Hello World!

I am a Postdoctoral Research Associate in the First Light research group at University College London (UCL). The main focus of my research is to study the evolution of the physical properties of very distant galaxies using state-of-the-art telescopes around the world.

I am interested in high-redshift (distant) galaxies that are in the very early stages of their evolution. To do this, I use the VANDELS dataset, which is a survey of small patches of the sky using the Very Large Telescope (VLT) in Chile. The VANDELS survey targeted thousands of galaxies to obtain very high quality spectra that enables studying their properties in incredible detail.

I am also interested in studying distant radio galaxies (massive galaxies that appear very bright at radio wavelengths) and using them to study the evolution of both galaxies and the large-scale structure of the universe. At redshifts (z) of 6 and above, into the epoch of reionisation (EoR), a bright radio galaxy can be used as a background to search for the elusive 21-cm absorption signal from the neutral hydrogen that pervaded the universe at that time. Constraining when and how the universe made a phase transition from neutral to completely ionised is one of the most exciting challenges in cosmology today and radio galaxies at z > 6 may hold some clues!

On this page you can find more information about my research interests, what I like to do in my free time, a short CV and my contact information.


Physical properties of Helium II emitting galaxies in VANDELS

Galaxies in the early Universe that emit copius amounts of Helium II are likely to be dominated by very massive stars that have very few metals. Such galaxies represent a population of the first galaxies that may have formed in the Universe, and studying large samples can reveal the physics that dominates within the earliest galaxies to appear in the Universe.
The paper reporting the Helium II emitting galaxies from VANDELS can be found here:
The properties of He II λ1640 emitters at z = 2.5-5 from the VANDELS survey, 2020

Discovery of the most distant radio galaxy to date

In June 2018, my research team discovered the most distant radio galaxy observed to date, named TGSS J1530+1049, at a distance of 12.7 billion light years away (redshift = 5.72)! In comparison, the age of the Universe is 13.6 billion years. Therefore, this is a galaxy that was formed within the first 7% of the Universe's lifetime! This discovery broke the distance record for a radio galaxy after almost 20 years. Radio galaxies are some of the most massive galaxies in the Universe and harbour a supermassive black hole in their centres that is actively eating up the gas and dust that surrounds it. Discovering such an object at such a large distance from us poses some interesting challenges about how and when the seeds of this galaxy and the supermassive black hole were sown, and how they evolved to be so massive in such a short period of time after the Big Bang.
The paper reporting this discovery has now been published in the Monthly Notices of the Royal Astronomical Society and can be found here:
Discovery of a radio galaxy at z = 5.72, 2018

In the media:
Astronomy Now: Most distant radio galaxy, host to a voracious black hole, is found
Phys.org: The most distant radio galaxy discovered
Astronomie.nl: Astronomen ontdekken verst verwijderde radiostelsel ooit (Astronomers discover the most distant radio galaxy ever)
BBC Brasil: Radiogaláxia mais distante da Terra é descoberta com participação de brasileiro - e dá mais pistas sobre o Big Bang (Most distant radio galaxy is discovered with Brazilian participation - and gives more clues about the Big Bang)
Media INAF: Scoperta la radiogalassia più lontana (The most distant radio galaxy discovered)

High-redshift extreme spectrum project (HiZESP)

We have started a large campaign to hunt for distant radio galaxies by taking advantage of the new all-sky surveys at low radio frequencies using telescopes such as the Giant Metrewave Radio Telescope (GMRT) in India, the Very Large Array (VLA) in USA and the Low Frequency Array (LOFAR) in the Netherlands and all of Europe. Early results from this project can be found here:
A search for faint high-redshift radio galaxy candidates at 150 MHz, 2018

In addition to studying these sources at radio wavelengths, it is essential to also observe them at optical and infrared wavelengths. As part of this project, we have been awarded observing time on telescopes all over the world to a) obtain spectra and determine redshifts of candidate high-redshift radio galaxies and b) observe our targets at near-infrared wavelengths to study the underlying stellar populations.

The telescopes being used for this project include the Hobby-Eberly Telescope (HET), Gemini North, William Herschel Telescope (WHT) and the Large Binocular Telescope (LBT). The paper reporting these observations has now been accepted for publication in the Monthly Notices of the Royal Astronomical Society and can be found here:
The nature of faint radio galaxies at high redshifts, 2019

Modelling luminosities and sizes of radio sources across cosmic time

One of the first projects of my PhD was to build a model capable of tracking the evolution of radio galaxies from first principles, and predicting the luminosity and size distribution of radio sources at any given epoch. This model included recipes for a host of physical phenomenon and the results can be found here:
Modelling the luminosities and sizes of radio sources: radio luminosity function at z = 6, 2017

Other interests

In addition to astronomy, I have had the pleasure to be a part of various activities in and around town. Here you can find some of the things that I care about!

Leiden International Short Film Experience (LISFE)

The 10th edition of LISFE at the artsy cinema, Het Kijkhuis, was a wrap this spring and it was a huge success! LISFE has grown from a day or two of screening short-films in a student centre in Leiden to one of the biggest national level short-film festivals in The Netherlands! LISFE received over 800 films from 70 countries for the 2018 edition and we are looking forward to expand and grow again this year. Click on the image on the left to know more!

Leiden Football Factory

After achieving the second place in the lower divisions of the Dutch Amateur Leauge, the new football (soccer) season starts again this autumn and we will be back to challenge for the division title! Click on the image on the left to follow updates (hopefully you click only when we've won a few games)!

Astronomy on Tap Leiden

Astronomy on Tap is a unique concept that combines an astronomy public talk with the joy of drinking beer in the local pub! I gave a public talk about distant radio galaxies and their supermassive black holes on 30 July, 2018! Join us at AoT at Grand Cafe de Burcht on the last Monday of every month starting at 8pm to learn more about astronomy while chugging pints with your mates.

Public Engagement = Fun!

Here at Leiden Observatory, we take public engagement activities very seriously and believe it to be an integral part of astronomy research. I am involved with our outreach wing called Universe Awareness (Unawe), founded by one of my co-supervisors George Miley. One of my personal best experiences was giving a talk about my research to 5th graders at American School The Hague. Follow the link by clicking on the image to find out more!

Short CV

Here you can find a short version of my CV:

Research positions

Postdoctoral Research Associate, UCL, UK, March 2020 -
Postdoctoral Researcher, INAF-OA Roma, Italy, Feb 2019 - Feb 2020


PhD Astronomy and Astrophysics, Leiden Observatory, The Netherlands, 2014 - 2019
MSc Astrophysics, University College London, UK, 2014

First author publications

Some successful observing proposals

  • LUCI MOS (Large Binocular Telescope) PI, 11 hours
  • MUSE (Very Large Telescope), PI, 8 hours
  • XSHOOTER (Very Large Telescope), PI, 4 hours DDT
  • William Herschel Telescope, PI, 7 dark nights
  • Very Large Array A-configuration, Co-I/contact person, 9+ hours of priority-A time
  • Gemini North, Co-I, 14 hours

Contact Me

Here is where you can find me both physically and online.

Office Address

Pearson Building
University College London
Gower Street, London

Email and phone

Email: aayush [dot] saxena [at] ucl [dot] ac [dot] uk

If you'd like to get in touch, either to find out more about my research or to complain about anything that you did not like on this website, why not send me an email on the address listed above?