Weekly issue

Week 8, 2026

Feb 16–22, 2026

Week 8, 2026 includes 6 curated papers, centered on LRD, QSO, high-z.

2602.15935v1

Little Red Dots as Globular Clusters in Formation

John Chisholm, Danielle A. Berg, Michael Boylan-Kolchin, Anna de Graaff, Lukas J. Furtak, Vasily Kokorev, Jorryt Matthee, Julian B. Muñoz, Rohan P. Naidu, Andreas A. C. Sander

Theme match 5/5

Digest

Proposes Little Red Dots as globular clusters caught in formation, where a very young cluster supplies the rest-UV while a short-lived supermassive star powers the cool, optical modified blackbody that creates the hallmark V-shaped SED. Using the z≈5–7 UV luminosity function and standard evolutionary mass loss, the authors evolve LRDs into a present-day GC mass function with a turnover at log10(M*/Msun)=5.3 and an exponential high-mass cutoff, and infer a total number density ≈0.3 Mpc^-3 consistent with local GCs. The observed LRD redshift window aligns with ages of metal-poor GCs and predicts multiple-population chemistry (He, N enhanced; Na–O and Al–Mg anti-correlations) as a test. A key caveat is that the required temperatures and bolometric luminosities likely demand optically thick, continuum-driven winds not fully captured by current SMS models.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect the SED decomposition of A2744-45924 to see how a young cluster plus an SMS reproduces the V-shape; note the mismatch near ~3500 Å that points to the need for cooler SMS/wind treatments.
Figure 2: Check LRDs in the Teff–Lbol plane against SMS tracks and the Hayashi/Eddington lines to gauge the implied radii (~500–2500 au) and near/super-Eddington output, underscoring missing dense-wind physics.
Figure 3: Follow the transformation from the observed LRD UV LF to the z=0 GC mass function; verify the turnover at log10(M*/Msun)=5.3 and high-mass exponential cutoff against MW and Virgo data.
Figure 4: Compare LRD redshift distribution to GC age/metallicity bins to see the demographic match to metal-poor GCs and the absence of an obvious metal-rich counterpart.

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2602.15929v1

Toward Black Hole Stars: supermassive black hole growth in nuclear clusters via stellar-object and gas accretion

Konstantinos Kritos, Joseph Silk

Theme match 5/5

Digest

Models SMBH growth in nuclear star clusters where runaway BH mergers seed IMBHs and continued stellar-object plus gas accretion builds compact, parsec-scale nuclei linked to Little Red Dots. Monte Carlo loss-cone calculations show MS-star TDEs dominate early feeding while stellar-mass BH plunges take over later, yielding a TDE rate about an order of magnitude above compact-object captures. The framework predicts detectable high‑z MS TDEs with peak luminosity–timescale tracks overlapping ENTs/ANTs, and a low‑frequency GW background with occasional BH‑EMRIs. Dense gas cocoons produce nuclei with comparable masses in gas, stars, and central “black hole star,” matching LRD spectral inferences.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Trace how the mass accretion budget shifts from MS TDEs to BH captures with time and SMBH mass; use the ten-realization error bars and the duty-cycle inset to gauge flare visibility windows for MS vs giants.
Figure 2: Compare model MS‑TDE peak luminosities and decay times to the ENT/ANT regions and Eddington lines; identify which stellar masses and evolutionary epochs place events in the extreme‑flare locus and note the late‑time turnover as turnoff masses drop.
Figure 3: Read off the GW energy density from BH/NS/WD captures versus frequency and compare to LISA/LGWA sensitivity curves to assess detectability; use the inset strains to connect individual capture channels to the stochastic background and contrast with light/heavy MBH‑seed merger backgrounds.

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2602.17329v1

MIDIS: The identification of deep MIRI-red sources as candidates for extreme Balmer-break and line emitting galaxies at high-z

I. Jermann, G. Brammer, S. Gillman, T. R. Greve, L. A. Boogaard, J. Melinder, R. A. Meyer, P. G. Pérez-González, P. Rinaldi, J. L. Colina, G. Östlin, G. Wright, J. Álvarez-Márquez, A. Bik, K. I. Caputi, A. Crespo Gómez, L. Costantin, J. Hjorth, E. Iani, S. Kendrew, A. Labiano, D. Langeroodi, F. Peissker, C. Prieto-Jiménez, J. P. Pye, T. V. Tikkanen, F. Walter, P. van der Werf, T. Henning, M. Shuntov

Theme match 4/5

Digest

Using the deepest 5.6 μm MIRI imaging of the HUDF (2.4 arcmin²), MIDIS defines “MIRI‑red” sources as 5σ F560W detections with mF444W−mF560W ≥ 0.5 and empirically calibrates the background, finding pipeline S/N is overestimated and achieving 92% purity and 54% completeness at 28.75 mag. Seven MIRI‑red candidates are found (including an F115W dropout), with colors consistent with extreme rest‑optical line emitters requiring EW0(Hα) ≥ 750 Å or EW0(Hβ+[OIII]) ≥ 600 Å, or with high‑z Balmer breaks ≥1.6. An extreme MIRI‑only candidate undetected in F444W implies EW0(Hα) ∼ 6000 Å and EW0(Hβ+[OIII]) ∼ 4000 Å, or an LRD‑like Balmer break ≈6.3. Fewer detections than extrapolated from Hα/Hβ+[OIII] luminosity functions and the absence of z>10 LRDs underscore the rarity of such systems and the value of mid‑IR selection for isolating the most extreme cases.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Use the field mosaic and Deep/Shallow contours to see where the seven MIRI‑red candidates (magenta squares) sit relative to the deepest F560W coverage and to ALMA Band 3/6 contours—check any positional coincidences that would favor dusty/AGN interpretations.
Figure 2: Inspect the bright‑source mask; it leaves 91.3% of the MIDIS Deep area usable—verify that candidates avoid masked edges where background estimation and color selection could be biased.
Figure 3: Background noise versus aperture size compares empty‑aperture scatter (black) to variance‑map errors before/after rescaling (red); this quantifies the S/N overestimation and justifies the empirically rescaled photometric uncertainties used for the selection.
Figure 4: Purity and completeness curves versus F560W magnitude/flux; at 28.75 mag the survey reaches 92% purity and 54% completeness—use this to gauge the reliability of the seven candidates and the expected number missed at fainter levels.

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2602.16775v1

Causal Reversal in the $M_\unicode{x25CF}\unicode{x2013}σ_0$ Relation: Implications for High-Redshift Supermassive Black Hole Mass Estimates

Benjamin L. Davis, Saakshi More, Zehao Jin, Mario Pasquato, Andrea Valerio Macciò, Feng Yuan

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Digest

Using NIHAO cosmological zoom-ins, the authors apply causal-discovery tools to track the time evolution of the M•–σ0 connection and related host properties. Splitting 55 galaxies into 28 star-forming and 27 quenched via an sSFR cut and the SFR-turnover epoch, they find a temporal inversion of causality: during the star-forming phase M• drives host galaxy properties, while after quenching host properties drive M•—mirroring the observational spiral vs. elliptical trends. Leveraging this, they propose causally informed high‑z scaling relations that yield SMBH masses ≈2 dex lower than estimates based on the local M•–σ0, defusing claims of “overmassive” early black holes.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect the sSFR–M* cut that separates 28 star-forming from 27 quenched NIHAO galaxies and the pairplot’s clear bimodality across variables; this sets the causal-regime bins used later.
Figure 2: Follow the single-galaxy track in SFR vs M* with time coloring; the SFR peak and subsequent decline mark the transition from the SMBH-driving to host-driving phase.
Figure 3: Read the edge/path marginal matrices and DAGs for star-forming vs quenched samples; verify the flip from M•→(host properties) to (host properties)→M• and note which variables connect directly to σ0 and M•.
Figure 4: Compare the NIHAO-based pairplots to the observational sample from Paper I under the same variable set; check that the morphology-based trends align with the simulation-defined star-forming vs quenched splits.

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2602.15952v1

Gas Accretion versus BH Merger driven Growth Modes of Supermassive Black Holes and Implications for the Little Red Dots

Paramita Barai

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Digest

Cosmological hydrodynamical boxes (50 Mpc)^3 are used to separate merger- from gas-accretion–driven SMBH growth and test feedback choices against SMBH–host coevolution. Seeded at 10^5 Msun, black holes first build up via BH–BH mergers to ~10^7 Msun; only after 7–9 Gyr does accretion reach Eddington, triggering 600–700 Myr bursts that amplify masses by 10^2–10^3 to 10^9–10^10 Msun. AGN-feedback-driven central gas depletion then curtails growth, keeping SMBHs below 10^10 Msun by z=0 and moving systems upward toward the M_BH–M_star relation from below. Implication for JWST little red dots: normal-mass objects are consistent with merger-dominated histories, while overmassive systems require Eddington or super-Eddington accretion episodes.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

MBH(t) decomposed into merger versus accretion contributions: verify the early merger-dominated rise to ~10^7 Msun and pinpoint the handoff to accretion-driven growth.
Eddington ratio or accretion rate versus cosmic time: identify the 7–9 Gyr transition to f_Edd ~ 1 and the ensuing 600–700 Myr burst responsible for 10^2–10^3 mass jumps.
Tracks in the M_BH–M_star plane: show systems starting below the relation and migrating upward; highlight which tracks map to normal-mass versus overmassive LRD analogs.
Central gas mass and outflow/feedback diagnostics versus time: demonstrate AGN-feedback-driven gas depletion that caps SMBH masses below 10^10 Msun by z=0.
Parameter-sweep comparison across BH feedback efficiencies/velocities: assess robustness of the merger-then-accretion sequence and how feedback tunes final masses.

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2602.14496v1

Back to Normal Again: Possible Destinies of JWST overmassive SMBHs and "Little Red Dots" in the View of Shin-Uchuu Simulation

Haojie Hu, Hiroto Yanagisawa, Moka Nishigaki, Tomokazu Kiyota, Tomoaki Ishiyama, Ken Ohsuga

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Digest

Using Shin-Uchuu halo merger trees with phenomenological prescriptions for BH growth and galaxy evolution, the authors evolve JWST “overmassive” SMBHs and LRD analogs (e.g., GN-z11, CEERS-20496, UNZ1, Abell-2744-QSO1). They find initially overmassive SMBHs undergo stunted accretion that reduces M_BH/M_*, while lower-mass SMBHs pass through super-Eddington phases that lift the ratio toward ~0.01; tracks converge near M_BH ≈ 10^8 Msun with M_BH/M_* ≈ 0.01 before moving onto local relations at later times. This points to global regulation encoded by observed SFR/BHAR distributions and active–quiescent fractions, implying many LRD-like systems can return to normal without fine-tuned feedback. A noted caveat is that the late-time approach to local relations is influenced by the adoption of low‑z empirical relations in the modeling.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 3: Follow GN-z11, CEERS-20496, UNZ1, and Abell-2744-QSO1 tracks to see when growth is super-Eddington (red stars) versus quasar/radio modes and how M_BH/M_* declines or rises before converging near 10^8 Msun and ~1%.
Figure 2: Inspect halo and stellar-mass assembly histories selected for each object; check how the merger-tree scatter brackets the observed M_* of the SMBH/LRD sample and the implied gas supply history.
Figure 1: Examine the adopted redshift- and mass-dependent quiescent fractions and BH active fractions; assess how the small high-mass active fraction constrains early fueling and helps drive the stunted-growth phase.
Figure 4: Compare the model SFR–M_* distribution and SMHM ratios to UniverseMachine and SDSS fits to verify that the phenomenological galaxy model reproduces main-sequence trends that underpin the ~1% M_BH/M_* convergence.