scholarly journals The Nature of the Dense Core Population in the Pipe Nebula: A Survey of NH 3 , CCS, and HC 5 N Molecular Line Emission

2008 ◽  
Vol 174 (2) ◽  
pp. 396-425 ◽  
Author(s):  
J. M. Rathborne ◽  
C. J. Lada ◽  
A. A. Muench ◽  
J. F. Alves ◽  
M. Lombardi
Keyword(s):  
Line Emission ◽  
Dense Core ◽  
Molecular Line

scholarly journals Quantitative inference of the H2 column densities from 3 mm molecular emission: case study towards Orion B

2020 ◽  
Vol 645 ◽  
pp. A27 ◽  
Author(s):  
Pierre Gratier ◽  
Jérôme Pety ◽  
Emeric Bron ◽  
Antoine Roueff ◽  
Jan H. Orkisz ◽  
...  
Keyword(s):  
Molecular Cloud ◽  
Column Density ◽  
Global Analysis ◽  
Line Emission ◽  
Dense Core ◽  
Supervised Machine Learning ◽  
Physical Parameters ◽  
Wide Field ◽  
Molecular Line ◽  
Core Conditions

Context. Based on the finding that molecular hydrogen is unobservable in cold molecular clouds, the column density measurements of molecular gas currently rely either on dust emission observation in the far-infrared, which requires space telescopes, or on star counting, which is limited in angular resolution by the stellar density. The (sub)millimeter observations of numerous trace molecules can be effective using ground-based telescopes, but the relationship between the emission of one molecular line and the H2 column density is non-linear and sensitive to excitation conditions, optical depths, and abundance variations due to the underlying physico- chemistry. Aims. We aim to use multi-molecule line emission to infer the H2 molecular column density from radio observations. Methods. We propose a data-driven approach to determine the H2 gas column densities from radio molecular line observations. We use supervised machine-learning methods (random forest) on wide-field hyperspectral IRAM-30m observations of the Orion B molecular cloud to train a predictor of the H2 column density, using a limited set of molecular lines between 72 and 116 GHz as input, and the Herschel-based dust-derived column densities as “ground truth” output. Results. For conditions similar to those of the Orion B molecular cloud, we obtained predictions of the H2 column density within a typical factor of 1.2 from the Herschel-based column density estimates. A global analysis of the contributions of the different lines to the predictions show that the most important lines are 13CO(1–0), 12CO(1–0), C18O(1–0), and HCO+(1–0). A detailed analysis distinguishing between diffuse, translucent, filamentary, and dense core conditions show that the importance of these four lines depends on the regime, and that it is recommended that the N2H+(1–0) and CH3OH(20–10) lines be added for the prediction of the H2 column density in dense core conditions. Conclusions. This article opens a promising avenue for advancing direct inferencing of important physical parameters from the molecular line emission in the millimeter domain. The next step will be to attempt to infer several parameters simultaneously (e.g., the column density and far-UV illumination field) to further test the method.

scholarly journals Molecular line emission in NGC 1068 imaged with ALMA

2014 ◽  
Vol 570 ◽  
pp. A28 ◽  
Author(s):  
S. Viti ◽  
S. García-Burillo ◽  
A. Fuente ◽  
L. K. Hunt ◽  
A. Usero ◽  
...  
Keyword(s):  
Line Emission ◽  
Molecular Line ◽  
Ngc 1068

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.

scholarly journals Molecular line emission in HH54: a coherent view from near to far infrared

2006 ◽  
Vol 459 (3) ◽  
pp. 821-835 ◽  
Author(s):  
T. Giannini ◽  
C. McCoey ◽  
B. Nisini ◽  
S. Cabrit ◽  
A. Caratti o Garatti ◽  
...  
Keyword(s):  
Line Emission ◽  
Far Infrared ◽  
Molecular Line

scholarly journals Molecular Line Studies of Dense Core Motions

1992 ◽  
Vol 150 ◽  
pp. 217-222
Author(s):  
Yuefang Wu
Keyword(s):  
Line Width ◽  
Dense Core ◽  
Emission Region ◽  
Molecular Line ◽  
Dense Cores ◽  
Chemical Effects ◽  
Size Relationship ◽  
Molecular Lines ◽  
Line Widths

Molecular lines have revealed various supporting motions in dense cores. Line widths and emission region sizes of NH3 and CS in the same kind of cores or of the same line in cores with or without sources are different and can not be explained with the line width- size relationship. Outflows in dense cores show rich characteristics which can account for the NH3 emission difference between the two kinds of the cores; CS emission is consistent with the chemical effects in shocked regions. Rotation exists in both kinds of cores and may be related to the observed polarities and collimations of outflows.

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 Molecular Line Emission as a Tool for Galaxy Observations (LEGO)

2017 ◽  
Vol 605 ◽  
pp. L5 ◽  
Author(s):  
Jens Kauffmann ◽  
Paul F. Goldsmith ◽  
Gary Melnick ◽  
Volker Tolls ◽  
Andres Guzman ◽  
...  
Keyword(s):  
Line Emission ◽  
Molecular Line

scholarly journals Molecules with ALMA at Planet-forming Scales (MAPS). II. CLEAN Strategies for Synthesizing Images of Molecular Line Emission in Protoplanetary Disks

2021 ◽  
Vol 257 (1) ◽  
pp. 2 ◽  
Author(s):  
Ian Czekala ◽  
Ryan A. Loomis ◽  
Richard Teague ◽  
Alice S. Booth ◽  
Jane Huang ◽  
...  
Keyword(s):  
Line Emission ◽  
Protoplanetary Disks ◽  
Molecular Line
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