Travelling back through time DR ASANTHA COORAY With Drs Julie Wardlow and Joseph Smidt from his research group, Professor Asantha Cooray describes the areas of study by which they are seeking to expand knowledge of far distant galaxies and star formation Can you begin by outlining your research goals? Cooray: The fi rst goal for my team is to search for the fi rst galaxies in the distant, early Universe. The fi rst galaxies are expected to be small in size and mass compared to later ones and their distance at almost the edge of the observable Universe makes them hard to see individually with existing observatories. So we look for signals in the sky that suggest their presence through aggregate effects, such as small variations in the total light emitted by them. Such searches for fi rst galaxies are best done at short infrared (like a galaxy), a foreground mass (such as wavelengths in the electromagnetic spectrum. another galaxy, or a cluster of galaxies) and A second research goal is to study the dust- our telescopes on Earth. The light from the enshrouded star formation in distant galaxies. background source has to pass through, or Since optical light is absorbed by dust, such very close to, the foreground mass in order observations are best done at long infrared to reach us. However, as Einstein theorised, wavelengths again from space. Why is there a need to investigate zodiacal the path that light takes is affected by the dust cloud? How does the Zodiacal dust, intervening mass, in much the same way as How will infrared wavelengths further Extragalactic Background and Reionisation light is defl ected by the lens in spectacles. This understanding of star formation? Apparatus (ZEBRA) mission concept study defl ection of the light from the background address this? galaxy is called gravitational lensing. It enables Wardlow: Optical light (that our eyes see) is us to see galaxies that are much fainter than absorbed by dust (think about trying to peer Smidt: Contributions from dust to astronomical we would normally even be able to detect and through a smoke-fi lled room), so that even the observations are not always trivial. Zodiacal study them in much more detail than would biggest optical telescopes cannot see into the light is a main contaminant for total infrared otherwise be possible. densest regions of star-formation. However, background intensity experiments that we are infrared light can travel through this dust, so we doing to search for the cumulative signature of From your research, what do you consider the use infrared telescopes to see through the dust fi rst galaxies at the edge of the Universe. For biggest revelation in the evolution of galaxy and into the heart of star-formation regions. example, the Zodiacal dust cloud is a cloud of and star formation? Infrared light is also particularly useful for dust fi lling the inner regions of our Solar System studying galaxies that are millions of light-years that refl ects light from the Sun, creating a bright Wardlow: That is a tough one! Recently, we away, in the distant universe. diffuse glow across the sky. This glow needs to have been looking a lot at distant galaxies be subtracted out from infrared observations to that are undergoing huge amounts of star- FIGURE 1. A region of the sky as surveyed in near-infra- correctly understand physics from outside the formation in very short timescales. We have red light by the Spitzer Space Telescope. Cooray group is Solar system, as from extra-galactic sources. been able to pinpoint these galaxies, detecting using deep and wide images such as these to detect the them at optical as well as infrared wavelengths, integrated light from the fi rst galaxies in the Universe. Cooray: In principle, we would like to measure and calculate exactly how far away they are. the total near-infrared background intensity, These galaxies are strange: they are much and look for the signatures of fi rst galaxies in more numerous in the distant Universe than regions where the dust content is small. ZEBRA nearby, and it is hard to discern how they fi t aims to travel to the outer Solar system, as into galaxy evolutionary scenarios and what part of a planetary mission to Jupiter or Saturn, could have caused such massive amounts of to make astrophysical measurements related star-formation. to the Universe without contamination from Zodiacal light. Smidt: Initially, it was hoped that the earliest stars and galaxies of the universe made the What is the signifi cance of gravitational dominant contributions to the fl uctuations in the lensing? infrared background light we measure. Instead, it has turned out that major contributor is the Wardlow: Gravitational lensing occurs when emission from previously unknown faint (dwarf) there is alignment of a background source galaxies at much later times. WWW.RESEARCHMEDIA.EU 21 DR ASANTHA COORAY Cool science The Cooray Group at the University of California in Irvine has a single mission: to discover how the original galaxies in the universe formed. Their programme of astrophysics research goes beyond the state-of-the-art SINCE THE FIRST infrared space telescopes were of the atmosphere with rockets. This wide range of PIONEERING PROGRAMMES sent into orbit in the 1980s, infrared technology observing systems enables probes into previously in astronomy has transformed knowledge of uncharted parts of the universe: “For the fi rst time, Cooray is a member of the team from US the Universe. Able to capture heat energy even we can quantify in detail the number of galaxies that contributed to the UK-led Spectral and from exceedingly cool objects in space, infrared that are hidden from traditional observations of Photometric Imaging Receiver, known as SPIRE, detection provides much more complete the Universe at optical wavelengths, what the one of the three instruments of the Herschel information than previous visible light technology: properties of such galaxies are and the rates at Space Observatory, and he participates in two in space, visible light is scattered by dust and which stars are forming in them,” Cooray asserts. major programmes on the Herschel platform. gases, which obscures images, but infrared can detect and display the tiny signs of galaxies and the birth of stars beyond the dust and gases. The Cooray Group at the University of California The team would like to understand how galaxies fi rst formed in the Irvine campus studies the signatures of ancient galaxies detected with near-infrared light and Universe and what kind and amount of stars were present measures clustering in star-forming galaxies detected with far-infrared light: “We would like The group aims to fi nd the fi rst ever galaxies The fi rst is the Herschel multi-tiered extra- to understand how galaxies fi rst formed and in the Universe and to study the formation of galactic survey (HerMES) studying the evolution what kind and amount of stars were present in new stars in far-off galaxies. Dr Julie Wardlow, a of galaxies, the biggest project on the Space those galaxies,” states Asantha Cooray, Professor group member, studies distant galaxies that are Observatory. Two undergraduates from his group of Physics in the Department of Physics and undergoing huge bursts of star formation: “When co-authored some of the fi rst science observation Astronomy at the University of California and we look at distant galaxies we are looking back in papers from the survey, an achievement of which head and mentor of the Group. time,”, she explains. “We have found that typical Cooray is very proud. distant galaxies look different from typical nearby The group has access to the massive datasets of galaxies, which shows that there is some kind The second major Herschel programme in which the large space observing telescopes, including the of evolution in galaxy types and star formation Cooray is the US (NASA) Principle Investigator is Hubble Space Telescope, which uses ultraviolet processes over the history of the Universe. Only the Herschel-Astrophysical Terahertz Large Area and near-infrared and is 569 km from Earth; by studying distant galaxies can we unravel the Survey, known as H-ATLAS, carried out with fi ve the European Space Agency’s Herschel Space drivers behind this evolution and the physics that US and 25 European institutions to explore, with Observatory, which uses far-infrared and is controls it,” she enthuses. far-infrared and sub-millimetre wavelengths, usually about 1.5 million kilometres from Earth; further back in time than any previous mission and NASA’s near- and mid-infrared Spitzer Space As well as post-doctoral fellows, Cooray’s Group – for this the H-ATLAS team managed to secure Telescope, which is currently nearly 160 million comprises undergraduate and post-graduate 600 hours’ observing time on an area of the sky kilometres from Earth - this varies as Spitzer students. Over the last fi ve years the Group has four times larger than all the other extra-galactic follows the Earth in its movements around the produced more than 90 journal publications; the surveys combined – H-ATLAS was featured on Sun. The Cooray Group, with collaborators at the members work together and on some important the BBC’s Bang Goes the Theory programme, NASA’s Jet Propulsion Laboratory, also fl y purpose- international collaborative programmes in which in which Cooray explained the principles of built small telescopes and instruments to the top Cooray is a key participant. gravitational lensing. 22 INTERNATIONAL INNOVATION INTELLIGENCE NEAR- AND FAR-INFRARED BACKGROUND LIGHT AND THE ASTROPHYSICAL AND COSMOLOGICAL Cooray is also a member of the science team – effect of the diffused light from Zodiacal dust is IMPLICATIONS alongside the astrophysicist Brian May, who is also compounded by Extragalactic Background Light, known as a guitarist with Queen – in the Zodiacal the total accumulated energy of all sources of OBJECTIVES dust, Extragalactic Background and Reionisation light, the stars and galaxies, beyond our galaxy, Apparatus (ZEBRA) mission concept study aimed over all time.