NASA | GSFC | STScI | HubbleSite | 2021 Sep 22
When the universe was about 3 billion years old, just 20% of its current age, it experienced the most prolific period of star birth in its history. But when NASA's Hubble Space Telescope and the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile gazed toward cosmic objects in this period, they found something odd: six early, massive, "dead" galaxies that had run out of the cold hydrogen gas needed to make stars.These images are composites from NASA's Hubble Space Telescope and the
Atacama Large Millimeter/submillimeter Array (ALMA). The boxed and pullout
images show two of the six, distant, massive galaxies where scientists found
star formation has ceased due to the depletion of a fuel source – cold hydrogen
gas. Image Processing: Joseph DePasquale (STScI)
Without more fuel for star formation, these galaxies were literally running on empty. ...
This study is a classic example of the harmony between Hubble and ALMA observations. Hubble pinpointed where in the galaxies the stars exist, showing where they formed in the past. By detecting the cold dust that serves as a proxy for the cold hydrogen gas, ALMA showed astronomers where stars could form in the future if enough fuel were present.
The study of these early, distant, dead galaxies was part of the appropriately named REQUIEM program, which stands for Resolving QUIEscent Magnified Galaxies At High Redshift. (Redshift happens when light is stretched by the expansion of space and appears shifted toward the red part of the spectrum. The farther away a galaxy is with respect to the observer, the redder it appears.)
The REQUIEM team uses extremely massive foreground galaxy clusters as natural telescopes. The immense gravity of a galaxy cluster warps space, bending and magnifying light from background objects. When an early, massive and very distant galaxy is positioned behind such a cluster, it appears greatly stretched and magnified, allowing astronomers to study details that would otherwise be impossible to see. This is called "strong gravitational lensing."
Only by combining the exquisite resolution of Hubble and ALMA with this strong lensing was the REQUIEM team able to able to understand the formation of these six galaxies, which appear as they did only a few billion years after the big bang. ...
ALMA Scientists Uncover the Mystery of
Early Massive Galaxies Running on Empty
ALMA | NRAO | 2021 Sep 22
Early massive galaxies—those that formed in the three billion years following the Big Bang—should have contained large amounts of cold hydrogen gas, the fuel required to make stars. But scientists observing the early Universe with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Hubble Space Telescope have spotted something strange: half a dozen early massive galaxies that ran out of fuel. ...This composite image of galaxy cluster MACSJ 0138 shows data from the Atacama
Large Millimeter/submillimeter Array (ALMA) and NASA’s Hubble Space Telescope.
The magnified section shows a bright orange/red dot, which traces cold dust
observed in radio using ALMA. This cold dust helps scientists to understand, by
inference, the amount of cold hydrogen gas present in the galaxies in the cluster.
Credit: ALMA (ESO/NAOJ/NRAO)/S. Dagnello (NRAO), STScI, K. Whitaker et al
Known as “quenched” galaxies—or galaxies that have shut down star formation—the six galaxies selected for observation from the REsolving QUIEscent Magnified galaxies at high redshift, or the REQUIEM survey, are inconsistent with what astronomers expect of the early Universe. ...
To better understand how the galaxies formed and died, the team observed them using Hubble, which revealed details about the stars residing in the galaxies. Concurrent observations with ALMA revealed the galaxies’ continuum emission—a tracer of dust—at millimeter wavelengths, allowing the team to infer the amount of gas in the galaxies. The use of the two telescopes is by careful design, as the purpose of REQUIEM is to use strong gravitational lensing as a natural telescope to observe dormant galaxies with higher spatial resolution. This, in turn, gives scientists a clear view of galaxies’ internal goings-on, a task often impossible with those running on empty. ...
Quenching of Star Formation from a Lack of Inflowing Gas to Galaxies ~ Katherine E. Whitaker et al