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Sample records for adjacent molecular cloud

  1. Identifying Nearby Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Rathborne, J. M.; Shah, R. Y., Jackson, J. M.; Bania, T. M.; Clemens, D. P.; Johnson, A. M.; Flynn, E.; Bonaventura, N.; Simon, R.; Meyer, M. H.

    2004-12-01

    Recent molecular surveys, such as the BU-FCRAO Galactic Ring Survey, are revealing the complex structure and dynamics of clouds within the Galactic plane. Yet, difficulties often remain in separating molecular clouds along a line of sight. Identification of nearby clouds is facilitated through the combination of molecular datasets and extinction maps. Star counts at optical and infrared (IR) wavelengths indirectly trace extinction, and when morphologically similar to molecular emission, unambiguously reveal nearby clouds. Here we present the methodology and data used to separate and determine the relative distance to two molecular clouds along the same line of sight (GRSMC 45.60+0.30 and GRSMC 45.46+0.05). We use a combination of optical and near-IR star count maps (derived from the US Naval Observatory and 2MASS catalogs, respectively) and molecular data from the BU-FCRAO Galactic Ring Survey.

  2. Interstellar molecular clouds

    NASA Astrophysics Data System (ADS)

    Bally, J.

    1986-04-01

    The physical properties of the molecular phase of the interstellar medium are studied with regard to star formation and the structure of the Galaxy. Most observations of molecular clouds are made with single-dish, high-surface precision radio telescopes, with the best resolution attainable at 0.2 to 1 arcmin; the smallest structures that can be resolved are of order 10 to the 17th cm in diameter. It is now believed that: (1) most of the mass of the Galaxy is in the form of giant molecular clouds; (2) the largest clouds and those responsible for most massive star formation are concentrated in spiral arms; (3) the molecular clouds are the sites of perpetual star formation, and are significant in the chemical evolution of the Galaxy; (4) giant molecular clouds determine the evolution of the kinematic properties of galactic disk stars; (5) the total gas content is diminishing with time; and (6) most clouds have supersonic internal motions and do not form stars on a free-fall time scale. It is concluded that though progress has been made, more advanced instruments are needed to inspect the processes operating within stellar nurseries and to study the distribution of the molecular clouds in more distant galaxies. Instruments presently under construction which are designed to meet these ends are presented.

  3. THE CALIFORNIA MOLECULAR CLOUD

    SciTech Connect

    Lada, Charles J.; Lombardi, Marco; Alves, Joao F. E-mail: mlombard@eso.or

    2009-09-20

    We present an analysis of wide-field infrared extinction maps of a region in Perseus just north of the Taurus-Auriga dark cloud complex. From this analysis we have identified a massive, nearby, but previously unrecognized, giant molecular cloud (GMC). Both a uniform foreground star density and measurements of the cloud's velocity field from CO observations indicate that this cloud is likely a coherent structure at a single distance. From comparison of foreground star counts with Galactic models, we derive a distance of 450 +- 23 pc to the cloud. At this distance the cloud extends over roughly 80 pc and has a mass of {approx} 10{sup 5} M{sub sun}, rivaling the Orion (A) molecular cloud as the largest and most massive GMC in the solar neighborhood. Although surprisingly similar in mass and size to the more famous Orion molecular cloud (OMC) the newly recognized cloud displays significantly less star formation activity with more than an order of magnitude fewer young stellar objects than found in the OMC, suggesting that both the level of star formation and perhaps the star formation rate in this cloud are an order of magnitude or more lower than in the OMC. Analysis of extinction maps of both clouds shows that the new cloud contains only 10% the amount of high extinction (A{sub K} > 1.0 mag) material as is found in the OMC. This, in turn, suggests that the level of star formation activity and perhaps the star formation rate in these two clouds may be directly proportional to the total amount of high extinction material and presumably high density gas within them and that there might be a density threshold for star formation on the order of n(H{sub 2}) {approx} a few x 10{sup 4} cm{sup -3}.

  4. Turbulence in molecular clouds

    NASA Astrophysics Data System (ADS)

    Dickman, R. L.

    The basic aim of this paper is to offer a primer of basic concepts and methods of analysis for observationally-oriented individuals who wish to work in the rapidly developing area of molecular cloud turbulence. First the difficulties which beset early attempts to determine the nature of gas motions within molecular clouds are reviewed. Some aspects of turbulence as a hydrodynamic phenomenon are considered next along with an introduction to the statistical vocabulary of the subject which is required to understand the methods for analyzing observational data. A simple and useful approximation for estimating the velocity correlation length of a molecular cloud is also described. The paper concludes with a final perspective, which considers the extent to which size-velocity dispersion correlations can serve as a probe of chaotic velocity fields in molecular clouds.

  5. Interstellar molecular clouds.

    PubMed

    Bally, J

    1986-04-11

    The interstellar medium in our galaxy contains matter in a variety of states ranging from hot plasma to cold and dusty molecular gas. The molecular phase consists of giant clouds, which are the largest gravitationally bound objects in the galaxy, the primary reservoir of material for the ongoing birth of new stars, and the medium regulating the evolution of galactic disks.

  6. HNCO in molecular clouds

    SciTech Connect

    Jackson, J.M.; Armstrong, J.T.; Barrett, A.H.

    1984-05-15

    In a survey of 18 molecular clouds, HNCO J/sub K/-1K1..-->..J'/sub K/'-1K'1 = 5/sub 05/..-->..4/sub 05/ and 4/sub 04/..-->..3/sub 03/ emission was etected in seven clouds, and possibly in one other. Emission in these transitions originates in high-density regions (n> or approx. =10/sup 6/ cm/sup -3/). The molecule's excitation requirements allow us to derive limits to excitation temperatures an optical depths. We discuss the possibility of clumping with respect to the beam and compare our results with data from other molecular species. The HNCO emission from Sgr A is an ordder of magnitude larger than the other detected sources as is the ratio ..delta..T +- /sub A/(HNCO 5/sub 05/..-->..4/sub 04/)/..delta..T +- /sub A/(C/sup 18/O 1..-->..0). HNCO is probably a constituent of most molecular clouds.

  7. CLOUD PEAK PRIMITIVE AREA AND ADJACENT AREAS, WYOMING.

    USGS Publications Warehouse

    Kiilsgaard, Thor H.; Patten, Lowell L.

    1984-01-01

    The results of a mineral survey of the Cloud Peak Primitive Area and adjacent areas in Wyoming indicated little promise for the occurrence of mineral resources. There are some prospect workings, particularly in the northern part of the area, but in none of them were there indications that ore had been mined. Samples from the workings, from nearby rocks and sediments from streams that drain the area did not yield any metal values of significance. The crystalline rocks that underlie the area do not contain oil and gas or coal, products that are extracted from the younger rocks that underlie basins on both sides of the study area.

  8. Chemical evolution of molecular clouds

    NASA Technical Reports Server (NTRS)

    Prasad, Sheo S.; Tarafdar, Sankar P.; Villere, Karen R.; Huntress, Wesley T., Jr.

    1987-01-01

    The principles behind the coupled chemical-dynamical evolution of molecular clouds are described. Particular attention is given to current problems involving the simplest species (i.e., C. CO, O2, and H2) in quiescent clouds. The results of a comparison made between the molecular abundances in the Orion ridge and the hot core (Blake, 1986) are presented.

  9. Physical conditions in molecular clouds

    NASA Technical Reports Server (NTRS)

    Evans, Neal J., II

    1989-01-01

    Recent developments have complicated the picture of the physical conditions in molecular clouds. The discoveries of widespread emission from high-J lines of CD and 12-micron IRAS emission have revealed the presence of considerably hotter gas and dust near the surfaces of molecular clouds. These components can complicate interpretation of the bulk of the cloud gas. Commonly assumed relations between column density or mean density and cloud size are called into question by conflicting results and by consideration of selection effects. Analysis of density and density structure through molecular excitation has shown that very high densities exist in star formation regions, but unresolved structure and possible chemical effects complicate the interpretation. High resolution far-IR and submillimeter observations offer a complementary approach and are beginning to test theoretical predictions of density gradients in clouds.

  10. ASTROCHEMICAL CORRELATIONS IN MOLECULAR CLOUDS

    SciTech Connect

    Gaches, Brandt A. L.; Offner, Stella S. R.; Rosolowsky, Erik W.; Bisbas, Thomas G. E-mail: soffner@astro.umass.edu E-mail: tb@star.ucl.ac.uk

    2015-02-01

    We investigate the spectral correlations between different species used to observe molecular clouds. We use hydrodynamic simulations and a full chemical network to study the abundances of over 150 species in typical Milky Way molecular clouds. We perform synthetic observations in order to produce emission maps of a subset of these tracers. We study the effects of different lines of sight and spatial resolution on the emission distribution and perform a robust quantitative comparison of the species to each other. We use the Spectral Correlation Function (SCF), which quantifies the root mean squared difference between spectra separated by some length scale, to characterize the structure of the simulated cloud in position-position-velocity (PPV) space. We predict the observed SCF for a broad range of observational tracers, and thus identify homologous species. In particular, we show that the pairs C and CO, C{sup +} and CN, and NH{sub 3} and H{sub 2}CS have very similar SCFs. We measure the SCF slope variation as a function of beam size for all species and demonstrate that the beam size has a distinct effect on different species emission. However, for beams of up to 10'', placing the cloud at 1 kpc, the change is not large enough to move the SCF slopes into different regions of parameter space. The results from this study provide observational guidance for choosing the best tracer to probe various cloud length scales.

  11. Molecular Clouds: Observation to Experiment

    SciTech Connect

    Kane, J O; Ryutov, D D; Mizuta, A; Remington, B A; Pound, M W

    2004-05-06

    Our ongoing investigation of how 'Pillars' and other structure form in molecular clouds irradiated by ultraviolet (UV) stars has revealed that the Rayleigh-Taylor instability is strongly suppressed by recombination in the photoevaporated outflow, that clumps and filaments may be key, that the evolution of structure is well-modeled by compressible hydrodynamics, and that directionality of the UV radiation may have significant effects. We discuss a generic, flexible set of laboratory experiments that can address these issues.

  12. AceCloud: Molecular Dynamics Simulations in the Cloud.

    PubMed

    Harvey, M J; De Fabritiis, G

    2015-05-26

    We present AceCloud, an on-demand service for molecular dynamics simulations. AceCloud is designed to facilitate the secure execution of large ensembles of simulations on an external cloud computing service (currently Amazon Web Services). The AceCloud client, integrated into the ACEMD molecular dynamics package, provides an easy-to-use interface that abstracts all aspects of interaction with the cloud services. This gives the user the experience that all simulations are running on their local machine, minimizing the learning curve typically associated with the transition to using high performance computing services.

  13. Molecular disorganization of axons adjacent to human lacunar infarcts.

    PubMed

    Hinman, Jason D; Lee, Monica D; Tung, Spencer; Vinters, Harry V; Carmichael, S Thomas

    2015-03-01

    Cerebral microvascular disease predominantly affects brain white matter and deep grey matter, resulting in ischaemic damage that ranges from lacunar infarcts to white matter hyperintensities seen on magnetic resonance imaging. These lesions are common and result in both clinical stroke syndromes and accumulate over time, resulting in cognitive deficits and dementia. Magnetic resonance imaging studies suggest that these lesions progress over time, accumulate adjacent to prior lesions and have a penumbral region susceptible to further injury. The pathological correlates of this adjacent injury in surviving myelinated axons have not been previously defined. In this study, we sought to determine the molecular organization of axons in tissue adjacent to lacunar infarcts and in the regions surrounding microinfarcts, by determining critical elements in axonal function: the morphology and length of node of Ranvier segments and adjacent paranodal segments. We examined post-mortem brain tissue from six patients with lacunar infarcts and tissue from two patients with autosomal dominant retinal vasculopathy and cerebral leukoencephalopathy (previously known as hereditary endotheliopathy with retinopathy, nephropathy and stroke) who accumulate progressive white matter ischaemic lesions in the form of lacunar and microinfarcts. In axons adjacent to lacunar infarcts yet extending up to 150% of the infarct diameter away, both nodal and paranodal length increase by ∼20% and 80%, respectively, reflecting a loss of normal cell-cell adhesion and signalling between axons and oligodendrocytes. Using premorbid magnetic resonance images, brain regions from patients with retinal vasculopathy and cerebral leukoencephalopathy that harboured periventricular white matter hyperintensities were selected and the molecular organization of axons was determined within these regions. As in regions adjacent to lacunar infarcts, nodal and paranodal length in white matter of these patients is

  14. Molecular disorganization of axons adjacent to human lacunar infarcts

    PubMed Central

    Lee, Monica D.; Tung, Spencer; Vinters, Harry V.; Carmichael, S. Thomas

    2015-01-01

    Cerebral microvascular disease predominantly affects brain white matter and deep grey matter, resulting in ischaemic damage that ranges from lacunar infarcts to white matter hyperintensities seen on magnetic resonance imaging. These lesions are common and result in both clinical stroke syndromes and accumulate over time, resulting in cognitive deficits and dementia. Magnetic resonance imaging studies suggest that these lesions progress over time, accumulate adjacent to prior lesions and have a penumbral region susceptible to further injury. The pathological correlates of this adjacent injury in surviving myelinated axons have not been previously defined. In this study, we sought to determine the molecular organization of axons in tissue adjacent to lacunar infarcts and in the regions surrounding microinfarcts, by determining critical elements in axonal function: the morphology and length of node of Ranvier segments and adjacent paranodal segments. We examined post-mortem brain tissue from six patients with lacunar infarcts and tissue from two patients with autosomal dominant retinal vasculopathy and cerebral leukoencephalopathy (previously known as hereditary endotheliopathy with retinopathy, nephropathy and stroke) who accumulate progressive white matter ischaemic lesions in the form of lacunar and microinfarcts. In axons adjacent to lacunar infarcts yet extending up to 150% of the infarct diameter away, both nodal and paranodal length increase by ∼20% and 80%, respectively, reflecting a loss of normal cell-cell adhesion and signalling between axons and oligodendrocytes. Using premorbid magnetic resonance images, brain regions from patients with retinal vasculopathy and cerebral leukoencephalopathy that harboured periventricular white matter hyperintensities were selected and the molecular organization of axons was determined within these regions. As in regions adjacent to lacunar infarcts, nodal and paranodal length in white matter of these patients is

  15. Astrochemical Correlations in Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Gaches, Brandt A.L.; Offner, Stella

    2014-06-01

    We investigate the spectral correlations between different chemical tracers used to observe molecular clouds. We study a 600 Solar Mass molecular cloud with Mach number 6.6 modeled using the magnetohydrodynamic code ORION. The chemical abundances are calculated by 3D-PDR, a three-dimensional astrochemical code using a full network of 3300 reactions and 215 species. We take synthetic observations of 16 different species using the non-LTE radiative transfer code RADMC-3D. The effects of different lines of sight and spatial resolution on the emission maps of the 16 different species will be discussed in this talk.We use the Spectral Correlation Function to quantify the structure of the simulated cloud in position-position-velocity space, which measures the average rms velocity between spectra separated by a given length scale. This statistic has been shown to be sensitive to global hydrodynamic parameters, such as the sonic Mach number and velocity dispersion. The SCF is analytically fit by a power law, with the slope being the one free parameter. We verify that the SCF is generally insensitive to the sightline through the cloud. We discover that the beam size has a distinct effect on different chemical tracers. However, the change is not large enough to move the SCF slopes into different parts of the parameter space. This is the first quantitative 3D study of the spectral similarity of a variety of species. We predict the observed SCF for a broad range of observational tracers, and thus, identify complementary species. In particular, we show that the pairs C and CO, C+ and CN, NH3 and H2CS have very similar SCFs. The results from this study will also give observers a guide for selecting which chemical tracers would be best for observing different length scales.

  16. TURBULENCE DECAY AND CLOUD CORE RELAXATION IN MOLECULAR CLOUDS

    SciTech Connect

    Gao, Yang; Law, Chung K.; Xu, Haitao

    2015-02-01

    The turbulent motion within molecular clouds is a key factor controlling star formation. Turbulence supports molecular cloud cores from evolving to gravitational collapse and hence sets a lower bound on the size of molecular cloud cores in which star formation can occur. On the other hand, without a continuous external energy source maintaining the turbulence, such as in molecular clouds, the turbulence decays with an energy dissipation time comparable to the dynamic timescale of clouds, which could change the size limits obtained from Jean's criterion by assuming constant turbulence intensities. Here we adopt scaling relations of physical variables in decaying turbulence to analyze its specific effects on the formation of stars. We find that the decay of turbulence provides an additional approach for Jeans' criterion to be achieved, after which gravitational infall governs the motion of the cloud core. This epoch of turbulence decay is defined as cloud core relaxation. The existence of cloud core relaxation provides a more complete understanding of the effect of the competition between turbulence and gravity on the dynamics of molecular cloud cores and star formation.

  17. FORMATION OF MASSIVE MOLECULAR CLOUD CORES BY CLOUD-CLOUD COLLISION

    SciTech Connect

    Inoue, Tsuyoshi; Fukui, Yasuo

    2013-09-10

    Recent observations of molecular clouds around rich massive star clusters including NGC 3603, Westerlund 2, and M20 revealed that the formation of massive stars could be triggered by a cloud-cloud collision. By using three-dimensional, isothermal, magnetohydrodynamics simulations with the effect of self-gravity, we demonstrate that massive, gravitationally unstable, molecular cloud cores are formed behind the strong shock waves induced by cloud-cloud collision. We find that the massive molecular cloud cores have large effective Jeans mass owing to the enhancement of the magnetic field strength by shock compression and turbulence in the compressed layer. Our results predict that massive molecular cloud cores formed by the cloud-cloud collision are filamentary and threaded by magnetic fields perpendicular to the filament.

  18. Fragmentation in filamentary molecular clouds

    NASA Astrophysics Data System (ADS)

    Contreras, Yanett; Garay, Guido; Rathborne, Jill M.; Sanhueza, Patricio

    2016-02-01

    Recent surveys of dust continuum emission at sub-mm wavelengths have shown that filamentary molecular clouds are ubiquitous along the Galactic plane. These structures are inhomogeneous, with overdensities that are sometimes associated with infrared emission and active of star formation. To investigate the connection between filaments and star formation, requires an understanding of the processes that lead to the fragmentation of filaments and a determination of the physical properties of the overdensities (clumps). In this paper, we present a multiwavelength study of five filamentary molecular clouds, containing several clumps in different evolutionary stages of star formation. We analyse the fragmentation of the filaments and derive the physical properties of their clumps. We find that the clumps in all filaments have a characteristic spacing consistent with the prediction of the `sausage' instability theory, regardless of the complex morphology of the filaments or their evolutionary stage. We also find that most clumps have sufficient mass and density to form high-mass stars, supporting the idea that high-mass stars and clusters form within filaments.

  19. A Simple Model for the Cloud Adjacency Effect and the Apparent Bluing of Aerosols Near Clouds

    NASA Technical Reports Server (NTRS)

    Marshak, Alexander; Wen, Guoyong; Coakley, James A., Jr.; Remer, Lorraine A.; Loeb,Norman G.; Cahalan, Robert F.

    2008-01-01

    In determining aerosol-cloud interactions, the properties of aerosols must be characterized in the vicinity of clouds. Numerous studies based on satellite observations have reported that aerosol optical depths increase with increasing cloud cover. Part of the increase comes from the humidification and consequent growth of aerosol particles in the moist cloud environment, but part comes from 3D cloud-radiative transfer effects on the retrieved aerosol properties. Often, discerning whether the observed increases in aerosol optical depths are artifacts or real proves difficult. The paper provides a simple model that quantifies the enhanced illumination of cloud-free columns in the vicinity of clouds that are used in the aerosol retrievals. This model is based on the assumption that the enhancement in the cloud-free column radiance comes from enhanced Rayleigh scattering that results from the presence of the nearby clouds. The enhancement in Rayleigh scattering is estimated using a stochastic cloud model to obtain the radiative flux reflected by broken clouds and comparing this flux with that obtained with the molecules in the atmosphere causing extinction, but no scattering.

  20. Little Massive Substructure in CMZ Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Kauffmann, J.; Pillai, T.; Zhang, Q.; Menten, K. M.; Goldsmith, P. F.; Lu, X.; Guzman, A. E.

    2016-05-01

    The Central Molecular Zone (CMZ; inner ˜100pc) hosts some of the most dense and massive molecular clouds of the Milky Way. Studying these clouds can potentially lead to a better understanding of the dense clouds seen in the central starburst regions in nearby galaxies or in the early universe. The clouds share an unusual feature: they form stars at an unusually slow rate compared to other Milky Way clouds of similar mass and density. Here we use interferometer data from ALMA and the SMA to show that this reduced star formation rate is a consequence of the cloud density structure: CMZ clouds have unusually flat density slopes. The clouds do, for example, exceed the average density of the Orion A molecular cloud by an order of magnitude on spatial scales ˜5 pc, but the cores of CMZ clouds with ˜0.1 pc radius often have masses and densities lower than what is found in the Orion KL region. This relative absence of highest-density gas probably explains the suppression of star formation. The clouds are relatively turbulent, and ALMA observations of H2CO and SiO indicate that the turbulence is induced by high-velocity shocks. We speculate that these shocks might prevent the formation of high-mass cores.

  1. The chemical composition of interstellar molecular clouds

    NASA Technical Reports Server (NTRS)

    Irvine, W. M.; Hjalmarson, A.

    1984-01-01

    Quantitative molecular abundances are becoming available for dense interstellar clouds and circumstellar envelopes, revealing both similarities across a wide range of source conditions and significant differences in the chemistries involved. As understanding concerning the processes that lead to particular compositions increases, it may become possible to relate these findings to the evolution of molecular clouds and hence to the chemistry of regions in which stellar and planetary formation is in progress. Attention is given to the results of a recently completed spectral scan of the Orion molecular cloud, as well as the envelope around the evolved star IRC + 10216, published by Johansson et al. (1983).

  2. Diffuse Molecular Cloud Chemistry: Successes and Challenges

    NASA Astrophysics Data System (ADS)

    Sonnentrucker, Paule

    2014-06-01

    Diffuse molecular clouds are transitional objects thought to form the bridge between the diffuse atomic medium and dense molecular clouds. As a result, their study is critical to advancing our understanding of how molecular clouds form from, and disperse back into, the interstellar medium (ISM). Due to their intrinsically low opacities, diffuse molecular clouds were thought to harbor relatively simple physics and chemistry. However, numerous ground- and space-based observations obtained over a wide wavelength range have uncovered an unexpected molecular complexity that is partially unaccounted for in theories of interstellar clouds and of star and planet formation. The discrepancies between diffuse cloud model predictions and astronomical observations are usually driven by only a few- but major- unknowns: the intrinsic complexity of the observed gas structure in the ISM, a complexity often only partially accounted for in theories, the uncertainties attached to various reaction rates or chemical pathways included in current theories, or the limitations attached to available astronomical instrumentation. I will show how concerted efforts between the astronomical, the theoretical and the laboratory communities have successfully reconciled differences between theoretical predictions and astronomical observations of diffuse molecular clouds and I will discuss how such collaborative efforts need to be pursued in order to address some of the challenges posed by recent astronomical observations.

  3. Theory of grain alignment in molecular clouds

    NASA Technical Reports Server (NTRS)

    Roberge, Wayne G.

    1993-01-01

    Research accomplishments are presented and include the following: (1) mathematical theory of grain alignment; (2) super-paramagnetic alignment of molecular cloud grains; and (3) theory of grain alignment by ambipolar diffusion.

  4. DISTRIBUTION OF WATER VAPOR IN MOLECULAR CLOUDS

    SciTech Connect

    Melnick, Gary J.; Tolls, Volker; Snell, Ronald L.; Bergin, Edwin A.; Hollenbach, David J.; Kaufman, Michael J.; Li Di; Neufeld, David A. E-mail: vtolls@cfa.harvard.edu E-mail: ebergin@umich.edu E-mail: mkaufman@email.sjsu.edu E-mail: neufeld@pha.jhu.edu

    2011-01-20

    We report the results of a large-area study of water vapor along the Orion Molecular Cloud ridge, the purpose of which was to determine the depth-dependent distribution of gas-phase water in dense molecular clouds. We find that the water vapor measured toward 77 spatial positions along the face-on Orion ridge, excluding positions surrounding the outflow associated with BN/KL and IRc2, display integrated intensities that correlate strongly with known cloud surface tracers such as CN, C{sub 2}H, {sup 13}CO J = 5-4, and HCN, and less well with the volume tracer N{sub 2}H{sup +}. Moreover, at total column densities corresponding to A{sub V}< 15 mag, the ratio of H{sub 2}O to C{sup 18}O integrated intensities shows a clear rise approaching the cloud surface. We show that this behavior cannot be accounted for by either optical depth or excitation effects, but suggests that gas-phase water abundances fall at large A{sub V}. These results are important as they affect measures of the true water-vapor abundance in molecular clouds by highlighting the limitations of comparing measured water-vapor column densities with such traditional cloud tracers as {sup 13}CO or C{sup 18}O. These results also support cloud models that incorporate freeze out of molecules as a critical component in determining the depth-dependent abundance of water vapor.

  5. Carbon depletion in turbulent molecular cloud cores

    NASA Astrophysics Data System (ADS)

    Boland, W.; de Jong, T.

    1982-10-01

    Observations of dense molecular cores indicate that about 10% of the carbon is still in the gas phase (depletion factor of about 0.1) in spite of the fact that the depletion time - the time needed for heavy elements to freeze out on dust grains - is several orders of magnitude smaller than the cloud lifetime. To resolve this problem, it is suggested that the material in molecular cloud cores is circulated by turbulence and that every time a parcel of gas and dust reaches the outer layers of the core, dust mantles that have formed by accretion in the center are evaporated and/or photodesorbed. The observed mild degree of depletion results because the circulation time and the depletion time are of the same order of magnitude. Since the time to reach molecular equilibrium in the outer layers of a cloud core is short compared with the circulation time the dust plays no role in the chemistry. In the center of a cloud core, the time to convert C to CO is of the order of the circulation time, so that an appreciable fraction of the gaseous carbon remains in atomic form. From a brief discussion of the energetics, it is concluded that the turbulence observed in molecular cloud cores can be maintained during the lifetime of the cloud if the envelope collapses onto the core at a rate of about 0.000001 solar mass per year.

  6. Carbon Isotope Chemistry in Molecular Clouds

    NASA Technical Reports Server (NTRS)

    Robertson, Amy N.; Willacy, Karen

    2012-01-01

    Few details of carbon isotope chemistry are known, especially the chemical processes that occur in astronomical environments like molecular clouds. Observational evidence shows that the C-12/C-13 abundance ratios vary due to the location of the C-13 atom within the molecular structure. The different abundances are a result of the diverse formation pathways that can occur. Modeling can be used to explore the production pathways of carbon molecules in an effort to understand and explain the chemical evolution of molecular clouds.

  7. Molecular clouds and galactic spiral structure

    NASA Technical Reports Server (NTRS)

    Dame, T. M.

    1984-01-01

    Galactic CO line emission at 115 GHz was surveyed in order to study the distribution of molecular clouds in the inner galaxy. Comparison of this survey with similar H1 data reveals a detailed correlation with the most intense 21 cm features. To each of the classical 21 cm H1 spiral arms of the inner galaxy there corresponds a CO molecular arm which is generally more clearly defined and of higher contrast. A simple model is devised for the galactic distribution of molecular clouds. The modeling results suggest that molecular clouds are essentially transient objects, existing for 15 to 40 million years after their formation in a spiral arm, and are largely confined to spiral features about 300 pc wide.

  8. Molecular clouds in the Carina arm

    NASA Technical Reports Server (NTRS)

    Cohen, R. S.; Grabelsky, D. A.; May, J.; Alvarez, H.; Bronfman, L.; Thaddeus, P.

    1985-01-01

    From a new survey of the 2.6 mm line of CO in the southern Milky Way, 37 molecular clouds were identified along the Carina arm from l = 282 deg to 336 deg with masses generally greater than 10 to the 5th solar mass. The clouds lie approximately every 700 pc along a spiral segment that is nearly 25 kpc long and has a pitch of about 10 deg. The total mass of these clouds is 40 x 10 to the 6th solar mass, or rougly 1 x 10 to the 6th solar mass each on average. The abrupt tangent point in molecular clouds at l = 280 deg and the characteristic loop structure in the l-v diagram are unmistakable evidence of a CO spiral arm in Carina. This arm apparently connects with the northern hemisphere Sagittarius arm to form a single 10 deg spiral which extends more than two-thirds of the way around the Galaxy.

  9. Magnetic diffusion in clumpy molecular clouds

    NASA Astrophysics Data System (ADS)

    Elmegreen, B. G.; Combes, F.

    1992-06-01

    Magnetic diffusion in a clumpy cloud is slower than in a uniform cloud with the same average density and field strength, by the square root of the clump filling factor, f. This implies that giant molecular clouds can maintain their supporting magnetic fields for at least 6/sq rt f free fall times, while allowing a moderate rate of star formation in the dense cores. The f dependence also implies that clouds or cloud cores larger than a thermal Jeans mass will lose their flux more slowly compared to the free-fall time than smaller cores because the larger regions have supersonic virialized motions, and this inevitably leads to small scale clumpy structure by nonlinear effects. Thus star formation may proceed rapidly via diffusion in uniform cores that have primarily thermal motions (large f), while the surrounding clumpy cloud can be supported by the field for a relatively long time (small f). The slower magnetic diffusion rate for clumpy clouds compared to uniform clouds also affects the local heating rate for neutral gas in a shock, giving more of a J-type than C-type structure by shortening the magnetic precursor and causing clump collisions at speeds exceeding the internal Alfven speed.

  10. Structures in Molecular Clouds: Modeling

    SciTech Connect

    Kane, J O; Mizuta, A; Pound, M W; Remington, B A; Ryutov, D D

    2006-04-20

    We attempt to predict the observed morphology, column density and velocity gradient of Pillar II of the Eagle Nebula, using Rayleigh Taylor (RT) models in which growth is seeded by an initial perturbation in density or in shape of the illuminated surface, and cometary models in which structure is arises from a initially spherical cloud with a dense core. Attempting to mitigate suppression of RT growth by recombination, we use a large cylindrical model volume containing the illuminating source and the self-consistently evolving ablated outflow and the photon flux field, and use initial clouds with finite lateral extent. An RT model shows no growth, while a cometary model appears to be more successful at reproducing observations.

  11. Molecular clouds. [significance in stellar evolution

    NASA Technical Reports Server (NTRS)

    Thaddeus, P.

    1977-01-01

    An attempt is made to understand star formation in the context of the dense interstellar molecular gas from which stars are made. Attention is given to how molecular observations (e.g., UV spectroscopy and radio 21-cm and recombination line observations) provide data on the physical state of the dense interstellar gas; observations of H II regions, stellar associations, and dark nebulae are discussed. CO clouds are studied with reference to radial velocity, temperature, density, ionization, magnetic field.

  12. Cloud-cloud collision in the Galactic center 50 km s-1 molecular cloud

    NASA Astrophysics Data System (ADS)

    Tsuboi, Masato; Miyazaki, Atsushi; Uehara, Kenta

    2015-12-01

    We performed a search of star-forming sites influenced by external factors, such as SNRs, H II regions, and cloud-cloud collisions (CCCs), to understand the star-forming activity in the Galactic center region using the NRO Galactic Center Survey in SiO v = 0, J = 2-1, H13CO+J = 1-0, and CS J = 1-0 emission lines obtained with the Nobeyama 45 m telescope. We found a half-shell-like feature (HSF) with a high integrated line intensity ratio of ∫TB(SiO v = 0, J = 2-1)dv/∫TB(H13CO+J = 1-0)dv ˜ 6-8 in the 50 km s-1 molecular cloud; the HSF is a most conspicuous molecular cloud in the region and harbors an active star-forming site where several compact H II regions can be seen. The high ratio in the HSF indicates that the cloud contains huge shocked molecular gas. The HSF can be also seen as a half-shell feature in the position-velocity diagram. A hypothesis explaining the chemical and kinetic properties of the HSF is that the feature originates from a CCC. We analyzed the CS J = 1-0 emission line data obtained with the Nobeyama Millimeter Array to reveal the relation between the HSF and the molecular cloud cores in the cloud. We made a cumulative core mass function (CMF) of the molecular cloud cores within the HSF. The CMF in the CCC region is not truncated at least up to ˜2500 M⊙, although the CMF of the non-CCC region reaches the upper limit of ˜1500 M⊙. Most massive molecular cores with Mgas > 750 M⊙ are located only around the ridge of the HSF and adjoin the compact H II region. These may be a sign of massive star formation induced by CCCs in the Galactic center region.

  13. Model calculations for diffuse molecular clouds. [interstellar hydrogen cloud model

    NASA Technical Reports Server (NTRS)

    Glassgold, A. E.; Langer, W. D.

    1974-01-01

    A steady state isobaric cloud model is developed. The pressure, thermal, electrical, and chemical balance equations are solved simultaneously with a simple one dimensional approximation to the equation of radiative transfer appropriate to diffuse clouds. Cooling is mainly by CII fine structure transitions, and a variety of heating mechanisms are considered. Particular attention is given to the abundance variation of H2. Inhomogeneous density distributions are obtained because of the attenuation of the interstellar UV field and the conversion from atomic to molecular hyrodgen. The effects of changing the model parameters are described and the applicability of the model to OAO-3 observations is discussed. Good qualitative agreement with the fractional H2 abundance determinations has been obtained. The observed kinetic temperatures near 80 K can also be achieved by grain photoelectron heating. The problem of the electron density is solved taking special account of the various hydrogen ions as well as heavier ones.

  14. Star formation relations in nearby molecular clouds

    SciTech Connect

    Evans, Neal J. II; Heiderman, Amanda; Vutisalchavakul, Nalin

    2014-02-20

    We test some ideas for star formation relations against data on local molecular clouds. On a cloud by cloud basis, the relation between the surface density of star formation rate and surface density of gas divided by a free-fall time, calculated from the mean cloud density, shows no significant correlation. If a crossing time is substituted for the free-fall time, there is even less correlation. Within a cloud, the star formation rate volume and surface densities increase rapidly with the corresponding gas densities, faster than predicted by models using the free-fall time defined from the local density. A model in which the star formation rate depends linearly on the mass of gas above a visual extinction of 8 mag describes the data on these clouds, with very low dispersion. The data on regions of very massive star formation, with improved star formation rates based on free-free emission from ionized gas, also agree with this linear relation.

  15. Formation of giant molecular clouds in global spiral structures: The role of orbital dynamics and cloud-cloud collisions

    NASA Technical Reports Server (NTRS)

    Roberts, W. W., Jr.; Stewart, G. R.

    1987-01-01

    The different roles played by orbital dynamics and dissipative cloud-cloud collisions in the formation of giant molecular clouds (GMCs) in a global spiral structure are investigated. The interstellar medium (ISM) is simulated by a system of particles, representing clouds, which orbit in a spiral-perturbed, galactic gravitational field. The overall magnitude and width of the global cloud density distribution in spiral arms is very similar in the collisional and collisionless simulations. The results suggest that the assumed number density and size distribution of clouds and the details of individual cloud-cloud collisions have relatively little effect on these features. Dissipative cloud-cloud collisions play an important steadying role for the cloud system's global spiral structure. Dissipative cloud-cloud collisions also damp the relative velocity dispersion of clouds in massive associations and thereby aid in the effective assembling of GMC-like complexes.

  16. Molecular abundances in the Sagittarius A molecular cloud.

    PubMed

    Minh, Y C; Irvine, W M; Friberg, P

    1992-01-01

    We have obtained column densities for HCO+, HCO, HCS+, C3H2, HC5N, SiO, OCS, HCOOH, CH3CH2OH, and CH3CCH toward Sgr A. The fractional abundance of SiO relative to molecular hydrogen in Sgr A is comparable to that for the Orion plateau, approximately 10(-7)-10(-8), which may be a typical value for hot clouds. The abundances of HCO, CH3CH2OH and CH3CCH all appear to be enhanced relative to other molecular clouds such as Sgr B2.

  17. What can simulated molecular clouds tell us about real molecular clouds?

    NASA Astrophysics Data System (ADS)

    Duarte-Cabral, A.; Dobbs, C. L.

    2016-06-01

    We study the properties of giant molecular clouds (GMCs) from a smoothed particle hydrodynamics simulation of a portion of a spiral galaxy, modelled at high resolution, with robust representations of the physics of the interstellar medium. We examine the global molecular gas content of clouds, and investigate the effect of using CO or H2 densities to define the GMCs. We find that CO can reliably trace the high-density H2 gas, but misses less dense H2 clouds. We also investigate the effect of using 3D CO densities versus CO emission with an observer's perspective, and find that CO-emission clouds trace well the peaks of the actual GMCs in 3D, but can miss the lower density molecular gas between density peaks which is often CO-dark. Thus, the CO emission typically traces smaller clouds within larger GMC complexes. We also investigate the effect of the galactic environment (in particular the presence of spiral arms), on the distribution of GMC properties, and we find that the mean properties are similar between arm and inter-arm clouds, but the tails of some distributions are indicative of intrinsic differences in the environment. We find highly filamentary clouds (similar to the giant molecular filaments of our Galaxy) exclusively in the inter-arm region, formed by galactic shear. We also find that the most massive GMC complexes are located in the arm, and that as a consequence of more frequent cloud interactions/mergers in the arm, arm clouds are more sub-structured and have higher velocity dispersions than inter-arm clouds.

  18. OH{sup +} IN DIFFUSE MOLECULAR CLOUDS

    SciTech Connect

    Porras, A. J.; Federman, S. R.; Welty, D. E.; Ritchey, A. M. E-mail: aporras@live.unc.edu E-mail: aritchey@astro.washington.edu

    2014-01-20

    Near ultraviolet observations of OH{sup +} and OH in diffuse molecular clouds reveal a preference for different environments. The dominant absorption feature in OH{sup +} arises from a main component seen in CH{sup +} (that with the highest CH{sup +}/CH column density ratio), while OH follows CN absorption. This distinction provides new constraints on OH chemistry in these clouds. Since CH{sup +} detections favor low-density gas with small fractions of molecular hydrogen, this must be true for OH{sup +} as well, confirming OH{sup +} and H{sub 2}O{sup +} observations with the Herschel Space Telescope. Our observed correspondence indicates that the cosmic ray ionization rate derived from these measurements pertains to mainly atomic gas. The association of OH absorption with gas rich in CN is attributed to the need for a high enough density and molecular fraction before detectable amounts are seen. Thus, while OH{sup +} leads to OH production, chemical arguments suggest that their abundances are controlled by different sets of conditions and that they coexist with different sets of observed species. Of particular note is that non-thermal chemistry appears to play a limited role in the synthesis of OH in diffuse molecular clouds.

  19. Masses, luminosities and dynamics of galactic molecular clouds

    NASA Technical Reports Server (NTRS)

    Solomon, P. M.; Rivolo, A. R.; Mooney, T. J.; Barrett, J. W.; Sage, L. J.

    1987-01-01

    Star formation in galaxies takes place in molecular clouds and the Milky Way is the only galaxy in which it is possible to resolve and study the physical properties and star formation activity of individual clouds. The masses, luminosities, dynamics, and distribution of molecular clouds, primarily giant molecular clouds in the Milky Way are described and analyzed. The observational data sets are the Massachusetts-Stony Brook CO Galactic Plane Survey and the IRAS far IR images. The molecular mass and infrared luminosities of glactic clouds are then compared with the molecular mass and infrared luminosities of external galaxies.

  20. Instabilities of rare rotating cold molecular clouds

    SciTech Connect

    Nekrasov, A. K.

    2009-03-15

    New electromagnetic streaming instabilities of rare rotating molecular clouds induced by the relative drift of ions, electrons, and dust grains in the equilibrium state are studied. The cases of a weak and strong collisional coupling of neutrals and ions in the perturbed state are involved. The dust grains are considered as unmagnetized having weak collisional coupling with neutrals in perturbations. The compressibility is taken into account. Axisymmetric perturbations with growth rates much larger than the rotation frequency are found.

  1. MOLECULAR TRACERS OF TURBULENT SHOCKS IN GIANT MOLECULAR CLOUDS

    SciTech Connect

    Pon, A.; Johnstone, D.; Kaufman, M. J. E-mail: Douglas.Johnstone@nrc-cnrc.gc.ca

    2012-03-20

    Giant molecular clouds contain supersonic turbulence and simulations of magnetohydrodynamic turbulence show that these supersonic motions decay in roughly a crossing time, which is less than the estimated lifetimes of molecular clouds. Such a situation requires a significant release of energy. We run models of C-type shocks propagating into gas with densities around 10{sup 3} cm{sup -3} at velocities of a few km s{sup -1}, appropriate for the ambient conditions inside of a molecular cloud, to determine which species and transitions dominate the cooling and radiative energy release associated with shock cooling of turbulent molecular clouds. We find that these shocks dissipate their energy primarily through CO rotational transitions and by compressing pre-existing magnetic fields. We present model spectra for these shocks, and by combining these models with estimates for the rate of turbulent energy dissipation, we show that shock emission should dominate over emission from unshocked gas for mid to high rotational transitions (J > 5) of CO. We also find that the turbulent energy dissipation rate is roughly equivalent to the cosmic-ray heating rate and that the ambipolar diffusion heating rate may be significant, especially in shocked gas.

  2. Morphological diagnostics of star formation in molecular clouds

    NASA Astrophysics Data System (ADS)

    Beaumont, Christopher Norris

    Molecular clouds are the birth sites of all star formation in the present-day universe. They represent the initial conditions of star formation, and are the primary medium by which stars transfer energy and momentum back to parsec scales. Yet, the physical evolution of molecular clouds remains poorly understood. This is not due to a lack of observational data, nor is it due to an inability to simulate the conditions inside molecular clouds. Instead, the physics and structure of the interstellar medium are sufficiently complex that interpreting molecular cloud data is very difficult. This dissertation mitigates this problem, by developing more sophisticated ways to interpret morphological information in molecular cloud observations and simulations. In particular, I have focused on leveraging machine learning techniques to identify physically meaningful substructures in the interstellar medium, as well as techniques to inter-compare molecular cloud simulations to observations. These contributions make it easier to understand the interplay between molecular clouds and star formation. Specific contributions include: new insight about the sheet-like geometry of molecular clouds based on observations of stellar bubbles; a new algorithm to disambiguate overlapping yet morphologically distinct cloud structures; a new perspective on the relationship between molecular cloud column density distributions and the sizes of cloud substructures; a quantitative analysis of how projection effects affect measurements of cloud properties; and an automatically generated, statistically-calibrated catalog of bubbles identified from their infrared morphologies.

  3. The chemical evolution of molecular clouds

    NASA Technical Reports Server (NTRS)

    Iglesias, E.

    1977-01-01

    The nonequilibrium chemistry of dense molecular clouds (10,000 to 1 million hydrogen molecules per cu cm) is studied in the framework of a model that includes the latest published chemical data and most of the recent theoretical advances. In this model the only important external source of ionization is assumed to be high-energy cosmic-ray bombardment; standard charge-transfer reactions are taken into account as well as reactions that transfer charge from molecular ions to trace-metal atoms. Schemes are proposed for the synthesis of such species as NCO, HNCO, and CN. The role played by adsorption and condensation of molecules on the surface of dust grains is investigated, and effects on the chemical evolution of a dense molecular cloud are considered which result from varying the total density or the elemental abundances and from assuming negligible or severe condensation of gaseous species on dust grains. It is shown that the chemical-equilibrium time scale is given approximately by the depletion times of oxygen and nitrogen when the condensation efficiency is negligible; that this time scale is probably in the range from 1 to 4 million years, depending on the elemental composition and initial conditions in the cloud; and that this time scale is insensitive to variations in the total density.

  4. Nitrogen sulfide in giant molecular clouds.

    PubMed

    McGonagle, D; Irvine, W M

    1997-03-10

    We report a survey for nitrogen sulfide (NS) toward regions of massive star formation. NS was observed by means of its 2 pi 1/2, J = 3/2 --> 1/2, J = 5/2 --> 3/2, and J = 7/2 --> 5/2 transitions at 69, 115, and 161 GHz, respectively, and was detected toward 12 of 14 giant molecular clouds (GMCs) observed. Analysis of the hyperfine component relative line strengths suggests that NS emission is optically thin toward these sources, with the possible exception of Sgr B2(M). The fractional abundance of NS relative to molecular hydrogen is best defined for the Orion molecular cloud, where it is typically (1-4) x 10(-10), which is about an order of magnitude larger than found by some recent gas-phase chemistry models developed for quiescent clouds. Toward OMC-1, the NS integrated intensity is strongly peaked toward KL, but also extends all along the Orion ridge, resembling the distribution of SO and CH3OH. We have identified a spectral feature seen toward several sources as the ortho-NKK = 4(04) --> 3(13) J = 3 --> 2, fine-structure component of methylene (CH2; cf. Hollis, Jewell, & Lovas). We also report the first detection of the SO+ 2 pi 1/2, J = 3/2 --> 1/2, parity-e transition toward W51(MS) and L134N.

  5. Nitrogen sulfide in giant molecular clouds

    NASA Technical Reports Server (NTRS)

    McGonagle, D.; Irvine, W. M.

    1997-01-01

    We report a survey for nitrogen sulfide (NS) toward regions of massive star formation. NS was observed by means of its 2 pi 1/2, J = 3/2 --> 1/2, J = 5/2 --> 3/2, and J = 7/2 --> 5/2 transitions at 69, 115, and 161 GHz, respectively, and was detected toward 12 of 14 giant molecular clouds (GMCs) observed. Analysis of the hyperfine component relative line strengths suggests that NS emission is optically thin toward these sources, with the possible exception of Sgr B2(M). The fractional abundance of NS relative to molecular hydrogen is best defined for the Orion molecular cloud, where it is typically (1-4) x 10(-10), which is about an order of magnitude larger than found by some recent gas-phase chemistry models developed for quiescent clouds. Toward OMC-1, the NS integrated intensity is strongly peaked toward KL, but also extends all along the Orion ridge, resembling the distribution of SO and CH3OH. We have identified a spectral feature seen toward several sources as the ortho-NKK = 4(04) --> 3(13) J = 3 --> 2, fine-structure component of methylene (CH2; cf. Hollis, Jewell, & Lovas). We also report the first detection of the SO+ 2 pi 1/2, J = 3/2 --> 1/2, parity-e transition toward W51(MS) and L134N.

  6. The Formation of Molecular Clouds: Insights from Numerical Models

    NASA Astrophysics Data System (ADS)

    Heitsch, Fabian

    2010-10-01

    Galactic star formation occurs at a surprisingly low rate. Yet, recent large-scale surveys of dark clouds in the Galaxy show that one rarely finds molecular clouds without young stellar objects, suggesting that star formation should occur rapidly upon molecular cloud formation. This rapid onset challenges the traditional concept of ``slow'' star formation in long-lived molecular clouds. It also imposes strong constraints on the physical properties of the parental clouds, mandating that a cloud's structure and dynamics controlling stellar birth must arise during its formation. This requires a new approach to study initial conditions of star formation, namely addressing the formation of molecular clouds. Taking into account the observational constraints, I will outline the physics of flow-driven molecular cloud formation. I will discuss the relevance and the limitations of this scenario for setting the star formation efficiency in our Galaxy and beyond.

  7. Two regimes of cloud water over the Okhotsk Sea and the adjacent regions around Japan in summer

    NASA Astrophysics Data System (ADS)

    Shimada, Teruhisa; Iwasaki, Toshiki

    2015-03-01

    This study derived two regimes of cloud water with a dipole structure between over the Okhotsk Sea and over the adjacent regions around Japan in summer by using a climate index for cool summer. When the Okhotsk high develops, clouds are confined to a thin low-level layer owing to the enhanced stability in the lower atmosphere induced by the downward motion associated with the Okhotsk high. The resulting optically thin clouds allow more downward shortwave radiation to reach the surface of the Okhotsk Sea. In contrast, the low-level easterly winds blowing toward the Japanese Islands and the Eurasian continent enhance cloud formation. This is due to the convergence of the water vapor flux induced by the easterly winds associated with the Okhotsk high and the southerly winds associated with the Baiu frontal zone and the Pacific high and due to the orographic uplift of air mass. When a cyclonic circulation occurs over the Okhotsk Sea, a thick layer of low-level clouds extending close to the sea surface is formed. The convergence of the water vapor flux over the subarctic sea surface temperature (SST) frontal zone and the cool SST promote fog formation, and upward motion associated with the cyclonic circulation supports the high cloud water content from the lower to the upper troposphere. The resulting optically thick clouds reduce the downward shortwave radiation at the surface of the Okhotsk Sea. Over the regions around Japan, water vapor flux diverges owing to dry air originating from land and cloud water decreases.

  8. A search for HCCN in molecular clouds.

    PubMed

    McGonagle, D; Irvine, W M

    1996-06-01

    We have conducted a deep search for HCCN towards the dark cloud TMC-l and several GMC's via its N(J) = 1(2)-->0(1) transition. HCCN was not detected in any of these sources. Towards TMC-l, assuming optically thin emission, the total column density upper limit is NHCCN < or = 2 x 10(12) cm-2, which corresponds to a fractional abundance upper limit with respect to molecular hydrogen of fHCCN < or = 2 x 10(-10). We find the abundance ratio of HCN:HCCN:HCCCN in TMC-l to be l : <0.01 : 0.3, which suggests that carbon-chain growth by the addition of single carbon atoms may not be efficient under dark cloud conditions. The HCCN abundance limit also places constraints on the branching ratio for the products of the dissociative electron recombination H3C2N+ + e.

  9. A search for HCCN in molecular clouds

    NASA Technical Reports Server (NTRS)

    McGonagle, D.; Irvine, W. M.

    1996-01-01

    We have conducted a deep search for HCCN towards the dark cloud TMC-l and several GMC's via its N(J) = 1(2)-->0(1) transition. HCCN was not detected in any of these sources. Towards TMC-l, assuming optically thin emission, the total column density upper limit is NHCCN < or = 2 x 10(12) cm-2, which corresponds to a fractional abundance upper limit with respect to molecular hydrogen of fHCCN < or = 2 x 10(-10). We find the abundance ratio of HCN:HCCN:HCCCN in TMC-l to be l : <0.01 : 0.3, which suggests that carbon-chain growth by the addition of single carbon atoms may not be efficient under dark cloud conditions. The HCCN abundance limit also places constraints on the branching ratio for the products of the dissociative electron recombination H3C2N+ + e.

  10. Molecular clouds in the Carina arm

    NASA Technical Reports Server (NTRS)

    Grabelsky, D. A.

    1986-01-01

    Results from the first large-scale survey in the CO(J = 1 to 0) line of the Vela-Carina-Centaurus region of the Southern Milky Way are reported. The observations, made with the Columbia University 1.2 m millimeter-wave telescope at Cerro Tololo, were spaced every beamwidth (0.125 deg) in the range 270 deg is less than or = l is less than or = 300 deg and -1 deg less than or = b less then or = 1 deg, with latitude extensions to cover all Carina arm emission beyond absolute b = 1 deg. In a concurrent survey made with the same telescope, every half-degree in latitude and longitude was sampled. Both surveys had a spectral coverage of 330 km/s with a resolution of 1.3 km/s. The Carina arm is the dominant feature in the data. Its abrupt tangent at l is approx. = 280 deg and characteristic loop in the l,v diagram are unmistakable evidence for CO spiral structure. When the emission is integrated over velocity and latitude, the height of the step seen in the tangent direction suggests that the arm-interarm contrast is at least 13:1. Comparison of the CO and H I data shows close agreement between these two species in a segment of the arm lying outside the solar circle. The distribution of the molecular layer about the galactic plane in the outer Galaxy is determined. Between R = 10.5 and 12.5 kpc, the average CO midplane dips from z = -48 to -167 pc below the b = 0 deg plane, following a similar well-known warping of the H I layer. In the same range of radii the half-thickness of the CO layer increases from 112 to 182 pc. Between l = 270 deg and 300 deg, 27 molecular clouds are identified and cataloged along with heliocentric distances and masses. An additional 16 clouds beyond 300 deg are cataloged from an adjoining CO survey made with the same telescope. The average mass for the Carina arm clouds is 1.4x 10(6)M (solar), and the average intercloud spacing along the arm is 700 pc. Comparison of the distribution of the Carina arm clouds with that of similarly massive

  11. Warm Dust in the RCRA Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Leene, A.; Beichman, C. A.

    The authors report on IRAS observations of a portion of the R CrA molecular cloud. The observations show IR emission coinciding with an area of low optical extinction. The 60 - 100 μm color temperature of this dust is 21K. The 12 - 25 μm color temperature is however 400K. The emission of this warm dust extends over an area of 0.3 square degrees. This high temperature can not be explained by normal equilibrium processes. The observations imply the existence of very small grains, which are heated by single photon absorptions.

  12. The composition of interstellar molecular clouds.

    PubMed

    Irvine, W M

    1999-01-01

    We consider four-aspects of interstellar chemistry for comparison with comets: molecular abundances in general, relative abundances of isomers (specifically, HCN and HNC), ortho/para ratios for molecules, and isotopic fractionation, particularly for the ratio hydrogen/deuterium. Since the environment in which the solar system formed is not well constrained, we consider both isolated dark clouds where low mass stars may form and the "hot cores" that are the sites of high mass star formation. Attention is concentrated on the gas phase, since the grains are considered elsewhere in this volume.

  13. Molecular oxygen in the ρ Ophiuchi cloud

    NASA Astrophysics Data System (ADS)

    Larsson, B.; Liseau, R.; Pagani, L.; Bergman, P.; Bernath, P.; Biver, N.; Black, J. H.; Booth, R. S.; Buat, V.; Crovisier, J.; Curry, C. L.; Dahlgren, M.; Encrenaz, P. J.; Falgarone, E.; Feldman, P. A.; Fich, M.; Florén, H. G.; Fredrixon, M.; Frisk, U.; Gahm, G. F.; Gerin, M.; Hagström, M.; Harju, J.; Hasegawa, T.; Hjalmarson, Å.; Johansson, L. E. B.; Justtanont, K.; Klotz, A.; Kyrölä, E.; Kwok, S.; Lecacheux, A.; Liljeström, T.; Llewellyn, E. J.; Lundin, S.; Mégie, G.; Mitchell, G. F.; Murtagh, D.; Nordh, L. H.; Nyman, L.-Å.; Olberg, M.; Olofsson, A. O. H.; Olofsson, G.; Olofsson, H.; Persson, G.; Plume, R.; Rickman, H.; Ristorcelli, I.; Rydbeck, G.; Sandqvist, A. A.; Schéele, F. V.; Serra, G.; Torchinsky, S.; Tothill, N. F.; Volk, K.; Wiklind, T.; Wilson, C. D.; Winnberg, A.; Witt, G.

    2007-05-01

    Context: Molecular oxygen, O2, has been expected historically to be an abundant component of the chemical species in molecular clouds and, as such, an important coolant of the dense interstellar medium. However, a number of attempts from both ground and from space have failed to detect O2 emission. Aims: The work described here uses heterodyne spectroscopy from space to search for molecular oxygen in the interstellar medium. Methods: The Odin satellite carries a 1.1 m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O2. Starting in 2002, the star forming molecular cloud core ρ {Oph A} was observed with Odin for 34 days during several observing runs. Results: We detect a spectral line at v_LSR =+3.5 km s-1 with Δ v_FWHM=1.5 km s-1, parameters which are also common to other species associated with ρ {Oph A}. This feature is identified as the O2 (NJ = 11 - 1_0) transition at 118 750.343 MHz. Conclusions: The abundance of molecular oxygen, relative to H{2} , is 5 × 10-8 averaged over the Odin beam. This abundance is consistently lower than previously reported upper limits. Based on observations with Odin, a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Étude Spatiale (CNES). The Swedish Space Corporation has been the industrial prime contractor and also is operating the satellite. Appendix A is only available in electronic form at http://www.aanda.org

  14. Inverse Hubble flows in molecular clouds

    NASA Astrophysics Data System (ADS)

    Toalá, Jesús A.; Vázquez-Semadeni, Enrique; Colín, Pedro; Gómez, Gilberto C.

    2015-02-01

    Motivated by recent numerical simulations of molecular cloud (MC) evolution, in which the clouds engage in global gravitational contraction, and local collapse events culminate significantly earlier than the global collapse, we investigate the growth of density perturbations embedded in a collapsing background, to which we refer as an inverse Hubble flow (IHF). We use the standard procedure for the growth of perturbations in a universe that first expands (the usual Hubble flow) and then recollapses (the IHF). We find that linear density perturbations immersed in an IHF grow faster than perturbations evolving in a static background (the standard Jeans analysis). A fundamental distinction between the two regimes is that, in the Jeans case, the time τnl for a density fluctuation to become non-linear increases without limit as its initial value approaches zero, while in the IHF case τnl ≤ τff always, where τff is the free-fall time of the background density. We suggest that this effect, although moderate, implies that small-scale density fluctuations embedded in globally collapsing clouds must collapse earlier than their parent cloud, regardless of whether the initial amplitude of the fluctuations is moderate or strongly non-linear, thus allowing the classical mechanism of Hoyle fragmentation to operate in multi-Jeans-mass MCs. More fundamentally, our results show that, contrary to the standard paradigm that fluctuations of all scales grow at the same rate in the linear regime, the hierarchical nesting of the fluctuations of different scales does affect their growth even in the linear stage.

  15. Large molecular cloud in Lupus far from the Galactic plane

    SciTech Connect

    Nyman, L.A.; Thaddeus, P.; Bronfman, L.; Cohen, R.S.

    1987-03-01

    The detection of a large molecular cloud at a distance of more than 200 pc from the Galactic plane, situated above a prominent hole in the CO distribution in the plane, is reported. The cloud has a radial velocity of -41 km/s, much larger than is characteristic of most local, high-latitude gas. The cloud's displacement above the plane is the largest for any cloud yet detected. The mass of the cloud is about 100,000 solar masses, and its gravitational potential energy is about 7 x 10 to the 50th ergs. A single event may have created both the cloud and the nearby hole. 27 references.

  16. Weekly cycle of lightning and associated patterns of rainfall, cloud, and aerosols over Korea and adjacent oceans during boreal summer

    NASA Astrophysics Data System (ADS)

    Kim, J.; Kim, K.

    2011-12-01

    In this study, we analyze the weekly cycle of lightning over Korea and adjacent oceans and associated variations of aerosols, clouds, precipitation, and atmospheric circulations, using aerosol optical depth (AOD) from the NASA Moderate resolution Imaging Spectroradiometer (MODIS) and Multi-angle Imaging SpectroRadiometer (MISR), cloud properties from MODIS, precipitation and storm height from Tropical Rainfall Measuring Mission (TRMM) satellite, and lightning data from the Korean Lightning Detection Network (KLDN) during 9-year from 2002 to 2010. Lightning data was divided into three approximately equal areas, land area of Korea, and two adjacent oceans, Yellow Sea and South Sea. Preliminary results show that the number of lightning increases during the middle of the week over land area. AOD data also shows moderately significant midweek increase at about the same time as lightning peaks. These results are consistent with the recent studies showing the invigoration of storms with more ice hydrometeors by aerosols, and subsequently wash out of aerosols by rainfall. Frequency of lightning strokes tend to peak at weekend in coastal area and over South Sea, indicating local weekly anomalous circulation between land and adjacent ocean. On the other hand, lightning frequency over Yellow Sea appears to have very strong weekly cycle with midweek peak on around Wednesday. It is speculated that the midweek peak of lightning over Yellow Sea was related with aerosol transport from adjacent land area. AOD data also suggests midweek peak over Yellow Sea, however, the weekly cycle of AOD was not statistically significant. Changes in weekly cycle of lightning from pre-monsoon to monsoon season, as well as associated clouds and circulation patterns are also discussed.

  17. Weekly Cycle of Lightning and Associated Patterns of Rainfall, Cloud, and Aerosols over Korea and Adjacent Oceans during Boreal Summer

    NASA Technical Reports Server (NTRS)

    Kim, Ji-In; Kim, Kyu-Myong

    2011-01-01

    In this study, we analyze the weekly cycle of lightning over Korea and adjacent oceans and associated variations of aerosols, clouds, precipitation, and atmospheric circulations, using aerosol optical depth (AOD) from the NASA Moderate resolution Imaging Spectroradiometer (MODIS) and Multi-angle Imaging SpectroRadiometer (MISR), cloud properties from MODIS, precipitation and storm height from Tropical Rainfall Measuring Mission (TRMM) satellite, and lightning data from the Korean Lightning Detection Network (KLDN) during 9-year from 2002 to 2010. Lightning data was divided into three approximately equal areas, land area of Korea, and two adjacent oceans, Yellow Sea and South Sea. Preliminary results show that the number of lightning increases during the middle of the week over Yellow Sea. AOD data also shows moderately significant midweek increase at about the same time as lightning peaks. These results are consistent with the recent studies showing the invigoration of storms with more ice hydrometeors by aerosols, and subsequently wash out of aerosols by rainfall. Frequency of lightning strokes tend to peak at weekend in land area and over South Sea, indicating local weekly anomalous circulation between land and adjacent ocean. On the other hand, lightning frequency over Yellow Sea appears to have very strong weekly cycle with midweek peak on around Wednesday. It is speculated that the midweek peak of lightning over Yellow Sea was related with aerosol transport from adjacent land area. AOD data also suggests midweek peak over Yellow Sea, however, the weekly cycle of AOD was not statistically significant. Changes in weekly cycle of lightning from pre-monsoon to monsoon season, as well as associated clouds and circulation patterns are also discussed.

  18. Star Formation in High-Latitude Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Magnus McGehee, Peregrine

    2015-08-01

    Galactic star formation preferentially occurs within the dense molecular clouds that reside primarily near the disk mid-plane and are thus seen in projection against the Milky Way. A population of molecular clouds are seen at higher Galactic latitude although distance determinations are required in order to identify those that are actually in extraplanar environments.We review the known high-latitude star formation regions (MBM 12, LDN 1642, and HRK 81.4-77.8) and discuss the nature and environment of other high-latitude molecular clouds. Distances to each of these structures are deduced from optical reddening profiles derived from analysis of Sloan Digital Sky Survey photometry. In particular, we examine those molecular clouds found within the complex of intermediate and high velocity HI clouds that span the Northern 2nd Galactic Quadrant: the Draco clouds, the IVC pair at (l+b) = 135+51 and 135+54, and IREC 306.

  19. Molecular clouds in galaxies with different Z - Fragmentation of diffuse clouds driven by opacity

    NASA Technical Reports Server (NTRS)

    Franco, Jose; Cox, Donald P.

    1986-01-01

    Molecular clouds are formed from diffuse interstellar clouds when the external ultraviolet radiation field is prevented from penetrating into the cloud. The opacity is provided mainly by dust grains and the required column density to the cloud center is larger than about 5 x 10 to the 20th (solar Z/Z)/sq cm. This high-opacity criterion could have a significant impact on the radial trends observed in spiral galaxies, and on the distinctions between spiral and dwarf irregular galaxies.

  20. Model For Dense Molecular Cloud Cores

    NASA Technical Reports Server (NTRS)

    Doty, Steven D.; Neufeld, David A.

    1997-01-01

    We present a detailed theoretical model for the thermal balance, chemistry, and radiative transfer within quiescent dense molecular cloud cores that contain a central protostar. In the interior of such cores, we expect the dust and gas temperatures to be well coupled, while in the outer regions CO rotational emissions dominate the gas cooling and the predicted gas temperature lies significantly below the dust temperature. Large spatial variations in the gas temperature are expected to affect the gas phase chemistry dramatically; in particular, the predicted water abundance varies by more than a factor of 1000 within cloud cores that contain luminous protostars. Based upon our predictions for the thermal and chemical structure of cloud cores, we have constructed self-consistent radiative transfer models to compute the line strengths and line profiles for transitions of (12)CO, (13)CO, C(18)O, ortho- and para-H2(16)O, ortho- and para-H2(18)O, and O I. We carried out a general parameter study to determine the dependence of the model predictions upon the parameters assumed for the source. We expect many of the far-infrared and submillimeter rotational transitions of water to be detectable either in emission or absorption with the use of the Infrared Space Observatory (ISO) and the Submillimeter Wave Astronomy Satellite. Quiescent, radiatively heated hot cores are expected to show low-gain maser emission in the 183 GHz 3(sub 13)-2(sub 20) water line, such as has been observed toward several hot core regions using ground-based telescopes. We predict the (3)P(sub l) - (3)P(sub 2) fine-structure transition of atomic oxygen near 63 micron to be in strong absorption against the continuum for many sources. Our model can also account successfully for recent ISO observations of absorption in rovibrational transitions of water toward the source AFGL 2591.

  1. MHD Turbulence in the Taurus Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Heyer, M.; Gong, H.; Brunt, C.; Ostriker, E.

    2005-12-01

    The presence of MHD turbulence in the Taurus Molecular Cloud is examined from 12CO and 13CO J=1-0 imaging observations using the FCRAO 14 meter telescope. The degree of velocity anisotropy is measured from velocity structure functions derived separately along the x and y axes using Principal Component Analysis of spectroscopic imaging data (Brunt & Heyer 2002). Such anisotropy is predicted from model descriptions and computational simulations of MHD turbulence in the case of strong magnetic fields (Goldreich & Sridhar 1995; Cho, Lazarian, & Vishniac 2002; Vestuto, Ostriker, & Stone 2003). Within a subfield of the Taurus image where the column densities are low, this velocity anisotropy is largest along an angle that is coincident with the local magnetic field direction determined independently from optical polarization of background stars.The structure function derived from data perpendicular to the local field shows a shallower scaling exponent and a larger scaling coefficient than the values that describe the structure function constructed along the magnetic field as predicted by the MHD models. This alignment provides strong evidence that the magnetic field is a significant dynamical force within this column density regime of the Taurus cloud.

  2. Water vapor in the Orion Molecular Cloud

    NASA Technical Reports Server (NTRS)

    Knacke, R. F.; Larson, H. P.

    1991-01-01

    Infrared observations of interstellar gas-phase H2O in the spectrum of the BN object in Orion are reported. There are absorptions (S/N = 2-5) at the positions of four of the strong lines in the 000-001 nu3 vibration-rotation band. With an estimated excitation temperature of 150 K, the column density of gaseous H2O toward BN in the OMC-1 cloud is (2 + or - 1) x 10 to the 17th/sq cm. The intensities of the lines imply an ortho/para ratio of 1 + or - 0.5 indicating recent sublimation of H2O from low-temperature grains. The results give gas-phase abundance ratios of H2O/CO roughly 0.03 + or - 0.02 and HDO/H2O = 0.001-0.0001 toward BN. The velocities of the H2O absorptions agree with those of the ridge source and CO outflow, but the position along the line of sight is not well constrained. The gas/solid ratio is H2O(gas)/H20(ice) = 0.05 or less. Less than 1 percent of the oxygen is in H2O gas (assuming total cosmic abundance). Most of the H2O in the line of sight to BN, and by inference in quiescent regions of molecular clouds generally, is frozen on grains.

  3. Filaments in the Lupus molecular clouds

    NASA Astrophysics Data System (ADS)

    Benedettini, M.; Schisano, E.; Pezzuto, S.; Elia, D.; André, P.; Könyves, V.; Schneider, N.; Tremblin, P.; Arzoumanian, D.; di Giorgio, A. M.; Di Francesco, J.; Hill, T.; Molinari, S.; Motte, F.; Nguyen-Luong, Q.; Palmeirim, P.; Rivera-Ingraham, A.; Roy, A.; Rygl, K. L. J.; Spinoglio, L.; Ward-Thompson, D.; White, G. J.

    2015-10-01

    We have studied the filaments extracted from the column density maps of the nearby Lupus 1, 3, and 4 molecular clouds, derived from photometric maps observed with the Herschel satellite. Filaments in the Lupus clouds have quite low column densities, with a median value of ˜1.5 × 1021 cm-2 and most have masses per unit length lower than the maximum critical value for radial gravitational collapse. Indeed, no evidence of filament contraction has been seen in the gas kinematics. We find that some filaments, that on average are thermally subcritical, contain dense cores that may eventually form stars. This is an indication that in the low column density regime, the critical condition for the formation of stars may be reached only locally and this condition is not a global property of the filament. Finally, in Lupus we find multiple observational evidences of the key role that the magnetic field plays in forming filaments, and determining their confinement and dynamical evolution.

  4. Centroid velocity statistics of molecular clouds

    NASA Astrophysics Data System (ADS)

    Bertram, Erik; Konstandin, Lukas; Shetty, Rahul; Glover, Simon C. O.; Klessen, Ralf S.

    2015-02-01

    We compute structure functions and Fourier spectra of 2D centroid velocity maps in order to study the gas dynamics of typical molecular clouds in numerical simulations. We account for a simplified treatment of time-dependent chemistry and the non-isothermal nature of the gas and use a 3D radiative transfer tool to model the CO line emission in a post-processing step. We perform simulations using three different initial mean number densities of n0 = 30, 100 and 300 cm-3 to span a range of typical values for dense gas clouds in the solar neighbourhood. We compute slopes of the centroid velocity increment structure functions (CVISF) and of Fourier spectra for different chemical components: the total density, H2 number density, 12CO number density as well as the integrated intensity of 12CO (J = 1 → 0) and 13CO (J = 1 → 0). We show that optical depth effects can significantly affect the slopes derived for the CVISF, which also leads to different scaling properties for the Fourier spectra. The slopes of CVISF and Fourier spectra for H2 are significantly steeper than those for the different CO tracers, independent of the density and the numerical resolution. This is due to the larger space-filling factor of H2 as it is better able to self-shield in diffuse regions, leading to a larger fractal co-dimension compared to CO.

  5. NONIDEAL MAGNETOHYDRODYNAMIC TURBULENT DECAY IN MOLECULAR CLOUDS

    SciTech Connect

    Downes, T. P.; O'Sullivan, S.

    2009-08-20

    It is well known that nonideal magnetohydrodynamic (MHD) effects are important in the dynamics of molecular clouds: both ambipolar diffusion and possibly the Hall effect have been identified as significant. We present the results of a suite of simulations with a resolution of 512{sup 3} of turbulent decay in molecular clouds, incorporating a simplified form of both ambipolar diffusion and the Hall effect simultaneously. The initial velocity field in the turbulence is varied from being super-Alfvenic and hypersonic, through to trans-Alfvenic but still supersonic. We find that ambipolar diffusion increases the rate of decay of the turbulence increasing the decay from t {sup -1.25} to t {sup -1.4}. The Hall effect has virtually no impact in this regard. The power spectra of density, velocity, and the magnetic field are all affected by the nonideal terms, being steepened significantly when compared with ideal MHD turbulence with exponents. The density power-spectra components change from {approx}1.4 to {approx}2.1 for the ideal and nonideal simulations respectively, and power spectra of the other variables all show similar modifications when nonideal effects are considered. Again, the dominant source of these changes is ambipolar diffusion rather than the Hall effect. There is also a decoupling between the velocity field and the magnetic field at short length scales. The Hall effect leads to enhanced magnetic reconnection, and hence less power, at short length scales. The dependence of the velocity dispersion on the characteristic length scale is studied and found not to be power law in nature.

  6. Supernova Driving. III. Synthetic Molecular Cloud Observations

    NASA Astrophysics Data System (ADS)

    Padoan, Paolo; Juvela, Mika; Pan, Liubin; Haugbølle, Troels; Nordlund, Åke

    2016-08-01

    We present a comparison of molecular clouds (MCs) from a simulation of supernova (SN) driven interstellar medium (ISM) turbulence with real MCs from the Outer Galaxy Survey. The radiative transfer calculations to compute synthetic CO spectra are carried out assuming that the CO relative abundance depends only on gas density, according to four different models. Synthetic MCs are selected above a threshold brightness temperature value, T B,min = 1.4 K, of the J = 1 - 0 12CO line, generating 16 synthetic catalogs (four different spatial resolutions and four CO abundance models), each containing up to several thousands MCs. The comparison with the observations focuses on the mass and size distributions and on the velocity-size and mass-size Larson relations. The mass and size distributions are found to be consistent with the observations, with no significant variations with spatial resolution or chemical model, except in the case of the unrealistic model with constant CO abundance. The velocity-size relation is slightly too steep for some of the models, while the mass-size relation is a bit too shallow for all models only at a spatial resolution dx ≈ 1 pc. The normalizations of the Larson relations show a clear dependence on spatial resolution, for both the synthetic and the real MCs. The comparison of the velocity-size normalization suggests that the SN rate in the Perseus arm is approximately 70% or less of the rate adopted in the simulation. Overall, the realistic properties of the synthetic clouds confirm that SN-driven turbulence can explain the origin and dynamics of MCs.

  7. Supernova Driving. III. Synthetic Molecular Cloud Observations

    NASA Astrophysics Data System (ADS)

    Padoan, Paolo; Juvela, Mika; Pan, Liubin; Haugbølle, Troels; Nordlund, Åke

    2016-08-01

    We present a comparison of molecular clouds (MCs) from a simulation of supernova (SN) driven interstellar medium (ISM) turbulence with real MCs from the Outer Galaxy Survey. The radiative transfer calculations to compute synthetic CO spectra are carried out assuming that the CO relative abundance depends only on gas density, according to four different models. Synthetic MCs are selected above a threshold brightness temperature value, T B,min = 1.4 K, of the J = 1 ‑ 0 12CO line, generating 16 synthetic catalogs (four different spatial resolutions and four CO abundance models), each containing up to several thousands MCs. The comparison with the observations focuses on the mass and size distributions and on the velocity–size and mass–size Larson relations. The mass and size distributions are found to be consistent with the observations, with no significant variations with spatial resolution or chemical model, except in the case of the unrealistic model with constant CO abundance. The velocity–size relation is slightly too steep for some of the models, while the mass–size relation is a bit too shallow for all models only at a spatial resolution dx ≈ 1 pc. The normalizations of the Larson relations show a clear dependence on spatial resolution, for both the synthetic and the real MCs. The comparison of the velocity–size normalization suggests that the SN rate in the Perseus arm is approximately 70% or less of the rate adopted in the simulation. Overall, the realistic properties of the synthetic clouds confirm that SN-driven turbulence can explain the origin and dynamics of MCs.

  8. RE-EXAMINING LARSON'S SCALING RELATIONSHIPS IN GALACTIC MOLECULAR CLOUDS

    SciTech Connect

    Heyer, Mark; Krawczyk, Coleman; Duval, Julia; Jackson, James M.

    2009-07-10

    The properties of Galactic molecular clouds tabulated by Solomon et al. (SRBY) are re-examined using the Boston University-FCRAO Galactic Ring Survey of {sup 13}CO J = 1-0 emission. These new data provide a lower opacity tracer of molecular clouds and improved angular and spectral resolution compared with previous surveys of molecular line emission along the Galactic Plane. We calculate giant molecular cloud (GMC) masses within the SRBY cloud boundaries assuming local thermodynamic equilibrium (LTE) conditions throughout the cloud and a constant H{sub 2} to {sup 13}CO abundance, while accounting for the variation of the {sup 12}C/{sup 13}C with galactocentric radius. The LTE-derived masses are typically five times smaller than the SRBY virial masses. The corresponding median mass surface density of molecular hydrogen for this sample is 42 M{sub sun} pc{sup -2}, which is significantly lower than the value derived by SRBY (median 206 M{sub sun} pc{sup -2}) that has been widely adopted by most models of cloud evolution and star formation. This discrepancy arises from both the extrapolation by SRBY of velocity dispersion, size, and CO luminosity to the 1 K antenna temperature isophote that likely overestimates the GMC masses and our assumption of constant {sup 13}CO abundance over the projected area of each cloud. Owing to the uncertainty of molecular abundances in the envelopes of clouds, the mass surface density of GMCs could be larger than the values derived from our {sup 13}CO measurements. From velocity dispersions derived from the {sup 13}CO data, we find that the coefficient of the cloud structure functions, v{sup 0} = {sigma}{sub v}/R {sup 1/2}, is not constant, as required to satisfy Larson's scaling relationships, but rather systematically varies with the surface density of the cloud as {approx}{sigma}{sup 0.5} as expected for clouds in self-gravitational equilibrium.

  9. Observations of chemical differentiation in clumpy molecular clouds.

    PubMed

    Buckle, Jane V; Rodgers, Steven D; Wirström, Eva S; Charnley, Steven B; Markwick-Kemper, Andrew J; Butner, Harold M; Takakuwa, Shigehisa

    2006-01-01

    We have extensively mapped a sample of dense molecular clouds (L1512, TMC-1C, L1262, Per7, L1389, L1251E) in lines of HC3N, CH3OH, SO and C18O. We demonstrate that a high degree of chemical differentiation is present in all of the observed clouds. We analyse the molecular maps for each cloud, demonstrating a systematic chemical differentiation across the sample, which we relate to the evolutionary state of the cloud. We relate our observations to the cloud physical, kinematical and evolutionary properties, and also compare them to the predictions of simple chemical models. The implications of this work for understanding the origin of the clumpy structures and chemical differentiation observed in dense clouds are discussed.

  10. Deuterium fractionation in the Ophiuchus molecular cloud

    NASA Astrophysics Data System (ADS)

    Punanova, A.; Caselli, P.; Pon, A.; Belloche, A.; André, Ph.

    2016-03-01

    Context. In cold (T< 25 K) and dense (nH> 104 cm-3) interstellar clouds, molecules such as CO are significantly frozen onto dust grain surfaces. Deuterium fractionation is known to be very efficient in these conditions as CO limits the abundance of H3+, which is the starting point of deuterium chemistry. In particular, N2D+ is an excellent tracer of dense and cold gas in star-forming regions. Aims: We measure the deuterium fraction, RD, and the CO depletion factor, fd, towards a number of starless and protostellar cores in the L1688 region of the Ophiuchus molecular cloud complex and search for variations based upon environmental differences across L1688. The kinematic properties of the dense gas traced by the N2H+ and N2D+ (1-0) lines are also discussed. Methods: Deuterium fraction has been measured via observations of the J = 1-0 transition of N2H+ and N2D+ towards 33 dense cores in different regions of L1688. We estimated the CO depletion factor using C17O(1-0) and 850 μm dust continuum emission from the SCUBA survey. We carried out all line observations with the IRAM 30 m antenna. Results: The dense cores show large (≃2-40%) deuterium fractions with significant variations between the sub-regions of L1688. The CO depletion factor also varies from one region to another (between ≃1 and 7). Two different correlations are found between deuterium fraction and CO depletion factor: cores in regions A, B2, and I show increasing RD with increasing fd, similar to previous studies of deuterium fraction in pre-stellar cores; cores in regions B1, B1B2, C, E, F, and H show a steeper RD - fd correlation with large deuterium fractions occurring in fairly quiescent gas with relatively low CO freeze-out factors. These are probably recently formed, centrally concentrated starless cores, which have not yet started the contraction phase towards protostellar formation. We also find that the deuterium fraction is affected by the amount of turbulence, dust temperature, and

  11. The emerging role of cloud computing in molecular modelling.

    PubMed

    Ebejer, Jean-Paul; Fulle, Simone; Morris, Garrett M; Finn, Paul W

    2013-07-01

    There is a growing recognition of the importance of cloud computing for large-scale and data-intensive applications. The distinguishing features of cloud computing and their relationship to other distributed computing paradigms are described, as are the strengths and weaknesses of the approach. We review the use made to date of cloud computing for molecular modelling projects and the availability of front ends for molecular modelling applications. Although the use of cloud computing technologies for molecular modelling is still in its infancy, we demonstrate its potential by presenting several case studies. Rapid growth can be expected as more applications become available and costs continue to fall; cloud computing can make a major contribution not just in terms of the availability of on-demand computing power, but could also spur innovation in the development of novel approaches that utilize that capacity in more effective ways.

  12. Dynamical Simulations of Molecular Clouds in the Galactic Center

    NASA Astrophysics Data System (ADS)

    Salas, Jesus; Morris, Mark

    2016-06-01

    The formation of the central massive cluster of young stars orbiting the Galactic black hole, Sgr A*, has been modeled by several groups by invoking an almost radially infalling molecular cloud that interacts with the black hole and creates a dense, gaseous disk in which stars can then form. However, the dynamical origin of such a cloud remains an open question. We present simulations of the central 30-100 pc of the Milky Way, starting from a population of molecular clouds located in a disk with scale height of ~30 pc, using the N-body/smoothed-particle hydrodynamics code, Gadget2. We followed the dynamical evolution of clouds in a galactic potential that includes a bar to explore whether cloud collisions or a succession of cloud scatterings can remove sufficient angular momentum from a massive cloud to endow it with a predominantly radial orbit. Initial results illustrate the importance of tidal shear; while dense cloud cores remain identifiable for extended periods of time, much of the molecular mass ends up in tidal streams, so cannot be deflected onto low angular momentum orbits by their mutual interactions. At the completion of our ongoing computations, we will report on whether the cloud cores can undergo sufficient scattering to achieve low-angular-momentum orbits.

  13. The interaction of T-Tauri stars with molecular clouds

    NASA Technical Reports Server (NTRS)

    Silk, J.; Norman, C.

    1980-01-01

    Winds from T-Tauri stars may provide an important dynamical input into cold molecular clouds. If the frequency of T-Tauri stars exceeds 20/cu pc, wind-driven shells collide and form ram-pressure-confined clumps. The supersonic clump motions can account for cloud line widths. Clumps collide inelastically, coalescing and eventually becoming Jeans unstable. For characteristic dark cloud temperatures low-mass stars form, and it is speculated that in this manner clouds can be self-sustaining for 10 million to 100 million yr. Only when either the gas supply is exhausted or an external trigger stimulates massive star formation (for example, by heating the cloud or enhancing the clump collision rate), will the cloud eventually be disrupted. A natural consequence of this model is that dark cloud lifetimes are identified with the duration of low-mass star formation, inferred to exceed 10 million yr from studies of nearby star clusters. Other implications include the prediction of the existence of embedded low-mass stars in turbulent cloud cores, the presence of an internal source of radiation in dark clouds, and a clumpy structure for cold molecular clouds.

  14. A quantitative analysis of IRAS maps of molecular clouds

    NASA Technical Reports Server (NTRS)

    Wiseman, Jennifer J.; Adams, Fred C.

    1994-01-01

    We present an analysis of IRAS maps of five molecular clouds: Orion, Ophiuchus, Perseus, Taurus, and Lupus. For the classification and description of these astrophysical maps, we use a newly developed technique which considers all maps of a given type to be elements of a pseudometric space. For each physical characteristic of interest, this formal system assigns a distance function (a pseudometric) to the space of all maps: this procedure allows us to measure quantitatively the difference between any two maps and to order the space of all maps. We thus obtain a quantitative classification scheme for molecular clouds. In this present study we use the IRAS continuum maps at 100 and 60 micrometer(s) to produce column density (or optical depth) maps for the five molecular cloud regions given above. For this sample of clouds, we compute the 'output' functions which measure the distribution of density, the distribution of topological components, the self-gravity, and the filamentary nature of the clouds. The results of this work provide a quantitative description of the structure in these molecular cloud regions. We then order the clouds according to the overall environmental 'complexity' of these star-forming regions. Finally, we compare our results with the observed populations of young stellar objects in these clouds and discuss the possible environmental effects on the star-formation process. Our results are consistent with the recently stated conjecture that more massive stars tend to form in more 'complex' environments.

  15. DISCOVERY OF THE PIGTAIL MOLECULAR CLOUD IN THE GALACTIC CENTER

    SciTech Connect

    Matsumura, Shinji; Oka, Tomoharu; Tanaka, Kunihiko; Nagai, Makoto; Kamegai, Kazuhisa; Hasegawa, Tetsuo

    2012-09-01

    This paper reports the discovery of a helical molecular cloud in the central molecular zone (CMZ) of our Galaxy. This 'pigtail' molecular cloud appears at (l, b, V{sub LSR}) {approx_equal} (-0.{sup 0}7, + 0.{sup 0}0, - 70 to -30 km s{sup -1}), with a spatial size of {approx}20 Multiplication-Sign 20 pc{sup 2} and a mass of (2-6) Multiplication-Sign 10{sup 5} M{sub Sun }. This is the third helical gaseous nebula found in the Galactic center region to date. Line intensity ratios indicate that the pigtail molecular cloud has slightly higher temperature and/or density than the other normal clouds in the CMZ. We also found a high-velocity wing emission near the footpoint of this cloud. We propose a formation model of the pigtail molecular cloud. It might be associated with a magnetic tube that is twisted and coiled because of the interaction between clouds in the innermost x{sub 1} orbit and ones in the outermost x{sub 2} orbit.

  16. STAR FORMATION IN TURBULENT MOLECULAR CLOUDS WITH COLLIDING FLOW

    SciTech Connect

    Matsumoto, Tomoaki; Dobashi, Kazuhito; Shimoikura, Tomomi

    2015-03-10

    Using self-gravitational hydrodynamical numerical simulations, we investigated the evolution of high-density turbulent molecular clouds swept by a colliding flow. The interaction of shock waves due to turbulence produces networks of thin filamentary clouds with a sub-parsec width. The colliding flow accumulates the filamentary clouds into a sheet cloud and promotes active star formation for initially high-density clouds. Clouds with a colliding flow exhibit a finer filamentary network than clouds without a colliding flow. The probability distribution functions (PDFs) for the density and column density can be fitted by lognormal functions for clouds without colliding flow. When the initial turbulence is weak, the column density PDF has a power-law wing at high column densities. The colliding flow considerably deforms the PDF, such that the PDF exhibits a double peak. The stellar mass distributions reproduced here are consistent with the classical initial mass function with a power-law index of –1.35 when the initial clouds have a high density. The distribution of stellar velocities agrees with the gas velocity distribution, which can be fitted by Gaussian functions for clouds without colliding flow. For clouds with colliding flow, the velocity dispersion of gas tends to be larger than the stellar velocity dispersion. The signatures of colliding flows and turbulence appear in channel maps reconstructed from the simulation data. Clouds without colliding flow exhibit a cloud-scale velocity shear due to the turbulence. In contrast, clouds with colliding flow show a prominent anti-correlated distribution of thin filaments between the different velocity channels, suggesting collisions between the filamentary clouds.

  17. Molecular heterogeneity in adjacent cells in triple-negative breast cancer

    PubMed Central

    Huebschman, Michael L; Lane, Nancy L; Liu, Huaying; Sarode, Venetia R; Devlin, Judith L; Frenkel, Eugene P

    2015-01-01

    Purpose This study interrogates the molecular status of individual cells in patients with triple-negative breast cancers and explores the molecular identification and characterization of these tumors to consider the exploitation of a potential-targeted therapeutic approach. Patients and methods Hyperspectral immunologic cell by cell analysis was applied to touch imprint smears obtained from fresh tumors of breast cancer patients. Results Cell by cell analysis confirms significant intratumoral molecular heterogeneity in cancer markers with differences from polymerase chain reaction marker reporting. The individual cell heterogeneity was recognized in adjacent cells examined with panels of ten molecular markers in each single cell and included some markers that are considered to express “stem-cell” character. In addition, heterogeneity did not relate either to the size or stage of the primary tumor or to the site from within the cancer. Conclusion There is a very significant molecular heterogeneity when “adjacent cells” are examined in triple-negative breast cancer, thereby making a successful targeted approach unlikely. In addition, it is not reasonable to consider that these changes will provide an answer to tumor dormancy. PMID:26316815

  18. CO mapping of the Orion molecular cloud: The influence of star formation on cloud structure

    NASA Technical Reports Server (NTRS)

    Schloerb, F. P.; Snell, R. L.; Goldsmith, P. F.; Morgan, J. A.

    1986-01-01

    Regions of massive star formation have long been believed to have a profound influence on the structure of their surrounding molecular clouds. The ways in which massive star formation has altered the structure and kinematics of the Orion Molecular Cloud are discussed. The data to be discussed consists of a large scale map of the CO J=1-0 emission from approximately 3 square degrees of OMC-1. During 1985, the Five College Radio Astronomy Observatory 14M antenna was used to map a 2 deg x 1 deg region centered on alpha(1950) = 5(h)33(m)00(s) delta(1950) = -5 deg 30 min. The region mapped in 1985 covers the well known HII regions M42, M43, and NGC1977, and the CO map contains abundant evidence of the interaction between these regions and the molecular cloud. Indeed, the global structure of the cloud appears to have been strongly influenced by the continuous formation of massive stars within the cloud. Individual instances of some of these features are discussed. There appear to be two classes of features which are indicative of this interaction: CO bright rims and CO holes. During 1986, we have undertaken further mapping of OMC-1 to the south of the region covered by the 1985 map. This portion of the cloud contains significant regions of star formation, but O star formation has not occured and large HII regions have not developed to alter the appearance of the cloud. A detailed map of this region is thus an opportunity to view the structure of the molecular cloud before it has been altered by massive star formation. Preliminary analysis of data obtained in this region suggests that the structure and kinematics of the southern portion of the Orion cloud are indeed dramatically different from those of the region previously mapped. Comparison of the two regions thus supports models of the development of structure in molecular clouds through interaction with the HII regions formed within them.

  19. OH 18 cm TRANSITION AS A THERMOMETER FOR MOLECULAR CLOUDS

    SciTech Connect

    Ebisawa, Yuji; Inokuma, Hiroshi; Yamamoto, Satoshi; Sakai, Nami; Menten, Karl M.; Maezawa, Hiroyuki

    2015-12-10

    We have observed the four hyperfine components of the 18 cm OH transition toward the translucent cloud eastward of Heiles Cloud 2 (HCL2E), the cold dark cloud L134N, and the photodissociation region of the ρ-Ophiuchi molecular cloud with the Effelsberg 100 m telescope. We have found intensity anomalies among the hyperfine components in all three regions. In particular, an absorption feature of the 1612 MHz satellite line against the cosmic microwave background has been detected toward HCL2E and two positions of the ρ-Ophiuchi molecular cloud. On the basis of statistical equilibrium calculations, we find that the hyperfine anomalies originate from the non-LTE population of the hyperfine levels, and can be used to determine the kinetic temperature of the gas over a wide range of H{sub 2} densities (10{sup 2}–10{sup 7} cm{sup −3}). Toward the center of HCL2E, the gas kinetic temperature is determined to be 53 ± 1 K, and it increases toward the cloud peripheries (∼60 K). The ortho-to-para ratio of H{sub 2} is determined to be 3.5 ± 0.9 from the averaged spectrum for the eight positions. In L134N, a similar increase of the temperature is also seen toward the periphery. In the ρ-Ophiuchi molecular cloud, the gas kinetic temperature decreases as a function of the distance from the exciting star HD 147889. These results demonstrate a new aspect of the OH 18 cm line that can be used as a good thermometer of molecular cloud envelopes. The OH 18 cm line can be used to trace a new class of warm molecular gas surrounding a molecular cloud, which is not well traced by the emission of CO and its isotopologues.

  20. OH 18 cm Transition as a Thermometer for Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Ebisawa, Yuji; Inokuma, Hiroshi; Sakai, Nami; Menten, Karl M.; Maezawa, Hiroyuki; Yamamoto, Satoshi

    2015-12-01

    We have observed the four hyperfine components of the 18 cm OH transition toward the translucent cloud eastward of Heiles Cloud 2 (HCL2E), the cold dark cloud L134N, and the photodissociation region of the ρ-Ophiuchi molecular cloud with the Effelsberg 100 m telescope. We have found intensity anomalies among the hyperfine components in all three regions. In particular, an absorption feature of the 1612 MHz satellite line against the cosmic microwave background has been detected toward HCL2E and two positions of the ρ-Ophiuchi molecular cloud. On the basis of statistical equilibrium calculations, we find that the hyperfine anomalies originate from the non-LTE population of the hyperfine levels, and can be used to determine the kinetic temperature of the gas over a wide range of H2 densities (102-107 cm-3). Toward the center of HCL2E, the gas kinetic temperature is determined to be 53 ± 1 K, and it increases toward the cloud peripheries (˜60 K). The ortho-to-para ratio of H2 is determined to be 3.5 ± 0.9 from the averaged spectrum for the eight positions. In L134N, a similar increase of the temperature is also seen toward the periphery. In the ρ-Ophiuchi molecular cloud, the gas kinetic temperature decreases as a function of the distance from the exciting star HD 147889. These results demonstrate a new aspect of the OH 18 cm line that can be used as a good thermometer of molecular cloud envelopes. The OH 18 cm line can be used to trace a new class of warm molecular gas surrounding a molecular cloud, which is not well traced by the emission of CO and its isotopologues.

  1. Witnessing molecular cloud formation from HI gas in high-latitude clouds

    NASA Astrophysics Data System (ADS)

    Tachihara, Kengo; Hattori, Momo; Yamamoto, Hiroaki; Okamoto, Ryuji; Hayakawa, Takahiro; Fukui, Yasuo

    2015-08-01

    The formation of molecular cloud is a fundamental process in terms of the cycle and evolution of matter in the universe. Its detail process is, however, not well understood yet, despite the importance for the investigation of initial condition of molecular clouds. From the observational point of view, it can be best studied in high-latitude clouds where obstacles of the galactic contamination and strong UV radiation decline. It is known that the atomic interstellar gas consist of warm neutral medium (WNM) and cold neutral medium (CNM), and the molecular gas formation is believed to take place in the dense CNM, which is suggested to have small-scale structures by theoretical calculations (e.g., Inoue & Inutsuka 2012). In order to avoid confusions of many overlapping structures, relatively high resolution HI data of the GALFA survey at high-latitude clouds MBM 53-55 are used. We decompose the multiple velocity components at the interface region between molecular and atomic clouds, and succeeded to resolve ~ 1 pc scale atomic CNM with a density of ~ 10 cm-3. As compared with the CO data obtained by the NANTEN telescope, small fraction of the HI components with small velocity dispersions appear to have counterpart molecular gas. The physical properties of these small-scale HI gas give us clues of not only the conditions of molecular formation but also the origins of cloud structures and interstellar turbulence.

  2. Unmixing multiple adjacent fluorescent targets with multispectral excited fluorescence molecular tomography.

    PubMed

    Zhou, Yuan; Guang, Huizhi; Pu, Huangsheng; Zhang, Jiulou; Luo, Jianwen

    2016-06-20

    Fluorescence molecular tomography (FMT) can visualize biological activities at cellular and molecular levels in vivo, and has been extensively used in drug delivery and tumor detection research of small animals. The ill-posedness of the FMT inverse problem makes it difficult to reconstruct and unmix multiple adjacent fluorescent targets that have different functional features but are labeled with the same fluorochrome. A method based on independent component analysis for multispectral excited FMT was proposed in our previous study. It showed that double fluorescent targets with certain edge-to-edge distance (EED) could be unmixed by the method. In this study, the situation is promoted to unmix multiple adjacent fluorescent targets (i.e., more than two fluorescent targets and EED=0). Phantom experiments on the resolving ability of the proposed algorithm demonstrate that the algorithm performs well in unmixing multiple adjacent fluorescent targets in both lateral and axial directions. And also, we recovered the locational information of each independent fluorescent target and described the variable trends of the corresponding fluorescent targets under the excitation spectrum. This method is capable of unmixing multiple fluorescent targets with small EED but labeled with the same fluorochrome, and may be used in imaging of nonspecific probe targeting and metabolism of drugs. PMID:27409108

  3. GIANT MOLECULAR CLOUD FORMATION IN DISK GALAXIES: CHARACTERIZING SIMULATED VERSUS OBSERVED CLOUD CATALOGS

    SciTech Connect

    Benincasa, Samantha M.; Pudritz, Ralph E.; Wadsley, James; Tasker, Elizabeth J.

    2013-10-10

    We present the results of a study of simulated giant molecular clouds (GMCs) formed in a Milky Way-type galactic disk with a flat rotation curve. This simulation, which does not include star formation or feedback, produces clouds with masses ranging between 10{sup 4} M{sub ☉} and 10{sup 7} M{sub ☉}. We compare our simulated cloud population to two observational surveys: the Boston University-Five College Radio Astronomy Observatory Galactic Ring Survey and the BIMA All-Disk Survey of M33. An analysis of the global cloud properties as well as a comparison of Larson's scaling relations is carried out. We find that simulated cloud properties agree well with the observed cloud properties, with the closest agreement occurring between the clouds at comparable resolution in M33. Our clouds are highly filamentary—a property that derives both from their formation due to gravitational instability in the sheared galactic environment, as well as to cloud-cloud gravitational encounters. We also find that the rate at which potentially star-forming gas accumulates within dense regions—wherein n{sub thresh} ≥ 10{sup 4} cm{sup –3}—is 3% per 10 Myr, in clouds of roughly 10{sup 6} M{sub ☉}. This suggests that star formation rates in observed clouds are related to the rates at which gas can be accumulated into dense subregions within GMCs via filamentary flows. The most internally well-resolved clouds are chosen for listing in a catalog of simulated GMCs—the first of its kind. The cataloged clouds are available as an extracted data set from the global simulation.

  4. Aberrant gene expression in mucosa adjacent to tumor reveals a molecular crosstalk in colon cancer

    PubMed Central

    2014-01-01

    Background A colorectal tumor is not an isolated entity growing in a restricted location of the body. The patient’s gut environment constitutes the framework where the tumor evolves and this relationship promotes and includes a complex and tight correlation of the tumor with inflammation, blood vessels formation, nutrition, and gut microbiome composition. The tumor influence in the environment could both promote an anti-tumor or a pro-tumor response. Methods A set of 98 paired adjacent mucosa and tumor tissues from colorectal cancer (CRC) patients and 50 colon mucosa from healthy donors (246 samples in total) were included in this work. RNA extracted from each sample was hybridized in Affymetrix chips Human Genome U219. Functional relationships between genes were inferred by means of systems biology using both transcriptional regulation networks (ARACNe algorithm) and protein-protein interaction networks (BIANA software). Results Here we report a transcriptomic analysis revealing a number of genes activated in adjacent mucosa from CRC patients, not activated in mucosa from healthy donors. A functional analysis of these genes suggested that this active reaction of the adjacent mucosa was related to the presence of the tumor. Transcriptional and protein-interaction networks were used to further elucidate this response of normal gut in front of the tumor, revealing a crosstalk between proteins secreted by the tumor and receptors activated in the adjacent colon tissue; and vice versa. Remarkably, Slit family of proteins activated ROBO receptors in tumor whereas tumor-secreted proteins transduced a cellular signal finally activating AP-1 in adjacent tissue. Conclusions The systems-level approach provides new insights into the micro-ecology of colorectal tumorogenesis. Disrupting this intricate molecular network of cell-cell communication and pro-inflammatory microenvironment could be a therapeutic target in CRC patients. PMID:24597571

  5. Linking numerical simulations of molecular cloud structure with observations.

    NASA Astrophysics Data System (ADS)

    Kainulainen, Jouni

    2015-08-01

    Understanding the physical processes that control the life-cycle of the cold interstellar medium (ISM) is one of the key themes in the astrophysics of galaxies today. This importance derives from the role of the cold ISM as the birthplace of new stars, and consequently, as an indivisible constituent of galaxy evolution. In the current paradigm of turbulence-regulated ISM, star formation is controlled by the internal structure of individual molecular clouds, which in turn is set by a complex interplay of turbulence, gravity, and magnetic fields in the clouds. It is in the very focus of the field to determine how these processes give rise to the observed structure of molecular clouds. In this talk, I will review our current efforts to confront this paradigm with the goal of observationally constraining how different processes regulate molecular cloud structure and star formation. At the heart of these efforts lies the use of numerical simulations of gravo-turbulent media to A) define physically meaningful characteristics that are sensitive to the different cloud-shaping processes, and B) determine if and how such characteristics can be recovered by observations. I will show in my talk how this approach has recently led to new constraints for some fundamental measures of the molecular cloud structure. Such constraints allow us to assess the roles of turbulence and gravity in controlling the ISM structure and star formation. I will also highlight specific recent results, focusing on the nature of filamentary structures within molecular clouds. These results may provide a novel set of observational constraints with which to challenge the turbulence-regulated ISM paradigm. Finally, I will discuss the current challenges and open questions in understanding the link between molecular cloud structure and star formation, and speculate on key directions to aim the near-future studies.

  6. 13CO Molecular Clouds and Clumps in the Galactic Plane

    NASA Astrophysics Data System (ADS)

    Lee, Y.; Stark, A. A.

    2004-12-01

    Using the 13CO Bell Laboratories Survey for one third of galactic plane, (l, b) = (-5° to 117°, -1° to +1°), and our revised cloud identification code, 13CO clouds have been identified and cataloged as a function of threshold temperature; 1,400 of molecular clouds with 1 K threshold temperature and with a 4-threshold number of pixels, 629 clouds with 2 K threshold temperature, and 263 clouds with 3 K. Clouds with the brightest cores (TR*(13CO) > 3 K) are confined to the 5 Kpc Molecular Ring (l<40°) and l=80° region. In addition to cloud identification, dense clump regions can be located using this 13CO survey and then combined with existing UMass-Stony Brook 12CO data for the first quadrant of the Galactic Plane. Numbers of identified clumps are 3,156 with 0.4 threshold 13CO optical depth, 2,134 with 0.6, 1,190 with 0.8, and 662 with 1.0. It is found that the hot clumps are heavily crowded between l = 10° to 20°. Good correlation is found between 13CO integrated intensity and column density. We discuss some statistical characteristics of clouds, cores, and the column density distribution.

  7. Molecular clumps in the W51 giant molecular cloud

    NASA Astrophysics Data System (ADS)

    Parsons, H.; Thompson, M. A.; Clark, J. S.; Chrysostomou, A.

    2012-08-01

    In this paper, we present a catalogue of dense molecular clumps located within the W51 giant molecular cloud (GMC). This work is based on Heterodyne Array Receiver Programme 13CO J = 3-2 observations of the W51 GMC and uses the automated CLUMPFIND algorithm to decompose the region into a total of 1575 clumps of which 1130 are associated with the W51 GMC. We clearly see the distinct structures of the W51 complex and the high-velocity stream previously reported. We find the clumps have characteristic diameters of 1.4 pc, excitation temperatures of 12 K, densities of 5.6 × 1021 cm-2, surface densities 0.02 g cm-2 and masses of 90 M⊙. We find a total mass of dense clumps within the GMC of 1.5 × 105 M⊙, with only 1 per cent of the clumps detected by number and 4 per cent by mass found to be supercritical. We find a clump-forming efficiency of 14 ± 1 per cent for the W51 GMC and a supercritical clump-forming efficiency of 0.5-0.5+2.3 per cent. Looking at the clump mass distribution, we find it is described by a single power law with a slope of α=2.4-0.1+0.2 above ˜100 M⊙. By comparing locations of supercritical clumps and young clusters, we see that any future star formation is likely to be located away from the currently active W51A region.

  8. Spectral Line Survey toward a Molecular Cloud in IC10

    NASA Astrophysics Data System (ADS)

    Nishimura, Yuri; Shimonishi, Takashi; Watanabe, Yoshimasa; Sakai, Nami; Aikawa, Yuri; Kawamura, Akiko; Yamamoto, Satoshi

    2016-10-01

    We have conducted a spectral line survey observation in the 3 mm band toward the low-metallicity dwarf galaxy IC10 with the 45 m radio telescope of the Nobeyama Radio Observatory to explore its chemical composition at a molecular-cloud scale (∼80 pc). The CS, SO, CCH, HCN, HCO+, and HNC lines are detected for the first time in this galaxy in addition to the CO and 13CO lines, while the c-C3H2, CH3OH, CN, C18O, and N2H+ lines are not detected. The spectral intensity pattern is found to be similar to those observed toward molecular clouds in the Large Magellanic Cloud (LMC), whose metallicity is as low as IC10. Nitrogen-bearing species are deficient in comparison with the Galactic molecular clouds due to a lower elemental abundance of nitrogen. CCH is abundant in comparison with Galactic translucent clouds, whereas CH3OH may be deficient. These characteristic trends for CCH and CH3OH are also seen in the LMC, and seem to originate from photodissociation regions more extended in the peripheries of molecular clouds due to the lower metallicity condition.

  9. Gravity, Turbulence and the scaling "laws" in molecular clouds

    NASA Astrophysics Data System (ADS)

    Ballesteros-Paredes, Javier

    2015-08-01

    The so-called Larson scaling laws found empirically in molecular clouds have been generally interpreted as evidence that the clouds are turbulent, and hence fractal. However, recent observations and models of cloud formation suggest that a) these relations are the result of strong observational biases, and thus should be replaced by a single, more general one, and b) that the actual source of the non-thermal motions is gravitational collapse of the clouds, so that the turbulent, chaotic component of the motions is only a by-product of the collapse, with no significant "support" role for the clouds, and that the scale-free nature of the motions is of gravitational, rather than turbulent, origin.

  10. Association of Presolar Grains with Molecular Cloud Material in IDPs

    NASA Technical Reports Server (NTRS)

    Messenger, S.; Keller, L. P.

    2005-01-01

    Anhydrous interplanetary dust particles (IDPs) collected in the stratosphere appear chemically, mineralogically, and texturally primitive in comparison to meteorites. Particles that escape significant atmospheric entry heating have highly unequilibrated mineralogy, are volatile element rich, and, overall, appear to have escaped significant parent body hydrothermal alteration. These IDPs are comprised of the building blocks of the solar system. The strongest evidence that anhydrous IDPs are primitive is that they contain abundant stardust and molecular cloud material. In particular, presolar silicates were first identified in IDPs and are present in abundances (450-5,500 ppm) that are well above that observed in primitive meteorites (less than 170 ppm). The most fragile (cluster) IDPs also commonly exhibit large H and N isotopic anomalies that likely originated by isotopic fractionation during extremely low temperature chemical reactions in a presolar cold molecular cloud. The D/H ratios exceed that of most primitive meteorites, and in rare cases reach values directly observed from simple gas phase molecules in cold molecular clouds. The most extreme D- and N-15-enrichments are usually observed at the finest spatial scales (0.5-2 microns) that can be measured. These observations suggest that D and N-15 hotspots are in fact preserved nuggets of molecular cloud material, and that the materials within them also have presolar origins. The advanced capabilities of the NanoSIMS ion microprobe now enable us to test this hypothesis. Here, we report two recent examples of presolar silicates found to be directly associated with molecular cloud material.

  11. Formation of young massive clusters from turbulent molecular clouds

    NASA Astrophysics Data System (ADS)

    Fujii, Michiko; Portegies Zwart, Simon

    2015-08-01

    We simulate the formation and evolution of young star clusters using smoothed-particle hydrodynamics (SPH) and direct N-body methods. We start by performing SPH simulations of the giant molecular cloud with a turbulent velocity field, a mass of 10^4 to 10^6 M_sun, and a density between 17 and 1700 cm^-3. We continue the SPH simulations for a free-fall time scale, and analyze the resulting structure of the collapsed cloud. We subsequently replace a density-selected subset of SPH particles with stars. As a consequence, the local star formation efficiency exceeds 30 per cent, whereas globally only a few per cent of the gas is converted to stars. The stellar distribution is very clumpy with typically a dozen bound conglomerates that consist of 100 to 10000 stars. We continue to evolve the stars dynamically using the collisional N-body method, which accurately treats all pairwise interactions, stellar collisions and stellar evolution. We analyze the results of the N-body simulations at 2 Myr and 10 Myr. From dense massive molecular clouds, massive clusters grow via hierarchical merging of smaller clusters. The shape of the cluster mass function that originates from an individual molecular cloud is consistent with a Schechter function with a power-law slope of beta = -1.73 at 2 Myr and beta = -1.67 at 10 Myr, which fits to observed cluster mass function of the Carina region. The superposition of mass functions have a power-law slope of < -2, which fits the observed mass function of star clusters in the Milky Way, M31 and M83. We further find that the mass of the most massive cluster formed in a single molecular cloud with a mass of M_g scales with 6.1 M_g^0.51 which also agrees with recent observation in M51. The molecular clouds which can form massive clusters are much denser than those typical in the Milky Way. The velocity dispersion of such molecular clouds reaches 20 km/s and it is consistent with the relative velocity of the molecular clouds observed near NGC 3603

  12. Correlation between Gas and Dust in Molecular Clouds: L977

    NASA Astrophysics Data System (ADS)

    Alves, João; Lada, Charles J.; Lada, Elizabeth A.

    1999-04-01

    We report observations of the J=(1-0) C18O molecular emission line toward the L977 molecular cloud. To study the correlation between C18O emission and dust extinction we constructed a Gaussian smoothed map of the infrared extinction measured by Alves et al. at the same angular resolution (50") as our molecular-line observations. This enabled a direct comparison of C18O integrated intensities and column densities with dust extinction over a relatively large range of cloud depth (2cloud depths corresponding to AV<~10 mag. For cloud depths above this threshold there is a notable break in the linear correlation. Although either optically thick C18O emission or extremely low (Tex<5 K) excitation temperatures at high extinctions could produce this departure from linearity, CO depletion in the denser, coldest regions of L977 may be the most likely cause of the break in the observed correlation. We directly derive the C18O abundance in this cloud over a broad range of cloud depths and find it to be virtually the same as that derived for IC 5146 from the data of Lada et al. In regions of very high extinction (AV>10 mag), such as dense cores, our results suggest that C18O would be a very poor tracer of mass. Consequently, using C18O as a column density tracer in molecular clouds can lead to a 10% to 30% underestimation of overall cloud mass. We estimate the minimum total column density required to shield C18O from the interstellar radiation field to be 1.6+/-0.5 mag of visual extinction.

  13. Molecular Clouds, Star Formation and Galactic Structure.

    ERIC Educational Resources Information Center

    Scoville, Nick; Young, Judith S.

    1984-01-01

    Radio observations show that the gigantic clouds of molecules where stars are born are distributed in various ways in spiral galaxies, perhaps accounting for the variation in their optical appearance. Research studies and findings in this area are reported and discussed. (JN)

  14. Cosmic-ray ionisation of dense molecular clouds

    NASA Astrophysics Data System (ADS)

    Vaupre, Solenn

    2015-07-01

    Cosmic rays (CR) are of tremendous importance in the dynamical and chemical evolution of interstellar molecular clouds, where stars and planets form. CRs are likely accelerated in the shells of supernova remnants (SNR), thus molecular clouds nearby can be irradiated by intense fluxes of CRs. CR protons have two major effects on dense molecular clouds: 1) when they encounter the dense medium, high-energy protons (>280 MeV) create pions that decay into gamma-rays. This process makes SNR-molecular cloud associations intense GeV and/or TeV sources whose spectra mimic the CR spectrum. 2) at lower energies, CRs penetrate the cloud and ionise the gas, leading to the formation of molecular species characteristic of the presence of CRs, called tracers of the ionisation. Studying these tracers gives information on low-energy CRs that are unaccessible to any other observations. I studied the CR ionisation of molecular clouds next to three SNRs: W28, W51C and W44. These SNRs are known to be interacting with the nearby clouds, from the presence of shocked gas, OH masers and pion-decay induced gamma-ray emission. My work includes millimeter observations and chemical modeling of tracers of the ionisation in these dense molecular clouds. In these three regions, we determined an enhanced CR ionisation rate, supporting the hypothesis of an origin of the CRs in the SNR nearby. The evolution of the CR ionisation rate with the distance to the SNR brings valuable constraints on the propagation properties of low-energy CRs. The method used relies on observations of the molecular ions HCO+ and DCO+, which shows crucial limitations at high ionisation. Therefore, I investigated, both through modeling and observations, the chemical abundances of several other species to try and identity alternative tracers of the ionisation. In particular, in the W44 region, observations of N2H+ bring additional constraints on the physical conditions, volatile abundances in the cloud, and the ionisation

  15. TWO POPULATIONS OF MOLECULAR CLOUDS IN THE ANTENNAE GALAXIES

    SciTech Connect

    Wei, Lisa H.; Keto, Eric; Ho, Luis C.

    2012-05-10

    Super star clusters-extremely massive clusters found predominately in starburst environments-are essential building blocks in the formation of galaxies and thought to dominate star formation in the high-redshift universe. However, the transformation from molecular gas into these ultracompact star clusters is not well understood. To study this process, we used the Submillimeter Array and the Plateau de Bure Interferometer to obtain high angular resolution ({approx}1.''5 or 160 pc) images of the Antennae overlap region in CO(2-1) to search for the molecular progenitors of the super star clusters. We resolve the molecular gas distribution into a large number of clouds, extending the differential cloud mass function down to a 5{sigma} completeness limit of 3.8 Multiplication-Sign 10{sup 5} M{sub Sun }. We identify a distinct break in the mass function around log M{sub mol}/M{sub Sun} Almost-Equal-To 6.5, which separates the molecular clouds into two distinct populations. The smaller, less massive clouds reside in more quiescent areas in the region, while the larger, more massive clouds cluster around regions of intense star formation. A broken power-law fit to the mass function yields slopes of {alpha} = -1.39 {+-} 0.10 and {alpha} = -1.44 {+-} 0.14 for the low- and high-mass cloud population, well matched to the mass function found for super star clusters in the Antennae galaxies. We find large velocity gradients and velocity dispersions at the locations of intense star formation, suggestive of compressive shocks. It is likely that these environmental factors contribute to the formation of the observed massive molecular clouds and super star clusters in the Antennae galaxies.

  16. Giant molecular cloud scaling relations: the role of the cloud definition

    NASA Astrophysics Data System (ADS)

    Khoperskov, S. A.; Vasiliev, E. O.; Ladeyschikov, D. A.; Sobolev, A. M.; Khoperskov, A. V.

    2016-01-01

    We investigate the physical properties of molecular clouds in disc galaxies with different morphologies: a galaxy without prominent structure, a spiral barred galaxy and a galaxy with flocculent structure. Our N-body/hydrodynamical simulations take into account non-equilibrium H2 and CO chemical kinetics, self-gravity, star formation and feedback processes. For the simulated galaxies, the scaling relations of giant molecular clouds, or so-called Larson's relations, are studied for two types of cloud definition (or extraction method): the first is based on total column density position-position (PP) data sets and the second is indicated by the CO (1-0) line emission used in position-position-velocity (PPV) data. We find that the cloud populations obtained using both cloud extraction methods generally have similar physical parameters, except that for the CO data the mass spectrum of clouds has a tail with low-mass objects M ˜ 103-104 M⊙. Owing toa varying column density threshold, the power-law indices in the scaling relations are significantly changed. In contrast, the relations are invariant to the CO brightness temperature threshold. Finally, we find that the mass spectra of clouds for PPV data are almost insensitive to the galactic morphology, whereas the spectra for PP data demonstrate significant variation.

  17. HCO emission from H II-molecular cloud interface regions.

    PubMed

    Schenewerk, M S; Snyder, L E; Hollis, J M; Jewell, P R; Ziurys, L M

    1988-05-15

    A survey of well-known molecular clouds in the four strongest HCO NK-,K+ = 1(01)-0(00) hyperfine transitions has been carried out to determine the prevalence of HCO and to study its chemistry. HCO emission was observed in seven molecular clouds. Three of these, NGC 2264, W49, and NGC 7538, were not previously known sources of HCO. In addition, NGC 2024 and Sgr B2 were mapped and shown to have extensive HCO emission. The survey results show the HCO abundance to be enhanced in H II-molecular cloud interface regions and support a correlation between C+ and HCO emission. The strength of the HCO emission in NGC 2024 is interpreted in terms of this enhancement and the source structure and proximity to Earth.

  18. Waves on the surface of the Orion molecular cloud.

    PubMed

    Berné, Olivier; Marcelino, Núria; Cernicharo, José

    2010-08-19

    Massive stars influence their parental molecular cloud, and it has long been suspected that the development of hydrodynamical instabilities can compress or fragment the cloud. Identifying such instabilities has proved difficult. It has been suggested that elongated structures (such as the 'pillars of creation') and other shapes arise because of instabilities, but alternative explanations are available. One key signature of an instability is a wave-like structure in the gas, which has hitherto not been seen. Here we report the presence of 'waves' at the surface of the Orion molecular cloud near where massive stars are forming. The waves seem to be a Kelvin-Helmholtz instability that arises during the expansion of the nebula as gas heated and ionized by massive stars is blown over pre-existing molecular gas. PMID:20725034

  19. Waves on the surface of the Orion molecular cloud.

    PubMed

    Berné, Olivier; Marcelino, Núria; Cernicharo, José

    2010-08-19

    Massive stars influence their parental molecular cloud, and it has long been suspected that the development of hydrodynamical instabilities can compress or fragment the cloud. Identifying such instabilities has proved difficult. It has been suggested that elongated structures (such as the 'pillars of creation') and other shapes arise because of instabilities, but alternative explanations are available. One key signature of an instability is a wave-like structure in the gas, which has hitherto not been seen. Here we report the presence of 'waves' at the surface of the Orion molecular cloud near where massive stars are forming. The waves seem to be a Kelvin-Helmholtz instability that arises during the expansion of the nebula as gas heated and ionized by massive stars is blown over pre-existing molecular gas.

  20. Carbon chemistry in dense molecular clouds: Theory and observational constraints

    NASA Technical Reports Server (NTRS)

    Blake, Geoffrey A.

    1990-01-01

    For the most part, gas phase models of the chemistry of dense molecular clouds predict the abundances of simple species rather well. However, for larger molecules and even for small systems rich in carbon these models often fail spectacularly. Researchers present a brief review of the basic assumptions and results of large scale modeling of the carbon chemistry in dense molecular clouds. Particular attention is to the influence of the gas phase C/O ratio in molecular clouds, and the likely role grains play in maintaining this ratio as clouds evolve from initially diffuse objects to denser cores with associated stellar and planetary formation. Recent spectral line surveys at centimeter and millimeter wavelengths along with selected observations in the submillimeter have now produced an accurate inventory of the gas phase carbon budget in several different types of molecular clouds, though gaps in our knowledge clearly remain. The constraints these observations place on theoretical models of interstellar chemistry can be used to gain insights into why the models fail, and show also which neglected processes must be included in more complete analyses. Looking toward the future, larger molecules are especially difficult to study both experimentally and theoretically in such dense, cold regions, and some new methods are therefore outlined which may ultimately push the detectability of small carbon chains and rings to much heavier species.

  1. A Survey for Distributed Star Formation in the Rosette Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Muench, August A.; Lada, Elizabeth A.; Phelps, Randy

    1999-08-01

    We propose to conduct a sensitive survey of a 1.4 deg^2 region of the Rosette Molecular Cloud (RMC) in the J(1.1(mu)m), H(1.6(mu)m), and K(2.2(mu)m) near-infrared bands (NIR) using ONIS on the 2.1m telescope. The main science goal of this survey is to determine whether or not a low mass, distributed mode of star formation exists within the cloud. An initial NIR survey using SQIID on the 1.3m telescope (Phelps & Lada, 1997) identified seven young embedded clusters. However the SQIID survey was not sensitive enough to determine whether or not a low- mass distributed population of stars is also present in the cloud. Therefore a more sensitive survey is required to determine which mode of star formation (distributed or clustered) dominates the star formation in the RMC. Additionally, our survey will allow us to investigate if the luminosity functions of the isolated stars are different from the cluster luminosity functions. We will also be able to investigate the influence of the adjacent HII nebulae on the distributed mode of star formation and how the nebulae may act as a trigger for sequential star formation. Our proposed survey will provide an important database for investigating the different modes of star formation in giant molecular clouds.

  2. Molecular Complexity in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Acharyya, Kinsuk; Herbst, Eric

    2016-07-01

    Recently, we studied chemical complexity in the Large and Small Magellanic clouds. These are irregular satellite galaxies of the Milky Way. Both are metal- and dust-poor, although the SMC is significantly poorer in both. The dust temperature in these galaxies could also be higher compared to our Galaxy; this can have a profound effect on the synthesis of molecules in these galaxies. Our simulations show that the cold, dense regions of the LMC and SMC can have a rich chemistry. We found major gas phase species, as well as water and CO2 ices, could be found in abundant quantity. In this presentation I will discuss the complex organic molecules that are found in abundant quantity in our Galaxy, and how their abundance varies in the Magellanic clouds. This comparison will help us to understand the role of metallicity and dust grain temperature in the formation of complex organic molecules.

  3. Schmidt's conjecture and star formation in molecular clouds

    SciTech Connect

    Lada, Charles J.; Forbrich, Jan; Lombardi, Marco; Roman-Zuniga, Carlos; Alves, João F. E-mail: marco.lombardi@unimi.it E-mail: jan.forbrich@univie.ac.at

    2013-12-01

    We investigate Schmidt's conjecture (i.e., that the star formation rate (SFR) scales in a power-law fashion with the gas density) for four well-studied local molecular clouds (giant molecular clouds, GMCs). Using the Bayesian methodology, we show that a local Schmidt scaling relation of the form Σ{sub ∗}(A{sub K})=κA{sub K}{sup β} (protostars pc{sup –2}) exists within (but not between) GMCs. Further, we find that the Schmidt scaling law does not by itself provide an adequate description of star formation activity in GMCs. Because the total number of protostars produced by a cloud is given by the product of Σ{sub *}(A {sub K}) and S'(> A {sub K}), the differential surface area distribution function, integrated over the entire cloud, the cloud's structure plays a fundamental role in setting the level of its star formation activity. For clouds with similar functional forms of Σ{sub *}(A {sub K}), observed differences in their total SFRs are primarily due to the differences in S'(> A {sub K}) between the clouds. The coupling of Σ{sub *}(A {sub K}) with the measured S'(> A {sub K}) in these clouds also produces a steep jump in the SFR and protostellar production above A{sub K} ∼ 0.8 mag. Finally, we show that there is no global Schmidt law that relates the SFR and gas mass surface densities between GMCs. Consequently, the observed Kennicutt-Schmidt scaling relation for disk galaxies is likely an artifact of unresolved measurements of GMCs and not a result of any underlying physical law of star formation characterizing the molecular gas.

  4. The COMPLETE Survey of Nearby Star-Forming Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Di Francesco, J.; Goodman, A. A.; Alves, J.; Arce, H.; Caselli, P.; Heyer, M. H.; Johnstone, D.; Schnee, S.; Tafalla, M.; Wilson, T. L.

    2002-12-01

    We report on the preliminary data and ongoing progress of the COMPLETE* Survey of Nearby Star-Forming Molecular Clouds, an international effort to provide the astronomical community with uniform, wide-field observations of molecular line emission, dust continuum emission, and dust extinction across the Ophiuchus, Perseus, and Serpens molecular clouds. Such observations of ~10 square degrees are now only feasible with the recent simultaneous availability of multi-element mapping instruments at various facilities. Extensive data of 12CO and 13CO J = 1-0 rotational transition emission across the 3 clouds will be obtained this winter using the 32-element SEQUOIA array of the Five College Radio Astronomy Observatory (FCRAO). Complementary 850 micron thermal continuum emission from dust within these same regions may be obtained this winter using the 37-element Long-Wave SCUBA array of the James Clerk Maxwell Telescope (JCMT). Dust extinction maps of these regions are being compiled initially using Two-Micron All Sky Survey (2MASS) data. The resulting COMPLETE database, accessible freely to the public through a pilot program of the National Virtual Observatory, will allow for comprehensive studies of the relationships between star formation and the physical conditions within molecular clouds, especially in conjunction with sensitive near- to mid-infrared data of these regions expected from the SIRTF Legacy program ``Cores to Disks" (c2d). (* COMPLETE = CO-ordinated Molecular Probe Line, Thermal Emission, and Extinction)

  5. Effects of cloud variability on TROPOMI molecular and cloud property products

    NASA Astrophysics Data System (ADS)

    Gimeno García, Sebastián; Schreier, Franz; Trautmann, Thomas; Loyola, Diego; Heinze, Rieke

    In order to guarantee high signal-to-noise ratios, the design of spectrometers aboard spaceborne platforms is a tradeoff between spectral and spatial resolution. Since molecular absorption is highly spectrally dependent, atmospheric composition instruments favor spectral over spatial resolution. The TROPOMI instrument aboard Sentinel 5 Precursor (S5P) will have a spatial resolution of about 7x7 km2 at nadir, which clearly outperforms the resolution of previous atmospheric missions (320x40 km2 for GOME/ERS-2, 120x30 km2 for SCIAMACHY/ENVISAT and 80x40 km2 for GOME-2/Metop-A,B). However, inside a TROPOMI ground pixel there may still be a considerable amount of unresolved cloud variability. In this work, we present a sensitivity study of measured reflectivities as a function of the unresolved cloud variability. For this purpose, we simulate virtual measurements of a TROPOMI-like instrument in cloudy scenes at different spatial resolutions by means of the three-dimensional (3D) radiative transfer model MoCaRT (Monte Carlo Radiative Transfer). The reference inside-pixel cloud microphysical properties are provided by the PArallelized Large-Eddy-Simulation Model (PALM) at a spatial resolution of 10x10 m2 in a 6.4x6.4 km2 domain. The retrieval algorithms of both, atmospheric molecules and cloud properties rely on one-dimensional radiative transfer (RT) models which do not account for neither cloud variability nor 3D RT effects. Moreover, the quality of atmospheric gas retrievals strongly depends on the accuracy of the cloud information. Accordingly, we first analyze the 3D effects on the cloud products by ingesting the 3D simulated spectra (around the oxygen A-band) to the ROCINN_CAL cloud algorithm. In a second step, the impact of the cloud variability on the ozone product is assessed (which also include the indirect impact on cloud properties).

  6. The cyanopolyynes as a chemical clock for molecular clouds

    NASA Technical Reports Server (NTRS)

    Stahler, S. W.

    1984-01-01

    A new method is proposed for determining the ages of molecular clouds. The method utilizes the properties of the long-chain organic molecules known as the cyanopolyynes (HC/2k + 1/N, k = 0, 1, 2, 3 ...), which are found in a variety of clouds. The observed regular abundance decline of these molecules as a function of chain length suggests that they are formed sequentially. If so, the age of the cloud can be read off as the time to grow the longest chain present. Although the creation process for the chains is still unknown, the age can be obtained from knowledge of the chain destruction mechanism. Destruction is probably due to adsorption onto the surfaces of interstellar grains. Using the known properties of grains, the age can be obtained from the cloud density and the abundance ratios of the cyanopolyynes. As a first application, minimum ages for the four dark clouds B335, TMC-1, TMC-2, and L183 are obtained. These minimum ages are 1.3 x 10 to the 6th yr, 9.7 x 10 to the 5th yr, 3.4 x 10 to the 5th yr, and 3.3 x 10 to the 5th yr, respectively. In each case, the ages are greater than or equal to the cloud's free-fall collapse time. These four clouds are therefore either in a state of hydrostatic balance or have only recently begun to collapse, following an earlier period of hydrostatic support.

  7. An estimate of star formation efficiency in molecular clouds

    NASA Technical Reports Server (NTRS)

    Rengarajan, T. N.

    1984-01-01

    From the existing data in the literature it is shown that there is a linear correlation between cloud mass derived from CO observations and the associated luminosity obtained from far-IR observations over a large luminosity range of 10 to the 4th to 10 to the 8th solar luminosities. The mean value of luminosity per unit mass for a giant molecular cloud is 5.6 solar-L/solar-M. The star-forming efficiency of the molecular cloud over its lifetime of 5-10 x 10 to the 7th yr is found to be 0.2-0.3, which yields the present star-forming rate of 6-11 solar masses per year. Furthermore, the integral luminosity distribution is a power-law with an exponent of about -0.5. The correlation between cloud mass and the far-IR luminosity observed for a sample of nuclei of external galaxies corresponds to molecular clouds similar to those in the Galaxy.

  8. Interaction between Cassiopeia A and Nearby Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Kilpatrick, C. D.; Bieging, J. H.; Rieke, G. H.

    2014-12-01

    We present spectroscopy of the supernova remnant Cassiopeia A (Cas A) observed at infrared wavelengths from 10 to 40 μm with the Spitzer Space Telescope and at millimeter wavelengths in 12CO and 13CO J =2-1 (230 and 220 GHz) with the Heinrich Hertz Submillimeter Telescope. The IR spectra demonstrate high-velocity features toward a molecular cloud coincident with a region of bright radio continuum emission along the northern shock front of Cas A. The millimeter observations indicate that CO emission is broadened by a factor of two in some clouds toward Cas A, particularly to the south and west. We believe that these features trace interactions between the Cas A shock front and nearby molecular clouds. In addition, some of the molecular clouds that exhibit broadening in CO lie 1'-2' away from the furthest extent of the supernova remnant shock front. We propose that this material may be accelerated by ejecta with velocity significantly larger than the observed free-expansion velocity of the Cas A shock front. These observations may trace cloud interactions with fast-moving outflows such as the bipolar outflow along the southwest to northeast axis of the Cas A supernova remnant, as well as fast-moving knots seen emerging in other directions.

  9. Interaction between Cassiopeia A and nearby molecular clouds

    SciTech Connect

    Kilpatrick, C. D.; Bieging, J. H.; Rieke, G. H.

    2014-12-01

    We present spectroscopy of the supernova remnant Cassiopeia A (Cas A) observed at infrared wavelengths from 10 to 40 μm with the Spitzer Space Telescope and at millimeter wavelengths in {sup 12}CO and {sup 13}CO J =2-1 (230 and 220 GHz) with the Heinrich Hertz Submillimeter Telescope. The IR spectra demonstrate high-velocity features toward a molecular cloud coincident with a region of bright radio continuum emission along the northern shock front of Cas A. The millimeter observations indicate that CO emission is broadened by a factor of two in some clouds toward Cas A, particularly to the south and west. We believe that these features trace interactions between the Cas A shock front and nearby molecular clouds. In addition, some of the molecular clouds that exhibit broadening in CO lie 1'-2' away from the furthest extent of the supernova remnant shock front. We propose that this material may be accelerated by ejecta with velocity significantly larger than the observed free-expansion velocity of the Cas A shock front. These observations may trace cloud interactions with fast-moving outflows such as the bipolar outflow along the southwest to northeast axis of the Cas A supernova remnant, as well as fast-moving knots seen emerging in other directions.

  10. STUDIES OF MOLECULAR CLOUDS ASSOCIATED WITH H II REGIONS: S175

    SciTech Connect

    Azimlu, Mohaddesseh; Fich, Michel; McCoey, Carolyn

    2009-06-15

    We are studying the impact of H II regions on star formation in their associated molecular clouds. In this paper, we present James Clerk Maxwell Telescope R x A molecular line observations of S175 and environs. This is the first within a sample of 10 H II regions and their surrounding molecular clouds selected for our study. We first make 7' x 7' maps in {sup 12}CO(2-1), which are used to investigate the structure of the cloud and to identify individual clumps. Single point observations were made in {sup 13}CO(2-1) and CS(5-4) at the peak of the {sup 12}CO(2-1) emission within each clump in order to measure the physical properties of the gas. Densities, temperatures, clump masses, peak velocities, and line widths were measured and calculated using these observations. We have identified two condensations (S175A and S175B) in the molecular cloud associated with this H II region. S175A is adjacent to the ionization front and is expected to be affected by the H II region, while S175B is too distant to be disturbed. We compare the structure and gas properties of these two regions to investigate how the molecular gas has been affected by the H II region. S175A has been heated by the H II region and partially compressed by the ionized gas front, but contrary to our expectation it is a quiescent region while S175B is very turbulent and dynamically active. Our investigation for the source of turbulence in S175B resulted in the detection of an outflow within this region.

  11. Cloud fluid compression and softening in spiral arms and the formation of giant molecular cloud complexes

    NASA Technical Reports Server (NTRS)

    Cowie, L. L.

    1981-01-01

    With regard to the galactodynamics of the cloudy interstellar medium, the paper considers the response of such a gas to a forcing potential in the tight-winding density wave theory. The cloud fluid is treated in the hydrodynamic limit with an equation of state which softens at high densities. It is shown that in the inner regions of the galaxy, cooling of the cloud fluid in the arms can result in gravitational instability and the formation of large bound complexes of clouds which are identified with the giant molecular clouds (GMCs). Masses, dimensions, distributions, and scale heights of the GMCs are predicted by the theory. It is suggested that the interstellar gas density in the disk is regulated by the gravitational instability mechanism in the arms which siphons material into star formation. Implications for the evolution of individual GMCs and for galactic morphology are discussed.

  12. The Chemistry and Excitation of Water in Molecular Clouds

    NASA Technical Reports Server (NTRS)

    Hollenbach, David

    2003-01-01

    We model the chemistry and thermal balance of opaque molecular clouds exposed to an external flux of ultraviolet photons. We include the processes of gas phase and grain surface chemical reactions; in particular we examine closely the freezing of atoms and molecules onto grain surfaces and the desorption of molecules from grain surfaces as a function of depth into a molecular cloud. We find that on the surface of a molecular cloud the gas phase water abundances are low because of photodissociation, and the grain phase water (ice) abundance is low because of photodesorption of water from the grain surfaces. Deeper into the cloud, at A(sub v) less than or approximately 2-8 depending on the strength of the external ultraviolet flux, the gas phase water abundance increases with depth as the photodissociation rates decline due to dust attenuation of the ultraviolet field. However, beyond A(sub v) less than or approximately 2-8 the gas phase water abundance declines because the water freezes as water ice on the grains, and photodesorption is no longer effective in clearing the ice. A peak water abundance of about 10(exp -6) to 10(exp -7) occurs at about A(sub v) approximately 2-8, relatively independent of the gas density and the ultraviolet field. We show that such a model matches very closely the observations of the Submillimeter Wave Astronomical Satellite (SWAS), a NASA Small Explorer Mission. The model elucidates several mechanisms that have been recently invoked to understand gas phase chemistry in clouds, including-the freeze-out of molecules onto grain surface, the desorption of these molecules from the surfaces, and the abundance gradients of molecules as functions of depth into molecular clouds.

  13. Supersonic turbulence and structure of interstellar molecular clouds.

    PubMed

    Boldyrev, Stanislav; Nordlund, Ake; Padoan, Paolo

    2002-07-15

    The interstellar medium provides a unique laboratory for highly supersonic, driven hydrodynamic turbulence. We propose a theory of such turbulence, test it by numerical simulations, and use the results to explain observational scaling properties of interstellar molecular clouds, the regions where stars are born.

  14. Primordial Molecular Cloud Material in Metal-Rich Carbonaceous Chondrites

    NASA Astrophysics Data System (ADS)

    Taylor, G. J.

    2016-03-01

    The menagerie of objects that make up our Solar System reflects the composition of the huge molecular cloud in which the Sun formed, a late addition of short-lived isotopes from an exploding supernova or stellar winds from a neighboring massive star, heating and/or alteration by water in growing planetesimals that modified and segregated the primordial components, and mixing throughout the Solar System. Outer Solar System objects, such as comets, have always been cold, hence minimizing the changes experienced by more processed objects. They are thought to preserve information about the molecular cloud. Elishevah Van Kooten (Natural History Museum of Denmark and the University of Copenhagen) and co-authors in Denmark and at the University of Hawai'i, measured the isotopic compositions of magnesium and chromium in metal-rich carbonaceous chondrites. They found that the meteorites preserve an isotopic signature of primordial molecular cloud materials, providing a potentially detailed record of the molecular cloud's composition and of materials that formed in the outer Solar System.

  15. Tidal disruption of open clusters in their parent molecular clouds

    NASA Technical Reports Server (NTRS)

    Long, Kevin

    1989-01-01

    A simple model of tidal encounters has been applied to the problem of an open cluster in a clumpy molecular cloud. The parameters of the clumps are taken from the Blitz, Stark, and Long (1988) catalog of clumps in the Rosette molecular cloud. Encounters are modeled as impulsive, rectilinear collisions between Plummer spheres, but the tidal approximation is not invoked. Mass and binding energy changes during an encounter are computed by considering the velocity impulses given to individual stars in a random realization of a Plummer sphere. Mean rates of mass and binding energy loss are then computed by integrating over many encounters. Self-similar evolutionary calculations using these rates indicate that the disruption process is most sensitive to the cluster radius and relatively insensitive to cluster mass. The calculations indicate that clusters which are born in a cloud similar to the Rosette with a cluster radius greater than about 2.5 pc will not survive long enough to leave the cloud. The majority of clusters, however, have smaller radii and will survive the passage through their parent cloud.

  16. Irradiation of dust in molecular clouds. IV. ACR doses

    NASA Astrophysics Data System (ADS)

    Yeghikyan, A. G.; Barsamyan, L.

    2013-09-01

    The fluxes of anomalous cosmic rays inside typical molecular clouds produced during collisions of stars with clouds are calculated. The charged particles formed in the cloud in the neighborhood of the star are accelerated in a shock front in the astrosphere by known statistical mechanisms to energies on the order of a few 100 MeV. It is shown that protons and α-particles with energies in the 1 keV ≤ E ≤ 10 GeV range penetrate deeply enough that, over the time of 1-5 hundred thousand years a star is passing through a cloud, they produce sufficient irradiation doses for the ice mantle of dust particles such that the cumulative effect owing to multiple passages would exceed a threshold value on the order of 0.1-1 eV/amu. The possible use of these results for astrophysical interpretation of laboratory experiments on the irradiation of H2O:CH3OH:NH3:CO ice mixtures is discussed. The complex organic substances formed by radiation-chemical transformation may play an important role in the prebiological evolution of the dust component of molecular clouds.

  17. Sandqvist 187 - A dense molecular cloud in Norma

    NASA Technical Reports Server (NTRS)

    Alvarez, H.; Bronfman, L.; Cohen, R.; Garay, G.; Graham, J.; Thaddeus, P.

    1986-01-01

    Observations of Sandqvist 187, an elongated dust cloud in the southern constellation Norma are presented and discussed. The cloud contains two Herbig-Haro objects, HH 56 and HH 57. HH 57 currently displays on its NE edge a 17th mag variable star of the FU Ori type. Using the Columbia University 1.2 m millimeter-wave telescope at Cerro Tololo, the region is mapped and an extended CO cloud which envelops and is elongated along the optical dust cloud is found. The position of maximum CO emission coincides with HH 56 and HH 57. Assuming a distance of 0.7 kpc, the total mass of the cloud is found to be close to 500 solar masses. The CO spectra show evidence of a molecular flow. Photographs and CCD images obtained mostly with the CTIO 4 m telescope show the detailed optical structure of the dark cloud's core region. The Herbig-Haro object HH 56 appears to be related to an emission-line star embedded in the small nebula Reipurth 13, not to the FU Ori star in HH 57.

  18. Chemical evolution of giant molecular clouds in simulations of galaxies

    NASA Astrophysics Data System (ADS)

    Richings, Alexander J.; Schaye, Joop

    2016-08-01

    We present an analysis of giant molecular clouds (GMCs) within hydrodynamic simulations of isolated, low-mass (M* ˜ 109 M⊙) disc galaxies. We study the evolution of molecular abundances and the implications for CO emission and the XCO conversion factor in individual clouds. We define clouds either as regions above a density threshold n_{H, min} = 10 {cm}^{-3}, or using an observationally motivated CO intensity threshold of 0.25 {K} {km} {s}^{-1}. Our simulations include a non-equilibrium chemical model with 157 species, including 20 molecules. We also investigate the effects of resolution and pressure floors (i.e. Jeans limiters). We find cloud lifetimes up to ≈ 40 Myr, with a median of 13 Myr, in agreement with observations. At one-tenth solar metallicity, young clouds ( ≲ 10-15 Myr) are underabundant in H2 and CO compared to chemical equilibrium, by factors of ≈3 and one to two orders of magnitude, respectively. At solar metallicity, GMCs reach chemical equilibrium faster (within ≈ 1 Myr). We also compute CO emission from individual clouds. The mean CO intensity, ICO, is strongly suppressed at low dust extinction, Av, and possibly saturates towards high Av, in agreement with observations. The ICO-Av relation shifts towards higher Av for higher metallicities and, to a lesser extent, for stronger UV radiation. At one-tenth solar metallicity, CO emission is weaker in young clouds ( ≲ 10-15 Myr), consistent with the underabundance of CO. Consequently, XCO decreases by an order of magnitude from 0 to 15 Myr, albeit with a large scatter.

  19. Anatomy of the GEM OB1 molecular cloud complex

    NASA Astrophysics Data System (ADS)

    Carpenter, John Michael

    1994-05-01

    I have conducted an extensive study of the Gem OB1 molecular cloud complex in order to determine the global morphology of the molecular gas and how the morphology is correlated with the distribution of embedded star forming regions. The distribution and properties of the molecular gas were determined through molecular line surveys in (12)CO(J = 1-0), (13)CO(J = 1-0), and CS(J = 2-1), and the embedded stellar content was traced using the IRAS point source catalog and a J, H, and K band imaging survey of a portion of the cloud complex. The global morphology of the cloud complex is dominated by a series of arc and ring shaped structures found on nearly all resolved spatial scales from approximately 1 pc to possibly even 100 pc. Several of these arc-shaped structures are found on the periphery of optical H II regions and the physical properties of these features are consistent with being swept up molecular material. Other arc-shaped features are found without associated optical counterparts, but possess morphological and kinematic evidence that suggests that these structures also represent swept up regions of molecular gas. The large scale CS mapping found 13 cores of dense molecular gas with masses ranging from 40 M(solar mass) to 2600 M(solar mass). These cores are preferentially found within the arcs of molecular gas found in the (12)CO and (13)CO surveys, which suggests that the cores formed as this molecular gas was swept up. Twelve of the thirteen cores are associated with a IRAS point source or a cluster of stars. This indicates that star formation must proceed rapidly after the formation of dense cores that have masses exceeding at least approximately 50 M, and that dense cores must be continually formed throughout the lifetime of the Gem OB1 cloud complex if massive star formation is to continue. These observations suggest that once massive stars form, the evolution of cloud complexes and the subsequent formation of massive stars and embedded stellar clusters

  20. Supernova feedback in molecular clouds: global evolution and dynamics

    NASA Astrophysics Data System (ADS)

    Körtgen, Bastian; Seifried, Daniel; Banerjee, Robi; Vázquez-Semadeni, Enrique; Zamora-Avilés, Manuel

    2016-07-01

    We use magnetohydrodynamical simulations of converging warm neutral medium flows to analyse the formation and global evolution of magnetized and turbulent molecular clouds subject to supernova feedback from massive stars. We show that supernova feedback alone fails to disrupt entire, gravitationally bound, molecular clouds, but is able to disperse small-sized (˜10 pc) regions on time-scales of less than 1 Myr. Efficient radiative cooling of the supernova remnant as well as strong compression of the surrounding gas result in non-persistent energy and momentum input from the supernovae. However, if the time between subsequent supernovae is short and they are clustered, large hot bubbles form that disperse larger regions of the parental cloud. On longer time-scales, supernova feedback increases the amount of gas with moderate temperatures (T ≈ 300-3000 K). Despite its inability to disrupt molecular clouds, supernova feedback leaves a strong imprint on the star formation process. We find an overall reduction of the star formation efficiency by a factor of 2 and of the star formation rate by roughly factors of 2-4.

  1. Polarization of far-infrared radiation from molecular clouds

    NASA Technical Reports Server (NTRS)

    Novak, G.; Gonatas, D. P.; Hildebrand, R. H.; Platt, S. R.; Dragovan, M.

    1989-01-01

    The paper reports measurements of the polarization of far-infrared emission from dust in nine molecular clouds. Detections were obtained in Mon R2, in the Kleinmann-Low (KL) nebula in Orion, and in Sgr A. Upper limits were set for six other clouds. A comparison of the 100 micron polarization of KL with that previously measured at 270 microns provides new evidence that the polarization is due to emission from magnetically aligned dust grains. Comparing the results for Orion with measurements at optical wavelengths, it is inferred that the magnetic field direction in the outer parts of the Orion cloud is the same as that in the dense core. This direction is nearly perpendicular to the ridge of molecular emission and is parallel to both the molecular outflow in KL and the axis of rotation of the cloud core. In Mon R2, the field direction which the measurements imply does not agree withthat derived from 0.9-2.2 micron polarimetry. The discrepancy is attributed to scattering in the near-infrared. In Orion and Sgr A, where comparisons are possible, the measurements are in good agreement with 10 micron polarization measurements.

  2. Search for molecular oxygen in dense interstellar clouds.

    PubMed

    Goldsmith, P F; Snell, R L; Erickson, N R; Dickman, R L; Schloerb, F P; Irvine, W M

    1985-02-15

    We have carried out a search for the 234 GHz N = 2 --> 0, J = 1 --> 1 transition of 16O18O using the 13.7 m FCRAO radio telescope. No emission was detected toward six giant molecular clouds. Observations of the 220 GHz J = 2 --> 1 transition of C18O yield column densities for this species 1-3 x 10(16) cm-2; the resulting limits on the [O2]/[CO] ratio lie between <0.5 and <4. According to various chemical models, the ratio of molecular oxygen to carbon monoxide is primarily sensitive to the age of a cloud and to its carbon to oxygen ratio. For ages exceeding 3 x 10(6) yr and total carbon-to-oxygen ratio < 1, [O2]/[CO] can approach unity. Our best limits can be interpreted as indicating that the observed clouds are not chemically "mature" or that [carbon]/[oxygen] > 1. However, significant exploitation of molecular oxygen as a tracer of cloud structure and evolution will require more sensitive observations, which may be best carried out from above Earth's atmosphere.

  3. Rosette: Understanding Star Formation in Molecular Cloud Complexes

    NASA Astrophysics Data System (ADS)

    Wang, Junfeng

    2010-09-01

    We propose Chandra imaging of three embedded clusters in the Rosette Molecular Cloud (RMC) complex. With complementary existing Spitzer and FLAMINGOS infrared surveys, the Chandra observation is critical for us to: (1) create a complete census of the young stars in the cloud; (2) study the spatial distribution of the young stars in different evolutionary stages within the RMC and the disk frequency in the embedded clusters; (3) construct X-ray Luminosity Function (XLF) and Initial Mass Function (IMF) for the clusters to examine XLF/IMF variations; (4) elucidate star formation history in this complex.

  4. Sulphur-bearing species in molecular clouds

    NASA Astrophysics Data System (ADS)

    Bilalbegović, G.; Baranović, G.

    2015-01-01

    We study several molecules that could help in the solution of the missing sulphur problem in dense clouds and circumstellar regions, as well as in the clarification of the sulphur chemistry in comets. These sulphur molecules are the trimer (CH2S)3 and the tetramer (CH2S)4 of thioformaldehyde, pentathian S5CH2, hexathiepan S6CH2, thiirane C2H4S, trisulfane HSSSH, and thioacetone (CH3)2CS. Infrared spectra of these species are calculated using the density functional theory methods. The majority of calculated bands belong to the mid-infrared, with some of them occurring in the near- and far-infrared region. We suggest that some of unidentified spectral features measured by Infrared Space Observatory in several active galactic nuclei and starburst galaxies could be caused by 1,3,5-trithiane ((CH2S)3), 1,3,5,7-tetrathiocane ((CH2S)4), and thiirane (C2H4S). The objects whose unidentified infrared features we compare with calculated bands are NGC 253, M82, NGC 1068, Circinus, Arp 220, 30 Doradus, Orion KL, and Sgr B2.

  5. KINEMATICS OF SHOCKED MOLECULAR GAS ADJACENT TO THE SUPERNOVA REMNANT W44

    SciTech Connect

    Sashida, Tomoro; Oka, Tomoharu; Tanaka, Kunihiko; Aono, Kazuya; Matsumura, Shinji; Nagai, Makoto; Seta, Masumichi

    2013-09-01

    We mapped molecular gas toward the supernova remnant W44 in the HCO{sup +} J = 1-0 line with the Nobeyama Radio Observatory 45 m telescope and in the CO J = 3-2 line with the Atacama Submillimeter Telescope Experiment 10 m telescope. High-velocity emission wings were detected in both lines over the area where the radio shell of W44 overlaps with the molecular cloud in the plane of the sky. We found that the average velocity distributions of the wing emission can be fit by a uniform expansion model. The best-fit expansion velocities are 12.2 {+-} 0.3 km s{sup -1} and 13.2 {+-} 0.2 km s{sup -1} in HCO{sup +} and CO, respectively. The non-wing CO J = 3-2 component is also fit by the same model with an expansion velocity of 4.7 {+-} 0.1 km s{sup -1}. This component might be dominated by a post-shock higher-density region where the shock velocity had slowed down. The kinetic energy of the shocked molecular gas is estimated to be (3.5 {+-} 1.3) Multiplication-Sign 10{sup 49} erg. Adding this and the energy of the previously identified H I shell, we conclude that (1.2 {+-} 0.2) Multiplication-Sign 10{sup 50} erg has been converted into gas kinetic energy from the initial baryonic energy of the W44 supernova. We also found ultra-high-velocity CO J = 3-2 wing emission with a velocity width of {approx}100 km s{sup -1} at (l, b) = (+34. Degree-Sign 73, -0. Degree-Sign 47). The origin of this extremely high velocity wing is a mystery.

  6. Two Models of Magnetic Support for Photoevaporated Molecular Clouds

    SciTech Connect

    Ryutov, D; Kane, J; Mizuta, A; Pound, M; Remington, B

    2004-05-05

    The thermal pressure inside molecular clouds is insufficient for maintaining the pressure balance at an ablation front at the cloud surface illuminated by nearby UV stars. Most probably, the required stiffness is provided by the magnetic pressure. After surveying existing models of this type, we concentrate on two of them: the model of a quasi-homogeneous magnetic field and the recently proposed model of a ''magnetostatic turbulence''. We discuss observational consequences of the two models, in particular, the structure and the strength of the magnetic field inside the cloud and in the ionized outflow. We comment on the possible role of reconnection events and their observational signatures. We mention laboratory experiments where the most significant features of the models can be tested.

  7. Giant Molecular Cloud Collisions as Triggers of Star Formation

    NASA Astrophysics Data System (ADS)

    Wu, Benjamin; Tan, Jonathan C.; Van Loo, Sven; nakamura, fumitaka; Bruderer, Simon

    2016-01-01

    We investigate a potentially dominant mechanism for galactic star formation: triggering via collisions between giant molecular clouds (GMCs). We create detailed numerical simulations of this process, utilizing the Enzo code with magnetohydrodynamics (MHD), including non-ideal effects, and adaptive mesh refinement (AMR) to explore how cloud collisions trigger formation of dense filaments, clumps and stars. We implement photo-dissociation region (PDR) based density/temperature/extinction-dependent heating and cooling functions that span the atomic to molecular transition and can return detailed diagnostic information. We first carried out a parameter space study via a suite of 2D simulations, which track the fate of an initially stable clump embedded within one of the clouds. We have then extended these calculations to 3D, including introduction of initial turbulence into the clouds and magnetically-regulated sub-grid models for star formation. Different magnetic field strengths and orientations are considered, as is the role of cloud collisions at various velocities and impact parameters. We examine the effects of including ambipolar diffusion. Between isolated and colliding cases, the density and kinematic structure are visualized and characterized, in addition to magnetic field configuration. We discuss observational diagnostics of cloud collisions, focusing on 13CO(J=2-1), 13CO(J=3-2), and 12CO(J=8-7) integrated intensity maps and spectra, which we synthesize from our simulation outputs. We find the ratio of J=8-7 to lower-J emission to be a powerful diagnostic probe of GMC collisions. We also analyze magnetic field orientation relative to filamentary structure, comparing to observations within the Galaxy. Finally, we examine the level of star formation activity that is induced by collisions and distinguishing kinematic properties of the stars that form by this mechanism.

  8. Molecular Clouds in the North American and Pelican Nebulae: Structures

    NASA Astrophysics Data System (ADS)

    Zhang, Shaobo; Xu, Ye; Yang, Ji

    2014-03-01

    We present observations of a 4.25 deg2 area toward the North American and Pelican Nebulae in the J = 1-0 transitions of 12CO, 13CO, and C18O. Three molecules show different emission areas with their own distinct structures. These different density tracers reveal several dense clouds with a surface density of over 500 M ⊙ pc-2 and a mean H2 column density of 5.8, 3.4, and 11.9 × 1021 cm-2 for 12CO, 13CO, and C18O, respectively. We obtain a total mass of 5.4 × 104 M ⊙ (12CO), 2.0 × 104 M ⊙ (13CO), and 6.1 × 103 M ⊙ (C18O) in the complex. The distribution of excitation temperature shows two phases of gas: cold gas (~10 K) spreads across the whole cloud; warm gas (>20 K) outlines the edge of the cloud heated by the W80 H II region. The kinetic structure of the cloud indicates an expanding shell surrounding the ionized gas produced by the H II region. There are six discernible regions in the cloud: the Gulf of Mexico, Caribbean Islands and Sea, and Pelican's Beak, Hat, and Neck. The areas of 13CO emission range within 2-10 pc2 with mass of (1-5) × 103 M ⊙ and line width of a few km s-1. The different line properties and signs of star-forming activity indicate they are in different evolutionary stages. Four filamentary structures with complicated velocity features are detected along the dark lane in LDN 935. Furthermore, a total of 611 molecular clumps within the 13CO tracing cloud are identified using the ClumpFind algorithm. The properties of the clumps suggest that most of the clumps are gravitationally bound and at an early stage of evolution with cold and dense molecular gas.

  9. Distances of Four High-Galactic Latitude Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Montgomery, Sharon L.; Rombach, C. E.; Birney, C. Y.; Burrows, D. N.

    2006-12-01

    The Sun is embedded within a large, irregularly-shaped region of plasma called the Local Bubble that formed when relatively nearby stars exploded as supernovae several million years ago. Lallement et al. (2003) have traced its convoluted boundary by using the equivalent widths of NaD lines in 1005 distant stars. To avoid directional bias, however, they intentionally avoided targeting stars that shared lines-of-sight with clouds visible on IR, X-ray, or radio maps. Thus, to complement their study, we have determined the distances and radial velocities of four molecular clouds that were also classified as soft X-ray shadows by Snowden et al. (2000). We targeted these objects since X-ray shadows are expected to lie at or near the bubble’s boundary. Thus, their distances and radial velocities provide information about the bubble’s edge. In addition, a small fraction of the clouds that are also shadows may prove to lie well within the bubble. The number and nature of such interlopers places constraints on the bubble’s history. The clouds' distances and radial velocities were determined using moderately high-resolution spectra of 88 bright, early-type stars lying near the clouds. The spectra were obtained using the Sandiford Cassegrain-Echelle spectrograph of the 2.1m Otto Struve Telescope. We then searched the stars’ spectra for interstellar Na-D lines and used their known distances to bracket the distances to the clouds. We use the derived distances to calculate the density and pressure of the Local Bubble in the direction of these clouds.

  10. Cold Water Vapor in the Barnard 5 Molecular Cloud

    NASA Technical Reports Server (NTRS)

    Wirstrom, E. S.; Charnley, S. B.; Persson, C. M.; Buckle, J. V.; Cordiner, M. A.; Takakuwa, S.

    2014-01-01

    After more than 30 yr of investigations, the nature of gas-grain interactions at low temperatures remains an unresolved issue in astrochemistry. Water ice is the dominant ice found in cold molecular clouds; however, there is only one region where cold ((is) approximately 10 K) water vapor has been detected-L1544. This study aims to shed light on ice desorption mechanisms under cold cloud conditions by expanding the sample. The clumpy distribution of methanol in dark clouds testifies to transient desorption processes at work-likely to also disrupt water ice mantles. Therefore, the Herschel HIFI instrument was used to search for cold water in a small sample of prominent methanol emission peaks. We report detections of the ground-state transition of o-H2O (J = 110-101) at 556.9360 GHz toward two positions in the cold molecular cloud, Barnard 5. The relative abundances of methanol and water gas support a desorption mechanism which disrupts the outer ice mantle layers, rather than causing complete mantle removal.

  11. COLD WATER VAPOR IN THE BARNARD 5 MOLECULAR CLOUD

    SciTech Connect

    Wirström, E. S.; Persson, C. M.; Charnley, S. B.; Cordiner, M. A.; Buckle, J. V.; Takakuwa, S.

    2014-06-20

    After more than 30 yr of investigations, the nature of gas-grain interactions at low temperatures remains an unresolved issue in astrochemistry. Water ice is the dominant ice found in cold molecular clouds; however, there is only one region where cold (∼10 K) water vapor has been detected—L1544. This study aims to shed light on ice desorption mechanisms under cold cloud conditions by expanding the sample. The clumpy distribution of methanol in dark clouds testifies to transient desorption processes at work—likely to also disrupt water ice mantles. Therefore, the Herschel HIFI instrument was used to search for cold water in a small sample of prominent methanol emission peaks. We report detections of the ground-state transition of o-H{sub 2}O (J = 1{sub 10}-1{sub 01}) at 556.9360 GHz toward two positions in the cold molecular cloud, Barnard 5. The relative abundances of methanol and water gas support a desorption mechanism which disrupts the outer ice mantle layers, rather than causing complete mantle removal.

  12. H2 distribution during the formation of multiphase molecular clouds

    NASA Astrophysics Data System (ADS)

    Valdivia, Valeska; Hennebelle, Patrick; Gérin, Maryvonne; Lesaffre, Pierre

    2016-03-01

    Context. H2 is the simplest and the most abundant molecule in the interstellar medium (ISM), and its formation precedes the formation of other molecules. Aims: Understanding the dynamical influence of the environment and the interplay between the thermal processes related to the formation and destruction of H2 and the structure of the cloud is mandatory to understand correctly the observations of H2. Methods: We performed high-resolution magnetohydrodynamical colliding-flow simulations with the adaptive mesh refinement code RAMSES in which the physics of H2 has been included. We compared the simulation results with various observations of the H2 molecule, including the column densities of excited rotational levels. Results: As a result of a combination of thermal pressure, ram pressure, and gravity, the clouds produced at the converging point of HI streams are highly inhomogeneous. H2 molecules quickly form in relatively dense clumps and spread into the diffuse interclump gas. This in particular leads to the existence of significant abundances of H2 in the diffuse and warm gas that lies in between clumps. Simulations and observations show similar trends, especially for the HI-to-H2 transition (H2 fraction vs. total hydrogen column density). Moreover, the abundances of excited rotational levels, calculated at equilibrium in the simulations, turn out to be very similar to the observed abundances inferred from FUSE results. This is a direct consequence of the presence of the H2 enriched diffuse and warm gas. Conclusions: Our simulations, which self-consistently form molecular clouds out of the diffuse atomic gas, show that H2 rapidly forms in the dense clumps and, due to the complex structure of molecular clouds, quickly spreads at lower densities. Consequently, a significant fraction of warm H2 exists in the low-density gas. This warm H2 leads to column densities of excited rotational levels close to the observed ones and probably reveals the complex intermix between

  13. IRAS observations of giant molecular clouds in the Milky Way

    NASA Technical Reports Server (NTRS)

    Mozurkewich, D.; Thronson, H. A., Jr.

    1986-01-01

    The IRAS data base has been used to study infrared radiation from molecular clouds in our galaxy. The sample of clouds was restricted to those with reliably determined molecular masses from large area, multi-isotope CO maps. They were normalized to X(CO-13)= 2x10 to the -6. Flux densities at 60 microns and 100 microns were determined by integrating the flux density within rectangles drawn on the sky flux plates after subtracting a suitable background. The rectangles were chosen to be coextensive with the areas mapped in CO. Color corrections were made and luminosites calculated by assuming the optical depths were proportional to frequency. The flux densities were converted to dust masses with a value for 4a rho/3Q = .04 g/cm at 100 microns.

  14. The Structure and Evolution of Self-Gravitating Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Holliman, John Herbert, II

    1995-01-01

    We present a theoretical formalism to evaluate the structure of molecular clouds and to determine precollapse conditions in star-forming regions. Models consist of pressure-bounded, self-gravitating spheres of a single -fluid ideal gas. We treat the case without rotation. The analysis is generalized to consider states in hydrostatic equilibrium maintained by multiple pressure components. Individual pressures vary with density as P_i(r) ~ rho^{gamma {rm p},i}(r), where gamma_{rm p},i is the polytropic index. Evolution depends additionally on whether conduction occurs on a dynamical time scale and on the adiabatic index gammai of each component, which is modified to account for the effects of any thermal coupling to the environment of the cloud. Special attention is given to properly representing the major contributors to dynamical support in molecular clouds: the pressures due to static magnetic fields, Alfven waves, and thermal motions. Straightforward adjustments to the model allow us to treat the intrinsically anisotropic support provided by the static fields. We derive structure equations, as well as perturbation equations for performing a linear stability analysis. The analysis provides insight on the nature of dynamical motions due to collapse from an equilibrium state and estimates the mass of condensed objects that form in such a process. After presenting a set of general results, we describe models of star-forming regions that include the major pressure components. We parameterize the extent of ambipolar diffusion. The analysis contributes to the physical understanding of several key results from observations of these regions. Commonly observed quantities are explicitly cross-referenced with model results. We theoretically determine density and linewidth profiles on scales ranging from that of molecular cloud cores to that of giant molecular clouds (GMCs). The model offers an explanation of the mean pressures in GMCs, which are observed to be high relative

  15. The Draco Nebula, a Molecular Cloud Associated with a High Velocity Cloud?

    NASA Technical Reports Server (NTRS)

    Mebold, U.; Kalberla, P. W. M.

    1984-01-01

    Extended and very faint bright nebulae are found in high galactic latitudes at the Palomar Observatory Sky Survey. Such a nebula, located in the constellation Draco and called Draco Nebula or Dracula, was found to be in detailed positional coincidence with a 21 cm emission line feature. Estimates of the minimum visual extinction from star counts ON and OFF Dracula and an estimated visual surface brightness indicate that Dracula fits the relation SBV = 24.2 - 2.5 log AV for dust clouds located above the galactic plane and reflecting the integrated starlight of the galactic disk. Hence Dracula is probably a reflection nebula. Indicators of molecular hydrogen in Dracula, molecules such as CO, were searched for by using a 2.5-m mm-telescope. Molecular hydrogen column densities were estimated. The dynamics of CO clumps was studied. Dracula has a close positional and possibly even astrophysical relationship to the high velocity cloud phenomenon.

  16. Molecular cloud-scale star formation in NGC 300

    SciTech Connect

    Faesi, Christopher M.; Lada, Charles J.; Forbrich, Jan; Menten, Karl M.; Bouy, Hervé

    2014-07-01

    We present the results of a galaxy-wide study of molecular gas and star formation in a sample of 76 H II regions in the nearby spiral galaxy NGC 300. We have measured the molecular gas at 250 pc scales using pointed CO(J = 2-1) observations with the Atacama Pathfinder Experiment telescope. We detect CO in 42 of our targets, deriving molecular gas masses ranging from our sensitivity limit of ∼10{sup 5} M {sub ☉} to 7 × 10{sup 5} M {sub ☉}. We find a clear decline in the CO detection rate with galactocentric distance, which we attribute primarily to the decreasing radial metallicity gradient in NGC 300. We combine Galaxy Evolution Explorer far-ultraviolet, Spitzer 24 μm, and Hα narrowband imaging to measure the star formation activity in our sample. We have developed a new direct modeling approach for computing star formation rates (SFRs) that utilizes these data and population synthesis models to derive the masses and ages of the young stellar clusters associated with each of our H II region targets. We find a characteristic gas depletion time of 230 Myr at 250 pc scales in NGC 300, more similar to the results obtained for Milky Way giant molecular clouds than the longer (>2 Gyr) global depletion times derived for entire galaxies and kiloparsec-sized regions within them. This difference is partially due to the fact that our study accounts for only the gas and stars within the youngest star-forming regions. We also note a large scatter in the NGC 300 SFR-molecular gas mass scaling relation that is furthermore consistent with the Milky Way cloud results. This scatter likely represents real differences in giant molecular cloud physical properties such as the dense gas fraction.

  17. Enhanced OH in C-Type Shock Waves in Molecular Clouds.

    PubMed

    Wardle

    1999-11-10

    Cosmic-ray and X-ray ionizations in molecular gas produce a weak far-ultraviolet flux through the radiative decay of H2 molecules that have been excited by collisions with energetic electrons (the Prasad-Tarafdar mechanism). I consider the effect of this dissociating flux on the oxygen chemistry in C-type shocks. Typically, a few percent of the water molecules produced within the shock front are dissociated before the gas has cooled to 50 K. The resulting column density of warm OH rises from 1015 to 1016 cm-2 as the ionization rate is increased from 10-17 s-1 (typical of dark clouds) to 10-15 s-1 (adjacent to supernova remnants). These column densities produce substantial emission in the far-infrared rotational transitions of OH and are consistent with the OH/H2O ratios inferred from Infrared Space Observatory observations of emission from molecular shocks. For high ionization rates, the column of warm OH is sufficient to explain the OH(1720 MHz) masers that occur where molecular clouds are being shocked by supernova remnants. The predicted abundance of OH throughout the shock front will enable C-type shocks to be examined with high spectral resolution through radio observations of the four hyperfine ground-state transitions of OH at 18 cm and heterodyne measurements of emission in the far-infrared (e.g., from the Stratospheric Observatory for Infrared Astronomy).

  18. The system of molecular clouds in the Gould Belt

    NASA Astrophysics Data System (ADS)

    Bobylev, V. V.

    2016-08-01

    Based on high-latitude molecular clouds with highly accurate distance estimates taken from the literature, we have redetermined the parameters of their spatial orientation. This systemcan be approximated by a 350 × 235 × 140 pc ellipsoid inclined by the angle i = 17° ± 2° to the Galactic plane with the longitude of the ascending node l Ω = 337° ± 1°. Based on the radial velocities of the clouds, we have found their group velocity relative to the Sun to be ( u 0, v 0, w 0) = (10.6, 18.2, 6.8) ± (0.9, 1.7, 1.5) km s-1. The trajectory of the center of the molecular cloud system in the past in a time interval of ~60 Myr has been constructed. Using data on masers associated with low-mass protostars, we have calculated the space velocities of the molecular complexes in Orion, Taurus, Perseus, and Ophiuchus. Their motion in the past is shown to be not random.

  19. SEQUENTIAL STAR FORMATION IN THE Sh 254-258 MOLECULAR CLOUD: HEINRICH HERTZ TELESCOPE MAPS OF CO J = 2-1 AND 3-2 EMISSION

    SciTech Connect

    Bieging, John H.; Peters, William L.; Schlottman, Keith; Kulesa, Craig; Vila Vilaro, Baltasar

    2009-09-15

    The molecular cloud associated with the Sh 254-258 group of five small H II regions appears to be forming a (late)-OB association. We have mapped the associated molecular cloud in the J = 2-1 line of the CO and {sup 13}CO molecules over 0.{sup 0}75 x 1{sup 0}, and the CO J = 3-2 line toward the two main peaks, with the University of Arizona Heinrich Hertz Submillimeter Telescope. The data are analyzed with a statistical equilibrium code to estimate physical properties of the molecular gas. We compare the molecular cloud morphology with images at optical, IR, and radio wavelengths. From this analysis, we propose a scenario for sequential formation of the stars exciting the H II regions, triggered by the compression of the molecular gas as a consequence of the expansion of the adjacent H II regions.

  20. Sequential Star Formation in the Sh 254-258 Molecular Cloud: Heinrich Hertz Telescope Maps of CO J = 2-1 and 3-2 Emission

    NASA Astrophysics Data System (ADS)

    Bieging, John H.; Peters, William L.; Vila Vilaro, Baltasar; Schlottman, Keith; Kulesa, Craig

    2009-09-01

    The molecular cloud associated with the Sh 254-258 group of five small H II regions appears to be forming a (late)-OB association. We have mapped the associated molecular cloud in the J = 2-1 line of the CO and 13CO molecules over 0fdg75 × 1°, and the CO J = 3-2 line toward the two main peaks, with the University of Arizona Heinrich Hertz Submillimeter Telescope. The data are analyzed with a statistical equilibrium code to estimate physical properties of the molecular gas. We compare the molecular cloud morphology with images at optical, IR, and radio wavelengths. From this analysis, we propose a scenario for sequential formation of the stars exciting the H II regions, triggered by the compression of the molecular gas as a consequence of the expansion of the adjacent H II regions.

  1. A hierarchical method for molecular docking using cloud computing.

    PubMed

    Kang, Ling; Guo, Quan; Wang, Xicheng

    2012-11-01

    Discovering small molecules that interact with protein targets will be a key part of future drug discovery efforts. Molecular docking of drug-like molecules is likely to be valuable in this field; however, the great number of such molecules makes the potential size of this task enormous. In this paper, a method to screen small molecular databases using cloud computing is proposed. This method is called the hierarchical method for molecular docking and can be completed in a relatively short period of time. In this method, the optimization of molecular docking is divided into two subproblems based on the different effects on the protein-ligand interaction energy. An adaptive genetic algorithm is developed to solve the optimization problem and a new docking program (FlexGAsDock) based on the hierarchical docking method has been developed. The implementation of docking on a cloud computing platform is then discussed. The docking results show that this method can be conveniently used for the efficient molecular design of drugs.

  2. A hierarchical method for molecular docking using cloud computing.

    PubMed

    Kang, Ling; Guo, Quan; Wang, Xicheng

    2012-11-01

    Discovering small molecules that interact with protein targets will be a key part of future drug discovery efforts. Molecular docking of drug-like molecules is likely to be valuable in this field; however, the great number of such molecules makes the potential size of this task enormous. In this paper, a method to screen small molecular databases using cloud computing is proposed. This method is called the hierarchical method for molecular docking and can be completed in a relatively short period of time. In this method, the optimization of molecular docking is divided into two subproblems based on the different effects on the protein-ligand interaction energy. An adaptive genetic algorithm is developed to solve the optimization problem and a new docking program (FlexGAsDock) based on the hierarchical docking method has been developed. The implementation of docking on a cloud computing platform is then discussed. The docking results show that this method can be conveniently used for the efficient molecular design of drugs. PMID:23017886

  3. Global Studies of Molecular Clouds in the Galaxy, the Magellanic Cloud and M31

    NASA Technical Reports Server (NTRS)

    Thaddeus, Patrick

    1998-01-01

    Over the past five years we have used our extensive CO surveys of the Galaxy and M31 in conjunction with spacecraft observations to address central problems in galactic structure and the astrophysics of molecular clouds. These problems included the nature of the molecular ring and its relation to the spiral arms and central bar, the cosmic ray distribution, the origin of the diffuse X-ray background, the distribution and properties of x-ray sources and supernova remnants, and the Galactic stellar mass distribution. For many of these problems, the nearby spiral M31 provided an important complementary perspective.

  4. Anisotropy Lengthens the Decay Time of Turbulence in Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Hansen, Charles E.; McKee, Christopher F.; Klein, Richard I.

    2011-09-01

    The decay of isothermal turbulence with velocity anisotropy is investigated using computational simulations and synthetic observations. We decompose the turbulence into isotropic and anisotropic components with total velocity dispersions σiso and σani, respectively. We find that the decay rate of the turbulence depends on the crossing time of the isotropic component only. A cloud of size L with significant anisotropy in its turbulence has a dissipation time, t diss = L/(2σiso). This translates into turbulent energy decay rates on the cloud scale that can be much lower for anisotropic turbulence than for isotropic turbulence. To help future observations determine whether observed molecular clouds have the level of anisotropy required to maintain the observed level of turbulence over their lifetimes, we performed a principal component analysis on our simulated clouds. Even with projection effects washing out the anisotropic signal, there is a measurable difference in the axis-constrained principal component analysis performed in directions parallel and perpendicular to the direction of maximum velocity dispersion. When this relative difference, ψ, is 0.1, there is enough anisotropy for the dissipation time to triple the expected isotropic value. We provide a fit for converting ψ into an estimate for the dissipation time, t diss.

  5. ANISOTROPY LENGTHENS THE DECAY TIME OF TURBULENCE IN MOLECULAR CLOUDS

    SciTech Connect

    Hansen, Charles E.; McKee, Christopher F.; Klein, Richard I.

    2011-09-01

    The decay of isothermal turbulence with velocity anisotropy is investigated using computational simulations and synthetic observations. We decompose the turbulence into isotropic and anisotropic components with total velocity dispersions {sigma}{sub iso} and {sigma}{sub ani}, respectively. We find that the decay rate of the turbulence depends on the crossing time of the isotropic component only. A cloud of size L with significant anisotropy in its turbulence has a dissipation time, t{sub diss} = L/(2{sigma}{sub iso}). This translates into turbulent energy decay rates on the cloud scale that can be much lower for anisotropic turbulence than for isotropic turbulence. To help future observations determine whether observed molecular clouds have the level of anisotropy required to maintain the observed level of turbulence over their lifetimes, we performed a principal component analysis on our simulated clouds. Even with projection effects washing out the anisotropic signal, there is a measurable difference in the axis-constrained principal component analysis performed in directions parallel and perpendicular to the direction of maximum velocity dispersion. When this relative difference, {psi}, is 0.1, there is enough anisotropy for the dissipation time to triple the expected isotropic value. We provide a fit for converting {psi} into an estimate for the dissipation time, t{sub diss}.

  6. Infrared reflection nebulae in Orion Molecular Cloud 2

    NASA Technical Reports Server (NTRS)

    Pendleton, Yvonne; Werner, M. W.; Capps, R.; Lester, D.

    1986-01-01

    New observations of Orion Molecular Cloud 2 have been made from 1 to 100 microns using the NASA Infrared Telescope Facility and the Kuiper Airborne Observatory. An extensive program of polarimetry, photometry, and spectrophotometry has shown that the extended emission regions associated with two of the previously known near-infrared sources, IRS 1 and IRS 4, are infrared reflection nebulae, and that the compact sources IRS 1 and IRS 4 are the main luminosity sources in the cloud. The constraints from the far-infrared observations and an analysis of the scattered light from the IRS 1 nebula show that OMC-2/IRS 1 can be characterized by L of 500 solar luminosities or less and T of roughly 1000 K. The near-infrared albedo of the grains in the IRS 1 nebula is greater than 0.08.

  7. Infrared reflection nebulae in Orion molecular cloud 2

    NASA Technical Reports Server (NTRS)

    Pendleton, Y.; Werner, M. W.; Capps, R.; Lester, D.

    1986-01-01

    New obervations of Orion Molecular Cloud-2 have been made from 1-100 microns using the NASA Infrared Telescope Facility and the Kuiper Airborne Observatory. An extensive program of polarimetry, photometry and spectrophotometry has shown that the extended emission regions associated with two of the previously known near infrared sources, IRS1 and IRS4, are infrared reflection nebulae, and that the compact sources IRS1 and IRS4 are the main luminosity sources in the cloud. The constraints from the far infrared observations and an analysis of the scattered light from the IRS1 nebula show that OMC-2/IRS1 can be characterized by L less than or equal to 500 Solar luminosities and T approx. 1000 K. The near infrared (1-5) micron albedo of the grains in the IRS1 nebula is greater than 0.08.

  8. THE FORMATION OF FILAMENTARY BUNDLES IN TURBULENT MOLECULAR CLOUDS

    SciTech Connect

    Moeckel, Nickolas; Burkert, Andreas E-mail: burkert@usm.uni-muenchen.de

    2015-07-01

    The classical picture of a star-forming filament is a near-equilibrium structure with its collapse dependent on its gravitational criticality. Recent observations have complicated this picture, revealing filaments to be a mess of apparently interacting subfilaments with transsonic internal velocity dispersions and mildly supersonic intra-subfilament dispersions. How structures like this form is unresolved. Here, we study the velocity structure of filamentary regions in a simulation of a turbulent molecular cloud. We present two main findings. First, the observed complex velocity features in filaments arise naturally in self-gravitating hydrodynamic simulations of turbulent clouds without the need for magnetic or other effects. Second, a region that is filamentary only in projection and is in fact made of spatially distinct features can display these same velocity characteristics. The fact that these disjoint structures can masquerade as coherent filaments in both projection and velocity diagnostics highlights the need to continue developing sophisticated filamentary analysis techniques for star formation observations.

  9. Molecular clouds in the North American and Pelican Nebulae: structures

    SciTech Connect

    Zhang, Shaobo; Xu, Ye; Yang, Ji

    2014-03-01

    We present observations of a 4.25 deg{sup 2} area toward the North American and Pelican Nebulae in the J = 1-0 transitions of {sup 12}CO, {sup 13}CO, and C{sup 18}O. Three molecules show different emission areas with their own distinct structures. These different density tracers reveal several dense clouds with a surface density of over 500 M {sub ☉} pc{sup –2} and a mean H{sub 2} column density of 5.8, 3.4, and 11.9 × 10{sup 21} cm{sup –2} for {sup 12}CO, {sup 13}CO, and C{sup 18}O, respectively. We obtain a total mass of 5.4 × 10{sup 4} M {sub ☉} ({sup 12}CO), 2.0 × 10{sup 4} M {sub ☉} ({sup 13}CO), and 6.1 × 10{sup 3} M {sub ☉} (C{sup 18}O) in the complex. The distribution of excitation temperature shows two phases of gas: cold gas (∼10 K) spreads across the whole cloud; warm gas (>20 K) outlines the edge of the cloud heated by the W80 H II region. The kinetic structure of the cloud indicates an expanding shell surrounding the ionized gas produced by the H II region. There are six discernible regions in the cloud: the Gulf of Mexico, Caribbean Islands and Sea, and Pelican's Beak, Hat, and Neck. The areas of {sup 13}CO emission range within 2-10 pc{sup 2} with mass of (1-5) × 10{sup 3} M {sub ☉} and line width of a few km s{sup –1}. The different line properties and signs of star-forming activity indicate they are in different evolutionary stages. Four filamentary structures with complicated velocity features are detected along the dark lane in LDN 935. Furthermore, a total of 611 molecular clumps within the {sup 13}CO tracing cloud are identified using the ClumpFind algorithm. The properties of the clumps suggest that most of the clumps are gravitationally bound and at an early stage of evolution with cold and dense molecular gas.

  10. GASEOUS CO ABUNDANCE-AN EVOLUTIONARY TRACER FOR MOLECULAR CLOUDS

    SciTech Connect

    Liu Tie; Wu Yuefang; Zhang Huawei E-mail: ywu@pku.edu.cn

    2013-09-20

    Planck cold clumps are among the most promising objects to investigate the initial conditions of the evolution of molecular clouds. In this work, by combing the dust emission data from the survey of the Planck satellite with the molecular data of {sup 12}CO/{sup 13}CO/C{sup 18}O (1-0) lines from observations with the Purple Mountain Observatory 13.7 m telescope, we investigate the CO abundance, CO depletion, and CO-to-H{sub 2} conversion factor of 674 clumps in the early cold cores sample. The median and mean values of the CO abundance are 0.89 Multiplication-Sign 10{sup -4} and 1.28 Multiplication-Sign 10{sup -4}, respectively. The mean and median of CO depletion factor are 1.7 and 0.9, respectively. The median value of X{sub CO-to-H{sub 2}} for the whole sample is 2.8 Multiplication-Sign 10{sup 20} cm{sup -2} K{sup -1} km{sup -1} s. The CO abundance, CO depletion factor, and CO-to-H{sub 2} conversion factor are strongly (anti-)correlated to other physical parameters (e.g., dust temperature, dust emissivity spectral index, column density, volume density, and luminosity-to-mass ratio). To conclude, the gaseous CO abundance can be used as an evolutionary tracer for molecular clouds.

  11. A source model for the L134N molecular cloud

    NASA Technical Reports Server (NTRS)

    Swade, Daryl A.; Schloerb, F. P.

    1992-01-01

    The dark molecular cloud L134N is observed at millimeter wavelengths in the CS (J = 3-2), OCS (J = 7-6), and HDO (1 sub 11-1 sub 10) transitions. The CS (J = 3-2) transition was observed at four positions within the cloud, while the other two transitions were observed at one position each. Fractional abundances in the LTE approximation are calculated for each emission line detected. L134N appears to have a high-density core characterized by NH3, C3H2, and H(C-13)O(+) emission maps. A lower density envelope characterized by C(0-18), CS (J = 2-1), and SO emission surrounds the core. There appears to be a gas-phase oxygen abundance gradient in L134N with atomic oxygen depleted in the high-density core. Observed molecular distributions within L134N can be explained by a model in which chemical and physical processes in icy-dust-grain mantles influence the gas-phase molecular abundances.

  12. Striations in molecular clouds: streamers or MHD waves?

    NASA Astrophysics Data System (ADS)

    Tritsis, Aris; Tassis, Konstantinos

    2016-11-01

    Dust continuum and molecular observations of the low column density parts of molecular clouds have revealed the presence of elongated structures which appear to be well aligned with the magnetic field. These so-called striations are usually assumed to be streams that flow towards or away from denser regions. We perform ideal magnetohydrodynamic (MHD) simulations adopting four models that could account for the formation of such structures. In the first two models striations are created by velocity gradients between ambient, parallel streamlines along magnetic field lines. In the third model striations are formed as a result of a Kelvin-Helmholtz instability perpendicular to field lines. Finally, in the fourth model striations are formed from the non-linear coupling of MHD waves due to density inhomogeneities. We assess the validity of each scenario by comparing the results from our simulations with previous observational studies and results obtained from the analysis of CO (J = 1-0) observations from the Taurus molecular cloud. We find that the first three models cannot reproduce the density contrast and the properties of the spatial power spectrum of a perpendicular cut to the long axes of striations. We conclude that the non-linear coupling of MHD waves is the most probable formation mechanism of striations.

  13. A source model for the L134N molecular cloud

    NASA Astrophysics Data System (ADS)

    Swade, Daryl A.; Schloerb, F. P.

    1992-06-01

    The dark molecular cloud L134N is observed at millimeter wavelengths in the CS (J = 3-2), OCS (J = 7-6), and HDO (111-1 sub 10) transitions. The CS (J = 3-2) transition was observed at four positions within the cloud, while the other two transitions were observed at one position each. Fractional abundances in the LTE approximation are calculated for each emission line detected. L134N appears to have a high-density core characterized by NH3, C3H2, and H(C-13)O(+) emission maps. A lower density envelope characterized by C(0-18), CS (J = 2-1), and SO emission surrounds the core. There appears to be a gas-phase oxygen abundance gradient in L134N with atomic oxygen depleted in the high-density core. Observed molecular distributions within L134N can be explained by a model in which chemical and physical processes in icy-dust-grain mantles influence the gas-phase molecular abundances.

  14. Global Studies of Molecular Clouds in the Galaxy, The Magellanic Clouds, and M31

    NASA Technical Reports Server (NTRS)

    Thaddeus, Patrick

    1999-01-01

    Over the course of this grant we used various spacecraft surveys of the Galaxy and M31 in conjunction with our extensive CO spectral line surveys to address central problems in galactic structure and the astrophysics of molecular clouds. These problems included the nature of the molecular ring and its relation to the spiral arms and central bar, the cosmic ray distribution, the origin of the diffuse X-ray background, the distribution and properties of x-ray sources and supernova remnants, and the Galactic stellar mass distribution. For many of these problems, the nearby spiral M31 provided an important complementary perspective. Our CO surveys of GMCs (Galactic Molecular Clouds) were crucial for interpreting Galactic continuum surveys from satellites such as GRO (Gamma Ray Observatory), ROSAT (Roentgen Satellite), IRAS (Infrared Astronomy Satellite), and COBE (Cosmic Background Explorer Satellite) because they provided the missing dimension of velocity or kinematic distance. GMCs are a well-defined and widespread population of objects whose velocities we could readily measure throughout the Galaxy. Through various emission and absorption mechanisms involving their gas, dust, or associated Population I objects, GMCs modulate the galactic emission in virtually every major wavelength band. Furthermore, the visibility. of GMCs at so many wavelengths provided various methods of resolving the kinematic distance ambiguity for these objects in the inner Galaxy. Summaries of our accomplishments in each of the major wavelength bands discussed in our original proposal are given

  15. Nonequilibrium chemistry in shocked molecular clouds. [interstellar gases

    NASA Technical Reports Server (NTRS)

    Iglesias, E. R.; Silk, J.

    1978-01-01

    The gas-phase chemistry is studied behind a 10-km/s shock propagating into a dense molecular cloud. The principal conclusions are that: the concentrations of certain molecules (CO, NH3, HCN, N2) are unperturbed by the shock; other molecules (H2CO, CN, HCO(+)) are greatly decreased in abundance; and substantial amounts of H2O, HCO, and CH4 are produced. Approximately 1 million yr (independent of the density) must elapse after shock passage before chemical equilibrium is attained.

  16. Observing simulations: molecular clouds and their journey in the galaxy

    NASA Astrophysics Data System (ADS)

    Duarte-Cabral, A.; Dobbs, C. L.

    2016-05-01

    In order to have a global picture of the cycle of matter in galaxies, we need to understand the interplay of large-scale galactic phenomena with the formation of giant molecular clouds (GMCs) and, ultimately, their subsequent star formation (SF). In this work, we study the population of GMCs within a smoothed particle hydrodynamics (SPH) simulation of a spiral galaxy, and investigate the link between the GMC properties and position with respect to spiral arms, both directly from the simulation (with the 3D densities of H2 and CO) and from an observer's perspective (with CO emission in PPV space).

  17. FilFinder: Filamentary structure in molecular clouds

    NASA Astrophysics Data System (ADS)

    Koch, Eric W.; Rosolowsky, Erik W.

    2016-08-01

    FilFinder extracts and analyzes filamentary structure in molecular clouds. In particular, it is capable of uniformly extracting structure over a large dynamical range in intensity. It returns the main filament properties: local amplitude and background, width, length, orientation and curvature. FilFinder offers additional tools to, for example, create a filament-only image based on the properties of the radial fits. The resulting mask and skeletons may be saved in FITS format, and property tables may be saved as a CSV, FITS or LaTeX table.

  18. Supernova Driving. II. Compressive Ratio in Molecular-cloud Turbulence

    NASA Astrophysics Data System (ADS)

    Pan, Liubin; Padoan, Paolo; Haugbølle, Troels; Nordlund, Åke

    2016-07-01

    The compressibility of molecular cloud (MC) turbulence plays a crucial role in star formation models, because it controls the amplitude and distribution of density fluctuations. The relation between the compressive ratio (the ratio of powers in compressive and solenoidal motions) and the statistics of turbulence has been previously studied systematically only in idealized simulations with random external forces. In this work, we analyze a simulation of large-scale turbulence (250 pc) driven by supernova (SN) explosions that has been shown to yield realistic MC properties. We demonstrate that SN driving results in MC turbulence with a broad lognormal distribution of the compressive ratio, with a mean value ≈0.3, lower than the equilibrium value of ≈0.5 found in the inertial range of isothermal simulations with random solenoidal driving. We also find that the compressibility of the turbulence is not noticeably affected by gravity, nor are the mean cloud radial (expansion or contraction) and solid-body rotation velocities. Furthermore, the clouds follow a general relation between the rms density and the rms Mach number similar to that of supersonic isothermal turbulence, though with a large scatter, and their average gas density probability density function is described well by a lognormal distribution, with the addition of a high-density power-law tail when self-gravity is included.

  19. Molecular cloud formation in high-shear, magnetized colliding flows

    NASA Astrophysics Data System (ADS)

    Fogerty, E.; Frank, A.; Heitsch, F.; Carroll-Nellenback, J.; Haig, C.; Adams, M.

    2016-08-01

    The colliding flows (CF) model is a well-supported mechanism for generating molecular clouds. However, to-date most CF simulations have focused on the formation of clouds in the normal-shock layer between head-on colliding flows. We performed simulations of magnetized colliding flows that instead meet at an oblique-shock layer. Oblique shocks generate shear in the post-shock environment, and this shear creates inhospitable environments for star formation. As the degree of shear increases (i.e. the obliquity of the shock increases), we find that it takes longer for sink particles to form, they form in lower numbers, and they tend to be less massive. With regard to magnetic fields, we find that even a weak field stalls gravitational collapse within forming clouds. Additionally, an initially oblique collision interface tends to reorient over time in the presence of a magnetic field, so that it becomes normal to the oncoming flows. This was demonstrated by our most oblique shock interface, which became fully normal by the end of the simulation.

  20. Molecular Anions in Protostars, Prestellar Cores and Dark Clouds

    NASA Technical Reports Server (NTRS)

    Cordiner, Martin; Charnley, Steven; Buckle, Jane; Wash, Catherine; Millar, Tom

    2011-01-01

    From our recent survey work using the Green Bank Telescope, microwave emission lines from the hydrocarbon anion C6H(-) and its parent neutral C6H have been detected in six new sources. Using HC3N = 10(exp -9) emission maps, we targeted the most carbon-chain-rich sources for our anion survey, which included the low-mass Class 0 protostar L1251A-IRS3, the prestellar cores L1389-SMM1 and L1512, and the interstellar clouds Ll172A, TMC-1C and L1495B. Derived [C6H(-)]/[C6H] anion-to-neutral ratios are approximately 1-10. The greatest C6H(-) column densities are found in the quiescent clouds TMC-1C and L1495B, but the anion-to-neutral ratios are greatest in the prestellar cores and protostars. These results are interpreted in terms of the physical and chemical properties of the sources, and the implications for molecular cloud chemistry are discussed.

  1. Molecular evidence for species-level distinctions in clouded leopards.

    PubMed

    Buckley-Beason, Valerie A; Johnson, Warren E; Nash, Willliam G; Stanyon, Roscoe; Menninger, Joan C; Driscoll, Carlos A; Howard, JoGayle; Bush, Mitch; Page, John E; Roelke, Melody E; Stone, Gary; Martelli, Paolo P; Wen, Ci; Ling, Lin; Duraisingam, Ratna K; Lam, Phan V; O'Brien, Stephen J

    2006-12-01

    Among the 37 living species of Felidae, the clouded leopard (Neofelis nebulosa) is generally classified as a monotypic genus basal to the Panthera lineage of great cats. This secretive, mid-sized (16-23 kg) carnivore, now severely endangered, is traditionally subdivided into four southeast Asian subspecies (Figure 1A). We used molecular genetic methods to re-evaluate subspecies partitions and to quantify patterns of population genetic variation among 109 clouded leopards of known geographic origin (Figure 1A, Tables S1 ans S2 in the Supplemental Data available online). We found strong phylogeographic monophyly and large genetic distances between N. n. nebulosa (mainland) and N. n. diardi (Borneo; n = 3 individuals) with mtDNA (771 bp), nuclear DNA (3100 bp), and 51 microsatellite loci. Thirty-six fixed mitochondrial and nuclear nucleotide differences and 20 microsatellite loci with nonoverlapping allele-size ranges distinguished N. n. nebulosa from N. n. diardi. Along with fixed subspecies-specific chromosomal differences, this degree of differentiation is equivalent to, or greater than, comparable measures among five recognized Panthera species (lion, tiger, leopard, jaguar, and snow leopard). These distinctions increase the urgency of clouded leopard conservation efforts, and if affirmed by morphological analysis and wider sampling of N. n. diardi in Borneo and Sumatra, would support reclassification of N. n. diardi as a new species (Neofelis diardi).

  2. Molecular evidence for species-level distinctions in clouded leopards.

    PubMed

    Buckley-Beason, Valerie A; Johnson, Warren E; Nash, Willliam G; Stanyon, Roscoe; Menninger, Joan C; Driscoll, Carlos A; Howard, JoGayle; Bush, Mitch; Page, John E; Roelke, Melody E; Stone, Gary; Martelli, Paolo P; Wen, Ci; Ling, Lin; Duraisingam, Ratna K; Lam, Phan V; O'Brien, Stephen J

    2006-12-01

    Among the 37 living species of Felidae, the clouded leopard (Neofelis nebulosa) is generally classified as a monotypic genus basal to the Panthera lineage of great cats. This secretive, mid-sized (16-23 kg) carnivore, now severely endangered, is traditionally subdivided into four southeast Asian subspecies (Figure 1A). We used molecular genetic methods to re-evaluate subspecies partitions and to quantify patterns of population genetic variation among 109 clouded leopards of known geographic origin (Figure 1A, Tables S1 ans S2 in the Supplemental Data available online). We found strong phylogeographic monophyly and large genetic distances between N. n. nebulosa (mainland) and N. n. diardi (Borneo; n = 3 individuals) with mtDNA (771 bp), nuclear DNA (3100 bp), and 51 microsatellite loci. Thirty-six fixed mitochondrial and nuclear nucleotide differences and 20 microsatellite loci with nonoverlapping allele-size ranges distinguished N. n. nebulosa from N. n. diardi. Along with fixed subspecies-specific chromosomal differences, this degree of differentiation is equivalent to, or greater than, comparable measures among five recognized Panthera species (lion, tiger, leopard, jaguar, and snow leopard). These distinctions increase the urgency of clouded leopard conservation efforts, and if affirmed by morphological analysis and wider sampling of N. n. diardi in Borneo and Sumatra, would support reclassification of N. n. diardi as a new species (Neofelis diardi). PMID:17141620

  3. A Large Scale Survey of Molecular Clouds at Nagoya University

    NASA Astrophysics Data System (ADS)

    Mizuno, A.; Onishi, T.; Yamaguchi, N.; Hara, A.; Hayakawa, T.; Kato, S.; Mizuno, N.; Abe, R.; Saito, H.; Yamaguchi, R.; Mine, Y.; Moriguchi, Y.; Mano, S.; Matsunaga, K.; Tachihara, K.; Kawamura, A.; Yonekura, Y.; Ogawa, H.; Fukui, Y.

    1999-10-01

    Large scale 12CO and 13CO (J=1-0) surveys have been carried out by using two 4-m radio telescopes at Nagoya University since 1990 in order to obtain a complete sample of the Galactic molecular clouds. The southern survey started in 1996 with one of the telescopes, named "NANTEN", installed at the Las Campanas Observatory in Chile. The observations made at a grid spacing of 2' - 8' with a 2.'7 beam allow us to identify and resolve the individual star forming dense cores within 1-2 kpc of the sun. The present coverage in the 12CO and 13CO are ~ 7% and ~ 21% of the sky, respectively. The data are used to derive physical parameters of dense cores and to study the mass spectrum, morphology, and conditions for star formation. For example, the survey revealed that the cloud mass function is fairly universal for various regions (e.g., Yonekura et al. 1998, ApJS, 110, 21), and that star forming clouds tend to be characterized by low Mvir/MLTE (e.g., Kawamura et al. 1998, ApJS, 117, 387; Mizuno et al. 1999, PASJ, in press). The survey will provide invaluable database of southern star and planet forming regions, one of the important scientific targets of ALMA.

  4. Dense molecular clouds in the SN 2008fp host galaxy

    NASA Astrophysics Data System (ADS)

    Cox, N. L. J.; Patat, F.

    2014-05-01

    Context. Supernovae (SNe) offer a unique opportunity to study physical properties, small-scale structure, and complex organic chemistry of the interstellar medium (ISM) in different galaxies. Aims: Interstellar absorption features, such as atomic and molecular lines as well as diffuse interstellar bands (DIBs), can be used to study the physical properties of extra-galactic diffuse interstellar clouds. Methods: We used optical high-resolution spectroscopy to study the properties of the ISM in the SN 2008fp host galaxy, ESO 428-G14. The properties of intervening dust were investigated via spectropolarimetry. Results: The spectra of SN 2008fp reveal a complex of diffuse atomic clouds at radial velocities in line with the systematic velocities of the host galaxy. In addition, a translucent (AV ~ 1.5 mag) cloud is detected at a heliocentric velocity of 1770 km s-1 (redshifted by 70 km s-1 with respect to the system velocity). This cold dense cloud is rich in dense atomic gas tracers, molecules, as well as DIBs. We have detected both C2 and C3 for the first time in a galaxy beyond the Local Group. The CN (0, 0) band-line ratios are consistent with an excitation temperature of T = 2.9 ± 0.4 K. The interstellar polarisation law deviates significantly from what is observed in the Galaxy, indicating substantial differences in the host dust/size composition. No variations over a period of about one month are observed in any of the ISM tracers. Conclusions: The lack of variability in the extra-galactic absorption line profiles implies that the absorbing material is not circumstellar and thus not directly affected by the SN event. It also shows that there are no significant density variation in the small-scale structure of the molecular cloud down to 100 AU. C2 is used to probe the cold diffuse ISM density and temperature. Here we also use observations of CN in a distant galaxies, though for now still in a limited way, for in situ measurements of the cosmic background

  5. Infrared Star Counts Do Not Indicate Distances to Galactic Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Finn, Susanna C.; Jackson, J. M.

    2008-05-01

    Molecular clouds are important objects for studying Galactic structure. Star formation occurs in molecular clouds and through observations of other galaxies, we know that they are largely confined to spiral arms. Therefore, with precise distance measurements toward molecular clouds in our Galaxy, the spiral structure of the Milky Way can in principle be deduced. However, current distance measurements to molecular clouds are fraught with errors. Kinematic distance measurements rely on the measured radial velocity of a cloud as well as the rotation of the Milky Way, both of which are uncertain. Therefore, it is important to find new methods independent of velocity for finding distances to molecular clouds. One potential method is the use of star counts. Because molecular clouds extinct stars, stars behind the cloud appear dimmer or completely disappear. Accordingly, one would expect to find fewer stars toward a molecular cloud than in a region without clouds. A cloud nearer to the observer would have a smaller overall stellar areal density. Conversely, a more distant cloud would have more stars in front of it. Because of the large extinctions, this method will work best in the infrared. This method was tested using the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). Star count maps were made for all four GLIMPSE bands (3.6, 4.5, 5.8, and 8.0 microns). Results show that a lack of star counts in a field does not correlate with distance to the cloud, contrary to expectation. One reason for this failure is that bright emission from many star-forming clouds artificially lowers the number of detected stars due to the difficulty of extracting point sources from regions of extended bright emission. Another reason is the superposition of multiple clouds along the same line of sight. Funding for this research was provided by NSF grant AST-0507657.

  6. 74 MHz nonthermal emission from molecular clouds: evidence for a cosmic ray dominated region at the galactic center.

    PubMed

    Yusef-Zadeh, F; Wardle, M; Lis, D; Viti, S; Brogan, C; Chambers, E; Pound, M; Rickert, M

    2013-10-01

    We present 74 MHz radio continuum observations of the Galactic center region. These measurements show nonthermal radio emission arising from molecular clouds that is unaffected by free–free absorption along the line of sight. We focus on one cloud, G0.13-0.13, representative of the population of molecular clouds that are spatially correlated with steep spectrum (α(327MHz)(74MHz) = 1.3 ± 0.3) nonthermal emission from the Galactic center region. This cloud lies adjacent to the nonthermal radio filaments of the Arc near l 0.2° and is a strong source of 74 MHz continuum, SiO (2-1), and Fe I Kα 6.4 keV line emission. This three-way correlation provides the most compelling evidence yet that relativistic electrons, here traced by 74 MHz emission, are physically associated with the G0.13-0.13 molecular cloud and that low-energy cosmic ray electrons are responsible for the Fe I Kα line emission. The high cosmic ray ionization rate 10(–1)3 s(–1) H(–1) is responsible for heating the molecular gas to high temperatures and allows the disturbed gas to maintain a high-velocity dispersion. Large velocity gradient (LVG) modeling of multitransition SiO observations of this cloud implies H2 densities 10(4–5) cm(–3) and high temperatures. The lower limit to the temperature of G0.13-0.13 is 100 K, whereas the upper limit is as high as 1000 K. Lastly, we used a time-dependent chemical model in which cosmic rays drive the chemistry of the gas to investigate for molecular line diagnostics of cosmic ray heating. When the cloud reaches chemical equilibrium, the abundance ratios of HCN/HNC and N2H+/HCO+ are consistent with measured values. In addition, significant abundance of SiO is predicted in the cosmic ray dominated region of the Galactic center. We discuss different possibilities to account for the origin of widespread SiO emission detected from Galactic center molecular clouds.

  7. Exploring Grain Alignment Mechanisms in Giant Molecular Clouds using GPIPS

    NASA Astrophysics Data System (ADS)

    Jameson, Katherine; Clemens, D.; Pinnick, A.; Pavel, M.; Moreau, J.; Taylor, B.

    2009-01-01

    The linear polarization of starlight along a line of sight arises from the alignment of anisotropic dust grains with the local magnetic field direction. The exact process which aligns the dust grains with the local magnetic field is still unknown. However, an understanding of the alignment mechanism is necessary to be able to interpret polarization maps as tracers of the galactic magnetic field. Recent arguments suggest that radiative aligned torques (RATs) dominate alignment in giant molecular clouds (GMCs), including the infrared dark cloud cores (IRDCs) within them. To test RAT theory, a nearby GMC at l = 53, b = 0 was chosen to be observed this past June as part of the Galactic Plane Infrared Polarization Survey (GPIPS). The cloud covers a 1 x 2 degree region of the galactic plane ( 200 GPIPS field-of-views), and displays regions of varying extinction, morphology, and radiation environments as seen using the GLIMPSE, MIPS, and GRS 13CO data. With an average sampling of 100 stars per GPIPS field-of-view (10’ x 10'), we expect 20,000 stars will show detectable polarizations -a factor of 600 greater than in previous polarimetric studies. A plot of degree of NIR polarization P(%) vs. I/Imax, found using GRS 13CO data, is ideal for comparison to the models of Cho & Lazarian (2005). Approximate Av values are found using the 2MASS color excesses, EH-K. This aids in the generation of a plot of P(%)/Av vs. Av in dark clouds, to compare to the results of Arce et al. (1998) to test the notion that grains are aligned only for a few skin-depths. This work is partially supported by NSF grant AST-0607500.

  8. A Uniform Catalog of Molecular Clouds in the Milky Way

    NASA Astrophysics Data System (ADS)

    Rice, Thomas S.; Goodman, Alyssa A.; Bergin, Edwin A.; Beaumont, Christopher; Dame, T. M.

    2016-05-01

    The all-Galaxy CO survey of Dame et al. is by far the most uniform, large-scale Galactic CO survey. Using a dendrogram-based decomposition of this survey, we present a catalog of 1064 massive molecular clouds throughout the Galactic plane. This catalog contains 2.5 × 108 solar masses, or {25}-5.8+10.7% of the Milky Way's estimated H2 mass. We track clouds in some spiral arms through multiple quadrants. The power index of Larson's first law, the size-linewidth relation, is consistent with 0.5 in all regions—possibly due to an observational bias—but clouds in the inner Galaxy systematically have significantly (˜30%) higher linewidths at a given size, indicating that their linewidths are set in part by the Galactic environment. The mass functions of clouds in the inner Galaxy versus the outer Galaxy are both qualitatively and quantitatively distinct. The inner Galaxy mass spectrum is best described by a truncated power law with a power index of γ = -1.6 ± 0.1 and an upper truncation mass of M 0 = (1.0 ± 0.2) × 107 M ⊙, while the outer Galaxy mass spectrum is better described by a non-truncating power law with γ = -2.2 ± 0.1 and an upper mass of M 0 = (1.5 ± 0.5) × 106 M ⊙, indicating that the inner Galaxy is able to form and host substantially more massive GMCs than the outer Galaxy. Additionally, we have simulated how the Milky Way would appear in CO from extragalactic perspectives, for comparison with CO maps of other galaxies.

  9. RESOLVED MAGNETIC FIELD MAPPING OF A MOLECULAR CLOUD USING GPIPS

    SciTech Connect

    Marchwinski, Robert C.; Pavel, Michael D.; Clemens, Dan P. E-mail: pavelmi@bu.edu

    2012-08-20

    We present the first resolved map of plane-of-sky magnetic field strength for a quiescent molecular cloud. GRSMC 45.60+0.30 subtends 40 Multiplication-Sign 10 pc at a distance of 1.88 kpc, masses 16,000 M{sub Sun }, and exhibits no star formation. Near-infrared background starlight polarizations were obtained for the Galactic Plane Infrared Polarization Survey using the 1.8 m Perkins telescope and the Mimir instrument. The cloud area of 0.78 deg{sup 2} contains 2684 significant starlight polarizations for Two Micron All Sky Survey matched stars brighter than 12.5 mag in the H band. Polarizations are generally aligned with the cloud's major axis, showing an average position angle dispersion of 15 {+-} 2 Degree-Sign and polarization of 1.8 {+-} 0.6%. The polarizations were combined with Galactic Ring Survey {sup 13}CO spectroscopy and the Chandrasekhar-Fermi method to estimate plane-of-sky magnetic field strengths, with an angular resolution of 100 arcsec. The average plane-of-sky magnetic field strength across the cloud is 5.40 {+-} 0.04 {mu}G. The magnetic field strength map exhibits seven enhancements or 'magnetic cores'. These cores show an average magnetic field strength of 8.3 {+-} 0.9 {mu}G, radius of 1.2 {+-} 0.2 pc, intercore spacing of 5.7 {+-} 0.9 pc, and exclusively subcritical mass-to-flux ratios, implying their magnetic fields continue to suppress star formation. The magnetic field strength shows a power-law dependence on gas volume density, with slope 0.75 {+-} 0.02 for n{sub H{sub 2}} {>=}10 cm{sup -3}. This power-law index is identical to those in studies at higher densities, but disagrees with predictions for the densities probed here.

  10. High spectral resolution observations of fluorescent molecular hydrogen in molecular clouds

    NASA Technical Reports Server (NTRS)

    Burton, Michael G.; Geballe, T. R.; Brand, P. W. J. L.; Moorhouse, A.

    1990-01-01

    The 1-0 S(1) line of molecular hydrogen has been observed at high spectral resolution in several sources where the emission was suspected of being fluorescent. In NGC 2023, the Orion Bar, and Parsamyan 18, the S(1) line is unresolved, and the line center close to the rest velocity of the ambient molecular cloud. Such behavior is expected for UV-excited line emission. The H2 line widths in molecular clouds thus can serve as diagnostic for shocked and UV-excitation mechanisms. If the lines are broader than several km/s or velocity shifts are observed across a source it is likely that shocks are responsible for the excitation of the gas.

  11. Characterization of molecular structural changes in pectin during juice cloud destabilization in frozen concentrated orange juice

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Pectin comprises one of the major components of cloud material in citrus juices. Juice cloud is a complex mixture of polysaccharides, proteins and lower molecular weight compounds that are responsible for the turbid appearance of citrus juices. The stability of juice cloud depends on a number of fac...

  12. The alignment of molecular cloud magnetic fields with the spiral arms in M33.

    PubMed

    Li, Hua-bai; Henning, Thomas

    2011-11-24

    The formation of molecular clouds, which serve as stellar nurseries in galaxies, is poorly understood. A class of cloud formation models suggests that a large-scale galactic magnetic field is irrelevant at the scale of individual clouds, because the turbulence and rotation of a cloud may randomize the orientation of its magnetic field. Alternatively, galactic fields could be strong enough to impose their direction upon individual clouds, thereby regulating cloud accumulation and fragmentation, and affecting the rate and efficiency of star formation. Our location in the disk of the Galaxy makes an assessment of the situation difficult. Here we report observations of the magnetic field orientation of six giant molecular cloud complexes in the nearby, almost face-on, galaxy M33. The fields are aligned with the spiral arms, suggesting that the large-scale field in M33 anchors the clouds.

  13. The alignment of molecular cloud magnetic fields with the spiral arms in M33

    NASA Astrophysics Data System (ADS)

    Li, Hua-Bai; Henning, Thomas

    2011-11-01

    The formation of molecular clouds, which serve as stellar nurseries in galaxies, is poorly understood. A class of cloud formation models suggests that a large-scale galactic magnetic field is irrelevant at the scale of individual clouds, because the turbulence and rotation of a cloud may randomize the orientation of its magnetic field. Alternatively, galactic fields could be strong enough to impose their direction upon individual clouds, thereby regulating cloud accumulation and fragmentation, and affecting the rate and efficiency of star formation. Our location in the disk of the Galaxy makes an assessment of the situation difficult. Here we report observations of the magnetic field orientation of six giant molecular cloud complexes in the nearby, almost face-on, galaxy M33. The fields are aligned with the spiral arms, suggesting that the large-scale field in M33 anchors the clouds.

  14. MIXING OF CLUMPY SUPERNOVA EJECTA INTO MOLECULAR CLOUDS

    SciTech Connect

    Pan Liubin; Desch, Steven J.; Scannapieco, Evan; Timmes, F. X.

    2012-09-01

    Several lines of evidence, from isotopic analyses of meteorites to studies of the Sun's elemental and isotopic composition, indicate that the solar system was contaminated early in its evolution by ejecta from a nearby supernova. Previous models have invoked supernova material being injected into an extant protoplanetary disk, or isotropically expanding ejecta sweeping over a distant (>10 pc) cloud core, simultaneously enriching it and triggering its collapse. Here, we consider a new astrophysical setting: the injection of clumpy supernova ejecta, as observed in the Cassiopeia A supernova remnant, into the molecular gas at the periphery of an H II region created by the supernova's progenitor star. To track these interactions, we have conducted a suite of high-resolution (1500{sup 3} effective) three-dimensional numerical hydrodynamic simulations that follow the evolution of individual clumps as they move into molecular gas. Even at these high resolutions, our simulations do not quite achieve numerical convergence, due to the challenge of properly resolving the small-scale mixing of ejecta and molecular gas, although they do allow some robust conclusions to be drawn. Isotropically exploding ejecta do not penetrate into the molecular cloud or mix with it, but, if cooling is properly accounted for, clumpy ejecta penetrate to distances {approx}10{sup 18} cm and mix effectively with large regions of star-forming molecular gas. In fact, the {approx}2 M{sub Sun} of high-metallicity ejecta from a single core-collapse supernova is likely to mix with {approx}2 Multiplication-Sign 10{sup 4} M{sub Sun} of molecular gas material as it is collapsing. Thus, all stars forming late ( Almost-Equal-To 5 Myr) in the evolution of an H II region may be contaminated by supernova ejecta at the level {approx}10{sup -4}. This level of contamination is consistent with the abundances of short-lived radionuclides and possibly some stable isotopic shifts in the early solar system and is

  15. Bacterial community composition in Brazilian Anthrosols and adjacent soils characterized using culturing and molecular identification.

    PubMed

    O'Neill, B; Grossman, J; Tsai, M T; Gomes, J E; Lehmann, J; Peterson, J; Neves, E; Thies, J E

    2009-07-01

    Microbial community composition was examined in two soil types, Anthrosols and adjacent soils, sampled from three locations in the Brazilian Amazon. The Anthrosols, also known as Amazonian dark earths, are highly fertile soils that are a legacy of pre-Columbian settlement. Both Anthrosols and adjacent soils are derived from the same parent material and subject to the same environmental conditions, including rainfall and temperature; however, the Anthrosols contain high levels of charcoal-like black carbon from which they derive their dark color. The Anthrosols typically have higher cation exchange capacity, higher pH, and higher phosphorus and calcium contents. We used culture media prepared from soil extracts to isolate bacteria unique to the two soil types and then sequenced their 16S rRNA genes to determine their phylogenetic placement. Higher numbers of culturable bacteria, by over two orders of magnitude at the deepest sampling depths, were counted in the Anthrosols. Sequences of bacteria isolated on soil extract media yielded five possible new bacterial families. Also, a higher number of families in the bacteria were represented by isolates from the deeper soil depths in the Anthrosols. Higher bacterial populations and a greater diversity of isolates were found in all of the Anthrosols, to a depth of up to 1 m, compared to adjacent soils located within 50-500 m of their associated Anthrosols. Compared to standard culture media, soil extract media revealed diverse soil microbial populations adapted to the unique biochemistry and physiological ecology of these Anthrosols. PMID:19381712

  16. Mapping the Orion Molecular Cloud Complex in Radio Frequencies

    NASA Astrophysics Data System (ADS)

    Castelaz, Michael W.; Lemly, C.

    2013-01-01

    The purpose of this research project was to create a large-scale intensity map of the Orion Molecular Cloud Complex at a radio frequency of 1420 MHz. A mapping frequency of 1420 MHz was chosen because neutral hydrogen, which is the primary component of the Orion Molecular Complex, naturally emits radio waves at this frequency. The radio spectral data for this project were gathered using a 4.6-m radio telescope whose spectrometer was tuned to 1420 MHz and whose beam width was 2.7 degrees. The map created for this project consisted of an eight-by-eight grid centered on M42 spanning 21.6 degrees per side. The grid consisted of 64 individual squares spanning 2.7 degrees per side (corresponding to the beam width of the telescope). Radio spectra were recorded for each of these individual squares at an IF gain of 18. Each spectrum consisted of intensity on an arbitrary scale from 0 to 10 plotted as a function frequencies ranging from -400 kHz to +100 kHz around the origin of 1420 MHz. The data from all 64 radio spectra were imported into Wolfram Alpha, which was used to fit Gaussian functions to the data. The peak intensity and the frequency at which this peak intensity occurs could then be extracted from the Gaussian functions. Other helpful quantities that could be calculated from the Gaussian functions include flux (integral of Gaussian function over frequency range), average value of intensity (flux integral divided by frequency range), and half maximum of intensity. Because all of the radio spectra were redshifted, the velocities of the hydrogen gas clouds of the Orion Molecular Cloud Complex could be calculated using the Doppler equation. The data extracted from the Gaussian functions were then imported into Mathcad to create 2D grayscale maps with right ascension (RA) on the x-axis, declination on the y-axis, and intensity (or flux, etc.) represented on a scale from black to white (with white representing the highest intensities). These 2D maps were then imported

  17. Using Morphological, Molecular and Climatic Data to Delimitate Yews along the Hindu Kush-Himalaya and Adjacent Regions

    PubMed Central

    Poudel, Ram C.; Möller, Michael; Gao, Lian-Ming; Ahrends, Antje; Baral, Sushim R.; Liu, Jie; Thomas, Philip; Li, De-Zhu

    2012-01-01

    Background Despite the availability of several studies to clarify taxonomic problems on the highly threatened yews of the Hindu Kush-Himalaya (HKH) and adjacent regions, the total number of species and their exact distribution ranges remains controversial. We explored the use of comprehensive sets of morphological, molecular and climatic data to clarify taxonomy and distributions of yews in this region. Methodology/Principal Findings A total of 743 samples from 46 populations of wild yew and 47 representative herbarium specimens were analyzed. Principle component analyses on 27 morphological characters and 15 bioclimatic variables plus altitude and maximum parsimony analysis on molecular ITS and trnL-F sequences indicated the existence of three distinct species occurring in different ecological (climatic) and altitudinal gradients along the HKH and adjacent regions Taxus contorta from eastern Afghanistan to the eastern end of Central Nepal, T. wallichiana from the western end of Central Nepal to Northwest China, and the first report of the South China low to mid-elevation species T. mairei in Nepal, Bhutan, Northeast India, Myanmar and South Vietnam. Conclusion/Significance The detailed sampling and combination of different data sets allowed us to identify three clearly delineated species and their precise distribution ranges in the HKH and adjacent regions, which showed no overlap or no distinct hybrid zone. This might be due to differences in the ecological (climatic) requirements of the species. The analyses further provided the selection of diagnostic morphological characters for the identification of yews occurring in the HKH and adjacent regions. Our work demonstrates that extensive sampling combined with the analysis of diverse data sets can reliably address the taxonomy of morphologically challenging plant taxa. PMID:23056501

  18. Giant molecular clouds in the Large Magellanic Cloud seen in sub-parsec scales by ALMA

    NASA Astrophysics Data System (ADS)

    Kawamura, Akiko; Onishi, Toshikazu; Harada, Ryohei; Morioka, Yuuki; Tokuda, Kazuki; Meixner, Margaret; Indebetouw, Remy; Sewilo, Marta; Nayak, Omnarayani; Saigo, Kazuya; Fukui, Yasuo

    2015-08-01

    Stars are formed in dense clumps of giant molecular clouds (GMCs), and kinetic energy and heavy elements are ejected from stars back into the interstellar medium through stellar winds and supernova explosions. This cycle drives the evolution of galaxies and thus, it is important to understand GMC evolution and star formation activities to obtain deeper knowledge of galaxy evolution.The Large Magellanic Cloud (LMC) offers an ideal laboratory to study how the interstellar medium evolves and how stars are formed throughout a galaxy at an unrivaled closeness to us with its nearly face-on view. It is known that young populous clusters like R136 are still being formed, making it possible to study also populous cluster formation, which is not currently observed in the Galaxy. We conducted a survey of the GMCs in the LMC by NANTEN and classified them into three types according to the activities of massive star formation, corresponding the evolutional sequence of the GMCs. One of the features of the GMCs in the LMC is that there are a large number of GMCs without active massive star formation unlike those of the Galaxy. Thus, the LMC is one of the most suitable galaxies to study the evolution of GMCs by investigating the star formation and natal GMCs with various star formation activities.We have started to obtain ALMA data of molecular cloud distributions in CO lines with sub-parsec to parsec scales for different types of GMCs, for example, one of the most active on-going star forming regions, N159 E/W, cluster forming GMCs like N206, and without active massive star formation, GMC 225, etc. The detailed studies of 13CO(2-1) observations, for e.g. in N159 West, show that many filaments are straight or curved distributions with a typical width of 0.5-1.0 pc and a length of 5-10 pc. N159W-S located toward an intersection of two filaments, where we also detected molecular outflows, we set up a hypothesis that the two filaments collided with each other ˜105 yrs ago and

  19. Dynamical Evolution of Supernova Remnants Breaking Through Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Cho, Wankee; Kim, Jongsoo; Koo, Bon-Chul

    2015-04-01

    We carry out three-dimensional hydrodynamic simulations of the supernova remnants (SNRs) produced inside molecular clouds (MCs) near their surface using the HLL code tep{har83}. We explore the dynamical evolution and the X-ray morphology of SNRs after breaking through the MC surface for ranges of the explosion depths below the surface and the density ratios of the clouds to the intercloud media (ICM). We find that if an SNR breaks out through an MC surface in its Sedov stage, the outermost dense shell of the remnant is divided into several layers. The divided layers are subject to the Rayleigh-Taylor instability and fragmented. On the other hand, if an SNR breaks through an MC after the remnant enters the snowplow phase, the radiative shell is not divided to layers. We also compare the predictions of previous analytic solutions for the expansion of SNRs in stratified media with our one-dimensional simulations. Moreover, we produce synthetic X-ray surface brightness in order to research the center-bright X-ray morphology shown in thermal composite SNRs. In the late stages, a breakout SNR shows the center-bright X-ray morphology inside an MC in our results. We apply our model to the observational results of the X-ray morphology of the thermal composite SNR 3C 391.

  20. Mass-density relationship in molecular cloud clumps

    NASA Astrophysics Data System (ADS)

    Donkov, Sava; Veltchev, Todor V.; Klessen, Ralf S.

    2011-12-01

    We study the mass-density relationship n ∝ mx in molecular cloud condensations (clumps), considering various equipartition relations between their gravitational, kinetic, internal and magnetic energies. Clumps are described statistically, with a density distribution that reflects a lognormal probability density function in turbulent cold interstellar medium. The clump mass-density exponent x derived at different scales L varies in most of the cases within the range -2.5 ≲x≲-0.2, with a pronounced scale dependence and in consistency with observations. When derived from the global size-mass relationship ? for set of clumps, generated at all scales, the clump mass-density exponent has typical values -3.0 ≲x(γglob) ≲-0.3 that depend on the forms of energy, included in the equipartition relations, and on the velocity scaling law, whereas the description of clump geometry is important when magnetic energy is taken into account.

  1. An infrared study of Orion Molecular Cloud-2 (OMC-2)

    SciTech Connect

    Johnson, J.J.; Gehrz, R.D.; Jones, T.J.; Hackwell, J.A.; Grasdalen, G.L. The Aerospace Corp., Space Sciences Laboratory, Los Angeles, CA Wyoming Infrared Observatory, Laramie )

    1990-08-01

    This paper reports 1.2-23 micron photometry for 11 discrete sources in Orion Molecular Cloud-2 (OMC-2). These data, combined with H and K photometric and K polarimetric images, are used to model the cluster sources. Most appear to be young stars of roughly solar mass. Some have circumstellar dust reradiation or reflection nebulosity. A model based on single scattering of light from an exciting star explains some features of the IRS 1 nebula, the largest reflection nebula in OMC-2. However, the red colors and high surface brightness of the IRS 1 nebula require a cool excitation source that is more luminous than far-infrared observations would indicate. 34 refs.

  2. MOLECULAR CLOUDS IN THE TRIFID NEBULA M20: POSSIBLE EVIDENCE FOR A CLOUD-CLOUD COLLISION IN TRIGGERING THE FORMATION OF THE FIRST GENERATION STARS

    SciTech Connect

    Torii, K.; Enokiya, R.; Sano, H.; Yoshiike, S.; Hanaoka, N.; Ohama, A.; Furukawa, N.; Dawson, J. R.; Moribe, N.; Oishi, K.; Nakashima, Y.; Okuda, T.; Yamamoto, H.; Kawamura, A.; Mizuno, N.; Onishi, T.; Fukui, Y.; Maezawa, H.; Mizuno, A.

    2011-09-01

    A large-scale study of the molecular clouds toward the Trifid Nebula, M20, has been made in the J = 2-1 and J = 1-0 transitions of {sup 12}CO and {sup 13}CO. M20 is ionized predominantly by an O7.5 star HD164492. The study has revealed that there are two molecular components at separate velocities peaked toward the center of M20 and that their temperatures-30-50 K as derived by a large velocity gradient analysis-are significantly higher than the 10 K of their surroundings. We identify the two clouds as the parent clouds of the first generation stars in M20. The mass of each cloud is estimated to be {approx}10{sup 3} M{sub sun} and their separation velocity is {approx}8 km s{sup -1} over {approx}1-2 pc. We find that the total mass of stars and molecular gas in M20 is less than {approx}3.2 x 10{sup 3} M{sub sun}, which is too small by an order of magnitude to gravitationally bind the system. We argue that the formation of the first generation stars, including the main ionizing O7.5 star, was triggered by the collision between the two clouds in a short timescale of {approx}1 Myr, a second example alongside Westerlund 2, where a super-star cluster may have been formed due to cloud-cloud collision triggering.

  3. Molecular Clouds in the Trifid Nebula M20: Possible Evidence for a Cloud-Cloud Collision in Triggering the Formation of the First Generation Stars

    NASA Astrophysics Data System (ADS)

    Torii, K.; Enokiya, R.; Sano, H.; Yoshiike, S.; Hanaoka, N.; Ohama, A.; Furukawa, N.; Dawson, J. R.; Moribe, N.; Oishi, K.; Nakashima, Y.; Okuda, T.; Yamamoto, H.; Kawamura, A.; Mizuno, N.; Maezawa, H.; Onishi, T.; Mizuno, A.; Fukui, Y.

    2011-09-01

    A large-scale study of the molecular clouds toward the Trifid Nebula, M20, has been made in the J = 2-1 and J = 1-0 transitions of 12CO and 13CO. M20 is ionized predominantly by an O7.5 star HD164492. The study has revealed that there are two molecular components at separate velocities peaked toward the center of M20 and that their temperatures—30-50 K as derived by a large velocity gradient analysis—are significantly higher than the 10 K of their surroundings. We identify the two clouds as the parent clouds of the first generation stars in M20. The mass of each cloud is estimated to be ~103 M sun and their separation velocity is ~8 km s-1 over ~1-2 pc. We find that the total mass of stars and molecular gas in M20 is less than ~3.2 × 103 M sun, which is too small by an order of magnitude to gravitationally bind the system. We argue that the formation of the first generation stars, including the main ionizing O7.5 star, was triggered by the collision between the two clouds in a short timescale of ~1 Myr, a second example alongside Westerlund 2, where a super-star cluster may have been formed due to cloud-cloud collision triggering.

  4. Chemistry in Magnetohydrodynamic Shock Waves in Diffuse Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Peimbert, Antonio

    1998-09-01

    Absorption observations of the CH+ molecule with column densities of up to 1014 cm-2 in diffuse molecular clouds in many lines of sight are reviewed, and compared to the reddening and to abundances and velocity shifts of molecules like CH. Special attention is placed on the observations of the line of sight towards ς Ophiuchi where high quality observations of many chemical species are available. The problem of the required CH+ is described, and many formation mechanisms from the literature are reviewed, finding that none of them is particularly apt at describing the observations towards ς-Oph. Two fluid J-type shock models are studied as an alternative. The necessary conditions for their formation are discussed, and it is shown how they are expected to be present widely in the interstellar medium. Plane parallel numerical integrations, for the particular case in which the magnetic field is perpendicular to the shock velocity, are employed to study the region of phase-space of initial conditions that will produce 2 fluid shocks. A chemical network is developed and formation of key molecules like CH+, CH and OH, along with the excited roto-vibrational levels of H2, are studied under the shock dynamics. These models are then compared to the observations of the different lines of sight, showing they are capable of reproducing the features of the observations towards most of those clouds. An attempt to model the line of sight towards ς-Oph is done, finding that a shock with a shock speed vs = 9.0km/s going through a cloud with a density of nH = 14cm-3 with a magnetic field of B = 4.7μG does a reasonable job at satisfying most of the observations with the exception of the highest rotational excited states of molecular hydrogen for which observations are available. There is a small family of solutions capable of explaining the observed results which make specific predictions for the velocity profiles of the H2 lines of various excited levels. New observations with

  5. The Two Molecular Clouds in RCW 38: Evidence for the Formation of the Youngest Super Star Cluster in the Milky Way Triggered by Cloud-Cloud Collision

    NASA Astrophysics Data System (ADS)

    Fukui, Y.; Torii, K.; Ohama, A.; Hasegawa, K.; Hattori, Y.; Sano, H.; Ohashi, S.; Fujii, K.; Kuwahara, S.; Mizuno, N.; Dawson, J. R.; Yamamoto, H.; Tachihara, K.; Okuda, T.; Onishi, T.; Mizuno, A.

    2016-03-01

    We present distributions of two molecular clouds having velocities of 2 and 14 km s-1 toward RCW 38, the youngest super star cluster in the Milky Way, in the 12CO J = 1-0 and 3-2 and 13CO J = 1-0 transitions. The two clouds are likely physically associated with the cluster as verified by the high intensity ratio of the J = 3-2 emission to the J = 1-0 emission, the bridging feature connecting the two clouds in velocity, and their morphological correspondence with the infrared dust emission. The velocity difference is too large for the clouds to be gravitationally bound. We frame a hypothesis that the two clouds are colliding with each other by chance to trigger formation of the ˜20 O stars that are localized within ˜0.5 pc of the cluster center in the 2 km s-1 cloud. We suggest that the collision is currently continuing toward part of the 2 km s-1 cloud where the bridging feature is localized. This is the third super star cluster alongside Westerlund 2 and NGC 3603 where cloud-cloud collision has triggered the cluster formation. RCW 38 is the youngest super star cluster in the Milky Way, holding a possible sign of on-going O star formation, and is a promising site where we may be able to witness the moment of O star formation.

  6. Statistical properties of dense molecular clouds in the Galactic center region

    NASA Astrophysics Data System (ADS)

    Miyazaki, A.; Tsuboi, M.

    We report physical properties of molecular clouds from the Galactic center r egion survey in CS J = 1-0 with the Nobeyama 45-m telescope (Tsuboi, Handa, an d Ukita, 1996). We identified over 70 molecular cloud cores in the region. We determined the statistical properties such as size-line width and LTE mass -virial theorem mass relations for the clouds. The size-line width relation is obscure in this survey data because of narrow in the radius range of the observed clouds. But the line width of the Galactic center cloud is about fi ve times larger than that of the disk clouds (Solomon et al.1987). Virial th eorem masses of the Galactic center clouds are 1-2 order of magnitude larger than the LTE masses. These are consistent with the results for larger size c louds around the Galactic center from CO J = 2-1 (Oka 1996).

  7. A wide-latitude CO survey of molecular clouds in the northern Milky Way

    NASA Technical Reports Server (NTRS)

    Dame, T. M.; Thaddeus, P.

    1985-01-01

    A wide-latitude, low angular resolution survey of CO along most of the first Galactic quadrant and part of the second was undertaken in order to investigate molecular clouds associated with the Great Rift and the diffuse component of Galactic gamma rays. The main nearby clouds have masses between a few times 10,000 and a few times 100,000 solar masses, versus a few times a million solar masses for the largest complexes elsewhere. The CO emission in the survey comes nearly equally from local clouds associated with the Great Rift and from distant clouds in the inner arms of the Galaxy 4-7 kpc from the Galactic center. The half-thickness at half-intensity of the local molecular cloud layer is greater than 50 pc and is estimated to be 75 + or - 25 pc. The results strongly support the notion that all dark nebulae are molecular clouds, and vice-versa.

  8. A New Method for Constraining Molecular Cloud Thickness: A Study of Taurus, Perseus, and Ophiuchus

    NASA Astrophysics Data System (ADS)

    Qian, Lei; Li, Di; Offner, Stella; Pan, Zhichen

    2015-09-01

    The core velocity dispersion (CVD) is a potentially useful tool for studying the turbulent velocity field of molecular clouds. CVD is based on centroid velocities of dense gas clumps, thus is less prone to density fluctuation and reflects more directly the cloud velocity field. Prior work demonstrated that the Taurus molecular cloud CVD resembles the well-known Larson's linewidth-size relation of molecular clouds. In this work, we studied the dependence of the CVD on the line-of-sight thickness of molecular clouds, a quantity which cannot be measured by direct means. We produced a simple statistical model of cores within clouds and analyzed the CVD of a variety of hydrodynamical simulations. We show that the relation between the CVD and the 2D projected separation of cores ({L}2{{D}}) is sensitive to the cloud thickness. When the cloud is thin, the index of the {CVD}-{L}2{{D}} relation (γ in the relation {CVD}˜ {L}2{{D}}γ ) reflects the underlying energy spectrum (E(k)˜ {k}-β ) in that γ ˜ (β -1)/2. The {CVD}-{L}2{{D}} relation becomes flatter (γ \\to 0) for thicker clouds. We used this result to constrain the thicknesses of Taurus, Perseus, and Ophiuchus. We conclude that Taurus has a ratio of cloud depth to cloud length smaller than about 1/10-1/8, i.e., it is a sheet. A simple geometric model fit to the linewidth-size relation indicates that the Taurus cloud has a ˜0.7 pc line-of-sight dimension. In contrast, Perseus and Ophiuchus are thicker and have ratios of cloud depth to cloud length larger than about 1/10-1/8.

  9. MOLECULAR OXYGEN IN OORT CLOUD COMET 1P/HALLEY

    SciTech Connect

    Rubin, M.; Altwegg, K.; Dishoeck, E. F. van; Schwehm, G.

    2015-12-10

    Recently, the ROSINA mass spectrometer suite on board the European Space Agency's Rosetta spacecraft discovered an abundant amount of molecular oxygen, O{sub 2}, in the coma of Jupiter family comet 67P/Churyumov–Gerasimenko of O{sub 2}/H{sub 2}O = 3.80 ± 0.85%. It could be shown that O{sub 2} is indeed a parent species and that the derived abundances point to a primordial origin. Crucial questions are whether the O{sub 2} abundance is peculiar to comet 67P/Churyumov–Gerasimenko or Jupiter family comets in general, and also whether Oort cloud comets such as comet 1P/Halley contain similar amounts of molecular oxygen. We investigated mass spectra obtained by the Neutral Mass Spectrometer instrument during the flyby by the European Space Agency's Giotto probe of comet 1P/Halley. Our investigation indicates that a production rate of O{sub 2} of 3.7 ± 1.7% with respect to water is indeed compatible with the obtained Halley data and therefore that O{sub 2} might be a rather common and abundant parent species.

  10. The CH+ abundance in turbulent, diffuse molecular clouds

    NASA Astrophysics Data System (ADS)

    Myers, Andrew T.; McKee, Christopher F.; Li, Pak Shing

    2015-11-01

    The intermittent dissipation of interstellar turbulence is an important energy source in the diffuse interstellar medium. Though on average smaller than the heating rates due to cosmic rays and the photoelectric effect on dust grains, the turbulent cascade can channel large amounts of energy into a relatively small fraction of the gas that consequently undergoes significant heating and chemical enrichment. In particular, this mechanism has been proposed as a solution to the long-standing problem of the high abundance of CH+ along diffuse molecular sight lines, which steady-state, low-temperature models underproduce by over an order of magnitude. While much work has been done on the structure and chemistry of these small-scale dissipation zones, comparatively little attention has been paid to relating these zones to the properties of the large-scale turbulence. In this paper, we attempt to bridge this gap by estimating the temperature and CH+ column density along diffuse molecular sight lines by post-processing three-dimensional magnetohydrodynamic(s) turbulence simulations. Assuming reasonable values for the cloud density (bar{n}H = 30 cm-3), size (L = 20 pc), and velocity dispersion (σv = 2.3 km s-1), we find that our computed abundances compare well with CH+ column density observations, as well as with observations of emission lines from rotationally excited H2 molecules.

  11. Molecular Oxygen in Oort Cloud Comet 1P/Halley

    NASA Astrophysics Data System (ADS)

    Rubin, M.; Altwegg, K.; van Dishoeck, E. F.; Schwehm, G.

    2015-12-01

    Recently, the ROSINA mass spectrometer suite on board the European Space Agency's Rosetta spacecraft discovered an abundant amount of molecular oxygen, O2, in the coma of Jupiter family comet 67P/Churyumov-Gerasimenko of O2/H2O = 3.80 ± 0.85%. It could be shown that O2 is indeed a parent species and that the derived abundances point to a primordial origin. Crucial questions are whether the O2 abundance is peculiar to comet 67P/Churyumov-Gerasimenko or Jupiter family comets in general, and also whether Oort cloud comets such as comet 1P/Halley contain similar amounts of molecular oxygen. We investigated mass spectra obtained by the Neutral Mass Spectrometer instrument during the flyby by the European Space Agency's Giotto probe of comet 1P/Halley. Our investigation indicates that a production rate of O2 of 3.7 ± 1.7% with respect to water is indeed compatible with the obtained Halley data and therefore that O2 might be a rather common and abundant parent species.

  12. Collapse of Rotating Magnetized Molecular Cloud Cores and Mass Outflows

    NASA Astrophysics Data System (ADS)

    Tomisaka, Kohji

    2002-08-01

    The collapse of rotating magnetized molecular cloud cores is studied with axisymmetric magnetohydrodynamic (MHD) simulations. Because of the change of the equation of state of the interstellar gas, molecular cloud cores experience several phases during the collapse. In the earliest isothermal runaway collapse (n<~1010 H2 cm-3), a pseudodisk is formed, and it continues to contract until an opaque core is formed at the center. In this disk, a number of MHD fast and slow shock pairs appear whose wave fronts are parallel to the disk. We assume that the interstellar gas obeys a polytropic equation of state with the exponent of Γ>1 above the critical density at which the core becomes optically thick against the thermal radiation from dusts ncr~1010 cm-3. After the equation of state becomes hard, an adiabatic quasi-static core forms at the center (the first core), which is separated from the isothermal contracting pseudodisk by the accretion shock front facing radially outward. By the effect of the magnetic tension, the angular momentum is transferred from the disk midplane to the surface. The gas with an excess angular momentum near the surface is finally ejected, which explains the molecular bipolar outflow. Two types of outflows are found. When the poloidal magnetic field is strong (its energy is comparable to the thermal one), a U-shaped outflow is formed, in which gas is mainly outflowing through a region whose shape looks like a capital letter U at a finite distance from the rotation axis. The gas is accelerated by the centrifugal force and the magnetic pressure gradient of the toroidal component. The other is a turbulent outflow in which magnetic field lines and velocity fields seem to be randomly oriented. In this case, globally the gas moves out almost perpendicularly from the disk, and the outflow looks like a capital letter I. In this case, although the gas is launched by the centrifugal force, the magnetic force working along the poloidal field lines plays an

  13. A survey for Galactic supernova remnant/molecular cloud interactions ssing carbon monoxide

    NASA Astrophysics Data System (ADS)

    Kilpatrick, Charles; Rieke, George; Bieging, John

    2016-06-01

    Supernova remnants are one of the primary engines through which stars add energy to the interstellar medium. The efficiency of this transfer of energy is enhanced where supernova remnants encounter dense interstellar gas, such as in molecular clouds. Unique signatures have been observed toward these supernova remnant/molecular cloud interactions in the form of unusual molecular line profiles and bright non-thermal radiation. The sites of these interactions also provide some of the best examples for evidence of cosmic-ray acceleration and Galactic sources of very high-energy gamma-rays. Despite the large number of individual studies that examine supernova remnant/molecular cloud interactions, very little is known about their overall rates and characteristics. This lack of information limits the usefulness of individual supernova remnant/molecular cloud interactions to enhance our understanding of supernova feedback and cosmic-ray acceleration. I will discuss recent work studying large populations of supernova remnants in the 12CO J = 2 ‑ 1 and J = 3 ‑ 2 lines and the observational signatures associated with molecular shocks from supernova ejecta. Broadened molecular lines and molecular line ratios indicative of warm gas can be used to identify and characterize populations of supernova remnant/molecular cloud interactions. From this large sample, I will discuss new constraints on the energetic processes to which supernova remnants contribute, especially the rate of GeV and TeV gamma-ray production associated with supernova remnant/molecular cloud interfaces.

  14. Nearby molecular clouds; Proceedings of the Specialized Colloquium, Toulouse, France, September 17-21, 1984

    NASA Astrophysics Data System (ADS)

    Serra, G.

    Papers are presented on molecular line observations of nearby dark clouds at high galactic latitudes, a comparison of optical appearance and infrared emission of extended dust clouds, correlations between NH3 (1.1) and far IR emission, and the dissipation of kinetic energy in clumpy magnetic clouds. Also considered are large and small scale structures of molecular clouds in the Taurus-Persens complex, radio continuum and molecular line studies of dense cores in dark clouds, star counts and ammonia observations in the central Taurus region, and frosts, in the Rho Oph molecular cloud. Other topics include IRAS observations of star formation in nearby molecular clouds, warm dust in the RCRA molecular cloud, the coexistence of spectral features of dust particles and of ionized gas as found in IRAS data, and CO observations of high velocity gas around S187. Papers are also presented on mass outflows from T Tauri stars and their interaction with the environment, an overview of Herbig-Haro objects, upper limits to coronal emission from X-ray detected T Tauri stars, VLA observations of the OH and H2O masers in the young star cluster NGC 2017 IR, and two ZAMS AOV stars in CHA I.

  15. POPULATIONS OF YOUNG STELLAR OBJECTS IN NEARBY MOLECULAR CLOUDS

    SciTech Connect

    Hsieh, Tien-Hao; Lai, Shih-Ping E-mail: slai@phys.nthu.edu.tw

    2013-03-01

    We develop a new method for identifying young stellar objects (YSOs) from star-forming regions using the photometry data from Spitzer's c2d Legacy Project. The aim is to obtain YSO lists as complete as possible for studying statistical properties such as the star formation rate (SFR) and lifetimes of YSOs in different evolutionary stages. The largest obstacle in identifying YSOs comes from background galaxies with similar spectral energy distributions to YSOs. Traditionally, selected color-color and color-magnitude criteria are used to separate YSOs and galaxies. However, since there is no obvious boundary between YSOs and galaxies in color-color diagrams and color-magnitude diagrams (CMDs), those criteria may exclude faint YSOs near the boundary. In this paper, we separate the YSOs and galaxies in a multi-dimensional (multi-D) magnitude space, which is equivalent to using all variations of CMDs simultaneously. Comparing sources from molecular clouds to Spitzer's SWIRE data, which have a negligible amount of YSOs, we can naturally identify YSO candidates (YSOc) located outside of the galaxy-populated regions in the multi-D space. In the five c2d surveyed clouds, we select 322 new YSOc and miss/exclude 33 YSOc compared to Evans et al., and this results in 1313 YSOc in total. As a result, SFR increases 28% correspondingly, but the lifetimes of YSOs in different evolutionary stages remain unchanged. Compared to theories by Krumholz and McKee, our derived SFR suggests that star formation at a large scale is dominated by supersonic turbulence rather than magnetic fields. Furthermore, we identify seven new very low luminosity objects.

  16. The Far Infrared Lines of OH as Molecular Cloud Diagnostics

    NASA Technical Reports Server (NTRS)

    Smith, Howard A.

    2004-01-01

    Future IR missions should give some priority to high resolution spectroscopic observations of the set of far-IR transitions of OH. There are 15 far-IR lines arising between the lowest eight rotational levels of OH, and ISO detected nine of them. Furthermore, ISO found the OH lines, sometimes in emission and sometimes in absorption, in a wide variety of galactic and extragalactic objects ranging from AGB stars to molecular clouds to active galactic nuclei and ultra-luminous IR galaxies. The ISO/LWS Fabry-Perot resolved the 119 m doublet line in a few of the strong sources. This set of OH lines provides a uniquely important diagnostic for many reasons: the lines span a wide wavelength range (28.9 m to 163.2 m); the transitions have fast radiative rates; the abundance of the species is relatively high; the IR continuum plays an important role as a pump; the contribution from shocks is relatively minor; and, not least, the powerful centimeter-wave radiation from OH allows comparison with radio and VLBI datasets. The problem is that the large number of sensitive free parameters, and the large optical depths of the strongest lines, make modeling the full set a difficult job. The SWAS montecarlo radiative transfer code has been used to analyze the ISO/LWS spectra of a number of objects with good success, including in both the lines and the FIR continuum; the DUSTY radiative transfer code was used to insure a self-consistent continuum. Other far IR lines including those from H2O, CO, and [OI] are also in the code. The OH lines all show features which future FIR spectrometers should be able to resolve, and which will enable further refinements in the details of each cloud's structure. Some examples are given, including the case of S140, for which independent SWAS data found evidence for bulk flows.

  17. Magnetic Field of the Vela C Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Kusune, Takayoshi; Sugitani, Koji; Nakamura, Fumitaka; Watanabe, Makoto; Tamura, Motohide; Kwon, Jungmi; Sato, Shuji

    2016-10-01

    We have performed extensive near-infrared (JHK s) imaging polarimetry toward the Vela C molecular cloud, which covers the five high-density sub-regions (North, Centre-Ridge, Centre-Nest, South-Ridge, and South-Nest) with distinct morphological characteristics. The obtained polarization vector map shows that three of these sub-regions have distinct plane-of-the-sky (POS) magnetic-field characteristics according to the morphological characteristics. (1) In the Centre-Ridge sub-region, a dominating ridge, the POS magnetic field is mostly perpendicular to the ridge. (2) In the Centre-Nest sub-region, a structure having a slightly extended nest of filaments, the POS magnetic field is nearly parallel to its global elongation. (3) In the South-Nest sub-region, which has a network of small filaments, the POS magnetic field appears to be chaotic. By applying the Chandrasekhar–Fermi method, we derived the POS magnetic field strength as ∼70–310 μG in the Centre-Ridge, Centre-Nest, and South-Ridge sub-regions. In the South-Nest sub-region, the dispersion of polarization angles is too large to apply the C-F method. Because the velocity dispersion in this sub-region is not greater than those in the other sub-regions, we suggest that the magnetic field in this sub-region is weaker than those in other sub-regions. We also discuss the relationship between the POS magnetic field (configuration and strength) and the cloud structure of each sub-region.

  18. Molecular Gas, Giant Molecular Clouds, and Star Formation in Early-type Galaxies

    NASA Astrophysics Data System (ADS)

    Bureau, Martin

    2015-08-01

    I will first briefly review the molecular gas content of early-type galaxies, revealing that they unexpectedly harbour much cold gas, with a variety of morphologies. Second, I will show that the star formation efficiency (Kennicutt-Schmidt relation) of early-type galaxies is lower than that of spirals, and will discuss possible dynamical causes. Third, I will discuss the molecular line ratios of early-type galaxies (multiple transitions, isotopologues, and molecular tracers) and their implications (via modeling) for the physical conditions in the gas, revealing unexpected correlations with galaxy properties and both small-scale (e.g. star formation density) and large-scale (e.g. galaxy environment) dependencies. Last, I will present the first study of individually-resolved molecular clouds in an early-type galaxy (e.g. Larson's relations), again revealing differences with respect to standard star-forming late-type galaxies, in particular more luminous, denser, and higher velocity dispersion clouds associated with a gas higher surface density.

  19. Dissipation of Molecular Cloud Turbulence by Magnetohydrodynamic Shockwaves

    NASA Astrophysics Data System (ADS)

    Lehmann, Andrew; Wardle, Mark

    2015-08-01

    The character of star formation is intimately related to the supersonic magnetohydrodynamic (MHD) turbulent dynamics of the giant molecular clouds in which stars form. A significant amount of the turbulent energy dissipates in low velocity shock waves. These shocks cause molecular line cooling of the compressed and heated gas, and so their radiative signatures probe the nature of the turbulence. In MHD fluids the three distinct families of shocks—fast, intermediate and slow—differ in how they compress and heat the molecular gas, and so observational differences between them may also distinguish driving modes of turbulent regions.Here we use a two-fluid model to compare the characteristics of one-dimensional fast and slow MHD shocks. Fast MHD shocks are magnetically driven, forcing ion species to stream through the neutral gas ahead of the shock front. This magnetic precursor heats the gas sufficiently to create a large, warm transition zone where all the fluid variables only weakly change in the shock front. In contrast, slow MHD shocks are driven by gas pressure where neutral species collide with ion species in a thin hot slab that closely resembles an ordinary gas dynamic shock.We computed observational diagnostics for fast and slow shocks at velocities vs = 2-4 km/s and preshock Hydrogen nuclei densities n(H) = 102-4 cm-3. We followed the abundances of molecules relevant for a simple oxygen chemistry and include cooling by CO, H2 and H2O. Estimates of intensities of CO rotational lines show that high-J lines, above J = 6→5, are more strongly excited in slow MHD shocks. We discuss how these shocks could help interpret recently observed anomalously strong mid- and high-J CO lines emitted by warm gas in the Milky Way and external galaxies, and implications for simulations of MHD turbulence.

  20. Molecular clouds in Orion and Monoceros. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Maddalena, R. J.

    1986-01-01

    About one-eighth of a well-sampled 850 deg. sq. region of Orion and Monoceros shows CO emission coming from either local clouds (d < 1 kpc) lying as much as 25 deg. from the galactic plane or from more distant objects located within a few degrees of the plane. Local giant clouds associated with Orion A and B have enhanced temperatures and densities near their western edges possibly due to compression by a high pressure region created by approx.10 supernovae that occurred in the Orion OB association. Another giant cloud associated with Mon R2 may be related to the Orion clouds. Two filamentary clouds (one possibly 300 pc long but 10 pc wide) may represent a new class of object. An expanding ring of clouds concentric with the H II region ionized by lambda Ori probably constitute fragments of the original cloud from which lambda Ori formed; the gas pressure of the H II region and the rocket effect probably disrupted the original cloud. At a distance of 3 kpc, a large (250 x 100 pc) and massive (7-11x10 to the 5th power solar mass) cloud was found with the unusual combination of low temperatures (T sub R < 2.7 K) and wide spectral lines (approx. 7 km /sec). Most of the signs of star formation expected for such a massive cloud being absent, this may be a young cloud that has not yet started to form stars. The approx. 15 large clouds found in the outer galaxy (1 approx. 206 deg. - 220 deg.) probably lie in two spiral arms. The distribution of outer galaxy clouds and a comparison of the properties of these clouds and those of local clouds are given.

  1. Constructing multiscale gravitational energy spectra from molecular cloud surface density PDF - interplay between turbulence and gravity

    NASA Astrophysics Data System (ADS)

    Li, Guang-Xing; Burkert, Andreas

    2016-09-01

    Gravity is believed to be important on multiple physical scales in molecular clouds. However, quantitative constraints on gravity are still lacking. We derive an analytical formula which provides estimates on multiscale gravitational energy distribution using the observed surface density probability distribution function (PDF). Our analytical formalism also enables one to convert the observed column density PDF into an estimated volume density PDF, and to obtain average radial density profile ρ(r). For a region with N_col ˜ N^{-γ _N}, the gravitational energy spectra is E_p(k)˜ k^{-4(1 - 1/γ _N)}. We apply the formula to observations of molecular clouds, and find that a scaling index of -2 of the surface density PDF implies that ρ ˜ r-2 and Ep(k) ˜ k-2. The results are valid from the cloud scale (a few parsec) to around ˜ 0.1 pc. Because of the resemblance the scaling index of the gravitational energy spectrum and the that of the kinetic energy power spectrum of the Burgers turbulence (where E ˜ k-2), our result indicates that gravity can act effectively against turbulence over a multitude of physical scales. This is the critical scaling index which divides molecular clouds into two categories: clouds like Orion and Ophiuchus have shallower power laws, and the amount of gravitational energy is too large for turbulence to be effective inside the cloud. Because gravity dominates, we call this type of cloud g-type clouds. On the other hand, clouds like the California molecular cloud and the Pipe nebula have steeper power laws, and turbulence can overcome gravity if it can cascade effectively from the large scale. We call this type of cloud t-type clouds. The analytical formula can be used to determine if gravity is dominating cloud evolution when the column density PDF can be reliably determined.

  2. STELLAR 'EGGS' EMERGE FROM MOLECULAR CLOUD (Star-Birth Clouds in M16)

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This eerie, dark structure, resembling an imaginary sea serpent's head, is a column of cool molecular hydrogen gas (two atoms of hydrogen in each molecule) and dust that is an incubator for new stars. The stars are embedded inside finger-like protrusions extending from the top of the nebula. Each 'fingertip' is somewhat larger than our own solar system. The pillar is slowly eroding away by the ultraviolet light from nearby hot stars, a process called 'photoevaporation'. As it does, small globules of especially dense gas buried within the cloud is uncovered. These globules have been dubbed 'EGGs' -- an acronym for 'Evaporating Gaseous Globules'. The shadows of the EGGs protect gas behind them, resulting in the finger-like structures at the top of the cloud. Forming inside at least some of the EGGs are embryonic stars -- stars that abruptly stop growing when the EGGs are uncovered and they are separated from the larger reservoir of gas from which they were drawing mass. Eventually the stars emerge, as the EGGs themselves succumb to photoevaporation. The stellar EGGS are found, appropriately enough, in the 'Eagle Nebula' (also called M16 -- the 16th object in Charles Messier's 18th century catalog of 'fuzzy' permanent objects in the sky), a nearby star-forming region 6,500 light-years away in the constellation Serpens. The picture was taken on April 1, 1995 with the Hubble Space Telescope Wide Field and Planetary Camera 2. The color image is constructed from three separate images taken in the light of emission from different types of atoms. Red shows emission from singly-ionized sulfur atoms. Green shows emission from hydrogen. Blue shows light emitted by doubly- ionized oxygen atoms. Credit: Jeff Hester and Paul Scowen (Arizona State University), and NASA Image files in GIF and JPEG format and captions may be accessed on Internet via anonymous ftp from oposite.stsci.edu in /pubinfo:

  3. Loops Adjacent to Catalytic Region and Molecular Stability of Man1312.

    PubMed

    Zhou, Haiyan; Yong, Jie; Gao, Han; Yuan, Zhihui; Yang, Wenjiao; Tian, Yun; Wu, Yongyao

    2016-09-01

    Hemicelluloses are the second major polysaccharides in nature and can be converted to ethanol product by a variety of enzymes including mannanases. Mannanase is an important enzyme that hydrolyses mannose-containing polysaccharides which are abundant in plants. An optimized mannanase could help to improve conversion process and make the technology efficiently and competitively. In this work, the effects of loops adjacent to active region on enzymic properties of Man1312 were investigated. Loop 6 and 10 are two loops neighboring to Man1312 catalytic region, and deletion mutagenesis and residue substitution were performed on both loops. Deletion on sites S145, Q148, N244, and S255 and substitution on sites N146, S147, S156, and T157 gave significant increased stability to enzyme. The quadruplet mutant ManD4I4 combined all the mutations and had higher optimal temperature and T m value by 5 and 4 °C than Man1312, respectively. From our data, we are able to conclude the loops of enzymes are important to design mutagenesis and obtain improved properties, especially the loops neighboring to catalytic region from tertiary structure. In our experiment, residue deletion and substitution on loops neighboring to catalytic region made significant improvement on enzyme properties.

  4. The H I Probability Distribution Function and the Atomic-to-molecular Transition in Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Imara, Nia; Burkhart, Blakesley

    2016-10-01

    We characterize the column-density probability distribution functions (PDFs) of the atomic hydrogen gas, H i, associated with seven Galactic molecular clouds (MCs). We use 21 cm observations from the Leiden/Argentine/Bonn Galactic H i Survey to derive column-density maps and PDFs. We find that the peaks of the H i PDFs occur at column densities in the range ˜1-2 × 1021 {{cm}}-2 (equivalently, ˜0.5-1 mag). The PDFs are uniformly narrow, with a mean dispersion of {σ }{{H}{{I}}}≈ {10}20 {{cm}}-2 (˜0.1 mag). We also investigate the H i-to-H2 transition toward the cloud complexes and estimate H i surface densities ranging from 7 to 16 {M}⊙ {{pc}}-2 at the transition. We propose that the H i PDF is a fitting tool for identifying the H i-to-H2 transition column in Galactic MCs.

  5. Molecular emission towards RCW38 and RCW120; Possible candidates of the star formation via cloud-cloud collision

    NASA Astrophysics Data System (ADS)

    Torii, Kazufumi; Fukui, Yasuo; Furukawa, Naoko; Akio, Ohama; Hasegawa, Keisuke

    2012-04-01

    Understanding the formation of high-mass stars is one of the most pressing issues in modern astronomy. Recent observations towards the young cluster Trifid Neubla (M20) have revealed that two molecular clouds of 10^3 Mo are physically associated with the cluster, and the cloud-cloud collision process as the mechanism of the cluster formation was proposed (Torii et al. 2011). A large relative velocity of ~10 km/s between these two clouds is much larger than the permitted gravitational binding velocity of the constituent clouds. It is a crucial next step that we identify other examples of cloud-cloud collision to further constrain triggered-formed stars. In this proposal, we will observe two well-known bubble-shaped HII regions RCW 38 and RCW 120, located within 2 kpc, from the Sun in CO J=1-0 with Mopra. High spatial resolutions of ~0.1-0.2 pc enable to describe the detailed velocity components and therefore to establish unambiguous association with the optical and infrared nebula just like in M20. We request 26 hours in total.

  6. EFFECTS OF MAGNETIC FIELD STRENGTH AND ORIENTATION ON MOLECULAR CLOUD FORMATION

    SciTech Connect

    Heitsch, Fabian; Hartmann, Lee W.; Stone, James M.

    2009-04-10

    We present a set of numerical simulations addressing the effects of magnetic field strength and orientation on the flow-driven formation of molecular clouds. Fields perpendicular to the flows sweeping up the cloud can efficiently prevent the formation of massive clouds but permit the buildup of cold, diffuse filaments. Fields aligned with the flows lead to substantial clouds, whose degree of fragmentation and turbulence strongly depends on the background field strength. Adding a random field component leads to a 'selection effect' for molecular cloud formation: high column densities are only reached at locations where the field component perpendicular to the flows is vanishing. Searching for signatures of colliding flows should focus on the diffuse, warm gas, since the cold gas phase making up the cloud will have lost the information about the original flow direction because the magnetic fields redistribute the kinetic energy of the inflows.

  7. Bipolar flows, molecular gas disks, and the collapse and accretion of rotating interstellar clouds

    NASA Technical Reports Server (NTRS)

    Boss, Alan P.

    1987-01-01

    Rigorous numerical models of the collapse and accretion of rotating, axisymmetric, isothermal interstellar clouds are studied. The results show that molecular gas disks and evacuated bipolar cavities both appear to be natural consequences of the collapse of rotating interstellar clouds. Dynamically significant magnetic fields may not be necessary for explaining either phenomenon. The models strongly support theoretical models of the type where an isotropic wind from a pre-main sequence star is extrinsically collimated by a rotationally derived molecular gas cloud. The models imply that collimation should be strongest on small scales where rotational effects are most important, i.e., in the dense region of the molecular gas disk.

  8. The structure of the high-latitude molecular cloud toward HD 210121

    NASA Technical Reports Server (NTRS)

    Gredel, Roland; Van Dishoeck, Ewine F.; De Vries, Cor P.; Black, John H.

    1992-01-01

    Optical absorption line observations and millimeter emission of the high-latitude cloud toward the star HD 21021 are reported. The cloud was mapped with the ESO submillimeter telescope. Maps of (C-12)O and (C-13)O emission are presented and the line profiles and velocity structure of the cloud are discussed. The optical absorption line observations allow an independent determination of the H2 column density along the line of sight. The molecular column densities found in this cloud were consistent with those measured in diffuse and translucent clouds. Attention is given to the physical and chemical properties of the cloud with reference to chemical models. Analysis indicates that small fluctuations in H2 column density and other factors can produce large variations of CO abundance and column density in clouds where carbon is just being transformed into CO.

  9. Contraction Signatures toward Dense Cores in the Perseus Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Campbell, J. L.; Friesen, R. K.; Martin, P. G.; Caselli, P.; Kauffmann, J.; Pineda, J. E.

    2016-03-01

    We report the results of an HCO+ (3-2) and N2D+ (3-2) molecular line survey performed toward 91 dense cores in the Perseus molecular cloud using the James Clerk Maxwell Telescope, to identify the fraction of starless and protostellar cores with systematic radial motions. We quantify the HCO+ asymmetry using a dimensionless asymmetry parameter δv, and identify 20 cores with significant blue or red line asymmetries in optically thick emission indicative of collapsing or expanding motions, respectively. We separately fit the HCO+ profiles with an analytic collapse model and determine contraction (expansion) speeds toward 22 cores. Comparing the δv and collapse model results, we find that δv is a good tracer of core contraction if the optically thin emission is aligned with the model-derived systemic velocity. The contraction speeds range from subsonic (0.03 km s-1) to supersonic (0.4 km s-1), where the supersonic contraction speeds may trace global rather than local core contraction. Most cores have contraction speeds significantly less than their free-fall speeds. Only 7 of 28 starless cores have spectra well-fit by the collapse model, which more than doubles (15 of 28) for protostellar cores. Starless cores with masses greater than the Jeans mass (M/MJ > 1) are somewhat more likely to show contraction motions. We find no trend of optically thin non-thermal line width with M/MJ, suggesting that any undetected contraction motions are small and subsonic. Most starless cores in Perseus are either not in a state of collapse or expansion, or are in a very early stage of collapse.

  10. Turbulent Flows within Self-gravitating Magnetized Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Balsara, D. S.; Crutcher, R. M.; Pouquet, A.

    2001-08-01

    Self-gravitating magnetized flows are explored numerically in slab geometry. In this approximation, the derivatives are computed only in one dimension but all three components of vector fields are retained. This is done for a range of fiducial values for the interstellar medium at the scale of molecular clouds. The overall characteristic scale of the turbulence, its Mach number, and the initial ratio of longitudinal to transverse turbulent velocities, as well as the extent of the initial density bulges within the fluid, are the main parameters of the study. Simulations have been performed with and without ambipolar drift. No external forcing is included. Velocity, density, and magnetic perturbations develop self-consistently to comparable levels in all cases. This includes those cases where the medium is initially static. However, a fully random flow produces substantially more density contrast with nested substructures. Collapse eventually occurs after typically three free-fall times. The magnetic field slows down the collapse as expected. For higher Mach numbers, the collapse is faster, and yet the peak densities reached in the final collapsed objects are lower. We have also modeled the effects of ambipolar drift in the presence of cosmic ray ionization and far-ultraviolet ionization. Because the turbulent timescales are shorter than the ambipolar drift timescales, we find that ambipolar drift does not play a significant role in gravitational collapse in a turbulent medium of the type modeled in our simulations.

  11. Comparing simulated emission from molecular clouds using experimental design

    SciTech Connect

    Yeremi, Miayan; Flynn, Mallory; Loeppky, Jason; Rosolowsky, Erik; Offner, Stella

    2014-03-10

    We propose a new approach to comparing simulated observations that enables us to determine the significance of the underlying physical effects. We utilize the methodology of experimental design, a subfield of statistical analysis, to establish a framework for comparing simulated position-position-velocity data cubes to each other. We propose three similarity metrics based on methods described in the literature: principal component analysis, the spectral correlation function, and the Cramer multi-variate two-sample similarity statistic. Using these metrics, we intercompare a suite of mock observational data of molecular clouds generated from magnetohydrodynamic simulations with varying physical conditions. Using this framework, we show that all three metrics are sensitive to changing Mach number and temperature in the simulation sets, but cannot detect changes in magnetic field strength and initial velocity spectrum. We highlight the shortcomings of one-factor-at-a-time designs commonly used in astrophysics and propose fractional factorial designs as a means to rigorously examine the effects of changing physical properties while minimizing the investment of computational resources.

  12. Dynamics of molecular clouds: observations, simulations, and NIF experiments

    NASA Astrophysics Data System (ADS)

    Kane, Jave O.; Martinez, David A.; Pound, Marc W.; Heeter, Robert F.; Casner, Alexis; Mancini, Roberto C.

    2015-02-01

    For over fifteen years astronomers at the University of Maryland and theorists and experimentalists at LLNL have investigated the origin and dynamics of the famous Pillars of the Eagle Nebula, and similar parsec-scale structures at the boundaries of HII regions in molecular hydrogen clouds. Eagle Nebula was selected as one of the National Ignition Facility (NIF) Science programs, and has been awarded four NIF shots to study the cometary model of pillar formation. These experiments require a long-duration drive, 30 ns or longer, to drive deeply nonlinear ablative hydrodynamics. The NIF shots will feature a new long-duration x-ray source prototyped at the Omega EP laser, in which multiple hohlraums are driven with UV light in series for 10 ns each and reradiate the energy as an extended x-ray pulse. The new source will be used to illuminate a science package with directional radiation mimicking a cluster of stars. The scaled Omega EP shots tested whether a multi-hohlraum concept is viable — whether earlier time hohlraums would degrade later time hohlraums by preheat or by ejecting ablated plumes that would deflect the later beams. The Omega EP shots illuminated three 2.8 mm long by 1.4 mm diameter Cu hohlraums for 10 ns each with 4.3 kJ per hohlraum. At NIF each hohlraum will be 4 mm long by 3 mm in diameter and will be driven with 80 kJ per hohlraum.

  13. Supernova Driving. I. The Origin of Molecular Cloud Turbulence

    NASA Astrophysics Data System (ADS)

    Padoan, Paolo; Pan, Liubin; Haugbølle, Troels; Nordlund, Åke

    2016-05-01

    Turbulence is ubiquitous in molecular clouds (MCs), but its origin is still unclear because MCs are usually assumed to live longer than the turbulence dissipation time. Interstellar medium (ISM) turbulence is likely driven by supernova (SN) explosions, but it has never been demonstrated that SN explosions can establish and maintain a turbulent cascade inside MCs consistent with the observations. In this work, we carry out a simulation of SN-driven turbulence in a volume of (250 pc)3, specifically designed to test if SN driving alone can be responsible for the observed turbulence inside MCs. We find that SN driving establishes a velocity scaling consistent with the usual scaling laws of supersonic turbulence, suggesting that previous idealized simulations of MC turbulence, driven with a random, large-scale volume force, were correctly adopted as appropriate models for MC turbulence, despite the artificial driving. We also find that the same scaling laws extend to the interiors of MCs, and that the velocity-size relation of the MCs selected from our simulation is consistent with that of MCs from the Outer-Galaxy Survey, the largest MC sample available. The mass-size relation and the mass and size probability distributions also compare successfully with those of the Outer Galaxy Survey. Finally, we show that MC turbulence is super-Alfvénic with respect to both the mean and rms magnetic-field strength. We conclude that MC structure and dynamics are the natural result of SN-driven turbulence.

  14. Supernova Driving. I. The Origin of Molecular Cloud Turbulence

    NASA Astrophysics Data System (ADS)

    Padoan, Paolo; Pan, Liubin; Haugbølle, Troels; Nordlund, Åke

    2016-05-01

    Turbulence is ubiquitous in molecular clouds (MCs), but its origin is still unclear because MCs are usually assumed to live longer than the turbulence dissipation time. Interstellar medium (ISM) turbulence is likely driven by supernova (SN) explosions, but it has never been demonstrated that SN explosions can establish and maintain a turbulent cascade inside MCs consistent with the observations. In this work, we carry out a simulation of SN-driven turbulence in a volume of (250 pc)3, specifically designed to test if SN driving alone can be responsible for the observed turbulence inside MCs. We find that SN driving establishes a velocity scaling consistent with the usual scaling laws of supersonic turbulence, suggesting that previous idealized simulations of MC turbulence, driven with a random, large-scale volume force, were correctly adopted as appropriate models for MC turbulence, despite the artificial driving. We also find that the same scaling laws extend to the interiors of MCs, and that the velocity–size relation of the MCs selected from our simulation is consistent with that of MCs from the Outer-Galaxy Survey, the largest MC sample available. The mass–size relation and the mass and size probability distributions also compare successfully with those of the Outer Galaxy Survey. Finally, we show that MC turbulence is super-Alfvénic with respect to both the mean and rms magnetic-field strength. We conclude that MC structure and dynamics are the natural result of SN-driven turbulence.

  15. Anomalous Microwave Emission in the Perseus Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Villadsen, Jackie; Tibbs, C.; Cleary, K.; Readhead, A. C.; Scaife, A.; Keating, G.; Sieth, M.; Stevenson, M.; Perrott, Y.; Grainge, K.

    2013-01-01

    Anomalous microwave emission is a form of radio emission that peaks at tens of GHz. This emission, primarily observed in Galactic sources, most likely comes from spinning dust grains with an electric dipole moment. This explanation is based on the remarkable spatial correlation between large-scale 15-GHz emission and long-wavelength infrared emission, discovered in 1997 at the Owens Valley Radio Observatory and since confirmed by many subsequent observations. Anomalous emission presents a new window on the physical conditions in the interstellar medium, especially the properties of very small dust grains. It is also a foreground for studies of the cosmic microwave background. This emission mechanism has so far been studied mostly on large spatial scales - tens of arcminutes to degrees. I present arcminute-resolution 30-GHz observations of known anomalous emission regions in the Perseus molecular cloud, and combine these data with 15-GHz observations in order to understand spectral properties. I also compare the radio observations to infrared data in order to clarify the environmental conditions that lead to anomalous emission.

  16. Molecular clouds toward the super star cluster NGC 3603; possible evidence for a cloud-cloud collision in triggering the cluster formation

    SciTech Connect

    Fukui, Y.; Ohama, A.; Hanaoka, N.; Furukawa, N.; Torii, K.; Hasegawa, K.; Fukuda, T.; Soga, S.; Moribe, N.; Kuroda, Y.; Hayakawa, T.; Kuwahara, T.; Yamamoto, H.; Okuda, T.; Dawson, J. R.; Mizuno, N.; Kawamura, A.; Onishi, T.; Maezawa, H.; Mizuno, A.

    2014-01-01

    We present new large field observations of molecular clouds with NANTEN2 toward the super star cluster NGC 3603 in the transitions {sup 12}CO(J = 2-1, J = 1-0) and {sup 13}CO(J = 2-1, J = 1-0). We suggest that two molecular clouds at 13 km s{sup –1} and 28 km s{sup –1} are associated with NGC 3603 as evidenced by higher temperatures toward the H II region, as well as morphological correspondence. The mass of the clouds is too small to gravitationally bind them, given their relative motion of ∼20 km s{sup –1}. We suggest that the two clouds collided with each other 1 Myr ago to trigger the formation of the super star cluster. This scenario is able to explain the origin of the highest mass stellar population in the cluster, which is as young as 1 Myr and is segregated within the central sub-pc of the cluster. This is the second super star cluster along with Westerlund 2 where formation may have been triggered by a cloud-cloud collision.

  17. MOLECULAR HYDROGEN EMISSION FROM THE BOUNDARIES OF THE TAURUS MOLECULAR CLOUD

    SciTech Connect

    Goldsmith, Paul F.; Velusamy, Thangasamy; Li Di; Langer, William D.

    2010-06-01

    We report Spitzer Space Telescope observations of the four lowest rotational transitions of H{sub 2} in three portions of the boundary of the Taurus molecular cloud. Emission in the two lowest transitions, S(0) and S(1), was detected in almost all pointing directions, while the S(2) and S(3) lines were marginally detected only after further averaging of data. The widespread detection of lines coming from levels 510 K and 1016 K above the molecular ground state is indicative of gas at a temperature of at least 200 K containing column densities (1-5) x 10{sup 18} cm{sup -2} of H{sub 2}. For the region with the simplest geometry, we have used the Meudon PDR code to model the chemistry, radiative transfer, and excitation of molecular hydrogen. We conclude that models with acceptable values of the UV interstellar radiation field can reproduce the amount of H{sub 2} in the lowest excited state, but cannot account for the degree of excitation of the H{sub 2}. The unexpectedly high degree of excitation of the H{sub 2} in the boundary layer of a molecular cloud, which cannot be explained by the presence of stellar sources, points to an enhanced heating rate which may be the result of, e.g., dissipation of turbulence. We have in one boundary region been able to obtain the ortho-to-para ratio (OPR) for H{sub 2}, which by modeling and possible detection of the S(2) and S(3) lines has a range 1.0 {>=} OPR {>=} 0.15, although this result must be treated with caution. The fact that the ortho-to-para ratio is lower than that expected for equilibrium at the gas kinetic temperature may be indicative of circulation of material from cold, purely molecular regions into the boundary layer, possibly due to turbulent diffusion. The explanation of these data may thus be suggestive of processes that are having a significant effect on the structure and evolution of molecular clouds and the star formation that takes place within them.

  18. Molecular Hydrogen Emission from the Boundaries of the Taurus Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Goldsmith, Paul F.; Velusamy, Thangasamy; Li, Di; Langer, William D.

    2010-06-01

    We report Spitzer Space Telescope observations of the four lowest rotational transitions of H2 in three portions of the boundary of the Taurus molecular cloud. Emission in the two lowest transitions, S(0) and S(1), was detected in almost all pointing directions, while the S(2) and S(3) lines were marginally detected only after further averaging of data. The widespread detection of lines coming from levels 510 K and 1016 K above the molecular ground state is indicative of gas at a temperature of at least 200 K containing column densities (1-5) × 1018 cm-2 of H2. For the region with the simplest geometry, we have used the Meudon PDR code to model the chemistry, radiative transfer, and excitation of molecular hydrogen. We conclude that models with acceptable values of the UV interstellar radiation field can reproduce the amount of H2 in the lowest excited state, but cannot account for the degree of excitation of the H2. The unexpectedly high degree of excitation of the H2 in the boundary layer of a molecular cloud, which cannot be explained by the presence of stellar sources, points to an enhanced heating rate which may be the result of, e.g., dissipation of turbulence. We have in one boundary region been able to obtain the ortho-to-para ratio (OPR) for H2, which by modeling and possible detection of the S(2) and S(3) lines has a range 1.0 >= OPR >= 0.15, although this result must be treated with caution. The fact that the ortho-to-para ratio is lower than that expected for equilibrium at the gas kinetic temperature may be indicative of circulation of material from cold, purely molecular regions into the boundary layer, possibly due to turbulent diffusion. The explanation of these data may thus be suggestive of processes that are having a significant effect on the structure and evolution of molecular clouds and the star formation that takes place within them.

  19. Investigating the Life Cycle of Molecular Clouds in the Andromeda Galaxy

    NASA Astrophysics Data System (ADS)

    Beerman, Lori; Dalcanton, Julianne; Schruba, Andreas; Leroy, Adam K.; Johnson, Lent C.; Weisz, Daniel R.; Fouesneau, Morgan; PHAT Collaboration

    2015-01-01

    There is currently a great divide between high resolution studies of stellar clusters and molecular clouds in the Milky Way, and those done in extragalactic systems, where individual stars and clouds cannot usually be resolved. For my thesis work, I combined several astronomical data sets to investigate the life cycle of molecular clouds in the Andromeda Galaxy. The primary data sets I used are the Panchromatic Hubble Andromeda Treasury (PHAT), which catalogued over 200 million stars, and a molecular cloud catalogue that is constructed from new high spatial/spectral resolution (20 pc, 1 km/s) CARMA observations. Several ancillary data sets, including H-alpha and Spitzer IR emission maps were also used, taking advantage of broad wavelength coverage to search for indicators of star formation with different timescales. Comparisons were also made with the PHAT cluster sample, and the youngest (<10 Myr) stellar clusters were used as an additional star formation indicator. The ages and masses of these clusters were determined by fitting the color-magnitude diagrams (CMDs) of their resolved stars to theoretical isochrones. The distribution of the youngest clusters shows a strong correlation with the molecular cloud distribution, while no correlation is evident for clusters greater than 30 Myr. Each molecular cloud in the sample was then classified as a star-forming cloud or a non-star forming cloud, based on the presence of any one of several star formation indicators. About 60% of the clouds in the sample were found to be associated with massive star formation. Based on the comparison between these observations and the results from a Monte Carlo simulation, I will also demonstrate how we can constrain the timescales for the relative phases in a cloud's life.

  20. Star Formation in the Molecular Cloud Associated with the Monkey Head Nebula: Sequential or Spontaneous?

    NASA Astrophysics Data System (ADS)

    Chibueze, J. O.; Imura, K.; Omodaka, T.; Handa, T.; Nagayama, T.; Fujisawa, K.; Sunada, K.; Nakano, M.; Kamezaki, T.; Yamaguchi, Y.

    2013-03-01

    We mapped the NH3 (1,1), (2,2), and (3,3) lines of the molecular cloud associated with the Monkey Head Nebula (MHN) with 1'.6 angular resolution using Kashima 34 m telescope. Its kinetic temperature distribution was contrary to what is expected for a molecular cloud at the edge of an expanding H II region and suggested that the massive star associated with S252A compact HII region formed spontaneously rather than through a sequential process.

  1. On the origin of the Orion and Monoceros molecular cloud complexes

    NASA Technical Reports Server (NTRS)

    Franco, J.; Tenorio-Tagle, G.; Bodenheimer, P.; Rozyczka, M.; Mirabel, I. F.

    1988-01-01

    A detailed model for the origin of the Orion and Monoceros cloud complexes is presented, showing that a single high-velocity H I cloud-galaxy collision can explain their main observed features. The collision generates massive shocked layers, and self-gravity can then provide the conditions for the transformation of these layers into molecular clouds. The clouds formed by the collision maintain the motion of their parental shocked gas and reach positions located far away from the plane. According to this model, both the Orion and Monoceros complexes were formed some 60 million yr ago, when the original shocked layer was fragmented by Galactic tidal forces.

  2. A large catalog of accurate distances to molecular clouds from PS1 photometry

    SciTech Connect

    Schlafly, E. F.; Rix, H.-W.; Martin, N. F.; Green, G.; Finkbeiner, D. P.; Bell, E. F.; Burgett, W. S.; Chambers, K. C.; Hodapp, K. W.; Kaiser, N.; Magnier, E. A.; Tonry, J. L.; Draper, P. W.; Metcalfe, N.; Price, P. A.

    2014-05-01

    Distance measurements to molecular clouds are important but are often made separately for each cloud of interest, employing very different data and techniques. We present a large, homogeneous catalog of distances to molecular clouds, most of which are of unprecedented accuracy. We determine distances using optical photometry of stars along lines of sight toward these clouds, obtained from PanSTARRS-1. We simultaneously infer the reddenings and distances to these stars, tracking the full probability distribution function using a technique presented in Green et al. We fit these star-by-star measurements using a simple dust screen model to find the distance to each cloud. We thus estimate the distances to almost all of the clouds in the Magnani et al. catalog, as well as many other well-studied clouds, including Orion, Perseus, Taurus, Cepheus, Polaris, California, and Monoceros R2, avoiding only the inner Galaxy. Typical statistical uncertainties in the distances are 5%, though the systematic uncertainty stemming from the quality of our stellar models is about 10%. The resulting catalog is the largest catalog of accurate, directly measured distances to molecular clouds. Our distance estimates are generally consistent with available distance estimates from the literature, though in some cases the literature estimates are off by a factor of more than two.

  3. 13CO filaments in the Taurus molecular cloud

    NASA Astrophysics Data System (ADS)

    Panopoulou, G. V.; Tassis, K.; Goldsmith, P. F.; Heyer, M. H.

    2014-11-01

    We have carried out a search for filamentary structures in the Taurus molecular cloud using 13CO line emission data from the Five Colleges Radio Astronomy Observatory survey of ˜100 deg2. We have used the topological analysis tool, Discrete Persistent Structures Extractor (DISPERSE), and post-processed its results to include a more strict definition of filaments that requires an aspect ratio of at least 3:1 and cross-section intensity profiles peaked on the spine of the filament. In the velocity-integrated intensity map only 10 of the hundreds of filamentary structures identified by DISPERSE comply with our criteria. Unlike Herschel analyses, which find a characteristic width for filaments of ˜0.1 pc, we find a much broader distribution of profile widths in our structures, with a peak at 0.4 pc. Furthermore, even if the identified filaments are cylindrical objects, their complicated velocity structure and velocity dispersions imply that they are probably gravitationally unbound. Analysis of velocity channel maps reveals the existence of hundreds of `velocity-coherent' filaments. The distribution of their widths is peaked at lower values (0.2 pc) while the fluctuation of their peak intensities is indicative of stochastic origin. These filaments are suppressed in the integrated intensity map due to the blending of diffuse emission from different velocities. Conversely, integration over velocities can cause filamentary structures to appear. Such apparent filaments can also be traced, using the same methodology, in simple simulated maps consisting of randomly placed cores. They have profile shapes similar to observed filaments and contain most of the simulated cores.

  4. Methanol in the Starless Core, Taurus Molecular Cloud-1

    NASA Astrophysics Data System (ADS)

    Soma, Tatsuya; Sakai, Nami; Watanabe, Yoshimasa; Yamamoto, Satoshi

    2015-04-01

    To explore the formation mechanisms of gas phase CH3OH in cold starless cores, we have conducted high spectral resolution observations toward the cyanopolyyne peak of Taurus Molecular Cloud-1 (TMC-1 CP) with the IRAM 30 m telescope, the Green Bank Telescope, and the Nobeyama 45 m telescope. The spectral lines of CH3OH toward TMC-1 CP are found to have a double-peaked profile separated by 0.5 km s-1. Since the double-peaked profile is observed for 13CH3OH, it is not due to optical depth and/or self-absorption effects. The spectral line profile of CH3OH is much different from those of C34S, C3S, and HC7N observed toward this source. The H2 densities of the emitting region of CH3OH for the blueshifted and redshifted components are derived to be (1.7 ± 0.5) × 104 cm-3 and (4.3 ± 1.2) × 104 cm-3, respectively. These densities are similar to or slightly lower than those found for the other molecules. These results suggest a chemical differentiation between CH3OH and the other molecules, which has indeed been confirmed by mapping observations of the CH3OH and C34S lines. These results are consistent with the general idea that CH3OH is formed on dust grains and is liberated into the gas phase by non-thermal desorption. The grain-surface origin of CH3OH is further confirmed by the CH3OH/13CH3OH ratio. Weak shocks caused by accreting diffuse gas to the TMC-1 filament, photoevaporation caused by cosmic-ray induced UV radiation, and the desorption of excess reaction energy in the formation of CH3OH on dust grains are discussed for the desorption mechanisms.

  5. The properties of bound and unbound molecular cloud populations formed in galactic disc simulations

    NASA Astrophysics Data System (ADS)

    Ward, Rachel L.; Benincasa, Samantha M.; Wadsley, James; Sills, Alison; Couchman, H. M. P.

    2016-01-01

    We explore the effect of galactic environment on properties of molecular clouds. Using clouds formed in a large-scale galactic disc simulation, we measure the observable properties from synthetic column density maps. We confirm that a significant fraction of unbound clouds forms naturally in a galactic disc environment and that a mixed population of bound and unbound clouds can match observed scaling relations and distributions for extragalactic molecular clouds. By dividing the clouds into inner and outer disc populations, we compare their distributions of properties and test whether there are statistically significant differences between them. We find that clouds in the outer disc have lower masses, sizes, and velocity dispersions as compared to those in the inner disc for reasonable choices of the inner/outer boundary. We attribute the differences to the strong impact of galactic shear on the disc stability at large galactocentric radii. In particular, our Toomre analysis of the disc shows a narrowing envelope of unstable masses as a function of radius, resulting in the formation of smaller, lower mass fragments in the outer disc. We also show that the star formation rate is affected by the environment of the parent cloud, and is particularly influenced by the underlying surface density profile of the gas throughout the disc. Our work highlights the strengths of using galaxy-scale simulations to understand the formation and evolution of cloud properties - and the star formation within them - in the context of their environment.

  6. Understanding star formation in molecular clouds. III. Probability distribution functions of molecular lines in Cygnus X

    NASA Astrophysics Data System (ADS)

    Schneider, N.; Bontemps, S.; Motte, F.; Ossenkopf, V.; Klessen, R. S.; Simon, R.; Fechtenbaum, S.; Herpin, F.; Tremblin, P.; Csengeri, T.; Myers, P. C.; Hill, T.; Cunningham, M.; Federrath, C.

    2016-03-01

    The probability distribution function of column density (N-PDF) serves as a powerful tool to characterise the various physical processes that influence the structure of molecular clouds. Studies that use extinction maps or H2 column-density maps (N) that are derived from dust show that star-forming clouds can best be characterised by lognormal PDFs for the lower N range and a power-law tail for higher N, which is commonly attributed to turbulence and self-gravity and/or pressure, respectively. While PDFs from dust cover a large dynamic range (typically N ~ 1020-24 cm-2 or Av~ 0.1-1000), PDFs obtained from molecular lines - converted into H2 column density - potentially trace more selectively different regimes of (column) densities and temperatures. They also enable us to distinguish different clouds along the line of sight through using the velocity information. We report here on PDFs that were obtained from observations of 12CO, 13CO, C18O, CS, and N2H+ in the Cygnus X North region, and make a comparison to a PDF that was derived from dust observations with the Herschel satellite. The PDF of 12CO is lognormal for Av ~ 1-30, but is cut for higher Av because of optical depth effects. The PDFs of C18O and 13CO are mostly lognormal up to Av ~ 1-15, followed by excess up to Av ~ 40. Above that value, all CO PDFs drop, which is most likely due to depletion. The high density tracers CS and N2H+ exhibit only a power law distribution between Av ~ 15 and 400, respectively. The PDF from dust is lognormal for Av ~ 3-15 and has a power-law tail up to Av ~ 500. Absolute values for the molecular line column densities are, however, rather uncertain because of abundance and excitation temperature variations. If we take the dust PDF at face value, we "calibrate" the molecular line PDF of CS to that of the dust and determine an abundance [CS]/[H2] of 10-9. The slopes of the power-law tails of the CS, N2H+, and dust PDFs are -1.6, -1.4, and -2.3, respectively, and are thus consistent

  7. The turbulent interstellar medium and pressure-bounded molecular clouds

    NASA Technical Reports Server (NTRS)

    Maloney, Philip

    1988-01-01

    The existence of turbulence throughout the interstellar medium suggests that an appropriate value for the average pressure may be P/K larger than about 10,000. Negative-index polytropic models of interstellar clouds in equilibrium with an external medium at these pressures are predicted to have sizes, line widths, masses, and size-line width and size-density relations in good agreement with those observed and inferred for dark clouds. Thus these observed features of interstellar clouds do not require that they be completely self-gravitating or 'virialized' in the commonly used sense.

  8. A First Look at the Disk Population in the Auriga-California Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Broekhoven-Fiene, Hannah; Matthews, Brenda C.; Harvey, Paul M.

    2014-01-01

    The Auriga-California Molecular Cloud (AMC) is one of two nearby (within 500 pc) giant molecular clouds, the other being the Orion A Molecular Cloud (OMC). We aim to study the properties of circumstellar disks in the AMC to compare the planet formation potential and processes within the AMC to those for other clouds. A first look with measurements from Spitzer observations suggests that AMC disk properties, such as the distribution of disk luminosities and the evolution of the mid-IR excesses, are not vastly different from those in other regions. Follow-up observations in the submm, mm and cm can be used to measure disk masses and the degree of grain growth from spectral slopes to more completely characterize the disk population.

  9. IDENTIFICATION OF AMBIENT MOLECULAR CLOUDS ASSOCIATED WITH GALACTIC SUPERNOVA REMNANT IC 443

    SciTech Connect

    Lee, Jae-Joon; Koo, Bon-Chul; Snell, Ronald L.; Yun, Min S.; Heyer, Mark H.; Burton, Michael G.

    2012-04-10

    The Galactic supernova remnant (SNR) IC 443 is one of the most studied core-collapse SNRs for its interaction with molecular clouds. However, the ambient molecular clouds with which IC 443 is interacting have not been thoroughly studied and remain poorly understood. Using the Five College Radio Astronomy Observatory 14 m telescope, we obtained fully sampled maps of the {approx}1 Degree-Sign Multiplication-Sign 1 Degree-Sign region toward IC 443 in the {sup 12}CO J = 1-0 and HCO{sup +} J = 1-0 lines. In addition to the previously known molecular clouds in the velocity range v{sub LSR} = -6 to -1 km s{sup -1} (-3 km s{sup -1} clouds), our observations reveal two new ambient molecular cloud components: small ({approx}1') bright clouds in v{sub LSR} = -8 to -3 km s{sup -1} (SCs) and diffuse clouds in v{sub LSR} = +3 to +10 km s{sup -1} (+5 km s{sup -1} clouds). Our data also reveal the detailed kinematics of the shocked molecular gas in IC 443; however, the focus of this paper is the physical relationship between the shocked clumps and the ambient cloud components. We find strong evidence that the SCs are associated with the shocked clumps. This is supported by the positional coincidence of the SCs with shocked clumps and other tracers of shocks. Furthermore, the kinematic features of some shocked clumps suggest that these are the ablated material from the SCs upon the impact of the SNR shock. The SCs are interpreted as dense cores of parental molecular clouds that survived the destruction by the pre-supernova evolution of the progenitor star or its nearby stars. We propose that the expanding SNR shock is now impacting some of the remaining cores and the gas is being ablated and accelerated, producing the shocked molecular gas. The morphology of the +5 km s{sup -1} clouds suggests an association with IC 443. On the other hand, the -3 km s{sup -1} clouds show no evidence for interaction.

  10. On the virial theorem for turbulent molecular clouds

    NASA Technical Reports Server (NTRS)

    Mckee, Christopher F.; Zweibel, Ellen G.

    1992-01-01

    An Eulerian, rather than Lagrangian, form of the virial theorem is derived for a turbulent, magnetized cloud embedded in a steady, turbulent, low-density intercloud medium. The role of turbulent pressure in cloud confinement is clarified, and it is shown that, in the absence of a magnetic field, a cloud can be at a somewhat lower pressure than the intercloud medium. Simple forms for the magnetic term in the virial equation are obtained. Radiation pressure is considered; its effects are relatively small under average conditions in the interstellar medium. Under typical conditions, external pressure and magnetic fields are shown to have a relatively small effect on virial estimates of the mass of self-gravitating clouds.

  11. THE PHYSICAL CONDITIONS IN A PRE-SUPER STAR CLUSTER MOLECULAR CLOUD IN THE ANTENNAE GALAXIES

    SciTech Connect

    Johnson, K. E.; Indebetouw, R.; Evans, A. S.; Leroy, A. K.; Brogan, C. L.; Hibbard, J.; Sheth, K.; Whitmore, B. C.

    2015-06-10

    We present an analysis of the physical conditions in an extreme molecular cloud in the Antennae merging galaxies. This cloud has properties consistant with those required to form a globular cluster. We have obtained ALMA CO and 870 μm observations of the Antennae galaxy system with ∼0.″5 resolution. This cloud stands out in the data with a radius of ≲24 pc and mass of >5 × 10{sup 6} M{sub ⊙}. The cloud appears capable of forming a globular cluster, but the lack of associated thermal radio emission indicates that star formation has not yet altered the environment. The lack of thermal radio emission places the cloud in an early stage of evolution, which we expect to be short-lived (≲1 Myr) and thus rare. Given its mass and kinetic energy, for the cloud to be confined (as its appearance strongly suggests) it must be subject to an external pressure of P/k{sub B} ≳ 10{sup 8} K cm{sup −3}–10,000 times higher than typical interstellar pressure. This would support theories that high pressures are required to form globular clusters and may explain why extreme environments like the Antennae are preferred environments for generating such objects. Given the cloud temperature of ∼25 K, the internal pressure must be dominated by non-thermal processes, most likely turbulence. We expect the molecular cloud to collapse and begin star formation in ≲1 Myr.

  12. The Physical Conditions in a Pre-super Star Cluster Molecular Cloud in the Antennae Galaxies

    NASA Astrophysics Data System (ADS)

    Johnson, K. E.; Leroy, A. K.; Indebetouw, R.; Brogan, C. L.; Whitmore, B. C.; Hibbard, J.; Sheth, K.; Evans, A. S.

    2015-06-01

    We present an analysis of the physical conditions in an extreme molecular cloud in the Antennae merging galaxies. This cloud has properties consistant with those required to form a globular cluster. We have obtained ALMA CO and 870 μm observations of the Antennae galaxy system with ˜0.″5 resolution. This cloud stands out in the data with a radius of ≲24 pc and mass of >5 × 106 M⊙. The cloud appears capable of forming a globular cluster, but the lack of associated thermal radio emission indicates that star formation has not yet altered the environment. The lack of thermal radio emission places the cloud in an early stage of evolution, which we expect to be short-lived (≲1 Myr) and thus rare. Given its mass and kinetic energy, for the cloud to be confined (as its appearance strongly suggests) it must be subject to an external pressure of P/kB ≳ 108 K cm-3-10,000 times higher than typical interstellar pressure. This would support theories that high pressures are required to form globular clusters and may explain why extreme environments like the Antennae are preferred environments for generating such objects. Given the cloud temperature of ˜25 K, the internal pressure must be dominated by non-thermal processes, most likely turbulence. We expect the molecular cloud to collapse and begin star formation in ≲1 Myr.

  13. The Chemistry of Interstellar Argonium and Other Probes of the Molecular Fraction in Diffuse Clouds

    NASA Astrophysics Data System (ADS)

    Neufeld, David A.; Wolfire, Mark G.

    2016-08-01

    We present a general parameter study in which the abundance of interstellar argonium (ArH+) is predicted using a model for the physics and chemistry of diffuse interstellar gas clouds. Results have been obtained as a function of UV radiation field, cosmic-ray ionization rate, and cloud extinction. No single set of cloud parameters provides an acceptable fit to the typical ArH+, OH+, and {{{H}}}2{{{O}}}+ abundances observed in diffuse clouds within the Galactic disk. Instead, the observed abundances suggest that ArH+ resides primarily in a separate population of small clouds of total visual extinction of at most 0.02 mag per cloud, within which the column-averaged molecular fraction is in the range {10}-5{--}{10}-2, while OH+ and {{{H}}}2{{{O}}}+ reside primarily in somewhat larger clouds with a column-averaged molecular fraction ˜0.2. This analysis confirms our previous suggestion that the argonium molecular ion is a unique tracer of almost purely atomic gas.

  14. Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites

    PubMed Central

    Van Kooten, Elishevah M. M. E.; Wielandt, Daniel; Schiller, Martin; Nagashima, Kazuhide; Thomen, Aurélien; Olsen, Mia B.; Nordlund, Åke; Krot, Alexander N.; Bizzarro, Martin

    2016-01-01

    The short-lived 26Al radionuclide is thought to have been admixed into the initially 26Al-poor protosolar molecular cloud before or contemporaneously with its collapse. Bulk inner Solar System reservoirs record positively correlated variability in mass-independent 54Cr and 26Mg*, the decay product of 26Al. This correlation is interpreted as reflecting progressive thermal processing of in-falling 26Al-rich molecular cloud material in the inner Solar System. The thermally unprocessed molecular cloud matter reflecting the nucleosynthetic makeup of the molecular cloud before the last addition of stellar-derived 26Al has not been identified yet but may be preserved in planetesimals that accreted in the outer Solar System. We show that metal-rich carbonaceous chondrites and their components have a unique isotopic signature extending from an inner Solar System composition toward a 26Mg*-depleted and 54Cr-enriched component. This composition is consistent with that expected for thermally unprocessed primordial molecular cloud material before its pollution by stellar-derived 26Al. The 26Mg* and 54Cr compositions of bulk metal-rich chondrites require significant amounts (25–50%) of primordial molecular cloud matter in their precursor material. Given that such high fractions of primordial molecular cloud material are expected to survive only in the outer Solar System, we infer that, similarly to cometary bodies, metal-rich carbonaceous chondrites are samples of planetesimals that accreted beyond the orbits of the gas giants. The lack of evidence for this material in other chondrite groups requires isolation from the outer Solar System, possibly by the opening of disk gaps from the early formation of gas giants. PMID:26858438

  15. Isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites.

    PubMed

    Van Kooten, Elishevah M M E; Wielandt, Daniel; Schiller, Martin; Nagashima, Kazuhide; Thomen, Aurélien; Larsen, Kirsten K; Olsen, Mia B; Nordlund, Åke; Krot, Alexander N; Bizzarro, Martin

    2016-02-23

    The short-lived (26)Al radionuclide is thought to have been admixed into the initially (26)Al-poor protosolar molecular cloud before or contemporaneously with its collapse. Bulk inner Solar System reservoirs record positively correlated variability in mass-independent (54)Cr and (26)Mg*, the decay product of (26)Al. This correlation is interpreted as reflecting progressive thermal processing of in-falling (26)Al-rich molecular cloud material in the inner Solar System. The thermally unprocessed molecular cloud matter reflecting the nucleosynthetic makeup of the molecular cloud before the last addition of stellar-derived (26)Al has not been identified yet but may be preserved in planetesimals that accreted in the outer Solar System. We show that metal-rich carbonaceous chondrites and their components have a unique isotopic signature extending from an inner Solar System composition toward a (26)Mg*-depleted and (54)Cr-enriched component. This composition is consistent with that expected for thermally unprocessed primordial molecular cloud material before its pollution by stellar-derived (26)Al. The (26)Mg* and (54)Cr compositions of bulk metal-rich chondrites require significant amounts (25-50%) of primordial molecular cloud matter in their precursor material. Given that such high fractions of primordial molecular cloud material are expected to survive only in the outer Solar System, we infer that, similarly to cometary bodies, metal-rich carbonaceous chondrites are samples of planetesimals that accreted beyond the orbits of the gas giants. The lack of evidence for this material in other chondrite groups requires isolation from the outer Solar System, possibly by the opening of disk gaps from the early formation of gas giants.

  16. The virial balance of clumps and cores in molecular clouds

    NASA Astrophysics Data System (ADS)

    Dib, Sami; Vázquez-Semadeni, Enrique; Kim, Jongsoo; Burkert, Andreas; Shadmehri, Mohsen

    We analyse the virial balance of clumps and cores in a set of three-dimensional, driven, isothermal, magnetohydrodynamical simulations of molecular clouds. We apply a clump finding algorithm based on a density threshold and a friend of friend approach to isolate clumps and cores in the simulation box. For each clump, we calculate all the terms which enter the virial equation in its Eulerian form (EVT): 1/2 ddot I_E=2E_th+E_k-τ_th-τ_k+E_m+τ_m-1/2 dΦ/dt, where the left hand side is the second time derivative of the clump moment of inertia and on the right hand side the terms are (from left to right), the thermal volume energy, volume kinetic energy, surface thermal energy, surface kinetic energy, volume magnetic energy, surface magnetic energy, gravitational term and first time derivative of the flux of moment of inertia through the clump boundary. We also calculate for each clump and core other stability indicators commonly used in both observational and theoretical work such as the Jeans number J[c], mass-to magnetic flux ratio (normalized to the critical value for collapse) μ_[c] and the gravitational parameter α_[vir]. We show that :a) Clumps and cores are dynamical, out of equilibrium structures, b) Surface energy terms are as important as the volume ones in the overall energy balance, c) Not all clumps that have infall like motions are gravitationally bound, d) The near equality of the temporal terms in the EVT enables the usage of the other terms as a stability indicator (gravity versus other energies), and e) We establish the relationships between the classical parameters J[c], μ_[c] and α_[vir] which are used to compare the ratios of gravitational to thermal, magnetic, and kinetic energy in clumps to their counterparts in the EVT (i.e., for example J[c] is compared to IWI /I E[th] -?τ [th] I). Thus, we propose a method to test the clumps stability based on observations of their derived dynamical, thermal and magnetic properties.

  17. METHANOL IN THE STARLESS CORE, TAURUS MOLECULAR CLOUD-1

    SciTech Connect

    Soma, Tatsuya; Sakai, Nami; Watanabe, Yoshimasa; Yamamoto, Satoshi

    2015-04-01

    To explore the formation mechanisms of gas phase CH{sub 3}OH in cold starless cores, we have conducted high spectral resolution observations toward the cyanopolyyne peak of Taurus Molecular Cloud-1 (TMC-1 CP) with the IRAM 30 m telescope, the Green Bank Telescope, and the Nobeyama 45 m telescope. The spectral lines of CH{sub 3}OH toward TMC-1 CP are found to have a double-peaked profile separated by 0.5 km s{sup −1}. Since the double-peaked profile is observed for {sup 13}CH{sub 3}OH, it is not due to optical depth and/or self-absorption effects. The spectral line profile of CH{sub 3}OH is much different from those of C{sup 34}S, C{sub 3}S, and HC{sub 7}N observed toward this source. The H{sub 2} densities of the emitting region of CH{sub 3}OH for the blueshifted and redshifted components are derived to be (1.7 ± 0.5) × 10{sup 4} cm{sup −3} and (4.3 ± 1.2) × 10{sup 4} cm{sup −3}, respectively. These densities are similar to or slightly lower than those found for the other molecules. These results suggest a chemical differentiation between CH{sub 3}OH and the other molecules, which has indeed been confirmed by mapping observations of the CH{sub 3}OH and C{sup 34}S lines. These results are consistent with the general idea that CH{sub 3}OH is formed on dust grains and is liberated into the gas phase by non-thermal desorption. The grain-surface origin of CH{sub 3}OH is further confirmed by the CH{sub 3}OH/{sup 13}CH{sub 3}OH ratio. Weak shocks caused by accreting diffuse gas to the TMC-1 filament, photoevaporation caused by cosmic-ray induced UV radiation, and the desorption of excess reaction energy in the formation of CH{sub 3}OH on dust grains are discussed for the desorption mechanisms.

  18. From Gas to Stars in Energetic Environments: Chemistry of Clumps in Giant Molecular Clouds Within the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Anderson, Crystal N.; Meier, David S.; Ott, Juergen; Hughes, Annie; Wong, Tony H.

    2015-01-01

    We present parsec scale interferometric maps of HCN and HCO^{+} emission from dense gas in the star-forming region 30 Doradus, obtained using the Australia Telescope Compact Array (ATCA). This extreme star-forming region, located in the Large Magellanic Cloud (LMC), is characterized by a very intense ultraviolet ionizing radiation field and sub-solar metallicity, both of which are expected to impact molecular cloud structure. We detect 13 bright, dense clumps within the 30 Doradus-10 giant molecular cloud. Some of the clumps are aligned along a filamentary structure with a characteristic spacing that is consistent with formation via the varicose fluid instability. Our analysis shows that the filament is gravitationally unstable and collapsing to form stars. There is a good correlation between HCO^{+} emission in the filament and signatures of recent star formation activity including H_{2}O masers and young stellar objects (YSOs). We present detailed comparisons of clump properties (masses, linewidths, sizes) in 30Dor-10 to those in other star forming regions of the LMC (N159, N113, N105, N44). Our analysis shows that the 30 Doradus-10 clumps have similar mass but wider linewidths and similar HCN/HCO^{+} (1-0) line ratios as clumps detected in other LMC star-forming regions. Our results suggest that the dense molecular gas clumps in the interior of 30Dor-10 are well-shielded against the intense ionizing field that is present in the 30 Doradus region. We also present preliminary results from follow up observations with the ATCA of a several molecular lines detected from the brightest clumps in 30 Doradus-10, N113 and N159W. The maps cover the following dense gas, photo-dominated regions (PDRs), and shock tracers: HCN, HCO^{+}, C_{2}H, SiO, HNCO, SiS, N_{2}H^{+}, CS, CH_{3}H, CH_{3}CN, {13}^CS, OCS, H_{2}, {34}^CS. These giant molecular clouds have varying radiation fields and energetics. We compare the chemistry within these giant molecular clouds to one another to

  19. Compression and ablation of the photo-irradiated molecular cloud the Orion Bar

    NASA Astrophysics Data System (ADS)

    Goicoechea, Javier R.; Pety, Jérôme; Cuadrado, Sara; Cernicharo, José; Chapillon, Edwige; Fuente, Asunción; Gerin, Maryvonne; Joblin, Christine; Marcelino, Nuria; Pilleri, Paolo

    2016-09-01

    The Orion Bar is the archetypal edge-on molecular cloud surface illuminated by strong ultraviolet radiation from nearby massive stars. Our relative closeness to the Orion nebula (about 1,350 light years away from Earth) means that we can study the effects of stellar feedback on the parental cloud in detail. Visible-light observations of the Orion Bar show that the transition between the hot ionized gas and the warm neutral atomic gas (the ionization front) is spatially well separated from the transition between atomic and molecular gas (the dissociation front), by about 15 arcseconds or 6,200 astronomical units (one astronomical unit is the Earth-Sun distance). Static equilibrium models used to interpret previous far-infrared and radio observations of the neutral gas in the Orion Bar (typically at 10-20 arcsecond resolution) predict an inhomogeneous cloud structure comprised of dense clumps embedded in a lower-density extended gas component. Here we report one-arcsecond-resolution millimetre-wave images that allow us to resolve the molecular cloud surface. In contrast to stationary model predictions, there is no appreciable offset between the peak of the H2 vibrational emission (delineating the H/H2 transition) and the edge of the observed CO and HCO+ emission. This implies that the H/H2 and C+/C/CO transition zones are very close. We find a fragmented ridge of high-density substructures, photoablative gas flows and instabilities at the molecular cloud surface. The results suggest that the cloud edge has been compressed by a high-pressure wave that is moving into the molecular cloud, demonstrating that dynamical and non-equilibrium effects are important for the cloud evolution.

  20. Compression and ablation of the photo-irradiated molecular cloud the Orion Bar

    NASA Astrophysics Data System (ADS)

    Goicoechea, Javier R.; Pety, Jérôme; Cuadrado, Sara; Cernicharo, José; Chapillon, Edwige; Fuente, Asunción; Gerin, Maryvonne; Joblin, Christine; Marcelino, Nuria; Pilleri, Paolo

    2016-09-01

    The Orion Bar is the archetypal edge-on molecular cloud surface illuminated by strong ultraviolet radiation from nearby massive stars. Our relative closeness to the Orion nebula (about 1,350 light years away from Earth) means that we can study the effects of stellar feedback on the parental cloud in detail. Visible-light observations of the Orion Bar show that the transition between the hot ionized gas and the warm neutral atomic gas (the ionization front) is spatially well separated from the transition between atomic and molecular gas (the dissociation front), by about 15 arcseconds or 6,200 astronomical units (one astronomical unit is the Earth–Sun distance). Static equilibrium models used to interpret previous far-infrared and radio observations of the neutral gas in the Orion Bar (typically at 10–20 arcsecond resolution) predict an inhomogeneous cloud structure comprised of dense clumps embedded in a lower-density extended gas component. Here we report one-arcsecond-resolution millimetre-wave images that allow us to resolve the molecular cloud surface. In contrast to stationary model predictions, there is no appreciable offset between the peak of the H2 vibrational emission (delineating the H/H2 transition) and the edge of the observed CO and HCO+ emission. This implies that the H/H2 and C+/C/CO transition zones are very close. We find a fragmented ridge of high-density substructures, photoablative gas flows and instabilities at the molecular cloud surface. The results suggest that the cloud edge has been compressed by a high-pressure wave that is moving into the molecular cloud, demonstrating that dynamical and non-equilibrium effects are important for the cloud evolution.

  1. The heating of interstellar clouds by vibrationally excited molecular hydrogen

    NASA Technical Reports Server (NTRS)

    Stecher, T. P.; Williams, D. A.

    1972-01-01

    The possibility that vibrationally excited H2 may be collisionally de-excited, so providing a heating mechanism for interstellar clouds which operates by coupling the stellar radiation to the gas, is discussed. The majority of excitations in the Lyman and Werner bands of H2 return the molecules to the ground electronic state in a vibrationally excited level, the most favored level being 7. The heating rate obtained in this way is compared with other mechanisms which have been postulated, and the results of calculations of temperature as a function of depth into clouds of different densities are presented. It appears that this mechanism is a significant one, which should be taken into account in detailed models of dense clouds.

  2. Variations in the HCN/HNC abundance ratio in the Orion molecular cloud.

    PubMed

    Goldsmith, P F; Irvine, W M; Hjalmarson, A; Elldér, J

    1986-11-01

    We have used observations of the rare isotopes of HCN and HNC to determine the relative abundance of these two chemical isomers along the central ridge of the Orion molecular cloud. The abundance ratio [HCN]/[HNC] decreases by more than an order of magnitude from the relatively warm plateau and hot core sources toward the KL nebula to the colder, more quiescent clouds to the north and south. Even in the cooler regions, however, the ratio is an order of magnitude larger than that found in previous investigations of cold dark clouds. We determine the kinetic temperature in the regions we have studied from new observations of methylacetylene (CH3CCH), together with other recent estimates of the gas temperature near KL. The results suggest that the warmer portions of the cloud are dominated by different chemical pathways than those in the general interstellar cloud material.

  3. Clumpy molecular clouds - A dynamic model self-consistently regulated by T Tauri star formation

    NASA Technical Reports Server (NTRS)

    Norman, C.; Silk, J.

    1980-01-01

    A model is proposed which can account for the longevity, energetics, and dynamical structure of dark molecular clouds. Recent observations of a high space density of T Tauri stars in some dark clouds provide the basis for the assertion that high-velocity winds from these low mass pre-main-sequence stars provide a continuous dynamic input into molecular clouds. It is postulated that as clumps are driven above the Jeans mass, both by coalescence and the enhancement of ram pressure through continuing acceleration by protostellar winds, collapse is followed by the formation of low-mass stars that generate additional protostellar winds. Finally, it is found that star formation occurs on a relatively slow time scale, comparable to the cloud lifetime

  4. Cometary impacts, molecular clouds, and the motion of the sun perpendicular to the galactic plane

    NASA Technical Reports Server (NTRS)

    Thaddeus, P.; Chanan, G. A.

    1985-01-01

    The stochastic nature of the mass extinction model of Rampino and Stothers (1984), based on the vertical oscillation of the solar system about the plane of the Galaxy, can accommodate a few events with large phase discrepancies. The degree of modulation is crucial in that it depends on the scale height of the population of molecular clouds relative to the amplitude of the solar system and tends to zero if this ratio is large and encounters are entirely random. Here data are presented here from CO surveys of molecular clouds both within and beyond the solar circle which permit explicit calculation of the strength of the modulation. The cloud layer near the sun it too extended and, as a consequence, the modulation of cloud encounters is too weak for a statistically significant period to be extracted from the nine extinctions analyzed by Rampino and Stothers.

  5. THERMAL INSTABILITY BEHIND A SHOCK WAVE IN H I AND MOLECULAR CLOUDS

    SciTech Connect

    Aota, Takuhiro; Aikawa, Yuri; Inoue, Tsuyoshi

    2013-09-20

    We performed one-dimensional hydrodynamic simulations with detailed cooling, heating, and chemical processes to examine the thermal stability of shocked gas in cold neutral medium (CNM) and molecular clouds. We find that both CNM and molecular clouds can be thermally unstable in the cooling layer behind the shock wave. The characteristic wavelength of the thermal instability ranges from 10{sup –5} pc to 0.1 pc in the CNM, and from 10{sup –7} pc to 0.1 pc in the molecular clouds. This coincides with the size of observed tiny scale structures in the CNM and molecular clouds, indicating that the thermal instability in the shocked gas could be a formation mechanism of these tiny structures in the interstellar medium. We have also calculated the e-folding number of the thermal instability to estimate the amplification of the density fluctuation in the shocked gas. Density perturbations in the CNM grow by a factor of exp (5) ≅ 150, whereas the perturbations in the molecular clouds grow only by a factor of a few behind a high Mach number shock. The amplification factor is larger at lower densities and higher velocities. Formation of very small scale structures by thermal instability in shocked gas is more effective in lower densities.

  6. STAR FORMATION IN THE MOLECULAR CLOUD ASSOCIATED WITH THE MONKEY HEAD NEBULA: SEQUENTIAL OR SPONTANEOUS?

    SciTech Connect

    Chibueze, James O.; Imura, Kenji; Omodaka, Toshihiro; Handa, Toshihiro; Kamezaki, Tatsuya; Yamaguchi, Yoshiyuki; Nagayama, Takumi; Sunada, Kazuyoshi; Fujisawa, Kenta; Nakano, Makoto; Sekido, Mamoru

    2013-01-01

    We mapped the (1,1), (2,2), and (3,3) lines of NH{sub 3} toward the molecular cloud associated with the Monkey Head Nebula (MHN) with a 1.'6 angular resolution using a Kashima 34 m telescope operated by the National Institute of Information and Communications Technology (NICT). The kinetic temperature of the molecular gas is 15-30 K in the eastern part and 30-50 K in the western part. The warmer gas is confined to a small region close to the compact H II region S252A. The cooler gas is extended over the cloud even near the extended H II region, the MHN. We made radio continuum observations at 8.4 GHz using the Yamaguchi 32 m radio telescope. The resultant map shows no significant extension from the H{alpha} image. This means that the molecular cloud is less affected by the MHN, suggesting that the molecular cloud did not form by the expanding shock of the MHN. Although the spatial distribution of the Wide-field Infrared Survey Explorer and Two Micron All Sky Survey point sources suggests that triggered low- and intermediate-mass star formation took place locally around S252A, but the exciting star associated with it should be formed spontaneously in the molecular cloud.

  7. Star Formation in the Molecular Cloud Associated with the Monkey Head Nebula: Sequential or Spontaneous?

    NASA Astrophysics Data System (ADS)

    Chibueze, James O.; Imura, Kenji; Omodaka, Toshihiro; Handa, Toshihiro; Nagayama, Takumi; Fujisawa, Kenta; Sunada, Kazuyoshi; Nakano, Makoto; Kamezaki, Tatsuya; Yamaguchi, Yoshiyuki; Sekido, Mamoru

    2013-01-01

    We mapped the (1,1), (2,2), and (3,3) lines of NH3 toward the molecular cloud associated with the Monkey Head Nebula (MHN) with a 1.'6 angular resolution using a Kashima 34 m telescope operated by the National Institute of Information and Communications Technology (NICT). The kinetic temperature of the molecular gas is 15-30 K in the eastern part and 30-50 K in the western part. The warmer gas is confined to a small region close to the compact H II region S252A. The cooler gas is extended over the cloud even near the extended H II region, the MHN. We made radio continuum observations at 8.4 GHz using the Yamaguchi 32 m radio telescope. The resultant map shows no significant extension from the Hα image. This means that the molecular cloud is less affected by the MHN, suggesting that the molecular cloud did not form by the expanding shock of the MHN. Although the spatial distribution of the Wide-field Infrared Survey Explorer and Two Micron All Sky Survey point sources suggests that triggered low- and intermediate-mass star formation took place locally around S252A, but the exciting star associated with it should be formed spontaneously in the molecular cloud.

  8. A LOW-METALLICITY MOLECULAR CLOUD IN THE LOWER GALACTIC HALO

    SciTech Connect

    Hernandez, Audra K.; Wakker, Bart P.; French, David; Benjamin, Robert A.; Kerp, Juergen; Lockman, Felix J.; O'Toole, Simon; Winkel, Benjamin E-mail: wakker@astro.wisc.edu E-mail: benjamin@astro.wisc.edu E-mail: fjlockman@nrao.edu E-mail: bwinkel@mpifr.de

    2013-11-01

    We find evidence for the impact of infalling, low-metallicity gas on the Galactic disk. This is based on FUV absorption line spectra, 21 cm emission line spectra, and far-infrared (FIR) mapping to estimate the abundance and physical properties of IV21 (IVC135+54-45), a galactic intermediate-velocity molecular cloud that lies ∼300 pc above the disk. The metallicity of IV21 was estimated using observations toward the subdwarf B star PG1144+615, located at a projected distance of 16 pc from the cloud's densest core, by measuring ion and H I column densities for comparison with known solar abundances. Despite the cloud's bright FIR emission and large column densities of molecular gas as traced by CO, we find that it has a sub-solar metallicity of log (Z/Z{sub ☉}) = –0.43 ± 0.12 dex. IV21 is thus the first known sub-solar metallicity cloud in the solar neighborhood. In contrast, most intermediate-velocity clouds (IVC) have near-solar metallicities and are believed to originate in the Galactic Fountain. The cloud's low metallicity is also atypical for Galactic molecular clouds, especially in light of the bright FIR emission which suggest a substantial dust content. The measured I{sub 100{sub μm}}/N(H I) ratio is a factor of three below the average found in high latitude H I clouds within the solar neighborhood. We argue that IV21 represents the impact of an infalling, low-metallicity high-velocity cloud that is mixing with disk gas in the lower Galactic halo.

  9. Internal structure of a cold dark molecular cloud inferred from the extinction of background starlight.

    PubMed

    Alves, J F; Lada, C J; Lada, E A

    2001-01-11

    Stars and planets form within dark molecular clouds, but little is understood about the internal structure of these clouds, and consequently about the initial conditions that give rise to star and planet formation. The clouds are primarily composed of molecular hydrogen, which is virtually inaccessible to direct observation. But the clouds also contain dust, which is well mixed with the gas and which has well understood effects on the transmission of light. Here we use sensitive near-infrared measurements of the light from background stars as it is absorbed and scattered by trace amounts of dust to probe the internal structure of the dark cloud Barnard 68 with unprecedented detail. We find the cloud's density structure to be very well described by the equations for a pressure-confined, self-gravitating isothermal sphere that is critically stable according to the Bonnor-Ebert criteria. As a result we can precisely specify the physical conditions inside a dark cloud on the verge of collapse to form a star. PMID:11196632

  10. Internal structure of a cold dark molecular cloud inferred from the extinction of background starlight.

    PubMed

    Alves, J F; Lada, C J; Lada, E A

    2001-01-11

    Stars and planets form within dark molecular clouds, but little is understood about the internal structure of these clouds, and consequently about the initial conditions that give rise to star and planet formation. The clouds are primarily composed of molecular hydrogen, which is virtually inaccessible to direct observation. But the clouds also contain dust, which is well mixed with the gas and which has well understood effects on the transmission of light. Here we use sensitive near-infrared measurements of the light from background stars as it is absorbed and scattered by trace amounts of dust to probe the internal structure of the dark cloud Barnard 68 with unprecedented detail. We find the cloud's density structure to be very well described by the equations for a pressure-confined, self-gravitating isothermal sphere that is critically stable according to the Bonnor-Ebert criteria. As a result we can precisely specify the physical conditions inside a dark cloud on the verge of collapse to form a star.

  11. Giant Molecular Clouds and Star Formation in the Non-Grand Design Spiral Galaxy NGC 6946

    NASA Astrophysics Data System (ADS)

    Rebolledo, David; Wong, T.; Leroy, A.

    2012-01-01

    Although the internal physical properties of molecular clouds have been extensively studied (Solomon et al. 1987), a more detailed understanding of their origin and evolution in different types of galaxies is needed. In order to disentangle the details of this process, we performed CO(1-0) CARMA observations of the eastern part of the multi-armed galaxy NGC 6946. Although we found no evidence of an angular offset between molecular gas, atomic gas and star formation regions in our observations (Tamburro et al. 2008), we observe a clear radial progression from regions where molecular gas dominates over atomic gas (for r ≤ 2.8 kpc) to regions where the gas becomes mainly atomic (5.6 kpc ≤ r ≤ 7.6 kpc) when azimuthally averaged. In addition, we found that the densest concentrations of molecular gas are located on arms, particularly where they appear to intersect, which is in concordance with the predictions by simulations of the spiral galaxies with an active potential (Clarke & Gittins 2006; Dobbs & Bonnell 2008). At CO(1-0) resolution (140 pc), we were able to find CO emitting complexes with masses greater than those of typical Giant Molecular Clouds (105-106 M⊙). To identify GMCs individually and make a more detailed study of their physical properties, we made D array observations of CO(2-1) toward the densest concentrations of gas, achieving a resolution similar to GMCs sizes found in other galaxies (Bolatto et al. 2008). We present first results about differences in properties of the on-arm clouds and inter-arm clouds. We found that, in general, on-arm clouds present broader line widths, are more massive and more active in star formation than inter-arm clouds. We investigated if the velocity dispersion observed in CO(1-0) emitting complexes reflects velocity differences between unresolved smaller clouds, or if it corresponds to actual internal turbulence of the gas observed.

  12. A Wide Latitude CO Survey of Molecular Clouds in the Northern Milky Way

    NASA Technical Reports Server (NTRS)

    Dame, T. M.; Thaddeus, P.

    1984-01-01

    It is now well established that molecular clouds are an important part of the interstellar medium, containing much or most of the dense, cold component of the gas, and producing the massive stars and supernovae responsible for the diffuse, hot component. It would therefore appear essential in formulating a complete picture of the local interstellar medium to have some knowledge of the distribution and properties of nearly molecular clouds. The Goddard-Columbia 1.2 meter telescope was used to carry out a wide latitude, low angular resolution survey of CO along most of the first galactic quadrant and a small part of the second. A plane-of-the-sky map, which resulted from numerically integrating the survey over radial velocity, is presented. The Great Rift and the Aquila Rift molecular clouds of the Milky Way are discussed.

  13. GIANT MOLECULAR CLOUDS AND STAR FORMATION IN THE TIDAL MOLECULAR ARM OF NGC 4039

    SciTech Connect

    Espada, D.; Komugi, S.; Muller, E.; Nakanishi, K.; Saito, M.; Tatematsu, K.; Iguchi, S.; Hasegawa, T.; Mizuno, N.; Iono, D.; Kawamura, A.; Akiyama, E.; Hiramatsu, M.; Nagai, H.; Miura, R. E.; Matsushita, S.; Trejo, A.; Chapillon, E.; Takahashi, S.; Su, Y. N.; and others

    2012-12-01

    The properties of tidally induced arms provide a means to study molecular cloud formation and the subsequent star formation under environmental conditions which, in principle, are different from quasi-stationary spiral arms. We report the properties of a newly discovered molecular gas arm of likely tidal origin at the south of NGC 4039 and the overlap region in the Antennae galaxies, with a resolution of 1.''68 Multiplication-Sign 0.''85, using the Atacama Large Millimeter/submillimeter Array science verification CO(2-1) data. The arm extends 3.4 kpc (34'') and is characterized by widths of {approx}<200 pc (2'') and velocity widths of typically {Delta}V {approx_equal} 10-20 km s{sup -1}. About 10 clumps are strung out along this structure, most of them unresolved, with average surface densities of {Sigma}{sub gas} {approx_equal} 10-100 M{sub Sun} pc{sup -2}, and masses of (1-8) Multiplication-Sign 10{sup 6} M{sub Sun }. These structures resemble the morphology of beads on a string, with an almost equidistant separation between the beads of about 350 pc, which may represent a characteristic separation scale for giant molecular associations. We find that the star formation efficiency at a resolution of 6''(600 pc) is in general a factor of 10 higher than in disk galaxies and other tidal arms and bridges. This arm is linked, based on the distribution and kinematics, to the base of the western spiral arm of NGC 4039, but its morphology is different to that predicted by high-resolution simulations of the Antennae galaxies.

  14. Cluster-formation in the Rosette molecular cloud at the junctions of filaments

    NASA Astrophysics Data System (ADS)

    Schneider, N.; Csengeri, T.; Hennemann, M.; Motte, F.; Didelon, P.; Federrath, C.; Bontemps, S.; Di Francesco, J.; Arzoumanian, D.; Minier, V.; André, Ph.; Hill, T.; Zavagno, A.; Nguyen-Luong, Q.; Attard, M.; Bernard, J.-Ph.; Elia, D.; Fallscheer, C.; Griffin, M.; Kirk, J.; Klessen, R.; Könyves, V.; Martin, P.; Men'shchikov, A.; Palmeirim, P.; Peretto, N.; Pestalozzi, M.; Russeil, D.; Sadavoy, S.; Sousbie, T.; Testi, L.; Tremblin, P.; Ward-Thompson, D.; White, G.

    2012-04-01

    Aims: For many years feedback processes generated by OB-stars in molecular clouds, including expanding ionization fronts, stellar winds, or UV-radiation, have been proposed to trigger subsequent star formation. However, hydrodynamic models including radiation and gravity show that UV-illumination has little or no impact on the global dynamical evolution of the cloud. Instead, gravitational collapse of filaments and/or merging of filamentary structures can lead to building up dense high-mass star-forming clumps. However, the overall density structure of the cloud has a large influence on this process, and requires a better understanding. Methods: The Rosette molecular cloud, irradiated by the NGC 2244 cluster, is a template region for triggered star-formation, and we investigated its spatial and density structure by applying a curvelet analysis, a filament-tracing algorithm (DisPerSE), and probability density functions (PDFs) on Herschel column density maps, obtained within the HOBYS key program. Results: The analysis reveals not only the filamentary structure of the cloud but also that all known infrared clusters except one lie at junctions of filaments, as predicted by turbulence simulations. The PDFs of sub-regions in the cloud show systematic differences. The two UV-exposed regions have a double-peaked PDF we interprete as caused by shock compression, while the PDFs of the center and other cloud parts are more complex, partly with a power-law tail. A deviation of the log-normal PDF form occurs at AV ≈ 9m for the center, and around 4m for the other regions. Only the part of the cloud farthest from the Rosette nebula shows a log-normal PDF. Conclusions: The deviations of the PDF from the log-normal shape typically associated with low- and high-mass star-forming regions at AV ≈ 3-4m and 8-10m, respectively, are found here within the very same cloud. This shows that there is no fundamental difference in the density structure of low- and high-mass star

  15. Fluorescent whitening agents in Tokyo Bay and adjacent rivers: their application as anthropogenic molecular markers in coastal environments.

    PubMed

    Hayashi, Yuko; Managaki, Satoshi; Takada, Hideshige

    2002-08-15

    Two kinds of stilbene-type fluorescent whitening agents (i.e., DSBP and DAS1), minor components of laundry detergents, were analyzed in surface waters of Tokyo Bay and adjacent rivers and in sewage effluents to examine their usefulness as molecular markers in the marine environment. Sensitive determination using HPLC (high performance liquid chromatography) with fluorescence detection with postcolumn UV radiator was employed. DSBP and DAS1 were found in Tokyo rivers at concentrations of a few microg/L and approximately 1 microg/L, respectively. DSBP and DAS1 were widely distributed in Tokyo Bay waters at concentrations in the range of 0.019-0.264 microg/L and 0.021-0.127 microg/L, respectively. Comparison of these concentrations with those in sewage effluents (DSBP: 8 microg/L and DAS1: 2.5 microg/L on average) yielded sewage dilutions in Tokyo Bay on the order of 10(2). FWAs-salinity diagram in the Tamagawa Estuary showed fairly conservative behaviors of the FWAs with approximately 20% and approximately 10% removal of DSBP and DAS1, respectively. This is thought to be caused by photodegradation. The persistent nature of FWAs and their widespread distribution in coastal environments demonstrates the utility of FWAs in tracing the behavior of water from rivers and sewage outfalls. The DSBP/DAS1 ratio showed a decreasing trend from sewage effluents, to rivers, to Tokyo Bay, indicating selective photodegradation of DSBP. The DSBP/DAS1 ratio is proposed as an index of the degree of photodegradation and residence time and freshness of water mass in coastal environments.

  16. Analysis of Bell Laboratories tco Galactic Plane Survey: List of Molecular Clouds and Clumps

    NASA Astrophysics Data System (ADS)

    Lee, Y.; Stark, A.

    Using the Bell Laboratories Galactic plane survey in the J=1-0 transition of 13CO, (l, b) = (-5o to 117o, -1o to +1o), and our cloud identification code, 13CO clouds have been identified and cataloged as a function of threshold temperature. We identified 1400 of molecular clouds with 1 K threshold temperature and with a 4-pixel threshold, 629 clouds with 2 K threshold temperature, and 263 clouds with 3 K. Clouds with the hottest cores (TR*( 13CO) > 3 K) are confined to the 6 kpc Molecular Ring (l<40o) and l=80o region. In addition to cloud identification, cloud core regions can also be located within the cloud complex. Dense core regions are also located using this 13CO survey and then combined with existing UMass-Stony Brook 13CO data for the first quadrant of the Galactic Plane (l, b) = (+8o to 89o.9, -1o to +1o). The optical depth of 13CO is estimated for each channel and pixel from the ratio of the 13CO and 13CO brightness assuming LTE. We also estimate the column density channel by channel (with a velocity step of 1 km s-1) with the LTE assumption, generating the column density cube data for the first quadrant of the Galactic Plane. The highest column density (a lower limit) is estimated to be 9.3×1016 cm-2 (km s-1)-1, which is one of the densest parts of the Galactic Ring region.

  17. Dynamical evolution and molecular abundances of interstellar clouds

    NASA Technical Reports Server (NTRS)

    Prasad, Sheo S.; Heere, Karen R.; Tarafdar, Shankar P.

    1991-01-01

    Dynamical models are presented that start with interstellar gas in an initial diffuse state and consider their gravitational collapse and the formation of dense cores. Frozen-in tangled magnetic fields are included to mimic forces that might oppose gravitational contraction and whose effectiveness may increase with increasing core densities. Results suggest the possibility that dense cloud cores may be dynamically evolving ephemeral objects, such that their lifespan at a given core density decreases as that density increases.

  18. Discovery of molecular hydrogen in a high-velocity cloud of the Galactic halo.

    PubMed

    Richter, P; de Boer, K S; Widmann, H; Kappelmann, N; Gringel, W; Grewing, M; Barnstedt, J

    1999-11-25

    The Milky Way's halo contains clouds of neutral hydrogen with high radial velocities which do not follow the general rotational motion of the Galaxy. Few distances to these high-velocity clouds are known, so even gross properties such as total mass are hard to determine. As a consequence, there is no generally accepted theory regarding their origin. One idea is that they result from gas that has cooled after being ejected from the Galaxy through fountain-like flows powered by supernovae; another is that they are composed of gas, poor in heavy elements, which is falling onto the disk of the Milky Way from intergalactic space. The presence of molecular hydrogen, whose formation generally requires the presence of dust (and therefore gas, enriched in heavy elements), could help to distinguish between these possibilities. Here we report the discovery of molecular hydrogen absorption in a high-velocity cloud along the line of sight to the Large Magellanic Cloud. We also derive for the same cloud an iron abundance which is half of the solar value. From these data, we conclude that gas in this cloud originated in the disk of the Milky Way.

  19. Ambiguities in the identification of giant molecular cloud complexes from longitude-velocity diagrams

    NASA Technical Reports Server (NTRS)

    Adler, David S.; Roberts, William W., Jr.

    1992-01-01

    Techniques which use longitude-velocity diagrams to identify molecular cloud complexes in the disk of the Galaxy are investigated by means of model Galactic disks generated from N-body cloud-particle simulations. A procedure similar to the method used to reduce the low-level emission in Galactic l-v diagrams is employed to isolate complexes of emission in the model l-v diagram (LVCs) from the 'background'clouds. The LVCs produced in this manner yield a size-line-width relationship with a slope of 0.58 and a mass spectrum with a slope of 1.55, consistent with Galactic observations. It is demonstrated that associations identified as LVCs are often chance superpositions of clouds spread out along the line of sight in the disk of the model system. This indicates that the l-v diagram cannot be used to unambiguously determine the location of molecular cloud complexes in the model Galactic disk. The modeling results also indicate that the existence of a size-line-width relationship is not a reliable indicator of the physical nature of cloud complexes, in particular, whether the complexes are gravitationally bound objects.

  20. STAR FORMATION RATES IN MOLECULAR CLOUDS AND THE NATURE OF THE EXTRAGALACTIC SCALING RELATIONS

    SciTech Connect

    Lada, Charles J.; Forbrich, Jan; Lombardi, Marco; Alves, Joao F. E-mail: jforbrich@cfa.harvard.edu E-mail: joao.alves@univie.ac.at

    2012-02-01

    In this paper, we investigate scaling relations between star formation rates and molecular gas masses for both local Galactic clouds and a sample of external galaxies. We specifically consider relations between the star formation rates and measurements of dense, as well as total, molecular gas masses. We argue that there is a fundamental empirical scaling relation that directly connects the local star formation process with that operating globally within galaxies. Specifically, the total star formation rate in a molecular cloud or galaxy is linearly proportional to the mass of dense gas within the cloud or galaxy. This simple relation, first documented in previous studies, holds over a span of mass covering nearly nine orders of magnitude and indicates that the rate of star formation is directly controlled by the amount of dense molecular gas that can be assembled within a star formation complex. We further show that the star formation rates and total molecular masses, characterizing both local clouds and galaxies, are correlated over similarly large scales of mass and can be described by a family of linear star formation scaling laws, parameterized by f{sub DG}, the fraction of dense gas contained within the clouds or galaxies. That is, the underlying star formation scaling law is always linear for clouds and galaxies with the same dense gas fraction. These considerations provide a single unified framework for understanding the relation between the standard (nonlinear) extragalactic Schmidt-Kennicutt scaling law, that is typically derived from CO observations of the gas, and the linear star formation scaling law derived from HCN observations of the dense gas.

  1. DETECTION OF STAR FORMATION IN THE UNUSUALLY COLD GIANT MOLECULAR CLOUD G216-2.5

    SciTech Connect

    Megeath, S. T.; Allgaier, E.; Allen, T.; Young, E.; Pipher, J. L.; Wilson, T. L.

    2009-04-15

    The giant molecular cloud G216-2.5, also known as Maddalena's cloud or the Maddalena-Thaddeus cloud, is distinguished by an unusual combination of high gas mass (1-6 x 10{sup 5} M {sub sun}), low kinetic temperatures (10 K), and the lack of bright far-IR emission. Although star formation has been detected in neighboring satellite clouds, little evidence for star formation has been found in the main body of this cloud. Using a combination of mid-IR observations with the IRAC and Multiband Imaging Photometer for Spitzer instruments onboard the Spitzer Space Telescope, and near-IR images taken with the Flamingos camera on the KPNO 2.1 m telescope, we identify a population of 41 young stars with disks and 33 protostars in the center of the cloud. Most of the young stellar objects are coincident with a filamentary structure of dense gas detected in CS (2 {yields} 1). These observations show that the main body of G216 is actively forming stars, although at a low stellar density comparable to that found in the Taurus cloud.

  2. Detection of Star Formation in the Unusually Cold Giant Molecular Cloud G216-2.5

    NASA Astrophysics Data System (ADS)

    Megeath, S. T.; Allgaier, E.; Young, E.; Allen, T.; Pipher, J. L.; Wilson, T. L.

    2009-04-01

    The giant molecular cloud G216-2.5, also known as Maddalena's cloud or the Maddalena-Thaddeus cloud, is distinguished by an unusual combination of high gas mass (1-6 × 105 M sun), low kinetic temperatures (10 K), and the lack of bright far-IR emission. Although star formation has been detected in neighboring satellite clouds, little evidence for star formation has been found in the main body of this cloud. Using a combination of mid-IR observations with the IRAC and Multiband Imaging Photometer for Spitzer instruments onboard the Spitzer Space Telescope, and near-IR images taken with the Flamingos camera on the KPNO 2.1 m telescope, we identify a population of 41 young stars with disks and 33 protostars in the center of the cloud. Most of the young stellar objects are coincident with a filamentary structure of dense gas detected in CS (2 → 1). These observations show that the main body of G216 is actively forming stars, although at a low stellar density comparable to that found in the Taurus cloud. Based on observations made with ESO telescopes at the La Silla Observatory.

  3. Studying the Formation and Development of Molecular Clouds: With the CCAT Heterodyne Array Instrument (CHAI)

    NASA Technical Reports Server (NTRS)

    Goldsmith, Paul F.

    2012-01-01

    Surveys of all different types provide basic data using different tracers. Molecular clouds have structure over a very wide range of scales. Thus, "high resolution" surveys and studies of selected nearby clouds add critical information. The combination of large-area and high resolution allows Increased spatial dynamic range, which in turn enables detection of new and perhaps critical morphology (e.g. filaments). Theoretical modeling has made major progress, and suggests that multiple forces are at work. Galactic-scale modeling also progressing - indicates that stellar feedback is required. Models must strive to reproduce observed cloud structure at all scales. Astrochemical observations are not unrelated to questions of cloud evolution and star formation but we are still learning how to use this capability.

  4. The dependence of star formation on initial conditions and molecular cloud structure

    NASA Astrophysics Data System (ADS)

    Bate, Matthew R.

    2009-07-01

    We investigate the dependence of stellar properties on the initial kinematic structure of the gas in star-forming molecular clouds. We compare the results from two large-scale hydrodynamical simulations of star cluster formation that resolve the fragmentation process down to the opacity limit, the first of which was reported by Bate, Bonnell & Bromm. The initial conditions of the two calculations are identical, but in the new simulation the power spectrum of the velocity field imposed on the cloud initially and allowed to decay is biased in favour of large-scale motions. Whereas the calculation of Bate et al. began with a power spectrum P(k) ~ k-4 to match the Larson scaling relations for the turbulent motions observed in molecular clouds, the new calculation begins with a power spectrum P(k) ~ k-6. Despite this change to the initial motions in the cloud and the resulting density structure of the molecular cloud, the stellar properties resulting from the two calculations are indistinguishable. This demonstrates that the results of such hydrodynamical calculations of star cluster formation are relatively insensitive to the initial conditions. It is also consistent with the fact that the statistical properties of stars and brown dwarfs (e.g. the stellar initial mass function) are observed to be relatively invariant within our Galaxy and do not appear to depend on environment.

  5. Magnetohydrodynamic simulations of a jet drilling an H I cloud: Shock induced formation of molecular clouds and jet breakup

    SciTech Connect

    Asahina, Yuta; Ogawa, Takayuki; Matsumoto, Ryoji; Kawashima, Tomohisa; Furukawa, Naoko; Enokiya, Rei; Yamamoto, Hiroaki; Fukui, Yasuo

    2014-07-01

    The formation mechanism of the jet-aligned CO clouds found by NANTEN CO observations is studied by magnetohydrodynamical (MHD) simulations taking into account the cooling of the interstellar medium. Motivated by the association of the CO clouds with the enhancement of H I gas density, we carried out MHD simulations of the propagation of a supersonic jet injected into the dense H I gas. We found that the H I gas compressed by the bow shock ahead of the jet is cooled down by growth of the cooling instability triggered by the density enhancement. As a result, a cold dense sheath is formed around the interface between the jet and the H I gas. The radial speed of the cold, dense gas in the sheath is a few km s{sup –1} almost independent of the jet speed. Molecular clouds can be formed in this region. Since the dense sheath wrapping the jet reflects waves generated in the cocoon, the jet is strongly perturbed by the vortices of the warm gas in the cocoon, which breaks up the jet and forms a secondary shock in the H I-cavity drilled by the jet. The particle acceleration at the shock can be the origin of radio and X-ray filaments observed near the eastern edge of the W50 nebula surrounding the galactic jet source SS433.

  6. The effects of flow-inhomogeneities on molecular cloud formation: Local versus global collapse

    SciTech Connect

    Carroll-Nellenback, Jonathan J.; Frank, Adam; Heitsch, Fabian

    2014-07-20

    Observational evidence from local star-forming regions mandates that star formation occurs shortly after, or even during, molecular cloud formation. Models of molecular cloud formation in large-scale converging flows have identified the physical mechanisms driving the necessary rapid fragmentation. They also point to global gravitational collapse driving supersonic turbulence in molecular clouds. Previous cloud formation models have focused on turbulence generation, gravitational collapse, magnetic fields, and feedback. Here, we explore the effect of structure in the flow on the resulting clouds and the ensuing gravitational collapse. We compare two extreme cases, one with a collision between two smooth streams, and one with streams containing small clumps. We find that structured converging flows lead to a delay of local gravitational collapse ({sup c}ore formation{sup )}. Hence, the cloud has more time to accumulate mass, eventually leading to a strong global collapse, and thus to a high core formation rate. Uniform converging flows fragment hydrodynamically early on, leading to the rapid onset of local gravitational collapse and an overall low core formation rate. This is also mirrored in the core mass distribution: the uniform initial conditions lead to more low-mass cores than the clumpy initial conditions. Kinetic (E{sub k} ) and gravitational energy (E{sub g} ) budgets suggest that collapse is only prevented for E{sub k} >> E{sub g} , which occurs for large scales in the smooth flow, and for small scales for the clumpy flow. Whenever E{sub k} ≈ E{sub g} , we observe gravitational collapse on those scales. Signatures of chemical abundance variations evolve differently for the gas phase and for the stellar population. For smooth flows, the forming cloud is well mixed, while its stellar population retains more information about the initial metallicities. For clumpy flows, the gas phase is less well mixed, while the stellar population has lost most of the

  7. Broad-wing molecular lines without internal energy sources. [in interstellar clouds

    NASA Technical Reports Server (NTRS)

    Blitz, Leo; Magnani, Loris; Wandel, Amri

    1988-01-01

    The discovery of broad CO wings in four high-latitude molecular clouds which do not have associated internal energy sources is reported. The velocity width of the wings is as much as five times greater than the width of the cloud cores. Neither visible stars brighter than the background population, optical nebulosity, nor IRAS point sources are found at the position of the wings, except for one case with an IRAS source 3 arcmin from the peak position of the wings. The possibility that the wings are the result of conductive interfaces resulting from cold molecular clouds in a hotter ambient medium is examined, and it is concluded that the expected column density of such gas is more than three orders of magnitude smaller than that observed.

  8. Cold Atomic Hydrogen, Narrow Self-Absorption, and the Age of Molecular Clouds

    NASA Technical Reports Server (NTRS)

    Goldsmith, Paul F.

    2006-01-01

    This viewgraph presentation reviews the history, and current work on HI and its importance in star formation. Through many observations of HI Narrow Self Absorption (HINSA) the conclusions are drawn and presented. Local molecular clouds have HI well-mixed with molecular constituents This HI is cold, quiescent, and must be well-shielded from the UV radiation field The density and fractional abundance (wrt H2) of the cold HI are close to steady state values The time required to convert these starless clouds from purely HI initial state to observed present composition is a few to ten million years This timescale is a lower limit - if dense clouds being swept up from lower density regions by shocks, the time to accumulate material to get A(sub v) is approximately 1 and provide required shielding may be comparable or longer

  9. Optical observations related to the molecular chemistry in diffuse interstellar clouds

    NASA Technical Reports Server (NTRS)

    Federman, S. R.

    1987-01-01

    Observations, which have been published since 1979, of molecular species in diffuse clouds are discussed. Particular attention is given to the ultraviolet measurements of CO with the Copernicus and IUE satellites and to ground-based optical measurements of CH, CH(+), CN, and 02. These data encompass large enough samples to test the chemical schemes expected to occur in diffuse clouds. Upper limits for other species (e.g., H2O, H2O(+), and C3) place restrictions on the pathways for molecular production. Moreover, analysis of the rotational distribution of the C2 molecule results in the determination of the physical conditions of the cloud. These parameters, including density, temperature, and the intensity of the radiation field, are necessary for modeling the chemistry.

  10. CO at Low-metallicity: Molecular Clouds in the dwarf galaxy WLM

    NASA Astrophysics Data System (ADS)

    Hunter, Deidre Ann; Rubio, Monica; Cigan, Phil; Cortes, Juan R.; Elmegreen, Bruce; Brinks, Elias; Simpson, Caroline E.; Young, Lisa

    2015-01-01

    Metallicity is not a passive result of galaxy evolution, but a crucial driver. Dwarf galaxies are low in heavy elements, which has important consequences for the ability to form cold, dense clouds that form stars. Molecular cores shrink and atomic envelopes grow in star-forming clouds as the metallicity drops. We are testing this picture of changing structure with metallicity with Herschel [CII]158 micron images of the photo-dissociation regions and ALMA maps of CO in star-forming regions in 4 dwarf irregular galaxies. These galaxies cover a range in metallicity from 13% solar to 5% solar. Here we report on the structure of the molecular clouds in WLM, a dwarf galaxy at 13% solar abundance where we for the first time detected CO emission at such a low heavy element abundance.The Herschel part of this work was supported by grant RSA #1433776 from JPL.

  11. Star formation efficiencies of molecular clouds in a galactic centre environment

    NASA Astrophysics Data System (ADS)

    Bertram, Erik; Glover, Simon C. O.; Clark, Paul C.; Klessen, Ralf S.

    2015-08-01

    We use the AREPO moving mesh code to simulate the evolution of molecular clouds exposed to a harsh environment similar to that found in the galactic centre (GC), in an effort to understand why the star formation efficiency (SFE) of clouds in this environment is so small. Our simulations include a simplified treatment of time-dependent chemistry and account for the highly non-isothermal nature of the gas and the dust. We model clouds with a total mass of 1.3 × 105 M⊙ and explore the effects of varying the mean cloud density and the virial parameter, α = Ekin/|Epot|. We vary the latter from α = 0.5 to 8.0, and so many of the clouds that we simulate are gravitationally unbound. We expose our model clouds to an interstellar radiation field (ISRF) and cosmic ray flux (CRF) that are both a factor of 1000 higher than the values found in the solar neighbourhood. As a reference, we also run simulations with local solar neighbourhood values of the ISRF and the CRF in order to better constrain the effects of the extreme conditions in the GC on the SFE. Despite the harsh environment and the large turbulent velocity dispersions adopted, we find that all of the simulated clouds form stars within less than a gravitational free-fall time. Increasing the virial parameter from α = 0.5 to 8.0 decreases the SFE by a factor of ˜4-10, while increasing the ISRF/CRF by a factor of 1000 decreases the SFE again by a factor of ˜2-6. However, even in our most unbound clouds, the SFE remains higher than that inferred for real GC clouds. We therefore conclude that high levels of turbulence and strong external heating are not enough by themselves to lead to a persistently low SFE at the centre of the Galaxy.

  12. Red Fluorescent Line Emission from Hydrogen Molecules in Diffuse Molecular Clouds

    NASA Technical Reports Server (NTRS)

    Neufeld, David A.; Spaans, Marco

    1996-01-01

    We have modeled the fluorescent pumping of electronic and vibrational emissions of molecular hydrogen (H2) within diffuse molecular clouds that are illuminated by ultraviolet continuum radiation. Fluorescent line intensities are predicted for transitions at ultraviolet, infrared, and red visible wavelengths as functions of the gas density, the visual extinction through the cloud, and the intensity of the incident UV continuum radiation. The observed intensity in each fluorescent transition is roughly proportional to the integrated rate of H2 photodissociation along the line of sight. Although the most luminous fluorescent emissions detectable from ground-based observatories lie at near-infrared wavelengths, we argue that the lower sky brightness at visible wavelengths makes the red fluorescent transitions a particularly sensitive probe. Fabry-Perot spectrographs of the type that have been designed to observe very faint diffuse Ha emissions are soon expected to yield sensitivities that will be adequate to detect H2 vibrational emissions from molecular clouds that are exposed to ultraviolet radiation no stronger than the mean radiation field within the Galaxy. Observations of red H2 fluorescent emission together with cospatial 21 cm H I observations could serve as a valuable probe of the gas density in diffuse molecular clouds.

  13. A study of the clumpiness in the Monoceros R2 molecular cloud

    NASA Astrophysics Data System (ADS)

    1996-04-01

    The study of clumpiness in the Monoceros R2 molecular cloud, and attempts to investigate the use of dust emission as well as gas tracers to study this, are addressed. A progress in developing the technique of dust temperature distribution by inversion of the emitted spectrum using the Mobius theorem is reported.

  14. The magnetic evolution of the Taurus molecular clouds. I - Large-scale properties

    NASA Astrophysics Data System (ADS)

    Heyer, Mark H.; Vrba, Frederick J.; Snell, Ronald L.; Schloerb, F. P.; Strom, Stephen E.; Goldsmith, Paul F.; Strom, Karen M.

    1987-10-01

    Finely sampled maps of the (C-13)O J = 1-0 emission from five dark clouds within the Taurus molecular cloud complex were made, and polarization measurements of the optical emission were obtained from background and embedded stars to determine the direction of the interstellar magnetic field towards these regions. The clouds are found to have flattened morphologies with the direction of their minor axis parallel to the direction of the magnetic field, as expected if the lateral contraction of the gas is inhibited by magnetic pressures. In addition, each cloud appears to be rotating about an axis parallel to the magnetic field direction as predicted by detailed calculations of the magnetic braking process. It is believed that the magnetic field has played a significant part in the evolution of these regions, which are characterized by mean densities of about 1000-5000/cu cm. In addition, the clouds are determined to be in virial equilibrium based on the extent and mean line-width of (C-13)O J = 1-0 emission and the masses derived from molecular hydrogen column densities.

  15. Molecular cloud/HII region interfaces in the star forming region NGC 6357.

    NASA Astrophysics Data System (ADS)

    Massi, F.; Brand, J.; Felli, M.

    1997-04-01

    We have performed ^12^CO(1-0), ^12^CO(2-1), ^13^CO(1-0), ^13^CO(2-1), C^18^O(1-0), C^18^O(2-1), HCO^+^(1-0) and H^13^CO^+^(1-0) observations towards two selected areas in the star forming complex NGC 6357 with angular resolutions from 21" to 55". In particular, we have mapped the molecular gas around the two HII regions G353.1+0.6 and G353.2+0.9 in the ^12^CO(1-0) and ^13^CO(1-0) transitions with a resolution of ~43". This improves on the coarser ^12^CO(1-0) observations previously carried out by others. We have also studied the physical properties of gas along strips through the molecular cloud/HII region interfaces. For G353.1+0.6, the observations confirm that an ionization front is eroding a warm, dense molecular cloud located to the north of the optical nebula. The molecular gas appears fragmented on a scale size >0.5pc and not all the components are related to the HII region. There is evidence of a density increase near the front and indications of temperature gradients toward the exciting stars. This is further suggested by the presence of ^12^CO(1-0) self-absorption produced by a cooler external layer. The isotopic ratio X(^13^CO)/X(C^18^O) decreases from the inner part of the clouds towards the front, contrary to what is theoretically predicted and observed in many other regions. This may be due to excitation or optical depths effects. An evolutionary scenario is proposed where the exciting stars form at the edge of a molecular cloud. The morphology of G353.2+0.9 is rather different from what previously believed. Only a weak "bar" of molecular material was found to the south of the sharp ionization front observed optically and in the radio-continuum, and most of the molecular emission arises from regions behind or to the north of the HII region. This indicates that we are viewing a late stage "blister" configuration face-on. This region is fragmented on a scale size >0.5pc, and a warm, dense and compact molecular fragment coincides with the elephant trunk

  16. The James Clerk Maxwell telescope Legacy Survey of the Gould Belt: a molecular line study of the Ophiuchus molecular cloud

    NASA Astrophysics Data System (ADS)

    White, Glenn J.; Drabek-Maunder, Emily; Rosolowsky, Erik; Ward-Thompson, Derek; Davis, C. J.; Gregson, Jon; Hatchell, Jenny; Etxaluze, Mireya; Stickler, Sarah; Buckle, Jane; Johnstone, Doug; Friesen, Rachel; Sadavoy, Sarah; Natt, Kieran. V.; Currie, Malcolm; Richer, J. S.; Pattle, Kate; Spaans, Marco; Francesco, James Di; Hogerheijde, M. R.

    2015-02-01

    CO, 13CO, and C18O J = 3-2 observations are presented of the Ophiuchus molecular cloud. The 13CO and C18O emission is dominated by the Oph A clump, and the Oph B1, B2, C, E, F, and J regions. The optically thin(ner) C18O line is used as a column density tracer, from which the gravitational binding energy is estimated to be 4.5 × 1039 J (2282 M⊙ km2 s-2). The turbulent kinetic energy is 6.3 × 1038 J (320 M⊙ km2 s-2), or seven times less than this, and therefore the Oph cloud as a whole is gravitationally bound. 30 protostars were searched for high-velocity gas, with 8 showing outflows, and 20 more having evidence of high-velocity gas along their lines of sight. The total outflow kinetic energy is 1.3 × 1038 J (67 M⊙ km2 s-2), corresponding to 21 per cent of the cloud's turbulent kinetic energy. Although turbulent injection by outflows is significant, but does not appear to be the dominant source of turbulence in the cloud. 105 dense molecular clumplets were identified, which had radii ˜0.01-0.05 pc, virial masses ˜0.1-12 M⊙, luminosities ˜0.001-0.1 K km s-1 pc-2, and excitation temperatures ˜10-50 K. These are consistent with the standard Giant Molecular Cloud (GMC) based size-linewidth relationships, showing that the scaling laws extend down to size scales of hundredths of a parsec, and to subsolar-mass condensations. There is however no compelling evidence that the majority of clumplets are undergoing free-fall collapse, nor that they are pressure confined.

  17. X-Ray Shadows by High-latitude Molecular Clouds. I. Cartography

    NASA Astrophysics Data System (ADS)

    Kuntz, K. D.; Snowden, S. L.; Verter, F.

    1997-07-01

    We have observed X-ray shadowing by nine nearby high-latitude molecular clouds with the ROSAT PSPC. The 1/4 keV emission from the Local Bubble is used to calculate an average electron density, ne, toward all of our sample clouds. Given the uniformity of emission within the Local Bubble, and previously determined cloud distances, one can determine whether the clouds are within or without the Local Bubble. We confirm that three of the sample clouds, MBM 12, MBM 16, and possibly MBM 20, which have been thought to be within the Local Bubble, are actually within. A combination of 1/4 keV and ne measures suggest that MBM 6 and LDN 1563 may also lie within the Local Bubble or its boundary layer. The shadows cast by the clouds at 3/4 keV and 1.5 keV imply little if any foreground emission in those bands, and produce lower limits for the distance to the hotter emission component responsible for the observed flux. The results are in agreement with previous estimates for the distances to the Loop I Bubble and the Eridion Bubble.

  18. Diversity of extrasolar planets and diversity of molecular cloud cores. I. Semimajor axes

    SciTech Connect

    Jin, Liping; Li, Min E-mail: minli09@mails.jlu.edu.cn

    2014-03-01

    We show that the diversity of extrasolar planetary systems may be related to the diversity of molecular cloud cores. In previous studies of planet formation, artificial initial conditions of protoplanetary disks or steady state disks, such as the minimum mass nebula model, have often been used so that the influence of cloud core properties on planet formation is not realized. To specifically and quantitatively demonstrate our point, we calculate the dependence of disk properties on cloud core properties and show that the boundary of the giant planet formation region in a disk is a function of cloud core properties with the conventional core accretion model of giant planet formation. The gravitational stability of a disk depends on the properties of its progenitor cloud core. We also compare our calculations with observations of extrasolar planets. From the observational data of cloud cores, our model could infer the range and most frequent values of observed semimajor axes of extrasolar planets. Our calculations suggest that planet formation at the snowline alone could not completely explain the semimajor axis distribution. If the current observations are not biased, our calculations indicate that the planet formation at the snowline is inefficient. We suggest that there will be more observed planets with semimajor axis <9 AU than >9 AU, even with a longer duration of observations, if the planet formation at the snowline is inefficient.

  19. A low fraction of nitrogen in molecular form in a dark cloud.

    PubMed

    Maret, S; Bergin, E A; Lada, C J

    2006-07-27

    Nitrogen is the fifth most abundant element in the Universe. In the interstellar medium, it has been thought to be mostly molecular (N2). However, N2 has no observable rotational or vibrational transitions, so its abundance in the interstellar medium remains poorly known. In comets, the N2 abundance is very low, while the elemental nitrogen abundance is deficient with respect to the solar value. Moreover, large nitrogen isotopic anomalies are observed in meteorites and interstellar dust particles. Here we report the N2H+ (and by inference the N2) abundance inside a cold dark molecular cloud. We find that only a small fraction of nitrogen in the gas phase is molecular, with most of it being atomic. Because the compositions of comets probably reflect those of dark clouds, this result explains the low N2 abundance in comets. We argue that the elemental nitrogen abundance deficiency in comets can be understood if the atomic oxygen abundance is lower than predicted by present chemical models. Furthermore, the lack of molecular nitrogen in molecular clouds explains the nitrogen anomalies in meteorites and interstellar dust particles, as nitrogen fractionation is enhanced if gaseous nitrogen is atomic.

  20. Numerical Simulations of Turbulent Molecular Clouds Regulated by Reprocessed Radiation Feedback from Nascent Super Star Clusters

    NASA Astrophysics Data System (ADS)

    Skinner, M. Aaron; Ostriker, Eve C.

    2015-08-01

    Radiation feedback from young star clusters embedded in giant molecular clouds (GMCs) is believed to be important to the control of star formation. For the most massive and dense clouds, including those in which super star clusters (SSCs) are born, pressure from reprocessed radiation exerted on dust grains may disperse a significant portion of the cloud mass back into the interstellar medium. Using our radiation hydrodynamics code, Hyperion, we conduct a series of numerical simulations to test this idea. Our models follow the evolution of self-gravitating, strongly turbulent clouds in which collapsing regions are replaced by radiating sink particles representing stellar clusters. We evaluate the dependence of the star formation efficiency (SFE) on the size and mass of the cloud and κ, the opacity of the gas to infrared (IR) radiation. We find that the single most important parameter determining the evolutionary outcome is κ, with κ ≳ 15 cm2 g-1 needed to disrupt clouds. For κ =20-40 cm2 g-1, the resulting SFE = 50%-70% is similar to empirical estimates for some SSC-forming clouds. The opacities required for GMC disruption likely apply only in dust-enriched environments. We find that the subgrid model approach of boosting the direct radiation force L/c by a “trapping factor” equal to a cloud's mean IR optical depth can overestimate the true radiation force by factors of ∼ 4-5. We conclude that feedback from reprocessed IR radiation alone is unlikely to significantly reduce star formation within GMCs unless their dust abundances or cluster light-to-mass ratios are enhanced.

  1. Warm neutral halos around molecular clouds. V - OH (1665 and 1667 MHz) observations

    NASA Technical Reports Server (NTRS)

    Wannier, Peter G.; Andersson, B.-G.; Federman, S. R.; Lewis, B. M.; Viala, Y. P.; Shaya, E.

    1993-01-01

    Ten strip maps of 1665- and 1667-MHz OH emission, traversing the outer boundaries of five molecular clouds, were made. The OH emission is found to be significantly extended relative to CO, from which it inferred that OH is to be found in abundance in the shell of partly atomic, partly molecular gas surrounding the dense molecular clouds. The fractional OH abundance is calculated using existing H I and CO observations, and detailed source models which include a complete chemistry network and a radiative transfer code. It is concluded that the extended OH is formed, not by the exothermic reaction of O with H3(+), but by the endothermic reaction, H(+) + O yields H + O(+).

  2. IMAGING OF THE CCS 22.3 GHz EMISSION IN THE TAURUS MOLECULAR CLOUD COMPLEX

    SciTech Connect

    Roy, Nirupam; Momjian, Emmanuel; Datta, Abhirup; Sarma, Anuj P.

    2011-09-20

    Thioxoethenylidene (CCS) is an abundant interstellar molecule and a good tracer of high density and evolutionary stage of dense molecular clouds. It is also a suitable candidate for Zeeman splitting observations for its high splitting factor and narrow thermal line widths. We report here Expanded Very Large Array 22.3 GHz observations of three dense molecular cores TMC-1, TMC-1C, and L1521B in the Taurus molecular cloud complex to image the CCS 2{sub 1}-1{sub 0} transition. For all three sources, the clumpy CCS emission is most likely tracing the starless cores. However, these compact structures account for only {approx}1%-13% of the integrated emission detected in single-dish observations, indicating the presence of significant large-scale diffuse emission in favorable conditions for producing CCS.

  3. Formation of Pillars at the Boundaries between H II Regions and Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Mizuta, Akira; Kane, Jave O.; Pound, Marc W.; Remington, Bruce A.; Ryutov, Dmitri D.; Takabe, Hideaki

    2006-08-01

    We investigate numerically the hydrodynamic instability of an ionization front (IF) accelerating into a molecular cloud, with imposed initial perturbations of different amplitudes. When the initial amplitude is small, the imposed perturbation is completely stabilized and does not grow. When the initial perturbation amplitude is large enough, roughly, the ratio of the initial amplitude to wavelength is greater than 0.02, portions of the IF temporarily separate from the molecular cloud surface, locally decreasing the ablation pressure. This causes the appearance of a large, warm H I region and triggers nonlinear dynamics of the IF. The local difference of the ablation pressure and acceleration enhances the appearance and growth of a multimode perturbation. The stabilization usually seen at the IF in the linear regime does not work due to the mismatch of the modes of the perturbations at the cloud surface and of the density in the H II region above the cloud surface. Molecular pillars are observed in the late stages of the large amplitude perturbation case. The velocity gradient in the pillars is in reasonably good agreement with that observed in the Eagle Nebula. The initial perturbation is imposed in three different ways: in density, in incident photon number flux, and in the surface shape. All cases show both stabilization for a small initial perturbation and large growth of the second harmonic by increasing amplitude of the initial perturbation above a critical value.

  4. Formation of Pillars at the Boundaries between HII Regions and Molecular Clouds

    SciTech Connect

    Mizuta, A; Kane, J O; Pound, M W; Remington, B A; Ryutov, D D; Takabe, H

    2006-04-20

    We investigate numerically the hydrodynamic instability of an ionization front (IF) accelerating into a molecular cloud, with imposed initial perturbations of different amplitudes. When the initial amplitude is small, the imposed perturbation is completely stabilized and does not grow. When the initial perturbation amplitude is large enough, roughly the ratio of the initial amplitude to wavelength is greater than 0.02, portions of the IF temporarily separate from the molecular cloud surface, locally decreasing the ablation pressure. This causes the appearance of a large, warm HI region and triggers nonlinear dynamics of the IF. The local difference of the ablation pressure and acceleration enhances the appearance and growth of a multimode perturbation. The stabilization usually seen at the IF in the linear regimes does not work due to the mismatch of the modes of the perturbations at the cloud surface and in density in HII region above the cloud surface. Molecular pillars are observed in the late stages of the large amplitude perturbation case. The velocity gradient in the pillars is in reasonably good agreement with that observed in the Eagle Nebula. The initial perturbation is imposed in three different ways: in density, in incident photon number flux, and in the surface shape. All cases show both stabilization for a small initial perturbation and large growth of the second harmonic by increasing amplitude of the initial perturbation above a critical value.

  5. Chemical Imaging of Molecular Clouds and Comets with the FCRAO 14m Telescope

    NASA Astrophysics Data System (ADS)

    Schloerb, F. Peter

    1999-10-01

    Focal plane array receivers enable single dish telescopes to obtain sensitive maps of sources efficiently. In this paper, we summarize results of the detailed mapping of the chemistry of molecular cloud cores and comets with the focal plane array on the FCRAO 14m antenna by a number of investigators. Surveys of the emission from approximately 20 different molecular species have been carried out in GMC cores and dark clouds. The GMC core chemistry is remarkably homogeneous and rather similar from source to source. Time dependent chemical modelling finds good agreement with the observations at early evolutionary stages (t ~ 105 yr) suggesting that the GMC cores are dynamically evolving objects. Surveys of dark cloud cores have revealed significant abundance variations within the sources. The pattern of variations is best explained by small differences in the chemical evolutionary age within the source, with a typical value for the entire cloud also in the vicinity of ~105 years. Images of the molecular emission from comets provide important clues about the physical processes and chemistry of the cometary coma. Chemical models reveal that HCO+ is created in the coma via ion-molecule chemistry; its detailed distribution reflects its interaction with the solar wind and provides important tests of MHD models of these effects.

  6. CO-to-H2 conversion factor of molecular clouds using X-ray shadows

    NASA Astrophysics Data System (ADS)

    Sofue, Yoshiaki; Kataoka, Jun

    2016-06-01

    A new method to determine the CO-to-H2 conversion factor XCO using absorption of diffuse X-ray emission by local molecular clouds was developed. It was applied to the Ophiuchus (G353+17) and Corona Australis (G359-18) clouds using CO line and soft X-ray archival data. We obtained a value XCO = 1.85 ± 0.45 × 1020 H2 cm-2 (K km s-1)-1 as the average of least-χ2 fitting results for R4 (0.7 keV) and R5 (0.8 keV) bands.

  7. Dust and molecular properties of the low-opacity cloud LYNDS 1563

    NASA Astrophysics Data System (ADS)

    Clark, Frank O.; Laureijs, R. J.; Wardell, Lauri L.

    1991-03-01

    Optical, molecular, and far-infrared data are analyzed for L1563, estimated peak Ab 2.5 mag. The cloud is detected by IRAS at 12, 25, 60, and 100 microns, and with CO, (C-13)O, and H2CO molecules. A column density comparison yields an estimate of the temperature of the classical dust grains of 15.6 + or - 1 K, while the color temperature derived from the ratio I(60)/I(100) is 26 K. Both dust and color temperatures decrease toward the cloud center.

  8. Molecular cloud origin for the oxygen isotope heterogeneity in the solar system.

    PubMed

    Yurimoto, Hisayoshi; Kuramoto, Kiyoshi

    2004-09-17

    Meteorites and their components have anomalous oxygen isotopic compositions characterized by large variations in 18O/16O and 17O/16O ratios. On the basis of recent observations of star-forming regions and models of accreting protoplanetary disks, we suggest that these variations may originate in a parent molecular cloud by ultraviolet photodissociation processes. Materials with anomalous isotopic compositions were then transported into the solar nebula by icy dust grains during the collapse of the cloud. The icy dust grains drifted toward the Sun in the disk, and their subsequent evaporation resulted in the 17O- and 18O-enrichment of the inner disk gas. PMID:15375265

  9. FORMATION PUMPING OF MOLECULAR HYDROGEN IN DARK CLOUDS

    SciTech Connect

    Islam, Farahjabeen; Viti, Serena; Cecchi-Pestellini, Cesare; Casu, Silvia E-mail: sv@star.ucl.ac.u E-mail: scasu@ca.astro.i

    2010-12-10

    Many theoretical and laboratory studies predict H{sub 2} to be formed in highly excited rovibrational states. The consequent relaxation of excited levels via a cascade of infrared transitions might be observable in emission from suitable interstellar regions. In this work, we model H{sub 2} formation pumping in standard dense clouds, taking into account the H/H{sub 2} transition zone, through an accurate description of chemistry and radiative transfer. The model includes recent laboratory data on H{sub 2} formation, as well as the effects of the interstellar UV field, predicting the populations of gas-phase H{sub 2} molecules and their IR emission spectra. Calculations suggest that some vibrationally excited states of H{sub 2} might be detectable toward lines of sight where significant destruction of H{sub 2} occurs, such as X-ray sources, and provides a possible explanation as to why observational attempts resulted in no detections reported to date.

  10. Observational Approach to Molecular Cloud Evolutation with the Submillimeter-Wave CI Lines

    NASA Astrophysics Data System (ADS)

    Oka, T.; Yamamoto, S.

    Neutral carbon atoms (CI) play important roles both in chemistry and cooling processes of interstellar molecular clouds. It is thus crucial to explore its large area distribution to obtain information on formation processes and thermal balance of molecular clouds. However, observations of the submillimeter-wave CI lines have been limited to small areas around some representative objects. We have constructed a 1.2 m submillimeter-wave telescope at the summit of Mt.Fuji. The telescope was designed for the exclusive use of surveying molecular clouds in two submillimeter-wave CI lines, 3 P1 -3 P0 (492GHz) and 3 P2 -3 P1 (809 GHz), of atomic carbon. A superconductor-insulator-superconductor (SIS) mixer receiver was equipped on the Nasmyth focus of the telescope. The receiver noise temperatures [Trx(DSB)] are 300 K and 1000 K for the 492 GHz and the 809 GHz mixers, respectively. The intermediate frequency is centered at 2 GHz, having a 700 MHz bandwidth. An acousto-optical spectrometer (AOS) with 1024 channel outputs is used as a receiver backend. The telescope was installed at Nishi-yasugawara (alt. 3725 m), which is 200 m north of the highest peak, Kengamine (3776 m), in July 1998. It has b en operatede successfully during 4 observing seasons in a remote way from the Hongo campus of the University of Tokyo. We have already observed more than 40 square degrees of the sky with the CI 492 GHz line. The distribution of CI emission is found to be different from those of the 13 CO or C1 8 O emission in some clouds. These differences are discussed in relation to formation processes of molecular clouds.

  11. Physical Properties of the 1.1 mm selected Giant Molecular Clouds in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Takekoshi, Tatsuya

    2015-08-01

    The first 1.1 mm continuum survey toward the Small Magellanic Cloud (SMC) is performed with the AzTEC instrument installed on the ASTE 10 m telescope. This survey covers 4.5 square degrees of the SMC, and achieves the 1σ noise levels of 5-13 mJy beam-1. As a result of the analysis, 44 extended objects are identified. The 1.1 mm extended emission has good spatial correlation with 160 μm, indicating that the origin of the 1.1 mm continuum is thermal emission from cold dust component. Spectral energy distribution analysis are performed assuming single-temperature thermal emission from the cold dust component. Assuming a gas-to-dust ratio of 1000, the 1.1 mm objects have gas mass ranges from 7×103 to 4×105 M⊙, which is typical mass range of giant molecular clouds (GMCs), implying that the detected objects are dust-selected GMCs. The 1.1 mm objects show good spatial correlation with the 24 μm and CO emission, and the physical properties are very similar to that of our Galaxy and the Large Magellanic Cloud. The existences of star formation activity or CO detection provide the information about the evolutionary sequence. Comparisions with signs of star-formation and CO emission provide information about the evolutionary sequence. We found 2, 8, 13, and 21 samples of the starless/CO-detected, starless/CO-dark, star-forming/CO-dark, and star-forming/CO-detected objects, respectively. This result implies the existence of three main evolutionary phases, and the starless/CO-dark samples can be explained as the youngest evolution phase of GMCs. The deficiency of the starless/CO-detected samples suggests that the detectable amount of CO forms after the onset of star formation in the low metallicity environment of the SMC.

  12. A note on compressibility and energy cascade in turbulent molecular clouds

    NASA Technical Reports Server (NTRS)

    Fleck, R. C., Jr.

    1983-01-01

    Observed velocity-size correlations are reexamined in the light of an improved theory of turbulent energy cascade that is developed. It is shown that observed velocity-size correlations cannot be compared with the Kolmogorov law, which is based on incompressible turbulent flow. The fact that the log v-log(l/rho) scaling law (v the turbulent velocity, l the associated region size, and rho the fluid density) predicted for compressible energy cascade is always steeper than that observed in molecular clouds indicates the injection rather than the dissipation of mechanical energy at smaller scales of motion. It is also shown that the concept of strict energy cascade may not be generally applicable in the interstellar medium. The agreement between theory and observation turns out to be best for small cool clouds and cloud cores, suggesting that, for these regions at least, the dominant process in establishing the observed v-l-rho correlation is a turbulent energy cascade.

  13. Large scale IRAM 30 m CO-observations in the giant molecular cloud complex W43

    NASA Astrophysics Data System (ADS)

    Carlhoff, P.; Nguyen Luong, Q.; Schilke, P.; Motte, F.; Schneider, N.; Beuther, H.; Bontemps, S.; Heitsch, F.; Hill, T.; Kramer, C.; Ossenkopf, V.; Schuller, F.; Simon, R.; Wyrowski, F.

    2013-12-01

    We aim to fully describe the distribution and location of dense molecular clouds in the giant molecular cloud complex W43. It was previously identified as one of the most massive star-forming regions in our Galaxy. To trace the moderately dense molecular clouds in the W43 region, we initiated W43-HERO, a large program using the IRAM 30 m telescope, which covers a wide dynamic range of scales from 0.3 to 140 pc. We obtained on-the-fly-maps in 13CO (2-1) and C18O (2-1) with a high spectral resolution of 0.1 km s-1 and a spatial resolution of 12''. These maps cover an area of ~1.5 square degrees and include the two main clouds of W43 and the lower density gas surrounding them. A comparison to Galactic models and previous distance calculations confirms the location of W43 near the tangential point of the Scutum arm at approximately 6 kpc from the Sun. The resulting intensity cubes of the observed region are separated into subcubes, which are centered on single clouds and then analyzed in detail. The optical depth, excitation temperature, and H2 column density maps are derived out of the 13CO and C18O data. These results are then compared to those derived from Herschel dust maps. The mass of a typical cloud is several 104 M⊙ while the total mass in the dense molecular gas (>102 cm-3) in W43 is found to be ~1.9 × 106 M⊙. Probability distribution functions obtained from column density maps derived from molecular line data and Herschel imaging show a log-normal distribution for low column densities and a power-law tail for high densities. A flatter slope for the molecular line data probability distribution function may imply that those selectively show the gravitationally collapsing gas. Appendices are available in electronic form at http://www.aanda.orgThe final datacubes (13CO and C18O) for the entire survey are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/560/A24

  14. Shocks, Superbubbles, and Filaments: Investigations into Large Scale Gas Motions in Giant Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Pon, Andrew Richard

    2013-12-01

    Giant molecular clouds (GMCs), out of which stars form, are complex, dynamic systems, which both influence and are shaped by the process of star formation. In this dissertation, I examine three different facets of the dynamical motions within GMCs. Collapse modes in different dimensional objects. Molecular clouds contain lower dimensional substructures, such as filaments and sheets. The collapse properties of finite filaments and sheets differ from those of spherical objects as well as infinite sheets and filaments. I examine the importance of local collapse modes of small central perturbations, relative to global collapse modes, in different dimensional objects to elucidate whether strong perturbations are required for molecular clouds to fragment to form stars. I also calculate the dependence of the global collapse timescale upon the aspect ratio of sheets and filaments. I find that lower dimensional objects are more readily fragmented, and that for a constant density, lower dimensional objects and clouds with larger aspect ratios collapse more slowly. An edge-driven collapse mode also exists in sheets and filaments and is most important in elongated filaments. The failure to consider the geometry of a gas cloud is shown to lead to an overestimation of the star formation rate by up to an order of magnitude. Molecular tracers of turbulent energy dissipation. Molecular clouds contain supersonic turbulence that simulations predict will decay rapidly via shocks. I use shock models to predict which species emit the majority of the turbulent energy dissipated in shocks and find that carbon monoxide, CO, is primarily responsible for radiating away this energy. By combining these shock models with estimates for the turbulent energy dissipation rate of molecular clouds, I predict the expected shock spectra of CO from molecular clouds. I compare the results of these shock models to predictions for the emission from the unshocked gas in GMCs and show that mid

  15. A comparative study of giant molecular clouds in M51, M33, and the Large Magellanic Cloud

    SciTech Connect

    Hughes, Annie; Meidt, Sharon E.; Colombo, Dario; Schinnerer, Eva; Pety, Jerôme; Dumas, Gaëlle; Schuster, Karl F.; Leroy, Adam K.; Dobbs, Clare L.; García-Burillo, Santiago; Thompson, Todd A.; Kramer, Carsten

    2013-12-10

    We compare the properties of giant molecular clouds (GMCs) in M51 identified by the Plateau de Bure Interferometer Whirlpool Arcsecond Survey with GMCs identified in wide-field, high-resolution surveys of CO emission in M33 and the Large Magellanic Cloud (LMC). We find that GMCs in M51 are larger, brighter, and have higher velocity dispersions relative to their sizes than equivalent structures in M33 and the LMC. These differences imply that there are genuine variations in the average mass surface density 〈Σ{sub H{sub 2}}〉 of the different GMC populations. To explain this, we propose that the pressure in the interstellar medium surrounding the GMCs plays a role in regulating their density and velocity dispersion. We find no evidence for a correlation between size and linewidth in M51, M33, or the LMC when the CO emission is decomposed into GMCs, although moderately robust correlations are apparent when regions of contiguous CO emission (with no size limitation) are used. Our work demonstrates that observational bias remains an important obstacle to the identification and study of extragalactic GMC populations using CO emission, especially in molecule-rich galactic environments.

  16. Gravitational fragmentation caught in the act: the filamentary Musca molecular cloud

    NASA Astrophysics Data System (ADS)

    Kainulainen, J.; Hacar, A.; Alves, J.; Beuther, H.; Bouy, H.; Tafalla, M.

    2016-02-01

    Context. Filamentary structures are common in molecular clouds. Explaining how they fragment to dense cores is a missing step in understanding their role in star formation. Aims: We perform a case study of whether low-mass filaments are close to hydrostatic prior to their fragmentation, and whether their fragmentation agrees with gravitational fragmentation models. To accomplish this, we study the ~6.5 pc long Musca molecular cloud, which is an ideal candidate for a filament at an early stage of fragmentation. Methods: We employ dust extinction mapping, in conjunction with near-infrared JHKS-band data from the CTIO/NEWFIRM instrument, and 870 μm dust continuum emission data from the APEX/LABOCA instrument to estimate column densities in Musca. We use the data to identify fragments from the cloud and to determine the radial density distribution of its filamentary part. We compare the cloud's morphology with 13CO and C18O line emission observed with the APEX/SHeFI instrument. Results: The Musca cloud is pronouncedly fragmented at its ends, but harbors a remarkably well-defined, ~1.6 pc long filament in its center region. The line mass of the filament is 21-31 M⊙ pc-1 and the full width at half maximum (FWHM) 0.07 pc. The radial profile of the filament can be fitted with a Plummer profile, which has the power-index of 2.6 ± 11% and is flatter than that of an infinite hydrostatic filament. The profile can also be fitted with a hydrostatic cylinder truncated by external pressure. These models imply a central density of ~5-10 × 104 cm-3. The fragments in the cloud have a mean separation of ~0.4 pc, in agreement with gravitational fragmentation. These properties, together with the subsonic and velocity-coherent nature of the cloud, suggest a scenario in which an initially hydrostatic cloud is currently gravitationally fragmenting. The fragmentation started a few tenths of a Myr ago from the ends of the cloud, leaving its center still relatively nonfragmented

  17. JCMT SCUBA-Diving in Nearby Molecular Clouds: The Case for Large Systematic Surveys with FIRST

    NASA Astrophysics Data System (ADS)

    Johnstone, D.

    2001-07-01

    Results from two sub-millimeter surveys of the nearby molecular clouds rho Oph, Taurus, Orion A and Orion B are presented. Combining large area (100's of square arc-minute) JCMT continuum emission images at 450 microns (8") and 850 microns (14"), sensitive to ~ 0.01 Msolar condensations, with molecular line data (CO isotopes, formaldehyde, etc.) allows for a glimpse into the physical properties of molecular clouds on small scales. Both barely resolved condensations and large scale features are visible in the maps, revealing the variety of dynamical events which operate in star forming regions. The important physics associated with these regions, as evidenced by the survey results, are discussed. Equilibrium Bonnor-Ebert models are fit to the compact clumps found in the dust continuum images in order to derive their physical properties - mass, temperature, and bounding pressure. The cumulative mass functions for the clumps in both Orion B and rho Oph are remarkably similar to the stellar IMF. The survey results are used to argue for a strong multi-wavelength and multi-instrument survey component to the FIRST mission in order to best unlock the secrets of star formation in molecular clouds.

  18. Cosmic-ray slowing down in molecular clouds: Effects of heavy nuclei

    NASA Astrophysics Data System (ADS)

    Chabot, Marin

    2016-01-01

    Context. A cosmic ray (CR) spectrum propagated through ISM contains very few low-energy (<100 MeV) particles. Recently, a local CR spectrum, with strong low energy components, has been proposed to be responsible for the over production of H3+ molecule in some molecular clouds. Aims: We aim to explore the effects of the chemical composition of low-energy cosmic rays (CRs) when they slow down in dense molecular clouds without magnetic fields. We considered both ionization and solid material processing rates. Methods: We used galatic CR chemical composition from proton to iron. We propagated two types of CR spectra through a cloud made of H2: those CR spectra with different contents of low energy CRs and those assumed to be initially identical for all CR species. The stopping and range of ions in matter (SRIM) package provided the necessary stopping powers. The ionization rates were computed with cross sections from recent semi-empirical laws, while effective cross sections were parametrized for solid processing rates using a power law of the stopping power (power 1 to 2). Results: The relative contribution to the cloud ionization of proton and heavy CRs was found identical everywhere in the irradiated cloud, no matter which CR spectrum we used. As compared to classical calculations, using protons and high-energy behaviour of ionization processes (Z2 scaling), we reduced absolute values of ionization rates by few a tens of percents but only in the case of spectrum with a high content of low-energy CRs. We found, using the same CR spectrum, the solid material processing rates to be reduced between the outer and inner part of thick cloud by a factor 10 (as in case of the ionization rates) or by a factor 100, depending on the type of process.

  19. Temperature gradients in the Cepheus B molecular cloud - a multi-line analysis

    NASA Astrophysics Data System (ADS)

    Deiss, B. M.; Beuther, H.; Kramer, C.

    The Cepheus B molecular cloud is a prime candidate to study the effect of sequential star formation on molecular clouds: it is located at the edge of an H ii region (S155) and an OB association (Cepheus OB3), and it comprises a hot-core region with an embedded compact H ii region and NIR cluster suggesting on-going star formation. The bulk of the cloud, however, appears to be in a 'calm' state where star formation has not (yet) started. We conducted on-the-fly maps of the (2-1) and (3-2) low-J transitions of the CO isotopomers 12CO, 13CO, and C18O (Beuther et al. 1999, to appear in A&A); the observations were carried out with the 3 m KOSMA submillimeter telescope at Gornergrat, Switzerland (Kramer et al. 1998, SPIE, Conf.Proc., Kona, Vol 3350). We present line ratio maps as well as spectra at selected positions, where the latter sample regions of Cepheus B each having different physical conditions. The line ratio distribution is a measure for the variation of the excitation conditions. Adopting an escape probability integration scheme the data can be fitted reasonably treating each of the CO isotopomers seperately. From that we derive differing kinetic temperatures at each of the projected positions. This strongly indicates a temperature gradient along the line-of-sight since different isotopomers trace different layers of the cloud due to their differing optical depths. The temperature difference between the cooler inner parts of the cloud and the cloud's 'surface' amounts up to 40 K. We also found a lateral west-to-east 'surface' temperature decrease from 70 K at the hot-core region down to 40 K.

  20. ALMA RESOLVES 30 DORADUS: SUB-PARSEC MOLECULAR CLOUD STRUCTURE NEAR THE CLOSEST SUPER STAR CLUSTER

    SciTech Connect

    Indebetouw, Remy; Brogan, Crystal; Leroy, Adam; Hunter, Todd; Kepley, Amanda E-mail: cbrogan@nrao.edu; and others

    2013-09-01

    We present Atacama Large (sub)Millimeter Array observations of 30 Doradus-the highest resolution view of molecular gas in an extragalactic star formation region to date ({approx}0.4 pc Multiplication-Sign 0.6 pc). The 30Dor-10 cloud north of R136 was mapped in {sup 12}CO 2-1, {sup 13}CO 2-1, C{sup 18}O 2-1, 1.3 mm continuum, the H30{alpha} recombination line, and two H{sub 2}CO 3-2 transitions. Most {sup 12}CO emission is associated with small filaments and clumps ({approx}<1 pc, {approx}10{sup 3} M{sub Sun} at the current resolution). Some clumps are associated with protostars, including ''pillars of creation'' photoablated by intense radiation from R136. Emission from molecular clouds is often analyzed by decomposition into approximately beam-sized clumps. Such clumps in 30 Doradus follow similar trends in size, linewidth, and surface density to Milky Way clumps. The 30 Doradus clumps have somewhat larger linewidths for a given size than predicted by Larson's scaling relation, consistent with pressure confinement. They extend to a higher surface density at a given size and linewidth compared to clouds studied at 10 pc resolution. These trends are also true of clumps in Galactic infrared-dark clouds; higher resolution observations of both environments are required. Consistency of clump masses calculated from dust continuum, CO, and the virial theorem reveals that the CO abundance in 30 Doradus clumps is not significantly different from the Large Magellanic Cloud mean, but the dust abundance may be reduced by {approx}2. There are no strong trends in clump properties with distance from R136; dense clumps are not strongly affected by the external radiation field, but there is a modest trend toward lower dense clump filling fraction deeper in the cloud.

  1. ALMA Resolves 30 Doradus: Sub-parsec Molecular Cloud Structure near the Closest Super Star Cluster

    NASA Astrophysics Data System (ADS)

    Indebetouw, Rémy; Brogan, Crystal; Chen, C.-H. Rosie; Leroy, Adam; Johnson, Kelsey; Muller, Erik; Madden, Suzanne; Cormier, Diane; Galliano, Frédéric; Hughes, Annie; Hunter, Todd; Kawamura, Akiko; Kepley, Amanda; Lebouteiller, Vianney; Meixner, Margaret; Oliveira, Joana M.; Onishi, Toshikazu; Vasyunina, Tatiana

    2013-09-01

    We present Atacama Large (sub)Millimeter Array observations of 30 Doradus—the highest resolution view of molecular gas in an extragalactic star formation region to date (~0.4 pc × 0.6 pc). The 30Dor-10 cloud north of R136 was mapped in 12CO 2-1, 13CO 2-1, C18O 2-1, 1.3 mm continuum, the H30α recombination line, and two H2CO 3-2 transitions. Most 12CO emission is associated with small filaments and clumps (lsim1 pc, ~103 M ⊙ at the current resolution). Some clumps are associated with protostars, including "pillars of creation" photoablated by intense radiation from R136. Emission from molecular clouds is often analyzed by decomposition into approximately beam-sized clumps. Such clumps in 30 Doradus follow similar trends in size, linewidth, and surface density to Milky Way clumps. The 30 Doradus clumps have somewhat larger linewidths for a given size than predicted by Larson's scaling relation, consistent with pressure confinement. They extend to a higher surface density at a given size and linewidth compared to clouds studied at 10 pc resolution. These trends are also true of clumps in Galactic infrared-dark clouds; higher resolution observations of both environments are required. Consistency of clump masses calculated from dust continuum, CO, and the virial theorem reveals that the CO abundance in 30 Doradus clumps is not significantly different from the Large Magellanic Cloud mean, but the dust abundance may be reduced by ~2. There are no strong trends in clump properties with distance from R136; dense clumps are not strongly affected by the external radiation field, but there is a modest trend toward lower dense clump filling fraction deeper in the cloud.

  2. Disruption of Molecular Clouds by Expansion of Dusty H II Regions

    NASA Astrophysics Data System (ADS)

    Kim, Jeong-Gyu; Kim, Woong-Tae; Ostriker, Eve C.

    2016-03-01

    Dynamical expansion of H II regions around star clusters plays a key role in dispersing the surrounding dense gas and therefore in limiting the efficiency of star formation in molecular clouds. We use a semianalytic method and numerical simulations to explore expansion of spherical dusty H II regions and surrounding neutral shells and the resulting cloud disruption. Our model for shell expansion adopts the static solutions of Draine for dusty H II regions and considers the contact outward forces on the shell due to radiation and thermal pressures, as well as the inward gravity from the central star and the shell itself. We show that the internal structure we adopt and the shell evolution from the semianalytic approach are in good agreement with the results of numerical simulations. Strong radiation pressure in the interior controls the shell expansion indirectly by enhancing the density and pressure at the ionization front. We calculate the minimum star formation efficiency ɛmin required for cloud disruption as a function of the cloud's total mass and mean surface density. Within the adopted spherical geometry, we find that typical giant molecular clouds in normal disk galaxies have ɛmin ≲ 10%, with comparable gas and radiation pressure effects on shell expansion. Massive cluster-forming clumps require a significantly higher efficiency of ɛmin ≳ 50% for disruption, produced mainly by radiation-driven expansion. The disruption time is typically of the order of a free-fall timescale, suggesting that the cloud disruption occurs rapidly once a sufficiently luminous H II region is formed. We also discuss limitations of the spherical idealization.

  3. Ultraviolet illuminated molecular cloud boundaries: Extended (C II) 158 micrometer emission toward L1630

    NASA Technical Reports Server (NTRS)

    Jaffe, D. T.; Zhou, S.; Howe, J. E.; Herrmann, F.; Madden, S. C.; Poglitsch, A.; Vanderwerf, P. P.; Stacey, G. J.

    1994-01-01

    The construction of a large scale map of the 158 micrometer C+ line toward the L1630/Orion B molecular cloud, covering an approximately 35' by 45' area which includes the NGC 2024 H II region, zeta-Ori, the reflection nebula NGC 2023, and the Horsehead nebula, is reported. Emission in the C II line is very widespread. The line was detected at levels in excess of a few 0.0001 erg/sq cm/s/sr over almost the entire mapped region. Extended emission associated with the NGC 2024 H II region and its envelope accounts for more than half of the C II flux. Over this approximately 1.5 by 2.5 pc region, the amount of gas phase carbon in the form of C+ is comparable to the amount of carbon in CO. This result, together with the C II distribution implies that C II emission arises on the surface of clumps throughout the cloud rather than in a single layer at the H II region boundary. Away from the H II region, most of the C II emission comes from the western edge of the L1630 cloud and probably results from excitation by external OB stars. The overall extent of the C II emission is comparable to that of millimeter molecular lines but the distributions are different in detail. The difference in C II and molecular line distributions, in particular, the larger extent of the C II emission west of NGC 2024 implies large variations in the ratio of the C II and J = 1 towards 0 intensities. Models of photon dominated regions can explain the relation between C II and CO intensities only if the cloud edges and cloud interior are considered separately. A method for using C II and radio continuum emission to characterize the relationship between OB stars and photon dominated regions is proposed.

  4. Ultraviolet-illuminated molecular cloud boundaries: Extended (C II) 158 micron emission toward L1630

    NASA Technical Reports Server (NTRS)

    Jaffe, D. T.; Zhou, S.; Howe, J. E.; Herrmann, F.; Madden, S. C.; Poglitsch, A.; Van Der Werf, P. P.; Stacey, G. J.

    1994-01-01

    We have made a large-scale map of the 158 micrometers C(+) line toward the L1630/Orion B molecular cloud. The map covers a approximately 35 min x 45 min area which includes the NGC 2024 H II region, zeta Ori, the reflection nebula NGC 2023, and the Horsehead nebula. Emission in the (C II) line is very widespread. The line was detected at levels in excess of a few 10(exp -4) ergs/sq cm/s/sr over almost the entire mapped region. Extended emission associated with the NGC 2024 H II region and its envelope accounts for more than half of the (C II) flux. Over this approximately 1.5 x 2.5 pc region, the amount of gas-phase carbon in the form of C(+) is comparable to the amount of carbon in CO. This result, together with the (C II) distribution, implies that (C II) emission arises on the surfaces of clumps throughout the cloud rather than in a single layer at the H II region boundary. Away from the H II region, most of the (C II) emission comes from the western edge of the L1630 cloud and probably results from excitation by external OB stars. The overall extent of the (C II) emission is comparable to that of millimeter molecular lines, but the distributions are different in detail. The difference in (C II) and molecular line distributions, in particular, the larger extent of the (C II) emission west of NGC 2024 implies large variations in the radio of the (C II) and CO J = 1 goes to 0 intensities. Models of photon-dominated regions can explain the relation between (C II) and CO intensities only if one considers the cloud edges and cloud interior separately. We propose a method for using (C II) and radio continuum emission to characterize the relationship between OB stars and photon-dominated regions.

  5. Understanding star formation in molecular clouds. II. Signatures of gravitational collapse of IRDCs

    NASA Astrophysics Data System (ADS)

    Schneider, N.; Csengeri, T.; Klessen, R. S.; Tremblin, P.; Ossenkopf, V.; Peretto, N.; Simon, R.; Bontemps, S.; Federrath, C.

    2015-06-01

    We analyse column density and temperature maps derived from Herschel dust continuum observations of a sample of prominent, massive infrared dark clouds (IRDCs) i.e. G11.11-0.12, G18.82-0.28, G28.37+0.07, and G28.53-0.25. We disentangle the velocity structure of the clouds using 13CO 1→0 and 12CO 3→2 data, showing that these IRDCs are the densest regions in massive giant molecular clouds (GMCs) and not isolated features. The probability distribution function (PDF) of column densities for all clouds have a power-law distribution over all (high) column densities, regardless of the evolutionary stage of the cloud: G11.11-0.12, G18.82-0.28, and G28.37+0.07 contain (proto)-stars, while G28.53-0.25 shows no signs of star formation. This is in contrast to the purely log-normal PDFs reported for near and/or mid-IR extinction maps. We only find a log-normal distribution for lower column densities, if we perform PDFs of the column density maps of the whole GMC in which the IRDCs are embedded. By comparing the PDF slope and the radial column density profile of three of our clouds, we attribute the power law to the effect of large-scale gravitational collapse and to local free-fall collapse of pre- and protostellar cores for the highest column densities. A significant impact on the cloud properties from radiative feedback is unlikely because the clouds are mostly devoid of star formation. Independent from the PDF analysis, we find infall signatures in the spectral profiles of 12CO for G28.37+0.07 and G11.11-0.12, supporting the scenario of gravitational collapse. Our results are in line with earlier interpretations that see massive IRDCs as the densest regions within GMCs, which may be the progenitors of massive stars or clusters. At least some of the IRDCs are probably the same features as ridges (high column density regions with N> 1023 cm-2 over small areas), which were defined for nearby IR-bright GMCs. Because IRDCs are only confined to the densest (gravity dominated

  6. Depletions and extinction curves for lines of sight through the outer edges of truly dense molecular clouds

    NASA Technical Reports Server (NTRS)

    Joseph, C. L.

    1986-01-01

    Observations of a few moderately reddened (0.3 is less than E(B-V) is less than 0.6) lines of sight through the outer edges of truly dense molecular clouds, not only show the overall depletions in these clouds to be as much as 0.5 (dex) greater than in comparably reddened diffuse clouds, but reveal a possible tendency for certain species to deplete preferentially. Possible methods of depletions are discussed.

  7. Effects of an Embedded B-Star Wind on the Properties of a Molecular Cloud: Ophiuchus

    NASA Astrophysics Data System (ADS)

    Chen, How-Huan; Goodman, A. A.

    2014-01-01

    Supernovae are often considered to be one of the main drivers of turbulence in molecular clouds. But, recent studies (Arce et al. 2010; Arce et al. 2011) find that stellar feedback from not-especially-massive B-type stars, which are much more long-lived and numerous than stars which go supernova, can account for at least half of the turbulent energy in one large nearby molecular cloud, Perseus. In the Ophiuchus cloud, we find dust emission and H-alpha mapping showing a prominent HII region surrounded by a shell of denser, warmer gas. The center of the shell coincides with rho Ophiuchii, a multiple-star system with four B-type stars forming two pairs of close binaries. In this work, we seek answers to two questions: 1) whether the energy embedded in the shell structure plausibly comes from the B-star cluste, and if so, 2) how this energy compares to the total turbulent energy in the Ophiuchus cloud.

  8. Studying the molecular gas towards the R Coronae Australis dark cloud

    NASA Astrophysics Data System (ADS)

    Paron, S.; Celis Peña, M.; Ortega, M. E.; Cunningham, M.; Jones, P. A.; Rubio, M.

    2016-08-01

    The R Coronae Australis dark cloud is one of the closest star-forming regions to the Sun. The cloud is known to be very active in star formation, harboring many Herbig-Haro objects (HHs) and Molecular Hydrogen emission-line Objects (MHOs). In this work we present results from molecular observations (a 5.5 map of CO J=3--2 and HCO J=4--3, and a single spectrum of NH J=4--3) obtained with the Atacama Submillimeter Telescope Experiment (ASTE) towards the RCrA dark cloud with an angular and spectral resolution of 22 and 0.11 km s, respectively. From the CO J=3--2 line we found kinematical spectral features strongly suggesting the presence of outflows towards a region populated by several HHs and MHOs. Moreover, most of these objects lie within an HCO maximum, suggesting that its emission arises from an increasement of its abundance due to the chemistry triggered by the outflow activity. Additionally, we are presenting the first reported detection of NH in the J=4--3 line towards the RCrA dark cloud.

  9. CLOUDS, a protocol for deriving a molecular proton density via NMR.

    PubMed

    Grishaev, Alexander; Llinás, Miguel

    2002-05-14

    We demonstrate the feasibility of computing realistic spatial proton distributions for proteins in solution from experimental NMR nuclear Overhauser effect data only and with minimal assignments. The method, CLOUDS, relies on precise and abundant interproton distance restraints calculated via a relaxation matrix analysis of sets of experimental nuclear Overhauser effect spectroscopy crosspeaks. The MIDGE protocol was adapted for this purpose. A gas of unassigned, unconnected H atoms is condensed into a structured proton distribution (cloud) via a molecular dynamics simulated-annealing scheme in which the internuclear distances and van der Waals repulsive terms are the only active restraints. Proton densities are generated by combining a large number of such clouds, each computed from a different trajectory. After filtering by reference to the cloud closest to the mean, a minimal dispersion proton density (foc) is identified. The latter affords a quasi-continuous hydrogen-only probability distribution that conveys immediate information on the protein surface topology (grooves, protrusions, potential binding site cavities, etc.), directly related to the molecular structure. Feasibility of the method was tested on NMR data measured on two globular protein domains of low regular secondary structure content, the col 2 domain of human matrix metalloproteinase-2 and the kringle 2 domain of human plasminogen, of 60 and 83 amino acid residues, respectively.

  10. LONG-LIVED MAGNETIC-TENSION-DRIVEN MODES IN A MOLECULAR CLOUD

    SciTech Connect

    Basu, Shantanu; Dapp, Wolf B. E-mail: wdapp@uwo.c

    2010-06-10

    We calculate and analyze the longevity of magnetohydrodynamic (MHD) wave modes that occur in the plane of a magnetic thin sheet. Initial turbulent conditions applied to a magnetically subcritical cloud are shown to lead to relatively rapid energy decay if ambipolar diffusion is introduced at a level corresponding to partial ionization primarily by cosmic rays. However, in the flux-freezing limit, as may be applicable to photoionized molecular cloud envelopes, the turbulence persists at 'nonlinear' levels in comparison with the isothermal sound speed c {sub s}, with one-dimensional rms material motions in the range of {approx} 2 c {sub s}-5 c {sub s} for cloud sizes in the range of {approx} 2 pc-16 pc. These fluctuations persist indefinitely, maintaining a significant portion of the initial turbulent kinetic energy. We find the analytic explanation for these persistent fluctuations. They are magnetic-tension-driven modes associated with the interaction of the sheet with the external magnetic field. The phase speed of such modes is quite large, allowing residual motions to persist without dissipation in the flux-freezing limit, even as they are nonlinear with respect to the sound speed. We speculate that long-lived large-scale MHD modes such as these may provide the key to understanding observed supersonic motions in molecular clouds.

  11. Atomic carbon near the molecular cloud/H II region interface in S 140

    NASA Astrophysics Data System (ADS)

    Hernichel, J.; Krause, D.; Roehrig, R.; Stutzki, J.; Winnewisser, G.

    1992-06-01

    We have observed the (CI) 3P1 - 3P0 fine structure line of atomic carbon at 492 GHz in the edge-on interface between the molecular cloud L 1204 and the S 140 H II region with the KOSMA telescope on Gornergrat, Switzerland. We find that the (CI)-emission near the interface consists of a narrow velocity component with position and line width similar to that of the ambient molecular cloud material, superimposed on a wider component (FWHM is approximately equal to 15 km/s) exhibiting a line profile similar to that of the higher velocity material visible in CO and carrying most of the CI column density. The velocity integrated (CI) emission peaks near the edge of the cloud facing the exciting star. This finding is in contrast to earlier results by Keene et al. (1985) who missed the wide velocity component in their observations. The relative CI/CO abundance is strongly enhanced in the high velocity material (100 percent) relative to the ambient cloud material (11 percent).

  12. Tycho SN 1572: A Naked Ia Supernova Remnant Without an Associated Ambient Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Tian, W. W.; Leahy, D. A.

    2011-03-01

    The historical supernova remnant (SNR) Tycho SN 1572 originates from the explosion of a normal Type Ia supernova that is believed to have originated from a carbon-oxygen white dwarf in a binary system. We analyze the 21 cm continuum, H I, and 12CO-line data from the Canadian Galactic Plane Survey in the direction of SN 1572 and the surrounding region. We construct H I absorption spectra to SN 1572 and three nearby compact sources. We conclude that SN 1572 has no molecular cloud interaction, which argues against previous claims that a molecular cloud is interacting with the SNR. This new result does not support a recent claim that dust, newly detected by AKARI, originates from such an SNR-cloud interaction. We suggest that the SNR has a kinematic distance of 2.5-3.0 kpc based on a nonlinear rotational curve model. Very high energy γ-ray emission from the remnant has been detected by the VERITAS telescope, so our result shows that its origin should not be an SNR-cloud interaction. Both radio and X-ray observations support that SN 1572 is an isolated Type Ia SNR.

  13. TYCHO SN 1572: A NAKED Ia SUPERNOVA REMNANT WITHOUT AN ASSOCIATED AMBIENT MOLECULAR CLOUD

    SciTech Connect

    Tian, W. W.; Leahy, D. A.

    2011-03-10

    The historical supernova remnant (SNR) Tycho SN 1572 originates from the explosion of a normal Type Ia supernova that is believed to have originated from a carbon-oxygen white dwarf in a binary system. We analyze the 21 cm continuum, H I, and {sup 12}CO-line data from the Canadian Galactic Plane Survey in the direction of SN 1572 and the surrounding region. We construct H I absorption spectra to SN 1572 and three nearby compact sources. We conclude that SN 1572 has no molecular cloud interaction, which argues against previous claims that a molecular cloud is interacting with the SNR. This new result does not support a recent claim that dust, newly detected by AKARI, originates from such an SNR-cloud interaction. We suggest that the SNR has a kinematic distance of 2.5-3.0 kpc based on a nonlinear rotational curve model. Very high energy {gamma}-ray emission from the remnant has been detected by the VERITAS telescope, so our result shows that its origin should not be an SNR-cloud interaction. Both radio and X-ray observations support that SN 1572 is an isolated Type Ia SNR.

  14. An x-ray search for PMS stars in translucent molecular clouds

    NASA Technical Reports Server (NTRS)

    Caillault, Jean-Pierre

    1994-01-01

    The work outlined in this paper identifies 108 plausible T Tauri candidates in the regions of two high latitude translucent molecular clouds. Follow-up optical spectroscopy of these candidates is needed to resolve the question of whether or not star formation is present in these clouds. We have recently submitted a proposal to use the Kitt Peak National Observatory 2.1 meter telescope to take medium resolution spectra of the 14 PMS candidate X-ray sources in MBM 40 to determine spectral types and search for indicators of youth (strong Li absorption; H alpha emission) and we will submit a similar proposal to study the X-ray sources in MBM 55. Only spectra will provide an unambiguous determination of their pedigree. As part of an ongoing study of star formation at high galactic latitude we intend to analyze data in the ROSAT archives to investigate the possibility of star formation in all of the high latitude translucent molecular clouds observed. We believe that this project may yield a significant increase in our understanding of the star formation process for low-mass stars and of the nature of the translucent clouds.

  15. The Spitzer Survey of Interstellar Clouds in the Gould Belt. VI. The Auriga-California Molecular Cloud Observed with IRAC and MIPS

    NASA Astrophysics Data System (ADS)

    Broekhoven-Fiene, Hannah; Matthews, Brenda C.; Harvey, Paul M.; Gutermuth, Robert A.; Huard, Tracy L.; Tothill, Nicholas F. H.; Nutter, David; Bourke, Tyler L.; DiFrancesco, James; Jørgensen, Jes K.; Allen, Lori E.; Chapman, Nicholas L.; Dunham, Michael M.; Merín, Bruno; Miller, Jennifer F.; Terebey, Susan; Peterson, Dawn E.; Stapelfeldt, Karl R.

    2014-05-01

    We present observations of the Auriga-California Molecular Cloud (AMC) at 3.6, 4.5, 5.8, 8.0, 24, 70, and 160 μm observed with the IRAC and MIPS detectors as part of the Spitzer Gould Belt Legacy Survey. The total mapped areas are 2.5 deg2 with IRAC and 10.47 deg2 with MIPS. This giant molecular cloud is one of two in the nearby Gould Belt of star-forming regions, the other being the Orion A Molecular Cloud (OMC). We compare source counts, colors, and magnitudes in our observed region to a subset of the SWIRE data that was processed through our pipeline. Using color-magnitude and color-color diagrams, we find evidence for a substantial population of 166 young stellar objects (YSOs) in the cloud, many of which were previously unknown. Most of this population is concentrated around the LkHα 101 cluster and the filament extending from it. We present a quantitative description of the degree of clustering and discuss the relative fraction of YSOs in earlier (Class I and F) and later (Class II) classes compared to other clouds. We perform simple SED modeling of the YSOs with disks to compare the mid-IR properties to disks in other clouds and identify 14 classical transition disk candidates. Although the AMC is similar in mass, size, and distance to the OMC, it is forming about 15-20 times fewer stars.

  16. The Spitzer survey of interstellar clouds in the gould belt. VI. The Auriga-California molecular cloud observed with IRAC and MIPS

    SciTech Connect

    Broekhoven-Fiene, Hannah; Matthews, Brenda C.; Harvey, Paul M.; Gutermuth, Robert A.; Huard, Tracy L.; Miller, Jennifer F.; Tothill, Nicholas F. H.; Nutter, David; Bourke, Tyler L.; DiFrancesco, James; Jørgensen, Jes K.; Allen, Lori E.; Chapman, Nicholas L.; Dunham, Michael M.; Merín, Bruno; Terebey, Susan; Peterson, Dawn E.; and others

    2014-05-01

    We present observations of the Auriga-California Molecular Cloud (AMC) at 3.6, 4.5, 5.8, 8.0, 24, 70, and 160 μm observed with the IRAC and MIPS detectors as part of the Spitzer Gould Belt Legacy Survey. The total mapped areas are 2.5 deg{sup 2} with IRAC and 10.47 deg{sup 2} with MIPS. This giant molecular cloud is one of two in the nearby Gould Belt of star-forming regions, the other being the Orion A Molecular Cloud (OMC). We compare source counts, colors, and magnitudes in our observed region to a subset of the SWIRE data that was processed through our pipeline. Using color-magnitude and color-color diagrams, we find evidence for a substantial population of 166 young stellar objects (YSOs) in the cloud, many of which were previously unknown. Most of this population is concentrated around the LkHα 101 cluster and the filament extending from it. We present a quantitative description of the degree of clustering and discuss the relative fraction of YSOs in earlier (Class I and F) and later (Class II) classes compared to other clouds. We perform simple SED modeling of the YSOs with disks to compare the mid-IR properties to disks in other clouds and identify 14 classical transition disk candidates. Although the AMC is similar in mass, size, and distance to the OMC, it is forming about 15-20 times fewer stars.

  17. Theory of molecular formation by radiative association in interstellar clouds

    NASA Technical Reports Server (NTRS)

    Bates, D. R.

    1983-01-01

    A theory of molecular formation by radiative association is presented which is consistent with angular momentum being conserved during the encounter and which incorporates explicitly the long-range attraction between the reactants. It is pointed out that the activated complex would not have a Boltzmann energy distribution should the rotational and kinetic temperatures of the reactants differ, and it is shown how allowance for this may be made. Account is taken of the inaccessibility of a considerable fraction of the nuclear spin states of the complex. Methods are given for treating the effect which the finiteness of the dissociation frequency may have on the association rate. Calculations on some reactions of interest are performed. A very simple semiempirical formula for the rate coefficient for radiative association is also given.

  18. Ionized carbon in side-illuminated molecular clouds.

    PubMed

    Boreiko, R T; Betz, A L; Zmuidzinas, J

    1990-04-10

    We have observed the 2P3/2-2P1/2 fine-structure line of C II at 1900 GHz in five sources with ionization fronts nearly perpendicular to the plane of the sky. The LSR velocity of the C II emission is generally in good agreement with that observed for molecular species such as CO. However, the observed line widths of 3-14 km s-1 are typically wider than those of molecular lines and often show rapid spatial variations in the regions observed. In some sources this may indicate that part of the C II emanates from an ionized gas component, while for others it suggests an association between C II emission and an outflow. The C II brightness temperatures are typically equal to or slighty higher than the dust temperature at all locations observed. In the optically thin approximation, C II excitation temperatures are > or = 100 K and column densities are < or = 10(18) cm-2 for all sources except M17, which has a more intense and complicated line profile with a larger spatial extent than any other source observed. The quoted column density estimates derived in the optically thin limit appear to be somewhat lower than those predicted by models of photodissociation regions for sources with a side-illuminated geometry, but uncertainties in the UV flux and geometry of the ionization front preclude a definitive comparison. The estimated column densities would be higher if the C II emission were somewhat optically thick, in which case the ionized carbon would be more in equilibrium with the dust at temperatures lower than predicted by current models.

  19. Disk-Halo interaction: The molecular clouds in the Galactic center region

    NASA Astrophysics Data System (ADS)

    Riquelme, D.; Martín-Pintado, J.; Mauersberger, R.; Amo-Baladrón, M. A.; Martín, S.; Bronfman, L.

    2012-07-01

    From a large-scale study of the Galactic center (GC) region in SiO(2 - 1), HCO+(1 - 0), and H13CO+(1 - 0), we identify shock regions as traced by the enhancement of SiO emission. We selected 9 positions called by us as "interaction regions", because they mark the places where gas in the GC could be interacting with gas coming from higher latitude ("disk-halo interaction") or from larger galactocentric radius. These positions were studied using the 12C/13C isotopic ratio to trace gas accretion/ejection. We found a systematically higher 12C/13C isotopic ratio (> 40) toward the interaction regions than for the GC "standard" molecular clouds (20 - 25). These high isotopic ratios are consistent with the accretion of the gas from higher galactic latitudes or from larger galactocentric distances. There are two kinetic temperature regimes (one warm at ~ 200 K and one cold at ~ 40 K) for all the positions, except for the positions associated to the giant molecular loops where only the warm component is present. Relative molecular abundances suggest that the heating mechanism in the GC is related to shocks. We mapped one molecular cloud placed at the foot points of the giant molecular loops in 3-mm molecular lines to reveal the morphology, chemical composition and the kinematics of the shocked gas.

  20. Cosmic Rays and MHD Turbulence Generation in Interstellar Giant Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Schlickeiser, R.; Caglar, M.; Lazarian, A.

    2016-06-01

    The diffusive propagation of nonrelativistic cosmic ray (CR) protons undergoing energy losses by ionization in a dense homogeneous infinitely extended interstellar molecular cloud (MC) is investigated. The steady-state transport equation for the differential number density of nonrelativistic CR protons is solved with the boundary condition that at the edge of cloud it agrees with the interstellar CR number density. It is shown that giant interstellar MCs with column depths much greater than about 7\\cdot {10}22 cm‑2 are an efficient sink of nonrelativistic CRs. At small penetration depths the CRs lose energy by ionizing and heating the molecular gas, whereas at large penetration depths they are collectively dissipated by the streaming instability, which transfers one-half of the energy density of the incoming interstellar nonrelativistic CRs to Alfvénic magnetic field turbulence.

  1. Warm neutral halos around molecular clouds. VI - Physical and chemical modeling

    NASA Technical Reports Server (NTRS)

    Andersson, B.-G.; Wannier, P. G.

    1993-01-01

    A combined physical and chemical modeling of the halos around molecular clouds is presented, with special emphasis on the H-to-H2 transition. On the basis of H I 21 cm observations, it is shown that the halos are extended. A physical model is employed in conjunction with a chemistry code to provide a self-consistent description of the gas. The radiative transfer code provides a check with H I, CO, and OH observations. It is concluded that the warm neutral halos are not gravitationally bound to the underlying molecular clouds and are isobaric. It is inferred from the observed extent of the H I envelopes and the large observed abundance of OH in them that the generally accepted rate for H2 information on grains is too large by a factor of two to three.

  2. Gaps in globular cluster streams: giant molecular clouds can cause them too

    NASA Astrophysics Data System (ADS)

    Amorisco, Nicola C.; Gómez, Facundo A.; Vegetti, Simona; White, Simon D. M.

    2016-11-01

    As a result of their internal dynamical coherence, thin stellar streams formed by disrupting globular clusters (GCs) can act as detectors of dark matter (DM) substructure in the Galactic halo. Perturbations induced by close flybys amplify into detectable density gaps, providing a probe both of the abundance and of the masses of DM subhaloes. Here, we use N-body simulations to show that the Galactic population of giant molecular clouds (GMCs) can also produce gaps (and clumps) in GC streams, and so may confuse the detection of DM subhaloes. We explore the cases of streams analogous to the observed Palomar 5 and GD1 systems, quantifying the expected incidence of structure caused by GMC perturbations. Deep observations should detect such disturbances regardless of the substructure content of the Milky Way's halo. Detailed modelling will be needed to demonstrate that any detected gaps or clumps were produced by DM subhaloes rather than by molecular clouds.

  3. SUPERNOVA REMNANT KES 17: AN EFFICIENT COSMIC RAY ACCELERATOR INSIDE A MOLECULAR CLOUD

    SciTech Connect

    Gelfand, Joseph D.; Castro, Daniel; Slane, Patrick O.; Temim, Tea; Hughes, John P.; Rakowski, Cara E-mail: cara.rakowski@gmail.com

    2013-11-10

    The supernova remnant Kes 17 (SNR G304.6+0.1) is one of a few but growing number of remnants detected across the electromagnetic spectrum. In this paper, we analyze recent radio, X-ray, and γ-ray observations of this object, determining that efficient cosmic ray acceleration is required to explain its broadband non-thermal spectrum. These observations also suggest that Kes 17 is expanding inside a molecular cloud, though our determination of its age depends on whether thermal conduction or clump evaporation is primarily responsible for its center-filled thermal X-ray morphology. Evidence for efficient cosmic ray acceleration in Kes 17 supports recent theoretical work concluding that the strong magnetic field, turbulence, and clumpy nature of molecular clouds enhance cosmic ray production in supernova remnants. While additional observations are needed to confirm this interpretation, further study of Kes 17 is important for understanding how cosmic rays are accelerated in supernova remnants.

  4. TRACING THE MAGNETIC FIELD MORPHOLOGY OF THE LUPUS I MOLECULAR CLOUD

    SciTech Connect

    Franco, G. A. P.; Alves, F. O. E-mail: falves@mpe.mpg.de

    2015-07-01

    Deep R-band CCD linear polarimetry collected for fields with lines of sight toward the Lupus I molecular cloud is used to investigate the properties of the magnetic field within this molecular cloud. The observed sample contains about 7000 stars, almost 2000 of them with a polarization signal-to-noise ratio larger than 5. These data cover almost the entire main molecular cloud and also sample two diffuse infrared patches in the neighborhood of Lupus I. The large-scale pattern of the plane-of-sky projection of the magnetic field is perpendicular to the main axis of Lupus I, but parallel to the two diffuse infrared patches. A detailed analysis of our polarization data combined with the Herschel/SPIRE 350 μm dust emission map shows that the principal filament of Lupus I is constituted by three main clumps that are acted on by magnetic fields that have different large-scale structural properties. These differences may be the reason for the observed distribution of pre- and protostellar objects along the molecular cloud and the cloud’s apparent evolutionary stage. On the other hand, assuming that the magnetic field is composed of large-scale and turbulent components, we find that the latter is rather similar in all three clumps. The estimated plane-of-sky component of the large-scale magnetic field ranges from about 70 to 200 μG in these clumps. The intensity increases toward the Galactic plane. The mass-to-magnetic flux ratio is much smaller than unity, implying that Lupus I is magnetically supported on large scales.

  5. General analytic results for nonlinear waves and solitons in molecular clouds

    NASA Technical Reports Server (NTRS)

    Adams, Fred C.; Fatuzzo, Marco; Watkins, Richard

    1994-01-01

    We study nonlinear wave phenomena in self-gravitating fluid systems, with a particular emphasis on applications to molecular clouds. This paper presents analytical results for one spatial dimension. We show that a large class of physical systems can be described by theories with a 'charge density' q(rho); this quantity replaces the density on the right-hand side of the Poisson equation for the gravitational potential. We use this formulation to prove general results about nonlinear wave motions in self-gravitating systems. We show that in order for stationary waves to exist, the total charge (the integral of the charge density over the wave profile) must vanish. This 'no-charge' property for solitary waves is related to the capability of a system to be stable to gravitational perturbations for arbitrarily long wavelengths. We find necessary and sufficient conditions on the charge density for the existence of solitary waves and stationary waves. We study nonlinear wave motions for Jeans-type theories (where q(rho) = rho-rho(sub 0)) and find that nonlinear waves of large amplitude are confined to a rather narrow range of wavelengths. We also study wave motions for molecular clouds threaded by magnetic fields and show how the allowed range of wavelengths is affected by the field strength. Since the gravitational force in one spatial dimension does not fall off with distance, we consider two classes of models with more realistic gravity: Yukawa potentials and a pseudo two-dimensional treatment. We study the allowed types of wave behavior for these models. Finally, we discuss the implications of this work for molecular cloud structure. We argue that molecular clouds can support a wide variety of wave motions and suggest that stationary waves (such as those considered in this paper) may have already been observed.

  6. Tracing the Magnetic Field Morphology of the Lupus I Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Franco, G. A. P.; Alves, F. O.

    2015-07-01

    Deep R-band CCD linear polarimetry collected for fields with lines of sight toward the Lupus I molecular cloud is used to investigate the properties of the magnetic field within this molecular cloud. The observed sample contains about 7000 stars, almost 2000 of them with a polarization signal-to-noise ratio larger than 5. These data cover almost the entire main molecular cloud and also sample two diffuse infrared patches in the neighborhood of Lupus I. The large-scale pattern of the plane-of-sky projection of the magnetic field is perpendicular to the main axis of Lupus I, but parallel to the two diffuse infrared patches. A detailed analysis of our polarization data combined with the Herschel/SPIRE 350 μm dust emission map shows that the principal filament of Lupus I is constituted by three main clumps that are acted on by magnetic fields that have different large-scale structural properties. These differences may be the reason for the observed distribution of pre- and protostellar objects along the molecular cloud and the cloud’s apparent evolutionary stage. On the other hand, assuming that the magnetic field is composed of large-scale and turbulent components, we find that the latter is rather similar in all three clumps. The estimated plane-of-sky component of the large-scale magnetic field ranges from about 70 to 200 μG in these clumps. The intensity increases toward the Galactic plane. The mass-to-magnetic flux ratio is much smaller than unity, implying that Lupus I is magnetically supported on large scales. Based on observations collected at the Observatório do Pico dos Dias, operated by Laboratório Nacional de Astrofísica (LNA/MCTI, Brazil).

  7. Squeezed between shells: The fate of the Lupus I molecular cloud

    NASA Astrophysics Data System (ADS)

    Gaczkowski, Benjamin; Preibisch, Thomas; Stanke, Thomas

    2015-08-01

    Today molecular cloud formation is attributed to collisions of large-scale flows in the ISM. Such flows can be driven by stellar feedback processes and supernovae. The numerous massive stars in the three sub-groups of the Sco-Cen OB-association created a huge system of expanding loop-like H I structures around each of the sub-groups. The Lupus I molecular cloud is situated in the middle between the Upper-Scorpius (USco) and the Upper-Centaurus-Lupus (UCL) sub-groups. At this location the expanding USco H I shell interacts with a bubble driven by the winds of the remaining B-stars of UCL. With a distance of 150 pc Lupus I represents the nearest example where we can study how such a collision process forms and influences new dense clouds in the ISM. We present LABOCA continuum sub-mm observations of Lupus I, complemented by Herschel and Planck data from which we constructed column density and temperature maps to characterize the cloud in a multi-wavelength approach. All maps revealed that the cloud can be divided into two distinct regions. The northern part that has on average lower densities and higher temperatures as well as no active star formation and the center-south part with dozens of pre-stellar and protostellar cores where density and temperature reach their maximum and minimum, respectively. The column density PDFs from the Herschel data show double-peaked profiles for all parts of the cloud. In those parts with active star formation also a power-law tail is found. With LABOCA the PDFs follow the denser parts of the cloud showing good agreement with those from Herschel for the second lognormal component and the power-law tail. The distribution of the 15 cores we found with LABOCA confirms that only the center-south part of Lupus I is actively forming stars whereas the north is quiescent. We argue that the main driving agents in the formation process of Lupus I are the advancing USco H I shell in whose edge the cloud is most likely embedded colliding with

  8. LUMINOSITY FUNCTIONS OF SPITZER-IDENTIFIED PROTOSTARS IN NINE NEARBY MOLECULAR CLOUDS

    SciTech Connect

    Kryukova, E.; Megeath, S. T.; Allen, T. S.; Gutermuth, R. A.; Pipher, J.; Allen, L. E.; Myers, P. C.; Muzerolle, J.

    2012-08-15

    We identify protostars in Spitzer surveys of nine star-forming (SF) molecular clouds within 1 kpc: Serpens, Perseus, Ophiuchus, Chamaeleon, Lupus, Taurus, Orion, Cep OB3, and Mon R2, which combined host over 700 protostar candidates. These clouds encompass a variety of SF environments, including both low-mass and high-mass SF regions, as well as dense clusters and regions of sparsely distributed star formation. Our diverse cloud sample allows us to compare protostar luminosity functions in these varied environments. We combine near- and mid-infrared photometry from the Two Micron All Sky Survey and Spitzer to create 1-24 {mu}m spectral energy distributions (SEDs). Using protostars from the c2d survey with well-determined bolometric luminosities, we derive a relationship between bolometric luminosity, mid-IR luminosity (integrated from 1-24 {mu}m), and SED slope. Estimations of the bolometric luminosities for protostar candidates are combined to create luminosity functions for each cloud. Contamination due to edge-on disks, reddened Class II sources, and galaxies is estimated and removed from the luminosity functions. We find that luminosity functions for high-mass SF clouds (Orion, Mon R2, and Cep OB3) peak near 1 L{sub Sun} and show a tail extending toward luminosities above 100 L{sub Sun }. The luminosity functions of the low-mass SF clouds (Serpens, Perseus, Ophiuchus, Taurus, Lupus, and Chamaeleon) do not exhibit a common peak, however the combined luminosity function of these regions peaks below 1 L{sub Sun }. Finally, we examine the luminosity functions as a function of the local surface density of young stellar objects. In the Orion molecular clouds, we find a significant difference between the luminosity functions of protostars in regions of high and low stellar density, the former of which is biased toward more luminous sources. This may be the result of primordial mass segregation, although this interpretation is not unique. We compare our luminosity

  9. The L1457 molecular/atomic cloud complex: H I and CO maps.

    PubMed

    Moriarty-Schieven, G H; Andersson, B G; Wannier, P G

    1997-02-01

    L1457 is the closest known molecular cloud (65 pc), and it lies near the edge of the local hot bubble and well out of the Galactic plane (b approximately -34 degrees). We have mapped an 8 degrees x 8 degrees region at 35' resolution and a 3 degrees x 5 degrees region at approximately 2' resolution in H I 21 cm emission. We have also mapped a 2 degrees x 4 degrees region at 2' resolution in 12CO J = 1-0. We find that there is an extended component of atomic gas, clearly associated with the molecular complex and comparable to it in total mass. The H I structure at small scales in the vicinity of the molecular clouds is remarkable, consisting largely of long, narrow filaments less than 20' (0.2 pc) in width and 1 degree-4 degrees in length. A thin (<10') limb-brightened atomic halo is seen to surround the CO at some velocities, but it is ill-defined at other velocities. The halo may be disturbed by external pressure, perhaps from the hot gas in the local bubble. The molecular clouds are part of a large structure approximately 5 degrees x 3 degrees in extent with a small "funnel-shaped" extension to the south. The structure, which we call the L1457 atomic/molecular complex, is dominated by H I in the north and H2 in the south extension. Roughly one-half the mass of the complex is molecular. The structure of this complex at both large- and small-scale suggests that the south end has been recently compressed.

  10. Submillimeter and far infrared line observations of M17 SW: A clumpy molecular cloud penetrated by UV radiation

    NASA Technical Reports Server (NTRS)

    Stutzki, J.; Stacey, G. J.; Genzel, R.; Harris, A. I.; Jaffe, d. T.; Lugten, J. B.

    1987-01-01

    Millimeter, submillimeter, and far infrared spectroscopic observations of the M17 SW star formation region are discussed. The results require the molecular cloud near the interface to be clumpy or filamentary. As a consequence, far ultraviolet radiation from the central OB stellar cluster can penetrate into the dense molecular cloud to a depth of several pc, thus creating bright and extended (CII) emission from the photodissociated surfaces of dense atomic and molecular clumps or sheets. The extended (CII) emission throughout the molecular cloud SW of the M17 complex has a level 20 times higher than expected from a single molecular cloud interface exposed to an ultraviolet radiation field typical of the solar neighborhood. This suggests that the molecular cloud as a whole is penetrated by ultraviolet radiation and has a clumpy or filamentary structure. The number of B stars expected to be embedded in the M17 molecular cloud probably can provide the UV radiation necessary for the extended (CII) emission. Alternatively, the UV radiation could be external, if the interstellar radiation in the vicinity of M17 is higher than in the solar neighborhood.

  11. Striations in the Taurus molecular cloud: Kelvin-Helmholtz instability or MHD waves?

    NASA Astrophysics Data System (ADS)

    Heyer, M.; Goldsmith, P. F.; Yıldız, U. A.; Snell, R. L.; Falgarone, E.; Pineda, J. L.

    2016-10-01

    The origin of striations aligned along the local magnetic field direction in the translucent envelope of the Taurus molecular cloud is examined with new observations of 12CO and 13CO J = 2-1 emission obtained with the 10-m Submillimeter Telescope of the Arizona Radio Observatory. These data identify a periodic pattern of excess blue and redshifted emission that is responsible for the striations. For both 12CO and 13CO, spatial variations of the J = 2-1 to J = 1-0 line ratio are small and are not spatially correlated with the striation locations. A medium comprised of unresolved CO emitting substructures (cells) with a beam area filling factor less than unity at any velocity is required to explain the average line ratios and brightness temperatures. We propose that the striations are generated from the modulation of velocities and beam filling factor of the cells as a result of either the Kelvin-Helmholtz instability or magnetosonic waves propagating through the envelope of the Taurus molecular cloud. Both processes are likely common features in molecular clouds that are sub-Alfvénic and may explain low column density, cirrus-like features similarly aligned with the magnetic field observed throughout the interstellar medium in far-infrared surveys of dust emission.

  12. A YOUNG GIANT MOLECULAR CLOUD FORMED AT THE INTERFACE OF TWO COLLIDING SUPERSHELLS: OBSERVATIONS MEET SIMULATIONS

    SciTech Connect

    Dawson, J. R.; Ntormousi, E.; Fierlinger, K.

    2015-01-20

    Dense, star-forming gas is believed to form at the stagnation points of large-scale interstellar medium flows, but observational examples of this process in action are rare. We here present a giant molecular cloud (GMC) sandwiched between two colliding Milky Way supershells, which we argue shows strong evidence of having formed from material accumulated at the collision zone. Combining {sup 12}CO, {sup 13}CO, and C{sup 18}O(J = 1-0) data with new high-resolution, three-dimensional hydrodynamical simulations of colliding supershells, we discuss the origin and nature of the GMC (G288.5+1.5), favoring a scenario in which the cloud was partially seeded by pre-existing denser material, but assembled into its current form by the action of the shells. This assembly includes the production of some new molecular gas. The GMC is well interpreted as non-self-gravitating, despite its high mass (M{sub H{sub 2}}∼1.7×10{sup 5} M{sub ⊙}), and is likely pressure confined by the colliding flows, implying that self-gravity was not a necessary ingredient for its formation. Much of the molecular gas is relatively diffuse, and the cloud as a whole shows little evidence of star formation activity, supporting a scenario in which it is young and recently formed. Drip-like formations along its lower edge may be explained by fluid dynamical instabilities in the cooled gas.

  13. LARGE-SCALE CO MAPS OF THE LUPUS MOLECULAR CLOUD COMPLEX

    SciTech Connect

    Tothill, N. F. H.; Loehr, A.; Stark, A. A.; Lane, A. P.; Harnett, J. I.; Bourke, T. L.; Myers, P. C.; Parshley, S. C.; Wright, G. A.; Walker, C. K.

    2009-11-01

    Fully sampled degree-scale maps of the {sup 13}CO 2-1 and CO 4-3 transitions toward three members of the Lupus Molecular Cloud Complex-Lupus I, III, and IV-trace the column density and temperature of the molecular gas. Comparison with IR extinction maps from the c2d project requires most of the gas to have a temperature of 8-10 K. Estimates of the cloud mass from {sup 13}CO emission are roughly consistent with most previous estimates, while the line widths are higher, around 2 km s{sup -1}. CO 4-3 emission is found throughout Lupus I, indicating widespread dense gas, and toward Lupus III and IV. Enhanced line widths at the NW end and along the edge of the B 228 ridge in Lupus I, and a coherent velocity gradient across the ridge, are consistent with interaction between the molecular cloud and an expanding H I shell from the Upper-Scorpius subgroup of the Sco-Cen OB Association. Lupus III is dominated by the effects of two HAe/Be stars, and shows no sign of external influence. Slightly warmer gas around the core of Lupus IV and a low line width suggest heating by the Upper-Centaurus-Lupus subgroup of Sco-Cen, without the effects of an H I shell.

  14. Herbig-haro objects and mid-infrared outflows in the VELA C molecular cloud

    SciTech Connect

    Zhang, Miaomiao; Wang, Hongchi; Henning, Thomas

    2014-08-01

    We have performed a deep [S II] λλ6717/6731 wide field Herbig-Haro (HH) object survey toward the Vela C molecular cloud with a sky coverage of about 2 deg{sup 2}. In total, 18 new HH objects, HH 1090-1107, are discovered and the two previously known HH objects, HH 73-74, are also detected in our [S II] images. We also present an investigation of mid-infrared outflows in the Vela C molecular cloud using the Wide-field Infrared Survey Explorer images taken from AllWISE data release. Using the method suggested by Zhang and Wang, 11 extended green objects (EGOs) are identified to be the mid-infrared outflows, including 6 new mid-infrared outflows that have not been detected previously at other wavelengths and 5 mid-infrared counterparts of the HH objects detected in this work. Using the AllWISE Source Catalog and the source classification scheme suggested by Koenig et al., we have identified 56 young stellar object (YSO) candidates in the Vela C molecular cloud. The possible driving sources of the HH objects and EGOs are discussed based on the morphology of HH objects and EGOs and the locations of HH objects, EGOs and YSO candidates. Finally we associate 12 HH objects and 5 EGOs with 10 YSOs and YSO candidates. The median length of the outflows in Vela C is 0.35 pc and the outflows seem to be oriented randomly.

  15. Low-Mass Star Formation: From Molecular Cloud Cores to Protostars and Protoplanetary Disks

    NASA Astrophysics Data System (ADS)

    Inutsuka, S.-I.; Machida, M.; Matsumoto, T.; Tsukamoto, Y.; Iwasaki, K.

    2016-05-01

    This review describes realistic evolution of magnetic field and rotation of the protostars, dynamics of outflows and jets, and the formation and evolution of protoplanetary disks. Recent advances in the protostellar collapse simulations cover a huge dynamic range from molecular cloud core density to stellar density in a self-consistent manner and account for all the non-ideal magnetohydrodynamical effects, such as Ohmic resistivity, ambipolar diffusion, and Hall current. We explain the emergence of the first core, i.e., the quasi-hydrostatic object that consists of molecular gas, and the second core, i.e., the protostar. Ohmic dissipation largely removes the magnetic flux from the center of a collapsing cloud core. A fast well-collimated bipolar jet along the rotation axis of the protostar is driven after the magnetic field is re-coupled with warm gas (˜103 K) around the protostar. The circumstellar disk is born in the "dead zone", a region that is de-coupled from the magnetic field, and the outer radius of the disk increases with that of the dead zone during the early accretion phase. The rapid increase of the disk size occurs after the depletion of the envelope of molecular cloud core. The effect of Hall current may create two distinct populations of protoplanetary disks.

  16. Geometry-independent Determination of Radial Density Distributions in Molecular Cloud Cores and Other Astronomical Objects

    NASA Astrophysics Data System (ADS)

    Krčo, Marko; Goldsmith, Paul F.

    2016-05-01

    We present a geometry-independent method for determining the shapes of radial volume density profiles of astronomical objects whose geometries are unknown, based on a single column density map. Such profiles are often critical to understand the physics and chemistry of molecular cloud cores, in which star formation takes place. The method presented here does not assume any geometry for the object being studied, thus removing a significant source of bias. Instead, it exploits contour self-similarity in column density maps, which appears to be common in data for astronomical objects. Our method may be applied to many types of astronomical objects and observable quantities so long as they satisfy a limited set of conditions, which we describe in detail. We derive the method analytically, test it numerically, and illustrate its utility using 2MASS-derived dust extinction in molecular cloud cores. While not having made an extensive comparison of different density profiles, we find that the overall radial density distribution within molecular cloud cores is adequately described by an attenuated power law.

  17. MOLECULAR RINGS AROUND INTERSTELLAR BUBBLES AND THE THICKNESS OF STAR-FORMING CLOUDS

    SciTech Connect

    Beaumont, Christopher N.; Williams, Jonathan P. E-mail: jpw@ifa.hawaii.ed

    2010-02-01

    The winds and radiation from massive stars clear out large cavities in the interstellar medium. These bubbles, as they have been called, impact their surrounding molecular clouds and may influence the formation of stars therein. Here we present James Clerk Maxwell Telescope observations of the J = 3-2 line of CO in 43 bubbles identified with Spitzer Space Telescope observations. These spectroscopic data reveal the three-dimensional structure of the bubbles. In particular, we show that the cold gas lies in a ring, not a sphere, around the bubbles indicating that the parent molecular clouds are flattened with a typical thickness of a few parsecs. We also mapped seven bubbles in the J = 4-3 line of HCO{sup +} and find that the column densities inferred from the CO and HCO{sup +} line intensities are below that necessary for 'collect and collapse' models of induced star formation. We hypothesize that the flattened molecular clouds are not greatly compressed by expanding shock fronts, which may hinder the formation of new stars.

  18. Herbig-Haro Objects and Mid-infrared Outflows in the Vela C Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Zhang, Miaomiao; Wang, Hongchi; Henning, Thomas

    2014-08-01

    We have performed a deep [S II] λλ6717/6731 wide field Herbig-Haro (HH) object survey toward the Vela C molecular cloud with a sky coverage of about 2 deg2. In total, 18 new HH objects, HH 1090-1107, are discovered and the two previously known HH objects, HH 73-74, are also detected in our [S II] images. We also present an investigation of mid-infrared outflows in the Vela C molecular cloud using the Wide-field Infrared Survey Explorer images taken from AllWISE data release. Using the method suggested by Zhang & Wang, 11 extended green objects (EGOs) are identified to be the mid-infrared outflows, including 6 new mid-infrared outflows that have not been detected previously at other wavelengths and 5 mid-infrared counterparts of the HH objects detected in this work. Using the AllWISE Source Catalog and the source classification scheme suggested by Koenig et al., we have identified 56 young stellar object (YSO) candidates in the Vela C molecular cloud. The possible driving sources of the HH objects and EGOs are discussed based on the morphology of HH objects and EGOs and the locations of HH objects, EGOs and YSO candidates. Finally we associate 12 HH objects and 5 EGOs with 10 YSOs and YSO candidates. The median length of the outflows in Vela C is 0.35 pc and the outflows seem to be oriented randomly.

  19. Large-Scale CO and [C I] Emission in the ρ Ophiuchi Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Kulesa, Craig A.; Hungerford, Aimee L.; Walker, Christopher K.; Zhang, Xiaolei; Lane, Adair P.

    2005-05-01

    We present a comprehensive study of the ρ Ophiuchi molecular cloud that addresses aspects of the physical structure and condition of the molecular cloud and its photodissociation region (PDR) by combining far-infrared and submillimeter-wave observations with a wide range of angular scale and resolution. We present 1600 arcmin2 maps (2.3 pc2) with 0.1 pc resolution in submillimeter CO (4-->3) and [C I] (3P1-->3P0) line emission from the Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) and pointed observations in the CO (7-->6) and [C I] (3P2-->3P1) lines. Within the large-scale maps, smaller spectral line maps of 3000 AU resolution over ~90 arcmin2 (0.2 pc2) of the cloud in CO, CS, HCO+, and their rare isotopomers are made at the Heinrich Hertz Telescope (HHT) in Arizona. Comparison of CO, HCO+, and [C I] maps with far-infrared observations of atomic and ionic species from the Infrared Space Observatory (ISO) far-infrared and submillimeter continuum emission and near-infrared H2 emission allows clearer determination of the physical and chemical structure of the ρ Oph PDR, since each species probes a different physical region of the cloud structure. Although a homogeneous plane-parallel PDR model can reproduce many of the observations described here, the excitation conditions needed to produce the observed HCO+ and [O I] emission imply inhomogeneous structure. Strong chemical gradients are observed in HCO+ and CS; the former is ascribed to a local enhancement in the H2 ionization rate, and the latter is principally due to shocks. Under the assumption of a simple two-component gas model for the cloud, we find that [C II] and [C I] emission predominantly arises from the lower density envelopes (103-104 cm-3) that surround denser cloud condensations, or ``clumps.'' The distribution of [C I] is very similar to that of C18O and is generally consistent with illumination from the ``far'' side of the cloud. A notable exception is found at the western edge

  20. Dust extinction and molecular gas in the dark cloud IC 5146

    NASA Astrophysics Data System (ADS)

    Lada, Charles J.; Lada, Elizabeth A.; Clemens, Dan P.; Bally, John

    1994-07-01

    In this paper we describe a powerful method for mapping the distribution of dust through a molecular cloud using data obtained in large-scale, multiwavelength, infrared imaging surveys. This method combines direct measurements of near-infrared color excess and certain techniques of star counting to derive mean extinctions and map the dust column density distribution through a cloud at higher angular resolutions and greater optical depths than those achieved previously by optical star counting. We report the initial results of the application of this method to a dark cloud complex near the cluster IC 5146, where we have performed coordinated, near-infrared, JHK imaging and (13)CO, C(18)O, and CS millimeter-wave, molecular-line surveys of a large portion of the complex. More than 4000 stars were detected in our JHK survey of the cloud. Of these, all but about a dozen appear to be field stars not associated with the cloud. Star count maps at J band show a striking and detailed anticorrelation between the surface density of J-band sources and CO and CS molecular-line emission. We used the (H-K) colors and positions of nearly 1300 sources to directly measure and map the extinction and thus trace the dust column density through the cloud at an effective angular resolution of 1 min .5. We report an interesting correlation between the measured dispersion in our extinction determinations and the extinction. Modeling this relation indicates that effects of small-scale cloud structure dominate the uncertainties in our measurements. Moreover, we demonstrate that such observations can be used to place constraints on the nature of the spatial distribution of extinction on scales smaller than our resolution. In particular, we show that models in which the dust is distributed uniformly or in discrete high-extinction clumps on scales smaller than (1 min .5) are inconsistent with the observations. We have derived extinctions at the same positions and at the same angular resolution

  1. Dust extinction and molecular gas in the dark cloud IC 5146

    NASA Technical Reports Server (NTRS)

    Lada, Charles J.; Lada, Elizabeth A.; Clemens, Dan P.; Bally, John

    1994-01-01

    In this paper we describe a powerful method for mapping the distribution of dust through a molecular cloud using data obtained in large-scale, multiwavelength, infrared imaging surveys. This method combines direct measurements of near-infrared color excess and certain techniques of star counting to derive mean extinctions and map the dust column density distribution through a cloud at higher angular resolutions and greater optical depths than those achieved previously by optical star counting. We report the initial results of the application of this method to a dark cloud complex near the cluster IC 5146, where we have performed coordinated, near-infrared, JHK imaging and (13)CO, C(18)O, and CS millimeter-wave, molecular-line surveys of a large portion of the complex. More than 4000 stars were detected in our JHK survey of the cloud. Of these, all but about a dozen appear to be field stars not associated with the cloud. Star count maps at J band show a striking and detailed anticorrelation between the surface density of J-band sources and CO and CS molecular-line emission. We used the (H-K) colors and positions of nearly 1300 sources to directly measure and map the extinction and thus trace the dust column density through the cloud at an effective angular resolution of 1 min .5. We report an interesting correlation between the measured dispersion in our extinction determinations and the extinction. Modeling this relation indicates that effects of small-scale cloud structure dominate the uncertainties in our measurements. Moreover, we demonstrate that such observations can be used to place constraints on the nature of the spatial distribution of extinction on scales smaller than our resolution. In particular, we show that models in which the dust is distributed uniformly or in discrete high-extinction clumps on scales smaller than (1 min .5) are inconsistent with the observations. We have derived extinctions at the same positions and at the same angular resolution

  2. Collapse and fragmentation of molecular cloud cores. 2: Collapse induced by stellar shock waves

    NASA Technical Reports Server (NTRS)

    Boss, Alan P.

    1995-01-01

    The standard scenario for low-mass star formation involves 'inside-out' collapse of a dense molecular cloud core following loss of magnetic field support through ambipolar diffusion. However, isotopic anomalies in presolar grains and meteoritical inclusions imply that the collapse of the presolar cloud may have been triggered by a stellar shock wave. This paper explores 'outside-in' collapse, that is, protostellar collapse initiated directly by the compression of quiescent dense cloud cores impacted by relatively slow stellar shock waves. A second-order accurate, gravitational hydrodynamics code has been used to study both the spherically symmetrical and three-dimensional evolution of initially centrally condensed, isothermal, self-gravitating, solar-mass cloud cores that are struck by stellar shock waves with velocities up to 25 km/s and postshock temperatures of 10 to 10,000 K. The models show that such mild shock waves do not completely shred and destroy the cloud, and that the dynamical ram pressure can compress the cloud to the verge of self-gravitational collapse. However, compression caused by a high postshock temperature is a considerably more effective means of inducing collapse. Shock-induced collapse produces high initial mass accretion rates (greater than 10(exp -4) solar mass/yr in a solar-mass cloud) that decline rapidly to much lower values, depending on the presence (approximately 10(exp -6) solar mass/yr) or absence (approximately 10(exp -8) to 10(exp -7) solar mass/yr) of an infinite reservoir of mass. Stellar mass accretion rates approximately 10(exp -7) solar mass/yr have been previously inferred from the luminosities of T Tauri stars; balanced mass accretion (stellar rate = envelope rate) at approximately 10(exp -7) solar mass/yr could then be possible if accretion occurs from a finite mass reservoir. Fluid tracers are used to determine what fraction of the stellar shock material is incorporated into the resulting protostellar object and disk

  3. Atomic Oxygen Abundance in Molecular Clouds: Absorption Toward Sagittarius B2

    NASA Technical Reports Server (NTRS)

    Lis, D. C.; Keene, Jocelyn; Phillips, T. G.; Schilke, P.; Werner, M. W.; Zmuidzinas, J.

    2001-01-01

    We have obtained high-resolution (approximately 35 km/s) spectra toward the molecular cloud Sgr B2 at 63 micrometers, the wavelength of the ground-state fine-structure line of atomic oxygen (O(I)), using the ISO-LWS instrument. Four separate velocity components are seen in the deconvolved spectrum, in absorption against the dust continuum emission of Sgr B2. Three of these components, corresponding to foreground clouds, are used to study the O(I) content of the cool molecular gas along the line of sight. In principle, the atomic oxygen that produces a particular velocity component could exist in any, or all, of three physically distinct regions: inside a dense molecular cloud, in the UV illuminated surface layer (PDR) of a cloud, and in an atomic (H(I)) gas halo. For each of the three foreground clouds, we estimate, and subtract from the observed O(I) column density, the oxygen content of the H(I) halo gas, by scaling from a published high-resolution 21 cm spectrum. We find that the remaining O(I) column density is correlated with the observed (13)CO column density. From the slope of this correlation, an average [O(I)]/[(13)CO] ratio of 270 +/- 120 (3-sigma) is derived, which corresponds to [O(I)]/[(13)CO] = 9 for a CO to (13)CO abundance ratio of 30. Assuming a (13)CO abundance of 1x10(exp -6) with respect to H nuclei, we derive an atomic oxygen abundance of 2.7x10(exp -4) in the dense gas phase, corresponding to a 15% oxygen depletion compared to the diffuse ISM in our Galactic neighborhood. The presence of multiple, spectrally resolved velocity components in the Sgr B2 absorption spectrum allows, for the first time, a direct determination of the PDR contribution to the O(I) column density. The PDR regions should contain O(I) but not (13)CO, and would thus be expected to produce an offset in the O(I)-(13)CO correlation. Our data do not show such an offset, suggesting that within our beam O(I) is spatially coexistent with the molecular gas, as traced by (13)CO

  4. The gas properties of the W3 giant molecular cloud: a HARP study

    NASA Astrophysics Data System (ADS)

    Polychroni, D.; Moore, T. J. T.; Allsopp, J.

    2012-06-01

    We present 12CO, 13CO and C18O J= 3 → 2 maps of the W3 giant molecular cloud (GMC) made at the James Clerk Maxwell Telescope. We combine these observations with Five College Radio Astronomy Observatory CO J= 1→0 data to produce the first map of molecular-gas temperatures across a GMC and the most accurate determination of the mass distribution in W3 yet obtained. We measure excitation temperatures in the part of the cloud dominated by triggered star formation (the high-density layer, HDL) of 15-30 K, while in the rest of the cloud, which is relatively unaffected by triggering (low-density layer), the excitation temperature is generally less than 12 K. We identify a temperature gradient in the HDL which we associate with an age sequence in the embedded massive star-forming regions. We measure the mass of the cloud to be 4.4 ± 0.4 × 105 M⊙, in agreement with previous estimates. Existing submillimetre continuum data are used to derive the fraction of gas mass in dense clumps as a function of position in the cloud. This fraction, which we interpret as a clump formation efficiency (CFE), is significantly enhanced across the HDL, probably due to the triggering. Finally, we measure the 3D rms Mach number, ?, as a function of position and find a correlation between ? and the CFE within the HDL only. This correlation is interpreted as due to feedback from the newly formed stars, and a change in its slope between the three main star-forming regions is construed as another evolutionary effect. We conclude that triggering has affected the star formation process in the W3 GMC primarily by creating additional dense structures that can collapse into stars. Any traces of changes in CFE due to additional turbulence have since been overruled by the feedback effects of the star-forming process itself.

  5. Evolution of prolate molecular clouds at H II boundaries - II. Formation of BRCs of asymmetrical morphology

    NASA Astrophysics Data System (ADS)

    Kinnear, T. M.; Miao, J.; White, G. J.; Sugitani, K.; Goodwin, S.

    2015-06-01

    A systematic investigation on the evolution of a prolate cloud at an H II boundary is conducted using smoothed particle hydrodynamics in order to understand the mechanism for a variety of irregular morphological structures found at the boundaries of various H II regions. The prolate molecular clouds in this investigation are set with their semimajor axes at inclinations between 0° and 90° to a plane-parallel ionizing radiation flux. A set of four parameters, the number density n, the ratio of major to minor axis γ, the inclination angle ϕ and the incident flux FEUV, are used to define the initial state of the simulated clouds. The dependence of the evolution of a prolate cloud under radiation-driven implosion (RDI) on each of the four parameters is investigated. It is found that (i) in addition to the well-studied standard type A, B or C bright-rimmed clouds (BRCs), many other types such as asymmetrical BRCs, filamentary structures and irregular horse-head structures could also be developed at H II boundaries with only simple initial conditions; (ii) the final morphological structures are very sensitive to the four initial parameters, especially to the initial density and the inclination; (iii) the previously defined ionizing radiation penetration depth can still be used as a good indicator of the final morphology. Based on the simulation results, the formation time-scales and masses of the early RDI-triggered star formation from clouds of different initial conditions are also estimated. Finally a unified mechanism for the various morphological structures found in many different H II boundaries is suggested.

  6. NARROW Na AND K ABSORPTION LINES TOWARD T TAURI STARS: TRACING THE ATOMIC ENVELOPE OF MOLECULAR CLOUDS

    SciTech Connect

    Pascucci, I.; Simon, M. N.; Edwards, S.; Heyer, M.; Rigliaco, E.; Hillenbrand, L.; Gorti, U.; Hollenbach, D.

    2015-11-20

    We present a detailed analysis of narrow Na i and K i absorption resonance lines toward nearly 40 T Tauri stars in Taurus with the goal of clarifying their origin. The Na i λ5889.95 line is detected toward all but one source, while the weaker K i λ7698.96 line is detected in about two-thirds of the sample. The similarity in their peak centroids and the significant positive correlation between their equivalent widths demonstrate that these transitions trace the same atomic gas. The absorption lines are present toward both disk and diskless young stellar objects, which excludes cold gas within the circumstellar disk as the absorbing material. A comparison of Na i and CO detections and peak centroids demonstrates that the atomic gas and molecular gas are not co-located, the atomic gas being more extended than the molecular gas. The width of the atomic lines corroborates this finding and points to atomic gas about an order of magnitude warmer than the molecular gas. The distribution of Na i radial velocities shows a clear spatial gradient along the length of the Taurus molecular cloud filaments. This suggests that absorption is associated with the Taurus molecular cloud. Assuming that the gradient is due to cloud rotation, the rotation of the atomic gas is consistent with differential galactic rotation, whereas the rotation of the molecular gas, although with the same rotation axis, is retrograde. Our analysis shows that narrow Na i and K i absorption resonance lines are useful tracers of the atomic envelope of molecular clouds. In line with recent findings from giant molecular clouds, our results demonstrate that the velocity fields of the atomic and molecular gas are misaligned. The angular momentum of a molecular cloud is not simply inherited from the rotating Galactic disk from which it formed but may be redistributed by cloud–cloud interactions.

  7. Gas Kinematics on Giant Molecular Cloud Scales in M51 with PAWS: Cloud Stabilization through Dynamical Pressure

    NASA Astrophysics Data System (ADS)

    Meidt, Sharon E.; Schinnerer, Eva; García-Burillo, Santiago; Hughes, Annie; Colombo, Dario; Pety, Jérôme; Dobbs, Clare L.; Schuster, Karl F.; Kramer, Carsten; Leroy, Adam K.; Dumas, Galle; Thompson, Todd A.

    2013-12-01

    We use the high spatial and spectral resolution of the PAWS CO(1-0) survey of the inner 9 kpc of the iconic spiral galaxy M51 to examine the effects of gas streaming motions on the star-forming properties of individual giant molecular clouds (GMCs). We compare our view of gas flows in M51—which arise due to departures from axisymmetry in the gravitational potential (i.e., the nuclear bar and spiral arms)—with the global pattern of star formation as traced by Hα and 24 μm emission. We find that the dynamical environment of GMCs strongly affects their ability to form stars, in the sense that GMCs situated in regions with large streaming motions can be stabilized, while similarly massive GMCs in regions without streaming go on to efficiently form stars. We argue that this is the result of reduced surface pressure felt by clouds embedded in an ambient medium undergoing large streaming motions, which prevent collapse. Indeed, the variation in gas depletion time expected based on the observed streaming motions throughout the disk of M51 quantitatively agrees with the variation in the observed gas depletion time scale. The example of M51 shows that streaming motions, triggered by gravitational instabilities in the form of bars and spiral arms, can alter the star formation law; this can explain the variation in gas depletion time among galaxies with different masses and morphologies. In particular, we can explain the long gas depletion times in spiral galaxies compared with dwarf galaxies and starbursts. We suggest that adding a dynamical pressure term to the canonical free-fall time produces a single star formation law that can be applied to all star-forming regions and galaxies across cosmic time.

  8. Gas kinematics on giant molecular cloud scales in M51 with PAWS: Cloud stabilization through dynamical pressure

    SciTech Connect

    Meidt, Sharon E.; Schinnerer, Eva; Hughes, Annie; Colombo, Dario; Pety, Jérôme; Schuster, Karl F.; Dumas, Galle; Dobbs, Clare L.; Kramer, Carsten; Leroy, Adam K.; Thompson, Todd A.

    2013-12-10

    We use the high spatial and spectral resolution of the PAWS CO(1-0) survey of the inner 9 kpc of the iconic spiral galaxy M51 to examine the effects of gas streaming motions on the star-forming properties of individual giant molecular clouds (GMCs). We compare our view of gas flows in M51—which arise due to departures from axisymmetry in the gravitational potential (i.e., the nuclear bar and spiral arms)—with the global pattern of star formation as traced by Hα and 24 μm emission. We find that the dynamical environment of GMCs strongly affects their ability to form stars, in the sense that GMCs situated in regions with large streaming motions can be stabilized, while similarly massive GMCs in regions without streaming go on to efficiently form stars. We argue that this is the result of reduced surface pressure felt by clouds embedded in an ambient medium undergoing large streaming motions, which prevent collapse. Indeed, the variation in gas depletion time expected based on the observed streaming motions throughout the disk of M51 quantitatively agrees with the variation in the observed gas depletion time scale. The example of M51 shows that streaming motions, triggered by gravitational instabilities in the form of bars and spiral arms, can alter the star formation law; this can explain the variation in gas depletion time among galaxies with different masses and morphologies. In particular, we can explain the long gas depletion times in spiral galaxies compared with dwarf galaxies and starbursts. We suggest that adding a dynamical pressure term to the canonical free-fall time produces a single star formation law that can be applied to all star-forming regions and galaxies across cosmic time.

  9. Gamma-Ray Observations of the Orion Molecular Clouds with the Fermi Large Area Telescope

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Allafort, A.; Antolini, E.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Ferrara, E. C.; Harding, A. K.; Troja, E.

    2012-01-01

    We report on the gamma-ray observations of giant molecular clouds Orion A and B with the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. The gamma-ray emission in the energy band between approx 100 MeV and approx 100 GeV is predicted to trace the gas mass distribution in the clouds through nuclear interactions between the Galactic cosmic rays (CRs) and interstellar gas. The gamma-ray production cross-section for the nuclear interaction is known to approx 10% precision which makes the LAT a powerful tool to measure the gas mass column density distribution of molecular clouds for a known CR intensity. We present here such distributions for Orion A and B, and correlate them with those of the velocity-integrated CO intensity (W(sub CO)) at a 1 deg 1 deg pixel level. The correlation is found to be linear over a W(sub CO) range of approx 10-fold when divided in three regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The W(sub CO)-to-mass conversion factor, X(sub CO), is found to be approx 2.3 10(exp 20) / sq cm (K km/s)(exp -1) for the high-longitude part of Orion A (l > 212 deg), approx 1.7 times higher than approx 1.3 10(exp 20) found for the rest of Orion A and B. We interpret the apparent high X(sub CO) in the high-longitude region of Orion A in the light of recent works proposing a nonlinear relation between H2 and CO densities in the diffuse molecular gas.W(sub CO) decreases faster than the H2 column density in the region making the gas "darker" to W(sub CO).

  10. The structures of embedded clusters in the Perseus, Serpens and Ophiuchus molecular clouds

    NASA Astrophysics Data System (ADS)

    Schmeja, S.; Kumar, M. S. N.; Ferreira, B.

    2008-09-01

    The young stellar population data of the Perseus, Ophiuchus and Serpens molecular clouds are obtained from the Spitzer Cores to Discs (c2d) legacy survey in order to investigate the spatial structure of embedded clusters using the nearest-neighbour (NN) and minimum-spanning tree method. We identify the embedded clusters in these clouds as density enhancements and analyse the clustering parameter with respect to source luminosity and evolutionary stage. This analysis shows that the older Class 2/3 objects are more centrally condensed than the younger Class 0/1 protostars, indicating that clusters evolve from an initial hierarchical configuration to a centrally condensed one. Only IC 348 and the Serpens core, the older clusters in the sample, show signs of mass segregation (indicated by the dependence of on the source magnitude), pointing to a significant effect of dynamical interactions after a few Myr. The structure of a cluster may also be linked to the turbulent energy in the natal cloud as the most centrally condensed cluster is found in the cloud with the lowest Mach number and vice versa. In general, these results agree well with theoretical scenarios of star cluster formation by gravoturbulent fragmentation.

  11. Star formation in a turbulent framework: from giant molecular clouds to protostars

    NASA Astrophysics Data System (ADS)

    Guszejnov, Dávid; Hopkins, Philip F.

    2016-06-01

    Turbulence is thought to be a primary driving force behind the early stages of star formation. In this framework large, self-gravitating, turbulent clouds fragment into smaller clouds which in turn fragment into even smaller ones. At the end of this cascade we find the clouds which collapse into protostars. Following this process is extremely challenging numerically due to the large dynamical range, so in this paper we propose a semi-analytic framework which is able to model star formation from the largest, giant molecular cloud scale, to the final protostellar size scale. Because of the simplicity of the framework it is ideal for theoretical experimentation to explore the principal processes behind different aspects of star formation, at the cost of introducing strong assumptions about the collapse process. The basic version of the model discussed in this paper only contains turbulence, gravity and crude assumptions about feedback; nevertheless it can reproduce the observed core mass function and provide the protostellar system mass function (PSMF), which shows a striking resemblance to the observed initial mass function (IMF), if a non-negligible fraction of gravitational energy goes into turbulence. Furthermore we find that to produce a universal IMF protostellar feedback must be taken into account otherwise the PSMF peak shows a strong dependence on the background temperature.

  12. Testing molecular-cloud fragmentation theories: self-consistent analysis of OH Zeeman observations

    NASA Astrophysics Data System (ADS)

    Mouschovias, Telemachos Ch.; Tassis, Konstantinos

    2009-11-01

    The ambipolar-diffusion theory of star formation predicts the formation of fragments in molecular clouds with mass-to-flux ratios greater than that of the parent-cloud envelope. By contrast, scenarios of turbulence-induced fragmentation do not yield such a robust prediction. Based on this property, Crutcher et al. recently proposed an observational test that could potentially discriminate between fragmentation theories. However, the analysis applied to the data severely restricts the discriminative power of the test: the authors conclude that they can only constrain what they refer to as the `idealized' ambipolar-diffusion theory that assumes initially straight-parallel magnetic field lines in the parent cloud. We present an original, self-consistent analysis of the same data taking into account the non-uniformity of the magnetic field in the cloud envelopes, which is suggested by the data themselves, and we discuss important geometrical effects that must be accounted for in using this test. We show quantitatively that the quality of current data does not allow for a strong conclusion about any fragmentation theory. Given the discriminative potential of the test, we urge for more and better-quality data.

  13. Is 1E 1740.7-2942 inside the Dense Molecular Cloud? Constraints from ASCA Data

    NASA Astrophysics Data System (ADS)

    Churazov, E.; Gilfanov, M.; Sunyaev, R.

    1996-06-01

    The discovery of the molecular cloud (Bally & Leventhal; Mirabel et al.) in the direction of bright and hard X-ray source 1E 1740.7-2942 raised the hypothesis that the unique properties of this object are related to the presence of a dense gas near the compact source. In particular, Bondi-Hoyle accretion onto a single black hole (Bally & Leventhal; Mirabel et al.) or onto a black hole in a binary system (Chen, Gehrels, & Leventhal) has been discussed. We have shown below that the weakness of the 6.4 keV line in the Advanced Satellite for Cosmology and Astrophysics (ASCA) data strongly constrains averaged column density of the gas surrounding the source to the values NH <= 2 x 1022 cm-2. If most of the low-energy absorption in the direction of the source (NH ~ 1023 cm-2) is due to the dense molecular cloud, then the compact source must be located behind the cloud. This would imply that Bondi-Hoyle accretion is unlikely the mechanism responsible for feeding the compact source.

  14. Equiparatition of energy for turbulent astrophysical fluids: Accounting for the unseen energy in molecular clouds

    NASA Technical Reports Server (NTRS)

    Zweibel, Ellen G.; Mckee, Christopher F.

    1995-01-01

    Molecular clouds are observed to be partially supported by turbulent pressure. The kinetic energy of the turbulence is directly measurable, but the potential energy, which consists of magnetic, thermal, and gravitational potential energy, is largly unseen. We have extended previous results on equipartition between kinetic and potential energy to show that it is likely to be a very good approximation in molecular clouds. We have used two separate approaches to demonstrate this result: For small-amplitude perturbations of a static equilibrium, we have used the energy principle analysis of Bernstein et al. (1958); this derivation applies to perturbations of arbitary wavelength. To treat perturbations of a nonstatic equilibrium, we have used the Lagrangian analysis of Dewar (1970); this analysis applies only to short-wavelength perturbations. Both analysis assume conservation of energy. Wave damping has only a small effect on equipartition if the wave frequency is small compared to the neutral-ion collision frequency; for the particular case we considered, radiative losses have no effect on equipartition. These results are then incorporated in a simple way into analyses of cloud equilibrium and global stability. We discuss the effect of Alfvenic turbulence on the Jeans mass and show that it has little effect on the magnetic critical mass.

  15. CO near the Pleiades: Encounter of a star cluster with a small molecular cloud

    NASA Technical Reports Server (NTRS)

    Bally, J.; White, R. E.

    1986-01-01

    Although there is a large amount of interstellar matter near the Pleiades star cluster, the observed dust and gas is not a remnant of the placental molecular cloud from which the star cluster was formed. Carbon monoxide (CO) associated with the visible reflection nebulae was discovered by Cohen (1975). Its radial velocity differs from that of the cluster by many times the cluster escape velocity, which implies that the cloud-cluster association is the result of a chance encounter. This circumstance and the proximity of the Pleiades to the sun creates an unique opportunity for study of interstellar processes at high spatial resolution. To study the molecular component of the gas, a 1.7 square degree field was mapped with the AT&T Bell Laboratories 7-meter antenna (1.7' beam) on a 1' grid in the J=1.0 C(12)O line, obtaining over 6,000 spectra with 50 kHz resolution. The cloud core was mapped in the J=1-0 line of C(13)O. Further observations include an unsuccessful search for CS (J=2-1) at AT&T BL, and some C(12)O J=2-1 spectra obtained at the Millimeter Wave Observatory of the University of Texas.

  16. Soft gamma-ray repeaters: Black holes in giant molecular clouds?

    NASA Technical Reports Server (NTRS)

    Grindlay, Jonathan E.

    1994-01-01

    The BATSE discovery of the near-simultaneous turnon of a soft gamma-ray repeater (SGR) source, located to apporximately 5 deg and possibly SGR 1900+14, and a new hard X-ray transient GRS 1915+105 (discovered by Granat), suggests they may be associated. Published positions for both the SGR and GRS sources do not preclude spatial coincidence for the two sources, or the GRS transient may be associated with another SGR source. We outline a model for SGR sources as due to thermal instabilities in spherical accretion onto black holes in giant molecular clouds. We show that the SIGMA position for the GRS 1915 source is consistent with it being in a giant molecular cloud and compare this possible identification with that suggested for the `1E' source in the Galactic center region. Our model would predict a strong concentration of SGR sources toward the Galactic plane (consistent with both SGR 1900+14 and SGR 1806-20) and so would require the only other known 'SGR,' the GRB 790305 superburst source apparently in the Large Magellanic Cloud, to be fundamentally different. We note that the recently discovered radio/infrared counterpart for the SGR 1806-20 may be consistent with this model, rather than the compact suprernova remnant/pulsar model suggested by Kulkarni and Frail.

  17. Evidence for grain growth in molecular clouds: A Bayesian examination of the extinction law in Perseus

    NASA Astrophysics Data System (ADS)

    Foster, Jonathan B.; Mandel, Kaisey S.; Pineda, Jaime E.; Covey, Kevin R.; Arce, Héctor G.; Goodman, Alyssa A.

    2013-01-01

    We investigate the shape of the extinction law in two 1° square fields of the Perseus molecular cloud complex. We combine deep red-optical (r, i and z band) observations obtained using Megacam on the MMT with UKIRT (United Kingdom Infrared Telescope) Infrared Deep Sky Survey near-infrared (J, H and K band) data to measure the colours of background stars. We develop a new hierarchical Bayesian statistical model, including measurement error, intrinsic colour variation, spectral type and dust reddening, to simultaneously infer parameters for individual stars and characteristics of the population. We implement an efficient Markov chain Monte Carlo algorithm utilizing generalized Gibbs sampling to compute coherent probabilistic inferences. We find a strong correlation between the extinction (AV) and the slope of the extinction law (parametrized by RV). Because the majority of the extinction towards our stars comes from the Perseus molecular cloud, we interpret this correlation as evidence of grain growth at moderate optical depths. The extinction law changes from the `diffuse' value of RV ˜ 3 to the `dense cloud' value of RV ˜ 5 as the column density rises from AV = 2 to 10 mag. This relationship is similar for the two regions in our study, despite their different physical conditions, suggesting that dust grain growth is a fairly universal process.

  18. A Systematic Deuteration Survey in the Gemini OB1 Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Shirley, Yancy L.

    2014-01-01

    Recent maps of dust continuum emission from molecular clouds at submillimeter wavelengths have made it possible to survey and to study the chemistry of entire core and clump populations within a single cloud. One very strong chemical process in star-forming regions is the fractionation of deuterium in molecules which results in an increase in the deuterium ratio many orders of magnitude over the ISM [D]/[H] ratio and provides a chemical probe of cold, dense regions. We present a survey of DCO+ 3-2 emission toward the clump population in the high-mass, star-forming Gemini OB1 molecular cloud complex identified from 1.1 mm continuum imaging by the Bolocam Galactic Plane Survey (BGPS). The peak 1.1 mm continuum positions of 52 clumps were observed with the 10m Heinrich Hertz Submillimeter Telescope operated by the Arizona Radio Observatory. We compare to observations of HCO+ and H13CO+ from the BGPS spectroscopic survey of Shirley et al. to determine the deuterium ratio. We find that DCO+ emission is detected toward 90% of the clumps with a median deuterium ratio of a few percent. DCO+ fractionation anti-correlates with gas kinetic temperature and linewidth, a measure of the amount of turbulence within the clumps.

  19. Giant Molecular Clouds and Star Formation in the Non-Grand Design Spiral Galaxy NGC 6946

    NASA Astrophysics Data System (ADS)

    Rebolledo, David; Wong, Tony; Leroy, Adam

    2011-10-01

    Although the internal physical properties of molecular clouds have been extensively studied (Solomon et al. 1987), a more detailed understanding of their origin and evolution in different types of galaxies is needed. In order to disentangle the details of this process, we performed CO(1→0) CARMA observations of the eastern part of the multi-armed galaxy NGC 6946. Our goal was to determine if azimuthal segregation of various gas and star formation tracers occurs in this kind of spiral galaxy (Tamburro et al. 2008). Although we found no evidence of an angular offset between molecular gas, atomic gas and star formation regions in our observations, we observe a clear radial progression from regions where molecular gas dominates over atomic gas (for r ≤ 2.8 kpc) to regions where the gas becomes mainly atomic (5.6 kpc ≤ r ≤ 7.6 kpc) when azimuthally averaged. In addition, we found that the densest concentrations of molecular gas are located on arms, particularly where they appear to intersect. This result is in concordance with the behavior predicted by simulations of the spiral galaxies with an active potential (Clarke & Gittins 2006; Dobbs & Bonnell 2008). Since NGC 6946 is located at a distance of 5.5 Mpc, the linear resolution of the map corresponds to 140 pc. At such resolution, we were able to find CO emitting complexes with masses greater than those of typical Giant Molecular Clouds (105-106 M⊙). To identify GMCs individually and make a more detailed study of their physical properties, we made D array observations of CO(2→1) toward the densest concentrations of gas located in the prominent spiral arms. We achieved a linear resolution of 50 pc at 1 mm in D array, similar to GMCs sizes found in other galaxies (Bolatto et al. 2008). We present first results about possible differences in the properties of the on-arm clouds and the inter-arm clouds. While inter-arm GMAs in grand-design galaxies are thought to be formed by fragmentation of more massive on

  20. The Molecular Clouds Fueling A 1/5 Solar Metallicity Starburst

    NASA Astrophysics Data System (ADS)

    Kepley, Amanda A.; Leroy, Adam K.; Johnson, Kelsey E.; Sandstrom, Karin; Chen, C.-H. Rosie

    2016-09-01

    Using the Atacama Large Millimeter/submillimeter Array, we have made the first high spatial and spectral resolution observations of the molecular gas and dust in the prototypical blue compact dwarf galaxy II Zw 40. The {}12{CO}(2-1) and {}12{CO}(3-2) emission is clumpy and distributed throughout the central star-forming region. Only one of eight molecular clouds has associated star formation. The continuum spectral energy distribution is dominated by free-free and synchrotron; at 870 μm, only 50% of the emission is from dust. We derive a CO-to-H2 conversion factor using several methods, including a new method that uses simple photodissocation models and resolved CO line intensity measurements to derive a relationship that uniquely predicts {α }{co} for a given metallicity. We find that the CO-to-H2 conversion factor is 4-35 times that of the Milky Way (18.1-150.5 {M}⊙ {({{K}}{km}{{{s}}}-1{{pc}}2)}-1). The star formation efficiency of the molecular gas is at least 10 times higher than that found in normal spiral galaxies, which is likely due to the burst-dominated star formation history of II Zw 40 rather than an intrinsically higher efficiency. The molecular clouds within II Zw 40 resemble those in other strongly interacting systems like the Antennae: overall they have high size-linewidth coefficients and molecular gas surface densities. These properties appear to be due to the high molecular gas surface densities produced in this merging system rather than to increased external pressure. Overall, these results paint a picture of II Zw 40 as a complex, rapidly evolving system whose molecular gas properties are dominated by the large-scale gas shocks from its ongoing merger.

  1. The Molecular Clouds Fueling A 1/5 Solar Metallicity Starburst

    NASA Astrophysics Data System (ADS)

    Kepley, Amanda A.; Leroy, Adam K.; Johnson, Kelsey E.; Sandstrom, Karin; Chen, C.-H. Rosie

    2016-09-01

    Using the Atacama Large Millimeter/submillimeter Array, we have made the first high spatial and spectral resolution observations of the molecular gas and dust in the prototypical blue compact dwarf galaxy II Zw 40. The {}12{CO}(2-1) and {}12{CO}(3-2) emission is clumpy and distributed throughout the central star-forming region. Only one of eight molecular clouds has associated star formation. The continuum spectral energy distribution is dominated by free–free and synchrotron; at 870 μm, only 50% of the emission is from dust. We derive a CO-to-H2 conversion factor using several methods, including a new method that uses simple photodissocation models and resolved CO line intensity measurements to derive a relationship that uniquely predicts {α }{co} for a given metallicity. We find that the CO-to-H2 conversion factor is 4–35 times that of the Milky Way (18.1–150.5 {M}ȯ {({{K}}{km}{{{s}}}-1{{pc}}2)}-1). The star formation efficiency of the molecular gas is at least 10 times higher than that found in normal spiral galaxies, which is likely due to the burst-dominated star formation history of II Zw 40 rather than an intrinsically higher efficiency. The molecular clouds within II Zw 40 resemble those in other strongly interacting systems like the Antennae: overall they have high size–linewidth coefficients and molecular gas surface densities. These properties appear to be due to the high molecular gas surface densities produced in this merging system rather than to increased external pressure. Overall, these results paint a picture of II Zw 40 as a complex, rapidly evolving system whose molecular gas properties are dominated by the large-scale gas shocks from its ongoing merger.

  2. A dynamical transition from atomic to molecular intermediate-velocity clouds

    NASA Astrophysics Data System (ADS)

    Röhser, T.; Kerp, J.; Winkel, B.; Boulanger, F.; Lagache, G.

    2014-04-01

    Context. Towards the high galactic latitude sky, the far-infrared (FIR) intensity is tightly correlated to the total hydrogen column density which is made up of atomic (H i) and molecular hydrogen (H2). Above a certain column density threshold, atomic hydrogen turns molecular. Aims: We analyse gas and dust properties of intermediate-velocity clouds (IVCs) in the lower galactic halo to explore their transition from the atomic to the molecular phase. Driven by observations, we investigate the physical processes that transform a purely atomic IVC into a molecular one. Methods: Data from the Effelsberg-Bonn H i-Survey (EBHIS) are correlated to FIR wavebands of the Planck satellite and IRIS. Modified black-body emission spectra are fitted to deduce dust optical depths and grain temperatures. We remove the contribution of atomic hydrogen to the FIR intensity to estimate molecular hydrogen column densities. Results: Two IVCs show different FIR properties, despite their similarity in H i, such as narrow spectral lines and large column densities. One FIR bright IVC is associated with H2, confirmed by 12CO (1 → 0) emission; the other IVC is FIR dim and shows no FIR excess, which indicates the absence of molecular hydrogen. Conclusions: We propose that the FIR dim and bright IVCs probe the transition between the atomic and molecular gas phase. Triggered by dynamical processes, this transition happens during the descent of IVCs onto the galactic disk. The most natural driver is ram pressure exerted onto the cloud by the increasing halo density. Because of the enhanced pressure, the formation timescale of H2 is reduced, allowing the formation of large amounts of H2 within a few Myr. Based on observations obtained with Planck (http://www.esa.int/Planck), an ESA science mission with instruments and contributions directly funded by ESA Member States, NASA, and Canada.

  3. Cold and warm atomic gas around the Perseus molecular cloud. I. Basic properties

    SciTech Connect

    Stanimirović, Snežana; Murray, Claire E.; Miller, Jesse; Lee, Min-Young

    2014-10-01

    Using the Arecibo Observatory, we have obtained neutral hydrogen (HI) absorption and emission spectral pairs in the direction of 26 background radio continuum sources in the vicinity of the Perseus molecular cloud. Strong absorption lines were detected in all cases, allowing us to estimate spin temperature (T{sub s} ) and optical depth for 107 individual Gaussian components along these lines of sight. Basic properties of individual H I clouds (spin temperature, optical depth, and the column density of the cold and warm neutral medium (CNM and WNM), respectively) in and around Perseus are very similar to those found for random interstellar lines of sight sampled by the Millennium H I survey. This suggests that the neutral gas found in and around molecular clouds is not atypical. However, lines of sight in the vicinity of Perseus have, on average, a higher total H I column density and the CNM fraction, suggesting an enhanced amount of cold H I relative to an average interstellar field. Our estimated optical depth and spin temperature are in stark contrast with the recent attempt at using Planck data to estimate properties of the optically thick H I. Only ∼15% of lines of sight in our study have a column density weighted average spin temperature lower than 50 K, in comparison with ≳ 85% of Planck's sky coverage. The observed CNM fraction is inversely proportional to the optical depth weighted average spin temperature, in excellent agreement with the recent numerical simulations by Kim et al. While the CNM fraction is, on average, higher around Perseus relative to a random interstellar field, it is generally low, between 10%-50%. This suggests that extended WNM envelopes around molecular clouds and/or significant mixing of CNM and WNM throughout molecular clouds are present and should be considered in the models of molecule and star formation. Our detailed comparison of H I absorption with CO emission spectra shows that only 3 of the 26 directions are clear

  4. Atmospheric organic matter in clouds: exact masses and molecular formula identification using ultrahigh resolution FT-ICR mass spectrometry

    NASA Astrophysics Data System (ADS)

    Zhao, Y.; Hallar, A. G.; Mazzoleni, L. R.

    2013-08-01

    Clouds alter the composition of atmospheric aerosol by acting as a medium for interactions between gaseous and particulate phase substances. To determine the cloud water atmospheric organic matter (AOM) composition and study the cloud processing of aerosols, two samples of supercooled clouds were collected at Storm Peak Laboratory near Steamboat Spring, Colorado (3220 m a.s.l.). Approximately 3000 molecular formulas were assigned to ultrahigh resolution mass spectra of the samples after using a reverse phase extraction procedure to isolate the AOM components from the cloud water. Nitrogen containing compounds (CHNO compounds), sulfur containing compounds (CHOS and CHNOS compounds) and other oxygen containing compounds (CHO compounds) with molecular weights up to 700 Da were observed. Average oxygen-to-carbon ratios of ~0.6 indicate a slightly more oxidized composition than most water-soluble organic carbon identified in aerosol studies, which may result from aqueous oxidation in the clouds. The AOM composition indicates significant influences from biogenic secondary organic aerosol (SOA) and residential wood combustion. We observed 60% of the cloud water CHO molecular formulas to be identical to SOA samples of α-pinene, β-pinene, d-limonene, and β-caryophyllene ozonolysis. CHNO compounds had the highest number frequency and relative abundances and are associated with residential wood combustion and NOx oxidation. We observed multiple nitrogen atoms in the assigned molecular formulas for the nighttime cloud sample composite indicating the significance of nighttime emissions or NOx oxidation on the AOM composition. Several CHOS and CHNOS compounds with reduced sulfur (in addition to the commonly observed oxidized sulfur containing compounds) were also observed, however further investigation is needed to determine the origin of the reduced sulfur containing compounds. Overall, the molecular composition determined using ultrahigh resolution Fourier transform ion

  5. Boundary conditions for the paleoenvironment: Chemical and physical processes in the pre-solar nebula. [molecular clouds, interstellar matter, and abundance

    NASA Technical Reports Server (NTRS)

    Irvine, W. M.; Schloerb, F. P.

    1985-01-01

    Two additional hyperfine components of the interstellar radical C3H were detected. In addition, methanol was discovered in interstellar clouds. The abundance of HCCN and various chemical isomers in molecular clouds was investigated.

  6. Molecular clouds and star formation in the inner galaxy - A comparison of CO, H II, and far-infrared surveys

    NASA Technical Reports Server (NTRS)

    Myers, P. C.; Dame, T. M.; Thaddeus, P.; Cohen, R. S.; Silverberg, R. F.; Dwek, E.; Hauser, M. G.

    1986-01-01

    Surveys of the galactic plane over galactic latitudes from -1 degree to +1 degree and galactic longitudes from 12 degrees to 60 degrees are compared in the CO line at 2.6 mm, in the far-infrared (FIR) continuum at 150 micrometers and 250 micrometers, and in the radio continuum and H 110-alpha recombination line at 6 cm. The main purposes are to determine the degree of association between FIR sources, H II regions, and molecular clouds in the first quadrant and to describe and analyze the stellar content of these molecular clouds. Among the conclusions it is noted that most FIR sources coincide with HII regions, and nearly all H II regions coincide with molecular clouds, and that clouds in the inner galaxy are probably several tens of millions of years old and may have been producing O stars for only about the most recent 20 percent of their lives.

  7. Submillimeter and far-infrared line observations of M17 SW - A clumpy molecular cloud penetrated by ultraviolet radiation

    NASA Technical Reports Server (NTRS)

    Stutzki, J.; Genzel, R.; Harris, A. I.; Stacey, G. J.; Jaffe, D. T.

    1988-01-01

    Millimeter, submillimeter, and far-IR spectroscopic observations of the M17 SW star formation region are reported. Strong forbidden C II 158 micron and CO J = 7 - 6 line emission arises in an H II region/molecular cloud interface of several pc thickness. Weaker forbidden C II emission appears to be extended over 15 pc throughout the molecular cloud. CO J = 14 - 13 and forbidden O I 145 micron spectra indicate high temperatures and densities for both molecular and atomic gas in the interface. The results require the molecular cloud near the interface to be clumpy or filamentary. The extended forbidden C II emission throughout the molecular cloud has a level around 20 times higher than expected from a single molecular cloud interface exposed to an ultraviolet radiation field typical of the solar neighborhood. The high gas temperature of molecular material in the UV-illuminated interface region suggests that CO self-shielding and heating of CO by photoelectrons are important.

  8. A Multi-Wavelength Study of Molecular Clouds and Starless Cores

    NASA Astrophysics Data System (ADS)

    Schnee, S. L.; Goodman, A. A.

    2005-12-01

    The physical properties of star-forming regions are best studied with a suite of measurements at a variety of wavelengths. My thesis is centered on combining several maps of the emission and/or extinction from dust with molecular line transition on scales as large as that of entire molecular clouds and as small as that of individual star-forming cores. As part of the COMPLETE Survey of Star-Forming Regions we have made a new set of dust temperature and column density maps for the Perseus, Ophiuchus and Serpens molecular clouds. Using the newly recalibrated IRAS data (IRIS) and 2MASS maps, we have determined the conversion from 100 micron optical depth to visual extinction, and found that this conversion is significantly different between clouds. In addition, we show that using IRAS maps to determine the column density of dust results in significant errors for AV > 1 due to temperature variations along the line of sight. The observed scatter between column density derived from pairs of emission maps and column density derived from the NIR colors of background stars can be reproduced without the inclusion of emission from transiently heated dust grains and without including the effects of variable dust emission properties. Using SCUBA and MAMBO maps of TMC-1C, a starless core in Taurus, we have mapped the dust temperature, column density, and emissivity spectral index at ˜ 14 arcsecond resolution. The density profile is consistent with that of a Bonnor-Ebert sphere, and the temperature varies from 7 to 12 K. By combining the dust emission maps with molecular line maps we show that TMC-1C is out of virial equilibrium and contracting at a rate slower than the sound speed.

  9. Modelling the structure of molecular clouds - I. A multiscale energy equipartition

    NASA Astrophysics Data System (ADS)

    Veltchev, Todor V.; Donkov, Sava; Klessen, Ralf S.

    2016-07-01

    We present a model for describing the general structure of molecular clouds (MCs) at early evolutionary stages in terms of their mass-size relationship. Sizes are defined through threshold levels at which equipartitions between gravitational, turbulent and thermal energy |W| ˜ f(Ekin + Eth) take place, adopting interdependent scaling relations of velocity dispersion and density and assuming a lognormal density distribution at each scale. Variations of the equipartition coefficient 1 ≤ f ≤ 4 allow for modelling of star-forming regions at scales within the size range of typical MCs (≳4 pc). Best fits are obtained for regions with low or no star formation (Pipe, Polaris) as well for such with star-forming activity but with nearly lognormal distribution of column density (Rosette). An additional numerical test of the model suggests its applicability to cloud evolutionary times prior to the formation of first stars.

  10. Observations of the interstellar ice grain feature in the Taurus molecular clouds

    SciTech Connect

    Whittet, D.C.B.; Bode, H.F.; Longmore, A.J.; Baines, D.W.T.; Evans, A.

    1983-01-01

    Although water ice was originally proposed as a major constituent of the interstellar grain population (e.g. Oort and van de Hulst, 1946), the advent of infrared astronomy has shown that the expected absorption due to O-H stretching vibrations at 3 ..mu..m is illusive. Observations have in fact revealed that the carrier of this feature is apparently restricted to regions deep within dense molecular clouds (Merrill et al., 1976; Willner et al., 1982). However, the exact carrier of this feature is still controversial, and many questions remain as to the conditions required for its appearance. It is also uncertain whether it is restricted to circumstellar shells, rather than the general cloud medium. Detailed discussion of the 3 ..mu..m band properties is given elsewhere in this volume. 15 references, 4 figures.

  11. Molecular clouds in the centers of galaxies: Constraints from HCN and CO-13 line emission

    NASA Technical Reports Server (NTRS)

    Aalto, S.; Black, J. H.; Booth, R. S.; Johansson, L. E. B.

    1993-01-01

    We have searched for HCN J=1-0 line emission in the centers of 12 galaxies and have detected it in 10 of them. We have obtained complementary data on J=1-0 and 2-1 transitions of CO-12 and CO-13 in these systems. The ratio of integrated intensities, I(CO 1-0)/I(HCN 1-0) = 25 +/- 11 for this sample. We find that HCN emission of this strength can be produced under conditions of subthermal excitation. In combination with the line ratios in CO and CO-13, HCN puts constraints on the mean conditions of molecular clouds and on the mix of cloud types within the projected beam.

  12. Search for old neutron stars in molecular clouds: Cygnus rift and Cygnus OB7.

    NASA Astrophysics Data System (ADS)

    Belloni, T.; Zampieri, L.; Campana, S.

    1997-03-01

    We present the results of a systematic search for old isolated neutron stars (ONSs) in the direction of two giant molecular clouds in Cygnus (Rift and OB7). From theoretical calculations, we expect the detection of a large number of ONSs with the PSPC on board ROSAT. By analyzing the PSPC pointings in the direction of the clouds, we find four sources characterized by count rates (~10^-3^ct/s) and spectral properties consistent with the hypothesis that the X-ray radiation is produced by ONSs and also characterized by the absence of any measurable optical counterpart within their error circle in the digitized red plates of the Palomar All Sky Survey. The importance of follow-up deep observations in the direction of these ONS candidates is discussed. The observational and theoretical approach presented here could be fruitfully applied also to the systematic search for ONSs in other regions of the Galaxy.

  13. FERMI LARGE AREA TELESCOPE OBSERVATIONS OF SUPERNOVA REMNANTS INTERACTING WITH MOLECULAR CLOUDS

    SciTech Connect

    Castro, Daniel; Slane, Patrick

    2010-07-01

    We report the detection of {gamma}-ray emission coincident with four supernova remnants (SNRs) using data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. G349.7+0.2, CTB 37A, 3C 391, and G8.7-0.1 are SNRs known to be interacting with molecular clouds, as evidenced by observations of hydroxyl (OH) maser emission at 1720 MHz in their directions. SNR shocks are expected to be sites of cosmic-ray acceleration, and clouds of dense material can provide effective targets for production of {gamma}-rays from {pi}{sup 0} decay. The observations reveal unresolved sources in the direction of G349.7+0.2, CTB 37A, and 3C 391, and a possibly extended source coincident with G8.7-0.1, all with significance levels greater than 10{sigma}.

  14. Molecular characterization of sulfate-reducing bacteria community in surface sediments from the adjacent area of Changjiang Estuary

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Zhen, Yu; Mi, Tiezhu; He, Hui; Yu, Zhigang

    2016-02-01

    Sulfate-reducing bacteria (SRB), which obtain energy from dissimilatory sulfate reduction, play a vital role in the carbon and sulfur cycles. The dissimilatory sulfite reductase (Dsr), catalyzing the last step in the sulfate reduction pathway, has been found in all known SRB that have been tested so far. In this study, the diversity of SRB was investigated in the surface sediments from the adjacent area of Changjiang Estuary by PCR amplification, cloning and sequencing of the dissimilatory sulfite reductase beta subunit gene ( dsrB). Based on dsrB clone libraries constructed in this study, diversified SRB were found, represented by 173 unique OTUs. Certain cloned sequences were associated with Desulfobacteraceae, Desulfobulbaceae, and a large fraction (60%) of novel sequences that have deeply branched groups in the dsrB tree, indicating that novel SRB inhabit the surface sediments. In addition, correlations of the SRB assemblages with environmental factors were analyzed by the linear model-based redundancy analysis (RDA). The result revealed that temperature, salinity and the content of TOC were most closely correlated with the SRB communities. More information on SRB community was obtained by applying the utility of UniFrac to published dsrB gene sequences from this study and other 9 different kinds of marine environments. The results demonstrated that there were highly similar SRB genotypes in the marine and estuarine sediments, and that geographic positions and environmental factors influenced the SRB community distribution.

  15. Spitzer Infrared Spectrograph Detection of Molecular Hydrogen Rotational Emission towards Translucent Clouds

    NASA Astrophysics Data System (ADS)

    Ingalls, James G.; Bania, T. M.; Boulanger, F.; Draine, B. T.; Falgarone, E.; Hily-Blant, P.

    2011-12-01

    Using the Infrared Spectrograph on board the Spitzer Space Telescope, we have detected emission in the S(0), S(1), and S(2) pure-rotational (v = 0-0) transitions of molecular hydrogen (H2) toward six positions in two translucent high Galactic latitude clouds, DCld 300.2-16.9 and LDN 1780. The detection of these lines raises important questions regarding the physical conditions inside low-extinction clouds that are far from ultraviolet radiation sources. The ratio between the S(2) flux and the flux from polycyclic aromatic hydrocarbons (PAHs) at 7.9 μm averages 0.007 for these six positions. This is a factor of about four higher than the same ratio measured toward the central regions of non-active Galaxies in the Spitzer Infrared Nearby Galaxies Survey. Thus, the environment of these translucent clouds is more efficient at producing rotationally excited H2 per PAH-exciting photon than the disks of entire galaxies. Excitation analysis finds that the S(1) and S(2) emitting regions are warm (T >~ 300 K), but comprise no more than 2% of the gas mass. We find that UV photons cannot be the sole source of excitation in these regions and suggest mechanical heating via shocks or turbulent dissipation as the dominant cause of the emission. The clouds are located on the outskirts of the Scorpius-Centaurus OB association and may be dissipating recent bursts of mechanical energy input from supernova explosions. We suggest that pockets of warm gas in diffuse or translucent clouds, integrated over the disks of galaxies, may represent a major source of all non-active galaxy H2 emission.

  16. Molecular clouds and the large-scale structure of the galaxy

    NASA Technical Reports Server (NTRS)

    Thaddeus, Patrick; Stacy, J. Gregory

    1990-01-01

    The application of molecular radio astronomy to the study of the large-scale structure of the Galaxy is reviewed and the distribution and characteristic properties of the Galactic population of Giant Molecular Clouds (GMCs), derived primarily from analysis of the Columbia CO survey, and their relation to tracers of Population 1 and major spiral features are described. The properties of the local molecular interstellar gas are summarized. The CO observing programs currently underway with the Center for Astrophysics 1.2 m radio telescope are described, with an emphasis on projects relevant to future comparison with high-energy gamma-ray observations. Several areas are discussed in which high-energy gamma-ray observations by the EGRET (Energetic Gamma-Ray Experiment Telescope) experiment aboard the Gamma Ray Observatory will directly complement radio studies of the Milky Way, with the prospect of significant progress on fundamental issues related to the structure and content of the Galaxy.

  17. The Structure of a Low-metallicity Giant Molecular Cloud Complex

    NASA Astrophysics Data System (ADS)

    Leroy, Adam K.; Bolatto, Alberto; Bot, Caroline; Engelbracht, Charles W.; Gordon, Karl; Israel, Frank P.; Rubio, Mónica; Sandstrom, Karin; Stanimirović, Snežana

    2009-09-01

    To understand the impact of low metallicities on giant molecular cloud (GMC) structure, we compare far-infrared dust emission, CO emission, and dynamics in the star-forming complex N83 in the Wing of the Small Magellanic Cloud (SMC). Dust emission (measured by Spitzer as part of the Spitzer Survey of the SMC and Surveying the Agents of a Galaxy's Evolution in the SMC surveys) probes the total gas column independent of molecular line emission and traces shielding from photodissociating radiation. We calibrate a method to estimate the dust column using only the high-resolution Spitzer data and verify that dust traces the interstellar medium in the H I-dominated region around N83. This allows us to resolve the relative structures of H2, dust, and CO within a GMC complex, one of the first times such a measurement has been made in a low-metallicity galaxy. Our results support the hypothesis that CO is photodissociated while H2 self-shields in the outer parts of low-metallicity GMCs, so that dust/self-shielding is the primary factor determining the distribution of CO emission. Four pieces of evidence support this view. First, the CO-to-H2 conversion factor averaged over the whole cloud is very high 4-11 × 1021 cm-2 (K km s-1)-1, or 20-55 times the Galactic value. Second, the CO-to-H2 conversion factor varies across the complex, with its lowest (most nearly Galactic) values near the CO peaks. Third, bright CO emission is largely confined to regions of relatively high line-of-sight extinction, AV gsim 2 mag, in agreement with photodissociation region models and Galactic observations. Fourth, a simple model in which CO emerges from a smaller sphere nested inside a larger cloud can roughly relate the H2 masses measured from CO kinematics and dust.

  18. THE YOUNG STELLAR OBJECT POPULATION IN THE VELA-D MOLECULAR CLOUD

    SciTech Connect

    Strafella, F.; Maruccia, Y.; Maiolo, B.; Lorenzetti, D.; Giannini, T.; Elia, D.; Molinari, S.; Pezzuto, S.; Massi, F.; Olmi, L.

    2015-01-10

    We investigate the young stellar population in the Vela Molecular Ridge, Cloud-D, a star-forming region observed by both the Spitzer/NASA and Herschel/ESA space telescopes. The point-source, band-merged, Spitzer-IRAC catalog complemented with MIPS photometry previously obtained is used to search for candidate young stellar objects (YSOs), also including sources detected in less than four IRAC bands. Bona fide YSOs are selected by using appropriate color-color and color-magnitude criteria aimed at excluding both Galactic and extragalactic contaminants. The derived star formation rate and efficiency are compared with the same quantities characterizing other star-forming clouds. Additional photometric data, spanning from the near-IR to the submillimeter, are used to evaluate both bolometric luminosity and temperature for 33 YSOs located in a region of the cloud observed by both Spitzer and Herschel. The luminosity-temperature diagram suggests that some of these sources are representative of Class 0 objects with bolometric temperatures below 70 K and luminosities of the order of the solar luminosity. Far-IR observations from the Herschel/Hi-GAL key project for a survey of the Galactic plane are also used to obtain a band-merged photometric catalog of Herschel sources intended to independently search for protostars. We find 122 Herschel cores located on the molecular cloud, 30 of which are protostellar and 92 of which are starless. The global protostellar luminosity function is obtained by merging the Spitzer and Herschel protostars. Considering that 10 protostars are found in both the Spitzer and Herschel lists, it follows that in the investigated region we find 53 protostars and that the Spitzer-selected protostars account for approximately two-thirds of the total.

  19. A Spitzer view of the giant molecular cloud Mon OB1 East/NGC 2264

    SciTech Connect

    Rapson, V. A.; Pipher, J. L.; Gutermuth, R. A.; Megeath, S. T.; Allen, T. S.; Myers, P. C.; Allen, L. E.

    2014-10-20

    We present Spitzer 3.6, 4.5, 5.8, 8.0, and 24 μm images of the Mon OB1 East giant molecular cloud, which contains the young star forming region NGC 2264, as well as more extended star formation. With Spitzer data and Two Micron All Sky Survey photometry, we identify and classify young stellar objects (YSOs) with dusty circumstellar disks and/or envelopes in Mon OB1 East by their infrared-excess emission and study their distribution with respect to cloud material. We find a correlation between the local surface density of YSOs and column density of molecular gas as traced by dust extinction that is roughly described as a power law in these quantities. NGC 2264 follows a power-law index of ∼2.7, exhibiting a large YSO surface density for a given gas column density. Outside of NGC 2264 where the surface density of YSOs is lower, the power law is shallower and the region exhibits a larger gas column density for a YSO surface density, suggesting the star formation is more recent. In order to measure the fraction of cloud members with circumstellar disks/envelopes, we estimate the number of diskless pre-main-sequence stars by statistical removal of background star detections. We find that the disk fraction of the NGC 2264 region is 45%, while the surrounding, more distributed regions show a disk fraction of 19%. This may be explained by the presence of an older, more dispersed population of stars. In total, the Spitzer observations provide evidence for heterogenous, non-coeval star formation throughout the Mon OB1 cloud.

  20. Molecular Line Studies of Ballistic Stellar Interlopers Burrowing through Dense Interstellar Clouds

    NASA Astrophysics Data System (ADS)

    Rosen, Anna; Sahai, R.; Claussen, M.; Morris, M.

    2010-01-01

    When an intermediate-mass star speeds through a dense interstellar cloud at a high velocity, it can produce a cometary or bow shock structure due to the cloud being impacted by the intense stellar wind. This class of objects, recently discovered in an HST imaging survey, has been dubbed "ballistic stellar interlopers" (Sahai et al. 2009). Using the ARO's 12m and SMT 10m millimeter-wave dishes, we have obtained molecular line emission data towards 10 stellar interloper sources, in order to identify and characterize the dense clouds with which the interlopers are interacting. We have made small "on-the-fly" maps in the 12CO (J=2-1) and 13CO (J=2-1) lines for each cloud, and obtained spectra of high-density tracers such as N2H+ (J=3-2), HCO+ (J=3-2), CN(N=2-1), and SO(J=5-4), which probe a range of physical conditions in the interstellar clouds being impacted by the interlopers. The data have been reduced and analyzed, and preliminary estimates of the cloud temperatures (9-22 K) and 13CO optical depths (0.18-0.37) have been made. The maps, which show the emission as a function of radial velocity and spatial offset from the location of the interlopers, have helped us distinguish between the clouds interacting with the interlopers, and those which are unrelated but happen to lie along the line of sight. These data will now enable us to carry out high-resolution mm-wave interferometric observations of the interlopers in the future. This research was performed at JPL under the Minority Education Initiatives program. RS and MM were funded by a Long Term Space Astrophysics award from NASA for this work. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Special thanks goes to John Bieging and Bill Peters of the Arizona Radio Observatory.

  1. CARMA LARGE AREA STAR FORMATION SURVEY: OBSERVATIONAL ANALYSIS OF FILAMENTS IN THE SERPENS SOUTH MOLECULAR CLOUD

    SciTech Connect

    Fernández-López, M.; Looney, L.; Lee, K.; Segura-Cox, D.; Arce, H. G.; Plunkett, A.; Mundy, L. G.; Storm, S.; Teuben, P. J.; Pound, M.; Isella, A.; Kauffmann, J.; Tobin, J. J.; Rosolowsky, E.; Kwon, W.; Ostriker, E.; Tassis, K.; Shirley, Y. L.

    2014-08-01

    We present the N{sub 2}H{sup +} (J = 1 → 0) map of the Serpens South molecular cloud obtained as part of the CARMA Large Area Star Formation Survey. The observations cover 250 arcmin{sup 2} and fully sample structures from 3000 AU to 3 pc with a velocity resolution of 0.16 km s{sup –1}, and they can be used to constrain the origin and evolution of molecular cloud filaments. The spatial distribution of the N{sub 2}H{sup +} emission is characterized by long filaments that resemble those observed in the dust continuum emission by Herschel. However, the gas filaments are typically narrower such that, in some cases, two or three quasi-parallel N{sub 2}H{sup +} filaments comprise a single observed dust continuum filament. The difference between the dust and gas filament widths casts doubt on Herschel ability to resolve the Serpens South filaments. Some molecular filaments show velocity gradients along their major axis, and two are characterized by a steep velocity gradient in the direction perpendicular to the filament axis. The observed velocity gradient along one of these filaments was previously postulated as evidence for mass infall toward the central cluster, but these kind of gradients can be interpreted as projection of large-scale turbulence.

  2. Cosmic ray induced ionisation of a molecular cloud shocked by the W28 supernova remnant

    NASA Astrophysics Data System (ADS)

    Vaupré, S.; Hily-Blant, P.; Ceccarelli, C.; Dubus, G.; Gabici, S.; Montmerle, T.

    2014-08-01

    Cosmic rays are an essential ingredient in the evolution of the interstellar medium, as they dominate the ionisation of the dense molecular gas, where stars and planets form. However, since they are efficiently scattered by the galactic magnetic fields, many questions remain open, such as where exactly they are accelerated, what is their original energy spectrum, and how they propagate into molecular clouds. In this work we present new observations and discuss in detail a method that allows us to measure the cosmic ray ionisation rate towards the molecular clouds close to the W28 supernova remnant. To perform these measurements, we use CO, HCO+, and DCO+ millimetre line observations and compare them with the predictions of radiative transfer and chemical models away from thermodynamical equilibrium. The CO observations allow us to constrain the density, temperature, and column density towards each observed position, while the DCO+/HCO+ abundance ratios provide us with constraints on the electron fraction and, consequently, on the cosmic ray ionisation rate. Towards positions located close to the supernova remnant, we find cosmic ray ionisation rates much larger (≳100) than those in standard galactic clouds. Conversely, towards one position situated at a larger distance, we derive a standard cosmic ray ionisation rate. Overall, these observations support the hypothesis that the γ rays observed in the region have a hadronic origin. In addition, based on CR diffusion estimates, we find that the ionisation of the gas is likely due to 0.1-1 GeV cosmic rays. Finally, these observations are also in agreement with the global picture of cosmic ray diffusion, in which the low-energy tail of the cosmic ray population diffuses at smaller distances than the high-energy counterpart.

  3. Evidence for nucleosynthetic enrichment of the protosolar molecular cloud core by multiple supernova events

    PubMed Central

    Schiller, Martin; Paton, Chad; Bizzarro, Martin

    2015-01-01

    The presence of isotope heterogeneity of nucleosynthetic origin amongst meteorites and their components provides a record of the diverse stars that contributed matter to the protosolar molecular cloud core. Understanding how and when the solar system’s nucleosynthetic heterogeneity was established and preserved within the solar protoplanetary disk is critical for unraveling the earliest formative stages of the solar system. Here, we report calcium and magnesium isotope measurements of primitive and differentiated meteorites as well as various types of refractory inclusions, including refractory inclusions (CAIs) formed with the canonical 26Al/27Al of ~5 × 10−5 (26Al decays to 26Mg with a half-life of ~0.73 Ma) and CAIs that show fractionated and unidentified nuclear effects (FUN-CAIs) to understand the origin of the solar system’s nucleosynthetic heterogeneity. Bulk analyses of primitive and differentiated meteorites along with canonical and FUN-CAIs define correlated, mass-independent variations in 43Ca, 46Ca and 48Ca. Moreover, sequential dissolution experiments of the Ivuna carbonaceous chondrite aimed at identifying the nature and number of presolar carriers of isotope anomalies within primitive meteorites have detected the presence of multiple carriers of the short-lived 26Al nuclide as well as carriers of anomalous and uncorrelated 43Ca, 46Ca and 48Ca compositions, which requires input from multiple and recent supernovae sources. We infer that the solar system’s correlated nucleosynthetic variability reflects unmixing of old, galactically-inherited homogeneous dust from a new, supernovae-derived dust component formed shortly prior to or during the evolution of the giant molecular cloud parental to the protosolar molecular cloud core. This implies that similarly to 43Ca, 46Ca and 48Ca, the short-lived 26Al nuclide was heterogeneously distributed in the inner solar system at the time of CAI formation. PMID:25684790

  4. ABUNDANCE OF {sup 26}Al AND {sup 60}Fe IN EVOLVING GIANT MOLECULAR CLOUDS

    SciTech Connect

    Vasileiadis, Aristodimos; Nordlund, Ake; Bizzarro, Martin

    2013-05-20

    The nucleosynthesis and ejection of radioactive {sup 26}Al (t{sub 1/2} {approx} 0.72 Myr) and {sup 60}Fe, (t{sub 1/2} {approx} 2.5 Myr) into the interstellar medium is dominated by the stellar winds of massive stars and supernova type II explosions. Studies of meteorites and their components indicate that the initial abundances of these short-lived radionuclides in the solar protoplanetary disk were higher than the background levels of the galaxy inferred from {gamma}-ray astronomy and models of the galactic chemical evolution. This observation has been used to argue for a late-stage addition of stellar debris to the solar system's parental molecular cloud or, alternatively, the solar protoplanetary disk, thereby requiring a special scenario for the formation of our solar system. Here, we use supercomputers to model-from first principles-the production, transport, and admixing of freshly synthesized {sup 26}Al and {sup 60}Fe in star-forming regions within giant molecular clouds. Under typical star formation conditions, the levels of {sup 26}Al in most star-forming regions are comparable to that deduced from meteorites, suggesting that the presence of short-lived radionuclides in the early solar system is a generic feature of the chemical evolution of giant molecular clouds. The {sup 60}Fe/{sup 26}Al yield ratio of Almost-Equal-To 0.2 calculated from our simulations is consistent with the galactic value of 0.15 {+-} 0.06 inferred from {gamma}-ray astronomy but is significantly higher than most current solar system measurements indicate. We suggest that estimates based on differentiated meteorites and some chondritic components may not be representative of the initial {sup 60}Fe abundance of the bulk solar system.

  5. Star formation in Carina OB1: Observations of a giant molecular cloud associated with the eta Carinae Nebula

    NASA Technical Reports Server (NTRS)

    Grabelsky, D. A.; Cohen, R. S.; Thaddeus, P.

    1987-01-01

    A giant molecular cloud associated with the eta Carinae nebula was fully mapped in CO with the Columbia Millimeter-Wave Telescope at Cerro Tololo. The cloud comples has a mass of roughly 700,000 solar mass and extends about 140 pc along the Galactic plane, with the giant Carina HII region situated at one end of the complex. Clear evidence of interaction between the HII region and the molecular cloud is found in the relative motions of the ionized gas, the molecular gas, and the dust; simple energy and momentum considerations suggest that the HII region is responsible for the observed motion of a cloud fragment. The molecular cloud complex appears to be the parent material of the entire Car OB1 Association which, in addition to the young clusters in the Carine nebula, includes the generally older cluster NGC 3325, NGC 3293, and IC 2581. The overall star formation efficiency in the cloud complex is estimated to be approximately 0.02.

  6. Search for H2COH+ and H2(13)CO in dense interstellar molecular clouds.

    PubMed

    Minh, Y C; Irvine, W M; McGonagle, D

    1993-01-01

    We have searched for the 2 mm transitions of H2COH+ (2(02) - 1(01)) and H2(13)CO (2(02) - 1(01), 2(12) - 1(11), and 2(11) - 1(10)) toward the dense interstellar molecular clouds Orion A, TMC-1 and L134N using the FCRAO 14m telescope. None of the transitions have been detected except the H2(13)CO transitions toward Orion-KL. We set upper limits for the abundances of the protonated formaldehyde ion (H2COH+), which are close to the abundances expected from ion-molecule chemistry.

  7. Isolated and companion young brown dwarfs in the taurus and chamaeleon molecular clouds

    PubMed

    Tamura; Itoh; Oasa; Nakajima

    1998-11-01

    Infrared imaging observations have detected a dozen faint young stellar objects (YSOs) in the Taurus and Chamaeleon molecular clouds whose near-infrared colors are similar to those of classical T Tauri stars (TTS). They are around four magnitudes fainter than low-luminosity YSOs in Taurus detected in earlier surveys and as much as eight magnitudes fainter than typical TTS. The extreme faintness of the objects and their lower luminosity relative to previously identified brown dwarfs in the Pleiades indicate that these faint YSOs are very young brown dwarfs on the order of 1 million years old.

  8. Observations of Rotational Transitions of OH from ORION-MOLECULAR-CLOUD-1

    NASA Astrophysics Data System (ADS)

    Melnick, G.

    In the Orion Molecular Cloud, the conditions needed to excite the higher rotational transitions of OH into emission are usually associated with gas that has been compressed and heated by the passage of a shock wave. According to the shock models of Draine, Roberge, and Dalgarno (1983), up to several percent of the preshock O2 and O are converted into OH in the ≡103K post-shocked gas. Assuming that oxygen is present in its cosmic abundance in the preshock gas, this implies a possible column density of hot OH of between about 4×1016 and 1017cm-2.

  9. A High-Mass Cold Core in the Auriga-California Giant Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Magnus McGehee, Peregrine; Paladini, Roberta; Pelkonen, Veli-Matti; Toth, Viktor; Sayers, Jack

    2015-08-01

    The Auriga-California Giant Molecular Cloud is noted for its relatively low star formation rate, especially at the high-mass end of the Initial Mass Function. We combine maps acquired by the Caltech Submillimeter Observatory's Multiwavelength Submillimeter Inductance Camera [MUSIC] in the wavelength range 0.86 to 2.00 millimeters with Planck and publicly-available Herschel PACS and SPIRE data in order to characterize the mass, dust properties, and environment of the bright core PGCC G163.32-8.41.

  10. Search for H2COH+ and H2(13)CO in dense interstellar molecular clouds

    NASA Technical Reports Server (NTRS)

    Minh, Y. C.; Irvine, W. M.; McGonagle, D.

    1993-01-01

    We have searched for the 2 mm transitions of H2COH+ (2(02) - 1(01)) and H2(13)CO (2(02) - 1(01), 2(12) - 1(11), and 2(11) - 1(10)) toward the dense interstellar molecular clouds Orion A, TMC-1 and L134N using the FCRAO 14m telescope. None of the transitions have been detected except the H2(13)CO transitions toward Orion-KL. We set upper limits for the abundances of the protonated formaldehyde ion (H2COH+), which are close to the abundances expected from ion-molecule chemistry.

  11. VizieR Online Data Catalog: CO survey of molecular clouds. III. Serpens (Burleigh+, 2013)

    NASA Astrophysics Data System (ADS)

    Burleigh, K. J.; Bieging, J. H.; Chromey, A.; Kulesa, C.; Peters, W. L.

    2014-02-01

    We mapped about 1.04deg2 of Serpens Main in the 12molecular cloud mapping project with the Arizona Radio Observatory. The observations were made between 2008 November and 2010 June with the Heinrich Hertz Submillimeter Telescope (HHT) on Mt. Graham, AZ, at an elevation of 3200m. The HHT has a 10m diameter paraboloidal dish and observes in the frequency range from 210 to 500GHz. (2 data files).

  12. The Spitzer Survey of Interstellar Clouds in the Gould Belt. VI. The Auriga-California Molecular Cloud Observed with IRAC and MIPS

    NASA Technical Reports Server (NTRS)

    Broekhoven-Fiene, Hannah; Matthews, Brenda C.; Harvey, Paul M.; Gutermuth, Robert A.; Huard, Tracy L.; Tothill, Nicholas F. H.; Nutter, David; Bourke, Tyler L.; DiFrancesco, James; Jorgensen, Jes K.; Allen, Lori E.; Chapman, Nicholas L.; Dunham, Michael M.; Merin, Bruno; Miller, Jennifer F.; Terebey, Susan; Peterson, Dawn E.; Stapelfeldt, Karl R.

    2014-01-01

    We present observations of the Auriga-California Molecular Cloud (AMC) at 3.6, 4.5, 5.8, 8.0, 24, 70 and 160 micrometers observed with the IRAC and MIPS detectors as part of the Spitzer Gould Belt Legacy Survey. The total mapped areas are 2.5 deg(exp 2) with IRAC and 10.47 deg2 with MIPS. This giant molecular cloud is one of two in the nearby Gould Belt of star-forming regions, the other being the Orion A Molecular Cloud (OMC). We compare source counts, colors and magnitudes in our observed region to a subset of the SWIRE data that was processed through our pipeline. Using color-magnitude and color-color diagrams, we find evidence for a substantial population of 166 young stellar objects (YSOs) in the cloud, many of which were previously unknown. Most of this population is concentrated around the LkH(alpha) 101 cluster and the filament extending from it. We present a quantitative description of the degree of clustering and discuss the fraction of YSOs in the region with disks relative to an estimate of the diskless YSO population. Although the AMC is similar in mass, size and distance to the OMC, it is forming about 15 - 20 times fewer stars.

  13. The Detection of a Hot Molecular Core in the Large Magellanic Cloud with ALMA

    NASA Astrophysics Data System (ADS)

    Shimonishi, Takashi; Onaka, Takashi; Kawamura, Akiko; Aikawa, Yuri

    2016-08-01

    We report the first detection of a hot molecular core outside our Galaxy based on radio observations with ALMA toward a high-mass young stellar object (YSO) in a nearby low metallicity galaxy, the Large Magellanic Cloud (LMC). Molecular emission lines of CO, C17O, HCO+, H13CO+, H2CO, NO, SiO, H2CS, 33SO, 32SO2, 34SO2, and 33SO2 are detected from a compact region (˜0.1 pc) associated with a high-mass YSO, ST11. The temperature of molecular gas is estimated to be higher than 100 K based on rotation diagram analysis of SO2 and 34SO2 lines. The compact source size, warm gas temperature, high density, and rich molecular lines around a high-mass protostar suggest that ST11 is associated with a hot molecular core. We find that the molecular abundances of the LMC hot core are significantly different from those of Galactic hot cores. The abundances of CH3OH, H2CO, and HNCO are remarkably lower compared to Galactic hot cores by at least 1-3 orders of magnitude. We suggest that these abundances are characterized by the deficiency of molecules whose formation requires the hydrogenation of CO on grain surfaces. In contrast, NO shows a high abundance in ST11 despite the notably low abundance of nitrogen in the LMC. A multitude of SO2 and its isotopologue line detections in ST11 imply that SO2 can be a key molecular tracer of hot core chemistry in metal-poor environments. Furthermore, we find molecular outflows around the hot core, which is the second detection of an extragalactic protostellar outflow. In this paper, we discuss the physical and chemical characteristics of a hot molecular core in the low metallicity environment.

  14. Feedback of the HBe star IL Cep on nearby molecular cloud and star formation

    NASA Astrophysics Data System (ADS)

    Zhang, Si-Ju; Wu, Yuefang; Li, Jin Zeng; Yuan, Jing-Hua; Liu, Hong-Li; Dong, Xiaoyi; Huang, Ya-Fang

    2016-06-01

    We present investigations of the feedback of a luminous Herbig Be star, IL Cep. We mapped the vicinity of IL Cep in the J = 1-0 transitions of 12CO, 13CO and C18O molecular lines with the Purple Mountain Observatory 13.7 m telescope. Archival data from Wide-field Infrared Survey Explorer were also employed. A parsec-scale cavity that has probably been excavated by the dominant HBe star, IL Cep, is revealed. An expanding shell-like structure featured by 12CO(J = 1-0) emission was found surrounding the cavity, which embeds several 13CO(J = 1-0) molecular clumps. The density and velocity gradients imply strong stellar winds from exciting stars, this is consistent with the morphology of molecular cloud. The 12CO(J = 1-0) spectra show broad blue wings with a width of about 3.5 km s-1. We suggest that the broad blue wings could be emission from the molecular gas shocked by stellar winds, while the main narrow component may originate from pre-shocked gas. Several bright bow-shaped rims have been detected at 12 μm, which serve as the interface of the molecular cloud facing UV dissipation from the exciting stars. The rims all have an orientation facing IL Cep, this may indicate the pre-dominant effects of IL Cep on its surroundings. A very young star candidate (about 104.8 yr) was found in the head of one bright rim, but its triggered origin is uncertain. All results achieved in this paper suggest that IL Cep has violent effects on its surroundings.

  15. STAR-FORMING CLOUD COMPLEXES IN THE CENTRAL MOLECULAR ZONE OF NGC 253

    SciTech Connect

    Sakamoto, Kazushi; Matsushita, Satoki; Mao, Rui-Qing; Peck, Alison B.; Sawada, Tsuyoshi; Wiedner, Martina C.

    2011-07-01

    We report 350 and 230 GHz observations of molecular gas and dust in the starburst nucleus of NGC 253 at 20-40 pc (1''-2'') resolution. The data contain CO(3-2), HCN(4-3), CO(2-1), {sup 13}CO(2-1), C{sup 18}O(2-1), and continuum at 0.87 mm and 1.3 mm toward the central kiloparsec. The CO(2-1) size of the galaxy's central molecular zone (CMZ) is measured to be about 300 pcx100 pc at the half-maximum of intensity. Five clumps of dense and warm gas stand out in the CMZ at arcsecond resolution, and they are associated with compact radio sources due to recent massive star formation. They contribute one-third of the CO emission in the central 300 pc and have {sup 12}CO peak brightness temperatures around 50 K, molecular gas column densities on the order of 10{sup 4} M{sub sun} pc{sup -2}, gas masses on the order of 10{sup 7} M{sub sun} in the size scale of 20 pc, volume-averaged gas densities of n{sub H{sub 2}} {approx} 4000 cm{sup -3}, and high HCN-to-CO ratios suggestive of higher fractions of dense gas than in the surrounding environment. It is suggested that these are natal molecular cloud complexes of massive star formation. The CMZ of NGC 253 is also compared with that of our Galaxy in CO(2-1) at the same 20 pc resolution. Their overall gas distributions are strikingly similar. The five molecular cloud complexes appear to be akin to such molecular complexes as Sgr A, Sgr B2, Sgr C, and the l = 1.{sup 0}3 cloud in the Galactic center. On the other hand, the starburst CMZ in NGC 253 has higher temperatures and higher surface (and presumably volume) densities than its non-starburst cousin.

  16. Study of interstellar molecular clouds using formaldehyde absorption toward extragalactic radio sources

    SciTech Connect

    Araya, E. D.; Andreev, N.; Dieter-Conklin, N.; Goss, W. M.

    2014-04-01

    We present new Very Large Array 6 cm H{sub 2}CO observations toward four extragalactic radio continuum sources (B0212+735, 3C 111, NRAO 150, and BL Lac) to explore the structure of foreground Galactic clouds as revealed by absorption variability. This project adds a new epoch in the monitoring observations of the sources reported by Marscher and collaborators in the mid-1990s. Our new observations confirm the monotonic increase in H{sub 2}CO absorption strength toward NRAO 150. We do not detect significant variability of our 2009 spectra with respect to the 1994 spectra of 3C111, B0212+735, and BL Lac; however, we find significant variability of the 3C111 2009 spectrum with respect to archive observations conducted in 1991 and 1992. Our analysis supports that changes in absorption lines could be caused by chemical and/or geometrical gradients in the foreground clouds and not necessarily by small-scale (∼10 AU) high-density molecular clumps within the clouds.

  17. COSMIC-RAY STREAMING FROM SUPERNOVA REMNANTS AND GAMMA-RAY EMISSION FROM NEARBY MOLECULAR CLOUDS

    SciTech Connect

    Yan Huirong; Lazarian, A.; Schlickeiser, R.

    2012-02-01

    High-energy gamma-ray emission has been detected recently from supernova remnants (SNRs) and their surroundings. The existence of molecular clouds near some of the SNRs suggests that the gamma rays originate predominantly from p-p interactions with cosmic rays (CRs) accelerated at a closeby SNR shock wave. Here we investigate the acceleration of CRs and the gamma-ray production in the cloud self-consistently by taking into account the interactions of the streaming instability and the background turbulence both at the shock front and in the ensuing propagation to the clouds. We focus on the later evolution of SNRs, when the conventional treatment of the streaming instability is valid but the magnetic field is enhanced due to Bell's current instability and/or the dynamo generation of magnetic field in the precursor region. We calculate the time dependence of the maximum energy of the accelerated particles. This result is then used to determine the diffusive flux of the runaway particles escaping the shock region, from which we obtain the gamma spectrum consistent with observations. Finally, we check the self-consistency of our results by comparing the required level of diffusion with the level of the streaming instability attainable in the presence of turbulence damping. The energy range of CRs subject to the streaming instability is able to produce the observed energy spectrum of gamma rays.

  18. Gas distribution, star formation and giant molecular cloud evolution in nearby spiral galaxies

    NASA Astrophysics Data System (ADS)

    Rebolledo Lara, David Andres

    2013-12-01

    In this thesis, I present a detailed study of the resolved properties of the cold gas in nearby galaxies at different size scales, starting from the whole galactic disk to the size of the Giant Molecular Clouds (GMCs). Differences in the shape and width of global CO and HI spectra of resolved disks of spiral galaxies are systematically investigated using a nearby sample for which high-resolution CO and HI maps are available. I find that CO line widths can be wider than HI widths in galaxies where the rotation curve declines in the outer parts, while they can be narrower in galaxies where the CO does not adequately sample the flat part of the rotation curve. Limited coverage of the CO emission by the telescope beam can mimic the latter effect. A physically based prescription linking the CO and HI radial profiles with the stellar disk is consistent with these findings. Then, I present an analysis performed on high spatial resolution observations of Giant Molecular Clouds in the three nearby spiral galaxies NGC 6946, NGC 628 and M101 obtained with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). Using the automated CPROPS algorithm I identified 112 CO cloud complexes in the CO(1 → 0) map and 145 GMCs in the CO(2 → 1) maps. The properties of the GMCs are similar to values found in other extragalactic studies. Clouds located on-arm present in general higher star formation rates than clouds located in inter-arm regions. Also, I find differences in the distribution of star formation efficiencies in the disk of these galaxies. These differences may be related to the underlying dynamical process that drives the observed spiral arm structure in the disks. In this scenario, in galaxies with nearly symmetric arm shape (e. g., NGC 628), the spiral shocks are triggering star formation along the arms. On other hand, galaxies with flocculent or multi-arm spiral structure (e. g., NGC 6946 and M101) show regions of high star formation efficiency at specific

  19. The dynamical evolution of molecular clouds near the Galactic Centre - I. Orbital structure and evolutionary timeline

    NASA Astrophysics Data System (ADS)

    Kruijssen, J. M. Diederik; Dale, James E.; Longmore, Steven N.

    2015-02-01

    We recently proposed that the star-forming potential of dense molecular clouds in the Central Molecular Zone (CMZ, i.e. the central few 100 pc) of the Milky Way is intimately linked to their orbital dynamics, potentially giving rise to an absolute-time sequence of star-forming clouds. In this paper, we present an orbital model for the gas stream(s) observed in the CMZ. The model is obtained by integrating orbits in the empirically constrained gravitational potential and represents a good fit (χ _red^2=2.0) to the observed position-velocity distribution of dense (n > several 103 cm-3) gas, reproducing all of its key properties. The orbit is also consistent with observational constraints not included in the fitting process, such as the 3D space velocities of Sgr B2 and the Arches and Quintuplet clusters. It differs from previous, parametric models in several respects: (1) the orbit is open rather than closed due to the extended mass distribution in the CMZ, (2) its orbital velocity (100-200 km s-1) is twice as high as in previous models, and (3) Sgr A* coincides with the focus of the (eccentric) orbit rather than being offset. Our orbital solution supports the recently proposed scenario in which the dust ridge between G0.253+0.016 (`the Brick') and Sgr B2 represents an absolute-time sequence of star-forming clouds, of which the condensation was triggered by the tidal compression during their most recent pericentre passage. We position the clouds on a common timeline and find that their pericentre passages occurred 0.30-0.74 Myr ago. Given their short free-fall times (tff ˜ 0.34 Myr), the quiescent cloud G0.253+0.016 and the vigorously star-forming complex Sgr B2 are separated by a single free-fall time of evolution, implying that star formation proceeds rapidly once collapse has been initiated. We provide the complete orbital solution, as well as several quantitative predictions of our model (e.g. proper motions and the positions of star formation `hotspots'). The

  20. Global collapse of molecular clouds as a formation mechanism for the most massive stars

    NASA Astrophysics Data System (ADS)

    Peretto, N.; Fuller, G. A.; Duarte-Cabral, A.; Avison, A.; Hennebelle, P.; Pineda, J. E.; André, Ph.; Bontemps, S.; Motte, F.; Schneider, N.; Molinari, S.

    2013-07-01

    The relative importance of primordial molecular cloud fragmentation versus large-scale accretion still remains to be assessed in the context of massive core/star formation. Studying the kinematics of the dense gas surrounding massive-star progenitors can tell us the extent to which large-scale flow of material impacts the growth in mass of star-forming cores. Here we present a comprehensive dataset of the 5500(±800) M⊙ infrared dark cloud SDC335.579-0.272 (hereafter SDC335), which exhibits a network of cold, dense, parsec-long filaments. Atacama Large Millimeter Array (ALMA) Cycle 0 observations reveal two massive star-forming cores, MM1 and MM2, sitting at the centre of SDC335 where the filaments intersect. With a gas mass of 545(-385+770) M⊙ contained within a source diameter of 0.05 pc, MM1 is one of the most massive, compact protostellar cores ever observed in the Galaxy. As a whole, SDC335 could potentially form an OB cluster similar to the Trapezium cluster in Orion. ALMA and Mopra single-dish observations of the SDC335 dense gas furthermore reveal that the kinematics of this hub-filament system are consistent with a global collapse of the cloud. These molecular-line data point towards an infall velocity Vinf = 0.7( ± 0.2) km s-1, and a total mass infall rate Ṁinf ≃ 2.5(±1.0) × 10-3 M⊙ yr-1 towards the central pc-size region of SDC335. This infall rate brings 750(±300) M⊙ of gas to the centre of the cloud per free-fall time (tff = 3 × 105 yr). This is enough to double the mass already present in the central pc-size region in 3.5-1.0+2.2 × tff. These values suggest that the global collapse of SDC335 over the past million year resulted in the formation of an early O-type star progenitor at the centre of the cloud's gravitational potential well.

  1. The role of orbital dynamics and cloud-cloud collisions in the formation of giant molecular clouds in global spiral structures

    NASA Technical Reports Server (NTRS)

    Roberts, William W., Jr.; Stewart, Glen R.

    1987-01-01

    The role of orbit crowding and cloud-cloud collisions in the formation of GMCs and their organization in global spiral structure is investigated. Both N-body simulations of the cloud system and a detailed analysis of individual particle orbits are used to develop a conceptual understanding of how individual clouds participate in the collective density response. Detailed comparisons are made between a representative cloud-particle simulation in which the cloud particles collide inelastically with one another and give birth to and subsequently interact with young star associations and stripped down simulations in which the cloud particles are allowed to follow ballistic orbits in the absence of cloud-cloud collisions or any star formation processes. Orbit crowding is then related to the behavior of individual particle trajectories in the galactic potential field. The conceptual picture of how GMCs are formed in the clumpy ISMs of spiral galaxies is formulated, and the results are compared in detail with those published by other authors.

  2. A CORRELATION BETWEEN SURFACE DENSITIES OF YOUNG STELLAR OBJECTS AND GAS IN EIGHT NEARBY MOLECULAR CLOUDS

    SciTech Connect

    Gutermuth, R. A.; Pipher, J. L.; Megeath, S. T.; Allen, T. S.; Myers, P. C.; Allen, L. E.

    2011-10-01

    We report the discovery and characterization of a power-law correlation between the local surface densities of Spitzer-identified, dusty young stellar objects (YSOs) and the column density of gas (as traced by near-IR extinction) in eight molecular clouds within 1 kpc and with 100 or more known YSOs. This correlation, which appears in data smoothed over size scales of {approx}1 pc, varies in quality from cloud to cloud; those clouds with tight correlations, MonR2 and Ophiuchus, are fit with power laws of slope 2.67 and 1.87, respectively. The spread in the correlation is attributed primarily to local gas disruption by stars that formed there or to the presence of very young subregions at the onset of star formation. We explore the ratio of the number of Class II to Class I sources, a proxy for the star formation age of a region, as a function of gas column density; this analysis reveals a declining Class II to Class I ratio with increasing column density. We show that the observed star-gas correlation is consistent with a star formation law where the star formation rate per area varies with the gas column density squared. We also propose a simple picture of thermal fragmentation of dense gas in an isothermal, self-gravitating layer as an explanation for the power law. Finally, we briefly compare the star-gas correlation and its implied star formation law with other recent proposed of star formation laws at similar and larger size scales from nearby star-forming regions.

  3. EXTENSIVE [C I] MAPPING TOWARD THE ORION-A GIANT MOLECULAR CLOUD

    SciTech Connect

    Shimajiri, Yoshito; Oshima, Tai; Kawabe, Ryohei; Sakai, Takeshi; Kohno, Kotaro; Tsukagoshi, Takashi; Momose, Munetake; Kitamura, Yoshimi; Saito, Masao

    2013-09-10

    We have carried out wide-field (0.17 deg{sup 2}) and high-angular resolution (21.''3 {approx} 0.04 pc) observations in the [C I] line toward the Orion-A giant molecular cloud with the Atacama Submillimeter Telescope Experiment 10 m telescope in the On-The-Fly mode. The overall features of the [C I] emission are similar to those of the {sup 12}CO (J = 1-0) emission by Shimajiri et al. in 2011; the total intensity ratio of the [C I] to CO emission ranges from 0.05 to 0.2. The optical depth of the [C I] emission is found to be 0.1-0.75, suggesting optically thin emission. The column density of the [C I] emission is estimated to be (1.0-19) Multiplication-Sign 10{sup 17} cm{sup -2}. These results are consistent with the results of the previous [C I] observations with a low-angular resolution of 2.'2. In the nearly edge-on photon-dominated regions (PDRs) and their candidates of the Orion Bar, DLSF, M 43 Shell, and Region D, the distributions of the [C I] emission coincide with those of the {sup 12}CO emission, inconsistent with the prediction by the plane-parallel PDR model. In addition, the [C I] distribution in the Orion A cloud is found to be more similar to those of the {sup 13}CO (J = 1-0), C{sup 18}O (J = 1-0), and H{sup 13}CO{sup +} (J = 1-0) lines than that of the {sup 12}CO (J = 1-0) line, suggesting that the [C I] emission is not limited to the cloud surface, but is tracing the dense, inner parts of the cloud.

  4. THE NATURE OF CARBON DIOXIDE BEARING ICES IN QUIESCENT MOLECULAR CLOUDS

    SciTech Connect

    Whittet, D. C. B.; Cook, A. M.; Chiar, J. E.; Pendleton, Y. J.; Shenoy, S. S.; Gerakines, P. A.

    2009-04-10

    The properties of the ices that form in dense molecular clouds represent an important set of initial conditions in the evolution of interstellar and preplanetary matter in regions of active star formation. Of the various spectral features available for study, the bending mode of solid CO{sub 2} near 15 {mu}m has proven to be a particularly sensitive probe of physical conditions, especially temperature. We present new observations of this absorption feature in the spectrum of Q21-1, a background field star located behind a dark filament in the Cocoon Nebula (IC 5146). We show the profile of the feature to be consistent with a two-component (polar + nonpolar) model for the ices, based on spectra of laboratory analogs with temperatures in the range 10-20 K. The polar component accounts for {approx}85% of the CO{sub 2} in the line of sight. We compare for the first time 15 {mu}m profiles in three widely separated dark clouds (Taurus, Serpens, and IC 5146), and show that they are indistinguishable to within observational scatter. Systematic differences in the observed CO{sub 2}/H{sub 2}O ratio in the three clouds have little or no effect on the 15 {mu}m profile. The abundance of elemental oxygen in the ices appears to be a unifying factor, displaying consistent behavior in the three clouds. We conclude that the ice formation process is robust and uniformly efficient, notwithstanding compositional variations arising from differences in how the O is distributed between the primary species (H{sub 2}O, CO{sub 2}, and CO) in the ices.

  5. The CO Transition from Diffuse Molecular Gas to Dense Clouds: Preliminary Results

    NASA Astrophysics Data System (ADS)

    Rice, Johnathan S.; Federman, Steven

    2016-06-01

    The atomic to molecular transitions occurring in diffuse interstellar gas surrounding molecular clouds are affected by the local physical conditions (density and temperature) and the radiation field penetrating the material. The material is closely connected to CO-dark gas, which is not associated with emission from H I at 21 cm or from CO at 2.6 mm. Using optical observations of CH, CH+ and CN absorption from McDonald Observatory and the European Southern Observatory in conjunction with UV observations of CO and H2 absorption from FUSE, we explore the changing environment between diffuse and dense gas, emphasizing trends in column density, excitation temperature, gas density, and velocity structure. This presentation will focus on the completed analysis involving H2 and on the preliminary results of CO for our sample.

  6. Opacity broadening and interpretation of suprathermal CO linewidths: Macroscopic turbulence and tangled molecular clouds

    NASA Astrophysics Data System (ADS)

    Hacar, A.; Alves, J.; Burkert, A.; Goldsmith, P.

    2016-06-01

    Context. Since their first detection in the interestellar medium, (sub-)millimeter line observations of different CO isotopic variants have routinely been employed to characterize the kinematic properties of the gas in molecular clouds. Many of these lines exhibit broad linewidths that greatly exceed the thermal broadening expected for the low temperatures found within these objects. These observed suprathermal CO linewidths are assumed to originate from unresolved supersonic motions inside clouds. Aims: The lowest rotational J transitions of some of the most abundant CO isotopologues, 12CO and 13CO, are found to present large optical depths. In addition to well-known line saturation effects, these large opacities present a non-negligible contribution to their observed linewidths. Typically overlooked in the literature, in this paper we aim to quantify the impact of these opacity broadening effects on the current interpretation of the CO suprathermal line profiles. Methods: Combining large-scale observations and LTE modeling of the ground J = 1-0 transitions of the main 12CO, 13CO, C18O isotopologues, we have investigated the correlation of the observed linewidths as a function of the line opacity in different regions of the Taurus molecular cloud. Results: Without any additional contributions to the gas velocity field, a large fraction of the apparently supersonic (ℳ ~ 2-3) linewidths measured in both 12CO and 13CO (J = 1-0) lines can be explained by the saturation of their corresponding sonic-like, optically thin C18O counterparts assuming standard isotopic fractionation. Combined with the presence of multiple components detected in some of our C18O spectra, these opacity effects also seem to be responsible for most of the highly supersonic linewidths (ℳ > 8-10) detected in some of the broadest 12CO and 13CO spectra in Taurus. Conclusions: Our results demonstrate that most of the suprathermal 12CO and 13CO linewidths reported in nearby clouds like Taurus

  7. The initial mass function of star clusters that form in turbulent molecular clouds

    NASA Astrophysics Data System (ADS)

    Fujii, M. S.; Portegies Zwart, S.

    2015-05-01

    We simulate the formation and evolution of young star clusters using the combination of smoothed particle hydrodynamics (SPH) simulations and direct N-body simulations. We start by performing SPH simulations of the giant molecular cloud (GMC) with a turbulent velocity field, a mass of 4 × 104 to 5 × 106 M⊙, and a density between ρ ˜ 1.7 × 103 and 170 cm-3. We continue the hydrodynamical simulations for a free-fall time-scale (tff ≃ 0.83 and 2.5 Myr), and analyse the resulting structure of the collapsed cloud. We subsequently replace a density-selected subset of SPH particles with stars by adopting a local star formation efficiency proportional to ρ1/2. As a consequence, the local star formation efficiency exceeds 30 per cent, whereas globally only a few per cent of the gas is converted to stars. The stellar distribution by the time gas is converted to stars is very clumpy, with typically a dozen bound conglomerates that consist of 100-104 stars. We continue to evolve the stars dynamically using the collisional N-body method, which accurately treats all pairwise interactions, stellar collisions and stellar evolution. We analyse the results of the N-body simulations when the stars have an age of 2 and 10 Myr. During the dynamical simulations, massive clusters grow via hierarchical merging of smaller clusters. The shape of the cluster mass function that originates from an individual molecular cloud is consistent with a Schechter function with a power-law slope of β = -1.73 at 2 Myr and β = -1.67 at 10 Myr, which fits to observed cluster mass function of the Carina region. The superposition of mass functions have a power-law slope of ≲ -2, which fits the observed mass function of star clusters in the Milky Way, M31 and M83. We further find that the mass of the most massive cluster formed in a single molecular cloud with a mass of Mg scales with 6.1 M_g^{0.51} which also agrees with recent observation of the GMC and young clusters in M51.

  8. Giant Molecular Clouds and High-Mass Star Formation in the Milky Way

    NASA Technical Reports Server (NTRS)

    1998-01-01

    We are conducting an extensive investigation of high-mass (OB) star formation within the dense cores of giant molecular clouds (GMCS) throughout the first Galactic quadrant of the Milky Way using enhanced resolution Infrared Astronomical Satellite (IRAS) images in combination with high-resolution ground-based observations in millimeter wave molecular transitions and radio continuum. As part of this investigation several resolution enhancement algorithms are applied to the IRAS data, including the HIgh RESolution (HIRES) algorithm developed at the IRAS Processing and Analysis Center (IPAC), as well as others ("pixon" image reconstruction). In addition, as part of a related study, we have completed a large survey of the CO emission in the first Galactic quadrant using the 15-element array detector (QUARRY) with the Five College Radio Astronomy Observatory (FCRAO) 14 m antenna, which provides sampling at an angular resolution of 50", comparable to that attained in the reprocessed IRAS data. Both of these data sets are compared with a sample of ultra-compact (UC) H II regions taken from a high-resolution multi-wavelength (6 and 20 cm) radio survey of the Galactic plane using the NRAO Very Large Array (VLA). Selected regions are observed in 1.3 mm continuum, which has proven to be particularly sensitive to the dust column density. Extensive observations of molecular clouds at high resolution in CO, CS and HCN are combined with the reprocessed IRAS high-resolution images to give a more complete picture of the physical conditions and kinematics of high-mass star forming GMCS. Our goals are to study in detail the morphology, structure, and rate of high-mass star formation within GMCs throughout the Galactic disk from the inner edge of the molecular ring to the outer Galaxy.

  9. Colliding filaments and a massive dense core in the Cygnus OB 7 molecular cloud

    SciTech Connect

    Dobashi, Kazuhito; Shimoikura, Tomomi; Akisato, Ko; Ohashi, Kenjiro; Nakagomi, Keisuke; Matsumoto, Tomoaki; Saito, Hiro

    2014-12-10

    We report the results of molecular line observations carried out toward a massive dense core in the Cyg OB 7 molecular cloud. The core has an extraordinarily large mass (∼1.1 × 10{sup 4} M {sub ☉}) and size (∼2 × 5 pc{sup 2}), but there is no massive young star forming therein. We observed this core in various molecular lines such as C{sup 18}O(J = 1-0) using the 45 m telescope at Nobeyama Radio Observatory. We find that the core has an elongated morphology consisting of several filaments and core-like structures. The filaments are massive (10{sup 2}-10{sup 3} M {sub ☉}), and they are apparently colliding with one another. Some candidates for young stellar objects are distributed around their intersection, suggesting that the collisions of the filaments may have influenced their formation. To understand the formation and evolution of such colliding filaments, we performed numerical simulations using the adaptive mesh refinement technique, adopting the observed core parameters (the mass and size) as the initial conditions. The results indicate that the filaments are formed as seen in other earlier simulations for small cores in the literature, but we could not reproduce the collisions of the filaments simply by assuming a large initial mass and size. We find that collisions of the filaments occur only when there is a large velocity gradient in the initial core, in a sense compressing it. We suggest that the observed core was actually compressed by an external effect, e.g., shocks from nearby supernova remnants, including HB 21 which has been suggested to be interacting with the Cyg OB 7 molecular cloud.

  10. Gravity Binding and Pressure Bounding of HII Regions and Molecular Clouds in Interacting Galaxies

    NASA Astrophysics Data System (ADS)

    Beckman, John Etienne; Zaragoz-Cardiel, Javier; Font, Joan; Amram, Philippe; Camps-Fariña, Artemi

    2015-08-01

    We have observed a sample of 12 interacting galaxies using the Fabry-Perot interferometer GHαFaS (Galaxy Hα Fabry-Perot system) on the 4.2m William Herschel Telescope (WHT) at the Observatorio del Roque de los Muchachos, La Palma, deriving maps in Hα surface brightness, velocity and velocity dispersion. We extracted the physical parameters (Hα luminosities, velocity dispersions, and effective radii) of 1300 HII regions for the full sample with techniques for which velocity tagging is an essential step. We found two populations of HII regions, with a break at a gas mass of 106.5 solar masses. The mean density of the regions falls with radius for smaller masses, but rises with radius for larger masses. This is because in the lower mass range the HII regions are pressure bounded while in the upper range they are gravitationally bound. This analysis is underscored by using the turbulent velocity dispersion to show that the virial parameter for the regions shows values consistent with gravitational equilibrium in the upper range only. We were able to use ALMA observations of the molecular clouds in one of our objects, the Antennae galaxies, showing that for clouds with masses above 106.5 solar masses their densities increase with mass. The mass functions of the molecular clouds and HII regions in the Antennae show bimodal distributions, with the break at 106.5 solar masses clearly in evidence. We draw two conclusions of interest. Firstly the classical Larson scaling relation between surface density and mass does not operate in the upper mass range, implying higher star formation efficiency there. Secondly the similarity in the mass functions and density radius relations for the GMC’s and HII regions suggests that, at least in the upper mass range, the former remain gravitationally bound even after massive star formation has occurred.

  11. An Analysis of the Deuterium Fractionation of Star-forming Cores in the Perseus Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Friesen, R. K.; Kirk, H. M.; Shirley, Y. L.

    2013-03-01

    We have performed a pointed survey of N2D+ 2-1 and N2D+ 3-2 emission toward 64 N2H+-bright starless and protostellar cores in the Perseus molecular cloud using the Arizona Radio Observatory Submillimeter Telescope and Kitt Peak 12 m telescope. We find a mean deuterium fractionation in N2H+, RD = N(N2D+)/N(N2H+), of 0.08, with a maximum RD = 0.2. In detected sources, we find no significant difference in the deuterium fractionation between starless and protostellar cores, nor between cores in clustered or isolated environments. We compare the deuterium fraction in N2H+ with parameters linked to advanced core evolution. We only find significant correlations between the deuterium fraction and increased H2 column density, as well as with increased central core density, for all cores. Toward protostellar sources, we additionally find a significant anticorrelation between RD and bolometric temperature. We show that the Perseus cores are characterized by low CO depletion values relative to previous studies of star-forming cores, similar to recent results in the Ophiuchus molecular cloud. We suggest that the low average CO depletion is the dominant mechanism that constrains the average deuterium fractionation in the Perseus cores to small values. While current equilibrium and dynamic chemical models are able to reproduce the range of deuterium fractionation values we find in Perseus, reproducing the scatter across the cores requires variation in parameters such as the ionization fraction or the ortho-to-para-H2 ratio across the cloud, or a range in core evolution timescales.

  12. Into the Darkness: Interstellar Extinction Near the Cepheus OB3 Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Fitzpatrick, Edward L.; Jacklin, S.; Massa, D.

    2014-01-01

    We present the results of a followup investigation to a study performed by Massa and Savage (1984, ApJ, 279, 310) of the properties of UV interstellar extinction in the region of the Cepheus OB3 molecular cloud. That study was performed using UV photometry and spectro-photometry from the ANS and IUE satellites. We have extended this study into the IR, utilizing the uniform database of IR photometry available from the 2MASS project. This is a part of a larger program whose goal is to study the properties of extinction in localized regions, where we hope to find clues to dust grain growth and destruction processes through spatial correlations of extinction with distinct environmental properties. Similarly to Massa and Savage’s UV results, we find that the IR extinction properties on the Cepheus OB3 region vary systematically with the apparent proximity of the target stars to the molecular cloud. We also find that the UV extinction and the IR extinction are crudely correlated. The methodology leading to these results and their implications are discussed.

  13. Calibrating column density tracers with gamma-ray observations of the ρ Ophiuchi molecular cloud

    NASA Astrophysics Data System (ADS)

    Abrahams, Ryan; Teachey, Alex; Paglione, Timothy

    2016-01-01

    Likelihood analyses of gamma-ray counts maps require modeling a variety of presumed emission sources including their spatial extents and spectral shapes. The differences between the observed counts maps and these models often result in significant, spatially coherent residuals. These residuals are distinct from the "dark gas", and persist despite accounting for other gas phases using dust maps or various measures. Given the goal to understand the underlying cosmic ray (CR) density, spectrum, and its spatial variation through the Galactic disk, the distribution and column density of the gas with which the CRs interact must be sensitively constrained. We present a study of the gamma-ray emission from the ρ Ophiuchi molecular cloud seen by Fermi, and compare this emission to a number of column density tracers, including near IR stellar extinction and dust emission. This nearby molecular cloud exhibits a broad dynamic range in extinction, notably atypical dust properties, and a number of embedded B stars which heat the dust and may also act as local CR sources

  14. CONSTRAINTS ON FREE-FREE EMISSION FROM ANOMALOUS MICROWAVE EMISSION SOURCES IN THE PERSEUS MOLECULAR CLOUD

    SciTech Connect

    Tibbs, C. T.; Paladini, R.; Dickinson, C.; Davies, R. D.; Davis, R. J.; Watson, R. A.; Mason, B. S.; Casassus, S.; Cleary, K.

    2013-06-20

    We present observations performed with the Green Bank Telescope at 1.4 and 5 GHz of three strips coincident with the anomalous microwave emission features previously identified in the Perseus molecular cloud at 33 GHz with the Very Small Array. With these observations we determine the level of the low frequency ({approx}1-5 GHz) emission. We do not detect any significant extended emission in these regions and we compute conservative 3{sigma} upper limits on the fraction of free-free emission at 33 GHz of 27%, 12%, and 18% for the three strips, indicating that the level of the emission at 1.4 and 5 GHz cannot account for the emission observed at 33 GHz. Additionally, we find that the low frequency emission is not spatially correlated with the emission observed at 33 GHz. These results indicate that the emission observed in the Perseus molecular cloud at 33 GHz, is indeed in excess over the low frequency emission, hence confirming its anomalous nature.

  15. Constraints on Free-Free Emission from Anomalous Microwave Emission Sources in the Perseus Molecular Cloud

    NASA Astrophysics Data System (ADS)

    Tibbs, C. T.; Paladini, R.; Dickinson, C.; Mason, B. S.; Casassus, S.; Cleary, K.; Davies, R. D.; Davis, R. J.; Watson, R. A.

    2013-06-01

    We present observations performed with the Green Bank Telescope at 1.4 and 5 GHz of three strips coincident with the anomalous microwave emission features previously identified in the Perseus molecular cloud at 33 GHz with the Very Small Array. With these observations we determine the level of the low frequency (~1-5 GHz) emission. We do not detect any significant extended emission in these regions and we compute conservative 3σ upper limits on the fraction of free-free emission at 33 GHz of 27%, 12%, and 18% for the three strips, indicating that the level of the emission at 1.4 and 5 GHz cannot account for the emission observed at 33 GHz. Additionally, we find that the low frequency emission is not spatially correlated with the emission observed at 33 GHz. These results indicate that the emission observed in the Perseus molecular cloud at 33 GHz, is indeed in excess over the low frequency emission, hence confirming its anomalous nature.

  16. Molecular Clouds and Massive Star Formation in the Norma Spiral Arm

    NASA Astrophysics Data System (ADS)

    García, P.; Bronfman, L.; May, J.

    2006-06-01

    The Norma spiral arm in the Southern Galaxy contains the most massive molecular clouds as well as the most FIR luminous regions of massive star formation in the Galactic disk. The tangent region of this arm, at a well defined distance of ≈ 4.5 kpc from the Sun, is ideal to study in detail the process of massive star formation in GMCs (Bronfman et al. 1988, ApJ, 324, 248). We present maps of the major GMCs in ^{12}CO and C^{18}O obtained with the Nanten 4-m telescope, at a resolution of 2.5 arcmin. We have obtained also CS (2-1) and CS(5-4) maps of several OB star formation regions embedded in these GMCs (Bronfman et al. 1996, A&AS, 115, 81). What is the contribution from embedded OB stars to the total FIR emission from these GMCs? What is the fraction of cloud molecular gas involved in massive star formation?

  17. High-dynamic-range extinction mapping of infrared dark clouds. Dependence of density variance with sonic Mach number in molecular clouds

    NASA Astrophysics Data System (ADS)

    Kainulainen, J.; Tan, J. C.

    2013-01-01

    Context. Measuring the mass distribution of infrared dark clouds (IRDCs) over the wide dynamic range of their column densities is a fundamental obstacle in determining the initial conditions of high-mass star formation and star cluster formation. Aims: We present a new technique to derive high-dynamic-range, arcsecond-scale resolution column density data for IRDCs and demonstrate the potential of such data in measuring the density variance - sonic Mach number relation in molecular clouds. Methods: We combine near-infrared data from the UKIDSS/Galactic Plane Survey with mid-infrared data from the Spitzer/GLIMPSE survey to derive dust extinction maps for a sample of ten IRDCs. We then examine the linewidths of the IRDCs using 13CO line emission data from the FCRAO/Galactic Ring Survey and derive a column density - sonic Mach number relation for them. For comparison, we also examine the relation in a sample of nearby molecular clouds. Results: The presented column density mapping technique provides a very capable, temperature independent tool for mapping IRDCs over the column density range equivalent to AV ≃ 1-100 mag at a resolution of 2″. Using the data provided by the technique, we present the first direct measurement of the relationship between the column density dispersion, σN/⟨N⟩, and sonic Mach number, ℳs, in molecular clouds. We detect correlation between the variables with about 3-σ confidence. We derive the relation σN/⟨N⟩ ≈ (0.047 ± 0.016)ℳs, which is suggestive of the correlation coefficient between the volume density and sonic Mach number, σρ/⟨ρ⟩ ≈ (0.20-0.22+0.37)ℳs, in which the quoted uncertainties indicate the 3-σ range. When coupled with the results of recent numerical works, the existence of the correlation supports the picture of weak correlation between the magnetic field strength and density in molecular clouds (i.e., B ∝ ρ0.5). While our results remain suggestive because of the small number of clouds in our

  18. X-RAY EMISSION FROM STELLAR JETS BY COLLISION AGAINST HIGH-DENSITY MOLECULAR CLOUDS: AN APPLICATION TO HH 248

    SciTech Connect

    López-Santiago, J.; Ustamujic, S.; Castro, A. I. Gómez de; Bonito, R.; Orlando, S.; Orellana, M.; Miceli, M.; Albacete-Colombo, J. F.

    2015-06-10

    We investigate the plausibility of detecting X-ray emission from a stellar jet that impacts a dense molecular cloud, a scenario that may be typical for classical T Tauri stars with jets in dense star-forming complexes. We first model the impact of a jet against a dense cloud using two-dimensional axisymmetric hydrodynamic simulations, exploring different configurations of the ambient environment. Then, we compare our results with XMM-Newton observations of the Herbig–Haro object HH 248, where extended X-ray emission aligned with the optical knots is detected at the edge of the nearby IC 434 cloud. Our simulations show that a jet can produce plasma with temperatures up to 10{sup 7} K, consistent with production of X-ray emission, after impacting a dense cloud. We find that jets denser than the ambient medium but less dense than the cloud produce detectable X-ray emission only at impact with the cloud. From an exploration of the model parameter space, we constrain the physical conditions (jet density and velocity and cloud density) that reproduce the intrinsic luminosity and emission measure of the X-ray source possibly associated with HH 248 well. Thus, we suggest that the extended X-ray source close to HH 248 corresponds to a jet impacting a dense cloud.

  19. Molecular clouds in the Carina arm - Large-scale properties of molecular gas and comparison with H I

    NASA Technical Reports Server (NTRS)

    Grabelsky, D. A.; Cohen, R. S.; Bronfman, L.; Thaddeus, P.; May, J.

    1987-01-01

    Results from the first large-scale survey in the CO (J = 1 - 0) line of the Vela-Carina-Centaurus region of the southern Milky Way are reported. The results demonstrate that molecular clouds in the Galaxy are largely confined to the spiral arms and that CO is therefore an extremely good tracer of the large-scale structure of the system. The Carina arm is the dominant feature in the data. Its abrupt tangent at l of roughly 280 deg and characteristic loop in the (l, v) diagram are unmistakable evidence for CO spiral structure. When the emission is integrated over velocity and latitude, the height of the step seen in the tangent direction indicate that the arm-interarm contrast is at least 13:1.

  20. Molecular gas and stars in the translucent cloud MBM 18 (LDN 1569)

    NASA Astrophysics Data System (ADS)

    Brand, J.; Wouterloot, J. G. A.; Magnani, L.

    2012-11-01

    Context. We investigate star formation in translucent, high-latitude clouds. Aims: Our aim is to understand the star-formation history and rate in the solar neighbourhood. Methods: We used spectroscopic observations of newly found candidate Hα emission-line stars to establish their pre-main-sequence nature. The environment was studied through molecular line observations of the cloud (MBM 18/LDN 1569) in which the stars are presumably embedded. Results: Ten candidate Hα emission-line stars were found in an objective grism survey of a ~1 square degree region in MBM 18, of which seven have been observed spectroscopically in this study. Four of these have weak (| W(Hα)| ≲ 5 Å) Hα emission, and six out of seven have spectral types M1-M4 V. One star is of type F7-G1 V, and has Hα in absorption. The spectra of three of the M-stars may show an absorption line of LiI, although none of these is an unambiguous detection. The M-stars lie at distances between ~60 pc and 250 pc, while most distance determinations of MBM 18 found in the literature agree on 120-150 pc. For the six M-stars a good fit is obtained with pre-main-sequence isochrones indicating ages between 7.5 and 15 Myr. The mass of the molecular material, derived from the integrated 12CO(1-0) emission, is ~160 M⊙ (for a distance of 120 pc). This is much smaller than the virial mass (~103 M⊙), and the cloud is not gravitationally bound. Using a clump-finding routine, we identify 12 clumps from the CO-data, with masses between 2.2 and 22 M⊙. All clumps have a virial mass at least six times higher than their CO-mass, and thus none are in gravitational equilibrium. A similar situation is found from higher-resolution CO-observations of the northern part of the cloud. Conclusions: Considering the relative weakness or absence of the Hα emission, the absence of other emission lines, and the lack of clear LiI absorption, the targets are not T Tauri stars. With ages between 7.5 and 15 Myr they are old enough to

  1. Molecular clouds and star formation : a multiwavelength study of Perseus, Serpens, and Ophiuchus

    NASA Astrophysics Data System (ADS)

    Enoch, Melissa Lanae

    NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.In this thesis I utilize large-scale millimeter and mid- to far-infrared surveys to address a number of outstanding questions regarding the formation of low mass stars in molecular clouds. Continuum [lambda] = 1.1 mm maps completed with Bolocam at a resolution of 31" cover the largest areas observed to date at millimeter or submillimeter wavelengths in three molecular clouds: 7.5 deg(2) in Perseus (140 pc(2) at the adopted distance of d = 250 pc), 10.8 deg(2) (50 pc(2) at d = 125 pc) in Ophiuchus, and 1.5 deg(2) (30 pc(2) at d = 125 pc) in Serpens. These surveys are sensitive to dense substructures with mean density n [...] 2 - 3 x 10(4) cm(-3). A total of 122 cores are detected in Perseus, 44 in Ophiuchus, and 35 in Serpens above mass detection limits of 0.1 - 0.2 Msun. Combining with Spitzer mid- and far-infrared maps from the c2d Legacy program provides wavelength coverage from [lambda] = 1.25-1100 micron, and enables the assembly of an unbiased, complete sample of the youngest star forming objects in three environments. This sample includes 108 prestellar cores, 43 Class 0 sources and 94 Class I sources.The approximately equal number of starless cores and embedded protostars in each cloud implies a starless core lifetime of 2 - 4 x 10(5) yr, only a few free-fall timescales. This timescale, considerably shorter than the timescale predicted by the classic scenario of magnetic field support in which core evolution is moderated by ambipolar diffusion, suggests that turbulence is the dominant process controlling the formation and evolution of dense cores. However, dense cores in all three clouds are found only at high cloud column densities, where [...] 7 mag, and the fraction of cloud mass in these cores is less than 10%, indicating that magnetic fields must play some role as well. Measured angular deconvolved sizes of the majority of starless cores are

  2. A Search for O2 in CO-depleted Molecular Cloud Cores with Herschel

    NASA Astrophysics Data System (ADS)

    Wirström, Eva S.; Charnley, Steven B.; Cordiner, Martin A.; Ceccarelli, Cecilia

    2016-10-01

    The general lack of molecular oxygen in molecular clouds is an outstanding problem in astrochemistry. Extensive searches with the Submillimeter Astronomical Satellite, Odin, and Herschel have only produced two detections; upper limits to the O2 abundance in the remaining sources observed are about 1000 times lower than predicted by chemical models. Previous atomic oxygen observations and inferences from observations of other molecules indicated that high abundances of O atoms might be present in dense cores exhibiting large amounts of CO depletion. Theoretical arguments concerning the oxygen gas–grain interaction in cold dense cores suggested that, if O atoms could survive in the gas after most of the rest of the heavy molecular material has frozen out onto dust, then O2 could be formed efficiently in the gas. Using Herschel HIFI, we searched a small sample of four depletion cores—L1544, L694-2, L429, and Oph D—for emission in the low excitation O2 N J = 33–12 line at 487.249 GHz. Molecular oxygen was not detected and we derive upper limits to its abundance in the range of N(O2)/N(H2) ≈ (0.6{--}1.6) × {10}-7. We discuss the absence of O2 in the light of recent laboratory and observational studies.

  3. CH 3 GHz Observations of Molecular Clouds along the Galactic Plane

    NASA Astrophysics Data System (ADS)

    Magnani, Loris; Lugo, Samantha; Dame, T. M.

    2005-12-01

    Spectra in the CH 2Π1/2, J=1/2, F=1-1 transition at 3335 MHz were obtained in three five-point crosses centered on the Galactic plane at l=50deg, 100°, and 110°. The lines of sight traversed both giant molecular clouds (GMCs) and local, smaller entities. This transition is a good tracer of low-density molecular gas, and the line profiles are very similar to CO(1-0) data at nearly the same resolution. In addition, the CH 3335 MHz line can be used to calibrate the CO-H2 conversion factor (XCO) in low-density molecular gas. Although this technique underestimates XCO in GMCs, our results are within a factor of 2 of XCO values calibrated for GMCs by other techniques. The similarity of CH and CO line profiles, and that of XCO values derived from CH and more traditional techniques, implies that most of the molecular gas along the observed lines of sight is at relatively low densities (n<=103 cm-3).

  4. NEWLY IDENTIFIED EXTENDED GREEN OBJECTS (EGOs) FROM THE SPITZER GLIMPSE II SURVEY. II. MOLECULAR CLOUD ENVIRONMENTS

    SciTech Connect

    Chen Xi; Gan Conggui; Shen Zhiqiang; Ellingsen, Simon P.; Titmarsh, Anita; He Jinhua

    2013-06-01

    We have undertaken a survey of molecular lines in the 3 mm band toward 57 young stellar objects using the Australia Telescope National Facility Mopra 22 m radio telescope. The target sources were young stellar objects with active outflows (extended green objects (EGOs)) newly identified from the GLIMPSE II survey. We observe a high detection rate (50%) of broad line wing emission in the HNC and CS thermal lines, which combined with the high detection rate of class I methanol masers toward these sources (reported in Paper I) further demonstrates that the GLIMPSE II EGOs are associated with outflows. The physical and kinematic characteristics derived from the 3 mm molecular lines for these newly identified EGOs are consistent with these sources being massive young stellar objects with ongoing outflow activity and rapid accretion. These findings support our previous investigations of the mid-infrared properties of these sources and their association with other star formation tracers (e.g., infrared dark clouds, methanol masers and millimeter dust sources) presented in Paper I. The high detection rate (64%) of the hot core tracer CH{sub 3}CN reveals that the majority of these new EGOs have evolved to the hot molecular core stage. Comparison of the observed molecular column densities with predictions from hot core chemistry models reveals that the newly identified EGOs from the GLIMPSE II survey are members of the youngest hot core population, with an evolutionary time scale of the order of 10{sup 3} yr.

  5. An excursion-set model for the structure of giant molecular clouds and the interstellar medium

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip F.

    2012-07-01

    The interstellar medium (ISM) is governed by supersonic turbulence on a range of scales. We use this simple fact to develop a rigorous excursion-set model for the formation, structure and time evolution of dense gas structures [e.g. giant molecular clouds (GMCs), massive clumps and cores]. Supersonic turbulence drives the density distribution in non-self-gravitating regions to a lognormal with dispersion increasing with Mach number. We generalize this to include scales ≳h (the disc scale-height), and use it to construct the statistical properties of the density field smoothed on a scale R. We then compare conditions for self-gravitating collapse including thermal, turbulent and rotational (disc shear) support (reducing to the Jeans/Toomre criterion on small/large scales). We show that this becomes a well-defined barrier crossing problem. As such, an exact 'bound object mass function' can be derived, from scales of the sonic length to well above the disc Jeans mass. This agrees remarkably well with observed GMC mass functions in the Milky Way and other galaxies, with the only inputs being the total mass and size of the galaxies (to normalize the model). This explains the cut-off of the mass function and its power-law slope (close to, but slightly shallower than, -2). The model also predicts the linewidth-size and size-mass relations of clouds and the dependence of residuals from these relations on mean surface density/pressure, in excellent agreement with observations. We use this to predict the spatial correlation function/clustering of clouds and, by extension, star clusters; these also agree well with observations. We predict the size/mass function of 'bubbles' or 'holes' in the ISM, and show that this can account for the observed H I hole distribution without requiring any local feedback/heating sources. We generalize the model to construct time-dependent 'merger/fragmentation trees' which can be used to follow cloud evolution and construct semi

  6. GIANT MOLECULAR CLOUDS IN THE EARLY-TYPE GALAXY NGC 4526

    SciTech Connect

    Utomo, Dyas; Blitz, Leo; Davis, Timothy; Rosolowsky, Erik; Bureau, Martin; Cappellari, Michele; Sarzi, Marc

    2015-04-10

    We present a high spatial resolution (≈20 pc) of {sup 12}CO(2 −1) observations of the lenticular galaxy NGC 4526. We identify 103 resolved giant molecular clouds (GMCs) and measure their properties: size R, velocity dispersion σ{sub v}, and luminosity L. This is the first GMC catalog of an early-type galaxy. We find that the GMC population in NGC 4526 is gravitationally bound, with a virial parameter α ∼ 1. The mass distribution, dN/dM ∝ M{sup −2.39±0.03}, is steeper than that for GMCs in the inner Milky Way, but comparable to that found in some late-type galaxies. We find no size–line width correlation for the NGC 4526 clouds, in contradiction to the expectation from Larson’s relation. In general, the GMCs in NGC 4526 are more luminous, denser, and have a higher velocity dispersion than equal-size GMCs in the Milky Way and other galaxies in the Local Group. These may be due to higher interstellar radiation field than in the Milky Way disk and weaker external pressure than in the Galactic center. In addition, a kinematic measurement of cloud rotation shows that the rotation is driven by the galactic shear. For the vast majority of the clouds, the rotational energy is less than the turbulent and gravitational energy, while the four innermost clouds are unbound and will likely be torn apart by the strong shear at the galactic center. We combine our data with the archival data of other galaxies to show that the surface density Σ of GMCs is not approximately constant, as previously believed, but varies by ∼3 orders of magnitude. We also show that the size and velocity dispersion of the GMC population across galaxies are related to the surface density, as expected from the gravitational and pressure equilibrium, i.e., σ{sub v} R{sup −1/2} ∝ Σ{sup 1/2}.

  7. Present-day star formation: From molecular cloud cores to protostars and protoplanetary disks

    NASA Astrophysics Data System (ADS)

    Inutsuka, Shu-ichiro

    2012-10-01

    Essential physical processes in the formation of protostars and protoplanetary disks are described. Recent advances in non-ideal magnetohydrodynamics simulations, which cover a huge dynamic range from molecular cloud core density (104/cc) to stellar density (1022/cc) in a self-consistent manner, enable us to study the realistic evolution of the magnetic field and rotation of protostars and the dynamics of outflows and jets. First we emphasize the importance of radiative heating and cooling, and describe thermal evolution in a self-gravitationally collapsing cloud. The increased pressure at the center creates the first hydrostatic core, which consists of molecular gas. After the dissociation of molecular hydrogen triggers the second gravitational collapse at the center of the first core, a protostar is quickly formed and the first core gradually transforms into a circumstellar disk that eventually accretes onto the central protostar. The importance of the short-lived first core formed in the early collapsing phase is emphasized in the contexts of driving magnetohydrodynamical bipolar outflows and self-gravitational fragmentation into binary or multiple stars. When the central density becomes sufficiently high (1012/cc), ohmic dissipation largely removes the magnetic flux from a collapsing cloud core, and the strongly twisted magnetic field lines are straightened. The magnetic field lines are twisted and amplified again for much higher density (1016/cc) where the magnetic field is recoupled with warm gas (˜103 K). Finally, protostars at their formation epoch have magnetic fields of 0.1-1 kG, which is comparable to observed values of pre-main-sequence stars. A substantially reduced magnetic flux at the center results in passively wound-up magnetic field lines just after the formation of a protostar. This is followed by driving of a fast bipolar jet along the rotation axis by the resultant magnetic pressure due to excessive winding. Strong collimation of the jet is

  8. A New Outer Galaxy Molecular Cloud Catalog: Applications to Galactic Structure

    NASA Astrophysics Data System (ADS)

    Kerton, C. R.; Brunt, C. M.; Pomerleau, C.

    2001-12-01

    We have generated a new molecular cloud catalog from a reprocessed version of the Five College Radio Astronomy (FCRAO) Observatory Outer Galaxy Survey (OGS) of 12CO (J=1--0) emission. The catalog has been used to develop a technique that uses the observed angular size-linewidth relation (ASLWR) as a distance indicator to molecular cloud ensembles. The new technique is a promising means to map out the large-scale structure of our Galaxy using the new high spatial dynamic range CO surveys currently available. The catalog was created using a two-stage object-identification algorithm. We first identified contiguous emission structures of a specified minimum number of pixels above a specified temperature threshold. Each structure so defined was then examined and localized emission enhancements within each structure were identified as separate objects. The resulting cloud catalog, contains basic data on 14595 objects. From the OGS we identified twenty-three cloud ensembles. For each, bisector fits to angular size vs. linewidth plots were made. The fits vary in a systematic way that allows a calibration of the fit parameters with distance to be made. Our derived distances to the ensembles are consistent with the distance to the Perseus Arm, and the accurate radial velocity measurements available from the same data are in accord with the known non-circular motions at the location of the Perseus Arm. The ASLWR method was also successfully applied to data from the Boston University/FCRAO Galactic Ring Survey (GRS) of 13CO(J=1--0) emission. Based upon our experience with the GRS and OGS, the ASLWR technique should be usable in any data set with sufficient spatial dynamic range to allow it to be properly calibrated. C.P. participated in this study through the Women in Engineering and Science (WES) program of NRC Canada. The Dominion Radio Astrophysical Observatory is a National Facility operated by the National Research Council. The Canadian Galactic Plane Survey is a Canadian

  9. THE STRUCTURE OF A LOW-METALLICITY GIANT MOLECULAR CLOUD COMPLEX

    SciTech Connect

    Leroy, Adam K.; Bolatto, Alberto; Bot, Caroline; Engelbracht, Charles W.; Gordon, Karl; Israel, Frank P.; Rubio, Monica; Sandstrom, Karin; Stanimirovic, Snezana

    2009-09-01

    To understand the impact of low metallicities on giant molecular cloud (GMC) structure, we compare far-infrared dust emission, CO emission, and dynamics in the star-forming complex N83 in the Wing of the Small Magellanic Cloud (SMC). Dust emission (measured by Spitzer as part of the Spitzer Survey of the SMC and Surveying the Agents of a Galaxy's Evolution in the SMC surveys) probes the total gas column independent of molecular line emission and traces shielding from photodissociating radiation. We calibrate a method to estimate the dust column using only the high-resolution Spitzer data and verify that dust traces the interstellar medium in the H I-dominated region around N83. This allows us to resolve the relative structures of H{sub 2}, dust, and CO within a GMC complex, one of the first times such a measurement has been made in a low-metallicity galaxy. Our results support the hypothesis that CO is photodissociated while H{sub 2} self-shields in the outer parts of low-metallicity GMCs, so that dust/self-shielding is the primary factor determining the distribution of CO emission. Four pieces of evidence support this view. First, the CO-to-H{sub 2} conversion factor averaged over the whole cloud is very high 4-11 x 10{sup 21} cm{sup -2} (K km s{sup -1}){sup -1}, or 20-55 times the Galactic value. Second, the CO-to-H{sub 2} conversion factor varies across the complex, with its lowest (most nearly Galactic) values near the CO peaks. Third, bright CO emission is largely confined to regions of relatively high line-of-sight extinction, A{sub V} {approx}> 2 mag, in agreement with photodissociation region models and Galactic observations. Fourth, a simple model in which CO emerges from a smaller sphere nested inside a larger cloud can roughly relate the H{sub 2} masses measured from CO kinematics and dust.

  10. H2, H3+ and the age of molecular clouds and prestellar cores.

    PubMed

    Pagani, L; Lesaffre, P; Roueff, E; Jorfi, M; Honvault, P; González-Lezana, T; Faure, A

    2012-11-13

    Measuring the age of molecular clouds and prestellar cores is a difficult task that has not yet been successfully accomplished although the information is of paramount importance to help in understanding and discriminating between different formation scenarios. Most chemical clocks suffer from unknown initial conditions and are therefore difficult to use. We propose a new approach based on a subset of deuterium chemistry that takes place in the gas phase and for which initial conditions are relatively well known. It relies primarily on the conversion of H(3)(+) into H(2)D(+) to initiate deuterium enrichment of the molecular gas. This conversion is controlled by the ortho/para ratio of H(2) that is thought to be produced with the statistical ratio of 3 and subsequently slowly decays to an almost pure para-H(2) phase. This slow decay takes approximately 1 Myr and allows us to set an upper limit on the age of molecular clouds. The deuterium enrichment of the core takes longer to reach equilibrium and allows us to estimate the time necessary to form a dense prestellar core, i.e. the last step before the collapse of the core into a protostar. We find that the observed abundance and distribution of DCO(+) and N(2)D(+) argue against quasi-static core formation and favour dynamical formation on time scales of less than 1 Myr. Another consequence is that ortho-H(2) remains comparable to para-H(2) in abundance outside the dense cores.

  11. Properties of the galactic molecular cloud ensemble from observations of /sup 13/CO

    SciTech Connect

    Liszt, H.S.; Delin, X.; Burton, W.B.

    1981-10-15

    We have observed galactic /sup 13/CO over the region b = 0/sup 0/, l = 28/sup 0/--40/sup 0/, at 3' spacings of the 36 foot (11 m) telescope antenna pattern. The major results of interpretation of these observations are as follows: (1) The size distribution of molecular clouds, inferred from correction measured sizes of features for the bias introduced by sampling only at b = 0/sup 0/, is characterized by the moments < or approx. =25 pc, /sup 1/2/< or approx. =27 pc, /sup 1/3/< or approx. =29 pc. (2) The smallest mean density of hydrogen molecules derived for the region Rroughly-equal5 kpc consistent with available constraints is roughly-equal2.5 cm/sup -3/. Higher values may easily be derived; lower ones are difficult to justify. (3) The radial abundance variations of the /sup 13/CO emissivity follows the general behavior established earlier from /sup 12/CO, but with prominent enhancements (in the longitude region observed) at Rroughly-equal9--10 kpc and Rroughly-equal7--8 kpc. (4) Comparison of the longitudinal variation of terminal velocities measured in /sup 13/CO and in H I indicates that the galactic kinematics of the dense centered molecular clouds are essentially identical to those found for H I. (5) Comparison of /sup 13/CO and H I integrated intensities indicates that one may find substantial regions over each of which the atomic and molecular intensities may be strongly positively or anticorrelated, or statistically independent. Reasons for this behavior are summarized here and considered in more detail by Liszt, Burton, and Bania.

  12. Molecular diversity and distribution pattern of ciliates in sediments from deep-sea hydrothermal vents in the Okinawa Trough and adjacent sea areas

    NASA Astrophysics Data System (ADS)

    Zhao, Feng; Xu, Kuidong

    2016-10-01

    In comparison with the macrobenthos and prokaryotes, patterns of diversity and distribution of microbial eukaryotes in deep-sea hydrothermal vents are poorly known. The widely used high-throughput sequencing of 18S rDNA has revealed a high diversity of microeukaryotes yielded from both living organisms and buried DNA in marine sediments. More recently, cDNA surveys have been utilized to uncover the diversity of active organisms. However, both methods have never been used to evaluate the diversity of ciliates in hydrothermal vents. By using high-throughput DNA and cDNA sequencing of 18S rDNA, we evaluated the molecular diversity of ciliates, a representative group of microbial eukaryotes, from the sediments of deep-sea hydrothermal vents in the Okinawa Trough and compared it with that of an adjacent deep-sea area about 15 km away and that of an offshore area of the Yellow Sea about 500 km away. The results of DNA sequencing showed that Spirotrichea and Oligohymenophorea were the most diverse and abundant groups in all the three habitats. The proportion of sequences of Oligohymenophorea was the highest in the hydrothermal vents whereas Spirotrichea was the most diverse group at all three habitats. Plagiopyleans were found only in the hydrothermal vents but with low diversity and abundance. By contrast, the cDNA sequencing showed that Plagiopylea was the most diverse and most abundant group in the hydrothermal vents, followed by Spirotrichea in terms of diversity and Oligohymenophorea in terms of relative abundance. A novel group of ciliates, distinctly separate from the 12 known classes, was detected in the hydrothermal vents, indicating undescribed, possibly highly divergent ciliates may inhabit this environment. Statistical analyses showed that: (i) the three habitats differed significantly from one another in terms of diversity of both the rare and the total ciliate taxa, and; (ii) the adjacent deep sea was more similar to the offshore area than to the

  13. The Relationship Between Molecular Gas, H I, and Star Formation in the Low-mass, Low-metallicity Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Jameson, Katherine E.; Bolatto, Alberto D.; Leroy, Adam K.; Meixner, Margaret; Roman-Duval, Julia; Gordon, Karl; Hughes, Annie; Israel, Frank P.; Rubio, Monica; Indebetouw, Remy; Madden, Suzanne C.; Bot, Caroline; Hony, Sacha; Cormier, Diane; Pellegrini, Eric W.; Galametz, Maud; Sonneborn, George

    2016-07-01

    The Magellanic Clouds provide the only laboratory to study the effects of metallicity and galaxy mass on molecular gas and star formation at high (˜20 pc) resolution. We use the dust emission from HERITAGE Herschel data to map the molecular gas in the Magellanic Clouds, avoiding the known biases of CO emission as a tracer of {{{H}}}2. Using our dust-based molecular gas estimates, we find molecular gas depletion times ({τ }{{dep}}{{mol}}) of ˜0.4 Gyr in the Large Magellanic Cloud and ˜0.6 in the Small Magellanic Cloud at 1 kpc scales. These depletion times fall within the range found for normal disk galaxies, but are shorter than the average value, which could be due to recent bursts in star formation. We find no evidence for a strong intrinsic dependence of the molecular gas depletion time on metallicity. We study the relationship between the gas and the star formation rate across a range of size scales from 20 pc to ≥1 kpc, including how the scatter in {τ }{{dep}}{{mol}} changes with the size scale, and discuss the physical mechanisms driving the relationships. We compare the metallicity-dependent star formation models of Ostriker et al. and Krumholz to our observations and find that they both predict the trend in the data, suggesting that the inclusion of a diffuse neutral medium is important at lower metallicity.

  14. Gas-phase chemistry in dense interstellar clouds including grain surface molecular depletion and desorption

    NASA Technical Reports Server (NTRS)

    Bergin, E. A.; Langer, W. D.; Goldsmith, P. F.

    1995-01-01

    We present time-dependent models of the chemical evolution of molecular clouds which include depletion of atoms and molecules onto grain surfaces and desorption, as well as gas-phase interactions. We have included three mechanisms to remove species from the grain mantles: thermal evaporation, cosmic-ray-induced heating, and photodesorption. A wide range of parameter space has been explored to examine the abundance of species present both on the grain mantles and in the gas phase as a function of both position in the cloud (visual extinction) and of evolutionary state (time). The dominant mechanism that removes molecules from the grain mantles is cosmic-ray desorption. At times greater than the depletion timescale, the abundances of some simple species agree with abundances observed in the cold dark cloud TMC-1. Even though cosmic-ray desorption preserves the gas-phase chemistry at late times, molecules do show significant depletions from the gas phase. Examination of the dependence of depletion as a function of density shows that when the density increases from 10(exp 3)/cc to 10(exp 5)/cc several species including HCO(+), HCN, and CN show gas-phase abundance reductions of over an order of magnitude. The CO: H2O ratio in the grain mantles for our standard model is on the order of 10:1, in reasonable agreement with observations of nonpolar CO ice features in rho Ophiuchus and Serpens. We have also examined the interdependence of CO depletion with the space density of molecular hydrogen and binding energy to the grain surface. We find that the observed depletion of CO in Taurus in inconsistent with CO bonding in an H2O rich mantle, in agreement with observations. We suggest that if interstellar grains consist of an outer layer of CO ice, then the binding energies for many species to the grain mantle may be lower than commonly used, and a significant portion of molecular material may be maintained in the gas phase.

  15. Structure analysis of simulated molecular clouds with the Δ-variance

    DOE PAGES

    Bertram, Erik; Klessen, Ralf S.; Glover, Simon C. O.

    2015-05-27

    Here, we employ the Δ-variance analysis and study the turbulent gas dynamics of simulated molecular clouds (MCs). Our models account for a simplified treatment of time-dependent chemistry and the non-isothermal nature of the gas. We investigate simulations using three different initial mean number densities of n0 = 30, 100 and 300 cm-3 that span the range of values typical for MCs in the solar neighbourhood. Furthermore, we model the CO line emission in a post-processing step using a radiative transfer code. We evaluate Δ-variance spectra for centroid velocity (CV) maps as well as for integrated intensity and column density mapsmore » for various chemical components: the total, H2 and 12CO number density and the integrated intensity of both the 12CO and 13CO (J = 1 → 0) lines. The spectral slopes of the Δ-variance computed on the CV maps for the total and H2 number density are significantly steeper compared to the different CO tracers. We find slopes for the linewidth–size relation ranging from 0.4 to 0.7 for the total and H2 density models, while the slopes for the various CO tracers range from 0.2 to 0.4 and underestimate the values for the total and H2 density by a factor of 1.5–3.0. We demonstrate that optical depth effects can significantly alter the Δ-variance spectra. Furthermore, we report a critical density threshold of 100 cm-3 at which the Δ-variance slopes of the various CO tracers change sign. We thus conclude that carbon monoxide traces the total cloud structure well only if the average cloud density lies above this limit.« less

  16. The dense gas mass fraction of molecular clouds in the Milky Way

    SciTech Connect

    Battisti, Andrew J.; Heyer, Mark H. E-mail: heyer@astro.umass.edu

    2014-01-10

    The mass fraction of dense gas within giant molecular clouds (GMCs) of the Milky Way is investigated using {sup 13}CO data from the Five College Radio Astronomy Observatory Galactic Plane Surveys and the Bolocam Galactic Plane Survey (BGPS) of 1.1 mm dust continuum emission. A sample of 860 compact dust sources are selected from the BGPS catalog and kinematically linked to 344 clouds of extended (>3') {sup 13}CO J = 1-0 emission. Gas masses are tabulated for the full dust source and subregions within the dust sources with mass surface densities greater than 200 M {sub ☉} pc{sup –2}, which are assumed to be regions of enhanced volume density. Masses of the parent GMCs are calculated assuming optically thin {sup 13}CO J = 1-0 emission and local thermodynamic equilibrium conditions. The mean fractional mass of dust sources to host GMC mass is 0.11{sub −0.06}{sup +0.12}. The high column density subregions comprise 0.07{sub −0.05}{sup +0.13} of the mass of the cloud. Owing to our assumptions, these values are upper limits to the true mass fractions. The fractional mass of dense gas is independent of GMC mass and gas surface density. The low dense gas mass fraction suggests that the formation of dense structures within GMCs is the primary bottleneck for star formation. The distribution of velocity differences between the dense gas and the low density material along the line of sight is also examined. We find a strong, centrally peaked distribution centered on zero velocity displacement. This distribution of velocity differences is modeled with radially converging flows toward the dense gas position that are randomly oriented with respect to the observed line of sight. These models constrain the infall velocities to be 2-4 km s{sup –1} for various flow configurations.

  17. Structure analysis of simulated molecular clouds with the Δ-variance

    SciTech Connect

    Bertram, Erik; Klessen, Ralf S.; Glover, Simon C. O.

    2015-05-27

    Here, we employ the Δ-variance analysis and study the turbulent gas dynamics of simulated molecular clouds (MCs). Our models account for a simplified treatment of time-dependent chemistry and the non-isothermal nature of the gas. We investigate simulations using three different initial mean number densities of n0 = 30, 100 and 300 cm-3 that span the range of values typical for MCs in the solar neighbourhood. Furthermore, we model the CO line emission in a post-processing step using a radiative transfer code. We evaluate Δ-variance spectra for centroid velocity (CV) maps as well as for integrated intensity and column density maps for various chemical components: the total, H2 and 12CO number density and the integrated intensity of both the 12CO and 13CO (J = 1 → 0) lines. The spectral slopes of the Δ-variance computed on the CV maps for the total and H2 number density are significantly steeper compared to the different CO tracers. We find slopes for the linewidth–size relation ranging from 0.4 to 0.7 for the total and H2 density models, while the slopes for the various CO tracers range from 0.2 to 0.4 and underestimate the values for the total and H2 density by a factor of 1.5–3.0. We demonstrate that optical depth effects can significantly alter the Δ-variance spectra. Furthermore, we report a critical density threshold of 100 cm-3 at which the Δ-variance slopes of the various CO tracers change sign. We thus conclude that carbon monoxide traces the total cloud structure well only if the average cloud density lies above this limit.

  18. Resolving Giant Molecular Clouds in NGC 300: A First Look with the Submillimeter Array

    NASA Astrophysics Data System (ADS)

    Faesi, Christopher M.; Lada, Charles J.; Forbrich, Jan

    2016-04-01

    We present the first high angular resolution study of giant molecular clouds (GMCs) in the nearby spiral galaxy NGC 300, based on observations from the Submillimeter Array (SMA). We target eleven 500 pc sized regions of active star formation within the galaxy in the 12CO(J = 2-1) line at 40 pc spatial and 1 km s-1 spectral resolution and identify 45 individual GMCs. We characterize the physical properties of these GMCs, and find that they are similar to GMCs in the disks of the Milky Way and other nearby spiral galaxies. For example, the GMC mass spectrum in our sample has a slope of 1.80 ± 0.07. Twelve clouds are spatially resolved by our observations, of which ten have virial mass estimates that agree to within a factor of two with mass estimates derived directly from 12CO integrated intensity, suggesting that the majority of these GMCs are bound. The resolved clouds show consistency with Larson’s fundamental relations between size, linewidth, and mass observed in the Milky Way. We find that the linewidth scales with the size as ΔV ∝ R0.52±0.20, and the median surface density in the subsample is 54 M⊙ pc-2. We detect 13CO in four GMCs and find a mean 12CO/13CO flux ratio of 6.2. Our interferometric observations recover between 30% and 100% of the integrated intensity from the APEX single dish 12CO observations of Faesi et al., suggesting the presence of low-mass GMCs and/or diffuse gas below our sensitivity limit. The fraction of APEX emission recovered increases with the SMA total intensity, as well as with the star formation rate.

  19. A search for pre-main sequence stars in the high-latitude molecular clouds. II - A survey of the Einstein database

    NASA Technical Reports Server (NTRS)

    Caillault, Jean-Pierre; Magnani, Loris

    1990-01-01

    The preliminary results are reported of a survey of every EINSTEIN image which overlaps any high-latitude molecular cloud in a search for X-ray emitting pre-main sequence stars. This survey, together with complementary KPNO and IRAS data, will allow the determination of how prevalent low mass star formation is in these clouds in general and, particularly, in the translucent molecular clouds.

  20. DISSOCIATIVE RECOMBINATION OF PROTONATED FORMIC ACID: IMPLICATIONS FOR MOLECULAR CLOUD AND COMETARY CHEMISTRY

    SciTech Connect

    Vigren, E.; Hamberg, M.; Zhaunerchyk, V.; Larsson, M.; Thomas, R. D.; Af Ugglas, M.; Kashperka, I.; Geppert, W. D.; Kaminska, M.; Semaniak, J.; Millar, T. J.; Walsh, C.; Roberts, H.

    2010-02-01

    At the heavy ion storage ring CRYRING in Stockholm, Sweden, we have investigated the dissociative recombination of DCOOD{sup +}{sub 2} at low relative kinetic energies, from approx1 meV to 1 eV. The thermal rate coefficient has been found to follow the expression k(T) = 8.43 x 10{sup -7} (T/300){sup -0.78} cm{sup 3} s{sup -1} for electron temperatures, T, ranging from approx10 to approx1000 K. The branching fractions of the reaction have been studied at approx2 meV relative kinetic energy. It has been found that approx87% of the reactions involve breaking a bond between heavy atoms. In only 13% of the reactions do the heavy atoms remain in the same product fragment. This puts limits on the gas-phase production of formic acid, observed in both molecular clouds and cometary comae. Using the experimental results in chemical models of the dark cloud, TMC-1, and using the latest release of the UMIST Database for Astrochemistry improves the agreement with observations for the abundance of formic acid. Our results also strengthen the assumption that formic acid is a component of cometary ices.

  1. H I ZEEMAN EXPERIMENTS OF SHOCKED ATOMIC GAS IN TWO SUPERNOVA REMNANTS INTERACTING WITH MOLECULAR CLOUDS

    SciTech Connect

    Koo, Bon-Chul; Heiles, Carl; Stanimirovic, Snezana; Troland, Tom

    2010-07-15

    We have carried out observations of Zeeman splitting of the H I 21 cm emission line from shocked atomic gas in the supernova remnants (SNRs) IC 443 and W51C using the Arecibo telescope. The observed shocked atomic gas is expanding at {approx}100 km s{sup -1} and this is the first Zeeman experiment of such fast-moving, shocked atomic gas. The emission lines, however, are very broad and the systematic error due to baseline curvature hampers an accurate measurement of field strengths. We derive an upper limit of 100-150 {mu}G on the strength of the line-of-sight field component. These two SNRs are interacting with molecular clouds, but the derived upper limits are considerably smaller than the field strengths expected from a strongly shocked dense cloud. We discuss the implications and conclude that either the magnetic field within the telescope beam is mostly randomly oriented or the high-velocity H I emission is from a shocked interclump medium of relatively low density.

  2. Examining molecular clouds in the Galactic Centre region using X-ray reflection spectra simulations.

    NASA Astrophysics Data System (ADS)

    Walls, M.; Chernyakova, M.; Terrier, R.; Goldwurm, A.

    2016-09-01

    In the centre of our galaxy lies a super-massive black hole, identified with the radio source Sagittarius A⋆. This black hole has an estimated mass of around 4 million solar masses. Although Sagittarius A⋆ is quite dim in terms of total radiated energy, having a luminosity that is a factor of 1010 lower than its Eddington luminosity, there is now compelling evidence that this source was far brighter in the past. Evidence derived from the detection of reflected X-ray emission from the giant molecular clouds in the galactic centre region. However, the interpretation of the reflected emission spectra cannot be done correctly without detailed modelling of the reflection process. Attempts to do so can lead to an incorrect interpretation of the data. In this paper we present the results of a Monte Carlo simulation code we developed in order to fully model the complex processes involved in the emerging reflection spectra. The simulated spectra can be compared to real data in order to derive model parameters and constrain the past activity of the black hole. In particular we apply our code to observations of Sgr B2, in order to constrain the position and density of the cloud and the incident luminosity of the central source. The results of the code have been adapted to be used in Xspec by a large community of astronomers.

  3. Atmospheric organic matter in clouds: exact masses and molecular formula identification using ultrahigh-resolution FT-ICR mass spectrometry

    NASA Astrophysics Data System (ADS)

    Zhao, Y.; Hallar, A. G.; Mazzoleni, L. R.

    2013-12-01

    Clouds alter the composition of atmospheric aerosol by acting as a medium for interactions between gas- and particulate-phase substances. To determine the cloud water atmospheric organic matter (AOM) composition and study the cloud processing of aerosols, two samples of supercooled clouds were collected at the Storm Peak Laboratory near Steamboat Springs, Colorado (3220 m a.s.l.). Approximately 3000 molecular formulas were assigned to ultrahigh-resolution mass spectra of the samples after using a reversed-phase extraction procedure to isolate the AOM components from the cloud water. Nitrogen-containing compounds (CHNO compounds), sulfur-containing compounds (CHOS and CHNOS compounds) and other oxygen-containing compounds (CHO compounds) with molecular weights up to 700 Da were observed. Average oxygen-to-carbon ratios of ∼0.6 indicate a slightly more oxidized composition than most water-soluble organic carbon identified in aerosol studies, which may result from aqueous oxidation in the clouds. The AOM composition indicates significant influences from biogenic secondary organic aerosol (SOA) and residential wood combustion. We observed 60% of the cloud water CHO molecular formulas to be identical to SOA samples of α-pinene, β-pinene, d-limonene, and β-caryophyllene ozonolysis. CHNO compounds had the highest number frequency and relative abundances and are associated with residential wood combustion and NOx oxidation. Multiple nitrogen atoms in the assigned molecular formulas for the nighttime cloud sample composite were observed, indicating the significance of nitrate radical reactions on the AOM composition. Several CHOS and CHNOS compounds with reduced sulfur (in addition to the commonly observed oxidized sulfur-containing compounds) were also observed; however further investigation is needed to determine the origin of the reduced sulfur-containing compounds. Overall, the molecular composition determined using ultrahigh-resolution Fourier-transform ion

  4. From the H II Region to the Molecular Cloud: Determining Physical Conditions in Star Forming Regions

    NASA Astrophysics Data System (ADS)

    Abel, N. P.

    2004-12-01

    Infrared missions such as Spitzer offer new insights into the chemical evolution and star formation history of the universe. Although objects such as starburst galaxies, which are among the most luminous objects in the universe, are the primary focus, OMC-1, a lower luminosity region with superb spatial resolution, serves as a benchmark to test the physics of newly formed O stars interacting with the surrounding molecular environment. The classical approach in determining conditions in the ionized, photodissociated, and molecular regions is to treat each problem separately. In actuality, however, this is a single continuous phenomenon, linked through the transport of gas and radiation. Here we self-consistently calculate the physical conditions and emission from the hot HII region to the cold, molecular gas as a continuous hydrostatic layer. The ion states of the first 30 elements, along with the abundances of 70 molecules, are determined with the temperature and electron density. The grain physics is treated self-consistently, with grain charge transfer, single photon heating, and PAH effects all included. Additionally, level populations of all the rotational/vibrational levels of the ground electronic state of molecular hydrogen are determined (see the dissertation talk of Gargi Shaw). As a benchmark, we consider the physical conditions through OMC-1 1' west of the Trapezium, where emission-line observations of the HII region and the PDR/molecular cloud all exist. Accurately interpreting this spectrum will give us confidence that we can apply our calculations to more luminous and distant starburst galaxies. We predict the sometimes significant contribution of the HII region to important PDR emission-line diagnostics. This has consequences for the interpretation of IR observations, the deduced values of n(H) and G0 in PDRs, and hence the overall conditions in star forming regions. All calculations were developed with the spectral synthesis code Cloudy, which is

  5. Chemistry in Infrared Dark Cloud Clumps: A Molecular Line Survey at 3 mm

    NASA Astrophysics Data System (ADS)

    Sanhueza, Patricio; Jackson, James M.; Foster, Jonathan B.; Garay, Guido; Silva, Andrea; Finn, Susanna C.

    2012-09-01

    We have observed 37 Infrared Dark Clouds (IRDCs), containing a total of 159 clumps, in high-density molecular tracers at 3 mm using the 22 m ATNF Mopra Telescope located in Australia. After determining kinematic distances, we eliminated clumps that are not located in IRDCs and clumps with a separation between them of less than one Mopra beam. Our final sample consists of 92 IRDC clumps. The most commonly detected molecular lines are (detection rates higher than 8%) N2H+, HNC, HN13C, HCO+, H13CO+, HCN, C2H, HC3N, HNCO, and SiO. We investigate the behavior of the different molecular tracers and look for chemical variations as a function of an evolutionary sequence based on Spitzer IRAC and MIPS emission. We find that the molecular tracers behave differently through the evolutionary sequence and some of them can be used to yield useful relative age information. The presence of HNC and N2H+ lines does not depend on the star formation activity. On the other hand, HC3N, HNCO, and SiO are predominantly detected in later stages of evolution. Optical depth calculations show that in IRDC clumps the N2H+ line is optically thin, the C2H line is moderately optically thick, and HNC and HCO+ are optically thick. The HCN hyperfine transitions are blended, and, in addition, show self-absorbed line profiles and extended wing emission. These factors combined prevent the use of HCN hyperfine transitions for the calculation of physical parameters. Total column densities of the different molecules, except C2H, increase with the evolutionary stage of the clumps. Molecular abundances increase with the evolutionary stage for N2H+ and HCO+. The N2H+/HCO+ and N2H+/HNC abundance ratios act as chemical clocks, increasing with the evolution of the clumps.

  6. Two-level hierarchical fragmentation in the northern filament of the Orion Molecular Cloud 1

    NASA Astrophysics Data System (ADS)

    Teixeira, P. S.; Takahashi, S.; Zapata, L. A.; Ho, P. T. P.

    2016-03-01

    Context. The filamentary structure of molecular clouds may set important constraints on the mass distribution of stars forming within them. It is therefore important to understand which physical mechanism dominates filamentary cloud fragmentation and core formation. Aims: Orion A is the nearest giant molecular cloud, and its so-called ∫-shaped filament is a very active star-forming region that is a good target for such a study. We have recently reported on the collapse and fragmentation properties of the northernmost part of this structure, located ~2.4 pc north of Orion KL - Orion Molecular Cloud (OMC) 3. As part of our project to study the ∫-shaped filament, we analyze the fragmentation properties of the northern OMC 1 filament (located ≲0.3 pc north of Orion KL). This filament is a dense structure previously identified by JCMT/SCUBA submillimeter continuum and VLA NH3 observations and was shown to have fragmented into clumps. Our aim is to search for cores and young protostars embedded within OMC 1n and to study how the filament is fragmenting to form them. Methods: We observed OMC 1North (hereafter OMC 1n) with the Submillimeter Array (SMA) at 1.3 mm and report on our analysis of the continuum data. Results: We discovered 24 new compact sources, ranging in mass from 0.1 to 2.3, in size from 400 to 1300 au, and in density from 2.6 × 107 to 2.8 × 106 cm-3. The masses of these sources are similar to those of the SMA protostars in OMC 3, but their typical sizes and densities are lower by a factor of ten. Only 8% of the new sources have infrared counterparts, but there are five associated CO molecular outflows. These sources are thus likely in the Class 0 evolutionary phase but it cannot be excluded that some of the sources might still be pre-stellar cores. The spatial analysis of the protostars shows that they are divided into small groups that coincide with previously identified JCMT/SCUBA 850 μm and VLA NH3 clumps, which are separated by a quasi

  7. NEW X-RAY-SELECTED PRE-MAIN-SEQUENCE MEMBERS OF THE SERPENS MOLECULAR CLOUD

    SciTech Connect

    Oliveira, Isa; Van der Laan, Margriet; Brown, Joanna M.

    2013-11-01

    The study of young stars no longer surrounded by disks can greatly add to our understanding of how protoplanetary disks evolve and planets form. We have used VLT/FLAMES optical spectroscopy to confirm the youth and membership of 19 new young diskless stars in the Serpens Molecular Cloud, identified at X-ray wavelengths. Spectral types, effective temperatures, and stellar luminosities were determined using optical spectra and optical/near-infrared photometry. Stellar masses and ages were derived based on pre-main-sequence evolutionary tracks. The results yield remarkable similarities for age and mass distribution between the diskless and disk-bearing stellar populations in Serpens. We discuss the important implications these similarities may have on the standard picture of disk evolution.

  8. Far Infrared Line Profiles from Photodissociation Regions and Warm Molecular Clouds

    NASA Technical Reports Server (NTRS)

    Boreiko, R. T.; Betz, A. L.

    1998-01-01

    This report summarizes the work done under NASA Grant NAG2-1056 awarded to the University of Colorado. The aim of the project was to analyze data obtained over the past several years with the University of Colorado far-infrared heterodyne spectrometer aboard the Kuiper Airborne Observatory. Of particular interest were observations of CO and ionized carbon (C II) in photodissociation regions (PDRS) at the interface between UV-ionized H II regions and the neutral molecular clouds supporting star formation. These data, obtained with a heterodyne spectrometer having a resolution of 3.2 MHz, which is equivalent to a velocity resolution of 0.2 km s(exp -1) at 60 microns and 1.0 km s(exp -1) at 300 microns, were analyzed to obtain physical parameters such as density and temperature in the observed PDR.

  9. Unfolding the laws of star formation: the density distribution of molecular clouds.

    PubMed

    Kainulainen, Jouni; Federrath, Christoph; Henning, Thomas

    2014-04-11

    The formation of stars shapes the structure and evolution of entire galaxies. The rate and efficiency of this process are affected substantially by the density structure of the individual molecular clouds in which stars form. The most fundamental measure of this structure is the probability density function of volume densities (ρ-PDF), which determines the star formation rates predicted with analytical models. This function has remained unconstrained by observations. We have developed an approach to quantify ρ-PDFs and establish their relation to star formation. The ρ-PDFs instigate a density threshold of star formation and allow us to quantify the star formation efficiency above it. The ρ-PDFs provide new constraints for star formation theories and correctly predict several key properties of the star-forming interstellar medium.

  10. Methanol Maser Emission in W75N and Orion Molecular Cloud 2 (OMC 2)

    NASA Astrophysics Data System (ADS)

    Goetz, J. A.; Brubaker, D. W.; Clerc, C. A.

    2001-12-01

    We present data of Class I methanol maser emission at 44 GHz centered on two star forming regions, W75N and Orion Molecular Cloud 2 (OMC 2). The Northeast Radio Observatory Corporation (NEROC) Haystack 37-m radio telescope was used to search for emission in the 70 to 61 A+ transition of CH3OH as part of a larger project lead by Dr. Preethi Pratap (MIT Haystack Observatory). This project focuses on detecting maser activity in positions that are offset from known young stellar objects. In addition to detecting the known methanol maser source in each region, a previously undetected maser source was observed to the southwest of W75N IRAS 1.

  11. A SEARCH FOR CO-EVOLVING ION AND NEUTRAL GAS SPECIES IN PRESTELLAR MOLECULAR CLOUD CORES

    SciTech Connect

    Tassis, Konstantinos; Hezareh, Talayeh; Willacy, Karen

    2012-11-20

    A comparison between the widths of ion and neutral molecule spectral lines has been recently used to estimate the strength of the magnetic field in turbulent star-forming regions. However, the ion (HCO{sup +}) and neutral (HCN) species used in such studies may not be necessarily co-evolving at every scale and density, and thus, may not trace the same regions. Here, we use coupled chemical/dynamical models of evolving prestellar molecular cloud cores including non-equilibrium chemistry, with and without magnetic fields, to study the spatial distribution of HCO{sup +} and HCN, which have been used in observations of spectral line width differences to date. In addition, we seek new ion-neutral pairs that are good candidates for such observations, because they have similar evolution and are approximately co-spatial in our models. We identify three such good candidate pairs: HCO{sup +}/NO, HCO{sup +}/CO, and NO{sup +}/NO.

  12. Environmental Catastrophes in the Earth's History Due to Solar Systems Encounters with Giant Molecular Clouds

    NASA Technical Reports Server (NTRS)

    Pavlov, Alexander A.

    2011-01-01

    In its motion through the Milky Way galaxy, the solar system encounters an average density (>=330 H atoms/cubic cm) giant molecular cloud (GMC) approximately every 108 years, a dense (approx 2 x 103 H atoms/cubic cm) GMC every approx 109 years and will inevitably encounter them in the future. However, there have been no studies linking such events with severe (snowball) glaciations in Earth history. Here we show that dramatic climate change can be caused by interstellar dust accumulating in Earth's atmosphere during the solar system's immersion into a dense (approx ,2 x 103 H atoms/cubic cm) GMC. The stratospheric dust layer from such interstellar particles could provide enough radiative forcing to trigger the runaway ice-albedo feedback that results in global snowball glaciations. We also demonstrate that more frequent collisions with less dense GMCs could cause moderate ice ages.

  13. Metastability of isoformyl ions in collisions with helium and hydrogen. [in interstellar molecular clouds

    NASA Technical Reports Server (NTRS)

    Green, S.

    1984-01-01

    The stability of HOC(+) ions under conditions in interstellar molecular clouds is considered. In particular, the possibility that collisions with helium or hydrogen will induce isomerization to the stable HCO(+) form is examined theoretically. Portions of the electronic potential energy surfaces for interaction with He and H atoms are obtained from standard quantum mechanical calculations. Collisions with He atoms are found to be totally ineffective for inducing isomerization. Collisions with H atoms are found to be ineffective at low interstellar temperatures owing to a small (about 500 K) barrier in the entrance channel; at higher temperatures where this barrier can be overcome, however, collisions with hydrogen atoms do result in conversion to the stable HCO(+) form. Although detailed calculations are not presented, it is argued that low-energy collisions with H2 molecules are also ineffective in destroying the metastable ion.

  14. High-resolution surveys of the Sagittarius a molecular cloud complex in ammonia, carbon monoxide, and isocyanic acid

    SciTech Connect

    Armstrong, J.T.; Barrett, A.H.

    1985-03-01

    We have observed the Sagittarius A molecular cloud complex in 10 molecular transitions. We find that excitation temperatures of CO and HNCO are in the range 10--30 K, with the CO temperatures slightly higher, while the rotation temperature T/sub rot/(NH/sub 3/ (2--1)) is approx.35 K. In contrast, T/sub rot/(NH/sub 3/ (6--3)) is approx.80 K. All these temperatures are relatively uniform across the complex. The masses of individual clouds are estimated by two methods; the resulting estimates are in good agreement in most cases. The three largest clouds have masses of densities approx.3--5 x 10/sup 5/ M/sub sun/, while four smaller features have masses of approx.10/sup 5/ M/sub sun/. The resulting estimated mean number densities are approx.10/sup 4/--10/sup 5/ cm/sup -3/.

  15. The carbon inventory in a quiescent, filamentary molecular cloud in G328

    SciTech Connect

    Burton, Michael G.; Ashley, Michael C. B.; Braiding, Catherine; Storey, John W. V.; Kulesa, Craig; Hollenbach, David J.; Wolfire, Mark; Glück, Christian; Rowell, Gavin

    2014-02-20

    We present spectral line images of [C I] 809 GHz, CO J = 1-0 115 GHz and H I 1.4 GHz line emission, and calculate the corresponding C, CO and H column densities, for a sinuous, quiescent giant molecular cloud about 5 kpc distant along the l = 328° sightline (hereafter G328) in our Galaxy. The [C I] data comes from the High Elevation Antarctic Terahertz telescope, a new facility on the summit of the Antarctic plateau where the precipitable water vapor falls to the lowest values found on the surface of the Earth. The CO and H I data sets come from the Mopra and Parkes/ATCA telescopes, respectively. We identify a filamentary molecular cloud, ∼75 × 5 pc long with mass ∼4 × 10{sup 4} M {sub ☉} and a narrow velocity emission range of just 4 km s{sup –1}. The morphology and kinematics of this filament are similar in CO, [C I], and H I, though in the latter appears as self-absorption. We calculate line fluxes and column densities for the three emitting species, which are broadly consistent with a photodissociation region model for a GMC exposed to the average interstellar radiation field. The [C/CO] abundance ratio averaged through the filament is found to be approximately unity. The G328 filament is constrained to be cold (T {sub Dust} < 20 K) by the lack of far-IR emission, to show no clear signs of star formation, and to only be mildly turbulent from the narrow line width. We suggest that it may represent a GMC shortly after formation, or perhaps still in the process of formation.

  16. The XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST)

    NASA Astrophysics Data System (ADS)

    Feigelson, Eric; Guedel, M.

    2007-12-01

    The XMM-Newton Extended Survey of the Taurus Molecular Cloud is an exceptionally large and growing X-ray survey of the Taurus Molecular Cloud (TMC). Now comprising 31 1/2-degree diameter fields, observed with the three XMM-Newton EPIC cameras. High-resolution spectroscopy has been obtained for about ten T Tauri stars (TTS) with the RGS instruments, and the Optical Monitor secured an optical/UV survey. XEST detects essentially the entire surveyed TTS population of the TMC in X-rays including about half of the observed (8/16) brown dwarfs and Class I protostars (8/20). Several new candidate members are identified. The X-ray luminosity (LX) of TTS shows related correlations with both stellar bolometric luminosity and mass. Classical TTS show suppressed X-ray output in the CCD band by a factor of about 2. These statistical results confirm results from other star formation regions. Different from previous reports on TMC, XEST identifies no activity-rotation relation. Brown dwarfs are found to follow trends set by TTS, both for accreting and non-accreting objects. But a decrease of the fractional luminosity, LX/Lbol, is seen with decreasing mass indicating weakened heating efficiency in the substellar domain. XEST reports five members of the class of "Two-Absorber X-Ray" (TAX) sources which reveal a double-peaked spectrum originating from two unrelated sources with different absorption column densities. The softer emission is thought to be related to jets, as explicitly seen in DG Tau. RGS spectroscopy shows a systematic "X-ray soft excess" in classical TTS, suggesting excessive cool (1-2 MK) plasma due to accretion, although the excess seems to correlate with magnetic activity as well. XEST has been supported by the Space Science Institute (Bern/Switz.).

  17. THE LIFE AND DEATH OF DENSE MOLECULAR CLUMPS IN THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Seale, Jonathan P.; Looney, Leslie W.; Wong, Tony; Ott, Juergen; Klein, Uli; Pineda, Jorge L.

    2012-05-20

    We report the results of a high spatial (parsec) resolution HCO{sup +} (J = 1 {yields} 0) and HCN (J = 1 {yields} 0) emission survey toward the giant molecular clouds of the star formation regions N 105, N 113, N 159, and N 44 in the Large Magellanic Cloud (LMC). The HCO{sup +} and HCN observations at 89.2 and 88.6 GHz, respectively, were conducted in the compact configuration of the Australia Telescope Compact Array. The emission is imaged into individual clumps with masses between 10{sup 2} and 10{sup 4} M{sub Sun} and radii of <1 pc to {approx}2 pc. Many of the clumps are coincident with indicators of current massive star formation, indicating that many of the clumps are associated with deeply embedded forming stars and star clusters. We find that massive young stellar object (YSO) bearing clumps tend to be larger ({approx}>1 pc), more massive (M {approx}> 10{sup 3} M{sub Sun }), and have higher surface densities ({approx}1 g cm{sup -2}), while clumps without signs of star formation are smaller ({approx}<1 pc), less massive (M {approx}< 10{sup 3} M{sub Sun }), and have lower surface densities ({approx}0.1 g cm{sup -2}). The dearth of massive (M > 10{sup 3} M{sub Sun }) clumps not bearing massive YSOs suggests that the onset of star formation occurs rapidly once the clump has attained physical properties favorable to massive star formation. Using a large sample of LMC massive YSO mid-IR spectra, we estimate that {approx}2/3 of the massive YSOs for which there are Spitzer mid-IR spectra are no longer located in molecular clumps; we estimate that these young stars/clusters have destroyed their natal clumps on a timescale of at least {approx}3 Multiplication-Sign 10{sup 5} yr.

  18. Planck intermediate results. XXXV. Probing the role of the magnetic field in the formation of structure in molecular clouds

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Alves, M. I. R.; Arnaud, M.; Arzoumanian, D.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Banday, A. J.; Barreiro, R. B.; Bartolo, N.; Battaner, E.; Benabed, K.; Benoît, A.; Benoit-Lévy, A.; Bernard, J.-P.; Bersanelli, M.; Bielewicz, P.; Bock, J. J.; Bonavera, L.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bracco, A.; Burigana, C.; Calabrese, E.; Cardoso, J.-F.; Catalano, A.; Chiang, H. C.; Christensen, P. R.; Colombo, L. P. L.; Combet, C.; Couchot, F.; Crill, B. P.; Curto, A.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Dickinson, C.; Diego, J. M.; Dole, H.; Donzelli, S.; Doré, O.; Douspis, M.; Ducout, A.; Dupac, X.; Efstathiou, G.; Elsner, F.; Enßlin, T. A.; Eriksen, H. K.; Falceta-Gonçalves, D.; Falgarone, E.; Ferrière, K.; Finelli, F.; Forni, O.; Frailis, M.; Fraisse, A. A.; Franceschi, E.; Frejsel, A.; Galeotta, S.; Galli, S.; Ganga, K.; Ghosh, T.; Giard, M.; Gjerløw, E.; González-Nuevo, J.; Górski, K. M.; Gregorio, A.; Gruppuso, A.; Gudmundsson, J. E.; Guillet, V.; Harrison, D. L.; Helou, G.; Hennebelle, P.; Henrot-Versillé, S.; Hernández-Monteagudo, C.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Holmes, W. A.; Hornstrup, A.; Huffenberger, K. M.; Hurier, G.; Jaffe, A. H.; Jaffe, T. R.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Knoche, J.; Kunz, M.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Lattanzi, M.; Lawrence, C. R.; Leonardi, R.; Levrier, F.; Liguori, M.; Lilje, P. B.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; Maino, D.; Mandolesi, N.; Mangilli, A.; Maris, M.; Martin, P. G.; Martínez-González, E.; Masi, S.; Matarrese, S.; Melchiorri, A.; Mendes, L.; Mennella, A.; Migliaccio, M.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, J. A.; Naselsky, P.; Nati, F.; Netterfield, C. B.; Noviello, F.; Novikov, D.; Novikov, I.; Oppermann, N.; Oxborrow, C. A.; Pagano, L.; Pajot, F.; Paladini, R.; Paoletti, D.; Pasian, F.; Perotto, L.; Pettorino, V.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Pratt, G. W.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reinecke, M.; Remazeilles, M.; Renault, C.; Renzi, A.; Ristorcelli, I.; Rocha, G.; Rossetti, M.; Roudier, G.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savelainen, M.; Savini, G.; Scott, D.; Soler, J. D.; Stolyarov, V.; Sudiwala, R.; Sutton, D.; Suur-Uski, A.-S.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Vielva, P.; Villa, F.; Wade, L. A.; Wandelt, B. D.; Wehus, I. K.; Ysard, N.; Yvon, D.; Zonca, A.

    2016-02-01

    Within ten nearby (d < 450 pc) Gould belt molecular clouds we evaluate statistically the relative orientation between the magnetic field projected on the plane of sky, inferred from the polarized thermal emission of Galactic dust observed by Planck at 353 GHz, and the gas column density structures, quantified by the gradient of the column density, NH. The selected regions, covering several degrees in size, are analysed at an effective angular resolution of 10' FWHM, thus sampling physical scales from 0.4 to 40 pc in the nearest cloud. The column densities in the selected regions range from NH≈ 1021 to1023 cm-2, and hence they correspond to the bulk of the molecular clouds. The relative orientation is evaluated pixel by pixel and analysed in bins of column density using the novel statistical tool called "histogram of relative orientations". Throughout this study, we assume that the polarized emission observed by Planck at 353 GHz is representative of the projected morphology of the magnetic field in each region, i.e., we assume a constant dust grain alignment efficiency, independent of the local environment. Within most clouds we find that the relative orientation changes progressively with increasing NH, from mostly parallel or having no preferred orientation to mostly perpendicular. In simulations of magnetohydrodynamic turbulence in molecular clouds this trend in relative orientation is a signature of Alfvénic or sub-Alfvénic turbulence, implying that the magnetic field is significant for the gas dynamics at the scales probed by Planck. We compare the deduced magnetic field strength with estimates we obtain from other methods and discuss the implications of the Planck observations for the general picture of molecular cloud formation and evolution.

  19. On the probability distribution function of the mass surface density of molecular clouds. II.

    NASA Astrophysics Data System (ADS)

    Fischera, Jörg

    2014-11-01

    The probability distribution function (PDF) of the mass surface density of molecular clouds provides essential information about the structure of molecular cloud gas and condensed structures out of which stars may form. In general, the PDF shows two basic components: a broad distribution around the maximum with resemblance to a log-normal function, and a tail at high mass surface densities attributed to turbulence and self-gravity. In a previous paper, the PDF of condensed structures has been analyzed and an analytical formula presented based on a truncated radial density profile, ρ(r) = ρc/ (1 + (r/r0)2)n/ 2 with central density ρc and inner radius r0, widely used in astrophysics as a generalization of physical density profiles. In this paper, the results are applied to analyze the PDF of self-gravitating, isothermal, pressurized, spherical (Bonnor-Ebert spheres) and cylindrical condensed structures with emphasis on the dependence of the PDF on the external pressure pext and on the overpressure q-1 = pc/pext, where pc is the central pressure. Apart from individual clouds, we also consider ensembles of spheres or cylinders, where effects caused by a variation of pressure ratio, a distribution of condensed cores within a turbulent gas, and (in case of cylinders) a distribution of inclination angles on the mean PDF are analyzed. The probability distribution of pressure ratios q-1 is assumed to be given by P(q-1) ∝ q-k1/ (1 + (q0/q)γ)(k1 + k2) /γ, where k1, γ, k2, and q0 are fixed parameters. The PDF of individual spheres with overpressures below ~100 is well represented by the PDF of a sphere with an analytical density profile with n = 3. At higher pressure ratios, the PDF at mass surface densities Σ ≪ Σ(0), where Σ(0) is the central mass surface density, asymptotically approaches the PDF of a sphere with n = 2. Consequently, the power-law asymptote at mass surface densities above the peak steepens from Psph(Σ) ∝ Σ-2 to Psph(Σ) ∝ Σ-3. The

  20. Recent Advances in the Collapse and Fragmentation of Turbulent Molecular Cloud Cores

    SciTech Connect

    Klein, R L; Fisher, R; Krumholz, M; McKee, C F

    2002-12-16

    The formation of Giant Molecular Clouds (GMCs) sets the stage for the formation of protostellar systems by the gravitational collapse of dense regions within the GMC that fragment into smaller core components that in turn condense into stars. Developing a comprehensive theory of star formation remains one of the most elusive, and most important, goals of theoretical astrophysics. Inherent in the difficulty in attaining this goal is that the gravitational collapse depends critically upon initial conditions within the cores which only recently have been known with sufficient accuracy to permit a realistic theoretical attack on the problem. Observations of stars in the vicinity of the Sun show that binary systems are prevalent and appear to be a general outcome of the collapse and fragmentation process. Despite years of progress, theoretical studies have still not determined why binary stars occur with such frequency, or indeed, even what processes determine the transition from single stars to binaries and thence to multiple stellar systems. One of the major goals of this research is to understand the nature of the formation of binary and multiple stellar systems with typical low mass stars 0.2 to 3 M{sub {circle_dot}} and the physical properties of these systems. Basic questions concerning this process remain unanswered. What determines the fraction of an unstable cloud that will fragment into protostellar objects? What determines the pattern of stellar clustering into binaries and multiple systems? Even after fragmentation occurs, we have little understanding of the subsequent collapse. Consequently, it is unclear how the mass distribution of fragments maps onto eventual stellar masses, something we must understand to explain the stellar initial mass function (IMF). We will first discuss the development of the numerical methodology that will contribute to answering these questions. This technology consists of a 3D parallel, adaptive mesh refinement (AMR) self

  1. Alcohol chemistry in the Galactic Center molecular clouds. A gigantic Hot Core

    NASA Astrophysics Data System (ADS)

    Requena Torres, M. A.; Martín-Pintado, J.; Rodríguez-Franco, A.; Martín, S.; Rodríguez-FerńNdez, N. J.

    We have carried out a systematic study of CH3OH, C2H5OH, (CH3)2O, HCOOCH3, HCOOH, CH3COOH, H2CO and CS in different Galactic Center (GC) molecular clouds. Figure 1 shows the relative abundances of those molecules with respect to CH3OH in the GC as function of the CH3OH abundance. The CH3OH abundance between sources in the GC varies in nearly two orders of magnitude. The abundance ratio of these molecules relative to CH3OH is basically independent of the CH3OH abundances and only varies in a factor of ~ 4 - 8. The abundance ratio of CS relative to CH3OH seem to vary by a factor of 60. Our data are compared with observations of the same molecules in short-lived objects like the hot cores. The abundance and the abundance ratios of the complex molecules relative to CH3OH in massive hot cores are similar to that found in the GC clouds. Alcohol related chemistry is believed to be driven by gas phase reactions after evaporation of alcohols from grain mantles. Gas phase chemistry based in the ejection of alcohols from grains (see Charnley et al. 1995; Horn et al. (2004)) can not explain the observed abundances of HCOOCH3 in the GC and the rather constant relative abundances of the other complex molecules. Our data suggest that basically all the molecules related to alcohol chemistry could be produced on grain mantles and/or depleted from gas phase after their formation. This interpretation requires frequent shocks in the GC region to keep the high abundances of these molecules in gas phase and a rather uniform average composition of the icy grain mantles. The molecular clouds associated with the Sickle and the Thermal Radio Arches (TRA), which seem to be affected by UV radiation, see Rodriguez-Fernandez et al. (2001), show lower abundances of C2H5OH relative to CH3OH which could be explained by shock ejection and photo dissociation conditions.

  2. The low-mass population of the ρ Ophiuchi molecular cloud

    NASA Astrophysics Data System (ADS)

    Alves de Oliveira, C.; Moraux, E.; Bouvier, J.; Bouy, H.; Marmo, C.; Albert, L.

    2010-06-01

    Context. Star formation theories are currently divergent regarding the fundamental physical processes that dominate the substellar regime. Observations of nearby young open clusters allow the brown dwarf (BD) population to be characterised down to the planetary mass regime, which ultimately must be accommodated by a successful theory. Aims: We hope to uncover the low-mass population of the ρ Ophiuchi molecular cloud and investigate the properties of the newly found brown dwarfs. Methods: We used near-IR deep images (reaching completeness limits of approximately 20.5 mag in J and 18.9 mag in H and Ks) taken with the Wide Field IR Camera (WIRCam) at the Canada France Hawaii Telescope (CFHT) to identify candidate members of ρ Oph in the substellar regime. A spectroscopic follow-up of a small sample of the candidates allows us to assess their spectral type and subsequently their temperature and membership. Results: We select 110 candidate members of the ρ Ophiuchi molecular cloud, from which 80 have not previously been associated with the cloud. We observed a small sample of these and spectroscopically confirm six new brown dwarfs with spectral types ranging from M6.5 to M8.25. Based on observations obtained with WIRCam, a joint project of CFHT, Taiwan, Korea, Canada, France, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institute National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii. Based on observations made at the ESO La Silla and Paranal Observatory under program 083.C-0092. Based in part on data collected at Subaru Telescope, and obtained from the SMOKA, which is operated by the Astronomy Data Center, National Astronomical Observatory of Japan. Research supported by the Marie Curie Research Training Network CONSTELLATION under grant No. MRTN-CT- 2006-035890.Table 4 is only available in electronic form at the CDS via

  3. XMM-Newton Study of the Fe K Emission from Molecular Clouds in the Galactic Centre

    NASA Astrophysics Data System (ADS)

    Ponti, Gabriele; Terrier, R.; Goldwurm, A.; Belanger, G.; Trap, G.

    2010-03-01

    The study of the X-ray emission from the Galactic Centre (GC) Molecular Clouds (MC), within 15 arcmin from SgrA*, will be presented. We use XMM-Newton data (about 1.2 Ms of observation time) spanning about 8 years. The MC spectra show all the features characteristic of reflection: intense FeKα, with EW of about 0.7-1 keV, and the associated Kβ line; flat power law continuum and significant FeK edge. The diffuse lowly ionised FeK emission follows the MC distribution, nevertheless not all MC are FeK emitters. The long baseline monitoring allows the characterisation of the temporal evolution of the MC emission, showing a complex pattern of significant variations. In particular, we observe an apparent super-luminal motion of a light front illuminating a Molecular nebula. This might be due to a source outside the MC (such as SgrA* or a bright and long outburst of a X-ray binary), while it can not be due to low energy cosmic rays or a source located inside the cloud. We also observe a decrease of the X-ray emission from G0.11-0.11, behaviour similar to the one of SgrB2. The line intensities, clouds dimensions, columns densities and positions with respect to SgrA*, are consistent with being produced by the same SgrA* flare. The required high luminosity (about 1.5×1039 erg s-1) can hardly be produced by an binary system, while it is in agreement with a flare of SgrA* fading about 100 years ago. The low intensity of the FeK emission coming from the 50 and the 20 km s^-1 MC places an upper limit of 3×1035 erg s^-1 to the mean luminosity of SgrA* in the last 60-90 years. The FeK emission and variations from these MC might have been produced by a single flare of SgrA*.

  4. Dense molecular clumps associated with the Large Magellanic Cloud supergiant shells LMC 4 and LMC 5

    SciTech Connect

    Fujii, Kosuke; Mizuno, Norikazu; Minamidani, Tetsuhiro; Onishi, Toshikazu; Muraoka, Kazuyuki; Kawamura, Akiko; Muller, Erik; Tatematsu, Ken'ichi; Hasegawa, Tetsuo; Miura, Rie E.; Ezawa, Hajime; Dawson, Joanne; Tosaki, Tomoka; Sakai, Takeshi; Tsukagoshi, Takashi; Tanaka, Kunihiko; Fukui, Yasuo

    2014-12-01

    We investigate the effects of supergiant shells (SGSs) and their interaction on dense molecular clumps by observing the Large Magellanic Cloud (LMC) star-forming regions N48 and N49, which are located between two SGSs, LMC 4 and LMC 5. {sup 12}CO (J = 3-2, 1-0) and {sup 13}CO(J = 1-0) observations with the ASTE and Mopra telescopes have been carried out toward these regions. A clumpy distribution of dense molecular clumps is revealed with 7 pc spatial resolution. Large velocity gradient analysis shows that the molecular hydrogen densities (n(H{sub 2})) of the clumps are distributed from low to high density (10{sup 3}-10{sup 5} cm{sup –3}) and their kinetic temperatures (T {sub kin}) are typically high (greater than 50 K). These clumps seem to be in the early stages of star formation, as also indicated from the distribution of Hα, young stellar object candidates, and IR emission. We found that the N48 region is located in the high column density H I envelope at the interface of the two SGSs and the star formation is relatively evolved, whereas the N49 region is associated with LMC 5 alone and the star formation is quiet. The clumps in the N48 region typically show high n(H{sub 2}) and T {sub kin}, which are as dense and warm as the clumps in LMC massive cluster-forming areas (30 Dor, N159). These results suggest that the large-scale structure of the SGSs, especially the interaction of two SGSs, works efficiently on the formation of dense molecular clumps and stars.

  5. Dense Molecular Clumps Associated with the Large Magellanic Cloud Supergiant Shells LMC 4 and LMC 5

    NASA Astrophysics Data System (ADS)

    Fujii, Kosuke; Minamidani, Tetsuhiro; Mizuno, Norikazu; Onishi, Toshikazu; Kawamura, Akiko; Muller, Erik; Dawson, Joanne; Tatematsu, Ken'ichi; Hasegawa, Tetsuo; Tosaki, Tomoka; Miura, Rie E.; Muraoka, Kazuyuki; Sakai, Takeshi; Tsukagoshi, Takashi; Tanaka, Kunihiko; Ezawa, Hajime; Fukui, Yasuo

    2014-12-01

    We investigate the effects of supergiant shells (SGSs) and their interaction on dense molecular clumps by observing the Large Magellanic Cloud (LMC) star-forming regions N48 and N49, which are located between two SGSs, LMC 4 and LMC 5. 12CO (J = 3-2, 1-0) and 13CO(J = 1-0) observations with the ASTE and Mopra telescopes have been carried out toward these regions. A clumpy distribution of dense molecular clumps is revealed with 7 pc spatial resolution. Large velocity gradient analysis shows that the molecular hydrogen densities (n(H2)) of the clumps are distributed from low to high density (103-105 cm-3) and their kinetic temperatures (T kin) are typically high (greater than 50 K). These clumps seem to be in the early stages of star formation, as also indicated from the distribution of Hα, young stellar object candidates, and IR emission. We found that the N48 region is located in the high column density H I envelope at the interface of the two SGSs and the star formation is relatively evolved, whereas the N49 region is associated with LMC 5 alone and the star formation is quiet. The clumps in the N48 region typically show high n(H2) and T kin, which are as dense and warm as the clumps in LMC massive cluster-forming areas (30 Dor, N159). These results suggest that the large-scale structure of the SGSs, especially the interaction of two SGSs, works efficiently on the formation of dense molecular clumps and stars.

  6. Understanding star formation in molecular clouds. I. Effects of line-of-sight contamination on the column density structure

    NASA Astrophysics Data System (ADS)

    Schneider, N.; Ossenkopf, V.; Csengeri, T.; Klessen, R. S.; Federrath, C.; Tremblin, P.; Girichidis, P.; Bontemps, S.; André, Ph.

    2015-03-01

    Column-density maps of molecular clouds are one of the most important observables in the context of molecular cloud- and star-formation (SF) studies. With the Herschel satellite it is now possible to precisely determine the column density from dust emission, which is the best tracer of the bulk of material in molecular clouds. However, line-of-sight (LOS) contamination from fore- or background clouds can lead to overestimating the dust emission of molecular clouds, in particular for distant clouds. This implies values that are too high for column density and mass, which can potentially lead to an incorrect physical interpretation of the column density probability distribution function (PDF). In this paper, we use observations and simulations to demonstrate how LOS contamination affects the PDF. We apply a first-order approximation (removing a constant level) to the molecular clouds of Auriga and Maddalena (low-mass star-forming), and Carina and NGC 3603 (both high-mass SF regions). In perfect agreement with the simulations, we find that the PDFs become broader, the peak shifts to lower column densities, and the power-law tail of the PDF for higher column densities flattens after correction. All corrected PDFs have a lognormal part for low column densities with a peak at Av ~ 2 mag, a deviation point (DP) from the lognormal at Av(DP) ~ 4-5 mag, and a power-law tail for higher column densities. Assuming an equivalent spherical density distribution ρ ∝ r- α, the slopes of the power-law tails correspond to αPDF = 1.8, 1.75, and 2.5 for Auriga, Carina, and NGC 3603. These numbers agree within the uncertainties with the values of α ≈ 1.5,1.8, and 2.5 determined from the slope γ (with α = 1-γ) obtained from the radial column density profiles (N ∝ rγ). While α ~ 1.5-2 is consistent with a structure dominated by collapse (local free-fall collapse of individual cores and clumps and global collapse), the higher value of α > 2 for NGC 3603 requires a physical

  7. COLLAPSE AND FRAGMENTATION OF MAGNETIC MOLECULAR CLOUD CORES WITH THE ENZO AMR MHD CODE. I. UNIFORM DENSITY SPHERES

    SciTech Connect

    Boss, Alan P.; Keiser, Sandra A.

    2013-02-20

    Magnetic fields are important contributors to the dynamics of collapsing molecular cloud cores, and can have a major effect on whether collapse results in a single protostar or fragmentation into a binary or multiple protostar system. New models are presented of the collapse of magnetic cloud cores using the adaptive mesh refinement code Enzo2.0. The code was used to calculate the ideal magnetohydrodynamics (MHD) of initially spherical, uniform density, and rotation clouds with density perturbations, i.e., the Boss and Bodenheimer standard isothermal test case for three-dimensional (3D) hydrodynamics codes. After first verifying that Enzo reproduces the binary fragmentation expected for the non-magnetic test case, a large set of models was computed with varied initial magnetic field strengths and directions with respect to the cloud core axis of rotation (parallel or perpendicular), density perturbation amplitudes, and equations of state. Three significantly different outcomes resulted: (1) contraction without sustained collapse, forming a denser cloud core; (2) collapse to form a single protostar with significant spiral arms; and (3) collapse and fragmentation into binary or multiple protostar systems, with multiple spiral arms. Comparisons are also made with previous MHD calculations of similar clouds with a barotropic equations of state. These results for the collapse of initially uniform density spheres illustrate the central importance of both magnetic field direction and field strength for determining the outcome of dynamic protostellar collapse.

  8. Large-scale CO (J = 4-3) mapping toward the Orion-A giant molecular cloud

    NASA Astrophysics Data System (ADS)

    Ishii, Shun; Seta, Masumichi; Nagai, Makoto; Miyamoto, Yusuke; Nakai, Naomasa; Nagasaki, Taketo; Arai, Hitoshi; Imada, Hiroaki; Miyagawa, Naoki; Maezawa, Hiroyuki; Maehashi, Hideki; Bronfman, Leonardo; Finger, Ricardo

    2016-02-01

    We have mapped the Orion-A giant molecular cloud in the CO (J = 4-3) line with the Tsukuba 30 cm submillimeter telescope. The map covered a 7.125 deg2 area with a 9' resolution, including main components of the cloud such as the Orion Nebula, OMC-2/3, and L1641-N. The most intense emission was detected toward the Orion KL region. The integrated intensity ratio betwee