NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/sci/astro/8313

Internet Message Format | 1992-07-25 | 4.9 KB

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From: [e-mail] (Bert_Rust_x3811)
Newsgroups: sci.astro
Subject: grav lensing (MG1654) and Supermassive stars ...
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Date: 24 Jul 92 20:39:55 GMT
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Organization: National Institute of Standards and Technology, Gaithersburg, MD
Lines: 82

Thanks to James Annis for the reference to the Lawrence ApJ Suppl. paper
(but it was vol 61 not 62).

I counted 51 Core Double (CD) sources, rather than 50, with 20 of them
bent, rather than 17.  However I put a question mark beside three of
those bent CDs because they didn't much look like CDs.  In fact, I had
question marks beside 7 out of the total 51 because they didn't look
like CDs.  In at least two cases, I couldn't find any trace of the core.
In other cases, including some which I accepted without question, the
core was indicated  by only one contour so it must have been very
weak w.r.t. the lobes.

The sample also included a class called triples (T) in which the center
source was usually quite pronounced.  If I were going to try to do
anything statistical with these data, I would have included them also
to boost the number in the sample.  That was my original intention,
but after looking closer at the data and trying to draw the angles with
a straightedge, I gave up the idea, and in fact I can't agree that this
sample is "the very best comparison sample to look at."  Not only did
I find myself questioning the authors classification in some cases, but
in others, either the core or the lobes exhibited complex structure so
I couldn`t decide how to draw the lines.

Another thing that bothered me about the sample was that I couldn't
figure out which one was MG1654, but that was probably due to my own
ignorance and the fact that I really didn't read all of the text.

There is no doubt that some of the sources are seriously bent, but in
at least two of the most severely bent cases, the core was almost merged
with one of the lobes which again makes me question the classification.
It is also certain that not all those sources are double lobed QSOs.
Of the cores, 8 were identified as galaxies, 5 were said to be stellar
in appearance (presumably QSOs) and the remaining 38 were empty fields.

I mean no disrespect toward the observers, but I don't believe that I
can get meaningful probabilities from this sample. (Why is real data
always so damned messy?).  What I would like to see is a sample of
optically identified radio QSOs with maps like those in the Lawrence
paper.  Surely someone must have done that with the 3CR and/or 4C QSOs.
It would be nice if someone had already done this study years ago --
someone with no preconceptions about gravitational lenses and QSO
ejections.

I'm not sure that Tom really suggested that his alternate interpretation
of MG1654 was that of a "quasar radio lobe spraying the galaxy."  An
interpretation more consistent with Arp's recent work would be that
the galaxy is a disturbed or active galaxy that has ejected the QSO and
that the thing labelled "Jet" in the Sky and Tel. article represents
a secondary ejection.  Is there something in the observational data
that precludes such an interpretation?

To Don Wells:  You keep reiterating your faith in hydrodynamical
modelling because it produces such pretty pictures that look like all
those maps from the VLA.  But all those maps are two-dimensional
projections, and it is well known that reconstructing a three-dimensionl
distribution from a two-dimensional projection is an ill-posed problem.
In such cases, it is not usually difficult to find a model consistent
with the observations.  The problem is that there are lots and lots
of models that do the job equally well.  If the modellers have, so far,
come up with only one, they are probably being bullied into line by
the most talented or agressive ones who set the pace for the others.
I am always amused when I overhear these guys arguing among themselves
at a poster session or AAS coctail hour.  They are so forceful and
certain of their models.  It would be educational for all of them to
spend a year or two working on climate and weather models, or some
other laboratory situation where three-dimensional data can be measured.
I know some damned good mathematicians and numerical analysts who
do that kind of hydronamical modelling, and they are usually more
modest in their claims than most of the stuff I see in ApJ.

Even if the plasma jet models are basically correct, how do they
preclude the ejection of compact objects?  Do you think the plasma
jet modellers completely understand AGNs, or any other kind of GNs for
that matter?  Why couldn't the plasa jets be precursors for or trailers
behind a compact object?  Please don't tell me to go read a whole bunch
of junky mathematics papers in ApJ to find out.  If I want to read
about PDE modelling, I'll go to a real mathematics journal.

Bert W. Rust
Appl. and Comp. Math. Div.
NIST
[e-mail]