arXiv subjects

D. Rouan

Publications and source records attributed to D. Rouan.

At least 19 recordsLinked to original sources

arXiv2026

Dust production in the harsh environment of Sgr A* - MIRI/JWST observation of the O-rich asymptotic giant branch star IRS~3

Studies of the interstellar medium (ISM) have frequently revealed signatures of the dust produced in the envelopes of asymptotic giant branch (AGB) stars, demonstrating a connection between the dust composition of the ISM and that of AGB stellar envelopes. Investigating this relationship in the extreme, radiation-dominated environment surrounding Sgr A*, the center of our own galaxy, reveals how such conditions might influence dust composition and the recycling of material in galactic centers. IRS 3, the brightest L band source in the Galactic center and most prominent AGB star within the inner parsec of the Milky Way, is embedded in a dusty envelope with an estimated radius of $\sim$10000 AU. We aim to conduct a comprehensive spectral analysis to more tightly constrain the dust composition and line-emitting species within the envelope of IRS 3 in the immediate vicinity of Sgr A*. In 2025, we observed the inner parsec of the Milky Way with the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST) as part of the guaranteed time observations (GTO) program Mid-Infrared Characterisation of Nearby Iconic galaxy Centres (MICONIC). We used the MIRI Medium Resolution Spectrometer (MRS) to study the spectroscopic characteristics of the AGB star IRS 3, located about 0.17 parsecs in projection from Sgr A*.

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arXiv2026

MICONIC: The spatial relationship between star formation and the AGN in Centaurus A revealed by JWST/MIRI

Centaurus A (Cen A), the nearest active radio galaxy, hosts a warped dust disc formed in a gas-rich merger. We present JWST/MIRI imaging in three filters, F560W, F770W, and F1130W, of this central disc over a ~4 x 2 kpc region to characterise its resolved mid-infrared stellar populations. The images reveal a system of extended dusty structures, previously identified with Spitzer as an "oval dusty shell", now resolved into multiple loop-like features that are brightest in F1130W and closely associated with the warped disc. Colour-magnitude and colour-colour diagnostics reveal a distinct population of 928 red point sources with strong infrared excess, accounting for ~36 per cent of sources with high-quality photometry in all three bands, spatially confined to the disc. These sources exhibit rising mid-infrared spectral slopes indicative of emission from warm dust. Their colours and spatial distribution are consistent with a population dominated by embedded young stellar objects, tracing recent (~10^5-10^6 yr) star formation within the disc. The strong geometric alignment of these sources with the disc, together with the lack of correlation with the radio jet, suggests that star formation in the central regions of Cen A is primarily regulated by merger-accreted gas, with no strong evidence for AGN jet-ISM interactions.

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arXiv2026

MICONIC: The multiphase circumnuclear region of Centaurus A as seen with JWST/MIRI MRS observations. I. Spectral inventory and properties of the warm molecular disk

Supermassive black holes power Active Galactic Nuclei (AGN), injecting energy that regulates accretion and shapes host galaxies. We investigate the morphology, excitation, and kinematics of molecular hydrogen (H2) in the inner circumnuclear disk of Centaurus A, the nearest radio galaxy. We present JWST/MIRI MRS integral-field spectroscopy of the central 170x100 pc2 at 0.3"-0.7" (5-12 pc) resolution, focusing on pure rotational H2 lines. The spectra show strong nuclear continuum and bright H2 emission from S(1) to S(8), including the first S(8) detection in Centaurus A. Optically thin nuclear lines enable maps of temperature, column density, and ortho-to-para ratio from spaxel-level excitation-diagram fitting. Warm H2 shows a complex morphology, dominating the central region where CO emission is weak or undetected. Low-excitation H2 lines trace an inhomogeneous ring with a 20-pc-radius cavity aligned with the jet's near side, suggesting that the jet affects the morphology of the molecular disk. Higher-excitation lines form filamentary structures around the AGN. Kinematics are rotational with an S-shaped distortion, indicating non-circular motions or a warped disk. A coherent, low-dispersion (70 km/s) streamer spirals inward. A power-law temperature distribution yields a warm (100-2000 K) H2 mass of (5.6+/-1.4)e5 Msun and a dynamical mass of 5e8 Msun within 100 pc. Shock excitation is supported by enhanced H2/continuum and H2/PAH ratios, elevated [Ne III]/[Ne II], and sub-equilibrium ortho-to-para ratios (1.6-2.4). Turbulent dissipation can balance H2 cooling and likely dominates heating beyond 30 pc. In the inner 100 pc of Centaurus A, AGN feeding and feedback are linked: shocks excite H2, regulate the gas temperature, and prevent cooling below 100 K, explaining the weak CO emission and lack of a massive outflow. These shocks may drive angular momentum loss and help fuel the nucleus.

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arXiv2026

MICONIC: JWST/MIRI-MRS reveals heavily reprocessed PAH emission in the circum-nuclear disc of Centaurus A

Polycyclic aromatic hydrocarbons (PAHs) are key dust components in galaxies and play a fundamental role in the physics of the interstellar medium (ISM), yet their response to AGN feedback remains debated. We present a spatially resolved analysis of PAHs in the central $7^{\prime\prime}\times12^{\prime\prime}$ ($\sim100\times200$ pc$^2$) of Centaurus A. We use JWST/MIRI-MRS observations at 5-28 $\mu$m from the MIRI European consortium GTO program MICONIC, with angular resolution of $0.35^{\prime\prime}-1^{\prime\prime}$ (about 6-17 pc). We derive PAH moment-0 maps via local continuum subtraction and extract one-dimensional spectra from five regions of interest, including the nucleus, the circumnuclear disc, and a PAH-deficient region. The spectra are decomposed into continuum, emission lines, and PAHs to measure feature intensities and equivalent widths (EWs). PAH emission is primarily distributed in a ring-like structure with localized enhancements at $\sim40$ pc from the nucleus. A distinct PAH-deficient region is observed to the north-west, roughly perpendicular to the jet axis, and coincident with enhanced ionized-gas velocity dispersion and inflowing molecular streamers. The 11.3/7.7 $\mu$m and 6.2/7.7 $\mu$m ratios exceed model predictions for pericondensed PAHs, indicating processed populations with more open structures. The 11.3/12.7 $\mu$m ratio suggests a dominance of solo hydrogen sites and partial dehydrogenation, particularly in the PAH-deficient region, where shocks likely drive erosion. The largest EWs are found in the ring, while reduced values in the deficient region point to partial destruction; in the nucleus, low EWs are mainly due to continuum dilution.

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arXiv2026

First Observation of CO$_2$ Emission and foreground absorption Toward the Galactic Center with JWST

CO$_2$ is an important, stable, and abundant molecule in the Universe, but it is very difficult to detect because it has no observable pure rotational transitions. The unique sensitivity and resolution of the James Webb Space Telescope (JWST) provide a fresh way to investigate it. CO$_2$ is typically found in the solid phase (ice) on grain mantles in dense molecular clouds, but is less commonly detected in the gas phase (compared to common molecules such as CO and H$_2$O) and has mostly been found in protostellar and proto-planetary environments. Here, we report and characterize the first observations of gas-phase CO$_2$ absorption toward two IR-bright regions of the Galactic Center, thanks to the high sensitivity of JWST. Using an LTE model we find a CO$_2$ gas excitation temperature between 20 and 50~K, a column density around 2$\times$10$^{15}$~cm$^{-2}$ and a radial velocity consistent with 0. We also report: 1) simultaneous detections of C$_2$H$_2$ and HCN absorption bands (near 13.7 and 14.0 $\mu$m, respectively), with column densitiy ratios of 1:3 and 3:2 with respect to gas-phase CO$_2$, and 2) CO$_2$ ice absorption with a ice-to-gas ratio of 90, consistent with previous findings. We conclude that the absorbing medium is likely in the foreground, most likely from one or more somewhat clumpy cloud(s), located between 0.15 and 4~kpc away from Earth. Additionally, we detected point-like CO$_2$ emission likely associated with a Galactic Center star (IRS~11SW), which is also spatially coincident with a previously reported X-ray source, raising the possibility that the system is a symbiotic binary.

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arXiv2025

Interstellar medium phases and abundances in the central parsec: A JWST MIRI/MRS view of the Galactic center

We used newly obtained observations from the Mid-Infrared Instrument (MIRI) equipped with the Medium Resolution Spectrometer (MRS) aboard the James Webb Space Telescope (JWST) to extract spectra covering the entire spectral range from 5 to 27~$\mu$m in the CND and in the CC. We used the photoionization code CLOUDY to generate synthetic spectra with the same spectral range and resolution, simulating a wide range of gas phases and abundances. We then determined the contribution of each phase to the spectra. Once the abundances and contribution from each phase of the gas were determined, we identified four dominant phases and performed a spatial analysis to determine their contribution to each spaxel of the datacubes. We find that in both the CND and the CC, the bulk of the emission originates from warm ionized gas with temperatures of between $10^4$ and $10^{4.8}$~K. In the CND, molecular gas contributes significantly to the flux and is spatially structured, while the CC shows minimal molecular gas content, as is expected from these regions. Coronal gas is detected in both regions at the interface between molecular and warm ionized gas. The observed abundance pattern (enhanced CNO and $\alpha$ elements with suppressed Fe) indicates a chemically young environment, recently enriched by core-collapse supernovae and stellar winds, with a limited contribution from older Type Ia supernovae. This favors a scenario of massive, recent star formation rather than cumulative long-term enrichment.

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arXiv2025

Detection of CO$_2$, CO, and H$_2$O in the atmosphere of the warm sub-Saturn HAT-P-12b

The chemical composition of warm gas giant exoplanet atmospheres (with Teq < 1000 K) is not well known due to the lack of observational constraints. HAT-P-12 b is a warm, sub-Saturn-mass transiting exoplanet that is ideal for transmission spectroscopy. One transit of HAT-P-12 b was observed with JWST NIRSpec in the 2.87--5.10 $\mu$m range with a resolving power of $\sim$1000. The JWST data are combined with archival observations from HST WFC3 covering the 1.1--1.7 $\mu$m range. The data were analysed using two data reduction pipelines and two atmospheric retrieval tools. Atmospheric simulations using chemical forward models were performed. CO2, CO, and H2O are detected at 12.2, 4.1, and 6.0 $\sigma$ confidence, respectively. Their volume mixing ratios are consistent with an atmosphere of $\sim10\times$ solar metallicity and production of CO2 by photochemistry. CH4 is not detected and seems to be lacking, which could be due to a high intrinsic temperature with strong vertical mixing or other phenomena. SO2 is also not detected and its production seems limited by low upper atmosphere temperatures ($\sim$500 K at $P<10^{-3}$ bar derived from one-dimensional retrievals), insufficient to produce it in detectable quantities ($\gtrsim$ 800 K required according to photochemical models). Retrievals indicate the presence of clouds between 2 and 269 mbar. This study points towards an atmosphere for HAT-P-12 b that could be enriched in carbon and oxygen with respect to its host star. When including the production of CO2 via photochemistry, an atmospheric metallicity that is close to Saturn's can explain the observations. Metallicities inferred for other gas giant exoplanets based on their CO2 mixing ratios may need to account for its photochemical production pathways. This may impact studies on mass-metallicity trends and links between exoplanet atmospheres, interiors, and formation history.

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arXiv2025

Evidence for SiO cloud nucleation in the rogue planet PSO J318

Silicate clouds are known to significantly impact the spectra of late L-type brown dwarfs, with observable absorption features at ~ 10 micron. JWST has reopened our window to the mid-infrared with unprecedented sensitivity, bringing the characterization of silicates into focus again. Using JWST, we characterize the planetary-mass brown dwarf PSO J318.5338-22.8603, concentrating on any silicate cloud absorption the object may exhibit. PSO J318's spectrum is extremely red, and its flux is variable, both of which are likely hallmarks of cloud absorption. We present JWST NIRSpec PRISM, G395H, and MIRI MRS observations from 1-18 micron. We introduce a method based on PSO J318's brightness temperature to generate a list of cloud species that are likely present in its atmosphere. We then test for their presence with petitRADTRANS retrievals. Using retrievals and grids from various climate models, we derive bulk parameters from PSO J318's spectra, which are mutually compatible. Our retrieval results point to a solar to slightly super-solar atmospheric C/O, a slightly super-solar metallicity, and a 12C/13C below ISM values. The atmospheric gravity proves difficult to constrain for both retrievals and grid models. Retrievals describing the flux of PSO J318 by mixing two 1-D models (``two-column models'') appear favored over single-column models; this is consistent with PSO J318's variability. The JWST spectra also reveal a pronounced absorption feature at 10 micron. This absorption is best reproduced by introducing a high-altitude cloud layer of small (<0.1 micron), amorphous SiO grains. The retrieved particle size and location of the cloud is consistent with SiO condensing as cloud seeding nuclei. High-altitude clouds comprised of small SiO particles have been suggested in previous studies, therefore the SiO nucleation we potentially observe in PSO J318 could be a more wide-spread phenomenon.

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arXiv2025

JWST/MIRI observations of the young TWA 27 system: hydrocarbon disk chemistry, silicate clouds, evidence for a CPD

The Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST) enables the characterisation of young self-luminous gas giants at previously inaccessible wavelengths, revealing physical processes in gas, dust, and clouds. We characterise the young planetary system TWA 27 (2M1207) in the mid-infrared (MIR), studying the atmosphere and disk spectra of the M9 brown dwarf TWA 27A and its L6 planetary-mass companion TWA 27b. We obtained data with the MIRI Medium Resolution Spectrometer (MRS) from 4.9 to 20 um, and MIRI Imaging in the F1000W and F1500W filters. We applied high-contrast imaging methods to extract the companion's spectral energy distribution up to 15 um at 0.78 arcsec separation and a contrast of 60. Combining these with published JWST/NIRSpec spectra, we analysed the 1-20 um range using self-consistent atmospheric grids and 0D slab models for molecular disk emission. The atmosphere of TWA 27A is well fitted by a BT-SETTL model with Teff 2780 K, log g 4.3, plus a 740 K blackbody for the inner disk rim. The disk shows at least 11 organic molecules, with no water or silicate dust emission detected. The atmosphere of TWA 27b is matched by a Teff 1400 K low-gravity model with extinction, best fit by the ExoREM grid. MIRI spectra and photometry for TWA 27b reveal a silicate cloud absorption feature between 8-10 um and significant (>5 sigma) infrared excess at 15 um consistent with circumplanetary disk emission. These MIRI observations provide new insights into TWA 27, revealing diverse features to study the formation and evolution of circumplanetary disks and young dusty atmospheres.

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arXiv2025

MICONIC: JWST/MIRI MRS reveals a fast ionized gas outflow in the central region of Centaurus A

We present a kinematical study of the ionized and molecular gas in the central region (~7-14"~100-200pc) of the nearby radio galaxy Cen A. We used JWST/MIRI MRS 5-28$\mu$m observations taken as part of the MIR Characterization of Nearby Iconic galaxy Centers (MICONIC) of the MIRI EC. The two gas phases present contrasting morphologies and kinematics. The brightest emission from the ionized gas, traced with a range of IP lines ([Fe II] to [Ne VI]), is extended along the direction of the radio jet. We also detected emission from low IP emission lines and H$_2$ transitions in the galaxy disk. Both gas phases present rotational motions but also complex kinematics. The observations reveal several ionized gas kinematical features that are consistent with simulation predictions of a jet-driven bubble and outflow interacting with the galaxy ISM. These include broad components in the nuclear line profiles ($\sigma$~600km/s), high velocities (~ +1000, -1400km/s) confined within the nuclear region, velocities of hundreds of km/s in several directions in the central 2", and enhanced velocity dispersions perpendicular to the radio jet. Moreover, we find evidence of shock excitation in the nuclear region based on MIR line ratios. We compared the ionized gas mass outflow rate with Cen A's AGN luminosity and radio jet power and demonstrate that both mechanisms provide sufficient energy to launch the outflow. The noncircular motions observed in the H$_2$ lines can be reproduced with either a warped rotating disk model or a radial component. The latter might be to related to gas streamers detected in cold molecular gas. There is no clear indication of a fast nuclear H$_2$ outflow, only a weak blueshifted component. This could be due to a relatively low nuclear warm H$_2$ column density and/or the limited geometrical coupling of Cen A's inner radio jet with the circumnuclear disk of the galaxy. (Abridged)

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arXiv2025

Evidence for a sub-jovian planet in the young TWA7 disk

Planets are thought to form from dust and gas in protoplanetary disks, and debris disks are the remnants of planet formation. Aged a few Myr up to a few Gyr, debris disks have lost their primordial gas, and their dust is produced by steady-state collisions between larger, rocky bodies. Tens of debris disks, with sizes of tens, sometimes hundreds of au, have been resolved with high spatial resolution, high contrast imagers at optical/near-IR or (sub)-millimeter interferometers. They commonly show cavities, ring-like structures, and gaps, which are often regarded as indirect signatures of the presence of planets that gravitationally interact with unseen planetesimals. However, no planet responsible for these features has been detected yet, probably because of the limited sensitivity (typically 2-10 MJ) of high contrast imaging instruments prior to JWST. We have used the unprecedented sensitivity of JWST/MIRI in the thermal IR to search for such planets in the disk of the ~ 6.4 Myr old star TWA 7. With its pole-on orientation, this three-ring debris disk is indeed ideally suited for such a detection. We unambiguously detected a source 1.5 arsec from the star, that is best interpreted as a cold, sub-Jupiter mass planet. Its estimated mass (~ 0.3 MJ) and position (~ 52 au, de-projected) can thoroughly account for the main disk structures.

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arXiv2024

The Galaxy Activity, Torus, and Outflow Survey (GATOS). Black hole mass estimation using machine learning

The detailed feeding and feedback mechanisms of Active Galactic Nuclei (AGN) are not yet well known. For low-luminosity and obscured AGN, as well as late-type galaxies, determining the central black hole (BH) masses is challenging. Our goal with the GATOS sample is to study circum-nuclear regions and better estimate BH masses with more precision than scaling relations offer. Using ALMA's high spatial resolution, we resolve CO(3-2) emissions within ~100 pc around the supermassive black hole (SMBH) in seven GATOS galaxies to estimate their BH masses when sufficient gas is present. We study seven bright ($L_{AGN}(14-150\mathrm{keV}) \geq 10^{42}\mathrm{erg/s}$), nearby (<28 Mpc) galaxies from the GATOS core sample. For comparison, we searched the literature for previous BH mass estimates and made additional calculations using the \mbh~ - $\sigma$ relation and the fundamental plane of BH activity. We developed a supervised machine learning method to estimate BH masses from position-velocity diagrams or first-moment maps using ALMA CO(3-2) observations. Numerical simulations with a wide range of parameters created the training, validation, and test sets. Seven galaxies provided enough gas for BH mass estimations: NGC4388, NGC5506, NGC5643, NGC6300, NGC7314, NGC7465, and NGC~7582. Our BH masses, ranging from 6.39 to 7.18 log$(M_{BH}/M_\odot)$, align with previous estimates. Additionally, our machine learning method provides robust error estimations with confidence intervals and offers greater potential than scaling relations. This work is a first step toward an automated \mbh estimation method using machine learning.

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arXiv2024

Molecular gas stratification and disturbed kinematics in the Seyfert galaxy MCG-05-23-16 revealed by JWST and ALMA

Understanding the processes that drive the morphology and kinematics of molecular gas in galaxies is crucial for comprehending star formation and, ultimately, galaxy evolution. Using data obtained with the James Webb Space Telescope (JWST) and the Atacama Large Millimeter/submillimeter Array (ALMA), we study the behavior of the warm molecular gas at temperatures of hundreds of Kelvin and the cold molecular gas at tens of Kelvin in the galaxy MCG$-$05$-$23$-$16, which hosts an active galactic nucleus (AGN). Hubble Space Telescope (HST) images of this spheroidal galaxy, classified in the optical as S0, show a dust lane resembling a nuclear spiral and a surrounding ring. These features are also detected in CO(2$-$1) and H2, and their morphologies and kinematics are consistent with rotation plus local inward gas motions along the kinematic minor axis in the presence of a nuclear bar. The H2 transitions 0-0 S(3), 0-0 S(4), and 0-0 S(5), which trace warmer and more excited gas, show more disrupted kinematics than 0-0 S(1) and 0-0 S(2), including clumps of high-velocity dispersion (of up to $\sim$ 160 km/s), in regions devoid of CO(2$-$1). The kinematics of one of these clumps, located at $\sim$ 350 pc westward from the nucleus, are consistent with outflowing gas, possibly driven by localized star formation traced by Polycyclic Aromatic Hydrocarbon (PAH) emission at 11.3 ${\mu}$m. Overall, we observe a stratification of the molecular gas, with the colder gas located in the nuclear spiral, ring, and connecting arms, while most warmer gas with higher velocity-dispersion fills the inter-arm space. The compact jet, approximately 200 pc in size, detected with Very Large Array (VLA) observations, does not appear to significantly affect the distribution and kinematics of the molecular gas, possibly due to its limited intersection with the molecular gas disc.

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arXiv2024

A biconical ionised gas outflow and evidence for positive feedback in NGC 7172 uncovered by MIRI/JWST

We present observations of the type-2 Seyfert NGC7172 obtained with the medium-resolution spectrometer (MRS) of the Mid-Infrared Instrument (MIRI) on board of the JWST. This galaxy hosts one of the lowest ionised gas mass outflow rates (Mout~0.005 M/yr) in a sample of six AGN with similar bolometric luminosities (log Lbol~44erg/s) within the Galactic Activity, Torus and Outflow Survey (GATOS). We aim to understand the properties of the ionised gas outflow, mainly using the emission lines from the neon transitions, that cover a broad range of ionisation potentials (IP) from ~20 eV to ~130 eV. We applied parametric and non-parametric methods to characterise the line emission and kinematics. The low excitation lines (IP<25eV, e.g.[NeII]) trace the rotating disc emission. The high excitation lines (IP>90eV, e.g.[NeV]), which are likely photoionised exclusively by the AGN, are expanding in the direction nearly perpendicular to the disc of the galaxy, with maximum projected velocities of ~350-500 km/s. In particular, [NeV] and [NeVI] lines reveal a biconical ionised gas outflow emerging N-S from the nuclear region, extending at least ~2.5"N and 3.8"S (projected distance of ~450 and 680 pc). Most of the emission arising in the northern part of the cone was not previously detected due to obscuration. Given the almost face-on orientation of the outflow and the almost edge-on orientation of the galaxy, NGC7172 may be a case of weak coupling. Nevertheless, we found evidence for positive feedback in two distinct outflowing clumps at projected distances of 3.1" and 4.3" (i.e. ~560 and 780 pc) SW from the AGN. We estimated a star formation rate in these regions using the [NeII] and [NeIII] luminosities of 0.08 M/yr, that is ~10% of that found in the circumnuclear ring. The star formation activity might have been triggered by the interaction between the ionised gas outflow and the ISM of the galaxy.

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arXiv2024

VLTI/GRAVITY Interferometric Measurements of Innermost Dust Structure Sizes around AGNs

We present new VLTI/GRAVITY near-infrared interferometric measurements of the angular size of the innermost hot dust continuum for 14 type 1 AGNs. The angular sizes are resolved on scales of ~0.7 mas and the inferred ring radii range from 0.028 to 1.33 pc, comparable to those reported previously and a factor 10-20 smaller than the mid-infrared sizes in the literature. Combining our new data with previously published values, we compile a sample of 25 AGN with bolometric luminosity ranging from $10^{42}$ to $10^{47} \rm erg~s^{-1}$, with which we study the radius-luminosity (R-L) relation for the hot dust structure. Our interferometric measurements of radius are offset by a factor 2 from the equivalent relation derived through reverberation mapping. Using a simple model to explore the dust structure's geometry, we conclude that this offset can be explained if the 2 um emitting surface has a concave shape. Our data show that the slope of the relation is in line with the canonical $R \propto L^{0.5}$ when using an appropriately non-linear correction for bolometric luminosity. In contrast, using optical luminosity or applying a constant bolometric correction to it results in a significant deviation in the slope, suggesting a potential luminosity dependence on the spectral energy distribution. Over four orders of magnitude in luminosity, the intrinsic scatter around the R-L relation is 0.2 dex, suggesting a tight correlation between innermost hot dust structure size and the AGN luminosity.

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arXiv2024

MICONIC: JWST/MIRI MRS observations of the nuclear and circumnuclear regions of Mrk231

We present JWST/MIRI MRS spatially resolved $\sim 5-28\,\mu$m observations of the central ~4-8kpc of the ultraluminous infrared galaxy and broad absorption line quasar Mrk231. These are part of the Mid-Infrared Characterization of Nearby Iconic galaxy Centers (MICONIC) program of the MIRI European Consortium guaranteed time observations. No high excitation lines (i.e., [MgV] at 5.61$\mu$m or [NeV] at 14.32$\mu$m) typically associated with the presence of an active galactic nucleus (AGN) are detected in the nuclear region of Mrk231. This is likely due to the intrinsically X-ray weak nature of its quasar. Some intermediate ionization potential lines, for instance, [ArIII] at 8.99$\mu$m and [SIV] at 10.51$\mu$m, are not detected either, even though they are clearly observed in a star-forming region ~920pc south-east of the AGN. Thus, the strong nuclear mid-infrared (mid-IR) continuum is also in part hampering the detection of faint lines in the nuclear region. The nuclear [NeIII]/[NeII]line ratio is consistent with values observed in star-forming galaxies. Moreover, we resolve for the first time the nuclear starburst in the mid-IR low-excitation line emission (size of ~400pc, FWHM). Several pieces of evidence also indicate that it is partly obscured even at these wavelengths. At the AGN position, the ionized and warm molecular gas emission lines have modest widths (W_80~300km/s). There are, however, weak blueshifted wings reaching velocities v_02~-400km/s in [NeII]. The nuclear starburst is at the center of a large (~8kpc), massive rotating disk with widely-spread, low velocity outflows. Given the high star formation rate of Mrk231, we speculate that part of the nuclear outflows and the large-scale non-circular motions observed in the mid-IR are driven by its powerful nuclear starburst.

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arXiv2024

GATOS: missing molecular gas in the outflow of NGC5728 revealed by JWST

The ionisation cones of NGC5728 have a deficit of molecular gas based on millimetre observations of CO(2-1) emission. Although photoionisation from the active nucleus may lead to suppression of this transition, warm molecular gas can still be present. We report the detection of eight mid-infrared rotational H$_2$ lines throughout the central kiloparsec, including the ionisation cones, using integral field spectroscopic observations with JWST/MIRI MRS. The H$_2$ line ratios, characteristic of a power-law temperature distribution, indicate that the gas is warmest where it enters the ionisation cone through disk rotation, suggestive of shock excitation. In the nucleus, where the data can be combined with an additional seven ro-vibrational H$_2$ transitions, we find that moderate velocity (30 km s$^{-1}$) shocks in dense ($10^5$ cm$^{-3}$) gas, irradiated by an external UV field ($G_0 = 10^3$), do provide a good match to the full set. The warm molecular gas in the ionisation cone that is traced by the H$_2$ rotational lines has been heated to temperatures $>200$ K. Outside of the ionisation cone the molecular gas kinematics are undisturbed. However, within the ionisation cone, the kinematics are substantially perturbed, indicative of a radial flow, but one that is quantitatively different from the ionised lines. We argue that this outflow is in the plane of the disk, implying a short 50 pc acceleration zone up to speeds of about 400 km s$^{-1}$ followed by an extended deceleration over $\sim$700 pc where it terminates. The deceleration is due to both the radially increasing galaxy mass, and mass-loading as ambient gas in the disk is swept up.

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arXiv2024

The size-luminosity relation of local active galactic nuclei from interferometric observations of the broad-line region

By using the GRAVITY instrument with the near-infrared (NIR) Very Large Telescope Interferometer (VLTI), the structure of the broad (emission-)line region (BLR) in active galactic nuclei (AGNs) can be spatially resolved, allowing the central black hole (BH) mass to be determined. This work reports new NIR VLTI/GRAVITY interferometric spectra for four type 1 AGNs (Mrk 509, PDS 456, Mrk 1239, and IC 4329A) with resolved broad-line emission. Dynamical modelling of interferometric data constrains the BLR radius and central BH mass measurements for our targets and reveals outflow-dominated BLRs for Mrk 509 and PDS 456. We present an updated radius-luminosity (R-L) relation independent of that derived with reverberation mapping (RM) measurements using all the GRAVITY-observed AGNs. We find our R-L relation to be largely consistent with that derived from RM measurements except at high luminosity, where BLR radii seem to be smaller than predicted. This is consistent with RM-based claims that high Eddington ratio AGNs show consistently smaller BLR sizes. The BH masses of our targets are also consistent with the standard $M_\mathrm{BH}$-$\sigma_*$ relation. Model-independent photocentre fitting shows spatial offsets between the hot dust continuum and the BLR photocentres (ranging from $\sim$17 $\mu$as to 140 $\mu$as) that are generally perpendicular to the alignment of the red- and blueshifted BLR photocentres. These offsets are found to be related to the AGN luminosity and could be caused by asymmetric K-band emission of the hot dust, shifting the dust photocentre. We discuss various possible scenarios that can explain this phenomenon.

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