Cze�� wszytkie,

On Fri, 4 Jan 2002, Andrzej Marecki wrote:

Paper: astro-ph/0201034

http://de.arXiv.org/abs/astro-ph/0201034

From: M.Rowan-Robinson m.rrobinson@ic.ac.uk Date: Thu, 3 Jan 2002 16:29:08 GMT (64kb)

Title: Do Type Ia Supernovae prove Lambda > 0 ? Authors: Michael Rowan-Robinson Comments: 10 pages, 10 figures. Accepted for publication by MNRAS

Well, the principle of checking things like extinction and reanalysing the data is a good one, especially given that just a fraction of a magnitude makes the difference between an Omega_m=1 and a Lambda model, as far as the SNeIa data go.

But assuming that all RR's corrections regarding extinction are correct, the real result of the paper (section 7.(4)) is just that the rejection of the Omega_m=1 model is "only" 2.8-4.6\sigma (instead of 6-10(?)\sigma).

Well, 3\sigma (double sided) is 99.7% 4\sigma (double sided) is 99.994%

Still strong evidence in favour of non-zero \Lambda!

Our constraint (RMB02, the proofs are still sitting on my desk... mea culpa) http://de.arXiv.org/abs/astro-ph/0106135 rejecting Omega_Lambda=0 is itself "only" 3\sigma. Our result is totally independent of the SNeIa results, it's a standard ruler, not a standard candle, and there are also the weak gravitational lensing constraints, plus the very nice result from our friend Roman Juszkiewicz, simply from galaxies' relative velocities, constraining Omega_m=0.35\pm 0.15 (if large-scale bias is zero) http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?bibcode=2000Sci...287..109J... so while RR is right that people should remain skeptical and to suggest that a sociological warning is a good idea, his analysis does nothing to suggest that the present "fashion" is wrong.

And I think the referee should have hassled him on his Hubble diagram. (Fig 10)

* He said that he himself finds z=1.4 for the SN 1997ff, but he plots it for z=1.7. If he trusted his own analysis, he would have put the spot at z=1.4, much closer to the (0.3,0.7) curve.

* He didn't put *error bars* on the high z points of Fig 10. The error bars put by Riess et al. 2001 on SN 1997ff are *big*, particularly in the magnitude direction. The uncertainties in modelling gravitational lens time delays are still big - and should have been plotted.

* It's rather unphysical to write "v" for velocities greater than c. "zc" is correct, redshifts can be equal to or greater than 1. But velocities of massive objects cannot be greater than or equal to c, unless you redefine velocity as v= d_(d_comoving)/d_(t_cosmological), but this is a definition which would only have very special uses in restricted contexts, and certainly not on this diagram.

* He should have labelled "luminosity distance", not just "distance".

So you can relax :-), Andrzej: (0.3,0.7) is still the best local cosmological parameter estimate to use when looking for global cosmological parameters!

Pozdrawiam, Boud