ABSTRACT Large-scale gaseous filaments with lengths up to the order of 100 pc are on the upper end of the filamentary hierarchy of the Galactic interstellar medium (ISM). Their association with ...respect to the Galactic structure and their role in Galactic star formation are of great interest from both an observational and theoretical point of view. Previous "by-eye" searches, combined together, have started to uncover the Galactic distribution of large filaments, yet inherent bias and small sample size limit conclusive statistical results from being drawn. Here, we present (1) a new, automated method for identifying large-scale velocity-coherent dense filaments, and (2) the first statistics and the Galactic distribution of these filaments. We use a customized minimum spanning tree algorithm to identify filaments by connecting voxels in the position-position-velocity space, using the Bolocam Galactic Plane Survey spectroscopic catalog. In the range of , we have identified 54 large-scale filaments and derived mass ( ), length (10-276 pc), linear mass density (54-8625 pc−1), aspect ratio, linearity, velocity gradient, temperature, fragmentation, Galactic location, and orientation angle. The filaments concentrate along major spiral arms. They are widely distributed across the Galactic disk, with 50% located within 20 pc from the Galactic mid-plane and 27% run in the center of spiral arms. An order of 1% of the molecular ISM is confined in large filaments. Massive star formation is more favorable in large filaments compared to elsewhere. This is the first comprehensive catalog of large filaments that can be useful for a quantitative comparison with spiral structures and numerical simulations.
We report a sample of 463 high-mass starless clump (HMSC) candidates within and . This sample has been singled out from 10,861 ATLASGAL clumps. None of these sources are associated with any known ...star-forming activities collected in SIMBAD and young stellar objects identified using color-based criteria. We also make sure that the HMSC candidates have neither point sources at 24 and 70 m nor strong extended emission at 24 m. Most of the identified HMSCs are infrared dark, and some are even dark at 70 m. Their distribution shows crowding in Galactic spiral arms and toward the Galactic center and some well-known star-forming complexes. Many HMSCs are associated with large-scale filaments. Some basic parameters were attained from column density and dust temperature maps constructed via fitting far-infrared and submillimeter continuum data to modified blackbodies. The HMSC candidates have sizes, masses, and densities similar to clumps associated with Class II methanol masers and H ii regions, suggesting that they will evolve into star-forming clumps. More than 90% of the HMSC candidates have densities above some proposed thresholds for forming high-mass stars. With dust temperatures and luminosity-to-mass ratios significantly lower than that for star-forming sources, the HMSC candidates are externally heated and genuinely at very early stages of high-mass star formation. Twenty sources with equivalent radii pc and mass surface densities g cm−2 could be possible high-mass starless cores. Further investigations toward these HMSCs would undoubtedly shed light on comprehensively understanding the birth of high-mass stars.
ABSTRACT
We present observations toward a high-mass (
), low-luminosity (
)
dark molecular core G28.34 S-A at 3.4 mm, using the IRAM 30 m telescope and the NOEMA interferometer. We report the ...detection of
line emission, which is spatially resolved in this source at a linear resolution of ∼0.1 pc, while the 3.4 mm continuum image does not resolve any internal sub-structures. The SiO emission exhibits two W–E oriented lobes centering on the continuum peak. Corresponding to the redshifted and blueshifted gas with velocities up to
relative to the quiescent cloud, these lobes clearly indicate the presence of a strong bipolar outflow from this
dark core, a source previously considered as one of the best candidates of “starless” core. Our SiO detection is consistent with ALMA archival data of
, whose high-velocity blueshifted gas reveals a more compact lobe spatially closer to the dust center. This outflow indicates that the central source may be in an early evolutionary stage of forming a high-mass protostar. We also find that the low-velocity components (in the range of
) have an extended, NW–SE oriented distribution. Discussing the possible accretion scenarios of the outflow-powering young stellar object, we argue that molecular line emission and the molecular outflows may provide a better indication of the accretion history of the forming young stellar object, than snapshot observations of the present bolometric luminosity. This is particularly significant for cases of episodic accretion, which may occur during the collapse of the parent molecular core.
Abstract
We studied the unique kinematic properties in massive filament G352.63-1.07 at 10
3
au spatial scale with the dense molecular tracers observed with the Atacama Large Millimeter/submillimeter ...Array. We find the central massive core M1 (12
M
⊙
) being separated from the surrounding filament with a velocity difference of
v
−
v
¯
sys
=
−
2
km
s
−
1
and a transverse separation within 3″. Meanwhile, as shown in multiple dense-gas tracers, M1 has a spatial extension closely aligned with the main filament and is connected to the filament toward both its ends. M1 thus represents a very beginning state for a massive, young star-forming core escaping from the parental filament, within a timescale of ∼4000 yr. Based on its kinetic energy (3.5 × 10
44
erg), the core escape is unlikely solely due to the original filament motion or magnetic field but requires more energetic events such as a rapid intense anisotropic collapse. The released energy also seems to noticeably increase the environmental turbulence. This may help the filament to become stabilized again.
全球暖化的議題，各國教育努力推動節能減碳教育，鼓勵依校園情境提供「節能減碳」課程，提升學生節能減碳的素養能力。本研究以臺中市一所國小校園情境，規劃反怠速方案教學計劃，透過混合研究法搜集行動方案教學的文件資料、研究團隊手札、四年級學生訪談資料、以及「節能減碳之認知、態度及行為量表」前後測驗 ...統計資料，揭露行動方案教學之研究過程與描述研究結果，藉以了解如何在國小校園推動節能減碳教育，提升學童節能減碳之素養。研究結果指出校園本位化方案教學有助於節能減碳教育之實施、教師參與研究團隊促進教師教育專業發展並有利行動方案教學推動、多元化的方案教學活動引起學生對節能減碳的學習興趣、及教學後學童節能減碳之素養有顯著差異，顯示該方案教學能提升學生節能減碳之素養。本研究依據取得之結論，對後續之研究提出建議。 Energy saving and carbon emission reduction education has become an important issue in education because of global warming. It is necessary that energy saving and carbon emission reduction education be situated in school context to practice into teaching and learning. This study aims to explore how implementing anti-idling project in an elementary school affects students’ knowledge, attitude, and behavior regarding saving energy and carbon emission reduction education. The project was implemented in an elementary school and 107 fourth-grade students were studied. By conducting mixed methods research, teaching materials, interview data, and surveys were collected through the project. First, situated learning would have crucial influences on energy saving and carbon emission reduction teaching project. Second, research community would affect the success of this project. Third, the students’ knowledge, attitude, and behavior toward energy saving and carbon emission reduction education have changed after the anti-idling teaching project. Based on the findings, suggestions for energy saving and carbon emission reduction education in schools are provided.
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