Cosmic rays in early Star-Forming Galaxies and their effects on the Interstellar Medium
Ellis [email protected] 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)
International Cosmic Ray Conference, Busan, Korea, July 2017
EQ J100054+023435 – Multiwavelength image with HST, Spitzer, Chandra, Keck, Galex, CFHT, Subaru, UKIRT, JCMT, VLA & IRAM. Credit NASA (2008)
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)
3
> 10 M� yr�1à many Supernovae à abundant cosmic rays
Starburst Galaxies at High Redshift
• Starburst galaxies characterized by high star formation rates (SFR)
• 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
> 10 M� yr�1à many Supernovae à abundant cosmic rays
Starburst Galaxies at High Redshift
• Starburst galaxies characterized by high star formation rates (SFR)
• 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
3
> 10 M� yr�1
Density field Radiation field Magnetic field
à many Supernovae à abundant cosmic rays
1000 M� yr�1
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
4
@n
@t= r · [D(E, r, t)rn] +Q(r, E)
• As a first estimate, assume Bohm diffusion ~1 scattering per gyro-radius
D =1
3c rL ' c rL
Cosmic Ray Diffusion & Containment
• Strong containment• Steady-state solution
with cosmic ray densities
• Around ~1012 times high than free-streaming case
5
10�2 10�1 100 101 102
r/kpc
10�38
10�35
10�32
10�29
10�26
10�23
10�20
10�17
dN
dE
dV/e
rg·c
m�
3 eV
�1
Free-streaming profile
Saturated magnetic field, steady-state profile
Cosmic Ray Interactions (Direct)
6
+ pion multiplicities at higher energies
p+ � ! p+ e+ + e� .
p+ � ! �+ !(p+ ⇡0 ! p+ 2�
n+ ⇡+ ! n+ µ+ + ⌫µ
n+ e+ + ⌫e + ⌫̄µ + ⌫µ
Photopion Interaction
Interactions with Radiation Fields (p𝛄)
Photopair Interaction
Interaction by particles scattering off ambient photons (starlight, CMB…)
p+ p !
8>>>>>><
>>>>>>:
p+�+ !
8><
>:
p+ p+ ⇡0
p+ p+ ⇡+
p+ n+ ⇡+
n+�++ !(n+ p+ ⇡+
n+ n+ 2(⇡+)
Cosmic Ray Interactions (Direct)
7
+ pion multiplicities at higher energies
Neutron and photon interactions produce pions
Pions decay to photons, muons, neutrinos, electrons, positrons,
antineutrinosn+ � ! ⇡’s ⇡ ! �, µ, e, ⌫ . . .
Interactions with Matter (pp)
p+ p !
8>>>>>><
>>>>>>:
p+�+ !
8><
>:
p+ p+ ⇡0
p+ p+ ⇡+
p+ n+ ⇡+
n+�++ !(n+ p+ ⇡+
n+ n+ 2(⇡+)
Cosmic Ray Interactions (Direct)
7
+ pion multiplicities at higher energies
Neutron and photon interactions produce pions
Pions decay to photons, muons, neutrinos, electrons, positrons,
antineutrinosn+ � ! ⇡’s ⇡ ! �, µ, e, ⌫ . . .
Interactions with Matter (pp)Dominates
Cosmic Ray Interactions (Indirect)
8
Electron Injection
Qe(�e) '⌥
6
400 me
mpQp(�p)
(Schober+ 2015, Lacki & Beck 2013)
Injection profile can be estimated from the CR source term
Cosmic Ray Interactions (Indirect)
8
Electron Injection
Qe(�e) '⌥
6
400 me
mpQp(�p)
(Schober+ 2015, Lacki & Beck 2013)
Sunyaev-Zel’dovich (SZ) Effect X-Ray Emission
Injection profile can be estimated from the CR source term
Inverse-Compton scattering off CMB CMB Photon
X-Ray Photon
Energetic electronsLSZ ⇡ 1048erg s�1
(upper limit)
Energy Deposition
• Absorption coefficient: energy absorbed at a point• Cross section depends on interaction (radiation/particles)
• In general, can account for attenuation from emission up to absorption point by RT
• Then heating is ~ energy absorbed at a point after attenuation
• Cross section: Klein-Nishina (X-rays)… Thomson limit with UV9
H(r) = F0 ↵(r) exp
✓�Z r
re
↵(r0) dr0◆
I⌫(r) = I⌫,0 exp
✓�Z r
r0
n(r0)�⌫dr0◆
↵(r) = n(r)�
Radiation
Energy Deposition
• Absorption coefficient: energy absorbed at a point• Cross section depends on interaction (radiation/particles)
10
↵(r) = n(r)�
Cosmic Rays
SZ X-rays
– Cross section is dominating ppinteraction
– Scale to account for the containment
– Emission profile from CR electron secondary injection
– Heating then as per conventional treatment (previous slide)
No B field
With B field
Energy Deposition
11
Stellar heating around 10-22 erg cm-3 s-1
X-ray heating
Cosmic Rays (saturated B field)
Note – Cosmic ray MC calculation using 1000 points
CR Heating: ISM
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
• Cosmic rays: charged energetic particles (assume protons)
• Sources: supernova remnants (SNRs) can accelerate CRs up to 1017-18 eV
• Diffusive shock acceleration
13
Emax
qBR
Adapted from Jacobsen+2015
Backup: Star-Forming Galaxies at High-z
14
Magnetic Field
10�4 10�3 10�2 10�1 100 101
Age of Galaxy/Myr
10�31
10�27
10�23
10�19
10�15
10�11
10�7
10�3
Mag
neti
cF
ield
Stre
ngth
/G
• Two scale components:– Local scale, ~10-3 pc– Galactic ordered field ~1kpc
• SN driven
• Initial B field ~10-20 G permeates protogalaxy (Sigl+1997; Howard & Kulsrud 1997)
• Turbulent dynamo drives B field up to µG levels seen in current epoch (Schober+2013) Model follows J. Schober + 2013
SNe à Turbulence à B field
Backup: Cosmic Ray Interactions
15
1010 1012 1014 1016 1018 1020
Energy/eV
10�4
10�3
10�2
10�1
100
101
102
103
104
105
E↵e
ctiv
ePat
hLen
gth/
Mpc
1
2
3
4
5
6
7
8
Particle Path Lengths
CMB & cosmological
losses
Interactions with stellar radiation
fields
Interactions with density fields
Backup: Cosmic Ray Diffusion
• Fundamental diffusion solution (Gaussian)
• Principle of superposition
16
Z tmax
0n(t)dt
n1(t)
n2(t) = n1(t+ dt)
n3(t) = n2(t+ dt) = n1(t+ 2dt)
ni(t) = · · · = n1(t+ (i� 1)dt)
⌃i{Time (to deal with continuous injection)
n(r, t) =Q(rs)
(4⇡Dt)3/2exp
⇢� (r � rs)2
4Dt
�
Backup: Cosmic Ray Diffusion
• Fundamental diffusion solution (Gaussian)
• Principle of superposition
17
x
x
xx
x x
xx
xx
x x
xxx
x
x
xx
x
x
x
x
Space (to deal with source distribution –weighted by galaxy density profile)
n(r, t) =Q(rs)
(4⇡Dt)3/2exp
⇢� (r � rs)2
4Dt
�
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