Radio continuum surveys


One way to study galaxy evolution is with radio continuum surveys. Galaxies release radio continuum emission if they are star forming or if they have an active nucleus.

This page describes the radio continuum survey work I conducted during my first postdoctoral research position at the Faculty of Science (PMF), University of Zagreb, Croatia (2014-2018). For my current work in this area, see Galaxy evolution with MeerKAT.

At the University of Zagreb, I worked with the ZGal research group led by Vernesa Smolcic. We studied galaxy evolution by mapping large parts of the sky with radio telescopes such as the Very Large Array (VLA).

I also worked as part of two large international collaborations: COSMOS and XXL.

The ZGal research group at the University of Zagreb. Image credit: Petar Krajačić Vilovic. Left to right: Krešimir Tisanić, Ivan Delvecchio, Lana Ceraj, Vernesa Smolčić, Oskari Miettinen, Mladen Novak, Jacinta Delhaize.


The Cosmic Evolution Survey (COSMOS) is an international team of astronomers collecting information across the entire electromagnetic spectrum for a two-square-degree patch of sky called the COSMOS field.

Our research group (ZGal) at the University of Zagreb were responsible for leading a new radio continuum survey of the COSMOS field. To do this, we observed the field for 400 hours using the Karl G. Jansky Very Large Array (VLA) telescope in New Mexico, USA. The survey is called the VLA-COSMOS 3GHz Large Project.

The VLA telescope (foreground; courtesy of NRAO/AUI) and a 3GHz image of the sky from the VLA-COSMOS 3GHz Large Project. Image composition: Vernesa Smolčić.

This was some of the most sensitive, high resolution and wide-field radio data available at the time. By combining it with the plethora of other high-quality multiwavelength data available in the COSMOS field, it provides a powerful resource with which to study galaxy evolution.

In June 2017 the Astronomy & Astrophysics journal published a special edition dedicated to the first suite of publications from our survey. You can read the full press release and watch some short videos about our work here.

My first-author publication in the series focused on the infrared-radio correlation of galaxies. There is a close relationship between the amount of radio light and the amount of far-infrared light that galaxies emit. Using the VLA-COSMOS 3GHz Large Project and data from the Herschel Space Observatory, I found that this correlation has seemingly changed slightly over the history of the Universe. This is important to know because it will change our measurements of the amount of star formation occurring in distant galaxies – which is an important parameter in galaxy evolution studies.

I explain this work for a general audience (no astronomy knowledge needed!) in this short video:


The XXL is a very large sky survey with the XMM-Newton X-ray telescope. It covers two 25 square-degree patches of sky. The international XXL team are working to obtain observations of these sky fields at many different wavelengths of light.

I was part of a sub-team responsible for running a 2.1GHz radio continuum survey of the Southern XXL field. To do this, we used 220 hours of time with the Australia Telescope Compact Array (ATCA) in New South Wales, Australia in 2012 and 2014.

We found 6287 radio-detected galaxies in the resulting map. We found the counterparts to these objects in similar maps at different wavelengths in order to study the physical properties of these galaxies.

You can find the publication on the pilot survey here and on the full survey here.

Observing the XXL field with the Australia Telescope Compact Array remotely from my ‘home office’ in Zagreb on Christmas eve 2014. With PhD student Nikola Baran.

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