Are the Galaxies with Indefinitely Flat Circular Velocities Located Inside Large Dark Matter Haloes?

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper titled:  Are the Galaxies with Indefinitely Flat Circular Velocities  Located Inside Large Dark Matter Haloes?  needs major revisions.

1.    This paper seems to be very confusingly written.
In the introduction  we can read :

A recent study using weak gravitational lensing reveals the rotation curves of some isolated galaxies for very large distance from the galactic centres. This provides strong evidence supporting Modifed Newtonian Dynamics (MOND) and challenging the standard cold dark matter model.

However  in the introduction we can read :

Observational evidence shows that our universe contains a lot of invisible mass. One possible solution to the invisible mass problem is that there exists a large amount of unknown dark matter.

In  fact the confusion extends to the entire introduction. The reviewer does not  understand  if the authors  support MOND, another modified gravity or the dark matter paradigm.  What is the aim of the authors ? In any way the reviewer estimates that the abstract and the introduction must be completely rewritten  for a much better homogeneity and understanding.

2.    The figure 1 is really   problematic.
The authors affirm: By comparing with the observed rotation velocities using the lensing data, we can see that this scenario generally agrees with the 
observations.

This  statement does not appear obvious for the reviewer. First,  the  sentence “By comparing with the observed rotation velocities using the lensing data”   requires some detailed explanation.  Secondly  the values  rc=30 kpc and beta=0.35 are  arbitrary. Are these values the same in the four cases? And if these parameters are changed, what is the impact on the theoretical curves ?  Moreover   the error bars are very large and  it seems that any theoretical curve can eventually agree with the observational cases (even a keplerian curve!).

3.     Another enigm for the rewiever is the scale displayed in the figure 1.  Does each individual galaxy really extend from the center to 3 Mpc (i.e. the size of a galaxy cluster and  the galaxies are all mixed up) ?

 All these questions have to be answered   before the reviewer takes his  decision on the acceptance  of the paper.

Author Response

Comment 1: 

This paper seems to be very confusingly written.
In the introduction  we can read :

A recent study using weak gravitational lensing reveals the rotation curves of some isolated galaxies for very large distance from the galactic centres. This provides strong evidence supporting Modifed Newtonian Dynamics (MOND) and challenging the standard cold dark matter model.

However  in the introduction we can read :

Observational evidence shows that our universe contains a lot of invisible mass. One possible solution to the invisible mass problem is that there exists a large amount of unknown dark matter.

In  fact the confusion extends to the entire introduction. The reviewer does not  understand  if the authors  support MOND, another modified gravity or the dark matter paradigm.  What is the aim of the authors ? In any way the reviewer estimates that the abstract and the introduction must be completely rewritten  for a much better homogeneity and understanding.

Response 1:

Thanks for your comments and feedback. To provide an unbiased introduction about MOND and dark matter paradigm, we only briefly state some positive and negative evidence of MOND and dark matter paradigm. The aim of this study is to show that the new rotation curve data is also compatible with the dark matter paradigm, but not only MOND. We have no strong conclusion on which paradigm is true. We have largely rewritten the introduction and part of the abstract to clarify our view on this issue. We have changed to a more neutral term “gravitational mass problem” to illustrate the missing mass or dark matter problem.

 

Comment 2: 

The figure 1 is really  problematic.
The authors affirm: By comparing with the observed rotation velocities using the lensing data, we can see that this scenario generally agrees with the 
observations.

This  statement does not appear obvious for the reviewer. First,  the  sentence “By comparing with the observed rotation velocities using the lensing data”   requires some detailed explanation.  Secondly  the values  rc=30 kpc and beta=0.35 are  arbitrary. Are these values the same in the four cases? And if these parameters are changed, what is the impact on the theoretical curves ?  Moreover   the error bars are very large and  it seems that any theoretical curve can eventually agree with the observational cases (even a keplerian curve!).

Response 2:

The values of rc and beta are arbitrary. The value of beta is degenerate with another unknown parameter temperature T. Therefore, we have used the average value of beta = 0.65 to perform the analysis. Since the asymptotic velocities mainly depend on beta and T only, one can always tune the value of temperature T to match the asymptotic velocities. Therefore, the choice of beta is not important and we have taken the average value beta = 0.65 appeared in galaxy groups and galaxy clusters. The value of rc is not important. We have added one more value of rc = 100 kpc for demonstration in Fig. 1. The only change is the rising part of the rotation velocities at small R and the positions where the rotation velocities become flat. We have added more discussions about these issues in the revised version. Also, we have added one more part to illustrate the comparison using the conventional NFW model. We have demonstrated why the conventional NFW model fails in describing the data. Although the error bars are very large for R > 2000 kpc, one can still see that the data do not agree with the conventional NFW model and the Keplerian decline. The disagreements can mainly be found at R = 500-1500 kpc, where the error bars are not very large. We have revised Fig. 1 to illustrate these changes.

 

Comment 3:

Another enigm for the rewiever is the scale displayed in the figure 1.  Does each individual galaxy really extend from the center to 3 Mpc (i.e. the size of a galaxy cluster and  the galaxies are all mixed up) ?

 All these questions have to be answered   before the reviewer takes his  decision on the acceptance  of the paper.

 

Response 3:

Thanks for the question. The data really extend to more than 2 to 3 Mpc. These data are generated from Mistele et al. (2024) using weak lensing. This is the reason why we propose the possibility that the galaxies are indeed located inside the dark matter halos with the size of a galaxy group.

Reviewer 2 Report

Comments and Suggestions for Authors

The more years pass, the darker our universe becomes. The concept of dark matter is very old. In fact, it emerged when Zwicky measured the velocities of the Coma galaxy cluster. While this appears to be the most plausible explanation, until a dark matter particle is discovered, exploring alternative explanations is not unreasonable. The most well-known alternative to the dark matter paradigm is certainly the so-called MOND theory, proposed by Milgrom. A recent paper, analyzing the rotation curves of some isolated galaxies, argues that the measurements are in perfect agreement with what is predicted by the MOND theory. The authors of this work want to show that the same results can be reproduced in the standard gravitational framework and the cold dark matter interpretation still remains viable. To achieve their goal, they hypothesize that these isolated galaxies are located in dark matter haloes with the size of a galaxy group. Using the hydrostatic gas model commonly adopted in galaxy clusters and galaxy groups they obtain constant circular velocities. So they argue that even these recent experimental data can be explained by the standard cold dark matter model. I think that the situation is really not simple. Dark matter explains not only the rotation curves of galaxies but also many inexplicable things close to the big bang. On the other hand, however, the years are passing and it seems really incredible that no dark particle has ever been observed in 100 years. I think the paper is professionally written and properly referenced. The abstract and conclusions clearly describe the content of the work. It seems mathematically correct. In my opinion, it can be published in its present form.

Author Response

Comment:

The more years pass, the darker our universe becomes. The concept of dark matter is very old. In fact, it emerged when Zwicky measured the velocities of the Coma galaxy cluster. While this appears to be the most plausible explanation, until a dark matter particle is discovered, exploring alternative explanations is not unreasonable. The most well-known alternative to the dark matter paradigm is certainly the so-called MOND theory, proposed by Milgrom. A recent paper, analyzing the rotation curves of some isolated galaxies, argues that the measurements are in perfect agreement with what is predicted by the MOND theory. The authors of this work want to show that the same results can be reproduced in the standard gravitational framework and the cold dark matter interpretation still remains viable. To achieve their goal, they hypothesize that these isolated galaxies are located in dark matter haloes with the size of a galaxy group. Using the hydrostatic gas model commonly adopted in galaxy clusters and galaxy groups they obtain constant circular velocities. So they argue that even these recent experimental data can be explained by the standard cold dark matter model. I think that the situation is really not simple. Dark matter explains not only the rotation curves of galaxies but also many inexplicable things close to the big bang. On the other hand, however, the years are passing and it seems really incredible that no dark particle has ever been observed in 100 years. I think the paper is professionally written and properly referenced. The abstract and conclusions clearly describe the content of the work. It seems mathematically correct. In my opinion, it can be published in its present form.

 

Response:

Thanks for recognizing the paper. Based on the comments from another reviewer, we have made some changes.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors The manuscript has been improved as the reviewer intended. It is now OK for
publication.