Ten billion years of cosmic evolution at hand

Along seven years of precise observations from Calar Alto Observatory (CAHA, Almeria, Spain), and thanks to a technique that decomposes stellar energy into its constituent colours by means of astronomical filters, the ALHAMBRA project has been able not only to identify and classify, but also to compute the distance to more than half million galaxies, all this with unprecedented precision. As a result, the ALHAMBRA survey allows reconstructing the most realistic tridimensional view of the universe up to date. Some months ago, a first, restricted data harvest was made public (the subset dubbed ALHAMBRA-Gold). Now, the whole ALHAMBRA data yield is offered to the scientific community.

The ALHAMBRA survey is such an ambitious scientific project that it has required the contribution of scientists from sixteen institutions all around the world. Directed by Mariano Moles (CEFCA, Teruel, Spain), and nurtured at the Astrophysical Institute of Andalusia (IAA-CSIC, Granada, Spain), it was devised to trace the evolution of the universe during the last ten billion years.

“ALHAMBRA makes a key step towards working out candent problems of cosmology and astrophysics through photometric surveys, a technique that allows reaching the required precision for the distance to the objects detected”, points out Mariano Moles (CEFCA), principal investigator of ALHAMBRA. “Thus, the non-biased character of this kind of surveys allows deducing relevant data at all cosmic scales. In this sense, the ALHAMBRA project acts as a pathfinder for the new long-reach surveys that are being proposed right now”, adds this scientist.

The vision of the universe given by ALHAMBRA will allow, on the one hand, studying how the stellar content of galaxies has changed with time, i.e., knowing how, when and how much they have aged. Deducing a univocal relation among morphology, stellar content and age for galaxies will point towards the comprehension of the physical processes that drive the universe at these scales.

On the other hand, ALHAMBRA sheds light on how galaxies are distributed in the universe. “During the last thirteen billion years, gravitation has been ruling the formation of structures such as galaxies or stars”, points out Alberto Molino, researcher at the Astrophysical Institute of Andalusia (IAA-CSIC) and a member of the ALHAMBRA team. “Studying how galaxies are located reveals the physical conditions in the universe in ancient epochs. This is something similar to deducing where and how the seeds were laid, from the study of a mature wood of trees seen today”, states Molino.

Furthermore, when looking deep into the further reaches of the universe, the ALHAMBRA observations have gone through enormous regions of our own Galaxy. Thus, the data allow exploring the cosmic history of the Galaxy from a census of the stars in the Galactic halo, discovering variable stars, counting the frequency of binary star systems or listing stars that may host other planets.

The publication of the data will give free access to all the ALHAMBRA power not only to the scientific community, but also to universities, science museums, astronomical societies or schools around the world.

The scientific value of the ALHAMBRA legacy will make this Spanish project an international reference for the study of galaxy properties, and it will also boost future generations of surveys, such as JPAS, that will extend this work from several sky areas to a complete study of all the observable universe.

Finally, ALHAMBRA displays, once more, the key role of Spanish astronomical observatories. Specially Calar Alto Observatory, that has shown itself as an indispensable first line facility, capable of providing the most exact and representative image of our universe up to now. The success of the observational part of the project lies on the quality of the Zeiss 3.5 m reflecting telescope at Calar Alto, on the outstanding features of its wide-field imager LAICA, and on the performance of the experienced staff of Calar Alto, that has operated the instruments in an optimised working scheme.

“It is fair acknowledging and thanking the effort and performance of Calar Alto staff during these years, to get ALHAMBRA data in the best possible conditions”, underlines Mariano Moles (CEFCA).

Images:

An example of the deep images taken at Calar Alto for the ALHAMBRA Survey.

The 3.5 m Zeiss reflector at Calar Alto Observatory.

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