The Composition and Distribution of Dust along the Line of Sight toward the Galactic Center

By J. Chiar, A. Tielens, D. Whittet, W. Schutte, A. Boogert, D. Lutz, E. V. van Dishoeck, M. Bernstein. 2000

245 citations recorded by the source corpus.

We discuss the composition of dust and ice along the line of sight to the Galactic center (GC) based on analysis of mid-infrared spectra (2.4-13 μm) from the Short Wavelength Spectrometer on the Infrared Space Observatory (ISO). We have analyzed dust absorption features arising in the molecular cloud material and the diffuse interstellar medium along the lines of sight toward Sgr A* and the Quintuplet sources, GCS 3 and GCS 4. It is evident from the depth of the 3.0 μm H2O and the 4.27 μm CO2 ice features that there is more molecular cloud material along the line of sight toward Sgr A* than toward GCS 3 and GCS 4. In fact, Sgr A* has a rich infrared ice spectrum with evidence for the presence of solid CH4, NH3, and possibly HCOOH. Hydrocarbon dust in the diffuse interstellar medium along the line of sight to the GC is characterized by absorption features centered at 3.4, 6.85, and 7.25 μm. Ground-based studies have identified the 3.4 μm feature with aliphatic hydrocarbons, and ISO has given us the first meaningful observations of the corresponding modes at longer wavelengths. The integrated strengths of these three features suggest that hydrogenated amorphous carbon is their carrier. We attribute an absorption feature centered at 3.28 μm in the GCS 3 spectrum to the C–H stretch in aromatic hydrocarbons. This feature is not detected, and its C–C stretch counterpart appears to be weaker, in the Sgr A* spectrum. A key question now is whether or not aromatics are a widespread component of the diffuse interstellar medium, analogous to aliphatic hydrocarbons.

Subfields: Astronomy and Astrophysics, Atmospheric Science, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/26d96007d6c0ba6ec95afbec50a02bcc0e42e15f

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. E. Dishoeck
2. Lee Armus
3. A. Tielens
4. L. Allen
5. R. Genzel
6. D. M. Alexander
7. R. Gutermuth
8. K. Oberg

In Atmospheric Science

1. E. Dishoeck
2. B. Draine
3. A. Tielens
4. K. Oberg
5. E. F. Dishoeck
6. L. Allamandola
7. A. Boogert
8. C. Salyk

In Spectroscopy

1. E. Dishoeck
2. A. Tielens
3. B. Draine
4. K. Oberg
5. R. Gutermuth
6. A. Boogert
7. L. Allen
8. D. Whittet

Citations in the corpus

• Interstellar Ice: The Infrared Space Observatory Legacy (2004, background): “These sources are believed to lie behind 29 mag of visual extinction and are in a region known as the Infrared Quintuplet, containing several bright and many faint IR sources whose nature is still unknown (Chiar et al. 2000).”
• ISO Spectroscopy of Gas and Dust: From Molecular Clouds to Protoplanetary Disks (2004, background): “PAHs have also been seen in absorption at 6.2 µm in the diffuse medium toward objects in the Galactic Center and several dusty late-type Wolf-Rayet stars (Schutte et al. 1998).”
• The Mid-Infrared Properties of Starburst Galaxies from Spitzer-IRS Spectroscopy (2006, background): “Their detection in NGC 4945 suggests that crystalline silicates are perhaps a more common component of the ISM and not just limited to ULIRG nuclei.”
• INTERSTELLAR DUST GRAINS (2003, methodology): “An absorption feature at 6.2µm (see Figure 4) has been observed (Schutte et al. 1998, Chiar et al. 2000).”
• Observations of the Icy Universe (2015, background): “…(crystalline) 41, 42, 43 a reference to a publication contributing strongly to its identification or profile characterization: 1: Taban et al. 2003, 2: Keane et al. 2001a, 3: Chiar et al. 2000, 4: Dartois & d’Hendecourt 2001, 5: Knacke et al. 1982, 6: Pendleton et al. 1990, 7: Gillett & Forrest…”
• Diffuse Atomic and Molecular Clouds (2006, background): “There have been some detections of the UIB bands in absorption (Sellgren et al. 1995, Bregman et al. 2000, Chiar et al. 2000, Song et al. 2003), but these have been in dense cloud sightlines or toward the Galactic Center, where both dense and diffuse gas are present.”
• Infrared Emission from Interstellar Dust. II. The Diffuse Interstellar Medium (2000, unknown): “7 B 2.9matic 6.2 km absorption feature has been detected in several objects, including both local sources and Galactic center sources (Schutte et al. 1998 ; Chiar et al. 2000).”
• The c2d Spitzer Spectroscopic Survey of Ices around Low-Mass Young Stellar Objects. I. H2O and the 5-8 μm Bands (2007, background): “A band at 6.85 µm is detected in lines of sight toward the Galactic Center (GC), tracing a large column of diffuse dust (Chiar et al. 2000).”
• Ice absorption features in the 5-8 μm region toward embedded protostars (2001, background): “10), which has also been tentatively identified with PAH absorption (Schutte et al. 1998; Chiar et al. 2000).”
• The evolution of amorphous hydrocarbons in the ISM: dust modelling from a new vantage point (2013, background): “Observations of a 3.3 μm aromatic CH band in absorption would be possible along lines of sight where the emission bands are weak or absent (e.g., towards young stellar objects and the Galactic centre, Smith et al. 1989; Sellgren et al. 1995; Brooke et al. 1999; Chiar et al. 2000).”
• The Organic Refractory Material in the Diffuse Interstellar Medium: Mid-Infrared Spectroscopic Constraints (2002, background): “Recent studies of the Galactic center by Chiar et al. (2000), in which an analysis is presented of the di†use and dense components to decouple the two, are consistent with our results for the di†use dust component of the ISM.”
• The global dust modelling framework THEMIS (The Heterogeneous dust Evolution Model for Interstellar Solids) (2017, background): “Firstly, observations of silicate dust in the ISM towards the Galactic Centre indicate that they are a mix of amorphous olivine-type and pyroxene-type silicates (e.g., Chiar et al. 2000).”
• Infrared Extinction toward Nearby Star-forming Regions (2007, background): “Broad ice absorption features at 3 and 6µm are seen toward Sgr A* and are attributed to foreground molecular cloud material (Chiar et al. 2000).”
• LINE DERIVED INFRARED EXTINCTION TOWARD THE GALACTIC CENTER (2011, background): “The depth is similar to that obtained by Chiar et al. (2000) of ∆τSi 9.7 = 3.46 and by Roche & Aitken (1985) of τSi 9.7 = 3.6.”
• INTERSTELLAR EXTINCTION LAW TOWARD THE GALACTIC CENTER III: J, H, KS BANDS IN THE 2MASS AND THE MKO SYSTEMS, AND 3.6, 4.5, 5.8, 8.0 μm IN THE SPITZER/IRAC SYSTEM (2009, background): “Lutz et al. (1996) compared the observed fluxes and expected fluxes predicted for the H ii region in an aperture of 14′′ × 20′′ centered on Sgr A∗.”