AGN dust emission as a standard candle in the LSST era

Lead Research Organisation: University of Southampton
Department Name: School of Physics and Astronomy


What is the universe made of and how did it come to be as we see it today? Modern cosmology evolved out of generations of philosophers and scientists who tried to answer these two questions. According to our current understanding the universe as we know it started out with a "Big Bang" 13.8 billion years ago and has been expanding ever since. While it was extremely hot initially, the expansion cooled the matter, and gravity worked its way to form stars and galaxies as we see them today.

While this has been the standard picture since at least 1964, marked by the discovery of the Big Bang afterglow, we have come to realise that the two dominant factors of the universe are completely unknown: About 85% of the matter is invisible "dark matter" and not formed of the atoms or elementary particles we know of. With the help of this huge "extra mass" we may expect that gravity eventually slows down the expansion that started during the Big Bang. However, over the last 20 years strong evidence has been found that an unknown force, the "dark energy", started pulling the universe apart, leading to an ever increasing rate of expansion. This dark energy accounts for almost 70% of the energy in the universe.

So, what is behind this mysterious dark sector? Despite being observationally different phenomena, both dark matter and dark energy challenge our foundation of physics. Could it be that some of our best tested theories, like general relativity, need to be reconsidered on cosmological scales?

This project aims at facilitating cosmology with a new tool. Our most precise measurements of the cosmological model come from the young universe and need to be extrapolated to the present. Yet, measurements in the local, present day universe show signs of tension with these extrapolations. It is unclear as of yet if this tension is a fact of unknown problems with the current cosmological probes or if they are pointing towards new physics that will help us understanding the dark universe.

Most direct cosmological probes rely on the measurement of distances. For this, "standard candles" are invoked where the degree of dimming with distance relates to the expansion of the universe while the light was travelling to us. The currently most favoured candles are a special type of supernova explosions; however they need a complicated set of calibration to make them absolute probes of the local cosmological parameters. Here a new type of standard candles will be established that can be calibrated against themselves and potentially solve the question where the tension in cosmological parameters between the different methods come from: new physics or unknown errors. These new standard candles are supermassive black holes in the centre of galaxies that swallow matter from its surrounding. As the matter is being accreted, it lights up and part of this radiation comes from a generic, standardised region, making it a standard candle. We will use computer simulations and new sets of observations to exploit this new tool for cosmology. We will also make use of the new data to address fundamental questions related to the accretion process onto supermassive black holes.

Planned Impact

Outreach and Public Engagement is not only responsible for informing our audiences what public funding has achieved, but it is also extremely important in inspiring the future human capital needed for the country's science and technology needs, both in terms of new students and skilled workers for Astronomy-based industry. The School of Physics and Astronomy reaches over 18,000 students and members of public a year with all its outreach and public engagement activities. Our activities encompass both small-scale events, targeted at small, specialised audiences, and large-scale public open-days. The flagship astronomy outreach activity is the inflatable "astrodome", an extremely popular mobile planetarium that visits local/regional schools and colleges, and other venues. It provides material relevant to the KS1-3, GCSE and A-level science and physics curricula. We regularly provide astronomy content for the Science Learning Centre South West, which opened in 2004 and provides continuing professional development opportunities for teachers. Thus we have been able to provide input and support to the teachers which can have much longer-term value for their future teaching of basic scientific principles.

The University has well-resourced Research and Innovation Service (R&IS), a mechanism that ensures effective uptake and dissemination of research results and knowledge exchange, via the commercialisation process. The R&IS has developed a sophisticated process for the identification, commercialisation and exploitation of IP developed at the university. Astrophysics has led the way and has developed the spin-out company Symetrica, a commercial spin-out company based on the Southampton Astronomy Group's instrumentation development for INTEGRAL, and which will continue to employ >25 people in the UK and the US, and has a forecast turnover of more than £10m for 2013-14 with recognition as an example of best practice. Symetrica is a technological leader in the field of radioactive isotope identification. This distinguished body of work on the design of technology for gamma-ray detection and imaging has informed new counter- terrorism practices. Technological advances arising from the research have been crucial to delivering significant benefits in the fields of homeland security and nuclear safety the latter particularly in the wake of the 2011 Fukushima disaster.


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Description As part of the grant, the idea of using infrared light emitted from the environment of supermassive black holes in the centres of galaxies as cosmological probes has been further developed. In a 2017 paper, I demonstrated how an optical and infrared sky survey would be able to constrain dark matter and dark energy and independently test our cosmological model. Since then two large sky surveys (VEILS and VOILETTE) to measure the size of the infrared emission region in several 100 galaxies have been started to put the theory to the test. In addition, I became a member of the AGN Science Collaboration of the upcoming LSST observatory. As part of the team, I contributed to a recent white paper to make sure the survey to be started in the 2020s will be setup in a way to facilitate the science goals laid out in the proposal.
Exploitation Route As part of the VEILS survey, we are required to prepare annual data releases of optical and infrared images, photometric catalogues, and light curves. Those data will be available to the community via the ESO archive and can be exploited by any scientist.
Sectors Other

Description Affiliate PI of LSST:UK 
Organisation Large Synoptic Survey Telescope Corporation
Country United States 
Sector Charity/Non Profit 
PI Contribution I am expected to facilitate reverberation mapping of AGN with LSST and undertake simulations to prepare for the observations.
Collaborator Contribution LSST:UK provided me with membership in LSST to join the relevant Science Collaboration within LSST. It is the gateway to actually influence the observation strategy and receive primary data access during operations.
Impact none to date.
Start Year 2016
Description DES-VEILS External Collaboration agreement 
Organisation Dark Energy Survey (DES)
Country Global 
Sector Charity/Non Profit 
PI Contribution Share infrared AGN light curves from VEILS with the DES AGN collaboration
Collaborator Contribution Share of optical AGN light curves from DES with the VEILS AGN collaboration
Impact none yet
Start Year 2018
Description Member of the LSST AGN Science Collaboration 
Organisation LSST Corporation
Country United States 
Sector Charity/Non Profit 
PI Contribution I am providing input into the planning of LSST operations from a point of view of AGN. This also involves contributions to the white paper on AGN with LSST that is currently been written.
Collaborator Contribution The LSST AGN SC provides the platform to shape and influence the operational strategy of LSST to facilities my science goals.
Impact none to date.
Start Year 2016