Radial distribution of cosmic ray density in the Galactic plane - PowerPoint PPT Presentation

Radial distribution of cosmic ray density in the Galactic plane Ruizhi Yang with Felix Aharonian and Carmelo Evoli (P.R.D 93, 123007 and A&A 600, 107) 35 th international Cosmic Ray Conference Busan, 2017. 18. 7

Diffuse emission in the plane • Gamma-ray emission in the plane (|b|<5 o ): Point sources+ CR interaction with gas + ICs +isotropic • CR interaction with gas dominates in the plane. • Gamma-ray map + gas distribution -> CR distribution • Gas Tracers : 1. HI and CO: With distance information. Various of biases (spin temperature of HI, dark gas problem in Molecular clouds, unknown X_co .etc) 2. Dust opacity : all sky coverage, free of “dark gas” problem, without distance information

Gamma-ray sky Gamma-ray counts map Point source contribution Dust opacity map (gas column)

Fit with dust column template Hardening of spectrum toward inner galaxy. (| b|<5 o ) 10 -9 φ (E) (erg s -1 cm -2 ) 10 -10 10 -11 l=[5 o :15 o ] l=[85 o :95 o ] l=[175 o :185 o ] 10 -12 0.1 1 10 100 Energy(GeV)

Fit with dust column template Hardening of spectrum toward inner galaxy. 2.9 photon index above 2 GeV 2.6 2.3 0 50 100 150 200 250 300 350 Galactic Longitude ( o )

Fit with gas ring template • Use kinematic distances. • 6 Galactocentric gas rings (|b|<5 o ). • CO conversion factor left free in the fit.

Fit with gas ring template SED in different rings

Fit with gas ring template Index distributions 2.9 photon index above 2 GeV 2.6 2.3 0 5 10 15 20 25 30 Distance to GC (kpc)

Fit with gas ring template Emissivities per H (CR density) 10 -26 emissivity per H atom (>1GeV) (ph sr -1 s -1 ) CMZ Sgr B 10 -27 0 5 10 15 20 25 30 Distance to GC (kpc)

Fit with gas ring template CRs SED in different rings. r < 8kpc 4kpc < r <6kpc r > 8kpc 10 4 Flux × E 2 (m -2 s -1 sr -1 GeV) Orion B GeV excess 10 3 10 2 1 10 100 1000 Energy(GeV)

Source distributions 10 -26 emissivity per H atom (>1GeV) (ph sr -1 s -1 ) CMZ Sgr B OB stars (Bronfman00) SNRs (Green15) 10 -27 0 5 10 15 20 25 30 Distance to GC (kpc) Peak coincide with OB stars

OB stars as CR sources? • GCR distribution reveal a similar peak to that of OB stars. • Most of OB stars exist in associations or clusters, stellar wind/ SNRs in such structure form bubbles/superbubbles and can accelerate CRs (e.g., Bykov 14). • Isotope measurement favor a superbubble origin. (W.R Binns 2016) • Could be visible in gamma-ray due to CR-gas interaction. • So far the only detection is Cygnus cocoon. A few more powerful systems: NGC 3603, Westerlund 1, Westerlund 2. RSGC 1 … ..

Cygnus cocoon 35 10 -9 48.000 φ (E)(erg s -1 cm -2 ) 44.000 LAT PSR J2030+4415 Cygnus Cocoon 10 -10 Declination LAT PSR J2032+4127 gamma Cygni 40.000 LAT PSR J2021+4026 TXS 2016+386 MG2 J201534+3710 PSR J2030+3641 36.000 10 -11 1 10 100 1000 B2 2023+33 LAT PSR J2028+3332 PSR J1952+3252 32.000 Energy(GeV) 4C +31.56 1 315.000 310.000 305.000 300.000 Right ascension Spectral Index of -2.2, up to 500 GeV with PASS 8 data. 8 46 84 122 160 198 236 274 312 350 388 Fermi LAT counts map (>1 GeV)

NGC 3603 (sky maps) -58:00:00.0 -58:00:00.0 PSR J1125-5825 PSR J1124-5916 -60:00:00.0 -60:00:00.0 PSR J1125-6014 Declination PSR J1055-6028 Declination 3FGL J1111.9-6038 PSR J1112-6103 LAT PSR J1135-6055 PSR J1105-6107 PSR J1119-6127 3FGL J1112.0-6135 -62:00:00.0 -62:00:00.0 PMN J1047-6217 -64:00:00.0 -64:00:00.0 AT20G J112319-641735 40:00.0 30:00.0 20:00.0 10:00.0 11:00:00.0 10:50:00.0 40:00.0 30:00.0 20:00.0 10:00.0 11:00:00.0 10:50:00.0 Right ascension Right ascension 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Counts map (>10 GeV) Residual map (>10 GeV), known source removed

NGC 3603 (SEDs and CR content) 10 -10 10 -10 n e = 2 cm -3 NGC 3603 n e = 10 cm -3 3FGL J1111.9-6038 E 2 dN/dE (erg cm -2 s -1 ) φ (E)(erg s -1 cm -2 ) 10 -11 10 -11 10 -12 10 -12 1 10 100 0.1 1 10 100 1000 Energy(GeV) Energy(GeV) Gamma-ray SEDs Compared with LIS emissivities Index ~ -2.3, up tp 300 GeV

NGC 3603 (gas content) -58:00:00.0 -58:00:00.0 -60:00:00.0 -60:00:00.0 Declination Declination -62:00:00.0 -62:00:00.0 -64:00:00.0 -64:00:00.0 40:00.0 30:00.0 20:00.0 10:00.0 11:00:00.0 10:50:00.0 40:00.0 30:00.0 20:00.0 10:00.0 11:00:00.0 10:50:00.0 Right ascension Right ascension .00e+21 1.90e+21 2.79e+21 3.70e+21 4.60e+21 5.50e+21 6.40e+21 7.30e+21 8.21e+21 9.10e+21 1.00e+2 .00e+00 3.99e+20 7.98e+20 1.20e+21 1.60e+21 2.00e+21 2.40e+21 2.80e+21 3.20e+21 3.60e+21 4.00e+2 CO+HI (0 ~ 20 km/s) HII gas Tentative correlation with HII distribution

Westerlund 2 (Preliminary results) -54:00:00.0 -54:00:00.0 -56:00:00.0 -56:00:00.0 Declination Declination LAT PSR J1044-5737 LAT PSR J1044-5737 LAT PSR J1023-5746 LAT PSR J1023-5746 PSR J1023-5746 PSR J1019-5749 PSR J1019-5749 PSR J1028-5819 -58:00:00.0 -58:00:00.0 PSR J1028-5819 PSR J1028-5819 PSR J1048-5832 PSR J1048-5832 1FGL J1018.6-5856 1FGL J1018.6-5856 PSR J1016-5857 PSR J1016-5857 SNR G284.3-0.3 PSR B1046-58 PSR J1044-5737 SNR G286.5-1.2 Eta Carinae Eta Carinae -60:00:00.0 -60:00:00.0 PSR J1055-6028 PSR J1055-6028 PSR J0955-61 11:00:00.0 50:00.0 40:00.0 30:00.0 20:00.0 10:00.0 10:00:00.0 9:50:00.0 11:00:00.0 50:00.0 40:00.0 30:00.0 20:00.0 10:00.0 10:00:00.0 9:50:00.0 Right ascension Right ascension 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Counts map (>10 GeV) Residual map (>10 GeV), known source removed

Westerlund 2 (Preliminary results) 10 -10 φ (E)(erg s -1 cm -2 ) 10 -11 10 -12 Westerlund 2 FGES J1023.3-5747 HESS J1023-575 10 -13 1 10 100 1000 10000 Energy(GeV) • Index ~ -2.1, up tp 300 GeV. • FGES J1023 is the GeV counterpart of HESS J1023, which has a much smaller spatial extension, is believed to be a PWN.

Conclusions and implications • Spatial variation of CR density and spectral shape • The results derived in outskirts of Galaxy is consistent with direct measurement • A maximal CR density at 4-6 kpc. • A lower CR level in GC region. • The main conclusions are consistent with ApJS (2016) 223, 26 from LAT collaboration • The maximum at 4-6 kpc coincides with the maximum of OB stars, may be caused by higher injection rate by OB star clusters. • A lower CR density in GC region, may be connected with strong advection therein. • The hardening in the inner galaxy may also be caused by strong wind (probably CR driven). • Evidence for OB star cluster as an substantial (even dominate) CR source.

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