| 1. |
- Sanhueza, Patricio, et al.
(författare)
-
The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). I. Pilot Survey: Clump Fragmentation
- 2019
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 886:2
-
Tidskriftsartikel (refereegranskat)abstract
- © 2019. The American Astronomical Society. All rights reserved. The ALMA Survey of 70 μm dark High-mass clumps in Early Stages (ASHES) is designed to systematically characterize the earliest stages and constrain theories of high-mass star formation. Twelve massive (>500 M⊙ ), cold (≤15 K), 3.6-70 μm dark prestellar clump candidates, embedded in infrared dark clouds, were carefully selected in the pilot survey to be observed with the Atacama Large Millimeter/submillimeter Array (ALMA). We have mosaicked each clump (∼1 arcmin2) in continuum and line emission with the 12 m, 7 m, and Total Power (TP) arrays at 224 GHz (1.34 mm), resulting in ∼1.″2 resolution (∼4800 au, at the average source distance). As the first paper in the series, we concentrate on the continuum emission to reveal clump fragmentation. We detect 294 cores, from which 84 (29%) are categorized as protostellar based on outflow activity or "warm core" line emission. The remaining 210 (71%) are considered prestellar core candidates. The number of detected cores is independent of the mass sensitivity range of the observations and, on average, more massive clumps tend to form more cores. We find a large population of low-mass ( 30 M⊙) prestellar cores (maximum mass 11 M⊙). From the prestellar core mass function, we derive a power-law index of 1.17 ± 0.10, which is slightly shallower than Salpeter. We used the minimum spanning tree (MST) technique to characterize the separation between cores and their spatial distribution, and to derive mass segregation ratios. While there is a range of core masses and separations detected in the sample, the mean separation and mass per clump are well explained by thermal Jeans fragmentation and are inconsistent with turbulent Jeans fragmentation. Core spatial distribution is well described by hierarchical subclustering rather than centrally peaked clustering. There is no conclusive evidence of mass segregation. We test several theoretical conditions and conclude that overall, competitive accretion and global hierarchical collapse scenarios are favored over the turbulent core accretion scenario.
|
|
| 2. |
- Taniguchi, KotomiFF, et al.
(författare)
-
Carbon Chain Chemistry in Hot-core Regions around Three Massive Young Stellar Objects Associated with 6.7 GHz Methanol Masers
- 2021
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 908:1
-
Tidskriftsartikel (refereegranskat)abstract
- We have carried out observations of CCH (N = 1 - 0), CH3CN (J = 5 - 4), and three C-13 isotopologues of HC3N (J = 10 - 9) toward three massive young stellar objects (MYSOs), G12.89+0.49, G16.86-2.16, and G28.28-0.36, with the Nobeyama 45 m radio telescope. Combined with previous results on HC5N, the column density ratios of N(CCH)/N(HC5N), hereafter the CCH/HC5N ratios, in the MYSOs are derived to be similar to 15. This value is lower than that in a low-mass warm carbon chain chemistry (WCCC) source by more than one order of magnitude. We compare the observed CCH/HC5N ratios with hot-core model calculations. The observed ratios in the MYSOs can be best reproduced by models when the gas temperature is similar to 85 K, which is higher than in L1527, a low-mass WCCC source (similar to 35 K). These results suggest that carbon-chain molecules detected around the MYSOs exist at least partially in higher temperature regions than those in low-mass WCCC sources. There is no significant difference in column density among the three C-13 isotopologues of HC3N in G12.89+0.49 and G16.86-2.16, while (HCCCN)-C-13 is more abundant than the others in G28.28-0.36. We discuss carbon-chain chemistry around the three MYSOs based on the CCH/HC5N ratio and the C-13 isotopic fractionation of HC3N.
|
|
| 3. |
- Taniguchi, Kotomi, et al.
(författare)
-
Chemical Differentiation around Five Massive Protostars Revealed by ALMA: Carbon-chain Species and Oxygen/Nitrogen-bearing Complex Organic Molecules
- 2023
-
Ingår i: Astrophysical Journal, Supplement Series. - 1538-4365 .- 0067-0049. ; 267:1
-
Tidskriftsartikel (refereegranskat)abstract
- We present Atacama Large Millimeter/submillimeter Array Band 3 data toward five massive young stellar objects (MYSOs), and investigate relationships between unsaturated carbon-chain species and saturated complex organic molecules (COMs). An HC5N (J = 35-34) line has been detected from three MYSOs, where nitrogen (N)-bearing COMs (CH2CHCN and CH3CH2CN) have been detected. The HC5N spatial distributions show compact features and match with a methanol (CH3OH) line with an upper-state energy around 300 K, which should trace hot cores. The hot regions are more extended around the MYSOs where N-bearing COMs and HC5N have been detected compared to two MYSOs without these molecular lines, while there are no clear differences in the bolometric luminosity and temperature. We run chemical simulations of hot-core models with a warm-up stage, and compare with the observational results. The observed abundances of HC5N and COMs show good agreements with the model at the hot-core stage with temperatures above 160 K. These results indicate that carbon-chain chemistry around the MYSOs cannot be reproduced by warm carbon-chain chemistry, and a new type of carbon-chain chemistry occurs in hot regions around MYSOs.
|
|
| 4. |
- Taniguchi, Kotomi, et al.
(författare)
-
Digging into the Interior of Hot Cores with the ALMA (DIHCA). III. The Chemical Link between NH 2 CHO, HNCO, and H 2 CO
- 2023
-
Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 950:1
-
Tidskriftsartikel (refereegranskat)abstract
- We have analyzed the NH2CHO, HNCO, H2CO, and CH3CN (13CH3CN) molecular lines at an angular resolution of ∼0.″3 obtained by the Atacama Large Millimeter/submillimeter Array Band 6 toward 30 high-mass star-forming regions. The NH2CHO emission has been detected in 23 regions, while the other species have been detected toward 29 regions. A total of 44 hot molecular cores (HMCs) have been identified using the moment 0 maps of the CH3CN line. The fractional abundances of the four species have been derived at each HMC. In order to investigate pure chemical relationships, we have conducted a partial correlation test to exclude the effect of temperature. Strong positive correlations between NH2CHO and HNCO (ρ = 0.89) and between NH2CHO and H2CO (0.84) have been found. These strong correlations indicate their direct chemical links; dual-cyclic hydrogen addition and abstraction reactions between HNCO and NH2CHO and gas-phase formation of NH2CHO from H2CO. Chemical models including these reactions can reproduce the observed abundances in our target sources.
|
|
| 5. |
- Taniguchi, Kotomi, et al.
(författare)
-
Vibrationally Excited Lines of HC3N Associated with the Molecular Disk around the G24.78+0.08 A1 Hypercompact H ii Region
- 2022
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 931:2
-
Tidskriftsartikel (refereegranskat)abstract
- We have analyzed Atacama Large Millimeter/submillimeter Array Band 6 data of the hypercompact H ii region G24.78+0.08 A1 (G24 HC H ii) and report the detection of vibrationally excited lines of HC3N (v (7) = 2, J = 24 - 23). The spatial distribution and kinematics of a vibrationally excited line of HC3N (v (7) = 2, J = 24 - 23, l = 2e) are found to be similar to the CH3CN vibrationally excited line (v (8) = 1), which indicates that the HC3N emission is tracing the disk around the G24 HC H ii region previously identified by the CH3CN lines. We derive the (CH3CN)-C-13/(HCCCN)-C-13 abundance ratios around G24 and compare them to the CH3CN/HC3N abundance ratios in disks around Herbig Ae and T Tauri stars. The (CH3CN)-C-13/(HCCCN)-C-13 ratios around G24 (similar to 3.0-3.5) are higher than the CH3CN/HC3N ratios in the other disks (similar to 0.03-0.11) by more than 1 order of magnitude. The higher CH3CN/HC3N ratios around G24 suggest that the thermal desorption of CH3CN in the hot dense gas and efficient destruction of HC3N in the region irradiated by the strong UV radiation are occurring. Our results indicate that the vibrationally excited HC3N lines can be used as a disk tracer of massive protostars at the HC H ii region stage, and the combination of these nitrile species will provide information of not only chemistry but also physical conditions of the disk structures.
|
|
| 6. |
- Umehata, Hideki, et al.
(författare)
-
ALMA Reveals Strong [C II] Emission in a Galaxy Embedded in a Giant Ly alpha Blob at z=3.1
- 2017
-
Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 834:2
-
Tidskriftsartikel (refereegranskat)abstract
- We report the result from observations conducted with the Atacama Large Millimeter/submillimeter Array (ALMA) to detect [C II] 158 mu m fine structure line emission from galaxies embedded in one of the most spectacular Ly alpha blobs (LABs) at z = 3.1, SSA22-LAB1. Of three dusty star-forming galaxies previously discovered by ALMA 860 mu m dust continuum survey toward SSA22-LAB1, we detected the [C II] line from one, LAB1-ALMA3 at z = 3.0993 +/- 0.0004. No line emission was detected, associated with the other ALMA continuum sources or from three rest-frame UV/optical selected z(spec) similar or equal to 3.1 galaxies within the field of view. For LAB1-ALMA3, we find relatively bright [C II] emission compared to the infrared luminosity (L-[C II]/LIR approximate to 0.01) and an extremely high [C II] 158 mu m and [N II] 205 mu m emission line ratio (L[C II]/L[N II] > 55). The relatively strong [C II] emission may be caused by abundant photodissociation regions and sub-solar metallicity, or by shock heating. The origin of the unusually strong [C II] emission could be causally related to the location within the giant LAB, although the relationship between extended Ly alpha emission and interstellar medium conditions of associated galaxies is yet to be understand.
|
|
| 7. |
- Watakabe, Shirou, et al.
(författare)
-
Operation trial of hydrogenous gas injection of COURSE50 project at an experimental blast furnace
- 2013
-
Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 53:12, s. 2065-2071
-
Tidskriftsartikel (refereegranskat)abstract
- COURSE50 (CO2 ultimate reduction in steelmaking process by innovative technology for Cool Earth 50) carried out COG and reformed COG (RCOG) injection operation trials at LKAB's experimental blast furnace in Luleå in cooperation with LKAB and Swerea MEFOS. Operation trials were successfully carried out. Input of C in both COG and RCOG injection periods decreased comparing the base period, because ofincrease in H2 reduction instead of C direct reduction that is a huge endothermic reaction. However poor penetration depth of injected gas from shaft tuyere made furnace efficiency worse. Hot top gas injection increased temperature of top gas and upper part of the furnace. Efficiency of hot top gas injection was not clear as sinter degradation did not occur in the base period.
|
|
