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[1004.2244] Regarding the Line-of-Sight Baryonic Acoustic Feature in the Sloan Digital Sky Survey and Baryon Oscillation Spectroscopic Survey Luminous Red Galaxy Samples
 
Authors:Eyal A. Kazin, Michael R. Blanton, Roman Scoccimarro, Cameron K. McBride, Andreas A. Berlind
Abstract:We analyze the line-of-sight baryonic acoustic feature in the two-point correlation function {\xi} of the Sloan Digital Sky Survey (SDSS) luminous red galaxy (LRG) sample (0.16 < z < 0.47). By defining a narrow line-of-sight region, rp < 5.5 Mpc/h, where rp is the transverse separation component, we measure a strong excess of clustering at ~ 110 Mpc/h, as previously reported in the literature. We also test these results in an alternative coordinate system, by defining the line-of-sight as {\theta} < 3{\deg}, where {\theta} is the opening angle. This clustering excess appears much stronger than the feature in the better-measured monopole. A fiducial {\Lambda}CDM non-linear model in redshift-space predicts a much weaker signature. We use realistic mock catalogs to model the expected signal and noise. We find that the line-of-sight measurements can be explained well by our mocks as well as by a featureless {\xi} = 0. We conclude that there is no convincing evidence that the strong clustering measurement is the line-of-sight baryonic acoustic feature. We also evaluate how detectable such a signal would be in the upcoming Baryon Oscillation Spectroscopic Survey LRG volume (BOSS). Mock LRG catalogs (z < 0.6) suggest that: (i) the narrow line- of-sight cylinder and cone defined above probably will not reveal a detectable acoustic feature in BOSS; (ii) a clustering measurement as high as that in the current sample can be ruled out (or confirmed) at a high confidence level using a BOSS-sized data set; and (iii) an analysis with wider angular cuts, which provide better signal-to-noise ratios, can nevertheless be used to compare line-of-sight and transverse distances, and thereby constrain the expansion rate H(z) and diameter distance DA(z).
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Syksy Rasanen



Joined: 02 Mar 2005
Posts: 128
Affiliation: University of Helsinki

PostPosted: April 19 2010  Reply with quote

This paper has more on the claimed measurement of the radial baryon acoustic oscillation signal mentioned at http://cosmocoffee.info/viewtopic.php?t=1301&highlight=.

The authors independently redo the analysis of Gaztanaga, Cabre and Hui, and obtain basically the same results as far as the data is concerned. However, they argue that the detection of the radial mode is not statistically significant, and discuss expected improvement from future surveys.

In particular, they claim that the model with the oscillation signal does not provide a fit to the data that would be decisively better than a completely featureless spectrum (their table 2 on the last page). This seems straightforward.

As for predictions for future surveys, I wonder about using ΛCDM simulations to set error bars, given that the large-scale statistical properties of the observed distribution are different from those in simulations: http://cosmocoffee.info/viewtopic.php?t=1543&highlight= - see also 0903.0950.
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Patrick McDonald



Joined: 06 Nov 2004
Posts: 17
Affiliation: CITA

PostPosted: April 19 2010  Reply with quote

I think its safe to say that the people making this kind of projection based on simulations don't believe there is any real evidence for disagreement.
There is good reason for this. There are plenty of very reliable-seeming analyses on the relevant scales for these projections which show absolutely beautiful precision agreement between the theory and observations, e.g., recent SDSS power spectrum measurements by Percival and Reid. I, and I'm sure more direct experts in observational galaxy clustering, generally flip through papers making wild-sounding claims for disagreement, looking for signs of believability, and don't find anything to make me doubt the standard analyses. The present paper is a pretty good example - when the original claims about the radial BAO feature came out, lots of people were interested and looked into it, but pretty quickly figured out that the arguments supporting the claims were flawed. Especially if the authors have not *done their job* of self-refereeing and presenting results that are free of pretty elementary problems, I think most people decide they've already wasted too much time on the paper by the time they figure this out and don't want to waste more by writing public comments, although that unfortunately dooms lots of other people to making the same mistake.
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Syksy Rasanen



Joined: 02 Mar 2005
Posts: 128
Affiliation: University of Helsinki

PostPosted: April 19 2010  Reply with quote

Do you think that the papers on the statistics of the large-scale distribution (the fractal dimension analysis and other work mentioned in http://cosmocoffee.info/viewtopic.php?t=1543&highlight=) have elementary errors and lack believability? What do you think those errors are?
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