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Sample records for cluster forming clump

  1. Physical Conditions in Massive-Cluster-Forming Molecular Clumps

    NASA Astrophysics Data System (ADS)

    Schap, William; Barnes, Peter; Ginsburg, Adam; Ordonez, Tony

    2015-08-01

    The CHaMP project has identified a uniform sample of 303 massive (20-8000 M⊙), dense (200-30,000 cm-3) molecular clumps in a large sector of the southern Milky Way that includes much of the Carina Arm. These are the kinds of clumps that are likely to be the precursors to IRDCs, large stellar clusters, and massive stars. We report new results of the physical conditions in these clouds based on the J=1-0 emission at 3mm from the HCN molecule. Analysis of the HCN emission from these clumps reveals that the physical conditions in the gas (i.e., the excitation temperature, optical depth, and column density) do not follow the molecular line emissivity in a straightforward way. This means that large fractions of the molecular meterial involved in massive cluster formation, while not completely "dark", are under-luminous and easily missed in certain studies. Furthermore, the existence of significant amounts of under-luminous gas has important consequences for the interpretation of wider correlations, such as the star-formation efficiency (SFE, ie the stellar-to-gas mass ratio in a cloud) and, on the larger scale, the Kennicutt-Schmidt relation. Therefore, some widely-used correlations may have hidden biases that depend on the hitherto poorly-characterised spatial variations in physical conditions, illustrated by our results.

  2. Outflow Feedback Regulated Massive Star Formation in Parsec-Scale Cluster Forming Clumps

    SciTech Connect

    Wang, Peng; Li, Zhi-Yun; Abel, Tom; Nakamura, Fumitaka; /Niigata U.

    2010-02-15

    We investigate massive star formation in turbulent, magnetized, parsec-scale clumps of molecular clouds including protostellar outflow feedback using three dimensional numerical simulations of effective resolution 2048{sup 3}. The calculations are carried out using a block structured adaptive mesh refinement code that solves the ideal MHD equations including self-gravity and implements accreting sink particles. We find that, in the absence of regulation by magnetic fields and outflow feedback, massive stars form readily in a turbulent, moderately condensed clump of {approx} 1,600 M{sub {circle_dot}} (containing {approx} 10{sup 2} initial Jeans masses), along with a cluster of hundreds of lower mass stars. The massive stars are fed at high rates by (1) transient dense filaments produced by large-scale turbulent compression at early times, and (2) by the clump-wide global collapse resulting from turbulence decay at late times. In both cases, the bulk of the massive star's mass is supplied from outside a 0.1 pc-sized 'core' that surrounds the star. In our simulation, the massive star is clump-fed rather than core-fed. The need for large-scale feeding makes the massive star formation prone to regulation by outflow feedback, which directly opposes the feeding processes. The outflows reduce the mass accretion rates onto the massive stars by breaking up the dense filaments that feed the massive star formation at early times, and by collectively slowing down the global collapse that fuel the massive star formation at late times. The latter is aided by a moderate magnetic field of strength in the observed range (corresponding to a dimensionless clump mass-to-flux ratio {lambda} {approx} a few); the field allows the outflow momenta to be deposited more efficiently inside the clump. We conclude that the massive star formation in our simulated turbulent, magnetized, parsec-scale clump is outflow-regulated and clump-fed (ORCF for short). An important implication is that the

  3. The connection between prestellar cores and filaments in cluster-forming clumps of the Aquila Rift complex

    NASA Astrophysics Data System (ADS)

    Könyves, Vera; André, Philippe; Maury, Anaëlle

    2015-08-01

    One of the main goals of the Herschel Gould Belt survey (André et al. 2010) is to elucidate the physicalmechanisms responsible for the formation and evolution of prestellar cores in molecular clouds. In theAquila cloud complex imaged with Herschel/SPIRE-PACS between 70-500 μm, we have recently identifieda complete sample of 651 starless cores, 446 of them are gravitationally-bound prestellar cores, likelyforming stars in the future. We also detected 58 protostellar cores (Könyves et al. 2010 and 2015, subm.- see http://gouldbelt-herschel.cea.fr/archives). This region is dominated by two (proto)clusters which arecurrently active sites of clustered star formation (SF): the filamentary Serpens South cloud and the W40HII region. The latter is powered by massive young stars, and a 2nd-generation SF can be witnessed inthe surroundings (Maury et al. 2011).Our Herschel observations also provide an unprecedented census of filaments in Aquila and suggest aclose connection between them and the formation process of prestellar cores, where both structures arehighly concentrated around the protoclusters. About 10-20% of the gas mass is in the form of filamentsbelow Av~7, while ~50-75% of the dense gas mass above Av~7-10 is in filamentary structures.Furthermore, ~90% of our prestellar cores are located above a background column density correspondingto Av~7, and ~75% of them lie within the densest filamentary structures with supercritical masses per unitlength >16 M⊙/pc. Indeed, a strong correlation is found between the spatial distribution of prestellar coresand the densest filaments.Comparing the statistics of cores and filaments with the number of young stellar objects found by Spitzerin the same complex, we also infer a typical timescale ~1 Myr for the formation and evolution of bothprestellar cores and filaments.In summary, our Herschel findings in Aquila support a filamentary paradigm for the early stages of SF,where the cores result from the gravitational fragmentation

  4. GAS CLUMPING IN THE OUTSKIRTS OF {Lambda}CDM CLUSTERS

    SciTech Connect

    Nagai, Daisuke; Lau, Erwin T.

    2011-04-10

    Recent Suzaku X-ray observations revealed that the observed entropy profile of the intracluster medium (ICM) deviates significantly from the prediction of hydrodynamical simulations of galaxy clusters. In this work, we show that gas clumping introduces significant biases in X-ray measurements of the ICM profiles in the outskirts of galaxy clusters. Using hydrodynamical simulations of galaxy cluster formation in a concordance {Lambda}CDM model, we demonstrate that gas clumping leads to an overestimate of the observed gas density and causes flattening of the entropy profile. Our results suggest that gas clumping must be taken into account when interpreting X-ray measurements of cluster outskirts.

  5. Stellar age spreads in clusters as imprints of cluster-parent clump densities

    SciTech Connect

    Parmentier, G.; Grebel, E. K.; Pfalzner, S.

    2014-08-20

    It has recently been suggested that high-density star clusters have stellar age distributions much narrower than that of the Orion Nebula Cluster, indicating a possible trend of narrower age distributions for denser clusters. We show this effect to likely arise from star formation being faster in gas with a higher density. We model the star formation history of molecular clumps in equilibrium by associating a star formation efficiency per free-fall time, ε{sub ff}, to their volume density profile. We focus on the case of isothermal spheres and we obtain the evolution with time of their star formation rate. Our model predicts a steady decline of the star formation rate, which we quantify with its half-life time, namely, the time needed for the star formation rate to drop to half its initial value. Given the uncertainties affecting the star formation efficiency per free-fall time, we consider two distinct values: ε{sub ff} = 0.1 and ε{sub ff} = 0.01. When ε{sub ff} = 0.1, the half-life time is of the order of the clump free-fall time, τ{sub ff}. As a result, the age distributions of stars formed in high-density clumps have smaller full-widths at half-maximum than those of stars formed in low-density clumps. When the star formation efficiency per free-fall time is 0.01, the half-life time is 10 times longer, i.e., 10 clump free-fall times. We explore what happens if the duration of star formation is shorter than 10τ{sub ff}, that is, if the half-life time of the star formation rate cannot be defined. There, we build on the invariance of the shape of the young cluster mass function to show that an anti-correlation between the clump density and the duration of star formation is expected. We therefore conclude that, regardless of whether the duration of star formation is longer than the star formation rate half-life time, denser molecular clumps yield narrower star age distributions in clusters. Published densities and stellar age spreads of young clusters and star-forming

  6. Stellar Age Spreads in Clusters as Imprints of Cluster-parent Clump Densities

    NASA Astrophysics Data System (ADS)

    Parmentier, G.; Pfalzner, S.; Grebel, E. K.

    2014-08-01

    It has recently been suggested that high-density star clusters have stellar age distributions much narrower than that of the Orion Nebula Cluster, indicating a possible trend of narrower age distributions for denser clusters. We show this effect to likely arise from star formation being faster in gas with a higher density. We model the star formation history of molecular clumps in equilibrium by associating a star formation efficiency per free-fall time, epsilonff, to their volume density profile. We focus on the case of isothermal spheres and we obtain the evolution with time of their star formation rate. Our model predicts a steady decline of the star formation rate, which we quantify with its half-life time, namely, the time needed for the star formation rate to drop to half its initial value. Given the uncertainties affecting the star formation efficiency per free-fall time, we consider two distinct values: epsilonff = 0.1 and epsilonff = 0.01. When epsilonff = 0.1, the half-life time is of the order of the clump free-fall time, τff. As a result, the age distributions of stars formed in high-density clumps have smaller full-widths at half-maximum than those of stars formed in low-density clumps. When the star formation efficiency per free-fall time is 0.01, the half-life time is 10 times longer, i.e., 10 clump free-fall times. We explore what happens if the duration of star formation is shorter than 10τff, that is, if the half-life time of the star formation rate cannot be defined. There, we build on the invariance of the shape of the young cluster mass function to show that an anti-correlation between the clump density and the duration of star formation is expected. We therefore conclude that, regardless of whether the duration of star formation is longer than the star formation rate half-life time, denser molecular clumps yield narrower star age distributions in clusters. Published densities and stellar age spreads of young clusters and star-forming regions

  7. Clusters of Small Clumps Can Explain the Peculiar Properties of Giant Clumps in High-redshift Galaxies

    NASA Astrophysics Data System (ADS)

    Behrendt, M.; Burkert, A.; Schartmann, M.

    2016-03-01

    Giant clumps are a characteristic feature of observed high-redshift disk galaxies. We propose that these kiloparsec-sized clumps have a complex substructure and are the result of many smaller clumps self-organizing themselves into clump clusters (CCs). This bottom-up scenario is in contrast to the common top-down view that these giant clumps form first and then sub-fragment. Using a high-resolution hydrodynamical simulation of an isolated, fragmented massive gas disk and mimicking the observations from Genzel et al. at z ˜ 2, we find remarkable agreement in many details. The CCs appear as single entities of sizes {R}{HWHM} ≃ \\0.9-1.4 kpc and masses ˜(1.5-3) × \\quad {10}9 {M}⊙ , representative of high-z observations. They are organized in a ring around the center of the galaxy. The origin of the observed clumps’ high intrinsic velocity dispersion {σ }{intrinsic} ≃ \\50-100 {km} {{{s}}}-1 is fully explained by the internal irregular motions of their substructure in our simulation. No additional energy input, e.g., via stellar feedback, is necessary. Furthermore, in agreement with observations, we find a small velocity gradient {V}{grad}\\quad ≃ 8-27 {km} {{{s}}}-1 {{kpc}}-1 along the CCs in the beam-smeared velocity residual maps, which corresponds to net prograde and retrograde rotation with respect to the rotation of the galactic disk. The CC scenario could have strong implications for the internal evolution, lifetimes, and the migration timescales of the observed giant clumps, bulge growth, and active galactic nucleus activity, stellar feedback, and the chemical enrichment history of galactic disks.

  8. Modeling active galactic nucleus feedback in cool-core clusters: The formation of cold clumps

    SciTech Connect

    Li, Yuan; Bryan, Greg L.

    2014-07-10

    We perform high-resolution (15-30 pc) adaptive mesh simulations to study the impact of momentum-driven active galactic nucleus (AGN) feedback in cool-core clusters, focusing in this paper on the formation of cold clumps. The feedback is jet-driven with an energy determined by the amount of cold gas within 500 pc of the super-massive black hole. When the intracluster medium in the core of the cluster becomes marginally stable to radiative cooling, with the thermal instability to the free-fall timescale ratio t{sub TI}/t{sub ff} < 3-10, cold clumps of gas start to form along the propagation direction of the AGN jets. By tracing the particles in the simulations, we find that these cold clumps originate from low entropy (but still hot) gas that is accelerated by the jet to outward radial velocities of a few hundred km s{sup –1}. This gas is out of hydrostatic equilibrium and so can cool. The clumps then grow larger as they decelerate and fall toward the center of the cluster, eventually being accreted onto the super-massive black hole. The general morphology, spatial distribution, and estimated Hα morphology of the clumps are in reasonable agreement with observations, although we do not fully replicate the filamentary morphology of the clumps seen in the observations, probably due to missing physics.

  9. ATLASGAL - towards a complete sample of massive star forming clumps

    NASA Astrophysics Data System (ADS)

    Urquhart, J. S.; Moore, T. J. T.; Csengeri, T.; Wyrowski, F.; Schuller, F.; Hoare, M. G.; Lumsden, S. L.; Mottram, J. C.; Thompson, M. A.; Menten, K. M.; Walmsley, C. M.; Bronfman, L.; Pfalzner, S.; König, C.; Wienen, M.

    2014-09-01

    By matching infrared-selected, massive young stellar objects (MYSOs) and compact H II regions in the Red MSX Source survey to massive clumps found in the submillimetre ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) survey, we have identified ˜1000 embedded young massive stars between 280° < ℓ < 350° and 10° < ℓ < 60° with | b | < 1.5°. Combined with an existing sample of radio-selected methanol masers and compact H II regions, the result is a catalogue of ˜1700 massive stars embedded within ˜1300 clumps located across the inner Galaxy, containing three observationally distinct subsamples, methanol-maser, MYSO and H II-region associations, covering the most important tracers of massive star formation, thought to represent key stages of evolution. We find that massive star formation is strongly correlated with the regions of highest column density in spherical, centrally condensed clumps. We find no significant differences between the three samples in clump structure or the relative location of the embedded stars, which suggests that the structure of a clump is set before the onset of star formation, and changes little as the embedded object evolves towards the main sequence. There is a strong linear correlation between clump mass and bolometric luminosity, with the most massive stars forming in the most massive clumps. We find that the MYSO and H II-region subsamples are likely to cover a similar range of evolutionary stages and that the majority are near the end of their main accretion phase. We find few infrared-bright MYSOs associated with the most massive clumps, probably due to very short pre-main-sequence lifetimes in the most luminous sources.

  10. MOLECULAR CLUMPS AND INFRARED CLUSTERS IN THE S247, S252, AND BFS52 REGIONS

    SciTech Connect

    Shimoikura, Tomomi; Dobashi, Kazuhito; Saito, Hiro; Nakamura, Fumitaka; Matsumoto, Tomoaki; Nishimura, Atsushi; Kimura, Kimihiro; Onishi, Toshikazu; Ogawa, Hideo

    2013-05-01

    We present results of the observations carried out toward the S247, S252, and BFS52 H II regions with various molecular lines using the 1.85 m radio telescope and the 45 m telescope at Nobeyama Radio Observatory. There are at least 11 young infrared clusters (IR clusters) within the observed region. We found that there are two velocity components in {sup 12}CO (J = 2-1), and also that their spatial distributions show an anti-correlation. The IR clusters are located at their interfaces, suggesting that two distinct clouds with different velocities are colliding with each other, which may have induced the cluster formation. Based on {sup 13}CO (J = 1-0) and C{sup 18}O (J = 1-0) observations, we identified 16 clumps in and around the three H II regions. Eleven of the clumps are associated with the IR clusters and the other five clumps are not associated with any known young stellar objects. We investigated variations in the velocity dispersions of the 16 clumps as a function of the distance from the center of the clusters or the clumps. Clumps with clusters tend to have velocity dispersions that increase with distance from the cluster center, while clumps without clusters show a flat velocity dispersion over the clump extents. A {sup 12}CO outflow has been found in some of the clumps with IR clusters but not in the other clumps, supporting a strong relation of these clumps to the broader velocity dispersion region. We also estimated a mean star formation efficiency of {approx}30% for the clumps with IR clusters in the three H II regions.

  11. Entropy flattening, gas clumping, and turbulence in galaxy clusters

    SciTech Connect

    Fusco-Femiano, R.; Lapi, A.

    2014-03-10

    Several physical processes and formation events are expected in cluster outskirts, a vast region up to now essentially not covered by observations. The recent Suzaku (X-ray) and Planck (Sunyaev-Zel'dovich (SZ) effect) observations out to the virial radius have highlighted in these peripheral regions a rather sharp decline of the intracluster gas temperature, an entropy flattening in contrast with the theoretically expected power law increase, the break of the hydrostatic equilibrium even in some relaxed clusters, a derived gas mass fraction above the cosmic value measured from several cosmic microwave background experiments, and a total X-ray mass lower than the weak lensing mass determinations. Here we present the analysis of four clusters (A1795, A2029, A2204, and A133) with the SuperModel that includes a nonthermal pressure component due to turbulence to sustain the hydrostatic equilibrium also in the cluster outskirts. In this way, we obtain a correct determination of the total X-ray mass and of the gas mass fraction; this in turn allows us to determine the level of the gas clumping that can affect the shape of the entropy profiles reported by the Suzaku observations. Our conclusion is that the role of the gas clumping is very marginal and that the observed entropy flattening is due to the rapid decrement of the temperature in the cluster outskirts caused by non-gravitational effects. Moreover, we show that the X-ray/SZ joint analysis from ROSAT and Planck data, as performed in some recent investigations, is inadequate for discriminating between a power law increase and a flattening of the entropy.

  12. MAPS OF MASSIVE CLUMPS IN THE EARLY STAGE OF CLUSTER FORMATION: TWO MODES OF CLUSTER FORMATION, COEVAL OR NON-COEVAL?

    SciTech Connect

    Higuchi, Aya E.; Saito, Masao; Mauersberger, Rainer; Kawabe, Ryohei; Kurono, Yasutaka; Naoi, Takahiro

    2013-03-10

    We present maps of seven young massive molecular clumps within five target regions in C{sup 18}O (J = 1-0) line emission, using the Nobeyama 45 m telescope. These clumps, which are not associated with clusters, lie at distances between 0.7 and 2.1 kpc. We find C{sup 18}O clumps with radii of 0.5-1.7 pc, masses of 470-4200 M{sub Sun }, and velocity widths of 1.4-3.3 km s{sup -1}. All of the clumps are massive and approximately in virial equilibrium, suggesting they will potentially form clusters. Three of our target regions are associated with H II regions (CWHRs), while the other two are unassociated with H II regions (CWOHRs). The C{sup 18}O clumps can be classified into two morphological types: CWHRs with a filamentary or shell-like structure and spherical CWOHRs. The two CWOHRs have systematic velocity gradients. Using the publicly released WISE database, Class I and Class II protostellar candidates are identified within the C{sup 18}O clumps. The fraction of Class I candidates among all YSO candidates (Class I+Class II) is {>=}50% in CWHRs and {<=}50% in CWOHRs. We conclude that effects from the H II regions can be seen in (1) the spatial distributions of the clumps: filamentary or shell-like structure running along the H II regions; (2) the velocity structures of the clumps: large velocity dispersion along shells; and (3) the small age spreads of YSOs. The small spreads in age of the YSOs show that the presence of H II regions tends to trigger coeval cluster formation.

  13. A super lithium-rich red-clump star in the open cluster Trumpler 5

    NASA Astrophysics Data System (ADS)

    Monaco, L.; Boffin, H. M. J.; Bonifacio, P.; Villanova, S.; Carraro, G.; Caffau, E.; Steffen, M.; Ahumada, J. A.; Beletsky, Y.; Beccari, G.

    2014-04-01

    Context. The existence of lithium-rich low-mass red giant stars still represents a challenge for stellar evolution models. Stellar clusters are privileged environments for this kind of investigation. Aims: To investigate the chemical abundance pattern of the old open cluster Trumpler 5, we observed a sample of four red-clump stars with high-resolution optical spectrographs. One of them (#3416) reveals extremely strong lithium lines in its spectrum. Methods: One-dimensional, local thermodynamic equilibrium analysis was performed on the spectra of the observed stars. A 3D-NLTE analysis was performed to derive the lithium abundance of star #3416. Results: Star #3416 is super Li-rich with A(Li) = 3.75 dex. The lack of 6Li enrichment (6Li/7Li < 2%), the low carbon isotopic ratio (12C/13C = 14 ± 3), and the lack of evidence for radial velocity variation or enhanced rotational velocity (vsini = 2.8 km s-1) all suggest that lithium production has occurred in this star through the Cameron & Fowler mechanism. Conclusions: We identified a super Li-rich core helium-burning, red-clump star in an open cluster. Internal production is the most likely cause of the observed enrichment. Given the expected short duration of a star's Li-rich phase, enrichment is likely to have occurred at the red clump or in the immediately preceding phases, namely during the He-flash at the tip of the red giant branch (RGB) or while ascending the brightest portion of the RGB. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 088.D-0045(A).Appendix A is available in electronic form at http://www.aanda.org

  14. Properties of massive star-forming clumps with infall motions

    NASA Astrophysics Data System (ADS)

    He, Yu-Xin; Zhou, Jian-Jun; Esimbek, Jarken; Ji, Wei-Guang; Wu, Gang; Tang, Xin-Di; Komesh, Toktarkhan; Yuan, Ye; Li, Da-Lei; Baan, W. A.

    2016-09-01

    In this work, we aim to characterize high-mass clumps with infall motions. We selected 327 clumps from the Millimetre Astronomy Legacy Team 90-GHz survey, and identified 100 infall candidates. Combined with the results of He et al., we obtained a sample of 732 high-mass clumps, including 231 massive infall candidates and 501 clumps where infall is not detected. Objects in our sample were classified as pre-stellar, proto-stellar, H II or photodissociation region (PDR). The detection rates of the infall candidates in the pre-stellar, proto-stellar, H II and PDR stages are 41.2 per cent, 36.6 per cent, 30.6 per cent and 12.7 per cent, respectively. The infall candidates have a higher H2 column density and volume density compared with the clumps where infall is not detected at every stage. For the infall candidates, the median values of the infall rates at the pre-stellar, proto-stellar, H II and PDR stages are 2.6 × 10-3, 7.0 × 10-3, 6.5 × 10-3 and 5.5 × 10-3 M⊙ yr-1, respectively. These values indicate that infall candidates at later evolutionary stages are still accumulating material efficiently. It is interesting to find that both infall candidates and clumps where infall is not detected show a clear trend of increasing mass from the pre-stellar to proto-stellar, and to the H II stages. The power indices of the clump mass function are 2.04 ± 0.16 and 2.17 ± 0.31 for the infall candidates and clumps where infall is not detected, respectively, which agree well with the power index of the stellar initial mass function (2.35) and the cold Planck cores (2.0).

  15. Properties of massive star-forming clumps with infall motions

    NASA Astrophysics Data System (ADS)

    He, Yu-Xin; Zhou, Jian-Jun; Esimbek, Jarken; Ji, Wei-Guang; Wu, Gang; Tang, Xin-Di; Komesh, Toktarkhan; Yuan, Ye; Li, Da-Lei; Baan, W. A.

    2016-06-01

    In this work, we aim to characterise high-mass clumps with infall motions. We selected 327 clumps from the Millimetre Astronomy Legacy Team 90-GHz (MALT90) survey, and identified 100 infall candidates. Combined with the results of He et al. (2015), we obtained a sample of 732 high-mass clumps, including 231 massive infall candidates and 501 clumps where infall is not detected. Objects in our sample were classified as pre-stellar, proto-stellar, HII or photo-dissociation region (PDR). The detection rates of the infall candidates in the pre-stellar, proto-stellar, HII and PDR stages are 41.2%, 36.6%, 30.6% and 12.7%, respectively. The infall candidates have a higher H2 column density and volume density compared with the clumps where infall is not detected at every stage. For the infall candidates, the median values of the infall rates at the pre-stellar, proto-stellar, HII and PDR stages are 2.6×10-3, 7.0×10-3, 6.5×10-3 and 5.5×10-3 M⊙ yr-1, respectively. These values indicate that infall candidates at later evolutionary stages are still accumulating material efficiently. It is interesting to find that both infall candidates and clumps where infall is not detected show a clear trend of increasing mass from the pre-stellar to proto-stellar, and to the HII stages. The power indices of the clump mass function (ClMF) are 2.04±0.16 and 2.17±0.31 for the infall candidates and clumps where infall is not detected, respectively, which agree well with the power index of the stellar initial mass function (2.35) and the cold Planck cores (2.0).

  16. An extremely young massive clump forming by gravitational collapse in a primordial galaxy

    NASA Astrophysics Data System (ADS)

    Zanella, A.; Daddi, E.; Le Floc'h, E.; Bournaud, F.; Gobat, R.; Valentino, F.; Strazzullo, V.; Cibinel, A.; Onodera, M.; Perret, V.; Renaud, F.; Vignali, C.

    2015-05-01

    When cosmic star formation history reaches a peak (at about redshift z ~ 2), galaxies vigorously fed by cosmic reservoirs are dominated by gas and contain massive star-forming clumps, which are thought to form by violent gravitational instabilities in highly turbulent gas-rich disks. However, a clump formation event has not yet been observed, and it is debated whether clumps can survive energetic feedback from young stars, and afterwards migrate inwards to form galaxy bulges. Here we report the spatially resolved spectroscopy of a bright off-nuclear emission line region in a galaxy at z = 1.987. Although this region dominates star formation in the galaxy disk, its stellar continuum remains undetected in deep imaging, revealing an extremely young (less than ten million years old) massive clump, forming through the gravitational collapse of more than one billion solar masses of gas. Gas consumption in this young clump is more than tenfold faster than in the host galaxy, displaying high star-formation efficiency during this phase, in agreement with our hydrodynamic simulations. The frequency of older clumps with similar masses, coupled with our initial estimate of their formation rate (about 2.5 per billion years), supports long lifetimes (about 500 million years), favouring models in which clumps survive feedback and grow the bulges of present-day galaxies.

  17. An extremely young massive clump forming by gravitational collapse in a primordial galaxy.

    PubMed

    Zanella, A; Daddi, E; Le Floc'h, E; Bournaud, F; Gobat, R; Valentino, F; Strazzullo, V; Cibinel, A; Onodera, M; Perret, V; Renaud, F; Vignali, C

    2015-05-01

    When cosmic star formation history reaches a peak (at about redshift z ≈ 2), galaxies vigorously fed by cosmic reservoirs are dominated by gas and contain massive star-forming clumps, which are thought to form by violent gravitational instabilities in highly turbulent gas-rich disks. However, a clump formation event has not yet been observed, and it is debated whether clumps can survive energetic feedback from young stars, and afterwards migrate inwards to form galaxy bulges. Here we report the spatially resolved spectroscopy of a bright off-nuclear emission line region in a galaxy at z = 1.987. Although this region dominates star formation in the galaxy disk, its stellar continuum remains undetected in deep imaging, revealing an extremely young (less than ten million years old) massive clump, forming through the gravitational collapse of more than one billion solar masses of gas. Gas consumption in this young clump is more than tenfold faster than in the host galaxy, displaying high star-formation efficiency during this phase, in agreement with our hydrodynamic simulations. The frequency of older clumps with similar masses, coupled with our initial estimate of their formation rate (about 2.5 per billion years), supports long lifetimes (about 500 million years), favouring models in which clumps survive feedback and grow the bulges of present-day galaxies. PMID:25951282

  18. The global chemical properties of high-mass star forming clumps at different evolutionary stages

    NASA Astrophysics Data System (ADS)

    Zhang, Yan-Jun; Zhou, Jian-Jun; Esimbek, Jarken; He, Yu-Xin; Li, Da-Lei; Tang, Xin-Di; Ji, Wei-Guang; Yuan, Ye; Guo, Wei-Hua

    2016-06-01

    A total of 197 relatively isolated high-mass star-forming clumps were selected from the Millimeter Astronomy Legacy Team 90 GHz (MALT90) survey data and their global chemical evolution investigated using four molecular lines, N2H+ (1--0), HCO+ (1--0), HCN (1-0), and HNC (1-0). The results suggest that the global averaged integrated intensity ratios I(HCO+)/I(HNC), I(HCN)/I(HNC), I(N2H+)/I(HCO+), and I(N2H+)/ I(HCN) are promising tracers for evolution of high-mass star-forming clumps. The global averaged column densities and abundances of N2H+, HCO+, HCN, and HNC increase as clumps evolve. The global averaged abundance ratios X(HCN)/X(HNC) could be used to trace evolution of high-mass star forming clumps, X(HCO+)/X(HNC) is more suitable for distinguishing high-mass star-forming clumps in prestellar (stage A) from those in protostellar (stage B) and HII/PDR region (stage C). These results suggest that the global averaged integrated intensity ratios between HCN (1-0), HNC (1-0), HCO+ (1--0) and N2H+ (1--0) are more suitable for tracing the evolution of high-mass star forming clumps. We also studied the chemical properties of the target high-mass star-forming clumps in each spiral arm of the Galaxy, and got results very different from those above. This is probably due to the relatively small sample in each spiral arm. For high-mass star-forming clumps in Sagittarius arm and Norma-Outer arm, comparing two groups located on one arm with different Galactocentric distances, the clumps near the Galactic Center appear to be younger than those far from the Galactic center, which may be due to more dense gas concentrated near the Galactic Center, and hence more massive stars being formed there.

  19. Properties of Star-forming Clumps in Galaxy Disks at z>1 from CANDELS

    NASA Astrophysics Data System (ADS)

    Ravindranath, Swara; Closson Ferguson, Henry; Guo, Yicheng

    2015-08-01

    Galaxies at z>1 often exhibit clumpy morphology, and the massive star-forming clumps are thought to be the result of violent disk instability in the gas-rich, turbulent galaxy disks. Their dynamical evolution happens on timescales much shorter compared to secular processes, transforming them into the more regular Hubble types. In order to study this transition, we have identified all the clumpy galaxies at 1clump-finder algorithm to identify the clumps, and used PSF photometry to obtain the flux of individual clumps across the optical and NIR wavelengths. In this presentation, I will present some of the results on the properties of clumps, their rest-frame colors, ages, and masses. I will discuss the trends in the observed properties with radius within galaxies, with redshift, and with the properties of the host galaxies, and discuss how these trends compare to the general predictions from theories of violent disk instabilities.

  20. KIC 8263801: A clump star in the Kepler open cluster NGC 6866 field?

    NASA Astrophysics Data System (ADS)

    Abedigamba, O. P.

    2016-07-01

    In this paper we study the field of Kepler open cluster NGC 6866 using the data obtained from Kepler mission collected for a period of 4 years. We search for the red clump (RC) stars amongst the red giant (RG) stars showing solar-like oscillations using median gravity-mode period spacings (ΔP). We find a RG star KIC 8263801 having median gravity-mode period spacing 173.7 ± 6.4 s. We claim based on the median gravity-mode period spacing that KIC 8263801 is a secondary red clump (SRC) star which is massive enough to have ignited Helium burning in a non degenerate core. In the literature, no classification for KIC 8263801 has been provided. This is the first time that a star located in the field of NGC 6866 is classified in this manner.

  1. The JCMT Gould Belt Survey: Evidence for Dust Grain Evolution in Perseus Star-forming Clumps

    NASA Astrophysics Data System (ADS)

    Chen, Michael Chun-Yuan; Di Francesco, J.; Johnstone, D.; Sadavoy, S.; Hatchell, J.; Mottram, J. C.; Kirk, H.; Buckle, J.; Berry, D. S.; Broekhoven-Fiene, H.; Currie, M. J.; Fich, M.; Jenness, T.; Nutter, D.; Pattle, K.; Pineda, J. E.; Quinn, C.; Salji, C.; Tisi, S.; Hogerheijde, M. R.; Ward-Thompson, D.; Bastien, P.; Bresnahan, D.; Butner, H.; Chrysostomou, A.; Coude, S.; Davis, C. J.; Drabek-Maunder, E.; Duarte-Cabral, A.; Fiege, J.; Friberg, P.; Friesen, R.; Fuller, G. A.; Graves, S.; Greaves, J.; Gregson, J.; Holland, W.; Joncas, G.; Kirk, J. M.; Knee, L. B. G.; Mairs, S.; Marsh, K.; Matthews, B. C.; Moriarty-Schieven, G.; Mowat, C.; Pezzuto, S.; Rawlings, J.; Richer, J.; Robertson, D.; Rosolowsky, E.; Rumble, D.; Schneider-Bontemps, N.; Thomas, H.; Tothill, N.; Viti, S.; White, G. J.; Wouterloot, J.; Yates, J.; Zhu, M.

    2016-07-01

    The dust emissivity spectral index, β, is a critical parameter for deriving the mass and temperature of star-forming structures and, consequently, their gravitational stability. The β value is dependent on various dust grain properties, such as size, porosity, and surface composition, and is expected to vary as dust grains evolve. Here we present β, dust temperature, and optical depth maps of the star-forming clumps in the Perseus Molecular Cloud determined from fitting spectral energy distributions to combined Herschel and JCMT observations in the 160, 250, 350, 500, and 850 μm bands. Most of the derived β and dust temperature values fall within the ranges of 1.0–2.7 and 8–20 K, respectively. In Perseus, we find the β distribution differs significantly from clump to clump, indicative of grain growth. Furthermore, we also see significant localized β variations within individual clumps and find low-β regions correlate with local temperature peaks, hinting at the possible origins of low-β grains. Throughout Perseus, we also see indications of heating from B stars and embedded protostars, as well evidence of outflows shaping the local landscape.

  2. THE SINS SURVEY OF z {approx} 2 GALAXY KINEMATICS: PROPERTIES OF THE GIANT STAR-FORMING CLUMPS

    SciTech Connect

    Genzel, R.; Foerster Schreiber, N. M.; Genel, S.; Tacconi, L. J.; Buschkamp, P.; Davies, R.; Eisenhauer, F.; Kurk, J.; Newman, S.; Jones, T.; Shapiro, K.; Lilly, S. J.; Carollo, C. M.; Renzini, A.; Bouche, N.; Burkert, A.; Cresci, G.; Ceverino, D.; Dekel, A.; Hicks, E.

    2011-06-01

    We have studied the properties of giant star-forming clumps in five z {approx} 2 star-forming disks with deep SINFONI AO spectroscopy at the ESO VLT. The clumps reside in disk regions where the Toomre Q-parameter is below unity, consistent with their being bound and having formed from gravitational instability. Broad H{alpha}/[N II] line wings demonstrate that the clumps are launching sites of powerful outflows. The inferred outflow rates are comparable to or exceed the star formation rates, in one case by a factor of eight. Typical clumps may lose a fraction of their original gas by feedback in a few hundred million years, allowing them to migrate into the center. The most active clumps may lose much of their mass and disrupt in the disk. The clumps leave a modest imprint on the gas kinematics. Velocity gradients across the clumps are 10-40 km s{sup -1} kpc{sup -1}, similar to the galactic rotation gradients. Given beam smearing and clump sizes, these gradients may be consistent with significant rotational support in typical clumps. Extreme clumps may not be rotationally supported; either they are not virialized or they are predominantly pressure supported. The velocity dispersion is spatially rather constant and increases only weakly with star formation surface density. The large velocity dispersions may be driven by the release of gravitational energy, either at the outer disk/accreting streams interface, and/or by the clump migration within the disk. Spatial variations in the inferred gas phase oxygen abundance are broadly consistent with inside-out growing disks, and/or with inward migration of the clumps.

  3. Clumped X-ray emission around radio galaxies in Abell clusters

    NASA Technical Reports Server (NTRS)

    Burns, Jack O.; Rhee, George; Owen, Frazer N.; Pinkney, Jason

    1994-01-01

    We have made a comparison of the X-ray and radio morphologies for a sample of 41 rich cluster fields using Einstein Observatory Imaging Proportional Counter (IPC) and Very Large Array (VLA) 20 cm images. Surprisingly, we find that 75% of the radio galaxies have a statistically significant X-ray peak or subclump within 5 min of the radio galaxy position. The X-ray luminosity and the generally extended nature of the X-ray subclumps suggest that these subclumps are overdense regions emitting free-free radiation, although there is also evidence for Active Galactic Nuclei (AGN) X-ray emission coming from some of the more compact, high surface brightness X-ray peaks. Some interesting correlations with radio morphology were also discovered. For clusters which contain wide-angle-tailed radio sources associated with centrally dominant galaxies, there are significant elongations or clumps in the central X-ray emission which are unusual for this type of cluster. We suggest that cluster radio galaxies are pointers to particular clusters or regions within clusters that have recently undergone mergers between cluster subsystems.

  4. Distance moduli of open cluster NGC 6819 from Red Giant Clump stars

    NASA Astrophysics Data System (ADS)

    Abedigamba, O. P.; Balona, L. A.; Medupe, R.

    2016-07-01

    In this paper we study Kepler open cluster NGC 6819 using Kepler data of Red Giant Clump (RGC) single member (SM) stars. The Kepler data spans a period of 4 years starting in 2009. In particular, we derive distance moduli for each individual RGC star, from which we get the mean distance modulus of μ0 = 11.520 ± 0.105 mag for the cluster when we use reddening from the Kepler Input Catalogue (KIC) for each RGC star. A value of μ0 = 11.747 ± 0.086 mag is obtained when uniform reddening value E(B - V) = 0.15 is used for the cluster. The values of μ0 obtained with RGC stars are in agreement with the values in the literature with other methods. We report for the case of Kepler open cluster NGC 6819 that RGC stars can be used as 'distance candles' as has been done in the literature with other open clusters.

  5. Molecular emission in dense massive clumps from the star-forming regions S231-S235

    NASA Astrophysics Data System (ADS)

    Ladeyschikov, D. A.; Kirsanova, M. S.; Tsivilev, A. P.; Sobolev, A. M.

    2016-04-01

    The paper is concerned with the study of the star-forming regions S231-S235 in radio lines of molecules of the interstellar medium—carbon monoxide (CO), ammonia (NH3), cyanoacetylene (HC3N), in maser lines—methanol (CH3OH) and water vapor (H2O). The regions S231-S235 belong to the giant molecular cloudG174+2.5. The goal of this paper is to search for new sources of emission toward molecular clumps and to estimate their physical parameters from CO and NH3 molecular lines. We obtained new detections ofNH3 andHC3Nlines in the sources WB89673 and WB89 668 which indicates the presence of high-density gas. From the CO line, we derived sizes, column densities, and masses of molecular clumps. From the NH3 line, we derived gas kinetic temperatures and number densities in molecular clumps. We determined that kinetic temperatures and number densities of molecular gas are within the limits 16-30 K and 2.8-7.2 × 103 cm-3 respectively. The shock-tracing line of CH3OH molecule at a frequency of 36.2 GHz was detected in WB89 673 for the first time.

  6. Gas density fluctuations in the Perseus Cluster: clumping factor and velocity power spectrum

    NASA Astrophysics Data System (ADS)

    Zhuravleva, I.; Churazov, E.; Arévalo, P.; Schekochihin, A. A.; Allen, S. W.; Fabian, A. C.; Forman, W. R.; Sanders, J. S.; Simionescu, A.; Sunyaev, R.; Vikhlinin, A.; Werner, N.

    2015-07-01

    X-ray surface brightness fluctuations in the core of the Perseus Cluster are analysed, using deep observations with the Chandra observatory. The amplitude of gas density fluctuations on different scales is measured in a set of radial annuli. It varies from 7 to 12 per cent on scales of ˜10-30 kpc within radii of 30-220 kpc from the cluster centre. Using a statistical linear relation between the observed amplitude of density fluctuations and predicted velocity, the characteristic velocity of gas motions on each scale is calculated. The typical amplitudes of the velocity outside the central 30 kpc region are 90-140 km s-1 on ˜20-30 kpc scales and 70-100 km s-1 on smaller scales ˜7-10 kpc. The velocity power spectrum (PS) is consistent with cascade of turbulence and its slope is in a broad agreement with the slope for canonical Kolmogorov turbulence. The gas clumping factor estimated from the PS of the density fluctuations is lower than 7-8 per cent for radii ˜30-220 kpc from the centre, leading to a density bias of less than 3-4 per cent in the cluster core. Uncertainties of the analysis are examined and discussed. Future measurements of the gas velocities with the Astro-H, Athena and Smart-X observatories will directly measure the gas density-velocity perturbation relation and further reduce systematic uncertainties in this analysis.

  7. The Kinematic and Chemical Properties of a Potential Core-forming Clump: Perseus B1-E

    NASA Astrophysics Data System (ADS)

    Sadavoy, S. I.; Shirley, Y.; Di Francesco, J.; Henning, Th.; Currie, M. J.; André, Ph.; Pezzuto, S.

    2015-06-01

    We present 13CO and {{C}18}O (1-0), (2-1), and (3-2) maps toward the core-forming Perseus B1-E clump using observations from the James Clerk Maxwell Telescope, the Submillimeter Telescope of the Arizona Radio Observatory, and the IRAM 30 m telescope. We find that the 13CO and {{C}18}O line emission both have very complex velocity structures, indicative of multiple velocity components within the ambient gas. The (1-0) transitions reveal a radial velocity gradient across B1-E of ˜ 1 km {{s}-1} p{{c}-1} that increases from northwest to southeast, whereas the majority of the Perseus cloud has a radial velocity gradient increasing from southwest to northeast. In contrast, we see no evidence of a velocity gradient associated with the denser Herschel-identified substructures in B1-E. Additionally, the denser substructures have much lower systemic motions than the ambient clump material, which indicates that they are likely decoupled from the large-scale gas. Nevertheless, these substructures themselves have broad line widths (˜0.4 km {{s}-1}) similar to that of the {{C}18}O gas in the clump, which suggests they inherited their kinematic properties from the larger-scale, moderately dense gas. Finally, we find evidence of {{C}18}O depletion only toward one substructure, B1-E2, which is also the only object with narrow (transonic) line widths. We suggest that as prestellar cores form, their chemical and kinematic properties are linked in evolution, such that these objects must first dissipate their turbulence before they deplete in CO.

  8. EVIDENCE FOR INFLOW IN HIGH-MASS STAR-FORMING CLUMPS

    SciTech Connect

    Reiter, Megan; Shirley, Yancy L.; Wu Jingwen; Brogan, Crystal; Wootten, Alwyn; Tatematsu, Ken'ichi E-mail: yshirley@as.arizona.edu E-mail: cbrogan@nrao.edu E-mail: k.tatematsu@nao.ac.jp

    2011-10-10

    We analyze the HCO{sup +} 3-2 and H{sup 13}CO{sup +} 3-2 line profiles of 27 high-mass star-forming regions to identify asymmetries that are suggestive of mass inflow. Three quantitative measures of line asymmetry are used to indicate whether a line profile is blue, red, or neither-the ratio of the temperature of the blue and red peaks, the line skew, and the dimensionless parameter {delta}v. We find nine HCO{sup +} 3-2 line profiles with a significant blue asymmetry and four with significant red asymmetric profiles. Comparing our HCO{sup +} 3-2 results to HCN 3-2 observations from Wu et al., we find that eight of the blue and three of the red have profiles with the same asymmetry in HCN. The eight sources with blue asymmetries in both tracers are considered strong candidates for inflow. Quantitative measures of the asymmetry (e.g., {delta}v) tend to be larger for HCN. This, combined with possible HCO{sup +} abundance enhancements in outflows, suggests that HCN may be a better tracer of inflow. Understanding the behavior of common molecular tracers like HCO{sup +} in clumps of different masses is important for properly analyzing the line profiles seen in a sample of sources representing a broad range of clump masses. Such studies will soon be possible with the large number of sources with possible self-absorption seen in spectroscopic follow-up observations of clumps identified in the Bolocam Galactic Plane Survey.

  9. Calibrating the Optical Luminosity of Red Clump Stars: An Archival Study of Star Clusters

    NASA Astrophysics Data System (ADS)

    Grocholski, Aaron

    2010-09-01

    The core helium burning stars of the red clump {RC} are a conspicuous feature in the color-magnitude diagram of many stellar populations. Its ease of identification, along with its relative brightness {M_I 0} make the RC a popular feature for HST studies of stellar populations in galaxies out to a few Mpc. Such studies generally interpret the data through comparison to theoretical isochrones. For accurate results, the theoretical predictions must be calibrated to match the RC properties of observed populations of known age and metallicity. However, no large scale studies of the luminosity of the RC currently exist in the optical bands. We propose to remedy this situation with an archival study of RC properties in star clusters in the Milky Way, LMC, and SMC. We will focus on HST images of globular clusters, but we will augment the sample with ground-based open cluster observations to extend the coverage of parameter space. The goal is to build a large and homogeneous database, through new analysis and incorporation of literature data, of cluster ages, abundances, distances, and RC photometry. This database will allow us to explore the variations in the RC luminosity as a function of age and [Fe/H] over the full range of parameter space where the RC exists, for both the V and I bands. The results will provide a fundamental calibration for all future HST studies of stellar populations and distances of nearby galaxies using the RC. They will also allow for verification or improvement of theoretical models for red giant phase evolution. This in turn will help many subjects, from stellar modeling to population synthesis and fitting of spectral energy distributions of distant galaxies.

  10. Understanding the star-forming environment in stellar clusters

    NASA Astrophysics Data System (ADS)

    Wang, Shiya

    The main goal of this thesis is to investigate the physical conditions of the star-forming environment in stellar clusters, especially for the formation of low-mass cluster members. Embedded, young, and intermediate-mass stellar clusters around Herbig Ae/Be stars are sampled. Mid- and near-infrared observations identifying young stars and millimeter interferometric observations probing dense molecular gas and dust continuum are presented. These observations are used to reveal the large-scale young stellar population around the vicinity where the sampled clusters form, probe the physical conditions of dense molecular clumps which are capable of forming individual low-mass cluster members, and examine the influence of the most massive star in the cluster on its siblings and natal cluster-forming cloud. This study shows that stars within the cluster tend to seem younger than those outside the cluster, suggesting a higher and continuous star-forming rate within the cluster than outside, or massive stars are initiated later than low-mass stars within the same cloud. A thorough investigation of young stars and dense gas toward the MWC 1080 cluster further suggests a domination of the most massive star in the cluster on both the natal cloud dispersal and its low-mass cluster members. As active outflows and winds from the Herbig Ae/Be stars increase the non-thermal motion in the cloud, low-mass cluster members are formed within denser and more turbulent cores, than isolated low-mass star-forming cores. In addition, the strong gas dispersal from the Herbig Ae/Be stars also helps the removal of the circumstellar material around nearby low-mass stars. This makes these low-mass cluster members appear older. In summary, this thesis provides the observational evidence showing how the most massive star in the cluster affects the formation and evolution of low-mass cluster members and the physical conditions of star formation in the cluster.

  11. STAR-FORMING GAS IN YOUNG CLUSTERS

    SciTech Connect

    Myers, Philip C.

    2010-05-10

    Initial conditions for star formation in clusters are estimated for protostars whose masses follow the initial mass function from 0.05 to 10 solar masses. Star-forming infall is assumed equally likely to stop at any moment, due to gas dispersal dominated by stellar feedback. For spherical infall, the typical initial condensation must have a steep density gradient, as in low-mass cores, surrounded by a shallower gradient, as in the clumps around cores. These properties match observed column densities in cluster-forming regions when the mean infall stopping time is 0.05 Myr and the accretion efficiency is 0.5. The infall duration increases with final protostar mass, from 0.01 to 0.3 Myr, and the mass accretion rate increases from 3 to 300 x 10{sup -6} solar masses yr{sup -1}. The typical spherical accretion luminosity is {approx}5 solar luminosities, reducing the 'luminosity problem' to a factor of {approx}3. The initial condensation density gradient changes from steep to shallow at radius 0.04 pc, enclosing 0.9 solar masses, with mean column density 2 x 10{sup 22} cm{sup -2} and with effective central temperature 16 K. These initial conditions are denser and warmer than those for isolated star formation.

  12. The Bolocam Galactic Plane Survey. XIV. Physical Properties of Massive Starless and Star-forming Clumps

    NASA Astrophysics Data System (ADS)

    Svoboda, Brian E.; Shirley, Yancy L.; Battersby, Cara; Rosolowsky, Erik W.; Ginsburg, Adam G.; Ellsworth-Bowers, Timothy P.; Pestalozzi, Michele R.; Dunham, Miranda K.; Evans, Neal J., II; Bally, John; Glenn, Jason

    2016-05-01

    We sort 4683 molecular clouds between 10° < ℓ < 65° from the Bolocam Galactic Plane Survey based on observational diagnostics of star formation activity: compact 70 μm sources, mid-IR color-selected YSOs, H2O and CH3OH masers, and UCH ii regions. We also present a combined NH3-derived gas kinetic temperature and H2O maser catalog for 1788 clumps from our own GBT 100 m observations and from the literature. We identify a subsample of 2223 (47.5%) starless clump candidates (SCCs), the largest and most robust sample identified from a blind survey to date. Distributions of flux density, flux concentration, solid angle, kinetic temperature, column density, radius, and mass show strong (>1 dex) progressions when sorted by star formation indicator. The median SCC is marginally subvirial (α ∼ 0.7) with >75% of clumps with known distance being gravitationally bound (α < 2). These samples show a statistically significant increase in the median clump mass of ΔM ∼ 170–370 M ⊙ from the starless candidates to clumps associated with protostars. This trend could be due to (i) mass growth of the clumps at \\dot{M}∼ 200{--}440 M ⊙ Myr‑1 for an average freefall 0.8 Myr timescale, (ii) a systematic factor of two increase in dust opacity from starless to protostellar phases, and/or (iii) a variation in the ratio of starless to protostellar clump lifetime that scales as ∼M ‑0.4. By comparing to the observed number of CH3OH maser containing clumps, we estimate the phase lifetime of massive (M > 103 M ⊙) starless clumps to be 0.37 ± 0.08 Myr (M/103 M ⊙)‑1 the majority (M < 450 M ⊙) have phase lifetimes longer than their average freefall time.

  13. Star Formation in the Perseus Molecular Cloud: A Detailed Look at Star-Forming Clumps with Herschel

    NASA Astrophysics Data System (ADS)

    Sadavoy, Sarah I.

    2013-08-01

    This dissertation presents new Herschel observations at 70 micron, 160 micron, 250 micron, 350 micron, and 500 micron of the Perseus molecular cloud from the Herschel Gould Belt Survey. The Perseus molecular cloud is a nearby star-forming region consisting of seven main star-forming clumps. The Herschel observations are used to characterize and contrast the properties of these clumps, and to study their embedded core populations. First, we probed the exceptionally young clump, B1-E. Using complementary molecular line data, we demonstrate that B1-E is likely fragmenting into a first generation of dense cores in relative isolation. Such a core formation region has never been observed before. Second, we use complementary long wavelength observations at 850 micron to study the dust properties in the larger, more active B1 clump. We find that Herschel data alone cannot constrain well the dust properties of cold dust emission and that long wavelength observations are needed. Additionally, we find evidence of dust grain growth towards the dense cores in B1, where the dust emissivity index, beta, varies from the often assumed value of beta = 2. In the absence of long wavelength observations, however, assuming beta = 2 is preferable over measuring beta with the Herschel-only bands. Finally, we use the source extraction code, getsources, to identify the core populations within each clump from the Herschel data. In addition, we use complementary archival infrared observations to study their populations of young stellar objects (YSOs). We find that the more massive clumps have an excess of older stage YSOs, suggesting that these regions contracted first. Starless cores are typically associated with peaks in the column density, where those found towards regions of higher column density also have higher average densities and colder temperatures. Starless cores associated with a strong, local interstellar radiation field, however, have higher temperatures. We find that the clumps

  14. Multi-Physics Feedback Simulations with Realistic Initial Conditions of the Formation of Star Clusters: From Large Scale Magnetized Clouds to Turbulent Clumps to Cores to Stars

    NASA Astrophysics Data System (ADS)

    Klein, R. I.; Li, P.; McKee, C. F.

    2015-10-01

    Multi-physics zoom-in adaptive mesh refinement simulations with feedback and realistic initial conditions, starting from large scale turbulent molecular clouds through the formation of clumps and cores to the formation os stellar clusters are presented. I give a summary of results at the different scales undergoing gravitational collapse from cloud to core to cluster formation. Detailed comparisons with observations are made at each stage of the simulations. In particular, properties of the magnetized clumps are compared with recent observations of Crutcher et al. 2010 and Crutcher 2012 and the magnetic field orientation in cloud clumps relative to the global mean field of the inter-cloud medium (Li et al. 2009). The Initial Mass Function (IMF) obtained is compared with the Chabrier IMF and the protostellar mass function of the cluster is compared with different theories.

  15. On the Cluster Physics of Sunyaev-Zel'dovich and X-Ray Surveys. IV. Characterizing Density and Pressure Clumping due to Infalling Substructures

    NASA Astrophysics Data System (ADS)

    Battaglia, N.; Bond, J. R.; Pfrommer, C.; Sievers, J. L.

    2015-06-01

    Understanding the outskirts of galaxy clusters at the virial radius (R200) and beyond is critical for an accurate determination of cluster masses, structure growth, and to ensure unbiased cosmological parameter estimates from cluster surveys. This problem has drawn renewed interest due to recent determinations of gas mass fractions beyond R200, which appear to be considerably larger than the cosmic mean. Here, we use a large suite of cosmological hydrodynamical simulations to study the inhomogeneity of the intra-cluster medium and employ different variants of simulated physics, including radiative gas physics and thermal feedback by active galactic nuclei. We find that density and pressure clumping closely trace each other as a function of radius, but the bias on density remains on average \\lt 20% within R200. At larger radii, clumping increases steeply due to the continuous infall of coherent structures that have not yet passed the accretion shock. Density and pressure clumping increase with cluster mass and redshift, which probes on average dynamically younger objects that are still in the process of assembling. The angular power spectra of gas density and pressure show that the clumping signal is dominated by large-scale cosmic filaments that reach from the cosmic web into the clusters, signaling the presence of gravitationally driven “super clumping.” While the prolateness of the gravitational halo potential implies an approximate radial correlation of these gaseous large-scale structures, gas density and pressure lose coherence on small scales across different radii due to dissipative gas physics. In contrast, the angular power spectrum of dark matter shows an almost uniform size distribution due to unimpeded subhalos. We provide a synopsis of the radial dependence of the clusters’ non-equilibrium measures (kinetic pressure support, ellipticity, and clumping) that all increase sharply beyond R200.

  16. Observations of Protostellar Outflow Feedback in Clustered Star Formation

    NASA Astrophysics Data System (ADS)

    Nakamura, F.

    2016-05-01

    We discuss the role of protostellar outflow feedback in clustered star formation using the observational data of recent molecular outflow surveys toward nearby cluster-forming clumps. We found that for almost all clumps, the outflow momentum injection rate is significantly larger than the turbulence dissipation rate. Therefore, the outflow feedback is likely to maintain supersonic turbulence in the clumps. For less massive clumps such as B59, L1551, and L1641N, the outflow kinetic energy is comparable to the clump gravitational energy. In such clumps, the outflow feedback probably affects significantly the clump dynamics. On the other hand, for clumps with masses larger than about 200 M⊙, the outflow kinetic energy is significantly smaller than the clump gravitational energy. Since the majority of stars form in such clumps, we conclude that outflow feedback cannot destroy the whole parent clump. These characteristics of the outflow feedback support the scenario of slow star formation.

  17. Interferometric Mapping of Magnetic Fields: The ALMA View of the Massive Star-forming Clump W43-MM1

    NASA Astrophysics Data System (ADS)

    Cortes, Paulo C.; Girart, Josep M.; Hull, Charles L. H.; Sridharan, Tirupati K.; Louvet, Fabien; Plambeck, Richard; Li, Zhi-Yun; Crutcher, Richard M.; Lai, Shih-Ping

    2016-07-01

    Here, we present the first results from ALMA observations of 1 mm polarized dust emission toward the W43-MM1 high-mass star-forming clump. We have detected a highly fragmented filament with source masses ranging from 14 M {}ȯ to 312 M {}ȯ , where the largest fragment, source A, is believed to be one of the most massive in our Galaxy. We found a smooth, ordered, and detailed polarization pattern throughout the filament, which we used to derived magnetic field morphologies and strengths for 12 out of the 15 fragments detected ranging from 0.2 to 9 mG. The dynamical equilibrium of each fragment was evaluated finding that all the fragments are in a super-critical state that is consistent with previously detected infalling motions toward W43-MM1. Moreover, there are indications suggesting that the field is being dragged by gravity as the whole filament is collapsing.

  18. A UKIDSS-based search for low-mass stars and small stellar clumps in off-cloud parts of young star-forming regions *

    NASA Astrophysics Data System (ADS)

    Perger, M.; Lodieu, N.; Martín, E. L.; Barrado Y Navascués, D.

    2011-07-01

    The form and universality of the mass function of young and nearby star-forming regions is still under debate. Its relation to the stellar density, its mass peak and the dependency on most recent models shows significant differencies for the various regions and remains unclear up to date. We aim to get a more complete census of two of such regions. We investigate yet unexplored areas of Orion and Taurus-Auriga, observed by the UKIDSS survey. In the latter, we search for low-mass stars via photometric and proper motion criteria and signs for variability. In Orion, we search for small stellar clumps via nearest-neighbor methods. Highlights in Taurus would be the finding of the missing low-mass stars and the detection of a young cluster T dwarf. In Orion, we discovered small stellar associations of its OB1b and OB1c populations. Combined with what is known in literature, we will provide by this investigations a general picture of the results of the star-forming processes in large areas of Taurus and Orion and probe the most recent models. Based on data of the UKIRT (operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the U.K.) Infrared Deep Sky Survey (UKIDSS).Supported by the Marie Curie Research Training Network `CONSTELLATION' under grant no. MRTN-CT-2006-035890.

  19. The growth of the galaxy cluster Abell 85: mergers, shocks, stripping and seeding of clumping

    NASA Astrophysics Data System (ADS)

    Ichinohe, Y.; Werner, N.; Simionescu, A.; Allen, S. W.; Canning, R. E. A.; Ehlert, S.; Mernier, F.; Takahashi, T.

    2015-04-01

    We present the results of deep Chandra, XMM-Newton and Suzaku observations of the nearby galaxy cluster Abell 85, which is currently undergoing at least two mergers, and in addition shows evidence for gas sloshing which extends out to r ≈ 600 kpc. One of the two infalling subclusters, to the south of the main cluster centre, has a dense, X-ray bright cool core and a tail extending to the south-east. The northern edge of this tail is strikingly smooth and sharp (narrower than the Coulomb mean free path of the ambient gas) over a length of 200 kpc, while towards the south-west the boundary of the tail is blurred and bent, indicating a difference in the plasma transport properties between these two edges. The thermodynamic structure of the tail strongly supports an overall north-westward motion. We propose, that a sloshing-induced tangential, ambient, coherent gas flow is bending the tail eastwards. The brightest galaxy of this subcluster is at the leading edge of the dense core, and is trailed by the tail of stripped gas, suggesting that the cool core of the subcluster has been almost completely destroyed by the time it reached its current radius of r ≈ 500 kpc. The surface-brightness excess, likely associated with gas stripped from the infalling southern subcluster, extends towards the south-east out to at least r500 of the main cluster, indicating that the stripping of infalling subclusters may seed gas inhomogeneities. The second merging subcluster appears to be a diffuse non-cool-core system. Its merger is likely supersonic with a Mach number of ≈1.4.

  20. Apex determination and detection of stellar clumps in the open cluster M 67

    NASA Astrophysics Data System (ADS)

    Vereshchagin, S. V.; Chupina, N. V.; Sariya, Devesh P.; Yadav, R. K. S.; Kumar, Brijesh

    2014-08-01

    We determined the cluster’s apex coordinates, studied the substructures and performed membership analysis in the central part (34‧×33‧) of the open cluster M 67. We used the individual stellar apexes method developed earlier and classical technique of proper motion diagrams in coordinate system connected with apex. The neighbour-to-neighbour distance technique was applied to detect space details. The membership list was corrected and some stars were excluded from the most probable members list. The apex coordinates have been determined as: A0=132.97° ± 0.81° and D0=11.85° ± 0.90°. The 2D-space star density field was analysed and high degree of inhomogeneity was found.

  1. Controversial age spreads from the main sequence turn-off and red clump in intermediate-age clusters in the LMC

    NASA Astrophysics Data System (ADS)

    Niederhofer, F.; Bastian, N.; Kozhurina-Platais, V.; Hilker, M.; de Mink, S. E.; Cabrera-Ziri, I.; Li, C.; Ercolano, B.

    2016-02-01

    Most star clusters at an intermediate age (1-2 Gyr) in the Large and Small Magellanic Clouds show a puzzling feature in their color-magnitude diagrams (CMD) that is not in agreement with a simple stellar population. The main sequence turn-off of these clusters is much broader than expected from photometric uncertainties. One interpretation of this feature is that age spreads of the order of 200-500 Myr exist within individual clusters, although this interpretation is highly debated. Such large age spreads should affect other parts of the CMD, which are sensitive to age, as well. In this study, we analyze the CMDs of a sample of 12 intermediate-age clusters in the Large Magellanic Cloud that all show an extended turn-off using archival optical data taken with the Hubble Space Telescope. We fit the star formation history of the turn-off region and the red clump region independently. We find that in most cases, the age spreads inferred from the red clumps are smaller than those that result from the turn-off region. However, the age ranges that result from the red clump region are broader than expected for a single age. Only two out of 12 clusters in our sample show a red clump which seems to be consistent with a single age. As our results are ambiguous, by fitting the star formation histories to the red clump regions, we cannot ultimately tell if the extended main sequence turn-off feature is the result of an age spread or not. However, we do find that the width of the extended main sequence turn-off feature is correlated with the age of the clusters in a way which would be unexplained in the so-called age spread interpretation, but which may be expected if stellar rotation is the cause of the spread at the turn-off. Based on observations made with the NASA/ESA Hubble Space Telescope, and obtained from the Hubble Legacy Archive, which is a collaboration between the Space Telescope Science Institute (STScI/NASA), the Space Telescope European Coordinating Facility (ST

  2. Lithium Inventory of 2 Solar Mass Red Clump Stars in Open Clusters: A Test of the Helium Flash Mechanism

    NASA Technical Reports Server (NTRS)

    Carlberg, Joleen K.; Cunha, Katia; Smith, Verne V.

    2016-01-01

    The temperature distribution of field Li-rich red giants suggests the presence of a population of Li-rich red clump (RC) stars. One proposed explanation for this population is that all stars with masses near 2 solar mass experience a shortlived phase of Li-richness at the onset of core He-burning. Many of these stars have low C-12/C-13, a signature of deep mixing that is presumably associated with the Li regeneration. To test this purported mechanism of Li enrichment, we measured abundances in 38 RC stars and 6 red giant branch (RGB) stars in four open clusters selected to have RC masses near 2 solar mass. We find six Li-rich stars (A(Li) greater than or equal to 1.50 dex) of which only two may be RC stars. None of the RC stars have Li exceeding the levels observed in the RGB stars, but given the brevity of the suggested Li-rich phase and the modest sample size, it is probable that stars with larger Li-enrichments were missed simply by chance. However, we find very few stars in our sample with low C-12/C-13. Such low C-12/C-13, seen in many field Li-rich stars, should persist even after lithium has returned to normal low levels. Thus, if Li synthesis during the He flash occurs, it is a rare, but potentially long-lived occurrence rather than a short-lived phase for all stars. We estimate a conservative upper limit of the fraction of stars going through a Li-rich phase to be less than 47%, based on stars that have low C-12/C-13 for their observed A(Li).

  3. Lithium Inventory of 2 M ⊙ Red Clump Stars in Open Clusters: A Test of the Helium Flash Mechanism

    NASA Astrophysics Data System (ADS)

    Carlberg, Joleen K.; Cunha, Katia; Smith, Verne V.

    2016-08-01

    The temperature distribution of field Li-rich red giants suggests the presence of a population of Li-rich red clump (RC) stars. One proposed explanation for this population is that all stars with masses near 2 M ⊙ experience a short-lived phase of Li-richness at the onset of core He-burning. Many of these stars have low 12C/13C, a signature of deep mixing that is presumably associated with the Li regeneration. To test this purported mechanism of Li enrichment, we measured abundances in 38 RC stars and 6 red giant branch (RGB) stars in four open clusters selected to have RC masses near 2 M ⊙. We find six Li-rich stars (A(Li) ≥ 1.50 dex) of which only two may be RC stars. None of the RC stars have Li exceeding the levels observed in the RGB stars, but given the brevity of the suggested Li-rich phase and the modest sample size, it is probable that stars with larger Li-enrichments were missed simply by chance. However, we find very few stars in our sample with low 12C/13C. Such low 12C/13C, seen in many field Li-rich stars, should persist even after lithium has returned to normal low levels. Thus, if Li synthesis during the He flash occurs, it is a rare, but potentially long-lived occurrence rather than a short-lived phase for all stars. We estimate a conservative upper limit of the fraction of stars going through a Li-rich phase to be \\lt 47 % , based on stars that have low 12C/13C for their observed A(Li).

  4. Radiative Feedback of Forming Star Clusters on Their GMC Environments: Theory and Simulation

    NASA Astrophysics Data System (ADS)

    Howard, C. S.; Pudritz, R. E.; Harris, W. E.

    2013-07-01

    Star clusters form from dense clumps within a molecular cloud. Radiation from these newly formed clusters feeds back on their natal molecular cloud through heating and ionization which ultimately stops gas accretion into the cluster. Recent studies suggest that radiative feedback effects from a single cluster may be sufficient to disrupt an entire cloud over a short timescale. Simulating cluster formation on a large scale, however, is computationally demanding due to the high number of stars involved. For this reason, we present a model for representing the radiative output of an entire cluster which involves randomly sampling an initial mass function (IMF) as the cluster accretes mass. We show that this model is able to reproduce the star formation histories of observed clusters. To examine the degree to which radiative feedback shapes the evolution of a molecular cloud, we use the FLASH adaptive-mesh refinement hydrodynamics code to simulate cluster formation in a turbulent cloud. Unlike previous studies, sink particles are used to represent a forming cluster rather than individual stars. Our cluster model is then coupled with a raytracing scheme to treat radiative transfer as the clusters grow in mass. This poster will outline the details of our model and present preliminary results from our 3D hydrodynamical simulations.

  5. 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.

  6. SMOOTH(ER) STELLAR MASS MAPS IN CANDELS: CONSTRAINTS ON THE LONGEVITY OF CLUMPS IN HIGH-REDSHIFT STAR-FORMING GALAXIES

    SciTech Connect

    Wuyts, Stijn; Foerster Schreiber, Natascha M.; Genzel, Reinhard; Lutz, Dieter; Guo Yicheng; Giavalisco, Mauro; Barro, Guillermo; Faber, Sandra M.; Kocevski, Dale D.; Koo, David C.; McGrath, Elizabeth; Dekel, Avishai; Ferguson, Henry C.; Grogin, Norman A.; Koekemoer, Anton M.; Lotz, Jennifer; Hathi, Nimish P.; Huang, Kuang-Han; Newman, Jeffrey A.; and others

    2012-07-10

    We perform a detailed analysis of the resolved colors and stellar populations of a complete sample of 323 star-forming galaxies (SFGs) at 0.5 < z < 1.5 and 326 SFGs at 1.5 < z < 2.5 in the ERS and CANDELS-Deep region of GOODS-South. Galaxies were selected to be more massive than 10{sup 10} M{sub Sun} and have specific star formation rates (SFRs) above 1/t{sub H} . We model the seven-band optical ACS + near-IR WFC3 spectral energy distributions of individual bins of pixels, accounting simultaneously for the galaxy-integrated photometric constraints available over a longer wavelength range. We analyze variations in rest-frame color, stellar surface mass density, age, and extinction as a function of galactocentric radius and local surface brightness/density, and measure structural parameters on luminosity and stellar mass maps. We find evidence for redder colors, older stellar ages, and increased dust extinction in the nuclei of galaxies. Big star-forming clumps seen in star formation tracers are less prominent or even invisible in the inferred stellar mass distributions. Off-center clumps contribute up to {approx}20% to the integrated SFR, but only 7% or less to the integrated mass of all massive SFGs at z {approx} 1 and z {approx} 2, with the fractional contributions being a decreasing function of wavelength used to select the clumps. The stellar mass profiles tend to have smaller sizes and M20 coefficients, and higher concentration and Gini coefficients than the light distribution. Our results are consistent with an inside-out disk growth scenario with brief (100-200 Myr) episodic local enhancements in star formation superposed on the underlying disk. Alternatively, the young ages of off-center clumps may signal inward clump migration, provided this happens efficiently on the order of an orbital timescale.

  7. Annihilations of superheavy dark matter in superdense clumps

    SciTech Connect

    Berezinsky, V.; Dokuchaev, V.; Eroshenko, Yu.; Kachelriess, M.; Solberg, M. A.

    2010-05-15

    Superheavy dark matter (SHDM) exchanges energy with its environment much slower than particles with masses close to the electroweak scale and has therefore different small-scale clustering properties. Using the neutralino as candidate for the SHDM, we find that free-streaming allows the formation of DM clumps of all masses down to {approx}260m{sub {chi}}in the case of bino. If small-scale clumps evolve from a nonstandard, spiky spectrum of perturbations, DM clumps may form during the radiation-dominated era. These clumps are not destroyed by tidal interactions and can be extremely dense. In the case of a bino, a 'gravithermal catastrophe' can develop in the central part of the most dense clumps, increasing further the central density and thus the annihilation signal. In the case of a Higgsino, the annihilation signal is enhanced by the Sommerfeld effect. As a result annihilations of superheavy neutralinos in dense clumps may lead to observable fluxes of annihilation products in the form of ultrahigh energy particles, for both cases, Higgsinos and binos, as lightest supersymmetric particles.

  8. Interstellar Clump Behavior and Magnetic Effects in Small Clumps

    NASA Astrophysics Data System (ADS)

    Vallée, Jacques P.

    2000-07-01

    Cold, dusty molecular clumps (0.01 pcclumps. There are universal physical relations in clumps governing mean parameters such as gas density n, diameter D, magnetic field B, and gas line width σ, with the forms ~Dc, ~p, ~k, <σ>~q. For clumps with diameters <0.5 pc, one finds c=-1.5+/-0.1, p=-1.5+/-0.1, k=1.0+/-0.2. These exponent values differ from those found by Larson for molecular clouds with sizes greater than 1 pc. These differences in c and k could be indicative of ongoing accretion processes in shocked media as a prelude to star formation. The energy distribution in clumps reveals the following: the support against gravitational collapse in clumps with sizes greater than 0.1 pc comes mainly from turbulent energy, while smaller clumps with sizes less than 0.1 pc are supported by both magnetic and turbulent energies. The clump size of 0.1 pc is critical in many other respects.

  9. The morphology of the sub-giant branch and red clump reveal no sign of age spreads in intermediate-age clusters

    NASA Astrophysics Data System (ADS)

    Bastian, N.; Niederhofer, F.

    2015-04-01

    A recent surprise in stellar cluster research, made possible through the precision of Hubble Space Telescope photometry, was that some intermediate-age (1-2 Gyr) clusters in the Large and Small Magellanic Clouds have main-sequence turn-off (MSTO) widths that are significantly broader than would be expected for a simple stellar population (SSP). One interpretation of these extended MSTOs (eMSTOs) is that age spreads of the order of ˜500 Myr exist within the clusters, radically redefining our view of stellar clusters, which are traditionally thought of as single-age, single-metallicity stellar populations. Here we test this interpretation by studying other regions of the CMD that should also be affected by such large age spreads, namely the width of the sub-giant branch (SGB) and the red clump (RC). We study two massive clusters in the LMC that display the eMSTO phenomenon (NGC 1806 and NGC 1846) and show that both have SGB and RC morphologies that are in conflict with expectations if large age spreads exist within the clusters. We conclude that the SGB and RC widths are inconsistent with extended star formation histories within these clusters, hence age spreads are not likely to be the cause of the eMSTO phenomenon. Our results are in agreement with recent studies that also have cast doubt on whether large age spreads can exist in massive clusters; namely the failure to find age spreads in young massive clusters, a lack of gas/dust detected within massive clusters, and homogeneous abundances within clusters that exhibit the eMSTO phenomenon.

  10. VLT-SINFONI sub-kpc study of the star formation in local LIRGs and ULIRGs. Analysis of the global ΣSFR structure and characterisation of individual star-forming clumps

    NASA Astrophysics Data System (ADS)

    Piqueras López, J.; Colina, L.; Arribas, S.; Pereira-Santaella, M.; Alonso-Herrero, A.

    2016-05-01

    identified a total of 95 individual star-forming clumps in our sample of U/LIRGs, with sizes that range within ~60-400 pc and ~300-1500 pc, and extinction-corrected Paα luminosities of ~105-107 L⊙ and ~106-108 L⊙ in LIRGs and ULIRGs, respectively. The ΣSFR of the clumps presents a wide range of values within 1-90 M⊙ yr-1 kpc-2 and 0.1-100 M⊙ yr-1 kpc-2 for LIRGs and ULIRGs. Star-forming clumps in LIRGs are about ten times larger and thousands of times more luminous than typical clumps in spiral galaxies, which is consistent with expected photon-bounded conditions in ionized nebulae that surround young stellar clusters. Clumps in ULIRGs have sizes similar (×0.5-1) to those of high-z clumps, having Paα luminosities similar to some high-z clumps, and about 10 times less luminous than the most luminous high-z clumps identified so far. This could be an indication that the most luminous giant clumps in high-z star-forming galaxies are forming stars with a higher surface density rate than low-z compact ULIRGs. We also observed a change in the slope of the L-r relation, from η = 3.04 of local samples to η = 1.88 from high-z observations. A likely explanation is that most luminous galaxies are interacting and merging, and therefore their size represents a combination of the distribution of the star-forming clumps within each galaxy in the system plus the additional effect of the projected distance between the galaxies. As a consequence, this produces an overall size that is larger than that of individual clumps, or galaxies (for integrated measurements) Final data products are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/590/A67

  11. Lithopanspermia in star-forming clusters.

    PubMed

    Adams, Fred C; Spergel, David N

    2005-08-01

    This paper considers the lithopanspermia hypothesis in star-forming groups and clusters, where the chances of biological material spreading from one solar system to another is greatly enhanced (relative to action in the field) because of the close proximity of the systems and lower relative velocities. These effects more than compensate for the reduced time spent in such crowded environments. This paper uses approximately 300,000 Monte Carlo scattering calculations to determine the cross sections for rocks to be captured by binaries and provides fitting formulae for other applications. We assess the odds of transfer as a function of the ejection speed v (eject) and number N(.) of members in the birth aggregate. The odds of any given ejected meteoroid being recaptured by another solar system are relatively low, about 1:10(3)-10(6) over the expected range of ejection speeds and cluster sizes. Because the number of ejected rocks (with mass m > 10 kg) per system can be large, N (R) approximately 10(16), virtually all solar systems are likely to share rocky ejecta with all of the other solar systems in their birth cluster. The number of ejected rocks that carry living microorganisms is much smaller and less certain, but we estimate that N (B) approximately 10(7) rocks can be ejected from a biologically active solar system. For typical birth environments, the capture of life-bearing rocks is expected to occur N (bio) asymptotically equal to 10-16,000 times (per cluster), depending on the ejection speeds. Only a small fraction (f (imp) approximately 10(4)) of the captured rocks impact the surfaces of terrestrial planets, so that N (lps) asymptotically equal to 10(3)-1.6 lithopanspermia events are expected per cluster (under favorable conditions). Finally, we discuss the question of internal versus external seeding of clusters and the possibility of Earth seeding young clusters over its biologically active lifetime. PMID:16078868

  12. Cloud Structure of Galactic OB Cluster-forming Regions from Combining Ground- and Space-based Bolometric Observations

    NASA Astrophysics Data System (ADS)

    Lin, Yuxin; Liu, Hauyu Baobab; Li, Di; Zhang, Zhi-Yu; Ginsburg, Adam; Pineda, Jaime E.; Qian, Lei; Galván-Madrid, Roberto; McLeod, Anna Faye; Rosolowsky, Erik; Dale, James E.; Immer, Katharina; Koch, Eric; Longmore, Steve; Walker, Daniel; Testi, Leonardo

    2016-09-01

    We have developed an iterative procedure to systematically combine the millimeter and submillimeter images of OB cluster-forming molecular clouds, which were taken by ground-based (CSO, JCMT, APEX, and IRAM-30 m) and space telescopes (Herschel and Planck). For the seven luminous (L\\gt {10}6 L ⊙) Galactic OB cluster-forming molecular clouds selected for our analyses, namely W49A, W43-Main, W43-South, W33, G10.6-0.4, G10.2-0.3, and G10.3-0.1, we have performed single-component, modified blackbody fits to each pixel of the combined (sub)millimeter images, and the Herschel PACS and SPIRE images at shorter wavelengths. The ∼10″ resolution dust column density and temperature maps of these sources revealed dramatically different morphologies, indicating very different modes of OB cluster-formation, or parent molecular cloud structures in different evolutionary stages. The molecular clouds W49A, W33, and G10.6-0.4 show centrally concentrated massive molecular clumps that are connected with approximately radially orientated molecular gas filaments. The W43-Main and W43-South molecular cloud complexes, which are located at the intersection of the Galactic near 3 kpc (or Scutum) arm and the Galactic bar, show a widely scattered distribution of dense molecular clumps/cores over the observed ∼10 pc spatial scale. The relatively evolved sources G10.2-0.3 and G10.3-0.1 appear to be affected by stellar feedback, and show a complicated cloud morphology embedded with abundant dense molecular clumps/cores. We find that with the high angular resolution we achieved, our visual classification of cloud morphology can be linked to the systematically derived statistical quantities (i.e., the enclosed mass profile, the column density probability distribution function (N-PDF), the two-point correlation function of column density, and the probability distribution function of clump/core separations). In particular, the massive molecular gas clumps located at the center of G10

  13. Cloud Structure of Galactic OB Cluster-forming Regions from Combining Ground- and Space-based Bolometric Observations

    NASA Astrophysics Data System (ADS)

    Lin, Yuxin; Liu, Hauyu Baobab; Li, Di; Zhang, Zhi-Yu; Ginsburg, Adam; Pineda, Jaime E.; Qian, Lei; Galván-Madrid, Roberto; McLeod, Anna Faye; Rosolowsky, Erik; Dale, James E.; Immer, Katharina; Koch, Eric; Longmore, Steve; Walker, Daniel; Testi, Leonardo

    2016-09-01

    We have developed an iterative procedure to systematically combine the millimeter and submillimeter images of OB cluster-forming molecular clouds, which were taken by ground-based (CSO, JCMT, APEX, and IRAM-30 m) and space telescopes (Herschel and Planck). For the seven luminous (L\\gt {10}6 L ⊙) Galactic OB cluster-forming molecular clouds selected for our analyses, namely W49A, W43-Main, W43-South, W33, G10.6-0.4, G10.2-0.3, and G10.3-0.1, we have performed single-component, modified blackbody fits to each pixel of the combined (sub)millimeter images, and the Herschel PACS and SPIRE images at shorter wavelengths. The ˜10″ resolution dust column density and temperature maps of these sources revealed dramatically different morphologies, indicating very different modes of OB cluster-formation, or parent molecular cloud structures in different evolutionary stages. The molecular clouds W49A, W33, and G10.6-0.4 show centrally concentrated massive molecular clumps that are connected with approximately radially orientated molecular gas filaments. The W43-Main and W43-South molecular cloud complexes, which are located at the intersection of the Galactic near 3 kpc (or Scutum) arm and the Galactic bar, show a widely scattered distribution of dense molecular clumps/cores over the observed ˜10 pc spatial scale. The relatively evolved sources G10.2-0.3 and G10.3-0.1 appear to be affected by stellar feedback, and show a complicated cloud morphology embedded with abundant dense molecular clumps/cores. We find that with the high angular resolution we achieved, our visual classification of cloud morphology can be linked to the systematically derived statistical quantities (i.e., the enclosed mass profile, the column density probability distribution function (N-PDF), the two-point correlation function of column density, and the probability distribution function of clump/core separations). In particular, the massive molecular gas clumps located at the center of G10.6-0.4 and

  14. THE CONTRIBUTIONS OF INTERACTIVE BINARY STARS TO DOUBLE MAIN-SEQUENCE TURNOFFS AND DUAL RED CLUMP OF INTERMEDIATE-AGE STAR CLUSTERS

    SciTech Connect

    Yang Wuming; Bi Shaolan; Tian Zhijia; Li Tanda; Liu Kang; Meng Xiangcun E-mail: woomyang@gmail.com

    2011-04-20

    Double or extended main-sequence turnoffs (DMSTOs) and dual red clump (RC) were observed in intermediate-age clusters, such as in NGC 1846 and 419. The DMSTOs are interpreted as that the cluster has two distinct stellar populations with differences in age of about 200-300 Myr but with the same metallicity. The dual RC is interpreted as a result of a prolonged star formation. Using a stellar population-synthesis method, we calculated the evolution of a binary-star stellar population. We found that binary interactions and merging can reproduce the dual RC in the color-magnitude diagrams of an intermediate-age cluster, whereas in actuality only a single population exists. Moreover, the binary interactions can lead to an extended main-sequence turnoff (MSTO) rather than DMSTOs. However, the rest of the main sequence, subgiant branch, and first giant branch are hardly spread by the binary interactions. Part of the observed dual RC and extended MSTO may be the results of binary interactions and mergers.

  15. Molecular gas of Planck cold dust clumps

    NASA Astrophysics Data System (ADS)

    Wu, Yuefang

    2015-08-01

    To probe dynamical processes and physical properties of Planck Cold Clumps, survey and mapping of 674 most reliable Planck cold dust clumps with J=1-0 of CO,13CO and C18O were made at PMO 13.7 m telescope. More than 600 molecular cores were obtained, which are mainly located in seven molecular complexes divided by Dame (1987). Parameters of cores in different regions are with some difference, showing different evolutional status and environment of the cores. As a whole they are quiescent. Some are with star forming activities. J=1-0 lines of HCO+ and HCN at CO emission peaks were also observed at PMO, of which 24 were mapped with IRAM 30 m telescope. Several cores were also observed with J=2-1 of CO and 13CO using CSO. Core splits were detected. Combining with infrared data more than 70% of CO cores are identified as starless. Planck cold clumps seem to be ideal samples to search for candidates of massive prestellar cores and pre-clusters.

  16. Cooperation, clumping and the evolution of multicellularity.

    PubMed

    Biernaskie, Jay M; West, Stuart A

    2015-08-22

    The evolution of multicellular organisms represents one of the major evolutionary transitions in the history of life. A potential advantage of forming multicellular clumps is that it provides an efficiency benefit to pre-existing cooperation, such as the production of extracellular 'public goods'. However, this is complicated by the fact that cooperation could jointly evolve with clumping, and clumping could have multiple consequences for the evolution of cooperation. We model the evolution of clumping and a cooperative public good, showing that (i) when considered separately, both clumping and public goods production gradually increase with increasing genetic relatedness; (ii) in contrast, when the traits evolve jointly, a small increase in relatedness can lead to a major shift in evolutionary outcome—from a non-clumping state with low public goods production to a cooperative clumping state with high values of both traits; (iii) high relatedness makes it easier to get to the cooperative clumping state and (iv) clumping can be inhibited when it increases the number of cells that the benefits of cooperation must be shared with, but promoted when it increases relatedness between those cells. Overall, our results suggest that public goods sharing can facilitate the formation of well-integrated cooperative clumps as a first step in the evolution of multicellularity. PMID:26246549

  17. THE LIFE AND DEATH OF DENSE MOLECULAR CLUMPS IN THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Seale, Jonathan P.; Looney, Leslie W.; Wong, Tony; Ott, Juergen; Klein, Uli; Pineda, Jorge L.

    2012-05-20

    We report the results of a high spatial (parsec) resolution HCO{sup +} (J = 1 {yields} 0) and HCN (J = 1 {yields} 0) emission survey toward the giant molecular clouds of the star formation regions N 105, N 113, N 159, and N 44 in the Large Magellanic Cloud (LMC). The HCO{sup +} and HCN observations at 89.2 and 88.6 GHz, respectively, were conducted in the compact configuration of the Australia Telescope Compact Array. The emission is imaged into individual clumps with masses between 10{sup 2} and 10{sup 4} M{sub Sun} and radii of <1 pc to {approx}2 pc. Many of the clumps are coincident with indicators of current massive star formation, indicating that many of the clumps are associated with deeply embedded forming stars and star clusters. We find that massive young stellar object (YSO) bearing clumps tend to be larger ({approx}>1 pc), more massive (M {approx}> 10{sup 3} M{sub Sun }), and have higher surface densities ({approx}1 g cm{sup -2}), while clumps without signs of star formation are smaller ({approx}<1 pc), less massive (M {approx}< 10{sup 3} M{sub Sun }), and have lower surface densities ({approx}0.1 g cm{sup -2}). The dearth of massive (M > 10{sup 3} M{sub Sun }) clumps not bearing massive YSOs suggests that the onset of star formation occurs rapidly once the clump has attained physical properties favorable to massive star formation. Using a large sample of LMC massive YSO mid-IR spectra, we estimate that {approx}2/3 of the massive YSOs for which there are Spitzer mid-IR spectra are no longer located in molecular clumps; we estimate that these young stars/clusters have destroyed their natal clumps on a timescale of at least {approx}3 Multiplication-Sign 10{sup 5} yr.

  18. Small-scale clumps in the Galactic halo

    SciTech Connect

    Berezinsky, V. S.; Dokuchaev, V. I. Eroshenko, Yu. N.

    2010-01-15

    A mass function of small-scale dark matter clumps is calculated. We take into account the tidal destruction of clumps at early stages of structure formation starting from a time of clump detachment from the Universe expansion. Only a small fraction of these clumps, {approx}0.1%, in each logarithmic mass interval {Delta} log M {approx} 1 survives the stage of hierarchical clustering. We calculate the probability of surviving of the remnants of dark matter clumps in the Galaxy by modelling the tidal destruction of the small-scale clumps by disk and stars. It is demonstrated that a substantial fraction of clump remnants may survive through the tidal destruction during the lifetime of the Galaxy if a radius of core is rather small. The resulting mass spectrum of survived clumps is extended down to the mass of the core of the cosmologically produced clumps with a minimal mass. The survived dense remnants of tidally destructed clumps provides a large contribution to the annihilation signal in the Galaxy. We describe the anisotropy of dark matter clump distribution caused by tidal destruction of clumps in the Galactic disk. A corresponding annihilation of dark matter particles in small-scale clumps produces the anisotropic gamma-ray signal with respect to the Galactic disk.

  19. Photoevaporation of Clumps in Photodissociation Regions

    NASA Technical Reports Server (NTRS)

    Gorti, Uma; Hollenbach, David; DeVincenzi, D. (Technical Monitor)

    2002-01-01

    We present the results of an investigation of the effects of Far Ultraviolet (FUV) radiation (6.0eV < hv < 13.6eV) from hot early type OB stars on clumps in star-forming molecular clouds. Clumps in FUV-illuminated regions (or photodissociation regions or PDRs) undergo external heating and photodissociation as they are exposed to the FUV field, resulting in a loss of cold, molecular lump mass as it is converted to warm atomic gas. The heating, if rapid, creates strong photoevaporative mass flows off the clump surfaces, and drives shocks into the clumps, compressing them to high densities. The clumps lose mass on relatively short timescales. The evolution of an individual clump is found to be sensitive to three dimensionless parameters: Nc0, the ratio of the initial column density of the clump to the column N(0) approx. 10(exp 21) cm(exp -2) of a warm FUV-heated surface region; upsilon, the ratio of the sound speed in the heated surface to that in the cold clump material: and t(FUV)t(c), the ratio of the "turn-on time" t(FUV) of the heating flux on a clump to its initial sound crossing-time t(c). The evolution also depends on whether a confining interclump medium exists, or whether the interclump region has negligible pressure, as is the case for turbulence-generated clumps. In this paper, we use spherical 1-D numerical hydrodynamic models as well as approximate analytical models to study the dependence of clump photoevaporation on the physical parameters of the clump, and to derive the dynamical evolution, mass loss rates and photoevaporative timescales of a clump for a variety of astrophysical situations. Turbulent clumps evolve so that their column densities are equal to a critical value determined by the local FUV field, and typically have short photo evaporation timescales, approx. 10(exp 4-5) years for a 1 M(solar mass) clump in a typical star-forming region (Nc0 = 10, upsilon = 10). Clumps with insufficient magnetic pressure support, and in strong FUV fields

  20. How did the Virgo cluster form?

    NASA Astrophysics Data System (ADS)

    Sorce, Jenny G.; Gottlöber, Stefan; Hoffman, Yehuda; Yepes, Gustavo

    2016-08-01

    While the Virgo cluster is the nearest galaxy cluster and therefore the best observed one, little is known about its formation history. In this paper, a set of cosmological simulations that resemble the Local Universe is used to shed the first light on this mystery. The initial conditions for these simulations are constrained with galaxy peculiar velocities of the second catalogue of the Cosmicflows project using algorithms developed within the Constrained Local UniversE Simulation project. Boxes of 500 h-1 Mpc on a side are set to run a series of dark matter only constrained simulations. In each simulation, a unique dark matter halo can be reliably identified as Virgo's counterpart. The properties of these Virgo haloes are in agreement at a 10-20 per cent level with the global properties of the observed Virgo cluster. Their zero-velocity masses agree at 1σ with the observational mass estimate. In all the simulations, the matter falls on to the Virgo objects along a preferential direction that corresponds to the observational filament and the slowest direction of collapse. A study of the mass accretion history of the Virgo candidates reveals the most likely formation history of the Virgo cluster, namely a quiet accretion over the last 7 Gyr.

  1. Clumped isotope thermometry and catagenesis

    NASA Astrophysics Data System (ADS)

    Eiler, J. M.; Clog, M. D.; Dallas, B.; Douglas, P. M.; Piasecki, A.; Sessions, A. L.; Stolper, D. A.

    2014-12-01

    Clumped- and site-specific isotopic compositions of organic compounds can constrain their formation temperatures, sources, and chemical reaction histories. The large number of isotopologues of organic molecules may allow for the isotopic composition of a single compound to illuminate many processes. For example, it is possible that clumping or site specific effects in different parts of the same molecule will differ in blocking temperature, such that a molecule's full isotopic structure could simultaneously constrain conditions of biosynthesis, catagenic 'cracking', and storage in the crust. Recent innovations in high-resolution mass spectrometry and methods of IR and NMR spectroscopy make it possible to explore these questions. Methane is the first organic molecule to have its clumped isotope geochemistry analyzed in a variety of natural environments and controlled experiments. Methane generated through catagenic cracking of kerogen and other organic matter forms in equilibrium with respect to isotopic clumping, and preserves that state through later storage or migration, up to temperatures of ~250 ˚C. This kinetic behavior permits a variety of useful geological applications. But it is unexpected because the bulk stable isotope composition of thermogenic methane is thought to reflect kinetic isotope effects on irreversible reactions. Our observations imply a new interpretation of the chemical physics of catagenic methane formation. Additional instrument and methods developments are currently extending the measurement of isotopic clumping and position specific effects to larger alkanes, other hydrocarbon compounds, and amino acids. These measurements will ultimately expand our capacity to understand the formational conditions and fates of organic molecules in high- and low-temperature environments through geological time.

  2. Statistical clumped isotope signatures

    PubMed Central

    Röckmann, T.; Popa, M. E.; Krol, M. C.; Hofmann, M. E. G.

    2016-01-01

    High precision measurements of molecules containing more than one heavy isotope may provide novel constraints on element cycles in nature. These so-called clumped isotope signatures are reported relative to the random (stochastic) distribution of heavy isotopes over all available isotopocules of a molecule, which is the conventional reference. When multiple indistinguishable atoms of the same element are present in a molecule, this reference is calculated from the bulk (≈average) isotopic composition of the involved atoms. We show here that this referencing convention leads to apparent negative clumped isotope anomalies (anti-clumping) when the indistinguishable atoms originate from isotopically different populations. Such statistical clumped isotope anomalies must occur in any system where two or more indistinguishable atoms of the same element, but with different isotopic composition, combine in a molecule. The size of the anti-clumping signal is closely related to the difference of the initial isotope ratios of the indistinguishable atoms that have combined. Therefore, a measured statistical clumped isotope anomaly, relative to an expected (e.g. thermodynamical) clumped isotope composition, may allow assessment of the heterogeneity of the isotopic pools of atoms that are the substrate for formation of molecules. PMID:27535168

  3. Statistical clumped isotope signatures.

    PubMed

    Röckmann, T; Popa, M E; Krol, M C; Hofmann, M E G

    2016-01-01

    High precision measurements of molecules containing more than one heavy isotope may provide novel constraints on element cycles in nature. These so-called clumped isotope signatures are reported relative to the random (stochastic) distribution of heavy isotopes over all available isotopocules of a molecule, which is the conventional reference. When multiple indistinguishable atoms of the same element are present in a molecule, this reference is calculated from the bulk (≈average) isotopic composition of the involved atoms. We show here that this referencing convention leads to apparent negative clumped isotope anomalies (anti-clumping) when the indistinguishable atoms originate from isotopically different populations. Such statistical clumped isotope anomalies must occur in any system where two or more indistinguishable atoms of the same element, but with different isotopic composition, combine in a molecule. The size of the anti-clumping signal is closely related to the difference of the initial isotope ratios of the indistinguishable atoms that have combined. Therefore, a measured statistical clumped isotope anomaly, relative to an expected (e.g. thermodynamical) clumped isotope composition, may allow assessment of the heterogeneity of the isotopic pools of atoms that are the substrate for formation of molecules. PMID:27535168

  4. A submillimetre survey of the kinematics of the Perseus molecular cloud - III. Clump kinematics

    NASA Astrophysics Data System (ADS)

    Curtis, Emily I.; Richer, John S.

    2011-01-01

    We explore the kinematic properties of dense continuum clumps in the Perseus molecular cloud, derived from our wide-field C18O J = 3 → 2 data across four regions - NGC 1333, IC 348/HH 211, L1448 and L1455. Two distinct populations are examined, identified using the automated algorithms CLFIND (85 clumps) and GAUSSCLUMPS (122 clumps) on existing SCUBA 850-μm data. These kinematic signatures are compared to the clumps' dust continuum properties. We calculate each clump's non-thermal linewidth and virial mass from the associated C18O J = 3 → 2 spectrum. The clumps have supersonic linewidths, <σNT/cs>= 1.76 ± 0.09 (CLFIND population) and 1.71 ± 0.05 (with GAUSSCLUMPS). The linewidth distributions suggest the C18O line probes a lower density `envelope' rather than a dense inner core. Similar linewidth distributions for protostellar and starless clumps imply protostars do not have a significant impact on their immediate environment. The proximity to an active young stellar cluster seems to affect the linewidths: those in NGC 1333 are greater than elsewhere. In IC 348 the proximity to the old infrared cluster has little influence, with the linewidths being the smallest of all. The virial analysis suggests that the clumps are bound and close to equipartition, with virial masses similar to the masses derived from the continuum emission. In particular, the starless clumps occupy the same parameter space as the protostars, suggesting they are true stellar precursors and will go on to form stars. We also search for ordered C18O velocity gradients across the face of each core. Approximately one-third have significant detections, which we mainly interpret in terms of rotation. However, we note a correlation between the directions of the identified gradients and outflows across the protostars, indicating we may not have a purely rotational signature. The fitted gradients are in the range ? to 16 km s-1 pc-1, larger than found in previous work, probably as a result of the

  5. Anatomy of a high-mass star forming cloud: The G24.78+0.08 (proto)stellar cluster

    NASA Astrophysics Data System (ADS)

    Cesaroni, R.; Codella, C.; Furuya, R. S.; Testi, L.

    2003-04-01

    We present the results of an interferometric and single-dish study of G24.78+0.08, a region associated with high-mass star formation. Observations have been carried out in several molecular species, which are suitable to trace environments with different densities and temperatures. Evidence for this region to contain a cluster of very young massive stellar objects has been presented in a previous paper (Furuya et al. \\cite{furu}). We suggest that the embedded stars might be too young to have affected the surrounding molecular cloud significantly on a large scale. This gives us the opportunity to investigate the configuration of the cloud as it was prior to the star formation episode. We assess that the (proto)stellar cluster lies at the center of a molecular clump with diameter of ~ 2 pc: to a good approximation this may be described as a spherically symmetric clump with density profile of the type nH_2~ R-1.8. Inside 0.5 pc from the center, instead, the gas is much more inhomogeneous and concentrated in a few high-density cores surrounding the (proto)stars. Our findings indicate that a self-regulating formation mechanism for the high-mass stars in G24.78 is plausible: in the proposed scenario star formation would occur from inside-out collapse of the parsec-scale clump, followed by infall reversal due to outflows powered by the newly formed massive stars. We also find that one of the two bipolar outflows powered by the embedded YSOs is more extended and hence older than the other, thus confirming the evolutionary sequence proposed in our previous article.

  6. Dense molecular clumps associated with the Large Magellanic Cloud supergiant shells LMC 4 and LMC 5

    SciTech Connect

    Fujii, Kosuke; Mizuno, Norikazu; Minamidani, Tetsuhiro; Onishi, Toshikazu; Muraoka, Kazuyuki; Kawamura, Akiko; Muller, Erik; Tatematsu, Ken'ichi; Hasegawa, Tetsuo; Miura, Rie E.; Ezawa, Hajime; Dawson, Joanne; Tosaki, Tomoka; Sakai, Takeshi; Tsukagoshi, Takashi; Tanaka, Kunihiko; Fukui, Yasuo

    2014-12-01

    We investigate the effects of supergiant shells (SGSs) and their interaction on dense molecular clumps by observing the Large Magellanic Cloud (LMC) star-forming regions N48 and N49, which are located between two SGSs, LMC 4 and LMC 5. {sup 12}CO (J = 3-2, 1-0) and {sup 13}CO(J = 1-0) observations with the ASTE and Mopra telescopes have been carried out toward these regions. A clumpy distribution of dense molecular clumps is revealed with 7 pc spatial resolution. Large velocity gradient analysis shows that the molecular hydrogen densities (n(H{sub 2})) of the clumps are distributed from low to high density (10{sup 3}-10{sup 5} cm{sup –3}) and their kinetic temperatures (T {sub kin}) are typically high (greater than 50 K). These clumps seem to be in the early stages of star formation, as also indicated from the distribution of Hα, young stellar object candidates, and IR emission. We found that the N48 region is located in the high column density H I envelope at the interface of the two SGSs and the star formation is relatively evolved, whereas the N49 region is associated with LMC 5 alone and the star formation is quiet. The clumps in the N48 region typically show high n(H{sub 2}) and T {sub kin}, which are as dense and warm as the clumps in LMC massive cluster-forming areas (30 Dor, N159). These results suggest that the large-scale structure of the SGSs, especially the interaction of two SGSs, works efficiently on the formation of dense molecular clumps and stars.

  7. Cluster speckle structures through multiple apertures forming a closed curve

    NASA Astrophysics Data System (ADS)

    Mosso, E.; Tebaldi, M.; Lencina, A.; Bolognini, N.

    2010-04-01

    In this work, cluster-like speckle patterns are analyzed. These patterns are generated when a diffuser illuminated by coherent light is imaged by a lens having a pupil mask with multiple apertures forming a closed curve. We show that the cluster structure results from the complex modulation produced inside each speckle which is generated by multiple interferences of light through the apertures. In particular, when the apertures are uniformly distributed along a closed curve, the resulting image speckle cluster replicates the pupil aperture distribution. Experimental results and theoretical simulations show that cluster features depend on the apertures distribution and the size of the closed curves.

  8. HUBBLE SPIES HUGE CLUSTERS OF STARS FORMED

    NASA Technical Reports Server (NTRS)

    2002-01-01

    BY ANCIENT ENCOUNTER This stunningly beautiful image [right] taken with the NASA Hubble Space Telescope shows the heart of the prototypical starburst galaxy M82. The ongoing violent star formation due to an ancient encounter with its large galactic neighbor, M81, gives this galaxy its disturbed appearance. The smaller picture at upper left shows the entire galaxy. The image was taken in December 1994 by the Kitt Peak National Observatory's 0.9-meter telescope. Hubble's view is represented by the white outline in the center. In the Hubble image, taken by the Wide Field and Planetary Camera 2, the huge lanes of dust that crisscross M82's disk are another telltale sign of the flurry of star formation. Below the center and to the right, a strong galactic wind is spewing knotty filaments of hydrogen and nitrogen gas. More than 100 super star clusters -- very bright, compact groupings of about 100,000 stars -- are seen in this detailed Hubble picture as white dots sprinkled throughout M82's central region. The dark region just above the center of the picture is a huge dust cloud. A collaboration of European and American scientists used these clusters to date the ancient interaction between M82 and M81. About 600 million years ago, a region called 'M82 B' (the bright area just below and to the left of the central dust cloud) exploded with new stars. Scientists have discovered that this ancient starburst was triggered by the violent encounter with M81. M82 is a bright (eighth magnitude), nearby (12 million light-years from Earth) galaxy in the constellation Ursa Major (the Great Bear). The Hubble picture was taken Sept. 15, 1997. The natural-color composite was constructed from three Wide Field and Planetary Camera 2 exposures, which were combined in chromatic order: 4,250 seconds through a blue filter (428 nm); 2,800 seconds through a green filter (520 nm); and 2,200 seconds through a red (820 nm) filter. Credits for Hubble image: NASA, ESA, R. de Grijs (Institute of

  9. Confronting the outflow-regulated cluster formation model with observations

    SciTech Connect

    Nakamura, Fumitaka; Li, Zhi-Yun E-mail: zl4h@virginia.edu

    2014-03-10

    Protostellar outflows have been shown theoretically to be capable of maintaining supersonic turbulence in cluster-forming clumps and keeping the star formation rate per free-fall time as low as a few percent. We aim to test two basic predictions of this outflow-regulated cluster formation model, namely, (1) the clump should be close to virial equilibrium and (2) the turbulence dissipation rate should be balanced by the outflow momentum injection rate, using recent outflow surveys toward eight nearby cluster-forming clumps (B59, L1551, L1641N, Serpens Main Cloud, Serpens South, ρ Oph, IC 348, and NGC 1333). We find, for almost all sources, that the clumps are close to virial equilibrium and the outflow momentum injection rate exceeds the turbulence momentum dissipation rate. In addition, the outflow kinetic energy is significantly smaller than the clump gravitational energy for intermediate and massive clumps with M {sub cl} ≳ a few × 10{sup 2} M {sub ☉}, suggesting that the outflow feedback is not enough to disperse the clump as a whole. The number of observed protostars also indicates that the star formation rate per free-fall time is as small as a few percent for all clumps. These observationally based results strengthen the case for outflow-regulated cluster formation.

  10. Abundant cyanopolyynes as a probe of infall in the Serpens South cluster-forming region

    NASA Astrophysics Data System (ADS)

    Friesen, R. K.; Medeiros, L.; Schnee, S.; Bourke, T. L.; Francesco, J. Di; Gutermuth, R.; Myers, P. C.

    2013-12-01

    We have detected bright HC7N J = 21 - 20 emission towards multiple locations in the Serpens South cluster-forming region using the K-Band Focal Plane Array at the Robert C. Byrd Green Bank Telescope. HC7N is seen primarily towards cold filamentary structures that have yet to form stars, largely avoiding the dense gas associated with small protostellar groups and the main central cluster of Serpens South. Where detected, the HC7N abundances are similar to those found in other nearby star-forming regions. Towards some HC7N `clumps', we find consistent variations in the line centroids relative to NH3 (1,1) emission, as well as systematic increases in the HC7N non-thermal line widths, which we argue reveal infall motions on to dense filaments within Serpens South with minimum mass accretion rates of M ˜ 2-5 M⊙ Myr-1. The relative abundance of NH3 to HC7N suggests that the HC7N is tracing gas that has been at densities n ˜ 104 cm-3 for time-scales t ≲ 1-2 × 105 yr. Since HC7N emission peaks are rarely co-located with those of either NH3 or continuum, it is likely that Serpens South is not particularly remarkable in its abundance of HC7N, but instead the serendipitous mapping of HC7N simultaneously with NH3 has allowed us to detect HC7N at low abundances in regions where it otherwise may not have been looked for. This result extends the known star-forming regions containing significant HC7N emission from typically quiescent regions, like the Taurus molecular cloud, to more complex, active environments.

  11. IRDC G030.88+00.13: A TALE OF TWO MASSIVE CLUMPS

    SciTech Connect

    Zhang Qizhou; Wang Ke

    2011-05-20

    Massive stars (M {approx}>10 M{sub sun}) form from collapse of parsec-scale molecular clumps. How molecular clumps fragment to give rise to massive stars in a cluster with a distribution of masses is unclear. We search for cold cores that may lead to future formation of massive stars in a massive (>10{sup 3} M{sub sun}), low luminosity (4.6 x 10{sup 2} L{sub sun}) infrared dark cloud (IRDC) G030.88+00.13. The NH{sub 3} data from the Very Large Array (VLA) and Green Bank Telescope reveal that the extinction feature seen in the infrared consists of two distinctive clumps along the same line of sight. The C1 clump at 97 km s{sup -1} coincides with the extinction in the Spitzer 8 and 24 {mu}m. Therefore, it is responsible for the majority of the IRDC. The C2 clump at 107 km s{sup -1} is more compact and has a peak temperature of 45 K. Compact dust cores and H{sub 2}O masers revealed in the Submillimeter Array and VLA observations are mostly associated with C2, and none are within the IRDC in C1. The luminosity indicates that neither the C1 nor C2 clump has yet to form massive protostars. But C1 might be at a precluster forming stage. The simulated observations rule out 0.1 pc cold cores with masses above 8 M{sub sun} within the IRDC. The core masses in C1 and C2 and those in high-mass protostellar objects suggest an evolutionary trend that the mass of cold cores increases over time. Based on our findings, we propose an empirical picture of massive star formation that protostellar cores and the embedded protostars undergo simultaneous mass growth during the protostellar evolution.

  12. THE STRUCTURAL EVOLUTION OF FORMING AND EARLY STAGE STAR CLUSTERS

    SciTech Connect

    Jaehnig, Karl O.; Da Rio, Nicola; Tan, Jonathan C. E-mail: ndario@ufl.edu

    2015-01-10

    We study the degree of angular substructure in the stellar position distribution of young members of Galactic star-forming regions, looking for correlations with distance from cluster center, surface number density of stars, and local dynamical age. To this end we adopt the catalog of members in 18 young (∼1-3 Myr) clusters from the Massive Young Star-Forming Complex Study in Infrared and X-ray Survey and the statistical analysis of the angular dispersion parameter, δ{sub ADP,} {sub N}. We find statistically significant correlation between δ{sub ADP,} {sub N} and physical projected distance from the center of the clusters, with the centers appearing smoother than the outskirts, consistent with more rapid dynamical processing on local dynamical, free-fall or orbital timescales. Similarly, smoother distributions are seen in regions of higher surface density, or older dynamical ages. These results indicate that dynamical processing that erases substructure is already well-advanced in young, sometimes still-forming, clusters. Such observations of the dissipation of substructure have the potential to constrain theoretical models of the dynamical evolution of young and forming clusters.

  13. The Structural Evolution of Forming and Early Stage Star Clusters

    NASA Astrophysics Data System (ADS)

    Jaehnig, Karl; Da Rio, Nicola; Tan, Jonathan C.

    2016-05-01

    We study the degree of angular substructure in the stellar position distribution of young members of Galactic star-forming regions, looking for correlations with distance from cluster center, surface number density of stars, and local dynamical age. To this end we adopt the catalog of members in 18 young (∼1-3 Myr) clusters from the Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) Survey and the statistical analysis of the Angular Dispersion Parameter, δADP. We find statistically significant correlation between δADP and physical projected distance from the center of the clusters, with the centers appearing smoother than the outskirts, consistent with more rapid dynamical processing on local dynamical, free-fall or orbital timescales. Similarly, smoother distributions are seen in regions of higher surface density, or older dynamical ages. These results indicate that dynamical processing that erases substructure is already well-advanced in young, sometimes still-forming, clusters. Such observations of the dissipation of substructure have the potential to constrain theoretical models of the dynamical evolution of young and forming clusters.

  14. Mass-density relationship in molecular cloud clumps

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  15. Automatic style clustering of printed characters in form images

    NASA Astrophysics Data System (ADS)

    Liu, Changsong; Ding, Xiaoqing

    2005-01-01

    Style is an important feature of printed or handwritten characters. But it is not studied thoroughly compared with character recognition. In this paper, we try to learn how many typical styles exist in a kind of real world form images. A hierarchical clustering method has been developed and tested. A cross recognition error rate constraint is proposed to reduce the false combinations in the hierarchical clustering process, and a cluster selecting method is used to delete redundant or unsuitable clusters. Only a similarity measure between any patterns is needed by the algorithm. It is tested on a template matching based similarity measure which can be extended to any other feature and distance measure easily. The detailed comparing on every step"s effects is shown in the paper. Total 16 kinds of typical styles are found out, and by giving each character in each style a prototype for recognition, a 0.78% error rate is achieved by recognizing the testing set.

  16. Automatic style clustering of printed characters in form images

    NASA Astrophysics Data System (ADS)

    Liu, Changsong; Ding, Xiaoqing

    2004-12-01

    Style is an important feature of printed or handwritten characters. But it is not studied thoroughly compared with character recognition. In this paper, we try to learn how many typical styles exist in a kind of real world form images. A hierarchical clustering method has been developed and tested. A cross recognition error rate constraint is proposed to reduce the false combinations in the hierarchical clustering process, and a cluster selecting method is used to delete redundant or unsuitable clusters. Only a similarity measure between any patterns is needed by the algorithm. It is tested on a template matching based similarity measure which can be extended to any other feature and distance measure easily. The detailed comparing on every step"s effects is shown in the paper. Total 16 kinds of typical styles are found out, and by giving each character in each style a prototype for recognition, a 0.78% error rate is achieved by recognizing the testing set.

  17. THE PROPERTIES OF THE STAR-FORMING INTERSTELLAR MEDIUM AT z = 0.8-2.2 FROM HiZELS: STAR FORMATION AND CLUMP SCALING LAWS IN GAS-RICH, TURBULENT DISKS

    SciTech Connect

    Swinbank, A. M.; Smail, Ian; Theuns, T.; Sobral, D.; Best, P. N.; Geach, J. E.

    2012-12-01

    We present adaptive optics assisted integral field spectroscopy of nine H{alpha}-selected galaxies at z = 0.84-2.23 drawn from the HiZELS narrowband survey. Our observations map the kinematics of these star-forming galaxies on {approx}kpc scales. We demonstrate that within the interstellar medium of these galaxies, the velocity dispersion of the star-forming gas ({sigma}) follows a scaling relation {sigma}{proportional_to}{Sigma}{sup 1/n} {sub SFR} + constant (where {Sigma}{sub SFR} is the star formation surface density and the constant includes the stellar surface density). Assuming the disks are marginally stable (Toomre Q = 1), this follows from the Kennicutt-Schmidt relation ({Sigma}{sub SFR} = A{Sigma} {sup n} {sub gas}), and we derive best-fit parameters of n = 1.34 {+-} 0.15 and A = 3.4{sup +2.5} {sub -1.6} Multiplication-Sign 10{sup -4} M {sub Sun} yr{sup -1} kpc{sup -2}, consistent with the local relation, and implying cold molecular gas masses of M {sub gas} = 10{sup 9-10} M {sub Sun} and molecular gas fractions of M {sub gas}/(M {sub gas} + M {sub *}) = 0.3 {+-} 0.1, with a range of 10%-75%. We also identify 11 {approx}kpc-scale star-forming regions (clumps) within our sample and show that their sizes are comparable to the wavelength of the fastest growing mode. The luminosities and velocity dispersions of these clumps follow the same scaling relations as local H II regions, although their star formation densities are a factor {approx}15 {+-} 5 Multiplication-Sign higher than typically found locally. We discuss how the clump properties are related to the disk, and show that their high masses and luminosities are a consequence of the high disk surface density.

  18. Star Formation in Massive Clusters via Bondi Accretion

    NASA Astrophysics Data System (ADS)

    Murray, Norman; Chang, Philip

    2012-02-01

    Essentially all stars form in giant molecular clouds (GMCs). However, inside GMCs, most of the gas does not participate in star formation; rather, denser gas accumulates in clumps in the GMC, with the bulk of the stars in a given GMC forming in a few of the most massive clumps. In the Milky Way, these clumps have masses M cl <~ 5 × 10-2 of the GMC, radii r cl ~ 1 pc, and free-fall times τcl ~ 2 × 105 yr. We show that clumps inside GMCs should accrete at a modified Bondi accretion rate, which depends on clump mass as \\dot{M}_{cl}\\sim M_{cl}^{5/4}. This rate is initially rather slow, usually slower than the initial star formation rate inside the clump (we adopt the common assumption that inside the clump, \\dot{M}_*=\\epsilon _ffM_{cl}/\\tau _{cl}, with epsilonff ≈ 0.017). However, after ~2 GMC free-fall times τGMC, the clump accretion rate accelerates rapidly; formally, the clump can accrete the entire GMC in ~3τGMC. At the same time, the star formation rate accelerates, tracking the Bondi accretion rate. If the GMC is disrupted by feedback from the largest clump, half the stars in that clump form in the final τGMC before the GMC is disrupted. The theory predicts that the distribution of effective star formation rates, measured per GMC free-fall time, is broad, ranging from ~0.001 up to 0.1 or larger and that the mass spectrum of star clusters is flatter than that of clumps, consistent with observations.

  19. STAR-FORMING GALAXY EVOLUTION IN NEARBY RICH CLUSTERS

    SciTech Connect

    Tyler, K. D.; Rieke, G. H.; Bai, L.

    2013-08-20

    Dense environments are known to quench star formation in galaxies, but it is still unknown what mechanism(s) are directly responsible. In this paper, we study the star formation of galaxies in A2029 and compare it to that of Coma, combining indicators at 24 {mu}m, H{alpha}, and UV down to rates of 0.03 M{sub Sun} yr{sup -1}. We show that A2029's star-forming galaxies follow the same mass-SFR relation as the field. The Coma cluster, on the other hand, has a population of galaxies with star formation rates (SFRs) significantly lower than the field mass-SFR relation, indicative of galaxies in the process of being quenched. Over half of these galaxies also host active galactic nuclei. Ram-pressure stripping and starvation/strangulation are the most likely mechanisms for suppressing the star formation in these galaxies, but we are unable to disentangle which is dominating. The differences we see between the two clusters' populations of star-forming galaxies may be related to their accretion histories, with A2029 having accreted its star-forming galaxies more recently than Coma. Additionally, many early-type galaxies in A2029 are detected at 24 {mu}m and/or in the far-UV, but this emission is not directly related to star formation. Similar galaxies have probably been classified as star forming in previous studies of dense clusters, possibly obscuring some of the effects of the cluster environment on true star-forming galaxies.

  20. From gas to stars in energetic environments: dense gas clumps in the 30 Doradus region within the Large Magellanic Cloud

    SciTech Connect

    Anderson, Crystal N.; Meier, David S.; Ott, Jürgen; Hughes, Annie; Wong, Tony; Looney, Leslie; Henkel, Christian; Chen, Rosie; Indebetouw, Remy; Muller, Erik; Pineda, Jorge L.; Seale, Jonathan

    2014-09-20

    We present parsec-scale interferometric maps of HCN(1-0) and HCO{sup +}(1-0) emission from dense gas in the star-forming region 30 Doradus, obtained using the Australia Telescope Compact Array. This extreme star-forming region, located in the Large Magellanic Cloud (LMC), is characterized by a very intense ultraviolet ionizing radiation field and sub-solar metallicity, both of which are expected to impact molecular cloud structure. We detect 13 bright, dense clumps within the 30 Doradus-10 giant molecular cloud. Some of the clumps are aligned along a filamentary structure with a characteristic spacing that is consistent with formation via varicose fluid instability. Our analysis shows that the filament is gravitationally unstable and collapsing to form stars. There is a good correlation between HCO{sup +} emission in the filament and signatures of recent star formation activity including H{sub 2}O masers and young stellar objects (YSOs). YSOs seem to continue along the same direction of the filament toward the massive compact star cluster R136 in the southwest. We present detailed comparisons of clump properties (masses, linewidths, and sizes) in 30Dor-10 to those in other star forming regions of the LMC (N159, N113, N105, and N44). Our analysis shows that the 30Dor-10 clumps have similar masses but wider linewidths and similar HCN/HCO{sup +} (1-0) line ratios as clumps detected in other LMC star-forming regions. Our results suggest that the dense molecular gas clumps in the interior of 30Dor-10 are well shielded against the intense ionizing field that is present in the 30 Doradus region.

  1. Massive star clusters in a z=1 star-forming galaxy seen at a 100 pc scale thanks to strong gravitational lensing

    NASA Astrophysics Data System (ADS)

    Dessauges-Zavadsky, Miroslava; Cava, Antonio; Richard, Johan; Schaerer, Daniel; Egami, Eiichi

    2015-08-01

    Deep and high-resolution imaging has revealed clumpy, rest-frame UV morphologies among z=1-3 galaxies. The majority of these galaxies has been shown to be dominated by ordered disk rotation, which led to the conclusion that the observed giant clumps, resolved on kpc-scales, are generated from disk fragmentation due to gravitational instability. State-of-the-art numerical simulations show that they may occupy a relevant role in galaxy evolution, contributing to the galactic bulge formation. Despite the high resolution attained by the most advanced ground- and space-based facilities, as well as in numerical simulations, the intrinsic typical masses and scale sizes of these star-forming clumps remain unconstrained, since they are barely resolved at z=1-3.Thanks to the amplification and stretching power provided by strong gravitational lensing, we are likely to reach the spatial resolving power for unveiling the physics of these star-forming regions. We report on the study of clumpy star formation observed in the Cosmic Snake, a strongly lensed galaxy at z=1, representative of the typical star-forming population close to the peak of Universe activity. About 20 clumps are identified in the HST images. Benefiting from extreme amplification factors up to 100, they are resolved down to an intrinsic scale of 100 pc, never reached before at z=1.The HST multi-wavelength analysis of these individual star clusters allows us to determine their intrinsic physical properties, showing stellar masses (Ms) from 106 to 108.3 Msun, sizes from 100 to 400 pc, and ages from 106 to 108.5 yr. The masses we find are in line with the new, very high resolution numerical simulations, which also suggest that the massive giant clumps previously observed at high redshift with Ms as high as 109-10 Msun may suffer from low resolution effects, being unresolved conglomerates of less massive star clusters. We also compare our results with those of massive young clusters in nearby galaxies. Our approved

  2. Solvated electrons formed in methanol cluster in ethane

    SciTech Connect

    Takahashi, K.; Bartels, D. M.; Jonah, C. D.; Dimitrijevic, N. A.

    2000-03-09

    The authors have studied the spectral shift of the solvated electron in MeOH/C{sub 2}H{sub 6} mixture using pulse radiolysis. The solvated electrons were formed by ionizing the solution. The spectral shift can be explained in terms of MeOH cluster size formed in the solution. With increasing temperature at constant mole fraction of MeOH, the spectral maximum shifts toward low energy. The width at red side increased with increasing temperature, however, there is no significant changes in the blue side of the spectra with temperature.

  3. Extra-nuclear starbursts: young luminous Hinge clumps in interacting galaxies

    SciTech Connect

    Smith, Beverly J.; Giroux, Mark L.; Soria, Roberto; Struck, Curtis; Swartz, Douglas A.; Yukita, Mihoko E-mail: girouxm@etsu.edu E-mail: curt@iastate.edu

    2014-03-01

    Hinge clumps are luminous knots of star formation near the base of tidal features in some interacting galaxies. We use archival Hubble Space Telescope (HST) UV/optical/IR images and Chandra X-ray maps along with Galaxy Evolution Explorer UV, Spitzer IR, and ground-based optical/near-IR images to investigate the star forming properties in a sample of 12 hinge clumps in five interacting galaxies. The most extreme of these hinge clumps have star formation rates of 1-9 M {sub ☉} yr{sup –1}, comparable to or larger than the 'overlap' region of intense star formation between the two disks of the colliding galaxy system the Antennae. In the HST images, we have found remarkably large and luminous sources at the centers of these hinge clumps. These objects are much larger and more luminous than typical 'super star clusters' in interacting galaxies, and are sometimes embedded in a linear ridge of fainter star clusters, consistent with star formation along a narrow caustic. These central sources have FWHM diameters of ∼70 pc, compared to ∼3 pc in 'ordinary' super star clusters. Their absolute I magnitudes range from M{sub I} ∼ – 12.2 to –16.5; thus, if they are individual star clusters they would lie near the top of the 'super star cluster' luminosity function of star clusters. These sources may not be individual star clusters, but instead may be tightly packed groups of clusters that are blended together in the HST images. Comparison to population synthesis modeling indicates that the hinge clumps contain a range of stellar ages. This is consistent with expectations based on models of galaxy interactions, which suggest that star formation may be prolonged in these regions. In the Chandra images, we have found strong X-ray emission from several of these hinge clumps. In most cases, this emission is well-resolved with Chandra and has a thermal X-ray spectrum, thus it is likely due to hot gas associated with the star formation. The ratio of the extinction

  4. On the onset of secondary stellar generations in giant star-forming regions and massive star clusters

    SciTech Connect

    Palouš, J.; Wünsch, R.; Tenorio-Tagle, G.

    2014-09-10

    Here we consider the strong evolution experienced by the matter reinserted by massive stars, both in giant star-forming regions driven by a constant star formation rate and in massive and coeval superstar clusters. In both cases we take into consideration the changes induced by stellar evolution on the number of massive stars, the number of ionizing photons, and the integrated mechanical luminosity of the star-forming regions. The latter is at all times compared with the critical luminosity that defines, for a given size, the lower mechanical luminosity limit above which the matter reinserted via strong winds and supernova explosions suffers frequent and recurrent thermal instabilities that reduce its temperature and pressure and inhibit its exit as part of a global wind. Instead, the unstable reinserted matter is compressed by the pervasive hot gas, and photoionization maintains its temperature at T ∼ 10{sup 4} K. As the evolution proceeds, more unstable matter accumulates and the unstable clumps grow in size. Here we evaluate the possible self-shielding of thermally unstable clumps against the UV radiation field. Self-shielding allows for a further compression of the reinserted matter, which rapidly develops a high-density neutral core able to absorb in its outer skin the incoming UV radiation. Under such conditions the cold (T ∼ 10 K) neutral cores soon surpass the Jeans limit and become gravitationally unstable, creating a new stellar generation with the matter reinserted by former massive stars. We present the results of several calculations of this positive star formation feedback scenario promoted by strong radiative cooling and mass loading.

  5. On the Onset of Secondary Stellar Generations in Giant Star-forming Regions and Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Palouš, J.; Wünsch, R.; Tenorio-Tagle, G.

    2014-09-01

    Here we consider the strong evolution experienced by the matter reinserted by massive stars, both in giant star-forming regions driven by a constant star formation rate and in massive and coeval superstar clusters. In both cases we take into consideration the changes induced by stellar evolution on the number of massive stars, the number of ionizing photons, and the integrated mechanical luminosity of the star-forming regions. The latter is at all times compared with the critical luminosity that defines, for a given size, the lower mechanical luminosity limit above which the matter reinserted via strong winds and supernova explosions suffers frequent and recurrent thermal instabilities that reduce its temperature and pressure and inhibit its exit as part of a global wind. Instead, the unstable reinserted matter is compressed by the pervasive hot gas, and photoionization maintains its temperature at T ~ 104 K. As the evolution proceeds, more unstable matter accumulates and the unstable clumps grow in size. Here we evaluate the possible self-shielding of thermally unstable clumps against the UV radiation field. Self-shielding allows for a further compression of the reinserted matter, which rapidly develops a high-density neutral core able to absorb in its outer skin the incoming UV radiation. Under such conditions the cold (T ~ 10 K) neutral cores soon surpass the Jeans limit and become gravitationally unstable, creating a new stellar generation with the matter reinserted by former massive stars. We present the results of several calculations of this positive star formation feedback scenario promoted by strong radiative cooling and mass loading.

  6. The physical state of selected cold clumps

    NASA Astrophysics Data System (ADS)

    Parikka, A.; Juvela, M.; Pelkonen, V.-M.; Malinen, J.; Harju, J.

    2015-05-01

    Context. The study of prestellar cores is essential to understanding the initial stages of star formation. With Herschel more cold clumps have been detected than ever before. For this study we have selected 21 cold clumps from 20 Herschel fields observed as a follow-up on original Planck detections. We have observed these clumps in 13CO (1-0), C18O (1-0), and N2H+ (1-0) lines. Aims: Our aim is to find out if these cold clumps are prestellar. We have examined to what extent independent analysis of the dust and the molecular lines lead to similar conclusions about the masses of these objects. Methods: We calculate the clump masses and densities from the dust continuum and molecular line observations and compare these to each other and to the virial and Bonnor-Ebert masses calculated for each clump. Finally we examine two of the fields with radiative transfer models to estimate CO abundances. Results: When excitation temperatures could be estimated, the column densities derived from molecular line observations were comparable to those from dust continuum data. The median column density estimates are 4.2 × 1021 cm-2 and 5.5 × 1021 cm-2 for the line and dust emission data, respectively. The calculated abundances, column densities, volume densities, and masses all have large uncertainties and one must be careful when drawing conclusions. Abundance of 13CO was found in modeling the two clumps in the field G131.65+9.75 to be close to the usual value of 10-6. The abundance ratio of 13CO and C18O was ~10. Molecular abundances could only be estimated with modeling, relying on dust column density data. Conclusions: The results indicate that most cold clumps, even those with dust color temperatures close to 11 K, are not necessarily prestellar. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendices are available in electronic form at http://www.aanda.org

  7. Properties of dense cores in clustered massive star-forming regions at high angular resolution

    NASA Astrophysics Data System (ADS)

    Sánchez-Monge, Álvaro; Palau, Aina; Fontani, Francesco; Busquet, Gemma; Juárez, Carmen; Estalella, Robert; Tan, Jonathan C.; Sepúlveda, Inma; Ho, Paul T. P.; Zhang, Qizhou; Kurtz, Stan

    2013-07-01

    We aim at characterizing dense cores in the clustered environments associated with intermediate-/high-mass star-forming regions. For this, we present a uniform analysis of Very Large Array NH3 (1,1) and (2,2) observations towards a sample of 15 intermediate-/high-mass star-forming regions, where we identify a total of 73 cores, classify them as protostellar, quiescent starless, or perturbed starless, and derive some physical properties. The average sizes and ammonia column densities of the total sample are ˜0.06 pc and ˜1015 cm-2, respectively, with no significant differences between the starless and protostellar cores, while the linewidth and rotational temperature of quiescent starless cores are smaller, ˜1.0 km s-1 and 16 K, than linewidths and temperatures of protostellar (˜1.8 km s-1 and 21 K), and perturbed starless (˜1.4 km s-1 and 19 K) cores. Such linewidths and temperatures for these quiescent starless cores in the surroundings of intermediate-/high-mass stars are still significantly larger than the typical linewidths and rotational temperatures measured in starless cores of low-mass star-forming regions, implying an important non-thermal component. We confirm at high angular resolutions (spatial scales ˜0.05 pc) the correlations previously found with single-dish telescopes (spatial scales ≳ 0.1 pc) between the linewidth and the rotational temperature of the cores, as well as between the rotational temperature and the linewidth with respect to the bolometric luminosity. In addition, we find a correlation between the temperature of each core and the incident flux from the most massive star in the cluster, suggesting that the large temperatures measured in the starless cores of our sample could be due to heating from the nearby massive star. A simple virial equilibrium analysis seems to suggest a scenario of a self-similar, self-gravitating, turbulent, virialized hierarchy of structures from clumps (˜0.1-10 pc) to cores (˜0.05 pc). A closer

  8. Submillimeter Array High-angular Resolution Observations of the Monoceros R2 Star-forming Cluster

    NASA Astrophysics Data System (ADS)

    Dierickx, M.; Jiménez-Serra, I.; Rivilla, V. M.; Zhang, Q.

    2015-04-01

    We present the first high-angular resolution study of the MonR2 star-forming complex carried out with the Submillimeter Array at (sub-)millimeter wavelengths. We image the continuum and molecular line emission toward the young stellar objects in MonR2 at 0.85 and 1.3 mm, with resolutions ranging from 0.″ 5 to ˜3″. While free-free emission dominates the IRS1 and IRS2 continuum, dust thermal emission prevails for IRS3 and IRS5, giving envelope masses of ˜0.1-0.3 {{M}⊙ }. IRS5 splits into at least two sub-arcsecond scale sources, IRS5B and the more massive IRS5A. Our 12CO(2-1) images reveal 11 previously unknown molecular outflows in the MonR2 clump. Comparing these outflows with known IR sources in the IRS5 and IRS3 subclusters allows for tentative identification of driving stars. Line images of molecular species such as CH3CN or CH3OH show that, besides IRS3 (a well-known hot molecular core), IRS5 is also a chemically active source in the region. The gas excitation temperature derived from CH3CN lines toward IRS5 is 144 ± 15 K, indicating a deeply embedded protostar at the hot-core evolutionary stage. Spectral energy distribution fitting of IRS5 gives a mass of ˜7 M ⊙ and a luminosity of 300 {{L}⊙ } for the central source. The derived physical properties of the CO outflows suggest that they contribute to the turbulent support of the MonR2 complex and to the gas velocity dispersion in the clump’s center. The detection of a large number of CO outflows widespread across the region supports the competitive accretion scenario as origin of the MonR2 star cluster.

  9. Identification of protostellar clusters in the inner part of the milky way : Interaction between the ISM and star forming regions.

    NASA Astrophysics Data System (ADS)

    Beuret, M.; Billot, N.; Cambrésy, L.; Elia, D.; Molinari, S.; Pezzuto, S.; Pestalozzi, M.; Schisano, E.

    2014-12-01

    Interactions between the interstellar medium (ISM) and young stellar objects (YSO) need to be investigated to better understand star formation. We used the Minimum Spanning Tree (MST) method to identify protostellar clusters in the inner part of galactic plane. Using heliocentric distance estimates, we obtained about 230 clusters over a 140 × 2 square degree region. Most of these clusters are correlated with Infrared Dark Cloud (IRDC) or H II regions. We conclude that clustering is more important for protostars than for prestellar clumps and that a strong correlation can be established between the distribution of H II regions, known star formation complexes and the YSOs identified in the Hi-GAL data.

  10. Diamond-like phases formed from fullerene-like clusters

    NASA Astrophysics Data System (ADS)

    Belenkov, E. A.; Greshnyakov, V. A.

    2015-11-01

    The geometrically optimized structure and properties of thirteen diamond-like carbon phases formed by linking or combining fullerene-like clusters (C4, C6, C8, C12, C16, C24, or C48) have been investigated. Atoms in the structures of these phases are located in crystallographically equivalent positions. The calculations have been performed using the density functional theory in the generalized gradient approximation. The calculated values of the structural characteristics and properties (sublimation energies, bulk moduli, band gaps, X-ray diffraction patterns) of the studied diamond-like phases differ significantly from the corresponding values for cubic diamond.

  11. Hippocampal cells encode places by forming small anatomical clusters.

    PubMed

    Nakamura, N H; Fukunaga, M; Akama, K T; Soga, T; Ogawa, S; Pavlides, C

    2010-03-31

    The hippocampus has been hypothesized to function as a "spatial" or "cognitive" map, however, the functional cellular organization of the spatial map remains a mystery. The majority of electrophysiological studies, thus far, have supported the view of a random-type organization in the hippocampus. However, using immediate early genes (IEGs) as an indicator of neuronal activity, we recently observed a cluster-type organization of hippocampal principal cells, whereby a small number ( approximately 4) of nearby cells were activated in rats exposed to a restricted part of an environment. To determine the fine structure of these clusters and to provide a 3D image of active hippocampal cells that encode for different parts of an environment, we established a functional mapping of IEGs zif268 and Homer1a, using in situ hybridization and 3D-reconstruction imaging methods. We found that, in rats exposed to the same location twice, there were significantly more double IEG-expressing cells, and the clusters of nearby cells were more "tightly" formed, in comparison to rats exposed to two different locations. We propose that spatial encoding recruits specific cell ensembles in the hippocampus and that with repeated exposure to the same place the ensembles become better organized to more accurately represent the "spatial map." PMID:20060034

  12. Hippocampal cells encode places by forming small anatomical clusters

    PubMed Central

    Nakamura, Nozomu H.; Fukunaga, Masaki; Akama, Keith T.; Soga, Tomoko; Ogawa, Sonoko; Pavlides, Constantine

    2010-01-01

    The hippocampus has been hypothesized to function as a “spatial” or “cognitive” map, however, the functional cellular organization of the spatial map remains a mystery. The majority of electrophysiological studies, thus far, have supported the view of a random-type organization in the hippocampus. However, using immediate early genes (IEGs) as an indicator of neuronal activity, we recently observed a cluster-type organization of hippocampal principal cells, whereby a small number (~4) of nearby cells were activated in animals exposed to a restricted part of an environment. To determine the fine structure of these clusters and to provide a 3D image of active hippocampal cells that encode for different parts of an environment, we established a functional mapping of immediate early genes (IEGs) zif268 and Homer1a, using in situ hybridization and 3D-reconstruction imaging methods. We found that, in animals exposed to the same location twice, there were significantly more double IEG-expressing cells, and the clusters of nearby cells were more “tightly” formed, in comparison to animals exposed to two different locations. We propose that spatial encoding recruits specific cell ensembles in the hippocampus and that with repeated exposure to the same place the ensembles become better organized to more accurately represent the “spatial map”. PMID:20060034

  13. Chemical Diagnostics of the Massive Star Cluster-forming Cloud G33.92+0.11 I. 13CS, CH3OH, CH3CN, OCS, H2S, SO2, and SiO

    NASA Astrophysics Data System (ADS)

    Minh, Young Chol; Liu, Hauyu Baobab; Galvań-Madrid, Roberto

    2016-06-01

    Large chemical diversity was found in the gas clumps associated with the massive star cluster-forming G33.92+0.11 region with sub-arcsecond angular resolution (0.″6–0.″8) observations with ALMA. The most prominent gas clumps are associated with the dust emission peaks A1, A2, and A5. The close correlation between CH3OH and OCS in the emission distributions strongly suggests that these species share a common origin of hot core grain mantle evaporation. The latest generation of star clusters are forming in the A5 clump, as indicated by multiple SiO outflows and its rich hot core chemistry. We also found a narrow SiO emission associated with the outflows, which may trace a cooled component of the outflows. Part of the chemical complexity may have resulted from the accreting gas from the ambient clouds, especially in the northern part of A1 and the southern part of A2. The chemical diversity found in this region is believed to mainly result from the different chemical evolutionary timescales of massive star formation. In particular, the abundance ratio between CH3OH and CH3CN may be a good chemical clock for the early phase of star formation.

  14. Stellar Clusters Forming in the Blue Dwarf Galaxy NGC 5253

    NASA Astrophysics Data System (ADS)

    2004-11-01

    ; it is located at a distance of about 11 million light-years in the direction of the southern constellation Centaurus. Some time ago a group of European astronomers [1] decided to take a closer look at this object and to study star-forming processes in the primordial-like environment of this galaxy. True, NGC 5253 does contains some dust and heavier elements, but significantly less than our own Milky Way galaxy. However, it is quite extreme as a site of intense star formation, a profuse "starburst galaxy" in astronomical terminology, and a prime object for detailed studies of large-scale star formation. ESO PR Photo 31a/04 provides an impressive view of NGC 5253. This composite image is based on a near-infrared exposure obtained with the multi-mode ISAAC instrument mounted on the 8.2-m VLT Antu telescope at the ESO Paranal Observatory (Chile), as well as two images in the optical waveband obtained from the Hubble Space Telescope data archive (located at ESO Garching). The VLT image (in the K-band at wavelength 2.16 μm) is coded red, the HST images are blue (V-band at 0.55 μm) and green (I-band at 0.79 μm), respectively. The enormous light-gathering capability and the fine optical quality of the VLT made it possible to obtain the very detailed near-infrared image (cf. PR Photo 31b/04) during an exposure lasting only 5 min. The excellent atmospheric conditions of Paranal at the time of the observation (seeing 0.4 arcsec) allow the combination of space- and ground-based data into a colour photo of this interesting object. A major dust lane is visible at the western (right) side of the galaxy, but patches of dust are visible all over, together with a large number of colourful stars and stellar clusters. The different colour shades are indicative of the ages of the objects and the degree of obscuration by interstellar dust. The near-infrared VLT image penetrates the dust clouds much better than the optical HST images, and some deeply embedded objects that are not

  15. SUBMILLIMETER OBSERVATIONS OF DENSE CLUMPS IN THE INFRARED DARK CLOUD G049.40-00.01

    SciTech Connect

    Kang, Miju; Choi, Minho; Bieging, John H.; Rho, Jeonghee; Tsai, Chao-Wei

    2011-12-20

    We obtained 350 and 850 {mu}m continuum maps of the infrared dark cloud G049.40-00.01. Twenty-one dense clumps were identified within G049.40-00.01 based on the 350 {mu}m continuum map with an angular resolution of about 9.''6. We present submillimeter continuum maps and report physical properties of the clumps. The masses of clumps range from 50 to 600 M{sub Sun }. About 70% of the clumps are associated with bright 24 {mu}m emission sources, and they may contain protostars. The two most massive clumps show extended, enhanced 4.5 {mu}m emission indicating vigorous star-forming activity. The clump-size-mass distribution suggests that many of them are forming high-mass stars. G049.40-00.01 contains numerous objects in various evolutionary stages of star formation, from pre-protostellar clumps to H II regions.

  16. Superdense cosmological dark matter clumps

    SciTech Connect

    Berezinsky, V.; Dokuchaev, V.; Eroshenko, Yu.; Kachelriess, M.; Solberg, M. Aa.

    2010-05-15

    The formation and evolution of superdense clumps (or subhalos) is studied. Such clumps of dark matter (DM) can be produced by many mechanisms, most notably by spiky features in the spectrum of inflationary perturbations and by cosmological phase transitions. Being produced very early during the radiation-dominated epoch, superdense clumps evolve as isolated objects. They do not belong to hierarchical structures for a long time after production, and therefore they are not destroyed by tidal interactions during the formation of larger structures. For DM particles with masses close to the electroweak mass scale, superdense clumps evolve towards a power-law density profile {rho}(r){proportional_to}r{sup -1.8} with a central core. Superdense clumps cannot be composed of standard neutralinos, since their annihilations would overproduce the diffuse gamma radiation. If the clumps are constituted of superheavy DM particles and develop a sufficiently large central density, the evolution of their central part can lead to a ''gravithermal catastrophe.'' In such a case, the initial density profile turns into an isothermal profile with {rho}{proportional_to}r{sup -2} and a new, much smaller core in the center. Superdense clumps can be observed by gamma radiation from DM annihilations and by gravitational wave detectors, while the production of primordial black holes and cascade nucleosynthesis constrain this scenario.

  17. The Herschel Virgo Cluster Survey. XVIII. Star-forming dwarf galaxies in a cluster environment

    NASA Astrophysics Data System (ADS)

    Grossi, M.; Hunt, L. K.; Madden, S. C.; Hughes, T. M.; Auld, R.; Baes, M.; Bendo, G. J.; Bianchi, S.; Bizzocchi, L.; Boquien, M.; Boselli, A.; Clemens, M.; Corbelli, E.; Cortese, L.; Davies, J.; De Looze, I.; di Serego Alighieri, S.; Fritz, J.; Pappalardo, C.; Pierini, D.; Rémy-Ruyer, A.; Smith, M. W. L.; Verstappen, J.; Viaene, S.; Vlahakis, C.

    2015-02-01

    To assess the effects of the cluster environment on the different components of the interstellar medium, we analyse the far-infrared (FIR) and submillimetre (submm) properties of a sample of star-forming dwarf galaxies detected by the Herschel Virgo Cluster Survey (HeViCS). We determine dust masses and dust temperatures by fitting a modified black body function to the spectral energy distributions (SEDs). Stellar and gas masses, star formation rates (SFRs), and metallicities are obtained from the analysis of a set of ancillary data. Dust is detected in 49 out of a total 140 optically identified dwarfs covered by the HeViCS field; considering only dwarfs brighter than mB = 18 mag, this gives a detection rate of 43%. After evaluating different emissivity indices, we find that the FIR-submm SEDs are best-fit by β = 1.5, with a median dust temperature Td = 22.4 K. Assuming β = 1.5, 67% of the 23 galaxies detected in all five Herschel bands show emission at 500 μm in excess of the modified black-body model. The fraction of galaxies with a submillimetre excess decreases for lower values of β, while a similarly high fraction (54%) is found if a β-free SED modelling is applied. The excess is inversely correlated with SFR and stellar masses. To study the variations in the global properties of our sample that come from environmental effects, we compare the Virgo dwarfs to other Herschel surveys,such as the Key Insights into Nearby Galaxies: Far-Infrared Survey with Herschel (KINGFISH), the Dwarf Galaxy Survey (DGS), and the HeViCS Bright Galaxy Catalogue (BGC). We explore the relations between stellar mass and Hi fraction, specific star formation rate, dust fraction, gas-to-dust ratio over a wide range of stellar masses (from 107 to 1011 M⊙) for both dwarfs and spirals. Highly Hi-deficient Virgo dwarf galaxies are mostly characterised by quenched star formation activity and lower dust fractions giving hints for dust stripping in cluster dwarfs. However, to explain the

  18. Glass Frit Clumping And Dusting

    SciTech Connect

    Steimke, J. L.

    2013-09-26

    DWPF mixes a slurry of glass frit (Frit 418) and dilute (1.5 wt%) formic acid solution with high level waste in the Slurry Mix Evaporator (SME). There would be advantages to introducing the frit in a non-slurry form to minimize water addition to the SME, however, adding completely dry frit has the potential to generate dust which could clog filters or condensers. Prior testing with another type of frit, Frit 320, and using a minimal amount of water reduced dust generation, however, the formation of hard clumps was observed. To examine options and behavior, a TTQAP [McCabe and Stone, 2013] was written to initiate tests that would address these concerns. Tests were conducted with four types of glass frit; Frit 320, DWPF Frit 418, Bekeson Frit 418 and Multi-Aspirator Frit 418. The last two frits are chemically identical to DWPF Frit 418 but smaller particles were removed by the respective vendors. Test results on Frit Clumping and Dusting are provided in this report. This report addresses the following seven questions. Short answers are provided below with more detailed answers to follow. 1. Will the addition of a small amount of water, 1.5 wt%, to dry DWPF Frit 418 greatly reduce the dust generation during handling at DWPF? a. Yes, a small scale test showed that adding a little water to the frit greatly reduced dust generation during handling. 2. Will the addition of small amounts of water to the frit cause clumping that will impair frit handling at DWPF? a. No, not with Frit 418. Although clumps were observed to form when 1.5 wt% water was mixed with DWPF Frit 418, then compressed and air-dried overnight, the clumps were easily crushed and did not form the hardened material noted when Frit 320 was tested. 3. What is the measured size distribution of dust generated when dry frit is handled? (This affects the feasibility and choice of processing equipment for removing the dust generating fraction of the frit before it is added to the SME.) a. The size distribution for

  19. Remarks on the clump theory

    SciTech Connect

    Krommes, J.A.

    1986-07-01

    Further details are provided of a soon-to-be published dialog (Phys. Fluids 29 (July, 1986)) which discussed the role of the small scales in fluid clump theory. It is argued that the approximation of the clump lifetime which is compatible with exponentially rapid separation of adjacent orbits is inappropriate for the description of the dynamically important large scales. Various other remarks are made relating to the analytic treatment of strong drift-wave-like turbulence.

  20. Small scale clustering of late forming dark matter

    NASA Astrophysics Data System (ADS)

    Agarwal, S.; Corasaniti, P.-S.; Das, S.; Rasera, Y.

    2015-09-01

    We perform a study of the nonlinear clustering of matter in the late-forming dark matter (LFDM) scenario in which dark matter results from the transition of a nonminimally coupled scalar field from radiation to collisionless matter. A distinct feature of this model is the presence of a damped oscillatory cutoff in the linear matter power spectrum at small scales. We use a suite of high-resolution N-body simulations to study the imprints of LFDM on the nonlinear matter power spectrum, the halo mass and velocity functions and the halo density profiles. The model largely satisfies high-redshift matter power spectrum constraints from Lyman-α forest measurements, while it predicts suppressed abundance of low-mass halos (˜109- 1010 h-1 M⊙ ) at all redshifts compared to a vanilla Λ CDM model. The analysis of the LFDM halo velocity function shows a better agreement than the Λ CDM prediction with the observed abundance of low-velocity galaxies in the local volume. Halos with mass M ≳1011 h-1 M⊙ show minor departures of the density profiles from Λ CDM expectations, while smaller-mass halos are less dense, consistent with the fact that they form later than their Λ CDM counterparts.

  1. THE STRUCTURE OF THE STAR-FORMING CLUSTER RCW 38

    SciTech Connect

    Winston, E.; Wolk, S. J.; Bourke, T. L.; Spitzbart, B.; Megeath, S. T.; Gutermuth, R.

    2011-12-20

    We present a study of the structure of the high-mass star-forming region RCW 38 and the spatial distribution of its young stellar population. Spitzer Infrared Array Camera (IRAC) photometry (3-8 {mu}m) is combined with Two Micron All Sky Survey near-IR data to identify young stellar objects (YSOs) by IR-excess emission from their circumstellar material. Chandra X-ray data are used to identify class III pre-main-sequence stars lacking circumstellar material. We identify 624 YSOs: 23 class 0/I and 90 flat spectrum protostars, 437 class II stars, and 74 class III stars. We also identify 29 (27 new) O star candidates over the IRAC field. Seventy-two stars exhibit IR-variability, including 7 class 0/I and 12 flat spectrum YSOs. A further 177 tentative candidates are identified by their location in the IRAC [3.6] versus [3.6]-[5.8] color-magnitude diagram. We find strong evidence of subclustering in the region. Three subclusters were identified surrounding the central cluster, with massive and variable stars in each subcluster. The central region shows evidence of distinct spatial distributions of the protostars and pre-main-sequence stars. A previously detected IR cluster, DB2001{sub O}bj36, has been established as a subcluster of RCW 38. This suggests that star formation in RCW 38 occurs over a more extended area than previously thought. The gas-to-dust ratio is examined using the X-ray derived hydrogen column density, N{sub H} and the K-band extinction, and found to be consistent with the diffuse interstellar medium, in contrast with Serpens and NGC 1333. We posit that the high photoionizing flux of massive stars in RCW 38 affects the agglomeration of the dust grains.

  2. Robustness of a partially interdependent network formed of clustered networks

    NASA Astrophysics Data System (ADS)

    Shao, Shuai; Huang, Xuqing; Stanley, H. Eugene; Havlin, Shlomo

    2014-03-01

    Clustering, or transitivity, a behavior observed in real-world networks, affects network structure and function. This property has been studied extensively, but most of this research has been limited to clustering in single networks. The effect of clustering on the robustness of coupled networks, on the other hand, has received much less attention. Only the case of a pair of fully coupled networks with clustering has recently received study. Here we generalize the study of clustering of a fully coupled pair of networks and apply it to a partially interdependent network of networks with clustering within the network components. We show, both analytically and numerically, how clustering within networks affects the percolation properties of interdependent networks, including the percolation threshold, the size of the giant component, and the critical coupling point at which the first-order phase transition changes to a second-order phase transition as the coupling between the networks is reduced. We study two types of clustering, one proposed by Newman [Phys. Rev. Lett. 103, 058701 (2009), 10.1103/PhysRevLett.103.058701] in which the average degree is kept constant while the clustering is changed, and the other by Hackett et al. [Phys. Rev. E 83, 056107 (2011), 10.1103/PhysRevE.83.056107] in which the degree distribution is kept constant. The first type of clustering is studied both analytically and numerically, and the second is studied numerically.

  3. Fuzzy clustering of facial form for prototyping environmental protection equipment

    SciTech Connect

    Robinson, D.G.

    1994-07-01

    Emphasis on the human-to-aircraft interface has magnified in importance as the performance envelope of today`s aircraft has continued to expand. A major problem is that there has been a corresponding increase in the need for better fitting protection equipment and unfortunately it has become increasingly difficult for aircrew members to find equipment that will provide this level of fit. While protection equipment has, historically had poor fit characteristics, the issue has grown tremendously with the recent increase in the numbers of minorities and women. Fundamental to this problem are the archaic methods for sizing individual equipment and the methods for establishing a sizing system. This paper documents recent investigations by the author into developing new methods to overcome these problems. Research centered on the development of a new statistically based method for describing form and the application of fuzzy clustering using the new shape descriptors. A sizing system was developed from the application of the research, prototype masks were constructed and the hardware tested under flight conditions.

  4. HUBBLE SPIES HUGE CLUSTERS OF STARS FORMED BY ANCIENT ENCOUNTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    NASA's Hubble Space Telescope snapped these two views of the heart of the galaxy M82. The image at left was taken in visible light; the picture at right, in infrared light. In the infrared view, the telescope's Near Infrared Camera and Multi-Object Spectrometer peered through thick dust lanes to find some of the galaxy's more than 100 super star clusters. The clusters are the larger pink and yellow dots scattered throughout the picture. They were formed during a violent collision with the galaxy M81 about 600 million years ago. The galaxy is 12 million light-years from Earth in the constellation Ursa Major. The pictures were taken Sept. 15, 1997. Credits: NASA, ESA, R. de Grijs (Institute of Astronomy, Cambridge, UK) NOTE TO EDITORS: For additional information, please contact Richard de Grijs, Institute of Astronomy, Cambridge University, Madingley Road, Cambridge CB3 0HA, UK, +44(0)1223-337528 (phone), +44(0)1223-337523 (fax), grijs@ast.cam.ac.uk (e-mail). The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA). This image is issued jointly by NASA and ESA. Electronic images, animation and additional information are available at: http://oposite.stsci.edu/pubinfo/pr/2001/08 and via links in http://oposite.stsci.edu/pubinfo/latest.html http://oposite.stsci.edu/pubinfo/pictures.html http://hubble.stsci.edu/go/news http://hubble.esa.int To receive STScI press releases electronically, send an Internet electronic mail message to public-request@stsci.edu. Leave the subject line blank, and type the word subscribe in the body of the message. The system will respond with a confirmation of the subscription, and you will receive new press releases as they are issued. Please subscribe using the email account

  5. A comparison of the structure of solute clusters formed during thermal ageing and irradiation.

    PubMed

    Hyde, J M; Sha, G; Marquis, E A; Morley, A; Wilford, K B; Williams, T J

    2011-05-01

    Nanometre scale clusters form in Cu-containing reactor pressure vessel (RPV) steels during neutron irradiation. These clusters have a deleterious effect on mechanical properties, which can result in embrittlement and limit the reactor operating life. Thermal ageing of RPV steels can also induce the formation of solute clusters but it is not clear how similar these are to those formed during irradiation. In this work atom probe tomography, combined with detailed structural assessments of the structure of solute clusters, is used to address this issue. A series of thermal ageing heat treatments has been performed on several high- and low-Ni RPV welds to produce 1-4 nm diameter solute clusters. The same materials have also been neutron irradiated. The results show that CuMnNiSi enriched clusters formed during thermal ageing have, on average, higher Cu contents and lower Mn, Ni and Si contents than those found in irradiation-induced clusters. The effect of increasing bulk Ni is to encourage the formation of clusters with significantly higher Ni content, slightly higher Mn and Si contents and significantly lower Cu contents. At very high doses and dose rates MnNiSi enriched clusters can form even in high-Cu welds. Despite differences in the compositions of individual clusters formed during irradiation and during thermal ageing, clusters in both exhibit similar structure. In particular, well developed clusters in both materials have Cu-enriched cores whose peripheries are enriched in Ni, Mn and, in most cases, Si. PMID:21227587

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

    NASA Astrophysics Data System (ADS)

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

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

  7. Forming Centaurus A's High M/L Globular Clusters

    NASA Astrophysics Data System (ADS)

    Sauda Bovill, Mia; Hyazinth Puzia, Thomas; Ricotti, Massimo; Taylor, Matthew Alan

    2015-08-01

    Using a set of high resolution N-body simulations, we develop a formation model for the high M/L globular clusters recently found around Centaurus A. In our model, the high M/L clusters are not true globular clusters, but rather the stripped cores of dwarf galaxies which underwent an epoch of efficient, concentrated star formation, possibly before or during the epoch of reionization. Given the known stellar masses of these objects, their halos virialized with relatively high masses and high redshift, falling into the Centaurus A with > 109 Msolar. These criteria give us a distribution of surviving subhalos which is consistent with the number and three dimensional distribution of the high M/L clusters within 100 pc of Centaurus A.

  8. Composition and topology of activity cliff clusters formed by bioactive compounds.

    PubMed

    Stumpfe, Dagmar; Dimova, Dilyana; Bajorath, Jürgen

    2014-02-24

    The assessment of activity cliffs has thus far mostly focused on compound pairs, although the majority of activity cliffs are not formed in isolation but in a coordinated manner involving multiple active compounds and cliffs. However, the composition of coordinated activity cliff configurations and their topologies are unknown. Therefore, we have identified all activity cliff configurations formed by currently available bioactive compounds and analyzed them in network representations where activity cliff configurations occur as clusters. The composition, topology, frequency of occurrence, and target distribution of activity cliff clusters have been determined. A limited number of large cliff clusters with unique topologies were identified that were centers of activity cliff formation. These clusters originated from a small number of target sets. However, most clusters were of small to moderate size. Three basic topologies were sufficient to describe recurrent activity cliff cluster motifs/topologies. For example, frequently occurring clusters with star topology determined the scale-free character of the global activity cliff network and represented a characteristic activity cliff configuration. Large clusters with complex topology were often found to contain different combinations of basic topologies. Our study provides a first view of activity cliff configurations formed by currently available bioactive compounds and of the recurrent topologies of activity cliff clusters. Activity cliff clusters of defined topology can be selected, and from compounds forming the clusters, SAR information can be obtained. The SAR information of activity cliff clusters sharing a/one specific activity and topology can be compared. PMID:24437577

  9. STAR CLUSTERS IN A NUCLEAR STAR FORMING RING: THE DISAPPEARING STRING OF PEARLS

    SciTech Connect

    Väisänen, Petri; Barway, Sudhanshu; Randriamanakoto, Zara

    2014-12-20

    An analysis of the star cluster population in a low-luminosity early-type galaxy, NGC 2328, is presented. The clusters are found in a tight star forming nuclear spiral/ring pattern and we also identify a bar from structural two-dimensional decomposition. These massive clusters are forming very efficiently in the circumnuclear environment and they are young, possibly all less than 30 Myr of age. The clusters indicate an azimuthal age gradient, consistent with a ''pearls-on-a-string'' formation scenario, suggesting bar-driven gas inflow. The cluster mass function has a robust down turn at low masses at all age bins. Assuming clusters are born with a power-law distribution, this indicates extremely rapid disruption at timescales of just several million years. If found to be typical, it means that clusters born in dense circumnuclear rings do not survive to become old globular clusters in non-interacting systems.

  10. Stellar Clusters in the NGC 6334 Star-Forming Complex

    NASA Astrophysics Data System (ADS)

    Feigelson, Eric D.; Martin, Amanda L.; McNeill, Collin J.; Broos, Patrick S.; Garmire, Gordon P.

    2009-07-01

    The full stellar population of NGC 6334, one of the most spectacular regions of massive star formation in the nearby Galaxy, has not been well sampled in past studies. We analyze here a mosaic of two Chandra X-ray Observatory images of the region using sensitive data analysis methods, giving a list of 1607 faint X-ray sources with arcsecond positions and approximate line-of-sight absorption. About 95% of these are expected to be cluster members, most lower mass pre-main-sequence stars. Extrapolating to low X-ray levels, the total stellar population is estimated to be 20,000-30,000 pre-main-sequence stars. The X-ray sources show a complicated spatial pattern with ~10 distinct star clusters. The heavily obscured clusters are mostly associated with previously known far-infrared sources and radio H II regions. The lightly obscured clusters are mostly newly identified in the X-ray images. Dozens of likely OB stars are found, both in clusters and dispersed throughout the region, suggesting that star formation in the complex has proceeded over millions of years. A number of extraordinarily heavily absorbed X-ray sources are associated with the active regions of star formation.

  11. STELLAR CLUSTERS IN THE NGC 6334 STAR-FORMING COMPLEX

    SciTech Connect

    Feigelson, Eric D.; Martin, Amanda L.; McNeill, Collin J.; Broos, Patrick S.; Garmire, Gordon P.

    2009-07-15

    The full stellar population of NGC 6334, one of the most spectacular regions of massive star formation in the nearby Galaxy, has not been well sampled in past studies. We analyze here a mosaic of two Chandra X-ray Observatory images of the region using sensitive data analysis methods, giving a list of 1607 faint X-ray sources with arcsecond positions and approximate line-of-sight absorption. About 95% of these are expected to be cluster members, most lower mass pre-main-sequence stars. Extrapolating to low X-ray levels, the total stellar population is estimated to be 20,000-30,000 pre-main-sequence stars. The X-ray sources show a complicated spatial pattern with {approx}10 distinct star clusters. The heavily obscured clusters are mostly associated with previously known far-infrared sources and radio H II regions. The lightly obscured clusters are mostly newly identified in the X-ray images. Dozens of likely OB stars are found, both in clusters and dispersed throughout the region, suggesting that star formation in the complex has proceeded over millions of years. A number of extraordinarily heavily absorbed X-ray sources are associated with the active regions of star formation.

  12. High-Redshift Clusters form NVSS: The TexOx Cluster (TOC) Survey

    SciTech Connect

    Croft, S; Rawlings, S; Hill, G J

    2003-02-11

    The TexOx Cluster (TOC) Survey uses overdensities of radiosources in the NVSS to trace clusters of galaxies. The links between radiosources and rich environments make this a powerful way to find clusters which may potentially be overlooked by other selection techniques. By including constraints from optical surveys, TOC is an extremely efficient way to find clusters at high redshift. One such field, TOC J0233.3+3021, contains at least one galaxy cluster (at z {approx} 1.4) and has been detected using the Sunyaev-Zel'dovich (SZ) effect. Even in targeted deep optical observations, however, distinguishing the cluster galaxies from the background is difficult, especially given the tendency of TOC to select fields containing multiple structures at different redshifts.

  13. The Spatial Distribution of the Young Stellar Clusters in the Star-forming Galaxy NGC 628

    NASA Astrophysics Data System (ADS)

    Grasha, K.; Calzetti, D.; Adamo, A.; Kim, H.; Elmegreen, B. G.; Gouliermis, D. A.; Aloisi, A.; Bright, S. N.; Christian, C.; Cignoni, M.; Dale, D. A.; Dobbs, C.; Elmegreen, D. M.; Fumagalli, M.; Gallagher, J. S., III; Grebel, E. K.; Johnson, K. E.; Lee, J. C.; Messa, M.; Smith, L. J.; Ryon, J. E.; Thilker, D.; Ubeda, L.; Wofford, A.

    2015-12-01

    We present a study of the spatial distribution of the stellar cluster populations in the star-forming galaxy NGC 628. Using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey), we have identified 1392 potential young (≲ 100 Myr) stellar clusters within the galaxy using a combination of visual inspection and automatic selection. We investigate the clustering of these young stellar clusters and quantify the strength and change of clustering strength with scale using the two-point correlation function. We also investigate how image boundary conditions and dust lanes affect the observed clustering. The distribution of the clusters is well fit by a broken power law with negative exponent α. We recover a weighted mean index of α ˜ -0.8 for all spatial scales below the break at 3.″3 (158 pc at a distance of 9.9 Mpc) and an index of α ˜ -0.18 above 158 pc for the accumulation of all cluster types. The strength of the clustering increases with decreasing age and clusters older than 40 Myr lose their clustered structure very rapidly and tend to be randomly distributed in this galaxy, whereas the mass of the star cluster has little effect on the clustering strength. This is consistent with results from other studies that the morphological hierarchy in stellar clustering resembles the same hierarchy as the turbulent interstellar medium.

  14. The Evolution of the Globular Cluster System in a Triaxial Galaxy: Can a Galactic Nucleus Form by Globular Cluster Capture?

    NASA Astrophysics Data System (ADS)

    Capuzzo-Dolcetta, Roberto

    1993-10-01

    Among the possible phenomena inducing evolution of the globular cluster system in an elliptical galaxy, dynamical friction due to field stars and tidal disruption caused by a central nucleus is of crucial importance. The aim of this paper is the study of the evolution of the globular cluster system in a triaxial galaxy in the presence of these phenomena. In particular, the possibility is examined that some galactic nuclei have been formed by frictionally decayed globular clusters moving in a triaxial potential. We find that the initial rapid growth of the nucleus, due mainly to massive clusters on box orbits falling in a short time scale into the galactic center, is later slowed by tidal disruption induced by the nucleus itself on less massive clusters in the way described by Ostriker, Binney, and Saha. The efficiency of dynamical friction is such to carry to the center of the galaxy enough globular cluster mass available to form a compact nucleus, but the actual modes and results of cluster-cluster encounters in the central potential well are complicated phenomena which remains to be investigated. The mass of the resulting nucleus is determined by the mutual feedback of the described processes, together with the initial spatial, velocity, and mass distributions of the globular cluster family. The effect on the system mass function is studied, showing the development of a low- and high-mass turnover even with an initially flat mass function. Moreover, in this paper is discussed the possibility that the globular cluster fall to the galactic center has been a cause of primordial violent galactic activity. An application of the model to M31 is presented.

  15. THERE ARE NO STARLESS MASSIVE PROTO-CLUSTERS IN THE FIRST QUADRANT OF THE GALAXY

    SciTech Connect

    Ginsburg, A.; Bally, J.; Battersby, C.; Bressert, E.

    2012-10-20

    We search the {lambda} = 1.1 mm Bolocam Galactic Plane Survey for clumps containing sufficient mass to form {approx}10{sup 4} M{sub Sun} star clusters. Eighteen candidate massive proto-clusters are identified in the first Galactic quadrant outside of the central kiloparsec. This sample is complete to clumps with mass M{sub clump} > 10{sup 4} M{sub Sun} and radius r {approx}< 2.5 pc. The overall Galactic massive cluster formation rate is CFR(M{sub cluster} > 10{sup 4}) {approx}<5 Myr{sup -1}, which is in agreement with the rates inferred from Galactic open clusters and M31 massive clusters. We find that all massive proto-clusters in the first quadrant are actively forming massive stars and place an upper limit of {tau}{sub starless} < 0.5 Myr on the lifetime of the starless phase of massive cluster formation. If massive clusters go through a starless phase with all of their mass in a single clump, the lifetime of this phase is very short.

  16. Dynamics of disklike clusters formed in a magnetorheological fluid under a rotational magnetic field.

    PubMed

    Nagaoka, Yutaka; Morimoto, Hisao; Maekawa, Toru

    2005-03-01

    We investigate the cluster formations and dynamics in a magnetorheological fluid under a rotational magnetic field focusing on the case of a relatively high volume fraction. We find that isotropic disklike clusters, which rotate more slowly than the field rotation, are formed at low Mason numbers (the ratio of viscous to magnetic forces) and, what is more, we show short rod clusters, which rotate stably thanks to the low Mason numbers and circulate along the surface of the disklike clusters. The circulation velocity of the surface particles is much higher than the rotational surface velocity of the rigid disklike clusters. PMID:15903473

  17. Predicted Sizes of Pressure-supported HI Clouds in the Outskirts of the Virgo Cluster

    NASA Astrophysics Data System (ADS)

    Burkhart, Blakesley; Loeb, Abraham

    2016-06-01

    Using data from the ALFALFA AGES Arecibo HI survey of galaxies and the Virgo cluster X-ray pressure profiles from XMM-Newton, we investigate the possibility that starless dark HI clumps, also known as “dark galaxies,” are supported by external pressure in the surrounding intercluster medium. We find that the starless HI clump masses, velocity dispersions, and positions allow these clumps to be in pressure equilibrium with the X-ray gas near the virial radius of the Virgo cluster. We predict the sizes of these clumps to range from 1 to 10 kpc, in agreement with the range of sizes found for spatially resolved HI starless clumps outside of Virgo. Based on the predicted HI surface density of the Virgo sources, as well as a sample of other similar resolved ALFALFA HI dark clumps with follow-up optical/radio observations, we predict that most of the HI dark clumps are on the cusp of forming stars. These HI sources therefore mark the transition between starless HI clouds and dwarf galaxies with stars.

  18. CO depletion in ATLASGAL-selected high-mass clumps

    NASA Astrophysics Data System (ADS)

    Giannetti, A.; Wyrowski, F.; Brand, J.; Csengeri, T.; Fontani, F.; Walmsley, C. M.; Nguyen Luong, Q.; Beuther, H.; Schuller, F.; Güsten, R.; Menten, K. M.

    2016-05-01

    In the low-mass regime, it is found that the gas-phase abundances of C-bearing molecules in cold starless cores rapidly decrease with increasing density. Here the molecules tend to stick to the grains, forming ice mantles. We study CO depletion in the TOP100 sample of the ATLASGAL survey, and investigate its correlation with evolutionary stage and with the physical parameters of the sources. We use low-J emission lines of CO isotopologues and the dust continuum emission to infer the depletion factor fD. RATRAN one-dimensional models were also used to determine fD and to investigate the presence of depletion above a density threshold. The isotopic ratios and optical depth were derived with a Bayesian approach. We find a significant number of clumps with a large CO depletion, up to ˜20. Larger values are found for colder clumps, thus for earlier evolutionary phases. For massive clumps in the earliest stages of evolution we estimate the radius of the region where CO depletion is important to be a few tenths of a pc. CO depletion in high-mass clumps seems to behave as in the low-mass regime, with less evolved clumps showing larger values for the depletion than their more evolved counterparts, and increasing for denser sources.

  19. Carbonate clumped isotope bond reordering and geospeedometry

    NASA Astrophysics Data System (ADS)

    Passey, Benjamin H.; Henkes, Gregory A.

    2012-10-01

    Carbonate clumped isotope thermometry is based on the preference of 13C and 18O to form bonds with each other. At elevated temperatures such bond ordering is susceptible to resetting by diffusion of C and O through the solid mineral lattice. This type of bond reordering has the potential to obscure primary paleoclimate information, but could also provide a basis for reconstructing shallow crustal temperatures and cooling rates. We determined Arrhenius parameters for solid-state reordering of C-O bonds in two different calcites through a series of laboratory heating experiments. We find that the calcites have different susceptibilities to solid-state reordering. Reaction progress follows a first order rate law in both calcites, but only after an initial period of non-first order reaction that we suggest relates to annealing of nonequilibrium defects when the calcites are first heated to experimental temperature. We show that the apparent equilibrium temperature equations (or "closure temperature" equations) for carbonate clumped isotope reordering are analogous Dodson's equations for first order loss of daughter isotopes. For each calcite, the sensitivity of apparent equilibrium temperature to cooling rate is sufficiently high for inference of cooling rates within a factor of ˜5 or better for cooling rates ranging from tens of degrees per day to a few degrees per million years. However, because the calcites have different susceptibilities to reordering, each calcite defines its own cooling rate-apparent equilibrium temperature relationship. The cooling rates of Carrara marble inferred from carbonate clumped isotope geospeedometry are 10-6-10-3 degrees per annum and are in broad agreement with rates inferred from thermochronometric methods. Cooling rates for 13C-depleted calcites from the late Neoproterozoic Doushantou cap carbonates in south China are on the order of 102-104 degrees per annum, consistent with rapid cooling following formation of these calcites by a

  20. The simultaneous formation of massive stars and stellar clusters

    NASA Astrophysics Data System (ADS)

    Smith, Rowan J.; Longmore, Steven; Bonnell, Ian

    2009-12-01

    We show that massive stars and stellar clusters are formed simultaneously, the global evolution of the forming cluster is what allows the central stars to become massive. We predict that massive star-forming clumps, such as those observed in Motte et al., contract and grow in mass leading to the formation of massive stars. This occurs as mass is continually channelled from large radii on to the central protostars, which can become massive through accretion. Using smoothed particle hydrodynamic simulations of massive star-forming clumps in a giant molecular cloud, we show that clumps are initially diffuse and filamentary, and become more concentrated as they collapse. Simulated interferometry observations of our data provide an explanation as to why young massive star-forming regions show more substructure than older ones. The most massive stars in our model are found within the most bound cluster. Most of the mass accreted by the massive stars was originally distributed throughout the clump at low densities and was later funnelled to the star due to global infall. Even with radiative feedback no massive pre-stellar cores are formed. The original cores are of intermediate mass and gain their additional mass in the protostellar stage. We also find that cores which form low-mass stars exist within the volume from which the high-mass stars accrete, but are largely unaffected by this process.

  1. Cluster separability in front-form particle dynamics

    SciTech Connect

    Coester, F.

    1986-01-01

    In relativistic quantum dynamics, the group structure demands that some transformations other than the time evolutions depend on dynamics. It is possible to choose the representation of a kinematic subgroup to be independent of the dynamics, leading to different ''forms of dynamics'' which are unitarily equivalen. In the ''front-form'' dynamics the kinematic subgroup leaves the light front invariant, and the rotations about any transverse axis are dynamical transformations. In the front form the kinematic subgroup includes the Lorentz transformations. The existence and construction of packing transformations in front-form particle dynamics are shown, and the general features of front-form dynamics needed for that purpose are reviewed. 5 refs. (LEW)

  2. Study of Galactic clumps with millimeter / submillimeter continuum and molecular emission: Early stages of massive star formation

    NASA Astrophysics Data System (ADS)

    Merello, Manuel Antonio

    2014-09-01

    Massive stars play a key role in the evolution of the Galaxy; hence they are important objects of study in astrophysics. Although they are rare compared to low mass stars, they are the principal source of heavy elements and UV radiation, affecting the process of formation of stars and planets, and the physical, chemical, and morphological structure of galaxies. Star clusters form in dense "clumps" (few parsecs in size) within giant molecular clouds, while individual stars form in cores (subparsec scale). An important step in the observational study of massive star formation is the identification and characterization of clumps. More detailed studies can then show how these clumps fragment into cores. Studies of clumps in our Galaxy will provide fundamental guidelines for the analysis of other galaxies, where individual clumps and cores cannot be resolved, and provide a catalog of interesting sources for observations of the Milky Way with a new generation of instruments, such as the Atacama Large Millimeter/Submillimeter Array. Large-scale blind surveys of the Galactic plane at millimeter and submillimeter wavelengths have recently been completed, allowing us to identify star forming clumps and improve our understanding of the early stages of massive stars. One of these studies, the Bolocam Galactic Plane Survey (BGPS), mapped the continuum emission at 1.1 mm over a large region of the northern Galactic plane at a resolution of 33", identifying 8559 compact sources throughout the Galaxy. In this dissertation, I present observations of a sample of sources from the BGPS catalog, obtained with the Submillimeter High Angular Resolution Camera II (SHARC-II). I present in this work 107 continuum emission maps at 350 μm at high angular resolution (8.500) toward clump-like sources and construct a catalog of BGPS substructures. I estimate clump properties such as temperatures and multiplicity of substructures, and compare my results with 350 μm continuum maps from the Hi

  3. The clustering evolution of dusty star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Cowley, William I.; Lacey, Cedric G.; Baugh, Carlton M.; Cole, Shaun

    2016-09-01

    We present predictions for the clustering of galaxies selected by their emission at far-infrared (FIR) and sub-millimetre wavelengths. This includes the first predictions for the effect of clustering biases induced by the coarse angular resolution of single-dish telescopes at these wavelengths. We combine a new version of the GALFORM model of galaxy formation with a self-consistent model for calculating the absorption and re-emission of radiation by interstellar dust. Model galaxies selected at 850μm reside in dark matter haloes of mass Mhalo ˜ 1011.5-1012 h-1 M⊙, independent of redshift (for 0.2 ≲ z ≲ 4) or flux (for 0.25 ≲ S850 μm ≲ 4 mJy). At z ˜ 2.5, the brightest galaxies (S850 μm > 4 mJy) exhibit a correlation length of r0=5.5_{-0.5}^{+0.3} h-1 Mpc, consistent with observations. We show that these galaxies have descendants with stellar masses M⋆ ˜ 1011 h-1 M⊙ occupying haloes spanning a broad range in mass Mhalo ˜ 1012-1014 h-1 M⊙. The FIR emissivity at shorter wavelengths (250, 350 and 500 μm) is also dominated by galaxies in the halo mass range Mhalo ˜ 1011.5-1012 h-1 M⊙, again independent of redshift (for 0.5 ≲ z ≲ 5). We compare our predictions for the angular power spectrum of cosmic infrared background anisotropies at these wavelengths with observations, finding agreement to within a factor of ˜2 over all scales and wavelengths, an improvement over earlier versions of the model. Simulating images at 850 μm, we show that confusion effects boost the measured angular correlation function on all scales by a factor of ˜4. This has important consequences, potentially leading to inferred halo masses being overestimated by an order of magnitude.

  4. The clustering evolution of dusty star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Cowley, William I.; Lacey, Cedric G.; Baugh, Carlton M.; Cole, Shaun

    2016-05-01

    We present predictions for the clustering of galaxies selected by their emission at far infra-red (FIR) and sub-millimetre wavelengths. This includes the first predictions for the effect of clustering biases induced by the coarse angular resolution of single-dish telescopes at these wavelengths. We combine a new version of the GALFORM model of galaxy formation with a self-consistent model for calculating the absorption and re-emission of radiation by interstellar dust. Model galaxies selected at 850 μm reside in dark matter halos of mass Mhalo ˜ 1011.5 - 1012 h-1 M⊙, independent of redshift (for 0.2 ≲ z ≲ 4) or flux (for 0.25 ≲ S850μm ≲ 4 mJy). At z ˜ 2.5, the brightest galaxies (S850μm > 4 mJy) exhibit a correlation length of r0=5.5_{-0.5}^{+0.3} h-1 Mpc, consistent with observations. We show that these galaxies have descendants with stellar masses M⋆ ˜ 1011 h-1 M⊙ occupying halos spanning a broad range in mass Mhalo ˜ 1012 - 1014 h-1 M⊙. The FIR emissivity at shorter wavelengths (250, 350 and 500 μm) is also dominated by galaxies in the halo mass range Mhalo ˜ 1011.5 - 1012 h-1 M⊙, again independent of redshift (for 0.5 ≲ z ≲ 5). We compare our predictions for the angular power spectrum of cosmic infra-red background anisotropies at these wavelengths with observations, finding agreement to within a factor of ˜2 over all scales and wavelengths, an improvement over earlier versions of the model. Simulating images at 850 μm, we show that confusion effects boost the measured angular correlation function on all scales by a factor of ˜4. This has important consequences, potentially leading to inferred halo masses being overestimated by an order of magnitude.

  5. Generation of self-clusters of galectin-1 in the farnesyl-bound form.

    PubMed

    Yamaguchi, Kazumi; Niwa, Yusuke; Nakabayashi, Takakazu; Hiramatsu, Hirotsugu

    2016-01-01

    Ras protein is involved in a signal transduction cascade in cell growth, and cluster formation of H-Ras and human galectin-1 (Gal-1) complex is considered to be crucial to achieve its physiological roles. It is considered that the complex is formed through interactions between Gal-1 and the farnesyl group (farnesyl-dependent model), post-translationally modified to the C-terminal Cys, of H-Ras. We investigated the role of farnesyl-bound Gal-1 in the cluster formation by analyzing the structure and properties of Gal-1 bound to farnesyl thiosalicylic acid (FTS), a competitive inhibitor of the binding of H-Ras to Gal-1. Gal-1 exhibited self-cluster formation upon interaction with FTS, and small- and large-size clusters were formed depending on FTS concentration. The galactoside-binding pocket of Gal-1 in the FTS-bound form was found to play an important role in small-size cluster formation. Large-size clusters were likely formed by the interaction among the hydrophobic sites of Gal-1 in the FTS-bound form. The present results indicate that Gal-1 in the FTS-bound form has the ability to form self-clusters as well as intrinsic lectin activity. Relevance of the self-clustering of FTS-bound Gal-1 to the cluster formation of the H-Ras-Gal-1complex was discussed by taking account of the farnesyl-dependent model and another (Raf-dependent) model. PMID:27624845

  6. Nano-clustered Pd catalysts formed on GaN surface for green chemistry

    NASA Astrophysics Data System (ADS)

    Hirayama, Motoi; Ueta, Yukiko; Konishi, Tomoya; Tsukamoto, Shiro

    2011-05-01

    We have succeeded in observing Pd nano-clusters, catalytic prime elements, on a GaN(0 0 0 1) surface by a scanning tunneling microscope for the first time. After the sample was reused, we found that nano-clusters (width: 11 nm, height: 2.2 nm) existed on the surface which still kept the catalytic activity, resulting that the neutral Pd atoms formed the nano-cluster. Moreover, the S-termination contributed to the formation of the dense and flat structure consisting of the Pd nano-clusters.

  7. Clumped isotope thermometry of cryogenic cave carbonates

    NASA Astrophysics Data System (ADS)

    Kluge, Tobias; Affek, Hagit P.; Zhang, Yi Ge; Dublyansky, Yuri; Spötl, Christoph; Immenhauser, Adrian; Richter, Detlev K.

    2014-02-01

    Freezing of cave pool water that is increasingly oversaturated with dissolved carbonate leads to precipitation of a very specific type of speleothems known as cryogenic cave carbonates (CCC). At present, two different environments for their formation have been proposed, based on their characteristic carbon and oxygen isotope ratios. Rapidly freezing thin water films result in the fast precipitation of fine-grained carbonate powder (CCCfine). This leads to rapid physicochemical changes including CO2 degassing and CaCO3 precipitation, resulting in significantly 13C-enriched carbonates. Alternatively, slow carbonate precipitation in ice-covered cave pools results in coarse crystalline CCC (CCCcoarse) yielding strongly 18O-depleted carbonate. This is due to the formation of relatively 18O-enriched ice causing the gradual depletion of 18O in the water from which the CCC precipitates. Cryogenic carbonates from Central European caves were found to have been formed primarily during the last glacial period, specifically during times of permafrost thawing, based on the oxygen isotope ratios and U-Th dating. Information about the precise conditions of CCCcoarse formation, i.e. whether these crystals formed under equilibrium or disequilibrium conditions with the parent fluid, however, is lacking. An improved understanding of CCCcoarse formation will increase the predictive value of this paleo-permafrost archive. Here we apply clumped isotopes to investigate the formation conditions of cryogenic carbonates using well-studied CCCcoarse from five different cave systems in western Germany. Carbonate clumped isotope measurements yielded apparent temperatures between 3 and 18 °C and thus exhibit clear evidence of isotopic disequilibrium. Although the very negative carbonate δ18O values can only be explained by gradual freezing of pool water accompanied by preferential incorporation of 18O into the ice, clumped isotope-derived temperatures significantly above expected freezing

  8. Metabolic Adaptations of Azospirillum brasilense to Oxygen Stress by Cell-to-Cell Clumping and Flocculation

    PubMed Central

    Bible, Amber N.; Khalsa-Moyers, Gurusahai K.; Mukherjee, Tanmoy; Green, Calvin S.; Mishra, Priyanka; Purcell, Alicia; Aksenova, Anastasia; Hurst, Gregory B.

    2015-01-01

    The ability of bacteria to monitor their metabolism and adjust their behavior accordingly is critical to maintain competitiveness in the environment. The motile microaerophilic bacterium Azospirillum brasilense navigates oxygen gradients by aerotaxis in order to locate low oxygen concentrations that can support metabolism. When cells are exposed to elevated levels of oxygen in their surroundings, motile A. brasilense cells implement an alternative response to aerotaxis and form transient clumps by cell-to-cell interactions. Clumping was suggested to represent a behavior protecting motile cells from transiently elevated levels of aeration. Using the proteomics of wild-type and mutant strains affected in the extent of their clumping abilities, we show that cell-to-cell clumping represents a metabolic scavenging strategy that likely prepares the cells for further metabolic stresses. Analysis of mutants affected in carbon or nitrogen metabolism confirmed this assumption. The metabolic changes experienced as clumping progresses prime cells for flocculation, a morphological and metabolic shift of cells triggered under elevated-aeration conditions and nitrogen limitation. The analysis of various mutants during clumping and flocculation characterized an ordered set of changes in cell envelope properties accompanying the metabolic changes. These data also identify clumping and early flocculation to be behaviors compatible with the expression of nitrogen fixation genes, despite the elevated-aeration conditions. Cell-to-cell clumping may thus license diazotrophy to microaerophilic A. brasilense cells under elevated oxygen conditions and prime them for long-term survival via flocculation if metabolic stress persists. PMID:26407887

  9. Metabolic adaptations of Azospirillum brasilense to oxygen stress by cell-to-cell clumping and flocculation.

    PubMed

    Bible, Amber N; Khalsa-Moyers, Gurusahai K; Mukherjee, Tanmoy; Green, Calvin S; Mishra, Priyanka; Purcell, Alicia; Aksenova, Anastasia; Hurst, Gregory B; Alexandre, Gladys

    2015-12-01

    The ability of bacteria to monitor their metabolism and adjust their behavior accordingly is critical to maintain competitiveness in the environment. The motile microaerophilic bacterium Azospirillum brasilense navigates oxygen gradients by aerotaxis in order to locate low oxygen concentrations that can support metabolism. When cells are exposed to elevated levels of oxygen in their surroundings, motile A. brasilense cells implement an alternative response to aerotaxis and form transient clumps by cell-to-cell interactions. Clumping was suggested to represent a behavior protecting motile cells from transiently elevated levels of aeration. Using the proteomics of wild-type and mutant strains affected in the extent of their clumping abilities, we show that cell-to-cell clumping represents a metabolic scavenging strategy that likely prepares the cells for further metabolic stresses. Analysis of mutants affected in carbon or nitrogen metabolism confirmed this assumption. The metabolic changes experienced as clumping progresses prime cells for flocculation, a morphological and metabolic shift of cells triggered under elevated-aeration conditions and nitrogen limitation. The analysis of various mutants during clumping and flocculation characterized an ordered set of changes in cell envelope properties accompanying the metabolic changes. These data also identify clumping and early flocculation to be behaviors compatible with the expression of nitrogen fixation genes, despite the elevated-aeration conditions. Cell-to-cell clumping may thus license diazotrophy to microaerophilic A. brasilense cells under elevated oxygen conditions and prime them for long-term survival via flocculation if metabolic stress persists. PMID:26407887

  10. Kinematics and dynamics of the MKW/AWM poor clusters

    NASA Technical Reports Server (NTRS)

    Beers, Timothy C.; Kriessler, Jeffrey R.; Bird, Christina M.; Huchra, John P.

    1995-01-01

    We report 472 new redshifts for 416 galaxies in the regions of the 23 poor clusters of galaxies originally identified by Morgan, Kayser, and White (MKW), and Albert, White, and Morgan (AWM). Eighteen of the poor clusters now have 10 or more available redshifts within 1.5/h Mpc of the central galaxy; 11 clusters have at least 20 available redshifts. Based on the 21 clusters for which we have sufficient velocity information, the median velocity scale is 336 km/s, a factor of 2 smaller than found for rich clusters. Several of the poor clusters exhibit complex velocity distributions due to the presence of nearby clumps of galaxies. We check on the velocity of the dominant galaxy in each poor cluster relative to the remaining cluster members. Significantly high relative velocities of the dominant galaxy are found in only 4 of 21 poor clusters, 3 of which we suspect are due to contamination of the parent velocity distribution. Several statistical tests indicate that the D/cD galaxies are at the kinematic centers of the parent poor cluster velocity distributions. Mass-to-light ratios for 13 of the 15 poor clusters for which we have the required data are in the range 50 less than or = M/L(sub B(0)) less than or = 200 solar mass/solar luminosity. The complex nature of the regions surrounding many of the poor clusters suggests that these groupings may represent an early epoch of cluster formation. For example, the poor clusters MKW7 and MKWS are shown to be gravitationally bound and likely to merge to form a richer cluster within the next several Gyrs. Eight of the nine other poor clusters for which simple two-body dynamical models can be carried out are consistent with being bound to other clumps in their vicinity. Additional complex systems with more than two gravitationally bound clumps are observed among the poor clusters.

  11. Kinematics and dynamics of the MKW/AWM poor clusters

    NASA Astrophysics Data System (ADS)

    Beers, Timothy C.; Kriessler, Jeffrey R.; Bird, Christina M.; Huchra, John P.

    1995-03-01

    We report 472 new redshifts for 416 galaxies in the regions of the 23 poor clusters of galaxies originally identified by Morgan, Kayser, and White (MKW), and Albert, White, and Morgan (AWM). Eighteen of the poor clusters now have 10 or more available redshifts within 1.5/h Mpc of the central galaxy; 11 clusters have at least 20 available redshifts. Based on the 21 clusters for which we have sufficient velocity information, the median velocity scale is 336 km/s, a factor of 2 smaller than found for rich clusters. Several of the poor clusters exhibit complex velocity distributions due to the presence of nearby clumps of galaxies. We check on the velocity of the dominant galaxy in each poor cluster relative to the remaining cluster members. Significantly high relative velocities of the dominant galaxy are found in only 4 of 21 poor clusters, 3 of which we suspect are due to contamination of the parent velocity distribution. Several statistical tests indicate that the D/cD galaxies are at the kinematic centers of the parent poor cluster velocity distributions. Mass-to-light ratios for 13 of the 15 poor clusters for which we have the required data are in the range 50 less than or = M/LB(0) less than or = 200 solar mass/solar luminosity. The complex nature of the regions surrounding many of the poor clusters suggests that these groupings may represent an early epoch of cluster formation. For example, the poor clusters MKW7 and MKWS are shown to be gravitationally bound and likely to merge to form a richer cluster within the next several Gyrs. Eight of the nine other poor clusters for which simple two-body dynamical models can be carried out are consistent with being bound to other clumps in their vicinity. Additional complex systems with more than two gravitationally bound clumps are observed among the poor clusters.

  12. CLUSTER FORMATION TRIGGERED BY FILAMENT COLLISIONS IN SERPENS SOUTH

    SciTech Connect

    Nakamura, Fumitaka; Kawabe, Ryohei; Shinnaga, Hiroko; Sugitani, Koji; Tanaka, Tomohiro; Kimura, Kimihiko; Tokuda, Kazuki; Kozu, Minato; Okada, Nozomi; Hasegawa, Yutaka; Ogawa, Hideo; Nishitani, Hiroyuki; Mizuno, Izumi; Dobashi, Kazuhito; Shimoikura, Tomomi; Shimajiri, Yoshito; Kameno, Seiji; Momose, Munetake; Nakajima, Taku; and others

    2014-08-20

    The Serpens South infrared dark cloud consists of several filamentary ridges, some of which fragment into dense clumps. On the basis of CCS (J{sub N} = 4{sub 3}-3{sub 2}), HC{sub 3}N (J = 5-4), N{sub 2}H{sup +} (J = 1-0), and SiO (J = 2-1, v = 0) observations, we investigated the kinematics and chemical evolution of these filamentary ridges. We find that CCS is extremely abundant along the main filament in the protocluster clump. We emphasize that Serpens South is the first cluster-forming region where extremely strong CCS emission is detected. The CCS-to-N{sub 2}H{sup +} abundance ratio is estimated to be about 0.5 toward the protocluster clump, whereas it is about 3 in the other parts of the main filament. We identify six dense ridges with different V {sub LSR}. These ridges appear to converge toward the protocluster clump, suggesting that the collisions of these ridges may have triggered cluster formation. The collisions presumably happened within a few × 10{sup 5} yr because CCS is abundant only for a short time. The short lifetime agrees with the fact that the number fraction of Class I objects, whose typical lifetime is 0.4 × 10{sup 5} yr, is extremely high, about 70% in the protocluster clump. In the northern part, two ridges appear to have partially collided, forming a V-shape clump. In addition, we detected strong bipolar SiO emission that is due to the molecular outflow blowing out of the protostellar clump, as well as extended weak SiO emission that may originate from the filament collisions.

  13. ALMA OBSERVATIONS OF THE IRDC CLUMP G34.43+00.24 MM3: HOT CORE AND MOLECULAR OUTFLOWS

    SciTech Connect

    Sakai, Takeshi; Sakai, Nami; Yamamoto, Satoshi; Foster, Jonathan B.; Sanhueza, Patricio; Jackson, James M.; Kassis, Marc; Furuya, Kenji; Aikawa, Yuri; Hirota, Tomoya

    2013-09-20

    We have observed a cluster forming clump (MM3) associated with the infrared dark cloud G34.43+00.24 in the 1.3 mm continuum and the CH{sub 3}OH, CS, {sup 13}CS, SiO, CH{sub 3}CH{sub 2}CN, and HCOOCH{sub 3} lines with the Atacama Large Millimeter/submillimeter Array and in K-band with the Keck telescope. We have found a young outflow toward the center of this clump in the SiO, CS, and CH{sub 3}OH lines. This outflow is likely driven by a protostar embedded in a hot core, which is traced by the CH{sub 3}CH{sub 2}CN, HCOOCH{sub 3}, {sup 13}CS, and high excitation CH{sub 3}OH lines. The size of the hot core is about 800 × 300 AU in spite of its low mass (<1.1 M {sub ☉}), suggesting a high accretion rate or the presence of multiple star system harboring a few hot corinos. The outflow is highly collimated, and the dynamical timescale is estimated to be less than 740 yr. In addition, we have also detected extended emission of SiO, CS, and CH{sub 3}OH, which is not associated with the hot core and the outflow. This emission may be related to past star formation activity in the clump. Although G34.43+00.24 MM3 is surrounded by a dark feature in infrared, it has already experienced active formation of low-mass stars in an early stage of clump evolution.

  14. The luminosity of Population III star clusters

    NASA Astrophysics Data System (ADS)

    DeSouza, Alexander L.; Basu, Shantanu

    2015-06-01

    We analyse the time evolution of the luminosity of a cluster of Population III protostars formed in the early Universe. We argue from the Jeans criterion that primordial gas can collapse to form a cluster of first stars that evolve relatively independently of one another (i.e. with negligible gravitational interaction). We model the collapse of individual protostellar clumps using non-axisymmetric numerical hydrodynamics simulations. Each collapse produces a protostar surrounded by a massive disc (i.e. Mdisc /M* ≳ 0.1), whose evolution we follow for a further 30-40 kyr. Gravitational instabilities result in the fragmentation and the formation of gravitationally bound clumps within the disc. The accretion of these fragments by the host protostar produces accretion and luminosity bursts on the order of 106 L⊙. Within the cluster, we show that a simultaneity of such events across several protostellar cluster members can elevate the cluster luminosity to 5-10 times greater than expected, and that the cluster spends ˜15 per cent of its star-forming history at these levels. This enhanced luminosity effect is particularly enabled in clusters of modest size with ≃10-20 members. In one such instance, we identify a confluence of burst events that raise the luminosity to nearly 1000 times greater than the cluster mean luminosity, resulting in L > 108 L⊙. This phenomenon arises solely through the gravitational-instability-driven episodic fragmentation and accretion that characterizes this early stage of protostellar evolution.

  15. Clump formation through colliding stellar winds in the Galactic Centre

    NASA Astrophysics Data System (ADS)

    Calderón, D.; Ballone, A.; Cuadra, J.; Schartmann, M.; Burkert, A.; Gillessen, S.

    2016-02-01

    The gas cloud G2 is currently being tidally disrupted by the Galactic Centre supermassive black hole, Sgr A*. The region around the black hole is populated by ˜30 Wolf-Rayet stars, which produce strong outflows. We explore the possibility that gas clumps, such as G2, originate from the collision of stellar winds via the non-linear thin shell instability. Following an analytical approach, we study the thermal evolution of slabs formed in the symmetric collision of winds, evaluating whether instabilities occur, and estimating possible clump masses. We find that the collision of relatively slow (≲750 km s-1) and strong (˜10-5 M⊙ yr-1) stellar winds from stars at short separations (<10 mpc) is a process that indeed could produce clumps of G2's mass and above. Such short separation encounters of single stars along their known orbits are not common in the Galactic Centre, making this process a possible but unlikely origin for G2. We also discuss clump formation in close binaries such as IRS 16SW and in asymmetric encounters as promising alternatives that deserve further numerical study.

  16. Cluster and nebular properties of the central star-forming region of NGC 1140

    NASA Astrophysics Data System (ADS)

    Moll, S. L.; Mengel, S.; de Grijs, R.; Smith, L. J.; Crowther, P. A.

    2007-12-01

    We present new high spatial resolution Hubble Space Telescope/Advanced Camera for Surveys (ACS) imaging of NGC 1140 and high spectral resolution Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph spectroscopy of its central star-forming region. The central region contains several clusters, the two brightest of which are clusters 1 and 6 from Hunter, O'Connell & Gallagher, located within star-forming knots A and B, respectively. A nebular analysis indicates that the knots have a Large Magellanic Cloud-like metallicity of 12 + logO/H = 8.29 +/-0.09. According to continuum-subtracted Hα ACS imaging, cluster 1 dominates the nebular emission of the brighter knot A. Conversely, negligible nebular emission in knot B originates from cluster 6. Evolutionary synthesis modelling implies an age of 5 +/-1 Myr for cluster 1, from which a photometric mass of (1.1 +/-0.3) × 106Msolar is obtained. For this age and photometric mass, the modelling predicts the presence of ~5900 late O stars within cluster 1. Wolf-Rayet (WR) features are observed in knot A, suggesting 550 late-type nitrogen-rich (WNL) and 200 early-type carbon-rich (WCE) stars. Therefore, N(WR)/N(O) ~ 0.1, assuming that all the WR stars are located within cluster 1. The velocity dispersions of the clusters were measured from constituent red supergiants as σ ~ 23 +/-1kms-1 for cluster 1 and σ ~ 26 +/-1kms-1 for cluster 6. Combining σ with half-light radii of 8 +/- 2 and 6.0 +/-0.2 pc measured from the F625W ACS image implies virial masses of (10 +/-3) × 106 and (9.1 +/-0.8) × 106Msolar for clusters 1 and 6, respectively. The most likely reason for the difference between the dynamical and photometric masses of cluster 1 is that the velocity dispersion of knot A is not due solely to cluster 1, as assumed, but has an additional component associated with cluster 2. E-mail: s.moll@sheffield.ac.uk Based on observations collected at the European Southern Observatory, Chile, under programme ESO 71.B-0058(A

  17. Combinatorial effects on clumped isotopes and their significance in biogeochemistry

    NASA Astrophysics Data System (ADS)

    Yeung, Laurence Y.

    2016-01-01

    The arrangement of isotopes within a collection of molecules records their physical and chemical histories. Clumped-isotope analysis interrogates these arrangements, i.e., how often rare isotopes are bound together, which in many cases can be explained by equilibrium and/or kinetic isotope fractionation. However, purely combinatorial effects, rooted in the statistics of pairing atoms in a closed system, are also relevant, and not well understood. Here, I show that combinatorial isotope effects are most important when two identical atoms are neighbors on the same molecule (e.g., O2, N2, and D-D clumping in CH4). When the two halves of an atom pair are either assembled with different isotopic preferences or drawn from different reservoirs, combinatorial effects cause depletions in clumped-isotope abundance that are most likely between zero and -1‰, although they could potentially be -10‰ or larger for D-D pairs. These depletions are of similar magnitude, but of opposite sign, to low-temperature equilibrium clumped-isotope effects for many small molecules. Enzymatic isotope-pairing reactions, which can have site-specific isotopic fractionation factors and atom reservoirs, should express this class of combinatorial isotope effect, although it is not limited to biological reactions. Chemical-kinetic isotope effects, which are related to a bond-forming transition state, arise independently and express second-order combinatorial effects related to the abundance of the rare isotope. Heteronuclear moeties (e.g., Csbnd O and Csbnd H), are insensitive to direct combinatorial influences, but secondary combinatorial influences are evident. In general, both combinatorial and chemical-kinetic factors are important for calculating and interpreting clumped-isotope signatures of kinetically controlled reactions. I apply this analytical framework to isotope-pairing reactions relevant to geochemical oxygen, carbon, and nitrogen cycling that may be influenced by combinatorial

  18. Disequilibrium in Clumped Isotopes Caused by Diagenesis in Tertiary Carbonates

    NASA Astrophysics Data System (ADS)

    Murray, S.; Swart, P. K.

    2015-12-01

    This work examines the clumped isotopes and carbonate associated sulfate (CAS) within a system which is being altered from aragonite to calcite and being subjected to partial dolomitization within the marine realm. Samples were collected from Clino, a ≈670m long core which represents slope carbonates composed of varying percentages of aragonite, low-magnesium calcite (LMC), and dolomite. The concentrations of these endmembers differ dramatically over short distances and are associated with varying degrees of marine diagenesis. In the deeper water portion of the core, previous work has shown no evidence of exposure throughout nor is there any evidence for hydrothermal fluids existing in the Bahamas. Bulk samples were collected from the portions of the core in which dolomite was most prominent. Samples were treated and measured for CAS and for their clumped isotope value. They were then subjected to a series of buffered acetic acid leaches to remove the aragonite and LMC portion of the sample. There were up to three treatments per sample with the resulting sediment measured on XRD to determine its % dolomite composition. These treatments were then also measured for clumped isotopes. The δ34S of the sediments yielded values of up to 10‰ more positive than contemporaneous sweater and implicate bacterial sulfate reduction in the formation of these dolomites. Clumped isotope results of the separates allowed for the calculation of end-member formation temperatures for the LMC and dolomite, whilst using a mixing model to account for non-linearity in ∆47 between end-member combinations and varying ∆47-temperature equations. In contrast to other dolomites in the Bahamas proposed to have formed by massive flow of normal seawater, the Clino temperatures values were significantly elevated compared to the presumed equilibrium values. These data suggest that BSR may result in carbonates with clumped isotopic values significant elevated to equilibrium.

  19. A lower fragmentation mass scale in high-redshift galaxies and its implications on giant clumps: a systematic numerical study

    NASA Astrophysics Data System (ADS)

    Tamburello, Valentina; Mayer, Lucio; Shen, Sijing; Wadsley, James

    2015-11-01

    We study the effect of sub-grid physics, galaxy mass, structural parameters and resolution on the fragmentation of gas-rich galaxy discs into massive star-forming clumps. The initial conditions are set up with the aid of the ARGO cosmological hydrodynamical simulation. Blast-wave feedback does not suppress fragmentation, but reduces both the number of clumps and the duration of the unstable phase. Once formed, bound clumps cannot be destroyed by our feedback model. Widespread fragmentation is promoted by high gas fractions and low halo concentrations. Yet giant clumps M > 108 M⊙ lasting several hundred Myr are rare and mainly produced by clump-clump mergers. They occur in massive discs with maximum rotational velocities Vmax > 250 km s-1 at z ˜ 2, at the high-mass end of the observed galaxy population at those redshifts. The typical gaseous and stellar masses of clumps in all runs are in the range ˜107-108 M⊙ for galaxies with disc mass in the range 1010-8 × 1010 M⊙. Clumps sizes are usually in the range 100-400 pc, in agreement with recent clump observations in lensed high-z galaxies. We argue that many of the giant clumps identified in observations are not due to in situ fragmentation, or are the result of blending of smaller structures owing to insufficient resolution. Using an analytical model describing local collapse inside spiral arms, we can predict the characteristic gaseous masses of clumps at the onset of fragmentation (˜3-5 × 107 M⊙) quite accurately, while the conventional Toomre mass overestimates them. Due to their moderate masses, clumps which migrate to the centre have marginal effect on bulge growth.

  20. Searching for star-forming dwarf galaxies in the Antlia cluster

    NASA Astrophysics Data System (ADS)

    Vaduvescu, O.; Kehrig, C.; Bassino, L. P.; Smith Castelli, A. V.; Calderón, J. P.

    2014-03-01

    Context. The formation and evolution of dwarf galaxies in clusters need to be understood, and this requires large aperture telescopes. Aims: In this sense, we selected the Antlia cluster to continue our previous work in the Virgo, Fornax, and Hydra clusters and in the Local Volume (LV). Because of the scarce available literature data, we selected a small sample of five blue compact dwarf (BCD) candidates in Antlia for observation. Methods: Using the Gemini South and GMOS camera, we acquired the Hα imaging needed to detect star-forming regions in this sample. With the long-slit spectroscopic data of the brightest seven knots detected in three BCD candidates, we derived their basic chemical properties. Using archival VISTA VHS survey images, we derived KS magnitudes and surface brightness profile fits for the whole sample to assess basic physical properties. Results: FS90-98, FS90-106, and FS90-147 are confirmed as BCDs and cluster members, based on their morphology, KS surface photometry, oxygen abundance, and velocity redshift. FS90-155 and FS90-319 did not show any Hα emission, and they could not be confirmed as dwarf cluster star-forming galaxies. Based on our data, we studied some fundamental relations to compare star forming dwarfs (BCDs and dIs) in the LV and in the Virgo, Fornax, Hydra, and Antlia clusters. Conclusions: Star-forming dwarfs in nearby clusters appear to follow same fundamental relations in the near infrared with similar objects in the LV, specifically the size-luminosity and the metallicity-luminosity, while other more fundamental relations could not be checked in Antlia due to lack of data. Based on observations acquired at Gemini South (GS-2010A-Q-51 and GS-2012A-Q-59) and ESO VISTA Hemisphere Survey (VHS).

  1. Study for Planck Cold Clumps with molecular lines

    NASA Astrophysics Data System (ADS)

    Wu, Yuefang

    2014-07-01

    To probe dynamical processes and physical properties of Planck Cold Clumps, we have observed 674 of the most reliable 915 sources with J=1-0 of CO,13CO and C18O using PMO 13.7 m telescope of Purple Mountain Observatory. J=1-0 lines of HCO+ and HCN at CO emission peaks were also observed, of which 24 were mapped with IRAM 30 m telescope. Results show excitation temperatures are from 4 to 17 K, and column densities range from 1020 to 4.5x1023 cm-2. Planck cold clumps have the smallest line width among samples of IRDCs, weak IRAS, EGOs, UC HII candidates and methanol maser chosen cores. However the lines are still wider than those of low-mass cores and have non-thermal supersonic dispersion. Filament is the majority in their morphologies and fragmented structures were found with dense molecular lines. More than 70% of CO cores are starless. Planck cold clumps seem to be ideal samples to search for candidates of massive prestellar cores and pre-clusters.

  2. Rotational support of giant clumps in high-z disc galaxies

    NASA Astrophysics Data System (ADS)

    Ceverino, Daniel; Dekel, Avishai; Mandelker, Nir; Bournaud, Frederic; Burkert, Andreas; Genzel, Reinhard; Primack, Joel

    2012-03-01

    We address the internal support against total free-fall collapse of the giant clumps that form by violent gravitational instability in high-z disc galaxies. Guidance is provided by an analytic model, where the protoclumps are cut from a rotating disc and collapse to equilibrium while preserving angular momentum. This model predicts prograde clump rotation, which dominates the support if the clump has contracted to a surface density contrast ≳10. This is confirmed in hydro adaptive mesh refinement zoom-in simulations of galaxies in a cosmological context. In most high-z clumps, the centrifugal force dominates the support, ?, where Vrot is the rotation velocity and the circular velocity Vcirc measures the potential well. The clump spin indeed tends to be in the sense of the global disc angular momentum, but substantial tilts are frequent, reflecting the highly warped nature of the high-z discs. Most clumps are in Jeans equilibrium, with the rest of the support provided by turbulence, partly driven by the gravitational instability itself. The general agreement between model and simulations indicates that angular momentum loss or gain in most clumps is limited to a factor of 2. Simulations of isolated gas-rich discs that resolve the clump substructure reveal that the cosmological simulations may overestimate ? by ˜30 per cent, but the dominance of rotational support at high z is not a resolution artefact. In turn, isolated gas-poor disc simulations produce at z= 0 smaller gaseous non-rotating transient clouds, indicating that the difference in rotational support is associated with the fraction of cold baryons in the disc. In our current cosmological simulations, the clump rotation velocity is typically more than twice the disc dispersion, Vrot˜ 100 km s-1, but when beam smearing of ≥0.1 arcsec is imposed, the rotation signal is reduced to a small gradient of ≤30 km s-1 kpc-1 across the clump. The velocity dispersion in the simulated clumps is comparable to the

  3. The star-forming history of the young cluster NGC 2264

    NASA Technical Reports Server (NTRS)

    Adams, M. T.; Strom, K. M.; Strom, S. E.

    1983-01-01

    UBVRI H-alpha photographic photometry was obtained for a sample of low-mass stars in the young open cluster NGC 2264 in order to investigate the star-forming history of this region. A theoretical H-R diagram was constructed for the sample of probable cluster members. Isochrones and evolutionary tracks were adopted from Cohen and Kuhi (1979). Evidence for a significant age spread in the cluster was found amounting to over ten million yr. In addition, the derived star formation rate as a function of stellar mass suggests that the principal star-forming mass range in NGC 2264 has proceeded sequentially in time from the lowest to the highest masses. The low-mass cluster stars were the first cluster members to form in significant numbers, although their present birth rate is much lower now than it was about ten million yr ago. The star-formation rate has risen to a peak at successively higher masses and then declined.

  4. The structure and evolution of a forming galaxy cluster at z = 1.62

    NASA Astrophysics Data System (ADS)

    Hatch, N. A.; Muldrew, S. I.; Cooke, E. A.; Hartley, W. G.; Almaini, O.; Simpson, C. J.; Conselice, C. J.

    2016-06-01

    We present a comprehensive picture of the Cl 0218.3-0510 protocluster at z = 1.623 across 10 comoving Mpc. Using filters that tightly bracket the Balmer and 4000 Å breaks of the protocluster galaxies we obtain precise photometric redshifts resulting in a protocluster galaxy sample that is 89 ± 5 per cent complete and has a contamination of only 12 ± 5 per cent. Both star-forming and quiescent protocluster galaxies are located, which allows us to map the structure of the forming cluster for the first time. The protocluster contains six galaxy groups, the largest of which is the nascent cluster. Only a small minority of the protocluster galaxies are in the nascent cluster (11 per cent) or in the other galaxy groups (22 per cent), as most protocluster galaxies reside between the groups. Unobscured star-forming galaxies predominantly reside between the protocluster's groups, whereas red galaxies make up a large fraction of the groups' galactic content, so observing the protocluster through only one of these types of galaxies results in a biased view of the protocluster's structure. The structure of the protocluster reveals how much mass is available for the future growth of the cluster and we use the Millennium Simulation, scaled to a Planck cosmology, to predict that Cl 0218.3-0510 will evolve into a 2.7^{+3.9}_{-1.7}× 10^{14} M_{{⊙}} cluster by the present day.

  5. A lower fragmentation mass scale for clumps in high redshift galaxies: a systematic numerical study

    NASA Astrophysics Data System (ADS)

    Tamburello, Valentina; Mayer, Lucio; Shen, Sijing; Wadsley, James

    2015-08-01

    We perform a systematic study of the effect of sub-grid physics, resolution and structural parameters on the fragmentation of gas-rich galaxy discs into massive star forming clumps due to gravitational instability. We use the state-of-the-art zoom-in cosmological hydrodynamical simulation ARGO (Fiacconi et al. 2015) to set up the initial conditions of our models, and then carry out 26 high resolution controlled simulations of high-z galaxies using the GASOLINE2 code, which includes a modern, numerically robust SPH implementation.We find that when blast-wave feedback is included, the formation of long-lived, gravitationally bound clumps requires disc gas fractions of at least 50% and massive discs, which should have Vmax > 200 km/s at z ˜ 2, more massive than the typical galaxies expected at those redshifts.Less than 50 Myr after formation, clumps have stellar masses in the range 4 × 106 - 5 × 107 M⊙.Formation of clumps with mass exceeding ˜108 M⊙ is a rare occurrence, since it requires mergers between multiple massive clumps, as we verified by tracing back in time the particles belonging to such clumps. Such mergers happen after a few orbital times (˜200-300 Myr), but normally clumps migrate inward and are tidally disrupted on shorter timescales.Clump sizes are in the range 100-500 pc. We argue that giant clumps identified in observations (˜109 M⊙ and 1 kpc in size) might either have a different origin, such as minor mergers and clumpy gas accretion, or their sizes and masses may be overestimated due to resolution issues.Using an analytical model, already developed to explain the fragmentation scale in gravitationally unstable 3D protoplanetary discs, we can predict fairly accurately the characteristic gaseous masses of clumps soon after fragmentation, when standard Toome analysis becomes invalid.Due to their modest size, clumps have little effect on bulge growth as they migrate to the center. In our unstable discs a small bulge can form irrespective of

  6. ATLASGAL - properties of compact H II regions and their natal clumps

    NASA Astrophysics Data System (ADS)

    Urquhart, J. S.; Thompson, M. A.; Moore, T. J. T.; Purcell, C. R.; Hoare, M. G.; Schuller, F.; Wyrowski, F.; Csengeri, T.; Menten, K. M.; Lumsden, S. L.; Kurtz, S.; Walmsley, C. M.; Bronfman, L.; Morgan, L. K.; Eden, D. J.; Russeil, D.

    2013-10-01

    We present a complete sample of molecular clumps containing compact and ultracompact H II (UC H II) regions between ℓ = 10° and 60° and |b| < 1°, identified by combining the APEX Telescope Large Area Survey of the Galaxy submm and CORNISH radio continuum surveys with visual examination of archival infrared data. Our sample is complete to optically thin, compact and UC H II regions driven by a zero-age main-sequence star of spectral type B0 or earlier embedded within a 1000 M⊙ clump. In total we identify 213 compact and UC H II regions, associated with 170 clumps. Unambiguous kinematic distances are derived for these clumps and used to estimate their masses and physical sizes, as well as the Lyman continuum fluxes and sizes of their embedded H II regions. We find a clear lower envelope for the surface density of molecular clumps hosting massive star formation of 0.05 g cm-2, which is consistent with a similar sample of clumps associated with 6.7 GHz masers. The mass of the most massive embedded stars is closely correlated with the mass of their natal clump. Young B stars appear to be significantly more luminous in the ultraviolet than predicted by current stellar atmosphere models. The properties of clumps associated with compact and UC H II regions are very similar to those associated with 6.7 GHz methanol masers and we speculate that there is little evolution in the structure of the molecular clumps between these two phases. Finally, we identify a significant peak in the surface density of compact and UC H II-regions associated with the W49A star-forming complex, noting that this complex is truly one of the most massive and intense regions of star formation in the Galaxy.

  7. Recombination clumping factor during cosmic reionization

    SciTech Connect

    Kaurov, Alexander A.; Gnedin, Nickolay Y. E-mail: gnedin@fnal.gov

    2014-06-01

    We discuss the role of recombinations in the intergalactic medium, and the related concept of the clumping factor, during cosmic reionization. The clumping factor is, in general, a local quantity that depends on both the local overdensity and the scale below which the baryon density field can be assumed smooth. That scale, called the filtering scale, depends on over-density and local thermal history. We present a method for building a self-consistent analytical model of inhomogeneous reionization, assuming the linear growth rate of the density fluctuation, which simultaneously accounts for these effects. We show that taking into account the local clumping factor introduces significant corrections to the total recombination rate, compared to the model with a globally uniform clumping factor.

  8. Doubly charged CO2 clusters formed by ionization of doped helium nanodroplets☆

    PubMed Central

    Daxner, Matthias; Denifl, Stephan; Scheier, Paul; Echt, Olof

    2014-01-01

    Helium nanodroplets are doped with carbon dioxide and ionized by electrons. Doubly charged cluster ions are, for the first time, identified based on their characteristic patterns of isotopologues. Thanks to the high mass resolution, large dynamic range, and a novel method to eliminate contributions from singly charged ions from the mass spectra, we are able to observe doubly charged cluster ions that are smaller than the ones reported in the past. The likely mechanism by which doubly charged ions are formed in doped helium droplets is discussed. PMID:25844051

  9. Clustered quantum dots in single GaN islands formed at threading dislocations

    NASA Astrophysics Data System (ADS)

    Schmidt, Gordon; Veit, Peter; Berger, Christoph; Bertram, Frank; Dadgar, Armin; Strittmatter, André; Christen, Jürgen

    2016-05-01

    We give direct evidence of distinct quantum dot states clustered but also spatially separated in single GaN islands. Resulting from GaN layer growth on top of AlN, the islands are predominantly formed in close vicinity to threading dislocation bundles. Detailed analysis of the inner optical and structural properties, performed by nanoscale cathodoluminescence, reveals various sharp quantum dot emission lines from different regions in an otherwise continuous island. Thickness fluctuations found within these islands are made responsible for the clustering of quantum dot states.

  10. The rate and latency of star formation in dense, massive clumps in the Milky Way

    NASA Astrophysics Data System (ADS)

    Heyer, M.; Gutermuth, R.; Urquhart, J. S.; Csengeri, T.; Wienen, M.; Leurini, S.; Menten, K.; Wyrowski, F.

    2016-04-01

    Context. Newborn stars form within the localized, high density regions of molecular clouds. The sequence and rate at which stars form in dense clumps and the dependence on local and global environments are key factors in developing descriptions of stellar production in galaxies. Aims: We seek to observationally constrain the rate and latency of star formation in dense massive clumps that are distributed throughout the Galaxy and to compare these results to proposed prescriptions for stellar production. Methods: A sample of 24 μm-based Class I protostars are linked to dust clumps that are embedded within molecular clouds selected from the APEX Telescope Large Area Survey of the Galaxy. We determine the fraction of star-forming clumps, f∗, that imposes a constraint on the latency of star formation in units of a clump's lifetime. Protostellar masses are estimated from models of circumstellar environments of young stellar objects from which star formation rates are derived. Physical properties of the clumps are calculated from 870 μm dust continuum emission and NH3 line emission. Results: Linear correlations are identified between the star formation rate surface density, ΣSFR, and the quantities ΣH2/τff and ΣH2/τcross, suggesting that star formation is regulated at the local scales of molecular clouds. The measured fraction of star forming clumps is 23%. Accounting for star formation within clumps that are excluded from our sample due to 24 μm saturation, this fraction can be as high as 31%, which is similar to previous results. Dense, massive clumps form primarily low mass (<1-2 M⊙) stars with emergent 24 μm fluxes below our sensitivity limit or are incapable of forming any stars for the initial 70% of their lifetimes. The low fraction of star forming clumps in the Galactic center relative to those located in the disk of the Milky Way is verified. Full Tables 2-4 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130

  11. GAS RESERVOIRS AND STAR FORMATION IN A FORMING GALAXY CLUSTER AT zbsime0.2

    SciTech Connect

    Jaffe, Yara L.; Poggianti, Bianca M.; Verheijen, Marc A. W.; Deshev, Boris Z.; Van Gorkom, Jacqueline H.

    2012-09-10

    We present first results from the Blind Ultra-Deep H I Environmental Survey of the Westerbork Synthesis Radio Telescope. Our survey is the first direct imaging study of neutral atomic hydrogen gas in galaxies at a redshift where evolutionary processes begin to show. In this Letter we investigate star formation, H I content, and galaxy morphology, as a function of environment in Abell 2192 (at z = 0.1876). Using a three-dimensional visualization technique, we find that Abell 2192 is a cluster in the process of forming, with significant substructure in it. We distinguish four structures that are separated in redshift and/or space. The richest structure is the baby cluster itself, with a core of elliptical galaxies that coincides with (weak) X-ray emission, almost no H I detections, and suppressed star formation. Surrounding the cluster, we find a compact group where galaxies pre-process before falling into the cluster, and a scattered population of 'field-like' galaxies showing more star formation and H I detections. This cluster proves to be an excellent laboratory to understand the fate of the H I gas in the framework of galaxy evolution. We clearly see that the H I gas and the star formation correlate with morphology and environment at z {approx} 0.2. In particular, the fraction of H I detections is significantly affected by the environment. The effect starts to kick in in low-mass groups that pre-process the galaxies before they enter the cluster. Our results suggest that by the time the group galaxies fall into the cluster, they are already devoid of H I.

  12. A Clumped Isotope Calibration for Lacustrine Carbonates

    NASA Astrophysics Data System (ADS)

    Mitsunaga, B. A.; Mering, J. A.; Petryshyn, V. A.; Dunbar, R. B.; Cohen, A. S.; Liu, X.; Kaufman, D. S.; Eagle, R.; Tripati, A.

    2014-12-01

    Our capacity to understand Earth's environmental history is highly dependent on the accuracy of past climate reconstructions. Unfortunately, many terrestrial proxies—tree rings, speleothems, leaf margin analyses, etc.—are influenced by the effects of both temperature and precipitation. Methods that can isolate the effects of temperature alone are needed, and clumped isotope thermometry has the potential to be a useful tool for determining terrestrial climates. Multiple studies have shown that the fraction of 13C—18O bonds in carbonates is inversely related to the temperature at which the rocks formed and may be a useful proxy for reconstructing temperatures on land. An in-depth survey of lacustrine carbonates, however, has not yet been published. Therefore we have been measuring the abundance of 13C18O16O in the CO2 produced by the dissolution of modern lake samples' carbonate minerals in phosphoric acid and comparing results to independently known estimates of lake water temperature and air temperature. Some of the sample types we have investigated include endogenic carbonates, freshwater gastropods, bivalves, microbialites, and ooids.

  13. Thermodynamic stability and structural properties of cluster crystals formed by amphiphilic dendrimers

    NASA Astrophysics Data System (ADS)

    Lenz, Dominic A.; Mladek, Bianca M.; Likos, Christos N.; Blaak, Ronald

    2016-05-01

    We pursue the goal of finding real-world examples of macromolecular aggregates that form cluster crystals, which have been predicted on the basis of coarse-grained, ultrasoft pair potentials belonging to a particular mathematical class [B. M. Mladek et al., Phys. Rev. Lett. 46, 045701 (2006)]. For this purpose, we examine in detail the phase behavior and structural properties of model amphiphilic dendrimers of the second generation by means of monomer-resolved computer simulations. On augmenting the density of these systems, a fluid comprised of clusters that contain several overlapping and penetrating macromolecules is spontaneously formed. Upon further compression of the system, a transition to multi-occupancy crystals takes place, the thermodynamic stability of which is demonstrated by means of free-energy calculations, and where the FCC is preferred over the BCC-phase. Contrary to predictions for coarse-grained theoretical models in which the particles interact exclusively by effective pair potentials, the internal degrees of freedom of these molecules cause the lattice constant to be density-dependent. Furthermore, the mechanical stability of monodisperse BCC and FCC cluster crystals is restricted to a bounded region in the plane of cluster occupation number versus density. The structural properties of the dendrimers in the dense crystals, including their overall sizes and the distribution of monomers are also thoroughly analyzed.

  14. Thermodynamic stability and structural properties of cluster crystals formed by amphiphilic dendrimers.

    PubMed

    Lenz, Dominic A; Mladek, Bianca M; Likos, Christos N; Blaak, Ronald

    2016-05-28

    We pursue the goal of finding real-world examples of macromolecular aggregates that form cluster crystals, which have been predicted on the basis of coarse-grained, ultrasoft pair potentials belonging to a particular mathematical class [B. M. Mladek et al., Phys. Rev. Lett. 46, 045701 (2006)]. For this purpose, we examine in detail the phase behavior and structural properties of model amphiphilic dendrimers of the second generation by means of monomer-resolved computer simulations. On augmenting the density of these systems, a fluid comprised of clusters that contain several overlapping and penetrating macromolecules is spontaneously formed. Upon further compression of the system, a transition to multi-occupancy crystals takes place, the thermodynamic stability of which is demonstrated by means of free-energy calculations, and where the FCC is preferred over the BCC-phase. Contrary to predictions for coarse-grained theoretical models in which the particles interact exclusively by effective pair potentials, the internal degrees of freedom of these molecules cause the lattice constant to be density-dependent. Furthermore, the mechanical stability of monodisperse BCC and FCC cluster crystals is restricted to a bounded region in the plane of cluster occupation number versus density. The structural properties of the dendrimers in the dense crystals, including their overall sizes and the distribution of monomers are also thoroughly analyzed. PMID:27250325

  15. Cluster form factor calculation in the ab initio no-core shell model

    SciTech Connect

    Navratil, Petr

    2004-11-01

    We derive expressions for cluster overlap integrals or channel cluster form factors for ab initio no-core shell model (NCSM) wave functions. These are used to obtain the spectroscopic factors and can serve as a starting point for the description of low-energy nuclear reactions. We consider the composite system and the target nucleus to be described in the Slater determinant (SD) harmonic oscillator (HO) basis while the projectile eigenstate to be expanded in the Jacobi coordinate HO basis. This is the most practical case. The spurious center of mass components present in the SD bases are removed exactly. The calculated cluster overlap integrals are translationally invariant. As an illustration, we present results of cluster form factor calculations for <{sup 5}He vertical bar{sup 4}He+n>, <{sup 5}He vertical bar{sup 3}H+d>, <{sup 6}Li vertical bar{sup 4}He+d>, <{sup 6}Be vertical bar{sup 3}He+{sup 3}He>, <{sup 7}Li vertical bar{sup 4}He+{sup 3}H>, <{sup 7}Li vertical bar{sup 6}Li+n>, <{sup 8}Be vertical bar{sup 6}Li+d>, <{sup 8}Be vertical bar{sup 7}Li+p>, <{sup 9}Li vertical bar{sup 8}Li+n>, and <{sup 13}C vertical bar{sup 12}C+n>, with all the nuclei described by multi-({Dirac_h}/2{pi}){omega} NCSM wave functions.

  16. The Clumped Isotope Composition of Biogenic Methane.

    NASA Astrophysics Data System (ADS)

    Sessions, A. L.; Douglas, P. M.; Eiler, J. M.; Stolper, D. A.

    2015-12-01

    The excess or lack of 13CH3D, a doubly substituted ("clumped") isotopologue of methane, relative to that expected for a random distribution of isotopes across molecules, is a function of the processes that generated the methane. For high-temperature thermogenic methane, which typically achieves internal equilibrium, an excess of 13CH3D is expected and the amount of excess can serve as a thermometer. In contrast, biogenic methane often - though not always - has a smaller excess of clumped isotopologues, and sometimes even a deficit of clumped species ("anti-clumped"). The effect presumably arises from kinetic isotope effects accompanying enzymatic reactions in the methanogenic pathway, though the particular reaction(s) has not yet been positively identified. The decrease in clumping is also known to correlate with both the reversibility of the pathway and the methane flux. In this talk, we will present recent data bearing on the origin and utility of biologic fractionations of clumped isotopologues in methane. Preliminary data suggest that methane deriving from the fermentative pathway is enriched in D-bearing isotopologues, at the same level of clumping, relative to that derived from the CO2-reductive pathway. This property offers another potential means to distinguish biogenic methane sources in the environment. Recently, we have also begun to measure the 12CH2D2 isotopologue, for which equilibrium and kinetic isotope effects are predicted to be distinct from 13CH3D. Preliminary data suggest that the combination of both doubly-substituted isotopologues will be especially useful for disentangling mixtures containing biogenic gas.

  17. The G305 star-forming complex: the central star clusters Danks 1 and Danks 2

    NASA Astrophysics Data System (ADS)

    Davies, Ben; Clark, J. S.; Trombley, Christine; Figer, Donald F.; Najarro, Francisco; Crowther, Paul A.; Kudritzki, Rolf-Peter; Thompson, Mark; Urquhart, James S.; Hindson, Luke

    2012-01-01

    The G305 H II complex (G305.4+0.1) is one of the most massive star-forming structures yet identified within the Galaxy. It is host to many massive stars at all stages of formation and evolution, from embedded molecular cores to post-main-sequence stars. Here, we present a detailed near-infrared analysis of the two central star clusters Danks 1 and Danks 2, using Hubble Space Telescope+NICMOS imaging and Very Large Telescope+ISAAC spectroscopy. We find that the spectrophotometric distance to the clusters is consistent with the kinematic distance to the G305 complex, an average of all measurements giving a distance of 3.8 ± 0.6 kpc. From analysis of the stellar populations and the pre-main-sequence stars, we find that Danks 2 is the elder of the two clusters, with an age of 3+3- 1 Myr. Danks 1 is clearly younger with an age of 1.5+1.5- 0.5 Myr, and is dominated by three very luminous H-rich Wolf-Rayet stars which may have masses ≳100 M⊙. The two clusters have mass functions consistent with the Salpeter slope, and total cluster masses of 8000 ± 1500 and 3000 ± 800 M⊙ for Danks 1 and Danks 2, respectively. Danks 1 is significantly the more compact cluster of the two, and is one of the densest clusters in the Galaxy with log (ρ/M⊙ pc-3) = 5.5+0.5- 0.4. In addition to the clusters, there is a population of apparently isolated Wolf-Rayet stars within the molecular cloud's cavity. Our results suggest that the star-forming history of G305 began with the formation of Danks 2, and subsequently Danks 1, with the origin of the diffuse evolved population currently uncertain. Together, the massive stars at the centre of the G305 region appear to be clearing away what is left of the natal cloud, triggering a further generation of star formation at the cloud's periphery.

  18. Defect clusters formed from large collision cascades in fcc metals irradiated with spallation neutrons

    NASA Astrophysics Data System (ADS)

    Satoh, Y.; Matsuda, Y.; Yoshiie, T.; Kawai, M.; Matsumura, H.; Iwase, H.; Abe, H.; Kim, S. W.; Matsunaga, T.

    2013-11-01

    Fcc pure metals were irradiated with spallation neutrons (energies up to 500 MeV) at room temperature to a neutron fluence of 1 × 1018 n m-2 at KENS, High Energy Accelerator Research Organization (KEK). Defect clusters induced by large collision cascades were examined using transmission electron microscopy (TEM). In Au, large groups of defects included more than 10 clusters, and the damage zone extended over 50 nm, which was larger than that induced by fusion neutron irradiation (<20 nm). Although small stacking fault tetrahedra (SFT) are formed in subcascades by fission and fusion neutron irradiation, dislocation loops were also observed in the present experiments. Large dislocation loops (>10 nm) were identified as vacancy type by the conventional inside-outside contrast method. Because of the low neutron fluence, spatial overlapping of collision cascades was ignored. Large vacancy loops are formed through cooperative reactions among subcascades in a single collision cascade with large recoil energy.

  19. Clustered streamlined forms in Athabasca Valles, Mars: Evidence for sediment deposition during floodwater ponding

    USGS Publications Warehouse

    Burr, D.

    2005-01-01

    A unique clustering of layered streamlined forms in Athabasca Valles is hypothesized to reflect a significant hydraulic event. The forms, interpreted as sedimentary, are attributed to extensive sediment deposition during ponding and then streamlining of this sediment behind flow obstacles during ponded water outflow. These streamlined forms are analogous to those found in depositional basins and other loci of ponding in terrestrial catastrophic flood landscapes. These terrestrial streamlined forms can provide the best opportunity for reconstructing the history of the terrestrial flooding. Likewise, the streamlined forms in Athabasca Valles may provide the best opportunity to reconstruct the recent geologic history of this young Martian outflow channel. ?? 2005 Elsevier B.V. All rights reserved.

  20. Photothermolysis by laser-induced microbubbles generated around gold nanorod clusters selectively formed in leukemia cells

    NASA Astrophysics Data System (ADS)

    Lapotko, Dmitri; Lukianova-Hleb, Ekaterina; Zhdanok, Sergei; Rostro, Betty; Simonette, Rebecca; Hafner, Jason; Konopleva, Marina; Andreeff, Michael; Conjusteau, Andre; Oraevsky, Alexander

    2008-02-01

    In an effort of developing clinical LANTCET (laser-activated nano-thermolysis as cell elimination technology) we achieved selective destruction of individual tumor cells through laser generation of vapor microbubbles around clusters of light absorbing gold nanorods (GNR) selectively formed in target tumor cells. Among all gold nanoparticles, nanorods offer the highest optical absorption in the near-infrared. We applied covalent conjugates of gold nanorods with targeting vectors such as monoclonal antibodies CD33 (specific for Acute Myeloid Leukemia), while GNR conjugates with polyethylene-glycol (PEG) were used as nonspecific targeting control. GNR clusters were formed inside the tumor cells at 37 °C due to endocytosis of large concentration of nanorods accumulated on the surface of tumor cells targeted at 4 °C. Formation of GNR clusters significantly reduces the threshold of tumor cell damage making LANTCET safe for normal cells. Appearance of GNR clusters was verified directly with optical resonance scattering microscopy. LANTCET was performed in vitro with living cells of (1) model myeloid K562 cells (CD33 positive), (2) primary human bone marrow CD33-positive blast cells from patients diagnosed with acute myeloid leukemia. Laser-induced microbubbles were generated and detected with a photothermal microscope equipped with a tunable Ti-Sa pulsed laser. GNT cluster formation caused a 100-fold decrease in the threshold optical fluence for laser microbubble generation in tumor cells compared with that in normal cells under the same targeting and irradiation conditions. Combining imaging based on resonance optical scattering with photothermal imaging of microbubbles, we developed a method for detection, image-guided treatment and monitoring of LANTCET. Pilot experiments were performed in flow mode bringing LANTCET closer to reality of clinical procedure of purging tumor cells from bone marrow grafts.

  1. The role of low-mass star clusters in forming the massive stars in DR 21

    NASA Astrophysics Data System (ADS)

    Rivilla, V. M.; Jiménez-Serra, I.; Martín-Pintado, J.; Sanz-Forcada, J.

    2014-01-01

    We have studied the young low-mass pre-main sequence (PMS) stellar population associated with the massive star-forming region DR 21 by using archival X-ray Chandra observations and by complementing them with existing optical and infrared (IR) surveys. The Chandra observations have revealed for the first time a new highly extincted population of PMS low-mass stars previously missed in observations at other wavelengths. The X-ray population exhibits three main stellar density peaks, coincident with the massive star-forming regions, being the DR 21 core the main peak. The cross-correlated X-ray/IR sample exhibits a radial `Spokes-like' stellar filamentary structure that extends from the DR 21 core towards the northeast. The near-IR data reveal a centrally peaked structure for the extinction, which exhibits its maximum in the DR 21 core and gradually decreases with the distance to the N-S cloud axis and to the cluster centre. We find evidence of a global mass segregation in the full low-mass stellar cluster, and of a stellar age segregation, with the youngest stars still embedded in the N-S cloud, and more evolved stars more spatially distributed. The results are consistent with the scenario where an elongated overall potential well created by the full low-mass stellar cluster funnels gas through filaments feeding stellar formation. Besides the full gravitational well, smaller scale local potential wells created by dense stellar sub-clusters of low-mass stars are privileged in the competition for the gas of the common reservoir, allowing the formation of massive stars. We also discuss the possibility that a stellar collision in the very dense stellar cluster revealed by Chandra in the DR 21 core is the origin of the large-scale and highly energetic outflow arising from this region.

  2. Formation of phase space holes and clumps.

    PubMed

    Lilley, M K; Nyqvist, R M

    2014-04-18

    It is shown that the formation of phase space holes and clumps in kinetically driven, dissipative systems is not restricted to the near threshold regime, as previously reported and widely believed. Specifically, we observe hole-clump generation from the edges of an unmodulated phase space plateau, created via excitation, phase mixing and subsequent dissipative decay of a linearly unstable bulk plasma mode in the electrostatic bump-on-tail model. This has now allowed us to elucidate the underlying physics of the hole-clump formation process for the first time. Holes and clumps develop from negative energy waves that arise due to the sharp gradients at the interface between the plateau and the nearly unperturbed, ambient distribution and destabilize in the presence of dissipation in the bulk plasma. We confirm this picture by demonstrating that the formation of such nonlinear structures in general does not rely on a "seed" wave, only on the ability of the system to generate a plateau. In addition, we observe repetitive cycles of plateau generation and erosion, the latter due to hole-clump formation and detachment, which appear to be insensitive to initial conditions and can persist for a long time. We present an intuitive discussion of why this continual regeneration occurs. PMID:24785043

  3. Pollen clumping and wind dispersal in an invasive angiosperm.

    PubMed

    Martin, Michael D; Chamecki, Marcelo; Brush, Grace S; Meneveau, Charles; Parlange, Marc B

    2009-09-01

    Pollen dispersal is a fundamental aspect of plant reproductive biology that maintains connectivity between spatially separated populations. Pollen clumping, a characteristic feature of insect-pollinated plants, is generally assumed to be a detriment to wind pollination because clumps disperse shorter distances than do solitary pollen grains. Yet pollen clumps have been observed in dispersion studies of some widely distributed wind-pollinated species. We used Ambrosia artemisiifolia (common ragweed; Asteraceae), a successful invasive angiosperm, to investigate the effect of clumping on wind dispersal of pollen under natural conditions in a large field. Results of simultaneous measurements of clump size both in pollen shedding from male flowers and airborne pollen being dispersed in the atmosphere are combined with a transport model to show that rather than being detrimental, clumps may actually be advantageous for wind pollination. Initial clumps can pollinate the parent population, while smaller clumps that arise from breakup of larger clumps can cross-pollinate distant populations. PMID:21622356

  4. Local-density-driven clustered star formation

    NASA Astrophysics Data System (ADS)

    Parmentier, G.; Pfalzner, S.

    2013-01-01

    Context. A positive power-law trend between the local surface densities of molecular gas, Σgas, and young stellar objects, Σ ⋆ , in molecular clouds of the solar neighbourhood has recently been identified. How it relates to the properties of embedded clusters, in particular to the recently established radius-density relation, has so far not been investigated. Aims: We model the development of the stellar component of molecular clumps as a function of time and initial local volume density. Our study provides a coherent framework able to explain both the molecular-cloud and embedded-cluster relations quoted above. Methods: We associate the observed volume density gradient of molecular clumps to a density-dependent free-fall time. The molecular clump star formation history is obtained by applying a constant star formation efficiency per free-fall time, ɛff. Results: For the volume density profiles typical of observed molecular clumps (i.e. power-law slope ≃ -1.7), our model gives a star-gas surface-density relation of the form Σ⋆ ∝ Σgas2, which agrees very well with the observations. Taking the case of a molecular clump of mass M0 ≃ 104 M⊙ and radius R ≃ 6 pc experiencing star formation during 2 Myr, we derive what star formation efficiency per free-fall time matches the normalizations of the observed and predicted (Σ ⋆ , Σgas) relations best. We find ɛff ≃ 0.1. We show that the observed growth of embedded clusters, embodied by their radius-density relation, corresponds to a surface density threshold being applied to developing star-forming regions. The consequences of our model in terms of cluster survivability after residual star-forming gas expulsion are that, owing to the locally high star formation efficiency in the inner part of star-forming regions, global star formation efficiency as low as 10% can lead to the formation of bound gas-free star clusters.

  5. Metabolic Adaptations of Azospirillum brasilense to Oxygen Stress by Cell-to-Cell Clumping and Flocculation

    SciTech Connect

    Bible, Amber N.; Khalsa-Moyers, Gurusahai K.; Mukherjee, Tanmoy; Green, Calvin S.; Mishra, Priyanka; Purcell, Alicia; Aksenova, Anastasia; Hurst, Gregory B.; Alexandre, Gladys

    2015-09-25

    The ability of bacteria to monitor their metabolism and adjust their behavior accordingly is critical to maintain competitiveness in the environment. The motile microaerophilic bacteriumAzospirillum brasilensenavigates oxygen gradients by aerotaxis in order to locate low oxygen concentrations that can support metabolism. When cells are exposed to elevated levels of oxygen in their surroundings, motileA. brasilensecells implement an alternative response to aerotaxis and form transient clumps by cell-to-cell interactions. Clumping was suggested to represent a behavior protecting motile cells from transiently elevated levels of aeration. Using the proteomics of wild-type and mutant strains affected in the extent of their clumping abilities, we show that cell-to-cell clumping represents a metabolic scavenging strategy that likely prepares the cells for further metabolic stresses. Analysis of mutants affected in carbon or nitrogen metabolism confirmed this assumption. The metabolic changes experienced as clumping progresses prime cells for flocculation, a morphological and metabolic shift of cells triggered under elevated-aeration conditions and nitrogen limitation. The analysis of various mutants during clumping and flocculation characterized an ordered set of changes in cell envelope properties accompanying the metabolic changes. These data also identify clumping and early flocculation to be behaviors compatible with the expression of nitrogen fixation genes, despite the elevated-aeration conditions. Finally, cell-to-cell clumping may thus license diazotrophy to microaerophilicA. brasilensecells under elevated oxygen conditions and prime them for long-term survival via flocculation if metabolic stress persists.

  6. Metabolic Adaptations of Azospirillum brasilense to Oxygen Stress by Cell-to-Cell Clumping and Flocculation

    DOE PAGESBeta

    Bible, Amber N.; Khalsa-Moyers, Gurusahai K.; Mukherjee, Tanmoy; Green, Calvin S.; Mishra, Priyanka; Purcell, Alicia; Aksenova, Anastasia; Hurst, Gregory B.; Alexandre, Gladys

    2015-09-25

    The ability of bacteria to monitor their metabolism and adjust their behavior accordingly is critical to maintain competitiveness in the environment. The motile microaerophilic bacteriumAzospirillum brasilensenavigates oxygen gradients by aerotaxis in order to locate low oxygen concentrations that can support metabolism. When cells are exposed to elevated levels of oxygen in their surroundings, motileA. brasilensecells implement an alternative response to aerotaxis and form transient clumps by cell-to-cell interactions. Clumping was suggested to represent a behavior protecting motile cells from transiently elevated levels of aeration. Using the proteomics of wild-type and mutant strains affected in the extent of their clumping abilities,more » we show that cell-to-cell clumping represents a metabolic scavenging strategy that likely prepares the cells for further metabolic stresses. Analysis of mutants affected in carbon or nitrogen metabolism confirmed this assumption. The metabolic changes experienced as clumping progresses prime cells for flocculation, a morphological and metabolic shift of cells triggered under elevated-aeration conditions and nitrogen limitation. The analysis of various mutants during clumping and flocculation characterized an ordered set of changes in cell envelope properties accompanying the metabolic changes. These data also identify clumping and early flocculation to be behaviors compatible with the expression of nitrogen fixation genes, despite the elevated-aeration conditions. Finally, cell-to-cell clumping may thus license diazotrophy to microaerophilicA. brasilensecells under elevated oxygen conditions and prime them for long-term survival via flocculation if metabolic stress persists.« less

  7. Physical and Chemical Properties of Protocluster Clumps and Massive Young Stellar Objects Associated to Infrared Dark Clouds

    NASA Astrophysics Data System (ADS)

    Gomez Gonzalez, Laura

    2012-01-01

    The study of high-mass stars is important not only because of the effects they produce in their environment through outflows, expanding HII regions, stellar winds, and eventually supernova shock waves, but also because they play a crucial role in estimating star formation rates in other galaxies. Although we have an accepted evolutionary scenario that explains (isolated) low-mass star formation, the processes that produce massive stars (M_star > 8 M_sol) and star clusters, especially their earliest stages, are not well understood. The newly discovered class of interstellar clouds now termed infrared dark clouds (IRDCs) represent excellent laboratories to study the earliest stages of high-mass star formation given that some of the clumps within them are known to have high masses (~100's M_sol), high densities (n > 10^5 cm^-3), and low temperatures (10-20K) as expected for the birthplaces of high-mass stars. Some questions remain unanswered: Do IRDCs harbor the very early stages of high-mass star formation, i.e., the pre-protocluster phase? If so, how do they compare with low-mass star formation sites? Is there chemical differentiation in IRDC clumps? What is the mass distribution of IRDCs? In this dissertation and for the first time, a catalog of 12529 IRDC candidates at 24 um has been created using archival data from the MIPSGAL/Spitzer survey, as a first step in searching for the massive pre-protocluster clumps. From this catalog, a sample of ~60 clumps has been selected in order to perform single-pointing observations with the IRAM 30m, Effelsberg 100m, and APEX 12m telescopes. One IRDC clump seems to be a promising candidate for being in the pre-protocluster phase. In addition, molecular line mapping observations have been performed on three clumps within IRDCs and a detailed chemical study of 10 molecular lines has been carried out. A larger difference in column densities and abundances has been found between these clumps and high-m! ass protostellar objects

  8. MAGNETIC FIELD IN THE ISOLATED MASSIVE DENSE CLUMP IRAS 20126+4104

    SciTech Connect

    Shinnaga, Hiroko; Phillips, Thomas G.; Novak, Giles; Vaillancourt, John E.; Machida, Masahiro N.; Kataoka, Akimasa; Tomisaka, Kohji; Davidson, Jacqueline; Houde, Martin; Dowell, C. Darren; Leeuw, Lerothodi

    2012-05-10

    We measured polarized dust emission at 350 {mu}m toward the high-mass star-forming massive dense clump IRAS 20126+4104 using the SHARC II Polarimeter, SHARP, at the Caltech Submillimeter Observatory. Most of the observed magnetic field vectors agree well with magnetic field vectors obtained from a numerical simulation for the case when the global magnetic field lines are inclined with respect to the rotation axis of the dense clump. The results of the numerical simulation show that rotation plays an important role on the evolution of the massive dense clump and its magnetic field. The direction of the cold CO 1-0 bipolar outflow is parallel to the observed magnetic field within the dense clump as well as the global magnetic field, as inferred from optical polarimetry data, indicating that the magnetic field also plays a critical role in an early stage of massive star formation. The large-scale Keplerian disk of the massive (proto)star rotates in an almost opposite sense to the clump's envelope. The observed magnetic field morphology and the counterrotating feature of the massive dense clump system provide hints to constrain the role of magnetic fields in the process of high-mass star formation.

  9. Slow formation of [3Fe-4S](1+) clusters in mutant forms of Desulfovibrio africanus ferredoxin III.

    PubMed

    Hannan, J P; Busch, J L; James, R; Thomson, A J; Moore, G R; Davy, S L

    2000-02-25

    Desulfovibrio africanus ferredoxin III (Da FdIII) readily interconverts between a 7Fe and an 8Fe form with Asp-14 believed to provide a cluster ligand in the latter form. To investigate the factors important for cluster interconversion in Fe/S cluster-containing proteins we have studied two variants of Da FdIII produced by site-directed mutagenesis, Asp14Glu and Asp14His, with cluster incorporation performed in vitro. Characterisation of these proteins by UV/visible, EPR and (1)H NMR spectroscopies revealed that the formation of the stable 7Fe form of these proteins takes some time to occur. Evidence is presented which indicates the [4Fe-4S](2+) cluster is incorporated prior to the [3Fe-4S](1+) cluster. PMID:10692579

  10. SELF-CONVERGENCE OF RADIATIVELY COOLING CLUMPS IN THE INTERSTELLAR MEDIUM

    SciTech Connect

    Yirak, Kristopher; Frank, Adam; Cunningham, Andrew J.

    2010-10-10

    Isolated regions of higher density populate the interstellar medium (ISM) on all scales-from molecular clouds, to the star-forming regions known as cores, to heterogeneous ejecta found near planetary nebulae and supernova remnants. These clumps interact with winds and shocks from nearby energetic sources. Understanding the interactions of shocked clumps is vital to our understanding of the composition, morphology, and evolution of the ISM. The evolution of shocked clumps is well understood in the limiting 'adiabatic' case where physical processes such as self-gravity, heat conduction, radiative cooling, and magnetic fields are ignored. In this paper, we address the issue of evolution and convergence when one of these processes-radiative cooling-is included. Numeric convergence studies demonstrate that the evolution of an adiabatic clump is well captured by roughly 100 cells per clump radius. The presence of radiative cooling, however, imposes limits on the problem due to the removal of thermal energy. Numerical studies which include radiative cooling typically adopt the 100-200 cells per clump radius resolution. In this paper, we present the results of a convergence study for radiatively cooling clumps undertaken over a broad range of resolutions, from 12 to 1536 cells per clump radius, employing adaptive mesh refinement (AMR) in a two-dimensional axisymmetric geometry (2.5 dimensions). We also provide a fully three-dimensional simulation, at 192 cells per clump radius, which supports our 2.5 dimensional results. We find no appreciable self-convergence at {approx}100 cells per clump radius as small-scale differences owing to increasingly resolving the cooling length have global effects. We therefore conclude that self-convergence is an insufficient criterion to apply on its own when addressing the question of sufficient resolution for radiatively cooled shocked clump simulations. We suggest the adoption of alternate criteria to support a statement of sufficient

  11. THE CLUSTERING AND HALO MASSES OF STAR-FORMING GALAXIES AT z < 1

    SciTech Connect

    Dolley, Tim; Brown, Michael J. I.; Pimbblet, Kevin A.; Palamara, David P.; Beare, Richard; Weiner, Benjamin J.; Jannuzi, Buell T.; Brodwin, Mark; Kochanek, C. S.; Dey, Arjun; Atlee, David W.

    2014-12-20

    We present clustering measurements and halo masses of star-forming galaxies at 0.2 < z < 1.0. After excluding active galactic nuclei (AGNs), we construct a sample of 22,553 24 μm sources selected from 8.42 deg{sup 2} of the Spitzer MIPS AGN and Galaxy Evolution Survey of Boötes. Mid-infrared imaging allows us to observe galaxies with the highest star formation rates (SFRs), less biased by dust obscuration afflicting the optical bands. We find that the galaxies with the highest SFRs have optical colors that are redder than typical blue cloud galaxies, with many residing within the green valley. At z > 0.4 our sample is dominated by luminous infrared galaxies (LIRGs, L {sub TIR} > 10{sup 11} L {sub ☉}) and is composed entirely of LIRGs and ultraluminous infrared galaxies (ULIRGs, L {sub TIR} > 10{sup 12} L {sub ☉}) at z > 0.6. We observe weak clustering of r {sub 0} ≈ 3-6 h {sup –1} Mpc for almost all of our star-forming samples. We find that the clustering and halo mass depend on L {sub TIR} at all redshifts, where galaxies with higher L {sub TIR} (hence higher SFRs) have stronger clustering. Galaxies with the highest SFRs at each redshift typically reside within dark matter halos of M {sub halo} ≈ 10{sup 12.9} h {sup –1} M {sub ☉}. This is consistent with a transitional halo mass, above which star formation is largely truncated, although we cannot exclude that ULIRGs reside within higher mass halos. By modeling the clustering evolution of halos, we connect our star-forming galaxy samples to their local descendants. Most star-forming galaxies at z < 1.0 are the progenitors of L ≲ 2.5 L {sub *} blue galaxies in the local universe, but star-forming galaxies with the highest SFRs (L {sub TIR} ≳ 10{sup 11.7} L {sub ☉}) at 0.6 < z < 1.0 are the progenitors of early-type galaxies in denser group environments.

  12. Enteropathogenic Escherichia coli: identification of a gene cluster coding for bundle-forming pilus morphogenesis.

    PubMed Central

    Sohel, I; Puente, J L; Ramer, S W; Bieber, D; Wu, C Y; Schoolnik, G K

    1996-01-01

    Sequence flanking the bfpA locus on the enteroadherent factor plasmid of the enteropathogenic Escherichia coli (EPEC) strain B171-8 (O111:NM) was obtained to identify genes that might be required for bundle-forming pilus (BFP) biosynthesis. Deletion experiments led to the identification of a contiguous cluster of at least 12 open reading frames, including bfpA, that could direct the synthesis of a morphologically normal BFP filament. Within the bfp gene cluster, we identified open reading frames that share homology with other type IV pilus accessory genes and with genes required for transformation competence and protein secretion. Immediately upstream of the bfp gene cluster, we identified a potential replication origin including genes that are predicted to encode proteins homologous with replicase and resolvase. Restriction fragment length polymorphism analysis of DNA from six additional EPEC serotypes showed that the organization of the bfp gene cluster and its juxtaposition with a potential plasmid origin of replication are highly conserved features of the EPEC biotype. PMID:8626330

  13. The initial mass function of star clusters that form in turbulent molecular clouds

    NASA Astrophysics Data System (ADS)

    Fujii, M. S.; Portegies Zwart, S.

    2015-05-01

    We simulate the formation and evolution of young star clusters using the combination of smoothed particle hydrodynamics (SPH) simulations and direct N-body simulations. We start by performing SPH simulations of the giant molecular cloud (GMC) with a turbulent velocity field, a mass of 4 × 104 to 5 × 106 M⊙, and a density between ρ ˜ 1.7 × 103 and 170 cm-3. We continue the hydrodynamical simulations for a free-fall time-scale (tff ≃ 0.83 and 2.5 Myr), and analyse the resulting structure of the collapsed cloud. We subsequently replace a density-selected subset of SPH particles with stars by adopting a local star formation efficiency proportional to ρ1/2. As a consequence, the local star formation efficiency exceeds 30 per cent, whereas globally only a few per cent of the gas is converted to stars. The stellar distribution by the time gas is converted to stars is very clumpy, with typically a dozen bound conglomerates that consist of 100-104 stars. We continue to evolve the stars dynamically using the collisional N-body method, which accurately treats all pairwise interactions, stellar collisions and stellar evolution. We analyse the results of the N-body simulations when the stars have an age of 2 and 10 Myr. During the dynamical simulations, massive clusters grow via hierarchical merging of smaller clusters. The shape of the cluster mass function that originates from an individual molecular cloud is consistent with a Schechter function with a power-law slope of β = -1.73 at 2 Myr and β = -1.67 at 10 Myr, which fits to observed cluster mass function of the Carina region. The superposition of mass functions have a power-law slope of ≲ -2, which fits the observed mass function of star clusters in the Milky Way, M31 and M83. We further find that the mass of the most massive cluster formed in a single molecular cloud with a mass of Mg scales with 6.1 M_g^{0.51} which also agrees with recent observation of the GMC and young clusters in M51.

  14. Planck early results. XXII. The submillimetre properties of a sample of Galactic cold clumps

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Balbi, A.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoît, A.; Bernard, J.-P.; Bersanelli, M.; Bhatia, R.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Cabella, P.; Cantalupo, C. M.; Cardoso, J.-F.; Catalano, A.; Cayón, L.; Challinor, A.; Chamballu, A.; Chiang, L.-Y.; Christensen, P. R.; Clements, D. L.; Colombi, S.; Couchot, F.; Coulais, A.; Crill, B. P.; Cuttaia, F.; Danese, L.; Davies, R. D.; de Bernardis, P.; de Gasperis, G.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Désert, F.-X.; Dickinson, C.; Doi, Y.; Donzelli, S.; Doré, O.; Dörl, U.; Douspis, M.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Falgarone, E.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Galeotta, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Hansen, F. K.; Harrison, D.; Helou, G.; Henrot-Versillé, S.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hovest, W.; Hoyland, R. J.; Huffenberger, K. M.; Ikeda, N.; Jaffe, A. H.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kitamura, Y.; Kneissl, R.; Knox, L.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Laureijs, R. J.; Lawrence, C. R.; Leach, S.; Leonardi, R.; Leroy, C.; Linden-Vørnle, M.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; MacTavish, C. J.; Maffei, B.; Malinen, J.; Mandolesi, N.; Mann, R.; Maris, M.; Marshall, D. J.; Martin, P.; Martínez-González, E.; Masi, S.; Matarrese, S.; Matthai, F.; Mazzotta, P.; McGehee, P.; Melchiorri, A.; Mendes, L.; Mennella, A.; Meny, C.; Mitra, S.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; Osborne, S.; Pagani, L.; Pajot, F.; Paladini, R.; Pasian, F.; Patanchon, G.; Pelkonen, V.-M.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Poutanen, T.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Reach, W. T.; Rebolo, R.; Reinecke, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savini, G.; Scott, D.; Seiffert, M. D.; Smoot, G. F.; Starck, J.-L.; Stivoli, F.; Stolyarov, V.; Sudiwala, R.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Torre, J.-P.; Toth, V.; Tristram, M.; Tuovinen, J.; Umana, G.; Valenziano, L.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Ysard, N.; Yvon, D.; Zacchei, A.; Zonca, A.

    2011-12-01

    within factors of a few, to the gas linear mass densities. The analysis of this small set of cold clumps already probes a broad variety of structures in the C3PO sample, probably associated with different evolutionary stages, from cold and starless clumps, to young protostellar objects still embedded in their cold surrounding cloud. Because of the all-sky coverage and its sensitivity, Planck is able to detect and locate the coldest spots in massive elongated structures that may be the long-searched for progenitors of stellar clusters. Appendix A is available in electronic form at http://www.aanda.orgCorresponding author: I. Ristorcelli, e-mail: isabelle.ristorcelli@irap.omp.eu

  15. The Distance to the Galactic Center Derived from Infrared Photometry of Bulge Red Clump Stars

    NASA Astrophysics Data System (ADS)

    Nishiyama, Shogo; Nagata, Tetsuya; Sato, Shuji; Kato, Daisuke; Nagayama, Takahiro; Kusakabe, Nobuhiko; Matsunaga, Noriyuki; Naoi, Takahiro; Sugitani, Koji; Tamura, Motohide

    2006-08-01

    On the basis of the near-infrared observations of bulge red clump stars near the Galactic center, we have determined the galactocentric distance to be R0=7.52+/-0.10 (stat) +/-0.35 (sys) kpc. We observed the red clump stars at |l|<~1.0d and 0.7d<~|b|<~1.0d with the IRSF 1.4 m telescope and the SIRIUS camera in the H and KS bands. After extinction and population corrections, we obtained (m-M)0=14.38+/-0.03 (stat) +/- 0.10 (sys). The statistical error is dominated by the uncertainty of the intrinsic local red clump stars' luminosity. The systematic error is estimated to be +/-0.10, including uncertainties in extinction and population correction, zero point of photometry, and the fitting of the luminosity function of the red clump stars. Our result, R0=7.52 kpc, is in excellent agreement with the distance determined geometrically with the star orbiting the massive black hole in the Galactic center. The recent result based on the spatial distribution of globular clusters is also consistent with our result. In addition, our study exhibits that the distance determination to the Galactic center with the red clump stars, even if the error of the population correction is taken into account, can achieve an uncertainty of about 5%, which is almost the same level as that in recent geometrical determinations.

  16. Ejection of gaseous clumps from gravitationally unstable protostellar disks

    NASA Astrophysics Data System (ADS)

    Vorobyov, E. I.

    2016-05-01

    Aims: We investigate the dynamics of gaseous clumps formed via gravitational fragmentation in young protostellar disks, focusing on the fragments that are ejected from the disk via many-body gravitational interaction. Methods: Numerical hydrodynamics simulations were employed to study the evolution of young protostellar disks that were formed from the collapse of rotating pre-stellar cores. Results: The protostellar disks that formed in our models undergo gravitational fragmentation driven by continuing mass-loading from parental collapsing cores. Several fragments can be ejected from the disk during the early evolution, but the low-mass fragments (<15 MJup) disperse, which creates spectacular bow-type structures while passing through the disk and collapsing core. The least massive fragment that survived the ejection (21 MJup) straddles the planetary-mass limit, while the most massive ejected fragments (145 MJup) can break up into several pieces, leading to the ejection of wide separation binary clumps in the brown-dwarf mass range. About half of the ejected fragments are gravitationally bound, the majority are supported by rotation against gravity, and all fragments have the specific angular momentum that is much higher than that expected for brown dwarfs. We found that the internal structure of the ejected fragments is distinct from what would be expected for gravitationally contracting clumps formed via molecular cloud fragmentation, which can help in differentiating their origin. Conclusions: The ejection of fragments is an important process, which is inherent to massive protostellar disks, and which produces freely floating pre-brown dwarf cores, regulates the disk and stellar masses and, potentially, enriches the intracluster medium with processed dust and complex organics.

  17. The Hercules Cluster Environment Impact on the Chemical History of Star-Forming Galaxies

    NASA Astrophysics Data System (ADS)

    Petropoulou, V.; VíLchez, J. M.; Iglesias-Páramo, J.; Papaderos, P.

    In this work we study the effects of the Hercules cluster environment on the chemical history of star-forming (SF) galaxies. For this purpose we have derived the gas metallicities, the mean stellar metallicities and ages, the masses and the luminosities of our sample of galaxies. We have found that our Hercules SF galaxies are either chemically evolved spirals with nearly flat oxygen gradients, or less metal-rich dwarf galaxies which appear to be the "newcomers" in the cluster. Most Hercules SF galaxies follow well defined mass-metallicity and luminosity-metallicity sequences; nevertheless significant outliers to these relations have been identified, illustrating how environmental effects can provide a physical source of dispersion in these fundamental relations.

  18. Clumped Isotopes in Bahamian Dolomites: A Rosetta Stone?

    NASA Astrophysics Data System (ADS)

    Murray, S.; Swart, P. K.; Arienzo, M. M.

    2014-12-01

    Low temperature dolomite formation continues to be an enigmatic process. However, with the advent of the clumped isotope technique, there is an opportunity to determine the temperature of formation as well as the δ18O of the fluid (δ18Ow) from which it formed. By using samples with a well constrained geologic and thermal history, we have attempted to accurately develop a technique for the application of clumped isotopes to varying dolomite systems. Samples for this study were taken from two cores, one from the island of San Salvador and one on Great Bahama Bank (known as Clino), located on the eastern and western edges respectively of the Bahamian Archipelago. Both cores penetrate through Pleistocene to Miocene aged carbonates. The San Salvador core has a 110m section of pure, near stoichiometric dolomite, while the Clino core is of a mixed carbonate composition with varying abundances (0% - 50%) of calcian dolomite (42-46 mol % MgCO3). The water temperature profile of the Bahamas can be assumed over time due to the stable geology and no influence of higher temperature waters. Because of its location and the present burial depth, the largest influence on dolomite formation has been changes in sea level. As the dolomites from San Salvador are 100% dolomite, the Δ47 was determined directly. The Clino dolomites however were only partially dolomitized and so were treated with buffered acetic acid to remove non-dolomite carbonates. This was carried out in stages, using X-ray diffraction to determine composition, followed by the measurement of Δ47 after each leaching episode. Because the dolomite formation temperature and δ18Ow can be constrained, it becomes possible to evaluate the applicability of the multitude of clumped isotope correction schemes that have been applied to various dolomite samples. Also tested were several different equations which link temperature to the δ18O of the dolomite allowing the δ18O of the water to be calculated. This is a necessary

  19. Massive cold cloud clusters

    NASA Astrophysics Data System (ADS)

    Toth, L. Viktor; Marton, Gabor; Zahorecz, Sarolta

    2015-08-01

    The all-sky Planck catalogue of Galactic Cold Clumps (PGCC, Planck 2015 results XXVIII 2015) allows an almost unbiased study of the early phases of star-formation in our Galaxy. Several thousand of the clumps have also distance estimates allowing a mass, and density determination. The nature of Planck clumps varies from IRDCs to tiny nearby cold clouds with masses ranging from one to several tens of thousands solar masses. Some of the clumps are embedded in GMCs, others are isolated. Some are close or even very close to OB associations, while others lay far from any UV luminous objects.The small scale clustering of these objects was studied with the improved Minimum Spanning Tree method of Cartwright & Whitworth identifying groups in 3D space. As a result also massive cold cloud clusters were identified. We analyse the MST structures, and discuss their relation to ongoing and future massive star formation.

  20. HOW TO FIND YOUNG MASSIVE CLUSTER PROGENITORS

    SciTech Connect

    Bressert, E.; Longmore, S.; Testi, L.; Ginsburg, A.; Bally, J.; Battersby, C.

    2012-10-20

    We propose that bound, young massive stellar clusters form from dense clouds that have escape speeds greater than the sound speed in photo-ionized gas. In these clumps, radiative feedback in the form of gas ionization is bottled up, enabling star formation to proceed to sufficiently high efficiency so that the resulting star cluster remains bound even after gas removal. We estimate the observable properties of the massive proto-clusters (MPCs) for existing Galactic plane surveys and suggest how they may be sought in recent and upcoming extragalactic observations. These surveys will potentially provide a significant sample of MPC candidates that will allow us to better understand extreme star-formation and massive cluster formation in the Local Universe.

  1. How to Find Young Massive Cluster Progenitors

    NASA Astrophysics Data System (ADS)

    Bressert, E.; Ginsburg, A.; Bally, J.; Battersby, C.; Longmore, S.; Testi, L.

    2012-10-01

    We propose that bound, young massive stellar clusters form from dense clouds that have escape speeds greater than the sound speed in photo-ionized gas. In these clumps, radiative feedback in the form of gas ionization is bottled up, enabling star formation to proceed to sufficiently high efficiency so that the resulting star cluster remains bound even after gas removal. We estimate the observable properties of the massive proto-clusters (MPCs) for existing Galactic plane surveys and suggest how they may be sought in recent and upcoming extragalactic observations. These surveys will potentially provide a significant sample of MPC candidates that will allow us to better understand extreme star-formation and massive cluster formation in the Local Universe.

  2. Physical properties of Planck Cold Dust Clumps

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Liu, T.; Meng, F.; Yuan, J.; Zhang, T.; Chen, P.; Hu, R.; Li, D.; Qin, S.; Ju, B.

    2016-05-01

    To explore physical properties of Planck cold dust clumps, 674 of the pilot samples were observed at the 13.7 m telescope of Purple Mountain Observatory (PMO) in J = 1 - 0 transitions of CO, 13CO and C18O. HCO+, HCN and N2H+ emissions were also observed with PMO 13.7 m and IRAM 30 m telescopes. They are real cold and quiescent with mean Tk ˜ 10 K and mean FWHM of 13CO (1-0) 1.27 km s-1. Column density ranges from 1020 to 1022 cm-2. Gas of the Planck clumps extends molecular space in the Milky Way. Turbulence dominates in cores. Filament structure is the majority and most of the cores are starless. Ten percent of the cores show asymmetric emission features including blue- and red- profiles. Planck clumps include different cold or low luminosity sources. Dense cores constitute an ideal sample for studying initial state of star formation while the diffuse clumps are suitable for investigating the formation of cores.

  3. Familial clustering of the ataxic form of Creutzfeldt-Jakob disease with Hirano bodies.

    PubMed Central

    Cartier, L; Gálvez, S; Gajdusek, D C

    1985-01-01

    A family cluster of the ataxic form of Creutzfeldt-Jakob disease with one probable and two autopsy proven cases that occurred in a single generation between 1974 and 1982 is reported. The clinical characteristics of the cases are closely similar to those of kuru patients, with a fair correlation between the prominent truncal ataxia and the intense devastation of the cerebellar cortex most marked in the vermis. Pathologically, the marked hippocampal involvement rarely seen in typical transmissible Creutzfeldt-Jakob disease and the finding of Hirano bodies in the Ammon's horn without specific Alzheimer's senile changes are noteworthy features. Images PMID:2984334

  4. Carbonate clumped isotope thermometry in continental tectonics

    NASA Astrophysics Data System (ADS)

    Huntington, Katharine W.; Lechler, Alex R.

    2015-04-01

    Reconstructing the thermal history of minerals and fluids in continental environments is a cornerstone of tectonics research. Paleotemperature constraints from carbonate clumped isotope thermometry have provided important tests of geodynamic, structural, topographic and basin evolution models. The thermometer is based on the 13C-18O bond ordering in carbonates (mass-47 anomaly, Δ47) and provides estimates of the carbonate formation temperature independent of the δ18O value of the water from which the carbonate grew; Δ47 is measured simultaneously with conventional measurements of carbonate δ13C and δ18O values, which together constrain the isotopic composition of the parent water. Depending on the geologic setting of carbonate growth, this information can help constrain paleoenvironmental conditions or basin temperatures and fluid sources. This review examines how clumped isotope thermometry can shed new light on problems in continental tectonics, focusing on paleoaltimetry, basin evolution and structural diagenesis applications. Paleoaltimetry is inherently difficult, and the precision in carbonate growth temperature estimates is at the limit of what is useful for quantitative paleoelevation reconstruction. Nevertheless, clumped isotope analyses have enabled workers to address previously intractable problems and in many settings offer the best chance of understanding topographic change from the geologic record. The portion of the shallow crust residing at temperatures up to ca. 200 °C is important as host to economic resources and records of tectonics and climate, and clumped isotope thermometry is one of the few proxies that can access this critical range with sensitivity to temperature alone. Only a handful of studies to date have used clumped isotopes to investigate diagenesis and other sub-surface processes using carbonate crystallization temperatures or the sensitivity of Δ47 values to a sample's thermal history. However, the thermometer is

  5. The Spiderweb Galaxy: A Forming Massive Cluster Galaxy at z ~ 2

    NASA Astrophysics Data System (ADS)

    Miley, George K.; Overzier, Roderik A.; Zirm, Andrew W.; Ford, Holland C.; Kurk, Jaron; Pentericci, Laura; Blakeslee, John P.; Franx, Marijn; Illingworth, Garth D.; Postman, Marc; Rosati, Piero; Röttgering, Huub J. A.; Venemans, Bram P.; Helder, Eveline

    2006-10-01

    We present a deep image of the radio galaxy MRC 1138-262 taken with the Hubble Space Telescope (HST) at a redshift of z=2.2. The galaxy is known to have properties of a cD galaxy progenitor and be surrounded by a 3 Mpc-sized structure, identified with a protocluster. The morphology shown on the new deep HST ACS image is reminiscent of a spider's web. More than 10 individual clumpy features are observed, apparently star-forming satellite galaxies in the process of merging with the progenitor of a dominant cluster galaxy 11 Gyr ago. There is an extended emission component, implying that star formation was occurring over a 50×40 kpc region at a rate of more than 100 Msolar yr-1. A striking feature of the newly named ``Spiderweb galaxy'' is the presence of several faint linear galaxies within the merging structure. The dense environments and fast galaxy motions at the centers of protoclusters may stimulate the formation of these structures, which dominate the faint resolved galaxy populations in the Hubble Ultra Deep Field. The new image provides a unique testbed for simulations of forming dominant cluster galaxies.

  6. Heat conduction boundary layers of condensed clumps in cooling flows

    NASA Astrophysics Data System (ADS)

    Boehringer, H.; Fabian, A. C.

    1989-04-01

    The structure of heat conduction boundary layers of gaseous condensations embedded in the hot intergalactic gas in clusters of galaxies is investigated by means of steady, one-dimensional, hydrodynamic models. It is assumed that heat conduction is effective only on scales much smaller than the total region of the cooling flow. Models are calculated for an arbitrary scaling factor, accounting for the reduction in heat conduction efficiency compared to the classical Spitzer case. The results imply a lower limit to the size spectrum of the condensations. The enhancement of cooling in the ambient medium due to heat conduction losses is calculated for a range of clump parameters. The luminosity of several observable emission lines, the extreme ultraviolet (EUV) and soft X-ray emission spectrum, and the column density of some important ions are determined for the model boundary layers and compared with observations.

  7. Clump detections and limits on moons in Jupiter's ring system.

    PubMed

    Showalter, Mark R; Cheng, Andrew F; Weaver, Harold A; Stern, S Alan; Spencer, John R; Throop, Henry B; Birath, Emma M; Rose, Debi; Moore, Jeffrey M

    2007-10-12

    The dusty jovian ring system must be replenished continuously from embedded source bodies. The New Horizons spacecraft has performed a comprehensive search for kilometer-sized moons within the system, which might have revealed the larger members of this population. No new moons were found, however, indicating a sharp cutoff in the population of jovian bodies smaller than 8-kilometer-radius Adrastea. However, the search revealed two families of clumps in the main ring: one close pair and one cluster of three to five. All orbit within a brighter ringlet just interior to Adrastea. Their properties are very different from those of the few other clumpy rings known; the origin and nonrandom distribution of these features remain unexplained, but resonant confinement by Metis may play a role. PMID:17932287

  8. X-RAY EMISSION LINE PROFILES FROM WIND CLUMP BOW SHOCKS IN MASSIVE STARS

    SciTech Connect

    Ignace, R.; Waldron, W. L.; Cassinelli, J. P.; Burke, A. E. E-mail: wwaldron@satx.rr.com E-mail: burke.alexander@gmail.com

    2012-05-01

    The consequences of structured flows continue to be a pressing topic in relating spectral data to physical processes occurring in massive star winds. In a preceding paper, our group reported on hydrodynamic simulations of hypersonic flow past a rigid spherical clump to explore the structure of bow shocks that can form around wind clumps. Here we report on profiles of emission lines that arise from such bow shock morphologies. To compute emission line profiles, we adopt a two-component flow structure of wind and clumps using two 'beta' velocity laws. While individual bow shocks tend to generate double-horned emission line profiles, a group of bow shocks can lead to line profiles with a range of shapes with blueshifted peak emission that depends on the degree of X-ray photoabsorption by the interclump wind medium, the number of clump structures in the flow, and the radial distribution of the clumps. Using the two beta law prescription, the theoretical emission measure and temperature distribution throughout the wind can be derived. The emission measure tends to be power law, and the temperature distribution is broad in terms of wind velocity. Although restricted to the case of adiabatic cooling, our models highlight the influence of bow shock effects for hot plasma temperature and emission measure distributions in stellar winds and their impact on X-ray line profile shapes. Previous models have focused on geometrical considerations of the clumps and their distribution in the wind. Our results represent the first time that the temperature distribution of wind clump structures are explicitly and self-consistently accounted for in modeling X-ray line profile shapes for massive stars.

  9. Burial Diagenesis Effects on Clumped Isotope Signatures of Coexisting Dolomites and Calcites

    NASA Astrophysics Data System (ADS)

    Winkelstern, I. Z.; Lohmann, K. C.

    2014-12-01

    Carbonate clumped isotope paleothermometry is a promising method for diagenetic and deep time paleoclimate studies, but original clumped isotope (Δ47) compositions can be altered by fluid and thermal diagenetic processes. Previous work shows Δ47 resetting of calcite occurs at temperatures exceeding 100°C over time periods of millions of years, but such thermally-driven effects have not been considered for dolomite. Differences between calcite and dolomite temperature calibrations are also largely unquantified, and the effect of burial diagenesis on dolomite Δ47 has not been measured. Coexisting calcites and dolomites in a ~4500 meter core from Andros Island, Bahamas, offer a unique opportunity to address these questions. These dolomites and calcites formed over a time span from the Cretaceous to Pleistocene under near-surface temperature conditions. Clumped isotope analysis of this material reveals that where these carbonate phases are buried to depths greater than ~3000 meters, realistic surface temperatures (~25 °C) are not preserved. Moreover, these phases do not record reasonable geothermal conditions (> 80 °C), but rather record temperatures between 40 and 60°C. Here we evaluate whether this Δ47 "error" is due to solid-state resetting of clumped isotopes, emplacement of minor burial cements, fabric retentive recrystallization, or some combination thereof. Our results show that clumped isotope compositions of both calcite and dolomite respond similarly to diagenetic resetting of primary values under conditions of burial. These data further emphasize the need to constrain the diagenetic history of samples used for clumped isotope work. The similar Δ47 temperatures recorded by each carbonate type suggest that dolomites and calcites are equally viable temperature proxy sources under shallow burial conditions, yet both seem equally susceptible to "resetting" of their primary clumped isotope abundances.

  10. Stability of Galactic Gaseous Disks and the Formation of Massive Clusters

    SciTech Connect

    Escala, Andres; Larson, Richard B.

    2008-08-21

    We study gravitational instabilities in disks, with special attention to the most massive clumps that form because they are expected to be the progenitors of globular-type clusters. The maximum unstable mass is set by rotation and depends only on the surface density and orbital frequency of the disk. We propose that the formation of massive clusters is related to this largest scale in galaxies not stabilized by rotation. Using data from the literature, we predict that globular-like clusters can form in nuclear starburst disks and protogalactic disks but not in typical spiral galaxies, in agreement with observations.

  11. Spectroscopic and functional characterization of iron-sulfur cluster-bound forms of Azotobacter vinelandii (Nif)IscA.

    PubMed

    Mapolelo, Daphne T; Zhang, Bo; Naik, Sunil G; Huynh, Boi Hanh; Johnson, Michael K

    2012-10-16

    The mechanism of [4Fe-4S] cluster assembly on A-type Fe-S cluster assembly proteins, in general, and the specific role of (Nif)IscA in the maturation of nitrogen fixation proteins are currently unknown. To address these questions, in vitro spectroscopic studies (UV-visible absorption/CD, resonance Raman and Mössbauer) have been used to investigate the mechanism of [4Fe-4S] cluster assembly on Azotobacter vinelandii(Nif)IscA, and the ability of (Nif)IscA to accept clusters from NifU and to donate clusters to the apo form of the nitrogenase Fe-protein. The results show that (Nif)IscA can rapidly and reversibly cycle between forms containing one [2Fe-2S](2+) and one [4Fe-4S](2+) cluster per homodimer via DTT-induced two-electron reductive coupling of two [2Fe-2S](2+) clusters and O(2)-induced [4Fe-4S](2+) oxidative cleavage. This unique type of cluster interconversion in response to cellular redox status and oxygen levels is likely to be important for the specific role of A-type proteins in the maturation of [4Fe-4S] cluster-containing proteins under aerobic growth or oxidative stress conditions. Only the [4Fe-4S](2+)-(Nif)IscA was competent for rapid activation of apo-nitrogenase Fe protein under anaerobic conditions. Apo-(Nif)IscA was shown to accept clusters from [4Fe-4S] cluster-bound NifU via rapid intact cluster transfer, indicating a potential role as a cluster carrier for delivery of clusters assembled on NifU. Overall the results support the proposal that A-type proteins can function as carrier proteins for clusters assembled on U-type proteins and suggest that they are likely to supply [2Fe-2S] clusters rather than [4Fe-4S] for the maturation of [4Fe-4S] cluster-containing proteins under aerobic or oxidative stress growth conditions. PMID:23003323

  12. Far-ultraviolet morphology of star-forming filaments in cool core brightest cluster galaxies

    NASA Astrophysics Data System (ADS)

    Tremblay, G. R.; O'Dea, C. P.; Baum, S. A.; Mittal, R.; McDonald, M. A.; Combes, F.; Li, Y.; McNamara, B. R.; Bremer, M. N.; Clarke, T. E.; Donahue, M.; Edge, A. C.; Fabian, A. C.; Hamer, S. L.; Hogan, M. T.; Oonk, J. B. R.; Quillen, A. C.; Sanders, J. S.; Salomé, P.; Voit, G. M.

    2015-08-01

    We present a multiwavelength morphological analysis of star-forming clouds and filaments in the central (≲50 kpc) regions of 16 low-redshift (z < 0.3) cool core brightest cluster galaxies. New Hubble Space Telescope imaging of far-ultraviolet continuum emission from young (≲10 Myr), massive (≳5 M⊙) stars reveals filamentary and clumpy morphologies, which we quantify by means of structural indices. The FUV data are compared with X-ray, Lyα, narrow-band Hα, broad-band optical/IR, and radio maps, providing a high spatial resolution atlas of star formation locales relative to the ambient hot (˜107-8 K) and warm ionized (˜104 K) gas phases, as well as the old stellar population and radio-bright active galactic nucleus (AGN) outflows. Nearly half of the sample possesses kpc-scale filaments that, in projection, extend towards and around radio lobes and/or X-ray cavities. These filaments may have been uplifted by the propagating jet or buoyant X-ray bubble, or may have formed in situ by cloud collapse at the interface of a radio lobe or rapid cooling in a cavity's compressed shell. The morphological diversity of nearly the entire FUV sample is reproduced by recent hydrodynamical simulations in which the AGN powers a self-regulating rain of thermally unstable star-forming clouds that precipitate from the hot atmosphere. In this model, precipitation triggers where the cooling-to-free-fall time ratio is tcool/tff ˜ 10. This condition is roughly met at the maximal projected FUV radius for more than half of our sample, and clustering about this ratio is stronger for sources with higher star formation rates.

  13. Integrin-Matrix Clusters Form Podosome-like Adhesions in the Absence of Traction Forces

    PubMed Central

    Yu, Cheng-han; Rafiq, Nisha Bte Mohd; Krishnasamy, Anitha; Hartman, Kevin L.; Jones, Gareth E.; Bershadsky, Alexander D.; Sheetz, Michael P.

    2013-01-01

    Summary Matrix-activated integrins can form different adhesion structures. We report that nontransformed fibroblasts develop podosome-like adhesions when spread on fluid Arg-Gly-Asp peptide (RGD)-lipid surfaces, whereas they habitually form focal adhesions on rigid RGD glass surfaces. Similar to classic macrophage podosomes, the podosome-like adhesions are protrusive and characterized by doughnut-shaped RGD rings that surround characteristic core components including F-actin, N-WASP, and Arp2/Arp3. Furthermore, there are 18 podosome markers in these adhesions, though they lack matrix metalloproteinases that characterize invadopodia and podosomes of Src-transformed cells. When nontransformed cells develop force on integrin-RGD clusters by pulling RGD lipids to prefabricated rigid barriers (metal lines spaced by 1–2 μm), these podosomes fail to form and instead form focal adhesions. The formation of podosomes on fluid surfaces is mediated by local activation of phosphoinositide 3-kinase (PI3K) and the production of phosphatidylinositol-(3,4,5)-triphosphate (PIP3) in a FAK/PYK2-dependent manner. Enrichment of PIP3 precedes N-WASP activation and the recruitment of RhoA-GAP ARAP3. We propose that adhesion structures can be modulated by traction force development and that production of PIP3 stimulates podosome formation and subsequent RhoA downregulation in the absence of traction force. PMID:24290759

  14. THE CLUSTERED NATURE OF STAR FORMATION. PRE-MAIN-SEQUENCE CLUSTERS IN THE STAR-FORMING REGION NGC 602/N90 IN THE SMALL MAGELLANIC CLOUD

    SciTech Connect

    Gouliermis, Dimitrios A.; Gennaro, Mario; Schmeja, Stefan; Dolphin, Andrew E.; Tognelli, Emanuele; Prada Moroni, Pier Giorgio

    2012-03-20

    Located at the tip of the wing of the Small Magellanic Cloud (SMC), the star-forming region NGC 602/N90 is characterized by the H II nebular ring N90 and the young cluster of pre-main-sequence (PMS) and early-type main-sequence stars NGC 602, located in the central area of the ring. We present a thorough cluster analysis of the stellar sample identified with Hubble Space Telescope/Advanced Camera for Surveys in the region. We show that apart from the central cluster low-mass PMS stars are congregated in 13 additional small, compact sub-clusters at the periphery of NGC 602, identified in terms of their higher stellar density with respect to the average background density derived from star counts. We find that the spatial distribution of the PMS stars is bimodal, with an unusually large fraction ({approx}60%) of the total population being clustered, while the remaining is diffusely distributed in the intercluster area, covering the whole central part of the region. From the corresponding color-magnitude diagrams we disentangle an age difference of {approx}2.5 Myr between NGC 602 and the compact sub-clusters, which appear younger, on the basis of comparison of the brighter PMS stars with evolutionary models, which we accurately calculated for the metal abundance of the SMC. The diffuse PMS population appears to host stars as old as those in NGC 602. Almost all detected PMS sub-clusters appear to be centrally concentrated. When the complete PMS stellar sample, including both clustered and diffused stars, is considered in our cluster analysis, it appears as a single centrally concentrated stellar agglomeration, covering the whole central area of the region. Considering also the hot massive stars of the system, we find evidence that this agglomeration is hierarchically structured. Based on our findings, we propose a scenario according to which the region NGC 602/N90 experiences an active clustered star formation for the last {approx}5 Myr. The central cluster NGC 602 was

  15. A detailed study of the high-mass clump interacting with the bubble N10

    NASA Astrophysics Data System (ADS)

    Ma, Yingxiu; Zhou, Jianjun; Esimbek, Jarken; Ji, Weiguang; Wu, Gang; Yuan, Ye

    2013-06-01

    We performed a detailed study of the high-mass clump interacting with bubble N10 based on the spectral lines 12CO(3-2), HCO+(4-3), N2H+(4-3) and CH3OH(7(0,7)-6(0,6)) and continuum emission data at 450 μm and 850 μm released by CADC and Spitzer. A blue-shifted optically thick line 12CO(3-2) seems to indicate that the outer envelope of the high-mass clump is still falling toward the center. Detection of CH3OH(7(0,7)-6(0,6)) suggests that a hot core has formed around YSO N10-7. The position-velocity diagram of N2H+(4-3) indicates that the cold dense core of the clump has not been destroyed by the star formation activities. The mass of N10-7 is about 27.44 M ⊙. The ratio HCO+(4-3)/N2H+(4-3) in the outer part of the clump is larger than that in the inner part of it. The reason may be that the CO abundance relative to N2H+(4-3) is increased in the outer part of the high-mass clump, and more N2H+(4-3) were converted into HCO+(4-3).

  16. Nonequilibrium clumped isotope signals in microbial methane

    NASA Astrophysics Data System (ADS)

    Wang, David T.; Gruen, Danielle S.; Lollar, Barbara Sherwood; Hinrichs, Kai-Uwe; Stewart, Lucy C.; Holden, James F.; Hristov, Alexander N.; Pohlman, John W.; Morrill, Penny L.; Könneke, Martin; Delwiche, Kyle B.; Reeves, Eoghan P.; Sutcliffe, Chelsea N.; Ritter, Daniel J.; Seewald, Jeffrey S.; McIntosh, Jennifer C.; Hemond, Harold F.; Kubo, Michael D.; Cardace, Dawn; Hoehler, Tori M.; Ono, Shuhei

    2015-04-01

    Methane is a key component in the global carbon cycle, with a wide range of anthropogenic and natural sources. Although isotopic compositions of methane have traditionally aided source identification, the abundance of its multiply substituted “clumped” isotopologues (for example, 13CH3D) has recently emerged as a proxy for determining methane-formation temperatures. However, the effect of biological processes on methane’s clumped isotopologue signature is poorly constrained. We show that methanogenesis proceeding at relatively high rates in cattle, surface environments, and laboratory cultures exerts kinetic control on 13CH3D abundances and results in anomalously elevated formation-temperature estimates. We demonstrate quantitatively that H2 availability accounts for this effect. Clumped methane thermometry can therefore provide constraints on the generation of methane in diverse settings, including continental serpentinization sites and ancient, deep groundwaters.

  17. Nonequilibrium clumped isotope signals in microbial methane

    USGS Publications Warehouse

    Wang, David T.; Gruen, Danielle S.; Lollar, Barbara Sherwood; Hinrichs, Kai-Uwe; Stewart, Lucy C.; Holden, James F.; Hristov, Alexander N.; Pohlman, John W.; Morrill, Penny L.; Könneke, Martin; Delwiche, Kyle B.; Reeves, Eoghan P.; Sutcliffe, Chelsea N.; Ritter, Daniel J.; Seewald, Jeffrey S.; McIntosh, Jennifer C.; Hemond, Harold F.; Kubo, Michael D.; Cardace, Dawn; Hoehler, Tori M.; Ono, Shuhei

    2015-01-01

    Methane is a key component in the global carbon cycle with a wide range of anthropogenic and natural sources. Although isotopic compositions of methane have traditionally aided source identification, the abundance of its multiply-substituted “clumped” isotopologues, e.g., 13CH3D, has recently emerged as a proxy for determining methane-formation temperatures; however, the impact of biological processes on methane’s clumped isotopologue signature is poorly constrained. We show that methanogenesis proceeding at relatively high rates in cattle, surface environments, and laboratory cultures exerts kinetic control on 13CH3D abundances and results in anomalously elevated formation temperature estimates. We demonstrate quantitatively that H2 availability accounts for this effect. Clumped methane thermometry can therefore provide constraints on the generation of methane in diverse settings, including continental serpentinization sites and ancient, deep groundwaters.

  18. The Census of High- and Medium-mass Protostars (CHaMP): From Molecular Clouds to Massive Young Clusters

    NASA Astrophysics Data System (ADS)

    Barnes, Peter

    2015-08-01

    I review the major science outcomes to date of the Galactic Census of High- and Medium-mass Protostars, and also report the latest observational results on this unbiased, uniform sample of massive, cluster-forming molecular clumps, based on new mm-wave and IR data. These clouds represent the vast, subthermally-excited population of clumps predicted by Narayanan et al (2008) to dominate the molecular mass of disk galaxies. Besides confirming their existence, we have presented evidence that these massive clumps probably spend a large fraction (90-95%) of their long lives (possibly up to 100 Myr) in a mostly quiescent, low star formation rate (SFR) state, which is likely ended when a density or internal pressure threshold is crossed, after which vigorous, massive cluster formation consumes the densest gas with a high SFR, dispersing the embedding envelope. New results presented in two posters at this Symposium include (1) the first analysis of HCN emission from the dense gas using a full LTE solution for the column density from the hyperfine line ratios (Schap et al), which identifies low-luminosity but high-column areas that significantly increase the clumps' mass estimates, and (2) the first deep photometry of clusters in this sample based on NIR AAT and CTIO data and MIR Warm Spitzer IRAC data (Dallilar et al), which gives basic cluster parameters such as mass and luminosity as well as the associated star formation efficiency (SFE).

  19. The long lives of giant clumps and the birth of outflows in gas-rich galaxies at high redshift

    SciTech Connect

    Bournaud, Frédéric; Renaud, Florent; Daddi, Emanuele; Duc, Pierre-Alain; Elbaz, David; Gabor, Jared M.; Juneau, Stéphanie; Kraljic, Katarina; Le Floch', Emeric; Dekel, Avishai; Elmegreen, Bruce G.; Elmegreen, Debra M.; Teyssier, Romain

    2014-01-01

    Star-forming disk galaxies at high redshift are often subject to violent disk instability, characterized by giant clumps whose fate is yet to be understood. The main question is whether the clumps disrupt within their dynamical timescale (≤50 Myr), like the molecular clouds in today's galaxies, or whether they survive stellar feedback for more than a disk orbital time (≈300 Myr) in which case they can migrate inward and help building the central bulge. We present 3.5-7 pc resolution adaptive mesh refinement simulations of high-redshift disks including photoionization, radiation pressure, and supernovae feedback. Our modeling of radiation pressure determines the mass loading and initial velocity of winds from basic physical principles. We find that the giant clumps produce steady outflow rates comparable to and sometimes somewhat larger than their star formation rate, with velocities largely sufficient to escape the galaxy. The clumps also lose mass, especially old stars, by tidal stripping, and the stellar populations contained in the clumps hence remain relatively young (≤200 Myr), as observed. The clumps survive gaseous outflows and stellar loss, because they are wandering in gas-rich turbulent disks from which they can reaccrete gas at high rates compensating for outflows and tidal stripping, overall keeping realistic and self-regulated gaseous and stellar masses. The outflow and accretion rates have specific timescales of a few 10{sup 8} yr, as opposed to rapid and repeated dispersion and reformation of clumps. Our simulations produce gaseous outflows with velocities, densities, and mass loading consistent with observations, and at the same time suggest that the giant clumps survive for hundreds of Myr and complete their migration to the center of high-redshift galaxies. These long-lived clumps are gas-dominated and contain a moderate mass fraction of stars; they drive inside-out disk evolution, thickening, spheroid growth, and fueling of the central

  20. Multi-seeded multi-mode formation of embedded clusters in the RMC: Clusters formed in swept-up shells

    NASA Astrophysics Data System (ADS)

    Li, J. Z.; Smith, M. D.

    2005-03-01

    This is the first of a series of three papers on clustered star formation in the Rosette Molecular Complex. Here we investigate star formation in the interfacing layers between the expanding Rosette Nebula and its surrounding cloud, based on an analysis of the spatially complete and unbiased 2MASS data. Two medium-mass infrared clusters with ages of around 1 Myr are identified in the south and south-east arcs of the fragmented shell. The majority of the candidate cluster members in these radiation and pressure-confined regions are found to be almost uniformly distributed, roughly following the compression layers traced by the distribution of optical depth at 100 μm, and may well develop into gravitationally unbound systems upon their emergence from the parental cloud. These expanding shells are believed to be playing important roles in impeding the emerging young open cluster NGC 2244 from intruding immediately and deeply into the ambient molecular cloud, where sequential formation of massive clusters is taking place. This publication makes use of 2MASS, the Two Micron All Sky Survey, a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by the National Aeronautics and Space administration and the National Science Foundation.

  1. Multi-wavelength characterisation of z ~ 2 clustered, dusty star-forming galaxies discovered by Planck

    NASA Astrophysics Data System (ADS)

    Flores-Cacho, I.; Pierini, D.; Soucail, G.; Montier, L.; Dole, H.; Pointecouteau, E.; Pelló, R.; Le Floc'h, E.; Nesvadba, N.; Lagache, G.; Guery, D.; Cañameras, R.

    2016-01-01

    that Planck data can be used to detect the emission from clustered, dusty star-forming galaxies at high z, and, thus, to pierce through the early growth of cluster-scale structures.

  2. Centenarian scientists: an unusual cluster newly formed in the 20th century.

    PubMed

    Sri Kantha, S

    2001-12-01

    From biographical data sources on ranking scientists, I was able to identify 35 centenarians. Among these, only one (Michel Chevereul from France) lived before the 20th century. Since the remaining 34 individuals became centenarians only from 1965, I propose that centenarian scientists are an unusual cluster, first formed in the 20th century. Among these, all except one (Alice Hamilton) were men. Six centenarian scientists, including Hamilton, had received professional medical training. The nationality ranks of the 34 centenarian scientists identified in the 20th century show 26 Americans, 6 British, one German and one French. Four of the 26 Americans were immigrants from Europe. At least three centenarians, namely Michael Heidelberger, Nathaniel Kleitman and Victor Hamburger, belong to the 'Nobel class' category, being pioneers in the disciplines of immunochemistry, sleep physiology and neuroembryology respectively. PMID:11918440

  3. METAL FORMING AND FABRICATION CLUSTER--AN INVESTIGATION AND DEVELOPMENT OF THE CLUSTER CONCEPT AS A PROGRAM IN VOCATIONAL EDUCATION AT THE SECONDARY LEVEL.

    ERIC Educational Resources Information Center

    MALEY, DONALD

    THIS COURSE OUTLINE ON METAL FORMING AND FABRICATION IS PART OF THE FINAL REPORT ON "CLUSTER CONCEPT" COURSES IN VOCATIONAL EDUCATION FOR SECONDARY EDUCATION (ED 010 301). EACH JOB ENTRY TASK WAS ANALYZED FOR HUMAN REQUIREMENTS (COMMUNICATION,MEASUREMENT, MATHEMATICS, SCIENCE, SKILLS, AND INFORMATION) NECESSARY TO PERFORMANCE OF THE TASK. THE TASK…

  4. Spherical cluster ensembles with fractal structure in LaSrMnO: New form of self-organization in solids

    NASA Astrophysics Data System (ADS)

    Okunev, V. D.; Samoilenko, Z. A.; Szymczak, H.; Szymczak, R.; Burkhovetski, V. V.; Lewandowski, S. J.

    2013-04-01

    The growth of La0.7Sr0.3MnO3 films in magnetron plasma, in special conditions, leads to the appearance of ensembles of micron-sized spherical crystalline clusters with fractal structure, which we consider to be a new form of self-organization in solids. Each ensemble contains 105-106 elementary clusters, 100-250 Å in diameter. Interaction of the clusters in the ensemble is realized through the interatomic chemical bonds, intrinsic to the manganites. Integration of peripheral areas of interacting clusters results in the formation of common intercluster medium in the ensemble. We argue that the ensembles with fractal structure built into paramagnetic disordered matrix have ferromagnetic properties. Absence of sharp borders between elementary clusters and the presence of common intercluster medium inside each ensemble permits to rearrange magnetic order and to change the volume of the ferromagnetic phase, providing automatically a high sensitivity of the material to the external field.

  5. ATCA survey of ammonia in the galactic center: The temperatures of dense gas clumps between Sgr A* and Sgr B2

    SciTech Connect

    Ott, Jürgen; Weiß, Axel; Henkel, Christian; Staveley-Smith, Lister; Meier, David S. E-mail: aweiss@mpifr-bonn.mpg.de E-mail: Lister.Staveley-Smith@uwa.edu.au

    2014-04-10

    We present a large-scale, interferometric survey of ammonia (1, 1) and (2, 2) toward the Galactic center observed with the Australia Telescope Compact Array. The survey covers Δℓ ∼ 1° (∼150 pc at an assumed distance of 8.5 kpc) and Δb ∼ 0.°2 (∼30 pc) which spans the region between the supermassive black hole Sgr A* and the massive star forming region Sgr B2. The resolution is ∼20'' (∼0.8 pc) and emission at scales ≳ 2' (≳ 3.2 pc) is filtered out due to missing interferometric short spacings. Consequently, the data represent the denser, compact clouds and disregards the large-scale, diffuse gas. Many of the clumps align with the 100 pc dust ring and mostly anti-correlate with 1.2 cm continuum emission. We present a kinetic temperature map of the dense gas. The temperature distribution peaks at ∼38 K with a width at half maximum between 18 K and 61 K (measurements sensitive within T {sub kin} ∼ 10-80 K). Larger clumps are on average warmer than smaller clumps which suggests internal heating sources. Our observations indicate that the circumnuclear disk ∼1.5 pc around Sgr A* is supplied with gas from the 20 km s{sup –1} molecular cloud. This gas is substantially cooler than gas ∼3-15 pc away from Sgr A*. We find a strong temperature gradient across Sgr B2. Ammonia column densities correlate well with SCUBA 850 μm fluxes, but the relation is shifted from the origin, which may indicate a requirement for a minimum amount of dust to form and shield ammonia. Around the Arches and Quintuplet clusters we find shell morphologies with UV-influenced gas in their centers, followed by ammonia and radio continuum layers.

  6. Size, Kinetics, and Free Energy of Clusters Formed by Ultraweak Carbohydrate-Carbohydrate Bonds.

    PubMed

    Witt, Hannes; Savić, Filip; Oelkers, Marieelen; Awan, Shahid I; Werz, Daniel B; Geil, Burkhard; Janshoff, Andreas

    2016-04-12

    Weak noncovalent intermolecular interactions play a pivotal role in many biological processes such as cell adhesion or immunology, where the overall binding strength is controlled through bond association and dissociation dynamics as well as the cooperative action of many parallel bonds. Among the various molecules participating in weak bonds, carbohydrate-carbohydrate interactions are probably the most ancient ones allowing individual cells to reversibly enter the multicellular state and to tell apart self and nonself cells. Here, we scrutinized the kinetics and thermodynamics of small homomeric Lewis X-Lewis X ensembles formed in the contact zone of a membrane-coated colloidal probe and a solid supported membrane ensuring minimal nonspecific background interactions. We used an atomic force microscope to measure force distance curves at Piconewton resolution, which allowed us to measure the force due to unbinding of the colloidal probe and the planar membrane as a function of contact time. Applying a contact model, we could estimate the free binding energy of the formed adhesion cluster as a function of dwell time and thereby determine the precise size of the contact zone, the number of participating bonds, and the intrinsic rates of association and dissociation in the presence of calcium ions. The unbinding energy per bond was found to be on the order of 1 kBT. Approximately 30 bonds were opened simultaneously at an off-rate of koff = 7 ± 0.2 s(-1). PMID:27074683

  7. A multinuclear copper(I) cluster forms the dimerization interface in copper-loaded human copper chaperone for superoxide dismutase.

    PubMed

    Stasser, Jay P; Siluvai, Gnana S; Barry, Amanda N; Blackburn, Ninian J

    2007-10-23

    Copper binding and X-ray aborption spectroscopy studies are reported on untagged human CCS (hCCS; CCS = copper chaperone for superoxide dismutase) isolated using an intein self-cleaving vector and on single and double Cys to Ala mutants of the hCCS MTCQSC and CSC motifs of domains 1 (D1) and 3 (D3), respectively. The results on the wild-type protein confirmed earlier findings on the CCS-MBP (maltose binding protein) constructs, namely, that Cu(I) coordinates to the CXC motif, forming a cluster at the interface of two D3 polypeptides. In contrast to the single Cys to Ser mutations of the CCS-MBP protein (Stasser, J. P., Eisses, J. F., Barry, A. N., Kaplan, J. H., and Blackburn, N. J. (2005) Biochemistry 44, 3143-3152), single Cys to Ala mutations in D3 were sufficient to eliminate cluster formation and significantly reduce CCS activity. Analysis of the intensity of the Cu-Cu cluster interaction in C244A, C246A, and C244/246A variants suggested that the nuclearity of the cluster was greater than 2 and was most consistent with a Cu4S6 adamantane-type species. The relationship among cluster formation, oligomerization, and metal loading was evaluated. The results support a model in which Cu(I) binding converts the apo dimer with a D2-D2 interface to a new dimer connected by cluster formation at two D3 CSC motifs. The predominance of dimer over tetramer in the cluster-containing species strongly suggests that the D2 dimer interface remains open and available for sequestering an SOD1 monomer. This work implicates the copper cluster in the reactive form and adds detail to the cluster nuclearity and how copper loading affects the oligomerization states and reactivity of CCS for its partner SOD1. PMID:17902702

  8. A Multinuclear Copper(I) Cluster Forms the Dimerization Interface in Copper-Loaded Human Copper Chaperone for Superoxide Dismutase

    SciTech Connect

    Stasser, J.P.; Siluvai, G.S.; Barry, A.N.; Blackburn, N.J.

    2009-06-04

    Copper binding and X-ray aborption spectroscopy studies are reported on untagged human CCS (hCCS; CCS = copper chaperone for superoxide dismutase) isolated using an intein self-cleaving vector and on single and double Cys to Ala mutants of the hCCS MTCQSC and CSC motifs of domains 1 (D1) and 3 (D3), respectively. The results on the wild-type protein confirmed earlier findings on the CCS-MBP (maltose binding protein) constructs, namely, that Cu(I) coordinates to the CXC motif, forming a cluster at the interface of two D3 polypeptides. In contrast to the single Cys to Ser mutations of the CCS-MBP protein (Stasser, J. P., Eisses, J. F., Barry, A. N., Kaplan, J. H., and Blackburn, N. J. (2005) Biochemistry 44, 3143-3152), single Cys to Ala mutations in D3 were sufficient to eliminate cluster formation and significantly reduce CCS activity. Analysis of the intensity of the Cu-Cu cluster interaction in C244A, C246A, and C244/246A variants suggested that the nuclearity of the cluster was greater than 2 and was most consistent with a Cu4S6 adamantane-type species. The relationship among cluster formation, oligomerization, and metal loading was evaluated. The results support a model in which Cu(I) binding converts the apo dimer with a D2-D2 interface to a new dimer connected by cluster formation at two D3 CSC motifs. The predominance of dimer over tetramer in the cluster-containing species strongly suggests that the D2 dimer interface remains open and available for sequestering an SOD1 monomer. This work implicates the copper cluster in the reactive form and adds detail to the cluster nuclearity and how copper loading affects the oligomerization states and reactivity of CCS for its partner SOD1.

  9. The initial conditions of stellar protocluster formation - II. A catalogue of starless and protostellar clumps embedded in IRDCs in the Galactic longitude range 15° ≤ l ≤ 55°

    NASA Astrophysics Data System (ADS)

    Traficante, A.; Fuller, G. A.; Peretto, N.; Pineda, J. E.; Molinari, S.

    2015-08-01

    We present a catalogue of starless and protostellar clumps associated with infrared dark clouds (IRDCs) in a 40° wide region of the inner Galactic plane (|b| ≤ 1°). We have extracted the far-infrared (FIR) counterparts of 3493 IRDCs with known distance in the Galactic longitude range 15° ≤ l ≤ 55° and searched for the young clumps using Herschel infrared Galactic plane survey, the survey of the Galactic plane carried out with the Herschel satellite. Each clump is identified as a compact source detected at 160, 250 and 350 μm. The clumps have been classified as protostellar or starless, based on their emission (or lack of emission) at 70 μm. We identify 1723 clumps, 1056 (61 per cent) of which are protostellar and 667 (39 per cent) starless. These clumps are found within 764 different IRDCs, 375 (49 per cent) of which are only associated with protostellar clumps, 178 (23 per cent) only with starless clumps, and 211 (28 per cent) with both categories of clumps. The clumps have a median mass of ˜250 M⊙ and range up to >104 M⊙ in mass and up to 105 L⊙ in luminosity. The mass-radius distribution shows that almost 30 per cent of the starless clumps identified in this survey could form high-mass stars; however these massive clumps are confined in only ≃4 per cent of the IRDCs. Assuming a minimum mass surface density threshold for the formation of high-mass stars, the comparison of the numbers of massive starless clumps and those already containing embedded sources suggests an upper limit lifetime for the starless phase of ˜105 yr for clumps with a mass M > 500 M⊙.

  10. Clumps and Temporal Changes in the Jovian Ring System as Viewed by New Horizons

    NASA Astrophysics Data System (ADS)

    Showalter, Mark R.; Cheng, A. F.; Weaver, H. A.; Stern, S. A.; Spencer, J. R.; Throop, H.; Birath, E. M.; Rose, D.; Moore, J. M.

    2007-10-01

    New Horizons obtained 400 ring images of the Jovian ring system using the Long Range Reconnaissance Imager (LORRI). This camera has a broad bandpass spanning wavelengths λ = 0.35 to 0.85 µm. The ring was imaged at phase angles 7°-159°. In addition, one sequence of near-IR spectra (λ = 1.25 to 2.5 µm) was obtained by the Linear Etalon Imaging Spectral Array (LEISA) for compositional studies. Two ring rotation movies during Jupiter approach were used to search for small moons embedded within the system. These bodies might serve as source bodies for the prevalent ring dust. No moons were detected down to a threshold of 500 m radius, suggesting a sharp cutoff in the population of inner Jovian moons below 8-km Adrastea. Although this search focused on the main Jovian ring, any 1-km moons from orbital radius r = 100,000 km to beyond the orbit of Amalthea (r = 181,000 km) should have been detected multiple times. More surprisingly, the ring revealed two clusters of tiny clumps, one pair and one set of three. These are definitively not moons because they have longitudinal extents of a few tenths of a degree. Separations between clumps are 2 to 4° but are not uniform. These clump families both orbit within a brightness peak just interior to the orbit of Adrastea, at r = 128,740 km. Their origin is unknown. They are not visible at high phase angles, indicating that they are composed primarily of larger "parent” bodies, not dust. They are definitely not related to a clump detected in Cassini images of the Jovian ring from December 2000, indicating that at least some ring clumps are transient. The large quadrant asymmetries reported in earlier images from Voyager and Galileo are completely absent in the new data.

  11. Clumped Methane Isotopologue Temperatures of Microbial Methane

    NASA Astrophysics Data System (ADS)

    Ono, S.; Wang, D. T.; Gruen, D.; Delwiche, K.; Hemond, H.; Pohlman, J.

    2014-12-01

    We will report the abundance of 13CH3D, a clumped isotopologue of methane, in microbial methane sampled from natural environments. They yield some expected and some unexpected results reflecting both equilibrium and kinetic isotope effects controlling the abundance of 13CH3D in low temperature environments. The four isotopologues of methane (12CH4, 13CH4, 12CH3D and 13CH3D) were measured by a tunable infrared spectroscopy method at a precision of 0.2‰ and accuracy of 0.5‰ (Ono et al., 2014). Similar to carbonate clumped isotope thermometry, clumped isotopologues of methane become more stable at lower temperatures. The equilibrium constant for the isotope exchange reaction 13CH4 + 12CH3D ⇌ 13CH3D + 12CH4 deviates from unity by +6.3 to +3.5 ‰ for methane equilibrated between 4 and 121 °C, a range expected for microbial methanogenesis. This would be measurably-distinct from a thermogenic methane signal, which typically have apparent 13CH3D-based temperatures ranging from 150 to 220 °C (+3.0 to +2.2 ‰ clumped isotope effect; Ono et al., 2014; Stolper et al. 2014). Marine samples, such as methane clathrates and porewater methane from the Cascadia margin, have 13CH3D-based temperatures that appear to be consistent with isotopic equilibration at in situ temperatures that are reasonable for deep sedimentary environments. In contrast, methane from freshwater environments, such as a lake and a swamp, yield apparent temperatures that are much higher than the known or inferred environmental temperature. Mixing of two or more distinct sources of methane could potentially generate this high temperature bias. We suggest, however, that this high-temperature bias likely reflects a kinetic isotope fractionation intrinsic to methanogenesis in fresh water environments. In contrast, the low-temperature signals from marine methane could be related to the slow metabolic rates and reversibility of microbial methanogenesis and methanotrophy in marine sedimentary environments

  12. Gravitational microlensing as a probe for dark matter clumps

    NASA Astrophysics Data System (ADS)

    Fedorova, E.; Sliusar, V. M.; Zhdanov, V. I.; Alexandrov, A. N.; Del Popolo, A.; Surdej, J.

    2016-04-01

    Extended dark matter (DM) substructures may play the role of microlenses in the Milky Way and in extragalactic gravitational lens systems (GLSs). We compare microlensing effects caused by point masses (Schwarzschild lenses) and extended clumps of matter using a simple model for the lens mapping. A superposition of the point mass and the extended clump is also considered. For special choices of the parameters, this model may represent a cusped clump of cold DM, a cored clump of self-interacting dark matter (SIDM) or an ultra-compact minihalo of DM surrounding a massive point-like object. We built the resulting micro-amplification curves for various parameters of one clump moving with respect to the source in order to estimate differences between the light curves caused by clumps and by point lenses. The results show that it may be difficult to distinguish between these models. However, some region of the clump parameters can be restricted by considering the high amplification events at the present level of photometric accuracy. Then we estimate the statistical properties of the amplification curves in extragalactic GLSs. For this purpose, an ensemble of amplification curves is generated yielding the autocorrelation functions (ACFs) of the curves for different choices of the system parameters. We find that there can be a significant difference between these ACFs if the clump size is comparable with typical Einstein radii; as a rule, the contribution of clumps makes the ACFs less steep.

  13. Astrophysics. Multiple images of a highly magnified supernova formed by an early-type cluster galaxy lens.

    PubMed

    Kelly, Patrick L; Rodney, Steven A; Treu, Tommaso; Foley, Ryan J; Brammer, Gabriel; Schmidt, Kasper B; Zitrin, Adi; Sonnenfeld, Alessandro; Strolger, Louis-Gregory; Graur, Or; Filippenko, Alexei V; Jha, Saurabh W; Riess, Adam G; Bradac, Marusa; Weiner, Benjamin J; Scolnic, Daniel; Malkan, Matthew A; von der Linden, Anja; Trenti, Michele; Hjorth, Jens; Gavazzi, Raphael; Fontana, Adriano; Merten, Julian C; McCully, Curtis; Jones, Tucker; Postman, Marc; Dressler, Alan; Patel, Brandon; Cenko, S Bradley; Graham, Melissa L; Tucker, Bradley E

    2015-03-01

    In 1964, Refsdal hypothesized that a supernova whose light traversed multiple paths around a strong gravitational lens could be used to measure the rate of cosmic expansion. We report the discovery of such a system. In Hubble Space Telescope imaging, we have found four images of a single supernova forming an Einstein cross configuration around a redshift z = 0.54 elliptical galaxy in the MACS J1149.6+2223 cluster. The cluster's gravitational potential also creates multiple images of the z = 1.49 spiral supernova host galaxy, and a future appearance of the supernova elsewhere in the cluster field is expected. The magnifications and staggered arrivals of the supernova images probe the cosmic expansion rate, as well as the distribution of matter in the galaxy and cluster lenses. PMID:25745167

  14. The Milky Way Project and ATLASGAL: The Distribution and Physical Properties of Cold Clumps Near Infrared Bubbles

    NASA Astrophysics Data System (ADS)

    Kendrew, Sarah; Beuther, Henrik; Simpson, Robert; Csengeri, Timea; Wienen, Marion; Lintott, Chris. J.; Povich, Matthew S.; Beaumont, Chris; Schuller, Frédéric

    2016-07-01

    We present a statistical study of the distribution and physical properties of cold, dense material in and around the inner Galactic Plane near-infrared bubbles as cataloged by the Milky Way Project citizen scientists. Using data from the Atacama Pathfinder Experiment (APEX) Telescope Large Area Survey of the Galaxy 870 μm survey, we show that 48 ± 2% of all cold clumps in the studied survey region (| l| ≤slant 65^\\circ , | b| ≤slant 1^\\circ ) are found in close proximity to a bubble, and 25 ± 2% appear directly projected toward a bubble rim. A two-point correlation analysis confirms the strong correlation of massive cold clumps with expanding bubbles. It shows an overdensity of clumps along bubble rims that grows with increasing bubble size, which shows how interstellar medium material is reordered on large scales by bubble expansion around regions of massive star formation. The highest column density clumps appear to be resistent to the expansion, remaining overdense toward the bubbles’ interior rather than being swept up by the expanding edge. Spectroscopic observations in ammonia show that cold dust clumps near bubbles appear to be denser, hotter, and more turbulent than those in the field, offering circumstantial evidence that bubble-associated clumps are more likely to be forming stars. These observed differences in physical conditions persist beyond the region of the bubble rims.

  15. Characterization of [4Fe-4S]-containing and cluster-free forms of Streptomyces WhiD

    PubMed Central

    Crack, Jason C.; den Hengst, Chris D.; Jakimowicz, Piotr; Subramanian, Sowmya; Johnson, Michael K.; Buttner, Mark J.; Thomson, Andrew J.; Le Brun, Nick E.

    2009-01-01

    WhiD, a member of the WhiB-like (Wbl) family of iron-sulfur proteins found exclusively within the actinomycetes, is required for the late stages of sporulation in Streptomyces coelicolor. Like all other Wbl proteins, WhiD has not so far been purified in a soluble form that contains a significant amount of cluster and characterization has relied on cluster-reconstituted protein. Thus, a major goal in Wbl research is to obtain and characterize native protein containing iron-sulfur clusters. Here we report the analysis of S. coelicolor WhiD purified anaerobically from E. coli as a soluble protein containing a single [4Fe-4S]2+ cluster ligated by four cysteines. Upon exposure to oxygen, spectral features associated with the [4Fe-4S] cluster were lost in a slow reaction that unusually yielded apo-WhiD directly without significant concentrations of cluster intermediates. This process was found to be highly pH dependent with an optimal stability observed between pH 7.0 and 8.0. Low molecular weight thiols, including a mycothiol analogue and thioredoxin, exerted a small but significant protective effect against WhiD cluster loss, an activity that could be of physiological importance. [4Fe-4S]2+ WhiD was found to react much more rapidly with superoxide than with either oxygen or hydrogen peroxide, which may also be of physiological significance. Loss of the [4Fe-4S] cluster to form apo-protein destabilized the protein fold significantly, but did not lead to complete unfolding. Finally, apo-WhiD exhibited negligible activity in an insulin-based disulfide reductase assay demonstrating that it does not function as a general protein disulfide reductase. PMID:19954209

  16. Massive Clumps in Local Galaxies: Comparisons with High-redshift Clumps

    NASA Astrophysics Data System (ADS)

    Elmegreen, Bruce G.; Elmegreen, Debra Meloy; Sánchez Almeida, J.; Muñoz-Tuñón, C.; Dewberry, J.; Putko, J.; Teich, Y.; Popinchalk, M.

    2013-09-01

    Local UV-bright galaxies in the Kiso survey include clumpy systems with kiloparsec-size star complexes that resemble clumpy young galaxies in surveys at high redshift. We compare clump masses and underlying disks in several dozen galaxies from each of these surveys to the star complexes and disks of normal spirals. Photometry and spectroscopy for the Kiso and spiral sample come from the Sloan Digital Sky Survey. We find that the largest Kiso clumpy galaxies resemble Ultra Deep Field (UDF) clumpies in terms of the star formation rates, clump masses, and clump surface densities. Clump masses and surface densities in normal spirals are smaller. If the clump masses are proportional to the turbulent Jeans mass in the interstellar medium, then for the most luminous galaxies in the sequence of normal:Kiso:UDF, the turbulent speeds and surface densities increase in the proportions 1.0:4.7:5.0 and 1.0:4.0:5.1, respectively, for fixed restframe B-band absolute magnitude. For the least luminous galaxies in the overlapping magnitude range, the turbulent speed and surface density trends are 1.0:2.7:7.4 and 1.0:1.4:3.0, respectively. We also find that while all three types have radially decreasing disk intensities when measured with ellipse-fit azimuthal averages, the average profiles are more irregular for UDF clumpies (which are viewed in their restframe UV) than for Kiso galaxies (viewed at g-band), and major axis intensity scans are even more irregular for the UDF than Kiso galaxies. Local clumpy galaxies in the Kiso survey appear to be intermediate between UDF clumpies and normal spirals.

  17. Stellar clustering as induced by a supernova

    NASA Technical Reports Server (NTRS)

    Baierlein, R.; Schwing, E.; Herbst, W.

    1981-01-01

    A possible mechanism for the fragmentation of the expanding shock wave from a supernova to form stellar clusters is considered. A model of supernova shell expansion is constructed in which the ratio of magnetic field intensity to gas density remains constant during the one-dimensional compression of the interstellar medium by the shock, and the gas and field adjust to a quasi-equilibrium within the shell following shock passage. It is shown that the quasi-equilibrium, which may be considered as an isothermal atmosphere, is unstable to a hydromagnetic instability representing a form of the Parker instability, which results in a clumping of gas at intervals on the order of parsecs. The length and time scales of the instability are consistent with the clustering of newly formed stars observed in Canis Major R1, where there is evidence for supernova-induced star formation.

  18. The clump mass function of the dense clouds in the Carina nebula complex

    NASA Astrophysics Data System (ADS)

    Pekruhl, S.; Preibisch, T.; Schuller, F.; Menten, K.

    2013-02-01

    Context. The question how the initial conditions in a star-forming region affect the resulting mass function of the forming stars is one of the most fundamental open topics in star formation theory. Aims: We want to characterize the properties of the cold dust clumps in the Carina nebula complex, which is one of the most massive star forming regions in our Galaxy and shows a very high level of massive star feedback. We derive the clump mass function (ClMF), explore the reliability of different clump extraction algorithms, and investigate the influence of the temperatures within the clouds on the resulting shape of the ClMF. Methods: We analyze a 1.25° × 1.25° wide-field submillimeter map obtained with LABOCA at the APEX telescope, which provides the first spatially complete survey of the clouds in the Carina nebula complex. We use the three clump-finding algorithms CLUMPFIND, GAUSSCLUMPS and SExtractor to identify individual clumps and determine their total fluxes. In addition to assuming a common "typical" temperature for all clouds, we also employ an empirical relation between cloud column densities and temperature to determine an estimate of the individual clump temperatures, and use this to determine individual clump masses. Results: We find that the ClMFs resulting from the different extraction methods show considerable differences in their shape. While the ClMF based on the CLUMPFIND extraction is very well described by a power-law (for clump masses well above the completeness limit), the ClMFs based on the extractions with GAUSSCLUMPS and SExtractor are better represented by a log-normal distribution. We also find that the use of individual clump temperatures leads to a shallower ClMF slope than the (often used) assumption of a common temperature (e.g. 20 K) of all clumps. Conclusions: The power-law of dN/dM ∝ M-1.95 we find for the CLUMPFIND sample is in good agreement with ClMF slopes found in previous studies of the ClMFs of other regions. The

  19. Clumped isotopes’ thermometry in land gastropod carbonate shells

    NASA Astrophysics Data System (ADS)

    Zaarur, S.; Affek, H. P.

    2009-12-01

    The carbonate ‘clumped isotope’ (Δ47) thermometer is based on the dependence of the abundance of 13C-18O bonds in carbonates on the carbonate formation temperature. We repeated at higher analytical precision the original thermometer calibration experiments of Ghosh et al., (2006) using carbonates precipitated synthetically by slow degassing of CO2 from saturated Ca(HCO3)2 solutions at a temperature range of 8°C to 70°C. Our data fall within error of the original calibration and generally confirms it. However, the samples precipitated at lower temperatures are slightly shifted, forming a line with a lower slope, fitting better the theoretical calibration thermometer predicted by Guo et al., (in press). We tested the Δ47 thermometer in land gastropods (snails) by analyzing modern gastropod shells from various geographical locations in comparison to the gastropods’ growing season temperatures. No significant inhomogeneity was observed within an individual shell. Segments growing at different stages in the gastropods’ life (e.g., inner part of the helix reflecting young gastropod growth and outer shell that grew at older gastropod age) revealed no significant variations within a specimen in either Δ47 or δ18O, whereas δ13C varied significantly (0.5 ‰) implying a change in the gastropods’ food source. Inter-species comparison revealed significant δ13C and δ18O variations among specimens collected at the same location (Sphincterochila zonata and Trochoidea simulate, south Israel, and Pleurodonte acuta and Orthalicus undutus, Jamaica) but no significant interspecies variations in Δ47, providing a strong indication for carbonate precipitation in isotopic equilibrium. Gastropod shells do not grow year-round, with most gastropods being dormant during dry cold seasons. ‘Clumped isotopes’ values are therefore expected to record the temperature of the gastropods’ growth season. Hence gastropod ecology and preferred growth conditions has to be taken

  20. Gangliosides GM1 and GM3 in the Living Cell Membrane Form Clusters Susceptible to Cholesterol Depletion and Chilling

    PubMed Central

    Fujita, Akikazu; Cheng, Jinglei; Hirakawa, Minako; Furukawa, Koichi; Kusunoki, Susumu

    2007-01-01

    Presence of microdomains has been postulated in the cell membrane, but two-dimensional distribution of lipid molecules has been difficult to determine in the submicrometer scale. In the present paper, we examined the distribution of gangliosides GM1 and GM3, putative raft molecules in the cell membrane, by immunoelectron microscopy using quick-frozen and freeze-fractured specimens. This method physically immobilized molecules in situ and thus minimized the possibility of artifactual perturbation. By point pattern analysis of immunogold labeling, GM1 was shown to make clusters of <100 nm in diameter in normal mouse fibroblasts. GM1-null fibroblasts were not labeled, but developed a similar clustered pattern when GM1 was administered. On cholesterol depletion or chilling, the clustering of both endogenous and exogenously-loaded GM1 decreased significantly, but the distribution showed marked regional heterogeneity in the cells. GM3 also showed cholesterol-dependent clustering, and although clusters of GM1 and GM3 were found to occasionally coincide, these aggregates were separated in most cases, suggesting the presence of heterogeneous microdomains. The present method enabled to capture the molecular distribution of lipids in the cell membrane, and demonstrated that GM1 and GM3 form clusters that are susceptible to cholesterol depletion and chilling. PMID:17392511

  1. The Spherically Symmetric Gravitational Collapse of a Clump of Solids in a Gas

    NASA Astrophysics Data System (ADS)

    Shariff, Karim; Cuzzi, Jeffrey N.

    2015-05-01

    In the subject of planetesimal formation, several mechanisms have been identified that create dense particle clumps in the solar nebula. The present work is concerned with the gravitational collapse of such clumps, idealized as being spherically symmetric. Fully nonlinear simulations using the two-fluid model are carried out (almost) up to the time when a central density singularity forms. We refer to this as the collapse time. The end result of the study is a parametrization of the collapse time, in order that it may be compared with timescales for various disruptive effects to which clumps may be subject in a particular situation. An important effect that determines the collapse time is that as the clump compresses, it also compresses the gas due to drag. This increases gas pressure, which retards particle collapse and can lead to oscillation in the size and density of the clump. In the limit of particles perfectly coupled to the gas, the characteristic ratio of gravitational force to gas pressure becomes relevant and defines a two-phase Jeans parameter, {{J}t}, which is the classical Jeans parameter with the speed of sound replaced by an effective wave speed in the coupled two-fluid medium. The parameter {{J}t} remains useful even away from the perfect coupling limit because it makes the simulation results insensitive to the initial density ratio of particles to gas (Φ0) as a separate parameter. A simple ordinary differential equation model is developed. It takes the form of two coupled non-linear oscillators and reproduces key features of the simulations. Finally, a parametric study of the time to collapse is performed and a formula (fit to the simulations) is developed. In the incompressible limit {{J}t}\\to 0, collapse time equals the self-sedimentation time, which is inversely proportional to the Stokes number. As {{J}t} increases, the collapse time decreases with {{J}t} and eventually becomes approximately equal to the dynamical time. Values of collapse

  2. The physical conditions in IRDC clumps from Herschel/HIFI observations of H2O

    NASA Astrophysics Data System (ADS)

    Shipman, R. F.; van der Tak, F. F. S.; Wyrowski, F.; Herpin, F.; Frieswijk, W.

    2014-10-01

    Context. The earliest phases of high-mass star formation are poorly understood. Aims: Our goal is to determine the physical conditions and kinematic structure of massive starforming cloud clumps. Methods: We analyse H2O 557 GHz line profiles observed with HIFI toward four positions in two infrared-dark cloud clumps. By comparison with ground-based C17O, N2H+, CH3OH, and NH3 line observations, we constrain the volume density and kinetic temperature of the gas and estimate the column density and abundance of H2O and N2H+. Results: The observed water lines are complex with emission and absorption components. The absorption is redshifted and consistent with a cold envelope, while the emission is interpreted as resulting from proto-stellar outflows. The gas density in the clumps is ~107 cm-3. The o-H2O outflow column density is 0.3-3.0 × 1014 cm-2. The o-H2O absorption column density is between 1.5 × 1014 and 2.6 × 1015 cm-2 with cold o-H2O abundances between 1.5 × 10-9 and 3.1 × 10-8. Conclusions: All clumps have high gas densities (~107 cm-3) and display infalling gas. Three of the four clumps have outflows. The clumps form an evolutionary sequence as probed by H2O N2H+, NH3, and CH3OH. We find that G28-MM is the most evolved, followed by G11-MM and then G28-NH3. The least evolved clump is G11-NH3 which shows no signposts of starformation; G11-NH3 is a high-mass pre-stellar core. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia with important participation of NASA.Tables 4, 6, 8, 10, 11, and Appendix A are available in electronic form at http://www.aanda.orgFinal Herschel and APEX data used in the paper (FITS files) 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/570/A51

  3. The luminosity function of star clusters in 20 star-forming galaxies based on Hubble legacy archive photometry

    SciTech Connect

    Whitmore, Bradley C.; Bowers, Ariel S.; Lindsay, Kevin; Ansari, Asna; Evans, Jessica; Chandar, Rupali; Larsen, Soeren

    2014-04-01

    Luminosity functions (LFs) have been determined for star cluster populations in 20 nearby (4-30 Mpc), star-forming galaxies based on Advanced Camera for Surveys source lists generated by the Hubble Legacy Archive (HLA). These cluster catalogs provide one of the largest sets of uniform, automatically generated cluster candidates available in the literature at present. Comparisons are made with other recently generated cluster catalogs demonstrating that the HLA-generated catalogs are of similar quality, but in general do not go as deep. A typical cluster LF can be approximated by a power law, dN/dL∝L {sup α}, with an average value for α of –2.37 and rms scatter = 0.18 when using the F814W ('I') band. A comparison of fitting results based on methods that use binned and unbinned data shows good agreement, although there may be a systematic tendency for the unbinned (maximum likelihood) method to give slightly more negative values of α for galaxies with steeper LFs. We find that galaxies with high rates of star formation (or equivalently, with the brightest or largest numbers of clusters) have a slight tendency to have shallower values of α. In particular, the Antennae galaxy (NGC 4038/39), a merging system with a relatively high star formation rate (SFR), has the second flattest LF in the sample. A tentative correlation may also be present between Hubble type and values of α, in the sense that later type galaxies (i.e., Sd and Sm) appear to have flatter LFs. Hence, while there do appear to be some weak correlations, the relative similarity in the values of α for a large number of star-forming galaxies suggests that, to first order, the LFs are fairly universal. We examine the bright end of the LFs and find evidence for a downturn, although it only pertains to about 1% of the clusters. Our uniform database results in a small scatter (≈0.4 to 0.5 mag) in the correlation between the magnitude of the brightest cluster (M {sub brightest}) and log of the number

  4. The clumped isotope geothermometer in soil and paleosol carbonate

    NASA Astrophysics Data System (ADS)

    Quade, J.; Eiler, J.; Daëron, M.; Achyuthan, H.

    2013-03-01

    We studied both modern soils and buried paleosols in order to understand the relationship of temperature (T°C(47)) estimated from clumped isotope compositions (Δ47) of soil carbonates to actual surface and burial temperatures. Carbonates from modern soils with differing rainfall seasonality were sampled from Arizona, Nevada, Tibet, Pakistan, and India. T°C(47) obtained from these soils shows that soil carbonate forms in the warmest months of the year, in the late morning to afternoon, and probably in response to intense soil dewatering. T°C(47) obtained from modern soil carbonate ranges from 10.8 to 39.5 °C. On average, T°C(47) exceeds mean annual temperature by 10-15 °C due to summertime bias in soil carbonate formation, and to summertime ground heating by incident solar radiation. Secondary controls on T°C(47) are soil depth and shading. Site mean annual air temperature (MAAT) across a broad range (0-30 °C) of site temperatures is highly correlated with T°C(47) from soils, following the equation: MAAT(°C)=1.20(T°C(47)0)-21.72(r2=0.92) where T°C(47)0 is the effective air temperature at the site estimated from T°C(47). The effective air temperature represents the air temperature required to account for the T°C(47) at each site, after consideration of variations in T°C(47) with soil depth and ground heating. The highly correlated relationship in this equation should now permit mean annual temperature in the past to be reconstructed from T°C(47) in paleosol carbonate, assuming one is studying paleosols that formed in environments generally similar in seasonality and ground cover to our calibration sites. T°C(47)0 decreases systematically with elevation gain in the Himalaya, following the equation: elevation(m)=-229(T°C(47)0)+9300(r2=0.95) Assuming that temperature varied similarly with elevation in the past, this equation can be used to reconstruct paleoelevation from clumped isotope analysis of ancient soil carbonates. We also measured T°C(47

  5. HerMES: Cosmic Infrared Background Anisotropies and the Clustering of Dusty Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Viero, M. P.; Wang, L.; Zemcov, M.; Addison, G.; Amblard, A.; Arumugam, V.; Aussel, H.; Béthermin, M.; Bock, J.; Boselli, A.; Buat, V.; Burgarella, D.; Casey, C. M.; Clements, D. L.; Conley, A.; Conversi, L.; Cooray, A.; De Zotti, G.; Dowell, C. D.; Farrah, D.; Franceschini, A.; Glenn, J.; Griffin, M.; Hatziminaoglou, E.; Heinis, S.; Ibar, E.; Ivison, R. J.; Lagache, G.; Levenson, L.; Marchetti, L.; Marsden, G.; Nguyen, H. T.; O'Halloran, B.; Oliver, S. J.; Omont, A.; Page, M. J.; Papageorgiou, A.; Pearson, C. P.; Pérez-Fournon, I.; Pohlen, M.; Rigopoulou, D.; Roseboom, I. G.; Rowan-Robinson, M.; Schulz, B.; Scott, D.; Seymour, N.; Shupe, D. L.; Smith, A. J.; Symeonidis, M.; Vaccari, M.; Valtchanov, I.; Vieira, J. D.; Wardlow, J.; Xu, C. K.

    2013-07-01

    We present measurements of the auto- and cross-frequency power spectra of the cosmic infrared background (CIB) at 250, 350, and 500 μm (1200, 860, and 600 GHz) from observations totaling ~70 deg2 made with the SPIRE instrument aboard the Herschel Space Observatory. We measure a fractional anisotropy δI/I = 14% ± 4%, detecting signatures arising from the clustering of dusty star-forming galaxies in both the linear (2-halo) and nonlinear (1-halo) regimes; and that the transition from the 2- to 1-halo terms, below which power originates predominantly from multiple galaxies within dark matter halos, occurs at k θ ~ 0.10-0.12 arcmin-1 (l ~ 2160-2380), from 250 to 500 μm. New to this paper is clear evidence of a dependence of the Poisson and 1-halo power on the flux-cut level of masked sources—suggesting that some fraction of the more luminous sources occupy more massive halos as satellites, or are possibly close pairs. We measure the cross-correlation power spectra between bands, finding that bands which are farthest apart are the least correlated, as well as hints of a reduction in the correlation between bands when resolved sources are more aggressively masked. In the second part of the paper, we attempt to interpret the measurements in the framework of the halo model. With the aim of fitting simultaneously with one model the power spectra, number counts, and absolute CIB level in all bands, we find that this is achievable by invoking a luminosity-mass relationship, such that the luminosity-to-mass ratio peaks at a particular halo mass scale and declines toward lower and higher mass halos. Our best-fit model finds that the halo mass which is most efficient at hosting star formation in the redshift range of peak star-forming activity, z ~ 1-3, is log(M peak/M ⊙) ~ 12.1 ± 0.5, and that the minimum halo mass to host infrared galaxies is log(M min/M ⊙) ~ 10.1 ± 0.6. Herschel is an ESA space observatory with science instruments provided by European

  6. HerMES: COSMIC INFRARED BACKGROUND ANISOTROPIES AND THE CLUSTERING OF DUSTY STAR-FORMING GALAXIES

    SciTech Connect

    Viero, M. P.; Zemcov, M.; Bock, J.; Cooray, A.; Dowell, C. D.; Wang, L.; Addison, G.; Amblard, A.; Arumugam, V.; Aussel, H.; Bethermin, M.; Casey, C. M.; Clements, D. L.; Conley, A.; Conversi, L.; De Zotti, G.; Farrah, D.; and others

    2013-07-20

    We present measurements of the auto- and cross-frequency power spectra of the cosmic infrared background (CIB) at 250, 350, and 500 {mu}m (1200, 860, and 600 GHz) from observations totaling {approx}70 deg{sup 2} made with the SPIRE instrument aboard the Herschel Space Observatory. We measure a fractional anisotropy {delta}I/I = 14% {+-} 4%, detecting signatures arising from the clustering of dusty star-forming galaxies in both the linear (2-halo) and nonlinear (1-halo) regimes; and that the transition from the 2- to 1-halo terms, below which power originates predominantly from multiple galaxies within dark matter halos, occurs at k{sub {theta}} {approx} 0.10-0.12 arcmin{sup -1} (l {approx} 2160-2380), from 250 to 500 {mu}m. New to this paper is clear evidence of a dependence of the Poisson and 1-halo power on the flux-cut level of masked sources-suggesting that some fraction of the more luminous sources occupy more massive halos as satellites, or are possibly close pairs. We measure the cross-correlation power spectra between bands, finding that bands which are farthest apart are the least correlated, as well as hints of a reduction in the correlation between bands when resolved sources are more aggressively masked. In the second part of the paper, we attempt to interpret the measurements in the framework of the halo model. With the aim of fitting simultaneously with one model the power spectra, number counts, and absolute CIB level in all bands, we find that this is achievable by invoking a luminosity-mass relationship, such that the luminosity-to-mass ratio peaks at a particular halo mass scale and declines toward lower and higher mass halos. Our best-fit model finds that the halo mass which is most efficient at hosting star formation in the redshift range of peak star-forming activity, z {approx} 1-3, is log(M{sub peak}/M{sub Sun }) {approx} 12.1 {+-} 0.5, and that the minimum halo mass to host infrared galaxies is log(M{sub min}/M{sub Sun }) {approx} 10

  7. Lanthanide, thorium, and uranium oxide clusters formed by DLV/FTICR

    SciTech Connect

    Pires de Matos, A.; Marcalo, J.; Leal, J.P.

    1995-12-31

    In this work the formation of clusters of all the lanthanides (except promethium), thorium and uranium by direct laser vaporization (DLV) of surface oxidized metallic targets in a vacuum of about 2 x 10{sup -8} Torr. The cluster ions were obtained using a Nd:YAG laser pulse (ca. 30 mJ at the fundamental 1064 nm wavelength) and the ions were stored in the trap of an Extrel (Waters) FTMS 2001-DT Fourier transform ion cyclotron resonance (FTICR) spectrometer.

  8. THE BLAST VIEW OF THE STAR-FORMING REGION IN AQUILA (l = 45{sup 0}, b = 0{sup 0})

    SciTech Connect

    Rivera-Ingraham, Alana; Martin, Peter G.; Netterfield, Calvin B.; Ade, Peter A. R.; Griffin, Matthew; Hargrave, Peter C.; Mauskopf, Philip; Bock, James J.; Chapin, Edward L.; Halpern, Mark; Marsden, Gaelen; Scott, Douglas; Devlin, Mark J.; Dicker, Simon R.; Klein, Jeff; Rex, Marie; Gundersen, Joshua O.; Hughes, David H.; Olmi, Luca; Patanchon, Guillaume

    2010-11-01

    We have carried out the first general submillimeter analysis of the field toward GRSMC 45.46+0.05, a massive star-forming region in Aquila. The deconvolved 6 deg{sup 2} (3{sup 0} x 2{sup 0}) maps provided by BLAST in 2005 at 250, 350, and 500 {mu}m were used to perform a preliminary characterization of the clump population previously investigated in the infrared, radio, and molecular maps. Interferometric CORNISH data at 4.8 GHz have also been used to characterize the Ultracompact H II regions (UCHIIRs) within the main clumps. By means of the BLAST maps, we have produced an initial census of the submillimeter structures that will be observed by Herschel, several of which are known Infrared Dark Clouds. Our spectral energy distributions of the main clumps in the field, located at {approx}7 kpc, reveal an active population with temperatures of T{approx} 35-40 K and masses of {approx}10{sup 3} M{sub sun} for a dust emissivity index {beta} = 1.5. The clump evolutionary stages range from evolved sources, with extended H II regions and prominent IR stellar population, to massive young stellar objects, prior to the formation of an UCHIIR. The CORNISH data have revealed the details of the stellar content and structure of the UCHIIRs. In most cases, the ionizing stars corresponding to the brightest radio detections are capable of accounting for the clump bolometric luminosity, in most cases powered by embedded OB stellar clusters.

  9. Clumps of hydrogenous planetoids as the dark matter of galaxies

    NASA Astrophysics Data System (ADS)

    Gibson, Carl H.; Schild, Rudolph E.

    2011-11-01

    Hydrodynamic gravitational condensation theory and quasar-microlensing observations lead to the conclusion that the baryonic mass of most galaxies is dominated by dense clumps of hydrogenous planetoids. Star microlensing collaborations fail to detect planetoids as the dominant dark matter component of the inner Galaxy halo (within ≈ 30 kpc) by an unjustified uniform- number-density assumption that underestimates the average value. At plasma neutralization and photon decoupling, existing proto-galaxies should fragment at both proto-globular-cluster (PGC) ≈ 105M⊙ and terrestrial-mass scales ≈ 10-6M⊙, from Gibson's 1996 hydro-gravitational theory. Schild's 1996 interpretation was that the mass of the lens galaxy is dominated by "rogue planets ... likely to be the missing mass", from measured twinkling frequencies of the lensed quasar Q0957+561 A,B images and their time-delayed difference. Schild's findings of a 1.1 year image time delay with dominant planetoid image-twinkling-period are confirmed herein by three observatories.

  10. Observational constraints on star cluster formation theory. I. The mass-radius relation

    NASA Astrophysics Data System (ADS)

    Pfalzner, S.; Kirk, H.; Sills, A.; Urquhart, J. S.; Kauffmann, J.; Kuhn, M. A.; Bhandare, A.; Menten, K. M.

    2016-02-01

    Context. Stars form predominantly in groups usually denoted as clusters or associations. The observed stellar groups display a broad spectrum of masses, sizes, and other properties, so it is often assumed that there is no underlying structure in this diversity. Aims: Here we show that the assumption of an unstructured multitude of cluster or association types might be misleading. Current data compilations of clusters in the solar neighbourhood show correlations among cluster mass, size, age, maximum stellar mass, etc. In this first paper we take a closer look at the correlation of cluster mass and radius. Methods: We use literature data to explore relations in cluster and molecular core properties in the solar neighbourhood. Results: We show that for embedded clusters in the solar neighbourhood a clear correlation exists between cluster mass and half-mass radius of the form Mc = CRcγ with γ = 1.7 ± 0.2. This correlation holds for infrared K-band data, as well as for X-ray sources and clusters containing a hundred stars up to those consisting of a few tens of thousands of stars. The correlation is difficult to verify for clusters containing fewer than 30 stars owing to low-number statistics. Dense clumps of gas are the progenitors of the embedded clusters. We find almost the same slope for the mass-size relation of dense, massive clumps as for the embedded star clusters. This might point to a direct translation from gas to stellar mass: however, it is difficult to relate size measurements for clusters (stars) to those for gas profiles. Taking multiple paths for clump mass into cluster mass into account, we obtain an average star-formation efficiency of 18%+9.3-5.7 for the embedded clusters in the solar neighbourhood. Conclusions: The derived mass-radius relation gives constraints for the theory of clustered star formation. Analytical models and simulations of clustered star formation have to reproduce this relation in order to be realistic.

  11. The Influence of Kinetic Growth Factors on the Clumped Isotope Composition of Calcite

    NASA Astrophysics Data System (ADS)

    Hunt, J. D.; Watkins, J. M.; Tripati, A.; Ryerson, F. J.; DePaolo, D. J.

    2014-12-01

    Clumped isotope paleothermometry is based on the association of 13C and 18O within carbonate minerals. Although the influence of temperature on equilibrium 13C-18O bond ordering has been studied, recent oxygen isotope studies of inorganic calcite demonstrate that calcite grown in laboratory experiments and in many natural settings does not form in equilibrium with water. It is therefore likely that the carbon and clumped isotope composition of these calcite crystals are not representative of true thermodynamic equilibrium. To isolate kinetic clumped isotope effects that arise at the mineral-solution interface, clumped isotopic equilibrium of DIC species must be maintained. This can be accomplished by dissolving the enzyme carbonic anhydrase (CA) into the solution, thereby reducing the time required for isotopic equilibration of DIC species by approximately two orders of magnitude between pH 7.7 and 9.3. We conduct calcite growth experiments aimed specifically at measuring the pH-dependence of kinetic clumped isotope effects during non-equilibrium precipitation of calcite. We precipitated calcite from aqueous solution at a constant pH and controlled supersaturation over the pH range 7.7-9.3 in the presence of CA. For each experiment, a gas mixture of N2 and CO2 is bubbled through a beaker of solution without seed crystals. As CO2 from the gas dissolves into solution, calcite crystals grow on the beaker walls. The pH of the solution is maintained by use of an autotitrator with NaOH as the titrant. We control the temperature, pH, the pCO2 of the gas inflow, and the gas inflow rate, and monitor the total alkalinity, the pCO2 of the gas outflow, and the amount of NaOH added. A constant crystal growth rate of ~1.6 mmol/m2/hr is maintained over all experiments. Results from these experiments are compared to predictions from a recently-developed isotopic ion-by-ion growth model of calcite. The model describes the rate, temperature and pH dependence of oxygen isotope uptake

  12. Using Spinning Dust Emission To Constrain The Evolution Of Dust Grains In Cold Clumps

    NASA Astrophysics Data System (ADS)

    Tibbs, C.; Paladini, R.; Cleary, K.; Grainge, K.; Muchovej, S.; Pearson, T.; Perrott, Y.; Rumsey, C.; Scaife, A.; Stevenson, M.; Villadsen, J.

    Within many molecular clouds in our Galaxy there are cold, dense regions known as cold clumps in which stars form. These dense environments provide a great location in which to study dust grain evolution. Given the low temperatures (˜10-15 K) and high densities (˜105 cm-3 ), these environments are dark at mid-infrared (IR) wavelengths and emit strongly at wavelengths ≥160 µm. The lack of mid-IR emission can be attributed to one of two reasons: i) a deficit of the small dust grains that emit stochastically at mid-IR wavelengths; or ii) small dust grains are present, but due to the high densities, the stellar photons cannot penetrate deep enough into the clumps to excite them. Using mid-IR observations alone it is impossible to distinguish between these two scenarios. However, by using spinning dust emission at cm wavelengths it is possible to break this degeneracy, because if small dust grains are present in these clumps, then even though stellar photons cannot excite them to emit at mid-IR wavelengths, these dust grains will be spunup by collisions and hence emit spinning dust radiation. If spinning dust were detected in these clumps it would prove that there are small dust grains present and that the lack of mid-IR emission is due to a lack of stellar photons. Conversely, a lack of spinning dust emission would indicate a deficit of small dust grains in these clumps. Since small dust grains require harsh radiation fields to be destroyed, a lack of small dust grains is likely a result of dust grain coagulation. With this in mind, we present preliminary results illustrating our method of using spinning dust observations to determine the evolution of small dust grains in these environments.

  13. Spherical cluster ensembles with fractal structure in LaSrMnO: New form of self-organization in solids

    SciTech Connect

    Okunev, V. D.; Samoilenko, Z. A.; Burkhovetski, V. V.; Szymczak, H.; Szymczak, R.; Lewandowski, S. J.

    2013-04-28

    The growth of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} films in magnetron plasma, in special conditions, leads to the appearance of ensembles of micron-sized spherical crystalline clusters with fractal structure, which we consider to be a new form of self-organization in solids. Each ensemble contains 10{sup 5}-10{sup 6} elementary clusters, 100-250 A in diameter. Interaction of the clusters in the ensemble is realized through the interatomic chemical bonds, intrinsic to the manganites. Integration of peripheral areas of interacting clusters results in the formation of common intercluster medium in the ensemble. We argue that the ensembles with fractal structure built into paramagnetic disordered matrix have ferromagnetic properties. Absence of sharp borders between elementary clusters and the presence of common intercluster medium inside each ensemble permits to rearrange magnetic order and to change the volume of the ferromagnetic phase, providing automatically a high sensitivity of the material to the external field.

  14. IN-SPIRALING CLUMPS IN BLUE COMPACT DWARF GALAXIES

    SciTech Connect

    Elmegreen, Bruce G.; Zhang Hongxin; Hunter, Deidre A.

    2012-03-10

    Giant star formation clumps in dwarf irregular galaxies can have masses exceeding a few percent of the galaxy mass enclosed inside their orbital radii. They can produce sufficient torques on dark matter halo particles, halo stars, and the surrounding disk to lose their angular momentum and spiral into the central region in 1 Gyr. Pairs of giant clumps with similarly large relative masses can interact and exchange angular momentum to the same degree. The result of this angular momentum loss is a growing central concentration of old stars, gas, and star formation that can produce a long-lived starburst in the inner region, identified with the blue compact dwarf (BCD) phase. This central concentration is proposed to be analogous to the bulge in a young spiral galaxy. Observations of star complexes in five local BCDs confirm the relatively large clump masses that are expected for this process. The observed clumps also seem to contain old field stars, even after background light subtraction, in which case the clumps may be long-lived. The two examples with clumps closest to the center have the largest relative clump masses and the greatest contributions from old stars. An additional indication that the dense central regions of BCDs are like bulges is the high ratio of the inner disk scale height to the scale length, which is comparable to 1 for four of the galaxies.

  15. Quantitative characterization of clumping in Scots pine crowns

    PubMed Central

    Stenberg, Pauline; Mõttus, Matti; Rautiainen, Miina; Sievänen, Risto

    2014-01-01

    Background and Aims Proper characterization of the clumped structure of forests is needed for calculation of the absorbed radiation and photosynthetic production by a canopy. This study examined the dependency of crown-level clumping on tree size and growth conditions in Scots pine (Pinus sylvestris), and determined the ability of statistical canopy radiation models to quantify the degree of self-shading within crowns as a result of the clumping effect. Methods Twelve 3-D Scots pine trees were generated using an application of the LIGNUM model, and the crown-level clumping as quantified by the crown silhouette to total needle area ratio (STARcrown) was calculated. The results were compared with those produced by the stochastic approach of modelling tree crowns as geometric shapes filled with a random medium. Key Results Crown clumping was independent of tree height, needle area and growth conditions. The results supported the capability of the stochastic approach in characterizing clumping in crowns given that the outer shell of the tree crown is well represented. Conclusions Variation in the whole-stand clumping index is induced by differences in the spatial pattern of trees as a function of, for example, stand age rather than by changes in the degree of self-shading within individual crowns as they grow bigger. PMID:24431344

  16. Microlensing Optical Depth towards the Galactic Bulge Using Clump Giants from the MACHO Survey

    SciTech Connect

    Popowski, P; Griest, K; Thomas, C L; Cook, K H; Bennett, D P; Becker, A C; Alves, D R; Minniti, D; Drake, A J; Alcock, C; Allsman, R A; Axelrod, T S; Freeman, K C; Geha, M; Lehner, M J; Marshall, S L; Nelson, C A; Peterson, B A; Quinn, P J; Stubbs, C W; Sutherland, W; Vandehei, T; Welch, D

    2005-07-14

    Using 7 years of MACHO survey data, we present a new determination of the optical depth to microlensing towards the Galactic bulge. We select the sample of 62 microlensing events (60 unique) on clump giant sources and perform a detailed efficiency analysis. We use only the clump giant sources because these are bright bulge stars and are not as strongly affected by blending as other events. Using a subsample of 42 clump events concentrated in an area of 4.5 deg{sup 2} with 739000 clump giant stars, we find {tau} = 2.17{sub -0.38}{sup +0.47} x 10{sup -6} at (l,b) = (1{sup o}.50, -2{sup o}.68), somewhat smaller than found in most previous MACHO studies, but in excellent agreement with recent theoretical predictions. We also present the optical depth in each of the 19 fields in which we detected events, and find limits on optical depth for fields with no events. The errors in optical depth in individual fields are dominated by Poisson noise. We measure optical depth gradients of (1.06 {+-} 0.71) x 10{sup -6}deg{sup -1} and (0.29 {+-} 0.43) x 10{sup -6}deg{sup -1} in the galactic latitude b and longitude l directions, respectively. Finally, we discuss the possibility of anomalous duration distribution of events in the field 104 centered on (l,b) = (3{sup o}.11, -3{sup o}.01) as well as investigate spatial clustering of events in all fields.

  17. Preservation of carbonate clumped isotopes in sedimentary paleoclimate archives

    NASA Astrophysics Data System (ADS)

    Henkes, G. A.; Passey, B. H.; Grossman, E. L.; Shenton, B.; Perez-Huerta, A.

    2014-12-01

    Carbonate clumped isotope thermometry is increasingly used to reconstruct paleotemperatures of ancient terrestrial environments. One promising application is elucidating paleoelevation from carbonate archives such as paleosols, lacustrine marls, and fossil freshwater shells. Unlike conventional stable isotope approaches (e.g., mineral δ18O or δD), clumped isotope thermometry is independent of the isotopic composition of the precipitating waters and can therefore be used to reconstruct elevation by both the temperature-altitude relationship and the rainfall δ18O-altitude relationship. However, interpretation of clumped isotope data is not without its own complications. Like conventional stable isotopes, clumped isotope paleotemperatures can be effectively reset to warmer values by dissolution/reprecipitation-type diagenesis during sedimentary burial. It is also known that carbonate clumped isotope bonds (i.e., 13C-18O) are susceptible to 'reordering' in the solid mineral lattice at warmer burial temperatures, with laboratory studies of natural carbonates indicating activation of this phenomenon at temperatures as low as 100 °C over geologic timescales. A challenge in applying carbonate clumped isotope thermometry to natural samples is now evaluating terrestrial archives with respect to both types of alteration: 'open-system' alteration and 'closed-system' bond reordering. In this talk we will review our experimental efforts to constrain the kinetics of clumped isotope reordering, with relevance to low-temperature carbonates like fossil shells and early diagenetic minerals, and present new laboratory data that further inform our theoretical framework for the mechanism(s) of 13C-18O bond reordering. Together with traditional analytical and petrographic screening for recrystallization, empirical and laboratory studies of carbonate clumped isotope reordering represent the next steps in evaluating isotopic records of paleoclimate, paleobiology, and paleoelevation

  18. Star-Forming Brightest Cluster Galaxies at 0.25 < z < 1.25: A Transitioning Fuel Supply

    DOE PAGESBeta

    McDonald, M.; Stalder, B.; Bayliss, M.; Allen, S. W.; Applegate, D. E.; Ashby, M. L. N.; Bautz, M.; Benson, B. A.; Bleem, L. E.; Brodwin, M.; et al

    2016-01-22

    In this paper, we present a multiwavelength study of the 90 brightest cluster galaxies (BCGs) in a sample of galaxy clusters selected via the Sunyaev Zel'dovich effect by the South Pole Telescope, utilizing data from various ground- and space-based facilities. We infer the star-formation rate (SFR) for the BCG in each cluster—based on the UV and IR continuum luminosity, as well as the [O ii]λλ3726,3729 emission line luminosity in cases where spectroscopy is available—and find seven systems with SFR > 100 M⊙ yr-1. We find that the BCG SFR exceeds 10 M⊙ yr-1 in 31 of 90 (34%) cases at 0.25 < z < 1.25, compared to ~1%–5% at z ~ 0 from the literature. At z ≳ 1, this fraction increases tomore » $${92}_{-31}^{+6}$$%, implying a steady decrease in the BCG SFR over the past ~9 Gyr. At low-z, we find that the specific SFR in BCGs is declining more slowly with time than for field or cluster galaxies, which is most likely due to the replenishing fuel from the cooling ICM in relaxed, cool core clusters. At z ≳ 0.6, the correlation between the cluster central entropy and BCG star formation—which is well established at z ~ 0—is not present. Instead, we find that the most star-forming BCGs at high-z are found in the cores of dynamically unrelaxed clusters. We use data from the Hubble Space Telescope to investigate the rest-frame near-UV morphology of a subsample of the most star-forming BCGs, and find complex, highly asymmetric UV morphologies on scales as large as ~50–60 kpc. Finally, the high fraction of star-forming BCGs hosted in unrelaxed, non-cool core clusters at early times suggests that the dominant mode of fueling star formation in BCGs may have recently transitioned from galaxy–galaxy interactions to ICM cooling.« less

  19. Star-forming Brightest Cluster Galaxies at 0.25 > z > 1.25: A Transitioning Fuel Supply

    NASA Astrophysics Data System (ADS)

    McDonald, M.; Stalder, B.; Bayliss, M.; Allen, S. W.; Applegate, D. E.; Ashby, M. L. N.; Bautz, M.; Benson, B. A.; Bleem, L. E.; Brodwin, M.; Carlstrom, J. E.; Chiu, I.; Desai, S.; Gonzalez, A. H.; Hlavacek-Larrondo, J.; Holzapfel, W. L.; Marrone, D. P.; Miller, E. D.; Reichardt, C. L.; Saliwanchik, B. R.; Saro, A.; Schrabback, T.; Stanford, S. A.; Stark, A. A.; Vieira, J. D.; Zenteno, A.

    2016-02-01

    We present a multiwavelength study of the 90 brightest cluster galaxies (BCGs) in a sample of galaxy clusters selected via the Sunyaev Zel’dovich effect by the South Pole Telescope, utilizing data from various ground- and space-based facilities. We infer the star-formation rate (SFR) for the BCG in each cluster—based on the UV and IR continuum luminosity, as well as the [O ii]λλ3726,3729 emission line luminosity in cases where spectroscopy is available—and find seven systems with SFR > 100 M⊙ yr-1. We find that the BCG SFR exceeds 10 M⊙ yr-1 in 31 of 90 (34%) cases at 0.25 < z < 1.25, compared to ˜1%-5% at z ˜ 0 from the literature. At z ≳ 1, this fraction increases to {92}-31+6%, implying a steady decrease in the BCG SFR over the past ˜9 Gyr. At low-z, we find that the specific SFR in BCGs is declining more slowly with time than for field or cluster galaxies, which is most likely due to the replenishing fuel from the cooling ICM in relaxed, cool core clusters. At z ≳ 0.6, the correlation between the cluster central entropy and BCG star formation—which is well established at z ˜ 0—is not present. Instead, we find that the most star-forming BCGs at high-z are found in the cores of dynamically unrelaxed clusters. We use data from the Hubble Space Telescope to investigate the rest-frame near-UV morphology of a subsample of the most star-forming BCGs, and find complex, highly asymmetric UV morphologies on scales as large as ˜50-60 kpc. The high fraction of star-forming BCGs hosted in unrelaxed, non-cool core clusters at early times suggests that the dominant mode of fueling star formation in BCGs may have recently transitioned from galaxy-galaxy interactions to ICM cooling.

  20. Hydrogen abstraction in the neutral molecular cluster of benzophenone and hydrogen donors formed in a supersonic free jet expansion

    SciTech Connect

    Matsushita, Yoshihisa; Kajii, Yoshizumi; Obi, Kinichi

    1992-08-06

    This paper discusses how benzophenone undergoes photoreduction to form benzophenone ketyl radical by an intracellular reaction in the benzophenone 1,4-cyclohexadiene mixed expansion in a supersonic free jet expansion. No ketyl radical fluorescence is observed when triethylamine, 2-propanol, or ethanol is the hydrogen donor; thus the normal molecular cluster activity depends on the nature of the hydrogen donor. 36 refs., 5 figs.

  1. CLUMPY GALAXIES IN CANDELS. I. THE DEFINITION OF UV CLUMPS AND THE FRACTION OF CLUMPY GALAXIES AT 0.5 < z < 3

    SciTech Connect

    Guo, Yicheng; Koo, David C.; Barro, Guillermo; Faber, Sandra M.; Fang, Jerome J.; Bell, Eric F.; Conselice, Christopher J.; Giavalisco, Mauro; Lu, Yu; Mandelker, Nir; Dekel, Avishai; McIntosh, Daniel M.; Primack, Joel R.; Ceverino, Daniel; and others

    2015-02-10

    Although giant clumps of stars are thought to be crucial to galaxy formation and evolution, the most basic demographics of clumps are still uncertain, mainly because the definition of clumps has not been thoroughly discussed. In this paper, we carry out a study of the basic demographics of clumps in star-forming galaxies at 0.5 < z < 3, using our proposed physical definition that UV-bright clumps are discrete star-forming regions that individually contribute more than 8% of the rest-frame UV light of their galaxies. Clumps defined this way are significantly brighter than the H II regions of nearby large spiral galaxies, either individually or blended, when physical spatial resolution and cosmological dimming are considered. Under this definition, we measure the fraction of star-forming galaxies that have at least one off-center clump (f {sub clumpy}) and the contributions of clumps to the rest-frame UV light and star formation rate (SFR) of star-forming galaxies in the CANDELS/GOODS-S and UDS fields, where our mass-complete sample consists of 3239 galaxies with axial ratio q > 0.5. The redshift evolution of f {sub clumpy} changes with the stellar mass (M {sub *}) of the galaxies. Low-mass (log (M {sub *}/M {sub ☉}) < 9.8) galaxies keep an almost constant f {sub clumpy} of ∼60% from z ∼ 3 to z ∼ 0.5. Intermediate-mass and massive galaxies drop their f {sub clumpy} from 55% at z ∼ 3 to 40% and 15%, respectively, at z ∼ 0.5. We find that (1) the trend of disk stabilization predicted by violent disk instability matches the f {sub clumpy} trend of massive galaxies; (2) minor mergers are a viable explanation of the f {sub clumpy} trend of intermediate-mass galaxies at z < 1.5, given a realistic observability timescale; and (3) major mergers are unlikely responsible for the f {sub clumpy} trend in all masses at z < 1.5. The clump contribution to the rest-frame UV light of star-forming galaxies shows a broad peak around galaxies with log (M {sub *}/M {sub

  2. The clump mass function of the dense clouds in the Carina Nebula

    NASA Astrophysics Data System (ADS)

    Pekruhl, Stephanie

    2013-07-01

    Stars form in dense, cold regions of dust and gas, called Molecular Clouds. The question how the initial conditions in these star-forming regions affect the resulting mass function of the forming stars is one of the most fundamental open problems in the theory of star formation. Therefore in this work we want to characterize the properties of the cold cloud structures in the Carina Nebula (NGC 3372). The Carina Nebula represents with a distance of 2.3kpc one of the nearest massive Galactic star forming regions, hosting at least 65 O-type stars. Therefore it is the best site to study in detail the physics of violent massive star formation. The feedback of the numerous hot stars disperses the parental cloud but also triggers the formation of new generations of stars. We use a 1.25° × 1.25° wide-field sub-millimetre map of the Carina Nebula obtained with LABOCA (870μm) at the APEX telescope to investigate its Clump Mass Function (ClMF). New deeper LABOCA maps of two selected regions experiencing different levels of stellar feedback will allow, due to their higher sensitivity, a more complete look on the cloud structures and the influence of the hot stars. To determine the ClMF of the Carina Nebula we use the three common clump-finding algorithms CLUMPFIND, GAUSSCLUMPS, and SExtractor. Each of these programs leads to a sample of clumps, whose positions, sizes, and intensities are calculated. For a reliable mass estimate the knowledge about the temperatures within the clumps is very important. In addition to the commonly used approach to assume a "typical" temperature for all clouds, we derive an empirical relation between cloud column density and temperature to determine an estimate of the individual clump temperatures. For all three samples we find clump temperatures between 8.5 K and 18.5 K. With these temperatures we are able to determine the individual clump masses. For masses above ∼50 M⊙ we find a power-law for all three ClMFs, with a power-law index

  3. A cluster in the making: ALMA reveals the initial conditions for high-mass cluster formation

    NASA Astrophysics Data System (ADS)

    Rathborne, Jill

    2015-08-01

    Despite their importance, very little is known about the formation of star clusters. An understanding of their formation requires observations of their natal dust and gas well before the onset of star formation. In recent Galactic Plane surveys, one object, G0.253+0.016, stands out as extreme. Identified as a cold, dense, massive molecular clump devoid of prevalent star-formation, it has exactly the properties expected for a clump that may form an Arches-like cluster. Located at a distance of ~8.5 kpc, G0.253+0.016 lies ~100 pc from the Galactic Centre, in the Central Molecular Zone (CMZ).In this talk I will showcase our recent ALMA data of the 90 GHz continuum and line emission toward G0.253+0.016. The data are spectacular reveal a complex network of structures: there is emission on all spatial scales, the morphology of which ranges from small, compact regions to extended, filamentary structures that are seen in both emission and absorption. A statistical analysis of the structure within G0.253+0.016 demonstrates the dominance of turbulence. The talk will summarise our recent results and the emerging picture of cluster formation in the extreme, high-pressure environment of the CMZ that is revealed by the new ALMA data.

  4. Probing the Dragonfish star-forming complex: the ionizing population of the young massive cluster Mercer 30

    NASA Astrophysics Data System (ADS)

    de la Fuente, D.; Najarro, F.; Borissova, J.; Ramírez Alegría, S.; Hanson, M. M.; Trombley, C.; Figer, D. F.; Davies, B.; Garcia, M.; Kurtev, R.; Urbaneja, M. A.; Smith, L. C.; Lucas, P. W.; Herrero, A.

    2016-04-01

    It has recently been claimed that the nebula, Dragonfish, is powered by a superluminous but elusive OB association. However, systematic searches in near-infrared photometric surveys have found many other cluster candidates in this region of the sky. Among these, the first confirmed young massive cluster was Mercer 30, where Wolf-Rayet stars were found.We perform a new characterization of Mercer 30 with unprecedented accuracy, combining NICMOS/HST and VVV photometric data with multi-epoch ISAAC/VLT H- and K-band spectra. Stellar parameters for most of spectroscopically observed cluster members are found through precise non-LTE atmosphere modeling with the CMFGEN code. Our spectrophotometric study for this cluster yields a new, revised distance of d = (12.4 ± 1.7) kpc and a total of QHMc30 ≈ 6.70 × 1050 s-1 Lyman ionizing photons. A cluster age of (4.0 ± 0.8) Myr is found through isochrone fitting, and a total mass of (1.6 ± 0.6) × 104M⊙ is estimated, thanks to our extensive knowledge of the post-main-sequence population. As a consequence, membership of Mercer 30 to the Dragonfish star-forming complex is confirmed, allowing us to use this cluster as a probe for the whole complex, which turns out to be extremely large (~400 pc across) and located at the outer edge of the Sagittarius-Carina spiral arm (~11 kpc from the Galactic center). The Dragonfish complex hosts 19 young clusters or cluster candidates (including Mercer 30 and a new candidate presented in this work) and an estimated minimum of nine field Wolf-Rayet stars. All these contributions account for, at least 73% of the ionization of the Dragonfish nebula and leaves little or no room for the alleged superluminous OB association; alternative explanations are discussed. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under programs IDs 179.B-2002, 081.D-0471, 083.D-0765, 087.D-0957, and 089.D-0989.

  5. Probing the Dragonfish star-forming complex: the ionizing population of the young massive cluster Mercer 30

    NASA Astrophysics Data System (ADS)

    de la Fuente, D.; Najarro, F.; Borissova, J.; Ramírez Alegría, S.; Hanson, M. M.; Trombley, C.; Figer, D. F.; Davies, B.; Garcia, M.; Kurtev, R.; Urbaneja, M. A.; Smith, L. C.; Lucas, P. W.; Herrero, A.

    2016-05-01

    It has recently been claimed that the nebula, Dragonfish, is powered by a superluminous but elusive OB association. However, systematic searches in near-infrared photometric surveys have found many other cluster candidates in this region of the sky. Among these, the first confirmed young massive cluster was Mercer 30, where Wolf-Rayet stars were found.We perform a new characterization of Mercer 30 with unprecedented accuracy, combining NICMOS/HST and VVV photometric data with multi-epoch ISAAC/VLT H- and K-band spectra. Stellar parameters for most of spectroscopically observed cluster members are found through precise non-LTE atmosphere modeling with the CMFGEN code. Our spectrophotometric study for this cluster yields a new, revised distance of d = (12.4 ± 1.7) kpc and a total of QHMc30 ≈ 6.70 × 1050 s-1 Lyman ionizing photons. A cluster age of (4.0 ± 0.8) Myr is found through isochrone fitting, and a total mass of (1.6 ± 0.6) × 104M⊙ is estimated, thanks to our extensive knowledge of the post-main-sequence population. As a consequence, membership of Mercer 30 to the Dragonfish star-forming complex is confirmed, allowing us to use this cluster as a probe for the whole complex, which turns out to be extremely large (~400 pc across) and located at the outer edge of the Sagittarius-Carina spiral arm (~11 kpc from the Galactic center). The Dragonfish complex hosts 19 young clusters or cluster candidates (including Mercer 30 and a new candidate presented in this work) and an estimated minimum of nine field Wolf-Rayet stars. All these contributions account for, at least 73% of the ionization of the Dragonfish nebula and leaves little or no room for the alleged superluminous OB association; alternative explanations are discussed. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under programs IDs 179.B-2002, 081.D-0471, 083.D-0765, 087.D-0957, and 089.D-0989.

  6. The Amyloid Precursor Protein Forms Plasmalemmal Clusters via Its Pathogenic Amyloid-β Domain

    PubMed Central

    Schreiber, Arne; Fischer, Sebastian; Lang, Thorsten

    2012-01-01

    The amyloid precursor protein (APP) is a large, ubiquitous integral membrane protein with a small amyloid-β (Aβ) domain. In the human brain, endosomal processing of APP produces neurotoxic Aβ-peptides, which are involved in Alzheimer's disease. Here, we show that the Aβ sequence exerts a physiological function when still present in the unprocessed APP molecule. From the extracellular site, Aβ concentrates APP molecules into plasmalemmal membrane protein clusters. Moreover, Aβ stabilization of clusters is a prerequisite for their targeting to endocytic clathrin structures. Therefore, we conclude that the Aβ domain directly mediates a central step in APP trafficking, driving its own conversion into neurotoxic peptides. PMID:22455924

  7. DYNAMO survey: An upclose view of turbulent disks with massive starforming clumps

    NASA Astrophysics Data System (ADS)

    Fisher, David B.

    2015-08-01

    In this talk I will discuss properties of extremely gas rich, turbulent disk galaxies in the DYNAMO survey, an IFU survey of Halpha in ~100 galaxies at z~0.1. DYNAMO galaxies are selected to have the highest Halpha luminosity at their redshift, yet are not AGNs. Follow up results from HST, and kinematic maps from Keck and Gemini show that many DYNAMO galaxies are clumpy, rotating disks, with large internal velocity dispersion, similar to galaxies at z=1-2. In this talk I will show that gas fractions in DYNAMO galaxies are 20-40%, much higher than typical local Universe galaxies (1-8%). The gas fraction of DYNAMO galaxies is similar to that of z=1-2 disks (eg. PHIBBS survey). The DYNAMO galaxies offer a sample of galaxies gas rich, clumpy, turbulent disks at z~0.1. Using DYNAMO galaxies we can therefore constrain the properties of individual clumps with much higher precision than in z=2 galaxies. Unlike high redshift observations in our data the Jeans length is resolved, and we can therefore measure the size of star forming regions with much greater security. I will therefore show how effects from resolution are likely to affect the measurement of clump propoerties, and present an analysis of the sizes and luminosities of star forming regions of massive star forming clumps using HST maps of ionized gas. I will show that in gas rich disk galaxies the sizes of clumps is directly linked to the gas fraction and velocity dispersion of the disk, both predictions of the theory that instabilities lead to clumpy disks.

  8. Does Bi form clusters in GaAs1 - xBi x alloys?

    NASA Astrophysics Data System (ADS)

    Punkkinen, M. P. J.; Laukkanen, P.; Kuzmin, M.; Levämäki, H.; Lång, J.; Tuominen, M.; Yasir, M.; Dahl, J.; Lu, S.; Delczeg-Czirjak, E. K.; Vitos, L.; Kokko, K.

    2014-11-01

    GaAs1 - xBi x alloys attract significant interest due to their potentiality for several applications, including solar cells. Recent experiments link the crucial optical properties of these alloys to Bi clustering at certain Bi compositions. Using ab initio calculations, we show that there is no thermodynamical driving force for the formation of small GaBi clusters incorporating As substitutional sites. However, the Ga vacancies should gather Bi atoms leading to small Bi clusters, and the Ga vacancies can act as nucleation centers for phase separation. The formation energy of the GaAs1 - xBi x with respect to GaAs and GaBi shows a maximum at intermediate Bi concentrations. Thermodynamics and kinetics of the GaAs1 - xBi x film growth is discussed. High Bi solubility is obtained, if the Bi atoms on the energetically favorable atom positions in the subsurface layer are relatively frozen. The Ga vacancy concentration may be increased by the incorporation of Bi. The Bi atoms can also prevent the out diffusion of Ga vacancies.

  9. Nanopore integrated with Au clusters formed under electron beam irradiation for single molecule analysis

    NASA Astrophysics Data System (ADS)

    Choi, Seong Soo; Park, Myoung Jin; Han, Chul Hee; Kim, Sung In; Yoo, Jung Ho; Park, Kyung Jin; Park, Nam Kyou; Kim, Yong-Sang

    2016-02-01

    Recently the single molecules such as protein and deoxyribonucleic acid (DNA) have been successfully characterized using a solidstate nanopore with an electrical detection technique. However, the optical plasmonic nanopore has yet to be fabricated. The optical detection technique can be better utilized as next generation ultrafast geneome sequencing devices due to the possible utilization of the current optical technique for genome sequencing. In this report, we have investigated the Au nanopore formation under the electron beam irradiation on an Au aperture. The circular-type nanoopening with ~ 5 nm diameter on the diffused membrane is fabricated by using 2 keV electron beam irradiation by using field emission scanning electron microscopy (FESEM). We found the Au cluster on the periphery of the drilled aperture under a 2 keV electron beam irradiation. Immediately right after electron beam irradiation, no Au cluster and no Au crystal lattice structure on the diffused plane are observed. However, after the sample was kept for ~ 6 months under a room environment, the Au clusters are found on the diffused membrane and the Au crystal lattice structures on the diffused membrane are also found using high resolution transmission electron microscopy. These phenomena can be attributed to Ostwald ripening. In addition, the Au nano-hole on the 40 nm thick Au membrane was also drilled by using 200 keV scanning transmission electron microscopy.

  10. Mid-infrared Extinction Mapping of Infrared Dark Clouds. II. The Structure of Massive Starless Cores and Clumps

    NASA Astrophysics Data System (ADS)

    Butler, Michael J.; Tan, Jonathan C.

    2012-07-01

    We develop the mid-infrared extinction (MIREX) mapping technique of Butler & Tan (Paper I), presenting a new method to correct for the Galactic foreground emission based on observed saturation in independent cores. Using Spitzer GLIMPSE 8 μm images, this allows us to accurately probe mass surface densities, Σ, up to ~= 0.5 g cm-2 with 2'' resolution and mitigate one of the main sources of uncertainty associated with Galactic MIREX mapping. We then characterize the structure of 42 massive starless and early-stage cores and their surrounding clumps, selected from 10 infrared dark clouds, measuring Σcl(r) from the core/clump centers. We first assess the properties of the core/clump at a scale where the total enclosed mass as projected on the sky is M cl = 60 M ⊙. We find that these objects have a mean radius of R cl ~= 0.1 pc, mean \\bar{\\Sigma }_cl = 0.3\\:g\\:cm^{-2} and, if fitted by a power-law (PL) density profile \\rho _cl\\propto r^{-k_\\rho ,cl}, a mean value of k ρ, cl = 1.1. If we assume a core is embedded in each clump and subtract the surrounding clump envelope to derive the core properties, then we find a mean core density PL index of k ρ, c = 1.6. We repeat this analysis as a function of radius and derive the best-fitting PL plus uniform clump envelope model for each of the 42 core/clumps. The cores have typical masses of Mc ~ 100 M ⊙ and \\bar{\\Sigma }_c\\sim 0.1\\:g\\:cm^{-2}, and are embedded in clumps with comparable mass surface densities. We also consider Bonnor-Ebert density models, but these do not fit the observed Σ profiles as well as PLs. We conclude that massive starless cores exist and are well described by singular polytropic spheres. Their relatively low values of Σ and the fact that they are IR dark may imply that their fragmentation is inhibited by magnetic fields rather than radiative heating. Comparing to massive star-forming cores and clumps, there is tentative evidence for an evolution toward higher densities and steeper