A most detailed view into distant stellar nurseries

Press release of the University of Bonn with participation of MPIA regarding the VLA-COSMOS 3 GHz project

14. Juni 2017
Just like in human civilizations the birth rate in the Universe fluctuated over time. When the Universe had reached 2.5 Billion years of its current age of approximately 13.8 Billion years, galaxies produced the majority of all stars ever formed. An international team of astronomers including reasearcher from the Argelander-Institute for Astronomy at the University of Bonn and the Max-Planck-Institute for Astronomy Heidelberg has now vastly improved on previous estimates. The Karl G. Jansky Very Large Array Telescope in New Mexico (USA) allowed to undertake a survey of distant galaxies that produced unprecendentedly detailed and deep radio views over a very large celestial area. The results will now be published in a special edition of the journal „Astronomy & Astrophysics“.  

The international team observed almost 11,000 galaxies over an area equivalent to about nine full moons on the sky. Thanks to these unique data the life cycle of galaxies over the past 13 Billion years could be reconstructed. „The radio light from a galaxy can show us at least two very important things,” said the lead investigator of the project, Associate-Professor Vernesa Smolčić from the University of Zagreb. „Radio light helps us to see straight through dust clouds and so reveals new stars forming within galaxies. It can also show us highly energetic signatures of growing supermassive black holes.“

Contrary to visible light, radio-light is not blocked by the large clouds of interstellar dust that often reside in galaxies. This means that radio waves can be used to detect newborn stars within galaxies in a way usually not possible at other wavelengths.

The VLA-COSMOS project started with Dr. Eva Schinnerer at the Max-Planck Institute for Astronomy Heidelberg as principal investigator already back in 2004 with a first radio survey of a celestial area called „COSMOS“. The tremendous scientific success of this project motivated the team – now led by Prof. Smolčić who at that time was based as a researcher at the Argelander-Institute for Astronomy at the University of Bonn – to apply for a large follow-up survey. This effort only became possible thanks to a major technological upgrade the Karl G. Jansky Very Large Array (VLA) Telescope in New Mexico (USA) had undergone in the meanwhile.

The   astronomers   combined   the   new   radio   data   with   optical,   infrared, and X-ray information from many of the world’s leading telescopes. „The synergy of sensitive, multi-wavelength  data  allowed  us to investigate  the  properties  of  galaxies  shining  at  radio wavelengths  out to about 13 billion years into the universe’s past,” said Dr. Alexander Karim who is responsible for the VLA-COSMOS survey at the Argelander-Institute for Astronomy at the University of Bonn.

The team found that the rate of production of new stars within galaxies was the highest when the universe was about 2.5  billion years old – a  fifth of its current age. During that period, about a quarter of all newborn stars were being created in massive galaxies. They also found that up to 20 percent more star formation was occurring in galaxies in the early universe, compared to what was previously thought.

Moreover, a very distant but vigurously star forming population of galaxies – so called submillimeter-galaxies – were found to be substantially larger than previously expected. The exact reasons for this have not been entirely clarified yet but they could be linked to collisions and gravitational interactions between galaxies. 

The new radio survey has also provided a unique insight into galaxies containing actively growing  supermassive  black  holes  in  their  centers.  These galaxies are called Active Galactic Nuclei, or AGN for short. Matter orbiting around and falling into the black hole can release huge amounts of energy. Using the new radio data, the astronomers discovered more than 1000 AGN. Only their radio emission signatures betray their hidden black hole activity. They are particularly interesting because of their influence on the fate of their host galaxies but even on their cosmic environment. The astronomers compared the AGN heating process   assumed in cosmological simulations to what they detected in the new  radio data. They found a strong similarity between the two. „Physical  processes associated with emission from these supermassive black holes may heat the gas in and around the galaxy, preventing the formation of new stars and halting the runaway growth of galaxies”, says Dr. Schinnerer from the MPI for Astronomy in Heidelberg. Dr. Karim adds: „The VLA-COSMOS survey marks an important milestone on our way towards the next generation large area sky surveys.”

Original press release with additional images, videos and all contact persons:

German press release of Bonn University at the Informationsdienst Wissenschaft (idw):

English version of the press release of Bonn University at Informationsdienst Wissenschaft (idw):

Scientific publications belonging to the project:
The VLA-COSMOS 3 GHz Large Project, „Astronomy & Astrophysics“

Project funding:

  • ERC Starting Grant project (‘CoSMass’): Constraining Stellar Mass and Supermassive Black Hole Growth through Cosmic Times: Paving the way for the next generation sky surveys (European Union’s Seventh Framework program under grant agreement 337595)
  • CIG project (‘AGN feedback’): Constraining AGN feedback through cosmic times: Paving the way for the next generation radio facilities (European Union’s Seventh Framework program under grant agreement 333654)
  • Deutsche Foschungsgemeinschaft (DFG): grant BE 1837/13-1 (‘The Cosmic Evolution of Black Hole and Stellar Mass Growth Probed Through Radio Observations’) and Collaborative Research Council 956 (“Conditions and Impact of Star Formation”) sub-project A1.


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