Distribution Of Molecular Gas Research Articles

New Insights into the H ii Region G18.88–0.49: Hub–Filament System and Accreting Filaments

Abstract We present an analysis of multiwavelength observations of an area of 0.°27 × 0.°27 around the Galactic H ii region G18.88−0.49, which is powered by an O-type star (age ∼ 105 yr). The Herschel column density map reveals a shell-like feature of extension ∼12 pc × 7 pc and mass ∼2.9 × 104 M ⊙ around the H ii region; its existence is further confirmed by the distribution of molecular (12CO, 13CO, C18O, and NH3) gas at [60, 70] km s−1. Four subregions are studied toward this shell-like feature and show a mass range of ∼0.8–10.5 × 103 M ⊙. These subregions associated with dense gas are dominated by nonthermal pressure and supersonic nonthermal motions. The shell-like feature is associated with the H ii region, Class I protostars, and a massive protostar candidate, illustrating the ongoing early phases of star formation (including massive stars). The massive protostar is found toward the position of the 6.7 GHz methanol maser, and is associated with outflow activity. Five parsec-scale filaments are identified in the column density and molecular maps and appear to be radially directed to the dense parts of the shell-like feature. This configuration is referred to as a “hub–filament” system. Significant velocity gradients (0.8–1.8 km s−1 pc−1) are observed along each filament, suggesting that the molecular gas flows toward the central hub along the filaments. Overall, our observational findings favor a global nonisotropic collapse scenario as discussed in Motte et al., which can explain the observed morphology and star formation in and around G18.88−0.49.

Molecular Gas Outflow in the Starburst Galaxy NGC 1482

Abstract Galactic winds are essential to the regulation of star formation in galaxies. To study the distribution and dynamics of molecular gas in wind, we imaged the nearby starburst galaxy NGC 1482 in CO (J = 1 → 0) at a resolution of 1″ (≈100 pc) using the Atacama Large Millimeter/submillimeter Array. Molecular gas is detected in a nearly edge-on disk with a radius of 3 kpc and a biconical outflow emerging from the central 1 kpc starburst and extending to at least 1.5 kpc perpendicular to the disk. In the outflow, CO gas is distributed approximately as a cylindrically symmetrical envelope surrounding the warm and hot ionized gas traced by Hα and soft X-rays. The velocity, mass outflow rate, and kinetic energy of the molecular outflow are , , and , respectively. is comparable to the star formation rate ( ) and E w is ∼1% of the total energy released by stellar feedback in the past , which is the dynamical timescale of the outflow. The results indicate that the wind is starburst driven.

HAWC+ Far-infrared Observations of the Magnetic Field Geometry in M51 and NGC 891

Abstract Stratospheric Observatory for Infrared Astronomy High-resolution Airborne Wideband Camera Plus polarimetry at 154 μm is reported for the face-on galaxy M51 and the edge-on galaxy NGC 891. For M51, the polarization vectors generally follow the spiral pattern defined by the molecular gas distribution, the far-infrared (FIR) intensity contours, and other tracers of star formation. The fractional polarization is much lower in the FIR-bright central regions than in the outer regions, and we rule out loss of grain alignment and variations in magnetic field strength as causes. When compared with existing synchrotron observations, which sample different regions with different weighting, we find the net position angles are strongly correlated, the fractional polarizations are moderately correlated, but the polarized intensities are uncorrelated. We argue that the low fractional polarization in the central regions must be due to significant numbers of highly turbulent segments across the beam and along lines of sight in the beam in the central 3 kpc of M51. For NGC 891, the FIR polarization vectors within an intensity contour of 1500 are oriented very close to the plane of the galaxy. The FIR polarimetry is probably sampling the magnetic field geometry in NGC 891 much deeper into the disk than is possible with NIR polarimetry and radio synchrotron measurements. In some locations in NGC 891, the FIR polarization is very low, suggesting we are preferentially viewing the magnetic field mostly along the line of sight, down the length of embedded spiral arms. There is tentative evidence for a vertical field in the polarized emission off the plane of the disk.

The SEDIGISM survey: First Data Release and overview of the Galactic structure

ABSTRACT The SEDIGISM (Structure, Excitation and Dynamics of the Inner Galactic Interstellar Medium) survey used the APEX telescope to map 84 deg2 of the Galactic plane between ℓ = −60° and +31° in several molecular transitions, including 13CO (2 – 1) and C18O (2 – 1), thus probing the moderately dense (∼103 cm−3) component of the interstellar medium. With an angular resolution of 30 arcsec and a typical 1σ sensitivity of 0.8–1.0 K at 0.25 km s−1 velocity resolution, it gives access to a wide range of structures, from individual star-forming clumps to giant molecular clouds and complexes. The coverage includes a good fraction of the first and fourth Galactic quadrants, allowing us to constrain the large-scale distribution of cold molecular gas in the inner Galaxy. In this paper, we provide an updated overview of the full survey and the data reduction procedures used. We also assess the quality of these data and describe the data products that are being made publicly available as part of this First Data Release (DR1). We present integrated maps and position–velocity maps of the molecular gas and use these to investigate the correlation between the molecular gas and the large-scale structural features of the Milky Way such as the spiral arms, Galactic bar and Galactic Centre. We find that approximately 60 per cent of the molecular gas is associated with the spiral arms and these appear as strong intensity peaks in the derived Galactocentric distribution. We also find strong peaks in intensity at specific longitudes that correspond to the Galactic Centre and well-known star-forming complexes, revealing that the 13CO emission is concentrated in a small number of complexes rather than evenly distributed along spiral arms.

Molecular gas in the central region of NGC 7213

We present a multi-wavelength study (from X-ray to mm) of the nearby low-luminosity active galactic nucleus NGC 7213. We combine the information from the different bands to characterise the source in terms of contribution from the AGN and the host-galaxy interstellar medium. This approach allows us to provide a coherent picture of the role of the AGN and its impact, if any, on the star formation and molecular gas properties of the host galaxy. We focused our study on archival ALMA Cycle 1 observations, where the CO(2–1) emission line has been used as a tracer of the molecular gas. Using the 3DBAROLO code on ALMA data, we performed the modelling of the molecular gas kinematics traced by the CO(2–1) emission, finding a rotationally dominated pattern. The molecular gas mass of the host galaxy was estimated from the integrated CO(2–1) emission line obtained with APEX data, assuming an αCO conversion factor. Had we used the ALMA data, we would have underestimated the gas masses by a factor ∼3, given the filtering out of the large-scale emission in interferometric observations. We also performed a complete X-ray spectral analysis on archival observations, revealing a relatively faint and unobscured AGN. The AGN proved to be too faint to significantly affect the properties of the host galaxy, such as star formation activity and molecular gas kinematics and distribution.

The Formation of a Stellar Association in the NGC 7000/IC 5070 Complex: Results from Kinematic Analysis of Stars and Gas

Abstract We examine the clustering and kinematics of young stellar objects (YSOs) in the North America/Pelican Nebulae, as revealed by Gaia astrometry, in relation to the structure and motions of the molecular gas, as indicated in molecular-line maps. The Gaia parallaxes and proper motions allow us to significantly refine previously published lists of YSOs, demonstrating that many of the objects previously thought to form a distributed population turn out to be nonmembers. The members are subdivided into at least six spatio-kinematic groups, each of which is associated with its own molecular cloud component or components. Three of the groups are expanding, with velocity gradients of 0.3–0.5 km s−1 pc−1, up to maximum velocities of ∼8 km s−1 away from the groups’ centers. The two known O-type stars associated with the region, 2MASS J20555125+4352246 and HD 199579, are rapidly escaping one of these groups, following the same position–velocity relation as the low-mass stars. We calculate that a combination of gas expulsion and tidal forces from the clumpy distribution of molecular gas could impart the observed velocity gradients within the groups. However, on a global scale, the relative motions of the groups do not appear either divergent or convergent. The velocity dispersion of the whole system is consistent with the kinetic energy gained due to gravitational collapse of the complex. Most of the stellar population has ages similar to the freefall timescales for the natal clouds. Thus, we suggest the nearly freefall collapse of a turbulent molecular cloud as the most likely scenario for star formation in this complex.

Discovery of a [C i]-faint, CO-bright Galaxy: ALMA Observations of the Merging Galaxy NGC 6052

Abstract We report sensitive [C i] 3 P 1–3 P 0 and 12CO J = 4–3 observations of the nearby merging galaxy NGC 6052 using the Morita (Atacama Compact) Array of the Atacama Large Millimeter/submillimeter Array (ALMA). We detect 12CO J = 4–3 toward the northern part of NGC 6052, but [C i] 3 P 1–3 P 0 is not detected with a [C i] 3 P 1–3 P 0 to 12CO J = 4–3 line luminosity ratio of ≲0.07. According to models of photodissociation regions, the unusual weakness of [C i] 3 P 1–3 P 0 relative to 12CO J = 4–3 can be explained if the interstellar medium has a hydrogen density larger than , conditions that might arise naturally in the ongoing merging process in NGC 6052. Its [C I] 3 P 1–3 P 0 emission is also weaker than expected given the molecular gas mass inferred from previous measurements of 12CO J = 1–0 and 12CO J = 2–1. This suggests that [C I]3 P 1–3 P 0 may not be a reliable tracer of molecular gas mass in this galaxy. NGC 6052 is a unique laboratory to investigate how the merger process impacts the molecular gas distribution.

Uncovering distinct environments in an extended physical system around the W33 complex

ABSTRACT We present a multiwavelength investigation of a large-scale physical system containing the W33 complex. The extended system (∼50 pc × 37 pc) is selected based on the distribution of molecular gas at [29.6, 60.2] km s−1 and of 88 ATLASGAL 870-μm dust clumps at d ∼2.6 kpc. The extended system/molecular cloud traced in the maps of 13CO and C18O emission contains several H ii regions excited by OB stars (age ∼0.3–1.0 Myr) and a thermally supercritical filament (fs1, length ∼17 pc). The filament, which is devoid of ionized gas, shows a dust temperature (Td) of ∼19 K, while the H ii regions have a Td of ∼21–29 K. It suggests the existence of two distinct environments in the cloud. The distribution of Class I young stellar objects (mean age ∼0.44 Myr) traces the early stage of star formation (SF) towards the cloud. At least three velocity components (around 35, 45 and 53 km s−1) are investigated towards the system. The analysis of 13CO and C18O reveals spatial and velocity connections of cloud components at around 35 and 53 km s−1. The observed positions of previously known sources, W33 Main, W33 A and O4–7I stars, are found towards a complementary distribution of these two cloud components. The filament fs1 and a previously known object W33 B are seen towards the overlapping areas of the clouds, where ongoing SF activity is evident. A scenario related to converging/colliding flows from two different velocity components appears to explain well the observed indications of SF activity in the system.

Central kiloparsec of NGC 1326 observed with SINFONI

Gas inflow processes in the vicinity of galactic nuclei play a crucial role in galaxy evolution and supermassive black hole growth. Exploring the central kiloparsec of galaxies is essential to shed more light on this subject. We present near-infraredH- andK-band results of the nuclear region of the nearby galaxy NGC 1326, observed with the integral-field spectrograph SINFONI mounted on the Very Large Telescope. The field of view covers 9″ × 9″ (650 × 650 pc2). Our work is concentrated on excitation conditions, morphology, and stellar content. The nucleus of NGC 1326 was classified as a LINER, however in our data we observed an absence of ionised gas emission in the centralr ∼ 3″. We studied the morphology by analysing the distribution of ionised and molecular gas, and thereby detected an elliptically shaped, circum-nuclear star-forming ring at a mean radius of 300 pc. We estimate the starburst regions in the ring to be young with dominating ages of < 10 Myr. The molecular gas distribution also reveals an elongated east to west central structure about 3″ in radius, where gas is excited by slow or mild shock mechanisms. We calculate the ionised gas mass of 8 × 105M⊙completely concentrated in the nuclear ring and the warm molecular gas mass of 187M⊙, from which half is concentrated in the ring and the other half in the elongated central structure. The stellar velocity fields show pure rotation in the plane of the galaxy. The gas velocity fields show similar rotation in the ring, but in the central elongated H2structure they show much higher amplitudes and indications of further deviation from the stellar rotation in the central 1″ aperture. We suggest that the central 6″ elongated H2structure might be a fast-rotating central disc. The CO(3–2) emission observations with the Atacama Large Millimeter/submillimeter Array reveal a central 1″ torus. In the central 1″ of the H2velocity field and residual maps, we find indications for a further decoupled structure closer to a nuclear disc, which could be identified with the torus surrounding the supermassive black hole.

SHARP – VI. Evidence for CO (1–0) molecular gas extended on kpc-scales in AGN star-forming galaxies at high redshift

ABSTRACT We present a study of the stellar host galaxy, CO (1–0) molecular gas distribution and AGN emission on 50–500 pc-scales of the gravitationally lensed dust-obscured AGN MG J0751+2716 and JVAS B1938+666 at redshifts 3.200 and 2.059, respectively. By correcting for the lensing distortion using a grid-based lens modelling technique, we spatially locate the different emitting regions in the source plane for the first time. Both AGN host galaxies have 300–500 pc-scale size and surface brightness consistent with a bulge/pseudo-bulge, and 2 kpc-scale AGN radio jets that are embedded in extended molecular gas reservoirs that are 5–20 kpc in size. The CO (1–0) velocity fields show structures possibly associated with discs (elongated velocity gradients) and interacting objects (off-axis velocity components). There is evidence for a decrement in the CO (1–0) surface brightness at the location of the host galaxy, which may indicate radiative feedback from the AGN, or offset star formation. We find CO–H2 conversion factors of around αCO = 1.5 ± 0.5 (K km s−1 pc2)−1, molecular gas masses of >3 × 1010 M⊙, dynamical masses of ∼1011 M⊙, and gas fractions of around 60 per cent. The intrinsic CO line luminosities are comparable to those of unobscured AGN and dusty star-forming galaxies at similar redshifts, but the infrared luminosities are lower, suggesting that the targets are less efficient at forming stars. Therefore, they may belong to the AGN feedback phase predicted by galaxy formation models, because they are not efficiently forming stars considering their large amount of molecular gas.

Large-scale Molecular Gas Distribution in the M17 Cloud Complex: Dense Gas Conditions of Massive Star Formation?

Abstract The non-uniform distribution of gas and protostars in molecular clouds is caused by combinations of various physical processes that are difficult to separate. We explore this non-uniform distribution in the M17 molecular cloud complex that hosts massive star formation activity using the 12CO (J = 1–0) and 13CO (J = 1–0) emission lines obtained with the Nobeyama 45 m telescope. Differences in clump properties such as mass, size, and gravitational boundedness reflect the different evolutionary stages of the M17-H ii and M17-IRDC clouds. Clumps in the M17-H ii cloud are denser, more compact, and more gravitationally bound than those in M17-IRDC. While M17-H ii hosts a large fraction of very dense gas (27%) that has a column density larger than the threshold of ∼1 g cm−2 theoretically predicted for massive star formation, this very dense gas is deficient in M17-IRDC (0.46%). Our HCO+ (J = 1–0) and HCN (J = 1–0) observations with the Taeduk Radio Astronomy Observatory 14 m telescope trace all gas with a column density higher than 3 × 1022 cm−2, confirming the deficiency of high-density (≳105 cm−3) gas in M17-IRDC. Although M17-IRDC is massive enough to potentially form massive stars, its deficiency of very dense gas and gravitationally bound clumps can explain the current lack of massive star formation.

The Gas–Star Formation Cycle in Nearby Star-forming Galaxies. I. Assessment of Multi-scale Variations

Abstract The processes regulating star formation in galaxies are thought to act across a hierarchy of spatial scales. To connect extragalactic star formation relations from global and kiloparsec-scale measurements to recent cloud-scale resolution studies, we have developed a simple, robust method that quantifies the scale dependence of the relative spatial distributions of molecular gas and recent star formation. In this paper, we apply this method to eight galaxies with ∼1″ resolution molecular gas imaging from the Physics at High Angular resolution in Nearby GalaxieS–ALMA (PHANGS–ALMA) survey and PdBI Arcsecond Whirlpool Survey (PAWS) that have matched resolution, high-quality narrowband Hα imaging. At a common scale of 140 pc, our massive (log(M ⋆[M ⊙]) = 9.3–10.7), normally star-forming (SFR[M ⊙ yr−1] = 0.3–5.9) galaxies exhibit a significant reservoir of quiescent molecular gas not associated with star formation as traced by Hα emission. Galactic structures act as backbones for both molecular gas and H ii region distributions. As we degrade the spatial resolution, the quiescent molecular gas disappears, with the most rapid changes occurring for resolutions up to ∼0.5 kpc. As the resolution becomes poorer, the morphological features become indistinct for spatial scales larger than ∼1 kpc. The method is a promising tool to search for relationships between the quiescent or star-forming molecular reservoir and galaxy properties, but requires a larger sample size to identify robust correlations between the star-forming molecular gas fraction and global galaxy parameters.

ALMA images the many faces of the NGC 1068 torus and its surroundings

Aims. We investigate the fueling and the feedback of nuclear activity in the nearby (D = 14 Mpc) Seyfert 2 barred galaxy NGC 1068 by studying the distribution and kinematics of molecular gas in the torus and its connections to the host galaxy disk. Methods. We used the Atacama Large Millimeter Array (ALMA ) to image the emission of a set of molecular gas tracers in the circumnuclear disk (CND) and the torus of the galaxy using the CO(2–1), CO(3–2), and HCO+(4–3) lines and their underlying continuum emission with high spatial resolutions (0.03″ − 0.09″ ≃ 2 − 6 pc). These transitions, which span a wide range of physical conditions of molecular gas (n(H2)⊂103 − 107 cm−3), are instrumental in revealing the density radial stratification and the complex kinematics of the gas in the torus and its surroundings. Results. The ALMA images resolve the CND as an asymmetric ringed disk of D ≃ 400 pc in size and ≃1.4 × 108 M⊙ in mass. The CND shows a marked deficit of molecular gas in its central ≃130 pc region. The inner edge of the ring is associated with the presence of edge-brightened arcs of NIR polarized emission, which are identified with the current working surface of the ionized wind of the active galactic nucleus (AGN). ALMA proves the existence of an elongated molecular disk/torus in NGC 1068 of Mtorusgas ≃ 3 × 105 M⊙, which extends over a large range of spatial scales D ≃ 10 − 30 pc around the central engine. The new observations evidence the density radial stratification of the torus: the HCO+(4–3) torus, with a full size DHCO+(4 − 3) = 11 ± 0.6 pc, is a factor of between two and three smaller than its CO(2–1) and CO(3–2) counterparts, which have full sizes of DCO(3 − 2) = 26 ± 0.6 pc and DCO(2 − 1) = 28 ± 0.6 pc, respectively. This result brings into light the many faces of the molecular torus. The torus is connected to the CND through a network of molecular gas streamers detected inside the CND ring. The kinematics of molecular gas show strong departures from circular motions in the torus, the gas streamers, and the CND ring. These velocity field distortions are interconnected and are part of a 3D outflow that reflects the effects of AGN feedback on the kinematics of molecular gas across a wide range of spatial scales around the central engine. In particular, we estimate through modeling that a significant fraction of the gas inside the torus (≃ 0.4 − 0.6 × Mtorusgas) and a comparable amount of mass along the gas streamers are outflowing. However, the bulk of the mass, momentum, and energy of the molecular outflow of NGC 1068 is contained at larger radii in the CND region, where the AGN wind and the radio jet are currently pushing the gas assembled at the Inner Lindblad Resonance (ILR) ring of the nuclear stellar bar. Conclusions. In our favored scenario a wide-angle AGN wind launched from the accretion disk of NGC1068 is currently impacting a sizable fraction of the gas inside the torus. However, a large gas reservoir (≃1.2 − 1.8 × 105 M⊙), which lies close to the equatorial plane of the torus, remains unaffected by the feedback of the AGN wind and can therefore continue fueling the AGN for at least ≃1 − 4 Myr. Nevertheless, AGN fueling currently seems thwarted on intermediate scales (15 pc ≤r ≤ 50 pc).

Cloud–cloud collisions in the common foot point of molecular loops 1 and 2 in the Galactic Center

Abstract Recent large-area, deep CO surveys in the Galactic disk have revealed the formation of ~50 high-mass stars or clusters triggered by cloud–cloud collisions (CCCs). Although the Galactic Center (GC)—which contains the highest volume density of molecular gas—is the most favorable place for cloud collisions, systematic studies of CCCs in that region are still untouched. Here we report for the first time evidence of CCCs in the common foot point of molecular loops 1 and 2 in the GC. We have investigated the distribution of molecular gas toward the foot point by using a methodology for identifying CCCs, and we have discovered clear signatures of CCCs. Using the estimated displacements and relative velocities of the clouds, we find the elapsed time since the beginnings of the collisions to be 105–106yr. We consider possible origins for previously reported peculiar velocity features in the foot point and discuss star formation triggered by CCCs in the GC.

ALMA Unveils Widespread Molecular Gas Clumps in the Ram Pressure Stripped Tail of the Norma Jellyfish Galaxy

Abstract We present the first high-resolution map of the cold molecular gas distribution as traced by CO(2−1) emission with ALMA in a long ram pressure stripped tail. The Norma cluster galaxy ESO 137-001 is undergoing a strong interaction with the surrounding intracluster medium and is one of the nearest jellyfish galaxies with a long multiphase and multicomponent tail. We have mapped the full extent of the tail at 1″ (350 pc) angular resolution and found a rich distribution of mostly compact CO regions extending to nearly 60 kpc in length and 25 kpc in width. In total, about 109 M ⊙ of molecular gas was detected with ALMA. From comparison with previous APEX observations, we also infer the presence of a substantial extended molecular component in the tail. The ALMA CO features are found predominantly at the heads of numerous small-scale (∼1.5 kpc) fireballs (i.e., star-forming clouds with linear streams of young stars extending toward the galaxy) but also large-scale (∼8 kpc) superfireballs and double-sided fireballs that have additional diffuse ionized gas tails extending in the direction opposite the stellar tails. The new data help to shed light on the origin of the molecular tail; CO filaments oriented in the direction of the tail are likely young molecular features formed in situ, whereas large CO features tilted with respect to the tail may have originated from dense gas complexes that were gradually pushed away from the disk.

A Superluminous Supernova in High Surface Density Molecular Gas within the Bar of a Metal-rich Galaxy

We report the Atacama Large Millimeter/submillimeter Array (ALMA) observations of the metal rich host galaxy of superluminous supernova (SLSN) PTF10tpz, a barred spiral galaxy at z=0.03994. We find the CO(1-0) emission to be confined within the bar of the galaxy. The distribution and kinematics of molecular gas in the host galaxy resemble gas flows along two lanes running from the tips of the bar towards the galaxy center. These gas lanes end in a gaseous structure in the inner region of the galaxy, likely associated with an inner Lindblad resonance. The interaction between the large-scale gas flows in the bar and the gas in the inner region plausibly leads to the formation of massive molecular clouds and consequently massive clusters. This in turn can result in formation of massive stars, and thus the likely progenitor of the SLSN in a young, massive cluster. This picture is consistent with SLSN PTF10tpz being located near the inner structure. We find the molecular gas in the vicinity of the SLSN to have high surface densities, comparable with those in interacting galaxies or starburst regions in nearby galaxies. This lends support to high densities being favorable conditions for formation of SLSNe progenitors.

Complex distribution and velocity field of molecular gas in NGC 1316 as revealed by the Morita Array of ALMA

Abstract We present the results of 12CO(J = 1–0) mosaicing observations of the cD galaxy NGC 1316 at kiloparsec resolution performed with the Morita Array of the Atacama Large Millimeter/submillimeter Array (ALMA). We reveal the detailed distribution of the molecular gas in the central region for the first time: a shell structure in the northwest, a barely resolved blob in the southeast of the center, and some clumps between them. The total molecular gas mass obtained with a standard Milky Way CO-to-H2 conversion factor is $(5.62 \pm 0.53) \times 10^{8}\, M_{\odot }$, which is consistent with previous studies. The disturbed velocity field of the molecular gas suggests that the molecular gas was injected very recently (<1 Gyr) if it has an external origin, and is in the process of settling into a rotating disk. Assuming that a low-mass gas-rich galaxy has accreted, the gas-to-dust ratio and H2-to-H i ratio are unusually low (∼28) and high (∼5.6), respectively. To explain these ratios additional processes should be taken into account, such as effective dust formation and conversion from atomic to molecular gas during the interaction. We also discuss the interaction between the nuclear jet and the molecular gas.

A Chandra and ALMA study of X-ray-irradiated gas in the central ∼100 pc of the Circinus galaxy

Abstract We report on a study of X-ray-irradiated gas in the central ∼100 pc of the Circinus galaxy, which hosts a Compton-thick active galactic nucleus (AGN), at 10 pc resolution using Chandra and ALMA. Based on ∼200 ks Chandra/ACIS-S data, we created an image of the Fe Kα line at 6.4 keV, tracing X-ray-irradiated dense gas. The ALMA data in Bands 6 (∼270 GHz) and 7 (∼350 GHz) cover five molecular lines: CO(J = 3–2), HCN(J = 3–2), HCN(J = 4–3), HCO+(J = 3–2), and HCO+(J = 4–3). The detailed spatial distribution of dense molecular gas was revealed, and compared to the iron line image. The molecular gas emission appeared faint in regions with bright iron emission. Motivated by this, we quantitatively discuss the possibility that the molecular gas is efficiently dissociated by AGN X-ray irradiation (i.e., creating an X-ray-dominated region). Based on a non-local thermodynamic equilibrium model, we constrained the molecular gas densities and found that they are as low as interpreted by X-ray dissociation. Furthermore, judging from inactive star formation reported in the literature, we suggest that the X-ray emission has the potential to suppress star formation, particularly in the proximity of the AGN.

Constraints on the Collimated X-ray Emission of SS 433 from the Reflection on Molecular Clouds

We calculate X-ray signal that should arise due to reflection of the putative collimated X-ray emission of the Galactic supercritical accretor SS 433 on molecular clouds in its vicinity. The molecular gas distribution in the region of interest has been constructed based on the data of the BU-FCRAO GRS in $^{13}$CO $J=1\rightarrow0$ emission line, while the collimated emission was assumed to be aligned with the direction of the relativistic jets, which are continuously launched by the system. We consider all the available $Chandra$ observations covering the regions possibly containing the reflection signal and put constraints on the apparent face-on luminosity of SS 433 above 4 keV. No signatures of the predicted signal have been found in the analysed regions down to a 4-8 keV surface brightness level of $\sim 10^{-11}$ erg/s/cm$^2$/deg$^2$. This translates into the limit on the apparent face-on 2-10 keV luminosity of SS 433 $L_{X,2-10}\lesssim 8\times10^{38}$ erg/s, provided that the considered clouds do fall inside the illumination cone of the collimated emission. This, however, might not be the case due to persisting uncertainty in the line-of-sight distances to SS 433 $d_{SS433}$ (4.5-5.5 kpc) and to the considered molecular clouds. For half-opening angle of the collimation cone larger than or comparable to the amplitude of the jets' precession ($\approx21\deg$), the stringent upper limit quoted above is most relevant if $d_{SS433}<5$ kpc, provided that the kinematic distances to the considered molecular clouds are sufficiently accurate. Dropping the last assumption, a more conservative constraint is $L_{X,2-10}\lesssim10^{40}$ erg/s for $d_{SS433}=4.65-4.85$ kpc (and yet worse outside this range). We conclude that SS 433 is not likely to belong to the brightest ultraluminous X-ray sources if it could be observed face-on, unless its X-ray emission is highly collimated. (Abridged)

WISDOM project – IV. A molecular gas dynamical measurement of the supermassive black hole mass in NGC 524

ABSTRACT We present high angular resolution (0.3 arcsec or $37\, \mathrm{pc}$) Atacama Large Millimeter/submillimeter Array observations of the CO(2–1) line emission from a central disc in the early-type galaxy NGC 524. This disc is shown to be dynamically relaxed, exhibiting ordered rotation about a compact $1.3\, \mathrm{mm}$ continuum source, which we identify as emission from an active supermassive black hole (SMBH). There is a hole at the centre of the disc slightly larger than the SMBH sphere of influence. An azimuthal distortion of the observed velocity field is found to be due to either a position angle warp or radial gas flow over the inner 2${^{\prime\prime}_{.}}$5. By forward-modelling the observations, we obtain an estimate of the SMBH mass of $4.0^{+3.5}_{-2.0}\times 10^8\,$ M⊙, where the uncertainties are at the 3σ level. The uncertainties are dominated by the poorly constrained inclination and the stellar mass-to-light ratio of this galaxy, and our measurement is consistent with the established correlation between SMBH mass and stellar velocity dispersion. Our result is roughly half that of the previous stellar dynamical measurement, but is consistent within the uncertainties of both. We also present and apply a new tool for modelling complex molecular gas distributions.