Tabatabaei, F. S., Braine, J., Xilouris, E. M., Kramer, C., Boquien, M., Combes, E., Henkel, C., Relano, M., Verley, S., Gratier, P., Israel, F., Wiedner, M. C., Roellig, M., Schuster, K. F. and van der Werf, P. (2014). Variation in the dust emissivity index across M33 with Herschel and Spitzer (HerM 33es). Astron. Astrophys., 561. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

We study the wavelength dependence of the dust emission as a function of position and environment across the disk of M33 using Spitzer and Herschel photometric data. M33 is a Local Group spiral with slightly subsolar metallicity, which makes it an ideal stepping-stone to less regular and lower-metallicity objects such as dwarf galaxies and, probably, young-universe objects. Expressing the emissivity of the dust as a power law, the power-law exponent (beta) was estimated from two independent approaches designed to properly treat the degeneracy between beta and the dust temperature (T). Both beta and T are higher in the inner than in the outer disk, contrary to reported beta - T anti-correlations found in other sources. In the cold + warm dust model, the warm component and the ionized gas (H alpha) have a very similar distribution across the galaxy, demonstrating that the model separates the components in an appropriate way. Both cold-and warm-dust column densities are high in star-forming regions and reach their maxima toward the giant star-forming complexes NGC 604 and NGC595. beta declines from close to 2 in the center to about 1.3 in the outer disk. beta is positively correlated with star formation and with the molecular gas column, as traced by the H alpha and CO emission. The lower dust-emissivity index in the outer parts of M33 is most likely related to the reduced metallicity (different grain composition) and possibly to a different size distribution. It is not due to the decrease in stellar radiation field or temperature in a simple way because the far-infrared-bright regions in the outer disk also have a low beta. Like most spirals, M33 has a (decreasing) radial gradient in star formation and molecular-to-atomic gas ratio such that the regions bright in H alpha or CO tend to trace the inner disk, which makes it difficult to distinguish between their effects on the dust. The assumption of a constant emissivity index beta is obviously not appropriate.

Item Type: Journal Article
Creators:
CreatorsEmailORCIDORCID Put Code
Tabatabaei, F. S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Braine, J.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Xilouris, E. M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Kramer, C.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Boquien, M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Combes, E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Henkel, C.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Relano, M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Verley, S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Gratier, P.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Israel, F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Wiedner, M. C.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Roellig, M.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Schuster, K. F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
van der Werf, P.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-451744
DOI: 10.1051/0004-6361/201321441
Journal or Publication Title: Astron. Astrophys.
Volume: 561
Date: 2014
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:
KeywordsLanguage
SPECTRAL ENERGY-DISTRIBUTIONS; LOCAL GALAXY ANDROMEDA; STAR-FORMATION; INFRARED-EMISSION; INTERSTELLAR DUST; GAS; SPACE; EVOLUTION; COOL; EXPLOITATIONMultiple languages
Astronomy & AstrophysicsMultiple languages
URI: http://kups.ub.uni-koeln.de/id/eprint/45174

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