Issue |
A&A
Volume 467, Number 3, June I 2007
|
|
---|---|---|
Page(s) | 1117 - 1123 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20065815 | |
Published online | 19 March 2007 |
An evolutionary sequence of expanding hydrogen shells in galaxy discs
1
Dpto. Física Teórica y del Cosmos, Universidad de Granada, Avda. Fuentenueva s/n, 18071 Granada, Spain e-mail: mrelano@ugr.es
2
Instituto de Astrofísica de Canarias, C. Vía Láctea s/n, 38200 La Laguna, Tenerife, Spain
3
Consejo Superior de Investigaciones Científicas (CSIC), Spain e-mail: jeb@ll.iac.es
4
Observatoire du mont Mégantic, LAE, Université de Montréal, C. P. 6128 succ. centre ville, Montréal, Québec, H3C 3J7, Canada e-mail: [odaigle;carignan]@ASTRO.UMontreal.CA
Received:
13
June
2006
Accepted:
12
March
2007
Aims.Large HI shells, with diameters of hundreds of pc and expansion velocities of 10–20 km s-1 have been detected in their hundreds in the Milky Way and are well observed features of local gas rich galaxies. These shells could well be predicted as a result of the impact of OB associations on the ISM, but doubt has been cast on this scenario by the apparent absence of OB stars close to the centres of a large fraction of these shells in recent observations of the SMC. Here we present observational evidence within an energetically consistent framework which strongly supports the scenario in which OB associations do produce the giant HI shells.
Methods.Using Fabry-Perot scanned Hα
emission line mapping of nearby galaxy discs, we have detected, in
all the H ii regions where the observations yield sufficient
angular resolution and S:N ratio, dominant Hα shells with radii a few tens of pc, expanding
at velocities of 50-100 km s-1, and with gas masses of 10105
. In previous studies, we found
that stellar winds alone can account for the energetics of most of
the Hα shells, which form initially before the stars explode as
SNe. We have applied a simple dynamically
consistent framework in which we can extrapolate the properties of the
observed Hα shells to a few 107 yr after the formation of the OB stars.
The framework includes the dynamical inputs of both winds and SNe on the
surrounding ISM. The results give quantitative statistical support to the
hypothesis that the Hα emitting shells are generic progenitors of the
HI shells.
Results.The results are in good agreement with the ranges of masses
(~106 ), velocities (up to ~20km s-1), and
diameters (up to ~500 pc) of representative HI shells observed in
nearby galaxies. The combined effects of stellar winds, acting during
the first few 106 yr, and SN explosions, “switching on”
subsequently, are required to yield the observed parameters.
Key words: ISM: H ii regions / ISM: kinematics and dynamics / ISM: bubbles / galaxies: general
© ESO, 2007
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