Hostname: page-component-586b7cd67f-vdxz6 Total loading time: 0 Render date: 2024-11-26T04:44:03.707Z Has data issue: false hasContentIssue false
  • English
  • Français

High-energy Galactic phenomena and the interstellar medium

Published online by Cambridge University Press:  04 August 2017

Catherine J. Cesarsky
Catherine J. Cesarsky*
Affiliation:
Service d'Astrophysique Centre d'Etudes Nucléaires de Saclay, France

Extract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

Gamma rays of energy in the range 30 MeV-several GeV, observed by the satellites SAS-2 and COS-B, are emitted in the interstellar medium as a result of interactions with gas of cosmic-ray nuclei in the GeV range (π° decay γ rays) and cosmic-ray electrons of energy > 30 MeV (bremsstrahlung γ rays). W. Hermsen has presented at this conference the γ ray maps of the Galaxy in three “colours” constructed by the COS-B collaboration; the information in such maps is supplemented by radio-continuum studies (see lecture by R. Beck), and is a useful tool for studying the distribution of gas, cosmic rays (c.r.) and magnetic fields in the Galaxy. The variables in this problem are many:large-scale (~ 1 kpc) and small-scale (~10 pc) distributions of c.r. nuclei, of c.r. electrons, of atomic and molecular hydrogen, of magnetic fields, fraction of the observed radiation due to localized sources, etc. Of these, only the distribution - or at least the column densities - of atomic hydrogen are determined in a reliable way. Estimates of the amount of molecular hydrogen can be derived from CO observations or from galaxy counts. The radio and gamma-ray data are not sufficient to disentangle all the other variables in a unique fashion, unless a number of assumptions are made (e.g. Paul et al. 1976). Still, the COS-B team has been able to show that :

a) there is a correlation between the gamma-ray emission from local regions, as observed at intermediate latitudes, and the total column density of dust, as measured by galaxy counts. The simplest interpretation is that the density of c.r. nuclei and electrons is uniform within 500 pc of the sun, and that dust and gas are well mixed. Then, γ rays can be used as excellent tracers of local gas complexes (Lebrun et al. 1982, Strong et al. 1982).

b) In the same way, the simplest interpretation of the γ-ray emission at energy > 300 MeV from the inner Galaxy, is that c.r. nuclei and electrons are distributed uniformly as well : there is no need for an enhanced density of c.r. in the 3–6 kpc ring; on the contrary, even assuming a uniform density of c.r., the γ-ray data are in conflict with the highest estimates of molecular hydrogen in the radio-astronomy literature (Mayer-Hasselwander et al. 1982).

c) In the outer Galaxy, the gradient of c.r. which had become apparent in the early SAS-2 data can now, with COS-B data, be studied in three energy ranges. A gradient in the c.r. distribution is only required to explain the low-energy radiation, which is dominated by bremsstrahlung from relativistic electrons (Bloemen et al., in preparation).

Type
PART II: COMPOSITION, STRUCTURE AND KINEMATICS
Information
Symposium - International Astronomical Union , Volume 106: The Milky Way Galaxy , 1985 , pp. 225 - 233
Copyright
Copyright © Reidel 1985 

References

Arnaud, M., Rothenflug, R., and Rocchia, R., 1983, Physica Scripta (in press).Google Scholar
Axford, W.I. 1981, Proc. 17th Int. Cosmic Ray Conf., Paris, 12, p. 155.Google Scholar
Bignami, G. and Hermsen, W. 1983, Ann. Rev. Astron. Astrophys., in press.Google Scholar
Bignami, G.F., Caraveo, P.A., Lamb, R.C. 1983, Astrophys. J; (Lett.), in press.Google Scholar
Blandford, R.D. and Ostriker, J.P. 1980, Astrophys. J. 237, p. 703.Google Scholar
Bobalsky, 1977, 1978 is short for the following 4 papers:Google Scholar
Blandford, R.D. and Ostriker, J.P. 1978, Astrophys. J. 221, p.L29.Google Scholar
Bell, A.R., 1978 M.N.R.A.S. 1982, p. 147.CrossRefGoogle Scholar
Axford, W.I., Leer, E. and Skadron, G. 1977, Proc. 15th Int. Cosmic Ray Conf. Plovdiv 11, p. 132.Google Scholar
Krymsky, G.F. 1977, Dokl. Akad. Nauk. SSSR, 234, p. 1306.Google Scholar
Bogdan, T.J., Völk, H. 1983, Astron. Astrophys. 122, p. 129.Google Scholar
Caraveo, P.A. et al. 1983, preprint.Google Scholar
Caraveo, P.A. et al. 1981, Proc. 17th Int. Cosmic Ray Conf., Paris, 1, p. 139.Google Scholar
Cassé, M. and Paul, J.A. 1980, Astrophys. J. 237, p. 236.Google Scholar
Cesarsky, C.J. and Montmerle, T. 1983, Space Sci. Rev. 36, p. 173 Google Scholar
Cox, D.P. 1981, Astrophys. J. 245, p. 534.CrossRefGoogle Scholar
Cox, D.P. and Anderson, P.R. 1982, Astrophys. J. 253, p. 268.CrossRefGoogle Scholar
Cox, D.P. and Smith, B.W. 1974, Astrophys. J. 189, p. L105.Google Scholar
Drury, L.O.'C. 1983, Rep. Progr. Phys., in press.Google Scholar
Eichler, D. 1979, Astrophys. J. 229, p. 419.CrossRefGoogle Scholar
Ellison, D. 1981, Ph.D. Thesis, Catholic University.Google Scholar
Fermi, E. 1949, Phys. Rev. 75, p. 1169.Google Scholar
Fichtel, C.E. et al. 1975, Astrophys. J. 198, p. 163.Google Scholar
Hayakawa, S. et al. 1979, in COSPAR X-Ray Astronomy, ed. Baity, W.A. and Peterson, L.E., Pergamon Press, p. 319.Google Scholar
Hermsen, W. and Bloemen, J.B.G.M. 1983, Leiden Workshop on Southern Galactic Surveys, Reidel, p. 65 Google Scholar
Inoue, H. et al. 1979, Astrophys. J. 227, L85.Google Scholar
Jenkins, E.B. 1978a, Astrophys. J. 219, p. 845.CrossRefGoogle Scholar
Jenkins, E.B. 1978b, Astrophys. J. 220, p. 107.CrossRefGoogle Scholar
Lagage, P.O. and Cesarsky, C.J. 1983, Astron. Astrophys., in press.Google Scholar
Lebrun, F. et al. 1982, Astron. Astrophys. 107, p. 390.Google Scholar
Lebrun, F. et al. 1983, Astrophys. J., in press.Google Scholar
Mayer-Hasselwander, H.A. et al. 1982, Astron. Astrophys. 105, p. 164.Google Scholar
McCammon, D. et al. 1983, Astrophys. J. 269, p. 107.CrossRefGoogle Scholar
McKee, C.F. and Ostriker, J.P. 1977, Ap. J. 218, p. 148.Google Scholar
McKenzie, J.F. and Völk, H.J. 1982, Astron. Astrophys. 116, p. 191.Google Scholar
Moffat, A.F.J. et al. 1983, Astrophys. J. (Lett.), in press.Google Scholar
Montmerle, T. 1979, Astrophys. J. 231, p. 95.CrossRefGoogle Scholar
Montmerle, T. and Cesarsky, C.J. 1980, Non-Solar Gamma Rays, Pergamon Press, p. 61.Google Scholar
Montmerle, T. et al. 1983, Astrophys. J. 269, p. 182.Google Scholar
Moraal, H. and Axford, W.I. 1983, Astron. Astrophys., in press.Google Scholar
Morfill, G.E. et al. 1981, Astrophys. J. 246, p. 810.Google Scholar
Paul, J., Cassé, M. and Cesarsky, C.J. 1976, Astrophys. J. 207, p. 62.Google Scholar
Rocchia, R. et al. 1983, submitted to Astron. Astrophys.Google Scholar
Strong, A.W. et al. 1982, Astron. Astrophys. 115, p. 404.Google Scholar
Swanenburg, B.N. et al., 1981, Astrophys. J. 243, p. L69.Google Scholar
Webber, W., 1983, Composition and Origin of Cosmic Rays, Reidel, p. 25.Google Scholar