Galaxy Evolution in Isolation

Abstract

Galaxy evolution is driven by both internal processes, such as AGN feedback and stellar winds, and external environmental processes, which include tidal interactions and ram pressure stripping. In dense environments both processes occur simultaneously, making it difficult to isolate their individual effects on galaxy evolution. Isolated galaxies act as a natural control sample for investigating galaxy evolution with minimal environmental influence. This project aimed to identify an isolated sample of galaxies within the MaNGA survey using the nearest neighbour distance measured against the NASA Sloan Atlas and to compare the u-r colours of isolated and typical environment galaxies to investigate whether isolation produces any difference in stellar population properties. The NASA Sloan Atlas data was restricted across the sky region (130 to 160 degrees RA, 0 to 20 degrees Dec) and redshift range (0.005 < z < 0.05), returning 3790 galaxies. A magnitude limit of Mr < -18.4 was applied to reduce the effects of Malmquist bias and produced a volume limited catalogue. The MaNGA sample consisted of 247 galaxies across the same region. Three dimensional nearest neighbour distances were computed using astropy match_coordinates_3d function, with a threshold of d > 3.442Mpc (median + 1.5 sigma) used to classify 21 galaxies as isolated. The mean u-r colour of isolated galaxies was found to be 1.87 +/- 0.070, compared to 1.88 +/- 0.03 for galaxies in typical environments. The difference of 0.015 +/- 0.076 is smaller than the combined uncertainty showing that there was no clear colour separation within current sample. Although the initial hypothesis that isolated galaxies would exhibit bluer colours is not supported, the absence of a strong colour separation is likely due to the small sample size rather than indicating that galaxy environment has no influence on colour evolution. Despite the limitation, this project demonstrates a reproducible nearest neighbour methodology for identifying isolated galaxy populations using large datasets. Future work should extend the analysis to a larger SDSS catalogue and utilise MaNGA's spectroscopy to compare stellar age between isolated and typical environment.