Radiation fields in the Milky Way and their role in High-Energy Astrophysics Richard Tuffs, Ruizhi Yang, & Felix Aharonian (MPI-Kernphysik Heidelberg) Cristina Popescu & Giovanni Natale (Jeremiah Horrocks Institute, Preston) ESA, Planck HFI & LFI Consortia

External Galaxy (NGC 891) - 25 and 60 micron: Compact SF regions trace UV emissivity (especially 25 & 60 micron) - diffuse FIR traces luminosity of young and old stars (especially micron) => HE & VHE Inverse Compton - Diffuse submm traces dust (and gas) column (850 micron with Planck) => HE & VHE pion-decay emission

Radiation Transfer Calculation: Model Geometry (Generic) (follows Popescu et al. 2011)

- axisymmetric RT calculation with full treatment of anisotropic scattering and non-equilibrium thermal dust emission -RT in diffuse ISM uses dust model of Weingartner & Draine 2001 (calibrated on local Cirrus) - MIR/FIR/submm emission from SF regions described according to templates fixed empirically from observations of SF complexes in the Milky Way - A fraction F of UV allowed to freely escape from SF regions according to a geometric covering factor F - no use of CO and HI gas tracers - no use of stellar counts - Explicit fit of all geometric parameters, F and SFR and optical/NIR emissivities to dust emission in 850, 550, 350, 100, 60, 25 & 12 micron bands (Planck & IRAS) and to direct stellar light measured by COBE (4.5 – 1.2 micron) Popescu et al. (2000) silicate inner disk Silicate outer disk Graphite outer disk graphite inner disk

- axisymmetric RT calculation with full treatment of anisotropic scattering and non-equilibrium thermal dust emission -RT in diffuse ISM uses dust model of Weingartner & Draine 2001 (calibrated on local Cirrus) - MIR/FIR/submm emission from SF regions described according to templates fixed empirically from observations of SF complexes in the Milky Way - A fraction F of UV allowed to freely escape from SF regions according to a geometric covering factor F - no use of CO and HI gas tracers - no use of stellar counts - Explicit fit of all geometric parameters, F and SFR and optical/NIR emissivities to dust emission in 850, 550, 350, 100, 60, 25 & 12 micron bands (Planck & IRAS) and to direct stellar light measured by COBE (4.5 – 1.2 micron) Fit to High Latitude Cirrus (Popescu et al. 2011)

- axisymmetric RT calculation with full treatment of anisotropic scattering and non-equilibrium thermal dust emission -RT in diffuse ISM uses dust model of Weingartner & Draine 2001 (calibrated on local Cirrus) - MIR/FIR/submm emission from SF regions described according to templates fixed empirically from observations of SF complexes in the Milky Way - A fraction F of UV allowed to freely escape from SF regions according to a geometric covering factor F - no use of CO and HI gas tracers - no use of stellar counts - Explicit fit of all geometric parameters, F and SFR and optical/NIR emissivities to dust emission in 850, 550, 350, 100, 60, 25 & 12 micron bands (Planck & IRAS) and to direct stellar light measured by COBE (4.5 – 1.2 micron) Popescu et al. (2011)

- axisymmetric RT calculation with full treatment of anisotropic scattering and non-equilibrium thermal dust emission -RT in diffuse ISM uses dust model of Weingartner & Draine 2001 (calibrated on local Cirrus) - MIR/FIR/submm emission from SF regions described according to templates fixed empirically from observations of SF complexes in the Milky Way - A fraction F of UV allowed to freely escape from SF regions according to a geometric covering factor F - no use of CO and HI gas tracers - no use of stellar counts - Explicit fit of all geometric parameters, F and SFR and optical/NIR emissivities to dust emission in 850, 550, 350, 100, 60, 25 & 12 micron bands (Planck & IRAS) and to direct stellar light measured by COBE (4.5 – 1.2 micron)

- axisymmetric RT calculation with full treatment of anisotropic scattering and non-equilibrium thermal dust emission -RT in diffuse ISM uses dust model of Weingartner & Draine 2001 (calibrated on local Cirrus) - MIR/FIR/submm emission from SF regions described according to templates fixed empirically from observations of SF complexes in the Milky Way - A fraction F of UV allowed to freely escape from SF regions according to a geometric covering factor F - no use of CO and HI gas tracers - no use of stellar counts - Explicit fit of all geometric parameters, F and SFR and optical/NIR emissivities to dust emission in 850, 550, 350, 100, 60, 25 & 12 micron bands (Planck & IRAS) and to direct stellar light measured by COBE (4.5 – 1.2 micron) Green et al. (2015) Using 8 million stars (Pan-STARRS1)

- axisymmetric RT calculation with full treatment of anisotropic scattering and non-equilibrium thermal dust emission -RT in diffuse ISM uses dust model of Weingartner & Draine 2001 (calibrated on local Cirrus) - MIR/FIR/submm emission from SF regions described according to templates fixed empirically from observations of SF complexes in the Milky Way - A fraction F of UV allowed to freely escape from SF regions according to a geometric covering factor F - no use of CO and HI gas tracers - no use of stellar counts - Explicit fit of all geometric parameters, F and SFR and optical/NIR emissivities to dust emission in 850, 550, 350, 100, 60, 25 & 12 micron bands (Planck & IRAS) and to direct stellar light measured by COBE (4.5 – 1.2 micron)

60 micron 25 micron

Two dust disk structure found: (1) “Young” dust disk - scale length 3.5kpc - tapered: scale height varies from 50 to 80pc from R=0 to R=8kpc (2) “Old” dust disk - scale length 4.9kpc - constant scale height of 140pc Face-on opacity of both disks decreases from R=4.5 to R=0 850 micron

Predicted Total Flux Predicted local Interstellar Radiation Field

Solution for diffuse Interstellar Radiation Field

Comparison with GALPROP solution for radiation fields

Eb = 0.01TeV Eb = 10TeV Effect of Radiation Fields on diffuse High Energy Inverse Compton Emission from the Milky Way Common reference energy spectrum dN(E)/dE = ^-12 (E/GeV)^(-3) exp(-E/Eb)cm^-2s^-1 GeV^-1 (normalisation from the local electron flux measurements by Pamela at 10GeV; Adriani et al. 2011)

Volume within which ISRF component exceeds CMB component

Abramowski et al. (2014)

J1641: E^-3.14 energy spectrum; no cut off

J1641: E^-2.54 energy spectrum; no cut off

J1641: E^-2.54 energy spectrum (ISRF+CMB) with 100TeV cutoff (solid line) E^-3.14 energy spectrum (ISRF+CMB) with no cutoff (dashed line)

Pair production opacity of the Milky Way Transmission curve for source at Galactic Centre Transmission curve for source at distance of 8 kpc and longitude 45 deg

ISRF Opacity for 40 TeV photons from Extragalactic Sources

ESA, Herschel PACS & SPIRE Consortia

- Clouds selected from Planck dust column maps with |l| > 30 degrees - Fermi-LAT Pass 8 data over 7 years Fermi stacking analysis on 158 Cirrus clouds Planck dust column Fermi 0.1-1GeV Fermi 1-10GeVFermi GeV

MIR Radiation Fields in the inner 10pc of the Milky Way HESS collaboration 2016 (see presentation by Aion Viana ) towards Sgr A* ring 0.35deg from Sgr A*

ISO-SWS (Lutz et al. 1996) Spaceborne aperture photometry MSX 19 micron

MSX 19 micron Inner 1.2 x 1.2 pc with 0.02pc FWHM VLT/VISIR 8.6/11.3/12.8 micron (Viehmann et al. 2006) VLT/VISIR 19 micron (Viehmann et al. 2006)

Summary -An axisymmetric self consistent 2 dust-disk radiation transfer solution to the global morphology from 1.2 to 850 micron exists -Predicted mid-plane ISRF high than before, especially in the central regions. IC scattering of the ISRF exceeds that off the CMB everywhere within the solar circle, with consequence for modelling both diffuse gamma-ray emission and gamma-rays from CR sources. -High latitude transclucent clouds (“Cirrus”) have been detected by Fermi/LAT from 0.1 to 100Gev, and are a likely source of high latitude Inverse Compton as well as pion emission - MIR/FIR Radiation fields within the inner 10pc have been severely underestimated in the past and have the potential to constrain the geometry of central gamma-ray emitters via analysis of modulation of the VHE spectrum via pair-production opacity

High latitude Cirrus Silicate Graphite PAH