Velocity resolved [CII] spectroscopy of the center and the BCLMP302 region of M33 (HerM33es)

Abstract : We aim to understand the contribution of the ionized, atomic and molecular phases of the ISM to the [CII] emission from clouds near the dynamical center and the BCLMP302 HII region in the north of the nearby galaxy M33 at a spatial resolution of 50pc. We combine high resolution [CII] spectra taken with the HIFI spectrometer onboard the Herschel satellite with [CII] Herschel-PACS maps and ground-based observations of CO(2-1) and HI. All data are at a common spatial resolution of 50pc. Typically, the [CII] lines have widths intermediate between the narrower CO(2-1) and broader HI line profiles. We decomposed the [CII] spectra in terms of contribution from molecular and atomic gas detected in CO(2-1) and HI, respectively. We find that the relative contribution of molecular and atomic gas traced by CO(2-1) and HI varies depends mostly on the local physical conditions and geometry. We estimate that 11-60% and 5-34% of the [CII] intensities in the center and in BCLMP302, respectively, arise at velocities showing no CO(2-1) or HI emission and could arise in CO-dark molecular gas. The deduced strong variation in the [CII] emission not associated with CO and HI cannot be explained in terms of differences in A_v, far-ultraviolet radiation field, and metallicity between the two studied regions. Hence the relative amounts of diffuse (CO-dark) and dense molecular gas possibly vary on spatial scales smaller than 50pc. Based on the emission measure observed at radio wavelengths we estimate the contribution of ionized gas at a few positions to lie between 10-25%. The correlations between the intensities of tracers corresponding to the same velocity range as [CII], differ from the correlation derived from PACS data. The results in this paper emphasize the need for velocity-resolved observations to discern the contribution of different components of the ISM to [CII] emission. (abridged)
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Astronomy and Astrophysics - A&A, EDP Sciences, 2016, 586, pp.id.A37. <10.1051/0004-6361/201527366>
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https://hal.archives-ouvertes.fr/hal-01238993
Contributeur : Marie-Paule Pomies <>
Soumis le : lundi 7 décembre 2015 - 12:49:13
Dernière modification le : mercredi 28 septembre 2016 - 16:19:50

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B., Mookerjea, F., Israel, C., Kramer, T., Nikola, J. Braine, et al.. Velocity resolved [CII] spectroscopy of the center and the BCLMP302 region of M33 (HerM33es). Astronomy and Astrophysics - A&A, EDP Sciences, 2016, 586, pp.id.A37. <10.1051/0004-6361/201527366>. <hal-01238993>

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