What Do Radio Emission Constraints Tell Us About Little Red Dots as Tidal Disruption Events?
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe manuscript presents a proposal to explain the nature of the recently reported little red dots (LRDs), a phenomenon still under active investigation within the astronomical community. The abstract notes that the most widely discussed interpretations include active galactic nuclei (AGN) and star-forming activity in dusty galaxies. The paper cites recent works supporting these scenario, as well as other explanations suggesting that the nature of some LRDs could also be associated with tidal disruption events (TDEs), particularly in dense clusters. As stated in the second paragraph on page 2, the study takes the work of Bellovary (2024) as a starting point, reinforces this hypothesis with similar studies (e.g., Ramirez-Ruiz et al. 2009), and then focuses on the presence -or absence- of radio emission, referencing works such as Horesh et al. (2021), Sfaradi et al. (2022), and Alexander et al. (2020), among others.
The results, based on upper-limit estimates, are rather inconclusive and focus exclusively on the radio properties of the sample, leaving aside other aspects previously reported, such as the spectral energy distribution (SED; Wang et al. 2025), Balmer breaks (Braggen et al. 2024), source size, and detection limits (Casey et al. 2024), all of which are references cited within the manuscript. Nevertheless, although the results are marginal, and acknowledging that other proposed hypotheses have likewise not yet succeeded in explaining the true nature of LRDs, the scenario explored in the current draft cannot be ruled out. It may therefore be considered for publication as a potential explanation for some of these phenomena. This interpretation will require stronger support from future observations, improved sampling, and advances in observational technology.
Minor comments:
1. The sentence "Thus, it is not implausible that these high-redshift sources cannot be explained with a sole universal model, but could be disguising various kinds of astrophysical objects and processes" (line 171) could be replaced with a clearer, more direct alternative that avoids the double negative: "These high-redshift sources may reflect a diversity of astrophysical objects and processes rather than a single universal model."
2. Similarly, the expression "...would predict one TDE for ~1000 galaxies per year" (line 161) should be presented in the formal notation: 10⁻³galaxy⁻¹yr⁻¹, consistent with the format used elsewhere in the text.
3. Regarding the term "delayed launch" (line 164), although a couple of references are mentioned, this concept has not been developed consistently within the context of the present study. Given that only one of the sources analysed shows detectable radio emission, it would be advisable either to discuss the term in greater detail or to remove it from that paragraph altogether.
4. In the caption of Fig. 1, the RQ/RL threshold is mentioned, but the meaning of this transition is not visually evident in the figure itself until one examines the individual cases described in the Materials and Methods section (which could be more appropriately titled Methodology). It is recommended to explicitly describe in the caption the nature of the populations located above and below this threshold.
5. The last paragraph of the conclusions, that TDEs are acknowledged as plausible candidates to explain some LRDs, is premature to refer to "subsets" of these objects, since their nature has not yet been identified or catalogued. However, if the authors imply the existence of subsets and should future analyses confirm that LRDs do not represent an entirely homogeneous population (as acknowledged in the final paragraph of the manuscript), it is recommended that the authors explicitly clarify throughout the text that the proposed scenario is intended as a plausible explanation for a subset of LRDs, rather than for the population as a whole. Nevertheless, if the authors intend to propose it as an explanation for the entire population of LRDs, this should be stated explicitly and without ambiguity, and more proof would be needed. The paragraph should be completely reformulated to maintain consistency with the text and with the limited scope of the results.
Author Response
We thank the anonymous reviewer for their prompt and constructive comments and suggestions to improve our manuscript. Below we address (A) each of the referee’s questions/suggestions (Q). We denoted changes in the revised manuscript with boldface characters.
Q1. The sentence "Thus, it is not implausible that these high-redshift sources cannot be explained with a sole universal model, but could be disguising various kinds of astrophysical objects and processes" (line 171) could be replaced with a clearer, more direct alternative that avoids the double negative: "These high-redshift sources may reflect a diversity of astrophysical objects and processes rather than a single universal model."
A1. We corrected the text according to the Reviewer’s suggestion.
Q2. Similarly, the expression "...would predict one TDE for ~1000 galaxies per year" (line 161) should be presented in the formal notation: 10⁻³galaxy⁻¹yr⁻¹, consistent with the format used elsewhere in the text.
A2. The expression was corrected to match the formats in the paper.
Q3. Regarding the term "delayed launch" (line 164), although a couple of references are mentioned, this concept has not been developed consistently within the context of the present study. Given that only one of the sources analysed shows detectable radio emission, it would be advisable either to discuss the term in greater detail or to remove it from that paragraph altogether.
A3. We removed the phrase ‘delayed launch’ from the sentence.
Q4. In the caption of Fig. 1, the RQ/RL threshold is mentioned, but the meaning of this transition is not visually evident in the figure itself until one examines the individual cases described in the Materials and Methods section (which could be more appropriately titled Methodology). It is recommended to explicitly describe in the caption the nature of the populations located above and below this threshold.
A4. We added an explanation to the RQ/RL boundary in the caption. We changed the section title from Materials and Methods to Methodology.
Q5. The last paragraph of the conclusions, that TDEs are acknowledged as plausible candidates to explain some LRDs, is premature to refer to "subsets" of these objects, since their nature has not yet been identified or catalogued. However, if the authors imply the existence of subsets and should future analyses confirm that LRDs do not represent an entirely homogeneous population (as acknowledged in the final paragraph of the manuscript), it is recommended that the authors explicitly clarify throughout the text that the proposed scenario is intended as a plausible explanation for a subset of LRDs, rather than for the population as a whole. Nevertheless, if the authors intend to propose it as an explanation for the entire population of LRDs, this should be stated explicitly and without ambiguity, and more proof would be needed. The paragraph should be completely reformulated to maintain consistency with the text and with the limited scope of the results.
A5. We modified the respective paragraph in Results and discussion to match the statements in Conclusions.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear all, the paper is very nicely written. Just a few remarks
Abstract
* L14: are there other observation of LRD in other wavelengths that could constraint your model?
Introduction
* L25 where the disagreement with AGN has been quoted?
* L37 what is the dichotomy here quoted?
* L46 what Massive Black Hole means? Could you quote the range in masses?
* L59-60 radio detected TDE not energetic in radio? Or not bright?
* L75 - why the overall TDE rate is reported? Why is that so relevant?
Material and methods
* Table1 - TDE references? I would add a caption to explain where the values were taken from?
* L103 - where is the comparison?
* L116 - what is TDE_1? and TDE_2?
* L119 - what is the average sample?
Results and discussions
* L133 - could you put the value of the detected TDE on the plots?
* L140 typo on “luminosty”
* L141 - please order the references (first 18 than 19) - same In Figure2
* L144-145 - could you put the values of the detected TDE on the plots?
Author Response
We thank the anonymous reviewer for their prompt and constructive comments and suggestions to improve our manuscript. Below we address (A) each of the referee’s questions/suggestions (Q). We denoted changes in the revised manuscript with boldface characters.
Q1. L14: are there other observation of LRD in other wavelengths that could constraint your model?
A1. Considering that LRDs are not generally detected in the X-ray and far infrared bands either (as presented in the Introduction), these additional constraints could be utilised in future works, however, such analysis is beyond the scope of the manuscript.
Q2. L25 where the disagreement with AGN has been quoted?
A2. The details were already listed following this sentence, however, to clarify, we added additional citations to this statement.
Q3. L37 what is the dichotomy here quoted?
A3. We supplemented the sentence with the respective information (colours, spectral shape).
Q4. L46 what Massive Black Hole means? Could you quote the range in masses?
A4. We added the mass ranges and the respective citation to the text.
Q5. L59-60 radio detected TDE not energetic in radio? Or not bright?
A5. We corrected the term energetic to bright.
Q6. L75 - why the overall TDE rate is reported? Why is that so relevant?
A6. We included the overall value, i.e. the one not divided to RQ/RL populations, for comparison. We supplemented the sentence accordingly.
Q7. Table1 - TDE references? I would add a caption to explain where the values were taken from?
A7. We added the citation in the table caption.
Q8. L103 - where is the comparison?
A8. We extended the sentence accordingly.
Q9. L116 - what is TDE_1? and TDE_2?
A9. We extended the previous sentence to introduce these variables.
Q10. L119 - what is the average sample?
A10. We corrected this expression from average sample to mixed sample to better describe the mixed RQ-RL population.
Q11. L133 - could you put the value of the detected TDE on the plots?
A11. We added the luminosity and flux density of the only radio-detected LRD known so far to Fig.1. and Fig.2., respectively.
Q12. L140 typo on “luminosty”
A12. We corrected the word.
Q13. L141 - please order the references (first 18 than 19) - same In Figure2
A13. We corrected the citations to follow numerical order.
Q14. L144-145 - could you put the values of the detected TDE on the plots?
A14. As these sources were only mentioned for comparison solely for the spectral properties, and would make Fig. 1. overly crowded, we respectfully decline this request.
Reviewer 3 Report
Comments and Suggestions for AuthorsDear authors and referee,
The manuscript by Perger et al. entitled "What Do Radio Emission Constraints Tell Us About Little Red Dots as Tidal Disruption Events?" submitted as a brief communication to Universe presents an interesting discussion on the possibility of Little Red Dots, a mysterious population of sources at high redshifts discovered in JWST observations to be explained by TDEs occurring regularly in dense star clusters. The main methods employ analysis of existing radio observations of LRDs.
This paper definitely adds an interesting argument to the very intense and hot discussion on the nature of Little Red Dots and is definitely worth publishing. I do not see any serious flaws in the methodology or analysis presented in the paper.
My only concern, which I would recommend the authors to address in the revised manuscript will be a discussion on the apparent lack of (rest-frame) optical variability of known LRDs, many of which had multiple epochs of observations by JWST survey programs. I think that adding a paragraph or a subsection on this subject will definitely strengthen the manuscript's conclusions.
To be mentioned here as well -- the two recent papers on local Universe's analogs of Little Red Dots (Lin et al. arXiv:2507.10659 and Ji et al. arXiv:2507.23774) deal with much brighter sources, which also do not display long-term optical variability (they are bright enough to be measured using ZTF and even ATLAS). I would recommend mentioning these sources as well and perhaps discuss their radio properties -- to my knowledge, they remain undetected in GHz-band radio surveys (VLASS, RACS).
Author Response
We thank the anonymous reviewer for their prompt and constructive comments and suggestions to improve our manuscript. Below we address (A) the referee’s suggestions (Q).
Q. My only concern, which I would recommend the authors to address in the revised manuscript will be a discussion on the apparent lack of (rest-frame) optical variability of known LRDs, many of which had multiple epochs of observations by JWST survey programs. I think that adding a paragraph or a subsection on this subject will definitely strengthen the manuscript's conclusions.
To be mentioned here as well -- the two recent papers on local Universe's analogs of Little Red Dots (Lin et al. arXiv:2507.10659 and Ji et al. arXiv:2507.23774) deal with much brighter sources, which also do not display long-term optical variability (they are bright enough to be measured using ZTF and even ATLAS). I would recommend mentioning these sources as well and perhaps discuss their radio properties -- to my knowledge, they remain undetected in GHz-band radio surveys (VLASS, RACS).
A. We appreciate and acknowledge the suggestion of the Reviewer. However, a detailed examination of such properties are beyond the scope of the manuscript. We intended this short communication paper to specifically focus on the radio-quiescence of LRDs, independently from their individual optical properties. Similarly, as this work explores the possible nature of LRDs at high redshifts, their lower-redshift analogues do not fit the message of the paper. On the other hand, we are also convinced that the suggested topic by itself deserves an independent, detailed analysis in the future.
