Interstellar Silicate Absorption Bands

Hackwell, J. A.; Gehrz, R. D.; Woolf, N. J.

doi:10.1038/227822a0

Cited by 45 publications

(15 citation statements)

References 8 publications

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“…The detection of silicates in the galactic ISM had been reported several years earlier, first in emission in the Trapezium region of the Orion Nebula (Stein & Gillett 1969), then in absorption toward the Galactic center (Hackwell et al 1970), and shortly thereafter toward the Becklin-Neugebauer object and Kleinmann-Low Nebula (Gillett & Forrest 1973). The numerous IRS studies of the many galaxy types and models discussed in Section 3 typically invoked silicate grains (e.g., see Hao et al 2007;Levenson et al 2007;Spoon et al 2007; Thompson et al 2009).…”

Section: Modeling the M81 Nucleus Silicate Emissionmentioning

confidence: 99%

Anomalous Silicate Dust Emission in the Type 1 Liner Nucleus of M81

Smith

et al. 2010

ApJ

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We report the detection and successful modeling of the unusual 9.7 μm Si-O stretching silicate emission feature in the type 1 (i.e., face-on) LINER nucleus of M81. Using the Infrared Spectrograph (IRS) instrument on Spitzer, we determine the feature in the central 230 pc of M81 to be in strong emission, with a peak at ∼10.5 μm. This feature is strikingly different in character from the absorption feature of the galactic interstellar medium, and from the silicate absorption or weak emission features typical of galaxies with active star formation. We successfully model the high signal-to-noise ratio IRS spectra with porous silicate dust using laboratory-acquired mineral spectra. We find that the most probable fit uses micron-sized, porous grains of amorphous silicate and amorphous carbon. In addition to silicate dust, there is weak polycyclic aromatic hydrocarbon (PAH) emission present (particularly at 11.3 μm, arising from the C-H out-of-plane bending vibration of relatively large PAHs of ∼500-1000 C atoms) whose character reflects the low-excitation active galactic nucleus environment, with some evidence that small PAHs of ∼100-200 C atoms (responsible for the 7.7 μm C-C stretching band) in the immediate vicinity of the nucleus have been preferentially destroyed. Analysis of the infrared fine structure lines confirms the LINER character of the M81 nucleus. Four of the infrared H 2 rotational lines are detected and fit to an excitation temperature of T ∼ 800 K. Spectral maps of the central 230 pc in the [Ne ii] 12.8 μm line, the H 2 17 μm line, and the 11.3 μm PAH C-H bending feature reveal arc-or spiral-like structures extending from the core. We also report on epochal photometric and spectroscopic observations of M81, whose nuclear intensity varies in time across the spectrum due to what is thought to be inefficient, subEddington accretion onto its central black hole. We find that, contrary to the implications of earlier photometry, the nucleus has not varied over a period of two years at these infrared wavelengths to a precision of about 1%.

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Section: Modeling the M81 Nucleus Silicate Emissionmentioning

confidence: 99%

Anomalous Silicate Dust Emission in the Type 1 Liner Nucleus of M81

Smith

et al. 2010

ApJ

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“…It was later shown by Gilman (1969) that grains around oxygen-rich cool giants are mainly silicates such as Al 2 SiO 3 and Mg 2 SiO 4 . Silicates were first detected in emission in M stars (Woolf & Ney 1969;Knacke et al 1969), in the Trapezium region of the Orion Nebula , and in comet Bennett 1969i (Maas, Ney, & Woolf 1970) and in absorption toward the Galactic center (Hackwell, Gehrz, & Woolf 1970) and toward the Becklin-Neugebauer object and Kleinmann-Low Nebula (Gillett & Forrest 1973). Silicates are now known to be ubiquitous and are seen in interstellar clouds, in circumstellar disks around young stellar objects (YSOs), in main-sequence and evolved stars, in H ii regions, and in interplanetary and cometary dust.…”

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confidence: 99%

On Ultrasmall Silicate Grains in the Diffuse Interstellar Medium

Draine

2001

The Astrophysical Journal

210

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The abundance of both amorphous and crystalline silicates in very small grains is limited by the fact that the 10 mm silicate emission feature is not detected in the diffuse interstellar medium (ISM). On the basis of the observed IR emission spectrum for the diffuse ISM, the observed ultraviolet extinction curve, and the 10 mm silicate absorption profile, we obtain upper limits on the abundances of ultrasmall ( ) amorphous and a Շ 15 A crystalline silicate grains. Contrary to previous work, as much as ∼10% of interstellar Si could be in silicate grains without violating observational constraints. Not more than ∼5% of the Si can be in a Շ 15 A crystalline silicates (of any size).

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“…It was first observed in the late sixties as an emission feature in the infrared (IR) spectra of several evolved stars [11]. Shortly thereafter it was observed in absorption in the interstellar medium (ISM; [12,13]). Since then, it has been found in many astrophysical environments including the solar system and extrasolar planetary systems (e.g., [14] and references therein), the circumstellar regions of both young stellar objects and evolved intermediate mass stars (asymptotic giant branch [AGB] stars, and planetary nebulae; e.g., [15,16]); many lines of sight through the interstellar medium in our own galaxy (e.g., [17,18]; in nearby and distant galaxies (e.g., [19]).…”

Section: Pos(lcdu 2013)002mentioning

confidence: 99%

Modeling Cosmic Dust: How to Use Optical "Constants"

Speck¹

2014

Proceedings of the Life Cycle of Dust in the Universe: Observations, Theory, and Laboratory Experiments — PoS(LCDU2013)

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In order to determine the precise nature of cosmic dust, we use a combination of multi-wavelength ground-and space-based spectroscopy, imaging, laboratory data and modeling. Dust grains scatter, absorb and re-radiate light according to their optical properties, which are sensitive to e.g. the temperature, chemical composition, size, shape, and lattice structure of the dust grains. For example, graphite and diamond are both polymorphs of carbon, and will form under very similar conditions, but their interactions with light are very different. This work provides a primer on how to apply basic physics concepts to understanding how we measure and use the optical properties of candidate cosmic dust species. We discuss the way in which measurements are made, how simplifying assumptions commonly made in astronomy may cause problems and how measurable and calculable parameters from laboratory experiments can be directly or indirectly compared to parameters derived from astronomical observations. Finally, we examine the simplifying assumptions with the most commonly used "synthetic" optical properties for cosmic dust and highlight forthcoming laboratory data as a potential replacement. * Speaker.

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Interstellar Silicate Absorption Bands

Abstract: Interstellar silicate absorption is observed in the direction of the galactic centre. Most interstellar silicon seems to be in silicate form.

Cited by 45 publications

References 8 publications

Anomalous Silicate Dust Emission in the Type 1 Liner Nucleus of M81

Anomalous Silicate Dust Emission in the Type 1 Liner Nucleus of M81

On Ultrasmall Silicate Grains in the Diffuse Interstellar Medium

Modeling Cosmic Dust: How to Use Optical "Constants"

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