By Marián Moreno Otero
“We need to see whether there are microhalos of dark matter around galaxies, as predicted by theory, but which we don’t in practice observe”
“The construction of 30 metre class telescopes is a challenge for computational engineering, electrónics, optics, and mechanics”
“Nowdays, Astronomy is a bet for technological development and, ultimately, for making the most of the resources beyond what is capable of allowing our planet”
Since he obtained his doctorate in Astrophysics from the University of La Laguna (Tenerife, Spain) in 1994, José Antonio de Diego Onsurbe has always felt a link to the Canaries and he says that he wouldn’t mind coming to live in Tenerife again. After finishing his thesis he joined the Institute of Astronomy of the National Autonomous University of México (IA-UNAM) in 1995, where he is now a staff researcher, and where he has give courses in extragalactic astrophysics, active nuclei of galaxies, gravitational lenses, and high redshift galaxies. At the present time he is in charge of a technology development project, and has been named Head of the Deartment of Science Communication at the IA-UNAM. During his stay at the IAC he has collaborated with the researchers Jordi Cepa Nogué and Ángel Bongiovanni in the statistical analysis of data bases of extragalactic sources. According to him “there are still many outstanding questions in this field, such as those related to galaxy evolution as a function of morphology, and the formation of microhalos of dark matter around galaxies”.
Question: During your stay at the IAC you collaborated in the research group on the OTELO project. What are the aims of this project?
Answer: OTELO is a deep survey of the sky over area of about one square degree. It uses narrow tuneable filters on the OSIRIS instrument on the Gran Telescopio CANARIAS (GTC). This survey is designed to detect objects with emission lines. For example emitters of Lyman-alpha and active galactic nuclei (AGN). The aims of the project are multiple: to determine the abundances of chemical elements using the ratios of their emission lines; to study the chemical evolution of galaxies, and in particular the differences between the different morphological types (irregulars, ellipticals, spirals, dwarfs); identify the galaxies by their morphology and estimate their redshifts, which give us an estimate of their distances; deduce their rates of star formation ( which depend on the abundances of the elements previously estimated); and study certain aspects of galaxy evolution, such as the distribution of galaxies with bursts of star formation as a function of redshift.
Q: With the OTELO project you can detect nearby galaxies and also distant galaxies. What do researchers consider “nearby” and “distant” in this case?
A: Whether a distance is considered short or long depends on the context. In astronomy, and particularly in extragalactic astronomy, when we talk about short distances we are referring to the local universe, where relativistic effects due to the overall expansion of the universe are small, out to a distance of some 1000 million light years, which means a redshift of from z = 0 to between z = 0.05 and 0.1. This means that the galaxies we observe have ages comparable to that of the universe itself, which is close to 13,800 million years. ON the other hand when we speak of large distances we are talking about galaxies which emitted their light when the age of the universe was less than some 10%-20” of its present age, that is to say around 2,000 million years after the Big Bang.
Q: You have been able to detect primitive galaxies, formed more than 13,000 million years ago, with a new method which can examine the oldest phases of the Universe. Explain how this method Works.
A: The radiation from the galaxies is absorbed at different wavelengths, especially in the ultra-violet, due to the neutral hydrogen between the galaxies and us. The limit of this absorption, which can sometimes be total, is at 912 Å. This is termed the Lyman limit.
Young galaxies have massive, recently formed stars, which emit ultraviolet light which can ionize hydrogen, which then recombines, emitting the Lyman-alpha line, at 1,216 Å. As we observe at different distances we can see the lines displaced towards the red. To detect these objects we have used, among other methods, the technique called dropouts. This is essentially comparing two neighbouring filters: the galaxy is not detected in one of them because the light it emits is absorbed by the hydrogen, but is detected brightly in the neighbouring filter where the light is not absorbed. They are usually rather narrow filters, of the order of 100 Å in width, such as those used on the Japanese 8,2 m telescope SUBARU, at the Mauna Kea Observatory (Hawaii).
But with OSIRIS we can use filters of only 12ª width, much narrower than those used previously, allowing us to find candidates with higher sensitivity and with fewer biases introduced by the width and the transmission of the filter. We have shown this using simulations. We have also made observations on a set of candidates, and we are now in the follow-up phase to find out more about them.
Q: What new information will this give us about galaxy evolution?
There are really a lot of questions to answer about the evolution of galaxies. For example about their morphology: we see that galaxies tend to be spirals or ellipticals, although there are other types, such as the irregulars. The spirals contain interstellar gas, dust, young stars, and old stars, while the ellipticals contain only old stars. The spirals are thus forming their stars continuously during the lifetime of the universe whereas the ellipticals formed them rapidly in a period of some 1,000 million years, and then stopped producing them. What caused these differences. We don’t understand well why some galaxies have evolved differently from others.
Another important point is that the theories predict the formation of microhalos of dark matter around galaxies. In principle these should be detected as galaxies emitting very feebly. However these microhalos are not observed. So that we need to keep researching to see if they exist, why they are not observed, and how they are distributed.
Q: If you had to pick out just one of the most important revolutions in astronomy, which would you choose?
A: This is a difficult question because there have been many revolutions throughout history, which have been very important. Rather than choosing one, I will mention several, and then say which I consider fundamental.
For example in the neolithic age the calendar was invented. This allowed societies to settle down because they could predict the best times to sow and harvest, which was an important revolution in human history. Much later, in the 19th century, Franhofer and Kirchhoff showed that the Sun and the stars are formed of the same elements we find on Earth. In the 1920’s Hubble discovered that some of the nebulae we see in the sky are galaxies different from our own, and this increased the size of the known universe in an extraordinary way. Some decades later, in 1965, Penzias and Wilson detected the microwave background radation, and we must not forget the gravity of Newton and Einstein. In the present year gravitational waves have been detected.
Nevertheless in my opinion the most important revolution occurred in the 16th Century when Copernicus and Galileo displaced the Earth from the centre of the universe, showed that the heavens are changeable, as shown by the satellites of Jupiter, and sunspots… With this, Aristotelian astronomy, which until then had been the paradigm, was substituted by a system based on the support or refutation of theories, a system of proofs. This initiated the modern scientific method, which is applied in all branches of science, not only in astronomy.
Q: In your opinion, what is the importance of science, and in particular of astronomy, for society?
A: As a society we must be aware of the importance of science for development and what is the best way to invest in this. Astronomy is not only a way to satisfy our curiosity as human beings. Today it is a way to invest in the future via technological development, and in the final instance to use resources beyond those available to us on this planet. Some examples of the technological contribution of astronomy are in conventional navigation systems, in GPS, and in the treatment of images in medicine or the digital cameras of mobile phones.
In the future the construction of 30 meters class telescopes will imply challenges for computer engineering, electronics, optics and mechanics. Scientific collaboration at national and international level required by these projects as well as by space projects, open doors to collaboration in the political, industrial and commercial fields, not only academic collaboration.
For all countries, including those which, for historical reasons or through insufficient investment, have fallen behind in scientific advance, access to data bases is increasingly free, and this gives a window of opportunity for development.
Fortunately this development does not need huge investments in equipment, so that countries which are not fully competitive technologically or financially can take part. Analysis algorithms can be applied to all types of data, for example oceanographic, climatological, financial data, etc.
