On Ultrasmall Silicate Grains in the Diffuse Interstellar Medium

Li, Aigen; Draine, B. T.

doi:10.1086/319640

Cited by 210 publications

(226 citation statements)

References 28 publications

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“…2, we show the PAH absorption cross-sections suggested by Li & Draine (2001); Malloci et al (2007); this work, as well as the cross-section of a particular PAH molecule, Coronene (Mulas, priv. comm.).…”

Section: Cross Sections Of Pahssupporting

confidence: 52%

“…Both emission components can only be explained by considering dust particles that are small enough to be stochastically heated. A step forward was taken in the dust models by Désert et al (1990); Siebenmorgen & Krügel (1992); Dwek et al (1997); Li & Draine (2001); and Draine & Li (2007). In these models, very small grains and PAHs are treated as an essential grain component along with the (so far) standard carbon and silicate mixture of large grains.…”

Section: Introductionmentioning

confidence: 99%

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Dust in the diffuse interstellar medium

Siebenmorgen

Вощинников

Bagnulo

2014

A&A

112

123

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We present a model for the diffuse interstellar dust that explains the observed wavelength-dependence of extinction, emission, and the linear and circular polarisation of light. The model is set up with a small number of parameters. It consists of a mixture of amorphous carbon and silicate grains with sizes from the molecular domain of 0.5 up to about 500 nm. Dust grains with radii larger than 6 nm are spheroids. Spheroidal dust particles have a factor 1.5-3 greater absorption cross section in the far-infrared than spherical grains of the same volume do. Mass estimates derived from submillimetre observations that ignore this effect are overestimated by the same amount. In the presence of a magnetic field, spheroids may be partly aligned and polarise light. We find that polarisation spectra help to determine the upper particle radius of the otherwise rather unconstrained dust size distribution. Stochastically heated small grains of graphite, silicates, and polycyclic aromatic hydrocarbons (PAHs) are included. We tabulate parameters for PAH emission bands in various environments. They show a trend with the hardness of the radiation field that can be explained by the ionisation state or hydrogenation coverage of the molecules. For each dust component its relative weight is specified so that absolute element abundances are not direct input parameters. The model is compared to the average properties of the Milky Way, which seem to represent dust in the solar neighbourhood. It is then applied to specific sight lines towards four particular stars, with one of them located in the reflection nebula NGC 2023. For these sight lines, we present ultra-high signal-to-noise linear and circular spectro-polarimetric observations obtained with FORS at the VLT. Using prolate rather than oblate grains gives a better fit to observed spectra; the axial ratio of the spheroids is typically two and aligned silicates are the dominant contributors to the polarisation.

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Section: Cross Sections Of Pahssupporting

confidence: 52%

Section: Introductionmentioning

confidence: 99%

Dust in the diffuse interstellar medium

Siebenmorgen

Вощинников

Bagnulo

2014

A&A

112

123

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“…However, evidence for the existence of crystalline silicon has not yet been observed. (Li & Draine 2001, 2002 It is interesting that the luminescence of forsterite is very similar to ERE of the Red Rectangle (peak at 652-684 nm, half width 70-90 nm). Generally, the ERE from interstellar dust consists of a broad, featureless emission band peaking anywhere from 610-820 nm, with a width of 60-100 nm.…”

Section: Similarity To Ere Of the Red Rectangle Spectrummentioning

confidence: 96%

Thermoluminescence of simulated interstellar matter after gamma-ray irradiation

Koike¹,

Nakagawa²,

Koike

et al. 2002

A&A

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Abstract. Interstellar matter is known to be strongly irradiated by cosmic radiation and several types of cosmic ray particles. Simulated interstellar matter, such as synthesized forsterite (Mg 2 SiO 4 ), enstatite (MgSiO 3 ) and magnesite (MgCO 3 ), has been irradiated with 60 Co gamma-rays in liquid nitrogen, and also irradiated with fast neutrons at 10 K and 70 K by making use of the low-temperature irradiation facility of the Kyoto University Reactor (KUR-LTL. Maximum fast neutron dose is 10 17 n f /cm 2 ). After irradiation, samples are stored in liquid nitrogen for several months to allow the decay of induced radioactivity. We measured the luminescence spectra of the gamma ray irradiated samples during warming to 370 K using a spectrophotometer. For the forsterite and magnesite, the spectra exhibit a rather intense peak at about 645-655 nm and 660 nm respectively, whereas luminescence scarcely appeared in the natural olivine sample. The spectra of forsterite is very similar to the ERE of the Red Rectangle.

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“…The mean size of PAHs (a 0 = 6.4 Å) corresponds to 120 C atoms. Note that, contrary to carbonaceous dust, for which the PAH bands give a constraint on the abundance and size of very small particles, only an upper limit can be set regarding the abundance of very small silicate dust (see Li & Draine 2001b). In our model, we do not include very small silicate particles.…”

Section: The Modelmentioning

confidence: 99%

“…In fact, throughout the dust lifecycle, from dense molecular cores to the diffuse ISM, the grain populations are the result of complex, non-equilibrium evolutionary processes and it appears natural to consider that carbon dust is amorphous, as observations have clearly demonstrated for silicate grains (e.g. Li & Draine 2001b;Kemper et al 2005;Li et al 2007). We follow this train of thought in this work and examine the possibility that all carbonaceous grains (except PAH) are amorphous and partially hydrogenated in the interstellar medium.…”

Section: Introductionmentioning

confidence: 99%

The global dust SED: tracing the nature and evolution of dust with DustEM

Compiègne

Verstraete

Jones

et al. 2010

A&A

411

724

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The Planck and Herschel missions are currently measuring the far-infrared to millimeter emission of dust, which combined with existing IR data, will for the first time provide the full spectral energy distribution (SED) of the galactic interstellar medium dust emission, from the mid-IR to the mm range, with an unprecedented sensitivity and down to spatial scales ∼30 . Such a global SED will allow a systematic study of the dust evolution processes (e.g. grain growth or fragmentation) that directly affect the SED because they redistribute the dust mass among the observed grain sizes. The dust SED is also affected by variations of the radiation field intensity. Here we present a versatile numerical tool, DustEM, that predicts the emission and extinction of dust grains given their size distribution and their optical and thermal properties. In order to model dust evolution, DustEM has been designed to deal with a variety of grain types, structures and size distributions and to be able to easily include new dust physics. We use DustEM to model the dust SED and extinction in the diffuse interstellar medium at high-galactic latitude (DHGL), a natural reference SED that will allow us to study dust evolution. We present a coherent set of observations for the DHGL SED, which has been obtained by correlating the IR and HI-21 cm data. The dust components in our DHGL model are (i) polycyclic aromatic hydrocarbons; (ii) amorphous carbon and (iii) amorphous silicates. We use amorphous carbon dust, rather than graphite, because it better explains the observed high abundances of gas-phase carbon in shocked regions of the interstellar medium. Using the DustEM model, we illustrate how, in the optically thin limit, the IRAS/Planck HFI (and likewise Spitzer/Herschel for smaller spatial scales) photometric band ratios of the dust SED can disentangle the influence of the exciting radiation field intensity and constrain the abundance of small grains (a < ∼ 10 nm) relative to the larger grains. We also discuss the contributions of the different grain populations to the IRAS, Planck (and similarly to Herschel) channels. Such information is required to enable a study of the evolution of dust as well as to systematically extract the dust thermal emission from CMB data and to analyze the emission in the Planck polarized channels. The DustEM code described in this paper is publically available.

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On Ultrasmall Silicate Grains in the Diffuse Interstellar Medium

Cited by 210 publications

References 28 publications

Dust in the diffuse interstellar medium

Dust in the diffuse interstellar medium

Thermoluminescence of simulated interstellar matter after gamma-ray irradiation

The global dust SED: tracing the nature and evolution of dust with DustEM

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