Dr. Joel E. Tohline
202 Nicholson Hall
Department of Physics and Astronomy
Louisiana State University
Baton Rouge, LA 70803-4001 USA

Dear Joel,

Your paper entitled "A Link Between Cosmic Ray Flux and the 
Formation of Star Clusters During Galaxy-Galaxy Interactions" by 
Joel E. Tohline, Nick Z. Scoville, and Andrew W. Strong was sent 
to a competent referee, and a copy of the report is enclosed for 
your consideration. I think the report can be summarized as a
judgment that the paper's argument is too speculative in its
present form, and would benefit from an illustrative, but 
specific, model.

Please supply a detailed cover letter that lists the changes you 
have made to the manuscript and submit the revised manuscript to 
the Chicago FTP site.

The Astrophysical Journal has adopted a policy that manuscript
files become inactive, and are considered to have been withdrawn,
a year after the most recent referee's report goes to the authors,
provided a revised version has not been received since then.

Regards,

Ethan T. Vishniac, Scientific Editor
The Astrophysical Journal
Phone:410-516-7269
Fax:410-516-5096
ethan@tarkus.pha.jhu.edu

*************************************************



                      Report of Referee

  A Link between Cosmic Ray Flux and the Formation of Star Clusters
              During Galaxy-Galaxy Interactions

       by J. E. Tohline, N. Z. Scoville, and A. W. Strong

The main point of this paper is the following suggestion: During
galaxy-galaxy interactions, cosmic ray flux in molecular gas 
clouds declines. As a result, magnetic field is decoupled from the 
gas and clouds collapse to become clusters. While I find this 
suggestion is interesting, I am not convinced that would really 
happen. The authors describe in pp. 13-15 arguments which support 
their suggestion.  They argue that during the galaxy-galaxy 
interactions, gas clouds are "simply" displaced from the disk to 
the intergalactic space where cosmic ray flux is much lower. Also 
they show that if cosmic rays confined in the disk spread 
"uniformly" over halo, the ionization rate due to cosmic rays 
reduces significantly. However, I regard that their arguments are 
mostly based on conjectures rather than physical proofs.

As the authors acknowledge in the paper, galaxy-galaxy 
interactions may induce many dynamical and other processes which 
affect the outcome in the context of cosmic ray flux. Here is 
the list of some (which the authors have pointed in the text too). 

   1) When clouds are displaced from disk, magnetic field is 
dragged with them and so are the cosmic rays.   It is difficult 
to picture that clouds are simply displaced without dragging
magnetic field and cosmic rays. 

   2) During the displacement, magnetic field is amplified by 
stretching and twisting. Yet the expected scale of the dynamically 
evolved magnetic field still far exceeds the gyro-radius of
low energy cosmic rays which are important for ionization.

So it is not clear at all to me how cosmic ray flux will be 
reduced in gas clouds during galaxy-galaxy interactions. In 
addition, the interaction may naturally induce some activities 
which would result in the increase of cosmic ray flux. For instance, 
collisions of gas clumps in two interacting galaxies will produce 
shocks which can serve as the sites of further cosmic ray 
acceleration. Hence it does not seem likely that the cosmic rays 
are simply de-coupled in the displaced clouds. Instead,
I even see the other possibilities that magnetic field become 
stronger and more comic rays are produced, so it may work in the 
other way.

However, my arguments here are equally based on conjectures. I do 
not mean to discard either the authors' suggestion (or mine). I 
am simply not convinced with the authors' suggestion. So I suggest 
the authors provide more detailed calculations which support their 
suggestion. For instance, they might build up a model for the 
evolution of clouds as well as magnetic field in interacting 
galaxies, and the evolution of cosmic ray flux based on the leaky 
box model. And then they may prove that cosmic ray flux decreases 
indeed.

Another point I would like to make is that the paper contains too 
much review of previous work (for instance, Section 3) as well as 
the stuffs which are not directly relevant to the main point of 
the paper (for instance, Appendix). The paper needs to be focused 
reducing those parts and provide more realistic model calculations 
to support the main point.

At this point I can not recommend the current version of the paper 
for publication.