Bibcode
Cappa, C.; Niemela, V. S.; Amorín, R.; Vasquez, J.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 477, Issue 1, January I 2008, pp.173-183
Advertised on:
1
2008
Revista
Número de citas
22
Número de citas referidas
20
Descripción
Aims:We analyze the distribution of the interstellar matter in the
environs of the H ii region Gum 31, excited by the open cluster NGC
3324, located in the complex Carina region, with the aim of
investigating the action of the massive stars on the surrounding neutral
material. Methods: We use neutral hydrogen 21-cm line data, radio
continuum images at 0.843, 2.4 and 4.9 GHz, 12CO(1-0)
observations, and IRAS and MSX infrared data. Results: Adopting a
distance of 3 kpc for the H ii region and the ionizing cluster, we
derived an electron density of 33±3 cm-3 and an
ionized mass of (3.3±1.1)×103 M&sun;
based on the radio continuum data at 4.9 GHz. The H i 21-cm line images
revealed an H i shell surrounding the H ii region. The H i structure is
10.0 ± 1.7 pc in radius, has a neutral mass of 1500 ± 500
M&sun;, and is expanding at 11 km s-1. The
associated molecular gas amounts to (1.1 ±
0.5)×105 M&sun;, being its volume density of
about 350 cm-3. This molecular shell could represent the
remains of the cloud where the young open cluster NGC 3324 was born or
could have originated by the shock front associated with the H ii
region. The difference between the ambient density and the electron
density of the H ii region suggests that the H ii region is expanding.
The distributions of the ionized and molecular material, along with that
of the emission in the MSX band A, suggest that a photodissociation
region has developed at the interface between the ionized and molecular
gas. The copious UV photon flux from the early type stars in NGC 3324
keeps the H ii region ionized. The characteristics of a relatively large
number of the IRAS, MSX, and 2MASS point sources projected onto the
molecular envelope are compatible with protostellar candidates, showing
the presence of active star forming regions. Very probably, the
expansion of the H ii region has triggered stellar formation in the
molecular shell.
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Casiana
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