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Thread: How accurately will GAIA measure the Hubble constant and will it be model dependent?

  1. #1
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    How accurately will GAIA measure the Hubble constant and will it be model dependent?

    GAIA DR2 is due out in about a month.

    Planck has measured the Hubble constant to be about 67-68km/s/Mpc. Riess and team have found about 73.2km/s/Mpc from the distance ladder, but uses the assumption of a deceleration parameter of q=-0.55. Another possibility which is ATM and won't be discussed much here is that the q=-1 leading to an estimated 75.5km/s/Mpc from Riess' analysis.

    Does anyone know the answers to...How accurately will GAIA determine the Hubble constant? Will it be model dependent or model independent? Is GAIA likely to be able to help resolve the tension between the first two values above?

    Thankyou.
    Last edited by slang; 2018-Mar-20 at 10:12 PM. Reason: strike-through added by moderator
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

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    As far as I know GAIA will not measure the Hubble constant at all. It will however provide a better foundation of the cosmological distance ladder by more accurately measuring the distance to nearby Cephids.

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    glappkaeft has Bingo. Gaia will provide improved distances to Cepheids, RR Lyraes, and other stars in the Milky Way, which can in turn be used to calibrate the first steps on the cosmological distance ladder; and that improved calibration can, in turn, provide more accurate values for the Hubble Constant, based on a variety of indicators which are too distant for Gaia to measure them directly.

    A somewhat detailed discussion of parallax measurements, and the improvement that Gaia will provide, can be found in

    http://spiff.rit.edu/classes/ladder/.../parallax.html

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    I Agree

    Quote Originally Posted by glappkaeft View Post
    As far as I know GAIA will not measure the Hubble constant at all. It will however provide a better foundation of the cosmological distance ladder by more accurately measuring the distance to nearby Cephids.
    The acronym is GAIA Data Release 2 and the relevant link is here:


    https://www.cosmos.esa.int/web/gaia/dr2

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    Quote Originally Posted by StupendousMan View Post
    glappkaeft has Bingo. Gaia will provide improved distances to Cepheids, RR Lyraes, and other stars in the Milky Way, which can in turn be used to calibrate the first steps on the cosmological distance ladder; and that improved calibration can, in turn, provide more accurate values for the Hubble Constant, based on a variety of indicators which are too distant for Gaia to measure them directly.

    A somewhat detailed discussion of parallax measurements, and the improvement that Gaia will provide, can be found in

    http://spiff.rit.edu/classes/ladder/.../parallax.html
    Thanks, great link.

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    Quote Originally Posted by John Mendenhall View Post
    The acronym is GAIA Data Release 2 and the relevant link is here:


    https://www.cosmos.esa.int/web/gaia/dr2
    I was speaking about GAIA in general and not about DR2.

    When we are sharing good sources on the subject I really recommend "Measuring the Universe: The Cosmological Distance Ladder" by Stephen Webb. It's an academic overview on the history and current thinking about cosmological distances. Its a bit old (1999) so it doesn't cover the latest research and is rather expensive but I found it so good I borrowed it twice from different university libraries. Hopefully something similar will come out a few years after GAIA final data release.

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    Thanks, John, StupendousMan and Glappkaeft,

    So, is it likely that there is an improved, more reliable distance ladder as a result of GAIA - and that teams such as Riess' can then improve on the accuracy of their Hubble constant value, but will still have to use a deceleration parameter assumption?

    Apparently DR1 confirmed the distance ladder value, so if DR2 does the same is it likely just to reduce the error in the 73.2km/s/Mpc value, and perhaps increase the tension problem between distance ladder and Planck determinations? If so, could be interesting for cosmology...
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

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    Quote Originally Posted by john hunter View Post
    GAIA DR2 is due out in about a month.

    Planck has measured the Hubble constant to be about 67-68km/s/Mpc. Riess and team have found about 73.2km/s/Mpc from the distance ladder, but uses the assumption of a deceleration parameter of q=-0.55. Another possibility which is ATM and won't be discussed much here is that the q=-1 leading to an estimated 75.5km/s/Mpc from Riess' analysis.

    Does anyone know the answers to...How accurately will GAIA determine the Hubble constant? Will it be model dependent or model independent? Is GAIA likely to be able to help resolve the tension between the first two values above?

    Thankyou.

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    Whoops

    Quote Originally Posted by glappkaeft View Post
    I was speaking about GAIA in general and not about DR2.

    When we are sharing good sources on the subject I really recommend "Measuring the Universe: The Cosmological Distance Ladder" by Stephen Webb. It's an academic overview on the history and current thinking about cosmological distances. Its a bit old (1999) so it doesn't cover the latest research and is rather expensive but I found it so good I borrowed it twice from different university libraries. Hopefully something similar will come out a few years after GAIA final data release.
    Yes, of course. The DR2 reference was Hunter's in post #1. Sorry.
    Last edited by John Mendenhall; 2018-Mar-20 at 12:03 PM. Reason: bad error

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    DR2 was released on Wednesday.

    Does anyone know if a group has done the analysis yet on the DR2 data, which would give a better foundation for the distance ladder method. If so is there an improved value for the Hubble constant yet from the distance ladder?
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

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    Quote Originally Posted by john hunter View Post
    DR2 was released on Wednesday.

    Does anyone know if a group has done the analysis yet on the DR2 data, which would give a better foundation for the distance ladder method. If so is there an improved value for the Hubble constant yet from the distance ladder?
    I did not see such a paper, but if you'd like to employ your big data skills, the data is out there waiting for such research to be done on it.
    Forming opinions as we speak

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    It seems that, only about a week after the GAIA DR2 release, there has now been an analysis by Riess et al.

    https://arxiv.org/abs/1804.10655

    In the abstract there is:

    "Including the DR2 parallaxes with all prior distance ladder data raises the current tension between the late and early Universe route to the Hubble constant to 3.8 sigma (99.99 %)."

    Their value from the distance ladder is more or less unchanged but possibly amended to 73.52 (1.62) from 73.24 (1.74), and as the error is smaller that's what's probably increased the tension to 3.8 sigma...which represents a more serious problem, and a need for reconciliation with Planck.

    Interesting time for cosmology!
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

  13. #13
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    It's not just through getting a better handle on the bottom rung(s) of the distance ladder that Gaia will contribute to cosmology.

    Krone-Martins+ (2018) (link): "Gaia DR2 Gravitational Lens Systems I: New lensed quasar candidates around known quasars" points to an indirect contribution: the more lensed quasars the more opportunities to estimate H0 by a method that's independent of the formal distance ladder ...

  14. #14
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    Good link Jean,

    It might take a while, but it will be interesting to see how the H(0) values from the different methods, including the GAIA data, compare.
    "...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes

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