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Title: Constraints on dark matter annihilation in clusters of galaxies with the Fermi large area telescope

Abstract

Nearby clusters and groups of galaxies are potentially bright sources of high-energy gamma-ray emission resulting from the pair-annihilation of dark matter particles. However, no significant gamma-ray emission has been detected so far from clusters in the first 11 months of observations with the Fermi Large Area Telescope. We interpret this non-detection in terms of constraints on dark matter particle properties. In particular for leptonic annihilation final states and particle masses greater than ~ 200 GeV, gamma-ray emission from inverse Compton scattering of CMB photons is expected to dominate the dark matter annihilation signal from clusters, and our gamma-ray limits exclude large regions of the parameter space that would give a good fit to the recent anomalous Pamela and Fermi-LAT electron-positron measurements. We also present constraints on the annihilation of more standard dark matter candidates, such as the lightest neutralino of supersymmetric models. The constraints are particularly strong when including the fact that clusters are known to contain substructure at least on galaxy scales, increasing the expected gamma-ray flux by a factor of ~ 5 over a smooth-halo assumption. Here, we also explore the effect of uncertainties in cluster dark matter density profiles, finding a systematic uncertainty in the constraints ofmore » roughly a factor of two, but similar overall conclusions. Finally, in this work, we focus on deriving limits on dark matter models; a more general consideration of the Fermi-LAT data on clusters and clusters as gamma-ray sources is forthcoming.« less

Authors:
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Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
Contributing Org.:
The Fermi-LAT Collaboration
OSTI Identifier:
1357563
Grant/Contract Number:  
AC02-76SF00515
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Cosmology and Astroparticle Physics
Additional Journal Information:
Journal Volume: 2010; Journal Issue: 05; Journal ID: ISSN 1475-7516
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; gamma ray experiments; galaxy clusters; supersymmetry and cosmology; dark energy theory

Citation Formats

Ackermann, M., Ajello, M., Allafort, A., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bechtol, K., Bellazzini, R., Blandford, R. D., Bloom, E. D., Bonamente, E., Borgland, A. W., Bouvier, A., Brandt, T. J., Bregeon, J., Brigida, M., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caraveo, P. A., Carrigan, S., Casandjian, J. M., Cecchi, C., Charles, E., Chekhtman, A., Cheung, C. C., Chiang, J., Ciprini, S., Claus, R., Cohen-Tanugi, J., Cominsky, L. R., Conrad, J., Angelis, A. de, Palma, F. de, Silva, E. do Couto e., Drell, P. S., Drlica-Wagner, A., Dubois, R., Dumora, D., Edmonds, Y., Farnier, C., Favuzzi, C., Fegan, S. J., Frailis, M., Fukazawa, Y., Fusco, P., Gargano, F., Gasparrini, D., Gehrels, N., Germani, S., Giglietto, N., Giordano, F., Glanzman, T., Godfrey, G., Grenier, I. A., Guiriec, S., Gustafsson, M., Harding, A. K., Hayashida, M., Horan, D., Hughes, R. E., Jeltema, T. E., Jóhannesson, G., Johnson, A. S., Johnson, W. N., Kamae, T., Katagiri, H., Kataoka, J., Knödlseder, J., Kuss, M., Lande, J., Latronico, L., Lee, S. -H, Garde, M. Llena, Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Madejski, G. M., Makeev, A., Mazziotta, M. N., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Moiseev, A. A., Monte, C., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nolan, P. L., Norris, J. P., Nuss, E., Ohno, M., Ohsugi, T., Omodei, N., Orlando, E., Ormes, J. F., Panetta, J. H., Pepe, M., Pesce-Rollins, M., Piron, F., Porter, T. A., Profumo, S., Rainò, S., Razzano, M., Reposeur, T., Ritz, S., Rodriguez, A. Y., Roth, M., Sadrozinski, H. F. -W, Sander, A., Scargle, J. D., Sgrò, C., Siskind, E. J., Smith, P. D., Spandre, G., Spinelli, P., Starck, J. -L, Strickman, M. S., Suson, D. J., Takahashi, H., Tanaka, T., Thayer, J. B., Thayer, J. G., Tibaldo, L., Torres, D. F., Tosti, G., Usher, T. L., Vasileiou, V., Vitale, V., Waite, A. P., Wang, P., Winer, B. L., Wood, K. S., Yang, Z., Ylinen, T., and Ziegler, M. Constraints on dark matter annihilation in clusters of galaxies with the Fermi large area telescope. United States: N. p., 2010. Web. doi:10.1088/1475-7516/2010/05/025.
Ackermann, M., Ajello, M., Allafort, A., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bechtol, K., Bellazzini, R., Blandford, R. D., Bloom, E. D., Bonamente, E., Borgland, A. W., Bouvier, A., Brandt, T. J., Bregeon, J., Brigida, M., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caraveo, P. A., Carrigan, S., Casandjian, J. M., Cecchi, C., Charles, E., Chekhtman, A., Cheung, C. C., Chiang, J., Ciprini, S., Claus, R., Cohen-Tanugi, J., Cominsky, L. R., Conrad, J., Angelis, A. de, Palma, F. de, Silva, E. do Couto e., Drell, P. S., Drlica-Wagner, A., Dubois, R., Dumora, D., Edmonds, Y., Farnier, C., Favuzzi, C., Fegan, S. J., Frailis, M., Fukazawa, Y., Fusco, P., Gargano, F., Gasparrini, D., Gehrels, N., Germani, S., Giglietto, N., Giordano, F., Glanzman, T., Godfrey, G., Grenier, I. A., Guiriec, S., Gustafsson, M., Harding, A. K., Hayashida, M., Horan, D., Hughes, R. E., Jeltema, T. E., Jóhannesson, G., Johnson, A. S., Johnson, W. N., Kamae, T., Katagiri, H., Kataoka, J., Knödlseder, J., Kuss, M., Lande, J., Latronico, L., Lee, S. -H, Garde, M. Llena, Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Madejski, G. M., Makeev, A., Mazziotta, M. N., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Moiseev, A. A., Monte, C., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nolan, P. L., Norris, J. P., Nuss, E., Ohno, M., Ohsugi, T., Omodei, N., Orlando, E., Ormes, J. F., Panetta, J. H., Pepe, M., Pesce-Rollins, M., Piron, F., Porter, T. A., Profumo, S., Rainò, S., Razzano, M., Reposeur, T., Ritz, S., Rodriguez, A. Y., Roth, M., Sadrozinski, H. F. -W, Sander, A., Scargle, J. D., Sgrò, C., Siskind, E. J., Smith, P. D., Spandre, G., Spinelli, P., Starck, J. -L, Strickman, M. S., Suson, D. J., Takahashi, H., Tanaka, T., Thayer, J. B., Thayer, J. G., Tibaldo, L., Torres, D. F., Tosti, G., Usher, T. L., Vasileiou, V., Vitale, V., Waite, A. P., Wang, P., Winer, B. L., Wood, K. S., Yang, Z., Ylinen, T., & Ziegler, M. Constraints on dark matter annihilation in clusters of galaxies with the Fermi large area telescope. United States. doi:10.1088/1475-7516/2010/05/025.
Ackermann, M., Ajello, M., Allafort, A., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bechtol, K., Bellazzini, R., Blandford, R. D., Bloom, E. D., Bonamente, E., Borgland, A. W., Bouvier, A., Brandt, T. J., Bregeon, J., Brigida, M., Bruel, P., Buehler, R., Buson, S., Caliandro, G. A., Cameron, R. A., Caraveo, P. A., Carrigan, S., Casandjian, J. M., Cecchi, C., Charles, E., Chekhtman, A., Cheung, C. C., Chiang, J., Ciprini, S., Claus, R., Cohen-Tanugi, J., Cominsky, L. R., Conrad, J., Angelis, A. de, Palma, F. de, Silva, E. do Couto e., Drell, P. S., Drlica-Wagner, A., Dubois, R., Dumora, D., Edmonds, Y., Farnier, C., Favuzzi, C., Fegan, S. J., Frailis, M., Fukazawa, Y., Fusco, P., Gargano, F., Gasparrini, D., Gehrels, N., Germani, S., Giglietto, N., Giordano, F., Glanzman, T., Godfrey, G., Grenier, I. A., Guiriec, S., Gustafsson, M., Harding, A. K., Hayashida, M., Horan, D., Hughes, R. E., Jeltema, T. E., Jóhannesson, G., Johnson, A. S., Johnson, W. N., Kamae, T., Katagiri, H., Kataoka, J., Knödlseder, J., Kuss, M., Lande, J., Latronico, L., Lee, S. -H, Garde, M. Llena, Longo, F., Loparco, F., Lovellette, M. N., Lubrano, P., Madejski, G. M., Makeev, A., Mazziotta, M. N., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Moiseev, A. A., Monte, C., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Nolan, P. L., Norris, J. P., Nuss, E., Ohno, M., Ohsugi, T., Omodei, N., Orlando, E., Ormes, J. F., Panetta, J. H., Pepe, M., Pesce-Rollins, M., Piron, F., Porter, T. A., Profumo, S., Rainò, S., Razzano, M., Reposeur, T., Ritz, S., Rodriguez, A. Y., Roth, M., Sadrozinski, H. F. -W, Sander, A., Scargle, J. D., Sgrò, C., Siskind, E. J., Smith, P. D., Spandre, G., Spinelli, P., Starck, J. -L, Strickman, M. S., Suson, D. J., Takahashi, H., Tanaka, T., Thayer, J. B., Thayer, J. G., Tibaldo, L., Torres, D. F., Tosti, G., Usher, T. L., Vasileiou, V., Vitale, V., Waite, A. P., Wang, P., Winer, B. L., Wood, K. S., Yang, Z., Ylinen, T., and Ziegler, M. Thu . "Constraints on dark matter annihilation in clusters of galaxies with the Fermi large area telescope". United States. doi:10.1088/1475-7516/2010/05/025. https://www.osti.gov/servlets/purl/1357563.
@article{osti_1357563,
title = {Constraints on dark matter annihilation in clusters of galaxies with the Fermi large area telescope},
author = {Ackermann, M. and Ajello, M. and Allafort, A. and Baldini, L. and Ballet, J. and Barbiellini, G. and Bastieri, D. and Bechtol, K. and Bellazzini, R. and Blandford, R. D. and Bloom, E. D. and Bonamente, E. and Borgland, A. W. and Bouvier, A. and Brandt, T. J. and Bregeon, J. and Brigida, M. and Bruel, P. and Buehler, R. and Buson, S. and Caliandro, G. A. and Cameron, R. A. and Caraveo, P. A. and Carrigan, S. and Casandjian, J. M. and Cecchi, C. and Charles, E. and Chekhtman, A. and Cheung, C. C. and Chiang, J. and Ciprini, S. and Claus, R. and Cohen-Tanugi, J. and Cominsky, L. R. and Conrad, J. and Angelis, A. de and Palma, F. de and Silva, E. do Couto e. and Drell, P. S. and Drlica-Wagner, A. and Dubois, R. and Dumora, D. and Edmonds, Y. and Farnier, C. and Favuzzi, C. and Fegan, S. J. and Frailis, M. and Fukazawa, Y. and Fusco, P. and Gargano, F. and Gasparrini, D. and Gehrels, N. and Germani, S. and Giglietto, N. and Giordano, F. and Glanzman, T. and Godfrey, G. and Grenier, I. A. and Guiriec, S. and Gustafsson, M. and Harding, A. K. and Hayashida, M. and Horan, D. and Hughes, R. E. and Jeltema, T. E. and Jóhannesson, G. and Johnson, A. S. and Johnson, W. N. and Kamae, T. and Katagiri, H. and Kataoka, J. and Knödlseder, J. and Kuss, M. and Lande, J. and Latronico, L. and Lee, S. -H and Garde, M. Llena and Longo, F. and Loparco, F. and Lovellette, M. N. and Lubrano, P. and Madejski, G. M. and Makeev, A. and Mazziotta, M. N. and Michelson, P. F. and Mitthumsiri, W. and Mizuno, T. and Moiseev, A. A. and Monte, C. and Monzani, M. E. and Morselli, A. and Moskalenko, I. V. and Murgia, S. and Nolan, P. L. and Norris, J. P. and Nuss, E. and Ohno, M. and Ohsugi, T. and Omodei, N. and Orlando, E. and Ormes, J. F. and Panetta, J. H. and Pepe, M. and Pesce-Rollins, M. and Piron, F. and Porter, T. A. and Profumo, S. and Rainò, S. and Razzano, M. and Reposeur, T. and Ritz, S. and Rodriguez, A. Y. and Roth, M. and Sadrozinski, H. F. -W and Sander, A. and Scargle, J. D. and Sgrò, C. and Siskind, E. J. and Smith, P. D. and Spandre, G. and Spinelli, P. and Starck, J. -L and Strickman, M. S. and Suson, D. J. and Takahashi, H. and Tanaka, T. and Thayer, J. B. and Thayer, J. G. and Tibaldo, L. and Torres, D. F. and Tosti, G. and Usher, T. L. and Vasileiou, V. and Vitale, V. and Waite, A. P. and Wang, P. and Winer, B. L. and Wood, K. S. and Yang, Z. and Ylinen, T. and Ziegler, M.},
abstractNote = {Nearby clusters and groups of galaxies are potentially bright sources of high-energy gamma-ray emission resulting from the pair-annihilation of dark matter particles. However, no significant gamma-ray emission has been detected so far from clusters in the first 11 months of observations with the Fermi Large Area Telescope. We interpret this non-detection in terms of constraints on dark matter particle properties. In particular for leptonic annihilation final states and particle masses greater than ~ 200 GeV, gamma-ray emission from inverse Compton scattering of CMB photons is expected to dominate the dark matter annihilation signal from clusters, and our gamma-ray limits exclude large regions of the parameter space that would give a good fit to the recent anomalous Pamela and Fermi-LAT electron-positron measurements. We also present constraints on the annihilation of more standard dark matter candidates, such as the lightest neutralino of supersymmetric models. The constraints are particularly strong when including the fact that clusters are known to contain substructure at least on galaxy scales, increasing the expected gamma-ray flux by a factor of ~ 5 over a smooth-halo assumption. Here, we also explore the effect of uncertainties in cluster dark matter density profiles, finding a systematic uncertainty in the constraints of roughly a factor of two, but similar overall conclusions. Finally, in this work, we focus on deriving limits on dark matter models; a more general consideration of the Fermi-LAT data on clusters and clusters as gamma-ray sources is forthcoming.},
doi = {10.1088/1475-7516/2010/05/025},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 05,
volume = 2010,
place = {United States},
year = {2010},
month = {5}
}

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Works referenced in this record:

Multi-frequency analysis of neutralino dark matter annihilations in the Coma cluster
journal, July 2006


Gamma rays from clusters and groups of galaxies: Cosmic rays versus dark matter
journal, July 2009


Gamma Rays from Dark Matter Annihilations Strongly Constrain the Substructure in Halos
journal, October 2009


An anomalous positron abundance in cosmic rays with energies 1.5–100 GeV
journal, April 2009

  • Adriani, O.; Barbarino, G. C.; Bazilevskaya, G. A.
  • Nature, Vol. 458, Issue 7238
  • DOI: 10.1038/nature07942

Measurement of the Cosmic Ray e + + e Spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope
journal, May 2009


Energy Spectrum of Cosmic-Ray Electrons at TeV Energies
journal, December 2008


On possible interpretations of the high energy electron–positron spectrum measured by the Fermi Large Area Telescope
journal, September 2009


Dark Matter Interpretation of Recent Electron and Positron Data
journal, July 2009


Dark Matter interpretations of the excesses after FERMI
journal, May 2010


FERMI DISCOVERY OF GAMMA-RAY EMISSION FROM NGC 1275
journal, June 2009


FERMI LARGE AREA TELESCOPE GAMMA-RAY DETECTION OF THE RADIO GALAXY M87
journal, November 2009


The Mass Function of an X‐Ray Flux–limited Sample of Galaxy Clusters
journal, March 2002

  • Reiprich, Thomas H.; Bohringer, Hans
  • The Astrophysical Journal, Vol. 567, Issue 2
  • DOI: 10.1086/338753

Statistics of X-ray observables for the cooling-core and non-cooling core galaxy clusters
journal, April 2007


OBSERVATIONS OF MILKY WAY DWARF SPHEROIDAL GALAXIES WITH THE FERMI -LARGE AREA TELESCOPE DETECTOR AND CONSTRAINTS ON DARK MATTER MODELS
journal, February 2010


THE LARGE AREA TELESCOPE ON THE FERMI GAMMA-RAY SPACE TELESCOPE MISSION
journal, May 2009


Parameter estimation in astronomy through application of the likelihood ratio
journal, March 1979


The Likelihood Analysis of EGRET Data
journal, April 1996

  • Mattox, J. R.; Bertsch, D. L.; Chiang, J.
  • The Astrophysical Journal, Vol. 461
  • DOI: 10.1086/177068

Fitting the gamma-ray spectrum from dark matter with DMFIT: GLAST and the galactic center region
journal, November 2008


Searching for Dark Matter with X‐Ray Observations of Local Dwarf Galaxies
journal, October 2008

  • Jeltema, T. E.; Profumo, S.
  • The Astrophysical Journal, Vol. 686, Issue 2
  • DOI: 10.1086/591495

Fermi Large Area Telescope Measurements of the Diffuse Gamma-Ray Emission at Intermediate Galactic Latitudes
journal, December 2009


A Universal Density Profile from Hierarchical Clustering
journal, December 1997

  • Navarro, Julio F.; Frenk, Carlos S.; White, Simon D. M.
  • The Astrophysical Journal, Vol. 490, Issue 2
  • DOI: 10.1086/304888

The X‐Ray Concentration–Virial Mass Relation
journal, July 2007

  • Buote, David A.; Gastaldello, Fabio; Humphrey, Philip J.
  • The Astrophysical Journal, Vol. 664, Issue 1
  • DOI: 10.1086/518684

TeV γ -rays and the largest masses and annihilation cross sections of neutralino dark matter
journal, November 2005


FIVE-YEAR WILKINSON MICROWAVE ANISOTROPY PROBE OBSERVATIONS: COSMOLOGICAL INTERPRETATION
journal, February 2009

  • Komatsu, E.; Dunkley, J.; Nolta, M. R.
  • The Astrophysical Journal Supplement Series, Vol. 180, Issue 2
  • DOI: 10.1088/0067-0049/180/2/330

Magic Gamma-Ray Telescope Observation of the Perseus Cluster of Galaxies: Implications for Cosmic Rays, dark Matter, and ngc 1275
journal, January 2010


Fermi Large Area Telescope Search for Photon Lines from 30 to 200 GeV and Dark Matter Implications
journal, March 2010


Clumps and streams in the local dark matter distribution
journal, August 2008


The Aquarius Project: the subhaloes of galactic haloes
journal, December 2008


What Mass Are the Smallest Protohalos?
journal, July 2006


Thermal decoupling of WIMPs from first principles
journal, April 2007


Particle models and the small-scale structure of dark matter
journal, October 2009


The Dark Matter Annihilation Signal from Galactic Substructure: Predictions for GLAST
journal, October 2008

  • Kuhlen, Michael; Diemand, Jürg; Madau, Piero
  • The Astrophysical Journal, Vol. 686, Issue 1
  • DOI: 10.1086/590337

The first WIMPy halos
journal, August 2005

  • Green, Anne M.; Hofmann, Stefan; Schwarz, Dominik J.
  • Journal of Cosmology and Astroparticle Physics, Vol. 2005, Issue 08
  • DOI: 10.1088/1475-7516/2005/08/003

The subhalo populations of ΛCDM dark haloes
journal, December 2004


The Mass of the Coma Cluster from Weak Lensing in the Sloan Digital Sky Survey
journal, December 2007

  • Kubo, Jeffrey M.; Stebbins, Albert; Annis, James
  • The Astrophysical Journal, Vol. 671, Issue 2
  • DOI: 10.1086/523101

Dark matter distribution in the Coma cluster from galaxy kinematics: breaking the mass–anisotropy degeneracy
journal, August 2003


The dark matter halo of NGC 1399 – CDM or MOND?
journal, December 2007


Dynamics of the Globular Cluster System Associated with M49 (NGC 4472): Cluster Orbital Properties and the Distribution of Dark Matter
journal, July 2003

  • Cote, Patrick; McLaughlin, Dean E.; Cohen, Judith G.
  • The Astrophysical Journal, Vol. 591, Issue 2
  • DOI: 10.1086/375488

Resolving the Structure of Cold Dark Matter Halos
journal, May 1998

  • Moore, B.; Governato, F.; Quinn, T.
  • The Astrophysical Journal, Vol. 499, Issue 1
  • DOI: 10.1086/311333

    Works referencing / citing this record:

    Search for γ -ray emission from dark matter particle interactions from the Andromeda and Triangulum galaxies with the Fermi Large Area Telescope
    journal, June 2019


    A stacked analysis of brightest cluster galaxies observed with the Fermi Large Area Telescope
    journal, December 2012

    • Dutson, K. L.; White, R. J.; Edge, A. C.
    • Monthly Notices of the Royal Astronomical Society, Vol. 429, Issue 3
    • DOI: 10.1093/mnras/sts477

    γ -rays from annihilating dark matter in galaxy clusters: stacking versus single source analysis: Gamma-rays from dark matter in clusters
    journal, July 2012


    Constraining extended gamma-ray emission from galaxy clusters: Extended gamma-ray emission in clusters
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    The impact of recent advances in laboratory astrophysics on our understanding of the cosmos
    journal, February 2012


    Improved constraints on the primordial power spectrum at small scales from ultracompact minihalos
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    The impact of recent advances in laboratory astrophysics on our understanding of the cosmos
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    A stacked analysis of brightest cluster galaxies observed with the Fermi Large Area Telescope
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    • Dutson, K. L.; White, R. J.; Edge, A. C.
    • Monthly Notices of the Royal Astronomical Society, Vol. 429, Issue 3
    • DOI: 10.1093/mnras/sts477

    Improved constraints on the primordial power spectrum at small scales from ultracompact minihalos
    journal, June 2012


    Search for γ -ray emission from dark matter particle interactions from the Andromeda and Triangulum galaxies with the Fermi Large Area Telescope
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    γ -rays from annihilating dark matter in galaxy clusters: stacking versus single source analysis: Gamma-rays from dark matter in clusters
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