Molecular clouds as the origin of the Fermi Gamma-ray GeV excess - PowerPoint PPT Presentation

Molecular clouds as the origin of the Fermi Gamma-ray GeV excess July 18, 2017 ICRC 2017, Busan, Korea Iris Gebauer , Peter L. Biermann, Wim de Boer, Leo Bosse, Alexander Neumann INSTITUT FÜR EXPERIMENTELLE KERNPHYSIK KIT – Universität des Landes Baden-Württemberg und Software-Entwurf und -Qualität 9/22/12 1 www.kit.edu nationales Forschungszentrum in der Helmholtz-Gemeinschaft Institut für Programmstrukturen und Datenorganisation

THE FERMI GEV EXCESS Daylan et al. Calore et al., 1402.6703 1411.4647 Spectral shape of excess Spatial distribution in latitude compatible with 35 GeV DM compatible with generalized particle annihilating into bb. NFW profile July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 2 Institut für Experimentelle Kernphysik

USUAL APPROACH: SPATIAL TEMPLATES ● Calculate diffuse emission (π 0 , bremsstrahlung, inverse Compton) from spatial templates using models like Galprop or Dragon ● Based on astronomical data on gas distributions/ISRF → models do not describe galactic center well THIS STUDY: SPECTRAL TEMPLATES ● Calculate diffuse emission from spectral templates of known physical processes (π 0 , bremsstrahlung, inverse Compton), use local cosmic ray measurements and gamma-rays to determine interstellar cosmic ray spectra spectra. ● Derive spatial distribution of fit components from Fermi data. → allows to determine if new physical processes are required → fit is over-constrained July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 3 Institut für Experimentelle Kernphysik

PROPGATED COSMIC RAYS (PCR) Simplest possible approach: assume local cosmic ray spectra are representative for Galaxy → independent of transport model. Gamma-ray template Proton flux template Propagated cosmic rays (PCR): π 0 production by propagated cosmic ray protons in the diffuse interstellar medium, following an E -2.85 spectrum consistent with the AMS-02 data above 20 GV. July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 4 Institut für Experimentelle Kernphysik

BREMSSTRAHLUNG (BR) Electron flux template Gamma-ray template E -0.81 E -3.21 1 GeV Bremsstrahlung (BR): cosmic ray electrons emit bremsstrahlung in the interstellar gas. The interstellar electron spectrum follows E -3.21 , consistent with the AMS-02 data. Below 1 GeV, where ionization losses dominate, a harder spectrum of E -0.81 is required by the gamma-ray data. July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 5 Institut für Experimentelle Kernphysik

INVERSE COMPTON (IC) Gamma-ray template Electron flux template E -0.81 E -3.21 1 GeV Inverse Compton scattering (IC): photons from the interstellar radiation field (starlight, dust emission, CMB) scatter off cosmic ray electrons. July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 6 Institut für Experimentelle Kernphysik

SOURCE COSMIC RAYS (SCR) Proton flux template CRs accelerated in sources see high density gas in shock wave and surrounding ISM E -2.1 → expect copious π 0 production with a spectrum from 1/E 2.1 protons [Völk, Berezhko, 1309.3955, de Boer et al., 1407.4114, 1509.05310, Biermann et al. 1009.5592, Hillas, J. Phys. G31 (2005) 95] July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 7 Institut für Experimentelle Kernphysik

SOURCE COSMIC RAYS Gamma-ray template Proton flux template SCR spectrum E -2.1 agrees with Fermi bubbles. Source cosmic rays (SCR): π 0 production by freshly accelerated protons in the vicinity of cosmic ray sources, following a hard E -2.1 spectrum. The SCR template agrees with the Fermi bubbles shown as the blue band. July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 8 Institut für Experimentelle Kernphysik

MOLECULAR CLOUDS CO Skymap from Planck Satellite (by measurement of CO rotation lines) Central Molecular Total mass fraction Zone (CMZ) in MCs: ~ 40% Size CMZ: -1.5° < l < 2° -0.5° < b < 0.5° Mass CMZ: 5.10 7 M ʘ Molecular clouds are accompanied (Black hole GC: 4.10 6 M ʘ ) by strong magnetic fields July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 9 Institut für Experimentelle Kernphysik

MOLECULAR CLOUD COSMIC RAYS (MCR) Earth's magnetic field leads to position dependent cutoff of low rigidity cosmic rays. Geomagnetic cutoff in AMS-01 data. July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 10 Institut für Experimentelle Kernphysik

MOLECULAR CLOUD COSMIC RAYS (MCR) Earth's magnetic field leads to position dependent cutoff of low rigidity cosmic rays. proton spectrum outside clouds A similar effect is expected for molecular clouds: the magnetic moment of the cloudlets will prevent low rigidity cosmic rays from entering the dense cores. Only over-cutoff protons can enter the dense cores and produce π 0 . proton spectrum inside clouds July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 11 Institut für Experimentelle Kernphysik

MOLECULAR CLOUD COSMIC RAYS (MCR) Gamma-ray template Proton flux template Position dependent Above cutoff: cutoff [6GV, 14GV] MCR follows PCR due to magnetic spectrum deflection → no CR in MCs below cutoff Molecular cloud cosmic rays (MCR): π 0 production by propagated cosmic ray protons in the dense cores of molecular clouds. July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 12 Institut für Experimentelle Kernphysik

ALTERNATIVELY: TEST DARK MATTER HYPOTHESIS Gamma-ray template Alternatively, to test the Dark Matter (DM) hypothesis an additional gamma-ray template expected for a DM candidate with a mass of 45 GeV annihilating into bb quark pairs is used instead of the MCR template. July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 13 Institut für Experimentelle Kernphysik

RESULTS MC hypothesis Halo Scutum- Centaurus CMZ arm best fit for 45 GeV → bb DM hypothesis Halo Scutum- Centaurus arm CMZ July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 14 Institut für Experimentelle Kernphysik

RESULTS: DARK MATTER HYPOTHESIS vs MOLECULAR CLOUDS Molecular clouds DM: 45 GeV → bb 5 templates 5 templates + isotropic background + isotropic background + variable MC cutoff value July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 15 Institut für Experimentelle Kernphysik

THE MCR TEMPLATE DISTRIBUTION “GeV-excess” is longitudinally extended, tracing the rectangular shape of the Galactic bar July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 16 Institut für Experimentelle Kernphysik

CORRELATION BETWEEN MCR AND CO ROTATION LINES CO surveys are the primary way of identifying molecular clouds (low J transitions). We use the Planck measurements on the CO J CMZ 2 →1 emission. Planck 2013 results. XIII. Galactic CO emission”, Astron. Astrophys. Centaurus 571 (2014) A13 Cygnus arm Spiral arms The MCR template traces molecular clouds. Calore et al., Along latitude the GeV-excess shows 1411.4647 indeed the morphology of a generalized NFW profile. July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 17 Institut für Experimentelle Kernphysik

THE DM TEMPLATE DISTRIBUTION rectangular shape is incompatible with the expected spherical morphology of DM July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 18 Institut für Experimentelle Kernphysik

THE DM TEMPLATE DISTRIBUTION The DM sky map does not resemble the expected spherical DM halo profile but has a morphology similar to the CO sky map. July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 19 Institut für Experimentelle Kernphysik

THE SCR TEMPLATE DISTRIBUTION July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 20 Institut für Experimentelle Kernphysik

THE SCR TEMPLATE DISTRIBUTION SCR traces Spiral arms Fermi Bar [40..-30deg] bubbles, bar and spiral arms Cygnus Centaurus arm July 18th, Molecular clouds as the origin of the Fermi GeV-excess (contribution DM-035) Iris Gebauer 21 Institut für Experimentelle Kernphysik