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2. Abstract A complete sample of point source emissions in the spiral type galaxies NGC300 and M31 have been catalogued and analysed. This study has identified a total of 72 and 864 point source emissions in both NGC300 and M#!. New high-sensitivity and resolution radio-continuum images of NGC300 and M31 at λ=20~cm have been created as part of this study. These new images were produced by merging archived 20~cm radio-continuum data sourced from ATCA and the VLA. Images presented in this thesis are extremely sensitive and feature high angular resolution (<10”).

3. Outline Overview of Instruments Data reduction process Results – NGC 300 – M31

4. Electromagnetic Spectrum

5. Radio-Telescopes The quality of the image is directly dependent upon the amount of flux gathered. A larger dish will collect more flux, improving the image.

6. Bigger is not always better…

7. Radio-Interferometers Rather then build bigger, we build more. A baseline is defined as the distance between 2 individual dishes. Creates a synthesized single dish telescope.

8. Effects of Baselines Array configurations with longer baselines produce higher resolution images – Intrinsic structure of sources can be studied – Image artifacts may be introduced Array configurations with shorter baselines produce lower resolution images – Extended sources are more apparent ie. Extended Emission

9. Instruments Used - ATCA The Australian Telescope Compact Array Made up of six 25 meter diameter dishes Longest baseline supported is 6 kilometers

10. Instruments Used - VLA The Very Large Array Made up of twenty-seven 22 meter diameter dishes Longest baseline supported is 36 kilometers

11. Merging Observations Merging multiple observations together is possible Observations with different array configurations can produce images with both intrinsic and extended structure to sources

12. Data Reduction Process Two main data reduction software packages were used – Astronomical Image Processing System (AIPS) Use was limited to preprocessing of VLA only – Multichannel Image Reconstruction, Image Analysis and Display (miriad)

13. Miriad - Overview Actual data reduction is comprised of a number of individual steps.

14. Miriad - Flagging Primary Calibrator 1934-638 with data points to be flagged

15. Miriad - Calibration Calibration is necessary to establish a flux density scale and correct for instrument gains over time Achieve this by observing significantly strong and are well understood sources By comparing results measured to what we expect the results to be, we can deduce certain corrections which need to be made, and apply these corrections to our data

16. Example - Primary Calibrator Before CalibrationAfter Calibration

17. Miriad - Invert This task actually produces a “dirty” map from a set of calibrated sources A number of additional parameters can be specified to alter processing – How to weigh baselines of varying length – Enable image mosaicing

18. Example – “Dirty” Map

19. Miriad - Cleaning “Dirty” images suffer from artifacts which degrade the quality of the image These artifacts can be removed from these “dirty” images – Miriad tasks CLEAN and MOSSDI both use an SDI CLEAN algorithmic approach Most computationally expensive stage of the imaging process

20. Miriad - Restor Produces a final cleaned image based on the outputs of previous tasks

21. Part 3 - Results NGC 300

22. NGC 300 - Observations Used PUT A TABLE HERE SUMMARISING: – PROJECT CODE – VLA/ATCA – RA AND DEC – DATE

23. NGC 300 - Final Image

24. NGC 300 - Sources A total of 72 distinct sources were identified This new source catalogue was compare to a previously defined catalogue (Payne et al., 2004) – 8 previously defined sources, out of 48, were not present in our catalogue

25. Part 3 - Results M31

26. M31 - Observations Used 15 individual VLA Projects were used Observations conducted between October 1983 and September 1996 Contains 57 individual pointings

27. M31 – Final Image

28. M31 - Sources Across 17 individual images from 15 VLA projects, 864 unique sources were identified. These sources were compared to those listed in Gelfand (2004), which describes sources at λ = 92cm – 118 sources were found to be common to both lists

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