Weekly issue

Week 51, 2025

Dec 15–21, 2025

Week 51, 2025 includes 12 curated papers, centered on high-z, spectroscopy, LRD.

2512.16365v1

The AGN nature of strong CIII emitters in the Early Universe with JWST

F. Arevalo-Gonzalez, R. Tripodi, M. Llerena, L. Pentericci, A. Plat, G. Barro, R. O. Amorín, B. Backhaus, A. Calabrò, N. J. Cleri, M. Dickinson, J. S. Dunlop, S. L. Finkelstein, M. Giavalisco, M. Hirschmann, J. Kartaltepe, A. M. Koekemoer, R. A. Lucas, L. Napolitano, E. Piconcelli, A. J. Taylor, F. Tombesi, J. R. Trump, X. Wang

Theme match 5/5

Digest

Builds a z=5–7 sample of 61 CIII] emitters from NIRSpec/prism (CEERS, JADES, RUBIES, CAPERS) and classifies them with UV-line diagnostics (EW(CIII])–CIII]/HeII; EW(CIV)–CIV/HeII) plus checks for broad Balmer lines, finding the OHNO optical diagram has low AGN/SF separation power. They report 29/61 with at least one secure AGN indicator and 13 additional AGN candidates from the CIII]-based diagnostic, and identify five Little Red Dots (one newly reported). The population shows strong CIII] with median EW 22.8 Å (12.5–51.5 Å), and at fixed MUV the line is stronger by ~0.67 dex than a 3<z<4 control (median 4.7 Å), implying rapid evolution. CIII] emitters span the star-forming main sequence, with the highest EWs common below the sequence, underscoring the utility of UV diagnostics for the early AGN census while cautioning against OHNO at these redshifts/resolution.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

UV diagnostic planes: EW(CIII]) vs CIII]/HeII and EW(CIV) vs CIV/HeII with AGN/SF demarcations—inspect where the 29 secure AGN and 13 candidates land and where LRDs cluster.
OHNO diagram ([OIII]/Hβ vs [NeIII]/[OII])—verify the claimed overlap of AGN and SFG loci and quantify the misclassification rate relative to UV diagnostics.
EW(CIII]) vs MUV (and/or histogram) with the z=3–4 control overlay—check the median 22.8 Å and the ~0.67 dex EW offset at fixed MUV.
Example NIRSpec/prism spectra for AGN-flagged sources—look for broad Balmer components (e.g., Hβ, Hγ) and note measured FWHM supporting AGN classification.
SFR–M* plane from Bagpipes fits—confirm that CIII] emitters span the main sequence and that the largest EWs concentrate below the sequence.

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2512.15853v1

From "The Cliff" to "Virgil": Mapping the Spectral Diversity of Little Red Dots with JWST/NIRSpec

Guillermo Barro, Pablo G. Perez-Gonzalez, Dale Kocevski, Jonathan R. Trump, Mark Dickinson, Pablo Arrabal Haro, Madisyn Brooks, Callum T. Donnan, James S. Dunlop, Steven L. Finkelstein, Maximilien Franco, Giovanni Gandolfi, Mauro Giavalisco, Norman A. Grogin, Michaela Hirschmann, Jeyhan S. Kartaltepe, Anton M. Koekemoer, Rebecca L. Larson, Gene C. K. Leung, Ray A. Lucas, Elizabeth J. McGrath, Casey Papovich, Borja Perez-Diaz, Rachel S. Somerville, Elizabeth Taylor, Anthony J. Taylor, Roberta Tripodi, L. Y. Aaron Yung, Xin Wang

Theme match 5/5

Digest

Using uniform photometric cuts and public NIRSpec/PRISM spectra across six JWST deep fields, the authors assemble 118 Little Red Dots and map their population-wide continuum and line diversity. They uncover a clear color–slope sequence: bluer LRDs (βν,UV ≈ 0.3) show power-law optical SEDs, while redder LRDs (βν,UV ≈ 1.1) develop strong Balmer breaks and curvature; up to 90% show broad Balmer lines and ~60% of known BLAGNs meet the LRD criteria. Emission-line ratios shift from high Hα/Hβ and low [OIII]/Hβ in the reddest LRDs to the opposite in the bluest, with stronger narrow-line EWs toward the blue, indicating a progression from AGN- to host-dominated emission. A two-component model (gas-enshrouded BH + host) reproduces this sequence by tuning BH luminosity/obscuration and host-to-BH contrast, offering a unified framework for early BH growth in LRDs.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect how the barro25 color–color box captures nearly all spectroscopic LRDs across six fields, the placement of prior BLAGNs, and the brown-dwarf exclusion—this sets selection completeness and contamination context.
Figure 2: Examine a single LRD with a sharp Balmer break to see why [0.3–0.9 μm] color can far exceed the fitted optical slope, emphasizing that breaks, not just slopes, drive the red sequence.
Figure 3: Read the UV-slope versus optical-color plane and the curvature coding to verify the trend from blue, power-law SEDs to red, highly curved spectra; note where extreme-break literature objects land.
Figure 4: Step through the five [0.3–0.9 μm] bins to visualize the spectral sequence—declining Balmer-break strength and curvature toward the blue—and compare with stacked templates carried between panels.

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2512.14066v1

Primordial Black Holes as Seeds for Extremely Overmassive AGN Observed by JWST

Saiyang Zhang, Boyuan Liu, Volker Bromm, Florian Kühnel

Theme match 5/5

Digest

High-resolution cosmological simulations with a massive PBH seed (MBH=5×10^7 M⊙) couple accretion/feedback to Pop III/II star formation to test LRD-like systems such as Abell 2744–QSO1 at z≈7. The PBH accelerates halo assembly but its thermal feedback delays first stars to z≲10 and drives short, bursty star-formation episodes while outflows purge metals and inflows resupply pristine gas. This cycle sustains low accretion (∼1–10% Eddington), subsolar metallicities (Z/Z⊙≲10^−2), and extreme MBH/M⋆ during both early star-forming and quenched phases. The tracks match A2744–QSO1’s low-Z and overmassive-BH constraints, pointing to massive PBHs as a viable channel for the most extreme LRDs.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect the radial density and metallicity profiles at the final snapshot to see the steep inner density cusp and persistently subsolar gas metallicity across the central 100–300 pc, and compare the Pop III vs. Pop II spatial distribution relative to the PBH.
Figure 2: Compare BH accretion histories (as Eddington fractions) to the observed range for A2744–QSO1 and note how star formation occurs in short, feedback-regulated bursts; check the impact of including full stellar feedback and the Pop III/Pop II decomposition.
Figure 3: Follow the redshift-colored tracks of metallicity versus MBH/M⋆ for central and 300 pc apertures to verify that the simulations enter the observed A2744–QSO1 zone of low Z and extreme mass ratio at early times.

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2512.13957v1

From ASTRID to BRAHMA -- The role of overmassive black holes in little red dots in cosmological simulations

Patrick LaChance, Aklant Kumar Bhowmick, Rupert A. C. Croft, Tiziana Di Matteo, Yihao Zhou, Fabio Pacucci, Laura Blecha, Paul Torrey, Yueying Ni, Nianyi Chen, Simeon Bird

Theme match 5/5

Digest

Using BRAHMA, the authors test whether overmassive black holes (MBH/M*≈0.1) can explain little red dots by post-processing AGN emission with a dense, surrounding gas cloud. They obtain an LRD number density of 2.04±0.32×10^-4 Mpc^-3 at z=5–8, with rest-visible light dominated by the AGN and a very strong Balmer break. Elevated BH masses cool the accretion discs, shifting the SED peak to longer wavelengths and brightening the rest-visible, while minimal dust (A_V=0.21±0.12) keeps IR re-emission below ALMA limits. ASTRID, with systematically smaller BHs, yields LRD counts over two orders of magnitude lower, pointing to dense-gas–enshrouded, overmassive BHs as necessary to match both properties and abundances.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Compare incident vs transmitted AGN SEDs through different gas cloud setups to see how the dense-enshrouded model deepens the Balmer break and suppresses X-rays, and how changing AGN temperature shifts the SED peak into the rest-visible.
Figure 2: Inspect Red1/Red2 color–color and color–magnitude selections to verify where BRAHMA LRDs land relative to the cut lines, and contrast BRAHMA’s distribution with the much sparser ASTRID contours.
Figure 3: In the mock JWST image+spectra, check that the AGN component dominates the rest-visible continuum and produces the strong Balmer break, while the dashed (pre-dust) vs solid curves show how little dust is required.
Figure 4: Read the MBH/M*–based panel colored by rest-visible color to see BRAHMA LRDs clustering at MBH/M*~0.1, and compare against literature AGN fits, X-ray–based estimates, and the local relation to underscore the ‘overmassive’ regime.

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2512.18421v1

The evolution of obscured AGN across cosmic time -- A large quasar survey for the 2040s

Tanya Urrutia, Darshan Kakkad, Paula Sánchez-Sáez, Mojtaba Raouf, Swayamtrupta Panda, Sarah E. I. Bosman, Francisco Pozo Nunez, Annagrazia Puglisi, Sophia Flury, Dragana Ilic, Andjelka B. Kovacevic, Mamta Pandey-Pommier, Giustina Vietri, Sarath Satheesh-Sheeba, Francesco Salvestrini, Susanna Bisogni, Eduardo Bañados, Ana Monreal Ibero, Sabine Thater, Pratika Dayal, Filippo D'Ammando, José Afonso, Paramita Barai, Valentin Ivanov

Theme match 4/5

Digest

White paper proposing a 2040s optical MOS program to repeatedly spectroscopically observe >50 million quasar/AGN candidates out to z≈6.5 by combining radio, IR, X-ray, variability, and astrometric selections. The unified, variability+spectroscopy framework is designed to fold in dust-reddened systems (e.g., LRD-like, red/FeLoBAL quasars), radio-selected sources, and CL AGN to measure how the obscured fraction depends on luminosity and redshift from Cosmic Noon into reionization. The plan leverages Euclid/Roman imaging, SKA-Wide radio identifications, LSST variability, and NewAthena X-rays, and argues for a WST-class 10–15 m, R≈1500, 20–30k-fiber facility achieving S/N>5 to 25 mag even for NH≈10^24 cm⁻2. The payoff is a bias-corrected, time-resolved census of early black-hole growth and obscuration evolution across cosmic time.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Projected completeness across the luminosity–redshift plane comparing single-method selections (radio/IR/X-ray/variability/astrometry) versus the combined strategy, to see how obscured classes (LRDs, red quasars, FeLoBALs, Type 2) are recovered uniformly.
Survey yield maps from Euclid, SKA-Wide, LSST, and NewAthena: expected surface densities and total counts per redshift bin, including the >100k red-quasar candidates from early Euclid and the >50k SKA EoR candidates, to gauge where the 50M total comes from.
Instrument performance for a WST-like facility: S/N versus magnitude at R≈1500 and exposure time, showing reach to r≈25 and detectability of broad emission/absorption features under heavy extinction (NH≈10^24 cm⁻2).
Cadence and multi-epoch plan: expected numbers of changing-look events and BLR re-emergence detections versus revisit spacing, illustrating how time-domain spectroscopy constrains obscuration physics.
Target selection and cross-match flow: decision tree integrating radio/IR/X-ray/variability/astrometry inputs with de-duplication and prioritization, clarifying how diverse AGN candidates enter a single spectroscopic program.

Tags

2512.18000v1

The Clustering of Little Red Dots from Ultra-Strongly Self-Interacting Dark Matter

M. Grant Roberts, Aarna Garg, Tesla Jeltema, Stefano Profumo

Theme match 4/5

Digest

This Letter computes the large‑scale clustering of Little Red Dots at z~5 assuming their SMBH seeds arise from gravothermal collapse in ultra‑strongly self‑interacting dark matter. Weighting the uSIDM‑predicted LRD mass function with the Tinker halo bias yields an effective bias b_eff ≈ 4.5, implying characteristic host halos of ~8×10^10 Msun and a population distinct from luminous high‑z quasars. The prediction is robust—b_eff is effectively insensitive to uSIDM microphysics (σ/m and fraction f) and independent of the assumed duty cycle—providing a clean observational target. Upcoming JWST samples can directly measure LRD clustering to test the uSIDM origin scenario.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect how the uSIDM LRD mass function (colored points) compares to SIDM simulations and Kokorev et al. data; use the slope/normalization—and the horizontal Eddington‑ratio shift bars—to see which BH‑mass ranges dominate the number‑density weighting that feeds into b_eff.
Figure 2: Read b_eff from the gray band of power‑law mass‑function fits and map it to a characteristic halo mass via the red Tinker bias curve; compare with the orange (Schindler et al.) and blue (Pizzati et al.) bands to gauge whether LRDs prefer lower‑mass halos than quasars.
Figure 3: Check that b_eff from the full uSIDM mass functions clusters tightly around ~4.5 despite varied microphysics, confirming the stated insensitivity and the implied host‑halo mass near 8×10^10 Msun.

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2512.17997v1

Pulsational Instability of Quasi-Stars: Interpreting the Variability of Little Red Dots

Matteo Cantiello, Jake B. Hassan, Rosalba Perna, Philip J. Armitage, Mitchell C. Begelman, Yan-Fei Jiang, Taeho Ryu, Richard H. D. Townsend

Theme match 4/5

Digest

Uses MESA+GYRE to test whether quasi-star envelopes that could power Little Red Dots become radially unstable and pulsate. Finds a Quasi-Star Instability Strip with a blue edge at Teff ≈ 5000–5200 K: hotter models are stable (consistent with non-variable R2211‑RX2 at ≈5000 K), cooler ones are κ‑driven unstable in H/He ionization zones. Fundamental modes have 20–180 yr periods and first overtones 10–30 yr, matching the co-moving variability and L–T hysteresis of lensed LRD R2211‑RX1. The implied pulsation-enhanced winds could shorten the quasi-star phase and regulate the seed BH’s terminal mass.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1 (HR diagram tracks): Identify where models cross Teff ≈ 5000–5200 K and how radius lines and BH-mass color coding map onto the proposed blue edge of the instability strip; compare stable (hotter) versus unstable (cooler) track segments relevant to RX2 vs RX1.
Instability-strip map (Teff–Lum or Teff–parameter plane): Locate the ‘Quasi-Star Instability Strip,’ mark the blue edge near 5000–5200 K, and see which envelope masses fall into unstable territory.
Mode stability and growth-rate diagram (GYRE): Inspect which radial modes (ℓ=0, n_p=1 and 2) are unstable and their e-folding rates across Teff; confirm κ‑mechanism driving regions from work integrals in H/He ionization zones.
Period–mass (or period–Teff) scaling: Read off fundamental (20–180 yr) and first-overtone (10–30 yr) periods versus M⋆ ≈10^4–10^5 M⊙ and check consistency with RX1’s co-moving timescale.
Nonlinear pulsation cycle: Follow time-dependent MESA loops in the luminosity–temperature plane to verify the clockwise/counter-clockwise hysteresis morphology and amplitude compared to RX1.

Tags

2512.14822v1

HELM's deep: Highly Extincted Low-Mass galaxies seen by JWST

L. Bisigello, G. Gandolfi, A. Grazian, G. Rodighiero, G. Girardi, A. Renzini, A. Vietri, E. McGrath, B. Holwerda, Abdurro'uf, M. Castellano, M. Giulietti, C. Gruppioni, N. Hathi, A. M. Koekemoer, R. Lucas, F. Pacucci, P. G. Pérez-González, L. Y. A. Yung, P. Arrabal Haro, B. E. Backhaus, M. Bagley, M. Dickinson, S. Finkelstein, J. Kartaltepe, A. Kirkpatrick, C. Papovich, N. Pirzkal

Theme match 4/5

Digest

Using CEERS imaging, the authors assemble 1361 highly extincted low-mass (HELM) systems via posterior-weighted SED fits, defining dwarfs with M* < 10^8.5 Msun and Av > 1 mag or objects exceeding an Av–M* threshold. After removing contaminants—including brown dwarfs, little red dots, and z > 8.5 ultra-high‑z lookalikes—the sample is mostly at z < 1 (tail to z = 7.2) with median M* ≈ 10^7 Msun and Av ≈ 2 mag. HELM galaxies have Re comparable to non‑dusty dwarfs and show no Av–(b/a) trend, arguing against simple projection, while a prolate or disk‑on‑oblate geometry remains plausible. They sit in slightly more clustered environments and are mildly less star‑forming, hinting—pending spectroscopic confirmation—that interactions may drive their high attenuation.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect the Av–M* plane to see how HELM objects sit well above the McLure (2018) relation and the exact red selection line; compare against literature dusty samples and note the spectroscopically confirmed HELM point for scale.
Figure 2: Check how the HELM selection is performed on the full posterior (not point medians) and how pre/post quality and contaminant cuts reshape the number-density side panels—useful for judging sample purity and boundary cases.
Figure 3: Read off the normalized redshift and stellar‑mass distributions; confirm the z < 1 dominance, the tail to z ≈ 7.2, and compare medians across HELM subsamples to understand where dusty dwarfs concentrate in M*–z space.
Figure 4: Examine the HELM fraction versus redshift, and versus redshift at fixed mass, to quantify how common dusty dwarfs are relative to CEERS peers and whether incidence rises in specific z or mass bins.

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2512.14844v1

Doubling NIRSpec/IFS capability to calibrate the single epoch black hole mass relation at high redshift

Eleonora Parlanti, Bartolomeo Trefoloni, Stefano Carniani, Francesco D'Eugenio, Michele Perna, Giulia Tozzi, Hannah Übler, Giacomo Venturi, Sandra Zamora

Theme match 3/5

Digest

Presents a NIRSpec/IFU reduction that exploits the red signal on NRS2 for medium‑resolution gratings, effectively doubling the usable wavelength coverage and recovering Hα beyond the nominal range; the authors also note the exposure‑time trade‑off when using adjacent dispersers. Applied to five z≈2 quasars with reverberation‑mapped MBH, the extended cubes enable joint Hβ–Hα measurements at R≈1000. Hβ‑based single‑epoch masses best match RM, while Hα recipes show ≈0.5 dex larger scatter; for the least‑massive, high‑λEdd object (MBH,RM≈10^7.5 M⊙, λEdd=0.8) all SE estimators overpredict by ~1 dex, suggesting a bias at high accretion. The work delivers the first high‑z SE calibrations from Hβ and Hα for the newfound early‑BH population, with uncertainties still limited by sample size.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1 (RM332 G140M/F100LP): Verify that emission falls on NRS2 beyond the nominal cutoff and that Hα is detected alongside the [O III]–Hβ complex; use the insets to gauge S/N and how far past the red limit the recovery extends.
Figure 2 (P330‑E calibrator): Check flux consistency of the extended G140M/F100LP response across cycles and field positions; this validates the throughput stability needed for reliable Hα fluxes in the extended region.
Figure 3 (wavelength‑dependent corrections): Inspect the G140M/F100LP and G235M/F170LP correction curves used to stitch the extended coverage; the smoothness and rise at long wavelengths indicate where the extended tail remains photometrically trustworthy.
Figure 4 (flux ratio test): Compare nominal‑range fluxes to those from the extended filter to quantify systematics; look for departures from unity toward the red end that set the error budget for SE mass scaling based on Hα.

Tags

2512.16981v1

The accretion of quasars at the epoch of reionisation: $JWST$ catches the primeval monsters slowly feasting

B. Trefoloni, E. Nardini, S. Carniani, E. Lusso, A. Marconi, E. Parlanti, A. Sacchi, A. Shlentsova, M. Signorini, G. Risaliti, S. Zamora

Theme match 2/5

Digest

Using NIRSpec’s 0.6–5.3 μm coverage, the authors fit accretion-disc models to rest-UV/optical spectra of eight luminous z≥5.9 quasars to obtain self-consistent MBH and LAD with tightened uncertainties (~0.2 and ~0.1 dex). They find a mean Eddington ratio ⟨log λEdd⟩ = −0.9 with ~0.2 dex scatter, indicating these bright EoR quasars are typically sub‑Eddington. Compared to single‑epoch recipes, the AD approach avoids C IV biases by anchoring to Hβ/Mg II and continuum windows while shrinking systematics. Assuming the sample represents optically selected blue QSOs, only ~0.2% appear super‑Eddington, challenging the prevailing near/super‑Eddington picture.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

NIRSpec PRISM spectra for each QSO across rest 1200–6700 Å: mark continuum windows and show line fits to Mg II and Hβ–[O III]; verify line widths used for SE comparisons and the clean avoidance of C IV.
AD SED fits overlaid on the spectra: locate the SED peak and show best‑fit/posterior ranges for MBH and LAD; note any assumptions on efficiency/spin and their impact on the fit.
AD‑based vs single‑epoch MBH and LAD comparison plots: check offsets, scatter, and any luminosity/redshift trends that could bias SE calibrations at z≈6–8.
Distribution of λEdd for the eight QSOs: confirm the mean −0.9 dex, ~0.2 dex dispersion, and quantify the tiny super‑Eddington tail (~0.2%).
Sample overview figure (z–L3000 plane): place these eight objects among other surveys to see why NIRSpec coverage captures both Mg II and Hβ at z≥5.9.

Tags

2512.15881v1

Shedding the envelope: JWST reveals a kiloparsec-scale [OIII]-weak Balmer shell around a z=7.64 quasar

Julien Wolf, Eduardo Bañados, Xiaohui Fan, Antoine Dumont, James E. Davies, David S. N. Rupke, Jinyi Yang, Weizhe Liu, Silvia Belladitta, Aaron Barth, Sarah Bosman, Tiago Costa, Frederick B. Davies, Roberto Decarli, Dominika Ďurovčíková, Anna-Christina Eilers, Hyunsung D. Jun, Yichen Liu, Federica Loiacono, Alessandro Lupi, Chiara Mazzucchelli, Maria Pudoka, Sofía Rojas-Ruiz, Jan-Torge Schindler, Wei Leong Tee, Benny Trakhtenbrot, Fabian Walter, Huanian Zhang

Theme match 2/5

Digest

JWST/NIRSpec IFU mapping of the z=7.64 quasar J0313−1806 reveals a kiloparsec-scale Hβ-bright shell (r ≈ 1.8 kpc) that is strikingly [O III]-weak, with a 3σ limit of log10([O III]/Hβ) = −1.15. The unresolved nucleus shows no detectable [O III] and yields M_BH = 1.63×10^9 Msun and λ_Edd ≈ 0.80 from Hβ. Photoionization modeling favors a thin, clumpy, dense outflowing shell where [O III] is collisionally de-excited, interpreted as a fossil of a recent blowout. This points to episodic feedback operating in one of the earliest luminous quasars and highlights dense ISM phases as key to early spectral phenomenology.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect the quasar Hβ fit and strong Fe II to see how the Hβ-based M_BH and λ_Edd are anchored, and note the absence of narrow [O III] despite broad Balmer emission.
Figure 2: Check the wavelength-dependent PSF scaling against the PSF star; this validates that extended residuals are not PSF mismatch artifacts near Hβ.
Figure 3: Study the PSF-subtracted residual map and region A to confirm that the extended emission is real and roughly ring-like around the quasar position.
Figure 4: Use the Hβ moment maps to trace the shell geometry: flux peaking near the quasar, a coherent velocity gradient consistent with expansion/rotation, and σ patches >600 km/s at the edges indicating turbulence in the shell.

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2512.14441v1

A sub-ppm upper limit on the cosmological variations of the fine structure constant alpha

S. Muller, A. Beelen, M. Guelin, J. H. Black, F. Combes, H. L. Bethlem, M. Gerin, C. Henkel, K. M. Menten, M. T. Murphy, W. Ubachs, N. Wozny

Theme match 2/5

Digest

Simultaneous ALMA spectroscopy of CH ground-state doublets and H2O toward the lens absorbers at z_abs=0.88582 (PKS 1830-211) and 0.68466 (B 0218+357) compares velocity centroids to test for cosmological variation of the fine-structure constant. Bulk shifts are Δv = −0.048 ± 0.028 km s−1 toward PKS 1830-211 (NE) and −0.13 ± 0.14 km s−1 toward B 0218+357 (SW), with tightly correlated CH–H2O opacities across many narrow components. Using independent limits on Δμ/μ for these systems, the shifts imply 3σ bounds |Δα/α| < 0.55 ppm and 1.5 ppm at look-back times ≈ half the age of the Universe. These single-system limits are 2–4× tighter than previous high-z constraints, enabled by the simultaneous setup that minimizes calibration, variability, and chemical-segregation biases.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Fig. 1 (CH level diagram): Identify which Λ-doublet and hyperfine components fall in the ALMA setup and their relative strengths—crucial for understanding the later hyperfine deconvolution and line-weighting in velocity comparisons.
Fig. 2 (Multi-epoch spectra): Compare CH and H2O profiles for PKS 1830-211 NE/SW and B 0218+357 SW across observing dates; verify the stability of component centroids despite intrinsic variability, the alignment of CH–H2O features, and the role of the H2^18O spectrum in checking opacity scaling.
Fig. 3 (Opacity overlays and common fit): Inspect the hyperfine-deconvolved CH profile overlaid with H2O scaled by the opacity ratio; the common fit visualizes the small bulk offset, the two-dex span in optical depths, and the isolated PKS 1830-211(SW) component used as a clean test case.