I've always had an interest in observational cosmology, in particular the study of the content and structure of the universe. Pursuing this line of enquiry through sky surveys has a long tradition. You could say Hipparchus started it all in the second century BC when the unexpected appearance of a new star stimulated him to make the first reliable star survey. The extragalactic universe entered the picture with the Messier catalog of nebulae. Famously, William Herschel, possibly the greatest observer of all time, sought to understand the structure of the heavens by compiling large catalogues of nebulae.

“ The ARI is unique in the UK in having its own research-sized optical ground based telescope. ” Professor Chris Collins, Director of the Astrophysics Research Institute

All those pioneering attempts were frustrated because their catalogs only listed positions: crucially, they had no information on distance. That had to await the efforts of Vesto Slipher and Edwin Hubble in the 1920s. In a nutshell, they developed the technique of using a galaxy's redshift, which is due to the expansion of the universe, to find its distance.

As data on galaxy redshifts slowly accumulated, astronomers began to realize that large-scale surveys would be needed to map out the structure of the universe. Ten years ago I took part in a galaxy redshift survey organized as a key project by the European Southern Observatory (ESO).

  Your 1997 paper, with Elena Zucca (Bologna Observatory, Italy) as the lead author, is ranked #7 in this analysis (Zucca E, et al., "The ESO Slice Project (ESP) galaxy redshift survey .2. The luminosity function and mean galaxy density," Astron. Astrophys. 326:477-88, 1997). What was the purpose of this ESO survey?

In the 1980s, when I was with the Royal Observatory, Edinburgh, I worked with colleagues to produce the Edinburgh-Durham catalog of galaxies in the southern hemisphere. The ESO Slice Survey covered about 23 square degrees of the sky and its target objects were taken from the Edinburgh-Durham catalog. We obtained reliable redshifts for 3,342 galaxies, which was a considerable achievement at that time. It provided one of the first accurate determinations of the luminosity function and mean galaxy density in our "local" neighborhood, where galaxy redshifts are ~0.1 or lower.

The galaxy luminosity function describes the relative number of galaxies of different luminosities. Our data showed clear evidence for voids and clumps in the distribution of galaxies. In observational cosmology the luminosity function is central to any understanding of galaxy evolution. We found, for example, a striking difference at the faint end for galaxies with and without emission lines: the volume density of emission-line galaxies becomes higher at faint magnitudes, which implies that there is an evolutionary effect at higher redshifts.

Let me first explain how we did this survey. It used the Two-degree Field (2dF) multifiber spectrograph on the Anglo-Australian Telescope. This is an awesome instrument. It is capable of observing 400 pre-selected objects simultaneously over a 2° field by using optical fibers to feed the light from 400 galaxies to two spectrographs where the spectra are recorded onto CCD. The throughput of this instrument is staggering: we recorded as many as 4000 galaxy spectra in one night, more than in the whole of the ESO Slice Survey, which took more than 20 nights to complete.

This 2dFGRS survey is designed to get the redshifts, and thereby the distances, of about 250,000 galaxies. Those galaxies were selected from the Automated Plate Measuring Machine (APM) galaxy catalog, compiled in 1990 and 1991 by scanning 390 photographic plates from the UK Schmidt Telescope. Paper #1 is fundamental in that it describes all of the technical and statistical aspects of the survey so that astrophysicists can make the correct interpretation of the properties of galaxies. In survey work of this kind you must be absolutely meticulous at hunting down sources of error and bias that you might otherwise attribute erroneously to intrinsic evolutionary effects. We all took the greatest care to account for those. As an historical aside, note that William Herschel got the structure of the Milky Way entirely wrong (he had the Sun at the center) because he had no idea that interstellar obscuration had biased his survey.

Will Percival (Royal Observatory, Edinburgh) headed the 2dFGRS Team on that investigation. We believe that the cosmological structure we see in the universe today began with the gravitational amplification of small density perturbations when the universe was much younger – before the formation of the first galaxies, in fact. Today that aspect of observational cosmology is dealt with beautifully by the cosmic microwave background observations such as the Wilkinson Microwave Anisotropy Probe.

What's so fascinating is that the power spectrum of the galaxy distribution should also reflect the spectrum of the linear density perturbations present in the early universe. Paper #2 is important, and deservedly highly cited, because we as optical astronomers were ahead of the curve on this one! By fitting the observed power spectrum to models we provided a measure of the matter content of the universe.

Our results showed that baryons account for only ~15% of the matter content of the universe. It's worth noting that in observational cosmology we now place great store on measuring the fundamental parameters using a variety of complementary techniques.

Yes it has. A good example is paper #15 in the analysis, by Ian Lewis and the 2dFGRS Team (Lewis I, et al., "The 2dF Galaxy Redshift Survey: the environmental dependence of galaxy star formation rates near clusters," Monthly Notices of the Royal Astronomical Society 334:673-83, 2002). The spectra in the survey form a dataset of unprecedented richness and variety for studying the astrophysical conditions in galaxies. This allows us to study any correlation between spectral properties (such as the strength of emission lines) as a function of external variables, such as local density.

Paper #15 is a study of 17 galaxy clusters in which we determine environmental factors governing star formation in galaxies by investigating a correlation between star formation rates and the local density around galaxies. We concluded that star formation rates depend on distance from the cluster center, even for galaxies located well outside the central regions of clusters. It appears that the environment in denser regions serves to reduce star formation. This will have a profound effect on the evolution of the universe, because as more and more galaxies are found in clusters as time passes, star formation will decline with cosmic time. This is just one example of how 2dFGRS is contributing to fundamental astrophysics.

We have particular strengths in galaxy evolution and in the stellar populations in galaxies; studies of galaxy clusters—where we lead the largest ever European Hubble Space Telescope Treasury Project—and studies of active galactic nuclei.

We also lead a new survey of the central regions of the Milky Way, using the new SCUBA 2 instrument on the James Clerk Maxwell Telescope in Hawaii to unlock the secrets of how stars form.

We are particularly strong in time-domain astrophysics—the study of cosmic explosions and celestial objects which rapidly vary in brightness (things that really go "bang" in the night!). For example we have a team of specialists working on Gamma Ray bursts—the most violent events in the universe since the Big Bang itself, but which in fact only last for tens of minutes. We also lead research in the related area of novae and supernovae stellar explosions.

The ARI is unique in the UK in having its own research-sized optical ground based telescope. The robotic Liverpool Telescope, designed and built on Merseyside and located on La Palma in the Canary Islands, has a 2-m optical mirror and is operated from the ARI as a national facility. The telescope is utilized on its own and as part of a wider network of robotic telescopes on Hawaii and Australia (RoboNet), which together provide 24-hour coverage for monitoring variable sources. It is this capability which makes the ARI world leaders in time-domain astrophysics and at the forefront of new developments in robotic telescope networks, such as our guaranteed access to time on the Las Cumbres Observatory Global Telescope Network.

We also take public outreach of our research very seriously, principally through: (i) National Schools' Observatory—a web-based facility for schools (currently 650 and rising) which enables children to carry out their own observations on the Liverpool Telescope from their classroom as part of their science lessons; and (ii) the local astronomy visitors center Spaceport, opened in 2005, which has close to 100,000 visitors per year and was developed in partnership with Mersey Travel.

LJMU won the 2005 Queen's Anniversary prize for Higher and Further Education exclusively for the work of the ARI. This is one of the UK's most prestigious educational awards and part of the Honors system. The prize attests to the astronomical excellence of the ARI's science, the delivery of innovative teaching programs, the development of the Liverpool Telescope, and our enhancement of the public engagement in science.

Surveys like 2dFGRS have done a great job in charting the galaxy distribution to unprecedented depths. However, even such a landmark project doesn’t really probe much beyond the cosmic doorstep. Over the next decade we hope to carry out multi-wavelength studies of representative samples of galaxies at a distance close to 10 billion light years from Earth, about three quarters of the way to the Big Bang itself. Such data will help astronomers solve vexing questions such as how structure forms and the nature of dark matter and dark energy.

Making progress in answering questions about how the universe began is even harder; however, a big leap forward will happen next year with the launch of European Space Agency's Planck satellite, which will map the Cosmic Microwave Background with improved sensitivity and angular resolution and will test the energy scale of inflationary models of the early universe.