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arxiv: 2606.29608 · v1 · pith:MUZ3ME5Qnew · submitted 2026-06-28 · 🌌 astro-ph.GA

The Lockman-SpReSO Project: A Deep X-ray Spectral View of a FIR-selected AGN Population

Mauricio El\'ias-Ch\'avez , Takamitsu Miyaji , Mart\'in Herrera-Endoqui , Irene Cruz-Gonz\'alez , Yair Krongold , H\'ector Hern\'andez-Toledo , Mirjana Povic , Bereket Assefa
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Mauro Gonz\'alez-Otero Castalia Alenka Negrete Miguel Cervi\~no J. Antonio de Diego Miguel S\'anchez-Portal Erika Ben\'itez Jordi Cepa Jos\'e Antonio V\'azquez Mata Monica I. Rodriguez Emilio J. Alfaro J. Jes\'us Gonz\'alez Carmen P. Padilla-Torres J. Ignacio Gonz\'alez-Serrano Vladimir \'Avila-Reese \'Angel Bongiovanni A. M. Perez Garcia
This is my paper

Pith reviewed 2026-06-30 01:49 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords AGNX-ray spectraobscured AGNCompton-thickreceding torusFIR selectionsoft excessLockman Hole
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The pith

FIR-selected AGNs show an increasing obscured fraction with redshift and a luminosity-dependent covering factor supporting the receding torus.

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

The paper performs X-ray spectral fitting on 94 AGNs drawn from a far-infrared selected sample in the Lockman Hole, spanning redshifts 0.07 to 5. It reports that the fraction of sources with high column densities rises at higher redshifts, identifies one strong and two borderline Compton-thick candidates, and detects soft excess emission in ten objects. A fitted relation shows the dust covering factor declining with rising 2-10 keV luminosity, which the authors interpret as evidence for a receding torus. The FIR selection is noted to favor detection of dusty, star-forming hosts and heavily obscured nuclei compared with purely X-ray surveys.

Core claim

In a sample of 94 FIR-selected AGNs observed with deep XMM-Newton data, the fraction of obscured sources increases toward higher redshift; soft excess is found in ten AGNs with mean temperature 0.12 keV; the X-ray Baldwin effect appears in both obscured and unobscured subsamples; and the torus covering factor follows f_cov = (-0.1 ± 0.01) × log(L_{2-10 keV}/10^{44} erg s^{-1}) + (0.65 ± 0.01), consistent with the receding-torus picture, while one strong and two borderline Compton-thick candidates are identified.

What carries the argument

X-ray spectral models (absorbed power-law plus reflection and soft excess, with XCLUMPY applied to candidate Compton-thick sources) applied to FIR-cross-matched sources to extract intrinsic column density, luminosity, iron-line equivalent width, and covering factor.

If this is right

  • The obscured AGN fraction increases with redshift in this population.
  • Soft excess emission appears in 10 sources with average temperature 0.12 ± 0.02 keV.
  • Covering factor declines with X-ray luminosity according to the quoted linear relation.
  • One strong and two borderline Compton-thick AGN candidates are present.
  • The X-ray Baldwin effect is detected in both obscured and unobscured subsamples.

Where Pith is reading between the lines

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

  • FIR selection may provide a more complete census of obscured AGNs than X-ray flux-limited surveys alone.
  • The observed luminosity-covering factor trend could be tested by repeating the analysis on purely optical or mid-infrared selected samples at similar redshifts.
  • If the redshift trend holds, models of AGN feedback and galaxy evolution will need to incorporate stronger obscuration at early cosmic times.

Load-bearing premise

The chosen spectral models and the FIR selection introduce no major systematic biases in the derived column densities, luminosities, or covering factors across the full redshift range.

What would settle it

An independent measurement of column densities in a comparable FIR-selected sample at z > 2 that shows no rise in the obscured fraction would falsify the reported redshift trend.

Figures

Figures reproduced from arXiv: 2606.29608 by A. M. Perez Garcia, \'Angel Bongiovanni, Bereket Assefa, Carmen P. Padilla-Torres, Castalia Alenka Negrete, Emilio J. Alfaro, Erika Ben\'itez, H\'ector Hern\'andez-Toledo, Irene Cruz-Gonz\'alez, J. Antonio de Diego, J. Ignacio Gonz\'alez-Serrano, J. Jes\'us Gonz\'alez, Jordi Cepa, Jos\'e Antonio V\'azquez Mata, Mart\'in Herrera-Endoqui, Mauricio El\'ias-Ch\'avez, Mauro Gonz\'alez-Otero, Miguel Cervi\~no, Miguel S\'anchez-Portal, Mirjana Povic, Monica I. Rodriguez, Takamitsu Miyaji, Vladimir \'Avila-Reese, Yair Krongold.

Figure 2
Figure 2. Figure 2: Photon count distribution in the 0.3 − 10 keV band for the complete X-ray catalog, with a median (green dashed line) of 529. from each individual PN observation for every object in our sample. For our analysis, we used the xspec program (version 12.13.1). We manually selected the source and background regions using the task evselect, defining circular areas with a radius of 15 and 30 arcsec￾onds, respectiv… view at source ↗
Figure 3
Figure 3. Figure 3: 2 − 10 keV absorption-corrected rest-frame luminosity versus red￾shift. Sources classified as AGNs are highlighted with green circles. Blue and red circles represent sources with spectroscopic (𝑧spec) and photometric (𝑧phot) redshifts, respectively. The luminosity regimes for quasars, Seyfert galaxies, and low-luminosity AGN (LLAGN) are indicated with dotted lines. 3.2 Complex Spectral Fitting To explore t… view at source ↗
Figure 4
Figure 4. Figure 4: Distribution of the spectral fitting parameters for the AGN sample. Left panel: distribution of the reduced 𝜒 2 values obtained from the X-ray spectral fits, showing that most sources cluster around 𝜒 2 red ∼ 1, indicating that the adopted spectral models provide an overall good description of the data. Right panel: distribution of the photon index Γ. Tbabs*(po*zphabs + zgauss) Tbabs*(po*zphabs + zgauss + … view at source ↗
Figure 5
Figure 5. Figure 5: Fitted X-ray spectrum and residuals of source 206710 at 𝑧 = 1.113. The left panel shows the spectrum fitted with a simple absorbed power-law and a neutral iron line (model-3); the central panel includes a reflection component (model-5); and the right panel incorporates an additional blackbody component to account for the soft excess emission (model-4). log 𝑁H = (1.0 ± 0.5)𝑧 + (21.2 ± 0.6) (6) To quantify t… view at source ↗
Figure 6
Figure 6. Figure 6: Hydrogen column density distribution as a function of redshift for our AGN sample. Green stars, yellow arrows, and purple circles indicate sources with robust 𝑁H measurements, only 𝑁H upper-limits, and Compton￾thick AGN candidates, respectively. The shaded blue region represents the 1𝜎 confidence interval of the linear regression fit (blue line) for the sources with robust 𝑁H measurements. The red curves s… view at source ↗
Figure 7
Figure 7. Figure 7: Upper-panels: Unfolded X-ray spectra and residuals of the three strongest CT-AGN candidates modelled with XCLUMPY. The black points with error bars represent the binned data, as described in Section 3. The red lines correspond to the best-fitting models. Individual spectral components are overplotted: the intrinsic X-ray emission (blue dot-dashed line), reflected continuum (green dot-dashed line), Fe K𝛼 em… view at source ↗
Figure 8
Figure 8. Figure 8: Distribution of the Fe K𝛼 equivalent width as a function of hard X-ray luminosity for both obscured (red circles) and unobscured (blue cir￾cles) AGN populations. The upper panel shows the full sample, while the central and lower panels display the unobscured and obscured subsamples, respectively. The solid lines represent the linear regression fits for each sam￾ple without upper-limits, with the shaded reg… view at source ↗
Figure 9
Figure 9. Figure 9: Upper-panel: angular width histogram. Lower-panel: distribution of the Fe K𝛼 equivalent width as a function of the torus angular width for both obscured (red circles) and unobscured (blue circles) AGNs. We included the average error bar at 90 per cent of confidence for the whole sample. From Equation 11, we can infer that the expected obscured frac￾tion at a luminosity of 1044 erg s−1 is approximately 0.65… view at source ↗
Figure 10
Figure 10. Figure 10: Distribution of the dust covering factor as a function of hard X-ray luminosity. The black line represents the linear regression fit, with the shaded region indicating the 95 per cent confidence interval. The red line shows the regression obtained by dividing the sample into seven equally distributed luminosity bins, represented by red stars. The colour bar indicates the redshift of each source. The avera… view at source ↗
Figure 12
Figure 12. Figure 12: Star-formation rate derived from the CIGALE SED fitting as a function of the absorption-corrected 2−10 keV X-ray luminosity for the AGN sample. Dark arrows are used for those sources with SFR upper-limits. 6.4 Star formation and X-ray emission One of the main characteristics of the AGN population analysed in this work is that it is selected from a parent far-infrared sample from the Lockman-SpReSO project… view at source ↗
read the original abstract

We present a detailed X-ray spectral analysis of the active galactic nucleus (AGN) population in the Lockman-SpReSO project, a multiwavelength campaign of FIR sources in the Lockman Hole field. Using deep XMM-Newton observations cross-matched with FIR-selected galaxies, we characterize 94 AGNs based on their X-ray spectral properties. The sample is distributed over a large redshift range of $z = 0.07-5$, and reaches a flux limit of $5 \times 10^{-16}\, \mathrm{erg\, s^{-1}\, cm^{-2}}$ in the $0.3-10\, \mathrm{keV}$ band. We model the X-ray spectra using absorbed power-law, reflection, and soft excess components to estimate intrinsic column densities ($N_{\mathrm{H}}$), rest-frame $2-10\, \mathrm{keV}$ luminosities, and iron line equivalent widths $(EW)$. Additionally, we included an advanced model fitting for Compton-thick AGNs (CT-AGNs) using the XCLUMPY model. Our results show an increase in the fraction of obscured AGNs toward higher redshifts, including the identification of one strong and two borderline CT-AGN candidates with $N_{\mathrm{H}} \gtrsim 10^{24}\, \mathrm{cm^{-2}}$. Soft excess emission is detected in 10 AGNs, with an average blackbody temperature of $0.12 \pm 0.02\, \mathrm{keV}$. We also detect the X-ray Baldwin effect in both obscured and unobscured populations, and we found a strong correlation between the torus angular width $(\sigma_\mathrm{tor})$, dust covering factor $(f_{\mathrm{cov}})$, and X-ray luminosity, described by $f_{\mathrm{cov}} = (-0.1 \pm 0.01) \times \log(L_{2-10\, \mathrm{keV}}/(10^{44}\, \mathrm{erg\, s^{-1}})) + (0.65 \pm 0.01)$, supporting the receding torus scenario. While consistent with deep X-ray surveys, the FIR selection favours the identification of dusty star-forming host galaxies and heavily obscured AGNs.

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.

Referee Report

2 major / 2 minor

Summary. The manuscript presents a detailed X-ray spectral analysis of 94 AGNs identified in the Lockman-SpReSO FIR-selected sample in the Lockman Hole, using deep XMM-Newton data spanning z=0.07-5 down to a 0.3-10 keV flux limit of 5×10^{-16} erg s^{-1} cm^{-2}. Spectra are modeled with absorbed power-law plus reflection and soft-excess components, with XCLUMPY applied to CT-AGN candidates, yielding N_H, rest-frame 2-10 keV luminosities, iron-line EWs, and torus parameters. Key results include an increasing fraction of obscured AGNs with redshift, soft excess detected in 10 sources (mean kT=0.12±0.02 keV), the X-ray Baldwin effect in both obscured and unobscured subsamples, one strong and two borderline CT-AGN candidates, and the correlation f_cov = (-0.1±0.01)×log(L_{2-10 keV}/10^{44} erg s^{-1}) + (0.65±0.01) interpreted as support for the receding-torus scenario.

Significance. If the spectral fits remain unbiased across the redshift range, the work supplies a useful FIR-selected view of AGN obscuration evolution and torus geometry that complements X-ray flux-limited surveys. The explicit reporting of fit uncertainties, the use of XCLUMPY for CT sources, and the detection of soft excess in a quantified subset are concrete strengths. The reported correlation supplies a falsifiable, quantitative test of the receding-torus picture in a dust-biased host population.

major comments (2)
  1. [Abstract / modeling description paragraph] Abstract and modeling description: the headline claims—an increasing obscured fraction with redshift and the quoted f_cov–L_{2-10} correlation—rest on the assumption that the chosen spectral models return unbiased N_H, L_{2-10}, and f_cov across z=0.07-5. The FIR selection explicitly favors dusty, star-forming hosts, and the observed 0.3-10 keV band shifts to rest-frame energies >1-30 keV at z>2, reducing leverage on soft absorption and soft-excess components. No quantitative test (e.g., redshift-binned simulation recovery or completeness correction) is described that would demonstrate the trends are not selection artifacts.
  2. [Abstract] Abstract: the correlation is presented as a direct fit to the sample (slope −0.1±0.01, intercept 0.65±0.01) rather than a prediction from an independent physical model. Without an explicit statement of how selection effects or luminosity-dependent completeness were folded into the fit, it is unclear whether the slope is robust or partly induced by the FIR flux limit and the z-dependent band shift.
minor comments (2)
  1. [Abstract] The abstract states the flux limit but does not specify the precise energy band or exposure times used for the 94 sources; a short table or sentence giving the median exposure and the number of counts per source would improve reproducibility.
  2. [Results] The definition of “obscured” (presumably N_H > 10^{22} cm^{-2}) and the exact redshift bins used for the fraction trend should be stated explicitly in the results section.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their constructive and detailed report. We address each major comment below and indicate the revisions we will make to improve clarity and transparency regarding potential biases and the interpretation of the reported correlation.

read point-by-point responses

  1. Referee: [Abstract / modeling description paragraph] Abstract and modeling description: the headline claims—an increasing obscured fraction with redshift and the quoted f_cov–L_{2-10} correlation—rest on the assumption that the chosen spectral models return unbiased N_H, L_{2-10}, and f_cov across z=0.07-5. The FIR selection explicitly favors dusty, star-forming hosts, and the observed 0.3-10 keV band shifts to rest-frame energies >1-30 keV at z>2, reducing leverage on soft absorption and soft-excess components. No quantitative test (e.g., redshift-binned simulation recovery or completeness correction) is described that would demonstrate the trends are not selection artifacts.

    Authors: We agree that the robustness of the derived parameters across the redshift range merits explicit discussion. The spectral models (absorbed power law plus reflection and soft excess, with XCLUMPY for CT candidates) follow standard practice validated in the literature. We did not perform redshift-binned recovery simulations in the submitted manuscript. In revision we will add a dedicated paragraph in the discussion section addressing possible biases from the FIR selection and the observed-frame band shift at high z. We will also note the consistency of our obscured-fraction trend with independent X-ray-selected surveys as supporting evidence that the redshift evolution is not an artifact. Full Monte-Carlo completeness simulations lie beyond the scope of the present work but will be flagged as a limitation. revision: partial

  2. Referee: [Abstract] Abstract: the correlation is presented as a direct fit to the sample (slope −0.1±0.01, intercept 0.65±0.01) rather than a prediction from an independent physical model. Without an explicit statement of how selection effects or luminosity-dependent completeness were folded into the fit, it is unclear whether the slope is robust or partly induced by the FIR flux limit and the z-dependent band shift.

    Authors: The quoted relation is an empirical linear fit performed directly on the measured (L_{2-10}, f_cov) points in our sample. We will revise both the abstract and the results section to state this explicitly and to add a short discussion of how the FIR flux limit and the redshift-dependent band shift could in principle affect the recovered slope. We will also note that while the negative correlation is consistent with the receding-torus picture, a full forward-modeling analysis that folds in selection functions would be required to rule out completeness-driven contributions. These clarifications will be incorporated without changing the reported fit coefficients. revision: yes

Circularity Check

0 steps flagged

No significant circularity; empirical fits and trends are direct outputs of spectral modeling on the observed sample.

full rationale

The paper reports X-ray spectral fits (absorbed power-law, reflection, soft excess, XCLUMPY) applied to 94 FIR-selected AGNs across z=0.07-5, yielding measured N_H, L_{2-10}, f_cov, and an observed increase in obscured fraction. The quoted correlation f_cov = (-0.1±0.01)×log(L_{2-10 keV}/10^{44}) + (0.65±0.01) is presented as a fit to the sample data supporting the receding-torus scenario, not as a first-principles prediction or quantity derived from prior self-citations. No load-bearing self-citation chains, self-definitional loops, or renaming of known results appear in the provided text; all central claims remain independent empirical results from the current dataset and modeling choices.

Axiom & Free-Parameter Ledger

3 free parameters · 2 axioms · 0 invented entities

The work rests on standard X-ray spectral models and the assumption that FIR selection primarily traces dusty hosts without introducing unmodeled biases; the correlation coefficients are fitted directly to the observed sample.

free parameters (3)
  • covering factor slope = -0.1
    Fitted coefficient -0.1 in the reported f_cov vs luminosity relation
  • covering factor intercept = 0.65
    Fitted constant term 0.65 in the same relation
  • soft excess temperature = 0.12
    Average blackbody temperature reported as 0.12 keV from 10 sources
axioms (2)
  • domain assumption Standard absorbed power-law, reflection, and XCLUMPY models accurately recover intrinsic N_H and luminosities
    Invoked when modeling all 94 spectra and identifying CT-AGNs
  • domain assumption FIR selection does not introduce redshift-dependent completeness biases that affect the obscured fraction trend
    Implicit in the claim of increasing obscured fraction with redshift

pith-pipeline@v0.9.1-grok · 6109 in / 1645 out tokens · 32641 ms · 2026-06-30T01:49:27.182545+00:00 · methodology

discussion (0)

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Reference graph

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