Shape-univ June 2002

shape-univ@cosmo.torun.pl

3 participants
6 discussions

xi(r) from Hoyle's P(k)
by Gary Mamon 01 Jul '02

01 Jul '02

Dear all, I finally computed the correlation function extpected from Hoyle etal.'s P(k) obtained from their analysis of the 2QZ-10k quasar sample. I used the final part of eq. (21.40) of Peebles (1993) book to convert P(k) to xi(r). I now understand that last equation as resulting from the integral over angles of the previsou integral (which is in fact triple: dk dtheta dphi). I extended the P(k) beyond the values of Hoyle et al in two ways: 1) I used the theoretical BBKS (Bardeen et al. 84, appendix) P(k) (black & white plot). Notice that Hoyle's points are about a factor of 10000 too high so the P(k) is highly discontinuous. 2) I moved up the BBKS P(k) on each side of the Hoyle range so as to make the whole P(k) continuous. 3) Same as 2) with a step in log k decreased from 0.075 (Hoyle et al.'s step) to 0.01. (see 4th attached file). The three xi(r) plots are attached. The calculation were done with Omega = 0.3, h = 0.7, Omegab = 0.04. Even though Hoyle's peak is at 2 pi h / 89 Mpc, the 1st plot shows xi(r) with peaks at 67, 127 and 255 h-1 Mpc, close to what we (Boud really) gave in RMB02. This gives us some confidence that Boud's calculations are not completely wrong :-) and that there is no simple relation such as peak in xi at 2 pi / k_peak, where k_peak is the peak in P(k). However, in the 2nd plot, the peaks are very narrow and marginally significant at 90.6, 107.6, 109.3, 127.8, 180.6 and 255.0 h-1 Mpc. Finally, in the 3rd plot, it is hard to distinguish anything! However, with some imagination, one can guess excess broad power around 140 h-1 Mpc and a finer excess around 255 h-1 Mpc... Let me know what you think. all the best Gary

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smoothed xi(r)
by Gary Mamon 30 Jun '02

30 Jun '02

Hi again, Attached you will find the same xi(r) as case 3 of the previous e-mail with, in red, it's smoothing by a 15 h-1 Mpc gaussian. I must admit that I worked avery quickly and there may be errors... cheers Gary

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xi(r) from P(k)
by Gary Mamon 13 Jun '02

13 Jun '02

Hi everyone, For my talk at the IAP colloquium on July 2, it would be nice if I could show the xi(r) expected from the 2dFGRS and 2QZ P(k)'s (that are quite similar). I want to see how strong and where will the wiggles be in the xi(r) derived from the P(k). Does anyone have time to do this? By the way, I don't understand the formulation given in Peebles's book (1993, PoPC), eq. 21-40 (p. 509). If P(k) = <|delta(k)|^2>, then shouldn't the right-hand-side of the 2nd line in eq. 21-40 be sin(kr) instead of sin(kr/(kr)? cheers Gary P.S. I agree with Boud that doing ML estimation or chi2 estimation on xi(r)s is dangerous because the separation bins are not truly independent.

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seminar at Mt Stromlo
by Gary Mamon 04 Jun '02

04 Jun '02

Dear all, My talk at Mt Stromlo went very well. Brian Schmidt of supernovae fame made a good remark. Instead of looking for peaks, which could simply require that the xi(r)'s in different z bins are similar (he thought of using a maximum likelihood technique). He was referring to Alcock & Paczynski... Matthew Colless mentioned that both 2dF galaxies (2dFGRS) and quasars (2QZ) show a feature in P(k) at 2pi/89 h Mpc-1. Matthew's postdoc, Roberto de Propris, showed me a plot of the correlation function of the superposition of many pencil beams drawn through the 2dFGRS. He has access to the full 250k sample, and avoided computing a complete xi(r) using all 30 billion separations. There is a feature around 250 Mpc, but there are also stronger features elsewhere, but not at 130 h-1 Mpc. It thus appears that Broadhurst et al. were lucky back in 1990. cheers Gary

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comments from Brian Boyle
by Gary Mamon 03 Jun '02

03 Jun '02

Dear all, Brian Boyle (PI of 2dF quasar survey) came to my talk at Macquarie University. He seemed to like our analysis. His main comment was: "Have you tried repeating your correlation function analysis by replacing the scambled redshifts with a smoothed redshift distribution?" This is what I gathered you (Boud) have done these last few days (extrapolating from Boud's often cryptic messages). I answered that we are in the process of doing just that, and our *** preliminary *** result is that the 125 h-1 Mpc feature comes out strongly in the 1st z-bin, but that we did not have yet any conclusion on Omega,Lambda. cheers Gary

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w_Q \approx -1.5 ??? (DE-V0.04)
by Boud Roukema 02 Jun '02

02 Jun '02

Cze�� wszystkim, I've done a bit more documentation. Now you should be able to download, compile and run DE-V0.04: http://www.astro.uni.torun.pl/~boud/DE/ and get some nice correlation function plots averaged from all six high completeness 2QZ fields, very similar to the ones in RMB2002. They're not exactly the same, because (i) the random number seeds are almost certainly different and (ii) there are probably small changes like different numerical accuracy on different computers, and small changes made to the programs since the time the results of the paper were obtained. Guess what? I couldn't wait to work on the next step, even when the documentation for the earlier steps is not finished... So I wrote DEdNdzfull (in DEscramble.f) which instead of using (scrambling) the z distribution of just the individual field being analysed, uses the full z distribution of the 2QZ-10K catalogue. It seems to me that this is a better way of producing the "true" redshift selection effects for this particular catalogue than the idea I had before of passing a "typical" QSO spectrum through the optical u, b_J and r filters. The z-scrambling technique means that some *real* signal may have been cancelled out, so the results were conservative. Now, with a more "neutral" z distribution for the "randoms", the signal should in principle be stronger - if it is real. Well, the resulting signal is spectacular! :) :) :) :) We still have a lot of work to do (I have to get plot_cf working), but it seems clear that (0.3,0.7,-1.0) gives a bad fit, and that (0.3,0.7,w_Q) with w_Q \approx -1.5 is likely to give a better fit and signal, which would greatly upset all the theorists! Anyway... during today's session you should hopefully be able to calculate these functions and see for yourself... Na popo�udnie o 14:00 godz, boud

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Shape-univ June 2002