Can We Trust the Dust? Evidence of Dust Segregation in Molecular Clouds

Padoan, Paolo; Cambrésy, L.; Juvela, M.; Kritsuk, Alexei G.; Langer, W. D.; Norman, Michael L.

doi:10.1086/507068

Cited by 42 publications

(48 citation statements)

References 39 publications

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“…The changes in dustgrain properties within dense clouds and small scale variations in the gas-to-dust ratio remain possible sources of uncertainty when any dust tracers are used to infer the distribution of total cloud mass (e.g. Padoan et al 2006b). On the other hand, by providing high resolution images of the dust distribution the near-infrared scattering also provides a useful tool for the study of these questions.…”

Section: Discussionmentioning

confidence: 99%

A Corona Australis cloud filament seen in NIR scattered light

Juvela¹,

Pelkonen²,

Padoan³

et al. 2008

A&A

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Context. Using state-of-art near-infrared (NIR) instrumentation the near-infrared light scattered from interstellar clouds can be mapped over large areas. Measurement of the surface brightness provides information on the line-of-sight dust column density. Scattered light therefore provides an important tool to study the mass distribution of quiescent, interstellar clouds at high, even subarcsecond resolution. Aims. We test the assumption that light scattering is the dominant contributor to the surface brightness in all NIR bands. Furthermore, we want to show that scattered light can be used for an accurate estimation of dust column densities in clouds with extinction in the range A V = 1-15 m . Methods. We have obtained NIR images of a quiescent filament in the Corona Australis molecular cloud. The observations provide maps of diffuse surface brightness in the J, H, and Ks photometric bands. Assuming that the main contributor is indeed scattered light, we convert surface brightness data into a map of dust column density. The same observations provide colour excesses for a large number of background stars. These data are used to derive an extinction map of the cloud. The two, largely independent tracers of the cloud structure are compared. Results. In regions where the extinction is below A V ∼ 15 m , both diffuse surface brightness and background stars lead to similar column density estimates. The existing differences can be explained as a result of normal observational errors and bias in the sampling of extinctions provided by the background stars. There is no indication that thermal dust-emission would have a significant contribution even in the Ks band. The results show that, below A V ∼ 15 mag , scattered light provides a reliable way to map cloud structure. Compared with the use of background stars, it can provide data of a significantly higher spatial resolution.

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Section: Discussionmentioning

confidence: 99%

A Corona Australis cloud filament seen in NIR scattered light

Juvela¹,

Pelkonen²,

Padoan³

et al. 2008

A&A

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“…More recently, several studies have suggested that dust grains in GMCs or neutral galactic disks should exhibit similar fluctu-E-mail:hlee2@mit.edu ations (Padoan et al 2006;Hopkins 2014b;Hopkins & Conroy 2015) -in terms of the aerodynamic drag equations, a grain of diameter ∼ 0.1−1 µm in a typical GMC is analogous to a meter-sized boulder in a protoplanetary disk. And observations have identified small-scale (∼ 0.01−1 pc) fluctuations in the local dust-to-gas ratio of large grains in a number of nearby molecular clouds (Thoraval et al 1997(Thoraval et al , 1999Abergel et al 2002;Flagey et al 2009;Boogert et al 2013).…”

Section: Introductionmentioning

confidence: 99%

The dynamics of charged dust in magnetized molecular clouds

Lee

Hopkins

Squire

2017

Monthly Notices of the Royal Astronomical Society

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We study the dynamics of large, charged dust grains in turbulent giant molecular clouds (GMCs). Massive dust grains behave as aerodynamic particles in primarily neutral dense gas, and thus are able to produce dramatic small-scale fluctuations in the dust-to-gas ratio. Hopkins & Lee (2016) directly simulated the dynamics of neutral dust grains in super-sonic MHD turbulence, typical of GMCs, and showed that the dust-to-gas fluctuations can exceed factor ∼ 1000 on small scales, with important implications for star formation, stellar abundances, and dust behavior and growth. However, even in primarily neutral gas in GMCs, dust grains are negatively charged and Lorentz forces are non-negligible. Therefore, we extend our previous study by including the effects of Lorentz forces on charged grains (in addition to drag). For small charged grains (sizes 0.1 µm), Lorentz forces suppress dust-to-gas ratio fluctuations, while for large grains (sizes 1 µm), Lorentz forces have essentially no effect, trends that are well explained with a simple theory of dust magnetization. In some special intermediate cases, Lorentz forces can enhance dust-gas segregation. Regardless, for the physically expected scaling of dust charge with grain size, we find the most important effects depend on grain size (via the drag equation) with Lorentz forces/charge as a second-order correction. We show that the dynamics we consider are determined by three dimensionless numbers in the limit of weak background magnetic fields: the turbulent Mach number, a dust drag parameter (proportional to grain size) and a dust Lorentz parameter (proportional to grain charge); these allow us to generalize our simulations to a wide range of conditions.

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“…The same phenomenon of "preferential concentration" is wellknown in both laboratory experiments and simulations of terrestrial turbulence (Squires & Eaton 1991;Rouson & Eaton 2001;Monchaux et al 2010Monchaux et al , 2012Pan et al 2011). Because the dynamics are scale-free, the same phenomena governing pebbles and boulders in a protoplanetary disk should apply tosubmicron size dust in a giant molecular cloud (Padoan et al 2006;Yoshimoto & Goto 2007;Bec et al 2009;Olla 2010;Hopkins 2016a). And indeed, dust-to-gas ratio fluctuations on scales of ∼0.003-10 pc have been measured in many nearby molecular clouds and insome galaxy nuclei (e.g., Orion, Taurus, and many more;see Thoraval et al 1997Thoraval et al , 1999Abergel et al 2002;MivilleDeschênes et al 2002;Padoan et al 2006;Flagey et al 2009;Pineda et al 2010;Nyland et al 2013); thedependence on dust grain size is in good agreement with the predictions of turbulent concentration (Padoan et al 2006;Hopkins 2014).…”

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confidence: 88%

Are the Formation and Abundances of Metal-poor Stars the Result of Dust Dynamics?

Hopkins

Conroy

2017

ApJ

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Large dust grains can fluctuate dramatically in their local density, relative to the gas, in neutralturbulent disks. Small, high-redshift galaxies (before reionization) represent ideal environments for this process. We show via simple arguments and simulations that order-of-magnitude fluctuations are expected in local abundances of large grains (>100 Å) under these conditions. This can have important consequences for star formation and stellar metal abundances in extremely metal-poor stars. Low-mass stars canform in dust-enhanced regions almost immediately after some dust formseven if the galaxy-average metallicity is too low for fragmentation to occur. We argue that the metal abundances of these "promoted" stars may contain interesting signaturesas the CNO abundances (concentrated in large carbonaceous grains and ices) and Mg and Si (in large silicate grains) can be enhanced and/or fluctuate almost independently. Remarkably, the otherwise puzzling abundance patterns of some metal-poor stars can be wellfit by standardIMF-averaged core-collapse SNe yieldsif we allow for fluctuating local dust-to-gas ratios. We also show that the observed log-normaldistribution of enhancements in these species agrees with our simulations. Moreover, we confirm that Mg and Si are correlated in these stars;theabundance ratios are similar to those in local silicate grains. Meanwhile [Mg/Ca], predicted to be nearly invariant from pure SNe yields, shows very large enhancements and variations up to factors of 100 as expected in the dust-promoted model, preferentially in the [C/Fe]-enhanced metal-poor stars. Together, this suggests that (1) dust exists in second-generation star formation, (2) local dust-to-gas ratio fluctuations occur inprotogalaxies and can be important for star formation, and (3) the light element abundances of these stars may be affected by the local chemistry of dust where they formed, rather than directly tracing nucleosynthesis from earlier populations.

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Can We Trust the Dust? Evidence of Dust Segregation in Molecular Clouds

Cited by 42 publications

References 39 publications

A Corona Australis cloud filament seen in NIR scattered light

A Corona Australis cloud filament seen in NIR scattered light

The dynamics of charged dust in magnetized molecular clouds

Are the Formation and Abundances of Metal-poor Stars the Result of Dust Dynamics?

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