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Gamma-rays from dark matter annihilations strongly constrain the substructure in halos
Stockholm University, Faculty of Science, Department of Physics. (The Oskar Klein Centre for Cosmoparticle Physics)
CITA, Toronto.
Stockholm University, Faculty of Science, Department of Physics. (The Oskar Klein Centre for Cosmoparticle Physics)
2009 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 18, 181302- p.Article in journal (Refereed) Published
Abstract [en]

Recently, it has been shown that electrons and positrons from dark matter (DM) annihilations provide an excellent fit to the Fermi, PAMELA, and HESS data. Using this DM model, which requires an enhancement of the annihilation cross section over its standard value to match the observations, we show that it immediately implies an observable level of gamma-ray emission for the Fermi telescope from nearby galaxy clusters such as Virgo and Fornax. We show that this DM model implies a peculiar feature from final state radiation that is a distinctive signature of DM. Using the EGRET upper limit on the gamma-ray emission from Virgo, we constrain the minimum mass of substructures within DM halos to be > 5x10^-3 M_sun -- about four orders of magnitudes larger than the expectation for cold dark matter. This limits the cutoff scale in the linear matter power spectrum to k < 35/kpc which can be explained by e.g., warm dark matter. Very near future Fermi observations will strongly constrain the minimum mass to be > 10^3 M_sun: if the true substructure cutoff is much smaller than this, the DM interpretation of the Fermi/PAMELA/HESS data must be wrong. To address the problem of astrophysical foregrounds, we performed high-resolution, cosmological simulations of galaxy clusters that include realistic cosmic ray (CR) physics. We compute the dominating gamma-ray emission signal resulting from hadronic CR interactions and find that it follows a universal spectrum and spatial distribution. If we neglect the anomalous enhancement factor and assume standard values for the cross section and minimum subhalo mass, the same model of DM predicts comparable levels of the gamma-ray emission from DM annihilations and CR interactions. This suggests that spectral subtraction techniques could be applied to detect the annihilation signal.

Place, publisher, year, edition, pages
2009. Vol. 103, no 18, 181302- p.
National Category
Subatomic Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-32501DOI: 10.1103/PhysRevLett.103.181302ISI: 000271352400009OAI: oai:DiVA.org:su-32501DiVA: diva2:280758
Available from: 2010-01-25 Created: 2009-12-11 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Gamma-Ray Emission from Galaxy Clusters: DARK MATTER AND COSMIC-RAYS
Open this publication in new window or tab >>Gamma-Ray Emission from Galaxy Clusters: DARK MATTER AND COSMIC-RAYS
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The quest for the first detection of a galaxy cluster in the high energy gamma-ray regime is ongoing, and even though clusters are observed in several other wave-bands, there is still no firm detection in gamma-rays.

To complement the observational efforts we estimate the gamma-ray contributions from both annihilating dark matter and cosmic-ray (CR) proton as well as CR electron induced emission.

Using high-resolution simulations of galaxy clusters, we find a universal concave shaped CR proton spectrum independent of the simulated galaxy cluster. Specifically, the gamma-ray spectra from decaying neutral pions, which are produced by CR protons, dominate the cluster emission. Furthermore, based on our derived flux and luminosity functions, we identify the galaxy clusters with the brightest galaxy clusters in gamma-rays. While this emission is challenging to detect using the Fermi satellite, major observations with Cherenkov telescopes in the near future may put important constraints on the CR physics in clusters.

To extend these predictions, we use a dark matter model that fits the recent electron and positron data from Fermi, PAMELA, and H.E.S.S. with remarkable precision, and make predictions about the expected gamma-ray flux from nearby clusters. In order to remain consistent with the EGRET upper limit on the gamma-ray emission from Virgo, we constrain the minimum mass of substructures for cold dark matter halos. In addition, we find comparable levels of gamma-ray emission from CR interactions and dark matter annihilations without Sommerfeld enhancement.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2010. 117 p.
Keyword
Galaxy clusters, gamma-rays, cosmic-rays, dark matter
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-42453 (URN)978-91-7447-141-0 (ISBN)
Public defence
2010-10-01, FB53, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted.Available from: 2010-09-09 Created: 2010-08-31 Last updated: 2010-09-03Bibliographically approved

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