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Accurate measurement of z = 8.68 galaxy

  1. Sep 6, 2015 #1


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    Lyman-alpha Emission from a Luminous z=8.68 Galaxy: Implications for Galaxies as Tracers of Cosmic Reionization
    Adi Zitrin, Ivo Labbe, Sirio Belli, Rychard Bouwens, Richard S. Ellis, Guido Roberts-Borsani, Daniel P. Stark, Pascal A. Oesch, Renske Smit
    (Submitted on 9 Jul 2015, last revised 13 Aug 2015)
    We report the discovery of Lyman-alpha emission (Lyα) in the bright galaxy EGSY-2008532660 (hereafter EGSY8p7) using the MOSFIRE spectrograph at the Keck Observatory...
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  3. Sep 7, 2015 #2


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    Z = 8.68? Wow, that's pretty old...
  4. Sep 7, 2015 #3


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    Yes it is! In the commentary I've seen the point was made that the special value of this work is in the reliability and precision of the measurement.
    There may be other cases where the astronomers THINK they have found z ≈ 9 galaxies, but either did not find Lyman-alpha light to work with or did not make use of as fine a spectrograph. Here the level of confidence is high. So it is a kind of landmark (although older galaxies may already have been discovered.)
  5. Sep 8, 2015 #4
    Just how old? I calculated 570,000 years after the Big Bang, 13.23 billion years ago, and a co-moving distance of 9333.95 Mpc (3x1010 light years)
  6. Sep 8, 2015 #5
    Hi, I think there should be no misconceptions about young and old objects in the universe.
    570,000 years after the Big Bang should be named pretty "Young" (in the early universe)
    Against it, our Milky Way seems to be pretty "Old", namely approx. 13.7 billion years.

    But really fantastic, observing the galaxy's strong 0.1216 μm UV lya-emission @ 1.1776 μm, stretched by redshift of z = 8.68+1 = 9.68
    (all the more precisely detected by an earth-bound telescope)!

    But to me questions arise: The work of
    Roberts-Borsani, G. W., Bouwens, R. J., Oesch, P. A., et al.
    2015, arXiv, 1506.00854

    is cited, where they report the space-based IR-Spitzer detection of this galaxy EGSY-2008532660:
    They additionally found strong Oxygen emission in the 4.5 μm band (the green line @0.56 μm stretched to 5.4 μm)
    So much Oxygen in such a young galaxy?
    Also the flux in the 3.6-4.5 μm bands (i.e. rest λ 0.37-0.46 μm) is pretty bright, much brighter than in UV
    and in that λ-range the angular diameter is as large as 2" x 2" instead approx. 0.5" x 0.5" in UV
    as can be seen on page 5, fig. 3.
    Obviously our universe is fairly a curved one, where above z ≈ 1...1.5 the objects again appear larger and brighter
    Just from these observations EGSY-2008532660 seems to be a normal galaxy with a normal spectral energy distribution,
    where the UV-flux is generally 1...2 orders of magnitude lower than that at 0.6...1.0 μm.
  7. Sep 15, 2015 #6
    Hi grauitate:

    I find your conclusion fascinating that this new astronomoical data implies the universe is not flat. From the data you found in the Zitrin et all article, can you calculate a rough estimate for the curvature?
  8. Sep 15, 2015 #7


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    You dropped some factors of 10. I think it is 0.579 GY, which is 579,000,000 years after the big bang.
  9. Sep 15, 2015 #8
    You're right phyzguy. I actually calculated 0.57 GY and left off a comma and 3 zeros when I converted it. I'll be standing in the corner in shame now...
  10. Sep 15, 2015 #9
    Cheer up, you might have a bright future as a politician.
  11. Sep 15, 2015 #10
    Not so severe, I overlooked it too! My calculation gives roughly t = t0 (1- (z2 + 2z)/(z2 + 2z +2)) = 289.3 Million years after BB.
    So still rather young! Only 2.1 ... 4.2 % of evolution-time gone.

    Unfortunately the paper of Zitrin et al. unveils no angular size of EGSY8p7 in UV (or do I overlook it ?).
    But the EGSY-2008532660 (here-after the EGSY8p7) was measured in arXiv 1506.00854 in IR at 3.6/4.5 μm and was found to be approx. 2" in diameter in the 4" x 4" stamp, and as I suggested this as an normal galaxy which bright core of ≈ 10 kpc should appear at approx. 0.5" at that distance in a flat universe - then the enlargement factor would be in the range 2"/0.5" = 4. Sorry and shame on me, except this general enlargement phenomenon which I connect to a curved universe in the moment I do not have the proper formulas available for presentation to derive a reliable value of curvature from that, not even an estimate.
    (as far as I found there are a lot of angular size data available from the 2009 SEDS-project, e.g. https://www.cfa.harvard.edu/SEDS/presentations.html,
    in 5 x 5 arcmin stamps - this will be future work to estimate enlargement factors from there and then a cautious value of curvature)
  12. Sep 20, 2015 #11
    Hi @grauitate:

    Thanks very much for your response to my question. I hope that within the next few years there will be an estimate about a curvature value.

  13. Sep 20, 2015 #12


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    Buzz Bloom and gravitate, I think you are confused. The fact that distant objects appear larger than you would calculate from a naive flat space model is a consequence of the expansion of the universe, and does not require the universe to be curved. In fact a factor of 4 magnification for an object at this distance is about what the Lambda-CDM model of an expanding flat universe predicts. I suggest David Hogg's "Distance Measures in Cosmology" for an explanation of how to do these calculations.
  14. Sep 20, 2015 #13
    Hi phyzguy:

    If I understand your post correctly, you are saying that the particular results from Zitrin et al. do not imply curvature. I am not skilled enough to evaluate Zitrin et al. regarding this point, and I thank you for the citation.

    I do understand that if a curvature term Ωk is included with ΩΛ, Ωm, and Ωr, in the equation relating t and a, and if Ωk is large enough, one would expect to see changes in the calculation of the corresponding relationship between z and brightness relative to a value for Ωk = 0.

  15. Sep 21, 2015 #14
    Thank you, phyzguy and Buzz Bloom, for your responses to my estimation and assumption of a curved universe.
    And by the way thanks to the inventors and operators of this nice forum.

    I took it just from observational results. For me the most natural explanation of the enlargement phenomenon wihich can be observed from far distant galaxies with redshifts larger than 1...1.2 is that the universe in total is curved, as can be assumed e.g. by the sum of all lensing effects, which enlarge and enlight galaxies that are far behind a foreground galaxy or a galaxy cluster (including pretty much of dark matter). This is a true curvature effect where the rays of the light take the line of the geodetics that are stamped by the foreground masses. Extrapolating this to very early galaxies like e.g. this z = 8.68 EGSY8p7 at a youth of ≈ 0.3 ...0.6 Gy means that we observe it through the mass and dark matter of nearly the entire later and accordingly older universe which performs like a giant magnification lens.
    On the other hand, of course, we have the calculations made for an expanding flat universe, which, as mentioned by phyzguy, are thoroughly described in David Hogg's "Distance Measures in Cosmology": Amazingly here we find a similar enlargement effect: Of course, early galaxies appear closer, larger and brighter (at their rest-wavelength) to us, because at the time of their light emission the universe was much smaller and therefore the distances between the galaxies as well. This sounds very plausible and evident.

    Now, may be the confusion comes neither from grauitate nor from Buzz Bloom, but from the principle of equivalence by Einstein: By no means the observer in the windowless lift-cabin cannot decide whether she or he feels heavy-weight, either by an accelerated motion or by a stationary gravitational field. It is left to here or him as a matter of taste, what's might be right. The same it is with redshift: Only by observing the increasing redshifts we cannot decide if its due to the accelerated receiding motion of the galaxies in a flat universe (Doppler-shift) or if its due to galaxies resting in a mean constant and inherent isotropic gravitational field of an entire curved universe (gravitational-shift). So it still keeps a matter of taste ... :olduhh:
  16. Sep 22, 2015 #15


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    No, this is not correct. The equivalence principle is local; it applies in a small region of spacetime. The cosmological redshift observations are not limited to a small region of spacetime, so the equivalence principle does not apply.
  17. Sep 23, 2015 #16
    Sorry PeterDonis, general speaking, my answer for the first is: If the Equivalence Principle (EPx) ist not regarded as the most important prerequisite of General Relativity and does not apply to the Standard Model of Cosmology, then something must be wrong completely !
    Insofar I'm really worried about our todays cosmology, because the EP does not appear at all.
    (xthe numerical concordance of heavy and inertial masses is measured today as around equal to the 10-13, see e.g. https://en.wikipedia.org/wiki/Equivalence_principle)

    Yes of course, the EP is assumed to function only local, but only in one or two dimensional more or less asymmetrical gravity fields, where over comparably short distances asymmetric forces appear, e.g. where the one-dimensional gravitational acceleration g in the lift-cabin differs slightly from the bottom to the top - therefore strictly speaking the EP it is valid here only locally for one discrete point in an unsymmetric gravitational field.

    But in a mean curved (and then consequently gravitationally closed) universe (we spoke of in the previous reply) you don't have these asymmetrical conditions. In an equilibrated universe that owns the isotropic and mean constant acceleration of IaI = Hc ≅ 7e-10 m/s2 all points are equal and flat, also in time. Therefore you can subject the EP directly to the cosmological redshift and it works.
    (of course, inside larger masses like e.g. the sun, the solar system, a star cluster or an entire galaxy you have again these unsymmetrical conditions, where the EP then can work only local, but far outside you have these smoothed conditions of IaI where the EP is perfectly valid in the environment all over the world in any direction and at any time).
  18. Sep 23, 2015 #17


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    I didn't say the EP doesn't apply to cosmology. I said the EP is local. It applies to any small region of spacetime, anywhere in the universe. But the redshift observations you are talking about are not limited to a single small region of spacetime, so the EP doesn't apply to them.

    I don't understand what this means. The EP is valid in any small region of spacetime, and applies to any phenomena involving any physical fields/objects you like, as long as the phenomena are limited to a single small region of spacetime.

    You are misunderstanding the EP. It does not require any change in g; in fact the definition of a "small local region of spacetime" is precisely that it is a region small enough that g does not vary. Phenomena like gravitational time dilation--the variation in the rate of time flow between the bottom and top of the "lift-cabin"--do not require g to vary; they only require altitude (i.e., vertical position, where "vertical" is defined relative to the direction of g) to vary. The top of the lift-cabin is at a higher altitude in the constant g field than the bottom; that's why time flows faster there.

    In the universe as a whole, there is no "g" field anyway; the concept doesn't even apply in cosmology. It only applies in stationary spacetimes, and the spacetime of the universe as a whole is not stationary, because the universe is expanding.

    In cosmology, the definition of a "local" region of spacetime--one within which the EP applies--is that the effects of the expansion of the universe are negligible. That means the region has to be small enough that the relative velocity of "comoving" objects is negligible. When you are talking about cosmological redshifts, you are talking about light from objects whose relative velocity, compared to us, is certainly not negligible--if it were, there would be no redshift! So any observations of redshifts must involve a region of spacetime that is too large for the EP to apply.

    No, it isn't. See above.
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