arXiv subjects

Martin Bureau

Publications and source records attributed to Martin Bureau.

At least 19 recordsLinked to original sources

arXiv2026

JWST Detects a Dusty AGB-like Source Before the Type Ia-CSM Supernova 2026sqf

Supernova (SN) 2026sqf recently appeared in the nearby face-on spiral galaxy NGC 3310 and has shown signs of strong interaction with a circumstellar medium (CSM). Such intense interaction, rare among nearby SNe, offers a valuable opportunity to reveal details on the origin and nature of its progenitor system. We analyzed the early-phase spectra and light curves (LCs) of SN 2026sqf. The general shapes of the observed spectra, the strengths of the emission lines, and the LC evolution all suggest that SN 2026sqf belongs to the rare SN Ia-CSM subclass. If confirmed, this would be the closest known member of this class, at D~19 Mpc. We also report the first candidate progenitor system for a thermonuclear supernova identified in JWST pre-explosion imaging, and the first evidence for a (probable) carbon-rich AGB donor to the exploding white dwarf (WD). Our results are consistent with the expectation that SNe Ia-CSM emerge from a system consisting of a WD and an AGB star undergoing a common-envelope phase. The CSM mass and dust content are consistent with expectations for an AGB environment, but the narrow-line width exceeds superwind expansion velocities, favoring an episodic ejection. Binary interaction shortly before the explosion is a natural explanation, though the channel and timescale remain uncertain. Late-time follow-up, especially with JWST, will test the identification and the conclusions of our early-phase analysis.

astro-ph.SR↗

arXiv2026

An automated method for planetary nebula detection with SIGNALS: first applications to NGC 4214 and NGC 4449

Utilising the optical imaging Fourier transform spectrograph SITELLE, the Star-formation, Ionized Gas and Nebular Abundances Legacy Survey (SIGNALS) is designed to study the connection between star-forming regions and their environments. Targeting $31$ local star-forming galaxies, its data products also lend themselves to planetary nebula (PN) surveys. We present here a new pipeline to find PNe using automated emission-line diagnostics and morphology tests, that is able to distinguish PNe from contaminants with an accuracy similar to that of past visual methods. We also perform thorough completeness tests using mock PNe inserted into the data cubes with full spectra. We apply these tools to a pilot sample of two dwarf irregular galaxies from the SIGNALS survey, NGC 4214 and NGC 4449, with other galaxies to follow. For these two galaxies, we identify $25$ PNe (including $6$ new discoveries) and $23$ PNe (including $13$ new discoveries), respectively, and calculate PN luminosity function distances of $3.09^{+0.25}_{-0.46}$ and $3.91^{+0.33}_{-0.52}$ Mpc, respectively, the latter consistent with previous estimates. We also calculate the bolometric PN specific frequency of our galaxies ($\alpha_\mathrm{bol}$), as well as a newly defined $V$-band PN specific frequency ($\alpha_\mathrm{V}$) based solely on the galaxies' total luminosities in that band.

astro-ph.GA↗

arXiv2026

WISDOM Project -- XXVIII. Molecular gas measurement of the supermassive black hole mass of the galaxy NGC 1387

Supermassive black hole (SMBH) masses can be measured using molecular gas kinematics. Here we present high angular resolution ($0.12$ arcsec or $\approx11$ pc) Atacama Large Millimeter/submillimeter Array observations of the $^{12}$CO(2-1) line emission of the early-type galaxy NGC 1387. The observations reveal a face-on, regularly-rotating central molecular gas disc with a diameter of $\approx18$ arcsec ($\approx1.7$ kpc) and a central depression slightly larger than the SMBH sphere of influence. We forward model the CO data cube in a Bayesian framework with the \textsc{Kinematic Molecular Simulation} code, and use \textit{Hubble Space Telescope} data to constrain the stellar gravitational potential contribution to the molecular gas kinematics. We infer a SMBH mass of $1.10^{+1.71}_{-0.95}[\text{stat},3\sigma]^{+2.45}_{-1.09}[\text{sys}]\times10^8$ M$_\odot$ and a F160W-filter stellar mass-to-light ratio of $0.90^{+0.44}_{-0.35}[\text{stat}, 3\sigma]^{+0.46}_{-0.36}[\text{sys}]$ M$_\odot$/L$_{\odot,\text{F160W}}$. This SMBH mass is consistent with the SMBH mass -- stellar velocity dispersion relation.

astro-ph.GA↗

arXiv2026

WISDOM Project - XXVII. Giant molecular clouds of the lenticular galaxy NGC 1387: similarities with spiral galaxy clouds

Molecular gas is crucial to understanding star formation and galaxy evolution, but the giant molecular clouds (GMCs) of early-type galaxies (ETGs) have rarely been studied. Here, we present analyses of the spatially resolved GMCs of the lenticular galaxy NGC 1387, exploiting high spatial resolution (0.15" or 14 pc) 12CO(2-1) line observations from the Atacama Large Millimeter/submillimeter Array. We identify 1285 individual GMCs and measure the fundamental properties (radius, velocity dispersion, and molecular gas mass) of each with a modified version of the CPROPStoo package. Unusually for an ETG, the GMCs of NGC 1387 follow scaling relations very similar to those of the Milky Way disc and Local Group galaxy clouds, and most are virialised. GMCs with large masses and radii and/or small galactocentric distances have their angular momenta aligned with the large-scale galactic rotation, while other GMCs do not. These results show that ETGs have more diversified GMC properties than previously thought. We discuss potential reasons for such diversity, and viewing-angle dependency is a plausible candidate.

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arXiv2026

Extragalactic planetary nebulae -- tracers of kinematics and stellar populations out to 100 Mpc

Extragalactic planetary nebulae (xPNe) in galaxies beyond the Local Universe serve as discrete tracers for studying the element abundances and kinematics of galaxies covering a wide range of morphologies and masses at a variety of angular distances, from the centre well out into their haloes. They are direct stellar probes to identify the galaxy progenitors of haloes and the intracluster light. Even with new facilities, reaching higher angular resolution and sensitivity, xPNe are the only stellar tracers that can be directly and singularly detected and characterised out to 100 Mpc distance, making them crucial for tracing halo and intracluster light assembly. New wide-field spectroscopic instruments at 10+meter-class telescopes will allow the unprecedented characterisation of xPN populations from galaxy centres to their diffuse outskirts. Panoramic integral-field spectroscopy will enable the simultaneous study of xPN and stellar population properties, establishing their use as age- and metallicity-tracers while also improving post-AGB stellar evolution models.

astro-ph.GA↗

arXiv2026

Stellar-mass black holes on the millimetre fundamental plane of black hole accretion

Recent work revealed the existence of a galaxy "millimetre fundamental plane of black hole accretion", a tight correlation between nuclear $1$mm luminosity, intrinsic $2$ - $10$keV X-ray luminosity and supermassive black hole mass, originally discovered for nearby low- and high-luminosity active galactic nuclei. Here we use mm and X-ray data of $5$ X-ray binaries (XRBs) to demonstrate that these stellar-mass black holes also lie on the mm fundamental plane, as they do at radio wavelengths. One source for which we have multi-epoch observations shows evidence of deviations from the plane after a state change, suggesting that the plane only applies to XRBs in the hard state, as is true again at radio wavelengths. We show that both advection-dominated accretion flows and compact jet models predict the existence of the plane across the entire range of black hole masses, although these models vary in their ability to accurately predict the XRB black hole masses.

astro-ph.GA↗

arXiv2025

Neural Deprojection of Galaxy Stellar Mass Profiles

We introduce a neural approach to dynamical modeling of galaxies that replaces traditional imaging-based deprojections with a differentiable mapping. Specifically, we train a neural network to translate Nuker profile parameters into analytically deprojectable Multi Gaussian Expansion components, enabling physically realistic stellar mass models without requiring optical observations. We integrate this model into SuperMAGE, a differentiable dynamical modelling pipeline for Bayesian inference of supermassive black hole masses. Applied to ALMA data, our approach finds results consistent with state-of-the-art models while extending applicability to dust-obscured and active galaxies where optical data analysis is challenging.

astro-ph.GA↗

arXiv2025

WISDOM Project -- XXV. Improving the CO-dynamical supermassive black hole mass measurement in the galaxy NGC 1574 using high spatial resolution ALMA observations

We present a molecular gas dynamical supermassive black hole (SMBH) mass measurement in the nearby barred lenticular galaxy NGC 1574, using Atacama Large Millimeter/sub-millimeter Array observations of the $^{12}$CO(2-1) emission line with synthesised beam full-widths at half-maximum of $0.''078\times0.''070$ ($\approx7.5\times6.7$ pc$^2$). The observations are the first to spatially resolve the SMBH's sphere of influence (SoI), resulting in an unambiguous detection of the Keplerian velocity increase due to the SMBH towards the centre of the gas disc. We also detect a previously known large-scale kinematic twist of the CO velocity map, due to a position angle (PA) warp and possible mild non-circular motions, and we resolve a PA warp within the central $0.''2\times0.''2$ of the galaxy, larger than that inferred from previous intermediate-resolution data. By forward modelling the data cube, we infer a SMBH mass of $(6.2\pm1.2)\times10^7$ M$_\odot$ ($1\sigma$ confidence interval), slightly smaller than but statistically consistent with the SMBH mass derived from the previous intermediate-resolution data that did not resolve the SoI, and slightly outside the $1\sigma$ scatter of the SMBH mass -- stellar velocity dispersion relation. Our measurement thus emphasises the importance of observations that spatially resolve the SMBH SoI for accurate SMBH mass measurements and gas dynamical modelling.

astro-ph.GA↗

arXiv2025

WISDOM project -- XXIII. Star-formation efficiencies of eight early-type galaxies and bulges observed with SITELLE and ALMA

Early-type galaxies (ETGs) are known to harbour dense spheroids of stars with scarce star formation (SF). Approximately a quarter of these galaxies have rich molecular gas reservoirs yet do not form stars efficiently. These gas-rich ETGs have properties similar to those of bulges at the centres of spiral galaxies. We use spatially-resolved observations (~ 100 pc resolution) of warm ionised-gas emission lines (Hbeta, [O III], [N II], Halpha and [S II]) from the imaging Fourier transform spectrograph SITELLE at the Canada-France-Hawaii Telescope and cold molecular gas (12CO(2-1) or 12CO(3-2)) from the Atacama Large Millimeter/submillimeter Array (ALMA) to study the SF properties of 8 ETGs and bulges. We use the ionised-gas emission lines to classify the ionisation mechanisms and demonstrate a complete absence of regions dominated by SF ionisation in these ETGs and bulges, despite abundant cold molecular gas. The ionisation classifications also show that our ETGs and bulges are dominated by old stellar populations. We use the molecular gas surface densities and Halpha-derived SF rates (in spiral galaxies outside of the bulges) or upper limits (in ETGs and bulges) to constrain the depletion times (inverse of the SF efficiencies), suggesting again suppressed SF in our ETGs and bulges. Finally, we use the molecular gas velocity fields to measure the gas kinematics, and show that bulge dynamics, particularly the strong shear due to the deep and steep gravitational potential wells, is an important SF-regulation mechanism for at least half of our sample galaxies.

astro-ph.GA↗

arXiv2025

The resolved star-formation efficiency of early-type galaxies

Understanding how and why star formation varies between galaxies is fundamental to our comprehension of galaxy evolution. In particular, the star-formation efficiency (SFE; star-formation rate or SFR per unit cold gas mass) has been shown to vary substantially both across and within galaxies. Early-type galaxies (ETGs) constitute an extreme case, as about a quarter have detectable molecular gas reservoirs but little to no detectable star formation. In this work, we present a spatially-resolved view of the SFE in ten ETGs, combining state-of-the-art Atacama Large Millimeter/submillimeter Array (ALMA) and Multi Unit Spectroscopic Explorer (MUSE) observations. Optical spectroscopic line diagnostics are used to identify the ionized emission regions dominated by star-formation, and reject regions where the ionization arises primarily from other sources. We identify very few regions where the ionization is consistent with pure star formation. Using ${\rm H}\alpha$ as our SFR tracer, we find that previous integrated measurements of the star-formation rate based on UV and 22$\mu$m emission are systematically higher than the SFR measured from ${\rm H}\alpha$. However, for the small number of regions where ionization is primarily associated with star formation, the SFEs are around 0.4 dex higher than those measured in star-forming galaxies at a similar spatial resolution (with depletion times ranging from $10^8$ to $10^{10}$ yr). Whilst the SFE of ETGs is overall low, we find that the SFEs of individual regions within ETGs can be similar to, or higher than, similar sized regions within star-forming galaxies.

astro-ph.GA↗

arXiv2025

WISDOM Project -- XXII. A 5% precision CO-dynamical supermassive black hole mass measurement in the galaxy NGC 383

We present a measurement of the supermassive black hole (SMBH) mass of the nearby lenticular galaxy NGC 383, based on Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the $^{12}$CO(2-1) emission line with an angular resolution of $0.''050\times0.''024$ ($\approx16\times8$ pc$^2$). These observations spatially resolve the nuclear molecular gas disc down to $\approx41,300$ Schwarzschild radii and the SMBH sphere of influence by a factor of $\approx24$ radially, better than any other SMBH mass measurement using molecular gas to date. The high resolution enables us to probe material with a maximum circular velocity of $\approx1040$ km/s, even higher than those of the highest-resolution SMBH mass measurements using megamasers. We detect a clear Keplerian increase (from the outside in) of the line-of-sight rotation velocities, a slight offset between the gas disc kinematic (i.e. the position of the SMBH) and morphological (i.e. the centre of the molecular gas emission) centres, an asymmetry of the innermost rotation velocity peaks and evidence for a mild position angle warp and/or non-circular motions within the central $\approx0.''3$. By forward modelling the mass distribution and ALMA data cube, we infer a SMBH mass of $(3.58\pm0.19)\times10^9$ M$_\odot$ ($1\sigma$ confidence interval), more precise ($5\%$) but consistent within $\approx1.4\sigma$ with the previous measurement using lower-resolution molecular gas data. Our measurement emphasises the importance of high spatial resolution observations for precise SMBH mass determinations.

astro-ph.GA↗

arXiv2024

WISDOM project XX -- Strong shear tearing molecular clouds apart in NGC 524

Early-type galaxies (ETGs) are known to harbour dense spheroids of stars but scarce star formation (SF). Approximately a quarter of these galaxies have rich molecular gas reservoirs yet do not form stars efficiently. We study here the ETG NGC~524, with strong shear suspected to result in a smooth molecular gas disc and low star-formation efficiency (SFE). We present new spatially-resolved observations of the \textsuperscript{12}CO(2-1)-emitting cold molecular gas from the Atacama Large Millimeter/sub-millimeter Array (ALMA) and of the warm ionised-gas emission lines from SITELLE at the Canada-France-Hawaii Telescope. Although constrained by the resolution of the ALMA observations ($\approx37$~pc), we identify only $52$ GMCs with radii ranging from $30$ to $140$~pc, a low mean molecular gas mass surface density $\langle\Sigma_{\rm gas}\rangle\approx125$~M$_\odot$~pc$^{-2}$ and a high mean virial parameter $\langle\alpha_{\rm obs,vir}\rangle\approx5.3$. We measure spatially-resolved molecular gas depletion times ($\tau_{\rm dep}\equiv1/{\rm SFE}$) with a spatial resolution of $\approx100$~pc within a galactocentric distance of $1.5$~kpc. The global depletion time is $\approx2.0$~Gyr but $\tau_{\rm dep}$ increases toward the galaxy centre, with a maximum $\tau_{\rm dep,max}\approx5.2$~Gyr. However, no pure \ion{H}{II} region is identified in NGC~524 using ionised-gas emission-line ratio diagnostics, so the $\tau_{\rm dep}$ inferred are in fact lower limits. Measuring the GMC properties and dynamical states, we conclude that shear is the dominant mechanism shaping the molecular gas properties and regulating SF in NGC~524. This is supported by analogous analyses of the GMCs in a simulated ETG similar to NGC~524.

astro-ph.GA↗

arXiv2024

WISDOM Project -- XXI. Giant molecular clouds in the central region of the barred spiral galaxy NGC 613: a steep size -- linewidth relation

NGC~613 is a nearby barred spiral galaxy with a nuclear ring. Exploiting high spatial resolution ($\approx20$ pc) Atacama Large Millimeter/sub-millimeter Array $^{12}$CO(1-0) observations, we study the giant molecular clouds (GMCs) in the nuclear ring and its vicinity, identifying $158$ spatially- and spectrally-resolved GMCs. The GMC sizes ($R_{\mathrm{c}}$) are comparable to those of the clouds in the Milky Way (MW) disc, but their gas masses, observed linewidths ($\sigma_{\mathrm{obs,los}}$) and gas mass surface densities are larger. The GMC size -- linewidth relation ($\sigma_{\mathrm{obs,los}}\propto R_{\mathrm{c}}^{0.77}$) is steeper than that of the clouds of the MW disc and centre, and the GMCs are on average only marginally gravitationally bound (with a mean virial parameter $\langle\alpha_{\mathrm{obs,vir}}\rangle\approx1.7$). We discuss the possible origins of the steep size -- linewidth relation and enhanced observed linewidths of the clouds and suggest that a combination of mechanisms such as stellar feedback, gas accretion and cloud-cloud collisions, as well as the gas inflows driven by the large-scale bar, may play a role.

astro-ph.GA↗

arXiv2024

WISDOM Project -- XIX. Figures of merit for supermassive black hole mass measurements using molecular gas and/or megamaser kinematics

The mass ($M_\mathrm{BH}$) of a supermassive black hole (SMBH) can be measured using spatially-resolved kinematics of the region where the SMBH dominates gravitationally. The most reliable measurements are those that resolve the smallest physical scales around the SMBHs. We consider here three metrics to compare the physical scales probed by kinematic tracers dominated by rotation: the radius of the innermost detected kinematic tracer $R_\mathrm{min}$ normalised by respectively the SMBH's Schwarzschild radius ($R_\mathrm{Schw}\equiv 2GM_\mathrm{BH}/c^2$, where $G$ is the gravitational constant and $c$ the speed of light), sphere-of-influence (SOI) radius ($R_\mathrm{SOI}\equiv GM_\mathrm{BH}/\sigma_\mathrm{e}^2$, where $\sigma_\mathrm{e}$ is the stellar velocity dispersion within the galaxy's effective radius) and equality radius [the radius $R_\mathrm{eq}$ at which the SMBH mass equals the enclosed stellar mass, $M_\mathrm{BH}=M_*(R_\mathrm{eq})$, where $M_*(R)$ is the stellar mass enclosed within the radius $R$]. All metrics lead to analogous simple relations between $R_\mathrm{min}$ and the highest circular velocity probed $V_\mathrm{c}$. Adopting these metrics to compare the SMBH mass measurements using molecular gas kinematics to those using megamaser kinematics, we demonstrate that the best molecular gas measurements resolve material that is physically closer to the SMBHs in terms of $R_\mathrm{Schw}$ but is slightly farther in terms of $R_\mathrm{SOI}$ and $R_\mathrm{eq}$. However, molecular gas observations of nearby galaxies using the most extended configurations of the Atacama Large Millimeter/sub-millimeter Array can resolve the SOI comparably well and thus enable SMBH mass measurements as precise as the best megamaser measurements.

astro-ph.GA↗

arXiv2024

WISDOM Project -- XXVI. Cross-checking supermassive black hole mass estimates from ALMA CO gas kinematics and SINFONI stellar kinematics in the galaxy NGC 4751

We present high angular resolution ($0.19''$ or $\approx24$ pc) ALMA observations of the $^{12}$CO(3-2) line emission of the galaxy NGC 4751. The data provide evidence for the presence of a central SMBH. Assuming a constant mass-to-light ratio ($M/L$), we infer a SMBH mass $M_\text{BH}=3.43^{+0.45}_{-0.44}[\text{stat},3\sigma]^{+0.22}_{-0.64}[\text{sys}]\times10^9$ M$_\odot$ and a F160W filter stellar $M/L_{F160W}=2.68\pm0.11[\text{stat},3\sigma]^{+0.10}_{-0.80}[\text{sys}]$ M$_\odot$/L$_{\odot,\text{F160W}}$, where the first uncertainties are statistical and the second systematic. Assuming a linearly spatially-varying $M/L$, we infer $M_\text{BH}=2.79^{+0.75}_{-0.57}[\text{stat},3\sigma]^{+0.75}_{-0.45}[\text{syst}]\times10^9$ M$_\odot$ and $(M/L_\text{F160W})/(\text{M}_\odot/\text{L}_{\odot,\text{F160W}})=3.07^{+0.27}_{-0.35}[\text{stat},3\sigma]^{+0.08}_{-1.14}[\text{sys}]-0.09^{+0.08}_{-0.06}[\text{stat},3\sigma]^{+0.08}_{-0.01}[\text{sys}](R/\text{arcsec})$, where $R$ is the galactocentric radius. We also present SMBH mass estimates using the Jeans Anisotropic Modelling (JAM) method and Very Large Telescope Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) stellar kinematics. Assuming a cylindrically-aligned velocity ellipsoid (JAM$_\text{cyl}$) we infer $M_\text{BH}=(2.52\pm 0.36)\times10^9$ M$_\odot$, while assuming a spherically-aligned velocity ellipsoid (JAM$_\text{sph}$) we infer $M_\text{BH}=(3.24\pm0.87)\times10^9$ M$_\odot$. The SMBH mass assuming a constant $M/L$ is statistically consistent with that of JAM$_\text{sph}$, whereas the mass assuming a linearly-varying $M/L$ is consistent with both JAM$_\text{cyl}$ and JAM$_\text{sph}$ (within the uncertainties). Our derived masses are larger than (and inconsistent with) one previous stellar dynamical measurement using the Schwarzschild orbit-superposition method and the same SINFONI kinematics.

astro-ph.GA↗

arXiv2024

The MASSIVE survey -- XIX. Molecular gas measurements of the supermassive black hole masses in the elliptical galaxies NGC 1684 and NGC 0997

Supermassive black hole (SMBH) masses can be measured by observing their dynamical effects on tracers, such as molecular gas. We present high angular resolution Atacama Large Millimeter/submillimeter Array (ALMA) observations of the $^{12}$CO(2-1) line emission of the early-type galaxies (ETGs) NGC 1684 and NGC 0997, obtained as part of the MASSIVE survey, a volume-limited integral-field spectroscopic study of the most massive local ETGs. NGC 1684 has a regularly-rotating central molecular gas disc, with a spatial extent of $\approx 6 "$ ($\approx1.8$ kpc) in radius and a central hole slightly larger than the expected SMBH sphere of influence. We forward model the data cube in a Bayesian framework with the Kinematic Molecular Simulation (KinMS) code and infer a SMBH mass of $1.40^{+0.44}_{-0.39}\times10^9$ M$_\odot$ ($3\sigma$ confidence interval) and a F110W-filter stellar mass-to-light ratio of $(2.50\pm0.05)$ M$_\odot/\text{L}_{\odot,\text{F110W}}$. NGC 0997 has a regularly-rotating central molecular gas disc, with a spatial extent of $\approx5 "$ ($\approx2.2$ kpc) in radius and a partially-filled central hole much larger than the expected SMBH sphere of influence, thus preventing a robust SMBH mass determination. With the same modelling method, we nevertheless constrain the SMBH mass to be in the range $4.0\times10^7$ to $1.8\times10^9$ M$_\odot$ and the F160W-filter stellar mass-to-light ratio to be $(1.52\pm0.11)$ M$_\odot/\text{L}_{\odot,\text{F160W}}$. Both SMBH masses are consistent with the SMBH mass -- stellar velocity dispersion ($M_{\text{BH}}$ -- $\sigma_\text{e}$) relation, suggesting that the over-massive SMBHs present in other very massive ETGs are fairly uncommon.

astro-ph.GA↗

arXiv2023

WISDOM Project -- XVI. The link between circumnuclear molecular gas reservoirs and active galactic nucleus fuelling

We use high-resolution data from the millimetre-Wave Interferometric Survey of Dark Object Masses (WISDOM) project to investigate the connection between circumnuclear gas reservoirs and nuclear activity in a sample of nearby galaxies. Our sample spans a wide range of nuclear activity types including radio galaxies, Seyfert galaxies, low-luminosity active galactic nuclei (AGN) and inactive galaxies. We use measurements of nuclear millimetre continuum emission along with other archival tracers of AGN accretion/activity to investigate previous claims that at, circumnuclear scales (<100 pc), these should correlate with the mass of the cold molecular gas. We find that the molecular gas mass does not correlate with any tracer of nuclear activity. This suggests the level of nuclear activity cannot solely be regulated by the amount of cold gas around the supermassive black hole (SMBH). This indicates that AGN fuelling, that drives gas from the large scale galaxy to the nuclear regions, is not a ubiquitous process and may vary between AGN type, with timescale variations likely to be very important. By studying the structure of the central molecular gas reservoirs, we find our galaxies have a range of nuclear molecular gas concentrations. This could indicate that some of our galaxies may have had their circumnuclear regions impacted by AGN feedback, even though they currently have low nuclear activity. On the other hand, the nuclear molecular gas concentrations in our galaxies could instead be set by secular processes.

astro-ph.GA↗

arXiv2023

WISDOM project -- XVIII. Molecular gas distributions and kinematics of three megamaser galaxies

The co-evolution of galaxies and supermassive black holes (SMBHs) underpins our understanding of galaxy evolution, but different methods to measure SMBH masses have only infrequently been cross-checked. We attempt to identify targets to cross-check two of the most accurate methods, megamaser and cold molecular gas dynamics. Three promising galaxies are selected from all those with existing megamaser SMBH mass measurements. We present Atacama Large Millimeter/sub-millimeter Array (ALMA) 12CO(2-1) and 230-GHz continuum observations with angular resolutions of about 0.5". Every galaxy has an extended rotating molecular gas disc and 230-GHz continuum source(s), but all also have irregularities and/or non-axisymmetric features: NGC1194 is highly inclined and has disturbed and lopsided central 12CO(2-1) emission; NGC3393 has a nuclear disc with fairly regular but patchy 12CO(2-1) emission with little gas near the kinematic major axis, faint emission in the very centre and two brighter structures reminiscent of a nuclear ring and/or spiral; NGC5765B has a strong bar and very bright 12CO(2-1) emission concentrated along two bisymmetric offset dust lanes and two bisymmetric nuclear spiral arms. 12CO(2-1) and 12CO(3-2) observations with the James Clerk Maxwell Telescope are compared with the ALMA observations. Because of the disturbed gas kinematics and the impractically long integration times required for higher angular resolution observations, none of the three galaxies is suitable for a future SMBH mass measurement. Nonetheless, increasing the number of molecular gas observations of megamaser galaxies is valuable, and the ubiquitous disturbances suggest a link between large-scale gas properties and the existence of megamasers.

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