Cosmic rays in early Star-Forming Galaxies and their effects on the Interstellar Medium Ellis Owen ellis.owen.12@ucl.ac.uk Mullard Space Science Laboratory, University College London, United Kingdom National Tsing Hua University, Taiwan (ROC) Collaborators: Kinwah Wu (UCL-MSSL, UK) Idunn Jacobsen (UCL-MSSL, UK) Pooja Surajbali (MPIK, Heidelberg, Germany) EQ J100054+023435 – Multiwavelength image with HST, Spitzer, Chandra, Keck, Galex, CFHT, Subaru, UKIRT, JCMT, VLA & IRAM. Credit NASA (2008) International Cosmic Ray Conference, Busan, Korea, July 2017
Outline • Early Star-Forming Galaxies • Propagation and Interaction of Cosmic Rays – Direct – Indirect • Energy Deposition and Cosmic Ray Heating • Remarks 2
Starburst Galaxies at High Redshift • Starburst galaxies characterized by high star formation rates (SFR) > 10 M � yr � 1 à many Supernovae à abundant cosmic rays 3
Starburst Galaxies at High Redshift • Starburst galaxies characterized by high star formation rates (SFR) > 10 M � yr � 1 à many Supernovae à abundant cosmic rays • Why are high redshifts of interest? – Galaxies with very high SFRs seem to be abundant at high redshifts – Possible implications on cosmic reionization (Sazonov & Sunyaev 2015) 3
Starburst Galaxies at High Redshift • Starburst galaxies characterized by high star formation rates (SFR) > 10 M � yr � 1 à many Supernovae à abundant cosmic rays • Why are high redshifts of interest? – Galaxies with very high SFRs seem to be abundant at high redshifts – Possible implications on cosmic reionization (Sazonov & Sunyaev 2015) • Parametric model protogalaxy, very active to demonstrate concept • SFR = , environment defined by 1000 M � yr � 1 Density field Radiation field Magnetic field 3
Energy Transport by Cosmic Rays • Cosmic rays may be influenced by magnetic fields – Low & Intermediate energies – Larmor radius • Can hamper their propagation into intergalactic space – Containment vs. Diffusion ∂ n ∂ t = r · [ D ( E, r, t ) r n ] + Q ( r, E ) • As a first estimate, assume Bohm diffusion ~1 scattering per gyro-radius D = 1 3 c r L ' c r L 4
Cosmic Ray Diffusion & Containment 10 − 17 • Strong containment Saturated magnetic field, d E d V / erg · cm − 3 eV − 1 steady-state profile 10 − 20 • Steady-state solution 10 − 23 with cosmic ray 10 − 26 densities 10 − 29 Around ~10 12 times • Free-streaming profile 10 − 32 high than free- 10 − 35 d N streaming case 10 − 38 10 − 2 10 − 1 10 0 10 1 10 2 r/ kpc 5
Cosmic Ray Interactions (Direct) Interactions with Radiation Fields ( p 𝛅 ) Interaction by particles scattering off ambient photons (starlight, CMB…) Photopion Interaction ( p + π 0 → p + 2 γ + pion multiplicities at p + γ → ∆ + → higher energies n + π + → n + µ + + ν µ n + e + + ν e + ¯ ν µ + ν µ Photopair Interaction p + γ → p + e + + e − 6
Cosmic Ray Interactions (Direct) Interactions with Matter ( pp ) 8 8 p + p + π 0 > > > < > p + ∆ + p + p + π + > → > > < + pion multiplicities > p + n + π + p + p → : at higher energies ( > n + p + π + > > n + ∆ ++ → > > n + n + 2( π + ) > : Pions decay to photons, muons, Neutron and photon neutrinos, electrons, positrons, interactions produce pions antineutrinos n + γ → π ’s π → γ , µ, e, ν . . . 7
Cosmic Ray Interactions (Direct) Interactions with Matter ( pp ) Dominates 8 8 p + p + π 0 > > > < > p + ∆ + p + p + π + > → > > < + pion multiplicities > p + n + π + p + p → : at higher energies ( > n + p + π + > > n + ∆ ++ → > > n + n + 2( π + ) > : Pions decay to photons, muons, Neutron and photon neutrinos, electrons, positrons, interactions produce pions antineutrinos n + γ → π ’s π → γ , µ, e, ν . . . 7
Cosmic Ray Interactions (Indirect) Electron Injection Injection profile can be estimated from the CR source term 400 m e Q e ( γ e ) ' Υ Q p ( γ p ) 6 m p (Schober+ 2015, Lacki & Beck 2013) 8
Cosmic Ray Interactions (Indirect) Electron Injection Injection profile can be estimated from the CR source term 400 m e Q e ( γ e ) ' Υ Q p ( γ p ) 6 m p (Schober+ 2015, Lacki & Beck 2013) Sunyaev-Zel’dovich (SZ) Effect X-Ray Emission Inverse-Compton scattering off CMB CMB Photon Energetic L SZ ≈ 10 48 erg s − 1 electrons (upper limit) X-Ray Photon 8
Energy Deposition • Absorption coefficient: energy absorbed at a point α ( r ) = n ( r ) σ • Cross section depends on interaction (radiation/particles) Radiation • In general, can account for attenuation from emission up to absorption point by RT Z r ✓ ◆ n ( r 0 ) σ ν dr 0 I ν ( r ) = I ν , 0 exp − r 0 • Then heating is ~ energy absorbed at a point after attenuation Z r ✓ ◆ H ( r ) = F 0 α ( r ) exp α ( r 0 ) dr 0 − r e • Cross section: Klein-Nishina (X-rays)… Thomson limit with UV 9
Energy Deposition • Absorption coefficient: energy absorbed at a point α ( r ) = n ( r ) σ • Cross section depends on interaction (radiation/particles) Cosmic Rays – Cross section is dominating pp With B field interaction – Scale to account for the containment SZ X-rays No B field – Emission profile from CR electron secondary injection – Heating then as per conventional treatment (previous slide) 10
Energy Deposition CR Heating: ISM Cosmic Rays (saturated B field) X-ray heating Stellar heating around 10 -22 erg cm -3 s -1 Note – Cosmic ray MC calculation using 1000 points 11
Summary & Remarks • Cosmic rays are abundant in star forming galaxies – Of particular interest at high redshift • Containment by magnetic field appears to be important global effect – Focuses CR heating into ISM above conventional stellar heating • Accompanied by an X-ray heating effect due to SZ effect – Higher than direct CR heating outside the galaxy • Impacts – Subsequent star formation (e.g. by heating star forming regions) – Thermal properties of surroundings – Pre-heating IGM during reionization 12
Backup: Cosmic Ray Sources/Hillas Criterion E max ≤ qBR • Cosmic rays: charged energetic particles (assume protons) • Sources: supernova remnants (SNRs) can accelerate CRs up to 10 17-18 eV • Diffusive shock acceleration Adapted from Jacobsen+2015 13
Backup: Star-Forming Galaxies at High-z Magnetic Field SNe à Turbulence à B field • Two scale components: 10 − 3 – Local scale, ~10 -3 pc Magnetic Field Strength/G 10 − 7 – Galactic ordered field ~1kpc 10 − 11 • SN driven 10 − 15 10 − 19 Initial B field ~10 -20 G • permeates protogalaxy 10 − 23 (Sigl+1997; Howard & Kulsrud 1997) 10 − 27 • Turbulent dynamo drives B 10 − 31 10 − 4 10 − 3 10 − 2 10 − 1 10 0 10 1 field up to µG levels seen in Age of Galaxy/Myr current epoch (Schober+2013) Model follows J. Schober + 2013 14
Backup: Cosmic Ray Interactions Interactions with Particle Path Lengths stellar radiation fields 10 5 4 E ff ective Path Length/Mpc 10 4 3 10 3 CMB & 7 cosmological 10 2 5 losses 10 1 6 8 10 0 2 10 − 1 10 − 2 1 10 − 3 10 − 4 10 10 10 12 10 14 10 16 10 18 10 20 Energy/eV Interactions with density fields 15
Backup: Cosmic Ray Diffusion • Fundamental diffusion solution (Gaussian) − ( r − r s ) 2 ⇢ � Q ( r s ) n ( r, t ) = (4 π Dt ) 3 / 2 exp 4 Dt • Principle of superposition Time (to deal with continuous injection) n 1 ( t ) Σ i { n 2 ( t ) = n 1 ( t + dt ) n 3 ( t ) = n 2 ( t + dt ) = n 1 ( t + 2 dt ) n i ( t ) = · · · = n 1 ( t + ( i − 1) dt ) Z t max n ( t ) dt 0 16
Backup: Cosmic Ray Diffusion • Fundamental diffusion solution (Gaussian) − ( r − r s ) 2 ⇢ � Q ( r s ) n ( r, t ) = (4 π Dt ) 3 / 2 exp 4 Dt • Principle of superposition Space (to deal with source distribution – weighted by galaxy density profile) x x x x x x x x x x x x x x x x x x x x x x x 17
Backup: Energy Deposition Heating: Cross-Check with GALPROP Cosmic Ray Heating Galprop Comparison γ − Ray Emission / erg cm − 3 s − 1 Cosmic Rays (saturated B field) X-ray heating Stellar heating Cosmic Rays (initial) 18
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