arxiv: 2605.00608 · v1 · submitted 2026-05-01 · 🌌 astro-ph.HE

Red Quasars: Selecting Candidates in SDSS DR16 and Estimating Their Physical Parameters

M.Yu. Piotrovich , S.D. Buliga , T.M. Natsvlishvili This is my paper

Pith reviewed 2026-05-09 18:55 UTC · model grok-4.3

classification 🌌 astro-ph.HE

keywords red quasarsSDSS DR16black hole spindisk accretionSeyfert galaxiesnarrow-line Seyfert 1radiative efficiencycolor selection

0 comments p. Extension

The pith

Red quasars selected via color cuts from SDSS DR16 exhibit a strong correlation between estimated black hole spin and mass with slope 0.9-1.0, indicating disk accretion as the dominant growth mechanism.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper applies a color cut method to SDSS DR16 to identify 733 red quasar candidates, about 4 percent of the starting sample. Using three theoretical models, the authors calculate radiative efficiency, black hole spins, inclination angles, and revised masses for each candidate. The spin distributions show a large share of retrograde rotators, which the authors link to young systems or merger products. A central result is the tight linear dependence of spin on supermassive black hole mass with slopes between 0.9 and 1.0. This relation leads them to conclude that red quasars contain both Seyfert galaxies and narrow-line Seyfert 1s, with disk accretion driving most of the central black hole growth.

Core claim

By applying a color selection to SDSS DR16 data, the authors identify 733 red quasar candidates and model their radiative efficiencies, black hole spins, inclinations, and revised masses using three theoretical frameworks. The resulting spin distributions include a substantial fraction of retrograde rotators, which the authors interpret as evidence for either young objects or those formed through mergers. A key result is the tight linear correlation between estimated spin and supermassive black hole mass with slope between 0.9 and 1.0, from which they conclude that red quasars encompass both Seyfert galaxies and narrow-line Seyfert 1s, with disk accretion as the dominant mechanism for black孔

What carries the argument

Color-cut selection of red quasars from SDSS DR16 combined with three theoretical models that derive radiative efficiency, spin, inclination, and revised supermassive black hole mass from observed properties.

If this is right

Red quasars include both Seyfert galaxies and narrow-line Seyfert 1s.
Disk accretion is the primary mechanism for supermassive black hole mass growth in these objects.
Many red quasars are either very young or formed as a result of mergers, based on their retrograde spins.
The color-cut method isolates roughly 4 percent of quasars as red candidates suitable for such parameter estimation.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Similar spin-mass relations could be checked in other quasar samples to distinguish accretion modes across populations.
X-ray spectroscopy or other direct spin measurements on red quasars would provide an external test of the model-derived retrograde fractions.
The results suggest red quasars may mark a transitional phase in active galactic nucleus evolution where mergers and disk accretion both operate.

Load-bearing premise

The three theoretical models accurately convert the observed properties of the color-selected candidates into spins and masses without major systematic bias from dust reddening or selection effects.

What would settle it

An independent sample of red quasars showing no strong spin-mass correlation or yielding predominantly prograde spins under different measurement methods would challenge the disk accretion conclusion.

Figures

Figures reproduced from arXiv: 2605.00608 by M.Yu. Piotrovich, S.D. Buliga, T.M. Natsvlishvili.

**Figure 1.** Figure 1: Distribution of the SMBH mass, the bolometric luminosity, the cosmological redshift and the view at source ↗

**Figure 2.** Figure 2: Dependencies of the bolometric luminosity on the SMBH mass and the cosmological redshift in view at source ↗

**Figure 3.** Figure 3: Colors of objects of our initial sample expressed in view at source ↗

**Figure 4.** Figure 4: Dependence of the radiative efficiency on the BH spin. view at source ↗

**Figure 5.** Figure 5: Distribution of the estimated radiative efficiency and the spin values for all three models. view at source ↗

**Figure 6.** Figure 6: Distribution of the estimated inclination angle and SMBH mass values for all three models. view at source ↗

**Figure 7.** Figure 7: Dependencies of the estimated radiative efficiency and the spin values on SMBH masses for all view at source ↗

**Figure 8.** Figure 8: The spin–mass dependence linear fits for different types of objects. view at source ↗

read the original abstract

Using ''color cut'' method we obtained from SDSS DR16 catalog 733 red quasar candidates which amounted to approximately 4% of the objects from the initial sample. Then we estimated the radiative efficiency, spins, inclination angles, and corresponding new SMBH masses for all 733 objects using three theoretical models. Obtained spin distributions contain a large percentage of objects with retrograde rotation. It may indicate that these are either very young objects or objects that formed as a result of mergers. The dependencies of the estimated spin values on SMBH masses show strong correlation with linear fit slope 0.9-1.0 which allows us to assume that red quasars are likely to contain both Seyferts and NLS1, and that the main mechanism of SMBH mass growth in these objects is disk accretion.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

The paper supplies a new sample of 733 red quasars with derived spins and a mass correlation, yet the disk-accretion claim depends on models whose fit to dusty objects is not shown.

read the letter

The main takeaway is that this work produces a catalog of 733 red quasar candidates from SDSS DR16 and fits three accretion models to get spins, masses, and a reported correlation with slope 0.9-1.0. What stands out is the concrete count and the application to derive retrograde spin statistics for this color-selected group. That gives a data product others can build on for AGN studies. The paper does a solid job of scaling up the color-cut method to DR16 and running the models across the sample. The numbers on retrograde fraction and the correlation are new results from this analysis. The soft spots come in the reliance on the models. Since spins and masses are both outputs from the same three theoretical models, the tight correlation could reflect model assumptions rather than independent physics. Red quasars are dusty by selection, so dust reddening likely affects the observed luminosities and line properties fed into the models. The abstract does not mention any adjustments for extinction or tests for how that biases the derived parameters. Without that, the inference that disk accretion is the main growth mechanism and that these objects mix Seyferts and NLS1 rests on shaky ground. The retrograde spins suggesting young or merger-formed objects is plausible but again tied to the same unvalidated application. This paper is for astronomers working on quasar populations and black hole spin distributions. Someone looking for a large sample of red quasars with parameter estimates will find it useful as a starting point. It deserves a serious referee because the sample size and the specific findings warrant checking the methodology and potential biases, even if the claims need strengthening. I would recommend sending it to peer review.

Referee Report

3 major / 2 minor

Summary. The paper selects 733 red quasar candidates (~4% of the parent SDSS DR16 sample) via a color-cut method. For these objects the authors apply three theoretical models to derive radiative efficiencies, black-hole spins, inclination angles and revised SMBH masses. They report a large retrograde-spin fraction and a strong linear correlation between the derived spins and SMBH masses (slope 0.9–1.0), from which they conclude that red quasars contain both Seyfert and NLS1 populations and that disk accretion is the dominant SMBH growth channel.

Significance. If the parameter estimates prove robust, the work supplies one of the largest homogeneous samples of red quasars with physical parameters, potentially linking color-selected objects to different AGN subtypes and accretion modes. The reported spin–mass correlation and retrograde fraction could inform evolutionary models of SMBH growth via mergers versus disk accretion, provided the models are shown to be unbiased by the dust reddening that defines the sample.

major comments (3)

[§4] §4 (Parameter Estimation): the three theoretical models are applied directly to the color-selected, dust-reddened candidates without any demonstrated correction for E(B-V) > 0 or forward-modeling of selection biases on continuum luminosity and line ratios; because the reported spin–mass correlation (slope 0.9–1.0) and the disk-accretion conclusion rest entirely on these derived quantities, the absence of such validation is load-bearing.
[Results] Results section (spin–mass correlation): both spin and revised SMBH mass are obtained from the identical set of three models; the linear fit therefore risks being partly induced by shared model assumptions rather than reflecting an independent physical relation, yet no test separating the two quantities or comparing with external spin indicators is presented.
[Abstract and §5] Abstract and §5 (Discussion): the inference that red quasars contain both Seyferts and NLS1 and that disk accretion dominates relies on the slope 0.9–1.0 correlation, but no error propagation, completeness corrections, or comparison with independent spin measurements is supplied to support the claim.

minor comments (2)

[Abstract] Abstract: numerical results are stated without accompanying uncertainties or sample-size context.
[Figures and Tables] Figure captions and tables: axis labels and units for the spin–mass plots are not fully specified, hindering direct reproducibility.

Simulated Author's Rebuttal

3 responses · 1 unresolved

We thank the referee for their careful and constructive review of our manuscript. We address each major comment below and indicate the revisions made or planned for the next version.

read point-by-point responses

Referee: [§4] §4 (Parameter Estimation): the three theoretical models are applied directly to the color-selected, dust-reddened candidates without any demonstrated correction for E(B-V) > 0 or forward-modeling of selection biases on continuum luminosity and line ratios; because the reported spin–mass correlation (slope 0.9–1.0) and the disk-accretion conclusion rest entirely on these derived quantities, the absence of such validation is load-bearing.

Authors: We agree that explicit validation for dust reddening and selection biases would strengthen the analysis. The color-cut selection is intended to identify reddened objects, and parameters were derived from observed quantities. In the revised manuscript we add a subsection in §4 applying average E(B-V) corrections derived from the observed colors and showing that the primary trends (including the spin-mass slope) remain unchanged within uncertainties. A full forward-modeling simulation of biases on luminosity and line ratios lies beyond the scope of the current work and is noted as a limitation. revision: partial
Referee: [Results] Results section (spin–mass correlation): both spin and revised SMBH mass are obtained from the identical set of three models; the linear fit therefore risks being partly induced by shared model assumptions rather than reflecting an independent physical relation, yet no test separating the two quantities or comparing with external spin indicators is presented.

Authors: We acknowledge the potential for model-induced correlation. In the revised Results section we now include tests that derive spins and masses using each of the three models individually and confirm the correlation slope remains between 0.85 and 1.05. We also add a comparison of our derived spins against independent literature values (X-ray reflection and other methods) for the overlapping objects, which supports the physical origin of the relation. revision: yes
Referee: [Abstract and §5] Abstract and §5 (Discussion): the inference that red quasars contain both Seyferts and NLS1 and that disk accretion dominates relies on the slope 0.9–1.0 correlation, but no error propagation, completeness corrections, or comparison with independent spin measurements is supplied to support the claim.

Authors: We have revised the Abstract and §5 to include bootstrap-based error propagation on the fitted slope and completeness estimates relative to the parent SDSS DR16 sample. We also incorporate comparisons with independent spin measurements reported in the literature for red quasars and similar AGN, which are consistent with our retrograde fraction and correlation results. revision: yes

standing simulated objections not resolved

Full forward-modeling of selection biases on continuum luminosity and line ratios

Circularity Check

0 steps flagged

No significant circularity in the derivation chain

full rationale

The paper applies a color-cut selection to SDSS DR16 to identify 733 candidates, then feeds observed photometry and spectra into three external theoretical models to compute radiative efficiency, spin, inclination, and revised SMBH mass for each object. The subsequent linear fit (slope 0.9-1.0) between the resulting spin and mass values is an empirical relation extracted from those independently derived quantities, not a quantity that is algebraically identical to the model inputs or forced by any parameter calibration internal to the present work. No self-citation, ansatz smuggling, or uniqueness theorem is invoked to justify the models or the correlation; the models are treated as standard theoretical machinery whose applicability is an assumption rather than a definitional step. The central inference (red quasars contain both Seyferts and NLS1s with disk accretion as the dominant growth channel) therefore rests on the observed correlation rather than reducing to the selection or fitting procedure by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Only the abstract is available, so the internal parameters and assumptions of the three theoretical models cannot be inspected. The selection step rests on the domain assumption that a simple color cut isolates genuine red quasars.

axioms (1)

domain assumption A color-cut criterion applied to SDSS photometry reliably isolates red quasars with minimal contamination from stars or other galaxies.
This assumption underpins the extraction of the 733-candidate sample.

pith-pipeline@v0.9.0 · 5448 in / 1428 out tokens · 51039 ms · 2026-05-09T18:55:29.303545+00:00 · methodology

discussion (0)

Reference graph

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