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Universe simulations show Webb telescope can reveal distant galaxies hidden in the glow of Quasars

High red shift quasar and companion galaxy

This artist’s illustration portrays two galaxies that existed in the first billion years of the universe. The larger galaxy on the left hosts a bright quasar at its center, whose glow is fueled by the hot matter surrounding a supermassive black hole. Scientists calculate that the resolution and infrared sensitivity of NASA’s upcoming James Webb Space Telescope will allow it to detect a dusty host galaxy like this despite the quasar’s light beam. Credit: J. Olmsted (STScI)

Webb’s observations will search for dusty galaxies from the first billion years of the universe.

The brightest objects in the young and distant universe are quasars. These cosmic beacons are powered by supermassive black holes that consume material at a ferocious rate. Quasars are so bright that they can eclipse the entire host galaxy, making it difficult to study those galaxies and compare them to galaxies without quasars.

A new theoretical study examines how well NASAIt is imminent James Webb space telescope, slated for launch in 2021, will be able to separate light from host galaxies from the bright central quasar. Researchers find that Webb could detect host galaxies that existed only 1 billion years after the big bang.

This video zooms in on a highly detailed simulation of the universe called BlueTides. Just like the iconic Powers of Ten video, each pass covers a distance 10 times shorter than the previous one. The first frame spans about 200 million light years while the fourth and final frame spans only 200,000 light years and contains two galaxies. The researchers used this simulation to study the properties of galaxies that contain quasars, bright galactic nuclei powered by the accumulation of supermassive black holes. Credits: Y. Ni (Carnegie Mellon University) and L. Hustak (STScI)

Quasars are the brightest objects in the universe and among the most energetic. They mirror entire galaxies of billions of stars. A supermassive black hole it is at the heart of every quasar, but not every black hole is a quasar. Only black holes that feed most voraciously can power a quasar. The material falling into the supermassive black hole heats up and makes a quasar in the universe shine like a lighthouse.

Although quasars are known to reside at the center of galaxies, it has been difficult to tell what these galaxies look like and how they compare to galaxies without quasars. The challenge is that the quasar’s glow makes it difficult or impossible to tease the light of the surrounding host galaxy. It’s like looking directly into a car headlight and trying to figure out what kind of car it’s connected to.

A new study[1] suggests that NASA’s James Webb Space Telescope, scheduled for launch in 2021, will be able to detect the host galaxies of some distant quasars despite their small size and dark dust.

Infrared images simulated by Webb and Hubble

These simulated images show what a quasar and its host galaxy would look like at NASA’s upcoming James Webb Space Telescope (top) and the Hubble Space Telescope (bottom) at infrared wavelengths of 1.5 and 1.6 microns. respectively. Webb’s largest mirror will provide more than 4 times the resolution, allowing astronomers to separate light from the galaxy from overwhelming light from the central quasar. The individual images span approximately 2 arc seconds into the sky, representing a distance of 36,000 light years with a red shift of 7. Credit: M. Marshall (University of Melbourne)

“We want to know what kind of galaxies these quasars live in. This can help us answer questions like: How can black holes grow so large so fast? Is there a relationship between the mass of the galaxy and the mass of the black hole, as seen in ‘near universe?’ said lead author Madeline Marshall of the University of Melbourne in Australia, who led her work within the ARC Center of Excellence in All Sky Astrophysics in 3 Dimensions.

Answering these questions is challenging for a variety of reasons. In particular, the more distant a galaxy is, the more its light has been stretched to longer wavelengths by the expansion of the universe. As a result, ultraviolet light from the black hole’s accretion disk or from the galaxy’s young stars is shifted to infrared wavelengths.

In a recent study[2], astronomers used NASA’s near-infrared capabilities Hubble Space Telescope to study known quasars in the hope of detecting the surrounding glow of their host galaxies, without significant detection. This suggests that the dust inside the galaxies is obscuring the light from their stars. Webb’s infrared detectors will be able to peer through the dust and discover hidden galaxies.

“Hubble just doesn’t go far enough into the infrared to see host galaxies. This is where Webb will truly excel,” said Rogier Windhorst of Arizona State University in Tempe, co-author of the Hubble study.

To determine what Webb should see, the team used a state-of-the-art computer simulation called BlueTides, developed by a team led by Tiziana Di Matteo at Carnegie Mellon University in Pittsburgh, Pennsylvania.

“BlueTides is designed to study the formation and evolution of galaxies and quasars in the first billion years of the universe’s history. Its large cosmic volume and high spatial resolution allow us to study those rare host quasars on a statistical basis.” , said Yueying Ni of Carnegie Mellon University, who ran the BlueTides simulation. BlueTides provides good agreement with current observations and allows astronomers to predict what Webb should see.

The team found that galaxies hosting quasars tended to be smaller than average, covering only about 1/30 the diameter of the quasars. Milky Way despite containing almost the same mass as our galaxy. “The host galaxies are surprisingly tiny compared to the average galaxy at the time,” Marshall said.

The galaxies in the simulation also tended to form stars rapidly, up to 600 times faster than the current star-forming rate in the Milky Way. “We have found that these systems grow very fast. They are like precocious children: they do everything early “, explained co-author Di Matteo.

The team then used these simulations to determine what Webb’s cameras would see if the observatory studied these distant systems. They found that it would be possible to distinguish the host galaxy from the quasar, although it was still difficult due to the galaxy’s small size in the sky.

“Webb will open up the opportunity to observe these very distant host galaxies for the first time,” Marshall said.

They also considered what Webb’s spectrographs could derive from these systems. Spectral studies, which break down incoming light into its component colors or wavelengths, would be able to reveal the chemical composition of the dust in these systems. Learning how many heavy elements they contain could help astronomers understand their star formation histories, as most of the chemical elements are produced in stars.

Webb could also determine whether host galaxies are isolated or not. The Hubble study found that most quasars had detectable companion galaxies, but was unable to determine if those galaxies were actually nearby or if they were random overlaps. Webb’s spectral capabilities will allow astronomers to measure redshifts, and thus distances, of those apparent companion galaxies to determine if they are at the same distance as the quasar.

Ultimately, Webb’s observations should provide new insight into these extreme systems. Astronomers still struggle to understand how a black hole can grow to weigh a billion times as much as our Sun in just a billion years. “These large black holes shouldn’t exist that early because there wasn’t enough time for them to get so massive,” said co-author Stuart Wyithe of the University of Melbourne.

Future quasar studies will also be fueled by synergies between multiple upcoming observatories. Infrared investigations with the European Space Agency’s Euclid mission, as well as the Vera C. Rubin Earth Observatory, a facility of the National Science Foundation / Department of Energy currently under construction on Cerro Pachón in the Atacama Desert in Chile. Both observers will significantly increase the number of known distant quasars. Those new quasars will then be examined by Hubble and Webb to gain new insights into the formative years of the universe.


  1. “The host galaxies of z = 7 quasars: predictions from the BlueTides simulation” by Madeline A Marshall, Yueying Ni, Tiziana Di Matteo, J Stuart B Wyithe, Stephen Wilkins, Rupert A C Croft and Jussi K Kuusisto, 5 October 2020, Royal Astronomical Society Monthly Notices.
    DOI: 10.1093 / mnras / staa2982
  2. “Limits to Rest-frame Ultraviolet Emission from Far-infrared-luminous z sime 6 Quasar Hosts” by MA Marshall, M. Mechtley, RA Windhorst, SH Cohen, RA Jansen, L. Jiang, VR Jones, JSB Wyithe1, X. Fan , NP Hathi, K. Jahnke, WC Keel, AM Koekemoer, V. Marian, K. Ren, J. Robinson, HJA Röttgering, RE Ryan Jr., E. Scannapieco, DP Schneider, G. Schneider, BM Smith and H. Yan, August 27, 2020, The Astrophysical Journal.
    DOI: 10.3847 / 1538-4357 / abaa4c

The Bluetides simulation (PI project: Tiziana Di Matteo at Carnegie Mellon University) was performed at the Blue Waters supported petascale processing facility, which is supported by the National Science Foundation.

The James Webb Space Telescope will be the world’s leading space science observatory when it launches in 2021. Webb will solve the mysteries of our solar system, look beyond distant worlds around other stars, and probe the mysterious structures and origins of our universe and the our place inside. Webb is a NASA-led international program with its partners, the European Space Agency (ESA) and Canadian Space Agency.

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