CYGNUS project: CYprus models for Galaxies and their Nuclear Spectra 


One of the most important and challenging areas of research in modern Astrophysics concerns the study of the sequence of events that led to the formation of galaxies and the supermassive black holes that usually reside at their centres. Understanding of the complex astrophysics that led to the observed distribution of galaxies, both in terms of properties and numbers, is usually sought within the framework of the standard ΛCDM (Lambda Cold Dark Matter) cosmological model (e.g. Lacey et al 2016).  

It is now clear that in order to understand the numerous processes that govern galaxy formation and evolution (star formation in quiescence and in mergers, accretion onto supermassive black holes and feedback associated with them) we need multi-wavelength or panchromatic observations of galaxies at all cosmic epochs. This is mainly due to the presence of cosmic dust in the interstellar medium of galaxies, which significantly affects their ultraviolet to millimetre spectra. The necessity of characterizing the panchromatic emission of galaxies has led to a series of surveys, at all wavelengths from X-ray to radio, of ever improving sensitivity, resolution and sky coverage. Most of these surveys can only be carried out from space, which has largely become possible over the last two or three decades with missions such as ISO, Spitzer, AKARI, Herschel, Planck, WISE, GALEX. At the same time, significant progress has been made in the development of models (stellar population synthesis models, radiative transfer models) and model fitting techniques that can be used to aid the interpretation of the resulting observations.  

The spectra of galaxies are usually decomposed into a number of components. It is widely acknowledged that radiative transfer models that take into account the effects of cosmic dust in a realistic geometry are needed for proper interpretation of the data and the self-consistent determination of a number of physical quantities of interest, such as the stellar mass of a galaxy, its current star formation rate and the fraction of its bolometric luminosity that is due to accretion onto a supermassive black hole. A number of radiative transfer models for the components of emission in galaxies, as well as methods of fitting them to data, are currently available. However, as the volume and quality of observational data improves, new challenges arise.  

 The Astrophysics and High Performance Computing group at European University Cyprus has, over the last two decades, developed a niche in radiative transfer models of galaxies, mainly due to the work of its director (Andreas Efstathiou). Some of these models are currently available publicly through the CYGNUS (CYprus models for Galaxies and their Nuclear Spectra) project. Over the last decade, our expertise has enabled us to become involved in a number of prestigious observational projects with our network of international collaborators. A fine example of this is our recent discovery of a dust-enshrouded tidal disruption event in the galaxy merger Arp 299 (Mattila, Perez-Torres et al, 2018, Science) where we have made a significant contribution to the interpretation of the spectral energy distribution of this event using the CYGNUS models.  

Through the CYGNUS project, we will develop further the CYGNUS models, develop a new method for fitting them to data using a Markov Chain Monte Carlo (MCMC) code and test the method with a large sample of galaxies with excellent photometry and infrared spectrophotometry from Spitzer. This will improve our ability to network with international collaborators and enable us to consolidate our position as one of the leading groups in the world in the development of radiative transfer models of galaxies and SED (Spectral Energy Distribution) fitting. This will also put us in a very strong position to secure more funding from Horizon 2020 and participate in projects with forthcoming missions such as JWST (due for launch in 2021) and SPICA (which has just been selected as a candidate for ESA’s fifth medium class mission in its Cosmic Vision science programme: a letter from the SPICA PI is included in the Annex). It is important to note that both JWST and SPICA will provide very powerful infrared spectroscopic data, so our approach to studying samples of galaxies with spectroscopy from Spitzer as well as Herschel provides excellent preparation for the JWST and SPICA era.