Weekly archive

LRDigest

Weekly digests of little red dots and JWST-selected AGN papers, with curated reading notes and archive pages.

Browse weekly issues, then open each paper page for the abstract, digest, figures, and PDFs.

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Weekly issue

Week 30, 2025

Jul 21–27, 2025

Week 30, 2025 includes 4 curated papers, centered on high-z, LRD, QSO.

2507.15556v1

Signatures of Exploding Supermassive PopIII Stars at High Redshift in JWST, EUCLID and Roman Space Telescope

Cédric Jockel, Kyohei Kawaguchi, Sho Fujibayashi, Masaru Shibata

Theme match 5/5

Digest

Semi-analytic models, anchored to stellar-evolution and GR collapse simulations, follow ejecta–CSM shocks from exploding supermassive Pop III stars to predict light curves, spectra, and photometry. The events peak at ~10^45–10^47 erg/s and last 10–200 yr in the source frame (observed 250–3000 yr), yielding quasi-persistent variability indistinguishable from little red dots/AGN on 0.5–9(1+z) yr baselines. Bright explosions should be detectable in long-wavelength JWST filters to z≤20 at 24–26 mag, with pulsating SMSs to z≤15; Euclid and Roman reach z<11–12. Deep fields could constrain the event rate to ~10^-11 Mpc^-3 yr^-1 and yield several hundred (Euclid) to dozens (Roman) detections, directly testing heavy-seed SMBH pathways.

Open paper pagearXiv abstractarXiv PDFHighlighted PDF

Key figures to inspect

  • Figure 1: Use the phase cartoon to track how a GR-unstable SMS forms a BH, ejects a core-driven outflow, sweeps up the bloated atmosphere, and transitions to an ejecta–CSM shock; note how core/atmosphere fractions set the eventual ejecta mass budget.
  • Figure 2: Inspect the ejecta, shocked shell, and CSM density profiles with forward/reverse shock jump conditions to read off diffusion timescales and where radiation should remain thermalized versus become non-thermal.
  • Figure 3: Bolometric light curves (thermal vs non-thermal phases) show quasi-persistence and compare directly to two high‑z AGN luminosities; use these panels to infer detectability windows and observer-frame durations from the optically thick/thin transition.
  • Figure 4: Parameter-space map of peak optically thick-phase luminosity versus ejecta mass and kinetic energy; identify which model combinations exceed survey limits and note the gray region where thin-shock luminosity dominates (model validity boundary).

Tags

  • LRD
  • BH seeds
  • simulation

Digest

This work builds an improved, unified framework for the halo mass function seeded by cosmic string loops, treating arbitrary loop-velocity distributions and capturing both spherical and filamentary growth. From this mass function, it isolates halos that meet direct-collapse conditions at high redshift, producing black-hole seeds of ~10^4–10^5 Msun. For reasonable string parameters, the predicted seed abundance reproduces the observed number density of JWST’s Little Red Dots, offering a non-Gaussian small-scale route to early SMBH growth. Because loop formation lacks large acoustic waves, the scenario avoids CMB spectral-distortion bounds, and a velocity–tension phase diagram (including fragmentation into “beads”) clarifies where this channel dominates.

Open paper pagearXiv abstractarXiv PDFHighlighted PDF

Key figures to inspect

  • Fig. 1: Use the three-phase schematic of stationary accretion (Regions I/II vs III) to see when the point-mass approximation is trustworthy and how the growth mode changes with time.
  • Fig. 2: Read the contours of the redshift where the point-mass limit holds versus loop-formation redshift and Gμ; compare to the loop-decay track to pinpoint regimes where stationary accretion fails and moving/filamentary treatment is required.
  • Fig. 3: Compare the growth histories across increasing loop velocities to watch the transition from spherical accretion to a single long filament, and finally to filament fragmentation into ‘beads’; note which channel actually governs the final halo mass relevant for direct collapse.
  • Fig. 4: Examine the (Gμ, v) phase map showing stationary → filamentary → bead-fragmentation regimes; combined with the assumed velocity distribution (Eq. 22), it highlights that most loops fragment and identifies the parameter space that maximizes heavy-seed and LRD yields.

Tags

  • LRD
  • BH seeds

2507.17738v1

Beyond the Dot: an LRD-like nucleus at the Heart of an IR-Bright Galaxy and its implications for high-redshift LRDs

Pierluigi Rinaldi, George H. Rieke, Zihao Wu, Carys J. E. Gilbert, Fabio Pacucci, Luigi Barchiesi, Stacey Alberts, Stefano Carniani, Andrew J. Bunker, Rachana Bhatawdekar, Francesco D'Eugenio, Zhiyuan Ji, Benjamin D. Johnson, Kevin Hainline, Vasily Kokorev, Nimisha Kumari, Edoardo Iani, Jianwei Lyu, Roberto Maiolino, Eleonora Parlanti, Brant E. Robertson, Yang Sun, Cristian Vignali, Christina C. Williams, Christopher N. A. Willmer, Yongda Zhu

Theme match 4/5

Digest

The authors present WISEA J123635.56+621424.2 (“the Saguaro”) at z=2.0145 in GOODS‑North as an LRD analog: a compact, LRD‑like nucleus with a face‑on spiral host and a clear V‑shaped nuclear SED from NIRSpec. Redshifting the system to z≈7 renders the host undetectable via surface‑brightness dimming, reproducing a canonical LRD appearance and implying many high‑z LRDs could be visible galactic nuclei embedded in extended hosts. A stack of rest‑UV images for 99 photometrically selected LRDs reveals faint diffuse emission and mild radial growth with redshift, consistent with galaxy size evolution. A simple analytic model shows surface‑brightness dimming alone can explain the compact morphology, arguing LRDs are a short‑lived, AGN‑dominated phase rather than a distinct population.

Open paper pagearXiv abstractarXiv PDFHighlighted PDF

Key figures to inspect

  • Figure 1: Use the PRISM spectrum and G235H zoom to locate the V‑break and inspect Hα+[N II] (line widths and [N II]/Hα separation), while the slit‑overlay RGB confirms the nuclear origin of the PRISM flux and the contrast between the compact nucleus and the face‑on spiral host in the postage stamps.
  • Figure 2: Examine the SED decomposition where a star‑forming LIRG template is fit and subtracted—verify that the residual (nuclear) SED shows the sharp blue‑to‑red turnover characteristic of LRDs and assess how much of the long‑wavelength flux is host‑dominated.
  • Figure 3: Check the agreement between PRISM spectroscopy and GALFITM AGN–host photometry; confirm the continuum shape across the HST–JWST transition and that the decomposition reproduces the PRISM flux level of the nucleus.
  • Figure 4: Inspect row‑by‑row 1D spectral extractions to see how continuum and lines peak at the trace center and fade outward, quantifying the AGN dominance in central rows versus increasing host contribution off‑nucleus.

Tags

  • LRD
  • v-shaped SED

2507.16921v1

ALMA survey of a massive node of the Cosmic Web at $z\sim 3$. II. A dynamically cold and massive disk galaxy in the proximity of a hyperluminous quasar

A. Pensabene, S. Cantalupo, W. Wang, C. Bacchini, F. Fraternali, M. Bischetti, C. Cicone, R. Decarli, G. Pezzulli, M. Galbiati, T. Lazeyras, N. Ledos, G. Quadri, A. Travascio

Theme match 2/5

Digest

High-resolution (∼0.3″) ALMA Band-3 CO(4–3) and 3‑mm continuum mapping of the MQN01 node isolates a massive companion, MQN01‑QC, ∼10 kpc and −300 km s⁻¹ from the hyperluminous quasar CTS G18.01 (z=3.251). Kinematic modeling of the cold gas yields a dynamical mass of 2.5×10^11 M⊙ within ≈4 kpc and a dynamically cold disk with Vrot/σ≈11, establishing the first quasar companion confirmed as a massive rotating disk at this epoch. Despite the proximity, the disk shows no clear tidal disturbances, while the quasar’s CO(4–3) profile exhibits a broad blueshifted wing consistent with a powerful molecular outflow or interaction. The system suggests dynamically cold disks can persist even in dense, early cosmic‑web nodes and hints the quasar may be a satellite in an incipient merger.

Open paper pagearXiv abstractarXiv PDFHighlighted PDF

Key figures to inspect

  • Figure 1: Compare the PSF‑subtracted JWST/NIRCam view with the ALMA 3‑mm map to verify the MQN01‑QC centroid, its projected ∼10 kpc separation from CTS G18.01, and the alignment between stellar light and dust continuum within the 0.3″ beam.
  • Figure 2: Inspect the CO(4–3) line profiles—multi‑Gaussian fit for the quasar and the 3DBarolo rotating‑disk model for MQN01‑QC—to see the ∼−300 km s⁻¹ offset of the companion and the quasar’s broad blueshifted wing; check residuals to gauge model adequacy.
  • Figure 3: Use the moment 0/1/2 maps to confirm an ordered velocity gradient across MQN01‑QC and low dispersions consistent with Vrot/σ≈11, and to contrast this with the higher‑σ emission near the quasar position.
  • Figure 4: Examine the modified‑blackbody SED fits to assess dust temperatures and masses for the quasar and MQN01‑QC, and how assumptions on Td shift inferred continuum‑based ISM properties.

Tags

  • luminous quasar
  • outflows
  • ALMA/mm