PHOTOEVAPORATING PROPLYD-LIKE OBJECTS IN CYGNUS OB2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wright, Nicholas J.; Drake, Jeremy J.; Guarcello, Mario G.

2012-02-20

We report the discovery of 10 proplyd-like objects in the vicinity of the massive OB association Cygnus OB2. They were discovered in IPHAS H{alpha} images and are clearly resolved in broadband Hubble Space Telescope/Advanced Camera for Surveys, near-IR, and Spitzer mid-IR images. All exhibit the familiar tadpole shape seen in photoevaporating objects such as the Orion proplyds, with a bright ionization front at the head facing the central cluster of massive stars and a tail stretching in the opposite direction. Many also show secondary ionization fronts, complex tail morphologies, or multiple heads. We consider the evidence that these are eithermore » proplyds or 'evaporating gaseous globules' (EGGs) left over from a fragmenting molecular cloud, but find that neither scenario fully explains the observations. Typical sizes are 50,000-100,000 AU, larger than the Orion proplyds, but in agreement with the theoretical scaling of proplyd size with distance from the ionizing source. These objects are located at projected separations of {approx}6-14 pc from the OB association, compared to {approx}0.1 pc for the Orion proplyds, but are clearly being photoionized by the {approx}65 O-type stars in Cyg OB2. Central star candidates are identified in near- and mid-IR images, supporting the proplyd scenario, though their large sizes and notable asymmetries are more consistent with the EGG scenario. A third possibility is therefore considered that these are a unique class of photoevaporating partially embedded young stellar objects that have survived the destruction of their natal molecular cloud. This has implications for the properties of stars that form in the vicinity of massive stars.« less

Irradiated interfaces in the Ara OB1, Carina, Eagle Nebula, and Cyg OB2 massive star formation regions

DOE PAGES

Hartigan, P.; Palmer, J.; Cleeves, L. I.

2012-09-05

Regions of massive star formation offer some of the best and most easily-observed examples of radiation hydrodynamics. Boundaries where fully-ionized H II regions transition to neutral/molecular photodissociation regions (PDRs) are of particular interest because marked temperature and density contrasts across the boundaries lead to evaporative flows and fluid dynamical instabilities that can evolve into spectacular pillar-like structures. Furthermore, when detached from their parent clouds, pillars become ionized globules that often harbor one or more young stars. H2 molecules at the interface between a PDR and an H II region absorb ultraviolet light from massive stars, and the resulting fluoresced infraredmore » emission lines are an ideal way to trace this boundary independent of obscuring dust. This paper presents H2 images of four regions of massive star formation that illustrate different types of PDR boundaries. The Ara OB1 star formation region contains a striking long wall that has several wavy structures which are present in H2, but the emission is not particularly bright because the ambient UV fluxes are relatively low. In contrast, the Carina star formation region shows strong H2 fluorescence both along curved walls and at the edges of spectacular pillars that in some cases have become detached from their parent clouds. The less-spectacular but more well-known Eagle Nebula has two regions that have strong fluorescence in addition to its pillars. And while somewhat older than the other regions, Cyg OB2 has the highest number of massive stars of the regions surveyed and contains many isolated, fluoresced globules that have head–tail morphologies which point towards the sources of ionizing radiation. Our images provide a collection of potential astrophysical analogs that may relate to ablated interfaces observed in laser experiments of radiation hydrodynamics.« less

Globules and pillars in Cygnus X. I. Herschel far-infrared imaging of the Cygnus OB2 environment

NASA Astrophysics Data System (ADS)

Schneider, N.; Bontemps, S.; Motte, F.; Blazere, A.; André, Ph.; Anderson, L. D.; Arzoumanian, D.; Comerón, F.; Didelon, P.; Di Francesco, J.; Duarte-Cabral, A.; Guarcello, M. G.; Hennemann, M.; Hill, T.; Könyves, V.; Marston, A.; Minier, V.; Rygl, K. L. J.; Röllig, M.; Roy, A.; Spinoglio, L.; Tremblin, P.; White, G. J.; Wright, N. J.

2016-06-01

The radiative feedback of massive stars on molecular clouds creates pillars, globules and other features at the interface between the H II region and molecular cloud. Optical and near-infrared observations from the ground as well as with the Hubble or Spitzer satellites have revealed numerous examples of such cloud structures. We present here Herschel far-infrared observations between 70 μm and 500 μm of the immediate environment of the rich Cygnus OB2 association, performed within the Herschel imaging survey of OB Young Stellar objects (HOBYS) program. All of the observed irradiated structures were detected based on their appearance at 70 μm, and have been classified as pillars, globules, evaporating gasous globules (EGGs), proplyd-like objects, and condensations. From the 70 μm and 160 μm flux maps, we derive the local far-ultraviolet (FUV) field on the photon dominated surfaces. In parallel, we use a census of the O-stars to estimate the overall FUV-field, that is 103-104 G0 (Habing field) close to the central OB cluster (within 10 pc) and decreases down to a few tens G0, in a distance of 50 pc. From a spectral energy distribution (SED) fit to the four longest Herschel wavelengths, we determine column density and temperature maps and derive masses, volume densities and surface densities for these structures. We find that the morphological classification corresponds to distinct physical properties. Pillars and globules are massive (~500 M⊙) and large (equivalent radius r ~ 0.6 pc) structures, corresponding to what is defined as "clumps" for molecular clouds. EGGs and proplyd-likeobjects are smaller (r ~ 0.1 and 0.2 pc) and less massive (~10 and ~30 M⊙). Cloud condensations are small (~0.1 pc), have an average mass of 35 M⊙, are dense (~6 × 104 cm-3), and can thus be described as molecular cloud "cores". All pillars and globules are oriented toward the Cyg OB2 association center and have the longest estimated photoevaporation lifetimes, a few million

Molecular clouds without detectable CO

NASA Technical Reports Server (NTRS)

Blitz, Leo; Bazell, David; Desert, F. Xavier

1990-01-01

The clouds identified by Desert, Bazell, and Boulanger (DBB clouds) in their search for high-latitude molecular clouds were observed in the CO (J = 1-0) line, but only 13 percent of the sample was detected. The remaining 87 percent are diffuse molecular clouds with CO abundances of about 10 to the -6th, a typical value for diffuse clouds. This hypothesis is shown to be consistent with Copernicus data. The DBB clouds are shown to ben an essentially complete catalog of diffuse molecular clouds in the solar vicinity. The total molecular surface density in the vicinity of the sun is then only about 20 percent greater than the 1.3 solar masses/sq pc determined by Dame et al. (1987). Analysis of the CO detections indicates that there is a sharp threshold in extinction of 0.25 mag before CO is detectable and is derived from the IRAS I(100) micron threshold of 4 MJy/sr. This threshold is presumably where the CO abundance exhibits a sharp increase

Molecular clouds without detectable CO

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blitz, L.; Bazell, D.; Desert, F.X.

1990-03-01

The clouds identified by Desert, Bazell, and Boulanger (DBB clouds) in their search for high-latitude molecular clouds were observed in the CO (J = 1-0) line, but only 13 percent of the sample was detected. The remaining 87 percent are diffuse molecular clouds with CO abundances of about 10 to the -6th, a typical value for diffuse clouds. This hypothesis is shown to be consistent with Copernicus data. The DBB clouds are shown to be an essentially complete catalog of diffuse molecular clouds in the solar vicinity. The total molecular surface density in the vicinity of the sun is thenmore » only about 20 percent greater than the 1.3 solar masses/sq pc determined by Dame et al. (1987). Analysis of the CO detections indicates that there is a sharp threshold in extinction of 0.25 mag before CO is detectable and is derived from the IRAS I(100) micron threshold of 4 MJy/sr. This threshold is presumably where the CO abundance exhibits a sharp increase 18 refs.« less

Age, size, and position of H ii regions in the Galaxy. Expansion of ionized gas in turbulent molecular clouds

NASA Astrophysics Data System (ADS)

Tremblin, P.; Anderson, L. D.; Didelon, P.; Raga, A. C.; Minier, V.; Ntormousi, E.; Pettitt, A.; Pinto, C.; Samal, M. R.; Schneider, N.; Zavagno, A.

2014-08-01

Aims: This work aims to improve the current understanding of the interaction between H ii regions and turbulent molecular clouds. We propose a new method to determine the age of a large sample of OB associations by investigating the development of their associated H ii regions in the surrounding turbulent medium. Methods: Using analytical solutions, one-dimensional (1D), and three-dimensional (3D) simulations, we constrained the expansion of the ionized bubble depending on the turbulence level of the parent molecular cloud. A grid of 1D simulations was then computed in order to build isochrone curves for H ii regions in a pressure-size diagram. This grid of models allowed us to date a large sample of OB associations that we obtained from the H ii Region Discovery Survey (HRDS). Results: Analytical solutions and numerical simulations showed that the expansion of H ii regions is slowed down by the turbulence up to the point where the pressure of the ionized gas is in a quasi-equilibrium with the turbulent ram pressure. Based on this result, we built a grid of 1D models of the expansion of H ii regions in a profile based on Larson's laws. We take the 3D turbulence into account with an effective 1D temperature profile. The ages estimated by the isochrones of this grid agree well with literature values of well known regions such as Rosette, RCW 36, RCW 79, and M 16. We thus propose that this method can be used to find ages of young OB associations through the Galaxy and also in nearby extra-galactic sources.

An anomalous extinction law in the Cep OB3b young cluster: Evidence for dust processing during gas dispersal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allen, Thomas S.; Prchlik, Jakub J.; Megeath, S. Thomas

We determine the extinction law through Cep OB3b, a young cluster of 3000 stars undergoing gas dispersal. The extinction is measured toward 76 background K giants identified with MMT/Hectospec spectra. Color excess ratios were determined toward each of the giants using V and R photometry from the literature, g, r, i, and z photometry from the Sloan Digital Sky Survey and J, H, and K{sub s} photometry from the Two Micron All Sky Survey. These color excess ratios were then used to construct the extinction law through the dusty material associated with Cep OB3b. The extinction law through Cep OB3bmore » is intermediate between the R{sub V} = 3.1 and R{sub V} = 5 laws commonly used for the diffuse atomic interstellar medium and dense molecular clouds, respectively. The dependence of the extinction law on line-of-sight A{sub V} is investigated and we find the extinction law becomes shallower for regions with A{sub V} > 2.5 mag. We speculate that the intermediate dust law results from dust processing during the dispersal of the molecular cloud by the cluster.« less

Molecular Cloud Evolution VI. Measuring cloud ages

NASA Astrophysics Data System (ADS)

Vázquez-Semadeni, Enrique; Zamora-Avilés, Manuel; Galván-Madrid, Roberto; Forbrich, Jan

2018-06-01

In previous contributions, we have presented an analytical model describing the evolution of molecular clouds (MCs) undergoing hierarchical gravitational contraction. The cloud's evolution is characterized by an initial increase in its mass, density, and star formation rate (SFR) and efficiency (SFE) as it contracts, followed by a decrease of these quantities as newly formed massive stars begin to disrupt the cloud. The main parameter of the model is the maximum mass reached by the cloud during its evolution. Thus, specifying the instantaneous mass and some other variable completely determines the cloud's evolutionary stage. We apply the model to interpret the observed scatter in SFEs of the cloud sample compiled by Lada et al. as an evolutionary effect so that, although clouds such as California and Orion A have similar masses, they are in very different evolutionary stages, causing their very different observed SFRs and SFEs. The model predicts that the California cloud will eventually reach a significantly larger total mass than the Orion A cloud. Next, we apply the model to derive estimated ages of the clouds since the time when approximately 25% of their mass had become molecular. We find ages from ˜1.5 to 27 Myr, with the most inactive clouds being the youngest. Further predictions of the model are that clouds with very low SFEs should have massive atomic envelopes constituting the majority of their gravitational mass, and that low-mass clouds (M ˜ 103-104M⊙) end their lives with a mini-burst of star formation, reaching SFRs ˜300-500 M⊙ Myr-1. By this time, they have contracted to become compact (˜1 pc) massive star-forming clumps, in general embedded within larger GMCs.

A Catalog of Distances to Molecular Clouds from Pan-STARRS1

NASA Astrophysics Data System (ADS)

Schlafly, Eddie; Green, G.; Finkbeiner, D. P.; Rix, H.

2014-01-01

We present a catalog of distances to molecular clouds, derived from PanSTARRS-1 photometry. We simultaneously infer the full probability distribution function of reddening and distance of the stars towards these clouds using the technique of Green et al. (2013) (see neighboring poster). We fit the resulting measurements using a simple dust screen model to infer the distance to each cloud. The result is a large, homogeneous catalog of distances to molecular clouds. For clouds with heliocentric distances greater than about 200 pc, typical statistical uncertainties in the distances are 5%, with systematic uncertainty stemming from the quality of our stellar models of about 10%. We have applied this analysis to many of the most well-studied clouds in the δ > -30° sky, including Orion, California, Taurus, Perseus, and Cepheus. We have also studied the entire catalog of Magnani, Blitz, and Mundy (1985; MBM), though for about half of those clouds we can provide only upper limits on the distances. We compare our distances with distances from the literature, when available, and find good agreement.

A Deuteration Survey of Starless Clumps in GemOB1 and the First Quadrant

NASA Astrophysics Data System (ADS)

Henrici, Andrew; Shirley, Yancy L.; Svoboda, Brian

2018-01-01

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. Recent maps of dust continuum emission at (sub)millimeter wavelengths have identified tens of thousands of dense clumps of gas and dust. By comparing these regions to infrared and radio surveys, we have identified starless clump candidates which have no evidence for embedded star formation. These objects represent the earliest phase of star formation throughout the Milky Way. One benefit of the Milky Way surveys is that it is also possible to study the chemistry of entire core and clump populations within a single cloud. We used the 10m Heinrich Hertz Submillimeter Telescope to survey starless clump candidates in the First Quadrant identified from the Bolocam Galactic Plane Survey 1.1 mm continuum in the deuterated molecular transitions of DCO+ 3-2 and N2D+ 3-2. We also survey the entire clump population of the Gemini OB1 molecular cloud. In both surveys, we compared detection statistics and compare deuteration fraction to physical properties of the clumps and their evolutionary stage. High resolution ALMA observations of 9 starless clump candidates of the same lines are used to analyze how the cold deuterated gas is spatially distributed in these clumps.

Cool neutral hydrogen in the direction of an anonymous OB association

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bania, T.M.

1983-08-01

H I self-absorption is seen in the direction l = 55./sup 0/6 probably physically associated with an anonymous OB association which has the Cepheid GY Sagittae as a member. The cool H I is in two clouds at least 15 pc in diameter located 3.25 kpc from the Sun. If their temperature is approx. =50 K, the cloud masses are approx. =10/sup 3/ M/sub sun/. The neutral atomic hydrogen clouds are probably warm envelopes surrounding cold molecular cloud cores because CO observations in this region show two molecular clouds nearly coincident with the absorbing H i gas. Since the OBmore » association is only approx. =10/sup 7/ years old, these clouds are likely to be part of the original cloud complex from which the stellar cluster formed. The H i clouds are part of the larger Arecibo survey of self-absorption which suggests that many of the Arecibo clouds are associated with heretofore unidentified star clusters. Even if this is generally not the case, the Arecibo objects have accurate kinematic distances and thus provide a new sample of cool H I clouds whose thermodynamic properties can be studied.« less

Chemical transitions for interstellar C2 and CN in cloud envelopes

NASA Technical Reports Server (NTRS)

Federman, S. R.; Strom, C. J.; Lambert, D. L.; Cardelli, Jason A.; Smith, V. V.; Joseph, C. L.

1994-01-01

Observations were made of absorption from CH, C2, and CN toward moderately reddened stars in Sco, OB2, Ceo OB3, and Taurus/Auriga. For these directions, most of the reddening is associated with a single cloud complex, for example, the rho Ophiuchus molecular cloud, and as a result, the observations probe moderately dense material. When combined with avaliable data for nearby directions, the survey provides the basis for a comprehensive analysis of the chemistry for these species. The chemical transitions affecting C2 and CN in cloud envelopes were analyzed. The depth into a cloud at which a transition takes place was characterized by tau(sub uv), the grain optical depth at 1000 A. One transition at tau(sub uv) approx. = 2, which arises from, the conversion of C(+) into CO, affects the chemistries for both molecules because of the key role this ion plays. A second one involving production terms in the CN chemistry occurs at tau(sub uv) of approx. = 3; neutral reactions which C2 and CH is more important at larger values for tau(sub uv). The transition from photodissociation to chemical destruction takes place at tau(sub uv) approx. = 4.5 for C2 and CN. The observational data for stars in Sco OB2, Cep OB3, and Taurus/Auriga were studied with chemical rate equations containing the most important production and destruction mechanisms. Because the sample of stars in Sco OB2 includes sight lines with A(sub v) ranging from 1-4 mag, sight lines dominated by photochemistry could be analyzed separately from those controlled by gas-phase destruction. The analysis yielded values for two poorly known rate constants for reactions involved in the production of CN; the reactions are C2 + N yields CN + C and C(+) + NH yields all products. The other directions were analyzed with the inferred values. The predicted column densities for C2 and CN agree with the observed values to better than 50%, and in most instances 20%. When combining the estimates for density and temperature derived

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.

Leptin Reduces the Expression and Increases the Phosphorylation of the Negative Regulators of GLUT4 Traffic TBC1D1 and TBC1D4 in Muscle of ob/ob Mice

PubMed Central

Sáinz, Neira; Rodríguez, Amaia; Catalán, Victoria; Becerril, Sara; Ramírez, Beatriz; Lancha, Andoni; Burgos-Ramos, Emma; Gómez-Ambrosi, Javier; Frühbeck, Gema

2012-01-01

Leptin improves insulin sensitivity in skeletal muscle. Our goal was to determine whether proteins controlling GLUT4 traffic are altered by leptin deficiency and in vivo leptin administration in skeletal muscle of wild type and ob/ob mice. Leptin-deficient ob/ob mice were divided in three groups: control, leptin-treated (1 mg/kg/d) and leptin pair-fed ob/ob mice. Microarray analysis revealed that 1,546 and 1,127 genes were regulated by leptin deficiency and leptin treatment, respectively. Among these, we identified 24 genes involved in intracellular vesicle-mediated transport in ob/ob mice. TBC1 domain family, member 1 (Tbc1d1), a negative regulator of GLUT4 translocation, was up-regulated (P = 0.001) in ob/ob mice as compared to wild types. Importantly, leptin treatment reduced the transcript levels of Tbc1d1 (P<0.001) and Tbc1d4 (P = 0.004) in the leptin-treated ob/ob as compared to pair-fed ob/ob animals. In addition, phosphorylation levels of TBC1D1 and TBC1D4 were enhanced in leptin-treated ob/ob as compared to control ob/ob (P = 0.015 and P = 0.023, respectively) and pair-fed ob/ob (P = 0.036 and P = 0.034, respectively) mice. Despite similar GLUT4 protein expression in wild type and ob/ob groups a different immunolocalization of this protein was evidenced in muscle sections. Leptin treatment increased GLUT4 immunoreactivity in gastrocnemius and extensor digitorum longus sections of leptin-treated ob/ob mice. Moreover, GLUT4 protein detected in immunoprecipitates from TBC1D4 was reduced by leptin replacement compared to control ob/ob (P = 0.013) and pair-fed ob/ob (P = 0.037) mice. Our findings suggest that leptin enhances the intracellular GLUT4 transport in skeletal muscle of ob/ob animals by reducing the expression and activity of the negative regulators of GLUT4 traffic TBC1D1 and TBC1D4. PMID:22253718

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.

Wide-field 12CO (J=2-1) and 13CO (J=2-1) Observations toward the Aquila Rift and Serpens Molecular Cloud Complexes. I. Molecular Clouds and Their Physical Properties

NASA Astrophysics Data System (ADS)

Nakamura, Fumitaka; Dobashi, Kazuhito; Shimoikura, Tomomi; Tanaka, Tomohiro; Onishi, Toshikazu

2017-03-01

We present the results of wide-field 12CO (J=2{--}1) and 13CO (J=2{--}1) observations toward the Aquila Rift and Serpens molecular cloud complexes (25^\\circ < l< 33^\\circ and 1^\\circ < b< 6^\\circ ) at an angular resolution of 3.‧4 (≈ 0.25 pc) and at a velocity resolution of 0.079 km s-1 with velocity coverage of -5 {km} {{{s}}}-1< {V}{LSR}< 35 {km} {{{s}}}-1. We found that the 13CO emission better traces the structures seen in the extinction map, and derived the {X}{13{CO}}-factor of this region. Applying SCIMES to the 13CO data cube, we identified 61 clouds and derived their mass, radii, and line widths. The line width-radius relation of the identified clouds basically follows those of nearby molecular clouds. The majority of the identified clouds are close to virial equilibrium, although the dispersion is large. By inspecting the 12CO channel maps by eye, we found several arcs that are spatially extended to 0.°2-3° in length. In the longitude-velocity diagrams of 12CO, we also found two spatially extended components that appear to converge toward Serpens South and the W40 region. The existence of two components with different velocities and arcs suggests that large-scale expanding bubbles and/or flows play a role in the formation and evolution of the Serpens South and W40 cloud.

THE SPITZER SPACE TELESCOPE SURVEY OF THE ORION A AND B MOLECULAR CLOUDS. II. THE SPATIAL DISTRIBUTION AND DEMOGRAPHICS OF DUSTY YOUNG STELLAR OBJECTS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Megeath, S. T.; Kryukova, E.; Gutermuth, R.

2016-01-15

We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc{sup −2} to over 10,000 pc{sup −2}, with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifyingmore » clusters and groups as continuous regions with surface densities ≥10 pc{sup −2}, we find that 59% of the YSOs are in the largest cluster, the Orion Nebula Cluster (ONC), while 13% of the YSOs are found in a distributed population. A lower fraction of protostars in the distributed population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups shows that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only ∼2 Myr in age. We find that the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or dynamical interactions in dense, clustered regions.« less

Glycerol-3-Phosphate Acyltransferase 1 Deficiency in ob/ob Mice Diminishes Hepatic Steatosis but Does Not Protect Against Insulin Resistance or Obesity

PubMed Central

Wendel, Angela A.; Li, Lei O.; Li, Yue; Cline, Gary W.; Shulman, Gerald I.; Coleman, Rosalind A.

2010-01-01

OBJECTIVE Hepatic steatosis is strongly associated with insulin resistance, but a causal role has not been established. In ob/ob mice, sterol regulatory element binding protein 1 (SREBP1) mediates the induction of steatosis by upregulating target genes, including glycerol-3-phosphate acyltransferase-1 (Gpat1), which catalyzes the first and committed step in the pathway of glycerolipid synthesis. We asked whether ob/ob mice lacking Gpat1 would have reduced hepatic steatosis and improved insulin sensitivity. RESEARCH DESIGN AND METHODS Hepatic lipids, insulin sensitivity, and hepatic insulin signaling were compared in lean (Lep+/?), lean-Gpat1−/−, ob/ob (Lepob/ob), and ob/ob-Gpat1−/− mice. RESULTS Compared with ob/ob mice, the lack of Gpat1 in ob/ob mice reduced hepatic triacylglycerol (TAG) and diacylglycerol (DAG) content 59 and 74%, respectively, but increased acyl-CoA levels. Despite the reduction in hepatic lipids, fasting glucose and insulin concentrations did not improve, and insulin tolerance remained impaired. In both ob/ob and ob/ob-Gpat1−/− mice, insulin resistance was accompanied by elevated hepatic protein kinase C-ε activation and blunted insulin-stimulated Akt activation. CONCLUSIONS These results suggest that decreasing hepatic steatosis alone does not improve insulin resistance, and that factors other than increased hepatic DAG and TAG contribute to hepatic insulin resistance in this genetically obese model. They also show that the SREBP1-mediated induction of hepatic steatosis in ob/ob mice requires Gpat1. PMID:20200319

1.0 Mm Maps and Radial Density Distributions of Southern Hii/molecular Cloud Complexes

NASA Technical Reports Server (NTRS)

Cheung, L. H.; Frogel, J. A.; Gezar, D. Y.; Hauser, M. G.

1980-01-01

Several 1.0 continuum mapping observations were made of seven southern hemisphere h12/molecular cloud complexes with 65 arcsec resolution. The radial density distribution of the clouds with central luminosity sources was determined observationally. Strong similarities in morphology and general physical conditions were found to exist among all of the southern clouds in the sample.

Case Study of Data Mining in Observational Astronomy: The Search for New OB Stars in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Larkin, Cormac; Vink, Jorick; Kalari, Venu; Groh, Jose

2018-01-01

OB stars are the most luminous and massive stars, living short lives and exerting a disproportionate influence on their environments. They are key to understanding progenitors of gravitational wave sources and reionization of the early Universe. To detect new OB stars, we combine photometric catalog data with TLUSTY and ATLAS9 stellar atmospheres. This method is also believed to be sensitive to elusive “stripped” stars, thought to lose their hydrogen envelope through binary interaction.OB stars are intrinsically luminous, so complete populations are assumed for local group galaxies such as the Small Magellanic Cloud. Our findings challenge this, as we find 26 new OB candidates. Spectroscopy of 7 candidates shows a 100% detection rate. Most interestingly, 5 of our candidates are consistent with “stripped” stars.To date only 5 “stripped” candidates have been found serendipitously (e.g. HD 45166) as current methods are not sensitive to them. Our work doubles the sample of detected candidates, highlighting that our approach is the first to identify them in a targeted, systematic way. The finding of “stripped” stars could rewrite our understanding of the early Universe, offering an alternative hypothesis to Wolf-Rayet driven cosmic reionization.

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.

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.

ALMA Observations of a Quiescent Molecular Cloud in the Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

Wong, Tony; Hughes, Annie; Tokuda, Kazuki; Indebetouw, Rémy; Bernard, Jean-Philippe; Onishi, Toshikazu; Wojciechowski, Evan; Bandurski, Jeffrey B.; Kawamura, Akiko; Roman-Duval, Julia; Cao, Yixian; Chen, C.-H. Rosie; Chu, You-hua; Cui, Chaoyue; Fukui, Yasuo; Montier, Ludovic; Muller, Erik; Ott, Juergen; Paradis, Deborah; Pineda, Jorge L.; Rosolowsky, Erik; Sewiło, Marta

2017-12-01

We present high-resolution (subparsec) observations of a giant molecular cloud in the nearest star-forming galaxy, the Large Magellanic Cloud. ALMA Band 6 observations trace the bulk of the molecular gas in 12CO(2-1) and the high column density regions in 13CO(2-1). Our target is a quiescent cloud (PGCC G282.98-32.40, which we refer to as the “Planck cold cloud” or PCC) in the southern outskirts of the galaxy where star formation activity is very low and largely confined to one location. We decompose the cloud into structures using a dendrogram and apply an identical analysis to matched-resolution cubes of the 30 Doradus molecular cloud (located near intense star formation) for comparison. Structures in the PCC exhibit roughly 10 times lower surface density and five times lower velocity dispersion than comparably sized structures in 30 Dor, underscoring the non-universality of molecular cloud properties. In both clouds, structures with relatively higher surface density lie closer to simple virial equilibrium, whereas lower surface-density structures tend to exhibit supervirial line widths. In the PCC, relatively high line widths are found in the vicinity of an infrared source whose properties are consistent with a luminous young stellar object. More generally, we find that the smallest resolved structures (“leaves”) of the dendrogram span close to the full range of line widths observed across all scales. As a result, while the bulk of the kinetic energy is found on the largest scales, the small-scale energetics tend to be dominated by only a few structures, leading to substantial scatter in observed size-line-width relationships.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heyer, Mark; Krawczyk, Coleman; Duval, Julia

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.more » 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.« less

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

Ablation of ghrelin receptor in leptin-deficient ob/ob mice has paradoxical effects on glucose homeostasis when compared with ablation of ghrelin in ob/ob mice.

PubMed

Ma, Xiaojun; Lin, Yuezhen; Lin, Ligen; Qin, Guijun; Pereira, Fred A; Haymond, Morey W; Butte, Nancy F; Sun, Yuxiang

2012-08-01

The orexigenic hormone ghrelin is important in diabetes because it has an inhibitory effect on insulin secretion. Ghrelin ablation in leptin-deficient ob/ob (Ghrelin(-/-):ob/ob) mice increases insulin secretion and improves hyperglycemia. The physiologically relevant ghrelin receptor is the growth hormone secretagogue receptor (GHS-R), and GHS-R antagonists are thought to be an effective strategy for treating diabetes. However, since some of ghrelin's effects are independent of GHS-R, we have utilized genetic approaches to determine whether ghrelin's effect on insulin secretion is mediated through GHS-R and whether GHS-R antagonism indeed inhibits insulin secretion. We investigated the effects of GHS-R on glucose homeostasis in Ghsr-ablated ob/ob mice (Ghsr(-/-):ob/ob). Ghsr ablation did not rescue the hyperphagia, obesity, or insulin resistance of ob/ob mice. Surprisingly, Ghsr ablation worsened the hyperglycemia, decreased insulin, and impaired glucose tolerance. Consistently, Ghsr ablation in ob/ob mice upregulated negative β-cell regulators (such as UCP-2, SREBP-1c, ChREBP, and MIF-1) and downregulated positive β-cell regulators (such as HIF-1α, FGF-21, and PDX-1) in whole pancreas; this suggests that Ghsr ablation impairs pancreatic β-cell function in leptin deficiency. Of note, Ghsr ablation in ob/ob mice did not affect the islet size; the average islet size of Ghsr(-/-):ob/ob mice is similar to that of ob/ob mice. In summary, because Ghsr ablation in leptin deficiency impairs insulin secretion and worsens hyperglycemia, this suggests that GHS-R antagonists may actually aggravate diabetes under certain conditions. The paradoxical effects of ghrelin ablation and Ghsr ablation in ob/ob mice highlight the complexity of the ghrelin-signaling pathway.

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.

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.

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

Crystal Structures of RMI1 and RMI2, Two OB-Fold Regulatory Subunits of the BLM Complex

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Feng; Yang, Yuting; Singh, Thiyam Ramsing

Mutations in BLM, a RecQ-like helicase, are linked to the autosomal recessive cancer-prone disorder Bloom's syndrome. BLM associates with topoisomerase (Topo) III{alpha}, RMI1, and RMI2 to form the BLM complex that is essential for genome stability. The RMI1-RMI2 heterodimer stimulates the dissolution of double Holliday junction into non-crossover recombinants mediated by BLM-Topo III{alpha} and is essential for stabilizing the BLM complex. However, the molecular basis of these functions of RMI1 and RMI2 remains unclear. Here we report the crystal structures of multiple domains of RMI1-RMI2, providing direct confirmation of the existence of three oligonucleotide/oligosaccharide binding (OB)-folds in RMI1-RMI2. Our structuralmore » and biochemical analyses revealed an unexpected insertion motif in RMI1N-OB, which is important for stimulating the dHJ dissolution. We also revealed the structural basis of the interaction between RMI1C-OB and RMI2-OB and demonstrated the functional importance of the RMI1-RMI2 interaction in genome stability maintenance.« less

Reduction of protein tyrosine phosphatase 1B increases insulin-dependent signaling in ob/ob mice.

PubMed

Gum, Rebecca J; Gaede, Lori L; Koterski, Sandra L; Heindel, Matthew; Clampit, Jill E; Zinker, Bradley A; Trevillyan, James M; Ulrich, Roger G; Jirousek, Michael R; Rondinone, Cristina M

2003-01-01

Protein tyrosine phosphatase 1B (PTP1B) is a negative regulator of insulin receptor (IR) signal transduction and a drug target for treatment of type 2 diabetes. Using PTP1B antisense oligonucleotides (ASOs), effects of decreased PTP1B levels on insulin signaling in diabetic ob/ob mice were examined. Insulin stimulation, prior to sacrifice, resulted in no significant activation of insulin signaling pathways in livers from ob/ob mice. However, in PTP1B ASO-treated mice, in which PTP1B protein was decreased by 60% in liver, similar stimulation with insulin resulted in increased tyrosine phosphorylation of the IR and IR substrate (IRS)-1 and -2 by threefold, fourfold, and threefold, respectively. IRS-2-associated phosphatidylinositol 3-kinase activity was also increased threefold. Protein kinase B (PKB) serine phosphorylation was increased sevenfold in liver of PTP1B ASO-treated mice upon insulin stimulation, while phosphorylation of PKB substrates, glycogen synthase kinase (GSK)-3alpha and -3beta, was increased more than twofold. Peripheral insulin signaling was increased by PTP1B ASO, as evidenced by increased phosphorylation of PKB in muscle of insulin-stimulated PTP1B ASO-treated animals despite the lack of measurable effects on muscle PTP1B protein. These results indicate that reduction of PTP1B is sufficient to increase insulin-dependent metabolic signaling and improve insulin sensitivity in a diabetic animal model.

Fast Molecular Cloud Destruction Requires Fast Cloud Formation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mac Low, Mordecai-Mark; Burkert, Andreas; Ibáñez-Mejía, Juan C., E-mail: mordecai@amnh.org, E-mail: burkert@usm.lmu.de, E-mail: ibanez@ph1.uni-koeln.de

A large fraction of the gas in the Galaxy is cold, dense, and molecular. If all this gas collapsed under the influence of gravity and formed stars in a local free-fall time, the star formation rate in the Galaxy would exceed that observed by more than an order of magnitude. Other star-forming galaxies behave similarly. Yet, observations and simulations both suggest that the molecular gas is indeed gravitationally collapsing, albeit hierarchically. Prompt stellar feedback offers a potential solution to the low observed star formation rate if it quickly disrupts star-forming clouds during gravitational collapse. However, this requires that molecular cloudsmore » must be short-lived objects, raising the question of how so much gas can be observed in the molecular phase. This can occur only if molecular clouds form as quickly as they are destroyed, maintaining a global equilibrium fraction of dense gas. We therefore examine cloud formation timescales. We first demonstrate that supernova and superbubble sweeping cannot produce dense gas at the rate required to match the cloud destruction rate. On the other hand, Toomre gravitational instability can reach the required production rate. We thus argue that, although dense, star-forming gas may last only around a single global free-fall time; the dense gas in star-forming galaxies can globally exist in a state of dynamic equilibrium between formation by gravitational instability and disruption by stellar feedback. At redshift z ≳ 2, the Toomre instability timescale decreases, resulting in a prediction of higher molecular gas fractions at early times, in agreement with the observations.« less

Shocking Changes to Molecular Clouds

NASA Astrophysics Data System (ADS)

Melnick, Gary J.

1998-05-01

Supersonic motions are commonly observed in molecular clouds as evidenced by larger-than-thermal line widths measured in most species. The shocks that ensue can profoundly effect these clouds, not only dynamically, but chemically. Because shocks compress and heat the gas, chemical reactions that are extremely slow at typical molecular cloud temperatures (T ~ 10-30 K) can proceed rapidly in the wake of a shock. In many cases, compositional changes brought on by a passing shock can endure long after the gas has cooled and returned to its pre-shock state. We have used a coupled time-dependent chemical and dynamical model to investigate the lifetime of such chemical relics in the wake of non-dissociative shocks. Using a Monte Carlo cloud simulation, we explore the effects of stochastic shock activity on molecular gas over a cloud lifetime. Particular attention is paid to the chemistry of H_2O and O_2, two molecules which are predicted to have abundances that are significantly affected by shock-heated gas. Both pure gas-phase and gas-grain chemistry are considered. In agreement with previous studies, we find that shocks with velocities in excess of 10 km s(-1) can chemically process all oxygen not locked in CO into H_2O on timescales of a shock passage time ( ~ \\:few hundred years). For pure gas-phase models, the high water abundance lingers for ~ (4-7) x 10(5) yr, independent of the gas density. A density dependence for the lifetime of H_2O is found in gas-grain models as the water molecules deplete onto grains at the depletion timescale. We demonstrate that the time-averaged abundance of H_2O and O_2 (as well as other tracers, such as SiO and CH_3OH) is a sensitive function of the frequency of shocks. As such, the abundance of H_2O, and to a lesser extent O_2, can be used to trace the shock history in molecular clouds. Equally important, we find that depletion of shock-produced water onto grains can be quite large and is comparable to that observed in molecular

Star formation in evolving molecular clouds

NASA Astrophysics Data System (ADS)

Völschow, M.; Banerjee, R.; Körtgen, B.

2017-09-01

Molecular clouds are the principle stellar nurseries of our universe; they thus remain a focus of both observational and theoretical studies. From observations, some of the key properties of molecular clouds are well known but many questions regarding their evolution and star formation activity remain open. While numerical simulations feature a large number and complexity of involved physical processes, this plethora of effects may hide the fundamentals that determine the evolution of molecular clouds and enable the formation of stars. Purely analytical models, on the other hand, tend to suffer from rough approximations or a lack of completeness, limiting their predictive power. In this paper, we present a model that incorporates central concepts of astrophysics as well as reliable results from recent simulations of molecular clouds and their evolutionary paths. Based on that, we construct a self-consistent semi-analytical framework that describes the formation, evolution, and star formation activity of molecular clouds, including a number of feedback effects to account for the complex processes inside those objects. The final equation system is solved numerically but at much lower computational expense than, for example, hydrodynamical descriptions of comparable systems. The model presented in this paper agrees well with a broad range of observational results, showing that molecular cloud evolution can be understood as an interplay between accretion, global collapse, star formation, and stellar feedback.

Light-element nucleosynthesis in a molecular cloud interacting with a supernova remnant and the origin of beryllium-10 in the protosolar nebula

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tatischeff, Vincent; Duprat, Jean; De Séréville, Nicolas, E-mail: Vincent.Tatischeff@csnsm.in2p3.fr

The presence of short-lived radionuclides (t {sub 1/2} < 10 Myr) in the early solar system provides important information about the astrophysical environment in which the solar system formed. The discovery of now extinct {sup 10}Be (t {sub 1/2} = 1.4 Myr) in calcium-aluminum-rich inclusions (CAIs) with Fractionation and Unidentified Nuclear isotope anomalies (FUN-CAIs) suggests that a baseline concentration of {sup 10}Be in the early solar system was inherited from the protosolar molecular cloud. In this paper, we investigate various astrophysical contexts for the nonthermal nucleosynthesis of {sup 10}Be by cosmic-ray-induced reactions. We first show that the {sup 10}Be recordedmore » in FUN-CAIs cannot have been produced in situ by irradiation of the FUN-CAIs themselves. We then show that trapping of Galactic cosmic rays (GCRs) in the collapsing presolar cloud core induced a negligible {sup 10}Be contamination of the protosolar nebula, the inferred {sup 10}Be/{sup 9}Be ratio being at least 40 times lower than that recorded in FUN-CAIs ({sup 10}Be/{sup 9}Be ∼ 3 × 10{sup –4}). Irradiation of the presolar molecular cloud by background GCRs produced a steady-state {sup 10}Be/{sup 9}Be ratio ≲ 1.3 × 10{sup –4} at the time of the solar system formation, which suggests that the presolar cloud was irradiated by an additional source of CRs. Considering a detailed model for CR acceleration in a supernova remnant (SNR), we find that the {sup 10}Be abundance recorded in FUN-CAIs can be explained within two alternative scenarios: (1) the irradiation of a giant molecular cloud by CRs produced by ≳ 50 supernovae exploding in a superbubble of hot gas generated by a large star cluster of at least 20,000 members, and (2) the irradiation of the presolar molecular cloud by freshly accelerated CRs escaped from an isolated SNR at the end of the Sedov-Taylor phase. In the second picture, the SNR resulted from the explosion of a massive star that ran away from its parent OB

The giant molecular cloud Monoceros R2. 1: Shell structure

NASA Technical Reports Server (NTRS)

Xie, Taoling; Goldsmith, Paul F.

1994-01-01

We have obtained a 45 sec resolution, Nyquist-sampled map in CO J = 1-0 covering approximately a 3 deg x 3 deg region of the giant molecular cloud Monoceros R2. The map consists of 167,000 spectra observed with the 15 element focal-plane array system on the FCRAO 14 m telescope. The data reveal that the large-scale structure of Mon R2 is dominated by a is approximately 30 pc diameter largely hemispherical shell containing approximately 4 x 10(exp 4) solar mass of molecular material and expanding at approximately 3-4 km s(exp -1) with symmetric axis roughly along the line of sight. The dynamical timescale of the shell is estimated to be approximately 4 x 10(exp 6) yr, which is consistent with the age of main-sequence stars powering the clusters of reflection nebulea in this region. There is no evidence for a redshifted shell on the far side of the interior 'bubble,' which is largely devoid of molecular material. Distortions of the shell are obvious, suggesting inhomogeneity of the cloud and possible presence of a magnetic field prior to its formation. Dense clumps in Mon R2, including the main core and the GGD 12-15 core, appear to be condensations located on the large shell. The reflection nebulea with their illuminating stars as well as embedded IRAS sources suggest that triggered star formation has taken place over a large part of the Mon R2 shell.

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.

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.

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.

Sterculic Oil, a Natural SCD1 Inhibitor, Improves Glucose Tolerance in Obese ob/ob Mice

PubMed Central

Ortinau, Laura C.; Pickering, R. Taylor; Nickelson, Karen J.; Stromsdorfer, Kelly L.; Naik, Chaitasi Y.; Haynes, Rebecca A.; Bauman, Dale E.; Rector, R. Scott; Fritsche, Kevin L.; Perfield, James W.

2012-01-01

Obesity and its metabolic complications are associated with increased expression/activity of stearoyl-CoA desaturase-1 (SCD1), a major regulator of lipid metabolism. Reduction or ablation of this enzyme is associated with an improved metabolic profile and has gained attention as a target for pharmaceutical development. Sterculic oil (SO) is a known inhibitor of SCD1 and may provide a natural approach for treating obesity and/or insulin resistance. The purpose of this study was to evaluate the effects of SO consumption in leptin-deficient ob/ob mice, a model of obesity and insulin resistance. Five-week-old male mice received either an AIN-93G (control) or an AIN-93G diet containing 0.5% SO. After 9 weeks, SO supplementation did not alter food intake or body weight; however, the desaturase indices, a proxy of SCD1 activity, were reduced in liver and adipose tissue of SO-supplemented animals. This reduction was associated with improved glucose and insulin tolerance and attenuated hepatic inflammation in obese ob/ob mice, while no appreciable changes were observed in lean control mice receiving SO. Future studies are needed to better understand the mechanism(s) by which SO is functioning to improve glucose metabolism and to further explore the nutraceutical potential and health implications of SO supplementation. PMID:23209931

The star-forming content of the W3 giant molecular cloud

NASA Astrophysics Data System (ADS)

Moore, T. J. T.; Bretherton, D. E.; Fujiyoshi, T.; Ridge, N. A.; Allsopp, J.; Hoare, M. G.; Lumsden, S. L.; Richer, J. S.

2007-08-01

We have surveyed a ˜0.9 square degree area of the W3 giant molecular cloud (GMC) and star-forming region in the 850-μm continuum, using the Submillimetre Common-User Bolometer Array on the James Clerk Maxwell Telescope. A complete sample of 316 dense clumps were detected with a mass range from around 13 to 2500 M⊙. Part of the W3 GMC is subject to an interaction with the H ii region and fast stellar winds generated by the nearby W4 OB association. We find that the fraction of total gas mass in dense, 850-μm traced structures is significantly altered by this interaction, being around 5-13 per cent in the undisturbed cloud but ˜25-37 per cent in the feedback-affected region. The mass distribution in the detected clump sample depends somewhat on assumptions of dust temperature and is not a simple, single power law but contains significant structure at intermediate masses. This structure is likely to be due to crowding of sources near or below the spatial resolution of the observations. There is little evidence of any difference between the index of the high-mass end of the clump mass function in the compressed region and in the unaffected cloud. The consequences of these results are discussed in terms of current models of triggered star formation.

The Molecular Gas Environment in the 20 km s{sup −1} Cloud in the Central Molecular Zone

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Xing; Gu, Qiusheng; Zhang, Qizhou

We recently reported a population of protostellar candidates in the 20 km s{sup −1} cloud in the Central Molecular Zone of the Milky Way, traced by H{sub 2}O masers in gravitationally bound dense cores. In this paper, we report molecular line studies with high angular resolution (∼3″) of the environment of star formation in this cloud. Maps of various molecular line transitions as well as the continuum at 1.3 mm are obtained using the Submillimeter Array. Five NH{sub 3} inversion lines and the 1.3 cm continuum are observed with the Karl G. Jansky Very Large Array. The interferometric observations aremore » complemented with single-dish data. We find that the CH{sub 3}OH, SO, and HNCO lines, which are usually shock tracers, are better correlated spatially with the compact dust emission from dense cores among the detected lines. These lines also show enhancement in intensities with respect to SiO intensities toward the compact dust emission, suggesting the presence of slow shocks or hot cores in these regions. We find gas temperatures of ≳100 K at 0.1 pc scales based on RADEX modeling of the H{sub 2}CO and NH{sub 3} lines. Although no strong correlations between temperatures and linewidths/H{sub 2}O maser luminosities are found, in high-angular-resolution maps we note several candidate shock-heated regions offset from any dense cores, as well as signatures of localized heating by protostars in several dense cores. Our findings suggest that at 0.1 pc scales in this cloud star formation and strong turbulence may together affect the chemistry and temperature of the molecular gas.« less

Water in dense molecular clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wannier, P.G.; Kuiper, T.B.H.; Frerking, M.A.

1991-08-01

The G.P. Kuiper Airborne Observatory (KAO) was used to make initial observations of the half-millimeter ground-state transition of water in seven giant molecular clouds and in two late-type stars. No significant detections were made, and the resulting upper limits are significantly below those expected from other, indirect observations and from several theoretical models. The implied interstellar H2O/CO abundance is less than 0.003 in the cores of three giant molecular clouds. This value is less than expected from cloud chemistry models and also than estimates based on HDO and H3O(+) observations. 78 refs.

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.

Clustering the Orion B giant molecular cloud based on its molecular emission

PubMed Central

Bron, Emeric; Daudon, Chloé; Pety, Jérôme; Levrier, François; Gerin, Maryvonne; Gratier, Pierre; Orkisz, Jan H.; Guzman, Viviana; Bardeau, Sébastien; Goicoechea, Javier R.; Liszt, Harvey; Öberg, Karin; Peretto, Nicolas; Sievers, Albrecht; Tremblin, Pascal

2017-01-01

Context Previous attempts at segmenting molecular line maps of molecular clouds have focused on using position-position-velocity data cubes of a single molecular line to separate the spatial components of the cloud. In contrast, wide field spectral imaging over a large spectral bandwidth in the (sub)mm domain now allows one to combine multiple molecular tracers to understand the different physical and chemical phases that constitute giant molecular clouds (GMCs). Aims We aim at using multiple tracers (sensitive to different physical processes and conditions) to segment a molecular cloud into physically/chemically similar regions (rather than spatially connected components), thus disentangling the different physical/chemical phases present in the cloud. Methods We use a machine learning clustering method, namely the Meanshift algorithm, to cluster pixels with similar molecular emission, ignoring spatial information. Clusters are defined around each maximum of the multidimensional Probability Density Function (PDF) of the line integrated intensities. Simple radiative transfer models were used to interpret the astrophysical information uncovered by the clustering analysis. Results A clustering analysis based only on the J = 1 – 0 lines of three isotopologues of CO proves suffcient to reveal distinct density/column density regimes (nH ~ 100 cm−3, ~ 500 cm−3, and > 1000 cm−3), closely related to the usual definitions of diffuse, translucent and high-column-density regions. Adding two UV-sensitive tracers, the J = 1 − 0 line of HCO+ and the N = 1 − 0 line of CN, allows us to distinguish two clearly distinct chemical regimes, characteristic of UV-illuminated and UV-shielded gas. The UV-illuminated regime shows overbright HCO+ and CN emission, which we relate to a photochemical enrichment effect. We also find a tail of high CN/HCO+ intensity ratio in UV-illuminated regions. Finer distinctions in density classes (nH ~ 7 × 103 cm−3 ~ 4 × 104 cm−3) for the

Clustering the Orion B giant molecular cloud based on its molecular emission.

PubMed

Bron, Emeric; Daudon, Chloé; Pety, Jérôme; Levrier, François; Gerin, Maryvonne; Gratier, Pierre; Orkisz, Jan H; Guzman, Viviana; Bardeau, Sébastien; Goicoechea, Javier R; Liszt, Harvey; Öberg, Karin; Peretto, Nicolas; Sievers, Albrecht; Tremblin, Pascal

2018-02-01

Previous attempts at segmenting molecular line maps of molecular clouds have focused on using position-position-velocity data cubes of a single molecular line to separate the spatial components of the cloud. In contrast, wide field spectral imaging over a large spectral bandwidth in the (sub)mm domain now allows one to combine multiple molecular tracers to understand the different physical and chemical phases that constitute giant molecular clouds (GMCs). We aim at using multiple tracers (sensitive to different physical processes and conditions) to segment a molecular cloud into physically/chemically similar regions (rather than spatially connected components), thus disentangling the different physical/chemical phases present in the cloud. We use a machine learning clustering method, namely the Meanshift algorithm, to cluster pixels with similar molecular emission, ignoring spatial information. Clusters are defined around each maximum of the multidimensional Probability Density Function (PDF) of the line integrated intensities. Simple radiative transfer models were used to interpret the astrophysical information uncovered by the clustering analysis. A clustering analysis based only on the J = 1 - 0 lines of three isotopologues of CO proves suffcient to reveal distinct density/column density regimes ( n H ~ 100 cm -3 , ~ 500 cm -3 , and > 1000 cm -3 ), closely related to the usual definitions of diffuse, translucent and high-column-density regions. Adding two UV-sensitive tracers, the J = 1 - 0 line of HCO + and the N = 1 - 0 line of CN, allows us to distinguish two clearly distinct chemical regimes, characteristic of UV-illuminated and UV-shielded gas. The UV-illuminated regime shows overbright HCO + and CN emission, which we relate to a photochemical enrichment effect. We also find a tail of high CN/HCO + intensity ratio in UV-illuminated regions. Finer distinctions in density classes ( n H ~ 7 × 10 3 cm -3 ~ 4 × 10 4 cm -3 ) for the densest regions are also

Chromium (D-phenylalanine)3 improves obesity-induced cardiac contractile defect in ob/ob mice.

PubMed

Dong, Feng; Yang, Xiaoping; Sreejayan, Nair; Ren, Jun

2007-11-01

Low-molecular weight chromium compounds, such as chromium picolinate [Cr(pic)(3)], improve insulin sensitivity, although toxicity is a concern. We synthesized a novel chromium complex, chromium (d-phenylalanine)(3) [Cr(d-phe)(3)], in an attempt to improve insulin sensitivity with reduced toxicity. The aim of this study was to compare the two chromium compounds on cardiac contractile function in ob/ob obese mice. C57BL lean and ob/ob obese mice were randomly divided into three groups: H(2)O, Cr(d-phe)(3), or Cr(pic)(3) (45 mug/kg per day orally for 6 months). The glucose tolerance test displayed improved glucose clearance by Cr(d-phe)(3) but not Cr(pic)(3). Myocytes from ob/ob mice exhibited depressed peak shortening (PS) and maximal velocity of shortening/relengthening (+/-dL/dt), prolonged time-to-PS and time-to-90% relengthening (TR90), reduced electrically stimulated rise in intracellular Ca(2+) (Deltafura-2 fluorescence intensity), and slowed intracellular Ca(2+) decay. Although a 3-month Cr(d-phe)(3) treatment for a separate group of ob/ob and lean 2-month-old mice only rectified reduced +/-dL/dt in ob/ob mice, all mechanical and intracellular Ca(2+) abnormalities were significantly attenuated or ablated by 6 months of Cr(d-phe)(3) but not Cr(pic)(3) treatment (except TR90). Sarco(endo)plasmic reticulum Ca(2+) ATPase activity and Na(+)-Ca(2+) exchanger expression were depressed in ob/ob mice, which were reversed by both Cr(d-phe)(3) and Cr(pic)(3), with a more pronounced effect from Cr(d-phe)(3). Cr(d-phe)(3) corrected reduced insulin-stimulated glucose uptake and improved basal phosphorylation of Akt and insulin receptor, as well as insulin-stimulated phosphorylation of Akt and insulin receptor in ob/ob myocytes. Heart homogenates from ob/ob mice had enhanced oxidative stress and protein carbonyl formation compared with the lean group, which were attenuated by both Cr(d-phe)(3) and Cr(pic)(3). Our data suggest that the new Cr(d-phe)(3) compound possesses

[Cii] emission from L1630 in the Orion B molecular cloud.

PubMed

Pabst, C H M; Goicoechea, J R; Teyssier, D; Berné, O; Ochsendorf, B B; Wolfire, M G; Higgins, R D; Riquelme, D; Risacher, C; Pety, J; Le Petit, F; Roueff, E; Bron, E; Tielens, A G G M

2017-10-01

L1630 in the Orion B molecular cloud, which includes the iconic Horsehead Nebula, illuminated by the star system σ Ori, is an example of a photodissociation region (PDR). In PDRs, stellar radiation impinges on the surface of dense material, often a molecular cloud, thereby inducing a complex network of chemical reactions and physical processes. Observations toward L1630 allow us to study the interplay between stellar radiation and a molecular cloud under relatively benign conditions, that is, intermediate densities and an intermediate UV radiation field. Contrary to the well-studied Orion Molecular Cloud 1 (OMC1), which hosts much harsher conditions, L1630 has little star formation. Our goal is to relate the [Cii] fine-structure line emission to the physical conditions predominant in L1630 and compare it to studies of OMC1. The [Cii] 158 μ m line emission of L1630 around the Horsehead Nebula, an area of 12' × 17', was observed using the upgraded German Receiver for Astronomy at Terahertz Frequencies (upGREAT) onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). Of the [Cii] emission from the mapped area 95%, 13 L ⊙ , originates from the molecular cloud; the adjacent Hii region contributes only 5%, that is, 1 L ⊙ . From comparison with other data (CO(1-0)-line emission, far-infrared (FIR) continuum studies, emission from polycyclic aromatic hydrocarbons (PAHs)), we infer a gas density of the molecular cloud of n H ∼ 3 · 10 3 cm -3 , with surface layers, including the Horsehead Nebula, having a density of up to n H ∼ 4 · 10 4 cm -3 . The temperature of the surface gas is T ∼ 100 K. The average [Cii] cooling efficiency within the molecular cloud is 1.3 · 10 -2 . The fraction of the mass of the molecular cloud within the studied area that is traced by [Cii] is only 8%. Our PDR models are able to reproduce the FIR-[Cii] correlations and also the CO(1-0)-[Cii] correlations. Finally, we compare our results on the heating efficiency of the

[Cii] emission from L1630 in the Orion B molecular cloud

PubMed Central

Pabst, C. H. M.; Goicoechea, J. R.; Teyssier, D.; Berné, O.; Ochsendorf, B. B.; Wolfire, M. G.; Higgins, R. D.; Riquelme, D.; Risacher, C.; Pety, J.; Le Petit, F.; Roueff, E.; Bron, E.; Tielens, A. G. G. M.

2017-01-01

Context L1630 in the Orion B molecular cloud, which includes the iconic Horsehead Nebula, illuminated by the star system σ Ori, is an example of a photodissociation region (PDR). In PDRs, stellar radiation impinges on the surface of dense material, often a molecular cloud, thereby inducing a complex network of chemical reactions and physical processes. Aims Observations toward L1630 allow us to study the interplay between stellar radiation and a molecular cloud under relatively benign conditions, that is, intermediate densities and an intermediate UV radiation field. Contrary to the well-studied Orion Molecular Cloud 1 (OMC1), which hosts much harsher conditions, L1630 has little star formation. Our goal is to relate the [Cii] fine-structure line emission to the physical conditions predominant in L1630 and compare it to studies of OMC1. Methods The [Cii] 158 μm line emission of L1630 around the Horsehead Nebula, an area of 12′ × 17′, was observed using the upgraded German Receiver for Astronomy at Terahertz Frequencies (upGREAT) onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). Results Of the [Cii] emission from the mapped area 95%, 13 L⊙, originates from the molecular cloud; the adjacent Hii region contributes only 5%, that is, 1 L⊙. From comparison with other data (CO(1-0)-line emission, far-infrared (FIR) continuum studies, emission from polycyclic aromatic hydrocarbons (PAHs)), we infer a gas density of the molecular cloud of nH ∼ 3 · 103 cm−3, with surface layers, including the Horsehead Nebula, having a density of up to nH ∼ 4 · 104 cm−3. The temperature of the surface gas is T ∼ 100 K. The average [Cii] cooling efficiency within the molecular cloud is 1.3 · 10−2. The fraction of the mass of the molecular cloud within the studied area that is traced by [Cii] is only 8%. Our PDR models are able to reproduce the FIR-[Cii] correlations and also the CO(1-0)-[Cii] correlations. Finally, we compare our results on the

A model for the infrared emission from an OB star cluster environment

NASA Technical Reports Server (NTRS)

Leisawitz, D.

1991-01-01

A model for the infrared emission from the neighborhood of an OB star cluster is described. The distribution of gas and dust around the stars, properties of the dust, and the cluster and interstellar radiation fields are variable. The model can be applied to regions around clusters embedded to various degrees in their parental molecular clouds (i.e., compact H II regions, blister-type H II regions, and the tenuous H II regions ionized by naked O stars). The model is used to simulate IRAS observations of a typical blister H II region. Infrared surface brightness and spectral energy distributions are predicted and the impact of limited spatial resolution is illustrated. The model results are shown to be consistent with observations of the exemplary outer Galaxy OB cluster NGC 7380. It is planned to use the model as a diagnostic tool to probe the physical conditions and dust properties in star-formation regions and, ultimately, in an interpretation of the spectral energy distributions of spiral galaxies.

Structural anatomy of telomere OB proteins.

PubMed

Horvath, Martin P

2011-10-01

Telomere DNA-binding proteins protect the ends of chromosomes in eukaryotes. A subset of these proteins are constructed with one or more OB folds and bind with G+T-rich single-stranded DNA found at the extreme termini. The resulting DNA-OB protein complex interacts with other telomere components to coordinate critical telomere functions of DNA protection and DNA synthesis. While the first crystal and NMR structures readily explained protection of telomere ends, the picture of how single-stranded DNA becomes available to serve as primer and template for synthesis of new telomere DNA is only recently coming into focus. New structures of telomere OB fold proteins alongside insights from genetic and biochemical experiments have made significant contributions towards understanding how protein-binding OB proteins collaborate with DNA-binding OB proteins to recruit telomerase and DNA polymerase for telomere homeostasis. This review surveys telomere OB protein structures alongside highly comparable structures derived from replication protein A (RPA) components, with the goal of providing a molecular context for understanding telomere OB protein evolution and mechanism of action in protection and synthesis of telomere DNA.

OH 18 cm TRANSITION AS A THERMOMETER FOR MOLECULAR CLOUDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ebisawa, Yuji; Inokuma, Hiroshi; Yamamoto, Satoshi

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 frommore » 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.« less

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

MOLECULAR OXYGEN IN OORT CLOUD COMET 1P/HALLEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

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 bymore » 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.« less

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.

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.

Antisense protein tyrosine phosphatase 1B reverses activation of p38 mitogen-activated protein kinase in liver of ob/ob mice.

PubMed

Gum, Rebecca J; Gaede, Lori L; Heindel, Matthew A; Waring, Jeffrey F; Trevillyan, James M; Zinker, Bradley A; Stark, Margery E; Wilcox, Denise; Jirousek, Michael R; Rondinone, Cristina M; Ulrich, Roger G

2003-06-01

Phosphorylation of stress-activated kinase p38, a MAPK family member, was increased in liver of ob/ob diabetic mice relative to lean littermates. Treatment of ob/ob mice with protein tyrosine phosphatase 1B (PTP1B) antisense oligonucleotides (ASO) reduced phosphorylation of p38 in liver-to below lean littermate levels-and normalized plasma glucose while reducing plasma insulin. Phosphorylation of ERK, but not JNK, was also decreased in ASO-treated mice. PTP1B ASO decreased TNFalpha protein levels and phosphorylation of the transcription factor cAMP response element binding protein (CREB) in liver, both of which can occur through decreased phosphorylation of p38 and both of which have been implicated in insulin resistance or hyperglycemia. Decreased p38 phosphorylation was not directly due to decreased phosphorylation of the kinases that normally phosphorylate p38-MKK3 and MKK6. Additionally, p38 phosphorylation was not enhanced in liver upon insulin stimulation of ASO-treated ob/ob mice (despite increased activation of other signaling molecules) corroborating that p38 is not directly affected via the insulin receptor. Instead, decreased phosphorylation of p38 may be due to increased expression of MAPK phosphatases, particularly the p38/ERK phosphatase PAC1 (phosphatase of activated cells). This study demonstrates that reduction of PTP1B protein using ASO reduces activation of p38 and its substrates TNFalpha and CREB in liver of diabetic mice, which correlates with decreased hyperglycemia and hyperinsulinemia.

Turbulence and star formation in molecular clouds

NASA Astrophysics Data System (ADS)

Larson, R. B.

1981-03-01

Consideration is given to the turbulence properties of molecular clouds and their implications for star formation. Data for 54 molecular clouds and condensations is presented which reveals cloud velocity dispersion and region size to follow a power-law relation, similar to the Kolmogoroff law for subsonic turbulence. Examination of the dynamics of the molecular clouds for which mass determinations are available reveals essentially all of them to be gravitationally bound, and to approximately satisfy the virial theorem. The observation of moderate scatter in the dispersion-size relation is noted to imply that most regions have not collapsed much since formation, suggesting that processes of turbulent hydrodynamics have played an important role in producing the observed substructures. A lower limit to the size of subcondensations at which their internal motions are no longer supersonic is shown to predict a minimum protostellar mass on the order of a few tenths of a solar mass, while massive protostellar clumps are found to develop complex internal structures, probably leading to the formation of prestellar condensation nuclei. The observed turbulence of molecular clouds is noted to imply lifetimes of less than 10 million years.

Completing the Mapping of the W3 Giant Molecular Cloud; Testing Models and the Importance of Triggered Star Formation

NASA Astrophysics Data System (ADS)

Moore, Toby; Allsopp, James; Jones, Huw

2006-05-01

It is proposed to complete the R. Gehrz's mapping of W3 at both IRAC and MIPS 24um wavelengths. W3 is an outer galaxy Giant Molecular Cloud comprising of two regions; a quiescent, spontaneously star forming region and a region compressed by the W4 OB association containing the majority of star formation and all of the high mass star formation. Currently only the high-density region, Lada( put date) is mapped, but for a scientifically-valid comparision between the triggered and spontaneous modes we require the remainder of the cloud to be mapped. Triggered star formation is vitally important as it provides a mechanism for understanding the massive disparity between the low star formation efficiencies of galaxies such as our own andmore violent events such as galaxy mergers. Currently we have mapped the majority of the cloud at 850 um using SCUBA and the whole cloud using the CO(J=1-0) with the 12CO, 13CO and C18O isotomers. From these studies we have identified and measured the masses of 230 clumps. Without Spitzer data we have no way of determining which of these clumps have formed stars. This project forms the final crucial piece which when added to our current observations of the mass in the cloud will quantify the local star formation efficiency for each region. This is the first part of an ongoing much larger study into triggered star formation. We used Aztec (1.1mm continuum) on the JCMT in January 2006 to map two more clouds and Spitzer data on these from other observers has either been recently released or is about to be. In 2007, we will expand on the knowledge gained from this with the SCUBA2 JCMT Galactic Plane Survey (JPS) in which we are collaborators.

Structural anatomy of telomere OB proteins

PubMed Central

Horvath, Martin P.

2015-01-01

Telomere DNA-binding proteins protect the ends of chromosomes in eukaryotes. A subset of these proteins are constructed with one or more OB folds and bind with G+T-rich single-stranded DNA found at the extreme termini. The resulting DNA-OB protein complex interacts with other telomere components to coordinate critical telomere functions of DNA protection and DNA synthesis. While the first crystal and NMR structures readily explained protection of telomere ends, the picture of how single-stranded DNA becomes available to serve as primer and template for synthesis of new telomere DNA is only recently coming into focus. New structures of telomere OB fold proteins alongside insights from genetic and biochemical experiments have made significant contributions towards understanding how protein-binding OB proteins collaborate with DNA-binding OB proteins to recruit telomerase and DNA polymerase for telomere homeostasis. This review surveys telomere OB protein structures alongside highly comparable structures derived from replication protein A (RPA) components, with the goal of providing a molecular context for understanding telomere OB protein evolution and mechanism of action in protection and synthesis of telomere DNA. PMID:21950380

Emodin, an 11β-hydroxysteroid dehydrogenase type 1 inhibitor, regulates adipocyte function in vitro and exerts anti-diabetic effect in ob/ob mice

PubMed Central

Wang, Yue-jing; Huang, Su-ling; Feng, Ying; Ning, Meng-meng; Leng, Ying

2012-01-01

Aim: Emodin (1,3,8-trihydroxy-6-methylanthraquinone) is a potent and selective inhibitor of 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) with the ability to ameliorate metabolic disorders in diet-induced obese mice. In the present study, we investigated the effects of emodin on adipocyte function and the underlying mechanisms in vitro, and its anti-diabetic effects in ob/ob mice. Methods: 3T3-L1 adipocytes were used for in vitro studies. 11β-HSD1A activity was evaluated with a scintillation proximity assay. The adipogenesis, glucose uptake, lipolysis and adiponectin secretion were investigated in 3T3-L1 adipocytes treated with emodin in the presence of active (corticosterone) or inactive glucocorticoid (11-dehydrocorticosterone). For in vivo studies, ob/ob mice were administered emodin (25 and 50 mg·kg−1·d−1, ip) for 26 d. On the last day of administration, the serum was collected and the mesenteric and perirenal fat were dissected for analyses. Results: Emodin inhibited the 11β-HSD1 activity in 3T3-L1 adipocytes in concentration- and time-dependent manners (the IC50 values were 7.237 and 4.204 μmol/L, respectively, after 1 and 24 h treatment. In 3T3-L1 adipocytes, emodin (30 μmol/L) suppressed 11-dehydrocorticosterone-induced adipogenesis without affecting corticosterone-induced adipogenesis; emodin (3 μmol/L) reduced 11-dehydrocorticosterone-stimulated lipolysis, but had no effect on corticosterone-induced lipolysis. Moreover, emodin (3 μmol/L) partly reversed the impaired insulin-stimulated glucose uptake and adiponectin secretion induced by 11-dehydrocorticosterone but not those induced by corticosterone. In ob/ob mice, long-term emodin administration decreased 11β-HSD1 activity in mesenteric adipose tissues, lowered non-fasting and fasting blood glucose levels, and improved glucose tolerance. Conclusion: Emodin improves the inactive glucocorticoid-induced adipose tissue dysfunction by selective inhibition on 11β-HSD1 in adipocyte in vitro

A Catalog of Molecular Clouds in the Milky Way Galaxy

NASA Astrophysics Data System (ADS)

Wahl, Matthew; Koda, J.

2010-01-01

We have created a complete catalog of molecular clouds in the Milky Way Galaxy. This is an extension of our previous study (Koda et al. 2006) which used a preliminary data set from The Boston University Five College Radio Astronomy Observatory Galactic Ring Survey (BUFCRAO GRS). This work is of the complete data set from this GRS. The data covers the inner part of the northern Galactic disk between galactic longitudes 15 to 56 degrees, galactic latitudes -1.1 to 1.1 degrees, and the entire Galactic velocities. We used the standard cloud identification method. This method searches the data cube for a peak in temperature above a specified value, and then searches around that peak in all directions until the extents of the cloud are found. This method is iterated until all clouds are found. We prefer this method over other methods, because of its simplicity. The properties of our molecular clouds are very similar to those based on a more evolved method (Rathborne et al. 2009).

RCW 36 in the Vela Molecular Ridge: Evidence for high-mass star-cluster formation triggered by cloud-cloud collision

NASA Astrophysics Data System (ADS)

Sano, Hidetoshi; Enokiya, Rei; Hayashi, Katsuhiro; Yamagishi, Mitsuyoshi; Saeki, Shun; Okawa, Kazuki; Tsuge, Kisetsu; Tsutsumi, Daichi; Kohno, Mikito; Hattori, Yusuke; Yoshiike, Satoshi; Fujita, Shinji; Nishimura, Atsushi; Ohama, Akio; Tachihara, Kengo; Torii, Kazufumi; Hasegawa, Yutaka; Kimura, Kimihiro; Ogawa, Hideo; Wong, Graeme F.; Braiding, Catherine; Rowell, Gavin; Burton, Michael G.; Fukui, Yasuo

2018-02-01

A collision between two molecular clouds is one possible candidate for high-mass star formation. The H II region RCW 36, located in the Vela molecular ridge, contains a young star cluster (˜ 1 Myr old) and two O-type stars. We present new CO observations of RCW 36 made with NANTEN2, Mopra, and ASTE using 12CO(J = 1-0, 2-1, 3-2) and 13CO(J = 2-1) emission lines. We have discovered two molecular clouds lying at the velocities VLSR ˜ 5.5 and 9 km s-1. Both clouds are likely to be physically associated with the star cluster, as verified by the good spatial correspondence among the two clouds, infrared filaments, and the star cluster. We also found a high intensity ratio of ˜ 0.6-1.2 for CO J = 3-2/1-0 toward both clouds, indicating that the gas temperature has been increased due to heating by the O-type stars. We propose that the O-type stars in RCW 36 were formed by a collision between the two clouds, with a relative velocity separation of 5 km s-1. The complementary spatial distributions and the velocity separation of the two clouds are in good agreement with observational signatures expected for O-type star formation triggered by a cloud-cloud collision. We also found a displacement between the complementary spatial distributions of the two clouds, which we estimate to be 0.3 pc assuming the collision angle to be 45° relative to the line-of-sight. We estimate the collision timescale to be ˜ 105 yr. It is probable that the cluster age found by Ellerbroek et al. (2013b, A&A, 558, A102) is dominated by the low-mass members which were not formed under the triggering by cloud-cloud collision, and that the O-type stars in the center of the cluster are explained by the collisional triggering independently from the low-mass star formation.

RCW 36 in the Vela Molecular Ridge: Evidence for high-mass star-cluster formation triggered by cloud-cloud collision

NASA Astrophysics Data System (ADS)

Sano, Hidetoshi; Enokiya, Rei; Hayashi, Katsuhiro; Yamagishi, Mitsuyoshi; Saeki, Shun; Okawa, Kazuki; Tsuge, Kisetsu; Tsutsumi, Daichi; Kohno, Mikito; Hattori, Yusuke; Yoshiike, Satoshi; Fujita, Shinji; Nishimura, Atsushi; Ohama, Akio; Tachihara, Kengo; Torii, Kazufumi; Hasegawa, Yutaka; Kimura, Kimihiro; Ogawa, Hideo; Wong, Graeme F.; Braiding, Catherine; Rowell, Gavin; Burton, Michael G.; Fukui, Yasuo

2018-05-01

A collision between two molecular clouds is one possible candidate for high-mass star formation. The H II region RCW 36, located in the Vela molecular ridge, contains a young star cluster (˜ 1 Myr old) and two O-type stars. We present new CO observations of RCW 36 made with NANTEN2, Mopra, and ASTE using 12CO(J = 1-0, 2-1, 3-2) and 13CO(J = 2-1) emission lines. We have discovered two molecular clouds lying at the velocities VLSR ˜ 5.5 and 9 km s-1. Both clouds are likely to be physically associated with the star cluster, as verified by the good spatial correspondence among the two clouds, infrared filaments, and the star cluster. We also found a high intensity ratio of ˜ 0.6-1.2 for CO J = 3-2/1-0 toward both clouds, indicating that the gas temperature has been increased due to heating by the O-type stars. We propose that the O-type stars in RCW 36 were formed by a collision between the two clouds, with a relative velocity separation of 5 km s-1. The complementary spatial distributions and the velocity separation of the two clouds are in good agreement with observational signatures expected for O-type star formation triggered by a cloud-cloud collision. We also found a displacement between the complementary spatial distributions of the two clouds, which we estimate to be 0.3 pc assuming the collision angle to be 45° relative to the line-of-sight. We estimate the collision timescale to be ˜ 105 yr. It is probable that the cluster age found by Ellerbroek et al. (2013b, A&A, 558, A102) is dominated by the low-mass members which were not formed under the triggering by cloud-cloud collision, and that the O-type stars in the center of the cluster are explained by the collisional triggering independently from the low-mass star formation.

Variation of z-height of the molecular clouds on the Galactic Plane

NASA Astrophysics Data System (ADS)

Lee, Y.; Stark, A. A.

2002-12-01

Using the Bell Laboratories Galactic plane in the J=1-0 transition of 13CO, (l, b) = (-5o to 117o, -1o to +1o), and cloud identification code, 13CO clouds have been identified and cataloged as a function of threshold temperature. Distance estimates to the identified clouds have been made with several criteria. Minimum and maximum distances to each identified cloud are determined from a set of all the possible distances of a cloud. Several physical parameters can be determined with distances, such as z-height [D sin (b)], CO luminosity, virial mass and so forth. We select the clouds with a ratio of maximum and minimum of CO luminosities less than 3. The number of selected clouds is 281 out of 1400 identified clouds with 1 K threshold temperature. These clouds are mostly located on the tangential positions in the inner Galaxy, and some are in the Outer Galaxy. It is found that the z-height of lower luminosity clouds (less massive clouds) is systimatically larger than that of high-luminosity clouds (more massive clouds). We claim that this is the first observational evidence of the z-height variation depending on the luminosities (or masses) of molecular clouds on the Galactic plane. Our results could be a basis explaining the formation mechanism of massive clouds, such as giant molecular clouds.

[C II] emission from L1630 in the Orion B molecular cloud

NASA Astrophysics Data System (ADS)

Pabst, C. H. M.; Goicoechea, J. R.; Teyssier, D.; Berné, O.; Ochsendorf, B. B.; Wolfire, M. G.; Higgins, R. D.; Riquelme, D.; Risacher, C.; Pety, J.; Le Petit, F.; Roueff, E.; Bron, E.; Tielens, A. G. G. M.

2017-10-01

Context. L1630 in the Orion B molecular cloud, which includes the iconic Horsehead Nebula, illuminated by the star system σ Ori, is an example of a photodissociation region (PDR). In PDRs, stellar radiation impinges on the surface of dense material, often a molecular cloud, thereby inducing a complex network of chemical reactions and physical processes. Aims: Observations toward L1630 allow us to study the interplay between stellar radiation and a molecular cloud under relatively benign conditions, that is, intermediate densities and an intermediate UV radiation field. Contrary to the well-studied Orion Molecular Cloud 1 (OMC1), which hosts much harsher conditions, L1630 has little star formation. Our goal is to relate the [C II] fine-structure line emission to the physical conditions predominant in L1630 and compare it to studies of OMC1. Methods: The [C II] 158 μm line emission of L1630 around the Horsehead Nebula, an area of 12' × 17', was observed using the upgraded German Receiver for Astronomy at Terahertz Frequencies (upGREAT) onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). Results: Of the [C II] emission from the mapped area 95%, 13 L⊙, originates from the molecular cloud; the adjacent H II region contributes only 5%, that is, 1 L⊙. From comparison with other data (CO (1 - 0)-line emission, far-infrared (FIR) continuum studies, emission from polycyclic aromatic hydrocarbons (PAHs)), we infer a gas density of the molecular cloud of nH 3 × 103 cm-3, with surface layers, including the Horsehead Nebula, having a density of up to nH 4 × 104 cm-3. The temperature of the surface gas is T 100 K. The average [C II] cooling efficiency within the molecular cloud is 1.3 × 10-2. The fraction of the mass of the molecular cloud within the studied area that is traced by [C II] is only 8%. Our PDR models are able to reproduce the FIR-[C II] correlations and also the CO (1 - 0)-[C II] correlations. Finally, we compare our results on the

Featured Image: A Molecular Cloud Outside Our Galaxy

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2018-06-01

What do molecular clouds look like outside of our own galaxy? See for yourself in the images above and below of N55, a molecular cloud located in the Large Magellanic Cloud (LMC). In a recent study led by Naslim Neelamkodan (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan), a team of scientists explore N55 to determine how its cloud properties differ from clouds within the Milky Way. The image above reveals the distribution of infrared-emitting gas and dust observed in three bands by the Spitzer Space Telescope. Overplotted in cyan are observations from the Atacama Submillimeter Telescope Experiment tracing the clumpy, warm molecular gas. Below, new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) reveal the sub-parsec-scale molecular clumps in greater detail, showing the correlation of massive clumps with Spitzer-identified young stellar objects (crosses). The study presented here indicates that this cloud in the LMC is the site of massive star formation, with properties similar to equivalent clouds in the Milky Way. To learn more about the authors findings, check out the article linked below.CitationNaslim N. et al 2018 ApJ 853 175. doi:10.3847/1538-4357/aaa5b0

Thermogenesis, fatty acid synthesis with oxidation, and inflammation in the brown adipose tissue of ob/ob (-/-) mice.

PubMed

Martins, Fabiane Ferreira; Bargut, Thereza Cristina Lonzetti; Aguila, Marcia Barbosa; Mandarim-de-Lacerda, Carlos Alberto

2017-03-01

Brown adipose tissue (BAT) is specialized in heat production, but its metabolism in ob/ob mice is still a matter of debate. We aimed to verify ob/ob mice BAT using C57Bl/6 male mice (as the wild-type, WT) and leptin-deficient ob/ob mice (on the C57Bl/6 background strain), at three months of age (n=10/group). At euthanasia, animals had their interscapular BAT weighed, and prepared for analysis (Western blot, and RT-qPCR). In comparison with the WT group, the ob/ob group showed reduced thermogenic signaling markers (gene expression of beta 3-adrenergic receptor, beta3-AR; PPARgamma coactivator 1 alpha, PGC1alpha, and uncoupling protein 1, UCP1). The ob/ob group also showed impaired gene expression for lipid utilization (perilipin was increased, while other markers were diminished: carnitine palmitoyltransferase-1b, CPT-1b; cluster of differentiation 36, CD36; fatty acid binding protein 4, FABP4; fatty acid synthase, FAS, and sterol regulatory element-binding protein 1c, SREBP1c), and altered protein expression of insulin signaling (diminished pAKT, TC10, and GLUT-4). Lastly, the ob/ob group showed increased gene expression of markers of inflammation (interleukin 1 beta, IL-1beta; IL-6, tumor necrosis factor alpha, TNFalpha; and monocyte chemotactic protein-1, MCP-1). In conclusion, the ob/ob mice have decreased thermogenic markers associated with reduced gene expression related to fatty acid synthesis, mobilization, and oxidation. There were also alterations in insulin signaling and protein and gene expressions of inflammation. The findings suggest that the lack of substrate for thermogenesis and the local inflammation negatively regulated thermogenic signaling in the ob/ob mice. Copyright © 2016 Elsevier GmbH. All rights reserved.

Clustering the Orion B giant molecular cloud based on its molecular emission

NASA Astrophysics Data System (ADS)

Bron, Emeric; Daudon, Chloé; Pety, Jérôme; Levrier, François; Gerin, Maryvonne; Gratier, Pierre; Orkisz, Jan H.; Guzman, Viviana; Bardeau, Sébastien; Goicoechea, Javier R.; Liszt, Harvey; Öberg, Karin; Peretto, Nicolas; Sievers, Albrecht; Tremblin, Pascal

2018-02-01

Context. Previous attempts at segmenting molecular line maps of molecular clouds have focused on using position-position-velocity data cubes of a single molecular line to separate the spatial components of the cloud. In contrast, wide field spectral imaging over a large spectral bandwidth in the (sub)mm domain now allows one to combine multiple molecular tracers to understand the different physical and chemical phases that constitute giant molecular clouds (GMCs). Aims: We aim at using multiple tracers (sensitive to different physical processes and conditions) to segment a molecular cloud into physically/chemically similar regions (rather than spatially connected components), thus disentangling the different physical/chemical phases present in the cloud. Methods: We use a machine learning clustering method, namely the Meanshift algorithm, to cluster pixels with similar molecular emission, ignoring spatial information. Clusters are defined around each maximum of the multidimensional probability density function (PDF) of the line integrated intensities. Simple radiative transfer models were used to interpret the astrophysical information uncovered by the clustering analysis. Results: A clustering analysis based only on the J = 1-0 lines of three isotopologues of CO proves sufficient to reveal distinct density/column density regimes (nH 100 cm-3, 500 cm-3, and >1000 cm-3), closely related to the usual definitions of diffuse, translucent and high-column-density regions. Adding two UV-sensitive tracers, the J = 1-0 line of HCO+ and the N = 1-0 line of CN, allows us to distinguish two clearly distinct chemical regimes, characteristic of UV-illuminated and UV-shielded gas. The UV-illuminated regime shows overbright HCO+ and CN emission, which we relate to a photochemical enrichment effect. We also find a tail of high CN/HCO+ intensity ratio in UV-illuminated regions. Finer distinctions in density classes (nH 7 × 103 cm-3, 4 × 104 cm-3) for the densest regions are also

Peripheral nervous system insulin resistance in ob/ob mice

PubMed Central

2013-01-01

Background A reduction in peripheral nervous system (PNS) insulin signaling is a proposed mechanism that may contribute to sensory neuron dysfunction and diabetic neuropathy. Neuronal insulin resistance is associated with several neurological disorders and recent evidence has indicated that dorsal root ganglion (DRG) neurons in primary culture display altered insulin signaling, yet in vivo results are lacking. Here, experiments were performed to test the hypothesis that the PNS of insulin-resistant mice displays altered insulin signal transduction in vivo. For these studies, nondiabetic control and type 2 diabetic ob/ob mice were challenged with an intrathecal injection of insulin or insulin-like growth factor 1 (IGF-1) and downstream signaling was evaluated in the DRG and sciatic nerve using Western blot analysis. Results The results indicate that insulin signaling abnormalities documented in other “insulin sensitive” tissues (i.e. muscle, fat, liver) of ob/ob mice are also present in the PNS. A robust increase in Akt activation was observed with insulin and IGF-1 stimulation in nondiabetic mice in both the sciatic nerve and DRG; however this response was blunted in both tissues from ob/ob mice. The results also suggest that upregulated JNK activation and reduced insulin receptor expression could be contributory mechanisms of PNS insulin resistance within sensory neurons. Conclusions These findings contribute to the growing body of evidence that alterations in insulin signaling occur in the PNS and may be a key factor in the pathogenesis of diabetic neuropathy. PMID:24252636

Dust scattering from the Taurus Molecular Cloud

NASA Astrophysics Data System (ADS)

Narayan, Sathya; Murthy, Jayant; Karuppath, Narayanankutty

2017-04-01

We present an analysis of the diffuse ultraviolet emission near the Taurus Molecular Cloud based on observations made by the Galaxy Evolution Explorer. We used a Monte Carlo dust scattering model to show that about half of the scattered flux originates in the molecular cloud with 25 per cent arising in the foreground and 25 per cent behind the cloud. The best-fitting albedo of the dust grains is 0.3, but the geometry is such that we could not constrain the phase function asymmetry factor (g).

H2, CO, and dust absorption through cold molecular clouds

NASA Astrophysics Data System (ADS)

Lacy, John H.; Sneden, Chris; Kim, Hwihyun; Jaffe, Daniel Thomas

2017-06-01

We have made observations with IGRINS on the Harlan J. Smith telescope at McDonald Observatory of near-infrared absorption by H2, CO, and dust toward stars behind molecular clouds, primarily the TMC. Prior to these observations, the abundance of H2 in molecular clouds, relative to the commonly used tracer CO, had only been measured toward a few embedded stars, which may be surrounded by atypical gas. The new observations provide a representative sample of these molecules in cold molecular gas. We find N(H2)/Av ~ 0.9e+21, N(CO)/Av ~ 1.6e+17, and H2/CO ~ 6000. The measured H2/CO ratio is consistent with that measured toward embedded stars in various molecular clouds, but half that derived from mm-wave observations of CO emission and star counts or other determinations of Av.

Properties and rotation of molecular clouds in M 33

NASA Astrophysics Data System (ADS)

Braine, J.; Rosolowsky, E.; Gratier, P.; Corbelli, E.; Schuster, K.-F.

2018-04-01

The sample of 566 molecular clouds identified in the CO(2-1) IRAM survey covering the disk of M 33 is explored in detail. The clouds were found using CPROPS and were subsequently catalogued in terms of their star-forming properties as non-star-forming (A), with embedded star formation (B), or with exposed star formation (C, e.g., presence of Hα emission). We find that the size-linewidth relation among the M 33 clouds is quite weak but, when comparing with clouds in other nearby galaxies, the linewidth scales with average metallicity. The linewidth and particularly the line brightness decrease with galactocentric distance. The large number of clouds makes it possible to calculate well-sampled cloud mass spectra and mass spectra of subsamples. As noted earlier, but considerably better defined here, the mass spectrum steepens (i.e., higher fraction of small clouds) with galactocentric distance. A new finding is that the mass spectrum of A clouds is much steeper than that of the star-forming clouds. Further dividing the sample, this difference is strong at both large and small galactocentric distances and the A vs. C difference is a stronger effect than the inner vs. outer disk difference in mass spectra. Velocity gradients are identified in the clouds using standard techniques. The gradients are weak and are dominated by prograde rotation; the effect is stronger for the high signal-to-noise clouds. A discussion of the uncertainties is presented. The angular momenta are low but compatible with at least some simulations. Finally, the cloud velocity gradients are compared with the gradient of disk rotation. The cloud and galactic gradients are similar; the cloud rotation periods are much longer than cloud lifetimes and comparable to the galactic rotation period. The rotational kinetic energy is 1-2% of the gravitational potential energy and the cloud edge velocity is well below the escape velocity, such that cloud-scale rotation probably has little influence on the

Molecular clouds toward three Spitzer bubbles S116, S117, and S118: Evidence for a cloud-cloud collision which formed the three H II regions and a 10 pc scale molecular cavity

NASA Astrophysics Data System (ADS)

Fukui, Yasuo; Ohama, Akio; Kohno, Mikito; Torii, Kazufumi; Fujita, Shinji; Hattori, Yusuke; Nishimura, Atsushi; Yamamoto, Hiroaki; Tachihara, Kengo

2018-05-01

We carried out a molecular-line study toward the three Spitzer bubbles S116, S117, and S118, which show active formation of high-mass stars. We found molecular gas consisting of two components with a velocity difference of ˜5 km s-1. One of them, the small cloud, has a typical velocity of -63 km s-1 and the other, the large cloud, has one of -58 km s-1. The large cloud has a nearly circular intensity depression, the size of which is similar to that of the small cloud. We present an interpretation that its cavity was created by a collision between the two clouds and that this collision compressed the gas into a dense layer elongating along the western rim of the small cloud. In this scenario, the O stars including those in the three Spitzer bubbles were formed in the interface layer compressed by the collision. Assuming that the relative motion of the clouds has a tilt of 45° to the line of sight, we estimate that the collision continued for the last 1 Myr at a relative velocity of ˜10 km s-1. In the S116-S117-S118 system the H II regions are located outside of the cavity. This morphology is ascribed to the density-bound distribution of the large cloud which caused the H II regions to expand more easily toward the outer part of the large cloud than towards the inside of the cavity. The present case proves that a cloud-cloud collision creates a cavity without the action of O-star feedback, and suggests that the collision-compressed layer is highly filamentary.

Role of estrogen receptor signaling in skeletal response to leptin in female ob/ob mice.

PubMed

Turner, Russell T; Philbrick, Kenneth A; Kuah, Amida F; Branscum, Adam J; Iwaniec, Urszula T

2017-06-01

Leptin, critical in regulation of energy metabolism, is also important for normal bone growth, maturation and turnover. Compared to wild type (WT) mice, bone mass is lower in leptin-deficient ob/ob mice. Osteopenia in growing ob/ob mice is due to decreased bone accrual, and is associated with reduced longitudinal bone growth, impaired cancellous bone maturation and increased marrow adipose tissue (MAT). However, leptin deficiency also results in gonadal dysfunction, disrupting production of gonadal hormones which regulate bone growth and turnover. The present study evaluated the role of increased estrogen in mediating the effects of leptin on bone in ob/ob mice. Three-month-old female ob/ob mice were randomized into one of the 3 groups: (1) ob/ob  + vehicle (veh), (2) ob/ob  + leptin (leptin) or (3) ob/ob  + leptin and the potent estrogen receptor antagonist ICI 182,780 (leptin + ICI). Age-matched WT mice received vehicle. Leptin (40 µg/mouse, daily) and ICI (10 µg/mouse, 2×/week) were administered by subcutaneous injection for 1 month and bone analyzed by X-ray absorptiometry, microcomputed tomography and static and dynamic histomorphometry. Uterine weight did not differ between ob/ob mice and ob/ob mice receiving leptin + ICI, indicating that ICI successfully blocked the uterine response to leptin-induced increases in estrogen levels. Compared to leptin-treated ob/ob mice, ob/ob mice receiving leptin + ICI had lower uterine weight; did not differ in weight loss, MAT or bone formation rate; and had higher longitudinal bone growth rate and cancellous bone volume fraction. We conclude that increased estrogen signaling following leptin treatment is dispensable for the positive actions of leptin on bone and may attenuate leptin-induced bone growth. © 2017 Society for Endocrinology.

Submillimeter Array {sup 12}CO (2-1) Imaging of the NGC 6946 Giant Molecular Clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Ya-Lin; Sakamoto, Kazushi; Pan, Hsi-An, E-mail: yalinwu@email.arizona.edu

2017-04-10

We present a {sup 12}CO (2–1) mosaic map of the spiral galaxy NGC 6946 by combining data from the Submillimeter Array and the IRAM 30 m telescope. We identify 390 giant molecular clouds (GMCs) from the nucleus to 4.5 kpc in the disk. GMCs in the inner 1 kpc are generally more luminous and turbulent, some of which have luminosities >10{sup 6} K km s{sup −1} pc{sup 2} and velocity dispersions >10 km s{sup −1}. Large-scale bar-driven dynamics likely regulate GMC properties in the nuclear region. Similar to the Milky Way and other disk galaxies, GMC mass function of NGCmore » 6946 has a shallower slope (index > −2) in the inner region, and a steeper slope (index < −2) in the outer region. This difference in mass spectra may be indicative of different cloud formation pathways: gravitational instabilities might play a major role in the nuclear region, while cloud coalescence might be dominant in the outer disk. Finally, the NGC 6946 clouds are similar to those in M33 in terms of statistical properties, but they are generally less luminous and turbulent than the M51 clouds.« less

Characterising the Structure of Molecular Clouds

NASA Astrophysics Data System (ADS)

Wong, Graeme Francis

The Interstellar Medium contains the building blocks of matter in our Galaxy and plays a vital role in the evolution of low mass star formation. The poorly studied molecular clouds of Lupus and Chamaeleon contain ongoing low mass star formation, and are in close proximity to our Solar System. While on the other hand the Carina molecular cloud, poorly observed in radio wavelength, is an active region of star formation and host some of the brightest stars known within our Galaxy. Using tracers like carbon monoxide, atomic neutral carbon, and ammonia, we are able to measure the temperature and density of the gas cloud. This information allows us to understand the initial conditions of the formation of low mass stars. Observations conducted with the 22-m Mopra radio telescope (located at the edge of the Warrumbungle Mountains near Coonabarabran), in the Carbon monoxide (CO) isotopologues 12 CO, 13 CO, C17O, and C18O (1-0) transitions, have mapped the Chamaeleon II cloud, an intermediate mass cloud within the Chamaeleon. Through the sub-arcminute maps, comparisons have been made to previous low resolution (2.5') maps which have been to resolve some of the dense clumps previously identified. Optical depth, column density, and excitation temperature derived from the CO maps, are consistent with previous results. A detailed comparison between identified C18O clumps have shown the different conditions occurring within the clumps, some of which contain or are located near a population of young stellar objects. The Northern region of the Carina Nebular Complex, was observed with NANTEN2, a 4-m radio telescope (located in the Chilean Atacama desert), in the 12CO (4-3) and [C I] 3P1-3P0 emission lines. Previous observations towards this region has either been at poor resolution or had limited coverage. The presented observations, strike a balance between the two; observing in sub-arcmin resolution (0.6') and with an area of 0.9° X 0.5° mapped. Excitation temperature of the 12

Effect of leptin administration on myelination in ob/ob mouse cerebrum after birth.

PubMed

Hashimoto, Ryuju; Matsumoto, Akihiro; Udagawa, Jun; Hioki, Kyoji; Otani, Hiroki

2013-01-09

Brain weight and size are known to be reduced in adult leptin-deficient Lep/Lep (OB) mice when compared with the wild-type (+/+) mice (C57BL/6: B6). We here analyzed leptin's effects on myelination by examining morphometrically the myelin sheath (MS) in the cerebrum of postnatal day (P) 14 and P28 OB that had received leptin 1 nmol/capita/day from P7 to P14 or P28 (OB+lep), in comparison with OB and B6. We examined myelin basic protein (MBP) mRNA levels and the differentiation of oligodendrocytes by comparing the number of oligodendrocyte precursor cells (OPCs) and the mature oligodendrocytes in the cerebrum between OB, OB+lep, and B6 on P14 and P28. MBP-mRNA expression was lower in OB than in B6 on P14 and P28. On P14, it was higher in OB+lep than in OB but was still lower than in B6, whereas on P28 it was even higher in OB+lep than in B6. On P28, the radii of myelinated axons were larger in OB than in B6 and OB+lep. The MS on P28 was significantly thinner in OB than in B6, but there was no significant difference between OB and OB+lep. There were significantly fewer mature oligodendrocytes in OB and OB+lep than in B6 on P28, whereas on P14 there were significantly fewer OPCs in OB and OB+lep than in B6. Our results suggested that leptin regulates the myelination of oligodendrocytes and that the replenishment of leptin in OB recovered myelination but did not affect the differentiation of OPCs from P7 to P28.

Young star clusters in nearby molecular clouds

NASA Astrophysics Data System (ADS)

Getman, K. V.; Kuhn, M. A.; Feigelson, E. D.; Broos, P. S.; Bate, M. R.; Garmire, G. P.

2018-06-01

The SFiNCs (Star Formation in Nearby Clouds) project is an X-ray/infrared study of the young stellar populations in 22 star-forming regions with distances ≲ 1 kpc designed to extend our earlier MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray) survey of more distant clusters. Our central goal is to give empirical constraints on cluster formation mechanisms. Using parametric mixture models applied homogeneously to the catalogue of SFiNCs young stars, we identify 52 SFiNCs clusters and 19 unclustered stellar structures. The procedure gives cluster properties including location, population, morphology, association with molecular clouds, absorption, age (AgeJX), and infrared spectral energy distribution (SED) slope. Absorption, SED slope, and AgeJX are age indicators. SFiNCs clusters are examined individually, and collectively with MYStIX clusters, to give the following results. (1) SFiNCs is dominated by smaller, younger, and more heavily obscured clusters than MYStIX. (2) SFiNCs cloud-associated clusters have the high ellipticities aligned with their host molecular filaments indicating morphology inherited from their parental clouds. (3) The effect of cluster expansion is evident from the radius-age, radius-absorption, and radius-SED correlations. Core radii increase dramatically from ˜0.08 to ˜0.9 pc over the age range 1-3.5 Myr. Inferred gas removal time-scales are longer than 1 Myr. (4) Rich, spatially distributed stellar populations are present in SFiNCs clouds representing early generations of star formation. An appendix compares the performance of the mixture models and non-parametric minimum spanning tree to identify clusters. This work is a foundation for future SFiNCs/MYStIX studies including disc longevity, age gradients, and dynamical modelling.

Photoionization-regulated star formation and the structure of molecular clouds

NASA Technical Reports Server (NTRS)

Mckee, Christopher F.

1989-01-01

A model for the rate of low-mass star formation in Galactic molecular clouds and for the influence of this star formation on the structure and evolution of the clouds is presented. The rate of energy injection by newly formed stars is estimated, and the effect of this energy injection on the size of the cloud is determined. It is shown that the observed rate of star formation appears adequate to support the observed clouds against gravitational collapse. The rate of photoionization-regulated star formation is estimated and it is shown to be in agreement with estimates of the observed rate of star formation if the observed molecular cloud parameters are used. The mean cloud extinction and the Galactic star formation rate per unit mass of molecular gas are predicted theoretically from the condition that photionization-regulated star formation be in equilibrium. A simple model for the evolution of isolated molecular clouds is developed.

Sirtuin-2 Regulates Sepsis Inflammation in ob/ob Mice

PubMed Central

Wang, Xianfeng; Buechler, Nancy L.; Martin, Ayana; Wells, Jonathan; Yoza, Barbara; McCall, Charles E.; Vachharajani, Vidula

2016-01-01

Objective Obesity increases morbidity and resource utilization in sepsis patients. Sepsis transitions from early/hyper-inflammatory to late/hypo-inflammatory phase. Majority of sepsis-mortality occurs during the late sepsis; no therapies exist to treat late sepsis. In lean mice, we have shown that sirtuins (SIRTs) modulate this transition. Here, we investigated the role of sirtuins, especially the adipose-tissue abundant SIRT-2 on transition from early to late sepsis in obese with sepsis. Methods Sepsis was induced using cecal ligation and puncture (CLP) in ob/ob mice. We measured microvascular inflammation in response to lipopolysaccharide/normal saline re-stimulation as a “second-hit” (marker of immune function) at different time points to track phases of sepsis in ob/ob mice. We determined SIRT-2 expression during different phases of sepsis. We studied the effect of SIRT-2 inhibition during the hypo-inflammatory phase on immune function and 7-day survival. We used a RAW264.7 (RAW) cell model of sepsis for mechanistic studies. We confirmed key findings in diet induced obese (DIO) mice with sepsis. Results We observed that the ob/ob-septic mice showed an enhanced early inflammation and a persistent and prolonged hypo-inflammatory phase when compared to WT mice. Unlike WT mice that showed increased SIRT1 expression, we found that SIRT2 levels were increased in ob/ob mice during hypo-inflammation. SIRT-2 inhibition in ob/ob mice during the hypo-inflammatory phase of sepsis reversed the repressed microvascular inflammation in vivo via activation of endothelial cells and circulating leukocytes and significantly improved survival. We confirmed the key finding of the role of SIRT2 during hypo-inflammatory phase of sepsis in this project in DIO-sepsis mice. Mechanistically, in the sepsis cell model, SIRT-2 expression modulated inflammatory response by deacetylation of NFκBp65. Conclusion SIRT-2 regulates microvascular inflammation in obese mice with sepsis and may

Molecular clouds in the extreme outer galaxy

NASA Technical Reports Server (NTRS)

Digel, S.; De Geus, E.; Thaddeus, P.

1994-01-01

We present observation of 11 molecular clouds with kinematic Galactocentric distances of 18-28 kpc. The most distant is approximately 10 kpc farther from the Galactic center than any previously known and apparently lies beyond the edge of the optical disk. All are associated with much larger H I concentrations, with typical offsets of approximately 40 pc from the H I peaks. CO observations with the CfA 1.2 m and National Radio Astronomy Observatory (NRAO) 12 m telescopes indicate typical sizes of 20-40 pc, velocity widths of 1-3 km/s, and kinetic temperatures of 10-25 K. They apparently have lower CO luminosities than clouds near the solar circle with similar properties. Some may have associated infrared sources, but owing to the great distances of the clouds, the only general conclusion that can be made about star formation is that stars earlier than B1 are absent. The apparent scarcity of clouds like these indicates that their contribution to the mass of the ISM beyond R = 18 kpc is not significant.

H2 emission as a tracer of molecular hydrogen: Large-scale observations of Orion

NASA Technical Reports Server (NTRS)

Luhman, M. L.; Jaffe, D. T.; Keller, L. D.; Pak, Soojong

1994-01-01

We have detected extremely extended (greater than 1.5 deg, or 12 pc) near-infrared H2 line emission from the Orion A molecular cloud. We have mapped emission in the 1.601 micrometer(s) upsilon = 6 - 4 Q(1) and 2.121 micrometer(s) upsilon = 1 - 0 S(1) lines of H2 along a approx. 2 deg R.A. cut and from a 6' x 6' region near theta(sup 1) Ori C. The surface brightness of the extended H2 line emission is 10(exp -6) to 10(exp -5) ergs/s/sq. cm/sr. Based on the distribution and relative strengths of the H2 lines, we conclude that UV fluorescene is most likely the dominant H2 emission mechanism in the outer parts of the Orion cloud. Shock-heated gas does not make a major contribution to the H2 emission in this region. The fluorescent component of the total H2 upsilon = 1 - 0 S(1) luminosity from Orion is 30-40 solar luminosity. Molecular hydrogen excited by UV radiation from nearby OB stars contributes 98%-99% of the global H2 line emission from the Orion molecular cloud, even though this cloud has a powerful shock-excited H2 source in its core. The ability to detect large-scale H2 directly opens up new possibilities for the study of molecular clouds.

The Monoceros R2 Molecular Cloud

NASA Astrophysics Data System (ADS)

Carpenter, J. M.; Hodapp, K. W.

2008-12-01

The Monoceros R2 region was first recognized as a chain of reflection nebulae illuminated by A- and B-type stars. These nebulae are associated with a giant molecular cloud that is one of the closest massive star forming regions to the Sun. This chapter reviews the properties of the Mon R2 region, including the namesake reflection nebulae, the large scale molecula= r cloud, global star formation activity, and properties of prominent star forming regions in the cloud.

Cool Star Beginnings: YSOs in the Perseus Molecular Cloud

NASA Astrophysics Data System (ADS)

Young, Kaisa E.; Young, Chadwick H.

2015-01-01

Nearby molecular clouds, where there is considerable evidence of ongoing star formation, provide the best opportunity to observe stars in the earliest stages of their formation. The Perseus molecular cloud contains two young clusters, IC 348 and NGC 1333 and several small dense cores of the type that produce only a few stars. Perseus is often cited as an intermediate case between quiescent low-mass and turbulent high-mass clouds, making it perhaps an ideal environment for studying ``typical low-mass star formation. We present an infrared study of the Perseus molecular cloud with data from the Spitzer Space Telescope as part of the ``From Molecular Cores to Planet Forming Disks (c2d) Legacy project tep{eva03}. By comparing Spitzer's near- and mid-infrared maps, we identify and classify the young stellar objects (YSOs) in the cloud using updated extinction corrected photometry. Virtually all of the YSOs in Perseus are forming in the clusters and other smaller associations at the east and west ends of the cloud with very little evidence of star formation in the midsection even in areas of high extinction.

NOEMA Observations of a Molecular Cloud in the Low-metallicity Galaxy Kiso 5639

NASA Astrophysics Data System (ADS)

Elmegreen, Bruce G.; Herrera, Cinthya; Rubio, Monica; Elmegreen, Debra Meloy; Sánchez Almeida, Jorge; Muñoz-Tuñón, Casiana; Olmo-García, Amanda

2018-06-01

A giant star-forming region in a metal-poor dwarf galaxy has been observed in optical lines with the 10 m Gran Telescopio Canarias (GTC) and in the emission line of CO(1–0) with the Northern Extended Millimeter Array (NOEMA) mm-wave interferometer. The metallicity was determined to be 12+{log}({{O}}/{{H}})=7.83+/- 0.09, from which we estimate a conversion factor of α CO ∼ 100 M ⊙ pc‑2(K km s‑1)‑1 and a molecular cloud mass of ∼2.9 × 107 M ⊙. This is an enormous concentration of molecular mass at one end of a small galaxy, suggesting a recent accretion. The molecular cloud properties seem normal: the surface density, 120 M ⊙ pc‑2, is comparable to that of a standard giant molecular cloud; the cloud’s virial ratio of ∼1.8 is in the star formation range; and the gas consumption time, 0.5 Gyr, at the present star formation rate is typical for molecular regions. The low metallicity implies that the cloud has an average visual extinction of only 0.8 mag, which is close to the threshold for molecule formation. With such an extinction threshold, molecular clouds in metal-poor regions should have high surface densities and high internal pressures. If high pressure is associated with the formation of massive clusters, then metal-poor galaxies such as dwarfs in the early universe could have been the hosts of metal-poor globular clusters.

Squeezed between shells? The origin of the Lupus I molecular cloud. II. APEX CO and GASS H I observations

NASA Astrophysics Data System (ADS)

Gaczkowski, B.; Roccatagliata, V.; Flaischlen, S.; Kröll, D.; Krause, M. G. H.; Burkert, A.; Diehl, R.; Fierlinger, K.; Ngoumou, J.; Preibisch, T.

2017-12-01

Context. Lupus I cloud is found between the Upper Scorpius (USco) and Upper Centaurus-Lupus (UCL) subgroups of the Scorpius-Centaurus OB association, where the expanding USco H I shell appears to interact with a bubble currently driven by the winds of the remaining B stars of UCL. Aims: We investigate whether the Lupus I molecular could have formed in a colliding flow, and in particular, how the kinematics of the cloud might have been influenced by the larger scale gas dynamics. Methods: We performed APEX 13CO(2-1)and C18O(2-1) line observations of three distinct parts of Lupus I that provide kinematic information on the cloud at high angular and spectral resolution. We compare those results to the atomic hydrogen data from the GASS H I survey and our dust emission results presented in the previous paper. Based on the velocity information, we present a geometric model for the interaction zone between the USco shell and the UCL wind bubble. Results: We present evidence that the molecular gas of Lupus Iis tightly linked to the atomic material of the USco shell. The CO emission in Lupus Iis found mainly at velocities between vLSR = 3-6 km s-1, which is in the same range as the H I velocities. Thus, the molecular cloud is co-moving with the expanding USco atomic H I shell. The gas in the cloud shows a complex kinematic structure with several line-of-sight components that overlay each other. The nonthermal velocity dispersion is in the transonic regime in all parts of the cloud and could be injected by external compression. Our observations and the derived geometric model agree with a scenario in which Lupus Iis located in the interaction zone between the USco shell and the UCL wind bubble. Conclusions: The kinematics observations are consistent with a scenario in which the Lupus Icloud formed via shell instabilities. The particular location of Lupus I between USco and UCL suggests that counterpressure from the UCL wind bubble and pre-existing density enhancements

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.

Resolved Giant Molecular Clouds in Nearby Spiral Galaxies: Insights from the CANON CO (1-0) Survey

NASA Astrophysics Data System (ADS)

Donovan Meyer, Jennifer; Koda, Jin; Momose, Rieko; Mooney, Thomas; Egusa, Fumi; Carty, Misty; Kennicutt, Robert; Kuno, Nario; Rebolledo, David; Sawada, Tsuyoshi; Scoville, Nick; Wong, Tony

2013-08-01

We resolve 182 individual giant molecular clouds (GMCs) larger than 2.5 × 105 M ⊙ in the inner disks of 5 large nearby spiral galaxies (NGC 2403, NGC 3031, NGC 4736, NGC 4826, and NGC 6946) to create the largest such sample of extragalactic GMCs within galaxies analogous to the Milky Way. Using a conservatively chosen sample of GMCs most likely to adhere to the virial assumption, we measure cloud sizes, velocity dispersions, and 12CO (J = 1-0) luminosities and calculate cloud virial masses. The average conversion factor from CO flux to H2 mass (or X CO) for each galaxy is 1-2 × 1020 cm-2 (K km s-1)-1, all within a factor of two of the Milky Way disk value (~2 × 1020 cm-2 (K km s-1)-1). We find GMCs to be generally consistent within our errors between the galaxies and with Milky Way disk GMCs; the intrinsic scatter between clouds is of order a factor of two. Consistent with previous studies in the Local Group, we find a linear relationship between cloud virial mass and CO luminosity, supporting the assumption that the clouds in this GMC sample are gravitationally bound. We do not detect a significant population of GMCs with elevated velocity dispersions for their sizes, as has been detected in the Galactic center. Though the range of metallicities probed in this study is narrow, the average conversion factors of these galaxies will serve to anchor the high metallicity end of metallicity-X CO trends measured using conversion factors in resolved clouds; this has been previously possible primarily with Milky Way measurements.

CO abundance variations in the Orion Molecular Cloud

NASA Astrophysics Data System (ADS)

Ripple, F.; Heyer, M. H.; Gutermuth, R.; Snell, R. L.; Brunt, C. M.

2013-05-01

Infrared stellar photometry from the Two Micron All-Sky Survey (2MASS) and spectral line imaging observations of 12CO and 13CO J = 1-0 line emission from the Five College Radio Astronomy Observatory (FCRAO) 14-m telescope are analysed to assess the variation of the CO abundance with physical conditions throughout the Orion A and Orion B molecular clouds. Three distinct Av regimes are identified in which the ratio between the 13CO column density and visual extinction changes corresponding to the photon-dominated envelope, the strongly self-shielded interior, and the cold, dense volumes of the clouds. Within the strongly self-shielded interior of the Orion A cloud, the 13CO abundance varies by 100 per cent with a peak value located near regions of enhanced star formation activity. The effect of CO depletion on to the ice mantles of dust grains is limited to regions with Av > 10 mag and gas temperatures less than ˜20 K as predicted by chemical models that consider thermal evaporation to desorb molecules from grain surfaces. Values of the molecular mass of each cloud are independently derived from the distributions of Av and 13CO column densities with a constant 13CO-to-H2 abundance over various extinction ranges. Within the strongly self-shielded interior of the cloud (Av> 3 mag), 13CO provides a reliable tracer of H2 mass with the exception of the cold, dense volumes where depletion is important. However, owing to its reduced abundance, 13CO does not trace the H2 mass that resides in the extended cloud envelope, which comprises 40-50 per cent of the molecular mass of each cloud. The implied CO luminosity to mass ratios, M/LCO, are 3.2 and 2.9 for Orion A and Orion B, respectively, which are comparable to the value (2.9), derived from γ-ray observations of the Orion region. Our results emphasize the need to consider local conditions when applying CO observations to derive H2 column densities.

Star formation induced by cloud-cloud collisions and galactic giant molecular cloud evolution

NASA Astrophysics Data System (ADS)

Kobayashi, Masato I. N.; Kobayashi, Hiroshi; Inutsuka, Shu-ichiro; Fukui, Yasuo

2018-05-01

Recent millimeter/submillimeter observations towards nearby galaxies have started to map the whole disk and to identify giant molecular clouds (GMCs) even in the regions between galactic spiral structures. Observed variations of GMC mass functions in different galactic environments indicates that massive GMCs preferentially reside along galactic spiral structures whereas inter-arm regions have many small GMCs. Based on the phase transition dynamics from magnetized warm neutral medium to molecular clouds, Kobayashi et al. (2017, ApJ, 836, 175) proposes a semi-analytical evolutionary description for GMC mass functions including a cloud-cloud collision (CCC) process. Their results show that CCC is less dominant in shaping the mass function of GMCs than the accretion of dense H I gas driven by the propagation of supersonic shock waves. However, their formulation does not take into account the possible enhancement of star formation by CCC. Millimeter/submillimeter observations within the Milky Way indicate the importance of CCC in the formation of star clusters and massive stars. In this article, we reformulate the time-evolution equation largely modified from Kobayashi et al. (2017, ApJ, 836, 175) so that we additionally compute star formation subsequently taking place in CCC clouds. Our results suggest that, although CCC events between smaller clouds are more frequent than the ones between massive GMCs, CCC-driven star formation is mostly driven by massive GMCs ≳ 10^{5.5} M_{⊙} (where M⊙ is the solar mass). The resultant cumulative CCC-driven star formation may amount to a few 10 percent of the total star formation in the Milky Way and nearby galaxies.

Star formation history of Canis Major OB1. II. A bimodal X-ray population revealed by XMM-Newton

NASA Astrophysics Data System (ADS)

Santos-Silva, T.; Gregorio-Hetem, J.; Montmerle, T.; Fernandes, B.; Stelzer, B.

2018-02-01

Aims: The Canis Major OB1 Association has an intriguing scenario of star formation, especially in the region called Canis Major R1 (CMa R1) traditionally assigned to a reflection nebula, but in reality an ionized region. This work is focussed on the young stellar population associated with CMa R1, for which our previous results from ROSAT, optical, and near-infrared data had revealed two stellar groups with different ages, suggesting a possible mixing of populations originated from distinct star formation episodes. Methods: The X-ray data allow the detected sources to be characterized according to hardness ratios, light curves, and spectra. Estimates of mass and age were obtained from the 2MASS catalogue and used to define a complete subsample of stellar counterparts for statistical purposes. Results: A catalogue of 387 XMM-Newton sources is provided, of which 78% are confirmed as members or probable members of the CMa R1 association. Flares (or similar events) were observed for 13 sources and the spectra of 21 bright sources could be fitted by a thermal plasma model. Mean values of fits parameters were used to estimate X-ray luminosities. We found a minimum value of log(LX [erg/s] ) = 29.43, indicating that our sample of low-mass stars (M⋆ ≤ 0.5 M⊙), which are faint X-ray emitters, is incomplete. Among the 250 objects selected as our complete subsample (defining our "best sample"), 171 are found to the east of the cloud, near Z CMa and dense molecular gas, of which 50% of them are young (<5 Myr) and 30% are older (>10 Myr). The opposite happens to the west, near GU CMa, in areas lacking molecular gas: among 79 objects, 30% are young and 50% are older. These findings confirm that a first episode of distributed star formation occurred in the whole studied region 10 Myr ago and dispersed the molecular gas, while a second, localized episode (<5 Myr) took place in the regions where molecular gas is still present.

NEAR INFRARED DIFFUSE INTERSTELLAR BANDS TOWARD THE CYGNUS OB2 ASSOCIATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamano, Satoshi; Kondo, Sohei; Sameshima, Hiroaki

2016-04-10

We obtained the near-infrared (NIR) high-resolution (R ≡ λ/Δλ ∼ 20,000) spectra of the seven brightest early-type stars in the Cygnus OB2 association for investigating the environmental dependence of diffuse interstellar bands (DIBs). The WINERED spectrograph mounted on the Araki 1.3 m telescope in Japan was used to collect data. All 20 of the known DIBs within the wavelength coverage of WINERED (0.91 < λ < 1.36 μm) were clearly detected along all lines of sight because of their high flux density in the NIR wavelength range and the large extinction. The equivalent widths (EWs) of DIBs were not correlated with the column densities of C{sub 2} molecules,more » which trace the patchy dense component, suggesting that the NIR DIB carriers are distributed mainly in the diffuse component. On the basis of the correlations among the NIR DIBs both for stars in Cyg OB2 and stars observed previously, λλ10780, 10792, 11797, 12623, and 13175 are found to constitute a “family,” in which the DIBs are correlated well over the wide EW range. In contrast, the EW of λ10504 is found to remain almost constant over the stars in Cyg OB2. The extinction estimated from the average EW of λ10504 (A{sub V} ∼ 3.6 mag) roughly corresponds to the lower limit of the extinction distribution of OB stars in Cyg OB2. This suggests that λ10504 is absorbed only by the foreground clouds, implying that the carrier of λ10504 is completely destroyed in Cyg OB2, probably by the strong UV radiation field. The different behaviors of the DIBs may be caused by different properties of the DIB carriers.« less

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

PubMed

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

2016-09-08

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 H 2 vibrational emission (delineating the H/H 2 transition) and the edge of the observed CO and HCO + emission. This implies that the H/H 2 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.

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.

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. Copyright © 2013 Elsevier Inc. All rights reserved.

RESOLVED GIANT MOLECULAR CLOUDS IN NEARBY SPIRAL GALAXIES: INSIGHTS FROM THE CANON CO (1-0) SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Donovan Meyer, Jennifer; Koda, Jin; Mooney, Thomas

We resolve 182 individual giant molecular clouds (GMCs) larger than 2.5 Multiplication-Sign 10{sup 5} M{sub Sun} in the inner disks of 5 large nearby spiral galaxies (NGC 2403, NGC 3031, NGC 4736, NGC 4826, and NGC 6946) to create the largest such sample of extragalactic GMCs within galaxies analogous to the Milky Way. Using a conservatively chosen sample of GMCs most likely to adhere to the virial assumption, we measure cloud sizes, velocity dispersions, and {sup 12}CO (J = 1-0) luminosities and calculate cloud virial masses. The average conversion factor from CO flux to H{sub 2} mass (or X{sub CO})more » for each galaxy is 1-2 Multiplication-Sign 10{sup 20} cm{sup -2} (K km s{sup -1}){sup -1}, all within a factor of two of the Milky Way disk value ({approx}2 Multiplication-Sign 10{sup 20} cm{sup -2} (K km s{sup -1}){sup -1}). We find GMCs to be generally consistent within our errors between the galaxies and with Milky Way disk GMCs; the intrinsic scatter between clouds is of order a factor of two. Consistent with previous studies in the Local Group, we find a linear relationship between cloud virial mass and CO luminosity, supporting the assumption that the clouds in this GMC sample are gravitationally bound. We do not detect a significant population of GMCs with elevated velocity dispersions for their sizes, as has been detected in the Galactic center. Though the range of metallicities probed in this study is narrow, the average conversion factors of these galaxies will serve to anchor the high metallicity end of metallicity-X{sub CO} trends measured using conversion factors in resolved clouds; this has been previously possible primarily with Milky Way measurements.« less

Two Molecular Clouds near M17

NASA Astrophysics Data System (ADS)

Wilson, T. L.; Hanson, M. M.; Muders, D.

2003-06-01

We present fully sampled images in the C18O J=2-1 line extending over 13'×23', made with the Heinrich Hertz Telescope (HHT) on Mount Graham, AZ. The HHT has a resolution of 35" at the line frequency. This region includes two molecular clouds. Cloud A, to the north, is more compact, while cloud B is to the west of the H II region M17. Cloud B contains the well-known source M17SW. In C18O we find 13 maxima in cloud A and 39 in cloud B. Sixteen sources in cloud B are in M17SW, mapped previously with higher resolution. In cloud B, sources outside M17SW have line widths comparable to those in M17SW. In comparison, cloud A has lower C18O line intensities and smaller line widths but comparable densities and sizes. Maps of the cores of these clouds were also obtained in the J=5-4 line of CS, which traces higher H2 densities. Our images of the cores of clouds A and B show that for VLSR<=20 km s-1, the peaks of the CS emission are shifted closer to the H II region than the C18O maxima, so higher densities are found toward the H II region. Our CS data give additional support to the already strong evidence that M17SW and nearby regions are heated and compressed by the H II region. Our data show that cloud A has a smaller interaction with the H II region. We surmise that M17SW was an initially denser region, and the turn-on of the H II region will make this the next region of massive star formation. Outside of M17SW, the only other obvious star formation region may be in cloud A, since there is an intense millimeter dust continuum peak found by Henning et al. (1998) but no corresponding C18O maximum. If the CO/H2 ratio is constant, the dust must have a temperature of ~100 K or the H2 density is greater than 106 cm-3 or both to reconcile the C18O and dust data. Alternatively, if the CO/H2 ratio is low, perhaps much of the CO is depleted.

IRAM 30 m large scale survey of {sup 12}CO(2-1) and {sup 13}CO(2-1) emission in the Orion molecular cloud

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berné, O.; Cernicharo, J.; Marcelino, N., E-mail: olivier.berne@irap.omp.eu

2014-11-01

Using the IRAM 30 m telescope, we have surveyed a 1 × 0.°8 part of the Orion molecular cloud in the {sup 12}CO and {sup 13}CO (2-1) lines with a maximal spatial resolution of ∼11'' and spectral resolution of ∼0.4 km s{sup –1}. The cloud appears filamentary, clumpy, and with a complex kinematical structure. We derive an estimated mass of the cloud of 7700 M {sub ☉} (half of which is found in regions with visual extinctions A{sub V} below ∼10) and a dynamical age for the nebula of the order of 0.2 Myr. The energy balance suggests that magneticmore » fields play an important role in supporting the cloud, at large and small scales. According to our analysis, the turbulent kinetic energy in the molecular gas due to outflows is comparable to turbulent kinetic energy resulting from the interaction of the cloud with the H II region. This latter feedback appears negative, i.e., the triggering of star formation by the H II region is inefficient in Orion. The reduced data as well as additional products such as the column density map are made available online (http://userpages.irap.omp.eu/∼oberne/Olivier{sub B}erne/Data).« less

Kinematics of OB-associations in Gaia epoch

NASA Astrophysics Data System (ADS)

Mel'nik, A. M.; Dambis, A. K.

2017-12-01

We use stellar proper motions from the Tycho-Gaia Astrometric Solution (TGAS) catalogue to study the kinematics of OB-associations. The TGAS proper motions of OB-associations generally agree well with the Hipparcos proper motions. The parameters of the Galactic rotation curve obtained with TGAS and Hipparcos proper motions agree within the errors. The average one-dimensional velocity dispersion inside 18 OB-associations with more than 10 TGAS stars is σv = 3.9 km s-1, which is considerably smaller, by a factor of 0.4, than the velocity dispersions derived from Hipparcos data. The effective contribution from orbital motions of binary OB-stars into the velocity dispersion σv inside OB-associations is σb = 1.2 km s-1. The median virial and stellar masses of OB-associations are equal to 7.1 × 105 and 9.0 × 103 M⊙, respectively. Thus, OB-associations must be unbound objects, provided they do not include a lot of dense gas. The median star-formation efficiency is ε = 2.1 per cent. Nearly one-third of stars of OB-associations must lie outside their tidal radius. We found that the Per OB1 and Car OB1 associations are expanding with the expansion started in a small region of 11-27 pc 7-10 Myr ago. The average expansion velocity is 6.3 km s-1.

Discovery of Molecular and Atomic Clouds Associated with the Magellanic Superbubble 30 Doradus C

NASA Astrophysics Data System (ADS)

Sano, H.; Yamane, Y.; Voisin, F.; Fujii, K.; Yoshiike, S.; Inaba, T.; Tsuge, K.; Babazaki, Y.; Mitsuishi, I.; Yang, R.; Aharonian, F.; Rowell, G.; Filipović, M. D.; Mizuno, N.; Tachihara, K.; Kawamura, A.; Onishi, T.; Fukui, Y.

2017-07-01

We analyzed the 2.6 mm CO and 21 cm H I lines toward the Magellanic superbubble 30 Doradus C, in order to reveal the associated molecular and atomic gas. We uncovered five molecular clouds in a velocity range from 251 to 276 km s-1 toward the western shell. The non-thermal X-rays are clearly enhanced around the molecular clouds on a parsec scale, suggesting possible evidence for magnetic field amplification via shock-cloud interaction. The thermal X-rays are brighter in the eastern shell, where there are no dense molecular or atomic clouds, opposite to the western shell. The TeV γ-ray distribution may spatially match the total interstellar proton column density as well as the non-thermal X-rays. If the hadronic γ-ray is dominant, the total energy of the cosmic-ray protons is at least ˜ 1.2× {10}50 erg with the estimated mean interstellar proton density ˜60 cm-3. In addition, the γ-ray flux associated with the molecular cloud (e.g., MC3) could be detected and resolved by the Cherenkov Telescope Array (CTA). This should permit CTA to probe the diffusion of cosmic-rays into the associated dense ISM.

Resolving the substructure of molecular clouds in the LMC

NASA Astrophysics Data System (ADS)

Wong, Tony; Hughes, Annie; Tokuda, Kazuki; Indebetouw, Remy; Wojciechowski, Evan; Bandurski, Jeffrey; MC3 Collaboration

2018-01-01

We present recent wide-field CO and 13CO mapping of giant molecular clouds in the Large Magellanic Cloud with ALMA. Our sample exhibits diverse star-formation properties, and reveals comparably diverse molecular cloud properties including surface density and velocity dispersion at a given scale. We first present the results of a recent study comparing two GMCs at the extreme ends of the star formation activity spectrum. Our quiescent cloud exhibits 10 times lower surface density and 5 times lower velocity dispersion than the active 30 Doradus cloud, yet in both clouds we find a wide range of line widths at the smallest resolved scales, spanning nearly the full range of line widths seen at all scales. This suggests an important role for feedback on sub-parsec scales, while the energetics on larger scales are dominated by clump-to-clump relative velocities. We then extend our analysis to four additional clouds that exhibit intermediate levels of star formation activity.

ALMA Reveals Molecular Cloud N55 in the Large Magellanic Cloud as a Site of Massive Star Formation

NASA Astrophysics Data System (ADS)

Naslim, N.; Tokuda, K.; Onishi, T.; Kemper, F.; Wong, T.; Morata, O.; Takada, S.; Harada, R.; Kawamura, A.; Saigo, K.; Indebetouw, R.; Madden, S. C.; Hony, S.; Meixner, M.

2018-02-01

We present the molecular cloud properties of N55 in the Large Magellanic Cloud using 12CO(1–0) and 13CO(1–0) observations obtained with Atacama Large Millimeter Array. We have done a detailed study of molecular gas properties, to understand how the cloud properties of N55 differ from Galactic clouds. Most CO emission appears clumpy in N55, and molecular cores that have young stellar objects (YSOs) show larger linewidths and masses. The massive clumps are associated with high and intermediate mass YSOs. The clump masses are determined by local thermodynamic equilibrium and virial analysis of the 12CO and 13CO emissions. These mass estimates lead to the conclusion that (a) the clumps are in self-gravitational virial equilibrium, and (b) the 12CO(1–0)-to-H2 conversion factor, {X}{CO}, is 6.5 × 1020 cm‑2 (K km s‑1)‑1. This CO-to-H2 conversion factor for N55 clumps is measured at a spatial scale of ∼0.67 pc, which is about two times higher than the {X}{CO} value of the Orion cloud at a similar spatial scale. The core mass function of N55 clearly show a turnover below 200 {M}ȯ , separating the low-mass end from the high-mass end. The low-mass end of the 12CO mass spectrum is fitted with a power law of index 0.5 ± 0.1, while for 13CO it is fitted with a power law index 0.6 ± 0.2. In the high-mass end, the core mass spectrum is fitted with a power index of 2.0 ± 0.3 for 12CO, and with 2.5 ± 0.4 for 13CO. This power law behavior of the core mass function in N55 is consistent with many Galactic clouds.

The simulation of molecular clouds formation in the Milky Way

NASA Astrophysics Data System (ADS)

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

2013-01-01

Using 3D hydrodynamic calculations we simulate formation of molecular clouds in the Galaxy. The simulations take into account molecular hydrogen chemical kinetics, cooling and heating processes. Comprehensive gravitational potential accounts for contributions from the stellar bulge, two- and four-armed spiral structure, stellar disc, dark halo and takes into account self-gravitation of the gaseous component. Gas clouds in our model form in the spiral arms due to shear and wiggle instabilities and turn into molecular clouds after t ≳ 100 Myr. At the times t ˜ 100-300 Myr the clouds form hierarchical structures and agglomerations with the sizes of 100 pc and greater. We analyse physical properties of the simulated clouds and find that synthetic statistical distributions like mass spectrum, `mass-size' relation and velocity dispersion are close to those observed in the Galaxy. The synthetic l-v (galactic longitude-radial velocity) diagram of the simulated molecular gas distribution resembles observed one and displays a structure with appearance similar to molecular ring of the Galaxy. Existence of this structure in our modelling can be explained by superposition of emission from the galactic bar and the spiral arms at ˜3-4 kpc.

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.

Helical magnetic fields in molecular clouds?. A new method to determine the line-of-sight magnetic field structure in molecular clouds

NASA Astrophysics Data System (ADS)

Tahani, M.; Plume, R.; Brown, J. C.; Kainulainen, J.

2018-06-01

Context. Magnetic fields pervade in the interstellar medium (ISM) and are believed to be important in the process of star formation, yet probing magnetic fields in star formation regions is challenging. Aims: We propose a new method to use Faraday rotation measurements in small-scale star forming regions to find the direction and magnitude of the component of magnetic field along the line of sight. We test the proposed method in four relatively nearby regions of Orion A, Orion B, Perseus, and California. Methods: We use rotation measure data from the literature. We adopt a simple approach based on relative measurements to estimate the rotation measure due to the molecular clouds over the Galactic contribution. We then use a chemical evolution code along with extinction maps of each cloud to find the electron column density of the molecular cloud at the position of each rotation measure data point. Combining the rotation measures produced by the molecular clouds and the electron column density, we calculate the line-of-sight magnetic field strength and direction. Results: In California and Orion A, we find clear evidence that the magnetic fields at one side of these filamentary structures are pointing towards us and are pointing away from us at the other side. Even though the magnetic fields in Perseus might seem to suggest the same behavior, not enough data points are available to draw such conclusions. In Orion B, as well, there are not enough data points available to detect such behavior. This magnetic field reversal is consistent with a helical magnetic field morphology. In the vicinity of available Zeeman measurements in OMC-1, OMC-B, and the dark cloud Barnard 1, we find magnetic field values of - 23 ± 38 μG, - 129 ± 28 μG, and 32 ± 101 μG, respectively, which are in agreement with the Zeeman measurements. Tables 1 to 7 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http

Molecular Cloud Structures and Massive Star Formation in N159

NASA Astrophysics Data System (ADS)

Nayak, O.; Meixner, M.; Fukui, Y.; Tachihara, K.; Onishi, T.; Saigo, K.; Tokuda, K.; Harada, R.

2018-02-01

The N159 star-forming region is one of the most massive giant molecular clouds (GMCs) in the Large Magellanic Cloud (LMC). We show the 12CO, 13CO, CS molecular gas lines observed with ALMA in N159 west (N159W) and N159 east (N159E). We relate the structure of the gas clumps to the properties of 24 massive young stellar objects (YSOs) that include 10 newly identified YSOs based on our search. We use dendrogram analysis to identify properties of the molecular clumps, such as flux, mass, linewidth, size, and virial parameter. We relate the YSO properties to the molecular gas properties. We find that the CS gas clumps have a steeper size–linewidth relation than the 12CO or 13CO gas clumps. This larger slope could potentially occur if the CS gas is tracing shocks. The virial parameters of the 13CO gas clumps in N159W and N159E are low (<1). The threshold for massive star formation in N159W is 501 M ⊙ pc‑2, and the threshold for massive star formation in N159E is 794 M ⊙ pc‑2. We find that 13CO is more photodissociated in N159E than N159W. The most massive YSO in N159E has cleared out a molecular gas hole in its vicinity. All the massive YSO candidates in N159E have a more evolved spectral energy distribution type in comparison to the YSO candidates in N159W. These differences lead us to conclude that the giant molecular cloud complex in N159E is more evolved than the giant molecular cloud complex in N159W.

Molecular cloud-scale star formation in NGC 300

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faesi, Christopher M.; Lada, Charles J.; Forbrich, Jan

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 tomore » 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.« less

Probes of turbulent driving mechanisms in molecular clouds from fluctuations in synchrotron intensity

NASA Astrophysics Data System (ADS)

Herron, C. A.; Federrath, C.; Gaensler, B. M.; Lewis, G. F.; McClure-Griffiths, N. M.; Burkhart, Blakesley

2017-04-01

Previous studies have shown that star formation depends on the driving of molecular cloud turbulence, and differences in the driving can produce an order of magnitude difference in the star formation rate. The turbulent driving is characterized by the parameter ζ, with ζ = 0 for compressive, curl-free driving (e.g. accretion or supernova explosions), and ζ = 1 for solenoidal, divergence-free driving (e.g. Galactic shear). Here we develop a new method to measure ζ from observations of synchrotron emission from molecular clouds. We calculate statistics of mock synchrotron intensity images produced from magnetohydrodynamic simulations of molecular clouds, in which the driving was controlled to produce different values of ζ. We find that the mean and standard deviation of the log-normalized synchrotron intensity are sensitive to ζ, for values of ζ between 0 (curl-free driving) and 0.5 (naturally mixed driving). We quantify the dependence of zeta on the direction of the magnetic field relative to the line of sight. We provide best-fitting formulae for ζ in terms of the log-normalized mean and standard deviation of synchrotron intensity, with which ζ can be determined for molecular clouds that have similar Alfvénic Mach number to our simulations. These formulae are independent of the sonic Mach number. Signal-to-noise ratios larger than 5, and angular resolutions smaller than 5 per cent of the cloud diameter, are required to apply these formulae. Although there are no firm detections of synchrotron emission from molecular clouds, by combining Green Bank Telescope and Very Large Array observations it should be possible to detect synchrotron emission from molecular clouds, thereby constraining the value of ζ.

CO line ratios in molecular clouds: the impact of environment

NASA Astrophysics Data System (ADS)

Peñaloza, Camilo H.; Clark, Paul C.; Glover, Simon C. O.; Klessen, Ralf S.

2018-04-01

Line emission is strongly dependent on the local environmental conditions in which the emitting tracers reside. In this work, we focus on modelling the CO emission from simulated giant molecular clouds (GMCs), and study the variations in the resulting line ratios arising from the emission from the J = 1-0, J = 2-1, and J = 3-2 transitions. We perform a set of smoothed particle hydrodynamics simulations with time-dependent chemistry, in which environmental conditions - including total cloud mass, density, size, velocity dispersion, metallicity, interstellar radiation field (ISRF), and the cosmic ray ionization rate (CRIR) - were systematically varied. The simulations were then post-processed using radiative transfer to produce synthetic emission maps in the three transitions quoted above. We find that the cloud-averaged values of the line ratios can vary by up to ±0.3 dex, triggered by changes in the environmental conditions. Changes in the ISRF and/or in the CRIR have the largest impact on line ratios since they directly affect the abundance, temperature, and distribution of CO-rich gas within the clouds. We show that the standard methods used to convert CO emission to H2 column density can underestimate the total H2 molecular gas in GMCs by factors of 2 or 3, depending on the environmental conditions in the clouds.

BOREAS TF-8 NSA-OJP and SSA-OBS Ceilometer Data

NASA Technical Reports Server (NTRS)

Moore, Kathleen E.; Hall, Forrest G. (Editor); Huemmrich, Karl (Editor); Fitzjarrald, David R.

2000-01-01

The BOREAS TF-8 team used ceilometers to collect data on the fraction of the sky covered with clouds and the cloud height. Included with these data is the surface-based lifting condensation level, derived from temperature and humidity values acquired at the flux tower at the NSA-OJP site. Ceilo-meter data were collected at the NSA-OJP site in 1994 and at the NSA-OJP and SSA-OBS sites in 1996. The data are available in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884).

Ablation of ghrelin receptor in leptin-deficient ob/ob mice has paradoxical effects on glucose homeostasis when compared with ablation of ghrelin in ob/ob mice

USDA-ARS?s Scientific Manuscript database

The orexigenic hormone ghrelin is important in diabetes because it has an inhibitory effect on insulin secretion. Ghrelin ablation in leptin-deficient ob/ob (Ghrelin(-/-):ob/ob) mice increases insulin secretion and improves hyperglycemia. The physiologically relevant ghrelin receptor is the growth ...

Morphological and biochemical alterations of skeletal muscles from the genetically obese (ob/ob) mouse.

PubMed

Kemp, J G; Blazev, R; Stephenson, D G; Stephenson, G M M

2009-08-01

Knowledge of the morphological and biochemical alterations occurring in skeletal muscles of obese animals is relatively limited, particularly with respect to non-limb muscles and relationship to fibre type. Sternomastoid (SM; fast-twitch), extensor digitorum longus (EDL; fast-twitch), and soleus (SOL; mixed) muscles of ob/ob mouse (18-22 weeks) were examined with respect to size (mass, muscle mass-to-body mass ratio, cross-sectional area (CSA)), fibre CSA, protein content, myosin heavy chain (MHC) content, MHC isoform (MHC(i)) composition, MHC(i)-based fibre type composition, and lactate dehydrogenase isoenzyme (LDH(iso)) composition. Compared with (control) muscles from lean mice, all the three muscles from ob/ob mice were smaller in size (by 13-30%), with SM and EDL being the most affected. The CSA of IIB and IIB+IID fibres (the predominant fibre types in SM and EDL muscles) was markedly smaller (by approximately 30%) in ob/ob mice, consistent with differences in muscle size. Total protein content (normalised to muscle mass) was significantly lower in EDL (-9.7%) and SOL (-14.1%) muscles of ob/ob mice, but there were no differences between SM, EDL, and SOL muscles from the two animal groups with respect to MHC content (also normalised to muscle mass). Electrophoretic analyses of MHC(i) composition in whole muscle homogenates and single muscle fibres showed a shift towards slower MHC(i) content, slower MHC(i) containing fibres, and a greater proportion of hybrid fibres in all the three muscles of ob/ob mice, with a shift towards a more aerobic-oxidative phenotype also observed with respect to LDH(iso) composition. This study showed that SM, EDL, and SOL muscles of ob/ob mice display size reductions to an extent that seems to be largely related to fibre type composition, and a shift in fibre type composition that may result from a process of structural remodelling, as suggested by the increased proportion of hybrid fibres in muscles of ob/ob mice.

DEEPLY EMBEDDED PROTOSTELLAR POPULATION IN THE 20 km s{sup −1} CLOUD OF THE CENTRAL MOLECULAR ZONE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lu, Xing; Gu, Qiusheng; Zhang, Qizhou

2015-12-01

We report the discovery of a population of deeply embedded protostellar candidates in the 20 km s{sup −1} cloud, one of the massive molecular clouds in the Central Molecular Zone (CMZ) of the Milky Way, using interferometric submillimeter continuum and H{sub 2}O maser observations. The submillimeter continuum emission shows five 1 pc scale clumps, each of which further fragments into several 0.1 pc scale cores. We identify 17 dense cores, among which 12 are gravitationally bound. Among the 18 H{sub 2}O masers detected, 13 coincide with the cores and probably trace outflows emanating from the protostars. There are also 5more » gravitationally bound dense cores without H{sub 2}O maser detection. In total, the 13 masers and 5 cores may represent 18 protostars with spectral types later than B1 or potentially growing more massive stars at earlier evolutionary stages, given the non-detection in the centimeter radio continuum. In combination with previous studies of CH{sub 3}OH masers, we conclude that the star formation in this cloud is at an early evolutionary phase, before the presence of any significant ionizing or heating sources. Our findings indicate that star formation in this cloud may be triggered by a tidal compression as it approaches pericenter, similar to the case of G0.253+0.016 but with a higher star formation rate, and demonstrate that high angular resolution, high-sensitivity maser, and submillimeter observations are promising techniques to unveil deeply embedded star formation in the CMZ.« less

Molecular clouds in the NGC 6334 and NGC 6357 region: Evidence for a 100 pc-scale cloud-cloud collision triggering the Galactic mini-starbursts

NASA Astrophysics Data System (ADS)

Fukui, Yasuo; Kohno, Mikito; Yokoyama, Keiko; Torii, Kazufumi; Hattori, Yusuke; Sano, Hidetoshi; Nishimura, Atsushi; Ohama, Akio; Yamamoto, Hiroaki; Tachihara, Kengo

2018-03-01

We carried out new CO (J = 1-0, 2-1, and 3-2) observations with NANTEN2 and ASTE in the region of the twin Galactic mini-starbursts NGC 6334 and NGC 6357. We detected two velocity molecular components of 12 km s-1 velocity separation, which is continuous over 3° along the plane. In NGC 6334 the two components show similar two-peaked intensity distributions toward the young H II regions and are linked by a bridge feature. In NGC 6357 we found spatially complementary distribution between the two velocity components as well as a bridge feature in velocity. Based on these results we hypothesize that the two clouds in the two regions collided with each other in the past few Myr and triggered the formation of the starbursts over ˜ 100 pc. We suggest that the formation of the starbursts happened toward the collisional region of extent ˜ 10 pc with initial high molecular column densities. For NGC 6334 we present a scenario which includes spatial variation of the colliding epoch due to non-uniform cloud separation. The scenario possibly explains the apparent age differences among the young O stars in NGC 6334, which range from 104 yr to 106 yr; the latest collision happened within 105 yr toward the youngest stars in NGC 6334 I(N) and I which exhibit molecular outflows without H II regions. For NGC 6357 the O stars were formed a few Myr ago, and the cloud dispersal by the O stars is significant. We conclude that cloud-cloud collision offers a possible explanation of the mini-starburst over a 100 pc scale.

Molecular clouds in the NGC 6334 and NGC 6357 region; Evidence for a 100-pc-scale cloud-cloud collision triggering the Galactic mini-starbursts

NASA Astrophysics Data System (ADS)

Fukui, Yasuo; Kohno, Mikito; Yokoyama, Keiko; Torii, Kazufumi; Hattori, Yusuke; Sano, Hidetoshi; Nishimura, Atsushi; Ohama, Akio; Yamamoto, Hiroaki; Tachihara, Kengo

2018-03-01

We carried out new CO (J = 1-0, 2-1, and 3-2) observations with NANTEN2 and ASTE in the region of the twin Galactic mini-starbursts NGC 6334 and NGC 6357. We detected two velocity molecular components of 12 km s-1 velocity separation, which is continuous over 3° along the plane. In NGC 6334 the two components show similar two-peaked intensity distributions toward the young H II regions and are linked by a bridge feature. In NGC 6357 we found spatially complementary distribution between the two velocity components as well as a bridge feature in velocity. Based on these results we hypothesize that the two clouds in the two regions collided with each other in the past few Myr and triggered the formation of the starbursts over ˜ 100 pc. We suggest that the formation of the starbursts happened toward the collisional region of extent ˜ 10 pc with initial high molecular column densities. For NGC 6334 we present a scenario which includes spatial variation of the colliding epoch due to non-uniform cloud separation. The scenario possibly explains the apparent age differences among the young O stars in NGC 6334, which range from 104 yr to 106 yr; the latest collision happened within 105 yr toward the youngest stars in NGC 6334 I(N) and I which exhibit molecular outflows without H II regions. For NGC 6357 the O stars were formed a few Myr ago, and the cloud dispersal by the O stars is significant. We conclude that cloud-cloud collision offers a possible explanation of the mini-starburst over a 100-pc scale.

Molecular clouds in the NGC 6334 and NGC 6357 region: Evidence for a 100 pc-scale cloud-cloud collision triggering the Galactic mini-starbursts

NASA Astrophysics Data System (ADS)

Fukui, Yasuo; Kohno, Mikito; Yokoyama, Keiko; Torii, Kazufumi; Hattori, Yusuke; Sano, Hidetoshi; Nishimura, Atsushi; Ohama, Akio; Yamamoto, Hiroaki; Tachihara, Kengo

2018-05-01

We carried out new CO (J = 1-0, 2-1, and 3-2) observations with NANTEN2 and ASTE in the region of the twin Galactic mini-starbursts NGC 6334 and NGC 6357. We detected two velocity molecular components of 12 km s-1 velocity separation, which is continuous over 3° along the plane. In NGC 6334 the two components show similar two-peaked intensity distributions toward the young H II regions and are linked by a bridge feature. In NGC 6357 we found spatially complementary distribution between the two velocity components as well as a bridge feature in velocity. Based on these results we hypothesize that the two clouds in the two regions collided with each other in the past few Myr and triggered the formation of the starbursts over ˜ 100 pc. We suggest that the formation of the starbursts happened toward the collisional region of extent ˜ 10 pc with initial high molecular column densities. For NGC 6334 we present a scenario which includes spatial variation of the colliding epoch due to non-uniform cloud separation. The scenario possibly explains the apparent age differences among the young O stars in NGC 6334, which range from 104 yr to 106 yr; the latest collision happened within 105 yr toward the youngest stars in NGC 6334 I(N) and I which exhibit molecular outflows without H II regions. For NGC 6357 the O stars were formed a few Myr ago, and the cloud dispersal by the O stars is significant. We conclude that cloud-cloud collision offers a possible explanation of the mini-starburst over a 100 pc scale.

The temperature of large dust grains in molecular clouds

NASA Technical Reports Server (NTRS)

Clark, F. O.; Laureijs, R. J.; Prusti, T.

1991-01-01

The temperature of the large dust grains is calculated from three molecular clouds ranging in visual extinction from 2.5 to 8 mag, by comparing maps of either extinction derived from star counts or gas column density derived from molecular observations to I(100). Both techniques show the dust temperature declining into clouds. The two techniques do not agree in absolute scale.

A Kennicutt-Schmidt relation at molecular cloud scales and beyond

NASA Astrophysics Data System (ADS)

Khoperskov, Sergey A.; Vasiliev, Evgenii O.

2017-06-01

Using N-body/gasdynamic simulations of a Milky Way-like galaxy, we analyse a Kennicutt-Schmidt (KS) relation, Σ _SFR ∝ Σ _gas^N, at different spatial scales. We simulate synthetic observations in CO lines and ultraviolet (UV) band. We adopt the star formation rate (SFR) defined in two ways: based on free fall collapse of a molecular cloud - ΣSFR, cl, and calculated by using a UV flux calibration - ΣSFR,UV. We study a KS relation for spatially smoothed maps with effective spatial resolution from molecular cloud scales to several hundred parsecs. We find that for spatially and kinematically resolved molecular clouds the Σ _{SFR, cl} ∝ σ _{gas}^N relation follows the power law with index N ≈ 1.4. Using UV flux as SFR calibrator, we confirm a systematic offset between the ΣSFR,UV and Σgas distributions on scales compared to molecular cloud sizes. Degrading resolution of our simulated maps for surface densities of gas and SFRs, we establish that there is no relation ΣSFR,UV -Σgas below the resolution ˜50 pc. We find a transition range around scales ˜50-120 pc, where the power-law index N increases from 0 to 1-1.8 and saturates for scales larger ˜120 pc. A value of the index saturated depends on a surface gas density threshold and it becomes steeper for higher Σgas threshold. Averaging over scales with size of ≳ 150 pc the power-law index N equals 1.3-1.4 for surface gas density threshold ˜5 M⊙ pc-2. At scales ≳ 120 pc surface SFR densities determined by using CO data and UV flux, ΣSFR,UV/SFR, cl, demonstrate a discrepancy about a factor of 3. We argue that this may be originated from overestimating (constant) values of conversion factor, star formation efficiency or UV calibration used in our analysis.

C3H2 observations as a diagnostic probe for molecular clouds

NASA Technical Reports Server (NTRS)

Avery, L. W.

1986-01-01

Recently the three-membered ring molecule, cyclopropenylidene, C3H2, has been identified in the laboratory and detected in molecular clouds by Thaddeus, Vrtilek and Gottlieb (1985). This molecule is wide-spread throughout the Galaxy and has been detected in 25 separate sources including cold dust clouds, circumstellar envelopes, HII regions, and the spiral arms observed against the Cas supernova remnant. In order to evaluate the potential of C3H2 as a diagnostic probe for molecular clouds, and to attempt to identify the most useful transitions, statistical equilibrium calculations were carried out for the lowest 24 levels of the ortho species and the lowest 10 levels of the para species. Many of the sources observed by Matthews and Irvine (1985) show evidence of being optically thick in the 1(10)-1(01) line. Consequently, the effects of radiative trapping should be incorporated into the equilibrium calculations. This was done using the Large Velocity Gradient approximation for a spherical cloud of uniform density. Some results of the calculations for T(K)=10K are given. Figures are presented which show contours of the logarithm of the ratio of peak line brightness temperatures for ortho-para pairs of lines at similar frequencies. It appears that the widespread nature of C3H2, the relatively large strength of its spectral lines, and their sensitivity to density and molecular abundance combine to make this a useful molecule for probing physical conditions in molecular clouds. The 1(10)-1(01) and 2(20)-2(11) K-band lines may be especially useful in this regard because of the ease with which they are observed and their unusual density-dependent emission/absorption properties.

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.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chibueze, James O.; Imura, Kenji; Omodaka, Toshihiro

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. Wemore » 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.« less

VizieR Online Data Catalog: M33 molecular clouds and young stellar clusters (Corbelli+, 2017)

NASA Astrophysics Data System (ADS)

Corbelli, E.; Braine, J.; Bandiera, R.; Brouillet, N.; Combes, F.; Druard, C.; Gratier, P.; Mata, J.; Schuster, K.; Xilouris, M.; Palla, F.

2017-04-01

Table 5 : Physical parameters for the 566 molecular clouds identified through the IRAM 30m CO J=2-1 survey of the star forming disk of M33. For each cloud the cloud type and the following properties are listed: celestial coordinates, galactocentric radius, cloud deconvolved effective radius and its uncertainty, CO(2-1) line velocity dispersion from CPROPS and its uncertainty, line velocity dispersion from a Gaussian fit, CO luminous mass and its uncertainty, and virial mass from a Gaussian fit. In the last column the identification number of the young stellar cluster candidates associated with the molecular cloud are listed. Notes: We identify up to four young stellar cluster candidates (YSCCs) associated with each molecular cloud and we list them according to the identification number of Sharma et al. (2011, Cat. J/A+A/545/A96) given also in Table 6. Table 6 : Physical parameters for the 630 young stellar cluster candidates identified via their mid-infrared emission in the star forming disk of M33. For each YSCC we list the type of source, the identified number of the molecular clouds associated with it (if any) and the corresponding cloud classes. In addition, for each YSCC we give the celestial coordinates, the bolometric, total infrared, FUV and Halpha luminosities, the estimated mass and age, the visual extinction, the galactocentric radius, the source size, and its flux at 24μm. (2 data files).

Interstellar C2, CH, and CN in translucent molecular clouds

NASA Technical Reports Server (NTRS)

Black, John H.; Van Dishoeck, Ewine F.

1989-01-01

Optical absorption-line techniques have been applied to the study of a number of translucent molecular clouds in which the total column densities are large enough that substantial molecular abundances can be maintained. Results are presented for a survey of absorption lines of interstellar C2, CH, and CN. Detections of CN through the A 2Pi-X 2Sigma(+) (1,O) and (2,O) bands of the red system are reported and compared with observations of the violet system for one line of sight. The population distributions in C2 provide diagnostic information on temperature and density. The measured column densities of the three species can be used to test details of the theory of molecule formation in clouds where photoprocesses still play a significant role. The C2 and CH column densities are strongly correlated with each other and probably also with the H2 column density. In contrast, the CN column densities are found to vary greatly from cloud to cloud. The observations are discussed with reference to detailed theoretical models.

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.

Molecule Formation at High Extinction and Low Metallicity in the Magellanic Clouds

NASA Technical Reports Server (NTRS)

Shull, J. Michael

2005-01-01

During 2005, our FUSE research group prepared two major FUSE surveys of interstellar molecular hydrogen: 1. Galactic Disk Sightlines. We measured N(H2) in rotational states J = 0 and 1 and in higher states, J = 2,3,4,5, sometimes up to J = l, for 139 sightlines to Galactic OB stars. 2. High-Latitude QSO sightlines. We surveyed 50 sightlines to high-latitude QSOs, finding H2 in most of them (44 of 50). 3 . Molecular Hydrogen in Infrared Cirrus. Related to the high-latitude H2 survey (#2), we examined the high-latitude infrared cirrus and its correlation with H2. In addition, we are accumulating H2 measurements for additional 0 stars in the Magellanic Clouds (LMC and SMC) to add to the previously published survey.

Molecular gas in the H II-region complex RCW 166: Possible evidence for an early phase of cloud-cloud collision prior to the bubble formation

NASA Astrophysics Data System (ADS)

Ohama, Akio; Kohno, Mikito; Fujita, Shinji; Tsutsumi, Daichi; Hattori, Yusuke; Torii, Kazufumi; Nishimura, Atsushi; Sano, Hidetoshi; Yamamoto, Hiroaki; Tachihara, Kengo; Fukui, Yasuo

2018-05-01

Young H II regions are an important site for the study of O star formation based on distributions of ionized and molecular gas. We reveal that two molecular clouds at ˜48 km s-1 and ˜53 km s-1 are associated with the H II regions G018.149-00.283 in RCW 166 by using the JCMT CO High-Resolution Survey (COHRS) of the 12CO(J = 3-2) emission. G018.149-00.283 comprises a bright ring at 8 μm and an extended H II region inside the ring. The ˜48 km s-1 cloud delineates the ring, and the ˜53 km s-1 cloud is located within the ring, indicating a complementary distribution between the two molecular components. We propose a hypothesis that high-mass stars within G018.149-00.283 were formed by triggering during cloud-cloud collision at a projected velocity separation of ˜5 km s-1. We argue that G018.149-00.283 is in an early evolutionary stage, ˜0.1 Myr after the collision according to the scheme detailed by Habe and Ohta (1992, PASJ, 44, 203), which will be followed by a bubble formation stage like RCW 120. We also suggest that nearby H II regions N21 and N22 are candidates for bubbles possibly formed by cloud-cloud collision. Inoue and Fukui (2013, ApJ, 774, L31) showed that the interface gas becomes highly turbulent and realizes a high-mass accretion rate of 10-3-10-4 M⊙ yr-1 by magnetohydrodynamical numerical simulations, which offers an explanation of the O-star formation. The fairly high frequency of cloud-cloud collision in RCW 166 is probably due to the high cloud density in this part of the Scutum arm.

Polarization models of filamentary molecular clouds.

NASA Astrophysics Data System (ADS)

Carlqvist, P.; Kristen, H.

1997-08-01

We study numerically the linear polarization and extinction of light from background stars in three types of models of elongated molecular clouds by following the development of the Stokes parameters. The clouds are assumed to be of cylindrical shape and penetrated by a helical magnetic field {vec}(B). In the first two models we study only the relative magnitude of the polarization assuming that the polarization is proportional to Bmu^, where primarily μ=2. Provided there is no background/foreground polarization present we find from the cylindrically symmetric Model I that the angle of polarization has a bimodal character with the polarization being either parallel with or perpendicular to the axis of the filament. For some magnetic-field geometries both angles may exist in one and the same filament. It is concluded that it is not a straightforward task to find the magnetic-field-line pattern from the polarization pattern. If a background/foreground polarization exists or, as in Model II, the filament is not cylindrically symmetric, the bimodal character of the angle of polarization is lost. By means of Model III we have, using semi-empirical methods based on the Davis-Greenstein mechanism, estimated the absolute degree of polarization in the filamentary molecular cloud L204. It is found that the polarization produced by the model is much less than the polarization observed. We therefore conclude that most of the polarization measured in the L204 cloud is not produced in the cloud itself but is constituted by a large-scale background/foreground polarization.

[CII] observations of H2 molecular layers in transition clouds

NASA Astrophysics Data System (ADS)

Velusamy, T.; Langer, W. D.; Pineda, J. L.; Goldsmith, P. F.; Li, D.; Yorke, H. W.

2010-10-01

We present the first results on the diffuse transition clouds observed in [CII] line emission at 158 μm (1.9 THz) towards Galactic longitudes near 340° (5 LOSs) & 20° (11 LOSs) as part of the HIFI tests and GOT C+ survey. Out of the total 146 [CII] velocity components detected by profile fitting we identify 53 as diffuse molecular clouds with associated 12CO emission but without 13CO emission and characterized by AV < 5 mag. We estimate the fraction of the [CII] emission in the diffuse HI layer in each cloud and then determine the [CII] emitted from the molecular layers in the cloud. We show that the excess [CII] intensities detected in a few clouds is indicative of a thick H2 layer around the CO core. The wide range of clouds in our sample with thin to thick H2 layers suggests that these are at various evolutionary states characterized by the formation of H2 and CO layers from HI and C+, respectively. In about 30% of the clouds the H2 column densities (“dark gas”) traced by the [CII] is 50% or more than that traced by 12CO emission. On the average ~25% of the total H2 in these clouds is in an H2 layer which is not traced by CO. We use the HI, [CII], and 12CO intensities in each cloud along with simple chemical models to obtain constraints on the FUV fields and cosmic ray ionization rates. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

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.

Mapping of the extinction in giant molecular clouds using optical star counts

NASA Astrophysics Data System (ADS)

Cambrésy, L.

1999-05-01

This paper presents large scale extinction maps of most nearby Giant Molecular Clouds of the Galaxy (Lupus, rho Ophiuchus, Scorpius, Coalsack, Taurus, Chamaeleon, Musca, Corona Australis, Serpens, IC 5146, Vela, Orion, Monoceros R1 and R2, Rosette, Carina) derived from a star count method using an adaptive grid and a wavelet decomposition applied to the optical data provided by the USNO-Precision Measuring Machine. The distribution of the extinction in the clouds leads to estimate their total individual masses M and their maximum of extinction. I show that the relation between the mass contained within an iso-extinction contour and the extinction is similar from cloud to cloud and allows the extrapolation of the maximum of extinction in the range 5.7 to 25.5 magnitudes. I found that about half of the mass is contained in regions where the visual extinction is smaller than 1 magnitude. The star count method used on large scale ( ~ 250 square degrees) is a powerful and relatively straightforward method to estimate the mass of molecular complexes. A systematic study of the all sky would lead to discover new clouds as I did in the Lupus complex for which I found a sixth cloud of about 10(4) M_⊙.

Genetically obese (ob/ob) mice are resistant to the lethal effects of thioacetamide hepatotoxicity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Won, Young-Suk; Song, Ji-Won; Lim, Jong-Hwan

Obesity increases the risk of chronic liver diseases, including viral hepatitis, alcohol-induced liver disease, and non-alcoholic steatohepatitis. In this study, we investigated the effects of obesity in acute hepatic failure using a murine model of thioacetamide (TA)-induced liver injury. Genetically obese ob/ob mice, together with non-obese ob/+ littermates, were subjected to a single intraperitoneal injection of TA, and examined for signs of hepatic injury. ob/ob mice showed a significantly higher survival rate, lower levels of serum alanine aminotransferase and aspartate aminotransferase, and less hepatic necrosis and apoptosis, compared with ob/+ mice. In addition, ob/ob mice exhibited significantly lower levels ofmore » malondialdehyde and significantly higher levels of glutathione and antioxidant enzyme activities compared with their ob/+ counterparts. Bioactivation analyses revealed reduced plasma clearance of TA and covalent binding of [{sup 14}C]TA to liver macromolecules in ob/ob mice. Together, these data demonstrate that genetically obese mice are resistant to TA-induced acute liver injury through diminished bioactivation of TA and antioxidant effects. - Highlights: • ob/ob mice are resistant to lethal doses of thioacetamide, compared to ob/+ mice. • ob/ob mice show reduced oxidative stress and enhanced antioxidant enzyme activity. • ob/ob mice exhibit diminished bioactivation of thioacetamide.« less

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.

Ob/ob Mouse Livers Show Decreased Oxidative Phosphorylation Efficiencies and Anaerobic Capacities after Cold Ischemia

PubMed Central

Tagaloa, Sherry; Zhang, Linda; Dare, Anna J.; MacDonald, Julia R.; Yeong, Mee-Ling; Bartlett, Adam S. J. R.; Phillips, Anthony R. J.

2014-01-01

Background Hepatic steatosis is a major risk factor for graft failure in liver transplantation. Hepatic steatosis shows a greater negative influence on graft function following prolonged cold ischaemia. As the impact of steatosis on hepatocyte metabolism during extended cold ischaemia is not well-described, we compared markers of metabolic capacity and mitochondrial function in steatotic and lean livers following clinically relevant durations of cold preservation. Methods Livers from 10-week old leptin-deficient obese (ob/ob, n = 9) and lean C57 mice (n = 9) were preserved in ice-cold University of Wisconsin solution. Liver mitochondrial function was then assessed using high resolution respirometry after 1.5, 3, 5, 8, 12, 16 and 24 hours of storage. Metabolic marker enzymes for anaerobiosis and mitochondrial mass were also measured in conjunction with non-bicarbonate tissue pH buffering capacity. Results Ob/ob and lean mice livers showed severe (>60%) macrovesicular and mild (<30%) microvesicular steatosis on Oil Red O staining, respectively. Ob/ob livers had lower baseline enzymatic complex I activity but similar adenosine triphosphate (ATP) levels compared to lean livers. During cold storage, the respiratory control ratio and complex I-fueled phosphorylation deteriorated approximately twice as fast in ob/ob livers compared to lean livers. Ob/ob livers also demonstrated decreased ATP production capacities at all time-points analyzed compared to lean livers. Ob/ob liver baseline lactate dehydrogenase activities and intrinsic non-bicarbonate buffering capacities were depressed by 60% and 40%, respectively compared to lean livers. Conclusions Steatotic livers have impaired baseline aerobic and anaerobic capacities compared to lean livers, and mitochondrial function indices decrease particularly from after 5 hours of cold preservation. These data provide a mechanistic basis for the clinical recommendation of shorter cold storage durations in steatotic donor

Time Evolution of the Giant Molecular Cloud Mass Functions across Galactic Disks

NASA Astrophysics Data System (ADS)

Kobayashi, Masato I. N.; Inutsuka, Shu-Ichiro; Kobayashi, Hiroshi; Hasegawa, Kenji

2017-01-01

We formulate and conduct the time-integration of time evolution equation for the giant molecular cloud mass function (GMCMF) including the cloud-cloud collision (CCC) effect. Our results show that the CCC effect is only limited in the massive-end of the GMCMF and indicate that future high resolution and sensitivity radio observations may constrain giant molecular cloud (GMC) timescales by observing the GMCMF slope in the lower mass regime.

Streaming motions and kinematic distances to molecular clouds

NASA Astrophysics Data System (ADS)

Ramón-Fox, F. G.; Bonnell, Ian A.

2018-02-01

We present high-resolution smoothed particle hydrodynamics simulations of a region of gas flowing in a spiral arm and identify dense gas clouds to investigate their kinematics with respect to a Milky Way model. We find that, on average, the gas in the arms can have a net radial streaming motion of vR ≈ -9 km s-1 and rotate ≈ 6 km s-1 slower than the circular velocity. This translates to average peculiar motions towards the Galaxy centre and opposite to Galactic rotation. These results may be sensitive to the assumed spiral arm perturbation, which is ≈ 3 per cent of the disc potential in our model. We compare the actual distance and the kinematic estimate and we find that streaming motions introduce systematic offsets of ≈1 kpc. We find that the distance error can be as large as ±2 kpc, and the recovered cloud positions have distributions that can extend significantly into the inter-arm regions. We conclude that this poses a difficulty in tracing spiral arm structure in molecular cloud surveys.

Reduced adiposity in ob/ob mice following total body irradiation and bone marrow transplantation.

PubMed

Ablamunits, Vitaly; Weisberg, Stuart P; Lemieux, Jacob E; Combs, Terry P; Klebanov, Simon

2007-06-01

The objective of this study was to assess long-term metabolic consequences of total body irradiation (TBI) and bone marrow transplantation. Severe obesity develops due to both hypertrophy and hyperplasia of adipocytes. We hypothesized that TBI would arrest adipose tissue growth and would affect insulin resistance (IR). We exposed 2-month-old female ob/ob mice to 8 Grays of TBI followed by bone marrow transplantation and tested the animals for body weight (BW) gain, body composition, blood glucose, and insulin sensitivity. Two months after TBI, irradiated mice stopped gaining BW, whereas non-treated mice continued to grow. At the age of 9.5 months, body mass of irradiated mice was 60.6 +/- 1.4 grams, which was only 61% of that in non-treated ob/ob controls (99.4 +/- 1.6 grams). Body composition measurements by DXA showed that decreased BW was primarily due to an impaired fat accumulation. This could not result from the production of leptin by bone marrow-derived adipocyte progenitors because inhibition of the obese phenotype was identical in recipients of both B6 and ob/ob bone marrow. Inability of the irradiated mice to accumulate fat was associated with hepatomegaly, lower levels of monocyte chemoattractant protein-1 expression in adipose tissue, and increased IR. Our data argue in favor of the hypothesis that inability of adipose tissue to expand may increase IR. This mouse model may be valuable for studies of late-onset radiation-induced IR in humans.

iNOS inhibits hair regeneration in obese diabetic (ob/ob) mice.

PubMed

Sasaki, Mari; Shinozaki, Shohei; Morinaga, Hironobu; Kaneki, Masao; Nishimura, Emi; Shimokado, Kentaro

2018-07-02

Previous studies have shown that androgenic alopecia is associated with metabolic syndrome and diabetes. However, the detailed mechanism whereby diabetes causes alopecia still remains unclear. We focused on the inflammatory response that is caused by diabetes or obesity, given that inflammation is a risk factor for hair loss. Inducible nitric oxide synthase (iNOS) is known to be upregulated under conditions of acute or chronic inflammation. To clarify the potential role of iNOS in diabetes-related alopecia, we generated obese diabetic iNOS-deficient (ob/ob; iNOS-KO mice). We observed that ob/ob; iNOS-KO mice were potentiated for the transition from telogen (rest phase) to anagen (growth phase) in the hair cycle compared with iNOS-proficient ob/ob mice. To determine the effect of nitric oxide (NO) on the hair cycle, we administered an iNOS inhibitor intraperitoneally (compound 1400 W, 10 mg/kg) or topically (10% aminoguanidine) in ob/ob mice. We observed that iNOS inhibitors promoted anagen transition in ob/ob mice. Next, we administered an NO donor (S-nitrosoglutathione, GSNO), to test whether NO has the telogen elongation effects. The NO donor was sufficient to induce telogen elongation in wild-type mice. Together, our data indicate that iNOS-derived NO plays a role in telogen elongation under the inflammatory conditions associated with diabetes in mice. Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.

Energy balance in adrenalectomized ob/ob mice: effects of dietary starch and glucose.

PubMed

Warwick, B P; Romsos, D R

1988-07-01

Effects of different carbohydrate types on energy balance, fatty acid synthesis, and plasma insulin concentrations in adrenalectomized ob/ob mice were investigated. Obese (ob/ob) and lean mice adrenalectomized at 4 wk of age received one of four high-carbohydrate powdered diets for 3 wk: stock, glucose, starch, or starch plus wheat bran. Adrenalectomy reduced energy intake of ob/ob mice equally independent of diet type, whereas energetic efficiency, in vivo rates of fatty acid synthesis in liver and white adipose tissue, and plasma insulin concentrations were substantially reduced to approach values in lean mice in all adrenalectomized ob/ob mice except those fed glucose. The ability of adrenalectomy to normalize energy balance in ob/ob mice depends on factors other than the reduced circulating concentration of glucocorticoids alone. Diet composition is a crucial factor, and striking differences exist between semipurified diets containing a simple sugar (glucose) and those containing a complex carbohydrate (starch), with no additional effect of dietary fiber (wheat bran).

STAR FORMATION IN TURBULENT MOLECULAR CLOUDS WITH COLLIDING FLOW

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsumoto, Tomoaki; Dobashi, Kazuhito; Shimoikura, Tomomi, E-mail: matsu@hosei.ac.jp

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 ismore » 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.« less

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.

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.

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

Proteomics Analysis of Skeletal Muscle from Leptin-Deficient ob/ob Mice Reveals Adaptive Remodeling of Metabolic Characteristics and Fiber Type Composition.

PubMed

Schönke, Milena; Björnholm, Marie; Chibalin, Alexander V; Zierath, Juleen R; Deshmukh, Atul S

2018-03-01

Skeletal muscle insulin resistance, an early metabolic defect in the pathogenesis of type 2 diabetes (T2D), may be a cause or consequence of altered protein expression profiles. Proteomics technology offers enormous promise to investigate molecular mechanisms underlying pathologies, however, the analysis of skeletal muscle is challenging. Using state-of-the-art multienzyme digestion and filter-aided sample preparation (MED-FASP) and a mass spectrometry (MS)-based workflow, we performed a global proteomics analysis of skeletal muscle from leptin-deficient, obese, insulin resistant (ob/ob) and lean mice in mere two fractions in a short time (8 h per sample). We identified more than 6000 proteins with 118 proteins differentially regulated in obesity. This included protein kinases, phosphatases, and secreted and fiber type associated proteins. Enzymes involved in lipid metabolism in skeletal muscle from ob/ob mice were increased, providing evidence against reduced fatty acid oxidation in lipid-induced insulin resistance. Mitochondrial and peroxisomal proteins, as well as components of pyruvate and lactate metabolism, were increased. Finally, the skeletal muscle proteome from ob/ob mice displayed a shift toward the "slow fiber type." This detailed characterization of an obese rodent model of T2D demonstrates an efficient workflow for skeletal muscle proteomics, which may easily be adapted to other complex tissues. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Magnetohydrodynamic Simulations of a Plunging Black Hole into a Molecular Cloud

NASA Astrophysics Data System (ADS)

Nomura, Mariko; Oka, Tomoharu; Yamada, Masaya; Takekawa, Shunya; Ohsuga, Ken; Takahashi, Hiroyuki R.; Asahina, Yuta

2018-05-01

Using two-dimensional magnetohydrodynamic simulations, we investigated the gas dynamics around a black hole (BH) plunging into a molecular cloud. In these calculations, we assumed a parallel-magnetic-field layer in the cloud. The size of the accelerated region is far larger than the Bondi–Hoyle–Lyttleton radius, being approximately inversely proportional to the Alfvén Mach number for the plunging BH. Our results successfully reproduce the “Y” shape in position–velocity maps of the “Bullet” in the W44 molecular cloud. The size of the Bullet is also reproduced within an order of magnitude using a reasonable parameter set. This consistency supports the shooting model of the Bullet, according to which an isolated BH plunged into a molecular cloud to form a compact broad-velocity-width feature.

The Global Evolution of Giant Molecular Clouds. I. Model Formulation and Quasi-Equilibrium Behavior

NASA Astrophysics Data System (ADS)

Krumholz, Mark R.; Matzner, Christopher D.; McKee, Christopher F.

2006-12-01

We present semianalytic dynamical models for giant molecular clouds evolving under the influence of H II regions launched by newborn star clusters. In contrast to previous work, we neither assume that clouds are in virial or energetic equilibrium, nor do we ignore the effects of star formation feedback. The clouds, which we treat as spherical, can expand and contract homologously. Photoionization drives mass ejection; the recoil of cloud material both stirs turbulent motions and leads to an effective confining pressure. The balance between these effects and the decay of turbulent motions through isothermal shocks determines clouds' dynamical and energetic evolution. We find that for realistic values of the rates of turbulent dissipation, photoevaporation, and energy injection by H II regions, the massive clouds where most molecular gas in the Galaxy resides live for a few crossing times, in good agreement with recent observational estimates that large clouds in Local Group galaxies survive roughly 20-30 Myr. During this time clouds remain close to equilibrium, with virial parameters of 1-3 and column densities near 1022 H atoms cm-2, also in agreement with observed cloud properties. Over their lives they convert 5%-10% of their mass into stars, after which point most clouds are destroyed when a large H II region unbinds them. In contrast, small clouds like those found in the solar neighborhood only survive ~1 crossing time before being destroyed.

Kefir improves fatty liver syndrome by inhibiting the lipogenesis pathway in leptin-deficient ob/ob knockout mice.

PubMed

Chen, H-L; Tung, Y-T; Tsai, C-L; Lai, C-W; Lai, Z-L; Tsai, H-C; Lin, Y-L; Wang, C-H; Chen, C-M

2014-09-01

Fatty liver disease is commonly associated with obesity, insulin resistance and diabetes. Severe fatty liver is sometimes accompanied by steatohepatitis and may lead to the development of hepatocellular carcinoma. At present, there is no effective treatment for non-alcoholic fatty liver disease (NAFLD); thus, recent investigations have focused on developing effective therapeutics to treat this condition. This study aimed to evaluate the effects of kefir on the hepatic lipid metabolism of ob/ob mice, which are commonly used to model fatty liver disease. In this study, we used leptin receptor-deficient ob/ob mice as an animal disease model of NAFLD. Six-week-old ob/ob mice were orally administered the dairy product kefir (140 mg kg(-1) of body weight (BW) per day) for 4 weeks. The data demonstrated that kefir improved fatty liver syndrome on BW, energy expenditure and basal metabolic rate by inhibiting serum glutamate oxaloacetate transaminase (GOT) and glutamate pyruvate transaminase (GPT) activities (P<0.05) and by decreasing the triglyceride (TG) and total cholesterol (TC) contents of the liver (P<0.05). Oral kefir administration also significantly reduced the macrovesicular fat quantity in liver tissue. In addition, kefir markedly decreased the expression of the genes sterol regulatory element-binding protein 1 (SREBP1), fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC) (P<0.05) but not the expression of peroxisome proliferator-activated receptor α (PPARα) or hepatic carnitine palmitoyltransferase-1α (CPT1α) in the livers of ob/ob mice. On the basis of these results, we conclude that kefir improves NAFLD on BW, energy expenditure and basal metabolic rate by inhibiting the lipogenesis pathway and that kefir may have the potential for clinical application to the prevention or treatment of NAFLD.

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.

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

Metabolic profiling of ob/ob mouse fatty liver using HR-MAS 1H-NMR combined with gene expression analysis reveals alterations in betaine metabolism and the transsulfuration pathway.

PubMed

Gogiashvili, Mikheil; Edlund, Karolina; Gianmoena, Kathrin; Marchan, Rosemarie; Brik, Alexander; Andersson, Jan T; Lambert, Jörg; Madjar, Katrin; Hellwig, Birte; Rahnenführer, Jörg; Hengstler, Jan G; Hergenröder, Roland; Cadenas, Cristina

2017-02-01

Metabolic perturbations resulting from excessive hepatic fat accumulation are poorly understood. Thus, in this study, leptin-deficient ob/ob mice, a mouse model of fatty liver disease, were used to investigate metabolic alterations in more detail. Metabolites were quantified in intact liver tissues of ob/ob (n = 8) and control (n = 8) mice using high-resolution magic angle spinning (HR-MAS) 1 H-NMR. In addition, after demonstrating that HR-MAS 1 H-NMR does not affect RNA integrity, transcriptional changes were measured by quantitative real-time PCR on RNA extracted from the same specimens after HR-MAS 1 H-NMR measurements. Importantly, the gene expression changes obtained agreed with those observed by Affymetrix microarray analysis performed on RNA isolated directly from fresh-frozen tissue. In total, 40 metabolites could be assigned in the spectra and subsequently quantified. Quantification of lactate was also possible after applying a lactate-editing pulse sequence that suppresses the lipid signal, which superimposes the lactate methyl resonance at 1.3 ppm. Significant differences were detected for creatinine, glutamate, glycine, glycolate, trimethylamine-N-oxide, dimethylglycine, ADP, AMP, betaine, phenylalanine, and uridine. Furthermore, alterations in one-carbon metabolism, supported by both metabolic and transcriptional changes, were observed. These included reduced demethylation of betaine to dimethylglycine and the reduced expression of genes coding for transsulfuration pathway enzymes, which appears to preserve methionine levels, but may limit glutathione synthesis. Overall, the combined approach is advantageous as it identifies changes not only at the single gene or metabolite level but also deregulated pathways, thus providing critical insight into changes accompanying fatty liver disease. Graphical abstract A Evaluation of RNA integrity before and after HR-MAS 1 H-NMR of intact mouse liver tissue. B Metabolite concentrations and gene expression

Giant molecular clouds as regions of particle acceleration

NASA Technical Reports Server (NTRS)

Dogiel, V. A.; Gurevich, A. V.; Istomin, Y. N.; Zybin, K. A.

1985-01-01

One of the most interesting results of investigations carried out on the satellites SAS-II and COS-B is the discovery of unidentified discrete gamma sources. Possibly a considerable part of them may well be giant molecular clouds. Gamma emission from clouds is caused by the processes with participation of cosmic rays. The estimation of the cosmic ray density in clouds has shown that for the energy E approx. = I GeV their density can 10 to 1000 times exceed the one in intercloud space. We have made an attempt to determine the mechanism which could lead to the increase in the cosmic ray density in clouds.

ALMA view of the massive dense clump in the Galactic center 50 km s-1 molecular cloud .

NASA Astrophysics Data System (ADS)

Uehara, K.; Tsuboi, M.; Kitamura, Y.; Miyawaki, R.; Miyazaki, A.

We observed the 50 km s-1 molecular cloud with a high angular resolution (˜1.5 arcsec) using ALMA in the H13CO+ J=1-0, C34S J=2-1, CS J=2-1 and SiO v=0 J=2-1 emission lines. This cloud is a candidate for the massive star forming region induced by cloud-cloud collision (CCC). We newly found a massive dense clump (DC1) with a size of ˜0.3 pc in the CCC region of the cloud in the H13CO+ J=1-0 map. The DC1 seems to be located on a line where the four HII regions line up. Furthermore, the DC1 has a broad velocity width covering ˜30 km s-1 and ˜60 km s-1 components in the CS J=2-1 map; the 30 km s-1 component has filamentary structures and the 60 km s-1 one a sheet-like structure. From the position-velocity diagrams of the H13CO+ J=1-0 and CS J=2-1 lines and the intensity ratio of T(SiO v=0 J=2-1)/T(H13CO+ J=1-0), i.e., a shock tracer, we consider that the DC1 has formed by the CCC between the filaments and the sheet-like gas. The LTE mass and virial parameter of the DC1 is estimated to be ˜1.3×104 M_ȯ and ˜5, respectively. These facts suggest that the DC1 is likely in a gravitationally bound state and may start massive star formation. We propose a scenario that the CCC induced the massive star formation in the HII region A ˜105 years ago and now causes the formation and collapse of the DC1; the clump would evolve to an HII region within ˜105 years.

A New Look at the Molecular Gas in M42 and M43: Possible Evidence for Cloud–Cloud Collision that Triggered Formation of the OB Stars in the Orion Nebula Cluster

NASA Astrophysics Data System (ADS)

Fukui, Yasuo; Torii, Kazufumi; Hattori, Yusuke; Nishimura, Atsushi; Ohama, Akio; Shimajiri, Yoshito; Shima, Kazuhiro; Habe, Asao; Sano, Hidetoshi; Kohno, Mikito; Yamamoto, Hiroaki; Tachihara, Kengo; Onishi, Toshikazu

2018-06-01

The Orion Nebula Cluster toward the H II region M42 is the most outstanding young cluster at the smallest distance (410 pc) among the rich high-mass stellar clusters. By newly analyzing the archival molecular data of the 12CO(J = 1–0) emission at 21″ resolution, we identified at least three pairs of complementary distributions between two velocity components at 8 and 13 km s‑1. We present a hypothesis that the two clouds collided with each other and triggered formation of the high-mass stars, mainly toward two regions including the nearly 10 O stars in M42 and the B star, NU Ori, in M43. The timescale of the collision is estimated to be ∼0.1 Myr by a ratio of the cloud size and velocity corrected for projection, which is consistent with the age of the youngest cluster members less than 0.1 Myr. The majority of the low-mass cluster members were formed prior to the collision in the last Myr. We discuss the implications of the present hypothesis and the scenario of high-mass star formation by comparing with the other eight cases of triggered O-star formation via cloud–cloud collision.

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

2013-10-03

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.

Not all stars form in clusters - measuring the kinematics of OB associations with Gaia

NASA Astrophysics Data System (ADS)

Ward, Jacob L.; Kruijssen, J. M. Diederik

2018-04-01

It is often stated that star clusters are the fundamental units of star formation and that most (if not all) stars form in dense stellar clusters. In this monolithic formation scenario, low-density OB associations are formed from the expansion of gravitationally bound clusters following gas expulsion due to stellar feedback. N-body simulations of this process show that OB associations formed this way retain signs of expansion and elevated radial anisotropy over tens of Myr. However, recent theoretical and observational studies suggest that star formation is a hierarchical process, following the fractal nature of natal molecular clouds and allowing the formation of large-scale associations in situ. We distinguish between these two scenarios by characterizing the kinematics of OB associations using the Tycho-Gaia Astrometric Solution catalogue. To this end, we quantify four key kinematic diagnostics: the number ratio of stars with positive radial velocities to those with negative radial velocities, the median radial velocity, the median radial velocity normalized by the tangential velocity, and the radial anisotropy parameter. Each quantity presents a useful diagnostic of whether the association was more compact in the past. We compare these diagnostics to models representing random motion and the expanding products of monolithic cluster formation. None of these diagnostics show evidence of expansion, either from a single cluster or multiple clusters, and the observed kinematics are better represented by a random velocity distribution. This result favours the hierarchical star formation model in which a minority of stars forms in bound clusters and large-scale, hierarchically structured associations are formed in situ.

Alterations in Oral [1-14C] 18:1n-9 Distribution in Lean Wild-Type and Genetically Obese (ob/ob) Mice

PubMed Central

Wang, Xinxia; Feng, Jie; Yu, Caihua; Shen, Qingwu W.; Wang, Yizhen

2015-01-01

Obesity may result from altered fatty acid (FA) disposal. Altered FA distribution in obese individuals is poorly understood. Lean wild-type C57BL/6J and obese C57BL/6Job/ob mice received an oral dose of [1-14C]18:1n-9 (oleic acid), and the radioactivity in tissues was evaluated at various time points. The 14C concentration decreased rapidly in gastrointestinal tract but gradually increased and peaked at 96 h in adipose tissue, muscle and skin in lean mice. The 14C concentration was constant in adipose tissue and muscle of obese mice from 4h to 168h. 14C-label content in adipose tissue was significantly affected by genotype, whereas muscle 14C-label content was affected by genotype, time and the interaction between genotype and time. There was higher total 14C retention (47.7%) in obese mice than in lean mice (9.0%) at 168 h (P<0.05). The 14C concentrations in the soleus and gastrocnemius muscle were higher in obese mice than in lean mice (P<0.05). Perirenal adipose tissue contained the highest 14C content in lean mice, whereas subcutaneous adipose tissue (SAT) had the highest 14C content and accounted for the largest proportion of total radioactivity among fat depots in obese mice. More lipid radioactivity was recovered as TAG in SAT from obese mice than from lean mice (P<0.05). Gene expression suggested acyl CoA binding protein and fatty acid binding protein are important for FA distribution in adipose tissue and muscle. The FA distribution in major tissues was altered in ob/ob mice, perhaps contributing to obesity. Understanding the disparity in FA disposal between lean and obese mice may reveal novel targets for the treatment and prevention of obesity. PMID:25826747

An unidentified TeV source in the vicinity of Cygnus OB2

NASA Astrophysics Data System (ADS)

Aharonian, F.; Akhperjanian, A.; Beilicke, M.; Bernlöhr, K.; Börst, H.; Bojahr, H.; Bolz, O.; Coarasa, T.; Contreras, J.; Cortina, J.; Denninghoff, S.; Fonseca, V.; Girma, M.; Götting, N.; Heinzelmann, G.; Hermann, G.; Heusler, A.; Hofmann, W.; Horns, D.; Jung, I.; Kankanyan, R.; Kestel, M.; Kettler, J.; Kohnle, A.; Konopelko, A.; Kornmeyer, H.; Kranich, D.; Krawczynski, H.; Lampeitl, H.; Lopez, M.; Lorenz, E.; Lucarelli, F.; Magnussen, N.; Mang, O.; Meyer, H.; Milite, M.; Mirzoyan, R.; Moralejo, A.; Ona, E.; Panter, M.; Plyasheshnikov, A.; Prahl, J.; Pühlhofer, G.; Rauterberg, G.; Reyes, R.; Rhode, W.; Ripken, J.; Röhring, A.; Rowell, G. P.; Sahakian, V.; Samorski, M.; Schilling, M.; Schröder, F.; Siems, M.; Sobzynska, D.; Stamm, W.; Tluczykont, M.; Völk, H. J.; Wiedner, C. A.; Wittek, W.; Uchiyama, Y.; Takahashi, T.; HEGRA Collaboration

2002-10-01

Deep observation ( ~ 113 hrs) of the Cygnus region at TeV energies using the HEGRA stereoscopic system of air Čerenkov telescopes has serendipitously revealed a signal positionally inside the core of the OB association Cygnus OB2, at the edge of the 95% error circle of the EGRET source 3EG J2033+4118, and ~ 0.5o north of Cyg X-3. The source centre of gravity is RA alphaJ2000: 20h 32m 07s+/- 9.2sstat +/-2.2ssys, Dec deltaJ2000: +41o 30' 30''+/- 2.0'stat +/- 0.4'sys. The source is steady, has a post-trial significance of +4.6sigma , indication for extension with radius 5.6' at the ~ 3sigma level, and has a differential power-law flux with hard photon index of -1.9 +/-0.3stat +/-0.3sys. The integral flux above 1 TeV amounts ~ 3% that of the Crab. No counterpart for the TeV source at other wavelengths is presently identified, and its extension would disfavour an exclusive pulsar or AGN origin. If associated with Cygnus OB2, this dense concentration of young, massive stars provides an environment conducive to multi-TeV particle acceleration and likely subsequent interaction with a nearby gas cloud. Alternatively, one could envisage gamma -ray production via a jet-driven termination shock.

The dependence of stellar age distributions on giant molecular cloud environment

NASA Astrophysics Data System (ADS)

Dobbs, C. L.; Pringle, J. E.; Naylor, T.

2014-01-01

In this Letter, we analyse the distributions of stellar ages in giant molecular clouds (GMCs) in spiral arms, interarm spurs and at large galactic radii, where the spiral arms are relatively weak. We use the results of numerical simulations of galaxies, which follow the evolution of GMCs and include star particles where star formation events occur. We find that GMCs in spiral arms tend to have predominantly young (<10 Myr) stars. By contrast, clouds which are the remainders of spiral arm giant molecular asssociations that have been sheared into interarm GMCs contain fewer young (<10 Myr) stars and more ˜20 Myr stars. We also show that clouds which form in the absence of spiral arms, due to local gravitational and thermal instabilities, contain preferentially young stars. We propose that the age distributions of stars in GMCs will be a useful diagnostic to test different cloud evolution scenarios, the origin of spiral arms and the success of numerical models of galactic star formation. We discuss the implications of our results in the context of Galactic and extragalactic molecular clouds.

The Carbon Isotope Ratio in Local Molecular Clouds

NASA Astrophysics Data System (ADS)

Goto, Miwa; Usuda, Tomonori; Takato, Naruhisa; Masahiko, Hayashi; Sakamoto, Seiichi; Mitchell, George

We report the carbon isotope ratio in nearby molecular clouds LkHα 101, AFGL 490, and Mon R2 IRS 3. The vibrational transition bands of 12CO ν = 2 ← 0 and 13CO ν = 1 ← 0 were observed with high resolution near-infrared spectroscopy (R = 23,000) to measure the relative abundance of 13CO to 12CO. The isotopic ratios are 12CO/13CO = 1379 (LkHα 101), 8649 (AFGL 490), and 158 (Mon R2 IRS 3), which is twice higher than in the solar neighborhood. The molecular clouds are with high visible extinction (AV = 10 70 mag), well shielded from destructive FUV field. It is questionable that the selective photo-destruction of 13CO plays a major role in biasing isotope ratio. Uncertainty in the Doppler parameters of the unresolved absorption lines, and possible emission filling of fundamental transitions are suspected to account for the high 12CO/13CO ratio. Higher resolution spectroscopy (R ~ 100,000) is the key to go for the accurate measurement of isotope ratio.

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

MOLECULAR CLOUDS AND CLUMPS IN THE BOSTON UNIVERSITY-FIVE COLLEGE RADIO ASTRONOMY OBSERVATORY GALACTIC RING SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rathborne, J. M.; Johnson, A. M.; Jackson, J. M.

2009-05-15

The Boston University-Five College Radio Astronomy Observatory (BU-FCRAO) Galactic Ring Survey (GRS) of {sup 13}CO J = 1 {yields} 0 emission covers Galactic longitudes 18{sup 0} < l < 55.{sup 0}7 and Galactic latitudes |b| {<=} 1{sup 0}. Using the SEQUOIA array on the FCRAO 14 m telescope, the GRS fully sampled the {sup 13}CO Galactic emission (46'' angular resolution on a 22'' grid) and achieved a spectral resolution of 0.21 km s{sup -1}. Because the GRS uses {sup 13}CO, an optically thin tracer, rather than {sup 12}CO, an optically thick tracer, the GRS allows a much better determination ofmore » column density and also a cleaner separation of velocity components along a line of sight. With this homogeneous, fully sampled survey of {sup 13}CO emission, we have identified 829 molecular clouds and 6124 clumps throughout the inner Galaxy using the CLUMPFIND algorithm. Here we present details of the catalog and a preliminary analysis of the properties of the molecular clouds and their clumps. Moreover, we compare clouds inside and outside of the 5 kpc ring and find that clouds within the ring typically have warmer temperatures, higher column densities, larger areas, and more clumps compared with clouds located outside the ring. This is expected if these clouds are actively forming stars. This catalog provides a useful tool for the study of molecular clouds and their embedded young stellar objects.« less

Complete Genome Sequence of Escherichia coli Strain M8, Isolated from ob/ob Mice

PubMed Central

Siddharth, Jay; Membrez, Mathieu; Chakrabarti, Anirikh; Betrisey, Bertrand; Chou, Chieh Jason

2017-01-01

ABSTRACT Escherichia coli is one of the common inhabitants of the mammalian gastrointestinal track. We isolated a strain from an ob/ob mouse and performed whole-genome sequencing, which yielded a chromosome of ~5.1 Mb and three plasmids of ~160 kb, ~6 kb, and ~4 kb. PMID:28572322

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.

Cyanide and isocyanide abundances in the cold, dark cloud TMC-1

NASA Technical Reports Server (NTRS)

Irvine, W. M.; Schloerb, F. P.

1984-01-01

Cold, dark molecular clouds are particularly useful for the study of interstellar chemistry because their physical parameters are better understood than those of heterogeneous, complex giant molecular clouds. Another advantage is their relatively small distance from the solar system. The present investigaation has the objective to provide accurate abundance ratios for several cyanides and isocyanides in order to constrain models of dark cloud chemistry. The relative abundances of such related species can be particularly useful for the study of chemical processes. The cloud TMC-1 considered in the current study has a remarkably high abundance of acetylene and polyacetylene derivatives. Data at 3 mm, corresponding to the J = 1 to 0 transitions of HCN, H(C-13)N, HN(C-13), HC(N-15), and H(N-15)C were obtained.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benincasa, Samantha M.; Pudritz, Ralph E.; Wadsley, James

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 simulatedmore » 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.« less

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

ULTRAVIOLET ESCAPE FRACTIONS FROM GIANT MOLECULAR CLOUDS DURING EARLY CLUSTER FORMATION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howard, Corey; Pudritz, Ralph; Klessen, Ralf

2017-01-01

The UV photon escape fraction from molecular clouds is a key parameter for understanding the ionization of the interstellar medium and extragalactic processes such as cosmic reionization. We present the ionizing photon flux and the corresponding photon escape fraction ( f {sub esc}) arising as a consequence of star cluster formation in a turbulent, 10{sup 6} M {sub ⊙} giant molecular cloud, simulated using the code FLASH. We make use of sink particles to represent young, star-forming clusters coupled with a radiative transfer scheme to calculate the emergent UV flux. We find that the ionizing photon flux across the cloudmore » boundary is highly variable in time and space due to the turbulent nature of the intervening gas. The escaping photon fraction remains at ∼5% for the first 2.5 Myr, followed by two pronounced peaks at 3.25 and 3.8 Myr with a maximum f {sub esc} of 30% and 37%, respectively. These peaks are due to the formation of large H ii regions that expand into regions of lower density, some of which reaching the cloud surface. However, these phases are short-lived, and f {sub esc} drops sharply as the H ii regions are quenched by the central cluster passing through high-density material due to the turbulent nature of the cloud. We find an average f {sub esc} of 15% with factor of two variations over 1 Myr timescales. Our results suggest that assuming a single value for f {sub esc} from a molecular cloud is in general a poor approximation, and that the dynamical evolution of the system leads to large temporal variation.« less

Hydrogen sulfide improves diabetic wound healing in ob/ob mice via attenuating inflammation.

PubMed

Zhao, Huichen; Lu, Shengxia; Chai, Jiachao; Zhang, Yuchao; Ma, Xiaoli; Chen, Jicui; Guan, Qingbo; Wan, Meiyan; Liu, Yuantao

2017-09-01

The proposed mechanisms of impaired wound healing in diabetes involve sustained inflammation, excess oxidative stress and compromised agiogenesis. Hydrogen sulfide (H 2 S) has been reported to have multiple biological activities. We aim to investigate the role of H 2 S in impaired wound healing in ob/ob mice and explore the possible mechanisms involved. Full-thickness skin dorsal wounds were created on ob/ob mice and C57BL/6 mice. Cystathionine-γ-lyase (CSE) expression and H 2 S production were determined in granulation tissues of the wounds. Effects of NaHS on wound healing were evaluated. Inflammation and angiogenesis in granulation tissues of the wounds were examined. CSE expression, and H 2 S content were significantly reduced in granulation tissues of wounds in ob/ob mice compared with control mice. NaHS treatment significantly improved wound healing in ob/ob mice, which was associated with reduced neutrophil and macrophage infiltration, decreased production of tumor necrosis factor (TNF)-α, interleukin (IL)-6. NaHS treatment decreased metalloproteinase (MMP)-9, whereas increased collagen deposition and vascular-like structures in granulation tissues of wounds in ob/ob mice. CSE down-regulation may play a role in the pathogenesis of diabetic impaired wound healing. Exogenous H 2 S could be a potential agent to improve diabetic impaired wound healing by attenuating inflammation and increasing angiogenesis. Copyright © 2017 Elsevier Inc. All rights reserved.

The Arizona Radio Observatory CO Mapping Survey of Galactic Molecular Clouds. V. The Sh2-235 Cloud in CO J=2-1, 13CO J=2-1, and CO J=3-2

NASA Astrophysics Data System (ADS)

Bieging, John H.; Patel, Saahil; Peters, William L.; Toth, L. Viktor; Marton, Gábor; Zahorecz, Sarolta

2016-09-01

We present the results of a program to map the Sh2-235 molecular cloud complex in the CO and 13CO J = 2 - 1 transitions using the Heinrich Hertz Submillimeter Telescope. The map resolution is 38″ (FWHM), with an rms noise of 0.12 K brightness temperature, for a velocity resolution of 0.34 km s-1. With the same telescope, we also mapped the CO J = 3 - 2 line at a frequency of 345 GHz, using a 64 beam focal plane array of heterodyne mixers, achieving a typical rms noise of 0.5 K brightness temperature with a velocity resolution of 0.23 km s-1. The three spectral line data cubes are available for download. Much of the cloud appears to be slightly sub-thermally excited in the J = 3 level, except for in the vicinity of the warmest and highest column density areas, which are currently forming stars. Using the CO and 13CO J = 2 - 1 lines, we employ an LTE model to derive the gas column density over the entire mapped region. Examining a 125 pc2 region centered on the most active star formation in the vicinity of Sh2-235, we find that the young stellar object surface density scales as approximately the 1.6-power of the gas column density. The area distribution function of the gas is a steeply declining exponential function of gas column density. Comparison of the morphology of ionized and molecular gas suggests that the cloud is being substantially disrupted by expansion of the H II regions, which may be triggering current star formation.

Dispersal of Giant Molecular Clouds by Photoionization and Radiation Pressure

NASA Astrophysics Data System (ADS)

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

2018-01-01

UV radiation feedback from young massive stars plays a key role in the evolution of giant molecular clouds (GMCs) by forming HII regions and driving their expansion. We present the results of radiation hydrodynamic simulations of star cluster formation in turbulent GMCs, focusing on the effects of photoionization and radiation pressure on regulating the net star formation efficiency (SFE) and lifetime of clouds. We find that the net SFE depends primarily on the initial gas surface density, $\\Sigma_0$, such that the net SFE increases from 4% to 50% as $\\Sigma_0$ increases from $20\\,M_{\\odot}\\,{\\rm pc}^{-2}$ to $1300\\,M_{\\odot}\\,{\\rm pc}^{-2}$. Cloud dispersal occurs within $10\\,{\\rm Myr}$ after the onset of radiation feedback, or within 0.7--4.0 free-fall times that increases with $\\Sigma_0$. Photoionization plays a dominant role in destroying molecular clouds typical of the Milky Way, while radiation pressure takes over in massive, dense clouds. Based on the analysis of mass loss processes by photoevaporation or momentum injection, we develop a semi-analytic model for cloud dispersal and compare it with the numerical results.

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.

Mouth of the Ob River, Russia

NASA Technical Reports Server (NTRS)

2002-01-01

These images from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra satellite shows the cause and effect of the large-scale seasonal flooding experienced on rivers throughout Siberia each year. Because many Siberian rivers flow from south to north, they flood regularly in the spring as meltwater from southern latitudes backs up against the still-frozen northern reaches of the rivers.These images show the Ob' River on the western edge of the Central Siberian Plateau. The images from June 20, 2002, show the mouth of the Ob' River (large river at left) where it empties into Kara Sea. In the false-color image, Vegetation appears in bright green, water appears dark blue or black, and ice appears bright blue. The ice is still choking the river's outlet to the sea.The effect of this ice block on the more southern stretches of the river can be seen in the images captured on June 17. In the false-color image, water is black, vegetation is in shades of gold and green, and clouds are pale orange. In the northernmost portion of the Ob' visible in this image (the Ob' runs southeast to northwest in the image), what is normally a fine mesh of braided streams and branches of the river channel has become almost a lake in places. The flood waters have engorged the river to 52 kilometers (32 miles) wide in places. Rivers can back up for hundreds of miles, and cause devastating flooding for towns and villages along the banks. Often, explosives are dropped into ice jams in an effort to free the river and give the flood waters a chance to escape. The spring and summer floods of 2002 have proven to be quite severe and perhaps as many as 100,000 people have been affected across the country. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

A Low-metallicity Molecular Cloud in the Lower Galactic Halo

NASA Astrophysics Data System (ADS)

Hernandez, Audra K.; Wakker, Bart P.; Benjamin, Robert A.; French, David; Kerp, Juergen; Lockman, Felix J.; O'Toole, Simon; Winkel, Benjamin

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 ⊙) = -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 100 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. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from MAST at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program No. 12275. The Green Bank Telescope is part of the National Radio Astronomy Observatory which is a Facility of the National Science Foundation, operated by Associated Universities, Inc.

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.

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

Impaired steroidogenesis in the testis of leptin-deficient mice (ob/ob -/-).

PubMed

Martins, Fabiane Ferreira; Aguila, Marcia Barbosa; Mandarim-de-Lacerda, Carlos Alberto

2017-06-01

The obesity and its comorbidities, including resistance to leptin, impacts the reproductive function. Testes express leptin receptors in the germ cells and Leydig cells. Then, leptin-deficient animals are obese and infertile. We aimed to evaluate the structure and steroidogenic pathway of the testis of deficient leptin mice. Three months old male C57BL/6 mice (wild-type, WT) and deficient leptin (ob/ob) mice had their testes dissected and prepared for analyses. Compared to the WT group, the ob/ob group showed a greater body mass with smaller testes, and alterations in the germinative epithelium: fewer spermatogonia, spermatocytes, and spermatids. The Sertoli cells and the germ cells showed condensed nuclei and nuclear fragmentation indicating cell death, in agreement with a low expression of the proliferating cell nuclear antigen and a high expression of Caspase3. In the ob/ob group, the sperm was absent in the seminiferous tubules, and the steroidogenic pathway was compromised (low 3Beta hydroxysteroid dehydrogenase and steroidogenic acute regulatory protein). Further, all hormone receptors involved in the testicular function were down expressed (androgen, estrogen, follicle-stimulating, luteinizing, aromatase, and nicotinamide adenine dinucleotide phosphate). In conclusion, the findings indicate significant morphological, hormonal and enzymatic changes in the testis of the ob/ob mice. The shifts in the enzymatic steroidogenic pathway and the enzymes related to spermatic activity support the insights about the failures in the fertility of these animals. The study provides new evidence and contributes to the understanding of how the lack of leptin and obesity might negatively modulate the testicular function leading to infertility. Copyright © 2017 Elsevier GmbH. All rights reserved.

On the physical mechanisms governing the cloud lifecycle in the Central Molecular Zone of the Milky Way

NASA Astrophysics Data System (ADS)

Jeffreson, S. M. R.; Kruijssen, J. M. D.; Krumholz, M. R.; Longmore, S. N.

2018-05-01

We apply an analytic theory for environmentally-dependent molecular cloud lifetimes to the Central Molecular Zone of the Milky Way. Within this theory, the cloud lifetime in the Galactic centre is obtained by combining the time-scales for gravitational instability, galactic shear, epicyclic perturbations and cloud-cloud collisions. We find that at galactocentric radii ˜45-120 pc, corresponding to the location of the `100-pc stream', cloud evolution is primarily dominated by gravitational collapse, with median cloud lifetimes between 1.4 and 3.9 Myr. At all other galactocentric radii, galactic shear dominates the cloud lifecycle, and we predict that molecular clouds are dispersed on time-scales between 3 and 9 Myr, without a significant degree of star formation. Along the outer edge of the 100-pc stream, between radii of 100 and 120 pc, the time-scales for epicyclic perturbations and gravitational free-fall are similar. This similarity of time-scales lends support to the hypothesis that, depending on the orbital geometry and timing of the orbital phase, cloud collapse and star formation in the 100-pc stream may be triggered by a tidal compression at pericentre. Based on the derived time-scales, this should happen in approximately 20 per cent of all accretion events onto the 100-pc stream.

Pillars of Creation among Destruction: Star Formation in Molecular Clouds near R136 in 30 Doradus

NASA Astrophysics Data System (ADS)

Kalari, Venu M.; Rubio, Mónica; Elmegreen, Bruce G.; Guzmán, Viviana V.; Zinnecker, Hans; Herrera, Cinthya N.

2018-01-01

We present new sensitive CO(2–1) observations of the 30 Doradus region in the Large Magellanic Cloud. We identify a chain of three newly discovered molecular clouds that we name KN1, KN2, and KN3 lying within 2–14 pc in projection from the young massive cluster R136 in 30 Doradus. Excited H2 2.12 μm emission is spatially coincident with the molecular clouds, but ionized Brγ emission is not. We interpret these observations as the tails of pillar-like structures whose ionized heads are pointing toward R136. Based on infrared photometry, we identify a new generation of stars forming within this structure.

The Anatomy of the Perseus Spiral Arm: 12 CO and IRAS Imaging Observations of the W3-W4-W5 Cloud Complex

NASA Technical Reports Server (NTRS)

Heyer, Mark H.; Terebey, S.

1998-01-01

Panoramic images of 12CO J = 1-0 and thermal dust emissions from the W3-W4-W5 region of the outer Galaxy are presented. These data and recently published H I 21 cm line emission images provide an approximate 1' resolution perspective to the dynamics and thermal energy content of the interstellar gas and dust components contained within a 9 deg. arc of the Perseus spiral arm. We tabulate the molecular properties of 1560 clouds identified as closed surfaces within the l-b-v CO data cube at a threshold of 0.9 K T* (sub R). Relative surface densities of the molecular (28:1) and atomic (2.5:1) gas components determined within the arm and interarm velocity intervals demonstrate that the gas component that enters the spiral arm is predominantly atomic. Molecular clouds must necessarily condense from the compressed atomic material that enters the spiral arm and are likely short lived within the interarm regions. From the distribution of centroid velocities of clouds, we determine a random cloud-to-cloud velocity dispersion of 4 km s (exp. -1) over the width of the spiral arm but find no clear evidence within the molecular gas for streaming motions induced by the spiral potential. The far-infrared images are analyzed with the CO J = 1-0 and H I 21 cm line emission. The enhanced UV (Ultraviolet) radiation field from members of the Cas OB6 association and embedded newborn stars provide a significant source of heating to the extended dust component within the Perseus arm relative to the quiescent cirrus regions. Much of the measured far-infrared flux (69% at 60 micrometers and 47% at 100 micrometers) originates from regions associated with star formation rather than the extended, infrared cirrus component.

Further RIOTS4 Characterization of Field OB Stars in the SMC

NASA Astrophysics Data System (ADS)

Oey, M. S.; Barnes, Jesse R.; Paggeot, Kevin J.; Dorigo Jones, John; Castro, Norberto; Simon-Diaz, Sergio; Kratter, Kaitlin M.; Moe, Maxwell; Szymanski, Michal

2018-06-01

We present recent results from the Runaways and O-Type Star Spectroscopic Survey of the SMC (RIOTS4), a survey quantifying properties of the field OB stars in the Small Magellanic Cloud (SMC). Based on PSF-fitting photometry and astrometry of OGLE-III I-band images, we quantify the degree of isolation for the target OB stars, classifying them as "tip-of-the-iceberg" stars accompanied by small, sparse, clusters; or as true, isolated field stars. Many of these field stars must be runaways, which we evaluate using GAIA DR2 proper motions. We measure v sin i using the IACOB code Fourier analysis, finding that the bimodal distribution of projected rotation velocities is less pronounced for O stars than early B stars. We examine rotation in relation to relative isolation and runaway status.

CO observations of dark clouds in Lupus

NASA Technical Reports Server (NTRS)

Murphy, D. C.; Cohen, R.; May, J.

1986-01-01

C-12O observations covering 170 square degrees toward the southern T Association Lupus have revealed the presence of an extended physically related complex of dark clouds which have recently formed low mass stars. The estimated mass of the clouds (about 30,000 solar masses) is comparable to that of the nearby Ophiuchus dust clouds. The Lupus clouds are projected onto a gap between two subgroups of the Scorpio-Centaurus OB association suggesting that this long accepted subgrouping may require reinterpretation.

Anomalous 13C isotope abundances in C3S and C4H observed toward the cold interstellar cloud, Taurus Molecular Cloud-1.

PubMed

Sakai, Nami; Takano, Shuro; Sakai, Takeshi; Shiba, Shoichi; Sumiyoshi, Yoshihiro; Endo, Yasuki; Yamamoto, Satoshi

2013-10-03

We have studied the abundances of the (13)C isotopic species of C3S and C4H in the cold molecular cloud, Taurus Molecular Cloud-1 (Cyanopolyyne Peak), by radioastronomical observations of their rotational emission lines. The CCCS/(13)CCCS and CCCS/C(13)CCS ratios are determined to be >206 and 48 ± 15, respectively. The CC(13)CS line is identified with the aid of laboratory microwave spectroscopy, and the range of the CCCS/CC(13)CS ratio is found to be from 30 to 206. The abundances of at least two (13)C isotopic species of C3S are thus found to be different. Similarly, it is found that the abundances of the four (13)C isotopic species of C4H are not equivalent. The CCCCH/(13)CCCCH, CCCCH/C(13)CCCH, CCCCH/CC(13)CCH, and CCCCH/CCC(13)CH ratios are evaluated to be 141 ± 44, 97 ± 27, 82 ± 15, and 118 ± 23, respectively. Here the errors denote 3 times the standard deviation. These results will constrain the formation pathways of C3S and C4H, if the nonequivalence is caused during the formation processes of these molecules. The exchange reactions after the formation of these two molecules may also contribute to the nonequivalence. In addition, we have confirmed that the (12)C/(13)C ratio of some species are significantly higher than the interstellar elemental (12)C/(13)C ratio of 60-70. The observations of the (13)C isotopic species provide us with rich information on chemical processes in cold interstellar clouds.

QUANTIFYING OBSERVATIONAL PROJECTION EFFECTS USING MOLECULAR CLOUD SIMULATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beaumont, Christopher N.; Offner, Stella S.R.; Shetty, Rahul

2013-11-10

The physical properties of molecular clouds are often measured using spectral-line observations, which provide the only probes of the clouds' velocity structure. It is hard, though, to assess whether and to what extent intensity features in position-position-velocity (PPV) space correspond to 'real' density structures in position-position-position (PPP) space. In this paper, we create synthetic molecular cloud spectral-line maps of simulated molecular clouds, and present a new technique for measuring the reality of individual PPV structures. Using a dendrogram algorithm, we identify hierarchical structures in both PPP and PPV space. Our procedure projects density structures identified in PPP space into correspondingmore » intensity structures in PPV space and then measures the geometric overlap of the projected structures with structures identified from the synthetic observation. The fractional overlap between a PPP and PPV structure quantifies how well the synthetic observation recovers information about the three-dimensional structure. Applying this machinery to a set of synthetic observations of CO isotopes, we measure how well spectral-line measurements recover mass, size, velocity dispersion, and virial parameter for a simulated star-forming region. By disabling various steps of our analysis, we investigate how much opacity, chemistry, and gravity affect measurements of physical properties extracted from PPV cubes. For the simulations used here, which offer a decent, but not perfect, match to the properties of a star-forming region like Perseus, our results suggest that superposition induces a ∼40% uncertainty in masses, sizes, and velocity dispersions derived from {sup 13}CO (J = 1-0). As would be expected, superposition and confusion is worst in regions where the filling factor of emitting material is large. The virial parameter is most affected by superposition, such that estimates of the virial parameter derived from PPV and PPP information typically

Observational Constraints for Modeling Diffuse Molecular Clouds

NASA Astrophysics Data System (ADS)

Federman, S. R.

2014-02-01

Ground-based and space-borne observations of diffuse molecular clouds suggest a number of areas where further improvements to modeling efforts is warranted. I will highlight those that have the widest applicability. The range in CO fractionation caused by selective isotope photodissociation, in particular the large 12C16O/13C16O ratios observed toward stars in Ophiuchus, is not reproduced well by current models. Our ongoing laboratory measurements of oscillator strengths and predissociation rates for Rydberg transitions in CO isotopologues may help clarify the situtation. The CH+ abundance continues to draw attention. Small scale structure seen toward ζ Per may provide additional constraints on the possible synthesis routes. The connection between results from optical transitions and those from radio and sub-millimeter wave transitions requires further effort. A study of OH+ and OH toward background stars reveals that these species favor different environments. This brings to focus the need to model each cloud along the line of sight separately, and to allow the physical conditions to vary within an individual cloud, in order to gain further insight into the chemistry. Now that an extensive set of data on molecular excitation is available, the models should seek to reproduce these data to place further constraints on the modeling results.

Hormone-sensitive lipase deficiency suppresses insulin secretion from pancreatic islets of Lep{sup ob/ob} mice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sekiya, Motohiro; Yahagi, Naoya, E-mail: nyahagi-tky@umin.ac.jp; Laboratory of Molecular Physiology on Energy Metabolism, Graduate School of Medicine, University of Tokyo, Tokyo 113-8655

2009-09-25

It has long been a matter of debate whether the hormone-sensitive lipase (HSL)-mediated lipolysis in pancreatic {beta}-cells can affect insulin secretion through the alteration of lipotoxicity. We generated mice lacking both leptin and HSL (Lep{sup ob/ob}/HSL{sup -/-}) and explored the role of HSL in pancreatic {beta}-cells in the setting of obesity. Lep{sup ob/ob}/HSL{sup -/-} developed elevated blood glucose levels and reduced plasma insulin levels compared with Lep{sup ob/ob}/HSL{sup +/+} in a fed state, while the deficiency of HSL did not affect glucose homeostasis in Lep{sup +/+} background. The deficiency of HSL exacerbated the accumulation of triglycerides in Lep{sup ob/ob} islets,more » leading to reduced glucose-stimulated insulin secretion. The deficiency of HSL also diminished the islet mass in Lep{sup ob/ob} mice due to decreased cell proliferation. In conclusion, HSL affects insulin secretary capacity especially in the setting of obesity.« less

All-trans retinoic acid stimulates gene expression of the cardioprotective natriuretic peptide system and prevents fibrosis and apoptosis in cardiomyocytes of obese ob/ob mice.

PubMed

Manolescu, Daniel-Constantin; Jankowski, Marek; Danalache, Bogdan A; Wang, Donghao; Broderick, Tom L; Chiasson, Jean-Louis; Gutkowska, Jolanta

2014-10-01

In hypertensive rodents, retinoic acid (RA) prevents adverse cardiac remodelling and improves myocardial infarction outcome, but its role in obesity-related changes of cardiac tissue are unclear. We hypothesized that all-trans RA (ATRA) treatment will improve the cardioprotective oxytocin-natriuretic peptides (OT-NP) system, preventing apoptosis and collagen accumulation in hearts of ob/ob mice, a mouse model of obesity and insulin resistance. Female 9-week-old B6.V-Lep/J ob/ob mice (n = 16) were divided into 2 groups: 1 group (n = 8) treated with 100 μg of ATRA dissolved in 100 μL of corn oil (vehicle) delivered daily (∼2 μg·g body weight(-1)·day(-1)) by stomach intubation for 16 days, and 1 group (n = 8) that received the vehicle alone. A group of nonobese littermate mice (n = 9) served as controls. Ob/ob mice exhibited obesity, hyperglycaemia, and downregulation of the cardiac OT-NP system, including the mRNA for the transcription factor GATA4, OT receptor and brain NP, and the protein expression for endothelial nitric oxide synthase. Hearts from ob/ob mice also demonstrated increased apoptosis and collagen accumulation. ATRA treatment induced weight loss and decreased adipocytes diameter in the visceral fat, thus reducing visceral obesity, which is associated with a high risk for cardiovascular disease. RA treatment was associated with a reduction in hyperglycemia and a normalization of the OT-NP system's expression in the hearts of ob/ob mice. Furthermore, ATRA treatment prevented apoptosis and collagen accumulation in hearts of ob/ob mice. The present study indicates that ATRA treatment was effective in restoring the cardioprotective OT-NP system and in preventing abnormal cardiac remodelling in the ob/ob mice.

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.

The wavelet transform as an analysis tool for structure identification in molecular clouds

NASA Astrophysics Data System (ADS)

Gill, Arnold Gerald

1993-01-01

Of the many methods used to attempt to understand the complex structure of giant molecular clouds, perhaps the most commonly used are the autocorrelation functions (ACF), the structure function, and the power spectrum. However, these do not give unique interpretations of structure, as is shown by explicit examples compared to the Taurus Molecular Complex. Thus, another, independent method of analysis is indicated. Here, the wavelet transform is presented, a relatively new technique less than 10 years old. It can be thought of as a band-pass filter that identifies structures of specific sizes. In addition, its mathematical properties allow it to be used to identify fractal structures and accurately identify the scaling exponent. This is shown by the wavelet transform identifying the fractal dimension of a hierarchical rain cloud model first proposed by Frisch et al. (1978). A wavelet analysis is then carried out for a range of astronomical CO data, including the clouds Orion A and B and NGC 7538 (in (12)CO) and Orion A and B, Mon R2, and L1551 (in (13)CO). The data analyzed consists of the velocities of the fitted Gaussians to the individual spectra, the halfwidths and amplitude of these Gaussians, and the total area of the spectral line. For most of the clouds investigated, each of these data types showed a very high degree of scaling coherence over a wide range of scales, from down at the beam spacing up to the full size of the cloud. The analysis carried out uses both the scaling and structure identification strengths of the wavelet transform The fragmentation parameters used by Scalo (1985) and the parameters of the geometric molecular cloud description introduced by Henriksen (1986) are calculated for each cloud. These results are all consistent with previous observations of these and other molecular clouds, though they are obtained individually for each cloud investigated. It is found that the uncertainties are of a magnitude that the differentiation of

VizieR Online Data Catalog: Molecular clouds with GLIMPSE/MIPSGAL data (Retes-Romero+, 2017)

NASA Astrophysics Data System (ADS)

Retes-Romero, R.; Mayya, Y. D.; Luna, A.; Carrasco, L.

2017-11-01

All of the 12 selected molecular clouds have GLIMPSE and MIPSGAL public data available. Typical Spitzer RGB images (3.6um, 8.0um, and 24um) of the resulting sample of clouds are shown in Figure 1, where the position of the IRAS source is identified. In order to define the parent molecular cloud that harbors the high-mass star-forming regions, we used 13CO(J=1-0) emission data from the Galactic Ring Survey (GRS) database (Jackson+ 2006ApJS..163..145J). The survey data have a velocity resolution of 0.21km/s, a typical (1σ) rms sensitivity of ~0.13K, a main beam efficiency of {eta}mb=0.48, and a beam of 46". The 13CO emission spectra for the line of sight (LOS) to the selected IRAS sources are shown in Figure 2, where the observed velocity of the CS(J=2-1) emission line (Bronfman+ 1996, J/A+AS/115/81) is also marked. (3 data files).

The Anatomy of the Perseus Spiral ARM: (sup 12)CO and IRAS Imaging Observations of the W3-W4-W5 Cloud Complex

NASA Technical Reports Server (NTRS)

Heyer, Mark H.; Terebey, S.; Oliversen, R. (Technical Monitor)

1998-01-01

Panoramic images of (sup l2)CO J = 1-0 and thermal dust emissions from the W3-W4-W5 region of the outer Galaxy are presented. These data and recently published H (sub I) 21 cm line emission images provide an approx. 1 min resolution perspective to the dynamics and thermal energy content of the interstellar gas and dust components contained within a 9 deg arc of the Perseus spiral arm. We tabulate the molecular properties of 1560 clouds identified as closed surfaces within the l-b-v CO data cube at a threshold of 0.9 K T(sup *)(sub R). Relative surface densities of the molecular (28:1) and atomic (2.5: 1) gas components determined within the arm and interarm velocity intervals demonstrate that the gas component that enters the spiral arm is predominantly atomic. Molecular clouds must necessarily condense from the compressed atomic material that enters the spiral arm and are likely short lived within the interarm regions. From the distribution of centroid velocities of clouds, we determine a random cloud-to-cloud velocity dispersion of 4 km/s over the width of the spiral arm but find no clear evidence within the molecular gas for streaming motions induced by the spiral potential. The far-infrared images are analyzed with the CO J = 1-0 and H (sub I) 21 cm line emission. The enhanced UV radiation field from members of the Cas OB6 association and embedded newborn stars provide a significant source of heating to the extended dust component within the Perseus arm relative to the quiescent cirrus regions. Much of the measured far-infrared flux (69% at 60 microns and 47% at 100 microns) originates from regions associated with star formation rather than the extended, infrared cirrus component.

Giant Molecular Clouds with High Abundance of Atomic Carbon and Cyano Radical in the Milky Way's Central Molecular Zone

NASA Astrophysics Data System (ADS)

Tanaka, Kunihiko; Oka, Tomoharu; Nagai, Makoto; Kamegai, Kazuhisa

2015-08-01

The central 400 pc region of the Milky Way Galaxy is the closest galactic central region to us, providing a unique opportunity to detailedly investigate gas dynamics, star formation activity, and chemistry under the extreme environment of galactic centers, where the presence of bar, intense UV/cosmic-ray fluxes, high degree of turbulence may significantly affect those processes. We report the results of molecular line surveys toward the Milky Way's central molecular zone (CMZ) performed with the ASTE 10m telescope, the Mopra 22m telescope, and the Nobeyama 45 m telescope. With the observations of the 500 GHz [CI] fine structure line of atomic carbon (C0), we have found a molecular cloud structure with remarkably bright [CI] emission in the Sgr A comlex in the innermost 20 pc region. The [CI] cloud is more extended than the GMCs in the region, and appears to connect the northern part of the 50 kms-1 (M-0.02-0.07) and the circumnuclear disk (CND), though no corresponding structures are visible in other molecular lines. The [C0]/[CO] abundance ratio is measured to be 0.5-2, which is 2-10 times those measured to the clouds at larger Galactic radii. This high ratio is close to the values measured toward centers of galaxies with starburst and AGN, suggesting that the chemical state of the cloud is similar to that in those active galaxies. We have also found a large scale gradient of the cyano radical (CN) abundance toward the Galactic center in the innermost 100 pc radius, showing near the Sgr A complex. We suggest that the cloud with high C0 and CN abundance is a feature formed as a result of inward transfer of diffuse molecular gas by the bar potential in the inner Galaxy, in which PDR-like chemical composition remains preserved, and that thus the [CI] cloud could be deeply related to formation of the GMCs and star formation in the CMZ. We also discuss other possible mechanisms to enhance C0 and CN abundances, including the enhanced cosmic-ray dissociation ratio.

Turbulence in molecular clouds - A new diagnostic tool to probe their origin

NASA Technical Reports Server (NTRS)

Canuto, V. M.; Battaglia, A.

1985-01-01

A method is presented to uncover the instability responsible for the type of turbulence observed in molecular clouds and the value of the physical parameters of the 'placental medium' from which turbulence originated. The method utilizes the observational relation between velocities and sizes of molecular clouds, together with a recent model for large-scale turbulence (constructed by Canuto and Goldman, 1985).

Tau hyperphosphorylation in the brain of ob/ob mice is due to hypothermia: Importance of thermoregulation in linking diabetes and Alzheimer's disease.

PubMed

Gratuze, Maud; El Khoury, Noura B; Turgeon, Andréanne; Julien, Carl; Marcouiller, François; Morin, Françoise; Whittington, Robert A; Marette, André; Calon, Frédéric; Planel, Emmanuel

2017-02-01

Over the last few decades, there has been a significant increase in epidemiological studies suggesting that type 2 diabetes (T2DM) is linked to a higher risk of Alzheimer's disease (AD). However, how T2DM affects AD pathology, such as tau hyperphosphorylation, is not well understood. In this study, we investigated the impact of T2DM on tau phosphorylation in ob/ob mice, a spontaneous genetic model of T2DM. Tau phosphorylation at the AT8 epitope was slightly elevated in 4-week-old ob/ob mice while 26-week-old ob/ob mice exhibited tau hyperphosphorylation at multiple tau phospho-epitopes (Tau1, CP13, AT8, AT180, PHF1). We then examined the mechanism of tau hyperphosphorylation and demonstrated that it is mostly due to hypothermia, as ob/ob mice were hypothermic and normothermia restored tau phosphorylation to control levels. As caffeine has been shown to be beneficial for diabetes, obesity and tau phosphorylation, we, therefore, used it as therapeutic treatment. Unexpectedly, chronic caffeine intake exacerbated tau hyperphosphorylation by promoting deeper hypothermia. Our data indicate that tau hyperphosphorylation is predominately due to hypothermia consequent to impaired thermoregulation in ob/ob mice. This study establishes a novel link between diabetes and AD, and reinforces the importance of recording body temperature to better assess the relationship between diabetes and AD. Copyright © 2016 Elsevier Inc. All rights reserved.

New massive members of Cygnus OB2

NASA Astrophysics Data System (ADS)

Berlanas, S. R.; Herrero, A.; Comerón, F.; Pasquali, A.; Motta, C. Bertelli; Sota, A.

2018-04-01

Context. The Cygnus complex is one of the most powerful star forming regions at a close distance from the Sun ( 1.4 kpc). Its richest OB association Cygnus OB2 is known to harbor many tens of O-type stars and hundreds of B-type stars, providing a large homogeneous population of OB stars that can be analyzed. Many studies of its massive population have been developed in the last decades, although the total number of OB stars is still incomplete. Aim. Our aim is to increase the sample of O and B members of Cygnus OB2 and its surroundings by spectroscopically classifying 61 candidates as possible OB-type members of Cygnus OB2, using new intermediate resolution spectroscopy. Methods: We have obtained intermediate resolution (R 5000) spectra for all of the OB-type candidates between 2013 and 2017. We thus performed a spectral classification of the sample using HeI-II and metal lines rates, as well as the Marxist Ghost Buster (MGB) software for O-type stars and the IACOB standards catalog for B-type stars. Results: From the whole sample of 61 candidates, we have classified 42 stars as new massive OB-type stars, earlier than B3, in Cygnus OB2 and surroundings, including 11 O-type stars. The other candidates are discarded as they display later spectral types inconsistent with membership in the association. We have also obtained visual extinctions for all the new confirmed massive OB members, placing them in a Hertzsprung-Russell Diagram using calibrations for Teff and luminosity. Finally, we have studied the age and extinction distribution of our sample within the region. Conclusions: We have obtained new blue intermediate-resolution spectra suitable for spectral classification of 61 OB candidates in Cygnus OB2 and surroundings. The confirmation of 42 new OB massive stars (earlier than B3) in the region allows us to increase the young massive population known in the field. We have also confirmed the correlation between age and Galactic longitude previously found in the

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.

Modelling dust polarization observations of molecular clouds through MHD simulations

NASA Astrophysics Data System (ADS)

King, Patrick K.; Fissel, Laura M.; Chen, Che-Yu; Li, Zhi-Yun

2018-03-01

The BLASTPol observations of Vela C have provided the most detailed characterization of the polarization fraction p and dispersion in polarization angles S for a molecular cloud. We compare the observed distributions of p and S with those obtained in synthetic observations of simulations of molecular clouds, assuming homogeneous grain alignment. We find that the orientation of the mean magnetic field relative to the observer has a significant effect on the p and S distributions. These distributions for Vela C are most consistent with synthetic observations where the mean magnetic field is close to the line of sight. Our results point to apparent magnetic disorder in the Vela C molecular cloud, although it can be due to either an inclination effect (i.e. observing close to the mean field direction) or significant field tangling from strong turbulence/low magnetization. The joint correlations of p with column density and of S with column density for the synthetic observations generally agree poorly with the Vela C joint correlations, suggesting that understanding these correlations requires a more sophisticated treatment of grain alignment physics.

25 Orionis: A Kinematically Distinct 10 Myr Old Group in Orion OB1a

NASA Astrophysics Data System (ADS)

Briceño, César; Hartmann, Lee; Hernández, Jesús; Calvet, Nuria; Vivas, A. Katherina; Furesz, Gabor; Szentgyorgyi, Andrew

2007-06-01

We report here on the photometric and kinematic properties of a well-defined group of nearly 200 low-mass pre-main-sequence stars, concentrated within ~1° of the early-B star 25 Ori, in the Orion OB1a subassociation. We refer to this stellar aggregate as the 25 Orionis group. The group also harbors the Herbig Ae/Be star V346 Ori and a dozen other early-type stars with photometry, parallaxes, and some with IR excess emission, indicative of group membership. The number of high- and low-mass stars is in agreement with expectations from a standard initial mass function. The velocity distribution for the low-mass stars shows a narrow peak at 19.7 km s-1, offset ~-10 km s-1 from the velocity characterizing the younger stars of the Ori OB1b subassociation, and -4 km s-1 from the velocity of widely spread young stars of the Ori OB1a population; this result provides new and compelling evidence that the 25 Ori group is a distinct kinematic entity, and that considerable space and velocity structure is present in the Ori OB1a subassociation. The low-mass members follow a well-defined band in the color-magnitude diagram, consistent with an isochronal age of ~7-10 Myr. The ~2 time drop in the overall Li I equivalent widths and accretion fraction between the younger Ori OB1b and the 25 Ori group is consistent with the latter being significantly older. In a simple-minded kinematic evolution scenario, the 25 Ori group may represent the evolved counterpart of the younger σ Ori cluster. The 25 Ori stellar aggregate is the most populous ~10 Myr sample yet known within 500 pc, setting it as an excellent laboratory to study the evolution of solar-like stars and protoplanetary disks. Based on observations obtained at the Llano del Hato National Astronomical Observatory of Venezuela, operated by CIDA for the Ministerio de Ciencia y Tecnología the MMT Observatory, a joint facility of the Smithsonian Institution and the University of Arizona; and the Fred Lawrence Whipple Observatory of

An origin of arc structures deeply embedded in dense molecular cloud cores

NASA Astrophysics Data System (ADS)

Matsumoto, Tomoaki; Onishi, Toshikazu; Tokuda, Kazuki; Inutsuka, Shu-ichiro

2015-04-01

We investigated the formation of arc-like structures in the infalling envelope around protostars, motivated by the recent Atacama Large Millimeter/Submillimeter Array (ALMA) observations of the high-density molecular cloud core, MC27/L1521F. We performed self-gravitational hydrodynamical numerical simulations with an adaptive mesh refinement code. A filamentary cloud with a 0.1 pc width fragments into cloud cores because of perturbations due to weak turbulence. The cloud core undergoes gravitational collapse to form multiple protostars, and gravitational torque from the orbiting protostars produces arc structures extending up to a 1000 au scale. As well as on a spatial extent, the velocity ranges of the arc structures, ˜0.5 km s-1, are in agreement with the ALMA observations. We also found that circumstellar discs are often misaligned in triple system. The misalignment is caused by the tidal interaction between the protostars when they undergo close encounters because of a highly eccentric orbit of the tight binary pair.

On the effective turbulence driving mode of molecular clouds formed in disc galaxies

NASA Astrophysics Data System (ADS)

Jin, Keitaro; Salim, Diane M.; Federrath, Christoph; Tasker, Elizabeth J.; Habe, Asao; Kainulainen, Jouni T.

2017-07-01

We determine the physical properties and turbulence driving mode of molecular clouds formed in numerical simulations of a Milky Way-type disc galaxy with parsec-scale resolution. The clouds form through gravitational fragmentation of the gas, leading to average values for mass, radii and velocity dispersion in good agreement with observations of Milky Way clouds. The driving parameter (b) for the turbulence within each cloud is characterized by the ratio of the density contrast (σ _{ρ /ρ _0}) to the average Mach number (M) within the cloud, b=σ _{ρ /ρ _0}/M. As shown in previous works, b ˜ 1/3 indicates solenoidal (divergence-free) driving and b ˜ 1 indicates compressive (curl-free) driving. We find that the average b value of all the clouds formed in the simulations has a lower limit of b > 0.2. Importantly, we find that b has a broad distribution, covering values from purely solenoidal to purely compressive driving. Tracking the evolution of individual clouds reveals that the b value for each cloud does not vary significantly over their lifetime. Finally, we perform a resolution study with minimum cell sizes of 8, 4, 2 and 1 pc and find that the average b value increases with increasing resolution. Therefore, we conclude that our measured b values are strictly lower limits and that a resolution better than 1 pc is required for convergence. However, regardless of the resolution, we find that b varies by factors of a few in all cases, which means that the effective driving mode alters significantly from cloud to cloud.

On the star-forming ability of Molecular Clouds

NASA Astrophysics Data System (ADS)

Anathpindika, S.; Burkert, A.; Kuiper, R.

2018-02-01

The star-forming ability of a molecular cloud depends on the fraction of gas it can cycle into the dense-phase. Consequently, one of the crucial questions in reconciling star formation in clouds is to understand the factors that control this process. While it is widely accepted that the variation in ambient conditions can alter significantly the ability of a cloud to spawn stars, the observed variation in the star-formation rate in nearby clouds that experience similar ambient conditions, presents an interesting question. In this work, we attempted to reconcile this variation within the paradigm of colliding flows. To this end we develop self-gravitating, hydrodynamic realizations of identical flows, but allowed to collide off-centre. Typical observational diagnostics such as the gas-velocity dispersion, the fraction of dense-gas, the column density distribution (N-PDF), the distribution of gas mass as a function of K-band extinction and the strength of compressional/solenoidal modes in the post-collision cloud were deduced for different choices of the impact parameter of collision. We find that a strongly sheared cloud is terribly inefficient in cycling gas into the dense phase and that such a cloud can possibly reconcile the sluggish nature of star formation reported for some clouds. Within the paradigm of cloud formation via colliding flows this is possible in case of flows colliding with a relatively large impact parameter. We conclude that compressional modes - though probably essential - are insufficient to ensure a relatively higher star-formation efficiency in a cloud.

AzTEC 1.1 mm OBSERVATIONS OF THE MBM12 MOLECULAR CLOUD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kim, M. J.; Kim, S.; Youn, S.

2012-02-10

We present 1.1 mm observations of the dust continuum emission from the MBM12 high-latitude molecular cloud observed with the Astronomical Thermal Emission Camera (AzTEC) mounted on the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. We surveyed 6.34 deg{sup 2} centered on MBM12, making this the largest area that has ever been surveyed in this region with submillimeter and millimeter telescopes. Eight secure individual sources were detected with a signal-to-noise ratio of over 4.4. These eight AzTEC sources can be considered to be real astronomical objects compared to the other candidates based on calculations of the false detection rate. Themore » distribution of the detected 1.1 mm sources or compact 1.1 mm peaks is spatially anti-correlated with that of the 100 {mu}m emission and the {sup 12}CO emission. We detected the 1.1 mm dust continuum emitting sources associated with two classical T Tauri stars, LkH{alpha}262 and LkH{alpha}264. Observations of spectral energy distributions (SEDs) indicate that LkH{alpha}262 is likely to be Class II (pre-main-sequence star), but there are also indications that it could be a late Class I (protostar). A flared disk and a bipolar cavity in the models of Class I sources lead to more complicated SEDs. From the present AzTEC observations of the MBM12 region, it appears that other sources detected with AzTEC are likely to be extragalactic and located behind MBM12. Some of these have radio counterparts and their star formation rates are derived from a fit of the SEDs to the photometric evolution of galaxies in which the effects of a dusty interstellar medium have been included.« less

SILCC-Zoom: the dynamic and chemical evolution of molecular clouds

NASA Astrophysics Data System (ADS)

Seifried, D.; Walch, S.; Girichidis, P.; Naab, T.; Wünsch, R.; Klessen, R. S.; Glover, S. C. O.; Peters, T.; Clark, P.

2017-12-01

We present 3D 'zoom-in' simulations of the formation of two molecular clouds out of the galactic interstellar medium. We model the clouds - identified from the SILCC simulations - with a resolution of up to 0.06 pc using adaptive mesh refinement in combination with a chemical network to follow heating, cooling and the formation of H2 and CO including (self-) shielding. The two clouds are assembled within a few million years with mass growth rates of up to ∼10-2 M⊙ yr-1 and final masses of ∼50 000 M⊙. A spatial resolution of ≲0.1 pc is required for convergence with respect to the mass, velocity dispersion and chemical abundances of the clouds, although these properties also depend on the cloud definition such as based on density thresholds, H2 or CO mass fraction. To avoid grid artefacts, the progressive increase of resolution has to occur within the free-fall time of the densest structures (1-1.5 Myr) and ≳200 time-steps should be spent on each refinement level before the resolution is progressively increased further. This avoids the formation of spurious, large-scale, rotating clumps from unresolved turbulent flows. While CO is a good tracer for the evolution of dense gas with number densities n ≥ 300 cm-3, H2 is also found for n ≲ 30 cm-3 due to turbulent mixing and becomes dominant at column densities around 30-50 M⊙ pc-2. The CO-to-H2 ratio steadily increases within the first 2 Myr, whereas XCO ≃ 1-4 × 1020 cm-2 (K km s-1)-1 is approximately constant since the CO(1-0) line quickly becomes optically thick.

On the fragmentation of filaments in a molecular cloud simulation

NASA Astrophysics Data System (ADS)

Chira, R.-A.; Kainulainen, J.; Ibáñez-Mejía, J. C.; Henning, Th.; Mac Low, M.-M.

2018-03-01

Context. The fragmentation of filaments in molecular clouds has attracted a lot of attention recently as there seems to be a close relation between the evolution of filaments and star formation. The study of the fragmentation process has been motivated by simple analytical models. However, only a few comprehensive studies have analysed the evolution of filaments using numerical simulations where the filaments form self-consistently as part of large-scale molecular cloud evolution. Aim. We address the early evolution of parsec-scale filaments that form within individual clouds. In particular, we focus on three questions: How do the line masses of filaments evolve? How and when do the filaments fragment? How does the fragmentation relate to the line masses of the filaments? Methods: We examine three simulated molecular clouds formed in kiloparsec-scale numerical simulations performed with the FLASH adaptive mesh refinement magnetohydrodynamic code. The simulations model a self-gravitating, magnetised, stratified, supernova-driven interstellar medium, including photoelectric heating and radiative cooling. We follow the evolution of the clouds for 6 Myr from the time self-gravity starts to act. We identify filaments using the DisPerSe algorithm, and compare the results to other filament-finding algorithms. We determine the properties of the identified filaments and compare them with the predictions of analytic filament stability models. Results: The average line masses of the identified filaments, as well as the fraction of mass in filamentary structures, increases fairly continuously after the onset of self-gravity. The filaments show fragmentation starting relatively early: the first fragments appear when the line masses lie well below the critical line mass of Ostriker's isolated hydrostatic equilibrium solution ( 16 M⊙ pc-1), commonly used as a fragmentation criterion. The average line masses of filaments identified in three-dimensional volume density cubes

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

PubMed

Li, Hua-bai; Henning, Thomas

2011-11-16

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. ©2011 Macmillan Publishers Limited. All rights reserved

Quiescent Giant Molecular Cloud Cores in the Galactic Center

NASA Technical Reports Server (NTRS)

Lis, D. C.; Serabyn, E.; Zylka, R.; Li, Y.

2000-01-01

We have used the Long Wavelength Spectrometer (LWS) aboard the Infrared Space Observatory (ISO) to map the far-infrared continuum emission (45-175 micrometer) toward several massive Giant Molecular Cloud (GMC) cores located near the Galactic center. The observed far-infrared and submillimeter spectral energy distributions imply low temperatures (approx. 15 - 22 K) for the bulk of the dust in all the sources, consistent with external heating by the diffuse ISRF and suggest that these GMCs do not harbor high- mass star-formation sites, in spite of their large molecular mass. Observations of FIR atomic fine structure lines of C(sub II) and O(sub I) indicate an ISRF enhancement of approx. 10(exp 3) in the region. Through continuum radiative transfer modeling we show that this radiation field strength is in agreement with the observed FIR and submillimeter spectral energy distributions, assuming primarily external heating of the dust with only limited internal luminosity (approx. 2 x 10(exp 5) solar luminosity). Spectroscopic observations of millimeter-wave transitions of H2CO, CS, and C-34S carried out with the Caltech Submillimeter Observatory (CSO) and the Institut de Radio Astronomie Millimetrique (IRAM) 30-meter telescope indicate a gas temperature of approx. 80 K, significantly higher than the dust temperatures, and density of approx. 1 x 10(exp 5)/cc in GCM0.25 + 0.01, the brightest submillimeter source in the region. We suggest that shocks caused by cloud collisions in the turbulent interstellar medium in the Galactic center region are responsible for heating the molecular gas. This conclusion is supported by the presence of wide-spread emission from molecules such as SiO, SO, and CH3OH, which are considered good shock tracers. We also suggest that the GMCs studied here are representative of the "typical", pre-starforming cloud population in the Galactic center.

Leptin Increases Striatal Dopamine D2 Receptor Binding in Leptin-Deficient Obese (ob/ob) Mice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pfaffly, J.; Michaelides, M.; Wang, G-J.

2010-06-01

Peripheral and central leptin administration have been shown to mediate central dopamine (DA) signaling. Leptin-receptor deficient rodents show decreased DA D2 receptor (D2R) binding in striatum and unique DA profiles compared to controls. Leptin-deficient mice show increased DA activity in reward-related brain regions. The objective of this study was to examine whether basal D2R-binding differences contribute to the phenotypic behaviors of leptin-deficient ob/ob mice, and whether D2R binding is altered in response to peripheral leptin treatment in these mice. Leptin decreased body weight, food intake, and plasma insulin concentration in ob/ob mice but not in wild-type mice. Basal striatal D2Rmore » binding (measured with autoradiography [{sup 3}H] spiperone) did not differ between ob/ob and wild-type mice but the response to leptin did. In wild-type mice, leptin decreased striatal D2R binding, whereas, in ob/ob mice, leptin increased D2R binding. Our findings provide further evidence that leptin modulates D2R expression in striatum and that these effects are genotype/phenotype dependent.« less

Time evolution of giant molecular cloud mass functions with cloud-cloud collisions and gas resurrection in various environments

NASA Astrophysics Data System (ADS)

Kobayashi, M. I. N.; Inutsuka, S.; Kobayashi, H.; Hasegawa, K.

We formulate the evolution equation for the giant molecular cloud (GMC) mass functions including self-growth of GMCs through the thermal instability, self-dispersal due to massive stars born in GMCs, cloud-cloud collisions (CCCs), and gas resurrection that replenishes the minimum-mass GMC population. The computed time evolutions obtained from this formulation suggest that the slope of GMC mass function in the mass range <105.5 Mȯ is governed by the ratio of GMC formation timescale to its dispersal timescale, and that the CCC process modifies only the massive end of the mass function. Our results also suggest that most of the dispersed gas contributes to the mass growth of pre-existing GMCs in arm regions whereas less than 60 per cent contributes in inter-arm regions.

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.

Gamma-ray observations of the Orion Molecular Clouds with the Fermi Large Area Telescope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackermann, M.; Ajello, M.; Allafort, A.

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 ~100 MeV and ~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 ~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. Wemore » present here such distributions for Orion A and B, and correlate them with those of the velocity-integrated CO intensity (W CO) at a 1° × 1° pixel level. The correlation is found to be linear over a W CO range of ~10-fold when divided in three regions, suggesting penetration of nuclear CRs to most of the cloud volumes. The W CO-to-mass conversion factor, X CO, is found to be ~2.3 × 10 20 cm -2(K km s –1) –1 for the high-longitude part of Orion A (l > 212°), ~1.7 times higher than ~1.3 × 10 20 found for the rest of Orion A and B. We interpret the apparent high X 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 CO decreases faster than the H 2 column density in the region making the gas "darker" to W CO.« less

Molecular Evidence for Species-Level Distinctions in Clouded Leopards

PubMed Central

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.

2017-01-01

Summary 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 [1–5]. This secretive, mid-sized (16–23 kg) carnivore, now severely endangered, is traditionally subdivided into four southeast Asian subspecies (Figure 1A) [4–8]. 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 and 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

A Business Case Analysis (BCA) of the One Box - One Wire (OB1) Joint Combined Technology Demonstration (JCTD)

DTIC Science & Technology

2009-03-01

Framework ( IATF ) as their guidance for information assurance. The IATF defines what high 5 OB1 is compatible with and intends to use legacy...standardized levels of security. The OB1 team using the IATF as guidance defines high robustness as proving to the maximum extent possible, that

A Herschel-SPIRE Survey of the MonR2 Giant Molecular Cloud

NASA Astrophysics Data System (ADS)

Pokhrel, Riwaj; Gutermuth, Robert A.; Ali, Babar; Megeath, S. Thomas; Pipher, Judith; Myers, Philip C.; Fischer, William J.; Henning, Thomas; Wolk, Scott J.; Allen, Lori; Tobin, John J.

2014-06-01

We present a new survey of the MonR2 giant molecular cloud with SPIRE on the Herschel Space Observatory. We cross-calibrated SPIRE data with Planck-HFI and accounted for its absolute offset and zero point correction. We fixed emissivity with the help of flux-error and flux ratio plots. As the best representation of cold dusty molecular clouds, we did greybody fits of the SEDs. We studied the nature of distribution of column densities above and below certain critical limit, followed by the mass and temperature distributions for different regions. We isolated the filaments and studied radial column density profile in this cloud.

The CIDA-QUEST large-scale survey of Orion OB1: evidence for rapid disk dissipation in a dispersed stellar population.

PubMed

Briceño, C; Vivas, A K; Calvet, N; Hartmann, L; Pacheco, R; Herrera, D; Romero, L; Berlind, P; Sánchez, G; Snyder, J A; Andrews, P

2001-01-05

We are conducting a large-scale, multiepoch, optical photometric survey [Centro de Investigaciones de Astronomia-Quasar Equatorial Survey Team (CIDA-QUEST)] covering about 120 square degrees to identify the young low-mass stars in the Orion OB1 association. We present results for an area of 34 square degrees. Using photometric variability as our main selection criterion, as well as follow-up spectroscopy, we confirmed 168 previously unidentified pre-main sequence stars that are about 0.6 to 0.9 times the mass of the sun (Mo), with ages of about 1 million to 3 million years (Ori OB1b) and about 3 million to 10 million years (Ori OB1a). The low-mass stars are spatially coincident with the high-mass (at least 3 Mo) members of the associations. Indicators of disk accretion such as Halpha emission and near-infrared emission from dusty disks fall sharply from Ori OB1b to Ori OB1a, indicating that the time scale for disk dissipation and possibly the onset of planet formation is a few million years.

Neuroglial metabolic compartmentation underlying leptin deficiency in the obese ob/ob mice as detected by magnetic resonance imaging and spectroscopy methods

PubMed Central

Delgado, Teresa C; Violante, Inês R; Nieto-Charques, Laura; Cerdán, Sebastián

2011-01-01

Manganese-Enhanced Magnetic Resonance Imaging (MEMRI), 1H and 13C High-Resolution-Magic Angle Spinning (HR-MAS) Spectroscopy, and genomic approaches were used to compare cerebral activation and neuronal and glial oxidative metabolism in ad libitum fed C57BL6/J leptin-deficient, genetically obese ob/ob mice. T1-weighted Magnetic Resonance Images across the hypothalamic Arcuate and the Ventromedial nuclei were acquired kinetically after manganese infusion. Neuroglial compartmentation was investigated in hypothalamic biopsies after intraperitoneal injections of [1-13C]glucose or [2-13C]acetate. Total RNA was extracted to determine the effects of leptin deficiency in the expression of representative genes coding for regulatory enzymes of hypothalamic energy pathways and glutamatergic neurotransmission. Manganese-Enhanced Magnetic Resonance Imaging revealed enhanced cerebral activation in the hypothalamic Arcuate and Ventromedial nuclei of the ob/ob mice. 13C HR-MAS analysis showed increased 13C accumulation in the hypothalamic glutamate and glutamine carbons of ob/ob mice after the administration of [1-13C]glucose, a primarily neuronal substrate. Hypothalamic expression of the genes coding for glucokinase, phosphofructokinase, pyruvate dehydrogenase, and glutamine synthase was not significantly altered while pyruvate kinase expression was slightly upregulated. In conclusion, leptin deficiency associated with obesity led to increased cerebral activation in the hypothalamic Arcuate and Ventromedial nuclei, concomitant with significant increases in neuronal oxidative metabolism and glutamatergic neurotransmission. PMID:21971349

Biogenic, urban, and wildfire influences on the molecular composition of dissolved organic compounds in cloud water

DOE PAGES

Cook, Ryan D.; Lin, Ying-Hsuan; Peng, Zhuoyu; ...

2017-12-21

Organic aerosol formation and transformation occurs within aqueous aerosol and cloud droplets, yet little is known about the composition of high molecular weight organic compounds in cloud water. Cloud water samples collected at Whiteface Mountain, New York, during August-September 2014 were analyzed by ultra-high-resolution mass spectrometry to investigate the molecular composition of dissolved organic carbon, with a focus on sulfur- and nitrogen-containing compounds. Organic molecular composition was evaluated in the context of cloud water inorganic ion concentrations, pH, and total organic carbon concentrations to gain insights into the sources and aqueous-phase processes of the observed high molecular weight organic compounds.more » Cloud water acidity was positively correlated with the average oxygen : carbon ratio of the organic constituents, suggesting the possibility for aqueous acid-catalyzed (prior to cloud droplet activation or during/after cloud droplet evaporation) and/or radical (within cloud droplets) oxidation processes. Many tracer compounds recently identified in laboratory studies of bulk aqueous-phase reactions were identified in the cloud water. Organosulfate compounds, with both biogenic and anthropogenic volatile organic compound precursors, were detected for cloud water samples influenced by air masses that had traveled over forested and populated areas. Oxidation products of long-chain (C 10-12) alkane precursors were detected during urban influence. Influence of Canadian wildfires resulted in increased numbers of identified sulfur-containing compounds and oligomeric species, including those formed through aqueous-phase reactions involving methylglyoxal. Light-absorbing aqueous-phase products of syringol and guaiacol oxidation were observed in the wildfire-influenced samples, and dinitroaromatic compounds were observed in all cloud water samples (wildfire, biogenic, and urban-influenced). Overall, the cloud water molecular composition

Biogenic, urban, and wildfire influences on the molecular composition of dissolved organic compounds in cloud water

NASA Astrophysics Data System (ADS)

Cook, Ryan D.; Lin, Ying-Hsuan; Peng, Zhuoyu; Boone, Eric; Chu, Rosalie K.; Dukett, James E.; Gunsch, Matthew J.; Zhang, Wuliang; Tolic, Nikola; Laskin, Alexander; Pratt, Kerri A.

2017-12-01

Organic aerosol formation and transformation occurs within aqueous aerosol and cloud droplets, yet little is known about the composition of high molecular weight organic compounds in cloud water. Cloud water samples collected at Whiteface Mountain, New York, during August-September 2014 were analyzed by ultra-high-resolution mass spectrometry to investigate the molecular composition of dissolved organic carbon, with a focus on sulfur- and nitrogen-containing compounds. Organic molecular composition was evaluated in the context of cloud water inorganic ion concentrations, pH, and total organic carbon concentrations to gain insights into the sources and aqueous-phase processes of the observed high molecular weight organic compounds. Cloud water acidity was positively correlated with the average oxygen : carbon ratio of the organic constituents, suggesting the possibility for aqueous acid-catalyzed (prior to cloud droplet activation or during/after cloud droplet evaporation) and/or radical (within cloud droplets) oxidation processes. Many tracer compounds recently identified in laboratory studies of bulk aqueous-phase reactions were identified in the cloud water. Organosulfate compounds, with both biogenic and anthropogenic volatile organic compound precursors, were detected for cloud water samples influenced by air masses that had traveled over forested and populated areas. Oxidation products of long-chain (C10-12) alkane precursors were detected during urban influence. Influence of Canadian wildfires resulted in increased numbers of identified sulfur-containing compounds and oligomeric species, including those formed through aqueous-phase reactions involving methylglyoxal. Light-absorbing aqueous-phase products of syringol and guaiacol oxidation were observed in the wildfire-influenced samples, and dinitroaromatic compounds were observed in all cloud water samples (wildfire, biogenic, and urban-influenced). Overall, the cloud water molecular composition depended on

Biogenic, urban, and wildfire influences on the molecular composition of dissolved organic compounds in cloud water

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cook, Ryan D.; Lin, Ying-Hsuan; Peng, Zhuoyu

Organic aerosol formation and transformation occurs within aqueous aerosol and cloud droplets, yet little is known about the composition of high molecular weight organic compounds in cloud water. Cloud water samples collected at Whiteface Mountain, New York, during August-September 2014 were analyzed by ultra-high-resolution mass spectrometry to investigate the molecular composition of dissolved organic carbon, with a focus on sulfur- and nitrogen-containing compounds. Organic molecular composition was evaluated in the context of cloud water inorganic ion concentrations, pH, and total organic carbon concentrations to gain insights into the sources and aqueous-phase processes of the observed high molecular weight organic compounds.more » Cloud water acidity was positively correlated with the average oxygen : carbon ratio of the organic constituents, suggesting the possibility for aqueous acid-catalyzed (prior to cloud droplet activation or during/after cloud droplet evaporation) and/or radical (within cloud droplets) oxidation processes. Many tracer compounds recently identified in laboratory studies of bulk aqueous-phase reactions were identified in the cloud water. Organosulfate compounds, with both biogenic and anthropogenic volatile organic compound precursors, were detected for cloud water samples influenced by air masses that had traveled over forested and populated areas. Oxidation products of long-chain (C 10-12) alkane precursors were detected during urban influence. Influence of Canadian wildfires resulted in increased numbers of identified sulfur-containing compounds and oligomeric species, including those formed through aqueous-phase reactions involving methylglyoxal. Light-absorbing aqueous-phase products of syringol and guaiacol oxidation were observed in the wildfire-influenced samples, and dinitroaromatic compounds were observed in all cloud water samples (wildfire, biogenic, and urban-influenced). Overall, the cloud water molecular composition

Odor-Induced Neuronal Rhythms in the Olfactory Bulb Are Profoundly Modified in ob/ob Obese Mice

PubMed Central

Chelminski, Yan; Magnan, Christophe; Luquet, Serge H.; Everard, Amandine; Meunier, Nicolas; Gurden, Hirac; Martin, Claire

2017-01-01

Leptin, the product of the Ob(Lep) gene, is a peptide hormone that plays a major role in maintaining the balance between food intake and energy expenditure. In the brain, leptin receptors are expressed by hypothalamic cells but also in the olfactory bulb, the first central structure coding for odors, suggesting a precise function of this hormone in odor-evoked activities. Although olfaction plays a key role in feeding behavior, the ability of the olfactory bulb to integrate the energy-related signal leptin is still missing. Therefore, we studied the fate of odor-induced activity in the olfactory bulb in the genetic context of leptin deficiency using the obese ob/ob mice. By means of an odor discrimination task with concomitant local field potential recordings, we showed that ob/ob mice perform better than wild-type (WT) mice in the early stage of the task. This behavioral gain of function was associated in parallel with profound changes in neuronal oscillations in the olfactory bulb. The distribution of the peaks in the gamma frequency range was shifted toward higher frequencies in ob/ob mice compared to WT mice before learning. More notably, beta oscillatory activity, which has been shown previously to be correlated with olfactory discrimination learning, was longer and stronger in expert ob/ob mice after learning. Since oscillations in the olfactory bulb emerge from mitral to granule cell interactions, our results suggest that cellular dynamics in the olfactory bulb are deeply modified in ob/ob mice in the context of olfactory learning. PMID:28154537

The kinematics of the Scorpius-Centaurus OB association from Gaia DR1

NASA Astrophysics Data System (ADS)

Wright, Nicholas J.; Mamajek, Eric E.

2018-05-01

We present a kinematic study of the Scorpius-Centaurus (Sco-Cen) OB association (Sco OB2) using Gaia DR1 parallaxes and proper motions. Our goal is to test the classical theory that OB associations are the expanded remnants of dense and compact star clusters disrupted by processes such as residual gas expulsion. Gaia astrometry is available for 258 out of 433 members of the association, with revised Hipparcos astrometry used for the remainder. We use these data to confirm that the three subgroups of Sco-Cen are gravitationally unbound and have non-isotropic velocity dispersions, suggesting that they have not had time to dynamically relax. We also explore the internal kinematics of the subgroups to search for evidence of expansion. We test Blaauw's classical linear model of expansion, search for velocity trends along the Galactic axes, compare the expanding and non-expanding convergence points, perform traceback analysis assuming both linear trajectories and using an epicycle approximation, and assess the evidence for expansion in proper motions corrected for virtual expansion/contraction. None of these methods provide coherent evidence for expansion of the subgroups, with no evidence to suggest that the subgroups had a more compact configuration in the past. We find evidence for kinematic substructure within the subgroups that supports the view that they were not formed by the disruption of individual star clusters. We conclude that Sco-Cen was likely to have been born highly substructured, with multiple small-scale star formation events contributing to the overall OB association, and not as single, monolithic burst of clustered star formation.

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.;

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.

Excitation and Disruption of a Giant Molecular Cloud by the Sepurnova Remnant 3C 391

NASA Technical Reports Server (NTRS)

Reach, W. T.; Rho, J.

1998-01-01

The ambient molecular gas at the distance of the remnant comprises a giant molecular cloud whose edge is closely parallel to a ridge of bright non-thermal radio continuum, which evidently delineates the blast-wave into the cloud.

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

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

2006-12-05

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).

RPA-1 from Leishmania amazonensis (LaRPA-1) structurally differs from other eukaryote RPA-1 and interacts with telomeric DNA via its N-terminal OB-fold domain.

PubMed

Pavani, R S; Fernandes, C; Perez, A M; Vasconcelos, E J R; Siqueira-Neto, J L; Fontes, M R; Cano, M I N

2014-12-20

Replication protein A-1 (RPA-1) is a single-stranded DNA-binding protein involved in DNA metabolism. We previously demonstrated the interaction between LaRPA-1 and telomeric DNA. Here, we expressed and purified truncated mutants of LaRPA-1 and used circular dichroism measurements and molecular dynamics simulations to demonstrate that the tertiary structure of LaRPA-1 differs from human and yeast RPA-1. LaRPA-1 interacts with telomeric ssDNA via its N-terminal OB-fold domain, whereas RPA from higher eukaryotes show different binding modes to ssDNA. Our results show that LaRPA-1 is evolutionary distinct from other RPA-1 proteins and can potentially be used for targeting trypanosomatid telomeres. Copyright © 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.

ALMA Observations of Molecular Clouds in Three Group-centered Elliptical Galaxies: NGC 5846, NGC 4636, and NGC 5044

NASA Astrophysics Data System (ADS)

Temi, Pasquale; Amblard, Alexandre; Gitti, Myriam; Brighenti, Fabrizio; Gaspari, Massimo; Mathews, William G.; David, Laurence

2018-05-01

We present new ALMA CO(2–1) observations of two well-studied group-centered elliptical galaxies: NGC 4636 and NGC 5846. In addition, we include a revised analysis of Cycle 0 ALMA observations of the central galaxy in the NGC 5044 group. We find evidence that molecular gas is a common presence in bright group-centered galaxies (BGG). CO line widths are broader than Galactic molecular clouds, and using the reference Milky Way X CO, the total molecular mass ranges from 2.6 × 105 M ⊙ in NGC 4636 to 6.1 × 107 M ⊙ in NGC 5044. Complementary observations using the ALMA Compact Array do not exhibit any detection of a CO diffuse component at the sensitivity level achieved by current exposures. The origin of the detected molecular features is still uncertain, but these ALMA observations suggest that they are the end product of the hot gas cooling process and not the result of merger events. Some of the molecular clouds are associated with dust features as revealed by HST dust extinction maps, suggesting that these clouds formed from dust-enhanced cooling. The global nonlinear condensation may be triggered via the chaotic turbulent field or buoyant uplift. The large virial parameter of the molecular structures and correlation with the warm ({10}3{--}{10}5 {{K}})/hot (≥106) phase velocity dispersion provide evidence that they are unbound giant molecular associations drifting in the turbulent field, consistent with numerical predictions of the chaotic cold accretion process. Alternatively, the observed large CO line widths may be generated by molecular gas flowing out from cloud surfaces due to heating by the local hot gas atmosphere.

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

Flooding of the Ob and Irtysh Rivers, Russia

NASA Technical Reports Server (NTRS)

2002-01-01

These images from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra satellite shows the cause and effect of the large-scale seasonal flooding experienced on rivers throughout Siberia each year. Because many Siberian rivers flow from south to north, they flood regularly in the spring as meltwater from southern latitudes backs up against the still-frozen northern reaches of the rivers.These images show the Ob' River on the western edge of the Central Siberian Plateau. The images from June 20, 2002, show the mouth of the Ob' River (large river at left) where it empties into Kara Sea. In the false-color image, Vegetation appears in bright green, water appears dark blue or black, and ice appears bright blue. The ice is still choking the river's outlet to the sea.The effect of this ice block on the more southern stretches of the river can be seen in the images captured on June 17. In the false-color image, water is black, vegetation is in shades of gold and green, and clouds are pale orange. In the northernmost portion of the Ob' visible in this image (the Ob' runs southeast to northwest in the image), what is normally a fine mesh of braided streams and branches of the river channel has become almost a lake in places. The flood waters have engorged the river to 52 kilometers (32 miles) wide in places. Rivers can back up for hundreds of miles, and cause devastating flooding for towns and villages along the banks. Often, explosives are dropped into ice jams in an effort to free the river and give the flood waters a chance to escape. The spring and summer floods of 2002 have proven to be quite severe and perhaps as many as 100,000 people have been affected across the country. Credit: Jacques Descloitres, MODIS Land Rapid Response Team, NASA/GSFC

Low-Frequency Carbon Recombination Lines in the Orion Molecular Cloud Complex

NASA Astrophysics Data System (ADS)

Tremblay, Chenoa D.; Jordan, Christopher H.; Cunningham, Maria; Jones, Paul A.; Hurley-Walker, Natasha

2018-05-01

We detail tentative detections of low-frequency carbon radio recombination lines from within the Orion molecular cloud complex observed at 99-129 MHz. These tentative detections include one alpha transition and one beta transition over three locations and are located within the diffuse regions of dust observed in the infrared at 100 μm, the Hα emission detected in the optical, and the synchrotron radiation observed in the radio. With these observations, we are able to study the radiation mechanism transition from collisionally pumped to radiatively pumped within the H ii regions within the Orion molecular cloud complex.

Hog millet (Panicum miliaceum L.)-supplemented diet ameliorates hyperlipidemia and hepatic lipid accumulation in C57BL/6J-ob/ob mice

PubMed Central

Park, Mi-Young; Jang, Hwan-Hee; Kim, Jung Bong; Yoon, Hyun Nye; Lee, Jin-Young; Lee, Young-Min; Kim, Jae-Hyun

2011-01-01

Dietary intake of whole grains reduces the incidence of chronic diseases such as obesity, diabetes, cardiovascular disease, and cancer. In an earlier study, we showed that Panicum miliaceum L. extract (PME) exhibited the highest anti-lipogenic activity in 3T3-L1 cells among extracts of nine different cereal grains tested. In this study, we hypothesized that PME in the diet would lead to weight loss and augmentation of hyperlipidemia by regulating fatty acid metabolism. PME was fed to ob/ob mice at 0%, 0.5%, or 1% (w/w) for 4 weeks. After the experimental period, body weight changes, blood serum and lipid profiles, hepatic fatty acid metabolism-related gene expression, and white adipose tissue (WAT) fatty acid composition were determined. We found that the 1% PME diet, but not the 0.5%, effectively decreased body weight, liver weight, and blood triglyceride and total cholesterol levels (P < 0.05) compared to obese ob/ob mice on a normal diet. Hepatic lipogenic-related gene (PPARα, L-FABP, FAS, and SCD1) expression decreased, whereas lipolysis-related gene (CPT1) expression increased in animals fed the 1% PME diet (P < 0.05). Long chain fatty acid content and the ratio of C18:1/C18:0 fatty acids decreased significantly in adipose tissue of animals fed the 1% PME diet (P < 0.05). Serum inflammatory mediators also decreased significantly in animals fed the 1% PME diet compared to those of the ob/ob control group (P < 0.05). These results suggest that PME is useful in the chemoprevention or treatment of obesity and obesity-related disorders. PMID:22259675

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.

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.

Switching performance of OBS network model under prefetched real traffic

NASA Astrophysics Data System (ADS)

Huang, Zhenhua; Xu, Du; Lei, Wen

2005-11-01

Optical Burst Switching (OBS) [1] is now widely considered as an efficient switching technique in building the next generation optical Internet .So it's very important to precisely evaluate the performance of the OBS network model. The performance of the OBS network model is variable in different condition, but the most important thing is that how it works under real traffic load. In the traditional simulation models, uniform traffics are usually generated by simulation software to imitate the data source of the edge node in the OBS network model, and through which the performance of the OBS network is evaluated. Unfortunately, without being simulated by real traffic, the traditional simulation models have several problems and their results are doubtable. To deal with this problem, we present a new simulation model for analysis and performance evaluation of the OBS network, which uses prefetched IP traffic to be data source of the OBS network model. The prefetched IP traffic can be considered as real IP source of the OBS edge node and the OBS network model has the same clock rate with a real OBS system. So it's easy to conclude that this model is closer to the real OBS system than the traditional ones. The simulation results also indicate that this model is more accurate to evaluate the performance of the OBS network system and the results of this model are closer to the actual situation.

Chronic ethanol consumption lessens the gain of body weight, liver triglycerides, and diabetes in obese ob/ob mice.

PubMed

Fromenty, Bernard; Vadrot, Nathalie; Massart, Julie; Turlin, Bruno; Barri-Ova, Nadège; Lettéron, Philippe; Fautrel, Alain; Robin, Marie-Anne

2009-10-01

Clinical studies suggest that moderate alcohol consumption can have beneficial effects, in particular regarding cardiovascular events, insulin resistance, and type 2 diabetes. In this study, lean and obese diabetic ob/ob mice were submitted or not to chronic ethanol intake via the drinking water for 6 months, which was associated with moderate levels of plasma ethanol. Plasma levels of alanine aminotransferase and aspartate aminotransferase were not increased by alcohol intake. Ethanol consumption progressively reduced the gain of body weight in ob/ob mice, but not in lean mice, and this was observed despite higher calorie intake. Increased plasma free fatty acids and glycerol in ethanol-treated ob/ob mice suggested peripheral lipolysis. Glycemia and insulinemia were significantly reduced, whereas adiponectinemia was increased in ethanol-treated ob/ob mice. Liver weight and triglycerides were significantly decreased in ethanol-treated ob/ob mice, and this was associated with less microvesicular steatosis. Hepatic levels of AMP-activated protein kinase and the phosphorylated form of acetyl-CoA carboxylase were higher in ethanol-treated ob/ob mice, suggesting better fatty acid oxidation. However, hepatic mRNA expression of several lipogenic genes was not reduced by ethanol consumption. Finally, mild oxidative stress was noticed in the liver of ethanol-treated mice, regardless of their genotype. Hence, our data are in keeping with clinical studies suggesting that moderate ethanol intake can have beneficial effects on type 2 diabetes and insulin sensitivity, at least in part through increased levels of plasma adiponectin. However, further studies are needed to determine whether long-term drinking of light-to-moderate amounts of ethanol is safe for the liver.

TRACING THE MAGNETIC FIELD MORPHOLOGY OF THE LUPUS I MOLECULAR CLOUD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Franco, G. A. P.; Alves, F. O., E-mail: franco@fisica.ufmg.br, 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 infraredmore » 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.« less

Gas-grain chemical models of star-forming molecular clouds as constrained by ISO and SWAS observations

NASA Astrophysics Data System (ADS)

Charnley, S. B.; Rodgers, S. D.; Ehrenfreund, P.

2001-11-01

We have investigated the gaseous and solid state molecular composition of dense interstellar material that periodically experiences processing in the shock waves associated with ongoing star formation. Our motivation is to confront these models with the stringent abundance constraints on CO2, H2O and O2, in both gas and solid phases, that have been set by ISO and SWAS. We also compare our results with the chemical composition of dark molecular clouds as determined by ground-based telescopes. Beginning with the simplest possible model needed to study molecular cloud gas-grain chemistry, we only include additional processes where they are clearly required to satisfy one or more of the ISO-SWAS constraints. When CO, N2 and atoms of N, C and S are efficiently desorbed from grains, a chemical quasi-steady-state develops after about one million years. We find that accretion of CO2 and H2O cannot explain the [CO2/H2O]ice ISO observations; as with previous models, accretion and reaction of oxygen atoms are necessary although a high O atom abundance can still be derived from the CO that remains in the gas. The observational constraints on solid and gaseous molecular oxygen are both met in this model. However, we find that we cannot explain the lowest H2O abundances seen by SWAS or the highest atomic carbon abundances found in molecular clouds; additional chemical processes are required and possible candidates are given. One prediction of models of this type is that there should be some regions of molecular clouds which contain high gas phase abundances of H2O, O2 and NO. A further consequence, we find, is that interstellar grain mantles could be rich in NH2OH and NO2. The search for these regions, as well as NH2OH and NO2 in ices and in hot cores, is an important further test of this scenario. The model can give good agreement with observations of simple molecules in dark molecular clouds such as TMC-1 and L134N. Despite the fact that S atoms are assumed to be continously

Giant Molecular Cloud Structure and Evolution

NASA Technical Reports Server (NTRS)

Hollenbach, David (Technical Monitor); Bodenheimer, P. H.

2003-01-01

Bodenheimer and Burkert extended earlier calculations of cloud core models to study collapse and fragmentation. The initial condition for an SPH collapse calculation is the density distribution of a Bonnor-Ebert sphere, with near balance between turbulent plus thermal energy and gravitational energy. The main parameter is the turbulent Mach number. For each Mach number several runs are made, each with a different random realization of the initial turbulent velocity field. The turbulence decays on a dynamical time scale, leading the cloud into collapse. The collapse proceeds isothermally until the density has increased to about 10(exp 13) g cm(exp -3). Then heating is included in the dense regions. The nature of the fragmentation is investigated. About 15 different runs have been performed with Mach numbers ranging from 0.3 to 3.5 (the typical value observed in molecular cloud cores is 0.7). The results show a definite trend of increasing multiplicity with increasing Mach number (M), with the number of fragments approximately proportional to (1 + M). In general, this result agrees with that of Fisher, Klein, and McKee who published three cases with an AMR grid code. However our results show that there is a large spread about this curve. For example, for M=0.3 one case resulted in no fragmentation while a second produced three fragments. Thus it is not only the value of M but also the details of the superposition of the various velocity modes that play a critical role in the formation of binaries. Also, the simulations produce a wide range of separations (10-1000 AU) for the multiple systems, in rough agreement with observations. These results are discussed in two conference proceedings.

Synthetic observations of molecular clouds in a galactic centre environment - I. Studying maps of column density and integrated intensity

NASA Astrophysics Data System (ADS)

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

2016-02-01

We run numerical simulations of molecular clouds, adopting properties similar to those found in the central molecular zone (CMZ) of the Milky Way. For this, we employ the moving mesh code AREPO and perform simulations which account for a simplified treatment of time-dependent chemistry and the non-isothermal nature of gas and dust. We perform simulations using an initial density of n0 = 103 cm-3 and a mass of 1.3 × 105 M⊙. Furthermore, we vary the virial parameter, defined as the ratio of kinetic and potential energy, α = Ekin/|Epot|, by adjusting the velocity dispersion. We set it to α = 0.5, 2.0 and 8.0, in order to analyse the impact of the kinetic energy on our results. We account for the extreme conditions in the CMZ and increase both the interstellar radiation field (ISRF) and the cosmic ray flux (CRF) by a factor of 1000 compared to the values found in the solar neighbourhood. We use the radiative transfer code RADMC-3D to compute synthetic images in various diagnostic lines. These are [C II] at 158 μm, [O I] (145 μm), [O I] (63 μm), 12CO (J = 1 → 0) and 13CO (J = 1 → 0) at 2600 and 2720 μm, respectively. When α is large, the turbulence disperses much of the gas in the cloud, reducing its mean density and allowing the ISRF to penetrate more deeply into the cloud's interior. This significantly alters the chemical composition of the cloud, leading to the dissociation of a significant amount of the molecular gas. On the other hand, when α is small, the cloud remains compact, allowing more of the molecular gas to survive. We show that in each case the atomic tracers accurately reflect most of the physical properties of both the H2 and the total gas of the cloud and that they provide a useful alternative to molecular lines when studying the interstellar medium in the CMZ.

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.

Recent Seismic Experiments of OBS in the South China Sea

NASA Astrophysics Data System (ADS)

Ruan, A.; Li, J.; Wu, Z.

2012-12-01

Since 2006 some research institutions of China have carried out some important seismic experiments by using ocean bottom seismometer(OBS) in the South China Sea (SCS) and obtained many concrete progresses in modeling the crustal structure of SCS and also in understanding of its formation and evolution as well. In 2006 three wide-angle profiles were completed in the northern margin, named OBS2006-1 across the northwestern sub-basin, OBS2006-2 parallel to the sea basin boundary and OBS2006-3 across the Dongsha Rise and Chaoshan Depression respectively. In 2010 two wide- angle profiles were completed, named OBS2010-1 and OBS 2010-2 both perpendicular to the northern off-shore faulting system. During 2009-2011 four wide-angle profiles were completed in the southern margin, named OBS973-1 from southern margin to the southwestern sub-basin, OBS973-2 from Liyue Bank to the southwestern sub-basin and OBS973-3 from Xisha to the southwestern sub-basin, OBS2011-2 from Xisha to Hainan Island respectively. In 2011 two 3D seismic array of OBS were completed in the Zhongnan-Changlong sea mount chain and Huangyan-Zhenbei sea mount chain respectively. Here we present some primary but important results as follows. (1) The velocity model of OBS2006-1 indicates that the crust under the continental slope decreases from 21km to 11km, and to 7.7km in the northwestern sub-basin with Moho depth ascends from 21km to 11km. The tectonic geometry and velocity structure of the northwestern sub-basin and its margins on both sides shows symmetrical and conjugate and indicates pure shear mode of continental margin rifting mechanism. (2) The velocity model of OBS2006-3 reveals remarkable thickness with maximum 8 km of the Mesozoic sediment in Chaoshan Depression in which velocity increases downward from 4.4 km/s at top to 5.3 km/s at the bottom. The buried depth of Moho decreases from 24-25 km under Dongsha Rise to 17 km in the lower slope and an obviously velocity abnormal is detected in the upper

Dynamical Timescale of Pre-collapse Evolution Inferred from Chemical Distribution in the Taurus Molecular Cloud-1 (TMC-1) Filament

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choi, Yunhee; Lee, Jeong-Eun; Bourke, Tyler L.

We present observations and analyses of the low-mass star-forming region, Taurus Molecular Cloud-1 (TMC-1). CS ( J = 2–1)/N{sub 2}H{sup +} ( J = 1–0) and C{sup 17}O ( J = 2–1)/C{sup 18}O ( J = 2–1) were observed with the Five College Radio Astronomy Observatory and the Seoul Radio Astronomy Observatory, respectively. In addition, Spitzer infrared data and 1.2 mm continuum data observed with Max-Planck Millimetre Bolometer are used. We also perform chemical modeling to investigate the relative molecular distributions of the TMC-1 filament. Based on Spitzer observations, there is no young stellar object along the TMC-1 filament, while five Classmore » II and one Class I young stellar objects are identified outside the filament. The comparison between column densities calculated from dust continuum and C{sup 17}O 2–1 line emission shows that CO is depleted much more significantly in the ammonia peak than in the cyanopolyyne peak, while the column densities calculated from the dust continuum are similar at the two peaks. N{sub 2}H{sup +} is not depleted much in either peak. According to our chemical calculation, the differential chemical distribution in the two peaks can be explained by different timescales required to reach the same density, i.e., by different dynamical processes.« less

Cygnus OB2 DANCe: A high-precision proper motion study of the Cygnus OB2 association

NASA Astrophysics Data System (ADS)

Wright, Nicholas J.; Bouy, Herve; Drew, Janet E.; Sarro, Luis Manuel; Bertin, Emmanuel; Cuillandre, Jean-Charles; Barrado, David

2016-08-01

We present a high-precision proper motion study of 873 X-ray and spectroscopically selected stars in the massive OB association Cygnus OB2 as part of the DANCe project. These were calculated from images spanning a 15 yr baseline and have typical precisions <1 mas yr-1. We calculate the velocity dispersion in the two axes to be σ _α (c) = 13.0^{+0.8}_{-0.7} and σ _δ (c) = 9.1^{+0.5}_{-0.5} km s-1, using a two-component, two-dimensional model that takes into account the uncertainties on the measurements. This gives a three-dimensional velocity dispersion of σ3D = 17.8 ± 0.6 km s-1 implying a virial mass significantly larger than the observed stellar mass, confirming that the association is gravitationally unbound. The association appears to be dynamically unevolved, as evidenced by considerable kinematic substructure, non-isotropic velocity dispersions and a lack of energy equipartition. The proper motions show no evidence for a global expansion pattern, with approximately the same amount of kinetic energy in expansion as there is in contraction, which argues against the association being an expanded star cluster disrupted by process such as residual gas expulsion or tidal heating. The kinematic substructures, which appear to be close to virial equilibrium and have typical masses of 40-400 M⊙, also do not appear to have been affected by the expulsion of the residual gas. We conclude that Cyg OB2 was most likely born highly substructured and globally unbound, with the individual subgroups born in (or close to) virial equilibrium, and that the OB association has not experienced significant dynamical evolution since then.

Cloud-scale Molecular Gas Properties in 15 Nearby Galaxies

NASA Astrophysics Data System (ADS)

Sun孙, Jiayi嘉懿; Leroy, Adam K.; Schruba, Andreas; Rosolowsky, Erik; Hughes, Annie; Kruijssen, J. M. Diederik; Meidt, Sharon; Schinnerer, Eva; Blanc, Guillermo A.; Bigiel, Frank; Bolatto, Alberto D.; Chevance, Mélanie; Groves, Brent; Herrera, Cinthya N.; Hygate, Alexander P. S.; Pety, Jérôme; Querejeta, Miguel; Usero, Antonio; Utomo, Dyas

2018-06-01

We measure the velocity dispersion, σ, and surface density, Σ, of the molecular gas in nearby galaxies from CO spectral line cubes with spatial resolution 45–120 pc, matched to the size of individual giant molecular clouds. Combining 11 galaxies from the PHANGS-ALMA survey with four targets from the literature, we characterize ∼30,000 independent sightlines where CO is detected at good significance. Σ and σ show a strong positive correlation, with the best-fit power-law slope close to the expected value for resolved, self-gravitating clouds. This indicates only a weak variation in the virial parameter α vir ∝ σ 2/Σ, which is ∼1.5–3.0 for most galaxies. We do, however, observe enormous variation in the internal turbulent pressure P turb ∝ Σσ 2, which spans ∼5 dex across our sample. We find Σ, σ, and P turb to be systematically larger in more massive galaxies. The same quantities appear enhanced in the central kiloparsec of strongly barred galaxies relative to their disks. Based on sensitive maps of M31 and M33, the slope of the σ–Σ relation flattens at Σ ≲ 10 M ⊙ pc‑2, leading to high σ for a given Σ and high apparent α vir. This echoes results found in the Milky Way and likely originates from a combination of lower beam-filling factors and a stronger influence of local environment on the dynamical state of molecular gas in the low-density regime.

Searching for self-enrichment in Cygnus OB2

NASA Astrophysics Data System (ADS)

Berlanas, Sara R.; Herrero, Artemio; Comerón, Fernando; Pasquali, Anna; Simón-Díaz, Sergio

2017-11-01

Cygnus OB2 is a rich and relatively close (d~1.4 kpc) OB association in our Galaxy. It represents an ideal testbed for our theories about self-enrichment processes produced by pollution of the interstellar medium by successive generations of massive stars. Comerón & Pasquali (2012, A&A, 543, A101) found a correlation between the age of young stellar groups in Cygnus OB2 and their Galactic longitude. If is associated with a chemical composition gradient, it could support these self-enrichment processes.

NARROW Na AND K ABSORPTION LINES TOWARD T TAURI STARS: TRACING THE ATOMIC ENVELOPE OF MOLECULAR CLOUDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pascucci, I.; Simon, M. N.; Edwards, S.

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 themore » 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.« less

The Shawmere anorthosite and OB-1 as lunar highland regolith simulants

NASA Astrophysics Data System (ADS)

Battler, Melissa M.; Spray, John G.

2009-12-01

Anorthosite constitutes a major component of the lunar crust and comprises an important, if not dominant, ingredient of the lunar regolith. Given the need for highland regolith simulants in preparation for lunar surface engineering activities, we have selected an appropriate terrestrial anorthosite and performed crushing trials to generate a particle size distribution comparable to Apollo 16 regolith sample 64 500. The root simulant is derived from a granoblastic facies of the Archean Shawmere Complex of the Kapuskasing Structural Zone of Ontario, Canada. The Shawmere exhibits minimal retrogression, is homogeneous and has an average plagioclase composition of An 78 (bytownite). Previous industrial interest in this calcic anorthosite has resulted in quarrying operations, which provide ease of extraction and access for potential large-scale simulant production. A derivative of the Shawmere involves the addition of olivine slag, crushed to yield a particle size distribution similar to that of the agglutinate and glass components of the Apollo sample. This simulant is referred to as OB-1. The Shawmere and OB-1 regolith simulants are lunar highland analogues, conceived to produce geotechnical properties of benefit to designing and testing drilling, excavation and construction equipment for future lunar surface operations.

Adipose Deficiency of Nrf2 in ob/ob Mice Results in Severe Metabolic Syndrome

PubMed Central

Xue, Peng; Hou, Yongyong; Chen, Yanyan; Yang, Bei; Fu, Jingqi; Zheng, Hongzhi; Yarborough, Kathy; Woods, Courtney G.; Liu, Dianxin; Yamamoto, Masayuki; Zhang, Qiang; Andersen, Melvin E.; Pi, Jingbo

2013-01-01

Nuclear factor E2–related factor 2 (Nrf2) is a transcription factor that functions as a master regulator of the cellular adaptive response to oxidative stress. Our previous studies showed that Nrf2 plays a critical role in adipogenesis by regulating expression of CCAAT/enhancer-binding protein β and peroxisome proliferator–activated receptor γ. To determine the role of Nrf2 in the development of obesity and associated metabolic disorders, the incidence of metabolic syndrome was assessed in whole-body or adipocyte-specific Nrf2-knockout mice on a leptin-deficient ob/ob background, a model with an extremely positive energy balance. On the ob/ob background, ablation of Nrf2, globally or specifically in adipocytes, led to reduced white adipose tissue (WAT) mass, but resulted in an even more severe metabolic syndrome with aggravated insulin resistance, hyperglycemia, and hypertriglyceridemia. Compared with wild-type mice, WAT of ob/ob mice expressed substantially higher levels of many genes related to antioxidant response, inflammation, adipogenesis, lipogenesis, glucose uptake, and lipid transport. Absence of Nrf2 in WAT resulted in reduced expression of most of these factors at mRNA or protein levels. Our findings support a novel role for Nrf2 in regulating adipose development and function, by which Nrf2 controls the capacity of WAT expansion and insulin sensitivity and maintains glucose and lipid homeostasis. PMID:23238296

Physical properties and scaling relations of molecular clouds: the effect of stellar feedback

NASA Astrophysics Data System (ADS)

Grisdale, Kearn; Agertz, Oscar; Renaud, Florent; Romeo, Alessandro B.

2018-06-01

Using hydrodynamical simulations of entire galactic discs similar to the Milky Way, reaching 4.6{ pc} resolution, we study the origins of observed physical properties of giant molecular clouds (GMCs). We find that efficient stellar feedback is a necessary ingredient in order to develop a realistic interstellar medium (ISM), leading to molecular cloud masses, sizes, velocity dispersions and virial parameters in excellent agreement with Milky Way observations. GMC scaling relations observed in the Milky Way, such as the mass-size (M-R), velocity dispersion-size (σ-R), and the σ-RΣ relations, are reproduced in a feedback driven ISM when observed in projection, with M∝R2.3 and σ∝R0.56. When analysed in 3D, GMC scaling relations steepen significantly, indicating potential limitations of our understanding of molecular cloud 3D structure from observations. Furthermore, we demonstrate how a GMC population's underlying distribution of virial parameters can strongly influence the scatter in derived scaling relations. Finally, we show that GMCs with nearly identical global properties exist in different evolutionary stages, where a majority of clouds being either gravitationally bound or expanding, but with a significant fraction being compressed by external ISM pressure, at all times.

Defatted safflower seed extract inhibits adipogenesis in 3T3-L1 preadipocytes and improves lipid profiles in C57BL/6J ob/ob mice fed a high-fat diet.

PubMed

Hwang, Eun-Young; Yu, Mi-Hee; Jung, Yeon-Seop; Lee, Sam-Pin; Shon, Jin Han; Lee, Syng-Ook

2016-09-01

In the present study, we hypothesized that defatted safflower seed which is known to be rich in polyphenols might influence adipogenesis and obesity-related disorders, and therefore the anti-adipogenic and hypolipidemic effects of ethanol extract from defatted safflower (Cathamus tinctorius L.) seeds (CSE) were investigated both in cultured 3T3-L1 preadipocytes and in C57BL/6J ob/ob mice fed a high-fat diet. CSE inhibited adipocyte differentiation of 3T3-L1 preadipocytes and decreased expression of the adipogenic transcription factors, SREBP1c and PPARγ, and their target genes. Six-week-old obese (ob/ob) mice were fed a high-fat diet and treated with CSE (50 or 100 mg/kg/day) by oral gavage for 6 weeks. Body fat mass (epididymal and perirenal white adipose tissues) in the CSE-treated groups was significantly lower than that in the high-fat diet control (HFD) group, whereas average daily food intake was not significantly different among the groups. Plasma and hepatic triglyceride levels and plasma low-density lipoprotein cholesterol level were also significantly lower in the CSE groups compared to the HFD group. These results suggest that CSE which decreases body fat mass and improves lipid profiles in plasma and liver, represents a potential treatment option for obesity and associated metabolic disorders, including hyperlipidemia. Copyright © 2016 Elsevier Inc. All rights reserved.

THE ARIZONA RADIO OBSERVATORY CO MAPPING SURVEY OF GALACTIC MOLECULAR CLOUDS. IV. THE NGC 1333 CLOUD IN PERSEUS IN CO J = 2-1 AND {sup 13}CO J = 2-1

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bieging, John H.; Revelle, Melissa; Peters, William L.

2014-09-01

We mapped the NGC 1333 section of the Perseus Molecular Cloud in the J = 2-1 emission lines of {sup 12}CO and {sup 13}CO over a 50' × 60' region (3.4 × 4.1 pc at the cloud distance of 235 pc), using the Arizona Radio Observatory Heinrich Hertz Submillimeter Telescope. The angular resolution is 38'' (0.04 pc) and velocity resolution is 0.3 km s{sup –1}. We compare our velocity moment maps with known positions of young stellar objects (YSOs) and (sub)millimeter dust continuum emission. The CO emission is brightest at the center of the cluster of YSOs, but is detectedmore » over the full extent of the mapped region at ≥10 × rms. The morphology of the CO channel maps shows a kinematically complex structure, with many elongated features extending from the YSO cluster outward by ∼1 pc. One notable feature appears as a narrow serpentine structure that curves and doubles back, with a total length of ∼3 pc. The {sup 13}CO velocity channel maps show evidence for many low-density cavities surrounded by partial shell-like structures, consistent with previous studies. Maps of the velocity moments show localized effects of bipolar outflows from embedded YSOs, as well as a large-scale velocity gradient around the central core of YSOs, suggestive of large-scale turbulent cloud motions determining the location of current star formation. The CO/{sup 13}CO intensity ratios show the distribution of the CO opacity, which exhibits a complex kinematic structure. Identified YSOs are located mainly at the positions of greatest CO opacity. The maps are available for download as FITS files.« less

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.

Star formation in massive Milky Way molecular clouds: Building a bridge to distant galaxies

NASA Astrophysics Data System (ADS)

Willis, Sarah Elizabeth

regions, indicating that they have a higher fraction of dense gas than the clouds that are forming primarily low mass stars. There is still significant spread at a given average gas density, indicating that the star formation history and dense gas fraction play important roles in determining an individual molecular cloud's place in a Sigma SFR vs. Sigmagas diagram. Zooming in, SigmaSFR vs. Sigma gas was examined within the individual clouds, revealing a decrease relative to the spread that is observed for the average over whole clouds. The dependence of SigmaSFR on Sigma gas increases significantly above AV ˜ 5 - 10 which is consistent with previous measurements of a threshold for star formation around AV = 8 or Sigma gas = 0.04 g cm-2. NGC 6334 was found to be consistent with a threshold for massive star formation at Sigmagas = 1 g cm-2.

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.;

Impaired contractile responses and altered expression and phosphorylation of Ca2+ sensitization proteins in gastric antrum smooth muscles from ob/ob mice

PubMed Central

Bhetwal, Bhupal P.; An, Changlong; Baker, Salah A.; Lyon, Kristin L.

2013-01-01

Diabetic gastroparesis is a common complication of diabetes, adversely affecting quality of life with symptoms of abdominal discomfort, nausea, and vomiting. The pathogenesis of this complex disorder is not well understood, involving abnormalities in the extrinsic and enteric nervous systems, interstitial cells of Cajal (ICCs), smooth muscles and immune cells. The ob/ob mouse model of obesity and diabetes develops delayed gastric emptying, providing an animal model for investigating how gastric smooth muscle dysfunction contributes to the pathophysiology of diabetic gastroparesis. Although ROCK2, MYPT1, and CPI-17 activities are reduced in intestinal motility disorders, their functioning has not been investigated in diabetic gastroparesis. We hypothesized that reduced expression and phosphorylation of the myosin light chain phosphatase (MLCP) inhibitory proteins MYPT1 and CPI-17 in ob/ob gastric antrum smooth muscles could contribute to the impaired antrum smooth muscle function of diabetic gastroparesis. Spontaneous and carbachol- and high K+-evoked contractions of gastric antrum smooth muscles from 7 to 12 week old male ob/ob mice were reduced compared to age- and strain-matched controls. There were no differences in spontaneous and agonist-evoked intracellular Ca2+ transients and myosin light chain kinase expression. The F-actin:G-actin ratios were similar. Rho kinase 2 (ROCK2) expression was decreased at both ages. Basal and agonist-evoked MYPT1 and myosin light chain 20 phosphorylation, but not CPI-17 phosphorylation, was reduced compared to age-matched controls. These findings suggest that reduced MLCP inhibition due to decreased ROCK2 phosphorylation of MYPT1 in gastric antrum smooth muscles contributes to the antral dysmotility of diabetic gastroparesis. PMID:23576331

Systemic anti-TNFalpha treatment restores diabetes-impaired skin repair in ob/ob mice by inactivation of macrophages.

PubMed

Goren, Itamar; Müller, Elke; Schiefelbein, Dana; Christen, Urs; Pfeilschifter, Josef; Mühl, Heiko; Frank, Stefan

2007-09-01

To date, diabetes-associated skin ulcerations represent a therapeutic problem of clinical importance. The insulin-resistant type II diabetic phenotype is functionally connected to obesity in rodent models of metabolic syndrome through the release of inflammatory mediators from adipose tissue. Here, we used the impaired wound-healing process in obese/obese (ob/ob) mice to investigate the impact of obesity-mediated systemic inflammation on cutaneous wound-healing processes. Systemic administration of neutralizing monoclonal antibodies against tumor necrosis factor (TNF)alpha (V1q) or monocyte/macrophage-expressed EGF-like module-containing mucin-like hormone receptor-like (Emr)-1 (F4/80) into wounded ob/ob mice at the end of acute wound inflammation initiated a rapid and complete neo-epidermal coverage of impaired wound tissue in the presence of a persisting diabetic phenotype. Wound closure in antibody-treated mice was paralleled by a marked attenuation of wound inflammation. Remarkably, anti-TNFalpha- and anti-F4/80-treated mice exhibited a strong reduction in circulating monocytic cells and reduced numbers of viable macrophages at the wound site. Our data provide strong evidence that anti-TNFalpha therapy, widely used in chronic inflammatory diseases in humans, might also exert effects by targeting "activated" TNFalpha-expressing macrophage subsets, and that inactivation or depletion of misbehaving macrophages from impaired wounds might be a novel therapeutic clue to improve healing of skin ulcers.

Filamentary flow and magnetic geometry in evolving cluster-forming molecular cloud clumps

NASA Astrophysics Data System (ADS)

Klassen, Mikhail; Pudritz, Ralph E.; Kirk, Helen

2017-02-01

We present an analysis of the relationship between the orientation of magnetic fields and filaments that form in 3D magnetohydrodynamic simulations of cluster-forming, turbulent molecular cloud clumps. We examine simulated cloud clumps with size scales of L ˜ 2-4 pc and densities of n ˜ 400-1000 cm-3 with Alfvén Mach numbers near unity. We simulated two cloud clumps of different masses, one in virial equilibrium, the other strongly gravitationally bound, but with the same initial turbulent velocity field and similar mass-to-flux ratio. We apply various techniques to analyse the filamentary and magnetic structure of the resulting cloud, including the DISPERSE filament-finding algorithm in 3D. The largest structure that forms is a 1-2 parsec-long filament, with smaller connecting sub-filaments. We find that our simulated clouds, wherein magnetic forces and turbulence are comparable, coherent orientation of the magnetic field depends on the virial parameter. Sub-virial clumps undergo strong gravitational collapse and magnetic field lines are dragged with the accretion flow. We see evidence of filament-aligned flow and accretion flow on to the filament in the sub-virial cloud. Magnetic fields oriented more parallel in the sub-virial cloud and more perpendicular in the denser, marginally bound cloud. Radiative feedback from a 16 M⊙ star forming in a cluster in one of our simulation's ultimately results in the destruction of the main filament, the formation of an H II region, and the sweeping up of magnetic fields within an expanding shell at the edges of the H II region.

Simulations of star-forming molecular clouds: observational predictions

NASA Astrophysics Data System (ADS)

Zhang, Shangjia; Hartmann, Lee; Kuznetsova, Aleksandra; Abelardo Zamora, Manuel

2018-01-01

Observations of protostellar molecular cloud cores can be used to test theories of star formation. However, observational results can be biased because of limited information: (a) only two spatial dimensions and one velocity dimension can be measured, (b) and cores generally are not spherically symmetric. We use numerical simulations of the formation and collapse of molecular gas with sink particles to make observational predictions. We use the radiative transfer code LIME to predict CO and NH3 channel maps. We find reasonable agreement with observed velocity structures and gradients but occasional large differences depending on viewing angle.

Is Molecular Cloud Turbulence Driven by External Supernova Explosions?

NASA Astrophysics Data System (ADS)

Seifried, Daniel; Walch, Stefanie; Haid, Sebastian; Girichidis, Philipp; Naab, Thorsten

2018-03-01

We present high-resolution (∼0.1 pc), hydrodynamical and magnetohydrodynamical simulations to investigate whether the observed level of molecular cloud (MC) turbulence can be generated and maintained by external supernova (SN) explosions. The MCs are formed self-consistently within their large-scale galactic environment following the non-equilibrium formation of H2 and CO, including (self-) shielding and important heating and cooling processes. The MCs inherit their initial level of turbulence from the diffuse ISM, where turbulence is injected by SN explosions. However, by systematically exploring the effect of individual SNe going off outside the clouds, we show that at later stages the importance of SN-driven turbulence is decreased significantly. This holds for different MC masses as well as for MCs with and without magnetic fields. The SN impact also decreases rapidly with larger distances. Nearby SNe (d ∼ 25 pc) boost the turbulent velocity dispersions of the MC by up to 70% (up to a few km s‑1). For d > 50 pc, however, their impact decreases fast with increasing d and is almost negligible. For all probed distances the gain in velocity dispersion decays rapidly within a few 100 kyr. This is significantly shorter than the average timescale for an MC to be hit by a nearby SN under solar neighborhood conditions (∼2 Myr). Hence, at these conditions SNe are not able to sustain the observed level of MC turbulence. However, in environments with high gas surface densities and SN rates, like the Central Molecular Zone, observed elevated MC dispersions could be triggered by external SNe.

Gravity, turbulence and the scaling ``laws'' in molecular clouds

NASA Astrophysics Data System (ADS)

Ballesteros-Paredes, Javier

The so-called Larson (1981) scaling laws found empirically in molecular clouds have been generally interpreted as evidence that the clouds are turbulent and fractal. In the present contribution we discussed how recent observations and models of cloud formation suggest that: (a) these relations are the result of strong observational biases due to the cloud definition itself: since the filling factor of the dense structures is small, by thresholding the column density the computed mean density between clouds is nearly constant, and nearly the same as the threshold (Ballesteros-Paredes et al. 2012). (b) When accounting for column density variations, the velocity dispersion-size relation does not appears anymore. Instead, dense cores populate the upper-left corner of the δ v-R diagram (Ballesteros-Paredes et al. 2011a). (c) Instead of a δ v-R relation, a more appropriate relation seems to be δ v 2 / R = 2 GMΣ, which suggest that clouds are in collapse, rather than supported by turbulence (Ballesteros-Paredes et al. 2011a). (d) These results, along with the shapes of the star formation histories (Hartmann, Ballesteros-Paredes & Heitsch 2012), line profiles of collapsing clouds in numerical simulations (Heitsch, Ballesteros-Paredes & Hartmann 2009), core-to-core velocity dispersions (Heitsch, Ballesteros-Paredes & Hartmann 2009), time-evolution of the column density PDFs (Ballesteros-Paredes et al. 2011b), etc., strongly suggest 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. This result calls into question if the scale-free nature of the motions has a turbulent, origin (Ballesteros-Paredes et al. 2011a; Ballesteros-Paredes et al. 2011b, Ballesteros-Paredes et al. 2012).

Winds of very low metallicity OB stars: crossing the frontier of the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Garcia, Miriam

2011-10-01

Very low metallicity massive stars are a key ingredient for our understanding of the early Universe because of their connection with the dominant conditions at that time, the reionization epoch and long-GRBs. In the studies of massive stars radiation driven winds play a crucial manifold role, being a chief agent of stellar evolution, altering the optical diagnostics for parameter determination and injecting radiative and mechanical energy into their surroundings. However, the theory of radiation driven winds has only be tested down to SMC metallicities and some important open questions remain: the existence of solar-metallicity stars with weak winds and very recent evidence of relatively strong winds in metal-poor stars.We have secured VLT optical spectra of a sample of early-type massive stars in IC 1613, a very metal poor { <0.1Zo} irregular galaxy of the Local Group that represents the next step towards low metallicities after the SMC. We request low resolution COS spectra {COS/FUV-G140L} of a sub-set of OB stars probing different wind regimes. The wind lines in the 1150-1800A range, together with the optical spectra, will allow us to derive consistently the photospheric and wind parameters of the sample. Results will be interpreted in the context of both evolutionary and radiatively driven winds theories, testing the current paradigm at unexplored low metallicities and increasing our knowledge of massive stars under conditions closer to those of the deep Universe.COS enhanced sensitivity will allow us to perform for the first time detailed studies of **resolved** OB stars in an environment with poorer metal content than the SMC.

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.

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

Accretion and outflow in the proplyd-like objects near Cygnus OB2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guarcello, M. G.; Drake, J. J.; Wright, N. J.

2014-09-20

Cygnus OB2 is the most massive association within 2 kpc from the Sun, hosting hundreds of massive stars, thousands of young low mass members, and some sights of active star formation in the surrounding cloud. Recently, 10 photoevaporating proplyd-like objects with tadpole-shaped morphology were discovered in the outskirts of the OB association, approximately 6-14 pc away from its center. The classification of these objects is ambiguous, being either evaporating residuals of the parental cloud that are hosting a protostar inside or disk-bearing stars with an evaporating disk, such as the evaporating proplyds observed in the Trapezium Cluster in Orion. Inmore » this paper, we present a study based on low-resolution optical spectroscopic observations made with the Optical System for Imaging and low Resolution Integrated Spectroscopy, mounted on the 10.4 m Gran Telescopio CANARIAS, of two of these protostars. The spectrum of one of the objects shows evidence of accretion but not of outflows. In the latter object, the spectra show several emission lines indicating the presence of an actively accreting disk with outflow. We present estimates of the mass loss rate and the accretion rate from the disk, showing that the former exceeds the latter as observed in other known objects with evaporating disks. We also show evidence of a strong variability in the integrated flux observed in these objects as well as in the accretion and outflow diagnostics.« less

Hierarchical Fragmentation in the Perseus Molecular Cloud: From the Cloud Scale to Protostellar Objects

NASA Astrophysics Data System (ADS)

Pokhrel, Riwaj; Myers, Philip C.; Dunham, Michael M.; Stephens, Ian W.; Sadavoy, Sarah I.; Zhang, Qizhou; Bourke, Tyler L.; Tobin, John J.; Lee, Katherine I.; Gutermuth, Robert A.; Offner, Stella S. R.

2018-01-01

We present a study of hierarchical structure in the Perseus molecular cloud, from the scale of the entire cloud (≳ 10 pc) to smaller clumps (∼1 pc), cores (∼0.05–0.1 pc), envelopes (∼300–3000 au), and protostellar objects (∼15 au). We use new observations from the Submillimeter Array (SMA) large project “Mass Assembly of Stellar Systems and their Evolution with the SMA (MASSES)” to probe the envelopes, and recent single-dish and interferometric observations from the literature for the remaining scales. This is the first study to analyze hierarchical structure over five scales in the same cloud complex. We compare the number of fragments with the number of Jeans masses in each scale to calculate the Jeans efficiency, or the ratio of observed to expected number of fragments. The velocity dispersion is assumed to arise either from purely thermal motions or from combined thermal and non-thermal motions inferred from observed spectral line widths. For each scale, thermal Jeans fragmentation predicts more fragments than observed, corresponding to inefficient thermal Jeans fragmentation. For the smallest scale, thermal plus non-thermal Jeans fragmentation also predicts too many protostellar objects. However, at each of the larger scales thermal plus non-thermal Jeans fragmentation predicts fewer than one fragment, corresponding to no fragmentation into envelopes, cores, and clumps. Over all scales, the results are inconsistent with complete Jeans fragmentation based on either thermal or thermal plus non-thermal motions. They are more nearly consistent with inefficient thermal Jeans fragmentation, where the thermal Jeans efficiency increases from the largest to the smallest scale.

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.

A Herschel-SPIRE Survey of the MonR2 Giant Molecular Cloud

NASA Astrophysics Data System (ADS)

Pokhrel, Riwaj; Gutermuth, Robert; Ali, Babar; Megeath, Thomas; Pipher, Judith; Myers, Philip; Fischer, William; Henning, Thomas; Wolk, Scott; Allen, Lori; Tobin, John

2015-08-01

We present a new survey of the MonR2 giant molecular cloud with SPIRE on the Herschel Space Observatory. We cross-calibrated SPIRE data with Planck-HFI and accounted for its absolute offset and zero point correction. We fixed emissivity with the help of flux-error and flux ratio plots. As the best representation of cold dusty molecular clouds, we did greybody fits of the SEDs. We studied the nature of distribution of column densities above and below certain critical limit, followed by the mass and temperature distributions for different regions. We used dendrograms as a technique to study the hierarchical structures in the GMC.

Supernova Remnant Kes 17: An Efficient Cosmic Ray Accelerator inside a Molecular Cloud

NASA Astrophysics Data System (ADS)

Gelfand, Joseph D.; Castro, Daniel; Slane, Patrick O.; Temim, Tea; Hughes, John P.; Rakowski, Cara

2013-11-01

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.

HP2 survey. III. The California Molecular Cloud: A sleeping giant revisited

NASA Astrophysics Data System (ADS)

Lada, Charles J.; Lewis, John A.; Lombardi, Marco; Alves, João

2017-10-01

We present new high resolution and dynamic range dust column density and temperature maps of the California Molecular Cloud derived from a combination of Planck and Herschel dust-emission maps, and 2MASS NIR dust-extinction maps. We used these data to determine the ratio of the 2.2 μm extinction coefficient to the 850 μm opacity and found the value to be close to that found in similar studies of the Orion B and Perseus clouds but higher than that characterizing the Orion A cloud, indicating that variations in the fundamental optical properties of dust may exist between local clouds. We show that over a wide range of extinction, the column density probability distribution function (pdf) of the cloud can be well described by a simple power law (I.e., PDFN ∝ AK -n) with an index (n = 4.0 ± 0.1) that represents a steeper decline with AK than found (n ≈ 3) in similar studies of the Orion and Perseus clouds. Using only the protostellar population of the cloud and our extinction maps we investigate the Schmidt relation, that is, the relation between the protostellar surface density, Σ∗, and extinction, AK, within the cloud. We show that Σ∗ is directly proportional to the ratio of the protostellar and cloud pdfs, I.e., PDF∗(AK)/PDFN(AK). We use the cumulative distribution of protostars to infer the functional forms for both Σ∗ and PDF∗. We find that Σ∗ is best described by two power-law functions. At extinctions AK ≲ 2.5 mag, Σ∗ ∝ AK β with β = 3.3 while at higher extinctions β = 2.5, both values steeper than those (≈2) found in other local giant molecular clouds (GMCs). We find that PDF∗ is a declining function of extinction also best described by two power-laws whose behavior mirrors that of Σ∗. Our observations suggest that variations both in the slope of the Schmidt relation and in the sizes of the protostellar populations between GMCs are largely driven by variations in the slope, n, of PDFN(AK). This confirms earlier studies

The parsec-scale relationship between ICO and AV in local molecular clouds

NASA Astrophysics Data System (ADS)

Lee, Cheoljong; Leroy, Adam K.; Bolatto, Alberto D.; Glover, Simon C. O.; Indebetouw, Remy; Sandstrom, Karin; Schruba, Andreas

2018-03-01

We measure the parsec-scale relationship between integrated CO intensity (ICO) and visual extinction (AV) in 24 local molecular clouds using maps of CO emission and dust optical depth from Planck. This relationship informs our understanding of CO emission across environments, but clean Milky Way measurements remain scarce. We find uniform ICO for a given AV, with the results bracketed by previous studies of the Pipe and Perseus clouds. Our measured ICO-AV relation broadly agrees with the standard Galactic CO-to-H2 conversion factor, the relation found for the Magellanic clouds at coarser resolution, and numerical simulations by Glover & Clark (2016). This supports the idea that CO emission primarily depends on shielding, which protects molecules from dissociating radiation. Evidence for CO saturation at high AV and a threshold for CO emission at low AV varies remains uncertain due to insufficient resolution and ambiguities in background subtraction. Resolution of order 0.1 pc may be required to measure these features. We use this ICO-AV relation to predict how the CO-to-H2 conversion factor (XCO) would change if the Solar Neighbourhood clouds had different dust-to-gas ratio (metallicity). The calculations highlight the need for improved observations of the CO emission threshold and H I shielding layer depth. They are also sensitive to the shape of the column density distribution. Because local clouds collectively show a self-similar distribution, we predict a shallow metallicity dependence for XCO down to a few tenths of solar metallicity. However, our calculations also imply dramatic variations in cloud-to-cloud XCO at subsolar metallicity.

Observations of OH and CO in the Orion Molecular Cloud

NASA Technical Reports Server (NTRS)

Viscuso, P. J.

1985-01-01

The results of millimeter and submillimeter observations of the BN-KL region of the Orion molecular cloud are reported. Observations were made with a 91 cm bent Cassegrain telescope fitted with an interferometer/grating spectrometer during flights at 13-14 km altitude in the NASA Kuiper Observatory. The data collected covered the 2Pi(1/2)J = 3/2 yields 1/2 and 2Pi(3/2)J = 7/2 yields 5/2 rotational transitions of OH. The measurements were made at 163 and 84 micron wavelengths, respectively. The OH emitting regions was estimated to have a temperature of 1000 K and a molecular hydrogen density of about 6 million/cu cm. Depopulation of the excited states of OH was caused primarily by collisional excitation. The OH fill factor for the region survey was about 10 percent, in line with predictions for a post-shocked region.

Observations of OH and CO in the Orion Molecular Cloud

NASA Astrophysics Data System (ADS)

Viscuso, P. J.

The results of millimeter and submillimeter observations of the BN-KL region of the Orion molecular cloud are reported. Observations were made with a 91 cm bent Cassegrain telescope fitted with an interferometer/grating spectrometer during flights at 13-14 km altitude in the NASA Kuiper Observatory. The data collected covered the 2Pi(1/2)J = 3/2 yields 1/2 and 2Pi(3/2)J = 7/2 yields 5/2 rotational transitions of OH. The measurements were made at 163 and 84 micron wavelengths, respectively. The OH emitting regions was estimated to have a temperature of 1000 K and a molecular hydrogen density of about 6 million/cu cm. Depopulation of the excited states of OH was caused primarily by collisional excitation. The OH fill factor for the region survey was about 10 percent, in line with predictions for a post-shocked region.

iPLA2β deficiency attenuates obesity and hepatic steatosis in ob/ob mice through hepatic fatty-acyl phospholipid remodeling.

PubMed

Deng, Xiuling; Wang, Jiliang; Jiao, Li; Utaipan, Tanyarath; Tuma-Kellner, Sabine; Schmitz, Gerd; Liebisch, Gerhard; Stremmel, Wolfgang; Chamulitrat, Walee

2016-05-01

PLA2G6 or GVIA calcium-independent PLA2 (iPLA2β) is identified as one of the NAFLD modifier genes in humans, and thought to be a target for NAFLD therapy. iPLA2β is known to play a house-keeping role in phospholipid metabolism and remodeling. However, its role in NAFLD pathogenesis has not been supported by results obtained from high-fat feeding of iPLA2β-null (PKO) mice. Unlike livers of human NAFLD and genetically obese rodents, fatty liver induced by high-fat diet is not associated with depletion of hepatic phospholipids. We therefore tested whether iPLA2β could regulate obesity and hepatic steatosis in leptin-deficient mice by cross-breeding PKO with ob/ob mice to generate ob/ob-PKO mice. Here we observed an improvement in ob/ob-PKO mice with significant reduction in serum enzymes, lipids, glucose, insulin as well as improved glucose tolerance, and reduction in islet hyperplasia. The improvement in hepatic steatosis measured by liver triglycerides, fatty acids and cholesterol esters was associated with decreased expression of PPARγ and de novo lipogenesis genes, and the reversal of β-oxidation gene expression. Notably, ob/ob livers contained depleted levels of lysophospholipids and phospholipids, and iPLA2β deficiency in ob/ob-PKO livers lowers the former, but replenished the latter particularly phosphatidylethanolamine (PE) and phosphatidylcholine (PC) that contained arachidonic (AA) and docosahexaenoic (DHA) acids. Compared with WT livers, PKO livers also contained increased PE and PC containing AA and DHA. Thus, iPLA2β deficiency protected against obesity and ob/ob fatty liver which was associated with hepatic fatty-acyl phospholipid remodeling. Our results support the deleterious role of iPLA2β in severe obesity associated NAFLD. Copyright © 2016 Elsevier B.V. All rights reserved.

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.

Kinematic Structure of Molecular Gas around High-mass YSO, Papillon Nebula, in N159 East in the Large Magellanic Cloud: A New Perspective with ALMA

NASA Astrophysics Data System (ADS)

Saigo, Kazuya; Onishi, Toshikazu; Nayak, Omnarayani; Meixner, Margaret; Tokuda, Kazuki; Harada, Ryohei; Morioka, Yuuki; Sewiło, Marta; Indebetouw, Remy; Torii, Kazufumi; Kawamura, Akiko; Ohama, Akio; Hattori, Yusuke; Yamamoto, Hiroaki; Tachihara, Kengo; Minamidani, Tetsuhiro; Inoue, Tsuyoshi; Madden, Suzanne; Galametz, Maud; Lebouteiller, Vianney; Chen, C.-H. Rosie; Mizuno, Norikazu; Fukui, Yasuo

2017-01-01

We present the ALMA Band 3 and Band 6 results of 12CO(2-1), 13CO(2-1), H30α recombination line, free-free emission around 98 GHz, and the dust thermal emission around 230 GHz toward the N159 East Giant Molecular Cloud (N159E) in the Large Magellanic Cloud (LMC). LMC is the nearest active high-mass star-forming face-on galaxy at a distance of 50 kpc and is the best target for studing high-mass star formation. ALMA observations show that N159E is the complex of filamentary clouds with the width and length of ˜1 pc and several parsecs. The total molecular mass is 0.92 × 105 M⊙ from the 13CO(2-1) intensity. N159E harbors the well-known Papillon Nebula, a compact high-excitation H II region. We found that a YSO associated with the Papillon Nebula has the mass of 35 M⊙ and is located at the intersection of three filamentary clouds. It indicates that the formation of the high-mass YSO was induced by the collision of filamentary clouds. Fukui et al. reported a similar kinematic structure toward two YSOs in the N159 West region, which are the other YSOs that have the mass of ≳35 M⊙. This suggests that the collision of filamentary clouds is a primary mechanism of high-mass star formation. We found a small molecular hole around the YSO in Papillon Nebula with a sub-parsec scale. It is filled by free-free and H30α emission. The temperature of the molecular gas around the hole reaches ˜80 K. It indicates that this YSO has just started the distruction of parental molecular cloud.

KINEMATIC STRUCTURE OF MOLECULAR GAS AROUND HIGH-MASS YSO, PAPILLON NEBULA, IN N159 EAST IN THE LARGE MAGELLANIC CLOUD: A NEW PERSPECTIVE WITH ALMA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saigo, Kazuya; Harada, Ryohei; Kawamura, Akiko

We present the ALMA Band 3 and Band 6 results of {sup 12}CO(2-1), {sup 13}CO(2-1), H30 α recombination line, free–free emission around 98 GHz, and the dust thermal emission around 230 GHz toward the N159 East Giant Molecular Cloud (N159E) in the Large Magellanic Cloud (LMC). LMC is the nearest active high-mass star-forming face-on galaxy at a distance of 50 kpc and is the best target for studing high-mass star formation. ALMA observations show that N159E is the complex of filamentary clouds with the width and length of ∼1 pc and several parsecs. The total molecular mass is 0.92 ×more » 10{sup 5} M {sub ⊙} from the {sup 13}CO(2-1) intensity. N159E harbors the well-known Papillon Nebula, a compact high-excitation H ii region. We found that a YSO associated with the Papillon Nebula has the mass of 35 M {sub ⊙} and is located at the intersection of three filamentary clouds. It indicates that the formation of the high-mass YSO was induced by the collision of filamentary clouds. Fukui et al. reported a similar kinematic structure toward two YSOs in the N159 West region, which are the other YSOs that have the mass of ≳35 M {sub ⊙}. This suggests that the collision of filamentary clouds is a primary mechanism of high-mass star formation. We found a small molecular hole around the YSO in Papillon Nebula with a sub-parsec scale. It is filled by free–free and H30 α emission. The temperature of the molecular gas around the hole reaches ∼80 K. It indicates that this YSO has just started the distruction of parental molecular cloud.« less

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

Optical polarimetry and molecular line studies of L1157 dark molecular cloud

NASA Astrophysics Data System (ADS)

Sharma, Ekta; Soam, Archana; Gopinathan, Maheswar

2018-04-01

Filaments are omnipresent in molecular clouds which are believed to fragment into cores. The detailed process of the evolution from filaments to cores depends critically on the physical conditions in the star forming region. This study aims at characterising gas motions using velocity structure and finding the dynamical importance of magnetic fields in the filament morphology. The plane-of-the-sky component of the magnetic field has been measured using optical polarization of the background stars. The orientation is found to be almost perpendicular to the filament implying its dynamical importance in the evolution of the cloud. Optical polarimetric results match very well with the sub millimetre polarization angles obtained in the inner core regions. The magnetic fields are found to have an orientation of 130° east with respect to north. The angular offset between the outflow axis and the magnetic field direction is found to be 25°. Values for parameters like the excitation temperature, optical depth and column densities have been derived using molecular lines. Optically thick lines show non-gaussian features. The non-thermal widths tell about the presence of turbulent motions whereas the C180 lines follow Gaussian features almost at all the locations observed in the filament.

Reduced inflammatory response and increased microcirculatory disturbances during hepatic ischemia-reperfusion injury in steatotic livers of ob/ob mice

PubMed Central

Hasegawa, Tadashi; Ito, Yoshiya; Wijeweera, Jayanthika; Liu, Jie; Malle, Ernst; Farhood, Anwar; McCuskey, Robert S.; Jaeschke, Hartmut

2016-01-01

Steatosis is a major risk factor for complications after liver surgery. Since neutrophil cytotoxicity is critical for ischemia-reperfusion injury in normal livers, the aim of the present study was to evaluate whether an exaggerated inflammatory response could cause the increased injury in steatotic livers. In C57Bl/6 mice, 60 min of warm hepatic ischemia triggered a gradual increase in hepatic neutrophil accumulation during reperfusion with peak levels of 100-fold over baseline at 12 h of reperfusion. Neutrophil extravasation and a specific neutrophil-induced oxidant stress (immunostaining for hypochlorous acid-modified epitopes) started at 6 h of reperfusion and peaked at 12–24 h. Ob/ob mice, which had a severe macrovesicular steatosis, suffered significantly higher injury (alanine transaminase activity: 18,000 ± 2,100 U/l; 65% necrosis) compared with lean littermates (alanine transaminase activity: 4,900 ± 720 U/l; 24% necrosis) at 6 h of reperfusion. However, 62% fewer neutrophils accumulated in steatotic livers. This correlated with an attenuated increase in mRNA levels of several proinflammatory genes in ob/ob mice during reperfusion. In contrast, sham-operated ob/ob mice had a 50% reduction in liver blood flow and 35% fewer functional sinusoids compared with lean littermates. These deficiencies in liver blood flow and the microcirculation were further aggravated only in ob/ob mice during reperfusion. The attenuated inflammatory response and reduced neutrophil-induced oxidant stress observed in steatotic livers during reperfusion cannot be responsible for the dramatically increased injury in ob/ob mice. In contrast, the aggravated injury appears to be mediated by ischemic necrosis due to massive impairment of blood and oxygen supply in the steatotic livers. PMID:17307725

Relationship between turbulence energy and density variance in the solar neighbourhood molecular clouds

NASA Astrophysics Data System (ADS)

Kainulainen, J.; Federrath, C.

2017-11-01

The relationship between turbulence energy and gas density variance is a fundamental prediction for turbulence-dominated media and is commonly used in analytic models of star formation. We determine this relationship for 15 molecular clouds in the solar neighbourhood. We use the line widths of the CO molecule as the probe of the turbulence energy (sonic Mach number, ℳs) and three-dimensional models to reconstruct the density probability distribution function (ρ-PDF) of the clouds, derived using near-infrared extinction and Herschel dust emission data, as the probe of the density variance (σs). We find no significant correlation between ℳs and σs among the studied clouds, but we cannot rule out a weak correlation either. In the context of turbulence-dominated gas, the range of the ℳs and σs values corresponds to the model predictions. The data cannot constrain whether the turbulence-driving parameter, b, and/or thermal-to-magnetic pressure ratio, β, vary among the sample clouds. Most clouds are not in agreement with field strengths stronger than given by β ≲ 0.05. A model with b2β/ (β + 1) = 0.30 ± 0.06 provides an adequate fit to the cloud sample as a whole. Based on the average behaviour of the sample, we can rule out three regimes: (i) strong compression combined with a weak magnetic field (b ≳ 0.7 and β ≳ 3); (ii) weak compression (b ≲ 0.35); and (iii) a strong magnetic field (β ≲ 0.1). When we include independent magnetic field strength estimates in the analysis, the data rule out solenoidal driving (b < 0.4) for the majority of the solar neighbourhood clouds. However, most clouds have b parameters larger than unity, which indicates a discrepancy with the turbulence-dominated picture; we discuss the possible reasons for this.

A Comparative Study of YSO Classification Techniques using WISE Observations of the KR 120 Molecular Cloud

NASA Astrophysics Data System (ADS)

Kang, Sung-Ju; Kerton, C. R.

2014-01-01

KR 120 (Sh2-187) is a small Galactic HII region located at a distance of 1.4 kpc that shows evidence for triggered star formation in the surrounding molecular cloud. We present an analysis of the young stellar object (YSO) population of the molecular cloud as determined using a variety of classification techniques. YSO candidates are selected from the WISE all sky catalog and classified as Class I, Class II and Flat based on 1) spectral index, 2) color-color or color-magnitude plots, and 3) spectral energy distribution (SED) fits to radiative transfer models. We examine the discrepancies in YSO classification between the various techniques and explore how these discrepancies lead to uncertainty in such scientifically interesting quantities such as the ratio of Class I/Class II sources and the surface density of YSOs at various stages of evolution.

HI-to-H2 Transitions in the Perseus Molecular Cloud

NASA Astrophysics Data System (ADS)

Bialy, Shmuel; Sternberg, Amiel; Lee, Min-Young; Le Petit, Franck; Roueff, Evelyne

2015-08-01

We use the Sternberg et al. theory for interstellar atomic to molecular hydrogen (H i-to-H2) conversion to analyze H i-to-H2 transitions in five (low-mass) star-forming and dark regions in the Perseus molecular cloud, B1, B1E, B5, IC348, and NGC1333. The observed H i mass surface densities of 6.3-9.2 {M}⊙ {{pc}}-2 are consistent with H i-to-H2 transitions dominated by H i-dust shielding in predominantly atomic envelopes. For each source, we constrain the dimensionless parameter α G, and the ratio {I}{UV}/n, of the FUV intensity to hydrogen gas density. We find α G values from 5.0 to 26.1, implying characteristic atomic hydrogen densities 11.8-1.8 cm-3, for {I}{UV}≈ 1 appropriate for Perseus. Our analysis implies that the dusty H i shielding layers are probably multiphased, with thermally unstable UNM gas in addition to cold CNM within the 21 cm kinematic radius.

Chemistry and structure of giant molecular clouds in energetic environments

NASA Astrophysics Data System (ADS)

Anderson, Crystal Nicole

2016-09-01

Throughout the years many studies on Galactic star formation have been conducted. This resulted in the idea that giant molecular clouds (GMCs) are hierarchical in nature with substructures spanning a large range of sizes. The physical processes that determine how molecular clouds fragment, form clumps/cores and then stars depends strongly on both recent radiative and mechanical feed- back from massive stars and, on longer term, from enhanced cooling due to the buildup of metals. Radiative and mechanical energy input from stellar populations can alter subsequent star formation over a large part of a galaxy and hence is relevant to the evolution of galaxies. Much of our knowledge of star formation on galaxy wide scales is based on scaling laws and other parametric descriptions. But to understand the overall evolution of star formation in galaxies we need to watch the feedback processes at work on giant molecular cloud (GMC) scales. By doing this we can begin to answer how strong feedback environments change the properties of the substructure in GMCs. Tests of Galactic star formation theory to other galaxies has been a challenging process due to the lack of resolution with current instruments. Thus, only the nearest galaxies allow us to resolve GMCs and their substructures. The Large Magellanic Cloud (LMC), is one of the closest low metallicity dwarf galaxies (D˜ 50 kpc) and is close enough that current instruments can resolve the sub- structure of its GMCs to <1pc. The LMC has a star cluster located near the GMC, 30Doradus, producing high levels of far ultra violet (FUV) radiation in the inter- stellar medium (ISM). The dwarf galaxy, NGC 5253, is also a close low metallicity galaxy (3.8 Mpc) with a super star cluster, which appears to be composed of several newborn globular clusters, located within the center of the galaxy. These huge, compact collections of massive stars and their supernovae have the potential to dump large amounts of FUV radiation and momentum

Molecular Line Emission as a Tool for Galaxy Observations (LEGO). I. HCN as a tracer of moderate gas densities in molecular clouds and galaxies

NASA Astrophysics Data System (ADS)

Kauffmann, Jens; Goldsmith, Paul F.; Melnick, Gary; Tolls, Volker; Guzman, Andres; Menten, Karl M.

2017-09-01

Trends observed in galaxies, such as the Gao & Solomon relation, suggest a linear relationship between the star formation rate and the mass of dense gas available for star formation. Validation of such trends requires the establishment of reliable methods to trace the dense gas in galaxies. One frequent assumption is that the HCN (J = 1-0) transition is unambiguously associated with gas at H2 densities ≫ 104 cm-3. If so, the mass of gas at densities ≫ 104 cm-3 could be inferred from the luminosity of this emission line, LHCN (1-0). Here we use observations of the Orion A molecular cloud to show that the HCN (J = 1-0) line traces much lower densities 103 cm-3 in cold sections of this molecular cloud, corresponding to visual extinctions AV ≈ 6 mag. We also find that cold and dense gas in a cloud like Orion produces too little HCN emission to explain LHCN (1-0) in star forming galaxies, suggesting that galaxies might contain a hitherto unknown source of HCN emission. In our sample of molecules observed at frequencies near 100 GHz (also including 12CO, 13CO, C18O, CN, and CCH), N2H+ is the only species clearly associated with relatively dense gas.

G Protein–Coupled Receptor Kinase 2, With β-Arrestin 2, Impairs Insulin-Induced Akt/Endothelial Nitric Oxide Synthase Signaling in ob/ob Mouse Aorta

PubMed Central

Taguchi, Kumiko; Matsumoto, Takayuki; Kamata, Katsuo; Kobayashi, Tsuneo

2012-01-01

In type 2 diabetes, impaired insulin-induced Akt/endothelial nitric oxide synthase (eNOS) signaling may decrease the vascular relaxation response. Previously, we reported that this response was negatively regulated by G protein–coupled receptor kinase 2 (GRK2). In this study, we investigated whether/how in aortas from ob/ob mice (a model of type 2 diabetes) GRK2 and β-arrestin 2 might regulate insulin-induced signaling. Endothelium-dependent relaxation was measured in aortic strips. GRK2, β-arrestin 2, and Akt/eNOS signaling pathway proteins and activities were mainly assayed by Western blotting. In ob/ob (vs. control [Lean]) aortas: 1) insulin-induced relaxation was reduced, and this deficit was prevented by GRK2 inhibitor, anti-GRK2 antibody, and an siRNA specifically targeting GRK2. The Lean aorta relaxation response was reduced to the ob/ob level by pretreatment with an siRNA targeting β-arrestin 2. 2) Insulin-stimulated Akt and eNOS phosphorylations were decreased. 3) GRK2 expression in membranes was elevated, and, upon insulin stimulation, this expression was further increased, but β-arrestin 2 was decreased. In ob/ob aortic membranes under insulin stimulation, the phosphorylations of Akt and eNOS were augmented by GRK2 inhibitor. In mouse aorta, GRK2 may be, upon translocation, a key negative regulator of insulin responsiveness and an important regulator of the β-arrestin 2/Akt/eNOS signaling, which is implicated in diabetic endothelial dysfunction. PMID:22688330

G protein-coupled receptor kinase 2, with β-arrestin 2, impairs insulin-induced Akt/endothelial nitric oxide synthase signaling in ob/ob mouse aorta.

PubMed

Taguchi, Kumiko; Matsumoto, Takayuki; Kamata, Katsuo; Kobayashi, Tsuneo

2012-08-01

In type 2 diabetes, impaired insulin-induced Akt/endothelial nitric oxide synthase (eNOS) signaling may decrease the vascular relaxation response. Previously, we reported that this response was negatively regulated by G protein-coupled receptor kinase 2 (GRK2). In this study, we investigated whether/how in aortas from ob/ob mice (a model of type 2 diabetes) GRK2 and β-arrestin 2 might regulate insulin-induced signaling. Endothelium-dependent relaxation was measured in aortic strips. GRK2, β-arrestin 2, and Akt/eNOS signaling pathway proteins and activities were mainly assayed by Western blotting. In ob/ob (vs. control [Lean]) aortas: 1) insulin-induced relaxation was reduced, and this deficit was prevented by GRK2 inhibitor, anti-GRK2 antibody, and an siRNA specifically targeting GRK2. The Lean aorta relaxation response was reduced to the ob/ob level by pretreatment with an siRNA targeting β-arrestin 2. 2) Insulin-stimulated Akt and eNOS phosphorylations were decreased. 3) GRK2 expression in membranes was elevated, and, upon insulin stimulation, this expression was further increased, but β-arrestin 2 was decreased. In ob/ob aortic membranes under insulin stimulation, the phosphorylations of Akt and eNOS were augmented by GRK2 inhibitor. In mouse aorta, GRK2 may be, upon translocation, a key negative regulator of insulin responsiveness and an important regulator of the β-arrestin 2/Akt/eNOS signaling, which is implicated in diabetic endothelial dysfunction.

Sucrose diet induced enzymatic and hormonal responses affecting carbohydrate, lipid and energy metabolism in two species differing in insulin availability: spiny and ob/ob mice.

PubMed

Shafrir, E; Trostler, N

1984-01-01

The low-insulin responding spiny mice (Acomys cahirinus), maintained on a 50% sucrose diet vs isocaloric regular diet, responded with an impressive increase in the activity of hepatic enzymes of glycolysis and lipogenesis and in hyperlipidemia. There was no hyperinsulinemia or hyperglycemia and spiny mice did not gain weight on sucrose due to loss of adipose tissue. Serum T3 levels rose 1.8 fold and the activity of the hepatic mitochondrial FAD-glycerol-3-phosphate oxidase became induced 2.6 fold representing the enhancement of multiple, T3-dependent, energy-consuming metabolic cycles. An increased TG lipolysis in adipose tissue was also observed. C57BL/6J ob/ob mice were markedly hyperinsulinemic and gained weight on sucrose almost as much as those on regular diet, without changes in serum glucose or insulin. Serum triglyceride level decreased, whereas liver triglycerides accumulated markedly. The extent of the increase in hepatic enzyme activities related to lipogenesis was much lower both in the ob/ob mice and their lean siblings, than in spiny mice, but the basal enzyme activities in ob/ob mice were remarkably elevated. Serum T3 level was also elevated already on the regular diet and rose only slightly on sucrose. Basal glycerol phosphate oxidase activity in ob/ob mice exceeded that in spiny mice and rose only marginally on sucrose. Adipose tissue lipolysis was not increased. Thus, sucrose diet by enhancing the T3 production appeared to activate protective mechanism against weight gain in normoinsulinemic spiny mice, whereas the full expression of these mechanisms appeared to be precluded by the hyperinsulinemia of ob/ob mice.(ABSTRACT TRUNCATED AT 250 WORDS)

Gas, dust, stars, star formation, and their evolution in M 33 at giant molecular cloud scales

NASA Astrophysics Data System (ADS)

Komugi, Shinya; Miura, Rie E.; Kuno, Nario; Tosaki, Tomoka

2018-06-01

We report on a multi-parameter analysis of giant molecular clouds (GMCs) in the nearby spiral galaxy M 33. A catalog of GMCs identifed in 12CO(J = 3-2) was used to compile associated 12CO(J = 1-0), dust, stellar mass, and star formation rate. Each of the 58 GMCs are categorized by their evolutionary stage. Applying the principal component analysis on these parameters, we construct two principal components, PC1 and PC2, which retain 75% of the information from the original data set. PC1 is interpreted as expressing the total interstellar matter content, and PC2 as the total activity of star formation. Young (< 10 Myr) GMCs occupy a distinct region in the PC1-PC2 plane, with lower interstellar medium (ISM) content and star formation activity compared to intermediate-age and older clouds. Comparison of average cloud properties in different evolutionary stages imply that GMCs may be heated or grow denser and more massive via aggregation of diffuse material in their first ˜ 10 Myr. The PCA also objectively identified a set of tight relations between ISM and star formation. The ratio of the two CO lines is nearly constant, but weakly modulated by massive star formation. Dust is more strongly correlated with the star formation rate than the CO lines, supporting recent findings that dust may trace molecular gas better than CO. Stellar mass contributes weakly to the star formation rate, reminiscent of an extended form of the Schmidt-Kennicutt relation with the molecular gas term substituted by dust.

Gas, dust, stars, star formation, and their evolution in M 33 at giant molecular cloud scales

NASA Astrophysics Data System (ADS)

Komugi, Shinya; Miura, Rie E.; Kuno, Nario; Tosaki, Tomoka

2018-04-01

We report on a multi-parameter analysis of giant molecular clouds (GMCs) in the nearby spiral galaxy M 33. A catalog of GMCs identifed in 12CO(J = 3-2) was used to compile associated 12CO(J = 1-0), dust, stellar mass, and star formation rate. Each of the 58 GMCs are categorized by their evolutionary stage. Applying the principal component analysis on these parameters, we construct two principal components, PC1 and PC2, which retain 75% of the information from the original data set. PC1 is interpreted as expressing the total interstellar matter content, and PC2 as the total activity of star formation. Young (< 10 Myr) GMCs occupy a distinct region in the PC1-PC2 plane, with lower interstellar medium (ISM) content and star formation activity compared to intermediate-age and older clouds. Comparison of average cloud properties in different evolutionary stages imply that GMCs may be heated or grow denser and more massive via aggregation of diffuse material in their first ˜ 10 Myr. The PCA also objectively identified a set of tight relations between ISM and star formation. The ratio of the two CO lines is nearly constant, but weakly modulated by massive star formation. Dust is more strongly correlated with the star formation rate than the CO lines, supporting recent findings that dust may trace molecular gas better than CO. Stellar mass contributes weakly to the star formation rate, reminiscent of an extended form of the Schmidt-Kennicutt relation with the molecular gas term substituted by dust.

Hydroxyl as a Tracer of Dark Gas in a Diffuse Molecular Cloud

NASA Astrophysics Data System (ADS)

White, Josh; Donate, Emmanuel; Magnani, Loris A.

2017-06-01

In an attempt to determine the extent of dark molecular gas at high Galactic latitudes, we have conducted a survey of OH at 18 cm in a region containing the diffuse molecular cloud MBM 53. Dark molecular gas is a term that refers to molecular hydrogen that is either difficult or impossible to detect by conventional spectroscopic means. While models of photo-dissociation regions predict that some molecular hydrogen is found under conditions where other species are too low in abundance to be detected by radio spectroscopy, recent estimates have predicted that as much dark molecular gas exists as that normally detected by CO(1-0) surveys. However, more sensitive surveys either in the CO(1-0) line or other tracers should detect some of this gas. We observed 44 lines of sight at 18 cm to see if very sensitive OH observations could detect some of the dark molecular gas in the Pegasus-Pisces region. Our data were taken with the 305 m Arecibo radiotelescope and have typical rms values of 6-7 mK. We compared our OH observations with the Georgia/Harvard-Smithsonian CfA high-latitude CO(1-0) survey. Of 8 OH detections at 1667 MHz, 5 were not detected by the CO survey and indicate that at least some of the dark molecular gas may be traced by sensitive OH observations.

Formation of compact HII regions possibly triggered by cloud-cloud collision

NASA Astrophysics Data System (ADS)

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

2015-08-01

Compact HII regions are ionized by young high-mass star(s) and ~1000 compact HII regions are cataloged in the Galaxy (Urquhart et al. MNRAS 443, 1555-1586 (2014)). Compact HII regions are one of the major populations of Galactic HII regions. The molecular environments around compact HII regions are however not well understood due to lack of extensive molecular surveys. In order to better understand formation of exciting stars and compact HII regions, we have carried out a systematic study of molecular clouds toward compact HII regions by using the 12CO datasets obtained with the JCMT and NANTEN2 telescopes for l = 10 - 56, and present here the first results.In one of the present samples, RCW166, we have discovered that the HII region is associated with two molecular clouds whose velocity separation is ~10 km s-1 the two clouds show complimentary spatial distributions, where one of the clouds have a cavity-like distribution apparently embracing the other. We present an interpretation that the two clouds collided with each other and the cavity-like distribution represents a hole created by the collision in the larger cloud as modeled by Habe and Ohta (1992). Similar molecular distributions are often found in the other compact HII regions in the present study.A recent study by Torii et al. (2015, arXiv:1503.00070) indicates that the Spitzer bubble RCW120 was formed by cloud-cloud collision where the inside of the cavity is fully ionized by the exiting stars. RCW166, on the other hand, shows that only a small part of the cavity, the compact HII region, is ionized. We thus suggest that RCW166 represents an evolutionary stage corresponding to an earlier phase of RCW120 in the collision scenario.

Extinction and Star Formation Study in Molecular Clouds with DENIS infrared data and USNO optical data

NASA Astrophysics Data System (ADS)

Cambrésy, Laurent

1999-11-01

This thesis consists in a study of molecular clouds, essentially of the point of view of the interstellar environment, but also of the one of the star formation. The original method to estimate extinction presented here is based on adaptive star counts as well as on a wavelet decomposition. For the first time, an extinction map of the whole sky is proposed (USNO-PMM optical data). Access to very large field maps offers the opportunity to analyze the interstellar matter distribution in various environments. A first result is that the contained mass in regions for which AV > 1 would not exceed half of the total cloud mass. Using DENIS data, it becomes possible to probe dense regions of clouds. For instance, star counts in the Chamaeleon complex show cores which were not resolved before. Moreover, the selection of stars with a strong infrared excess yields about fifty T Tauri candidates. From their luminosity function, I derived the average lifetime of circumstellar disc of low--mass stars: ~4cdot 106 years. It is difficult to understand the relation between extinction and molecular emission, but it appears clearly that molecular emission is a bad estimator of the column density for low extinction area. Actually, thresholds exist in the CO detection and I conclude that photodissociation, density and cloud geometry have important consequences on the CO emission when AV < 2. Investigation of the relation between extinction and far--infrared emission in Polaris leads to a four times larger emissivity in cold areas than in hot areas. This result explains the low temperatures in this cloud and implies severe restrictions concerning the use of far--infrared fluxes as an extinction estimator.

Hydrodynamic simulations of mechanical stellar feedback in a molecular cloud formed by thermal instability

NASA Astrophysics Data System (ADS)

Wareing, C. J.; Pittard, J. M.; Falle, S. A. E. G.

2017-09-01

We have used the AMR hydrodynamic code, mg, to perform 3D hydrodynamic simulations with self-gravity of stellar feedback in a spherical clumpy molecular cloud formed through the action of thermal instability. We simulate the interaction of the mechanical energy input from 15, 40, 60 and 120 M⊙ stars into a 100 pc diameter 16 500 M⊙ cloud with a roughly spherical morphology with randomly distributed high-density condensations. The stellar winds are introduced using appropriate non-rotating Geneva stellar evolution models. In the 15 M⊙ star case, the wind has very little effect, spreading around a few neighbouring clumps before becoming overwhelmed by the cloud collapse. In contrast, in the 40, 60 and 120 M⊙ star cases, the more powerful stellar winds create large cavities and carve channels through the cloud, breaking out into the surrounding tenuous medium during the wind phase and considerably altering the cloud structure. After 4.97, 3.97 and 3.01 Myr, respectively, the massive stars explode as supernovae (SNe). The wind-sculpted surroundings considerably affect the evolution of these SN events as they both escape the cloud along wind-carved channels and sweep up remaining clumps of cloud/wind material. The 'cloud' as a coherent structure does not survive the SN from any of these stars, but only in the 120 M⊙ case is the cold molecular material completely destabilized and returned to the unstable thermal phase. In the 40 and 60 M⊙ cases, coherent clumps of cold material are ejected from the cloud by the SN, potentially capable of further star formation.

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

Leptin differentially regulates STAT3 activation in the ob/ob mice adipose mesenchymal stem cells

USDA-ARS?s Scientific Manuscript database

Leptin-deficient genetically obese ob/ob mice exhibit adipocyte hypertrophy and hyperplasia as well as elevated adipose tissue and systemic inflammation. Studies have shown that multipotent stem cells isolated from adult adipose tissue can differentiate into adipocytes ex vivo and thereby contribute...

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

USDA-ARS?s Scientific Manuscript database

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...

SUPERNOVA DRIVING. III. SYNTHETIC MOLECULAR CLOUD OBSERVATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Padoan, Paolo; Juvela, Mika; Pan, Liubin

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 {sub B,min} = 1.4 K, of the J = 1 − 0 {sup 12}CO line, generating 16 synthetic catalogs (four different spatial resolutions and four CO abundance models), each containing up to several thousandsmore » 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.« less

Galactic kinematics of molecuar clouds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stark, A.A.

1979-01-01

The kinematics of molecular clouds in the galactic disk are studied to determine the magnitude of cloud-to-coud velocity dispersions and systematic streaming motions. Three observational programs are reported: (i) a strip map of 1 = 180/sup 0/ from b = -9/sup 0/ to +8/sup 0/ observed in CO J = 1 greater than or equal to 0 to an rms noise level of 0.1 K in 250 kHz filters; (ii) a 20-point map of the minor axis of M31, observed in CO J = 1 greater than or equal to 0 to an rms noise level of 20 mK inmore » 1 MHz filters; (iii) three maps in the molecular ring, centered at 1 = 34/sup 0/, 1 = 36/sup 0/ and 1 = 51/sup 0/, each about one degree square, sampled every 0.05/sup 0/ in /sup 13/CO J = 1 greater than or equal to 0 to an rms noise level of 0.1 K in 250 kHz filters. Molecular clouds typically have one dimensional cloud-to-cloud velocity dispersions of about 8 km s/sup -1/. This dispersion is independent of cloud mass over a range of 10/sup 2/M /sub solar/ < M/sub C < 10/sup 5/ /sup 5/M /sub solar/. Clouds more massive than about 10 /sup 5/ /sup 5/M /sub solar/ have a markedly smaller dispersion. These most massive clouds occur preferentially in spiral arms, and result in spiral arm CO emissivities several times that of interarm regions. Also associated with spiral arms are large-scale streaming motions, which amount to 100 km s/sup -1/ in one arm in M31.« less

No evidence of disk destruction by OB stars

NASA Astrophysics Data System (ADS)

Richert, Alexander J. W.; Feigelson, Eric

2015-01-01

It has been suggested that the hostile environments observed in massive star forming regions are inhospitable to protoplanetary disks and therefore to the formation of planets. The Orion Proplyds show disk evaporation by extreme ultraviolet (EUV) photons from Theta1 Orionis C (spectral type O6). In this work, we examine the spatial distributions of disk-bearing and non-disk bearing young stellar objects (YSOs) relative to OB stars in 17 massive star forming regions in the MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray) survey. Any tendency of disky YSOs, identified by their infrared excess, to avoid OB stars would reveal complete disk destruction.We consider a sample of MYStIX that includes 78 O3-O9 stars, 256 B stars, 5,606 disky YSOs, and 5,794 non-disky YSOs. For each OB star, we compare the cumulative distribution functions of distances to disky and non-disky YSOs. We find no significant avoidance of OB stars by disky YSOs. This result indicates that OB stars are not sufficiently EUV-luminous and long-lived to completely destroy a disk within its ordinary lifetime. We therefore conclude that massive star forming regions are not clearly hostile to the formation of planets.

GIANT MOLECULAR CLOUDS AND STAR FORMATION IN THE NON-GRAND DESIGN SPIRAL GALAXY NGC 6946

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rebolledo, David; Wong, Tony; Leroy, Adam

We present high spatial resolution observations of giant molecular clouds (GMCs) in the eastern part of the nearby spiral galaxy NGC 6946 obtained with the Combined Array for Research in Millimeter-wave Astronomy (CARMA). We have observed CO(1 {yields} 0), CO(2 {yields} 1) and {sup 13}CO(1 {yields} 0), achieving spatial resolutions of 5.''4 Multiplication-Sign 5.''0, 2.''5 Multiplication-Sign 2.''0, and 5.''6 Multiplication-Sign 5.''4, respectively, over a region of 6 Multiplication-Sign 6 kpc. This region extends from 1.5 kpc to 8 kpc galactocentric radius, thus avoiding the intense star formation in the central kpc. We have recovered short-spacing u-v components by using singlemore » dish observations from the Nobeyama 45 m and IRAM 30 m telescopes. Using the automated CPROPS algorithm, we identified 45 CO cloud complexes in the CO(1 {yields} 0) map and 64 GMCs in the CO(2 {yields} 1) maps. The sizes, line widths, and luminosities of the GMCs are similar to values found in other extragalactic studies. We have classified the clouds into on-arm and inter-arm clouds based on the stellar mass density traced by the 3.6 {mu}m map. Clouds located on-arm present in general higher star formation rates than clouds located in inter-arm regions. Although the star formation efficiency shows no systematic trend with galactocentric radius, some on-arm clouds-which are more luminous and more massive compared to inter-arm GMCs-are also forming stars more efficiently than the rest of the identified GMCs. We find that these structures appear to be located in two specific regions in the spiral arms. One of them shows a strong velocity gradient, suggesting that this region of high star formation efficiency may be the result of gas flow convergence.« less

Genetic ablation of phosphatidylcholine transfer protein/StarD2 in ob/ob mice improves glucose tolerance without increasing energy expenditure.

PubMed

Krisko, Tibor I; LeClair, Katherine B; Cohen, David E

2017-03-01

Phosphatidylcholine transfer protein (PC-TP; synonym StarD2) is highly expressed in liver and oxidative tissues. PC-TP promotes hepatic glucose production during fasting and aggravates glucose intolerance in high fat fed mice. However, because PC-TP also suppresses thermogenesis in brown adipose tissue (BAT), its direct contribution to obesity-associated diabetes in mice remains unclear. Here we examined the effects of genetic PC-TP ablation on glucose homeostasis in leptin-deficient ob/ob mice, which exhibit both diabetes and altered thermoregulation. Mice lacking both PC-TP and leptin (Pctp -/- ;ob/ob) were prepared by crossing Pctp -/- with ob/+ mice. Glucose homeostasis was assessed by standard assays, and energy expenditure was determined by indirect calorimetry using a comprehensive laboratory animal monitoring system, which also recorded physical activity and food intake. Body composition was determined by NMR and hepatic lipids by enzymatic assays. Core body temperature was measured using a rectal thermocouple probe. Pctp -/- ;ob/ob mice demonstrated improved glucose homeostasis, as evidenced by markedly improved glucose and pyruvate tolerance tests, without changes in insulin tolerance. However, there were no differences in EE at any ambient temperature. There were also no effects of PC-TP expression on physical activity, food intake or core body temperature. Improved glucose tolerance in Pctp -/- ;ob/ob mice in the absence of increases in energy expenditure or core body temperature indicates a direct pathogenic role for PC-TP in diabetes in leptin deficient mice. Copyright © 2016 Elsevier Inc. All rights reserved.

Resolving Molecular Clouds in the Nearby Galaxy NGC 300

NASA Astrophysics Data System (ADS)

Faesi, Christopher; Lada, Charles J.; Forbrich, Jan

2015-01-01

We present results from our ongoing Submillimeter Array (SMA) survey in which we resolve Giant Molecular Clouds (GMCs) for the first time in the nearby (D = 1.9 Mpc) spiral galaxy NGC 300. We have conducted CO(2-1) and 1.3 mm dust continuum observations of several massive star-forming regions in NGC 300, following up on the Atacama Pathfinder Experiment (APEX) survey of Faesi et al. (2014). We find that the unresolved CO sources detected with APEX at ~250 pc resolution typically resolve into one dominant GMC in our SMA observations, which have a resolution of ~3.5' (30 pc). The majority of sources are significantly detected in CO, but only one exhibits dust continuum emission. Comparing with archival H-alpha, GALEX far-ultraviolet, and Spitzer 24 micron images, we note physical offsets between the young star clusters, warm dust, and ionized and molecular gas components in these regions. We recover a widely varying fraction -- between 30% and almost 100% -- of the full APEX single dish flux with our interferometric observations. This implies that the fraction of CO-emitting molecular gas that is in a diffuse state (i.e. with characteristic spatial scales > 100 pc) differs greatly amongst star forming regions in NGC 300. We investigate potential trends in the implied diffuse molecular gas fraction with GMC properties and star formation activity. We compute virial masses and analyze the velocity structure of these resolved extragalactic GMCs and compare to results from surveys of the Milky Way and other nearby galaxies.

Spectral shifting strongly constrains molecular cloud disruption by radiation pressure on dust

NASA Astrophysics Data System (ADS)

Reissl, Stefan; Klessen, Ralf S.; Mac Low, Mordecai-Mark; Pellegrini, Eric W.

2018-03-01

Aim. We aim to test the hypothesis that radiation pressure from young star clusters acting on dust is the dominant feedback agent disrupting the largest star-forming molecular clouds and thus regulating the star-formation process. Methods: We performed multi-frequency, 3D, radiative transfer calculations including both scattering and absorption and re-emission to longer wavelengths for model clouds with masses of 104-107 M⊙, containing embedded clusters with star formation efficiencies of 0.009-91%, and varying maximum grain sizes up to 200 μm. We calculated the ratio between radiative and gravitational forces to determine whether radiation pressure can disrupt clouds. Results: We find that radiation pressure acting on dust almost never disrupts star-forming clouds. Ultraviolet and optical photons from young stars to which the cloud is optically thick do not scatter much. Instead, they quickly get absorbed and re-emitted by the dust at thermal wavelengths. As the cloud is typically optically thin to far-infrared radiation, it promptly escapes, depositing little momentum in the cloud. The resulting spectrum is more narrowly peaked than the corresponding Planck function, and exhibits an extended tail at longer wavelengths. As the opacity drops significantly across the sub-mm and mm wavelength regime, the resulting radiative force is even smaller than for the corresponding single-temperature blackbody. We find that the force from radiation pressure falls below the strength of gravitational attraction by an order of magnitude or more for either Milky Way or moderate starbust conditions. Only for unrealistically large maximum grain sizes, and star formation efficiencies far exceeding 50% do we find that the strength of radiation pressure can exceed gravity. Conclusions: We conclude that radiation pressure acting on dust does not disrupt star-forming molecular clouds in any Local Group galaxies. Radiation pressure thus appears unlikely to regulate the star

IRAS observations of dust heating and energy balance in the Rho Ophiuchi dark cloud

NASA Technical Reports Server (NTRS)

Greene, Thomas P.; Young, Erick T.

1989-01-01

The equilibrium process dust emission in the Rho Ophiuchi dark cloud is studied. The luminosity of the cloud is found to closely match the luminosity of the clouds's known embedded and external radiation sources. There is no evidence for a large population of undetected low-luminosity sources within the cloud and unknown external heating is also only a minor source of energy. Most of the cloud's luminosity is emitted in the mid-to-far-IR. Dust temperature maps indicate that the dust is not hot enough to heat the gas to observed temperatures. A simple cloud model with a radiation field composed of flux HD 147889, S1, and Sco OB2 associations predicts the observed IRAS 60 to 100 micron in-band flux ratios for a mean cloud density n(H2) = 1400. Flattened 12 and 25 micron observations show much extended emission in these bands, suggesting stochastic heating of very small grains or large molecules.

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.

Manta A New BroadBand OBS

NASA Astrophysics Data System (ADS)

Hello, Y.; Yegikyan, M.; Charvis, P.; Philippe, O.

2017-12-01

Manta is a new BroadBand OBS developed at Geoazur and commercialized by Osean. The design is inspired by 3-years autonomy MUG-OBS a Multiparameter Ocean Bottom System which carry a lot of sort of sensor types. As Mug-OBS, Manta-OBS rated 6000m is designed to resist a trawling. All the components are non corrosive such polyethylene, titanium and buoyancy is ensured by syntactic foam. Equipped in standard version with a Trillium compact OBS Manta has an autonomy of 18 months, but can accept on its 4 input channels any kind of signal as low as from an hydrophone or larger from other type of a seismometer or accelerometer. Tri-axial geophones unit (2 Hz or 4.5 Hz ) can replace the seismometer and will expend the lifespan for the instrument. The seismometer is encapsulated in a central well established by four panels of the main structure to protect it from sea current convection and is decoupled from main chassis. An health bulletin is recoverable by acoustic any time to facilitate the installation and during a visit when instrument is deployed. Main parameters for acquisition can be changed by acoustics command from surface at any time. Once at the bottom, release for the main sensor installation is programmed on a timer but controlled by the tilt of the OBS. If the tilt is too important based on programmed limits, sensor will not released automatically, but this can be forced by acoustic command after returning the tilt informations to the boat operator. Manta is equipped with flash light and AIS system for easy location at recovery, and can also send it's position by Iridium satellite in case of an unexpected ascent such caused by a possible trawling if deployed in shallow water. Clock drift calculation is automatically made against GPS time signal once the OBS return at the surface. The recovery of the OBS is initiated by an acoustic command. These new features made Manta a very versatile instrument for monitoring earthquakes.

Infrared Polarization of the Molecular Cloud Associated to IRAS 18236-1205

NASA Astrophysics Data System (ADS)

Luna, A.; Retes, R.; Devaraj, R.; Maya, Y. D.; Carrasco, L.

2017-07-01

We present the near-infrared polarization observations towards the star forming molecular cloud associated with the IRAS source 18236-1205, obtained with the near-infrared (NIR) imaging polarimeter POLICAN at the Guillermo Haro Astrophysical Observatory in Cananea, Sonora, México.

An evolutionary model for collapsing molecular clouds and their star formation activity. II. Mass dependence of the star formation rate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zamora-Avilés, Manuel; Vázquez-Semadeni, Enrique

We discuss the evolution and dependence on cloud mass of the star formation rate (SFR) and efficiency (SFE) of star-forming molecular clouds (MCs) within the scenario that clouds are undergoing global collapse and that the SFR is controlled by ionization feedback. We find that low-mass clouds (M {sub max} ≲ 10{sup 4} M {sub ☉}) spend most of their evolution at low SFRs, but end their lives with a mini-burst, reaching a peak SFR ∼10{sup 4} M {sub ☉} Myr{sup –1}, although their time-averaged SFR is only (SFR) ∼ 10{sup 2} M {sub ☉} Myr{sup –1}. The corresponding efficiencies aremore » SFE{sub final} ≲ 60% and (SFE) ≲ 1%. For more massive clouds (M {sub max} ≳ 10{sup 5} M {sub ☉}), the SFR first increases and then reaches a plateau because the clouds are influenced by stellar feedback since earlier in their evolution. As a function of cloud mass, (SFR) and (SFE) are well represented by the fits (SFR) ≈ 100(1 + M {sub max}/1.4 × 10{sup 5} M {sub ☉}){sup 1.68} M {sub ☉} Myr{sup –1} and (SFE) ≈ 0.03(M {sub max}/2.5 × 10{sup 5} M {sub ☉}){sup 0.33}, respectively. Moreover, the SFR of our model clouds follows closely the SFR-dense gas mass relation recently found by Lada et al. during the epoch when their instantaneous SFEs are comparable to those of the clouds considered by those authors. Collectively, a Monte Carlo integration of the model-predicted SFR(M) over a Galactic giant molecular cloud mass spectrum yields values for the total Galactic SFR that are within half an order of magnitude of the relation obtained by Gao and Solomon. Our results support the scenario that star-forming MCs may be in global gravitational collapse and that the low observed values of the SFR and SFE are a result of the interruption of each SF episode, caused primarily by the ionizing feedback from massive stars.« less

Compression of turbulent magnetized gas in giant molecular clouds

NASA Astrophysics Data System (ADS)

Birnboim, Yuval; Federrath, Christoph; Krumholz, Mark

2018-01-01

Interstellar gas clouds are often both highly magnetized and supersonically turbulent, with velocity dispersions set by a competition between driving and dissipation. This balance has been studied extensively in the context of gases with constant mean density. However, many astrophysical systems are contracting under the influence of external pressure or gravity, and the balance between driving and dissipation in a contracting, magnetized medium has yet to be studied. In this paper, we present three-dimensional magnetohydrodynamic simulations of compression in a turbulent, magnetized medium that resembles the physical conditions inside molecular clouds. We find that in some circumstances the combination of compression and magnetic fields leads to a rate of turbulent dissipation far less than that observed in non-magnetized gas, or in non-compressing magnetized gas. As a result, a compressing, magnetized gas reaches an equilibrium velocity dispersion much greater than would be expected for either the hydrodynamic or the non-compressing case. We use the simulation results to construct an analytic model that gives an effective equation of state for a coarse-grained parcel of the gas, in the form of an ideal equation of state with a polytropic index that depends on the dissipation and energy transfer rates between the magnetic and turbulent components. We argue that the reduced dissipation rate and larger equilibrium velocity dispersion has important implications for the driving and maintenance of turbulence in molecular clouds and for the rates of chemical and radiative processes that are sensitive to shocks and dissipation.

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.

Modelling CO emission - II. The physical characteristics that determine the X factor in Galactic molecular clouds

NASA Astrophysics Data System (ADS)

Shetty, Rahul; Glover, Simon C.; Dullemond, Cornelis P.; Ostriker, Eve C.; Harris, Andrew I.; Klessen, Ralf S.

2011-08-01

We investigate how the X factor, the ratio of the molecular hydrogen column density (?) to velocity-integrated CO intensity (W), is determined by the physical properties of gas in model molecular clouds (MCs). The synthetic MCs are results of magnetohydrodynamic simulations, including a treatment of chemistry. We perform radiative transfer calculations to determine the emergent CO intensity, using the large velocity gradient approximation for estimating the CO population levels. In order to understand why observations generally find cloud-averaged values of X = XGal˜ 2 × 1020 cm-2 K-1 km-1 s, we focus on a model representing a typical Milky Way MC. Using globally integrated ? and W reproduces the limited range in X found in observations and a mean value X = XGal= 2.2 × 1020 cm-2 K-1 km-1 s. However, we show that when considering limited velocity intervals, X can take on a much larger range of values due to CO line saturation. Thus, the X factor strongly depends on both the range in gas velocities and the volume densities. The temperature variations within individual MCs do not strongly affect X, as dense gas contributes most to setting the X factor. For fixed velocity and density structure, gas with higher temperatures T has higher W, yielding X ∝ T-1/2 for T ˜ 20-100 K. We demonstrate that the linewidth-size scaling relationship does not influence the X factor - only the range in velocities is important. Clouds with larger linewidths σ, regardless of the linewidth-size relationship, have a higher W, corresponding to a lower value of X, scaling roughly as X ∝σ-1/2. The 'mist' model, often invoked to explain a constant XGal consisting of optically thick cloudlets with well-separated velocities, does not accurately reflect the conditions in a turbulent MC. We propose that the observed cloud-averaged values of X ˜ XGal are simply a result of the limited range in ?, temperatures and velocities found in Galactic MCs - a nearly constant value of X therefore

THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Line, Michael R.; Parmentier, Vivien, E-mail: mrline@ucsc.edu

2016-03-20

We model the impact of nonuniform cloud cover on transit transmission spectra. Patchy clouds exist in nearly every solar system atmosphere, brown dwarfs, and transiting exoplanets. Our major findings suggest that fractional cloud coverage can exactly mimic high mean molecular weight atmospheres and vice versa over certain wavelength regions, in particular, over the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) bandpass (1.1–1.7 μm). We also find that patchy cloud coverage exhibits a signature that is different from uniform global clouds. Furthermore, we explain analytically why the “patchy cloud-high mean molecular weight” degeneracy exists. We also explore the degeneracy ofmore » nonuniform cloud coverage in atmospheric retrievals on both synthetic and real planets. We find from retrievals on a synthetic solar composition hot Jupiter with patchy clouds and a cloud-free high mean molecular weight warm Neptune that both cloud-free high mean molecular weight atmospheres and partially cloudy atmospheres can explain the data equally well. Another key finding is that the HST WFC3 transit transmission spectra of two well-observed objects, the hot Jupiter HD 189733b and the warm Neptune HAT-P-11b, can be explained well by solar composition atmospheres with patchy clouds without the need to invoke high mean molecular weight or global clouds. The degeneracy between high molecular weight and solar composition partially cloudy atmospheres can be broken by observing the molecular Rayleigh scattering differences between the two. Furthermore, the signature of partially cloudy limbs also appears as a ∼100 ppm residual in the ingress and egress of the transit light curves, provided that the transit timing is known to seconds.« less

Tumour necrosis factor-α inhibition with lenalidomide alleviates tissue oxidative injury and apoptosis in ob/ob obese mice.

PubMed

Zhu, Xiaoling; Jiang, Shasha; Hu, Nan; Luo, Fuling; Dong, Hailong; Kang, Yu-Ming; Jones, Kyla R; Zou, Yunzeng; Xiong, Lize; Ren, Jun

2014-07-01

Lenalidomide (Revlimid; Selleck Chemicals, Houston, TX, USA), an analogue of thalidomide, possesses potent cytokine modulatory capacity through inhibition of cytokines such as tumour necrosis factor (TNF)-α, a cytokine pivotal for the onset and development of complications in obesity and diabetes mellitus. The present study was designed to evaluate the effect of lenalidomide on oxidative stress, protein and DNA damage in multiple organs in an ob/ob murine model of obesity. To this end, C57BL/6 lean and ob/ob obese mice were administered lenalidomide (50 mg/kg per day, p.o.) for 5 days. Oxidative stress, protein and DNA damage were assessed using the conversion of reduced glutathione (GSH) to oxidized glutathione (GSSG), carbonyl formation and Comet assay, respectively. Apoptosis was evaluated using caspase 3 activity, and levels of Bax, Bcl-2, Bip, caspase 8, caspase 9 and TNF-α were assessed using western blot analysis. Lenalidomide treatment did not affect glucose clearance in lean or ob/ob mice. Obese mice exhibited a reduced GSH/GSSG ratio in the liver, gastrocnemius skeletal muscle and small intestine, as well as enhanced protein carbonyl formation, DNA damage and caspase 3 activity in the liver, kidney, skeletal muscle and intestine; these effects were alleviated by lenalidomide, with the exception of obesity-associated DNA damage in the liver and kidney. Western blot analysis revealed elevated TNF-α, Bax, Bcl-2, Bip, caspase 8 and caspase 9 in ob/ob mice with various degrees of reversal by lenalidomide treatment. Together, these data indicate that lenalidomide protects against obesity-induced tissue injury and protein damage, possibly in association with antagonism of cytokine production and cytokine-induced apoptosis and oxidative stress. © 2014 Wiley Publishing Asia Pty Ltd.

Magnetic suppression of turbulence and the star formation activity of molecular clouds

NASA Astrophysics Data System (ADS)

Zamora-Avilés, Manuel; Vázquez-Semadeni, Enrique; Körtgen, Bastian; Banerjee, Robi; Hartmann, Lee

2018-03-01

We present magnetohydrodynamic simulations aimed at studying the effect of the magnetic suppression of turbulence (generated through various instabilities during the formation of molecular clouds by converging) on the subsequent star formation (SF) activity. We study four magnetically supercritical models with magnetic field strengths B = 0, 1, 2, and 3 μG (corresponding to mass-to-flux ratios of ∞, 4.76, 2.38, and 1.59 times the critical value), with the magnetic field, initially being aligned with the flows. We find that, for increasing magnetic field strength, the clouds formed tend to be more massive, denser, less turbulent, and with higher SF activity. This causes the onset of SF activity in the non-magnetic or more weakly magnetized cases to be delayed by a few Myr in comparison to the more strongly magnetized cases. We attribute this behaviour to the suppression of the non-linear thin shell instability (NTSI) by the magnetic field, previously found by Heitsch and coworkers. This result is contrary to the standard notion that the magnetic field provides support to the clouds, thus reducing their star formation rate. However, our result is a completely non-linear one, and could not be foreseen from simple linear considerations.

EMBEDDED CLUSTERS IN THE LARGE MAGELLANIC CLOUD USING THE VISTA MAGELLANIC CLOUDS SURVEY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Romita, Krista; Lada, Elizabeth; Cioni, Maria-Rosa, E-mail: k.a.romita@ufl.edu, E-mail: elada@ufl.edu, E-mail: mcioni@aip.de

We present initial results of the first large-scale survey of embedded star clusters in molecular clouds in the Large Magellanic Cloud (LMC) using near-infrared imaging from the Visible and Infrared Survey Telescope for Astronomy Magellanic Clouds Survey. We explored a ∼1.65 deg{sup 2} area of the LMC, which contains the well-known star-forming region 30 Doradus as well as ∼14% of the galaxy’s CO clouds, and identified 67 embedded cluster candidates, 45 of which are newly discovered as clusters. We have determined the sizes, luminosities, and masses for these embedded clusters, examined the star formation rates (SFRs) of their corresponding molecularmore » clouds, and made a comparison between the LMC and the Milky Way. Our preliminary results indicate that embedded clusters in the LMC are generally larger, more luminous, and more massive than those in the local Milky Way. We also find that the surface densities of both embedded clusters and molecular clouds is ∼3 times higher than in our local environment, the embedded cluster mass surface density is ∼40 times higher, the SFR is ∼20 times higher, and the star formation efficiency is ∼10 times higher. Despite these differences, the SFRs of the LMC molecular clouds are consistent with the SFR scaling law presented in Lada et al. This consistency indicates that while the conditions of embedded cluster formation may vary between environments, the overall process within molecular clouds may be universal.« less

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.

On the probability distribution function of the mass surface density of molecular clouds. I

NASA Astrophysics Data System (ADS)

Fischera, Jörg

2014-05-01

The probability distribution function (PDF) of the mass surface density is an essential characteristic of the structure of molecular clouds or the interstellar medium in general. Observations of the PDF of molecular clouds indicate a composition of a broad distribution around the maximum and a decreasing tail at high mass surface densities. The first component is attributed to the random distribution of gas which is modeled using a log-normal function while the second component is attributed to condensed structures modeled using a simple power-law. The aim of this paper is to provide an analytical model of the PDF of condensed structures which can be used by observers to extract information about the condensations. The condensed structures are considered to be either spheres or cylinders with a truncated radial density profile at cloud radius rcl. The assumed profile is of the form ρ(r) = ρc/ (1 + (r/r0)2)n/ 2 for arbitrary power n where ρc and r0 are the central density and the inner radius, respectively. An implicit function is obtained which either truncates (sphere) or has a pole (cylinder) at maximal mass surface density. The PDF of spherical condensations and the asymptotic PDF of cylinders in the limit of infinite overdensity ρc/ρ(rcl) flattens for steeper density profiles and has a power law asymptote at low and high mass surface densities and a well defined maximum. The power index of the asymptote Σ- γ of the logarithmic PDF (ΣP(Σ)) in the limit of high mass surface densities is given by γ = (n + 1)/(n - 1) - 1 (spheres) or by γ = n/ (n - 1) - 1 (cylinders in the limit of infinite overdensity). Appendices are available in electronic form at http://www.aanda.org

Observations of SO in dark and molecular clouds

NASA Technical Reports Server (NTRS)

Rydbeck, O. E. H.; Hjalmarson, A.; Rydbeck, G.; Ellder, J.; Kollberg, E.; Irvine, W. M.

1980-01-01

The 1(0)-0(1) transition of SO at 30 GHz has been observed in several sources, including the first detection of sulfur monoxide in cold dark clouds without apparent internal energy sources. The SO transition appears to be an excellent tracer of structure in dark clouds, and the data support suggestions that self-absorption is important in determining emission profiles in such regions for large line-strength transitions. Column densities estimated from a comparison of the results for the two isotopic species indicate a high fractional abundance of SO in dark clouds.

Evolutionary Description of Giant Molecular Cloud Mass Functions on Galactic Disks

NASA Astrophysics Data System (ADS)

Kobayashi, Masato I. N.; Inutsuka, Shu-ichiro; Kobayashi, Hiroshi; Hasegawa, Kenji

2017-02-01

Recent radio observations show that giant molecular cloud (GMC) mass functions noticeably vary across galactic disks. High-resolution magnetohydrodynamics simulations show that multiple episodes of compression are required for creating a molecular cloud in the magnetized interstellar medium. In this article, we formulate the evolution equation for the GMC mass function to reproduce the observed profiles, for which multiple compressions are driven by a network of expanding shells due to H II regions and supernova remnants. We introduce the cloud-cloud collision (CCC) terms in the evolution equation in contrast to previous work (Inutsuka et al.). The computed time evolution suggests that the GMC mass function slope is governed by the ratio of GMC formation timescale to its dispersal timescale, and that the CCC effect is limited only in the massive end of the mass function. In addition, we identify a gas resurrection channel that allows the gas dispersed by massive stars to regenerate GMC populations or to accrete onto pre-existing GMCs. Our results show that almost all of the dispersed gas contributes to the mass growth of pre-existing GMCs in arm regions whereas less than 60% contributes in inter-arm regions. Our results also predict that GMC mass functions have a single power-law exponent in the mass range <105.5 {M}⊙ (where {M}⊙ represents the solar mass), which is well characterized by GMC self-growth and dispersal timescales. Measurement of the GMC mass function slope provides a powerful method to constrain those GMC timescales and the gas resurrecting factor in various environments across galactic disks.

A Multi-Fiber Spectroscopic Search for Low-mass Young Stars in Orion OB1

NASA Astrophysics Data System (ADS)

Loerincs, Jacqueline; Briceno, Cesar; Calvet, Nuria; Mateo, Mario L.; Hernandez, Jesus

2017-01-01

We present here results of a low resolution spectroscopic followup of candidate low-mass pre-main sequence stars in the Orion OB1 association. Our targets were selected from the CIDA Variability Survey of Orion (CVSO), and we used the Michigan/Magellan Fiber Spectrograph (M2FS) on the Magellan Clay 6.5m telescope to obtain spectra of 500 candidate T Tauri stars distributed in seven 0.5 deg diameter fields, adding to a total area of ~5.5 deg2. We identify young stars by looking at the distinctive Hα 6563 Å emission and Lithium Li I 6707 Å absorption features characteristic of young low mass pre-main sequence stars. Furthermore, by measuring the strength of their Hα emission lines, confirmed T Tauri stars can be classified as either Classical T Tauris (CTTS) or Weak-line T Tauris (WTTS), which give indication of whether the star is actively accreting material from a gas and dust disk surrounding the star, which may be the precursor of a planetary system. We confirm a total of 90 T Tauri stars, of which 50% are newly identified young members of Orion; out of the 49 new detections,15 are accreting CTTS, and of these all but one are found in the OB1b sub-region. This result is in line with our previous findings that this region is much younger than the more extended Orion OB1a sub-association. The M2FS results add to our growing census of young stars in Orion, that is allowing us to characterize in a systematic and consistent way the distribution of stellar ages across the entire complex, in order to building a complete picture of star formation in this, one of nearest most active sites of star birth.

Automated identification of OB associations in M31

NASA Technical Reports Server (NTRS)

Magnier, Eugene A.; Battinelli, Paolo; Lewin, Walter H. G.; Haiman, Zoltan; Paradijs, Jan Van; Hasinger, Guenther; Pietsch, Wolfgang; Supper, Rodrigo; Truemper, Joachim

1993-01-01

A new identification of OB associations in M31 has been performed using the Path Linkage Criterion (PLC) technique of Battinelli (1991). We found 174 associations with a very small contamination (less than 5%) by random clumps of stars. The expected total number and average size of OB associations in the region of M 31 covered by our data set (Magnier et al. 1992) are approximately 280 and approximately 90 pc, respectively. M31 associations therefore have sizes similar to those of OB associations observed in nearby galaxies, so that we can consider them to be classical OB associations. This list of OB associations will be used for the study of the spatial distribution of OB associations and their correlation with other objects. Taking into account the fact that we do not cover the entire disk of M31, we extrapolate a total number of association in M31 of approximately 420.

Star Formation in Galaxies

NASA Technical Reports Server (NTRS)

1987-01-01

Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.

Star cluster formation in a turbulent molecular cloud self-regulated by photoionization feedback

NASA Astrophysics Data System (ADS)

Gavagnin, Elena; Bleuler, Andreas; Rosdahl, Joakim; Teyssier, Romain

2017-12-01

Most stars in the Galaxy are believed to be formed within star clusters from collapsing molecular clouds. However, the complete process of star formation, from the parent cloud to a gas-free star cluster, is still poorly understood. We perform radiation-hydrodynamical simulations of the collapse of a turbulent molecular cloud using the RAMSES-RT code. Stars are modelled using sink particles, from which we self-consistently follow the propagation of the ionizing radiation. We study how different feedback models affect the gas expulsion from the cloud and how they shape the final properties of the emerging star cluster. We find that the star formation efficiency is lower for stronger feedback models. Feedback also changes the high-mass end of the stellar mass function. Stronger feedback also allows the establishment of a lower density star cluster, which can maintain a virial or sub-virial state. In the absence of feedback, the star formation efficiency is very high, as well as the final stellar density. As a result, high-energy close encounters make the cluster evaporate quickly. Other indicators, such as mass segregation, statistics of multiple systems and escaping stars confirm this picture. Observations of young star clusters are in best agreement with our strong feedback simulation.

Supernova Driving. IV. The Star-formation Rate of Molecular Clouds

NASA Astrophysics Data System (ADS)

Padoan, Paolo; Haugbølle, Troels; Nordlund, Åke; Frimann, Søren

2017-05-01

We compute the star-formation rate (SFR) in molecular clouds (MCs) that originate ab initio in a new, higher-resolution simulation of supernova-driven turbulence. Because of the large number of well-resolved clouds with self-consistent boundary and initial conditions, we obtain a large range of cloud physical parameters with realistic statistical distributions, which is an unprecedented sample of star-forming regions to test SFR models and to interpret observational surveys. We confirm the dependence of the SFR per free-fall time, SFRff, on the virial parameter, α vir, found in previous simulations, and compare a revised version of our turbulent fragmentation model with the numerical results. The dependences on Mach number, { M }, gas to magnetic pressure ratio, β, and compressive to solenoidal power ratio, χ at fixed α vir are not well constrained, because of random scatter due to time and cloud-to-cloud variations in SFRff. We find that SFRff in MCs can take any value in the range of 0 ≤ SFRff ≲ 0.2, and its probability distribution peaks at a value of SFRff ≈ 0.025, consistent with observations. The values of SFRff and the scatter in the SFRff-α vir relation are consistent with recent measurements in nearby MCs and in clouds near the Galactic center. Although not explicitly modeled by the theory, the scatter is consistent with the physical assumptions of our revised model and may also result in part from a lack of statistical equilibrium of the turbulence, due to the transient nature of MCs.

Penetration of Cosmic Rays into Dense Molecular Clouds: Role of Diffuse Envelopes

NASA Astrophysics Data System (ADS)

Ivlev, A. V.; Dogiel, V. A.; Chernyshov, D. O.; Caselli, P.; Ko, C.-M.; Cheng, K. S.

2018-03-01

A flux of cosmic rays (CRs) propagating through a diffuse ionized gas can excite MHD waves, thus generating magnetic disturbances. We propose a generic model of CR penetration into molecular clouds through their diffuse envelopes, and identify the leading physical processes controlling their transport on the way from a highly ionized interstellar medium to the dense interior of the cloud. The model allows us to describe a transition between a free streaming of CRs and their diffusive propagation, determined by the scattering on the self-generated disturbances. A self-consistent set of equations, governing the diffusive transport regime in an envelope and the MHD turbulence generated by the modulated CR flux, is characterized by two dimensionless numbers. We demonstrate a remarkable mutual complementarity of different mechanisms leading to the onset of the diffusive regime, which results in a universal energy spectrum of the modulated CRs. In conclusion, we briefly discuss implications of our results for several fundamental astrophysical problems, such as the spatial distribution of CRs in the Galaxy as well as the ionization, heating, and chemistry in dense molecular clouds. This paper is dedicated to the memory of Prof. Vadim Tsytovich.

Ice Jams the Ob River

NASA Technical Reports Server (NTRS)

2007-01-01

Russia's Ob River flows from south to north, and each summer, it thaws in the same direction. The result is that an ice jam sits downstream from thawed portions of the river, which is laden with heavy runoff from melted snow. On June 29, 2007, the Moderate Resolution Imaging Spectroradiometer (MODIS) flying on NASA's Terra satellite captured this image of the almost completely thawed Ob River. The scene is typical for early summer. South of the ice jam, the Gulf of Ob is swollen with pent-up run-off, and upstream from that, the river is widened as well. Unable to carve through frozen land, the river has little choice but to overflow its banks. For a comparison of early summer and autumn conditions, see Flooding on the Ob River in the Earth Observatory's Natural Hazards section. Besides the annual overflow, this image captures other circumstances of early summer. Sea ice is retreating from the Kara Sea. A lingering line of snow cover snakes its way along the Ob River, to the west. And while the land is lush and green in the south, it appears barren and brown in the north. Near the mouth of the river and the Kara Sea, the land is cold-adapted tundra, with diminutive plants and a short growing season. Just as the ice plugging the river had yet to thaw in the Far North's short summer, the tundra had not yet to greened up either. In this image it still appears lifeless beige. NASA image courtesy Jeff Schmaltz, MODIS Rapid Response Team, Goddard Space Flight Center

The effect of temperature mixing on the observable (T, β)-relation of interstellar dust clouds

NASA Astrophysics Data System (ADS)

Juvela, M.; Ysard, N.

2012-03-01

Context. Detailed studies of the shape of dust emission spectra are possible thanks to the current instruments capable of simultaneous observations in several sub-millimetre bands (e.g., Herschel and Planck). The relationship between the observed spectra and the intrinsic dust grain properties is known to be affected by the noise and the line-of-sight temperature variations. However, some controversy remains even on the basic effects resulting from the mixing of temperatures along the line-of-sight or within the instrument beam. Aims: Regarding the effect of temperature variations, previous studies have suggested either a positive or a negative correlation between the colour temperature TC and the observed spectral index βObs. Our aim is to show that both cases are possible and to determine the principal factors leading to either behaviour. Methods: We start by studying the behaviour of the sum of two or three modified black bodies at different temperatures. Then, with radiative transfer models of spherical clouds, we examine the probability distributions of the dust mass as a function of the physical dust temperature. With these results as a guideline, we examine the (TC, βobs) relations for different sets of clouds. Results: Even in the simple case of models consisting of two blackbodies at temperatures T0 and T0 + ΔT0, the correlation between TC and βobs can be either positive or negative. If one compares models where the temperature difference ΔT0 between the two blackbodies is varied, the correlation is negative. If the models differ in their mean temperature T0 rather than in ΔT0, the correlation remains positive. Radiative transfer models show that externally heated clouds have different mean temperatures but the widths of their temperature distributions are rather similar. Thus, in observations of samples of such clouds the correlation between TC and βObs is expected to be positive. The same result applies to clouds illuminated by external radiation

Cold and warm atomic gas around the Perseus molecular cloud. I. Basic properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stanimirović, Snežana; Murray, Claire E.; Miller, Jesse

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 randommore » 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