Decoupled Kinematics and Excitation in the Compton-thick AGN NGC 6552: Spatially Resolved KOOLS-IFU Observations

abstract · abstract

Hard X-ray selected Compton-thick AGNs provide a relatively obscuration-resistant census of accretion, but optical line diagnostics can be strongly shaped by extinction and geometry. Spatially resolved integral-field spectroscopy can mitigate these effects and provides direct constraints on outflow kinematics and ionization state on kiloparsec scales. We present KOOLS-IFU optical integral-field spectroscopy of NGC 6552 obtained on the 3.8 m Seimei Telescope. Using spatially resolved emission-line ratios and non-parametric [O III]5007 kinematics over the central ~2 kpc, we test whether ionized-gas kinematics are locally coupled to excitation. The [O III]5007 width W80 is broadly elevated across the inner region (~530-830 km/s) and declines monotonically with projected galactocentric distance, consistent with a centrally concentrated outflow that decelerates at larger radii. Despite this clear kinematic structure, neither W80 nor the velocity asymmetry parameter dv shows a statistically significant correlation with [O III]5007/Hbeta. Order-of-magnitude outflow energetics yield Edot_K/L_bol ~ 0.01%-0.28% (for assumed n_e = 50-1000 cm^-3), consistent with [O III]-based estimates tracing only the ionized phase of a multi-phase outflow. We conclude that in NGC 6552 both the total line broadening traced by W80 and dv are consistent with being governed primarily by spatial dynamical structure and line-of-sight superposition of multiple kinematic components, with no statistically significant coupling to excitation-driven processes detected at our sensitivity level. A positive W80-[O III]5007/Hbeta coupling does emerge in the small subset of bins for which the two-component fit is most strongly favored statistically, which deeper observations will be needed to confirm.

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The KOOLS-IFU field (Figure 1 ) covers the central ∼ 8.4 ′′ × 8.0 ′′ \sim 8.4^{\prime\prime}\times 8.0^{\prime\prime} region of NGC 6552 ( ∼ 4.3 × 4.1 \sim 4.3\times 4.1 kpc at z = 0.0260 z=0.0260 ). Bins with sufficient continuum S/N for emission-line analysis are concentrated within the central ∼ 2 \sim 2 kpc, enabling a spatially resolved view of ionized gas on kpc scales. Projected galactocentric distances are measured relative to the nucleus position defined from the background-subtracted JWST/MIRI F560W image [ 3 ] (cross in Figures 2 ).

S5.SS1: V.1 The Centrally Peaked W 80 W_{80} Profile / block 1 · html

Our optical results complement the mid-infrared integral-field findings of Álvarez-Márquez et al. [3] , who reported the first clear evidence for a nuclear outflow in NGC 6552 using JWST/MIRI MRS observations. In their analysis, the outflow was detected as a blue-shifted velocity component in high-excitation and coronal emission lines spanning ionization potentials of 27–187 eV, with an average peak velocity offset of − 127 ± 45 -127\pm 45 km s -1 and a maximal outflow velocity of 698 ± 80 698\pm 80 km s -1 . This mid-infrared outflow was spatially unresolved, confined to < 0.2 <0.2 kpc from the nucleus. In contrast, our KOOLS-IFU [ O iii ] λ ​ 5007 \lambda 5007 observations reveal that the kinematic disturbance extends well beyond this nuclear region: W 80 W_{80} is maximized near the nucleus ( ∼ 830 \sim 830 km s -1 ) and declines monotonically outward, yet remains elevated ( ≳ 600 \gtrsim 600 km s -1 ) out to projected radii of ∼ \sim 1.5 kpc before falling to ∼ \sim 530–590 km s -1 at the field edges. This monotonically declining profile suggests that the nuclear outflow launched within < 0.2 <0.2 kpc gradually decelerates as it propagates outward through the host ISM.

S6: VI Summary and Conclusions / block 1 · html

We have presented KOOLS-IFU optical integral-field spectroscopy of NGC 6552, a hard X-ray selected Compton-thick AGN, obtained on the 3.8 m Seimei Telescope. Using non-parametric [ O iii ] λ ​ 5007 \lambda 5007 kinematic measures and spatially resolved emission-line diagnostics over the central ∼ 2 \sim 2 kpc, we investigated whether kinematic broadening is coupled to the local excitation state. The [ O iii ] λ ​ 5007 \lambda 5007 non-parametric width W 80 W_{80} is broadly elevated across the inner region, spanning ∼ \sim 530–830 km s -1 , with high- W 80 W_{80} values at the smallest projected radii (Figure 2 ). The W 80 W_{80} radial profile declines monotonically from the nucleus outward (Figure 3 ). A weighted linear fit provides a good phenomenological description of the trend, albeit with substantial scatter ( χ ν 2 ≈ 7.4 \chi^{2}_{\nu}\approx 7.4 ), suggesting azimuthal variations and/or multiple kinematic components. Line-ratio maps of log ⁡ ( [ N ​ II ] / H ​ α ) \log([\mathrm{N\,II}]/\mathrm{H}\alpha) and log ⁡ ( [ O ​ III ] / H ​ β ) \log([\mathrm{O\,III}]/\mathrm{H}\beta) show spatially non-uniform structure within the field of view (Figure 4 ). The spatial footprint of bins that can be robustly classified on the BPT diagram is compact and primarily limited by the S/N of H β \beta , rather than necessarily indicating a sharp physical boundary in excitation. All N bins = 15 N_{\rm bins}=15 bins satisfying A/N > 3 >3 in all four BPT lines fall in the Seyfert region of the [ O iii ] λ ​ 5007 \lambda 5007 /H β \beta versus [ N ii ] λ ​ 6583 \lambda 6583 /H α \alpha diagram (Figure 5 ). Across these bins, W 80 W_{80} shows no statistically significant correlation with log ⁡ ( [ O ​ III ] / H ​ β ) \log([\mathrm{O\,III}]/\mathrm{H}\beta) (Spearman ρ = + 0.24 \rho=+0.24 , p = 0.41 p=0.41 ; Pearson r = + 0.22 r=+0.22 , p = 0.40 p=0.40 ; Table 2 and Figure 6 ). This conclusion is unchanged when controlling for projected radius or after subtracting radial trends. The velocity asymmetry parameter Δ ​ v \Delta v likewise shows no statistically significant correlation with log ⁡ ( [ O ​ III ] / H ​ β ) \log([\mathrm{O\,III}]/\mathrm{H}\beta) (Spearman ρ = − 0.40

S6: VI Summary and Conclusions / block 1 · html

Order-of-magnitude outflow energetics yield a kinetic coupling efficiency of E ˙ K / L bol ≈ 0.01 % \dot{E}_{K}/L_{\rm bol}\approx 0.01\% – 0.28 % 0.28\% (for n e = 50 n_{e}=50 – 1000 1000 cm -3 ), placing NGC 6552 near or below the 1% efficiency line on the E ˙ K \dot{E}_{K} – L bol L_{\rm bol} diagram (Figure 7 ).

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The BIC-based robustness check supports the main result of Section IV.4 that the velocity asymmetry Δ ​ v \Delta v is not coupled to the local excitation state in NGC 6552. The Δ ​ v \Delta v – log ⁡ ( [ O ​ III ] / H ​ β ) \log([\mathrm{O\,III}]/\mathrm{H}\beta) decoupling holds across all subsamples once shared radial dependence is controlled for.

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A positive W 80 W_{80} – log ⁡ ( [ O ​ III ] / H ​ β ) \log([\mathrm{O\,III}]/\mathrm{H}\beta) coupling, by contrast, emerges in the BIC-strong subsample ( Δ ​ BIC > 10 \Delta\mathrm{BIC}>10 , N bins = 7 N_{\mathrm{bins}}=7 ), with a partial Spearman coefficient that survives controlling for projected radius (Table 3 ). We do not adopt a fixed bin-number threshold below which such a correlation is disregarded. Our caution regarding this subsample reflects three factors. It is defined post hoc, its significance was evaluated across a range of Δ ​ BIC \Delta\mathrm{BIC} thresholds so that the look-elsewhere effect is non-negligible, and the absolute number of bins is small. The emergence of the correlation is nonetheless informative. Several bins that enter the full sample with a formal A/N > 2 >2 detection of the shifted component are preferred as single-component by the BIC, so the full-sample correlation is averaged over bins in which a second kinematic component is not statistically required. The full-sample null result of Section IV.4 is therefore the conservative outcome, while the BIC-strong subsample isolates the bins that most robustly trace the outflow.

A3.SS3: C.3 Implications for the Main Conclusions / block 1 · html

The primary kinematics–excitation test of this work is the full-sample test of Section IV.4 , which yields a null result. The positive W 80 W_{80} – log ⁡ ( [ O ​ III ] / H ​ β ) \log([\mathrm{O\,III}]/\mathrm{H}\beta) coupling discussed here is a secondary result that emerges only in the small BIC-strong subsample. If it is genuine, it would be consistent with a picture in which the bins that most robustly trace the outflow also sample the most actively AGN-photoionized gas. Confirming whether this coupling is real rather than a small-sample fluctuation requires a larger number of bins with robustly detected outflow components, which deeper observations would provide.

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Considering the typical seeing at the site ( ∼ 1.2 ′′ \sim 1.2^{\prime\prime} – 1.4 ′′ 1.4^{\prime\prime} ) and the field of view of each fiber (a regular hexagon with radius 0.42 ′′ 0.42^{\prime\prime} ), we combined data from three adjacent fibers and present the results throughout this work.

S5.SS2: V.2 Decoupling Between Kinematics and Ionization / block 2 · html

conclusion that the kinematic–excitation decoupling in NGC 6552 is not an artifact of using a single line ratio. A more complete assessment would benefit from multi-line mixing sequences and explicit two-component spectral decomposition.

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Figure 3: Results of the Spearman correlation tests between H 2 S(3)/PAH 11.3 versus T H2 ​ ( 3 , 1 ) T_{\rm H2}{\rm(3,1)} (H 2 temp.), [Fe ii ]/PAH 11.3 (Shocks), and [Ne iii ]/[Ne ii ] (AGN ion.), measured both along and perpendicular to the radio axis. The numbers in each cell correspond to the measured R S R_{\rm S} coefficients. Only correlations with statistical significance, defined by p < 0.05 p<0.05 (95% confidence level), are shown; cases that do not satisfy this criterion are marked as NC.

S3: 3 Results / block 1 · html

Detailed studies of individual sources based on MIRI/MRS have already been conducted for most objects in our sample ( Costa-Souza et al., 2024 ; Dasyra et al., 2024 ; Goold et al., 2024 ; Alonso-Herrero et al., 2025 ; Ogle et al., 2025 ; Riffel et al., 2025 ; Evangelista et al., 2026 ) . Here, we focus our analysis on the H 2 / PAH \mathrm{H_{2}/PAH} ratio and on the relation between the jet orientation and the gas kinematics.

S1: I Introduction / block 1 · html

This paper is the second in our series on the LINER active galactic nucleus (AGN) galaxy NGC 5005, and the first to present results based on deep Chandra observations of its nuclear region. NGC 5005 is a weakly barred spiral galaxy [SAB(r)] with a dust-enshrouded nucleus [ 37 ] , located at a distance of D ∼ D\sim 17 Mpc (NED; z z =0.003156, scale = 100 pc arcsec -1 ).

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We present results from a deep 255 ks Chandra ACIS observation of NGC 5005, a LINER-dominated galaxy previously reported to host broad H α \alpha emission. The data reveal extended X-ray emission with a roughly symmetric morphology, tracing diffuse structure out to ∼ \sim 800 pc at soft energies ( < < 3 keV), decreasing to ∼ \sim 400 pc at higher energies (6–7 keV). A prominent central peak in the 0.3–7 keV image, spatially coincident with a Seyfert-like nucleus identified in HST imaging, is interpreted as nuclear emission.

abstract · abstract

We present JWST NIRSpec and MIRI MRS observations of the central kiloparsec of M58 (NGC 4579), a nearby LINER galaxy hosting a low-luminosity AGN (LLAGN; $L_\mathrm{bol} \sim 10^{42}$ erg s$^{-1}$) with a low-power jet. These data provide an unprecedented view of the warm molecular gas phase and reveal clear signatures of feedback. We detect 44 H$_2$ lines, including bright pure rotational lines (S(1)-S(18)) and rovibrational lines up to $ν=2$, probing a wide range of excitation conditions. Excitation diagrams show that rotational lines follow a power-law temperature distribution with an exponential cutoff, consistent with heating by low-velocity shocks. H$_2$ rovibrational lines deviate from thermal models primarily because of sub-thermal excitation at low density. Additionally, there may be a 10% contribution powered by AGN X-ray photons in the nucleus. The dust lanes associated with the spiral inflow appear dynamically undisturbed but show signs of shock heating, while the inner $\sim$200 pc exhibits turbulent kinematics produced by outflowing molecular gas. These results reveal the subtle yet measurable impact of LLAGN feedback on the interstellar medium, demonstrating that even weak, vertically oriented jets and low radiative accretion rates can perturb molecular gas and regulate nuclear reservoirs. This study highlights JWST's transformative ability to uncover hidden modes of AGN feedback.

abstract · abstract

Heavily obscured Active Galactic Nuclei (AGN), especially Compton-thick sources with line-of-sight column density ($N_{\rm H,los}$) $>$ 10$^{24}$ cm$^{-2}$, are critical to understanding supermassive black hole (SMBH) growth and the origin of the Cosmic X-ray Background (CXB). However, their observed fraction remains significantly below model predictions, due to strong absorption bias, even in the hard X-ray (i.e., above 10 keV) band. We analyze a sample of 26 nearby ($z < 0.1$) AGN from the Swift-BAT 150-month catalog, selected via mid-IR to X-ray diagnostics and observed with NuSTAR and soft X-ray telescopes (Xmm-Newton, Chandra, or Swift-xrt). Using self-consistent torus models (MyTorus, Borus02, and UXCLUMPY), we aim to constrain $N_{\rm H,los}$, the average torus column density, and other geometrical parameters of the obscuring medium. A comparative analysis among the three torus models showed that while estimates of $N_{\rm{H,los}}$ were generally in agreement, Borus02 tended to classify a slightly larger number of sources as Compton-thick AGN (CT-AGN). Building on this comparison, we benchmark two prediction schemes -- a mid-IR/X-ray relation and a machine-learning model -- against our broadband best-fit $N_{\rm H,los}$ measurements to assess which approach more effectively bridges the gap between predicted and measured obscuration, finding that while the former works effectively in the heavily obscured region (log$\rm{N_H} \gtrsim$ 23.5 $\rm{cm^{-2}}$), the latter provides improved accuracy, particularly for Compton-thin to moderately thick regimes (log$\rm{N_H} \lesssim$ 23.5 $\rm{cm^{-2}}$).

abstract · abstract

We present a new stellar dynamical measurement of the supermassive black hole (SMBH) in the compact elliptical galaxy NGC 4486B, based on integral field spectroscopy with JWST/NIRSpec. The two-dimensional kinematic maps reveal a resolved double nucleus and a velocity dispersion peak offset from the photometric center. Utilizing two independent methods-Schwarzschild orbit-superposition and Jeans Anisotropic Modeling-we tightly constrain the black hole mass by fitting the full line-of-sight velocity distribution. Our axisymmetric Schwarzschild models yield a best-fit black hole mass of $M_{BH} = 3.6^{+0.7}_{-0.7} \times 10^8 \, M_{\odot}$, slightly lower but significantly more precise than previous estimates. However, since our models do not account for the non-equilibrium nature of the double nucleus, this value may represent a lower limit. Across all tested dynamical models, the inferred $M_{BH}/M_*$ ratio ranges from ~ 4-13%, providing robust evidence for an overmassive SMBH in NGC 4486B. Combined with the galaxy's location deep within the Virgo Cluster, our results support the interpretation that NGC 4486B is the tidally stripped remnant core of a formerly massive galaxy. As the JWST/NIRSpec field of view is insufficient to constrain the dark matter halo, we incorporate archival ground-based long-slit kinematics extending to 5 arcsec. While this provides some leverage on the dark matter content, the constraints remain relatively weak. We place only an upper limit on the dark matter fraction, with $M_{DM}/M_{*} < 0.5$ within 1 kpc-well beyond the effective radius. The inferred black hole mass remains unchanged with or without a dark matter halo.

abstract · abstract

We evaluate the underlying assumptions for the identification of Active Galactic Nuclei (AGNs) through near- and mid-infrared photometry and spectral energy distribution (SED) fitting out to z ~ 3. For massive galaxies, log(M) > 9.5, our high resolution spectra of the rest optical range generally confirm the results of SED fitting, which relies primarily on excesses above the stellar emission between 1 and 6 microns to identify AGN. However, the method is undermined if the redshift used for the SED fitting is incorrect. Low mass galaxies, log(M) < 9:5, can contain relatively warm dust that emits in the 4 - 6 micron range. We show that the potential contamination of AGN samples by purely star forming low-mass galaxies can be avoided by the use of the infrared properties of Haro 11 as a limiting star-forming SED template. However, relatively few star forming galaxies emit as strongly in the 3 - 6 micron range as this template, so this could result in missing some obscured AGNs to avoid a minor contamination. Including the behavior of the galaxies at rest lamda ~ 13.5 microns can mitigate this problem and yield more complete samples of bona fide AGN. JWST/MIRI supports this approach out to z ~ 0.6.

abstract · abstract

The study of heavily obscured supermassive black hole (SMBH) growth in late-stage galaxy mergers is challenging: column densities $N_{\mathrm{H}}>10^{24},\mathrm{cm}^{-2}$ can block most nuclear emission, leaving significant gaps in the SMBH growth census. Millimeter-wave continuum emission offers a potential window into this obscured phase, as it can trace Active Galactic Nuclei (AGN) activity through mechanisms less affected by dust extinction. In this work, we test whether the observed correlation between millimeter ($\sim200,\mathrm{GHz}$) and hard X-ray (14 - 150,keV) luminosities can be used to plausibly identify hidden AGN in local (Ultra)Luminous Infrared Galaxies (U)LIRGs, including systems hosting confirmed dual AGN. We identify three sources -- one confirmed AGN and two strong candidates -- presenting significant evidence of AGN activity. The confirmed dual AGN lie within $\sim3σ$ of the mm--X-ray correlation, suggesting this relation can be used to identify hidden pairs. By combining the position of each source relative to this correlation with independent star formation rate constraints, we propose a method to disentangle AGN and star formation contributions for sources with measured column densities. While our analysis is based on a small, heterogeneous local sample and relies on empirical scaling relations, these results indicate that millimeter continuum emission may provide a useful complementary diagnostic for obscured SMBH growth. ALMA observations at high angular resolutions are particularly valuable for this approach, while future facilities such as the ngVLA will be essential to test its robustness in larger and more distant samples.

S4: IV Summary and Conclusions / block 1 · html

This paper presents the NIRSpec IFU observations of six galaxies at z ∼ 6 z\sim 6 , obtained as part of the JWST GO 5645 program (the Aether project). The targets were originally identified by the SHELLQs project, as candidate obscured quasars with luminous ( ≳ 10 43 \gtrsim 10^{43} erg s -1 ) but narrow ( ≲ \lesssim 500 km s -1 ) Ly α \alpha emission. The NIRSpec spectra revealed that two objects (G03 and G04) have broad line components (FWHM > 3000 >3000 km s -1 ) only in permitted Balmer lines, indicating the presence of AGN. The remaining four objects (G08, G12, G13, and G14) show similar profiles in the permitted and forbidden lines.

S4: IV Summary and Conclusions / block 1 · html

We combined the above sample with similar SHELLQs objects presented in Matsuoka et al. [64] , and analyzed their Ly α \alpha and H α \alpha luminosities. Overall, we found that the dust-extinction correction inferred from the Balmer decrement would result in unreasonably high values of L Ly ​ α L_{\rm Ly\alpha} . This may indicate that the line-emitting gas consists of multiple zones. We also found that the presence of broad permitted lines is strongly coupled with Ly α \alpha luminosity. The inferred AGN fraction is > > 77 % and < < 15 % (1 σ \sigma confidence level) above and below L Ly ​ α = 10 44 L_{\rm Ly\alpha}=10^{44} erg s -1 , respectively. The fairly sharp transition in AGN fraction may be explained by the relatively high LAE number density at z ∼ 6 z\sim 6 and a sharp fall-off of the (non-AGN) LAE LF at the luminous end. The IGM and/or dust absorption of Ly α \alpha photons may also be at work.