EDP Sciences
Free access
Volume 463, Number 2, February IV 2007
Page(s) 635 - 640
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20066572

A&A 463, 635-640 (2007)
DOI: 10.1051/0004-6361:20066572

IRAS 08572+3915: constraining the aromatic versus aliphatic content of interstellar HACs

E. Dartois1, T. R. Geballe2, T. Pino3, A.-T. Cao3, A. Jones1, D. Deboffle1, V. Guerrini4, Ph. Bréchignac3, and L. d'Hendecourt1

1  Institut d'Astrophysique Spatiale, UMR-8617, Université Paris-Sud, bâtiment 121, 91405 Orsay Cedex, France
    e-mail: emmanuel.dartois@ias.u-psud.fr
2  Gemini Observatory, 670 North Aòhoku Place, Hilo, HI 96720, USA
3  Laboratoire de Photophysique Moléculaire, UPR 3361, Université Paris-Sud, bâtiment 210, 91405 Orsay Cedex, France
4  Service d'Aéronomie, UMR 7620, Route des Gatines, BP 3, 91371 Verrières Le Buisson, France

(Received 16 October 2006 / Accepted 22 November 2006)

We analyze dust features present in the mid-infrared (Spitzer) and recently published L-band (UKIRT) spectra of the infrared galaxy IRAS 08572+3915. The line of sight toward the AGN nucleus crosses a high column density of carbonaceous dust whose characteristic absorption features appear clearly. They provide a real insight into the chemical environment of the diffuse interstellar medium. Thanks to the moderate redshift of IRAS 08572+3915, the wavelength of the aromatic CH stretching mode is free of major telluric lines, and a strong observational constraint of H $_{\rm sp2} $/H $_{\rm sp3} \le 0.08$ has been determined. This limit clearly shows that the bonding of hydrogen atoms in interstellar hydrogenated amorphous carbon is highly aliphatic. The presence of a broad absorption feature centered at 6.2 $\mu$m, probably arising from olefinic/aromatic structures, corresponds to the backbone of this carbonaceous material, which is the major carbon-containing component of the interstellar medium along this line of sight.

Key words: ISM: abundances -- ISM: dust, extinction -- galaxies: individual: IRAS 08572+3915 -- galaxies: ISM

© ESO 2007