Weekly issue

Week 43, 2025

Oct 20–26, 2025

Week 43, 2025 includes 5 curated papers, centered on QSO, high-z, LRD.

2510.21709v1

From nuclear star clusters to Little Red Dots: black hole growth, mergers, and tidal disruptions

Konstantinos Kritos, Joseph Silk

Theme match 5/5

Digest

The authors build a simple nuclear star cluster framework in which Little Red Dots host massive black hole seeds that grow through self-consistent tidal disruptions, black hole captures/mergers, and gas accretion. Calibrated to the observed LRD number density, the model predicts at z=4–6 at least a few tens of tidal disruption events and at least a few black hole captures, with the TDE rate roughly an order of magnitude higher than the capture rate. Episodic gas inflow accelerates early growth and correlates with enhanced loss‑cone feeding, offering a path to rapid SMBH assembly while remaining compatible with the generally low X‑ray luminosities of LRDs. The work also quantifies uncertainties on these event-rate estimates.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect the radial density and velocity-dispersion profiles of stars vs stellar‑mass BHs to see where the stellar cusp and BH subcluster form, how the influence radii are set, and how loss‑cone vs evaporation fluxes pick out where TDEs/EMRIs originate.
Figure 2: Compare runs with and without gas accretion; the 20 gas‑inflow episodes drive step‑like SMBH growth and simultaneous spikes in loss‑cone rates—use this to gauge how inflow modulates TDE and capture activity over time.
Figure 3: Use the schematic plus time‑evolution panel to trace mass flow channels (stars, BH remnants, and gas) into the central BH; the inset highlights how discrete inflow episodes imprint on the SMBH growth history.
Figure 4: Check the cumulative counts and time‑resolved rates of TDEs, EMRI captures, and BH binaries; verify the predicted TDE ≫ capture ratio (~10:1) and that 3‑body binary formation stays sub‑dominant (<1 event).

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2510.18142v1

Ultra-Strongly Self-Interacting Dark Matter: From Phenomenology to Astrophysical Observables

M. Grant Roberts, Wolfgang Altmannshofer, Pierce Giffin, Stefano Profumo

Theme match 5/5

Digest

Introduces a minimal two-component SIDM model with a light vector mediator, analytic relic accounting (annihilation plus interconversion), and an ETHOS mapping evolved with CLASS, constrained by dwarf/LSB rotation curves and strong cluster lensing. The viable window features a dominant SIDM with σ_eff/m ≈ 20–40 cm^2 g^-1 at dwarf velocities while satisfying cluster bounds <0.13 cm^2 g^-1, plus a subpercent uSIDM fraction that undergoes rapid gravothermal collapse to seed early SMBHs and the “little red dots.” The small-scale matter power spectrum remains consistent with Lyman-α and satellite counts but exhibits distinctive, non-standard cutoffs that future data could test. The allowed space is organized chiefly by the mediator-to-DM mass ratio and the late-time uSIDM fraction, and is further bounded by direct-detection limits.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1 (process diagrams): Contrast number-conserving self-scattering, annihilation, and χ1χ1 ↔ χ2χ2 interconversion to see why conversion is rate-suppressed, motivating the simplified Boltzmann treatment for relic fractions.
Figure 2 (cross-section hierarchy vs x): Verify that conversion is many orders below annihilation and that the non-relativistic expansion matches the full result at large x, underpinning the analytic yields and the freeze-out uSIDM fraction.
Constraints panel (rotation curves + cluster lensing): Inspect σ/m as a function of velocity—look for the band giving 20–40 cm^2 g^-1 at v_dwarf and <0.13 cm^2 g^-1 at v_cluster—to see the microphysics region that survives data.
Power spectrum figure (ETHOS → CLASS): Examine P(k) to locate the small-scale cutoff and any non-monotonic features compatible with Lyman-α and satellite counts; note scales where deviations from CDM are largest.
Parameter-space map (m_med/m_DM vs f_u): Identify the narrow allowed window satisfying astrophysical and cosmological bounds and mark slices testable by sub-GeV direct detection under kinetic mixing.

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2510.17952v1

Evolutionary Tracks and Spectral Properties of Quasi-stars and Their Correlation with Little Red Dots

Andrew D. Santarelli, Ebraheem Farag, Earl P. Bellinger, Priyamvada Natarajan, Rohan P. Naidu, Claire B. Campbell, Matthew E. Caplan

Theme match 5/5

Digest

Using the MESA-QUEST framework, the authors build evolutionary tracks and spectra for quasi-stars as candidates for the red, compact Little Red Dots seen at z≈3–10. The models settle onto a late-stage Hayashi track lasting about 20 Myr and yield practical scaling relations linking quasi-star mass to Lbol and Lbol to Teff. Synthetic spectra from these models broadly match the continuum of exemplar LRDs (MoM-BH*-1 and UNCOVER-45924), including blackbody-like SEDs with strong Balmer breaks and stellar absorption features. Coupling the short lifetimes with the observed LRD number densities, they argue quasi-stars could be a common pathway to assembling early supermassive black holes.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Evolution tracks on the HR and Kiel diagrams: verify when the model enters the late-stage Hayashi track, how long it stays there, and how BH mass growth maps onto Teff–log g; note the ATLAS9 coverage region and constant-radius lines.
Scaling relations panel: inspect the fitted M_QS–Lbol and Lbol–Teff relations along the Hayashi track and how to use them to estimate quasi-star masses from observed LRD luminosities/temperatures.
Observed vs synthetic spectra for MoM-BH*-1: check the continuum shape, Balmer break amplitude, and presence of Ca H&K/Ca II triplet absorption against the model envelope spectrum.
Observed vs synthetic spectra for UNCOVER-45924: assess how well the quasi-star model reproduces the NIR SED slope and Balmer absorption, and whether any galaxy light component is required.
Dust attenuation test (if shown): look for comparisons with simple dust corrections to confirm the conclusion that attenuation is minimal for LRD continua.

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2510.22403v1

SHELLQs-JWST: Revealing the Spectra of Extended Emission in 12 z > 6 Quasar Host Galaxies using the JWST NIRSpec Fixed Slit

Camryn L. Phillips, Michael A. Strauss, Masafusa Onoue, Xuheng Ding, John D. Silverman, Yoshiki Matsuoka, Takuma Izumi, Junya Arita, Kentaro Aoki, Shunsuke Baba, Masatoshi Imanishi, Nobunari Kashikawa, Toshihiro Kawaguchi, Chien-Hsiu Lee, Mahoshi Sawamura, Yoshiki Toba, Feige Wang, Jinyi Yang

Theme match 2/5

Digest

JWST/NIRSpec Fixed Slit (F290LP/G395M) spectra of 12 SHELLQs quasars at 6.0 < z < 6.4 are PSF-modeled with a wavelength-dependent double-Gaussian and subtracted to isolate host emission, revealing extended lines in 10/12 and extended stellar continuum in 5/12. The hosts show [OIII]5008 kinematics including a 132 ± 19 km/s ionized outflow in one system and 52 ± 12 km/s rotation in another, while narrow Hα implies SFRs ≈7–111 M⊙/yr, largely consistent with the z ≈ 6 main sequence. On the R3N2 BPT plane, line ratios fall in AGN-like regions by low-z standards but overlap with other z ≈ 6 quasar hosts, indicating these ratios cannot cleanly separate AGN from star-formation ionization at high z. Together, the results argue that low-luminosity AGN produce little short-timescale (~10 Myr) impact on typical galaxy properties at z ≈ 6.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 2 (PSF residuals comparison): Verify that the double-Gaussian plus smoothed residuals model removes the nuclear light across wavelength, minimizing wing residuals so that extended [OIII]/Hα features are not PSF leakage.
Figure 4 (PSF width vs. wavelength): Inspect the chromatic ‘wiggles’ and Level-3 broadening; this justifies modeling/subtracting the PSF in individual Level-2 dithers before coadding to preserve faint, spatially extended host emission.
Figure 3 (single-wavelength PSF fit): Check that the summed double-Gaussian closely matches the spatial profile with near-zero residuals—key for trustworthy kinematic measurements (e.g., the 132 km/s outflow, 52 km/s rotation).
Figure 1 (centroid/amplitude/width with λ): See the chromatic centroid shifts and width trends in the calibration star that motivate a wavelength-dependent PSF and explain systematic patterns in the rectified data.
BPT (R3N2) placement figure: Identify where hosts lie on log10([OIII]5008/Hβ) vs. log10([NII]6584/Hα); note their apparent AGN-like locus at low z yet overlap with z ≈ 6 hosts, underscoring the diagnostic’s ambiguity at early times.

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2510.19904v1

The Synthetic Absorption Line Spectral Almanac (SALSA)

Dylan Nelson, Celine Peroux, Philipp Richter, Matthew M. Pieri, Sebastian Lopez, Rongmon Bordoloi, Siwei Zou, Joseph N. Burchett, Rebecca L. Davies, Rahul Ramesh, Matthew C. Smith, Sanchayeeta Borthakur, Christopher W. Churchill

Theme match 2/5

Digest

SALSA introduces a first-of-its-kind, large-scale library of synthetic absorption-line spectra through the ISM, CGM, and IGM, generated with a mesh-free Voronoi ray-tracing algorithm applied to cosmological hydrodynamical simulations. The public platform spans ions from HI/MgII to CIV/OVI/NeVIII, multiple instruments (SDSS-BOSS, KECK-HIRES, UVES, COS, DESI, 4MOST, WEAVE, XSHOOTER), redshifts 0–~6, and simulations including IllustrisTNG (TNG50, TNG-Cluster), EAGLE, and SIMBA, with ancillary equivalent widths, column densities, and galaxy–absorber metadata. Example spectra show how multi-component kinematics in CIV and NeVIII emerge at high resolution, enabling apples-to-apples comparisons, stacking tests, and survey optimization. By tying absorber profiles to underlying 3D gas structure, SALSA becomes a versatile community resource for interpreting quasar absorption and galaxy–halo correlations.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Use the NeVIII column-density map and single sightline crossing a galaxy’s virial radius to connect bubble-like CGM morphology from feedback to the resulting NeVIII 780/770 Å and CIV 1548/1550 Å absorption profiles—i.e., how 3D structure imprints velocity components.
Figure 2: Inspect the ion–redshift–instrument coverage grid to plan virtual surveys—identify which transitions fall in-band for a chosen spectrograph at each snapshot, and what catalog combinations (ion/line/z) are downloadable.
Figure 3: Browse the 121-spectrum CIV gallery ordered by equivalent width to gauge the diversity of IGM→CGM→ISM absorbers and how profile shape and blending evolve with increasing EW; useful for stacking and completeness experiments.
Figure 4: Compare the same CIV systems observed as SDSS-BOSS vs KECK-HIRES to see how low-resolution blending hides narrow velocity components and alters inferred EW/column structure, illustrating instrument-driven systematics.