scholarly journals Observations of Interstellar CH at 9 cm Wavelength

1976 ◽  
Vol 29 (3) ◽  
pp. 211 ◽  
Author(s):  
FF Gardner ◽  
BJ Robinson ◽  
MW Sinclair
Keyword(s):  
Transition Temperature ◽  
Ground State ◽  
Molecular Clouds ◽  
Hii Regions ◽  
The Galaxy ◽  
Galactic Sources

The 9 cm ground-state lines of CH have been observed in southern galactic sources, mainly HII regions. The F = 0-1 transition at 3264 MHz has been detected in emission in 16 sources; the F = 1-1 transition at 3335 MHz has been seen in absorption in 5 sources and in emission in 2 others. Where the F = 1-1 transition is in absorption the transition temperature is positive and below about 100 K. The F = 0-1 transition is generally inverted, with a transition temperature between -10 and 0 K. The column densities of CH are in the vicinity of lO'4 cm-2, slightly below those for OH but many times those for H2CO. There is no correlation between apparent optical depths of CH and those for OH or H2CO absorption. There is also no enhancement of CH in the dense molecular clouds near the centre of the Galaxy.

Spectra of the 10-01 Transition of Sulfur Monoxide in Interstellar Clouds

1980 ◽  
Vol 87 ◽  
pp. 71-76
Author(s):  
O.E.H. Rydbeck ◽  
Å. Hjalmarson ◽  
G. Rydbeck ◽  
J. Elldér ◽  
E. Kollberg ◽  
...  
Keyword(s):  
Ground State ◽  
Molecular Clouds ◽  
Zeeman Splitting ◽  
Hii Regions ◽  
Interstellar Clouds ◽  
Dark Clouds ◽  
Isotopic Species ◽  
Fractional Abundance ◽  
Sulfur Monoxide ◽  
The Magnetic Field

Emission from SO towards a number of HII regions and molecular clouds with embedded energy sources has been reported by several authors (e.g., Gottlieb et al. 1978; Clark et al. 1978; Wannier and Phillips 1977; and references therein; cf. also Loren et al., 1974; Loren et al. 1975; Lada et al. 1974). Transitions observed include the 45→44, 43→32, 32→21, 23→12, 22→11, 12→11, and 10→01, with the latter (to the ground state) seen only in Sgr B2. Recently Rydbeck et al. (1980) have detected SO in cold, dark clouds and have made the first astronomical measurements of the 10→01 transition in a variety of sources, including the corresponding 34SO line. The latter authors find that the 10→01 transition of SO is an excellent tracer of structure in dark clouds, and they discuss the fractional abundance [SO]/[H2] on the basis of column densities derived from observations of the two isotopic species. They also set limits to the magnetic field strength in dark clouds from the absence of observed Zeeman splitting. We shall provide here additional spectra and information on observing procedures, and shall discuss the rest frequencies for the SO and 34SO 10→01 transitions.

scholarly journals The Galactic deuterium gradient

2009 ◽  
Vol 5 (S268) ◽  
pp. 179-180
Author(s):  
Donald Lubowich ◽  
Jay M. Pasachoff
Keyword(s):  
Molecular Clouds ◽  
Galactic Center ◽  
The Sun ◽  
Abundance Gradient ◽  
The Galaxy ◽  
Low Metallicity ◽  
Galactic Sources

AbstractThe Galactic deuterium abundance gradient has been determined from observations of DCN in Galactic molecular clouds. This is the only way to observe D throughout the Galaxy because the molecular clouds are not limited to the 2 kpc region around the Sun observed with FUSE and from DI. We used an astrochemistry model and the DCN/HCN ratios to estimate the underlying D/H ratios in 16 molecular clouds including five in the Galactic Center. The resulting positive Galactic D gradient and reduced Galactic Center D/H ratio imply that there are no significant Galactic sources of D, there is continuous infall of low-metallicity gas into the Galaxy, and that deuterium is cosmological.

scholarly journals Detecting dark photons from atomic rearrangement in the galaxy

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
James Eiger ◽  
Michael Geller
Keyword(s):  
Dark Matter ◽  
Ground State ◽  
Bound State ◽  
Current Data ◽  
Dark Sector ◽  
Atomic Process ◽  
The Galaxy ◽  
Atomic States ◽  
Atomic Rearrangement

Abstract We study a new dark sector signature for an atomic process of “rearrangement” in the galaxy. In this process, a hydrogen-like atomic dark matter state together with its anti-particle can rearrange to form a highly-excited bound state. This bound state will then de-excite into the ground state emitting a large number of dark photons that can be measured in experiments on Earth through their kinetic mixing with the photon. We find that for DM masses in the GeV range, the dark photons have enough energy to pass the thresholds of neutrino observatories such as Borexino and Super-Kamiokande that can probe for our scenario even when our atomic states constitute a small fraction of the total DM abundance. We study the corresponding bounds on the parameters of our model from current data as well as the prospects for future detectors.

A Thermal Source with Strong 1612 MHz OH Emission

1969 ◽  
Vol 1 (5) ◽  
pp. 211-212
Author(s):  
B. J. Robinson ◽  
W. M. Goss ◽  
R. N. Manchester
Keyword(s):  
Ground State ◽  
Hii Regions ◽  
Thermal Source ◽  
Strong Source ◽  
Galactic Longitude

During 1968 we have found at Parkes several types of emission in the lines of the 18 cm quadruplet of the ground-state OH molecule. This note describes a strong source of 1612 MHz emission near galactic longitude 331°.OH emission was originally detected in the vicinity of HII regions, and a search of a large number of HII regions showed that about a third had associated OH emission. This type of emission is usually strongest at 1665 MHz, and is also seen at 1667 MHz and weakly on one of the satellite lines.

scholarly journals The global star formation law: from dense cores to extreme starbursts

2006 ◽  
Vol 2 (S237) ◽  
pp. 331-335
Author(s):  
Yu Gao
Keyword(s):  
Star Formation ◽  
Linear Correlation ◽  
Molecular Clouds ◽  
High Redshift ◽  
Gas Content ◽  
Molecular Gas ◽  
Giant Molecular Clouds ◽  
Active Star ◽  
Dense Cores ◽  
The Galaxy

AbstractActive star formation (SF) is tightly related to the dense molecular gas in the giant molecular clouds' dense cores. Our HCN (measure of the dense molecular gas) survey in 65 galaxies (including 10 ultraluminous galaxies) reveals a tight linear correlation between HCN and IR (SF rate) luminosities, whereas the correlation between IR and CO (measure of the total molecular gas) luminosities is nonlinear. This suggests that the global SF rate depends more intimately upon the amount of dense molecular gas than the total molecular gas content. This linear relationship extends to both the dense cores in the Galaxy and the hyperluminous extreme starbursts at high-redshift. Therefore, the global SF law in dense gas appears to be linear all the way from dense cores to extreme starbursts, spanning over nine orders of magnitude in IR luminosity.

scholarly journals Mapping the 13CO/C18O abundance ratio in the massive star-forming region G29.96−0.02

2018 ◽  
Vol 617 ◽  
pp. A14 ◽  
Author(s):  
S. Paron ◽  
M. B. Areal ◽  
M. E. Ortega
Keyword(s):  
Molecular Clouds ◽  
Abundance Ratio ◽  
High Mass ◽  
Local Thermal Equilibrium ◽  
Mass Star ◽  
Galactocentric Distance ◽  
Star Forming ◽  
Physical Conditions ◽  
The Galaxy ◽  
Molecular Abundances

Aims. Estimating molecular abundances ratios from directly measuring the emission of the molecules toward a variety of interstellar environments is indeed very useful to advance our understanding of the chemical evolution of the Galaxy, and hence of the physical processes related to the chemistry. It is necessary to increase the sample of molecular clouds, located at different distances, in which the behavior of molecular abundance ratios, such as the 13CO/C18O ratio, is studied in detail. Methods. We selected the well-studied high-mass star-forming region G29.96−0.02, located at a distance of about 6.2 kpc, which is an ideal laboratory to perform this type of study. To study the 13CO/C18O abundance ratio (X13∕18) toward this region, we used 12CO J = 3–2 data obtained from the CO High-Resolution Survey, 13CO and C18O J = 3–2 data from the 13CO/C18O (J = 3–2) Heterodyne Inner Milky Way Plane Survey, and 13CO and C18O J = 2–1 data retrieved from the CDS database that were observed with the IRAM 30 m telescope. The distribution of column densities and X13∕18 throughout the extension of the analyzed molecular cloud was studied based on local thermal equilibrium (LTE) and non-LTE methods. Results. Values of X13∕18 between 1.5 and 10.5, with an average of about 5, were found throughout the studied region, showing that in addition to the dependency of X13∕18 and the galactocentric distance, the local physical conditions may strongly affect this abundance ratio. We found that correlating the X13∕18 map with the location of the ionized gas and dark clouds allows us to suggest in which regions the far-UV radiation stalls in dense gaseous components, and in which regions it escapes and selectively photodissociates the C18O isotope. The non-LTE analysis shows that the molecular gas has very different physical conditions, not only spatially throughout the cloud, but also along the line of sight. This type of study may represent a tool for indirectly estimating (from molecular line observations) the degree of photodissociation in molecular clouds, which is indeed useful to study the chemistry in the interstellar medium.

scholarly journals The relative orientation between the magnetic field and gas density structures in non-gravitating turbulent media

2020 ◽  
Vol 499 (4) ◽  
pp. 4785-4792
Author(s):  
Bastian Körtgen ◽  
Juan D Soler
Keyword(s):  
Magnetic Field ◽  
Molecular Clouds ◽  
Relative Orientation ◽  
Local Magnetic Field ◽  
Gas Formation ◽  
Initial Magnetization ◽  
The Galaxy ◽  
Dynamical Time ◽  
Isothermal Gas ◽  
The Magnetic Field

ABSTRACT Magnetic fields are a dynamically important agent for regulating structure formation in the interstellar medium. The study of the relative orientation between the local magnetic field and gas (column-) density gradient has become a powerful tool to analyse the magnetic field’s impact on the dense gas formation in the Galaxy. In this study, we perform numerical simulations of a non-gravitating, isothermal gas, where the turbulence is driven either solenoidally or compressively. We find that only simulations with an initially strong magnetic field (plasma-β < 1) show a change in the preferential orientation between the magnetic field and isodensity contours, from mostly parallel at low densities to mostly perpendicular at higher densities. Hence, compressive turbulence alone is not capable of inducing the transition observed towards nearby molecular clouds. At the same high initial magnetization, we find that solenoidal modes produce a sharper transition in the relative orientation with increasing density than compressive modes. We further study the time evolution of the relative orientation and find that it remains unchanged by the turbulent forcing after one dynamical time-scale.

3.3 GHz Ground-State Transitions of CH towards Southern HII Regions–1. An Atlas of CH Profiles

1985 ◽  
Vol 6 (1) ◽  
pp. 6-33 ◽  
Author(s):  
J. B. Whiteoak ◽  
F. F. Gardner ◽  
Gwenyth A. Manefield ◽  
B. Höglund ◽  
L. E. B. Johansson
Keyword(s):  
Radio Telescope ◽  
Ground State ◽  
Hii Regions ◽  
State Transitions ◽  
Space Observatory ◽  
Onsala Space Observatory

SummaryThe Parkes 64-m radio telescope equipped with a 3 GHz maser on loan from the Onsala Space Observatory has been used to observe the three ground-state transitions of CH (at 3264, 3335 and 3349 MHz) towards a total of 74 HII regions, mostly at southern declinations. In this paper the regions and related characteristics are listed, and the CH spectra displayed.

Sign in / Sign up

Export Citation Format

Share Document