Interstellar Matter Kinematics in the Magellanic Clouds

A Ph.D. Dissertation by Charles W. Danforth

Johns Hopkins University, Baltimore, MD, USA

Dissertation Summary (15 pages, ps format, 11Mb)

Abstract:

I study the ISM of the Magellanic Clouds using three different and complimentary datasets. The first is a set of 141 far-ultraviolet (FUV) spectra taken by the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite of sight lines toward hot, OB stars in the Magellanic Clouds. I use these stars as background sources and study the absorption in the intervening ISM. Secondly, I use a collection of emission-line images of the Magellanic Clouds in Halpha and red continuum light to provide a morphological context for the FUV absorption data. Finally, I present a set of 99 longslit echelle optical emission spectra to act as a bridge between the kinematics seen in the absorption spectra and the morphology seen in the images. I use the combination of optical images and optical spectra to classify each sight line into a set of morphological categories. The diagnostic power of this combined dataset is immense.

I use these datasets to search for global patterns in the Magellanic ISM. In particular, I measure the velocities, widths, and column depths of the absorption features in five different FUV transitions and two optical transitions. Various other data from the literature is added to this and I search for correlations. The picture that emerges is one of a three-phase ISM with cold, warm, and hot phases. The kinematics and distribution of each phase bear little resemblance to each other.

Additionally, I use the high velocity resolution to perform two more focussed investigations on the global dataset. First, I study the ionization structure along sight lines, a good probe of temperature and radiation properties in the ISM. I find that the different morphological classes of objects exhibit different ionization characteristics and that the LMC and SMC show different ranges of ionization. I undertake a similar project to study dust depletion in the ISM of the Magellanic Clouds. Again, different classes of objects display different characteristic profiles and depletion values.

Finally, I carry out two investigations of specific ISM structures using small subsets of the emission and absorption data. These show how detailed analysis of the data can shed unprecedented light on the structure and properties of the ISM at smaller scales. In the first case, I investigate the interaction between the ISM and the wind of an luminous blue variable and determine that it is moving through the disk of the LMC at a high speed.

In the second case, I use several emission and absorption spectra to probe the properties of a bright HII region in the SMC and the supernova remnant (SNR) which lies in front of it. I determine the three-dimensional geometry of the region, determine key shock parameters of the SNR, and find that the nebular ISM is fairly quiescent. The FUV flux from the many massive stars within the HII region photoionize the material in the SNR and make optical investigation very difficult. I discuss the implications of SNRs in HII regions and what effect this might have on the search for more distant objects.

Thesis Advisor: Dr. William P. Blair


Dissertation Summary (15 pages, ps format, 11Mb)


Charles Danforth
Last modified: Tue May 20 10:04:34 MDT 2008