Observations of Interstellar Carbon Compounds

Abstract

Abstract. Infrared absorption and emission features observed spectroscopically in our Galaxy allow to probe the composition of solid dust grains, their evolution and thus follow the cycling of matter in the Galaxy. Many observables do reveal the presence of large amounts of carbonaceous particles in space, other than the PAH-like emission lines. The carbonaceous materials observed include amorphous carbons, diamondoids showing in emission for a few specific sources, and the recently detected fullerenes. An important hydrogenated amorphous carbon component (HAC or a-C:H), traced by the 2940 cm −1 structured absorption feature is observed against Galactic background sources. Since the discovery of this feature in the early eighties (Allen 1981), the observation of a-C:H has been extended to the mid-infrared by space observatories, giving insight into additional associated features. They are also observed in external galaxies, showing the ubiquitous nature of these components. We will focus on astronomical observations of organic matter other than PAHs, amorphous carbons and associated laboratory dust analogues relevant to astrophysical applications.

Complex organics in space from Solar System to distant galaxies

“…5 The 3.4 µm feature is seen in absorption against the background infrared continuum along two lines of sight (GC IRS8 and GCS3) towards the galactic center. Figure adapted from Dartois (2011) can be quite reliably determined. The strength of the 3.4 µm feature suggests that at least 15 % of all the carbon atoms are in the form of aliphatic compounds (Dartois 2011).…”

“…Figure adapted from Dartois (2011) can be quite reliably determined. The strength of the 3.4 µm feature suggests that at least 15 % of all the carbon atoms are in the form of aliphatic compounds (Dartois 2011).…”

THE ORIGIN OF THE 3.4 μm FEATURE IN WILD 2 COMETARY PARTICLES AND IN ULTRACARBONACEOUS INTERPLANETARY DUST PARTICLES

“…The examination of these samples has provided many unexpected findings, including the presence of refractory minerals (Simon et al 2008), the presence of chondrule-like objects ) and low abundance of presolar grains (Stadermann & Floss 2008). Indigenous organic materials are also observed in Wild 2 samples (Sandford et al 2006;Matrajt et al 2008;Cody et al 2008Cody et al , 2011Gallien et al 2008;Wirick et al 2009;De Gregorio et al 2010, 2011Clemett et al 2010;Nakamura-Messenger et al 2011). The abundance of organic matter in the Wild 2 samples was lower than expected because the most of the submicron material was destroyed upon capture .…”

“…We calculated the ratio for the four samples we analyzed and compared them with the published data of other samples, including CCs, the DISM, comet Hartley 2 and asteroid 24 Themis ( Table 2). Given that the carrier of the 3.4 µm interstellar absorption band appears to be widespread throughout the Galaxy and is present in several others (Pendleton 1997;Wright et al 1996;Imanishi & Dudley 2000;Dartois et al 2004;Dartois 2011;Godard et al 2012), we used the interstellar CH 2 /CH 3 ratio measured in the past by Sandford et al (1991), Pendleton et al (1994) and Pendleton & Allamandola (2002) for the comparison. Another tool that we used for the comparison is the presence of O and N in the organic materials.…”

“…The abundance of organic matter in the Wild 2 samples was lower than expected because the most of the submicron material was destroyed upon capture . Coordinated analyses of organic material have shown that the organic material in the Wild 2 particles is very diverse in its morphology, isotopic and chemical composition, abundance, spatial distribution and complexity De Gregorio et al 2010, 2011Nakamura-Messenger et al 2011). Infrared spectroscopy (Sandford et al 2006;Keller et al 2006;Muñoz Caro et al 2008;Bajt et al 2009) has shown that aliphatics are present in most tracks and particles.…”