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Astron. Astrophys. 332, 55-70 (1998)

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7. Summary

We analyzed the [FORMULA] keV and [FORMULA] keV ROSAT all-sky-survey data and evaluated the photoelectric absorption of the neutral matter traced by H gas as given by the Leiden/Dwingeloo survey. The main results are:

  1. At high latitudes near [FORMULA] the temperature of the distant X-ray MK plasma is kT = 0.13-0.14 keV (Sect. 3.2), a value in agreement with other published X-ray temperatures obtained towards different directions of the galactic sky. Hence, we found that the thermal X-ray component is, in a first approximation, isothermal.
  2. The photoelectric-absorption-corrected [FORMULA] keV count rate decreases with increasing latitude and towards the galactic anticenter, (Sect. 3.5), indicating that a significant fraction of the galactic [FORMULA] keV emission originates in the halo.
  3. We modelled an isothermal flattened X-ray halo based on hydrostatic equilibrium considerations (Sect. 4.1). An X-ray halo component with a scale height of [FORMULA] and a radial scale length of [FORMULA] in addition to an extragalactic power-law ([FORMULA]) component - both absorbed by galactic neutral matter - can reproduce the [FORMULA] keV RASS data down to its data accuracy limit (Sect. 4.2).
  4. The RASS [FORMULA] keV large-scale intensity distribution is consistent with this X-ray plasma halo model (Sect. 6).

(Since our analysis is restricted to latitudes above [FORMULA] and to directions away from the galactic bulge, we note that our results are largely restricted to information contributed from a volume within about 4 kpc from the Sun.)

Finally, assuming that the X-ray halo model is valid for the entire Galaxy, we obtain a total halo X-ray luminosity of [FORMULA]. This value is comparable to luminosities found for the X-ray halos of M51 and NGC1566 by Ehle (1996). This may be an indication of a common X-ray halo-producing mechanism, as for example a galactic fountain by stellar activity (e.g. Bregman 1980), where hot material is transported up and radially outward, reproducing the X-ray parameters determined.

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© European Southern Observatory (ESO) 1998

Online publication: March 10, 1998