[astro-ph/0501171] Detection of the Baryon Acoustic Peak in the Large-Scale Correlation Function of SDSS Luminous Red Galaxies

Authors:  D. J. Eisenstein, I. Zehavi, D. W. Hogg, R. Scoccimarro, M. R. Blanton, R. C. Nichol, R. Scranton, H. Seo, M. Tegmark, Z. Zheng, S. Anderson, J. Annis, N. Bahcall, J. Brinkmann, S. Burles, F. J. Castander, A. Connolly, I. Csabai, M. Doi,
Abstract:  We present the large-scale correlation function measured from a spectroscopic sample of 46,748 luminous red galaxies from the Sloan Digital Sky Survey. The survey region covers 0.72 h^{-3} Gpc^3 over 3816 square degrees and 0.16<z<0.47, making it the best sample yet for the study of large-scale structure. We find a well-detected peak in the correlation function at 100h^{-1} Mpc separation that is an excellent match to the predicted shape and location of the imprint of the recombination-epoch acoustic oscillations on the low-redshift clustering of matter. This detection demonstrates the linear growth of structure by gravitational instability between z=1000 and the present and confirms a firm prediction of the standard cosmological theory. The acoustic peak provides a standard ruler by which we can measure the ratio of the distances to z=0.35 and z=1089 to 4% fractional accuracy and the absolute distance to z=0.35 to 5% accuracy. From the overall shape of the correlation function, we measure the matter density Omega_mh^2 to 8% and find agreement with the value from cosmic microwave background (CMB) anisotropies. Independent of the constraints provided by the CMB acoustic scale, we find Omega_m = 0.273 +- 0.025 + 0.123 (1+w_0) + 0.137 Omega_K. Including the CMB acoustic scale, we find that the spatial curvature is Omega_K=-0.010+-0.009 if the dark energy is a cosmological constant. More generally, our results provide a measurement of cosmological distance, and hence an argument for dark energy, based on a geometric method with the same simple physics as the microwave background anisotropies. The standard cosmological model convincingly passes these new and robust tests of its fundamental properties.
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Anze Slosar
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[astro-ph/0501171] Detection of the Baryon Acoustic Peak in

Post by Anze Slosar » January 15 2005

This is definitely and important paper and I am surprised nobody has put up any comments. It claims to see the evidence for baryon wiggles in the correlation function (where wiggles beomes just a bump) of LRGs from SDSS.

So do people buy this detection? I am quite convinced, but have only two minor questions:
  • In fig 4 the red and black curve become a bit discrepant after 150Mpc... In particular red curve seems to see another peak (while black seems to go too a bit too low so they exactly cancel to produce the expected power... Is this just a statistical anomaly? It seems to me that they couldn't claim the detection of the peak from the red curve alone (although they do say it is a bit noiser).
  • In conclusions they say something along the lines that the existence of this peak at the right place puts very strong constraints on alternative theories of gravity. How strong? Is this a definite no-no for things like Brans-Dicke and similar (not that I know much about these)?

Rich Savage
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Re: [astro-ph/0501171] Detection of the Baryon Acoustic Peak

Post by Rich Savage » January 18 2005

Hi Anze!

This is a really interesting paper; for those who missed the release last week, both SDSS and 2dFGRS released results on this sort of topic on the same day. The 2dF paper is also on Astro-ph (astro-ph/0501174). Both detect evidence for baryon oscillations at about the 4-sigma level.

Bob Nichol gave a talk on this at the RAS meeting last week (and a longer one here at Sussex today). I think it's pretty clear that both Sloan and 2dF have detected something in the galaxy power spectrum, and that something looks like the first acoustic peak of the baryon oscillations. Importantly, the 2dF sample is totally different to the SDSS one, so we have two essentially independent results here.

This type of measurement looks to have a lot of power as a standard ruler test of cosmology. People are already looking to build multi-object spectrographs to go and really nail the wiggles.
Anze Slosar wrote: In fig 4 the red and black curve become a bit discrepant after 150Mpc... In particular red curve seems to see another peak (while black seems to go too a bit too low so they exactly cancel to produce the expected power... Is this just a statistical anomaly? It seems to me that they couldn't claim the detection of the peak from the red curve alone (although they do say it is a bit noiser).
Looking at fig 4, I'd be inclined to say they were running out of sensitivity by above 150Mpc. From figures 2 and 3, you can see there aren't many data points out there (and those that are there are pretty correlated).

All interesting stuff! :-)

Best regards,

Rich

Håvard Alnes
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[astro-ph/0501171] Detection of the Baryon Acoustic Peak in

Post by Håvard Alnes » January 20 2005

What about the rather large value for h found in the 2dF paper?

h = 0.766 +/- 0.032

(From the concluding section, found by combining 2dF results with CMB data)

Should it be taken seriously?

-h

Anze Slosar
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[astro-ph/0501171] Detection of the Baryon Acoustic Peak in

Post by Anze Slosar » January 22 2005

Well, yes, there seems to be some kind (1−2 sigma?) discrepancy between 2dF and SDSS: 2dF gets considerably lower [tex]\Omega_m[/tex] as well.

Håvard Alnes
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[astro-ph/0501171] Detection of the Baryon Acoustic Peak in

Post by Håvard Alnes » February 01 2005

I guess these differences have been there also in the earlier SPSS vs 2dF data. For instance, M.Tegmark et al (astro-ph/0310723) write after finding h=0.70+−0.04, compared to the WMAP + 2dF result of h=0.73+−0.03:

"indeed, our value for h is about 1 sigma lower. This is because the SDSS has a slightly bluer slope compared to that of 2dFGRS, favouring slightly higher omega_m values. (...) this slight difference might be linked to differences in modelling of non-linear redshift space distortions and bias. (...)"

Now, I suppose the new data and the *new analysis* of the 2dF data just increased this difference in the power spectrum (especially since the error bars went down).

The question, then, is whether this difference reflects uncertainties in the galaxy surveys (and especially the bias modelling), or if it is a sign of new and exiting physics... :)

-h

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