Probing Galaxy Evolution with AKARI

Davidge, Helen Rosemary (2017). Probing Galaxy Evolution with AKARI. PhD thesis The Open University.



This thesis presents the first detailed analysis of three extragalactic fields observed by the infrared satellite, AKARI. AKARI is the only telescope able to observe deeply in the Spitzer/IRAC - Spitzer/MIPS band gap of 8-24 microns. The first analysis of these extragalactic fields, was to perform galaxy number counts, the most basic statistical property of galaxy populations. Presented are the counts at 3, 4, 7, 11, 15 and 18 microns. These number counts were compared with published results and galaxy evolution models. These models are dependent on both the Spectral Energy Distribution (SED) templates and evolution of the galaxy types. The phenomenological backwards evolution model of Pearson 2005 appeared to be consistent with the number counts. To probe this, number counts were extracted from below the survey limit by performing Probability of Deflection (P(D)) fluctuation analysis. The Pearson model was found to be consistent with the 11 microns P(D) analysis but not with the 15 microns. The results from the 15 microns P(D) analysis indicates that the Pearson model under predicts the evolution of star forming galaxies. Multi-wavelength band-merged catalogues for the two deep extragalactic fields were created using AKARI data from the work of this thesis and ancillary data. The separation of galaxy type using AKARI/IRC filter colours was explored. For z < 2 a separation criteria was found for Active Galactic Nuclei (AGN), but to accurately classify galaxy type, SED fitting is required. Submm-selected galaxies detected by AKARI were found to resemble scaled-up normal local spiral galaxies, rather than starbursts, consistent with them lying on the high-redshift `main sequence' unlike local ultraluminous infrared galaxies. The thesis concludes by measuring the percentage of the far-infrared Cosmic Infrared Background (CIB) resolved by AKARI mid-infrared galaxies. By performing stacking analysis on a Herschel/SPIRE 250 microns image of AKARI galaxy positions, it was found that AKARI mid-infrared galaxies resolve ~10% of the 250 micron CIB.

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