Multi-wavelength analysis of the dust emission   in the Small
 Magellanic Cloud

Bot, Caroline; Boulanger, F.; Lagache, G.; Cambrésy, L.; Egret, D.

doi:10.1051/0004-6361:20035918

Cited by 66 publications

(86 citation statements)

References 29 publications

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“…Indeed, there is no clear evidence that the BG abundance relative to gas varies significantly in the MW, independent of large scale variations that may be due to metallicity gradients. A comparison between the abundance of large grains in the MW and the Magellanic Clouds shows a systematic decrease of the BG abundance with metallicity, as expected (see Bernard et al 2008;Bot et al 2004). While the BG abundance could vary on large scales within galaxies if large metallicity gradients are present, no significant variations are expected on the size scales of giant molecular clouds.…”

Section: A V Vs N H Correlationssupporting

confidence: 75%

“…Following the large-scale, low angular resolution surveys by IRAS and DIRBE (e.g., Sauvage et al 1990; Sakon et al 2006), recent systematic, higher angular resolution IR observations of the LMC and SMC conducted by Spitzer (see Meixner et al 2006;Bernard et al 2008;Bot et al 2004) and Akari now permit the efficient separation of the diffuse emission from that of point sources. This is an important prerequisite for understanding the physics of dust emission, since the emission depends strongly on the intensity of the local interstellar radiation field (ISRF) and on the relative distribution of dust and stars.…”

Section: Introductionmentioning

confidence: 99%

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Extinction and dust/gas ratio in LMC molecular clouds

Dobashi

Bernard

Hughes

et al. 2008

A&A

125

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Aims. The goal of this paper is to measure the dust content and distribution in the Large Magellanic Cloud (LMC) by comparing extinction maps produced in the near-infrared wavelengths and the spatial distribution of the neutral and molecular gas, as traced by H i and CO observations.Methods. In order to derive an extinction map of the LMC, we have developed a new method to measure the color excess of dark clouds, using the 2MASS all-sky survey. Classical methods to measure the color excess (including the NICE method) tend to underestimate the true color excess if the clouds are significantly contaminated by unreddened foreground stars, as is the case in the LMC. We propose a new method that uses the color of the X percentile reddest stars and which is robust against such contamination. Using this method, it is possible to infer the positions of dark clouds with respect to the star distribution by comparing the observed color excess as a function of the percentile used and that predicted by a model. Results. On the basis of the resulting extinction map, we perform a correlation analysis for a set of dark molecular clouds. Assuming similar infrared absorption properties for the dust in the neutral and molecular phases, we derive the absorption-to-column density ratio A V N H and the CO-to-H 2 conversion factor X CO . We show that A V N H increases from the outskirts of the LMC towards the 30 Dor star-forming region. This can be explained either by a systematic increase of the dust abundance, or by the presence of an additional gas component not traced by H i or CO, but strongly correlated to the H i distribution. If dust abundance is allowed to vary, the derived X CO factors for the selected regions are several times lower than those derived from a virial analysis of the CO data. This could indicate that molecular clouds in the LMC are not gravitationally bound, or that they are bounded by substantial external pressure. However, the X CO values derived from absorption can be reconciled with the virial results assuming a constant value for the dust abundance and the existence of an additional, unseen gas component. These results are in agreement with those derived for the LMC from diffuse far-infrared emission.

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Section: A V Vs N H Correlationssupporting

confidence: 75%

Section: Introductionmentioning

confidence: 99%

Extinction and dust/gas ratio in LMC molecular clouds

Dobashi

Bernard

Hughes

et al. 2008

A&A

125

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“…Part of the excess observed in the SMC could be dust colder than can be extrapolated from far-infrared data points. In particular, a ∼60 μm excess has been reported in the Magellanic Clouds (Bot et al 2004;Bernard et al 2008). This 60 μm excess could be a significant part of the total emission in the SMC and bias dust models toward high temperatures.…”

Section: Integrated Spectra Of the Magellanic Cloudsmentioning

confidence: 93%

Submillimeter to centimeter excess emission from the Magellanic Clouds

Bot

Ysard

Paradis

et al. 2010

A&A

Self Cite

115

140

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Context. Dust emission at sub-millimeter to centimeter wavelengths is often simply the Rayleigh-Jeans tail of dust particles at thermal equilibrium and is used as a cold mass tracer in various environments, including nearby galaxies. However, well-sampled spectral energy distributions of the nearby, star-forming Magellanic Clouds have a pronounced (sub-)millimeter excess. Aims. This study attempts to confirm the existence of this millimeter excess above expected dust, free-free and synchrotron emission and to explore different possibilities for its origin. Methods. We model near-infrared to radio spectral energy distributions of the Magellanic Clouds with dust, free-free, and synchrotron emission. A millimeter excess emission is confirmed above these components and its spectral shape and intensity are analyzed in light of different scenarios: very cold dust, cosmic microwave background (CMB) fluctuations, a change of the dust spectral index and spinning dust emission. Results. We show that very cold dust or CMB fluctuations are very unlikely explanations for the observed excess in these two galaxies. The excess in the Large Magellanic Cloud can be satisfactorily explained either by a change of the spectral index related to intrinsic properties of amorphous grains, or by spinning dust emission. In the Small Magellanic Cloud, however, the excess is larger and the dust grain model including TLS/DCD effects cannot reproduce the observed emission in a simple way. A possible solution was achieved with spinning dust emission, but many assumptions on the physical state of the interstellar medium had to be made. Conclusions. Further studies, with higher resolution data from Planck and Herschel are needed to probe the origin of this observed submillimeter-centimeter excess more definitely. Our study shows that the different possible origins will be best distinguished where the excess is the highest, as is the case in the Small Magellanic Cloud.

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“…Note that some of the past attempts at constraining the equilibrium temperature of the large grains in the LMC used the IRAS 60 μm emission. Emission at 60 μm is highly contaminated by out-of-equilibrium emission from very small grains (VSGs) and this is even more the case in the Magellanic Clouds, due to the presence of the 70 μm excess (Bot et al 2004;Bernard et al 2008). Combining the IRAS 60 μm and 100 μm data therefore strongly over-estimates the temperature and accordingly under-estimates the abundances of all types of dust particles.…”

Section: Temperature Determinationmentioning

confidence: 99%

Planckearly results. XVII. Origin of the submillimetre excess dust emission in the Magellanic Clouds

Ade¹,

Aghanim²,

Arnaud³

et al. 2011

A&A

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125

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The integrated spectral energy distributions (SED) of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) appear significantly flatter than expected from dust models based on their far-infrared and radio emission. The still unexplained origin of this millimetre excess is investigated here using the Planck data. The integrated SED of the two galaxies before subtraction of the foreground (Milky Way) and background (CMB fluctuations) emission are in good agreement with previous determinations, confirming the presence of the millimetre excess. In the context of this preliminary analysis we do not propose a full multi-component fitting of the data, but instead subtract contributions unrelated to the galaxies and to dust emission. The background CMB contribution is subtracted using an internal linear combination (ILC) method performed locally around the galaxies. The foreground emission from the Milky Way is subtracted as a Galactic H i template, and the dust emissivity is derived in a region surrounding the two galaxies and dominated by Milky Way emission. After subtraction, the remaining emission of both galaxies correlates closely with the atomic and molecular gas emission of the LMC and SMC. The millimetre excess in the LMC can be explained by CMB fluctuations, but a significant excess is still present in the SMC SED. The Planck and IRAS-IRIS data at 100 μm are combined to produce thermal dust temperature and optical depth maps of the two galaxies.Corresponding author: J.-P. Bernard, e-mail: jean-philippe.bernard@cesr.frArticle published by EDP Sciences A17, page 1 of 17 A&A 536, A17 (2011) The LMC temperature map shows the presence of a warm inner arm already found with the Spitzer data, but which also shows the existence of a previously unidentified cold outer arm. Several cold regions are found along this arm, some of which are associated with known molecular clouds. The dust optical depth maps are used to constrain the thermal dust emissivity power-law index (β). The average spectral index is found to be consistent with β =1.5 and β =1.2 below 500 μm for the LMC and SMC respectively, significantly flatter than the values observed in the Milky Way. Also, there is evidence in the SMC of a further flattening of the SED in the sub-mm, unlike for the LMC where the SED remains consistent with β =1.5. The spatial distribution of the millimetre dust excess in the SMC follows the gas and thermal dust distribution. Different models are explored in order to fit the dust emission in the SMC. It is concluded that the millimetre excess is unlikely to be caused by very cold dust emission and that it could be due to a combination of spinning dust emission and thermal dust emission by more amorphous dust grains than those present in our Galaxy.

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Multi-wavelength analysis of the dust emission in the Small Magellanic Cloud

Cited by 66 publications

References 29 publications

Extinction and dust/gas ratio in LMC molecular clouds

Extinction and dust/gas ratio in LMC molecular clouds

Submillimeter to centimeter excess emission from the Magellanic Clouds

Planckearly results. XVII. Origin of the submillimetre excess dust emission in the Magellanic Clouds

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