1. Cosmic rays, γ and ν in star-forming galaxies
Xiang-Yu Wang
Nanjing University
Collaborators: X. C. Chang, F. K. Peng, Q. W. Tang

2. CRs in our Galaxy

3. Cosmic ray (CR) luminosity in galaxies
Energy density 1 eV/cm^3 ， equipartition of the magnetic and CR
-- a major energetic component
Diffuse Galactic gamma-rays are produced dominantly by CRs
CRs represent a major form
(but not well-studied) of galactic feedback, regulating the formation and evolution of galaxies

4. 1. Evidence of cosmic rays in other galaxies?

5. Gamma-ray messenger

6. Gamma-ray emission from starburst galaxies
Abdo et al. 2010

7. Cosmic rays accelerated by SNRs
Cygnus Loop ( GeV)
Supernova explosions induce shocks (SNRs)
Cosmic rays are accelerated across these shock fronts
GeV Gamma-rays are produced by Cosmic rays

8. Are galaxies CR calorimeters?
Galaxies are typically calorimeters for lepton CRs, explaining the FIR- radio linear correlation
How about protons?

9. Correlation between gamma-ray and infrared luminosities
Several nearby star-forming galaxies detected
Gamma-ray and infrared luminosity well correlated
Naturally expected if more CR energy is converted into gamma-rays in more luminous galaxies
Ackermann et al. 2012

10. CR calorimeter? “calorimetry fraction limit”
Best target: (ultra) luminous infrared galaxies
Lacki et al. 2011

11. GeV emission from LIRG NGC 2146
Tang, Wang XY & Tam 2014
A luminous infrared galaxy – CR calorimeter ?
using the 68 month Fermi data
5.5σ detection of gamma-ray emission above 200 MeV

12. NGC2146—a likely calorimeter ?
assuming ESN,51 η0.05=1, for proton calorimeter limit : L GeV/L8-100μm=1.5e-4.
NGC 2146 is likely a proton calorimeter !
cosmic rays accelerated in NGC 2146 lose most of their energy into secondary pions
Tang, Wang XY & Tam 2014
2018/12/5

13. Arp 220- the nearest ULIRG: must be calorimeter!
A prototype of ULIRG: LIR=1.4*1012Lsun
D=78Mpc
n~104cm-3
Possible AGN
SN rate: 4+-2/yr
Long predicted to be GeV sources
(e.g.,Torres 2004; Lacki+ 2011; Yoast-Hull+2015)
tpp<tescape
Hubble image of Arp 220
作为对比，银河系的红外光度为1.4*10^10 Lsun，超新星爆发率为0.03/yr，恒星形成率为1 Msun/yr
天文年会报告

14. Fermi observation- PASS 8
Peng, Wang XY et al. 2016, ApJL

15. LC and SED of Arp 220
Favor cosmic Rays origin

16. Efficiency of powering CRs
Cosmic Rays injection power
GeV emission luminosity from CRs
Efficiency of powering CRs of SRNs

17. Is there direct evidence for cosmic ray origin?

18. Pion-decay evidence in supernova remnants
Science, 2013
p+p->p+p+ p0
p0->γ+γ

19. Gamma-ray count map around LMC in 60 MeV-2.45 GeV
Tang, Peng, Liu, Tam, Wang XY, 2017
LMC is the brightest external galaxies in gamma-ray emission
LMC is near enough that individual star-forming regions can be resolved
The high Galactic latitude of LMC also leads to a low level of contamination due to the Galactic diffuse gamma-ray emission.

20. Spectrum of the LMC disk component
Tang, Peng, Liu, Tam, Wang XY, 2017

21. fit with pion-decay model
Tang, Peng, Liu, Tam, Wang XY, 2017

22. 3. Neutrinos from CRs in galaxies ?

23. Arriving directions isotropic distribution dominated
Favor extragalactic origin

24. Starburst galaxy scenario
Loeb & Waxman 2006
Cosmic rays are accelerated by SNR shocks
Normalized with the local 1.4 GHz energy production rate
But, Normal SNRs can only accelerate CR to PeV, while IceCube neutrinos need 100 PeV CRs ?
Eν ~ 0.04 Ep: PeV neutrino ⇔ 20-30(1+z) PeV CR proton

25. Hypernova remnant scenario
(Liu, Wang et al. 2014)
Normal SNRs can hardly accelerate CR to PeV
Hypernovae can accelerate CR protons to 10^18 eV (Wang et al. 2007)
Semi-relativistic (v~c, or Γβ≥1) outflow
Proton
ISM
Hypernova
remnant

26. PeV Neutrino production
(Liu, Wang XY et al. 2014)
CR protons collide with the surrounding gas and produce neutrinos
Proton
ISM
Two escape ways: 1) diffusion 2) advection
pp efficiency in star-forming galaxies & starburst galaxies
See also He et al. 2013

27. Detailed calculation
Chang, Liu & Wang 2015
Use infrared luminosity function obtained by Herschel PEP/HerMES (Gruppioni et al. 2013)
Sum up contributions by different galaxy populations
Star-forming galaxies also contribute significantly to the diffuse gamma-ray background

28. Normal SNR + HNR
(Chakraborty and Izaguirre 15; Senno+ 15)
With normal SNRs, can explain the low energy IceCube data (softer spectrum)
IceCube
(Chakraborty and Izaguirre 15)

29. Tension with the gamma-ray background
Scenarios： 1）overestimate blazar contribution to EGB ? 2）hidden sources in gamma- rays (e.g. choked jets)
arXiv:

30. Internal Υ-ray absorption in starbursts
Chang & Wang XY 2014

31. Taking into account the synchrotron loss of secondary pairs
Chang & Wang XY 2014

32. High-redshift sources
Assuming sources are at z=4-10 Considering EBL absorption
Xiao et al. 2016

33. Fermi Search for GeV Flares Associated with the IceCube Track-like Neutrinos
Peng & Wang XY 2017
Fermi/LAT upper limits:

34. Put constraints on the source density
Favor low-luminosity,
high-density candidates
high-density source case
(e.g. 4x10-4Mpc-3;
starburst galaxies)
low-density case
(e.g. 4x10-9Mpc-3
FSRQ)
Peng & Wang XY 2017

35. Summary
GeV-emitting star-forming/starburst galaxies are huge reserviors of CRs
Starburst/ULIRGs (e.g. Arp 220) are likely calorimeters of CRs
Star-forming/starburst galaxies may also be, at least partly, the sources of HE neutrinos observed by IceCube