scholarly journals Hydride spectroscopy of the diffuse interstellar medium: new clues on the gas fraction in molecular form and cosmic ray ionization rate in relation to H 3 +

2012 ◽  
Vol 370 (1978) ◽  
pp. 5174-5185 ◽  
Author(s):  
M. Gerin ◽  
F. Levrier ◽  
E. Falgarone ◽  
B. Godard ◽  
P. Hennebelle ◽  
...  
Keyword(s):  
Molecular Form ◽  
Chemical Properties ◽  
Cosmic Ray ◽  
Building Blocks ◽  
Ionization Rate ◽  
Spectral Lines ◽  
Interstellar Gas ◽  
Interstellar Molecules ◽  
Star Forming ◽  
Star Forming Regions

The Herschel-guaranteed time key programme PRobing InterStellar Molecules with Absorption line Studies (PRISMAS) 1 is providing a survey of the interstellar hydrides containing the elements C, O, N, F and Cl. As the building blocks of interstellar molecules, hydrides provide key information on their formation pathways. They can also be used as tracers of important physical and chemical properties of the interstellar gas that are difficult to measure otherwise. This paper presents an analysis of two sight-lines investigated by the PRISMAS project, towards the star-forming regions W49N and W51. By combining the information extracted from the detected spectral lines, we present an analysis of the physical properties of the diffuse interstellar gas, including the electron abundance, the fraction of gas in molecular form, and constraints on the cosmic ray ionization rate and the gas density.

scholarly journals A new proxy to estimate the cosmic ray ionization rate in dense cores

2020 ◽  
Vol 495 (1) ◽  
pp. L7-L11
Author(s):  
S Bovino ◽  
S Ferrada-Chamorro ◽  
A Lupi ◽  
D R G Schleicher ◽  
P Caselli
Keyword(s):  
Spatial Scales ◽  
Cosmic Ray ◽  
Ionization Rate ◽  
Fundamental Parameter ◽  
Star Forming ◽  
Star Forming Regions ◽  
Dense Cores ◽  
Statistical Relevance ◽  
Theoretical Predictions ◽  
Diffuse Clouds

ABSTRACT Cosmic rays are a global source of ionization, and the ionization fraction represents a fundamental parameter in the interstellar medium. Ions couple to magnetic fields, and affect the chemistry and the dynamics of star-forming regions as well as planetary atmospheres. However, the cosmic ray ionization rate represents one of the bottlenecks for astrochemical models, and its determination is one of the most puzzling problems in astrophysics. While for diffuse clouds reasonable values have been provided from ${\mathrm{ H}_3}^+$ observations, for dense clouds, due to the lack of rotational transitions, this is not possible, and estimates are strongly biased by the employed model. We present here an analytical expression, obtained from first principles, to estimate the cosmic ray ionization rate from observational quantities. The theoretical predictions are validated with high-resolution 3D numerical simulations and applied to the well-known core L1544; we obtained an estimate of ζ2 ∼ 2–3 × 10−17 s−1. Our results and the analytical formulae provided represent the first model-independent robust tool to probe the cosmic ray ionization rate in the densest part of star-forming regions (on spatial scales of R ≤ 0.05 pc). An error analysis is presented to give statistical relevance to our study.

Using H 3 + and H 2 D + as probes of star-forming regions

2006 ◽  
Vol 364 (1848) ◽  
pp. 3101-3106 ◽  
Author(s):  
Floris F.S van der Tak
Keyword(s):  
Cosmic Ray ◽  
Ionization Rate ◽  
High Mass ◽  
Mass Star ◽  
Future Prospects ◽  
Star Forming ◽  
Star Forming Regions ◽  
Chemical Conditions ◽  
Physical And Chemical ◽  
Kinematic Properties

The and H 2 D + ions are important probes of the physical and chemical conditions in regions of the interstellar medium where new stars are forming. This paper reviews how observations of these species and of heavier ions such as HCO + and H 3 O + can be used to derive chemical and kinematic properties of nearby pre-stellar cores and the cosmic ray ionization rate towards more distant regions of high-mass star formation. Future prospects in the field are outlined at the end.

scholarly journals Ionization: a possible explanation for the difference of mean disk sizes in star-forming regions

2020 ◽  
Vol 639 ◽  
pp. A86
Author(s):  
M. Kuffmeier ◽  
B. Zhao ◽  
P. Caselli
Keyword(s):  
Cosmic Ray ◽  
Ionization Rate ◽  
Ohmic Dissipation ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Difference ◽  
Protostellar Collapse ◽  
Different Levels ◽  
Collapse Phase ◽  
Ionization Rates

Context. Surveys of protoplanetary disks in star-forming regions of similar age revealed significant variations in average disk mass in some regions. For instance, disks in the Orion Nebular Cluster (ONC) and Corona Australis (CrA) are on average smaller than disks observed in Lupus, Taurus, Chamaeleon I, or Ophiuchus. Aims. In contrast to previous models that studied the truncation of disks at a late stage of their evolution, we investigate whether disks may already be born with systematically smaller disk sizes in more massive star-forming regions as a consequence of higher ionization rates. Methods. Assuming various cosmic-ray ionization rates, we computed the resistivities for ambipolar diffusion and Ohmic dissipation with a chemical network, and performed 2D nonideal magnetohydrodynamical protostellar collapse simulations. Results. A higher ionization rate leads to stronger magnetic braking, and hence to the formation of smaller disks. Accounting for recent findings that protostars act as forges of cosmic rays and considering only mild attenuation during the collapse phase, we show that a high average cosmic-ray ionization rate in star-forming regions such as the ONC or CrA can explain the detection of smaller disks in these regions. Conclusions. Our results show that on average, a higher ionization rate leads to the formation of smaller disks. Smaller disks in regions of similar age can therefore be the consequence of different levels of ionization, and may not exclusively be caused by disk truncation through external photoevaporation. We strongly encourage observations that allow measuring the cosmic-ray ionization degrees in different star-forming regions to test our hypothesis.

scholarly journals Complex chemistry in star-forming regions

2008 ◽  
Vol 4 (S251) ◽  
pp. 123-124 ◽  
Author(s):  
Robin T. Garrod ◽  
Susanna L. Widicus Weaver ◽  
Eric Herbst
Keyword(s):  
Cosmic Ray ◽  
Building Blocks ◽  
Complex Molecules ◽  
Warm Up ◽  
Star Forming ◽  
Star Forming Regions ◽  
Surface Mobility ◽  
Complex Chemistry ◽  
Grain Surface ◽  
Complex Organic

AbstractWe present a new gas-grain chemical model that allows the grain-surface formation of saturated, complex, organic species from their constituent functional-groups–basic building blocks that derive from the cosmic ray-induced photodissociation of the granular ice mantles. The surface mobility of the funtional-group radicals is crucial to the reactions, and much of the formation of complex molecules occurs at the intermediate temperatures (~20–40 K) attained during the warm-up of the hot core. Our model traces the evolution of a large range of detected, and as yet un-detected, complex molecules.

scholarly journals Survey of ortho-H2D+ in high-mass star-forming regions

2020 ◽  
Vol 644 ◽  
pp. A34
Author(s):  
G. Sabatini ◽  
S. Bovino ◽  
A. Giannetti ◽  
F. Wyrowski ◽  
M. A. Órdenes ◽  
...  
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Strong Dependence ◽  
Cosmic Ray ◽  
High Mass ◽  
Clear Correlation ◽  
Mass Star ◽  
Large Sample ◽  
Star Forming ◽  
Star Forming Regions

Context. Deuteration has been suggested to be a reliable chemical clock of star-forming regions due to its strong dependence on density and temperature changes during cloud contraction. In particular, the H3+ isotopologues (e.g. ortho-H2D+) seem to act as good proxies of the evolutionary stages of the star formation process. While this has been widely explored in low-mass star-forming regions, in the high-mass counterparts only a few studies have been pursued, and the reliability of deuteration as a chemical clock remains inconclusive. Aims. We present a large sample of o-H2D+ observations in high-mass star-forming regions and discuss possible empirical correlations with relevant physical quantities to assess its role as a chronometer of star-forming regions through different evolutionary stages. Methods. APEX observations of the ground-state transition of o-H2D+ were analysed in a large sample of high-mass clumps selected from the ATLASGAL survey at different evolutionary stages. Column densities and beam-averaged abundances of o-H2D+ with respect to H2, X(o-H2D+), were obtained by modelling the spectra under the assumption of local thermodynamic equilibrium. Results. We detect 16 sources in o-H2D+ and find clear correlations between X(o-H2D+) and the clump bolometric luminosity and the dust temperature, while only a mild correlation is found with the CO-depletion factor. In addition, we see a clear correlation with the luminosity-to-mass ratio, which is known to trace the evolution of the star formation process. This would indicate that the deuterated forms of H3+ are more abundant in the very early stages of the star formation process and that deuteration is influenced by the time evolution of the clumps. In this respect, our findings would suggest that the X(o-H2D+) abundance is mainly affected by the thermal changes rather than density changes in the gas. We have employed these findings together with observations of H13CO+, DCO+, and C17O to provide an estimate of the cosmic-ray ionisation rate in a sub-sample of eight clumps based on recent analytical work. Conclusions. Our study presents the largest sample of o-H2D+ in star-forming regions to date. The results confirm that the deuteration process is strongly affected by temperature and suggests that o-H2D+ can be considered a reliable chemical clock during the star formation processes, as proved by its strong temporal dependence.

scholarly journals Interferometric Observations of Chemistry in High-Mass Star-Forming Regions

2000 ◽  
Vol 197 ◽  
pp. 125-133 ◽  
Author(s):  
Peter Schilke ◽  
Karl M. Menten ◽  
Friedrich Wyrowski ◽  
C. M. Walmsley
Keyword(s):  
Chemical Properties ◽  
High Mass ◽  
Mass Star ◽  
Line Density ◽  
Complex Molecules ◽  
Star Forming ◽  
Star Forming Regions ◽  
High Line ◽  
Interferometric Study ◽  
Very High

Single dish spectral line surveys of high mass star-forming regions provide spectra with a very high line density, and reveal the presence of many complex molecules. Besides the prototypical Orion BN/KL region, more and more regions get surveyed and we start to get a better idea of the chemical similarities and differences. Yet, single dish studies miss an important aspect of hot cores, which is revealed by higher resolution studies with interferometers: the cores are not chemically homogeneous, but a pronounced chemical substructure exists. As an example of such an interferometric study, we will present one particular set of objects, the UC HII W3(OH) and its neighboring hot core W3(H2O) (otherwise known as the Turner-Welch object), and discuss their chemical properties.

Radio observations of molecules in the interstellar gas

1981 ◽  
Vol 303 (1480) ◽  
pp. 469-486 ◽  
Keyword(s):  
Molecular Clouds ◽  
Large Scale ◽  
Heavy Atom ◽  
Linear Chain ◽  
Angular Size ◽  
Line Emission ◽  
Spectral Lines ◽  
Interstellar Gas ◽  
Interstellar Molecules ◽  
Branched Chains

Radio astronomers have succeeded since 1968 in identifying nearly 50 molecules in the dense concentrations of the interstellar gas now generally termed molecular clouds. Most interstellar molecules are stable compounds familiar to the terrestrial chemist, but nearly one-fifth are ions, radicals and acetylenic carbon chains so reactive in the laboratory that before being detected in Space they had rarely been observed or were entirely unknown. The heavy atom backbone of the known interstellar molecules is a linear chain of C, N, O or S (Si is found in two diatomic molecules) ; rings and branched chains are missing. The most readily observed spectral lines of most interstellar molecules are rotational transitions at millimetre wavelengths. These are generally excited by H 2 collisions, and depending on the H 2 number density, the levels can be either in rotational equilibrium, or far from it. Maser line emission from OH, H 2 0 , SiO and CH 3 OH - extremely intense, small sources typically much less than 1" in angular size, often polarized and sometimes time-dependent - are the most striking examples of nonequilibrium excitation. A number of rare isotopic species are observed in interstellar molecules, those ol C, N and O having been studied the most intensively. Isotopic ratios differing from those on Earth by two- or threefold apparently exist, and in all but one case can be attributed to stellar nucleosynthesis since the formation of the Solar System. Molecular clouds apparently constitute an appreciable fraction of the interstellar medium by mass and are the largest reservoir of matter in Nature subject to the chemical bond. They are of great astronomical interest because of their central role in star formation and galactic structure: it is possible that all stars form in molecular clouds, and as molecular clouds are largely restricted to the spiral arms, they provide a new and highly specific tracer of the large-scale structure of the galactic system.

scholarly journals Stellar Populations in the Nuclei of Spiral Galaxies

1983 ◽  
Vol 6 ◽  
pp. 147-156 ◽  
Author(s):  
R. W. O’Connell
Keyword(s):  
Spiral Galaxies ◽  
Stellar Populations ◽  
Potential Well ◽  
Interstellar Gas ◽  
Central Potential ◽  
Star Forming ◽  
Star Forming Regions

Spiral galaxies are a composite of two dynamical population types: the spheroidal and disk populations. These can be studied in isolation in E and Irr galaxies, respectively. It is natural to expect that the combination in a spiral of a dense spheroidal population, having a deep central potential well, with a repository of interstellar gas and dust in the disk gives rise to special conditions not usually found in E or Irr galaxies. And in fact, we find spectacular concentrations of star forming regions in some spiral nuclei.In this review, I will limit most of the discussion to later spiral types which are classified as “intermediate” in the Yerkes system (Morgan and Osterbrock 1969). Types earlier than Sbc usually have “k-nuclei,” where the spheroidal population dominates; excellent reviews are available for these types (van den Bergh 1975, Faber 1977).

scholarly journals Interferometric and single-dish observations of 44, 84 and 95 GHz Class I methanol masers

2017 ◽  
Vol 13 (S336) ◽  
pp. 239-242
Author(s):  
Carolina B. Rodríguez-Garza ◽  
Stanley E. Kurtz ◽  
Arturo I. Gómez-Ruiz ◽  
Peter Hofner ◽  
Esteban D. Araya ◽  
...  
Keyword(s):  
Massive Star ◽  
Wide Band ◽  
Hii Regions ◽  
Spectral Lines ◽  
Class I ◽  
Detection Rates ◽  
Very Large Array ◽  
Star Forming ◽  
Star Forming Regions ◽  
Methanol Masers

AbstractWe present observations of massive star-forming regions selected from the IRAS Point Source Catalog. The observations were made with the Very Large Array and the Large Millimeter Telescope to search for Class I methanol masers. We made interferometric observations of 125 massive star-forming regions in the 44 GHz methanol maser transition; 53 of the 125 fields showed emission. The data allow us to demonstrate associations, at arcsecond precision, of the Class I maser emission with outflows, HII regions and shocks traced by 4.5 μm emission. We made single-dish observations toward 38 of the 53 regions with 44 GHz masers detected to search for the methanol transitions at 84.5, 95.1, 96.7, 107.0, and 108.8 GHz. We find detection rates of 74, 55, 100, 3, and 45%, respectively. We used a wide-band receiver which revealed many other spectral lines that are common in star-forming regions.

scholarly journals Resolved Spectroscopy of Gravitationally Lensed Galaxies at z≃2

2014 ◽  
Vol 10 (S309) ◽  
pp. 247-250
Author(s):  
Tucker Jones
Keyword(s):  
Gas Phase ◽  
Gravitational Lensing ◽  
Gravitational Interaction ◽  
Interstellar Gas ◽  
Star Forming ◽  
Spatially Resolved ◽  
Star Forming Regions ◽  
Integral Field Spectroscopy ◽  
Isolated Galaxies ◽  
Spatially Resolved Spectroscopy

AbstractSpatially resolved spectroscopy is even more powerful when combined with magnification by gravitational lensing. I discuss observations of lensed galaxies at z≃2 with spatial resolution reaching 100 parsecs. Near-IR integral field spectroscopy reveals the kinematics, distribution and physical properties of star forming regions, and gas-phase metallicity gradients. Roughly two thirds of observed galaxies are isolated systems with coherent velocity fields, large velocity dispersion, multiple giant star-forming regions, and negative gas-phase metallicity gradients, suggestive of inside-out growth in gravitationally unstable disks. The remainder are undergoing mergers and have shallower metallicity gradients, indicating mixing of the interstellar gas via gravitational interaction. The metallicity gradients in isolated galaxies are consistent with simulations using standard feedback prescriptions, whereas simulations with enhanced feedback predict shallower gradients. These measurements therefore constrain the growth of galaxies from mergers and star formation as well as the regulatory feedback.

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