Аннотация
(abridged) The Magellanic Clouds provide a nearby laboratory for metal-poor
dwarf galaxies. The low dust abundance enhances the penetration of UV photons
into the interstellar medium (ISM), resulting in a relatively larger filling
factor of the ionized gas. Furthermore, there is likely a hidden molecular gas
reservoir probed by the CII157um line. We present Herschel/PACS maps in
several tracers, CII, OI63um,145um, NII122um, NIII57um, and OIII88um
in the HII region N11B in the Large Magellanic Cloud. Halpha and OIII5007A
images are used as complementary data to investigate the effect of dust
extinction. Observations are interpreted with photoionization models to infer
the gas conditions and estimate the ionized gas contribution to the CII
emission. Photodissociation regions (PDRs) are probed through polycyclic
aromatic hydrocarbons (PAHs). We first study the distribution and properties of
the ionized gas. We then constrain the origin of CII157um by comparing to
tracers of the low-excitation ionized gas and of PDRs. OIII is dominated by
extended emission from the high-excitation diffuse ionized gas; it is the
brightest far-infrared line, ~4 times brighter than CII. The extent of the
OIII emission suggests that the medium is rather fragmented, allowing far-UV
photons to permeate into the ISM to scales of >30pc. Furthermore, by comparing
CII with NII, we find that 95% of CII arises in PDRs, except toward the
stellar cluster for which as much as 15% could arise in the ionized gas. We
find a remarkable correlation between CII+OI and PAH emission, with CII
dominating the cooling in diffuse PDRs and OI dominating in the densest PDRs.
The combination of CII and OI provides a proxy for the total gas cooling in
PDRs. Our results suggest that PAH emission describes better the PDR gas
heating as compared to the total infrared emission.
Пользователи данного ресурса
Пожалуйста,
войдите в систему, чтобы принять участие в дискуссии (добавить собственные рецензию, или комментарий)