scholarly journals Chemical evolution of HC3N in dense molecular clouds

2019 ◽  
Vol 489 (4) ◽  
pp. 4497-4512
Author(s):  
Naiping Yu ◽  
Jun-Jie Wang ◽  
Jin-Long Xu
Keyword(s):  
Chemical Evolution ◽  
Molecular Clouds ◽  
Galactic Plane ◽  
Density Ratio ◽  
The Other ◽  
H Ii Regions ◽  
Evolutionary Trend ◽  
Dust Temperature ◽  
Uv Photons ◽  
Cloud Evolution

ABSTRACT We investigated the chemical evolution of HC3N in six dense molecular clouds, using archival available data from the Herschel infrared Galactic Plane Survey (Hi-GAL) and the Millimeter Astronomy Legacy Team Survey at 90 GHz (MALT90). Radio sky surveys of the Multi-Array Galactic Plane Imaging Survey (MAGPIS) and the Sydney University Molonglo Sky Survey (SUMSS) indicate these dense molecular clouds are associated with ultracompact H ii (UCH ii) regions and/or classical H ii regions. We find that in dense molecular clouds associated with normal classical H ii regions, the abundance of HC3N begins to decrease or reaches a plateau when the dust temperature gets hot. This implies UV photons could destroy the molecule of HC3N. On the other hand, in the other dense molecular clouds associated with UCH ii regions, we find the abundance of HC3N increases with dust temperature monotonously, implying HC3N prefers to be formed in warm gas. We also find that the spectra of HC3N (10-9) in G12.804−0.199 and RCW 97 show wing emissions, and the abundance of HC3N in these two regions increases with its non-thermal velocity width, indicating HC3N might be a shock origin species. We further investigated the evolutionary trend of N(N2H+)/N(HC3N) column density ratio, and found this ratio could be used as a chemical evolutionary indicator of cloud evolution after the massive star formation is started.

scholarly journals Giant Molecular Clouds in the Galaxy: The Massachusetts-Stony Brook CO Galactic Plane Survey

1987 ◽  
Vol 115 ◽  
pp. 499-499 ◽  
Author(s):  
P. M. Solomon
Keyword(s):  
Molecular Clouds ◽  
Galactic Plane ◽  
Far Infrared ◽  
Formation Mechanisms ◽  
H Ii Regions ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
The Galaxy ◽  
Two Populations ◽  
Spiral Arm

The CO Galactic Plane Survey consists of 40,572 spectral line observations in the region between 1 = 8° to 90° and b = −1°.05 to +1°.05 spaced every 3 arc minutes, carried out with the FCRAO 14-m antenna. The velocity coverage from −100 to +200 km/s includes emission from all galactic radii. This high resolution survey was designed to observe and identify essentially all molecular clouds or cloud components larger than 10 parsecs in the inner galaxy. There are two populations of molecular clouds which separate according to temperature. The warm clouds are closely associated with H II regions, exhibit a non-axisymmetric galactic distribution and are a spiral arm population. The cold clouds are a disk population, are not confined to any patterns in longitude-velocity space and must be widespread in the galaxy both in and out of spiral arms. The correlation between far infrared luminosities from IRAS, and molecular masses from CO is utilized to determine a luminosity to mass ratio for the clouds. A face-on picture of the galaxy locating the warm population is presented, showing ring like or spiral arm features at R ∼ 5, 7.5 and 9 kpc. The cloud size and mass spectrum will be discussed and evidence presented showing the presence of clusters of giant molecular clouds with masses of 106 to 107 M⊙. The two populations of clouds probably have different star forming luminosity functions. The implication of the two populations for star formation mechanisms will be discussed.

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 In Search of ≲ 5 K Galactic Molecular Gas

1980 ◽  
Vol 87 ◽  
pp. 113-114
Author(s):  
R. H. Rubin ◽  
Neal J. Evans ◽  
B. Zuckerman
Keyword(s):  
Molecular Clouds ◽  
Galactic Plane ◽  
Molecular Gas ◽  
H Ii Regions ◽  
Excitation Temperature ◽  
Molecular Component ◽  
Co Emission

Existing surveys of our galaxy are able to detect CO clouds with an excitation temperature Tex ≳ 5 K. We have made observations to determine if a substantial molecular component is colder than ∼ 5 K. We compared CO emission features with H2CO absorption against 17 continuum sources near the galactic plane. After elimination of features in the spectra that are probably associated with known H II regions, there were 39 clouds remaining, most of which show an excellent kinematic agreement between H2CO and CO. The results do not suggest the existence of a large amount of mass in ultra-cold molecular clouds.

scholarly journals Origin of CH+ in diffuse molecular clouds

2017 ◽  
Vol 600 ◽  
pp. A114 ◽  
Author(s):  
Valeska Valdivia ◽  
Benjamin Godard ◽  
Patrick Hennebelle ◽  
Maryvonne Gerin ◽  
Pierre Lesaffre ◽  
...  
Keyword(s):  
Velocity Distribution ◽  
Chemical Evolution ◽  
Molecular Clouds ◽  
Ambipolar Diffusion ◽  
The Other ◽  
Small Scale ◽  
Neutral Drift ◽  
Physical Conditions ◽  
Mhd Simulations ◽  
Ideal Mhd

Context. Molecular clouds are known to be magnetised and to display a turbulent and complex structure where warm and cold phases are interwoven. The turbulent motions within molecular clouds transport molecules, and the presence of magnetic fields induces a relative velocity between neutrals and ions known as the ion-neutral drift (vd). These effects all together can influence the chemical evolution of the clouds. Aims. This paper assesses the roles of two physical phenomena which have previously been invoked to boost the production of CH+ under realistic physical conditions: the presence of warm H2 and the increased formation rate due to the ion-neutral drift. Methods. We performed ideal magnetohydrodynamical (MHD) simulations that include the heating and cooling of the multiphase interstellar medium (ISM), and where we treat dynamically the formation of the H2 molecule. In a post-processing step we compute the abundances of species at chemical equilibrium using a solver that we developed. The solver uses the physical conditions of the gas as input parameters, and can also prescribe the H2 fraction if needed. We validate our approach by showing that the H2 molecule generally has a much longer chemical evolution timescale compared to the other species. Results. We show that CH+ is efficiently formed at the edge of clumps, in regions where the H2 fraction is low (0.3−30%) but nevertheless higher than its equilibrium value, and where the gas temperature is high (≳ 300 K). We show that warm and out of equilibrium H2 increases the integrated column densities of CH+ by one order of magnitude up to values still ~ 3−10 times lower than those observed in the diffuse ISM. We balance the Lorentz force with the ion-neutral drag to estimate the ion-drift velocities from our ideal MHD simulations. We find that the ion-neutral drift velocity distribution peaks around ~ 0.04 km s-1, and that high drift velocities are too rare to have a significant statistical impact on the abundances of CH+. Compared to previous works, our multiphase simulations reduce the spread in vd, and our self-consistent treatment of the ionisation leads to much reduced vd. Nevertheless, our resolution study shows that this velocity distribution is not converged: the ion-neutral drift has a higher impact on CH+ at higher resolution. On the other hand, our ideal MHD simulations do not include ambipolar diffusion, which would yield lower drift velocities. Conclusions. Within these limitations, we conclude that warm H2 is a key ingredient in the efficient formation of CH+ and that the ambipolar diffusion has very little influence on the abundance of CH+, mainly due to the small drift velocities obtained. However, we point out that small-scale processes and other non-thermal processes not included in our MHD simulation may be of crucial importance, and higher resolution studies with better controlled dissipation processes are needed.

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 Dirty H2 Molecular Clusters as the DIB Sources: Spectroscopic and Physical Properties

2013 ◽  
Vol 9 (S297) ◽  
pp. 378-380
Author(s):  
L. S. Bernstein ◽  
F. O. Clark ◽  
D. K. Lynch
Keyword(s):  
Single Molecule ◽  
Molecular Clouds ◽  
Rotational Temperature ◽  
Single Layer ◽  
Molecular Clusters ◽  
Microwave Emission ◽  
Giant Molecular Clouds ◽  
Induced Dipole ◽  
Spectral Profiles ◽  
Uv Photons

AbstractWe propose that the diffuse interstellar bands (DIBs) arise from absorption lines of electronic transitions in molecular clusters primarily composed of a single molecule, atom, or ion (“seed”), embedded in a single-layer shell of H2 molecules (Bernstein et al. 2013). Less abundant variants of the cluster, including two seed molecules and/or a two-layer shell of H2 molecules may also occur. The lines are broadened, blended, and wavelength-shifted by interactions between the seed and surrounding H2 shell. We refer to these clusters as CHCs (Contaminated H2 Clusters). CHC spectroscopy matches the diversity of observed DIB spectral profiles, and provides good fits to several DIB profiles based on a rotational temperature of 10 K. CHCs arise from ~cm-sized, dirty H2 ice balls, called CHIMPs (Contaminated H2 Ice Macro-Particles), formed in cold, dense, Giant Molecular Clouds (GMCs), and later released into the interstellar medium (ISM) upon GMC disruption. Attractive interactions, arising from Van der Waals and ion-induced dipole potentials, between the seeds and H2 molecules enable CHIMPs to attain cm-sized dimensions. When an ultraviolet (UV) photon is absorbed in the outer layer of a CHIMP, it heats the icy matrix and expels CHCs into the ISM. While CHCs are quickly destroyed by absorbing UV photons, they are replenished by the slowly eroding CHIMPs. Since CHCs require UV photons for their release, they are most abundant at, but not limited to, the edges of UV-opaque molecular clouds, consistent with the observed, preferred location of DIBs. An inherent property of CHCs, which can be characterized as nanometer size, spinning, dipolar dust grains, is that they emit in the radio-frequency region. Thus, CHCs offer a natural explanation to the anomalous microwave emission (AME) feature in the ~10-100 GHz spectral region.

scholarly journals Discovery of the Carina Flare with NANTEN; Evidence for a Supershell That Triggered the Formation of Stars and Massive Molecular Clouds

1999 ◽  
Vol 51 (6) ◽  
pp. 751-764 ◽  
Author(s):  
Yasuo Fukui ◽  
Toshikazu Onishi ◽  
Rihei Abe ◽  
Akiko Kawamura ◽  
Kengo Tachihara ◽  
...  
Keyword(s):  
Kinetic Energy ◽  
Molecular Clouds ◽  
Galactic Plane ◽  
Far Infrared ◽  
Infrared Emission ◽  
High Mass ◽  
Stellar Winds ◽  
Neutral Gas ◽  
Supernova Explosions ◽  
Current Kinetic

Abstract We present extensive observations of the Carina arm region in the 2.6 mm CO (J = 1−0) emission with the NANTEN telescope in Chile. The observations have revealed 120 molecular clouds which are distributed in an area of 283° < l < 293° and 2° .5 < b < 10°. Because of its vertical elongation to the galactic plane, the clouds are named the Carina flare. H I and far-infrared emission show a cavity-like distribution corresponding to the molecular clouds, and soft X-ray emission appears to fill this cavity. It is shown that the Carina flare represents a supershell at a distance of a few kpc that has been produced by about 20 supernova explosions, or equivalent stellar winds of OB stars, over the last ∼ 2×107 yr. The supershell consisting of molecular and atomic neutral gas involves a total mass and kinetic energy of ≳ 3×105M⊙ and ≳ 3×1050 erg, respectively, and the originally injected energy required is about 100-times this current kinetic energy in the shell. It is unique among supershells known previously because of the following aspects: i) it exhibits evidence for the triggered formation of intermediate-to-high-mass stars and massive molecular clouds of 102 − 104M⊙, and ii) the massive molecular clouds formed are located unusually far above the galactic plane at z ∼ 100–500 pc.

scholarly journals CO and OH in the Galactic Center Region

1980 ◽  
Vol 87 ◽  
pp. 111-112
Author(s):  
Junji Inatani ◽  
Nobuharu Ukita
Keyword(s):  
Emission Line ◽  
Intensity Ratio ◽  
Molecular Clouds ◽  
Galactic Center ◽  
Point Of View ◽  
The Other ◽  
Kinetic Temperature ◽  
Two Dimensional ◽  
Center Region ◽  
Dimensional Distribution

The two-dimensional distribution of molecular clouds in the galactic center region has been investigated in the CO 115 GHz line and in the OH 1665 and 1667 MHz lines. As the former is an emission line, we can find molecular clouds without the unavoidable bias to continuum sources which is inherent in a survey of OH absorption lines. Because the CO line is usually optically thick, the brightness temperature of the line is directly related to the kinetic temperature of the cloud. On the other hand, the real optical depth of the OH line can be obtained from the intensity ratio between 1665 and 1667 MHz lines (assuming LTE). From this point of view we have compared the CO and OH observational results.

scholarly journals Towards an anagraphical picture of high-energy Galactic neutrinos

2019 ◽  
Vol 209 ◽  
pp. 01003
Author(s):  
Antonio Marinelli ◽  
Dario Grasso ◽  
Sofia Ventura
Keyword(s):  
Short Duration ◽  
Molecular Clouds ◽  
Supernova Remnants ◽  
Cosmic Ray ◽  
High Energy ◽  
The Other ◽  
Molecular Gas ◽  
High Energy Neutrino ◽  
Neutrino Telescopes ◽  
Upper Limits

The TeV/PeV neutrino emission from our Galaxy is related to the distribution of cosmic-ray accelerators, their maximal energy of injection as well as the propagation of injected particles and their interaction with molecular gas. In the last years Interesting upper limits on the diffuse hadronic emission from the whole Galaxy, massive molecular clouds and Fermi Bubbles were set by the IceCube and ANTARES as well as HAWC and Fermi-LAT observations. On the other hand no evidence of Galactic point-like excess has been observed up to now by high-energy neutrino telescopes. This result can be related to the short duration of the PeV hadronic activity of the sources responsible for the acceleration of primary protons, possibly including supernova remnants. All these aspects will be discussed in this work.

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