Astronomy and Astrophysics – Astrophysics
Scientific paper
2004-10-07
Astrophys.J. 619 (2005) 291-296
Astronomy and Astrophysics
Astrophysics
5 pages, 4 figures, accepted in ApJ Part I (2004, October 6)
Scientific paper
10.1086/426540
We present Infrared Space Observatory (ISO) observations of several OH, CH and H2O rotational lines toward the bright infrared galaxies NGC253 and NGC1068. As found in the Galactic clouds in SgrB2 and Orion, the extragalactic far-IR OH lines change from absorption to emission depending on the physical conditions and distribution of gas and dust along the line of sight. As a result, most of the OH rotational lines that appear in absorption toward NGC253 are observed in emission toward NGC1068. We show that the far-IR spectrum of OH can be used as a powerful diagnostic to derive the physical conditions of extragalactic neutral gas. In particular, we find that a warm (Tk~150 K, n(H2)< 5 10^4 cm^-3) component of molecular gas with an OH abundance of 10^{-7} from the inner <15'' can qualitatively reproduce the OH lines toward NGC253. Similar temperatures but higher densities (5 10^5 cm^-3) are required to explain the OH emission in NGC1068.
Cernicharo Jose
Goicoechea Javier R.
Martín-Pintado Jesús
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