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Sample records for diffuse ionized halo

  1. ON THE ORIGINS OF THE DIFFUSE H{alpha} EMISSION: IONIZED GAS OR DUST-SCATTERED H{alpha} HALOS?

    SciTech Connect

    Seon, Kwang-Il; Witt, Adolf N.

    2012-10-20

    It is known that the diffuse H{alpha} emission outside of bright H II regions not only are very extended, but also can occur in distinct patches or filaments far from H II regions, and the line ratios of [S II] {lambda}6716/H{alpha} and [N II] {lambda}6583/H{alpha} observed far from bright H II regions are generally higher than those in the H II regions. These observations have been regarded as evidence against the dust-scattering origin of the diffuse H{alpha} emission (including other optical lines), and the effect of dust scattering has been neglected in studies on the diffuse H{alpha} emission. In this paper, we reexamine the arguments against dust scattering and find that the dust-scattering origin of the diffuse H{alpha} emission cannot be ruled out. As opposed to the previous contention, the expected dust-scattered H{alpha} halos surrounding H II regions are, in fact, in good agreement with the observed H{alpha} morphology. We calculate an extensive set of photoionization models by varying elemental abundances, ionizing stellar types, and clumpiness of the interstellar medium (ISM) and find that the observed line ratios of [S II]/H{alpha}, [N II]/H{alpha}, and He I {lambda}5876/H{alpha} in the diffuse ISM accord well with the dust-scattered halos around H II regions, which are photoionized by late O- and/or early B-type stars. We also demonstrate that the H{alpha} absorption feature in the underlying continuum from the dust-scattered starlight ({sup d}iffuse galactic light{sup )} and unresolved stars is able to substantially increase the [S II]/H{alpha} and [N II]/H{alpha} line ratios in the diffuse ISM.

  2. Diffuse low-ionization gas in the galactic halo casts doubts on z ≃ 0.03 WHIM detections

    NASA Astrophysics Data System (ADS)

    Nicastro, F.; Senatore, F.; Gupta, A.; Mathur, S.; Krongold, Y.; Elvis, M.; Piro, L.

    2016-05-01

    In this Letter, we demonstrate that the two claims of z ≃ 0.03 O VII K α absorption lines from Warm Hot Intergalactic Medium (WHIM) along the lines of sight to the blazars H 2356-309 (Buote et al.; Fang et al.) and Mkn 501 (Ren, Fang & Buote) are likely misidentifications of the z = 0 O II K β line produced by a diffuse Low-Ionization Metal Medium in the Galaxy's interstellar and circum-galactic mediums. We perform detailed modelling of all the available high signal-to-noise Chandra Low Energy Transmission Grating (LETG) and XMM-Newton Reflection Grating Spectrometer (RGS) spectra of H 2356-309 and Mkn 501 and demonstrate that the z ≃ 0.03 WHIM absorption along these two sightlines is statistically not required. Our results, however, do not rule out a small contribution from the z ≃ 0.03 O VII K α absorber along the line of sight to H 2356-309. In our model the temperature of the putative z = 0.031 WHIM filament is T = 3 × 105 K and the O VII column density is N_{O VII} ≲ 4× 10^{15} cm-2, twenty times smaller than the O VIIcolumn density previously reported, and now more consistent with the expectations from cosmological hydrodynamical simulations.

  3. The Contribution of Ionizing Starts to the Far-Infrared and Radio Emission in the Milky Way: Evidence for a Swept-up Shell and Diffuse Ionized Halo Around the W4 Chimney/Supershell

    NASA Technical Reports Server (NTRS)

    Terebey, Susan; Oliversen, R. (Technical Monitor)

    1999-01-01

    Normandeau have proposed that W4 is a galactic chimney, the only chimney to-date identified in our Galaxy. Using the recent approx. 1 min resolution IGA (Infrared Galaxy Atlas) and DRAO (Dominion Royal Astrophysical Observatory) CGPS (Canadian Galactic Plane Survey) galactic plane surveys we analyze the far-infrared and radio structure of the W 4 chimney/supershell. We show W4 has a swept-up partially ionized shell of gas and dust which is powered by the OCl 352 star cluster. Analysis of the dust column density establishes there is dense interstellar material below the shell, directly showing the dense material which caused the lower shell expansion to stall. Due to much lower densities above the Galactic plane, the upper W4 shell achieved 'breakout' to form a Galactic chimney. Although the shell appears ionization bounded, it is very inhomogenous and an ionized halo provides evidence of significant Lyman continuum leakage. A large fraction of the OCl 352 cluster photons escape to large distances and are available to ionize the WIM (warm ionized medium) component of the interstellar medium.

  4. Highly ionized gas in the Galactic halo

    NASA Technical Reports Server (NTRS)

    Shull, J. Michael; Slavin, Jonathan D.

    1994-01-01

    We reexamine the values of electron density n(sub e) and gas pressure P/k in the interstellar medium (ISM) of the Galactic halo, as inferred from C IV emission and absorption lines and using current C IV atomic data. In a homogeneous model with 4.7 less than or equal to log T less than or equal to 5.3, the data are consistent with 0.01 less than or equal to n(sub e) less than or equal to 0.02/cu cm and 2200 less than or equal to P/k less than or equal to 3700/cu cm K, a factor of 2-3 higher than advocated by Martin & Bowyer (1990) and comparable to the thermal pressure in the disk. If some of the C IV absorption arises from nonemitting, photoionized gas, then the inferred density and pressure will increase accordingly. The volume filling factor for homogeneous models ranges from 0.5% to 5%. Because of the constraints arising from filling factor and radiated power, most of the C IV must arise from gas near the peak of the cooling curve, at log t less than or equal to 5.6. We relate both emission-line and absorption-line observations to recent models in which turbulent mixing layers and isobarically cooling supernova remnants (SNRs) provide significant amounts of halo gas at approximately 10(exp 5.3) K and process 20-40 solar mass/yr with a power of approximately 10(exp 41) ergs/sec. Since the observed C IV and N V absorption scale heights have been reported to differ, at 4.9 kpc and 1.6 kpc, respectively, we examine inhomogeneous models with different exponential scale heights of T, P, and SN energy input. The ISM may change its character with distance above the Galactic plane, as superbubbles and mixing layers dominate over isolated SNRs as the source of the C IV. For appropiate scale heights, the midplane pressure is twice the homogeneous values quoted above. The O IV lambda 1034 diffuse emission line, which can be used as a temperature diagnostic of the hot gas, is predicted to be comparable in strength to that of C IV lambda 1549 (approximately 6000 photons

  5. Cosmological Halos: A Search for the Ionized Intergalactic Medium

    NASA Astrophysics Data System (ADS)

    Geller, Robert M.; Sault, Robert J.; Antonucci, Robert; Killeen, Neil E. B.; Ekers, Ron; Desai, Ketan; Whysong, David

    2000-08-01

    Standard big bang nucleosynthesis predicts the average baryon density of the universe to be a few percent of the critical density. Only about one-tenth of the predicted baryons have been seen. A plausible repository for the missing baryons is in a diffuse ionized intergalactic medium (IGM). In an attempt to measure the IGM, we searched for Thomson-scattered halos around strong high-redshift radio sources. Observations of the radio source 1935-692 were made with the Australia Telescope Compact Array. We assumed a uniform IGM, and isotropic steady emission of 1935-692 for a duration between 107 and 108 yr. A model of the expected halo visibility function was used in χ2 fits to place upper limits on ΩIGM. The upper limits varied depending on the methods used to characterize systematic errors in the data. The results are 2 σ limits of ΩIGM<0.65. While not yet at the sensitivity level to test primordial nucleosynthesis, improvements in the technique will probably allow this in future studies.

  6. Cosmological Halos: a Search for the Ionized Intergalactic Medium

    NASA Astrophysics Data System (ADS)

    Geller, Robert Maurice

    Standard big bang nucleosynthesis predicts the average baryon density of the Universe to be a few percent of the critical density. Only about one tenth of the predicted baryons have been seen. A plausible repository for the missing baryons is in a diffuse ionized intergalactic medium (IGM). In an attempt to measure the IGM we searched for Thomson-scattered halos around strong high redshift radio sources. Observations of the radio source 1935-692 were made with the Australia Telescope Compact Array. We assumed a uniform IGM, and isotropic steady emission of 1935-692 for a duration between 107-108 years. A model of the expected halo visibility function was used in χ2 fits to place upper limits on Ω IGM. The upper limits varied depending on the methods used to characterize systematic errors in the data. The results are 2σ limits of Ω IGM < 0.65. While not yet at the sensitivity level to test primordial nucleosynthesis, improvements on the technique will probably allow this in future studies.

  7. Observations of diffusion in the electron halo and strahl

    NASA Astrophysics Data System (ADS)

    Gurgiolo, Chris; Goldstein, Melvyn L.

    2016-12-01

    Observations of the three-dimensional solar wind electron velocity distribution functions (VDF) using ϕ-θ plots often show a tongue of electrons that begins at the strahl and stretches toward a new population of electrons, termed the proto-halo, that exists near the projection of the magnetic field opposite that associated with the strahl. The energy range in which the tongue and proto-halo are observed forms a "diffusion zone". The tongue first appears in energy generally near the lower-energy range of the strahl and in the absence of any clear core/halo signature. While the ϕ-θ plots give the appearance that the tongue and proto-halo are derived from the strahl, a close examination of their density suggests that their source is probably the upper-energy core/halo electrons which have been scattered by one or more processes into these populations.

  8. The ionization conditions in the Milky Way halo - Infalling gas toward the North Galactic Pole

    NASA Technical Reports Server (NTRS)

    Danly, Laura

    1992-01-01

    Observations of gas in the Milky Way halo are studied with an eye toward the theoretical predictions of the Galactic Fountain model for the production of halo gas. Data are shown that indicate significant variations in the ionization conditions in infalling halo gas in the northern galactic hemisphere. Understanding the nature of Milky Way halo gas plays a critical role in interpreting QSO absorption lines in the investigation of galaxies at high redshift.

  9. The ionization conditions in the Milky Way halo - Infalling gas toward the North Galactic Pole

    NASA Technical Reports Server (NTRS)

    Danly, Laura

    1992-01-01

    Observations of gas in the Milky Way halo are studied with an eye toward the theoretical predictions of the Galactic Fountain model for the production of halo gas. Data are shown that indicate significant variations in the ionization conditions in infalling halo gas in the northern galactic hemisphere. Understanding the nature of Milky Way halo gas plays a critical role in interpreting QSO absorption lines in the investigation of galaxies at high redshift.

  10. The COS-Halos Survey: Origins of the Highly Ionized Circumgalactic Medium of Star-Forming Galaxies

    NASA Astrophysics Data System (ADS)

    Werk, Jessica K.; Prochaska, J. Xavier; Cantalupo, Sebastiano; Fox, Andrew J.; Oppenheimer, Benjamin; Tumlinson, Jason; Tripp, Todd M.; Lehner, Nicolas; McQuinn, Matthew

    2016-12-01

    The total contribution of diffuse halo gas to the galaxy baryon budget strongly depends on its dominant ionization state. In this paper, we address the physical conditions in the highly ionized circumgalactic medium (CGM) traced by {{O}} {{VI}} absorption lines observed in COS-Halos spectra. We analyze the observed ionic column densities, absorption-line widths and relative velocities, along with the ratios of {{N}} {{V}}/{{O}} {{VI}} for 39 fitted Voigt profile components of O vi. We compare these quantities with the predictions given by a wide range of ionization models. Photoionization models that include only extragalactic UV background radiation are ruled out; conservatively, the upper limits to {{N}} {{V}}/{{O}} {{VI}} and measurements of {N}{{O}{{VI}}} imply unphysically large path lengths ≳100 kpc. Furthermore, very broad {{O}} {{VI}} absorption (b > 40 km s-1) is a defining characteristic of the CGM of star-forming L* galaxies. We highlight two possible origins for the bulk of the observed {{O}} {{VI}}: (1) highly structured gas clouds photoionized primarily by local high-energy sources or (2) gas radiatively cooling on large scales behind a supersonic wind. Approximately 20% of circumgalactic O vi does not align with any low-ionization state gas within ±50 km s-1 and is found only in halos with {M}{halo} < 1012 {M}⊙ . We suggest that this type of unmatched O vi absorption traces the hot corona itself at a characteristic temperature of {10}5.5 K. We discuss the implications of these very distinct physical origins for the dynamical state, gas cooling rates, and total baryonic content of L* gaseous halos.

  11. The kinematics of Milky Way halo gas. I - Observations of low-ionization species

    NASA Technical Reports Server (NTRS)

    Danly, Laura

    1989-01-01

    Ultraviolet interstellar line day observed with the IUE toward 70 halo stars and four extragalactic sight lines are analyzed in a study of the large-scale kinematic properties of the Milky Way halo gas. The motions of the low-ionization gas is focused on. Large systematic velocities are found, and a pronounced asymmetry in the absorption characteristics of halo gas toward the Galactic poles is indicated. In the north, substantial amounts of material are falling toward the disk at velocities up to about 120 km/s in the most extreme case. Toward the south, low-ionization material shows no extreme or systematic motions.

  12. The kinematics of Milky Way halo gas. I - Observations of low-ionization species

    NASA Technical Reports Server (NTRS)

    Danly, Laura

    1989-01-01

    Ultraviolet interstellar line day observed with the IUE toward 70 halo stars and four extragalactic sight lines are analyzed in a study of the large-scale kinematic properties of the Milky Way halo gas. The motions of the low-ionization gas is focused on. Large systematic velocities are found, and a pronounced asymmetry in the absorption characteristics of halo gas toward the Galactic poles is indicated. In the north, substantial amounts of material are falling toward the disk at velocities up to about 120 km/s in the most extreme case. Toward the south, low-ionization material shows no extreme or systematic motions.

  13. A diffusive model for halo width growth during vertical displacement events

    NASA Astrophysics Data System (ADS)

    Eidietis, N. W.; Humphreys, D. A.

    2011-07-01

    The electromagnetic loads produced by halo currents during vertical displacement events (VDEs) impose stringent requirements on the strength of ITER in-vessel components. A predictive understanding of halo current evolution is essential for ensuring the robust design of these components. A significant factor determining that evolution is the plasma resistance, which is a function of three quantities: the resistivities of the core and halo regions, and the halo region width. A diffusive model of halo width growth during VDEs has been developed, which provides one part of a physics basis for predictive halo current simulations. The diffusive model was motivated by DIII-D observations that VDEs with cold post-thermal quench plasma and a current decay time much faster than the vertical motion (type I VDE) possess much wider halo region widths than warmer plasma VDEs, where the current decay is much slower than the vertical motion (type II). A 2D finite element code is used to model the diffusion of toroidal halo current during selected type I and type II DIII-D VDEs. The model assumes a core plasma region within the last closed flux surface (LCFS) diffusing current into a halo plasma filling the vessel outside the LCFS. LCFS motion and plasma temperature are prescribed from experimental observations. The halo width evolution produced by this model compares favourably with experimental measurements of type I and type II toroidal halo current width evolution.

  14. Probing ionization conditions of Galactic halo gas using H-alpha observations of the Magellanic Stream

    NASA Astrophysics Data System (ADS)

    Barger, Kat; Madsen, Gregory J.; Fox, Andrew; Wakker, Bart P.; Bland-Hawthorn, Jonathan; Nidever, David L.; Lehner, Nicolas; Haffner, L. Matthew; Hill, Alex S.

    2017-01-01

    Galaxy interactions have greatly disturbed and redistributed the gas in the Magellanic System throughout the halos of the Milky Way. Using the Wisconsin H-alpha Mapper (WHAM) telescope, we have completed the highest sensitivity and kinematically resolved emission-line survey of the entire Magellanic Stream. These observations enable us to determine how the ionization conditions change over 100-degrees across the sky, including the region below the South Galactic Pole. We explore the sources of that ionization and find that photoionization from the Milky Way and Magellanic Clouds is insufficient to explain the observed H-alpha emission. We further investigate whether energetic processes associated with the Milky Way's center or interactions with the halo could provide the remaining ionization. The gas in the Magellanic Steam could supply enough gas to maintain or even boost the star formation in the Milky Way, but only if it can survive the journey to the Galaxy's disk.

  15. Diffuse ionizing radiation within HH jets

    SciTech Connect

    Esquivel, A.; Raga, A. C. E-mail: raga@nucleares.unam.mx

    2013-12-20

    We present numerical hydrodynamical simulations of a time-dependent ejection velocity precessing jet. The parameters used in our models correspond to a high excitation Herbig-Haro object, such as HH 80/81. We have included the transfer of ionizing radiation produced within the shocked regions of the jet. The radiative transfer is computed with a ray-tracing scheme from all the cells with an emissivity above a certain threshold. We show the development of a radiative precursor, and compare the morphology with a model without the diffuse radiation. Our simulations show that the morphology of the Hα emission is affected considerably if the diffuse ionizing radiation is accounted for. The predicted Hα position-velocity diagram (i.e., spatially resolved emission line profiles) from a model with the transfer of ionizing radiation has a relatively strong component at zero velocity, corresponding to the radiative precursor. Qualitatively similar 'zero velocity components' are observed in HH 80/81 and in the jet from Sanduleak's star in the Large Magellanic Cloud.

  16. The formation of low-ionization emission in the halo of NGC 891

    NASA Technical Reports Server (NTRS)

    Sokolowski, James; Bland-Hawthorn, Jonathan

    1993-01-01

    Imaging and Spectroscopic study first revealed the presence of a diffuse ionized medium (DIM), having unusual excitation, pervading the lower halo of the edge-on spiral galaxy NGC 891. Emission from this DIM is strongest northeast of the nucleus, at radii between 2 and 8 kpc (hereafter region 1). The (N2)(lambda)6583/H(alpha) and (S2)(lambda) (lambda)6716,6731/H(alpha) ratios increase dramatically with z in region 1, from 0.6 and 0.5 respectively at z is approximately equal to 500 pc to 1.1 and 1.0 at z is approximately equal to 1 kpc, while nondetections of (O1)(lambda)6300 and (O3)(lambda)5007 emission yield upper limits of (O1)(lambda)6300/H(alpha) less than or equal to 0.05 and (O3)(lambda)5007/H(alpha) less than or equal to 0.15 for z less than 1 kpc. Previous photoionization models, using the radiation field from disk O and B stars, have been successful in reproducing the elevated (N2)(lambda)6583/H(alpha) and (S2)(lambda)(lambda)6716.6731/H(alpha) ratios observed. However, these radiation bounded models also produce significant (O3)(lambda)5007 emission, in conflict with the observed upper limit. Here, we report the results of new, matter bounded models for the photoionization of the DIM in region 1 of NGC 891.

  17. Highly-Ionized Gas in the Galactic Halo: A FUSE Survey of O 6 Absorption toward 22 Halo Stars

    NASA Astrophysics Data System (ADS)

    Zsargo, J.; Sembach, K. R.; Howk, J. C.; Savage, B. D.

    2002-12-01

    Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of 22 Galactic halo stars are studied to determine the amount of O 6 in the Galactic halo between ~0.3 and ~10 kpc from the Galactic mid-plane. Strong O 6 λ 1031.93 absorption was detected toward 21 stars, and a reliable 3 σ upper limit was obtained toward HD 97991. The weaker member of the O 6 doublet at 1037.62 Å could be studied toward only six stars. The observed columns are reasonably consistent with a patchy exponential O 6 distribution with a mid-plane density of 1.7x10-8 cm-3 and scale height between 2.3 and 4 kpc. We do not see clear signs of strong high-velocity components in O 6 absorption along the Galactic sight lines, which indicates the general absence of high velocity O 6 within 2-5 kpc of the Galactic mid-plane. The correlation between the H 1 and O 6 intermediate velocity absorption is also poor. The O 6 velocity dispersions are much larger than the value of ~18 km/s expected from thermal broadening for gas at T ~ 3x105 K, the temperature at which O 6 is expected to reach its peak abundance in collisional ionization equilibrium. Turbulence, inflow, and outflow must have an effect on the shape of the O 6 profiles. Kinematical comparisons of O 6 with Ar 1 reveal that 9 of 21 sight lines are closely aligned in LSR velocity (|Δ VLSR| <=5 km/s ), while 8 of 21 exhibit significant velocity differences (|Δ VLSR| >= 15 km/s ). This dual behavior may indicate the presence of two different types of O 6-bearing environments toward the Galactic sight lines. Comparison of O 6 with other highly-ionized species suggests that the high ions are produced primarily by cooling hot gas in the Galactic fountain flow, and that turbulent mixing also has a significant contribution. The role of turbulent mixing is most important toward sight lines that sample supernova remnants like Loop I and IV. We are also able to show that the O 6 enhancement toward the Galactic center region that was observed in the FUSE

  18. Photoionization of the diffuse interstellar medium and galactic halo by OB associtations

    NASA Technical Reports Server (NTRS)

    Dove, James B.; Shull, J. Michael

    1994-01-01

    Assuming smoothly varying H I distributions in te Galactic disk, we have calculated the geometry of diffuse II regions due to OB associations in the Galactic plane. Near the solar circle, OB associations with a Lyman continuum (Lyc) photon luminosity Psi(sub Lyc) = 3.3 x 10(exp 7) cm(exp -2) s(exp -1), produce H II regions that are density bounded in the vertical direction (H II chimneys) allowing Lyc to escape the gaseous disk and penetrate into the Galactic halo. We provide analytic formulae for the Lyc escape fraction as functions of S(sub 0) O-star catalog of Garmany and a new Lyc stellar stellar Lyc stellar flux calibration, we find a production rate of Lyc photons by OB associations within 2.5 kpc of Psi(sub Lyc) = 3.3 x 10(exp 7) cm(exp -2) s(exp -1). Integrating the fraction of Lyc photons that escape the disk over our adopted luminosity function of OB associations, we estimate that approximately 7% of the ionizing photons, or Phi(sub Lyc) = 2.3 x 10(exp 6) cm(exp -2) s(exp -1), escape each side of the H I disk layer and penetrate the diffuse ionized medium ('Reynolds layer'). This flux is sufficient to explain the potoionization of this, although we have not constructed a model for the observed H-alpha emission and pulsar dispersion measures that is fully consistent with the absorption rate of Lyc in the H II layer. Since our quiescent model does not account for the effects of dynamic chimneys and superbubbles, which should enhance Lyc escape, we conclude the O stars are the probable source of ionizing radiation for the Reynolds layer. For a random distribution of OB associations throughout the disk, the Lyc flux is nearly uniform for heights Z is greater than approximately 0.8 kpc above the midplane.

  19. No evidence for large-scale outflows in the extended ionized halo of ULIRG Mrk273

    NASA Astrophysics Data System (ADS)

    Spence, R. A. W.; Zaurín, J. Rodríguez; Tadhunter, C. N.; Rose, M.; Cabrera-Lavers, A.; Spoon, H.; Muñoz-Tuñón, C.

    2016-06-01

    We present deep new Gran Telescopio Canarias (GTC) narrow-band images and William Herschel Telescope (WHT) long-slit spectroscopy of the merging system Mrk273 that show a spectacular extended halo of warm ionized gas out to a radius of ˜45 kpc from the system nucleus. Outside of the immediate nuclear regions (r > 6 kpc), there is no evidence for kinematic disturbance in the ionized gas: in the extended regions covered by our spectroscopic slits the emission lines are relatively narrow (full width at half-maximum, FWHM ≲ 350 km s-1) and velocity shifts small (|ΔV| ≲ 250 km s-1). This is despite the presence of powerful near-nuclear outflows (FWHM > 1000 km s-1; |ΔV| > 400 km s-1; r < 6 kpc). Diagnostic ratio plots are fully consistent with Seyfert 2 photoionization to the NE of the nuclear region, however to the SW the plots are more consistent with low-velocity radiative shock models. The kinematics of the ionized gas, combined with the fact that the main structures are aligned with low-surface-brightness tidal continuum features, are consistent with the idea that the ionized halo represents tidal debris left over from a possible triple-merger event, rather than a reservoir of outflowing gas.

  20. Lithium in halo stars - Constraining the effects of helium diffusion on globular cluster ages and cosmology

    NASA Technical Reports Server (NTRS)

    Deliyannis, Constantine P.; Demarque, Pierre

    1991-01-01

    Stellar evolutionary models with diffusion are used to show that observations of lithium in extreme halo stars provide crucial constraints on the magnitude of the effects of helium diffusion. The flatness of the observed Li-T(eff) relation severely constrains diffusion Li isochrones, which tend to curve downward toward higher T(eff). It is argued that Li observations at the hot edge of the plateau are particularly important in constraining the effects of helium diffusion; yet, they are currently few in number. It is proposed that additional observations are required there, as well as below 5500 K, to define more securely the morphology of the halo Li abundances. Implications for the primordial Li abundance are considered. It is suggested that a conservative upper limit to the initial Li abundance, due to diffusive effects alone, is 2.35.

  1. High S/N Observations of Low-Ionization Gas Through the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Meyer, D. M.; Roth, K. C.; Savage, B. D.; Lu, L.

    1993-12-01

    Optical absorption-line studies of extragalactic objects can now provide a sensitive probe of low-ionization gas over the full extent of the Galactic halo. Such work is particularly pertinent to a better understanding of the distances, metallicities, and sky coverage of the high-velocity clouds (HVCs) primarily observed in H I 21 cm emission. We have recently obtained high S/N, high resolution (20 km s(-1) ) KPNO 4-m echelle observations of the Ca II absorption toward the QSO 1821+643, the Seyfert galaxy Mkn 231, and SN 1993J in the galaxy M81. We detect a weak (W_lambda ~30 m Angstroms) Ca II component at an LSR velocity of -140 km s(-1) toward 1821+643 that corresponds to the Outer Arm H I HVC Complex. In the case of Mkn 231, we find no evidence of high-velocity Ca II absorption despite the location of this sightline near H I HVC Complex C. Our Ca II observations toward SN 1993J are especially exceptional in quality (S/N~500) and reveal absorption due to the Galactic halo, the disk of M81, and intergalactic material in the M81 group. Although the M81 disk gas dominates the absorption in the velocity region encompassing HVC Complex C, we do find a high-velocity component at +228 km s(-1) in Ca II that has also been seen in Mg II absorption with HST (Bowen et al. 1994, Ap. J. (Letters), in press). Our echelle spectra of SN 1993J also reveal detections of other interstellar atoms and molecules such as Ti II, Ca I, and CH(+) \\@. The Ti II measurement is particularly interesting in that it represents the first detection of Ti II toward an extragalactic object and indicates a Ti II scale height of about 1200 pc which is somewhat less than expected from observations of Ti II toward halo stars.

  2. The Vertical Structure of Diffuse Ionized Gas in Galactic Spiral Arms

    NASA Astrophysics Data System (ADS)

    Krishnarao, Dhanesh; Haffner, L. Matthew; Benjamin, Robert A.

    2017-01-01

    The Wisconsin H-Alpha Mapper provides the most sensitive velocity resolved observations of diffuse Hα, [S II] λ6716, and [N II] λ6584 emission in the Galaxy, tracing the warm (~8000K) ionized component of the interstellar medium. The vertical extent of this diffuse gas can directly impact the midplane pressure, influencing cold molecular clouds and star formation in the disk. Here, we analyze the vertical structure of the warm ionized medium around multiple spiral arm components of the Galaxy. Diffuse halo emission is isolated using longitude varying velocity channels guided by CO emission tracing cold molecular gas in the disk. We find exponential electron density squared (or emission measure) scale heights and analyze its behavior as a function of Galactocentric radius and the presence of cold molecular clouds and star forming regions in the disk. Statistical analysis of the behavior of [S II]/Hα and [N II]/Hα line ratios along some of these spiral arms disentangle the complex physical conditions of the warm ionized gas as a function of height and in-situ electron density. Some spiral arm sections, in particular the far Carina arm, have significantly larger (>3x) scale heights than previously studied arms that tend to increase as a function of Galactocentric radius.

  3. Small-scale Intensity Mapping: Extended Halos as a Probe of the Ionizing Escape Fraction and Faint Galaxy Populations during Reionization

    NASA Astrophysics Data System (ADS)

    Mas-Ribas, Lluís; Hennawi, Joseph F.; Dijkstra, Mark; Davies, Frederick B.; Stern, Jonathan; Rix, Hans-Walter

    2017-09-01

    We present a new method to quantify the value of the escape fraction of ionizing photons, and the existence of ultra-faint galaxies clustered around brighter objects during the epoch of cosmic reionization, using the diffuse Lyα, continuum, and Hα emission observed around galaxies at z∼ 6. We model the surface brightness profiles of the diffuse halos, considering the fluorescent emission powered by ionizing photons escaping from the central galaxies, and the nebular emission from satellite star-forming sources, by extending the formalisms developed in Mas-Ribas & Dijkstra and Mas-Ribas et al. The comparison between our predicted profiles and Lyα observations at z = 5.7 and z = 6.6 favors a low ionizing escape fraction, {f}{esc}{ion}∼ 5 % , for galaxies in the range -19≳ {M}{UV}≳ -21.5. However, uncertainties and possible systematics in the observations do not allow for firm conclusions. We predict Hα and rest-frame visible continuum observations with the James Webb Space Telescope (JWST), and show that it will be able to detect extended (a few tens of kiloparsecs) fluorescent Hα emission powered by ionizing photons escaping from a bright, L≳ 5{L}* , galaxy. Such observations could differentiate fluorescent emission from nebular emission by satellite sources. We discuss how observations and stacking several objects may provide unique constraints on the escape fraction for faint galaxies and/or the abundance of ultra-faint radiation sources.

  4. Helium Ionization in the Diffuse Ionized Gas Surrounding UCH ii Regions

    NASA Astrophysics Data System (ADS)

    Anish Roshi, D.; Churchwell, E.; Anderson, L. D.

    2017-04-01

    We present measurements of the singly ionized helium-to-hydrogen ratio ({n}{{He}+}/{n}{{{H}}+}) toward diffuse gas surrounding three ultracompact H ii (UCH ii) regions: G10.15-0.34, G23.46-0.20, and G29.96-0.02. We observe radio recombination lines of hydrogen and helium near 5 GHz using the GBT to measure the {n}{{He}+}/{n}{{{H}}+} ratio. The measurements are motivated by the low helium ionization observed in the warm ionized medium and in the inner Galaxy diffuse ionized regions. Our data indicate that the helium is not uniformly ionized in the three observed sources. Helium lines are not detected toward a few observed positions in sources G10.15-0.34 and G23.46-0.20, and the upper limits of the {n}{{He}+}/{n}{{{H}}+} ratio obtained are 0.03 and 0.05, respectively. The selected sources harbor stars of type O6 or hotter as indicated by helium line detection toward the bright radio continuum emission from the sources with mean {n}{{He}+}/{n}{{{H}}+} value 0.06 ± 0.02. Our data thus show that helium in diffuse gas located a few parsecs away from the young massive stars embedded in the observed regions is not fully ionized. We investigate the origin of the nonuniform helium ionization and rule out the possibilities (a) that the helium is doubly ionized in the observed regions and (b) that the low {n}{{He}+}/{n}{{{H}}+} values are due to additional hydrogen ionizing radiation produced by accreting low-mass stars. We find that selective absorption of ionizing photons by dust can result in low helium ionization but needs further investigation to develop a self-consistent model for dust in H ii regions.

  5. Helium Ionization in the Diffuse Ionized Gas Surrounding UCH ii Regions

    NASA Astrophysics Data System (ADS)

    Roshi, D. Anish; Churchwell, E.; Anderson, L. D.

    2017-04-01

    We present measurements of the singly ionized helium-to-hydrogen ratio ({n}{{He}+}/{n}{{{H}}+}) toward diffuse gas surrounding three ultracompact H ii (UCH ii) regions: G10.15-0.34, G23.46-0.20, and G29.96-0.02. We observe radio recombination lines of hydrogen and helium near 5 GHz using the GBT to measure the {n}{{He}+}/{n}{{{H}}+} ratio. The measurements are motivated by the low helium ionization observed in the warm ionized medium and in the inner Galaxy diffuse ionized regions. Our data indicate that the helium is not uniformly ionized in the three observed sources. Helium lines are not detected toward a few observed positions in sources G10.15-0.34 and G23.46-0.20, and the upper limits of the {n}{{He}+}/{n}{{{H}}+} ratio obtained are 0.03 and 0.05, respectively. The selected sources harbor stars of type O6 or hotter as indicated by helium line detection toward the bright radio continuum emission from the sources with mean {n}{{He}+}/{n}{{{H}}+} value 0.06 ± 0.02. Our data thus show that helium in diffuse gas located a few parsecs away from the young massive stars embedded in the observed regions is not fully ionized. We investigate the origin of the nonuniform helium ionization and rule out the possibilities (a) that the helium is doubly ionized in the observed regions and (b) that the low {n}{{He}+}/{n}{{{H}}+} values are due to additional hydrogen ionizing radiation produced by accreting low-mass stars. We find that selective absorption of ionizing photons by dust can result in low helium ionization but needs further investigation to develop a self-consistent model for dust in H ii regions.

  6. Properties of the highly ionized disk and halo gas toward two distant high-latitude stars

    NASA Technical Reports Server (NTRS)

    Savage, Blair D.; Sembach, K. R.

    1994-01-01

    absorption, part of the C IV absorption, and has very little associated Si IV absorption. In this gas N(C IV)/N(N V) is approximately 1 to 3. This gas is hot (T greater than 2 x 10(exp 5) K) and may be tracing the cooling gas of supernova (SN) bubbles or a Galactic fountain. The relative mixture of these two types of highly ionized gas varies from one sight line to the next. The two sight lines in this study sample halo gas in the solar neighborhood and have a smaller percentage of the more highly ionized gas than inner Galaxy sight lines.

  7. Neutral Atom Diffusion in a Partially Ionized Prominence Plasma

    NASA Technical Reports Server (NTRS)

    Gilbert, Holly

    2010-01-01

    The support of solar prominences is normally described in terms of a magnetic force on the prominence plasma that balances the solar gravitational force. Because the prominence plasma is only partially ionized. it is necessary to consider in addition the support of the neutral component of the prominence plasma. This support is accomplished through a frictional interaction between the neutral and ionized components of the plasma, and its efficacy depends strongly on the degree of ionization of the plasma. More specifically, the frictional force is proportional to the relative flow of neutral and ion species, and for a sufficiently weakly ionized plasma, this flow must be relatively large to produce a frictional force that balances gravity. A large relative flow, of course, implies significant draining of neutral particles from the prominence. We evaluate the importance of this draining effect for a hydrogen-helium plasma, and consider the observational evidence for cross-field diffusion of neutral prominence material,

  8. Neutral Atom Diffusion in a Partially Ionized Prominence Plasma

    NASA Technical Reports Server (NTRS)

    Gilbert, Holly

    2010-01-01

    The support of solar prominences is normally described in terms of a magnetic force on the prominence plasma that balances the solar gravitational force. Because the prominence plasma is only partially ionized. it is necessary to consider in addition the support of the neutral component of the prominence plasma. This support is accomplished through a frictional interaction between the neutral and ionized components of the plasma, and its efficacy depends strongly on the degree of ionization of the plasma. More specifically, the frictional force is proportional to the relative flow of neutral and ion species, and for a sufficiently weakly ionized plasma, this flow must be relatively large to produce a frictional force that balances gravity. A large relative flow, of course, implies significant draining of neutral particles from the prominence. We evaluate the importance of this draining effect for a hydrogen-helium plasma, and consider the observational evidence for cross-field diffusion of neutral prominence material,

  9. Ambipolar Diffusion Effects on Weakly Ionized Turbulence Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Li, Pak Shing; McKee, Christopher F.; Klein, Richard I.

    2011-04-01

    Ambipolar diffusion (AD) is a key process in molecular clouds (MCs). Non-ideal MHD turbulence simulations are technically very challenging because of the large Alfvén speed of ions in weakly ionized clouds. Using the Heavy-Ion Approximation method (Li, McKee & Klein 2006), we have carried out two-fluid simulations of AD in isothermal, turbulent boxes at a resolution of 5123, to investigate the effect of AD on the weakly ionized turbulence in MCs. Our simulation results show that the neutral gas component of the two-fluid system gradually transforms from an ideal MHD turbulence system to near a pure hydrodynamic turbulence system within the standard AD regime, in which the neutrals and ions are coupled over a flow time. The change of the turbulent state has a profound effect on the weakly ionized MCs.

  10. Irradiation spectrum and ionization-induced diffusion effects in ceramics

    SciTech Connect

    Zinkle, S.J.

    1997-08-01

    There are two main components to the irradiation spectrum which need to be considered in radiation effects studies on nonmetals, namely the primary knock-on atom energy spectrum and ionizing radiation. The published low-temperature studies on Al{sub 2}O{sub 3} and MgO suggest that the defect production is nearly independent of the average primary knock-on atom energy, in sharp contrast to the situation for metals. On the other hand, ionizing radiation has been shown to exert a pronounced influence on the microstructural evolution of both semiconductors and insulators under certain conditions. Recent work on the microstructure of ion-irradiated ceramics is summarized, which provides evidence for significant ionization-induced diffusion. Polycrystalline samples of MgO, Al{sub 2}O{sub 3}, and MgAl{sub 2}O{sub 4} were irradiated with various ions ranging from 1 MeV H{sup +} to 4 MeV Zr{sup +} ions at temperatures between 25 and 650{degrees}C. Cross-section transmission electron microscopy was used to investigate the depth-dependent microstructural of the irradiated specimens. Dislocation loop nucleation was effectively suppressed in specimens irradiated with light ions, whereas the growth rate of dislocation loops was enhanced. The sensitivity to irradiation spectrum is attributed to ionization-induced diffusion. The interstitial migration energies in MgAl{sub 2}O{sub 4} and Al{sub 2}O{sub 3} are estimated to be {le}0.4 eV and {le}0.8 eV, respectively for irradiation conditions where ionization-induced diffusion effects are expected to be negligible.

  11. The diffuse ionized interstellar medium perpendicular to the plane of NGC 891

    NASA Technical Reports Server (NTRS)

    Dettmar, Ralf-Juergen; Keppel, Jean; Roberts, Morton S.; Gallagher, John S., III

    1990-01-01

    In an attempt to study the structure and the properties of the diffuse ionized interstellar medium perpendicular to the plane of disk galaxies researchers obtained H alpha images and spectra of NGC 891. Perhaps the most remarkable property of the H alpha emission line in NGC 891 is its extension out of the plane of the galaxy: researchers are able to measure the H alpha line out to more than 30 seconds (1.4 kpc) from the midplane. This means that the ionized hydrogen extends at least four times higher than the neutral hydrogen layer. An anomalously large scale-height for the ionized gas of approx. equals 1 kpc is also found in the Milky Way. The echelle spectra show a changing ratio of NII to H alpha. This excludes the possibility that the large scaleheight of the emission is due to scattering of disk emission by dust high above the plane. The z-extent of the H alpha emission is confirmed by the imaging result. The large z-extent of the ionized gas is confined to the inner half of the visible disk. In this inner region the H alpha distribution also shows a filamentary structure of the diffuse ionized medium. These filaments, sticking out of the plane, originate in HII regions in the plane. The H alpha image also shows a large scale asymmetry if the NE and SW parts of the disk are compared. The NE part is more prominent and extended in H alpha. The same asymmetry is also seen in the radio continuum distribution. This correlation between the diffuse ionized medium and the distribution of relativistic electrons is one example of a relation between star formation processes in the disk and the various components of the halo. Thermal filaments or spurs which are related to HII regions are also known in the Galaxy. These filamentary structures perpendicular to the galactic planes may represent the chimneys which result in the supernova dominated model of the Interstellar Medium by Norman and Ikeuchi (1989).

  12. Ultraviolet Halos around Spiral Galaxies. I. Morphology

    NASA Astrophysics Data System (ADS)

    Hodges-Kluck, Edmund; Cafmeyer, Julian; Bregman, Joel N.

    2016-12-01

    We examine ultraviolet halos around a sample of highly inclined galaxies within 25 Mpc to measure their morphology and luminosity. Despite contamination from galactic light scattered into the wings of the point-spread function, we find that ultraviolet (UV) halos occur around each galaxy in our sample. Around most galaxies the halos form a thick, diffuse disk-like structure, but starburst galaxies with galactic superwinds have qualitatively different halos that are more extensive and have filamentary structure. The spatial coincidence of the UV halos above star-forming regions, the lack of consistent association with outflows or extraplanar ionized gas, and the strong correlation between the halo and galaxy UV luminosity suggest that the UV light is an extragalactic reflection nebula. UV halos may thus represent 106-107 M ⊙ of dust within 2-10 kpc of the disk, whose properties may change with height in starburst galaxies.

  13. Beryllium in the Galactic halo - Surface abundances from standard, diffusive, and rotational stellar evolution, and implications

    NASA Technical Reports Server (NTRS)

    Deliyannis, Constantine P.; Pinsonneault, Marc H.

    1990-01-01

    The recently observed upper limits to the beryllium abundances in population II stars are much lower than population I detections. This difference reflects an intrinsic difference in the initial abundances and is not caused by different degrees of depletion driven by stellar evolution processes from similar initial abundances. Evolutionary sequences of models from the early premain sequence to beyond the turnoff that correspond to halo dwarfs with Fe/H abundances of -1.3, -2.3, and -3.3 are constructed, and standard, diffusive, and rotational mechanisms are used to estimate a maximal possible beryllium depletion. Halo star models in the T(eff) range 6000 to 5000 K might be rotationally depleted by a factor of 1.5-2, and the total depletion should be no more than (conservatively) a factor of 3. Implications for cosmology, cosmic-ray theory, and Galactic chemical evolution are discussed.

  14. Constraints on the Galactic Halo Dark Matter From FERMI-LAT Diffuse Measurements

    DOE PAGES

    Ackermann, M.; Ajello, M.; Atwood, W. B.; ...

    2012-11-28

    For this study, we have performed an analysis of the diffuse gamma-ray emission with the Fermi Large Area Telescope (LAT) in the Milky Way halo region, searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal, constraints are presented. We consider both gamma rays produced directly in the dark matter annihilation/decay and produced by inverse Compton scattering of the e+/e– produced in the annihilation/decay. Conservative limits are derived requiring that the dark matter signal does not exceed the observed diffuse gamma-ray emission. A second set of more stringent limits is derivedmore » based on modeling the foreground astrophysical diffuse emission using the GALPROP code. Uncertainties in the height of the diffusive cosmic-ray halo, the distribution of the cosmic-ray sources in the Galaxy, the index of the injection cosmic-ray electron spectrum, and the column density of the interstellar gas are taken into account using a profile likelihood formalism, while the parameters governing the cosmic-ray propagation have been derived from fits to local cosmic-ray data. In conclusion, the resulting limits impact the range of particle masses over which dark matter thermal production in the early universe is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic ray anomalies as the annihilation of dark matter.« less

  15. Constraints on the Galactic Halo Dark Matter from Fermi-LAT Diffuse Measurements

    NASA Technical Reports Server (NTRS)

    Ackermann, M.; Ajello, M.; Atwood, W. B.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Blandford, R. D.; Bloom, E. D.; hide

    2012-01-01

    We have performed an analysis of the diffuse gamma-ray emission with the Fermi Large Area Telescope (LAT) in the Milky Way halo region, searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal, constraints are presented. We consider both gamma rays produced directly in the dark matter annihilation/decay and produced by inverse Compton scattering of the e+/e- produced in the annihilation/decay. Conservative limits are derived requiring that the dark matter signal does not exceed the observed diffuse gamma-ray emission. A second set of more stringent limits is derived based on modeling the foreground astrophysical diffuse emission using the GALPROP code. Uncertainties in the height of the diffusive cosmic-ray halo, the distribution of the cosmic-ray sources in the Galaxy, the index of the injection cosmic-ray electron spectrum, and the column density of the interstellar gas are taken into account using a profile likelihood formalism, while the parameters governing the cosmic-ray propagation have been derived from fits to local cosmic-ray data. The resulting limits impact the range of particle masses over which dark matter thermal production in the early universe is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic ray anomalies as the annihilation of dark matter.

  16. Constraints on the Galactic Halo Dark Matter From FERMI-LAT Diffuse Measurements

    SciTech Connect

    Ackermann, M.; Ajello, M.; Atwood, W. B.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Casandjian, J. M.; Cecchi, C.; Charles, E.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cuoco, A.; Cutini, S.; D’Ammando, F.; de Angelis, A.; de Palma, F.; Dermer, C. D.; do Couto e Silva, E.; Drell, P. S.; Drlica-Wagner, A.; Falletti, L.; Favuzzi, C.; Fegan, S. J.; Focke, W. B.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Germani, S.; Giglietto, N.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Guiriec, S.; Gustafsson, M.; Hadasch, D.; Hayashida, M.; Horan, D.; Hughes, R. E.; Jackson, M. S.; Jogler, T.; Jóhannesson, G.; Johnson, A. S.; Kamae, T.; Knödlseder, J.; Kuss, M.; Lande, J.; Latronico, L.; Lionetto, A. M.; Llena Garde, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Mazziotta, M. N.; McEnery, J. E.; Mehault, J.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Naumann-Godo, M.; Norris, J. P.; Nuss, E.; Ohsugi, T.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Pesce-Rollins, M.; Pierbattista, M.; Piron, F.; Pivato, G.; Poon, H.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Romoli, C.; Sbarra, C.; Scargle, J. D.; Sgrò, C.; Siskind, E. J.; Spandre, G.; Spinelli, P.; Stawarz, Łukasz; Strong, A. W.; Suson, D. J.; Tajima, H.; Takahashi, H.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Tibaldo, L.; Tinivella, M.; Tosti, G.; Troja, E.; Usher, T. L.; Vandenbroucke, J.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Wallace, E.; Wood, K. S.; Wood, M.; Yang, Z.; Zaharijas, G.; Zimmer, S.

    2012-11-28

    For this study, we have performed an analysis of the diffuse gamma-ray emission with the Fermi Large Area Telescope (LAT) in the Milky Way halo region, searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal, constraints are presented. We consider both gamma rays produced directly in the dark matter annihilation/decay and produced by inverse Compton scattering of the e+/e produced in the annihilation/decay. Conservative limits are derived requiring that the dark matter signal does not exceed the observed diffuse gamma-ray emission. A second set of more stringent limits is derived based on modeling the foreground astrophysical diffuse emission using the GALPROP code. Uncertainties in the height of the diffusive cosmic-ray halo, the distribution of the cosmic-ray sources in the Galaxy, the index of the injection cosmic-ray electron spectrum, and the column density of the interstellar gas are taken into account using a profile likelihood formalism, while the parameters governing the cosmic-ray propagation have been derived from fits to local cosmic-ray data. In conclusion, the resulting limits impact the range of particle masses over which dark matter thermal production in the early universe is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic ray anomalies as the annihilation of dark matter.

  17. CONSTRAINTS ON THE GALACTIC HALO DARK MATTER FROM FERMI-LAT DIFFUSE MEASUREMENTS

    SciTech Connect

    Ackermann, M.; Ajello, M.; Bechtol, K.; Blandford, R. D.; Bloom, E. D.; Borgland, A. W.; Bottacini, E.; Buehler, R.; Atwood, W. B.; Baldini, L.; Barbiellini, G.; Bastieri, D.; Buson, S.; Bellazzini, R.; Bregeon, J.; Bonamente, E.; Brandt, T. J.; Brigida, M.; Bruel, P.; and others

    2012-12-20

    We have performed an analysis of the diffuse gamma-ray emission with the Fermi Large Area Telescope (LAT) in the Milky Way halo region, searching for a signal from dark matter annihilation or decay. In the absence of a robust dark matter signal, constraints are presented. We consider both gamma rays produced directly in the dark matter annihilation/decay and produced by inverse Compton scattering of the e {sup +}/e {sup -} produced in the annihilation/decay. Conservative limits are derived requiring that the dark matter signal does not exceed the observed diffuse gamma-ray emission. A second set of more stringent limits is derived based on modeling the foreground astrophysical diffuse emission using the GALPROP code. Uncertainties in the height of the diffusive cosmic-ray halo, the distribution of the cosmic-ray sources in the Galaxy, the index of the injection cosmic-ray electron spectrum, and the column density of the interstellar gas are taken into account using a profile likelihood formalism, while the parameters governing the cosmic-ray propagation have been derived from fits to local cosmic-ray data. The resulting limits impact the range of particle masses over which dark matter thermal production in the early universe is possible, and challenge the interpretation of the PAMELA/Fermi-LAT cosmic ray anomalies as the annihilation of dark matter.

  18. HST/COS Observations of Ionized Gas Accretion at the Disk–Halo Interface of M33

    NASA Astrophysics Data System (ADS)

    Zheng, Y.; Peek, J. E. G.; Werk, J. K.; Putman, M. E.

    2017-01-01

    We report the detection of accreting ionized gas at the disk–halo interface of the nearby galaxy M33. We analyze Hubble Space Telescope/Cosmic Origins Spectrograph absorption-line spectra of seven ultraviolet-bright stars evenly distributed across the disk of M33. We find Si iv absorption components consistently redshifted relative to the bulk M33's ISM absorption along all the sightlines. The Si iv detection indicates an enriched, disk-wide, ionized gas inflow toward the disk. This inflow is most likely multi-phase as the redshifted components can also be observed in ions with lower ionization states (e.g., S ii, P ii, Fe ii, Si ii). Kinematic modeling of the inflow is consistent with an accreting layer at the disk–halo interface of M33, which has an accretion velocity of {110}-20+15 {km} {{{s}}}-1 at a distance of {1.5}-1.0+1.0 kpc above the disk. The modeling indicates a total mass of ∼3.9 × 107 M⊙ for the accreting material at the disk–halo interface on the near side of the M33 disk, with an accretion rate of ∼2.9 M⊙ yr‑1. The high accretion rate and the level of metal enrichment suggest the inflow is likely to be the fallback of M33 gas from a galactic fountain and/or the gas pulled loosed during a close interaction between M31 and M33. Our study of M33 is the first to unambiguously reveal the existence of a disk-wide, ionized gas inflow beyond the Milky Way, providing a better understanding of gas accretion in the vicinity of a galaxy disk.

  19. Massive Stars and the Ionization of the Diffuse Medium

    NASA Astrophysics Data System (ADS)

    Kahre, Lauren E.; Walterbos, Rene A. M.

    2015-08-01

    Diffuse ionized Gas (DIG, sometimes called the warm ionized medium or WIM) has been recognized as a major component of the interstellar medium (ISM) in disk galaxies. A general understanding of the characteristics of the DIG is emerging, but several questions remain unanswered. One of these is the ionization mechanism for this gas, believed to be connected to OB stars and HII regions. Using 5-band (NUV (2750 A), U, V, B, and I) photometric imaging data from the Hubble Space Telescope (HST) Legacy Extragalactic Ultraviolet Survey (LEGUS) and ground-based Halpha data from the Local Volume Legacy (LVL) survey and HST Halpha data from LEGUS, we will investigate the photoionization of HII regions and DIG in nearly 50 galaxies. The 5-band photometry will enable us to determine properties of the most massive stars and reddening corrections for specific regions within a galaxy. Luminosities and ages for groups and clusters will be obtained from SED-fitting of photometric data. For individual stars ages will be determined from isochrone-fitting using reddening-corrected color-magnitude diagrams. We can then obtain estimates of the ionizing luminosities by matching these photometric properties for massive stars and clusters to various stellar atmosphere models. We will compare these predictions to the inferred Lyman continuum production rates from reddening-corrected ground- and HST-based Halpha data for HII regions and DIG. This particular presentation will demonstrate the above process for a set of selected regions in galaxies within the LEGUS sample. It will subsequently be expanded to cover the full LEGUS sample, with the overall goals of obtaining a better understanding of the radiative energy feedback from massive stars on the ISM, particularly their ability to ionize the surrounding ISM over a wide range of spatial scales and SFR surface densities, and to connect the ionization of the ISM to HII region morphologies.

  20. A Rich Globular Cluster System in Dragonfly 17: Are Ultra-diffuse Galaxies Pure Stellar Halos?

    NASA Astrophysics Data System (ADS)

    Peng, Eric W.; Lim, Sungsoon

    2016-05-01

    Observations of nearby galaxy clusters at low surface brightness have identified galaxies with low luminosities, but sizes as large as L ⋆ galaxies, leading them to be dubbed “ultra-diffuse galaxies” (UDGs). The survival of UDGs in dense environments like the Coma cluster suggests that UDGs could reside in much more massive dark halos. We report the detection of a substantial population of globular clusters (GCs) around a Coma UDG, Dragonfly 17 (DF17). We find that DF17 has a high GC specific frequency of S N = 26 ± 13. The GC system is extended, with an effective radius of 12″ ± 2″, or 5.6 ± 0.9 kpc at Coma distance, 70% larger than the galaxy itself. We also estimate the mean of the GC luminosity function to infer a distance of {97}-14+17 Mpc, providing redshift-independent confirmation that one of these UDGs is in the Coma cluster. The presence of a rich GC system in DF17 indicates that, despite its low stellar density, star formation was intense enough to form many massive star clusters. If DF17's ratio of total GC mass to total halo mass is similar to those in other galaxies, then DF17 has an inferred total mass of ˜1011 M ⊙, only ˜10% the mass of the Milky Way, but extremely dominated by dark matter, with M/L V ≈ 1000. We suggest that UDGs like DF17 may be “pure stellar halos,” i.e., galaxies that formed their stellar halo components, but then suffered an early cessation in star formation that prevented the formation of any substantial central disk or bulge. Based on observations with the NASA/ESA Hubble Space Telescope obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  1. A reservoir of ionized gas in the galactic halo to sustain star formation in the Milky Way.

    PubMed

    Lehner, Nicolas; Howk, J Christopher

    2011-11-18

    Without a source of new gas, our Galaxy would exhaust its supply of gas through the formation of stars. Ionized gas clouds observed at high velocity may be a reservoir of such gas, but their distances are key for placing them in the galactic halo and unraveling their role. We have used the Hubble Space Telescope to blindly search for ionized high-velocity clouds (iHVCs) in the foreground of galactic stars. We show that iHVCs with 90 ≤ |v(LSR)| ≲ 170 kilometers per second (where v(LSR) is the velocity in the local standard of rest frame) are within one galactic radius of the Sun and have enough mass to maintain star formation, whereas iHVCs with |v(LSR)| ≳ 170 kilometers per second are at larger distances. These may be the next wave of infalling material.

  2. Detection of Extraplanar Diffuse Ionized Gas in M83

    NASA Astrophysics Data System (ADS)

    Boettcher, Erin; Gallagher, J. S., III; Zweibel, Ellen G.

    2017-08-01

    We present the first kinematic study of extraplanar diffuse ionized gas (eDIG) in the nearby, face-on disk galaxy M83 using optical emission-line spectroscopy from the Robert Stobie Spectrograph on the Southern African Large Telescope. We use a Markov Chain Monte Carlo method to decompose the [N ii]λ λ 6548, 6583, Hα, and [S ii]λ λ 6717, 6731 emission lines into H ii region and diffuse ionized gas emission. Extraplanar, diffuse gas is distinguished by its emission-line ratios ([N ii]λ6583/Hα ≳ 1.0) and its rotational velocity lag with respect to the disk ({{Δ }}v=-24 km s-1 in projection). With interesting implications for isotropy, the velocity dispersion of the diffuse gas, σ =96 km s-1, is a factor of a few higher in M83 than in the Milky Way and nearby, edge-on disk galaxies. The turbulent pressure gradient is sufficient to support the eDIG layer in dynamical equilibrium at an electron scale height of {h}z=1 kpc. However, this dynamical equilibrium model must be finely tuned to reproduce the rotational velocity lag. There is evidence of local bulk flows near star-forming regions in the disk, suggesting that the dynamical state of the gas may be intermediate between a dynamical equilibrium and a galactic fountain flow. As one of the first efforts to study eDIG kinematics in a face-on galaxy, this study demonstrates the feasibility of characterizing the radial distribution, bulk velocities, and vertical velocity dispersions in low-inclination systems. Based on observations made with the Southern African Large Telescope (SALT) under program 2015-2-SCI-004 (PI: E. Boettcher).

  3. Ionization and feedback in Lyα haloes around two radio galaxies at z ∼ 2.5

    NASA Astrophysics Data System (ADS)

    Morais, S. G.; Humphrey, A.; Villar-Martín, M.; Lagos, P.; Moyano, M.; Overzier, R.; di Serego Alighieri, S.; Vernet, J.; Fernandes, C. A. C.

    2017-03-01

    We present new spectroscopic observations of two high-redshift radio galaxies, TXS 0211-122 (z = 2.34) and TXS 0828+193 (z = 2.57), known to be associated with large Lyα haloes. The observations were taken with the slits placed perpendicularly to the radio axis. With access to pre-existing Keck II observations taken with the slit placed along the radio axis, we are able to compare the properties of the gas in different regions of the galaxies. In both objects, we detect spatially extended Lyα emission perpendicularly to the radio axis. In TXS 0211-122, the flux and velocity profiles of Lyα are strongly affected by H I absorption/scattering. In line with previous studies, we find evidence for outflowing gas along the radio axis which may be the result of jet-gas interactions. In the slit oriented perpendicularly to the radio axis we find less perturbed gas kinematics, suggesting outflows of ionized gas in this object are focused along the radio jet axis. Additionally, we find evidence for a giant, UV-emitting arc or shell-like structure surrounding the radio galaxy Lyα halo, possibly resulting from feedback activity. In TXS 0828+193, a large Lyα halo (∼56 kpc) is detected perpendicularly to the radio axis. Along both slit position angles we find evidence for outflowing gas, which we argue is part of an approximately spherical, expanding shell or bubble of gas powered by feedback activity in the central regions of the galaxy. Our results suggest a diversity in the spatial distribution of ionized outflows in powerful radio galaxies at z ∼ 2.5.

  4. Measurements of beam halo diffusion and population density in the Tevatron and in the Large Hadron Collider

    SciTech Connect

    Stancari, Giulio

    2015-03-01

    Halo dynamics influences global accelerator performance: beam lifetimes, emittance growth, dynamic aperture, and collimation efficiency. Halo monitoring and control are also critical for the operation of high-power machines. For instance, in the high-luminosity upgrade of the LHC, the energy stored in the beam tails may reach several megajoules. Fast losses can result in superconducting magnet quenches, magnet damage, or even collimator deformation. The need arises to measure the beam halo and to remove it at controllable rates. In the Tevatron and in the LHC, halo population densities and diffusivities were measured with collimator scans by observing the time evolution of losses following small inward or outward collimator steps, under different experimental conditions: with single beams and in collision, and, in the case of the Tevatron, with a hollow electron lens acting on a subset of bunches. After the LHC resumes operations, it is planned to compare measured diffusivities with the known strength of transverse damper excitations. New proposals for nondestructive halo population density measurements are also briefly discussed.

  5. Tracing Dense and Diffuse Neutral Hydrogen in the Halo of the Milky Way

    NASA Astrophysics Data System (ADS)

    Moss, V. A.; Lockman, F. J.; McClure-Griffiths, N. M.

    2017-01-01

    We have combined observations of Galactic high-velocity H i from two surveys: a very sensitive survey from the Green Bank 140 ft Telescope with limited sky coverage, and the less sensitive but complete Galactic All Sky Survey from the 64 m Parkes Radio Telescope. The two surveys preferentially detect different forms of neutral gas due to their sensitivity. We adopt a machine learning approach to divide our data into two populations that separate across a range in column density: (1) a narrow line-width population typical of the majority of bright high velocity cloud components, and (2) a fainter, broad line-width population that aligns well with that of the population found in the Green Bank survey. We refer to these populations as dense and diffuse gas, respectively, and find that diffuse gas is typically located at the edges and in the tails of high velocity clouds, surrounding dense components in the core. A fit to the average spectrum of each type of gas in the Galactic All Sky Survey data reveals the dense population to have a typical line width of ˜20 km s-1 and brightness temperature of ˜0.3 K, while the diffuse population has a typical line width of ˜30 km s-1 and a brightness temperature of ˜0.2 K. Our results confirm that most surveys of high velocity gas in the Milky Way halo are missing the majority of the ubiquitous diffuse gas, and that this gas is likely to contribute at least as much mass as the dense gas.

  6. Evidence for Halo Contributions to the 1/4 keV Diffuse Soft X-Ray Background

    NASA Astrophysics Data System (ADS)

    Bellm, E. C.

    2003-12-01

    The 1/4-keV diffuse soft X-ray background (SXRB) apparently originates in a thermal plasma at around 106 K, but the location of this emission has proven to be difficult to determine. The finite flux in the Galactic plane and similarity of the spectrum at all latitudes led to a model where essentially all of the observed flux originated in a local hot bubble (LHB) surrounding the Sun. Snowden et al. (1998) have proposed a three-component model of the SXRB from the ROSAT All-Sky Survey R12 (1/4 keV) map which consists of an unabsorbed local component, an absorbed halo component, and an absorbed power law to represent the known contribution from AGN, which is quite small. We have investigated whether this model is consistent with the lower-energy data available from sounding rocket flights in the B and Be bands. We find that the Snowden model provides better correspondence with the low-energy Wisconsin bands than the pure LHB model. The differences are subtle because the bulk of the intensity variation in the Snowden model is still due to differences in the extent of the local bubble. We have also investigated whether the observed band ratios are fit by the emission models used. We find that with current collisional ionization equilibrium models, depleted abundances are necessary to be consistent with the observed band ratios. We also show that the model predictions depend strongly on the model version, which does little to lend confidence to their predictions. This work was supported by a NSF-REU site grant (AST-0139563) to the University of Wisconsin-Madison.

  7. Radio-Optical Alignment and Recent Star Formation Associated with Ionized Filaments in the Halo of NGC 5128 (Centaurus A)

    NASA Astrophysics Data System (ADS)

    Rejkuba, M.; Minniti, D.; Courbin, F.; Silva, D. R.

    2002-01-01

    We used a direct CCD camera at the Magellan I telescope at Las Campanas Observatory and the Focal Reducer/Low Dispersion Spectrograph (FORS1) at the Antu Very Large Telescope (VLT) ESO Paranal Observatory to image fields centered on the inner and outer optical filaments in the halo of NGC 5128. In the V versus U-V color-magnitude diagrams we have identified young blue supergiants associated with these line-emitting filaments located between the inner radio lobe and the northern middle lobe. Around the outer filament, stars as young as 10 Myr were detected. They are principally aligned with the direction of the radio jet, but a vertical north-south alignment along the edge of the H I cloud is also present. Young stars in the inner filament field are found inside the bright knots of photoionized gas and are strongly aligned in the direction of the center of the galaxy at the same position angle as the inner radio jet. Fitting the Padova isochrones on UV color-magnitude diagrams, we find that blue stars around the inner filaments have ages similar to the ones around the outer filaments ~10-15 Myr and the same abundance of Z=0.004. The presence of young blue supergiants clearly shows that the bright blue knots in the northeastern halo of NGC 5128 are associations of young stars with photoionized gas. The temperature of the brightest stars is T~12,000-16,000 K, insufficient to account alone for the high excitation lines observed in the surrounding ionized gas. Thus, the optical emission jet is principally seen due to its alignment with the radio structure of the active galactic nucleus (AGN). The highly collimated star formation is present only in the northeastern halo of the galaxy, suggesting interaction of the jet with the gas clouds deposited during the last accretion event as the preferred triggering mechanism. From these observations, we infer a lower limit for the age of the NGC 5128 jet at 107 yr. The triggering of the star formation in the dense clouds in the

  8. IONIZED GAS IN THE FIRST 10 kpc OF THE INTERSTELLAR GALACTIC HALO: METAL ION FRACTIONS

    SciTech Connect

    Howk, J. Christopher; Consiglio, S. Michelle E-mail: smconsiglio@ucla.edu

    2012-11-10

    We present direct measures of the ionization fractions of several sulfur ions in the Galactic warm ionized medium (WIM). We obtained high-resolution ultraviolet absorption-line spectroscopy of post-asymptotic giant branch stars in the globular clusters Messier 3 [(l, b) = (42.{sup 0}2, +78.{sup 0}7), d = 10.2 kpc, and z = 10.0 kpc] and Messier 5 [(l, b) = (3.{sup 0}9, +46.{sup 0}8), d = 7.5 kpc, and z = +5.3 kpc] with the Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer to measure, or place limits on, the column densities of S I, S II, S III, S IV, S VI, and H I. These clusters also house millisecond pulsars, whose dispersion measures give an electron column density from which we infer the H II column in these directions. We find fractions of S{sup +2} in the WIM for the M 3 and M 5 sight lines x(S{sup +2}) {identical_to} N(S{sup +2})/N(S) = 0.33 {+-} 0.07 and 0.47 {+-} 0.09, respectively, with variations perhaps related to location. With negligible quantities of the higher ionization states, we conclude that S{sup +} and S{sup +2} account for all of the S in the WIM. We extend the methodology to study the ion fractions in the warm and hot ionized gas of the Milky Way, including the high ions Si{sup +3}, C{sup +3}, N{sup +4}, and O{sup +5}. The vast majority of the Galactic ionized gas is warm (T {approx} 10{sup 4} K) and photoionized (the WIM) or very hot (T > 4 Multiplication-Sign 10{sup 5} K) and collisionally ionized. The common tracer of ionized gas beyond the Milky Way, O{sup +5}, traces <1% of the total ionized gas mass of the Milky Way.

  9. Ortho effect in electron ionization mass spectrometry of N-acylanilines bearing a proximal halo substituent.

    PubMed

    Jariwala, Freneil B; Figus, Margaret; Attygalle, Athula B

    2008-08-01

    Electron ionization (EI) mass spectra are not very helpful for characterizing ortho, meta, and para isomers of underivatized haloanilines since their spectra are virtually identical. In contrast, when the amino group of chloro-, bromo-, or iodoanilines is transformed to an N-formyl, N-acetyl, or N-benzoyl derivative, the spectra of the derivatives reveal a highly dramatic loss of a halogen radical, instead of an HX elimination usually expected from an "ortho effect." For example, the spectra of N-formyl, N-acetyl, and N-benzoyl derivatives of ortho isomers of chloro-, bromo-, and iodoanilines show a very prominent peak at m/z 120, 134, and 196, respectively, for the loss of the corresponding halogen atom.

  10. The case for diffuse, collisionally ionized interstellar C IV and SI IV below Z = 1 KPC

    NASA Astrophysics Data System (ADS)

    Harris, Alan W.; Bromage, Gordon E.

    1986-09-01

    The results of a study of highly ionized gas in the galactic disc and disc/halo interface region are presented, based on IUE observations of C IV and Si IV absorption in a specially selected set of 19 co-directional sight-lines to early-type stars. Evidence is presented for a generally distributed, collisionally ionized phase of this gas having a density in the plane of ≡3×10-9cm-3 and a scale height in the range of 1 - 3 kpc. It is shown that the use in a restricted range of sight-line directions in studies such as this may reduce confusion resulting from inhomogeneities in the distribution of the highly ionized medium.

  11. ON THE DIFFUSE Lyα HALO AROUND Lyα EMITTING GALAXIES

    SciTech Connect

    Lake, Ethan; Zheng, Zheng; Sadoun, Raphael; Cen, Renyue; Momose, Rieko; Ouchi, Masami E-mail: zhengzheng@astro.utah.edu

    2015-06-10

    Lyα photons scattered by neutral hydrogen atoms in the circumgalactic media or produced in the halos of star-forming galaxies are expected to lead to extended Lyα emission around galaxies. Such low surface brightness Lyα halos (LAHs) have been detected by stacking Lyα images of high-redshift star-forming galaxies. We study the origin of LAHs by performing radiative transfer modeling of nine z = 3.1 Lyα emitters (LAEs) in a high resolution hydrodynamic cosmological galaxy formation simulation. We develop a method of computing the mean Lyα surface brightness profile of each LAE by effectively integrating over many different observing directions. Without adjusting any parameters, our model yields an average Lyα surface brightness profile in remarkable agreement with observations. We find that observed LAHs cannot be accounted for solely by photons originating from the central LAE and scattered to large radii by hydrogen atoms in the circumgalactic gas. Instead, Lyα emission from regions in the outer halo is primarily responsible for producing the extended LAHs seen in observations, which potentially includes both star-forming and cooling radiation. With the limit on the star formation contribution set by the ultraviolet halo measurement, we find that cooling radiation can play an important role in forming the extended LAHs. We discuss the implications and caveats of such a picture.

  12. The Massive Stellar Population in the Diffuse Ionized Gas of M33

    NASA Technical Reports Server (NTRS)

    Hoopes, Charles G.; Walterbos, Rene A. M.

    1995-01-01

    We compare Far-UV, H alpha, and optical broadband images of the nearby spiral galaxy M33, to investigate the massive stars associated with the diffuse ionized gas. The H-alpha/FUV ratio is higher in HII regions than in the DIG, possibly indicating that an older population ionizes the DIG. The broad-band colors support this conclusion. The HII region population is consistent with a young burst, while the DIG colors resemble an older population with constant star formation. Our results indicate that there may be enough massive field stars to ionize the DIG, without the need for photon leakage from HII regions.

  13. The disk-halo interface in edge-on spirals

    NASA Technical Reports Server (NTRS)

    Walterbos, Rene; Braun, Robert; Norman, Colin

    1993-01-01

    We are studying the disk-halo interface in several edge-on spiral galaxies through extensive imagery in H(alpha) and other emission lines from Diffuse Ionized Gas (DIG), also referred to as the Warm Ionized Medium (WIM). In addition, for the nearby Sc galaxy NGC4631 we have obtained x-ray observations with ROSAT, to map the distribution of hot (10(exp 6) - 10(exp 7)) gas in the disk and halo. Here we present initial results for two late-type spirals, NGC4244 and NGC4631.

  14. Laser action in runaway electron pre-ionized diffuse discharges

    NASA Astrophysics Data System (ADS)

    Panchenko, Alexei N.; Lomaev, Mikhail I.; Panchenko, Nikolai A.; Tarasenko, Viktor F.; Suslov, Alexei I.

    2015-12-01

    Formation features of run-away electron preionized diffuse discharge (REP DD) and REP DD properties in different experimental conditions are studied. It was shown that sufficient uniformity of REP DD allows its application as an excitation source of lasers on different gas mixtures at elevated pressure. Promising results of REP DD application for development of gas lasers are shown. Stimulated radiation in the IR, visible and UV spectral ranges was obtained in the diffuse discharge. Ultimate efficiency of non-chain HF(DF) chemical and nitrogen lasers on mixtures of SF6 with H2(D2) and N2 was achieved. New operation mode of nitrogen laser is demonstrated under REP DD excitation. Kinetic model of the REP DD in mixtures of nitrogen with SF6 is developed allowing to predict the radiation parameters of nitrogen laser at λ = 337,1 nm. Long-pulse operation of rare gas halide lasers was achieved.

  15. Thermal diffusion in partially ionized gases - The case of unequal temperatures. [in solar chromosphere

    NASA Technical Reports Server (NTRS)

    Geiss, J.; Burgi, A.

    1987-01-01

    Previous calculations of thermal diffusion coefficients in partially ionized gases are extended to the case of unequal neutral and ion temperatures and/or temperature gradients. Formulas are derived for the general case of a major gas as well as for minor atoms and ions. Strong enhancements of minor-ion thermal diffusion coefficients over their values in the fully ionized gas are found when the degree of ionization in the main gas is relatively low. However, compared to the case of equal temperatures, the enhancements are less strong when the neutrals are cooler than the ions. The specific case of the H-H(+) mixture, which is important in the study of solar and stellar atmospheres, is discussed as an application.

  16. The Contribution of Field OB Stars to the Ionization of the Diffuse Ionized Gas in M33

    NASA Astrophysics Data System (ADS)

    Hoopes, Charles G.; Walterbos, René A. M.

    2000-10-01

    We present a study of the ionizing stars associated with the diffuse ionized gas (DIG) and H II regions in the nearby spiral galaxy M33. We compare our Schmidt Hα image to the far-ultraviolet (FUV, 1520 Å) image from the Ultraviolet Imaging Telescope (UIT). The Hα/FUV ratio is higher in H II regions than in the DIG, suggesting an older population of ionizing stars in the DIG. Assuming ionization equilibrium, we convert the Hα flux to the number of Lyman continuum photons NLyc. When compared to models of evolving stellar populations, the NLyc/FUV ratio in H II regions is consistent with a young burst, while the DIG ratio resembles an older burst population, or a steady state population built up by constant star formation, which is probably a more accurate description of the stellar population in the field. The UIT data is complemented with archival FUV and optical images of a small portion of the disk of M33 obtained with WFPC2 on board the Hubble Space Telescope (HST). These images overlap low- and mid-luminosity H II regions as well as DIG, so we can investigate the stellar population in these environments. Using the HST FUV and optical photometry, we assign spectral types to the stars observed in DIG and H II regions. The photometry indicates that ionizing stars are present in the DIG. We compare the predicted ionizing flux with the amount required to produce the observed Hα emission, and we find that field OB stars in the HST images can account for 40%+/-12% of the ionization of the DIG, while the stars in H II regions can provide 107%+/-26% of the Hα luminosity of the H II regions. Due to the limited coverage of the HST data, we cannot determine if stars outside the HST fields ionize some of the DIG located in the HST fields, nor can we determine if photons from stars inside the HST fields leak out of the area covered by the HST fields. We do not find any correlation between leakage of ionizing photons and Hα luminosity for the H II regions in our HST

  17. Detection of a Diffuse Extended Halo-like Structure around 47 Tuc

    NASA Astrophysics Data System (ADS)

    Piatti, Andrés E.

    2017-09-01

    We constructed for the first time a stellar density profile of 47 Tucanae (47 Tuc) out of ∼5.5 times its tidal radius (r t ) using high-quality deep BV photometry. After carefully considering the influence of photometric errors, and Milky Way and Small Magellanic Cloud composite stellar population contamination, we found that the cluster stellar density profile reaches a nearly constant value from ∼1.7r t outward, which does not depend on the direction from the cluster’s center considered. These results visibly contrast with recent distinct theoretical predictions on the existence of tidal tails or on a density profile that falls as {r}-4 at large distances, and with observational outcomes of a clumpy structure as well. Our results suggest that the envelope of 47 Tuc is a halo-like, nearly constant low-density structure.

  18. The Burrell Schmidt Deep Virgo Survey: Tidal Debris, Galaxy Halos, and Diffuse Intracluster Light in the Virgo Cluster

    NASA Astrophysics Data System (ADS)

    Mihos, J. Christopher; Harding, Paul; Feldmeier, John J.; Rudick, Craig; Janowiecki, Steven; Morrison, Heather; Slater, Colin; Watkins, Aaron

    2017-01-01

    We present the results of a deep imaging survey of the Virgo cluster of galaxies, concentrated around the cores of Virgo subclusters A and B. The goal of this survey was to detect and study very low surface brightness features present in Virgo, including discrete tidal features, the faint halos of luminous galaxies, and the diffuse intracluster light (ICL). Our observations span roughly 16 degrees2 in two filters, reaching a 3σ limiting depth of {μ }B = 29.5 and {μ }V = 28.5 mag arcsec-2. At these depths, our limiting systematic uncertainties are astrophysical: variations in faint background sources as well as scattered light from galactic dust. We show that this dust-scattered light is well traced by deep far-infrared imaging, making it possible to separate it from true diffuse light in Virgo. We use our imaging to trace and measure the color of the diffuse tidal streams and ICL in the Virgo core near M87, in fields adjacent to the core including the M86/M84 region, and to the south of the core around M49 and subcluster B, along with the more distant W{}\\prime cloud around NGC 4365. Overall, the bulk of the projected ICL is found in the Virgo core and within the W{}\\prime cloud; we find little evidence for an extensive ICL component in the field around M49. The bulk of the ICL we detect is fairly red in color (B - V = 0.7-0.9), indicative of old, evolved stellar populations. Based on the luminosity of the observed ICL features in the cluster, we estimate a total Virgo ICL fraction of 7%-15%. This value is somewhat smaller than that expected for massive, evolved clusters, suggesting that Virgo is still in the process of growing its extended ICL component. We also trace the shape of M87's extremely boxy outer halo out to ˜150 kpc, and show that the current tidal stripping rate from low luminosity galaxies is insufficient to have built M87's outer halo over a Hubble time. We identify a number of previously unknown low surface brightness structures around

  19. Investigating the Diffuse Ionized Gas in the Magellanic Stream with Mapped WHAM Observations

    NASA Astrophysics Data System (ADS)

    Smart, Brianna; Haffner, L. Matthew; Barger, Kathleen; Hernandez, Mike

    2016-01-01

    We present early stages of an Hα survey of the Magellanic Stream using the Wisconsin H-Alpha Mapper (WHAM). While the neutral component of the Stream may extend 200° across the sky (Nidever et al. 2010), its ionized gas has not yet been studied in detail. Fox et al. 2014 find that the tidal debris in the Magellanic System contains twice as much ionized gas as neutral and may extend 30° away from the H I emission. However, such absorption-line studies are not sensitive to the overall morphology of the ionized gas. Using targeted Hα emission observations of the Magellanic Stream, Barger et al. 2015 find that although the warm ionized gas tracks the neutral gas, it often spans a few degrees away from the H I emission at slightly offset velocities. Using WHAM's unprecedented sensitivity to diffuse emission (~ 10s of mR) and its velocity resolution (12 km/s) to isolate Stream emission, we are now conducting the first full Hα survey of its ionized component. Here we present early results, including spatial and kinematic comparisons to the well-established neutral profile of the Stream. WHAM research and operations are supported through NSF Award AST-1108911.

  20. CAN THE LYMAN CONTINUUM LEAKED OUT OF H II REGIONS EXPLAIN DIFFUSE IONIZED GAS?

    SciTech Connect

    Seon, Kwang-Il

    2009-09-20

    We present an attempt to explain the diffuse Halpha emission of a face-on galaxy M 51 with the 'standard' photoionization model, in which the Lyman continuum (Lyc) escaping from H II regions propagates large distances into the diffuse interstellar medium (ISM). The diffuse Halpha emission of M 51 is analyzed using thin slab models and exponential disk models in the context of the 'on-the-spot' approximation. The scale height of the ionized gas needed to explain the diffuse Halpha emission with the scenario is found to be of the order of {approx}1-2 kpc, consistent with those of our Galaxy and edge-on galaxies. The model also provides a vertical profile, when the galaxy is viewed edge-on, consisting of two-exponential components. However, it is found that an incredibly low absorption coefficient of kappa{sub 0} {approx} 0.4-0.8 kpc{sup -1} at the galactic plane, or, equivalently, an effective cross section as low as sigma{sub eff} {approx} 10{sup -5} of the photoionization cross section at 912 A is required to allow the stellar Lyc photons to travel through the H I disk. Such a low absorption coefficient is out of accord with the properties of the ISM. Furthermore, we found that even the model that has the diffuse ionized gas (DIG) phase only and no H I gas phase shows highly concentrated Halpha emissions around H II regions, and can account for only {approx}<26% of the Halpha luminosity of the DIG. This result places a strong constraint on the ionizing source of the DIG. We also report that the Halpha intensity distribution functions not only of the DIG, but also of H II regions in M 51, appear to be lognormal.

  1. Extremely faint, diffuse satellite systems in the M31 halo: exceptional star clusters or tiny dwarf galaxies?

    NASA Astrophysics Data System (ADS)

    Mackey, Dougal

    2013-10-01

    Recent years have seen the discovery of a variety of low surface brightness, diffuse stellar systems in the Local Group. Of particular prominence are the ultra-faint dwarf satellites of the Milky Way and the extended globular clusters seen in M31, M33, and NGC 6822. As part of the major Pan-Andromeda Archaeological Survey {PAndAS} we have discovered several very faint and diffuse stellar satellites in the M31 halo. In Cycle 19 we obtained ACS/WFC imaging for one of these, PAndAS-48, which has revealed it to be a puzzling and unusual object. On the size-luminosity plane it falls between the extended clusters and ultra-faint dwarfs; however, its characteristics do not allow us to unambiguously class it as either type of system. If PAndAS-48 is an extended cluster then it is the most elliptical, isolated, metal-poor, and lowest-luminosity example yet uncovered. Conversely, while its properties are generally consistent with those observed for the faint dwarf satellites of the Milky Way, it would be a factor 2-3 smaller in spatial extent than its Galactic counterparts at comparable luminosity. Here we propose deep resolved imaging of the remaining five similar objects in our sample, with the aim of probing this hitherto poorly-explored region of parameter space in greater detail. If we are able to confirm any of these objects as faint dwarfs, they will provide the first insight into the behaviour of this class of object in a galaxy other than the Milky Way.

  2. The Impact of Diffuse Ionized Gas on Emission-line Ratios and Gas Metallicity Measurements

    NASA Astrophysics Data System (ADS)

    Zhang, Kai; Yan, Renbin; MaNGA Team

    2016-01-01

    Diffuse Ionized Gas (DIG) is prevalent in star-forming galaxies. Using a sample of galaxies observed by MaNGA, we demonstrate how DIG in star-forming galaxies impact the measurements of emission line ratios, hence the gas-phase metallicity measurements and the interpretation of diagnostic diagrams. We demonstrate that emission line surface brightness (SB) is a reasonably good proxy to separate HII regions from regions dominated by diffuse ionized gas. For spatially-adjacent regions or regions at the same radius, many line ratios change systematically with emission line surface brightness, reflecting a gradual increase of dominance by DIG towards low SB. DIG could significantly bias the measurement of gas metallicity and metallicity gradient. Because DIG tend to have a higher temperature than HII regions, at fixed metallicity DIG displays lower [NII]/[OII] ratios. DIG also show lower [OIII]/[OII] ratios than HII regions, due to extended partially-ionized regions that enhance all low-ionization lines ([NII], [SII], [OII], [OI]). The contamination by DIG is responsible for a substantial portion of the scatter in metallicity measurements. At different surface brightness, line ratios and line ratio gradients can differ systematically. As DIG fraction could change with radius, it can affect the metallicity gradient measurements in systematic ways. The three commonly used strong-line metallicity indicators, R23, [NII]/[OII], O3N2, are all affected in different ways. To make robust metallicity gradient measurements, one has to properly isolate HII regions and correct for DIG contamination. In line ratio diagnostic diagrams, contamination by DIG moves HII regions towards composite or LINER-like regions.

  3. The origin of the ionization of the diffuse interstellar medium in spiral galaxies. I. Photometric measurements

    NASA Astrophysics Data System (ADS)

    Zurita, A.; Rozas, M.; Beckman, J. E.

    2000-11-01

    We present a complete study of the diffuse ionized gas (DIG) in a sample of six spiral galaxies (NGC 157, NGC 3359, NGC 3631, NGC 6764, NGC 6951, NGC 7479) using very high quality Hα images which allow analysis down to very low surface brightness (between 0.3 and 2 pc cm-6). Separation of the diffuse Hα emission from that of the H II regions was performed using the most reliable method: subtracting from the integrated Hα flux of a complete galaxy the contribution from its fully catalogued population of H II regions. The integrated luminosity of the DIG is considerable ( ~ 1040-1042 erg s-1) and is a high fraction of the total Hα emission of each galaxy. Lower and upper limits to the DIG emission in Hα were derived. The lower limits vary from 25% to 50% and the upper limits from 45% to 70%, in our observed sample. Previous studies of a very small number of objects, showed that there is a spatial correlation between the DIG and the H II regions in spiral galaxies suggesting that the DIG is photoionized by Lyman continuum photons (Lyc) which leak from H II regions. Here we go further: we show that the correlation of the DIG is stronger with the most luminous H II regions and we propose a specific model for the ionization of the DIG: we show that the luminosity, in Lyc photons, leaking from the most luminous H II regions is enough to ionize the diffuse gas in a model where the H II regions with luminosities greater than LHα>= 1038.6 erg s-1 are density bounded (Beckman et al. \\cite{gordo}). This model predicts that a fraction of this flux escapes from the galaxy into the surrounding medium.

  4. Halos around planetary nebulae

    NASA Technical Reports Server (NTRS)

    Jewitt, D. C.; Danielson, G. E.; Kupferman, P. N.

    1986-01-01

    Preliminary results of a CCD survey designed to detect and investigate faint halos around planetary nebulae are reported. A TI 800 x 800 pixel CCD was used to take deep exposures of 44 planetary nebulae. The exposures were obtained through an H-alpha filter at the Cassegrain focus of the Palomar 1.5 m telescope. Spatial resolutions of 1 to 2 arcsec were obtained across 400 arcsec wide fields. The images, which are in many cases considerably deeper than any previously taken, reveal numerous planetary nebula halos. About two-thirds of the studied nebulae possess extensive outer halos, here defined as any extended emission beyond the 10 percent isophote. Ionized sulphur electron density measurements show that in some nebulae, the mass in the halo is comparable to the mass contained in the primary H II region. The data have been used to place constraints on the mode of origin of the halos. It is likely that the halos originate either by dynamical separation of a single ejected shell of gas or by the ejection of two or more such shells from the central star. It is possible but less likely that the halos are caused by excitation of the preplanetary stellar wind and improbable that the halos represent reflection nebulae.

  5. Facilitated Diffusion of Acetonitrile Revealed by Quantitative Breath Analysis Using Extractive Electrospray Ionization Mass Spectrometry

    PubMed Central

    Li, Ming; Ding, Jianhua; Gu, Haiwei; Zhang, Yan; Pan, Susu; Xu, Ning; Chen, Huanwen; Li, Hongmei

    2013-01-01

    By using silver cations (Ag+) as the ionic reagent in reactive extractive electrospray ionization mass spectrometry (EESI-MS), the concentrations of acetonitrile in exhaled breath samples from the volunteers including active smokers, passive smokers, and non-smokers were quantitatively measured in vivo, without any sample pretreatment. A limit of detection (LOD) and relative standard deviation (RSD) were 0.16 ng/L and 3.5% (n = 8), respectively, for the acetonitrile signals in MS/MS experiments. Interestingly, the concentrations of acetonitrile in human breath continuously increased for 1–4 hours after the smoker finished smoking and then slowly decreased to the background level in 7 days. The experimental data of a large number of (> 165) samples indicated that the inhaled acetonitrile is excreted most likely by facilitated diffusion, instead of simple diffusion reported previously for other volatile compounds. PMID:23386969

  6. Facilitated diffusion of acetonitrile revealed by quantitative breath analysis using extractive electrospray ionization mass spectrometry.

    PubMed

    Li, Ming; Ding, Jianhua; Gu, Haiwei; Zhang, Yan; Pan, Susu; Xu, Ning; Chen, Huanwen; Li, Hongmei

    2013-01-01

    By using silver cations (Ag⁺) as the ionic reagent in reactive extractive electrospray ionization mass spectrometry (EESI-MS), the concentrations of acetonitrile in exhaled breath samples from the volunteers including active smokers, passive smokers, and non-smokers were quantitatively measured in vivo, without any sample pretreatment. A limit of detection (LOD) and relative standard deviation (RSD) were 0.16 ng/L and 3.5% (n = 8), respectively, for the acetonitrile signals in MS/MS experiments. Interestingly, the concentrations of acetonitrile in human breath continuously increased for 1-4 hours after the smoker finished smoking and then slowly decreased to the background level in 7 days. The experimental data of a large number of (> 165) samples indicated that the inhaled acetonitrile is excreted most likely by facilitated diffusion, instead of simple diffusion reported previously for other volatile compounds.

  7. Highly ionized gas absorption in the disk and halo toward HD 167756 at 3.5 kilometers per second resolution

    NASA Technical Reports Server (NTRS)

    Savage, Blair D.; Sembach, Kenneth R.; Cardelli, Jason A.

    1994-01-01

    High-resolution spectra of interstellar Si IV, C IV, and N V absorption lines along the 4 kpc path to the inner Galaxy star HD 167756 at z = -0.85 kpc are presented. The spectra were obtained with the echelle mode of Goddard High Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope (HST) and have signal-to-noise ratios ranging from 23 to 38. The high resolution of the measurements full width at half maximum (FWHM = 3.5 km/s) results in fully resolved line profiles for the highly ionized gas absorption. The measurements provide information on the column density per unit velocity, N(v), as a function of velocity for Si IV, C IV, and N V. The C IV and N V profiles extend from -70 to +70 km/s, while the Si IV profiles extend from -40 to +70 km/s. The integrated logarithmic column densities are long N(Si IV) = 13.09 +/- 0.02, log N(C IV) = 13.83 +/- 0.02, and log N(N V) = 13.56 +/- 0.03. The N V profile is broad, asymmetric, and featureless, while the Si IV profile contains narrow absorption components near V(sub LSR) = -19, 0, +20, and +52 km/s with Doppler spread parameters, b about = 10-12 km/s. The C IV profile contains both broad and narrow structure. The high ion feature near +52 km/s is also detected in the low-ionization lines of Ca II, O I, Si II, and Fe II. The other narrow Si IV and C IV components occur within several km/s of components seen in low-ionization species. The sight line contains at least two types of highly ionized gas. One type gives rise to a broad N V profile, and the other results in the more structured Si IV profile. The C IV profile contains contributions from both types of highly ionized gas. The broad but asymmetric N V profile is well represented by a large Galactic scale height gas which is participating in Galactic rotation and has a combination of thermal and turbulent broadening with b(sub tot) about = 42 km/s. The C IV to N V abundance ratio of 1.0 +/- 0.3 for the gas implies T about 1.6 x 10(exp 5) K or about 8 x 10

  8. SDSS IV MaNGA: Deep observations of extra-planar, diffuse ionized gas around late-type galaxies from stacked IFU spectra

    NASA Astrophysics Data System (ADS)

    Jones, A.; Kauffmann, G.; D'Souza, R.; Bizyaev, D.; Law, D.; Haffner, L.; Bahé, Y.; Andrews, B.; Bershady, M.; Brownstein, J.; Bundy, K.; Cherinka, B.; Diamond-Stanic, A.; Drory, N.; Riffel, R. A.; Sánchez, S. F.; Thomas, D.; Wake, D.; Yan, R.; Zhang, K.

    2017-03-01

    We have conducted a study of extra-planar diffuse ionized gas using the first year data from the MaNGA IFU survey. We have stacked spectra from 49 edge-on, late-type galaxies as a function of distance from the midplane of the galaxy. With this technique we can detect the bright emission lines Hα, Hβ, [O ii]λλ3726, 3729, [O iii]λ5007, [N ii]λλ6549, 6584, and [S ii]λλ6717, 6731 out to about 4 kpc above the midplane. With 16 galaxies we can extend this analysis out to about 9 kpc, i.e. a distance of 2Re, vertically from the midplane. In the halo, the surface brightnesses of the [O ii] and Hα emission lines are comparable, unlike in the disk where Hα dominates. When we split the sample by specific star-formation rate, concentration index, and stellar mass, each subsample's emission line surface brightness profiles and ratios differ, indicating that extra-planar gas properties can vary. The emission line surface brightnesses of the gas around high specific star-formation rate galaxies are higher at all distances, and the line ratios are closer to ratios characteristic of H ii regions compared with low specific star-formation rate galaxies. The less concentrated and lower stellar mass samples exhibit line ratios that are more like H ii regions at larger distances than their more concentrated and higher stellar mass counterparts. The largest difference between different subsamples occurs when the galaxies are split by stellar mass. We additionally infer that gas far from the midplane in more massive galaxies has the highest temperatures and steepest radial temperature gradients based on their [N ii]/Hα and [O ii]/Hα ratios between the disk and the halo. SDSS IV.

  9. Implementation of cost-effective diffuse light source mechanism to reduce specular reflection and halo effects for resistor-image processing

    NASA Astrophysics Data System (ADS)

    Chen, Yung-Sheng; Wang, Jeng-Yau

    2015-09-01

    Light source plays a significant role to acquire a qualified image from objects for facilitating the image processing and pattern recognition. For objects possessing specular surface, the phenomena of reflection and halo appearing in the acquired image will increase the difficulty of information processing. Such a situation may be improved by the assistance of valuable diffuse light source. Consider reading resistor via computer vision, due to the resistor's specular reflective surface it will face with a severe non-uniform luminous intensity on image yielding a higher error rate in recognition without a well-controlled light source. A measurement system including mainly a digital microscope embedded in a replaceable diffuse cover, a ring-type LED embedded onto a small pad carrying a resistor for evaluation, and Arduino microcontrollers connected with PC, is presented in this paper. Several replaceable cost-effective diffuse covers made by paper bowl, cup and box inside pasted with white paper are presented for reducing specular reflection and halo effects and compared with a commercial diffuse some. The ring-type LED can be flexibly configured to be a full or partial lighting based on the application. For each self-made diffuse cover, a set of resistors with 4 or 5 color bands are captured via digital microscope for experiments. The signal-to-noise ratio from the segmented resistor-image is used for performance evaluation. The detected principal axis of resistor body is used for the partial LED configuration to further improve the lighting condition. Experimental results confirm that the proposed mechanism can not only evaluate the cost-effective diffuse light source but also be extended as an automatic recognition system for resistor reading.

  10. The diffusion of charged particles in the weakly ionized plasma with power-law kappa-distributions

    NASA Astrophysics Data System (ADS)

    Wang, Lan; Du, Jiulin

    2017-10-01

    We study the diffusion of charged particles in the weakly ionized plasma with the power-law κ-distributions and without the magnetic field. The electrons and ions have different κ-parameters. We obtain the expressions of both diffusion and mobility coefficients of electrons and ions respectively in the plasma. We find that these new transport coefficient formulae depend strongly on the κ-parameters in the power-law distributed plasma. When we take κ→∞, these formulae reduce to the classical forms in the weakly ionized plasma with a Maxwellian distribution.

  11. Directional Degradation of Spectralon Diffuser Under Ionizing Radiation for Calibration of Space-Based Sensors

    NASA Technical Reports Server (NTRS)

    Georgiev, G. T.; Butler, J. J.; Kowalewski, M. G.; Ding, L.

    2012-01-01

    Assessment of the effect of Vacuum Ultra Violet (VUV) irradiation on the Bidirectional Reflectance Distribution Function (BRDF) of Spectralon is presented in this paper. The sample was a 99% white Spectralon calibration standard irradiated with VUV source positioned at 60o off the irradiation direction for a total of 20 hours. The BRDF before and after VUV irradiation was measured and compared at number of wavelengths in the UV, VIS and IR. Non-isotropic directional degradation of Spectralon diffuser under ionizing radiation was detected at different BRDF measurement geometries primarily at UV spectral range. The 8o directional/hemispherical reflectance of the same sample was also measured and compared from 200nm to 2500nm. Index Terms BRDF, Reflectance, Multiangular, Spectralon, Remote Sensing

  12. Surface diffusion of In on Si(111): Evidence for surface ionization effects

    SciTech Connect

    Allen, C.E.; Ditchfield, R.; Seebauer, E.G.

    1996-01-01

    Second harmonic microscopy has been used to quantify the surface diffusion of In on Si(111). At temperatures near 50{percent} of the bulk melting temperature and in the coverage range 0{much_gt}{theta}{much_gt}0.7, the activation energy {ital E}{sub diff} and pre-exponential factor {ital D}{sub 0} lie at 42{plus_minus}0.5 kcal/mol and 3{times}10{sup 3{plus_minus}0.3} cm{sup 2}/s, respectively. These parameters, which are quite large, are explained semiquantitatively by reference to an adatom{endash}vacancy model recently developed for related systems. The present work, when compared with the results of these other systems, offers significant evidence for the effects of adatom{endash}vacancy ionization. {copyright} {ital 1996 American Vacuum Society}

  13. Injection to Rapid Diffusive Shock Acceleration at Perpendicular Shocks in Partially Ionized Plasmas

    NASA Astrophysics Data System (ADS)

    Ohira, Yutaka

    2016-08-01

    We present a three-dimensional hybrid simulation of a collisionless perpendicular shock in a partially ionized plasma for the first time. In this simulation, the shock velocity and upstream ionization fraction are v sh ≈ 1333 km s-1 and f i ˜ 0.5, which are typical values for isolated young supernova remnants (SNRs) in the interstellar medium. We confirm previous two-dimensional simulation results showing that downstream hydrogen atoms leak into the upstream region and are accelerated by the pickup process in the upstream region, and large magnetic field fluctuations are generated both in the upstream and downstream regions. In addition, we find that the magnetic field fluctuations have three-dimensional structures and the leaking hydrogen atoms are injected into the diffusive shock acceleration (DSA) at the perpendicular shock after the pickup process. The observed DSA can be interpreted as shock drift acceleration with scattering. In this simulation, particles are accelerated to v ˜ 100 v sh ˜ 0.3 c within ˜100 gyroperiods. The acceleration timescale is faster than that of DSA in parallel shocks. Our simulation results suggest that SNRs can accelerate cosmic rays to 1015.5 eV (the knee) during the Sedov phase.

  14. Implementation of a 3D halo neutral model in the TRANSP code and application to projected NSTX-U plasmas

    NASA Astrophysics Data System (ADS)

    Medley, S. S.; Liu, D.; Gorelenkova, M. V.; Heidbrink, W. W.; Stagner, L.

    2016-02-01

    A 3D halo neutral code developed at the Princeton Plasma Physics Laboratory and implemented for analysis using the TRANSP code is applied to projected National Spherical Torus eXperiment-Upgrade (NSTX-U plasmas). The legacy TRANSP code did not handle halo neutrals properly since they were distributed over the plasma volume rather than remaining in the vicinity of the neutral beam footprint as is actually the case. The 3D halo neutral code uses a ‘beam-in-a-box’ model that encompasses both injected beam neutrals and resulting halo neutrals. Upon deposition by charge exchange, a subset of the full, one-half and one-third beam energy components produce first generation halo neutrals that are tracked through successive generations until an ionization event occurs or the descendant halos exit the box. The 3D halo neutral model and neutral particle analyzer (NPA) simulator in the TRANSP code have been benchmarked with the Fast-Ion D-Alpha simulation (FIDAsim) code, which provides Monte Carlo simulations of beam neutral injection, attenuation, halo generation, halo spatial diffusion, and photoemission processes. When using the same atomic physics database, TRANSP and FIDAsim simulations achieve excellent agreement on the spatial profile and magnitude of beam and halo neutral densities and the NPA energy spectrum. The simulations show that the halo neutral density can be comparable to the beam neutral density. These halo neutrals can double the NPA flux, but they have minor effects on the NPA energy spectrum shape. The TRANSP and FIDAsim simulations also suggest that the magnitudes of beam and halo neutral densities are relatively sensitive to the choice of the atomic physics databases.

  15. Implementation of a 3D halo neutral model in the TRANSP code and application to projected NSTX-U plasmas

    SciTech Connect

    Medley, S. S.; Liu, D.; Gorelenkova, M. V.; Heidbrink, W. W.; Stagner, L.

    2016-01-12

    A 3D halo neutral code developed at the Princeton Plasma Physics Laboratory and implemented for analysis using the TRANSP code is applied to projected National Spherical Torus eXperiment-Upgrade (NSTX-U plasmas). The legacy TRANSP code did not handle halo neutrals properly since they were distributed over the plasma volume rather than remaining in the vicinity of the neutral beam footprint as is actually the case. The 3D halo neutral code uses a 'beam-in-a-box' model that encompasses both injected beam neutrals and resulting halo neutrals. Upon deposition by charge exchange, a subset of the full, one-half and one-third beam energy components produce first generation halo neutrals that are tracked through successive generations until an ionization event occurs or the descendant halos exit the box. The 3D halo neutral model and neutral particle analyzer (NPA) simulator in the TRANSP code have been benchmarked with the Fast-Ion D-Alpha simulation (FIDAsim) code, which provides Monte Carlo simulations of beam neutral injection, attenuation, halo generation, halo spatial diffusion, and photoemission processes. When using the same atomic physics database, TRANSP and FIDAsim simulations achieve excellent agreement on the spatial profile and magnitude of beam and halo neutral densities and the NPA energy spectrum. The simulations show that the halo neutral density can be comparable to the beam neutral density. These halo neutrals can double the NPA flux, but they have minor effects on the NPA energy spectrum shape. The TRANSP and FIDAsim simulations also suggest that the magnitudes of beam and halo neutral densities are relatively sensitive to the choice of the atomic physics databases.

  16. Diffuse Ionized Gas in the Magellanic System: Early Results from WHAM-South

    NASA Astrophysics Data System (ADS)

    Haffner, L. Matthew; Madsen, G. J.

    2011-01-01

    From its new vantage point at CTIO, the Wisconsin Hα Mapper is poised to explore the full distribution and kinematics of diffuse plasma in extended gaseous structures near the Magellanic Clouds. Shaped by the interaction between the Clouds and the Milky Way, the Bridge, Stream, and Leading Arm gas complexes have been studied extensively in 21 cm emission and optical/UV absorption. With spectral resolution of 12 km/s, WHAM is able to separate optical emission from these structures and brighter local gas near vLSR 0 km/s. Combined with its unprecedented sensitivity to the limit of atmospheric line confusion ( 10s of mR), we are embarking on a survey of the ionized component of the Magellanic System with WHAM. With observations of the southern component of our all-sky survey nearly completed, we have begun to examine some emission features toward the Magellanic System. Here we present a sample of several regions observed recently with WHAM in Hα. WHAM was built and continues to operate with ongoing support from NSF. The research presented here is currently funded by award AST-0607512 and an International Program Development Fund from the University of Sydney.

  17. Identifying Extraplanar Diffuse Ionized Gas in a Sample of MaNGA Galaxies

    NASA Astrophysics Data System (ADS)

    Hubbard, Ryan J.; Diamond-Stanic, Aleksandar M.; MaNGA Team

    2016-01-01

    The efficiency with which galaxies convert gas into stars is driven by the continuous cycle of accretion and feedback processes within the circumgalactic medium. Extraplanar diffuse ionized gas (eDIG) can provide insights into the tumultuous processes that govern the evolution of galactic disks because eDIG emission traces both inflowing and outflowing gas. With the help of state-of-the-art, spatially-resolved spectroscopy from MaNGA (Mapping Nearby Galaxies at Apache Point Observatory), we developed a computational method to identify eDIG based on the strength of and spatial extent of optical emission lines for a diverse sample of 550 nearby galaxies. This sample includes roughly half of the MaNGA galaxies that will become publicly available in summer 2016 as part of the Thirteenth Data Release of the Sloan Digital Sky Survey. We identified signatures of eDIG in 8% of the galaxies in this sample, and we found that these signatures are particularly common among galaxies with active star formation and inclination angles >45 degrees. Our analysis of the morphology, incidence, and kinematics of eDIG has important implications for current models of accretion and feedback processes that regulate star formation in galaxies. We acknowledge support from the Astrophysics REU program at the University of Wisconsin-Madison, the National Astronomy Consortium, and The Grainger Foundation.

  18. Testing a Dynamical Equilibrium Model of the Extraplanar Diffuse Ionized Gas in NGC 891

    NASA Astrophysics Data System (ADS)

    Boettcher, Erin; Zweibel, Ellen G.; Gallagher, J. S., III; Benjamin, Robert A.

    2016-12-01

    The observed scale heights of extraplanar diffuse ionized gas (eDIG) layers exceed their thermal scale heights by a factor of a few in the Milky Way and other nearby edge-on disk galaxies. Here, we test a dynamical equilibrium model of the eDIG layer in NGC 891, where we ask whether the thermal, turbulent, magnetic field, and cosmic-ray pressure gradients are sufficient to support the layer. In optical emission-line spectroscopy from the SparsePak integral field unit on the WIYN 3.5 m telescope, the Hα emission in position-velocity space suggests that the eDIG is found in a ring between galactocentric radii of {R}\\min ≤slant R≤slant 8 {kpc}, where {R}\\min ≥slant 2 {kpc}. We find that the thermal ({σ }{th}=11 km s-1) and turbulent ({σ }{turb}=25 km s-1) velocity dispersions are insufficient to satisfy the hydrostatic equilibrium equation given an exponential electron scale height of {h}z=1.0 {kpc}. Using a literature analysis of radio continuum observations from the CHANG-ES survey, we demonstrate that the magnetic field and cosmic-ray pressure gradients are sufficient to stably support the gas at R≥slant 8 kpc if the cosmic rays are sufficiently coupled to the system ({γ }{cr}=1.45). Thus, a stable dynamical equilibrium model is viable only if the eDIG is found in a thin ring around R = 8 kpc, and nonequilibrium models such as a galactic fountain flow are of interest for further study.

  19. An Unusual Lunar Halo

    ERIC Educational Resources Information Center

    Cardon, Bartley L.

    1977-01-01

    Discusses a photograph of an unusual combination of lunar halos: the 22-degree refraction halo, the circumscribed halo, and a reflection halo. Deduces the form and orientations of the ice crystals responsible for the observed halo features. (MLH)

  20. An Unusual Lunar Halo

    ERIC Educational Resources Information Center

    Cardon, Bartley L.

    1977-01-01

    Discusses a photograph of an unusual combination of lunar halos: the 22-degree refraction halo, the circumscribed halo, and a reflection halo. Deduces the form and orientations of the ice crystals responsible for the observed halo features. (MLH)

  1. Simulating 3D Stellar Winds and Diffuse X-ray Emissions from Gases in Non-equilibrium Ionization State

    NASA Astrophysics Data System (ADS)

    Long, Min; Sun, Wei; Niu, Shu; Zhou, Xin; Ji, Li

    2017-08-01

    We investigate the physical properties of stellar winds launched in super stellar clusters (SSCs). Chandra observations have detected the presence of diffuse X-ray emission caused by hot gas from such winds in SSCs, and provide the best probe for understanding interactions between the stellar winds and the complex nursery regions. However, the details of the origin of cluster winds, the mass and energy ejection, the formation of diffuse X-ray emission, the fraction of winds contribution to the distribution of diffuse X-ray emission still remain unclear. We developed a multiphysics hydrodynamic model including self-gravity, head conduction and performed 3D simulations with an unprecedented grid resolution due to adaptive mesh refinement (AMR) capability in a case study of NGC 3603, as a supplement to the analysis of the archived 500 ks Chandra observations. The synthetic emission will be computed by assuming the gas in a non-equilibrium ionization (NEI) state indicated by Chandra observation, not coronal ionization equilibrium (CIE) that most works assumed, by using a customized NEI calculation module based on AtomDB. The results will be compared to the Chandra observations.

  2. THE ORIGIN OF THE 6.4 keV LINE EMISSION AND H{sub 2} IONIZATION IN THE DIFFUSE MOLECULAR GAS OF THE GALACTIC CENTER REGION

    SciTech Connect

    Dogiel, V. A.; Chernyshov, D. O.; Tatischeff, V.; Terrier, R.

    2013-07-10

    We investigate the origin of the diffuse 6.4 keV line emission recently detected by Suzaku and the source of H{sub 2} ionization in the diffuse molecular gas of the Galactic center (GC) region. We show that Fe atoms and H{sub 2} molecules in the diffuse interstellar medium of the GC are not ionized by the same particles. The Fe atoms are most likely ionized by X-ray photons emitted by Sgr A* during a previous period of flaring activity of the supermassive black hole. The measured longitudinal intensity distribution of the diffuse 6.4 keV line emission is best explained if the past activity of Sgr A* lasted at least several hundred years and released a mean 2-100 keV luminosity {approx}> 10{sup 38} erg s{sup -1}. The H{sub 2} molecules of the diffuse gas cannot be ionized by photons from Sgr A*, because soft photons are strongly absorbed in the interstellar gas around the central black hole. The molecular hydrogen in the GC region is most likely ionized by low-energy cosmic rays, probably protons rather than electrons, whose contribution into the diffuse 6.4 keV line emission is negligible.

  3. Gauging Metallicity of Diffuse Gas under an Uncertain Ionizing Radiation Field

    NASA Astrophysics Data System (ADS)

    Chen, Hsiao-Wen; Johnson, Sean D.; Zahedy, Fakhri S.; Rauch, Michael; Mulchaey, John S.

    2017-06-01

    Gas metallicity is a key quantity used to determine the physical conditions of gaseous clouds in a wide range of astronomical environments, including interstellar and intergalactic space. In particular, considerable effort in circumgalactic medium (CGM) studies focuses on metallicity measurements because gas metallicity serves as a critical discriminator for whether the observed heavy ions in the CGM originate in chemically enriched outflows or in more chemically pristine gas accreted from the intergalactic medium. However, because the gas is ionized, a necessary first step in determining CGM metallicity is to constrain the ionization state of the gas which, in addition to gas density, depends on the ultraviolet background radiation field (UVB). While it is generally acknowledged that both the intensity and spectral slope of the UVB are uncertain, the impact of an uncertain spectral slope has not been properly addressed in the literature. This Letter shows that adopting a different spectral slope can result in an order of magnitude difference in the inferred CGM metallicity. Specifically, a harder UVB spectrum leads to a higher estimated gas metallicity for a given set of observed ionic column densities. Therefore, such systematic uncertainties must be folded into the error budget for metallicity estimates of ionized gas. An initial study shows that empirical diagnostics are available for discriminating between hard and soft ionizing spectra. Applying these diagnostics helps reduce the systematic uncertainties in CGM metallicity estimates.

  4. Nuclear Halos

    SciTech Connect

    Vogt, Erich

    2010-07-27

    We show that extreme nuclear halos are caused only by pairs of s-wave neutrons (or single s-wave neutrons) and that such states occur much more frequently in the periodic table than previously believed. Besides lingering long near zero neutron separation energy such extreme halos have very remarkable properties: they can contribute significantly to the nuclear density at more than twice the normal nuclear radius and their spreading width can be very narrow. The properties of these states are primarily determined by the ''thickness'' of the nuclear surface in the mean-free nuclear potential and thus their importance increases greatly as we approach the neutron drip line. We discuss what such extreme halos are, where they occur, what their properties are and some of their impact on nuclear observations.

  5. Solar wind ionization temperatures inferred from the charge state composition of diffuse particle events

    NASA Technical Reports Server (NTRS)

    Galvin, A. B.; Ipavich, F. M.; Gloeckler, G.; Hovestadt, D.; Klecker, B.; Scholer, M.

    1984-01-01

    Detailed measurements of the charge state composition of energetic heavy ions in the diffuse component are presented for the first time. Spectral characteristics and charge state measurements for 12 diffuse ion events observed upstream of the earth's bow shock are reported. One event is analyzed in order to illustrate the basic assumptions and general techniques involved in the determination of charge state composition from the data. The probable solar wind origin of the seed population of the diffuse component is used together with the charge state composition of these heavy ions to estimate the charge state composition in the concurrent solar wind, and hence to infer the equilibrium coronal temperatures associated with a variety of solar wind flows. The results are compared with predicted solar wind values.

  6. Terminal Velocity Infall in QSO Absorption Line Halos

    NASA Astrophysics Data System (ADS)

    Benjamin, Robert A.

    We explore the hypothesis that clouds detected in quasar absorption line systems are falling at a terminal velocity toward the center of high redshift gaseous galactic halos. Since both the ionization level and terminal velocity of halo clouds increase with increasing distance from the central galaxy, velocity resolved profiles of highly ionized gas are predicted to have a greater width than low ionization gas. A line of sight passing through the center of gaseous halo (an idealized damped Ly alpha system), yields low ionization absorption at the velocity of the galaxy, flanked by high ionization on either side. Reasonable halo parameters yield total velocity extents for C IV of Delta v_{C IV}=100-200 km s^{-1}, in agreement with many systems observed by Lu et al (1997). The remaining systems may better described by the rotating disk model of Prochaska & Wolfe (1998). Finally, observational tests are suggested for verifying or falsifying the terminal velocity hypothesis for these systems.

  7. Modeling of Pickup Ion Distributions in the Halley Cometo-Sheath: Empirical Rates of Ionization, Diffusion, Loss and Creation of Fast Neutral Atoms

    NASA Technical Reports Server (NTRS)

    Huddleston, D.; Neugebauer, M.; Goldstein, B.

    1994-01-01

    The shape of the velocity distribution of water-group ions observed by the Giotto ion mass spectrometer on its approach to comet Halley is modeled to derive empirical values for the rates on ionization, energy diffusion, and loss in the mid-cometosheath.

  8. Modeling of Pickup Ion Distributions in the Halley Cometo-Sheath: Empirical Rates of Ionization, Diffusion, Loss and Creation of Fast Neutral Atoms

    NASA Technical Reports Server (NTRS)

    Huddleston, D.; Neugebauer, M.; Goldstein, B.

    1994-01-01

    The shape of the velocity distribution of water-group ions observed by the Giotto ion mass spectrometer on its approach to comet Halley is modeled to derive empirical values for the rates on ionization, energy diffusion, and loss in the mid-cometosheath.

  9. Ionization of the Diffuse Interstellar Medium by O Stars and the Time Integrated Spectrum of a Supernova Remnant

    NASA Astrophysics Data System (ADS)

    Miller, Walter Warren, III

    1994-01-01

    The diffuse interstellar medium (DISM) fills the majority of the Galactic volume, contains roughly one-third of all interstellar matter, and acts as the ambient environment in which dense clouds, cosmic rays, and most stars evolve. Its pervasiveness ensures it an active role in many important Galactic mechanisms, establishing an urgency to understand thoroughly its nature and the interactions between this medium and the host of denser 'contaminants' that exist within it. The work presented in this dissertation demonstrates our efforts at better understanding processes that affect aspects of the DISM. First, we have explored the possibility that the diffuse ionized gas of the Galaxy is kept ionized by O stars, and that such gas consists of the dilute portions of O star HII regions in a multiple component interstellar medium. To make this exploration, we calculated the HII region structures for the known galactic O stars and compared the integral properties of the ensemble (dispersion and emission measures) with the observational data. With the simplified assumptions of our standard cloud model, good quantitative agreement is found for the electron density as a function of z and the dispersion measures to pulsars at high and low latitudes as well as quantitative agreement for summary measures such as the mean vertical column density of electrons, the average H-alpha surface brightness perpendicular to the galactic plane, and its decrease at high latitude. Second, we present preliminary results of a project that estimates the x-ray surface brightness of a galaxy due to a steady state population of supernova remnants. Previous estimates of the surface brightness contribution from supernova remnants, limited by x-ray observations, marginally threaten or eliminate popular ideas concerning the diffuse interstellar medium density in galaxies. We improve upon this analysis by accurately modeling remnant evolution numerically, making possible a detailed description of the

  10. A strong diffusive ion mode in dense ionized matter predicted by Langevin dynamics

    DOE PAGES

    Mabey, P.; Richardson, S.; White, T. G.; ...

    2017-01-30

    We determined the state and evolution of planets, brown dwarfs and neutron star crusts by the properties of dense and compressed matter. Furthermore, due to the inherent difficulties in modelling strongly coupled plasmas, however, current predictions of transport coefficients differ by orders of magnitude. Collective modes are a prominent feature, whose spectra may serve as an important tool to validate theoretical predictions for dense matter. With recent advances in free electron laser technology, X-rays with small enough bandwidth have become available, allowing the investigation of the low-frequency ion modes in dense matter. Here, we present numerical predictions for these ionmore » modes and demonstrate significant changes to their strength and dispersion if dissipative processes are included by Langevin dynamics. Notably, a strong diffusive mode around zero frequency arises, which is not present, or much weaker, in standard simulations. These results have profound consequences in the interpretation of transport coefficients in dense plasmas.« less

  11. A strong diffusive ion mode in dense ionized matter predicted by Langevin dynamics

    PubMed Central

    Mabey, P.; Richardson, S.; White, T. G.; Fletcher, L. B.; Glenzer, S. H.; Hartley, N. J.; Vorberger, J.; Gericke, D. O.; Gregori, G.

    2017-01-01

    The state and evolution of planets, brown dwarfs and neutron star crusts is determined by the properties of dense and compressed matter. Due to the inherent difficulties in modelling strongly coupled plasmas, however, current predictions of transport coefficients differ by orders of magnitude. Collective modes are a prominent feature, whose spectra may serve as an important tool to validate theoretical predictions for dense matter. With recent advances in free electron laser technology, X-rays with small enough bandwidth have become available, allowing the investigation of the low-frequency ion modes in dense matter. Here, we present numerical predictions for these ion modes and demonstrate significant changes to their strength and dispersion if dissipative processes are included by Langevin dynamics. Notably, a strong diffusive mode around zero frequency arises, which is not present, or much weaker, in standard simulations. Our results have profound consequences in the interpretation of transport coefficients in dense plasmas. PMID:28134338

  12. A strong diffusive ion mode in dense ionized matter predicted by Langevin dynamics

    NASA Astrophysics Data System (ADS)

    Mabey, P.; Richardson, S.; White, T. G.; Fletcher, L. B.; Glenzer, S. H.; Hartley, N. J.; Vorberger, J.; Gericke, D. O.; Gregori, G.

    2017-01-01

    The state and evolution of planets, brown dwarfs and neutron star crusts is determined by the properties of dense and compressed matter. Due to the inherent difficulties in modelling strongly coupled plasmas, however, current predictions of transport coefficients differ by orders of magnitude. Collective modes are a prominent feature, whose spectra may serve as an important tool to validate theoretical predictions for dense matter. With recent advances in free electron laser technology, X-rays with small enough bandwidth have become available, allowing the investigation of the low-frequency ion modes in dense matter. Here, we present numerical predictions for these ion modes and demonstrate significant changes to their strength and dispersion if dissipative processes are included by Langevin dynamics. Notably, a strong diffusive mode around zero frequency arises, which is not present, or much weaker, in standard simulations. Our results have profound consequences in the interpretation of transport coefficients in dense plasmas.

  13. A strong diffusive ion mode in dense ionized matter predicted by Langevin dynamics.

    PubMed

    Mabey, P; Richardson, S; White, T G; Fletcher, L B; Glenzer, S H; Hartley, N J; Vorberger, J; Gericke, D O; Gregori, G

    2017-01-30

    The state and evolution of planets, brown dwarfs and neutron star crusts is determined by the properties of dense and compressed matter. Due to the inherent difficulties in modelling strongly coupled plasmas, however, current predictions of transport coefficients differ by orders of magnitude. Collective modes are a prominent feature, whose spectra may serve as an important tool to validate theoretical predictions for dense matter. With recent advances in free electron laser technology, X-rays with small enough bandwidth have become available, allowing the investigation of the low-frequency ion modes in dense matter. Here, we present numerical predictions for these ion modes and demonstrate significant changes to their strength and dispersion if dissipative processes are included by Langevin dynamics. Notably, a strong diffusive mode around zero frequency arises, which is not present, or much weaker, in standard simulations. Our results have profound consequences in the interpretation of transport coefficients in dense plasmas.

  14. A strong diffusive ion mode in dense ionized matter predicted by Langevin dynamics

    DOE PAGES

    Mabey, Paul; Richardson, S.; White, T. G.; ...

    2017-01-30

    The state and evolution of planets, brown dwarfs and neutron star crusts is determined by the properties of dense and compressed matter. Due to the inherent difficulties in modelling strongly coupled plasmas, however, current predictions of transport coefficients differ by orders of magnitude. Collective modes are a prominent feature, whose spectra may serve as an important tool to validate theoretical predictions for dense matter. With recent advances in free electron laser technology, X-rays with small enough bandwidth have become available, allowing the investigation of the low-frequency ion modes in dense matter. Here, we present numerical predictions for these ion modesmore » and demonstrate significant changes to their strength and dispersion if dissipative processes are included by Langevin dynamics. Notably, a strong diffusive mode around zero frequency arises, which is not present, or much weaker, in standard simulations. Finally, our results have profound consequences in the interpretation of transport coefficients in dense plasmas.« less

  15. Diffuse gas in retired galaxies: nebular emission templates and constraints on the sources of ionization

    NASA Astrophysics Data System (ADS)

    Johansson, Jonas; Woods, Tyrone E.; Gilfanov, Marat; Sarzi, Marc; Chen, Yan-Mei; Oh, Kyuseok

    2016-10-01

    We present emission-line templates for passively-evolving (`retired') galaxies, useful for investigation of the evolution of the interstellar medium in these galaxies, and characterization of their high-temperature source populations. The templates are based on high signal-to-noise (>800) co-added spectra (3700-6800 Å) of ˜11 500 gas-rich Sloan Digital Sky Survey galaxies devoid of star formation and active galactic nuclei. Stacked spectra are provided for the entire sample and sub-samples binned by mean stellar age. In our previous paper, Johansson et al., these spectra provided the first measurements of the He II 4686 Å line in passively-evolving galaxies, and the observed He II/Hβ ratio constrained the contribution of accreting white dwarfs (the `single-degenerate' scenario) to the Type Ia supernova rate. In this paper, the full range of unambiguously detected emission lines are presented. Comparison of the observed [O I] 6300 Å/Hα ratio with photoionization models further constrains any high-temperature single-degenerate scenario for Type Ia supernovae (with 1.5 ≲ T/105 K ≲ 10) to ≲3-6 per cent of the observed rate in the youngest age bin (i.e. highest SN Ia rate). Hence, for the same temperatures, in the presence of an ambient population of post-asymptotic giant branch stars, we exclude additional high-temperature sources with a combined ionizing luminosity of ≈1.35 × 1030 L⊙/M⊙,* for stellar populations with mean ages of 1-4 Gyr. Furthermore, we investigate the extinction affecting both the stellar and nebular continuum. The latter shows about five times higher values. This contradicts isotropically distributed dust and gas that renders similar extinction values for both cases.

  16. Gas motions within high-velocity cloud Complex A reveal that it is dissolving into the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Huey-You, Cannan; Barger, Kathleen; Nidever, David L.; Rueff, Katherine Meredith

    2017-01-01

    A massive gas cloud, known as Complex A, is headed towards our Galaxy. This high-velocity cloud is made up of 2 million solar masses of neutral and ionized hydrogen. This cloud is traveling through the Galactic halo, which causes a headwind that damages the cloud. Light escaping the Milky Way’s disk also hits the cloud and ionizes it. Using 21-cm radio observations from the Green Bank Telescope, we studied the motions of the gas. We found that diffuse gas is lagging behind the denser parts of the cloud. These motions suggest that gas is being stripped off the cloud and that it is dissolving into the Galactic halo. This disruptive process means that less gas will safely reach the disk of Milky Way and therefore the cloud will provide less gas for making future stars.

  17. Neutral and ionized polycyclic aromatic hydrocarbons, diffuse interstellar bands and the ultraviolet extinction curve

    NASA Technical Reports Server (NTRS)

    Salama, Farid; Allamandola, Louis John

    1993-01-01

    Neutral naphthalene C10H8, phenanthrene C14H10 and pyrene C16H10 absorb strongly in the ultraviolet region and may contribute to the extinction curve. High abundances are required to produce detectable structures. The cations of these polycyclic aromatic hydrocarbons (PAHs) absorb in the visible C10H8(+) has 13 discrete absorption bands which fall between 6800 and 4500 A. The strongest band at 6741 A falls close to the weak 6742 A diffuse interstellar band (DIB). Five other weaker bands also match DIBs. The possibility that C10H8(+) is responsible for some of the DIBs can be tested by searching for new DIBs at 6520 and 6151 A, other strong naphthalene cation band positions. If C10H8(+) is indeed responsible for the 6742 A feature, it accounts for 0.3% of the cosmic carbon. The spectrum of C16H10(+) is dominated by a strong band at 4435 A in an Ar matrix and 4395 A in Ne, wavelengths which fall very close to the strongest DIB at 4430 A. If C16H10(+) or a closely related pyrene-like ion, is indeed responsible for the 4430 A feature, it accounts for 0.2% of the cosmic carbon. An intense, very broad UV-to-visible continuum is reported which is associated with both ions and could explain how PAHs convert interstellar UV and visible radiation into IR radiation.

  18. Neutral and ionized polycyclic aromatic hydrocarbons, diffuse interstellar bands and the ultraviolet extinction curve

    NASA Technical Reports Server (NTRS)

    Salama, Farid; Allamandola, Louis John

    1993-01-01

    Neutral naphthalene C10H8, phenanthrene C14H10 and pyrene C16H10 absorb strongly in the ultraviolet region and may contribute to the extinction curve. High abundances are required to produce detectable structures. The cations of these polycyclic aromatic hydrocarbons (PAHs) absorb in the visible C10H8(+) has 13 discrete absorption bands which fall between 6800 and 4500 A. The strongest band at 6741 A falls close to the weak 6742 A diffuse interstellar band (DIB). Five other weaker bands also match DIBs. The possibility that C10H8(+) is responsible for some of the DIBs can be tested by searching for new DIBs at 6520 and 6151 A, other strong naphthalene cation band positions. If C10H8(+) is indeed responsible for the 6742 A feature, it accounts for 0.3% of the cosmic carbon. The spectrum of C16H10(+) is dominated by a strong band at 4435 A in an Ar matrix and 4395 A in Ne, wavelengths which fall very close to the strongest DIB at 4430 A. If C16H10(+) or a closely related pyrene-like ion, is indeed responsible for the 4430 A feature, it accounts for 0.2% of the cosmic carbon. An intense, very broad UV-to-visible continuum is reported which is associated with both ions and could explain how PAHs convert interstellar UV and visible radiation into IR radiation.

  19. Universality in Molecular Halo Clusters

    NASA Astrophysics Data System (ADS)

    Stipanović, P.; Markić, L. Vranješ; Bešlić, I.; Boronat, J.

    2014-12-01

    The ground state of weakly bound dimers and trimers with a radius extending well into the classically forbidden region is explored, with the goal to test the predicted universality of quantum halo states. The focus of the study is molecules consisting of T ↓ , D ↓ , 3He, 4He, and alkali atoms, where the interaction between particles is much better known than in the case of nuclei, which are traditional examples of quantum halos. The study of realistic systems is supplemented by model calculations in order to analyze how low-energy properties depend on the interaction potential. The use of variational and diffusion Monte Carlo methods enabled a very precise calculation of both the size and binding energy of the trimers. In the quantum halo regime, and for large values of scaled binding energies, all clusters follow almost the same universal line. As the scaled binding energy decreases, Borromean states separate from tango trimers.

  20. Halo Star Lithium Depletion

    SciTech Connect

    Pinsonneault, M. H.; Walker, T. P.; Steigman, G.; Narayanan, Vijay K.

    1999-12-10

    The depletion of lithium during the pre-main-sequence and main-sequence phases of stellar evolution plays a crucial role in the comparison of the predictions of big bang nucleosynthesis with the abundances observed in halo stars. Previous work has indicated a wide range of possible depletion factors, ranging from minimal in standard (nonrotating) stellar models to as much as an order of magnitude in models that include rotational mixing. Recent progress in the study of the angular momentum evolution of low-mass stars permits the construction of theoretical models capable of reproducing the angular momentum evolution of low-mass open cluster stars. The distribution of initial angular momenta can be inferred from stellar rotation data in young open clusters. In this paper we report on the application of these models to the study of lithium depletion in main-sequence halo stars. A range of initial angular momenta produces a range of lithium depletion factors on the main sequence. Using the distribution of initial conditions inferred from young open clusters leads to a well-defined halo lithium plateau with modest scatter and a small population of outliers. The mass-dependent angular momentum loss law inferred from open cluster studies produces a nearly flat plateau, unlike previous models that exhibited a downward curvature for hotter temperatures in the 7Li-Teff plane. The overall depletion factor for the plateau stars is sensitive primarily to the solar initial angular momentum used in the calibration for the mixing diffusion coefficients. Uncertainties remain in the treatment of the internal angular momentum transport in the models, and the potential impact of these uncertainties on our results is discussed. The 6Li/7Li depletion ratio is also examined. We find that the dispersion in the plateau and the 6Li/7Li depletion ratio scale with the absolute 7Li depletion in the plateau, and we use observational data to set bounds on the 7Li depletion in main-sequence halo

  1. Diffuse Optical Spectroscopy for the Quantitative Assessment of Acute Ionizing Radiation Induced Skin Toxicity Using a Mouse Model

    PubMed Central

    Chin, Lee; Korpela, Elina; Kim, Anthony; Yohan, Darren; Niu, Carolyn; Wilson, Brian C.; Liu, Stanley K.

    2016-01-01

    Acute skin toxicities from ionizing radiation (IR) are a common side effect from therapeutic courses of external beam radiation therapy (RT) and negatively impact patient quality of life and long term survival. Advances in the understanding of the biological pathways associated with normal tissue toxicities have allowed for the development of interventional drugs, however, current response studies are limited by a lack of quantitative metrics for assessing the severity of skin reactions. Here we present a diffuse optical spectroscopic (DOS) approach that provides quantitative optical biomarkers of skin response to radiation. We describe the instrumentation design of the DOS system as well as the inversion algorithm for extracting the optical parameters. Finally, to demonstrate clinical utility, we present representative data from a pre-clinical mouse model of radiation induced erythema and compare the results with a commonly employed visual scoring. The described DOS method offers an objective, high through-put evaluation of skin toxicity via functional response that is translatable to the clinical setting. PMID:27284926

  2. Where have all the cluster halos gone?

    NASA Technical Reports Server (NTRS)

    Burns, Jack O.; Sulkanen, Martin E.; Gisler, Galen R.; Perley, Rick A.

    1992-01-01

    A new LF (330 MHz) VLA image of the Perseus cluster confirms the presence of a miniradio halo with diameter of about 430 kpc (H0 = 75 km/s Mpc) surrounding 3C 84. A careful comparison with the Coma cluster shows that there is no evidence for a similar, very extended halo in Perseus despite the large number of cluster radio galaxies which could power such a halo. These two clusters represent two classes of radio halos which differ by the absence (Coma) or presence (Perseus) of cooling inflows. It is argued that smaller halos as in Perseus result form insufficient clusterwide magnetic fields. A simple model is presented which suggests that cooling flows can suppress the diffusion of turbulently amplified B-fields outward from the cluster core. Such a suppression leads to the development of minihalos which are confined to the cores of cooling flow clusters.

  3. Borromean halo, Tango halo, and halo isomers in atomic nuclei

    NASA Astrophysics Data System (ADS)

    Izosimov, Igor

    2016-01-01

    Structure of the ground and excited states in halo-like nuclei is discussed. Both the Borromean and tango halo types can be observed for n-p configurations of atomic nuclei.Structure of the halo may be different for the different levels and resonances in atomic nuclei. Isobar analog, double isobar analog, configuration, and double configuration states can simultaneously have n-n, n-p, and p-p halo components in their wave functions. When the halo structure of the excited state differs from that of the ground state, or the ground state has non-halo structure, the γ-transition from the excited state to the ground state can be essentially hindered, i.e. the formation of a specific type of isomers (halo isomers) becomes possible. B(Mγ) and B(Eγ) values for γ-transitions in 6,7,8Li, 8,9,10Be, 8,10,11B, 10,11,12,13,14C, 13,14,15,16,17N, 15,16,17,19O, and 17F are analyzed. Special attention is given to nuclei which ground state does not exhibit halo structure but the excited state (halo isomer) may have one.

  4. The Halo

    NASA Image and Video Library

    2013-12-23

    NASA's Cassini spacecraft looks towards the dark side of Saturn's largest moon, Titan, capturing the blue halo caused by a haze layer that hovers high in the moon's atmosphere. The haze that permeates Titan's atmosphere scatters sunlight and produces the orange color seen here. More on Titan's orange and blue hazes can be found at PIA14913. This view looks towards the side of Titan (3,200 miles or 5,150 kilometers across) that leads in its orbit around Saturn. North on Titan is up and rotated 40 degrees to the left. Images taken using red, green and blue spectral filters were combined to create this natural-color view. The images were taken with the Cassini spacecraft narrow-angle camera on Nov. 3, 2013. The view was acquired at a distance of approximately 2.421 million miles (3.896 million kilometers) from Titan. Image scale is 14 miles (23 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA17180

  5. ORIGAMI: DELINEATING HALOS USING PHASE-SPACE FOLDS

    SciTech Connect

    Falck, Bridget L.; Neyrinck, Mark C.; Szalay, Alexander S.

    2012-08-01

    We present the ORIGAMI method of identifying structures, particularly halos, in cosmological N-body simulations. Structure formation can be thought of as the folding of an initially flat three-dimensional manifold in six-dimensional phase space. ORIGAMI finds the outer folds that delineate these structures. Halo particles are identified as those that have undergone shell-crossing along three orthogonal axes, providing a dynamical definition of halo regions that is independent of density. ORIGAMI also identifies other morphological structures: particles that have undergone shell-crossing along 2, 1, or 0 orthogonal axes correspond to filaments, walls, and voids, respectively. We compare this method to a standard friends-of-friends halo-finding algorithm and find that ORIGAMI halos are somewhat larger, more diffuse, and less spherical, though the global properties of ORIGAMI halos are in good agreement with other modern halo-finding algorithms.

  6. Effect of ion velocity on creation of point defects halos of latent tracks in LiF

    NASA Astrophysics Data System (ADS)

    Volkov, A. E.; Schwartz, K.; Medvedev, N. A.; Trautmann, C.

    2017-09-01

    Parameters of point defects halos (F-color centers) created due to decays of self-trapped valence holes generated in nanometric vicinities of trajectories of gold ions of 275 MeV and 2187 MeV in LiF are estimated in absorption spectroscopy experiments. Such ions have approximately the same electronic stopping: 24.6 keV/nm and 22.9 keV/nm, respectively. In contrast to the usual concept of the velocity effect that a slower ion produces larger structure changes due to a higher density of the deposited energy, the opposite effect occurs for the defect halo revealing a larger radius and a larger defect concentration for an ion of the higher velocity realizing the same energy loss. Spatial spreading of generated valence holes before their self-trapping (500 fs) forms the size of the defect halos around the trajectories of the applied ions. Simulations with Monte-Carlo code TREKIS show no significant difference in the initial spatial distributions of these valence holes by the times of finishing of ionization cascades (∼10 fs after the projectile passage) within the radii of the defect halos deduced from the experiments. Using these distributions as initial conditions for spatial spreading of generated valence holes and taking into account the difference between the defect halo radii, the diffusion coefficients of these holes near the trajectories of 275 and 2187 MeV Au ions in LiF are estimated showing about six times larger value in tracks of the faster ion for irradiations at room temperatures. Presence of H-color centers changes considerably the kinetics of the created defect ensemble in the defect halo resulting in differences between the defect halo parameters in LiF crystals irradiated at 8 K vs. 300 K.

  7. Accretion in the galactic halo

    NASA Astrophysics Data System (ADS)

    Stephens, Alex Courtney

    2000-10-01

    The Milky Way disk is enveloped in a diffuse, dynamically-hot collection of stars and star clusters collectively known as the ``stellar halo''. Photometric and chemical analyses suggest that these stars are ancient fossils of the galaxy formation epoch. Yet, little is known about the origin of this trace population. Is this system merely a vestige of the initial burst of star formation within the decoupled proto-Galaxy, or is it the detritus of cannibalized satellite galaxies? In an attempt to unravel the history of the Milky Way's stellar halo, I performed a detailed spectroscopic analysis of 55 metal-poor stars possessing ``extreme'' kinematic properties. It is thought that stars on orbits that either penetrate the remote halo or exhibit large retrograde velocities could have been associated with assimilated (or ``accreted'') dwarf galaxies. The hallmark of an accreted halo star is presumed to be a deficiency (compared with normal stars) of the α-elements (O, Mg, Si, Ca, Ti) with respect to iron, a consequence of sporadic bursts of star formation within the diminutive galaxies. Abundances for a select group of light metals (Li, Na, Mg, Si, Ca, Ti), iron-peak nuclides (Cr, Fe, Ni), and neutron-capture elements (Y, Ba) were calculated using line-strengths measured from high-resolution, high signal-to-noise spectral observations collected with the Keck I 10-m and KPNO 4-m telescopes. The abundances extracted from the spectra reveal: (1)The vast majority of outer halo stars possess supersolar [α/Fe] > 0.0) ratios. (2)The [α/Fe] ratio appears to decrease with increasing metallicity. (3)The outer halo stars have lower ratios of [α/Fe] than inner halo stars at a given metallicity. (4)At the largest metallicities, there is a large spread in the observed [α/Fe] ratios. (5)[α/Fe] anti-correlates with RAPO. (6)Only one star (BD+80° 245) exhibits the peculiar abundances expected of an assimilated star. The general conclusion extracted from these data is that the

  8. "Invisible" Galactic Halos.

    ERIC Educational Resources Information Center

    Lugt, Karel Vander

    1993-01-01

    Develops a simple core-halo model of a galaxy that exhibits the main features of observed rotation curves and quantitatively illustrates the need to postulate halos of dark matter. Uses only elementary mechanics. (Author/MVL)

  9. "Invisible" Galactic Halos.

    ERIC Educational Resources Information Center

    Lugt, Karel Vander

    1993-01-01

    Develops a simple core-halo model of a galaxy that exhibits the main features of observed rotation curves and quantitatively illustrates the need to postulate halos of dark matter. Uses only elementary mechanics. (Author/MVL)

  10. Halo CME

    NASA Image and Video Library

    2017-09-28

    A giant cloud appears to expand outward from the sun in all directions in this image from Sept. 28, 2012, which is called a halo CME. This kind of image occurs when a CME moves toward Earth – as here – or directly away from it. Credit: ESA/NASA/SOHO CME WEEK: What To See in CME Images Two main types of explosions occur on the sun: solar flares and coronal mass ejections. Unlike the energy and x-rays produced in a solar flare – which can reach Earth at the speed of light in eight minutes – coronal mass ejections are giant, expanding clouds of solar material that take one to three days to reach Earth. Once at Earth, these ejections, also called CMEs, can impact satellites in space or interfere with radio communications. During CME WEEK from Sept. 22 to 26, 2014, we explore different aspects of these giant eruptions that surge out from the star we live with. When a coronal mass ejection blasts off the sun, scientists rely on instruments called coronagraphs to track their progress. Coronagraphs block out the bright light of the sun, so that the much fainter material in the solar atmosphere -- including CMEs -- can be seen in the surrounding space. CMEs appear in these images as expanding shells of material from the sun's atmosphere -- sometimes a core of colder, solar material (called a filament) from near the sun's surface moves in the center. But mapping out such three-dimensional components from a two-dimensional image isn't easy. Watch the slideshow to find out how scientists interpret what they see in CME pictures. The images in the slideshow are from the three sets of coronagraphs NASA currently has in space. One is on the joint European Space Agency and NASA Solar and Heliospheric Observatory, or SOHO. SOHO launched in 1995, and sits between Earth and the sun about a million miles away from Earth. The other two coronagraphs are on the two spacecraft of the NASA Solar Terrestrial Relations Observatory, or STEREO, mission, which launched in 2006. The two

  11. Farside Halo

    NASA Image and Video Library

    2017-09-28

    There's no way to tell from this SOHO image whether the halo CME on March 5, 2013, originated from the front or far of the sun. But the STEREO spacecraft were watching the sun from the sides and showed it was from the far side. The bright planet is Venus. Credit: NASA/SOHO CME WEEK: What To See in CME Images Two main types of explosions occur on the sun: solar flares and coronal mass ejections. Unlike the energy and x-rays produced in a solar flare – which can reach Earth at the speed of light in eight minutes – coronal mass ejections are giant, expanding clouds of solar material that take one to three days to reach Earth. Once at Earth, these ejections, also called CMEs, can impact satellites in space or interfere with radio communications. During CME WEEK from Sept. 22 to 26, 2014, we explore different aspects of these giant eruptions that surge out from the star we live with. When a coronal mass ejection blasts off the sun, scientists rely on instruments called coronagraphs to track their progress. Coronagraphs block out the bright light of the sun, so that the much fainter material in the solar atmosphere -- including CMEs -- can be seen in the surrounding space. CMEs appear in these images as expanding shells of material from the sun's atmosphere -- sometimes a core of colder, solar material (called a filament) from near the sun's surface moves in the center. But mapping out such three-dimensional components from a two-dimensional image isn't easy. Watch the slideshow to find out how scientists interpret what they see in CME pictures. The images in the slideshow are from the three sets of coronagraphs NASA currently has in space. One is on the joint European Space Agency and NASA Solar and Heliospheric Observatory, or SOHO. SOHO launched in 1995, and sits between Earth and the sun about a million miles away from Earth. The other two coronagraphs are on the two spacecraft of the NASA Solar Terrestrial Relations Observatory, or STEREO, mission, which

  12. High-Resolution Height-Profile Analysis and Laser-Ionization Characterization of a Wide Range of Fullerenes in Laminar Diffusion Flames

    NASA Astrophysics Data System (ADS)

    Siegmann, K.; Hepp, H.; Sattler, K.

    Neutral fullerenes are detected online in laminar, atmospheric pressure methane diffusion flames using time-of-flight mass spectrometry combined with laser ionization. The intensity of the C60 signal shows a quadratic dependence of the laser-pulse energy, which is consistent with two-photon ionization. Poly-cyclic aromatic hydrocarbons (PAH) are also found in these flames. Height profiles of fullerenes are compared with height profiles of PAH and it is found that the concentration of fullerenes most strongly at a height where the concentration of PAH decreases the most. This height in the flame probably marks the burnout of the available hydrogen. Since all fullerenes, independent of their number of carbons, peak at the same height above burner, we conclude that fullerenes in flames do not grow by the addition of small molecules.

  13. Quantum Halo States in Helium Tetramers.

    PubMed

    Stipanović, Petar; Vranješ Markić, Leandra; Boronat, Jordi

    2017-01-12

    The universality of quantum halo states enables a comparison of systems from different fields of physics, as demonstrated in two- and three-body clusters. In the present work, we studied weakly bound helium tetramers in order to test whether some of these four-body realistic systems qualify as halos. Their ground-state binding energies and structural properties were thoroughly estimated using the diffusion Monte Carlo method with pure estimators. Helium tetramer properties proved to be less sensitive on the potential model than previously evaluated trimer properties. We predict the existence of realistic four-body halo (4)He2(3)He2, whereas (4)He4 and (4)He3(3)He are close to the border and thus can be used as prototypes of quasi-halo systems. Our results could be tested by the experimental determination of the tetramers' structural properties using a setup similar to the one developed for the study of helium trimers.

  14. Large Halos of Missing Baryons Around Galaxies

    NASA Astrophysics Data System (ADS)

    Bregman, Joel

    2009-10-01

    If galaxies had the cosmological baryon-to-dark matter ratio, they would have 3-30 times their observed baryon mass. These missing baryons are undetected, but some fraction may surround a galaxy with a hot diffuse halo extending to R_virial (250 kpc). A loosely bound gaseous halo could be stripped in a cluster or group environment, but should be relatively undisturbed around isolated late-type spirals. Existing observations of spirals are mainly of nearby systems, where only the inner parts fit in a field of view so a halo on the scale of R_virial would pass unnoticed. To detect or place limits on a large halo of missing baryons, we propose to observe isolated L* spirals sufficiently distant that we can detect emission to at least R_virial.

  15. Modeling of pickup ion distributions in the Halley cometosheath: Empirical limits on rates of ionization, diffusion, loss and creation of fast neutral atoms

    NASA Technical Reports Server (NTRS)

    Huddleston, D. E.; Neugebauer, M.; Goldstein, B. E.

    1994-01-01

    The shape of the velocity distribution of water group ions observed by the Giotto ion mass spectrometer on its approach to comet Halley is modeled to derive empirical values for the rates of ionization, energy diffusion, and loss in the midcometosheath. The model includes the effect of rapid pitch angle scattering into a bispherical shell distribution as well as the effect of the magnetization of the plasma on the charge exchange loss rate. It is found that the average rate of ionization of cometary neutrals in this region of the cometosheath appears to be of the order of a factor 3 faster than the `standard' rates approx. 1 x 10(exp -6)/s that are generally assumed to model the observations in most regions of the comet environment. For the region of the coma studied in the present work (approx. 1 - 2 x 10(exp 5) km from the nucleus), the inferred energy diffusion coefficient is D(sub 0) approx. equals 0.0002 to 0.0005 sq km/cu s, which is generally lower than values used in other models. The empirically obtained loss rate appears to be about an order of magnitude greater than can be explained by charge exchange with the `standard' cross section of approx. 2 x 10(exp -15)sq cm. However such cross sections are not well known and for water group ion/water group neutral interactions, rates as high as 8 x 10(exp -15) sq cm have previously been suggested in the literature. Assuming the entire loss rate is due to charge exchange yields a rate of creation of fast neutral atoms of the order of approx. 10(exp -4)/s or higher, depending on the level of velocity diffusion. The fast neutrals may, in turn, be partly responsible for the higher-than-expected ionization rate.

  16. Modeling of pickup ion distributions in the Halley cometosheath: Empirical limits on rates of ionization, diffusion, loss and creation of fast neutral atoms

    NASA Technical Reports Server (NTRS)

    Huddleston, D. E.; Neugebauer, M.; Goldstein, B. E.

    1994-01-01

    The shape of the velocity distribution of water group ions observed by the Giotto ion mass spectrometer on its approach to comet Halley is modeled to derive empirical values for the rates of ionization, energy diffusion, and loss in the midcometosheath. The model includes the effect of rapid pitch angle scattering into a bispherical shell distribution as well as the effect of the magnetization of the plasma on the charge exchange loss rate. It is found that the average rate of ionization of cometary neutrals in this region of the cometosheath appears to be of the order of a factor 3 faster than the `standard' rates approx. 1 x 10(exp -6)/s that are generally assumed to model the observations in most regions of the comet environment. For the region of the coma studied in the present work (approx. 1 - 2 x 10(exp 5) km from the nucleus), the inferred energy diffusion coefficient is D(sub 0) approx. equals 0.0002 to 0.0005 sq km/cu s, which is generally lower than values used in other models. The empirically obtained loss rate appears to be about an order of magnitude greater than can be explained by charge exchange with the `standard' cross section of approx. 2 x 10(exp -15)sq cm. However such cross sections are not well known and for water group ion/water group neutral interactions, rates as high as 8 x 10(exp -15) sq cm have previously been suggested in the literature. Assuming the entire loss rate is due to charge exchange yields a rate of creation of fast neutral atoms of the order of approx. 10(exp -4)/s or higher, depending on the level of velocity diffusion. The fast neutrals may, in turn, be partly responsible for the higher-than-expected ionization rate.

  17. Initial Stage of the Microwave Ionization Wave Within a 1D Model

    NASA Astrophysics Data System (ADS)

    Semenov, V. E.; Rakova, E. I.; Glyavin, M. Yu.; Nusinovich, G. S.

    2016-05-01

    The dynamics of the microwave breakdown in a gas is simulated numerically within a simple 1D model which takes into account such processes as the impact ionization of gas molecules, the attachment of electrons to neutral molecules, and plasma diffusion. Calculations are carried out for different spatial distributions of seed electrons with account for reflection of the incident electromagnetic wave from the plasma. The results reveal considerable dependence of the ionization wave evolution on the relation between the field frequency and gas pressure, as well as on the existence of extended rarefied halo of seed electrons. At relatively low gas pressures (or high field frequencies), the breakdown process is accompanied by the stationary ionization wave moving towards the incident electromagnetic wave. In the case of a high gas pressure (or a relatively low field frequency), the peculiarities of the breakdown are associated with the formation of repetitive jumps of the ionization front.

  18. SDSS-IV MaNGA: the impact of diffuse ionized gas on emission-line ratios, interpretation of diagnostic diagrams and gas metallicity measurements

    NASA Astrophysics Data System (ADS)

    Zhang, Kai; Yan, Renbin; Bundy, Kevin; Bershady, Matthew; Haffner, L. Matthew; Walterbos, René; Maiolino, Roberto; Tremonti, Christy; Thomas, Daniel; Drory, Niv; Jones, Amy; Belfiore, Francesco; Sánchez, Sebastian F.; Diamond-Stanic, Aleksandar M.; Bizyaev, Dmitry; Nitschelm, Christian; Andrews, Brett; Brinkmann, Jon; Brownstein, Joel R.; Cheung, Edmond; Li, Cheng; Law, David R.; Roman Lopes, Alexandre; Oravetz, Daniel; Pan, Kaike; Storchi Bergmann, Thaisa; Simmons, Audrey

    2017-04-01

    Diffuse ionized gas (DIG) is prevalent in star-forming galaxies. Using a sample of 365 nearly face-on star-forming galaxies observed by Mapping Nearby Galaxies at APO, we demonstrate how DIG in star-forming galaxies impacts the measurements of emission-line ratios, hence the interpretation of diagnostic diagrams and gas-phase metallicity measurements. At fixed metallicity, DIG-dominated low ΣHα regions display enhanced [S II]/Hα, [N II]/Hα, [O II]/Hβ and [O I]/Hα. The gradients in these line ratios are determined by metallicity gradients and ΣHα. In line ratio diagnostic diagrams, contamination by DIG moves H II regions towards composite or low-ionization nuclear emission-line region (LI(N)ER)-like regions. A harder ionizing spectrum is needed to explain DIG line ratios. Leaky H II region models can only shift line ratios slightly relative to H II region models, and thus fail to explain the composite/LI(N)ER line ratios displayed by DIG. Our result favours ionization by evolved stars as a major ionization source for DIG with LI(N)ER-like emission. DIG can significantly bias the measurement of gas metallicity and metallicity gradients derived using strong-line methods. Metallicities derived using N2O2 are optimal because they exhibit the smallest bias and error. Using O3N2, R23, N2 = [N II]/Hα and N2S2Hα to derive metallicities introduces bias in the derived metallicity gradients as large as the gradient itself. The strong-line method of Blanc et al. (IZI hereafter) cannot be applied to DIG to get an accurate metallicity because it currently contains only H II region models that fail to describe the DIG.

  19. Lyman-Werner UV escape fractions from primordial haloes

    NASA Astrophysics Data System (ADS)

    Schauer, Anna T. P.; Whalen, Daniel J.; Glover, Simon C. O.; Klessen, Ralf S.

    2015-12-01

    Population III (Pop III) stars can regulate star formation in the primordial Universe in several ways. They can ionize nearby haloes, and even if their ionizing photons are trapped by their own haloes, their Lyman-Werner (LW) photons can still escape and destroy H2 in other haloes, preventing them from cooling and forming stars. LW escape fractions are thus a key parameter in cosmological simulations of early reionization and star formation but have not yet been parametrized for realistic haloes by halo or stellar mass. To do so, we perform radiation hydrodynamical simulations of LW UV escape from 9-120 M⊙ Pop III stars in 105-107 M⊙ haloes with ZEUS-MP. We find that photons in the LW lines (i.e. those responsible for destroying H2 in nearby systems) have escape fractions ranging from 0 to 85 per cent. No LW photons escape the most massive halo in our sample, even from the most massive star. Escape fractions for photons elsewhere in the 11.18-13.6 eV energy range, which can be redshifted into the LW lines at cosmological distances, are generally much higher, being above 60 per cent for all but the least massive stars in the most massive haloes. We find that shielding of H2 by neutral hydrogen, which has been neglected in most studies to date, produces escape fractions that are up to a factor of 3 smaller than those predicted by H2 self-shielding alone.

  20. Halo particle confinement in the VLHC using optical stochastic cooling

    SciTech Connect

    Zholents, Alexander; Barletta, W.; Chattopadhyay, S.; Zolotorev, M.

    2000-06-01

    Beam halo particles following the extreme trajectories near the physical aperture limit radiate Smith-Purcell radiation when moving over a diffraction grating. This grating can be used as a pick-up and a kicker for optical stochastic cooling of the halo particles. In this application cooling would have the effect of slowing down the halo particle diffusion onto the aperture. Cooling efficiency would quickly diminish with the distance from the aperture and would only affect the halo particles. A preliminary analysis of this system is considered.

  1. Dwarf Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Colín, P.; Klypin, A.; Valenzuela, O.; Gottlöber, Stefan

    2004-09-01

    We study properties of dark matter halos at high redshifts z=2-10 for a vast range of masses with the emphasis on dwarf halos with masses of 107-109 h-1 Msolar. We find that the density profiles of relaxed dwarf halos are well fitted by the Navarro, Frenk, & White (NFW) profile and do not have cores. We compute the halo mass function and the halo spin parameter distribution and find that the former is very well reproduced by the Sheth & Tormen model, while the latter is well fitted by a lognormal distribution with λ0=0.042 and σλ=0.63. We estimate the distribution of concentrations for halos in a mass range that covers 6 orders of magnitude, from 107 to 1013 h-1 Msolar, and find that the data are well reproduced by the model of Bullock et al. The extrapolation of our results to z=0 predicts that present-day isolated dwarf halos should have a very large median concentration of ~35. We measure the subhalo circular velocity functions for halos with masses that range from 4.6×109 to 1013 h-1 Msolar and find that they are similar when normalized to the circular velocity of the parent halo. Dwarf halos studied in this paper are many orders of magnitude smaller than well-studied cluster- and Milky Way-sized halos. Yet, in all respects the dwarfs are just downscaled versions of the large halos. They are cuspy and, as expected, more concentrated. They have the same spin parameter distribution and follow the same mass function that was measured for large halos.

  2. Clouds Dominate the Galactic Halo

    NASA Astrophysics Data System (ADS)

    2003-01-01

    Using the exquisite sensitivity of the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT), astronomer Jay Lockman of the National Radio Astronomy Observatory (NRAO) in Green Bank, W. Va., has produced the best cross-section ever of the Milky Way Galaxy's diffuse halo of hydrogen gas. This image confirms the presence of discrete hydrogen clouds in the halo, and could help astronomers understand the origin and evolution of the rarefied atmosphere that surrounds our Galaxy. Lockman presented his findings at the American Astronomical Society meeting in Seattle, WA. Hydrogen Clouds Graphic Artist's Rendering of the Milky Way (background) with insert showing GBT image of cross-section of neutral atomic Hydrogen Credit: Kirk Woellert/National Science Foundation Patricia Smiley, NRAO. "The first observations with the Green Bank Telescope suggested that the hydrogen in the lower halo, the transition zone between the Milky Way and intergalactic space, is very clumpy," said Lockman. "The latest data confirm these results and show that instead of trailing away smoothly from the Galactic plane, a significant fraction of the hydrogen gas in the halo is concentrated in discrete clouds. There are even some filaments." Beyond the star-filled disk of the Milky Way, there exists an extensive yet diffuse halo of hydrogen gas. For years, astronomers have speculated about the origin and structure of this gas. "Even the existence of neutral hydrogen in the halo has been somewhat of a puzzle," Lockman remarked. "Unlike the Earth's atmosphere, which is hot enough to hold itself up against the force of gravity, the hydrogen in the halo is too cool to support itself against the gravitational pull of the Milky Way." Lockman points out that some additional factor has to be involved to get neutral hydrogen to such large distances from the Galactic plane. "This force could be cosmic rays, a supersonic wind, the blast waves from supernovae, or something we have not thought of

  3. The Halo of NGC 2438 scrutinized

    NASA Astrophysics Data System (ADS)

    Oettl, Silvia; Kimeswenger, Stefan

    2015-08-01

    Haloes and multiple shells around planetary nebulae trace the mass-loss history of the central star. The haloes provide us with information about abundances, ionization or kinematics. Detailed investigations of these haloes can be used to study the evolution of the old stellar population in our galaxy and beyond.Different observations show structures in the haloes like radial rays, blisters and rings (e.g., Ramos-Larios et al. 2012, MNRAS 423, 3753 or Matsuura et al. 2009, ApJ, 700, 1067). The origin of these features has been associated with ionization shadows (Balick 2004, AJ, 127, 2262). They can be observed in regions, where dense knots are opaque to stellar ionizing photons. In this regions we can see leaking UV photons.In this work, we present a detailed investigation of the multiple shell PN NGC 2438. We derive a complete data set of the main nebula. This allows us to analize the physical conditions from photoionization models, such as temperature, density and ionization, and clumping.Data from ESO (3.6m telescope - EFOSC1 - direct imaging and long slit spectroscopy) and from SAAO (spectroscopic observations using a small slit) were available. These data were supplemented by imaging data from the HST archive and by archival VLA observations. The low-excitation species are found to be dominated by clumps. The emission line ratios show no evidence for shocks. We find the shell in ionization equilibrium: a significant amount of UV radiation infiltrates the inner nebula. Thus the shell still seems to be ionized.The photoionization code CLOUDY was used to model the nebular properties and to derive a more accurate distance and ionized mass. The model supports the hypothesis that photoionization is the dominant process in this nebula, far out into the shell.If we want to use extragalactic planetary nebulae as probes of the old stellar population, we need to assess the potential impact of a halo on the evolution. Also the connection of observations and models must

  4. The Contribution of Ionizing Stars to the Far-Infrared and Radio Emission in the Galaxy

    NASA Technical Reports Server (NTRS)

    Terebey, S.; Fich, M.; Taylor, R.

    1999-01-01

    A summary of research activities carried out in this eighth and final progress report. The final report includes: this summary document, copies of three published research papers, plus a draft manuscript of a fourth research paper entitled "The Contribution of Ionizing Stars to the FarInfrared and Radio Emission in the Milky Way; Evidence for a Swept-up Shell and Diffuse Ionized Halo around the W4 Chimney/Supershell." The main activity during the final quarterly reporting period was research on W4, including analysis of the radio and far-infrared images, generation of shell models, a literature search, and preparation of a research manuscript. There will be additional consultation with co-authors prior to submission of the paper to the Astrophysical Journal. The results will be presented at the 4th Tetons Summer Conference on "Galactic Structure, Stars, and the ISM" in May 2000. In this fourth and last paper we show W4 has a swept-up partially ionized shell of gas and dust which is powered by the OCl 352 star cluster. Analysis shows there is dense interstellar material directly below the shell, evidence that that the lower W4 shell "ran into a brick wall" and stalled, whereas the upper W4 shell achieved "breakout" to form a Galactic chimney. An ionized halo is evidence of Lyman continuum leakage which ionizes the WIM (warm ionized medium). It has long been postulated that the strong winds and abundant ionizing photons from massive stars are responsible for much of the large scale structure in the interstellar medium (ISM), including the ISM in other galaxies. However standard HII region theory predicts few photons will escape the local HII region. The significance of W4 and this work is it provides a direct example of how stellar winds power a galactic chimney, which in turn leads to a low density cavity from which ionizing photons can escape to large distances to ionize the WIM.

  5. Star Formation in Edge-on Galaxies and its Relation to Radio Continuum Halos

    NASA Astrophysics Data System (ADS)

    Vargas, Carlos J.; Mora Partiarroyo, Silvia Carolina; Schmidt, Philip; Walterbos, Rene A. M.; Irwin, Judith; Wang, Daniel; Rand, Richard J.; Stein, Yelena; CHANG-ES

    2017-01-01

    We study the radio continuum emission in edge-on galaxies from the Continuum Halos in Nearby Galaxies -- an EVLA Survey (CHANG-ES), with a particular focus on the question of the correlation of radio synchroton halos with the star formation rate distribution across the galaxy disks. To determine the star formation rates we analyze the application of various SFR calibration methods, in particular those involving Hα and 24 μm emission for the galaxies in the sample. We test consistency of the published SFR calibrations by predicting thermal radio continuum maps that are compared with the observed radio data and with the derived spectral index maps, both before and after removal of the predicted thermal maps. In addition to published calibrations of the SFR from Hα and 24 μm data, we explore different mixtures of Hα and 24 μm maps that may be more applicable in the case of an edge-on galaxy perspective. We also discuss the correlation between the luminosity, morphology, and spectral indices of radio synchrotron halos with the distribution of SF in the galactic disks, and explore the connection with extra-planar diffuse ionized gas obtained from sensitive Hα images with the ARC 3.5m telescope for the entire sample. This research is supported by the National Science Foundation under Grant No 1650681 and AST - 1615594.

  6. Structure of Halo and Quasi-halo Helium-Helium-Alkali Trimers

    NASA Astrophysics Data System (ADS)

    Stipanović, Petar; Markić, Leandra Vranješ; Boronat, Jordi

    2017-05-01

    We report a diffusion Monte Carlo study of A^4He_2 and A^4He^3He trimers' structural properties, were A is one of the alkali atoms ^{6,7}Li, ^{23}Na, ^{39}K, ^{85}Rb or ^{133}Cs. Some of them are in a pure halo state, characterized by large spatial extent and universality, while some are close to the halo limit. The theoretical analysis of these trimers enables insight on how structural properties of weakly bound systems change when approaching the halo edge. For that purpose, two-variable distributions of inter-particle separations and angles were calculated. Extreme spatial extensions of some trimers with ^3He confirm their halo nature. Although all the considered systems are floppy, trimers with all bound dimer subsystems are less spread and have significantly lower percentage of quasi-linear configurations than those which have at least one unbound dimer subsystem.

  7. The dark halo of the milky Way

    PubMed

    Alcock

    2000-01-07

    Most of the matter in the Milky Way is invisible to astronomers. Precise numbers are elusive, but it appears that the dark component is 20 times as massive as the visible disk of stars and gas. This dark matter is distributed in space differently than the stars, forming a vast, diffuse halo, more spherical than disklike, which occupies more than 1000 times the volume of the disk of stars. The composition of this dark halo is unknown, but it may comprise a mixture of ancient, degenerate dwarf stars and exotic, hypothetical elementary particles.

  8. Optical and ultraviolet absorption studies of cool gas in the Milky Way halo

    NASA Technical Reports Server (NTRS)

    Danly, L.

    1990-01-01

    This paper focuses on the contributions from absorption techniques to the knowledge of halo gas with temperatures below 10 to the 5th K. The results from observations of the neutral and singly ionized species on the nature of cool gas in the halo, its structure and its kinematics are presented. An overview of past and optical and ultraviolet observational studies of halo gas is included.

  9. Abundances of Neutral and Ionized PAH Along The Lines-of-Sight of Diffuse and Translucent Interstellar Clouds

    NASA Technical Reports Server (NTRS)

    Salama, Farid; Galazutdinov, Gazinur; Krewloski, Jacek; Biennier, Ludovic; Beletsky, Yuri; Song, In-Ok

    2013-01-01

    The spectra of neutral and ionized PAHs isolated in the gas phase at low temperature have been measured in the laboratory under conditions that mimic interstellar conditions and are compared with a set of astronomical spectra of reddened, early type stars. The comparisons of astronomical and laboratory data provide upper limits for the abundances of neutral PAH molecules and ions along specific lines-of-sight. Something that is not attainable from infrared observations. We present the characteristics of the laboratory facility (COSmIC) that was developed for this study and discuss the findings resulting from the comparison of the laboratory data with high resolution, high S/N ratio astronomical observations. COSmIC combines a supersonic jet expansion with discharge plasma and cavity ringdown spectroscopy and provides experimental conditions that closely mimic the interstellar conditions. The column densities of the individual PAH molecules and ions probed in these surveys are derived from the comparison of the laboratory data with high resolution, high S/N ratio astronomical observations. The comparisons of astronomical and laboratory data lead to clear conclusions regarding the expected abundances for PAHs in the interstellar environments probed in the surveys. Band profile comparisons between laboratory and astronomical spectra lead to information regarding the molecular structures and characteristics associated with the DIB carriers in the corresponding lines-of-sight. These quantitative surveys of neutral and ionized PAHs in the optical range open the way for quantitative searches of PAHs and complex organics in a variety of interstellar and circumstellar environments.

  10. N-body dark matter haloes with simple hierarchical histories

    NASA Astrophysics Data System (ADS)

    Jiang, Lilian; Helly, John C.; Cole, Shaun; Frenk, Carlos S.

    2014-05-01

    We present a new algorithm which groups the subhaloes found in cosmological N-body simulations by structure finders such as SUBFIND into dark matter haloes whose formation histories are strictly hierarchical. One advantage of these `Dhaloes' over the commonly used friends-of-friends (FoF) haloes is that they retain their individual identity in the cases when FoF haloes are artificially merged by tenuous bridges of particles or by an overlap of their outer diffuse haloes. Dhaloes are thus well suited for modelling galaxy formation and their merger trees form the basis of the Durham semi-analytic galaxy formation model, GALFORM. Applying the Dhalo construction to the Λ cold dark matter Millennium II Simulation, we find that approximately 90 per cent of Dhaloes have a one-to-one, bijective match with a corresponding FoF halo. The remaining 10 per cent are typically secondary components of large FoF haloes. Although the mass functions of both types of haloes are similar, the mass of Dhaloes correlates much more tightly with the virial mass, M200, than FoF haloes. Approximately 80 per cent of FoF and bijective and non-bijective Dhaloes are relaxed according to standard criteria. For these relaxed haloes, all three types have similar concentration-M200 relations and, at fixed mass, the concentration distributions are described accurately by log-normal distributions.

  11. Low frequency follow up of radio haloes and relics in the GMRT Radio Halo Cluster Survey

    NASA Astrophysics Data System (ADS)

    Venturi, T.; Giacintucci, S.; Dallacasa, D.; Cassano, R.; Brunetti, G.; Macario, G.; Athreya, R.

    2013-03-01

    Aims: To gain insight into the origin of diffuse radio sources in galaxy clusters and their connection with cluster merger processes, we performed GMRT low frequency observations of the radio haloes, relics and new candidates belonging to the GMRT radio Halo cluster sample first observed at 610 MHz. Our main aim was to investigate their observational properties and integrated spectra at frequencies below 610 MHz. Methods: High sensitivity imaging was performed using the GMRT at 325 MHz and 240 MHz. The properties of the diffuse emission in each cluster were compared to our 610 MHz images and/or literature information available at other frequencies, in order to derive the integrated spectra over a wide frequency range. Results: Cluster radio haloes form a composite class in terms of spectral properties. Beyond the classical radio haloes, whose spectral index α is in the range ~1.2 ÷ 1.3 (S ∝ ν- α), we found sources with α ~ 1.6 ÷ 1.9. This result supports the idea that the spectra of the radiating particles in radio haloes is not universal and that inefficient mechanisms of particle acceleration are responsible for their origin. We also found a variety of brightness distributions, i.e. both centrally peaked and clumpy haloes. Even though the thermal and relativistic plasma tend to occupy the same cluster volume, in some cases a positional shift between the radio and X-ray peaks of emission is evident. Our observations also revealed diffuse cluster sources that cannot be easily classified as either haloes or relics. New candidate relics were found in A 1300 and in A 1682, and in some clusters "bridges" of radio emission have been detected, connecting the relic and radio halo emission. Finally, by combining our new data with information in the literature, we derived the Log LX - Log P325 MHz correlation for radio haloes, and investigated the possible correlation of the spectral index of radio haloes with the temperature of the intracluster medium.

  12. Abundances of Neutral and Ionized PAH Along The Lines-of-Sight of Diffuse and Translucent Interstellar Clouds

    NASA Astrophysics Data System (ADS)

    Salama, Farid; Galazutdinov, G.; Krelowski, J.; Biennier, L.; Beletsky, Y.; Song, I.

    2013-06-01

    The spectra of neutral and ionized PAHs isolated in the gas phase at low temperature have been measured in the laboratory under conditions that mimic interstellar conditions and are compared with a set of astronomical spectra of reddened, early type stars. The comparisons of astronomical and laboratory data provide upper limits for the abundances of neutral PAH molecules and ions along specific lines-of-sight. Something that is not attainable from infrared observations. We present the characteristics of the laboratory facility (COSmIC) that was developed for this study and discuss the findings resulting from the comparison of the laboratory data with high resolution, high S/N ratio astronomical observations. COSmIC combines a supersonic jet expansion with discharge plasma and cavity ringdown spectroscopy and provides experimental conditions that closely mimic the interstellar conditions. The column densities of the individual PAH molecules and ions probed in these surveys are derived from the comparison of the laboratory data with high resolution, high S/N ratio astronomical observations. The comparisons of astronomical and laboratory data lead to clear conclusions regarding the expected abundances for PAHs in the interstellar environments probed in the surveys. Band profile comparisons between laboratory and astronomical spectra lead to information regarding the molecular structures and characteristics associated with the DIB carriers in the corresponding lines-of-sight. These quantitative surveys of neutral and ionized PAHs in the optical range open the way for quantitative searches of PAHs and complex organics in a variety of interstellar and circumstellar environments. Acknowledgements: F.S. acknowledges the support of the Astrophysics Research and Analysis Program of the NASA Space Mission Directorate and the technical support provided by R. Walker at NASA ARC. J.K. acknowledges the financial support of the Polish State. The authors are deeply grateful to the

  13. THE RELATIONSHIP BETWEEN THE DENSE NEUTRAL AND DIFFUSE IONIZED GAS IN THE THICK DISKS OF TWO EDGE-ON SPIRAL GALAXIES

    SciTech Connect

    Rueff, Katherine M.; Howk, J. Christopher; Pitterle, Marissa; Hirschauer, Alec S.; Fox, Andrew J.; Savage, Blair D.

    2013-03-15

    We present high-resolution, optical images (BVI + H{alpha}) of the multiphase interstellar medium (ISM) in the thick disks of the edge-on spiral galaxies NGC 4013 and NGC 4302. Our images from the Hubble Space Telescope (HST), Large Binocular Telescope, and WIYN 3.5 m telescope reveal an extensive population of filamentary dust absorption seen to z {approx}2-2.5 kpc. Many of these dusty thick disk structures have characteristics reminiscent of molecular clouds found in the Milky Way disk. Our H{alpha} images show that the extraplanar diffuse ionized gas (DIG) in these galaxies is dominated by a smooth, diffuse component. The strongly filamentary morphologies of the dust absorption have no counterpart in the smoothly distributed H{alpha} emission. We argue that the thick disk DIG and dust-bearing filaments trace physically distinct phases of the thick disk ISM, the latter tracing a dense, warm or cold neutral medium. The dense, dusty matter in the thick disks of spiral galaxies is largely tracing matter ejected from the thin disk via energetic feedback from massive stars. The high densities of the gas may be a result of converging gas flows. This dense material fuels some thick disk star formation, as evidenced by the presence of thick disk H II regions.

  14. Galactic Halos of Hydrogen

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This image shows two companion galaxies, NGC 4625 (top) and NGC 4618 (bottom), and their surrounding cocoons of cool hydrogen gas (purple). The huge set of spiral arms on NGC 4625 (blue) was discovered by the ultraviolet eyes of NASA's Galaxy Evolution Explorer. Though these arms are nearly invisible when viewed in optical light, they glow brightly in ultraviolet. This is because they are bustling with hot, newborn stars that radiate primarily ultraviolet light.

    The vibrant spiral arms are also quite lengthy, stretching out to a distance four times the size of the galaxy's core. They are part of the largest ultraviolet galactic disk discovered so far.

    Astronomers do not know why NGC 4625 grew arms while NGC 4618 did not. The purple nebulosity shown here illustrates that hydrogen gas - an ingredient of star formation - is diffusely distributed around both galaxies. This means that other unknown factors led to the development of the arms of NGC 4625.

    Located 31 million light-years away in the constellation Canes Venatici, NGC 4625 is the closest galaxy ever seen with such a young halo of arms. It is slightly smaller than our Milky Way, both in size and mass. However, the fact that this galaxy's disk is forming stars very actively suggests that it might evolve into a more massive and mature galaxy resembling our own.

    The image is composed of ultraviolet, visible-light and radio data, from the Galaxy Evolution Explorer, the California Institute of Technology's Digitized Sky Survey, and the Westerbork Synthesis Radio Telescope, the Netherlands, respectively. Near-ultraviolet light is colored green; far-ultraviolet light is colored blue; and optical light is colored red. Radio emissions are colored purple.

  15. The halo fixator.

    PubMed

    Bono, Christopher M

    2007-12-01

    The halo fixator may be used for the definitive treatment of cervical spine trauma, preoperative reduction in the patient with spinal deformity, and adjunctive postoperative stabilization following cervical spine surgery. Halo fixation decreases cervical motion by 30% to 96%. Absolute contraindications include cranial fracture, infection, and severe soft-tissue injury at the proposed pin sites. Relative contraindications include severe chest trauma, obesity, advanced age, and a barrel-shaped chest. In children, a computed tomography scan of the head should be obtained before pin placement to determine cranial bone thickness. Complications of halo fixation include pin loosening, pin site infection, and skin breakdown. A concerning rate of life-threatening complications, such as respiratory distress, has been reported in elderly patients. Despite a paucity of contemporary data, recent retrospective studies have demonstrated acceptable results for halo fixation in managing some upper and lower cervical spine injuries.

  16. AHF: AMIGA'S HALO FINDER

    SciTech Connect

    Knollmann, Steffen R.; Knebe, Alexander

    2009-06-15

    Cosmological simulations are the key tool for investigating the different processes involved in the formation of the universe from small initial density perturbations to galaxies and clusters of galaxies observed today. The identification and analysis of bound objects, halos, is one of the most important steps in drawing useful physical information from simulations. In the advent of larger and larger simulations, a reliable and parallel halo finder, able to cope with the ever-increasing data files, is a must. In this work we present the freely available MPI parallel halo finder AHF. We provide a description of the algorithm and the strategy followed to handle large simulation data. We also describe the parameters a user may choose in order to influence the process of halo finding, as well as pointing out which parameters are crucial to ensure untainted results from the parallel approach. Furthermore, we demonstrate the ability of AHF to scale to high-resolution simulations.

  17. Halo vest instrumentation

    NASA Astrophysics Data System (ADS)

    Huston, Dryver R.; Krag, Martin

    1996-05-01

    The halo vest is a head and neck immobilization system that is often used on patients that are recovering from cervical trauma or surgery. The halo vest system consists of a rigid halo that is firmly attached to the skull, an upright support structure for stabilization and immobilization, and a torso-enveloping vest. The main purpose of this study was to measure the forces that are carried by the halo-vest structure as the subject undergoes various activities of daily living and external loading for different vest designs. A tethered strain gage load cell based instrumentation system was used to take these load measurements on ten different subjects. Three different halo-vest systems were evaluated. The primary difference between the vests was the amount of torso coverage and the use of shoulder straps. The loads were measured, analyzed and used to compare the vests and to create a model of halo-vest-neck mechanics. Future applications of this technology to standalone data logging, pin-load measuring and biofeedback applications are discussed.

  18. The HALO / HALO-2 Supernova Neutrino Detectors

    NASA Astrophysics Data System (ADS)

    Yen, Stanley; HALO Collaboration; HALO-2 Collaboration

    2016-09-01

    The Helium and Lead Observatory (HALO) is a dedicated supernova neutrino detector in SNOLAB, which is built from 79 tons of surplus lead and the helium-3 neutron detectors from the SNO experiment. It is sensitive primarily to electron neutrinos, and is thus complementary to water Cerenkov and organic scintillation detectors which are primarily sensitive to electron anti-neutrinos. A comparison of the rates in these complementary detectors will enable a flavor decomposition of the neutrino flux from the next galactic core-collapse supernova. We have tentative ideas to build a 1000-ton HALO-2 detector in the Gran Sasso laboratory by using the lead from the decommissioned OPERA detector. We are exploring several neutron detector technologies to supplement the existing helium-3 detectors. We welcome new collaborators to join us. This research is supported by the NRC and NSERC (Canada), the US DOE and NSF, and the German RISE program.

  19. Haloes seen in UVIS reflectance

    NASA Astrophysics Data System (ADS)

    Esposito, L. W.; Bradley, E. T.; Colwell, J. E.; Sremcevic, M.

    2012-12-01

    UVIS SOI reflectance spectra show bright 'haloes' around the locations of some of the strongest resonances in Saturn's A ring (Esposito etal 2005). UV spectra constrain the size and composition of the icy ring particles (Bradley etal 2010, 2012). We investigate the Janus 4:3, 5:3, 6:5 and Mimas 5:3 inner Lindblad resonances as well as at the Mimas 5:3 vertical resonance (bending wave location). Models of ring particle regolith evolution (Elliott and Esposito 2010) indicate the deeper regolith is made of older and purer ice. The strong resonances can cause streamline crowding (Lewis and Stewart 2005) which damps the interparticle velocity, allowing temporary clumps to grow, which in turn increase the velocity, eroding the clumps and releasing smaller particles and regolith (see the predator-prey model of Esposito etal 2012). This cyclic behavior, driven by the resonant perturbation from the moon, can yield collision velocities at particular azimuths greater than 1m/sec, sufficient to erode the aggregates (Blum 2006), exposing older, purer materials. Thus, the radial location of the strongest resonances can be where we find both large aggregates and disrupted fragments, in a balance maintained by the periodic moon forcing. If this stirring exposes older, and purer ice, the velocity threshold for eroding the aggregates can explain why only the strongest Lindblad resonances show haloes. Diffusion can explain the morphology of these haloes, although they are not well-resolved spatially by UVIS. Spectra determine the relative contributions of particle size and purity at these locations, for comparison to estimates from the regolith evolution models.

  20. Dark matter annihilation in the first galaxy haloes

    NASA Astrophysics Data System (ADS)

    Schön, S.; Mack, K. J.; Avram, C. A.; Wyithe, J. S. B.; Barberio, E.

    2015-08-01

    We investigate the impact of energy released from self-annihilating dark matter (DM) on heating of gas in the small, high-redshift DM haloes thought to host the first stars. A supersymmetric (SUSY)-neutralino-like particle is implemented as our DM candidate. The PYTHIA code is used to model the final, stable particle distributions produced during the annihilation process. We use an analytic treatment in conjunction with the code MEDEA2 to find the energy transfer and subsequent partition into heating, ionizing and Lyman α photon components. We consider a number of halo density models, DM particle masses and annihilation channels. We find that the injected energy from DM exceeds the binding energy of the gas within a 105-106 M⊙ halo at redshifts above 20, preventing star formation in early haloes in which primordial gas would otherwise cool. Thus we find that DM annihilation could delay the formation of the first galaxies.

  1. The Source of Ionization along the Magellanic Stream

    NASA Astrophysics Data System (ADS)

    Bland-Hawthorn, Joss; Sutherland, Ralph; Agertz, Oscar; Moore, Ben

    2007-12-01

    Since its discovery in 1996, the source of the bright Hα emission (up to 750 mR) along the Magellanic Stream has remained a mystery. There is no evidence of ionizing stars within the H I stream, and the extended hot halo is far too tenuous to drive strong shocks into the clouds. We now present a hydrodynamical model that explains the known properties of the Hα emission and provides new insights on the lifetime of the Stream clouds. The upstream clouds are gradually disrupted due to their interaction with the hot halo gas. The clouds that follow plow into gas ablated from the upstream clouds, leading to shock ionization at the leading edges of the downstream clouds. Since the following clouds also experience ablation, and weaker Hα (100-200 mR) is quite extensive, a disruptive cascade must be operating along much of the Stream. In our model, the clouds are evolving on timescales of 100-200 Myr, such that the Stream must be replenished by the Magellanic Clouds at a fairly constant rate. The ablated material falls onto the Galaxy as a warm drizzle, which suggests that diffuse ionized gas at 104 K may be an important constituent of galactic accretion. The observed Hα emission provides a new constraint on the rate of disruption of the Stream and, consequently, the infall rate of metal-poor gas onto the Galaxy. When the ionized component of the Stream is fully accounted for, the rate of gas accretion is 0.4 Msolar yr-1, roughly twice the rate deduced from H I observations alone.

  2. The flatness and sudden evolution of the intergalactic ionizing background

    NASA Astrophysics Data System (ADS)

    Muñoz, Joseph A.; Oh, S. Peng; Davies, Frederick B.; Furlanetto, Steven R.

    2016-01-01

    The ionizing background of cosmic hydrogen is an important probe of the sources and absorbers of ionizing radiation in the post-reionization universe. Previous studies show that the ionization rate should be very sensitive to changes in the source population: as the emissivity rises, absorbers shrink in size, increasing the ionizing mean free path and, hence, the ionizing background. By contrast, observations of the ionizing background find a very flat evolution from z ˜ 2-5, before falling precipitously at z ˜ 6. We resolve this puzzling discrepancy by pointing out that, at z ˜ 2-5, optically thick absorbers are associated with the same collapsed haloes that host ionizing sources. Thus, an increasing abundance of galaxies is compensated for by a corresponding increase in the absorber population, which moderates the instability in the ionizing background. However, by z ˜ 5-6, gas outside of haloes dominates the absorption, the coupling between sources and absorbers is lost, and the ionizing background evolves rapidly. Our halo-based model reproduces observations of the ionizing background, its flatness and sudden decline, as well as the redshift evolution of the ionizing mean free path. Our work suggests that, through much of their history, both star formation and photoelectric opacity in the universe track halo growth.

  3. The gamma-ray-flux PDF from galactic halo substructure

    SciTech Connect

    Lee, Samuel K.; Ando, Shin'ichiro; Kamionkowski, Marc E-mail: ando@tapir.caltech.edu

    2009-07-01

    One of the targets of the recently launched Fermi Gamma-ray Space Telescope is a diffuse gamma-ray background from dark-matter annihilation or decay in the Galactic halo. N-body simulations and theoretical arguments suggest that the dark matter in the Galactic halo may be clumped into substructure, rather than smoothly distributed. Here we propose the gamma-ray-flux probability distribution function (PDF) as a probe of substructure in the Galactic halo. We calculate this PDF for a phenomenological model of halo substructure and determine the regions of the substructure parameter space in which the PDF may be distinguished from the PDF for a smooth distribution of dark matter. In principle, the PDF allows a statistical detection of substructure, even if individual halos cannot be detected. It may also allow detection of substructure on the smallest microhalo mass scales, ∼ M{sub ⊕}, for weakly-interacting massive particles (WIMPs). Furthermore, it may also provide a method to measure the substructure mass function. However, an analysis that assumes a typical halo substructure model and a conservative estimate of the diffuse background suggests that the substructure PDF may not be detectable in the lifespan of Fermi in the specific case that the WIMP is a neutralino. Nevertheless, for a large range of substructure, WIMP annihilation, and diffuse background models, PDF analysis may provide a clear signature of substructure.

  4. Renormalized halo bias

    SciTech Connect

    Assassi, Valentin; Baumann, Daniel; Green, Daniel; Zaldarriaga, Matias E-mail: dbaumann@damtp.cam.ac.uk E-mail: matiasz@ias.edu

    2014-08-01

    This paper provides a systematic study of renormalization in models of halo biasing. Building on work of McDonald, we show that Eulerian biasing is only consistent with renormalization if non-local terms and higher-derivative contributions are included in the biasing model. We explicitly determine the complete list of required bias parameters for Gaussian initial conditions, up to quartic order in the dark matter density contrast and at leading order in derivatives. At quadratic order, this means including the gravitational tidal tensor, while at cubic order the velocity potential appears as an independent degree of freedom. Our study naturally leads to an effective theory of biasing in which the halo density is written as a double expansion in fluctuations and spatial derivatives. We show that the bias expansion can be organized in terms of Galileon operators which aren't renormalized at leading order in derivatives. Finally, we discuss how the renormalized bias parameters impact the statistics of halos.

  5. Halo Nonlinear Reconstruction

    NASA Astrophysics Data System (ADS)

    Yu, Yu; Zhu, Hong-Ming; Pen, Ue-Li

    2017-10-01

    We apply the nonlinear reconstruction method to simulated halo fields. For halo number density 2.77 × {10}-2 {({h}-1{Mpc})}-3 at z = 0, corresponding to the SDSS main sample density, we find that the scale where the noise saturates the linear signal is improved to k≳ 0.36 h {{Mpc}}-1, which is a factor of 2.29 improvement in scale, or 12 in number of linear modes. The improvement is less for higher redshift or lower halo density. We expect this to substantially improve the BAO accuracy of dense, low-redshift surveys, including the SDSS main sample, 6dFGS and 21 cm intensity mapping initiatives.

  6. Origins of Stellar Halos

    NASA Astrophysics Data System (ADS)

    Johnston, Kathryn V.

    2016-08-01

    This contribution reviews ideas about the origins of stellar halos. It includes discussion of the theoretical understanding of and observational evidence for stellar populations formed ``in situ'' (meaning formed in orbits close to their current ones), ``kicked-out'' (meaning formed in the inner galaxy in orbits unlike their current ones) and ``accreted'' (meaning formed in a dark matter halo other than the one they currently occupy). At this point there is general agreement that a significant fraction of any stellar halo population is likely ``accreted''. There is modest evidence for the presence of a ``kicked-out'' population around both the Milky Way and M31. Our theoretical understanding of and the observational evidence for an ``in situ'' population are less clear.

  7. The mass transfer kinetics in columns packed with Halo-ES shell particles.

    PubMed

    Gritti, Fabrice; Guiochon, Georges

    2011-02-18

    The average mesopore size of the new Halo-ES-Peptide shell particles is 160 Å, markedly larger than that of the classical Halo shell particles (90 Å). We found that this change causes a considerable decrease of the film mass transfer resistance measured for columns packed with these particles. We analyze data obtained by systematic measurements of the C term of the van Deemter equation for the peptide β-lipotropin (MW = 769 Da), the protein insulin (MW = 5800 Da), and a series of non-retained polystyrene standards (MW = 6400 and 13,200). The improvement in column performance is explained by an increase of the fraction of the external surface area of the shell that allows the entrance of the sample molecules inside the particle. The fraction of the shell surface accessible to a probe controls the rate of its external film mass transfer, i.e. its rate of transfer between the interstitial and the stagnant eluent. Although measurable, the increase in sample diffusivity through the porous shells does not account for the better performance of Halo-ES-peptide columns. Furthermore, the analysis of the HETPs data of small molecules (uracil, acetophenone, toluene, and naphthalene, MW< 150) reveals that the eddy diffusion (A) term of these new columns is 25% lower than that of the classical Halo columns. This result is consistent with the impact of intra-particle diffusivity on the eddy diffusion mechanism in packed columns. As shell diffusivity increases, so does the rate of transfer of sample molecules between the eluent stream-paths flowing through the packed particles and across the column diameter. Dispersion through short-range inter-channel and trans-column eddies is reduced. Copyright © 2010 Elsevier B.V. All rights reserved.

  8. The Outer Halo -- Halo Origins and Mass of the Galaxy

    NASA Astrophysics Data System (ADS)

    Morrison, Heather; Arabadjis, John; Dohm-Palmer, Robbie; Freeman, Ken; Harding, Paul; Mateo, Mario; Norris, John; Olszewski, Ed; Sneden, Chris

    2000-02-01

    Through our detection of distant halo stars, we are now well placed to map the regions of the Galactic halo where previously only satellite galaxies and a few globular clusters were known. Mapping this region is crucial for answering questions like: How and over what timescales was the Milky Way's stellar halo assembled? What is the total mass and shape of its dark halo? The Sagittarius dwarf has demonstrated that at least some of the stellar halo was accreted. But, HOW MUCH of the halo was accreted? Our previous efforts have proven that the Washington photometric system, in conjuction with spectroscopy, is capable of efficiently and unambiguously identifying halo stars out to 100 kpc or more. We require followup spectroscopy to map velocity substructure, which is more likely visible in the outer halo because of the long dynamical timescales, and to identify the rare objects in the extreme outer halo which will constrain the shape and size of its dark halo. We are applying for 4m/RCSP time at both CTIO and KPNO to observe faint outer-halo giant and BHB candidates.

  9. What's a Halo?

    MedlinePlus

    ... to school, doing schoolwork, and participating in extracurricular clubs, as long as they're feeling up to it and the doctor says it's OK. Your child's doctor will tell you what activities your child should avoid while in a halo brace. Sports will have to be put on hold for ...

  10. Stability of halo orbits.

    PubMed

    Howard, J E; Dullin, H R; Horányi, M

    2000-04-10

    We predict new populations of trapped nonequatorial ("halo") orbits of charged dust grains about an arbitrary axisymmetric planet. Simple equilibrium and stability conditions are derived, revealing dramatic differences between positively and negatively charged grains in prograde or retrograde orbits. Implications for the Cassini mission to Saturn are discussed.

  11. Detection of ultraviolet halos around highly inclined galaxies

    SciTech Connect

    Hodges-Kluck, Edmund; Bregman, Joel N.

    2014-07-10

    We report the discovery of diffuse ultraviolet light around late-type galaxies out to 5-20 kpc from the midplane using Swift and GALEX images. The emission is consistent with the stellar outskirts in the early-type galaxies but not in the late-type galaxies, where the emission is quite blue and consistent with a reflection nebula powered by light escaping from the galaxy and scattering off dust in the halo. Our results agree with expectations from halo dust discovered in extinction by Ménard et al. to within a few kpc of the disk and imply a comparable amount of hot and cold gas in galaxy halos (a few× 10{sup 8} M{sub ☉} within 20 kpc) if the dust resides primarily in Mg II absorbers. The results also highlight the potential of UV photometry to study individual galaxy halos.

  12. Halo-Formation at an Early Stage of Injection into High-Intensity Hadron Rings

    SciTech Connect

    Shimosaki, Yoshito

    2005-06-08

    Halo formation under a non-equilibrium state for a 2D Gaussian beam has been examined in terms of a transition of time-varying nonlinear resonances induced by the space-charge effect. Analytic approaches using an isolated resonance Hamiltonian are presented for estimating the location of the halo and the strength of the diffusion.

  13. Magnetic spiral arms in galaxy haloes

    NASA Astrophysics Data System (ADS)

    Henriksen, R. N.

    2017-08-01

    We seek the conditions for a steady mean field galactic dynamo. The parameter set is reduced to those appearing in the α2 and α/ω dynamo, namely velocity amplitudes, and the ratio of sub-scale helicity to diffusivity. The parameters can be allowed to vary on conical spirals. We analyse the mean field dynamo equations in terms of scale invariant logarithmic spiral modes and special exact solutions. Compatible scale invariant gravitational spiral arms are introduced and illustrated in an appendix, but the detailed dynamical interaction with the magnetic field is left for another work. As a result of planar magnetic spirals `lifting' into the halo, multiple sign changes in average rotation measures forming a regular pattern on each side of the galactic minor axis, are predicted. Such changes have recently been detected in the Continuum Halos in Nearby Galaxies-an EVLA Survey (CHANG-ES) survey.

  14. Halos in Martian Sandstone

    NASA Image and Video Library

    2017-05-30

    Pale zones called "halos" border bedrock fractures visible in this 2015 image from NASA's Curiosity Mars rover which has been darkened (a previously released image can be seen at PIA20268). Measurements overlaid on the image offer a sense of scale for the size of these fractures. The rover team determined that the halos are rich in silica, a clue to the duration of wet environmental conditions long ago. The location is on the lower slope of Mars' Mount Sharp. Curiosity's Navigation Camera (Navcam) acquired the component images of this mosaic on Aug. 23, 2015, during the 1.083rd Martian day, or sol, of the mission. The location is along the rover's path between "Marias Pass" and "Bridger Basin." In this region, the rover has found fracture zones to be associated with rock compositions enriched in silica, relative to surrounding bedrock. https://photojournal.jpl.nasa.gov/catalog/PIA21649

  15. Mixing between high velocity clouds and the galactic halo

    SciTech Connect

    Gritton, Jeffrey A.; Shelton, Robin L.; Kwak, Kyujin E-mail: rls@physast.uga.edu

    2014-11-01

    In the Galactic halo, metal-bearing Galactic halo material mixes into high velocity clouds (HVCs) as they hydrodynamically interact. This interaction begins long before the clouds completely dissipate and long before they slow to the velocity of the Galactic material. In order to make quantitative estimates of the mixing efficiency and resulting metal enrichment of HVCs, we made detailed two- and three-dimensional simulations of cloud-interstellar medium interactions. Our simulations track the hydrodynamics and time-dependent ionization levels. They assume that the cloud originally has a warm temperature and extremely low metallicity while the surrounding medium has a high temperature, low density, and substantial metallicity, but our simulations can be generalized to other choices of initial metallicities. In our simulations, mixing between cloud and halo gas noticeably raises the metallicity of the high velocity material. We present plots of the mixing efficiency and metal enrichment as a function of time.

  16. GALACTIC WARPS IN TRIAXIAL HALOS

    SciTech Connect

    Jeon, Myoungwon; Kim, Sungsoo S.; Ann, Hong Bae E-mail: sungsoo.kim@khu.ac.kr

    2009-05-10

    We study the behavior of galactic disks in triaxial halos both numerically and analytically to see if warps can be excited and sustained in triaxial potentials. We consider the following two scenarios: (1) galactic disks that are initially tilted relative to the equatorial plane of the halo (for a pedagogical purpose), and (2) tilted infall of dark matter relative to the equatorial plane of the disk and the halo. With numerical simulations of 100,000 disk particles in a fixed halo potential, we find that in triaxial halos, warps can be excited and sustained just as in spherical or axisymmetric halos but they show some oscillatory behavior and even can be transformed to a polar-ring system if the halo has a prolate-like triaxiality. The nonaxisymmetric component of the halo causes the disk to nutate, and the differential nutation between the inner and outer parts of the disk generally makes the magnitude of the warp slightly diminish and fluctuate. We also find that warps are relatively weaker in oblate and oblate-like triaxial halos, and since these halos are the halo configurations of disk galaxies inferred by cosmological simulations, our results are consistent with the fact that most of the observed warps are quite weak. We derive approximate formulae for the torques exerted on the disk by the triaxial halo and the dark matter torus, and with these formulae we successfully describe the behavior of the disks in our simulations. The techniques used in deriving these formulae could be applied for realistic halos with more complex structures.

  17. Search for Halo Axions

    SciTech Connect

    Daw, E. J.,; van Bibber, K.

    1998-01-01

    A collaboration of MIT, LLNL, Univ. of Florida, FNAL, UC Berkeley and INR Moscow have built a large-scale RF cavity axion detector. The experiment has been taking production data since February of 1996 and is sensitive enough to detect plausible dark matter axions comprising a reasonable fraction of the mass in our galactic halo. After a brief introduction to axion physics, I discuss details of our instrumentation, our analysis methodology, our run plan and future goals of the experiments.

  18. Rainbows, halos, and glories.

    NASA Astrophysics Data System (ADS)

    Greenler, R.

    Paperback edition of the book first published in 1980 (31.003.052). Contents: 1. Rainbows. 2. Ice-crystal refraction effects: halos, arcs, and spots. 3. Ice-crystal reflection effects: pillars, circles, and crosses. 4. Complex displays, past and present. 5. Scattering: light in the sky and color in the clouds. 6. Diffraction: the corona, the glory, and the specter of the Brocken. 7. Atmospheric refraction: mirages, twinkling stars, and the green flash.

  19. Probing the Structure and Kinematics of the Transition Layer between the Magellanic Stream and the Halo in H I

    NASA Astrophysics Data System (ADS)

    Nigra, Lou; Stanimirović, Snežana; Gallagher, John S., III; Wood, Kenneth; Nidever, David; Majewski, Steven

    2012-11-01

    The Magellanic Stream (MS) is a nearby laboratory for studying the fate of cool gas streams injected into a gaseous galactic halo. We investigate properties of the boundary layer between the cool MS gas and the hot Milky Way halo with 21 cm H I observations of a relatively isolated cloud having circular projection in the northern MS. Through averaging and modeling techniques, our observations, obtained with the Robert C. Byrd Green Bank Telescope, reach unprecedented 3σ sensitivity of ~1 × 1017 cm-2, while retaining the telescope's 9farcm1 resolution in the essential radial dimension. We find an envelope of diffuse neutral gas with FWHM of 60 km s-1, associated in velocity with the cloud core having FWHM of 20 km s-1, extending to 3.5 times the core radius with a neutral mass seven times that of the core. We show that the envelope is too extended to represent a conduction-dominated layer between the core and the halo. Its observed properties are better explained by a turbulent mixing layer driven by hydrodynamic instabilities. The fortuitous alignment of the NGC 7469 background source near the cloud center allows us to combine UV absorption and H I emission data to determine a core temperature of 8350 ± 350 K. We show that the H I column density and size of the core can be reproduced when a slightly larger cloud is exposed to Galactic and extragalactic background ionizing radiation. Cooling in the large diffuse turbulent mixing layer envelope extends the cloud lifetime by at least a factor of two relative to a simple hydrodynamic ablation case, suggesting that the cloud is likely to reach the Milky Way disk.

  20. MULTIPHASE GAS IN GALAXY HALOS: THE O VI LYMAN-LIMIT SYSTEM TOWARD J1009+0713

    SciTech Connect

    Tumlinson, J.; Thom, C.; Okrochkov, M.; Sembach, K. R.; Werk, J. K.; Prochaska, J. X.; Meiring, J. D.; Tripp, T. M.; O'Meara, J. M.

    2011-06-01

    We have serendipitously detected a strong O VI-bearing Lyman-limit system (LLS) at z{sub abs} = 0.3558 toward the quasi-stellar object (QSO) J1009+0713 (z{sub em} = 0.456) in our survey of low-redshift galaxy halos with the Hubble Space Telescope's (HST) Cosmic Origins Spectrograph. Its total rest-frame equivalent width of W{sub r} = 835 {+-} 49 mA and column density of log N(O VI) = 15.0 are the highest for an intervening absorber yet detected in any low-redshift QSO sightline, with absorption spanning at least four major kinematic component groups over 400 km s{sup -1} in its rest frame. HST/Wide Field Camera 3 images of the galaxy field show that the absorber is associated with two galaxies lying at 14 and 46 kpc from the QSO line of sight. The absorber is kinematically complex and there are no less than nine individual Mg II components spanning 200 km s{sup -1} in our Keck/HIRES optical data. The bulk of the absorbing gas traced by H I resides in two strong, blended component groups that possess a total log N(H I) {approx_equal} 18-18.8, but most of the O VI is associated with two outlying components with log N(H I) = 14.8 and 16.5. The ion ratios and column densities of C, N, O, Mg, Si, S, and Fe, except the O VI, can be accommodated into a simple photoionization model in which diffuse, low-metallicity halo gas is exposed to a photoionizing field from stars in the nearby galaxies that propagates into the halo at 10% efficiency. In this model, the clouds have neutral fractions of {approx}1%-10% and thus total hydrogen column densities of log N(H) {approx_equal} 19.5. Direct measurement of the gas metallicity is precluded by saturation of the main components of H I, but we constrain the metallicity firmly within the range 0.1-1 Z{sub sun}, and photoionization modeling indirectly indicates a subsolar metallicity of 0.05-0.5 Z{sub sun}. This highly ionized, multiphase, possibly low-metallicity halo gas resembles gas with similar properties in the Milky Way halo

  1. "Halo nevi" and UV radiation.

    PubMed

    Pustisek, Nives; Sikanić-Dugić, Nives; Hirsl-Hećej, Vlasta; Domljan, Mislav Luka

    2010-04-01

    Halo nevi, also termed Sutton nevi, are defined as benign melanocytic nevi that are surrounded by an area of depigmentation resembling a halo. Halo nevi are common in children and young adults, with a mean age at onset of 15 years. The incidence in the population is estimated to be approximately 1%. Affected individuals frequently have multiple lesions which are usually localized on the back. A familial tendency for halo nevi has been reported. The etiology of halo nevi is unknown. It is an autoimmune response and T lymphocytes are considered to play a key role in the progressive destruction of nevus cells. Halo nevi may be associated with autoimmune disorders such as vitiligo, Hashimoto thyroiditis, alopecia areata, celiac disease, atopic dermatitis and others. It has been proved that halo nevi are detected after an intense sun exposure especially after sunburns. The etiology of halo nevi, association with malignant melanoma and the role of sun exposure in the development of halo nevi are discussed.

  2. Jupiter's Ring Halo

    NASA Technical Reports Server (NTRS)

    1997-01-01

    A mosaic of four images taken through the clear filter (610 nanometers) of the solid state imaging (CCD) system aboard NASA's Galileo spacecraft on November 8, 1996, at a resolution of approximately 46 kilometers (km) per picture element (pixel) along the rings; however, because the spacecraft was only about 0.5 degrees above the ring plane, the image is highly foreshortened in the vertical direction. The images were obtained when Galileo was in Jupiter's shadow peering back toward the Sun; the ring was approximately 2,300,000 kilometers (km) away. The arc on the far right of the image is produced by sunlight scattered by small particles comprising Jupiter's upper atmospheric haze. The ring also efficiently scatters light, indicating that much of its brightness is due to particles that are microns or less in diameter. Such small particles are believed to have human-scale lifetimes, i.e., very brief compared to the solar system's age.

    Jupiter's ring system is composed of three parts -- a flat main ring, a lenticular halo interior to the main ring, and the gossamer ring, which lies exterior to the main ring. The near and far arms of Jupiter's main ring extend horizontally across the mosaic, joining together at the ring's ansa, on the far left side of the figure. The near arm of the ring appears to be abruptly truncated close to the planet, at the point where it passes into Jupiter's shadow.

    A faint mist of particles can be seen above and below the main rings; this vertically extended, toroidal 'halo' is unusual in planetary rings, and is probably caused by electromagnetic forces which can push small grains out of the ring plane. Halo material is present across this entire image, implying that it reaches more than 27,000 km above the ring plane. Because of shadowing, the halo is not visible close to Jupiter in the lower right part of the mosaic. In order to accentuate faint features in the image, different brightnesses are shown through color, with the brightest

  3. Jupiter's Ring Halo

    NASA Technical Reports Server (NTRS)

    1997-01-01

    A mosaic of four images taken through the clear filter (610 nanometers) of the solid state imaging (CCD) system aboard NASA's Galileo spacecraft on November 8, 1996, at a resolution of approximately 46 kilometers (km) per picture element (pixel) along the rings; however, because the spacecraft was only about 0.5 degrees above the ring plane, the image is highly foreshortened in the vertical direction. The images were obtained when Galileo was in Jupiter's shadow peering back toward the Sun; the ring was approximately 2,300,000 kilometers (km) away. The arc on the far right of the image is produced by sunlight scattered by small particles comprising Jupiter's upper atmospheric haze. The ring also efficiently scatters light, indicating that much of its brightness is due to particles that are microns or less in diameter. Such small particles are believed to have human-scale lifetimes, i.e., very brief compared to the solar system's age.

    Jupiter's ring system is composed of three parts -- a flat main ring, a lenticular halo interior to the main ring, and the gossamer ring, which lies exterior to the main ring. The near and far arms of Jupiter's main ring extend horizontally across the mosaic, joining together at the ring's ansa, on the far left side of the figure. The near arm of the ring appears to be abruptly truncated close to the planet, at the point where it passes into Jupiter's shadow.

    A faint mist of particles can be seen above and below the main rings; this vertically extended, toroidal 'halo' is unusual in planetary rings, and is probably caused by electromagnetic forces which can push small grains out of the ring plane. Halo material is present across this entire image, implying that it reaches more than 27,000 km above the ring plane. Because of shadowing, the halo is not visible close to Jupiter in the lower right part of the mosaic. In order to accentuate faint features in the image, different brightnesses are shown through color, with the brightest

  4. Jupiter Ring Halo

    NASA Image and Video Library

    1998-03-26

    A mosaic of four images taken through the clear filter (610 nanometers) of the solid state imaging (CCD) system aboard NASA's Galileo spacecraft on November 8, 1996, at a resolution of approximately 46 kilometers (km) per picture element (pixel) along the rings; however, because the spacecraft was only about 0.5 degrees above the ring plane, the image is highly foreshortened in the vertical direction. The images were obtained when Galileo was in Jupiter's shadow peering back toward the Sun; the ring was approximately 2,300,000 kilometers (km) away. The arc on the far right of the image is produced by sunlight scattered by small particles comprising Jupiter's upper atmospheric haze. The ring also efficiently scatters light, indicating that much of its brightness is due to particles that are microns or less in diameter. Such small particles are believed to have human-scale lifetimes, i.e., very brief compared to the solar system's age. Jupiter's ring system is composed of three parts -- a flat main ring, a lenticular halo interior to the main ring, and the gossamer ring, which lies exterior to the main ring. The near and far arms of Jupiter's main ring extend horizontally across the mosaic, joining together at the ring's ansa, on the far left side of the figure. The near arm of the ring appears to be abruptly truncated close to the planet, at the point where it passes into Jupiter's shadow. A faint mist of particles can be seen above and below the main rings; this vertically extended, toroidal "halo" is unusual in planetary rings, and is probably caused by electromagnetic forces which can push small grains out of the ring plane. Halo material is present across this entire image, implying that it reaches more than 27,000 km above the ring plane. Because of shadowing, the halo is not visible close to Jupiter in the lower right part of the mosaic. In order to accentuate faint features in the image, different brightnesses are shown through color, with the brightest being

  5. Toward a universal formulation of the halo mass function.

    PubMed

    Corasaniti, P S; Achitouv, I

    2011-06-17

    We compute the dark matter halo mass function using the excursion set formalism for a diffusive barrier with linearly drifting average which captures the main features of the ellipsoidal collapse model. We evaluate the non-Markovian corrections due to the sharp filtering of the linear density field in real space with a path-integral method. We find an unprecedented agreement with N-body simulation data with deviations ≲5% over the range of masses probed by the simulations. This indicates that the excursion set in combination with a realistic modeling of the collapse threshold can provide a robust estimation of the halo mass function.

  6. HALOE test and evaluation software

    NASA Technical Reports Server (NTRS)

    Edmonds, W.; Natarajan, S.

    1987-01-01

    Computer programming, system development and analysis efforts during this contract were carried out in support of the Halogen Occultation Experiment (HALOE) at NASA/Langley. Support in the major areas of data acquisition and monitoring, data reduction and system development are described along with a brief explanation of the HALOE project. Documented listings of major software are located in the appendix.

  7. The FUSE Survey of 0 VI in the Galactic Halo

    NASA Technical Reports Server (NTRS)

    Sonneborn, George; Savage, B. D.; Wakker, B. P.; Sembach, K. R.; Jenkins, E. B.; Moos, H. W.; Shull, J. M.

    2003-01-01

    This paper summarizes the results of the Far-Ultraviolet Spectroscopic Explorer (FUSE) program to study 0 VI in the Milky Way halo. Spectra of 100 extragalactic objects and two distant halo stars are analyzed to obtain measures of O VI absorption along paths through the Milky Way thick disk/halo. Strong O VI absorption over the velocity range from -100 to 100 km/s reveals a widespread but highly irregular distribution of O VI, implying the existence of substantial amounts of hot gas with T approx. 3 x 10(exp 5) K in the Milky Way thick disk/halo. The overall distribution of O VI is not well described by a symmetrical plane-parallel layer of patchy O VI absorption. The simplest departure from such a model that provides a reasonable fit to the observations is a plane-parallel patchy absorbing layer with an average O VI mid-plane density of n(sub 0)(O VI) = 1.7 x 10(exp -2)/cu cm, a scale height of approx. 2.3 kpc, and a approx. 0.25 dex excess of O VI in the northern Galactic polar region. The distribution of O VI over the sky is poorly correlated with other tracers of gas in the halo, including low and intermediate velocity H I, Ha emission from the warm ionized gas at approx. l0(exp 4) K, and hot X-ray emitting gas at approx. l0(exp 6) K . The O VI has an average velocity dispersion, b approx. 60 km/s and standard deviation of 15 km/s. Thermal broadening alone cannot explain the large observed profile widths. A combination of models involving the radiative cooling of hot fountain gas, the cooling of supernova bubbles in the halo, and the turbulent mixing of warm and hot halo gases is required to explain the presence of O VI and other highly ionized atoms found in the halo. The preferential venting of hot gas from local bubbles and superbubbles into the northern Galactic polar region may explain the enhancement of O VI in the North.

  8. The FUSE Survey of 0 VI in the Galactic Halo

    NASA Technical Reports Server (NTRS)

    Sonneborn, George; Savage, B. D.; Wakker, B. P.; Sembach, K. R.; Jenkins, E. B.; Moos, H. W.; Shull, J. M.

    2003-01-01

    This paper summarizes the results of the Far-Ultraviolet Spectroscopic Explorer (FUSE) program to study 0 VI in the Milky Way halo. Spectra of 100 extragalactic objects and two distant halo stars are analyzed to obtain measures of O VI absorption along paths through the Milky Way thick disk/halo. Strong O VI absorption over the velocity range from -100 to 100 km/s reveals a widespread but highly irregular distribution of O VI, implying the existence of substantial amounts of hot gas with T approx. 3 x 10(exp 5) K in the Milky Way thick disk/halo. The overall distribution of O VI is not well described by a symmetrical plane-parallel layer of patchy O VI absorption. The simplest departure from such a model that provides a reasonable fit to the observations is a plane-parallel patchy absorbing layer with an average O VI mid-plane density of n(sub 0)(O VI) = 1.7 x 10(exp -2)/cu cm, a scale height of approx. 2.3 kpc, and a approx. 0.25 dex excess of O VI in the northern Galactic polar region. The distribution of O VI over the sky is poorly correlated with other tracers of gas in the halo, including low and intermediate velocity H I, Ha emission from the warm ionized gas at approx. l0(exp 4) K, and hot X-ray emitting gas at approx. l0(exp 6) K . The O VI has an average velocity dispersion, b approx. 60 km/s and standard deviation of 15 km/s. Thermal broadening alone cannot explain the large observed profile widths. A combination of models involving the radiative cooling of hot fountain gas, the cooling of supernova bubbles in the halo, and the turbulent mixing of warm and hot halo gases is required to explain the presence of O VI and other highly ionized atoms found in the halo. The preferential venting of hot gas from local bubbles and superbubbles into the northern Galactic polar region may explain the enhancement of O VI in the North.

  9. Neutron halo in deformed nuclei

    SciTech Connect

    Zhou Shangui; Meng Jie; Ring, P.; Zhao Enguang

    2010-07-15

    Halo phenomena in deformed nuclei are investigated within a deformed relativistic Hartree Bogoliubov (DRHB) theory. These weakly bound quantum systems present interesting examples for the study of the interdependence between the deformation of the core and the particles in the halo. Contributions of the halo, deformation effects, and large spatial extensions of these systems are described in a fully self-consistent way by the DRHB equations in a spherical Woods-Saxon basis with the proper asymptotic behavior at a large distance from the nuclear center. Magnesium and neon isotopes are studied and detailed results are presented for the deformed neutron-rich and weakly bound nucleus {sup 44}Mg. The core of this nucleus is prolate, but the halo has a slightly oblate shape. This indicates a decoupling of the halo orbitals from the deformation of the core. The generic conditions for the occurrence of this decoupling effects are discussed.

  10. Baryonic distributions in galaxy dark matter halos

    NASA Astrophysics Data System (ADS)

    Richards, Emily E.

    In our best current understanding of the growth of structure in the Universe, visibly complex distributions of gas and stars form and evolve into a wide range of galaxies inside overdensities of dark matter. Re-creating the observed diversity in the organization of baryonic mass within dark matter halos represents a key challenge for galaxy formation models. In this dissertation, I constrain the distribution of baryonic and non-baryonic matter in a statistically representative sample of 44 nearby galaxies defined from the Extended Disk Galaxy Exploration Science (EDGES) survey to address the growth of galaxy disks in dark matter halos. I trace the gravitational potentials of each galaxy using rotation curves derived from new and archival radio synthesis observations of neutral hydrogen (HI). The measured rotation curves are decomposed into baryonic and dark matter halo components using 3.6 mum images for the stellar content, the HI observations for the atomic gas component, and, when available, CO data from the literature for the molecular gas component. The HI kinematics are supplemented with optical integral field spectroscopic (IFS) observations to measure the central ionized gas kinematics in 26 galaxies. Distributions of baryonic-to-total mass ratios are determined from the rotation curve decompositions under different assumptions about the contribution of the stellar component, and are compared to global and radial properties of the dominant stellar populations extracted from optical and near-infrared photometry. Galaxies are grouped into clusters of similar baryonic-to-total mass distributions to examine whether they also exhibit similar star and gas properties. The radial distribution of baryonic-to-total mass in a galaxy does not appear to correlate with any characteristics of its star formation history. This result encapsulates the challenge facing simulations to create galaxies which evolve with different star formation histories but similar

  11. Haloes gone MAD: The Halo-Finder Comparison Project

    NASA Astrophysics Data System (ADS)

    Knebe, Alexander; Knollmann, Steffen R.; Muldrew, Stuart I.; Pearce, Frazer R.; Aragon-Calvo, Miguel Angel; Ascasibar, Yago; Behroozi, Peter S.; Ceverino, Daniel; Colombi, Stephane; Diemand, Juerg; Dolag, Klaus; Falck, Bridget L.; Fasel, Patricia; Gardner, Jeff; Gottlöber, Stefan; Hsu, Chung-Hsing; Iannuzzi, Francesca; Klypin, Anatoly; Lukić, Zarija; Maciejewski, Michal; McBride, Cameron; Neyrinck, Mark C.; Planelles, Susana; Potter, Doug; Quilis, Vicent; Rasera, Yann; Read, Justin I.; Ricker, Paul M.; Roy, Fabrice; Springel, Volker; Stadel, Joachim; Stinson, Greg; Sutter, P. M.; Turchaninov, Victor; Tweed, Dylan; Yepes, Gustavo; Zemp, Marcel

    2011-08-01

    We present a detailed comparison of fundamental dark matter halo properties retrieved by a substantial number of different halo finders. These codes span a wide range of techniques including friends-of-friends, spherical-overdensity and phase-space-based algorithms. We further introduce a robust (and publicly available) suite of test scenarios that allow halo finder developers to compare the performance of their codes against those presented here. This set includes mock haloes containing various levels and distributions of substructure at a range of resolutions as well as a cosmological simulation of the large-scale structure of the universe. All the halo-finding codes tested could successfully recover the spatial location of our mock haloes. They further returned lists of particles (potentially) belonging to the object that led to coinciding values for the maximum of the circular velocity profile and the radius where it is reached. All the finders based in configuration space struggled to recover substructure that was located close to the centre of the host halo, and the radial dependence of the mass recovered varies from finder to finder. Those finders based in phase space could resolve central substructure although they found difficulties in accurately recovering its properties. Through a resolution study we found that most of the finders could not reliably recover substructure containing fewer than 30-40 particles. However, also here the phase-space finders excelled by resolving substructure down to 10-20 particles. By comparing the halo finders using a high-resolution cosmological volume, we found that they agree remarkably well on fundamental properties of astrophysical significance (e.g. mass, position, velocity and peak of the rotation curve). We further suggest to utilize the peak of the rotation curve, vmax, as a proxy for mass, given the arbitrariness in defining a proper halo edge. Airport code for Madrid, Spain

  12. Dark-Matter Halos of Tenuous Galaxies

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-03-01

    A series of recent deep-imaging surveys has revealed dozens of lurking ultra-diffuse galaxies (UDGs) in nearby galaxy clusters. A new study provides key information to help us understand the origins of these faint giants.What are UDGs?There are three main possibilities for how UDGs galaxies with the sizes of giants, but luminosities no brighter than those of dwarfs formed:They are tidal dwarfs, created in galactic collisions when streams of matter were pulled away from the parent galaxies and halos to form dwarfs.They are descended from normal galaxies and were then altered by tidal interactions with the galaxy cluster.They are ancient remnant systems large galaxies whose gas was swept away, putting an early halt to star formation. The gas removal did not, however, affect their large dark matter halos, which permitted them to survive in the cluster environment.The key to differentiating between these options is to obtain mass measurements for the UDGs how large are their dark matter halos? In a recent study led by Michael Beasley (Institute of Astrophysics of the Canary Islands, University of La Laguna), a team of astronomers has determined a clever approach for measuring these galaxies masses: examine their globular clusters.Masses from Globular ClustersVCC 1287s mass measurements put it outside of the usual halo-mass vs. stellar-mass relationships for nearby galaxies: it has a significantly higher halo mass than is normal, given its stellar mass. [Adapted from Beasley et al. 2016]Beasley and collaborators selected one UDG, VCC 1287, from the Virgo galaxy cluster, and they obtained spectra of the globular clusters around it using the OSIRIS spectrograph on the Great Canary Telescope. They then determined VCC 1287s total halo mass in two ways: first by using the dynamics of the globular clusters, and then by relying on a relation between total globular cluster mass and halo mass.The two masses they found are in good agreement with each other; both are around 80

  13. Halo Shape and its Relation to Environment

    NASA Astrophysics Data System (ADS)

    Gottlöber, S.; Turchaninov, V.

    Using high resolution DM simulations we study the shape of dark matter halos. Halos become more spherical with decreasing mass. This trend is even more pronounced for the inner part of the halo. Angular momentum and shape are correlated. The angular momenta of neighboring halos are correlated.

  14. The surface density of haloes

    NASA Astrophysics Data System (ADS)

    Del Popolo, A.; Lee, Xi-Guo

    We study the correlation between the central surface density and the core radius of the dark matter haloes of galaxies and clusters of galaxies. We find that the surface density within the halo characteristic radius r* is not a universal quantity as claimed by some authors (e.g., Milgrom 2009), but it correlates with several physical quantities (e.g., the halo mass M200, and the magnitude MB). The slope of the surface density-mass relation is 0.18 ± 0.05, leaving small room to the possibility of a constant surface density. Finally, we compare the results with MOND predictions.

  15. A Hot Gaseous Galaxy Halo Candidate with Mg X Absorption

    NASA Astrophysics Data System (ADS)

    Qu, Zhijie; Bregman, Joel N.

    2016-12-01

    The hot gas in galaxy halos may account for a significant fraction of missing baryons in galaxies, and some of these gases can be traced by high ionization absorption systems in QSO UV spectra. Using high S/N Hubble Space Telescope/Cosmic Origins Spectrograph spectra, we discovered a high ionization state system at z = 1.1912 in the sightline toward LBQS 1435-0134, and two-component absorption lines are matched for Mg x, Ne viii, Ne vi, O vi, Ne v, O v, Ne iv, O iv, N iv, O iii, and H i. Mg x, detected for the first time (5.8σ), is a particularly direct tracer of hot galactic halos, as its peak ion fraction occurs near 106.1 K, about the temperature of a virialized hot galaxy halo of mass ˜ 0.5{M}* . With Mg x and Ne viii, a photoionization model cannot reproduce the observed column densities with path lengths of galaxy halos. For collisional ionization models, one or two-temperature models do not produce acceptable fits, but a three-temperature model or a power-law model can produce the observed results. In the power-law model, {dN}/{dT}={10}4.4+/- 2.2-[Z/X]{T}1.55+/- 0.41 with temperatures in the range of {10}4.39+/- 0.13 {{K}}\\lt T\\lt {10}6.04+/- 0.05 {{K}}, the total hydrogen column density is 8.2× {10}19(0.3 {Z}⊙ /Z) {{cm}}-2 and the positive power-law index indicates most of the mass is at the high temperature end. We suggest that this absorption system is a hot volume-filled galaxy halo rather than interaction layers between the hot halo and cool clouds. The temperature dependence of the column density is likely due to the local mixture of multiple phase gases.

  16. Halo model and halo properties in Galileon gravity cosmologies

    SciTech Connect

    Barreira, Alexandre; Li, Baojiu; Hellwing, Wojciech A.; Baugh, Carlton M.; Lombriser, Lucas; Pascoli, Silvia E-mail: baojiu.li@durham.ac.uk E-mail: llo@roe.ac.uk E-mail: silvia.pascoli@durham.ac.uk

    2014-04-01

    We investigate the performance of semi-analytical modelling of large-scale structure in Galileon gravity cosmologies using results from N-body simulations. We focus on the Cubic and Quartic Galileon models that provide a reasonable fit to CMB, SNIa and BAO data. We demonstrate that the Sheth-Tormen mass function and linear halo bias can be calibrated to provide a very good fit to our simulation results. We also find that the halo concentration-mass relation is well fitted by a power law. The nonlinear matter power spectrum computed in the halo model approach is found to be inaccurate in the mildly nonlinear regime, but captures reasonably well the effects of the Vainshtein screening mechanism on small scales. In the Cubic model, the screening mechanism hides essentially all of the effects of the fifth force inside haloes. In the case of the Quartic model, the screening mechanism leaves behind residual modifications to gravity, which make the effective gravitational strength time-varying and smaller than the standard value. Compared to normal gravity, this causes a deficiency of massive haloes and leads to a weaker matter clustering on small scales. For both models, we show that there are realistic halo occupation distributions of Luminous Red Galaxies that can match both the observed large-scale clustering amplitude and the number density of these galaxies.

  17. WARM IONIZED GAS REVEALED IN THE MAGELLANIC BRIDGE TIDAL REMNANT: CONSTRAINING THE BARYON CONTENT AND THE ESCAPING IONIZING PHOTONS AROUND DWARF GALAXIES

    SciTech Connect

    Barger, K. A.; Haffner, L. M.; Bland-Hawthorn, J. E-mail: haffner@astro.wisc.edu

    2013-07-10

    The Magellanic System includes some of the nearest examples of galaxies disturbed by galaxy interactions. These interactions have redistributed much of their gas into the halos of the Milky Way (MW) and the Magellanic Clouds. We present Wisconsin H{alpha} Mapper kinematically resolved observations of the warm ionized gas in the Magellanic Bridge over the velocity range of +100 to +300 km s{sup -1} in the local standard of rest reference frame. These observations include the first full H{alpha} intensity map and the corresponding intensity-weighted mean velocity map of the Magellanic Bridge across (l, b) = (281 Degree-Sign .5, -30 Degree-Sign .0) to (302. Degree-Sign 5, -46. Degree-Sign 7). Using the H{alpha} emission from the Small Magellanic Cloud (SMC)-Tail and the Bridge, we estimate that the mass of the ionized material is between (0.7-1.7) Multiplication-Sign 10{sup 8} M{sub Sun }, compared to 3.3 Multiplication-Sign 10{sup 8} M{sub Sun} for the neutral mass over the same region. The diffuse Bridge is significantly more ionized than the SMC-Tail, with an ionization fraction of 36%-52% compared to 5%-24% for the Tail. The H{alpha} emission has a complex multiple-component structure with a velocity distribution that could trace the sources of ionization or distinct ionized structures. We find that incident radiation from the extragalactic background and the MW alone are insufficient to produced the observed ionization in the Magellanic Bridge and present a model for the escape fraction of the ionizing photons from both the SMC and Large Magellanic Cloud (LMC). With this model, we place an upper limit of 4.0% for the average escape fraction of ionizing photons from the LMC and an upper limit of 5.5% for the SMC. These results, combined with the findings of a half a dozen other studies for dwarf galaxies in different environments, provide compelling evidence that only a small percentage of the ionizing photons escape from dwarf galaxies in the present epoch to

  18. Ionizing radiation

    USDA-ARS?s Scientific Manuscript database

    This chapter gives a comprehensive review on ionizing irradiation of fresh fruits and vegetables. Topics include principles of ionizing radiation, its effects on pathogenic and spoilage microorganisms, shelf-life, sensory quality, nutritional and phytochemical composition, as well as physiologic and...

  19. Low-redshift Lyman-alpha absorption lines and the dark matter halos of disk galaxies

    NASA Technical Reports Server (NTRS)

    Maloney, Philip

    1992-01-01

    Ultraviolet observations of the low-redshift quasar 3C 273 using the Hubble Space Telescope have revealed many more Lyman-alpha absorption lines than would be expected from extrapolation of the absorption systems seen toward QSOs at z about 2. It is shown here that these absorption lines can plausibly be produced by gas at large radii in the disks of spiral and irregular galaxies; the gas is confined by the dark matter halos and ionized and heated by the extragalactic radiation field. This scenario does not require the extragalactic ionizing radiation field to decline as rapidly with decreasing z as the QSO emissivity. Observations of Ly-alpha absorption through the halos of known galaxies at low redshift will constrain both the extragalactic background and the properties of galactic halos.

  20. Low-redshift Lyman-alpha absorption lines and the dark matter halos of disk galaxies

    NASA Technical Reports Server (NTRS)

    Maloney, Philip

    1992-01-01

    Ultraviolet observations of the low-redshift quasar 3C 273 using the Hubble Space Telescope have revealed many more Lyman-alpha absorption lines than would be expected from extrapolation of the absorption systems seen toward QSOs at z about 2. It is shown here that these absorption lines can plausibly be produced by gas at large radii in the disks of spiral and irregular galaxies; the gas is confined by the dark matter halos and ionized and heated by the extragalactic radiation field. This scenario does not require the extragalactic ionizing radiation field to decline as rapidly with decreasing z as the QSO emissivity. Observations of Ly-alpha absorption through the halos of known galaxies at low redshift will constrain both the extragalactic background and the properties of galactic halos.

  1. Probing Milky Way's hot gas halo density distribution using the dispersion measure of pulsars

    NASA Astrophysics Data System (ADS)

    Zhezher, Ya. V.; Nugaev, E. Ya.; Rubtsov, G. I.

    2016-03-01

    A number of recent studies indicates a significant amount of ionized gas in a form of the hot gas halo around the Milky Way. The halo extends over the region of 100 kpc and may be acountable for the missing baryon mass. In this paper we calculate the contribution of the proposed halo to the dispersion measure (DM) of the pulsars. The Navarro, Frenk, and White (NFW), Maller and Bullock (MB), and Feldmann, Hooper, and Gnedin (FHG) density distibutions are considered for the gas halo. The data set includes pulsars with the distance known independently from the DM, e.g., pulsars in globular clusters, LMC, SMC and pulsars with known parallax. The results exclude the NFW distribution for the hot gas, while the more realisticMB and FHG models are compatible with the observed dispersion measure.

  2. THE SCALING RELATIONS AND THE FUNDAMENTAL PLANE FOR RADIO HALOS AND RELICS OF GALAXY CLUSTERS

    SciTech Connect

    Yuan, Z. S.; Han, J. L.; Wen, Z. L.

    2015-11-01

    Diffuse radio emission in galaxy clusters is known to be related to cluster mass and cluster dynamical state. We collect the observed fluxes of radio halos, relics, and mini-halos for a sample of galaxy clusters from the literature, and calculate their radio powers. We then obtain the values of cluster mass or mass proxies from previous observations, and also obtain the various dynamical parameters of these galaxy clusters from optical and X-ray data. The radio powers of relics, halos, and mini-halos are correlated with the cluster masses or mass proxies, as found by previous authors, while the correlations concerning giant radio halos are in general the strongest. We found that the inclusion of dynamical parameters as the third dimension can significantly reduce the data scatter for the scaling relations, especially for radio halos. We therefore conclude that the substructures in X-ray images of galaxy clusters and the irregular distributions of optical brightness of member galaxies can be used to quantitatively characterize the shock waves and turbulence in the intracluster medium responsible for re-accelerating particles to generate the observed diffuse radio emission. The power of radio halos and relics is correlated with cluster mass proxies and dynamical parameters in the form of a fundamental plane.

  3. Frost halos from supercooled water droplets

    PubMed Central

    Jung, Stefan; Tiwari, Manish K.; Poulikakos, Dimos

    2012-01-01

    Water freezing on solid surfaces is ubiquitous in nature. Even though icing/frosting impairs the performance and safety in many processes, its mechanism remains inadequately understood. Changing atmospheric conditions, surface properties, the complexity of icing physics, and the unorthodox behavior of water are the primary factors that make icing and frost formation intriguing and difficult to predict. In addition to its unquestioned scientific and practical importance, unraveling the frosting mechanism under different conditions is a prerequisite to develop “icephobic” surfaces, which may avoid ice formation and contamination. In this work we demonstrate that evaporation from a freezing supercooled sessile droplet, which starts explosively due to the sudden latent heat released upon recalescent freezing, generates a condensation halo around the droplet, which crystallizes and drastically affects the surface behavior. The process involves simultaneous multiple phase transitions and may also spread icing by initiating sequential freezing of neighboring droplets in the form of a domino effect and frost propagation. Experiments under controlled humidity conditions using substrates differing up to three orders of magnitude in thermal conductivity establish that a delicate balance between heat diffusion and vapor transport determines the final expanse of the frozen condensate halo, which, in turn, controls frost formation and propagation. PMID:23012410

  4. Escape fraction of ionizing photons from high-redshift galaxies in cosmological SPH simulations

    NASA Astrophysics Data System (ADS)

    Yajima, Hidenobu; Choi, Jun-Hwan; Nagamine, Kentaro

    2011-03-01

    Combing the three-dimensional radiative transfer (RT) calculation and cosmological smoothed particle hydrodynamics (SPH) simulations, we study the escape fraction of ionizing photons (fesc) of high-redshift galaxies at z= 3-6. Our simulations cover the halo mass range of Mh= 109-1012 M⊙. We post-process several hundred simulated galaxies with the Authentic Radiative Transfer (ART) code to study the halo mass dependence of fesc. In this paper, we restrict ourselves to the transfer of stellar radiation from local stellar population in each dark matter halo. We find that the average fesc steeply decreases as the halo mass increases, with a large scatter for the lower-mass haloes. The low-mass haloes with Mh˜ 109 M⊙ have large values of fesc (with an average of ˜0.4), whereas the massive haloes with Mh˜ 1011 M⊙ show small values of fesc (with an average of ˜0.07). This is because in our simulations, the massive haloes show more clumpy structure in gas distribution, and the star-forming regions are embedded inside these clumps, making it more difficult for the ionizing photons to escape. On the other hand, in low-mass haloes, there are often conical regions of highly ionized gas due to the shifted location of young star clusters from the centre of dark matter halo, which allows the ionizing photons to escape more easily than in the high-mass haloes. By counting the number of escaped ionizing photons, we show that the star-forming galaxies can ionize the intergalactic medium at z= 3-6. The main contributor to the ionizing photons is the haloes with Mh≲ 1010 M⊙ owing to their high fesc. The large dispersion in fesc suggests that there may be various sizes of H II bubbles around the haloes even with the same mass in the early stages of reionization. We also examine the effect of UV background radiation field on fesc using simple, four different treatments of UV background.

  5. Halo modelling in chameleon theories

    SciTech Connect

    Lombriser, Lucas; Koyama, Kazuya; Li, Baojiu E-mail: kazuya.koyama@port.ac.uk

    2014-03-01

    We analyse modelling techniques for the large-scale structure formed in scalar-tensor theories of constant Brans-Dicke parameter which match the concordance model background expansion history and produce a chameleon suppression of the gravitational modification in high-density regions. Thereby, we use a mass and environment dependent chameleon spherical collapse model, the Sheth-Tormen halo mass function and linear halo bias, the Navarro-Frenk-White halo density profile, and the halo model. Furthermore, using the spherical collapse model, we extrapolate a chameleon mass-concentration scaling relation from a ΛCDM prescription calibrated to N-body simulations. We also provide constraints on the model parameters to ensure viability on local scales. We test our description of the halo mass function and nonlinear matter power spectrum against the respective observables extracted from large-volume and high-resolution N-body simulations in the limiting case of f(R) gravity, corresponding to a vanishing Brans-Dicke parameter. We find good agreement between the two; the halo model provides a good qualitative description of the shape of the relative enhancement of the f(R) matter power spectrum with respect to ΛCDM caused by the extra attractive gravitational force but fails to recover the correct amplitude. Introducing an effective linear power spectrum in the computation of the two-halo term to account for an underestimation of the chameleon suppression at intermediate scales in our approach, we accurately reproduce the measurements from the N-body simulations.

  6. Analytical Estimates of the Dispersion Curve in Planar Ionization Fronts

    SciTech Connect

    Arrayas, Manuel; Trueba, Jose L.; Fontelos, Marco A.

    2009-04-27

    Fingers from ionization fronts for a hydrodynamic plasma model result from a balance between impact ionization and electron diffusion in a non-attaching gas. An analytical estimation of the size of the fingers and its dependence on both the electric field and electron diffusion coefficient can be done when the diffusion is low and the electric field is strong.

  7. The optical halo around NGC 253

    NASA Astrophysics Data System (ADS)

    Beck, R.; Hutschenreiter, G.; Wielebinski, R.

    1982-02-01

    A photographic technique of image enhancement and digital smoothing of P.D.S. scans are used to study the blue light from an extended halo surrounding NGC 253. The photographic technique, described by Malin (1978), is based on the fact that the true image is formed in the topmost surface layer of the emission of a plate, while the fog is found in deeper layers of the emulsion. The investigation made it possible to follow the distribution of light out to 10 kpc from the plane of the galaxy. Synchrotron emission is responsible for the bulk of radio continuum emission in NGC 253 (Beck et al., 1979). Moreover, the radio map at a wavelength of 3.4 cm shows a spur-like feature at the exact position where the diffuse loop of light is seen, indicating a similar emission origin.

  8. Building Halos by Digesting Satellites

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-05-01

    We think galactic halos are built through the addition of material from the smaller subhalos of satellites digested by their hosts. Though most of the stars in Milky-Way-mass halos were probably formed in situ, many were instead accumulated over time, as orbiting dwarf galaxies were torn apart and their stars flung throughout the host galaxy. A recent set of simulations has examined this brutal formation process.In the authors simulations, a subhalo first falls into the host halo. At this point, it can either survive to present day as a satellite galaxy, or it can be destroyed, its stars scattering throughout the host halo. [Deason et al. 2016]Subhalo FateThere are many open questions about the growth of Milky-Way-mass halos from the accretion of subhalos. Which subhalos are torn apart and accreted, and which ones survive intact? Are more small or large subhalos accreted? Does subhalo accretion affect the host galaxys metallicity? And what can we learn from all of this about the Milky Ways formation history?In a recently published study, a team of scientists from Stanford University and SLAC National Accelerator Laboratory set out to answer these questions using a suite of 45 zoom-in simulations of Milky-Way-mass halos. Led by Alis Deason, the team tracked the accretion history of these 45 test galaxies to determine how their halos were built.Piecing Together HistoryDeason and collaborators reach several new and interesting conclusions based on the outcomes of their simulations.Average accreted stellar mass from destroyed dwarfs for each host halo, as a function of the time of the last major accretion event. More stellar mass is accreted in more recent accretion events. [Deason et al. 2016]Most of the stellar mass accreted by the Milky-Way-mass halos typically comes from only one or two destroyed dwarfs. The accreted dwarfs are usually low-mass if they were accreted early on in the simulation (i.e., in the early universe), and high-mass if they were accreted

  9. Mapping Baryons in the Halo of NGC 1097

    NASA Astrophysics Data System (ADS)

    Bowen, David

    2012-10-01

    We propose observing 5 background QSOs whose sightlines pass through the halo of NGC 1097 at impact parameters of 53-183 kpc. NGC 1097 is a bright {-21.1} spiral galaxy that has the highest surface density of background, UV-bright QSOs in the nearby Universe. The galaxy hosts a low luminosity AGN at its core, surrounded by a ring of intense star-forming regions; there is also evidence from stellar tidal streams that the galaxy has recently cannibalized a number of dwarf galaxies, and a companion dwarf elliptical is still clearly merging with the outer disk. We aim to examine the physical conditions of gas that fills the halo of such an active galaxy. We will search primarily for Lya and SiIV absorption lines in the spectra of the background QSOs, as well as weak NV from hot gas. At the lowest impact parameters, we may also be able to find absorption lines from low ionization species. Our goals are to test whether the halo of NGC 1097 contains the same distribution of Lyman-alpha forest clouds seen at higher redshifts out to large distances from galaxies, and determine how the HI column density, covering fraction, and temperature of the gas decline with radius in a single galaxy halo. We will examine whether the velocities of the absorbers are consistent with those expected from gas co-rotating in the dark matter halo of the galaxy, or whether there exists a distribution of velocities that might indicate outflows from the galactic disk or from the central AGN, or, alternatively, from inflows from the IGM. Our map of Lya and SiIV around NGC 1097 will provide an important template for understanding the origin of higher redshift QSO absorption line systems.

  10. Reliability of the hypernephroma halo

    SciTech Connect

    Wong, W.S.; Cochran, S.T.; Waisman, J.

    1981-11-01

    The excretory urograms and renal arteriograms of 68 patients with renal adenocarcinoma and 84 patients with renal masses other than renal adenocarcinoma were reviewed. The radiographs were examined for the presence or absence of the ''hypernephroma halo.'' The sensitivity of this sign was observed to be only 6% and 35% on excretory urography and arteriography, respectively. The specificity was 92% and 77%. However, the overall accuracy for this sign was only 54% and 59%. The relation between the halo and its postulated structural correlate, the tumor capsule, was also examined. There was no significant association demonstrable. It was concluded that the hypernephroma halo is not a reliable sign for diagnosing renal adenocarcinoma and that it probably does not represent the tumor capsule.

  11. Flows of Baryons through the Milky Way Halo

    NASA Astrophysics Data System (ADS)

    Fox, Andrew J.

    2017-07-01

    The Milky Way provides an ideal opportunity to study baryon flows in the circumgalactic medium of a star-forming spiral galaxy. High velocity clouds (HVCs) seen in UV absorption toward background AGN probe the multi-phase ionized gas in the Galactic CGM. In this talk new observations from the Cosmic Origins Spectrograph (COS) on Hubble will be presented, focusing on two Galactic regions: the biconical outflow from the Galactic Center, which drives gas into the Fermi Bubbles, and the Smith Cloud, an accreting HVC close to the Galactic disk showing clear signs of fragmentation. These observations allow us to constrain the rates of gas circulation in the Galactic halo.

  12. The study of diffuse soft X-ray background

    NASA Astrophysics Data System (ADS)

    Gupta, Anjali

    The cosmic X-ray background was discovered at the dawn of the X-ray astronomy: during the first successful rocket flight launched to study the X-ray emission from the Moon, the presence of a residual diffuse emission was also "serendipitously" revealed. In the intervening decades, observations with improving angular and spectral resolution have enhanced our understanding of the components that make up this background. Above 1 keV, the emission is highly isotropic on large angular scales, has extragalactic origin, and about ~80 percent has been resolved into discrete sources (Mushotzky et al. 2000, Hasinger et al. 1998). Our current interpretation of the diffuse X-ray emission below 1 keV uses a combination of 5 components, solar wind charge exchange, Local Bubble, Galactic halo, intergalactic gas, and unresolved point sources. Resolving the different components is made particularly difficult by the similar spectral emission of most components, X-ray lines of heavily ionized metals, which are poorly resolved by the energy resolution of CCD cameras onboard current X-ray satellites with typical observing times. The goal of this investigation is to assess the integral emission of the major components of the diffuse Soft X-Ray Background. In the first part of my project, I analyzed the shadow observations performed with XMM-Newton and Suzaku X-ray observatories. Shadow observations offer a tool to separate the fore ground component, due to the Local Bubble and, possibly, charge exchange within the solar system, from the background component, due primarily to the Galactic Halo and unidentified point sources. In the second part of my project, I studied the contribution of unresolved point sources and intergalactic medium to the diffuse Soft X-ray Background.

  13. Prospects for detecting supersymmetric dark matter in the Galactic halo.

    PubMed

    Springel, V; White, S D M; Frenk, C S; Navarro, J F; Jenkins, A; Vogelsberger, M; Wang, J; Ludlow, A; Helmi, A

    2008-11-06

    Dark matter is the dominant form of matter in the Universe, but its nature is unknown. It is plausibly an elementary particle, perhaps the lightest supersymmetric partner of known particle species. In this case, annihilation of dark matter in the halo of the Milky Way should produce gamma-rays at a level that may soon be observable. Previous work has argued that the annihilation signal will be dominated by emission from very small clumps (perhaps smaller even than the Earth), which would be most easily detected where they cluster together in the dark matter haloes of dwarf satellite galaxies. Here we report that such small-scale structure will, in fact, have a negligible impact on dark matter detectability. Rather, the dominant and probably most easily detectable signal will be produced by diffuse dark matter in the main halo of the Milky Way. If the main halo is strongly detected, then small dark matter clumps should also be visible, but may well contain no stars, thereby confirming a key prediction of the cold dark matter model.

  14. Multiple Tracers of Structure, Substructure, and Dynamics of Galaxy Halos

    NASA Astrophysics Data System (ADS)

    Romanowsky, Aaron

    2015-08-01

    I will present a suite of results on the fundamental properties of galaxy halos, using a variety of observational tracers for a range of galaxy types, from giant ellipticals to spirals to dwarfs, along with comparisons to numerical simulations. The tracers include diffuse stellar light spectroscopy up to ~4 Re, resolved stellar photometry and spectroscopy, metal-poor and metal-rich globular cluster subpopulations, and planetary nebulae. The results include extended rotation and metallicity profiles, scaling relations for total angular momentum, shape inferences for the halos, orbital anisotropy estimates, kinematically "decoupled" halos, surprisingly homogeneous total mass profiles, and both detection and chemodynamical mapping of streams, shells, and other substructures. Connections are made to simulations of idealized galaxy mergers and of full cosmological formation histories, using the observed properties to make inferences about the assembly mechanisms of individual galaxies and of different galaxy types. Detailed models of stellar streams are used to infer their progenitor properties and to probe the gravitational potentials of the host galaxies. Novel observations are presented of compact stellar systems (globular clusters, ultra-compact dwarfs, compact ellipticals, and transition objects), with implications for the merger histories of their host halos.

  15. Halo Nucleus 11Be: A Spectroscopic Study via Neutron Transfer

    SciTech Connect

    Schmitt, Kyle; Jones, K. L.; Bey, A.; Ahn, S.H.; Bardayan, Daniel W; Blackmon, Jeffery C; Brown, S.; Chae, Kyung Yuk; Chipps, K.; Cizewski, J. A.; Kozub, R. L.; Liang, J Felix; Matei, Catalin; Matos, M.; Moazen, Brian H; Nesaraja, Caroline D; Nunes, F. M.; O'Malley, Patrick; Pain, Steven D; Peters, W. A.; Pittman, S. T.; Wilson, G.

    2012-01-01

    The best examples of halo nuclei, exotic systems with a diffuse nuclear cloud surrounding a tightly bound core, are found in the light, neutron-rich region, where the halo neutrons experience only weak binding and a weak, or no, potential barrier. Modern direct-reaction measurement techniques provide powerful probes of the structure of exotic nuclei. Despite more than four decades of these studies on the benchmark one-neutron halo nucleus 11Be, the spectroscopic factors for the two bound states remain poorly constrained. In the present work, the 10Be d;p reaction has been used in inverse kinematics at four beam energies to study the structure of 11Be. The spectroscopic factors extracted using the adiabatic model were found to be consistent across the four measurements and were largely insensitive to the optical potential used. The extracted spectroscopic factor for a neutron in an n j 2s1=2 state coupled to the ground state of 10Be is 0.71(5). For the first excited state at 0.32 MeV, a spectroscopic factor of 0.62(4) is found for the halo neutron in a 1p1=2 state.

  16. White Dwarfs in the Galaxy's Halo

    NASA Astrophysics Data System (ADS)

    Oppenheimer, B.; Murdin, P.

    2002-12-01

    The Galaxy's large spherical halo (see GALACTICMETAL-POOR HALO and HALO, GALACTIC) may harboras many as several hundred billion WHITE DWARFS, apopulation as large in number as the total number of stars in theGalaxy's disk (see DISK GALAXIES and GALACTIC THIN DISK). Although this assertion iscontroversial, several astronomical surveys provide strong support for it andthe implications affect fields ...

  17. Dermoscopy of halo nevus in own observation

    PubMed Central

    Szymszal, Jan

    2014-01-01

    Introduction Halo nevus (HN) is a rare dermatologic entity characterized by a typical whitish rim encircling the existing melanocytic nevus resembling a halo. The clinical picture is suggesting its diagnosis, but so far only several dermoscopic descriptions of halo nevus have existed in the PubMed database. Aim To present the clinical and dermoscopic characteristics of halo nevus observed in dermoscopy. Material and methods Fifteen patients were diagnosed clinically and dermoscopically with halo nevus during planned routine dermoscopic examinations of all melanocytic lesions in 2007–2013. All digital images stored in the computer database were analyzed retrospectively according to the procedure described in the study. The clinical and dermoscopic parameters such as the dermoscopic pattern, color of nevus, special features and description of the surrounding halo were analyzed statistically. Results We analyzed 22 halo nevi (9 in females, 13 in males) in 15 patients (7 females, 8 males) diagnosed during the dermoscopic examination. The mean age of patients during dermoscopic examinations was 18.2 years. Mean patients’ age at HN onset was 15.7 years. Halo nevi occurred the most often as a solitary lesion. The ratio of multiple halo nevi to solitary halo nevus was 5 : 10. Every third halo nevus was located on the posterior trunk upper. In 68.2% of HN cases, the surrounding rim (halo) was characterized by its homogenous, whitish color. Conclusions Dermoscopic patterns such as uniform globular and structureless constituted one-third each of them in all analyzed patterns. PMID:25097486

  18. Dermoscopy of halo nevus in own observation.

    PubMed

    Kamińska-Winciorek, Grażyna; Szymszal, Jan

    2014-06-01

    Halo nevus (HN) is a rare dermatologic entity characterized by a typical whitish rim encircling the existing melanocytic nevus resembling a halo. The clinical picture is suggesting its diagnosis, but so far only several dermoscopic descriptions of halo nevus have existed in the PubMed database. To present the clinical and dermoscopic characteristics of halo nevus observed in dermoscopy. Fifteen patients were diagnosed clinically and dermoscopically with halo nevus during planned routine dermoscopic examinations of all melanocytic lesions in 2007-2013. All digital images stored in the computer database were analyzed retrospectively according to the procedure described in the study. The clinical and dermoscopic parameters such as the dermoscopic pattern, color of nevus, special features and description of the surrounding halo were analyzed statistically. We analyzed 22 halo nevi (9 in females, 13 in males) in 15 patients (7 females, 8 males) diagnosed during the dermoscopic examination. The mean age of patients during dermoscopic examinations was 18.2 years. Mean patients' age at HN onset was 15.7 years. Halo nevi occurred the most often as a solitary lesion. The ratio of multiple halo nevi to solitary halo nevus was 5 : 10. Every third halo nevus was located on the posterior trunk upper. In 68.2% of HN cases, the surrounding rim (halo) was characterized by its homogenous, whitish color. Dermoscopic patterns such as uniform globular and structureless constituted one-third each of them in all analyzed patterns.

  19. Non-Gaussian halo assembly bias

    SciTech Connect

    Reid, Beth A.; Verde, Licia; Dolag, Klaus; Matarrese, Sabino; Moscardini, Lauro E-mail: liciaverde@icc.ub.edu E-mail: sabino.matarrese@pd.infn.it

    2010-07-01

    The strong dependence of the large-scale dark matter halo bias on the (local) non-Gaussianity parameter, f{sub NL}, offers a promising avenue towards constraining primordial non-Gaussianity with large-scale structure surveys. In this paper, we present the first detection of the dependence of the non-Gaussian halo bias on halo formation history using N-body simulations. We also present an analytic derivation of the expected signal based on the extended Press-Schechter formalism. In excellent agreement with our analytic prediction, we find that the halo formation history-dependent contribution to the non-Gaussian halo bias (which we call non-Gaussian halo assembly bias) can be factorized in a form approximately independent of redshift and halo mass. The correction to the non-Gaussian halo bias due to the halo formation history can be as large as 100%, with a suppression of the signal for recently formed halos and enhancement for old halos. This could in principle be a problem for realistic galaxy surveys if observational selection effects were to pick galaxies occupying only recently formed halos. Current semi-analytic galaxy formation models, for example, imply an enhancement in the expected signal of ∼ 23% and ∼ 48% for galaxies at z = 1 selected by stellar mass and star formation rate, respectively.

  20. The interstellar disk-halo connection in the spiral galaxy NGC 3079

    NASA Technical Reports Server (NTRS)

    Veilleux, Sylvain; Cecil, Gerald; Bland-Hawthorne, J.

    1995-01-01

    We discuss the morphology and excitation of ionized gas in the nearby Sc galaxy NGC 3079. The almost edge-on orientation is ideal for studying the vertical structure of the gaseous disk, and especially the diffuse ionized medium (DIM) found between the bright H II regions. We used the Hawaii Imaging Fabry-Perot Interferometer (HIFI) to map 150,000 H-alpha + (N II) lambda lambda 6548, 6583 emission-line profiles across the entire disk, with resolution 70 km/s at subarcsecond steps, down to a flux level of approximately 10(exp -17) ergs/s/sq cm (EM approximately equal to 4 cm(exp -6) pc). The DIM contributes approximately 30% of the total disk H-alpha emission within a radius of 10 kpc. The DIM has broader emission lines and larger (N II) H-alpha flux ratios than the adjacent H II regions. Within a radius of 5 kpc, we find that the X-shaped filaments reported in previous studies emerge from the inner (R approximately equal to 1.5 kpc) disk, and rise more than 4 kpc above the disk plane. The morphology, kinematics, and excitation of the filaments suggest that they form a biconic interface between the undisturbed disk gas, and gas entrained in the wide-angle outflow. The DIM beyond 5 kpc radius is more vertically extended than the thick ionized disk detected in our Galaxy and in a few nearby edge-on systems. After correcting for dust, the vertical profile of this DIM has an exponential scale height of about 1.1 kpc, similar to that of the H I disk. The (N II) lambda 6538/H-alpha flux ratio of the DIM increases monotonically with vertical height, reaching unity for absolute value of z greater than or approximately equal to 2.5 kpc. The flux required to keep the DIM ionized at R = 8 kpc is similar to that near the solar circle of our Galaxy. Highly dilute radiation from O stars in the galactic plane probably maintains the DIM. The total mass of the DIM is of order 10(exp 8) - 10(exp 9) solar mass, representing less than 1% of the total dynamical mass of NGC 3079

  1. The interstellar disk-halo connection in the spiral galaxy NGC 3079

    NASA Technical Reports Server (NTRS)

    Veilleux, Sylvain; Cecil, Gerald; Bland-Hawthorne, J.

    1995-01-01

    We discuss the morphology and excitation of ionized gas in the nearby Sc galaxy NGC 3079. The almost edge-on orientation is ideal for studying the vertical structure of the gaseous disk, and especially the diffuse ionized medium (DIM) found between the bright H II regions. We used the Hawaii Imaging Fabry-Perot Interferometer (HIFI) to map 150,000 H-alpha + (N II) lambda lambda 6548, 6583 emission-line profiles across the entire disk, with resolution 70 km/s at subarcsecond steps, down to a flux level of approximately 10(exp -17) ergs/s/sq cm (EM approximately equal to 4 cm(exp -6) pc). The DIM contributes approximately 30% of the total disk H-alpha emission within a radius of 10 kpc. The DIM has broader emission lines and larger (N II) H-alpha flux ratios than the adjacent H II regions. Within a radius of 5 kpc, we find that the X-shaped filaments reported in previous studies emerge from the inner (R approximately equal to 1.5 kpc) disk, and rise more than 4 kpc above the disk plane. The morphology, kinematics, and excitation of the filaments suggest that they form a biconic interface between the undisturbed disk gas, and gas entrained in the wide-angle outflow. The DIM beyond 5 kpc radius is more vertically extended than the thick ionized disk detected in our Galaxy and in a few nearby edge-on systems. After correcting for dust, the vertical profile of this DIM has an exponential scale height of about 1.1 kpc, similar to that of the H I disk. The (N II) lambda 6538/H-alpha flux ratio of the DIM increases monotonically with vertical height, reaching unity for absolute value of z greater than or approximately equal to 2.5 kpc. The flux required to keep the DIM ionized at R = 8 kpc is similar to that near the solar circle of our Galaxy. Highly dilute radiation from O stars in the galactic plane probably maintains the DIM. The total mass of the DIM is of order 10(exp 8) - 10(exp 9) solar mass, representing less than 1% of the total dynamical mass of NGC 3079

  2. STELLAR POPULATIONS IN THE OUTER HALO OF THE MASSIVE ELLIPTICAL M49

    SciTech Connect

    Mihos, J. Christopher; Harding, Paul; Rudick, Craig S.; Feldmeier, John J. E-mail: paul.harding@case.edu E-mail: jjfeldmeier@ysu.edu

    2013-02-20

    We use deep surface photometry of the giant elliptical M49 (NGC 4472), obtained as part of our survey for diffuse light in the Virgo Cluster, to study the stellar populations in its outer halo. Our data trace M49's stellar halo out to {approx}100 kpc (7r{sub e}), where we find that the shallow color gradient seen in the inner regions becomes dramatically steeper. The outer regions of the galaxy are quite blue (B - V {approx} 0.7); if this is purely a metallicity effect, it argues for extremely metal-poor stellar populations with [Fe/H] < -1. We also find that the extended accretion shells around M49 are distinctly redder than the galaxy's surrounding halo, suggesting that we are likely witnessing the buildup of both the stellar mass and metallicity in M49's outer halo due to late time accretion. While such growth of galaxy halos is predicted by models of hierarchical accretion, this growth is thought to be driven by more massive accretion events which have correspondingly higher mean metallicity than inferred for M49's halo. Thus the extremely metal-poor nature of M49's extended halo provides some tension against current models for elliptical galaxy formation.

  3. IONIZATION CHAMBER

    DOEpatents

    Redman, W.C.; Shonka, F.R.

    1958-02-18

    This patent describes a novel ionization chamber which is well suited to measuring the radioactivity of the various portions of a wire as the wire is moved at a uniform speed, in order to produce the neutron flux traverse pattern of a reactor in which the wire was previously exposed to neutron radiation. The ionization chamber of the present invention is characterized by the construction wherein the wire is passed through a tubular, straight electrode and radiation shielding material is disposed along the wire except at an intermediate, narrow area where the second electrode of the chamber is located.

  4. AXIAL RATIO OF EDGE-ON SPIRAL GALAXIES AS A TEST FOR BRIGHT RADIO HALOS

    SciTech Connect

    Singal, J.; Jones, E.; Dunlap, H.; Kogut, A.

    2015-01-20

    We use surface brightness contour maps of nearby edge-on spiral galaxies to determine whether extended bright radio halos are common. In particular, we test a recent model of the spatial structure of the diffuse radio continuum by Subrahmanyan and Cowsik which posits that a substantial fraction of the observed high-latitude surface brightness originates from an extended Galactic halo of uniform emissivity. Measurements of the axial ratio of emission contours within a sample of normal spiral galaxies at 1500 MHz and below show no evidence for such a bright, extended radio halo. Either the Galaxy is atypical compared to nearby quiescent spirals or the bulk of the observed high-latitude emission does not originate from this type of extended halo. (letters)

  5. Halo Coronal Mass Ejections and Geomagnetic Storms

    NASA Technical Reports Server (NTRS)

    Gopalswamy, Nat

    2009-01-01

    In this letter, I show that the discrepancies in the geoeffectiveness of halo coronal mass ejections (CMEs) reported in the literature arise due to the varied definitions of halo CMEs used by different authors. In particular, I show that the low geoeffectiveness rate is a direct consequence of including partial halo CMEs. The geoeffectiveness of partial halo CMEs is lower because they are of low speed and likely to make a glancing impact on Earth. Key words: Coronal mass ejections, geomagnetic storms, geoeffectiveness, halo CMEs.

  6. Halo Coronal Mass Ejections and Geomagnetic Storms

    NASA Technical Reports Server (NTRS)

    Gopalswamy, Nat

    2009-01-01

    In this letter, I show that the discrepancies in the geoeffectiveness of halo coronal mass ejections (CMEs) reported in the literature arise due to the varied definitions of halo CMEs used by different authors. In particular, I show that the low geoeffectiveness rate is a direct consequence of including partial halo CMEs. The geoeffectiveness of partial halo CMEs is lower because they are of low speed and likely to make a glancing impact on Earth. Key words: Coronal mass ejections, geomagnetic storms, geoeffectiveness, halo CMEs.

  7. A finite-volume fast diffusion-limited aggregation model for predicting the coagulation rate of mixed low-ionized system

    NASA Astrophysics Data System (ADS)

    Feng, Yu; Wang, Guang; Ruan, Leidan; Du, Ai

    2017-03-01

    Accompanied with the changing of coagulation time, the micro-structure of aerogel can be controlled by adding Polyacrylic acid (PAA) into sol system. We simulate the process of particles aggregation contains attracting molecular chains based on diffusion-limited cluster aggregation (DLCA). Compared with the normal coagulation system, the coagulation rate of the system that contains attracting chains are sped up first and then slowed down. The results of the stimulation point out that the interaction between particles and chains not only accelerates the motion of particles, but also separates the region and constrains the clusters' motion. These two effects are coexisting but the attracting interaction play a dominant role in the early state while the volume of chains has a dramatic influence on cluster's motion in late states.

  8. Hot halo gas in numerical simulations of galaxy mergers

    NASA Astrophysics Data System (ADS)

    Sinha, Manodeep

    Galaxy merger simulations have explored the behavior of gas within a galactic disk, yet the dynamics of hot gas within the galaxy halo has been neglected. We report on the results of high-resolution hydrodynamic simulations of colliding galaxies with hot halo gas. We explore a range of mass ratios, gas fractions and orbital configurations to constrain the shocks and the dynamics of the gas within the progenitor halos. We find that: (i) A strong shock is produced in the galaxy halos before the first passage, increasing the temperature of the gas by almost an order of magnitude to ˜ 10 6.3 K. (ii) The X-ray luminosity of the shock is strongly dependent on the gas fraction. It is ≳ 1039 erg/s for gas fractions larger than 10%. (iii) We find an analytic fit to the maximum X-ray luminosity of the shock as a function of merger parameters. This fit can be used in semi-analytic recipes for galaxy formation to estimate the total X-ray emission from shocks in merging galaxies. (iv) The hot diffuse gas in the simulation also produces X-ray luminosities as large as 1042 erg/s. This contributes to the total X-ray background in the Universe. (v) ˜ 10--20% of the initial gas mass is unbound from the galaxies for equal-mass mergers, while 3--5% of the gas mass is released for the 3:1 and 10:1 mergers. This unbound gas ends up far from the galaxy and can be a feasible mechanism for metal enrichment of the IGM. We use an analytical halo merger tree to estimate the fraction of gas mass lost over the history of the Universe.

  9. Halo Density Reduction by Baryonic Settling?

    NASA Astrophysics Data System (ADS)

    Jardel, J. R.; Sellwood, J. A.

    2009-02-01

    We test the proposal by El-Zant et al. that the dark matter density of halos could be reduced through dynamical friction acting on heavy baryonic clumps in the early stages of galaxy formation. Using N-body simulations, we confirm that the inner halo density cusp is flattened to 0.2 of the halo break radius by the settling of a single clump of mass gsim0.5% of the halo mass. We also find that an ensemble of 50 clumps, each having masses gsim0.2%, can flatten the cusp to almost the halo break radius on a timescale of ~9 Gyr, for a Navarro-Frenk-White profile halo of concentration 15. We summarize some of the difficulties that need to be overcome if this mechanism is to resolve the apparent conflict between the observed inner densities of galaxy halos and the predictions of ΛCDM.

  10. The Extended GMRT Radio Halo Survey. II. Further results and analysis of the full sample

    NASA Astrophysics Data System (ADS)

    Kale, R.; Venturi, T.; Giacintucci, S.; Dallacasa, D.; Cassano, R.; Brunetti, G.; Cuciti, V.; Macario, G.; Athreya, R.

    2015-07-01

    The intra-cluster medium contains cosmic rays and magnetic fields that are manifested through the large scale synchrotron sources, termed radio haloes, relics, and mini-haloes. The Extended Giant Metrewave Radio Telescope (GMRT) Radio Halo Survey (EGRHS) is an extension of the GMRT Radio Halo Survey (GRHS) designed to search for radio haloes using GMRT 610/235 MHz observations. The GRHS and EGRHS consists of 64 clusters in the redshift range 0.2-0.4 that have an X-ray luminosity larger than 5 × 1044 erg s-1 in the 0.1-2.4 keV band and declination, δ > -31° in the REFLEX and eBCS X-ray cluster catalogues. In this second paper in the series, GMRT 610/235 MHz data on the last batch of 11 galaxy clusters and the statistical analysis of the full sample are presented. A new mini-halo in RX J2129.6+0005 and candidate diffuse sources in Z5247, A2552, and Z1953 have been discovered. A unique feature of this survey are the upper limits on the detections of 1 Mpc sized radio haloes; 4 new are presented here, making a total of 31 in the survey. Of the sample, 58 clusters with adequately sensitive radio information were used to obtain the most accurate occurrence fractions so far. The occurrence fractions of radio haloes, mini-haloes and relics in our sample are ~22%, ~16% and ~5%, respectively. The P1.4 GHz-LX diagrams for the radio haloes and mini-haloes are presented. The morphological estimators - centroid shift (w), concentration parameter (c), and power ratios (P3/P0) derived from the Chandra X-ray images - are used as proxies for the dynamical states of the GRHS and EGRHS clusters. The clusters with radio haloes and mini-haloes occupy distinct quadrants in the c-w, c-P3/P0 and w-P3/P0 planes, corresponding to the more and less morphological disturbance, respectively. The non-detections span both the quadrants. Appendices are available in electronic form at http://www.aanda.org

  11. Baryonic Distributions in Galaxy Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Richards, Emily E.

    2016-01-01

    Understanding the role and significance of dark matter in the evolution of baryonic components (i.e., conversion of the gaseous disk into stars) is a critical aspect for realistic models of galaxy evolution. In an effort to address fundamental questions regarding the growth and distribution of stellar disks in dark matter halos in a statistical manner, we have undertaken a project correlating structural properties and star formation activity with the dark matter properties of the host galaxy. The project uses a statistical sample of 45 nearby galaxies which are optimally suited for rotation curve decomposition analysis. The dataset includes deep Spitzer 3.6μm images to trace the stellar distribution, neutral and ionized gas rotation curves to trace the total mass distribution, and optical images to examine the dominant stellar populations. Using a sub-set of galaxies from the full sample, we find that the distribution of the baryonic mass relative to the total mass is roughly self-similar in more massive galaxies when normalized by the average stellar disk scale length measured at 3.6μm. We additionally observe an emerging trend between total baryonic mass and the radius at which the total mass distribution transitions from baryon-dominated to dark matter-dominated. However, we find no significant correlation between the distribution of dark matter and structural properties of the stellar disk, such as changes in color or star formation activity.

  12. Evolution of Dwarf Spheroidal Satellites in the Common Surface-density Dark Halos

    NASA Astrophysics Data System (ADS)

    Okayasu, Yusuke; Chiba, Masashi

    2016-08-01

    We investigate the growth histories of dark matter halos associated with dwarf satellites in Local Group galaxies and the resultant evolution of the baryonic component. Our model is based on the recently proposed property that the mean surface density of a dark halo inside a radius at maximum circular velocity {V}{{\\max }} is universal over a large range of {V}{{\\max }}. Given that a surface density of 20 M ⊙ pc-2 well explains dwarf satellites in the Milky Way and Andromeda, we find that the evolution of the dark halo in this common surface-density scale is characterized by the rapid increase of the halo mass assembled by the redshift {z}{{TT}} of the tidal truncation by its host halo, at early epochs of {z}{{TT}}≳ 6 or {V}{{\\max }}≲ 22 km s-1. This mass growth of the halo is slow at lower {z}{{TT}} or larger {V}{{\\max }}. Taking into account the baryon content in this dark halo evolution, under the influence of the ionizing background radiation, we find that the dwarf satellites are divided into roughly two families: those with {V}{{\\max }}≲ 22 km s-1 having high star formation efficiency and those with larger {V}{{\\max }} having less efficient star formation. This semianalytical model is in agreement with the high-resolution numerical simulation for galaxy formation and with the observed star formation histories for Fornax and Leo II. This suggests that the evolution of a dark halo may play a key role in understanding star formation histories in dwarf satellites.

  13. Reionization histories of Milky Way mass halos

    SciTech Connect

    Li, Tony Y.; Wechsler, Risa H.; Abel, Tom; Alvarez, Marcelo A. E-mail: rwechsler@stanford.edu E-mail: malvarez@cita.utoronto.ca

    2014-04-20

    We investigate the connection between the reionization era and the present-day universe by examining the mass reionization histories of z = 0 dark matter halos. In a 600{sup 3} Mpc{sup 3} volume, we combine a dark matter N-body simulation with a three-dimensional seminumerical reionization model. This tags each particle with a reionization redshift, so that individual present-day halos can be connected to their reionization histories and environments. We find that the vast majority of present-day halos with masses larger than ∼ few × 10{sup 11} M {sub ☉} reionize earlier than the rest of the universe. We also find significant halo-to-halo diversity in mass reionization histories, and find that in realistic inhomogeneous models, the material within a given halo is not expected to reionize at the same time. In particular, the scatter in reionization times within individual halos is typically larger than the scatter among halos. From our fiducial reionization model, we find that the typical 68% scatter in reionization times within halos is ∼115 Myr for 10{sup 12±0.25} M {sub ☉} halos, decreasing slightly to ∼95 Myr for 10{sup 15±0.25} M {sub ☉} halos. We find a mild correlation between reionization history and environment: halos with shorter reionization histories are typically in more clustered environments, with the strongest trend on a scale of ∼20 Mpc. Material in Milky Way mass halos with short reionization histories is preferentially reionized in relatively large H II regions, implying reionization mostly by sources external to the progenitors of the present-day halo. We investigate the impact on our results of varying the reionization model parameters, which span a range of reionization scenarios with varying timing and morphology.

  14. Central 300 PC of the Galaxy Probed by the Infrared Spectra of H_3^+ and Co: I. Predominance of Warm and Diffuse Gas and High H_2 Ionization Rate

    NASA Astrophysics Data System (ADS)

    Oka, Takeshi; Geballe, Thomas R.; Goto, Miwa; Usuda, Tomonori; Indriolo, Nick

    2016-06-01

    A low-resolution 2.0-2.5 μm survey of ˜500 very red point-like objects in the Central Molecular Zone (CMZ) of our Galaxy, initiated in 2008, has revealed many new bright objects with featureless spectra that are suitable for high resolution absorption spectroscopy of H_3^+ and CO. We now have altogether 48 objects mostly close to the Galactic plane located from 142 pc to the west of Sgr A* to 120 pc east allowing us to probe dense and diffuse gas by H_3^+ and dense gas by CO. Our observations demonstrate that the warm (˜250 K) and diffuse (≤100 cm-3) gas with a large column length (≥30 pc) initially observed toward the brightest star in the CMZ, GCS3-2 of the Quintuplet Cluster, exists throughout the CMZ with the surface filling factor of ˜ 100% dominating the region. The column densities of CO in the CMZ are found to be much less than those in the three foreground spiral arms except in the directions of Sgr B and Sgr E complexes and indicate that the volume filling factor of dense clouds of 10% previously estimated is a gross overestimate for the front half of the CMZ. Nevertheless the predominance of the newly found diffuse molecular gas makes the term "Central Molecular Zone" even more appropriate. The ultra-hot X-rays emitting plasma which some thought to dominate the region must be non existent except near the stars and SNRs. Recently the H_2 fraction f(H_2) in diffuse gas of the CMZ has been reported to be ˜0.6. If we use this value, the cosmic ray H_2 ionization rate ζ of a few times 10-15 s-1 reported earlier^b on the assumption of f(H_2)=1 needs to be increased by a factor of ˜3 since the value is approximately inversely proportional to f(H_2)^2. Geballe, T. R., Oka, T., Lambridges, E., Yeh, S. C. C., Schlegelmilch, B., Goto, M., Westrick, C. W., WI07 at the 70th ISMS, Urbana, IL, USA,2015 Oka, T., Geballe, T. R., Goto, M., Usuda, T., McCall, B. J. 2005, ApJ, 632, 882 Le Petit, F., Ruaud, M., Bron, E., Godard, B., Roueff, E., Languignon, D., Le

  15. STRUCTURAL PROPERTIES OF NON-SPHERICAL DARK HALOS IN MILKY WAY AND ANDROMEDA DWARF SPHEROIDAL GALAXIES

    SciTech Connect

    Hayashi, Kohei; Chiba, Masashi E-mail: chiba@astr.tohoku.ac.jp

    2015-09-01

    We investigate the non-spherical density structure of dark halos of the dwarf spheroidal (dSph) galaxies in the Milky Way and Andromeda galaxies based on revised axisymmetric mass models from our previous work. The models we adopt here fully take into account velocity anisotropy of tracer stars confined within a flattened dark halo. Applying our models to the available kinematic data of the 12 bright dSphs, we find that these galaxies associate with, in general, elongated dark halos, even considering the effect of this velocity anisotropy of stars. We also find that the best-fit parameters, especially for the shapes of dark halos and velocity anisotropy, are susceptible to both the availability of velocity data in the outer regions and the effect of the lack of sample stars in each spatial bin. Thus, to obtain more realistic limits on dark halo structures, we require photometric and kinematic data over much larger areas in the dSphs than previously explored. The results obtained from the currently available data suggest that the shapes of dark halos in the dSphs are more elongated than those of ΛCDM subhalos. This mismatch needs to be solved by theory including baryon components and the associated feedback to dark halos as well as by further observational limits in larger areas of dSphs. It is also found that more diffuse dark halos may have undergone consecutive star formation history, thereby implying that dark-halo structure plays an important role in star formation activity.

  16. Predator-Prey model for haloes in Saturn's A ring

    NASA Astrophysics Data System (ADS)

    Esposito, Larry W.; Bradley, E. Todd; Colwell, Joshua E.; Madhusudhanan, Prasanna; Sremcevic, Miodrag

    2013-04-01

    UVIS SOI reflectance spectra show bright 'haloes' around the locations of some of the strongest resonances in Saturn's A ring (Esposito etal 2005). UV spectra constrain the size and composition of the icy ring particles (Bradley etal 2010, 2012). The correspondence of IR, UV spectroscopy, HSP wavelet analysis indicate that we detect the same phenomenon. We investigate the Janus 2:1. 4:3, 5:3, 6:5 and Mimas 5:3 inner Lindblad resonances as well as at the Mimas 5:3 vertical resonance (bending wave location). Models of ring particle regolith evolution (Elliott and Esposito 2010) indicate the deeper regolith is made of older and purer ice. The strong resonances can cause streamline crowding (Lewis and Stewart 2005) which damps the interparticle velocity, allowing temporary clumps to grow, which in turn increase the velocity, eroding the clumps and releasing smaller particles and regolith (see the predator-prey model of Esposito etal 2012). This cyclic behavior, driven by the resonant perturbation from the moon, can yield collision velocities at particular azimuths greater than 1m/sec, sufficient to erode the aggregates (Blum 2006), exposing older, purer materials: In the perturbed region, collisions erode the regolith, removing smaller particles. The released regolith material settles in the less perturbed neighboring regions. Diffusion spreads these ring particles with smaller regolith into a 'halo'. Thus, the radial location of the strongest resonances can be where we find both large aggregates and disrupted fragments, in a balance maintained by the periodic moon forcing. If this stirring exposes older, and purer ice, the velocity threshold for eroding the aggregates can explain why only the strongest Lindblad resonances show haloes. Diffusion can explain the morphology of these haloes, although they are not well-resolved spatially by UVIS.

  17. Determination of benzene, toluene, ethylbenzene and xylenes in indoor air at environmental levels using diffusive samplers in combination with headspace solid-phase microextraction and high-resolution gas chromatography-flame ionization detection.

    PubMed

    Elke, K; Jermann, E; Begerow, J; Dunemann, L

    1998-11-27

    An improved analytical method for passive air sampling is presented based on a combination of commercially available diffusive samplers with headspace solid-phase microextraction and high-resolution gas chromatography with flame ionization detection (HRGC-FID). This procedure is targeted for short-term BTEX (benzene, toluene, ethylbenzene and o-, m- and p-xylenes) determinations at environmental concentrations and can be applied for sampling intervals between 30 min and 24 h. The analytes are adsorbed onto the charcoal pad of a passive sampler and then extracted with carbon disulphide-methanol. After removal of the carbon disulphide by xanthation, the BTEXs are enriched on a Carboxen SPME fiber, thermally desorbed and analysed by HRGC-FID. Detection limits for a sampling interval of 2 h are between 0.4 and 2 micrograms/m3, within-series precision ranges between 6.6 and 12.8%, day-to-day precision is between 11.1 and 15.2%. The results obtained with this procedure are validated by comparison with active sampling. Detection limits and a further reduction of the sampling time are limited by blanks of the chemicals and the diffusive samplers. Procedures to eliminate these blanks are described in detail. Applications such as the determination of BTEXs in indoor air inside buildings, inside a train and a car are presented, indicating the usefulness of the described procedure for short-term measurements of environmental BTEX concentrations. An advantage of passive samplers is the storage stability for at least six months, which is essential for its use in large epidemiological studies.

  18. The Anemic Stellar Halo of M101

    NASA Astrophysics Data System (ADS)

    Holwerda, Benne

    2014-10-01

    Models of galaxy formation in a cosmological context predict that massive disk galaxies should have richly-structured extended stellar halos, containing ~10% of a galaxy's stars, originating in large part from the tidal disruption of dwarf galaxies. Observations of a number of nearby disk galaxies have generally agreed with these expectations. Recent new observations in integrated light with a novel array of low scattered-light telephoto lenses have failed to convincingly detect a stellar halo in the nearby massive face-on disk galaxy M101 (van Dokkum et al. 2014). They argue that any halo has to have <0.3% of the mass of the galaxy. This halo would be the least massive of any massive disk galaxy in the local Universe (by factors of several) -- such a halo is not predicted or naturally interpreted by the models, and would present a critical challenge to the picture of ubiquitous stellar halos formed from the debris of disrupting dwarf galaxies.We propose to resolve the stellar populations of this uniquely anemic stellar halo for 6 orbits with HST (ACS and WFC3), allowing us to reach surface brightness limits sufficient to clearly detect and characterize M101's stellar halo if it carries more than 0.1% of M101's mass. With resolved stellar populations, we can use the gradient of stellar populations as a function of radius to separate stellar halo from disk, which is impossible using integrated light observations. The resolved stellar populations will reveal the halo mass to much greater accuracy, measure the halo radial profile, constrain any halo lopsidedness, estimate the halo's stellar metallicity, and permit an analysis of outer disk stellar populations.

  19. Gas phase abundances and conditions along the sight line to the low-halo, inner galaxy star HD 167756

    NASA Technical Reports Server (NTRS)

    Cardelli, Jason A.; Sembach, Kenneth R.; Savage, Blair D.

    1995-01-01

    We present high-resolution (3.5 km/s) Goddard High Resolution Spectrograph (GHRS) measurements of the Mg II, Si II, Cr II, Fe II, and Zn II lines toward HD 167756, a low-latitude halo star at a distance of 4 kpc in the direction l = 351.5 deg, b = -12.3 and at a Galactic altitude of z = -0.85 kpc. Supplemental Na I, Ca II, and H I data are also presented for comparison with the UV lines. Our analysis centers on converting the observed absoprtion-line data into measures of the apparent column density per unit velocity. N(sub a)(v), over the velocity range -25 less than or = v(sub lsr) less than 30 km/s for each species observed. We use these N(sub a)(v) profiles to construct logarithmic abundance ratios of Mg II, Si II, Cr II, Fe II, and Ca II relative to Zn II, normalized to solar abundances, as a function of velocity. Compared to Zn, these species show an underabundance relative to their solar values, with the largest underabundances occurring in the v(sub lsr) approximately equals 5 km/s component(s), for which we find logarithmic abundances A(sub Si/Zn) greater than -0.38, A(Mg/Zn) = -0.82, A(sub Cr/Zn) = -1.18, and A(sub Fe/Zn) greater than 1.40 dex. We show that ionization effects, abundance gradients, or intrinsic abundance variability cannot be significant sources for the underabundances observed. The most likely explanation is gas phase depletion of elements onto dust grains. Comparisons with the gas phase abundances along other diffuse, warm gas sight lines, like the halo sight line to HD 93521, support this interpretation as do the derived physical properties of the sight line.

  20. Gas phase abundances and conditions along the sight line to the low-halo, inner galaxy star HD 167756

    NASA Technical Reports Server (NTRS)

    Cardelli, Jason A.; Sembach, Kenneth R.; Savage, Blair D.

    1995-01-01

    We present high-resolution (3.5 km/s) Goddard High Resolution Spectrograph (GHRS) measurements of the Mg II, Si II, Cr II, Fe II, and Zn II lines toward HD 167756, a low-latitude halo star at a distance of 4 kpc in the direction l = 351.5 deg, b = -12.3 and at a Galactic altitude of z = -0.85 kpc. Supplemental Na I, Ca II, and H I data are also presented for comparison with the UV lines. Our analysis centers on converting the observed absoprtion-line data into measures of the apparent column density per unit velocity. N(sub a)(v), over the velocity range -25 less than or = v(sub lsr) less than 30 km/s for each species observed. We use these N(sub a)(v) profiles to construct logarithmic abundance ratios of Mg II, Si II, Cr II, Fe II, and Ca II relative to Zn II, normalized to solar abundances, as a function of velocity. Compared to Zn, these species show an underabundance relative to their solar values, with the largest underabundances occurring in the v(sub lsr) approximately equals 5 km/s component(s), for which we find logarithmic abundances A(sub Si/Zn) greater than -0.38, A(Mg/Zn) = -0.82, A(sub Cr/Zn) = -1.18, and A(sub Fe/Zn) greater than 1.40 dex. We show that ionization effects, abundance gradients, or intrinsic abundance variability cannot be significant sources for the underabundances observed. The most likely explanation is gas phase depletion of elements onto dust grains. Comparisons with the gas phase abundances along other diffuse, warm gas sight lines, like the halo sight line to HD 93521, support this interpretation as do the derived physical properties of the sight line.

  1. Galaxy and Mass Assembly (GAMA): halo formation times and halo assembly bias on the cosmic web

    NASA Astrophysics Data System (ADS)

    Tojeiro, Rita; Eardley, Elizabeth; Peacock, John A.; Norberg, Peder; Alpaslan, Mehmet; Driver, Simon P.; Henriques, Bruno; Hopkins, Andrew M.; Kafle, Prajwal R.; Robotham, Aaron S. G.; Thomas, Peter; Tonini, Chiara; Wild, Vivienne

    2017-09-01

    We present evidence for halo assembly bias as a function of geometric environment (GE). By classifying Galaxy and Mass Assembly (GAMA) galaxy groups as residing in voids, sheets, filaments or knots using a tidal tensor method, we find that low-mass haloes that reside in knots are older than haloes of the same mass that reside in voids. This result provides direct support to theories that link strong halo tidal interactions with halo assembly times. The trend with GE is reversed at large halo mass, with haloes in knots being younger than haloes of the same mass in voids. We find a clear signal of halo downsizing - more massive haloes host galaxies that assembled their stars earlier. This overall trend holds independently of GE. We support our analysis with an in-depth exploration of the L-Galaxies semi-analytic model, used here to correlate several galaxy properties with three different definitions of halo formation time. We find a complex relationship between halo formation time and galaxy properties, with significant scatter. We confirm that stellar mass to halo mass ratio, specific star formation rate (SFR) and mass-weighed age are reasonable proxies of halo formation time, especially at low halo masses. Instantaneous SFR is a poor indicator at all halo masses. Using the same semi-analytic model, we create mock spectral observations using complex star formation and chemical enrichment histories, which approximately mimic GAMA's typical signal-to-noise ratio and wavelength range. We use these mocks to assert how well potential proxies of halo formation time may be recovered from GAMA-like spectroscopic data.

  2. Analysis of aldehydes in beer by gas-diffusion microextraction: characterization by high-performance liquid chromatography-diode-array detection-atmospheric pressure chemical ionization-mass spectrometry.

    PubMed

    Gonçalves, Luís Moreira; Magalhães, Paulo Jorge; Valente, Inês Maria; Pacheco, João Grosso; Dostálek, Pavel; Sýkora, David; Rodrigues, José António; Barros, Aquiles Araújo

    2010-06-11

    In this work, a recently developed extraction technique for sample preparation aiming the analysis of volatile and semi-volatile compounds named gas-diffusion microextraction (GDME) is applied in the chromatographic analysis of aldehydes in beer. Aldehydes-namely acetaldehyde (AA), methylpropanal (MA) and furfural (FA)-were simultaneously extracted and derivatized with 2,4-dinitrophenylhydrazine (DNPH), then the derivatives were separated and analyzed by high-performance liquid chromatography with spectrophotometric detection (HPLC-UV). The identity of the eluted compounds was confirmed by high-performance liquid chromatography-atmospheric pressure chemical ionization-mass-spectrometry detection in the negative ion mode (HPLC-APCI-MS). The developed methodology showed good repeatability (ca. 5%) and linearity as well as good limits of detection (AA-12.3, FA-1.5 and MA 5.4microgL(-1)) and quantification (AA-41, FA-4.9 and MA 18microgL(-1)); it also appears to be competitive in terms of speed and cost of analysis.

  3. The SAURON project - XVI. On the sources of ionization for the gas in elliptical and lenticular galaxies

    NASA Astrophysics Data System (ADS)

    Sarzi, Marc; Shields, Joseph C.; Schawinski, Kevin; Jeong, Hyunjin; Shapiro, Kristen; Bacon, Roland; Bureau, Martin; Cappellari, Michele; Davies, Roger L.; de Zeeuw, P. Tim; Emsellem, Eric; Falcón-Barroso, Jesús; Krajnović, Davor; Kuntschner, Harald; McDermid, Richard M.; Peletier, Reynier F.; van den Bosch, Remco C. E.; van de Ven, Glen; Yi, Sukyoung K.

    2010-03-01

    Following our study on the incidence, morphology and kinematics of the ionized gas in early-type galaxies, we now address the question of what is powering the observed nebular emission. To constrain the likely sources of gas excitation, we resort to a variety of ancillary data we draw from complementary information on the gas kinematics, stellar populations and galactic potential from the SAURON data, and use the SAURON-specific diagnostic diagram juxtaposing the [OIII] λ5007/Hβ and [NI] λλ5197, 5200/Hβ line ratios. We find a tight correlation between the stellar surface brightness and the flux of the Hβ recombination line across our sample, which points to a diffuse and old stellar source as the main contributor of ionizing photons in early-type galaxies, with post-asymptotic giant branch (pAGB) stars being still the best candidate based on ionizing balance arguments. The role of AGN photoionization is confined to the central 2-3arcsec of an handful of objects with radio or X-ray cores. OB-stars are the dominant source of photoionization in 10 per cent of the SAURON sample, whereas for another 10 per cent the intense and highly ionized emission is powered by the pAGB population associated to a recently formed stellar subcomponent. Fast shocks are not an important source of ionization for the diffuse nebular emission of early-type galaxies since the required shock velocities can hardly be attained in the potential of our sample galaxies. Finally, in the most massive and slowly or non-rotating galaxies in our sample, which can retain a massive X-ray halo, the finding of a spatial correlation between the hot and warm phases of the interstellar medium (ISM) suggests that the interaction with the hot ISM provides an additional source of ionization besides old ultraviolet-bright stars. This is also supported by a distinct pattern towards lower values of the [OIII]/Hβ ratio. These results lead us to investigate the relative role of stellar and AGN photoionization

  4. The galactic cosmic ray ionization rate

    PubMed Central

    Dalgarno, A.

    2006-01-01

    The chemistry that occurs in the interstellar medium in response to cosmic ray ionization is summarized, and a review of the ionization rates that have been derived from measurements of molecular abundances is presented. The successful detection of large abundances of H3+ in diffuse clouds and the recognition that dissociative recombination of H3+ is fast has led to an upward revision of the derived ionization rates. In dense clouds the molecular abundances are sensitive to the depletion of carbon monoxide, atomic oxygen, nitrogen, water, and metals and the presence of large molecules and grains. Measurements of the relative abundances of deuterated species provide information about the ion removal mechanisms, but uncertainties remain. The models, both of dense and diffuse clouds, that are used to interpret the observations may be seriously inadequate. Nevertheless, it appears that the ionization rates differ in dense and diffuse clouds and in the intercloud medium. PMID:16894166

  5. The galactic cosmic ray ionization rate.

    PubMed

    Dalgarno, A

    2006-08-15

    The chemistry that occurs in the interstellar medium in response to cosmic ray ionization is summarized, and a review of the ionization rates that have been derived from measurements of molecular abundances is presented. The successful detection of large abundances of H(3)(+) in diffuse clouds and the recognition that dissociative recombination of H(3)(+) is fast has led to an upward revision of the derived ionization rates. In dense clouds the molecular abundances are sensitive to the depletion of carbon monoxide, atomic oxygen, nitrogen, water, and metals and the presence of large molecules and grains. Measurements of the relative abundances of deuterated species provide information about the ion removal mechanisms, but uncertainties remain. The models, both of dense and diffuse clouds, that are used to interpret the observations may be seriously inadequate. Nevertheless, it appears that the ionization rates differ in dense and diffuse clouds and in the intercloud medium.

  6. Ionization-based detectors for gas chromatography.

    PubMed

    Poole, Colin F

    2015-11-20

    The gas phase ionization detectors are the most widely used detectors for gas chromatography. The column and makeup gases commonly used in gas chromatography are near perfect insulators. This facilitates the detection of a minute number of charge carriers facilitating the use of ionization mechanisms of low efficiency while providing high sensitivity. The main ionization mechanism discussed in this report are combustion in a hydrogen diffusion flame (flame ionization detector), surface ionization in a plasma (thermionic ionization detector), photon ionization (photoionization detector and pulsed discharge helium ionization detector), attachment of thermal electrons (electron-capture detector), and ionization by collision with metastable helium species (helium ionization detector). The design, response characteristics, response mechanism, and suitability for fast gas chromatography are the main features summarized in this report. Mass spectrometric detection and atomic emission detection, which could be considered as ionization detectors of a more sophisticated and complex design, are not discussed in this report. Copyright © 2015 Elsevier B.V. All rights reserved.

  7. Jupiter's Main Ring/Ring Halo

    NASA Technical Reports Server (NTRS)

    1997-01-01

    A mosaic of four images taken through the clear filter (610 nanometers) of the solid state imaging (CCD) system aboard NASA's Galileo spacecraft on November 8, 1996, at a resolution of approximately 46 kilometers (28.5 miles) per picture element (pixel) along Jupiter's rings. Because the spacecraft was only about 0.5 degrees above the ring plane, the image is highly foreshortened in the vertical direction. The images were obtained when Galileo was in Jupiter's shadow, peering back toward the Sun; the ring was approximately 2.3 million kilometers (1.4 million miles) away. The arc on the far right of the image is produced when sunlight is scattered by small particles comprising Jupiter's upper atmospheric haze. The ring also efficiently scatters light, indicating that much of its brightness is due to particles that are microns or less in diameter. Such small particles are believed to have human-scale lifetimes, i.e., very brief compared to the solar system's age.

    Jupiter's ring system is composed of three parts - - a flat main ring, a lenticular halo interior to the main ring, and the gossamer ring, outside the main ring. The near and far arms of Jupiter's main ring extend horizontally across the mosaic, joining together at the ring's ansa, on the figure's far left side. The near arm of the ring appears to be abruptly truncated close to the planet, at the point where it passes into Jupiter's shadow. Some radial structure is barely visible across the ring's ansa (top image). A faint mist of particles can be seen above and below the main rings. This vertically extended 'halo' is unusual in planetary rings, and is probably caused by electromagnetic forces pushing the smallest grains out of the ring plane. Because of shadowing, the halo is not visible close to Jupiter in the lower right part of the mosaic. To accentuate faint features in the bottom image of the ring halo, different brightnesses are shown through color. Brightest features are white or yellow and the

  8. Jupiter's Main Ring/Ring Halo

    NASA Technical Reports Server (NTRS)

    1997-01-01

    A mosaic of four images taken through the clear filter (610 nanometers) of the solid state imaging (CCD) system aboard NASA's Galileo spacecraft on November 8, 1996, at a resolution of approximately 46 kilometers (28.5 miles) per picture element (pixel) along Jupiter's rings. Because the spacecraft was only about 0.5 degrees above the ring plane, the image is highly foreshortened in the vertical direction. The images were obtained when Galileo was in Jupiter's shadow, peering back toward the Sun; the ring was approximately 2.3 million kilometers (1.4 million miles) away. The arc on the far right of the image is produced when sunlight is scattered by small particles comprising Jupiter's upper atmospheric haze. The ring also efficiently scatters light, indicating that much of its brightness is due to particles that are microns or less in diameter. Such small particles are believed to have human-scale lifetimes, i.e., very brief compared to the solar system's age.

    Jupiter's ring system is composed of three parts - - a flat main ring, a lenticular halo interior to the main ring, and the gossamer ring, outside the main ring. The near and far arms of Jupiter's main ring extend horizontally across the mosaic, joining together at the ring's ansa, on the figure's far left side. The near arm of the ring appears to be abruptly truncated close to the planet, at the point where it passes into Jupiter's shadow. Some radial structure is barely visible across the ring's ansa (top image). A faint mist of particles can be seen above and below the main rings. This vertically extended 'halo' is unusual in planetary rings, and is probably caused by electromagnetic forces pushing the smallest grains out of the ring plane. Because of shadowing, the halo is not visible close to Jupiter in the lower right part of the mosaic. To accentuate faint features in the bottom image of the ring halo, different brightnesses are shown through color. Brightest features are white or yellow and the

  9. Halo Microlensing and Dark Baryons

    NASA Astrophysics Data System (ADS)

    Crotts, A. P. S.

    1993-12-01

    (While Pierce lectures review past accomplishments, customarily, this talk concerns efforts which we have pursued for some years and which are now reaching fruition. We present elsewhere at this meeting results from research cited for the Prize.) Dark matter exists in the halos of spiral galaxies, and the least radical alternative for its identity is normal matter produced by primordial nucleosynthesis. This matter could easily be hidden in large, condensed objects. Paczynski pointed out in 1986 that if condensations of Galactic halo matter are sufficiently massive, they will produce detectable amplification of background starlight by gravitational lensing. Several groups recently reported possible detections of this effect after surveying large numbers of stars in the Galactic Bulge and LMC. The connection between these events and massive, dark halos is unclear and likely to remain so for some time, given the rate at which they are detected. Following Paczynski's realization, we stressed that a much higher event rate, a statistical control sample, sensitivity to a much broader mass range, and modulation of the predicted lensing rate with galactocentric distance can all be realized by a different experiment: observing the halo of M31 (and the Galaxy) using stars in M31. In some ways, M31 is a more difficult target than the LMC or the Bulge, given the faintness of its stars, but our observations in 1991 and 1993 indicate that these problems have been surmounted. We can detect stellar variability even under extremely crowded conditions like those in M31's inner disk, and can monitor a sufficient number of stars to study halo lensing. We present results from our initial survey which indicates that the required sensitivity can be reached to confirm or reject the hypothesis that sub-solar masses like those detected in our Galaxy make up the missing spiral galaxy mass. It is possible that we may use the data already obtained (and still being analyzed) to place

  10. Predator-Prey Model for Haloes in Saturn's Rings

    NASA Astrophysics Data System (ADS)

    Esposito, Larry W.; Colwell, Joshua; Sremcevic, Miodrag; Madhusudhanan, Prasanna

    Particles in Saturn’s rings have a tripartite nature: (1) a broad distribution of fragments from the disruption of a previous moon that accrete into (2) transient aggregates, resembling piles of rubble, covered by a (3) regolith of smaller grains that result from collisions and meteoritic grinding. Evidence for this triple architecture of ring particles comes from a multitude of Cassini observations. In a number of ring locations (including Saturn’s F ring, the shepherded outer edges of rings A and B and at the locations of the strongest density waves) aggregation and dis-aggregation are operating now. ISS, VIMS, UVIS spectroscopy and occultations show haloes around the strongest density waves. Based on a predator-prey model for ring dynamics, we offer the following explanation: •Cyclic velocity changes cause the perturbed regions to reach higher collision speeds at some orbital phases, which preferentially removes small regolith particles; •This forms a bright halo around the ILR, if the forcing is strong enough; •Surrounding particles diffuse back too slowly to erase the effect; they diffuse away to form the halo. The most rapid time scale is for forcing/aggregate growth/disaggregation; then irreversible regolith erosion; diffusion and/or ballistic transport; and slowest, meteoritic pollution/darkening. We observe both smaller and larger particles at perturbed regions. Straw, UVIS power spectral analysis, kittens and equinox objects show the prey (mass aggregates); while the haloes’ VIMS spectral signature, correlation length and excess variance are created by the predators (velocity dispersion) in regions stirred in the rings. Moon forcing triggers aggregation to create longer-lived aggregates that protect their interiors from meteoritic darkening and recycle the ring material to maintain the current purity of the rings. It also provides a mechanism for creation of new moons at resonance locations in the Roche zone, as proposed by Charnoz etal and

  11. Historical halo displays as past weather indicator

    NASA Astrophysics Data System (ADS)

    Neuhäuser, Dagmar; Neuhäuser, Ralph

    2017-04-01

    Certain halo displays like the 22° circle were known to indicate specific weather pattern since millennia - as specified in Babylonian omina, Aristotle's Meteorology, farmers' weather lore, etc. Today, it is known that halo phenomena are due to refraction and reflection of sun and moon light in ice crystals in cirrus and cirrostratus, so that halo observations do indicate atmospheric conditions like temperature, humidity, pressure etc. in a few km height. The Astronomical Diaries of Babylonia have recorded both halo phenomena (circles, parhelia, etc.) and weather conditions (rain, clouds, etc.), so that we can use them to show statistically, whether, which and how fast halo phenomena are related to weather - for the last few centuries BC for Babylonia. We can then also compare the observations of Babylonian priests in the given BC epoch (without air and light pollution) with the last few decades of the modern epoch (with air and light pollution), where amateur halo observers have systematically recorded such phenomena (in Europe). Weather and climate are known to be partly driven by solar activity. Hence, one could also consider whether there is an indirect relation between halo displays as weather proxy and aurorae as solar activity proxy - if low solar activity leads to low pressure systems, one could expect more halos, preliminary studies show such a hint. For the last few decades, we have many halo observations, satellite imaging of the aurora oval, and many data on solar activity. A statistically sufficient amount of aurora and halo observations should be available for the historic time to investigate such a possible connection: halos were recorded very often in antiquity and the medieval times (as found in chronicles etc.), and modern scholarly catalogs of aurorae also often contain unrecognized halo displays.

  12. Dark energy and dark matter haloes

    NASA Astrophysics Data System (ADS)

    Kuhlen, Michael; Strigari, Louis E.; Zentner, Andrew R.; Bullock, James S.; Primack, Joel R.

    2005-02-01

    We investigate the effect of dark energy on the density profiles of dark matter haloes with a suite of cosmological N-body simulations and use our results to test analytic models. We consider constant equation of state models, and allow both w>=-1 and w < -1. Using five simulations with w ranging from -1.5 to -0.5, and with more than ~1600 well-resolved haloes each, we show that the halo concentration model of Bullock et al. accurately predicts the median concentrations of haloes over the range of w, halo masses and redshifts that we are capable of probing. We find that the Bullock et al. model works best when halo masses and concentrations are defined relative to an outer radius set by a cosmology-dependent virial overdensity. For a fixed power spectrum normalization and fixed-mass haloes, larger values of w lead to higher concentrations and higher halo central densities, both because collapse occurs earlier and because haloes have higher virial densities. While precise predictions of halo densities are quite sensitive to various uncertainties, we make broad comparisons to galaxy rotation curve data. At fixed power spectrum normalization (fixed σ8), w > -1 quintessence models seem to exacerbate the central density problem relative to the standard w=-1 model. For example, models with w~=- 0.5 seem disfavoured by the data, which can be matched only by allowing extremely low normalizations, σ8<~ 0.6. Meanwhile w < -1 models help to reduce the apparent discrepancy. We confirm that the halo mass function of Jenkins et al. provides an excellent approximation to the abundance of haloes in our simulations and extend its region of validity to include models with w < -1.

  13. A study of halo and relic radio emission in merging clusters using the Murchison Widefield Array

    NASA Astrophysics Data System (ADS)

    George, L. T.; Dwarakanath, K. S.; Johnston-Hollitt, M.; Intema, H. T.; Hurley-Walker, N.; Bell, M. E.; Callingham, J. R.; For, Bi-Qing; Gaensler, B.; Hancock, P. J.; Hindson, L.; Kapińska, A. D.; Lenc, E.; McKinley, B.; Morgan, J.; Offringa, A.; Procopio, P.; Staveley-Smith, L.; Wayth, R. B.; Wu, Chen; Zheng, Q.

    2017-05-01

    We have studied radio haloes and relics in nine merging galaxy clusters using the Murchison Widefield Array (MWA). The images used for this study were obtained from the GaLactic and Extragalactic All-sky MWA (GLEAM) Survey which was carried out at five frequencies, viz. 88, 118, 154, 188 and 215 MHz. We detect diffuse radio emission in eight of these clusters. We have estimated the spectra of haloes and relics in these clusters over the frequency range 80-1400 MHz; the first such attempt to estimate their spectra at low frequencies. The spectra follow a power law with a mean value of α = -1.13 ± 0.21 for haloes and α = -1.2 ± 0.19 for relics, where S ∝ να. We reclassify two of the cluster sources as radio galaxies. The low-frequency spectra are thus an independent means of confirming the nature of cluster sources. Five of the nine clusters host radio haloes. For the remaining four clusters, we place upper limits on the radio powers of possible haloes in them. These upper limits are a factor of 2-20 below those expected from the LX-P1.4 relation. These limits are the lowest ever obtained and the implications of these limits to the hadronic model of halo emission are discussed.

  14. A study of halo and relic radio emission in merging clusters using the Murchison Widefield Array

    NASA Astrophysics Data System (ADS)

    George, L. T.; Dwarakanath, K. S.; Johnston-Hollitt, M.; Intema, H. T.; Hurley-Walker, N.; Bell, M. E.; Callingham, J. R.; For, Bi-Qing; Gaensler, B.; Hancock, P. J.; Hindson, L.; Kapińska, A. D.; Lenc, E.; McKinley, B.; Morgan, J.; Offringa, A.; Procopio, P.; Staveley-Smith, L.; Wayth, R. B.; Wu, Chen; Zheng, Q.

    2017-01-01

    We have studied radio haloes and relics in nine merging galaxy clusters using the Murchison Widefield Array (MWA). The images used for this study were obtained from the GaLactic and Extragalactic All-sky MWA (GLEAM) Survey which was carried out at 5 frequencies, viz. 88, 118, 154, 188 and 215 MHz. We detect diffuse radio emission in 8 of these clusters. We have estimated the spectra of haloes and relics in these clusters over the frequency range 80 - 1400 MHz; the first such attempt to estimate their spectra at low frequencies. The spectra follow a power law with a mean value of α = -1.13 ± 0.21 for haloes and α = -1.2 ± 0.19 for relics where, S∝να. We reclassify two of the cluster sources as radio galaxies. The low frequency spectra are thus an independent means of confirming the nature of cluster sources. Five of the nine clusters host radio haloes. For the remaining four clusters, we place upper limits on the radio powers of possible haloes in them. These upper limits are a factor of 2 - 20 below those expected from the LX - P1.4 relation. These limits are the lowest ever obtained and the implications of these limits to the hadronic model of halo emission are discussed.

  15. How unusual is the cool-core radio halo cluster CL1821+643?

    NASA Astrophysics Data System (ADS)

    Kale, Ruta; Parekh, Viral

    2016-07-01

    Massive galaxy clusters with cool cores typically host diffuse radio sources called mini-haloes, whereas, those with non-cool cores host radio haloes. We attempt to understand the unusual nature of the cool-core galaxy cluster CL1821+643, which hosts a megaparsec-scale radio halo, using new radio observations and morphological analysis of its intra-cluster medium. We present the Giant Metrewave Radio Telescope (GMRT) 610-MHz image of the radio halo. The spectral index α, defined as S ∝ ν-α, of the radio halo is 1.0 ± 0.1 over the frequency range of 323-610-1665 MHz. Archival Chandra X-ray data were used to make surface brightness and temperature maps. The morphological parameters Gini, M20 and concentration (C) were calculated on X-ray surface brightness maps by including and excluding the central quasar (H1821+643) in the cluster. We find that the cluster CL1821+643, excluding the quasar, is a non-relaxed cluster as seen in the morphological parameter planes. It occupies the same region as other merging radio halo clusters in the temperature versus morphology parameter plane. We conclude that this cluster has experienced a non-core-disruptive merger.

  16. NOT DEAD YET: COOL CIRCUMGALACTIC GAS IN THE HALOS OF EARLY-TYPE GALAXIES

    SciTech Connect

    Thom, Christopher; Tumlinson, Jason; Sembach, Kenneth R.; Werk, Jessica K.; Xavier Prochaska, J.; Peeples, Molly S.; Tripp, Todd M.; Katz, Neal S.; O'Meara, John M.; Ford, Amanda Brady; Dave, Romeel; Weinberg, David H.

    2012-10-20

    We report new observations of circumgalactic gas in the halos of early-type galaxies (ETGs) obtained by the COS-Halos Survey with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. We find that detections of H I surrounding ETGs are typically as common and strong as around star-forming galaxies, implying that the total mass of circumgalactic material is comparable in the two populations. For ETGs, the covering fraction for H I absorption above 10{sup 16} cm{sup -2} is {approx}40%-50% within {approx}150 kpc. Line widths and kinematics of the detected material show it to be cold (T {approx}< 10{sup 5} K) in comparison to the virial temperature of the host halos. The implied masses of cool, photoionized circumgalactic medium baryons may be up to 10{sup 9}-10{sup 11} M{sub Sun }. Contrary to some theoretical expectations, strong halo H I absorbers do not disappear as part of the quenching of star formation. Even passive galaxies retain significant reservoirs of halo baryons that could replenish the interstellar gas reservoir and eventually form stars. This halo gas may feed the diffuse and molecular gas that is frequently observed inside ETGs.

  17. Halo scale predictions of symmetron modified gravity

    SciTech Connect

    Clampitt, Joseph; Jain, Bhuvnesh; Khoury, Justin E-mail: bjain@physics.upenn.edu

    2012-01-01

    We offer predictions of symmetron modified gravity in the neighborhood of realistic dark matter halos. The predictions for the fifth force are obtained by solving the nonlinear symmetron equation of motion in the spherical NFW approximation. In addition, we compare the three major known screening mechanisms: Vainshtein, Chameleon, and Symmetron around such dark matter halos, emphasizing the significant differences between them and highlighting observational tests which exploit these differences. Finally, we demonstrate the host halo environmental screening effect (''blanket screening'') on smaller satellite halos by solving for the modified forces around a density profile which is the sum of satellite and approximate host components.

  18. The prodigious halo of the other Huygens.

    PubMed

    Können, Gunther P

    2015-02-01

    At the height of the ceremony in the Principality of Orange of the restoration of the sovereignty of the House of Nassau in 1665, a ceremony led by Christiaan's father, Constantijn Huygens, a "solar crown" appeared in the sky, apparently a divine sign of approval. A nearly forgotten contemporary color engraving of this miraculous event has survived. Constantijn seized the opportunity by using to his advantage the general euphoria among the citizens caused by the appearance. We argue that Constantijn knew exactly what was going on in the sky because of his son's work on halo theory. Given its brightness and its time of appearance, it seems plausible that the most prominent halo in the Orange halo display was a circumscribed halo rather than the more familiar but bleaker circular 22° halo. The same probably holds for most of the other high-sun halos that caused general consternation, dating from the Octavian halo of 44 BC, to the Chernobyl halo of 1986, and indeed up to bright high-sun halos of the present.

  19. The total mass of dark matter haloes

    NASA Astrophysics Data System (ADS)

    Anderhalden, Donnino; Diemand, Jürg

    2011-07-01

    The simple, conventional dark matter halo mass definitions commonly used in cosmological simulations ('virial' mass, FoF mass, M50, 100, 200, …) only capture part of the collapsed material and are therefore inconsistent with the halo mass concept used in analytical treatments of structure formation. Simulations have demonstrated that typical dark matter particle orbits extend out to about 90 per cent of their turnaround radius, which results in apocentre passages outside of the current 'virial' radius on the first and also on the second orbit. Here we describe how the formation history of haloes can be used to identify those particles which took part in the halo collapse, but are missed by conventional group finders because of their remote present location. These particles are added to the part of the halo already identified by FoF. The corrected masses of dark haloes are significantly higher (the median mass increase is 25 per cent) and there is a considerable shift of the halo mass function towards the Press and Schechter form. We conclude that meaningful quantitative comparisons between (semi-)analytic predictions of halo properties (e.g. mass functions, mass accretion rates, merger rates, spatial clustering, etc.) and simulation results will require using the same halo definition in both approaches.

  20. Unbound particles in dark matter halos

    SciTech Connect

    Behroozi, Peter S.; Loeb, Abraham; Wechsler, Risa H.

    2013-06-13

    We investigate unbound dark matter particles in halos by tracing particle trajectories in a simulation run to the far future (a = 100). We find that the traditional sum of kinetic and potential energies is a very poor predictor of which dark matter particles will eventually become unbound from halos. We also study the mass fraction of unbound particles, which increases strongly towards the edges of halos, and decreases significantly at higher redshifts. We discuss implications for dark matter detection experiments, precision calibrations of the halo mass function, the use of baryon fractions to constrain dark energy, and searches for intergalactic supernovae.

  1. Progress in understanding halo current at JET

    NASA Astrophysics Data System (ADS)

    Riccardo, V.; Arnoux, G.; Beaumont, P.; Hacquin, S.; Hobirk, J.; Howell, D.; Huber, A.; Joffrin, E.; Koslowski, R.; Lam, N.; Leggate, H.; Rachlew, E.; Sergienko, G.; Stephen, A.; Todd, T.; Zerbini, M.; Delogu, R.; Grando, L.; Marcuzzi, D.; Peruzzo, S.; Pomaro, N.; Sonato, P.; JET EFDA Contributors

    2009-05-01

    The poloidal distribution of the halo current density on the top dump plate in JET can now be measured thanks to a new set of Rogowskii coils. These are the first measurements in JET able to offer an insight in the width of the halo current interaction with the wall. Therefore they offer both validation of the assumption made for JET disruption design criteria and one additional point in the extrapolation of the expected halo current width, and hence halo current density (and related local electro-mechanical loads on in-vessel components) for ITER. During upward events, the measured current density is consistent with the measured total poloidal halo current. The halo footprint extends over most of the upper dump plate, converting to a halo current flux tube width of ~100 mm. A set of four toridal field pick-up coils installed 90° apart now allows a more accurate measurement of the poloidal halo current, in particular its toroidal peaking factor, and direct comparison between halo and plasma asymmetries.

  2. X-ray Haloes and Scattering by Interstellar Grains

    NASA Technical Reports Server (NTRS)

    Dwek, Eliahu

    2003-01-01

    The presence of dust in the general interstellar medium is inferred f r o m the general extinction of starlight, the diffuse infrared emission, and the elemental abundance constraints. X-ray haloes around X-ray sources, produced by small angle scattering from intervening interstellar dust particles provide a new probe into the nature of interstellar dust. In this talk I will review the physics of X-ray scattering by dust particles, and present an analysis of dust properties around select X-ray sources.

  3. Characterizing the X-Ray Spectrum of the Galactic Halo

    NASA Technical Reports Server (NTRS)

    2003-01-01

    The goal of this project is to determine the spectrum of the Galactic halo's soft X-ray emission. These photons are emitted by hot, diffuse gas hundreds to thousands of parsecs from the Galactic plane. Thus, the emission is weak, can be confused with locally produced photons, and must be distinguished from noise. My co-I has made significant progress on determining the background. I have been working on a complementary aspect of the project: computer simulations of the hot gas in the local and distant regions.

  4. X-ray Haloes and Scattering by Interstellar Grains

    NASA Technical Reports Server (NTRS)

    Dwek, Eliahu

    2003-01-01

    The presence of dust in the general interstellar medium is inferred from the general extinction of starlight, the diffuse infrared emission, and the elemental abundance constraints. X-ray haloes around X-ray sources, produced by small angle scattering from intervening interstellar dust particles provide a new probe into the nature of interstellar dust. In this talk I will review the physics of X-ray scattering by dust particles, and present an analysis of dust properties around select X-ray sources.

  5. Characterizing the X-Ray Spectrum of the Galactic Halo

    NASA Technical Reports Server (NTRS)

    2003-01-01

    The goal of this project is to determine the spectrum of the Galactic halo's soft X-ray emission. These photons are emitted by hot, diffuse gas hundreds to thousands of parsecs from the Galactic plane. Thus, the emission is weak, can be confused with locally produced photons, and must be distinguished from noise. My co-I has made significant progress on determining the background. I have been working on a complementary aspect of the project: computer simulations of the hot gas in the local and distant regions.

  6. X-ray Haloes and Scattering by Interstellar Grains

    NASA Technical Reports Server (NTRS)

    Dwek, Eliahu

    2003-01-01

    The presence of dust in the general interstellar medium is inferred f r o m the general extinction of starlight, the diffuse infrared emission, and the elemental abundance constraints. X-ray haloes around X-ray sources, produced by small angle scattering from intervening interstellar dust particles provide a new probe into the nature of interstellar dust. In this talk I will review the physics of X-ray scattering by dust particles, and present an analysis of dust properties around select X-ray sources.

  7. X-ray Haloes and Scattering by Interstellar Grains

    NASA Technical Reports Server (NTRS)

    Dwek, Eliahu

    2003-01-01

    The presence of dust in the general interstellar medium is inferred from the general extinction of starlight, the diffuse infrared emission, and the elemental abundance constraints. X-ray haloes around X-ray sources, produced by small angle scattering from intervening interstellar dust particles provide a new probe into the nature of interstellar dust. In this talk I will review the physics of X-ray scattering by dust particles, and present an analysis of dust properties around select X-ray sources.

  8. Computation of the halo mass function using physical collapse parameters: application to non-standard cosmologies

    SciTech Connect

    Achitouv, I.; Weller, J.; Wagner, C.; Rasera, Y. E-mail: cwagner@MPA-Garching.MPG.DE E-mail: yann.rasera@obspm.fr

    2014-10-01

    In this article we compare the halo mass function predicted by the excursion set theory with a drifting diffusive barrier against the results of N-body simulations for several cosmological models. This includes the standard ΛCDM case for a large range of halo masses, models with different types of primordial non-Gaussianity, and the Ratra-Peebles quintessence model of Dark Energy. We show that in all those cosmological scenarios, the abundance of dark matter halos can be described by a drifting diffusive barrier, where the two parameters describing the barrier have physical content. In the case of the Gaussian ΛCDM, the statistics are precise enough to actually predict those parameters at different redshifts from the initial conditions. Furthermore, we found that the stochasticity in the barrier is non-negligible making the simple deterministic spherical collapse model a bad approximation even at very high halo masses. We also show that using the standard excursion set approach with a barrier inspired by peak patches leads to inconsistent predictions of the halo mass function.

  9. Stellar haloes in Milky Way mass galaxies: from the inner to the outer haloes

    NASA Astrophysics Data System (ADS)

    Tissera, Patricia B.; Beers, Timothy C.; Carollo, Daniela; Scannapieco, Cecilia

    2014-04-01

    We present a comprehensive study of the chemical properties of the stellar haloes of Milky Way mass galaxies, analysing the transition between the inner to the outer haloes. We find the transition radius between the relative dominance of the inner-halo and outer-halo stellar populations to be ˜15-20 kpc for most of our haloes, similar to that inferred for the Milky Way from recent observations. While the number density of stars in the simulated inner-halo populations decreases rapidly with distance, the outer-halo populations contribute about 20-40 per cent in the fiducial solar neighbourhood, in particular at the lowest metallicities. We have determined [Fe/H] profiles for our simulated haloes; they exhibit flat or mild gradients, in the range [-0.002, -0.01] dex kpc-1. The metallicity distribution functions exhibit different features, reflecting the different assembly history of the individual stellar haloes. We find that stellar haloes formed with larger contributions from massive subgalactic systems have steeper metallicity gradients. Very metal-poor stars are mainly contributed to the halo systems by lower mass satellites. There is a clear trend among the predicted metallicity distribution functions that a higher fraction of low-metallicity stars are found with increasing radius. These properties are consistent with the range of behaviours observed for stellar haloes of nearby galaxies.

  10. The dust scattering halo of Cygnus X-3

    NASA Astrophysics Data System (ADS)

    Corrales, L. R.; Paerels, F.

    2015-10-01

    Dust grains scatter X-ray light through small angles, producing a diffuse halo image around bright X-ray point sources situated behind a large amount of interstellar material. We present analytic solutions to the integral for the dust scattering intensity, which allow for a Bayesian analysis of the scattering halo around Cygnus X-3. Fitting the optically thin 4-6 keV halo surface brightness profile yields the dust grain size and spatial distribution. We assume a power-law distribution of grain sizes (n ∝ a-p) and fit for p, the grain radius cut-off amax, and dust mass column. We find that a p ≈ 3.5 dust grain size distribution with amax ≈ 0.2 μm fits the halo profile relatively well, whether the dust is distributed uniformly along the line of sight or in clumps. We find that a model consisting of two dust screens, representative of foreground spiral arms, requires the foreground Perseus arm to contain 80 per cent of the total dust mass. The remaining 20 per cent of the dust, which may be associated with the outer spiral arm of the Milky Way, is located within 1 kpc of Cyg X-3. Regardless of which model was used, we found τ_sca ˜ 2 E_keV^{-2}. We examine the energy resolved haloes of Cyg X-3 from 1 to 6 keV and find that there is a sharp drop in scattering halo intensity when E < 2-3 keV, which cannot be explained with multiple scattering effects. We hypothesize that this may be caused by large dust grains or material with unique dielectric properties, causing the scattering cross-section to depart from the Rayleigh-Gans approximation that is used most often in X-ray scattering studies. The foreground Cyg OB2 association, which contains several evolved stars with large extinction values, is a likely culprit for grains of unique size or composition.

  11. GLOBAL PROPERTIES OF M31'S STELLAR HALO FROM THE SPLASH SURVEY. I. SURFACE BRIGHTNESS PROFILE

    SciTech Connect

    Gilbert, Karoline M.; Guhathakurta, Puragra; Bullock, James; Tollerud, Erik J.; Geha, Marla C.; Kalirai, Jason S.; Kirby, Evan N.; Tanaka, Mikito; Chiba, Masashi

    2012-11-20

    We present the surface brightness profile of M31's stellar halo out to a projected radius of 175 kpc. The surface brightness estimates are based on confirmed samples of M31 red giant branch stars derived from Keck/DEIMOS spectroscopic observations. A set of empirical spectroscopic and photometric M31 membership diagnostics is used to identify and reject foreground and background contaminants. This enables us to trace the stellar halo of M31 to larger projected distances and fainter surface brightnesses than previous photometric studies. The surface brightness profile of M31's halo follows a power law with index -2.2 {+-} 0.2 and extends to a projected distance of at least {approx}175 kpc ({approx}2/3 of M31's virial radius), with no evidence of a downward break at large radii. The best-fit elliptical isophotes have b/a = 0.94 with the major axis of the halo aligned along the minor axis of M31's disk, consistent with a prolate halo, although the data are also consistent with M31's halo having spherical symmetry. The fact that tidal debris features are kinematically cold is used to identify substructure in the spectroscopic fields out to projected radii of 90 kpc and investigate the effect of this substructure on the surface brightness profile. The scatter in the surface brightness profile is reduced when kinematically identified tidal debris features in M31 are statistically subtracted; the remaining profile indicates that a comparatively diffuse stellar component to M31's stellar halo exists to large distances. Beyond 90 kpc, kinematically cold tidal debris features cannot be identified due to small number statistics; nevertheless, the significant field-to-field variation in surface brightness beyond 90 kpc suggests that the outermost region of M31's halo is also comprised to a significant degree of stars stripped from accreted objects.

  12. X-ray scattered halo around IGR J17544–2619

    SciTech Connect

    Mao, Junjie; Ling, Zhixing; Zhang, Shuang-Nan

    2014-04-10

    X-ray photons coming from an X-ray point source not only arrive at the detector directly, but also can be strongly forward-scattered by the interstellar dust along the line of sight (LOS), leading to a detectable diffuse halo around the X-ray point source. The geometry of small-angle X-ray scattering is straightforward, namely, the scattered photons travel longer paths and thus arrive later than the unscattered ones; thus, the delay time of X-ray scattered halo photons can reveal information of the distances of the interstellar dust and the point source. Here we present a study of the X-ray scattered halo around IGR J17544–2619, which is one of the so-called supergiant fast X-ray transients. IGR J17544–2619 underwent a striking outburst when observed with Chandra on 2004 July 3, providing a near δ-function light curve. We find that the X-ray scattered halo around IGR J17544–2619 is produced by two interstellar dust clouds along the LOS. The one that is closer to the observer gives the X-ray scattered halo at larger observational angles, whereas the farther one, which is in the vicinity of the point source, explains the halo with a smaller angular size. By comparing the observational angle of the scattered halo photons with that predicted by different dust grain models, we are able to determine the normalized dust distance. With the delay times of the scattered halo photons, we can determine the point source distance, given a dust grain model. Alternatively, we can discriminate between the dust grain models, if the point source distance is known independently.

  13. X-Ray Scattered Halo around IGR J17544-2619

    NASA Astrophysics Data System (ADS)

    Mao, Junjie; Ling, Zhixing; Zhang, Shuang-Nan

    2014-04-01

    X-ray photons coming from an X-ray point source not only arrive at the detector directly, but also can be strongly forward-scattered by the interstellar dust along the line of sight (LOS), leading to a detectable diffuse halo around the X-ray point source. The geometry of small-angle X-ray scattering is straightforward, namely, the scattered photons travel longer paths and thus arrive later than the unscattered ones; thus, the delay time of X-ray scattered halo photons can reveal information of the distances of the interstellar dust and the point source. Here we present a study of the X-ray scattered halo around IGR J17544-2619, which is one of the so-called supergiant fast X-ray transients. IGR J17544-2619 underwent a striking outburst when observed with Chandra on 2004 July 3, providing a near δ-function light curve. We find that the X-ray scattered halo around IGR J17544-2619 is produced by two interstellar dust clouds along the LOS. The one that is closer to the observer gives the X-ray scattered halo at larger observational angles, whereas the farther one, which is in the vicinity of the point source, explains the halo with a smaller angular size. By comparing the observational angle of the scattered halo photons with that predicted by different dust grain models, we are able to determine the normalized dust distance. With the delay times of the scattered halo photons, we can determine the point source distance, given a dust grain model. Alternatively, we can discriminate between the dust grain models, if the point source distance is known independently.

  14. Detecting halo weakly interacting massive particles with a cryogenic phonon detector

    SciTech Connect

    Wang, N.; Barnes, P.D.; Cummings, A.; Emes, J. ); Giraud-Heraud, Y. ); Haller, E.E. ); Lange, A.; Ross, R.; Sadoulet, B.; Shutt, T.; Stubbs, C. )

    1991-04-15

    If dark matter in the halo is made of weakly interacting massive particles (WIMPs), it may be detected with a cryogenic phonon detector. Such a detector must have low energy threshold, high energy resolution, and, more importantly, good background rejection capability. It has been proposed that a good background rejection ratio can be obtained by a simultaneous measurement of phonons and ionization. To test this experimentally, we have built a 60 g Ge detector and have measured simultaneous phonon and ionization signals, each with 4 keV energy resolution. We present a simple estimate of the rejection ratios, and WIMP event rates that may be achieved by such a detector.

  15. The Galactic Warm Ionized Medium: the First Direct Measures of its Ionization and Abundances

    NASA Astrophysics Data System (ADS)

    Howk, J.

    2002-07-01

    The warm ionized medium {WIM} is the dominant gaseous component of the Galactic halo and represents an important sink of the radiative and kinetic energy output of stars and supernovae, though the source of its ionization remains unknown. We will use stis spectroscopy of the post-AGB stars ROB 162 and ZNG 1 in the globular clusters NGC 6397 and Messier 5 to measure directly the abundances and ionization states of several key metals in the Galactic WIM. These sight lines are unique: because the two clusters also contain pulsars with published radio dispersion measurements, these are the only sight lines for which we can derive the column densities of both HI, em and ionH2, as well as the columns of multiple ionization stages of the important metals S, P, and Fe. We will use the proposed stis observations with existing Ause data to derive the total gas-phase abundances of S, P, and Fe for the material along these sight lines with no ionization uncertainties. We will directly measure the ionization fractions of S and P in the WIM. We will also infer the dust content of the WIM. Our study of the ionization state and dust content of the WIM will provide the best yet constraints for models of this gas. Our work will also provide the best constraint for the fundamental ``cosmic'' reference abundance {averaged over these sight lines} of the undepleted elements S and P.

  16. Halo and reverse halo signs in canine pulmonary computed tomography.

    PubMed

    Secrest, Scott; Sakamoto, Kaori

    2014-01-01

    The halo sign (HS) and reverse halo sign (RHS) are radiologic signs identified on pulmonary computed tomography (CT) in people. The HS is described as a circular area of ground-glass attenuation surrounding a pulmonary nodule or mass. The RHS is defined as a focal, rounded area of ground-glass attenuation surrounded by a more or less complete ring of consolidation. These signs have been identified in a variety of diseases in people. The purpose of this retrospective study was to determine if the HS and RHS occur in dogs with pulmonary disease and to determine if they are associated with a particular disease process. In addition, the appearance of the HS and RHS was correlated with the histopathologic changes. Our results indicate that the HS and RHS are not common signs identified in dogs with pulmonary disease with an HS noted in five cases and an RHS in 4 of the 33 dogs that met the inclusion criteria. An association between the HS (P-value 0.8163) or RHS (P-value 0.5988) and neoplasia, infectious/inflammatory, and other disease processes was not identified using a Fisher's exact test. The HS was identified in neoplastic, infectious, and inflammatory conditions, with the RHS identified in neoplastic and infectious diseases and a lung lobe torsion. Histologically, the HS and RHS were caused by tumor extension, necrosis, and/or hemorrhage of the pulmonary parenchyma. © 2014 American College of Veterinary Radiology.

  17. The Dark Matter halo of the Milky Way, AD 2013

    SciTech Connect

    Nesti, Fabrizio; Salucci, Paolo E-mail: salucci@sissa.it

    2013-07-01

    We derive the mass model of the Milky Way (MW), crucial for Dark Matter (DM) direct and indirect detection, using recent data and a cored dark matter (DM) halo profile, which is favoured by studies of external galaxies. The method used consists in fitting a spherically symmetric model of the Galaxy with a Burkert DM halo profile to available data: MW terminal velocities in the region inside the solar circle, circular velocity as recently estimated from maser star forming regions at intermediate radii, and velocity dispersions of stellar halo tracers for the outermost Galactic region. The latter are reproduced by integrating the Jeans equation for every modeled mass distribution, and by allowing for different velocity anisotropies for different tracer populations. For comparison we also consider a Navarro-Frenk-White profile. We find that the cored profile is the preferred one, with a shallow central density of ρ{sub H} ∼ 4 × 10{sup 7}M{sub ☉}/kpc{sup 3} and a large core radius R{sub H} ∼ 10 kpc, as observed in external spirals and in agreement with the mass model underlying the Universal Rotation Curve of spirals. We describe also the derived model uncertainties, which are crucially driven by the poorly constrained velocity dispersion anisotropies of halo tracers. The emerging cored DM distribution has implications for the DM annihilation angular profile, which is much less boosted in the Galactic center direction with respect to the case of the standard ΛCDM, NFW profile. Using the derived uncertainties we discuss finally the limitations and prospects to discriminate between cored and cusped DM profile with a possible observed diffuse DM annihilation signal. The present mass model aims to characterize the present-day description of the distribution of matter in our Galaxy, which is needed to frame current crucial issues of Cosmology, Astrophysics and Elementary Particles.

  18. The Dual Origin Of Stellar Halos

    NASA Astrophysics Data System (ADS)

    Zolotov, Adi

    In the dominant Lambda+Cold Dark Matter cosmological paradigm, galaxy stellar halos are thought to form hierarchically from multiple accretion events, starting from the first structures to collapse in the Universe. This dissertation aims to make the first detailed theoretical predictions for the origin of galactic stellar halos. We focus on understanding the physical processes involved in halo formation using high-resolution, N-body + Smooth Particle Hydrodynamic simulations of disk galaxies in a cosmological context. These self-consistent simulations are used to study the competing importance of dissipative processes and dissipationless mergers in the formation of stellar halos. The relative contribution of each mechanism, and its specific role in assembling the inner and outer regions of halos is explored, as a function of galaxy mass and merging history. We show that the presence of both accreted and in situ stars in halos is a generic feature of galaxy formation. For L* galaxies, the relative contribution of each stellar population to a halo is shown to be a function of a galaxy's accretion history. Galaxies with recent mergers, like M31, will host relatively few in situ stars, while galaxies with more quiescent recent histories, like the Milky Way, will likely have a larger relative contribution from an in situ population. We show that in situ halo stars are more [alpha/Fe]-rich than accreted stars at the high [Fe/H] end of a halo's metallicity distribution function. In lower mass galaxies, M ˜ 1010 M, in situ stars dominate the stellarmass of halos. In these galaxies, in situ halo stars are, on average, younger and more metal-rich than accreted halo stars. Because in situ stars are dominant, these trends result in halos that are more metal-rich than simple accretion models predict. The halos of low mass galaxies do not extend out to the virial radii of the primary, as they do in more massive galaxies. We find that the ratio of luminous-halo mass to total

  19. THE PSEUDO-EVOLUTION OF HALO MASS

    SciTech Connect

    Diemer, Benedikt; Kravtsov, Andrey V.; More, Surhud

    2013-03-20

    A dark matter halo is commonly defined as a spherical overdensity of matter with respect to a reference density, such as the critical density or the mean matter density of the universe. Such definitions can lead to a spurious pseudo-evolution of halo mass simply due to redshift evolution of the reference density, even if its physical density profile remains constant over time. We estimate the amount of such pseudo-evolution of mass between z = 1 and 0 for halos identified in a large N-body simulation, and show that it accounts for almost the entire mass evolution of the majority of halos with M{sub 200{rho}-bar} Less-Than-Or-Equivalent-To 10{sup 12} h{sup -1} M{sub Sun} and can be a significant fraction of the apparent mass growth even for cluster-sized halos. We estimate the magnitude of the pseudo-evolution assuming that halo density profiles remain static in physical coordinates, and show that this simple model predicts the pseudo-evolution of halos identified in numerical simulations to good accuracy, albeit with significant scatter. We discuss the impact of pseudo-evolution on the evolution of the halo mass function and show that the non-evolution of the low-mass end of the halo mass function is the result of a fortuitous cancellation between pseudo-evolution and the absorption of small halos into larger hosts. We also show that the evolution of the low-mass end of the concentration-mass relation observed in simulations is almost entirely due to the pseudo-evolution of mass. Finally, we discuss the implications of our results for the interpretation of the evolution of various scaling relations between the observable properties of galaxies and galaxy clusters and their halo masses.

  20. HaloSat - A CubeSat to Study the Hot Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kaaret, Philip

    2017-08-01

    Observations of the nearby universe fail to locate about half of the normal matter (baryons) observed in the early universe. The missing baryons may be in hot galactic halos. HaloSat is a CubeSat designed to map oxygen line emission (O VII and O VIII) around the Milky Way in order to constrain the mass and spatial distribution of hot gas in the halo. HaloSat has a grasp competitive with current X-ray observatories. Its observing program will be optimized to minimize contributions from solar wind charge exchange (SWCX) emission that limit the accuracy of current measurements. We describe the current status of HaloSat.

  1. Combining two-dimensional diffusion-ordered nuclear magnetic resonance spectroscopy, imaging desorption electrospray ionization mass spectrometry, and direct analysis in real-time mass spectrometry for the integral investigation of counterfeit pharmaceuticals.

    PubMed

    Nyadong, Leonard; Harris, Glenn A; Balayssac, Stéphane; Galhena, Asiri S; Malet-Martino, Myriam; Martino, Robert; Parry, R Mitchell; Wang, May Dongmei; Fernández, Facundo M; Gilard, Véronique

    2009-06-15

    During the past decade, there has been a marked increase in the number of reported cases involving counterfeit medicines in developing and developed countries. Particularly, artesunate-based antimalarial drugs have been targeted, because of their high demand and cost. Counterfeit antimalarials can cause death and can contribute to the growing problem of drug resistance, particularly in southeast Asia. In this study, the complementarity of two-dimensional diffusion-ordered (1)H nuclear magnetic resonance spectroscopy (2D DOSY (1)H NMR) with direct analysis in real-time mass spectrometry (DART MS) and desorption electrospray ionization mass spectrometry (DESI MS) was assessed for pharmaceutical forensic purposes. Fourteen different artesunate tablets, representative of what can be purchased from informal sources in southeast Asia, were investigated with these techniques. The expected active pharmaceutical ingredient was detected in only five formulations via both nuclear magnetic resonance (NMR) and mass spectrometry (MS) methods. Common organic excipients such as sucrose, lactose, stearate, dextrin, and starch were also detected. The graphical representation of DOSY (1)H NMR results proved very useful for establishing similarities among groups of samples, enabling counterfeit drug "chemotyping". In addition to bulk- and surface-average analyses, spatially resolved information on the surface composition of counterfeit and genuine antimalarial formulations was obtained using DESI MS that was performed in the imaging mode, which enabled one to visualize the homogeneity of both genuine and counterfeit drug samples. Overall, this study suggests that 2D DOSY (1)H NMR, combined with ambient MS, comprises a powerful suite of instrumental analysis methodologies for the integral characterization of counterfeit antimalarials.

  2. Correlates of Halo Error in Teacher Evaluation.

    ERIC Educational Resources Information Center

    Moritsch, Brian G.; Suter, W. Newton

    1988-01-01

    An analysis of 300 undergraduate psychology student ratings of teachers was undertaken to assess the magnitude of halo error and a variety of rater, ratee, and course characteristics. The raters' halo errors were significantly related to student effort in the course, previous experience with the instructor, and class level. (TJH)

  3. Confounding among Measures of Leniency and Halo.

    ERIC Educational Resources Information Center

    Alliger, George M.; Williams, Kevin J.

    1989-01-01

    The interrelationships among halo and leniency rating errors were examined using simulated rating data. As leniency increased, halo decreased when measured by dimension intercorrelations but increased when measured by standard deviations across dimensions. Implications of these results for the use of the various measures are discussed. (SLD)

  4. Comments on the Measurement of Halo.

    ERIC Educational Resources Information Center

    Fisicaro, Sebastiano A.; Vance, Robert J.

    1994-01-01

    This article presents arguments that the correlation measure "r" of halo is not conceptually more appropriate than the standard deviation (SD) measure. It also describes conditions under which halo effects occur and when the SD and r measures can be used. Neither measure is uniformly superior to the other. (SLD)

  5. Confounding among Measures of Leniency and Halo.

    ERIC Educational Resources Information Center

    Alliger, George M.; Williams, Kevin J.

    1989-01-01

    The interrelationships among halo and leniency rating errors were examined using simulated rating data. As leniency increased, halo decreased when measured by dimension intercorrelations but increased when measured by standard deviations across dimensions. Implications of these results for the use of the various measures are discussed. (SLD)

  6. Comments on the Measurement of Halo.

    ERIC Educational Resources Information Center

    Fisicaro, Sebastiano A.; Vance, Robert J.

    1994-01-01

    This article presents arguments that the correlation measure "r" of halo is not conceptually more appropriate than the standard deviation (SD) measure. It also describes conditions under which halo effects occur and when the SD and r measures can be used. Neither measure is uniformly superior to the other. (SLD)

  7. Correlates of Halo Error in Teacher Evaluation.

    ERIC Educational Resources Information Center

    Moritsch, Brian G.; Suter, W. Newton

    1988-01-01

    An analysis of 300 undergraduate psychology student ratings of teachers was undertaken to assess the magnitude of halo error and a variety of rater, ratee, and course characteristics. The raters' halo errors were significantly related to student effort in the course, previous experience with the instructor, and class level. (TJH)

  8. Analytical halo model of galactic conformity

    NASA Astrophysics Data System (ADS)

    Pahwa, Isha; Paranjape, Aseem

    2017-09-01

    We present a fully analytical halo model of colour-dependent clustering that incorporates the effects of galactic conformity in a halo occupation distribution framework. The model, based on our previous numerical work, describes conformity through a correlation between the colour of a galaxy and the concentration of its parent halo, leading to a correlation between central and satellite galaxy colours at fixed halo mass. The strength of the correlation is set by a tunable 'group quenching efficiency', and the model can separately describe group-level correlations between galaxy colour (1-halo conformity) and large-scale correlations induced by assembly bias (2-halo conformity). We validate our analytical results using clustering measurements in mock galaxy catalogues, finding that the model is accurate at the 10-20 per cent level for a wide range of luminosities and length-scales. We apply the formalism to interpret the colour-dependent clustering of galaxies in the Sloan Digital Sky Survey (SDSS). We find good overall agreement between the data and a model that has 1-halo conformity at a level consistent with previous results based on an SDSS group catalogue, although the clustering data require satellites to be redder than suggested by the group catalogue. Within our modelling uncertainties, however, we do not find strong evidence of 2-halo conformity driven by assembly bias in SDSS clustering.

  9. Milky Way halo gas kinematics

    NASA Technical Reports Server (NTRS)

    Danly, L.

    1986-01-01

    Measurements of high resolution, short wavelength absorption data taken by IUE toward high latitude O and B stars are presented in a discussion of the large scale kinematic properties of Milky Way Halo gas. An analysis of these data demonstrates that: (1) the obsrved absorption widths (FWHM) of Si II are very large, ranging up to 150 Km/s for the most distant halo star; this is much larger than is generally appreciated from optical data; (2) the absorption is observed to be systematically negative in radial velocity, indicating that cool material is, on the whole, flowing toward the disk of the galaxy; (3) there is some evidence for asymmetry between the northern and southern galactic hemispheres, in accordance with the HI 21 cm data toward the galactic poles; (4) low column density gas with highly negative radial LSR velocity (V less than -70 km/s) can be found toward stars beyond 1-3 kpc in the northern galactic hemisphere in all four quadrants of galactic longitude; and (5) only the profiles toward stars in the direction of known high velocity HI features show a clear two component structure.

  10. Probing the galactic halo with ROSAT

    NASA Technical Reports Server (NTRS)

    Burrows, David N.; Mendenhall, J. A.

    1992-01-01

    We discuss the current status of ROSAT shadowing observations designed to search for emission from million degree gas in the halo of the Milky Way galaxy. Preliminary results indicate that million degree halo gas is observed in the 1/4 keV band in some directions, most notably toward the Draco cloud at (l,b) = (92 deg, +38 deg), but that the halo emission is patchy and highly anisotropic. Our current understanding of this halo emission is based on a small handful of observations which have been analyzed to date. Many more observations are currently being analyzed or are scheduled for observation within the next year, and we expect our understanding of this component of the galactic halo to improve dramatically in the near future.

  11. Probing the galactic halo with ROSAT

    NASA Technical Reports Server (NTRS)

    Burrows, D. N.; Mendenhall, J. A.

    1993-01-01

    We discuss the current status of ROSAT shadowing observations designed to search for emission from million degree gas in the halo of the Milky Way galaxy. Preliminary results indicate that million degree halo gas is observed in the 1/4 keV band in some directions, most notably toward the Draco cloud at (l,b) = (92 deg, +38 deg), but that the halo emission is patchy and highly anisotropic. Our current understanding of this halo emission is based on a small handful of observations which have been analyzed to date. Many more observations are currently being analyzed or are scheduled for observation within the next year, and we expect our understanding of this component of the galactic halo to improve dramatically in the near future.

  12. Smooth halos in the cosmic web

    NASA Astrophysics Data System (ADS)

    Gaite, José

    2015-04-01

    Dark matter halos can be defined as smooth distributions of dark matter placed in a non-smooth cosmic web structure. This definition of halos demands a precise definition of smoothness and a characterization of the manner in which the transition from smooth halos to the cosmic web takes place. We introduce entropic measures of smoothness, related to measures of inequality previously used in economy and with the advantage of being connected with standard methods of multifractal analysis already used for characterizing the cosmic web structure in cold dark matter N-body simulations. These entropic measures provide us with a quantitative description of the transition from the small scales portrayed as a distribution of halos to the larger scales portrayed as a cosmic web and, therefore, allow us to assign definite sizes to halos. However, these ``smoothness sizes'' have no direct relation to the virial radii. Finally, we discuss the influence of N-body discreteness parameters on smoothness.

  13. Smooth halos in the cosmic web

    SciTech Connect

    Gaite, José

    2015-04-01

    Dark matter halos can be defined as smooth distributions of dark matter placed in a non-smooth cosmic web structure. This definition of halos demands a precise definition of smoothness and a characterization of the manner in which the transition from smooth halos to the cosmic web takes place. We introduce entropic measures of smoothness, related to measures of inequality previously used in economy and with the advantage of being connected with standard methods of multifractal analysis already used for characterizing the cosmic web structure in cold dark matter N-body simulations. These entropic measures provide us with a quantitative description of the transition from the small scales portrayed as a distribution of halos to the larger scales portrayed as a cosmic web and, therefore, allow us to assign definite sizes to halos. However, these ''smoothness sizes'' have no direct relation to the virial radii. Finally, we discuss the influence of N-body discreteness parameters on smoothness.

  14. Halo-free Phase Contrast Microscopy

    PubMed Central

    Nguyen, Tan H.; Kandel, Mikhail; Shakir, Haadi M.; Best-Popescu, Catherine; Arikkath, Jyothi; Do, Minh N.; Popescu, Gabriel

    2017-01-01

    We present a new approach for retrieving halo-free phase contrast microscopy (hfPC) images by upgrading the conventional PC microscope with an external interferometric module, which generates sufficient data for reversing the halo artifact. Acquiring four independent intensity images, our approach first measures haloed phase maps of the sample. We solve for the halo-free sample transmission function by using a physical model of the image formation under partial spatial coherence. Using this halo-free sample transmission, we can numerically generate artifact-free PC images. Furthermore, this transmission can be further used to obtain quantitative information about the sample, e.g., the thickness with known refractive indices, dry mass of live cells during their cycles. We tested our hfPC method on various control samples, e.g., beads, pillars and validated its potential for biological investigation by imaging live HeLa cells, red blood cells, and neurons. PMID:28338086

  15. Concentrations of Simulated Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Child, Hillary

    2017-01-01

    We present the concentration-mass (c-M) relation of dark matter halos in two new high-volume high-resolution cosmological N-body simulations, Q Continuum and Outer Rim. Concentration describes the density of the central regions of halos; it is highest for low-mass halos at low redshift, decreasing at high mass and redshift. The shape of the c-M relation is an important probe of cosmology. We discuss the redshift dependence of the c-M relation, several different methods to determine concentrations of simulated halos, and potential sources of bias in concentration measurements. To connect to lensing observations, we stack halos, which also allows us to assess the suitability of the Navarro-Frenk-White profile and other profiles, such as Einasto, with an additional shape parameter. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1144082.

  16. Halo-free Phase Contrast Microscopy.

    PubMed

    Nguyen, Tan H; Kandel, Mikhail; Shakir, Haadi M; Best-Popescu, Catherine; Arikkath, Jyothi; Do, Minh N; Popescu, Gabriel

    2017-03-24

    We present a new approach for retrieving halo-free phase contrast microscopy (hfPC) images by upgrading the conventional PC microscope with an external interferometric module, which generates sufficient data for reversing the halo artifact. Acquiring four independent intensity images, our approach first measures haloed phase maps of the sample. We solve for the halo-free sample transmission function by using a physical model of the image formation under partial spatial coherence. Using this halo-free sample transmission, we can numerically generate artifact-free PC images. Furthermore, this transmission can be further used to obtain quantitative information about the sample, e.g., the thickness with known refractive indices, dry mass of live cells during their cycles. We tested our hfPC method on various control samples, e.g., beads, pillars and validated its potential for biological investigation by imaging live HeLa cells, red blood cells, and neurons.

  17. Halo-free Phase Contrast Microscopy

    NASA Astrophysics Data System (ADS)

    Nguyen, Tan H.; Kandel, Mikhail; Shakir, Haadi M.; Best-Popescu, Catherine; Arikkath, Jyothi; Do, Minh N.; Popescu, Gabriel

    2017-03-01

    We present a new approach for retrieving halo-free phase contrast microscopy (hfPC) images by upgrading the conventional PC microscope with an external interferometric module, which generates sufficient data for reversing the halo artifact. Acquiring four independent intensity images, our approach first measures haloed phase maps of the sample. We solve for the halo-free sample transmission function by using a physical model of the image formation under partial spatial coherence. Using this halo-free sample transmission, we can numerically generate artifact-free PC images. Furthermore, this transmission can be further used to obtain quantitative information about the sample, e.g., the thickness with known refractive indices, dry mass of live cells during their cycles. We tested our hfPC method on various control samples, e.g., beads, pillars and validated its potential for biological investigation by imaging live HeLa cells, red blood cells, and neurons.

  18. Extended hot-gas halos around starburst galaxies

    NASA Technical Reports Server (NTRS)

    Tomisaka, Kohji; Bregman, Joel N.

    1993-01-01

    A reanalysis of Einstein Imaging Proportional Counter (IPC) data and new observations from the Ginga Large Area (Proportional) counters (LAC) indicate the presence of extended X-ray emission (10-50 kpc) around the starburst galaxy M82. Here, we discuss our model of this emission, which was obtained by performing numerical hydrodynamic simulations of the starburst event to much later times and larger scales than were previously considered. For our models, we adopted a supernova rate of 0.1/yr, and an extended low-density static halo that is bound to the galaxy. There are three stages to the evolution of the wind-blown bubble and the propagation of the shock front: the bubble expands in an almost uniform density disk gas, with a deceleration of the shock front (t is less than or approximately 3.6 Myr); breakout from the disk and the upward acceleration of the shock front (3.6 Myr is less than or approximately t is less than or approximately 18 Myr); propagation into the halo, leading to a more spherical system and shock deceleration (18 Myr is less than or approximately t). For a halo density of 10(exp -3)/cu cm, the outflow reaches a distance of 40-50 kpc from the center of the starburst galaxy in 50 Myr. We calculated the time evolution of the X-ray luminosity and found that the extended starburst emits 3 x 10(exp 39) erg/s to 10(exp 40) in the Ginga LAC band and approximately 10(exp 41) erg/s in the Einstein band. The degree of the ionization equilibrium in the outflow and its effect on the iron K alpha line emission are discussed.

  19. Orbital anisotropy in cosmological haloes revisited

    NASA Astrophysics Data System (ADS)

    Wojtak, Radosław; Gottlöber, Stefan; Klypin, Anatoly

    2013-09-01

    The velocity anisotropy of particles inside dark matter (DM) haloes is an important physical quantity, which is required for the accurate modelling of mass profiles of galaxies and clusters of galaxies. It is typically measured using the ratio of the radial to tangential velocity dispersions at a given distance from the halo centre. However, this measure is insufficient to describe the dynamics of realistic haloes, which are not spherical and are typically quite elongated. Studying the velocity distribution in massive DM haloes in cosmological simulations, we find that in the inner parts of the haloes, the local velocity ellipsoids are strongly aligned with the major axis of the halo, the alignment being stronger for more relaxed haloes. In the outer regions of the haloes, the alignment becomes gradually weaker and the orientation is more random. These two distinct regions of different degree of the alignment coincide with two characteristic regimes of the DM density profile: a shallow inner cusp and a steep outer profile that are separated by a characteristic radius at which the density declines as ρ ∝ r-2. This alignment of the local velocity ellipsoids requires reinterpretation of features found in measurements based on the spherically averaged ratio of the radial to tangential velocity dispersions. In particular, we show that the velocity distribution in the central halo regions is highly anisotropic. For cluster-size haloes with mass 1014-1015 h-1 M⊙, the velocity anisotropy along the major axis is nearly independent of radius and is equal to β = 1 - σ ^2_perp/σ ^2_radial≈ 0.4, which is significantly larger than the previously estimated spherically averaged velocity anisotropy. The alignment of density and velocity anisotropies and the radial trends may also have some implications for the mass modelling based on kinematical data of objects such as galaxy clusters or dwarf spheroidals, where the orbital anisotropy is a key element in an unbiased mass

  20. Development of sprite streamers and preceding halos and elves

    NASA Astrophysics Data System (ADS)

    Sanmiya, Y.; Kobayashi, N.; Kudo, T.; Takahashi, Y.; Sato, M.; Shima, Y.; Yamada, T.; NHK Cosmic Shore Project; Stenbaek-Nielsen, H. C.; McHarg, M. G.; Kanmae, T.; Haaland, R.; Yair, Y.; Lyons, W. A.; Cummer, S. A.

    2012-04-01

    The relationship between diffuse glows such as elves and sprite halos and subsequent discrete structure of sprite streamers is considered to have a key to solve the generation mechanism of streamers. However, it's not easy to image at high frame rate both the diffuse and discrete structures simultaneously, since it requires high sensitivity, high spatial resolution and high signal-to-noise ratio. To capture the real spatial structure of TLEs without influence of atmospheric absorption, aircraft would be one of the best solutions. The aircraft can approach thunderstorm up to a few hundred km or less to image TLEs with high spatial resolution and can carry heavy high-speed cameras with huge size data memories. In the period of June 27 - July 10, 2011, a combined aircraft and ground-based campaign, in support of NHK Cosmic Shore project, was carried with two jet airplanes under collaboration between NHK, Japan Broadcasting Corporation, and universities. On 8 nights out of 16 standing-by, the jets took off from the airport near Denver, Colorado, and an airborne high speed camera captured over 40 TLE events at a frame rate of 8300 /sec. Here we introduce the latest analysis of a very complicated time development of sprite streamers and its relationship to the structures of preceding halos and elves, which are always showing some inhomogeneity, suggesting a mechanism to cause the large variation of sprite features.

  1. Ionized cluster beam deposition

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, A. R.

    1983-01-01

    Ionized Cluster Beam (ICB) deposition, a new technique originated by Takagi of Kyoto University in Japan, offers a number of unique capabilities for thin film metallization as well as for deposition of active semiconductor materials. ICB allows average energy per deposited atom to be controlled and involves impact kinetics which result in high diffusion energies of atoms on the growth surface. To a greater degree than in other techniques, ICB involves quantitative process parameters which can be utilized to strongly control the characteristics of films being deposited. In the ICB deposition process, material to be deposited is vaporized into a vacuum chamber from a confinement crucible at high temperature. Crucible nozzle configuration and operating temperature are such that emerging vapor undergoes supercondensation following adiabatic expansion through the nozzle.

  2. The Lyman-alpha glow of gas falling into the dark matter halo of a z = 3 galaxy.

    PubMed

    Weidinger, Michael; Møller, Palle; Fynbo, Johan Peter Uldall

    2004-08-26

    Quasars are the visible signatures of gas falling into the deep potential well of super-massive black holes in the centres of distant galaxies. It has been suggested that quasars are formed when two massive galaxies collide and merge, leading to the prediction that quasars should be found in the centres of regions of largest overdensity in the early Universe. In dark matter (DM)-dominated models of the early Universe, massive DM halos are predicted to attract the surrounding gas, which falls towards their centres. The neutral gas is not detectable in emission by itself, but gas falling into the ionizing cone of such a quasar will glow in the Lyman-alpha line of hydrogen, effectively imaging the DM halo. Here we present a Lyalpha image of a DM halo at redshift z = 3, along with a two-dimensional spectrum of the gaseous halo. Our observations are best understood in the context of the standard model for DM haloes; we infer a mass of (2 - 7) x 10(12) solar masses (M(\\circ)) for the halo.

  3. The impact of ionizing radiation on the formation of a supermassive star in the early Universe

    NASA Astrophysics Data System (ADS)

    Chon, Sunmyon; Latif, Muhammad A.

    2017-06-01

    A massive primordial halo near an intensely star-forming galaxy may collapse into a supermassive star (SMS) and leave a massive black hole seed of about 105 M⊙. To investigate the impact of ionizing radiation on the formation of an SMS from a nearby galaxy, we perform three-dimensional radiation hydrodynamical simulations by selecting a pair of massive dark matter haloes forming at z > 10. We find that rich structures such as clumps and filaments around the source galaxy shield the cloud from ionizing radiation. In fact, in some cases, cloud collapse is accelerated under ionizing radiation. This fact suggests that the ionization of the cloud's surroundings helps its collapse. Only strong radiation at the early stage of structure formation can halt the cloud collapse, but this is much stronger than observationally allowed value. We also explored the effect of ionizing radiation on a sample of 68 haloes by employing an analytical model and found that increase in the mean density of the gas between the SMS-forming cloud and the source galaxy protects the gas cloud from ionizing radiation as they approach each other. Thus, we conclude that ionizing radiation does not prevent the formation of an SMS in most of the cases.

  4. Testing the self-consistency of the excursion set approach to predicting the dark matter halo mass function.

    PubMed

    Achitouv, I; Rasera, Y; Sheth, R K; Corasaniti, P S

    2013-12-06

    The excursion set approach provides a framework for predicting how the abundance of dark matter halos depends on the initial conditions. A key ingredient of this formalism is the specification of a critical overdensity threshold (barrier) which protohalos must exceed if they are to form virialized halos at a later time. However, to make its predictions, the excursion set approach explicitly averages over all positions in the initial field, rather than the special ones around which halos form, so it is not clear that the barrier has physical motivation or meaning. In this Letter we show that once the statistical assumptions which underlie the excursion set approach are considered a drifting diffusing barrier model does provide a good self-consistent description both of halo abundance as well as of the initial overdensities of the protohalo patches.

  5. Ophthalmic halo reduced lenses design

    NASA Astrophysics Data System (ADS)

    Limon, Ofer; Zalevsky, Zeev

    2015-05-01

    The halo effect is a very problematic visual artifact occurring in extended depth of focus or multi-focal ophthalmic lenses such as e.g. intra-ocular (after cataract surgery) or contact lenses when used in dark illumination conditions. This artifact is generated due to surface structures added on top of those lenses in order to increase their depth of focus or to realize multiple focal lengths. In this paper we present novel solution that can resolve this major problem of ophthalmic lenses. The proposed solution involves modification to the surface structure that realizes the extended depth of focus. Our solution is fabricated and numerically and experimentally validated also in preliminary in-vivo trials.

  6. NUBEAM developments and 3d halo modeling

    NASA Astrophysics Data System (ADS)

    Gorelenkova, M. V.; Medley, S. S.; Kaye, S. M.

    2012-10-01

    Recent developments related to the 3D halo model in NUBEAM code are described. To have a reliable halo neutral source for diagnostic simulation, the TRANSP/NUBEAM code has been enhanced with full implementation of ADAS atomic physic ground state and excited state data for hydrogenic beams and mixed species plasma targets. The ADAS codes and database provide the density and temperature dependence of the atomic data, and the collective nature of the state excitation process. To be able to populate 3D halo output with sufficient statistical resolution, the capability to control the statistics of fast ion CX modeling and for thermal halo launch has been added to NUBEAM. The 3D halo neutral model is based on modification and extension of the ``beam in box'' aligned 3d Cartesian grid that includes the neutral beam itself, 3D fast neutral densities due to CX of partially slowed down fast ions in the beam halo region, 3D thermal neutral densities due to CX deposition and fast neutral recapture source. More details on the 3D halo simulation design will be presented.

  7. Halo assembly bias from Separate Universe simulations

    NASA Astrophysics Data System (ADS)

    Paranjape, Aseem; Padmanabhan, Nikhil

    2017-07-01

    We present a calibration of halo assembly bias using the Separate Universe technique. Specifically, we measure the response of halo abundances at fixed mass and concentration to the presence of an infinite-wavelength initial perturbation. We develop an analytical framework for describing the concentration dependence of this peak-background split halo bias - a measure of assembly bias - relying on the near-lognormal distribution of halo concentration at fixed halo mass. The combination of this analytical framework and the Separate Universe technique allows us to achieve very high precision in the calibration of the linear assembly bias b1, and qualitatively reproduces known trends such as the monotonic decrease (increase) of b1 with halo concentration at large (small) masses. The same framework extends to the concentration dependence of higher order bias parameters bn, and we present the first calibration of assembly bias in b2. Our calibrations are directly applicable in analytical Halo Model calculations that seek to robustly detect galaxy assembly bias in observational samples. We detect a non-universality in the b1-b2 relation arising from assembly bias, and suggest that simultaneous measurements of these bias parameters could be used to both detect the signature of assembly bias as well as mitigate its effects in cosmological analyses.

  8. Dark matter haloes: a multistream view

    NASA Astrophysics Data System (ADS)

    Ramachandra, Nesar S.; Shandarin, Sergei F.

    2017-09-01

    Mysterious dark matter constitutes about 85 per cent of all masses in the Universe. Clustering of dark matter plays a dominant role in the formation of all observed structures on scales from a fraction to a few hundreds of Mega-parsecs. Galaxies play a role of lights illuminating these structures so they can be observed. The observations in the last several decades have unveiled opulent geometry of these structures currently known as the cosmic web. Haloes are the highest concentrations of dark matter and host luminous galaxies. Currently the most accurate modelling of dark matter haloes is achieved in cosmological N-body simulations. Identifying the haloes from the distribution of particles in N-body simulations is one of the problems attracting both considerable interest and efforts. We propose a novel framework for detecting potential dark matter haloes using the field unique for dark matter-multistream field. The multistream field emerges at the non-linear stage of the growth of perturbations because the dark matter is collisionless. Counting the number of velocity streams in gravitational collapses supplements our knowledge of spatial clustering. We assume that the virialized haloes have convex boundaries. Closed and convex regions of the multistream field are hence isolated by imposing a positivity condition on all three eigenvalues of the Hessian estimated on the smoothed multistream field. In a single-scale analysis of high multistream field resolution and low softening length, the halo substructures with local multistream maxima are isolated as individual halo sites.

  9. Anisotropic halo model: implementation and numerical results

    NASA Astrophysics Data System (ADS)

    Sgró, Mario A.; Paz, Dante J.; Merchán, Manuel

    2013-07-01

    In the present work, we extend the classic halo model for the large-scale matter distribution including a triaxial model for the halo profiles and their alignments. In particular, we derive general expressions for the halo-matter cross-correlation function. In addition, by numerical integration, we obtain instances of the cross-correlation function depending on the directions given by halo shape axes. These functions are called anisotropic cross-correlations. With the aim of comparing our theoretical results with the simulations, we compute averaged anisotropic correlations in cones with their symmetry axis along each shape direction of the centre halo. From these comparisons we characterize and quantify the alignment of dark matter haloes on the Λcold dark matter context by means of the presented anisotropic halo model. Since our model requires multidimensional integral computation we implement a Monte Carlo method on GPU hardware which allows us to increase the precision of the results and it improves the performance of the computation.

  10. Halo bias in mixed dark matter cosmologies

    NASA Astrophysics Data System (ADS)

    LoVerde, Marilena

    2014-10-01

    The large-scale distribution of cold dark matter halos is generally assumed to trace the large-scale distribution of matter. In a universe with multiple types of matter fluctuations, as is the case with massive neutrinos, the relation between the halo field and the matter fluctuations may be more complicated. We develop a method for calculating the linear bias factor relating fluctuations in the halo number density to fluctuations in the mass density in the presence of multiple fluctuating components of the energy density. In the presence of massive neutrinos we find a small but pronounced feature in the halo bias near the neutrino free-streaming scale. The neutrino feature is a small step with amplitude that increases with halo mass and neutrino mass density. The scale-dependent halo bias lessens the suppression of the small-scale halo power spectrum and should therefore weaken constraints on neutrino mass from the galaxy autopower spectrum and correlation function. On the other hand, the feature in the bias is itself a novel signature of massive neutrinos that can be studied independently.

  11. Population Gradients in Stellar Halos from GHOSTS

    NASA Astrophysics Data System (ADS)

    Bailin, Jeremy; Monachesi, Antonela; Bell, Eric F.; de Jong, Roelof S.; Ghosts Survey

    2015-01-01

    We report on recent results from the Galaxy Halos, Outer disks, Substructure, Thick disks, and Star clusters (GHOSTS) survey, an HST ACS+WFC3 imaging survey to study stellar populations in and around 16 nearby spiral galaxies. By using HST resolution to resolve the stellar halos into individual red giant branch (RGB) stars, we are able to detect distinct stellar populations at several points throughout the halo of the half dozen massive highly-inclined galaxies in the sample. In approximately half of these galaxies, we detect a gradient in the color of the RGB; which we interpret as a metallicity gradient. Stellar halo formation models predict a wide variety of metallicity gradients: those in which the halos are dominated by stars formed in situ predict stronger gradients than we observe, while accretion-dominated halo models predict weaker or nonexistent gradients. Our measurements therefore provide a useful discriminator between stellar halo models, and at first look appear most consistent with the accretion-based model of Cooper et al. (2010).

  12. Angular momentum properties of haloes and their baryon content in the Illustris simulation

    NASA Astrophysics Data System (ADS)

    Zjupa, Jolanta; Springel, Volker

    2017-04-01

    The angular momentum properties of virialized dark matter haloes have been measured with good statistics in collisionless N-body simulations, but an equally accurate analysis of the baryonic spin is still missing. We employ the Illustris simulation suite, one of the first simulations of galaxy formation with full hydrodynamics that produces a realistic galaxy population in a sizeable volume, to quantify the baryonic spin properties for more than ∼320 000 haloes. We first compare the systematic differences between different spin parameter and halo definitions, and the impact of sample selection criteria on the derived properties. We confirm that dark-matter-only haloes exhibit a close to self-similar spin distribution in mass and redshift of lognormal form. However, the physics of galaxy formation radically changes the baryonic spin distribution. While the dark matter component remains largely unaffected, strong trends with mass and redshift appear for the spin of diffuse gas and the formed stellar component. With time, the baryons staying bound to the halo develop a misalignment of their spin vector with respect to dark matter, and increase their specific angular momentum by a factor of ∼1.3 in the non-radiative case and ∼1.8 in the full physics setup at z = 0. We show that this enhancement in baryonic spin can be explained by the combined effect of specific angular momentum transfer from dark matter on to gas during mergers and from feedback expelling low specific angular momentum gas from the halo. Our results challenge certain models for spin evolution and underline the significant changes induced by baryonic physics in the structure of haloes.

  13. A DISTANT RADIO MINI-HALO IN THE PHOENIX GALAXY CLUSTER

    SciTech Connect

    Van Weeren, R. J.; Andrade-Santos, F.; Forman, W. R.; Jones, C.; Intema, H. T.; Lal, D. V.; Brüggen, M.; De Gasperin, F.; Hoeft, M.; Nuza, S. E.; Röttgering, H. J. A.; Stroe, A.

    2014-05-10

    We report the discovery of extended radio emission in the Phoenix cluster (SPT-CL J2344-4243, z = 0.596) with the Giant Metrewave Radio Telescope (GMRT) at 610 MHz. The diffuse emission extends over a region of at least 400-500 kpc and surrounds the central radio source of the Brightest Cluster Galaxy, but does not appear to be directly associated with it. We classify the diffuse emission as a radio mini-halo, making it the currently most distant mini-halo known. Radio mini-halos have been explained by synchrotron emitting particles re-accelerated via turbulence, possibly induced by gas sloshing generated from a minor merger event. Chandra observations show a non-concentric X-ray surface brightness distribution, which is consistent with this sloshing interpretation. The mini-halo has a flux density of 17 ± 5 mJy, resulting in a 1.4 GHz radio power of (10.4 ± 3.5) × 10{sup 24} W Hz{sup –1}. The combined cluster emission, which includes the central compact radio source, is also detected in a shallow GMRT 156 MHz observation and together with the 610 MHz data we compute a spectral index of –0.84 ± 0.12 for the overall cluster radio emission. Given that mini-halos typically have steeper radio spectra than cluster radio galaxies, this spectral index should be taken as an upper limit for the mini-halo.

  14. THE DUAL ORIGIN OF STELLAR HALOS

    SciTech Connect

    Zolotov, Adi; Hogg, David W.; Willman, Beth; Brooks, Alyson M.; Brook, Chris B.; Stinson, Greg E-mail: bwillman@haverford.edu

    2009-09-10

    We investigate the formation of the stellar halos of four simulated disk galaxies using high-resolution, cosmological SPH + N-body simulations. These simulations include a self-consistent treatment of all the major physical processes involved in galaxy formation. The simulated galaxies presented here each have a total mass of {approx}10{sup 12} M{sub sun}, but span a range of merger histories. These simulations allow us to study the competing importance of in situ star formation (stars formed in the primary galaxy) and accretion of stars from subhalos in the building of stellar halos in a {lambda}CDM universe. All four simulated galaxies are surrounded by a stellar halo, whose inner regions (r < 20 kpc) contain both accreted stars, and an in situ stellar population. The outer regions of the galaxies' halos were assembled through pure accretion and disruption of satellites. Most of the in situ halo stars formed at high redshift out of smoothly accreted cold gas in the inner 1 kpc of the galaxies' potential wells, possibly as part of their primordial disks. These stars were displaced from their central locations into the halos through a succession of major mergers. We find that the two galaxies with recently quiescent merger histories have a higher fraction of in situ stars ({approx}20%-50%) in their inner halos than the two galaxies with many recent mergers ({approx}5%-10% in situ fraction). Observational studies concentrating on stellar populations in the inner halo of the Milky Way will be the most affected by the presence of in situ stars with halo kinematics, as we find that their existence in the inner few tens of kpc is a generic feature of galaxy formation.

  15. The Dual Origin of Galactic Stellar Halos

    NASA Astrophysics Data System (ADS)

    Zolotov, Adi

    2011-01-01

    Accreted stellar halos are a natural consequence of galaxy formation in a Lambda-CDM Universe, and contain unique fossil records of hierarchical galaxy formation. The properties of local Milky Way halo stars, however, suggest that the Galaxy's halo is composed of at least two distinct stellar populations, each exhibiting different spatial distributions, orbits, and metallicities. This observed dichotomy is the result of the assembly history of the halo, which likely formed through a process more complex than pure hierarchical accretions. In this talk I will describe the formation of stellar halos surrounding Milky Way-massed disk galaxies simulated using high-resolution cosmological Smooth Particle Hydrodynamics + N-Body simulations. We find that two competing physical processes - accretion of dwarf galaxies and in situ star formation - contribute to the formation of every stellar halo. While the outer regions (r > 20 kpc) of the halos were assembled solely through the accretion and disruption of satellites, in situ star formation supplements accretion in the formation of inner halos. The relative contribution of each stellar population to a halo is shown to be a function of a galaxy's merging history. Galaxies with recent mergers, like M31, will host relatively few in situ stars, while galaxies with more quiescent recent histories, like the Milky Way, will likely have a larger population of such stars. We show how the chemical abundance trends ([Fe/H] vs. [alpha/Fe]) of accreted and in situ stars diverge at the high [Fe/H] end of the metallicity distribution function, and discuss how such trends can be used to study and identify the observable imprints of the Milky Way's formation history.

  16. Effective field theory description of halo nuclei

    NASA Astrophysics Data System (ADS)

    Hammer, H.-W.; Ji, C.; Phillips, D. R.

    2017-10-01

    Nuclear halos emerge as new degrees of freedom near the neutron and proton driplines. They consist of a core and one or a few nucleons which spend most of their time in the classically-forbidden region outside the range of the interaction. Individual nucleons inside the core are thus unresolved in the halo configuration, and the low-energy effective interactions are short-range forces between the core and the valence nucleons. Similar phenomena occur in clusters of 4He atoms, cold atomic gases near a Feshbach resonance, and some exotic hadrons. In these weakly-bound quantum systems universal scaling laws for s-wave binding emerge that are independent of the details of the interaction. Effective field theory (EFT) exposes these correlations and permits the calculation of non-universal corrections to them due to short-distance effects, as well as the extension of these ideas to systems involving the Coulomb interaction and/or binding in higher angular-momentum channels. Halo nuclei exhibit all these features. Halo EFT, the EFT for halo nuclei, has been used to compute the properties of single-neutron, two-neutron, and single-proton halos of s-wave and p-wave type. This review summarizes these results for halo binding energies, radii, Coulomb dissociation, and radiative capture, as well as the connection of these properties to scattering parameters, thereby elucidating the universal correlations between all these observables. We also discuss how Halo EFT's encoding of the long-distance physics of halo nuclei can be used to check and extend ab initio calculations that include detailed modeling of their short-distance dynamics.

  17. COSMIC VORTICITY AND THE ORIGIN HALO SPINS

    SciTech Connect

    Libeskind, Noam I.; Steinmetz, Matthias; Gottloeber, Stefan; Hess, Steffen; Hoffman, Yehuda; Knebe, Alexander

    2013-04-01

    In the standard model of cosmology, structure emerges out of a non-rotational flow and the angular momentum of collapsing halos is induced by tidal torques. The growth of angular momentum in the linear and quasi-linear phases is associated with a shear, curl-free, flow and it is well described within the linear framework of tidal torque theory (TTT). However, TTT ceases to be applicable as halos approach turnaround when their ambient flow field becomes rotational. Subsequently, halos become embedded in a vortical flow field and the growth of their angular momentum is affected by the vorticity of their ambient velocity field. Using a cosmological simulation, we have examined the importance of the curl of the velocity field in determining halo spin, finding a significant alignment between the two: the vorticity tends to be perpendicular to the axis of the fastest collapse of the velocity shear tensor (e{sub 1}). This is independent of halo masses and cosmic web environment. Our results agree with previous findings on the tendency of halo spin to be perpendicular to e{sub 1}, and of the spin of (simulated) halos and (observed) galaxies to be aligned with the large-scale structure. It follows that angular momentum growth proceeds in two distinct phases. First, the angular momentum emerges out of a shear, curl-free, potential flow, as described by TTT. In the second phase, in which halos approach virialization, the angular momentum emerges out of a vortical flow and halo spin becomes partially aligned with the vorticity of the ambient flow field.

  18. Re-ionization and decaying dark matter

    NASA Technical Reports Server (NTRS)

    Dodelson, Scott; Jubas, Jay M.

    1991-01-01

    Gunn-Peterson tests suggest that the Universe was reionized after the standard recombination epoch. A systematic treatment is presented of the ionization process by deriving the Boltzmann equations appropriate to this regime. A compact solution for the photon spectrum is found in terms of the ionization ratio. These equations are then solved numerically for the Decaying Dark Matter scenario, wherein neutrinos with mass of order 30 eV radiatively decay producing photons which ionize the intergalactic medium. It was found that the neutrino mass and lifetime are severely constrained by Gunn-Peterson tests, observations of the diffuse photon spectrum in the ultraviolet regime, and the Hubble parameter.

  19. The statistics of Λ CDM halo concentrations

    NASA Astrophysics Data System (ADS)

    Neto, Angelo F.; Gao, Liang; Bett, Philip; Cole, Shaun; Navarro, Julio F.; Frenk, Carlos S.; White, Simon D. M.; Springel, Volker; Jenkins, Adrian

    2007-11-01

    We use the Millennium Simulation (MS) to study the statistics of Λ cold dark matter (ΛCDM) halo concentrations at z = 0. Our results confirm that the average halo concentration declines monotonically with mass; the concentration-mass relation is well fitted by a power law over three decades in mass, up to the most massive objects that form in a ΛCDM universe (~ 1015h-1Msolar). This is in clear disagreement with the predictions of the model proposed by Bullock et al. for these rare objects, and agrees better with the original predictions of Navarro, Frenk & White. The large volume surveyed, together with the unprecedented numerical resolution of the MS, allows us to estimate with confidence the distribution of concentrations and, consequently, the abundance of systems with unusual properties. About one in a hundred cluster haloes (M200 >~ 3 × 1014h-1Msolar) have concentrations exceeding c200 = 7.5, a result that may be useful in interpreting the likelihood of unusually strong massive gravitational lenses, such as Abell 1689, in the ΛCDM cosmogony. A similar fraction of about 1 per cent of galaxy-sized haloes (M200 ~ 1012h-1Msolar) have c200 < 4.5 and this could be relevant to models that attempt to reconcile the ΛCDM cosmology with rotation curves of low surface brightness galaxies by appealing to haloes of unexpectedly low concentration. We find that halo concentrations are independent of spin once haloes manifestly out of equilibrium have been removed from the sample. Compared to their relaxed brethren, the concentrations of out-of-equilibrium haloes tend to be lower and have more scatter, while their spins tend to be higher. A number of previously noted trends within the halo population are induced primarily by these properties of unrelaxed systems. Finally, we compare the result of predicting halo concentrations using the mass assembly history of the main progenitor with predictions based on simple arguments regarding the assembly time of all progenitors

  20. Halo Mergers in Phase-space

    NASA Astrophysics Data System (ADS)

    Taylor, J. E.

    I consider a very simple model for the evolution of the real space and phase-space density profiles of a dark matter halo as it acquires its mass. I show that this model, which assumes slow growth through gradual accretion, predicts structures much more concentrated than those found in self-consistent simulations of halo formation. By implication, major mergers must act to reduce the concentration of dark matter haloes, adding the orbital energy of the infalling satellite to the internal energy of the pre-existing system and causing it to expand at intermediate radii. This effect should be easy to detect in numerical simulations.

  1. Haloes around the Moon and the Sun

    NASA Astrophysics Data System (ADS)

    Gaina, Alex; Gaina, Danielle A.

    2008-10-01

    The authors observations of the Haloes around the Moon and the Sun during few last years are reported. A Historical review of the phenomenon is given since the observations by Benvenuto Cellini and Gaston Tissandier is given. A photograph (from eight available) of the Halo around the Sun observed in Chisinau on 21 May 2007 is included. The Halo from 21 May 2007 occured after a very fast increasing of the air temperature during one day by more than 15 Deg. The authors consider, that the phenomenon is due to scattering of light on Cirri clouds(7 km altitude), present on the sky during that day. They formed due to very fast heating.

  2. EFFECTS OF HOT HALO GAS ON STAR FORMATION AND MASS TRANSFER DURING DISTANT GALAXY–GALAXY ENCOUNTERS

    SciTech Connect

    Hwang, Jeong-Sun; Park, Changbom E-mail: cbp@kias.re.kr

    2015-06-01

    We use N-body/smoothed particle hydrodynamics simulations of encounters between an early-type galaxy (ETG) and a late-type galaxy (LTG) to study the effects of hot halo gas on the evolution for a case with the mass ratio of the ETG to LTG of 2:1 and the closest approach distance of ∼100 kpc. We find that the dynamics of the cold disk gas in the tidal bridge and the amount of the newly formed stars depend strongly on the existence of a gas halo. In the run of interacting galaxies not having a hot gas halo, the gas and stars accreted into the ETG do not include newly formed stars. However, in the run using the ETG with a gas halo and the LTG without a gas halo, a shock forms along the disk gas tidal bridge and induces star formation near the closest approach. The shock front is parallel to a channel along which the cold gas flows toward the center of the ETG. As a result, the ETG can accrete star-forming cold gas and newly born stars at and near its center. When both galaxies have hot gas halos, a shock is formed between the two gas halos somewhat before the closest approach. The shock hinders the growth of the cold gas bridge to the ETG and also ionizes it. Only some of the disk stars transfer through the stellar bridge. We conclude that the hot halo gas can give significant hydrodynamic effects during distant encounters.

  3. The diagnostic value of halo and reversed halo signs for invasive mold infections in compromised hosts.

    PubMed

    Georgiadou, Sarah P; Sipsas, Nikolaos V; Marom, Edith M; Kontoyiannis, Dimitrios P

    2011-05-01

    The halo sign is a CT finding of ground-glass opacity surrounding a pulmonary nodule or mass. The reversed halo sign is a focal rounded area of ground-glass opacity surrounded by a crescent or complete ring of consolidation. In severely immunocompromised patients, these signs are highly suggestive of early infection by an angioinvasive fungus. The halo sign and reversed halo sign are most commonly associated with invasive pulmonary aspergillosis and pulmonary mucormycosis, respectively. Many other infections and noninfectious conditions, such as neoplastic and inflammatory processes, may also manifest with pulmonary nodules associated with either sign. Although nonspecific, both signs can be useful for preemptive initiation of antifungal therapy in the appropriate clinical setting. This review aims to evaluate the diagnostic value of the halo sign and reversed halo sign in immunocompromised hosts and describes the wide spectrum of diseases associated with them.

  4. The Diagnostic Value of Halo and Reversed Halo Signs for Invasive Mold Infections in Compromised Hosts

    PubMed Central

    Georgiadou, Sarah P.; Sipsas, Nikolaos V.; Marom, Edith M.

    2011-01-01

    The halo sign is a CT finding of ground-glass opacity surrounding a pulmonary nodule or mass. The reversed halo sign is a focal rounded area of ground-glass opacity surrounded by a crescent or complete ring of consolidation. In severely immunocompromised patients, these signs are highly suggestive of early infection by an angioinvasive fungus. The halo sign and reversed halo sign are most commonly associated with invasive pulmonary aspergillosis and pulmonary mucormycosis, respectively. Many other infections and noninfectious conditions, such as neoplastic and inflammatory processes, may also manifest with pulmonary nodules associated with either sign. Although nonspecific, both signs can be useful for preemptive initiation of antifungal therapy in the appropriate clinical setting. This review aims to evaluate the diagnostic value of the halo sign and reversed halo sign in immunocompromised hosts and describes the wide spectrum of diseases associated with them. PMID:21467021

  5. Mechanism of branching in negative ionization fronts.

    PubMed

    Arrayás, Manuel; Fontelos, Marco A; Trueba, José L

    2005-10-14

    When a strong electric field is applied to nonconducting matter, narrow channels of plasma called streamers may form. Branchlike patterns of streamers have been observed in anode directed discharges. We explain a mechanism for branching as the result of a balance between the destabilizing effect of impact ionization and the stabilizing effect of electron diffusion on ionization fronts. The dispersion relation for transversal perturbation of a planar negative front is obtained analytically when the ratio D between the electron diffusion coefficient and the intensity of the externally imposed electric field is small. We estimate the spacing lambda between streamers and deduce a scaling law lambda approximately D(1/3).

  6. Modelling the Formation of HI Clouds in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    de Avillez, M. A.; Mac Low, M.-M.

    2001-05-01

    Large scale modelling of the cycle of gas between the disk and the halo has been carried out with a 3D adaptive mesh refinement code. The model includes a gravitational field provided by the stars in the disk, an ideal-gas equation of state, and an approximation for the cooling curve, assuming collisional ionization equilibrium. Supernovae are set up at the beginning of their Sedov phases at a rate compatible with observations. Sixty percent of the SNe are set up within associations and the rest are set up at random sites. After a transient startup period of roughly 200 Myr, dynamical balance between upward and downward flowing gas is reached. Gas at the disk-halo interface (z ~ 1.5 kpc) flows into the halo in a turbulent convective flow at a rate of ~ 6 Msun yr-1, forming a large scale fountain. Ascending gas cools into clouds, with a large range of velocities, which we identify with observed H i clouds. These in turn rain down upon the disk. The descending clouds interact with the thick gas disk and eventually impact onto the thin disk leading to its deformation and disruption. The sizes of the clouds vary from a few pc to several tens of pc and their distribution in the halo varies with z. Intermediate velocity clouds (IVCs) are mainly distributed between z=0.8 and 4.2 kpc, whereas a large fraction of high velocity clouds (HVCs) are found at greater heights. On average 55-60% of the clouds have negative velocities. During a period of 50 Myr, approximately 18% of the total number of clouds have velocities between -90 and -160 km/s, whereas only ~ 3% of the clouds have vz<-160 km/s. The bulk of the HI clouds detected in the simulations have intermediate positive (40 to 90 km/s) and negative (-40 to -90 km/s) velocities. The former constitutes ~20% and the latter constitutes 25-27% of the total number of HI clouds detected. Most of the clouds show a multiphase structure with a core of cold gas, having temperatures of some 103 K, embedded in a warmer phase. M

  7. The COS-Halos survey: physical conditions and baryonic mass in the low-redshift circumgalactic medium

    SciTech Connect

    Werk, Jessica K.; Prochaska, J. Xavier; Tejos, Nicolas; Tripp, Todd M.; Katz, Neal; Lehner, Nicolas; O'Meara, John M.; Ford, Amanda Brady; Oppenheimer, Benjamin D.; Davé, Romeel; Weinberg, David H.

    2014-09-01

    We analyze the physical conditions of the cool, photoionized (T ∼10{sup 4} K) circumgalactic medium (CGM) using the COS-Halos suite of gas column density measurements for 44 gaseous halos within 160 kpc of L ∼ L* galaxies at z ∼ 0.2. These data are well described by simple photoionization models, with the gas highly ionized (n {sub H} {sub II}/n {sub H} ≳ 99%) by the extragalactic ultraviolet background. Scaling by estimates for the virial radius, R {sub vir}, we show that the ionization state (tracked by the dimensionless ionization parameter, U) increases with distance from the host galaxy. The ionization parameters imply a decreasing volume density profile n {sub H} = (10{sup –4.2±0.25})(R/R {sub vir}){sup –0.8±0.3}. Our derived gas volume densities are several orders of magnitude lower than predictions from standard two-phase models with a cool medium in pressure equilibrium with a hot, coronal medium expected in virialized halos at this mass scale. Applying the ionization corrections to the H I column densities, we estimate a lower limit to the cool gas mass M{sub CGM}{sup cool}>6.5×10{sup 10} M {sub ☉} for the volume within R < R {sub vir}. Allowing for an additional warm-hot, O VI-traced phase, the CGM accounts for at least half of the baryons purported to be missing from dark matter halos at the 10{sup 12} M {sub ☉} scale.

  8. Cosmic Ray Propagation through the Magnetic Fields of the Galaxy with Extended Halo

    NASA Technical Reports Server (NTRS)

    Zhang, Ming

    2005-01-01

    In this project we perform theoretical studies of 3-dimensional cosmic ray propagation in magnetic field configurations of the Galaxy with an extended halo. We employ our newly developed Markov stochastic process methods to solve the diffusive cosmic ray transport equation. We seek to understand observations of cosmic ray spectra, composition under the constraints of the observations of diffuse gamma ray and radio emission from the Galaxy. The model parameters are directly are related to properties of our Galaxy, such as the size of the Galactic halo, particle transport in Galactic magnetic fields, distribution of interstellar gas, primary cosmic ray source distribution and their confinement in the Galaxy. The core of this investigation is the development of software for cosmic ray propagation models with the Markov stochastic process approach. Values of important model parameters for the halo diffusion model are examined in comparison with observations of cosmic ray spectra, composition and the diffuse gamma-ray background. This report summarizes our achievement in the grant period at the Florida Institute of Technology. Work at the co-investigator's institution, the University of New Hampshire, under a companion grant, will be covered in detail by a separate report.

  9. Charge form factors of two-neutron halo nuclei in halo EFT

    NASA Astrophysics Data System (ADS)

    Hagen, P.; Hammer, H.-W.; Platter, L.

    2013-09-01

    We set up a formalism to calculate the charge form factors of two-neutron halo nuclei with S -wave neutron-core interactions in the framework of the halo effective field theory. The method is applied to some known and suspected halo nuclei. In particular, we calculate the form factors and charge radii relative to the core to leading order in the halo EFT and compare to experiments where they are available. Moreover, we investigate the general dependence of the charge radius on the core mass and the one- and two-neutron separation energies.

  10. Changes in interstellar atomic abundances from the galactic plane to the halo

    NASA Technical Reports Server (NTRS)

    Jenkins, E. B.

    1982-01-01

    A few, specially selected interstellar absorption lines were measured in the high resolution, far ultraviolet spectra of 200 O and B type stars observed by the International Ultraviolet Explorer (IUE). For lines of sight extending beyond about 500 pc from the galactic plane, the abundance of singly ionized iron atoms increases relative to singly ionized sulfur. However, the relative abundances of singly ionized sulfur, silicon and aluminum do not seem to change appreciably. An explanation for the apparent increase of iron is the partial sputtering of material off the surfaces of dust grains by interstellar shocks. Another possibility might be that the ejecta from type I supernovae enrich the low density medium in the halo with iron.

  11. The galactic halo question: New size constraints from galactic gamma-ray data

    NASA Technical Reports Server (NTRS)

    Stecker, F. W.; Jones, F. C.

    1977-01-01

    The SAS-2 gamma-ray data is analyzed making use of recent CO line emission and other data for determining the large-scale distribution of galactic gas. A nonuniform distribution of cosmic rays in the galaxy is implied. This fact rules out large trapping halo models and extragalactic origin models. Detailed models of diffusion halos of various sizes perpendicular to the galactic plane are considered. In such models, the scale perpendicular to the plane has a strong effect in determining the radial distribution of cosmic rays. Such radial distributions are calculated for cylindrical coordinate models. The implied gamma-ray longitude distributions are then calculated and compared with the SAS-2 data for goodness-of-fit. Assuming the sources to be supernova remnants or pulsars, cosmic ray nucleon halo models with scale heights greater than 3 kpc are found to provide a poor fit to the gamma-ray longitude data (probability of 6% or less). Thin halo, or source dominated diffusion models are found to provide a good fit to the gamma-ray data, with an upper limit scale height of approximately 3 kpc.

  12. Detection of possible intervening Mg X associated with A hot gaseous galaxy halo

    NASA Astrophysics Data System (ADS)

    Qu, Zhijie; Bregman, Joel N.

    2017-08-01

    Galaxies may store a significant fraction of baryonic material in their hot halos, which can be traced by high ionization absorption systems in spectra of background QSOs. A hot halo of an L* galaxy has a virial temperature ~ 10^6 K, corresponding to the peak ionization fraction for Mg X. We discovered a Mg X absorption system, in the sightline towards LBQS 1435-0134, which also contains Ne VIII, Ne VI, O VI, Ne V, O V, Ne IV, O IV, N IV, O III, and H I. Further modeling shows that the highest ionization state ions, Mg X and Ne VIII, cannot be produced by the photoionization model. A collisional ionization model can reproduce the observations, and all of the ions can be accommodated in a three- temperature plasma or one gas with a power-law temperature distribution, dN / dT = 10^(4.4 +- 2.2 - [Z/X]) T^(1.55 +- 0.41) (for 10^(4.39 +- 0.13) K < T < 10^(6.04+-0.05) K). In the power-law temperature model, the total hydrogen column density is 8.2 * 10^19(0.3 Zsun/Z), and most of the gaseous mass is in the hot phase with the postive power index. The modeling results show that the gas is consistent with a hot volume-filled gaseous galaxy halo (N(H) <~ 10^20 cm^-2 and T ~ 10^6 K), which contains a baryonic mass that may be comparable or greater than the stellar mass (~10^11Msun assuming n200).

  13. A Halo Model Approach to the 21 cm and Lyα Cross-correlation

    NASA Astrophysics Data System (ADS)

    Feng, Chang; Cooray, Asantha; Keating, Brian

    2017-09-01

    We present a halo-model-based approach to calculate the cross-correlation between 21 {cm} H i intensity fluctuations and {Ly}α emitters (LAE) during the epoch of reionization (EoR). Ionizing radiation around dark matter halos are modeled as bubbles with the size and growth determined based on the reionization photon production, among other physical parameters. The cross-correlation shows a clear negative-to-positive transition, associated with transition from ionized to neutral hydrogen in the intergalactic medium during EoR. The cross-correlation is subject to several foreground contaminants, including foreground radio point sources important for 21 {cm} experiments and low-z interloper emission lines, such as {{H}}α , O iii, and O ii, for {Ly}α experiments. Our calculations show that by masking out high fluxes in the {Ly}α measurement, the correlated foreground contamination on the 21 {cm}–{Ly}α cross-correlation can be dramatically reduced. We forecast the detectability of 21 {cm}–{Ly}α cross-correlation at different redshifts and adopt a Fisher matrix approach to estimate uncertainties on the key EoR parameters that have not been well constrained by other observations of reionization. This halo-model-based approach enables us to explore the EoR parameter space rapidly for different 21 {cm} and {Ly}α experiments.

  14. Why are so many primitive stars observed in the Galaxy halo

    NASA Astrophysics Data System (ADS)

    Gibson, Carl H.; Nieuwenhuizen, Theo M.; Schild, Rudolph E.

    2013-03-01

    Small values of lithium observed in a small, primitive, Galaxy-Halo star SDSS J102915 + 172927 cannot be explained using the standard cold dark matter CDM theory of star formation, but are easily understood using the Gibson/Schild 1996 hydrogravitational- dynamics (HGD) theory. From HGD, primordial H-4He gas fragments into Earth-mass planets in trillion-planet proto-globular-star-cluster (PGC) clumps at the 300 Kyr time of transition from the plasma epoch, soon after the big bang. The first HGD stars formed from pristine, frictionally-merging, gas-planets within the gently stressed clumps of the early universe, burning most available lithium in brown-dwarfs and hot-stars before creating metals that permit cooler burning. The Caffau halo star is a present day example. CDM first stars (Population III) were massive and promptly exploded, re- ionizing the gas of the universe and seeding it with metals, thus making the observed star unexplainable. From HGD, CDM and its massive first stars, and re-ionization by Pop III supernovae, never happened. All stars are formed from planets in primordial clumps. HGD first stars (Pop III) were small and long-lived, and the largest ones were hot. We suggest such small HGD (Pop III) stars still form in the gently stressed Galaxy halo.

  15. Dark matter particles in the galactic halo

    SciTech Connect

    Bernabei, R. Belli, P.; Montecchia, F.; Nozzoli, F.; Cappella, F.; D'Angelo, A.; Incicchitti, A.; Prosperi, D.; Cerulli, R.; Dai, C. J.; He, H. L.; Kuang, H. H.; Ma, J. M.; Sheng, X. D.; Ye, Z. P.

    2009-12-15

    Arguments on the investigation of the DarkMatter particles in the galactic halo are addressed. Recent results obtained by exploiting the annual modulation signature are summarized and the perspectives are discussed.

  16. Studying stellar halos with future facilities

    NASA Astrophysics Data System (ADS)

    Greggio, Laura; Falomo, Renato; Uslenghi, Michela

    2016-08-01

    Stellar halos around galaxies retain fundamental evidence of the processes which lead to their build up. Sophisticated models of galaxy formation in a cosmological context yield quantitative predictions about various observable characteristics, including the amount of substructure, the slope of radial mass profiles and three dimensional shapes, and the properties of the stellar populations in the halos. The comparison of such models with the observations provides constraints on the general picture of galaxy formation in the hierarchical Universe, as well as on the physical processes taking place in the halos formation. With the current observing facilities, stellar halos can be effectively probed only for a limited number of nearby galaxies. In this paper we illustrate the progress that we expect in this field with the future ground based large aperture telescopes (E-ELT) and with space based facilities as JWST.

  17. Genesis Halo Orbit Station Keeping Design

    NASA Technical Reports Server (NTRS)

    Lo, M.; Williams, K.; Wilson, R.; Howell, K.; Barden, B.

    2000-01-01

    As the fifth mission of NASA's Directory Program, Genesis is designed to collect solar wind samples for approximately two years in a halo orbit near the Sun-Earth L(sub 1) Lagrange point for return to the Earth.

  18. Genesis Halo Orbit Station Keeping Design

    NASA Technical Reports Server (NTRS)

    Lo, M.; Williams, K.; Wilson, R.; Howell, K.; Barden, B.

    2000-01-01

    As the fifth mission of NASA's Directory Program, Genesis is designed to collect solar wind samples for approximately two years in a halo orbit near the Sun-Earth L(sub 1) Lagrange point for return to the Earth.

  19. The Vertical Structure of the Halo Rotation

    NASA Astrophysics Data System (ADS)

    Kinman, T. D.; Cacciari, C.; Bragaglia, A.; Buzzoni, A.; Spagna, A.

    New GSC-II proper motions of RR Lyrae and Blue Horizontal Branch (BHB) stars near the North Galactic Pole are used to show that the Galactic Halo 5 kpc above the Plane has a significantly retrograde galactic rotation.

  20. Solar Back-sided Halo CME

    NASA Image and Video Library

    The Sun erupted with several CMEs (coronal mass ejections) during a period just over a day (Nov. 8-9, 2012), the largest of which was a halo CME. This CME appears to have originated from an active ...

  1. Foxp3(+) regulatory T cells are increased in the early stages of halo nevi: clinicopathological features of 30 halo nevi.

    PubMed

    Park, H S; Jin, S A; Choi, Y-D; Shin, M-H; Lee, S E; Yun, S J

    2012-01-01

    There have been few clinical studies of the role of regulatory T cells (Tregs) in halo formation of halo nevus. To evaluate the clinicopathologic features and the presence of Tregs in halo nevi. We analyzed 30 halo nevi and performed immunohistochemical analysis using antibodies against CD4, CD8, CD25 and Foxp3. We also performed double immunohistochemical staining for Foxp3 and CD25. We found significant increases in Foxp3(+) Tregs, and the shorter the halo nevus duration, the more Foxp3(+) Tregs were detected. Also, the ratio of Foxp3 to CD8 T cells was increased in early stages of halo nevi. Double immunohistochemical staining suggested that the Tregs in the halo nevi were CD25(+)Foxp3(+) T cells. Foxp3(+) Tregs were greatly increased in the halo nevi. The shorter the halo nevi duration, the more Foxp3(+) Tregs were involved in the earlier developmental stages of halo nevi. Copyright © 2012 S. Karger AG, Basel.

  2. Contribution of globular clusters to halos

    NASA Astrophysics Data System (ADS)

    Bragaglia, Angela

    2017-03-01

    The contribution of massive star clusters to their hosting halo dramatically depends on their formation mechanism and their early evolution. Massive globular clusters in the Milky Way (and in other galaxies) have been shown to display peculiar chemical patterns (light-elements correlations and anti-correlations) indicative of a complex star formation, confirmed by photometric evidence (spread or split sequences). I use these chemical signatures to try to understand what is the fraction of halo stars originally born in globular clusters.

  3. On physical scales of dark matter halos

    SciTech Connect

    Zemp, Marcel

    2014-09-10

    It is common practice to describe formal size and mass scales of dark matter halos as spherical overdensities with respect to an evolving density threshold. Here, we critically investigate the evolutionary effects of several such commonly used definitions and compare them to the halo evolution within fixed physical scales as well as to the evolution of other intrinsic physical properties of dark matter halos. It is shown that, in general, the traditional way of characterizing sizes and masses of halos dramatically overpredicts the degree of evolution in the last 10 Gyr, especially for low-mass halos. This pseudo-evolution leads to the illusion of growth even though there are no major changes within fixed physical scales. Such formal size definitions also serve as proxies for the virialized region of a halo in the literature. In general, those spherical overdensity scales do not coincide with the virialized region. A physically more precise nomenclature would be to simply characterize them by their very definition instead of calling such formal size and mass definitions 'virial'. In general, we find a discrepancy between the evolution of the underlying physical structure of dark matter halos seen in cosmological structure formation simulations and pseudo-evolving formal virial quantities. We question the importance of the role of formal virial quantities currently ubiquitously used in descriptions, models, and relations that involve properties of dark matter structures. Concepts and relations based on pseudo-evolving formal virial quantities do not properly reflect the actual evolution of dark matter halos and lead to an inaccurate picture of the physical evolution of our universe.

  4. ANGULAR MOMENTUM ACQUISITION IN GALAXY HALOS

    SciTech Connect

    Stewart, Kyle R.; Brooks, Alyson M.; Bullock, James S.; Maller, Ariyeh H.; Diemand, Juerg; Wadsley, James; Moustakas, Leonidas A.

    2013-05-20

    We use high-resolution cosmological hydrodynamic simulations to study the angular momentum acquisition of gaseous halos around Milky-Way-sized galaxies. We find that cold mode accreted gas enters a galaxy halo with {approx}70% more specific angular momentum than dark matter averaged over cosmic time (though with a very large dispersion). In fact, we find that all matter has a higher spin parameter when measured at accretion than when averaged over the entire halo lifetime, and is well characterized by {lambda} {approx} 0.1, at accretion. Combined with the fact that cold flow gas spends a relatively short time (1-2 dynamical times) in the halo before sinking to the center, this naturally explains why cold flow halo gas has a specific angular momentum much higher than that of the halo and often forms ''cold flow disks.'' We demonstrate that the higher angular momentum of cold flow gas is related to the fact that it tends to be accreted along filaments.

  5. New views of the distant stellar halo

    NASA Astrophysics Data System (ADS)

    Sanderson, Robyn E.; Secunda, Amy; Johnston, Kathryn V.; Bochanski, John J.

    2017-10-01

    Currently, only a small number of Milky Way (MW) stars are known to exist beyond 100 kpc from the Galactic Centre. Though the distribution of these stars in the outer halo is believed to be sparse, they can provide evidence of more recent accretion events than in the inner halo and help map out the MW's dark matter halo to its virial radius. We have re-examined the outermost regions of 11 existing stellar halo models with two synthetic surveys: one mimicking present-day searches for distant M giants and another mimicking RR Lyra (RRL) projections for the Large Synoptic Survey Telescope (LSST). Our models suggest that colour and proper motion cuts currently used to select M giant candidates for follow-up successfully remove nearly all self-contamination from foreground halo dwarf stars and are useful for focusing observations on distant M giants, of which there are thousands to tens of thousands beyond 100 kpc in our models. We likewise expect that LSST will identify comparable numbers of RRLe at these distances. We demonstrate that several observable properties of both tracers, such as proximity of neighbouring stars, proper motions and distances (for RRLe), could help us separate different accreted dwarf galaxies from one another in the distant MW halo. We also discuss prospects for using ratios of M giants to RRLe as a proxy for accretion time, which in the future could provide new constraints on the recent accretion history of our Galaxy.

  6. MODIFIED GRAVITY SPINS UP GALACTIC HALOS

    SciTech Connect

    Lee, Jounghun; Zhao, Gong-Bo; Li, Baojiu; Koyama, Kazuya

    2013-01-20

    We investigate the effect of modified gravity on the specific angular momentum of galactic halos by analyzing the halo catalogs at z = 0 from high-resolution N-body simulations for a f(R) gravity model that meets the solar-system constraint. It is shown that the galactic halos in the f(R) gravity model tend to acquire significantly higher specific angular momentum than those in the standard {Lambda}CDM model. The largest difference in the specific angular momentum distribution between these two models occurs for the case of isolated galactic halos with mass less than 10{sup 11} h {sup -1} M {sub Sun }, which are likely least shielded by the chameleon screening mechanism. As the specific angular momentum of galactic halos is rather insensitive to other cosmological parameters, it can in principle be an independent discriminator of modified gravity. We speculate a possibility of using the relative abundance of low surface brightness galaxies (LSBGs) as a test of general relativity given that the formation of the LSBGs occurs in fast spinning dark halos.

  7. The Splashback Radius as a Physical Halo Boundary and the Growth of Halo Mass

    NASA Astrophysics Data System (ADS)

    More, Surhud; Diemer, Benedikt; Kravtsov, Andrey V.

    2015-09-01

    The boundaries of cold dark matter halos are commonly defined to enclose a density contrast Δ relative to a reference (mean or critical) density. We argue that a more physical halo boundary choice is the radius at which accreted matter reaches its first orbital apocenter after turnaround. This splashback radius, {R}{sp}, manifests itself as a sharp density drop in the halo outskirts, at a location that depends upon the mass accretion rate. We present calibrations of {R}{sp} and the enclosed mass, {M}{sp}, as a function of mass accretion rate and peak height. We find that {R}{sp} is in the range ≈ 0.8-1{R}200{{m}} for rapidly accreting halos and is ≈ 1.5{R}200{{m}} for slowly accreting halos. Thus, halos and their environmental effects can extend well beyond the conventionally defined “virial” radius. We show that {M}{sp} and {R}{sp} evolve relatively strongly compared to other commonly used definitions. In particular, {M}{sp} evolves significantly even for the smallest dwarf-sized halos at z = 0. We also contrast {M}{sp} with the mass enclosed within four scale radii of the halo density profile, {M}\\lt 4{r{{s}}}, which characterizes the inner halo. During the early stages of halo assembly, {M}{sp} and {M}\\lt 4{r{{s}}} evolve similarly, but in the late stages {M}\\lt 4{r{{s}}} stops increasing while {M}{sp} continues to grow significantly. This illustrates that halos at low z can have “quiet” interiors while continuing to accrete mass in their outskirts. We discuss potential observational estimates of the splashback radius and show that it may already have been detected in galaxy clusters.

  8. The effects of a hot gaseous halo in galaxy major mergers

    NASA Astrophysics Data System (ADS)

    Moster, Benjamin P.; Macciò, Andrea V.; Somerville, Rachel S.; Naab, Thorsten; Cox, T. J.

    2011-08-01

    Cosmological hydrodynamical simulations as well as observations indicate that spiral galaxies comprise five different components: dark matter halo, stellar disc, stellar bulge, gaseous disc and gaseous halo. While the first four components have been extensively considered in numerical simulations of binary galaxy mergers, the effect of a hot gaseous halo has usually been neglected even though it can contain up to 80 per cent of the total gas within the galaxy virial radius. We present a series of hydrodynamic simulations of major mergers of disc galaxies, that for the first time include a diffuse, rotating, hot gaseous halo. Through cooling and accretion, the hot halo can dissipate and refuel the cold gas disc before and after a merger. This cold gas can subsequently form stars, thus impacting the morphology and kinematics of the remnant. Simulations of isolated systems with total mass M˜ 1012 M⊙ show a nearly constant star formation rate of ˜5 M⊙ yr-1 if the hot gaseous halo is included, while the star formation rate declines exponentially if it is neglected. We conduct a detailed study of the star formation efficiency during mergers and find that the presence of a hot gaseous halo reduces the starburst efficiency (e= 0.5) compared to simulations without a hot halo (e= 0.68). The ratio of the peak star formation rate in mergers compared to isolated galaxies is reduced by almost an order of magnitude (from 30 to 5). Moreover, we find cases where the stellar mass of the merger remnant is lower than the sum of the stellar mass of the two progenitor galaxies when evolved in isolation. This suggests a revision to semi-analytic galaxy formation models which assume that a merger always leads to enhanced star formation. In addition, the bulge-to-total ratio after a major merger is decreased if hot gas is included in the halo, due to the formation of a more massive stellar disc in the remnant. We show that adding the hot gas component has a significant effect on the

  9. The two-component giant radio halo in the galaxy cluster Abell 2142

    NASA Astrophysics Data System (ADS)

    Venturi, T.; Rossetti, M.; Brunetti, G.; Farnsworth, D.; Gastaldello, F.; Giacintucci, S.; Lal, D. V.; Rudnick, L.; Shimwell, T. W.; Eckert, D.; Molendi, S.; Owers, M.

    2017-07-01

    Aims: We report on a spectral study at radio frequencies of the giant radio halo in A 2142 (z = 0.0909), which we performed to explore its nature and origin. The optical and X-ray properties of the cluster suggest that A 2142 is not a major merger and the presence of a giant radio halo is somewhat surprising. Methods: We performed deep radio observations of A 2142 with the Giant Metrewave Radio Telescope (GMRT) at 608 MHz, 322 MHz, and 234 MHz and with the Very Large Array (VLA) in the 1-2 GHz band. We obtained high-quality images at all frequencies in a wide range of resolutions, from the galaxy scale, i.e. 5'', up to 60'' to image the diffuse cluster-scale emission. The radio halo is well detected at all frequencies and extends out to the most distant cold front in A 2142, about 1 Mpc away from the cluster centre. We studied the spectral index in two regions: the central part of the halo, where the X-ray emission peaks and the two brightest dominant galaxies are located; and a second region, known as the ridge (in the direction of the most distant south-eastern cold front), selected to follow the bright part of the halo and X-ray emission. We complemented our deep observations with a preliminary LOw Frequency ARray (LOFAR) image at 118 MHz and with the re-analysis of archival VLA data at 1.4 GHz. Results: The two components of the radio halo show different observational properties. The central brightest part has higher surface brightess and a spectrum whose steepness is similar to those of the known radio halos, i.e. α1.78 GHz118 MHz = 1.33 ± 0.08 . The ridge, which fades into the larger scale emission, is broader in size and has considerably lower surface brightess and a moderately steeper spectrum, i.e. α1.78 GHz118 MHz 1.5. We propose that the brightest part of the radio halo is powered by the central sloshing in A 2142, in a process similar to what has been suggested for mini-halos, or by secondary electrons generated by hadronic collisions in the ICM. On

  10. Baryon cycling in the low-redshift circumgalactic medium: a comparison of simulations to the COS-Halos survey

    NASA Astrophysics Data System (ADS)

    Ford, Amanda Brady; Werk, Jessica K.; Davé, Romeel; Tumlinson, Jason; Bordoloi, Rongmon; Katz, Neal; Kollmeier, Juna A.; Oppenheimer, Benjamin D.; Peeples, Molly S.; Prochaska, Jason X.; Weinberg, David H.

    2016-06-01

    We analyse the low-redshift (z ≈ 0.2) circumgalactic medium (CGM) by comparing absorption-line data from the COS-Halos survey to absorption around a matched galaxy sample from two cosmological hydrodynamic simulations. The models include different prescriptions for galactic outflows, namely hybrid energy/momentum driven wind (ezw), and constant winds (cw). We compare equivalent widths, covering factors, ion ratios, and kinematics. Both wind models show generally ≲ 1σ agreement with these observations for H I and certain low-ionization metal lines, but poorer agreement with higher ionization metal lines including Si III and O VI that are well observed by COS-Halos. This suggests that both models predict too much cool, metal-enriched gas and not enough hot gas, and / or that metals are not sufficiently mixed. This may reflect our model assumption of ejecting outflows as cool and unmixing gas. Our ezw simulation includes a heuristic prescription to quench massive galaxies by superheating interstellar medium gas. This produces low-ionization absorption broadly consistent with observations, but substantial O VI absorption inconsistent with data, suggesting that gas around quenched galaxies in the real Universe does not cool. At impact parameters of ≲ 50 kpc, recycling winds dominate the absorption of low ions and even H I, while O VI generally arises from metals ejected ≳ 1 Gyr ago. The similarity between the wind models is surprising, since they differ substantially in the amount and phase distribution of halo gas. We show that this similarity owes mainly to our comparison at fixed stellar (not halo) mass, suggesting that CGM properties are more closely tied to galaxy's stellar (versus halo) mass.

  11. On the relevance of chaos for halo stars in the solar neighbourhood

    NASA Astrophysics Data System (ADS)

    Maffione, N. P.; Gómez, F. A.; Cincotta, P. M.; Giordano, C. M.; Cooper, A. P.; O'Shea, B. W.

    2015-11-01

    We show that diffusion due to chaotic mixing in the neighbourhood of the Sun may not be as relevant as previously suggested in erasing phase space signatures of past Galactic accretion events. For this purpose, we analyse solar neighbourhood-like volumes extracted from cosmological simulations that naturally account for chaotic orbital behaviour induced by the strongly triaxial and cuspy shape of the resulting dark matter haloes, among other factors. In the approximation of an analytical static triaxial model, our results show that a large fraction of stellar halo particles in such local volumes have chaos onset times (i.e. the time-scale at which stars commonly associated with chaotic orbits will exhibit their chaotic behaviour) significantly larger than a Hubble time. Furthermore, particles that do present a chaotic behaviour within a Hubble time do not exhibit significant diffusion in phase space.

  12. Halo occupation numbers and galaxy bias

    NASA Astrophysics Data System (ADS)

    Peacock, J. A.; Smith, R. E.

    2000-11-01

    We propose a heuristic model that displays the main features of realistic theories for galaxy bias. We first show that the low-order clustering statistics of the dark-matter distribution depend almost entirely on the locations and density profiles of dark-matter haloes. The quasi-linear mass correlations are in fact reproduced well by a model of independent randomly-placed haloes. The distribution of galaxies within the halo density field depends on: (i) the efficiency of galaxy formation, as manifested by the halo occupation number - the number of galaxies brighter than some sample limit contained in a halo of a given mass; (ii) the location of these galaxies within their halo. The first factor is constrained by the empirical luminosity function of groups. For the second factor, we assume that one galaxy marks the halo centre, with any remaining galaxies acting as satellites that trace the halo mass. This second assumption is essential if small-scale galaxy correlations are to remain close to a single power law, rather than flattening in the same way as the correlations of the overall density field. These simple assumptions amount to a recipe for non-local bias, in which the probability of finding a galaxy is not a simple function of its local mass density. We have applied this prescription to some CDM models of current interest, and find that the predictions are close to the observed galaxy correlations for a flat Ω=0.3 model (ΛCDM), but not for an Ω=1 model with the same power spectrum (τCDM). This is an inevitable consequence of cluster normalization for the power spectra: cluster-scale haloes of given mass have smaller core radii for high Ω, and hence display enhanced small-scale clustering. Finally, the pairwise velocity dispersion of galaxies in the ΛCDM model is lower than that of the mass, allowing cluster-normalized models to yield a realistic Mach number for the peculiar velocity field. This is largely due to the strong variation of galaxy

  13. New observations of the halo radial temperature structure in NGC 7662

    NASA Astrophysics Data System (ADS)

    Sandin, C.; Schönberner, D.; Roth, M. M.; Steffen, M.; Monreal-Ibero, A.; Böhm, P.; Tripphahn, U.

    We report on our studies of the physical structure of the planetary nebula (PN) NGC 7662. Using (3D) Integral Field Spectroscopy we have been able to measure the electron temperature more accurately and at a larger number of radial locations than before. Here we briefly present our method by which we find a strong positive temperature gradient with increasing radius. According to hydrodynamic models a hot halo, when compared to the central star, can be the product of the passage of an ionization front (e.g. Marten 1993). Such a gradient is not found in equilibrium models, and this finding - when confirmed for other objects - strongly advocates the use of hydrodynamic models when modeling PN halos.

  14. HaloSat- A CubeSat to Study the Hot Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kaaret, Philip

    We propose to develop, build, and fly HaloSat, a CubeSat capable of measuring the oxygen line emission from the hot Galactic halo. A dedicated CubeSat enables an instrument design and observing strategy to maximize the halo signal while minimizing foregrounds from solar wind charge exchange interactions within the solar system. We will use HaloSat to map the distribution of hot gas in the Milky Way and determine whether it fills an extended, and thus massive halo, or whether the halo is compact, and thus does not contribute significantly to the total mass of the Milky Way. HaloSat can be accomplished at modest cost using a CubeSat, a novel platform for space astrophysics missions. We will use a commercially available CubeSat bus and commercially available X-ray detectors to reduce development risk and minimize overall mission cost. HaloSat builds on the initiatives of GSFC/Wallops Flight Facility (WFF) in the development of CubeSats for low cost access to space and relies on the technical expertise of WFF personnel for spacecraft and mission design and operations. The team, from University of Iowa (UI), GSFC, Johns Hopkins, and CNRS (France), contains experts in X-ray detector development and data analysis and the astrophysics of hot plasmas and Galactic structure. The UI team will include a number of junior researchers (undergraduates, graduate students, and a postdoc) and help train them for future leadership roles on NASA space flight missions.

  15. Simulating Halos with the Caterpillar Project

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-04-01

    The Caterpillar Project is a beautiful series of high-resolution cosmological simulations. The goal of this project is to examine the evolution of dark-matter halos like the Milky Ways, to learn about how galaxies like ours formed. This immense computational project is still in progress, but the Caterpillar team is already providing a look at some of its first results.Lessons from Dark-Matter HalosWhy simulate the dark-matter halos of galaxies? Observationally, the formation history of our galaxy is encoded in galactic fossil record clues, like the tidal debris from disrupted satellite galaxies in the outer reaches of our galaxy, or chemical abundance patterns throughout our galactic disk and stellar halo.But to interpret this information in a way that lets us learn about our galaxys history, we need to first test galaxy formation and evolution scenarios via cosmological simulations. Then we can compare the end result of these simulations to what we observe today.This figure illustrates the difference that mass resolution makes. In the left panel, the mass resolution is 1.5*10^7 solar masses per particle. In the right panel, the mass resolution is 3*10^4 solar masses per particle [Griffen et al. 2016]A Computational ChallengeDue to how computationally expensive such simulations are, previous N-body simulations of the growth of Milky-Way-like halos have consisted of only one or a few halos each. But in order to establish a statistical understanding of how galaxy halos form and find out whether the Milky Ways halo is typical or unusual! it is necessary to simulate a larger number of halos.In addition, in order to accurately follow the formation and evolution of substructure within the dark-matter halos, these simulations must be able to resolve the smallest dwarf galaxies, which are around a million solar masses. This requires an extremely high mass resolution, which adds to the computational expense of the simulation.First OutcomesThese are the challenges faced by

  16. A Simple Apparatus for Determining Ionization and Solubility Product Constants.

    ERIC Educational Resources Information Center

    Gerardi, Gary

    1977-01-01

    Describes a simple conductivity apparatus for the determination of ionization and solubility product constants of various substances. The uses of the apparatus in determining the ionization constant of a weak monoprotic acid and in measuring the rate of diffusion of ions through a membrane are also presented. (HM)

  17. A Simple Apparatus for Determining Ionization and Solubility Product Constants.

    ERIC Educational Resources Information Center

    Gerardi, Gary

    1977-01-01

    Describes a simple conductivity apparatus for the determination of ionization and solubility product constants of various substances. The uses of the apparatus in determining the ionization constant of a weak monoprotic acid and in measuring the rate of diffusion of ions through a membrane are also presented. (HM)

  18. GRAVITATIONALLY CONSISTENT HALO CATALOGS AND MERGER TREES FOR PRECISION COSMOLOGY

    SciTech Connect

    Behroozi, Peter S.; Wechsler, Risa H.; Wu, Hao-Yi; Busha, Michael T.; Klypin, Anatoly A.; Primack, Joel R. E-mail: rwechsler@stanford.edu

    2013-01-20

    We present a new algorithm for generating merger trees and halo catalogs which explicitly ensures consistency of halo properties (mass, position, and velocity) across time steps. Our algorithm has demonstrated the ability to improve both the completeness (through detecting and inserting otherwise missing halos) and purity (through detecting and removing spurious objects) of both merger trees and halo catalogs. In addition, our method is able to robustly measure the self-consistency of halo finders; it is the first to directly measure the uncertainties in halo positions, halo velocities, and the halo mass function for a given halo finder based on consistency between snapshots in cosmological simulations. We use this algorithm to generate merger trees for two large simulations (Bolshoi and Consuelo) and evaluate two halo finders (ROCKSTAR and BDM). We find that both the ROCKSTAR and BDM halo finders track halos extremely well; in both, the number of halos which do not have physically consistent progenitors is at the 1%-2% level across all halo masses. Our code is publicly available at http://code.google.com/p/consistent-trees. Our trees and catalogs are publicly available at http://hipacc.ucsc.edu/Bolshoi/.

  19. An Unlikely Radio Halo in the Low X-Ray Luminosity Galaxy Cluster RXCJ1514.9-1523

    NASA Technical Reports Server (NTRS)

    Marketvitch, M.; ZuHone, J. A.; Lee, D.; Giacintucci, S.; Dallacasa, D.; Venturi, T.; Brunetti, G.; Cassano, R.; Markevitch, M.; Athreya, R. M.

    2011-01-01

    Aims: We report the discovery of a giant radio halo in the galaxy cluster RXCJ1514,9-1523 at z=0.22 with a relatively low X-ray luminosity, L(sub X) (0.1-2.4kev) approx. 7 x 10(exp 44) ergs/s. Methods: This faint, diffuse radio source is detected with the Giant Meterwave Radio Telescope at 327 MHz. The source is barely detected at 1.4 GHz in a NVSS pointing that we have reanalyzed. Results: The integrated radio spectrum of the halo is quite steep, with a slope alpha = 1.6 between 327 MHz and 1.4 GHz. While giant radio halos are common in more X-ray luminous cluster mergers, there is a less than 10% probability to detect a halo in systems with L(sub X) < 8 x 10(exp 44) ergs/s. The detection of a new giant halo in this borderline luminosity regime can be particularly useful for discriminating between the competing theories for the origin of ultrarelativistic electrons in clusters. Furthermore, if our steep radio spectral index is confirmed by future deeper radio observations, this cluster would provide another example of the very rare, new class of ultra-steep spectrum radio halos, predicted by the model in which the cluster cosmic ray electrons are produced by turbulent reacceleration.

  20. The interstellar halo of spiral galaxies: NGC 891

    NASA Technical Reports Server (NTRS)

    Kulkarni, Shrinivas R.; Rand, R. J.; Hester, J. Jeff

    1990-01-01

    Researchers have detected the Warm Ionized Medium (WIM) phase in the galaxy NGC 891. They found that the radial distribution of the WIM follows the molecular or young star distribution - an expected dependence. The amount of the WIM in this galaxy exceeds that in our Galaxy. The major surprize is the large thickness of the WIM phase - about 9 kpc instead 3 kpc as in our Galaxy. Clearly, this is the most significant result of the observations. The presence of low ionization gas at high z as well as at large galactocentric radii (where young stars are rare) is an important clue to the origin of the halo and observations such as the one reported here provide important data on this crucial question. In particular, the ionization of gas at high absolute z implies that either the UV photons manage to escape from the disk of the galaxy or that the extragalactic UV background plays an important role. The bulk of the WIM in spiral galaxies is a result of star-formation activity and thus these results can be understood by invoking a high star formation rate in NGC 891. Only the concerted action of supernovae can get the gas to the large z-heights as is observed in this galaxy. Support for this view comes from our detection of many worms i.e., bits and pieces of supershells in the form of kilo-parsec long vertical filaments. Researchers also saw a 600-pc size supershell located nearly one kpc above the plane of the galaxy.

  1. Halo Spin Parameter in Cosmological Simulations

    NASA Astrophysics Data System (ADS)

    Ahn, Jieun; Kim, Juhan; Shin, Jihye; Kim, Sungsoo S.; Choi, Yun-Young

    2014-04-01

    Using a cosmological ΛCDM simulation, we analyze the differences between the widely-used spin parameters suggested by Peebles and Bullock. The dimensionless spin parameter λ proposed by Peebles is theoretically well-justified but includes an annoying term, the potential energy, which cannot be directly obtained from observations and is computationally expensive to calculate in numerical simulations. The Bullock's spin parameter λ^' avoids this problem assuming the isothermal density profile of a virialized halo in the Newtonian potential model. However, we find that there exists a substantial discrepancy between λ and λ^' depending on the adopted potential model (Newtonian or Plummer) to calculate the halo total energy and that their redshift evolutions differ to each other significantly. Therefore, we introduce a new spin parameter, λ^{''}, which is simply designed to roughly recover the value of λ but to use the same halo quantities as used in λ^'. If the Plummer potential is adopted, the λ^{''} is related to the Bullock's definition as λ^{''} = 0.80× (1 + z)^{-1/12} λ^'. Hence, the new spin parameter λ^{''} distribution becomes consistent with a log-normal distribution frequently seen for the λ^' while its mean value is much closer to that of λ. On the other hand, in case of the Newtonian potential model, we obtain the relation of λ^{''}=(1+z)^{-1/8}λ^{'}; there is no significant difference at z = 0 as found by others but λ^{'} becomes more overestimated than λ or λ^{''} at higher redshifts. We also investigate the dependence of halo spin parameters on halo mass and redshift. We clearly show that although the λ^' for small-mass halos with M_h < 2× 10^{12} M_odot seems redshift independent after z=1, all the spin parameters explored, on the whole, show a stronger correlation with the increasing halo mass at higher redshifts.

  2. Dark Matter Properties and Halo Central Densities

    NASA Astrophysics Data System (ADS)

    Alam, S. M. Khairul; Bullock, James S.; Weinberg, David H.

    2002-06-01

    Using an analytic model calibrated against numerical simulations, we calculate the central densities of dark matter halos in a ``conventional'' cold dark matter model with a cosmological constant (LCDM) and in a ``tilted'' model (TLCDM) with slightly modified parameters motivated by recent analyses of Lyα forest data. We also calculate how warm dark matter (WDM) would modify these predicted densities by delaying halo formation and imposing phase-space constraints. As a measure of central density, we adopt the quantity ΔV/2, the density within the radius RV/2 at which the halo rotation curve falls to half of its maximum value, in units of the critical density. We compare the theoretical predictions to values of ΔV/2 estimated from the rotation curves of dark matter-dominated disk galaxies. Assuming that dark halos are described by Navarro-Frenk-White profiles, our results suggest that the conventional LCDM model predicts excessively high dark matter densities, unless there is some selection bias in the data toward the low-concentration tail of the halo distribution. A WDM model with particle mass 0.5-1 keV provides a better match to the observational data. However, the modified cold dark matter model, TLCDM, fits the data equally well, suggesting that the solution to the ``halo cores'' problem might lie in moderate changes to cosmological parameters rather than radical changes to the properties of dark matter. If cold dark matter halos have the steeper density profiles found by Moore et al., then neither conventional LCDM nor TLCDM can reproduce the observed central densities.

  3. The Milky Way, the Galactic Halo, and the Halos of Galaxies

    NASA Astrophysics Data System (ADS)

    Gerhard, Ortwin

    2016-08-01

    The Milky Way, ``our'' Galaxy, is currently the subject of intense study with many ground-based surveys, in anticipation of upcoming results from the Gaia mission. From this work we have been learning about the full three-dimensional structure of the Galactic box/peanut bulge, the distribution of stars in the bar and disk, and the many streams and substructures in the Galactic halo. The data indicate that a large fraction of the Galactic halo has been accreted from outside. Similarly, in many external galaxy halos there is now evidence for tidal streams and accretion of satellites. To study these features requires exquisite, deep photometry and spectroscopy. These observations illustrate how galaxy halos are still growing, and sometimes can be used to ``time'' the accretion events. In comparison with cosmological simulations, the structure of galaxy halos gives us a vivid illustration of the hierarchical nature of our Universe.

  4. HaloSat - A CubeSat to Study the Hot Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kaaret, Philip

    2017-01-01

    Observations of the nearby universe fail to locate about half of the baryons observed in the early universe. The missing baryons may be in hot galactic halos. HaloSat is a CubeSat designed to map oxygen line emission (O VII and O VIII) around the Milky Way in order to constrain the mass and spatial distribution of hot gas in the halo. HaloSat has a grasp competitive with current X-ray observatories. Its observing program will be optimized to minimize contributions from solar wind charge exchange (SWCX) emission that limit the accuracy of current measurements. We will describe the HaloSat mission concept, progress towards its implementation, and plans for archiving and distribution of the data.

  5. HaloSat - A CubeSat to Study the Hot Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kaaret, Philip

    2016-04-01

    Observations of the nearby universe fail to locate about half of the normal matter (baryons) observed in the early universe. The missing baryons may be in hot galactic halos. HaloSat is a CubeSat designed to map oxygen line emission (O VII and O VIII) around the Milky Way in order to constrain the mass and spatial distribution of hot gas in the halo. HaloSat has a grasp competitive with current X-ray observatories. Its observing program will be optimized to minimize contributions from solar wind charge exchange (SWCX) emission that limit the accuracy of current measurements. We will describe the HaloSat mission concept, progress towards its implementation, and plans for archiving and distribution of the data.

  6. Electric Properties of One-Neutron Halo Nuclei in Halo EFT

    NASA Astrophysics Data System (ADS)

    Braun, Jonas; Hammer, Hans-Werner

    2017-03-01

    We exploit the separation of scales in weakly-bound nuclei to compute E2 transitions and electric form factors in a halo effective field theory (EFT) framework. The relevant degrees of freedom are the core and the halo neutron. The EFT expansion is carried out in powers of R_{core}/R_{halo}, where R_{core} and R_{halo} denote the length scales of the core and halo, respectively. We include the strong s-wave and d-wave interactions by introducing dimer fields. The dimer propagators are regulated by employing the power divergence subtraction scheme and matched to the effective range expansion in the respective channel. Electromagnetic interactions are included via minimal substitution in the Lagrangian. We demonstrate that, depending on the observable and respective partial wave, additional local gauge-invariant operators contribute in LO, NLO and higher orders.

  7. Probing the galactic disk and halo. 2: Hot interstellar gas toward the inner galaxy star HD 156359

    NASA Technical Reports Server (NTRS)

    Sembach, Kenneth R.; Savage, Blair D.; Lu, Limin

    1995-01-01

    We present Goddard High Resolution Spectrograph intermediate-resolution measurements of the 1233-1256 A spectral region of HD 156396, a halo star at l = 328.7 deg, b = -14.5 deg in the inner Galaxy with a line-of sight distance of 11.1 kpc and a z-distance of -2.8 kpc. The data have a resolution of 18 km/s Full Width at Half Maximum (FWHM) and a signal-to-noise ratio of approximately 50:1. We detect interstellar lines of Mg II, S II, S II, Ge II, and N V and determine log N/(Mg II) = 15.78 +0.25, -0.27, log N(Si II) greater than 13.70, log N(S II) greater than 15.76, log N(Ge II) = 12.20 +0.09,-0.11, and log N(N v) = 14.06 +/- 0.02. Assuming solar reference abundances, the diffuse clouds containing Mg, S, and Ge along the sight line have average logarithmic depletions D(Mg) = -0.6 +/- 0.3 dex, D(S) greater than -0.2 dex, and D(Ge) = -0.2 +/- 0.2 dex. The Mg and Ge depletions are approximately 2 times smaller than is typical of diffuse clouds in the solar vicinity. Galactic rotational modeling of the N v profiles indicates that the highly ionized gas traced by this ion has a scale height of approximately 1 kpc if gas at large z-distances corotates with the underlying disk gas. Rotational modeling of the Si iv and C iv profiles measured by the IUE satellite yields similar scale height estimates. The scale height results contrast with previous studies of highly ionized gas in the outer Milky Way that reveal a more extended gas distribtion with h approximately equals 3-4 kpc. We detect a high-velocity feature in N v and Si II v(sub LSR) approximately equals + 125 km/s) that is probably created in an interface between warm and hot gas.

  8. Probing the galactic disk and halo. 2: Hot interstellar gas toward the inner galaxy star HD 156359

    NASA Technical Reports Server (NTRS)

    Sembach, Kenneth R.; Savage, Blair D.; Lu, Limin

    1995-01-01

    We present Goddard High Resolution Spectrograph intermediate-resolution measurements of the 1233-1256 A spectral region of HD 156396, a halo star at l = 328.7 deg, b = -14.5 deg in the inner Galaxy with a line-of sight distance of 11.1 kpc and a z-distance of -2.8 kpc. The data have a resolution of 18 km/s Full Width at Half Maximum (FWHM) and a signal-to-noise ratio of approximately 50:1. We detect interstellar lines of Mg II, S II, S II, Ge II, and N V and determine log N/(Mg II) = 15.78 +0.25, -0.27, log N(Si II) greater than 13.70, log N(S II) greater than 15.76, log N(Ge II) = 12.20 +0.09,-0.11, and log N(N v) = 14.06 +/- 0.02. Assuming solar reference abundances, the diffuse clouds containing Mg, S, and Ge along the sight line have average logarithmic depletions D(Mg) = -0.6 +/- 0.3 dex, D(S) greater than -0.2 dex, and D(Ge) = -0.2 +/- 0.2 dex. The Mg and Ge depletions are approximately 2 times smaller than is typical of diffuse clouds in the solar vicinity. Galactic rotational modeling of the N v profiles indicates that the highly ionized gas traced by this ion has a scale height of approximately 1 kpc if gas at large z-distances corotates with the underlying disk gas. Rotational modeling of the Si iv and C iv profiles measured by the IUE satellite yields similar scale height estimates. The scale height results contrast with previous studies of highly ionized gas in the outer Milky Way that reveal a more extended gas distribtion with h approximately equals 3-4 kpc. We detect a high-velocity feature in N v and Si II v(sub LSR) approximately equals + 125 km/s) that is probably created in an interface between warm and hot gas.

  9. Deep 230-470 MHz VLA observations of the mini-halo in the Perseus cluster

    NASA Astrophysics Data System (ADS)

    Gendron-Marsolais, M.; Hlavacek-Larrondo, J.; van Weeren, R. J.; Clarke, T.; Fabian, A. C.; Intema, H. T.; Taylor, G. B.; Blundell, K. M.; Sanders, J. S.

    2017-08-01

    We present a low-frequency view of the Perseus cluster with new observations from the Karl G. Jansky Very Large Array (JVLA) at 230-470 MHz. The data reveal a multitude of new structures associated with the mini-halo. The mini-halo seems to be influenced both by the AGN activity and the sloshing motion of the cool core cluster's gas. In addition, it has a filamentary structure similar to that seen in radio relics found in merging clusters. We present a detailed description of the data reduction and imaging process of the dataset. The depth and resolution of the observations allow us to conduct for the first time a detailed comparison of the mini-halo structure with the X-ray structure as seen in the Chandra X-ray images. The resulting image very clearly shows that the mini-halo emission is mostly contained behind the western cold front, similar to that predicted by simulations of gas sloshing in galaxy clusters, but fainter emission is also seen beyond, as if particles are leaking out. However, due to the proximity of the Perseus cluster, as well as the quality of the data at low radio frequencies and at X-ray wavelengths, we also find evidence of fine structure. This structure includes several radial radio filaments extending in different directions, a concave radio structure associated with the southern X-ray bay and sharp radio edges that correlate with X-ray edges. Mini-haloes are therefore not simply diffuse, uniform radio sources, but rather have a rich variety of complex structures. These results illustrate the high-quality images that can be obtained with the new JVLA at low radio frequencies, as well as the necessity to obtain deeper, higher fidelity radio images of mini-haloes in clusters to further understand their origin.

  10. Statistical Aspects of X-Class Halo and Non-Halo Events, 1996-2014

    NASA Technical Reports Server (NTRS)

    Wilson, Robert M.

    2016-01-01

    Of the 166 X-class events that occurred during the interval 1996-2014, 80 had associations with halo events, 68 had no associations with halo events, and 18 occurred during LASCO (Large Angle and Spectrometric COronagraph) data gaps. Both the duration and location of the X-class halo events proved to be statistically important parameters with respect to the geo-effectiveness of the events. Forty-four of the 80 X-class halo events occurred within 45 degrees of the Sun's central meridian and 47 of the 80 had duration greater than or equal to 30 minutes, whereas only 28 of the 68 X-class non-halo events occurred within 45 degrees of the Sun's central meridian (2 events have unknown location) and 22 of the 68 had duration greater than or equal to 30 minutes. Ignoring the 4 largest X-class flares greater than or equal to X4.0 during the LASCO data gaps, 17 of the remaining 20 were associated with halo events, and 14 of the 17 had at least one geo-magnetically disturbed day (Ap (i.e. NOAA's Ap* (ApStar)index: the major magnetic storms going back to 1932) greater than or equal to 25 nanotesias) within 1-5 days following the X-class halo event. Based on the hourly Dst (Disturbance storm time) index, the most geo-effective X-class halo event during the interval 1996-2014 was that of an X1.7 flare that occurred on 2001 March 29 at 0957, having an hourly Disturbance storm time minimum equal to minus 387 nanotesias. On average, the X-class halo events (80 events) were found to have a mean duration (42 minutes) slightly longer than the mean duration (29 minutes) of the X-class non-halo events (68 events) with the difference in the means being statistically important at the 1 percent level of significance.

  11. Sun-Earth L1 Region Halo-To-Halo Orbit and Halo-To-LisaJous Orbit Transfers

    NASA Technical Reports Server (NTRS)

    Roberts, Craig E.; DeFazio, Robert

    2004-01-01

    Practical techniques for designing transfer trajectories between Libration Point Orbits (LPOs) are presented. Motivation for development of these techniques was provided by a hardware contingency experienced by the Solar Heliospheric Observatory (SOHO), a joint mission of the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) orbiting the L1 point of the Sun-Earth system. A potential solution to the problem involved a transfer from SOHO s periodic halo orbit to a new LPO of substantially different dimensions. Assuming the SOHO halo orbit as the departure orbit, several practical LPO transfer techniques were developed to obtain new Lissajous or periodic halo orbits that satisfy mission requirements and constraints. While not implemented for the SOHO mission, practical LPO transfer techniques were devised that are generally applicable to current and future LPO missions.

  12. SCORCH I: The Galaxy-Halo Connection in the First Billion Years

    NASA Astrophysics Data System (ADS)

    Trac, Hy; Cen, Renyue; Mansfield, Philip

    2015-11-01

    SCORCH (Simulations and Constructions of the Reionization of Cosmic Hydrogen) is a new project to study the Epoch of Reionization (EoR). In this first paper, we probe the connection between observed high-redshift galaxies and simulated dark matter halos to better understand the primary source of ionizing radiation. High-resolution N-body simulations are run to quantify the abundance of dark matter halos as a function of mass M, accretion rate \\dot{M}, and redshift z. A new fit for the halo mass function dn/dM is ≈20% more accurate at the high-mass end. A novel approach is used to fit the halo accretion rate function {dn}/d\\dot{M} in terms of the halo mass function. Abundance matching against the observed galaxy luminosity function is used to estimate the luminosity-mass relation and the luminosity-accretion-rate relation. The inferred star formation efficiency is not monotonic with M nor \\dot{M}, but reaches a maximum value at a characteristic mass ˜ 2× {10}11 {M}⊙ and a characteristic accretion rate ˜ 6× {10}2 {M}⊙ {{{yr}}}-1 at z ≈ 6. We find a universal EoR luminosity-accretion-rate relation and construct a fiducial model for the galaxy luminosity function. The Schechter parameters evolve such that {φ }\\star decreases, {M}\\star is fainter, and α is steeper at higher redshifts. We forecast for the upcoming James Webb Space Telescope and show that with apparent magnitude limit {m}{{AB}}≈ 31 (32), it can observe ≳ 11 (24) unlensed galaxies per square degree per unit redshift at least down to {M}\\star at z ≲ 13 (14).

  13. Why are halo coronal mass ejections faster?

    NASA Astrophysics Data System (ADS)

    Zhang, Qing-Min; Guo, Yang; Chen, Peng-Fei; Ding, Ming-De; Fang, Cheng

    2010-05-01

    Halo coronal mass ejections (CMEs) have been to be significantly faster than normal CMEs, which is a long-standing puzzle. In order to solve the puzzle, we first investigate the observed properties of 31 limb CMEs that clearly display loop-shaped frontal loops. The observational results show a strong tendency that slower CMEs are weaker in white-light intensity. Then, we perform a Monte Carlo simulation of 20000 artificial limb CMEs that have an average velocity of ~523 km s-1. The Thomson scattering of these events is calculated when they are assumed to be observed as limb and halo events, respectively. It is found that the white-light intensity of many slow CMEs becomes remarkably reduced when they turn from being viewed as a limb event to being viewed as a halo event. When the intensity is below the background solar wind fluctuation, it is assumed that they would be missed by coronagraphs. The average velocity of “detectable" halo CMEs is ~922 km s-1 very close to the observed value. This also indicates that wider events are more likely to be recorded. The results soundly suggest that the higher average velocity of halo CMEs is due to that a majority of slow events and some of narrow fast events carrying less material are so faint that they are blended with the solar wind fluctuations, and therefore are not observed.

  14. A ''LIGHT'', CENTRALLY CONCENTRATED MILKY WAY HALO?

    SciTech Connect

    Rashkov, Valery; Pillepich, Annalisa; Deason, Alis J.; Madau, Piero; Rockosi, Constance M.; Mayer, Lucio

    2013-08-20

    We discuss a novel approach to ''weighing'' the Milky Way (MW) dark matter halo, one that combines the latest samples of halo stars selected from the Sloan Digital Sky Survey (SDSS) with state of the art numerical simulations of MW analogs. The fully cosmological runs employed in the present study include ''Eris'', one of the highest resolution hydrodynamical simulations of the formation of a M{sub vir} = 8 Multiplication-Sign 10{sup 11} M{sub Sun} late-type spiral, and the dark-matter-only M{sub vir} = 1.7 Multiplication-Sign 10{sup 12} M{sub Sun} ''Via Lactea II'' (VLII) simulation. Eris provides an excellent laboratory for creating mock SDSS samples of tracer halo stars, and we successfully compare their density, velocity anisotropy, and radial velocity dispersion profiles with the observational data. Most mock SDSS realizations show the same ''cold veil'' recently observed in the distant stellar halo of the MW, with tracers as cold as {sigma}{sub los} Almost-Equal-To 50 km s{sup -1} between 100 and 150 kpc. Controlled experiments based on the integration of the spherical Jeans equation as well as a particle tagging technique applied to VLII show that a ''heavy'' M{sub vir} Almost-Equal-To 2 Multiplication-Sign 10{sup 12} M{sub Sun} realistic host produces a poor fit to the kinematic SDSS data. We argue that these results offer added evidence for a ''light'', centrally concentrated MW halo.

  15. The angular momentum distribution in galactic halos

    NASA Astrophysics Data System (ADS)

    Quinn, P. J.; Zurek, W. H.

    1988-08-01

    N-body simulations are used to model the formation of individual galactic halos from scale-free density perturbations in universes dominated by cold, nondissipative dark matter. In well-mixed halos, the angular momentum distribution is shown to have a systematic behavior with power law index n corresponding to that found for circular rotation curves. For a given n, the distribution of angular momentum has the same trend with radius and energy as that implied for a halo in which all the matter has its maximum possible angular momentum. Dynamical mixing during the relaxation of the halo redistributes both angular momentum and binding energy in an orderly manner. The organized nature of the collapse means that relaxation is not completely violent and that the secondary infall paradigm, in its simplest form, needs to be modified to include the organizing effects of dynamical friction. It is shown that the Mestel hypothesis is not consistent with the final collapsed state of halos, but may be applicable to the collapse of the disks of spirals.

  16. A UNIVERSAL MODEL FOR HALO CONCENTRATIONS

    SciTech Connect

    Diemer, Benedikt; Kravtsov, Andrey V.

    2015-01-20

    We present a numerical study of dark matter halo concentrations in ΛCDM and self-similar cosmologies. We show that the relation between concentration, c, and peak height, ν, exhibits the smallest deviations from universality if halo masses are defined with respect to the critical density of the universe. These deviations can be explained by the residual dependence of concentration on the local slope of the matter power spectrum, n, which affects both the normalization and shape of the c-ν relation. In particular, there is no well-defined floor in the concentration values. Instead, the minimum concentration depends on redshift: at fixed ν, halos at higher z experience steeper slopes n, and thus have lower minimum concentrations. We show that the concentrations in our simulations can be accurately described by a universal seven-parameter function of only ν and n. This model matches our ΛCDM results to ≲ 5% accuracy up to z = 6, and matches scale-free Ω{sub m} = 1 models to ≲ 15%. The model also reproduces the low concentration values of Earth-mass halos at z ≈ 30, and thus correctly extrapolates over 16 orders of magnitude in halo mass. The predictions of our model differ significantly from all models previously proposed in the literature at high masses and redshifts. Our model is in excellent agreement with recent lensing measurements of cluster concentrations.

  17. Static galactic halo and galactic wind

    NASA Technical Reports Server (NTRS)

    Ko, Chung-Ming

    1993-01-01

    Although the exact state of the interstellar medium (ISM) in our Galaxy (other galaxies as well) is not clear at all, the 'common consensus' is that a rough pressure balance (or equipartition of energy) exists between different components and phases: cold, warm, hot phases of the ISM, magnetic field, cosmic rays, etc. If the halo of a galaxy is taken to be an extension of the ISM, then its structure is influenced by various ISM components. A 'complete' description of the halo is evidently very complicated. This paper gives a brief account on cosmic ray halo, which emphasizes the role played by cosmic rays. The interaction between cosmic rays and thermal plasma is facilitated by magnetic field. The cosmic rays are scattered by hydromagnetic waves (e.g., Alfven waves) which in turn can be generated by cosmic ray streaming instability. This constitutes a self-consistent picture. Since we are interested in the structure of the halo, we adopted a hydrodynamic model in which the cosmic rays and waves are described by their pressures. In general there are two classes of halos: static and dynamic.

  18. A "Light," Centrally Concentrated Milky Way Halo?

    NASA Astrophysics Data System (ADS)

    Rashkov, Valery; Pillepich, Annalisa; Deason, Alis J.; Madau, Piero; Rockosi, Constance M.; Guedes, Javiera; Mayer, Lucio

    2013-08-01

    We discuss a novel approach to "weighing" the Milky Way (MW) dark matter halo, one that combines the latest samples of halo stars selected from the Sloan Digital Sky Survey (SDSS) with state of the art numerical simulations of MW analogs. The fully cosmological runs employed in the present study include "Eris," one of the highest resolution hydrodynamical simulations of the formation of a M vir = 8 × 1011 M ⊙ late-type spiral, and the dark-matter-only M vir = 1.7 × 1012 M ⊙ "Via Lactea II" (VLII) simulation. Eris provides an excellent laboratory for creating mock SDSS samples of tracer halo stars, and we successfully compare their density, velocity anisotropy, and radial velocity dispersion profiles with the observational data. Most mock SDSS realizations show the same "cold veil" recently observed in the distant stellar halo of the MW, with tracers as cold as σlos ≈ 50 km s-1 between 100 and 150 kpc. Controlled experiments based on the integration of the spherical Jeans equation as well as a particle tagging technique applied to VLII show that a "heavy" M vir ≈ 2 × 1012 M ⊙ realistic host produces a poor fit to the kinematic SDSS data. We argue that these results offer added evidence for a "light," centrally concentrated MW halo.

  19. A Universal Model for Halo Concentrations

    NASA Astrophysics Data System (ADS)

    Diemer, Benedikt; Kravtsov, Andrey V.

    2015-01-01

    We present a numerical study of dark matter halo concentrations in ΛCDM and self-similar cosmologies. We show that the relation between concentration, c, and peak height, ν, exhibits the smallest deviations from universality if halo masses are defined with respect to the critical density of the universe. These deviations can be explained by the residual dependence of concentration on the local slope of the matter power spectrum, n, which affects both the normalization and shape of the c-ν relation. In particular, there is no well-defined floor in the concentration values. Instead, the minimum concentration depends on redshift: at fixed ν, halos at higher z experience steeper slopes n, and thus have lower minimum concentrations. We show that the concentrations in our simulations can be accurately described by a universal seven-parameter function of only ν and n. This model matches our ΛCDM results to <~ 5% accuracy up to z = 6, and matches scale-free Ωm = 1 models to <~ 15%. The model also reproduces the low concentration values of Earth-mass halos at z ≈ 30, and thus correctly extrapolates over 16 orders of magnitude in halo mass. The predictions of our model differ significantly from all models previously proposed in the literature at high masses and redshifts. Our model is in excellent agreement with recent lensing measurements of cluster concentrations.

  20. Globular Cluster Contributions to the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Martell, Sarah; Grebel, Eva; Lai, David

    2010-08-01

    The goal of this project is to confirm chemically that globular clusters are the source of as much as half the population of the Galactic halo. Using moderate-resolution spectroscopy from the SEGUE survey, we have identified a previously unknown population of halo field giants with distinctly strong CN features. CN variations are typically only observed in globular clusters, so these stars are interpreted as immigrants to the halo that originally formed in globular clusters. In one night of Keck/HIRES time, we will obtain high-quality, high- resolution spectra for five such stars, and determine abundances of O, Na, Mg, Al, alpha, iron-peak and neutron-capture elements. With this information we can state clearly whether these unusual CN-strong halo stars carry the full abundance pattern seen in CN-strong globular cluster stars, with depleted C, O, and Mg and enhanced N, Na, and Al. This type of coarse ``chemical tagging'' will allow a clearer division of the Galactic halo into contributions from globular clusters and from dwarf galaxies, and will place constraints on theoretical models of globular cluster formation and evolution.

  1. The settling of warped disks in oblate dark halos

    NASA Technical Reports Server (NTRS)

    Dubinski, John; Kuijken, Konrad

    1995-01-01

    When a galaxy forms, the disk may initially be tilted with respect to a flattened dark halo. The misalignment between the disk and the halo is a common explanation for galactic disk warps, since in this state disks have precessing bending modes which resemble real warps. The gravitational response of the halo has often been ignored, and its strength and effect on possible bending modes is unknown. We therefore calculate the response of an oblate halo to a precessing inclined exponential disk using a variety of techniques. We construct models with a rigid exponential disk precessing in a particle halo, a particle disk precessing inside a static bulge/halo potential, and a self-consistent model with a particle disk, bulge, and halo. When the disk: halo mass ratio is small (approximately 10%) within 5 exponential scale radii, the disk settles to the equatorial plane of the halo within five orbital times. When the disk and halo mass are comparable, the halo rapidly aligns with the disk within a few orbital times, while the disk inclination drops. The rapid response of the halo to an inclined precessing disk suggests that the warps seen in galactic disks are not due to a misalignment between the disk and the inner halo. If a galaxy forms inclined to the principal plane of a dark halo, either the disk will settle to a pricipal plane or the inner halo will twist to align with the disk. The outer halo will remain misaligned for a much longer time and therefore may still exert a torque. Warped bending modes may still exist if the misalignment of the outer halo persists for a Hubble time.

  2. The settling of warped disks in oblate dark halos

    NASA Technical Reports Server (NTRS)

    Dubinski, John; Kuijken, Konrad

    1995-01-01

    When a galaxy forms, the disk may initially be tilted with respect to a flattened dark halo. The misalignment between the disk and the halo is a common explanation for galactic disk warps, since in this state disks have precessing bending modes which resemble real warps. The gravitational response of the halo has often been ignored, and its strength and effect on possible bending modes is unknown. We therefore calculate the response of an oblate halo to a precessing inclined exponential disk using a variety of techniques. We construct models with a rigid exponential disk precessing in a particle halo, a particle disk precessing inside a static bulge/halo potential, and a self-consistent model with a particle disk, bulge, and halo. When the disk: halo mass ratio is small (approximately 10%) within 5 exponential scale radii, the disk settles to the equatorial plane of the halo within five orbital times. When the disk and halo mass are comparable, the halo rapidly aligns with the disk within a few orbital times, while the disk inclination drops. The rapid response of the halo to an inclined precessing disk suggests that the warps seen in galactic disks are not due to a misalignment between the disk and the inner halo. If a galaxy forms inclined to the principal plane of a dark halo, either the disk will settle to a pricipal plane or the inner halo will twist to align with the disk. The outer halo will remain misaligned for a much longer time and therefore may still exert a torque. Warped bending modes may still exist if the misalignment of the outer halo persists for a Hubble time.

  3. Ionization potentials of seaborgium

    SciTech Connect

    Johnson, E.; Pershina, V.; Fricke, B.

    1999-10-21

    Multiconfiguration relativistic Dirac-Fock values were calculated for the first six ionization potentials of seaborgium and of the other group 6 elements. No experimental ionization potentials are available for seaborgium. Accurate experimental values are not available for all of the other ionization potentials. Ionic radii for the 4+ through 6+ ions of seaborgium are also presented. The ionization potentials and ionic radii obtained will be used to predict some physiochemical properties of seaborgium and its compounds.

  4. The impact of stellar feedback on hot gas in galaxy haloes: the Sunyaev-Zel'dovich effect and soft X-ray emission

    NASA Astrophysics Data System (ADS)

    van de Voort, Freeke; Quataert, Eliot; Hopkins, Philip F.; Faucher-Giguère, Claude-André; Feldmann, Robert; Kereš, Dušan; Chan, T. K.; Hafen, Zachary

    2016-12-01

    The thermal Sunyaev-Zel'dovich (SZ) effect and soft X-ray emission are routinely observed around massive galaxies and in galaxy groups and clusters. We study these observational diagnostics of galaxy haloes for a suite of cosmological `zoom-in' simulations from the `Feedback In Realistic Environments' project, which spans a large range in halo mass (1010-13 M⊙). We explore the effect of stellar feedback on the hot gas observables. The properties of our simulated groups, such as baryon fractions, SZ flux, and X-ray luminosities (LX), are broadly consistent with existing observations, even though feedback from active galactic nuclei is not included. We make predictions for future observations of lower mass objects for both SZ and diffuse X-ray measurements, finding that they are not just scaled-down versions of massive galaxies, but more strongly affected by galactic winds driven by star formation. Low-mass haloes (≲1011 M⊙) retain a low fraction of their baryons, which results in a strong suppression of the SZ signal. Our simulations therefore predict a scaling with halo mass that is steeper than self-similar for haloes less massive than 1013 M⊙. For halo masses ≲1012 M⊙, LX is time variable and correlated primarily with the star formation rate (SFR). For these objects, the diffuse X-ray emission is powered mostly by galactic winds and the gas dominating the X-ray emission is flowing out with radial velocities close to the halo's circular velocity. For halo masses ≳1013 M⊙, on the other hand, LX is much less variable and not correlated with the SFR, because the emission originates from the quasi-hydrostatic, virialized halo gas.

  5. Ionization Energies of Lanthanides

    ERIC Educational Resources Information Center

    Lang, Peter F.; Smith, Barry C.

    2010-01-01

    This article describes how data are used to analyze the pattern of ionization energies of the lanthanide elements. Different observed pathways of ionization between different ground states are discussed, and the effects of pairing, exchange, and orbital interactions on ionization energies of the lanthanides are evaluated. When all the above…

  6. Ionization Energies of Lanthanides

    ERIC Educational Resources Information Center

    Lang, Peter F.; Smith, Barry C.

    2010-01-01

    This article describes how data are used to analyze the pattern of ionization energies of the lanthanide elements. Different observed pathways of ionization between different ground states are discussed, and the effects of pairing, exchange, and orbital interactions on ionization energies of the lanthanides are evaluated. When all the above…

  7. Stability of BEC galactic dark matter halos

    NASA Astrophysics Data System (ADS)

    Guzmán, F. S.; Lora-Clavijo, F. D.; González-Avilés, J. J.; Rivera-Paleo, F. J.

    2013-09-01

    In this paper we show that spherically symmetric BEC dark matter halos, with the sin r/r density profile, that accurately fit galactic rotation curves and represent a potential solution to the cusp-core problem are unstable. We do this by introducing back the density profiles into the fully time-dependent Gross-Pitaevskii-Poisson system of equations. Using numerical methods to track the evolution of the system, we found that these galactic halos lose mass at an approximate rate of half of its mass in a time scale of dozens of Myr. We consider this time scale is enough as to consider these halos are unstable and unlikely to be formed. We provide some arguments to show that this behavior is general and discuss some other drawbacks of the model that restrict its viability.

  8. Systematic Problems With Stellar Halo Modelling

    NASA Astrophysics Data System (ADS)

    Bailin, Jeremy

    2012-05-01

    Stellar halos contain a small fraction of the stellar mass of a galaxy. The dynamic range required to model the substructure within this small component while simultaneously modeling the main galaxy is currently unobtainable, which has lead to the prevalence of stellar halo models that tag stellar content onto dark matter particles in pure dark matter simulations, making it computationally feasible (e.g. Bullock & Johnston 2005; Cooper et al. 2010). Using paired simulations with identical initial conditions, we estimate the magnitude of the systematic effects these simplifications have on the structure of the halos. We find that (1) "painting" and (2) neglecting baryonic processes each introduce factor-of-several changes to the amount of substructure predicted. We therefore urge caution when interpreting differences between models and observations that are at this level.

  9. The Implication of MOND for Dark Haloes

    NASA Astrophysics Data System (ADS)

    Huang, Yi-Cheng; Kosowsky, A.

    2006-12-01

    It is always interesting that how much implication that Milgrom's relation could provide, even phenomenologically. With just one assumption that the gravitational acceleration goes like 1/r instead of Newton's law, 1/r2, when the acceleration is smaller than the value $10-10m/sec2, it is well known that MOND can give a better description of the rotational curves in spiral galaxies. In this research, we explore the configuration of the parameter space for the dark haloes by fitting the rotation curves of halo profiles with the exponential disk for stellar mass to that of MOND. In addition, we find that the baryon mass to the halo mass ratio is lower than the primordial ratio which gives that the total baryon mass is about 15% of the dark matter, and which is consistent with what we generally expect today.

  10. Polypoid Spitz Nevus With a Halo Reaction.

    PubMed

    Fernandez-Flores, Angel; Saeb-Lima, Marcela; Rodriguez-Peralto, José Luis

    2017-02-01

    Approximately, 2% of Spitz nevi are polypoid; between 3.6% and 7.4% present with a halo reaction. In tandem, these low percentages make the presence of a polypoid Spitz nevus with a halo reaction uncommon; we have not found reports of any previous cases. In the current report, we present a polypoid Spitz nevus with a halo reaction on the back of a 10-year-old male and discuss the morphologic findings. The lesion showed preserved nuclear expression of BAP1. There was no immunohistochemical expression of BRAF and ALK, while the melanocytic cells expressed p16. Comparative genomic hybridization was performed, and no significant aberrations were found. Only 2 small losses were evidenced in chromosome 8. The patient has been followed now for 2 years with no recurrence.

  11. Halo cold dark matter and microlensing

    SciTech Connect

    Gates, Evalyn; Turner, Michael S.

    1993-12-01

    There is good evidence that most of the baryons in the Universe are dark and some evidence that most of the matter in the Universe is nonbaryonic with cold dark matter (cdm) being a promising possibility. We discuss expectations for the abundance of baryons and cdm in the halo of our galaxy and locally. We show that in plausible cdm models the local density of cdm is at least $10^{-25}\\gcmm3$. We also discuss what one can learn about the the local cdm density from microlensing of stars in the LMC by dark stars in the halo and, based upon a suite of reasonable two-component halo models, conclude that microlensing is not a sensitive probe of the local cdm density.

  12. Coulomb dissociation of one- and two-neutron halos in halo EFT

    NASA Astrophysics Data System (ADS)

    Acharya, Bijaya; Phillips, Daniel

    2013-10-01

    In neutron halo nuclei the neutron distribution extends significantly beyond the region occupied by the nuclear ``core.'' Halo effective field theory (Halo-EFT) exploits the consequent separation of scales in order to predict relationships between low-energy observables in these systems as a systematic expansion in Rcore /Rhalo . This talk will discuss results for the Coulomb dissociation of neutron halo nuclei in this framework. In particular, we consider the Coulomb dissociation of 19C. We compute the reduced transition probability (dB (E 1) / dE) for excitation of the bound-state neutrons to the continuum up to N2LO in the Halo-EFT expansion. By comparing the predcition with data from RIKEN we are able to extract accurate results for 19C's one-neutron separation energy and asymptotic normalization coefficient. Good agreement between data and Halo-EFT is also found for the longitudinal momentum distribution of 19C. Results from ongoing work to extend ths calculation to two-neutron halos will also be presented. Supported by the US Department of Energy under grant DE-FG02- 93ER40756.

  13. Composition of interstellar clouds in the disk and halo. I - HD 93521

    NASA Technical Reports Server (NTRS)

    Spitzer, Lyman, Jr.; Fitzpatrick, Edward L.

    1993-01-01

    Interstellar column densities of Fe, S, Si, Mn, and Mg in their dominant ionization state, as well as of C(+) and S(2+), are presently derived from analyses of HST UV observations of the Galactic halo star HD 93521. Ratios of column densities for the dominant species yield approximations of the logarithmic depletion D(X) in the warm, primarily neutral H gas which produces each of the resolved components. Variations of D between components are highly correlated between elements; about two Fe atoms leave the grains for every Si atom, as if these atoms were primarily bound in the Fe2SiO4 molecules within the grain cores.

  14. Composition of interstellar clouds in the disk and halo. I - HD 93521

    NASA Technical Reports Server (NTRS)

    Spitzer, Lyman, Jr.; Fitzpatrick, Edward L.

    1993-01-01

    Interstellar column densities of Fe, S, Si, Mn, and Mg in their dominant ionization state, as well as of C(+) and S(2+), are presently derived from analyses of HST UV observations of the Galactic halo star HD 93521. Ratios of column densities for the dominant species yield approximations of the logarithmic depletion D(X) in the warm, primarily neutral H gas which produces each of the resolved components. Variations of D between components are highly correlated between elements; about two Fe atoms leave the grains for every Si atom, as if these atoms were primarily bound in the Fe2SiO4 molecules within the grain cores.

  15. Galaxy halo occupation at high redshift

    NASA Astrophysics Data System (ADS)

    Bullock, James S.; Wechsler, Risa H.; Somerville, Rachel S.

    2002-01-01

    We discuss how current and future data on the clustering and number density of z~3 Lyman-break galaxies (LBGs) can be used to constrain their relationship to dark matter haloes. We explore a three-parameter model in which the number of LBGs per dark halo scales like a power law in the halo mass: N(M)=(M/M1)S for M>Mmin. Here, Mmin is the minimum mass halo that can host an LBG, M1 is a normalization parameter, associated with the mass above which haloes host more than one observed LBG, and S determines the strength of the mass-dependence. We show how these three parameters are constrained by three observable properties of LBGs: the number density, the large-scale bias and the fraction of objects in close pairs. Given these three quantities, the three unknown model parameters may be estimated analytically, allowing a full exploration of parameter space. As an example, we assume a ΛCDM cosmology and consider the observed properties of a recent sample of spectroscopically confirmed LBGs. We find that the favoured range for our model parameters is Mmin~=(0.4-8)×1010h- 1Msolar, M1~=(6-10)×1012h- 1Msolar, and 0.9<~S<~1.1. The preferred region in Mmin expands by an order of magnitude, and slightly shallower slopes are acceptable if the allowed range of bg is permitted to span all recent observational estimates. We also discuss how the observed clustering of LBGs as a function of luminosity can be used to constrain halo occupation, although because of current observational uncertainties we are unable to reach any strong conclusions. Our methods and results can be used to constrain more realistic models that aim to derive the occupation function N(M) from first principles, and offer insight into how basic physical properties affect the observed properties of LBGs.

  16. Global Properties of M31's Stellar Halo from the SPLASH Survey. I. Surface Brightness Profile

    NASA Astrophysics Data System (ADS)

    Gilbert, Karoline M.; Guhathakurta, Puragra; Beaton, Rachael L.; Bullock, James; Geha, Marla C.; Kalirai, Jason S.; Kirby, Evan N.; Majewski, Steven R.; Ostheimer, James C.; Patterson, Richard J.; Tollerud, Erik J.; Tanaka, Mikito; Chiba, Masashi

    2012-11-01

    We present the surface brightness profile of M31's stellar halo out to a projected radius of 175 kpc. The surface brightness estimates are based on confirmed samples of M31 red giant branch stars derived from Keck/DEIMOS spectroscopic observations. A set of empirical spectroscopic and photometric M31 membership diagnostics is used to identify and reject foreground and background contaminants. This enables us to trace the stellar halo of M31 to larger projected distances and fainter surface brightnesses than previous photometric studies. The surface brightness profile of M31's halo follows a power law with index -2.2 ± 0.2 and extends to a projected distance of at least ~175 kpc (~2/3 of M31's virial radius), with no evidence of a downward break at large radii. The best-fit elliptical isophotes have b/a = 0.94 with the major axis of the halo aligned along the minor axis of M31's disk, consistent with a prolate halo, although the data are also consistent with M31's halo having spherical symmetry. The fact that tidal debris features are kinematically cold is used to identify substructure in the spectroscopic fields out to projected radii of 90 kpc and investigate the effect of this substructure on the surface brightness profile. The scatter in the surface brightness profile is reduced when kinematically identified tidal debris features in M31 are statistically subtracted; the remaining profile indicates that a comparatively diffuse stellar component to M31's stellar halo exists to large distances. Beyond 90 kpc, kinematically cold tidal debris features cannot be identified due to small number statistics; nevertheless, the significant field-to-field variation in surface brightness beyond 90 kpc suggests that the outermost region of M31's halo is also comprised to a significant degree of stars stripped from accreted objects. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California

  17. Conceptual design of hollow electron lenses for beam halo control in the Large Hadron Collider

    SciTech Connect

    Stancari, Giulio; Previtali, Valentina; Valishev, Alexander; Bruce, Roderik; Redaelli, Stefano; Rossi, Adriana; Salvachua Ferrando, Belen

    2014-06-26

    Collimation with hollow electron beams is a technique for halo control in high-power hadron beams. It is based on an electron beam (possibly pulsed or modulated in intensity) guided by strong axial magnetic fields which overlaps with the circulating beam in a short section of the ring. The concept was tested experimentally at the Fermilab Tevatron collider using a hollow electron gun installed in one of the Tevatron electron lenses. We are proposing a conceptual design for applying this technique to the Large Hadron Collider at CERN. A prototype hollow electron gun for the LHC was built and tested. The expected performance of the hollow electron beam collimator was based on Tevatron experiments and on numerical tracking simulations. Halo removal rates and enhancements of halo diffusivity were estimated as a function of beam and lattice parameters. Proton beam core lifetimes and emittance growth rates were checked to ensure that undesired effects were suppressed. Hardware specifications were based on the Tevatron devices and on preliminary engineering integration studies in the LHC machine. Required resources and a possible timeline were also outlined, together with a brief discussion of alternative halo-removal schemes and of other possible uses of electron lenses to improve the performance of the LHC.

  18. Reversed halo sign on high-resolution CT of cryptogenic organizing pneumonia: diagnostic implications.

    PubMed

    Kim, Sang Jin; Lee, Kyung Soo; Ryu, Young Hoon; Yoon, Young Cheol; Choe, Kyu Ok; Kim, Tae Sung; Sung, Ki Jun

    2003-05-01

    The aim of our study was to evaluate the usefulness of the reversed halo sign on high-resolution CT in the diagnosis of cryptogenic organizing pneumonia. Between 1996 and 2001, we saw 31 patients with biopsy-proven cryptogenic organizing pneumonia. During the same period, we also saw 30 patients with non-cryptogenic organizing pneumonia diseases, from which cryptogenic organizing pneumonia should be differentiated: Wegener's granulomatosis (n = 14), diffuse bronchioloalveolar carcinoma (n = 10), chronic eosinophilic pneumonia (n = 5), and Churg-Strauss syndrome (n = 1). Two independent observers analyzed CT findings and recorded how frequently the so-called reversed halo sign (central ground-glass opacity and surrounding air-space consolidation of crescentic and ring shape) was seen on high-resolution CT. The most common patterns of parenchymal abnormalities of cryptogenic organizing pneumonia were ground-glass opacity (28/31 patients, 90%) and consolidation (27/31, 87%). The ground-glass opacity pattern showed random distribution, and the consolidation pattern showed subpleural or peribronchovascular (20/27 patients, 74%) distribution with predominance in the middle or lower lung zone. The reversed CT halo sign was seen in six (19%) of 31 patients with cryptogenic organizing pneumonia and in none of the patients with the diseases that needed to be differentiated from cryptogenic organizing pneumonia on CT. The reversed halo sign, although seen only in one fifth of patients with the disease, appears relatively specific to make a diagnosis of cryptogenic organizing pneumonia on CT.

  19. Continuous flow synthesis of α-halo ketones: essential building blocks of antiretroviral agents.

    PubMed

    Pinho, Vagner D; Gutmann, Bernhard; Miranda, Leandro S M; de Souza, Rodrigo O M A; Kappe, C Oliver

    2014-02-21

    The development of a continuous flow process for the multistep synthesis of α-halo ketones starting from N-protected amino acids is described. The obtained α-halo ketones are chiral building blocks for the synthesis of HIV protease inhibitors, such as atazanavir and darunavir. The synthesis starts with the formation of a mixed anhydride in a first tubular reactor. The anhydride is subsequently combined with anhydrous diazomethane in a tube-in-tube reactor. The tube-in-tube reactor consists of an inner tube, made from a gas-permeable, hydrophobic material, enclosed in a thick-walled, impermeable outer tube. Diazomethane is generated in the inner tube in an aqueous medium, and anhydrous diazomethane subsequently diffuses through the permeable membrane into the outer chamber. The α-diazo ketone is produced from the mixed anhydride and diazomethane in the outer chamber, and the resulting diazo ketone is finally converted to the halo ketone with anhydrous ethereal hydrogen halide. This method eliminates the need to store, transport, or handle diazomethane and produces α-halo ketone building blocks in a multistep system without racemization in excellent yields. A fully continuous process allowed the synthesis of 1.84 g of α-chloro ketone from the respective N-protected amino acid within ~4.5 h (87% yield).

  20. X-Ray Dust Scattering At Small Angles: The Complete Halo Around GX13+1

    NASA Technical Reports Server (NTRS)

    Smith, Randall K.

    2007-01-01

    The exquisite angular resolution available with Chandra should allow precision measurements of faint diffuse emission surrounding bright sources, such as the X-ray scattering halos created by interstellar dust. However, the ACIS CCDs suffer from pileup when observing bright sources, and this creates difficulties when trying to extract the scattered halo near the source. The initial study of the X-ray halo around GX13+1 using only the ACIS-I detector done by Smith, Edgar & Shafer (2002) suffered from a lack of sensitivity within 50" of the source, limiting what conclusions could be drawn. To address this problem, observations of GX13+1 were obtained with the Chandra HRC-I and simultaneously with the RXTE PCA. Combined with the existing ACIS-I data, this allowed measurements of the X-ray halo between 2-1000". After considering a range of dust models, each assumed to be smoothly distributed with or without a dense cloud along the line of sight, the results show that there is no evidence in this data for a dense cloud near the source, as suggested by Xiang et al. (2005). In addition, although no model leads to formally acceptable results, the Weingartner & Draine (2001) and all but one of the composite grain models from Zubko, Dwek & Arendt (2004) give particularly poor fits.

  1. X-ray Dust Halos Seen With Extreme Dynamic Range: What Do We Learn?

    NASA Astrophysics Data System (ADS)

    Smith, Randall

    2008-03-01

    The exquisite angular resolution available with Chandra should allow precision measurements of faint diffuse emission surrounding bright sources, such as the X-ray scattering halos created by interstellar dust. However, the ACIS CCDs suffer from pileup when observing bright sources, and this creates difficulties when trying to extract the scattered halo near the source. The initial study of the X-ray halo around GX13+1 using only the ACIS-I detector done by Smith, Edgar & Shafer (2002) suffered from a lack of sensitivity within 50'' of the source, limiting what conclusions could be drawn. To address this problem, observations of GX13+1 were obtained with the Chandra HRC-I and simultaneously with the RXTE PCA. Combined with the existing ACIS-I data, this allowed measurements of the X-ray halo between 2-1000''. After considering a range of dust models, each assumed to be smoothly distributed with or without a dense cloud along the line of sight, the results show that there is no evidence in this data for a dense cloud near the source, as suggested by Xiang et al. 2005. Finally, although no model leads to formally acceptable results, the Weingartner & Draine (2001) and nearly all of the composite grain models from Zubko, Dwek & Arendt (2004) give poor fits. I thank Dr. Michael Juda of the HRC-I team for providing significant assistance; this work was supported by Chandra Observing Grant GO56144X.

  2. X-Ray Dust Scattering at Small Angles: The Complete Halo around GX13+1

    NASA Astrophysics Data System (ADS)

    Smith, Randall K.

    2008-07-01

    The exquisite angular resolution available with Chandra should allow precision measurements of faint diffuse emission surrounding bright sources, such as the X-ray scattering halos created by interstellar dust. However, the ACIS CCDs suffer from pileup when observing bright sources, and this creates difficulties when trying to extract the scattered halo near the source. The initial study of the X-ray halo around GX13+1 using only the ACIS-I detector performed by Smith, Edgar, & Shafer suffered from a lack of sensitivity within 50'' of the source, limiting what conclusions could be drawn. To address this problem, observations of GX13+1 were obtained with the Chandra HRC-I and simultaneously with the RXTE PCA. Combined with the existing ACIS-I data, this allowed measurements of the X-ray halo between 2'' and 1000''. After considering a range of dust models, each assumed to be smoothly distributed with or without a dense cloud along the line of sight; the results show that there is no evidence in these data for a dense cloud near the source, as suggested by Xiang et al. Finally, although no model leads to formally acceptable results, the Weingartner & Draine model and nearly all of the composite grain models from Zubko, Dwek, & Arendt give poor fits.

  3. Dark energy and extended dark matter halos

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.; Teerikorpi, P.; Valtonen, M. J.; Dolgachev, V. P.; Domozhilova, L. M.; Byrd, G. G.

    2012-03-01

    The cosmological mean matter (dark and baryonic) density measured in the units of the critical density is Ωm = 0.27. Independently, the local mean density is estimated to be Ωloc = 0.08-0.23 from recent data on galaxy groups at redshifts up to z = 0.01-0.03 (as published by Crook et al. 2007, ApJ, 655, 790 and Makarov & Karachentsev 2011, MNRAS, 412, 2498). If the lower values of Ωloc are reliable, as Makarov & Karachentsev and some other observers prefer, does this mean that the Local Universe of 100-300 Mpc across is an underdensity in the cosmic matter distribution? Or could it nevertheless be representative of the mean cosmic density or even be an overdensity due to the Local Supercluster therein. We focus on dark matter halos of groups of galaxies and check how much dark mass the invisible outer layers of the halos are able to host. The outer layers are usually devoid of bright galaxies and cannot be seen at large distances. The key factor which bounds the size of an isolated halo is the local antigravity produced by the omnipresent background of dark energy. A gravitationally bound halo does not extend beyond the zero-gravity surface where the gravity of matter and the antigravity of dark energy balance, thus defining a natural upper size of a system. We use our theory of local dynamical effects of dark energy to estimate the maximal sizes and masses of the extended dark halos. Using data from three recent catalogs of galaxy groups, we show that the calculated mass bounds conform with the assumption that a significant amount of dark matter is located in the invisible outer parts of the extended halos, sufficient to fill the gap between the observed and expected local matter density. Nearby groups of galaxies and the Virgo cluster have dark halos which seem to extend up to their zero-gravity surfaces. If the extended halo is a common feature of gravitationally bound systems on scales of galaxy groups and clusters, the Local Universe could be typical or even

  4. Rockstar: Phase-space halo finder

    NASA Astrophysics Data System (ADS)

    Behroozi, Peter; Wechsler, Risa; Wu, Hao-Yi

    2012-10-01

    Rockstar (Robust Overdensity Calculation using K-Space Topologically Adaptive Refinement) identifies dark matter halos, substructure, and tidal features. The approach is based on adaptive hierarchical refinement of friends-of-friends groups in six phase-space dimensions and one time dimension, which allows for robust (grid-independent, shape-independent, and noise-resilient) tracking of substructure. Our method is massively parallel (up to 10^5 CPUs) and runs on the largest current simulations (>10^10 particles) with high efficiency (10 CPU hours and 60 gigabytes of memory required per billion particles analyzed). Rockstar offers significant improvement in substructure recovery as compared to several other halo finders.

  5. PHYSICAL PROPERTIES OF COMPLEX C HALO CLOUDS

    SciTech Connect

    Hsu, W.-H.; Putman, M. E.; Peek, J. E. G.; Heitsch, F.; Clark, S. E.; Stanimirovic, S.

    2011-02-15

    Observations from the Galactic Arecibo L-band Feed Array H I (GALFA-H I) Survey of the tail of Complex C are presented and the halo clouds associated with this complex are cataloged. The properties of the Complex C clouds are compared to clouds cataloged at the tail of the Magellanic Stream to provide insight into the origin and destruction mechanism of Complex C. Magellanic Stream and Complex C clouds show similarities in their mass distributions (slope = -0.7 and -0.6 log (N( log (mass)))/ log (mass), respectively) and have a common line width of 20-30 km s{sup -1} (indicative of a warm component), which may indicate a common origin and/or physical process breaking down the clouds. The clouds cataloged at the tail of Complex C extend over a mass range of 10{sup 1.1}-10{sup 4.8} M{sub sun}, sizes of 10{sup 1.2}-10{sup 2.6} pc, and have a median volume density and pressure of 0.065 cm{sup -3} and (P/k) = 580 K cm{sup -3}. We do not see a prominent two-phase structure in Complex C, possibly due to its low metallicity and inefficient cooling compared to other halo clouds. Assuming that the Complex C clouds are in pressure equilibrium with a hot halo medium, we find a median halo density of 5.8 x 10{sup -4} cm{sup -3}, which given a constant distance of 10 kpc is at a z-height of {approx}3 kpc. Using the same argument for the Stream results in a median halo density of 8.4 x 10-{sup 5} (60 kpc/d) cm{sup -3}. These densities are consistent with previous observational constraints and cosmological simulations. We also assess the derived cloud and halo properties with three-dimensional grid simulations of halo H I clouds and find that the temperature is generally consistent within a factor of 1.5 and the volume densities, pressures, and halo densities are consistent within a factor of three.

  6. The rise of ionized gas in the Magellanic Stream

    NASA Astrophysics Data System (ADS)

    Hernandez, Michael; Barger, Kathleen; Smart, Brianna; Haffner, L. Matthew

    2017-01-01

    The Small and Large Magellanic Clouds are a pair of interacting galaxies near the Milky Way. Tidal interactions have stripped gas from these galaxies, leaving behind gaseous debris such as the Magellanic Stream. We explore the morphology and kinematics of the neutral and ionized hydrogen gas in the trailing stream traveling toward the Milky Way. This comparison provides us with insight into the physical processes that are affecting the gas flowing through the Galactic halo. This is done using mapped H-alpha emission-line spectroscopy, obtained with the Wisconsin H-alpha Mapper (WHAM), and archival 21-cm HI observations of the Stream near the Magellanic Clouds. We found that the neutral and ionized gas spatially and kinematically trace each other. With a map of the ionized gas in hand, we will continue to study the survival of this tidal relic.

  7. Search for and analysis of radioactive halos in lunar material

    NASA Technical Reports Server (NTRS)

    Gentry, R. V.

    1976-01-01

    The lunar halo search was conducted because halos in terrestrial minerals serve as pointers to localized radioactivity, and make possible analytical studies on the problems of isotopic dating and mode of crystallization of the host mineral. Ancillary studies were conducted on terrestrial halos and on certain samples of special origin such as tektites and meteorites.

  8. The Constant Error of the Halo in Educational Outcomes Research.

    ERIC Educational Resources Information Center

    Pike, Gary R.

    1999-01-01

    Research suggests correlations between student gains and college experiences may be an artifact of halo effect. A study examined whether halo error underlies students' self-reported gains, significance of the error, and its effect on the relationship between college experiences and educational outcomes. Results confirm halo error may be an…

  9. Comment on Halo Effects in Rating and Evaluation Research.

    ERIC Educational Resources Information Center

    Feeley, Thomas Hugh

    2002-01-01

    Considers the existence of halo effects in individuals' evaluations of target communicators across different dimensions. Notes that halo effects result from raters' inability to discriminate among conceptually distinct and theoretically independent aspects of a target's behavior. Discusses current conceptions of halo error and suggests several…

  10. Comment on Halo Effects in Rating and Evaluation Research.

    ERIC Educational Resources Information Center

    Feeley, Thomas Hugh

    2002-01-01

    Considers the existence of halo effects in individuals' evaluations of target communicators across different dimensions. Notes that halo effects result from raters' inability to discriminate among conceptually distinct and theoretically independent aspects of a target's behavior. Discusses current conceptions of halo error and suggests several…

  11. The Constant Error of the Halo in Educational Outcomes Research.

    ERIC Educational Resources Information Center

    Pike, Gary R.

    1999-01-01

    Research suggests correlations between student gains and college experiences may be an artifact of halo effect. A study examined whether halo error underlies students' self-reported gains, significance of the error, and its effect on the relationship between college experiences and educational outcomes. Results confirm halo error may be an…

  12. Simulating the 21 cm signal from reionization including non-linear ionizations and inhomogeneous recombinations

    NASA Astrophysics Data System (ADS)

    Hassan, Sultan; Davé, Romeel; Finlator, Kristian; Santos, Mario G.

    2016-04-01

    We explore the impact of incorporating physically motivated ionization and recombination rates on the history and topology of cosmic reionization and the resulting 21 cm power spectrum, by incorporating inputs from small-volume hydrodynamic simulations into our semi-numerical code, SIMFAST21, that evolves reionization on large scales. We employ radiative hydrodynamic simulations to parametrize the ionization rate Rion and recombination rate Rrec as functions of halo mass, overdensity and redshift. We find that Rion scales superlinearly with halo mass ({R_ion}∝ M_h^{1.41}), in contrast to previous assumptions. Implementing these scalings into SIMFAST21, we tune our one free parameter, the escape fraction fesc, to simultaneously reproduce recent observations of the Thomson optical depth, ionizing emissivity and volume-averaged neutral fraction by the end of reionization. This yields f_esc=4^{+7}_{-2} per cent averaged over our 0.375 h-1 Mpc cells, independent of halo mass or redshift, increasing to 6 per cent if we also constrain to match the observed z = 7 star formation rate function. Introducing superlinear Rion increases the duration of reionization and boosts small-scale 21 cm power by two to three times at intermediate phases of reionization, while inhomogeneous recombinations reduce ionized bubble sizes and suppress large-scale 21 cm power by two to three times. Gas clumping on sub-cell scales has a minimal effect on the 21 cm power. Superlinear Rion also significantly increases the median halo mass scale for ionizing photon output to ˜ 1010 M⊙, making the majority of reionizing sources more accessible to next-generation facilities. These results highlight the importance of accurately treating ionizing sources and recombinations for modelling reionization and its 21 cm power spectrum.

  13. Ionization structure of multiple-shell planetary nebulae. I. NGC 2438

    NASA Astrophysics Data System (ADS)

    Öttl, S.; Kimeswenger, S.; Zijlstra, A. A.

    2014-05-01

    Context. In recent times an increasing number of extended haloes and multiple shells around planetary nebulae have been discovered. These faint extensions to the main nebula trace the mass-loss history of the star, modified by the subsequent evolution of the nebula. Integrated models predict that some haloes may be recombining, and thus are not in ionization equilibrium. But parameters such as the ionization state and thus the contiguous excitation process are only poorly known. The haloes are very extended, but faint in surface brightness -103 times lower than the main nebula. The observational limits call for an extremely well studied main nebula, to model the processes in the shells and haloes of one object. NGC 2438 is a perfect candidate to explore the physical characteristics of the halo. Aims: The aim is to derive a complete data set of the main nebula. This allows us to derive the physical conditions from photoionization models, such as temperature, density and ionization, and clumping. These models are used to derive whether the halo is in ionization equilibrium. Methods: Long-slit spectroscopic data at various positions in the nebula were obtained at the ESO 3.6 m and the SAAO 1.9 m telescope. These data were supplemented by imaging data from the HST archive and from the ESO 3.6 m telescope and by archival VLA observations. The use of diagnostic diagrams draws limits for physical properties in the models. The photoionization code CLOUDY was used to model the nebular properties and to derive a more accurate distance and ionized mass. Results: We derive an accurate extinction EB - V = 0.16, and distance of 1.9 ± 0.2 kpc. This locates the nebula behind the nearby open cluster M46 and rules out membership. The low-excitation species are found to be dominated by clumps. The emission line ratios show no evidence for shocks. The filling factor increases with radius in the nebula. The electron densities in the main nebula are ~250 cm-3, dropping to ~10-30 in the

  14. Reputation, Halo, and Ratings of Counseling Programs

    ERIC Educational Resources Information Center

    Thoreson, Richard W.; And Others

    1975-01-01

    This study tests the hypothesis that previous ratings of programs in psychology reflect both an experimental psychology and general institutional halo bias. It was found that applied programs in counseling psychology do receive ratings that differ from overall ratings of psychology in general. Programs ranked as strong, good, and adequate are…

  15. Reputation, Halo, and Ratings of Counseling Programs

    ERIC Educational Resources Information Center

    Thoreson, Richard W.; And Others

    1975-01-01

    This study tests the hypothesis that previous ratings of programs in psychology reflect both an experimental psychology and general institutional halo bias. It was found that applied programs in counseling psychology do receive ratings that differ from overall ratings of psychology in general. Programs ranked as strong, good, and adequate are…

  16. The Hot Gaseous Halos of Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Bregman, J.

    2016-06-01

    In the Milky Way, absorption and emission line measurements of O VII and O VIII show that the halo environment is dominated by a nearly spherical halo of temperature 2 × 10^6 K, metallicity of 0.3-0.5 solar, and with a density decreasing as r^{-3/2}. The mass of the hot gas, estimated through extrapolation to the virial radius, is comparable to the stellar mass, but does not account for the missing mass. The Milky Way hot halo appears to be rotating at about 180 km/s, which is consistent with model expectations, depending on the time of infall. Around massive spiral galaxies, hot halos are seen in emission out to about 70 kpc in the best cases. These show similar gas density laws and metallicities in the range 0.1-0.5 solar. The gas mass is comparable to the stellar mass, but does not account for the missing baryons within the virial radius. If the density law can be extrapolated to about three virial radii, the missing baryons would be accounted for.

  17. Substructure of fuzzy dark matter haloes

    NASA Astrophysics Data System (ADS)

    Du, Xiaolong; Behrens, Christoph; Niemeyer, Jens C.

    2017-02-01

    We derive the halo mass function (HMF) for fuzzy dark matter (FDM) by solving the excursion set problem explicitly with a mass-dependent barrier function, which has not been done before. We find that compared to the naive approach of the Sheth-Tormen HMF for FDM, our approach has a higher cutoff mass and the cutoff mass changes less strongly with redshifts. Using merger trees constructed with a modified version of the Lacey & Cole formalism that accounts for suppressed small-scale power and the scale-dependent growth of FDM haloes and the semi-analytic GALACTICUS code, we study the statistics of halo substructure including the effects from dynamical friction and tidal stripping. We find that if the dark matter is a mixture of cold dark matter (CDM) and FDM, there will be a suppression on the halo substructure on small scales which may be able to solve the missing satellites problem faced by the pure CDM model. The suppression becomes stronger with increasing FDM fraction or decreasing FDM mass. Thus, it may be used to constrain the FDM model.

  18. WEIGHING THE GALACTIC DARK MATTER HALO: A LOWER MASS LIMIT FROM THE FASTEST HALO STAR KNOWN

    SciTech Connect

    Przybilla, Norbert; Tillich, Alfred; Heber, Ulrich; Scholz, Ralf-Dieter

    2010-07-20

    The mass of the Galactic dark matter halo is under vivid discussion. A recent study by Xue et al. revised the Galactic halo mass downward by a factor of {approx}2 relative to previous work, based on the line-of-sight velocity distribution of {approx}2400 blue horizontal-branch (BHB) halo stars. The observations were interpreted with a statistical approach using cosmological galaxy formation simulations, as only four of the six-dimensional phase-space coordinates were determined. Here we concentrate on a close investigation of the stars with the highest negative radial velocity from that sample. For one star, SDSSJ153935.67+023909.8 (J1539+0239 for short), we succeed in measuring a significant proper motion, i.e., full phase-space information is obtained. We confirm the star to be a Population II BHB star from an independent quantitative analysis of the Sloan Digital Sky Survey (SDSS) spectrum-providing the first non-LTE (NLTE) study of any halo BHB star-and reconstruct its three-dimensional trajectory in the Galactic potential. J1539+0239 turns out to be the fastest halo star known to date, with a Galactic rest-frame velocity of 694{sup +300}{sub -221} km s{sup -1} (full uncertainty range from Monte Carlo error propagation) at its current position. The extreme kinematics of the star allows a significant lower limit to be put on the halo mass in order to keep it bound, of M {sub halo} {>=} 1.7{sup +2.3}{sub -1.1} x 10{sup 12} M{sub sun}. We conclude that the Xue et al. results tend to underestimate the true halo mass as their most likely mass value is consistent with our analysis only at a level of 4%. However, our result confirms other studies that make use of the full phase-space information.

  19. Non-Gaussian halo mass function and non-spherical halo collapse: theory vs. simulations

    SciTech Connect

    Achitouv, Ixandra E.; Corasaniti, Pier Stefano E-mail: Pier-Stefano.Corasaniti@obspm.fr

    2012-02-01

    The mass distribution of dark matter halos is a sensitive probe of primordial non-Gaussianity (NG). We derive an analytical formula of the halo mass function by perturbatively computing excursion set path-integrals for a non-Gaussian density field with non-vanishing skewness, f{sub NL}. We assume a stochastic barrier model which captures the main features of the ellipsoidal collapse of halos. Contrary to previous results based on extensions of the Press-Schechter formalism to NG initial conditions, we find that the non-spherical collapse of halos directly alter the signature of primordial NG. This points toward a potential degeneracy between the effect of primordial non-Gaussianity and that of non-linear halo collapse. The inferred mass function is found to be in remarkable agreement with N-body simulations of NG local type. Deviations are well within numerical uncertainties for all values of f{sub NL}{sup loc} in the range of validity of the perturbative calculation (|f{sub nl}{sup loc}|∼<200). Moreover, the comparison with simulation results suggests that for |f{sub NL}|∼>30 the non-linear collapse of halos, as described by our barrier model, strongly deviates from that of Gaussian initial conditions. This is not surprising since the effect of non-linear gravitational processes may be altered by initially large NG. Hence, in the lack of prior theoretical knowledge, halo collapse model parameters should be included in statistical halo mass function data analysis which aim to constrain the signature of primordial NG.

  20. DISCOVERY OF A HALO AROUND THE HELIX NEBULA NGC 7293 IN THE WISE ALL-SKY SURVEY

    SciTech Connect

    Zhang Yong; Hsia, Chih-Hao; Kwok, Sun E-mail: xiazh@hku.hk

    2012-08-10

    We report the discovery of an extended halo ({approx}40' in diameter) around the planetary nebula NGC 7293 (the Helix Nebula) observed in the 12 {mu}m band from the Wide-field Infrared Survey Explorer all-sky survey. The mid-infrared halo has an axisymmetric structure with a sharp boundary to the northeast and a more diffuse boundary to the southwest, suggesting an interaction between the stellar wind and the interstellar medium (ISM). The symmetry axis of the halo is well aligned with that of a northeast arc, suggesting that the two structures are physically associated. We have attempted to fit the observed geometry with a model of a moving steady-state stellar wind interacting with the ISM. Possible combinations of the ISM density and the stellar velocity are derived from these fittings. The discrepancies between the model and the observations suggest that the stellar mass loss has a more complicated history, including possible time and angle dependences.

  1. The velocity shear tensor: tracer of halo alignment

    NASA Astrophysics Data System (ADS)

    Libeskind, Noam I.; Hoffman, Yehuda; Forero-Romero, Jaime; Gottlöber, Stefan; Knebe, Alexander; Steinmetz, Matthias; Klypin, Anatoly

    2013-01-01

    The alignment of dark matter (DM) haloes and the surrounding large-scale structure (LSS) is examined in the context of the cosmic web. Halo spin, shape and the orbital angular momentum of subhaloes are investigated relative to the LSS using the eigenvectors of the velocity shear tensor evaluated on a grid with a scale of 1 Mpc h-1, deep within the non-linear regime. Knots, filaments, sheets and voids are associated with regions that are collapsing along 3, 2, 1 or 0 principal directions simultaneously. Each halo is tagged with a web classification (i.e. knot halo, filament halo, etc.) according to the nature of the collapse at the halo position. The full distribution of shear eigenvalues is found to be substantially different from that tagged to haloes, indicating that the observed velocity shear is significantly biased. We find that larger mass haloes live in regions where the shear is more isotropic, namely the expansion or collapse is more spherical. A correlation is found between the halo shape and the eigenvectors of the shear tensor, with the longest (shortest) axis of the halo shape being aligned with the slowest (fastest) collapsing eigenvector. This correlation is web independent, suggesting that the velocity shear is a fundamental tracer of the halo alignment. A similar result is found for the alignment of halo spin with the cosmic web. It has been shown that high-mass haloes exhibit a spin flip with respect to the LSS: we find that the mass at which this spin flip occurs is web dependent and not universal as suggested previously. Although weaker than haloes, subhalo orbits too exhibit an alignment with the LSS, providing a possible insight into the highly correlated corotation of the Milky Way's satellite system. The present study suggests that the velocity shear tensor constitutes the natural framework for studying the directional properties of the non-linear LSS and those of haloes and galaxies.

  2. THE ESCAPE FRACTION OF IONIZING RADIATION FROM GALAXIES

    SciTech Connect

    Benson, Andrew; Venkatesan, Aparna; Shull, J. Michael E-mail: avenkatesan@usfca.edu

    2013-06-10

    The escape of ionizing radiation from galaxies plays a critical role in the evolution of gas in galaxies, and the heating and ionization history of the intergalactic medium. We present semi-analytic calculations of the escape fraction of ionizing radiation for both hydrogen and helium from galaxies ranging from primordial systems to disk-type galaxies that are not heavily dust-obscured. We consider variations in the galaxy density profile, source type, location, and spectrum, and gas overdensity/distribution factors. For sufficiently hard first-light sources, the helium ionization fronts closely track or advance beyond that of hydrogen. Key new results in this work include calculations of the escape fractions for He I and He II ionizing radiation, and the impact of partial ionization from X-rays from early active galactic nuclei or stellar clusters on the escape fractions from galaxy halos. When factoring in frequency-dependent effects, we find that X-rays play an important role in boosting the escape fractions for both hydrogen and helium, but especially for He II. We briefly discuss the implications of these results for recent observations of the He II reionization epoch at low redshifts, as well as the UV data and emission-line signatures from early galaxies anticipated from future satellite missions.

  3. Stellar discs in Aquarius dark matter haloes

    NASA Astrophysics Data System (ADS)

    DeBuhr, Jackson; Ma, Chung-Pei; White, Simon D. M.

    2012-10-01

    We investigate the gravitational interactions between live stellar discs and their dark matter haloes, using Λ cold dark matter haloes similar in mass to that of the Milky Way taken from the Aquarius Project. We introduce the stellar discs by first allowing the haloes to respond to the influence of a growing rigid disc potential from z = 1.3 to 1.0. The rigid potential is then replaced with star particles which evolve self-consistently with the dark matter particles until z = 0.0. Regardless of the initial orientation of the disc, the inner parts of the haloes contract and change from prolate to oblate as the disc grows to its full size. When the disc's normal is initially aligned with the major axis of the halo at z = 1.3, the length of the major axis contracts and becomes the minor axis by z = 1.0. Six out of the eight discs in our main set of simulations form bars, and five of the six bars experience a buckling instability that results in a sudden jump in the vertical stellar velocity dispersion and an accompanying drop in the m = 2 Fourier amplitude of the disc surface density. The bars are not destroyed by the buckling but continue to grow until the present day. Bars are largely absent when the disc mass is reduced by a factor of 2 or more; the relative disc-to-halo mass is therefore a primary factor in bar formation and evolution. A subset of the discs is warped at the outskirts and contains prominent non-coplanar material with a ring-like structure. Many discs reorient by large angles between z = 1 and 0, following a coherent reorientation of their inner haloes. Larger reorientations produce more strongly warped discs, suggesting a tight link between the two phenomena. The origins of bars and warps appear independent: some discs with strong bars show little disturbances at the outskirts, while the discs with the weakest bars show severe warps.

  4. Mapping Dark Matter Halos with Stellar Kinematics

    NASA Astrophysics Data System (ADS)

    Murphy, Jeremy; Gebhardt, K.; Greene, J. E.; Graves, G.

    2013-07-01

    Galaxies of all sizes form and evolve in the centers of dark matter halos. As these halos constitute the large majority of the total mass of a galaxy, dark matter certainly plays a central role in the galaxy's formation and evolution. Yet despite our understanding of the importance of dark matter, observations of the extent and shape of dark matter halos have been slow in coming. The paucity of data is particularly acute in elliptical galaxies. Happily, concerted effort over the past several years by a number of groups has been shedding light on the dark matter halos around galaxies over a wide range in mass. The development of new instrumentation and large surveys, coupled with the tantalizing evidence for a direct detection of dark matter from the AMS experiment, has brought on a golden age in the study of galactic scale dark matter halos. I report on results using extended stellar kinematics from integrated light to dynamically model massive elliptical galaxies in the local universe. I use the integral field power of the Mitchell Spectrograph to explore the kinematics of stars to large radii (R > 2.5 r_e). Once the line-of-sight stellar kinematics are measured, I employ orbit-based, axisymmetric dynamical modeling to explore a range of dark matter halo parameterizations. Globular cluster kinematics at even larger radii are used to further constrain the dynamical models. The dynamical models also return information on the anisotropy of the stars which help to further illuminate the primary formation mechanisms of the galaxy. Specifically, I will show dynamical modeling results for the first and second rank galaxies in the Virgo Cluster, M49 and M87. Although similar in total luminosity and ellipticity, these two galaxies show evidence for different dark matter halo shapes, baryon to dark matter fractions, and stellar anisotropy profiles. Moreover, the stellar velocity dispersion at large radii in M87 is significantly higher than the globular clusters at the same

  5. THE HALO OCCUPATION DISTRIBUTION OF SDSS QUASARS

    SciTech Connect

    Richardson, Jonathan; Chatterjee, Suchetana; Nagai, Daisuke; Zheng Zheng; Shen Yue

    2012-08-10

    We present an estimate of the projected two-point correlation function (2PCF) of quasars in the Sloan Digital Sky Survey (SDSS) over the full range of one- and two-halo scales, 0.02 h{sup -1} Mpc < r{sub p} < 120 h{sup -1} Mpc. This was achieved by combining data from SDSS DR7 on large scales and Hennawi et al. (with appropriate statistical corrections) on small scales. Our combined clustering sample is the largest spectroscopic quasar clustering sample to date, containing {approx}48, 000 quasars in the redshift range 0.4 {approx}< z {approx}< 2.5 with median redshift 1.4. We interpret these precise 2PCF measurements within the halo occupation distribution (HOD) framework and constrain the occupation functions of central and satellite quasars in dark matter halos. In order to explain the small-scale clustering, the HOD modeling requires that a small fraction of z {approx} 1.4 quasars, f{sub sat} = (7.4 {+-} 1.4) Multiplication-Sign 10{sup -4}, be satellites in dark matter halos. At z {approx} 1.4, the median masses of the host halos of central and satellite quasars are constrained to be M{sub cen} = 4.1{sup +0.3}{sub -0.4} Multiplication-Sign 10{sup 12} h{sup -1} M{sub Sun} and M{sub sat} = 3.6{sup +0.8}{sub -1.0} Multiplication-Sign 10{sup 14} h{sup -1} M{sub Sun }, respectively. To investigate the redshift evolution of the quasar-halo relationship, we also perform HOD modeling of the projected 2PCF measured by Shen et al. for SDSS quasars with median redshift 3.2. We find tentative evidence for an increase in the mass scale of quasar host halos-the inferred median mass of halos hosting central quasars at z {approx} 3.2 is M{sub cen} = 14.1{sup +5.8}{sub -6.9} Multiplication-Sign 10{sup 12} h{sup -1} M{sub Sun }. The cutoff profiles of the mean occupation functions of central quasars reveal that quasar luminosity is more tightly correlated with halo mass at higher redshifts. The average quasar duty cycle around the median host halo mass is inferred to be f{sub q

  6. The Impact of Theoretical Uncertainties in the Halo Mass Function and Halo

    SciTech Connect

    Wu, Hao-Yi; Zentner, Andrew R.; Wechsler, Risa H.; /KIPAC, Menlo Park /SLAC /Pittsburgh U. /KIPAC, Menlo Park /SLAC

    2010-06-04

    We study the impact of theoretical uncertainty in the dark matter halo mass function and halo bias on dark energy constraints from imminent galaxy cluster surveys. We find that for an optical cluster survey like the Dark Energy Survey, the accuracy required on the predicted halo mass function to make it an insignificant source of error on dark energy parameters is {approx}1%. The analogous requirement on the predicted halo bias is less stringent ({approx}5%), particularly if the observable-mass distribution can be well constrained by other means. These requirements depend upon survey area but are relatively insensitive to survey depth. The most stringent requirements are likely to come from a survey over a significant fraction of the sky that aims to observe clusters down to relatively low mass, M{sub th}{approx} 10{sup 13.7} h{sup -1} M{sub sun}; for such a survey, the mass function and halo bias must be predicted to accuracies of {approx}0.5% and {approx}1%, respectively. These accuracies represent a limit on the practical need to calibrate ever more accurate halo mass and bias functions. We find that improving predictions for the mass function in the low-redshift and low-mass regimes is the most effective way to improve dark energy constraints.

  7. Comparing halo bias from abundance and clustering

    NASA Astrophysics Data System (ADS)

    Hoffmann, K.; Bel, J.; Gaztañaga, E.

    2015-06-01

    We model the abundance of haloes in the ˜(3 Gpc h-1)3 volume of the MICE Grand Challenge simulation by fitting the universal mass function with an improved Jackknife error covariance estimator that matches theory predictions. We present unifying relations between different fitting models and new predictions for linear (b1) and non-linear (c2 and c3) halo clustering bias. Different mass function fits show strong variations in their performance when including the low mass range (Mh ≲ 3 × 1012 M⊙ h-1) in the analysis. Together with fits from the literature, we find an overall variation in the amplitudes of around 10 per cent in the low mass and up to 50 per cent in the high mass (galaxy cluster) range (Mh > 1014 M⊙ h-1). These variations propagate into a 10 per cent change in b1 predictions and a 50 per cent change in c2 or c3. Despite these strong variations, we find universal relations between b1 and c2 or c3 for which we provide simple fits. Excluding low-mass haloes, different models fitted with reasonable goodness in this analysis, show per cent level agreement in their b1 predictions, but are systematically 5-10 per cent lower than the bias directly measured with two-point halo-mass clustering. This result confirms previous findings derived from smaller volumes (and smaller masses). Inaccuracies in the bias predictions lead to 5-10 per cent errors in growth measurements. They also affect any halo occupation distribution fitting or (cluster) mass calibration from clustering measurements.

  8. Parametrizing the stellar haloes of galaxies

    NASA Astrophysics Data System (ADS)

    D'Souza, Richard; Kauffman, Guinevere; Wang, Jing; Vegetti, Simona

    2014-09-01

    We study the stellar haloes of galaxies out to 70-100 kpc as a function of stellar mass and galaxy type by stacking aligned r- and g-band images from a sample of 45 508 galaxies from Sloan Digital Sky Survey Data Release 9 in the redshift range 0.06 ≤ z ≤ 0.1 and in the mass range 1010.0 M⊙ < M* < 1011.4 M⊙. We derive surface brightness profiles to a depth of almost μr ˜ 32 mag arcsec-2. We find that the ellipticity of the stellar halo is a function of galaxy stellar mass and that the haloes of high-concentration galaxies are more elliptical than those of low-concentration galaxies. Where the g - r colour of the stellar halo can be measured, we find that the stellar light is always bluer than in the main galaxy. The colour of the stellar halo is redder for more massive galaxies. We further demonstrate that the full two-dimensional surface intensity distribution of our galaxy stacks can only be fit through multicomponent Sérsic models. Using the fraction of light in the outer component of the models as a proxy for the fraction of accreted stellar light, we show that this fraction is a function of stellar mass and galaxy type. The fraction of accreted stellar light rises from 30 to 70 per cent and from 2 to 25 per cent for high- and low-concentration galaxies, respectively, over the mass range 1010.0-1011.4 M⊙.

  9. PEEK-Halo effect in interbody fusion.

    PubMed

    Phan, Kevin; Hogan, Jarred A; Assem, Yusuf; Mobbs, Ralph J

    2016-02-01

    Recent developments have seen poly[aryl-ether-ether-ketone] (PEEK) being increasingly used in vertebral body fusion. More novel approaches to improve PEEK have included the introduction of titanium-PEEK (Ti-PEEK) composites and coatings. This paper aims to describe a potential complication of PEEK based implants relating to poorer integration with the surrounding bone, producing a "PEEK-Halo" effect which is not seen in Ti-PEEK composite implants. We present images from two patients undergoing anterior lumbar interbody fusion (ALIF). The first patient underwent an L5/S1 ALIF using a PEEK implant whilst the second patient underwent L4/L5 ALIF using a Ti-PEEK composite implant. Evidence of osseointegration was sought using CT imaging and confirmed using histological preparations of a sheep tibia model. The PEEK-Halo effect is demonstrated by a halo effect between the PEEK implant and the bone graft on CT imaging. This phenomenon is secondary to poor osseointegration of PEEK implants. The PEEK-Halo effect was not demonstrated in the second patient who received a Ti-PEEK composite graft. Histological analysis of graft/bone interface surfaces in PEEK versus Ti-PEEK implants in a sheep model further confirmed poorer osseointegration of the PEEK implant. In conclusion, the PEEK-Halo effect is seen secondary to minimal osseointegration of PEEK at the adjacent vertebral endplate following a PEEK implant insertion. This effect is not seen with Ti-PEEK implants, and may support the role of titanium in improving the bone-implant interface of PEEK substrates. Copyright © 2015 Elsevier Ltd. All rights reserved.

  10. The Circumgalactic Medium in Massive Halos

    NASA Astrophysics Data System (ADS)

    Chen, Hsiao-Wen

    This chapter presents a review of the current state of knowledge on the cool (T ˜ 104 K) halo gas content around massive galaxies at z ≈ 0. 2-2. Over the last decade, significant progress has been made in characterizing the cool circumgalactic gas in massive halos of M h ≈ 1012-14 M⊙ at intermediate redshifts using absorption spectroscopy. Systematic studies of halo gas around massive galaxies beyond the nearby universe are made possible by large spectroscopic samples of galaxies and quasars in public archives. In addition to accurate and precise constraints for the incidence of cool gas in massive halos, detailed characterizations of gas kinematics and chemical compositions around massive quiescent galaxies at z ≈ 0. 5 have also been obtained. Combining all available measurements shows that infalling clouds from external sources are likely the primary source of cool gas detected at d 100 d\\gtrsim 100 kpc from massive quiescent galaxies. The origin of the gas closer in is currently less certain, but SNe Ia driven winds appear to contribute significantly to cool gas found at d < 100 kpc. In contrast, cool gas observed at d 200 d\\lesssim 200 kpc from luminous quasars appears to be intimately connected to quasar activities on parsec scales. The observed strong correlation between cool gas covering fraction in quasar host halos and quasar bolometric luminosity remains a puzzle. Combining absorption-line studies with spatially resolved emission measurements of both gas and galaxies is the necessary next step to address remaining questions.

  11. Dark Matter Halos with VIRUS-P

    NASA Astrophysics Data System (ADS)

    Murphy, Jeremy; Gebhardt, K.

    2010-05-01

    We present new, two-dimensional stellar kinematic data on several of the most massive galaxies in the local universe. These data were taken with the integral field spectrograph, VIRUS-P, and extend to unprecedented radial distances. Once robust stellar kinematics are in hand, we run orbit-based axisymmetric dynamical models in order to constrain the stellar mass-to-light ratio and dark matter halo parameters. We have run a large set of dynamical models on the second rank galaxy in the Virgo cluster, M87, and find clear evidence for a massive dark matter halo. The two-dimensional stellar kinematics for several of our other targets, all first and second rank galaxies, are also presented. Dark matter halos are known to dominate the mass profile of elliptical galaxies somewhere between one to two effective radii, yet due to the low surface brightness at these radial distances, determining stellar dynamics is technologically challenging. To overcome this, constraints on the dark matter halo are often made with planetary nebulae or globular clusters at large radii. However, as results from different groups have returned contradictory results, it remains unclear whether different dynamical tracers always follow the stellar kinematics. Due to VIRUS-P's large field of view and on-sky fiber diameter, we are able to determine stellar kinematics at radial distances that overlap with other dynamical tracers. Understanding what the dynamics of stars, planetary nebula and globular clusters tell us about both the extent of the dark matter halo profile and the formation histories of the largest elliptical galaxies is a primary science driver for this work.

  12. Mass function and assembly of dark haloes: an approach to inventory isolated overdense regions in random fields

    NASA Astrophysics Data System (ADS)

    Firmani, C.; Avila-Reese, V.

    2013-07-01

    In order to attain a statistical description of the evolution of cosmic density fluctuations in agreement with results from the numerical simulations, we introduce a probability conditional formalism (CF) based on a complete inventory of isolated overdense regions in a density random field. This formalism is a useful tool for describing at the same time the mass function (MF) of virialized dark haloes, their mass aggregation histories (MAHs) and merging rates (MRs). The CF focuses on virialized regions in a self-consistent way rather than in mass elements, and it offers an economical description for a variety of random fields. Within the framework of the CF, we confirm that, for a Gaussian field, it is not possible to reproduce at the same time the MF, MAH and MR of haloes, for both a constant and moving barrier. Then, we develop an inductive method for constraining the cumulative conditional probability from a given halo MF description, and thus, using the CF, we calculate the halo MAHs and MRs. By applying this method to the MF measured in numerical simulations by Tinker et al., we find that a reasonable solution, justified by a mass conservation argument, is obtained if a rescaling - increment by ˜30 per cent - of the virial mass defined in simulations is introduced, and a (slight) deviation from Gaussianity is taken into account. Thus, both the MAH and MR obtained by a Monte Carlo merger tree agree now with the predictions of numerical simulations. We discuss the necessity of rescaling the virial mass in simulations when comparing with analytical approaches on the ground of the matter not accounted as part of the haloes and the halo mass limit due to numerical resolutions in the simulations. Our analysis supports the presence of a diffuse dark matter component that is not taken into account in the measured halo MFs inasmuch as it is not part of the collapsed structures.

  13. An analysis of the halo and relic radio emission from Abell 3376 from Murchison Widefield Array observations

    NASA Astrophysics Data System (ADS)

    George, L. T.; Dwarakanath, K. S.; Johnston-Hollitt, M.; Hurley-Walker, N.; Hindson, L.; Kapińska, A. D.; Tingay, S. J.; Bell, M.; Callingham, J. R.; For, Bi-Qing; Hancock, P. J.; Lenc, E.; McKinley, B.; Morgan, J.; Offringa, A.; Procopio, P.; Staveley-Smith, L.; Wayth, R. B.; Wu, Chen; Zheng, Q.; Bernardi, G.; Bowman, J. D.; Briggs, F.; Cappallo, R. J.; Corey, B. E.; Deshpande, A. A.; Emrich, D.; Goeke, R.; Greenhill, L. J.; Hazelton, B. J.; Kaplan, D. L.; Kasper, J. C.; Kratzenberg, E.; Lonsdale, C. J.; Lynch, M. J.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Oberoi, D.; Ord, S. M.; Prabu, T.; Rogers, A. E. E.; Roshi, A.; Shankar, N. Udaya; Srivani, K. S.; Subrahmanyan, R.; Waterson, M.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, C. L.

    2015-08-01

    We have carried out multiwavelength observations of the nearby (z = 0.046) rich, merging galaxy cluster Abell 3376 with the Murchison Widefield Array (MWA). As a part of the GaLactic and Extragalactic All-sky MWA Survey, this cluster was observed at 88, 118, 154, 188, and 215 MHz. The known radio relics, towards the eastern and western peripheries of the cluster, were detected at all the frequencies. The relics, with a linear extent of ˜1 Mpc each, are separated by ˜2 Mpc. Combining the current observations with those in the literature, we have obtained the spectra of these relics over the frequency range 80-1400 MHz. The spectra follow power laws, with α = -1.17 ± 0.06 and -1.37 ± 0.08 for the west and east relics, respectively (S∝να). Assuming the break frequency to be near the lower end of the spectrum we estimate the age of the relics to be ˜0.4 Gyr. No diffuse radio emission from the central regions of the cluster (halo) was detected. The upper limit on the radio power of any possible halo that might be present in the cluster is a factor of 35 lower than that expected from the radio power and X-ray luminosity correlation for cluster haloes. From this we conclude that the cluster halo is very extended (>500 kpc) and/or most of the radio emission from the halo has decayed. The current limit on the halo radio power is a factor of 10 lower than the existing upper limits with possible implications for models of halo formation.

  14. The COS-Halos Survey: Metallicities in the Low-redshift Circumgalactic Medium

    NASA Astrophysics Data System (ADS)

    Prochaska, J. Xavier; Werk, Jessica K.; Worseck, Gábor; Tripp, Todd M.; Tumlinson, Jason; Burchett, Joseph N.; Fox, Andrew J.; Fumagalli, Michele; Lehner, Nicolas; Peeples, Molly S.; Tejos, Nicolas

    2017-03-01

    We analyze new far-ultraviolet spectra of 13 quasars from the z˜ 0.2 COS-Halos survey that cover the H i Lyman limit of 14 circumgalactic medium (CGM) systems. These data yield precise estimates or more constraining limits than previous COS-Halos measurements on the H i column densities {N}{{H}{{I}}}. We then apply a Monte-Carlo Markov chain approach on 32 systems from COS-Halos to estimate the metallicity of the cool (T˜ {10}4 K) CGM gas that gives rise to low-ionization state metal lines, under the assumption of photoionization equilibrium with the extragalactic UV background. The principle results are: (1) the CGM of field L* galaxies exhibits a declining H i surface density with impact parameter {R}\\perp (at > 99.5 % confidence), (2) the transmission of ionizing radiation through CGM gas alone is 70 ± 7% (3) the metallicity distribution function of the cool CGM is unimodal with a median of {10}-0.51 {Z}⊙ and a 95% interval ≈ 1/50 {Z}⊙ to > 3 {Z}⊙ ; the incidence of metal-poor (< 1/100 {Z}⊙ ) gas is low, implying any such gas discovered along quasar sightlines is typically unrelated to L* galaxies; (4) we find an unexpected increase in gas metallicity with declining {N}{{H}{{I}}} (at > 99.9 % confidence) and, therefore, also with increasing {R}\\perp ; the high metallicity at large radii implies early enrichment; and (5) a non-parametric estimate of the cool CGM gas mass is {M}{CGM}{cool}=(9.2+/- 4.3)× {10}10 {M}⊙ , which together with new mass estimates for the hot CGM may resolve the galactic missing baryons problem. Future analyses of halo gas should focus on the underlying astrophysics governing the CGM, rather than processes that simply expel the medium from the halo. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with

  15. Halo mass distribution reconstruction across the cosmic web

    NASA Astrophysics Data System (ADS)

    Zhao, Cheng; Kitaura, Francisco-Shu; Chuang, Chia-Hsun; Prada, Francisco; Yepes, Gustavo; Tao, Charling

    2015-08-01

    We study the relation between halo mass and its environment from a probabilistic perspective. We find that halo mass depends not only on local dark matter density, but also on non-local quantities such as the cosmic web environment and the halo-exclusion effect. Given these accurate relations, we have developed the HADRON-code (Halo mAss Distribution ReconstructiON), a technique which permits us to assign halo masses to a distribution of haloes in three-dimensional space. This can be applied to the fast production of mock galaxy catalogues, by assigning halo masses, and reproducing accurately the bias for different mass cuts. The resulting clustering of the halo populations agree well with that drawn from the BigMultiDark N-body simulation: the power spectra are within 1σ up to scales of k = 0.2 h Mpc-1, when using augmented Lagrangian perturbation theory based mock catalogues. Only the most massive haloes show a larger deviation. For these, we find evidence of the halo-exclusion effect. A clear improvement is achieved when assigning the highest masses to haloes with a minimum distance separation. We also compute the two- and three-point correlation functions, and find an excellent agreement with N-body results. Our work represents a quantitative application of the cosmic web classification. It can have further interesting applications in the multitracer analysis of the large-scale structure for future galaxy surveys.

  16. Characteristic time for halo current growth and rotation

    NASA Astrophysics Data System (ADS)

    Boozer, Allen H.

    2015-10-01

    A halo current flows for part of its path through the plasma edge and for part through the chamber walls and during tokamak disruptions can be as large as tenths of the plasma current. The primary interest in halo currents is the large force that they can exert on machine components particularly if the toriodal rotation of the halo current resonates with a natural oscillation frequency of the tokamak device. Halo currents arise when required to slow down the growth of a kink that is too unstable to be stabilized by the chamber walls. The width of the current channel in the halo plasma is comparable to the amplitude of the kink, and the halo current grows linearly, not exponentially, in time. The current density in the halo is comparable to that of the main plasma body. The rocket force due to plasma flowing out of the halo and recombining on the chamber walls can cause the non-axisymmetric magnetic structure produced by the kink to rotate toroidally at a speed comparable to the halo speed of sound. Gerhardt's observations of the halo current in NSTX shot 141 687 [Nucl. Fusion 53, 023005 (2013)] illustrate many features of the theory of halo currents and are discussed as a summary of the theory.

  17. Characteristic time for halo current growth and rotation

    SciTech Connect

    Boozer, Allen H.

    2015-10-15

    A halo current flows for part of its path through the plasma edge and for part through the chamber walls and during tokamak disruptions can be as large as tenths of the plasma current. The primary interest in halo currents is the large force that they can exert on machine components particularly if the toriodal rotation of the halo current resonates with a natural oscillation frequency of the tokamak device. Halo currents arise when required to slow down the growth of a kink that is too unstable to be stabilized by the chamber walls. The width of the current channel in the halo plasma is comparable to the amplitude of the kink, and the halo current grows linearly, not exponentially, in time. The current density in the halo is comparable to that of the main plasma body. The rocket force due to plasma flowing out of the halo and recombining on the chamber walls can cause the non-axisymmetric magnetic structure produced by the kink to rotate toroidally at a speed comparable to the halo speed of sound. Gerhardt's observations of the halo current in NSTX shot 141 687 [Nucl. Fusion 53, 023005 (2013)] illustrate many features of the theory of halo currents and are discussed as a summary of the theory.

  18. Dynamics of the Disruption Halo Current Toroidal Asymmetry in NSTX

    SciTech Connect

    S.P. Gerhardt

    2012-09-27

    This paper describes the dynamics of disruption halo current non-axisymmetries in the lower divertor of the National Spherical Torus Experiment [M. Ono, et al. Nuclear Fusion 40, 557 (2000)]. While. The halo currents typically have a strongly asymmetric structure where they enter the divertor floor, and this asymmetry has been observed to complete up to 7 toroidal revolutions over the duration of the halo current pulse. However, the rotation speed and toroidal extend of the asymmetry can vary significantly during the pulse. The rotation speed, halo current pulse duration, and total number of revolutions tend to be smaller in cases with large halo currents. The halo current pattern is observed to become toroidally symmetric at the end of the halo current pulse. It is proposed that this symmeterization is due to the loss of most or all of the closed field line geometry in the final phase of the vertical displacement event.

  19. Can MACHOs probe the shape of the galaxy halo ?

    NASA Technical Reports Server (NTRS)

    Frieman, Joshua; Scoccimarro, Roman

    1994-01-01

    Microlensing searches in our galaxy have recently discovered several candidates in the direction of the Large Magellanic Cloud (LMC). We study the prospects for such searches to yield useful information about the flattening of the Galaxy dark matter halo, using a self-consistent oblate halo model and allowing for the possibility of misalignment between the disk and halo symmetry axes. The microlensing optical depth for the LMC, tau(LMC), depends sensitively on the disk-halo tilt angle in the Milky Way, as does the ratio tau(SMC)/tau(LMC). If the tilt angle is as large as 30 deg, a much larger spread in values for tau(LMC) is consistent with rotation curve constraints than previously thought. Disk-halo tilt and halo flattening do not significantly affect the massive compact halo object (MACHO) masses inferred from event durations.

  20. The global dark halo structure of the Andromeda galaxy

    NASA Astrophysics Data System (ADS)

    Hayashi, Kohei; Chiba, Masashi

    2014-01-01

    We set new limits on the global shape of the dark halo in the Andromeda galaxy based on axisymmetric mass models constructed by Hayashi & Chiba (2012). This is motivated by the fact that CDM models predict non-spherical virialized dark halos, which reflect the process of mass assembly in the galactic scale. Based on the application of our models to latest kinematical data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield not a spherical but a prolate shape for its dark halo. We also find that the prolate dark halo is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their galactic host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web.

  1. Diffuse gamma radiation

    NASA Technical Reports Server (NTRS)

    Fichtel, C. E.; Simpson, G. A.; Thompson, D. J.

    1977-01-01

    An examination of the intensity, energy spectrum, and spatial distribution of the diffuse gamma-radiation observed by SAS-2 satellite away from the galactic plane in the energy range above 35 MeV has shown that it consists of two components. One component is generally correlated with galactic latitudes, the atomic hydrogen column density was deduced from 21 cm measurements, and the continuum radio emission, believed to be synchrotron emission. It has an energy spectrum similar to that in the plane and joins smoothly to the intense radiation from the plane. It is therefore presumed to be of galactic origin. The other component is apparently isotropic, at least on a coarse scale, and has a steep energy spectrum. No evidence is found for a cosmic ray halo surrounding the galaxy in the shape of a sphere or oblate spheroid with galactic dimensions. Constraints for a halo model with significantly larger dimensions are set on the basis of an upper limit to the gamma-ray anisotropy.

  2. Effect of basic physical parameters to control plasma meniscus and beam halo formation in negative ion sources

    SciTech Connect

    Miyamoto, K.; Okuda, S.; Nishioka, S.; Hatayama, A.

    2013-09-14

    Our previous study shows that the curvature of the plasma meniscus causes the beam halo in the negative ion sources: the negative ions extracted from the periphery of the meniscus are over-focused in the extractor due to the electrostatic lens effect, and consequently become the beam halo. In this article, the detail physics of the plasma meniscus and beam halo formation is investigated with two-dimensional particle-in-cell simulation. It is shown that the basic physical parameters such as the H{sup −} extraction voltage and the effective electron confinement time significantly affect the formation of the plasma meniscus and the resultant beam halo since the penetration of electric field for negative ion extraction depends on these physical parameters. Especially, the electron confinement time depends on the characteristic time of electron escape along the magnetic field as well as the characteristic time of electron diffusion across the magnetic field. The plasma meniscus penetrates deeply into the source plasma region when the effective electron confinement time is short. In this case, the curvature of the plasma meniscus becomes large, and consequently the fraction of the beam halo increases.

  3. Discovery of a Giant Radio Halo in a New Planck Galaxy Cluster PLCKG171.9-40.7

    NASA Technical Reports Server (NTRS)

    Giacintucci, Simona; Kale, Ruta; Wik, Daniel R.; Venturi, Tiziana; Markevitch, Maxim

    2013-01-01

    We report the discovery of a giant radio halo in a new, hot, X-ray luminous galaxy cluster recently found by Planck, PLCKG171.9-40.7. The radio halo was found using Giant Metrewave Radio Telescope observations at 235 MHz and 610 MHz, and in the 1.4 GHz data from a NRAO Very Large Array Sky Survey pointing that we have reanalyzed. The diffuse radio emission is coincident with the cluster X-ray emission, has an extent of approx.1 Mpc and a radio power of approx. 5×10(exp 24)W/Hz at 1.4 GHz. Its integrated radio spectrum has a slope of alpha approx. = 1.8 between 235 MHz and 1.4 GHz, steeper than that of a typical giant halo. The analysis of the archival XMMNewton X-ray data shows that the cluster is hot (approx. 10 keV) and disturbed, consistent with X-ray selected clusters hosting radio halos. This is the first giant radio halo discovered in one of the new clusters found by Planck.

  4. DISCOVERY OF A GIANT RADIO HALO IN A NEW PLANCK GALAXY CLUSTER PLCKG171.9-40.7

    SciTech Connect

    Giacintucci, Simona; Kale, Ruta; Venturi, Tiziana; Wik, Daniel R.; Markevitch, Maxim

    2013-03-20

    We report the discovery of a giant radio halo in a new, hot, X-ray luminous galaxy cluster recently found by Planck, PLCKG171.9-40.7. The radio halo was found using Giant Metrewave Radio Telescope observations at 235 MHz and 610 MHz, and in the 1.4 GHz data from an NRAO Very Large Array Sky Survey pointing that we have reanalyzed. The diffuse radio emission is coincident with the cluster X-ray emission, and has an extent of {approx}1 Mpc and a radio power of {approx}5 Multiplication-Sign 10{sup 24} W Hz{sup -1} at 1.4 GHz. Its integrated radio spectrum has a slope of {alpha} Almost-Equal-To 1.8 between 235 MHz and 1.4 GHz, steeper than that of a typical giant halo. The analysis of the archival XMM-Newton X-ray data shows that the cluster is hot ({approx}10 keV) and disturbed, consistent with X-ray-selected clusters hosting radio halos. This is the first giant radio halo discovered in one of the new clusters found by Planck.

  5. Analytical instruments, ionization sources, and ionization methods

    DOEpatents

    Atkinson, David A.; Mottishaw, Paul

    2006-04-11

    Methods and apparatus for simultaneous vaporization and ionization of a sample in a spectrometer prior to introducing the sample into the drift tube of the analyzer are disclosed. The apparatus includes a vaporization/ionization source having an electrically conductive conduit configured to receive sample particulate which is conveyed to a discharge end of the conduit. Positioned proximate to the discharge end of the conduit is an electrically conductive reference device. The conduit and the reference device act as electrodes and have an electrical potential maintained between them sufficient to cause a corona effect, which will cause at least partial simultaneous ionization and vaporization of the sample particulate. The electrical potential can be maintained to establish a continuous corona, or can be held slightly below the breakdown potential such that arrival of particulate at the point of proximity of the electrodes disrupts the potential, causing arcing and the corona effect. The electrical potential can also be varied to cause periodic arcing between the electrodes such that particulate passing through the arc is simultaneously vaporized and ionized. The invention further includes a spectrometer containing the source. The invention is particularly useful for ion mobility spectrometers and atmospheric pressure ionization mass spectrometers.

  6. A Speeding Binary in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-04-01

    The recent discovery of a hyper-velocity binary star system in the halo of the Milky Way poses a mystery: how was this system accelerated to its high speed?Accelerating StarsUnlike the uniform motion in the Galactic disk, stars in the Milky Ways halo exhibit a huge diversity of orbits that are usually tilted relative to the disk and have a variety of speeds. One type of halo star, so-called hyper-velocity stars, travel with speeds that can approach the escape velocity of the Galaxy.How do these hyper-velocity stars come about? Assuming they form in the Galactic disk, there are multiple proposed scenarios through which they could be accelerated and injected into the halo, such as:Ejection after a close encounter with the supermassive black hole at the Galactic centerEjection due to a nearby supernova explosionEjection as the result of a dynamical interaction in a dense stellar population.Further observations of hyper-velocity stars are necessary to identify the mechanism responsible for their acceleration.J1211s SurpriseModels of J1211s orbit show it did not originate from the Galactic center (black dot). The solar symbol shows the position of the Sun and the star shows the current position of J1211. The bottom two panels show two depictions(x-y plane and r-z plane) of estimated orbits of J1211 over the past 10 Gyr. [Nmeth et al. 2016]To this end, a team of scientists led by Pter Nmeth (Friedrich Alexander University, Erlangen-Nrnberg) recently studied the candidate halo hyper-velocity star SDSS J121150.27+143716.2. The scientists obtained spectroscopy of J1211 using spectrographs at the Keck Telescope in Hawaii and ESOs Very Large Telescope in Chile. To their surprise, they discovered the signature of a companion in the spectra: J1211 is actually a binary!Nmeth and collaborators found that J1211, located roughly 18,000 light-years away, is moving at a rapid ~570 km/s relative to the galactic rest frame. The binary system consists of a hot (30,600 K) subdwarf and a

  7. Hot Stars in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Adelman, Saul J.; Upgren, Arthur R.; Adelman, Carol J.

    2011-03-01

    Participants; Preface; Foreword; Acknowledgements; Part I. Introductory Papers: 1. What is the galaxy's halo population?; 2. Theoretical properties of horizontal-branch stars; 3. A review of A-type horizontal-branch stars; Part II. Surveys: 4. A progress report on the Edinburgh-Cape object survey; 5. A 300 square degree survey of young stars at high galactic latitudes; 6. The isolation of a new sample of B stars in the halo; 7. A northern catalog of FHB/A stars; 8. Recent progress on a continuing survey of galactic globular clusters for blue stragglers; 9. UV observations with FAUST and the galactic model; 10. Hot stars at the South Galactic Pole; Part III. Clusters: 11. Population II horizontal branches: a photometric study of globular clusters; 12. The period-shift effect in Oosterhoff type II globular clusters; 13. UV photometry of hot stars in omega centauri; 14. Spectroscopic and UBV observations of blue stars at the NGP; 15. Population I horizontal branches: probing the halo-to-disk transition; Part IV. Stars: 16. Very hot subdwarf O stars; 17. Quantitative spectroscopy of the very hot subluminous O-stars: K646, PG1159-035, and KPD0005+5106; 18. Analyzing the helium-rich hot sdO stars in the Palomar Green Survey; 19. Late type companions of hot sd O stars; 20. Hot stars in globular clusters; 21. Faint blue stars from the Hamburg Schmidt Survey; 22. Stellar winds and the evolution of sdB's to sdO's; 23. Halo stars in the Vilnius photometric system; 24. Horizontal branch stars in the geneva photometric system; 25. Zeeman observations of FHB stars and hot subdwarf stars; 26. What does a FHB star's spectrum look like?; 27. A technique for distinguishing FHB stars from A-type stars; 28. eEemental abundances of halo A and interloper stars; 29. The mass of blue horizontal branch stars in the globular cluster NGC6397; 30. IUE observations of blue HB stars in the globular clusters M3 and NGC6752; 31. Metallicities and kinematics of the local RR lyraes: lukewarm stars

  8. Hot Stars in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Adelman, Saul J.; Upgren, Arthur R.; Adelman, Carol J.

    1994-08-01

    Participants; Preface; Foreword; Acknowledgements; Part I. Introductory Papers: 1. What is the galaxy's halo population?; 2. Theoretical properties of horizontal-branch stars; 3. A review of A-type horizontal-branch stars; Part II. Surveys: 4. A progress report on the Edinburgh-Cape object survey; 5. A 300 square degree survey of young stars at high galactic latitudes; 6. The isolation of a new sample of B stars in the halo; 7. A northern catalog of FHB/A stars; 8. Recent progress on a continuing survey of galactic globular clusters for blue stragglers; 9. UV observations with FAUST and the galactic model; 10. Hot stars at the South Galactic Pole; Part III. Clusters: 11. Population II horizontal branches: a photometric study of globular clusters; 12. The period-shift effect in Oosterhoff type II globular clusters; 13. UV photometry of hot stars in omega centauri; 14. Spectroscopic and UBV observations of blue stars at the NGP; 15. Population I horizontal branches: probing the halo-to-disk transition; Part IV. Stars: 16. Very hot subdwarf O stars; 17. Quantitative spectroscopy of the very hot subluminous O-stars: K646, PG1159-035, and KPD0005+5106; 18. Analyzing the helium-rich hot sdO stars in the Palomar Green Survey; 19. Late type companions of hot sd O stars; 20. Hot stars in globular clusters; 21. Faint blue stars from the Hamburg Schmidt Survey; 22. Stellar winds and the evolution of sdB's to sdO's; 23. Halo stars in the Vilnius photometric system; 24. Horizontal branch stars in the geneva photometric system; 25. Zeeman observations of FHB stars and hot subdwarf stars; 26. What does a FHB star's spectrum look like?; 27. A technique for distinguishing FHB stars from A-type stars; 28. eEemental abundances of halo A and interloper stars; 29. The mass of blue horizontal branch stars in the globular cluster NGC6397; 30. IUE observations of blue HB stars in the globular clusters M3 and NGC6752; 31. Metallicities and kinematics of the local RR lyraes: lukewarm stars

  9. The Geographic Distribution of Boulder Halo Craters at Mid-to-High Latitudes on Mars

    NASA Technical Reports Server (NTRS)

    Rader, L. X.; Fassett, C. I.; Levy, J. S.; King, I. R.; Chaffey, P. M.; Wagoner, C. M.; Hanlon, A. E.; Watters, J. L.; Kreslavsky, M. A.; Holt, J. W.; hide

    2017-01-01

    Extensive evidence exists for ground ice at mid-to-high latitudes on Mars, including results from neutron spectroscopy [1-3], thermal properties [4-5], geomorphology [e.g., 6-9], and the in situ observations of Mars Phoenix [10]. This ground ice has been hypothesized to be emplaced diffusively and fill pores [11], or to have accumulated by ice and dust deposition that draped or mantled the terrain [7, 12]. These two processes are not mutually exclusive; both potentially have occurred on Mars [5]. One of the landforms found in areas where ground ice is common on Mars are boulder halo craters [e.g., 13-15] (Figure 1), which are topographically muted impact craters that are filled by ice-rich regolith. They are outlined by boulders that trace a circular outline of the original crater rim. Boulder halos generally have distinctly higher boulder densities than the surrounding background plains and have few boulders in their interiors. The mechanism of boulder halo crater formation is somewhat uncertain. Our working model is that an impact event occurs with sufficient size to excavate to a depth greater than the boulder-poor, ice-rich soils. Excavated boulders are deposited around the crater's rim and in its proximal ejecta. Quite rapidly [14], the crater becomes infilled by icy soil. Rather than being buried, boulders in the halo remain at the surface, perhaps be-cause they 'float' relative to finer-grained materials [14, 16]. Regardless of the details of this process, the life-time of boulders at the surface is much greater than the timescale needed to remove most of the craters' topography. Physical weathering of rocks must be greatly out-paced by crater infilling (the opposite of what is typical, e.g., on the Moon [17]). The rapidity of this infilling is easiest to understand if icy mantling material is deposited and accumulates, rather than simply being added by pore filling of soils. If this model is correct, boulder halos only form when they excavate rock

  10. CONSTRAINING THE MILKY WAY'S HOT GAS HALO WITH O VII AND O VIII EMISSION LINES

    SciTech Connect

    Miller, Matthew J.; Bregman, Joel N. E-mail: jbregman@umich.edu

    2015-02-10

    The Milky Way hosts a hot (≈2 × 10{sup 6} K), diffuse, gaseous halo based on detections of z = 0 O VII and O VIII absorption lines in quasar spectra and emission lines in blank-sky spectra. Here we improve constraints on the structure of the hot gas halo by fitting a radial model to a much larger sample of O VII and O VIII emission line measurements from XMM-Newton/EPIC-MOS spectra compared to previous studies (≈650 sightlines). We assume a modified β-model for the halo density distribution and a constant-density Local Bubble from which we calculate emission to compare with the observations. We find an acceptable fit to the O VIII emission line observations with χ{sub red}{sup 2} (dof) = 1.08 (644) for best-fit parameters of n{sub o}r{sub c}{sup 3β}=1.35±0.24 cm{sup –3} kpc{sup 3β} and β = 0.50 ± 0.03 for the hot gas halo and negligible Local Bubble contribution. The O VII observations yield an unacceptable χ{sub red}{sup 2} (dof) = 4.69 (645) for similar best-fit parameters, which is likely due to temperature or density variations in the Local Bubble. The O VIII fitting results imply hot gas masses of M(<50 kpc) = 3.8{sub −0.3}{sup +0.3}×10{sup 9} M{sub ⊙} and M(<250 kpc) = 4.3{sub −0.8}{sup +0.9}×10{sup 10} M{sub ⊙}, accounting for ≲50% of the Milky Way's missing baryons. We also explore our results in the context of optical depth effects in the halo gas, the halo gas cooling properties, temperature and entropy gradients in the halo gas, and the gas metallicity distribution. The combination of absorption and emission line analyses implies a sub-solar gas metallicity that decreases with radius, but that also must be ≥0.3 Z {sub ☉} to be consistent with the pulsar dispersion measure toward the Large Magellanic Cloud.

  11. The halo of M 49 and its environment as traced by planetary nebulae populations

    NASA Astrophysics Data System (ADS)

    Hartke, J.; Arnaboldi, M.; Longobardi, A.; Gerhard, O.; Freeman, K. C.; Okamura, S.; Nakata, F.

    2017-07-01

    Context. The galaxy M 49 (NGC 4472) is the brightest early-type galaxy in the Virgo Cluster. It is located in subcluster B and has an unusually blue, metal-poor outer halo. Planetary nebulae (PNe) are excellent tracers of diffuse galaxy and intragroup light (IGL). Aims: We aim to present a photometric survey of PNe in the galaxy's extended halo to characterise its PN population, as well as the surrounding IGL of the subcluster B. Methods: PNe were identified based on their bright [OIII]5007 Å emission and absence of a broad-band continuum through automated detection techniques. Results: We identify 738 PNe out to a radius of 155 kpc from M 49's centre from which we define a complete sample of 624 PNe within a limiting magnitude of m5007,lim = 28.8. Comparing the PN number density to the broad-band stellar surface brightness profile, we find a variation of the PN-specific frequency (α-parameter) with radius. The outer halo beyond 60kpc has a 3.2 times higher α-parameter compared to the main galaxy halo (α2.5,innerM 49 = (3.20 ± 0.43) × 10-9 PN L-1⊙,bol), which is likely due to contribution from the surrounding blue IGL. We use the planetary nebulae luminosity function (PNLF) as an indicator of distance and stellar population. Its slope, which correlates empirically with galaxy type, varies within the inner halo. In the eastern quadrant of M 49, the PNLF slope is shallower, indicating an additional localised, bright PN population following an accretion event, likely that of the dwarf irregular galaxy VCC1249. We also determined a distance modulus of μPNLF = 31.29+ 0.07-0.08 for M 49, corresponding to a physical distance of 18.1 ± 0.6 Mpc, which agrees with a recent surface-brightness fluctuations distance. Conclusions: The PN populations in the outer halo of M 49 are consistent with the presence of a main Sérsic galaxy halo with a slight (B - V) colour gradient of 10-4 mag arcsec-1 surrounded by IGL with a very blue colour of (B - V) = 0.25 and a constant

  12. The Ionization Structure of Sharpless 2-264: Multiwavelength Observations of the λ Ori H II Region

    NASA Astrophysics Data System (ADS)

    Sahan, M.; Haffner, L. M.

    2016-06-01

    diffuse H ii region around λ Ori can be compared to studies of the WIM to provide important insight into the nature of the diffuse ionized gas throughout the disk and halo of the Galaxy.

  13. Dark Matter annihilations in halos and high-redshift sources of reionization of the universe

    SciTech Connect

    Poulin, Vivian; Serpico, Pasquale D.; Lesgourgues, Julien E-mail: Pasquale.Serpico@lapth.cnrs.fr

    2015-12-01

    It is well known that annihilations in the homogeneous fluid of dark matter (DM) can leave imprints in the cosmic microwave background (CMB) anisotropy power spectrum. However, the relevance of DM annihilations in halos for cosmological observables is still subject to debate, with previous works reaching different conclusions on this point. Also, all previous studies used a single type of parameterization for the astrophysical reionization, and included no astrophysical source for the heating of the intergalactic medium. In this work, we revisit these problems. When standard approaches are adopted, we find that the ionization fraction does exhibit a very particular (and potentially constraining) pattern, but the currently measurable τ{sub reio} is left almost unchanged: in agreement with most of the previous literature, for plausible halo models we find that the modification of the signal with respect to the one coming from annihilations in the smooth background is tiny, below cosmic variance within currently allowed parameter space. However, if different and probably more realistic treatments of the astrophysical sources of reionization and heating are adopted, a more pronounced effect of the DM annihilation in halos is possible. We thus conclude that within currently adopted baseline models the impact of the virialised DM structures cannot be uncovered by CMB power spectra measurements, but a larger impact is possible if peculiar models are invoked for the redshift evolution of the DM annihilation signal or different assumptions are made for the astrophysical contributions. A better understanding (both theoretical and observational) of the reionization and temperature history of the universe, notably via the 21 cm signal, seems the most promising way for using halo formation as a tool in DM searches, improving over the sensitivity of current cosmological probes.

  14. Dark Matter annihilations in halos and high-redshift sources of reionization of the universe

    NASA Astrophysics Data System (ADS)

    Poulin, Vivian; Serpico, Pasquale D.; Lesgourgues, Julien

    2015-12-01

    It is well known that annihilations in the homogeneous fluid of dark matter (DM) can leave imprints in the cosmic microwave background (CMB) anisotropy power spectrum. However, the relevance of DM annihilations in halos for cosmological observables is still subject to debate, with previous works reaching different conclusions on this point. Also, all previous studies used a single type of parameterization for the astrophysical reionization, and included no astrophysical source for the heating of the intergalactic medium. In this work, we revisit these problems. When standard approaches are adopted, we find that the ionization fraction does exhibit a very particular (and potentially constraining) pattern, but the currently measurable τreio is left almost unchanged: in agreement with most of the previous literature, for plausible halo models we find that the modification of the signal with respect to the one coming from annihilations in the smooth background is tiny, below cosmic variance within currently allowed parameter space. However, if different and probably more realistic treatments of the astrophysical sources of reionization and heating are adopted, a more pronounced effect of the DM annihilation in halos is possible. We thus conclude that within currently adopted baseline models the impact of the virialised DM structures cannot be uncovered by CMB power spectra measurements, but a larger impact is possible if peculiar models are invoked for the redshift evolution of the DM annihilation signal or different assumptions are made for the astrophysical contributions. A better understanding (both theoretical and observational) of the reionization and temperature history of the universe, notably via the 21 cm signal, seems the most promising way for using halo formation as a tool in DM searches, improving over the sensitivity of current cosmological probes.

  15. Intracranial halo pin penetration causing brain injury secondary to poor halo care technique: a case report and literature review

    PubMed Central

    Male, Kishore Reddy; Guha, Abhijit; James, Stuart; Ahuja, Sashin

    2008-01-01

    This is a case report of intra cranial penetration by halo pins resulting in cerebritis and fits secondary to incorrect halo care by the patient and his family. Halo pin penetration into the skull with brain injury is itself a rare incident. Previously documented case reports were in patients with a previous cranioplasties and they were highlight the fact that halo not to be used in cranioplasty patients. Cranial penetration of the halo pins has generally been secondary to a fall/medical condition as epilepsy. This incident how ever highlights the fact the halo care itself along with proper techniques used for tightening the halo pins by the carer plays a crucial role in preventing complications such as this. PMID:19068118

  16. Precise halo orbit design and optimal transfer to halo orbits from earth using differential evolution

    NASA Astrophysics Data System (ADS)

    Nath, Pranav; Ramanan, R. V.

    2016-01-01

    The mission design to a halo orbit around the libration points from Earth involves two important steps. In the first step, we design a halo orbit for a specified size and in the second step, we obtain an optimal transfer trajectory design to the halo orbit from an Earth parking orbit. Conventionally, the preliminary design for these steps is obtained using higher order analytical solution and the dynamical systems theory respectively. Refinements of the design are carried out using gradient based methods such as differential correction and pseudo arc length continuation method under the of circular restricted three body model. In this paper, alternative single level schemes are developed for both of these steps based on differential evolution, an evolutionary optimization technique. The differential evolution based scheme for halo orbit design produces precise halo orbit design avoiding the refinement steps. Further, in this approach, prior knowledge of higher order analytical solutions for the halo orbit design is not needed. The differential evolution based scheme for the transfer trajectory, identifies the precise location on the halo orbit that needs minimum energy for insertion and avoids exploration of multiple points. The need of a close guess is removed because the present scheme operates on a set of bounds for the unknowns. The constraint on the closest approach altitude from Earth is handled through objective function. The use of these schemes as the design and analysis tools within the of circular restricted three body model is demonstrated through case studies for missions to the first libration point of Sun-Earth system.

  17. The large, oxygen-rich halos of star-forming galaxies are a major reservoir of galactic metals.

    PubMed

    Tumlinson, J; Thom, C; Werk, J K; Prochaska, J X; Tripp, T M; Weinberg, D H; Peeples, M S; O'Meara, J M; Oppenheimer, B D; Meiring, J D; Katz, N S; Davé, R; Ford, A B; Sembach, K R

    2011-11-18

    The circumgalactic medium (CGM) is fed by galaxy outflows and accretion of intergalactic gas, but its mass, heavy element enrichment, and relation to galaxy properties are poorly constrained by observations. In a survey of the outskirts of 42 galaxies with the Cosmic Origins Spectrograph onboard the Hubble Space Telescope, we detected ubiquitous, large (150-kiloparsec) halos of ionized oxygen surrounding star-forming galaxies; we found much less ionized oxygen around galaxies with little or no star formation. This ionized CGM contains a substantial mass of heavy elements and gas, perhaps far exceeding the reservoirs of gas in the galaxies themselves. Our data indicate that it is a basic component of nearly all star-forming galaxies that is removed or transformed during the quenching of star formation and the transition to passive evolution.

  18. Deformed halo nuclei probed by breakup reactions

    NASA Astrophysics Data System (ADS)

    Nakamura, Takashi

    2013-07-01

    Breakup reactions play important roles in elucidating the structures near the drip lines, such as nuclear halo. The recent experimental results using the Coulomb and nuclear breakup reactions for the neutron-drip-line nuclei at the new-generation RI beam facility, RIBF at RIKEN, are presented. Focuses are put on the results on the newly found halo nucleus 31Ne, which is intriguing also in that this nucleus is in the island-of-inversion and thus could be strongly deformed. The results on other Ne/Mg/Si neutron rich isotopes ranging from N=20 towards N=28 are also briefly reported. The first breakup experiments using SAMURAI facility at RIBF and future perspectives are also presented.

  19. Cool Carbon Stars in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Gigoyan, K. S.

    2016-06-01

    In this paper we report current status of search and study for Faint High Latitude Carbon Stars (FHLCs). Data for more than 1800 spectroscopically confirmed FHLCs are known, which are found thanks to objective prism surveys and photometric selections. More than half of the detected objects belongs to group of dwarf Carbon (dC) stars. Many-sided investigations based on modern astrophysical databases are necessary to study the space distribution of different groups of the FHLC stars and their possible origin in the Halo of our Galaxy. We report about the selection of FHLCs by the spectroscopic surveys: First Byurakan Survey (FBS), Hamburg/ESO Survey (HES), LAMOST Pilot Survey and SDSS, as well as by photometric selection: APM Survey for Cool Carbon Stars in the Galactic Halo, SDSS and 2MASS JHK colours.

  20. Probing satellite haloes with weak gravitational lensing

    NASA Astrophysics Data System (ADS)

    Gillis, Bryan R.; Hudson, Michael J.; Hilbert, Stefan; Hartlap, Jan

    2013-02-01

    We demonstrate the possibility of detecting tidal stripping of dark matter subhaloes within galaxy groups using weak gravitational lensing. We have run ray-tracing simulations on galaxy catalogues from the Millennium Simulation to generate mock shape catalogues. The ray-tracing catalogues assume a halo model for galaxies and groups using various models with different distributions of mass between galaxy and group haloes to simulate different stages of group evolution. Using these mock catalogues, we forecast the lensing signals that will be detected around galaxy groups and satellite galaxies, as well as test two different methods for isolating the satellites' lensing signals. A key challenge is to determine the accuracy to which group centres can be identified. We show that with current and ongoing surveys, it will possible to detect stripping in groups of mass 1012-1015 M⊙.

  1. Stellar halos around Local Group galaxies

    NASA Astrophysics Data System (ADS)

    McConnachie, Alan W.

    2016-08-01

    The Local Group is now home to 102 known galaxies and candidates, with many new faint galaxies continuing to be discovered. The total stellar mass range spanned by this population covers a factor of close to a billion, from the faintest systems with stellar masses of order a few thousand to the Milky Way and Andromeda, with stellar masses of order 1011 M ⊙. Here, I discuss the evidence for stellar halos surrounding Local Group galaxies spanning from dwarf scales (with the case of the Andromeda II dwarf spheroidal), though to intermediate mass systems (M33) and finishing with M31. Evidence of extended stellar populations and merging is seen across the luminosity function, indicating that the processes that lead to halo formation are common at all mass scales.

  2. Magnetic braking in weakly ionized media

    NASA Technical Reports Server (NTRS)

    Konigl, Arieh

    1987-01-01

    The combined magnetic braking-ambipolar diffusion problem in weakly ionized, rigidly rotating disks is studied. An analytical solution is presented for a disk whose angular velocity and magnetic yield vectors are aligned with the symmetry axis, illustrating the effects of the relative azimuthal drift of neutrals and ions. The effects of radial drift are added, commenting on the ratio of the characteristic ambipolar diffusion and magnetic braking time scales in high-mass and low-mass disks. A numerical calculation is used to show the combined action of these two processes.

  3. Determining the Galactic Halo's Emission Measure from UV and X-Ray Observations

    NASA Astrophysics Data System (ADS)

    Lei, Shijun; Shelton, Robin L.; Henley, David B.

    2009-07-01

    We analyze a pair of Suzaku shadowing observations in order to determine the X-ray spectrum of the Galaxy's gaseous halo. Our data consist of an observation toward an absorbing filament in the southern Galactic hemisphere and an observation toward an unobscured region adjacent to the filament. We simultaneously fit the spectra with models having halo, local, and extragalactic components. The intrinsic intensities of the halo O VII triplet and O VIII Ly α emission lines are 9.98+1.10 -1.99 LU (line unit; photons cm-2 s-1 sr-1) and 2.66+0.37 -0.30 LU, respectively. These results imply the existence of hot gas with a temperature of ~106.0 K to ~107.0 K in the Galactic halo. Meanwhile, FUSE O VI observations for the same directions and SPEAR C IV observations for a nearby direction indicate the existence of hot halo gas at temperatures of ~105.0 K to ~106.0 K. This collection of data implies that the hot gas in the Galactic halo is not isothermal, but its temperature spans a relatively wide range from ~105.0 K to ~107.0 K. We therefore construct a differential emission measure (DEM) model for the halo's hot gas, consisting of two components. In each, dEM/dlog T is assumed to follow a power-law function of the temperature and the gas is assumed to be in collisional ionizational equilibrium. The low-temperature component (LTC) of the broken power-law DEM model covers the temperature range of 104.80-106.02 K with a slope of 0.30 and the high-temperature component (HTC) covers the temperature range of 106.02-107.02 K with a slope of -2.21. We compare our observations with predictions from models for hot gas in the halo. The observed spatial distribution of gas with temperatures in the range of our HTC is smoother than that of the LTC. We thus suggest that two types of sources contribute to our broken power-law model. We find that a simple model in which hot gas accretes onto the Galactic halo and cools radiatively cannot explain both the observed UV and X-ray portions of

  4. Accurate mass and velocity functions of dark matter haloes

    NASA Astrophysics Data System (ADS)

    Comparat, Johan; Prada, Francisco; Yepes, Gustavo; Klypin, Anatoly

    2017-08-01

    N-body cosmological simulations are an essential tool to understand the observed distribution of galaxies. We use the MultiDark simulation suite, run with the Planck cosmological parameters, to revisit the mass and velocity functions. At redshift z = 0, the simulations cover four orders of magnitude in halo mass from ˜1011M⊙ with 8783 874 distinct haloes and 532 533 subhaloes. The total volume used is ˜515 Gpc3, more than eight times larger than in previous studies. We measure and model the halo mass function, its covariance matrix w.r.t halo mass and the large-scale halo bias. With the formalism of the excursion-set mass function, we explicit the tight interconnection between the covariance matrix, bias and halo mass function. We obtain a very accurate (<2 per cent level) model of the distinct halo mass function. We also model the subhalo mass function and its relation to the distinct halo mass function. The set of models obtained provides a complete and precise framework for the description of haloes in the concordance Planck cosmology. Finally, we provide precise analytical fits of the Vmax maximum velocity function up to redshift z < 2.3 to push for the development of halo occupation distribution using Vmax. The data and the analysis code are made publicly available in the Skies and Universes data base.

  5. Is the Milky Way's hot halo convectively unstable?

    SciTech Connect

    Henley, David B.; Shelton, Robin L.

    2014-03-20

    We investigate the convective stability of two popular types of model of the gas distribution in the hot Galactic halo. We first consider models in which the halo density and temperature decrease exponentially with height above the disk. These halo models were created to account for the fact that, on some sight lines, the halo's X-ray emission lines and absorption lines yield different temperatures, implying that the halo is non-isothermal. We show that the hot gas in these exponential models is convectively unstable if γ < 3/2, where γ is the ratio of the temperature and density scale heights. Using published measurements of γ and its uncertainty, we use Bayes' theorem to infer posterior probability distributions for γ, and hence the probability that the halo is convectively unstable for different sight lines. We find that, if these exponential models are good descriptions of the hot halo gas, at least in the first few kiloparsecs from the plane, the hot halo is reasonably likely to be convectively unstable on two of the three sight lines for which scale height information is available. We also consider more extended models of the halo. While isothermal halo models are convectively stable if the density decreases with distance from the Galaxy, a model of an extended adiabatic halo in hydrostatic equilibrium with the Galaxy's dark matter is on the boundary between stability and instability. However, we find that radiative cooling may perturb this model in the direction of convective instability. If the Galactic halo is indeed convectively unstable, this would argue in favor of supernova activity in the Galactic disk contributing to the heating of the hot halo gas.

  6. Halo naevi with associated vitiligo-like depigmentations: pathogenetic hypothesis.

    PubMed

    van Geel, N; Speeckaert, R; Lambert, J; Mollet, I; De Keyser, S; De Schepper, S; Brochez, L

    2012-06-01

      In analogy with melanoma-associated leucoderma, halo naevi may trigger in some patients the development of additional depigmentations which are in distribution, extent and prognosis not in accordance with classic vitiligo.   The aim of this study was to support the hypothesis that in a subset of halo naevi patients vitiligo-like lesions develop directly linked to the halo phenomenon.   Forty-one patients with halo naevi were examined for the development of depigmentations not corresponding to typical vitiligo lesions.   We identified a subset of five halo naevi patients with additional subtle depigmentations. After the occurrence of multiple halo naevi, they developed leucoderma that showed a different disease pattern than vitiligo (variable asymmetric distribution, limited extent and lack of progression). Moreover, the characteristics of these halo naevi patients with associated leucoderma were different from classic vitiligo patients (high number of halo naevi, absence of family history for vitiligo and absence of autoimmune diseases) and the timing of occurrence of the leucoderma suggested a direct relation with the halo phenomenon.   In this article, we describe in a limited subset of patients with multiple halo naevi discrete depigmentations at distance from halo naevi which may result from a temporary autoimmune process directly linked to the halo phenomenon. This finding illustrates the collateral damage resulting from skin immunosurveillance and may have clinical consequences as the evolution pattern in this subset of patients is less progressive compared with vitiligo. We present clinical data that support this hypothesis and suggest to call it 'halo naevi-associated leucoderma'. © 2011 The Authors. Journal of the European Academy of Dermatology and Venereology © 2011 European Academy of Dermatology and Venereology.

  7. Prognostic value and clinical significance of halo naevi regarding vitiligo.

    PubMed

    van Geel, N; Vandenhaute, S; Speeckaert, R; Brochez, L; Mollet, I; De Cooman, L; Lambert, J

    2011-04-01

    Vitiligo and halo naevi can present together or separately. Whether they are different entities remains unclear. To assess the clinical significance of halo naevi, both with respect to the future development of vitiligo, and to the clinical profile and course of vitiligo. In total, 291 patients were included in this study: patients with only halo naevi (group 1; n=40), patients with generalized vitiligo without halo naevi (group 2; n=173) and patients with generalized vitiligo with halo naevi (group 3; n=78). Patients with only halo naevi (group 1) reported significantly less associated autoimmune disease (P=0·001), were less likely to have a family history of vitiligo (P=0·013) and were less likely to have presence of Koebner phenomenon (P<0·001) compared with patients with generalized vitiligo (groups 2+3). Multiple halo naevi (≥3) were significantly more frequently observed (P=0·002) in patients from group 1 compared with patients from group 3. In group 3, halo naevi were reported prior to the development of vitiligo in 61% (mean±SD time interval of 33·7±5·17months). No significant correlation was observed between the presence of halo naevi and the extent, activity or subtype of vitiligo. However, halo naevi in patients with vitiligo significantly reduced the risk for associated autoimmune diseases, and age at onset of vitiligo was significantly lower compared with patients with vitiligo without halo naevi (P<0·001). Our results support the hypothesis that halo naevi can represent a distinct condition. In a subset of patients, the occurrence of halo naevi may be an initiating factor in the pathogenesis of vitiligo. © 2011 The Authors. BJD © 2011 British Association of Dermatologists.

  8. Dynamic Colloidal Stabilization by Nanoparticle Halos

    NASA Astrophysics Data System (ADS)

    Karanikas, S.; Louis, A. A.

    2004-12-01

    We explore the conditions under which colloids can be stabilized by the addition of smaller particles. The largest repulsive barriers between colloids occur when the added particles repel each other with soft interactions, leading to an accumulation near the colloid surfaces. At lower densities these layers of mobile particles (nanoparticle halos) result in stabilization, but when too many are added, the interactions become attractive again. We systematically study these effects—accumulation repulsion, reentrant attraction, and bridging—by accurate integral equation techniques.

  9. Stellar Spirals in Triaxial Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Hu, Shaoran; Sijacki, Debora

    2017-03-01

    Two-armed grand-design spirals may form if the shape of its dark matter halo changes abruptly enough. The feasibility of such a mechanism is tested in realistic simulations. The interplay of such externally-driven spirals and self-induced transient spirals is then studied. Subhaloes are also found to lead to transient grand-design spiral structures when they impact the disk.

  10. Splashback Shells of Cold Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Mansfield, Philip; Kravtsov, Andrey V.; Diemer, Benedikt

    2017-05-01

    The density field in the outskirts of dark matter halos is discontinuous as a result of a caustic formed by matter at its first apocenter after infall. In this paper, we present an algorithm to identify the “splashback shell” formed by these apocenters in individual simulated halos using only a single snapshot of the density field. We implement this algorithm in the code Shellfish (SHELL Finding In Spheroidal Halos) and demonstrate that the code identifies splashback shells correctly and measures their properties with an accuracy of < 5 % for halos with more than 50,000 particles and mass accretion rates of {{{Γ }}}{DK14}> 0.5. Using Shellfish, we present the first estimates for several basic properties of individual splashback shells, such as radius, {R}{sp}, mass, and overdensity, and provide fits to the distribution of these quantities as functions of {{{Γ }}}{DK14}, {ν }200{{m}}, and z. We confirm previous findings that {R}{sp} decreases with increasing {{{Γ }}}{DK14}, but we show that, independent of accretion rate, it also decreases with increasing {ν }200{{m}}. We also study the 3D structures of these shells and find that they generally have non-ellipsoidal oval shapes. We find that splashback radii estimated by Shellfish are 20%-30% larger than those estimated in previous studies from stacked density profiles at high accretion rates. We demonstrate that the latter are biased low owing to the contribution of high-mass subhalos to these profiles, and we show that using the median instead of mean density in each radial bin mitigates the effect of substructure on density profiles and removes the bias.

  11. The Halo B2B Studio

    NASA Astrophysics Data System (ADS)

    Gorzynski, Mark; Derocher, Mike; Mitchell, April Slayden

    Research underway at Hewlett-Packard on remote communication resulted in the identification of three important components typically missing in existing systems. These missing components are: group nonverbal communication capabilities, high-resolution interactive data capabilities, and global services. Here we discuss some of the design elements in these three areas as part of the Halo program at HP, a remote communication system shown to be effective to end-users.

  12. The Vertical Structure of the Halo Rotation

    NASA Astrophysics Data System (ADS)

    Kinman, T. D.; Bragaglia, A.; Cacciari, C.; Buzzoni, A.; Spagna, A.

    New GSC-II proper motions and radial velocities of RR Lyrae and Blue Horizontal Branch stars near the North Galactic Pole are used to show that the Galactic Halo 5 kpc above the Plane has a significantly retrograde galactic rotation. Streaming motions cannot be excluded. Based on observations collected at the Kitt Peak and TNG Observatories. Funded by MIUR-Cofin 2001 (PI: Gratton).

  13. Oxygen vs. Age in Halo Field Stars

    NASA Astrophysics Data System (ADS)

    Laird, J. B.; Sneden, C.

    1996-04-01

    Oxygen abundances as a function of age are presented for a sample of halo field stars near the main sequence turn-off. We have measured oxygen abundances using the infrared oxygen triplet, and ages have previously been determined for these stars by Schuster & Nissen and Marquez & Schuster using Stromgren photometry and theoretical isochrones. The age spread observed among globular clusters and among the field stars indicates that the formation of the halo occurred over at least several billion years. The relatively shorter time scale for the contribution of Type Ia supernovae should have produced a significant decrease in the oxygen-to-iron (O/Fe) ratio over this time, leading to a significant variation in [O/Fe] among stars with different ages. We do not find the expected correlation of O/Fe and age. This result suggests that either the timescale for Type Ia supernovae is significantly longer than 1 Gyr or the stars of different ages formed in chemically isolated regions of the halo.

  14. Epicardial halo phenomenon: a guide for pericardiocentesis?

    PubMed

    Ristić, Arsen D; Wagner, Hans-Joachim; Maksimović, Ružica; Maisch, Bernhard

    2013-05-01

    The epicardial halo delineates the heart shadow in fluoroscopy. To establish whether the sign is applicable to pericardiocentesis guidance, three investigators evaluated its intensity as absent = grade 0, indistinct = 0.5, clear = 1, intensive = 2 in posterior-anterior (PA) and lateral fluoroscopies recorded before pericardiocentesis or cardiac catheterization (Philips Integris-II BH3000). Three populations were studied: (a) 32 patients with pericardial effusion (PE group), 53.1 % males, aged 53.9 ± 13.9 years; (b) 14 patients with perimyocarditis (PM group), 64.3 % males, aged 51.6 ± 14.4 years; and (c) 46 coronary patients (CAD group), no PE, 95.6 % males, aged 67.3 ± 11.8 years. The intensity of the halo phenomenon was highest in patients with PE, lowest in patients with CAD, and intermediate in patients with PM (median sum of grades in PA/lateral view: 4/5 vs. 2/2.5 vs. 3/3, respectively) (p < 0.01). The halo phenomenon correlated well with HR and echocardiographic PE size in both angiographic views. The correlation with body mass index (BMI) and age was significant only in the lateral view and with PE volume only in the PA view. The sensitivity of the halo sign for PE was 84.1 % in PA and 92.0 % in lateral views. In 10/32 PE patients, the evaluation of the sign was repeated after PE drainage, revealing lower grades both in PA and in lateral views (p < 0.01). In conclusion, the epicardial halo sign is highly sensitive for the detection of a PE; it correlates well in at least one angiographic projection with the PE volume, HR, age, BMI, and the PE size in echocardiography and could be therefore applied as a safety guide for pericardiocentesis.

  15. Biological Effects of Ionizing Radiation

    DOE R&D Accomplishments Database

    Ingram, M.; Mason, W. B.; Whipple, G. H.; Howland, J. W.

    1952-04-07

    This report presents a review of present knowledge and concepts of the biological effects of ionizing radiations. Among the topics discussed are the physical and chemical effects of ionizing radiation on biological systems, morphological and physiological changes observed in biological systems subjected to ionizing radiations, physiological changes in the intact animal, latent changes following exposure of biological systems to ionizing radiations, factors influencing the biological response to ionizing radiation, relative effects of various ionizing radiations, and biological dosimetry.

  16. Revisiting the Bulge-Halo Conspiracy. I. Dependence on Galaxy Properties and Halo Mass

    NASA Astrophysics Data System (ADS)

    Shankar, Francesco; Sonnenfeld, Alessandro; Mamon, Gary A.; Chae, Kyu-Hyun; Gavazzi, Raphael; Treu, Tommaso; Diemer, Benedikt; Nipoti, Carlo; Buchan, Stewart; Bernardi, Mariangela; Sheth, Ravi; Huertas-Company, Marc

    2017-05-01

    We carry out a systematic investigation of the total mass density profile of massive ({log} {M}{star}/{M}⊙ ≳ 11.3) early-type galaxies and its dependence on galactic properties and host halo mass with the aid of a variety of lensing/dynamical data and large mock galaxy catalogs. The latter are produced via semi-empirical models that, by design, are based on just a few basic input assumptions. Galaxies with measured stellar masses, effective radii, and Sérsic indices, are assigned, via abundance matching relations, host dark matter halos characterized by a typical ΛCDM profile. Our main results are as follows. (1) In line with observational evidence, our semi-empirical models naturally predict that the total, mass-weighted density slope at the effective radius γ‧ is not universal, steepening for more compact and/or massive galaxies, but flattening with increasing host halo mass. (2) Models characterized by a Salpeter or variable initial mass function (IMF) and uncontracted dark matter profiles are in good agreement with the data, while a Chabrier IMF and/or adiabatic contractions/expansions of the dark matter halos are highly disfavored. (3) Currently available data on the mass density profiles of very massive galaxies ({log} {M}{star}/{M}⊙ ≳ 12), with {M}{halo}≳ 3× {10}14 {M}⊙ , favor instead models with a stellar profile flatter than a Sérsic one in the very inner regions (r ≲ 3-5 kpc), and a cored NFW or Einasto dark matter profile with median halo concentration a factor of ˜2 or ≲1.3, respectively, higher than those typically predicted by N-body numerical simulations.

  17. Resolved Stellar Halos of M87 and NGC 5128

    NASA Astrophysics Data System (ADS)

    Bird, Sarah A.; Harris, William; Flynn, Chris; Blakeslee, John P.; Valtonen, Mauri

    2015-08-01

    We search halo fields of two giant elliptical galaxies: M87, using HST images at 10 kpc from the center, and NGC 5128 (Cen A), using VIMOS VLT images at 65 kpc from the center and archival HST data from 8 to 38 kpc from the center. We resolve thousands of red-giant-branch stars in these stellar halo fields using V and I filters, and, in addition, measure the metallicity using stellar isochrones. In Cen A, we find that the density of metal-rich and metal-poor halo stars falls off with the same slope in the de Vaucouleurs' law profile, from the inner halo of 8 kpc out to 70 kpc, with no sign of a transition to dominance by metal-poor stars. We also find that the metallicity distribution of the inner stellar halo of M87 is most similar to that of NGC 5128's inner stellar halo.

  18. Star formation activity in spiral galaxy disks and the properties of radio halos: Observational evidence for a direct dependence

    NASA Technical Reports Server (NTRS)

    Dahlem, Michael; Lisenfeld, Ute; Golla, Gotz

    1995-01-01

    In this article we address observationally the questions: how does star formation (SF) in the disks of galaxies lead to the creation of radio halos, and what minimum energy input into the interstellar medium (ISM) is needed to facilitate this? For the investigation we use a sample of five edge-on galaxies exhibiting radio continuum emmission in their halos and enhanced SF spread over large parts of their disks. In a detailed study of the two galaxies in our sample for which we have the best data, NGC 891 and NGC 4631, we show that the radio halos cut off abruptly at galactocentric radii smaller than those of the underlying thin radio disks. Our most important result is that the halo cutoffs are spatially coincident with the radii where the SF activity in the underlying disks drops sharply. The difference in radius of the emission distributions tracing ongoing SF in the disks (IRAS 50 micrometers, H alpha) versus that of the nonthermal radio continuum thin disks (tracing the distribution of cosmic-ray (CR) electrons) is typically a few kpc. This difference in extent is caused by CR diffusion. We have measured the CR diffusion coefficients in the thin disks of both NGC 891 and NGC 4631. For radial diffusion of CR electrons within the galactic disks the values are D(sub r) = 1.1-2.5 x 10 (exp 29) sq cm/s (NGC 4631) and D(sub r) = 1.2 x 10(exp 29) sq cm/s (NGC 891). For motions in the z-direction in areas within the thin disks where no outflows occur, we derive a firm upper limit of D(sub z) less than or equal to 0.2 x 10(exp 28) sq cm/s for NGC 891. The value for NGC 4631 is D(sub z = 1.4 x 10 (exp 28) sq cm/s. The other three galaxies in our sample, NGC 3044, NGC 4666, and NGC 5775 show (at the sensitivity of our data) less extended, more filamentary radio halos. Isolates spurs or filaments of nonthermal radio continuum emission in their halos are traced only above the most actively star-forming regions in the disks. This, in conjuction with the results obtained for

  19. Predator-Prey Model for Haloes in Saturn’s Rings

    NASA Astrophysics Data System (ADS)

    Esposito, Larry W.; Madhusudhanan, P.; Colwell, J. E.; Bradley, E.; Sremcevic, M.

    2013-10-01

    Particles in Saturn’s rings have a tripartite nature: (1) a broad distribution of fragments from the disruption of a previous moon that accrete into (2) transient aggregates, resembling piles of rubble, covered by a (3) regolith of smaller grains that result from collisions and meteoritic grinding. Evidence for this triple architecture of ring particles comes from a multitude of Cassini observations. In a number of ring locations (including Saturn’s F ring, the shepherded outer edges of rings A and B and at the locations of the strongest density waves) aggregation and dis-aggregation are operating now. ISS, VIMS, UVIS spectroscopy and occultations show haloes around the strongest density waves. Based on a predator-prey model for ring dynamics, we offer the following explanation: 1. Cyclic velocity changes cause the perturbed regions to reach higher collision speeds at some orbital phases, which preferentially removes small regolith particles; 2. This forms a bright halo around the ILR, if the forcing is strong enough; 3. Surrounding particles diffuse back too slowly to erase the effect; they diffuse away to form the halo. The most rapid time scale is for forcing/aggregate growth/disaggregation; then irreversible regolith erosion; diffusion and/or ballistic transport; and slowest, meteoritic pollution/darkening. We observe both smaller and larger particles at perturbed regions. Straw, UVIS power spectral analysis, kittens and equinox objects show the prey (mass aggregates); while the haloes’ VIMS spectral signature, correlation length and excess variance are created by the predators (velocity dispersion) in regions stirred in the rings. Moon forcing triggers aggregation to create longer-lived aggregates that protect their interiors from meteoritic darkening and recycle the ring material to maintain the current purity of the rings. It also provides a mechanism for creation of new moons at resonance locations in the Roche zone, as proposed by Charnoz etal and

  20. The distribution of warm ionized gas in NGC 891

    NASA Technical Reports Server (NTRS)

    Rand, Richard J.; Kulkarni, Shrinivas R.; Hester, J. Jeff

    1990-01-01

    Narrow-band imaging is presented of the edge-on spiral NGC 891 in the H-alpha and S II 6716, 6731 A forbidden lines. Emission from H II regions confined to the plane of the galaxy and from diffuse gas up to about 4 kpc off the plane is readily detected. The full radial extent of the diffuse emission in the plane is about 30 kpc. NGC 891 is found to have a surface density of diffuse ionized gas twice the Galactic value, a thicker ionized gas layer, and a larger surface density of ionized gas relative to neutral gas. These are interpreted as consequences of a relatively high level of star formation in this galaxy. Other star formation tracers indicate the same conclusion. Many vertical H-alpha filaments, or 'worms,' extending to over 2 kpc off the plane of the galaxy are seen. These worms are interpreted in terms of chimney models for the interstellar media of spirals.

  1. Data-Parallel Halo Finder Operator in PISTON

    SciTech Connect

    Widanagamaachchi, W. N.

    2012-08-01

    PISTON is a portable framework which supports the development of visualization and analysis operators using a platform-independent, data-parallel programming model. Operators such as isosurface, cut-surface and threshold have been implemented in this framework, with the exact same operator code achieving good parallel performance on different architectures. An important analysis operator in cosmology is the halo finder. A halo is a cluster of particles and is considered a common feature of interest found in cosmology data. As the number of cosmological simulations carried out in the recent past has increased, the resultant data of these simulations and the required analysis tasks have increased as well. As a consequence, there is a need to develop scalable and efficient tools to carry out the needed analysis. Therefore, we are currently implementing a halo finder operator using PISTON. Researchers have developed a wide variety of techniques to identify halos in raw particle data. The most basic algorithm is the friend-of-friends (FOF) halo finder, where the particles are clustered based on two parameters: linking length and halo size. In a FOF halo finder, all particles which lie within the linking length are considered as one halo and the halos are filtered based on the halo size parameter. A naive implementation of a FOF halo finder compares each and every particle pair, requiring O(n{sup 2}) operations. Our data-parallel halo finder operator uses a balanced k-d tree to reduce this number of operations in the average case, and implements the algorithm using only the data-parallel primitives in order to achieve portability and performance.

  2. The Angular Momentum Distribution within Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Chen, D.; Jing, Y.

    We study the angular momentum profile of dark matter halos for a statistical sample drawn from a set of high-resolution cosmological simulations of 2563 particles. Two typical Cold Dark Matter (CDM) models have been analyzed, and the halos are selected to have at least 3× 104 particles in order to reliably measure the angular momentum profile. In contrast with the recent claims of Bullock et al. (2001), we find that the degree of misalignment of angular momentum within a halo is very high. About 50 percent of halos have more than 10 percent of halo mass in the mass of negative angular momentum j. After the mass of negative j is excluded, the cumulative mass function M(halos (˜ 50%) which exhibit systematic deviations from the universal function. Our results, however, are broadly in good agreement with the recent work of van den Bosch et al. (2002). We also study the angular momentum profile of halos in a Warm Dark Matter (WDM) model and a Self-Interacting Dark Matter (SIDM) model. We find that the angular momentum profile of halos in the WDM is statistically indistinguishable from that in the CDM model, but the angular momentum of halos in the SIDM is reduced by the self-interaction of dark matter.

  3. Angular Momentum Profiles of Warm Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Bullock, James S.; Kravtsov, and Andrey V.; Colín, Pedro

    2002-01-01

    We compare the specific angular momentum profiles of virialized dark halos in cold dark matter (CDM) and warm dark matter (WDM) models, using high-resolution dissipationless simulations. The simulations were initialized using the same set of modes, except on small scales, where the power was suppressed in WDM below the filtering length. Remarkably, WDM as well as CDM halos are well described by the two-parameter angular momentum profile of Bullock and coworkers, even though the halo masses are below the filtering scale of the WDM. Although the best-fit shape parameters change quantitatively for individual halos in the two simulations, we find no systematic variation in profile shapes as a function of the dark matter type. The scatter in shape parameters is significantly smaller for the WDM halos, suggesting that substructure and/or merging history plays a role in producing scatter about the mean angular momentum distribution, but that the average angular momentum profiles of halos originate from larger scale phenomena or a mechanism associated with the virialization process. The known mismatch between the angular momentum distributions of dark halos and disk galaxies is, therefore, present in WDM as well as CDM models. Our WDM halos tend to have a less coherent (more misaligned) angular momentum structure and smaller spin parameters than do their CDM counterparts, although we caution that this result is based on a small number of halos.

  4. Two stellar components in the halo of the Milky Way.

    PubMed

    Carollo, Daniela; Beers, Timothy C; Lee, Young Sun; Chiba, Masashi; Norris, John E; Wilhelm, Ronald; Sivarani, Thirupathi; Marsteller, Brian; Munn, Jeffrey A; Bailer-Jones, Coryn A L; Fiorentin, Paola Re; York, Donald G

    2007-12-13

    The halo of the Milky Way provides unique elemental abundance and kinematic information on the first objects to form in the Universe, and this information can be used to tightly constrain models of galaxy formation and evolution. Although the halo was once considered a single component, evidence for its dichotomy has slowly emerged in recent years from inspection of small samples of halo objects. Here we show that the halo is indeed clearly divisible into two broadly overlapping structural components--an inner and an outer halo--that exhibit different spatial density profiles, stellar orbits and stellar metallicities (abundances of elements heavier than helium). The inner halo has a modest net prograde rotation, whereas the outer halo exhibits a net retrograde rotation and a peak metallicity one-third that of the inner halo. These properties indicate that the individual halo components probably formed in fundamentally different ways, through successive dissipational (inner) and dissipationless (outer) mergers and tidal disruption of proto-Galactic clumps.

  5. Squeezing the halo bispectrum: a test of bias models

    NASA Astrophysics Data System (ADS)

    Moradinezhad Dizgah, Azadeh; Chan, Kwan Chuen; Noreña, Jorge; Biagetti, Matteo; Desjacques, Vincent

    2016-09-01

    We study the halo-matter cross bispectrum in the presence of primordial non-Gaussianity of the local type. We restrict ourselves to the squeezed limit, for which the calculation are straightforward, and perform the measurements in the initial conditions of N-body simulations, to mitigate the contamination induced by nonlinear gravitational evolution. Interestingly, the halo-matter cross bispectrum is not trivial even in this simple limit as it is strongly sensitive to the scale-dependence of the quadratic and third-order halo bias. Therefore, it can be used to test biasing prescriptions. We consider three different prescription for halo clustering: excursion set peaks (ESP), local bias and a model in which the halo bias parameters are explicitly derived from a peak-background split. In all cases, the model parameters are fully constrained with statistics other than the cross bispectrum. We measure the cross bispectrum involving one halo fluctuation field and two mass overdensity fields for various halo masses and collapse redshifts. We find that the ESP is in reasonably good agreement with the numerical data, while the other alternatives we consider fail in various cases. This suggests that the scale-dependence of halo bias also is a crucial ingredient to the squeezed limit of the halo bispectrum.

  6. Milky Way is Surrounded by Huge Halo of Hot Gas

    NASA Image and Video Library

    2012-09-24

    Astronomers have used Chandra to find evidence that our Milky Way Galaxy is embedded in an enormous halo of hot gas that extends for hundreds of thousands of light years. This artist's illustration shows the halo of hot gas, in blue, around the Milky Way and two small neighboring galaxies. The mass of the halo is estimated to be comparable to the mass of all the stars in the Milky Way galaxy. If the size and mass of this gas halo is confirmed, it could be the solution to the "missing-baryon" problem for the Galaxy.

  7. Reversed Halo Sign: Presents in Different Pulmonary Diseases

    PubMed Central

    Zhan, Xi; Zhang, Lei; Wang, Zheng; Jin, Mulan; Liu, Min; Tong, Zhaohui

    2015-01-01

    Objective To observe the incidence of reversed halo sign in different pulmonary diseases and the pathological correspondence of reversed halo sign. Methods Retrospectively studied the high resolution computer tomography scans of all the patients who were admitted in our department with abnormal pulmonary imaging, from 1st of January 2011 to 31st of December 2013, and all the cases with reversed halo sign on the high resolution computer tomography were collected. Clinical data such as pathological findings and confirmed diagnosis of the patients with reversed halo sign on the high resolution computer tomography scan were collected and summarized. Results Of 1546 abnormal High resolution computer tomography scans 108 had a reverse halo sign present, including 108 cases were observed with reversed halo sign in the high resolution computer tomography, including 40 cases of pulmonary tuberculosis, 43 cases of cryptogenic organizing pneumonia, 16 cases of lung cancer, 7 cases of sarcoidosis, and 1 case of pulmonary cryptococcosis, 1 case of granulomatosis with polyangiitis. Reversed halo sign had a higher incidence in granulomatous diseases (16.28%) compared with non-granulomatous diseases (9.97%). Conclusions Reversed halo sign is relatively non specific; it can be observed in different lung diseases, and different phases of diseases; reversed halo sign is more commonly found in granulomatous diseases compared with non-granulomatous diseases, and is most commonly observed in pulmonary tuberculosis among the granulomatous diseases, and in cryptogenic organizing pneumonia among the non-granulomatous diseases. PMID:26083865

  8. Reversed Halo Sign: Presents in Different Pulmonary Diseases.

    PubMed

    Zhan, Xi; Zhang, Lei; Wang, Zheng; Jin, Mulan; Liu, Min; Tong, Zhaohui

    2015-01-01

    To observe the incidence of reversed halo sign in different pulmonary diseases and the pathological correspondence of reversed halo sign. Retrospectively studied the high resolution computer tomography scans of all the patients who were admitted in our department with abnormal pulmonary imaging, from 1st of January 2011 to 31st of December 2013, and all the cases with reversed halo sign on the high resolution computer tomography were collected. Clinical data such as pathological findings and confirmed diagnosis of the patients with reversed halo sign on the high resolution computer tomography scan were collected and summarized. Of 1546 abnormal High resolution computer tomography scans 108 had a reverse halo sign present, including 108 cases were observed with reversed halo sign in the high resolution computer tomography, including 40 cases of pulmonary tuberculosis, 43 cases of cryptogenic organizing pneumonia, 16 cases of lung cancer, 7 cases of sarcoidosis, and 1 case of pulmonary cryptococcosis, 1 case of granulomatosis with polyangiitis. Reversed halo sign had a higher incidence in granulomatous diseases (16.28%) compared with non-granulomatous diseases (9.97%). Reversed halo sign is relatively non specific; it can be observed in different lung diseases, and different phases of diseases; reversed halo sign is more commonly found in granulomatous diseases compared with non-granulomatous diseases, and is most commonly observed in pulmonary tuberculosis among the granulomatous diseases, and in cryptogenic organizing pneumonia among the non-granulomatous diseases.

  9. Light source halos in night vision goggles: psychophysical assessments

    NASA Astrophysics Data System (ADS)

    Craig, Greg; Macuda, Todd; Thomas, Paul; Allison, Rob; Jennings, Sion

    2005-05-01

    Anecdotal reports by pilots flying with Night Vision Goggles (NVGs) in urban environments suggest that halos produced by bright light sources impact flight performance. The current study developed a methodology to examine the impact of viewing distance on perceived halo size. This was a first step in characterizing the subtle phenomenon of halo. Observers provided absolute size estimates of halos generated by a red LED at several viewing distances. Physical measurements of these halos were also recorded. The results indicated that the perceived halo linear size decreased as viewing distance was decreased. Further, the data showed that halos subtended a constant visual angle on the goggles (1°48", +/-7") irrespective of distance up to 75". This invariance with distance may impact pilot visual performance. For example, the counterintuitive apparent contraction of halo size with decreasing viewing distance may impact estimates of closure rates and of the spatial layout of light sources in the scene. Preliminary results suggest that halo is a dynamic phenomenon that requires further research to characterize the specific perceptual effects that it might have on pilot performance.

  10. Effects of image intensifier halo on perceived layout

    NASA Astrophysics Data System (ADS)

    Zacher, James E.; Brandwood, Tracey; Thomas, Paul; Vinnikov, Margarita; Xu, Gancun; Jennings, Sion; Macuda, Todd; Palmisano, Stephan A.; Craig, Greg; Wilcox, Laurie; Allison, Robert S.

    2007-04-01

    Night vision devices (NVDs) or night-vision goggles (NVGs) based on image intensifiers improve nighttime visibility and extend night operations for military and increasingly civil aviation. However, NVG imagery is not equivalent to daytime vision and impaired depth and motion perception has been noted. One potential cause of impaired perceptions of space and environmental layout is NVG halo, where bright light sources appear to be surrounded by a disc-like halo. In this study we measured the characteristics of NVG halo psychophysically and objectively and then evaluated the influence of halo on perceived environmental layout in a simulation experiment. Halos are generated in the device and are not directly related to the spatial layout of the scene. We found that, when visible, halo image (i.e. angular) size was only weakly dependent on both source intensity and distance although halo intensity did vary with effective source intensity. The size of halo images surrounding lights sources are independent of the source distance and thus do not obey the normal laws of perspective. In simulation experiments we investigated the effect of NVG halo on judgements of observer attitude with respect to the ground during simulated flight. We discuss the results in terms of NVG design and of the ability of human operators to compensate for perceptual distortions.

  11. The clustering of baryonic matter. II: halo model and hydrodynamic simulations

    SciTech Connect

    Fedeli, C.; Semboloni, E.; Velliscig, M.; Daalen, M. Van; Schaye, J.; Hoekstra, H. E-mail: sembolon@strw.leidenuniv.nl E-mail: daalen@strw.leidenuniv.nl E-mail: hoekstra@strw.leidenuniv.nl

    2014-08-01

    We recently developed a generalization of the halo model in order to describe the spatial clustering properties of each mass component in the Universe, including hot gas and stars. In this work we discuss the complementarity of the model with respect to a set of cosmological simulations including hydrodynamics of different kinds. We find that the mass fractions and density profiles measured in the simulations do not always succeed in reproducing the simulated matter power spectra, the reason being that the latter encode information from a much larger range in masses than that accessible to individually resolved structures. In other words, this halo model allows one to extract information on the growth of structures from the spatial clustering of matter, that is complementary with the information coming from the study of individual objects. We also find a number of directions for improvement of the present implementation of the model, depending on the specific application one has in mind. The most relevant one is the necessity for a scale dependence of the bias of the diffuse gas component, which will be interesting to test with future detections of the Warm-Hot Intergalactic Medium. This investigation confirms the possibility to gain information on the physics of galaxy and cluster formation by studying the clustering of mass, and our next work will consist of applying the halo model to use future high-precision cosmic shear surveys to this end.

  12. Major substructure in the M31 Outer Halo: the East Cloud

    NASA Astrophysics Data System (ADS)

    McMonigal, B.; Bate, N. F.; Conn, A. R.; Mackey, A. D.; Lewis, G. F.; Irwin, M. J.; Martin, N. F.; McConnachie, A. W.; Ferguson, A. M. N.; Ibata, R. A.; Huxor, A. P.

    2016-02-01

    We present the first detailed analysis of the East Cloud, a highly disrupted diffuse stellar substructure in the outer halo of M31. The core of the substructure lies at a projected distance of ˜100 kpc from the centre of M31 in the outer halo, with possible extensions reaching right into the inner halo. Using Pan-Andromeda Archaeological Survey photometry of red giant branch stars, we measure the distance, metallicity and brightness of the cloud. Using Hubble Space Telescope data, we independently measure the distance and metallicity to the two globular clusters coincident with the East Cloud core, PA-57 and PA-58, and find their distances to be consistent with the cloud. Four further globular clusters coincident with the substructure extensions are identified as potentially associated. Combining the analyses, we determine a distance to the cloud of 814^{+20}_{-9} kpc, a metallicity of [Fe/H] = -1.2 ± 0.1, and a brightness of MV = -10.7 ± 0.4 mag. Even allowing for the inclusion of the potential extensions, this accounts for less than 20 per cent of the progenitor luminosity implied by the luminosity-metallicity relation. Using the updated techniques developed for this analysis, we also refine our estimates of the distance and brightness of the South-West Cloud, a separate substructure analysed in the previous work in this series.

  13. Galactic halo origin of the neutrinos detected by IceCube

    NASA Astrophysics Data System (ADS)

    Taylor, Andrew M.; Gabici, Stefano; Aharonian, Felix

    2014-05-01

    Recent IceCube results suggest that the first detection of very high energy astrophysical neutrinos have been accomplished. We consider these results at face value in a Galactic origin context. Emission scenarios from both the Fermi bubble and broader halo region are considered. We motivate that such an intensity of diffuse neutrino emission could be Galactic in origin if it is produced from an outflow into the halo region. This scenario requires cosmic ray transport within the outflow environment to be different to that inferred locally within the disk and that activity in the central part of the Galaxy accelerates cosmic rays to trans-"knee" energies before they escape into an outflow. The presence of a large reservoir of gas in a very extended halo around the Galaxy, recently inferred from x-ray observations, implies that the relatively modest acceleration power of 1039 erg s-1 in PeV energy cosmic rays may be sufficient to explain the observed neutrino flux. Such a luminosity is compatible with that required to explain the observed intensity of cosmic rays around the knee.

  14. The Outer Halos of Very Massive Galaxies: BCGs and their DSC in the Magneticum Simulations

    NASA Astrophysics Data System (ADS)

    Remus, Rhea-Silvia; Dolag, Klaus; Hoffmann, Tadziu

    2017-09-01

    Recent hydrodynamic cosmological simulations cover volumes up to Gpc^3 and resolve halos across a wide range of masses and environments, from massive galaxy clusters down to normal galaxies, while following a large variety of physical processes (star formation, chemical enrichment, AGN feedback) to allow a self-consistent comparison to observations at multiple wavelengths. Using the Magneticum simulations, we investigate the buildup of the diffuse stellar component (DSC) around massive galaxies within group and cluster environments. The DSC in our simulations reproduces the spatial distribution of the observed intracluster light (ICL) as well as its kinematic properties remarkably well. For galaxy clusters and groups we find that, although the DSC in almost all cases shows a clear separation from the brightest cluster galaxy (BCG) with regard to its dynamic state, the radial stellar density distribution in many halos is often characterized by a single Sersic profile, representing both the BCG component and the DSC, very much in agreement with current observational results. Interestingly, even in those halos that clearly show two components in both the dynamics and the spatial distribution of the stellar component, no correlation between them is evident.

  15. THE DISCOVERY OF A RADIO HALO IN PLCK G147.3–16.6 AT Z = 0.65

    SciTech Connect

    Van Weeren, R. J.; Jones, C.; Forman, W. R.; Intema, H. T.; Lal, D. V.; Bonafede, A.; Brüggen, M.; De Gasperin, F.; Röttgering, H. J. A.; Stroe, A.; Hoeft, M.; Nuza, S. E.

    2014-02-01

    Recent X-ray and Sunyaev-Zel'dovich (SZ) observations have dramatically increased the number of known distant galaxy clusters. In some merging, low-redshift (z < 0.4) clusters, centrally located, diffuse, extended radio emission (radio halos) has been found. Using the Giant Metrewave Radio Telescope (GMRT), we report the detection of diffuse radio emission in the binary-merging cluster PLCK G147.3–16.6 located at z = 0.65. We classify the emission as a giant radio halo due to its large physical extent of about 0.9 Mpc and its low-surface brightness. We measure an integrated flux density of 7.3 ± 1.1 mJy at 610 MHz for the radio halo, resulting in a 1.4 GHz radio power of 5.1 × 10{sup 24} W Hz{sup –1}. The radio halo power is consistent with that expected from the known correlation between X-ray luminosity or the cluster integrated SZ signal and radio power. Our observations also suggest that more of these distant radio halos could be discovered with the GMRT.

  16. Characterizing cosmic inhomogeneity with anomalous diffusion

    NASA Astrophysics Data System (ADS)

    Kraljic, D.

    2015-08-01

    Dark matter (DM) clustering at the present epoch is investigated from a fractal viewpoint in order to determine the scale where the self-similar scaling property of the DM halo distribution transits to homogeneity. Methods based on well-established `counts-in-cells' as well as new methods based on anomalous diffusion and random walks are investigated. Both are applied to DM haloes of the biggest N-body simulation in the `Dark Sky Simulations' (DS) catalogue and an equivalent randomly distributed catalogue. Results based on the smaller `Millennium Run' (MR) simulation are revisited and improved. It is found that the MR simulation volume is too small and prone to bias to reliably identify the onset of homogeneity. Transition to homogeneity is defined when the fractal dimension of the clustered and random distributions cannot be distinguished within the associated uncertainties. The `counts-in-cells' method applied to the DS then yields a homogeneity scale roughly consistent with previous work (˜150 h-1 Mpc). The characteristic length-scale for anomalous diffusion to behave homogeneously is found to be at about 250 h-1 Mpc. The behaviour of the fractal dimensions for a halo catalogue with the same two-point function as the original but with shuffled Fourier phases is investigated. The methods based on anomalous diffusion are shown to be sensitive to the phase information, whereas the `counts-in-cells' methods are not.

  17. In silico studies to explore the mutagenic ability of 5-halo/oxy/li-oxy-uracil bases with guanine of DNA base pairs.

    PubMed

    Jana, Kalyanashis; Ganguly, Bishwajit

    2014-10-16

    DNA nucleobases are reactive in nature and undergo modifications by deamination, oxidation, alkylation, or hydrolysis processes. Many such modified bases are susceptible to mutagenesis when formed in cellular DNA. The mutagenesis can occur by mispairing with DNA nucleobases by a DNA polymerase during replication. We have performed a study of mispairing of DNA bases with unnatural bases computationally. 5-Halo uracils have been studied as mispairs in mutagenesis; however, the reports on their different forms are scarce in the literature. The stability of mispairs with keto form, enol form, and ionized form of 5-halo-uracil has been computed with the M06-2X/6-31+G** level of theory. The enol form of 5-halo-uracil showed remarkable stability toward DNA mispair compared to the corresponding keto and ionized forms. (F)U-G mispair showed the highest stability in the series and (Halo)(U(enol/ionized)-G mispair interactions energies are more stable than the natural G-C basepair of DNA. To enhance the stability of DNA mispairs, we have introduced the hydroxyl group in the place of halogen atoms, which provides additional hydrogen-bonding interactions in the system while forming the 5-membered ring. The study has been further extended with lithiated 5-hydroxymethyl-uracil to stabilize the DNA mispair. (CH2OLi)U(ionized)-G mispair has shown the highest stability (ΔG = -32.4 kcal/mol) with multi O-Li interactions. AIM (atoms in molecules) and EDA (energy decomposition analysis) analysis has been performed to examine the nature of noncovalent interactions in such mispairs. EDA analysis has shown that electrostatic energy mainly contributes toward the interaction energy of mispairs. The higher stability achieved in these studied mispairs can play a pivotal role in the mutagenesis and can help to attain the mutation for many desired biological processes.

  18. Wide-Field Imaging of Galactic Halos with a Near-Infrared Rocket-Borne Telescope

    NASA Technical Reports Server (NTRS)

    Lange, Andrew E.

    2000-01-01

    We successfully completed both of the proposed flights by May of 1998, on schedule and on budget. In both flights the instrument worked flawlessly, achieving sensitivities slightly better than the specification (1 nW/sq m sr per pixel). The payload was recovered with only minor damage after both flights. The results from the first flight, which targeted the nearby edge-on spiral NCG 4565, have been published. Analysis of the data failed to detect any significant emission, from the halo around the galaxy, and set a very stringent 2 sigma lower limit on the M/L ratio of the halo of greater than 260 in solar units. The results from the second flight, which targeted the infamous NGC 5907, have taken longer to analyze because of an offset in the absolute pointing of the payload which broke the symmetry of the scan pattern about the galaxy, thus complicating the analysis, After careful analysis, Caltech graduate student, Sarah Yost, has recovered the full sensitivity of the experiment, setting a 2 sigma lower limit on the M/L ratio of the halo of greater than 280 in solar units. This result rules out the hypothesis that a significant portion of the halo around NGC 5907 is composed of low-mass stars, as previous observations had suggested. NITE probes directly the halo at 10 to 30 kpc from the disk, a region far too dim for other experiments. Our conclusion is that observations of a significant IR signature associated with the halo at less than approximately 5kpc radius where contaminated by tidally disrupted disk population of stars. In order to test the idea that we could study faint surface-brightness fluctuations in the diffuse background using NITE, we have analyzed the data from the 1997 flight which targeted NCG 4565 (this target is in a region of lower stellar confusion than is NGC 5907). We have detected a significant correlation in the noise at zero-lag, with an amplitude that corresponds to brightness fluctuations of 3.04 plus or minus 0.16 nW/sq m sr. This

  19. Mapping stellar content to dark matter haloes - II. Halo mass is the main driver of galaxy quenching

    NASA Astrophysics Data System (ADS)

    Zu, Ying; Mandelbaum, Rachel

    2016-04-01

    We develop a simple yet comprehensive method to distinguish the underlying drivers of galaxy quenching, using the clustering and galaxy-galaxy lensing of red and blue galaxies in Sloan Digital Sky Survey. Building on the iHOD framework developed by Zu & Mandelbaum, we consider two quenching scenarios: (1) a `halo' quenching model in which halo mass is the sole driver for turning off star formation in both centrals and satellites; and (2) a `hybrid' quenching model in which the quenched fraction of galaxies depends on their stellar mass, while the satellite quenching has an extra dependence on halo mass. The two best-fitting models describe the red galaxy clustering and lensing equally well, but halo quenching provides significantly better fits to the blue galaxies above 1011 h-2 M⊙. The halo quenching model also correctly predicts the average halo mass of the red and blue centrals, showing excellent agreement with the direct weak lensing measurements of locally brightest galaxies. Models in which quenching is not tied to halo mass, including an age-matching model in which galaxy colour depends on halo age at fixed M*, fail to reproduce the observed halo mass for massive blue centrals. We find similar critical halo masses responsible for the quenching of centrals and satellites (˜1.5 × 1012 h-1 M⊙), hinting at a uniform quenching mechanism for both, e.g. the virial shock heating of infalling gas. The success of the iHOD halo quenching model provides strong evidence that the physical mechanism that quenches star formation in galaxies is tied principally to the masses of their dark matter haloes rather than the properties of their stellar components.

  20. Electron ionization of acetylene.

    PubMed

    King, Simon J; Price, Stephen D

    2007-11-07

    Relative partial ionization cross sections and precursor specific relative partial ionization cross sections for fragment ions formed by electron ionization of C2H2 have been measured using time-of-flight mass spectrometry coupled with a 2D ion-ion coincidence technique. We report data for the formation of H+, H+2, C2+, C+/C2+ 2, CH+/C2H+2, CH+2, C+2, and C2H+ relative to the formation of C2H+2, as a function of ionizing electron energy from 30-200 eV. While excellent agreement is found between our data and one set of previously published absolute partial ionization cross sections, some discrepancies exist between the results presented here and two other recent determinations of these absolute partial ionization cross sections. We attribute these differences to the loss of some translationally energetic fragment ions in these earlier studies. Our relative precursor-specific partial ionization cross sections enable us, for the first time, to quantify the contribution to the yield of each fragment ion from single, double, and triple ionization. Analysis shows that at 50 eV double ionization contributes 2% to the total ion yield, increasing to over 10% at an ionizing energy of 100 eV. From our ion-ion coincidence data, we have derived branching ratios for charge separating dissociations of the acetylene dication. Comparison of our data to recent ab initio/RRKM calculations suggest that close to the double ionization potential C2H2+2 dissociates predominantly on the ground triplet potential energy surface (3Sigma*g) with a much smaller contribution from dissociation via the lowest singlet potential energy surface (1Delta g). Measurements of the kinetic energy released in the fragmentation reactions of C2H2+2 have been used to obtain precursor state energies for the formation of product ion pairs, and are shown to be in good agreement with available experimental data and with theory.

  1. Levy-Student distributions for halos in accelerator beams

    SciTech Connect

    Cufaro Petroni, Nicola; De Martino, Salvatore; De Siena, Silvio; Illuminati, Fabrizio

    2005-12-15

    We describe the transverse beam distribution in particle accelerators within the controlled, stochastic dynamical scheme of stochastic mechanics (SM) which produces time reversal invariant diffusion processes. This leads to a linearized theory summarized in a Schroedinger-like (SL) equation. The space charge effects have been introduced in recent papers by coupling this S-L equation with the Maxwell equations. We analyze the space-charge effects to understand how the dynamics produces the actual beam distributions, and in particular we show how the stationary, self-consistent solutions are related to the (external and space-charge) potentials both when we suppose that the external field is harmonic (constant focusing), and when we a priori prescribe the shape of the stationary solution. We then proceed to discuss a few other ideas by introducing generalized Student distributions, namely, non-Gaussian, Levy infinitely divisible (but not stable) distributions. We will discuss this idea from two different standpoints: (a) first by supposing that the stationary distribution of our (Wiener powered) SM model is a Student distribution; (b) by supposing that our model is based on a (non-Gaussian) Levy process whose increments are Student distributed. We show that in the case (a) the longer tails of the power decay of the Student laws and in the case (b) the discontinuities of the Levy-Student process can well account for the rare escape of particles from the beam core, and hence for the formation of a halo in intense beams.

  2. HIGH-TEMPERATURE IONIZATION IN PROTOPLANETARY DISKS

    SciTech Connect

    Desch, Steven J.; Turner, Neal J.

    2015-10-01

    We calculate the abundances of electrons and ions in the hot (≳500 K), dusty parts of protoplanetary disks, treating for the first time the effects of thermionic and ion emission from the dust grains. High-temperature ionization modeling has involved simply assuming that alkali elements such as potassium occur as gas-phase atoms and are collisionally ionized following the Saha equation. We show that the Saha equation often does not hold, because free charges are produced by thermionic and ion emission and destroyed when they stick to grain surfaces. This means the ionization state depends not on the first ionization potential of the alkali atoms, but rather on the grains’ work functions. The charged species’ abundances typically rise abruptly above about 800 K, with little qualitative dependence on the work function, gas density, or dust-to-gas mass ratio. Applying our results, we find that protoplanetary disks’ dead zone, where high diffusivities stifle magnetorotational turbulence, has its inner edge located where the temperature exceeds a threshold value ≈1000 K. The threshold is set by ambipolar diffusion except at the highest densities, where it is set by Ohmic resistivity. We find that the disk gas can be diffusively loaded onto the stellar magnetosphere at temperatures below a similar threshold. We investigate whether the “short-circuit” instability of current sheets can operate in disks and find that it cannot, or works only in a narrow range of conditions; it appears not to be the chondrule formation mechanism. We also suggest that thermionic emission is important for determining the rate of Ohmic heating in hot Jupiters.

  3. 77 FR 75672 - Manufacturer of Controlled Substances, Notice of Registration, Halo Pharmaceutical, Inc.

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-12-21

    ... Enforcement Administration Manufacturer of Controlled Substances, Notice of Registration, Halo Pharmaceutical... 47114, Halo Pharmaceutical, Inc., 30 North Jefferson Road, Whippany, New Jersey 07981, made application... determined that the registration of Halo Pharmaceutical, Inc., to manufacture the listed basic classes...

  4. 77 FR 16264 - Manufacturer of Controlled Substances, Notice of Registration; Halo Pharmaceutical Inc.

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-03-20

    ... Enforcement Administration Manufacturer of Controlled Substances, Notice of Registration; Halo Pharmaceutical... FR 77850, Halo Pharmaceutical Inc., 30 North Jefferson Road, Whippany, New Jersey 07981, made... determined that the registration of Halo Pharmaceutical Inc. to manufacture the listed basic classes...

  5. THE COS-HALOS SURVEY: AN EMPIRICAL DESCRIPTION OF METAL-LINE ABSORPTION IN THE LOW-REDSHIFT CIRCUMGALACTIC MEDIUM

    SciTech Connect

    Werk, Jessica K.; Prochaska, J. Xavier; Tripp, Todd M.; O'Meara, John M.; Peeples, Molly S.

    2013-02-15

    We present the equivalent width and column density measurements for low and intermediate ionization states of the circumgalactic medium (CGM) surrounding 44 low-z, L Almost-Equal-To L* galaxies drawn from the COS-Halos survey. These measurements are derived from far-UV transitions observed in HST/COS and Keck/HIRES spectra of background quasars within an impact parameter R < 160 kpc to the targeted galaxies. The data show significant metal-line absorption for 33 of the 44 galaxies, including quiescent systems, revealing the common occurrence of a cool (T Almost-Equal-To 10{sup 4}-10{sup 5} K), metal-enriched CGM. The detection rates and column densities derived for these metal lines decrease with increasing impact parameter, a trend we interpret as a declining metal surface density profile for the CGM. A comparison of the relative column densities of adjacent ionization states indicates that the gas is predominantly ionized. The large surface density in metals demands a large reservoir of metals and gas in the cool CGM (very conservatively, M {sup cool} {sub CGM} >