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)

Publications

2021

Kristensen MT, Pimbblet K, Gibson B, Penny S and Koudmani (submitted), "The effect of environment and merger history on AGN activity for dwarf galaxies in IllustrisTNG"

[BibTeX]

BibTeX:

@article{Kristensen2021,
  author = {Kristensen, Mikkel T. and Pimbblet, Kevin and Gibson, Brad and Penny, Samantha and Koudmani, Sophie},
  title = {The effect of environment and merger history on AGN activity for dwarf galaxies in IllustrisTNG},
  year = {submitted}
}

Keegans JD, Stancliffe RJ, Bilton LE, Cashmore CR, Gibson BK, Kristensen MT, Lawson TV, Pignatari M, Vaezzadeh I, Côté B and Chongchitnan S (2021), "Project ThaiPASS: international outreach blending astronomy and Python", Physics Education., feb, 2021. Vol. 56(3), pp. 035001. IOP Publishing.

[Abstract] [BibTeX] [DOI] [URL]

Abstract: We present our outreach program, the Thailand–UK Python+Astronomy Summer School (ThaiPASS), a collaborative project comprising UK and Thai institutions and assess its impact and possible application to schools in the United Kingdom. Since its inception in 2018, the annual ThaiPASS has trained around 60 Thai high-school students in basic data handling skills using Python in the context of various astronomy topics, using current research from the teaching team. Our impact assessment of the 5 day summer schools shows an overwhelmingly positive response from students in both years, with over 80% of students scoring the activities above average in all activities but one. We use this data to suggest possible future improvements. We also discuss how ThaiPASS may inspire further outreach and engagement activities within the UK and beyond.

BibTeX:

@article{Keegans2021,
  author = {James D Keegans and Richard J Stancliffe and Lawrence E Bilton and Claire R Cashmore and Brad K Gibson and Mikkel Theiss Kristensen and Thomas V Lawson and Marco Pignatari and Iraj Vaezzadeh and Benoit Côté and Siri Chongchitnan},
  title = {Project ThaiPASS: international outreach blending astronomy and Python},
  journal = {Physics Education},
  publisher = {IOP Publishing},
  year = {2021},
  volume = {56},
  number = {3},
  pages = {035001},
  url = {https://doi.org/10.1088/1361-6552/abdae7},
  doi = {10.1088/1361-6552/abdae7}
}

2020

Kristensen MT, Pimbblet K and Penny S (2020), "Environments of dwarf galaxies with optical AGN characteristics", mnras., August, 2020. Vol. 496(3), pp. 2577-2590.

[Abstract] [BibTeX] [DOI]

Abstract: This study aims to explore the relation between dwarf galaxies (M_* ≤ 510^9 M_odot) with AGNs and their environment by comparing neighbourhood parameters of AGN and non-AGN samples. Using the NASA-Sloan Atlas, both the local environment and the immediate environment of dwarf galaxies with z ≤ 0.055 are analysed. Of the 145,155 galaxies in the catalogue, 62,258 of them are classified as dwarf galaxies, and by employing two AGN selection methods based on emission line fluxes (BPT and WHAN), 4,476 are found to have AGN characteristics in their optical spectra. Regardless of selection method, this study finds no discernible differences in environment between AGN and non-AGN host dwarf galaxies and these results indicate that environment is not an important factor in triggering AGN activity in dwarf galaxies. This is in line with existing literature on environments of regular galaxies with AGNs and suggests universality in terms of reaction to environment across the mass regime. The biases of AGN selection in low-mass galaxies, and the biases of different measures of environment are also considered. It is found that there are several mass-trends in emission line ratios and that the SDSS fiber covers galaxies non-uniformly with redshift. These biases should be accounted for in future work by possibly including other wavelength regimes or mass-weighting of emission line ratios. Lastly, a discussion of the environment estimation methods is included since they may not gauge the desired properties due to factors such as time delay or using loosely constrained proxy parameters.

BibTeX:

@article{Kristensen2020,
  author = {Kristensen, Mikkel T. and Pimbblet, Kevin and Penny, Samantha},
  title = {Environments of dwarf galaxies with optical AGN characteristics},
  journal = {mnras},
  year = {2020},
  volume = {496},
  number = {3},
  pages = {2577-2590},
  doi = {10.1093/mnras/staa1719}
}

Older

Dahle H, Gladders MD, Sharon K, Bayliss MB, Wuyts E, Abramson LE, Koester BP, Groeneboom N, Brinckmann TE, Kristensen MT, Lindholmer MO, Nielsen A, Krogager JK and Fynbo JPU (2013), "SDSS J2222+2745: A Gravitationally Lensed Sextuple Quasar with a Maximum Image Separation of 15.''1 Discovered in the Sloan Giant Arcs Survey", apj., August, 2013. Vol. 773(2), pp. 146.

[BibTeX] [DOI]

BibTeX:

@article{Dahle2013,
  author = {Dahle, H. and Gladders, M. D. and Sharon, K. and Bayliss, M. B. and Wuyts, E. and Abramson, L. E. and Koester, B. P. and Groeneboom, N. and Brinckmann, T. E. and Kristensen, M. T. and Lindholmer, M. O. and Nielsen, A. and Krogager, J. -K. and Fynbo, J. P. U.},
  title = {SDSS J2222+2745: A Gravitationally Lensed Sextuple Quasar with a Maximum Image Separation of 15.''1 Discovered in the Sloan Giant Arcs Survey},
  journal = {apj},
  year = {2013},
  volume = {773},
  number = {2},
  pages = {146},
  doi = {10.1088/0004-637X/773/2/146}
}

Publications

2021

Kristensen MT, Pimbblet K, Gibson B, Penny S and Koudmani (2021), "The effect of environment and merger history on AGN activity for dwarf galaxies in IllustrisTNG", ApJ, December, 2021, Vol. 922, Issue 2, id.127, 19 pp.
Keegans JD, Stancliffe RJ, Bilton LE, Cashmore CR, Gibson BK, Kristensen MT, Lawson TV, Pignatari M, Vaezzadeh I, Côté B and Chongchitnan S (2021), "Project ThaiPASS: international outreach blending astronomy and Python", Physics Education., feb, 2021. Vol. 56(3), pp. 035001. IOP Publishing.

2020

Kristensen MT, Pimbblet K and Penny S (2020), "Environments of dwarf galaxies with optical AGN characteristics", MNRAS, August, 2020. Vol. 496(3), pp. 2577-2590.

Older

Dahle H, Gladders MD, Sharon K, Bayliss MB, Wuyts E, Abramson LE, Koester BP, Groeneboom N, Brinckmann TE, Kristensen MT, Lindholmer MO, Nielsen A, Krogager JK and Fynbo JPU (2013), "SDSS J2222+2745: A Gravitationally Lensed Sextuple Quasar with a Maximum Image Separation of 15.''1 Discovered in the Sloan Giant Arcs Survey", ApJ, August, 2013. Vol. 773(2), pp. 146.