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MORPHOLOGY OF INTERSTELLAR MEDIUM USING MULTI-WAVELENGTH OBSERVATIONS

Preethi, K (2016) MORPHOLOGY OF INTERSTELLAR MEDIUM USING MULTI-WAVELENGTH OBSERVATIONS. PhD thesis, Christ University.

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Abstract

The interstellar medium (ISM) is the matter that exists between the stars in a galactic system. The structure and composition of a galaxy can be understood by a study of the ISM. Our Galaxy is the only place where the observations of the ISM can be resolved and studied in great detail. There are various archived observations from space-based and groundbased telescopes spanning a large region of the electromagnetic spectrum. Combining these different observations with one another will help to study the ISM on a large scale. We have compiled some such observations and analyzed the column density data, to study the ISM and make the database available to the scientific community for further investigations. The data was taken from papers published over a span of 60 years (1951 to 2010). The column densities in these papers were derived using different methods and observations from various telescopes operating in different wavelengths. We compiled these diverse data into a single catalogue and analysed the data. We studied the correlations between the line of sight gas and dust and reported new correlations not published before (ApJS, 119(1), 8, 2012). We also studied the spatial distribution of the interstellar gas and dust and have estimated the corresponding exponential vertical scale heights. There also exists a wide range of photometric data from various telescopes which can be combined to cover a large range of wavelengths. We have made use of Galaxy Evolution Explorer (GALEX) photometric data in conjunction with Sloan Digital Sky Survey (SDSS) data to obtain the point sources observed by both missions. GALEX observed in two bands simultaneously, the far-ultraviolet (FUV: 1350 – 1750 Å) and the near-ultraviolet (NUV: 1750 – 2750 Å), while SDSS observed in five bands u, g, r, i and z, with effective wavelengths ranging from 3551 Å to 8931 Å. GALEX and SDSS together provide photometric data ranging from the far-ultraviolet to the near-infrared. We used a model-based approach to classify the point sources and to simultaneously determine the extinction towards each of these sources. We find that ~80 per cent of the point sources detected by both GALEX and SDSS are extragalactic. We have this photometric data towards ~1.6 million point sources with both GALEX and SDSS bands. By fitting various SED models to these data, we were able to classify them by type such as, main-sequence stars, red giants, white dwarfs, galaxies and quasars and also estimate the line of sight parameters, i.e. extinction, distance to Galactic sources and photometric redshift towards extragalactic sources (MNRAS, 437(1), 771, 2014). We then focused on the sources classified as white dwarfs and produced a catalogue of the same along with the best fit parameters. We have also constructed three dimensional extinction maps of the Milky Way Galaxy using the line of sight extinction and distances derived towards these white dwarfs, for every 100pc slice in distance and covering an area of 13,441 square degrees. The variation of extinction with Galactic latitude and distance is also studied and compared with other similar papers.

Item Type:Thesis (PhD)
Subjects:Thesis
Thesis > Ph.D > Physics
Thesis > Ph.D
ID Code:7844
Deposited By:Shaiju M C
Deposited On:18 May 2019 16:01
Last Modified:18 May 2019 16:01

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