Arp and Quasar-Galaxy alignments proposed statistical study

Morgoth wrote:
0.698 [1], which with a very rough back-of-the-envelope and horrendous
guestimate calculation, assuming a value of the deceleration parameter
of between 0 and -0.6 [2], works out at about 3-4000 Mpc.

I calculate this as 10*c which needs some explaining. OK, here it comes ...

Martin Hardcastle wrote:
If, as Joseph says, the apparent motion can be entirely explained in
terms of changes in structure (e.g. one component gets fainter and one
gets brighter, so the apparent mean position moves) then this isn't an
argument in favour of Arp's position.

However this sort of high rate of motion has to be considered more
easily consistent with Arp's view than with redshift being 100%
cosmological. While one object aiming right at us is possible, if too
many such objects are found then we start to look like a special place
in the universe.

You need to be careful in making this claim, because in the standard
model the high speed and alignment towards us also give rise to
Doppler boosting (SR effect leading to greater observed brightness).
So in a flux-limited sample of radio sources you will have more
aligned objects than you `should' have if the angles were completely
randomly distributed wrt the line of sight. This also leads to the
problem that the sources at large angles to the line of sight are too
faint (Doppler suppression) to allow component speeds to be measured
with VLBI.

Certainly. However there are other things that must also be the case if
this is a correct explanation. When plotted on a redshift-brightness
diagram the object should be correspondingly very high up due to this
enhanced brightness. Is this the case?

Ray Tomes

In article ,
Ray Tomes wrote:
However this sort of high rate of motion has to be considered more
easily consistent with Arp's view than with redshift being 100%
cosmological. While one object aiming right at us is possible, if too
many such objects are found then we start to look like a special place
in the universe.

Agreed.

Certainly. However there are other things that must also be the case if
this is a correct explanation. When plotted on a redshift-brightness
diagram the object should be correspondingly very high up due to this
enhanced brightness. Is this the case?

In the sense that most known superluminal quasars come from
flux-limited radio samples, and so are the brightest few objects in
their redshift range (and part of the sky surveyed), yes, it
necessarily is the case. But because we don't really have any other
sort of sample for this sort of work, you may not feel that that tells
you very much.

In order to make the test that you want to make, we'd need a
luminosity-limited sample in a fixed redshift range of quasars and
their presumed parent population, radio galaxies, and then we'd need
to measure component speeds in the jet for each one, and look at the
beaming effects, and see if the whole picture hangs together. It would
be a great thing to do, but it's simply not possible at the moment --
most of the objects would be too faint for motions to be measured even
if they were there. You can do some work on the statistics of core
brightnesses -- I did something in this area comparatively recently --
but even then you have to join together various different samples to
get what you need.

Martin
--
Martin Hardcastle Department of Physics, University of Bristol
A little learning is a dangerous thing; / Drink deep, or taste not the
Pierian spring; / There shallow draughts intoxicate the brain ...

In article ,
Ray Tomes wrote:
However this sort of high rate of motion has to be considered more
easily consistent with Arp's view than with redshift being 100%
cosmological. While one object aiming right at us is possible, if too
many such objects are found then we start to look like a special place
in the universe.

Agreed.

Certainly. However there are other things that must also be the case if
this is a correct explanation. When plotted on a redshift-brightness
diagram the object should be correspondingly very high up due to this
enhanced brightness. Is this the case?

In the sense that most known superluminal quasars come from
flux-limited radio samples, and so are the brightest few objects in
their redshift range (and part of the sky surveyed), yes, it
necessarily is the case. But because we don't really have any other
sort of sample for this sort of work, you may not feel that that tells
you very much.

In order to make the test that you want to make, we'd need a
luminosity-limited sample in a fixed redshift range of quasars and
their presumed parent population, radio galaxies, and then we'd need
to measure component speeds in the jet for each one, and look at the
beaming effects, and see if the whole picture hangs together. It would
be a great thing to do, but it's simply not possible at the moment --
most of the objects would be too faint for motions to be measured even
if they were there. You can do some work on the statistics of core
brightnesses -- I did something in this area comparatively recently --
but even then you have to join together various different samples to
get what you need.

Martin
--
Martin Hardcastle Department of Physics, University of Bristol
A little learning is a dangerous thing; / Drink deep, or taste not the
Pierian spring; / There shallow draughts intoxicate the brain ...