| dc.creator |
Cernicharo, José |
|
| dc.creator |
Goicoechea, Javier R. |
|
| dc.creator |
Pardo Carrión, Juan Ramón |
|
| dc.creator |
Asensio Ramos, Andrés |
|
| dc.date |
2008-01-03T16:14:27Z |
|
| dc.date |
2008-01-03T16:14:27Z |
|
| dc.date |
2006-05-10 |
|
| dc.date.accessioned |
2017-01-31T00:59:39Z |
|
| dc.date.available |
2017-01-31T00:59:39Z |
|
| dc.identifier |
The Astrophysical Journal, 642: 940-953 (2006) |
|
| dc.identifier |
1538-4357 |
|
| dc.identifier |
http://hdl.handle.net/10261/2652 |
|
| dc.identifier |
10.1086/501425 |
|
| dc.identifier.uri |
http://dspace.mediu.edu.my:8181/xmlui/handle/10261/2652 |
|
| dc.description |
Several condensations heated externally by nearby hot stars are present in the Sgr B2 region for which H2O far-IR lines are expected to probe only an external low-density and high temperature section. Millimeter-wave lines can penetrate deeper into them (higher densities and lower Tk). We have conducted a study combining H2O lines in both spectral regions using the ISO (far-IR lines) and the IRAM 30m telescope (183 GHz line). The far-IRH2O lines, seen in absorption, are optically thick. They form in the outermost gas in front of the far-IR continuum sources, probing a maximum visual extinction of ~5–10 mag. IR photons from the dust play a dominant role in their excitation. We
conclude, based on observations of the COJ = 7-6 line at 806.65 GHz, and the lack of emission from the far-IR CO lines, that the gas density has to be below ~10^4 cm^-3. Using the gas kinetic temperature and density derived from OH, CO, and other molecular species, we derive a water column density of (9 ± 3) x 10^16 cm^-2 in the absorbing gas, implying an abundance of ~(1-2) x 10^-5 in this region. The resulting relatively low H2O/OH abundance ratio,
~2–4, is a signature of UV photon-dominated surface layers traced by far-IR observations. As a consequence, the
temperature of the absorbing gas is high, Tk ~ 300-500 K, which allows very efficient neutral-neutral reactions producing H2O and OH. Finally, the 183.31 GHz data allow one to trace the inner, denser (n(H2) > 10^5-10^6 cm^-3), and colder (Tk ~ 40K) gas. The emission is very strong toward the cores with an estimated water vapor abundance of
a few x 10^-7. There is also moderate extended emission around Sgr B2 main condensations, in agreement with the
water vapor abundance derived from far-IR H2O lines. |
|
| dc.description |
We thank Spanish DGES and PNIE for funding support under grants PANAYA2000-1784, ESP2001-4516, AYA2002-10113-E, ESP2002-01627,AYA2003-02785-E and AYA2004-05792. CSO
observations were supported by NSF grant AST-9980846. J.R.G. was also supported by the French Direction de la Recherche in the
latest stages of the work. |
|
| dc.description |
Peer reviewed |
|
| dc.format |
1372655 bytes |
|
| dc.format |
application/pdf |
|
| dc.language |
eng |
|
| dc.publisher |
American Astronomical Society |
|
| dc.publisher |
University of Chicago Press |
|
| dc.rights |
openAccess |
|
| dc.subject |
Infrared: ISM |
|
| dc.subject |
ISM: individual (Sgr B2) |
|
| dc.subject |
ISM: lines and bands |
|
| dc.subject |
ISM: molecules |
|
| dc.subject |
Radiative transfer |
|
| dc.title |
Warm Water Vapor around Sagittarius B2 |
|
| dc.type |
Artículo |
|