PhD project

Environments of dwarf galaxies with AGN characteristics in observations and simulations

This thesis investigates the relation between environment and active galactic nuclei (AGN) activity for dwarf galaxies (M* <= 3 x 10^9 M_odot) in both observations and simulations. So far, it consists of three sub-projects: (i) NASA-Sloan Atlas dwarf galaxies with optical AGN characteristics, (ii) IllustrisTNG dwarf galaxy AGNs and their environmental histories, and (iii) a machine learning approach and spatially resolved MaNGA data to classify and characterise dwarf AGN.

Findings of project (i) has been published in MNRAS in August 2020, which found that there is not a statistical significant difference between environments of AGN and non-AGN dwarf galaxies. Project (ii)  has been published in ApJ in December 2021. Here, we found that dense environments and small mergers do play a role for a minority of dwarf galaxies – dense environments can be detrimental to developing AGN activity while minor mergers can enhance it. The last project (iii) is a preliminary study on what we can learn from using a random forest classifier to predict  the class of dwarf galaxies using spatially resolved MaNGA data and different mass bins as training sets.  So far,  this approach suggests that using properties of lower mass AGN as training sets agrees the most observational classifications, but higher mass training sets provide a more candidates. External properties are not important for prediciting AGN activity. 

Submitted May 2022 (preview).

BPT diagram of dwarf galaxies
From "Environments of dwarf galaxies with optical AGN characteristics"

BPT diagram for dwarf galaxies in the NASA-Sloan Atlas. Blue points are dwarf galaxies, red a dwarf galaxies in the AGN region of the diagram while grey points are AGNs with low signal-to-noise

Distance to 10th nearest neighbour distribution
From "The effect of environment and merger history on AGN activity for dwarf galaxies in IllustrisTNG"

Distribution of distance to 10th nearest neighbour for three TNG subsamples and one observational subsample.

Results of Kolmogorov Smirnov testing
From "The effect of environment and merger history on AGN activity for dwarf galaxies in IllustrisTNG"

These three figures show the different the p-values of the KS-testing suite for two different environmental measures: Time since last merger (for three different merger ratios) and distance to 10th nearest neighbour (for 6 different snapshots)