Non-standard grain properties, dark gas reservoir, and extended submillimeter excess, probed by Herschel in the Large Magellanic Cloud

By F. Galliano, S. Hony, J. Bernard, C. Bot, S. Madden, J. Roman-Duval, M. Galametz, Aigen Li, M. Meixner, C. Engelbracht and 6 more. 2011

177 citations recorded by the source corpus.

Context. Herschel provides crucial constraints on the IR SEDs of galaxies, allowing unprecedented accuracy on the dust mass estimates. However, these estimates rely on non-linear models and poorly-known optical properties. Aims. In this paper, we perform detailed modelling of the Spitzer and Herschel observations of the LMC, in order to: (i) systematically study the uncertainties and biases affecting dust mass estimates; and to (ii) explore the peculiar ISM properties of the LMC. Methods. To achieve these goals, we have modelled the spatially resolved SEDs with two alternate grain compositions, to study the impact of different submillimetre opacities on the dust mass. We have rigorously propagated the observational errors (noise and calibration) through the entire fitting process, in order to derive consistent parameter uncertainties. Results. First, we show that using the integrated SED leads to underestimating the dust mass by ≃50% compared to the value obtained with sufficient spatial resolution, for the region we studied. This might be the case, in general, for unresolved galaxies. Second, we show that Milky Way type grains produce higher gas-to-dust mass ratios than what seems possible according to the element abundances in the LMC. A spatial analysis shows that this dilemma is the result of an exceptional property: the grains of the LMC have on average a larger intrinsic submm opacity (emissivity index β ≃ 1.7 and opacity κ_(abs)(160 μm) = 1.6 m^2 kg^(-1)) than those of the Galaxy. By studying the spatial distribution of the gas-to-dust mass ratio, we are able to constrain the fraction of unseen gas mass between ≃10, and ≃100% and show that it is not sufficient to explain the gas-to-dust mass ratio obtained with Milky Way type grains. Finally, we confirm the detection of a 500 μm extended emission excess with an average relative amplitude of ≃15%, varying up to 40%. This excess anticorrelates well with the dust mass surface density. Although we do not know the origin of this excess, we show that it is unlikely the result of very cold dust, or CMB fluctuations.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/87e08350fdb049231be6d3acd4509463dd514489

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Citations in the corpus

An Overview of the Dwarf Galaxy Survey (2013, methodology): “…often-used graphite dust analog, which, along with silicate and PAH components, well-describes the dust composition of the Galaxy (e.g., Zubko et al. 2004; Draine & Li 2007) can lead to inexplicably large dust masses in low metallicity galaxies such as the LMC, as shown by Galliano et al. (2011).”
Dust spectral energy distributions of nearby galaxies: an insight from the Herschel Reference Survey (2014, background): “A very cold dust component was proposed by Galliano et al. (2003, 2005), showing that it would need to lie in a small number of dense parsec scale clumps, but Galliano et al. (2011) showed that this hypothesis was not verified in the LMC, where they had the spatial resolution to test it.”
THE EVOLVING INTERSTELLAR MEDIUM OF STAR-FORMING GALAXIES SINCE z = 2 AS PROBED BY THEIR INFRARED SPECTRAL ENERGY DISTRIBUTIONS (2012, background): “Dust masses based on different grain size compositions and opacities in the literature can vary even by a factor of ∼ 3, indicating that the absolute values should be treated with caution (e.g., Galliano et al. 2011).”
The Herschel Dwarf Galaxy Survey - I. Properties of the low-metallicity ISM from PACS spectroscopy (2015, methodology): “For the extended sample, we create LTIR and synthetic IRAS maps based on the model of Galliano et al. (2011) that we convolve to the largest beam (12′′, corresponding to the PACS 160 µm beam size).”
Gas-to-dust mass ratios in local galaxies over a 2 dex metallicity range (2013, methodology): “The submm emissivity index, β, for this grain composition is ∼2.0 (Galliano et al. 2011).”
The global dust modelling framework THEMIS (The Heterogeneous dust Evolution Model for Interstellar Solids) (2017, background): “Some later dust models followed this same basic approach but abandoned "astronomical" graphite in favour of physically morerealistic amorphous carbons (e.g., Zubko et al. 2004; Compiègne et al. 2011; Galliano et al. 2011).”
The dust content of galaxies from z = 0 to z = 9 (2016, methodology): “We can cite for instance the Draine et al. (2007), Galliano et al. (2011), GRASIL (Silva et al. 1998), CIGALE (Burgarella, Buat & Iglesias-Páramo 2005), and THEMIS (Jones et al. 2016) models.”
The CO-to-H2 Conversion Factor (2013, background): “…the translation of a SED into a dust mass relies almost entirely on dust grain properties (composition, mass emissivity, 30 size distribution) that have been derived for the Milky Way (Draine & Li 2001, 2007b), and are extremely uncertain even for local galaxies (e.g., Galliano et al. 2011).”
The evolution of the dust and gas content in galaxies (2013, background): “In addition, the underestimate by 50% of the dust mass of unresolved sources found by Galliano et al. (2011) may also explain the lower values found by us.”
HERSCHEL FAR-INFRARED AND SUBMILLIMETER PHOTOMETRY FOR THE KINGFISH SAMPLE OF NEARBY GALAXIES (2011, unknown): “3 (e.g., Bolatto et al. 2000; Galliano et al. 2005; Bot et al. 2010; Gordon et al. 2010; Ade et al. 2011a,b; Galametz et al. 2011; Galliano et al. 2011).”