Unveiling galaxies at cosmic dawn that were hiding behind the dust
Scientists serendipitously discover two heavily dust-enshrouded galaxies
that formed when the Universe was only 5% of its present age

Date:
September 22, 2021
Source:
Waseda University
Summary:
While investigating the data of young, distant galaxies observed
with the Atacama Large Millimeter/submillimeter Array, astronomers
noticed unexpected emissions coming from seemingly empty regions in
space that, a global research team confirmed, came actually from two
hitherto undiscovered galaxies heavily obscured by cosmic dust. This
discovery suggests that numerous such galaxies might still be hidden
in the early Universe, many more than researchers were expecting.



FULL STORY ==========================================================================
When astronomers peer deep into the night sky, they observe what the
Universe looked like a long time ago. Because the speed of light is
finite, studying the most distant observable galaxies allows us to
glimpse billions of years into the past when the Universe was very
young and galaxies had just started to form stars. Studying this "early Universe" is one of the last frontiers in astronomy and is essential
for constructing accurate and consistent astrophysics models.

A key goal of scientists is to identify all the galaxies in the first
billion years of cosmic history and to measure the rate at which galaxies
were growing by forming new stars.


========================================================================== Various efforts have been made over the past decades to observe
distant galaxies, which are characterized by electromagnetic emissions
that become strongly redshifted (shifted towards longer wavelengths)
before reaching the Earth. So far, our knowledge of early galaxies has
mostly relied on observations with the Hubble Space Telescope (HST)
and large ground-based telescopes, which probe their ultra-violet (UV) emission. However, recently, astronomers have started to use the unique capability of the Atacama Large Millimeter/submillimeter Array (ALMA)
telescope to study distant galaxies at submillimeter wavelengths. This
could be particularly useful for studying dusty galaxies missed in the
HST surveys due to the dust absorbing UV emission. Since ALMA observes
in submillimeter wavelengths, it can detect these galaxies by observing
the dust emissions instead.

In an ongoing large program called REBELS (Reionization-Era Bright
Emission Line Survey), astronomers are using ALMA to observe the
emissions of 40 target galaxies at cosmic dawn. Using this dataset,
they have recently discovered that the regions around some of these
galaxies contain more than meets the eye.

While analyzing the observed data for two REBELS galaxies, Dr. Yoshinobu Fudamoto of the Research Institute for Science and Engineering at Waseda University, Japan, and the National Astronomical Observatory of Japan
(NAOJ), noticed strong emission by dust and singly ionized carbon in
positions substantially offset from the initial targets. To his surprise,
even highly sensitive equipment like the HST couldn't detect any UV
emission from these locations. To understand these mysterious signals,
Fudamoto and his colleagues investigated matters further.

In their latest paper published in Nature, they presented a thorough
analysis, revealing that these unexpected emissions came from two
previously unknown galaxies located near the two original REBELS
targets. These galaxies are not visible in the UV or visible wavelengths
as they are almost completely obscured by cosmic dust. One of them
represents the most distant dust-obscured galaxy discovered so far.

What is most surprising about this serendipitous finding is that the
newly discovered galaxies, which formed more than 13 billion years ago,
are not strange at all when compared with typical galaxies at the same
epoch. "These new galaxies were missed not because they are extremely
rare, but only because they are completely dust-obscured," explains
Fudamoto. However, it is uncommon to find such "dusty" galaxies in the
early period of the Universe (less than 1 billion years after the Big
Bang), suggesting that the current census of early galaxy formation is
most likely incomplete, and would call for deeper, blind surveys. "It is possible that we have been missing up to one out of every five galaxies
in the early Universe so far," Fudamoto adds.

The researchers expect that the unprecedented capability of the James
Webb Space Telescope (JWST) and its strong synergy with ALMA would lead
to significant advances in this field in the coming years. "Completing
our census of early galaxies with the currently missing dust-obscured
galaxies, like the ones we found this time, will be one of the main
objectives of JWST and ALMA surveys in the near future," states Pascal
Oesch from University of Geneva.

Overall, this study constitutes an important step in uncovering when the
very first galaxies started to form in the early Universe, which in turn
shall help us understand where we are standing today.

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


========================================================================== Journal Reference:
1. Fudamoto, Y., Oesch, P.A., Schouws, S. et al. Normal, dust-obscured
galaxies in the epoch of reionization. Nature, 2021 DOI:
10.1038/s41586- 021-03846-z ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210922121803.htm

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