scholarly journals Latest results on dark matter searches with H.E.S.S

2019 ◽  
Vol 209 ◽  
pp. 01023 ◽  
Author(s):  
Lucia Rinchiuso
Keyword(s):  
Dark Matter ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Mass Range ◽  
High Energy ◽  
Galactic Centre ◽  
Final States ◽  
Cherenkov Telescopes ◽  
Observation Strategy ◽  
Very High Energy

The nature of Dark Matter (DM) is one of the most debated questions of contemporary physics. Ground-based arrays of Cherenkov telescopes such as the High Energy Spectroscopic System (H.E.S.S.) search for DM signatures through the detection of Very-High-Energy (VHE, E > 100 GeV) gamma-rays. DM particles could selfannihilate in dense environments producing VHE γ-rays in the final states that could be eventually detected by H.E.S.S.. The H.E.S.S. observation strategy for DM search focuses towards the Galactic Centre (GC) region and nearby dwarf galaxy satellites of the Milky Way. The GC dataset provides the most stringent constraints on the DM annihilation cross section in the mass range 300 GeV - 70 TeV. Searches have been carried out towards classical and ultra-faint dwarf galaxies to test specific heavy DM models. The latest results towards the GC and dwarf galaxies are shown.

scholarly journals The MUSE-Faint survey

2020 ◽  
Vol 635 ◽  
pp. A107
Author(s):  
Sebastiaan L. Zoutendijk ◽  
Jarle Brinchmann ◽  
Leindert A. Boogaard ◽  
Madusha L. P. Gunawardhana ◽  
Tim-Oliver Husser ◽  
...  
Keyword(s):  
Dark Matter ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Mass Range ◽  
Line Of Sight ◽  
Large Telescope ◽  
Stellar Cluster ◽  
Set Constraints ◽  
Very Large Telescope ◽  
Intrinsic Mean

Aims. It has been shown that the ultra-faint dwarf galaxy Eridanus 2 may host a stellar cluster in its centre. If this cluster is shown to exist, it can be used to set constraints on the mass and abundance of massive astrophysical compact halo objects (MACHOs) as a form of dark matter. Previous research has shown promising expectations in the mass range of 10−100 M⊙, but lacked spectroscopic measurements of the cluster. We aim to provide spectroscopic evidence regarding the nature of the putative star cluster in Eridanus 2 and to place constraints on MACHOs as a constituent of dark matter. Methods. We present spectroscopic observations of the central square arcminute of Eridanus 2 from MUSE-Faint, a survey of ultra-faint dwarf galaxies with the Multi Unit Spectroscopic Explorer on the Very Large Telescope. We derived line-of-sight velocities for possible member stars of the putative cluster and for stars in the centre of Eridanus 2. We discuss the existence of the cluster and determine new constraints for MACHOs using the Fokker–Planck diffusion approximation. Results. Out of 182 extracted spectra, we identify 26 member stars of Eridanus 2, seven of which are possible cluster members. We find intrinsic mean line-of-sight velocities of 79.7+3.1−3.8 km s−1 and 76.0+3.2−3.7 km s−1 for the cluster and the bulk of Eridanus 2, respectively, as well as intrinsic velocity dispersions of < 7.6 km s−1 (68% upper limit) and 10.3+3.9−3.2 km s−1, respectively. This indicates that the cluster most likely exists as a distinct dynamical population hosted by Eridanus 2 and that it does not have a surplus of dark matter over the background distribution. Among the member stars in the bulk of Eridanus 2, we find possible carbon stars, alluding to the existence of an intermediate-age population. We derived constraints on the fraction of dark matter that can consist of MACHOs with a given mass between 1 and 105 M⊙. For dark matter consisting purely of MACHOs, the mass of the MACHOs must be less than ∼7.6 M⊙ and ∼44 M⊙ at a 68- and 95% confidence level, respectively.

scholarly journals On the origin of the asymmetric dwarf galaxy distribution around andromeda

2019 ◽  
Vol 492 (1) ◽  
pp. 456-467
Author(s):  
Zhen Wan ◽  
William H Oliver ◽  
Geraint F Lewis ◽  
Justin I Read ◽  
Michelle L M Collins
Keyword(s):  
Milky Way ◽  
Dwarf Galaxies ◽  
Initial Conditions ◽  
Dwarf Galaxy ◽  
High Energy ◽  
Initial Position ◽  
Asymmetric Structures ◽  
Galaxy Distribution ◽  
Very High Energy ◽  
Radial Dispersion

ABSTRACT The dwarf galaxy distribution surrounding M31 is significantly anisotropic in nature. Of the 30 dwarf galaxies in this distribution, 15 form a disc-like structure and 23 are contained within the hemisphere facing the Milky Way. Using a realistic local potential, we analyse the conditions required to produce and maintain these asymmetries. We find that some dwarf galaxies are required to have highly eccentric orbits in order to preserve the presence of the hemispherical asymmetry with an appropriately large radial dispersion. Under the assumption that the dwarf galaxies originate from a single association or accretion event, we find that the initial size and specific energy of that association must both be relatively large in order to produce the observed hemispherical asymmetry. However if the association was large in physical size, the very high-energy required would enable several dwarf galaxies to escape from the M31 and be captured by the Milky Way. Furthermore, we find that associations that result in this structure have total specific energies concentrated around $E = V_{\rm esc}^{2} - V_{\rm init}^{2} \sim 200^2$ – $300^2\ \rm {km^2\ s^{-2}}$, implying that the initial velocity and initial position needed to produce the structure are strongly correlated. The overlap of initial conditions required to produce the radial dispersion, angular dispersion, and the planar structure is small and suggests that either they did not originate from a single accretion event, or that these asymmetric structures are short-lived.

scholarly journals NIHAO – XXV. Convergence in the cusp-core transformation of cold dark matter haloes at high star formation thresholds

2020 ◽  
Vol 499 (2) ◽  
pp. 2648-2661
Author(s):  
Aaron A Dutton ◽  
Tobias Buck ◽  
Andrea V Macciò ◽  
Keri L Dixon ◽  
Marvin Blank ◽  
...  
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Galaxy Formation ◽  
Cold Dark Matter ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Good Description ◽  
Good Match ◽  
Virial Mass ◽  
Density Threshold

ABSTRACT We use cosmological hydrodynamical galaxy formation simulations from the NIHAO project to investigate the response of cold dark matter (CDM) haloes to baryonic processes. Previous work has shown that the halo response is primarily a function of the ratio between galaxy stellar mass and total virial mass, and the density threshold above which gas is eligible to form stars, n[cm−3]. At low n all simulations in the literature agree that dwarf galaxy haloes are cuspy, but at high n ≳ 100 there is no consensus. We trace halo contraction in dwarf galaxies with n ≳ 100 reported in some previous simulations to insufficient spatial resolution. Provided the adopted star formation threshold is appropriate for the resolution of the simulation, we show that the halo response is remarkably stable for n ≳ 5, up to the highest star formation threshold that we test, n = 500. This free parameter can be calibrated using the observed clustering of young stars. Simulations with low thresholds n ≤ 1 predict clustering that is too weak, while simulations with high star formation thresholds n ≳ 5, are consistent with the observed clustering. Finally, we test the CDM predictions against the circular velocities of nearby dwarf galaxies. Low thresholds predict velocities that are too high, while simulations with n ∼ 10 provide a good match to the observations. We thus conclude that the CDM model provides a good description of the structure of galaxies on kpc scales provided the effects of baryons are properly captured.

scholarly journals Quantifying tidal stream disruption in a simulated Milky Way

2017 ◽  
Vol 470 (1) ◽  
pp. 522-538 ◽  
Author(s):  
Emily Sandford ◽  
Andreas H. W. Küpper ◽  
Kathryn V. Johnston ◽  
Jürg Diemand
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Galactic Halo ◽  
Mass Range ◽  
Galactic Centre ◽  
High Dimensions ◽  
Density Profiles ◽  
Upper Limits ◽  
Tidal Stream ◽  
Tidal Streams

Abstract Simulations of tidal streams show that close encounters with dark matter subhaloes induce density gaps and distortions in on-sky path along the streams. Accordingly, observing disrupted streams in the Galactic halo would substantiate the hypothesis that dark matter substructure exists there, while in contrast, observing collimated streams with smoothly varying density profiles would place strong upper limits on the number density and mass spectrum of subhaloes. Here, we examine several measures of stellar stream ‘disruption' and their power to distinguish between halo potentials with and without substructure and with different global shapes. We create and evolve a population of 1280 streams on a range of orbits in the Via Lactea II simulation of a Milky Way-like halo, replete with a full mass range of Λcold dark matter subhaloes, and compare it to two control stream populations evolved in smooth spherical and smooth triaxial potentials, respectively. We find that the number of gaps observed in a stellar stream is a poor indicator of the halo potential, but that (i) the thinness of the stream on-sky, (ii) the symmetry of the leading and trailing tails and (iii) the deviation of the tails from a low-order polynomial path on-sky (‘path regularity') distinguish between the three potentials more effectively. We furthermore find that globular cluster streams on low-eccentricity orbits far from the galactic centre (apocentric radius ∼30–80 kpc) are most powerful in distinguishing between the three potentials. If they exist, such streams will shortly be discoverable and mapped in high dimensions with near-future photometric and spectroscopic surveys.

scholarly journals The Making of Catalogues of Very-High-Energy γ-ray Sources

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 421
Author(s):  
Mathieu de Naurois
Keyword(s):  
Galactic Plane ◽  
Population Studies ◽  
High Energy ◽  
Cherenkov Telescopes ◽  
Background Rejection ◽  
Fine Grained ◽  
Very High Energy ◽  
Advanced Analysis ◽  
Γ Ray ◽  
Very High

Thirty years after the discovery of the first very-high-energy γ-ray source by the Whipple telescope, the field experienced a revolution mainly driven by the third generation of imaging atmospheric Cherenkov telescopes (IACTs). The combined use of large mirrors and the invention of the imaging technique at the Whipple telescope, stereoscopic observations, developed by the HEGRA array and the fine-grained camera, pioneered by the CAT telescope, led to a jump by a factor of more than ten in sensitivity. The advent of advanced analysis techniques led to a vast improvement in background rejection, as well as in angular and energy resolutions. Recent instruments already have to deal with a very large amount of data (petabytes), containing a large number of sources often very extended (at least within the Galactic plane) and overlapping each other, and the situation will become even more dramatic with future instruments. The first large catalogues of sources have emerged during the last decade, which required numerous, dedicated observations and developments, but also made the first population studies possible. This paper is an attempt to summarize the evolution of the field towards the building up of the source catalogues, to describe the first population studies already made possible, and to give some perspectives in the context of the upcoming, new generation of instruments.

scholarly journals Gamma-ray emission in radio galaxies, from MeV to TeV

2018 ◽  
Vol 14 (S342) ◽  
pp. 158-166
Author(s):  
Eleonora Torresi
Keyword(s):  
Gamma Ray ◽  
Radio Galaxies ◽  
High Energy ◽  
Cherenkov Telescopes ◽  
New Class ◽  
Very High Energy ◽  
Structure Complexity ◽  
The Impact ◽  
Jet Structure ◽  
Very High

AbstractThanks to the Fermi λ-ray satellite and the current Imaging Atmospheric Cherenkov Telescopes, radio galaxies have arisen as a new class of high- and very-high energy emitters. The favourable orientation of their jets makes radio galaxies extremely relevant in addressing important issues such as: (i) revealing the jet structure complexity; (ii) localising the emitting region(s) of high- and very-high energy radiation; (iii) understanding the physical processes producing these photons. In this review the main results on the λ-ray emission studies of radio galaxies from the MeV to TeV regimes will be presented, and the impact of future Cherenkov Telescope Array observations will be discussed.

scholarly journals In Pursuit of the Least Luminous Galaxies

2010 ◽  
Vol 2010 ◽  
pp. 1-11 ◽  
Author(s):  
Beth Willman
Keyword(s):  
Dark Matter ◽  
Milky Way ◽  
Field Survey ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Wide Field ◽  
Dark Matter Halos ◽  
The Past ◽  
Luminous Galaxies ◽  
Host Stars

The dwarf galaxy companions to the Milky Way are unique cosmological laboratories. With luminosities as low as10−7LMW, they inhabit the lowest mass dark matter halos known to host stars and are presently the most direct tracers of the distribution, mass spectrum, and clustering scale of dark matter. Their resolved stellar populations also facilitate detailed studies of their history and mass content. To fully exploit this potential requires a well-defined census of virtually invisible galaxies to the faintest possible limits and to the largest possible distances. I review the past and present impacts of survey astronomy on the census of Milky Way dwarf galaxy companions and discuss the future of finding ultra-faint dwarf galaxies around the Milky Way and beyond in wide-field survey data.

scholarly journals Way-out to the gravitino problem in intersecting D-brane Pati–Salam models

2016 ◽  
Vol 31 (19) ◽  
pp. 1650111 ◽  
Author(s):  
Andrea Addazi ◽  
Maxim Yu Khlopov
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
High Energy ◽  
Indirect Detection ◽  
Supersymmetric Particle ◽  
Cosmological Time ◽  
Neutrino Sector ◽  
Very High Energy ◽  
Very High ◽  
Parity Breaking

We discuss the gravitino problem in the context of the exotic see-saw mechanism for neutrinos and leptogenesis, UV completed by intersecting D-branes Pati–Salam models. In the exotic see-saw model, supersymmetry is broken at high scales M[Formula: see text] 109 GeV and this seems in contradiction with gravitino bounds from inflation and baryogenesis. However, if gravitino is the lightest stable supersymmetric particle, it will not decay into other SUSY particles, avoiding the gravitino problem and providing a good cold dark matter (CDM). Gravitini are super heavy dark particles and they can be produced by non-adiabatic expansion during inflation. Intriguingly, from bounds on the correct abundance of dark matter (DM), we also constrain the neutrino sector. We set a limit on the exotic instantonic coupling of [Formula: see text] 10[Formula: see text]–10[Formula: see text]. This also sets constrains on the Calabi–Yau compactifications and on the string scale. This model strongly motivates very high energy DM indirect detection of neutrini and photons of 10[Formula: see text]–10[Formula: see text] GeV: gravitini can decay on them in a cosmological time because of soft R-parity breaking effective operators.

scholarly journals Chemo-dynamical evolution of dwarf galaxies: from flat to cuspy dark matter density profiles

2009 ◽  
Vol 5 (H15) ◽  
pp. 78-78
Author(s):  
S. Pasetto ◽  
E. K. Grebel ◽  
P. Berczik ◽  
R. Spurzem
Keyword(s):  
Dark Matter ◽  
Dwarf Galaxies ◽  
Initial Conditions ◽  
Smooth Particle Hydrodynamic ◽  
Dynamical Evolution ◽  
Mass Range ◽  
Density Profiles ◽  
Hydrodynamic Approach ◽  
The Stability ◽  
Evolution With Time

A model of an isolated dwarf spherical galaxy (dSph) is considered in its chemo-dynamical evolution with time. The system is composed by 3 γ-model density profiles: gas, stellar and dark matter, and it is realized in a spherical symmetric equilibrium configuration. The total masses used in our simulations are covering the dwarf galaxies mass range. The stability of this configuration is first tested for the system evolving under the gravity effect alone and then evolved taking into account for the most relevant stellar astrophysical processes implemented with a Smooth Particle Hydrodynamic approach. The two different kinds of evolution are compared. The dark matter evolves naturally from a centrally cuspy density profile into a flatter one within a timescale of several Gyr. The effect manifests itself naturally, without any tuned initial conditions, as soon as few standard criteria on star formation are assumedand the SN feedback on the ISM has been adopted the prescription in (Cioffi & Shull 1991) and (Bradamante et al. 1998). This result is expected to be a possible natural explanation for the discrepancy between observations that want flatter dark matter profiles (e.g. de Block 2005), and N-body simulations that predict cuspy dark matter profiles (Navarro et al. 1997). Chemical considerations are presented as a tool to follow with observational parameters the theory predictions.

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