1. Gamma-ray Measurements of the distribution of Gas and Cosmic Ray in the Interstellar Space Yasushi Fukazawa Hiroshima University

2. Matter in the Galactic Plane Stars Atomic Gas (HI) Molecular Clouds (H 2 ) Ionized Gas (HII, X-ray Hot Gas) Dust Cosmic Ray 10 11 M. 10 9 M. 10 8 M. 10 7 M. 10M. All the interstellar medium can be traced by Gamma-ray. Opt. NIR 21cm CO X-ray FIR Radio Absorption-Free, Independent of physical and chemical states

3. Pi-0 decay (cosmic ray p) * (interstellar gas) Bremss (cosmic ray e) * (interstellar gas) IC (cosmic ray e) * (interstellar photon) Radio-synchrotron (cosmic ray e) * (interstellar B) 100 MeV 100 GeV Bremss(e) π 0 decay(p) Inverse Compton (e) Diffuse Gamma-Ray Emission along the Galactic Plane Study energy density and distribution of Cosmic-ray Proton, Electron, and Gas (and B), separately. COS-B Study the Galactic Structure and Formation in terms of Energetics ! (Mayer-Hasselwander et al. 1982)

4. EGRET (1991-2000) 20MeV-100GeV Detection of several molecular clouds Discovery of many pulsars and unidentified sources Detection of LMC OphuichusOrion π0 Hunter et al. 1994 Digel et al. 1995 Sreekumar et al. 1992

5. High energy tail Spectral variation between inner and outer galactic plane TeV (Whipple) Proton escape in the outer region ? Electron energy index flatter ? But high energy cut-off ? Hunter et al. 1997 l=0° l=180°

6. In order to resolve the emission more finely, we need much improved instruments of Gamma-ray GLAST (Gamma-ray Large Area Space Telescope) Launch 2005 USA, Japan, Italy, France Sparc chamber Silicon Strip Sensor Technological Improvement 4  4 array of Si-strip sensors (X) Si-strip(Y) Design and Development Hiroshima University (Japan) Large Area and Good Spatial Reso. Easy Assembly

7. EGRET GLAST Energy Band 30MeV--10GeV 20MeV--100GeV Field of View 0.5sr 2.4sr (20% of 4π) Effective Area 1,500cm2 11,000cm2 Energy Resolution 10% 10% Source Location 5—30arcmin 0.5—5arcmin Sensitivity ～ 1×10 -7 cm -2 s -1 2×10 -9 cm -2 s -1 (2years) Detected Sources 271 >10000 Basic Performance of GLAST EGRET(1991-1995) GLAST

8. EGRET 95% 5  source r = 7 ’ 5  source r = 7 ’ 30‘ Bright Sources r = 0.3 ’ EGRET GLAST GLAST Source Location and Resolution

9. ～ 50 Giant Molecular Clouds (D ～ 1kpc, M=10 5 M.) Distribution of cosmic-ray proton content among cloulds whose mass is well constrained Overall proton distribution 3×3 degree 2 mappinggrid e and p distribution Simulated spectra of GLAST SNRs Expected Observations

10. The difference of the distribution between p and e (cosmic-ray) e correlation with young SNRs or spiral arm? p uniform distribution ? Energy equipartition ? p and e content in other galaxies with different types p in clusters of galaxies ? H 2 /CO ratio in many molecular cloud (accurate molecular mass) ? Expected Results Any unobserved gas (e.g. Ionized gas with kT=10 5-6 K )? LMC simulation Interstellar Gas (LMC,SMC,M31,M82…) (Coma Cluster…) Energy density distribution of p and e Ionization Accelaration rate

12. Strong Correlation with HI column density Gamma-ray SpectrumGamma-ray Intensity Possible bump of π 0 decay Fichtel et al. 1983 Possible Detection of Molecular Cloud Main Results from SAS-2 and COS-B Orion Wolfendale 1980 Strong et al. 1982

13. Diffuse Gamma-Ray Emission along the Galactic Plane Discovery … OSO-3 (1967) Detailed Analysis SAS-2 (launch 1972, 35-200MeV) COS-B (launch 1975, 70MeV-5GeV) Image in Yamasaki D(COS-B) 100 MeV 100 GeV Bremss(e) π 0 decay(p) Inverse Compton (e)