A&A 411, 447-464 (2003)
3D mapping of the dense interstellar gas around the Local
R. Lallement1, B. Y. Welsh2, J. L. Vergely3, F. Crifo4 and D. Sfeir2
Service d'Aéronomie du CNRS, 91371 Verrières-le-Buisson, France
Astrophysics Group, Space Sciences Laboratory, UC Berkeley, CA 94720, USA
ACRI-ST, BP 234, 06504 Sofia-Antipolis, France
GEPI and URA 8111 du CNRS, Observatoire de Paris, 92195 Meudon, France
(Received 21 February 2003 / Accepted 30 July 2003 )
We present intermediate results from a long-term program of mapping
the neutral absorption characteristics of the
local interstellar medium, motivated by the availability of accurate
and consistent parallaxes from the Hipparcos satellite.
Equivalent widths of the interstellar
NaI D-line doublet at 5890 Å are presented for the lines-of-sight
towards some 311 new
target stars lying within ~350 pc of the Sun.
Using these data, together with
NaI absorption measurements towards a
further ~240 nearby targets published in
the literature (for many of them, in the directions of molecular clouds), and the ~450 lines-of-sight already
by (Sfeir et al. 1999), we show
3D absorption maps of the local distribution of neutral gas
towards 1005 sight-lines with
Hipparcos distances as
viewed from a variety of different galactic projections.
The data are synthesized by means of two complementary methods,
(i) by mapping of iso-equivalent width contours,
and (ii) by
density distribution calculation
from the inversion of column-densities,
method devised by Vergely et al. (2001).
Our present data confirms the view that the local cavity
is deficient in cold and neutral interstellar gas. The closest dense and cold
gas "wall", in the first quadrant,
is at ~55-60 pc. There are
a few isolated clouds at closer distance,
if the detected absorption is not produced by
The maps reveal narrow or wide "interstellar tunnels" which connect the Local Bubble
to surrounding cavities, as predicted by the model of Cox & Smith (1974).
In particular, one of these tunnels, defined by stars at 300 to 600 pc from
showing negligible sodium absorption, connects the well known CMa void
(Gry et al. 1985), which is part of
the Local Bubble, with the
supershell GSH 238+00+09 (Heiles 1998).
High latitude lines-of-sight with the smallest absorption are found
in two "chimneys", whose directions are perpendicular to the Gould belt plane.
The maps show that the Local Bubble is
"squeezed" by surrounding shells
in a complicated pattern
and suggest that its pressure is smaller than in those expanding regions.
We discuss the locations of several HI and molecular
clouds. Using comparisons between NaI and HI or CO velocities, in some cases we are able to improve the constraints
on their distances. According to the velocity criteria,
MBM 33-37, MBM 16-18, UT 3-7, and MBM 54-55 are closer than ~100 pc, and MBM 40 is closer than 80 pc.
Dense HI clouds are seen at less than 90 pc and 85 pc in the directions
of the MBM 12 and MBM 41-43 clouds respectively, but the
molecular clouds themselves may be far beyond.
The above closest molecular clouds
are located at the neutral boundary of the Bubble.
Only one translucent cloud, G192-67, is clearly embedded
within the LB and well isolated.
These maps of the distribution of local neutral interstellar
NaI gas are also briefly compared with the distribution of both interstellar
dust and neutral HI gas within 300 pc.
Galaxy: solar neighborhood --
ISM: atoms --
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