Plane Of The Sky Research Articles

Orion A’s complete 3D magnetic field morphology

Magnetic fields permeate the interstellar medium and are important in the star formation process. Determining the three-dimensional (3D) magnetic fields of molecular clouds will allow us to better understand their role in the evolution of these clouds and the formation of stars. We fully reconstruct the approximate 3D magnetic field morphology of the Orion A molecular cloud (on scales of a few to ∼100 pc) using Galactic magnetic field models, as well as available line-of-sight and plane-of-sky magnetic field observations. While previous studies identified the 3D magnetic field morphology of the Orion A cloud as an arc shape, in this study we provide the orientation of this arc-shaped field and its plane-of-sky direction for the first time. We find that this 3D field is a tilted, semi-convex (from our point of view) structure and mostly points in the direction of decreasing latitude and longitude on the plane of the sky from our vantage point. The previously identified bubbles and events in this region were key in shaping this arc-shaped magnetic field morphology.

3D magnetic-field morphology of the Perseus molecular cloud

Context.Despite recent observational and theoretical advances in mapping the magnetic fields associated with molecular clouds, their three-dimensional (3D) morphology remains unresolved. Multi-wavelength and multi-scale observations will allow us to paint a comprehensive picture of the magnetic fields of these star-forming regions.Aims.We reconstructed the 3D magnetic field morphology associated with the Perseus molecular cloud and compared it with predictions of cloud-formation models. These cloud-formation models predict a bending of magnetic fields associated with filamentary molecular clouds. We compared the orientation and direction of this field bending with our 3D magnetic-field view of the Perseus cloud.Methods.We used previous line-of-sight and plane-of-sky magnetic field observations as well as Galactic magnetic field models to reconstruct the complete 3D magnetic field vectors and morphology associated with the Perseus cloud.Results.We approximated the 3D magnetic field morphology of the cloud as a concave arc that points in the decreasing longitude direction in the plane of the sky (from our point of view). This field morphology preserves a memory of the Galactic magnetic field. In order to compare this morphology to cloud-formation model predictions, we assume that the cloud retains a memory of its most recent interaction. After incorporating velocity observations, we find that the line-of-sight magnetic field observations are consistent with predictions of shock-cloud-interaction models.Conclusions.To our knowledge, this is the first time that the 3D magnetic fields of a molecular cloud have been reconstructed. We find the 3D magnetic field morphology of the Perseus cloud to be consistent with the predictions of the shock-cloud-interaction model that describes the formation mechanism of filamentary molecular clouds.

The ESO-VLT MIKiS Survey Reloaded: Velocity Dispersion Profile and Rotation Curve of NGC 1904* *Based on observations collected at the European Southern Observatory, Cerro Paranal (Chile), under proposal 193.D-0232 (PI: Ferraro) and 0104.D-0636 (PI: Ferraro).

We present an investigation of the internal kinematic properties of M79 (NGC 1904). Our study is based on radial velocity measurements obtained from the ESO-VLT Multi-Instrument Kinematic Survey (MIKiS) of Galactic globular clusters for more than 1700 individual stars distributed between ∼0.″3 and 770″ (∼14 three-dimensional half-mass radii) from the center. Our analysis reveals the presence of ordered line-of-sight rotation with a rotation axis almost aligned along the east–west direction and a velocity peak of 1.5 km s−1 at ∼70″ from the rotation axis. The velocity dispersion profile is well described by the same King model that best fits the projected density distribution, with a constant central plateau at σ 0 ∼ 6 km s−1. To investigate the cluster rotation in the plane of the sky, we have analyzed the proper motions provided by the Gaia EDR3, finding a signature of rotation with a maximum amplitude of ∼2.0 km s−1 at ∼80″ from the cluster center. Analyzing the three-dimensional velocity distribution for a subsample of 130 stars, we confirm the presence of systemic rotation and find a rotation axis inclination angle of 37° with respect to the line of sight. As a final result, the comparison of the observed rotation curves with the results of a representative N-body simulation of a rotating star cluster shows that the present-day kinematic properties of NGC 1904 are consistent with those of a dynamically old system that has lost a significant fraction of its initial angular momentum.

Origin of the spectacular tidal shells of galaxy NGC 474

Context.The lenticular galaxy NGC 474 hosts a rich system of tidal shells and streams, some of which are exceptionally bright. Two teams recently presented spectroscopic observations of the brightest shells. These were the first shell spectra ever observed in integrated starlight. The authors studied the stellar populations of the shell, of the center of the galaxy, and of its globular clusters. The precise formation scenario for the tidal features of this prominent galaxy still remained unclear, however.Aims.Here, we add further clues on their formation from the radii of the shells, and we present a scenario for the formation of the tidal features that seems to be unique and can explain all available data.Methods.Shell radii were analyzed with the shell identification method, and we ran self-consistent simulations of the formation of the tidal features. We considered Newtonian as well as MOND gravity.Results.Observations suggest that the tidal features originate from the accretion of a spiral galaxy. According to the shell identification method, the merging galaxies first collided 1.3 Gyr ago and then again 0.9 Gyr ago, thereby forming the shells in two generations. This would also explain the young ages of stellar populations in the center of the galaxy and the young age of the globular clusters. The analytic models of shell propagation that underlie the shell identification method are verified by a simulation. The simulations reproduce the observed morphology of the tidal features well. The accreted spiral likely reached NGC 474 on the plane of the sky nearly radially from the south, its rotation axis pointing toward us. It probably had a stellar mass of about one-sixth of NGC 474, that is, 109.8 M⊙. Apparently, all tidal features in the galaxy originate from one merger.

Cloud-cloud collision as origin of the G31.41+0.31 massive protocluster

The G31.41+0.31 (G31) hot molecular core (HMC) is a high-mass protocluster showing accelerated infall and rotational spin-up that is well studied at high-angular resolution. To complement the accurate view of the small scale in G31, we traced the kinematics of the large-scale material by carrying out N2H+ (1–0) observations with the Institute de Radioastronomie Millimétrique 30m telescope of an area of ∼6 × 6 arcmin2 around the HMC. The N2H+ observations have revealed a large-scale (5 pc) hub-filament system (HFS) composed of at least four filamentary arms and a NNE–SSW velocity gradient (∼0.4 km s−1 pc−1) between the northern and southern filaments. The linewidth increases toward the hub at the center of the HFS reaching values of 2.5–3 km s−1 in the central 1 pc. The origin of the large-scale velocity gradient is likely a cloud-cloud collision. In this scenario, the filaments in G31 would have formed by compression resulting from the collision, and the rotation of the HMC observed at scales of 1000 au would have been induced by shear caused by the cloud-cloud collision at scales of a few parsecs. We conclude that G31 represents a HFS in a compressed layer with an orthogonal orientation to the plane of the sky, and it represents a benchmark for the filaments-to-clusters paradigm of star formation.

Follow-Up of Extended Shells around B[e] Stars

B[e] stars are massive B type emission line stars in different evolutionary stages ranging from pre-main sequence to post-main sequence. Due to their mass loss and ejection events these objects deposit huge amounts of mass and energy into their environment and enrich it with chemically processed material, contributing significantly to the chemical and dynamical evolution of their host galaxies. However, the large-scale environments of these enigmatic objects have not attracted much attention. The first and so far only catalog reporting the detection of extended shells around a sample of B[e] stars was an Hα imaging survey carried out in the year 2001, and was limited to bright targets in the northern hemisphere. We have recently started a follow-up of those targets to detect possible evolution of their nebulae in the plane of the sky over a baseline of two decades. Furthermore, we extend our survey to southern targets and fainter northern ones to complement and complete our knowledge on large-scale ejecta surrounding B[e] stars. Besides imaging in Hα and selected nebular lines, we utilize long-slit and 3D spectral observations across the nebulae to derive their physical properties. We discovered pronounced nebula structures around 15 more objects, resulting in a total of 27 B[e] stars with a large-scale nebula. Here we present our (preliminary) results for three selected objects: the two massive supergiants MWC137 and MWC 314, and the unclassified B[e] star MWC 819.

HR 6819 is a binary system with no black hole

Context. Two scenarios have been proposed to match the existing observational constraints of the object HR 6819. The system could consist of a close inner B-type giant plus a black hole (BH) binary with an additional Be companion in a wide orbit. Alternatively, it could be a binary composed of a stripped B star and a Be star in a close orbit. Either scenario makes HR 6819 a cornerstone object as the stellar BH closest to Earth, or as an example of an important transitional, non-equilibrium phase for Be stars with solid evidence for its nature. Aims. We aim to distinguish between the two scenarios for HR 6819. Both models predict two luminous stars but with very different angular separations and orbital motions. Therefore, the presence of bright sources in the 1−100 milliarcsec (mas) regime is a key diagnostic for determining the nature of the HR 6819 system. Methods. We obtained new high-angular resolution data with VLT/MUSE and VLTI/GRAVITY of HR 6819. The MUSE data are sensitive to bright companions at large scales, whilst the interferometric GRAVITY data are sensitive down to separations on mas scales and large magnitude differences. Results. The MUSE observations reveal no bright companion at large separations and the GRAVITY observations indicate the presence of a stellar companion at an angular separation of ∼1.2 mas that moves on the plane of the sky over a timescale compatible with the known spectroscopic 40-day period. Conclusions. We conclude that HR 6819 is a binary system and that no BH is present in the system. The unique nature of HR 6819, and its proximity to Earth make it an ideal system for quantitatively characterising the immediate outcome of binary interaction and probing how Be stars form.

The Long Filament of PSR J2030+4415

Abstract New X-ray and optical observations shed light on the remarkable X-ray filament of the gamma-ray pulsar PSR J2030+4415. Images of the associated Hα bow shock’s evolution over the past decade compared with its velocity structure provide an improved kinematic distance of ∼0.5 kpc. These velocities also imply that the pulsar spin axis lies ∼15° from the proper motion axis, which is close to the plane of the sky. The multi-bubble shock structure indicates that the bow shock standoff was compressed to a small value ∼20–30 yr ago when the pulsar broke through the bow shock to its present bubble. This compression allowed multi-TeV pulsar e ± to escape to the external interstellar medium (ISM), lighting up an external magnetic field structure as the filament. The narrow filament indicates excellent initial confinement and the full 15′ (2.2 pc = 7 lt-yr) projected length of the filament indicates rapid e ± propagation to its end. Spectral variation along the filament suggests that the injected particle energy evolved during the breakthrough event.

Imprints of the Jittering Jets Explosion Mechanism in the Morphology of the Supernova Remnant SNR 0540-69.3

I identify a point-symmetric structure in recently published VLT/MUSE velocity maps of different elements in a plane along the line of sight at the center of the supernova remnant SNR 0540-69.3, and argue that jittering jets that exploded this core collapse supernova shaped this point-symmetric structure. The four pairs of two opposite clumps that compose this point symmetric structure suggest that two to four pairs of jittering jets shaped the inner ejecta in this plane. In addition, intensity images of several spectral lines reveal a faint strip (the main jet-axis) that is part of this plane of jittering jets and its similarity to morphological features in a few other SNRs and in some planetary nebulae further suggests shaping by jets. My interpretation implies that in addition to instabilities, jets also mix elements in the ejecta of core collapse supernovae. Based on the point-symmetric structure and under the assumption that jittering jets exploded this supernova, I estimate the component of the neutron star natal kick velocity on the plane of the sky to be ≃ 235 km s−1, and at an angle of ≃47° to the direction of the main jet-axis. I analyze this natal kick direction together with 12 other SNRs in the frame of the jittering jets explosion mechanism.

Galactic magnetic X fields

Aims. Or aim in this note is to compare a recent explanation of the galactic X pattern in Faraday rotation to the pattern produced by the advection part of the classical dynamo. Methods. We find that the characteristic X magnetic field polarization in the plane of the sky, found in edge-on spiral galaxies, can develop magnetohydromagnetically from an initial disk magnetic field combined with wind and rotation. The rotation measure develops a corresponding X distribution in sign, but this distribution is not a universal behavior because it depends primarily on the velocity field. We use Cauchy evolution of an initial magnetic field to find the field at some later time. Results. A battery mechanism that requires the current to always flow out of a galaxy has been recently suggested. This contrasts with the conclusions of this paper. Conclusions. Either explanation has significant consequences for the structure of a spiral galaxy. If the battery mechanism applies, then we have a new method of producing a magnetic field independent of the traditional dynamo. If, however, the flow mechanism applies, then constraints concerning the presence and nature of a galactic wind, together with the signature of the mean radial magnetic field, can be inferred.

Expanding Bipolar X-Ray Structure After the 2006 Eruption of RS Oph

Abstract We report on the detection and analysis of extended X-ray emission by the Chandra X-ray Observatory stemming from the 2006 eruption of the recurrent nova RS Oph. The extended emission was detected 1254 and 1927 days after the start of the 2006 eruption and is consistent with a bipolar flow oriented in the East–West direction of the sky with opening angles of approximately 70°. The length of both lobes appeared to expand from 1.″3 in 2009 to 2.″0 in 2011, suggesting a projected expansion rate of 1.1 ± 0.1 mas day−1 and an expansion velocity of 4600 km s−1 (D/2.4 kpc) in the plane of the sky. This expansion rate is consistent with previous estimates from optical and radio observations of material in a similar orientation. The X-ray emission does not show any evidence of cooling between 2009 and 2011, consistent with free expansion of the material. This discovery suggests that some mechanism collimates ejecta away from the equatorial plane, and that after that material passes through the red giant wind, it expands freely into the cavity left by the 1985 eruption. We expect similar structures to arise from the latest eruption and to expand into the cavity shaped by the 2006 eruption.

Comparing the Heliospheric Cataloging, Analysis, and Techniques Service (HELCATS) Manual and Automatic Catalogues of Coronal Mass Ejections Using Solar Terrestrial Relations Observatory/Heliospheric Imager (STEREO/HI) Data

We present the results of a comparative study between automatic and manually compiled coronal mass ejection (CME) catalogues based on observations from the Heliospheric Imagers (HIs) onboard NASA’s Solar Terrestrial Relations Observatory (STEREO) spacecraft. Using the Computer Aided CME Tracking software (CACTus), CMEs are identified in HI data using an automatic feature-detection algorithm, while the Heliospheric Imagers Catalogue (HICAT) includes CMEs that are detected by visual inspection of HI images. Both catalogues were compiled as part of the EU FP7 Heliospheric Cataloguing, Analysis and Techniques Service (HELCATS) project ( ). We compare observational parameters of the CMEs from CACTus to those listed in HICAT, such as CME frequency, position angle (PA), and PA-width. We also compare CACTus-derived speeds to speeds derived from applying geometric modelling to the majority of the HICAT CMEs, the results of which are listed in the HELCATS Heliospheric Imagers Geometric Catalogue (HIGeoCAT). We find that both CACTus and HICAT catalogues contain a similar number of events when we exclude events narrower than 20∘, which are not included in the HICAT catalogue but are found to be identified by CACTus. PA-distributions are strongly peaked around 90∘ and 270∘, with a slightly larger CME frequency northwards of the equatorial plane (particularly for the STEREO-A versions of both catalogues). The CME PA-widths in both HICAT and CACTus catalogues peak at approximately 60∘. Manually derived speeds from HIGeoCAT and automatically derived speeds by CACTus correlate well for values lower than 1000 km s−1, in particular when CMEs are propagating close to the plane of the sky.

Dust Structure Nearby G229-03

The Sky View Virtual Observatory was used for the systematic search of dust structures within the far-infrared loop G229-03. The source (object) responsible for the formation of the cavity of interest was detected by the Set of Identifications, Measurements, and Bibliography for Astronomical Data (SIMBAD) database. The total mass of the loop was 8.50031 × 1029 kg which is about 0.425 times the mass of the Sun at a distance of 1300 pc. The size of the cavity was 3.67° × 3.6°, whereas its core size was 0.531° × 0.255° located at R.A. (J2000) = 7h10m0.8s and Dec.(J2000) =15h55m30s. The minimum and maximum temperatures were between 20.24 ± 1.16 K and 18.63 ± 1.96 K respectively. In the core region, the average temperature was 19.53 K, approximately equal to Gaussian center 19.267 K with an offset temperature of 0.4 K showing that the core region of the cavity is dynamically stable. The Far-infrared loop was found to be located within a 1° radius around the high-velocity cloud HVC oriented by 45° to the plane of the sky. The inclination angle of the core of the loop was greater than 60° whereas the inclination angle for the larger structure was 13.71°. The Gaussian distribution of temperature was well fitted with the center of 19.267 K which shows that the cavity was in thermal equilibrium and the outer region with offset temperature of about 35 K suggesting that the loop was dynamically unstable possibly due to high-velocity cloud

Multiwavelength and Dual-perspective Observations of Eruption and Untwisting of Two Homologous Magnetic Flux Ropes

Abstract In this paper, we present a detailed morphological, kinematic, and thermal analysis of two homologous magnetic flux ropes (MFRs) from NOAA 11515 on 2012 July 8–9. The study is based on multiwavelength and dual-perspective imaging observations from the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory Ahead spacecraft, which can reveal the structure and evolution of the two MFRs. We find that both of the MFRs show up in multiple passbands and their emissions mainly consist of a cold component peaking at a temperature of ∼0.4–0.6 MK and a hot component peaking at ∼7–8 MK. The two MFRs exhibit erupting, expanding, and untwisting motions that manifest distinctive features from two different viewpoints. Their evolution can be divided into two stages—a fast-eruption stage with speeds of about 105–125 km s−1 for MFR-1 and 50–65 km s−1 for MFR-2—and a slow-expansion (or untwisting) stage with speeds of about 10–35 km s−1 for MFR-1 and 10–30 km s−1 for MFR-2 in the plane of the sky. We also find that during the two-stage evolution, the high-temperature features mainly appear in the interface region between MFRs and ambient magnetic structures and also in the center of MFRs, which suggests that some heating processes take place in such places as magnetic reconnection and plasma compression. These observational results indicate that the eruption and untwisting processes of MFRs are coupled with the heating process, among which an energy conversion exists.

Mapping the Morphology and Kinematics of a Lyα-selected Nebula at z = 3.15 with MUSE

Abstract Recent wide-field integral-field spectroscopy has revealed the detailed properties of high-redshift Lyα nebulae, most often targeted due to the presence of an active galactic nucleus (AGN). Here, we use VLT/MUSE to resolve the morphology and kinematics of a nebula initially identified due to strong Lyα emission at z ∼ 3.2 (LABn06). Our observations reveal a two-lobed Lyα nebula, at least ∼173 pkpc in diameter, with a light-weighted centroid near a mid-infrared source (within ≈17.2 pkpc) that appears to host an obscured AGN. The Lyα emission near the AGN is also coincident in velocity with the kinematic center of the nebula, suggesting that the nebula is both morphologically and kinematically centered on the AGN. Compared to AGN-selected Lyα nebulae, the surface-brightness profile of this nebula follows a typical exponential profile at large radii (>25 pkpc), although at small radii, the profile shows an unusual dip at the location of the AGN. The kinematics and asymmetry are similar to, and the C iv and He ii upper limits are consistent with, other AGN-powered Lyα nebulae. Double-peaked and asymmetric line profiles suggest that Lyα resonant scattering may be important in this nebula. These results support the picture of the AGN being responsible for powering a Lyα nebula that is oriented roughly in the plane of the sky. Further observations will explore whether the central surface-brightness depression is indicative of either an unusual gas or dust distribution or variation in the ionizing output of the AGN over time.

Morpho-kinematics of the wind of asymptotic giant branch star L2 Pup

ABSTRACT Single-dish observations of asymptotic giant branch star L2 Pup have revealed exceptionally low mass-loss rate and expansion velocity, challenging interpretations in terms of standard wind models. Recent VLT and ALMA observations have drawn a detailed picture of the circumstellar envelope within ∼20 au from the centre of the star: a nearly edge-on rotating disc of gas and dust, probably hosting a planetary companion near the star. However, these observations provide no direct information on the wind escaping the gravity of the star. This article uses ALMA observations of the 12, 13CO(3-2), 29SiO(8-7), 12CO(2-1), and 28SiO(5-4) line emissions to shed new light on this issue. It shows the apparent normality of L2 Pup in terms of the formation of the nascent wind, with important line broadening within 4 au from the centre of the star, but no evidence for a wind flowing along the disc axis. At larger distances, up to some 200 au from the centre of the star, the wind morpho-kinematics is dominated by a disc, or equatorial enhancement, expanding isotropically and radially with a velocity not exceeding some 5 km s−1, inclined in the north-west/south-east direction with respect to the plane of the sky. In addition, outflows of lower density are observed on both sides of the disc, covering large solid angles about the disc axis, contributing about half the flux of the disc. Such morphology is at strong variance with the expectation of a pair of back-to-back outflows collimated by the central gas-and-dust disc.

A high-resolution view of the filament of gas between Abell 399 and Abell 401 from the Atacama Cosmology Telescope and MUSTANG-2

ABSTRACTWe report a significant detection of the hot intergalactic medium in the filamentary bridge connecting the galaxy clusters Abell 399 and Abell 401. This result is enabled by a low-noise, high-resolution map of the thermal Sunyaev–Zeldovich signal from the Atacama Cosmology Telescope (ACT) and Planck satellite. The ACT data provide the 1.65 arcmin resolution that allows us to clearly separate the profiles of the clusters, whose centres are separated by 37 arcmin, from the gas associated with the filament. A model that fits for only the two clusters is ruled out compared to one that includes a bridge component at >5σ. Using a gas temperature determined from Suzaku X-ray data, we infer a total mass of $(3.3\pm 0.7)\times 10^{14}\, \mathrm{M}_{\odot }$ associated with the filament, comprising about 8 per cent of the entire Abell 399–Abell 401 system. We fit two phenomenological models to the filamentary structure; the favoured model has a width transverse to the axis joining the clusters of ${\sim }1.9\, \mathrm{Mpc}$. When combined with the Suzaku data, we find a gas density of $(0.88\pm 0.24)\times 10^{-4}\, \mathrm{cm}^{-3}$, considerably lower than previously reported. We show that this can be fully explained by a geometry in which the axis joining Abell 399 and Abell 401 has a large component along the line of sight, such that the distance between the clusters is significantly greater than the $3.2\, \mathrm{Mpc}$ projected separation on the plane of the sky. Finally, we present initial results from higher resolution (12.7 arcsec effective) imaging of the bridge with the MUSTANG-2 receiver on the Green Bank Telescope.

Multiple components in the molecular outflow of the red supergiant NML Cyg

ABSTRACT Despite their large impact on stellar and galactic evolution, the properties of outflows from red supergiants are not well characterized. We used the Onsala 20m telescope to perform a spectral survey at 3 and 4 mm (68–116 GHz) of the red supergiant NML Cyg, alongside the yellow hypergiant IRC + 10420. Our observations of NML Cyg were combined with complementary archival data to enable a search for signatures of morphological complexity in the circumstellar environment, using emission lines from 15 molecular species. The recovered parameters imply the presence of three distinct, coherent, and persistent components, comprised of blue-shifted and red-shifted components, in addition to an underlying outflow centred at the stellar systemic velocity. Furthermore, to reproduce 12CO emission with 3D radiative transfer models required a spherical outflow with three superposed conical outflows, one towards and one away from the observer, and one in the plane of the sky. These components are higher in density than the spherical outflow by up to an order of magnitude. We hence propose that NML Cyg’s circumstellar environment consists of a small number of high-density large-scale coherent outflows embedded in a spherical wind. This would make the mass-loss history similar to that of VY CMa, and distinct from μ Cep, where the outflow contains many randomly distributed smaller clumps. A possible correlation between stellar properties, outflow structures, and content is critical in understanding the evolution of massive stars and their environmental impact.

Physically Motivated Fit to Mass Surface Density Profiles Observed in Galaxies

Abstract Polytropes have gained renewed interest because they account for several seemingly disconnected observational properties of galaxies. Here we study whether polytropes are also able to explain the stellar mass distribution within galaxies. We develop a code to fit surface density profiles using polytropes projected in the plane of the sky (propols). Sérsic profiles are known to be good proxies for the global shapes of galaxies and we find that, ignoring central cores, propols, and Sérsic profiles are indistinguishable within observational errors (within 5% over five orders of magnitude in surface density). The range of physically meaningful polytropes yields Sérsic indexes between 0.4 and 6. The code has been systematically applied to ∼750 galaxies with carefully measured mass density profiles and including all morphological types and stellar masses ( 7 < log [ M ⋆ / M ⊙ ] < 12 ). The propol fits are systematically better than Sérsic profiles when log ( M ⋆ / M ⊙ ) ≲ 9 and systematically worse when log ( M ⋆ / M ⊙ ) ≳ 10 . Although with large scatter, the observed polytropic indexes increase with increasing mass and tend to cluster around m = 5. For the most massive galaxies, propols are very good at reproducing their central parts, but they do not handle well cores and outskirts overall. Polytropes are self-gravitating systems in thermal meta-equilibrium as defined by the Tsallis entropy. Thus, the above results are compatible with the principle of maximum Tsallis entropy dictating the internal structure in dwarf galaxies and in the central region of massive galaxies.

Physical conditions in the warped accretion disk of a massive star

Young massive stars warm up the large amount of gas and dust that condenses in their vicinity, exciting a forest of lines from different molecular species. Their line brightness is a diagnostic tool of the gas’s physical conditions locally, which we use to set constraints on the environment where massive stars form. We made use of the Atacama Large Millimeter/submillimeter Array at frequencies near 349 GHz, with an angular resolution of 0′′.1, to observe the methyl cyanide (CH3CN) emission which arises from the accretion disk of a young massive star. We sample the disk midplane with twelve distinct beams, where we get an independent measure of the gas’s (and dust’s) physical conditions. The accretion disk extends above the midplane, showing a double-armed spiral morphology projected onto the plane of the sky, which we sample with ten additional beams: Along these apparent spiral features, gas undergoes velocity gradients of about 1 km s−1 per 2000 au. The gas temperature (T) rises symmetrically along each side of the disk, from about 98 K at 3000 au to 289 K at 250 au, following a power law with radius R−0.43. The CH3CN column density (N) increases from 9.2 × 1015 cm−2 to 8.7 × 1017 cm−2 at the same radii, following a power law with radius R−1.8. In the framework of a circular gaseous disk observed approximately edge-on, we infer an H2 volume density in excess of 4.8 ×109 cm−3 at a distance of 250 au from the star. We study the disk stability against fragmentation following the methodology by Kratter et al. (2010, ApJ, 708, 1585), which is appropriate under rapid accretion, and we show that the disk is marginally prone to fragmentation along its whole extent.