scholarly journals 4.5. Sub-mm [C I] and CO observations of molecular clouds presumably interacting by the G359.54+0.18 nonthermal filaments

1998 ◽  
Vol 184 ◽  
pp. 175-176
Author(s):  
J. Staguhn ◽  
J. Stutzki ◽  
S. P. Balm ◽  
A. A. Stark ◽  
A. P. Lane
Keyword(s):  
Molecular Clouds ◽  
Line Emission ◽  
Recombination Line ◽  
Molecular Line ◽  
Line Intensities ◽  
Angular Extent ◽  
H Ii Region ◽  
Morphological Differences ◽  
5 Ghz ◽  
Co Observations

We have investigated the physical properties of molecular clouds which are presumably interacting with the G359.54+0.18 Nonthermal Filaments and an associated H ii region east of the filaments (Staguhn et al., 1996). The sub-mm spectra of 12CO(3-2) were observed with the KOSMA 3 m telescope, while the 490 GHz [C i] 3P1 →3P0 observations were made with the AST/RO 1.7 m sub-mm telescope. Fig. 1 shows channel maps of the integrated CO and [C i] line intensities in the velocity range of the recombination line observed towards the nearby H ii region. This H ii region is traced by the VLA 5 GHz continuum observations which are shown as contours in the central parts of the maps. The G359.54+0.18 Nonthermal Filaments, situated further to the west, appear to be morphologically associated with the H ii region. The [C i] emission of the molecular cloud east of the filaments which is kinematically linked to the H ii region is anti-correlated with the molecular line emission over a large angular extent. It is unlikely that the large morphological differences between [C i] and CO in this region can be explained exclusively by a high abundance of neutral carbon in the surface regions of dense molecular clumps, as is usually the case in PDR regions near the Sun.

scholarly journals Understanding biases in measurements of molecular cloud kinematics using line emission

2020 ◽  
Vol 498 (2) ◽  
pp. 2440-2455
Author(s):  
Yuxuan (宇轩) Yuan (原) ◽  
Mark R Krumholz ◽  
Blakesley Burkhart
Keyword(s):  
Magnetic Field ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Velocity Dispersion ◽  
Signal To Noise Ratio ◽  
Line Emission ◽  
Molecular Line ◽  
Velocity Dispersions ◽  
Cloud Kinematics ◽  
Measurement Biases

ABSTRACT Molecular line observations using a variety of tracers are often used to investigate the kinematic structure of molecular clouds. However, measurements of cloud velocity dispersions with different lines, even in the same region, often yield inconsistent results. The reasons for this disagreement are not entirely clear, since molecular line observations are subject to a number of biases. In this paper, we untangle and investigate various factors that drive linewidth measurement biases by constructing synthetic position–position–velocity cubes for a variety of tracers from a suite of self-gravitating magnetohydrodynamic simulations of molecular clouds. We compare linewidths derived from synthetic observations of these data cubes to the true values in the simulations. We find that differences in linewidth as measured by different tracers are driven by a combination of density-dependent excitation, whereby tracers that are sensitive to higher densities sample smaller regions with smaller velocity dispersions, opacity broadening, especially for highly optically thick tracers such as CO, and finite resolution and sensitivity, which suppress the wings of emission lines. We find that, at fixed signal-to-noise ratio, three commonly used tracers, the J = 4 → 3 line of CO, the J = 1 → 0 line of C18O, and the (1,1) inversion transition of NH3, generally offer the best compromise between these competing biases, and produce estimates of the velocity dispersion that reflect the true kinematics of a molecular cloud to an accuracy of $\approx 10{{\ \rm per\ cent}}$ regardless of the cloud magnetic field strengths, evolutionary state, or orientations of the line of sight relative to the magnetic field. Tracers excited primarily in gas denser than that traced by NH3 tend to underestimate the true velocity dispersion by $\approx 20{{\ \rm per\ cent}}$ on average, while low-density tracers that are highly optically thick tend to have biases of comparable size in the opposite direction.

A Second Compact Radio Component Detected in the LMC HII Region N159

1994 ◽  
Vol 11 (1) ◽  
pp. 68-73 ◽  
Author(s):  
M. R. Hunt ◽  
J. B. Whiteoak
Keyword(s):  
Line Emission ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Recombination Line ◽  
Hii Region ◽  
Infrared Wavelengths ◽  
5 Ghz ◽  
Compact Array

AbstractThe Australia Telescope Compact Array has been used for observations, with arcsecond resolution, of the HII region N159 in the Large Magellanic Cloud. Images at 5 GHz reveal a second compact continuum component which has no obvious counterpart at optical and infrared wavelengths. Observations of HI 10α recombination-line emission, and HI and H2CO absorption, suggest that the object is a compact HII region embedded in a dense obscuring cloud on the edge of N159.

scholarly journals Extragalactic science with ALMA

2011 ◽  
Vol 7 (S284) ◽  
pp. 494-495
Author(s):  
George J. Bendo ◽  
Keyword(s):  
Molecular Clouds ◽  
High Redshift ◽  
Atacama Desert ◽  
Line Emission ◽  
Continuum Emission ◽  
Synchrotron Emission ◽  
Molecular Line ◽  
Molecular Lines ◽  
Nearby Galaxies ◽  
Detailed Imaging

AbstractThe Atacama Large Millimeter/submillimeter Array (ALMA) is a telescope comprising 66 antennas that is located in the Atacama Desert in Chile, one of the driest locations on Earth. When the telescope is fully operational, it will perform observations over ten receiver bands at wavelengths from 9.5-0.32 mm (31-950 GHz) with unprecedented sensitivities to continuum emission from cold (<20 K) dust, Bremsstrahlung, and synchrotron emission as well as submillimetre and millimetre molecular lines. With baselines out to 16km and dynamic reconfiguration, ALMA will achieve spatial resolutions ranging from 3″ to 0.010″, allowing for detailed imaging of continuum or molecular line emission from 0.1-1 kpc scale gas and dust discs in high-redshift sources or 10-100 pc scale molecular clouds and substructures within nearby galaxies. Science observations started on 30 September 2011 with 16 antennas and four receiver bands on baselines up to 400 m. The telescope's capabilities will steadily improve until full operations begin in 2013.

scholarly journals Radio emission during the formation of stellar clusters in M 33

2020 ◽  
Vol 639 ◽  
pp. A27
Author(s):  
Edvige Corbelli ◽  
Jonathan Braine ◽  
Fatemeh S. Tabatabaei
Keyword(s):  
Radio Emission ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Supernova Remnants ◽  
Line Emission ◽  
Radio Continuum ◽  
Stellar Clusters ◽  
Nonthermal Radio ◽  
Early Formation ◽  
5 Ghz

Aims. We investigate thermal and nonthermal radio emission associated with the early formation and evolution phases of young stellar clusters (YSCs) selected by their mid-infrared (MIR) emission at 24 μm in M 33. We consider regions in their early formation period, which are compact and totally embedded in the molecular cloud, and in the more evolved and exposed phase. Methods. Thanks to recent radio continuum surveys between 1.4 and 6.3 GHz we are able to find radio source counterparts to more than 300 star forming regions of M 33. We identify the thermal free–free component for YSCs and their associated molecular complexes using the Hα line emission. Results. A cross-correlation of MIR and radio continuum is established from bright to very faint sources, with the MIR-to-radio emission ratio that shows a slow radial decline throughout the M 33 disk. We confirm the nature of candidate embedded sources by recovering the associated faint radio continuum luminosities. By selecting exposed YSCs with reliable Hα flux, we establish and discuss the tight relation between Hα and the total radio continuum at 5 GHz over four orders of magnitude. This holds for individual YSCs as well as for the giant molecular clouds hosting them, and allows us to calibrate the radio continuum–star formation rate relation at small scales. On average, about half of the radio emission at 5 GHz in YSCs is nonthermal with large scatter. For exposed but compact YSCs and their molecular clouds, the nonthermal radio continuum fraction increases with source brightness, while for large HII regions the nonthermal fraction is lower and shows no clear trend. This has been found for YSCs with and without identified supernova remnants and underlines the possible role of massive stars in triggering particle acceleration through winds and shocks: these particles diffuse throughout the native molecular cloud prior to cloud dispersal.

scholarly journals Large-scale CO observations of a far-infrared loop in Pegasus; detection of a large number of very small molecular clouds possibly formed via shocks

2006 ◽  
Vol 2 (S237) ◽  
pp. 500-500
Author(s):  
Hiroaki Yamamoto ◽  
Akiko Kawamura ◽  
Kengo Tachihara ◽  
Norikazu Mizuno ◽  
Toshikazu Onishi ◽  
...  
Keyword(s):  
Molecular Clouds ◽  
Large Scale ◽  
Far Infrared ◽  
Grid Spacing ◽  
Angular Extent ◽  
Co Observations

Large-scale CO observations with the millimeter/submillimeter telescope NANTEN toward a whole FIR loop-like structure whose angular extent is ~20° × 20° around (l, b) ~(109°, − 45°) in Pegasus have been carried out in the 12CO (J = 1 − 0) at 4′ – 8′ grid spacing and the 12CO emitting region in the 13CO (J=1–0) at 2′ grid spacing. The diameter corresponds to ~25 pc at a distance of 100 pc, adopted from that of the star HD886(B2IV) near the center of the loop.

scholarly journals Radiative transfer of CO through clumpy molecular clouds with external UV heating

1991 ◽  
Vol 147 ◽  
pp. 504-504
Author(s):  
Jan A. Tauber ◽  
Paul F. Goldsmith
Keyword(s):  
Radiative Transfer ◽  
Molecular Clouds ◽  
Line Emission ◽  
Spectral Lines ◽  
Kinetic Temperature ◽  
Dynamical Structure ◽  
Hii Region ◽  
Line Intensities ◽  
Model Cloud ◽  
Uv Photons

We have developed a model which simulates the radiative transfer of molecular line emission through clumpy molecular clouds. The dynamical structure of the model cloud is based on the work of Kwan and Sanders (1986). The model incorporates the existence of an intense source of UV photons at the surface of the cloud. The UV source heats the clumps and creates kinetic temperature and CO abundance gradients within them. The amount of heating depends on the intensity of the UV field, which decreases from the surface to the core of the cloud due to attenuation by dust. We treat in detail the photochemistry and self-shielding properties of CO as a function of UV intensity and gas density in order to obtain the CO line intensities emerging from each clump. The line intensity emerging from the cloud is obtained by integrating the emission from all clumps along the line of sight, weighted by an area covering factor, and attenuated by the opacity of intervening clumps. The effects of the heating are significantly noticeable on the line intensities of CO transitions arising from levels with J between ∼ 3 and ∼ 7. We apply our model to the case of the Orion A molecular cloud, and in particular to observations of the J=3 →2 12CO and 13CO lines. The model is in general agreement with the observed enhanced intensity of the 12CO J=3 →2 transition relative to the J=1 →0 transition throughout the central ∼ 10′ region of Orion. It also produces centrally peaked spectral lines whose intensity is maximum in a shell-like distribution centered on the Trapezium HII region, as is observed.

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 Synthetic line and continuum observations of simulated turbulent clouds: the apparent widths of filaments

2020 ◽  
Vol 499 (3) ◽  
pp. 3728-3737
Author(s):  
F D Priestley ◽  
A P Whitworth
Keyword(s):  
Radial Velocity ◽  
Surface Density ◽  
Line Emission ◽  
Continuum Emission ◽  
Full Time ◽  
Molecular Line ◽  
Line Intensities ◽  
Hydrodynamical Simulations ◽  
Proper Account ◽  
Synthetic Line

ABSTRACT Filamentary structures are ubiquitous in observations of real molecular clouds and also in simulations of turbulent, self-gravitating gas. However, making comparisons between observations and simulations is complicated by the difficulty of estimating volume densities observationally. Here, we have post-processed hydrodynamical simulations of a turbulent isothermal molecular cloud, using a full time-dependent chemical network. We have then run radiative transfer models to obtain synthetic line and continuum intensities that can be compared directly with those observed. We find that filaments have a characteristic width of ${\sim }0.1 \, {\rm pc}$, both on maps of their true surface density and on maps of their $850\, {\rm \mu m}$ dust continuum emission in agreement with previous work. On maps of line emission from CO isotopologues, the apparent widths of filaments are typically several times larger because the line intensities are poorly correlated with the surface density. On maps of line emission from dense gas tracers such as N2H+ and HCN, the apparent widths of filaments are ${\la}0.1\, {\rm pc}$. Thus, current observations of molecular-line emission are compatible with the universal $0.1 \, {\rm pc}$ filament width inferred from Herschel observations, provided proper account is taken of abundance, optical depth, and excitation considerations. We find evidence for ${\sim}0.4 \, {\rm km \, s^{-1}}$ radial velocity differences across filaments. These radial velocity differences might be a useful indicator of the mechanism by which a filament has formed or is forming, for example the turbulent cloud scenario modelled here, as against other mechanisms such as cloud–cloud collisions.

scholarly journals Radiative transfer of CO through clumpy molecular clouds with external UV heating

1991 ◽  
Vol 147 ◽  
pp. 504-504
Author(s):  
Jan A. Tauber ◽  
Paul F. Goldsmith
Keyword(s):  
Radiative Transfer ◽  
Molecular Clouds ◽  
Line Emission ◽  
Spectral Lines ◽  
Kinetic Temperature ◽  
Dynamical Structure ◽  
Hii Region ◽  
Line Intensities ◽  
Model Cloud ◽  
Uv Photons

We have developed a model which simulates the radiative transfer of molecular line emission through clumpy molecular clouds. The dynamical structure of the model cloud is based on the work of Kwan and Sanders (1986). The model incorporates the existence of an intense source of UV photons at the surface of the cloud. The UV source heats the clumps and creates kinetic temperature and CO abundance gradients within them. The amount of heating depends on the intensity of the UV field, which decreases from the surface to the core of the cloud due to attenuation by dust. We treat in detail the photochemistry and self-shielding properties of CO as a function of UV intensity and gas density in order to obtain the CO line intensities emerging from each clump. The line intensity emerging from the cloud is obtained by integrating the emission from all clumps along the line of sight, weighted by an area covering factor, and attenuated by the opacity of intervening clumps. The effects of the heating are significantly noticeable on the line intensities of CO transitions arising from levels with J between ∼ 3 and ∼ 7. We apply our model to the case of the Orion A molecular cloud, and in particular to observations of the J=3 →2 12CO and 13CO lines. The model is in general agreement with the observed enhanced intensity of the 12CO J=3 →2 transition relative to the J=1 →0 transition throughout the central ∼ 10′ region of Orion. It also produces centrally peaked spectral lines whose intensity is maximum in a shell-like distribution centered on the Trapezium HII region, as is observed.

scholarly journals CO observations of the 30-Doradus region using SEST

1991 ◽  
Vol 148 ◽  
pp. 157-159
Author(s):  
R. S. Booth ◽  
L.E.B. Johansson
Keyword(s):  
Molecular Clouds ◽  
Small Areas ◽  
The Relationship ◽  
Co Observations ◽  
30 Doradus

Using the Swedish-ESO Submillimetre Telescope, we have mapped the CO (1-0) emission in two small areas of the LMC near 30 Dor. Some 20 molecular clouds have been identified and analysed. Cloud masses are calculated assuming virial equilibrium and the relationship between mass and CO luminosity is discussed.

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