidal disruption. Full article

(This article belongs to the Special Issue The Role of Halo Substructure in Gamma-Ray Dark Matter Searches)

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16 pages, 658 KiB

Open AccessArticle

Properties of Subhalos in the Interacting Dark Matter Scenario

by Ángeles Moliné, Jascha A. Schewtschenko, Miguel A. Sánchez-Conde, Alejandra Aguirre-Santaella, Sofía A. Cora and Mario G. Abadi

Galaxies 2019, 7(4), 80; https://doi.org/10.3390/galaxies7040080 - 21 Sep 2019

Cited by 2 | Viewed by 2733

Abstract

One possible and natural derivation from the collisionless cold dark matter (CDM) standard cosmological framework is the assumption of the existence of interactions between dark matter (DM) and photons or neutrinos. Such a possible interacting dark matter (IDM) model would imply a suppression [...] Read more.

One possible and natural derivation from the collisionless cold dark matter (CDM) standard cosmological framework is the assumption of the existence of interactions between dark matter (DM) and photons or neutrinos. Such a possible interacting dark matter (IDM) model would imply a suppression of small-scale structures due to a large collisional damping effect, even though the weakly-interacting massive particle (WIMP) can still be the DM candidate. Because of this, IDM models can help alleviate alleged tensions between standard CDM predictions and observations at small mass scales. In this work, we investigate the properties of the DM halo substructure or subhalos formed in a high-resolution cosmological N-body simulation specifically run within these alternative models. We also run its CDM counterpart, which allowed us to compare subhalo properties in both cosmologies. We show that, in the lower mass range covered by our simulation runs, both subhalo concentrations and abundances are systematically lower in IDM compared to the CDM scenario. Yet, as in CDM, we find that median IDM subhalo concentration values increase towards the innermost regions of their hosts for the same mass subhalos. Similarly to CDM, we find IDM subhalos to be more concentrated than field halos of the same mass. Our work has a direct application to studies aimed at the indirect detection of DM where subhalos are expected to boost the DM signal of their host halos significantly. From our results, we conclude that the role of the halo substructure in DM searches will be less important in interacting scenarios than in CDM, but is nevertheless far from being negligible. Full article

(This article belongs to the Special Issue The Role of Halo Substructure in Gamma-Ray Dark Matter Searches)

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17 pages, 1080 KiB

Open AccessEditor’s ChoiceArticle

Remnants of Galactic Subhalos and Their Impact on Indirect Dark-Matter Searches

by Martin Stref, Thomas Lacroix and Julien Lavalle

Galaxies 2019, 7(2), 65; https://doi.org/10.3390/galaxies7020065 - 4 Jun 2019

Cited by 17 | Viewed by 3518

Abstract

Dark-matter subhalos, predicted in large numbers in the cold-dark-matter scenario, should have an impact on dark-matter-particle searches. Recent results show that tidal disruption of these objects in computer simulations is overefficient due to numerical artifacts and resolution effects. Accounting for these results, we [...] Read more.

Dark-matter subhalos, predicted in large numbers in the cold-dark-matter scenario, should have an impact on dark-matter-particle searches. Recent results show that tidal disruption of these objects in computer simulations is overefficient due to numerical artifacts and resolution effects. Accounting for these results, we re-estimated the subhalo abundance in the Milky Way using semianalytical techniques. In particular, we showed that the boost factor for gamma rays and cosmic-ray antiprotons is increased by roughly a factor of two. Full article

(This article belongs to the Special Issue The Role of Halo Substructure in Gamma-Ray Dark Matter Searches)

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19 pages, 5998 KiB

Open AccessArticle

γ-ray and ν Searches for Dark-Matter Subhalos in the Milky Way with a Baryonic Potential

by Moritz Hütten, Martin Stref, Céline Combet, Julien Lavalle and David Maurin

Galaxies 2019, 7(2), 60; https://doi.org/10.3390/galaxies7020060 - 28 May 2019

Cited by 17 | Viewed by 3805

Abstract

The distribution of dark-matter (DM) subhalos in our galaxy remains disputed, leading to varying

γ

-ray and

ν

flux predictions from their annihilation or decay. In this work, we study how, in the inner galaxy, subhalo tidal disruption from the galactic baryonic potential [...] Read more.

The distribution of dark-matter (DM) subhalos in our galaxy remains disputed, leading to varying

γ

-ray and

ν

flux predictions from their annihilation or decay. In this work, we study how, in the inner galaxy, subhalo tidal disruption from the galactic baryonic potential impacts these signals. Based on state-of-the art modeling of this effect from numerical simulations and semi-analytical results, updated subhalo spatial distributions are derived and included in the CLUMPY code. The latter is used to produce a thousand realizations of the

γ

-ray and

ν

sky. Compared to predictions based on DM only, we conclude a decrease of the flux of the brightest subhalo by a factor of 2 to 7 for annihilating DM and no impact on decaying DM: the discovery prospects or limits subhalos can set on DM candidates are affected by the same factor. This study also provides probability density functions for the distance, mass, and angular distribution of the brightest subhalo, among which the mass may hint at its nature: it is most likely a dwarf spheroidal galaxy in the case of strong tidal effects from the baryonic potential, whereas it is lighter and possibly a dark halo for DM only or less pronounced tidal effects. Full article

(This article belongs to the Special Issue The Role of Halo Substructure in Gamma-Ray Dark Matter Searches)

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Review

Jump to: Research

27 pages, 3748 KiB

Open AccessReview

Gamma-Ray Dark Matter Searches in Milky Way Satellites—A Comparative Review of Data Analysis Methods and Current Results

by Javier Rico

Galaxies 2020, 8(1), 25; https://doi.org/10.3390/galaxies8010025 - 17 Mar 2020

Cited by 21 | Viewed by 3378

Abstract

If dark matter is composed of weakly interacting particles with mass in the GeV-TeV range, their annihilation or decay may produce gamma rays that could be detected by gamma-ray telescopes. Observations of dwarf spheroidal satellite galaxies of the Milky Way (dSphs) benefit from [...] Read more.

If dark matter is composed of weakly interacting particles with mass in the GeV-TeV range, their annihilation or decay may produce gamma rays that could be detected by gamma-ray telescopes. Observations of dwarf spheroidal satellite galaxies of the Milky Way (dSphs) benefit from the relatively accurate predictions of dSph dark matter content to produce robust constraints to the dark matter properties. The sensitivity of these observations for the search for dark matter signals can be optimized thanks to the use of advanced statistical techniques able to exploit the spectral and morphological peculiarities of the expected signal. In this paper, I review the status of the dark matter searches from observations of dSphs with the current generation of gamma-ray telescopes: Fermi-LAT, H.E.S.S, MAGIC, VERITAS and HAWC. I will describe in detail the general statistical analysis framework used by these instruments, putting in context the most recent experimental results and pointing out the most relevant differences among the different particular implementations. This will facilitate the comparison of the current and future results, as well as their eventual integration in a multi-instrument and multi-target dark matter search. Full article

(This article belongs to the Special Issue The Role of Halo Substructure in Gamma-Ray Dark Matter Searches)

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54 pages, 9674 KiB

Open AccessReview

Dark Matter Haloes and Subhaloes

by Jesús Zavala and Carlos S. Frenk

Galaxies 2019, 7(4), 81; https://doi.org/10.3390/galaxies7040081 - 25 Sep 2019

Cited by 103 | Viewed by 10618

Abstract

The development of methods and algorithms to solve the N-body problem for classical, collisionless, non-relativistic particles has made it possible to follow the growth and evolution of cosmic dark matter structures over most of the universe’s history. In the best-studied case—the cold [...] Read more.

The development of methods and algorithms to solve the N-body problem for classical, collisionless, non-relativistic particles has made it possible to follow the growth and evolution of cosmic dark matter structures over most of the universe’s history. In the best-studied case—the cold dark matter or CDM model—the dark matter is assumed to consist of elementary particles that had negligible thermal velocities at early times. Progress over the past three decades has led to a nearly complete description of the assembly, structure, and spatial distribution of dark matter haloes, and their substructure in this model, over almost the entire mass range of astronomical objects. On scales of galaxies and above, predictions from this standard CDM model have been shown to provide a remarkably good match to a wide variety of astronomical data over a large range of epochs, from the temperature structure of the cosmic background radiation to the large-scale distribution of galaxies. The frontier in this field has shifted to the relatively unexplored subgalactic scales, the domain of the central regions of massive haloes, and that of low-mass haloes and subhaloes, where potentially fundamental questions remain. Answering them may require: (i) the effect of known but uncertain baryonic processes (involving gas and stars), and/or (ii) alternative models with new dark matter physics. Here we present a review of the field, focusing on our current understanding of dark matter structure from N-body simulations and on the challenges ahead. Full article

(This article belongs to the Special Issue The Role of Halo Substructure in Gamma-Ray Dark Matter Searches)

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30 pages, 1694 KiB

Open AccessEditor’s ChoiceReview

Halo Substructure Boosts to the Signatures of Dark Matter Annihilation

by Shin’ichiro Ando, Tomoaki Ishiyama and Nagisa Hiroshima

Galaxies 2019, 7(3), 68; https://doi.org/10.3390/galaxies7030068 - 1 Jul 2019

Cited by 56 | Viewed by 4844

Abstract

The presence of dark matter substructure will boost the signatures of dark matter annihilation. We review recent progress on estimates of this subhalo boost factor—a ratio of the luminosity from annihilation in the subhalos to that originating the smooth component—based on both numerical [...] Read more.

The presence of dark matter substructure will boost the signatures of dark matter annihilation. We review recent progress on estimates of this subhalo boost factor—a ratio of the luminosity from annihilation in the subhalos to that originating the smooth component—based on both numerical N-body simulations and semi-analytic modelings. Since subhalos of all the scales, ranging from the Earth mass (as expected, e.g., the supersymmetric neutralino, a prime candidate for cold dark matter) to galaxies or larger, give substantial contribution to the annihilation rate, it is essential to understand subhalo properties over a large dynamic range of more than twenty orders of magnitude in masses. Even though numerical simulations give the most accurate assessment in resolved regimes, extrapolating the subhalo properties down in sub-grid scales comes with great uncertainties—a straightforward extrapolation yields a very large amount of the subhalo boost factor of ≳100 for galaxy-size halos. Physically motivated theoretical models based on analytic prescriptions such as the extended Press-Schechter formalism and tidal stripping modeling, which are well tested against the simulation results, predict a more modest boost of order unity for the galaxy-size halos. Giving an accurate assessment of the boost factor is essential for indirect dark matter searches and thus, having models calibrated at large ranges of host masses and redshifts, is strongly urged upon. Full article

(This article belongs to the Special Issue The Role of Halo Substructure in Gamma-Ray Dark Matter Searches)

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14 pages, 387 KiB

Open AccessReview

Radio-Frequency Searches for Dark Matter in Dwarf Galaxies

by Geoff Beck

Galaxies 2019, 7(1), 16; https://doi.org/10.3390/galaxies7010016 - 13 Jan 2019

Cited by 11 | Viewed by 3489

Abstract

Dwarf spheroidal galaxies have long been discussed as optimal targets for indirect dark matter searches. However, the majority of such studies have been conducted with gamma-ray instruments. In this review, we discuss the very recent progress that has been made in radio-based indirect [...] Read more.

Dwarf spheroidal galaxies have long been discussed as optimal targets for indirect dark matter searches. However, the majority of such studies have been conducted with gamma-ray instruments. In this review, we discuss the very recent progress that has been made in radio-based indirect dark matter searches. We look at existing work on this topic and discuss the future prospects that motivate continued work in this newly developing field that promises to become, in the light of the up-coming Square Kilometre Array, a prominent component of the hunt for dark matter. Full article

(This article belongs to the Special Issue The Role of Halo Substructure in Gamma-Ray Dark Matter Searches)

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