Max Tegmark's cosmology library: 2dF

We've done an independent analysis of the the 2dF galaxy redshift survey. Below you can get the power spectra, survey mask, and uniform galaxy sample described in the paper as well as some software, as a starting point for your own analysis.
Figure 26: Our 2dFGRS power spectrum measurements compared with theoretical models.

The astro-ph version, has low-res figures (1 and 6) because of the size limit, so please click here to download a PDF file with the final MNRAS published version of the paper. Click here if you are interested in other research of mine.

The power spectrum of galaxies in the 2dF 100k redshift survey


Max Tegmark, Andrew Hamilton & Yongzhong Xu


We compute the real-space power spectrum and the redshift-space distortions of galaxies in the 2dF 100k galaxy redshift survey using pseudo-Karhunen-Loeve eigenmodes and the stochastic bias formalism. Our results agree well with those published by the 2dFGRS team, and have the added advantage of producing easy-to-interpret uncorrelated minimum-variance measurements of the galaxy-galaxy, galaxy-velocity and velocity-velocity power spectra in 27 k-bands, with narrow and well-behaved window functions in the range 0.01h/Mpc < k < 0.8h/Mpc. We find no significant detection of baryonic wiggles, although our results are consistent with a standard flat Omega_Lambda=0.7 ``concordance'' model and previous tantalizing hints of baryonic oscillations. We measure the galaxy-matter correlation coefficient r > 0.4 and the redshift-distortion parameter beta=0.49+/-0.16 for r=1 (beta=0.47+/- 0.16 without finger-of-god compression). Since this is an apparent-magnitude limited sample, luminosity-dependent bias may cause a slight red-tilt in the power spectum. A battery of systematic error tests indicate that the survey is not only impressive in size, but also unusually clean, free of systematic errors at the level to which our tests are sensitive. Our measurements and window functions are available at together with the survey mask, radial selection function and uniform subsample of the survey that we have constructed.

Reference info:

astro-ph/0111575, MNRAS, 335, 887-908

Power spectrum

If you simply want to plot up the 13 band powers shown above for a chi-by-eye analysis or the like, use this table (from Figure 26 in the paper). The 5 columns are (k_eff,k_low,k_high,P,dP). If you want to do a quantitative analysis comparing to models, then use this table instead, which contains the 27 points from Figure 17 without unneccesary binning. The corresponding 27 window functions are the rows of this file. To compute chi2 as in the paper, evaluate p_i = P(k_i), where P(k) is your own model power spectrum and k_i are the 49 k-values from this file. Then compute
chi2 = sum_i [P_i-(Wp)_i]^2/dP_i^2,
where P_i and dP_i are the measurements and error bars you loaded above and W is the 27 x 49 window matrix. Note that if you want the window functions to look like in Figure 11 of the paper, which shows windows on the relative power (power relative to the prior), you need to multiply each window by the prior power spectrum we used, available in this file - the columns give (k,P). The resulting 27 window functions are plotted here, normalized to unit area.

Uniform galaxy sample

You'll find the uniform galaxy sample described in the paper in this file. The 5 columns are (ra,dec,cz,b_j,eta_type). If you'd like a file with additional fields, say the 2dFGRS team ID numbers, just let me know and I'll be happy to send it. This sample is strictly magnitude limited at b_j=19.27, so it's very easy to interpret and work with. Our fit for its radial selection function nbar(r) is in this file, where the columns are (r,nbar) and r is comoving distance. It's only valid for 10-650 Mpc/h. The only additional thing you need before you run off and compute your own power spectrum, trispectrum, genus curve or whatever is the angular mask below.

Angular mask

As the cutout to the left illustrates, the angular mask is pretty complicated. As described in the paper, it consists of 3614 spherical polygons. All the info you need is in this file. To help you along, I've put some demo software in tarball.tar.gz - the easiest way to figure out how it works is probably to run the enclosed code completeness_demo.f. If you have questions, please don't hesitate to ask.

If you'd like additional stuff that you can't find here, please drop me an email! And, needless to say, don't forget to visit the site of the 2dF galaxy redshift survey itself - it's terrific that the 2dFGRS team has made their data public, thereby making analyses like ours possible.

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This page was last modified October 7, 2002.