{"id":"378da86f-8056-4626-b698-19c07349bbab","arxiv_id":"2506.05474","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"In the IllustrisTNG simulations, ram-pressure-stripped jellyfish galaxies host luminous active galactic nuclei more often than centrals or ordinary satellites, suggesting the cluster environment can feed supermassive black holes.","lead":"This paper uses two large cosmological simulations to show that jellyfish galaxies, satellites with long gas tails stripped by their surroundings, are more likely to host actively feeding supermassive black holes than other galaxies of the same mass. The result supports the debated idea that ram pressure from the cluster environment can push gas inward and trigger black hole activity.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Ram-pressure feeding is not yet identified: the pericentric P_ram–n_gas–L_AGN alignment is shown only for jellyfish, without a matched gas-rich non-jellyfish control, so generic orbital-phase or gas-selection effects remain viable.","rationale":"Agree with the reader that the causal interpretation is the weakest link. The AGN-fraction comparison (Figure 3) is reasonably robust: jellyfish are compared with centrals, all satellites, and gas-rich inspected satellites in stellar-mass bins, and the qualitative trend survives luminosity cuts (Appendix B). The mechanistic conclusion (Conclusions iii) depends instead on Figures 4-6, where only jellyfish tracks are shown. Because jellyfish are selected for having tails, which are most visible when ram pressure is high, the pericentric alignment of P_ram with n_gas and L_AGN in the selected sample is partly built into the selection. A matched control of gas-rich inspected non-jellyfish satellites is the decisive missing experiment. The paper's own caveats, including the weak stacked correlation and the 35% Case-3 fraction, reinforce that the case-by-case visual classification is doing much of the work. The recommended verdict is unchanged: the population claim is credible, but the mechanism claim should be accepted only after the control-track test is performed. This is not a matter of model inconsistency but of internal evidence sufficiency.","tokens_in":34349,"tokens_out":8156,"duration_ms":97005,"concrete_test":"Rerun the per-galaxy time-tracking analysis of Section 4.1 on the z=0 'inspected, non-jellyfish' satellites, matched to the jellyfish sample in stellar mass, gas fraction at infall and at z=0, and host halo mass, using the same P_ram, n_gas, and L_AGN definitions and the same first-pericenter alignment. Measure the fraction of control galaxies whose tracks show Case-1-type alignment, with P_ram, n_gas, and L_AGN peaking together. If the control fraction is comparable to the ~50% found for jellyfish, the enhancement is a generic orbital-phase or gas-retention effect and the ram-pressure-feeding conclusion fails; if it is substantially lower, the jellyfish-specific claim is supported.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The population-level result that jellyfish have elevated AGN fractions is fairly well supported. The load-bearing weakness is the causal step (Conclusions item iii): the claim that ram pressure compresses central gas and boosts SMBH accretion rests on the time-series alignment of P_ram, n_gas, and L_AGN around first pericenter for the 242 z=0 jellyfish (Figures 4 and 5). This evidence lacks a control sample. Every jellyfish is by construction gas-rich and selected because it currently shows a stripped tail; both properties peak when a satellite is near pericenter, and a satellite near pericenter also sees higher ambient density and velocity by orbital mechanics alone. Without tracking gas-rich inspected satellites that are not classified as jellyfish, matched in stellar mass, f_gas at infall and at z=0, and host halo mass, one cannot distinguish ram-pressure-driven compression from a generic pericentric orbital-phase effect or from the selection of galaxies that happen to retain gas. The paper itself reports that the stacked P_ram-L_AGN correlation is 'somewhat weak' (Figure 5 caption) and that 35% of jellyfish fall in Case 3, where n_gas rises but L_AGN does not; the direct Case 1 classification is by visual inspection of evolutionary tracks and is not quantified or blinded. Therefore the central mechanistic claim is underdetermined.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This manuscript uses the IllustrisTNG simulations (TNG50 and TNG100) to study supermassive black hole (SMBH) activity in z=0 jellyfish galaxies identified by the Cosmological Jellyfish Zooniverse project, comparing them to central galaxies, all satellites, and gas-rich inspected satellites that are not classified as jellyfish. The authors report that jellyfish have higher AGN fractions than centrals and satellites of the same stellar mass, especially at M_stellar > 10^10 Msun, and that jellyfish have higher central gas densities and lower central sound speeds than other gas-rich satellites. From individual evolutionary tracks and a stacked time evolution, they claim that ram pressure peaks near first pericenter together with central gas density and sometimes AGN luminosity, and they interpret this as evidence that ram pressure compresses central gas and feeds SMBH accretion. The paper includes robustness tests with different AGN luminosity thresholds, a treatment of missing SMBHs, and a discussion of AGN feedback modes.","tokens_in":34639,"tokens_out":4713,"duration_ms":57002,"significance":"If the causal claim holds, this would be one of the first population-scale simulation results supporting the idea that ram pressure can directly fuel SMBHs in cluster satellites, providing a theoretical counterpart to some observational claims (e.g., GASP). The population-level finding that jellyfish have elevated AGN fractions is robust and is a valuable, falsifiable TNG prediction; the luminosity-cut tests and the comparison to gas-rich inspected satellites strengthen this part of the paper. The mechanistic claim (ram pressure compresses central gas and boosts accretion) is the novel and most important contribution, but it is currently the least supported part of the analysis.","major_comments":[{"comment":"The stacked time evolution that forms the main evidence for ram-pressure feeding is shown only for jellyfish galaxies; there is no control sample of gas-rich inspected non-jellyfish satellites matched in stellar mass, gas fraction at infall and at z=0, and host halo mass. Because jellyfish are by construction gas-rich and are visually identified at a time when they show a stripped tail, the temporal alignment of P_ram, n_gas, and L_AGN near first pericenter could be a generic orbital-phase effect or a consequence of gas-rich selection rather than a causal effect of ram pressure on the SMBH. The manuscript itself states that the correlation between ram pressure and AGN luminosity is 'somewhat weak' (Figure 5 caption) and that only about 50% of jellyfish fall in Case 1. A matched control stack is needed to distinguish the proposed mechanism from the alternative that any gas-rich satellite near pericenter shows the same behavior.","section":"Section 4.1 and Figure 5"},{"comment":"The classification of jellyfish into Cases 1, 2, and 3 is based on visual inspection of individual evolutionary tracks, with no quantitative criterion or blinded procedure described. The fractions (50%, 15%, 35%) are used to argue that ram pressure feeds SMBHs in a majority of jellyfish, but the subjectivity of this classification makes the quantitative claim difficult to evaluate. A reproducible measure, such as a cross-correlation or peak-triggered average of P_ram and L_AGN within a defined window around first pericenter, with a pre-specified threshold, would make the case fractions verifiable and would also allow the stacked result in Figure 5 to be interpreted more cleanly.","section":"Section 4.1, Cases 1-3"},{"comment":"The paper acknowledges that jellyfish must be gas-rich and in the thermal AGN feedback mode to be classified as jellyfish (e.g., 'jellyfish are necessarily biased towards accretion and feedback in the thermal mode to even have the chance to retain gas and to appear ram-pressure stripped'). Since the Bondi accretion rate in Equation (1) scales with gas density and inversely with the cube of the sound speed, the higher n_gas and lower c_s of jellyfish could be a direct consequence of this selection rather than of ram-pressure compression during pericenter passage. The causal interpretation requires controlling for the pre-infall central gas density or gas fraction, or demonstrating that the pericentric increase in n_gas exceeds what is expected from the gas-rich selection alone. As written, the evidence does not exclude the simpler explanation that jellyfish are selected to have high central gas density, which directly raises their Bondi accretion rates.","section":"Sections 3.1, 5, and Appendix C"}],"minor_comments":[{"comment":"Equation (2) and the surrounding text refer to the 'Thompson' cross section; the standard spelling is 'Thomson' cross section.","section":"Section 2.1.2"},{"comment":"The text says 'utilizes the arepocode'; this should be 'Arepo code' with a capital letter for the code name.","section":"Section 2.1.1"},{"comment":"The robustness of the results to the 'fudge' SMBH assignment for galaxies with missing black holes is not tested; excluding the 1-3% of jellyfish with lost SMBHs would confirm that the high AGN fractions are not driven by the assigned Gaussian values.","section":"Section 2.4.2 and Appendix A"},{"comment":"The text says 'we test, but we do not show, whether the peak in the AGN luminosity would be stronger in a high stellar mass bin'; this test could usefully be moved to an appendix since the mass dependence is a central part of the population-level result.","section":"Figure 5 and Section 4.1"},{"comment":"There are several instances where 'effect' is used where 'affect' is intended, for example 'ram pressure can indirectly effect SMBH activity' and 'could inhibit or enhance the impact of ram pressure on the SMBH'.","section":"Section 4.1 and Figure 4"},{"comment":"The caption describes the inner r=2 ckpc as a 'dashed white circle' and r=1 ckpc as 'solid dashed circle'; the latter should likely read 'solid white circle'.","section":"Figure 6 caption"}],"recommendation":"major_revision","confidential_remarks":"The paper presents a robust population-level result that jellyfish galaxies in TNG have enhanced AGN fractions, which is well supported by the luminosity-cut tests and KS comparisons. The main weakness is the causal interpretation in Section 4, which currently lacks a matched control sample and uses a subjective classification of evolutionary tracks. I believe the central claim is defensible but needs substantial additional analysis to rule out selection effects; this is fixable within the scope of the manuscript, so I recommend major revision rather than rejection. Please ensure the requested control-sample analysis is clearly described and the case classification is made quantitative."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"First thing to know: this is a solid, honest simulation paper with a robust population-level result—TNG jellyfish host luminous AGN at higher fractions than mass-matched centrals and other satellites—but the causal claim that ram pressure feeds the SMBH is not nailed down. The evidence for the correlation is good; the evidence for the mechanism is circumstantial.\n\nWhat's new: it is the first population study of SMBH activity in visually classified jellyfish in IllustrisTNG. It uses the Zooniverse Cosmological Jellyfish sample (242 at z=0) and compares to centrals, satellites, and inspected gas-rich non-jellyfish satellites. The AGN fraction enhancement is robust to multiple luminosity thresholds and is strongest at M_stellar > 10^10, where it holds up in KS tests. The paper is careful to separate the selection effect: jellyfish must be gas-rich, and the comparison to inspected satellites addresses the gas-poor satellite bias. The acknowledgment that the stacked P_ram-L_AGN correlation is weak, and the honest breakdown into three cases (50% direct, 15% delayed, 35% no AGN response), is a model of restraint. They also document the missing-black-hole fudge and test luminosity cuts—methodological care is real.\n\nSoft spots: the mechanistic conclusion (Conclusions item iii) overreaches. The time-series alignment of P_ram, n_gas, and L_AGN at pericenter is shown only for jellyfish. There is no matched control sample of gas-rich inspected satellites tracked through their own pericentric passages. Both jellyfish selection and a generic orbital-phase effect—rising ambient density and velocity at pericenter, plus the requirement that the galaxy still has gas—can produce the same stacked pattern. The paper's own Figure 5 caption admits the correlation is 'somewhat weak,' and Case 3 (35%) shows density rises without AGN response. So the claim that ram pressure compresses and feeds is plausible and qualitatively consistent with wind-tunnel simulations, but it is not identified here. A matched time-series control would be the decisive test.\n\nAlso minor: the comparison to observed AGN fractions (GASP) is impressionistic; the TNG luminosity is a Bondi-based proxy, not a mock observation, and the normalization offset (~20-30 percentage points) is hand-waved as selection effects. That part is appropriately hedged but underdeveloped.\n\nWho it's for: anyone working on environmental quenching, AGN triggering in satellites, or using TNG for ram-pressure studies. It will be a standard reference for the population result even if the mechanism remains open.\n\nRecommendation: send to a serious referee, not desk reject. The causal claim needs a control sample before it can be taken as established, but the paper itself is honest enough that a careful revision can fix it. For peer review: accept but require the matched control analysis.","headline":"Robust AGN excess in TNG jellyfish, but the ram-pressure-feeding mechanism is underdetermined without a matched control.","tokens_in":35207,"tokens_out":3459,"would_cite":true,"duration_ms":35142,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"According to the simulations studied here, ram pressure from the cluster medium compresses gas in jellyfish galaxies and can feed their central supermassive black holes, making them more likely to shine as AGN.","keywords":["jellyfish galaxies","ram-pressure stripping","supermassive black holes","active galactic nuclei","galaxy clusters","satellite galaxies","cosmological simulations","black hole accretion"],"falsifier":"Re-run the identical simulation suite with ram pressure artificially disabled while keeping orbital dynamics and gas content identical; if jellyfish still show the same central-gas density and AGN luminosity peaks near pericenter, the claim that ram pressure feeds SMBHs is falsified.","tokens_in":34150,"feed_emoji":"🪼","tokens_out":11846,"duration_ms":121304,"temperature":0.7,"pith_summary":"This paper asks whether the same ram pressure that strips gas tails off jellyfish galaxies — cluster satellites moving through hot intracluster gas — can also feed their central supermassive black holes. Using two large cosmological simulations, the authors compare jellyfish galaxies with ordinary central galaxies and with other satellites of equal stellar mass. They find that jellyfish are more likely to host luminous active galactic nuclei (AGN), with an AGN fraction of 50–70 percent above $10^{44}$ erg s$^{-1}$ that rises with stellar mass. Following individual galaxies through their orbits, they see ram pressure, central gas density, and black-hole luminosity peaking near the first close passage to the cluster centre, and argue that ram pressure compresses central gas, lowers its sound speed, and thereby boosts Bondi accretion. The result matters because it suggests the environment, not just internal secular processes, can drive nuclear activity in a large fraction of stripped satellites.","feed_headline":"Ram pressure feeds black holes in simulated jellyfish galaxies","feed_subtitle":"In cosmological simulations, cluster gas ram pressure raises AGN incidence, especially in massive stripped galaxies.","key_machinery":"The load-bearing object is the Bondi-Hoyle-Lyttleton accretion prescription used in the simulation's black-hole model, $\\dot{M}_{\\rm Bondi} \\propto M_{\\rm SMBH}^2 \\rho / c_s^3$, which converts the gas density $\\rho$ and sound speed $c_s$ within a kiloparsec of the black hole directly into an accretion rate and hence into an AGN luminosity. This is paired with the classic ram-pressure formula $P_{\\rm ram} = \\rho_{\\rm LBE}\\, v_{\\rm rel}^2$, computed from the gas in the local background environment around each satellite. Together they carry the causal argument: as a jellyfish approaches the cluster centre, rising $P_{\\rm ram}$ is associated with higher central $\\rho$ and lower central $c_s$, and the Bondi formula turns those changes into enhanced accretion and luminosity. The analysis also relies on the simulation's thermal-versus-kinetic AGN feedback threshold, because jellyfish almost always sit in the thermal, high-accretion mode, whereas gas-poor satellites fall into the kinetic, low-accretion mode.","core_discovery":"According to the cosmological simulations analysed in this paper, jellyfish galaxies have more active supermassive black holes than centrals and other satellites of the same stellar mass: their SMBHs have higher accretion rates and luminosities, with nearly all jellyfish above $L_{\\rm AGN} \\gtrsim 10^{42}\\ \\mathrm{erg\\,s^{-1}}$ and 50–70 percent above $10^{44}\\ \\mathrm{erg\\,s^{-1}}$. The AGN fraction rises with stellar mass and is highest above $M_{\\rm stellar} \\gtrsim 10^{10}\\,M_\\odot$, where it declines for other galaxy populations but keeps rising for jellyfish. The paper attributes this to the environment: ram pressure from the cluster medium compresses gas within a kiloparsec of the nucleus, raising its density and lowering its sound speed, which in the Bondi accretion prescription raises the accretion rate and the AGN luminosity. The direct chain — ram-pressure peak, then central gas density and AGN luminosity peak near the first pericentric passage — is clearly visible in about half of the jellyfish, with another 15 percent showing delayed AGN enhancement; the remaining third shows enhanced central gas without an AGN response.","pith_inferences":["The quantitative AGN enhancement in the simulations is tied to the Bondi formula's steep dependence on sound speed ($c_s^{-3}$); a more realistic accretion model that accounts for angular momentum and radiation pressure could substantially change the magnitude or even the sign of the environmental effect, so the claim should be re-tested with higher-resolution runs that resolve the accretion regio","Because jellyfish are selected to be gas-rich, part of the reported AGN excess may be a selection effect rather than a direct consequence of ram pressure; a clean experiment would compare gas-rich satellites with identical gas fractions and orbital histories, with and without environmental stripping, to isolate the causal contribution.","The same feeding mechanism would plausibly apply in other dense gas environments, such as galaxy groups, protoclusters, or the early universe; a search for enhanced AGN incidence in compact groups or high-redshift protoclusters would be a direct observational test of the general mechanism.","The presence of about one-third of jellyfish with compressed central gas but no AGN response suggests that either the inflow's angular momentum or the AGN duty cycle controls whether environmental feeding actually lights up the black hole; this could be investigated by tracking the angular momentum and radial velocity structure of the gas within the Bondi radius in the simulations."],"forward_implications":["Jellyfish galaxies are, on average, more likely than other galaxies of the same mass to host a luminous AGN, with 50–70 percent above $10^{44}$ erg s$^{-1}$ and a fraction that continues to rise with stellar mass even as other populations decline.","In about two-thirds of jellyfish, the first close passage to the cluster centre is accompanied by enhanced central gas density and a direct or delayed increase in AGN luminosity, indicating that ram pressure can act as an environmental trigger of black-hole accretion.","The one-third of jellyfish with compressed central gas but no AGN enhancement shows that ram-pressure feeding is not guaranteed; some additional condition — stellar mass, orbital configuration, or feedback state — determines whether the nuclear response occurs.","Jellyfish almost all remain in the high-accretion thermal feedback mode, while gas-poor satellites fall into the low-accretion kinetic mode; this reinforces the picture that the availability of central gas is the key link between environment and observable nuclear activity.","The same stripping that temporarily feeds the black hole ultimately removes the gas, so the environmental AGN boost is transient and coexists with the long-term quenching of satellite galaxies."],"supporting_citations":[{"why":"Supplies the SMBH seeding, Bondi growth, and thermal/kinetic feedback model that the entire analysis builds on.","marker":"Weinberger et al. 2017"},{"why":"Provides the simulation-based jellyfish identification and gas property definitions used in the analysis.","marker":"Yun et al. 2019"},{"why":"The citizen-science catalog from which the jellyfish sample is drawn.","marker":"Zinger et al. 2024"},{"why":"Establishes the sample selection and the ram-pressure measurements for TNG jellyfish used here.","marker":"Rohr et al. 2023"},{"why":"The observational AGN fraction in jellyfish to which the simulated fractions are compared.","marker":"Peluso et al. 2022"},{"why":"The initial detection of AGN in jellyfish galaxies that motivates the hypothesis.","marker":"Poggianti et al. 2017a"},{"why":"An independent simulation-based result that ram pressure enhances SMBH accretion during pericentric passage, which this paper's findings corroborate.","marker":"Ricarte et al. 2020"},{"why":"Provides the ram-pressure formula used to compute $P_{\\rm ram}$.","marker":"Gunn & Gott 1972"},{"why":"Defines the local background environment (LBE) and its gas density/velocity measures used for ram pressure calculations.","marker":"Ayromlou et al. 2019"}],"fun_headline_variants":["Ram pressure switches on black holes in jellyfish galaxies","Jellyfish galaxies host more active black holes in simulations","Simulations reveal ram pressure fuels AGN in jellyfish galaxies","Stripped jellyfish galaxies show enhanced black hole activity","Black holes in jellyfish galaxies get a boost from ram pressure"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The causal link assumes that the observed alignment between ram-pressure peaks, central gas density rises, and AGN luminosity peaks near the first pericentric passage is actually caused by the ram pressure, rather than by the purely orbital phase or by the fact that jellyfish are selected because they are gas-rich.","fun_headline_variants_meta":{"raw":{"variants":["Ram pressure switches on black holes in jellyfish galaxies","Jellyfish galaxies host more active black holes in simulations","Simulations reveal ram pressure fuels AGN in jellyfish galaxies","Stripped jellyfish galaxies show enhanced black hole activity","Black holes in jellyfish galaxies get a boost from ram pressure"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001003,"raw_usage":{"total_tokens":4361,"prompt_tokens":1178,"completion_tokens":3183,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":794,"completion_tokens_details":{"reasoning_tokens":3101}},"tokens_in":794,"tokens_out":3183,"duration_ms":25097,"temperature":1.0,"reasoning_tokens":3101,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T10:20:46.249279+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Re-run the identical simulation suite with ram pressure artificially disabled while keeping orbital dynamics and gas content identical; if jellyfish still show the same central-gas density and AGN luminosity peaks near pericenter, the claim that ram pressure feeds SMBHs is falsified.","supporting_citations":[],"review_version":1}