Diffuse interstellar bands and interstellar carbon chemistry in the Galaxy and beyond

Details Diffuse interstellar bands and interstellar carbon chemistry in the Galaxy and beyond Diffuse interstellar bands and interstellar carbon chemistry in the Galaxy and beyond

Jun 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006phdt........12c&link_type=abstract

PhD Thesis, Universiteit van Amsterdam, 2006

Astronomy and Astrophysics

Astronomy

Astrochemistry, Interstellar Medium (Ism), Diffuse Clouds, Diffuse Interstellar Band (Dib), Gas, Dust, Atoms, Molecules, Pah

Scientific paper

This thesis presents the results from a study on the behaviour of the diffuse interstellar bands (DIBs) and candidate DIB carriers in diffuse to translucent interstellar clouds probing a wide variety in local environmental conditions.
In the first part a study of a heavily reddened line of sight in the Galactic plane is presented. It shows that atomic lines, notably neutral potassium and sodium, trace the 6613 and 5797 DIBs very well and over a broad range in reddening, showing also that several different interstellar clouds contribute to the observed DIB profile. Next, a search for linear and circular polarisation of DIBs in several lines of sight exhibiting continuum polarisation is discussed. This chapter shows that the derived upper limits on the polarisation confirm that the carriers, for the six DIBs studied, are not likely to be directly related to grains or grain impurities.
The second part presents a study of DIBs in two Local Group members, the Large and Small Magellanic Clouds. A detailed analysis of the dust and gas is performed in order to understand the physical conditions of the diffuse interstellar medium in which DIBs reside. The strength and hardness of the UV field appear to govern the observed differences in DIB strength in the different lines of sight. The unique detection of a dozen strong, narrow DIBs in the spiral galaxy NGC 1448, towards SN2001el, shows that DIBs are present even beyond the Local Group. The observations also show that, like in our own Galaxy, different local physical environmental conditions occur that favour or prohibit the formation and survival of DIB carriers.
The final part presents results from detailed modelling of the translucent interstellar cloud towards HD147889 in the Rho Ophiuchus cloud complex and the subsequent PAH charge state distribution and emerging theoretical PAH absorption spectrum. In addition, the effects of metallicity, the UV radiation field and dust extinction on the PAH charge state are studied and the possible implications for the DIB carriers are discussed. The increased PAH ionization fraction in the LMC and SMC due to the lower metallicity is mitigated by the increased attenuation of UV photons by the dust in these galaxies. The observed differences in DIB strength within and between galaxies can be understood in terms of the fraction of the available carbon in PAHs and the subsequent ionisation fraction of these PAHs.

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