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Astronomy and Astrophysics 544 (2012) id.A55
Spectrally resolved CII emission in M~33 ({\tt HerM33es}): Physical conditions and kinematics around BCLMP 691
J. Braine 1, 2, 3, 4, P. Gratier 1, 2, 3, 4, C. Kramer 5, F. P. Israel, F. van der Tak 6, B. Mookerjea 7, M. Boquien 8, 9, F. Tabatabaei 10, P. van der Werf 11, C. Henkel 10

This work presents high spectral resolution observations of the \CII\ line at 158 \micron, one of the major cooling lines of the interstellar medium, taken with the HIFI heterodyne spectrometer on the Herschel satellite. In BCLMP 691, an \HII\ region far north (3.3 kpc) in the disk of M 33, the \CII\ and CO line profiles show similar velocities within $0.5 \kms$, while the \HI\ line velocities are systematically shifted towards lower rotation velocities by $\sim 5\kms$. Observed at the same $12"$ angular resolution, the \CII\ lines are broader than those of CO by about 50% but narrower than the \HI\ lines. The \CII\ line to far-infrared continuum ratio suggests a photoelectric heating efficiency of 1.1%. The data, together with published models indicate a UV field $G_0 \sim 100$ in units of the solar neighborhood value, a gas density $n_H \sim 1000 \cc$, and a gas temperature $T\sim 200$ K. Adopting these values, we estimate the C$^+$ column density to be $N_{C^+} \approx 1.3 \times 10^{17} \cmt$. The \CII\ emission comes predominantly from the warm neutral region between the \HII\ region and the cool molecular cloud behind it. From published abundances, the inferred C$^+$ column corresponds to a hydrogen column density of $N_H \sim 2 \times 10^{21} \cmt$. The CO observations suggest that $N_H = 2 N_{H_2} \sim 3.2 \times 10^{21} \cmt$ and 21cm measurements, also at $12"$ resolution, yield $N_\HI \approx 1.2 \times 10^{21} \cmt$ within the \CII\ velocity range. Thus, some H$_2$ not detected in CO must be present, in agreement with earlier findings based on the SPIRE 250 -- 500 $\mu$m emission.
1 :  Observatoire aquitain des sciences de l'univers (OASU)
CNRS : UMS2567 – INSU – Université Sciences et Technologies - Bordeaux I
2 :  Université Sciences et Technologies - Bordeaux 1
Université Sciences et Technologies - Bordeaux I
3 :  Laboratoire d'Astrophysique de Bordeaux (LAB)
CNRS : UMR5804 – INSU – Université Sciences et Technologies - Bordeaux I
4 :  Laboratoire d'astrodynamique, d'astrophysique et d'aéronomie de bordeaux (L3AB)
CNRS : UMR5804 – INSU – Université Sciences et Technologies - Bordeaux I
5 :  Instituto de RadioAstronomía Milimétrica (IRAM)
CNRS : UPS2074
6 :  Laboratoire d'Astrophysique de Grenoble (LAOG)
CNRS : UMR5571 – OSUG – INSU – Université Joseph Fourier - Grenoble I
7 :  KOSMA, I. Physikalisches Institut
Universität zu Köln
8 :  Astrophysique Interactions Multi-échelles (AIM - UMR 7158)
CNRS : UMR7158 – INSU – Université Paris VII - Paris Diderot – CEA : DSM/IRFU
9 :  Department of Astronomy
University of Massachusetts
10 :  Institut für Physik (Institut für Physik)
Universität Potsdam
11 :  Leiden Observatory
University of Leiden
Planète et Univers/Astrophysique/Astrophysique stellaire et solaire

Physique/Astrophysique/Astrophysique stellaire et solaire
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