Probing the diffuse interstellar medium with diffuse interstellar bands

Abstract

This work investigates the small scale structure of the Diffuse Interstellar Medium. To do this optical spectroscopy is used to obtain spectra of early type stars which are used as background targets with which the Diffuse Interstellar Medium (ISM) is probed. The spectra obtained contain the highly diagnostic Diffuse Interstellar Bands (DIBs), Na i D and Ca ii lines.

The maps I present here are of the Local Bubble, the Small Magellanic Cloud and the Large Magellanic Cloud. These are the first DIB maps of the solar neighbourhood and large portions of external galaxies. The spectra were obtained with the New Technology Telecsope (NTT) at La Silla Observatory in Chile (Local Bubble survey) and at the Anglo-Australian Telescope (AAT) at Siding Spring Observatory, NSW, Australia. The NTT spectra are long slit spectra of 239 individual targets, whilst the AAT spectra were obtained with the multi-fibre spectrograph 2dF/AAOmega (about 350 targets in each of the Magellanic Clouds).

I have successfully used the 5780 and 5797°A DIBs to map the ISM in the Local Bubble and the Magellanic Clouds. The 5797°A DIB traced neutral structures whereas the 5780°A DIB traced warmer and/or more highly irradiated gas, possibly residing in the skins of those neutral clouds It showed a more highly structured Local Bubble than revealed by the sodium maps, on sub parsec scales; tracing the walls of the Bubble and clearly showing the Bubble opening out into the Halo. In the Magellanic Clouds the DIBs trace molecular clouds surrounding regions of active star formation; they are weak or absent in quiescent molecular cloud complexes and hot gas bubbles.

Probing the diffuse interstellar medium with diffuse interstellar bands

Abstract

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