HERSCHEL/SPIRE SUBMILLIMETER SPECTRA OF LOCAL ACTIVE GALAXIES,Journal Articles
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abstract
We present the sub-millimeter spectra from 450 GHz to 1550 GHz of eleven
nearby active galaxies observed with the SPIRE Fourier Transform Spectrometer
(SPIRE/FTS) onboard Herschel. We detect CO transitions from J_up = 4 to 12, as
well as the two [CI] fine structure lines at 492 and 809 GHz and the [NII] 461
GHz line. We used radiative transfer models to analyze the observed CO spectral
line energy distributions (SLEDs). The FTS CO data were complemented with
ground-based observations of the low-J CO lines. We found that the warm
molecular gas traced by the mid-J CO transitions has similar physical
conditions (n_H2 ~ 10^3.2 - 10^3.9 cm^-3 and T_kin ~ 300 - 800 K) in most of
our galaxies. Furthermore, we found that this warm gas is likely producing the
mid-IR rotational H2 emission. We could not determine the specific heating
mechanism of the warm gas, however it is possibly related to the star-formation
activity in these galaxies. Our modeling of the [CI] emission suggests that it
is produced in cold (T_kin < 30 K) and dense (n_H2 > 10^3 cm^-3) molecular gas.
Transitions of other molecules are often detected in our SPIRE/FTS spectra. The
HF J=1-0 transition at 1232 GHz is detected in absorption in UGC05101 and in
emission in NGC7130. In the latter, near-infrared pumping, chemical pumping, or
collisional excitation with electrons are plausible excitation mechanisms
likely related to the AGN of this galaxy. In some galaxies few H2O emission
lines are present. Additionally, three OH+ lines at 909, 971, and 1033 GHz are
identified in NGC7130.
