A common column density threshold for scattering at 3.6<i>μ</i>m and water-ice in molecular clouds

Andersen, M.; Steinacker, Jürgen M.; Tothill, N.

doi:10.1051/0004-6361/201424011

Cited by 11 publications

(8 citation statements)

References 19 publications

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“…6) leading to J, H, and K colour ratios disagreeing with the observations made by Malinen et al (2013) and Foster & Goodman (2006). The need for an ice mantle coating the aggregate grains complies with the findings of Andersen et al (2014), who showed a correlation between the dust scattering efficiency and the H 2 O abundance in the Lupus IV molecular cloud complex.…”

Section: Cloudshinesupporting

confidence: 77%

Mantle formation, coagulation, and the origin of cloud/core shine

Ysard

Koehler

Jones

et al. 2016

A&A

135

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Context. Many dense interstellar clouds are observable in emission in the near-IR (J, H, and K photometric bands), commonly referred to as "Cloudshine", and in the mid-IR (Spitzer IRAC 3.6 and 4.5 μm bands), the so-called "Coreshine". These C-shine observations have usually been explained in terms of grain growth but no model has yet been able to self-consistently explain the dust spectral energy distribution from the near-IR to the submm. Aims. Our new core/mantle evolutionary dust model, The Heterogeneous dust Evolution Model at the IaS (THEMIS), has been shown to be valid in the far-IR and submm. We want to demonstrate its ability to reproduce the C-shine observations. Methods. Our starting point is a physically motivated core/mantle dust model. It consists of three dust populations: small polyaromatic-rich carbon grains, bigger core/mantle grains with mantles of aromatic-rich carbon, and cores made of either amorphous aliphatic-rich carbon or amorphous silicate. Then, we assume an evolutionary path where these grains, when entering denser regions, may first form a second aliphatic-rich carbon mantle (coagulation of small grains, accretion of carbon from the gas phase), second coagulate together to form large aggregates, and third accrete gas phase molecules coating them with an ice mantle. To compute the corresponding dust emission and scattering, we use a 3D Monte Carlo radiative transfer code. Results. We show that our global evolutionary dust modelling approach THEMIS allows us to reproduce C-shine observations towards dense starless clouds. Dust scattering and emission is most sensitive to the cloud central density and to the steepness of the cloud density profile. Varying these two parameters leads to changes that are stronger in the near-IR, in both the C-shine intensity and profile. Conclusions. With a combination of aliphatic-rich mantle formation and low-level coagulation into aggregates, we can selfconsistently explain the observed C-shine and far-IR/submm emission towards dense starless clouds.

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Section: Cloudshinesupporting

confidence: 77%

Mantle formation, coagulation, and the origin of cloud/core shine

Ysard

Koehler

Jones

et al. 2016

A&A

135

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“…Indirect evidence for a distinct population of much larger, micron-sized icy grains comes from diffuse scattered light observed toward dense cloud cores ("coreshine"; Andersen et al 2014). Such grains were also suggested as an alternative explanation of the long-wavelength wing of the 4.67 µm CO ice band ( §4.2; Dartois 2006).…”

Section: Grain Size and Mantle Thicknessmentioning

confidence: 99%

Observations of the Icy Universe

Boogert

Gerakines²,

Whittet

2015

Annu. Rev. Astron. Astrophys.

852

986

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Freeze-out of the gas phase elements onto cold grains in dense interstellar and circumstellar media builds up ice mantles consisting of molecules that are mostly formed in situ (H2O, NH3, CO2, CO, CH3OH, and more). This review summarizes the detected infrared spectroscopic ice features and compares the abundances across Galactic, extragalactic, and solar system environments. A tremendous amount of information is contained in the ice band profiles. Laboratory experiments play a critical role in the analysis of the observations. Strong evidence is found for distinct ice formation stages, separated by CO freeze out at high densities. The ice bands have proven to be excellent probes of the thermal history of their environment. The evidence for the long-held idea that processing of ices by energetic photons and cosmic rays produces complex molecules is weak. Recent state of the art observations show promise for much progress in this area with planned infrared facilities.Comment: To appear in Annual Review of Astronomy and Astrophysics, volume 53, 2015. Updated 08/May/2015: corrected numbers in elemental budget section, updated references and typo

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“…The dust mass is fixed in our modeling, which does not include ices, and corresponds to grain growth by coagulation with the density. Ice coatings may promote coagulation by changing the sticking coefficient of the grains and the scattering efficiency at coreshine wavelength (Andersen et al 2014;Lefèvre et al 2014). However, no icecoated dust distribution, able to produce efficient scattering at 8 µm , is publicly available presently.…”

Section: Compability Of the Modeling With Observationsmentioning

confidence: 99%

On the importance of scattering at 8 μm: Brighter than you think

Lefèvre

Pagani

Min

et al. 2016

A&A

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Context. Extinction and emission of dust models need for observational constraints to be validated. The coreshine phenomenon has already shown the importance of scattering in the 3 to 5 µm range and its ability to validate dust properties for dense cores. Aims. We want to investigate whether scattering can also play a role at longer wavelengths and to place even tighter constraints on the dust properties. Methods. We analyze the inversion of the Spitzer 8 µm map of the dense molecular cloud L183, to examine the importance of scattering as a potential contributor to the line-of-sight extinction.Results. The column density deduced from the inversion of the 8 µm map, when we neglect scattering, disagrees with all the other column density measurements of the same region. Modeling confirms that scattering at 8 µm is not negligible with an intensity of several hundred kJy sr −1 . This demonstrates the need of efficiently scattering dust grains at mid-infrared wavelengths up to 8 µm. Coagulated aggregates are good candidates and might also explain the discrepancy at high extinction between E(J − K) and τ 9.7 toward dense molecular clouds. Further investigation requires considering efficiently scattering dust grains including ices as realistic dust models.

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A common column density threshold for scattering at 3.6μm and water-ice in molecular clouds

Cited by 11 publications

References 19 publications

Mantle formation, coagulation, and the origin of cloud/core shine

Mantle formation, coagulation, and the origin of cloud/core shine

Observations of the Icy Universe

On the importance of scattering at 8 μm: Brighter than you think

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