scholarly journals A Dark-Cloud Complex in Aquila: Small Molecular Clouds Possibly Associated with the Aquila Rift

1999 ◽  
Vol 51 (6) ◽  
pp. 851-858 ◽  
Author(s):  
Akiko Kawamura ◽  
Toshikazu Onishi ◽  
Akira Mizuno ◽  
Hideo Ogawa ◽  
Yasuo Fukui
Keyword(s):  
Molecular Clouds ◽  
Velocity Dispersion ◽  
Galactic Plane ◽  
Dark Cloud ◽  
Dark Clouds ◽  
Order Of Magnitude ◽  
Virial Mass ◽  
The Individual ◽  
Cloud Complex ◽  
Gravitational Equilibrium

Abstract A 12CO(J = 1−0) survey for local molecular clouds was performed toward dark clouds in Aquila (26° < l ≤ 42° and −25° ≤ b < −2°) by using the 4-meter millimeter wave telescope, NANTEN, at Las Campanas Observatory, Chile. A cloud complex consisting of 64 small clouds has been discovered in −25° ≲ b ≲ −12°; at a distance of 220 pc, its height from the galactic plane is ∼ 50–100 pc and the total mass is ∼ 4 × 103M⊙. The spatial and velocity distributions of the complex suggest that it may be connected to the Great Rift in Aquila. This complex, as a whole, has a significantly large virial mass compared with the mass derived from the CO intensities by an order of magnitude, though H I gas of ∼ 104M⊙, possibly associated, may contribute to bind them gravitationally. The individual CO clouds have velocity dispersion and mass similar to those of the high-latitude clouds; also, the clouds are not in gravitational equilibrium. There is no indication of active star formation.

Polarimetric and photometric observations of CB54, with analysis of four other dark clouds

2021 ◽  
Vol 503 (4) ◽  
pp. 5274-5290
Author(s):  
A K Sen ◽  
V B Il’in ◽  
M S Prokopjeva ◽  
R Gupta
Keyword(s):  
Magnetic Field ◽  
Near Infrared ◽  
Galactic Plane ◽  
Photometric Data ◽  
Dust Particles ◽  
Dark Cloud ◽  
Dark Clouds ◽  
High Polarization ◽  
Field Parallel ◽  
Photometric Observations

ABSTRACT We present the results of our BVR-band photometric and R-band polarimetric observations of ∼40 stars in the periphery of the dark cloud CB54. From different photometric data, we estimate E(B − V) and E(J − H). After involving data from other sources, we discuss the extinction variations towards CB54. We reveal two main dust layers: a foreground, E(B − V) ≈ 0.1 mag, at ∼200 pc and an extended layer, $E(B-V) \gtrsim 0.3$ mag, at ∼1.5 kpc. CB54 belongs to the latter. Based on these results, we consider the reason for the random polarization map that we have observed for CB54. We find that the foreground is characterized by low polarization ($P \lesssim 0.5$ per cent) and a magnetic field parallel to the Galactic plane. The extended layer shows high polarization (P up to 5–7 per cent). We suggest that the field in this layer is nearly perpendicular to the Galactic plane and both layers are essentially inhomogeneous. This allows us to explain the randomness of polarization vectors around CB54 generally. The data – primarily observed by us in this work for CB54, by A. K. Sen and colleagues in previous works for three dark clouds CB3, CB25 and CB39, and by other authors for a region including the B1 cloud – are analysed to explore any correlation between polarization, the near-infrared, E(J − H), and optical, E(B − V), excesses, and the distance to the background stars. If polarization and extinction are caused by the same set of dust particles, we should expect good correlations. However, we find that, for all the clouds, the correlations are not strong.

scholarly journals Study of the 13CO/C18O abundance ratio towards the filamentary infrared dark cloud IRDC 34.43 + 0.24

2019 ◽  
Vol 36 ◽  
Author(s):  
M. B. Areal ◽  
S. Paron ◽  
M. E. Ortega ◽  
L. Duvidovich
Keyword(s):  
Molecular Clouds ◽  
Galactic Plane ◽  
Abundance Ratio ◽  
Young Stellar Objects ◽  
Molecular Gas ◽  
Accurate Analysis ◽  
Good Tool ◽  
Dark Cloud ◽  
Average Value ◽  
Far Ultraviolet

Abstract Nowadays, there are several observational studies about the 13CO/C18O abundance ratio ( $X^{13/18}$ ) towards nearby molecular clouds. These works give observational support to the C18O selective photodissociation due to the interaction between the far ultraviolet (FUV) radiation and the molecular gas. It is necessary to increase the sample of molecular clouds located at different distances and affected in different ways by nearby or embedded H ii regions and OB associations to study the selective photodissociation. Using 12CO, 13CO, and C18O J = 1–0 data obtained from the FOREST unbiased Galactic plane imaging survey performed with the Nobeyama 45-m telescope, we analyse the filamentary infrared dark cloud IRDC $34.43+0.24$ located at the distance of about 3.9 kpc. This infrared dark cloud (IRDC) is related to several H ii regions and young stellar objects. Assuming local thermodynamic equilibrium, we obtain: $0.8 \times 10^{16} <$ N(13CO) $<4 \times 10^{17}$ cm–2 (average value $= 4.2 \times 10^{16}$ cm–2), $0.6 \times 10^{15} <$ N(C18O) $<4.4 \times 10^{16}$ cm–2 (average value $= 5.0 \times 10^{15}$ cm–2), and 3 $<$ $X^{13/18}$ $<$ 30 (average $= 8$ ) across the whole IRDC. Larger values of $X^{13/18}$ were found towards portions of the cloud related to the H ii regions associated with the N61 and N62 bubbles and with the photodissociation regions, precisely the regions in which FUV photons are strongly interacting with the molecular gas. Our result represents an observational support to the C18O selectively photodissociation phenomenon occurring in a quite distant filamentary IRDC. Additionally, based on IR data from the Hi-GAL survey, the FUV radiation field was estimated in Habing units, and the dust temperature (T $_{dust}$ ) and H2 column density (N(H2)) distribution were studied. Using the average of N(H2), values in close agreement with the ‘canonical’ abundance ratios [H2]/[13CO] and [H2]/[C18O] were derived. However, the obtained ranges in the abundance ratios show that if an accurate analysis of the molecular gas is required, the use of the ‘canonical’ values may introduce some bias. Thus, it is important to consider how the gas is irradiated by the FUV photons across the molecular cloud. The analysis of $X^{13/18}$ is a good tool to perform that. Effects of beam dilution and clumpiness were studied.

Recent Results on Associations: Anatomy of CMa OB1 and Mon OB1

1980 ◽  
Vol 85 ◽  
pp. 33-49 ◽  
Author(s):  
William Herbst
Keyword(s):  
Molecular Clouds ◽  
Line Emission ◽  
T Tauri Stars ◽  
Molecular Line ◽  
Dark Clouds ◽  
T Tauri ◽  
Sky Survey ◽  
Objective Prism ◽  
Cloud Complex ◽  
Reflection Nebulae

Three types of associations are presently recognized. These are OB, R, and T, and represent, respectively, concentrations of O and B type stars, reflection nebulae, and T Tauri stars, in certain regions of the sky. OB and T associations are identified on objective prism plates; R associations may be found using direct plates such as those of the Palomar Sky Survey. All associations are intimately connected with what appear optically as dark clouds and are now detected as sources of molecular line emission and known as molecular clouds. Often, all three types of associations are found within the same cloud complex (eg, Mon OB1). However, there are also examples of T associations (Taurus) and R associations (Mon R2) which are not connected with recognized OB associations.

scholarly journals Magnetic Fields in Strongly Interacting Galaxy Systems

2004 ◽  
Vol 217 ◽  
pp. 436-438
Author(s):  
Krzysztof T. Chyży ◽  
Rainer Beck
Keyword(s):  
Magnetic Fields ◽  
Far Infrared ◽  
Total Power ◽  
X Rays ◽  
Dark Cloud ◽  
Star Forming ◽  
Dark Clouds ◽  
Extended Radio ◽  
Tidal Tails ◽  
Cloud Complex

We obtained VLA radio total power and polarization maps of a merging pair of galaxies NGC4038/39. The whole system is filled with bright extended radio emission with a high thermal fraction of ⋍ 50% at 10.45 GHz and very strong magnetic fields of ⋍ 20μG. A star-forming region at the southern end of the dark cloud complex extending between the galaxies has highly tangled magnetic fields reaching the strength of ⋍ 30μG, even larger than in both individual galaxies. The polarized components associated with the HI ridge at the base of one of the tidal tails and with the northern complex of dark clouds (weakly forming stars) have been identified. A relic magnetic spiral coincident with the northern galaxy has been found, too. Our data on the magnetic fields combined with those in HI, Hα, X-rays and in far infrared are used as a diagnostic tool to distinguish several physically distinct regions.

scholarly journals Nobeyama 45m CO Galactic Plane Survey: Filament properties and star formation in M17

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Atsushi Nishimura ◽  
Tomofumi Umemoto ◽  
Tetsuhiro Minamidani ◽  
Nario Kuno ◽  
Tomoka Tosaki ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Angular Resolution ◽  
Galactic Plane ◽  
Young Stellar Objects ◽  
Giant Molecular Clouds ◽  
Dark Cloud ◽  
Stellar Objects ◽  
Entire Area ◽  
Uv Photons ◽  
Velocity Channel

AbstractWe present the 12CO J=1–0, 13CO J=1–0, and C18O J=1–0 maps of the M17 giant molecular clouds (GMCs) obtained as a part of the Nobeyama 45m CO Galactic Plane Survey. The observations cover the entire area of M17 SW and M17 N clouds at an angular resolution of ~ 15″ which corresponds to ~ 0.15 pc. We found that the N cloud consists of a couple of twisted filaments, they are extended in parallel toward the Hii region. The typicall width of the filaments is ~0.5 pc in 13CO intensity map. Most of young stellar objects (YSOs) are located on the filaments which have a bright rim structure in 8μm at the filament edge facing the Hii region. Furthermore, the time scale of the YSOs formation on the bright rim is comparable with that of NGC 6618 cluster which provides UV photons for the region. This fact indicates that the cluster triggered to form YSOs in N cloud. We also investigated the geometry of the Hii region and GMCs by comparing spatial distribution of 12CO velocity channel map and infrared dark cloud, and then found that NGC 6618 is possibly formed by the cloud cloud colision.

scholarly journals Molecular Abundance Variations Among and Within Cold, Dark Molecular Clouds

1992 ◽  
Vol 150 ◽  
pp. 171-177 ◽  
Author(s):  
Masatoshi Ohishi ◽  
William M. Irvine ◽  
Norio Kaifu
Keyword(s):  
Chemical Evolution ◽  
Molecular Clouds ◽  
Dark Cloud ◽  
Dark Clouds ◽  
Cloud Cores ◽  
Molecular Abundances

The latest table of molecular abundances in the cold, dark clouds TMC-1 and L134N is presented. Molecular abundance variations between TMC-1 and L134N, those within TMC-1 and L134N, and those among 49 dark cloud cores surveyed by Suzuki et al. (1991) are interpreted as an effect of chemical evolution.

A [TSUP]13[/TSUP]CO ([ITAL]J[/ITAL] = 1–0) Search for Small Molecular Clouds toward the Chamaeleon-Musca Dark Cloud Complex

1998 ◽  
Vol 507 (1) ◽  
pp. L83-L87 ◽  
Author(s):  
Akira Mizuno ◽  
Takahiro Hayakawa ◽  
Nobuyuki Yamaguchi ◽  
Shigeo Kato ◽  
Atsushi Hara ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Dark Cloud ◽  
Cloud Complex

scholarly journals Magnetic Field Structure in Dark Clouds

1987 ◽  
Vol 115 ◽  
pp. 48-50
Author(s):  
M. Tamura ◽  
T. Nagata ◽  
S. Sato ◽  
M. Tanaka ◽  
N. Kaifu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Single Mode ◽  
Polarization Degree ◽  
List Type ◽  
Dark Cloud ◽  
Dark Clouds ◽  
Central Regions ◽  
Field Geometry ◽  
Cloud Complex ◽  
The Magnetic Field

The magnetic field geometry in the central regions of two dark clouds has been mapped by measuring the polarization at 2.2 μm of background stars and of stars embedded in the clouds. The observations were done with the Kyoto polarimeter on the Agematsu 1m IR telescope in December 1984 for Heiles Cloud 2 in the Taurus dark cloud complex, and on the UKIRT 3.8m in May and July 1985 for the ρ Ophiuchus dark cloud core. The main results are: i)Most of the stars in both regions show polarization and their maxima are 2.7% in Heiles Cloud 2 and 7.6% in ρ Oph, respectively. There are similar positive relations between polarization degree and extinct ion Av's.ii)The distribution of position angles for Heiles Cloud 2 shows a single mode at about 50° and that for ρ Oph shows a bimode, at about 50° and 150°.iii)The magnetic fields, as delineated by the infrared polarization, appear perpendicular to the flattened elongations of the molecular clouds.

scholarly journals Giant elephant trunks from giant molecular clouds

2019 ◽  
Author(s):  
Yoshiaki Sofue
Keyword(s):  
Molecular Clouds ◽  
Gas Flow ◽  
Galactic Plane ◽  
Kinetic Temperature ◽  
H Ii Regions ◽  
Giant Molecular Clouds ◽  
Elephant Trunk ◽  
Star Forming ◽  
Order Of Magnitude ◽  
Molecular Masses

Abstract We report the discovery of large elephant trunk (ET)-like objects, named giant elephant trunks (GETs), of molecular gas in star-forming complexes in the Scutum and Norma arms using the $^{12}$CO(J = 1–0)-line survey data with the Nobeyama 45 m telescope. In comparison with the CO maps of ETs in M$\, 16$ as derived from the same data, we discuss physical properties of the GETs. Their lengths are $\sim\!\! 20$ to $50\:$pc, an order of magnitude larger than ETs. GETs show a cometary structure coherently aligned parallel to the galactic plane, and emerge from the bow-shaped concave surface of giant molecular clouds (GMC) facing the H$\,$ ii regions, and point down-stream of the gas flow in the spiral arms. The molecular masses of the head clumps are $\sim 10^{3}$–$10^{4}\, M_{\odot}$, about three to four times the virial masses, indicating that the clumps are gravitationally stable. Jeans masses calculated for the derived density and assumed kinetic temperature are commonly sub-solar. We suggest that the GET heads are possible birth sites of stellar clusters, similarly to ET globules, but at much greater scale. We discuss the origin of the GETs by Rayleigh–Taylor instability due to deceleration of GMCs by low-density gas stagnated in the galactic shock waves as well as by pressure of the H$\,$ ii regions.

scholarly journals CO Isotope Line Shapes in Dark Clouds

1980 ◽  
Vol 87 ◽  
pp. 421-422
Author(s):  
P. C. Myers ◽  
R. B. Buxton ◽  
P.T.P. Ho
Keyword(s):  
Molecular Clouds ◽  
Velocity Dispersion ◽  
Giant Molecular Clouds ◽  
Low Velocity ◽  
Dark Clouds ◽  
Line Shapes ◽  
State Densities ◽  
Chemical Conditions ◽  
Non Gaussian ◽  
Physical And Chemical

The ratio of ground-state densities Ro ≡ N (13CO) / N (C18O) has been used to infer physical and chemical conditions in giant molecular clouds (Wannier et al. 1976) and dark clouds (Mahoney et al. 1976; Langer et al. 1979). In dark clouds Ro is found to vary from values near the terrestrial ratio [13C] [16O] / [12C] [18O] ∼ 5 at positions of high extinction to values ∼20 at positions of low extinction. In this paper we present high-resolution J = 1 → 0 spectra of CO, 13CO, and C18O at positions of high extinction in TMC-2, L134, and L134N. The C18O lines have non-Gaussian wings and are ∼ half as wide as the 13CO lines. We find that RO must vary across the line, from a minimum of R0 ∼ 4 at the peak of the C18O line to a maximum of RO ∼ 10 in the wings, unless the 13CO line has peak opacity ∼5. The variation of RO with position and with velocity is consistent with models of clouds which have a dense core with low velocity-dispersion and low fractionation, and a rarefied envelope with high velocity-dispersion and high fractionation.

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