Welcome to my homepage

Hi! I'm Thomas Jackson and I'm currently a third year PhD student at the Astronomisches Rechen Institut (ARI) at Heidelberg University. My PhD topic is on the assembly and growth processes of central galaxies in the low redshift Universe. I also have research interests in AGN host galaxy properties. I'm orginally from a farm on the edge of the Lake District, in the north of England. More information on me, such as my research, CV, publications, contact details and background can be found below. Feel free to contact me via email with any questions that aren't answered on this page.

The assembly and growth of central galaxies

One, current major question concerns the size evolution of massive, quiescent galaxies. Daddi et al. (2005) found that massive galaxies at high redshift have much smaller sizes than their low redshift counterparts despite similar stellar masses. This work has been extended to other galaxy populations across different redshifts, with similar results (e.g. van der Wel et al. 2014). Multiple theories have been suggested to explain this behaviour including major mergers or feedback from AGN or supernovae. Dry minor mergers, and thereby the accretion of satellite galaxies, has emerged as the favoured theory as the driver of this size evolution. Dynamical arguments and simulations have been used to show these processes (e.g. Naab et al. 2009), however observational evidence has, until recently, been lacking.

To address this, in Jackson et al. (2020a), we investigated the build up of galaxies and their dependence on both their stellar mass and their environment (given by the halo mass) as shown in the first figure below, where the times at which 10, 50 and 90 percent of their stellar masses were assembled depending on the stellar and halo mass. We take this a step further in Jackson et al. (in prep), where we will present evidence of widespread minor merger activity causing excesses of stellar mass and light in the profiles of massive galaxies (such as the example in the picture below). This accreted material in the outskirts of galaxies has very similar properties to the surrounding satellite population and thereby provides evidence of minor mergers predominantly driving the size growth of central galaxies.

Star forming properties of AGN host galaxies

Another major question in galaxy evolution is the role of accreting supermassive black holes in the middle of galaxies known as active galactic nuclei (AGN) and their contribution to the quenching/shutting down of star formation in the galaxy population. The majority of cosmological simulations require some form of this so-called AGN feedback in order to accurately reproduce properties of the local universe, e.g. the stellar mass function (Bower et al. 2006). However, finding observational signatures of this AGN feedback has so far proven difficult. Some studies have tried to directly link star formation and AGN activity (e.g. Rosario et al. 2012, Stanley et al. 2015), while others have tried to link AGN outflows with star formation (e.g. Harrison et al. 2012), each with mixed results.

Building on work from my masters degree, I am attempting to contribute towards answering this question using both observations and simulations simulataneously, by comparing the host galaxy properties of AGN samples. So far we (my collaborators and I) have found that introducing AGN feedback into simulations widens the specific star formation rate distributions of AGN samples (Scholtz et al. 2018, see the first figure below), which are then similar to those in the observed universe, both at high redshift and low redshift (Jackson et al. 2020b, see second figure below) and that these AGN form stars, on average, at slightly lower rates than the star forming main sequence. We are also currently investigating the direct effect AGN feedback has on star formation in simulations and the stellar population properties of low redshift AGN.


Dr. Anna Pasquali
Prof. David Alexander
Dr. David Rosario
Prof. Eva Grebel

Useful Links

Here are some links to some of the telescopes, simulations and data sets I use:

The EAGLE simulations
The IllustrisTNG simulations
The Subaru Hyper Suprime Cam Survey
The Swift-BAT catalogues
The Sloan Digital Sky Survey (SDSS)
The BAT AGN Spectroscopic Survey (BASS)

First Author Publications

Co-authored Publications

  • A correlation between BCG position angle and large scale structure spanning 10 Mpc
  • R. Smith, H. Choi, K. Kraljic, A. Pasquali, T. M. Jackson (in prep)

  • The imprint of cosmic web quenching on galaxy evolution
  • N. Winkel, A. Pasquali, K. Kraljic, R. Smith, A. Gallazzi, T. M. Jackson (in prep)

A bit more about me

Where I come from

I grew up on a small farm on the edge of the Lake District, which is, in my (not so neutral) opinion, possibly the most beautiful part of the UK. It consists of a couple of hundred mountains up to almost 1000m in altitude and around 15 big lakes, with hundreds of smaller ponds or tarns, all packed into an area of roughly 50km by 50km. Tourism and farming are the main industries there, with the climate being typically very, very wet, however on the few days of summer every year with 20/25 degrees and sunshine, you'll find plenty of outdoor activites such as hiking, kayaking, ghyll scrambling etc. Above are plenty of photographs taken by myself and below is a link to a podcast of an interview, giving a rough insight into life in the Lake District from James Rebanks, one of my favourite authors: James Rebanks - Interview

My hobbies

In my spare time when I'm not working on my PhD project or research, I love being outdoors. You'll find me often hiking on hills and mountains, playing sports (such as rugby) or doing garden work. I also enjoy fine food and drink, especially for cooking and baking all sorts of different dishes. To relax I usually like playing music on a number of instruments or listening to music (and sometimes dancing). Friends and family are also a big part of my life, so I spend a lot of my spare time with them, sometimes doing some of the above activities. I also like to keep up to date with and get involved in discussions about current affairs, including politics, climate change and equality.


Email: Thomas.Jackson@uni-heidelberg.de

Address: Thomas Jackson, ARI, Universitat Heidelberg, Moenchhofstr. 12-14, 69120 Heidelberg, Germany