Survey of the sky reveals newborn jets in distant galaxies

Astronomers using data from the ongoing VLA Sky Survey (VLASS) have found a number of distant galaxies with supermassive black holes in their cores that have launched powerful jets of radio-emitting material over the past two decades or so. The scientists compared the VLASS data with data from an earlier survey that also used the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) to come to their conclusion.

“We have found galaxies that showed no evidence of jets before, but now show clear indications that they have young, compact jets,” said Dr Kristina Nyland, who is an NRC postdoctoral fellow resident at the Naval Research Laboratory.

“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 like VLASS provides a measure of the role of powerful radio jets in shaping the life of galaxies in the over billions of years, ”Nyland said.

VLASS is a project that will examine the sky visible from the VLA, approximately 80% of the entire sky, three times in seven years. Observations began in 2017 and the first of three scans is now complete. Nyland and her 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.

They found around 2,000 objects appearing in VLASS images, but they were not detected in the first FIRST survey. From these, they selected 26 objects that had previously been classified as galaxies with active nuclei – powered by supermassive black holes – using optical and infrared observations. The FIRST observations of the 26 objects were made between 1994 and 2001. The VLASS observations were made in 2019. The intervals between the observations of the objects therefore varied from 18 to 25 years.

They 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.

“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 the ‘motors’ in the nuclei of these galaxies have launched new jets since the FIRST observations were made,” explained Dillon Dong of Caltech.

Black holes in the nucleus of galaxies are known to interact with the galaxies themselves and the two evolve together. Jets launched from regions close to black holes can affect the amount of star formation within the galaxy.

“Radio jets provide natural laboratories for learning the extreme physics of supermassive black holes, whose formation and growth are believed to be intrinsically linked to that of the galactic centers in which they reside,” said Pallavi Patil of the University of Virginia.

“Young jets like those 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,” Nyland said.

“VLASS has proven to be a key tool for the discovery of such jets, and we look forward to the results of its next two observation eras,” said Mark Lacy, of the National Radio Astronomy Observatory.

Nyland and his colleagues plan further studies of galaxies using the Very Long Baseline Array (VLBA), the Chandra X-ray Observatory, and visible light and infrared telescopes. The article was accepted in the publication by The Astrophysical Journal.