The Observational Astronomy group's research acivities address several topics in extragalactic astrophysics:
We study galaxy evolution using large spectroscopic and multi-wavelength imaging surveys of the galaxy population. These are particularly successful tools in trying to identify and disentangle the various processes responsible for the formation and subsequent evolution of galaxies. Such surveys allow us to systematically study galaxies at different cosmological epochs as a function of key parameters, such as dynamical, stellar and gas mass, environment, star formation activity, stellar age, stellar and gas-phase metallicity, size, morphology, dynamical state, AGN activity, dust content, etc. The ever more detailed observational picture of galaxy evolution provided by these studies plays a key role in further developing our understanding of galaxies.
Below we briefly discuss the two survey projects our group is closely involved with.
Galaxy And Mass Assembly (GAMA)
The central element of the GAMA project is a large spectroscopic survey of ∼270,000 galaxies that was conducted in the period 2008 – 2014 using 210 nights on the AAOmega multi-object spectrograph on the Anglo-Australian Telescope (AAT). The final spectroscopic dataset is described Liske et al. (2015). These data were combined with multi-wavelength photometric data from seven space-borne and ground-based facilities to create an extraordinarily rich legacy dataset for galaxy evolution studies. The analysis of these data is still ongoing, with more than 120 papers published so far (+ 48 papers in collaboration with other survey teams). J. Liske is a member of the collaboration’s three-person Executive as well as a member of its Scientific and Strategic Advisory Committee. We also maintain and host the GAMA database and website.
Wide Area VISTA Extragalactic Survey (WAVES)
The WAVES collaboration is currently designing and planning a new spectroscopic survey of ∼1.5 million galaxies to be carried out on 4MOST, a wide-field, high-multiplex spectrograph currently under construction for VISTA. WAVES is one of the ten 4MOST consortium surveys that will be carried out over a period of five years using the consortium’s guaranteed time on 4MOST. As described by Driver, Liske et al. (2019), WAVES is designed to study the growth of structure, mass and energy on scales of 1 kpc to 10 Mpc over a 7 Gyr timeline. In particular, WAVES will probe galaxy evolution in the low stellar mass, low halo mass and intermediate redshift regimes. J. Liske is one of the two Principal Investigators of WAVES.
Other survey projects
Below is a list of other past and present survey projects we are or have been involved with:
We are working towards the realisation of a new class of cosmological observations often referred to as "real-time cosmology". The idea is to use extremely precise measurements over a time span of several years to directly detect tiny changes in the Universe on cosmological scales due to its expansion. In particular, observations of the so-called "redshift drift" would provide a direct and dynamical measurement of the expansion history of the Universe, capable of providing independent evidence of its late-time acceleration. This experiment [see Liske (2018) for an accessible description] is currently not possible and requires the next generation of observational facilities currently under construction or in planning (Liske et al. 2008), in particular the Extremely Large Telescope in combination with an extremely stable high-resolution spectrograph (ANDES).
The Dark Matter Halo Mass Function
The mass function of dark matter halos is a robust prediction of the Cold Dark Matter (CDM) structure formation paradigm. As described by Driver, Liske et al. (2019), the Wide Area VISTA Extragalactic Survey (WAVES) is a planned spectroscopic survey of ~1.5 million galaxies designed to study the growth of structure, mass and energy on scales of 1 kpc to 10 Mpc over a 7 Gyr timeline. This survey will be used to identify ~70,000 groups of galaxies, to measure the masses of the dark matter halos inhabited by these groups, and thus to construct the mass function of dark matter halos over unprecedented regimes of halo mass and redshift. The low-mass end of this function will provide unique opportunities for studying the nature of dark matter (cold vs. warm vs. self-interacting), while the evolution of its high-mass end will trace the hierarchical growth of structure and thus constrain the expansion history of the Universe. J. Liske is one of the two Principal Investigators of WAVES.
4MOST (de Jong et al. 2019) is a state-of-the-art, high-multiplex, fibre-fed, optical spectroscopic survey facility currently under construction for ESO’s 4-m VISTA telescope. Its field-of-view will be large enough to survey a large fraction of the southern sky in a few years, and its multiplex of 2400 fibres enables surveys of millions of objects. During the first five years of operations 4MOST will be used to execute a comprehensive, integrated programme of both Galactic and extragalactic Public Surveys, including WAVES, which is co-led by J. Liske. We largely funded one of 4MOST's two low-resolution spectrographs, and we lead or contribute to several work packages in the areas of scientific planning and software development. J. Liske also served as the Chair of the 4MOST Science Coordination Board in the period 2015 – 2023.
ANDES (Marconi et al. 2018) is the optical and near-infrared high-resolution spectrograph for the Extremely Large Telescope, the world's largest optical and infrared telescope (currently under construction in Chile by the European Southern Observatory). This instrument will address a number of compelling science cases, including the characterisation of the atmospheres of extrasolar planets and the search for variations in some of the fundamental constants of physics. As a goal, this instrument will also be able to provide the first measurement of the so-called "redshift drift". The project has completed its conceptual design phase and is now in a preliminary detailed design phase. During the conceptual design phase, J. Liske led the Science Advisory Team's working group on cosmology and fundamental physics.