Using data from the Very Large Array Sky Survey (VLASS), astronomers have detected young radio-emitting jets from supermassive black holes in distant active galaxies.
An artist’s conception of a galaxy with an active nucleus propelling jets of material outward from the galaxy’s center. Image credit: Sophia Dagnello, NRAO / AUI / NSF.
VLASS is a project that will survey the sky visible from NSF’s Karl G. Jansky Very Large Array (VLA) — about 80% of the entire sky — three times over seven years. The observations began in 2017 and the first of the three scans now is complete.
Dr. Kristina Nyland, a postdoctoral researcher at the Naval Research Laboratory, and colleagues compared 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 found galaxies that showed no evidence of jets before but now show clear indications of having young, compact jets,” Dr. Nyland said.
“Jets like these can strongly affect the growth and evolution of their galaxies, but we still don’t understand all of the details.”
“Catching newborn jets with surveys like VLASS provides a measure of the role of powerful radio jets in shaping the lives of the galaxies over billions of years.”
Dr. Nyland and co-authors found about 2,000 objects that appear in the VLASS images, but were not detected in the earlier FIRST survey.
From these, they selected 26 objects that previously were categorized as quasars — galaxies with active nuclei powered by supermassive black holes — by optical and infrared observations.
They then chose 14 of these galaxies for more detailed observations with the VLA.
These observations provided higher-resolution images and also were done at multiple radio frequencies to get a more complete understanding of the objects’ characteristics.
VLA images of three galaxies in the study, comparing what was seen in the earlier FIRST survey and the later VLASS; the newly-appearing bright radio emission indicates that the galaxies launched new jets of material sometime 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 the VLASS observations is that the engines at the cores of these galaxies have launched new jets since the FIRST observations were made,” said Dr. Dillon Dong, an astronomer with Caltech.
“Radio jets provide natural laboratories for learning about the extreme physics of supermassive black holes, whose formation and growth are believed to be intrinsically linked to that of the galaxy centers in which they reside,” said Dr. Pallavi Patil, an astronomer at the National Radio Astronomy Observatory and the University of Virginia.
“Jets as young as the ones discovered in our study can provide us with a rare opportunity to gain new insights on how these interactions between the jets and their surroundings work,” Dr. Nyland added.
“VLASS has proven to be a key tool for discovering such jets, and we eagerly await the results of its next two observing epochs,” said Dr. Mark Lacy, an astronomer at the National Radio Astronomy Observatory.
The team’s results will be published in the Astrophysical Journal.
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Kristina Nyland et al. 2020. Quasars That Have Transitioned from Radio-quiet to Radio-loud on Decadal Timescales Revealed by VLASS and FIRST. ApJ, in press; arXiv: 2011.08872
