cosmic rays and magnetic field in the core and halo of the starburst m82… · 2019. 8. 7. ·...
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COSMIC RAYS AND MAGNETIC FIELD IN THE CORE AND HALO OF THE STARBURST M82:
IMPLICATIONS FOR GALACTIC WIND PHYSICS
Benjamin BuckmanTim Linden
Todd ThompsonArXix: Next Week
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QUESTION!
• Can cosmic rays propel a gas cloud?
• If the answer to the previous question was yes, explain.
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 2
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QUESTION!
• Can cosmic rays propel a gas cloud?
• If the answer to the previous question was yes, explain.
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 3
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QUESTION!
• Can cosmic rays propel a gas cloud?
• If the answer to the previous question was yes, explain.
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 4
𝑎𝑔𝑎𝑠 = −∇𝑃𝐶𝑅𝜌𝑔𝑎𝑠
Acceleration of gas from CRs is due to
the gradient of the CR pressure
mediated by the mangetic field
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COSMIC RAYS AND MAGNETIC FIELD IN THE CORE AND HALO OF THE STARBURST M82:
IMPLICATIONS FOR GALACTIC WIND PHYSICS
Benjamin BuckmanTim Linden
Todd ThompsonArXix: Next Week
![Page 6: COSMIC RAYS AND MAGNETIC FIELD IN THE CORE AND HALO OF THE STARBURST M82… · 2019. 8. 7. · STARBURST GALAXY M82 •Gamma-ray detection –Not resolved •Spatially resolved radio](https://reader035.vdocuments.mx/reader035/viewer/2022071406/60fd09d2fcef5d430162d0e3/html5/thumbnails/6.jpg)
STARBURST GALAXY M82
• Gamma-ray detection – Not resolved
• Spatially resolved radio halo measurements @ multiple wavelengths
• Viewed from edge-on
• Well studied galactic wind
• Starburst core – known SNR and dimension
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 6
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MODELING CR’S IN M82IMPORTANT INGREDIENTS
Transport
Wind
Diffusion
Energy Losses
𝐵
𝑛𝐻𝐼 , 𝑛𝐻𝐼𝐼ISRF
Injection
Primary Spectrum
Primary p/e ratioSNR
Source Distribution
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 7
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GALPROP
GALPROP►injection►propagation►energy losses ►secondaries
Cosmic ray Distribution
Radio Emission
•Synchrotron
•Free-Free
Gamma-ray Emission
•Bremsstrahlung
• Inverse Compton
•Pion-decay EmissionInjection
Transport
Energy Losses
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 8
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INPUT DISTRIBUTIONS
• Magnetic Field (𝐵) and Gas Density (𝑛)
– Constant inside ellipsoidal core
– Outside core: 𝐵 ∝ 𝑟−𝛽, 𝑛 ∝ 𝑟−2
• Interstellar Radiation Field
– Determined from exponential disk of sources (dust+stars)
• Cosmic-ray Sources
– Constant inside ellipsoidal core
– No sources outside core
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 9
Simulation box size:𝑅 ∈ [0,5] kpc, 𝑧 ∈ [−4,4] kpc
200pc
50 pc
Starburst core
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CONSTRAINING PARAMETERS
• Use integrated radio and gamma-ray emission to constrain properties in starburst core:
– Magnetic Field
– Gas Density
• Use extended radio halo to constrain halo properties:
– Magnetic field, 𝐵 ∝ 𝑟−𝛽
– Gas density
– CR advection velocity
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 10
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INTEGRATED EMISSION
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 11
gamma-ray radio
We replicated emission with our models
We constrain magnetic field and gas density
DEGENERACY in the core
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EXTENDED EMISSION
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 12
Wavelength
increases
Halo size
increases
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TIMESCALES
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week
• Electron Cooling Timescales
– 𝜏𝑖𝑜𝑛𝑖𝑧𝑎𝑡𝑖𝑜𝑛~106 𝜈𝑐𝑟𝑖𝑡
1 𝐺𝐻𝑧
1
2 𝐵
100 𝜇𝐺
−1
2 𝑛
100 𝑐𝑚−3
−1yr
– 𝜏𝑏𝑟𝑒𝑚𝑠𝑠~3 × 105𝑛
100 𝑐𝑚−3
−1yr
– 𝜏𝐼𝐶~3 × 105𝜈𝑐𝑟𝑖𝑡
1 𝐺𝐻𝑧
−1
2 𝐵
100 𝜇𝐺
1
2 𝑈𝑟𝑎𝑑
1000 𝑒𝑉 𝑐𝑚−3
−1yr
– 𝜏𝑠𝑦𝑛𝑐ℎ~106 𝜈𝑐𝑟𝑖𝑡
1 𝐺𝐻𝑧
−1
2 𝐵
100 𝜇𝐺
−3
2yr
𝐸
1 𝐺𝑒𝑉=
𝜈𝑐𝑟𝑖𝑡1 𝐺𝐻𝑧
12 𝐵
100 𝜇𝐺
−12
steepen
spectrum
13
Spectral index from
competition of
cooling timescales
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RADIO SPECTRAL INDEX ALONG MINOR AXIS
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 14
• Spectral index changes by >1.5
along the minor axis of M82
• Changing of cooling mechanism
can change spectral index by 1
at most
• Spectral steeping is due to the
galactic wind and changing
cooling mechanism
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SPECTRAL STEEPENING CONSTRAINS:
• Cosmic ray population
• Magnetic field
• Gas density
• Wind velocity
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 15
All along the minor
axis of M82
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COSMIC RAY SPECTRA
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 16
Colors denote distance from
core (0, 0.2, 0.5, 3.0) kpc
Protons Electrons+Positrons
Radio emission
spectral steepening
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GAS ACCELERATION
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 17
Cosmic Rays
Gravity𝑎𝑔𝑎𝑠 = −
∇𝑃𝐶𝑅𝜌𝑔𝑎𝑠
• Cosmic rays are
subdominant to gravity
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GAS ACCELERATION II
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 18
Cosmic Rays
Gravity
Magnetic Field
𝑎𝑔𝑎𝑠 = −∇𝑈𝐵𝜌𝑔𝑎𝑠
• Magnetic field is
dynamically relevant!
• May effect galactic
winds!
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SUMMARY
• Using GALPROP:
– Modeled integrated gamma-ray and radio data
– Modeled radio halo and constrained magnetic field, gas density, and wind velocity
• Cosmic rays are not able to drive galactic winds in starburst galaxies
• Magnetic fields are dynamically relevant to galactic winds!
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 19
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QUESTIONS?
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 20
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MAGNETIC FIELD VS GAS DENSITY
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 21
• Degeneracy due to:
• Relative gamma-
ray/radio
normalization
• Radio spectral index
• We chose 3 models to
exemplify behavior
• Magnetic Field must be
>150 microG
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EXTENDED EMISSION
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 22
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ENERGY DENSITY
B. J. Buckman [CCAPP, OSU] -- ArXiv: Next Week 23