Abstract
We report on a possible cloud–cloud collision in the DR 21 region, which we found through molecular observations with the Nobeyama 45 m telescope. We mapped an area of ∼8′ × 12′ around the ...region with 20 molecular lines including the 12CO(J = 1–0) and 13CO(J = 1–0) emission lines, and 16 of them were significantly detected. Based on the 12CO and 13CO data, we found five distinct velocity components in the observed region, and we call the molecular gas associated with these components “−42,”“−22,” “−3,” “9,” and “17” km s−1 clouds, after their typical radial velocities. The −3 km s−1 cloud is the main filamentary cloud ($\sim 31000\, M_{\odot }$) associated with young massive stars such as DR21 and DR21(OH), and the 9 km s−1 cloud is a smaller cloud ($\sim 3400\, M_{\odot }$) which may be an extension of the W75 region in the north. The other clouds are much smaller. We found a clear anticorrelation in the distributions of the −3 and 9 km s−1 clouds, and detected faint 12CO emission which had intermediate velocities bridging the two clouds at their intersection. These facts strongly indicate that the two clouds are colliding against each other. In addition, we found that DR21 and DR21(OH) are located in the periphery of the densest part of the 9 km s−1 cloud, which is consistent with results of recent numerical simulations of cloud–cloud collisions. We therefore suggest that the −3 and 9 km s−1 clouds are colliding, and that the collision induced the massive star formation in the DR21 cloud. The interaction of the −3 and 9 km s−1 clouds was previously suggested by Dickel, Dickel, and Wilson (1978, ApJ, 223, 840), and our results strongly support their hypothesis of the interaction.
We present the results of mapping observations toward a nearby starless filamentary cloud, the Taurus Molecular Cloud 1 (TMC-1), in the CCS ( , 45.379033 GHz) emission line, using the Nobeyama 45 m ...telescope. The map shows that the TMC-1 filament has a diameter of ∼0.1 pc and a length of ∼0.5 pc at a distance of 140 pc. The position-velocity diagrams of CCS clearly indicate the existence of velocity-coherent substructures in the filament. We identify 21 substructures that are coherent in the position-position-velocity space by eye. Most of the substructures are elongated along the major axis of the TMC-1 filament. The line densities of the subfilaments are close to the critical line density for the equilibrium (∼17 M☉ pc−1 for the excitation temperature of 10 K), suggesting that self-gravity should play an important role in the dynamics of the subfilaments.
A Statistical Study of Massive Cluster-forming Clumps Shimoikura, Tomomi; Dobashi, Kazuhito; Nakamura, Fumitaka ...
Astrophysical journal/The Astrophysical journal,
03/2018, Letnik:
855, Številka:
1
Journal Article
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Odprti dostop
We report results of the observations of 15 regions in several molecular lines for a statistical study of massive cluster-forming clumps. We identified 24 clumps based on the C18O (J = 1-0) data ...obtained by the NRO 45 m telescope, and found that 16 of them are associated with young clusters. The clumps associated with clusters have a typical mass, radius, and molecular density of ∼1 × 103 M☉, ∼0.5 pc, ∼1 × 105 cm−3, respectively. We categorized the clumps and clusters into four types according to the spatial coincidence of gas and star density, and discussed their evolutions: Clumps without clusters (Type 1), clumps showing good correlations with clusters (Type 2), clumps showing poor correlations with clusters (Type 3), and clusters with no associated clumps (Type 4). Analyses of the velocity structures and the chemical compositions imply that the clump + cluster systems should evolve from Type 1 to Type 4. We found that some of the Type 2 clumps are infalling on the clump-scale to form clusters at the clump center, which should commonly occur in the beginning of cluster formation. Interestingly, all of the identified Type 1 clumps are likely to be older than the Type 2 clumps in terms of chemical compositions, suggesting that they have been gravitationally stable for a long time, possibly being supported by the strong magnetic field of 1 mG. Type 1 clumps younger than the observed Type 2 clumps should be very rare to find because of their short lifetime.
We present maps in several molecular emission lines of a 1 square degree region covering the W40 and Serpens South molecular clouds belonging to the Aquila Rift complex. The observations were made ...with the 45 m telescope at the Nobeyama Radio Observatory. We found that the 12CO and 13CO emission lines consist of several velocity components with different spatial distributions. The component that forms the main cloud of W40 and Serpens South, which we call the "main component," has a velocity of VLSR 7 km s−1. There is another significant component at VLSR 40 km s−1, which we call the "40 km s−1 component." The latter component is mainly distributed around two young clusters: W40 and Serpens South. Moreover, the two components look spatially anticorrelated. Such spatial configuration suggests that the star formation in W40 and Serpens South was induced by the collision of the two components. We also discuss a possibility that the 40 km s−1 component consists of gas swept up by superbubbles created by SNRs and stellar winds from the Scorpius-Centaurus association.
We clarify the line-of-sight structure of the Taurus Molecular Cloud 1 (TMC-1) on the basis of the CCS (JN = 43−32) and HC3N (J = 5−4) spectral data observed at a very high velocity resolution and ...sensitivity of ΔV 0.0004 km s−1 (=61 Hz) and ΔTmb 40 mK. The data were obtained toward the cyanopolyyne peak with ∼30 hr integration using the Z45 receiver and the PolariS spectrometer installed in the Nobeyama 45 m telescope. Analyses of the optically thin F = 4−4 and 5−5 hyperfine lines of the HC3N emission show that the spectra consist of four distinct velocity components with a small line width ( 0.1 km s−1) at VLSR = 5.727, 5.901, 6.064, and 6.160 km s−1, which we call A, B, C, and D, respectively, in the order of increasing LSR velocities. Utilizing the velocity information of the four velocity components, we further analyzed the optically thicker CCS spectrum and the other hyperfine lines of the HC3N emission by solving the radiative transfer to investigate how the four velocity components overlap along the line of sight. Results indicate that they are located in the order of A, B, C, and D from far side to near side to the observer, indicating that TMC-1 is shrinking, moving inward as a whole.
Abstract
We have studied optical properties of interstellar dust around the Orion A molecular cloud to investigate the size distribution and the composition of dust grains. Orion A is one of the most ...studied molecular clouds in the solar vicinity (
d
≃ 400 pc). In this paper, we used optical and near-infrared photometric data. The optical data were obtained by
BVRI
bands imaging observations. The near-infrared data consisting of
JHK
S
bands were taken from 2MASS point source catalog. We produced some color excess maps around Orion A and measured their ratios such as
E
(
R
−
I
)/
E
(
B
−
V
). In order to investigate dust properties, we compared the observed ratios with results of simulation performed by Naoi et al. who calculated the extinction in the optical to near-infrared wavelengths based on a standard dust model. They assumed a power-law grain-size distribution with an upper cutoff radius and assumed
graphite
and
silicate
as dominant components. As a result, we found that the upper cutoff radius around Orion A is ≃0.3
μ
m, and
silicate
predominates compared with
graphite
(with the fraction of
silicate
grater than 93%). In addition, we further derived the total-to-selective extinction ratio
R
V
from the observed extinction of
A
V
and the color excess
E
(
B
−
V
), and compared it with the model calculations. Dust properties (i.e., the upper cutoff radius and the ratio of
graphite
/
silicate
) derived from
R
V
are almost consistent with those derived from the color excess ratios.
Abstract
We present the results of mapping observations covering a large area of 1 square degree around W 40 and Serpens South carried out in the 12CO (J = 1–0), 13CO (J = 1–0), C18O (J = 1–0), CCS ...(JN = 87–76), and N2H+ (J = 1–0) emission lines with the 45 m Nobeyama Radio Telescope. W 40 is a blistered H ii region, and Serpens South is an infrared dark cloud accompanied by a young cluster. The relation between these two regions, which are separated by ∼20′ on the sky, has not been recognizable so far. We found the C18O emission is distributed smoothly throughout the W 40 and Serpens South regions, and that the two regions seem to be physically connected. We divided the C18O emission into four groups in terms of the spatial distributions around the H ii region which we call 5, 6, 7, and 8 km s−1 components according to their typical LSR velocity, and propose a three-dimensional model of the W 40 and Serpens South complex. We found two elliptical structures in the position–velocity diagrams, which can be explained as part of two expanding shells. One of the shells is small inner shell just around the H ii region, and the other is a large outer shell corresponding to the boundary of the H ii region. Dense gas associated with the young cluster of Serpens South is likely to be located at the surface of the outer shell, indicating that the natal clump of the young cluster is interacting with the outer shell being compressed by the expansion of the shell. We suggest that the expansion of the shell induced the formation of the young cluster.
ABSTRACT
We have carried out mapping observations of molecular emission lines of HC3N and CH3OH toward two massive cluster-forming clumps, NGC 2264-C and NGC 2264-D, using the Nobeyama 45-m radio ...telescope. We derive an I(HC3N)/I(CH3OH) integrated intensity ratio map, showing a higher value at clumps including 2MASS (Two Micron All Sky Survey) point sources at the northern part of NGC 2264-D. Possible interpretations of the I(HC3N)/I(CH3OH) ratio are discussed. We have also observed molecular emission lines from CCS and N2H+ toward five positions in each clump. We investigate the N(N2H+)/N(CCS) and N(N2H+)/N(HC3N) column density ratios among the ten positions in order to test whether they can be used as chemical evolutionary indicators in these clumps. The N(N2H+)/N(CCS) ratio shows a very high value toward a bright embedded IR source (IRS1), whereas the N(N2H+)/N(HC3N) ratio at IRS1 is comparable with those at the other positions. These results suggest that ultraviolet radiation affects the chemistry around IRS1. We find that there are positive correlations between these column density ratios and the excitation temperatures of N2H+, which implies the chemical evolution of clumps. These chemical evolutionary indicators likely reflect the combination of evolution along the filamentary structure and evolution of each clump.
We have carried out interferometric observations of cyanopolyynes, HC3N, HC5N, and HC7N, in the 36 GHz band toward the G28.28−0.36 high-mass star-forming region using the Ka-band receiver of the Karl ...G. Jansky Very Large Array. The spatial distributions of HC3N and HC5N are obtained. HC5N emission is coincident with a 450 m dust continuum emission, and this clump with a diameter of ∼0.2 pc is located at a position ∼0.15 pc east of the 6.7 GHz methanol maser. HC7N is tentatively detected toward the clump. The HC3N:HC5N:HC7N column density ratios are estimated to be 1.0:∼0.3:∼0.2 at an HC7N peak position. We discuss possible natures of the 450 m continuum clump associated with the cyanopolyynes. This clump seems to contain deeply embedded low- or intermediate-mass protostellar cores, and the most likely formation mechanism of the cyanopolyynes is the mechanism of warm carbon-chain chemistry. In addition, HC3N and compact HC5N emission is detected at the edge of the 4.5 m emission, which possibly implies that such emission has a shock origin.
Abstract
We report the first clear detection of the Zeeman splitting of a CCS emission line at 45 GHz toward the nearby pre-stellar dense filament, Taurus Molecular Cloud 1 (TMC-1). We observed ...HC$_3$N non-Zeeman lines simultaneously with the CCS line, and did not detect any significant splitting of the HC$_3$N lines. Thus, we conclude that our detection of CCS Zeeman splitting is robust. The derived line-of-sight magnetic field strength is about $117 \pm 21 \, \mu$G, which corresponds to a normalized mass-to-magnetic flux ratio of 2.2 if we adopt an inclination angle of 45$^\circ$. Thus, we conclude that the TMC-1 filament is magnetically supercritical. Recent radiative transfer calculations of the CCS and HC$_3$N lines along the line of sight suggest that the filament is collapsing with a speed of $\sim$0.6 km s$^{-1}$, which is comparable to three times the isothermal sound speed. This infall velocity appears to be consistent with the evolution of a gravitationally infalling core.
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