Universität zu Köln

Mookerjea, B., Israel, F., Kramer, C., Nikola, T., Braine, J., Ossenkopf, V., Roellig, M., Henkel, C., van der Werf, P., van der Tak, F. and Wiedner, M. C. (2016). Velocity resolved [C ii] spectroscopy of the center and the BCLMP 302 region of M33 (HerM 33es). Astron. Astrophys., 586. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. The forbidden fine structure transition of C+ at 158 mu m is one of the major cooling lines of the interstellar medium (ISM). Aims. 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 50 pc. Methods. We combine high-resolution [Cii] spectra taken with the HIFI spectrometer onboard the Herschel satellite with [C ii] Herschel-PACS maps and ground-based observations of CO(2-1) and Hi. All data are at a common spatial resolution of 50 pc. Correlation coefficients between the integrated intensities of [Cii], CO(2-1) and Hi are estimated from the velocity-integrated PACS data and from the HIFI data. We decomposed the [Cii] spectra in terms of contribution from molecular and atomic gas detected in CO(2-1) and Hi, respectively. At a few positions, we estimated the contribution of ionized gas to [Cii] from the emission measure observed at radio wavelengths. Results. In both regions, the center and BCLMP302, the correlation seen in the [Cii], CO(2-1) and Hi intensities from structures of all sizes is significantly higher than the highest correlation in intensity obtained when comparing only structures of the same size. The correlations between the intensities of tracers corresponding to the same velocity range as [C ii], differ from the correlation derived from PACS data. Typically, the [C ii] lines have widths intermediate between the narrower CO(2-1) and broader Hi line profiles. A comparison of the spectra shows that the relative contribution of molecular and atomic gas traced by CO(2-1) and Hi varies substantially between positions and depends mostly on the local physical conditions and geometry. At the positions of the Hii regions, the ionized gas contributes between 10-25% of the observed [Cii] intensity. 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 H i 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 AV, far-ultraviolet radiation field, and metallicity between the two studied regions. Conclusions. The relative amounts of diffuse (CO-dark) and dense molecular gas possibly vary on spatial scales smaller than 50 pc. In both regions, a larger fraction of the molecular gas is traced by [C ii] than by the canonical tracer CO. Correlations between observed intensities of [Cii], CO, and Hi crucially depend on the spatial and spectral resolution of the data and need to be used carefully, in particular, for extragalactic studies. These results emphasize the need for velocity-resolved observations to discern the contribution of different components of the ISM to [Cii] emission.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Mookerjea, B. UNSPECIFIED UNSPECIFIED UNSPECIFIED Israel, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Kramer, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Nikola, T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Braine, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED Ossenkopf, V. UNSPECIFIED UNSPECIFIED UNSPECIFIED Roellig, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Henkel, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED van der Werf, P. UNSPECIFIED UNSPECIFIED UNSPECIFIED van der Tak, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Wiedner, M. C. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-285341
DOI:	10.1051/0004-6361/201527366
Journal or Publication Title:	Astron. Astrophys.
Volume:	586
Date:	2016
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language GROUP GALAXY M33; MU-M EMISSION; STAR-FORMATION; COLLISIONAL EXCITATION; MOLECULAR CLOUDS; CII EMISSION; HII-REGIONS; GAS; SPACE; LINE Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/28534