Science stories

October 3, 2020 • Science stories

Snakes and Butterflies



Imagine your eyes could see in the radio part of the electromagnetic spectrum and you went out and looked towards the constellation of Sextans, where the COSMOS field is located. You would be able to distinguish several weird shapes in the sky showing jets or lobes of radio emission, forming snakes, slugs, and butterflies. These extended radio Active Galactic Nuclei (AGN) have the nickname FR-type radio galaxies.


The latest work by Vardoulaki et al. ( of FR-type radio AGN in COSMOS uses the data from the 3 GHz VLA-COSMOS survey (Smolčić et al. 2017) to investigate the physical properties of the sources, their host galaxies and the large scale environment in order to find links with the shapes they display in the radio sky. 


You can read the publication here:


September 27, 2020 • Science stories

Relating mass and star formation rates

What's the relation between the mass of galaxies and their rate for star formation? The new paper by Sarah Leslie and collaborators measures this relation for 200,000 galaxies in the COSMOS field.

This relation between rate of star formation (SFR) and mass is called the main-sequence. It is observed across a large amount of cosmic time (redshifts). The paper by Leslie et al. provides a coherent measurement of this main-sequence up to redshift of 5 (about 13 billion years in the past). To do this, they use mean stacks of 3 GHz radio-continuum images to derive average SFRs for ∼ 200,000 mass-selected galaxies.

Check out her YouTube video explaining her paper:


July 12, 2019 • Science stories

New COSMOS Publication on Brightest Cluster Galaxy Progenitors

The brightest and most massive galaxies in the universe, the Brightest Cluster Galaxies (BCGs), tell a unique story of galaxy evolution. Today, BCGs are quiescent ellipticals hosted in relaxed galaxy clusters, with pasts fraught with mergers and high star formation rates (SFRs).

In a recent publication, Cooke et al. investigate how this active past may depend on local environment by estimating star formation in BCG progenitors in the COSMOS field out to a redshift of z ~ 3 (more than 11 billion years in the past).

April 3, 2018 • Science stories

COSMOS in the public eye

On 24-28th March 2018 the International Astronomical Union (IAU) held its huge Communicating Astronomy with the Public (CAP2018) conference in Fukuoka, Japan. COSMOS was represented at the meeting by team member Jacinta Delhaize from the University of Zagreb, who gave a talk on the various public outreach and communications initiatives of COSMOS.

She spoke about the various successes and challenges of engaging the public in such a large multi-national, multi-wavelength astronomical consortium. This is important because we think our data and science is great and we want to share it with everyone! The main challenge is that our astronomers, therefore the members of the public who we are trying to reach, are dispersed throughout the world over many different time zones and languages.

Therefore we mainly communicate our science using online platforms. We have this website and a presence on Facebook, Twitter and You Tube. We use these platforms to share our video blogs, news, press releases and more.

Stepping away from the virtual realm, we have our wonderful Artist-in-Residence Karel Nel, who creates renowned artworks inspired by COSMOS research. We also sometimes run public Astronomy on Tap events at the pub alongside our annual team meetings.

If you have any feedback or suggestions about other initiatives or website content you'd like to see, please let us know!

July 13, 2017 • Science stories

The dust properties of infant galaxies

The dust properties of infant galaxies

This new study uses the Hubble Space Telescope (HST) to characterize the dust properties of 10 galaxies living 12 billion years in the past. The new HST imaging data together with existing optical and ALMA (far-infrared) observations on COSMOS allowed the authors to measure the ultra-violet properties of these galaxies more accurately than ever. It turns out that these young galaxies have similar dust properties as the Small Magellanic Cloud, which is a metal-poor dwarf galaxy orbiting around our Milky Way.
Interested? - Read the whole paper:


March 30, 2017 • Science stories

The fate of massive Galaxies

The dominant processes that stop the formation of stars in galaxies is currently still unknown. Similarly, we do not know what grows galaxies after they stop their star formation and therefore should not change their size and mass anymore. Likely the life of very massive galaxies is very different than that of low-mass galaxies.

This new study on COSMOS targets to answering these questions for the most massive galaxies in our Universe by using the COSMOS/UltraVISTA near-infrared data.

Interested? Find the paper here or read the full article!

March 13, 2017 • Science stories

COSMOS unravelling the cosmic web

A team of researchers, led by Behnam Darvish, have been able to examine the cosmic web in great detail thanks to the plethora of high-quality COSMOS data available. The team have used the accurate photometric redshifts available within COSMOS, out to large cosmic distances, to map the density field within COSMOS. That is, they have determined the location of clusters of galaxies, filaments of the cosmic web and "normal" density regions called "the field." The cosmic web is the large-scale, complex network of galaxies, dark matter and gas that pervades throughout the Universe. The team found that a galaxy's position within the cosmic web plays an important role in determining the evolutionary pathway taken by the galaxy. They found that the cosmic web has a different influence on the rate of star formation within central galaxies (existing inside regions of high gravitational potential) compared to satellite galaxies (existing on the outskirts of these clusters). These findings will pave the way for exciting future work with upcoming telescopes such as LSST, Euclid, and WFIRST.

January 26, 2017 • Science stories

Do sub-millimeter galaxies (SMGs) live in over-dense regions in the early Universe?

A new study on COSMOS shows that between 35% and 60% of SMGs (i.e., highly star-forming galaxies) between z = 0 and z = 5 (1 billion years after the Big Bang) indeed reside in over-dense environments. However, the study also shows that the occurrence of SMGs occupying over-dense regions is lower at z < 3 compared to z > 3. This might indicate that highly star-forming galaxies can only be formed in high density regions at early cosmic epochs, while at later times, modest over-densities allow SMGs to form. For more information, check out their paper:

September 2, 2016 • Science stories

Record-breaking Galaxy Cluster Discovered

COSMOS data across many different wavelengths, including X-ray, infrared and radio, has been used to set the record for the most distant galaxy cluster ever discovered. We may be seeing the cluster, named CL J1001+0220, just after it's formation and while it is in the process of a big 'baby-boom' of star formation.

August 19, 2016 • Science stories

Spitzer to observe COSMOS for 1500 hours

A further 1500h of Spitzer time has been awarded to complete a survey of the COSMOS field. The program has been approved in Spitzer Cycle-13 to PI I. Labbe and COSMOS Co-I Karina Caputi. This will complete the legacy of Spitzer/IRAC over COSMOS by extending the deep coverage to cover the full 1.8 sq degree field, producing a nearly homogenous and contiguous map unparalleled in terms of area and depth. This will complement ongoing optical-to-NIR surveys and reconfirm COSMOS as a unique field for probing the bright end of the z=6-11 universe and the formation of large-scale structures.

August 10, 2016 • Science stories

ALMA to set its sights on COSMOS

Several hours of highly competitive Atacama Large Millimeter Array (ALMA) Cycle 4 time has been awarded to COSMOS astronomers to target various objects in the COSMOS field. ALMA is a revolutionary millimetre/sub-millimeter telescope and COSMOS astronomers will use it to gain a deeper understanding of how galaxies formed and evolved. They will study how the galaxy environment impacts star formation, examine the sizes and structures of enigmatic sub-millimetre galaxies, reveal the properties of galaxies in the high redshift Universe, and more. Congratulations to everyone involved! See the full article for details of the successful proposals.

July 28, 2016 • Science stories

Why do dead galaxies grow in size?

Quiescent galaxies do not form stars anymore, however, their population averaged size is increasing over time. Using stacked zCOSMOS spectra, Fagioli et al. measured their ages as a function of size and find that small galaxies are older than large ones. This indicates that the increase of the average size of quiescent galaxies with cosmic time is due to the addition of newly quenched, bigger star-forming galaxies at later times to the quiescent population. This is not true anymore for the most massive galaxies, which individually grow in size, possibly due to dry mergers.

May 13, 2016 • Science stories

Why do galaxies stop forming stars?

This new study uses the COSMOS survey to measure the local environment (density) around galaxies at z < 3 and connects it to their star formation rates. The study suggests that the shutdown of star formation due to galaxies falling into dense environment (e.g., causing stripping and heating of gas) is dominant at z < 1. At higher redshifts, quenching of star formation is likely triggered by galaxy internal processes (feedback, etc).

April 23, 2016 • Science stories

SPLASH as precursor of JWST

A new paper by COSMOS member Andreas Faisst and team shows how to use Spitzer colors to derive emission line properties of 3 < z < 6 galaxies. Optical emission lines at z > 4 cannot be measured spectroscopically with current facilities. Since emission lines "contaminate" the Spitzer 3.6um and 4.5um channels, these can be used to estimate optical line emission without the need of spectra. The study of emission lines provides important information about galaxy formation in the early universe and also provides a sample of galaxies for future JWST follow-up. The ApJ paper is in print and can be retrieved here:

March 22, 2016 • Science stories

Feedback in action in a quasar at z=1.5

Winds and outflows of gas in quasars are thought to have a significant impact on their host galaxies. A group of researchers, led by COSMOS's Marcella Brusa, have mapped the kinematics of quasar XID5395, a merging luminous quasar at z=1.5. The team identified this curious object using extensive COSMOS multiwavength data. They then observed XID5395 with the Subaru telescope and the ESO/SINFONI spectrograph and found the quasar to be in a turbulent situation. Winds up to 1300km/s, induced by the nuclear activity, are sweeping the surrounding gas outwards. It is thought that this will halt, or 'quench', star formation in the host galaxy of the quasar. XID5395 gives us a rare opportunity to see strong feedback in action and to study how this phenomenon impacts the evolutionary pathways of galaxies. Click here to read more about this galaxy caught in its life-changing phase.

March 22, 2016 • Science stories

Rare galaxies provide clues on cluster formation

COSMOS researcher Caitlin Casey has found that the formation of the most massive structures in the Universe — clusters of galaxies — happened with a bang! This conclusion was reached after looking in detail at galaxy protoclusters - collections of galaxies in the early Universe that may eventually form a galaxy cluster.

November 19, 2015 • Science stories

The Birth of Monsters

ESO’s VISTA survey telescope has spied a horde of previously hidden massive galaxies that existed when the Universe was in its infancy. By discovering and studying more of these galaxies than ever before, astronomers have, for the first time, found out exactly when such monster galaxies first appeared. Read the full press release here.

October 22, 2015 • Science stories

ALMA telescope unveils rapid formation of new stars in distant galaxies

Researchers have found that 'starburst' galaxies in the Universe 9 billion years ago were more efficient at forming stars than average galaxies today. 'Starburst' galaxies display unusually huge bursts of newly-formed stars and are likely caused by a collision between two large galaxies. A new study published in Astrophysical Journal letters on October 15, led by John Silverman at the Kavli Institute for the Physics and Mathematics of the Universe, has helped to understand exactly why such huge bursts of star formation occur. The researchers used the new, sensitive Atacama Large Millimeter Array (ALMA) in Chile to study carbon monoxide (CO) gas in seven starburst galaxies that existed when the Universe was only four billion years old. They found that the amount of CO gas in these galaxies is not special, but that these galaxies seem to be particularly efficient at turning their gas into stars. This study also relied on a variety of powerful telescopes available through the COSMOS survey, including the Spitzer Observatory, the Herschel Observatory and the Subaru Telescope.

July 13, 2015 • Science stories

A precocious black hole

A research team, led by ETH Zurich researcher Benny Trakhtenbrot, has discovered a gigantic black hole that is much more massive than we expect it to be.

June 25, 2015 • Science stories

Discovering a New Stage in the Galactic Lifecycle

CONFIRMED: Galaxies contained far less dust in the early stages of their evolution! Using ALMA, COSMOS team leader Peter Capak and collaborators picked up the signature of [CII] (emitted by gas) and continuum (emitted by dust) in nine 'normal' galaxies at redshift 5 to 6 - only 1 billion years after the Big Bang.

June 22, 2015 • Science stories

Detailed Shape and Evolutionary Behavior of the X-Ray Luminosity Function of Active Galactic Nuclei

We revealed the detailed shape and evolutionary behavior of the X-ray luminosity function of active galactic nuclei between 143 erg s-1. The two-break flat-top structures and overall downsizing is suggestive of a two-phase AGN evolution scenario, consisting of major merger triggerings and secular processes. Read the paper at