Computer Science
Scientific paper
Apr 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004phdt.........8g&link_type=abstract
PhD thesis, Université de Paris XI
Computer Science
9
Spectral Energy Distributions, Dwarf Galaxies, Interstellar Medium, Dust, Observational Techniques
Scientific paper
This thesis is devoted to the multi-wavelength observations and the modelling of dust, in nearby low-metallicity dwarf galaxies. The main motivations of this project are: (i) the study of dust properties - composition, size distribution, etc. - in non-solar interstellar media; (ii) the study of global spectral energy distributions of dwarf galaxies which are thought, due to their chemical youth, to be similar to primordial galaxies that we can not observe; and (iii) obtaining informations about the chemical evolution of these galaxies by studying the gas-to-dust mass ratio.
I begin with the detailed study of mid-infrared ISO spectra of these galaxies. The main spectral characteristics that we outline are: (i) the weakness of the aromatic band emission, compared to what is observed in normal starburst galaxies; (ii) the similarity with Galactic HII region spectra - a steep very small grain continuum and prominent ionic lines. After that, we study the spectra of a more diversified sample - spiral, starburst, dwarf galaxies and HII regions - in order to plot the band ratios. The 6.2/11.3, 7.7/11.3 and 8.6/11.3 correlations are, for the first time, established on such a large sample. They show that dwarf galaxies occupy a particular region in this diagram, different than the one occupied by Galactic HII regions, inducing a different PAH structure - ionization, hydrogenation, size, etc.
The second step of this project is the modelling of the spectral energy distributions of four dwarf galaxies (He 2-10, II Zw 40, NGC 1140, NG 1569), from ultraviolet to millimeter. In order to achieve this goal, I have added, to our own observations, data from the litterature. The modelling is done self-consistently, using constraints on dust emission, stellar radiation and on ionic lines. We synthesize the spectral energy distributions of these galaxies, as well as the corresponding extinction curves. The properties that we are able to outline are that: (i) the emission is dominated by small grains (3-4 nm) stochastically heated; (ii) the synthesized extinction curves exhibit some analogies with the magellanic cloud curves, by their slopes, and the strength of the 2175 angströms bump is weaker in three of the four galaxies; (iii) every spectral energy distribution have an excess in submillimeter emission that we attribute to a very cold dust component, embedded in dense cores, accounting for a large fraction of the total dust mass.
Moreover, this dissertation contains: (i) a presentation of the motivations to study galaxies' spectral energy distributions; (ii) a general description of the way that optical dust properties are modeled; (iii) a detailed description of ISOCAM data reduction; and (iv) a detailed description of the observation and the data reduction with the submillimeter bolometer arrays, SCUBA and MAMBO.
This dissertation is written essentially in french.
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