{"id":"c5ee5891-40ca-4eda-b13e-183c01b13427","arxiv_id":"2607.09647","paper_version":1,"verdict":"ACCEPT","confidence":"HIGH","novelty_score":6.0,"correctness_risk":"low","formal_verification":"none","parameter_count":3,"one_line_summary":"Spatially resolved JWST/NIRSpec IFU spectroscopy of five z~5 Little Red Dots shows blue continuum and narrow lines from extended hosts and red continuum plus broad Balmer features from compact cores.","lead":"JWST NIRSpec IFU maps of five Little Red Dots at z~5 separate a compact red core (broad Balmer lines and absorption) from an extended blue continuum co-spatial with narrow lines. This supplies direct spatial evidence that LRDs are composite systems of a central engine inside a host galaxy.","discovery_kind":"extension","skeptic_critique":{"model":"grok-4.5","headline":"No significant objection identified","rationale":"The paper's strongest claim is observational and map-based: blue continuum co-spatial with the narrow-line region, red continuum co-spatial with broad Balmer emission/absorption, and a central EW[OIII] depression. The reader's identification of continuum-decomposition purity as the weakest assumption is accurate and matches the authors' own caveat in Section 5. That caveat does not invalidate the maps, because the line components (narrow vs. broad) are fitted independently of the continuum model choice and still show the same spatial dichotomy (Figure 5 radial profiles vs. STPSF). Both continuum models tested by the authors yield similar maps, further reducing model dependence. Limitations (N=5, two marginally resolved sources, possible merger contribution in GS-13971) are real but already quantified and do not reverse the co-spatiality result. No hidden assumption, numerical error, or unacknowledged systematic rises to a load-bearing concern that would move the verdict away from ACCEPT. The concrete test above is a useful verification step but is expected to leave the claim intact.","tokens_in":16821,"tokens_out":614,"duration_ms":7933,"concrete_test":"Re-fit the PRISM continuum maps for GS-13971 and GN-12839 after forcing a pure single-component continuum (power-law only or blackbody only) and recompute the radial surface-brightness profiles of residual narrow [OIII] versus broad Hα; if the extended-versus-compact distinction disappears or the central EW[OIII] dip vanishes, residual mixing would be load-bearing. Otherwise the two-component spatial claim holds.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The reader's weakest assumption (possible residual mixing of blue continuum from the central engine into the host component) is real but already flagged by the authors in Section 5 and does not undercut the central observational claim. The claim rests primarily on the co-spatiality of independently fitted components: compact red continuum with broad Hα (and absorption) versus more extended blue continuum with narrow [OIII]/Hα, plus the central dip in EW[OIII] maps (Figures 3–6). These spatial associations are measured after continuum subtraction and line decomposition on a spaxel-by-spaxel basis; they survive even if some fraction of the blue light is engine-related. Sample size (N=5), marginal resolution for GN-9771 and GN-15498, and companion contamination in GS-13971 (Appendix B) are acknowledged limitations that reduce generality but do not reverse the co-spatiality result for the clearer targets. Methods (power-law+modified blackbody or empirical templates; Gaussian line fits with LMFIT; STPSF comparison) are standard and documented. No internal inconsistency or unacknowledged systematic that would falsify the two-component spatial picture is present.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.5","summary":"This paper presents JWST/NIRSpec IFU spectroscopy (PRISM + G395H) of five broad-Hα-selected Little Red Dots at z∼5 and performs a spaxel-by-spaxel spectral decomposition into a blue continuum, a red continuum, narrow emission lines ([O III], Hα, Hβ), broad Balmer emission, and Balmer absorption. Intensity and kinematic maps, wavelength-dependent half-light radii, radial surface-brightness profiles compared to STPSF models, and [O III] equivalent-width maps are used to test a two-component picture. The authors report that the blue continuum is co-spatial with the narrow-line region, while the red continuum is compact and co-spatial with broad Balmer emission and absorption, with a central dip in EW[O III]. They conclude that LRD emission arises from at least two distinct physical components: a red central engine embedded in a blue host galaxy.","tokens_in":17167,"tokens_out":1488,"duration_ms":19294,"significance":"If the spatial associations hold, the work supplies direct IFU evidence for a composite (central engine + host) interpretation of LRDs, moving the debate beyond integrated spectra and broadband imaging. The combination of continuum decomposition, line decomposition, PSF comparisons, and EW[O III] maps for the same targets is a clear observational advance. The result is falsifiable with deeper IFU data or larger samples and is already partially stress-tested by the authors via two continuum models that yield similar maps. Limitations (N=5, marginal resolution in two objects, companion contamination in GS-13971) reduce generality but do not erase the co-spatiality signal in the better-resolved systems. The paper is a useful contribution to the high-z AGN/host literature.","major_comments":[{"comment":"§4.1 and §5: The central claim is stated for the sample as a whole, yet the text itself reports that GS-13971, GN-12839, and (to a lesser extent) GN-16813 show extended blue continuum and [O III], while GN-9771 and GN-15498 have comparable blue/red sizes and compact narrow-line morphologies. The abstract and summary should more carefully qualify that the morphological separation is clear in a subset of the sample and only marginally resolved or continuum-dominated in the rest, so that the two-component spatial picture is not over-generalized from the three clearer targets.","section":"§4.1, §5, Abstract"},{"comment":"§3.1 and §5: The continuum decomposition (power-law + modified blackbody, or fixed Black Hole Star + host templates) is load-bearing for the blue/red maps. The paper notes that both models give similar maps and that some blue continuum may still originate from the central engine, but it does not quantify residual mixing (e.g., via mock IFU cubes with known host/engine fractions, or by reporting the fractional blue flux that could be reassigned to the engine without erasing the R1/2 or co-spatiality trends). A short robustness test or explicit upper bound on residual engine contribution to the blue maps would strengthen the claim that the extended blue light is host-dominated.","section":"§3.1, §5"},{"comment":"Appendix B / GS-13971: Extended [O III] and blue continuum around this object include at least four narrow-line companions, and the authors favor a merger interpretation over a single large rotating host. Because GS-13971 is presented as the clearest extended case (Figures 3, 5, 6), the main text should state more explicitly how much of the extended narrow-line and blue continuum flux is attributed to companions versus a genuine host, and whether the co-spatiality argument for this target survives after companion masking. Without that, the strongest morphological example partially rests on a system that may not be a clean host+engine geometry.","section":"Appendix B, §4.2, Figure 3"}],"minor_comments":[{"comment":"Figure 1 caption and ordering: spectra are ordered by UV prominence; a quantitative UV-to-optical continuum ratio or rest-UV slope in Table 1 would make that ordering reproducible.","section":"Figure 1, Table 1"},{"comment":"Eq. (1): the prior on α is written as (0, −5); clarify whether this is an open interval and the intended sign convention for a blue continuum (typically α < 0 in Fλ ∝ λ^α).","section":"§3.1, Eq. (1)"},{"comment":"GN-12839 Hα truncation: the chip-gap handling (tied narrow/broad velocity offsets) is described, but the impact on the broad-Hα intensity map and FWHM should be stated quantitatively (e.g., recovered fraction of the line profile).","section":"§3.2"},{"comment":"Figure 4: R1/2 uncertainties are 16–84th percentiles of the curve-of-growth; specify whether these include only measurement noise or also continuum-model parameter uncertainty.","section":"§4.1, Figure 4"},{"comment":"Figure 6 radial EW[O III] panel: profiles are normalized for comparison; also show absolute EW scales (or a second panel) so the depth of the central dip can be compared across targets in physical units.","section":"Figure 6"},{"comment":"Typographical consistency: “z~5” vs “z∼5”, “[Oiii]” vs “[O III]”, and “Ha” vs “Hα” appear in mixed forms in the abstract and body; standardize to journal style.","section":"Abstract, throughout"},{"comment":"References to overlapping-author continuum models (Sun et al. 2026; Naidu et al. 2025) are appropriate, but a brief sentence distinguishing what is newly measured here (spatial maps, EW rings) from what is assumed from those works would help non-specialist readers.","section":"§1, §3.1"}],"recommendation":"minor_revision","confidential_remarks":"The central observational result is sound and the paper is close to publishable. The three major points are about qualification and robustness rather than internal inconsistency; I would not block acceptance if the authors tighten the sample-level wording, add a short continuum-mixing robustness note, and clarify the GS-13971 companion contribution. Fit to a general astrophysics journal is good; novelty is incremental but timely given the LRD debate. No concerns about misconduct or undisclosed overlap beyond the expected shared-program context (GO 5664)."},"author_rebuttal":null,"desk_editor":{"model":"grok-4.5","letter":"The new thing here is the spaxel-by-spaxel NIRSpec IFU decomposition: blue continuum with narrow [OIII]/Hα versus compact red continuum with broad Hα (and absorption), plus the central dip in EW[OIII]. That is the first published spatial separation of those pieces for a broad-Hα LRD sample, not just another SED argument.\n\nThey do the work carefully. Both continuum models (power-law + modified blackbody, and the empirical BH-star + host templates) give similar maps. Radial profiles are compared to STPSF; R1/2 versus wavelength is shown; SNR>3 cuts are applied; GS-13971 companions are flagged in the appendix. The co-spatiality result is clearest for GS-13971, GN-12839, and GN-16813 and still visible, if weaker, in the other two. The EW[OIII] ring is a nice independent check that the red core is not the main [OIII] source. Methods are standard LMFIT Gaussians and documented enough to re-run.\n\nSoft spots are real but already owned by the authors. N=5, two objects only marginally resolved, and possible residual blue light from the engine itself (they say so in §5). That residual mixing does not erase the spatial associations after continuum subtraction and line decomposition. Companion contamination in GS-13971 is handled honestly. No circularity problem: they are testing a picture already in the literature with new IFU data, not inventing it from the fits. Citations are dense on the overlapping groups, which is expected given how fast this subfield is moving, not a red flag.\n\nThis is for people already deep in the LRD debate who need spatial evidence rather than another single-aperture spectrum. It organizes the V-shape, broad lines, and absorption under one geometric picture without overclaiming a unique physical model. I would send it to referees; the maps deserve a careful look and the limitations are proportionate. Worth reading and, for anyone writing on LRD hosts or BH growth at z~5, worth citing.","headline":"First clean IFU maps that put the red broad-line core and blue narrow-line host on the sky for five LRDs; the two-component picture holds for the clearer targets.","tokens_in":17815,"tokens_out":537,"would_cite":true,"duration_ms":5846,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.5","headline":"Little Red Dots are made of a compact red central engine sitting inside a more extended blue host galaxy.","keywords":["Little Red Dots","Active galactic nuclei","High-redshift galaxies","Supermassive black holes","AGN host galaxies","JWST","NIRSpec IFU"],"falsifier":"Higher-resolution or multi-wavelength maps that show red continuum, broad Balmer lines, and blue continuum all sharing one compact profile, with no extended blue or narrow-line component, would falsify the host-plus-engine decomposition.","tokens_in":17746,"feed_emoji":"🔴","tokens_out":885,"duration_ms":18779,"temperature":0.7,"pith_summary":"Little Red Dots are compact red sources found by JWST that show a V-shaped continuum, broad Balmer lines, and sometimes Balmer absorption. Their origin has been debated—evolved stars, dust-obscured black holes, or exotic single atmospheres. This paper tests the two-component idea by using JWST/NIRSpec integral-field spectroscopy to decompose, spaxel by spaxel, the blue continuum, red continuum, narrow lines, broad lines, and absorption in five broad-Hα LRDs at redshift about 5. The maps show blue continuum and narrow lines are co-spatial and more extended, while red continuum, broad Balmer emission, and absorption arise from a compact core; [O III] equivalent width also dips in that core. A sympathetic reader cares because this spatial separation would turn the conflicting spectral features into distinct physical regions rather than one unexplained object.","feed_headline":"JWST splits Little Red Dots into red cores and blue hosts","feed_subtitle":"Five z~5 maps put broad lines with compact red light and narrow lines with extended blue light.","key_machinery":"Spatially resolved spectral decomposition of NIRSpec IFU datacubes: each spaxel is fit as blue power-law plus red modified blackbody continuum, plus independent narrow lines, broad Balmer lines, and Balmer absorption, then mapped in intensity and kinematics.","core_discovery":"For five broad Hα-selected Little Red Dots at z~5 observed with NIRSpec IFU (prism plus G395H), the blue continuum is co-spatial with the narrow emission-line region while the red continuum comes from a compact core co-spatial with the broad Balmer emission and absorption. Maps of [O III] equivalent width show a clear central dip. The authors conclude that LRD light is produced by at least two distinct components: a red central engine embedded in a blue host galaxy.","pith_inferences":["If hosts are routinely more extended, deeper IFU or adaptive-optics imaging should resolve blue light around most LRDs once engine contrast is accounted for.","The central [O III] equivalent-width dip is a practical locator for the engine even when the continuum is barely resolved.","Single-atmosphere models that put continuum and lines in one dense structure would need to reproduce the observed spatial offset between blue/narrow and red/broad components.","Merger-like companions around at least one target imply that some extended narrow-line gas may be environmental rather than a settled host disk."],"forward_implications":["The V-shaped continuum is the sum of an extended blue host and a compact red engine, not a single continuum source.","Broad Balmer lines and absorption originate in the compact red core, favoring an AGN-like or black-hole-star engine.","Host light can be isolated by selecting high-[O III] equivalent-width regions away from the red core.","Diversity among LRD spectra can be explained by changing contrast between host and central engine.","Measured LRD sizes must be wavelength-dependent because different components dominate at different wavelengths."],"fun_headline_variants":["NIRSpec IFU maps five LRDs into red cores and blue hosts","Little Red Dots split: compact red engines in blue host galaxies","JWST places LRD broad lines in red cores, narrow lines in blue hosts","[OIII] dips mark red LRD cores against extended blue continuum","Spatial maps show LRD red continuum co-located with broad Balmer lines"],"cache_read_input_tokens":128,"weakest_assumption_plain":"The continuum fit cleanly separates host-galaxy light from central-engine light, without substantial leftover mixing of the two.","fun_headline_variants_meta":{"raw":{"variants":["NIRSpec IFU maps five LRDs into red cores and blue hosts","Little Red Dots split: compact red engines in blue host galaxies","JWST places LRD broad lines in red cores, narrow lines in blue hosts","[OIII] dips mark red LRD cores against extended blue continuum","Spatial maps show LRD red continuum co-located with broad Balmer lines"]},"model":"grok-4.5","effort":"low","cost_usd":0.00318,"raw_usage":{"total_tokens":1146,"prompt_tokens":828,"num_sources_used":0,"completion_tokens":82,"cost_in_usd_ticks":31800000,"prompt_tokens_details":{"text_tokens":828,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":236,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":828,"tokens_out":82,"duration_ms":3349,"temperature":1.0,"reasoning_tokens":236,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-07-13T01:28:14.356915+00:00","model_set":{"reader":"grok-4.5"},"falsifier":"Higher-resolution or multi-wavelength maps that show red continuum, broad Balmer lines, and blue continuum all sharing one compact profile, with no extended blue or narrow-line component, would falsify the host-plus-engine decomposition.","supporting_citations":[],"review_version":1}