Abstract
We study the magnetic field structures in six giant filaments associated with the spiral arms of the Milky Way by applying the velocity gradient technique (VGT) to the
13
CO spectroscopic ...data from the GRS, FUGIN, and SEDIGSM surveys. Unlike dust-polarized emission, the VGT allows us to separate the foreground and background using the velocity information, from which the orientation of the magnetic field can be reliably determined. We find that in most cases the magnetic fields stay aligned with the filament bodies, which are parallel to the disk midplane. Among these, G29, G47, and G51 exhibit smooth magnetic fields, and G24, G339, and G349 exhibit discontinuities. The fact that most filaments have magnetic fields that stay aligned with the Galactic disk midplane suggests that Galactic shear may be responsible for shaping the filaments. The fact that the magnetic field can stay regular at the resolution of our analysis (≲10 pc), where the turbulence crossing time is short compared to the shear time, suggests that turbulent motion cannot effectively disrupt the regular orientation of the magnetic field. The discontinuities found in some filaments can be caused by processes including filament reassembly, gravitational collapse, and stellar feedback.
Jurassic soft rocks are the main coal-bearing strata in western mining areas, which are rich in water and high in expansive minerals. The roof and floor of the coal seam are easily muddied and ...disintegrated when affected by water, and heave floor of roadway in soft rock has become one of the problems that restricts the safety and efficient production of coal mines in western mining areas. It is not ideal for the effect of the traditional roadway control theory on geological soft rock roadway support, and the deformation is difficult to control. Take the tailgate of 11506 working face of a coal mine in the western mining area as the research background. This surrounding rock conditions and the deformation characteristics of the roadway in tailgate of 11506 working face were analyzed systematically, and the optimization design of the support scheme of the water-rich soft rock roadway was carried out by using theoretical analysis and numerical simulation. The application of the support in the tailgate of 11506 working face was carried out. The results show that slip of the two sidewalls, support failure, stress concentration, and floor heave were failure characteristics in water-rich soft rock roadway. The optimization of the roadway section, thin guniting of the roadway surface, optimization of support components, and gradient support could effectively achieve the control of soft rock roadway deformation. The maximum floor heave during the roadway deformation monitoring period was 230 mm, which decreased about 75% compared with original support. The influence range of the advance abutment stress is 0~60 m, of which 0~30 m is the serious influence area. The research results have good engineering practice significance for the control of bottom bulge of the soft rock roadway in this coal mine and western mining area.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Abstract We report the detection of the ordered alignment between the magnetic field and kpc-scale bubbles in the nearby spiral galaxy, NGC 628. Applying the Velocity Gradient Technique on CO ...spectroscopic data from the ALMA-PHANGS, the magnetic field of NGC 628 is measured at the scale of 191 pc (∼4″). The large-scale magnetic field is oriented parallel to the spiral arms and curves around the galactic bubble structures in the mid-infrared emission observed by the James Webb Space Telescope. A total of 21 bubble structures have been identified at the edges of spiral arms with scales over 300 pc, which includes two kpc-scale structures. These bubbles are caused by supernova remnants and prolonged star formation and are similar to the outflow chimneys found in neutral hydrogen in galactic disks. At the edge of the bubbles, the shocks traced by the O iii emission present a curved magnetic field that parallels the bubble’s shell. The magnetic field follows the bubble expansion and binds the gas in the shell to trigger further star formation. By analyzing the larger sample of 1694 bubbles, we found a distinct radial-size distribution of bubbles in NGC 628 indicating the star formation history in the galaxy.
Abstract We report high angular resolution observations, made with the Atacama Large Millimeter Array in band 6, of high excitation molecular lines of CH 3 CN and SO 2 and of the H29 α radio ...recombination line toward the G345.0061+01.794 B HC H ii region in order to investigate the physical and kinematical characteristics of its surroundings. Emission was detected in all observed components of the J = 14 →13 rotational ladder of CH 3 CN and in the 30 4,26 –30 3,27 , and 32 4,28 –32 3,29 lines of SO 2 . The peak of the velocity-integrated molecular emission is located ∼0.″4 northwest of the peak of the continuum emission. The first-order moment images and channel maps show a velocity gradient of 1.1 km s −1 arcsec −1 across the source and a distinctive spot of blueshifted emission toward the peak of the zero-order moment. The rotational temperature is found to decrease from 252±24 K at the peak position to 166±16 K at its edge, indicating that our molecular observations are probing a hot molecular core that is internally excited. The emission in the H29 α line arises from a region of 0.″65 in size, where its peak coincides with that of the dust continuum. We model the kinematical characteristics of the “central blue spot” feature as due to infalling motions, suggesting a central mass of 172.8±8.8 M ⊙ . Our observations indicate that this HC H ii region is surrounded by a compact structure of hot molecular gas, which is rotating and infalling toward a central mass, that is most likely confining the ionized region. The observed scenario is reminiscent of a “butterfly pattern” with an approximately edge-on torus and ionized gas roughly parallel to its rotation axis.
Context. Recent observations suggest a scenario in which filamentary structures in the interstellar medium represent the first step towards clumps/cores and eventually star formation. The densest ...filaments would then fragment into prestellar cores owing to gravitational instability. Aims. We seek to understand the roles filamentary structures play in high-mass star formation. Methods. We mapped the integral-shaped filament (ISF) located at the northern end of the Orion A molecular cloud in NH3 (1, 1) and (2, 2). The observations were made using the 25 m radio telescope operated by the Xinjiang Astronomical Observatory, Chinese Academy of Sciences. The whole filamentary structure, about 1.2° × 0.6°, is uniformly and fully sampled. We investigate the morphology, fragmentation, kinematics, and temperature properties in this region. Results. We find that the morphology revealed by the map of velocity-integrated intensity of the NH3 (1, 1) line is closely associated with the dust ridge revealed by the Herschel Space Observatory. We identify 6 “lumps” related to the well known OMC-1 to 5 and 11 “sub-clumps” within the map. The clumps and sub-clumps are separated not randomly but in roughly equal intervals along the ISF. The average spacing of clumps is 11.30′ ± 1.31′ (1.36 ± 0.16 pc) and the average spacing of sub-clumps is 7.18′ ± 1.19′ (0.86 ± 0.14 pc). These spacings agree well with the predicted values of the thermal (0.86 pc) and turbulent sausage instability (1.43 pc) by adopting a cylindric geometry of the ISF with an inclination of 60° with respect to the line of sight. We also find a velocity gradient of about 0.6 km s−1 pc−1 that runs along the ISF which likely arises from an overall rotation of the Orion A molecular cloud. The inferred ratio between rotational and gravitational energy is well below unity. Furthermore, fluctuations are seen in the centroid velocity diagram along the ISF. The OMC-1 to 5 clouds are located close to the local extrema of the fluctuations, which suggests that there exist gas flows associated with these clumps in the ISF. The derived NH3 (1, 1) and (2, 2) rotation temperatures in the OMC-1 are about 30–40 K while lower temperatures (below 20 K) are obtained in the northern and southern parts of the ISF. In OMC-2, OMC-3, and the northern part of OMC-4, we find higher and lower temperatures at the boundaries and in the interior, respectively.
ABSTRACT
Investigating the physical and chemical structure of massive star-forming regions is critical for understanding the formation and early evolution of massive stars. We performed a detailed ...line survey toward six dense cores, named MM1, MM4, MM6, MM7, MM8, and MM11, in the G9.62+0.19 star-forming region resolved in Atacama Large Millimeter/submillimeter Array (ALMA) band 3 observations. Toward these cores, about 172 transitions have been identified and attributed to 16 species, including organic oxygen-, nitrogen-, and sulphur-bearing molecules and their isotopologues. Four dense cores, MM7, MM8, MM4, and MM11, are line-rich sources. Modelling of these spectral lines reveals that the rotational temperature lies in the range 72–115, 100–163, 102–204, and 84–123 K for MM7, MM8, MM4, and MM11, respectively. The molecular column densities are 1.6 × 1015–9.2 × 1017 cm−2 toward the four cores. The cores MM8 and MM4 show a chemical difference between oxygen- and nitrogen-bearing species, i.e. MM4 is rich in oxygen-bearing molecules, while nitrogen-bearing molecules, especially vibrationally excited HC3N lines, are mainly observed in MM8. The distinct initial temperatures at the accretion phase may lead to this N/O differentiation. Through analysing column densities and spatial distributions of O-bearing complex organic molecules (COMs), we found that C2H5OH and CH3OCH3 might have a common precursor, CH3OH. CH3OCHO and CH3OCH3 are likely chemically linked. In addition, the observed variation in HC3N and HC5N emission may indicate their different formation mechanisms in hot and cold regions.
Aims.
We investigate the role of selective dissociation in the process of star formation by comparing the physical parameters of protostellar-prestellar cores and the selected regions with the CO ...isotope distributions in photo-dissociation regions. We seek to understand whether there is a better connection between the evolutionary age of star forming regions and the effect of selective dissociation
Methods.
We used wide-field observations of the
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CO,
13
CO, and C
18
O (
J
= 1–0) emission lines to study the ongoing star formation activity in the Aquila molecular region, and we used the 70 and 250
μ
m data to describe the heating of the surrounding material and as an indicator of the evolutionary age of the core.
Results.
The protostellar-prestellar cores are found at locations with the highest C
18
O column densities and their increasing evolutionary age coincides with an increasing 70
μ
m/250
μ
m emission ratio at their location. The evolutionary age of the cores may also follow from the
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CO versus C
18
O abundance ratio, which decreases with increasing C
18
O column densities. The original mass has been estimated for nine representative star formation regions and the original mass of the region correlates well with the integrated 70
μ
m flux density. Similarly, the
X
13
CO
/
X
C
18
O
ratio, which provides the dissociation rate for these regions correlates with the 70
μ
m/250
μ
m flux density ratio and reflects the evolutionary age of the star formation activity.
ABSTRACT
A total of 188 high-mass outflows have been identified from a sample of 694 clumps from the Millimetre Astronomy Legacy Team 90 GHz survey, representing a detection rate of approximately ...27 per cent. The detection rate of outflows increases from the proto-stellar stage to the H ii stage, but decreases again at the photodissociation (PDR) stage suggesting that outflows are being switched off during the PDR stage. An intimate relationship is found between outflow action and the presence of masers, and water masers appear together with 6.7 GHz methanol masers. Comparing the infall detection rate of clumps with and without outflows, we find that outflow candidates have a lower infall detection rate. Finally, we find that outflow action has some influence on the local environment and the clump itself, and this influence decreases with increasing evolutionary time as the outflow action ceases.
We mapped the kinetic temperature structure of Orion KL in a ∼20″ (∼8000 au) sized region with para-H2CS 707 − 606, 726 − 625, and 725 − 624 making use of Atacama Large Millimeter/submillimeter Array ...Band 6 Science Verification data. The kinetic temperatures obtained with a resolution of 1 65 × 1 14 (∼550 au) are deduced by modeling the measured averaged velocity-integrated intensity ratios of para-H2CS 726 − 625/707 − 606 and 725 − 624/707 − 606 with a RADEX non-LTE model. The kinetic temperatures of the dense gas, derived from the para-H2CS line ratios at a spatial density of 107 cm−3, are high, ranging from 43 to >500 K with an unweighted average of ∼170 K. There is no evidence for internal sources playing an important role in the heating of the various structures identified in previous work, namely the elongated ridge, the northwestern clump, and the eastern region of the compact ridge, while the high temperatures in the western region of the compact ridge may be dominated by internal massive star formation. Significant gradients of kinetic temperature along molecular filaments traced by H2CS indicate that the dense gas is heated by the shocks induced by the enigmatic explosive event which occurred several hundred years ago and greatly affected the energetics of the Orion KL region. Thus, with the notable exception of the western region of the compact ridge, the high temperatures of the dense gas in Orion KL are probably caused by shocks from the explosive event, leading to a dominant component of externally heated dense gas.
An unbiased search of molecular outflows within the region of the CO High Resolution survey has identified 157 high-mass outflows from a sample of 770 APEX Telescope Large Area Survey of the Galaxy ...clumps with a detection rate of 20%. The detection rate of outflows increases for clumps with higher Mclump, Lbol, Lbol/Mclump, N H 2 , and Tdust compared to the clumps with no outflow. The detection rates of the outflow increase from protostellar (8%) to young stellar object clump (17%) to massive star-forming clump (29%). The detection rate 26% for quiescent clump is preliminary, because the sample of quiescent clumps is small. A statistical relation between the outflow and clump masses for our sample is log ( M out M ) = ( − 1.1 0.21 ) + ( 0.9 0.07 ) log ( M clump M ) . The detection rate of outflows and the outflow mass-loss rate show an increase with increasing Mclump, Lbol, N H 2 , and Tdust, which indicates that clumps with outflow with higher parameter values are at a more advanced evolutionary stage. The outflow mechanical force increases with increasing bolometric luminosities. No clear evidence has yet been found that higher-mass outflows have different launching conditions than low-mass outflows.
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