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  • Galaxy cluster at z=4.31

    From jacobnavia@21:1/5 to All on Fri Apr 27 22:49:22 2018
    ALMA sees very far. And at z=4.31, just 1.4 Gy after the supposed
    "bang"... it sees a galaxy cluster the mass of the coma cluster...

    http://www.eso.org/public/archives/releases/sciencepapers/eso1812/eso1812a.pdf

    Interesting read that article.

    Now, wait a minute. If that huge concentration of mass existed 1.4Gy
    after the "beginning" we should see an object in the CMB isn't it?

    If we look at that particular direction, do we see a change in the
    composition of the CMB?

    1.4 Gy after the big bang, that huge concentration of mass hasn't the
    time to move a lot, and should be there as a variation of the CMB light.

    If we take the CMB measurements of the Planck satellite, at that
    particular point in our horizon we should see this object.

    What is more interesting, besides the death of the nth cosmology we have produced, is that there is apparently an evolution or rather a change.
    Galaxies were much younger 12.7 Gy ago. And this forming cluster, that
    was already a heavyweight at that time, must be a gargantuan object now.

    The team identified 14 galaies, and they are producing stars at an
    incredible rate... the excesses of youth. :-)

    But can we extrapolate from a few objects to an universal evolution?

    Difficult. Until a lot of more observations are done, nobody can say
    with any satatistical relevance that "the universe" and galaxies were
    "younger" at that time. This is a young object, but observer bias is a
    reality: it is quite bright of course, given its huge dimensions and
    star formation rates. Other objects, less luminous, could be there and
    they could be old objects already then, 12.7 Gy ago.

    In any case, this is not just a galaxy (as I have repeatedly reported in
    this group) at this enormous distances that poses a huge problem. It is
    a CLUSTER of them... with an incredible mass. Clusters weren't supposed
    to exist before 10Gy ago. Now we find one at more than 12Gy!

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  • From Steve Willner@21:1/5 to jacobnavia on Thu May 3 21:37:38 2018
    In article <pbtgpb$hh1$1@dont-email.me>,
    jacobnavia <jacob@jacob.remcomp.fr> writes:
    ALMA sees very far. And at z=4.31, just 1.4 Gy after the supposed
    "bang"... it sees a galaxy cluster the mass of the coma cluster...

    http://www.eso.org/public/archives/releases/sciencepapers/eso1812/eso1812a.pdf

    Interesting read that article.

    Indeed.

    Now, wait a minute. If that huge concentration of mass existed 1.4Gy
    after the "beginning" we should see an object in the CMB isn't it?

    The authors don't say, but I gather the submm flux from the galaxies
    overwhelms the CMB signal. The South Pole Telescope, which
    discovered the cluster, is primarily a CMB instrument.

    If we take the CMB measurements of the Planck satellite, at that
    particular point in our horizon we should see this object.

    Combined with the signal from the galaxies. Planck presumably saw
    what ALMA and SPT saw but with lower angular resolution. The
    Herschel/SPIRE map in Extended Data Fig 1 is more interesting.

    . And this forming cluster, that
    was already a heavyweight at that time, must be a gargantuan object now.

    Expected halo mass at z=0 is about 10^15 solar masses, one of the
    largest. Not surprising considering this cluster is the strongest
    signal in about 1/18 of the sky.

    Until a lot of more observations are done, nobody can say
    with any satatistical relevance that "the universe" and galaxies were "younger" at that time.

    The galaxy population at high redshift is vastly different from the
    local population. In general, high-redshift galaxies are more
    compact, lower mass (for constant space density), more gas-rich, and
    more irregular than local ones. There is a vast literature on this
    subject.

    a CLUSTER of [galaxies]... with an incredible mass.

    Did you miss Fig 2 (right panel) in the paper? The mass is
    consistent with model expectations. The submm flux density is higher
    than the model would suggest (Fig 2 left panel), but the model
    ignores galaxy interactions. Those raise the star formation rate and
    therefore the submm flux density.

    --
    Help keep our newsgroup healthy; please don't feed the trolls.
    Steve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA

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  • From jacobnavia@21:1/5 to All on Fri May 4 05:32:15 2018
    Le 03/05/2018 à 22:37, Steve Willner a écrit :
    Did you miss Fig 2 (right panel) in the paper? The mass is
    consistent with model expectations.

    Well, I detect that I look at what I want to see, I did miss the right
    panel figure, because I read what it said about the LEFT panel:

    <quote>
    Most of the literature SMG overdensities are consistent with the model expectations, whereas SPT2349-56 lies vastly above the region spanned by
    the model.
    <end quote>

    So the models do not fit at all for the left panel.

    You point correctly that the right panel shows that the models could
    account for the same object!

    I did not read that. Observer bias from my side :-)

    Anyway, the question remains:

    how can you make a cluster of this mass in only 1.2Gy?

    And yes, many detected objects are young and bright in the far away
    universe, but since those objects are bright there could be an observer
    bias in our observations!

    Older and far less luminous objects could be abundant but beyond the
    powers of ALMA.

    You did not quote that part of my message...

    What is interesting is that there could be an evolution in the universe,
    and maybe the galaxy formation process started somewhere sometime in a
    huge undifferentiated gas cloud. Not a "big bang" but a beginning of an
    ongoing condensation process in our local cloud.

    With an ALMA version 2.0 maybe it will be possible to find out lensed
    galaxies in that cluster, and if we find them, we could start answering
    those questions. In any case, finding such a lensed galaxy in this
    cluster would definitely disprove any big bang.

    Thanks for your input.

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  • From Steve Willner@21:1/5 to jacobnavia on Fri May 11 10:44:31 2018
    The paper in question is now published at http://www.nature.com/articles/s41586-018-0025-2
    but you will need to pay or have a subscription.

    I am reluctant to respond further, but there seems to be one point of
    confusion I can clear up:

    In article <pcg6lb$48r$1@dont-email.me>,
    jacobnavia <jacob@jacob.remcomp.fr> writes:
    how can you make a cluster of this mass in only 1.2Gy?

    As noted, the models do so, as shown in Fig 2 (right panel).

    So the models do not fit at all for the left panel.

    Which shows something related to linear size. As was stated in the
    paper, the models for cluster size omit galaxy interactions, which
    will (it seems) make real clusters smaller than the models say.

    --
    Help keep our newsgroup healthy; please don't feed the trolls.
    Steve Willner Phone 617-495-7123 swillner@cfa.harvard.edu Cambridge, MA 02138 USA

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