From: annis@hale.ifa.hawaii.edu (James Annis)
Subject: Re: grav lensing (MG1654)
Organization: Institute for Astronomy, Hawaii
Date: Mon, 27 Jul 1992 11:27:56 GMT

Bert Rust (bwr@cam.nist.gov) did his own work on the Lawrence et al. 
radio survey...  and found the data messy. yeah, I have to agree. 

I do maintain that this sample is the best for comparison, though. The 
data published in the paper may not allow the comparison to be performed, 
true, but the sample is separate.  There are a couple of subtle effects 
going on, primary among which is the idea that these radio sources
have wavelength dependent radio emission (flux proportional to nu**-1, 
where -1 varies from 1 to -3, is common). If one looks at the brightest 
examples in the sky found at 300Mhz, it is not at all clear that
one is selecting the same population of radio sources that one finds when
looking at moderate sources at 5Ghz. The statistics built 
up from a survey of 3C objects may be applicable to those objects found in 
the MIT survey; then again, they may be misleading. 

The MIT radio survey will be very powerful eventually (when? a decade
maybe?) just because there is that large resevoir of unlensed, resolved
radio sources with which to compare the candidate lens systems.
One will be able to look at the unlensed source population and find
its overall properties and statistics. Then one will be able to compare the
lens systems and their individual characteristics to this population.
It may turn out, in fact, that the inferred lens system source objects
are not drawn from the same population as the radio survey as a whole found.
The question is interesting. And open.

If you were going to do the statistics right, you would get ahold of
the MIT data, and look at it interactively. They plotted their contours
at standard intervals which sometimes hid objects they claimed were visible.
You could obtain deeper radio images, in order, for instance, to turn the 
class called "Doubles" into  core-doubles (most likely). And you would make 
your own classifications, presumably with fewer classes then they used. 
It could be done. Perhaps it will be.

For now, I should bring up the numbers of objects they plotted. Lawrence 
et al found 632 in their survey, but they published only 460 contour plots.
What happened to the other 172? They don't say. Most are probably just
point sources. On the other hand, none of the candidate
lens systems currently published from this survey are plotted. 
(2116; MG1131; MG1654; MG0414 are the ones I know about.) 
I personally think that they refrained
from publishing anything that they thought might be a lensed system.
They did the hard work, why shouldn't they get the rewards...?
But it is in those 172 cases that I expect to find Tom's desired arcs. 
And they are not published. At their publishing rate of 1 per year, its 
going to be a long time before I can point to one. Oh well.

>An interpretation more consistent with Arp's recent work would be that
>the galaxy is a disturbed galaxy that has ejected the QSO 
>Is there something in the observational data that precludes such an 
> interpretation?

There is nothing that I know of in this data which precludes this 
interpretation. Proof is hard to come by in astronomy. Overwhelming 
evidence is what is usually substituted. This kind of evidence is not 
to be found in MG1654, so arguments about simplicity and plausibility 
will have to suffice.

By the way, when I do the calculation you asked about earlier, i find
that MG1654 has a "wingspan" of 52kpc, assuming H=75, q=0.1. I don't think 
that is a very big for a radio lobe system; it seems rather small to me, 
but this isn't my field. If there is a spherical shell about the galaxy
it has a radius of 3.5 kpc. Nothing here catches my eye as abnormal.

--

James Annis   			annis@galileo.ifa.hawaii.edu