Stability and Damping in the Disks of Massive Galaxies
Round 1
Reviewer 1 Report
I attached a file that indicates a few points where the presentation could be improved. This includes: elucidated of the problem with more modern references, more illustrative figures, and a little more detail in the presentation.
Comments for author File: 
Comments.pdf
Author Response
Please see attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This is a small review article an a limited set of methods to investigate disk stability. It is not introducing any really new result but "ideas" ( often introduced quite fenomenologically) explored in the literature and often not quantified by any support of numerical/dynamical simulations.
Could serve, on the other hand, as a short introduction to young researchers in the field to have a quick overview of few problems although the number of cited studies is often quite limited and not exhaustive. Many problems have a hydrodynamical nature and no reference if provided to simulations.
Few notes:
1. line 20: RMS not defined
2. line 26 insignificant should be quantified.. maybe negligible? But please quantify with some reference
3. line 27 mass-> what mass? stellar? gas? dust?
4. Line 68 By considering -> For example, by considering..
Section 4 in particular just introduces potential damping mechanisms often in a oversimpified way.
Subsection 4.2: the description of the ISM is quite naive sometimes expecially when its build up is explained as :
"The interstellar medium (ISM) is a mixture of gas and dust remaining from: a) the formation of
the galaxy; b) ejection by stars; and c) accretion from outside the galaxy."
a) is probably galaxy assembly throughout mergers and smooth accretion
b) is probably mechanical feedbak by stelar winds but no mention to supernovae feedback is found while critical to explain the metallicity and dust content of the ISM.
c) Accretion meaning by gas accretion from the CGM or throughout mergers?
The ISM structure is more complex that the provided picture and numerical studies on galaxy assembly and ISM build up are totally missing.
Section 5.
line 328: This remarkable stability appears to persist despite galactic mergers in the early Universe ->
This is another naive point as the merger rate changes with redshift while disk galaxies are found at even z>4. The stability of the disk should be explained cosmologically through minor/major mergers while estimates for the angular momentum stabilizing the disc and cooling it thanks to internal damping are effective when the galaxy is in a isolated evolutionary stage... time scales of al mechanisms and a comparison could be useful.
Note that during galaxy assembly minor mergers are occurring quite at any time... All the above considerations emerge clearly from modern cosmological simulations of galaxy formation with a proper hydrodynamical treatment ... all missing here.. significantly biasing the manuscript content
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
The paper Stability and Damping in the Disks of Massive Galaxies by J. H. Marr deals with the behaviour of star orbits in galactic disks, and in particular with the surprising stability of rotational orbits over timescales comparable to the Hubble time. The paper is well written, concise and to the point. The analysis of the damping mechanisms that stabilise rotational orbit is of interest. There are however a few points relevant to the science content that should be clarified by the author. I thereby recommend major revision.
p. 7: Eq. 3 should be checked and explained better, as it is not expressing conservation of energy in its present form. Please give indicative values of Δv and vdrift earlier in the paper.
l. 177ff: text should be rewritten and clarified. As a more general commentary, I am not sure that enforcing energy conservation is the best choice here. The problems of motion of a star across Oort clouds may be more appropriately treated as a form of dynamical friction. The author should at least discuss this possibility.
p. 7: consistency of units: ρ should be in kg/km3 ; also units that are more relevant to the context of the paper should be used. Δm in Eq. 2 is a quantity per unit time; in Eq. 3 is not. l. 190: Δv is given with the units an acceleration.
p. 9 vdrift/s per Myr: unclear
l. 167: "gravitational radius" has a widely used meaning that is much different from the meaning in this paper. Better reword.
p. 11 Eq. 12 is not rigorous. A simple multiplication of the star formation rate and of the death rate of stars is not properly giving the slope of the mass function of a stellar population. I suggest that the authors removes Eq. 12 and presents the calculation as only indicative.
p. 11, l. 318: I doubt that the situation discussed in the paper is applicable post merging. "despite galactic mergers" should be dropped.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Thank you for considering my review. I have no further suggestions.
Reviewer 2 Report
Paper ready for publication
Reviewer 3 Report
I think the author has answered to my questions.
