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

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

Sep 22, 2023 219 likes •438 views

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

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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)

35th international Cosmic Ray Conference Busan, 2017. 18. 7

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SLIDE 2

Diffuse emission in the plane

  • Gamma-ray emission in the plane (|b|<5o): 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

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SLIDE 3

Gamma-ray sky

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

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SLIDE 4

Fit with dust column template

10-12 10-11 10-10 10-9 0.1 1 10 100 φ(E) (erg s-1 cm-2) Energy(GeV) l=[5o:15o] l=[85o:95o] l=[175o:185o]

Hardening of spectrum toward inner galaxy. (| b|<5o)

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SLIDE 5

Fit with dust column template

Hardening of spectrum toward inner galaxy.

2.3 2.6 2.9 50 100 150 200 250 300 350 photon index above 2 GeV Galactic Longitude (o)

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SLIDE 6

Fit with gas ring template

  • Use kinematic distances.
  • 6 Galactocentric gas rings (|b|<5o).
  • CO conversion factor left free in the fit.
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SLIDE 7

Fit with gas ring template

SED in different rings

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SLIDE 8

Fit with gas ring template

2.3 2.6 2.9 5 10 15 20 25 30 photon index above 2 GeV Distance to GC (kpc)

Index distributions

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SLIDE 9

Fit with gas ring template

Emissivities per H (CR density)

10-27 10-26 5 10 15 20 25 30 emissivity per H atom (>1GeV) (ph sr-1 s-1) Distance to GC (kpc) CMZ Sgr B

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SLIDE 10

Fit with gas ring template

CRs SED in different rings.

102 103 104 1 10 100 1000 Flux × E2 (m-2s-1sr-1GeV) Energy(GeV) r < 8kpc 4kpc < r <6kpc r > 8kpc Orion B GeV excess

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SLIDE 11

Source distributions

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

Peak coincide with OB stars

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SLIDE 12

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…..

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SLIDE 13

Cygnus cocoon

8 46 84 122 160 198 236 274 312 350 388 315.000 310.000 305.000 300.000 48.000 44.000 40.000 36.000 32.000

Right ascension Declination gamma Cygni Cygnus Cocoon 35 LAT PSR J2032+4127 LAT PSR J2030+4415 PSR J2030+3641 LAT PSR J2028+3332 B2 2023+33 4C +31.56 LAT PSR J2021+4026 TXS 2016+386 MG2 J201534+3710 PSR J1952+3252 1

10-11 10-10 10-9 1 10 100 1000 φ(E)(erg s-1 cm-2) Energy(GeV)

Spectral Index of -2.2, up to 500 GeV with PASS 8 data. Fermi LAT counts map (>1 GeV)

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SLIDE 14

NGC 3603 (sky maps)

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 40:00.0 30:00.0 20:00.0 10:00.0 11:00:00.0 10:50:00.0

  • 58:00:00.0
  • 60:00:00.0
  • 62:00:00.0
  • 64:00:00.0

Right ascension Declination

3FGL J1112.0-6135 3FGL J1111.9-6038 PMN J1047-6217 PSR J1055-6028 AT20G J112319-641735 PSR J1105-6107 PSR J1112-6103 PSR J1119-6127 LAT PSR J1135-6055 PSR J1125-6014 PSR J1124-5916 PSR J1125-5825

Counts map (>10 GeV)

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 40:00.0 30:00.0 20:00.0 10:00.0 11:00:00.0 10:50:00.0

  • 58:00:00.0
  • 60:00:00.0
  • 62:00:00.0
  • 64:00:00.0

Right ascension Declination

Residual map (>10 GeV), known source removed

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SLIDE 15

NGC 3603 (SEDs and CR content)

10-12 10-11 10-10 1 10 100 φ(E)(erg s-1 cm-2) Energy(GeV) NGC 3603 3FGL J1111.9-6038

Gamma-ray SEDs Index ~ -2.3, up tp 300 GeV

10-12 10-11 10-10 0.1 1 10 100 1000 E2 dN/dE (erg cm-2 s-1 ) Energy(GeV)

ne = 2 cm-3 ne = 10 cm-3

Compared with LIS emissivities

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SLIDE 16

NGC 3603 (gas content)

.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 40:00.0 30:00.0 20:00.0 10:00.0 11:00:00.0 10:50:00.0

  • 58:00:00.0
  • 60:00:00.0
  • 62:00:00.0
  • 64:00:00.0

Right ascension Declination

CO+HI (0 ~ 20 km/s) HII gas

.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 40:00.0 30:00.0 20:00.0 10:00.0 11:00:00.0 10:50:00.0

  • 58:00:00.0
  • 60:00:00.0
  • 62:00:00.0
  • 64:00:00.0

Right ascension Declination

Tentative correlation with HII distribution

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SLIDE 17

Westerlund 2 (Preliminary results)

0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 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

  • 54:00:00.0
  • 56:00:00.0
  • 58:00:00.0
  • 60:00:00.0

Right ascension Declination PSR J1055-6028 PSR J1048-5832 Eta Carinae LAT PSR J1044-5737 PSR J1028-5819 LAT PSR J1023-5746 PSR J1019-5749 1FGL J1018.6-5856 PSR J1016-5857 PSR J0955-61 PSR J1055-6028 PSR J1048-5832 Eta Carinae LAT PSR J1044-5737 PSR J1028-5819 LAT PSR J1023-5746 PSR J1019-5749 1FGL J1018.6-5856 PSR J1016-5857

Counts map (>10 GeV)

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 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

  • 54:00:00.0
  • 56:00:00.0
  • 58:00:00.0
  • 60:00:00.0

Right ascension Declination PSR J1044-5737 PSR J1028-5819 PSR B1046-58 PSR J1023-5746 SNR G286.5-1.2 SNR G284.3-0.3

Residual map (>10 GeV), known source removed

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SLIDE 18

Westerlund 2 (Preliminary results)

10-13 10-12 10-11 10-10 1 10 100 1000 10000 φ(E)(erg s-1 cm-2) Energy(GeV) Westerlund 2 FGES J1023.3-5747 HESS J1023-575

  • 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.

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SLIDE 19

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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SLIDE 20

Thanks!