A Multiwavelength Dynamical State Analysis of ACT-CL J0019.6+0336

Round 1

Reviewer 1 Report

The article presents X-ray, radio and optical properties of the cluster of
galaxies ACT-CL J0019.6+0336, at z=0.266 showing a high S/N SZ emission. The authors investigate the level of distturbance of this cluster by studying 
several X-ray (XMM-Newton data) and optical (DES imaging and photometry)  morphological parameters. The results presented in this work are not very  conclusive. While the optical density map shows a clear bimodality, the morphological parameters indicate that J0019 may even be a relaxed galaxy system.

Taking into account all the data and information presented in this work, I
 provide some major corrections. Please, see file attached.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer. 

Thank you for these helpful comments. I have made the necessary changes as follows:

1. The velocity dispersion information analysis was added under section 3.4 with the appropriate analysis and discussion.
2. Flux values and spectroscopic redshifts were added in Table 2.
3. The abstract has been rewritten in a more conclusive way.
4. Flux values and spectroscopic redshifts were added in Table 2.
5. This info was added to the caption
6. This info was added to the caption and also referenced in the text.
7. A paragraph was added to the discussion including the results from section 3.4 and the conclusion was edited accordingly

Reviewer 2 Report

Comments to the authors

The paper presents the result of a follow up study of the radio observations of the cluster of galaxies ACTJ0019.6 using MeerKAT. Compiling X-ray and optical imaging data from the literature and combining with the radio image, they derived various morphological parameters. Although the data and analysis are fine and the parameters are useful, the authors do not present any concusive statement about the dynamics of the cluster. I would like to comment the following in order to improve the paper.

1. Title:

The title is not informative, although it might work as an internal circulation inside the team. 

2. Abstract: 

The first half is a general introduction to cluster research, may be removed. The authors state, the purpose of this paper is ".... to investigate the level of disturbance", but there is no description of the level nor any answer to the motivation throughout the paper.

3. Figures: 

MeerKAT data are excellent, but may better be displayed by presenting contour maps of 
A) full UV coverage (does "full resolution" mean this?), 
B) long baselines,
C) short baselines (must be equivalent to D. Are contours in Fig. 1 this? What is meant by "large scale filtered image contours"?), 
D) smoothed map of A (Fig. 1 contours are this?).  

4. Parameters and physics:

The authors present various morphology parameters, which are valuable. However, they are not used to derive conclusive physics of the cluster.

Moreover, if the authors aim at studying the cluster itself as the targeting object, and if their purpose is to understand dynamics of the cluster, at least the mass, potential/kinetic energies and velocity dispersions should be presented along with X-ray temperature (kT) and density (EM). They also mention about turbulence, while do not discuss it from their data such as the radio brightness, which can be used to estimate the magnetic fields, hence the strength of dynamo through the turbulence. 

The authors appear to believe that the cluster is a merger or on the way of merging. Then discussion of the masses of colliding clusters and mutual velocity would be crucial to clarify the undergoing dynamics. Is each cluster gravitationally bound, are both bound to each other (merging) or unstable (not merging), how is the Virial (dynamical) consideration related to the morphology parameters, etc.?

5. Discussion and conclusion: 

As above, inspite of the various calculated parameters, the result about the dynamics of the cluster is not well described, often stating "inconclusive" , "mixture of relaxed and unrelaxed", ..., I would suggest for the authors to state more clearly, what was the purpose of this paper, and what new aspect and physics of the cluster were obtained. Namely, what was followed up?

Author Response

Dear Reviewer

Thank you for the helpful comments. I have made the following changes to the paper:

1. The title has been changed to ' The dynamical state of ACT-CL J0019.6+0336 from multiwavelength data'
2. The abstract has been changed, shows more results, and is written in a conclusive way
3. The MeerKAT contours have not been added as the radio image is shown to emphasize the diffuse emission. This would be obstructed by the long baseline contours. Moreover, the long-baseline radio contours are shown in the optical image. The large-scale contours come from the filtering technique mentioned in the radio section (I've added a reference). 
4. Section 3.4 was added with a velocity dispersion study of 17 optically confirmed cluster members showing bimodality and an offset between the BCG velocity and the mean velocity. Moreover, we calculate the dynamical mass and find a discrepancy between the SZ mass, the X-ray mass, and the dynamical mass.
5. A paragraph was added to the discussion to include section 3.4's results and the conclusion was rewritten in a more conclusive way.      

Round 2

Reviewer 1 Report

I have reviewed the new material added to the manuscript, and I think  the article is now much more complete and convincing. However, I have a few comments:

1) Section 2.2. The authors should specify in the text the sky area contained the 17 SDSS spectroscopic redshift. This would help the readers to compare the coverage of the optical analysis with R500 and/or R200 of the cluster.

2) Caption of Fig. 4: The datum concerning the bin size is wrong. The text specify a bin size of 600 km/s, while the figure is made using a bin size about 350 km/s (<500 km/s for sure). This should be corrected.

3) In section 5, at the end of the third paragraph, the authors claim that "the cluster merger is occurring along this line". This is not strictly correct because the velocity histogram shows a clear bimodality and the BCG shows an offset in velocity. These facts indicate that the collision has a clear component in the line-of-sight direction. So, the merging is probably not contained in the plane of the sky and following the North-South direction. At least, not completely. Probably, the sentence "suggesting that the cluster merger is occurring along this line" can be modified as follows: "The bimodality detected in the velocity distribution and the offset of the BCG respect the mean velocity of the cluster suggest that the cluster merger has a clear component in the line-of-sight direction. However, the DES density maps, the MeerKAT and XMM surface brightness shape show an elongation in the north-south, which suggests that the collision also present a velocity component contained in the plane of the sky and follows this N-S axis."

I suggest the authors to implement these few corrections.

Author Response

Dear Reviewer

Thank you for your help in refining the presentation and clarity of the paper. I greatly appreciate it. I have made the appropriate changes according to the 3 points outlined below.

In terms of the English standard of the paper, while minor lapses in the English style remain, the paper has been widely reviewed and edited by the authors. More changes have been made throughout the paper to improve the English expressed, but if possible, can the reviewer provide guidance or examples on how else to improve the English? Alternatively, should this paper go through an extensive English revision through the service listed on the mdpi website? 

Reviewer 2 Report

The paper has been revised appropriately, just few minor revision:

Fig. 4: Please present the source of the data and  reference(s).  If you used the same data and figure as those by the other referee , is some  acknowledgement  not necessary?

Author Response

Dear Reviewer

Dear Reviewer

Thank you for your help in refining the presentation and clarity of the paper. I greatly appreciate it. I have made the appropriate changes according to the 2 points outlined below.

In terms of the English standard of the paper, while minor lapses in the English style remain, the paper has been widely reviewed and edited by the authors. More changes have been made throughout the paper to improve the English expressed, but if possible, can the reviewer provide guidance or examples on how else to improve the English? Alternatively, should this paper go through an extensive English revision through the service listed on the mdpi website?