21 March 2012

UltraVISTA - a treasure trove of data released to the community

COSMOS field

This picture shows a region of the sky known as the COSMOS field in the constellation of Sextans (The Sextant). More than 200 000 galaxies have been identified in this picture. Credit: ESO/UltraVISTA team. Acknowledgement: TERAPIX/CNRS/INSU/CASU

The European South Observatory (ESO)’s VISTA telescope has created the deepest wide-angle view of the sky ever made using infrared light. This new picture of an unremarkable patch of sky comes from the UltraVISTA survey and reveals more than 200,000 galaxies, forming just one part of a huge collection of fully processed images from all the VISTA surveys that is now being made available by ESO to astronomers worldwide. UltraVISTA is a treasure trove that is being used to study distant galaxies in the early Universe as well as for many other science projects.

ESO’s VISTA telescope has been trained on the same patch of sky repeatedly to slowly accumulate the very dim light of the most distant galaxies. In total more than six thousand separate exposures with a total effective exposure time of 55 hours, taken through five different coloured filters, have been combined to create this picture. This image from the UltraVISTA survey is the deepest infrared view of the sky of its size ever taken.

Data from the VISTA surveys — totalling more than 6 terabytes of images — are now being processed in data centres in the United Kingdom and France, and are flowing back into the ESO science archive and being made available to astronomers around the world.

Researchers at the Dark Cosmology Centre (DARK) are responsible for the narrow-band component of the UltraVISTA survey, with Johan P.U. Fynbo as a project PI.  The 16 narrow-band filters used on the telescope were funded in Denmark by DARK and the Instrument Center for Danish Astrophysics (IDA).

At DARK, Data Specialist Bo Milvang-Jensen and Johan are involved with the preparation and monitoring of the narrow-band observations, quality control in connection with the data reduction, and preparing the data for release to the community, as well as exploiting the data to study emission-line galaxies at various redshifts, including ultimately Lyman alpha-emitting galaxies at redshift 8.8.  In addition, PhD student, Johannes Zabl, assisted in preparing the data for release to the community.

DARK researchers exploiting the data from UltraVISTA

The newly-released data are already in use here at DARK: Zabl, together with Fynbo and Milvang-Jensen, will use X-shooter to observe a few narrow-band selected galaxies in April.  DARK Fellow Andrew Zirm has produced a photometric catalogue based on the UltraVISTA data as well as on existing public data at other wavelengths. He has also produced so-called photometric redshifts based on this catalogue.

PhD student, Allison Mann is working on finding galaxy pairs to study galaxy mergers using Zirm's catalogue.  PhD student, Jens-Kristian Krogager is working on other data -  Hubble Space Telescope slitless grism spectroscopy -  taken in the COSMOS field, and the plan is to integrate those spectra with Zirm's database. DARK Fellow, Kelly Denney and Milvang-Jensen (and others), have plans to look for active galactic nuclei (AGN) variablility using the UltraVISTA data.  And the uses of the data continue to be developed and involved in more and more projects at the Centre.

More than 200,000 galaxies in view

At first glance the UltraVISTA image looks unremarkable, a few bright stars and a sprinkling of fainter ones. But in fact almost all of those fainter objects are not stars in the Milky Way, but very remote galaxies, each containing billions of stars. Enlarging the image to fill the screen, and zooming in reveals more and more of them, and the image records more than 200,000 galaxies in total.

Observations from the VISTA infrared view

Highlights of VISTA’s deep infrared view of the COSMOS field

The expansion of the Universe shifts light from distant objects towards longer wavelengths. For starlight coming from the most distant galaxies that we can observe, this means that most of the light falls in the infrared part of the spectrum when it gets to Earth. As a highly sensitive infrared telescope with a wide field of view, VISTA is uniquely powerful for spotting distant galaxies in the early Universe. By studying galaxies in redshifted light at successively larger distances, astronomers can also trace how galaxies were built up and evolved over the history of the cosmos. 

Early studies of the UltraVISTA images, in combination with images from other telescopes, have revealed the presence of many galaxies that are seen when the Universe was less than a billion years old and a few are seen at even earlier times. More images: http://ultravista.org/images/field/.

Although the current UltraVISTA image is already the deepest infrared image of its size in existence, observations are continuing. In a few years from now, the final result will be significantly deeper still.

Surveys like this one are vital resources for astronomers, and ESO has put in place a programme so that the rich heritage from both VISTA and its visible-light companion, the VLT Survey Telescope (VST, eso1119), will be accessible to astronomers for decades to come.