Galaxy Group Ellipticity Confirms a Younger Cosmos
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors1- The manuscript has only one author but in header "RONG ET AL."?!
2- The manuscript is not written according to MDPI template. The author mentioned Fig 6, and 10 but the manuscript has only fig 1.
3- the abstract should has any reference please remove it.
4- Observation and simulation section need more specific details.
5- Split the section CONCLUSION AND DISCUSSION in to two separate sections, DISCUSSION and CONCLUSION.
Comments on the Quality of English LanguageLanguage is good.
Author Response
In the revised manuscript, all changes made are highlighted in bold.
1- The manuscript has only one author but in header "RONG ET AL."?!
--> We modified it in the revised manuscript with the MDPI template.
2- The manuscript is not written according to MDPI template. The author mentioned Fig 6, and 10 but the manuscript has only fig 1.
--> The revised manuscript is written with the MDPI template. Note that the figures referred to in the Discussion section, Fig. 6 and Fig. 10, are from the paper by Knebe et al. (2008), not from our manuscript. In the Discussion section, we recommend readers to refer to Fig. 6 and Fig. 10 in the paper by Knebe et al. (2008) for a visual understanding of the simulation results of the warm dark matter model.
3- the abstract should has any reference please remove it.
--> Done.
4- Observation and simulation section need more specific details.
--> In the revised manuscript, we have included additional details about the galaxy sample used for selecting the observational group sample, including the redshift and flux range of these galaxies. We have also briefly outlined the method used to calculate the stellar mass of each galaxy. Furthermore, we noted the exclusion of galaxy clusters near the survey boundaries. In addition, we have provided further information on the simulated sample, including details on the magnitude range of galaxies in the simulations. Readers are directed to Lim et al. (2017) for a comprehensive explanation of how the mock catalog was developed from simulations.
5- Split the section CONCLUSION AND DISCUSSION in to two separate sections, DISCUSSION and CONCLUSION.
--Done.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThe author compares the ellipticity of galaxy groups shown in the computer simulation against real ones and suggests that the disparity is due to the shorter time the real galaxy groups have had to relax into a more isotropic configuration.
The paper is clear and requires only minor changes. The motivation provided in lines 63-64 is somewhat weak. The explanation in lines 129-132 is unclear and potentially misleading; perhaps "faster relaxation" would be better than "long term relaxation."
Regarding the language, avoiding hyperbolic expressions (such as "imperative") could improve clarity.
Comments on the Quality of English Language
Sufficiently clear.
Regarding the language, avoiding hyperbolic expressions (such as "imperative") could improve clarity.
Author Response
In the revised manuscript, all changes made are highlighted in bold.
The author compares the ellipticity of galaxy groups shown in the computer simulation against real ones and suggests that the disparity is due to the shorter time the real galaxy groups have had to relax into a more isotropic configuration.
The paper is clear and requires only minor changes. The motivation provided in lines 63-64 is somewhat weak.
--> Our work is solely based on the study by Gu et al. (2024). In their study, Gu et al. found that the real Universe may be younger than expected by comparing the proportion of galaxy pairs with co-moving velocities in observations and simulations. While we could assess the age of the real Universe relative to theoretical expectations by examining other properties of galaxies in observations and simulations, such as metallicity and stellar population ages, the essence of Gu et al. (2024) lies in their work relying almost entirely on galaxy dynamics, which has less uncertainty compared to existing galaxy formation models and chemical evolution models. Their work primarily relies on galaxy dynamics, which is closely related to the cold dark matter model and clustering theory, with fewer uncertainties. Inspired by the work of Gu et al. (2024), we attempt to use the ellipticity of galaxy clusters to test the age of the real Universe, as the ellipticity of galaxy clusters is primarily related to the distribution of galaxies and is less dependent on galaxy formation models. Therefore, from this perspective, the work by Gu et al. (2024) is unique and serves as the sole motivation for our study. We have not found any other relevant work that allows for the measurement of the age of the Universe without relying on galaxy formation models or chemical evolution models.
The explanation in lines 129-132 is unclear and potentially misleading; perhaps "faster relaxation" would be better than "long term relaxation."
--> We change "long-term relaxation" to "faster relaxation" in the revised manuscript.
Regarding the language, avoiding hyperbolic expressions (such as "imperative") could improve clarity.
--> Done. We have modified the hyperbolic expressions, from "imperative" to "worth".
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsAuthors analyze the ellipticities of galaxy groups that are derived either from observation or from the theoretical simulations. Based on the analysis, the authors suggest the possibility of a younger age for our Universe and discuss the warm dark matter cosmology as a framework that explains found discrepancies. Some results of this paper are novel and might be published after replying to a few questions and suggestions.
- Could you please give mathematical definitions of shape?
- Are there cosmological phenomena or parameters that contradict the hypothesis of the earlier Universe? Could you please discuss them?
- Is it the first such analysis of ellipticities between data and simulations?
no comments
Author Response
In the revised manuscript, all changes made are highlighted in bold.
Authors analyze the ellipticities of galaxy groups that are derived either from observation or from the theoretical simulations. Based on the analysis, the authors suggest the possibility of a younger age for our Universe and discuss the warm dark matter cosmology as a framework that explains found discrepancies. Some results of this paper are novel and might be published after replying to a few questions and suggestions.
Could you please give mathematical definitions of shape?
--> We use cluster ellipticities to probe cosmic age. In section 3, we have clarified the definition of cluster ellipticity, epsilon=1-b/a, where a=sqrt(lambda1) and b=sqrt(lambda2) are the semi-major and semi-minor axes ratios of a cluster, and lambda1 and lambda2 are the two eigenvalues. We have also clarified how to estimate lambda1 and lambda2 with equation (1).
Are there cosmological phenomena or parameters that contradict the hypothesis of the earlier Universe? Could you please discuss them?
--> Done. Yes, Llorente de Andres' (2024) study on globular clusters suggests that the age of the universe today may be older than expected by theory. Furthermore, the latest findings from the JWST indicate the presence of significantly more massive galaxies at high redshifts than theoretical predictions, which could also suggest that the universe is older than expected by theory, as galaxies require sufficient time for star formation to grow in mass. These research results may contradict our findings and those of Gu et al. (2024), but it is worth noting that our work and that of Gu et al. (2024) rely almost exclusively on galaxy dynamics, meaning they are based solely on the framework of the cold dark matter model and clustering theory, with minimal uncertainties. In contrast, the studies on globular clusters and high-redshift galaxies mentioned earlier heavily rely on galaxy evolution models and chemical enrichment models, which have significant uncertainties. We discuss these in the Discussion section in the revised manuscript.
Is it the first such analysis of ellipticities between data and simulations?
--> Numerous studies have investigated the ellipticities of clusters in observations or simulations based on the distributions of galaxies, gas, or dark matter (e.g., Wang et al. 2008, MNRAS, 385, 1511; Shi et al. 2018, MNRAS, 475, 2421; Limousin et al. 2013, Space Science Reviews, 177, 155; Hopkins et al. 2005, ApJ, 618, 1). However, our work represents the first instance of using the same group finder to compare the simulated and observed cluster ellipticities with the 2D galaxy distributions. It is crucial and necessary to use the same group finder in simulations and observations, as different group finders often yield different member galaxies and ellipticities of galaxy clusters.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors responded to my questions well and the paper can be published.
Comments on the Quality of English Language-
