{"id":"90aad28e-db55-492a-b680-3270e1b50f0e","arxiv_id":"2501.05354","paper_version":1,"verdict":"UNVERDICTED","confidence":"HIGH","novelty_score":3.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"A review proposing that ESO multi-object and integral-field spectrographs can provide the redshift and multi-phase gas follow-up needed to exploit SKAO radio surveys.","lead":"This paper reviews how ESO's spectrographs can support the Square Kilometre Array in studying galaxy evolution. It recommends specific follow-up strategies and calls for joint planning between the two observatories.","discovery_kind":"review","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Feasibility claims in Figs. 2–3 equate 2h/1h optical–NIR magnitude limits with spectroscopic follow-up capability, but a continuum detection does not guarantee a secure redshift, so the quoted 100%/50% completeness fractions are not yet established.","rationale":"The reader's weakest_assumption is the accuracy of T-RECS counts and the optimism of the magnitude limits. I agree those are uncertainties, but they are not the most load-bearing because a factor-of-two error in T-RECS counts would not change the qualitative recommendation; 4MOST and MOONS would still be useful follow-up instruments. The stronger issue is the gap between 'detectable continuum' and 'secure redshift.' The article explicitly motivates MOS follow-up as redshift survey campaigns, yet Figures 2–3 define the detectable populations solely by broad-band magnitude cuts, and no redshift-extraction success rate is presented. The quantitative completeness fractions are then used to argue for a 'good match' between source counts and fibre densities. If realistic redshift success is substantially lower, the resource-allocation argument is weakened even if T-RECS is correct. The proposed mock-observation test would settle this directly. The paper deserves credit for citing ORCHIDSS as an approved 4MOST survey and for acknowledging that only 25–30% of radio AGN are reached by 4MOST, but that acknowledgment makes the absence of a redshift-yield estimate more conspicuous. Since the paper is a planning document without a novel testable scientific claim, the concern does not change the UNVERDICTED verdict, but it should be addressed before the quantitative figures are used to justify survey time allocations.","tokens_in":99,"tokens_out":6312,"duration_ms":133367,"concrete_test":"Take the T-RECS catalogue used in Figures 2–3, select sources above the EMU (S1.4>100 uJy), MIGHTEE (S1.4~10 uJy) and planned SKA-Mid WIDE (S1.4>20 uJy) limits, generate mock 2h 4MOST low-resolution and 1h MOONS spectra using the public exposure-time calculators and T-RECS SEDs, add realistic sky and noise, and run a standard redshift fitter with a conservative quality flag. Compare the secure-redshift fraction per radio-flux bin with the 'detectable' fractions from the paper's magnitude cuts; a shortfall greater than 20% in any bin relevant to the proposed follow-up strategy would directly falsify the completeness interpretation used to support the resource-allocation argument.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Figures 2 and 3 use 'detectable by 4MOST in two hours' and 'detectable by MOONS in one hour' as the selection for spectroscopic follow-up, with cuts rAB<22.5 and HAB<22. The text then concludes that 4MOST can detect all EMU/SKA all-sky galaxies and 25–30% of radio AGN, and MOONS all galaxies and ~50% of AGN, and uses these fractions to argue that the fibre densities provide a good match. The unstated step is that for a redshift survey the relevant quantity is the fraction of targets from which a secure redshift can be extracted, not the fraction with continuum S/N above some threshold. At r~22.5 or H~22, redshift success depends on emission/absorption line strength, spectral energy distribution, and sky-line residuals; many faint early-type or dusty sources, and most AGN-dominated spectra, yield ambiguous or failed redshifts. The figures contain no simulation of the observing/redshift-fitting process and no success-rate curve, so the plotted completeness is an upper bound rather than an expected yield. Because the paper's central recommendation is to allocate ESO time to radio-selected follow-up, an overestimate of redshift completeness by, say, a factor of two would weaken the quantitative case in Figs. 2–3 even if T-RECS number counts were correct.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"This manuscript, written by members of the ESO and SKAO communities, argues that ESO optical/near-infrared spectrographs and integral-field units can provide the follow-up observations needed to exploit forthcoming SKAO radio continuum and HI surveys. The paper identifies three classes of follow-up campaigns (large MOS redshift surveys, IFU/ALMA surveys of selected fields, and IFU/ALMA targeted studies), and illustrates the first class with quantitative comparisons: Figures 2 and 3 use the T-RECS simulation to show that 4MOST and MOONS can detect large fractions of radio-selected galaxies and AGN, and that fiber densities roughly match source densities at certain flux limits. The manuscript also discusses KMOS, MUSE, BlueMUSE, and future ELT instruments, and closes with operational recommendations for joint ESO–SKAO projects.","tokens_in":14178,"tokens_out":2576,"duration_ms":27936,"significance":"The paper is a timely and useful community-oriented synthesis. Its central claim—that ESO MOS/IFU facilities can and should play a key role in supporting SKAO radio surveys—is reasonable and well aligned with existing instrument plans. The concrete examples (ORCHIDSS, KMOS public surveys) and the explicit breakdown of short- and long-term timescales give the paper practical value for survey planners. The quantitative figures, based on the publicly available T-RECS simulation, provide a first-order feasibility check. However, the numerical claims are presented without uncertainty estimates or sensitivity tests, and the paper's conclusions would be more robust if the quoted completeness fractions were treated as upper limits rather than expected spectroscopic yields.","major_comments":[{"comment":"The paper equates the magnitude limits r_AB < 22.5 (4MOST, 2h) and H_AB < 22 (MOONS, 1h) with spectroscopic detectability, and then quotes completeness fractions such as '4MOST can detect all radio-selected galaxies' and 'MOONS is able to detect all radio sources associated with galaxies' as well as '~50% of the radio AGN populations.' However, a continuum detection at these limits does not guarantee that a secure redshift can be extracted; redshift success depends on line strength, spectral energy distribution, and sky-line residuals, and is typically well below 100% for faint sources, especially for passive or dusty systems and for AGN-dominated spectra. The figures contain no simulation of the redshift-fitting process and no success-rate curves, so the quoted fractions are upper limits on the target population rather than expected spectroscopic yields. Because the paper's quantitative case for allocating ESO time to radio-selected follow-up rests on these fractions, the authors should either reframe the claims as 'detectable in the continuum' upper limits or add a realistic estimate of redshift success rates based on existing surveys (e.g., GAMA, zCOSMOS, VANDELS) or a simple spectroscopic simulation.","section":"The role of MOS: 4MOST and MOONS (Figures 2 and 3)"},{"comment":"The quantitative match-ups between radio source densities and fiber densities rely entirely on the T-RECS simulation (Bonaldi et al., 2023) for number counts, flux–redshift distributions, and AGN fractions, but the paper provides no sensitivity analysis or comparison with observed source counts. The quoted percentages (25–30% for 4MOST AGN, ~50% for MOONS AGN) and the flux values at which fiber densities match source densities (e.g., S_1.4GHz ~ 10–20 uJy for MOONS galaxies) are presented without error bars or alternative model checks. Since a change in the simulated faint radio AGN population or in the assumed optical/NIR magnitude limits would directly alter the claimed completeness and the fiber-matching flux thresholds, the authors should at minimum add a brief discussion of T-RECS uncertainties (e.g., agreement with observed counts at 20–100 uJy, cosmic variance in the 1-deg2 fields) or soften the quantitative statements to indicate that they are indicative only.","section":"Figures 2, 3, and 4 (T-RECS dependence)"}],"minor_comments":[{"comment":"The abstract and introduction are clear, but the phrase 'Figure/uni00A01' in the Introduction should be formatted simply as 'Figure 1'.","section":"Abstract and Introduction"},{"comment":"There are several typographical errors: 'collegues' should be 'colleagues', 'sensitivy' should be 'sensitivity', and 'precusors' should be 'precursors'.","section":"Acknowledgements"},{"comment":"The caption states that in the top panel only surveys covering sky areas larger than the 4MOST field of view are shown, but the text does not explicitly define the sky areas of the SKA survey tiers; adding a sentence with the survey areas (deg^2) would help the reader interpret the vertical lines.","section":"Figure 2 caption"},{"comment":"Some references are incomplete (e.g., 'Chowdhury, A., Nissim, K & Chengalur, J. N. 2022' is missing a parenthesis after 'Nissim'), and the reference list would benefit from a consistent style for author lists.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"This is a Messenger-style overview article rather than a full research paper, and the requested revision is well within its scope: the authors need to qualify the completeness fractions as continuum-based upper limits and add a brief uncertainty discussion for T-RECS. The central recommendation is defensible and the paper is likely to be useful to the community after these changes. I would not require new simulations, but the text should not present the current quantitative claims without the caveats described in the major comments."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Read this as a community planning document, not a research paper. The pitch is that ESO's 4MOST and MOONS can efficiently follow up SKAO and precursor radio surveys, and the authors illustrate the match with T-RECS source counts and fibre densities. The pitch is plausible and worth taking seriously.\n\nWhat is actually new is modest: the T-RECS overlay plots in Figures 2–4. They give survey planners a quick visual sense of where fibre counts and magnitude limits align with expected radio source populations. The three-way classification of projects—wide redshift surveys, IFU/ALMA field surveys, targeted follow-ups—is sensible, and the short/medium/long timescale split is realistic. The paper is transparent about its workshop origins and does not oversell the facilities.\n\nThe main soft spot is the one flagged in the stress test. The figures use continuum detection limits (r<22.5 in two hours, H<22 in one hour) as the selection for spectroscopic follow-up, but a secure redshift needs lines, not just continuum. At those magnitudes, a non-negligible fraction of galaxies—and a larger fraction of AGN—will fail or yield ambiguous redshifts. So the quoted '100% of galaxies' and '~50% of AGN' completeness are upper bounds, not expected yields. The paper does not say this, and the text in Section 3 reads as if detection equals a measured redshift. That weakens the quantitative case a bit, but not the central recommendation: the fibre density comparison still shows the right order of magnitude. Also, the T-RECS-based numbers have no error bars; for a planning document that is acceptable, but I would treat the matches as approximate.\n\nWho gets value: astronomers planning southern-sky radio follow-up, and anyone writing a survey proposal that involves ESO and SKAO. It deserves a serious referee in a venue that handles technical/perspective pieces; the main changes I'd ask for are a caveat about redshift completeness and softer phrasing of 'detect'. I would not cite it for the quantitative claims (I'd go to T-RECS and the instrument papers), but I'd point people to it for orientation.","headline":"A useful, well-grounded planning document for ESO–SKAO follow-up, with the caveat that its completeness fractions are upper bounds.","tokens_in":14712,"tokens_out":3101,"would_cite":false,"duration_ms":30516,"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":"ESO's new multi-fibre spectrographs 4MOST and MOONS can supply the spectroscopy SKAO radio surveys need.","keywords":["SKAO","ESO","4MOST","MOONS","radio continuum surveys","HI surveys","integral field spectroscopy","T-RECS"],"falsifier":"Measure the actual optical magnitudes of radio-selected AGN in MIGHTEE fields and compare the fraction that 4MOST can reach in two hours with the predicted 25–30%; a strong mismatch would falsify the claimed completeness. A second check is to compare T-RECS cumulative counts with observed EMU and MIGHTEE counts at sub-10-microjansky radio fluxes.","tokens_in":44,"feed_emoji":"🔭","tokens_out":11313,"duration_ms":135646,"temperature":0.7,"pith_summary":"This paper argues that the scientific return of SKAO radio continuum and 21-cm hydrogen surveys will depend on optical and near-infrared spectroscopy from ESO, and that ESO's new multi-fibre spectrographs are quantitatively up to the task. Comparing the T-RECS simulation's predicted radio source counts with the fibre numbers, fields of view, and depth of 4MOST and MOONS, the authors find that 4MOST can spectroscopically cover essentially all radio-selected galaxies in wide surveys such as EMU and the planned SKA all-sky survey, while MOONS can cover galaxies and roughly half the radio AGN down to the deepest SKA-Mid flux limits. For resolved studies, they argue that integral-field spectrographs such as KMOS and MUSE, combined with ALMA, can deliver the multi-phase gas and stellar measurements needed to study galaxy assembly. If this is correct, survey planners should allocate ESO time to radio-selected targets and build joint ESO-SKAO proposals, archives, and virtual observing platforms.","feed_headline":"4MOST and MOONS can cover SKAO's radio survey redshift needs","feed_subtitle":"Matched fibre counts and survey depths show ESO's new spectrographs can shoulder the radio follow-up bottleneck.","key_machinery":"The quantitative match between the Tiered Radio Extragalactic Continuum Simulation (T-RECS) and the multiplex capabilities of ESO spectrographs is the argument's engine. T-RECS supplies predicted flux–redshift distributions and cumulative number counts for radio galaxies and radio AGN; the paper overlays the 4MOST and MOONS fibre numbers and depth limits ($r_{\\rm AB} < 22.5$ in two hours, $H_{\\rm AB} < 22$ in one hour) and the KMOS limit ($K_{\\rm AB} < 22.5$) to test whether the predicted radio source density can be followed in a single pass. Where the cumulative source density meets or falls below the fibre density, the ESO instrument can carry the follow-up without becoming the bottleneck; where it rises above, the paper states the resulting completeness fraction, such as the 25–30% for 4MOST on radio AGN.","core_discovery":"The central claim is that ESO's currently available and soon-to-be-operational spectroscopic facilities can and should serve as the follow-up workhorses for SKAO galaxy surveys. For the multi-object tier the claim is quantitative: in two hours, 4MOST (reaching $r_{\\rm AB} < 22.5$) can detect essentially all radio-selected galaxies from the EMU survey and the planned SKA all-sky survey, and its fibre density matches the predicted source density at those limits; 4MOST reaches only about 25–30% of the radio AGN population at all fluxes, which the authors count as a good match down to the MIGHTEE and SKA-Mid WIDE limits. In one hour, MOONS (reaching $H_{\\rm AB} < 22$) detects all radio-selected galaxies and about half the radio AGN down to the deepest SKA-Mid continuum depths, covering the redshift 1.5–2.5 window where key spectral features shift out of optical reach. For resolved studies, KMOS can follow complete HI-mass-selected spiral samples with $M_{\\rm HI} > 10^{7.5}$–$10^8\\,M_\\odot$ out to redshift 0.5, and MUSE and BlueMUSE together with ALMA can map the multi-phase baryon cycle. The paper closes with operational recommendations: joint proposal schemes, shared archival capabilities, and common virtual observing platforms.","pith_inferences":["If T-RECS underpredicts the faint radio AGN population, the 25–30% 4MOST AGN completeness would be an upper bound, so completing the AGN census would require a deeper or near-infrared spectroscopic tier.","The same fibre-density matching logic can be inverted to compute, for any radio survey depth, the sky area where 4MOST or MOONS becomes saturated, allowing survey footprints to be designed to avoid overcrowded or wasted fields.","A practical pilot would run a joint ESO-SKAO virtual observing platform on existing ASKAP and MeerKAT data to measure overheads and completeness before the SKA era begins.","The KMOS HI-size matching argument could be turned into a concrete target list of HI-selected spirals with $M_{\\rm HI} > 10^{7.5}$–$10^8\\,M_\\odot$ and $z < 0.5$, testable against WALLABY and LADUMA detections."],"forward_implications":["4MOST can provide spectroscopic redshifts for essentially all radio-selected galaxies in wide shallow surveys such as EMU and the planned SKA all-sky survey, easing host-galaxy identification and source classification.","MOONS extends the follow-up into the near-infrared, covering galaxies and roughly half the radio AGN across the redshift 1.5–2.5 epoch of peak star formation and black-hole activity.","KMOS and MUSE/BlueMUSE, combined with ALMA, can turn SKAO HI detections into spatially resolved multi-phase gas and stellar measurements.","Joint ESO-SKAO proposal schemes, shared archives, and common virtual observing platforms would shorten the path from radio survey data to scientific results."],"supporting_citations":[{"why":"Supplies the T-RECS simulation: the predicted radio source counts, flux-redshift distributions, and HI property distributions used in all the quantitative comparisons.","marker":"Bonaldi et al., 2023"},{"why":"Defines 4MOST capabilities and the two-hour depth limit used to compute the detectable fractions of radio sources.","marker":"de Jong et al., 2019"},{"why":"Defines MOONS capabilities and the one-hour near-infrared depth limit used to compute the detectable fractions of radio sources.","marker":"Cirasuolo et al., 2020"},{"why":"Supplies the KMOS detection limits and resolved-size criteria used for the HI-selected spiral follow-up argument.","marker":"Birkin et al., 2024"},{"why":"Provides the planned SKA-Mid radio continuum survey depths and survey nomenclature used as comparison points in the figures.","marker":"Prandoni & Seymour, 2015"},{"why":"Describes the SKAO HI surveys that motivate the need for optical and near-infrared spectroscopy and HI stacking.","marker":"Staveley-Smith & Oosterloo, 2015"},{"why":"Gives ORCHIDSS, the approved 4MOST community survey, as the working example of a MeerKAT/4MOST synergistic follow-up.","marker":"Duncan et al., 2023"}],"fun_headline_variants":["4MOST and MOONS match SKAO's radio survey needs","ESO's 4MOST, MOONS ready for SKAO follow-up","SKAO surveys find their spectroscopic match in ESO","Fiber counts align: ESO instruments for SKAO surveys","ESO spectrographs to shoulder SKAO radio follow-ups"],"cache_read_input_tokens":16896,"weakest_assumption_plain":"The matching exercise assumes that the T-RECS simulation predicts real radio source counts, flux-redshift distributions, and AGN fractions down to the planned SKA depths, and that the assumed optical and near-infrared magnitude limits are realistic for the stated exposure times.","fun_headline_variants_meta":{"raw":{"variants":["4MOST and MOONS match SKAO's radio survey needs","ESO's 4MOST, MOONS ready for SKAO follow-up","SKAO surveys find their spectroscopic match in ESO","Fiber counts align: ESO instruments for SKAO surveys","ESO spectrographs to shoulder SKAO radio follow-ups"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000318,"raw_usage":{"total_tokens":1805,"prompt_tokens":962,"completion_tokens":843,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":578,"completion_tokens_details":{"reasoning_tokens":752}},"tokens_in":578,"tokens_out":843,"duration_ms":7505,"temperature":1.0,"reasoning_tokens":752,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T21:12:10.494837+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the actual optical magnitudes of radio-selected AGN in MIGHTEE fields and compare the fraction that 4MOST can reach in two hours with the predicted 25–30%; a strong mismatch would falsify the claimed completeness. A second check is to compare T-RECS cumulative counts with observed EMU and MIGHTEE counts at sub-10-microjansky radio fluxes.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the T-RECS simulation: the predicted radio source counts, flux-redshift distributions, and HI property distributions used in all the quantitative comparisons."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Defines MOONS capabilities and the one-hour near-infrared depth limit used to compute the detectable fractions of radio sources."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the KMOS detection limits and resolved-size criteria used for the HI-selected spiral follow-up argument."},{"cited_title":"& Seymour, N","cited_arxiv_id":null,"evidence_quote":"Provides the planned SKA-Mid radio continuum survey depths and survey nomenclature used as comparison points in the figures."},{"cited_title":"& Oosterloo, T","cited_arxiv_id":null,"evidence_quote":"Describes the SKAO HI surveys that motivate the need for optical and near-infrared spectroscopy and HI stacking."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Gives ORCHIDSS, the approved 4MOST community survey, as the working example of a MeerKAT/4MOST synergistic follow-up."}],"review_version":1}