Special Issue "The Role of Halo Substructure in Gamma-Ray Dark Matter Searches"

A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (30 September 2019).

Special Issue Editors

Dr. Miguel A. Sánchez-Conde
E-Mail Website
Guest Editor
Institute for Theoretical Physics (IFT UAM/CSIC) and the Department of Theoretical Physics, Universidad Autónoma de Madrid, 28049 Madrid, Spain
Interests: gamma-ray dark matter searches; diffuse gamma-ray backgrounds; formation/evolution of CDM halos; CDM halo substructure; n-body cosmological simulations; large scale structure
Dr. Michele Doro
E-Mail Website
Guest Editor
Department of Physics and Astronomy G. GalileiVia Belzoni 7, I-35131 Padova (PD) Italy
Interests: gamma-ray astrophysics with MAGIC and CTA telescopes; dark matter searches with MAGIC and CTA; atmospheric calibration for IACTs

Special Issue Information

Dear Colleagues,

An important open question today is the understanding of the relevance that dark matter (DM) halo substructure may have for DM searches. In the standard cosmological framework, subhalos are predicted to be largely abundant inside larger halos, i.e., galaxies like ours, and are thought to form first and later merge to form larger structures. Dwarf satellite galaxies—the most massive exponents of halo substructure in our own galaxy—are already known to be excellent targets and, indeed, they are constantly scrutinized by current gamma-ray experiments in their search for DM annihilation signals. Lighter subhalos not massive enough to have a visible baryonic counterpart may be good targets as well given their typical number densities and distances. In addition, the clumpy distribution of subhalos residing in larger halos may boost the DM signals considerably.

In an era in which gamma-ray experiments possess, for the first time, the exciting potential of reaching the most relevant regions of the DM parameter space, a profound knowledge of the DM targets and scenarios being tested at present is mandatory if we aim for accurate predictions of DM-induced fluxes, for investing significant telescope observing time to selected targets, and for deriving robust conclusions from our DM search efforts. In this regard, a precise characterization of the statistical and structural properties of subhalos becomes critical.


With this Special Issue we aim to summarize where we stand today on our knowledge of the different aspects of the DM halo substructure; to identify what are the remaining big questions, how we could address these and, by doing so, to find new avenues for research. Thus, we welcome both review papers and focused research papers in the field. 

Some of the key topics that will be covered in this Special Issue of Galaxies are:

  • Formation and evolution of halo substructure: merging and accretion, survival and disruption.
  • Structural properties of subhalos. Subhalo DM density profiles, concentrations.
  • N-body cosmological simulations as a tool for understanding halo substructure.
  • Observations of dwarfs galaxies in the Milky Way. Current and upcoming surveys (DES, LSST...).
  • Indirect detection of DM in dwarf galaxies.
  • Search for ''dark satellites''. Unidentified gamma-ray sources.
  • Substructure boosts to DM annihilation signals.
  • Lensing as a probe of halo substructure.
  • Stellar gaps in stellar streams induced by DM subhalos.
Dr. Miguel A. Sánchez-Conde
Dr. Michele Doro
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Galaxies is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (7 papers)

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Research

Jump to: Review

Open AccessArticle
Gamma-Ray Sensitivity to Dark Matter Subhalo Modelling at High Latitudes
Galaxies 2019, 7(4), 90; https://doi.org/10.3390/galaxies7040090 - 26 Nov 2019
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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Open AccessArticle
Properties of Subhalos in the Interacting Dark Matter Scenario
Galaxies 2019, 7(4), 80; https://doi.org/10.3390/galaxies7040080 - 21 Sep 2019
Cited by 1
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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Open AccessArticle
Remnants of Galactic Subhalos and Their Impact on Indirect Dark-Matter Searches
Galaxies 2019, 7(2), 65; https://doi.org/10.3390/galaxies7020065 - 04 Jun 2019
Cited by 7
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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Open AccessArticle
γ-ray and ν Searches for Dark-Matter Subhalos in the Milky Way with a Baryonic Potential
Galaxies 2019, 7(2), 60; https://doi.org/10.3390/galaxies7020060 - 28 May 2019
Cited by 4
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

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Open AccessReview
Dark Matter Haloes and Subhaloes
Galaxies 2019, 7(4), 81; https://doi.org/10.3390/galaxies7040081 - 25 Sep 2019
Cited by 3
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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Open AccessReview
Halo Substructure Boosts to the Signatures of Dark Matter Annihilation
Galaxies 2019, 7(3), 68; https://doi.org/10.3390/galaxies7030068 - 01 Jul 2019
Cited by 9
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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Open AccessReview
Radio-Frequency Searches for Dark Matter in Dwarf Galaxies
Galaxies 2019, 7(1), 16; https://doi.org/10.3390/galaxies7010016 - 13 Jan 2019
Cited by 1
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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