Hubble finds early, massive galaxies running on empty

Date:
September 22, 2021
Source:
NASA/Goddard Space Flight Center
Summary:
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. Without more fuel
for star formation, these galaxies were literally running on empty.



FULL STORY ==========================================================================
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.


========================================================================== Without more fuel for star formation, these galaxies were literally
running on empty. The findings are published in the journal Nature.

"At this point in our universe, all galaxies should be forming lots
of stars.

It's the peak epoch of star formation," explained lead author Kate
Whitaker, assistant professor of astronomy at the University of
Massachusetts, Amherst.

Whitaker is also associate faculty at the Cosmic Dawn Center in
Copenhagen, Denmark. "So what happened to all the cold gas in these
galaxies so early on?" 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.

Using Nature's Own Telescopes 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.

"By using strong gravitational lensing as a natural telescope, we can find
the distant, most massive, and first galaxies to shut down their star formation," said Whitaker. "I like to think about it like doing science
of the 2030s or 40s -- with powerful next-generation space telescopes
-- but today instead by combining the capabilities of Hubble and ALMA,
which are boosted by strong lensing." "REQUIEM pulled together the
largest sample to date of these rare, strong- lensed, dead galaxies in
the early universe, and strong lensing is the key here," said Mohammad
Akhshik, principal investigator of the Hubble observing program. "It
amplifies the light across all wavelengths so that it's easier to detect,
and you also get higher spatial resolution when you have these galaxies stretched across the sky. You can essentially see inside of them at
much finer physical scales to figure out what's happening." Live Fast,
Die Young These sorts of dead galaxies don't appear to rejuvenate, even
through later minor mergers and accretions of nearby, small galaxies
and gas. Gobbling up things around them mostly just "puffs up" the
galaxies. If star formation does turn back on, Whitaker described it as
"a kind of a frosting." About 11 billion years later in the present-day universe, these formerly compact galaxies are thought to have evolved
to be larger but are still dead in terms of any new star formation.

These six galaxies lived fast and furious lives, creating their stars
in a remarkably short time. Why they shut down star formation so early
is still a puzzle.

Whitaker proposes several possible explanations: "Did a supermassive
black hole in the galaxy's center turn on and heat up all the gas? If
so, the gas could still be there, but now it's hot. Or it could have
been expelled and now it's being prevented from accreting back onto
the galaxy. Or did the galaxy just use it all up, and the supply is cut
off? These are some of the open questions that we'll continue to explore
with new observations down the road." The Hubble Space Telescope is
a project of international cooperation between NASA and ESA (European
Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI)
in Baltimore, Maryland, conducts Hubble science operations.

STScI is operated for NASA by the Association of Universities for Research
in Astronomy, in Washington, D.C.

========================================================================== Story Source: Materials provided by
NASA/Goddard_Space_Flight_Center. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Whitaker, K.E., Williams, C.C., Mowla, L. et al. Quenching of star
formation from a lack of inflowing gas to galaxies. Nature, 2021
DOI: 10.1038/s41586-021-03806-7 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210922121920.htm

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