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- Newsgroups: sci.physics
- Path: sparky!uunet!mcsun!sunic!ugle.unit.no!aun.uninett.no!nuug!nntp.uio.no!athena!jarleb
- From: jarleb@athena.uio.no (Jarle Brinchmann)
- Subject: Re: Request info on Cold Dark Matter
- Message-ID: <1993Jan8.151056.14346@ulrik.uio.no>
- Keywords: cold dark matter, cosmology
- Lines: 45
- Sender: jarleb@athena (Jarle Brinchmann)
- Nntp-Posting-Host: athena.uio.no
- Reply-To: jarleb@athena.uio.no (Jarle Brinchmann)
- Organization: Institute for Theoretical Astrophysics
- References: <1993Jan4.222138.7079@klaava.Helsinki.FI> <1iaigeINN8rn@darkstar.UCSC.EDU> <1id38oINNpoq@terminator.rs.itd.umich.edu>
- Date: Fri, 8 Jan 1993 15:10:56 GMT
- Lines: 45
-
-
- Chris Metzler writes:
-
- > 2. Hi Mike. Hope things have gone well since Varenna. I would take a
- > small amount of exception with your statement that "COBE results have
- > shown that minimal CDM is not correct, since it creates too much structure
- > at small scales if one normalizes the distribution to the large (COBE)
- > scales." I would take exception to this. Remember that the simulations
- > people have done which have told them that there's too much structure on
- > small scales assume that the collisionless particles in the N-body
- > simulations are accurate tracers of galaxies. I am NOT talking about
- > spatial bias (biased CDM) here. Galaxy formation simulations which include
- > both N-body and hydro suggest that there exists velocity bias even in
- > unbiased CDM models, whether from dynamical friction or from the
- > nature of the environment galaxies are born into. Thus, the whole
- > "pairwise-velocity-dispersions are too high" problem may not even exist.
- > You may be right, but I think the jury is still out; the impression
- > I'm starting to get from the CDM gurus is 'hey, maybe unbiased CDM
- > wasn't so bad after all.'
-
- Maybe this is because they are _CDM_ gurus :-) ? I recently read (or is
- reading) a preprint from A. Kashlinsky, in which he argues that with our
- current observations of high-z objects, there is not easy to get enough
- power on small scales with CDM. Not easy means virtually impossible in
- his opinion, but then he is not very supportive of CDM.....
-
- I think very many wants CDM to survive because it is quite well understood
- and it has survived comparatively long. But if we shall start to use models
- with mixed CDM and HDM or a non-zero cosmological constant, I see no
- aestethic reason for not having a tilted spectrum. IMHO both a mixed DM
- universe and a tilted spectrum contains some a priori unknown constants,
- and therefore I guess we can't say much. Too bad COBE gave us such results
- it would have been much more fun if we could make everything as simple as
- possible :-)
-
-
- Jarle.
-
-
- --
- ---------------------------------------
- Internet: jarleb@medusa.uio.no
- or Jarle.Brinchmann@astro.uio.no
- ---------------------------------------
-
-