Observations of the 1→0 Transition of CO Towards Southern HII Regions

1982 ◽  
Vol 4 (4) ◽  
pp. 434-440 ◽  
Author(s):  
J. B. Whiteoak ◽  
Robina E. Otrupcek ◽  
C. J. Rennie
Keyword(s):  
Radio Telescope ◽  
Molecular Cloud ◽  
Milky Way ◽  
Line Emission ◽  
Hii Regions ◽  
Hii Region ◽  
Giant Molecular Cloud ◽  
Molecular Lines ◽  
Csiro Division

The 4-m radio telescope of the CSIRO Division of Radiophysics at Epping is being used to survey the line emission associated with the 1→0 transition of CO (rest frequency 115.271 GHz) in the southern Milky Way. The programme includes mapping the CO distribution across giant molecular-cloud/HII-region complexes. As a first stage the emission has been observed towards bright southern HII regions. These results will not only serve as a basis for future extensive mapping but will also provide data which is directly comparable with observations of other molecular lines that have been made towards the HII regions.

scholarly journals 4.4. The Sagittarius C region mapped in CS(2→1) and (3→2) by the IRAM 30m telescope

1998 ◽  
Vol 184 ◽  
pp. 173-174
Author(s):  
C. Kramer ◽  
J. Staguhn ◽  
H. Ungerechts ◽  
A. Sievers
Keyword(s):  
Spatial Resolution ◽  
Radio Telescope ◽  
Molecular Cloud ◽  
High Spatial Resolution ◽  
Ionized Gas ◽  
Hii Region ◽  
Molecular Material ◽  
Giant Molecular Cloud ◽  
First Time

We study the interaction of a dense giant molecular cloud with the HII region Sagittarius C, and a prominent nonthermal filament (NTF). For this purpose, we mapped the CS(2→1) and (3→2) transitions simultaneously with the IRAM 30m radio telescope, using the on-the-fly observing mode, and covering a 20pc×37pc (8′ × 15′) region. The high spatial resolution, 0.7pc (16″) at 147 GHz, allows for the first time to analyze in detail the morphology and kinematics of the molecular material and its relation to the ionized gas.

scholarly journals Physical Contact between the +20 km s−1 Cloud and the Galactic Circumnuclear Disk

2016 ◽  
Vol 11 (S322) ◽  
pp. 145-146
Author(s):  
Shunya Takekawa ◽  
Tomoharu Oka ◽  
Kunihiko Tanaka
Keyword(s):  
Radio Telescope ◽  
Molecular Cloud ◽  
High Density ◽  
Physical Contact ◽  
Radio Observatory ◽  
Millimeter Wavelength ◽  
Giant Molecular Cloud ◽  
Molecular Lines ◽  
Circumnuclear Disk ◽  
Density Probe

AbstractWe report the discovery of physical contact between the Galactic circumnuclear disk (CND) and an adjacent giant molecular cloud. The central 10 pc of our Galaxy has been imaged in molecular lines at millimeter wavelength using the Nobeyama Radio Observatory 45 m radio telescope. In the position-velocity maps of several high-density probe lines, we have found an emission “bridge” connecting the +20 km s−1 cloud (M–0.13–0.08) and the negative longitude extension of the CND. The collision between the +20 km s−1 cloud and the CND may be responsible for the formation of the bridge. This event can promote mass accretion onto the CND and/or into the inner cavity.

scholarly journals Gas Content in the GMC G333: hierarchical structure of turbulence

2012 ◽  
Vol 8 (S292) ◽  
pp. 49-49
Author(s):  
N. Lo ◽  
M. R. Cunningham ◽  
P. A. Jones ◽  
L. Bronfman
Keyword(s):  
Carbon Monoxide ◽  
Hierarchical Structure ◽  
Molecular Cloud ◽  
Gas Content ◽  
Preliminary Results ◽  
Cloud Properties ◽  
Giant Molecular Cloud ◽  
Molecular Lines

AbstractWe present our preliminary results on the application of dendrogram statistics to the carbon monoxide PPV map of the giant molecular cloud G333. We obtain the dendrograms at various merging levels and found the clustering of branches is independent from the merging levels. The statistics of intensity distributions show gravity is possibly significant in this cloud and the gas may be sonic. Application of this method to other molecular lines data are required for further analysis of the cloud properties.

scholarly journals Formation of structures around HII regions: ionization feedback from massive stars

2012 ◽  
Vol 10 (H16) ◽  
pp. 590-590
Author(s):  
P. Tremblin ◽  
E. Audit ◽  
V. Minier ◽  
W. Schmidt ◽  
N. Schneider
Keyword(s):  
Uv Radiation ◽  
Molecular Cloud ◽  
Massive Stars ◽  
Hii Regions ◽  
Ionization Front ◽  
Hii Region ◽  
Data Archives ◽  
Density Enhancement ◽  
Rosette Nebula ◽  
Density Modulation

AbstractWe present a new model for the formation of dense clumps and pillars around HII regions based on shocks curvature at the interface between a HII region and a molecular cloud. UV radiation leads to the formation of an ionization front and of a shock ahead. The gas is compressed between them forming a dense shell at the interface. This shell may be curved due to initial interface or density modulation caused by the turbulence of the molecular cloud. Low curvature leads to instabilities in the shell that form dense clumps while sufficiently curved shells collapse on itself to form pillars. When turbulence is high compared to the ionized-gas pressure, bubbles of cold gas have sufficient kinetic energy to penetrate into the HII region and detach themselves from the parent cloud, forming cometary globules.Using computational simulations, we show that these new models are extremely efficient to form dense clumps and stable and growing elongated structures, pillars, in which star formation might occur (see Tremblin et al.2012a). The inclusion of turbulence in the model shows its importance in the formation of cometary globules (see Tremblin et al.2012b). Globally, the density enhancement in the simulations is of one or two orders of magnitude higher than the density enhancement of the classical “collect and collapse“ scenario. The code used for the simulation is the HERACLES code, that comprises hydrodynamics with various equation of state, radiative transfer, gravity, cooling and heating.Our recent observations with Herschel (see Schneider et al.2012a) and SOFIA (see Schneider et al.2012b) and additional Spitzer data archives revealed many more of these structures in regions where OB stars have already formed such as the Rosette Nebula, Cygnus X, M16 and Vela, suggesting that the UV radiation from massive stars plays an important role in their formation. We present a first comparison between the simulations described above and recent observations of these regions.

The Marseille Observatory Hα Survey: Comparisons by CO, 6 CM and IRAS Data

1998 ◽  
Vol 179 ◽  
pp. 186-188
Author(s):  
D. Russeil ◽  
P. Amram ◽  
Y.P. Georgelin ◽  
Y.M. Georgelin ◽  
M. Marcelin ◽  
...  
Keyword(s):  
Molecular Cloud ◽  
Large Scale ◽  
Galactic Plane ◽  
Photon Counting ◽  
Hii Regions ◽  
Radio Continuum ◽  
Line Of Sight ◽  
Ionized Gas ◽  
Hii Region ◽  
Pattern Determination

The Marseille Observatory Hα survey supplies Hα velocities of the ionized hydrogen over large zones of the sky towards the galactic plane. This survey, led at the ESO La Silla, uses a 36 cm telescope equiped with a scanning Fabry-Perot interferometer and a photon counting camera (Le Coarer et al. 1992). About 250 fields (39′×39′) toward the galactic plane have already been covered (see Figure 1) with a spatial resolution of 9″×9″ and a spectral resolution of 5 km s–1. This allows us to observe the discrete HII regions and the diffuse ionized gas widely distributed between them and to separate the distinct layers found along the line of sight. HII regions are often grouped on the molecular cloud surface, then CO, radio continuum and recombination lines surveys of the galactic plane are also essential to distinguish the HII region-molecular cloud complexes met on the line of sight, and in order to take dynamical effects into account, such as the champagne effect, for the kinematic distance determination. Indeed, the spiral structure pattern determination requires avoiding any artificial spread by clearly identifying the giant complexes composed of molecular clouds, HII regions, diffuse ionized hydrogen widely surrounding them, and exciting stars. On the other hand the ionized gas data (Hα and recombination lines) associated with IRAS data help us to study the nature of the young objects constituent of these complexes and to assess their detectability. We present two fields from the Hα survey and parallel large scale investigations.

scholarly journals ALMA CO observations of a giant molecular cloud in M 33: Evidence for high-mass star formation triggered by cloud–cloud collisions

2020 ◽  
Author(s):  
Hidetoshi Sano ◽  
Kisetsu Tsuge ◽  
Kazuki Tokuda ◽  
Kazuyuki Muraoka ◽  
Kengo Tachihara ◽  
...  
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Line Emission ◽  
High Mass ◽  
H Ii Regions ◽  
Mass Star ◽  
Star Forming ◽  
Spatially Resolved ◽  
Giant Molecular Cloud

Abstract We report the first evidence for high-mass star formation triggered by collisions of molecular clouds in M 33. Using the Atacama Large Millimeter/submillimeter Array, we spatially resolved filamentary structures of giant molecular cloud 37 in M 33 using 12CO(J = 2–1), 13CO(J = 2–1), and C18O(J = 2–1) line emission at a spatial resolution of ∼2 pc. There are two individual molecular clouds with a systematic velocity difference of ∼6 km s−1. Three continuum sources representing up to ∼10 high-mass stars with spectral types of B0V–O7.5V are embedded within the densest parts of molecular clouds bright in the C18O(J = 2–1) line emission. The two molecular clouds show a complementary spatial distribution with a spatial displacement of ∼6.2 pc, and show a V-shaped structure in the position–velocity diagram. These observational features traced by CO and its isotopes are consistent with those in high-mass star-forming regions created by cloud–cloud collisions in the Galactic and Magellanic Cloud H ii regions. Our new finding in M 33 indicates that cloud–cloud collision is a promising process for triggering high-mass star formation in the Local Group.

scholarly journals 4.8. Distribution of C18O and HNCO emission in the Sagittarius B2 molecular cloud

1998 ◽  
Vol 184 ◽  
pp. 181-182 ◽  
Author(s):  
Fumio Sato ◽  
Tetsuo Hasegawa ◽  
John B. Whiteoak ◽  
Masayoshi Shimizu
Keyword(s):  
Star Formation ◽  
Molecular Cloud ◽  
Massive Star ◽  
Galactic Center ◽  
Full Description ◽  
Massive Star Formation ◽  
Hii Region ◽  
The Galaxy ◽  
Molecular Lines ◽  
Star Formation Regions

Sgr B2, located at a distance of ∼100 pc from the Galactic center, is one of the most active, recent massive-star formation regions in the Galaxy. Based on the 13CO (J = 1–0) line data taken with the Nobeyama 45 m telescope, we presented a cloud collision scenario as the triggering mechanism of the burst of massive-star formation there (Hasegawa et al. 1994). In order to obtain further evidence supporting our model, we observed the Sgr B2 molecular cloud in various molecular lines with the 45 m telescope in 1992 February. Twelve points each with 20″ spacings were observed along several strips 3.67′ long at constant galactic longitudes through the major HII region complexes. Here we report the results of the two lines in the 110 GHz band, C18O (J = 1–0) and HNCO (50,5–40,4). Full description of the observations will be given elsewhere (Sato et al. 1997).

Observations of 115 GHz CO Emission Towards the Carina Nebula

1984 ◽  
Vol 5 (4) ◽  
pp. 552-557 ◽  
Author(s):  
J. B. Whiteoak ◽  
Robina E. Otrupcek
Keyword(s):  
Interstellar Medium ◽  
Radio Telescope ◽  
Molecular Clouds ◽  
Line Emission ◽  
Microwave Frequencies ◽  
Carina Nebula ◽  
Co Emission ◽  
Csiro Division

We have carried out a survey of the 115 GHz CO emission (J = 1→0 transition) towards the Carina nebula (NGC 3372) using the Epping 4 m radio telescope of the CSIRO Division of Radiophysics. Of all the molecules detected in the interstellar medium CO is perhaps the best tracer of molecular clouds. It is an abundant molecule (second only to H2) and its line emission at microwave frequencies occurs at relatively low excitation.

scholarly journals Magnetic Fields in Molecular Cloud Cores

1990 ◽  
Vol 140 ◽  
pp. 291-292
Author(s):  
Z.P. Zhou ◽  
X.W. Zheng
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Circular Polarization ◽  
Molecular Cloud ◽  
Zeeman Splitting ◽  
Hii Regions ◽  
Observational Evidence ◽  
Hii Region ◽  
Vlbi Observations ◽  
Cloud Cores

Strong circular polarization of OH masers at 1665 and 1667 MHz lines has been observed towards the molecular cloud cores associated with HII regions. Magnetic field strengths of a few mG are derived from the Zeeman splitting of OH lines. For instance, a magnetic field of about 4 mG in the masing region of W3(OH) has been estimated by OH-line Zeeman splitting (Davies, 1974). VLBI observations show that the OH maser spots project onto or very close to the surface of associated compact HII regions (Reid et al., 1986). The observational evidence demonstrates that the scales of OH maser components surrounding a compact HII region (R ~ 1016 cm) are about 1014 cm in diameter with an amplification pathlength of ~1015 cm. Hence the magnetic fields determined by the Zeeman splitting of OH maser lines appear partly very close to the associated HII region. Elitzur (1979) has theoretically obtained similar results as above.

scholarly journals LEGO – II. A 3 mm molecular line study covering 100 pc of one of the most actively star-forming portions within the Milky Way disc

2020 ◽  
Vol 497 (2) ◽  
pp. 1972-2001
Author(s):  
A T Barnes ◽  
J Kauffmann ◽  
F Bigiel ◽  
N Brinkmann ◽  
D Colombo ◽  
...  
Keyword(s):  
Column Density ◽  
Milky Way ◽  
Line Emission ◽  
Chemical Properties ◽  
Molecular Line ◽  
Star Forming ◽  
Emission Efficiency ◽  
Single Region ◽  
High Emission ◽  
Molecular Lines

ABSTRACT The current generation of (sub)mm-telescopes has allowed molecular line emission to become a major tool for studying the physical, kinematic, and chemical properties of extragalactic systems, yet exploiting these observations requires a detailed understanding of where emission lines originate within the Milky Way. In this paper, we present 60 arcsec (∼3 pc) resolution observations of many 3 mm band molecular lines across a large map of the W49 massive star-forming region (∼100 pc × 100 pc at 11 kpc), which were taken as part of the ‘LEGO’ IRAM-30m large project. We find that the spatial extent or brightness of the molecular line transitions are not well correlated with their critical densities, highlighting abundance and optical depth must be considered when estimating line emission characteristics. We explore how the total emission and emission efficiency (i.e. line brightness per H2 column density) of the line emission vary as a function of molecular hydrogen column density and dust temperature. We find that there is not a single region of this parameter space responsible for the brightest and most efficiently emitting gas for all species. For example, we find that the HCN transition shows high emission efficiency at high column density (1022 cm−2) and moderate temperatures (35 K), whilst e.g. N2H+ emits most efficiently towards lower temperatures (1022 cm−2; <20 K). We determine $X_{\mathrm{CO} (1-0)} \sim 0.3 \times 10^{20} \, \mathrm{cm^{-2}\, (K\, km\, s^{-1})^{-1}}$, and $\alpha _{\mathrm{HCN} (1-0)} \sim 30\, \mathrm{M_\odot \, (K\, km\, s^{-1}\, pc^2)^{-1}}$, which both differ significantly from the commonly adopted values. In all, these results suggest caution should be taken when interpreting molecular line emission.

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