Probing Non-thermal Cluster Emission with Gamma-Ray and Radio Data

Tesla JeltemaUniversity of California, Santa Cruz

Cosmic Rays: accelerated in accretion and merger shocks, AGN, and supernovae

- CR protons can survive for a long time- CR electrons lose energy quickly

Dark Matter: annihilation or decay of WIMPs to Standard Model particles Star Formation: emission associated to cosmic rays accelerated by supernovae in cluster galaxies

AGN: (not discussed here)

Non-Thermal Emission - Sources

Non-Thermal Emission - Mechanisms

Cosmic Rays

Hadronic production

or

turbulent reacceleration of lower energy e-

Dark Matter

or

(models for positron fraction)

Non-Thermal Emission - Observations

Emission from synchrotron (radio), IC scattering of CMB (X-ray or gamma-ray), and π0 decay (gamma-ray).

Radio: Mpc scale radio emission insome, but not all clusters

implies active e- production over a large area limits e- production in non-detections

Gamma-ray: diffuse emission not yet found

limits CR protons, dark matter, and total star formation

Preliminary

Zimmer for Fermi-LAT, TeV PA 2011

Constraints - Cosmic Rays The Fermi non-detection of clusters implies:

low cosmic ray densities of < 1-10% of the thermal energy density in nearby clusters.

high B fields in the hadronic model of radio halos. Turbulent acceleration model preferred.

Fermi limits to low CR densities and high magnetic fields

Jeltema & Profumo 2011

Constraints - Dark Matter The non-detection of both radio and gamma-ray emission limits the DM annihilation cross-section

conservative limits exclude thermal cross-section for low DM mass

excludes much of parameter space fitting e+ excess

Storm, Jeltema, Profumo, & Rudnick 2013

NFW only

best Fermi cluster limits

Example Radio Limits Example Fermi Limits

Ackermann et al. 2010

Star Formation - Predictions

Storm, Jeltema, & Profumo 2012

Gamma-ray luminosity correlates strongly with star formation rate (total IR or radio luminosity) for galaxies

Gives predicted minimum gamma-ray emission from cluster galaxies.

Ackermann et al. 2012

Star formation should account for at least 10% of gamma-ray emission from some clusters.