Size of voids?

Hello everyone!

I am interested in the size of the voids between the superclusters of
galaxies. Unfortunately, different articles give different values for
that. According to E. Saar, et al, The supercluster-void network V: The
regularity periodogram", Astr. And Astrophys., vol. 393, pp1-23 (2002),
the size of the voids is about 100-130 h^(-1) Mpc (they examined the
Abell supercluster), whereas according to astro-ph/0111581 Nov. 30,
2001, the size of the voids lies approximately between 25 h^(-1) and 50
h^(-1) (they studied the LCRS). Even for generously taking the low value
in the first and the high value in the second case, that is still a
factor of two difference!

The most obvious conclusion would be that the first paper talks about
the diameter and the second about the radius, but I checked carefully,
and both seem to mean the diameter. The second paper explains in the
beginning that there are different methods for determining the sizes of
voids, but I don't see how using these different methods could yield a
difference by a factor of 2 and more! There may also be the possible
explanation that in the Abell supercluster, the voids are simply larger
than in the region studied by the LCRS, but that possibility also looks
quite improbable to me.

So, what am I missing here, and what is the *real* size of the voids?


Bye,
Bjoern

"BF" == Bjoern Feuerbacher writes:

BF I am interested in the size of the voids between the superclusters
BF of galaxies. Unfortunately, different articles give different
BF values [...]. According to E. Saar, et al, The supercluster-void
BF network V: The regularity periodogram", Astr. And Astrophys.,
BF vol. 393, pp1-23 (2002), the size of the voids is about 100-130
BF h^(-1) Mpc (they examined the Abell supercluster), whereas
BF according to astro-ph/0111581 Nov. 30, 2001, the size of the voids
BF lies approximately between 25 h^(-1) and 50 h^(-1) (they studied
BF the LCRS). Even for generously taking the low value in the first
BF and the high value in the second case, that is still a factor of
BF two difference!

BF [...] There may also be the possible explanation that in the Abell
BF supercluster, the voids are simply larger than in the region
BF studied by the LCRS, but that possibility also looks quite
BF improbable to me.

BF So, what am I missing here, and what is the *real* size of the
BF voids?

Not that I am an expert, but do we expect them to be only one
characteristic size? There's a whole range in sizes for groups of
galaxies, ranging from the loose groups like the Local Group to rich
clusters like Coma. Why shouldn't we expect voids to have some range
of sizes as well?

--
Lt. Lazio, HTML police | e-mail:
No means no, stop rape. | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/sci.astro.html

Joseph Lazio wrote:
"BF" == Bjoern Feuerbacher writes:


BF I am interested in the size of the voids between the superclusters
BF of galaxies. Unfortunately, different articles give different
BF values [...]. According to E. Saar, et al, The supercluster-void
BF network V: The regularity periodogram", Astr. And Astrophys.,
BF vol. 393, pp1-23 (2002), the size of the voids is about 100-130
BF h^(-1) Mpc (they examined the Abell supercluster), whereas
BF according to astro-ph/0111581 Nov. 30, 2001, the size of the voids
BF lies approximately between 25 h^(-1) and 50 h^(-1) (they studied
BF the LCRS). Even for generously taking the low value in the first
BF and the high value in the second case, that is still a factor of
BF two difference!

BF [...] There may also be the possible explanation that in the Abell
BF supercluster, the voids are simply larger than in the region
BF studied by the LCRS, but that possibility also looks quite
BF improbable to me.

BF So, what am I missing here, and what is the *real* size of the
BF voids?

Not that I am an expert, but do we expect them to be only one
characteristic size? There's a whole range in sizes for groups of
galaxies, ranging from the loose groups like the Local Group to rich
clusters like Coma. Why shouldn't we expect voids to have some range
of sizes as well?

Err, they do indeed. As I mentioned above, both groups gave ranges for
the sizes of voids (about 100-130 h^(-1) Mpc in the first and about
25-50 h^(-1) Mpc in the second case).

The problem I see is that the lower range in the first case is still two
times the upper range in the second case! And both groups talked about
"typical" void sizes - and there, the factor was even more than two!


Bye,
Bjoern

In article ,
wrote:

I am interested in the size of the voids between the superclusters of
galaxies. Unfortunately, different articles give different values for
that. ...

..., but I don't see how using these different methods could yield a
difference by a factor of 2 and more! ...

For a lot of cosmological work a factor of 2 is pretty good.

If you follow papers on a subject over a few years you *might*
see different methods converge to a common value. This has happened
with the time since the Big Bang, it hasn't happened yet with
inter-cluster voids.

Perhaps the different methods are telling different things about
the voids and we haven't figured out the details as yet. That is
the challenge of reading current papers. You rarely have the complete
story.

If you want some perspective, read some review articles, here a
prominent worker looks at the literature and gives their determination
of which results are important and which are the hot problems.

Dark skies,

tom

--
We have discovered a therapy ( NOT a cure )
for the common cold. Play tuba for an hour.