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Astron. Astrophys. 352, 308-316 (1999)

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EUV mapping of the local interstellar medium: the Local Chimney revealed?

B.Y. Welsh 1, D.M. Sfeir 1,2, M.M. Sirk 1 and R. Lallement 2

1 Experimental Astrophysics Group, Space Sciences Laboratory, UC Berkeley, Berkeley, CA 94720, USA
2 Service d'Aeronomie du CNRS, 91371 Verrieres-le-Buisson, France

Received 30 August 1999 / Accepted 29 September 1999

Abstract

We discuss the galactic distribution of 450 sources detected by the EUVE satellite that have reliable distance estimates. Late-type stars dominate the nearby EUV source distribution, whereas the majority of EUV source detections with distances [FORMULA] 100pc are hot white dwarf stars. The galactic distribution of all these sources is non-uniform with number enhancements seen towards the Hyades cluster, in line-of-sight along the [FORMULA] CMa interstellar tunnel and towards high galactic latitudes in both hemispheres. A comparison of the distribution of these EUV sources with that of the neutral absorption boundary of the Local Bubble region derived from the interstellar NaI observations of Sfeir et al. (1999) reveals that vast majority of EUV sources are contained within this neutral boundary. However, at high galactic latitudes 20 extragalactic EUV sources have been detected along lines-of-sight with low neutral column density, and is consistent with the local interstellar cavity being "open-ended" in the galactic halo. This "Local Chimney" opens towards two regions of enhanced intensity of the 0.25 keV soft X-ray background emission at high galactic latitudes. Although the hot Local Bubble gas is still contained within a cold, neutral interstellar gas boundary in the galactic plane, it has probably expanded into the halo to produce the Local Chimney feature.

Key words: ISM: atoms, ions – ISM: clouds – Galaxy: solar neighbourhood

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© European Southern Observatory (ESO) 1999

Online publication: November 23, 1999
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