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Using data from the Very Large Array Sky Survey (VLASS), astronomers have detected young jets emitting radio from supermassive black holes in distant active galaxies.
An artist’s conception of a galaxy with an active core pushing jets of material outward from the center of the galaxy. Image credit: Sophia Dagnello, NRAO / AUI / NSF.
VLASS is a project that will examine the sky visible from NSF’s Karl G. Jansky Very Large Array (VLA) – about 80% of the entire sky – three times in seven years. Observations began in 2017 and the first of three scans is now complete.
Dr Kristina Nyland, a postdoctoral researcher at the Naval Research Laboratory, and colleagues compared the data from this scan with data from the FIRST survey that used the VLA to observe a smaller portion of the sky between 1993 and 2011.
“We have found galaxies that showed no evidence of jets before, but now show clear indications that they have young and compact jets,” said Dr Nyland.
“Jets like these can strongly influence the growth and evolution of their galaxies, but we still don’t understand all the details.”
“Capturing newborn jets with surveys such as VLASS provides a measure of the role of powerful radio jets in shaping the life of galaxies over billions of years.”
Dr Nyland and co-authors found about 2,000 objects appearing in the VLASS images, but they were not detected in the first FIRST survey.
From these, they selected 26 objects that had previously been classified as quasars – galaxies with active nuclei powered by supermassive black holes – using optical and infrared observations.
They then chose 14 of these galaxies for more detailed observations with the VLA.
These observations provided high resolution images and were also performed at multiple radio frequencies to gain a more complete understanding of the characteristics of the objects.
VLA images of three galaxies in the study, comparing what was seen in the first FIRST survey and the subsequent VLASS survey; the newly appeared radio light emission indicates that galaxies launched new jets of material at some point between the dates of the two observations. Image credit: Nyland et al. / Sophia Dagnello, NRAO / AUI / NSF.
“The data from these detailed observations tell us that the most likely cause of the difference in radio brightness between the FIRST and VLASS observations is that motors in the nuclei of these galaxies have launched new jets since the FIRST observations were made,” he said. Dr. Dillon Dong, Caltech astronomer.
“Radio jets provide natural laboratories for learning the extreme physics of supermassive black holes, the formation and growth of which are believed to be intrinsically linked to that of the galactic centers in which they reside,” said Dr. Pallavi Patil, astronomer at the National Radio Astronomy Observatory. and the University of Virginia.
“Young jets like the ones discovered in our study may provide us with a rare opportunity to gain new insights into how these interactions between jets and their surroundings work,” added Dr. Nyland.
“VLASS has proven to be a key tool for discovering such jets, and we look forward to the results of its next two observation eras,” said Dr. Mark Lacy, an astronomer at the National Radio Astronomy Observatory.
The team’s results will be published in Astrophysical Journal.
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Kristina Nyland et al. 2020. Quasars that have gone from radio-quiet to radio-loud on ten-year time scales revealed by VLASS and FIRST. ApJ, in print; arXiv: 2011.08872
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