Preparing to study the epoch of reionization

October 10, 2016, Harvard-Smithsonian Center for Astrophysics
One "tile" of the Murchison Wide-field Array telescope. In preparation for looking for the first generation of galaxies, the facility has published the first catalog of extragalactic sources of contamination in one of the fields of view. Credit: Murchison Wide-field Array

The epoch when the very first stars appeared is a key period of cosmic history. These stars began the manufacture of the chemical elements (those heavier than hydrogen and helium) and their light began the reionization of the neutral cosmic gas. These stars thus mark the dawn of the universe as we know it today and the start of the so-called Epoch of Reionization. The term "reionization" refers to the process whereby these atoms are prompted (by the ultraviolet light from new stars) to shed some of their electrons. Astronomers estimate that this period occurred a few hundred million years or so after the big bang.

Neutral hydrogen atoms were the dominant element in the universe from the time they first arose, about 380,000 years after the , until the Epoch of Reionization. Astronomers are now constructing facilities like the radio telescope Murchison Wide-field Array (MWA) to search for light from the hydrogen atoms at the dawn of this Epoch, a daunting task not only because the sources are so distant and faint, but also because there are so many other galaxies from much later cosmic times lying in the way and contaminating our lines-of-sight, as well as more local sources of contamination.

CfA astronomers Lincoln Greenhill, Justin Kasper (now at Michigan), and Avi Loeb were members of a large team of scientists that used the MWA during its early commissioning phase of operations to develop a catalog of foreground sources that could be likely sources of confusion. The MWA currently consists of 128 groupings ("tiles") of sixteen antennae each arranged in four-by-four squares and sensitive to radiation around a meter in wavelength. The unusual telescope pattern meant that the team had to learn how to properly reduce and analyze the complex resulting data, and much of the effort in this research was devoted to these tasks.

The astronomers successfully identified 7394 extragalactic sources which could be confused with earlier-epoch galaxies in their first field of the sky under study. Nearly all of these objects were associated with previously known galaxies, but twenty-five of them are previously unknown, and all of them have now been characterized. The results both demonstrate the practicality of the MWA performance and are a first step toward assembling a database for the precise subtraction of foreground radiation to uncover nascent galaxies in the early universe.

Explore further: Explaining why the universe can be transparent

More information: P. A. Carroll et al. A high reliability survey of discrete Epoch of Reionization foreground sources in the MWA EoR0 field, Monthly Notices of the Royal Astronomical Society (2016). DOI: 10.1093/mnras/stw1599

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cantdrive85
1.6 / 5 (7) Oct 10, 2016
This "study" is the equivalent of the preparations that are taking place to get ready to count the gold in the leprechauns pot o' gold at the end of the rainbow.
optical
Oct 10, 2016
This comment has been removed by a moderator.
RNP
4 / 5 (4) Oct 11, 2016
@optical
.... The space-time expands the faster, the more distant it is and once the speed of its expansion exceeds the speed of light, then all massive objects in it would disappear from our sight.


This is not true. In part because I think you are confusing the Hubble law, v=Hd, which is an approximation only applicable on (cosmologically) small scales, with the full relativistic, cosmological law (see http://hyperphysi...shf.html ). You can use the calculator on this web page to calculate the recession velocity at the redshift of the epoch of reionization (~10) to be ~0.984c. I.e. still LESS than the speed of light.

Indeed, at no redshift, however high, does the recession velocity exceed the speed of light.
optical
Oct 11, 2016
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RNP
1 / 5 (1) Oct 11, 2016
@optical
I can make no sense of what you are saying. You said that we can not see the epoch of reionization and I showed that we can. So what WAS your "objection"?
optical
Oct 11, 2016
This comment has been removed by a moderator.
RNP
3.7 / 5 (3) Oct 11, 2016
@optical
Try to imagine, the Universe is infinitely large, due to metric expansion the particle horizon would represent and infinitely small part of it. Therefore we would see an infinitely small part of Universe history. The observability of reionization epoch would have only meaning for https://www.physi....350249/


Sorry ,but that is pure nonsense.
RNP
3 / 5 (2) Oct 11, 2016
@optical

Try to imagine, the Universe is infinitely large, due to metric expansion the particle horizon would represent and infinitely small part of it. Therefore we would see an infinitely small part of Universe history. The observability of reionization epoch would have only meaning for https://www.physi....350249/


Who says they universe is infinitely large? Besides, we are looking back to z=10, a long way sure, but not infinite. What has the particle horizon got to do with it? You are also trying (but failing) to interpret cosmology using simple but misplaced analogies. You should actually try to learn modern cosmology before you make such extreme claims.

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