Weekly issue

Week 4, 2025

Jan 20–26, 2025

Week 4, 2025 includes 6 curated papers, centered on spectroscopy, obscured AGN, QSO.

2501.14026v1

Luminous Mid-IR Selected Type-2 Quasars at Cosmic Noon in SDSS Stripe82 I: Selection, Composite Photometry, and Spectral Energy Distributions

Ben Wang, Joseph F. Hennawi, Zheng Cai, Gordon T. Richards, Jan-Torge Schindler, Nadia L. Zakamska, Yuzo Ishikawa, Hollis B. Akins, Zechang Sun

Theme match 5/5

Digest

WISE W4>5 mJy selection in SDSS Stripe 82 yielded 24 candidates, with GNIRS (all) plus LRIS (18/24) confirming 23 luminous Type‑2 QSOs at 0.88<z<2.99, including 12 at z>2. Multi‑band photometry (DESI Legacy, PS1, UKIDSS, Spitzer, WISE) enables rest‑frame 0.1–10 μm composite photometry and AGNfitter SEDs. The IR is torus‑dominated with average L_torus ≈10^46.84 erg s−1; inferred L_bol spans 10^46.28–10^47.49 erg s−1 and Eddington masses ~10^8.18–10^9.39 M⊙, and the sample is redder with brighter tori than earlier Type‑2 SEDs. Their SED shapes closely resemble JWST “little red dots,” highlighting mid‑IR selection as an efficient path to luminous z>2 Type‑2s; a key open point is the origin of the rest‑UV/optical light (scattered, stellar, or a reddened disk).

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Selection plane: r versus r−W4 (and W4 flux>5 mJy) showing how the Stripe 82 cut isolates IR‑luminous, optically faint/red sources; check where confirmed Type‑2s lie relative to contaminants.
Spectroscopic confirmation panels: GNIRS+LRIS examples illustrating narrow‑line spectra and redshift measurements; compare success rate (96%) and the distribution across 0.88<z<2.99, emphasizing the z>2 subset.
Composite SED and AGNfitter decomposition: rest‑frame 0.1–10 μm photometry with model components, demonstrating torus dominance and the uncertain UV/optical component; read off average L_torus and L_bol range.
Redshift and photometry summary: histograms or tables of z, W4 fluxes, and optical magnitudes (r>23 or r−W4>8.38) to visualize sample definition and luminosity regime.
Comparison to JWST LRDs: overlaid median SEDs showing the similarity in optical‑IR slope/shape between these mid‑IR Type‑2 QSOs and LRDs, motivating selection strategies at higher z.

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2501.12449v1

Intervening nuclear obscuration changing the X-ray look of the $z\approx6$ QSO CFHQS J164121+375520

Fabio Vito, William Nielsen Brandt, Andrea Comastri, Roberto Gilli, Franz Bauer, Silvia Belladitta, George Chartas, Kazushi Iwasawa, Giorgio Lanzuisi, Bin Luo, Stefano Marchesi, Marco Mignoli, Federica Ricci, Ohad Shemmer, Cristiana Spingola, Cristian Vignali, Walter Boschin, Felice Cusano, Diego Paris

Theme match 5/5

Digest

The authors re-monitor the z=6.025 QSO CFHQS J164121+375520 (J1641) with Chandra and rest‑UV imaging in 2022–2024 after a dramatic X-ray dimming seen between 2018 and 2021. J1641 is now detected only in the hard 2–7 keV band, while its soft 0.5–2 keV flux has faded by >20× relative to 2018, establishing it as an X‑ray changing‑look quasar at z>6. They attribute the transition to intervening, ongoing Compton‑thick obscuration along our line of sight—potentially a thickened inner disk/failed wind or an occultation by dust‑free sub‑pc clouds—with the near‑constant rest‑UV light curve supporting obscuration over intrinsic fading. Catching such events in the reionization era offers a new handle on how rapidly growing SMBHs are fueled and shrouded.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1 (soft-band panels): Compare 2018 versus the 2022–2024 stack at 0.5–2 keV to see the disappearance of soft photons within the photometric aperture, which drives the >20× soft-band dimming and the changing‑look classification.
Figure 1 (hard-band panels): Inspect the 2–7 keV images to confirm J1641’s re‑detection only at higher observed energies in 2022–2024, consistent with heavy line‑of‑sight absorption while the source remained bright in 2018.
Figure 2 (X-ray/UV timeline): Read off the soft- and hard-band flux evolution—soft dropping by >20× while the hard band shows at most modest dimming—and the overplotted i‑band magnitudes, which remain stable, reinforcing an obscuration scenario.

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2501.13082v1

BlackTHUNDER -- A non-stellar Balmer break in a black hole-dominated little red dot at $z=7.04$

Xihan Ji, Roberto Maiolino, Hannah Übler, Jan Scholtz, Francesco D'Eugenio, Fengwu Sun, Michele Perna, Hannah Turner, Stefano Carniani, Santiago Arribas, Jake S. Bennett, Andrew Bunker, Stéphane Charlot, Giovanni Cresci, Mirko Curti, Eiichi Egami, Andy Fabian, Kohei Inayoshi, Yuki Isobe, Gareth Jones, Ignas Juodžbalis, Nimisha Kumari, Jianwei Lyu, Giovanni Mazzolari, Eleonora Parlanti, Brant Robertson, Bruno Rodríguez Del Pino, Raffaella Schneider, Debora Sijacki, Sandro Tacchella, Alessandro Trinca, Rosa Valiante, Giacomo Venturi, Marta Volonteri, Chris Willott, Callum Witten, Joris Witstok

Theme match 4/5

Digest

BlackTHUNDER analyzes JWST NIRSpec-IFU plus archival MSA data of the triply imaged lensed LRD Abell2744-QSO1 at z=7.04, confirming a smooth Balmer break and a broad Hβ from the BLR. The narrow Hβ dispersion gives M_dyn < 4×10^8 Msun, capping the stellar contribution to <10% of the optical continuum and favoring a non-stellar Balmer break produced by an AGN continuum filtered by very dense (n_H ~ 10^10 cm^-3), nearly dust-free gas likely in/around the BLR; a tentative 3σ Hβ absorption appears in the R2700 spectrum. The black hole is overmassive relative to both stellar and dynamical masses, with hints of variability and an initial reverberation-mapping attempt. This picture alleviates the extreme stellar-density problem for LRDs and may generalize to similar V-shaped continua.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Use the IFU maps and PRISM/grating spectra of the three lensed images to verify the smooth Balmer break, the presence of broad vs narrow Hβ, and the spatial compactness; in the R2700 panel, check the improved residuals when a narrow Hβ absorption component (∼3σ) is included.
Figure 2: Inspect the stellar–dynamical mass comparison to see why a purely stellar Balmer-break interpretation is unphysical for Abell2744-QSO1 (stellar mass would exceed M_dyn), and note the dynamical upper limit that constrains the stellar light fraction.
Figure 3: Examine the M_BH–M_* and M_BH–M_dyn planes to appreciate how Abell2744-QSO1 sits well above local scaling relations, underscoring a black hole-dominated system at early times.
Figure 4: Look at the Cloudy slab models showing how a dust-free, very dense screen imprints Balmer-line absorption and a Balmer break on an AGN continuum; adding a modest dust screen reproduces the rising optical slope typical of LRDs.

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2501.14072v1

Estimating Black Hole Masses in Obscured AGN from X-ray and Optical Emission Line Luminosities

S. LaMassa, I. Farrow, C. M. Urry, B. Trakhtenbrot, C. Auge, M. J. Koss, A. Peca, D. Sanders, T. J. Turner

Theme match 2/5

Digest

Tests a proxy-based black hole mass estimator for obscured AGN that infers FWHM_bHα from the narrow-line ratio L[O III]/L_nHβ and λL5100 from either intrinsic 2–10 keV X-rays or narrow lines, using 99 local Swift-BAT/BASS AGN. The two λL5100 proxies differ by a mean −0.32 ± 0.68 dex (narrow-line estimate lower than X-ray), implying ≈2× MBH uncertainty from the luminosity choice. Compared to virial masses from broad Paschen lines (14 Paα, 12 Paβ), the proxy MBH is higher by 0.39 ± 0.44 dex and 0.48 ± 0.51 dex, respectively, though still within the scatter. σ*-based MBH for 151 BASS AGN agrees on average within 0.08 dex but with large ≈0.74 dex scatter, so the method scales to large samples with overall ≈3–5× uncertainty and a possible mild high bias needing more data.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Check how far the red best-fit line deviates from the one-to-one line and where outliers drive the −0.32 ± 0.68 dex offset; this sets how much the choice of X-ray vs narrow-line λL5100 propagates into the virial MBH error budget.
Figure 2: Inspect the trend between log(L[O III]/L_nHβ) and FWHM(Paα/Paβ) relative to the dashed BM19+Kim10 expectation; the significant Paα (p≈0.03) but weaker Paβ correlation tests whether the BLR–NLR coupling holds for individual obscured AGN and hints at BLR extinction effects.
Figure 3: Compare MBH,[O III]/nHβ to Paα/Paβ-based MBH and note the systematic high offset; re-evaluate the trend when excluding green squares (den Brok 2022 entries without quality flags) to see how line-fit reliability impacts the bias.
Figure 4: Contrast σ*-derived MBH with Paα/Paβ results and with MBH,[O III]/nHβ; verify that MBH,[O III]/nHβ tracks M–σ on average (≈−0.08 dex) while Paβ shows a ≈0.38 dex high offset, and assess whether points fall within the 95% prediction band.

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2501.12567v1

Exploring quasar evolution with proximate molecular absorbers: Insights from the kinematics of highly ionized nitrogen

R. Cuellar, P. Noterdaeme, S. Balashev, S. López, V. D'Odorico, J. -K. Krogager

Theme match 2/5

Digest

X-shooter spectroscopy of 13 z≈2.5–3.3 quasars with proximate H2+HI absorbers finds NV in 9/13 (70%), far exceeding intervening DLA (~10%) and generic proximate (~30%) rates. High-ionization lines show blue-extended, broader kinematics decoupled from the neutral/low-ionized profiles, and NV/SiIV varies with velocity such that blueshifted components require higher ionization parameters. Redshifted systems lack NV and are interpreted as infall pre-feedback, while blueshifted proximate H2 systems trace outflow phases that can reach neutral/molecular gas. The authors argue that ionization state—not a fixed velocity threshold—should define “associated” versus “intervening” classifications.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1 (J0019−0137): Compare NV 1238 and SiIV 1393 AOD profiles to the low-ionization velocity window; note the extended blue wing and component-by-component NV/SiIV ratios versus the 5/50/95% low-ionization percentiles.
Figure 2: Contrast KS19 background with AGN spectra at 100 kpc vs 1 Mpc and inspect how HI shielding at N_HI≈10^18–10^21 cm⁻² alters flux above the N→N4+ edge, setting conditions for strong NV.
Figure 3: Cloudy grids of high-ion column densities versus ionization parameter for different stopping N_HI; identify the U range that reproduces observed NV while tracking sensitivity to the assumed median metallicity.
Figure 4: NV/SiIV color map in the U–N_HI plane with observed component crosses; use it to locate blueshifted components at higher U and gauge ~0.2 dex column-density uncertainties in the inferred parameter space.

Tags

2501.11491v1

MIDIS: Quantifying the AGN component of X-ray-detected galaxies

Steven Gillman, John P. Pye, Almudena Alonso-Herrero, Martin J. Ward, Leindert Boogaard, Tuomo V. Tikkanen, Luis Colina, G. Östlin, Pablo G. Pérez-González, Luca Costantin, Edoardo Iani, Pierluigi Rinaldi, Javier Álvarez-Márquez, A. Bik, Sarah E. I. Bosman, Alejandro Crespo Gómez, Andreas Eckart, Macarena García-Marín, Thomas R. Greve, Jens Hjorth, A. Labiano, Danial Langeroodi, J. Melinder, Florian Peißker, Fabian Walter, M. Güdel, Thomas Henning, P. -O. Lagage, Thomas P. Ray

Theme match 2/5

Digest

Using MIDIS MIRI 5.6 μm imaging in the HUDF cross-matched to the CDF-S 7 Ms catalog, the authors morphologically decompose 31 X-ray sources (24 AGN; z≈0.5–3) with visual, Sérsic+PSF, and non-parametric classifiers to isolate unresolved nuclear emission at rest-frame ~2 μm. They find ≥70% show an unresolved MIRI component with unresolved-to-total 2 μm flux fractions spanning ~0.2–0.9, and at Lx>10^43 erg s^-1 the 2 μm point-source luminosities align with local AGN relations. At lower X-ray luminosities, they report an excess 2 μm nuclear component relative to pre-JWST expectations, plausibly linked to Compton-thick AGN and/or compact nuclear starburst/merger activity. The work demonstrates that MIRI can robustly quantify nuclear IR emission in faint X-ray sources and clarifies the AGN/host balance across Cosmic Noon.

Open paper page arXiv abstract arXiv PDF Highlighted PDF

Key figures to inspect

Figure 1: Use the MIDIS false-color cutouts (F1000W/F770W/F560W) to verify which CDF-S XIDs exhibit red, compact MIR cores and to cross-check each target’s z and Lx; note IDs 695 and 758 lack reliable F1000W, affecting color inference.
Figure 2: Inspect Lx versus redshift with N_H coloring to see the flux-limited locus of the MIDIS subsample and where obscured systems sit relative to the full 7 Ms population.
Figure 3: Examine F210M/F560W and F480M/F560W color maps to identify centrally peaked red colors that betray unresolved hot-dust emission; compare with the PSF FWHM circles to judge true compactness.
Figure 4: Read off Sérsic+PSF fits at rest-frame ~2 μm (PSF and host magnitudes, Sérsic n, Gini–M20, residuals) to assess the measured PSF fractions and the diversity of host morphologies across representative XIDs.