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  • richardmitnick 10:15 am on November 8, 2016 Permalink | Reply
    Tags: , , , , Hubble finds galaxy GN-z11 as it was 13.4 billion years ago   

    From astrobites: “The Origins and Fate of the Most Distant Galaxy” 

    Astrobites bloc


    Nov 8, 2016
    Steph Greis

    Title: Dark-ages reionization & galaxy formation simulation VI: The origins and fate of the highest known redshift galaxy
    Authors: Simon J. Mutch, Chuanwu Liu, Gregory B. Poole et al.
    First Author’s Institution: University of Melbourne
    Status: submitted to MNRAS

    Looking into the far reaches of the observable Universe is like rewinding a very long video tape and gazing into the distant past. Since light has a speed limit, it takes time to reach us from the very distant sources, and since the Universe is expanding, the observed light is also stretched relative to when it was emitted – which is very useful for astronomers, as we can use the amount by which it has been stretched to figure out how far away a distant object is. This is known as the cosmological redshift.

    The Most Distant Galaxy

    The main protagonist in today’s paper was found using the Wide Field Camera 3 on-board the Hubble Space Telescope; its name: GN-z11, and yes, it has its own wikipedia page!

    Hubble Space Telescope astronomers, studying the northern hemisphere field from the Great Observatories Origins Deep Survey (GOODS), have measured the distance to the farthest galaxy ever seen. The survey field contains tens of thousands of galaxies stretching far back into time. Galaxy GN-z11, shown in the inset, is seen as it was 13.4 billion years in the past, just 400 million years after the big bang, when the universe was only three percent of its current age. The galaxy is ablaze with bright, young, blue stars, but looks red in this image because its light has been stretched to longer spectral wavelengths by the expansion of the universe.
    Date 11 February 2015 and 3 April 2015

    Oesch et al were recently able to identify this galaxy, at a redshift of just over 11, meaning that the light we observe from it left the galaxy GN-z11 when the Universe was a mere 400 million years old, and had been travelling for over 13.3 billion years before reaching our telescopes. While being the most distant galaxy ever discovered should be enough, this object was also found to be extremely luminous (hence making it possible to discover it at such an enormous distance in the first place): according to the authors of today’s paper, GN-z11 is approximately 3 times more luminous than a typical galaxy at redshifts 7-8, i.e. one that is closer than GN-z11 and hence would be expected to be brighter! This makes objects like GN-z11 extremely rare, and begs the question of how such a galaxy might have formed, and what it might evolve into?

    Comparisons to Models

    To answer these questions, the authors make use of a galaxy formation model to investigate whether such models would predict the existence of such extreme systems as GN-z11, and if so, what their properties, origins and possible fates are. By studying a volume of modelled cosmological space comparable to that probed for the discovery of GN-z11, they find two distant galaxies with ultraviolet brightnesses similar to those of GN-z11. This suggests that such luminous galaxies may in, fact, be more common during the early phases of galaxy formation than had previously been thought.

    Fig. 1: The ultraviolet luminosity function, indicating how many galaxies of a certain brightness can be found in a given volume at redshifts 6 (blue line), 8 (magenta) and 11.1 (grey). The x-axis indicates the brightness in UV (increasing to the right), while the y-axis gives a measure for how many galaxies there are within a certain volume of a given brightness). The luminosities of the two model analogue galaxies, DR-1 and DR-2, are indicated by a green circle and orange square respectively, while the location of GN-z11 is shown by the red pentagon. The locations and uncertainties of previous observations are show on both the redshift 6 and 8 lines. The good agreement between the observed values and the model predictions demonstrates the success of the model, and gives the authors confidence in the data for the two model analogue galaxies.

    Finding these model galaxies also allowed the authors to use them as analogues to learn more about the properties of GN-z11. But first they needed to check whether the Universe in their models was actually reproducing the observations in the real world. To do this, the authors compared how many bright galaxies the model predicted at lower redshifts, i.e. in the more recent history of the Universe, to how many had been observed. Finding good agreement between the observational data and the model results (see the magenta and blue lines in Fig. 1), the authors felt confident that they could trust the results of the very distant redshift 11 models. Hence they selected the two brightest model galaxies at redshift 11, calling them DR-1 and DR-2 (see Fig. 2). Both showed good agreement with the observational measurements of GN-z11 and hence by learning about their origins and eventual fate, it should be possible to learn more about GN-z11 itself. DR-1 and DR-2 are the two most massive galaxies in the simulations (at redshift ~11) and live in the two most massive subhaloes. They are rare outliers from the majority of the modelled galaxy population, not only in terms of their brightness, but also with their stellar masses and star formation rates.

    Fig. 2: The histories of the two model galaxies, DR-1 and DR-2 (green line and orange dashed line respectively) between redshifts 18 and 6, spanning the cosmic time period when the Universe was between 200 million and 1 billion years old. The available data points for GN-z11 are indicated at the appropriate redshift/time by a red pentagon. From top to bottom, the panels show: absolute ultraviolet magnitude, star formation rates, stellar mass, subhalo mass, fraction of cold gas within the galaxy, radius of the galaxy, mass ratios of any mergers. For comparison, thin grey lines and dots are also shown to indicate the histories of the ten next-most-luminous galaxies selected at redshift 11.

    The Origin of GN-z11

    Several interesting questions remain: how do such massive systems for so rapidly? The age of the Universe at redshift 11 is a mere few hundred million years which does not give these galaxies a lot of time to assemble themselves. And is their extreme brightness only a transient feature, e.g. due to a recent merger or other event? And if not, then how can the level of star formation required to produce such high numbers of new, ultraviolet luminous stars be sustained? This is where the simulated galaxies came in handy.

    By studying the simulations, the authors could determine that the subhalo in which DR-1 resides grew by a factor of 5 in just 65 million years in the time period immediately before redshift 11, resulting in a stellar mass growth of the galaxy by a factor of 9 during this period. Additionally, it appears that the analogue galaxies’ extreme brightness is not a transient feature but instead that their star formation rates and ultraviolet luminosities remain high, or even increase during their evolution. This is puzzling, however; high star formation rates should result in large amounts of energy from supernova being fed into the interstellar medium, which heats it and ejects cold gas from the galaxy – thereby curtailing star formation in a negative feedback cycle. What the authors found for the analogue galaxies, though, is that they have fewer such depletion events. This is likely due to the large reservoirs of cold gas available to these galaxies, which means that only a small fraction of the available material is used up during any one episode of star formation. Additionally, mergers are known to trigger rapid star formation which could deplete such gas reservoirs. However, the authors find that neither DR-1 nor DR-2 has experienced a major merger.

    The Fate of GN-z11

    Fast-forwarding the tape of cosmic evolution simulations to a time when the Universe was approximately 1 billion years old allows the authors to investigate what might become of galaxies like GN-z11. Interestingly, they find that both DR-1 and DR-2 continue to grow steadily, and they remain both massive and luminous. However, while they were clear outliers – booming at redshift 11 – by the time the Universe reaches 1 billion years of age, they are no longer among the brightest or most massive objects in the simulations.

    And so it appears that, even though GN-z11 was outstanding during the Universe’s early years, it is likely merely the progenitor of a more common massive galaxy in the slightly more evolved Universe…

    See the full article here .

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    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.
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  • richardmitnick 1:34 pm on March 3, 2016 Permalink | Reply
    Tags: , , Hubble finds galaxy GN-z11 as it was 13.4 billion years ago,   

    From Hubble: “Hubble Team Breaks Cosmic Distance Record” 

    NASA Hubble Banner

    NASA Hubble Telescope


    March 3, 2016
    Felicia Chou
    NASA Headquarters, Washington, D.C.

    Ann Jenkins / Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4488 / 410-338-4514
    jenkins@stsci.edu / villard@stsci.edu

    Pascal Oesch
    Yale University, New Haven, Connecticut

    Gabriel Brammer
    Space Telescope Science Institute, Baltimore, Maryland

    Garth Illingworth
    University of California, Santa Cruz, California

    NASA Hubble Distant Galaxy GN-z11
    Credit: NASA, ESA, P. Oesch (Yale University), G. Brammer (STScI), P. van Dokkum (Yale University), and G. Illingworth (University of California, Santa Cruz)
    Release Date: March 3, 2016

    By pushing NASA’s Hubble Space Telescope to its limits, an international team of astronomers has shattered the cosmic distance record by measuring the farthest galaxy ever seen in the universe. This surprisingly bright, infant galaxy, named GN-z11, is seen as it was 13.4 billion years in the past, just 400 million years after the big bang. GN-z11 is located in the direction of the constellation of Ursa Major.

    “We’ve taken a major step back in time, beyond what we’d ever expected to be able to do with Hubble. We see GN-z11 at a time when the universe was only three percent of its current age,” explained principal investigator Pascal Oesch of Yale University in New Haven, Connecticut. The team includes scientists from Yale University, the Space Telescope Science Institute (STScI) in Baltimore, Maryland, and the University of California in Santa Cruz, California.

    Astronomers are closing in on the first galaxies that formed in the universe. The new Hubble observations take astronomers into a realm that was once thought to be only reachable with NASA’s upcoming James Webb Space Telescope.

    NASA Webb telescope annotated

    This measurement provides strong evidence that some unusual and unexpectedly bright galaxies found earlier in Hubble images are really at extraordinary distances. Previously, the team had estimated GN-z11’s distance by determining its color through imaging with Hubble and NASA’s Spitzer Space Telescope.

    NASA Spitzer Telescope

    Now, for the first time for a galaxy at such an extreme distance, the team used Hubble’s Wide Field Camera 3 to precisely measure the distance to GN-z11 spectroscopically by splitting the light into its component colors.

    NASA Hubble WFC3

    Astronomers measure large distances by determining the redshift of a galaxy. This phenomenon is a result of the expansion of the universe; every distant object in the universe appears to be receding from us because its light is stretched to longer, redder wavelengths as it travels through expanding space to reach our telescopes. The greater the redshift, the farther the galaxy.

    “Our spectroscopic observations reveal the galaxy to be even farther away than we had originally thought, right at the distance limit of what Hubble can observe,” said Gabriel Brammer of STScI, second author of the study.

    Before astronomers determined the distance for GN-z11, the most distant galaxy measured spectroscopically had a redshift of 8.68 (13.2 billion years in the past). Now, the team has confirmed GN-z11 to be at a redshift of 11.1, nearly 200 million years closer to the time of the big bang. “This is an extraordinary accomplishment for Hubble. It managed to beat all the previous distance records held for years by much larger ground-based telescopes,” said investigator Pieter van Dokkum of Yale University. “This new record will likely stand until the launch of the James Webb Space Telescope.”

    The combination of Hubble’s and Spitzer’s imaging reveals that GN-z11 is 25 times smaller than the Milky Way and has just one percent of our galaxy’s mass in stars. However, the [then] newborn GN-z11 is growing fast, forming stars at a rate about 20 times greater than our galaxy does today. This makes such an extremely remote galaxy bright enough for astronomers to find and perform detailed observations with both Hubble and Spitzer.

    The results reveal surprising new clues about the nature of the very early universe. “It’s amazing that a galaxy so massive existed only 200 million to 300 million years after the very first stars started to form. It takes really fast growth, producing stars at a huge rate, to have formed a galaxy that is a billion solar masses so soon,” explained investigator Garth Illingworth of the University of California, Santa Cruz.

    These findings provide a tantalizing preview of the observations that the James Webb Space Telescope will perform after it is launched into space in 2018. “Hubble and Spitzer are already reaching into Webb territory,” Oesch said. “This new discovery shows that the Webb telescope will surely find many such young galaxies reaching back to when the first galaxies were forming,” added Illingworth.

    This discovery also has important consequences for NASA’s planned Wide-Field Infrared Survey Telescope (WFIRST), which will have the ability to find thousands of such bright, very distant galaxies.


    The team’s findings will appear in the March 8, 2016, edition of The Astrophysical Journal.

    The science team includes P. Oesch (Yale University), G. Brammer (STScI), P. van Dokkum (Yale University), G. Illingworth (University of California, Santa Cruz), R. Bouwens, I. Labbé, and M. Franx (Leiden University), I. Momcheva, M. Ashby, and G. Fazio (Harvard-Smithsonian Center for Astrophysics), V. Gonzalez (University of California, Riverside), B. Holden and D. Magee (UCO/Lick Observatory/University of California, Santa Cruz), R. Skelton (South African Astronomical Observatory), R. Smit (Durham University), L. Spitler (Macquarie University/Australian Astronomical Observatory), M. Trenti (University of Melbourne), and S. Willner (Harvard-Smithsonian Center for Astrophysics).

    See the full article here .

    Please help promote STEM in your local schools.

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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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