The LOFAR survey, based within the Netherlands, has released a bonanza of the latest sources. And with only 2% of the sky covered thus far, this is often only the start.
A unique sky survey at low radio frequencies has turned up quite 300,000 new sources, many of which are radio galaxies and quasars within the distant universe. And there’s far more to come: The discoveries, published during a special issue of Astronomy & Astrophysics, are supported just 2% of the eventual survey volume.
“For the primary time, we now have high-quality images of the radio sky at these low frequencies,” says Huub Röttgering (Leiden University, The Netherlands), PI of the LOFAR Surveys Key Science Project. “That’s an important breakthrough.”
The Low-Frequency Array (LOFAR), operated by ASTRON, Netherlands Institute for astronomy, maybe a novel instrument, consisting of some 100,000 simple antennas, grouped in 50 stations and connected to a central supercomputer through fiber optics. Most of the LOFAR stations are located within the Netherlands, but 12 of them are spread everywhere in Europe, from Ireland to Poland and from Sweden to France.
Eventually, the Low-frequency Two-meter Sky Survey (LoTSS) will map the entire northern sky, but the primary data release covers just 424 square degrees, centered on the handle of the large Dipper. a complete of 58 “radio pointings,” each 8 hours long, are administered at frequencies between 120 and 168 megahertz, yielding enough data to fill 10 million DVDs.
According to Röttgering, the most important problem has been removing the consequences of ionospheric turbulence, the radio equivalent of stars twinkling at visible wavelengths. Through clever mathematical tricks, scientists have sharpened the info to ascertain details 6 arcseconds across.
The new catalog has 325,694 radio sources, amid 58 high-resolution mosaic radio images. For about 70% of the sources, visible-light counterparts were found in existing data from the Sloan and Pan-STARRS surveys, giving astronomers rough distance estimates to the objects.
The radio waves from the galaxies that LOFAR has found are primarily generated by electrons spiraling along magnetic flux lines that thread jets coming from the galaxies’ central black holes. Once these electrons are spiraling for a short time, they hamper and emit lower-frequency radio waves, so LOFAR is seeing jet activity on for much longer timescales than existing higher-frequency radio surveys.
One intriguing result’s that each one relatively massive galaxies exhibit jet activity on the brink of their cores, which suggests that their central black holes are feeding more or less continuously. The new observations should shed light on the evolution of supermassive black holes over time. “Eventually, we hope to seek out the very first supermassive black holes within the history of the universe,” says Röttgering.
The 26 papers in Astronomy & Astrophysics, authored by quite 200 scientists from 18 countries, also cover LOFAR data on galaxy clusters. consistent with Annalisa Bonafede (University of Bologna, Italy), one surprising result’s that even isolated clusters that aren’t interacting with their neighbors still produce radio waves from charged particles speeding among the gas between galaxies, though the emissions are at a really low level.
The future Square Kilometre Array (SKA) features a low-frequency segment based in Australia, which can be even more sensitive than LOFAR, but it won’t see details as sharply. consistent with Röttgering, LOFAR’s high spatial resolution (it may discern details up to 0.5 arcseconds across under ideal circumstances) are going to be unsurpassed for an extended time to return.