Carbonaceous dust grains in luminous infrared galaxies. Spitzer/IRS reveals a-C:H as an abundant and ubiquitous ISM component

Details Carbonaceous dust grains in luminous infrared galaxies. Spitzer/IRS reveals a-C:H as an abundant and ubiquitous ISM component Carbonaceous dust grains in luminous infrared galaxies. Spitzer/IRS reveals a-C:H as an abundant and ubiquitous ISM component

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007a%26a...476.1235d&link_type=abstract

Astronomy and Astrophysics, Volume 476, Issue 3, December IV 2007, pp.1235-1242

Astronomy and Astrophysics

Astrophysics

20

Ism: Dust, Extinction, Galaxies: Ism, Methods: Laboratory

Scientific paper

Aims:The available ground- and space-based spectroscopic capabilities of observatories now allow us to extend Galactic interstellar medium composition studies to extragalactic cases. Absorptions in the mid-infrared shows evidence for silicate and carbonaceous grains in other galaxies. Methods: A set of extragalactic spectra of luminous infrared galaxies (LIRGs) has been extracted from the Spitzer database and compared to the spectra of laboratory-produced interstellar carbon dust analogues. Results: These highly obscured lines-of-sight display the characteristic absorptions at ~6.85 and 7.25 μm of the CH3/CH2 deformation modes of hydrogenated amorphous carbon (a-C:H) grains. They are compared to laboratory-produced a-C:H and imply carbon atom column densities in the solid phase exceeding ~1018 cm-2. Conclusions: These observations further demonstrate the ubiquitousness of a-C:H in the diffuse interstellar medium (DISM) of galaxies, for a long time almost only observed in the Milky-Way ISM lines-of-sights. Whereas PAH emission lines trace the re-processing of energetic young stellar radiation, the observed a-C:H features underline the existence of large masses of amorphous carbon dust in (extra-)galactic dust budgets. The difficulty in observing such an interstellar component in the mid-infrared is linked to its low absorption contrast (A_V/τ(6.85)≈ 625 ± 40) for the strongest band, which therefore requires high column densities to detect a-C:H grains. Such carbon grains might be present but spectroscopically hidden in many other galactic environments.
This research has made use of the SIMBAD
database, operated at CDS, Strasbourg, France, and of
the NASA/IPAC Extragalactic Database (NED) which is
operated by the Jet Propulsion Laboratory, California
Institute of Technology, under contract with the
National Aeronautics and Space Administration.

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