arXiv subjects

Takeshi Sakai

Publications and source records attributed to Takeshi Sakai.

At least 37 records · Page 2Linked to original sources

arXiv2024

Multiple chemical tracers finally unveil the intricate NGC\,1333 IRAS\,4A outflow system. FAUST XVI

The exploration of outflows in protobinary systems presents a challenging yet crucial endeavour, offering valuable insights into the dynamic interplay between protostars and their evolution. In this study, we examine the morphology and dynamics of jets and outflows within the IRAS\,4A protobinary system. This analysis is based on ALMA observations of SiO(5--4), H$_2$CO(3$_{0,3}$--2$_{0,3}$), and HDCO(4$_{1,4}$--3$_{1,3}$) with a spatial resolution of $\sim$150\,au. Leveraging an astrochemical approach involving the use of diverse tracers beyond traditional ones has enabled the identification of novel features and a comprehensive understanding of the broader outflow dynamics. Our analysis reveals the presence of two jets in the redshifted emission, emanating from IRAS\,4A1 and IRAS\,4A2, respectively. Furthermore, we identify four distinct outflows in the region for the first time, with each protostar, 4A1 and 4A2, contributing to two of them. We characterise the morphology and orientation of each outflow, challenging previous suggestions of bends in their trajectories. The outflow cavities of IRAS\,4A1 exhibit extensions of 10$''$ and 13$''$ with position angles (PA) of 0$^{\circ}$ and -12$^{\circ}$, respectively, while those of IRAS\,4A2 are more extended, spanning 18$''$ and 25$''$ with PAs of 29$^{\circ}$ and 26$^{\circ}$. We propose that the misalignment of the cavities is due to a jet precession in each protostar, a notion supported by the observation that the more extended cavities of the same source exhibit lower velocities, indicating they may stem from older ejection events.

astro-ph.GA↗

arXiv2024

The ALMA Survey of 70 $μ$m Dark High-mass Clumps in Early Stages (ASHES). XI. Statistical Study of Early Fragmentation

Fragmentation during the early stages of high-mass star formation is crucial for understanding the formation of high-mass clusters. We investigated fragmentation within thirty-nine high-mass star-forming clumps as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Survey of 70 $μ$m Dark High-mass Clumps in Early Stages (ASHES). Considering projection effects, we have estimated core separations for 839 cores identified from the continuum emission and found mean values between 0.08 and 0.32 pc within each clump. We find compatibility of the observed core separations and masses with the thermal Jeans length and mass, respectively. We also present sub-clump structures revealed by the 7 m-array continuum emission. Comparison of the Jeans parameters using clump and sub-clump densities with the separation and masses of gravitationally bound cores suggests that they can be explained by clump fragmentation, implying the simultaneous formation of sub-clumps and cores within rather than a step-by-step hierarchical fragmentation. The number of cores in each clump positively correlates with the clump surface density and the number expected from the thermal Jeans fragmentation. We also find that the higher the fraction of protostellar cores, the larger the dynamic range of the core mass, implying that the cores are growing in mass as the clump evolves. The ASHES sample exhibits various fragmentation patterns: aligned, scattered, clustered, and sub-clustered. Using the Q-parameter, which can help to distinguish between centrally condensed and subclustered spatial core distributions, we finally find that in the early evolutionary stages of high-mass star formation, cores tend to follow a subclustered distribution.

astro-ph.GA↗

arXiv2024

Observations of high-order multiplicity in a high-mass stellar protocluster

The dominant mechanism forming multiple stellar systems in the high-mass regime (M$_\ast \gtrsim $ 8 $M_{\odot}$) remained unknown because direct imaging of multiple protostellar systems at early phases of high-mass star formation is very challenging. High-mass stars are expected to form in clustered environments containing binaries and higher-order multiplicity systems. So far only a few high-mass protobinary systems, and no definitive higher-order multiples, have been detected. Here we report the discovery of one quintuple, one quadruple, one triple and four binary protostellar systems simultaneously forming in a single high-mass protocluster, G333.23--0.06, using Atacama Large Millimeter/submillimeter Array high-resolution observations. We present a new example of a group of gravitationally bound binary and higher-order multiples during their early formation phases in a protocluster. This provides the clearest direct measurement of the initial configuration of primordial high-order multiple systems, with implications for the in situ multiplicity and its origin. We find that the binary and higher-order multiple systems, and their parent cores, show no obvious sign of disk-like kinematic structure. We conclude that the observed fragmentation into binary and higher-order multiple systems can be explained by core fragmentation, indicating its crucial role in establishing the multiplicity during high-mass star cluster formation.

astro-ph.GA↗

arXiv2023

The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). X: Hot Gas Reveals Deeply Embedded Star Formation

Massive infrared dark clouds (IRDCs) are considered to host the earliest stages of high-mass star formation. In particular, 70 $μ$m dark IRDCs are the colder and more quiescent clouds. At a scale of about 5000 au using formaldehyde (H2CO) emission, we investigate the kinetic temperature of dense cores in 12 IRDCs obtained from the pilot ALMA Survey of 70 $μ$m dark High-mass clumps in Early Stages (ASHES). Compared to 1.3 mm dust continuum and other molecular lines, such as C18O and deuterated species, we find that H2CO is mainly sensitive to low-velocity outflow components rather than to quiescent gas expected in the early phases of star formation. The kinetic temperatures of these components range from 26 to 300 K. The Mach number reaches about 15 with an average value of about 4, suggesting that the velocity distribution of gas traced by H2CO is significantly influenced by a supersonic non-thermal component. In addition, we detect warm line emission from HC3N and OCS in 14 protostellar cores, which requires high excitation temperatures (Eu/k ~ 100 K). These results show that some of the embedded cores in the ASHES fields are in an advanced evolutionary stage, previously unexpected for 70 $μ$m dark IRDCs.

astro-ph.GA↗

arXiv2023

Digging into the Interior of Hot Cores with ALMA: Spiral Accretion into the High-mass Protostellar Core G336.01-0.82

We observed the high-mass star-forming core G336.01-0.82 at 1.3 mm and 0.05'' (~150 au) angular resolution with the Atacama Large Millimeter/submillimeter Array (ALMA) as part of the Digging into the Interior of Hot Cores with ALMA (DIHCA) survey. These high-resolution observations reveal two spiral streamers feeding a circumstellar disk at opposite sides in great detail. Molecular line emission from CH$_3$OH shows velocity gradients along the streamers consistent with infall. Similarly, a flattened envelope model with rotation and infall implies a mass larger than 10 M$_\odot$ for the central source and a centrifugal barrier of 300 au. The location of the centrifugal barrier is consistent with local peaks in the continuum emission. We argue that gas brought by the spiral streamers is accumulating at the centrifugal barrier, which can result in future accretion burst events. A total high infall rate of ~$4\times10^{-4}$ M$_\odot$ yr$^{-1}$ is derived by matching models to the observed velocity gradient along the streamers. Their contribution account for 20-50% the global infall rate of the core, indicating streamers play an important role in the formation of high-mass stars.

astro-ph.GA↗

arXiv2023

FAUST X: Formaldehyde in the Protobinary System [BHB2007] 11: Small Scale Deuteration

Context. Deuterium in H-bearing species is enhanced during the early stages of star formation, however, only a small number of high spatial resolution deuteration studies exist towards protostellar objects, leaving the small-scale structures unrevealed and understudied. Aims. We aim to constrain the deuterium fractionation ratios in a Class 0/I protostellar object in formaldehyde (H2CO), which has abundant deuterated isotopologues in this environment. Methods. We observed the Class 0/I protobinary system [BHB2007] 11, whose emission components are embedded in circumstellar disks that have radii of 2-3 au, using ALMA within the context of the Large Program FAUST. The system is surrounded by a complex filamentary structure connecting to the larger circumbinary disk. In this work we present the first study of formaldehyde D-fractionation towards this source with detections of H2CO 3(0,3)-2(0,2), combined with HDCO 4(2,2)-3(2,1), HDCO 4(1,4)-3(1,3) and D2CO 4(0,4)-3(0,3). These observations enable multiple velocity components associated with the methanol hotspots also uncovered by FAUST data, as well as the external envelope, to be resolved. In addition, based on the kinematics seen in the observations of the H2CO emission, we propose the presence of a second large scale outflow. Results. HDCO and D2CO are only found in the central regions of the core while H2CO is found more ubiquitously. From radiative transfer modelling, the column densities ranges found for H2CO, HDCO and D2CO are (3-8)x10$^{14}$ cm$^{-2}$, (0.8-2.9)x10$^{13}$ cm$^{-2}$ and (2.6-4.3)x10$^{12}$ cm$^{-2}$, respectively, yielding an average D/H ratio of 0.01-0.04. Following the results of kinematic modelling, the second large scale feature is inconsistent with a streamer-like nature and we thus tentatively conclude that the feature is an asymmetric molecular outflow launched by a wide-angle disk wind.

astro-ph.GA↗

arXiv2023

The ALMA Survey of 70 $μ$m Dark High-mass Clumps in Early Stages (ASHES). IX. Physical Properties and Spatial Distribution of Cores in IRDCs

The initial conditions found in infrared dark clouds (IRDCs) provide insights on how high-mass stars and stellar clusters form. We have conducted high-angular resolution and high-sensitivity observations toward thirty-nine massive IRDC clumps, which have been mosaicked using the 12m and 7m arrays from the Atacama Large Millimeter/submillimeter Array (ALMA). The targets are 70 $μ$m dark massive (220-4900 $M_\odot$), dense ($>$10$^4$ cm$^{-3}$), and cold ($\sim$10-20K) clumps located at distances between 2 and 6 kpc. We identify an unprecedented number of 839 cores, with masses between 0.05 and 81 $M_\odot$ using 1.3 mm dust continuum emission. About 55% of the cores are low-mass ($<$1 $M_\odot$), whereas $\lesssim$1% (7/839) are high-mass ($\gtrsim$27 $M_\odot$). We detect no high-mass prestellar cores. The most massive cores (MMC) identified within individual clumps lack sufficient mass to form high-mass stars without additional mass feeding. We find that the mass of the MMCs is correlated with the clump surface density, implying denser clumps produce more massive cores and a larger number of cores. There is no significant mass segregation except for a few tentative detections. In contrast, most clumps show segregation once the clump density is considered instead of mass. Although the dust continuum emission resolves clumps in a network of filaments, some of which consist of hub-filament systems, the majority of the MMCs are not found in the hubs. Our analysis shows that high-mass cores and MMCs have no preferred location with respect to low-mass cores at the earliest stages of high-mass star formation.

astro-ph.GA↗

arXiv2022

The ALMA Survey of 70 $μ\rm m$ Dark High-mass Clumps in Early Stages (ASHES). VII: Chemistry of Embedded Dense Cores

We present a study of chemistry toward 294 dense cores in 12 molecular clumps using the data obtained from the ALMA Survey of 70 $μ\rm m$ dark High-mass clumps in Early Stages (ASHES). We identified 97 protostellar cores and 197 prestellar core candidates based on the detection of outflows and molecular transitions of high upper energy levels ($E_{u}/k > 45$ K). The detection rate of the N$_{2}$D$^{+}$ emission toward the protostellar cores is 38%, which is higher than 9% for the prestellar cores, indicating that N$_{2}$D$^{+}$ does not exclusively trace prestellar cores. The detection rates of the DCO$^{+}$ emission are 35% for the prestellar cores and 49% for the protostellar cores, which are higher than those of N$_{2}$D$^{+}$, implying that DCO$^{+}$ appears more frequently than N$_{2}$D$^{+}$ in both prestellar and protostellar cores. Both N$_{2}$D$^{+}$ and DCO$^{+}$ abundances appear to decrease from the prestellar to protostellar stage. The DCN, C$_{2}$D and $^{13}$CS emission lines are rarely seen in the dense cores of early evolutionary phases. The detection rate of the H$_{2}$CO emission toward dense cores is 52%, three times higher than that of CH$_{3}$OH (17%). In addition, the H$_{2}$CO detection rate, abundance, line intensities, and line widths increase with the core evolutionary status, suggesting that the H$_{2}$CO line emission is sensitive to protostellar activity.

astro-ph.GA↗

arXiv2022

The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). VI. The core-scale CO-depletion

Studying the physical and chemical properties of cold and dense molecular clouds is crucial for the understanding of how stars form. Under the typical conditions of infrared dark clouds, CO is removed from the gas phase and trapped on to the surface of dust grains by the so-called depletion process. This suggests that the CO depletion factor ($f_{\rm D}$) can be a useful chemical indicator for identifying cold and dense regions (i.e., prestellar cores). We have used the 1.3 mm continuum and C$^{18}$O(2-1) data observed at the resolution of $\sim$5000 au in the ALMA Survey of 70 $μ$m Dark High-mass Clumps in Early Stages (ASHES) to construct averaged maps of $f_{\rm D}$ in twelve clumps to characterise the earliest stages of the high-mass star formation process. The average $f_{\rm D}$ determined for 277 of the 294 ASHES cores follows an unexpected increase from the prestellar to the protostellar stage. If we exclude the temperature effect due to the slight variations in the NH$_3$ kinetic temperature among different cores, we explain this result as a dependence primarily on the average gas density, which increases in cores where protostellar conditions prevail. This shows that $f_{\rm D}$ determined in high-mass star-forming regions at the core scale is insufficient to distinguish among prestellar and protostellar conditions for the individual cores, and should be complemented by information provided by additional tracers. However, we confirm that the clump-averaged $f_{\rm D}$ values correlates with the luminosity-to-mass ratio of each source, which is known to trace the evolution of the star formation process.

astro-ph.GA↗

arXiv2022

Nobeyama Survey of Inward Motions toward Cores in Orion Identified by SCUBA-2

In this study, 36 cores (30 starless and 6 protostellar) identified in Orion were surveyed to search for inward motions. We used the Nobeyama 45 m radio telescope, and mapped the cores in the $J = 1\rightarrow0$ transitions of HCO$^+$, H$^{13}$CO$^+$, N$_2$H$^+$, HNC, and HN$^{13}$C. The asymmetry parameter $δV$, which was the ratio of the difference between the HCO$^+$ and H$^{13}$CO$^+$ peak velocities to the H$^{13}$CO$^+$ line width, was biased toward negative values, suggesting that inward motions were more dominant than outward motions. Three starless cores (10% of all starless cores surveyed) were identified as cores with blue-skewed line profiles (asymmetric profiles with more intense blue-shifted emission), and another two starless cores (7%) were identified as candidate blue-skewed line profiles. The peak velocity difference between HCO$^+$ and H$^{13}$CO$^+$ of them was up to 0.9 km s$^{-1}$, suggesting that some inward motions exceeded the speed of sound for the quiescent gas ($\sim10-17$ K). The mean of $δV$ of the five aforementioned starless cores was derived to be $-$0.5$\pm$0.3. One core, G211.16$-$19.33North3, observed using the ALMA ACA in DCO$^+$ $J = 3\rightarrow2$ exhibited blue-skewed features. Velocity offset in the blue-skewed line profile with a dip in the DCO$^+$ $J = 3\rightarrow2$ line was larger ($\sim 0.5$ km s$^{-1}$) than that in HCO$^+$ $J = 1\rightarrow0$ ($\sim 0.2$ km s$^{-1}$), which may represent gravitational acceleration of inward motions. It seems that this core is at the last stage in the starless phase, judging from the chemical evolution factor version 2.0 (CEF2.0).

astro-ph.GA↗

arXiv2022

Digging into the Interior of Hot Cores with ALMA (DIHCA). II. Exploring the Inner Binary (Multiple) System Embedded in G335 MM1 ALMA1

We observed the high-mass protostellar core G335.579-0.272 ALMA1 at ${\sim}200$ au (0.05") resolution with the Atacama Large Millimeter/submillimeter Array (ALMA) at 226 GHz (with a mass sensitivity of $5σ=0.2$ M$_\odot$ at 10 K). We discovered that at least a binary system is forming inside this region, with an additional nearby bow-like structure (${\lesssim}1000$ au) that could add an additional member to the stellar system. These three sources are located at the center of the gravitational potential well of the ALMA1 region and the larger MM1 cluster. The emission from CH$_3$OH (and many other tracers) is extended ($>1000$ au), revealing a common envelope toward the binary system. We use CH$_2$CHCN line emission to estimate an inclination angle of the rotation axis of $26^\circ$ with respect to the line of sight based on geometric assumptions and derive a kinematic mass of the primary source (protostar+disk) of 3.0 M$_\odot$ within a radius of 230 au. Using SiO emission, we find that the primary source drives the large scale outflow revealed by previous observations. Precession of the binary system likely produces a change in orientation between the outflow at small scales observed here and large scales observed in previous works. The bow structure may have originated by entrainment of matter into the envelope due to widening or precession of the outflow, or, alternatively, an accretion streamer dominated by the gravity of the central sources. An additional third source, forming due to instabilities in the streamer, cannot be ruled out as a temperature gradient is needed to produce the observed absorption spectra.

astro-ph.GA↗

arXiv2022

FAUST III. Misaligned rotations of the envelope, outflow, and disks in the multiple protostellar system of VLA 1623$-$2417

We report a study of the low-mass Class-0 multiple system VLA 1623AB in the Ophiuchus star-forming region, using H$^{13}$CO$^+$ ($J=3-2$), CS ($J=5-4$), and CCH ($N=3-2$) lines as part of the ALMA Large Program FAUST. The analysis of the velocity fields revealed the rotation motion in the envelope and the velocity gradients in the outflows (about 2000 au down to 50 au). We further investigated the rotation of the circum-binary VLA 1623A disk as well as the VLA 1623B disk. We found that the minor axis of the circum-binary disk of VLA 1623A is misaligned by about 12 degrees with respect to the large-scale outflow and the rotation axis of the envelope. In contrast, the minor axis of the circum-binary disk is parallel to the large-scale magnetic field according to previous dust polarization observations, suggesting that the misalignment may be caused by the different directions of the envelope rotation and the magnetic field. If the velocity gradient of the outflow is caused by rotation, the outflow has a constant angular momentum and the launching radius is estimated to be $5-16$ au, although it cannot be ruled out that the velocity gradient is driven by entrainments of the two high-velocity outflows. Furthermore, we detected for the first time a velocity gradient associated with rotation toward the VLA 16293B disk. The velocity gradient is opposite to the one from the large-scale envelope, outflow, and circum-binary disk. The origin of its opposite gradient is also discussed.

astro-ph.GA↗

arXiv2021

The ALMA Survey of 70 $μ$m Dark High-mass Clumps in Early Stages (ASHES). V. Deuterated Molecules in the 70 $μ$m dark IRDC G14.492-00.139

We have observed the 70 $μ$m dark infrared dark cloud (IRDC) G14.492-00.139 in the N$_2$D$^+$ $J$=3--2, DCO$^+$ $J$=3--2, DCN $J$=3--2, and C$^{18}$O $J$=2--1 lines, using the Atacama Large Millimeter/submillimeter Array (ALMA) as part of the ALMA Survey of 70 $μ$m Dark High-mass Clumps in Early Stages (ASHES). We find that the spatial distribution is different among the observed emission from the deuterated molecular lines. The N$_2$D$^+$ emission traces relatively quiescent regions, while both the DCO$^+$ and DCN emission emanates mainly from regions with signs of active star-formation. In addition, the DCO$^+$/N$_2$D$^+$ ratio is found to be lower in several dense cores than in starless cores embedded in low-mass star-forming regions. By comparing the observational results with chemical model calculations, we discuss the origin of the low DCO$^+$/N$_2$D$^+$ ratio in this IRDC clump. The low DCO$^+$/N$_2$D$^+$ ratio can be explained if the temperature of the dense cores is in the range between the sublimation temperature of N$_2$ ($\sim$20 K) and CO ($\sim$25 K). The results suggest that the dense cores in G14.492-00.139 are warmer and denser than the dense cores in low-mass star-forming regions.

astro-ph.GA↗

arXiv2021

The ALMA Survey of 70 $μ$m Dark High-mass Clumps in Early Stages (ASHES). IV. Star formation signatures in G023.477

With a mass of $\sim$1000 $M_\odot$ and a surface density of $\sim$0.5 g cm$^{-2}$, G023.477+0.114 also known as IRDC 18310-4 is an infrared dark cloud (IRDC) that has the potential to form high-mass stars and has been recognized as a promising prestellar clump candidate. To characterize the early stages of high-mass star formation, we have observed G023.477+0.114 as part of the ALMA Survey of 70 $μ$m Dark High-mass Clumps in Early Stages (ASHES). We have conducted $\sim$1."2 resolution observations with the Atacama Large Millimeter/submillimeter Array (ALMA) at 1.3 mm in dust continuum and molecular line emission. We identified 11 cores, whose masses range from 1.1 $M_\odot$ to 19.0 $M_\odot$. Ignoring magnetic fields, the virial parameters of the cores are below unity, implying that the cores are gravitationally bound. However, when magnetic fields are included, the prestellar cores are close to virial equilibrium, while the protostellar cores remain sub-virialized. Star formation activity has already started in this clump. Four collimated outflows are detected in CO and SiO. H$_2$CO and CH$_3$OH emission coincide with the high-velocity components seen in the CO and SiO emission. The outflows are randomly oriented for the natal filament and the magnetic field. The position-velocity diagrams suggest that episodic mass ejection has already begun even in this very early phase of protostellar formation. The masses of the identified cores are comparable to the expected maximum stellar mass that this IRDC could form (8-19 $M_\odot$). We explore two possibilities on how IRDC G023.477+0.114 could eventually form high-mass stars in the context of theoretical scenarios.

astro-ph.GA↗

arXiv2021

Exploring the 100 au Scale Structure of the Protobinary System NGC 2264 CMM3 with ALMA

We have observed the young protostellar system NGC 2264 CMM3 in the 1.3 mm and 2.0 mm bands at a resolution of about 0.1$"$ (70 au) with ALMA. The structures of two distinct components, CMM3A and CMM3B, are resolved in the continuum images of both bands. CMM3A has an elliptical structure extending along the direction almost perpendicular to the known outflow, while CMM3B reveals a round shape. We have fitted two 2D-Gaussian components to the elliptical structure of CMM3A and CMM3B, and have separated the disk and envelope components for each source. The spectral index $α$ between 2.0 mm and 0.8 mm is derived to be 2.4-2.7 and 2.4-2.6 for CMM3A and CMM3B, respectively, indicating the optically thick dust emission and/or the grain growth. A velocity gradient in the disk/envelope direction is detected for CMM3A in the CH$_3$CN, CH$_3$OH, and $^{13}$CH$_3$OH lines detected in the 1.3 mm band, which can be interpreted as the rotation of the disk/envelope system. From this result, the protostellar mass of CMM3A is roughly evaluated to be $0.1- 0.5$ $M_\odot$ by assuming Keplerian rotation. The mass accretion rate is thus estimated to be $5\times10^{-5}$ - 4 $\times$ $10^{-3}$ $M_\odot$ yr$^{-1}$, which is higher than typical mass accretion rate of low-mass protostars. The OCS emission line shows a velocity gradient in both outflow direction and disk/envelope direction. A hint of outflow rotation is found, and the specific angular momentum of the outflow is estimated to be comparable to that of the disk. These results provide us with novel information on the initial stage of a binary/multiple system.

astro-ph.GA↗

arXiv2021

Diamond anvil cell with boron-doped diamond heater for high-pressure synthesis and in-situ transport measurements

Temperature and pressure are essential parameters in the synthesis, evaluation, and application of functional materials. This study proposes the addition of a heating function to a high-pressure diamond anvil cell (DAC) with in-situ measurement probes. The proposed DAC allows for simultaneous control of temperature and pressure within the sample space and can be used to synthesize functional materials under extreme conditions. The various components, namely the heater, thermometer, and measurement probes, were fabricated with a boron-doped diamond epitaxial film and could be used repeatedly. The developed DAC was used to successfully conduct the high-pressure annealing of La(O,F)BiS$_{2}$ single crystal and the high-pressure synthesis of EuFBiS$_{2}$ superconductors. The proposed technique shows promise for further exploration of superconductors to broaden the research field.

cond-mat.supr-con↗

arXiv2021

Molecular Cloud Cores with High Deuterium Fractions: Nobeyama Mapping Survey

We present the results of on-the-fly mapping observations of 44 fields containing 107 SCUBA-2 cores in the emission lines of molecules, N$_2$H$^+$, HC$_3$N, and CCS at 82$-$94 GHz using the Nobeyama 45-m telescope. This study aimed at investigating the physical properties of cores that show high deuterium fractions and might be close to the onset of star formation. We found that the distributions of the N$_2$H$^+$ and HC$_3$N line emissions are approximately similar to that of 850-$μ$m dust continuum emission, whereas the CCS line emission is often undetected or is distributed in a clumpy structure surrounding the peak position of the 850-$μ$m dust continuum emission. Occasionally (12%), we observe the CCS emission which is an early-type gas tracer toward the young stellar object, probably due to local high excitation. Evolution toward star formation does not immediately affect nonthermal velocity dispersion.

astro-ph.GA↗

arXiv2021

Gravity Driven Magnetic Field at ~1000 au Scales in High-mass Star Formation

A full understanding of high-mass star formation requires the study of one of the most elusive components of the energy balance in the interstellar medium: magnetic fields. We report ALMA 1.2 mm, high-resolution (700 au) dust polarization and molecular line observations of the rotating hot molecular core embedded in the high-mass star-forming region IRAS 18089-1732. The dust continuum emission and magnetic field morphology present spiral-like features resembling a whirlpool. The velocity field traced by the H13CO+ (J=3-2) transition line reveals a complex structure with spiral filaments that are likely infalling and rotating, dragging the field with them. We have modeled the magnetic field and find that the best model corresponds to a weakly magnetized core with a mass-to-magnetic-flux ratio (lambda) of 8.38. The modeled magnetic field is dominated by a poloidal component, but with an important contribution from the toroidal component that has a magnitude of 30% of the poloidal component. Using the Davis-Chandrasekhar-Fermi method, we estimate a magnetic field strength of 3.5 mG. At the spatial scales accessible to ALMA, an analysis of the energy balance of the system indicates that gravity overwhelms turbulence, rotation, and the magnetic field. We show that high-mass star formation can occur in weakly magnetized environments, with gravity taking the dominant role.

astro-ph.GA↗