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Scientists unveil 4.4 million galaxies in new map of the universe

About a million objects that have never been seen before.

Scientists unveil 4.4 million galaxies in new map of the universe
A composition radio (LoTSS-DR2) and optical (Hubble space telescope) image of the “jellyfish galaxy” NGC 4858 which is flying through a dense medium that is stripping material from the galaxy. Credits Ian Roberts Astron

Astronomers are constantly creating maps of the universe that both amaze and impress. These maps are not only pleasant to look at, but they also offer insights into our planetary systems and beyond.

Now, using the Low-Frequency Array (LOFAR), a pan-European radio telescope, Durham University researchers, with the aid of a team of international scientists, have mapped more than a quarter of the northern sky, according to a statement released by the institution on Friday.

The new map reveals about a million objects that have never been seen before with any telescope and almost four million objects that are new discoveries at radio wavelengths.

A new map of the universe

“This project is so exciting to work on. Each time we create a map our screens are filled with new discoveries and objects that have never before been seen by human eyes. Exploring the unfamiliar phenomena that glow in the energetic radio Universe is such an incredible experience and our team is thrilled to be able to release these maps publicly," said astronomer Timothy Shimwell of ASTRON and Leiden University.

The map showcases more than 4.4 million objects, the vast majority of which are billions of light-years away. These awe-inspiring celestial objects tend to be either galaxies that harbor massive black holes or are rapidly growing new stars.

Scientists unveil 4.4 million galaxies in new map of the universe
Astron

20,000 laptops worth of data

There are also a few colliding groups of distant galaxies and flaring stars. To get their images, researchers had to weed through 3,500 hours of data that make up 8 petabytes of disk space (this amounts to roughly 20,000 laptops). And there are actually more observations to shift through.

"This release is only 27% of the entire survey and we anticipate it will lead to many more scientific breakthroughs in the future, including examining how the largest structures in the Universe grow, how black holes form and evolve, the physics governing the formation of stars in distant galaxies and even detailing the most spectacular phases in the life of stars in our own Galaxy," concluded Shimwell.

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The study is published in the journal Astronomy and Astrophysics.

Abstract:

In this data release from the ongoing LOw-Frequency ARray (LOFAR) Two-metre Sky Survey we present 120–168 MHz images covering 27% of the northern sky. Our coverage is split into two regions centred at approximately 12h45m +44◦300 and 1h00m +28◦000 and spanning 4178 and 1457 square degrees respectively. The images were derived from 3451 h (7.6 PB) of LOFAR High Band Antenna data which were corrected for the direction-independent instrumental properties as well as direction-dependent ionospheric distortions during extensive, but fully automated, data processing. A catalogue of 4 396 228 radio sources is derived from our total intensity (Stokes I) maps, where the majority of these have never been detected at radio wavelengths before. At 600 resolution, our full bandwidth Stokes I continuum maps with a central frequency of 144 MHz have: a median rms sensitivity of 83 µJy beam−1; a flux density scale accuracy of approximately 10%; an astrometric accuracy of 0.200; and we estimate the point-source completeness to be 90% at a peak brightness of 0.8 mJy beam−1. By creating three 16 MHz bandwidth images across the band we are able to measure the in band spectral index of many sources, albeit with an error on the derived spectral index of >±0.2 which is a consequence of our flux density scale accuracy and small fractional bandwidth. Our circular polarisation (Stokes V) 2000 resolution 120–168 MHz continuum images have a median rms sensitivity of 95 µJy beam−1, and we estimate a Stokes I to Stokes V leakage of 0.056%. Our linear polarisation (Stokes Q and Stokes U) image cubes consist of 480 × 97.6 kHz wide planes and have a median rms sensitivity per plane of 10.8 mJy beam−1 at 40 and 2.2 mJy beam−1 at 2000; we estimate the Stokes I to Stokes Q/U leakage to be approximately 0.2%. Here we characterise and publicly release our Stokes I, Q, U and V images in addition to the calibrated UV-data to facilitate the thorough scientific exploitation of this unique dataset.

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