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  • richardmitnick 1:24 pm on March 16, 2017 Permalink | Reply
    Tags: , , , , , Epoch of Reionization, , When the Neighborhood Dwarf Galaxies were Kids   

    From astrobites: “When the Neighborhood Dwarf Galaxies were Kids’ 

    Astrobites bloc

    Astrobites

    Title: Local Group Ultra-Faint Dwarf Galaxies in the Reionization Era
    Authors: D. R. Weisz, M. Boylan-Kolchin
    First Author’s Institution: Department of Astronomy, University of California Berkeley, Berkeley, CA
    1
    No image credit
    Status: Submitted to MNRAS, [open access]

    The heavens bespeak a dark and quiet night, glinting here and there with distant stars and yet more distant galaxies. But in ages past, long before the birth of our stalwart Sun, before even the supernovae that spewed the calcium in our bones and the iron in our blood into the gas that formed the Sun and the Solar System, there was darkness. The cosmic dark ages reigned for nearly a million years before the first stars blinked blearily on.

    Then suddenly there came an age of light. We’re not entirely sure what exactly lit up the universe, but among the suspects are the first galaxies. Once practically invisible, they were lit aflame as the first stars began to burn hot and bright within them. They generated copious amounts of ultra-violet (UV) light, energetic enough to ionize the hydrogen in the universe. So much UV flux was generated that nearly all the hydrogen in the universe was ionized, leaving the universe clear and transparent and allowing us the majestic views of faraway galaxies that we take for granted today.

    2
    Figure 1. The role of small galaxies like the Milky Way’s newly discovered ultra-faint galaxies could have had in reionizing the universe. The top panel shows the number density of galaxies as a function of how bright they were in the ultra-violet (MUV), what we call the Salpeter function. The colors denote how the numbers changed with time; purple (z ~ 8) denotes when reionization occurred, and the lighter colors denote the subsequent evolution after reionization. Far more faint galaxies (less negative MUV) exist compared to brighter galaxies. Together, they produced most of the UV flux during reionization, as shown in the middle and bottom panels: the middle panel shows the density of UV photons (which is clearly highest at the faint end), and the bottom panel shows the cumulative fraction of the flux that galaxies brighter than a given MUV were generating. As much as 50-80% of the UV flux that reionized the universe may have come from galaxies fainter than MUV ~ -10! Figure taken from today’s paper.

    The authors of today’s paper investigate what role the newly discovered ultra-faint dwarf galaxies orbiting our Milky Way could have had during this epoch of reionization. For it turns out that our most careful galaxy counts—which we’ve codified into what we now call the Schechter function (see Figure 1)—tell us that the universe swarms with dwarf galaxies, which are at least a thousand times less massive than the more familiar grand spirals such as the Milky Way. The Milky Way itself is thought to be surrounded by several hundreds, if not thousands, of such galaxies. Dwarf galaxies are so numerous that together, they may have been able to provide much of the UV photons required. It was an age in which the smallest galaxies ruled the ultra-violet skies.


    Dwarf Galaxies with Messier 101 Allison Merritt Dragonfly Telephoto Array


    U Toronta Dragon Fly Telescope Array

    We don’t know for sure if dwarf galaxies can solve the mystery of reionization. The problem is that it’s extremely difficult to peer into the universe’s distant past, and literally impossible to observe the faint dwarfs that existed then. Our best observations hint that there were many more dwarfs in the past than in the present, before they were torn apart and cannibalized by larger galaxies.

    To work around these uncertainties, the authors did something simple. They worked out when the stars in the Milky Way’s ultra-faint dwarfs formed to determine how much UV light they’d give off during reionization. They then asked: If the Schechter function was valid for dwarfs as dim as the Milky Way’s faintest dwarfs used to be, how much UV light would they have produced? They found that dwarfs could have generated as much as 50-80% of the UV photons needed to reionize the universe.

    There’s hints, however, that such a simple extrapolation of the Schechter function to ultra-faint galaxies overestimates the number of bright UV-emitting dwarfs. The Schechter function predicts that we should see as many as ten times as many bright dwarfs around the Milky Way than we actually do. And it’s becoming clear that the smallest galaxies have trouble producing UV-generating stars. This would cause the Schechter function to “turn over” (see Figure 2) or predict fewer bright dwarfs (and hordes of small, dark galaxies). The authors show that the estimated reduction in bright dwarfs seen in simulations lowers the UV flux we should expect from small galaxies to about 10%.

    Although we haven’t yet gotten to the bottom of how large a role dwarf galaxies played in the ionization of the universe, it’s clear that the yet unobservable number of UV-bright dwarfs matters greatly in understanding how the history of the universe unfolded. The upcoming James Webb Space Telescope has the ability to detect galaxies from the epoch of reionization that are almost 100x fainter—still far short of the 10,000x increase in sensitivity we need to see the faint UV galaxies that preoccupied today’s authors. It’ll be a big step forward, but we’ll still have to hunt for other clues as to the true numbers of dwarf galaxies during reionization.

    3
    Figure 2. How a reduction in the number of ultra-faint dwarf galaxies can reduce their contribution to the reionization of the universe. The top panel shows different guesses as to the number density of galaxies of a given UV brightness. In black is the traditional Salpeter function, which predicts many faint UV galaxies, while the orange and purple curves are based on simulations that show a “turn-over” or reduction in the number of faint UV galaxies. The bottom panel shows that if there are just a few UV-faint galaxies, then they contribute only ~10% of the UV flux that reionized the universe. Figure taken from today’s paper.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 9:15 am on February 9, 2017 Permalink | Reply
    Tags: , , , , Epoch of Reionization, Faintest galaxies yet seen in the early universe, , , ,   

    From U Texas at Austin: “Astronomers Find Faintest Early Galaxies Yet, Probe How the Early Universe Lit Up” 

    U Texas Austin bloc

    University of Texas at Austin

    08 February 2017
    No writer credit

    Astronomers at The University of Texas at Austin have developed a new technique to discover the faintest galaxies yet seen in the early universe —10 times fainter than any previously seen.

    1
    A Hubble Space Telescope view of the galaxy cluster Abell 2744.

    These galaxies will help astronomers probe a little-understood, but important period in cosmic history. Their new technique helps probe the time a billion years after the Big Bang, when the early, dark universe was flooded with light from the first galaxies.

    Rachael Livermore and Steven Finkelstein of the UT Austin Astronomy Department, along with Jennifer Lotz of the Space Telescope Science Institute, went looking for these faint galaxies in images from Hubble Space Telescope’s Frontier Fields survey.

    2
    A Hubble Space Telescope view of the galaxy cluster MACS 0416 is annotated in cyan and magenta to show how it acts as a ‘gravitational lens,’ magnifying more distant background galaxies.

    “These galaxies are actually extremely common,” Livermore said. “It’s very satisfying being able to find them.”

    These faint, early galaxies gave rise to the Epoch of Reionization, when the energetic radiation they gave off bombarded the gas between all galaxies in the universe. This caused the atoms in this diffuse gas to lose their electrons (that is, become ionized).

    Finkelstein explained why finding these faint galaxies is so important. “We knew ahead of time that for our idea of galaxy-powered reionization to work, there had to be galaxies a hundred times fainter than we could see with Hubble,” he said, “and they had to be really, really common.” This was why the Hubble Frontier Fields program was created, he said.

    Lotz leads the Hubble Frontier Fields project, one of the telescope’s largest to date. In it, Hubble photographed several large galaxy clusters. These were selected to take advantage of their enormous mass which causes a useful optical effect, predicted by Albert Einstein. A galaxy cluster’s immense gravity bends space, which magnifies light from more-distant galaxies behind it as that light travels toward the telescope. Thus the galaxy cluster acts as a magnifying glass, or a “gravitational lens,” allowing astronomers to see those more-distant galaxies — ones they would not normally be able to detect, even with Hubble.

    Even then, though, the lensed galaxies were still just at the cusp of what Hubble could detect.

    “The main motivation for the Frontier Fields project was to search for these extremely faint galaxies during this critical period in the universe’s history,” Lotz said. “However, the primary difficulty with using the Frontier Field clusters as an extra magnifying glass is how to correct for the contamination from the light of the cluster galaxies.”

    Livermore elaborates: “The problem is, you’re trying to find these really faint things, but you’re looking behind these really bright things. The brightest galaxies in the universe are in clusters, and those cluster galaxies are blocking the background galaxies we’re trying to observe. So what I did was come up with a method of removing the cluster galaxies” from the images.

    Her method uses modeling to identify and separate light from the foreground galaxies (the cluster galaxies) from the light coming from the background galaxies (the more-distant, lensed galaxies).

    According to Lotz, “This work is unique in its approach to removing this light. This has allowed us to detect more and fainter galaxies than seen in previous studies, and to achieve the primary goal for the Frontier Fields survey.”

    Livermore and Finkelstein have used the new method on two of the galaxy clusters in the Frontier Fields project: Abell 2744 and MACS 0416. It enabled them to identify faint galaxies seen when the universe was about a billion years old, less than 10 percent of its current age — galaxies 100 times fainter than those found in the Hubble Ultra Deep Field, for instance, which is the deepest image of the night sky yet obtained.

    Their observations showed that these faint galaxies are extremely numerous, consistent with the idea that large numbers of extremely faint galaxies were the main power source behind reionization.

    There are four Frontier Fields clusters left, and the team plans to study them all with Livermore’s method. In future, she said, they would like to use the James Webb Space Telescope to study even fainter galaxies.

    The work is published in a recent issue of The Astrophysical Journal.

    See the full article here .

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    U Texas Arlington Campus

    In 1839, the Congress of the Republic of Texas ordered that a site be set aside to meet the state’s higher education needs. After a series of delays over the next several decades, the state legislature reinvigorated the project in 1876, calling for the establishment of a “university of the first class.” Austin was selected as the site for the new university in 1881, and construction began on the original Main Building in November 1882. Less than one year later, on Sept. 15, 1883, The University of Texas at Austin opened with one building, eight professors, one proctor, and 221 students — and a mission to change the world. Today, UT Austin is a world-renowned higher education, research, and public service institution serving more than 51,000 students annually through 18 top-ranked colleges and schools.

     
  • richardmitnick 3:01 pm on February 7, 2017 Permalink | Reply
    Tags: 21-centimeter cosmology, , , , Epoch of Reionization, , What ended the dark ages of the universe?   

    From Symmetry: “What ended the dark ages of the universe?” 

    Symmetry Mag
    Symmetry

    02/07/17
    Diana Kwon

    1
    NAOJ

    When we peer through our telescopes into the cosmos, we can see stars and galaxies reaching back billions of years. This is possible only because the intergalactic medium we’re looking through is transparent. This was not always the case.

    Around 380,000 years after the Big Bang came recombination, when the hot mass of particles that made up the universe cooled enough for electrons to pair with protons, forming neutral hydrogen. This brought on the dark ages, during which the neutral gas in the intergalactic medium absorbed most of the high-energy photons around it, making the universe opaque to these wavelengths of light.

    Then, a few hundred million years later, new sources of energetic photons appeared, stripping hydrogen atoms of their electrons and returning them to their ionized state, ultimately allowing light to easily travel through the intergalactic medium. After this era of reionization was complete, the universe was fully transparent once again.

    Physicists are using a variety of methods to search for the sources of reionization, and finding them will provide insight into the first galaxies, the structure of the early universe and possibly even the properties of dark matter.

    Energetic sources

    Current research suggests that most—if not all—of the ionizing photons came from the formation of the first stars and galaxies. “The reionization process is basically a competition between the rate at which stars produce ionizing radiation and the recombination rate in the intergalactic medium,” says Brant Robertson, a theoretical astrophysicist at the University of California, Santa Cruz.

    However, astronomers have yet to find these early galaxies, leaving room for other potential sources. The first stars alone may not have been enough. “There are undoubtedly other contributions, but we argue about how important those contributions are,” Robertson says.

    Active galactic nuclei, or AGN, could have been a source of reionization. AGN are luminous bodies, such as quasars, that are powered by black holes and release ultraviolet radiation and X-rays. However, scientists don’t yet know how abundant these objects were in the early universe.

    Another, more exotic possibility, is dark matter annihilation. In some models of dark matter, particles collide with each other, annihilating and producing matter and radiation. “If through this channel or something else we could find evidence for dark matter annihilation, that would be fantastically interesting, because it would immediately give you an estimate of the mass of the dark matter and how strongly it interacts with Standard Model particles,” says Tracy Slatyer, a particle physicist at MIT.

    Dark matter annihilation and AGN may have also indirectly aided reionization by providing extra heat to the universe.

    Probing the cosmic dawn

    To test their theories of the course of cosmic reionization, astronomers are probing this epoch in the history of the universe using various methods including telescope observations, something called “21-centimeter cosmology” and probing the cosmic microwave background.

    Astronomers have yet to find evidence of the most likely source of reionization—the earliest stars—but they’re looking.

    By assessing the luminosity of the first galaxies, physicists could estimate how many ionizing photons they could have released. “[To date] there haven’t been observations of the actual galaxies that are reionizing the universe—even Hubble can’t deliver any of those—but the hope is that the James Webb Space Telescope can,” says John Wise, an astrophysicist at Georgia Tech.

    Some of the most telling information will come from 21-centimeter cosmology, so called because it studies 21-centimeter radio waves. Neutral hydrogen gives off radio waves of this frequency, ionized hydrogen does not. Experiments such as the forthcoming Hydrogen Epoch of Reionization Array will detect neutral hydrogen using radio telescopes tuned to this frequency. This could provide clinching evidence about the sources of reionization.

    “The basic idea with 21-centimeter cosmology is to not look at the galaxies themselves, but to try to make direct measurements of the intergalactic medium—the hydrogen between the galaxies,” says Adrian Liu, a Hubble fellow at UC Berkeley. “This actually lets you, in principle, directly see reionization, [by seeing how] it affects the intergalactic medium.”

    By locating where the universe is ionized and where it is not, astronomers can create a map of how neutral hydrogen is distributed in the early universe. “If galaxies are doing it, then you would have ionized bubbles [around them]. If it is dark matter—dark matter is everywhere—so you’re ionizing everywhere, rather than having bubbles of ionizing gas,” says Steven Furlanetto, a theoretical astrophysicist at the University of California, Los Angeles.

    Physicists can also learn about sources of reionization by studying the cosmic microwave background, or CMB.

    When an atom is ionized, the electron that is released scatters and disrupts the CMB. Physicists can use this information to determine when reionization happened and put constraints on how many photons were needed to complete the process.

    For example, physicists reported last year that data released from the Planck satellite was able to lower its estimate of how much ionization was caused by sources other than galaxies. “Just because you could potentially explain it with star-forming galaxies, it doesn’t mean that something else isn’t lurking in the data,” Slatyer says. “We are hopefully going to get much better measurements of the reionization epoch using experiments like the 21-centimeter observations.”

    It is still too early to rule out alternative explanations for the sources of reionization, since astronomers are still at the beginning of uncovering this era in the history of our universe, Liu says. “I would say that one of the most fun things about working in this field is that we don’t know exactly what happened.”

    See the full article here .

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    Symmetry is a joint Fermilab/SLAC publication.


     
  • richardmitnick 8:38 am on December 29, 2016 Permalink | Reply
    Tags: , , , , DDM hypothesis, Epoch of Reionization, , , Institute for Nuclear Research in Moscow, , The Universe is losing dark matter and researchers have finally measured how much   

    From Science Alert: “The Universe is losing dark matter, and researchers have finally measured how much” 

    ScienceAlert

    Science Alert

    28 DEC 2016
    JOSH HRALA

    1
    MIPT

    Researchers from Russia have, for the first time, been able to measure the amount of dark matter the Universe has lost since the Big Bang some 13.7 billion years ago, and calculate that as much as 5 percent of dark matter could have deteriorated.

    The finding could explain one of the biggest mysteries in physics – why our Universe appears to function in a slightly different way than it did in the years just after the Big Bang, and it could also shed insight into how it might continue to evolve in future.

    “The discrepancy between the cosmological parameters in the modern Universe and the Universe shortly after the Big Bang can be explained by the fact that the proportion of dark matter has decreased,” said co-author Igor Tkachev, from the Institute for Nuclear Research in Moscow.

    “We have now, for the first time, been able to calculate how much dark matter could have been lost, and what the corresponding size of the unstable component would be.”

    The mystery surrounding dark matter was first brought up way back in the 1930s, when astrophysicists and astronomers observed that galaxies moved in weird ways, appearing to be under the effect of way more gravity than could be explained by the visible matter and energy in the Universe.

    This gravitational pull has to come from somewhere. So, researchers came up with a new type of ‘dark matter’ to describe the invisible mass responsible for the things they were witnessing.

    As of right now, the current hypothesis states that the Universe is made up of 4.9 percent normal matter – the stuff we can see, such as galaxies and stars – 26.8 percent dark matter, and 68.3 percent dark energy, a hypothetical type of energy that’s spread throughout the Universe, and which might be responsible for the Universe’s expansion.

    But even though the majority of matter predicted to be in the Universe is actually dark, very little is known about dark matter – in fact, scientists still haven’t been able to prove that it actually exists.

    One of the ways scientists study dark matter is by examining the cosmic microwave background (CMB), which some call the ‘echo of the Big Bang’.

    CMB per ESA/Planck
    CMB per ESA/Planck

    The CMB is the thermal radiation left over from the Big Bang, making it somewhat of an astronomical time capsule that researchers can use to understand the early, newly born Universe.

    The problem is that the cosmological parameters that govern how our Universe works – such as the speed of light and the way gravity works – appear to differ ever so slightly in the CMB compared to the parameters we know to exist in the modern Universe.

    “This variance was significantly more than margins of error and systematic errors known to us,” Tkachev explains. “Therefore, we are either dealing with some kind of unknown error, or the composition of the ancient universe is considerably different to the modern Universe.”

    One of the hypotheses that might explain why the early Universe was so different is the ‘decaying dark matter‘ [Nature] (DDM) hypothesis – the idea that dark matter has slowly been disappearing from the Universe.

    And that’s exactly what Tkachev and his colleagues set out to analyse on a mathematical level, looking for just how much dark matter might have decayed since the creation of the Universe.

    The study’s lead author, Dmitry Gorbunov, also from the Institute for Nuclear Research, explains:

    “Let us imagine that dark matter consists of several components, as in ordinary matter (protons, electrons, neutrons, neutrinos, photons). And one component consists of unstable particles with a rather long lifespan.

    In the era of the formation of hydrogen, hundreds of thousands of years after the Big Bang, they are still in the Universe, but by now (billions of years later), they have disappeared, having decayed into neutrinos or hypothetical relativistic particles. In that case, the amount of dark matter in the era of hydrogen formation and today will be different.”

    To come up with a figure, the team analysed data taken from the Planck Telescope observations on the CMB, and compared it to different dark matter models like DDM.

    ESA/Planck
    ESA/Planck

    They found that the DDM model accurately depicts the observational data found in the modern Universe over other possible explanations for why our Universe looks so different today compared to straight after the Big Bang.

    The team was able to take the study a step further by comparing the CMB data to the modern observational studies of the Universe and error-correcting for various cosmological effects – such as gravitational lensing, which can amplify regions of space thanks to the way gravity can bend light.

    In the end, they suggest that the Universe has lost somewhere between 2 and 5 percent of its dark matter since the Big Bang, as a result of these hypothetical dark matter particles decaying over time.

    “This means that in today’s Universe, there is 5 percent less dark matter than in the recombination era,” Tkachev concludes.

    “We are not currently able to say how quickly this unstable part decayed; dark matter may still be disintegrating even now, although that would be a different and considerably more complex model.”

    These findings suggest that dark matter decays over time, making the Universe move in different ways than it had in the past, though the findings call for more outside research before anything is said for certain.

    Even so, this research is another step closer to potentially understanding the nature of dark matter, and solving one of science’s greatest mysteries – why the Universe looks the way it does, and how it will evolve in the future.

    The team’s work was published in Physical Review D.

    See the full article here .

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  • richardmitnick 1:36 pm on October 27, 2016 Permalink | Reply
    Tags: , , Cosmic Horseshoe, Epoch of Reionization, ,   

    From UC Riverside: “The Cosmic Horseshoe Is Not the Lucky Beacon That Astronomers Had Hoped For” 

    UC Riverside bloc

    UC Riverside

    10.26.16

    A UC Riverside-lead team of astronomers used a new approach by using the gravitationally lensed galaxy to try to measure the escaping fraction of photons.

    1

    INTRODUCTION

    Around 380,000 years after the Big Bang, electrons and protons bound together to form hydrogen atoms for the first time. They make up more than 90% of the atoms in the universe, and can very efficiently absorb high-energy photons and become ionized. However, there were very few energetic sources to ionize these atoms in the early universe. One billion years after the Big Bang, the material between the galaxies was reionized (transparent). The main energy source of the reionization is widely believed to be massive stars formed within early galaxies. These stars had a short lifespan and were usually born in the midst of dense gas clouds, which made it very hard for ionizing photons to escape their host galaxies.

    Previous studies suggested that about 20 percent of these ionizing photons need to escape the dense-gas environment of their host galaxies to significantly contribute to the reionization of the material between galaxies. Unfortunately, a direct detection of these ionizing photons is very challenging and previous efforts have not been very successful. Therefore, the mechanisms leading to their escape are poorly understood.

    This has led many astrophysicists to use indirect methods to estimate the fraction of ionizing photons that escape the galaxies. In one popular method, the gas is assumed to have a “picket fence” distribution, where the space between the stars and the edges of galaxies is assumed to be composed of either regions of very little gas, which are transparent to ionizing light, or regions of dense gas, which are opaque. Researchers can determine the fraction of each of these regions by studying the light (spectra) emerging from the galaxies.

    In this new study, astronomers directly measured the fraction of ionizing photons escaping from the Cosmic Horseshoe. The Horseshoe is a distant galaxy that is gravitationally lensed. Gravitational lensing is the deformation and amplification of a background object by the curving of space and time due to the mass of a foreground galaxy”, said Kaveh Vasei, graduate student of astronomy at UC Riverside and lead author of the new study. “The details of the galaxy in the background are therefore magnified, allowing us to study its light and physical properties more clearly.”

    RESULTS

    Based on the picket fence model, an escape fraction of 40% for ionizing photons from the Horseshoe was expected. Therefore, the Horseshoe represented an ideal opportunity to get a clear, resolved image of leaking ionizing photons for the first time, to help us understand the mechanisms by which they escape their host galaxies.

    The research team obtained a deep-image of the Horseshoe with the Hubble Space Telescope in an ultraviolet filter, enabling them to directly detect escaping ionizing photons. Surprisingly, the image did not detect ionizing photons coming from the Horseshoe. This team constrained the fraction of escaping photons to be less than 8%, five times smaller than what had been inferred by indirect methods widely used by astronomers.

    “The study concludes that the previously determined fraction of escaping ionizing radiation of galaxies, as estimated by the most popular indirect method, is likely overestimated in many galaxies,” added Prof. Brian Siana, co-author of the research paper and a professor at UC Riverside. “The team is now focusing on direct determination the fraction of escaping ionizing photons that do not rely on indirect estimates.”

    This paper has been published in the Astrophysical Journal and is authored by Kaveh Vasei (UC Riverside), Brian Siana (UC Riverside), Alice E. Shapley (UCLA), Anna M. Quider (University of Cambridge, UK), Anahita Alavi (UC Riverside), Marc Rafelski (Goddard Space Flight Center / NASA), Charles C. Steidel (Caltech), Max Pettini (University of Cambridge, UK), Geraint F. Lewis (University of Sydney)

    See the full article here .

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    UC Riverside Campus

    The University of California, Riverside is one of 10 universities within the prestigious University of California system, and the only UC located in Inland Southern California.

    Widely recognized as one of the most ethnically diverse research universities in the nation, UCR’s current enrollment is more than 21,000 students, with a goal of 25,000 students by 2020. The campus is in the midst of a tremendous growth spurt with new and remodeled facilities coming on-line on a regular basis.

    We are located approximately 50 miles east of downtown Los Angeles. UCR is also within easy driving distance of dozens of major cultural and recreational sites, as well as desert, mountain and coastal destinations.

    See the full article here .

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    UC Riverside Campus

    The University of California, Riverside is one of 10 universities within the prestigious University of California system, and the only UC located in Inland Southern California.

    Widely recognized as one of the most ethnically diverse research universities in the nation, UCR’s current enrollment is more than 21,000 students, with a goal of 25,000 students by 2020. The campus is in the midst of a tremendous growth spurt with new and remodeled facilities coming on-line on a regular basis.

    We are located approximately 50 miles east of downtown Los Angeles. UCR is also within easy driving distance of dozens of major cultural and recreational sites, as well as desert, mountain and coastal destinations.

     
  • richardmitnick 11:15 am on October 12, 2016 Permalink | Reply
    Tags: , , , Epoch of Reionization, MWA,   

    From CfA: “Preparing to Study the Epoch of Reionization” 

    Harvard Smithsonian Center for Astrophysics


    Center For Astrophysics

    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 big bang, 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.

    1
    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. Murchison Wide-field Array

    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.

    Reference(s):

    A High Reliability Survey of Discrete Epoch of Reionization Foreground Sources in the MWA EoR0 Field, P. A. Carroll et al., MNRAS 461, 4151, 2016.

    See the full article here .

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    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

     
  • richardmitnick 1:54 pm on September 21, 2016 Permalink | Reply
    Tags: , , Epoch of Reionization, HERA,   

    From Many Worlds: “Out Of The Darkness” 

    NASA NExSS bloc

    NASA NExSS

    Many Words icon

    Many Worlds

    2016-09-21
    Marc Kaufman

    1
    http://www.cafescipa.org

    2
    Simulation of the “Dark Ages” of the universe, a period predicted by theorists to have lasted as long as several hundred million years after the Big Bang. The first hydrogen atoms in the universe had not yet coalesced into stars and galaxies. (NASA/WMAP)

    Before there were galaxies with stars and exoplanets, there were galaxies with stars and no planets. Before there were galaxies without planets, there were massive singular stars.

    And before that, there was darkness for more than 100 million years after the Big Bang — a cosmos without much, or at times any, light.

    So how did the lights get turned on, setting the stage for all that followed? Scientists have many theories but so far only limited data.

    In the coming years, that is likely to change substantially.

    First, the James Webb Space Telescope, scheduled to launch in 2018, will be able to look back at distant galaxies and stars that existed in small or limited numbers during the so called Dark Ages.

    NASA/ESA/CSA Webb Telescope annotated
    NASA/ESA/CSA Webb Telescope annotated

    They gradually became more prevalent and then suddenly (in astronomical terms) became common. Called the epoch of cosmic “reionization,” this period is an essential turning point in the evolution of the cosmos.

    Less well known but also about to begin pioneering work into how and when the lights came on will be an international consortium led by a team at the University of California, Berkeley. Unlike the space-based JWST, this effort will use an array of radio telescopes under construction in the South African desert. The currently small array will expand quickly now thanks in large part to a $9.6 million grant recently announced from the National Science Foundation.

    Named the Hydrogen Epoch of Reionization Array (HERA), the project will focus especially on the billion-year process that changed the fundamental particle physics of the universe to allow stars, galaxies and their light burst out like spring flowers after a long winter.

    hera
    Ultimate 350 dishes, UC Berkeley Hydrogen Epoch of Reionization Array (HERA), at the Karoo desert site, South Africa

    But unlike the JWST, which will be able to observe faint and very early individual galaxies and stars, HERA will be exploring the early universe as a near whole.

    3
    Before stars and galaxies became common, the universe went through a long period of darkness and semi-darkness, but ended with the “Epoch of Reionization.” (S.G. Djorgovski & Digital Media Center, Caltech)

    Aaron Parsons, an associate professor at Berkeley and principal investigator of the HERA project, said his team is now ready to grow their proof-of-concept array to a full-fledged observatory with 270 radio telescopes, with science that just might give some solid answers about how the lights came on.

    Parsons said they see their effort as a continuation of the earlier pioneering work that identified and mapped the cosmic microwave background radiation that was produced by another cosmos-changing event some 380,000 years after the Big Bang.

    “We have learned a ton about the cosmology of our universe from studies of the cosmic microwave background, but those experiments are observing just the thin shell of light that was emitted from a bunch of protons and electrons that finally combined into neutral hydrogen 380,000 years after the Big Bang,” Parsons said.

    “We know from these experiments that the universe started out neutral {at that point}, and we know that it ended ionized, and we are trying to map out how it transitioned between those two.”

    More specifically, here is what cosmologists and astrophysicists theorize or know happened:

    The Big Bang produced a scorching cauldron of particles that had electrical charge. That condition ended with the ‘recombination” event that joined protons and neutrons together to form atomic hydrogen, and as a result produced the cosmic microwave background radiation.

    What followed was 100 million or more years of abject darkness because the atomic hydrogen was neutral and unable to do much of anything. Some relatively few stars appeared in those Dark Ages, when enough gas clumped together and set off a star-forming gravitational collapse.

    Those stars, and later dwarf galaxies, emitted photons which had the effect of splitting (or ionizing) the hydrogen that surrounded them — creating bubbles of charged hydrogen (and some helium) in a vast ocean of neutral hydrogen.

    Much remains unknown about how and when the population of stars and galaxies grew over the ensuing hundreds of millions of years during this epoch of reionization. But a time came, an estimated one billion years after the Big Bang, when the islands of split hydrogen turned into a universe of split hydrogen. That made widescale star and galaxy formation possible.

    Many astronomers study primordial stars and galaxies to learn about this still mysterious process, but the HERA project will analyze instead how those earliest celestial objects changed the nature of intergalactic space. And that essentially means capturing tiny changes in the vast universe of uncharged hydrogen during and after the Dark Ages, since hydrogen was most of what was present.

    As Parsons explained it, the changes within hydrogen atoms they are looking for were weak and occurred only infrequently — perhaps once in 10 million years for a single atom of hydrogen. “But there’s an awful lot of hydrogen out there, and that allows the weakness to be an advantage. That means we can see through clouds, can see deep into the hydrogen clouds,” and that allows for observing on a much longer time scale.

    The goal of the HERA project is, most broadly, to trace those minute changes in hydrogen from about 100 million years after the Big Bang to one billion years after, when the epoch of reionization culminated with a conclusive turning on of the universe.

    3
    An artist rendering of the “bubbles” of ionized atoms theorized to have surrounded the earliest stars. As Parsons explained: “The first galaxies lit up and started ionizing bubbles of gas around them, and soon these bubbles started percolating and intersecting and making bigger and bigger bubbles. Eventually, they all intersected and you got this über bubble, leaving the universe as we observe it today.” (Illustration from Scientific American)

    The HERA array currently has 19 radio telescopes, will grow to 37 soon, and to 270 in 2018.

    UC Berkeley Hydrogen Epoch of Reionization Array (HERA), South Africa
    19 dishes, UC Berkeley Hydrogen Epoch of Reionization Array (HERA), at the Karoo desert site, South Africa

    The team hopes to some day expand to 350 telescopes. Each is a of radio dish looking fixedly upwards and measuring primordial radiation. It was originally emitted at a wavelength of 21 centimeters, a key spectral tracer for the neutral hydrogen atom. The photons have been been stretched by a factor of 10 or more since it was emitted some 13 billion years ago, making the detections more easily measured.

    The signal is nonetheless weak and has been difficult to measure. Previous experiments, such as the UC Berkeley-led Precision Array Probing the Epoch of Reionization (PAPER) in South Africa and the Murchison Widefield Array (MWA) in Australia, have not been sufficiently powerful and sensitive. But HERA is much more powerful and hopes are high.

    uc-berkeley-led-precision-array-probing-the-epoch-of-reionization-paper
    UC Berkeley led Precision Array Probing The Epoch Of Reionization (PAPER)

    SKA Murchison Widefield Array, in Western Australia
    SKA Murchison Widefield Array, in Western Australia

    The researchers will be looking for the boundaries between those bubbles of ionized hydrogen around early stars — which are invisible to HERA — and the surrounding neutral or atomic hydrogen being measured. By tuning the receiver to different wavelengths, they can map the bubble boundaries at different distances to follow the the evolution of the bubbles over time.

    HERA is being constructed at the Karoo desert site where PAPER was deployed. Joining the Berkeley team will be scientists from England, South Africa, Italy, MIT, the National Radio Astronomical Observatory, the University of Washington, Arizona State University and others.

    HERA was recently granted the status of a precursor telescope for the Square Kilometer Array (SKA), an ambitious project to build a vast collection of radio dishes around Africa and Australia — thereby creating the largest astronomical observatory of all time. HERA is located close by one of the South African SKA sites.

    See the full article here .

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    About Many Worlds

    There are many worlds out there waiting to fire your imagination.

    Marc Kaufman is an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer, and is the author of two books on searching for life and planetary habitability. While the “Many Worlds” column is supported by the Lunar Planetary Institute/USRA and informed by NASA’s NExSS initiative, any opinions expressed are the author’s alone.

    This site is for everyone interested in the burgeoning field of exoplanet detection and research, from the general public to scientists in the field. It will present columns, news stories and in-depth features, as well as the work of guest writers.

    About NExSS

    The Nexus for Exoplanet System Science (NExSS) is a NASA research coordination network dedicated to the study of planetary habitability. The goals of NExSS are to investigate the diversity of exoplanets and to learn how their history, geology, and climate interact to create the conditions for life. NExSS investigators also strive to put planets into an architectural context — as solar systems built over the eons through dynamical processes and sculpted by stars. Based on our understanding of our own solar system and habitable planet Earth, researchers in the network aim to identify where habitable niches are most likely to occur, which planets are most likely to be habitable. Leveraging current NASA investments in research and missions, NExSS will accelerate the discovery and characterization of other potentially life-bearing worlds in the galaxy, using a systems science approach.
    The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.

    President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

    Since that time, most U.S. space exploration efforts have been led by NASA, including the Apollo moon-landing missions, the Skylab space station, and later the Space Shuttle. Currently, NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle and Commercial Crew vehicles. The agency is also responsible for the Launch Services Program (LSP) which provides oversight of launch operations and countdown management for unmanned NASA launches. Most recently, NASA announced a new Space Launch System that it said would take the agency’s astronauts farther into space than ever before and lay the cornerstone for future human space exploration efforts by the U.S.

    NASA science is focused on better understanding Earth through the Earth Observing System, advancing heliophysics through the efforts of the Science Mission Directorate’s Heliophysics Research Program, exploring bodies throughout the Solar System with advanced robotic missions such as New Horizons, and researching astrophysics topics, such as the Big Bang, through the Great Observatories [Hubble, Chandra, Spitzer, and associated programs. NASA shares data with various national and international organizations such as from the [JAXA]Greenhouse Gases Observing Satellite.

     
  • richardmitnick 1:32 pm on September 16, 2016 Permalink | Reply
    Tags: , , Epoch of Reionization, HERA collaboration, , ,   

    From UC Berkeley and SKA: “Funding boost for SKA Precursor HERA telescope – What happened after the lights came on in the universe?” 

    UC Berkeley

    UC Berkeley

    SKA Square Kilometer Array

    SKA

    From SKA:
    Friday 21 September 2016, SKA Global Headquarters, UK – The Hydrogen Epoch of Reionisation Array (HERA) has been awarded international funding with a $9.5 million investment to expand its capabilities, as announced on Wednesday 14th September by the US National Science Foundation.

    1
    Image of the [beginnings of] HERA telescope at the Losberg Site in the Karoo desert. Credit: Danny Jacobs

    HERA, which was recently granted the status of SKA precursor telescope by SKA Organisation, currently has 19, 14-metre radio dishes at the SKA South Africa Losberg site near Carnarvon. With this fresh injection of $9.5 million, this will allow the array to expand to 220 radio dishes by 2018.

    HERA is an experiment focused on one science goal – detecting the Epoch of Reionization signal – and is not a general facility. As part of this effort, HERA is developing techniques, algorithms, calibration and processing pipelines and hardware optimised towards the detection of the power spectrum of the EOR, all of which will benefit SKA in designing and eventually operating the SKA-low telescope to be based in Australia.

    From UC Berkeley:

    September 14, 2016
    Robert Sanders

    An experiment to explore the aftermath of cosmic dawn, when stars and galaxies first lit up the universe, has received nearly $10 million in funding from the National Science Foundation to expand its detector array in South Africa.

    2
    The HERA collaboration expects eventually to expand to 330 radio dishes in the core array, each pointed straight up to measure radiation originally emitted some 13 billion years ago. Twenty outrigger dishes (not shown) are also planned, bringing the array up to 350 dishes total.

    The experiment, an international collaboration called the Hydrogen Epoch of Reionization Array, or HERA, currently has 19 14-meter (42-foot) radio dishes aimed at the southern sky near Carnarvon, South Africa, and will soon up that to 37. The $9.5 million in new funding will allow the array to expand to 240 radio dishes by 2018.

    Led by UC Berkeley, HERA will explore the billion-year period after hydrogen gas collapsed into the first stars, perhaps 100 million years after the Big Bang, through the ignition of stars and galaxies throughout the universe. These first brilliant objects flooded the universe with ultraviolet light that split or ionized all the hydrogen atoms between galaxies into protons and electrons to create the universe we see today.

    “The first galaxies lit up and started ionizing bubbles of gas around them, and soon these bubbles started percolating and intersecting and making bigger and bigger bubbles,“ said Aaron Parsons, a UC Berkeley associate professor of astronomy and principal investigator for HERA. “Eventually, they all intersected and you got this über bubble, leaving the universe as we observe it today: Between galaxies the gas is essentially all ionized.“

    That’s the theory, anyway. HERA hopes for the first time to observe this key cosmic milestone and then map the evolution of reionization to about 1 billion years after the Big Bang.

    “We have leaned a ton about the cosmology of our universe from studies of the cosmic microwave background, but those experiments are observing just the thin shell of light that was emitted from a bunch of protons and electrons that finally combined into neutral hydrogen 380,000 years after the Big Bang,“ he said. “We know from these experiments that the universe started out neutral, and we know that it ended ionized, and we are trying to map out how it transitioned between those two.“

    “Before the cosmic dawn, the universe glowed from the cosmic microwave background radiation, but there weren’t stars lighting up the universe,“ said David DeBoer, a research astronomer in UC Berkeley’s Radio Astronomy Laboratory. “At some point the neutral hydrogen seeded the stars and black holes and galaxies that relit the universe and led to the epoch of reionization.“

    3
    A 13.8-billion-year cosmic timeline indicates the era shortly after the Big Bang observed by the Planck satellite, the era of the first stars and galaxies observed by HERA and the era of galaxy evolution to be observed by NASA’s future James Webb Space Telescope. (HERA image)

    The HERA array, which could eventually expand to 350 telescopes, consists of radio dishes staring fixedly upwards, measuring radiation originally emitted at a wavelength of 21 centimeters – the hyperfine transition in the hydrogen atom – that has been red-shifted by a factor of 10 or more since it was emitted some 13 billion years ago. The researchers hope to detect the boundaries between bubbles of ionized hydrogen – invisible to HERA – and the surrounding neutral or atomic hydrogen.

    By tuning the receiver to different wavelengths, they can map the bubble boundaries at different distances or redshifts to visualize the evolution of the bubbles over time.

    “HERA can also tell us a lot about how galaxies form,“ Parsons said. “Galaxies are very complex organisms that feed back on themselves, regulating their own star formation and the gas that falls into them, and we don’t really understand how they live, especially at this early time when flowing hydrogen gas ends up as complex structures with spiral arms and black holes in the middle. The epoch of reionization is a bridge between the cosmology that we can theoretically calculate from first principles and the astrophysics we observe today and try to understand.“

    UC Berkeley’s partners in HERA are the University of Washington, UCLA, Arizona State University, the National Radio Astronomical Observatory, the University of Pennsylvania, the Massachusetts Institute of Technology, Brown University, the University of Cambridge in the UK, the Square Kilometer Array in South Africa and the Scuola Normale Superiore in Pisa, Italy.

    Other collaborators are the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, the University of KwaZulu Natal, the University of Western Cape and Rhodes University, all in South Africa, and California State Polytechnic University in Pomona.

    “Astronomers want to know what happened to the universe after it emerged from its so-called ‘dark ages’,” said Rich Barvainis, director of the National Science Foundation program that funds HERA. “HERA will help us answer that question, not by studying the primordial stars and galaxies themselves, but rather by studying how these objects changed the nature of intergalactic space.”

    Searching for a firefly on a searchlight

    The key to detecting these percolating bubbles of ionized gas from the epoch of reionization is a receiver that can detect radio signals from neutral hydrogen a million times fainter than nearby radio noise.

    “The foreground noise, mostly synchrotron emission from electrons spiraling in magnetic fields in our own galaxy, is about a million times stronger than the signal,“ DeBoer said. “This is a real problem, because it’s like looking for a firefly in front of an incredibly powerful searchlight. We are trying to see the firefly and filter out the searchlight.“

    Previous experiments, such as the UC Berkeley-led Precision Array Probing the Epoch of Reionization (PAPER) in South Africa and the Murchison Widefield Array (MWA) in Australia, have not been sensitive enough to detect this signal, but with larger dishes and better signal processing, HERA should do the trick.

    “HERA is a unique, next-generation instrument building on the heritage of PAPER,“ said Parsons, who helped build PAPER a decade ago when he was a graduate student working with the late UC Berkeley astronomer Donald Backer. “It is on the same site as PAPER, we are using a lot of the same equipment, but importantly we have brought together a lot more collaborators, including a lot of the U.S. team that has been working with MWA.“

    The strategy is to build a hexagonal array of radio dishes that minimizes the noise, such as radio reflections in the dishes and wires, that would obscure the signal. A supercomputer’s worth of field programmable gate arrays will cross-correlate the signals from the antennas to finely map a 10-degree swath of southern sky centered at minus-30 degrees latitude. Using a technique adopted from PAPER, they will employ this computer processing power to eliminate the slowly varying noise across the wavelength spectrum – 150-350 centimeters – to reveal the rapidly varying signal from neutral hydrogen as they tune across the radio spectrum.

    Astronomers have already discovered hints of reionization, Parsons said. Measurements of the polarization of the cosmic microwave background radiation show that some of the photons emitted at that early time in the universe have been scattered by intervening electrons possibly created by the first stars and galaxies. And galaxy surveys have turned up some very distant galaxies that show attenuation by intervening intergalactic neutral hydrogen, perhaps the last bit remaining before reionization was complete.

    “We have an indication that reionization should have happened, and we are getting hints of when it might have ended, but we don’t have anything telling us what is going on during it.,“ Parsons added. “That is what we hope to learn with HERA, the actual step-by-step process of how reionization happened.“

    Once astronomers know the reionization process, they can calculate the scattering of radiation from the era of recombination – the cosmic background radiation, or CMB – and remove some of the error that makes it hard to detect the gravitational waves produced by inflation shortly after the Big Bang.

    “There is a lot of cosmology you can do with HERA,“ Parsons said. “We have learned so much from the thin shell of the CMB, but here we will be looking at a full three-dimensional space. Something like 80 percent of the observable universe can be mapped using the 21-centimeter line, so this opens up the next generation of cosmology.“

    Parsons and DeBoer compare HERA to the first experiment to detect the cosmic microwave background radiation, the Cosmic Background Explorer, which achieved its goal in 1992 and won for its leaders – George Smoot of UC Berkeley and Lawrence Berkeley National Laboratory, and John Mather of NASA – the 2006 Nobel Prize in Physics.

    “Ultimately, the goal is to get to the point were we are actually making images, just like the CMB images we have seen,“ DeBoer said. “But that is really, really hard, and we need to learn a fair bit about what we are looking for and the instruments we need to get there. We hope that what we develop will allow the Square Kilometre Array or another big project to actually make these images and get much more science from this pivotal epoch in our cosmic history.“

    See the full SKA article here .
    See the UC Berkeley press release here .
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    Founded in the wake of the gold rush by leaders of the newly established 31st state, the University of California’s flagship campus at Berkeley has become one of the preeminent universities in the world. Its early guiding lights, charged with providing education (both “practical” and “classical”) for the state’s people, gradually established a distinguished faculty (with 22 Nobel laureates to date), a stellar research library, and more than 350 academic programs.

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  • richardmitnick 4:41 am on October 30, 2015 Permalink | Reply
    Tags: , , , Epoch of Reionization   

    From CAASTRO: “onospheric effects not detrimental to EoR detection from ground” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    30 October 2015

    Temp 1

    The Epoch of Reionisation (EoR) is the time in the early Universe when the first stars and galaxies formed and re-ionised the neutral hydrogen. Indirect information about the EoR has been obtained from the Cosmic Microwave Background [CMB] and spectra of the distant quasars.

    CMB Planck ESA
    CMB per ESA/Planck

    ESA Planck
    ESA/Planck

    However, the bulk of information about the physical parameters of the EoR is encoded in the 21cm line (1420 MHz) from neutral hydrogen redshifted into the low radio frequency range 200 – 50 MHz, for redshifts of 6 < z < 30.

    The observational approaches range from large interferometer arrays to single antenna experiments. The latter, so-called global EoR experiments, spatially average the signal from the entire visible sky and try to identify the tiny signature of the EoR (of order 100 milliKelvin, which is a few orders of magnitude smaller than the Galactic foregrounds) in the sky-averaged spectrum. This extremely challenging precision requires very long observations (hundreds of hours) to achieve a sufficiently high signal-to-noise ratio. Moreover, ground-based global EoR experiments are affected by frequency-dependent effects (i.e. absorption and refraction) due to the propagation of radio-waves in the Earth’s ionosphere. The amplitude of these effects changes in time. There has therefore been an ongoing discussion in the literature on the importance of ionospheric effects and whether the global EoR signature can feasibly be detected from the ground.

    Advanced Ligo
    MIT Advanced Ligo interferometry

    The team of CAASTRO researches at Curtin University, led by Dr Marcin Sokolowski, used three months’ worth of 2014/2015 data collected with the BIGHORNS system with a conical log-spiral antenna deployed at the Murchison Radio-astronomy Observatory to study the impact of the ionosphere on its capability to detect the global EoR signal.

    CAASTRO BIGHORNS
    BIGHORNS

    Comparison of data collected on different days at the same sidereal time enabled the researchers to infer some properties of the ionosphere, such as electron temperature (Te≈470 K at night-time) and amplitude and variability of ionospheric absorption of radio waves. Furthermore, the data sample shows that the sky-averaged spectrum indeed varies in time due to fluctuations of these ionospheric properties. Nevertheless, the data analysis indicates that averaging over very long observations (several days or even several weeks) suppresses the noise and leads to an improved signal-to-noise ratio. Therefore, the ionospheric effects and fluctuations are not fundamental impediments that prevent ground-based instruments, such as BIGHORNS, from integrating down to the precision required for global EoR experiments, provided that the ionospheric contribution is properly accounted for in the data analysis.

    Publication details:
    Marcin Sokolowski, Randall Wayth, Steven Tremblay, Steven Tingay et al. in ApJ (2015) The impact of the ionosphere on ground-based detection of the global Epoch of Reionisation signal

    See the full article here .

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    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.

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  • richardmitnick 5:28 am on October 20, 2015 Permalink | Reply
    Tags: , , , Epoch of Reionization,   

    From CAASTRO: “Interplanetary scintillation found to contaminate the EoR signal” 

    CAASTRO bloc

    CAASTRO ARC Centre of Excellence for All Sky Astrophysics

    20 October 2015
    No Writer Credit

    The Epoch of Reionisation (EoR) is a period in the early Universe when the first stars and galaxies began radiating. Before this time, the Universe existed in the Dark Ages, a time marked by a lack of radiating sources and a neutral hydrogen intergalactic medium. During the EoR, the ionising radiation from these first sources stripped the electrons from these hydrogen atoms, transitioning the Universe from dark and neutral to bright and ionised. The details of this transition promise to provide a wealth of information about structure formation in the Universe but the radio signal we are trying to detect to trace it is extremely weak. Much more prominent in the radio sky are the numerous foreground sources, such as Active Galactic Nuclei and radio galaxies, that ‘contaminate’ our signal. In the EoR experiments with the Murchison Widefield Array (MWA), and others, we use our knowledge of these bright foregrounds, along with some signal processing tricks, to discriminate the EoR signal from the contaminants.

    SKA Murchison Widefield Array
    SKA/MWA

    However, if the contaminants differ from our expectations, then residual signal may affect our ability to observe the early Universe. Interplanetary scintillation (IPS) is a potential candidate to create this kind of issue.

    Temp 1
    No image credit

    IPS is typically observed as the twinkling of radio sources due to their light interacting with solar plasma before reaching our telescopes. Electrons and other ionised particles (plasma) flowing in the solar wind interact with the light from distant objects, distorting and refracting the wavefronts. The constructive and destructive interference of these wavefront distortions, as seen by the telescope, apparently increases or decreases the strength of the signal, compared with expectations. Such behaviour has the potential to add unexpected and time-dependent power to the EoR data and to further contaminate the signal. Following the measurement of IPS in two bright radio sources in the MWA EoR field by Kaplan et al. (2015), Curtin University based CAASTRO members Dr Cathryn Trott and Prof Steven Tingay explored the importance of considering IPS contamination for EoR experiments in their recent publication.

    Taking a statistical approach, they took the measured spatial and temporal properties of IPS from results in the literature spanning 50 years and imprinted this signature on the expected, static properties of foreground radio sources in EoR data. The researchers found that IPS has different spatial and spectral properties to the static radio sources themselves, producing a unique, but low-level, signature in the EoR data. Having considered normal IPS conditions, they concluded that IPS would not be a major contributor to EoR contamination but that it should be considered in the modelling due to its distinct behaviour to avoid bias in the final results. This conclusion has potential implications for future, large-scale EoR experiments, such as with the Square Kilometre Array (SKA).

    SKA Square Kilometer Array

    See the full article here .

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    Astronomy is entering a golden age, in which we seek to understand the complete evolution of the Universe and its constituents. But the key unsolved questions in astronomy demand entirely new approaches that require enormous data sets covering the entire sky.

    In the last few years, Australia has invested more than $400 million both in innovative wide-field telescopes and in the powerful computers needed to process the resulting torrents of data. Using these new tools, Australia now has the chance to establish itself at the vanguard of the upcoming information revolution centred on all-sky astrophysics.

    CAASTRO has assembled the world-class team who will now lead the flagship scientific experiments on these new wide-field facilities. We will deliver transformational new science by bringing together unique expertise in radio astronomy, optical astronomy, theoretical astrophysics and computation and by coupling all these capabilities to the powerful technology in which Australia has recently invested.

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