Weekly issue

Week 21, 2025

May 19–25, 2025

Week 21, 2025 includes 6 curated papers, centered on LRD, spectroscopy, QSO.

2505.14025v1

Quasar identifications from the slitless spectra: a test from 3D-HST

Yuxuan Pang, Xue-Bing Wu, Yuming Fu, Rui Zhu, Tao Ji, Qinchun Ma, Xiaotong Feng

Theme match 5/5

Digest

Pang et al. build a slitless-spectrum QSO selector on 3D-HST/G141 by first flagging >6,000 sources with apparently broad lines and then using forward modeling to test whether the “broad” features require a point-like QSO component rather than size-broadened ELG lines. Calibrated on known QSOs, ELGs, and simulations, the criterion recovers ~90% of point-like QSOs with Hα/Hβ while keeping ELG contamination at ~5%. Applied to clean emission-line sources, it yields 19 QSO candidates at z=0.12–1.56 (12 X-ray detections) with broader UV colors and redder optical slopes than SDSS QSOs and MBH≈10^6.9–10^8.3 M⊙, consistent with normal QSOs rather than little red dots. The method boosts QSO completeness at z≈0.8–1.6 in 3D-HST and is directly portable to Euclid and CSST slitless surveys.

Open paper page arXiv abstract arXiv PDF

Key figures to inspect

Figure 1 — Walk through the two-step pipeline; focus on how the forward-model “QSO component reliability” gate is defined and where size-broadened ELG lines fail the test.
Figure 2 — Inspect the continuum-fit and thresholding on 1D spectra; compare the distorted versus clean examples to see how peaks are flagged and how apparent FWHM≥1200 km/s are distinguished from noise.
Figure 3 — Examine heavy-contamination cases in 2D spectra; compare the data, model, and contamination model to see how spurious broadening from overlaps is recognized and removed.
Figure 4 — Check the F140W–redshift distribution for the one-line vs two-line subsamples; note that most lie at 0.6–2.4 where Hα or Hβ+[O III] enters G141, setting the method’s most effective redshift window.

Tags

2505.14768v1

X-ray properties of massive compact relic galaxies

Orsolya E. Kovacs, Norbert Werner, Akos Bogdan, Jelle de Plaa

Theme match 4/5

Digest

Chandra and XMM-Newton data are used to map hot atmospheres around seven local compact ellipticals selected as red‑nugget analogs, probing BH–bulge–halo coupling. Only MRK 1216 and PGC 32873 show luminous, spatially extended halos enabling radial thermodynamic profiles, with MRK 1216’s RGS spectrum hinting at super‑solar α/Fe. The others have faint or undetected halos, several instead showing AGN‑like power‑law emission. On galaxy scaling planes, cEGs follow a slightly steeper M⋆–LX and sit on the lower edge of M⋆–Mvir, implying red nuggets—and possibly their LRD progenitors—host a diverse range of halo atmospheres.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Deep Chandra/XMM images and surface‑brightness profiles of MRK 1216 and PGC 32873: verify the spatially extended halo relative to the PSF and separate central point‑source from diffuse gas.
Radial thermodynamic profiles (kT, ne, entropy, pressure) for MRK 1216 and PGC 32873: read off cooling times/entropy floors and assess hydrostatic mass trends that place them on the low edge of M⋆–Mvir.
XMM‑RGS spectrum of MRK 1216: inspect α‑element (O/Ne/Mg/Si) to Fe line ratios supporting super‑solar α/Fe and check for multi‑temperature structure.
Spectral fits for the fainter cEGs: compare thermal vs power‑law components and photon indices to substantiate AGN‑like emission where halos are undetected.
Scaling‑relation panels (M⋆–LX and M⋆–Mvir): see the steeper M⋆–LX slope and cEG locus along the lower boundary of M⋆–Mvir relative to the general galaxy population.

Tags

2505.14676v1

A JWST View of the Overmassive Black Hole in NGC 4486B

Behzad Tahmasebzadeh, Matthew A. Taylor, Monica Valluri, Haruka Yoshino, Eugene Vasiliev, Michael J. Drinkwater, Solveig Thompson, Kristen Dage, Patrick Côté, Laura Ferrarese, Tatsuya Akiba, Vivienne Baldassare, Misty C. Bentz, John P. Blakeslee, Holger Baumgardt, Youkyung Ko, Chengze Liu, Ann-Marie Madigan, Eric W. Peng, Joel Roediger, Kaixiang Wang, Tyrone E. Woods

Theme match 4/5

Digest

Using JWST/NIRSpec IFU stellar kinematics plus archival long-slit data, the authors model the compact elliptical NGC 4486B and resolve a double nucleus with a velocity-dispersion peak offset from the photometric center. Axisymmetric Schwarzschild modeling of the full LOSVD yields M_BH = 3.6 ± 0.7 × 10^8 M_sun and a host ratio M_BH/M_* ≈ 4–13%, firmly placing the black hole in the overmassive regime. Dark matter within 1 kpc is weakly constrained (M_DM/M_* < 0.5), and the inferred M_BH is unchanged with or without a halo. The system’s location deep in Virgo supports a stripped-core origin, with the caveat that non-equilibrium double-nucleus dynamics are not modeled, so the mass may be a lower limit.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Compare the HST F850LP image to the NIRSpec IFU S/N map to see the resolved P1/P2 double nucleus and how the IFU coverage samples it; inspect the central vs outer pPXF fits to gauge LOSVD quality where dispersion is highest.
Figure 2: Examine GH moment maps (V, σ, h3, h4) to locate the off-center σ peak and assess how the best-fit Schwarzschild model reproduces asymmetries; contrast the baseline, peak-masked, and peak-shifted cases to test robustness.
Figure 3: Trace V and σ along the kinematic major axis, comparing JWST points to CFHT/SIS data from Kormendy et al. (1997); verify the amplitude and location of the dispersion peak and how the axisymmetric model tracks both datasets.
Figure 4: Inspect marginalized likelihoods for M_BH, M/L, DM circular velocity, and inclination; note the tight M_BH constraints and how data treatments (masking/shifting the peak) affect parameter posteriors and confidence intervals.

Tags

2505.12719v1

Composite spectrum of Little Red Dot from a standard inner disk and an unstable outer disk

Chenxuan Zhang, Qingwen Wu, Xiao Fan, Luis C. Ho, Jiancheng Wu, Huanian Zhang, Bing Lyu, Xinwu Cao, Jianmin Wang

Theme match 4/5

Digest

Builds SEDs for 29 broad-line LRDs and finds uniformly V-shaped continua with a narrow break around ν_b ≃ 10^{14.96±0.06} Hz (λ ≈ 2600–3800 Å). Models the SEDs as a composite of an inner standard thin disk plus an outer gravitationally unstable disk (Q≈1) that self-regulates to T≈2000–4000 K, naturally producing the near-IR/optical bump without invoking extreme dust. MCMC fits anchored by MBH from broad lines reproduce individual SEDs, including UNCOVER 25119 and PRIMER 33823 (whose MIRI 4.9–27.9 μm points trace the bump). Allowing for dense gas to explain strong Balmer breaks suppresses intrinsic optical–UV by only ≲2–3×, implying most LRDs are sub-Eddington and intrinsically weak.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1 (broken-power-law fits for UNCOVER 25119 and PRIMER 33823): Check how the V-shaped continuum is identified and where the inflection lies; note excluded line-contaminated and low-S/N points and the MIRI outliers for PRIMER 33823.
Figure 2 (inflection-wavelength histogram and normalized SED stack): Verify the tight clustering of λ_b ≈ 2600–3800 Å and the small scatter in the composite, which drives the common break-frequency claim.
Figure 3 (cartoon, temperature profile, and model spectrum): See how the outer Q≈1 disk attains T≈2000–4000 K and dominates the near-IR/optical bump; note the schematic showing how crossing a dense disk wind strengthens the Balmer break.
Figure 4 (MCMC SED fits for UNCOVER 25119 and PRIMER 33823): Inspect how the composite model matches photometry/spectroscopy, the recovery of the MIRI-traced bump, and constraints on ṁ and the critical radius given MBH from broad lines.

Tags

2505.18873v1

An upper limit of 10$^6$ M$_\odot$ in dust from ALMA observations in 60 Little Red Dots

Caitlin M. Casey, Hollis B. Akins, Steven L. Finkelstein, Maximilien Franco, Seiji Fujimoto, Daizhong Liu, Arianna S. Long, Georgios Magdis, Sinclaire M. Manning, Jed McKinney, Marko Shuntov, Takumi S. Tanaka

Theme match 3/5

Digest

ALMA Band-6 (1.3 mm) continuum follow-up of 60 of the reddest and brightest COSMOS-Web little red dots—preselected with MIRI F770W detections—finds no individual detections and a non-detection in the stack. The data reach a mean σ_rms≈22 μJy, with a stacked flux of S_1.3mm=2.1±2.9 μJy, implying 3σ limits of Mdust<10^6 M⊙ and Ldust≲10^11 L⊙, about 10× deeper than previous submm stacks. These results disfavor large, cold dust reservoirs in typical LRDs. They are consistent with compact, modest dust columns (A_V~2–4) or extreme Balmer breaks from very dense gas (n>10^9 cm^-3) enshrouding a central black hole.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect the JWST cutouts with ALMA contours to verify the absence of >3σ peaks at LRD centroids and to gauge the uniform 1σ RMS (21–23 μJy); also check for any offset positive contours that might hint at extended hosts or unrelated submm sources.
Figure 2: Read off how the 3σ per-source limit (≈66 μJy) and the stacked 3σ limit (≈10.8 μJy) map onto Mdust and LIR across dust temperatures and redshifts; note where the curves intersect Mdust≈10^6 M⊙ and how they compare to the Setton et al. (2025) constraints.
Figure 3: Compare the new stacked limit against previous LRD submm/NOEMA results (Labbé 2022; Akins 2024; Xiao 2025; Setton 2025), noting the rescaling to typical LRD luminosities and the consistency with the predicted low-luminosity dust SED; use the overplotted 30 K and 1500 K blackbodies to visualize why large cold…

Tags

2505.15923v1

Discovery and characterization of 25 new quasars at 4.6 < z < 6.9 from wide-field multi-band surveys

Silvia Belladitta, Eduardo Bañados, Zhang-Liang Xie, Roberto Decarli, Silvia Onorato, Jinyi Yang, Manuela Bischetti, Masafusa Onoue, Federica Loiacono, Laura N. Martínez-Ramírez, Chiara Mazzucchelli, Frederick B. Davies, Julien Wolf, Jan-Torge Schindler, Xiaohui Fan, Feige Wang, Fabian Walter, Tatevik Mkrtchyan, Daniel Stern, Emanuele P. Farina, Bram P. Venemans

Theme match 2/5

Digest

Targeted optical/IR/radio selections across wide-area surveys yield 25 new luminous quasars at 4.6<z<6.9 (six at z≥6.5; M1450 −25.4 to −27.0), plus new spectra for six independently discovered z>6.5 sources. Three are strong radio emitters, including a z=4.71 object with blazar-like traits (flat spectrum, radio-loudness ~1000, multi-frequency variability) and an SRG/eROSITA X-ray detection (f0.2–2.3 keV ≈1.3×10^−13 erg s^−1 cm^−2). NIR spectroscopy for seven 6.3<z<6.9 quasars gives MgII-based black hole masses of 10^8.58–10^9.14 Msun and Eddington ratios 0.74–2.2, with one source showing an extreme CIV–MgII velocity offset of ~9000 km s^−1. The sample also includes three HiBALs, one with a potential 48,000 km s^−1 outflow, expanding the rare jetted/outflowing quasar census that constrains early SMBH growth and feedback.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Inspect where the newly confirmed (yellow crosses) sit relative to the DELS+PS1 color cuts and the L/T dwarf histograms to see how the dropout tracks isolate z>6 objects and where contamination pressure is highest.
Figure 2: Scan the Lyman-break region for each of the 31 spectra to verify redshift placements, note weak-Lyα cases, and identify candidates with BAL troughs or damping-wing–like absorption shaping the continuum.
Figure 3: Use the NIR line fits to read off MgII-based MBH and CIV–MgII velocity shifts; find the z≈6.3 source with ~9000 km s−1 offset and evaluate how telluric bands affect the profile measurements and FWHM.
Figure 4: Compare radio SEDs of MQC J021 19, MQC J133 02, and PSO J200 13 to quantify spectral indices and variability; the near-simultaneous RACS_mid/VLASS points highlight flat-spectrum, blazar-like behavior and year-scale flux changes.