Science.gov

Sample records for magnetized galactic halo

  1. Magnetized galactic haloes and velocity lags

    NASA Astrophysics Data System (ADS)

    Henriksen, R. N.; Irwin, J. A.

    2016-06-01

    We present an analytic model of a magnetized galactic halo surrounding a Mestel gravitating disc. The magnetic field is taken to be in energy equipartition with the pressure dominant rotating halo gas (not with the cosmic rays), and the whole system is in a steady state. A more flexible `anisotropic equipartition' model is also explored. A definite pressure law is required to maintain the equilibrium, but the halo density is constant. The velocity/magnetic system is scale-free. The objective is to find the rotational velocity lag in such a halo. The magnetic field is not force-free so that angular momentum may be transported from the halo to the intergalactic medium. We find that the `X'-shaped structure observed for halo magnetic fields can be obtained together with a simple analytic formula for the rate of decline of the velocity with height z. The formula also predicts the change in lag with radius, r.

  2. Numerical simulation of the plasma and gravitational dynamics of a galactic magnetic monopole halo

    NASA Astrophysics Data System (ADS)

    Farouki, R.; Shapiro, S. L.; Wasserman, I.

    1984-09-01

    Numerical and analytical calculations designed to assess the viability of a Galactic magnetic monopole halo are presented. The dynamical interplay between magnetic currents and the Galactic magnetic field is treated self-consistently, taking full account of the temporal evolution of currents and fields. It is found that in general self-consistent bounds on the Galactic magnetic monopole flux based on the survival of the Galactic magnetic field are far less restrictive than the Parker limit. The halo models are consistent with monopole masses m(M) approximately equal to or less than 7 x 10 to the 19th GeV, and monopole fluxes in the range F(M) approximately equal to or greater than 3 x 10 to the -13th per sq cm per s. Topics for future, more detailed studies are enumerated and discussed.

  3. Collision of the Smith Cloud and its dark matter halo with the magnetized Galactic disk

    NASA Astrophysics Data System (ADS)

    Galyardt, Jason; Shelton, Robin L.

    2015-01-01

    The Smith Cloud is a massive High Velocity Cloud (HVC) that may have passed through the Milky Way disk in the recent past. Previous studies using hydrodynamic simulations suggest that a dark matter halo may have provided the confinement neccessary for the Smith Cloud to survive passage through the Galactic corona and disk. However, the models of the Galaxy that were used in these studies did not include a magnetic field, while magnetic fields are known to have confining properties. Other studies have shown that the Galactic magnetic field can inhibit mass exchange between the corona and the disk due to magnetic field compression. We extend upon these studies via FLASH magnetohydrodynamic simulations to consider the effects of a Galactic magnetic field on an infalling, dark matter confined HVC.

  4. Origin of strong magnetic fields in Milky Way-like galactic haloes

    NASA Astrophysics Data System (ADS)

    Beck, Alexander; Dolag, Klaus; Lesch, Harald

    2015-08-01

    An analytical model predicting the growth rates, the absolute growth times and the saturation values of the magnetic field strength within galactic haloes is presented. The analytical results are compared to cosmological MHD simulations of Milky Way-like galactic halo formation performed with the N-body / SPMHD code GADGET. The halo has a mass of approximately 3*10^{12} solar masses and a virial radius of approximately 270 kpc. The simulations in a LCDM cosmology also include radiative cooling, star formation, supernova feedback and the description of non-ideal MHD. A primordial magnetic seed field ranging from 10^{-10} to 10^{-34} G in strength agglomerates together with the gas within filaments and protohaloes.There, it is amplified within a couple of hundred million years up to equipartition with the corresponding turbulent energy. The magnetic field strength increases by turbulent small-scale dynamo action. The turbulence is generated by the gravitational collapse and by supernova feedback. Subsequently, a series of halo mergers leads to shock waves and amplification processes magnetizing the surrounding gas within a few billion years. At first, the magnetic energy grows on small scales and then self-organizes to larger scales.Magnetic field strengths of microG are reached in the center of the halo and drop to nG in the IGM. Analyzing the saturation levels and growth rates, the model is able to describe the process of magnetic amplification notably well and confirms the results of the simulations. Additionally, we investigate magnetic seed fields created self-consistently by supernova explosions naturally occuring during the star formation in galaxies. Within starforming regions and given typical dimensions and magnetic field strengths in canonical SN remnants, we inject a dipole-shape magnetic field at a rate of nG/Gyr.In our model for the evolution of galactic magnetic fields, the seed magnetic field determined self-consistently by the star formation process

  5. Origin of strong magnetic fields in Milky Way-like galactic haloes

    NASA Astrophysics Data System (ADS)

    Beck, A. M.; Lesch, H.; Dolag, K.; Kotarba, H.; Geng, A.; Stasyszyn, F. A.

    2012-05-01

    An analytical model predicting the growth rates, the absolute growth times and the saturation values of the magnetic field strength within galactic haloes is presented. The analytical results are compared to cosmological magnetohydrodynamics (MHD) simulations of Milky Way-like galactic halo formation performed with the N-body/SPMHD code GADGET. The halo has a mass of ≈3 × 1012 M⊙ and a virial radius of ≈270 kpc. The simulations in a Λ cold dark matter (ΛCDM) cosmology also include radiative cooling, star formation, supernova feedback and the description of non-ideal MHD. A primordial magnetic seed field ranging from 10-10 to 10-34 G in strength agglomerates together with the gas within filaments and protohaloes. There, it is amplified within a couple of hundred million years up to equipartition with the corresponding turbulent energy. The magnetic field strength increases by turbulent small-scale dynamo action. The turbulence is generated by the gravitational collapse and by supernova feedback. Subsequently, a series of halo mergers leads to shock waves and amplification processes magnetizing the surrounding gas within a few billion years. At first, the magnetic energy grows on small scales and then self-organizes to larger scales. Magnetic field strengths of ≈10-6 G are reached in the centre of the halo and drop to ≈10-9 G in the intergalactic medium. Analysing the saturation levels and growth rates, the model is able to describe the process of magnetic amplification notably well and confirms the results of the simulations.

  6. NEW CONSTRAINTS ON THE GALACTIC HALO MAGNETIC FIELD USING ROTATION MEASURES OF EXTRAGALACTIC SOURCES TOWARD THE OUTER GALAXY

    SciTech Connect

    Mao, S. A.; McClure-Griffiths, N. M.; Gaensler, B. M.; Brown, J. C.; Van Eck, C. L.; Stil, J. M.; Taylor, A. R.; Haverkorn, M.; Kronberg, P. P.; Shukurov, A.

    2012-08-10

    We present a study of the Milky Way disk and halo magnetic field, determined from observations of Faraday rotation measure (RM) toward 641 polarized extragalactic radio sources in the Galactic longitude range 100 Degree-Sign -117 Degree-Sign , within 30 Degree-Sign of the Galactic plane. For |b| < 15 Degree-Sign , we observe a symmetric RM distribution about the Galactic plane. This is consistent with a disk field in the Perseus arm of even parity across the Galactic mid-plane. In the range 15 Degree-Sign < |b| < 30 Degree-Sign , we find median RMs of -15 {+-} 4 rad m{sup -2} and -62 {+-} 5 rad m{sup -2} in the northern and southern Galactic hemispheres, respectively. If the RM distribution is a signature of the large-scale field parallel to the Galactic plane, then this suggests that the halo magnetic field toward the outer Galaxy does not reverse direction across the mid-plane. The variation of RM as a function of Galactic latitude in this longitude range is such that RMs become more negative at larger |b|. This is consistent with an azimuthal magnetic field of strength 2 {mu}G (7 {mu}G) at a height 0.8-2 kpc above (below) the Galactic plane between the local and the Perseus spiral arm. We propose that the Milky Way could possess spiral-like halo magnetic fields similar to those observed in M51.

  7. ANISOTROPY AS A PROBE OF THE GALACTIC COSMIC-RAY PROPAGATION AND HALO MAGNETIC FIELD

    SciTech Connect

    Qu, Xiao-bo; Zhang, Yi; Liu, Cheng; Hu, Hong-bo; Xue, Liang

    2012-05-01

    The anisotropy of cosmic rays (CRs) in the solar vicinity is generally attributed to CR streaming due to the discrete distribution of CR sources or local magnetic field modulation. Recently, the two-dimensional large-scale CR anisotropy has been measured by many experiments in the TeV-PeV energy range in both hemispheres. The tail-in excess along the tangential direction of the local spiral arm and the loss cone deficit pointing to the north Galactic pole direction agree with what have been obtained in tens to hundreds of GeV. The persistence of the two large-scale anisotropy structures in such a wide energy range suggests that the anisotropy might be due to global streaming of the Galactic CRs (GCRs). This work tries to extend the observed CR anisotropy picture from the solar system to the whole galaxy. In such a case, we can find a new interesting signature, a loop of GCR streaming, of the GCR propagation. We further calculate the overall GCR streaming induced magnetic field, and find a qualitative consistency with the observed structure of the halo magnetic field.

  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. The Evolution of Gas Clouds Falling in the Magnetized Galactic Halo: High-Velocity Clouds (HVCs) Originated in the Galactic Fountain

    NASA Astrophysics Data System (ADS)

    Kwak, Kyujin; Shelton, Robin L.; Raley, Elizabeth A.

    2009-07-01

    In the Galactic fountain scenario, supernovae and/or stellar winds propel material into the Galactic halo. As the material cools, it condenses into clouds. By using FLASH three-dimensional magnetohydrodynamic simulations, we model and study the dynamical evolution of these gas clouds after they form and begin to fall toward the Galactic plane. In our simulations, we assume that the gas clouds form at a height of z = 5 kpc above the Galactic midplane, then begin to fall from rest. We investigate how the cloud's evolution, dynamics, and interaction with the interstellar medium (ISM) are affected by the initial mass of the cloud. We find that clouds with sufficiently large initial densities (n >= 0.1 H atoms cm-3) accelerate sufficiently and maintain sufficiently large column densities as to be observed and identified as high-velocity clouds (HVCs) even if the ISM is weakly magnetized (1.3 μG). However, the ISM can provide noticeable resistance to the motion of a low-density cloud (n <= 0.01 H atoms cm-3) thus making it more probable that a low-density cloud will attain the speed of an intermediate-velocity cloud rather than the speed of an HVC. We also investigate the effects of various possible magnetic field configurations. As expected, the ISM's resistance is greatest when the magnetic field is strong and perpendicular to the motion of the cloud. The trajectory of the cloud is guided by the magnetic field lines in cases where the magnetic field is oriented diagonal to the Galactic plane. The model cloud simulations show that the interactions between the cloud and the ISM can be understood via analogy to the shock tube problem which involves shock and rarefaction waves. We also discuss accelerated ambient gas, streamers of material ablated from the clouds, and the cloud's evolution from a sphere-shaped to a disk- or cigar-shaped object.

  10. MAGNETIC FIELD TRANSPORT FROM DISK TO HALO VIA THE GALACTIC CHIMNEY PROCESS IN NGC 6946

    SciTech Connect

    Heald, George H.

    2012-08-01

    The interstellar medium (ISM) in galaxies is directly affected by the mass and energy outflows originating in regions of star formation. Magnetic fields are an essential ingredient of the ISM, but their connection to the gaseous medium and its evolution remains poorly understood. Here, we present the detection of a gradient in Faraday rotation measure (RM), co-located with a hole in the neutral hydrogen (H I) distribution in the disk of the nearby spiral galaxy NGC 6946. The gas kinematics in the same location show evidence for infall of cold gas. The combined characteristics of this feature point to a substantial vertical displacement of the initially plane-parallel-ordered magnetic field, driven by a localized star formation event. This reveals how the large-scale magnetic field pattern in galaxy disks is directly influenced by internal energetic phenomena. Conversely, magnetic fields are observed to be an important ingredient in disk-halo interactions, as predicted in MHD simulations. Turbulent magnetic fields at smaller spatial scales than the observed RM gradient will also be carried from the disk and provide a mechanism for the dynamo process to amplify the ordered magnetic field without quenching. We discuss the observational biases and suggest that this is a common feature of star-forming galaxies with active disk-halo flows.

  11. 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.

  12. 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

  13. 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.

  14. Dark matter particles in the galactic halo

    NASA Astrophysics Data System (ADS)

    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.

    2009-12-01

    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.

  15. 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.

  16. Experimental searches for galactic halo axions.

    PubMed

    van Bibber, Karl A; Kinion, S Darin

    2003-11-15

    A very light axion would be copiously produced during the Big Bang as a zero-temperature Bose gas, and it would possess vanishingly small couplings to matter and radiation. It thus represents an ideal cold dark matter candidate. Galactic halo axions may be detected by their resonant conversion to microwave photons in a high-Q cavity permeated by a strong magnetic field. A large-scale search for the axion is ongoing in the US with sufficient sensitivity to see axions of plausible model couplings. Dramatic breakthroughs in the development of near-quantum limited superconducting quantum interference device amplifiers promise to improve the sensitivity of the experiment by a factor of 30 in the near future. In Japan, a group has been developing a Rydberg atom single-quantum detector as an alternative to linear amplifiers for a microwave-cavity axion experiment. Should the axion be discovered, the predicted fine structure in the axion signal would be rich in information about the history of galactic formation. PMID:14667317

  17. 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

  18. Mapping the Galactic Halo. VIII. Quantifying Substructure

    NASA Astrophysics Data System (ADS)

    Starkenburg, Else; Helmi, Amina; Morrison, Heather L.; Harding, Paul; van Woerden, Hugo; Mateo, Mario; Olszewski, Edward W.; Sivarani, Thirupathi; Norris, John E.; Freeman, Kenneth C.; Shectman, Stephen A.; Dohm-Palmer, R. C.; Frey, Lucy; Oravetz, Dan

    2009-06-01

    We have measured the amount of kinematic substructure in the Galactic halo using the final data set from the Spaghetti project, a pencil-beam high-latitude sky survey. Our sample contains 101 photometrically selected and spectroscopically confirmed giants with accurate distance, radial velocity, and metallicity information. We have developed a new clustering estimator: the "4distance" measure, which when applied to our data set leads to the identification of one group and seven pairs of clumped stars. The group, with six members, can confidently be matched to tidal debris of the Sagittarius dwarf galaxy. Two pairs match the properties of known Virgo structures. Using models of the disruption of Sagittarius in Galactic potentials with different degrees of dark halo flattening, we show that this favors a spherical or prolate halo shape, as demonstrated by Newberg et al. using the Sloan Digital Sky Survey data. One additional pair can be linked to older Sagittarius debris. We find that 20% of the stars in the Spaghetti data set are in substructures. From comparison with random data sets, we derive a very conservative lower limit of 10% to the amount of substructure in the halo. However, comparison to numerical simulations shows that our results are also consistent with a halo entirely built up from disrupted satellites, provided that the dominating features are relatively broad due to early merging or relatively heavy progenitor satellites.

  19. 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

  20. GCN: a gaseous Galactic halo stream?

    NASA Astrophysics Data System (ADS)

    Jin, Shoko

    2010-10-01

    We show that a string of HI clouds that form part of the high-velocity cloud complex known as GCN is a probable gaseous stream extending over more than 50° in the Galactic halo. The radial velocity gradient along the stream is used to deduce transverse velocities as a function of distance, enabling a family of orbits to be computed. We find that a direction of motion towards the Galactic disc coupled with a mid-stream distance of ~20kpc provides a good match to the observed sky positions and radial velocities of the HI clouds comprising the stream. With an estimated mass of 105Msolar, its progenitor is likely to be a dwarf galaxy. However, no stellar counterpart has been found amongst the currently known Galactic dwarf spheroidal galaxies or stellar streams and the exact origin of the stream is therefore currently unknown.

  1. 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

  2. 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

  3. Large-scale gas dynamical processes affecting the origin and evolution of gaseous galactic halos

    NASA Technical Reports Server (NTRS)

    Shapiro, Paul R.

    1991-01-01

    Observations of galactic halo gas are consistent with an interpretation in terms of the galactic fountain model in which supernova heated gas in the galactic disk escapes into the halo, radiatively cools and forms clouds which fall back to the disk. The results of a new study of several large-scale gas dynamical effects which are expected to occur in such a model for the origin and evolution of galactic halo gas will be summarized, including the following: (1) nonequilibrium absorption line and emission spectrum diagnostics for radiatively cooling halo gas in our own galaxy, as well the implications of such absorption line diagnostics for the origin of quasar absorption lines in galactic halo clouds of high redshift galaxies; (2) numerical MHD simulations and analytical analysis of large-scale explosions ad superbubbles in the galactic disk and halo; (3) numerical MHD simulations of halo cloud formation by thermal instability, with and without magnetic field; and (4) the effect of the galactic fountain on the galactic dynamo.

  4. Massive black holes in galactic halos?

    NASA Technical Reports Server (NTRS)

    Lacey, C. G.; Ostriker, J. P.

    1985-01-01

    In the present attempt to resolve the problems posed by the composition of dark halos and the heating of stellar disks, under the assumption that galaxy halos are composed of massive black holes, it is noted that the black holes must have masses of the order of one million solar masses. The heating mechanism proposed yields predictions for the dependence of the velocity dispersion on time, and for the shape of the velocity ellipsoid, which are in good agreement with observations. Attention is given to the constraints set by dynamical friction causing black holes to spiral to the Galactic center, by the possible presence of dark matter in dwarf spheroidal galaxies, and by the accretion of interstellar gas by the black holes that produce luminous objects in the Galaxy.

  5. 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.

  6. Inhomogeneous chemical enrichment in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Kobayashi, Chiaki

    2016-08-01

    In a galaxy, chemical enrichment takes place in an inhomogeneous fashion, and the Galactic Halo is one of the places where the inhomogeneous effects are imprinted and can be constrained from observations. I show this using my chemodynamical simulations of Milky Way type galaxies. The scatter in the elemental abundances originate from radial migration, merging/accretion of satellite galaxies, local variation of star formation and chemical enrichment, and intrinsic variation of nucleosynthesis yields. In the simulated galaxies, there is no strong age-metallicity relation. This means that the most metal-poor stars are not always the oldest stars, and can be formed in chemically unevolved clouds at later times. The long-lifetime sources of chemical enrichment such as asymptotic giant branch stars or neutron star mergers can contribute at low metallicities. The intrinsic variation of yields are important in the early Universe or metal-poor systems such as in the Galactic halo. The carbon enhancement of extremely metal-poor (EMP) stars can be best explained by faint supernovae, the low [α/Fe] ratios in some EMP stars naturally arise from low-mass (~ 13 - 15M ⊙) supernovae, and finally, the [α/Fe] knee in dwarf spheroidal galaxies can be produced by subclasses of Type Ia supernovae such as SN 2002cx-like objects and sub-Chandrasekhar mass explosions.

  7. Carbon Stars in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Totten, E. J.; Irwin, M. J.

    1996-04-01

    A byproduct of the APM high redshift quasar survey (Irwin et al. 1991) was the discovery of ~ 20 distant (20-100kpc) cool AGB carbon stars (all N-type) at high Galactic latitude. In August we used the INT+IDS to survey the rest of the high latitude SGC sky visible from La Palma and found 10 more similar carbon stars. Before this work there were only a handful of published faint high latitude cool carbon stars known (eg. Margon et al., 1984, Mould et al., 1985) and there has been speculation as to their origin (eg. Sanduleak, 1980, van den Bergh & Lafontaine, 1984). Intermediate age carbon stars (3 -- 7 Gyrs) seem unlikely to have formed in the halo in isolation from other star forming regions so how did they get there ? One possiblity that we are investigating, is that they arise from either the disruption of tidally captured dSph galaxies or are a manifestion of the long sought after optical component of the Magellanic Stream. Lack of proper motion rules out the possibility of them being dwarf carbon stars (eg. Warren et al., 1992); indeed no N-type carbon stars have been found to be dwarf carbon stars. Our optical spectroscopy confirms their carbon star type (they are indistinguishable from cool AGB carbon stars in nearby dwarf galaxies) and hence probable large distances. We are extending our survey to the NGC region, obtaining radial velocities and good S:N fluxed spectra for all the carbon stars. This will enable us to investigate their kinematics, true spatial distribution and hence their origin. Even, in the event that these objects are somehow an integral part of the Galactic halo, then their velocities and large distances will enable direct studies of the velocity ellipsoid and rotation of the outer halo (eg. Green et al., 1994).

  8. 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

  9. Magnetic fields in halos of spiral galaxies and the interstellar disk-halo connection

    NASA Astrophysics Data System (ADS)

    Dettmar, Ralf-Jürgen

    2005-09-01

    Observations of magnetic fields in halos of edge-on disk galaxies are discussed in relation to the different gaseous phases of the interstellar medium. For this comparison the presence of diffuse ionized gas (DIG) is introduced as a valuable tracer for gaseous halos which are originating from the star-formation driven disk-halo connection of the interstellar medium. The distribution of extraplanar DIG correlates on local and global scales with cosmic rays and magnetic fields as inferred from observations of the non-thermal radio continuum radiation and its polarization. From the polarization a large scale and well ordered magnetic field in these gaseous halos can be deduced. These observations indicate the presence of physical processes which generate and maintain magnetic fields on galactic scales. The importance of differential rotation of the gaseous halos for such processes is briefly discussed and the possible influence of magnetic fields on the dynamics of dust particles is addressed.

  10. 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.

  11. Correlating galaxy colour and halo concentration: a tunable halo model of galactic conformity

    NASA Astrophysics Data System (ADS)

    Paranjape, Aseem; Kovač, Katarina; Hartley, William G.; Pahwa, Isha

    2015-12-01

    We extend the halo occupation distribution (HOD) framework to generate mock galaxy catalogues exhibiting varying levels of `galactic conformity', which has emerged as a potentially powerful probe of environmental effects in galaxy evolution. Our model correlates galaxy colours in a group with the concentration of the common parent dark halo through a `group quenching efficiency' ρ which makes older, more concentrated haloes at fixed mass preferentially host redder galaxies. We find that, for a specific value of ρ, this 1-halo conformity matches corresponding measurements in a group catalogue based on the Sloan Digital Sky Survey. Our mocks also display conformity at large separations from isolated objects, potentially an imprint of halo assembly bias. A detailed study - using mocks with assembly bias erased while keeping 1-halo conformity intact - reveals a rather nuanced situation, however. At separations ≲4 Mpc, conformity is mainly a 1-halo effect dominated by the largest haloes and is not a robust indicator of assembly bias. Only at very large separations (≳8 Mpc) does genuine 2-halo conformity, driven by the assembly bias of small haloes, manifest distinctly. We explain all these trends in standard halo model terms. Our model opens the door to parametrized HOD analyses that self-consistently account for galactic conformity at all scales.

  12. Could wormholes form in dark matter galactic halos?

    NASA Astrophysics Data System (ADS)

    Rahaman, Farook; Shit, G. C.; Sen, Banashree; Ray, Saibal

    2016-01-01

    We estimate expression for velocity as a function of the radial coordinate r by using polynomial interpolation based on the experimental data of rotational velocities at distant outer regions of galaxies. The interpolation technique has been used to estimate fifth degree polynomial followed by cubic spline interpolation. This rotational velocity is used to find the geometry of galactic halo regions within the framework of Einstein's general relativity. In this paper we have analyzed features of galactic halo regions based on two possible choices for the dark matter density profile, viz. Navarro, Frenk & White (NFW) type (Navarro et al. in Astrophys. J. 462:563, 1996) and Universal Rotation Curve (URC) (Castignani et al. in Nat. Sci. 4:265, 2012). It is argued that spacetime of the galactic halo possesses some of the characteristics needed to support traversable wormholes.

  13. Mixing between High Velocity Clouds and the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Gritton, Jeffrey A.; Shelton, Robin L.; Kwak, Kyujin

    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.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

    Lee, Samuel K.; Ando, Shin'ichiro; Kamionkowski, Marc

    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⊕, 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.

  16. The Milky Way, the Galactic halo, and the Halos of Galaxies

    NASA Astrophysics Data System (ADS)

    Gerhard, Ortwin

    2015-08-01

    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 in the Galactic halo. The data tell us that most of the Galactic bulge formed from the disk, and 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 see these features requires exquisite data - mostly very deep photometry, but some halo substructures have also been found with kinematic data. 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.

  17. 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.

  18. GAS CONDENSATION IN THE GALACTIC HALO

    SciTech Connect

    Joung, M. Ryan; Bryan, Greg L.; Putman, Mary E.

    2012-02-01

    Using adaptive mesh refinement (AMR) hydrodynamic simulations of vertically stratified hot halo gas, we examine the conditions under which clouds can form and condense out of the hot halo medium to potentially fuel star formation in the gaseous disk. We find that halo clouds do not develop from linear isobaric perturbations. This is a regime where the cooling time is longer than the Brunt-Vaeisaelae time, confirming previous linear analysis. We extend the analysis into the nonlinear regime by considering mildly or strongly nonlinear perturbations with overdensities up to 100, also varying the initial height, the cloud size, and the metallicity of the gas. Here, the result depends on the ratio of cooling time to the time required to accelerate the cloud to the sound speed (similar to the dynamical time). If the ratio exceeds a critical value near unity, the cloud is accelerated without further cooling and gets disrupted by Kelvin-Helmholtz and/or Rayleigh-Taylor instabilities. If it is less than the critical value, the cloud cools and condenses before disruption. Accreting gas with overdensities of 10-20 is expected to be marginally unstable; the cooling fraction will depend on the metallicity, the size of the incoming cloud, and the distance to the galaxy. Locally enhanced overdensities within cold streams have a higher likelihood of cooling out. Our results have implications on the evolution of clouds seeded by cold accretion that are barely resolved in current cosmological hydrodynamic simulations and absorption line systems detected in galaxy halos.

  19. 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.

  20. Does SEGUE/SDSS indicate a dual galactic halo?

    SciTech Connect

    Schönrich, Ralph; Asplund, Martin; Casagrande, Luca

    2014-05-01

    We re-examine recent claims of observational evidence for a dual Galactic halo in SEGUE/SDSS data, and trace them back to improper error treatment and neglect of selection effects. In particular, the detection of a vertical abundance gradient in the halo can be explained as a metallicity bias in distance. A similar bias and the impact of disk contamination affect the sample of blue horizontal branch stars. These examples highlight why non-volume complete samples require forward modeling from theoretical models or extensive bias-corrections. We also show how observational uncertainties produce the specific non-Gaussianity in the observed azimuthal velocity distribution of halo stars, which can be erroneously identified as two Gaussian components. A single kinematic component yields an excellent fit to the observed data, when we model the measurement process including distance uncertainties. Furthermore, we show that sample differences in proper motion space are the direct consequence of kinematic cuts and are enhanced when distance estimates are less accurate. Thus, their presence is neither proof of a separate population nor a measure of reliability for the applied distances. We conclude that currently there is no evidence from SEGUE/SDSS that would favor a dual Galactic halo over a single halo that is full of substructure.

  1. The Origin of the Hot Gas in the Galactic Halo: Testing Galactic Fountain Models' X-Ray Emission

    NASA Astrophysics Data System (ADS)

    Henley, David B.; Shelton, Robin L.; Kwak, Kyujin; Hill, Alex S.; Mac Low, Mordecai-Mark

    2015-02-01

    We test the X-ray emission predictions of galactic fountain models against XMM-Newton measurements of the emission from the Milky Way's hot halo. These measurements are from 110 sight lines, spanning the full range of Galactic longitudes. We find that a magnetohydrodynamical simulation of a supernova-driven interstellar medium, which features a flow of hot gas from the disk to the halo, reproduces the temperature but significantly underpredicts the 0.5-2.0 keV surface brightness of the halo (by two orders of magnitude, if we compare the median predicted and observed values). This is true for versions of the model with and without an interstellar magnetic field. We consider different reasons for the discrepancy between the model predictions and the observations. We find that taking into account overionization in cooled halo plasma, which could in principle boost the predicted X-ray emission, is unlikely in practice to bring the predictions in line with the observations. We also find that including thermal conduction, which would tend to increase the surface brightnesses of interfaces between hot and cold gas, would not overcome the surface brightness shortfall. However, charge exchange emission from such interfaces, not included in the current model, may be significant. The faintness of the model may also be due to the lack of cosmic ray driving, meaning that the model may underestimate the amount of material transported from the disk to the halo. In addition, an extended hot halo of accreted material may be important, by supplying hot electrons that could boost the emission of the material driven out from the disk. Additional model predictions are needed to test the relative importance of these processes in explaining the observed halo emission.

  2. 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.

  3. The SEGUE K Giant Survey. III. Quantifying Galactic Halo Substructure

    NASA Astrophysics Data System (ADS)

    Janesh, William; Morrison, Heather L.; Ma, Zhibo; Rockosi, Constance; Starkenburg, Else; Xue, Xiang Xiang; Rix, Hans-Walter; Harding, Paul; Beers, Timothy C.; Johnson, Jennifer; Lee, Young Sun; Schneider, Donald P.

    2016-01-01

    We statistically quantify the amount of substructure in the Milky Way stellar halo using a sample of 4568 halo K giant stars at Galactocentric distances ranging over 5-125 kpc. These stars have been selected photometrically and confirmed spectroscopically as K giants from the Sloan Digital Sky Survey’s Sloan Extension for Galactic Understanding and Exploration project. Using a position-velocity clustering estimator (the 4distance) and a model of a smooth stellar halo, we quantify the amount of substructure in the halo, divided by distance and metallicity. Overall, we find that the halo as a whole is highly structured. We also confirm earlier work using blue horizontal branch (BHB) stars which showed that there is an increasing amount of substructure with increasing Galactocentric radius, and additionally find that the amount of substructure in the halo increases with increasing metallicity. Comparing to resampled BHB stars, we find that K giants and BHBs have similar amounts of substructure over equivalent ranges of Galactocentric radius. Using a friends-of-friends algorithm to identify members of individual groups, we find that a large fraction (˜33%) of grouped stars are associated with Sgr, and identify stars belonging to other halo star streams: the Orphan Stream, the Cetus Polar Stream, and others, including previously unknown substructures. A large fraction of sample K giants (more than 50%) are not grouped into any substructure. We find also that the Sgr stream strongly dominates groups in the outer halo for all except the most metal-poor stars, and suggest that this is the source of the increase of substructure with Galactocentric radius and metallicity.

  4. Neutron stars and white dwarfs in galactic halos?

    NASA Technical Reports Server (NTRS)

    Ryu, Dongsu; Olive, Keith A.; Silk, Joseph

    1990-01-01

    The possibility that galactic halos are composed of stellar remnants such as neutron stars and white dwarfs is discussed. On the basis of a simple model for the evolution of galactic halos, researchers follow the history of halo matter, luminosity, and metal and helium abundances. They assume conventional yields for helium and the heavier elements. By comparing with the observational constraints, which may be considered as fairly conservative, it is found that, for an exponentially decreasing star formation rate (SFR) with e-folding time tau, only values between 6 x 10(8) less than similar to tau less than similar to 2 x 10(9) years are allowed together with a very limited range of masses for the initial mass function (IMF). Star formation is allowed for 2 solar mass less than similar to m less than similar to 8 solar mass if tau = 2 x 10(9) years, and for 4 solar mass less than similar to m less than similar to 6 solar mass if tau = 10(9) years. For tau = 6 x 10(8) years, the lower and upper mass limits merge to similar to 5 solar mass. Researchers conclude that, even though the possibility of neutron stars as halo matter may be ruled out, that of white dwarfs may still be a viable hypothesis, though with very stringent constraints on allowed parameters, that merits further consideration.

  5. Neutron stars and white dwarfs in galactic halos

    NASA Technical Reports Server (NTRS)

    Ryu, Dongsu; Olive, Keith A.; Silk, Joseph

    1989-01-01

    The possibility that galactic halos are composed of stellar remnants such as neutron stars and white dwarfs is discussed. On the basis of a simple model for the evolution of galactic halos, researchers follow the history of halo matter, luminosity, and metal and helium abundances. They assume conventional yields for helium and the heavier elements. By comparing with the observational constraints, which may be considered as fairly conservative, it is found that, for an exponentially decreasing star formation rate (SFR) with e-folding time tau, only values between 6 x 10(8) less than similar to tau less than similar to 2 x 10(9) years are allowed together with a very limited range of masses for the initial mass function (IMF). Star formation is allowed for 2 solar mass less than similar to m less than similar to 8 solar mass if tau = 2 x 10(9) years, and for 4 solar mass less than similar to m less than similar to 6 solar mass if tau = 10(9) years. For tau = 6 x 10(8) years, the lower and upper mass limits merge to similar to 5 solar mass. Researchers conclude that, even though the possibility of neutron stars as halo matter may be ruled out, that of white dwarfs may still be a viable hypothesis, though with very stringent constraints on allowed parameters, that merits further consideration.

  6. On the alleged duality of the Galactic halo

    NASA Astrophysics Data System (ADS)

    Schönrich, Ralph; Asplund, Martin; Casagrande, Luca

    2011-08-01

    We examine the kinematics of the Galactic halo based on SDSS/SEGUE data by Carollo et al. We find that their claims of a counter-rotating halo are the result of substantial biases in distance estimates (of the order of 50 per cent): the claimed retrograde component, which makes up only a tiny fraction of the entire sample, prone to contaminations, is identified as the tail of distance overestimates. The strong overestimates also result in a lift in the vertical velocity component, which explains the large altitudes those objects were claimed to reach. Errors are worst for the lowest metallicity stars, which explains the metal-poor nature of the artificial component. We also argue that measurement errors were not properly accounted for and that the use of Gaussian fitting on intrinsically non-Gaussian Galactic components invokes the identification of components that are distorted or even artificial. Our evaluation of the data leads to a revision of the estimated velocity ellipsoids and does not yield any reliable evidence for a counter-rotating halo component. If a distinct counter-rotating halo component exists, then it must be far weaker than claimed by Carollo et al. Finally, we note that their revised analysis presented in Beers et al. does not alleviate our main concerns.

  7. Distant Galactic Halo Substructures Observed by the Palomar Transient Factory

    NASA Astrophysics Data System (ADS)

    Sesar, Branimir

    2013-01-01

    Characterization of Galactic halo substructures is important as their kinematic and chemical properties help constrain the properties of the Galactic dark matter halo, the formation history of the Milky Way, and the galaxy formation process in general. The best practical choice for finding distant halo substructures are pulsating RR Lyrae stars, due to their intrinsic brightness (M_V = 0.6 mag) and distinct light curves. I will present kinematic and chemical properties of two distant halo substructures that were traced using RR Lyrae stars observed by the Palomar Transient Factory. One of these substructures, located at 90 kpc from the Sun in the Cancer constellation, consists of two groups of RR Lyrae stars moving away from the Galaxy at ~80 and ~20 km/s, respectively. The second substructure is located at ~65 kpc from the Sun in the Hercules constellation. The kinematics of RR Lyrae stars tracing this substructure suggest a presence of 2 or 3 stellar streams extending in the similar direction on the sky. Due to their spatial extent, both of these substructures are clearly disrupted and would be very difficult to detect using tradiitonal techniques such as the color-magnitude diagram filtering.

  8. RADIAL VELOCITIES OF GALACTIC HALO STARS IN VIRGO

    SciTech Connect

    Brink, Thomas G.; Mateo, Mario; Martinez-Delgado, David E-mail: mmateo@umich.ed

    2010-11-15

    We present multi-slit radial velocity measurements for 111 stars in the direction of the Virgo Stellar Stream (VSS). The stars were photometrically selected to be probable main-sequence stars in the Galactic halo. When compared with the radial velocity distribution expected for the halo of the Milky Way, as well as the distribution seen in a control field, we observe a significant excess of negative velocity stars in the field, which can likely be attributed to the presence of a stellar stream. This kinematic excess peaks at a Galactic standard of rest radial velocity of -75 km s{sup -1}. A rough distance estimate suggests that this feature extends from {approx}15 kpc out to, and possibly beyond, the {approx}30 kpc limit of the study. The mean velocity of these stars is incompatible with those of the VSS itself (V{sub gsr} {approx} 130 km s{sup -1}), which we weakly detect, but it is consistent with radial velocity measurements of nearby 2MASS M-giants and SDSS+SEGUE K/M-giants and blue horizontal branch stars that constitute the leading tidal tail of the Sagittarius dwarf spheroidal galaxy. Some oblate models for the shape of the Milky Way's dark matter halo predict that the leading arm of the Sagittarius Stream should pass through this volume, and have highly negative (V{sub gsr} {approx}< -200 km s{sup -1}) radial velocities, as it descends down from the northern Galactic hemisphere toward the Galactic plane. The kinematic feature observed in this study, if it is in fact Sagittarius debris, is not consistent with these predictions, and instead, like other leading stream radial velocity measurements, is consistent with a recently published triaxial halo model, or, if axisymmetry is imposed, favors a prolate shape for the Galactic halo potential. However, a rough distance estimate to the observed kinematic feature places it somewhat closer (D {approx} 15-30 kpc) than the Sagittarius models predict (D {approx} 35-45 kpc).

  9. Galactic evolution. II - Disk galaxies with massive halos

    NASA Technical Reports Server (NTRS)

    Ostriker, J. P.; Thuan, T. X.

    1975-01-01

    Models of galactic evolution are computed in which matter shed by dying halo stars accumulates in a smaller, more rapidly rotating disk. The models are simpler and more successful than one-zone (pure disk) models in that (1) the observed absence of low-metal-abundance low-mass dwarfs is expected, not anomalous and (2) the relative birthrate function (or IMF) need not be a strongly variable function of time in agreement with recent interpretations of observed stellar populations and neutral hydrogen in our own and other galaxies. Even a simple 'Salpeter' IMF for both disk and halo will produce an acceptable model. The model with a halo 'Salpeter' IMF, roughly one-quarter of the mass in the secondary disk, and approximately half the metals produced in the halo seems most compatible with observations of the metal abundance in low-mass stars, the deuterium abundance, halo planetary nebulae, and light from Population II stars, as well as with arguments on the stability of the disk.

  10. 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.

  11. 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.

  12. Discy dwarf disruption and the shape of the Galactic halo

    NASA Astrophysics Data System (ADS)

    Gibbons, S. L. J.; Belokurov, V.; Erkal, D.; Evans, N. W.

    2016-05-01

    The shape of the Galactic dark halo can, in principle, be inferred through modelling of stellar tidal streams in the Milky Way halo. The brightest and the longest of these, the Sagittarius stream, reaches out to large Galactocentric distances and hence can deliver the tightest constraints on the Galaxy's potential. In this contribution, we revisit the idea that the Sagittarius Stream was formed from a rotating progenitor. We demonstrate that the angle between the disc's angular momentum and the progenitor's orbital angular momentum does not remain constant throughout the disruption. Instead, it undergoes a dramatic evolution caused, in part, by the changes in the progenitor's moment of inertia tensor. We show that, even in a spherical potential, the streams produced as a result of a discy dwarf disruption appear to be `precessing'. Yet, this debris plane evolution is illusory as it is solely caused by the swaying and wobbling of the progenitor's disc. Stream plane precession is therefore not an unambiguous indicator of asphericity of the dark halo.

  13. Modelling galactic conformity with the colour-halo age relation in the Illustris simulation

    NASA Astrophysics Data System (ADS)

    Bray, Aaron D.; Pillepich, Annalisa; Sales, Laura V.; Zhu, Emily; Genel, Shy; Rodriguez-Gomez, Vicente; Torrey, Paul; Nelson, Dylan; Vogelsberger, Mark; Springel, Volker; Eisenstein, Daniel J.; Hernquist, Lars

    2016-01-01

    Comparisons between observational surveys and galaxy formation models find that dark matter haloes' mass can largely explain their galaxies' stellar mass. However, it remains uncertain whether additional environmental variables, known as assembly bias, are necessary to explain other galaxy properties. We use the Illustris simulation to investigate the role of assembly bias in producing galactic conformity by considering 18 000 galaxies with Mstellar > 2 × 109 M⊙. We find a significant signal of galactic conformity: out to distances of about 10 Mpc, the mean red fraction of galaxies around redder galaxies is higher than around bluer galaxies at fixed stellar mass. Dark matter haloes exhibit an analogous conformity signal, in which the fraction of haloes formed at earlier times (old haloes) is higher around old haloes than around younger ones at fixed halo mass. A plausible interpretation of galactic conformity is the combination of the halo conformity signal with the galaxy colour-halo age relation: at fixed stellar mass, particularly towards the low-mass end, Illustris' galaxy colours correlate with halo age, with the reddest galaxies (often satellites) preferentially found in the oldest haloes. We explain the galactic conformity effect with a simple semi-empirical model, assigning stellar mass via halo mass (abundance matching) and galaxy colour via halo age (age matching). Regarding comparison to observations, we conclude that the adopted selection/isolation criteria, projection effects, and stacking techniques can have a significant impact on the measured amplitude of the conformity signal.

  14. Baryonic dark clusters in galactic halos and their observable consequences

    NASA Technical Reports Server (NTRS)

    Wasserman, Ira; Salpeter, Edwin E.

    1994-01-01

    We consider the possibility that approximately 10% of the mass of a typical galaxy halo is in the form of massive (approximately 10(exp 7) solar masses), compact (escape speeds approximately 100 km/s) baryonic clusters made of neutron stars (approximately 10% by mass), black holes (less than or approximately equal to 1%) and brown dwarfs, asteroids, and other low-mass debris (approximately 90%). These general properties are consistent with several different observational and phenomenological constraints on cluster properties subject to the condition that neutron stars comprise approximately 1% of the total halo mass. Such compact, dark clusters could be the sites of a variety of collisional phenomena involving neutron stars. We find that integrated out to the Hubble distance approximately one neutron star-neutron star or neutron star-black hole collision occurs daily. Of order 0.1-1 asteroid-neutron star collisions may also happen daily in the halo of the Milky Way if there is roughly equal cluster mass per logarithmic particle mass interval between asteroids and brown dwarfs. These event rates are comparable to the frequency of gamma-ray burst detections by the Burst and Transient Source Experiment (BATSE) on the Compton Observatory, implying that if dark halo clusters are the sites of most gamma-ray bursts, perhaps approximately 90% of all bursts are extragalactic, but approximately 10% are galactic. It is possible that dark clusters of the kind discussed here could be detected directly by the Infrared Space Observatory (ISO) or Space Infrared Telescope Facility (SIRTF). If the clusters considered in this paper exist, they should produce spatially correlated gravitational microlensing of stars in the Large Magellanic Cloud (LMC). If 10% of the halo is in the form of dark baryonic clusters, and the remaining 90% is in brown dwarfs and other dark objects which are either unclustered or collected into low-mass clusters, then we expect that two events within

  15. An origin for multiphase gas in galactic winds and haloes

    NASA Astrophysics Data System (ADS)

    Thompson, Todd A.; Quataert, Eliot; Zhang, Dong; Weinberg, David H.

    2016-01-01

    The physical origin of high-velocity cool gas seen in galactic winds remains unknown. Following work by B. Wang, we argue that radiative cooling in initially hot thermally-driven outflows can produce fast neutral atomic and photoionized cool gas. The inevitability of adiabatic cooling from the flow's initial 107-108 K temperature and the shape of the cooling function for T ≲ 107 K imply that outflows with hot gas mass-loss rate relative to star formation rate of β =dot{M}_hot/dot{M}_star ≳ 0.5 cool radiatively on scales ranging from the size of the energy injection region to tens of kpc. We highlight the β and star formation rate surface density dependence of the column density, emission measure, radiative efficiency, and velocity. At rcool, the gas produces X-ray and then UV/optical line emission with a total power bounded by ˜10-2 L⋆ if the flow is powered by steady-state star formation with luminosity L⋆. The wind is thermally unstable at rcool, potentially leading to a multiphase medium. Cooled winds decelerate significantly in the extended gravitational potential of galaxies. The cool gas precipitated from hot outflows may explain its prevalence in galactic haloes. We forward a picture of winds whereby cool clouds are initially accelerated by the ram pressure of the hot flow, but are rapidly shredded by hydrodynamical instabilities, thereby increasing β, seeding radiative and thermal instability, and cool gas rebirth. If the cooled wind shocks as it sweeps up the circumgalactic medium, its cooling time is short, thus depositing cool gas far out into the halo. Finally, conduction can dominate energy transport in low-β hot winds, leading to flatter temperature profiles than otherwise expected, potentially consistent with X-ray observations of some starbursts.

  16. SMASH: Spitzer Merger History and Shape of the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Johnston, Kathryn; Scowcroft, Vicky; Madore, Barry; Freedman, Wendy; Scowcroft, Victoria; Clementini, Gisella; Cioni, Maria-Rosa; van der Marel, Roeland; Udalski, Andrzej; Pietrzynski, Grzegorz; Soszynski, Igor; Nidever, David; Kallivayalil, Nitya; Besla, Gurtina; Majewski, Steve; Monson, Andy; Seibert, Mark; Smith, Horace; Preston, George; Kollmeier, Juna; Bono, Giuseppe; Marengo, Massimo; Persson, Eric; Law, David; Grillmair, Carl; Cohen, Judy; Sesar, Branimir; Price-Whelan, Adrian; Fabrizio, Michele

    2013-10-01

    The existence of a period-luminosity relation for RR Lyrae variables as measured at IRAC mid-infrared wavelengths allows Spitzer to estimate distances to individual stars with 2% errors. The SMASH program will exploit this unprecedented opportunity to precisely map structures throughout the halo of our Galaxy. SMASH will construct the first 3-D map of one of the larger satellites of the Milky Way (Sagittarius), it will determine precise distances to four more satellites (Ursa Minor, Carina, Sculptor & Bootes) and make the only measurements of stars in tidal streams accurate enough to determine their individual positions within the debris. This proposal describes some of the ground-breaking science enabled by this program, from increased accuracy in determining the orbits of satellite galaxies, to revolutionary constraints on the mass, shape and orientation of our Milky Way's dark matter halo. The foundational importance of these data sets cannot be overstated. These Milky Way structures lie far beyond the reach of any current or proposed future direct parallax measurements. Moreover, the combination of the SMASH results with proper motions from ESA's upcoming astrometric mission, Gaia, can effectively stretch Gaia's horizon for full 6D phase-space maps of our Galaxy by nearly four orders of magnitude in volume! These data and the resulting distance measurements will become Spitzer's legacy to the Galactic Astronomy community for years to come.

  17. Observations of galactic magnetic fields

    NASA Astrophysics Data System (ADS)

    Beck, Rainer

    Magnetic fields are enchored in gas clouds. Field lines are tangled in spiral arms, but highly regular between the arms. The similarity of pitch angles between gaseous and magnetic arms suggests a coupling between the density wave and the magnetic wave. Observations of large-scale patterns in Faraday rotation favour a dynamo origin of the regular fields. Fields in barred galaxies do not reveal the strong shearing shocks observed in the cold gas, but swing smoothly from the upstream region into the bar. Magnetic fields are important for the dynamcis of gas clouds, for the formation of spiral structures, bars and halos, and for mass and angular momentum transport in central regions.

  18. Production and Recycling of Carbon in the Early Galactic Halo

    NASA Astrophysics Data System (ADS)

    Andersen, Johannes; Thidemann Hansen, Terese; Nordström, Birgitta

    2015-08-01

    Extremely metal-poor (EMP) stars - [Fe/H] below ~ -3 - are fossil records of the conditions in the early halo. High-resolution 8m-class spectroscopy has shown that the detailed abundance pattern of EMP giant stars is surprisingly uniform and essentially Solar (e.g. Bonifacio+ 2012), apart from the usual α-enhancement in the halo. In the simplest picture, iron is a proxy for both overall metallicity and time, so the EMP stars should form before the oldest and most metal-poor Galactic globular clusters, notably at the lowest metallicities ([Fe/H] ≲ -3.5).It is thus striking that 20-40% of the EMP giants are strongly enhanced in carbon - the CEMP stars (Lucatello+ 2006). This is conventionally ascribed to mass transfer from a former AGB binary companion, and from a limited compilation of data, Lucatello+ (2005) concluded that most or all CEMP stars are indeed binaries, similar to the classical Ba and CH stars (e.g. Jorissen+ 1998). However, most of the sample was of the inner-halo CEMP-s variety (C and s-process elements both enhanced), while CEMP-no stars dominate the outer halo (Carollo+ 2014). Our precise radial velocity monitoring for CEMP stars over 8 years shed light on this issue.Our data suggest a normal binary frequency for the CEMP-no stars; i.e. the C was not produced in a binary companion, but in sites at interstellar distances, e.g. ‘faint’ SNe, and imprinted on the natal clouds of the low-mass stars we observe. This has immediate implications for the formation of dust in primitive, high-redshift galaxies (Watson+ 2015) and the origin of C-enhanced DLAs (Cooke+ 2011, 2012). The CEMP-s binary orbits are also revealing, with periods up to several decades and generally low amplitudes and eccentricities, suggesting that EMP AGB stars have very large radii, facilitating extensive mass loss. More work on faint SNe and EMP AGB envelopes is needed!

  19. The Galactic Magnetic Field and its lensing of Ultrahigh Energy and Galactic Cosmic Rays

    NASA Astrophysics Data System (ADS)

    Farrar, Glennys

    2015-08-01

    It has long been recognized that magnetic fields play an important role in many astrophysical environments, but the magnetic field strength and structure has only been quantitatively determined for relatively few systems beyond our solar system.Our understanding of the Galactic magnetic field (GMF) has improved tremendously in recent years. The Jansson-Farrar (2012) (JF12) GMF model is the most realistic and comprehensive model available. It was constrained by fitting all-sky Faraday Rotation Measures of ~40k extragalactic sources, simultaneously with WMAP polarized (Q,U) and total synchrotron emission maps - together providing a total of more than 10,000 independent datapoints, each with measured astrophysical variance. In addition to disk and toroidal halo components, a previously overlooked coherent poloidal halo field proves to be necessary to account for the RM, Q and U data. Moreover a “striated” random component is needed in addition to a fully random component, in both disk and halo.The talk will give a concise review of the JF12 model and its derivation, with emphasis on which features of the GMF are well or poorly established. I will show that the data unambiguously demand a large scale coherent component to the halo field which is a diverging-spiral centered on the Galactic center, with field lines running from Southern to Northern hemispheres. The puzzles posed by the large scale coherent halo and disk magnetic fields, and their possible origins, will be discussed.Having a good model of the Galactic magnetic field is crucial for determining the sources of UHECRs, for modeling the transport of Galactic CRs (the halo field provides a heretofore-overlooked escape route for by diffusion along its field lines), and for calculating the background to dark matter and CMB-cosmology studies. I will present new results on the lensing effect of the GMF on UHECRs, which produces multiple images and dramatic magnification and demagnification that varies with

  20. HaloSat: A CubeSat to Map the Distribution of Baryonic Matter in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Miles, Drew M.

    2016-04-01

    Approximately half of predicted baryonic matter in the Milky Way remains unidentified. One possible explanation for the location of this missing matter is in an extended Galactic halo. HaloSat is a CubeSat that aims to constrain the mass and distribution of the halo’s baryonic matter by obtaining an all-sky map of O VII and O VIII emission in the hot gas associated with the halo of the Milky Way. HaloSat offers an improvement in the quality of measurements of oxygen line emission over existing X-ray observatories and an observation plan dedicated to mapping the hot gas in the Galactic halo. In addition to the missing baryon problem, HaloSat will assign a portion of its observations to the solar wind charge exchange (SWCX) in order to calibrate models of SCWX emission. We present here the current status of HaloSat and the progression of instrument development in anticipation of a 2018 launch.

  1. Precessing Gamma Jets in the extended and evaporating galactic halo as the sources of GRBs

    NASA Astrophysics Data System (ADS)

    Fargion, Daniele; Salis, Andrea

    1996-08-01

    Precessing Gamma Jets (GJ) in binary systems located in extended or evaporating galactic halos should be the sources of GRBs. The GJ are born by Inverse Compton Scattering (ICS) of thermal photons (optical, infrared,...) onto (power law) electron jets (from GeV energies and above) produced by spinning pulsars or black holes. The thermal photons are emitted by the binary companion (or by their nearby accreting disk). The collimated GJ beam is trembling with the characteristic pulsar millisecond period and it is bent by the companion magnetic field interactions, as a lighthouse, in a nearly conical shape within the characteristic Keplerian period; an additional nutation due to the asymmetric inertial momentum may lead, in general, to aperiodic behaviour of GRB signals. SGRs are GRBs seen at the periphery of the hard energy GJ beam core. The original birth locations of GJ (SNRs, planetary nebulae, globular clusters,...) are smeared out by the high escape velocity of the system; the Neutron Star (NS) high velocity is possibly due to the asymmetric jet precession, and consequent ``rowing'' acceleration, related to the eccentricity of the binary system. The GJ power is, for realistic parameters, comparable to that needed for GRBs in an extended or evaporating galactic halo. Their detailed spectra and time evolution fit the observed data. The expected GRB source number (within present BATSE sensitivity) is tens of thousands, compatible with the allowed presence of 10-20% GRB repeaters.

  2. CALET's sensitivity to Dark Matter annihilation in the galactic halo

    NASA Astrophysics Data System (ADS)

    Motz, H.; Asaoka, Y.; Torii, S.; Bhattacharyya, S.

    2015-12-01

    CALET (Calorimetric Electron Telescope), installed on the ISS in August 2015, directly measures the electron+positron cosmic rays flux up to 20 TeV. With its proton rejection capability of 1 : 105 and an aperture of 1200 cm2· sr, it will provide good statistics even well above one TeV, while also featuring an energy resolution of 2%, which allows it to detect fine structures in the spectrum. Such structures may originate from Dark Matter annihilation or decay, making indirect Dark Matter search one of CALET's main science objectives among others such as identification of signatures from nearby supernova remnants, study of the heavy nuclei spectra and gamma astronomy. The latest results from AMS-02 on positron fraction and total electron+positron flux can be fitted with a parametrization including a single pulsar as an extra power law source with exponential cut-off, which emits an equal amount of electrons and positrons. This single pulsar scenario for the positron excess is extrapolated into the TeV region and the expected CALET data for this case are simulated. Based on this prediction for CALET data, the sensitivity of CALET to Dark Matter annihilation in the galactic halo has been calculated. It is shown that CALET could significantly improve the limits compared to current data, especially for those Dark Matter candidates that feature a large fraction of annihilation directly into e+ + e-, such as the LKP (Lightest Kaluza-Klein particle).

  3. Are ancient dwarf satellites the building blocks of the Galactic halo?

    NASA Astrophysics Data System (ADS)

    Spitoni, E.; Vincenzo, F.; Matteucci, F.; Romano, D.

    2016-05-01

    According to the current cosmological cold dark matter paradigm, the Galactic halo could have been the result of the assemblage of smaller structures. Here we explore the hypothesis that the classical and ultra-faint dwarf spheroidal satellites of the Milky Way have been the building blocks of the Galactic halo by comparing their [α/Fe] and [Ba/Fe] versus [Fe/H] patterns with the ones observed in Galactic halo stars. The α elements deviate substantially from the observed abundances in the Galactic halo stars for [Fe/H] values larger than -2 dex, while they overlap for lower metallicities. On the other hand, for the [Ba/Fe] ratio, the discrepancy is extended at all [Fe/H] values, suggesting that the majority of stars in the halo are likely to have been formed in situ. Therefore, we suggest that [Ba/Fe] ratios are a better diagnostic than [α/Fe] ratios. Moreover, for the first time we consider the effects of an enriched infall of gas with the same chemical abundances as the matter ejected and/or stripped from dwarf satellites of the Milky Way on the chemical evolution of the Galactic halo. We find that the resulting chemical abundances of the halo stars depend on the assumed infall time-scale, and the presence of a threshold in the gas for star formation. In particular, in models with an infall time-scale for the halo around 0.8 Gyr coupled with a threshold in the surface gas density for the star formation (4 M⊙ pc-2), and the enriched infall from dwarf spheroidal satellites, the first halo stars formed show [Fe/H]>-2.4 dex. In this case, to explain [α/Fe] data for stars with [Fe/H]<-2.4 dex, we need stars formed in dSph systems.

  4. HUBBLE'S SEARCH FOR FAINT FIELD STARS IN GALACTIC HALO

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Left A NASA Hubble Space Telescope image of a randomly selected area of sky taken to search for faint red stars that might constitute dark matter in our Milky Way Galaxy. (Dark matter is material of an unknown type that makes up most of the mass of our galaxy). If the dark matter in our Galaxy was made of faint red stars -- as many scientists have previously conjectured -- then about 38 such stars should have been visible in this HST image. The simulated stars (diamond-shaped symbols), based on theoretical calculations, illustrate what scientists would have seen if the dark matter were locked-up in faint red stars. These surprising results rule out dim stars as an explanation for dark matter in our Galaxy. Right The unmodified HST image shows the region is actually so devoid of stars that far more distant background galaxies can easily be seen. The field is in the constellation Eridanus, far outside the plane of our Milky Way Galaxy. This region was chosen to highlight stars in the galactic halo, where dark matter exists, and to avoid the contribution of faint stars in the plane of the Galaxy. Technical Information: The image was constructed from seven exposures totaling almost three hours of searching by HST. The field shown is about 1.5 arc-minutes across. The image was taken in near-infrared light (814 nm) with the Wide Field Planetary Camera 2, on Feb 8, 1994. This observation is part of the HST parallel observing program. Credit: J Bahcall, Institute for Advance Study, Princeton and NASA

  5. An extremely primitive star in the Galactic halo.

    PubMed

    Caffau, Elisabetta; Bonifacio, Piercarlo; François, Patrick; Sbordone, Luca; Monaco, Lorenzo; Spite, Monique; Spite, François; Ludwig, Hans-G; Cayrel, Roger; Zaggia, Simone; Hammer, François; Randich, Sofia; Molaro, Paolo; Hill, Vanessa

    2011-09-01

    The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium; almost all other elements were subsequently created in stars and supernovae. The mass fraction of elements more massive than helium, Z, is known as 'metallicity'. A number of very metal-poor stars has been found, some of which have a low iron abundance but are rich in carbon, nitrogen and oxygen. For theoretical reasons and because of an observed absence of stars with Z < 1.5 × 10(-5), it has been suggested that low-mass stars cannot form from the primitive interstellar medium until it has been enriched above a critical value of Z, estimated to lie in the range 1.5 × 10(-8) to 1.5 × 10(-6) (ref. 8), although competing theories claiming the contrary do exist. (We use 'low-mass' here to mean a stellar mass of less than 0.8 solar masses, the stars that survive to the present day.) Here we report the chemical composition of a star in the Galactic halo with a very low Z (≤ 6.9 × 10(-7), which is 4.5 × 10(-5) times that of the Sun) and a chemical pattern typical of classical extremely metal-poor stars--that is, without enrichment of carbon, nitrogen and oxygen. This shows that low-mass stars can be formed at very low metallicity, that is, below the critical value of Z. Lithium is not detected, suggesting a low-metallicity extension of the previously observed trend in lithium depletion. Such lithium depletion implies that the stellar material must have experienced temperatures above two million kelvin in its history, given that this is necessary to destroy lithium. PMID:21886158

  6. TESTING GALACTIC MAGNETIC FIELD MODELS USING NEAR-INFRARED POLARIMETRY

    SciTech Connect

    Pavel, Michael D.; Clemens, D. P.; Pinnick, A. F. E-mail: clemens@bu.edu

    2012-04-10

    This work combines new observations of NIR starlight linear polarimetry with previously simulated observations in order to constrain dynamo models of the Galactic magnetic field. Polarimetric observations were obtained with the Mimir instrument on the Perkins Telescope in Flagstaff, AZ, along a line of constant Galactic longitude (l = 150 Degree-Sign ) with 17 pointings of the 10' Multiplication-Sign 10' field of view between -75 Degree-Sign < b < 10 Degree-Sign , with more frequent pointings toward the Galactic midplane. A total of 10,962 stars were photometrically measured and 1116 had usable polarizations. The observed distribution of polarization position angles with Galactic latitude and the cumulative distribution function of the measured polarizations are compared to predicted values. While the predictions lack the effects of turbulence and are therefore idealized, this comparison allows significant rejection of A0-type magnetic field models. S0 and disk-even halo-odd magnetic field geometries are also rejected by the observations, but at lower significance. New predictions of spiral-type, axisymmetric magnetic fields, when combined with these new NIR observations, constrain the Galactic magnetic field spiral pitch angle to -6 Degree-Sign {+-} 2 Degree-Sign .

  7. Are Pressure-Confined Clouds in Galactic Halos Possible for a Model of Lyman Alpha Clouds?

    NASA Astrophysics Data System (ADS)

    Miyahata, K.; Ikeuchi, S.

    Lanzetta et al (1995) found that most luminous galaxies at low redshifts produce Ly alpha absorptions at the mean impact parameter ~160h-1 kpc. Motivated by this observation, we propose the two-component protogalaxy model as a model for the Ly alpha cloud besed upon the previous work (MI 1995). In our model, the Ly alpha clouds are supposed to be stable cold clouds confined by the pressure of ambient hot gas in galactic halo. We determine the properties of these cold clouds and hot gas on the basis of theoretical and observational constraints. Especially, we take into account the stability of cold cloud in the galactic halo in addition to the general stability conditions in a two-component medium, and compare the derived quantities of Ly alpha cloud both cases in galactic halo and in intergalactic medium. We conclude that the condition that cloud is stable against both evaporation and tidal destruction by a hot galactic halo is very severe. As a result, at z ~0.5, it is concluded that a pressure-confined, stable spherical Ly alpha cloud of typical column density NHI = 1014 cm-2 cannot survive in the galactic halo, although much higher column density clouds of NHI = 1017 cm-2 can do there. We discuss how our result constraints an alternative model for a Ly alpha cloud which associates with galaxy observed by Lanzetta et.al.

  8. Armchair cartography - A map of the Galactic halo based on observations of local, metal-poor stars

    NASA Astrophysics Data System (ADS)

    Sommer-Larsen, Jesper; Zhen, Chen

    1990-01-01

    The velocity distribution of metal-poor halo stars in the solar neighborhood is studied to extract data on the global spatial and kinematic properties of the Galactic stellar halo. A global model of the solar neighborhood stars is constructed from observed positions and three-dimensional velocity of local, metal-poor halo stars in terms of a discrete sum of orbits. The characteristics of the reconstructed halo are examined and used to study the evolution of the halo subsystems.

  9. Advective and diffusive cosmic ray transport in galactic haloes

    NASA Astrophysics Data System (ADS)

    Heesen, Volker; Dettmar, Ralf-Jürgen; Krause, Marita; Beck, Rainer; Stein, Yelena

    2016-05-01

    We present 1D cosmic ray transport models, numerically solving equations of pure advection and diffusion for the electrons and calculating synchrotron emission spectra. We find that for exponential halo magnetic field distributions advection leads to approximately exponential radio continuum intensity profiles, whereas diffusion leads to profiles that can be better approximated by a Gaussian function. Accordingly, the vertical radio spectral profiles for advection are approximately linear, whereas for diffusion they are of `parabolic' shape. We compare our models with deep Australia Telescope Compact Array observations of two edge-on galaxies, NGC 7090 and 7462, at λλ 22 and 6 cm. Our result is that the cosmic ray transport in NGC 7090 is advection dominated with V=150^{+80}_{-30} km s^{-1}, and that the one in NGC 7462 is diffusion dominated with D=3.0± 1.0 × 10^{28}E_GeV^{0.5} cm^2 s^{-1}. NGC 7090 has both a thin and thick radio disc with respective magnetic field scale heights of hB1 = 0.8 ± 0.1 kpc and hB2 = 4.7 ± 1.0 kpc. NGC 7462 has only a thick radio disc with hB2 = 3.8 ± 1.0 kpc. In both galaxies, the magnetic field scale heights are significantly smaller than what estimates from energy equipartition would suggest. A non-negligible fraction of cosmic ray electrons can escape from NGC 7090, so that this galaxy is not an electron calorimeter.

  10. Ages, chemistry, and type 1A supernovae: Clues to the formation of the galactic stellar halo

    NASA Technical Reports Server (NTRS)

    Smecker-Hane, Tammy A.; Wyse, Rosemary F. G.

    1993-01-01

    We endeavor to resolve two conflicting constraints on the duration of the formation of the Galactic stellar halo - 2-3 Gyr age differences in halo stars, and the time scale inferred from the observed constant values of chemical element abundance ratios characteristic of enrichment by Type II supernovae - by investigating the time scale for the onset of Type Ia supernovae (SNIa) in the currently favored progenitor model - mergers of carbon and oxygen white dwarfs (CO WDs).

  11. 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

  12. Studies of the Hot Gas in the Galactic halo and Local Bubble

    NASA Technical Reports Server (NTRS)

    Shelton, Robin L.

    2003-01-01

    This paper presents a report on the progress made on Studies of the Hot Gas in the Galactic halo and Local Bubble at Johns Hopkins University. The broad goals of this project are to determine the physical conditions and history of the hot phase of the Galaxy's interstellar medium. Such gas resides in the Galactic halo, the Local Bubble surrounding the solar neighborhood, other bubbles, and supernova remnants. A better understanding of the hot gas and the processes occurring within it requires several types of work, including ultraviolet and X-ray data analyses and computer modeling.

  13. Wormhole solutions for f(G) gravity in galactic halo region

    NASA Astrophysics Data System (ADS)

    Sharif, M.; Ismat Fatima, H.

    2016-04-01

    In this paper, we study static spherically symmetric wormhole solutions in galactic halo region. Two observational results, Navarro-Frenk-White energy density profile in standard cosmological model and the observed flat rotational curves, are used to discuss traversable wormholes supported by galactic halo in modified Gauss-Bonnet gravity. We explore these solutions either by considering a viable f(G) model to construct shape function or by specifying the shape function to deduce f(G) model. We explore energy conditions and find physically acceptable wormhole solutions threaded by normal matter for all values of r. Finally, we investigate stability of the resulting wormhole solutions.

  14. Exploring the Hot Galactic Halo Using Shadows of High Latitude Clouds

    NASA Technical Reports Server (NTRS)

    Juda, M.; Petre, Robert (Technical Monitor)

    2001-01-01

    The objective of this proposal was to measure variations in the 1/4 keV emission from the galactic halo, using ROSAT (x-ray astronomy satellite) Position Sensitive Proportional Counters (PSPC) observations toward known enhancements in the absorbing column density along the line-of-sight out of the Galaxy. Target directions were selected to have a low total hydrogen column density but to also show significant gradients in the amount of absorbing material, as traced by Infrared Astronomical Satellite (IRAS) 100 micron emission, on angular scales that would be contained within the PSPC field of view. In addition, we restricted the galactic latitude of the target directions to be greater than 60 degrees or less than -60 degrees in order to enable a cleaner separation of Galactic halo emission from that of the Galactic disk. The observations would also provide a measurement of the brightness of the emission from the Local Bubble.

  15. Contributions to the Galactic halo from in-situ, kicked-out, and accreted stars

    NASA Astrophysics Data System (ADS)

    Sheffield, Allyson A.; Johnston, Kathryn V.; Cunha, Katia; Smith, Verne V.; Majewski, Steven R.

    2016-08-01

    We report chemical abundances for a sample of 66 M giants with high S/N high-resolution spectroscopy in the inner halo of the Milky Way. The program giant stars have radial velocities that vary significantly from those expected for stars moving on uniform circular orbits in the Galactic disk. Thus, based on kinematics, we expect a sample dominated by halo stars. Abundances are derived for α-elements and neutron capture elements. By analyzing the multi-dimensional abundance space, the formation site of the halo giants - in-situ or accreted - can be assessed. Of particular interest are a class of stars that form in-situ, deep in the Milky Way's gravitational potential well, but are ``kicked out'' of the disk into the halo due to a perturbation event. We find: (1) our sample is dominated by accreted stars and (2) tentative evidence of a small kicked-out population in our Milky Way halo sample.

  16. Subhalo statistics of galactic haloes: beyond the resolution limit

    NASA Astrophysics Data System (ADS)

    Cautun, Marius; Hellwing, Wojciech A.; van de Weygaert, Rien; Frenk, Carlos S.; Jones, Bernard J. T.; Sawala, Till

    2014-12-01

    We study the substructure population of Milky Way (MW)-mass haloes in the Λ cold dark matter (ΛCDM) cosmology using a novel procedure to extrapolate subhalo number statistics beyond the resolution limit of N-body simulations. The technique recovers the mean and the variance of the subhalo abundance, but not its spatial distribution. It extends the dynamic range over which precise statistical predictions can be made by the equivalent of performing a simulation with 50 times higher resolution, at no additional computational cost. We apply this technique to MW-mass haloes, but it can easily be applied to haloes of any mass. We find up to 20 per cent more substructures in MW-mass haloes than found in previous studies. Our analysis lowers the mass of the MW halo required to accommodate the observation that the MW has only three satellites with a maximum circular velocity Vmax ≥ 30 km s- 1 in the ΛCDM cosmology. The probability of having a subhalo population similar to that in the MW is 20 per cent for a virial mass, M200 = 1 × 1012 M⊙ and practically zero for haloes more massive than M200 = 2 × 1012 M⊙.

  17. The Abundance of Deuterium in the Warm Neutral Medium of the Lower Galactic Halo

    NASA Astrophysics Data System (ADS)

    Savage, Blair D.; Lehner, Nicolas; Fox, Andrew; Wakker, Bart; Sembach, Kenneth

    2007-04-01

    We use high-resolution ultraviolet spectra to obtain Milky Way interstellar column densities of H I, D I, O I, S II, Fe II, and P II toward the QSO HE 0226-4110 in the Galactic direction l=253.4deg and b=-65.77deg. We obtain D/H=21+8-6 ppm from an analysis of the strong damped Lyα line of H I and the weak higher Lyman series absorption of D I. Correcting for a small amount of foreground contamination from D and H in the Local Bubble we obtain D/H=22+8-6 for the warm neutral medium of the lower Galactic halo. The medium sampled has [O/H]=0.12+0.41-0.20 and [Fe/H]=-1.01+0.10-0.09. This suggests the abundances in the gas in the halo toward HE 0226-4110 are not affected by the infall of low-metallicity gas and that the gas originates in the disk and is elevated into the halo by energetic processes that erode but do not totally destroy the dust grains. We compare our result to measured values of D/H in other astrophysical sites. The value we measure in the halo gas is consistent with the hypothesis that for many Galactic disk lines of sight D is incorporated into dust. The high average value of D/H=23.1+/-2.4(1 σ) ppm measured along five sight lines through disk gas in the solar neighborhood is similar to D/H in the lower Galactic halo. These disk and halo observations imply the abundance of deuterium in the Galaxy has only been reduced by a factor of 1.12+/-0.13 since its formation. In contrast, current galactic chemical evolution models predict the astration reduction factor should be in the range from 1.39 to 1.83.

  18. Assembly history of subhalo populations in galactic and cluster sized dark haloes

    NASA Astrophysics Data System (ADS)

    Xie, Lizhi; Gao, Liang

    2015-12-01

    We make use of two suits of ultrahigh resolution N-body simulations of individual dark matter haloes from the Phoenix and the Aquarius Projects to investigate systematics of assembly history of subhaloes in dark matter haloes differing by a factor of 1000 in the halo mass. We have found that real progenitors which built up present-day subhalo population are relatively more abundant for high-mass haloes, in contrast to previous studies claiming a universal form independent of the host halo mass. That is mainly because of repeated counting of the `re-accreted' (progenitors passed through and were later re-accreted to the host more than once) and inclusion of the `ejected' progenitor population (progenitors were accreted to the host in the past but no longer members at present day) in previous studies. The typical accretion time for all progenitors vary strongly with the host halo mass, which is typical about z ˜ 5 for the galactic Aquarius and about z ˜ 3 for the cluster sized Phoenix haloes. Once these progenitors start to orbit their parent haloes, they rapidly lose their original mass but not their identifiers, more than 55 (50) per cent of them survive to present day for the Phoenix (Aquarius) haloes. At given redshift, survival fraction of the accreted subhalo is independent of the parent halo mass, whilst the mass-loss of the subhalo is more efficient in high-mass haloes. These systematics results in similarity and difference in the subhalo population in dark matter haloes of different masses at present day.

  19. Lyman-Alpha Absorption at Low Redshifts and Hot Gas in Galactic Haloes

    NASA Astrophysics Data System (ADS)

    Mo, H. J.

    1994-08-01

    Motivated by the recent observation of Lanzetta et al. that most luminous galaxies at low redshifts produce Lyα absorptions at impact parameter l <~ 160 h^-1^ kpc, we propose that these absorbers are clouds confined by the pressure of ambient hot gas in galactic haloes. We determine the properties of this hot gas and of the absorption systems on the basis of observational and theoretical constraints. The absorbing clouds need to be replenished on a time-scale of about one orbital time (~10^9^ yr) in the galactic halo. The pressure and temperature of the gas at radius r~100 kpc are P = (10-100) cm^-3^ K and T = 10^5.5-6.5^ K. The model requires that about 10 per cent of the gas in low-redshift galactic haloes be in the hot phase. Such gas in galactic haloes emits X-rays with a bolometric luminosity of the order of 10^37-40^1 erg s^-1^. The likelihood that such gas exists in current models of galaxy formation is discussed.

  20. IC 1257: A New Globular Cluster in the Galactic Halo

    NASA Technical Reports Server (NTRS)

    Harris, W. E.; Phelps, R. L.; Madore, B. F.; Pevunova, O.; Skiff, B. A.; Crute, C.; Wilson, B.

    1996-01-01

    New CCD photometry of the faint, compact star cluster IC 1257 (L = 17? = +/- 15?obtained with the Palomar 5m telescope, reveals that it is a highly reddened globular cluster well beyond the Galactic center.

  1. Compact binary mergers as the origin of r-process elements in the Galactic halo

    SciTech Connect

    Ishimaru, Yuhri; Wanajo, Shinya; Prantzos, Nikos

    2014-05-02

    Compact binary mergers (of double neutron star and black hole-neutron star systems) are suggested to be the major site of the r-process elements in the Galaxy by recent hydrodynamical and nucleosynthesis studies. It has been pointed out, however, that estimated long lifetimes of compact binaries are in conflict with the presence of r-process-enhanced stars at the metallicity [Fe/H] ∼ −3. To resolve this problem, we examine the role of compact binary mergers in the early Galactic chemical evolution on the assumption that our Galactic halo was formed from merging sub-halos. The chemical evolutions are modeled for sub-halos with their total stellar masses between 10{sup 4}M{sub ⊙} and 2 × 10{sup 8}M{sub ⊙}. The lifetimes of compact binaries are assumed to be 100 Myr (95%) and 1 Myr (5%) according to recent binary population synthesis studies. We find that the r-process abundances (relative to iron; [r/Fe]) start increasing at [Fe/H] ≤ −3 if the star formation rates are smaller for less massive sub-halos. Our models also suggest that the star-to-star scatter of [r/Fe]'s observed in Galactic halo stars can be interpreted as a consequence of greater gas outflow rates for less massive sub-halos. In addition, the sub-solar [r/Fe]'s (observed as [Ba/Fe] ∼ −1.5 for [Fe/H] < −3) are explained by the contribution from the short-lived (∼ 1 Myr) binaries. Our result indicates, therefore, that compact binary mergers can be potentially the origin of the r-process elements throughout the Galactic history.

  2. 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

    2008-11-01

    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. PMID:18987737

  3. Evidence for recent star formation in the galactic halo

    NASA Astrophysics Data System (ADS)

    Keenan, F. P.

    1986-09-01

    Observational data for PHL 346 obtained with the 2.5 m Issac Newton telescope on August 1985 are studied. Measured stellar Stromgren colors, hydrogen-line profiles, and helium and metal-line equivalent widths are compared with those predicted by local thermodynamic equilibrium model-atmosphere calculations. Effective temperature, surface gravity, microturbulent velocity, and helium and metal abundances for the star are derived. A mass of 13 + or - 2 solar masses, a lifetime of 11 x 10 to the 6th yr, a distance from the galactic plane of 8.7 + or - 1.5 kpc, and a velocity in the z direction of +56 + or - 10 km/s are calculated for the star. The data reveal that the star was not ejected from the galactic plane, but that it formed out of galactic fountain gas at about 6 kpc from the disc.

  4. Magnetic field structure and halo in NGC 4631

    NASA Astrophysics Data System (ADS)

    Mora, Silvia Carolina; Krause, Marita

    2013-12-01

    Context. All of the edge-on spiral galaxies observed so far present a similar magnetic field configuration, which consists of a plane-parallel field in the disk and an X-shaped field at larger z-distances from the plane of the galaxy. Only NGC 4631 seems to have a different field orientation in its disk. Along the eastern and western halves of the disk of NGC 4631 the magnetic field orientation is parallel to the galactic plane, but in the central region of the disk a vertical field seems to dominate. Aims: In order to clarify whether NGC 4631 has a unique magnetic field configuration in the central region along its disk, we present high-resolution Faraday-corrected polarization data. Methods: Radio continuum observations of NGC 4631 at 4.85 GHz were performed with the VLA. In addition, observations were made with the Effelsberg telescope at 4.85 GHz and at 8.35 GHz. These were analyzed together with archival VLA-data at 8.35 GHz. The single-dish and interferometer data were combined to recover the missing zero-spacings. Results: We determined an integrated total spectral index of αtot = -0.78 ± 0.04 and a nonthermal integrated spectral index of αnth = -0.87 ± 0.03. The vertical scale heights in NGC 4631 vary significantly in different regions within the galaxy and their mean values at 4.85 GHz are with 2.3 kpc (370 pc) for the thick (thin) disk higher than the mean values found so far in six other edge-on spiral galaxies. This may originate in the tidal interaction of NGC 4631 with its neighbouring galaxies. The rotation measures are characterized by a smooth large-scale distribution. Along the galactic plane the degree of Faraday depolarization is significantly high. We estimated a total magnetic field strength in the disk of NGC 4631 of Bt ≈ 9 ± 2 μG and an ordered field strength of Bord ≈ 2 ± 1 μG. The total field strengths in the halo are of the order of the total magnetic field strength in the disk, whereas the ordered field strengths in the halo

  5. The effect of active galactic nuclei feedback on the halo mass function

    NASA Astrophysics Data System (ADS)

    Cui, Weiguang; Borgani, Stefano; Murante, Giuseppe

    2014-06-01

    We investigate baryon effects on the halo mass function (HMF), with emphasis on the role played by active galactic nuclei (AGN) feedback. Haloes are identified with both friends-of-friends (FoF) and spherical overdensity (SO) algorithms. We embed the standard SO algorithm into a memory-controlled frame program and present the Python spherIcAl Overdensity code - PIAO (Chinese character: ). For both FoF and SO haloes, the effect of AGN feedback is that of suppressing the HMFs to a level even below that of dark matter (DM) simulations. The ratio between the HMFs in the AGN and in the DM simulations is ˜0.8 at overdensity Δc = 500, a difference that increases at higher overdensity Δc = 2500, with no significant redshift and mass dependence. A decrease of the halo masses ratio with respect to the DM case induces the decrease of the HMF in the AGN simulation. The shallower inner density profiles of haloes in the AGN simulation witnesses that mass reduction is induced by the sudden displacement of gas induced by thermal AGN feedback. We provide fitting functions to describe halo mass variations at different overdensities, which can recover the HMFs with a residual random scatter ≲5 per cent for halo masses larger than 1013 h-1 M⊙.

  6. A NEW DELIVERY ROUTE TO GALACTIC NUCLEI: WARM HALO CLOUD IMPACTS

    SciTech Connect

    McKernan, Barry; Ford, K. E. Saavik; Maller, Ariyeh

    2010-08-01

    We propose a new mechanism for the delivery of gas to the heart of galactic nuclei. We show that warm halo clouds (WHCs) must periodically impact galactic centers and potentially deliver a large ({approx}10{sup 4}-10{sup 6} M{sub sun}) mass of gas to the galactic nucleus in a singular event. The impact of an accreting WHC originating far in the galactic halo can, depending on mixing, produce a nuclear starburst of low-metallicity stars as well as low-luminosity accretion onto the central black hole. Based on multiphase cooling around a {Lambda}CDM distribution of halos, we calculate the nuclear impact rate, the mass captured by the central black hole, and the fraction of active nuclei for impacting cloud masses in the range 10{sup 4}-10{sup 6} M{sub sun}. If there is moderate braking during cloud infall, our model predicts an average fraction of low-luminosity active nuclei consistent with observations.

  7. Anisotropies at Ultra High Energies and the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Wolfendale, Arnold

    1999-08-01

    A measure of consistency is appearing in measurements of the anisotropy of arrival directions above 1017 eV and these show a Galactic Plane Enhancement and a S-N excess, to about 3.1018 eV. The implication is that Galactic particles predominate here. At higher energies, where an Extragalactic origin is preferred, a contender for the `sources' is exotic dark matter particles. However, an analysis of the anisotropy at the highest energies, or, rather, the lack of it, makes this interpretation highly unlikely. Instead, `bottom-up' acceleration, in galaxy-systems is preferred; the likely mass mixture of the primaries, above 1018 eV, helps to explain why strong clustering of arrival is not observed.

  8. X-ray detection of warm ionized matter in the Galactic halo

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    We report on a systematic investigation of the cold and mildly ionized gaseous baryonic metal components of our Galaxy, through the analysis of high-resolution Chandra and XMM-Newton spectra of two samples of Galactic and extragalactic sources. The comparison between lines of sight towards sources located in the disc of our Galaxy and extragalactic sources allows us for the first time to clearly distinguish between gaseous metal components in the disc and halo of our Galaxy. We find that a warm ionized metal medium (WIMM) permeates a large volume above and below the Galaxy's disc, perhaps up to the circum-galactic space. This halo WIMM imprints virtually the totality of the O I and O II absorption seen in the spectra of our extragalactic targets, has a temperature of T_{WIMM}^{Halo}=2900 ± 900 K, a density < n_H > _{WIMM}^{Halo} = 0.023 ± 0.009 cm-3 and a metallicity Z_{WIMM}^{Halo} = (0.4 ± 0.1) Z⊙. Consistently with previous works, we also confirm that the disc of the Galaxy contains at least two distinct gaseous metal components, one cold and neutral (the CNMM: cold neutral metal medium) and one warm and mildly ionized, with the same temperature of the halo WIMM, but higher density (< n_H > _{WIMM}^{Disc} = 0.09 ± 0.03 cm-3) and metallicity (Z_{WIMM}^{Disc} = 0.8 ± 0.1 Z⊙). By adopting a simple disc+sphere geometry for the Galaxy, we estimate masses of the CNMM and the total (disc + halo) WIMM of MCNMM ≲ 8 × 108 M⊙ and MWIMM ≃ 8.2 × 109 M⊙.

  9. A general relativistic approach to the Navarro Frenk White galactic halos

    NASA Astrophysics Data System (ADS)

    Matos, Tonatiuh; Núñez, Darío; Sussman, Roberto A.

    2004-11-01

    Although galactic dark matter halos are basically Newtonian structures, the study of their interplay with large-scale cosmic evolution and with relativistic effects, such as gravitational lenses, quintessence sources or gravitational waves, makes it necessary to obtain adequate relativistic descriptions for these self-gravitating systems. With this purpose in mind, we construct a post-Newtonian fluid framework for the 'Navarro Frenk White' (NFW) models of galactic halos that follow from N-body numerical simulations. Since these simulations are unable to resolve regions very near the halo centre, the extrapolation of the fitting formula leads to a spherically averaged 'universal' density profile that diverges at the origin. We remove this inconvenient feature by replacing a small central region of the NFW halo with an interior Schwarzschild solution with constant density, continuously matched to the remaining NFW spacetime. A model of a single halo, as an isolated object with finite mass, follows by smoothly matching the NFW spacetime to a Schwarzschild vacuum exterior along the virial radius, the physical 'cut-off' customarily imposed, as the mass associated with NFW profiles diverges asymptotically. Numerical simulations assume weakly interacting collisionless particles, hence we suggest that NFW halos approximately satisfy an 'ideal gas' type of equation of state, where mass-density is the dominant rest-mass contribution to matter-energy, with the internal energy contribution associated with an anisotropic kinetic pressure. We show that, outside the central core, this pressure and the mass density roughly satisfy a polytropic relation. Since stellar polytropes are the equilibrium configurations in Tsallis' non-extensive formalism of statistical mechanics, we argue that NFW halos might provide a rough empirical estimate of the free parameter q of Tsallis' formalism.

  10. Building the Galactic halo from globular clusters: evidence from chemically unusual red giants

    NASA Astrophysics Data System (ADS)

    Martell, S. L.; Smolinski, J. P.; Beers, T. C.; Grebel, E. K.

    2011-10-01

    We present a spectroscopic search for halo field stars that originally formed in globular clusters. Using moderate-resolution SDSS-III/SEGUE-2 spectra of 561 red giants with typical halo metallicities (-1.8 ≤ [Fe/H] ≤ -1.0), we identify 16 stars, 3% of the sample, with CN and CH bandstrength behavior indicating depleted carbon and enhanced nitrogen abundances relative to the rest of the data set. Since globular clusters are the only environment known in which stars form with this pattern of atypical light-element abundances, we claim that these stars are second-generation globular cluster stars that have been lost to the halo field via normal cluster mass-loss processes. Extrapolating from theoretical models of two-generation globular cluster formation, this result suggests that globular clusters contributed significant numbers of stars to the construction of the Galactic halo: we calculate that a minimum of 17% of the present-day mass of the stellar halo was originally formed in globular clusters. The ratio of CN-strong to CN-normal stars drops with Galactocentric distance, suggesting that the inner-halo population may be the primary repository of these stars. Full Tables 1 and 3 are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/534/A136

  11. Soft X-Ray Observations of the Galactic Halo

    NASA Technical Reports Server (NTRS)

    Shelton, Robin; Kuntz, K. D.

    2003-01-01

    In this project, my co-I (K.D. Kuntz) and I plan to extract the soft X-ray spectrum emitted by the hot gas along a high latitude line of sight. We plan to subtract off the local component (garnered from other observations) in order to isolate the halo component. We then plan to combine this spectral information with the ultraviolet resonance line emission produced by slightly cooler gas along the line of sight and use the two observations as a constraint on models. My co-I, K.D., Kuntz has been working on the determination of the instrumental background. I have not yet drawn any of the funds for this project. I have just moved from J h s Hopkins University to the University of Georgia and anticipate finishing the project while at the University of Georgia.

  12. Constraints on baryonic dark matter in the Galactic halo and Local Group

    NASA Technical Reports Server (NTRS)

    Richstone, Douglas; Gould, Andrew; Guhathakurta, Puragra; Flynn, Chris

    1992-01-01

    A four-color method and deep CCD data are used to search for very faint metal-poor stars in the direction of the south Galactic pole. The results make it possible to limit the contribution of ordinary old, metal-poor stars to the dynamical halo of the Galaxy or to the Local Group. The ratio of the mass of the halo to its ordinary starlight must be more than about 2000, unless the halo is very small. For the Local Group, this ratio is greater than about 400. If this local dark matter is baryonic, the process of compact-object formation must produce very few 'impurities' in the form of stars similar to those found in globular clusters. The expected number of unbound stars with MV not greater than 6 within 100 pc of the sun is less than 1 based on the present 90-percent upper limit to the Local Group starlight.

  13. Small-scale clumps in the Galactic halo

    SciTech Connect

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

    2010-01-15

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

  14. VizieR Online Data Catalog: The SEGUE K giant survey. III. Galactic halo (Janesh+, 2016)

    NASA Astrophysics Data System (ADS)

    Janesh, W.; Morrison, H. L.; Ma, Z.; Rockosi, C.; Starkenburg, E.; Xue, X. X.; Rix, H.-W.; Harding, P.; Beers, T. C.; Johnson, J.; Lee, Y. S.; Schneider, D. P.

    2016-03-01

    We statistically quantify the amount of substructure in the Milky Way stellar halo using a sample of 4568 halo K giant stars at Galactocentric distances ranging over 5-125kpc. These stars have been selected photometrically and confirmed spectroscopically as K giants from the Sloan Digital Sky Survey's Sloan Extension for Galactic Understanding and Exploration (SEGUE) project. Using a position-velocity clustering estimator (the 4distance) and a model of a smooth stellar halo, we quantify the amount of substructure in the halo, divided by distance and metallicity. Overall, we find that the halo as a whole is highly structured. We also confirm earlier work using blue horizontal branch (BHB) stars which showed that there is an increasing amount of substructure with increasing Galactocentric radius, and additionally find that the amount of substructure in the halo increases with increasing metallicity. Comparing to resampled BHB stars, we find that K giants and BHBs have similar amounts of substructure over equivalent ranges of Galactocentric radius. Using a friends-of-friends algorithm to identify members of individual groups, we find that a large fraction (~33%) of grouped stars are associated with Sgr, and identify stars belonging to other halo star streams: the Orphan Stream, the Cetus Polar Stream, and others, including previously unknown substructures. A large fraction of sample K giants (more than 50%) are not grouped into any substructure. We find also that the Sgr stream strongly dominates groups in the outer halo for all except the most metal-poor stars, and suggest that this is the source of the increase of substructure with Galactocentric radius and metallicity. (2 data files).

  15. Did globular clusters contribute to the stellar population of the Galactic halo?

    NASA Astrophysics Data System (ADS)

    Charbonnel, Corinne; Krause, Martin

    2016-08-01

    The origin of Galactic halo stars and the contribution of globular clusters (GC) to this stellar population have long been (and still are) debated. The discovery of multiple stellar populations with peculiar chemical properties in GCs both in the Milky Way and in Local Group galaxies recently brought a renewal on these questions. Indeed most of the scenarios that compete to reproduce the present-day GC characteristics call for fast expulsion of both gas and low-mass stars from these clusters in their early infancy. In this framework, the initial masses of GCs could have been 8 to 25 times higher than their present-day stellar mass, and they could have contributed to 5 to 20 % of the low-mass stars in the Galactic halo. Here we revisit these conclusions, which are in tension with observations of dwarf galaxies and of young massive star clusters in the Local Group. We come back in particular on the paradigm of gas expulsion from massive star clusters, and propose an alternative interpretation of the GC abundance properties. We conclude by proposing a major revision of the current concepts regarding the role massive star clusters play in the assembly of galactic haloes.

  16. A skewer survey of the Galactic halo from deep CFHT and INT images

    NASA Astrophysics Data System (ADS)

    Pila-Díez, B.; de Jong, J. T. A.; Kuijken, K.; van der Burg, R. F. J.; Hoekstra, H.

    2015-07-01

    We study the density profile and shape of the Galactic halo using deep multicolour images from the MENeaCS and CCCP projects, over 33 fields selected to avoid overlap with the Galactic plane. Using multicolour selection and point spread function homogenization techniques we obtain catalogues of F stars (near-main sequence turnoff stars) out to Galactocentric distances up to 60 kpc. Grouping nearby lines of sight, we construct the stellar density profiles through the halo in eight different directions by means of photometric parallaxes. Smooth halo models are then fitted to these profiles. We find clear evidence for a steepening of the density profile power law index around R = 20 kpc, from -2.50 ± 0.04 to -4.85 ± 0.04, and for a flattening of the halo towards the poles with best-fit axis ratio 0.79 ± 0.02. Furthermore, we cannot rule out a mild triaxiality (w ≥ 0.88 ± 0.07). We recover the signatures of well-known substructure and streams that intersect our lines of sight. These results are consistent with those derived from wider but shallower surveys, and augur well for upcoming, wide-field surveys of comparable depth to our pencil beam surveys.

  17. The sagittarius tidal stream and the shape of the galactic stellar halo

    NASA Astrophysics Data System (ADS)

    Newby, Matthew T.

    The stellar halo that surrounds our Galaxy contains clues to understanding galaxy formation, cosmology, stellar evolution, and the nature of dark matter. Gravitationally disrupted dwarf galaxies form tidal streams, which roughly trace orbits through the Galactic halo. The Sagittarius (Sgr) dwarf tidal debris is the most dominant of these streams, and its properties place important constraints on the distribution of mass (including dark matter) in the Galaxy. Stars not associated with substructures form the "smooth" component of the stellar halo, the origin of which is still under investigation. Characterizing halo substructures such as the Sgr stream and the smooth halo provides valuable information on the formation history and evolution of our galaxy, and places constraints on cosmological models. This thesis is primarily concerned with characterizing the 3-dimensional stellar densities of the Sgr tidal debris system and the smooth stellar halo, using data from the Sloan Digital Sky Survey (SDSS). F turnoff stars are used to infer distances, as they are relatively bright, numerous, and distributed about a single intrinsic brightness (magnitude). The inherent spread in brightnesses of these stars is overcome through the use of the recently-developed technique of statistical photometric parallax, in which the bulk properties of a stellar population are used to create a probability distribution for a given star's distance. This was used to build a spatial density model for the smooth stellar halo and tidal streams. The free parameters in this model are then fit to SDSS data with a maximum likelihood technique, and the parameters are optimized by advanced computational methods. Several computing platforms are used in this study, including the RPI SUR Bluegene and the Milkyway home volunteer computing project. Fits to the Sgr stream in 18 SDSS data stripes were performed, and a continuous density profile is found for the major Sgr stream. The stellar halo is found to

  18. The galactic halo in mixed dark matter cosmologies

    SciTech Connect

    Anderhalden, D.; Diemand, J.; Schneider, A.; Bertone, G.; Macciò, A.V. E-mail: diemand@physik.uzh.ch E-mail: maccio@mpia.de

    2012-10-01

    A possible solution to the small scale problems of the cold dark matter (CDM) scenario is that the dark matter consists of two components, a cold and a warm one. We perform a set of high resolution simulations of the Milky Way halo varying the mass of the WDM particle (m{sub WDM}) and the cosmic dark matter mass fraction in the WDM component ( f-bar {sub W}). The scaling ansatz introduced in combined analysis of LHC and astroparticle searches postulates that the relative contribution of each dark matter component is the same locally as on average in the Universe (e.g. f{sub W,s}un = f-bar {sub W}). Here we find however, that the normalised local WDM fraction (f{sub W,s}un / f-bar {sub W}) depends strongly on m{sub WDM} for m{sub WDM} < 1 keV. Using the scaling ansatz can therefore introduce significant errors into the interpretation of dark matter searches. To correct this issue a simple formula that fits the local dark matter densities of each component is provided.

  19. THE FRACTION OF GLOBULAR CLUSTER SECOND-GENERATION STARS IN THE GALACTIC HALO

    SciTech Connect

    Vesperini, Enrico; McMillan, Stephen L. W.; D'Antona, Francesca; D'Ercole, Annibale

    2010-08-01

    Many observational studies have revealed the presence of multiple stellar generations in Galactic globular clusters. These studies suggest that second-generation stars make up a significant fraction of the current mass of globular clusters, with the second-generation mass fraction ranging from {approx}50% to 80% in individual clusters. In this Letter, we carry out hydrodynamical simulations to explore the dependence of the mass of second-generation stars on the initial mass and structural parameters and stellar initial mass function (IMF) of the parent cluster. We then use the results of these simulations to estimate the fraction f{sub SG,H} of the mass of the Galactic stellar halo composed of second-generation stars that originated in globular clusters. We study the dependence of f{sub SG,H} on the parameters of the IMF of the Galactic globular cluster system. For a broad range of initial conditions, we find that the fraction of mass of the Galactic stellar halo in second-generation stars is always small, f{sub SG,H} < 4%-6% for a Kroupa-1993 IMF and f{sub SG,H} < 7%-9% for a Kroupa-2001 IMF.

  20. Modeling the evolution of galactic magnetic fields

    SciTech Connect

    Yar-Mukhamedov, D.

    2015-04-15

    An analytic model for evolution of galactic magnetic fields in hierarchical galaxy formation frameworks is introduced. Its major innovative components include explicit and detailed treatment of the physics of merger events, mass gains and losses, gravitational energy sources and delays associated with formation of large-scale magnetic fields. This paper describes the model, its implementation, and core results obtained by its means.

  1. New cluster members and halo stars of the Galactic globular cluster NGC 1851

    NASA Astrophysics Data System (ADS)

    Navin, Colin A.; Martell, Sarah L.; Zucker, Daniel B.

    2015-10-01

    NGC 1851 is an intriguing Galactic globular cluster, with multiple stellar evolutionary sequences, light and heavy element abundance variations and indications of a surrounding stellar halo. We present the first results of a spectroscopic study of red giant stars within and outside of the tidal radius of this cluster. Our results identify nine probable new cluster members (inside the tidal radius) with heliocentric radial velocities consistent with that of NGC 1851. We also identify, based on their radial velocities, four probable extratidal cluster halo stars at distances up to ˜3.1 times the tidal radius, which are supportive of previous findings that NGC 1851 is surrounded by an extended stellar halo. Proper motions were available for 12 of these 13 stars and all are consistent with that of NGC 1851. Apart from the cluster members and cluster halo stars, our observed radial velocity distribution agrees with the expected distribution from a Besançon disc/N-body stellar halo Milky Way model generated by the GALAXIA code, suggesting that no other structures at different radial velocities are present in our field. The metallicities of these stars are estimated using equivalent width measurements of the near-infrared calcium triplet absorption lines and are found, within the limitations of this method, to be consistent with that of NGC 1851. In addition we recover 110 red giant cluster members from previous studies based on their radial velocities and identify three stars with unusually high radial velocities.

  2. THE STELLAR METALLICITY DISTRIBUTION FUNCTION OF THE GALACTIC HALO FROM SDSS PHOTOMETRY

    SciTech Connect

    An, Deokkeun; Beers, Timothy C.; Johnson, Jennifer A.; Pinsonneault, Marc H.; Lee, Young Sun; Bovy, Jo; Ivezic, Zeljko; Carollo, Daniela; Newby, Matthew

    2013-01-20

    We explore the stellar metallicity distribution function of the Galactic halo based on SDSS ugriz photometry. A set of stellar isochrones is calibrated using observations of several star clusters and validated by comparisons with medium-resolution spectroscopic values over a wide range of metal abundance. We estimate distances and metallicities for individual main-sequence stars in the multiply scanned SDSS Stripe 82, at heliocentric distances in the range 5-8 kpc and |b| > 35 Degree-Sign , and find that the in situ photometric metallicity distribution has a shape that matches that of the kinematically selected local halo stars from Ryan and Norris. We also examine independent kinematic information from proper-motion measurements for high Galactic latitude stars in our sample. We find that stars with retrograde rotation in the rest frame of the Galaxy are generally more metal poor than those exhibiting prograde rotation, which is consistent with earlier arguments by Carollo et al. that the halo system comprises at least two spatially overlapping components with differing metallicity, kinematics, and spatial distributions. The observed photometric metallicity distribution and that of Ryan and Norris can be described by a simple chemical evolution model by Hartwick (or by a single Gaussian distribution); however, the suggestive metallicity-kinematic correlation contradicts the basic assumption in this model that the Milky Way halo consists primarily of a single stellar population. When the observed metallicity distribution is deconvolved using two Gaussian components with peaks at [Fe/H] Almost-Equal-To -1.7 and -2.3, the metal-poor component accounts for {approx}20%-35% of the entire halo population in this distance range.

  3. The Stellar Metallicity Distribution Function of the Galactic Halo from SDSS Photometry

    NASA Astrophysics Data System (ADS)

    An, Deokkeun; Beers, Timothy C.; Johnson, Jennifer A.; Pinsonneault, Marc H.; Lee, Young Sun; Bovy, Jo; Ivezić, Željko; Carollo, Daniela; Newby, Matthew

    2013-01-01

    We explore the stellar metallicity distribution function of the Galactic halo based on SDSS ugriz photometry. A set of stellar isochrones is calibrated using observations of several star clusters and validated by comparisons with medium-resolution spectroscopic values over a wide range of metal abundance. We estimate distances and metallicities for individual main-sequence stars in the multiply scanned SDSS Stripe 82, at heliocentric distances in the range 5-8 kpc and |b| > 35°, and find that the in situ photometric metallicity distribution has a shape that matches that of the kinematically selected local halo stars from Ryan & Norris. We also examine independent kinematic information from proper-motion measurements for high Galactic latitude stars in our sample. We find that stars with retrograde rotation in the rest frame of the Galaxy are generally more metal poor than those exhibiting prograde rotation, which is consistent with earlier arguments by Carollo et al. that the halo system comprises at least two spatially overlapping components with differing metallicity, kinematics, and spatial distributions. The observed photometric metallicity distribution and that of Ryan & Norris can be described by a simple chemical evolution model by Hartwick (or by a single Gaussian distribution); however, the suggestive metallicity-kinematic correlation contradicts the basic assumption in this model that the Milky Way halo consists primarily of a single stellar population. When the observed metallicity distribution is deconvolved using two Gaussian components with peaks at [Fe/H] ≈ -1.7 and -2.3, the metal-poor component accounts for ~20%-35% of the entire halo population in this distance range.

  4. Post Asymptotic Giant Branch and Central Stars of Planetary Nebulae in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Weston, Simon

    2012-01-01

    Post asymptotic giant branch (post-AGB) stars, central stars of planetary nebulae (CSPNe) and planetary nebulae (PNe) are important phases of stellar evolution as the material they feedback is the seed of subsequent star formation in a galaxy. The majority of low and intermediate mass stars are expected to evolve through these channels, however, it is uncertain how many actually do, and at what rate. The Galactic halo, with its older population, provides a direct test of evolutionary models for low mass stars. Birthrate estimates of PNe are uncertain and worse still, are in contradiction with accepted white dwarf (WD) birthrate estimates. Much of the uncertainty stems from the lack of complete samples and poorly determined distance estimates. New surveys such as the Sloan Digital Sky Survey (SDSS), Galaxy Evolutionary Explorer (GALEX) and the INT Photometric Ha Survey (IPHAS) have discovered many new PNe and have observed the far edges of the Galaxy. Improved methods of determining distances to CSPNe are presented here, using model atmospheres, evolutionary tracks and high resolution reddening maps utilising these revolutionary surveys. Locating the CSPN is non-trivial particularly for evolved PNe, as they are extended with their central star often displaced from the centre of the nebula. Therefore, photometric criteria are required to locate the CSPN in the nebula's field. Synthetic photometry of the CSPNe is derived from spectral energy distributions (SEDs) computed from a grid of model atmospheres covering the parameter range of CSPNe. The SEDs are convolved with filter transmission curves to compute synthetic magnitudes for a given photometric system which are then calibrated with standard stars and WDs. A further project borne out of a search for luminous central stars of faint PNe, resulted in a systematic search for post-AGB stars in the Galactic halo. In this work, new candidate halo post-AGB stars are discovered from a search through the SDSS spectroscopic

  5. Chemical and kinematic correlations in the galactic halo

    NASA Astrophysics Data System (ADS)

    James, Carol Renee

    2000-11-01

    Abundances and kinematics have been determined for sixty-one low metallicity ([Fe/H] < -1.30) stars in an attempt to find correlations between stellar chemistry and dynamics. Distances for program stars have been re-derived spectroscopically, and the computed stellar distances agree with the parallaxes reported by Hipparcos (ESA 1997). Stellar orbits were calculated using the Galactic mass model of Bahcall et al. (1983). We find that the general kinematic results (U, V, W, Rapo, Z max, eccentricity) are more extreme than previously thought, but in good agreement with recent studies of this nature. We have also adopted the chemical and kinematic results for 34 additional stars from the work of others to supplement our sample. Our LTE abundance results concur with previous studies. Specifically, we have found that the alpha-capture elements (Mg, Ca, and Ti) are consistently overabundant by 0.4 dex (i.e. [alpha/Fe] = +0.4) except in the cases of four stars: HD 134439, HD 134440, BD+80 245 and G4-36. Additionally, we have found a typical oxygen overabundance of +0.70 dex, and a sodium abundance of [Na/Fe] = -0.60 dex after an empirical correction for NLTE effects. We find no statistically sound correlations between various kinematic parameters and abundances. We confirm the unusual abundance signatures of HD 134439/HD 134440 and BD+80 245. The former stars are a proper-motion pair with mildly deficient alpha-capture abundances. The latter star possesses a pronounced alpha-capture deficiency combined with an extremely low Ba abundance. Its Na and O are apparently normal. We have also discovered a star with extremely unusual abundances: G4-36 possesses marked deficiencies in O, Mg, Al, Ca, Sr, and Ba, but overabundances of Fe-peak elements Mn, Ni, and Zn. We suggest that the nucleosynthetic origin of G4-36 is substantially different from that of BD+80 245 and the proper motion pair HD 134439/134440. All four unusual stars are in retrograde orbits, as are half the stars

  6. Neutron-capture element and Sc abundances in low- and high-alpha Galactic halo stars

    NASA Astrophysics Data System (ADS)

    Yong, David; Fishlock, Cherie; Karakas, Amanda

    2015-08-01

    Nissen & Schuster (2010) identified two samples of Galactic halo stars with distinct kinematic and chemical properties. The "high-alpha" population is associated with the dissipative monolithic collapse of a proto-Galactic gas cloud while the "low-alpha" population was likely accreted from dwarf galaxies having experienced slower star formation rates. For a subset of these stars, we measured precise abundances of Sc, Zr, La, Ce, Nd and Eu. We find differences in the abundance ratios of [Sc/Fe], [Zr/Fe], and [La/Zr] between the low- and high-alpha groups. The most intriguing result is that the low-alpha stars appear to have higher [Eu/Fe] ratios than the high-alpha stars, in contrast to the expectation that Eu should follow the alpha elements. These data challenge the hypothesis that the high-alpha stars formed in regions only enriched by massive stars and that the low-alpha received additional enrichment from SNeIa and low-mass AGB stars. This work has three main consequences for galaxy halos: 1. The new Eu data could be explained by different IMFs for the two halo populations; 2. The low [alpha/Fe] ratios in some, and perhaps all, dwarf galaxies may be driven (in part of in whole) by different IMFs rather than SNeIa contributions; 3. These data may provide important new constraints on the origin of Eu.

  7. May 2005 Halo CMEs and Galactic Cosmic Ray Flux Changes at Earth's Orbit

    NASA Astrophysics Data System (ADS)

    Ahluwalia, H. S.; Alania, M. V.; Wawrzynczak, A.; Ygbuhay, R. C.; Fikani, M. M.

    2014-05-01

    The pressure corrected hourly data from the global network of cosmic ray detectors, measurements of the interplanetary magnetic field (IMF) intensity ( B) at Earth's orbit and its components B x , B y , B z (in the geocentric solar ecliptic coordinates) are used to conduct a comprehensive study of the galactic cosmic ray (GCR) intensity fluctuations caused by the halo coronal mass ejection of 13 May 2005. Distinct differences exist in GCR timelines recorded by neutron monitors (NMs) and multidirectional muon telescopes (MTs), the latter respond to the high rigidity portion of the GCR differential rigidity spectrum. The Forbush decrease (FD) onset in MTs is delayed (˜5 h) with respect to the onset of a geomagnetic storm sudden commencement (SSC) and a large pre-increase is present in MT data before, during, and after the SSC onset, of unknown origin. The rigidity spectrum, for a range of GCR rigidities (≤200 GV), is a power law in rigidity (R) with a negative exponent ( γ=-1.05) at GCR minimum intensity, leading us to infer that the quasi-linear theory of modulation is inconsistent with observations at high rigidities (>1 GV); the results support the force field theory of modulation. At present, we do not have a comprehensive model for the FD explaining quantitatively all the observational features but we present a preliminary model listing physical processes that may contribute to a FD timeline. We explored the connections between different phases of the FD and the power spectra of IMF components but did not find a sustained relationship.

  8. Structure Formation inside Triaxial Dark Matter Halos: Galactic Disks, Bulges, and Bars

    NASA Astrophysics Data System (ADS)

    Heller, Clayton H.; Shlosman, Isaac; Athanassoula, E.

    2007-12-01

    We investigate formation and evolution of galactic disks immersed in assembling live DM halos. Models have been evolved from cosmological initial conditions and represent the collapse of an isolated density perturbation. The baryons include gas participating in star formation (SF) and stars with the energy feedback onto the ISM. We find that (1) the triaxial halo figure tumbling is insignificant and the angular momentum (J) is channeled into the internal circulation, while the baryonic collapse is stopped by the centrifugal barrier; (2) density response of the (disk) baryons is out of phase with DM, thus washing out the inner halo ellipticity; (3) the total J is neatly conserved, even in models accounting for stellar feedback; (4) the specific J for DM is nearly constant, while that for baryons is decreasing; (5) early stage of disk formation resembles the cat's cradle-a small amorphous disk fueled via radial string patterns-followed by growing oval disk whose shape varies with its orientation to the halo major axis; (6) the disk gas layer thins when the SF rate drops below ~5 Msolar yr-1 (7) about half of the baryons remain outside the disk SF region or in the halo as a hot gas; (8) rotation curves appear to be flat and account for the observed disk/halo contributions; (9) a range of bulge-dominated to bulgeless disks was obtained, depending on the stellar feedback parameter, ɛSF: smaller ɛSF leads to a larger and earlier bulge; lower density threshold for SF leads to a smaller, thicker disk; gas gravitational softening mimics a number of intrinsic processes within the ISM; (10) models are characterized by an extensive bar-forming activity; (11) nested bars form in response to the gas inflow along the primary bars, as shown by Heller, Shlosman, and Athanassoula.

  9. WEAK GALACTIC HALO-DWARF SPHEROIDAL CONNECTION FROM RR LYRAE STARS

    SciTech Connect

    Fiorentino, Giuliana; Bono, Giuseppe; Monelli, Matteo; Gallart, Carme; Martínez-Vásquez, Clara E.; Tolstoy, Eline; Salaris, Maurizio; Bernard, Edouard J.

    2015-01-01

    We discuss the role that dwarf galaxies may have played in the formation of the Galactic halo (Halo) using RR Lyrae stars (RRL) as tracers of their ancient stellar component. The comparison is performed using two observables (periods, luminosity amplitudes) that are reddening and distance independent. Fundamental mode RRL in 6 dwarf spheroidals (dSphs) and 11 ultra faint dwarf galaxies (∼1300) show a Gaussian period distribution well peaked around a mean period of (Pab) = 0.610 ± 0.001 days (σ = 0.03). The Halo RRL (∼15,000) are characterized by a broader period distribution. The fundamental mode RRL in all the dSphs apart from Sagittarius are completely lacking in High Amplitude Short Period (HASP) variables, defined as those having P ≲ 0.48 days and A{sub V} ≥ 0.75 mag. Such variables are not uncommon in the Halo and among the globular clusters and massive dwarf irregulars. To further interpret this evidence, we considered 18 globulars covering a broad range in metallicity (–2.3 ≲ [Fe/H] ≲ –1.1) and hosting more than 35 RRL each. The metallicity turns out to be the main parameter, since only globulars more metal-rich than [Fe/H] ∼ –1.5 host RRL in the HASP region. This finding suggests that dSphs similar to the surviving ones do not appear to be the major building-blocks of the Halo. Leading physical arguments suggest an extreme upper limit of ∼50% to their contribution. On the other hand, massive dwarfs hosting an old population with a broad metallicity distribution (Large Magellanic Cloud, Sagittarius) may have played a primary role in the formation of the Halo.

  10. Hidden Galactic Accretion: The Discovery of Low-Velocity Halo Clouds

    NASA Astrophysics Data System (ADS)

    Peek, J. E. G.; Putman, M. E.; Sommer-Larsen, J.; Heiles, C. E.; Stanimirovic, S.; Douglas, K.; Gibson, S.; Korpela, E.

    2007-12-01

    High-Velocity Clouds (HVCs) have been thought to be part of the Galactic accretion process since their discovery more than 40 years ago. Two modes through which HVCs may be generated and contribute to the ongoing growth of our Galaxy are (1) the tidal stripping of satellite galaxies and (2) the fragmented condensation of the Galaxy's hot baryonic halo. We have run cosmological Tree-SPH simulations of a Milky-Way sized galaxy, in which we can resolve clouds down to 10^5 M⊙, in an attempt to probe the cooling halo accretion process. The simulations show that this HVC generation mechanism can indeed reproduce the characteristics of observed population of HVCs, including the flux, velocity and cloud clustering properties. These simulations also predict an equally large population of halo clouds moving at lower radial velocities: Low-Velocity Halo Clouds (LVHCs). These clouds would not be observed as HVCs, but would rather be confused with local disk gas. Taking advantage of the known empirical result that HVCs have undetectably low infrared dust flux compared to their 21cm column, we search for these clouds in the preliminary GALFA-HI survey and IRAS. We announce the discovery of the first examples of these clouds, and describe their properties. This work was supported in part by NSF grant AST 04-06987 and NSF grant AST 07-09347.

  11. GALACTIC ARCHEOLOGY AND THE HIGH-REDSHIFT DETECTABILITY OF MILKY WAY HALO PROGENITOR GALAXIES

    SciTech Connect

    Okrochkov, Mikhail; Tumlinson, Jason

    2010-06-10

    Using a simple model of Milky Way halo formation and chemical evolution, we examine the criteria for observing Milky Way-like progenitor galaxies and the stellar populations within them with the James Webb Space Telescope (JWST). We determine that Milky Way progenitors are visible in deep fields (AB = 30-31) up to z = 7 with low dust content and up to z = 9 with no dust content. These models allow us to determine the fraction of Milky Way halo stars formed in galaxies that should be visible with Near-Infrared Camera on JWST, as a function of metallicity. We show that galaxies in which Galactic halo stars of metallicity above [Fe/H] = -2.5 formed can be detected. Galaxies that form stars with higher metallicities should be visible in deep fields and can be studied by combining observations within the Galaxy as well as external galaxies. We find that halo stars with [Fe/H] <-2.8 formed in progenitor galaxies that are not visible to JWST and that examining their remnants within the Milky Way provides the only realistic prospect of studying these ancient stellar populations. The oldest visible stellar populations are shown to be centrally concentrated, with the stars that formed in visible galaxies at z > 3 residing preferentially within the central 10 kpc region of the Galaxy.

  12. Beyond halo mass: galactic conformity as a smoking gun of central galaxy assembly bias

    NASA Astrophysics Data System (ADS)

    Hearin, Andrew P.; Watson, Douglas F.; van den Bosch, Frank C.

    2015-09-01

    Quenched central galaxies tend to reside in a preferentially quenched large-scale environment, a phenomenon that has been dubbed galactic conformity. Remarkably, this tendency persists out to scales far larger than the virial radius of the halo hosting the central. Therefore, conformity manifestly violates the widely adopted assumption that the dark matter halo mass Mvir exclusively governs galaxy occupation statistics. This paper is the first in a series studying the implications of the observed conformity signal for the galaxy-dark matter connection. We show that recent measurements of conformity on scales r ˜ 1-5 Mpc imply that central galaxy quenching statistics cannot be correctly predicted with the knowledge of Mvir alone. We also demonstrate that ejected (or `backsplash') satellites cannot give rise to the signal. We then invoke the age matching model, which is predicated on the co-evolution of galaxies and haloes. We find that this model produces a strong signal, and that central galaxies are solely responsible. We conclude that large-scale `two-halo' conformity represents a smoking gun of central galaxy assembly bias, and indicates that contemporary models of satellite quenching have systematically overestimated the influence of post-infall processes.

  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. Assembling the Largest, Most Distant Sample of Halo Wide Binaries for Galactic Structure and Dynamics

    NASA Astrophysics Data System (ADS)

    Coronado, J.; Chanamé, J.

    2015-10-01

    Samples of wide binaries (agtrsim \\ 100\\ AU) are a gold mine for Galactic studies. They have been used on a large list of applications in a diversity of fields. In the dynamical arena, wide binaries provided the first meaningful constraints on the mass and nature of disk dark matter and, more recently, they were used to close the remaining parameter space of MACHO-like halo dark matter not accessible to the micro-lensing campaigns. All these applications were possible when samples of these objects became large enough to not be dominated by random, chance alignments of two unrelated stars projected on the sky. Nevertheless, still today the largest available sample of the particularly valuable halo wide binaries free from selection biases, contains not much more than 100 systems, and conclusions on dark matter are very sensitive to this fact.

  15. MAPPING THE GALACTIC HALO WITH BLUE HORIZONTAL BRANCH STARS FROM THE TWO-DEGREE FIELD QUASAR REDSHIFT SURVEY

    SciTech Connect

    De Propris, Roberto; Harrison, Craig D.; Mares, Peter J.

    2010-08-20

    We use 666 blue horizontal branch stars from the 2Qz Redshift Survey to map the Galactic halo in four dimensions (position, distance, and velocity). We find that the halo extends to at least 100 kpc in Galactocentric distance, and obeys a single power-law density profile of index {approx}-2.5 in two different directions separated by about 150{sup 0} on the sky. This suggests that the halo is spherical. Our map shows no large kinematically coherent structures (streams, clouds, or plumes) and appears homogeneous. However, we find that at least 20% of the stars in the halo reside in substructures and that these substructures are dynamically young. The velocity dispersion profile of the halo appears to increase toward large radii while the stellar velocity distribution is non-Gaussian beyond 60 kpc. We argue that the outer halo consists of a multitude of low luminosity overlapping tidal streams from recently accreted objects.

  16. Inflow of halo gas from the direction of the Galactic north pole

    NASA Technical Reports Server (NTRS)

    De Boer, K. S.; Savage, B. D.

    1984-01-01

    A far-UV echelle spectrum has been obtained of the UV-bright star vZ1128 in the globular cluster M3. This cluster lies in a direction 11 deg off the Galactic north pole at a distance of about 10 kpc. Only the usually strong interstellar lines are recognizable in the faint spectrum, and they show absorption at velocities from near +40 km/s to -100 km/s. Since in the direction observed the line-of-sight component of the Milky Way rotation is negligible, the detected velocities demonstrate for this direction the motion of gas from the Milky Way halo toward the disk. Gas returning to the disk in a galactic fountainlike flow may explain the observations.

  17. Emission from the Local Galactic Halo in the 1/4 keV Band

    NASA Astrophysics Data System (ADS)

    Juda, M.

    1994-12-01

    Pointed observations with the ROSAT PSPC toward clouds at high galactic latitude provide a unique opportunity to probe emission from the local galactic halo in the 1/4 keV band. I present data from five fields toward clouds at |b| > 60(deg) identified through their IRAS 100 microns emission, two in the north galactic hemisphere and three in the south. In four of the five fields significant shadows are detected (2 north, 2 south). The derivation of the brightness of the shadowed component depends strongly on the assumed location and amount of absorbing material. Scaling the IRAS 100 microns emission by 10(20) H atom cm(-2) /MJy sr(-1) and correcting for the difference from the observed average 21 cm derived column density, the implied brightness of the distant emitting component is the same for the two northern latitude fields at { ~ 1.2*E(-3) counts s(-1) arcmin(-2}) ; this brightness is lower than that seen in the direction of Draco (Burrows & Mendenhall 1991, Snowden et al. 1991) and higher than in Ursa Major (Snowden et al. 1994). The two southern fields also have the same derived distant brightness at nearly the same level as the northern fields, { ~ 1.0*E(-3) counts s(-1) arcmin(-2}) . Approximately 20% of this emission may be attributed to an extragalactic background (Hasinger et al. 1993). The remaining emission, { ~ 0.8*E(-3) counts s(-1) arcmin(-2}) , would be provided by the local galactic halo. If these x-rays arise from a collisionally excited plasma at a temperature of 10(6) K the required emission measure is { ~ 0.0033 cm(-6) pc}. Burrows & Mendenhall 1991, Nature, 351, 629. Hasinger et al. 1993, A&A, 275, 1. Snowden et al. 1991, Science, 252, 1529. Snowden et al. 1994, ApJ, 430, 601.

  18. The interaction of high-velocity clouds with the galactic halo gas

    NASA Astrophysics Data System (ADS)

    Kerp, J.; Kalberla, P. M. W.

    The analysis of the new Leiden/Dwingeloo 21-cm line and the ROSAT all-sky-survey data provided evidence for the interaction of high-velocity clouds (HVCs) with the gas of the galactic halo. The quantitative correlation of both surveys gave evidence that the Milky Way is enclosed within a gaseous halo with a vertical scale height of 4.4 kpc and a radial scale length of 15 kpc. Within this gaseous halo, soft X-ray plasma (T ~= 10^{6.2} K) as well as cold neutral atomic hydrogen seems to coexist. Using this gaseous halo model we can derive the intensity distribution of the soft X-ray background across the entire sky. However, towards the prominent HVC complexes we found excess soft X-ray emission. These areas of enhanced X-ray emission are by a factor of 2 to 3 brighter than the total ``calm'' SXRB intensity. These soft X-ray enhancements, as well as the recently detected H alpha-emission of HVCs may indicate that the HVCs interact with their environment. In the X-ray regime the excess radiation releases about 1036 {erg}/{s}. Compared to the kinetic energy of an HVC complex with MHVC ~= 10^6 - 10^7 M_{\\odot} and Ekin ~= 1053 - 1054 {erg}/{s}, only a tiny fraction of the HVCs motion is transferred into heating of the HVC material. Our results indicate that the HVC matter itself is heated up, not only the surrounding gaseous halo medium, because the determined emission measures of EM ~= 0.015 cm^{-6} pc (T ~= 10^{6.2} - 10^{6.3}) K are an order of magnitude larger than the surrounding volume density.

  19. 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.

  20. V474 Car: A RARE HALO RS CVn BINARY IN RETROGRADE GALACTIC ORBIT

    SciTech Connect

    Bubar, Eric J.; Mamajek, Eric E.; Jensen, Eric L. N.; Walter, Frederick M.

    2011-04-15

    We report the discovery that the star V474 Car is an extremely active, high velocity halo RS CVn system. The star was originally identified as a possible pre-main-sequence star in Carina, given its enhanced stellar activity, rapid rotation (10.3 days), enhanced Li, and absolute magnitude which places it above the main sequence (MS). However, its extreme radial velocity (264 km s{sup -1}) suggested that this system was unlike any previously known pre-MS system. Our detailed spectroscopic analysis of echelle spectra taken with the CTIO 4 m finds that V474 Car is both a spectroscopic binary with an orbital period similar to the photometric rotation period and metal-poor ([Fe/H] {approx_equal}-0.99). The star's Galactic orbit is extremely eccentric (e {approx_equal} 0.93) with a perigalacticon of only {approx}0.3 kpc of the Galactic center-and the eccentricity and smallness of its perigalacticon are surpassed by only {approx}0.05% of local F/G-type field stars. The observed characteristics are consistent with V474 Car being a high-velocity, metal-poor, tidally locked, chromospherically active binary, i.e., a halo RS CVn binary, and one of only a few such specimens known.

  1. The Milky Way Halo and the First Stars: New Frontiers in Galactic Archaeology

    NASA Astrophysics Data System (ADS)

    Beers, Timothy C.; Tumlinson, Jason; O'Shea, Brian; Peruta, Carolyn; Carollo, Daniela

    2010-11-01

    We discuss plans for a new joint effort between observers and theorists to understand the formation of the Milky Way halo back to the first epochs of chemical evolution. New models based on high-resolution N-body simulations coupled to simple models of Galactic chemical evolution show that surviving stars from the epoch of the first galaxies remain in the Milky Way today and should bear the nucleosynthetic imprint of the first stars. We investigate the key physical influences on the formation of stars in the first galaxies and how they appear today, including the relationship between cosmic reionization and surviving Milky Way stars. These models also provide a physically motivated picture of the formation of the Milky Ways “outer halo,” which has been identified from recent large samples of stars from SDSS. The next steps are to use these models to guide rigorous gas simulations of Milky Way formation, including its disk, and to gradually build up the fully detailed theoretical “Virtual Galaxy” that is demanded by the coming generation of massive Galactic stellar surveys.

  2. The Abundance Pattern of Two Barium Stars in the Galactic Halo: HD 104340 and HD 206983

    NASA Astrophysics Data System (ADS)

    Junqueira, S.; Pereira, C. B.

    2001-07-01

    We present the abundance pattern of two barium stars in the Galactic halo, HD 104340 and HD 206983, based on high-resolution optical spectra. We also determined the spectroscopic stellar atmospheric parameters, temperature, and microturbulent velocity, as well as stellar surface gravity from a solution of excitation and ionization equilibria of Fe I and Fe II lines under the assumption of local thermodynamic equilibrium. The abundance analysis reveals HD 104340 to be a metal-poor K giant with [Fe/H]=-1.72 and HD 206983 also a metal-poor K giant with [Fe/H]=-1.43. From a set of Fe I lines, the radial velocity is found to be 263.3+/-0.6 km s-1 and -319.2+/-4.4 km s-1 for HD 104340 and HD 206983, respectively. Their high velocity, low metallicity, and high galactic latitude imply that both stars are members of a Galactic halo population. From our study and by using information from the literature we believe that HD 206983 is another member of a group known as metal-deficient barium stars. We compare the abundance pattern with the abundances of a halo population. We found that the abundances of the iron group, α-elements, manganese, copper, and zinc, as well as sodium and magnesium, of HD 104340 and HD 206983 follow the abundance pattern of a halo population. The heavy element abundance pattern of both stars shows enhancement by a factor of 4-8 with respect to the metal-poor stars with the same metallicity as that analyzed by us. We also discuss the abundances of the s-process elements and compare our results with other objects that display the same degree of enrichment due to neutron capture reactions, binary systems, and AGB stars, through a diagram of metallicity versus neutron exposure given by the [hs/ls] index. Based on the observations made with the 1.52 m telescope at the European Southern Observatory (La Silla, Chile) under agreement with Observatório Nacional (Brazil).

  3. Galactic and Intergalactic Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Klein, U.; Fletcher, A.

    This course-tested textbook conveys the fundamentals of magnetic fields and relativistic plasma in diffuse cosmic media, with a primary focus on phenomena that have been observed at different wavelengths. Theoretical concepts are addressed wherever necessary, with derivations presented in sufficient detail to be generally accessible. In the first few chapters the authors present an introduction to various astrophysical phenomena related to cosmic magnetism, with scales ranging from molecular clouds in star-forming regions and supernova remnants in the Milky Way, to clusters of galaxies. Later chapters address the role of magnetic fields in the evolution of the interstellar medium, galaxies and galaxy clusters. The book is intended for advanced undergraduate and postgraduate students in astronomy and physics and will serve as an entry point for those starting their first research projects in the field.

  4. Formation of a Giant Galactic Gaseous Halo: Metal-Absorption Lines and High-Velocity Clouds

    NASA Astrophysics Data System (ADS)

    Li, Fan

    1992-04-01

    A Galactic gaseous halo formed through the interstellar disk-halo connection is simulated by means of a two-dimensional axisymmetric hydrodynamic code based upon the chimney model of the interstellar medium, a new version of the galactic fountain. Galactic rotation, heating processes by diffuse UV flux, and radiative cooling processes are taken into account. The resulting gaseous halo can be divided into three categories, i.e., wind-type halo, bound-type halo, and cooled-type halo. In this way, we try to reproduce the column densities of C IV, N V, O VI, and Si IV in the observed absorption lines of halo stars. Assuming that the radiatively cooled halo gas condenses into clouds due to thermal instabilities, we can calculate their distribution and ballistic motions in the Galactic gravitational field. These correspond to the high- and intermediate-velocity clouds observed at high Galactic latitudes. We find that a cooled-type halo with a gas temperature between 5 X 10^5 and 10^6 K and a density between 10^-3 and 10^-2 cm^-3 at the disk-halo interface can reproduce the observational facts about our Galaxy. Supposing that the metal-absorption-line systems of QSOs arise from the halos of intervening galaxies formed by similar processes, we calculate features of the Ca II, Mg II, C IV, and Si IV absorption lines in various stages of galactic evolution. We conclude that C IV systems which are greater than 50 kpc in size correspond to the wind-type halo. On the other hand, Mg II and Ca II systems can only be detected in a very restricted region ( Metaxa, SMALL FAINT CLUSTERS IN THE LMC This is a short review of the main results of my Ph.D. thesis concerning some important problems on the dynamical properties of the LMC star clusters. The topic of this thesis was to find and study the dynamical paramters (tidal radius r_t core radius r_c concentration parameters log (r_t/r_c), and total mass M) for a large sample of small LMC clusters and to define their location in the

  5. Supernova explosions in magnetized, primordial dark matter haloes

    NASA Astrophysics Data System (ADS)

    Seifried, D.; Banerjee, R.; Schleicher, D.

    2014-05-01

    The first supernova explosions are potentially relevant sources for the production of the first large-scale magnetic fields. For this reason, we present a set of high-resolution simulations studying the effect of supernova explosions on magnetized, primordial haloes. We focus on the evolution of an initially small-scale magnetic field formed during the collapse of the halo. We vary the degree of magnetization, the halo mass, and the amount of explosion energy in order to account for expected variations as well as to infer systematical dependences of the results on initial conditions. Our simulations suggest that core collapse supernovae with an explosion energy of 1051 erg and more violent pair instability supernovae with 1053 erg are able to disrupt haloes with masses up to about 106 and 107 M⊙, respectively. The peak of the magnetic field spectra shows a continuous shift towards smaller k-values, i.e. larger length scales, over time reaching values as low as k = 4. On small scales, the magnetic energy decreases at the cost of the energy on large scales resulting in a well-ordered magnetic field with a strength up to ˜10-8 G depending on the initial conditions. The coherence length of the magnetic field inferred from the spectra reaches values up to 250 pc in agreement with those obtained from autocorrelation functions. We find the coherence length to be as large as 50 per cent of the radius of the supernova bubble. Extrapolating this relation to later stages, we suggest that significantly strong magnetic fields with coherence lengths as large as 1.5 kpc could be created. We discuss possible implications of our results on processes like recollapse of the halo, first galaxy formation, and the magnetization of the intergalactic medium.

  6. HOT GAS IN THE GALACTIC THICK DISK AND HALO NEAR THE DRACO CLOUD

    SciTech Connect

    Shelton, R. L.; Henley, D. B.; Dixon, W. V. E-mail: dbh@physast.uga.ed

    2010-10-10

    This paper examines the ultraviolet and X-ray photons generated by hot gas in the Galactic thick disk or halo in the Draco region of the northern hemisphere. Our analysis uses the intensities from four ions, C IV, O VI, O VII, and O VIII, sampling temperatures of {approx}10{sup 5} to {approx}3 x 10{sup 6} K. We measured the O VI, O VII, and O VIII intensities from FUSE and XMM-Newton data and subtracted off the local contributions in order to deduce the thick disk/halo contributions. These were supplemented with published C IV intensity and O VI column density measurements. Our estimate of the thermal pressure in the O VI-rich thick disk/halo gas, p{sub th}/k = 6500{sup +2500}{sub -2600} K cm{sup -3}, suggests that the thick disk/halo is more highly pressurized than would be expected from theoretical analyses. The ratios of C IV to O VI to O VII to O VIII intensities were compared with those predicted by theoretical models. Gas which was heated to 3 x 10{sup 6} K then allowed to cool radiatively cannot produce enough C IV or O VI-generated photons per O VII or O VIII-generated photon. Producing enough C IV and O VI emission requires heating additional gas to 10{sup 5} K < T < 10{sup 6} K. However, shock heating, which provides heating across this temperature range, overproduces O VI relative to the others. Obtaining the observed mix may require a combination of several processes, including some amount of shock heating, heat conduction, and mixing, as well as radiative cooling of very hot gas.

  7. The angular clustering of WISE-selected active galactic nuclei: Different halos for obscured and unobscured active galactic nuclei

    SciTech Connect

    Donoso, E.; Yan, Lin; Stern, D.; Assef, R. J.

    2014-07-01

    We calculate the angular correlation function for a sample of ∼170,000 active galactic nuclei (AGNs) extracted from the Wide-field Infrared Survey Explorer (WISE) catalog, selected to have red mid-IR colors (W1 – W2 > 0.8) and 4.6 μm flux densities brighter than 0.14 mJy). The sample is expected to be >90% reliable at identifying AGNs and to have a mean redshift of (z) = 1.1. In total, the angular clustering of WISE AGNs is roughly similar to that of optical AGNs. We cross-match these objects with the photometric Sloan Digital Sky Survey catalog and distinguish obscured sources with r – W2 > 6 from bluer, unobscured AGNs. Obscured sources present a higher clustering signal than unobscured sources. Since the host galaxy morphologies of obscured AGNs are not typical red sequence elliptical galaxies and show disks in many cases, it is unlikely that the increased clustering strength of the obscured population is driven by a host galaxy segregation bias. By using relatively complete redshift distributions from the COSMOS survey, we find that obscured sources at (z) ∼ 0.9 have a bias of b = 2.9 ± 0.6 and are hosted in dark matter halos with a typical mass of log (M/M {sub ☉} h {sup –1}) ∼ 13.5. In contrast, unobscured AGNs at (z) ∼ 1.1 have a bias of b = 1.6 ± 0.6 and inhabit halos of log (M/M {sub ☉} h {sup –1}) ∼ 12.4. These findings suggest that obscured AGNs inhabit denser environments than unobscured AGNs, and they are difficult to reconcile with the simplest AGN unification models, where obscuration is driven solely by orientation.

  8. Dynamics and X-Ray Emission of a Galactic Superwind Interacting with Disk and Halo Gas

    NASA Astrophysics Data System (ADS)

    Suchkov, A. A.; Balsara, D. S.; Heckman, T. M.; Leitherer, C.

    1993-12-01

    There is a general agreement that the conspicuous extranuclear x-ray, optical-line, and radio-continuum emission of starbursts is associated with powerful galactic superwinds blowing from their centers. However, despite the significant advances in observational studies of superwinds, there is no consensus on the nature of the emitting material and even on the emission mechanisms themselves. This is to a great extent a consequence of a poor understanding of dynamical processes in the starburst superwind regions. To address this issue, we have conducted two-dimensional hydrodynamical simulations of galactic superwinds. While previous similar studies have used a single (disk) component to represent the ISM of the starburst galaxy, we analyse the interaction of the wind with a two-component disk--halo ambient interstellar medium. This two-component representation is argued to be crucial for adequate modelling of starbursts. The emphasis of this study is on the geometry and structure of the wind region and the x-ray emission arising in the wind material and the shocked gas in the disk and the halo of the galaxy. The simulation results have shown that a clear-cut bipolar wind can easily develop under a range of very different conditions. On the other hand, a complex `filamentary' structure associated with the entrained dense disk material is found to arise within the hot bubble blown out by the wind. The flow pattern within the bubble is dominated equally by the central biconic outflow and a system of whirling motions related to the origin and development of the `filaments'. The `filament' parameters make them a good candidate for optical-emission-line filamentary gas observed in starburst halos. We find that the history of mass and energy deposition in the starburst region of the galaxy is crucial for wind dynamics. A ``mild'' early wind, which arises as a result of the cumulative effect of stellar winds from massive stars, produces a bipolar vertical cavity in the disk

  9. XMM-Newton Measurement of the Galactic Halo X-Ray Emission using a Compact Shadowing Cloud

    NASA Astrophysics Data System (ADS)

    Henley, David B.; Shelton, Robin L.; Cumbee, Renata S.; Stancil, Phillip C.

    2015-02-01

    Observations of interstellar clouds that cast shadows in the soft X-ray background can be used to separate the background Galactic halo emission from the local emission due to solar wind charge exchange (SWCX) and/or the Local Bubble (LB). We present an XMM-Newton observation of a shadowing cloud, G225.60-66.40, that is sufficiently compact that the on- and off-shadow spectra can be extracted from a single field of view (unlike previous shadowing observations of the halo with CCD-resolution spectrometers, which consisted of separate on- and off-shadow pointings). We analyzed the spectra using a variety of foreground models: one representing LB emission, and two representing SWCX emission. We found that the resulting halo model parameters (temperature T h ≈ 2 × 106 K, emission measure {E}h≈ 4 × 10-3 cm-6 pc) were not sensitive to the foreground model used. This is likely due to the relative faintness of the foreground emission in this observation. However, the data do favor the existence of a foreground. The halo parameters derived from this observation are in good agreement with those from previous shadowing observations, and from an XMM-Newton survey of the Galactic halo emission. This supports the conclusion that the latter results are not subject to systematic errors, and can confidently be used to test models of the halo emission.

  10. XMM-NEWTON MEASUREMENT OF THE GALACTIC HALO X-RAY EMISSION USING A COMPACT SHADOWING CLOUD

    SciTech Connect

    Henley, David B.; Shelton, Robin L.; Cumbee, Renata S.; Stancil, Phillip C.

    2015-02-01

    Observations of interstellar clouds that cast shadows in the soft X-ray background can be used to separate the background Galactic halo emission from the local emission due to solar wind charge exchange (SWCX) and/or the Local Bubble (LB). We present an XMM-Newton observation of a shadowing cloud, G225.60–66.40, that is sufficiently compact that the on- and off-shadow spectra can be extracted from a single field of view (unlike previous shadowing observations of the halo with CCD-resolution spectrometers, which consisted of separate on- and off-shadow pointings). We analyzed the spectra using a variety of foreground models: one representing LB emission, and two representing SWCX emission. We found that the resulting halo model parameters (temperature T {sub h} ≈ 2 × 10{sup 6} K, emission measure E{sub h}≈4×10{sup −3} cm{sup −6} pc) were not sensitive to the foreground model used. This is likely due to the relative faintness of the foreground emission in this observation. However, the data do favor the existence of a foreground. The halo parameters derived from this observation are in good agreement with those from previous shadowing observations, and from an XMM-Newton survey of the Galactic halo emission. This supports the conclusion that the latter results are not subject to systematic errors, and can confidently be used to test models of the halo emission.

  11. Domain wall model in the galactic Bose-Einstein condensate halo

    SciTech Connect

    Souza, J.C.C. de; Pires, M.O.C. E-mail: marcelo.pires@ufabc.edu.br

    2013-05-01

    We assume that the galactic dark matter halo, considered composed of an axionlike particles Bose-Einstein condensate [1], can present topological defects, namely domain walls, arising as the dark soliton solution for the Gross-Pitaevskii equation in a self-graviting potential. We investigate the influence that such substructures would have in the gravitational interactions within a galaxy. We find that, for the simple domain wall model proposed, the effects are too small to be identified, either by means of a local measurement of the gradient of the gravitational field or by analysing galaxy rotation curves. In the first case, the gradient of the gravitational field in the vicinity of the domain wall would be 10{sup −31} (m/s{sup 2})/m. In the second case, the ratio of the tangential velocity correction of a star due to the presence of the domain wall to the velocity in the spherical symmetric case would be 10{sup −8}.

  12. Light bending in the galactic halo by Rindler-Ishak method

    SciTech Connect

    Bhattacharya, Amrita; Nandi, Kamal K.; Isaev, Ruslan; Scalia, Massimo; Cattani, Carlo E-mail: subfear@gmail.com E-mail: ccattani@unisa.it

    2010-09-01

    After the work of Rindler and Ishak, it is now well established that the bending of light is influenced by the cosmological constant Λ appearing in the Schwarzschild-de Sitter spacetime. We show that their method, when applied to the exact Mannheim-Kazanas-de Sitter solution of the Weyl conformal gravity, nicely yields the expected answer together with several other physically interesting new terms. Apart from Λ, the solution is parametrized by a conformal parameter γ, which is known to play a dominant role in the galactic halo gravity. The application of the method yields exactly the same γ− correction to Schwarzschild bending as obtained by standard methods. Different cases are analyzed, which include some corrections to the special cases considered in the original paper by Rindler and Ishak.

  13. 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.

  14. Hot subdwarf stars in the Galactic halo Tracers of prominent events in late stellar evolution

    NASA Astrophysics Data System (ADS)

    Geier, Stephan; Kupfer, Thomas; Schaffenroth, Veronika; Heber, Ulrich

    2016-08-01

    Hot subdwarf stars (sdO/Bs) are the stripped cores of red giants located at the bluest extension of the horizontal branch. They constitute the dominant population of UV-bright stars in old stellar environments and are most likely formed by binary interactions. We perform the first systematic, spectroscopic analysis of a sample of those stars in the Galactic halo based on data from SDSS. In the course of this project we discovered 177 close binary candidates. A significant fraction of the sdB binaries turned out to have close substellar companions, which shows that brown dwarfs and planets can significantly influence late stellar evolution. Close hot subdwarf binaries with massive white dwarf companions on the other hand are good candidates for the progenitors of type Ia supernovae. We discovered a hypervelocity star, which not only turned out to be the fastest unbound star known in our Galaxy, but also the surviving companion of such a supernova explosion.

  15. Particle Dark Matter in the galactic halo: results from DAMA/LIBRA

    SciTech Connect

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

    2010-02-10

    The DAMA/LIBRA experiment at the Gran Sasso National Laboratory of the I.N.F.N. has confirmed with higher sensitivity the model independent evidence for Dark Matter (DM) particles in the galactic halo obtained by the former DAMA/NaI experiment by investigating the DM annual modulation signature. Considering the data collected by DAMA/LIBRA together with the data collected by the former DAMA/NaI (cumulative exposure of 0.82 tonxyr) a confidence level of 8.2 sigma has been achieved. The experiment is in data taking; a first upgrading of the set-up has been carried out in Spetember 2008 and a second one--aiming to decrease the experimental energy threshold--is foreseen in September 2010.

  16. Light bending in the galactic halo by Rindler-Ishak method

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Amrita; Isaev, Ruslan; Scalia, Massimo; Cattani, Carlo; Nandi, Kamal K.

    2010-09-01

    After the work of Rindler and Ishak, it is now well established that the bending of light is influenced by the cosmological constant Λ appearing in the Schwarzschild-de Sitter spacetime. We show that their method, when applied to the exact Mannheim-Kazanas-de Sitter solution of the Weyl conformal gravity, nicely yields the expected answer together with several other physically interesting new terms. Apart from Λ, the solution is parametrized by a conformal parameter γ, which is known to play a dominant role in the galactic halo gravity. The application of the method yields exactly the same γ- correction to Schwarzschild bending as obtained by standard methods. Different cases are analyzed, which include some corrections to the special cases considered in the original paper by Rindler and Ishak.

  17. Search for the Galactic Disk and Halo Components in the Arrival Directions of High-Energy Astrophysical Neutrinos

    NASA Astrophysics Data System (ADS)

    Troitsky, S. V.

    2015-12-01

    The arrival directions of 40 neutrino events with energies ≳100 TeV, observed by the IceCube experiment, are studied. Their distribution in the Galactic latitude and in the angular distance to the Galactic Center allow searching for the Milky-Way disk and halo-related components, respectively. No statistically significant evidence for the disk component is found, though even 100% disk origin of the flux is allowed at the 90% confidence level. Contrary, the Galactic Center-Anticenter dipole anisotropy, specific for dark-matter decays (annihilation) or for interactions of cosmic rays with the extended halo of the circumgalactic gas, is clearly favored over the isotropic distribution (the probability of fluctuation of the isotropic signal is ~2%).

  18. RR Lyrae in XSTPS: The halo density profile in the north galactic cap

    SciTech Connect

    Faccioli, L.; Smith, M. C.; Yuan, H.-B.; Liu, X.-W.; Zhang, H.-H.; Zhao, H.-B.; Yao, J.-S. E-mail: msmith@shao.ac.cn

    2014-06-20

    We present a catalog of RR Lyrae stars (RRLs) observed by the Xuyi Schmidt Telescope Photometric Survey (XSTPS). The area we consider is located in the north Galactic cap, covering ≈376.75 deg{sup 2} at α ≈ 150° and δ ≈ 27° down to a magnitude limit of i ≈ 19. Using the variability information afforded by the multi-epoch nature of our XSTPS data, combined with colors from the Sloan Digital Sky Survey, we are able to identify candidate RRLs. We find 318 candidates, derive distances to them, and estimate the detection efficiency. The majority of our candidates have more than 12 observations, and for these we are able to calculate periods. These also allow us to estimate our contamination level, which we predict is between 30% and 40%. Finally, we use the sample to probe the halo density profile in the 9-49 kpc range and find that it can be well fitted by a double power law. We find good agreement between this model and the models derived for the south Galactic cap using the Watkins et al. and Sesar et al. RRL data sets, after accounting for possible contamination in our data set from Sagittarius stream members. We consider non-spherical double power-law models of the halo density profile and again find agreement with literature data sets, although we have limited power to constrain the flattening due to our small survey area. Much tighter constraints will be placed by current and future wide-area surveys, most notably ESA's astrometric Gaia mission. Our analysis demonstrates that surveys with a limited number of epochs can effectively be mined for RRLs. Our complete sample is provided as accompanying online material; as an example the first few entries of each electronic table are shown in the text.

  19. RR Lyrae in XSTPS: The Halo Density Profile in the North Galactic Cap

    NASA Astrophysics Data System (ADS)

    Faccioli, L.; Smith, M. C.; Yuan, H.-B.; Zhang, H.-H.; Liu, X.-W.; Zhao, H.-B.; Yao, J.-S.

    2014-06-01

    We present a catalog of RR Lyrae stars (RRLs) observed by the Xuyi Schmidt Telescope Photometric Survey (XSTPS). The area we consider is located in the north Galactic cap, covering ≈376.75 deg2 at α ≈ 150° and δ ≈ 27° down to a magnitude limit of i ≈ 19. Using the variability information afforded by the multi-epoch nature of our XSTPS data, combined with colors from the Sloan Digital Sky Survey, we are able to identify candidate RRLs. We find 318 candidates, derive distances to them, and estimate the detection efficiency. The majority of our candidates have more than 12 observations, and for these we are able to calculate periods. These also allow us to estimate our contamination level, which we predict is between 30% and 40%. Finally, we use the sample to probe the halo density profile in the 9-49 kpc range and find that it can be well fitted by a double power law. We find good agreement between this model and the models derived for the south Galactic cap using the Watkins et al. and Sesar et al. RRL data sets, after accounting for possible contamination in our data set from Sagittarius stream members. We consider non-spherical double power-law models of the halo density profile and again find agreement with literature data sets, although we have limited power to constrain the flattening due to our small survey area. Much tighter constraints will be placed by current and future wide-area surveys, most notably ESA's astrometric Gaia mission. Our analysis demonstrates that surveys with a limited number of epochs can effectively be mined for RRLs. Our complete sample is provided as accompanying online material; as an example the first few entries of each electronic table are shown in the text.

  20. Deep brain transcranial magnetic stimulation using variable "Halo coil" system

    NASA Astrophysics Data System (ADS)

    Meng, Y.; Hadimani, R. L.; Crowther, L. J.; Xu, Z.; Qu, J.; Jiles, D. C.

    2015-05-01

    Transcranial Magnetic Stimulation has the potential to treat various neurological disorders non-invasively and safely. The "Halo coil" configuration can stimulate deeper regions of the brain with lower surface to deep-brain field ratio compared to other coil configurations. The existing "Halo coil" configuration is fixed and is limited in varying the site of stimulation in the brain. We have developed a new system based on the current "Halo coil" design along with a graphical user interface system that enables the larger coil to rotate along the transverse plane. The new system can also enable vertical movement of larger coil. Thus, this adjustable "Halo coil" configuration can stimulate different regions of the brain by adjusting the position and orientation of the larger coil on the head. We have calculated magnetic and electric fields inside a MRI-derived heterogeneous head model for various positions and orientations of the coil. We have also investigated the mechanical and thermal stability of the adjustable "Halo coil" configuration for various positions and orientations of the coil to ensure safe operation of the system.

  1. H II REGION DRIVEN GALACTIC BUBBLES AND THEIR RELATIONSHIP TO THE GALACTIC MAGNETIC FIELD

    SciTech Connect

    Pavel, Michael D.; Clemens, D. P. E-mail: clemens@bu.edu

    2012-12-01

    The relative alignments of mid-infrared traced Galactic bubbles are compared to the orientation of the mean Galactic magnetic field in the disk. The orientations of bubbles in the northern Galactic plane were measured and are consistent with random orientations-no preferential alignment with respect to the Galactic disk was found. A subsample of H II region driven Galactic bubbles was identified, and as a single population they show random orientations. When this subsample was further divided into subthermal and suprathermal H II regions, based on hydrogen radio recombination linewidths, the subthermal H II regions showed a marginal deviation from random orientations, but the suprathermal H II regions showed significant alignment with the Galactic plane. The mean orientation of the Galactic disk magnetic field was characterized using new near-infrared starlight polarimetry and the suprathermal H II regions were found to preferentially align with the disk magnetic field. If suprathermal linewidths are associated with younger H II regions, then the evolution of young H II regions is significantly affected by the Galactic magnetic field. As H II regions age, they cease to be strongly linked to the Galactic magnetic field, as surrounding density variations come to dominate their morphological evolution. From the new observations, the ratios of magnetic-to-ram pressures in the expanding ionization fronts were estimated for younger H II regions.

  2. Probing the galactic disk and halo. 1: The NGC 3783 sight line

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    We report a study of Galactic disk and halo absorption toward the Seyfert galaxy NGC 3783 which has Galactic coordinates l = 287.46 and b = +22.95. The data were obtained with the Goddard High Resolution Spectrograph operating at medium resolution with the Large Science Aperture, which produces a line spread function having a sharp core (full width at half maximum (FWHM) approximately 20 km/s) and broad wings extending to +/- 70 km/s. Ion species detected in absorption near zero LSR velocity include C IV and N V for high ions, and C I, Mg II, Si II, and S II for low ions. Absorption from a high-velocity cloud (HVC) at a velocity of +240 km/s along the sight line is also detected in the ion species of S II, Si II, and probably C I. This is the first reported case where S II and C I absorption has been detected in a HVC. The S II lines are especially useful since metal abundance estimates based on S are largely unaffected by dust grains. The study is aided by the availability of 21 cm emission data.

  3. THE ORIGIN OF THE HOT GAS IN THE GALACTIC HALO: CONFRONTING MODELS WITH XMM-NEWTON OBSERVATIONS

    SciTech Connect

    Henley, David B.; Shelton, Robin L.; Kwak, Kyujin; Joung, M. Ryan; Mac Low, Mordecai-Mark

    2010-11-01

    We compare the predictions of three physical models for the origin of the hot halo gas with the observed halo X-ray emission, derived from 26 high-latitude XMM-Newton observations of the soft X-ray background between l = 120{sup 0} and l = 240{sup 0}. These observations were chosen from a much larger set of observations as they are expected to be the least contaminated by solar wind charge exchange emission. We characterize the halo emission in the XMM-Newton band with a single-temperature plasma model. We find that the observed halo temperature is fairly constant across the sky ({approx}(1.8-2.4) x 10{sup 6} K), whereas the halo emission measure varies by an order of magnitude ({approx}0.0005-0.006 cm{sup -6} pc). When we compare our observations with the model predictions, we find that most of the hot gas observed with XMM-Newton does not reside in isolated extraplanar supernova (SN) remnants-this model predicts emission an order of magnitude too faint. A model of an SN-driven interstellar medium, including the flow of hot gas from the disk into the halo in a galactic fountain, gives good agreement with the observed 0.4-2.0 keV surface brightness. This model overpredicts the halo X-ray temperature by a factor of {approx}2, but there are a several possible explanations for this discrepancy. We therefore conclude that a major (possibly dominant) contributor to the halo X-ray emission observed with XMM-Newton is a fountain of hot gas driven into the halo by disk SNe. However, we cannot rule out the possibility that the extended hot halo of accreted material predicted by disk galaxy formation models also contributes to the emission.

  4. The role of neutron star mergers in the chemical evolution of the Galactic halo

    NASA Astrophysics Data System (ADS)

    Cescutti, G.; Romano, D.; Matteucci, F.; Chiappini, C.; Hirschi, R.

    2015-05-01

    Context. The dominant astrophysical production site of the r-process elements has not yet been unambiguously identified. The suggested main r-process sites are core-collapse supernovae and merging neutron stars. Aims: We explore the problem of the production site of Eu. We also use the information present in the observed spread in the Eu abundances in the early Galaxy, and not only its average trend. Moreover, we extend our investigations to other heavy elements (Ba, Sr, Rb, Zr) to provide additional constraints on our results. Methods: We adopt a stochastic chemical evolution model that takes inhomogeneous mixing into account. The adopted yields of Eu from merging neutron stars and from core-collapse supernovae are those that are able to explain the average [Eu/Fe]-[Fe/H] trend observed for solar neighbourhood stars, the solar abundance of Eu, and the present-day abundance gradient of Eu along the Galactic disc in the framework of a well-tested homogeneous model for the chemical evolution of the Milky Way. Rb, Sr, Zr, and Ba are produced by both the s- and r-processes. The r-process yields were obtained by scaling the Eu yields described above according to the abundance ratios observed in r-process rich stars. The s-process contribution by spinstars is the same as in our previous papers. Results: Neutron star binaries that merge in less than 10 Myr or neutron star mergers combined with a source of r-process generated by massive stars can explain the spread of [Eu/Fe] in the Galactic halo. The combination of r-process production by neutron star mergers and s-process production by spinstars is able to reproduce the available observational data for Sr, Zr, and Ba. We also show the first predictions for Rb in the Galactic halo. Conclusions: We confirm previous results that either neutron star mergers on a very short timescale or both neutron star mergers and at least a fraction of Type II supernovae have contributed to the synthesis of Eu in the Galaxy. The r

  5. 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.

  6. The Century Survey Galactic Halo Project III: A Complete 4300 DEG2 Survey of Blue Horizontal Branch Stars in the Metal-Weak Thick Disk and Inner Halo

    NASA Astrophysics Data System (ADS)

    Brown, Warren R.; Beers, Timothy C.; Wilhelm, Ronald; Allende Prieto, Carlos; Geller, Margaret J.; Kenyon, Scott J.; Kurtz, Michael J.

    2008-02-01

    We present a complete spectroscopic survey of 2414 2MASS-selected blue horizontal branch (BHB) candidates selected over 4300 deg2 of the sky. We identify 655 BHB stars in this non-kinematically selected sample. We calculate the luminosity function of field BHB stars, and find evidence for very few hot BHB stars in the field. The BHB stars located at a distance from the Galactic plane |Z| < 4 kpc trace what is clearly a metal-weak thick disk population, with a mean metallicity of [Fe/H] = -1.7, a rotation velocity gradient of dvrot/d|Z| = -28 ± 3.4 km s-1 in the region |Z| < 6 kpc, and a density scale height of hZ = 1.26 ± 0.1 kpc. The BHB stars located at 5 < |Z| < 9 kpc are a predominantly inner-halo population, with a mean metallicity of [Fe/H] = -2.0 and a mean Galactic rotation of -4 ± 31 km s-1. We infer the density of halo and thick disk BHB stars is 104 ± 37 kpc-3 near the Sun, and the relative normalization of halo to thick-disk BHB stars is 4 ± 1% near the Sun.

  7. Magnetic Field Generation in Galactic Plasmas

    NASA Astrophysics Data System (ADS)

    Opher, Merav; Cowley, Steve; Maron, Jason; McWilliams, James

    2000-10-01

    The origin of the magnetic field in the universe is one of the great problems in astrophysics. The observed magnetic fields in spiral galaxies, for example, are of the order of microgauss and are coherent over galactic scales. It is usually assumed that turbulent fluid motions will enhance a seed field. In the present work we investigate the growth of the magnetic field in plasmas with high magnetic Prandtl number (the ratio of viscosity to resistivity). This growth occurs initially at scales below the viscous scale [1]. Kinney et al. [2] showed that in 2D the field saturates at an amplitude independent of the mean scale of the field. We discuss the initial growth in the three dimensional case where the dynamics of the field are on scales less than the viscosity scale [3]. At low initial field, the field grows and the scale decreases until the resistive scale is reached. The field then grows at a reduced rate until it reaches an equilibrium with the mean scale at a resistive scale. At higher initial amplitude, the field saturates before the mean scale has decreased to the resistive scale. The subsequent evolution is a slow decrease of the scale to the resistive scale, at which point it reaches equilibrium and stops evolving. To explain the large scale coherence of galactic fields, an inverse cascade is necessary. There is no evidence of an inverse cascade. We will present results for extended physics models including tensor viscosity and ambipular diffusion. [1] R. Kulsrud, and S. Anderson, Astrophys. J., 396, 606 (1992); A. Gruzinov, S. Cowley, and R. Sudan, Phys.Rev.Lett., 77, 4342 (1996). [2] R. M. Kinney, B. Chandran, S. Cowley, J. C. McWilliams, Astrophys. J., accepted to publication (2000). [3] M. Opher, S. Cowley, R. M. Kinney, B. Chandran, J. Maron and J.C. McWilliams, in preparation (2000).

  8. Magnetic Field Generation in Galactic Plasmas

    NASA Astrophysics Data System (ADS)

    Opher, M.; Cowley, S.; Schekochihin, A.; Kinney, R. M.; Chandran, B.; Maron, J.; McWilliams, J. C.

    2001-05-01

    The origin of the magnetic field in the universe is one of the great problems in astrophysics. The observed magnetic fields in spiral galaxies, for example, are of the order of microgauss and are coherent over galactic scales. Its is usually assumed that turbulent fluid motions will enhance a seed field. In the present work we invetigate the growth of the magnetic field in plasmas with high magnetic Prandtl number (the ratio of viscosity to resistivity). This growth occur initially at scales below the viscous scale [1]. Kinney et al. [2] showed that in 2D the field saturates at an amplitude independent of the mean scale of the field. We discuss the initial growth in the three dimensional case where the dynamics of the field on scales less than the viscosity scale [3]. At low initial field, the field grows and the scale decreases until the resistive scale is reached. The field then grows at a reduced rate until it reaches an equilibrium with the mean scale at a resistive scale. At higher initial amplitude, the field saturates before the mean scale has decreased to the resistive scale. The subsequent evolution is a slow decrease of the scale to the resistive scale, at which point it reaches equilibrium and stops evolving. To explain the large scale coherence of galactic fields, an inverse cascade is necessary. There is no evidence of an inverse cascade. We will present results for extended physics models including tensor viscosity and ambipular diffusion. [1] R. Kulsrud, and S. Anderson, Astrophys. J., 396, 606 (1992); A. Gruzinov, S. Cowley, and R. Sudan, Phys.Rev.Lett., 77, 4342 (1996). [2] R. M. Kinney, B. Chandran, S. Cowley, J. C. McWilliams, Astrophys. J., accepted to publication (2000). [3] M. Opher, S. Cowley, A. Schekochihin, R. M. Kinney, B. Chandran, J. Maron and J.C. McWilliams, in preparation (2001).

  9. A study of ultraviolet absorption lines through the complete Galactic halo by the analysis of HST faint object spectrograph spectra of active Galactic nuclei, 1

    NASA Technical Reports Server (NTRS)

    Burks, Geoffrey S.; Bartko, Frank; Shull, J. Michael; Stocke, John T.; Sachs, Elise R.; Burbidge, E. Margaret; Cohen, Ross D.; Junkkarinen, Vesa T.; Harms, Richard J.; Massa, Derck

    1994-01-01

    The ultraviolet (1150 - 2850 A) spectra of a number of active galactic nuclei (AGNs) observed with the Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) have been used to study the properties of the Galactic halo. The objects that served as probes are 3C 273, PKS 0454-220, Pg 1211+143, CSO 251, Ton 951, and PG 1351+640. The equivalent widths of certain interstellar ions have been measured, with special attention paid to the C IV/C II and Si IV/Si II ratios. These ratios have been intercompared, and the highest values are found in the direction of 3C 273, where C IV/C II = 1.2 and Si IV/Si II greater than 1. These high ratios may be due to a nearby supernova remnant, rather than to ionized gas higher up in the Galactic halo. Our data give some support to the notion that QSO metal-line systems may arise from intervening galaxies which contain high supernova rates, galactic fountains, and turbulent mixing layers.

  10. F TURNOFF DISTRIBUTION IN THE GALACTIC HALO USING GLOBULAR CLUSTERS AS PROXIES

    SciTech Connect

    Newby, Matthew; Newberg, Heidi Jo; Simones, Jacob; Cole, Nathan; Monaco, Matthew E-mail: heidi@rpi.edu

    2011-12-20

    F turnoff stars are important tools for studying Galactic halo substructure because they are plentiful, luminous, and can be easily selected by their photometric colors from large surveys such as the Sloan Digital Sky Survey (SDSS). We describe the absolute magnitude distribution of color-selected F turnoff stars, as measured from SDSS data, for 11 globular clusters in the Milky Way halo. We find that the M{sub g} distribution of turnoff stars is intrinsically the same for all clusters studied, and is well fit by two half-Gaussian functions, centered at {mu} = 4.18, with a bright-side {sigma} = 0.36, and with a faint-side {sigma} = 0.76. However, the color errors and detection efficiencies cause the observed {sigma} of the faint-side Gaussian to change with magnitude due to contamination from redder main-sequence stars (40% at 21st magnitude). We present a function that will correct for this magnitude-dependent change in selected stellar populations, when calculating stellar density from color-selected turnoff stars. We also present a consistent set of distances, ages, and metallicities for 11 clusters in the SDSS Data Release 7. We calculate a linear correction function to Padova isochrones so that they are consistent with SDSS globular cluster data from previous papers. We show that our cluster population falls along the Milky Way age-metallicity relationship (AMR), and further find that isochrones for stellar populations on the AMR have very similar turnoffs; increasing metallicity and decreasing age conspire to produce similar turnoff magnitudes and colors for all old clusters that lie on the AMR.

  11. F Turnoff Distribution in the Galactic Halo Using Globular Clusters as Proxies

    NASA Astrophysics Data System (ADS)

    Newby, Matthew; Newberg, H. J.; Simones, J.; Monaco, M.; Cole, N.

    2012-01-01

    F turnoff stars are important tools for studying Galactic halo substructure because they are plentiful, luminous, and can be easily selected by their photometric colors from large surveys such as the Sloan Digital Sky Survey (SDSS). We describe the absolute magnitude distribution of color-selected F turnoff stars, as measured from SDSS data, for eleven globular clusters in the Milky Way halo. We find that the absolute magnitude distribution of turnoff stars is intrinsically the same for all clusters studied, and is well fit by two half Gaussian functions, centered at μ = 4.18, with a bright-side σ = 0.36, and with a faint-side σ = 0.76. However, the color errors and detection efficiencies cause the observed σ of the faint-side Gaussian to change with magnitude due to contamination from redder main sequence stars (40% at 21st magnitude). We present a function that will correct for this magnitude-dependent change in selected stellar populations, when calculating stellar density from color-selected turnoff stars. We also present a consistent set of distances, ages and metallicities for eleven clusters in the SDSS Data Release 7. We calculate a linear correction function to Padova isochrones so that they are consistent with SDSS globular cluster data from previous papers. We show that our cluster population falls along the theoretical Age-Metallicity Relationship (AMR), and further find that isochrones for stellar populations on the AMR have very similar turnoffs; increasing metallicity and decreasing age conspire to produce similar turnoff magnitudes and colors for all old clusters that lie on the AMR. This research was supported by NSF grant AST 10-09670 and the NASA/NY Space Grant.

  12. F Turnoff Distribution in the Galactic Halo Using Globular Clusters as Proxies

    NASA Astrophysics Data System (ADS)

    Newby, Matthew; Newberg, Heidi Jo; Simones, Jacob; Cole, Nathan; Monaco, Matthew

    2011-12-01

    F turnoff stars are important tools for studying Galactic halo substructure because they are plentiful, luminous, and can be easily selected by their photometric colors from large surveys such as the Sloan Digital Sky Survey (SDSS). We describe the absolute magnitude distribution of color-selected F turnoff stars, as measured from SDSS data, for 11 globular clusters in the Milky Way halo. We find that the Mg distribution of turnoff stars is intrinsically the same for all clusters studied, and is well fit by two half-Gaussian functions, centered at μ = 4.18, with a bright-side σ = 0.36, and with a faint-side σ = 0.76. However, the color errors and detection efficiencies cause the observed σ of the faint-side Gaussian to change with magnitude due to contamination from redder main-sequence stars (40% at 21st magnitude). We present a function that will correct for this magnitude-dependent change in selected stellar populations, when calculating stellar density from color-selected turnoff stars. We also present a consistent set of distances, ages, and metallicities for 11 clusters in the SDSS Data Release 7. We calculate a linear correction function to Padova isochrones so that they are consistent with SDSS globular cluster data from previous papers. We show that our cluster population falls along the Milky Way age-metallicity relationship (AMR), and further find that isochrones for stellar populations on the AMR have very similar turnoffs; increasing metallicity and decreasing age conspire to produce similar turnoff magnitudes and colors for all old clusters that lie on the AMR.

  13. A Method for Deriving Accurate Gas-Phase Abundances for the Multiphase Interstellar Galactic Halo

    NASA Astrophysics Data System (ADS)

    Howk, J. Christopher; Sembach, Kenneth R.; Savage, Blair D.

    2006-01-01

    We describe a new method for accurately determining total gas-phase abundances for the Galactic halo interstellar medium with minimal ionization uncertainties. For sight lines toward globular clusters containing both ultraviolet-bright stars and radio pulsars, it is possible to measure column densities of H I and several ionization states of selected metals using ultraviolet absorption line measurements and of H II using radio dispersion measurements. By measuring the ionized hydrogen column, we minimize ionization uncertainties that plague abundance measurements of Galactic halo gas. We apply this method for the first time to the sight line toward the globular cluster Messier 3 [(l,b)=(42.2d,+78.7d), d=10.2 kpc, z=10.0 kpc] using Far Ultraviolet Spectroscopic Explorer and Hubble Space Telescope ultraviolet spectroscopy of the post-asymptotic giant branch star von Zeipel 1128 and radio observations by Ransom et al. of recently discovered millisecond pulsars. The fraction of hydrogen associated with ionized gas along this sight line is 45%+/-5%, with the warm (T~104 K) and hot (T>~105 K) ionized phases present in roughly a 5:1 ratio. This is the highest measured fraction of ionized hydrogen along a high-latitude pulsar sight line. We derive total gas-phase abundances logN(S)/N(H)=-4.87+/-0.03 and logN(Fe)/N(H)=-5.27+/-0.05. Our derived sulfur abundance is in excellent agreement with recent solar system determinations of Asplund, Grevesse, & Sauval. However, it is -0.14 dex below the solar system abundance typically adopted in studies of the interstellar medium. The iron abundance is ~-0.7 dex below the solar system abundance, consistent with the significant incorporation of iron into interstellar grains. Abundance estimates derived by simply comparing S II and Fe II to H I are +0.17 and +0.11 dex higher, respectively, than the abundance estimates derived from our refined approach. Ionization corrections to the gas-phase abundances measured in the standard way are

  14. Magnetic fields and galactic star formation rates

    SciTech Connect

    Loo, Sven Van; Tan, Jonathan C.; Falle, Sam A. E. G.

    2015-02-10

    The regulation of galactic-scale star formation rates (SFRs) is a basic problem for theories of galaxy formation and evolution: which processes are responsible for making observed star formation rates so inefficient compared to maximal rates of gas content divided by dynamical timescale? Here we study the effect of magnetic fields of different strengths on the evolution of giant molecular clouds (GMCs) within a kiloparsec patch of a disk galaxy and resolving scales down to ≃0.5 pc. Including an empirically motivated prescription for star formation from dense gas (n{sub H}>10{sup 5} cm{sup −3}) at an efficiency of 2% per local free-fall time, we derive the amount of suppression of star formation by magnetic fields compared to the nonmagnetized case. We find GMC fragmentation, dense clump formation, and SFR can be significantly affected by the inclusion of magnetic fields, especially in our strongest investigated B-field case of 80 μG. However, our chosen kiloparsec-scale region, extracted from a global galaxy simulation, happens to contain a starbursting cloud complex that is only modestly affected by these magnetic fields and likely requires internal star formation feedback to regulate its SFR.

  15. An ancient F-type subdwarf from the halo crossing the Galactic plane

    NASA Astrophysics Data System (ADS)

    Scholz, R.-D.; Heber, U.; Heuser, C.; Ziegerer, E.; Geier, S.; Niederhofer, F.

    2015-02-01

    Aims: We selected the bluest object, WISE J0725-2351, from Luhman's new high proper motion (HPM) survey based on observations with the Wide-field Infrared Survey Explorer (WISE) for spectroscopic follow-up observations. Our aim was to unravel the nature of this relatively bright (V ~ 12, J ~ 11) HPM star (μ = 267 mas/yr). Methods: We obtained low- and medium-resolution spectra with the European Southern Observatory (ESO) New Technology Telescope (NTT)/EFOSC2 and Very Large Telescope (VLT)/X-Shooter instruments, investigated the radial velocity and performed a quantitative spectral analysis that allowed us to determine physical parameters. The fit of the spectral energy distribution based on the available photometry to low-metallicity model spectra and the similarity of our target to a metal-poor benchmark star (HD 84937) allowed us to estimate the distance and space velocity. Results: As in the case of HD 84937, we classified WISE J0725-2351 as sdF5: or a metal-poor turnoff star with [ Fe/H ] = -2.0 ± 0.2, Teff = 6250 ± 100 K, log g = 4.0 ± 0.2, and a possible age of about 12 Gyr. At an estimated distance of more than 400 pc, its proper motion translates to a tangential velocity of more than 500 km s-1. Together with its constant (on timescales of hours, days, and months) and large radial velocity (about +240 km s-1), the resulting Galactic restframe velocity is about 460 km s-1, implying a bound retrograde orbit for this extreme halo object that currently crosses the Galactic plane at high speed. Based on observations at the La Silla-Paranal Observatory of the European Southern Observatory for programmes 092.D-0040(A) and 093.D-0127(A).

  16. Very high energy gamma rays from active galactic nuclei: Cascading on the cosmic background radiation fields and the formation of pair halos

    NASA Technical Reports Server (NTRS)

    Aharonian, F. A.; Coppi, P. S.; Voelk, H. J.

    1994-01-01

    Recent high-energy gamma-ray observations (E(sub gamma) greater than 100 MeV) of blazar Active Galactic Nuclei (AGNs) show emission spectra with no clear upper energy cutoff. AGNs, considered to be possible sources for the observed flux of cosmic rays beyond 10(exp 19) eV, may well have emission extending into the very high energy (VHE), (E(sub gamma) greater than 100 GeV) domain. Because VHE gamma-rays are absorbed by pair production on the intergalactic background radiation fields, much of this emission may not be directly visible. The electromagnetic cascades initiated by absorbed VHE gamma-rays, however, may be observable. Since, most probably, the velocities of (e(+), e(-)) pairs produced in a cascade are quickly isotropized by an ambient random magnetic field, extended 'halos' (R greater than 1 Mpc) of pairs will be formed around AGNs with VHE emission. The cascade radiation from these pair halos is emitted isotropically and should be observable at energies below a few TeV. The halo radiation can be distinguished by its characteristic variation in spectrum and intensity with angular distance from the central source. This variation depends weakly on the details of the central source model, e.g., the orientation and beaming/opening angle of an emitting jet. Limiting or determining the intensity of the pair halo can thus serve as a model-independent bound on or measure of the VHE power of AGNs. Next-generation Cherenkov telescopes may be able to image a pair halo.

  17. An XMM-Newton Survey of the Soft X-Ray Background. III. The Galactic Halo X-Ray Emission

    NASA Astrophysics Data System (ADS)

    Henley, David B.; Shelton, Robin L.

    2013-08-01

    We present measurements of the Galactic halo's X-ray emission for 110 XMM-Newton sight lines selected to minimize contamination from solar wind charge exchange emission. We detect emission from few million degree gas on ~4/5 of our sight lines. The temperature is fairly uniform (median = 2.22 × 106 K, interquartile range = 0.63 × 106 K), while the emission measure and intrinsic 0.5-2.0 keV surface brightness vary by over an order of magnitude (~(0.4-7) × 10-3 cm-6 pc and ~(0.5-7) × 10-12 erg cm-2 s-1 deg-2, respectively, with median detections of 1.9 × 10-3 cm-6 pc and 1.5 × 10-12 erg cm-2 s-1 deg-2, respectively). The high-latitude sky contains a patchy distribution of few million degree gas. This gas exhibits a general increase in emission measure toward the inner Galaxy in the southern Galactic hemisphere. However, there is no tendency for our observed emission measures to decrease with increasing Galactic latitude, contrary to what is expected for a disk-like halo morphology. The measured temperatures, brightnesses, and spatial distributions of the gas can be used to place constraints on models for the dominant heating sources of the halo. We provide some discussion of such heating sources, but defer comparisons between the observations and detailed models to a later paper.

  18. 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. PMID:21868626

  19. Discussion on the energy content of the galactic dark matter Bose-Einstein condensate halo in the Thomas-Fermi approximation

    SciTech Connect

    De Souza, J.C.C.; Pires, M.O.C. E-mail: marcelo.pires@ufabc.edu.br

    2014-03-01

    We show that the galactic dark matter halo, considered composed of an axionlike particles Bose-Einstein condensate [6] trapped by a self-graviting potential [5], may be stable in the Thomas-Fermi approximation since appropriate choices for the dark matter particle mass and scattering length are made. The demonstration is performed by means of the calculation of the potential, kinetic and self-interaction energy terms of a galactic halo described by a Boehmer-Harko density profile. We discuss the validity of the Thomas-Fermi approximation for the halo system, and show that the kinetic energy contribution is indeed negligible.

  20. ASSEMBLY OF THE OUTER GALACTIC STELLAR HALO IN THE HIERARCHICAL MODEL

    SciTech Connect

    Murante, Giuseppe; Curir, Anna; Poglio, Eva; Villalobos, Alvaro E-mail: curir@oato.inaf.i E-mail: villalobos@oats.inaf.i

    2010-06-20

    We provide a set of numerical N-body simulations for studying the formation of the outer Milky Ways' stellar halo through accretion events. After simulating minor mergers of prograde and retrograde orbiting satellite halos with a dark matter main halo, we analyze the signal left by satellite stars in the rotation velocity distribution. The aim is to explore the orbital conditions where a retrograde signal in the outer part of the halo can be obtained, in order to give a possible explanation of the observed rotational properties of the Milky Way stellar halo. Our results show that, for satellites more massive than {approx}1/40 of the main halo, the dynamical friction has a fundamental role in assembling the final velocity distributions resulting from different orbits and that retrograde satellites moving on low-inclination orbits deposit more stars in the outer halo regions and therefore can produce the counter-rotating behavior observed in the outer Milky Way halo.

  1. Dynamics and X-ray emission of a galactic superwind interacting with disk and halo gas

    NASA Astrophysics Data System (ADS)

    Suchkov, Anatoly A.; Balsara, Dinshaw S.; Heckman, Timothy M.; Leitherer, Claus

    1994-08-01

    There is a general agreement that the conspicuous extranuclear X-ray, optical-line, and radio-contiuum emission of starbursts is associated with powerful galactic superwinds blowing from their centers. However, despite the significant advances in observational studies of superwinds, there is no consensus on the nature of the emitting material and even on the emission mechanisms themselves. This is to a great extent a consequence of a poor understanding of dynamical processes in the starburst superwind regions. To address this issue, we have conducted two-dimensional hydrodynamical simulations of galactic superwinds. While previous similar studies have used a single (disk) component to represent the ISM of the starburst galaxy, we analyze the interaction of the wind with a two-component disk-halo ambient interstellar medium and argue that this two-component representation is crucial for adequate modeling of starbursts. The emphasis of this study is on the geometry and structure of the wind region and the X-ray emission arising in the wind material and the shocked gas in the disk and the halo of the galaxy. The simulation results have shown that a clear-cut bipolar wind can easily develop under a range of very different conditions. On the other hand, a complex 'filamentary' structure associated with the entrained dense disk material is found to arise within the hot bubble blown out by the wind. The flow pattern within the bubble is dominated equally by the central biconic outflow and a system of whirling motions r elated to the origin and development of the 'filaments'. The filament parameters make them a good candidate for optical-emission-line filamentary gas observed in starburst halos. We find that the history of mass and energy deposition in the starburst region of the galaxy is crucial for wind dynamics. A 'mild' early wind, which arises as a result of the cumulative effect of stellar winds from massive stars, produces a bipolar vertical cavity in the disk and

  2. Dynamics and X-ray emission of a galactic superwind interacting with disk and halo gas

    NASA Technical Reports Server (NTRS)

    Suchkov, Anatoly A.; Balsara, Dinshaw S.; Heckman, Timothy M.; Leitherner, Claus

    1994-01-01

    There is a general agreement that the conspicuous extranuclear X-ray, optical-line, and radio-contiuum emission of starbursts is associated with powerful galactic superwinds blowing from their centers. However, despite the significant advances in observational studies of superwinds, there is no consensus on the nature of the emitting material and even on the emission mechanisms themselves. This is to a great extent a consequence of a poor understanding of dynamical processes in the starburst superwind regions. To address this issue, we have conducted two-dimensional hydrodynamical simulations of galactic superwinds. While previous similar studies have used a single (disk) component to represent the ISM of the starburst galaxy, we analyze the interaction of the wind with a two-component disk-halo ambient interstellar medium and argue that this two-component representation is crucial for adequate modeling of starbursts. The emphasis of this study is on the geometry and structure of the wind region and the X-ray emission arising in the wind material and the shocked gas in the disk and the halo of the galaxy. The simulation results have shown that a clear-cut bipolar wind can easily develop under a range of very different conditions. On the other hand, a complex 'filamentary' structure associated with the entrained dense disk material is found to arise within the hot bubble blown out by the wind. The flow pattern within the bubble is dominated equally by the central biconic outflow and a system of whirling motions r elated to the origin and development of the 'filaments'. The filament parameters make them a good candidate for optical-emission-line filamentary gas observed in starburst halos. We find that the history of mass and energy deposition in the starburst region of the galaxy is crucial for wind dynamics. A 'mild' early wind, which arises as a result of the cumulative effect of stellar winds from massive stars, produces a bipolar vertical cavity in the disk and

  3. Methods for Identifying Pair Halos

    NASA Astrophysics Data System (ADS)

    Wells, Brendan; Caputo, Regina; Atwood, William; Ritz, Steven M.

    2016-01-01

    The flux of very high energy gamma rays from active galactic nuclei (AGN) is attenuated via interactions with extragalactic background photons and is converted into e+e- pairs. With non-zero intergalactic magnetic fields, the electrons and positrons will deflect as they propagate and simultaneously lose energy by upscattering cosmic microwave background photons. "Pair halos," the visible consequences of these electromagnetic cascades, are faint and difficult to observe against their AGN counterparts. We investigate three methods for indirectly identifying pair halos, using a two-component approach to model the AGN core/halo image. We estimate each method's sensitivity by utilizing a new, detailed Monte Carlo pair-halo simulation.

  4. Planck early results. XXIV. Dust in the diffuse interstellar medium and the Galactic halo

    NASA Astrophysics Data System (ADS)

    Planck Collaboration; Abergel, A.; Ade, P. A. R.; Aghanim, N.; Arnaud, M.; Ashdown, M.; Aumont, J.; Baccigalupi, C.; Balbi, A.; Banday, A. J.; Barreiro, R. B.; Bartlett, J. G.; Battaner, E.; Benabed, K.; Benoît, A.; Bernard, J.-P.; Bersanelli, M.; Bhatia, R.; Blagrave, K.; Bock, J. J.; Bonaldi, A.; Bond, J. R.; Borrill, J.; Bouchet, F. R.; Boulanger, F.; Bucher, M.; Burigana, C.; Cabella, P.; Cantalupo, C. M.; Cardoso, J.-F.; Catalano, A.; Cayón, L.; Challinor, A.; Chamballu, A.; Chiang, L.-Y.; Chiang, C.; Christensen, P. R.; Clements, D. L.; Colombi, S.; Couchot, F.; Coulais, A.; Crill, B. P.; Cuttaia, F.; Danese, L.; Davies, R. D.; Davis, R. J.; de Bernardis, P.; de Gasperis, G.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.-M.; Désert, F.-X.; Dickinson, C.; Donzelli, S.; Doré, O.; Dörl, U.; Douspis, M.; Dupac, X.; Efstathiou, G.; Enßlin, T. A.; Eriksen, H. K.; Finelli, F.; Forni, O.; Frailis, M.; Franceschi, E.; Galeotta, S.; Ganga, K.; Giard, M.; Giardino, G.; Giraud-Héraud, Y.; González-Nuevo, J.; Górski, K. M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Hansen, F. K.; Harrison, D.; Helou, G.; Henrot-Versillé, S.; Herranz, D.; Hildebrandt, S. R.; Hivon, E.; Hobson, M.; Holmes, W. A.; Hovest, W.; Hoyland, R. J.; Huffenberger, K. M.; Jaffe, A. H.; Joncas, G.; Jones, A.; Jones, W. C.; Juvela, M.; Keihänen, E.; Keskitalo, R.; Kisner, T. S.; Kneissl, R.; Knox, L.; Kurki-Suonio, H.; Lagache, G.; Lamarre, J.-M.; Lasenby, A.; Laureijs, R. J.; Lawrence, C. R.; Leach, S.; Leonardi, R.; Leroy, C.; Linden-Vørnle, M.; Lockman, F. J.; López-Caniego, M.; Lubin, P. M.; Macías-Pérez, J. F.; MacTavish, C. J.; Maffei, B.; Maino, D.; Mandolesi, N.; Mann, R.; Maris, M.; Marshall, D. J.; Martin, P.; Martínez-González, E.; Masi, S.; Matarrese, S.; Matthai, F.; Mazzotta, P.; McGehee, P.; Meinhold, P. R.; Melchiorri, A.; Mendes, L.; Mennella, A.; Miville-Deschênes, M.-A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Munshi, D.; Murphy, A.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C. B.; Nørgaard-Nielsen, H. U.; Noviello, F.; Novikov, D.; Novikov, I.; O'Dwyer, I. J.; Osborne, S.; Pajot, F.; Paladini, R.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pinheiro Gonçalves, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Poutanen, T.; Prézeau, G.; Prunet, S.; Puget, J.-L.; Rachen, J. P.; Reach, W. T.; Reinecke, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rowan-Robinson, M.; Rubiño-Martín, J. A.; Rusholme, B.; Sandri, M.; Santos, D.; Savini, G.; Scott, D.; Seiffert, M. D.; Shellard, P.; Smoot, G. F.; Starck, J.-L.; Stivoli, F.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sygnet, J.-F.; Tauber, J. A.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Torre, J.-P.; Tristram, M.; Tuovinen, J.; Umana, G.; Valenziano, L.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L. A.; Wandelt, B. D.; Wilkinson, A.; Yvon, D.; Zacchei, A.; Zonca, A.

    2011-12-01

    This paper presents the first results from a comparison of Planck dust maps at 353, 545 and 857GHz, along with IRAS data at 3000 (100 μm) and 5000GHz (60 μm), with Green Bank Telescope 21-cm observations of Hi in 14 fields covering more than 800 deg2 at high Galactic latitude. The main goal of this study is to estimate the far-infrared to sub-millimeter (submm) emissivity of dust in the diffuse local interstellar medium (ISM) and in the intermediate-velocity (IVC) and high-velocity clouds (HVC) of the Galactic halo. Galactic dust emission for fields with average Hi column density lower than 2 × 1020 cm-2 is well correlated with 21-cm emission because in such diffuse areas the hydrogen is predominantly in the neutral atomic phase. The residual emission in these fields, once the Hi-correlated emission is removed, is consistent with the expected statistical properties of the cosmic infrared background fluctuations. The brighter fields in our sample, with an average Hi column density greater than 2 × 1020 cm-2, show significant excess dust emission compared to the Hi column density. Regions of excess lie in organized structures that suggest the presence of hydrogen in molecular form, though they are not always correlated with CO emission. In the higher Hi column density fields the excess emission at 857 GHz is about 40% of that coming from the Hi, but over all the high latitude fields surveyed the molecular mass faction is about 10%. Dust emission from IVCs is detected with high significance by this correlation analysis. Its spectral properties are consistent with, compared to the local ISM values, significantly hotter dust (T ~ 20K), lower submm dust opacity normalized per H-atom, and a relative abundance of very small grains to large grains about four times higher. These results are compatible with expectations for clouds that are part of the Galactic fountain in which there is dust shattering and fragmentation. Correlated dust emission in HVCs is not detected

  5. The gaseous galactic halo as inferred from the line spectra of the galaxies Markarian 509 and Fairall 9

    NASA Technical Reports Server (NTRS)

    York, D. G.; Songaila, A.; Blades, J. C.; Cowie, L. L.; Morton, D. C.; Wu, C.-C.

    1982-01-01

    Narrow interstellar absorption lines of S II 1259.52, Si II 1260.42, and Fe II 1608.46 due to gas in the disk and the halo of the Galaxy have been detected in the spectrum of the Seyfert galaxy Mrk 509 with the International Ultraviolet Explorer. This gas is also seen at higher resolution in the Ca II and Na I absorption lines in two components at LSR velocities of +6 and +62 km/s. In addition, narrow Ly-alpha and C IV absorption near the Seyfert redshift seem to be present in the spectrum. Si II 1260.42 absorption from the galactic disk and from the Magellanic Stream or the halo of the SMC have been detected with the IUE in the spectrum of Fairall 9. The observations of these two objects when combined with existing results are shown to be consistent with a corotating galactic halo having a height of less than 10 kpc at the sun.

  6. Changing Amplitudes: Detecting RR Lyrae Light Curve Shape Variations in the Galactic Disk and Inner Halo

    NASA Astrophysics Data System (ADS)

    De Lee, Nathan M.; Kinemuchi, K.; Pepper, J.; Rodriguez, J. E.

    2014-01-01

    In this poster we will discuss our ongoing program to use extant light curves from the Kilodegree Extremely Little Telescope (KELT) survey to find and characterize RR Lyrae (RRL) stars in the disk and inner halo of the Milky Way. RRL stars are of particular interest because they are standard candles and can be used to map out structure in the galaxy. The periods and shape of RRL light curves also contain information about their Oosterhoff type, which can probe galactic formation history, and metallicity respectively. Although there have been several large photometric surveys for RR Lyrae in the nearby galaxy (OGLE, NSVS, ASAS, and MACHO to name a few), they have each been limited in either sky coverage or number of epochs. The KELT survey represents a new generation of surveys that has many epochs over a large portion of the sky. KELT samples 60% of the sky in both northern and southern hemispheres, and has a long-time-baseline of 4-8 years with a very high cadence rate of less than 20 minutes. This translates into 4,000 to 9,000 epochs per light curve with completeness out to 3 kpc from the Sun. Recent results from both Kepler and ground based surveys results suggest that as many as 50% of RR Lyrae stars show long-term modulation of their light curve shapes (Blazhko effect). These stars combined with RRL stars that pulsate in more than one mode give a sample of objects that the KELT survey is uniquely suited to explore. This poster concentrates on a pilot project to examine RRL stars in a limited number of KELT fields. In particular, we focus on, detecting RR Lyrae, developing a light curve shape-metallicity relationship in the KELT band-pass, and some initial characterization of RRL with either amplitude-modulated or period-modulated light curves.

  7. PROBING THE OUTER GALACTIC HALO WITH RR LYRAE FROM THE CATALINA SURVEYS

    SciTech Connect

    Drake, A. J.; Djorgovski, S. G.; Graham, M. J.; Mahabal, A.; Donalek, C.; Williams, R.; Catelan, M.; Torrealba, G.; Belokurov, V.; Koposov, S. E.; Prieto, J. L.; Larson, S.; Christensen, E.; Beshore, E.

    2013-01-20

    We present analysis of 12,227 type-ab RR Lyraes (RRLs) found among the 200 million public light curves in Catalina Surveys Data Release 1. These stars span the largest volume of the Milky Way ever surveyed with RRLs, covering {approx}20,000 deg{sup 2} of the sky (0 Degree-Sign < {alpha} < 360 Degree-Sign , -22 Degree-Sign < {delta} < 65 Degree-Sign ) to heliocentric distances of up to 60 kpc. Each of the RRLs is observed between 60 and 419 times over a six-year period. Using period finding and Fourier fitting techniques we determine periods and apparent magnitudes for each source. We find that the periods are generally accurate to {sigma} = 0.002% in comparison to 2842 previously known RRLs and 100 RRLs observed in overlapping survey fields. We photometrically calibrate the light curves using 445 Landolt standard stars and show that the resulting magnitudes are accurate to {approx}0.05 mag using Sloan Digital Sky Survey (SDSS) data for {approx}1000 blue horizontal branch stars and 7788 RRLs. By combining Catalina photometry with SDSS spectroscopy, we analyze the radial velocity and metallicity distributions for >1500 of the RRLs. Using the accurate distances derived for the RRLs, we show the paths of the Sagittarius tidal streams crossing the sky at heliocentric distances from 20 to 60 kpc. By selecting samples of Galactic halo RRLs, we compare their velocity, metallicity, and distance with predictions from a recent detailed N-body model of the Sagittarius system. We find that there are some significant differences between the distances and structures predicted and our observations.

  8. Do gamma-ray bursts originate from an extended Galactic Halo of high-velocity neutron stars?

    NASA Technical Reports Server (NTRS)

    Hartmann, Dieter H.; Brown, Lawrence E.; The, Lih-Sin; Linder, Eric V.; Petrosian, Vahe; Blumenthal, George R.; Hurley, Kevin C.

    1994-01-01

    The gamma-ray burst brightness distribution is inhomogeneous and the distribution on the sky is nearly isotropic. These features argue against an association of gamma-ray bursts with those Galactic objects that are known to exhibit a strong concentration toward the Galactic center or plane. The observed statistical properties indicate a cosmological origin. Circumstantial evidence suggests that neutron stars are involved in the burst phenomenon. Here we consider Population II neutron stars in an extended Galactic Halo (EGH) as an alternative to cosmological scenarios. The Burst and Transient Source Experiment (BATSE) data indicate a small deviation from isotropy near the 2 sigma level of statistical significance. If confirmed for an increasing number of bursts, these anisotropies could rule out cosmological scenarios. On the other hand, EGH models require small anisotropies like those observed by BATSE. We consider simple distribution models to determine the generic properties such halos must have to be consistent with the observations and discuss the implications of the corresponding distance scale on burst models.

  9. A hadronic-leptonic model for the Fermi bubbles: Cosmic-rays in the galactic halo and radio emission

    SciTech Connect

    Fujita, Yutaka; Ohira, Yutaka; Yamazaki, Ryo

    2014-07-01

    We investigate non-thermal emission from the Fermi bubbles in a hadronic model. Cosmic-ray (CR) protons are accelerated at the forward shock of the bubbles. They interact with the background gas in the Galactic halo and create π{sup 0}-decay gamma-rays and secondary electrons through proton-proton interaction. We follow the evolution of the CR protons and electrons by calculating their distribution functions. We find that the spectrum and the intensity profiles of π{sup 0}-decay gamma-rays are consistent with observations. We predict that the shock front is located far ahead of the gamma-ray boundary of the Fermi bubbles. This naturally explains the fact that a clear temperature jump of thermal gas was not discovered at the gamma-ray boundary in recent Suzaku observations. We also consider re-acceleration of the background CRs in the Galactic halo at the shock front. We find that it can significantly affect the gamma-rays from the Fermi bubbles, unless the density of the background CRs is ≲ 10% of that in the Galactic disk. We indicate that secondary electrons alone cannot produce the observed radio emission from the Fermi bubbles. However, the radio emission from the outermost region of the bubbles can be explained if electrons are directly accelerated at the shock front with an efficiency of ∼0.1% of that of protons.

  10. Sturm und Drang: The turbulent, magnetic tempest in the Galactic center

    NASA Astrophysics Data System (ADS)

    Lacki, Brian C.

    2014-05-01

    The Galactic center central molecular zone (GCCMZ) bears similarities with extragalactic starburst regions, including a high supernova (SN) rate density. As in other starbursts like M82, the frequent SNe can heat the ISM until it is filled with a hot (˜ 4 × 107 K) superwind. Furthermore, the random forcing from SNe stirs up the wind, powering Mach 1 turbulence. I argue that a turbulent dynamo explains the strong magnetic fields in starbursts, and I predict an average B ˜70 μG in the GCCMZ. I demonstrate how the SN driving of the ISM leads to equipartition between various pressure components in the ISM. The SN-heated wind escapes the center, but I show that it may be stopped in the Galactic halo. I propose that the Fermi bubbles are the wind's termination shock.

  11. AN XMM-NEWTON SURVEY OF THE SOFT X-RAY BACKGROUND. III. THE GALACTIC HALO X-RAY EMISSION

    SciTech Connect

    Henley, David B.; Shelton, Robin L.

    2013-08-20

    We present measurements of the Galactic halo's X-ray emission for 110 XMM-Newton sight lines selected to minimize contamination from solar wind charge exchange emission. We detect emission from few million degree gas on {approx}4/5 of our sight lines. The temperature is fairly uniform (median = 2.22 Multiplication-Sign 10{sup 6} K, interquartile range = 0.63 Multiplication-Sign 10{sup 6} K), while the emission measure and intrinsic 0.5-2.0 keV surface brightness vary by over an order of magnitude ({approx}(0.4-7) Multiplication-Sign 10{sup -3} cm{sup -6} pc and {approx}(0.5-7) Multiplication-Sign 10{sup -12} erg cm{sup -2} s{sup -1} deg{sup -2}, respectively, with median detections of 1.9 Multiplication-Sign 10{sup -3} cm{sup -6} pc and 1.5 Multiplication-Sign 10{sup -12} erg cm{sup -2} s{sup -1} deg{sup -2}, respectively). The high-latitude sky contains a patchy distribution of few million degree gas. This gas exhibits a general increase in emission measure toward the inner Galaxy in the southern Galactic hemisphere. However, there is no tendency for our observed emission measures to decrease with increasing Galactic latitude, contrary to what is expected for a disk-like halo morphology. The measured temperatures, brightnesses, and spatial distributions of the gas can be used to place constraints on models for the dominant heating sources of the halo. We provide some discussion of such heating sources, but defer comparisons between the observations and detailed models to a later paper.

  12. Effects of the galactic magnetic field upon large scale anisotropies of extragalactic cosmic rays

    SciTech Connect

    Harari, D.; Mollerach, S.; Roulet, E. E-mail: mollerach@cab.cnea.gov.ar

    2010-11-01

    The large scale pattern in the arrival directions of extragalactic cosmic rays that reach the Earth is different from that of the flux arriving to the halo of the Galaxy as a result of the propagation through the galactic magnetic field. Two different effects are relevant in this process: deflections of trajectories and (de)acceleration by the electric field component due to the galactic rotation. The deflection of the cosmic ray trajectories makes the flux intensity arriving to the halo from some direction to appear reaching the Earth from another direction. This applies to any intrinsic anisotropy in the extragalactic distribution or, even in the absence of intrinsic anisotropies, to the dipolar Compton-Getting anisotropy induced when the observer is moving with respect to the cosmic rays rest frame. For an observer moving with the solar system, cosmic rays traveling through far away regions of the Galaxy also experience an electric force coming from the relative motion (due to the rotation of the Galaxy) of the local system in which the field can be considered as being purely magnetic. This produces small changes in the particles momentum that can originate large scale anisotropies even for an isotropic extragalactic flux.

  13. DETECTING TRIAXIALITY IN THE GALACTIC DARK MATTER HALO THROUGH STELLAR KINEMATICS

    SciTech Connect

    Rojas-Nino, Armando; Valenzuela, Octavio; Pichardo, Barbara; Aguilar, Luis A. E-mail: barbara@astro.unam.mx

    2012-10-01

    Assuming the dark matter halo of the Milky Way to be a non-spherical potential (i.e., triaxial, prolate, oblate), we show how the assembling process of the Milky Way halo may have left long-lasting stellar halo kinematic fossils due to the shape of the dark matter halo. In contrast with tidal streams, which are associated with recent satellite accretion events, these stellar kinematic groups will typically show inhomogeneous chemical and stellar population properties. However, they may be dominated by a single accretion event for certain mass assembling histories. If the detection of these peculiar kinematic stellar groups were confirmed, they would be the smoking gun for the predicted triaxiality of dark halos in cosmological galaxy formation scenarios.

  14. THE HALO OCCUPATION DISTRIBUTION OF X-RAY-BRIGHT ACTIVE GALACTIC NUCLEI: A COMPARISON WITH LUMINOUS QUASARS

    SciTech Connect

    Richardson, Jonathan; Chatterjee, Suchetana; Myers, Adam D.; Zheng Zheng; Hickox, Ryan E-mail: schatte1@uwyo.edu

    2013-09-10

    We perform halo occupation distribution (HOD) modeling of the projected two-point correlation function (2PCF) of high-redshift (z {approx} 1.2) X-ray-bright active galactic nuclei (AGNs) in the XMM-COSMOS field measured by Allevato et al. The HOD parameterization is based on low-luminosity AGNs in cosmological simulations. At the median redshift of z {approx} 1.2, we derive a median mass of 1.02{sub -0.23}{sup +0.21} Multiplication-Sign 10{sup 13} h{sup -1} M{sub sun} for halos hosting central AGNs and an upper limit of {approx}10% on the AGN satellite fraction. Our modeling results indicate (at the 2.5{sigma} level) that X-ray AGNs reside in more massive halos compared to more bolometrically luminous, optically selected quasars at similar redshift. The modeling also yields constraints on the duty cycle of the X-ray AGN, and we find that at z {approx} 1.2 the average duration of the X-ray AGN phase is two orders of magnitude longer than that of the quasar phase. Our inferred mean occupation function of X-ray AGNs is similar to recent empirical measurements with a group catalog and suggests that AGN halo occupancy increases with increasing halo mass. We project the XMM-COSMOS 2PCF measurements to forecast the required survey parameters needed in future AGN clustering studies to enable higher precision HOD constraints and determinations of key physical parameters like the satellite fraction and duty cycle. We find that N {sup 2}/A {approx} 5 Multiplication-Sign 10{sup 6} deg{sup -2} (with N the number of AGNs in a survey area of A deg{sup 2}) is sufficient to constrain the HOD parameters at the 10% level, which is easily achievable by upcoming and proposed X-ray surveys.

  15. Transonic galactic outflows in a dark matter halo with a central black hole and its application to the Sombrero galaxy

    NASA Astrophysics Data System (ADS)

    Igarashi, Asuka; Mori, Masao; Nitta, Shin-ya

    2014-10-01

    We have classified possible transonic solutions of galactic outflows in the gravitational potential of the dark matter halo (DMH) and supermassive black hole (SMBH) under the assumptions of isothermal, spherically symmetric and steady state. It is clarified that the gravity of SMBH adds a new branch of transonic solutions with the transonic point in very close proximity to the centre in addition to the outer transonic point generated by the gravity of DMH. Because these two transonic solutions have substantially different mass fluxes and starting points, these solutions may have different influences on the evolution of galaxies and the release of metals into intergalactic space. We have applied our model to the Sombrero galaxy and obtained a new type of galactic outflow: a slowly accelerated transonic outflow through the transonic point at very distant region (≃126 kpc). In this galaxy, previous works reported that although the trace of the galactic outflow is observed by X-ray, the gas density distribution is consistent with the hydrostatic state. We have clarified that the slowly accelerating outflow has a gas density profile quite similar to that of the hydrostatic solution in the widely spread subsonic region. Thus, the slowly accelerating transonic solution cannot be distinguished from the hydrostatic solution in the observed region (≤25 kpc) even if slow transonic flow exists. Our model provides a new perspective of galactic outflows and is applicable even to quiescent galaxies with inactive star formation.

  16. Collisions between Dark Matter Confined High Velocity Clouds and Magnetized Galactic Disks: The Smith Cloud

    NASA Astrophysics Data System (ADS)

    Galyardt, Jason; Shelton, Robin L.

    2016-01-01

    The Galaxy’s population of High Velocity Clouds (HVCs) may include a subpopulation that is confined by dark matter minihalos and falling toward the Galactic disk. We present the first magnetohydrodynamic simulational study of dark-matter-dominated HVCs colliding with a weakly magnetized galactic disk. Our HVCs have baryonic masses of 5 × 106M⊙ and dark matter minihalo masses of 0, 3 × 108, or 1 × 109 M⊙. They are modeled on the Smith Cloud, which is said to have collided with the disk 70 Myr ago. We find that, in all cases, the cloud’s collision with the galactic disk creates a hole in the disk, completely disperses the cloud, and forms a bubble-shaped structure on the far side of the disk. In contrast, when present, the dark matter minihalo continues unimpeded along its trajectory. Later, as the minihalo passes through the bubble structure and galactic halo, it accretes up to 6.0 × 105 M⊙ in baryonic material, depending on the strengths of the magnetic field and minihalo gravity. These simulations suggest that if the Smith Cloud is associated with a dark matter minihalo and collided with the Galactic disk, the minihalo has accreted the observed gas. However, if the Smith Cloud is dark-matter-free, it is on its first approach toward the disk. These simulations also suggest that the dark matter is most concentrated either at the head of the cloud or near the cloud, depending upon the strength of the magnetic field, a point that could inform indirect dark matter searches.

  17. Multipole analysis of IceCube data to search for dark matter accumulated in the Galactic halo

    NASA Astrophysics Data System (ADS)

    Aartsen, M. G.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Ahrens, M.; Altmann, D.; Anderson, T.; Arguelles, C.; Arlen, T. C.; Auffenberg, J.; Bai, X.; Barwick, S. W.; Baum, V.; Beatty, J. J.; Becker Tjus, J.; Becker, K.-H.; BenZvi, S.; Berghaus, P.; Berley, D.; Bernardini, E.; Bernhard, A.; Besson, D. Z.; Binder, G.; Bindig, D.; Bissok, M.; Blaufuss, E.; Blumenthal, J.; Boersma, D. J.; Bohm, C.; Bos, F.; Bose, D.; Böser, S.; Botner, O.; Brayeur, L.; Bretz, H.-P.; Brown, A. M.; Casey, J.; Casier, M.; Chirkin, D.; Christov, A.; Christy, B.; Clark, K.; Classen, L.; Clevermann, F.; Coenders, S.; Cowen, D. F.; Cruz Silva, A. H.; Danninger, M.; Daughhetee, J.; Davis, J. C.; Day, M.; de André, J. P. A. M.; De Clercq, C.; De Ridder, S.; Desiati, P.; de Vries, K. D.; de With, M.; DeYoung, T.; Díaz-Vélez, J. C.; Dunkman, M.; Eagan, R.; Eberhardt, B.; Eichmann, B.; Eisch, J.; Euler, S.; Evenson, P. A.; Fadiran, O.; Fazely, A. R.; Fedynitch, A.; Feintzeig, J.; Felde, J.; Feusels, T.; Filimonov, K.; Finley, C.; Fischer-Wasels, T.; Flis, S.; Franckowiak, A.; Frantzen, K.; Fuchs, T.; Gaisser, T. K.; Gallagher, J.; Gerhardt, L.; Gier, D.; Gladstone, L.; Glüsenkamp, T.; Goldschmidt, A.; Golup, G.; Gonzalez, J. G.; Goodman, J. A.; Góra, D.; Grandmont, D. T.; Grant, D.; Gretskov, P.; Groh, J. C.; Groß, A.; Ha, C.; Haack, C.; Haj Ismail, A.; Hallen, P.; Hallgren, A.; Halzen, F.; Hanson, K.; Hebecker, D.; Heereman, D.; Heinen, D.; Helbing, K.; Hellauer, R.; Hellwig, D.; Hickford, S.; Hill, G. C.; Hoffman, K. D.; Hoffmann, R.; Homeier, A.; Hoshina, K.; Huang, F.; Huelsnitz, W.; Hulth, P. O.; Hultqvist, K.; Hussain, S.; Ishihara, A.; Jacobi, E.; Jacobsen, J.; Jagielski, K.; Japaridze, G. S.; Jero, K.; Jlelati, O.; Jurkovic, M.; Kaminsky, B.; Kappes, A.; Karg, T.; Karle, A.; Kauer, M.; Kelley, J. L.; Kheirandish, A.; Kiryluk, J.; Kläs, J.; Klein, S. R.; Köhne, J.-H.; Kohnen, G.; Kolanoski, H.; Koob, A.; Köpke, L.; Kopper, C.; Kopper, S.; Koskinen, D. J.; Kowalski, M.; Kriesten, A.; Krings, K.; Kroll, G.; Kroll, M.; Kunnen, J.; Kurahashi, N.; Kuwabara, T.; Labare, M.; Larsen, D. T.; Larson, M. J.; Lesiak-Bzdak, M.; Leuermann, M.; Leute, J.; Lünemann, J.; Macías, O.; Madsen, J.; Maggi, G.; Maruyama, R.; Mase, K.; Matis, H. S.; McNally, F.; Meagher, K.; Medici, M.; Meli, A.; Meures, T.; Miarecki, S.; Middell, E.; Middlemas, E.; Milke, N.; Miller, J.; Mohrmann, L.; Montaruli, T.; Morse, R.; Nahnhauer, R.; Naumann, U.; Niederhausen, H.; Nowicki, S. C.; Nygren, D. R.; Obertacke, A.; Odrowski, S.; Olivas, A.; Omairat, A.; O'Murchadha, A.; Palczewski, T.; Paul, L.; Penek, Ö.; Pepper, J. A.; Pérez de los Heros, C.; Pfendner, C.; Pieloth, D.; Pinat, E.; Posselt, J.; Price, P. B.; Przybylski, G. T.; Pütz, J.; Quinnan, M.; Rädel, L.; Rameez, M.; Rawlins, K.; Redl, P.; Rees, I.; Reimann, R.; Resconi, E.; Rhode, W.; Richman, M.; Riedel, B.; Robertson, S.; Rodrigues, J. P.; Rongen, M.; Rott, C.; Ruhe, T.; Ruzybayev, B.; Ryckbosch, D.; Saba, S. M.; Sander, H.-G.; Sandroos, J.; Santander, M.; Sarkar, S.; Schatto, K.; Scheriau, F.; Schmidt, T.; Schmitz, M.; Schoenen, S.; Schöneberg, S.; Schönwald, A.; Schukraft, A.; Schulte, L.; Schulz, O.; Seckel, D.; Sestayo, Y.; Seunarine, S.; Shanidze, R.; Sheremata, C.; Smith, M. W. E.; Soldin, D.; Spiczak, G. M.; Spiering, C.; Stamatikos, M.; Stanev, T.; Stanisha, N. A.; Stasik, A.; Stezelberger, T.; Stokstad, R. G.; Stößl, A.; Strahler, E. A.; Ström, R.; Strotjohann, N. L.; Sullivan, G. W.; Taavola, H.; Taboada, I.; Tamburro, A.; Tepe, A.; Ter-Antonyan, S.; Terliuk, A.; Tešić, G.; Tilav, S.; Toale, P. A.; Tobin, M. N.; Tosi, D.; Tselengidou, M.; Unger, E.; Usner, M.; Vallecorsa, S.; van Eijndhoven, N.; Vandenbroucke, J.; van Santen, J.; Vehring, M.; Voge, M.; Vraeghe, M.; Walck, C.; Wallraff, M.; Weaver, Ch.; Wellons, M.; Wendt, C.; Westerhoff, S.; Whelan, B. J.; Whitehorn, N.; Wichary, C.; Wiebe, K.; Wiebusch, C. H.; Williams, D. R.; Wissing, H.; Wolf, M.; Wood, T. R.; Woschnagg, K.; Xu, D. L.; Xu, X. W.; Yanez, J. P.; Yodh, G.; Yoshida, S.; Zarzhitsky, P.; Ziemann, J.; Zierke, S.; Zoll, M.

    2015-01-01

    Dark matter which is bound in the Galactic halo might self-annihilate and produce a flux of stable final state particles, e.g. high energy neutrinos. These neutrinos can be detected with IceCube, a cubic-kilometer sized Cherenkov detector. Given IceCube's large field of view, a characteristic anisotropy of the additional neutrino flux is expected. In this paper we describe a multipole method to search for such a large-scale anisotropy in IceCube data. This method uses the expansion coefficients of a multipole expansion of neutrino arrival directions and incorporates signal-specific weights for each expansion coefficient. We apply the technique to a high-purity muon neutrino sample from the Northern Hemisphere. The final result is compatible with the null-hypothesis. As no signal was observed, we present limits on the self-annihilation cross-section averaged over the relative velocity distribution down to for a dark matter particle mass of 700-1,000 GeV and direct annihilation into . The resulting exclusion limits come close to exclusion limits from -ray experiments, that focus on the outer Galactic halo, for high dark matter masses of a few TeV and hard annihilation channels.

  18. Globular clusters and their contribution to the formation of the Galactic halo

    NASA Astrophysics Data System (ADS)

    Carretta, Eugenio

    2016-08-01

    This is a ``biased'' review because I will show recent evidence on the contribution of globular clusters (GCs) to the halo of our Galaxy seen through the lens of the new paradigm of multiple populations in GCs. I will show a few examples where the chemistry of multiple populations helps to answer hot questions including whether and how much GCs did contribute to the halo population, if we have evidence of the GCs-halo link, what are the strengths and weak points concerning this contribution.

  19. SOFIA/HAWC+: Mapping the Galactic Center Magnetic Field

    NASA Technical Reports Server (NTRS)

    Werner, Michael W.; Dowell, C. Darren; Chuss, D. T.; Morris, M. R.; Novak, G.

    2013-01-01

    Polarimetry of the far infrared emission from magnetically-aligned interstellar grains is one of the best ways of studying the magnetic field at the Galactic Center. We describe the HAWC+ instrument, under development for flight on SOFIA starting in 2015, which will provide a major advance in capability for these critically important measurements.

  20. A search for pair haloes around active galactic nuclei through a temporal analysis of Fermi-Large Area Telescope data

    NASA Astrophysics Data System (ADS)

    Prokhorov, D. A.; Moraghan, A.

    2016-04-01

    We develop a method to search for pair haloes around active galactic nuclei (AGN) through a temporal analysis of γ-ray data. The basis of our method is an analysis of the spatial distributions of photons coming from AGN flares and from AGN quiescent states and a further comparison of these two spatial distributions. This method can also be used for a reconstruction of a point spread function (PSF). We found no evidence for a pair halo component through this method by applying it to the Fermi-Large Area Telescope (LAT) data in the energy bands of 4.5-6, 6-10, and >10 GeV and set upper limits on the fraction of photons attributable to a pair halo component. An illustration of how to reconstruct the PSF of Fermi-LAT is given. We demonstrate that the PSF reconstructed by using this method is in good agreement with that which was obtained by using the γ-ray data taken by LAT in the direction of the Crab pulsar and nebula.

  1. The Segue K giant survey. II. A catalog of distance determinations for the Segue K giants in the galactic halo

    SciTech Connect

    Xue, Xiang-Xiang; Rix, Hans-Walter; Ma, Zhibo; Morrison, Heather L.; Harding, Paul; Beers, Timothy C.; Ivans, Inese I.; Jacobson, Heather R.; Johnson, Jennifer; Lee, Young Sun; Lucatello, Sara; Rockosi, Constance M.; Yanny, Brian; Zhao, Gang; Allende Prieto, Carlos

    2014-04-01

    We present an online catalog of distance determinations for 6036 K giants, most of which are members of the Milky Way's stellar halo. Their medium-resolution spectra from the Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration are used to derive metallicities and rough gravity estimates, along with radial velocities. Distance moduli are derived from a comparison of each star's apparent magnitude with the absolute magnitude of empirically calibrated color-luminosity fiducials, at the observed (g – r){sub 0} color and spectroscopic [Fe/H]. We employ a probabilistic approach that makes it straightforward to properly propagate the errors in metallicities, magnitudes, and colors into distance uncertainties. We also fold in prior information about the giant-branch luminosity function and the different metallicity distributions of the SEGUE K-giant targeting sub-categories. We show that the metallicity prior plays a small role in the distance estimates, but that neglecting the luminosity prior could lead to a systematic distance modulus bias of up to 0.25 mag, compared to the case of using the luminosity prior. We find a median distance precision of 16%, with distance estimates most precise for the least metal-poor stars near the tip of the red giant branch. The precision and accuracy of our distance estimates are validated with observations of globular and open clusters. The stars in our catalog are up to 125 kpc from the Galactic center, with 283 stars beyond 50 kpc, forming the largest available spectroscopic sample of distant tracers in the Galactic halo.

  2. The Century Survey Galactic Halo Project. II. Global Properties and the Luminosity Function of Field Blue Horizontal Branch Stars

    NASA Astrophysics Data System (ADS)

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J.; Kurtz, Michael J.; Allende Prieto, Carlos; Beers, Timothy C.; Wilhelm, Ronald

    2005-09-01

    We discuss a 175 deg2 spectroscopic survey for blue horizontal branch (BHB) stars in the Galactic halo. We use the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) to select BHB candidates, and we find that the 2MASS and SDSS color selection is 38% and 50% efficient, respectively, for BHB stars. Our samples include one likely runaway B7 star 6 kpc below the Galactic plane. The global properties of the BHB samples are consistent with membership in the halo population: the median metallicity is [Fe/H]=-1.7, the velocity dispersion is 108 km s-1, and the mean Galactic rotation of the BHB stars 3 kpc<|z|<15 kpc is -4+/-30 km s-1. We discuss the theoretical basis of the Preston, Shectman, and Beers MV-color relation for BHB stars and conclude that the intrinsic shape of the BHB MV-color relation results from the physics of stars on the horizontal branch. We calculate the luminosity function for the field BHB star samples using the maximum likelihood method of Efstathiou and coworkers, which is unbiased by density variations. The field BHB luminosity function exhibits a steep rise at bright luminosities, a peak between 0.8

  3. Galactic rotation curves, the baryon-to-dark-halo-mass relation and space-time scale invariance

    NASA Astrophysics Data System (ADS)

    Wu, Xufen; Kroupa, Pavel

    2015-01-01

    Low-acceleration space-time scale invariant dynamics (SID) predicts two fundamental correlations known from observational galactic dynamics: the baryonic Tully-Fisher relation and a correlation between the observed mass discrepancy and acceleration (MDA) in the low-acceleration regime for disc galaxies. SID corresponds to the deep Modified Newtonian Dynamics limit. The MDA data emerging in cold/warm dark matter (C/WDM) cosmological simulations disagree significantly with the tight MDA correlation of the observed galaxies. Therefore, the most modern simulated disc galaxies, which are delicately selected to have a quiet merging history in a standard dark matter cosmological model, still do not represent the correct rotation curves. Also, the observed tight correlation contradicts the postulated stochastic formation of galaxies in low-mass dark matter haloes. Moreover, we find that SID predicts a baryonic to apparent virial halo (dark matter) mass relation which agrees well with the correlation deduced observationally assuming Newtonian dynamics to be valid, while the baryonic to halo mass relation predicted from CDM models does not. The distribution of the observed ratios of dark matter halo masses to baryonic masses may be empirical evidence for the external field effect, which is predicted in SID as a consequence of the forces acting between two galaxies depending on the position and mass of a third galaxy. Applying the external field effect, we predict the masses of galaxies in the proximity of the dwarf galaxies in the Miller et al. sample. Classical non-relativistic gravitational dynamics is thus best described as being Milgromian, rather than Newtonian.

  4. On planetary nebulae as sources of carbon dust: Infrared emission from planetary nebulae of the galactic halo

    NASA Technical Reports Server (NTRS)

    Dinerstein, Harriet L.; Lester, Daniel F.

    1990-01-01

    Planetary nebulae of the galactic disk are generally seen to emit a thermal continuum due to dust grains heated by stellar and nebular photons. This continuum typically peaks between 25 and 60 micron m, so that the total power emitted by the dust is sampled well by the broad-band measurements made by IRAS. Researchers examine here the characteristics of the infrared emission from the four planetary nebulae which are believed on the basis of their low overall metallicities to belong to the halo population. These nebulae are of particular interest because they are the most metal-poor ionized nebulae known in our Galaxy, and offer the opportunity to probe possible dependences of the dust properties on nebular composition. Researchers present fluxes extracted from co-addition of the IRAS data, as well as ground-based near infrared measurements. Each of the four halo objects, including the planetary nebula in the globular cluster M15, is detected in at least one infrared band. Researchers compare the estimated infrared excesses of these nebulae (IRE, the ratio of measured infrared power to the power available in the form of resonantly-trapped Lyman alpha photons) to those of disk planetary nebulae with similar densities but more normal abundances. Three of the halo planetaries have IRE values similar to those of the disk nebulae, despite the fact that their Fe- and Si-peak gas phase abundances are factors of 10 to 100 lower. However, these halo nebulae have normal or elevated C/H ratios, due to nuclear processing and mixing in their red giant progenitors. Unlike the other halo planetaries, DDDM1 is deficient in carbon as well as in the other light metals. This nebula has a substantially lower IRE than the other halo planetaries, and may be truly dust efficient. Researchers suggest that the deficiency is due to a lack of the raw material for producing carbon-based grains, and that the main bulk constituent of the dust in these planetary nebulae is carbon.

  5. The connection between supernova remnants and the Galactic magnetic field: A global radio study of the axisymmetric sample

    NASA Astrophysics Data System (ADS)

    West, J. L.; Safi-Harb, S.; Jaffe, T.; Kothes, R.; Landecker, T. L.; Foster, T.

    2016-03-01

    The study of supernova remnants (SNRs) is fundamental to understanding the chemical enrichment and magnetism in galaxies, including our own Milky Way. In an effort to understand the connection between the morphology of SNRs and the Galactic magnetic field (GMF), we have examined the radio images of all known SNRs in our Galaxy and compiled a large sample that have an axisymmetric morphology, which we define to mean SNRs with a bilateral or barrel-shaped morphology, in addition to one-sided shells. We selected the cleanest examples and model each of these at their appropriate Galactic position using two GMF models, one of which includes a vertical halo component, and another that is oriented entirely parallel to the plane. Since the magnitude and relative orientation of the magnetic field changes with distance from the sun, we analyze a range of distances, from 0.5 to 10 kpc in each case. Using a physically motivated model of an SNR expanding into an ambient GMF that includes a vertical halo component, we find it is able to reproduce observed morphologies of many SNRs in our sample. These results strongly support the presence of an off-plane, vertical component to the GMF, and the importance of the Galactic field on SNR morphology. Our approach also provides a potentially new method for determining distances to SNRs, or conversely, distances to features in the large-scale GMF if SNR distances are known.

  6. Does the dark-matter halo induce chaos in the galactic disk?

    NASA Astrophysics Data System (ADS)

    Weinberg, Martin D.

    2013-07-01

    A three-dimensional galaxy disk will not have regular orbits (tori) everywhere. Therefore, there will be irregular, chaotic regions in addition to regular regions in the disk's phase space. In addition, galaxy formation in the standard LCDM scenario suggests a transition between disk-dominated and halo-dominated gravity at several disk scale lengths. These simple observations raise the following questions: 1) are there generic features of a exponential stellar disk induced by breaking of invariant tori? 2) do the chaotic regions in disks enable significant structural evolution in a galaxy lifetime? 3) does the orbital structure of disks indirectly depend on the dark matter halo especially in the transition region between the disk and dark-matter halo? In this talk, I present early results in my attempt to answer these questions using a new developed numerical technique based the mathematical construction used to prove the KAM theorem.

  7. Universality of galactic surface densities within one dark halo scale-length.

    PubMed

    Gentile, Gianfranco; Famaey, Benoit; Zhao, HongSheng; Salucci, Paolo

    2009-10-01

    It was recently discovered that the mean dark matter surface density within one dark halo scale-length (the radius within which the volume density profile of dark matter remains approximately flat) is constant across a wide range of galaxies. This scaling relation holds for galaxies spanning a luminosity range of 14 magnitudes and the whole Hubble sequence. Here we report that the luminous matter surface density is also constant within one scale-length of the dark halo. This means that the gravitational acceleration generated by the luminous component in galaxies is always the same at this radius. Although the total luminous-to-dark matter ratio is not constant, within one halo scale-length it is constant. Our finding can be interpreted as a close correlation between the enclosed surface densities of luminous and dark matter in galaxies. PMID:19794488

  8. The white dwarf luminosity function - A possible probe of the galactic halo

    NASA Technical Reports Server (NTRS)

    Tamanaha, Christopher M.; Silk, Joseph; Wood, M. A.; Winget, D. E.

    1990-01-01

    The dynamically inferred dark halo mass density, amounting to above 0.01 solar masses/cu pc at the sun's Galactocentric radius, can be composed of faint white dwarfs provided that the halo formed in a sufficiently early burst of star formation. The model is constrained by the observed disk white dwarf luminosity function which falls off below log (L/solar L) = -4.4, due to the onset of star formation in the disk. By using a narrow range for the initial mass function and an exponentially decaying halo star formation rate with an e-folding time equal to the free-fall time, all the halo dark matter is allowed to be in cool white dwarfs which lie beyond the falloff in the disk luminosity function. Although it is unlikely that all the dark matter is in these dim white dwarfs, a definite signature in the low-luminosity end of the white dwarf luminosity function is predicted even if they comprise only 1 percent of the dark matter. Current CCD surveys should answer the question of the existence of this population within the next few years.

  9. The age of the globular cluster NGC 288, the formation of the Galactic halo, and the second parameter

    SciTech Connect

    Bolte, M. )

    1989-06-01

    A differential comparison of precise CCD photometry in the globular clusters NGC 288, NGC 362, and NGC 1261 shows that differences exist in the positions of the main-sequence turnoff in these clusters that are most naturally explained if NGC 288 is some 3 billion yr older than NGC 362 and about 1 to 2 billion yr older than NGC 1261. This implies that the formation time for the Galactic halo is significantly longer than a freefall time. Consideration of the inferred ages and horizontal-branch morphologies of the clusters Pal 12, NGC 288, NGC 362, and NGC 1261, all with similar metal abundances, suggests that age may be the parameter that, after overall metal abundance, most determines horizontal-branch morphology. 56 refs.

  10. Tracing the Galactic Halo: Obtaining Bayesian mass estimates of the Galaxy in the presence of incomplete data

    NASA Astrophysics Data System (ADS)

    Eadie, Gwendolyn; Harris, William; Widrow, Lawrence; Springford, Aaron

    2016-08-01

    The mass and cumulative mass profile of the Galaxy are its most fundamental properties. Estimating these properties, however, is not a trivial problem. We rely on the kinematic information from Galactic satellites such as globular clusters and dwarf galaxies, and this data is incomplete and subject to measurement uncertainty. In particular, the complete 3D velocity vectors of objects are sometimes unavailable, and there may be selection biases due to both the distribution of objects around the Galaxy and our measurement position. On the other hand, the uncertainties of these data are fairly well understood. Thus, we would like to incorporate these uncertainties and the incomplete data into our estimate of the Milky Way's mass. The Bayesian paradigm offers a way to deal with both the missing kinematic data and measurement errors using a hierarchical model. An application of this method to the Milky Way halo mass profile, using the kinematic data for globular clusters and dwarf satellites, is shown.

  11. Reconstructing the Accretion History of the Galactic Halo Using Stellar Chemical Abundance Ratio Distributions

    NASA Astrophysics Data System (ADS)

    Lee, Duane M.; Johnston, Kathryn V.; Sen, Bodhisattva; Jessop, Will

    2016-08-01

    In this study we tested the prospects of using 2D chemical abundance ratio distributions (CARDs) found in stars of the stellar halo to determine its formation history. First, we used simulated data from eleven ``MW-like'' halos to generate satellite template sets of 2D CARDs of accreted dwarf satellites which are comprised of accreted dwarfs from various mass regimes and epochs of accretion. Next, we randomly drew samples of ~ 103-4 mock observations of stellar chemical abundance ratios ([α/Fe], [Fe/H]) from those eleven halos to generate samples of the underlying densities for our CARDs to be compared to our templates in our analysis. Finally, we used the expectation-maximization algorithm to derive accretion histories in relation to the satellite template set (STS) used and the sample size. For certain STS used we typically can identify the relative mass contributions of all accreted satellites to within a factor of 2. We also find that this method is particularly sensitive to older accretion events involving low-luminous dwarfs e.g. ultra-faint dwarfs - precisely those events that are too ancient to be seen by phase-space studies of stars and too faint to be seen by high-z studies of the early Universe. Since our results only exploit two chemical dimensions and near-future surveys promise to provide ~ 6-9 dimensions, we conclude that these new high-resolution spectroscopic surveys of the stellar halo will allow us (given the development of new CARD-generating dwarf models) to recover the luminosity function of infalling dwarf galaxies - and the detailed accretion history of the halo - across cosmic time.

  12. Reconstructing the Accretion History of the Galactic Halo Using Stellar Chemical Abundance Ratio Distributions

    NASA Astrophysics Data System (ADS)

    Lee, Duane Morris; Johnston, Kathryn V.; Sen, Bodhisattva; Jessop, Will

    2015-08-01

    In this study we tested the prospects of using 2D chemical abundance ratio distributions (CARDs) found in stars of the stellar halo to determine its formation history. First, we used simulated data from eleven ``MW-like'' halos to generate satellite template sets of 2D CARDs of accreted dwarf satellites which are comprised of accreted dwarfs from various mass regimes and epochs of accretion. Next, we randomly drew samples of ~103-4 mock observations of stellar chemical abundance ratios ([α/Fe], [Fe/H]) from those eleven halos to generate samples of the underlying densities for our CARDs to be compared to our templates in our analysis. Finally, we used the expectation-maximization algorithm to derive accretion histories in relation to the satellite template set (STS) used and the sample size. For certain STS used we typically can identify the relative mass contributions of all accreted satellites to within a factor of 2. We also find that this method is particularly sensitive to older accretion events involving low-luminous dwarfs e.g. ultra-faint dwarfs --- precisely those events that are too ancient to be seen by phase-space studies of stars and too faint to be seen by high-z studies of the early Universe. Since our results only exploit two chemical dimensions and near-future surveys promise to provide ~6-9 dimensions, we conclude that these new high-resolution spectroscopic surveys of the stellar halo will allow us (given the development of new CARD-generating dwarf models) to recover the luminosity function of infalling dwarf galaxies --- and the detailed accretion history of the halo --- across cosmic time.

  13. Pathways to massive black holes and compact star clusters in pre-galactic dark matter haloes with virial temperatures >~10000K

    NASA Astrophysics Data System (ADS)

    Regan, John A.; Haehnelt, Martin G.

    2009-06-01

    Large dynamic range numerical simulations of atomic cooling driven collapse of gas in pre-galactic dark matter haloes with Tvir ~ 10000 K show that the gas loses 90 per cent and more of its angular momentum before rotational support sets in. In a fraction of these haloes where the metallicity is low and ultraviolet (UV) radiation suppresses H2 cooling, conditions are thus very favourable for the rapid build-up of massive black holes. Depending on the progression of metal enrichment, the continued suppression of H2 cooling by external and internal UV radiation and the ability to trap the entropy produced by the release of gravitational energy, the gas at the centre of the halo is expected to form a supermassive star, a stellar-mass black hole accreting at super-Eddington accretion rates or a compact star-cluster undergoing collisional run-away of massive stars at its centre. In all three cases, a massive black hole of initially modest mass finds itself at the centre of a rapid inflow of gas with inflow rates of >~1Msolaryr-1. The massive black hole will thus grow quickly to a mass of 105- 106Msolar until further inflow is halted either by consumption of gas by star formation or by the increasing energy and momentum feedback from the growing massive black hole. Conditions for the formation of massive seed black holes in this way are most favourable in haloes with Tvir ~ 15000K and Vvir ~ 20 km s-1 with less massive haloes not allowing collapse of gas by atomic cooling and more massive haloes being more prone to fragmentation. This should imprint a characteristic mass on the mass spectrum of an early population of massive black hole seeds in pre-galactic haloes which will later grow into the observed population of supermassive black holes in galactic bulges.

  14. Neutrino mass and the origin of galactic magnetic fields

    SciTech Connect

    Enqvist, K. ); Semikoz, V. IZMIRAN, Academy of Sciences, Troitsk 142092 ); Shukurov, A. Computing Center, Moscow University, Moscow 119899 ); Sokoloff, D. Isaac Newton Institute, Cambridge University, Cambridge CB3 0EH )

    1993-11-15

    We compare two constraints on the strength of the cosmological primordial magnetic field: the one following from the restrictions on the Dirac neutrino spin flip in the early Universe, and another one based on the galactic dynamo theory for the Milky Way (presuming that the seed magnetic field has a relic origin). Since the magnetic field facilitates transitions between left- and right-handed neutrino states, thereby affecting [sup 4]He production at primordial nucleosynthesis, we can obtain a guaranteed [ital upper] limit on the strength of the relic magnetic field in the protogalaxy, [ital B][sub [ital c

  15. The WENSS & Dwingeloo surveys and the Galactic magnetic field

    NASA Astrophysics Data System (ADS)

    Schnitzeler, D. H. F. M.; Katgert, P.; Haverkorn, M.; de Bruyn, A. G.

    2007-01-01

    Aims:We investigate the structure of the Galactic magnetic field in the 2nd Galactic quadrant using radio continuum polarization data from the 325 MHz WENSS (WEsterbork Northern Sky Survey) survey in combination with earlier single-dish observations. Methods: We study gradients in polarization angle along Galactic longitude and latitude in the region 130° ⪉ l ⪉ 173° and -5° ⪉ b ⪉ 31°. These gradients were determined with a new method that we developed to efficiently and reliably fit linear gradients to periodic data like polarization angles. Since the WENSS data were obtained with a synthesis array they suffer from the "missing short spacing" problem. We have tried to repair this by adding an estimate of the large-scale emission based on the single-dish (Dwingeloo) data obtained by Brouw and Spoelstra. Combining all available data we derive a rotation measure map of the area, from which we estimate all 3 components of the magnetic field vector. Results: In the part of WENSS where large-scale structure in polarized intensity is relatively unimportant, we find that the magnetic field is predominantly perpendicular to the line-of-sight, and parallel to the Galactic plane. The magnetic field components along the line-of-sight and along Galactic latitude have comparable values, and the strength of these components is much smaller than the strength of the total magnetic field. Our observations also cover part of the so-called "fan" region, an area of strong polarized intensity, where large-scale structure is missing from our WENSS data. We tentatively show that Faraday rotation occurring in front of the Perseus arm is causing both the WENSS RM and the RM towards the fan region observed in previous single-dish surveys, and we suggest that the fan is formed by local emission that originates in front of the emission we see in WENSS.

  16. Wide-Field Imaging of Galactic Halos with a Near-Infrared Rocket-Borne Telescope

    NASA Astrophysics Data System (ADS)

    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

  17. Search for gravitational waves from primordial black hole binary coalescences in the galactic halo

    NASA Astrophysics Data System (ADS)

    Abbott, B.; Abbott, R.; Adhikari, R.; Ageev, A.; Allen, B.; Amin, R.; Anderson, S. B.; Anderson, W. G.; Araya, M.; Armandula, H.; Ashley, M.; Asiri, F.; Aufmuth, P.; Aulbert, C.; Babak, S.; Balasubramanian, R.; Ballmer, S.; Barish, B. C.; Barker, C.; Barker, D.; Barnes, M.; Barr, B.; Barton, M. A.; Bayer, K.; Beausoleil, R.; Belczynski, K.; Bennett, R.; Berukoff, S. J.; Betzwieser, J.; Bhawal, B.; Bilenko, I. A.; Billingsley, G.; Black, E.; Blackburn, K.; Blackburn, L.; Bland, B.; Bochner, B.; Bogue, L.; Bork, R.; Bose, S.; Brady, P. R.; Braginsky, V. B.; Brau, J. E.; Brown, D. A.; Bullington, A.; Bunkowski, A.; Buonanno, A.; Burgess, R.; Busby, D.; Butler, W. E.; Byer, R. L.; Cadonati, L.; Cagnoli, G.; Camp, J. B.; Cantley, C. A.; Cardenas, L.; Carter, K.; Casey, M. M.; Castiglione, J.; Chandler, A.; Chapsky, J.; Charlton, P.; Chatterji, S.; Chelkowski, S.; Chen, Y.; Chickarmane, V.; Chin, D.; Christensen, N.; Churches, D.; Cokelaer, T.; Colacino, C.; Coldwell, R.; Coles, M.; Cook, D.; Corbitt, T.; Coyne, D.; Creighton, J. D. E.; Creighton, T. D.; Crooks, D. R. M.; Csatorday, P.; Cusack, B. J.; Cutler, C.; D'Ambrosio, E.; Danzmann, K.; Daw, E.; Debra, D.; Delker, T.; Dergachev, V.; Desalvo, R.; Dhurandhar, S.; Credico, A. Di; Díaz, M.; Ding, H.; Drever, R. W. P.; Dupuis, R. J.; Edlund, J. A.; Ehrens, P.; Elliffe, E. J.; Etzel, T.; Evans, M.; Evans, T.; Fairhurst, S.; Fallnich, C.; Farnham, D.; Fejer, M. M.; Findley, T.; Fine, M.; Finn, L. S.; Franzen, K. Y.; Freise, A.; Frey, R.; Fritschel, P.; Frolov, V. V.; Fyffe, M.; Ganezer, K. S.; Garofoli, J.; Giaime, J. A.; Gillespie, A.; Goda, K.; González, G.; Goßler, S.; Grandclément, P.; Grant, A.; Gray, C.; Gretarsson, A. M.; Grimmett, D.; Grote, H.; Grunewald, S.; Guenther, M.; Gustafson, E.; Gustafson, R.; Hamilton, W. O.; Hammond, M.; Hanson, J.; Hardham, C.; Harms, J.; Harry, G.; Hartunian, A.; Heefner, J.; Hefetz, Y.; Heinzel, G.; Heng, I. S.; Hennessy, M.; Hepler, N.; Heptonstall, A.; Heurs, M.; Hewitson, M.; Hild, S.; Hindman, N.; Hoang, P.; Hough, J.; Hrynevych, M.; Hua, W.; Ito, M.; Itoh, Y.; Ivanov, A.; Jennrich, O.; Johnson, B.; Johnson, W. W.; Johnston, W. R.; Jones, D. I.; Jones, L.; Jungwirth, D.; Kalogera, V.; Katsavounidis, E.; Kawabe, K.; Kawamura, S.; Kells, W.; Kern, J.; Khan, A.; Killbourn, S.; Killow, C. J.; Kim, C.; King, C.; King, P.; Klimenko, S.; Koranda, S.; Kötter, K.; Kovalik, J.; Kozak, D.; Krishnan, B.; Landry, M.; Langdale, J.; Lantz, B.; Lawrence, R.; Lazzarini, A.; Lei, M.; Leonor, I.; Libbrecht, K.; Libson, A.; Lindquist, P.; Liu, S.; Logan, J.; Lormand, M.; Lubiński, M.; Lück, H.; Lyons, T. T.; Machenschalk, B.; Macinnis, M.; Mageswaran, M.; Mailand, K.; Majid, W.; Malec, M.; Mann, F.; Marin, A.; Márka, S.; Maros, E.; Mason, J.; Mason, K.; Matherny, O.; Matone, L.; Mavalvala, N.; McCarthy, R.; McClelland, D. E.; McHugh, M.; McNabb, J. W. C.; Mendell, G.; Mercer, R. A.; Meshkov, S.; Messaritaki, E.; Messenger, C.; Mitrofanov, V. P.; Mitselmakher, G.; Mittleman, R.; Miyakawa, O.; Miyoki, S.; Mohanty, S.; Moreno, G.; Mossavi, K.; Mueller, G.; Mukherjee, S.; Murray, P.; Myers, J.; Nagano, S.; Nash, T.; Nayak, R.; Newton, G.; Nocera, F.; Noel, J. S.; Nutzman, P.; Olson, T.; O'Reilly, B.; Ottaway, D. J.; Ottewill, A.; Ouimette, D.; Overmier, H.; Owen, B. J.; Pan, Y.; Papa, M. A.; Parameshwaraiah, V.; Parameswaran, A.; Parameswariah, C.; Pedraza, M.; Penn, S.; Pitkin, M.; Plissi, M.; Prix, R.; Quetschke, V.; Raab, F.; Radkins, H.; Rahkola, R.; Rakhmanov, M.; Rao, S. R.; Rawlins, K.; Ray-Majumder, S.; Re, V.; Redding, D.; Regehr, M. W.; Regimbau, T.; Reid, S.; Reilly, K. T.; Reithmaier, K.; Reitze, D. H.; Richman, S.; Riesen, R.; Riles, K.; Rivera, B.; Rizzi, A.; Robertson, D. I.; Robertson, N. A.; Robison, L.; Roddy, S.; Rollins, J.; Romano, J. D.; Romie, J.; Rong, H.; Rose, D.; Rotthoff, E.; Rowan, S.; Rüdiger, A.; Russell, P.; Ryan, K.; Salzman, I.; Sandberg, V.; Sanders, G. H.; Sannibale, V.; Sathyaprakash, B.; Saulson, P. R.; Savage, R.; Sazonov, A.; Schilling, R.; Schlaufman, K.; Schmidt, V.; Schnabel, R.; Schofield, R.; Schutz, B. F.; Schwinberg, P.; Scott, S. M.; Seader, S. E.; Searle, A. C.; Sears, B.; Seel, S.; Seifert, F.; Sengupta, A. S.; Shapiro, C. A.; Shawhan, P.; Shoemaker, D. H.; Shu, Q. Z.; Sibley, A.; Siemens, X.; Sievers, L.; Sigg, D.; Sintes, A. M.; Smith, J. R.; Smith, M.; Smith, M. R.; Sneddon, P. H.; Spero, R.; Stapfer, G.; Steussy, D.; Strain, K. A.; Strom, D.; Stuver, A.; Summerscales, T.; Sumner, M. C.; Sutton, P. J.; Sylvestre, J.; Takamori, A.; Tanner, D. B.; Tariq, H.; Taylor, I.; Taylor, R.; Taylor, R.; Thorne, K. A.; Thorne, K. S.; Tibbits, M.; Tilav, S.; Tinto, M.; Tokmakov, K. V.; Torres, C.; Torrie, C.; Traylor, G.; Tyler, W.; Ugolini, D.; Ungarelli, C.; Vallisneri, M.; van Putten, M.; Vass, S.; Vecchio, A.

    2005-10-01

    We use data from the second science run of the LIGO gravitational-wave detectors to search for the gravitational waves from primordial black hole binary coalescence with component masses in the range 0.2-1.0M⊙. The analysis requires a signal to be found in the data from both LIGO observatories, according to a set of coincidence criteria. No inspiral signals were found. Assuming a spherical halo with core radius 5 kpc extending to 50 kpc containing nonspinning black holes with masses in the range 0.2-1.0M⊙, we place an observational upper limit on the rate of primordial black hole coalescence of 63 per year per Milky Way halo (MWH) with 90% confidence.

  18. H I IN LOCAL GROUP DWARF GALAXIES AND STRIPPING BY THE GALACTIC HALO

    SciTech Connect

    Grcevich, Jana; Putman, Mary E E-mail: mputman@astro.columbia.edu

    2009-05-01

    We examine the H I content and environment of all of the Local Group dwarf galaxies (M {sub tot} < 10{sup 10} M {sub sun}), including the numerous newly discovered satellites of the Milky Way and M31. All of the new dwarfs, with the exception of Leo T, have no detected H I. The majority of dwarf galaxies within {approx}270 kpc of the Milky Way or Andromeda are undetected in H I (<10{sup 4} M {sub sun} for Milky Way dwarfs), while those further than {approx}270 kpc are predominantly detected with masses {approx}10{sup 5} to 10{sup 8} M {sub sun}. Analytical ram-pressure arguments combined with velocities obtained via proper motion studies allow for an estimate of the halo density of the Milky Way at several distances. This halo density is constrained to be greater than 2x 10{sup -4}-3 x 10{sup -4} cm{sup -3} out to distances of at least 70 kpc. This is broadly consistent with theoretical models of the diffuse gas in a Milky Way-like halo and is consistent with this component hosting a large fraction of a galaxy's baryons. Accounting for completeness in the dwarf galaxy count, gasless dwarf galaxies could have provided at most 2.1 x 10{sup 8} M {sub sun} of H I gas to the Milky Way, which suggests that most of our Galaxy's star formation fuel does not come from accreted small satellites in the current era.

  19. The Galactic Magnetic Field as Viewed from the VLA

    NASA Astrophysics Data System (ADS)

    van Eck, Cameron; Brown, Jo-Anne

    2009-05-01

    Interstellar magnetic fields play critical roles in many astrophysical processes. Yet despite their importance, our knowledge about magnetic fields in our Galaxy remains limited. For the field within the Milky Way much of what we do know comes from radio astronomy, through observations of polarization and Faraday rotation measures (RMs) of extragalactic sources and pulsars. A high angular density of RM measurements in several critical areas of the Galaxy is needed to clarify the Galactic magnetic field structure. Understanding the overall structure of the magnetic field will subsequently help us determine the origin and evolution of the field. In an effort to determine the overall structure of the field, Sun et al. (2008) produced 3 models of the Galactic magnetic field based on RM measurements available at the time. These models made distinct predictions for RMs in a region of the inner Galaxy at low Galactic latitude. Using observations made with the Very Large Array (VLA), we have determined RMs for sources in this critical region. In this talk we will present the results of our study and show how the RMs strongly support the ASS+RING model.

  20. Low-background balloon-borne direct search for ionizing massive particles as a component of the dark galactic halo matter

    NASA Astrophysics Data System (ADS)

    McGuire, Patrick Charles

    A dark matter (DM) search experiment was flown on the IMAX balloon payload, which tested the hypothesis that a minor component of the dark matter in the Galactic halo is composed of ionizing (dE/dx greater than 1 MeV/g/cm2 or sigma greater than 2 x 10-20 sq cm supermassive particles (mx is an element of (104, 1012)GeV/c2 that cannot penetrate the atmosphere due to their low velocities (beta belongs to (0.0003, 0.00025)). The DM search experiment consisted of a delayed coincidence between four approximately 2400 cm2 plastic scintillation detectors, with a total acceptance of approximately 100 cm2 sr. In order to search for ultra-slow particles which do not slow down in the IMAX telescope, the experiment contained TDCs which measured the time-delays Ti,i+1is an element of (0.3, 14.0)microseconds between hits in a successive counters to approximately 1 percent precision. Using the first 5 hours of data at float altitude (5 g/sq cm residual atmosphere), we observed approximately 5 candidate non-slowing dark matter events, consistent with the background from accidental coincidences of 4 events. This implies that the DM flux is less than 6.5 x 10-6 cm-2s-1sr-1 (95 percent C.L.). Similar results were also obtained for particles which slow down in the counter telescope. This experiment effectively closes much of a previously unconstrained 'window' in the mass/cross-section joint parameter space for massive particles as the dominant halo DM, and implies that for certain regions of this parameter space massive particles cannot be more than one part in 105 by mass of all the DM. These results can also directly constrain 'light' magnetic monopoles and neutra CHAMPs in a previously unconstrained mass region mx belongs to (106, 109) GeV.

  1. Dark matter annihilation and decay from non-spherical dark halos in galactic dwarf satellites

    NASA Astrophysics Data System (ADS)

    Hayashi, Kohei; Ichikawa, Koji; Matsumoto, Shigeki; Ibe, Masahiro; Ishigaki, Miho N.; Sugai, Hajime

    2016-09-01

    The dwarf spheroidal galaxies (dSphs) in the Milky Way are the primary targets in the indirect searches for particle dark matter. To set robust constraints on candidate dark matter particles, understanding the dark halo structure of these systems is of substantial importance. In this paper, we first evaluate the astrophysical factors for dark matter annihilation and decay for 24 dSphs, taking into account a non-spherical dark halo, using generalized axisymmetric mass models based on axisymmetric Jeans equations. First, from a fitting analysis of the most recent kinematic data available, our axisymmetric mass models are a much better fit than previous spherical ones, thus, our work should be the most realistic and reliable estimator for astrophysical factors. Secondly, we find that among analysed dSphs, the ultra-faint dwarf galaxies Triangulum II and Ursa Major II are the most promising but large uncertain targets for dark matter annihilation while the classical dSph Draco is the most robust and detectable target for dark matter decay. It is also found that the non-sphericity of luminous and dark components influences the estimate of astrophysical factors, even though these factors largely depend on the sample size, the prior range of parameters and the spatial extent of the dark halo. Moreover, owing to these effects, the constraints on the dark matter annihilation cross-section are more conservative than those of previous spherical works. These results are important for optimizing and designing dark matter searches in current and future multi-messenger observations by space and ground-based telescopes.

  2. The Outer Galactic Halo As Probed By RR Lyr Stars From the Palomar Transient Facility + Keck

    NASA Astrophysics Data System (ADS)

    Cohen, Judith; Sesar, Branimir; Banholzer, Sophianna

    2016-08-01

    We present initial results from our study of the outer halo of the Milky Way using a large sample of RR Lyr(ab) variables datamined from the archives of the Palomar Transient Facility. Of the 464 RR Lyr in our sample with distances exceeding 50 kpc, 62 have been observed spectroscopically at the Keck Observatory. vr and σ(vr ) are given as a function of distance between 50 and 110 kpc, and a very preliminary rather low total mass for the Milky Way out to 110 kpc of ~7+/-1.5×1011 M ⊙ is derived from our data.

  3. Inhomogeneous halo collapse and early Galactic chemical evolution - Globular cluster metallicities

    NASA Technical Reports Server (NTRS)

    Malinie, G.; Hartmann, D. H.; Mathews, G. J.

    1991-01-01

    A new solution to the observed Galactic globular cluster metallicity distribution is proposed by considering inhomogeneous collapse of a centrally condensed proto-Galaxy. In contrast to the standard one-zone model, it is shown that, for inhomogeneous models, the metallicity distribution can be reproduced without the need to decrease the nucleosynthetic yield for metal-poor stars. Chemical evolution in free fall is calculated analytically. A hybrid hydroparticle code is developed to study the effect of supernova induced pressure.

  4. Glow in the dark matter: observing galactic halos with scattered light.

    PubMed

    Davis, Jonathan H; Silk, Joseph

    2015-02-01

    We consider the observation of diffuse halos of light around the discs of spiral galaxies, as a probe of the interaction cross section between dark matter (DM) and photons. Using the galaxy M101 as an example, we show that for a scattering cross section at the level of 10(-23)(m/GeV)  cm(2) or greater dark matter in the halo will scatter light out from the more luminous center of the disc to larger radii, contributing to an effective increased surface brightness at the edges of the observed area on the sky. This allows us to set an upper limit on the DM-photon cross section using data from the Dragonfly instrument. We then show how to improve this constraint, and the potential for discovery, by combining the radial profile of DM-photon scattering with measurements at multiple wavelengths. Observation of diffuse light presents a new and potentially powerful way to probe the interactions of dark matter with photons, a way that is complementary to existing searches. PMID:25699431

  5. Glow in the Dark Matter: Observing Galactic Halos with Scattered Light

    NASA Astrophysics Data System (ADS)

    Davis, Jonathan H.; Silk, Joseph

    2015-02-01

    We consider the observation of diffuse halos of light around the discs of spiral galaxies, as a probe of the interaction cross section between dark matter (DM) and photons. Using the galaxy M101 as an example, we show that for a scattering cross section at the level of 10-23(m /GeV ) cm2 or greater dark matter in the halo will scatter light out from the more luminous center of the disc to larger radii, contributing to an effective increased surface brightness at the edges of the observed area on the sky. This allows us to set an upper limit on the DM-photon cross section using data from the Dragonfly instrument. We then show how to improve this constraint, and the potential for discovery, by combining the radial profile of DM-photon scattering with measurements at multiple wavelengths. Observation of diffuse light presents a new and potentially powerful way to probe the interactions of dark matter with photons, a way that is complementary to existing searches.

  6. Searching for planetary nebulae at the Galactic halo via J-PAS

    NASA Astrophysics Data System (ADS)

    Gonçalves, Denise R.; Aparício-Villegas, T.; Akras, S.; Cortesi, A.; Borges-Fernandes, M.; Daflon, S.; Pereira, C. B.; Lorenz-Martins, S.; Marcolino, W.; Kanaan, A.; Viironen, K.; de Oliveira, C. Mendes; Molino, A.; Ederoclite, A.

    2016-08-01

    The Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS) is a narrow-band imaging, very wide field cosmological survey. It will last 5 years and will observe 8500 sq. deg. of the sky. There will be 54 contiguous narrow-band filters of 145Å FWHM, from 3,500 to 10,000Å. Two broad-band filters will be added at the extremes, UV and IR, plus the 3-g, r, and i- SDSS filters. Thus, J-PAS can be an important tool to search for new planetary nebulae (PNe) at the halo, increasing their numbers, because only 14 of them have been convincingly identified in the literature. Halo PNe are able to reveal precious information for the study of stellar evolution and the early chemical conditions of the Galaxy. The characteristic low continuum and intense emission lines of PNe make them good objects to be searched by J-PAS. Though covering a significantly smaller sky area, data from the ALHAMBRA survey were used to test our J-PAS strategy to search for PNe. Our first results are shown in this contribution.

  7. 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.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Brandt, Theresa 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.; Chekhtman, A.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Conrad, J.; Cuoco, A.; Guiriec, Sylvain Germain; McEnery, Julie E.; Scargle. J. D.; Troja, Eleonora

    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.

  8. Searching for planetary nebulae at the Galactic halo via J-PAS and J-PLUS

    NASA Astrophysics Data System (ADS)

    Goncalves, Denise R.; Aparício-Villegas, Teresa; Akras, Stavros; Borges Fernandes, Marcelo; J-PAS Collaboration

    2015-08-01

    The Javalambre-Physics of the Accelerating Universe Astrophysical Survey (J-PAS) is a narrow-band imaging, very wide field cosmological survey to be carried out from a dedicated 2.5m telescope and a 4.7 sq.deg camera with 1.2Gpix. It will last 5 years and will observe 8500 sq.deg of Northern sky to a 5-σ magnitude depth for point sources, equivalent to i ~23.3 over an aperture of 2 arcsec2. The J-PAS filter system consists of 54 contiguous narrow band filters of 145-Å FWHM, from 3,500 to 10,000Å. Two broad-band filters will be added at the extremes, UV and IR, plus 3 SDSS g, r, and i filters. The Javalambre Photometric Local Universe Survye (J-PLUS) will be an auxiliary survey ofJ-PAS (mainly for calibration) with a dedicated 0.80m telescope. J-PLUS comprises 12 filters, including g, r, i and z SDSS ones. Though about 2,500 planetary nebulae (PNe, confirmed spectroscopically) are known in the Galaxy, only 14 objects have been convincingly identified as halo PNe. They were classified as such from their location, kinematics and chemistry. Halo PNe are able to reveal precious information for the study of low- and intermediate-mass star evolution and the early chemical conditions of the Galaxy. The characteristic low continuum and intense line emissions of PNe make them good objects to be searched by J-PAS, and even by J-PLUS. For instance, the halo PNe BoBn 1, DdDm 1 and PS 1, located somewhere between 11 and 24 kpc from the Sun, have B magnitudes of 16, 14 and 13.4, respectively. Such values are easily encompassed by J-PAS/J-PLUS, given the typical limit magnitude of the survey. Though covering a significantly smaller sky area, data from the ALHAMBRA survey were used to test our J-PAS/J-PLUS strategy to search for PNe. Our first results will be shown in this poster.

  9. Evolution of heavy-element abundances in the Galactic halo and disk

    NASA Technical Reports Server (NTRS)

    Mathews, G. J.; Cowan, J. J.; Schramm, D. N.

    1988-01-01

    The constraints on the universal energy density and cosmological constant from cosmochronological ages and the Hubble age are reviewed. Observational evidence for the galactic chemical evolution of the heavy-element chronometers is descirbed in the context of numerical models. The viability of the recently discovered Th/Nd stellar chronometer is discussed, along with the suggestion that high r-process abundances in metal-poor stars may have resulted from a primordial r-process, as may be required by some inhomogeneous cosmologies.

  10. On the Density of Primordial Black Holes in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Wright, Edward L.

    1996-03-01

    Calculations of the rate of local primordial black hole (PBH) explosions often assume that the PBHs can be highly concentrated into galaxies, thereby weakening the Page-Hawking limit on the cosmological density of PBHs. But if the PBHs are concentrated by a factor exceeding c/(H_{0 }R0) 4 x 10 , where R_{0 }= 8.5 kpc is the scale of the Milky Way, then the steady emission from the PBHs in the halo will produce an anisotropic high-latitude diffuse gamma-ray intensity larger than the observed anisotropy. This provides a limit on the rate density of evaporating PBHs of 0.4 pc -3 yr -1, which is more than 6 orders of magnitude lower than recent experimental limits. However, the weak observed anisotropic high-latitude diffuse gamma-ray intensity is consistent with the idea that the dark matter that closes the universe is Planck mass remnants of evaporated black holes.

  11. Enhanced tidal stripping of satellites in the galactic halo from dark matter self-interactions

    NASA Astrophysics Data System (ADS)

    Dooley, Gregory A.; Peter, Annika H. G.; Vogelsberger, Mark; Zavala, Jesús; Frebel, Anna

    2016-09-01

    We investigate the effects of self-interacting dark matter (SIDM) on the tidal stripping and evaporation of satellite galaxies in a Milky Way-like host. We use a suite of five zoom-in, dark-matter-only simulations, two with velocity-independent SIDM cross-sections, two with velocity-dependent SIDM cross-sections, and one cold dark matter (CDM) simulation for comparison. After carefully assigning stellar mass to satellites at infall, we find that stars are stripped at a higher rate in SIDM than in CDM. In contrast, the total bound dark matter mass-loss rate is minimally affected, with subhalo evaporation having negligible effects on satellites for viable SIDM models. Centrally located stars in SIDM haloes disperse out to larger radii as cores grow. Consequently, the half-light radius of satellites increases, stars become more vulnerable to tidal stripping, and the stellar mass function is suppressed. We find that the ratio of core radius to tidal radius accurately predicts the relative strength of enhanced SIDM stellar stripping. Velocity-independent SIDM models show a modest increase in the stellar stripping effect with satellite mass, whereas velocity-dependent SIDM models show a large increase in this effect towards lower masses, making observations of ultrafaint dwarfs prime targets for distinguishing between and constraining SIDM models. Due to small cores in the largest satellites of velocity-dependent SIDM, no identifiable imprint is left on the all-sky properties of the stellar halo. While our results focus on SIDM, the main physical mechanism of enhanced tidal stripping of stars apply similarly to satellites with cores formed via other means.

  12. Bright gamma-ray Galactic Center excess and dark dwarfs: Strong tension for dark matter annihilation despite Milky Way halo profile and diffuse emission uncertainties

    NASA Astrophysics Data System (ADS)

    Abazajian, Kevork N.; Keeley, Ryan E.

    2016-04-01

    We incorporate Milky Way dark matter halo profile uncertainties, as well as an accounting of diffuse gamma-ray emission uncertainties in dark matter annihilation models for the Galactic Center Extended gamma-ray excess (GCE) detected by the Fermi Gamma Ray Space Telescope. The range of particle annihilation rate and masses expand when including these unknowns. However, two of the most precise empirical determinations of the Milky Way halo's local density and density profile leave the signal region to be in considerable tension with dark matter annihilation searches from combined dwarf galaxy analyses for single-channel dark matter annihilation models. The GCE and dwarf tension can be alleviated if: one, the halo is very highly concentrated or strongly contracted; two, the dark matter annihilation signal differentiates between dwarfs and the GC; or, three, local stellar density measures are found to be significantly lower, like that from recent stellar counts, increasing the local dark matter density.

  13. SEGUE-2 LIMITS ON METAL-RICH OLD-POPULATION HYPERVELOCITY STARS IN THE GALACTIC HALO

    SciTech Connect

    Kollmeier, Juna A.; Gould, Andrew; Johnson, Jennifer A.; Rockosi, Constance; Beers, Timothy C.; Lee, Young Sun; Knapp, Gillian; Morrison, Heather; Harding, Paul; Weaver, Benjamin A.

    2010-11-01

    We present new limits on the ejection of metal-rich old-population hypervelocity stars (HVSs) from the Galactic center (GC) as probed by the SEGUE-2 survey. Our limits are a factor of 3-10 more stringent than previously reported, depending on stellar type. Compared to the known population of B-star ejectees, there can be no more than 30 times more metal-rich old-population F/G stars ejected from the GC. Because B stars comprise a tiny fraction of a normal stellar population, this places significant limits on the combination of the GC mass function and the ejection mechanism for HVSs. In the presence of a normal GC mass function, our results require an ejection mechanism that is about 5.5 times more efficient at ejecting B stars compared to low-mass F/G stars.

  14. X-ray absorption/emission line spectroscopy of the Galactic hot gaseous halo

    NASA Astrophysics Data System (ADS)

    Wang, Daniel

    2016-04-01

    There is an ongoing debate as to whether or not the Milky Way is surrounded by a large-scale, massive corona. Vastly different conclusions as to its extent and mass have been drawn from existing studies based on X-ray absorption and/or emission line spectroscopy. I will discuss my assessment of this issue, focusing on various uncertainties and potential problems in the present data, analyses, results, and interpretations.In particular, I will examine how different assumptions about the temperature distribution of the corona affect the inference of its physical scale. I will also discuss the external perspectives of galactic coronae obtained form observing nearby highly-inclined disk galaxies.

  15. 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.

  16. A NEW MILKY WAY HALO STAR CLUSTER IN THE SOUTHERN GALACTIC SKY

    SciTech Connect

    Balbinot, E.; Santiago, B. X.; Da Costa, L.; Maia, M. A. G.; Rocha-Pinto, H. J.; Majewski, S. R.; Nidever, D.; Thomas, D.; Wechsler, R. H.; Yanny, B.

    2013-04-20

    We report on the discovery of a new Milky Way (MW) companion stellar system located at ({alpha}{sub J2000,}{delta}{sub J2000}) = (22{sup h}10{sup m}43{sup s}.15, 14 Degree-Sign 56 Prime 58 Double-Prime .8). The discovery was made using the eighth data release of SDSS after applying an automated method to search for overdensities in the Baryon Oscillation Spectroscopic Survey footprint. Follow-up observations were performed using Canada-France-Hawaii-Telescope/MegaCam, which reveal that this system is comprised of an old stellar population, located at a distance of 31.9{sup +1.0}{sub -1.6} kpc, with a half-light radius of r{sub h}= 7.24{sup +1.94}{sub -1.29} pc and a concentration parameter of c = log{sub 10}(r{sub t} /r{sub c} ) = 1.55. A systematic isochrone fit to its color-magnitude diagram resulted in log (age yr{sup -1}) = 10.07{sup +0.05}{sub -0.03} and [Fe/H] = -1.58{sup +0.08}{sub -0.13}. These quantities are typical of globular clusters in the MW halo. The newly found object is of low stellar mass, whose observed excess relative to the background is caused by 95 {+-} 6 stars. The direct integration of its background decontaminated luminosity function leads to an absolute magnitude of M{sub V} = -1.21 {+-} 0.66. The resulting surface brightness is {mu}{sub V} = 25.90 mag arcsec{sup -2}. Its position in the M{sub V} versus r{sub h} diagram lies close to AM4 and Koposov 1, which are identified as star clusters. The object is most likely a very faint star cluster-one of the faintest and lowest mass systems yet identified.

  17. STELLAR ARCHEOLOGY IN THE GALACTIC HALO WITH ULTRA-FAINT DWARFS. VII. HERCULES

    SciTech Connect

    Musella, Ilaria; Ripepi, Vincenzo; Marconi, Marcella E-mail: ripepi@na.astro.it; and others

    2012-09-10

    We present the first time-series study of the ultra-faint dwarf galaxy Hercules. Using a variety of telescope/instrument facilities we secured about 50 V and 80 B epochs. These data allowed us to detect and characterize 10 pulsating variable stars in Hercules. Our final sample includes six fundamental-mode (ab-type) and three first-overtone (c-type) RR Lyrae stars, and one Anomalous Cepheid. The average period of the ab-type RR Lyrae stars, (P{sub ab}) = 0.68 days ({sigma} = 0.03 days), places Hercules in the Oosterhoff II group, as found for almost the totality of the ultra-faint dwarf galaxies investigated so far for variability. The RR Lyrae stars were used to obtain independent estimates of the metallicity, reddening, and distance to Hercules, for which we find [Fe/H] = -2.30 {+-} 0.15 dex, E(B - V) = 0.09 {+-} 0.02 mag, and (m - M){sub 0} = 20.6 {+-} 0.1 mag, in good agreement with the literature values. We have obtained a V, B - V color-magnitude diagram (CMD) of Hercules that reaches V {approx} 25 mag and extends beyond the galaxy's half-light radius over a total area of 40' Multiplication-Sign 36'. The CMD and the RR Lyrae stars indicate the presence of a population as old and metal-poor as (at least) the Galactic globular cluster M68.

  18. STELLAR ARCHAEOLOGY IN THE GALACTIC HALO WITH THE ULTRA-FAINT DWARFS. VI. URSA MAJOR II

    SciTech Connect

    Dall'Ora, M.; Ripepi, Vincenzo; Marconi, Marcella; Musella, Ilaria E-mail: ripepi@na.astro.it E-mail: ilaria@na.astro.it; and others

    2012-06-10

    We present a B, V color-magnitude diagram (CMD) of the Milky Way dwarf satellite Ursa Major II (UMa II), spanning the magnitude range from V {approx} 15 to V {approx} 23.5 mag and extending over an 18 Multiplication-Sign 18 arcmin{sup 2} area centered on the Galaxy. Our photometry goes down to about 2 mag below the Galaxy's main-sequence turnoff that we detected at V {approx} 21.5 mag. We have discovered a bona fide RR Lyrae variable star in UMa II, which we use to estimate a conservative dereddened distance modulus for the galaxy of (m - M){sub 0} = 17.70 {+-} 0.04 {+-} 0.12 mag, where the first error accounts for the uncertainties of the calibrated photometry, and the second reflects our lack of information on the metallicity of the star. The corresponding distance to UMa II is 34.7{sup +0.6}{sub -0.7}({sup +2.0}{sub -1.9}) kpc. Our photometry shows evidence of a spread in the Galaxy's subgiant branch, compatible with a spread in metal abundance in the range between Z = 0.0001 and Z = 0.001. Based on our estimate of the distance, a comparison of the fiducial lines of the Galactic globular clusters M68 and M5 ([Fe/H] = -2.27 {+-} 0.04 dex and -1.33 {+-} 0.02 dex, respectively), with the position on the CMD of spectroscopically confirmed Galaxy members, may suggest the existence of stellar populations of different metal abundance/age in the central region of UMa II.

  19. Stellar Archeology in the Galactic Halo with Ultra-faint Dwarfs. VII. Hercules

    NASA Astrophysics Data System (ADS)

    Musella, Ilaria; Ripepi, Vincenzo; Marconi, Marcella; Clementini, Gisella; Dall'Ora, Massimo; Scowcroft, Victoria; Moretti, Maria Ida; Di Fabrizio, Luca; Greco, Claudia; Coppola, Giuseppina; Bersier, David; Catelan, Márcio; Grado, Aniello; Limatola, Luca; Smith, Horace A.; Kinemuchi, Karen

    2012-09-01

    We present the first time-series study of the ultra-faint dwarf galaxy Hercules. Using a variety of telescope/instrument facilities we secured about 50 V and 80 B epochs. These data allowed us to detect and characterize 10 pulsating variable stars in Hercules. Our final sample includes six fundamental-mode (ab-type) and three first-overtone (c-type) RR Lyrae stars, and one Anomalous Cepheid. The average period of the ab-type RR Lyrae stars, langP abrang = 0.68 days (σ = 0.03 days), places Hercules in the Oosterhoff II group, as found for almost the totality of the ultra-faint dwarf galaxies investigated so far for variability. The RR Lyrae stars were used to obtain independent estimates of the metallicity, reddening, and distance to Hercules, for which we find [Fe/H] = -2.30 ± 0.15 dex, E(B - V) = 0.09 ± 0.02 mag, and (m - M)0 = 20.6 ± 0.1 mag, in good agreement with the literature values. We have obtained a V, B - V color-magnitude diagram (CMD) of Hercules that reaches V ~ 25 mag and extends beyond the galaxy's half-light radius over a total area of 40' × 36'. The CMD and the RR Lyrae stars indicate the presence of a population as old and metal-poor as (at least) the Galactic globular cluster M68. Based on data collected at the 2.5 m Isaac Newton Telescope, La Palma, Canary Islands, Spain, at the 4.2 m William Herschel Telescope, Roche de los Muchachos, Canary Islands, Spain, at the 2.2 m ESO/MPI telescope, La Silla, Chile, Proposal 079.D-0587, at the 2 m Liverpool Telescope, Roche de los Muchachos, Canary Islands, Spain, and at the 2 m Faulkes Telescope North, Haleakala Observatory, Hawaii, USA.

  20. BVRI and UBV Photometry of Metal-Poor and Horizontal-Branch Candidates in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    De Lee, N.; Beers, T. C.; Smith, H. A.; Marsteller, B.; Krugler, J.; Lee, Y.; Wilhelm, R.; Terndrup, D.

    2005-12-01

    We report on UBVRI CCD photometry that has been obtained over the course of the past seven years for a sample of over 1600 metal-poor (MP), field horizontal-branch (FHB), and other A-type candidates selected from two large objective-prism surveys, the HK survey of Beers and collaborators and the Hamburg/ESO stellar survey of Christlieb and colleagues. These stars either have, or soon will have, medium-resolution (1-2 Å) spectroscopy obtained with various 2.5m - 4m class telescopes, including the SOAR 4.1m. These observations are being employed for several purposes. In the case of the FHB/A stars, the UBV photometry is useful for separating out low-gravity stars from the high-gravity ones. The subsample of high-gravity A-type stars includes Blue Metal Poor stars, halo and thick-disk blue stragglers, main-sequence A-type dwarfs, and Am and Ap stars. These observations are also being used to derive photometric distance estimates that will aid studies of high-velocity hydrogen clouds in the Galaxy, as well as to refine Galactic mass measurements. The data for the low-metallicity objects will be used to obtain estimates of temperatures that are required for elemental abundance studies based on future high-resolution spectroscopic observations, as well as to estimate distances for use in kinematic studies. T.C.B. and Y.L. acknowledge partial support from grant AST 04-06784, as well as from grant PHY 02-16783, Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA), awarded by the US National Science Foundation.

  1. Highly Ionized Gas in the Galactic Halo and the High Velocity Clouds Toward PG 1116+215

    NASA Astrophysics Data System (ADS)

    Ganguly, R.; Sembach, K. R.; Tripp, T. M.; Savage, B. D.

    2003-12-01

    Recent observations of extragalactic objects with FUSE have revealed the presence of high ionization OVI absorption associated with high velocity clouds (HVCs), defined as gas which lies at absolute velocities beyond 100 km/s in the Local Standard of Rest. We have acquired high spectral resolution observations with STIS ( ˜ 10 km/s) and FUSE ( ˜ 20 km/s) of the quasar PG 1116+215. The spectra show absorption at Vlsr=184km/s from a wide range of ionization species:CIV, OI, OVI, MgII, SiII, SiIII, SiIV, and FeII. The strong and broad O VI absorption in this HVC extends from ˜ 120 to 230 km/s with a weak wing of absorption to 300km/s. Although the HVC is not seen in HI 21 cm emission down to N(HI) ˜ 2x1018 cm-2, it is seen in the HI Lyman series up to at least the 918.13Å line. In addition, we have non-detection constraints on the column denisties of CI, NI, NV, and SII. We can rule out photoionization in an ultra-low density (n ˜ 10-6 cm-3) Local Group medium adopted by some investigators to explain the O VI and O VII absorption detected in several directions. We are currently in the process of determining if these data either support or rule out other models of HVCs, such as the Warm-Hot Intergalactic Medium, Dark Matter dominated mini-halos, or interactions with a low density (10-4-10-5 cm-3) Galactic corona or Local Group medium. In addition, we will also use abundance infomation to study the enrichment history and constrain possible sources for the high velocity gas, such as tidal debris from cannibalized galaxies.

  2. Magnetic monopole plasma oscillations and the survival of Galactic magnetic fields

    SciTech Connect

    Parker, E.N.

    1987-10-01

    This paper explores the general nature of magnetic-monopole plasma oscillations as a theoretical possibility for the observed Galactic magnetic field in the presence of a high abundance of magnetic monopoles. The modification of the hydromagnetic induction equation by the monopole oscillations produces the half-velocity effect, in which the magnetic field is transported bodily with a velocity midway between the motion of the conducting fluid and the monopole plasma. Observational studies of the magnetic field in the Galaxy, and in other galaxies, exclude the half-velocity effect, indicating that the magnetic fields is not associated with monopole oscillations. In any case the phase mixing would destroy the oscillations in less than 100 Myr. The conclusion is that magnetic monopole oscillations do not play a significant role in the galactic magnetic fields. Hence the existence of galactic magnetic fields places a low limit on the monopole flux, so that their detection - if they exist at all - requires a collecting area at least as large as a football field. 47 references.

  3. GLOBULAR CLUSTERS IN THE OUTER GALACTIC HALO: NEW HUBBLE SPACE TELESCOPE/ADVANCED CAMERA FOR SURVEYS IMAGING OF SIX GLOBULAR CLUSTERS AND THE GALACTIC GLOBULAR CLUSTER AGE-METALLICITY RELATION

    SciTech Connect

    Dotter, Aaron; Anderson, Jay; Sarajedini, Ata

    2011-09-01

    Color-magnitude diagrams (CMDs) derived from Hubble Space Telescope (HST) Advanced Camera for Surveys F606W, F814W photometry of six globular clusters (GCs) are presented. The six GCs form two loose groupings in Galactocentric distance (R{sub GC}): IC 4499, NGC 6426, and Ruprecht 106 at {approx}15-20 kpc and NGC 7006, Palomar 15, and Pyxis at {approx}40 kpc. The CMDs allow the ages to be estimated from the main-sequence turnoff in every case. In addition, the age of Palomar 5 (R{sub GC} {approx} 18 kpc) is estimated using archival HST Wide Field Planetary Camera 2 V, I photometry. The age analysis reveals the following: IC 4499, Ruprecht 106, and Pyxis are 1-2 Gyr younger than inner halo GCs with similar metallicities; NGC 7006 and Palomar 5 are marginally younger than their inner halo counterparts; NGC 6426 and Palomar 15, the two most metal-poor GCs in the sample, are coeval with all the other metal-poor GCs within the uncertainties. Combined with our previous efforts, the current sample provides strong evidence that the Galactic GC age-metallicity relation consists of two distinct branches. One suggests a rapid chemical enrichment in the inner Galaxy while the other suggests prolonged GC formation in the outer halo. The latter is consistent with the outer halo GCs forming in dwarf galaxies and later being accreted by the Milky Way.

  4. Looking for building blocks of the Galactic halo: variable stars in the Fornax, Bootes I, Canes Venatici II dwarfs and in NGC 2419

    NASA Astrophysics Data System (ADS)

    Greco, Claudia; Clementini, Gisella; Held, E. V.; Poretti, E.; Catelan, M.; Federici, L.; Maio, M.; Gullieuszik, M.; Ripepi, V.; Dall'Ora, M.; Di Fabrizio, L.; Kinemuchi, K.; Di Crescienzo, M.; Marconi, M.; Musella, I.; Pritzl, B.; Rest, A.; De Lee, N.; Smith, H.

    2010-01-01

    Λ cold-dark-matter hierarchical models of galaxy formation suggest that the halo of the Milky Way (MW) has been assembled, at least in part, through accretion of protogalactic fragments partially resembling the present-day dwarf spheroidal (dSph) satellites of the MW. Investigation of the stellar populations of the MW's globular clusters (GCs) and dSph companions can thus provide excellent tests to infer the dominant Galaxy-formation scenario, whether merger/accretion or cloud collapse. Pulsating variable stars offer a very powerful tool in this context, since variables of different types allow tracing the different stellar generations in a galaxy and to reconstruct the galaxy's star-formation history and assembly back to the first epochs of galaxy formation. In particular, the RR Lyrae stars, belonging to the old population (t > 10 Gyr), witnessed the epoch of halo formation, and thus hold a crucial role to identify the MW satellites that may have contributed to build up the Galactic halo. In the MW, most GCs with an RR Lyrae population sharply divide into two distinct groups (Oosterhoff types I and II) based on the mean periods and relative proportion of fundamental-mode (RRab) and first-overtone (RRc) RR Lyrae stars. On the other hand, the Galactic-halo field RR Lyrae stars show a dominance of Oosterhoff I properties. Here, we investigate the Oosterhoff properties of a number of different stellar systems, starting from relatively undisturbed dwarf galaxies (the Fornax dSph and its globular clusters), through distorted and tidally disrupting ones (the Bootes and Canes Venatici II dSphs), to possible final relics of the disruption process (the Galactic globular cluster NGC 2419). We are addressing the crucial question of whether the RR Lyrae pulsation properties in these systems conform to the Oosterhoff dichotomy characterizing the MW variables. If they do not, the Galaxy's halo cannot have been assembled by dSph-like protogalactic fragments resembling the

  5. BLAZAR HALOS AS PROBE FOR EXTRAGALACTIC MAGNETIC FIELDS AND MAXIMAL ACCELERATION ENERGY

    SciTech Connect

    Dolag, K.; Kachelriess, M.; Ostapchenko, S.; Tomas, R.

    2009-09-20

    High-energy photons from blazars interact within tens of kpc with the extragalactic photon background, initiating electromagnetic pair cascades. The charged component of such cascades is deflected by extragalactic magnetic fields (EGMFs), leading to halos even around initially point-like sources. We calculate the intensity profile of the resulting secondary high-energy photons for different assumptions on the initial source spectrum and the strength of the EGMF, employing also fields found earlier in a constrained simulation of structure formation including magnetohydrodynamics processes. We find that the observation of halos around blazars like Mrk 180 probes an interesting range of EGMF strengths and acceleration models: in particular, blazar halos test if the photon energy spectrum at the source extends beyond {approx}100 TeV and how anisotropic this high-energy component is emitted.

  6. Wiggle Instability of Galactic Spiral Shocks: Effects of Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Kim, Yonghwi; Kim, Woong-Tae; Elmegreen, Bruce G.

    2015-08-01

    It has been suggested that the wiggle instability (WI) of spiral shocks in a galactic disk is responsible for the formation of gaseous feathers observed in grand-design spiral galaxies. We perform both a linear stability analysis and numerical simulations to investigate the effect of magnetic fields on the WI. The disk is assumed to be infinitesimally thin, isothermal, and non-self-gravitating. We control the strengths of magnetic fields and spiral-arm forcing using the dimensionless parameters β and {F}, respectively. By solving the perturbation equations as a boundary-eigenvalue problem, we obtain dispersion relations of the WI for various values of β =1-∞ and {F}=5% and 10%. We find that the WI arising from the accumulation of potential vorticity at disturbed shocks is suppressed, albeit not completely, by magnetic fields. The stabilizing effect of magnetic fields is not from the perturbed fields but from the unperturbed fields that reduce the density compression factor in the background shocks. When {F}=5% and β ≲ 10 or {F}=10% and β ∼ 5–10, the most unstable mode has a wavelength of ∼0.1–0.2 times the arm-to-arm separation, which appears consistent with a mean spacing of observed feathers.

  7. MAGNETIC FLUX PARADIGM FOR RADIO LOUDNESS OF ACTIVE GALACTIC NUCLEI

    SciTech Connect

    Sikora, Marek; Begelman, Mitchell C. E-mail: mitch@jila.colorado.edu

    2013-02-20

    We argue that the magnetic flux threading the black hole (BH), rather than BH spin or Eddington ratio, is the dominant factor in launching powerful jets and thus determining the radio loudness of active galactic nuclei (AGNs). Most AGNs are radio quiet because the thin accretion disks that feed them are inefficient in depositing magnetic flux close to the BH. Flux accumulation is more likely to occur during a hot accretion (or thick disk) phase, and we argue that radio-loud quasars and strong emission-line radio galaxies occur only when a massive, cold accretion event follows an episode of hot accretion. Such an event might be triggered by the merger of a giant elliptical galaxy with a disk galaxy. This picture supports the idea that flux accumulation can lead to the formation of a so-called magnetically choked accretion flow. The large observed range in radio loudness reflects not only the magnitude of the flux pressed against the BH, but also the decrease in UV flux from the disk, due to its disruption by the ''magnetosphere'' associated with the accumulated flux. While the strongest jets result from the secular accumulation of flux, moderate jet activity can also be triggered by fluctuations in the magnetic flux deposited by turbulent, hot inner regions of otherwise thin accretion disks, or by the dissipation of turbulent fields in accretion disk coronae. These processes could be responsible for jet production in Seyferts and low-luminosity AGNs, as well as jets associated with X-ray binaries.

  8. Wiggle Instability of Galactic Spiral Shocks: Effects of Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Kim, Yonghwi; Kim, Woong-Tae; Elmegreen, Bruce G.

    2015-08-01

    It has been suggested that the wiggle instability (WI) of spiral shocks in a galactic disk is responsible for the formation of gaseous feathers observed in grand-design spiral galaxies. We perform both a linear stability analysis and numerical simulations to investigate the effect of magnetic fields on the WI. The disk is assumed to be infinitesimally thin, isothermal, and non-self-gravitating. We control the strengths of magnetic fields and spiral-arm forcing using the dimensionless parameters β and {F}, respectively. By solving the perturbation equations as a boundary-eigenvalue problem, we obtain dispersion relations of the WI for various values of β =1-∞ and {F}=5% and 10%. We find that the WI arising from the accumulation of potential vorticity at disturbed shocks is suppressed, albeit not completely, by magnetic fields. The stabilizing effect of magnetic fields is not from the perturbed fields but from the unperturbed fields that reduce the density compression factor in the background shocks. When {F}=5% and β ≲ 10 or {F}=10% and β ˜ 5-10, the most unstable mode has a wavelength of ˜0.1-0.2 times the arm-to-arm separation, which appears consistent with a mean spacing of observed feathers.

  9. THE MASSIVE-BLACK-HOLE-VELOCITY-DISPERSION RELATION AND THE HALO BARYON FRACTION: A CASE FOR POSITIVE ACTIVE GALACTIC NUCLEUS FEEDBACK

    SciTech Connect

    Silk, Joseph; Nusser, Adi E-mail: adi@physics.technion.ac.i

    2010-12-10

    Force balance considerations put a limit on the rate of active galactic nucleus radiation momentum output, L/c, capable of driving galactic superwinds and reproducing the observed M{sub BH}-{sigma} relation between black hole mass and spheroid velocity dispersion. We show that black holes cannot supply enough momentum in radiation to drive the gas out by pressure alone. Energy-driven winds give a M{sub BH}-{sigma} scaling favored by a recent analysis but also fall short energetically once cooling is incorporated. We propose that outflow triggering of star formation by enhancing the intercloud medium turbulent pressure and squeezing clouds can supply the necessary boost and suggest possible tests of this hypothesis. Our hypothesis simultaneously can account for the observed halo baryon fraction.

  10. XMM-Newton and Suzaku X-Ray Shadowing Measurements of the Solar Wind Charge Exchange, Local Bubble, and Galactic Halo Emission

    NASA Astrophysics Data System (ADS)

    Henley, David B.; Shelton, Robin L.

    2015-07-01

    We present results from a sample of XMM-Newton and Suzaku observations of interstellar clouds that cast shadows in the soft X-ray background (SXRB)—the first uniform analysis of such a sample from these missions. By fitting to the on- and off-shadow spectra, we separated the foreground and Galactic halo components of the SXRB. We tested different foreground models—two solar wind charge exchange (SWCX) models and a Local Bubble (LB) model. We also examined different abundance tables. We found that Anders & Grevesse abundances, commonly used in previous SXRB studies, may result in overestimated foreground brightnesses and halo temperatures. We also found that assuming a single solar wind ionization temperature for a SWCX model can lead to unreliable results. We compared our measurements of the foreground emission with predictions of the SWCX emission from a smooth solar wind, finding only partial agreement. Using available observation-specific SWCX predictions and various plausible assumptions, we placed an upper limit on the LB's O vii intensity of ˜0.8 {{photons}} {{{cm}}}-2 {{{s}}}-1 {{{sr}}}-1 (90% confidence). Comparing the halo results obtained with SWCX and LB foreground models implies that, if the foreground is dominated by SWCX and is brighter than ˜1.5× {10}-12 {{erg}} {{{cm}}}-2 {{{s}}}-1 {{{deg}}}-2 (0.4-1.0 {{keV}}), then using an LB foreground model may bias the halo temperature upward and the 0.5-2.0 {{keV}} surface brightness downward by ˜(0.2-0.3)× {10}6 {{K}} and ˜(1-2)× {10}-12 {{erg}} {{{cm}}}-2 {{{s}}}-1 {{{deg}}}-2, respectively. Similarly, comparing results from different observatories implies that there may be uncertainties in the halo temperature and surface brightness of up to ˜0.2× {10}6 {{K}} and ˜25%, respectively, in addition to the statistical uncertainties. These uncertainties or biases may limit the ability of X-ray measurements to discriminate between Galactic halo models.

  11. XMM-Newton and Suzaku X-Ray Shadowing Measurements of the Solar Wind Charge Exchange, Local Bubble, and Galactic Halo Emission

    NASA Astrophysics Data System (ADS)

    Henley, David B.; Shelton, Robin L.

    2015-07-01

    We present results from a sample of XMM-Newton and Suzaku observations of interstellar clouds that cast shadows in the soft X-ray background (SXRB)—the first uniform analysis of such a sample from these missions. By fitting to the on- and off-shadow spectra, we separated the foreground and Galactic halo components of the SXRB. We tested different foreground models—two solar wind charge exchange (SWCX) models and a Local Bubble (LB) model. We also examined different abundance tables. We found that Anders & Grevesse abundances, commonly used in previous SXRB studies, may result in overestimated foreground brightnesses and halo temperatures. We also found that assuming a single solar wind ionization temperature for a SWCX model can lead to unreliable results. We compared our measurements of the foreground emission with predictions of the SWCX emission from a smooth solar wind, finding only partial agreement. Using available observation-specific SWCX predictions and various plausible assumptions, we placed an upper limit on the LB's O vii intensity of ∼0.8 {{photons}} {{{cm}}}-2 {{{s}}}-1 {{{sr}}}-1 (90% confidence). Comparing the halo results obtained with SWCX and LB foreground models implies that, if the foreground is dominated by SWCX and is brighter than ∼1.5× {10}-12 {{erg}} {{{cm}}}-2 {{{s}}}-1 {{{deg}}}-2 (0.4–1.0 {{keV}}), then using an LB foreground model may bias the halo temperature upward and the 0.5–2.0 {{keV}} surface brightness downward by ∼(0.2-0.3)× {10}6 {{K}} and ∼(1-2)× {10}-12 {{erg}} {{{cm}}}-2 {{{s}}}-1 {{{deg}}}-2, respectively. Similarly, comparing results from different observatories implies that there may be uncertainties in the halo temperature and surface brightness of up to ∼0.2× {10}6 {{K}} and ∼25%, respectively, in addition to the statistical uncertainties. These uncertainties or biases may limit the ability of X-ray measurements to discriminate between Galactic halo models.

  12. 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.

  13. Anomaly distribution of quasar magnitudes: a test of lensing by a hypothetic supergiant molecular cloud in the Galactic halo

    NASA Astrophysics Data System (ADS)

    Giraud, E.

    2012-07-01

    Context. An anomaly in the distribution of quasar magnitudes based on the Sloan Digital Sky survey, was reported by Longo. The angular size of this quasar anomaly is on the order of ±15° on the sky. A smooth low surface brightness structure detected in γ-rays and at 408 MHz, coincides with the sky location and extent of the anomaly, and is close to the northern component of a pair of γ-ray bubbles discovered in the Fermi Gamma-ray Space Telescope survey. Molecular clouds are thought to be illuminated by cosmic rays. Molecular gas in the Galaxy, in the form of cold H2, may be a significant component of dark matter as suggested by Pfenniger et al. Aims: I test the hypothesis that the magnitude anomaly in the quasar distribution, is due to lensing by a hypothetical supergiant molecular cloud (SGMC) either in or falling into the Galactic halo. Methods: A series of grid lens models are built by assuming that a SGMC is a fractal structure constructed with clumps of 10-3 M⊙, 10 AU in size, and considering various fractal dimensions. Local amplifications are computed by using the single-plane approximation. Results: A complex network of caustics due to the clumpy structure is present. Our best single plane lens model capable of explaining Longo's effect, at least in sparse regions, requires a mass (1.5-4.1) × 1010 M⊙ within 8.7 × 8.7 × (5-8.6) kpc3 at a lens plane distance of 20 kpc, and is constructed from a molecular-cloud building-block of 5 × 105 M⊙ within a scale of 30 pc expanded by fractal scaling with dimension D = 1.8-2 out to 5-8.6 kpc for the SGMC. The mass budget depends on the cloud depth and on the fractal dimension. Conclusions: If such a SGMC were found to exist, it may provide at least part of a lensing explanation for the luminous anomaly discovered in quasars and red galaxies.

  14. Pulsar rotation and dispersion measures and the galactic magnetic field.

    NASA Technical Reports Server (NTRS)

    Manchester, R. N.

    1972-01-01

    Use of observations of pulsar polarization and pulse time of arrival at frequencies between 250 and 500 MHz to determine rotation and dispersion measures for 19 and 21 pulsars, respectively. These measurements have been used to calculate mean line-of-sight components of the magnetic field in the path to the pulsars. These and other observations show that there is probably no contribution to the observed rotation measure from the pulsar itself. Low-latitude, low-dispersion pulsars are observed to have strong field components, and a strong dependence of rotation-measure sign on galactic longitude has been found. The observations are consistent with a relatively uniform field of about 3.5 microgauss directed toward about l = 90 deg in the local region, but appear to be inconsistent with the helical model for the local field.

  15. The radial velocity dispersion profile of the Galactic halo: constraining the density profile of the dark halo of the Milky Way

    NASA Astrophysics Data System (ADS)

    Battaglia, Giuseppina; Helmi, Amina; Morrison, Heather; Harding, Paul; Olszewski, Edward W.; Mateo, Mario; Freeman, Kenneth C.; Norris, John; Shectman, Stephen A.

    2005-12-01

    We have compiled a new sample of 240 halo objects with accurate distance and radial velocity measurements, including globular clusters, satellite galaxies, field blue horizontal branch (FHB) stars and red giant stars from the Spaghetti survey. The new data lead to a significant increase in the number of known objects for Galactocentric radii beyond 50 kpc, which allows a reliable determination of the radial velocity dispersion profile out to very large distances. The radial velocity dispersion shows an almost constant value of 120 km s-1 out to 30 kpc and then continuously declines down to 50 km s-1 at about 120 kpc. This fall-off puts important constraints on the density profile and total mass of the dark matter halo of the Milky Way. For a constant velocity anisotropy, the isothermal profile is ruled out, while both a dark halo following a truncated flat (TF) model of mass 1.2+1.8-0.5× 1012Msolar and a Navarro, Frenk & White (NFW) profile of mass 0.8+1.2-0.2× 1012Msolar and c= 18 are consistent with the data. The significant increase in the number of tracers combined with the large extent of the region probed by these has allowed a more precise determination of the Milky Way mass in comparison to previous works. We also show how different assumptions for the velocity anisotropy affect the performance of the mass models.

  16. Evidence for Distinct Components of the Galactic Stellar Halo from 838 RR Lyrae Stars Discovered in the LONEOS-I Survey

    SciTech Connect

    Miceli, A; Rest, A; Stubbs, C W; Hawley, S L; Cook, K H; Magnier, E A; Krisciunas, K; Bowell, E; Koehn, B

    2007-02-23

    We present 838 ab-type RR Lyrae stars from the Lowell Observatory Near Earth Objects Survey Phase I (LONEOS-I). These objects cover 1430 deg{sup 2} and span distances ranging from 3-30kpc from the Galactic Center. Object selection is based on phased, photometric data with 28-50 epochs. We use this large sample to explore the bulk properties of the stellar halo, including the spatial distribution. The period-amplitude distribution of this sample shows that the majority of these RR Lyrae stars resemble Oosterhoff type I, but there is a significant fraction (26%) which have longer periods and appear to be Oosterhoff type II. We find that the radial distributions of these two populations have significantly different profiles ({rho}{sub OoI} {approx} R{sup -2.26{+-}0.07} and {rho}{sub OoII} {approx} R{sup -2.88{+-}0.11}). This suggests that the stellar halo was formed by at least two distinct accretion processes and supports dual-halo models.

  17. Using red clump stars to decompose the galactic magnetic field with distance

    SciTech Connect

    Pavel, Michael D.

    2014-09-01

    A new method for measuring the large-scale structure of the Galactic magnetic field is presented. The Galactic magnetic field has been probed through the Galactic disk with near-infrared starlight polarimetry; however, the distance to each background star is unknown. Using red clump stars as near-infrared standard candles, this work presents the first attempt to decompose the line-of-sight structure of the sky-projected Galactic magnetic field. Two example lines of sight are decomposed: toward a field with many red clump stars and toward a field with few red clump stars. A continuous estimate of magnetic field orientation over several kiloparsecs of distance is possible in the field with many red clump stars, while only discrete estimates are possible in the sparse example. Toward the outer Galaxy, there is a continuous field orientation with distance that shows evidence of perturbation by the Galactic warp. Toward the inner Galaxy, evidence for a large-scale change in the magnetic field geometry is consistent with models of magnetic field reversals, independently derived from Faraday rotation studies. A photo-polarimetric method for identifying candidate intrinsically polarized stars is also presented. The future application of this method to large regions of the sky will begin the process of mapping the Galactic magnetic field in a way never before possible.

  18. Using Red Clump Stars to Decompose the Galactic Magnetic Field with Distance

    NASA Astrophysics Data System (ADS)

    Pavel, Michael D.

    2014-09-01

    A new method for measuring the large-scale structure of the Galactic magnetic field is presented. The Galactic magnetic field has been probed through the Galactic disk with near-infrared starlight polarimetry; however, the distance to each background star is unknown. Using red clump stars as near-infrared standard candles, this work presents the first attempt to decompose the line-of-sight structure of the sky-projected Galactic magnetic field. Two example lines of sight are decomposed: toward a field with many red clump stars and toward a field with few red clump stars. A continuous estimate of magnetic field orientation over several kiloparsecs of distance is possible in the field with many red clump stars, while only discrete estimates are possible in the sparse example. Toward the outer Galaxy, there is a continuous field orientation with distance that shows evidence of perturbation by the Galactic warp. Toward the inner Galaxy, evidence for a large-scale change in the magnetic field geometry is consistent with models of magnetic field reversals, independently derived from Faraday rotation studies. A photo-polarimetric method for identifying candidate intrinsically polarized stars is also presented. The future application of this method to large regions of the sky will begin the process of mapping the Galactic magnetic field in a way never before possible.

  19. Evidence for a Very Low-column Density Hole in the Galactic Halo in the Direction of the High Latitude Molecular Cloud MBM 16

    NASA Astrophysics Data System (ADS)

    Liu, W.; Galeazzi, M.; Ursino, E.

    2016-01-01

    Shadow observations are the only way to observe emission from the galactic halo (GH) and/or the circumgalactic medium (CGM) free of any foreground contamination from local hot bubble (LHB) and solar wind charge exchange (SWCX). We analyzed data from a shadow observation in the direction of the high latitude, neutral hydrogen cloud MBM 16 with Suzaku. We found that all emission can be accounted for by foreground emission from LHB and SWCX, plus power-law emission associated with unresolved point sources. The GH/CGM in the direction of MBM 16 is negligible or inexistent in our observation, with upper limits on the emission measure of 9× {10}-4 pc cm-6 (90% C.L.-solar metallicity), at the lowest end of current estimates.

  20. DETERMINATION OF THE POINT-SPREAD FUNCTION FOR THE FERMI LARGE AREA TELESCOPE FROM ON-ORBIT DATA AND LIMITS ON PAIR HALOS OF ACTIVE GALACTIC NUCLEI

    SciTech Connect

    Ackermann, M.; Ajello, M.; Allafort, A.; Bechtol, K.; Bloom, E. D.; Borgland, A. W.; Bottacini, E.; Buehler, R.; Asano, K.; Atwood, W. B.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Ballet, J.; Bastieri, D.; Bonamente, E.; Brandt, T. J.; Brigida, M.; Bruel, P. E-mail: mar0@uw.edu [Laboratoire Leprince-Ringuet, Ecole polytechnique, CNRS and others

    2013-03-01

    The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to detect photons with energies from Almost-Equal-To 20 MeV to >300 GeV. The pre-launch response functions of the LAT were determined through extensive Monte Carlo simulations and beam tests. The point-spread function (PSF) characterizing the angular distribution of reconstructed photons as a function of energy and geometry in the detector is determined here from two years of on-orbit data by examining the distributions of {gamma} rays from pulsars and active galactic nuclei (AGNs). Above 3 GeV, the PSF is found to be broader than the pre-launch PSF. We checked for dependence of the PSF on the class of {gamma}-ray source and observation epoch and found none. We also investigated several possible spatial models for pair-halo emission around BL Lac AGNs. We found no evidence for a component with spatial extension larger than the PSF and set upper limits on the amplitude of halo emission in stacked images of low- and high-redshift BL Lac AGNs and the TeV blazars 1ES0229+200 and 1ES0347-121.

  1. Balloon-borne direct search for ionizing massive particles as a component of the galactic halo dark matter (The Arizona-IMAX Collaboration)

    NASA Astrophysics Data System (ADS)

    McGuire, P. C.; Bowen, T.; Barker, D. L.; Halverson, P. G.; Kendall, K. R.; Metcalfe, T. S.; Norton, R. S.; Pifer, A. E.; Barbier, L. M.; Christian, E. R.; Krombel, K. E.; Mitchell, J. W.; Ormes, J. F.; Streitmatter, R. E.; Davis, A. J.; Labrador, A. W.; Mewaldt, R. A.; Schindler, S. M.; Golden, R. L.; Stochaj, S. J.; Webber, W. R.; Arizona-IMAX Collaboration

    1995-07-01

    A dark matter (DM) search experiment was flown on the IMAX balloon payload to search for a possible minor component of the dark matter in the Galactic halo: ionizing massive particles (IMPs) (mx>~104 GeV/c2) that cannot penetrate the atmosphere due to their low-velocities and high energy-loss. The DM search experiment consisted of a delayed coincidence between four large plastic scintillation detectors arranged in a vertical stack. In order to search for ultra-slow particles which do not slow down in the IMAX telescope, the experiment contained TDCs which measured the time-delay Ti,i+1∈(0.3, 14.0) μs between hits in successive counters to ~2% precision. We present IMP flux limits for non-slowing IMPs and also for IMPs which slow down significantly within the IMAX telescope. This experiment effectively closes much of a previously unconstrained ``window'' in the mass/cross-section joint parameter spaces for massive particles as the dominant halo DM.

  2. An explosion model for the formation of the radio halo of NGC 891

    NASA Astrophysics Data System (ADS)

    You, Jun-han; Allen, R. J.; Hu, Fu-xing

    1987-06-01

    The explosion model for the formation of the radio halo of NGC 891 proposed here are mainly based on two physical assumptions: a) the relativistic electrons belong to two families, a halo family and a disk family: the disk family originating in supernova events throughout the disk and the halo family, in a violent explosion of the galactic nucleus in the distant past. b) Energy equipartition, that is, the magnetic energy density be proportional to the number density of stars. On these two assumptions, the main observed features of the radio halo of NGC 891 can be satisfactorily explained.

  3. An explosion model for the formation of the radio halo of NGC 891

    NASA Astrophysics Data System (ADS)

    You, Jun-Han; Allen, R. J.; Hu, Fu-Xing

    1986-06-01

    The explosion model for the formation of the radio halo of NGC 891 proposed here is mainly based on two physical assumptions: (1) the relativistic electrons belong to two families, a halo family and a disk family, the disk family originating in supernova events throughout the disk, and the halo family in a violent explosion of the galactic nucleus in the distant past; and (2) energy equipartition, where the magnetic energy density is proportional to the number density of stars. On these two assumptions, the main observed features of the radio halo of NGC 891 can be satisfactorily explained.

  4. Analysis of HST/COS spectra of the bare C-O stellar core H1504+65 and a high-velocity twin in the Galactic halo

    NASA Astrophysics Data System (ADS)

    Werner, K.; Rauch, T.

    2015-12-01

    H1504+65 is an extremely hot white dwarf (effective temperature Teff = 200 000 K) with a carbon-oxygen dominated atmosphere devoid of hydrogen and helium. This atmospheric composition was hitherto unique among hot white dwarfs (WDs), and it could be related to recently detected cooler WDs with C or O dominated spectra. The origin of the H and He deficiency in H1504+65 is unclear. To further assess this problem, we performed ultraviolet spectroscopy with the Cosmic Origins Spectrograph (COS) aboard the Hubble Space Telescope (HST). In accordance with previous far-ultraviolet spectroscopy performed with the Far Ultraviolet Spectroscopic Explorer, the most prominent lines stem from C iv, O v-vi, and Ne vi-viii. Archival HST/COS spectra are utilized to prove that the supersoft X-ray source RX J0439.8-6809 is, considering the exotic composition, a twin of H1504+65 that is even hotter (Teff = 250 000 K). In contrast to earlier claims, we find that the star is not located in the Large Magellanic Cloud but a foreground object in the Galactic halo at a distance of 9.2 kpc, 5.6 kpc below the Galactic plane, receding with vrad = +220 km s-1. 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 NAS5-26666.

  5. Discovery and Photometric Observation of the Optical Counterpart of a Possible Galactic Halo X-Ray Transient, XTE J1118+480

    NASA Astrophysics Data System (ADS)

    Uemura, Makoto; Kato, Taichi; Matsumoto, Katsura; Yamaoka, Hitoshi; Takamizawa, Kesao; Sano, Yasuo; Haseda, Katsumi; Cook, Lewis M.; Buczynski, Denis; Masi, Gianluca

    2000-08-01

    We discovered an optical counterpart of about 13 mag of a soft X-ray transient, XTE J1118+480 on 2000 March 30. We performed astrometry and provided an accurate position of R.A. = 11h18m10.85s85, Decl. = +48deg02'12.9{' '}. The outbursting object has been identified with a 18.8 mag star in the USNO catalog. Our pre-discovery data shows another outburst during 2000 January, again coinciding with an outburst detected in X-rays. Through CCD time-series photometry, we found the presence of a periodic variation with an amplitude of 0.055 mag and a period of 0.17078 \\pm 0.00004 d$, which we consider to be a promising candidate of the orbital period. Because of the high galactic latitude and faint quiescence magnitude of 18.8, XTE J1118+480 is possibly the first firmly identified black hole candidate X-ray transient in the galactic halo.

  6. The Generation of Hot Galactic Halos: Multi-Phase Simulations including Collision-Induced Shock Heating, and Comparisons with Observations

    NASA Astrophysics Data System (ADS)

    Hearn, Nathan C.; Lamb, Susan A.

    2001-09-01

    The presence of hot halos around some colliding and supposed merging galaxies, as detected in X-rays, suggests that galaxy interactions may be responsible for the production of significant amounts of hot-phase interstellar gas in some systems. Possible mechanisms for producing this hot material are large-scale shock heating due to the collision itself, as well as the subsequent supernova explosions and intense stellar winds from the massive stars that are formed in collision-induced starbursts. We are using numerical simulations of galaxy collisions and mergers to explore the possible contribution of these various physical mechanisms. These simulations are compared with observations of real systems. Here we report on results from the application of a new N-body/smoothed particle hydrodynamics simulation code that has been constructed to allow the representation of multiple phases in the interstellar medium (Hearn et al, in preparation). This simulation code has been used to explore the generation of hot interstellar gas due to the large-scale shock heating that occurs during the collision and merger of two gas-rich disk galaxies. This current study allows us to place limits on the effect of the collision itself (as opposed to the results of subsequent star formation) on the generation of hot halos. We compare our numerical results to the extensive observations of the collisional merging system Arp 220 and, in particular, with our recent Chandra observations of its extended X-ray halo (McDowell et al, in preparation).

  7. The Ties that Bind? Galactic Magnetic Fields and Ram Pressure Stripping

    NASA Astrophysics Data System (ADS)

    Tonnesen, Stephanie; Stone, James

    2014-11-01

    One process affecting gas-rich cluster galaxies is ram pressure stripping (RPS), i.e., the removal of galactic gas through direct interaction with the intracluster medium (ICM). Galactic magnetic fields may have an important impact on the stripping rate and tail structure. We run the first magnetohydrodynamic (MHD) simulations of RPS that include a galactic magnetic field, using 159 pc resolution throughout our entire domain in order to resolve mixing throughout the tail. We find very little difference in the total amount of gas removed from the unmagnetized and magnetized galaxies, although a magnetic field with a radial component will initially accelerate stripped gas more quickly. In general, we find that magnetic fields in the disk lead to slower velocities in the stripped gas near the disk and faster velocities farther from the disk. We also find that magnetic fields in the galactic gas lead to larger unmixed structures in the tail. Finally, we discuss whether ram pressure stripped tails can magnetize the ICM. We find that the total magnetic energy density grows as the tail lengthens, likely through turbulence. There are μG-strength fields in the tail in all of our MHD runs, which survive to at least 100 kpc from the disk (the edge of our simulated region), indicating that the area-filling factor of magnetized tails in a cluster could be large.

  8. Quasar-microlensing versus star-microlensing evidence of small-planetary-mass objects as the dominant inner-halo galactic dark matter

    NASA Astrophysics Data System (ADS)

    Gibson, Carl H.; Schild, Rudolph E.

    2011-11-01

    We examine recent results of two kinds of microlensing experiments intended to detect galactic dark matter objects, and we suggest that the lack of short period star-microlensing events observed for stars near the Galaxy does not preclude either the "rogue planets" identified from quasar-microlensing by Schild 1996 as the missing-mass of a lens galaxy, or the "Primordial Fog Particles" (PFPs) in Proto-Globular-star-Cluster (PGC) clumps predicted by Gibson 1996 - 2000 as the dominant inner-halo galactic dark matter component from a new hydrodynamic gravitational structure formation theory. We point out that hydro-gravitational processes acting on a massive population of such micro-brown-dwarfs in their nonlinear accretional cascades to form stars gives intermittent lognormal number density np distributions for the PFPs within the PGC gas-stabilized-clumps. Hence, star-microlensing searches that focus on a small fraction of the sky assuming a uniform distribution for np are subject to vast underestimates of the mean ⟨np⟩mean. Sparse independent samples give modes 10-4 - 10-6 smaller than means of the highly skewed lognormal distributions expected. Quasar-microlensing searches with higher optical depths are less affected by np intermittency. We attempt to reconcile the results of the star-microlensing and quasar-microlensing studies, with particular reference to the necessarily hydrogenous and primordial small-planetary-mass range. We conclude that star microlensing searches cannot exclude and are unlikely even to detect these low-mass candidate-galactic-dark-matter-objects so easily observed by quasar-microlensing and so robustly predicted by the new theory.

  9. Bilateral symmetry in supernova remnants and the connection to the Galactic magnetic field

    NASA Astrophysics Data System (ADS)

    West, Jennifer Lorraine; Safi-Harb, Samar; Jaffe, Tess; Kothes, Roland; Foster, Tyler; Landecker, Tom

    2015-08-01

    Supernova explosions are some of the most significant and transformative events in our Universe. Understanding Supernova Remnants (SNRs), the leftover remains of these explosions, is fundamental to our understanding of the chemical enrichment and magnetism in galaxies, including our own Milky Way. We model the radio synchrotron emission from Galactic SNRs using the “Hammurabi” synchrotron modelling code. We incorporate current models of Galactic magnetic field and electron density to simulate the emission from the SNRs as a function of their position in the Galaxy. We do this in an effort to understand the connection between SNRs and their environment and to investigate the relationship between the angle of the symmetry axis of the SNR and the Galactic Magnetic field. This relationship has implications for understanding the magnetic field geometry and cosmic ray electron distribution in SNRs, and possibly even a new method for determining or constraining the distances to SNRs.

  10. Haloing in bimodal magnetic colloids: the role of field-induced phase separation.

    PubMed

    Magnet, C; Kuzhir, P; Bossis, G; Meunier, A; Suloeva, L; Zubarev, A

    2012-07-01

    If a suspension of magnetic micrometer-sized and nanosized particles is subjected to a homogeneous magnetic field, the nanoparticles are attracted to the microparticles and form thick anisotropic halos (clouds) around them. Such clouds can hinder the approach of microparticles and result in effective repulsion between them [M. T. López-López, A. Yu. Zubarev, and G. Bossis, Soft Matter 6, 4346 (2010)]. In this paper, we present detailed experimental and theoretical studies of nanoparticle concentration profiles and of the equilibrium shapes of nanoparticle clouds around a single magnetized microsphere, taking into account interactions between nanoparticles. We show that at a strong enough magnetic field, the ensemble of nanoparticles experiences a gas-liquid phase transition such that a dense liquid phase is condensed around the magnetic poles of a microsphere while a dilute gas phase occupies the rest of the suspension volume. Nanoparticle accumulation around a microsphere is governed by two dimensionless parameters--the initial nanoparticle concentration (φ(0)) and the magnetic-to-thermal energy ratio (α)--and the three accumulation regimes are mapped onto a α-φ(0) phase diagram. Our local thermodynamic equilibrium approach gives a semiquantitative agreement with the experiments on the equilibrium shapes of nanoparticle clouds. The results of this work could be useful for the development of the bimodal magnetorheological fluids and of the magnetic separation technologies used in bioanalysis and water purification systems. PMID:23005414

  11. OXYGEN ABUNDANCES IN NEARBY FGK STARS AND THE GALACTIC CHEMICAL EVOLUTION OF THE LOCAL DISK AND HALO

    SciTech Connect

    Ramirez, I.; Lambert, D. L.; Allende Prieto, C.

    2013-02-10

    Atmospheric parameters and oxygen abundances of 825 nearby FGK stars are derived using high-quality spectra and a non-local thermodynamic equilibrium analysis of the 777 nm O I triplet lines. We assign a kinematic probability for the stars to be thin-disk (P {sub 1}), thick-disk (P {sub 2}), and halo (P {sub 3}) members. We confirm previous findings of enhanced [O/Fe] in thick-disk (P {sub 2} > 0.5) relative to thin-disk (P {sub 1} > 0.5) stars with [Fe/H] {approx}< -0.2, as well as a 'knee' that connects the mean [O/Fe]-[Fe/H] trend of thick-disk stars with that of thin-disk members at [Fe/H] {approx}> -0.2. Nevertheless, we find that the kinematic membership criterion fails at separating perfectly the stars in the [O/Fe]-[Fe/H] plane, even when a very restrictive kinematic separation is employed. Stars with 'intermediate' kinematics (P {sub 1} < 0.7, P {sub 2} < 0.7) do not all populate the region of the [O/Fe]-[Fe/H] plane intermediate between the mean thin-disk and thick-disk trends, but their distribution is not necessarily bimodal. Halo stars (P {sub 3} > 0.5) show a large star-to-star scatter in [O/Fe]-[Fe/H], but most of it is due to stars with Galactocentric rotational velocity V < -200 km s{sup -1}; halo stars with V > -200 km s{sup -1} follow an [O/Fe]-[Fe/H] relation with almost no star-to-star scatter. Early mergers with satellite galaxies explain most of our observations, but the significant fraction of disk stars with 'ambiguous' kinematics and abundances suggests that scattering by molecular clouds and radial migration have both played an important role in determining the kinematic and chemical properties of solar neighborhood stars.

  12. Oxygen Abundances in Nearby FGK Stars and the Galactic Chemical Evolution of the Local Disk and Halo

    NASA Astrophysics Data System (ADS)

    Ramírez, I.; Allende Prieto, C.; Lambert, D. L.

    2013-02-01

    Atmospheric parameters and oxygen abundances of 825 nearby FGK stars are derived using high-quality spectra and a non-local thermodynamic equilibrium analysis of the 777 nm O I triplet lines. We assign a kinematic probability for the stars to be thin-disk (P 1), thick-disk (P 2), and halo (P 3) members. We confirm previous findings of enhanced [O/Fe] in thick-disk (P 2 > 0.5) relative to thin-disk (P 1 > 0.5) stars with [Fe/H] <~ -0.2, as well as a "knee" that connects the mean [O/Fe]-[Fe/H] trend of thick-disk stars with that of thin-disk members at [Fe/H] >~ -0.2. Nevertheless, we find that the kinematic membership criterion fails at separating perfectly the stars in the [O/Fe]-[Fe/H] plane, even when a very restrictive kinematic separation is employed. Stars with "intermediate" kinematics (P 1 < 0.7, P 2 < 0.7) do not all populate the region of the [O/Fe]-[Fe/H] plane intermediate between the mean thin-disk and thick-disk trends, but their distribution is not necessarily bimodal. Halo stars (P 3 > 0.5) show a large star-to-star scatter in [O/Fe]-[Fe/H], but most of it is due to stars with Galactocentric rotational velocity V < -200 km s-1 halo stars with V > -200 km s-1 follow an [O/Fe]-[Fe/H] relation with almost no star-to-star scatter. Early mergers with satellite galaxies explain most of our observations, but the significant fraction of disk stars with "ambiguous" kinematics and abundances suggests that scattering by molecular clouds and radial migration have both played an important role in determining the kinematic and chemical properties of solar neighborhood stars.

  13. Time delay and extended halo for constraints on the intergalactic magnetic field

    NASA Astrophysics Data System (ADS)

    Yang, Yuan-Pei; Dai, Zi-Gao

    2015-12-01

    Primary gamma rays emitted from extragalactic very-high-energy (VHE) sources, such as blazars, will generate cascade radiation in intergalactic space with a scale of ˜ 100 Mpc, for z ˜ 0.1 and Eγ ˜ 1TeV. These cascades proceed through electron-positron pair production and inverse Compton (IC) scattering in the cosmic background radiation fields, mainly cosmic microwave background (CMB) radiation and extragalactic background light in the voids of the universe. The existence of an intergalactic magnetic field (IGMF) would deflect paths of electron-positron pairs that scatter CMB photons, causing some observable effects, such as time delay, an extended halo, and a spectral change. Here we reanalyze the diffusion of an electron jet deflected by IGMF and propose a unified semi-analytical model. By using publicly available data from the Fermi/LAT detector and contemporaneous TeV observations, we find that the cascade photon flux is not significantly affected by the IGMF strength for non-variable blazars when the IGMF is weaker than ˜ 10-16 G. This result is clearly different from previous works that analyzed the extended halo and time delay separately for non-variable blazars and flaring blazars. By applying our model to two extreme blazars (1ES 0229+200 and 1ES 1218+304), we obtain the IGMF lower limit of order ≳ 10-13 ˜ 10-14 G in the non-variable case, which is a stronger constraint on the IGMF strength than previous works (≳ 10-16 ˜ 10-18 G), and ≳ 10-18 ˜ 10-19 G in the case of flaring blazars. Furthermore, we study the light curves and extended halo of the cascade photons by considering the effects of the IGMF.

  14. 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. PMID:22096191

  15. Detection of satellite remnants in the Galactic Halo with Gaia - II. A modified great circle cell method

    NASA Astrophysics Data System (ADS)

    Mateu, C.; Bruzual, G.; Aguilar, L.; Brown, A. G. A.; Valenzuela, O.; Carigi, L.; Velázquez, H.; Hernández, F.

    2011-07-01

    We propose an extension of the great circle cell count streamer finding method of Johnston et al. that can be applied to the future Gaia data base. The original method looks for streamers along great circles in the sky, our extension adds the kinematical restriction that velocity vectors should also be constrained to lie along these great circles, as seen by a Galactocentric observer. We show how to use these combined criteria starting from heliocentric observables. We test it by using the mock Gaia catalogue of Brown et al., which includes a realistic Galactic background and observational errors, but with the addition of detailed star formation histories for the simulated satellites. We investigate its success rate as a function of initial satellite luminosity, star formation history and orbit. We find that the inclusion of the kinematical restriction vastly enhances the contrast between a streamer and the background, even in the presence of observational errors, provided we use only data with good astrometric quality (fractional errors of 30 per cent or better). The global nature of the method diminishes the erasing effect of phase mixing and permits the recovery of merger events of reasonable dynamical age. Satellites with a star formation history different to that of the Galactic background are also better isolated. We find that satellites in the range of 108-109 L⊙ can be recovered even for events as old as ˜10 Gyr. Even satellites with 4-5 × 107 L⊙ can be recovered for certain combinations of dynamical ages and orbits.

  16. THE GALACTIC CENTER S-STARS AND THE HYPERVELOCITY STARS IN THE GALACTIC HALO: TWO FACES OF THE TIDAL BREAKUP OF STELLAR BINARIES BY THE CENTRAL MASSIVE BLACK HOLE?

    SciTech Connect

    Zhang Fupeng; Lu Youjun; Yu Qingjuan

    2013-05-10

    In this paper, we investigate the link between the hypervelocity stars (HVSs) discovered in the Galactic halo and the Galactic center (GC) S-stars, under the hypothesis that they are both the products of the tidal breakup of the same population of stellar binaries by the central massive black hole (MBH). By adopting several hypothetical models for binaries to be injected into the vicinity of the MBH and doing numerical simulations, we realize the tidal breakup processes of the binaries and their follow-up dynamical evolution. We find that many statistical properties of the detected HVSs and GC S-stars could be reproduced under some binary injecting models, and their number ratio can be reproduced if the stellar initial mass function is top-heavy (e.g., with slope {approx} - 1.6). The total number of the captured companions is {approx}50 that have masses in the range {approx}3-7 M{sub Sun} and semimajor axes {approx}< 4000 AU and survive to the present within their main-sequence lifetime. The innermost one is expected to have a semimajor axis {approx}300-1500 AU and a pericenter distance {approx}10-200 AU, with a significant probability of being closer to the MBH than S2. Future detection of such a close star would offer an important test to general relativity. The majority of the surviving ejected companions of the GC S-stars are expected to be located at Galactocentric distances {approx}< 20 kpc, and have heliocentric radial velocities {approx} - 500-1500 km s{sup -1} and proper motions up to {approx}5-20 mas yr{sup -1}. Future detection of these HVSs may provide evidence for the tidal breakup formation mechanism of the GC S-stars.

  17. Detection of satellite remnants in the Galactic halo with Gaia- III. Detection limits for ultrafaint dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Antoja, T.; Mateu, C.; Aguilar, L.; Figueras, F.; Antiche, E.; Hernández-Pérez, F.; Brown, A. G. A.; Valenzuela, O.; Aparicio, A.; Hidalgo, S.; Velázquez, H.

    2015-10-01

    We present a method to identify ultrafaint dwarf galaxies (UFDGs) candidates in the halo of the Milky Way using the future Gaia catalogue and we explore its detection limits and completeness. The method is based on the Wavelet Transform and searches for overdensities in the combined space of sky coordinates and proper motions, using kinematics in the search for the first time. We test the method with a Gaia mock catalogue that has the Gaia Universe Model Snapshot as a background, and use a library of around 30 000 UFDGs simulated as Plummer spheres with a single stellar population. For the UFDGs, we use a wide range of structural and orbital parameters that go beyond the range spanned by real systems, where some UFDGs may remain undetected. We characterize the detection limits as function of the number of observable stars by Gaia in the UFDGs with respect to that of the background and their apparent sizes in the sky and proper motion planes. We find that the addition of proper motions in the search improves considerably the detections compared to a photometric survey at the same magnitude limit. Our experiments suggest that Gaia will be able to detect UFDGs that are similar to some of the known UFDGs even if the limit of Gaia is around 2 mag brighter than that of SDSS, with the advantage of having a full-sky catalogue. We also see that Gaia could even find some UFDGs that have lower surface brightness than the SDSS limit.

  18. A SURVEY OF EXTRAGALACTIC FARADAY ROTATION AT HIGH GALACTIC LATITUDE: THE VERTICAL MAGNETIC FIELD OF THE MILKY WAY TOWARD THE GALACTIC POLES

    SciTech Connect

    Mao, S. A.; Gaensler, B. M.; Madsen, G. J.; Haverkorn, M.; Zweibel, E. G.; McClure-Griffiths, N. M.; Shukurov, A.; Kronberg, P. P.

    2010-05-10

    We present a study of the vertical magnetic field of the Milky Way toward the Galactic poles, determined from observations of Faraday rotation toward more than 1000 polarized extragalactic radio sources at Galactic latitudes |b| {>=} 77{sup 0}, using the Westerbork Radio Synthesis Telescope and the Australia Telescope Compact Array. We find median rotation measures (RMs) of 0.0 {+-} 0.5 rad m{sup -2} and +6.3 {+-} 0.7 rad m{sup -2} toward the north and south Galactic poles, respectively, demonstrating that there is no coherent vertical magnetic field in the Milky Way at the Sun's position. If this is a global property of the Milky Way's magnetism, then the lack of symmetry across the disk rules out pure dipole or quadrupole geometries for the Galactic magnetic field. The angular fluctuations in RM seen in our data show no preferred scale within the range {approx}0.{sup 0}1 to {approx}25{sup 0}. The observed standard deviation in RM of {approx}9 rad m{sup -2} then implies an upper limit of {approx}1 {mu}G on the strength of the random magnetic field in the warm ionized medium at high Galactic latitudes.

  19. GLOBAL GALACTIC DYNAMO DRIVEN BY COSMIC RAYS AND EXPLODING MAGNETIZED STARS

    SciTech Connect

    Hanasz, Michal; Woltanski, Dominik; Kowalik, Kacper

    2009-11-20

    We report the first results of the first global galactic-scale cosmic ray (CR)-MHD simulations of CR-driven dynamo. We investigate the dynamics of magnetized interstellar medium (ISM), which is dynamically coupled with CR gas. We assume that exploding stars deposit small-scale, randomly oriented, dipolar magnetic fields into the differentially rotating ISM, together with a portion of CRs, accelerated in supernova shocks. We conduct numerical simulations with the aid of a new parallel MHD code PIERNIK. We find that the initial magnetization of galactic disks by exploding magnetized stars forms favorable conditions for the CR-driven dynamo. We demonstrate that dipolar magnetic fields supplied on small supernova remnant scales can be amplified exponentially by the CR-driven dynamo, to the present equipartition values, and transformed simultaneously to large galactic scales. The resulting magnetic field structure in an evolved galaxy appears spiral in the face-on view and reveals the so-called X-shaped structure in the edge-on view.

  20. 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.

  1. Search for a dark matter annihilation signal from the galactic center halo with H.E.S.S.

    PubMed

    Abramowski, A; Acero, F; Aharonian, F; Akhperjanian, A G; Anton, G; Barnacka, A; de Almeida, U Barres; Bazer-Bachi, A R; Becherini, Y; Becker, J; Behera, B; Bernlöhr, K; Bochow, A; Boisson, C; Bolmont, J; Bordas, P; Borrel, V; Brucker, J; Brun, F; Brun, P; Bulik, T; Büsching, I; Carrigan, S; Casanova, S; Cerruti, M; Chadwick, P M; Charbonnier, A; Chaves, R C G; Cheesebrough, A; Chounet, L-M; Clapson, A C; Coignet, G; Conrad, J; Dalton, M; Daniel, M K; Davids, I D; Degrange, B; Deil, C; Dickinson, H J; Djannati-Ataï, A; Domainko, W; Drury, L O'C; Dubois, F; Dubus, G; Dyks, J; Dyrda, M; Egberts, K; Eger, P; Espigat, P; Fallon, L; Farnier, C; Fegan, S; Feinstein, F; Fernandes, M V; Fiasson, A; Fontaine, G; Förster, A; Füssling, M; Gallant, Y A; Gast, H; Gérard, L; Gerbig, D; Giebels, B; Glicenstein, J F; Glück, B; Goret, P; Göring, D; Hague, J D; Hampf, D; Hauser, M; Heinz, S; Heinzelmann, G; Henri, G; Hermann, G; Hinton, J A; Hoffmann, A; Hofmann, W; Hofverberg, P; Horns, D; Jacholkowska, A; de Jager, O C; Jahn, C; Jamrozy, M; Jung, I; Kastendieck, M A; Katarzyński, K; Katz, U; Kaufmann, S; Keogh, D; Kerschhaggl, M; Khangulyan, D; Khélifi, B; Klochkov, D; Kluźniak, W; Kneiske, T; Komin, Nu; Kosack, K; Kossakowski, R; Laffon, H; Lamanna, G; Lennarz, D; Lohse, T; Lopatin, A; Lu, C-C; Marandon, V; Marcowith, A; Masbou, J; Maurin, D; Maxted, N; McComb, T J L; Medina, M C; Méhault, J; Moderski, R; Moulin, E; Naumann, C L; Naumann-Godo, M; de Naurois, M; Nedbal, D; Nekrassov, D; Nguyen, N; Nicholas, B; Niemiec, J; Nolan, S J; Ohm, S; Olive, J-F; Wilhelmi, E de Oña; Opitz, B; Ostrowski, M; Panter, M; Arribas, M Paz; Pedaletti, G; Pelletier, G; Petrucci, P-O; Pita, S; Pühlhofer, G; Punch, M; Quirrenbach, A; Raue, M; Rayner, S M; Reimer, A; Reimer, O; Renaud, M; de los Reyes, R; Rieger, F; Ripken, J; Rob, L; Rosier-Lees, S; Rowell, G; Rudak, B; Rulten, C B; Ruppel, J; Ryde, F; Sahakian, V; Santangelo, A; Schlickeiser, R; Schöck, F M; Schönwald, A; Schwanke, U; Schwarzburg, S; Schwemmer, S; Shalchi, A; Sikora, M; Skilton, J L; Sol, H; Spengler, G; Stawarz, Ł; Steenkamp, R; Stegmann, C; Stinzing, F; Sushch, I; Szostek, A; Tavernet, J-P; Terrier, R; Tibolla, O; Tluczykont, M; Valerius, K; van Eldik, C; Vasileiadis, G; Venter, C; Vialle, J P; Viana, A; Vincent, P; Vivier, M; Völk, H J; Volpe, F; Vorobiov, S; Vorster, M; Wagner, S J; Ward, M; Wierzcholska, A; Zajczyk, A; Zdziarski, A A; Zech, A; Zechlin, H-S

    2011-04-22

    A search for a very-high-energy (VHE; ≥100  GeV) γ-ray signal from self-annihilating particle dark matter (DM) is performed towards a region of projected distance r∼45-150  pc from the Galactic center. The background-subtracted γ-ray spectrum measured with the High Energy Stereoscopic System (H.E.S.S.) γ-ray instrument in the energy range between 300 GeV and 30 TeV shows no hint of a residual γ-ray flux. Assuming conventional Navarro-Frenk-White and Einasto density profiles, limits are derived on the velocity-weighted annihilation cross section (σv) as a function of the DM particle mass. These are among the best reported so far for this energy range and in particular differ only little between the chosen density profile parametrizations. In particular, for the DM particle mass of ∼1  TeV, values for (σv) above 3×10(-25)  cm(3) s(-1) are excluded for the Einasto density profile. PMID:21599352

  2. The Galactic Magnetic Field and Ultra-High Energy Cosmic Rays

    NASA Astrophysics Data System (ADS)

    Urban, Federico R.

    The Galactic Magnetic Field is a peeving and importune screen between Ultra-High Energy Cosmic Rays and us cosmologists, engaged in the combat to unveil their properties and origin, as it deviates their paths towards the Earth in unpredictable ways. I will, in this order: briefly review the available field models on the market; explain a little trick which allows one to obtain cosmic rays deflection variances without even knowing what the (random) GMF model is; and argue that there is a lack of anisotropy in the large scales cosmic rays signal, which the Galactic field can do nothing about.

  3. The role of binaries in the enrichment of the early Galactic halo. III. Carbon-enhanced metal-poor stars - CEMP-s stars

    NASA Astrophysics Data System (ADS)

    Hansen, T. T.; Andersen, J.; Nordström, B.; Beers, T. C.; Placco, V. M.; Yoon, J.; Buchhave, L. A.

    2016-04-01

    natal clouds by an external (distant) source. This finding has important implications for our understanding of carbon enrichment in the early Galactic halo and some high-redshift damped lyman alpha (DLA) systems, and of the mass loss from extremely metal-poor AGB stars.

  4. The role of binaries in the enrichment of the early Galactic halo. II. Carbon-enhanced metal-poor stars: CEMP-no stars

    NASA Astrophysics Data System (ADS)

    Hansen, T. T.; Andersen, J.; Nordström, B.; Beers, T. C.; Placco, V. M.; Yoon, J.; Buchhave, L. A.

    2016-02-01

    Context. The detailed composition of most metal-poor halo stars has been found to be very uniform. However, a fraction of 20-70% (increasing with decreasing metallicity) exhibit dramatic enhancements in their abundances of carbon; these are the so-called carbon-enhanced metal-poor (CEMP) stars. A key question for Galactic chemical evolution models is whether this non-standard composition reflects that of the stellar natal clouds or is due to local, post-birth mass transfer of chemically processed material from a binary companion; CEMP stars should then all be members of binary systems. Aims: Our aim is to determine the frequency and orbital parameters of binaries among CEMP stars with and without over-abundances of neutron-capture elements - CEMP-s and CEMP-no stars, respectively - as a test of this local mass-transfer scenario. This paper discusses a sample of 24 CEMP-no stars, while a subsequent paper will consider a similar sample of CEMP-s stars. Methods: High-resolution, low S/N spectra of the stars were obtained at roughly monthly intervals over a time span of up to eight years with the FIES spectrograph at the Nordic Optical Telescope. Radial velocities of ~100 m s-1 precision were determined by cross-correlation after each observing night, allowing immediate, systematic follow-up of any variable object. Results: Most programme stars exhibit no statistically significant radial-velocity variation over this period and appear to be single, while four are found to be binaries with orbital periods of 300-2000 days and normal eccentricity; the binary frequency for the sample is 17 ± 9%. The single stars mostly belong to the recently identified low-C band, while the binaries have higher absolute carbon abundances. Conclusions: We conclude that the nucleosynthetic process responsible for the strong carbon excess in these ancient stars is unrelated to their binary status; the carbon was imprinted on their natal molecular clouds in the early Galactic interstellar

  5. MAGNETICALLY REGULATED GAS ACCRETION IN HIGH-REDSHIFT GALACTIC DISKS

    SciTech Connect

    Birnboim, Yuval

    2009-09-10

    Disk galaxies are in hydrostatic equilibrium along their vertical axis. The pressure allowing for this configuration consists of thermal, turbulent, magnetic, and cosmic-ray components. For the Milky Way the thermal pressure contributes {approx}10% of the total pressure near the plane, with this fraction dropping toward higher altitudes. Out of the rest, magnetic fields contribute {approx}1/3 of the pressure to distances of {approx}3 kpc above the disk plane. In this Letter, we attempt to extrapolate these local values to high-redshift, rapidly accreting, rapidly star-forming disk galaxies and study the effect of the extra pressure sources on the accretion of gas onto the galaxies. In particular, magnetic field tension may convert a smooth cold-flow accretion to clumpy, irregular star formation regions and rates. The infalling gas accumulates on the edge of the magnetic fields, supported by magnetic tension. When the mass of the infalling gas exceeds some threshold mass, its gravitational force cannot be balanced by magnetic tension anymore, and it falls toward the disk's plane, rapidly making stars. Simplified estimations of this threshold mass are consistent with clumpy star formation observed in SINS, UDF, GOODS, and GEMS surveys. We discuss the shortcomings of pure hydrodynamic codes in simulating the accretion of cold flows into galaxies, and emphasize the need for magnetohydrodynamic simulations.

  6. The Large Scale Structure of the Galactic Magnetic Field and High Energy Cosmic Ray Anisotropy

    NASA Astrophysics Data System (ADS)

    Alvarez-Muñiz, Jaime; Stanev, Todor

    2006-10-01

    Measurements of the magnetic field in our Galaxy are complex and usually difficult to interpret. A spiral regular field in the disk is favored by observations, however the number of field reversals is still under debate. Measurements of the parity of the field across the Galactic plane are also very difficult due to the presence of the disk field itself. In this work we demonstrate that cosmic ray protons in the energy range 1018 to 1019eV, if accelerated near the center of the Galaxy, are sensitive to the large scale structure of the Galactic Magnetic Field (GMF). In particular if the field is of even parity, and the spiral field is bi-symmetric (BSS), ultra high energy protons will predominantly come from the Southern Galactic hemisphere, and predominantly from the Northern Galactic hemisphere if the field is of even parity and axi-symmetric (ASS). There is no sensitivity to the BSS or ASS configurations if the field is of odd parity.

  7. Galactic ménage à trois: simulating magnetic fields in colliding galaxies

    NASA Astrophysics Data System (ADS)

    Kotarba, H.; Lesch, H.; Dolag, K.; Naab, T.; Johansson, P. H.; Donnert, J.; Stasyszyn, F. A.

    2011-08-01

    We present high-resolution simulations of a multiple merger of three disc galaxies, including the evolution of magnetic fields, performed with the N-body/smoothed particle hydrodynamics (SPH) code GADGET. For the first time, we embed the galaxies in a magnetized, low-density medium, thus modelling an ambient intergalactic medium (IGM). The simulations include radiative cooling and a model for star formation and supernova feedback. Magnetohydrodynamics is followed using the SPH method. The progenitor discs have initial magnetic seed fields in the range 10-9-10-6 G and the IGM has initial fields of 10-12-10-9 G. The simulations are compared to a run excluding magnetic fields. We show that the propagation of interaction-driven shocks depends significantly on the initial magnetic field strength. The shocks propagate faster in simulations with stronger initial field, suggesting that the shocks are supported by magnetic pressure. The Mach numbers of the shocks range from approximately M= 1.5 for the non-magnetized case up to M= 6 for the highest initial magnetization, resulting in higher temperatures of the shock-heated IGM gas. The magnetic field in the system saturates rapidly after the mergers at ˜10-6 G within the galaxies and ˜10-8 G in the IGM independent of the initial value. These field strengths agree with observed values and correspond to the equipartition value of the magnetic pressure with the turbulent pressure in the system. We also present synthetic radio and polarization maps for different phases of the evolution, showing that shocks driven by the interaction produce a high amount of polarized emission. These idealized simulations indicate that magnetic fields play an important role for the hydrodynamics of the IGM during galactic interactions. We also show that even weak seed fields are efficiently strengthened during multiple galactic mergers. This interaction-driven amplification might have been a key process for the magnetization of the Universe.

  8. Galactic cosmic ray currents and magnetic field irregularity degree in high-speed solar wind streams

    NASA Technical Reports Server (NTRS)

    Kuzmin, A. I.; Samsonov, I. S.; Samsonova, Z. N.

    1985-01-01

    Currents of galactic cosmic rays (GCR) obtained by global survey method are analyzed. The cases of almost total disappearance of GCR currents are compared with the results of direct measurements of the solar wind parameters. The conclusion is made on a restricted application of the convective-diffusive mechanism of the GCR modulation by the solar wind during the occurrence of stationary and regular magnetic fields in the interplanetary medium.

  9. A magnetic torsional wave near the Galactic Centre traced by a 'double helix' nebula.

    PubMed

    Morris, Mark; Uchida, Keven; Do, Tuan

    2006-03-16

    The magnetic field in the central few hundred parsecs of the Milky Way has a dipolar geometry and is substantially stronger than elsewhere in the Galaxy, with estimates ranging up to a milligauss (refs 1-6). Characterization of the magnetic field at the Galactic Centre is important because it can affect the orbits of molecular clouds by exerting a drag on them, inhibit star formation, and could guide a wind of hot gas or cosmic rays away from the central region. Here we report observations of an infrared nebula having the morphology of an intertwined double helix about 100 parsecs from the Galaxy's dynamical centre, with its axis oriented perpendicular to the Galactic plane. The observed segment is about 25 parsecs in length, and contains about 1.25 full turns of each of the two continuous, helically wound strands. We interpret this feature as a torsional Alfvén wave propagating vertically away from the Galactic disk, driven by rotation of the magnetized circumnuclear gas disk. The direct connection between the circumnuclear disk and the double helix is ambiguous, but the images show a possible meandering channel that warrants further investigation. PMID:16541066

  10. Magnetic Bubble Expansion as an Experimental Model for Extra-Galactic Radio Lobes

    NASA Astrophysics Data System (ADS)

    Lynn, Alan; Zhang, Yue; Hsu, Scott

    2010-11-01

    The Plasma Bubble Expansion Experiment (PBEX) is conducting laboratory experiments to address outstanding nonlinear plasma physics issues related to how magnetic energy and helicity carried by extra-galactic jets interacts with the intergalactic medium to form radio lobe structures. Experiments are being conducted in the 4 meter long, 50 cm diameter HELCAT linear plasma device at UNM. A pulsed magnetized coaxial gun (˜10 kV, ˜100 kA, ˜2 mWb) forms and injects magnetized plasma bubbles perpendicularly into a lower pressure weakly magnetized background plasma formed by a helicon and/or hot cathode source in HELCAT. Ideal MHD simulations show that an MHD shock develops ahead of the bubble as it propagates, and that the bubble develops asymmetries due to the background field [1]. Experimental data from plasma bubble injection into a background plasma, particularly magnetic probe measurements, will be discussed. [4pt] [1] W. Liu et al., Phys. Plasmas 15, 072905 (2008).

  11. The role of binaries in the enrichment of the early Galactic halo. I. r-process-enhanced metal-poor stars

    NASA Astrophysics Data System (ADS)

    Hansen, T. T.; Andersen, J.; Nordström, B.; Beers, T. C.; Yoon, J.; Buchhave, L. A.

    2015-11-01

    Context. The detailed chemical composition of most metal-poor halo stars has been found to be highly uniform, but a minority of stars exhibit dramatic enhancements in their abundances of heavy neutron-capture elements and/or of carbon. The key question for Galactic chemical evolution models is whether these peculiarities reflect the composition of the natal clouds, or if they are due to later (post-birth) mass transfer of chemically processed material from a binary companion. If the former case applies, the observed excess of certain elements was implanted within selected clouds in the early ISM from a production site at interstellar distances. Aims: Our aim is to determine the frequency and orbital properties of binaries among these chemically peculiar stars. This information provides the basis for deciding whether local mass transfer from a binary companion is necessary and sufficient to explain their unusual compositions. This paper discusses our study of a sample of 17 moderately (r-I) and highly (r-II) r-process-element enhanced VMP and EMP stars. Methods: High-resolution, low signal-to-noise spectra of the stars were obtained at roughly monthly intervals over eight years with the FIES spectrograph at the Nordic Optical Telescope. From these spectra, radial velocities with an accuracy of ~100 m s-1 were determined by cross-correlation against an optimized template. Results: Fourteen of the programme stars exhibit no significant radial-velocity variation over this temporal window, while three are binaries with orbits of typical eccentricity for their periods, resulting in a normal binary frequency of ~18 ± 6% for the sample. Conclusions: Our results confirm our preliminary conclusion from 2011, based on partial data, that the chemical peculiarity of the r-I and r-II stars is not caused by any putative binary companions. Instead, it was imprinted on the natal molecular clouds of these stars by an external, distant source. Models of the ISM in early galaxies

  12. A CONSTRAINT ON THE ORGANIZATION OF THE GALACTIC CENTER MAGNETIC FIELD USING FARADAY ROTATION

    SciTech Connect

    Law, C. J.; Brentjens, M. A.; Novak, G.

    2011-04-10

    We present new 6 and 20 cm Very Large Array (VLA) observations of polarized continuum emission of roughly 0.5 deg{sup 2} of the Galactic center (GC) region. The 6 cm observations detect diffuse linearly polarized emission throughout the region with a brightness of roughly 1 mJy per 15''x10'' beam. The Faraday rotation measure (RM) toward this polarized emission has structure on degree size scales and ranges from roughly +330 rad m{sup -2} east of the dynamical center (Sgr A) to-880 rad m{sup -2} west of the dynamical center. This RM structure is also seen toward several nonthermal radio filaments, which implies that they have a similar magnetic field orientation and constrains models for their origin. Modeling shows that the RM and its change with Galactic longitude are best explained by the high electron density and strong magnetic field of the GC region. Considering the emissivity of the GC plasma shows that while the absolute RM values are indirect measures of the GC magnetic field, the RM longitude structure directly traces the magnetic field in the central kiloparsec of the Galaxy. Combining this result with previous work reveals a larger RM structure covering the central {approx}2{sup 0} of the Galaxy. This RM structure is similar to that proposed by Novak and coworkers, but is shifted roughly 50 pc west of the dynamical center of the Galaxy. If this RM structure originates in the GC region, it shows that the GC magnetic field is organized on {approx}300 pc size scales. The pattern is consistent with a predominantly poloidal field geometry, pointing from south to north, that is perturbed by the motion of gas in the Galactic disk.

  13. A Constraint on the Organization of the Galactic Center Magnetic Field Using Faraday Rotation

    NASA Astrophysics Data System (ADS)

    Law, C. J.; Brentjens, M. A.; Novak, G.

    2011-04-01

    We present new 6 and 20 cm Very Large Array (VLA) observations of polarized continuum emission of roughly 0.5 deg2 of the Galactic center (GC) region. The 6 cm observations detect diffuse linearly polarized emission throughout the region with a brightness of roughly 1 mJy per 15''×10'' beam. The Faraday rotation measure (RM) toward this polarized emission has structure on degree size scales and ranges from roughly +330 rad m-2 east of the dynamical center (Sgr A) to-880 rad m-2 west of the dynamical center. This RM structure is also seen toward several nonthermal radio filaments, which implies that they have a similar magnetic field orientation and constrains models for their origin. Modeling shows that the RM and its change with Galactic longitude are best explained by the high electron density and strong magnetic field of the GC region. Considering the emissivity of the GC plasma shows that while the absolute RM values are indirect measures of the GC magnetic field, the RM longitude structure directly traces the magnetic field in the central kiloparsec of the Galaxy. Combining this result with previous work reveals a larger RM structure covering the central ~2° of the Galaxy. This RM structure is similar to that proposed by Novak and coworkers, but is shifted roughly 50 pc west of the dynamical center of the Galaxy. If this RM structure originates in the GC region, it shows that the GC magnetic field is organized on ~300 pc size scales. The pattern is consistent with a predominantly poloidal field geometry, pointing from south to north, that is perturbed by the motion of gas in the Galactic disk.

  14. 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.

  15. Gaseous Halos and the Interstellar Disk-Halo Connection

    NASA Astrophysics Data System (ADS)

    Dettmar, Ralf Jurgen

    The presence of diffuse ionized gas (DIG) in the halos of spiral galaxies is discussed in the framework of the disk-halo interaction. The halo DIG is typically correlated with the presence of other components of the ISM in the halo including X-ray hot gas, cosmic rays, and magnetic fields. All these tracers of an extraplanar ISM correlate well with star formation in the disk thus corroborating the paradigm of an ISM driven by multiple and clustered supernovae.

  16. A model for the magnetic field in the molecular disk at the Galactic center

    SciTech Connect

    Wardle, M.; Konigl, A. )

    1990-10-01

    A model for the magnetic field configuration in the Galactic center disk is presented. The field has an open geometry and represents the poloidal field detected at larger distances from the Galactic center, stretched and twisted by the effects of advection and shear in a magnetized accretion disk. It is concluded that the 100 micron polarization measurements of Hildebrand et al. (1990) imply that the radial and azimuthal components of the magnetic field in the disk are comparable and have opposite signs, consistent with the generation of B(phi) from B(r) by differential rotation. The polarization measurements indicate that the z-component of the field is smaller than both /B(phi)/ and /B(r)/; thus, they do not by themselves require that the field lines thread the disk. The field strengths of order 1 mG inferred from the Zeeman measurements and the fact that /B(phi)/ and /B(r)/ exceed B(z) imply that the field could remove the excess angular momentum of the accreted matter in the form of a centrifugally driven outflow. 31 refs.

  17. Modelling the Galactic magnetic field on the plane in two dimensions

    NASA Astrophysics Data System (ADS)

    Jaffe, T. R.; Leahy, J. P.; Banday, A. J.; Leach, S. M.; Lowe, S. R.; Wilkinson, A.

    2010-01-01

    We present a method for parametric modelling of the physical components of the Galaxy's magnetized interstellar medium, simulating the observables and mapping out the likelihood space using a Markov Chain Monte Carlo analysis. We then demonstrate it using total and polarized synchrotron emission data as well as rotation measures of extragalactic sources. With these three data sets, we define and study three components of the magnetic field: the large-scale coherent field, the small-scale isotropic random field and the ordered field. In this first paper, we use only data along the Galactic plane and test a simple two-dimensional (2D) logarithmic spiral model for the magnetic field that includes a compression and a shearing of the random component giving rise to an ordered component. We demonstrate with simulations that the method can indeed constrain multiple parameters yielding measures of, for example, the ratios of the magnetic field components. Though subject to uncertainties in thermal and cosmic ray electron densities and depending on our particular model parametrization, our preliminary analysis shows that the coherent component is a small fraction of the total magnetic field and an ordered component comparable in strength to the isotropic random component is required to explain the polarization fraction of synchrotron emission. We outline further work to extend this type of analysis to study the magnetic spiral arm structure, the details of the turbulence as well as the 3D structure of the magnetic field.

  18. Stochastic non-circular motion and outflows driven by magnetic activity in the Galactic bulge region

    NASA Astrophysics Data System (ADS)

    Suzuki, Takeru K.; Fukui, Yasuo; Torii, Kazufumi; Machida, Mami; Matsumoto, Ryoji

    2015-12-01

    By performing a global magnetohydrodynamical simulation for the Milky Way with an axisymmetric gravitational potential, we propose that spatially dependent amplification of magnetic fields possibly explains the observed noncircular motion of the gas in the Galactic centre region. The radial distribution of the rotation frequency in the bulge region is not monotonic in general. The amplification of the magnetic field is enhanced in regions with stronger differential rotation, because magnetorotational instability and field-line stretching are more effective. The strength of the amplified magnetic field reaches ≳0.5 mG, and radial flows of the gas are excited by the inhomogeneous transport of angular momentum through turbulent magnetic field that is amplified in a spatially dependent manner. In addition, the magnetic pressure-gradient force also drives radial flows in a similar manner. As a result, the simulated position-velocity diagram exhibits a time-dependent asymmetric parallelogram-shape owing to the intermittency of the magnetic turbulence; the present model provides a viable alternative to the bar-potential-driven model for the parallelogram shape of the central molecular zone. This is a natural extension into the central few 100 pc of the magnetic activity, which is observed as molecular loops at radii from a few 100 pc to 1 kpc. Furthermore, the time-averaged net gas flow is directed outward, whereas the flows are highly time dependent, which we discuss from a viewpoint of the outflow from the bulge.

  19. ASSESSING THE FEASIBILITY OF COSMIC-RAY ACCELERATION BY MAGNETIC TURBULENCE AT THE GALACTIC CENTER

    SciTech Connect

    Fatuzzo, M.; Melia, F. E-mail: fmelia@email.arizona.edu

    2012-05-01

    The presence of relativistic particles at the center of our Galaxy is evidenced by the diffuse TeV emission detected from the inner {approx}2 Degree-Sign of the Galaxy. Although it is not yet entirely clear whether the origin of the TeV photons is due to hadronic or leptonic interactions, the tight correlation of the intensity distribution with the distribution of molecular gas along the Galactic ridge strongly points to a pionic-decay process involving relativistic protons. In previous work, we concluded that point-source candidates, such as the supermassive black hole Sagittarius A* (identified with the High-Energy Stereoscopic System (HESS) source J1745-290) or the pulsar wind nebulae dispersed along the Galactic plane, could not account for the observed diffuse TeV emission from this region. Motivated by this result, we consider here the feasibility that the cosmic rays populating the Galactic center region are accelerated in situ by magnetic turbulence. Our results indicate that even in a highly conductive environment, this mechanism is efficient enough to energize protons within the intercloud medium to the {approx}>TeV energies required to produce the HESS emission.

  20. Mapping magnetic fields in the cold dust at the Galactic center

    NASA Astrophysics Data System (ADS)

    Chuss, David Thomas

    We present polarimetry results of the Galactic center with two complementary instruments: SPARO (Submillimeter Polarimeter for Antarctic Remote Observing), a 450 μm polarimeter with 6' resolution, and Hertz, a 350 μm polarimeter with 20' resolution operating on the Caltech Submillimeter Observatory. The design of SPARO is reviewed. A description of the data acquisition and analysis for SPARO is included. Finally, results are presented for the two instruments that are consistent with a model for the Galactic center magnetosphere in which an initially poloidal field has been sheared into a toroidal configuration in regions in which the energy density of gravity dominates that of magnetic fields. The SPARO data show that at low latitudes over much of the central 200 pc of the Galactic center, the field is toroidal. The Hertz data focus on the central 30 pc and find a clumpy matter distribution in which the dense regions are dominated by a toroidal field, while in the less dense regions, the field is preferentially poloidal. We use this model to estimate a characteristic field strength in this region of ˜3 mG.

  1. The energy spectrum and geometrical structure of Galactic turbulent magnetic field

    NASA Astrophysics Data System (ADS)

    Sun, Xiaohui; Gaensler, Bryan; Mcclure-Griffiths, Naomi; Purcell, Cormac; Hill, Alex; Burkhart, Blakesley; Lazarian, Alex

    2012-04-01

    The energy spectrum and geometrical structure of the turbulent magnetic field can offer a solid test of different theoretical models on the generation and evolution of Galactic magnetic fields. They are also pivotal to understanding the propagation of cosmic-ray particles. However, the energy spectrum has been difficult to determine and the geometrical structure has never been obtained so far, due to lack of proper methods and observations. We aim to infer these quantities by applying our newly developed techniques to polarisation images. These images are required to be observed with high angular resolution and broadband multi-channel polarimetry, which is possible only recently using the ATCA. As a pilot study, we plan to map the 2X2 degree high-latitude field centred at l=255.5 degree and b=-38 degree at 1.1-3.1 GHz in total intensity and polarisation.

  2. The energy spectrum and geometrical structure of Galactic turbulent magnetic field

    NASA Astrophysics Data System (ADS)

    Sun, Xiaohui; Gaensler, Bryan; Mcclure-Griffiths, Naomi; Purcell, Cormac; Hill, Alex; Burkhart, Blakesley; Lazarian, Alex

    2012-10-01

    The energy spectrum and geometrical structure of the turbulent magnetic field can offer a solid test of different theoretical models on the generation and evolution of Galactic magnetic fields. They are also pivotal to understanding the propagation of cosmic-ray particles. However, the energy spectrum has been difficult to determine and the geometrical structure has never been obtained so far, due to lack of proper methods and observations. We aim to infer these quantities by applying our newly developed techniques to polarisation images. These images are required to be observed with high angular resolution and broadband multi-channel polarimetry, which is possible only recently using the ATCA. As a pilot study, we plan to map the 2X2 degree high-latitude field centred at l=255.5 degree and b=-38 degree at 1.1-3.1 GHz in total intensity and polarisation.

  3. The spectrum of random magnetic fields in the mean field dynamo theory of the Galactic magnetic field

    NASA Technical Reports Server (NTRS)

    Kulsrud, Russell M.; Anderson, Stephen W.

    1992-01-01

    The fluctuation spectrum that must arise in a mean field dynamo generation of galactic fields if the initial field is weak is considered. A kinetic equation for its evolution is derived and solved. The spectrum evolves by transfer of energy from one magnetic mode to another by interaction with turbulent velocity modes. This kinetic equation is valid in the limit that the rate of evolution of the magnetic modes is slower than the reciprocal decorrelation time of the turbulent modes. This turns out to be the case by a factor greater than 3. Most of the fluctuation energy concentrates on small scales, shorter than the hydrodynamic turbulent scales. The fluctuation energy builds up to equipartition with the turbulent energy in times that are short compared to the e-folding time of the mean field. The turbulence becomes strongly modified before the dynamo amplification starts. Thus, the kinematic assumption of the mean dynamo theory is invalid. Thus, the galactic field must have a primordial origin, although it may subsequently be modified by dynamo action.

  4. Galactic dynamos

    NASA Astrophysics Data System (ADS)

    Moss, David

    There is a broad agreement between the predictions of galactic dynamo theory and observations; although there are still some unresolved difficulties, the theory appears to be robust. Now attention is turning from generic models to studies of particular features of the large-scale magnetic fields, and also to models for specific galaxies. The effects of noncircular flows, for example driven by the interaction of spiral arms and galactic bars with the dynamo, are of current interest.

  5. Tokamak halo currents

    SciTech Connect

    Boozer, Allen H.

    2013-08-15

    A halo current flows for part of its path through the plasma edge and for part through the chamber walls and 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. Two discordant constraints are central to the theory: (1) Halo currents must produce the magnetic field distribution required to maintain plasma force balance—a distribution that depends on the two angular coordinates of a torus. (2) Halo currents must flow along the magnetic field lines in the plasma, which implies a dependence on a linear combination of the two angular coordinates—only one angular coordinate is free. The physics basis of these two constraints is explained as is their application to the calculation of the properties of halo currents, such as their broad toroidal spectrum. Existing codes could be used to (1) provide detailed comparisons with experiments to validate that the critical elements of physics are adequately included, (2) allow more complete predictions for future machines such as ITER, and (3) design shunts and resistive elements to ensure halo currents follow paths that are the least damaging to the machine. The physics of halo currents implies that it may be possible to feedback stabilize resistive wall modes beyond the ideal-wall limit.

  6. The Origin of Galactic and Metagalactic Magnetic Fields: The Black Hole Accretion Disk Dynamo

    NASA Astrophysics Data System (ADS)

    Colgate, S.; Li, H.; Beckley, H.; Finn, J.; Pariev, V.

    1998-12-01

    The frequent star-disk collisions in the accretion disk forming the massive black hole of galaxies is an efficient, robust mechanism for generating the alpha -helicity in the alpha -Omega dynamo. In the rotating frame of the disk, these collisions result in axially directed, expanding plumes which "un-twist" due to their increased moment of inertia. We have demonstrated this flow field and its feasibility in the laboratory in preparation for a dynamo experiment using liquid sodium. The near-infinite number of rotations of the inner accretion disk and hence, amplification, ensures that this dynamo will saturate at the maximum accretion disk stress, where Bmax ~ 50 kG, corresponding to a luminosity, L ~ 10(46) ergs/s. The magnetic flux expelled as a collimated Poynting flux is sufficient to explain the magnetic flux of the galaxy as well as that of galactic clusters. The dissipation of a fraction of this magnetic energy is the likely source of the AGN/quasar phenomena.

  7. Accretion disk models for QSOs and active galactic nuclei - The role of magnetic viscosity

    NASA Technical Reports Server (NTRS)

    Sakimoto, P. J.; Coroniti, F. V.

    1981-01-01

    The inner regions of standard accretion disk models are known to be thermally unstable, and when scaled to quasar black hole masses, optically thin. Alternative accretion disk models are constructed under the assumption of a purely magnetic viscosity in the limiting cases of equipartition of gas and magnetic pressures and global flux conservation. The inner regions of these models are considerably denser than the standard model and therefore remain optically thick in all regions. The equipartition model is thermally stable throughout, while flux conservation leads to a localized thermal instability at the gas pressure/radiation pressure boundary and marginal stability as the radial distance approaches zero. The outer regions of quasar scaled accretion disks are strongly self-gravitating, leading to a vertical scale height which is smaller than that found in the inner region. Most of the outer region is gravitationally unstable, implying that the outer parts of galactic nuclei accretion disks are populated by dense self-gravitating gas clouds or possibly by stars.

  8. Artificial halos

    NASA Astrophysics Data System (ADS)

    Selmke, Markus

    2015-09-01

    Judged by their frequency and beauty, ice halos easily rival rainbows as a prominent atmospheric optics phenomenon. This article presents experimental halo demonstrations of varying complexity. Using a single commercially available hexagonal glass prism, a variety of artificial halos can be simulated. The experiments include laser beam path analysis, a modified classic spinning prism experiment, and a novel Monte-Carlo machine for three-dimensional rotations. Each of these experiments emulates different conditions of certain halo displays, and in combination, they allow a thorough understanding of these striking phenomena.

  9. The Outer Halo Metallicity Distribution

    NASA Astrophysics Data System (ADS)

    MA, ZHIBO; Morrison, H.; Harding, P.; Xue, X.; Rix, H.; Rockosi, C.; Johnson, J.; Lee, Y.; Cudworth, K.

    2012-01-01

    We present a new determination of the metallicity distribution function in the Milky Way halo, based on an in situ sample of more than 5000 K giants from SDSS/SEGUE. We have also measured the metallicity gradient in the halo, using our sample which stretches from 5 kpc to more than 100 kpc from the galactic center. The halo metallicity gradient has been a controversial topic in recent studies, but our in-situ study overcomes the problems caused in these studies by their extrapolations from local samples to the distant halo. We also describe our extensive checks of the log g and [Fe/H] measurements from the SEGUE Stellar Parameters pipeline, using globular and open cluster stars and SEGUE stars with follow-up high-resolution analysis. In addition, we present a new Bayesian estimate of distances to the K giants, which avoids the distance bias introduced by the red giant branch luminosity function.

  10. The Invariant Twist of Magnetic Fields in the Relativistic Jets of Active Galactic Nuclei

    NASA Technical Reports Server (NTRS)

    Contopoulos, Ioannis; Christodoulou, Dimitris M.; Kazanas, Demosthenes; Gabuzda, Denise C.

    2009-01-01

    The origin of cosmic magnetic (B) fields remains an open question. It is generally believed that very weak primordial B fields are amplified by dynamo processes, but it appears unlikely that the amplification proceeds fast enough to account for the fields presently observed in galaxies and galaxy clusters. In an alternative scenario, cosmic B fields are generated near the inner edges of accretion disks in Active Galactic Nuclei (AGNs) by azimuthal electric currents due to the difference between the plasma electron and ion velocities that arises when the electrons are retarded by interactions with photons. While dynamo processes show no preference for the polarity of the (presumably random) seed field that they amplify, this alternative mechanism uniquely relates the polarity of the poloidal B field to the angular velocity of the accretion disk, resulting in a unique direction for the toroidal B field induced by disk rotation. Observations of the toroidal fields of 29 AGN jets revealed by parsec-scale Faraday rotation measurements show a clear asymmetry that is consistent with this model, with the probability that this asymmetry came about by chance being less than 1 %. This lends support to the hypothesis that the Universe is seeded by B fields that are generated in AGN via this mechanism

  11. THE INVARIANT TWIST OF MAGNETIC FIELDS IN THE RELATIVISTIC JETS OF ACTIVE GALACTIC NUCLEI

    SciTech Connect

    Contopoulos, Ioannis; Christodoulou, Dimitris M.; Kazanas, Demosthenes E-mail: dimitris_christodoulou@uml.edu E-mail: gabuzda@physics.ucc.ie

    2009-09-10

    The origin of cosmic magnetic (B) fields remains an open question. It is generally believed that very weak primordial B fields are amplified by dynamo processes, but it appears unlikely that the amplification proceeds fast enough to account for the fields presently observed in galaxies and galaxy clusters. In an alternative scenario, cosmic B fields are generated near the inner edges of accretion disks in active galactic nuclei (AGNs) by azimuthal electric currents due to the difference between the plasma electron and ion velocities that arises when the electrons are retarded by interactions with photons. While dynamo processes show no preference for the polarity of the (presumably random) seed field that they amplify, this alternative mechanism uniquely relates the polarity of the poloidal B field to the angular velocity of the accretion disk, resulting in a unique direction for the toroidal B field induced by disk rotation. Observations of the toroidal fields of 29 AGN jets revealed by parsec-scale Faraday rotation measurements show a clear asymmetry that is consistent with this model, with the probability that this asymmetry came about by chance being less than 1%. This lends support to the hypothesis that the universe is seeded by B fields that are generated in AGNs via this mechanism and subsequently injected into intergalactic space by the jet outflows.

  12. Two Point Autocorrelation Analysis of Auger Highest Energy Events Backtracked in Galactic Magnetic Field

    NASA Astrophysics Data System (ADS)

    Petrov, Yevgeniy

    2009-10-01

    Searches for sources of the highest-energy cosmic rays traditionally have included looking for clusters of event arrival directions on the sky. The smallest cluster is a pair of events falling within some angular window. In contrast to the standard two point (2-pt) autocorrelation analysis, this work takes into account influence of the galactic magnetic field (GMF). The highest energy events, those above 50EeV, collected by the surface detector of the Pierre Auger Observatory between January 1, 2004 and May 31, 2009 are used in the analysis. Having assumed protons as primaries, events are backtracked through BSS/S, BSS/A, ASS/S and ASS/A versions of Harari-Mollerach-Roulet (HMR) model of the GMF. For each version of the model, a 2-pt autocorrelation analysis is applied to the backtracked events and to 105 isotropic Monte Carlo realizations weighted by the Auger exposure. Scans in energy, separation angular window and different model parameters reveal clustering at different angular scales. Small angle clustering at 2-3 deg is particularly interesting and it is compared between different field scenarios. The strength of the autocorrelation signal at those angular scales differs between BSS and ASS versions of the HMR model. The BSS versions of the model tend to defocus protons as they arrive to Earth whereas for the ASS, in contrary, it is more likely to focus them.

  13. 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)

  14. Mapping Hydrogen in the Galaxy, Galactic Halo, and Local Group with ALFA: The GALFA-H I Survey Starting with TOGS

    NASA Astrophysics Data System (ADS)

    Gibson, S. J.; Douglas, K. A.; Heiles, C.; Korpela, E. J.; Peek, J. E. G.; Putman, M. E.; Stanimirović, S.

    2008-08-01

    Radio observations of gas in the Milky Way and Local Group are vital for understanding how galaxies function as systems. The unique sensitivity of Arecibo's 305 m dish, coupled with the 7-beam Arecibo L-Band Feed Array (ALFA), provides an unparalleled tool for investigating the full range of interstellar phenomena traced by the H I 21 cm line. The GALFA (Galactic ALFA) H I Survey is mapping the entire Arecibo sky over a velocity range of -700 to +700 km s-1 with 0.2 km s-1 velocity channels and an angular resolution of 3.4'. We present highlights from the TOGS (Turn On GALFA Survey) portion of GALFA-H I, which is covering thousands of square degrees in commensal drift scan observations with the ALFALFA and AGES extragalactic ALFA surveys. This work is supported in part by the National Astronomy and Ionosphere Center, operated by Cornell University under cooperative agreement with the National Science Foundation.

  15. DOES GALACTIC MAGNETIC FIELD DISTURB THE CORRELATION OF THE HIGHEST ENERGY COSMIC RAYS WITH THEIR SOURCES?

    SciTech Connect

    Takami, Hajime; Sato, Katsuhiko

    2010-12-01

    The propagation trajectories of the highest energy cosmic rays (HECRs) are deflected by not only intergalactic magnetic field but also Galactic magnetic field (GMF). These magnetic fields can weaken the positive correlation between the arrival directions of HECRs and the positions of their sources. In order to explore the effect of GMF on the expected correlation, we simulate the arrival distribution of protons with energy above 6 x 10{sup 19} eV taking several GMF models into account, and then test the correlation between the protons and their sources assumed in the simulation. The dependence of the correlation signals on GMF models is also investigated. The correlation can be observed by accumulating {approx}200 protons in a half-hemisphere. The typical angular scale at which the positive signal of the correlation is maximized depends on the spiral component of the GMF model. That angular scale is {approx}5{sup 0} for bisymmetric spiral (BS) GMF models and {approx}7{sup 0} for axisymmetric spiral (AS) GMF models if the number density of HECR sources, n{sub s} , is {approx}10{sup -4} Mpc{sup -3}. An additional vertical (dipole) component of GMF affects these angular scales by 0.{sup 0}5-1{sup 0}. The difference between the correlation signal for the BS models and that for the AS models is prominent in the northern sky. The significance of the positive correlation depends on source distribution. The probability that the number of simulated HECR events correlating with sources is smaller than the number of random events correlating with the same sources by chance is much less than 10{sup -3} ({approx}3{sigma}) in almost all the source distributions with n{sub s} = 10{sup -4} Mpc{sup -3} for detection of under 200 protons, but {approx}10% of source distributions predict a chance probability more than 10{sup -3} in the AS GMF model. In addition, we also briefly discuss the effect of GMF for heavy-nuclei-dominated composition.

  16. Energetic secondary electrons and the nonthermal galactic radio background - A probe of the magnetic field in interstellar clouds

    NASA Technical Reports Server (NTRS)

    Marscher, A. P.; Brown, R. L.

    1978-01-01

    A previous analysis of the manifestations of charged-pion-decay secondary electrons in interstellar cloud material is extended to include those contributions to the Galactic radio and soft gamma-ray backgrounds that are directly attributable to energetic secondaries. The equilibrium distribution of secondary electrons in dense interstellar clouds is calculated, synchrotron emissivity from isolated interstellar clouds is examined, and it is shown how the value of the magnetic field in these clouds may be determined by observing the radio emission in their directions. The contribution that such clouds make to the integrated radio background is evaluated, and the Galactic distribution of bremsstrahlung gamma rays that arise from interactions of secondary electrons with thermal material in dense clouds is computed. The results indicate that a magnetic field of no more than 80 microgauss is characteristic of dense clouds and that the integrated synchrotron radiation from secondary electrons in interstellar clouds will contribute a significant fraction of the nonthermal brightness along the Galactic equator even if the mean cloud field is as low as 35 microgauss.

  17. The kinematics and morphology of cool galactic winds and halo gas from galaxies at 0.3 < z < 1.4

    NASA Astrophysics Data System (ADS)

    Rubin, Kate H. R.

    cool halo gas is typically studied along sightlines to background QSOs, the use of background galaxies offers several advantages over more traditional techniques. Because the background galaxy is spatially extended, we probe absorption over a large (> 4 h-170 kpc) area in the foreground halo, and find that the gas exhibits a large velocity dispersion and high covering fraction over this area. Spectroscopy of the foreground host galaxy reveals that it experienced a burst of star formation ˜1 Gyr ago, and we suggest that the absorbing gas in the halo was most likely ejected or tidally stripped during this past violent event. As such, these results again place a novel constraint on the radial extent of cool gas originating in the ISM of a distant galaxy.

  18. On the physical origin of galactic conformity

    NASA Astrophysics Data System (ADS)

    Hearin, Andrew P.; Behroozi, Peter S.; van den Bosch, Frank C.

    2016-09-01

    Correlations between the star formation rates (SFRs) of nearby galaxies (so-called galactic conformity) have been observed for projected separations up to 4 Mpc, an effect not predicted by current semi-analytic models. We investigate correlations between the mass accretion rates (dMvir/dt) of nearby haloes as a potential physical origin for this effect. We find that pairs of host haloes `know about' each others' assembly histories even when their present-day separation is greater than thirty times the virial radius of either halo. These distances are far too large for direct interaction between the haloes to explain the correlation in their dMvir/dt. Instead, halo pairs at these distances reside in the same large-scale tidal environment, which regulates dMvir/dt for both haloes. Larger haloes are less affected by external forces, which naturally gives rise to a mass dependence of the halo conformity signal. SDSS measurements of galactic conformity exhibit a qualitatively similar dependence on stellar mass, including how the signal varies with distance. Based on the expectation that halo accretion and galaxy SFR are correlated, we predict the scale-, mass- and redshift-dependence of large-scale galactic conformity, finding that the signal should drop to undetectable levels by z ≳ 1. These predictions are testable with current surveys to z ˜ 1; confirmation would establish a strong correlation between dark matter halo accretion rate and central galaxy SFR.

  19. Orbit bump by DC magnets and halo collimation for the RCS extraction

    NASA Astrophysics Data System (ADS)

    Tang, J. Y.

    2007-06-01

    The beam loss during the single turn extraction from a Rapid Cycling Synchrotron (RCS) with high beam power is of important concern. The extraction kickers are usually designed to have exigent total strength to avoid the beam loss. This will increase the construction cost or reduce the kickers' availability during operation. This paper introduces a method employing DC bump magnets and beam collimation during the early acceleration stage in order to reduce the requirement to the extraction kickers and the beam loss at the extraction. The orbit bump at the extraction septum produced by small DC magnets will collapse during the acceleration, and this will lower the requirement of the orbit separation by the kickers. At the same time, the similar orbit bump at the transverse collimators will allow the beam cleaning in the early acceleration stage and result in much smaller beam emittance at the extraction. The combined effect gives the low beam loss extraction with significantly lower kicker strength. The different ways of applying the method in the China Spallation Neutron Source are also presented.

  20. Identifying Remote Halo Giants in High-Latitude Fields with Kepler 2

    NASA Astrophysics Data System (ADS)

    Peterson, Ruth

    2015-08-01

    This talk describes halo-field K2 proposals submitted for C6, and planned for C8, C10, and C12, to identify red giants at distances from the Galactic plane between 10 and 100 kpc. This complements KASC WG8 Galactic Archaeology proposals by identifying and characterizing very remote halo red giants, and also in contributing to MAST a grid of high-resolution spectral calculations for giants useful for determining temperatures, gravities, and abundances from optical spectroscopy. Unlike previous surveys, our targets are unbiased in metallicity, consisting of all EPIC stars with SDSS ugriz photometry, g-r from 0.6 to 1.1, proximity > 12" (if present) to minimize contamination, and proper motion < 11 mas to remove most foreground stars. Kepler magnitudes Kp are between 16 and 18.5, where we establish that K2 can detect p-mode oscillations of red giants and measure the frequency of maximum power νmax. We also show that for these minimally-reddened stars, the g-r color alone yields the effective temperature Teff to 100K for giants with metallicity [Fe/H] below -1. We then illustrate how [Fe/H] will be estimated from νmax from the dependence of red-giant luminosity on metallicity at a given g-r.Only about 3% of these targets will be halo giants. The remainder will be intervening dwarfs, which at these magnitudes will be more than 1 kpc from the Galactic plane and thus members of the old halo population. This sample is valuable in its own right, for problems as diverse as the nature of the thick disk - halo transition and the occurrence of flaring on cool dwarfs so old that any original global magnetic dynamo has died away.

  1. ADP study of the structure of the IUE halo

    NASA Technical Reports Server (NTRS)

    Massa, Derck

    1992-01-01

    Results of a two year ADP study of gas in the Galactic halo are presented. This is partly a summary of 2 papers which were published in referred journals and partly a discussion of work currently underway.

  2. Checking for Energetic Flares on Old Halo K Dwarfs with Kepler 2

    NASA Astrophysics Data System (ADS)

    Peterson, Ruth

    2015-08-01

    This talk describes the unique opportunity offered by Kepler 2 (K2) observations of halo fields to establish whether energetic flaring occurs on stars so old that any global magnetic dynamo present at star formation has died away. Such work is being proposed to Living With a Star as a byproduct of identifying red giants at very large distances from the Galactic plane, 10 to 100 kpc. We have proposed the latter to K2 for the halo field C6, and plan to do so for the upcoming K2 halo fields C8, C10, and C12, to obtain hundreds of giants at these distances. To remove all metallicity bias, our targets include all K2 EPIC stars with Sloan SDSS ugriz photometry, g-r from 0.6 to 1.1, proximity > 12'' (if present) to minimize contamination, and proper motion below 11 mas to remove most foreground stars. Kepler magnitudes Kp are between 16 and 18.5, where long-cadence K2 observations can detect p-mode oscillations of red giants and measure the frequency of maximum power νmax. However, only about 3% of these targets will be halo giants. The remainder will be intervening dwarfs, which at these magnitudes will be more than 1 kpc from the Galactic plane and thus members of the old halo population. Both spotted stars and interacting binaries are recognizable from their light curves; single dwarfs show simple shot noise. Using the properties of superflares as seen in long-cadence Kepler data, we will identify flares and flaring stars among this sample of old halo K dwarfs. Subsequent C6 spectroscopy, if desired, can be pursued from both hemispheres, and need cover an area only four degrees square. Whether positive or negative, the results will constrain mechanisms for energetic flaring on the Sun.

  3. Topics in galactic dynamics

    NASA Astrophysics Data System (ADS)

    Little, Frank Blane

    1989-01-01

    The distant satellites of the Milky Way Galaxy are used to probe the distribution of dark matter in the Galactic halo. A new method of statistical analysis based on Bayes' theorem was devised, which directly yields confidence intervals for the mass of the Galaxy once the eccentricity distribution of the satellites is specified. Assuming an isotropic velocity distribution for 10 objects at distances of 50 to 140 kiloparsecs, mass results suggest that the Galaxy's massive dark halo extends to approximately less than 50 kiloparsecs from the Galactic center. A model galaxy with an artificial bar is used to explore the effect of dynamical friction on a galactic bar. An analytic formula is provided which correctly predicts angular momentum changes for a bar in interaction with a non self-gravitating disk. N-body simulations further show that disk self-gravity tends to make a bar without inner Lindblad resonances spin down more rapidly, and tends to make a bar dominated by inner Lindblad resonances spin up less rapidly. The long-term dynamical evolution of galactic bars is investigated using fully self gravitating bar-unstable disk-halo models. The models develop rapidly rotating bars which then slow down through transfers of angular momentum both to the outer disk and to the halo. The models suggest that the distance between the end of a bar and its corotation circle is proportional to the bar's age, and an approximate formula is presented which expresses this relationship. It is also concluded that the average tangential velocity within a barlike object drops by a factor of about 2 over approximately 45 initial rotation periods.

  4. Radio polarimetry of Galactic Centre pulsars

    NASA Astrophysics Data System (ADS)

    Schnitzeler, D. H. F. M.; Eatough, R. P.; Ferrière, K.; Kramer, M.; Lee, K. J.; Noutsos, A.; Shannon, R. M.

    2016-07-01

    To study the strength and structure of the magnetic field in the Galactic Centre (GC), we measured Faraday rotation of the radio emission of pulsars which are seen towards the GC. Three of these pulsars have the largest rotation measures (RMs) observed in any Galactic object with the exception of Sgr A⋆. Their large dispersion measures, RMs and the large RM variation between these pulsars and other known objects in the GC implies that the pulsars lie in the GC and are not merely seen in projection towards the GC. The large RMs of these pulsars indicate large line-of-sight magnetic field components between ˜ 16 and 33 μG; combined with recent model predictions for the strength of the magnetic field in the GC this implies that the large-scale magnetic field has a very small inclination angle with respect to the plane of the sky (˜12°). Foreground objects like the Radio Arc or possibly an ablated, ionized halo around the molecular cloud G0.11-0.11 could contribute to the large RMs of two of the pulsars. If these pulsars lie behind the Radio Arc or G0.11-0.11 then this proves that low-scattering corridors with lengths ≳100 pc must exist in the GC. This also suggests that future, sensitive observations will be able to detect additional pulsars in the GC. Finally, we show that the GC component in our most accurate electron density model oversimplifies structure in the GC.

  5. Radio polarimetry of Galactic centre pulsars

    NASA Astrophysics Data System (ADS)

    Schnitzeler, D. H. F. M.; Eatough, R. P.; Ferrière, K.; Kramer, M.; Lee, K. J.; Noutsos, A.; Shannon, R. M.

    2016-04-01

    To study the strength and structure of the magnetic field in the Galactic centre (GC) we measured Faraday rotation of the radio emission of pulsars which are seen towards the GC. Three of these pulsars have the largest rotation measures (RMs) observed in any Galactic object with the exception of Sgr A⋆. Their large dispersion measures, RMs and the large RM variation between these pulsars and other known objects in the GC implies that the pulsars lie in the GC and are not merely seen in projection towards the GC. The large RMs of these pulsars indicate large line-of-sight magnetic field components between ˜ 16 - 33 μG; combined with recent model predictions for the strength of the magnetic field in the GC this implies that the large-scale magnetic field has a very small inclination angle with respect to the plane of the sky (˜ 12°). Foreground objects like the Radio Arc or possibly an ablated, ionized halo around the molecular cloud G0.11-0.11 could contribute to the large RMs of two of the pulsars. If these pulsars lie behind the Radio Arc or G0.11-0.11 then this proves that low-scattering corridors with lengths ≳ 100 pc must exist in the GC. This also suggests that future, sensitive observations will be able to detect additional pulsars in the GC. Finally, we show that the GC component in our most accurate electron density model oversimplifies structure in the GC.

  6. Rotation Measures of Extragalactic Sources behind the Southern Galactic Plane: New Insights into the Large-Scale Magnetic Field of the Inner Milky Way

    NASA Astrophysics Data System (ADS)

    Brown, J. C.; Haverkorn, M.; Gaensler, B. M.; Taylor, A. R.; Bizunok, N. S.; McClure-Griffiths, N. M.; Dickey, J. M.; Green, A. J.

    2007-07-01

    We present new Faraday rotation measures (RMs) for 148 extragalactic radio sources behind the southern Galactic plane (253deg<=l<=356deg, |b|<=1.5deg), and use these data in combination with published data to probe the large-scale structure of the Milky Way's magnetic field. We show that the magnitudes of these RMs oscillate with longitude in a manner that correlates with the locations of the Galactic spiral arms. The observed pattern in RMs requires the presence of at least one large-scale magnetic reversal in the fourth Galactic quadrant, located between the Sagittarius-Carina and Scutum-Crux spiral arms. To quantitatively compare our measurements to other recent studies, we consider all available extragalactic and pulsar RMs in the region we have surveyed, and jointly fit these data to simple models in which the large-scale field follows the spiral arms. In the best-fitting model, the magnetic field in the fourth Galactic quadrant is directed clockwise in the Sagittarius-Carina spiral arm (as viewed from the north Galactic pole), but is oriented counterclockwise in the Scutum-Crux arm. This contrasts with recent analyses of pulsar RMs alone, in which the fourth-quadrant field was presumed to be directed counterclockwise in the Sagittarius-Carina arm. Also in contrast to recent pulsar RM studies, our joint modeling of pulsar and extragalactic RMs demonstrates that large numbers of large-scale magnetic field reversals are not required to account for observations.

  7. Rotation of tokamak halo currents

    SciTech Connect

    Boozer, Allen H.

    2012-05-15

    During tokamak disruptions, halo currents, which can be tenths of the total plasma current, can flow at the plasma edge along the magnetic field lines that intercept the chamber walls. Non-axisymmetric halo currents are required to maintain force balance as the plasma kinks when the edge safety factor drops to about two in a vertical displacement event. The plasma quickly assumes a definite toroidal velocity v{sub a}(r) with respect to that of the magnetic kink, v{sub k}, where v{sub a}(r) is set by the radial electric field required for ambipolarity. The plasma velocity, v{sub pl}=v{sub a}+v{sub k}, near the edge is influenced by the interaction with neutrals and with the potential in the halo required for quasi-neutrality on open magnetic field lines, and the plasma velocity in the core is influenced by external error fields. When plasma effects dominate magnetic locking, the magnetic kink should rotate at a diamagnetic speed of either the edge or the core. If the magnetic field lines of the halo plasma intercept the wall at locations of very different electrical conductivity, the toroidal rotation of the halo currents can intermittently stall at wall locations of high conductivity. Such stalling is seen in experiments. The toroidal phase difference between the stalled halo currents and the kink, which is expected to rotate smoothly, must satisfy {delta}{phi}<{+-}{pi}/2. A concern cited by ITER engineers is that the time varying force of the rotating halo could substantially increase the disruption loads on in-vessel components.

  8. Rotation of tokamak halo currents

    NASA Astrophysics Data System (ADS)

    Boozer, Allen H.

    2012-05-01

    During tokamak disruptions, halo currents, which can be tenths of the total plasma current, can flow at the plasma edge along the magnetic field lines that intercept the chamber walls. Non-axisymmetric halo currents are required to maintain force balance as the plasma kinks when the edge safety factor drops to about two in a vertical displacement event. The plasma quickly assumes a definite toroidal velocity va(r) with respect to that of the magnetic kink, vk, where va(r) is set by the radial electric field required for ambipolarity. The plasma velocity, vpl=va+vk, near the edge is influenced by the interaction with neutrals and with the potential in the halo required for quasi-neutrality on open magnetic field lines, and the plasma velocity in the core is influenced by external error fields. When plasma effects dominate magnetic locking, the magnetic kink should rotate at a diamagnetic speed of either the edge or the core. If the magnetic field lines of the halo plasma intercept the wall at locations of very different electrical conductivity, the toroidal rotation of the halo currents can intermittently stall at wall locations of high conductivity. Such stalling is seen in experiments. The toroidal phase difference between the stalled halo currents and the kink, which is expected to rotate smoothly, must satisfy δϕ <±π/2. A concern cited by ITER engineers is that the time varying force of the rotating halo could substantially increase the disruption loads on in-vessel components.

  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. How do galaxies get their magnetic fields?

    NASA Astrophysics Data System (ADS)

    Beck, Alexander; Dolag, Klaus; Lesch, Harald

    2015-08-01

    The origin of magnetic fields in high-redshift and present-day galaxies is a long-standing problem. In this talk, we present a model for the seeding and evolution of magnetic fields in protogalaxies. Supernova (SN) explosions during the assembly of a protogalaxy self-consistently provide magnetic seed fields, which are subsequently amplified by compression, shear flows and random motions.Our model explains the origin of strong magnetic fields of $\\mu$G amplitude within the first starforming protogalactic structures shortly after the first stars have formed.We present cosmological simulations with the GADGET code of Milky Way-like galactic halo formation using a standard LCDM cosmology and analyse the strength and distribution of the evolving magnetic field.Within starforming regions and given typical dimensions and magnetic field strengths in canonical SN remnants, we inject a dipole-shape magnetic field at a rate of nG/Gyr. Subsequently, the magnetic field strength increases exponentially on timescales of a few ten million years within the innermost regions of the halo.Furthermore, turbulent diffusion, shocks and gas motions transport the magnetic field towards the halo outskirts. At redshift z=0, the entire galactic structures are magnetized and the field amplitude is of the order of a few microG in the center of the halo and nG at the virial radius. Additionally, we analyse the intrinsic rotation measure (RM) of the forming galactic halo over redshift. The mean halo intrinsic RM peaks between redshifts z=4 and z=2 and reaches absolute values around 1000 rad/m^2. Towards redshift z=0, the intrinsic RM values decline to a mean value below 10 rad/m^2. At high redshifts, the distribution of individual starforming and thus magnetized regions is widespread leading to a widespread distribution of large intrinsic RMs. Our model for the evolution of galactic magnetic fields solves the joint problem of magnetic field seeding and subsequent amplification and distribution

  11. How do galaxies get their magnetic fields?

    NASA Astrophysics Data System (ADS)

    Beck, Alexander M.

    2016-06-01

    The origin of magnetic fields in high-redshift and present-day galaxies is a long-standing problem. In this talk, we present a model for the seeding and evolution of magnetic fields in protogalaxies. Supernova (SN) explosions during the assembly of a protogalaxy self-consistently provide magnetic seed fields, which are subsequently amplified by compression, shear flows and random motions.Our model explains the origin of strong magnetic fields of μG amplitude within the first starforming protogalactic structures shortly after the first stars have formed.We present cosmological simulations with the GADGET code of Milky Way-like galactic halo formation using a standard LCDM cosmology and analyse the strength and distribution of the evolving magnetic field.Within starforming regions and given typical dimensions and magnetic field strengths in canonical SN remnants, we inject a dipole-shape magnetic field at a rate of nG/Gyr. Subsequently, the magnetic field strength increases exponentially on timescales of a few ten million years within the innermost regions of the halo.Furthermore, turbulent diffusion, shocks and gas motions transport the magnetic field towards the halo outskirts. At redshift z=0, the entire galactic structures are magnetized and the field amplitude is of the order of a few microG in the center of the halo and nG at the virial radius. Additionally, we analyse the intrinsic rotation measure (RM) of the forming galactic halo over redshift. The mean halo intrinsic RM peaks between redshifts z=4 and z=2 and reaches absolute values around 1000 rad/m^2. Towards redshift z=0, the intrinsic RM values decline to a mean value below 10 rad/m^2. At high redshifts, the distribution of individual starforming and thus magnetized regions is widespread leading to a widespread distribution of large intrinsic RMs. Our model for the evolution of galactic magnetic fields solves the joint problem of magnetic field seeding and subsequent amplification and distribution. The

  12. Evidence for a Triaxial Milky Way Dark Matter Halo from the Sagittarius Stellar Tidal Stream

    NASA Astrophysics Data System (ADS)

    Law, David R.; Majewski, S. R.; Johnston, K. V.

    2010-01-01

    Observations of the lengthy tidal streams produced by the destruction of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) are capable of providing strong constraints on the shape of the Galactic gravitational potential. However, previous work, based on modeling different stream properties in axisymmetric Galactic models has yielded conflicting results: while the angular precession of the Sgr leading arm is most consistent with a spherical or slightly oblate halo, the radial velocities of stars in this arm are only reproduced by prolate halo models. We demonstrate that this apparent paradox can be resolved by instead adopting a triaxial potential. Our new Galactic halo model, which simultaneously fits all well-established phase space constraints from the Sgr stream, provides the first conclusive evidence for, and tentative measurement of, triaxiality in an individual dark matter halo. In this model, the minor axis of the dark halo is approximately coincident with the Galactic X axis connecting the Sun and the Galactic Center.

  13. Is the Milky Way's Hot Halo Convectively Unstable?

    NASA Astrophysics Data System (ADS)

    Henley, David B.; Shelton, Robin L.

    2014-03-01

    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.

  14. 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.

  15. Galactic Cosmic Ray Intensity Response to Interplanetary Coronal Mass Ejections/Magnetic Clouds in 1995-2009

    NASA Technical Reports Server (NTRS)

    Richardson, I. G.; Cane, H. V.

    2011-01-01

    We summarize the response of the galactic cosmic ray (CGR) intensity to the passage of the more than 300 interplanetary coronal mass ejections (ICMEs) and their associated shocks that passed the Earth during 1995-2009, a period that encompasses the whole of Solar Cycle 23. In approx.80% of cases, the GCR intensity decreased during the passage of these structures, i.e., a "Forbush decrease" occurred, while in approx.10% there was no significant change. In the remaining cases, the GCR intensity increased. Where there was an intensity decrease, minimum intensity was observed inside the ICME in approx.90% of these events. The observations confirm the role of both post-shock regions and ICMEs in the generation of these decreases, consistent with many previous studies, but contrary to the conclusion of Reames, Kahler, and Tylka (Astrophys. 1. Lett. 700, L199, 2009) who, from examining a subset of ICMEs with flux-rope-like magnetic fields (magnetic clouds) argued that these are "open structures" that allow free access of particles including GCRs to their interior. In fact, we find that magnetic clouds are more likely to participate in the deepest GCR decreases than ICMEs that are not magnetic clouds.

  16. The age of the halo as determined from halo field stars

    NASA Astrophysics Data System (ADS)

    Guo, Jin-Cheng; Liu, Chao; Liu, Ji-Feng

    2016-03-01

    The age of the Galactic halo is a critical parameter that can constrain the origin of the stellar halo. In general, the Galactic stellar halo is believed to be very old. However, different independent measurements and techniques based on various types of stars are required so that the age estimates of the Galactic halo are accurate, robust, and reliable. In this work, we provide a novel approach to determine the age of the halo with turn-off stars. We first carefully select 63 field halo turn-off stars from the literature. Then, we compare them with the GARSTEC model, which takes the process of atomic diffusion into account in the B - V vs. metallicity plane. Finally, we run Monte Carlo simulations to consider the uncertainty of the color index and obtain the age of 10.5 ± 1.5 Gyr. This result is in agreement with previous studies. Future works are needed to collect more turn-off samples with more accurate photometry to reduce the uncertainty of the age.

  17. Three-dimensional relativistic MHD simulations of active galactic nuclei jets: magnetic kink instability and Fanaroff-Riley dichotomy

    NASA Astrophysics Data System (ADS)

    Tchekhovskoy, Alexander; Bromberg, Omer

    2016-09-01

    Energy deposition by active galactic nuclei jets into the ambient medium can affect galaxy formation and evolution, the cooling of gas flows at the centres of galaxy clusters, and the growth of the supermassive black holes. However, the processes that couple jet power to the ambient medium and determine jet morphology are poorly understood. For instance, there is no agreement on the cause of the well-known Fanaroff-Riley (FR) morphological dichotomy of jets, with FRI jets being shorter and less stable than FRII jets. We carry out global 3D magnetohydrodynamic simulations of relativistic jets propagating through the ambient medium. We show that the flat density profiles of galactic cores slow down and collimate the jets, making them susceptible to the 3D magnetic kink instability. We obtain a critical power, which depends on the galaxy core mass and radius, below which jets become kink-unstable within the core, stall, and inflate cavities filled with relativistically hot plasma. Jets above the critical power stably escape the core and form powerful backflows. Thus, the kink instability controls the jet morphology and can lead to the FR dichotomy. The model-predicted dependence of the critical power on the galaxy optical luminosity agrees well with observations.

  18. Three-dimensional Relativistic MHD Simulations of Active Galactic Nuclei Jets: Magnetic Kink Instability and Fanaroff-Riley Dichotomy

    NASA Astrophysics Data System (ADS)

    Tchekhovskoy, Alexander; Bromberg, Omer

    2016-04-01

    Energy deposition by active galactic nuclei jets into the ambient medium can affect galaxy formation and evolution, the cooling of gas flows at the centres of galaxy clusters, and the growth of the supermassive black holes. However, the processes that couple jet power to the ambient medium and determine jet morphology are poorly understood. For instance, there is no agreement on the cause of the well-known Fanaroff-Riley (FR) morphological dichotomy of jets, with FRI jets being shorter and less stable than FRII jets. We carry out global 3D magnetohydrodynamic simulations of relativistic jets propagating through the ambient medium. We show that the flat density profiles of galactic cores slow down and collimate the jets, making them susceptible to the 3D magnetic kink instability. We obtain a critical power, which depends on the galaxy core mass and radius, below which jets become kink-unstable within the core, stall, and inflate cavities filled with relativistically-hot plasma. Jets above the critical power stably escape the galaxy cores and form powerful backflows. Thus, the kink instability controls the jet morphology and can lead to the FR dichotomy. The model-predicted dependence of the critical power on the galaxy optical luminosity agrees well with observations.

  19. A supernova scenario for magnetic fields and rotation measures in galaxies

    NASA Astrophysics Data System (ADS)

    Beck, Alexander; Dolag, Klaus; Lesch, Harald

    2015-08-01

    We present a model for the seeding and evolution of magnetic fields in protogalaxies. Supernova SN explosions during the assembly of a protogalaxy provide magnetic seed fields, which are subsequently amplified by compression, shear flows and random motions. Our model explains the origin of strong magnetic fields of microG amplitude within the first starforming protogalactic structures shortly after onset of star formation. We implement the model into the MHD version of the cosmological N-body / SPH simulation code GADGET and we couple the magnetic seeding directly to the underlying multi-phase description of star formation. We perform simulations of Milky Way-like galactic halo formation using a standard LCDM cosmology and analyse the strength and distribution of the subsequent evolving magnetic field.Within starforming regions and given typical dimensions and magnetic field strengths in canonical SN remnants, we inject a dipole-shape magnetic field at a rate of nG/Gyr.Subsequently, the magnetic field strength increases exponentially on timescales of a few ten million years within the innermost regions of the halo. Furthermore, turbulent diffusion, shocks and gas motions transport the magnetic field towards the halo outskirts. At redshift z=0, the entire galactic halo is magnetized and the field amplitude is of the order of a few microG in the center of the halo and nG at the virial radius. Additionally, we analyse the intrinsic rotation measure (RM) of the forming galactic halo over redshift. The mean halo intrinsic RM peaks between redshifts z=4 and z=2 and reaches absolute values around 1000 rad/m^2.While the halo virializes towards redshift z=0, the intrinsic RM values decline to a mean value below 10 rad/m^2. At high redshifts, the distribution of individual starforming and thus magnetized regions is widespread. This leads to a widespread distribution of large intrinsic RM values. In our model, galactic magnetic fields are a consequence of the star formation

  20. The Gaseous Halo of NGC 891

    NASA Astrophysics Data System (ADS)

    Hodges-Kluck, Edmund

    2014-08-01

    The halos of disk galaxies contain a substantial mass of diffuse gas whose properties (temperature, density, structure, and metallicity) are important to understanding how the intergalactic medium was enriched and the long-term star-formation potential of the galaxy. However, we still do not know whether most of the halo material was expelled from the galaxy in a 'galactic fountain' or is fresh infall from the circum/intergalactic medium. NGC 891 is a nearby (D=10 Mpc), edge-on Milky Way analog whose halo has been intensively studied. I will present our recent work in the X-ray and UV bands aimed at trying to determine the origin of the hot and cool components of the halo gas by measuring their metal content, and discuss whether results from NGC 891 can be generalized to other galaxies.

  1. The QUAX proposal: a search of galactic axion with magnetic materials

    NASA Astrophysics Data System (ADS)

    Ruoso, G.; Lombardi, A.; Ortolan, A.; Pengo, R.; Braggio, C.; Carugno, G.; Gallo, C. S.; Speake, C. C.

    2016-05-01

    Aim of the QUAX (QUaerere AXion) proposal is to exploit the interaction of cosmological axions with the spin of electrons in a magnetized sample. Their effect is equivalent to the application of an oscillating rf field with frequency and amplitude which are fixed by axion mass and coupling constant, respectively. The rf receiver module of the QUAX detector consists of magnetized samples with the Larmor resonance frequency tuned to the axion mass by a polarizing static magnetic field. The interaction of electrons with the axion-equivalent rf field produces oscillations in the total magnetization of the samples. To amplify such a tiny field, a pump field at the same frequency is applied in a direction orthogonal to the polarizing field. The induced oscillatory magnetization along the polarizing field is measured by a SQUID amplifier operated at its quantum noise level.

  2. Vertical Equilibrium, Energetics, and Star Formation Rates in Magnetized Galactic Disks Regulated by Momentum Feedback from Supernovae

    NASA Astrophysics Data System (ADS)

    Kim, Chang-Goo; Ostriker, Eve C.

    2015-12-01

    Recent hydrodynamic (HD) simulations have shown that galactic disks evolve to reach well-defined statistical equilibrium states. The star formation rate (SFR) self-regulates until energy injection by star formation feedback balances dissipation and cooling in the interstellar medium (ISM), and provides vertical pressure support to balance gravity. In this paper, we extend our previous models to allow for a range of initial magnetic field strengths and configurations, utilizing three-dimensional, magnetohydrodynamic (MHD) simulations. We show that a quasi-steady equilibrium state is established as rapidly for MHD as for HD models unless the initial magnetic field is very strong or very weak, which requires more time to reach saturation. Remarkably, models with initial magnetic energy varying by two orders of magnitude approach the same asymptotic state. In the fully saturated state of the fiducial model, the integrated energy proportions Eturb:Eth:δ Emag:\\bar Emag are 0.35:0.39:0.15:0.11, while the proportions of midplane support Pturb:Pth:δ Πmag:\\barΠmag are 0.49:0.18:0.18:0.15. Vertical profiles of total effective pressure satisfy vertical dynamical equilibrium with the total gas weight at all heights. We measure the "feedback yields" ηc≡ Pc/ΣSFR (in suitable units) for each pressure component, finding that ηturb∼ 3.5-4 and ηth∼ 1.1-1.4 are the same for MHD as in previous HD simulations, and δ ηmag∼ 1.3-1.5. These yields can be used to predict the equilibrium SFR for a local region in a galaxy based on its observed gas and stellar surface densities and velocity dispersions. As the ISM weight (or dynamical equilibrium pressure) is fixed, an increase in η from turbulent magnetic fields reduces the predicted ΣSFR by ∼ 20-30% relative to the HD case.

  3. 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

  4. A deployable high temperature superconducting coil (DHTSC) - A novel concept for producing magnetic shields against both solar flare and Galactic radiation during manned interplanetary missions

    NASA Technical Reports Server (NTRS)

    Cocks, F. Hadley

    1991-01-01

    The discovery of materials which are superconducting above 100 K makes possible the use of superconducting coils deployed beyong the hull of an interplanetary spacecraft to produce a magnetic shield capable of giving protection not only against solar flare radiation, but also even against Galactic radiation. Such deployed coils can be of very large size and can thus achieve the great magnetic moments required using only relatively low currents. Deployable high-temperature-superconducting coil magnetic shields appear to offer very substantial reductions in mass and energy compared to other concepts and could readily provide the radiation protection needed for a Mars mission or space colonies.

  5. Light-element abundance variations in the Milky Way halo

    NASA Astrophysics Data System (ADS)

    Martell, S. L.; Grebel, E. K.

    2010-09-01

    We present evidence for the contribution of high-mass globular clusters to the stellar halo of the Galaxy. Using SDSS-II/SEGUE spectra of over 1900 G- and K-type halo giants, we identify for the first time a subset of stars with CN bandstrengths significantly larger, and CH bandstrengths lower, than the majority of halo field stars, at fixed temperature and metallicity. Since CN bandstrength inhomogeneity and the usual attendant abundance variations are presently understood as a result of star formation in globular clusters, we interpret this subset of halo giants as a result of globular cluster dissolution into the Galactic halo. We find that 2.5% of our sample is CN-strong, and can infer based on recent models of globular cluster evolution that the fraction of halo field stars initially formed within globular clusters may be as large as 50%.

  6. The Galactic Bulge

    NASA Astrophysics Data System (ADS)

    Barbuy, B.

    2016-06-01

    The Galactic bulge is the least studied component of our Galaxy. Yet, its formation and evolution are key to understand the formation of the Galaxy itself. Studies on the Galactic bulge have increased significantly in the last years, but still there are many points of controversy. This volume contains several contributions from experts in different aspects of the bulge. Issues discussed include the following: the presence of an old spheroidal bulge, or identification of its old stellar population with the thick disk or halo; fraction of stars younger than 10 Gyr is estimated to be of < 5 to 22% depending on method and authors; multiple populations or only a metal-poor and a metal-rich ones; spheroidal or ellipsoidal distribution of RR Lyrae; formation of the bulge from early mergers or from secular evolution of the bar; different methods of mapping extinction; selection and identification of bulge globular clusters.

  7. Magnetic Field Strength in an Intermediate-velocity Ionized Filament in the First Galactic Quadrant

    NASA Astrophysics Data System (ADS)

    Stil, J. M.; Hryhoriw, A.

    2016-08-01

    We investigate the magnetic field in an intermediate-velocity filament for which the Hα intensity in the WHAM survey correlates with excess Faraday rotation of extragalactic radio sources over the length of the filament from b ≈ 20° to b ≈ 55°. The density-weighted mean magnetic field is 2.8 +/- 0.8 μ {{G}}, derived from rotation measures and an empirical relation between Hα emission measure and dispersion measure from Berkhuijsen et al. In view of the uncertainties in the derived magnetic field strength, we propose an alternative use of the available data, rotation measure, and emission measure, to derive a lower limit to the Alfvén speed, weighted by electron density {n}e3/2. We find lower limits to the Alfvén speed that are comparable to or larger than the sound speed in a {10}4 {{K}} plasma, and conclude that the magnetic field is dynamically important. We discuss the role of intermediate-velocity gas as a locus of Faraday rotation in the interstellar medium, and propose that this lower limit to the Alfvén speed may also be applicable to Faraday rotation by galaxy clusters.

  8. Evolution and Distribution of Magnetic Fields from Active Galactic Nuclei in Galaxy Clusters. II. The Effects of Cluster Size and Dynamical State

    NASA Astrophysics Data System (ADS)

    Xu, Hao; Li, Hui; Collins, David C.; Li, Shengtai; Norman, Michael L.

    2011-10-01

    Theory and simulations suggest that magnetic fields from radio jets and lobes powered by their central super massive black holes can be an important source of magnetic fields in the galaxy clusters. This is Paper II in a series of studies where we present self-consistent high-resolution adaptive mesh refinement cosmological magnetohydrodynamic simulations that simultaneously follow the formation of a galaxy cluster and evolution of magnetic fields ejected by an active galactic nucleus. We studied 12 different galaxy clusters with virial masses ranging from 1 × 1014 to 2 × 1015 M sun. In this work, we examine the effects of the mass and merger history on the final magnetic properties. We find that the evolution of magnetic fields is qualitatively similar to those of previous studies. In most clusters, the injected magnetic fields can be transported throughout the cluster and be further amplified by the intracluster medium (ICM) turbulence during the cluster formation process with hierarchical mergers, while the amplification history and the magnetic field distribution depend on the cluster formation and magnetism history. This can be very different for different clusters. The total magnetic energies in these clusters are between 4 × 1057 and 1061 erg, which is mainly decided by the cluster mass, scaling approximately with the square of the total mass. Dynamically older relaxed clusters usually have more magnetic fields in their ICM. The dynamically very young clusters may be magnetized weakly since there is not enough time for magnetic fields to be amplified.

  9. On the structure of the magnetic field near a black hole in active galactic nuclei

    NASA Astrophysics Data System (ADS)

    Beskin, V. S.; Zheltoukhov, A. A.

    2013-04-01

    Using the Grad-Shafranov equation, we consider a new analytical model of the black hole magnetosphere based on the assumption that the magnetic field is radial near the horizon and uniform (cylindrical) in the jet region. Within this model, we have managed to show that the angular velocity of particles ΩF near the rotation axis of the black hole can be smaller than ΩH/2. This result is consistent with the latest numerical simulations.

  10. The Prolate Dark Matter Halo of the Andromeda Galaxy

    NASA Astrophysics Data System (ADS)

    Hayashi, Kohei; Chiba, Masashi

    2014-07-01

    We present new limits on the global shape of the dark matter halo in the Andromeda galaxy using and generalizing non-spherical mass models developed by Hayashi & Chiba and compare our results with theoretical predictions of cold dark matter (CDM) models. 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. Applying our models to the latest kinematic data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield a prolate shape for its dark halo, irrespective of assumed density profiles. We also find that this prolate dark halo in Andromeda is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web. Therefore, our result is profound in understanding internal dynamics of halo tracers in Andromeda, such as orbital evolutions of tidal stellar streams, which play important roles in extracting the abundance of CDM subhalos through their dynamical effects on stream structures.

  11. The prolate dark matter halo of the Andromeda galaxy

    SciTech Connect

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

    2014-07-01

    We present new limits on the global shape of the dark matter halo in the Andromeda galaxy using and generalizing non-spherical mass models developed by Hayashi and Chiba and compare our results with theoretical predictions of cold dark matter (CDM) models. 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. Applying our models to the latest kinematic data of globular clusters and dwarf spheroidal galaxies in the Andromeda halo, we find that the most plausible cases for Andromeda yield a prolate shape for its dark halo, irrespective of assumed density profiles. We also find that this prolate dark halo in Andromeda is consistent with theoretical predictions in which the satellites are distributed anisotropically and preferentially located along major axes of their host halos. It is a reflection of the intimate connection between galactic dark matter halos and the cosmic web. Therefore, our result is profound in understanding internal dynamics of halo tracers in Andromeda, such as orbital evolutions of tidal stellar streams, which play important roles in extracting the abundance of CDM subhalos through their dynamical effects on stream structures.

  12. Millimeter Flares and VLBI Visibilities from Relativistic Simulations of Magnetized Accretion Onto the Galactic Center Black Hole

    NASA Astrophysics Data System (ADS)

    Dexter, Jason; Agol, Eric; Fragile, P. Chris

    2009-10-01

    The recent very long baseline interferometry (VLBI) observation of the Galactic center black hole candidate Sgr A* at 1.3 mm shows source structure on event-horizon scales. This detection enables a direct comparison of the emission region with models of the accretion flow onto the black hole. We present the first results from time-dependent radiative transfer of general relativistic MHD simulation data, and compare simulated synchrotron images at black hole spin a = 0.9 with the VLBI measurements. After tuning the accretion rate to match the millimeter flux, we find excellent agreement between predicted and observed visibilities, even when viewed face-on (i lsim 30°). VLBI measurements on 2000-3000 km baselines should constrain the inclination. The data constrain the accretion rate to be (1.0-2.3)×10-9 M sun yr-1 with 99% confidence, consistent with but independent of prior estimates derived from spectroscopic and polarimetric measurements. Finally, we compute light curves, which show that magnetic turbulence can directly produce flaring events with 0.5 hr rise times, 2-3.5 hr durations, and 40%-50% flux modulation, in agreement with observations of Sgr A* at millimeter wavelengths.

  13. Moving Groups in the Milky Way Halo and Disk Induced by the Bar and Spiral Arms

    NASA Astrophysics Data System (ADS)

    Schuster, William John

    2015-08-01

    In a previous study (Moreno et al. 2015), the use of a detailed Milky Way potential (observationally and dynamically constrained) has shown that the Galactic bar is able to efficiently concentrate stars of the stellar halo and disk into several main resonances. With the tools introduced here, the Galactic bar is shown to produce significant phase-space structure attracting stars to several main resonances. This new study is dedicated to the study of known groups of the Galactic halo and disk, and their relation to these resonances. Stars belonging to some known halo and disk moving groups have settled down along these bar resonant families, showing, in some cases, a likely Galactic secular origin. In general, the 2D resonant orbits of the disk produced by the bar, seem to dominate at large scale-heights (several kiloparsecs) into the Galactic halo. In particular, provisionally six of the members of the Kapteyn halo moving group seem to be associated with one of these resonances, and also the Groombridge 1830 (Eggen 1996a; Eggen & Sandage 1959) and especially the newer halo moving groups G21-22 and G18-39 (Silva et al. 2012) show some correlation with these resonances suggesting possible secular origins, while the halo moving group Ross 451 (Eggen 1996b) does not show any such correlation, indicating a more probable cosmological (non-secular) ancestry. All Galactic disk moving groups (such as Arcturus, Hercules, Castor, IC 2391, Hyades, Pleiades, and Ursa Major) show considerable association with these resonances.

  14. Possible existence of wormholes in the central regions of halos

    SciTech Connect

    Rahaman, Farook; Salucci, P.; Kuhfittig, P.K.F.; Ray, Saibal; Rahaman, Mosiur

    2014-11-15

    An earlier study (Rahaman, et al., 2014 and Kuhfittig, 2014) has demonstrated the possible existence of wormholes in the outer regions of the galactic halo, based on the Navarro–Frenk–White (NFW) density profile. This paper uses the Universal Rotation Curve (URC) dark matter model to obtain analogous results for the central parts of the halo. This result is an important compliment to the earlier result, thereby confirming the possible existence of wormholes in most of the spiral galaxies. - Highlights: • Earlier we showed possible existence of wormholes in the outer regions of halo. • We obtain here analogous results for the central parts of the galactic halo. • Our result is an important compliment to the earlier result. • This confirms possible existence of wormholes in most of the spiral galaxies.

  15. Simulations of Galactic Dynamos

    NASA Astrophysics Data System (ADS)

    Brandenburg, Axel

    We review our current understanding of galactic dynamo theory, paying particular attention to numerical simulations both of the mean-field equations and the original three-dimensional equations relevant to describing the magnetic field evolution for a turbulent flow. We emphasize the theoretical difficulties in explaining non-axisymmetric magnetic fields in galaxies and discuss the observational basis for such results in terms of rotation measure analysis. Next, we discuss nonlinear theory, the role of magnetic helicity conservation and magnetic helicity fluxes. This leads to the possibility that galactic magnetic fields may be bi-helical, with opposite signs of helicity and large and small length scales. We discuss their observational signatures and close by discussing the possibilities of explaining the origin of primordial magnetic fields.

  16. EVIDENCE FOR A TRIAXIAL MILKY WAY DARK MATTER HALO FROM THE SAGITTARIUS STELLAR TIDAL STREAM

    SciTech Connect

    Law, David R.; Majewski, Steven R.; Johnston, Kathryn V. E-mail: srm4n@virginia.ed

    2009-09-20

    Observations of the lengthy tidal streams produced by the destruction of the Sagittarius dwarf spheroidal (Sgr dSph) are capable of providing strong constraints on the shape of the Galactic gravitational potential. However, previous work, based on modeling different stream properties in axisymmetric Galactic models, has yielded conflicting results: while the angular precession of the Sgr leading arm is most consistent with a spherical or slightly oblate halo, the radial velocities of stars in this arm are reproduced only by prolate halo models. We demonstrate that this apparent paradox can be resolved by instead adopting a triaxial potential. Our new Galactic halo model, which simultaneously fits all well-established phase space constraints from the Sgr stream, provides the first conclusive evidence for, and tentative measurement of, triaxiality in an individual dark matter halo. The Milky Way halo within {approx}60 kpc is best characterized by a minor/major axis ratio of the isovelocity contours c/a {approx} 0.67, intermediate/major axis ratio b/a {approx} 0.83, and triaxiality parameter T {approx} 0.56. In this model, the minor axis of the dark halo is coincident with the Galactic X-axis connecting the Sun and the Galactic center to within {approx}15 deg., while the major axis also lies in the Galactic plane, approximately along the Galactic Y-axis.

  17. Evidence for a Triaxial Milky Way Dark Matter Halo from the Sagittarius Stellar Tidal Stream

    NASA Astrophysics Data System (ADS)

    Law, David R.; Majewski, Steven R.; Johnston, Kathryn V.

    2009-09-01

    Observations of the lengthy tidal streams produced by the destruction of the Sagittarius dwarf spheroidal (Sgr dSph) are capable of providing strong constraints on the shape of the Galactic gravitational potential. However, previous work, based on modeling different stream properties in axisymmetric Galactic models, has yielded conflicting results: while the angular precession of the Sgr leading arm is most consistent with a spherical or slightly oblate halo, the radial velocities of stars in this arm are reproduced only by prolate halo models. We demonstrate that this apparent paradox can be resolved by instead adopting a triaxial potential. Our new Galactic halo model, which simultaneously fits all well-established phase space constraints from the Sgr stream, provides the first conclusive evidence for, and tentative measurement of, triaxiality in an individual dark matter halo. The Milky Way halo within ~60 kpc is best characterized by a minor/major axis ratio of the isovelocity contours c/a ≈ 0.67, intermediate/major axis ratio b/a ≈ 0.83, and triaxiality parameter T ~ 0.56. In this model, the minor axis of the dark halo is coincident with the Galactic X-axis connecting the Sun and the Galactic center to within ~15°, while the major axis also lies in the Galactic plane, approximately along the Galactic Y-axis.

  18. 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

  19. Relativistic Dark Matter at the Galactic Center

    SciTech Connect

    Amin, Mustafa A.; Wizansky, Tommer; /SLAC

    2007-11-16

    In a large region of the supersymmetry parameter space, the annihilation cross section for neutralino dark matter is strongly dependent on the relative velocity of the incoming particles. We explore the consequences of this velocity dependence in the context of indirect detection of dark matter from the galactic center. We find that the increase in the annihilation cross section at high velocities leads to a flattening of the halo density profile near the galactic center and an enhancement of the annihilation signal.

  20. One dark matter mystery: halos in the cosmic web

    NASA Astrophysics Data System (ADS)

    Gaite, Jose

    2015-01-01

    The current cold dark matter cosmological model explains the large scale cosmic web structure but is challenged by the observation of a relatively smooth distribution of matter in galactic clusters. We consider various aspects of modeling the dark matter around galaxies as distributed in smooth halos and, especially, the smoothness of the dark matter halos seen in N-body cosmological simulations. We conclude that the problems of the cold dark matter cosmology on small scales are more serious than normally admitted.

  1. The halo Boltzmann equation

    NASA Astrophysics Data System (ADS)

    Biagetti, Matteo; Desjacques, Vincent; Kehagias, Alex; Racco, Davide; Riotto, Antonio

    2016-04-01

    Dark matter halos are the building blocks of the universe as they host galaxies and clusters. The knowledge of the clustering properties of halos is therefore essential for the understanding of the galaxy statistical properties. We derive an effective halo Boltzmann equation which can be used to describe the halo clustering statistics. In particular, we show how the halo Boltzmann equation encodes a statistically biased gravitational force which generates a bias in the peculiar velocities of virialized halos with respect to the underlying dark matter, as recently observed in N-body simulations.

  2. Galaxy Formation in Triaxial Halos: Black Hole-Bulge-Dark Halo Correlation

    NASA Astrophysics Data System (ADS)

    El-Zant, Amr A.; Shlosman, Isaac; Begelman, Mitchell C.; Frank, Juhan

    2003-06-01

    The masses of supermassive black holes (SBHs) show correlations with bulge properties in disk and elliptical galaxies. We study the formation of galactic structure within flat-core, mildly triaxial halos and show that these correlations can be understood within the framework of a baryonic component modifying the orbital structure in the underlying potential. In particular, we find that terminal properties of bulges and their central SBHs are constrained by the destruction of box orbits in the harmonic cores of dark halos and the emergence of progressively less eccentric loop orbits there. SBH masses, M•, should exhibit a tighter correlation with bulge velocity dispersions, σB, than with bulge masses, MB, in accord with observations, if there is a significant scatter in the MH-σH relation for the halo. In the context of this model the observed M•-σB relation implies that halos should exhibit a Faber-Jackson type relationship between their masses and velocity dispersions. The most important prediction of our model is that halo properties determine the bulge and SBH parameters. The model also has important implications for galactic morphology and the process of disk formation.

  3. MHF: MLAPM Halo Finder

    NASA Astrophysics Data System (ADS)

    Gill, Stuart P. D.; Knebe, Alexander

    2015-11-01

    MHF is a Dark Matter halo finder that is based on the refinement grids of MLAPM. The grid structure of MLAPM adaptively refines around high-density regions with an automated refinement algorithm, thus naturally "surrounding" the Dark Matter halos, as they are simply manifestations of over-densities within (and exterior) to the underlying host halo. Using this grid structure, MHF restructures the hierarchy of nested isolated MLAPM grids into a "grid tree". The densest cell in the end of a tree branch marks center of a prospective Dark Matter halo. All gravitationally bound particles about this center are collected to obtain the final halo catalog. MHF automatically finds halos within halos within halos.

  4. Stellar halos: a rosetta stone for galaxy formation and cosmology

    NASA Astrophysics Data System (ADS)

    Inglis Read, Justin

    2015-08-01

    Stellar halos make up about a percent of the total stellar mass in galaxies. Yet their old age and long phase mixing times make them living fossil records of galactic history. In this talk, I review the latest simulations of structure formation in our standard Lambda Cold Dark Matter cosmology. I discuss the latest predictions for stellar halos and the relationship between the stellar halo light and the underlying dark matter. Finally, I discuss how these simulations compare to observations of the Milky Way and Andromeda and, ultimately, what this means for our cosmological model and the formation history of the Galaxy.

  5. Searching for Tidal Tails in Galactic Dwarf Spheroidal Galaxies

    NASA Astrophysics Data System (ADS)

    Martínez-Delgado, David; Aparicio, A.; Gomez-Flechoso, Maria A.

    The formation of the Galactic halo is currently best explained by the combination of two scenarios which previously were regarded as competing models. Based on the kinematics of metal-poor halo field stars, Eggen, Lynden-Bell & Sandage (ELS, 1962) proposed that the halo formed during a rapid, smooth collapse from a homogeneous primordial medium. Searle & Zinn (SZ, 1978) argued a halo formation via the gradual merging of many sub-galactic fragments. The SZ scenario has been strengthened by the observational evidence accumulated during the past decade. The discovery of the Sagittarius dwarf galaxy (Ibata, Gilmore & Irwin 1994), in a process of dissolving into the Galactic halo, argued in favour that accretion events can take place in the Milky Way. The possibility that accretion events may leave observable fossil records in the halo is also supported by theoretical models of tidally disrupted dSph satellites (Johnston, Spergel & Hernquist 1995; Oh, Lin & Aarseth 1995; Piatek & Pryor 1995). We present our preliminary results of a long-term project to investigate the process of accretion and tidal disruption of dSph satellites in the Galactic halo and, in particular, to search for new tidal tails in a sample of nearby dSph satellites of the Milky Way. The presence of a possible tidal debris in Ursa Minor and Sculptor dSphs and the results of our survey for a tidal extension along the NW semimajor axis of Saggitarius is discussed.

  6. SUBSTRUCTURE IN THE STELLAR HALOS OF THE AQUARIUS SIMULATIONS

    SciTech Connect

    Helmi, Amina; Cooper, A. P.; Cole, S.; Frenk, C. S.; White, S. D. M.; Navarro, J. F.

    2011-05-20

    We characterize the substructure in the simulated stellar halos of Cooper et al. which were formed by the disruption of satellite galaxies within the cosmological N-body simulations of galactic halos of the Aquarius project. These stellar halos exhibit a wealth of tidal features: broad overdensities and very narrow faint streams akin to those observed around the Milky Way. The substructures are distributed anisotropically on the sky, a characteristic that should become apparent in the next generation of photometric surveys. The normalized RMS of the density of stars on the sky appears to be systematically larger for our halos compared with the value estimated for the Milky Way from main-sequence turnoff stars in the Sloan Digital Sky Survey. We show that this is likely to be due in part to contamination by faint QSOs and redder main-sequence stars, and might suggest that {approx}10% of the Milky Way halo stars have formed in situ.

  7. On detecting halo assembly bias with galaxy populations

    NASA Astrophysics Data System (ADS)

    Lin, Yen-Ting; Mandelbaum, Rachel; Huang, Yun-Hsin; Huang, Hung-Jin; Dalal, Neal; Diemer, Benedikt; Kravtsov, Andrey

    2016-01-01

    The fact that the clustering and concentration of dark matter halos depend not only on their mass, but also the formation epoch, is a prominent, albeit subtle, feature of the cold dark matter structure formation theory, and is known as assembly bias. At low mass scales (~1012 Msun), early-forming halos are predicted to be more strongly clustered than the late-forming ones. In this study we aim to robustly detect the signature of assembly bias observationally, making use of formation time indicators of central galaxies in low mass halos as a proxy for the halo formation history. Weak gravitational lensing is employed to ensure our early- and late-forming halo samples have similar masses, and are free of contamination of satellites from more massive halos. For the two formation time indicators used (resolved star formation history and current specific star formation rate), we do not find convincing evidence of assembly bias. We attribute the lack of detection to the possibility that these indicators do not correlate well with the halo formation history, and suggest alternatives that should perform better for future studies. In addition, we have developed a method to constrain the probability distribution function of halo mass of a given galaxy sample, and also demonstrate that the abundance matching-based halo mass assignments to galaxy groups and clusters may be biased, likely due to interlopers from more massive galactic systems.

  8. EVOLUTION AND DISTRIBUTION OF MAGNETIC FIELDS FROM ACTIVE GALACTIC NUCLEI IN GALAXY CLUSTERS. I. THE EFFECT OF INJECTION ENERGY AND REDSHIFT

    SciTech Connect

    Xu Hao; Li Hui; Li Shengtai; Collins, David C.; Norman, Michael L. E-mail: hli@lanl.go E-mail: dcollins@physics.ucsd.ed

    2010-12-20

    We present a series of cosmological magnetohydrodynamic simulations that simultaneously follow the formation of a galaxy cluster and evolution of magnetic fields ejected by an active galactic nucleus (AGN). Specifically, we investigate the influence of both the epoch of the AGN (z {approx} 3-0.5) and the AGN energy ({approx}3 x 10{sup 57}- 2 x 10{sup 60} erg) on the final magnetic field distribution in a relatively massive cluster (M{sub vir} {approx} 10{sup 15} M{sub sun}). We find that as long as the AGN magnetic fields are ejected before the major mergers in the cluster formation history, magnetic fields can be transported throughout the cluster and can be further amplified by the intracluster medium (ICM) turbulence caused by hierarchical mergers during the cluster formation process. The total magnetic energy in the cluster can reach {approx}10{sup 61} erg, with micro Gauss fields distributed over the {approx}Mpc scale. The amplification of the total magnetic energy by the ICM turbulence can be significant, up to {approx}1000 times in some cases. Therefore even weak magnetic fields from AGNs can be used to magnetize the cluster to the observed level. The final magnetic energy in the ICM is determined by the ICM turbulent energy, with a weak dependence on the AGN injection energy. We discuss the properties of magnetic fields throughout the cluster and the synthetic Faraday rotation measure maps they produce. We also show that high spatial resolution over most of the magnetic regions of the cluster is very important to capture the small-scale dynamo process and maintain the magnetic field structure in our simulations.

  9. Evolution and Distribution of Magnetic Fields from Active Galactic Nuclei in Galaxy Clusters. I. The Effect of Injection Energy and Redshift

    NASA Astrophysics Data System (ADS)

    Xu, Hao; Li, Hui; Collins, David C.; Li, Shengtai; Norman, Michael L.

    2010-12-01

    We present a series of cosmological magnetohydrodynamic simulations that simultaneously follow the formation of a galaxy cluster and evolution of magnetic fields ejected by an active galactic nucleus (AGN). Specifically, we investigate the influence of both the epoch of the AGN (z ~ 3-0.5) and the AGN energy (~3 × 1057- 2 × 1060 erg) on the final magnetic field distribution in a relatively massive cluster (M vir ~ 1015 M sun). We find that as long as the AGN magnetic fields are ejected before the major mergers in the cluster formation history, magnetic fields can be transported throughout the cluster and can be further amplified by the intracluster medium (ICM) turbulence caused by hierarchical mergers during the cluster formation process. The total magnetic energy in the cluster can reach ~1061 erg, with micro Gauss fields distributed over the ~Mpc scale. The amplification of the total magnetic energy by the ICM turbulence can be significant, up to ~1000 times in some cases. Therefore even weak magnetic fields from AGNs can be used to magnetize the cluster to the observed level. The final magnetic energy in the ICM is determined by the ICM turbulent energy, with a weak dependence on the AGN injection energy. We discuss the properties of magnetic fields throughout the cluster and the synthetic Faraday rotation measure maps they produce. We also show that high spatial resolution over most of the magnetic regions of the cluster is very important to capture the small-scale dynamo process and maintain the magnetic field structure in our simulations.

  10. INSIGHT INTO THE FORMATION OF THE MILKY WAY THROUGH COLD HALO SUBSTRUCTURE. III. STATISTICAL CHEMICAL TAGGING IN THE SMOOTH HALO

    SciTech Connect

    Schlaufman, Kevin C.; Rockosi, Constance M.; Rashkov, Valery; Madau, Piero; Lee, Young Sun; Beers, Timothy C.; Prieto, Carlos Allende; Bizyaev, Dmitry E-mail: crockosi@ucolick.org E-mail: pmadau@ucolick.org E-mail: beers@pa.msu.edu E-mail: dmbiz@apo.nmsu.edu

    2012-04-10

    We find that the relative contribution of satellite galaxies accreted at high redshift to the stellar population of the Milky Way's smooth halo increases with distance, becoming observable relative to the classical smooth halo about 15 kpc from the Galactic center. In particular, we determine line-of-sight-averaged [Fe/H] and [{alpha}/Fe] in the metal-poor main-sequence turnoff (MPMSTO) population along every Sloan Extension for Galactic Understanding and Exploration (SEGUE) spectroscopic line of sight. Restricting our sample to those lines of sight along which we do not detect elements of cold halo substructure (ECHOS), we compile the largest spectroscopic sample of stars in the smooth component of the halo ever observed in situ beyond 10 kpc. We find significant spatial autocorrelation in [Fe/H] in the MPMSTO population in the distant half of our sample beyond about 15 kpc from the Galactic center. Inside of 15 kpc however, we find no significant spatial autocorrelation in [Fe/H]. At the same time, we perform SEGUE-like observations of N-body simulations of Milky Way analog formation. While we find that halos formed entirely by accreted satellite galaxies provide a poor match to our observations of the halo within 15 kpc of the Galactic center, we do observe spatial autocorrelation in [Fe/H] in the simulations at larger distances. This observation is an example of statistical chemical tagging and indicates that spatial autocorrelation in metallicity is a generic feature of stellar halos formed from accreted satellite galaxies.

  11. Dark filaments in the galaxy NGC 253: A boiling galactic disk

    NASA Astrophysics Data System (ADS)

    Sofue, Yoshiaki; Wakamatsu, Ken-Ichi; Malin, David F.

    1994-12-01

    We study the morphology of dark lanes and filaments in the dust-rich galaxy NGC 253 using an unsharp-masked B-band optical photograph. Dust features are classified as 'arcs,' which have heights and scale radius of about 100 to 300 pc, connecting two or more dark clouds, and 'loops' and 'bubbles,' which are developed forms of arcs, expanding into the disk-halo interface. These have diameters of a few hundred pc to approximately 1 kpc. Among the bubbles, we notice a peculiar round-shaped bubble above the nucleus, which could be a large-diameter (approximately 300 pc) supernova remnant exploded in the halo over the nucleus. We also find 'vertical dust streamers,' which comprise bunches of narrow filaments with a thickness of a few tens of pc and are almost perpendicular to the galactic plane, extending coherently for 1 to 2 kpc toward the halo. Finally, we note 'short vertical dust filaments' (or spicules) are found in the central region. We interpret these features as due to three-dimensional structures of gas extending from the disk into the halo. We propose a 'boiling disk' model where the filamentary features are produced by star-forming activity in the disk as well as the influence of magnetic fluxes. We discuss the implication of the model for the chemical evolution of the interstellar medium (ISM) in a galaxy disk.

  12. The linear filaments of the radio arc near the Galactic center

    NASA Technical Reports Server (NTRS)

    Yusef-Zadeh, Farhad; Morris, Mark

    1987-01-01

    High-resolution radio continuum VLA images of a segment of the Galactic center arc centered at G0.16-0.15 at wavelengths of both 6 and 20 cm are presented. In this segment, the highest multiplicity of filaments, the largest degree of linear polarization, and a maximum rotation measure of -5500 rad/sq m between wavelengths 6.166 and 6.363 cm are found. The large 'helical segments' which surround the filamentary system are also shown and discussed. Based on a number of intriguing characteristics of the filamentary system, including the helical component and possible twisting of some of the filaments, a picture is considered in which the geometry of the magnetic structure is that of a cylindrically symmetric, force-free field anchored to the halo of the Galaxy. An analogy with solar flare filaments is used to discuss some aspects of the Galactic center filaments.

  13. 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.

  14. SECULAR DAMPING OF STELLAR BARS IN SPINNING DARK MATTER HALOS

    SciTech Connect

    Long, Stacy; Shlosman, Isaac; Heller, Clayton

    2014-03-01

    We demonstrate using numerical simulations of isolated galaxies that growth of stellar bars in spinning dark matter halos is heavily suppressed in the secular phase of evolution. In a representative set of models, we show that for values of the cosmological spin parameter λ ≳ 0.03, bar growth (in strength and size) becomes increasingly quenched. Furthermore, the slowdown of the bar pattern speed weakens considerably with increasing λ until it ceases completely. The terminal structure of the bars is affected as well, including extent and shape of their boxy/peanut bulges. The essence of this effect lies in the modified angular momentum exchange between the disk and the halo facilitated by the bar. For the first time we have demonstrated that a dark matter halo can emit and not purely absorb angular momentum. Although the halo as a whole is not found to emit, the net transfer of angular momentum from the disk to the halo is significantly reduced or completely eliminated. The paradigm shift implies that the accepted view that disks serve as sources of angular momentum and halos serve as sinks must be revised. Halos with λ ≳ 0.03 are expected to form a substantial fraction, based on the lognormal distribution of λ. The dependence of secular bar evolution on halo spin, therefore, implies profound corollaries for the cosmological evolution of galactic disks.

  15. Secular Damping of Stellar Bars in Spinning Dark Matter Halos

    NASA Astrophysics Data System (ADS)

    Long, Stacy; Shlosman, Isaac; Heller, Clayton

    2014-03-01

    We demonstrate using numerical simulations of isolated galaxies that growth of stellar bars in spinning dark matter halos is heavily suppressed in the secular phase of evolution. In a representative set of models, we show that for values of the cosmological spin parameter λ >~ 0.03, bar growth (in strength and size) becomes increasingly quenched. Furthermore, the slowdown of the bar pattern speed weakens considerably with increasing λ until it ceases completely. The terminal structure of the bars is affected as well, including extent and shape of their boxy/peanut bulges. The essence of this effect lies in the modified angular momentum exchange between the disk and the halo facilitated by the bar. For the first time we have demonstrated that a dark matter halo can emit and not purely absorb angular momentum. Although the halo as a whole is not found to emit, the net transfer of angular momentum from the disk to the halo is significantly reduced or completely eliminated. The paradigm shift implies that the accepted view that disks serve as sources of angular momentum and halos serve as sinks must be revised. Halos with λ >~ 0.03 are expected to form a substantial fraction, based on the lognormal distribution of λ. The dependence of secular bar evolution on halo spin, therefore, implies profound corollaries for the cosmological evolution of galactic disks.

  16. Galactic antiprotons from photinos

    NASA Technical Reports Server (NTRS)

    Stecker, F. W.; Rudaz, S.; Walsh, T. F.

    1985-01-01

    Stable photinos, the photino being the supersymmetry partner of the photon, can explain both the 'missing mass' in galactic halos and the cosmic-ray antiproton spectrum up to the highest energies observed so far. This requires a photino mass around 15 GeV; significantly higher masses are cosmologically disfavored. As a consequence, the observed cosmic-ray antiproton-to-proton ratio is predicted to decrease abruptly just above the measured energy range, at E = m(x). If observed, this striking effect would strongly support the hypothesis that photinos make up the missing matter in the galaxy and also lead to a measurement of the photino mass from cosmic-ray data.

  17. 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

  18. Tests and consequences of disk plus halo models of gamma-ray burst sources

    NASA Technical Reports Server (NTRS)

    Smith, I. A.

    1995-01-01

    The gamma-ray burst observations made by the Burst and Transient Source Experiment (BATSE) and by previous experiments are still consistent with a combined Galactic disk (or Galactic spiral arm) plus extended Galactic halo model. Testable predictions and consequences of the disk plus halo model are discussed here; tests performed on the expanded BATSE database in the future will constrain the allowed model parameters and may eventually rule out the disk plus halo model. Using examples, it is shown that if the halo has an appropriate edge, BATSE will never detect an anisotropic signal from the halo of the Andromeda galaxy. A prediction of the disk plus halo model is that the fraction of the bursts observed to be in the 'disk' population rises as the detector sensitivity improves. A careful reexamination of the numbers of bursts in the two populations for the pre-BATSE databases could rule out this class of models. Similarly, it is predicted that different satellites will observe different relative numbers of bursts in the two classes for any model in which there are two different spatial distribiutions of the sources, or for models in which there is one spatial distribution of the sources that is sampled to different depths for the two classes. An important consequence of the disk plus halo model is that for the birthrate of the halo sources to be small compared to the birthrate of the disk sources, it is necessary for the halo sources to release many orders of magnitude more energy over their bursting lifetime than the disk sources. The halo bursts must also be much more luminous than the disk bursts; if this disk-halo model is correct, it is necessary to explain why the disk sources do not produce halo-type bursts.

  19. Halo-Independent Comparison of Direct Dark Matter Detection Data

    DOE PAGESBeta

    Del Nobile, Eugenio

    2014-01-01

    We review the halo-independent formalism that allows comparing data from different direct dark matter detection experiments without making assumptions on the properties of the dark matter halo. We apply this method to spin-independent WIMP-nuclei interactions, for both isospin-conserving and isospin-violating couplings, and to WIMPs interacting through an anomalous magnetic moment.

  20. PROGRESSIVELY MORE PROLATE DARK MATTER HALO IN THE OUTER GALAXY AS TRACED BY FLARING H I GAS

    SciTech Connect

    Banerjee, Arunima; Jog, Chanda J. E-mail: cjjog@physics.iisc.ernet.in

    2011-05-01

    A galactic disk in a spiral galaxy is generally believed to be embedded in an extended dark matter halo, which dominates its dynamics in the outer parts. However, the shape of the halo is not clearly understood. Here we show that the dark matter halo in the Milky Way is prolate in shape. Further, it is increasingly more prolate at larger radii, with the vertical-to-planar axis ratio monotonically increasing to 2.0 at 24 kpc. This is obtained by modeling the observed steeply flaring atomic hydrogen gas layer in the outer Galactic disk, where the gas is supported by pressure against the net gravitational field of the disk and the halo. The resulting prolate-shaped halo can explain several long-standing puzzles in galactic dynamics, for example, it permits long-lived warps thus explaining their ubiquitous nature.

  1. Resolved Stellar Halos of M87 and NGC 5128: Metallicities from the Red-Giant Branch

    NASA Astrophysics Data System (ADS)

    Bird, Sarah A.

    2016-08-01

    We have searched halo fields of two giant elliptical galaxies: M87, using HST images at 10 kpc from the galactic 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 have resolved thousands of red-giant-branch (RGB) stars in these stellar halo fields using V and I filters, and, in addition, measured the metallicity using stellar isochrones. The metallicity distribution function (MDF) of the inner stellar halo of M87 is similar to that of NGC 5128's stellar halo.

  2. Ghostly Halos in Dwarf Galaxies: a probe of star formation in the Early Universe

    NASA Astrophysics Data System (ADS)

    Kang, Hoyoung; Ricotti, Massimo

    2016-01-01

    We carry out numerical simulations to characterize the size, stellar mass, and stellar mass surface density of extended stellar halos in dwarf galaxies as a function of dark matter halo mass. We expect that for galaxies smaller than a critical value, these ghostly halos will not exist because the smaller galactic subunits that build it up, do not form any stars. The detection of ghostly halos around isolated dwarf galaxies is a sensitive test of the efficiency of star formation in the first galaxies and of whether ultra-faint dwarf satellites of the Milky Way are fossils of the first galaxies.

  3. Cold dark matter halos

    NASA Astrophysics Data System (ADS)

    Dubinski, John Joseph

    The dark halos arising in the Cold Dark Matter (CDM) cosmology are simulated to investigate the relationship between the structure and kinematics of dark halos and galaxies. Realistic cosmological initial conditions and tidal field boundary conditions are used in N-body simulations of the collapse of density peaks to form dark halos. The core radii of dark halos are no greater than the softening radius, rs = 1.4 kpc. The density profiles can be fit with an analytical Hernquist (1990) profile with an effective power law which varies between -1 in the center to -4 at large radii. The rotation curves of dark halos resemble the flat rotation curves of spiral galaxies in the observed range, 1.5 approximately less than r approximately less than 30 kpc. The halos are strongly triaxial and very flat with (c/a) = 0.50 and (b/a) = 0.71. The distribution of ellipticities for dark halos reaches a maximum at epsilon = 0.5 in contrast to the distribution for elliptical galaxies which peaks at epsilon = 0.2 suggesting that ellipticals are much rounder than dark halos. Dark halos are generally flatter than their progenitor density peaks. The final shape and orientation of a dark halo are largely determined by tidal torquing and are sensitive to changes in the strength and orientation of a tidal field. Dark halos are pressure supported objects with negligible rotational support as indicated by the mean dimensionless spin, lamda = 0.042 +/- 0.024. The angular momentum vector tends to align with the true minor axis of dark halos. Elliptical galaxies have a similar behavior implied by the observation of the tendency for alignment of the rotation vector and the apparent minor axis. The origin of this behavior may be traced to the tendency for tidal torques to misalign with the major axis of a density peak. Tidal torques are found to isotropize the velocity ellipsoids of dark halos at large radii, contrary to the expectation of radially anisotropic velocity ellipsoids in cold collapse

  4. EFFECT OF DARK MATTER HALO SUBSTRUCTURES ON GALAXY ROTATION CURVES

    SciTech Connect

    Roy, Nirupam

    2010-11-01

    In this paper, the effect of halo substructures on galaxy rotation curves is investigated using a simple model of dark matter clustering. A dark matter halo density profile is developed based only on the scale-free nature of clustering that leads to a statistically self-similar distribution of the substructures at the galactic scale. A semi-analytical method is used to derive rotation curves for such a clumpy dark matter density profile. It is found that the halo substructures significantly affect the galaxy velocity field. Based on the fractal geometry of the halo, this self-consistent model predicts a Navarro-Frenk-White-like rotation curve and a scale-free power spectrum of the rotation velocity fluctuations.

  5. Magnetic fields in damped Ly-alpha systems

    NASA Technical Reports Server (NTRS)

    Wolfe, A. M.; Lanzetta, K. M.; Oren, A. L.

    1992-01-01

    The probability of Faraday rotation in various types of metal-line absorbers is computed by combining the incidence of Faraday rotation in a sample of radio-selected QSOs with the incidence of foreground metal-line absorption. The sample is divided into subsets with and without damped Ly-alpha absorption. The probability of Faraday rotation is significantly higher in the damped subset. The probability is higher in the damped subset than in nondamped subsets selected on the basis of Mg II or C IV absorption. From evidence linking damped systems to the progenitors of galactic disks and the Mg II systems to the progenitors of galactic halos, it is concluded that magnetic fields were significantly higher in protogalactic disks than in protogalactic halos. It is estimated that the B fields in two damped Ly-alpha systems with z of about 2 are a few micro-Gauss.

  6. Linking the Halo to its Surroundings

    NASA Astrophysics Data System (ADS)

    Arimoto, N.

    The Galactic halo is unlikely built up from galaxy populations similar to the dwarf spheroidal galaxies (dSph's) in the Local Group, but it is possible that the halo was formed by accreted dwarf galaxies that had much larger mass and higher star formation rates such as the Saggitarius dSph. Cosmological simulations show that dSph galaxies formed via hierarchical clustering of numerous smaller building blocks. Stars formed at the galaxy centre tend to form from metal-rich infall gas, which builds up the metallicity gradients. Infalling gas has larger rotational velocity and smaller velocity dispersion due to the dissipative processes, resulting the two distinct old stellar populations of different chemical and kinematic properties, which are recently discovered in the Sculptor dSph galaxy.

  7. The Shapes, Orientation, and Alignment of Galactic Dark Matter Subhalos

    NASA Astrophysics Data System (ADS)

    Kuhlen, Michael; Diemand, Jürg; Madau, Piero

    2007-12-01

    We present a study of the shapes, orientations, and alignments of Galactic dark matter subhalos in the Via Lactea simulation of a Milky Way-size ΛCDM host halo. Whereas isolated dark matter halos tend to be prolate, subhalos are predominantly triaxial. Overall subhalos are more spherical than the host halo, with minor-to-major and intermediate-to-major axis ratios of 0.68 and 0.83, respectively. Like isolated halos, subhalos tend to be less spherical in their central regions. The principal axis ratios are independent of subhalo mass when the shapes are measured within a physical scale such as rVmax, the radius of the peak of the circular velocity curve. Subhalos tend to be slightly more spherical closer to the host halo center. The spatial distribution of the subhalos traces the prolate shape of the host halo when they are selected by the largest Vmax they ever had, i.e., before they experienced strong tidal mass loss. The subhalos' orientation is not random: the major axis tends to align with the direction toward the host halo center. This alignment disappears for halos beyond 3r200 and is more pronounced when the shapes are measured in the outer regions of the subhalos. The radial alignment is preserved during a subhalo's orbit and they become elongated during pericenter passage, indicating that the alignment is likely caused by the host halo's tidal forces. These tidal interactions with the host halo act to make subhalos rounder over time.

  8. An Improved Catalog of Halo Wide Binary Candidates

    NASA Astrophysics Data System (ADS)

    Allen, Christine; Monroy-Rodríguez, Miguel A.

    2014-08-01

    We present an improved catalog of halo wide binaries compiled from an extensive literature search. Most of our binaries stem from the common proper motion binary catalogs by Allen et al. and Chanamé & Gould, but we have also included binaries from the lists of Ryan and Zapatero-Osorio & Martín. All binaries were carefully checked and their distances and systemic radial velocities are included when available. Probable membership to the halo population was tested by means of reduced proper motion diagrams for 251 candidate halo binaries. After eliminating obvious disk binaries, we ended up with 211 probable halo binaries, 150 of which have radial velocities available. We compute galactic orbits for these 150 binaries and calculate the time they spend within the galactic disk. Considering the full sample of 251 candidate halo binaries as well as several subsamples, we find that the distribution of angular separations (or expected major semiaxes) follows a power law f(a) ~ a -1 (Oepik's relation) up to different limits. For the 50 most disk-like binaries, those that spend their entire lives within z = ±500 pc, this limit is found to be 19,000 AU (0.09 pc), while for the 50 most halo-like binaries, those that spend on average only 18% of their lives within z = ±500 pc, the limit is 63,000 AU (0.31 pc). In a companion paper, we employ this catalog to establish limits on the masses of the halo massive perturbers (massive compact halo objects).

  9. An improved catalog of halo wide binary candidates

    SciTech Connect

    Allen, Christine; Monroy-Rodríguez, Miguel A.

    2014-08-01

    We present an improved catalog of halo wide binaries compiled from an extensive literature search. Most of our binaries stem from the common proper motion binary catalogs by Allen et al. and Chanamé and Gould, but we have also included binaries from the lists of Ryan and Zapatero-Osorio and Martín. All binaries were carefully checked and their distances and systemic radial velocities are included when available. Probable membership to the halo population was tested by means of reduced proper motion diagrams for 251 candidate halo binaries. After eliminating obvious disk binaries, we ended up with 211 probable halo binaries, 150 of which have radial velocities available. We compute galactic orbits for these 150 binaries and calculate the time they spend within the galactic disk. Considering the full sample of 251 candidate halo binaries as well as several subsamples, we find that the distribution of angular separations (or expected major semiaxes) follows a power law f(a) ∼ a {sup –1} (Oepik's relation) up to different limits. For the 50 most disk-like binaries, those that spend their entire lives within z = ±500 pc, this limit is found to be 19,000 AU (0.09 pc), while for the 50 most halo-like binaries, those that spend on average only 18% of their lives within z = ±500 pc, the limit is 63,000 AU (0.31 pc). In a companion paper, we employ this catalog to establish limits on the masses of the halo massive perturbers (massive compact halo objects).

  10. Kinematic imprint of clumpy disk formation on halo objects

    NASA Astrophysics Data System (ADS)

    Inoue, Shigeki

    2013-02-01

    Context. Clumpy disk galaxies in the distant universe, at redshift of z ≳ 1, have been observed to host several giant clumps in their disks. They are thought to correspond to early formative stages of disk galaxies. On the other hand, halo objects, such as old globular clusters and halo stars, are likely to consist of the oldest stars in a galaxy (age ≳ 10 Gyr), clumpy disk formation can thus be presumed to take place in a pre-existing halo system. Aims: Giant clumps orbit in the same direction in a premature disk and are so massive that they may be expected to interact gravitationally with halo objects and exercise influence on the kinematic state of the halo. Accordingly, I scrutinize the possibility that the clumps leave a kinematic imprint of the clumpy disk formation on a halo system. Methods: I perform a restricted N-body calculation with a toy model to study the kinematic influence on a halo by orbital motions of clumps and the dependence of the results on masses (mass loss), number, and orbital radii of the clumps. Results: I show that halo objects can catch clump motions and acquire disky rotation in a dynamical friction time scale of the clumps, ~0.5 Gyr. The influence of clumps is limited within a region around the disk, while the halo system shows vertical gradients of net rotation velocity and orbital eccentricity. The significance of the kinematic influence strongly depends on the clump masses; the lower limit of postulated clump mass would be ~5 × 108 M⊙. The result also depends on whether the clumps are subjected to rapid mass loss or not, which is an open question under debate in recent studies. The existence of such massive clumps is not unrealistic. I therefore suggest that the imprints of past clumpy disk formation could remain in current galactic halos.

  11. The Primordial Origin Model of Magnetic Fields in Spiral Galaxies

    NASA Astrophysics Data System (ADS)

    Sofue, Yoshiaki; Machida, Mami; Kudoh, Takahiro

    2010-10-01

    We propose a primordial-origin model for composite configurations of global magnetic fields in spiral galaxies. We show that a uniform tilted magnetic field wound up into a rotating disk galaxy can evolve into composite magnetic configurations comprising bisymmetric spiral (S = BSS), axisymmetric spiral (A = ASS), plane-reversed spiral (PR), and/or ring (R) fields in the disk, and vertical (V) fields in the center. By MHD simulations we show that these composite galactic fields are indeed created from a weak primordial uniform field, and that different configurations can co-exist in the same galaxy. We show that spiral fields trigger the growth of two-armed gaseous arms. The centrally accumulated vertical fields are twisted and produce a jet toward the halo. We found that the more vertical was the initial uniform field, the stronger was the formed magnetic field in the galactic disk.

  12. Galactic energetic particles and their radiative yields in clusters

    NASA Astrophysics Data System (ADS)

    Rephaeli, Yoel; Sadeh, Sharon

    2016-05-01

    As energetic particles diffuse out of radio and star-forming galaxies (SFGs), their intracluster density builds up to a level that could account for a substantial part or all the emission from a radio halo. We calculate the particle time-dependent, spectro-spatial distributions from a solution of a diffusion equation with radio galaxies as sources of electrons and SFGs as sources of both electrons and protons. Whereas strong radio galaxies are typically found in the cluster (e.g., Coma) core, the fraction of SFGs increases with distance from the cluster center. Scaling particle escape rates from their sources to the reasonably well determined Galactic rates, and for realistic gas density and magnetic field spatial profiles, we find that predicted spectra and spatial profiles of radio emission from primary and secondary electrons are roughly consistent with those deduced from current measurements of the Coma halo (after subtraction of emission from the relic Coma A). Nonthermal x-ray emission is predicted to be mostly by Compton scattering of electrons from radio galaxies off the CMB, whereas γ -ray emission is primarily from the decay of neutral pions produced in interactions of protons from SFGs with protons in intracluster gas.

  13. DO HOT HALOS AROUND GALAXIES CONTAIN THE MISSING BARYONS?

    SciTech Connect

    Anderson, Michael E.; Bregman, Joel N. E-mail: jbregman@umich.ed

    2010-05-01

    Galaxies are missing most of their baryons, and many models predict these baryons lie in a hot halo around galaxies. We establish observationally motivated constraints on the mass and radii of these halos using a variety of independent arguments. First, the observed dispersion measure of pulsars in the Large Magellanic Cloud allows us to constrain the hot halo around the Milky Way: if it obeys the standard Navarro, Frenk, and White (NFW) profile, it must contain less than 4%-5% of the missing baryons from the Galaxy. This is similar to other upper limits on the Galactic hot halo, such as the soft X-ray background and the pressure around high-velocity clouds. Second, we note that the X-ray surface brightness of hot halos with NFW profiles around large isolated galaxies is high enough that such emission should be observed, unless their halos contain less than 10%-25% of their missing baryons. Third, we place constraints on the column density of hot halos using nondetections of O VII absorption along active galactic nucleus (AGN) sightlines: in general they must contain less than 70% of the missing baryons or extend to no more than 40 kpc. Flattening the density profile of galactic hot halos weakens the surface brightness constraint so that a typical L{sub *} galaxy may hold half its missing baryons in its halo, but the O VII constraint remains unchanged, and around the Milky Way a flattened profile may only hold 6%-13% of the missing baryons from the Galaxy ((2-4) x 10{sup 10} M{sub sun}). We also show that AGN and supernovae at low to moderate redshift-the theoretical sources of winds responsible for driving out the missing baryons-do not produce the expected correlations with the baryonic Tully-Fisher relationship and, therefore, are insufficient to explain the missing baryons from galaxies. We conclude that most of missing baryons from galaxies do not lie in hot halos around the galaxies, and that the missing baryons never fell into the potential wells of

  14. The starformation driven interstellar disk-halo connection

    NASA Astrophysics Data System (ADS)

    Dettmar, Ralf-Jürgen

    2005-08-01

    The evidence for starformation in the disks of spiral galaxies driving the disk-halo interaction is briefly reviewed. It is argued that diffuse ionized gas (DIG) in the halos of edge-on disk galaxies traces the presence of extraplanar gas well since it correlates with the star formation rate in the underlying disk as well as with other gaseous phases and components of the ISM such as X-ray hot gas, cosmic rays, and magnetic fields. The dependence on the starformation rate is demonstrated using a survey of H+ halos with more than 70 objects. This survey allows us to establish a minimum energy release per unit area that is required to start the disk-halo mass exchange. Observations of extraplanar HII regions let us conclude that also molecular hydrogen must be present. In addition, well ordered magnetic field in the gaseous halos can be deduced from the polarization of synchrotron radiocontinuum maps.

  15. Study of galactic rotation curves in wormhole spacetime

    NASA Astrophysics Data System (ADS)

    Rahaman, Farook; Sen, Banashree; Chakraborty, Koushik; Shit, G. C.

    2016-03-01

    The spacetime of the galactic halo region is described by a wormhole like line element. We assume violation of Null Energy Condition (NEC) in the galactic halo. The Einstein Field equations are solved for two different conditions of pressure and density to obtain physical parameters like tangential velocity of test particles and parameters related to the wormhole geometry. The theoretical rotation curve of the test particles is plotted and compared the same with an observed rotation curve. We obtain a satisfactory fit between the observed curve and the curve obtained from the present theory for the radial distances in the range 9 Kpc to 100 Kpc.

  16. The end of the MACHO era, revisited: New limits on MACHO masses from halo wide binaries

    SciTech Connect

    Monroy-Rodríguez, Miguel A.; Allen, Christine

    2014-08-01

    In order to determine an upper bound for the mass of the massive compact halo objects (MACHOs), we use the halo binaries contained in a recent catalog by Allen and Monroy-Rodríguez. To dynamically model their interactions with massive perturbers, a Monte Carlo simulation is conducted, using an impulsive approximation method and assuming a galactic halo constituted by massive particles of a characteristic mass. The results of such simulations are compared with several subsamples of our improved catalog of candidate halo wide binaries. In accordance with Quinn et al., we also find our results to be very sensitive to the widest binaries. However, our larger sample, together with the fact that we can obtain galactic orbits for 150 of our systems, allows a more reliable estimate of the maximum MACHO mass than that obtained previously. If we employ the entire sample of 211 candidate halo stars we, obtain an upper limit of 112 M{sub ☉}. However, using the 150 binaries in our catalog with computed galactic orbits, we are able to refine our fitting criteria. Thus, for the 100 most halo-like binaries we obtain a maximum MACHO mass of 21-68 M{sub ☉}. Furthermore, we can estimate the dynamical effects of the galactic disk using binary samples that spend progressively shorter times within the disk. By extrapolating the limits obtained for our most reliable—albeit smallest—sample, we find that as the time spent within the disk tends to zero, the upper bound of the MACHO mass tends to less than 5 M{sub ☉}. The non-uniform density of the halo has also been taken into account, but the limit obtained, less than 5 M{sub ☉}, does not differ much from the previous one. Together with microlensing studies that provide lower limits on the MACHO mass, our results essentially exclude the existence of such objects in the galactic halo.

  17. Galactic Conformity Beyond the Virial Radius in Observations and Simulations

    NASA Astrophysics Data System (ADS)

    Bray, Aaron D.; Primus Team, Illustris Team

    2016-01-01

    We report on the presence of galactic conformity at distances out to 10 Mpc in the Illustris suite of simulations, as well as on a search for conformity in the PRIMUS redshift survey. Galactic conformity, where red galaxies preferentially surround other red galaxies at fixed mass, is used as a probe of galaxy assembly bias — the picture in which environmental factors and assembly history, other than dark matter halo mass, are necessary to understand the halo occupation statistics of galaxies. Using the Illustris suite of simulations, we demonstrate how a galactic conformity signal at z = 0 can arise from a combination of the underlying dark matter clustering as a function of halo formation age and a galaxy color-halo age relation. With observations from the PRIMUS redshift survey, we probe the deprojected 3D galactic conformity signal as a function of redshift over the range 0.2 < z < 1. Together, these results motivate further observations to discern the effect size of to discern the effect size of the galactic conformity signal, its variation in redshift, and what baryonic processes, such as feedback or accretion, play a dominant role in its creation.

  18. THE STRUCTURE OF THE MILKY WAY'S HOT GAS HALO

    SciTech Connect

    Miller, Matthew J.; Bregman, Joel N. E-mail: jbregman@umich.edu

    2013-06-20

    The Milky Way's million degree gaseous halo contains a considerable amount of mass that, depending on its structural properties, can be a significant mass component. In order to analyze the structure of the Galactic halo, we use XMM-Newton Reflection Grating Spectrometer archival data and measure O VII K{alpha} absorption-line strengths toward 26 active galactic nuclei, LMC X-3, and two Galactic sources (4U 1820-30 and X1735-444). We assume a {beta}-model as the underlying gas density profile and find best-fit parameters of n{sub circle} = 0.46{sup +0.74}{sub -0.35} cm{sup -3}, r{sub c} = 0.35{sup +0.29}{sub -0.27} kpc, and {beta} = 0.71{sup +0.13}{sub -0.14}. These parameters result in halo masses ranging between M(18 kpc) = 7.5{sub -4.6}{sup +}2{sup 2.0} x 10{sup 8} M{sub Sun} and M (200 kpc) = 3.8{sub -0.5}{sup +6.0} x 10{sup 10} M{sub Sun} assuming a gas metallicity of Z = 0.3 Z{sub Sun }, which are consistent with current theoretical and observational work. The maximum baryon fraction from our halo model of f{sub b} = 0.07{sup +0.03}{sub -0.01} is significantly smaller than the universal value of f{sub b} = 0.171, implying the mass contained in the Galactic halo accounts for 10%-50% of the missing baryons in the Milky Way. We also discuss our model in the context of several Milky Way observables, including ram pressure stripping in dwarf spheroidal galaxies, the observed X-ray emission measure in the 0.5-2 keV band, the Milky Way's star formation rate, spatial and thermal properties of cooler gas ({approx}10{sup 5} K), and the observed Fermi bubbles toward the Galactic center. Although the metallicity of the halo gas is a large uncertainty in our analysis, we place a lower limit on the halo gas between the Sun and the Large Magellanic Cloud (LMC). We find that Z {approx}> 0.2 Z{sub Sun} based on the pulsar dispersion measure toward the LMC.

  19. Galactic Winds

    NASA Astrophysics Data System (ADS)

    Veilleux, Sylvain

    Galactic winds have become arguably one of the hottest topics in extragalactic astronomy. This enthusiasm for galactic winds is due in part to the detection of winds in many, if not most, high-redshift galaxies. Galactic winds have also been invoked by theorists to (1) suppress the number of visible dwarf galaxies and avoid the "cooling catastrophe" at high redshift that results in the overproduction of massive luminous galaxies, (2) remove material with low specific angular momentum early on and help enlarge gas disks in CDM + baryons simulations, (3) reduce the dark mass concentrations in galaxies, (4) explain the mass-metallicity relation of galaxies from selective loss of metal-enriched gas from smaller galaxies, (5) enrich and "preheat" the ICM, (6) enrich the IGM without disturbing the Lyαforest significantly, and (7) inhibit cooling flows in galaxy clusters with active cD galaxies. The present paper highlights a few key aspects of galactic winds taken from a recent ARAA review by Veilleux, Cecil, &Bland-Hawthorn (2005; herafter VCBH). Readers interested in a more detailed discussion of this topic are encouraged to refer to the original ARAA article.

  20. CHANG-ES. VII. Magnetic Outflows from the Virgo Cluster Galaxy NGC 4388

    NASA Astrophysics Data System (ADS)

    Damas-Segovia, A.; Beck, R.; Vollmer, B.; Wiegert, T.; Krause, M.; Irwin, J.; Weżgowiec, M.; Li, J.; Dettmar, R.-J.; English, J.; Wang, Q. D.

    2016-06-01

    We investigate the effects of ram pressure on the ordered magnetic field of a galaxy hosting a radio halo and strong nuclear outflows. New radio images in total and polarized intensity of the edge-on Virgo galaxy NGC 4388 were obtained within the CHANG-ES EVLA project. The unprecedented noise level reached allows us to detect striking new features of the ordered magnetic field. The nuclear outflow extends far into the halo to about 5 kpc from the center and is spatially correlated with the {{H}}α and X-ray emission. For the first time, the southern outflow is detected. Above and below both spiral arms we find extended blobs of polarized emission with an ordered field oriented perpendicular to the disk. The synchrotron lifetime of the cosmic-ray electrons (CREs) in these regions yields a mean outflow velocity of 270+/- 70 {km} {{{s}}}-1, in agreement with a galactic wind scenario. The observed symmetry of the polarized halo features in NGC 4388 excludes a compression of the halo gas by the ram pressure of the intracluster medium (ICM). The assumption of equilibrium between the halo pressure and the ICM ram pressure yields an estimate of the ICM density that is consistent with both the ICM density derived from X-ray observations and the recent Planck Sunyaev–Zel’dovich measurements. The detection of a faint radio halo around cluster galaxies could thus be used for an estimate of ICM ram pressure.

  1. The Halo of the Milky Way

    SciTech Connect

    Newberg, Heidi Jo; Yanny, Brian; /Rensselaer Poly. /Fermilab

    2005-02-01

    The authors show that the star counts in the spheroid of the Milky Way are not symmetric about the l = 0{sup o}, l = 180{sup o} plane. The minimum counts are found towards l = 155{sup o}. The Galactic longitude of maximum star counts depends on the magnitude and color selection of the halo stars. They interpret this as evidence that the spheroid population is triaxial with a major axis oriented 65{sup o} from the line of sight from the Sun to the Galactic center, and approximately perpendicular to the Galactic bar. Large local star concentrations from tidal debris and possible tidal debris are also observed. A full understanding of the Galactic spheroid population awaits position information and three dimensional space velocities for a representative set of stars in every substructure. Tangential velocities for many stars will be provided by current and planned astrometry missions, but no planned mission will measure stars faint enough to unravel the more distant parts of the spheroid, which contain the majority of the spatial substructure. This paper uses data from the Sloan Digital Sky Survey (SDSS) public data release DR3.

  2. Haloes light and dark: dynamical models of the stellar halo and constraints on the mass of the Galaxy

    NASA Astrophysics Data System (ADS)

    Williams, A. A.; Evans, N. W.

    2015-11-01

    We develop a flexible set of action-based distribution functions (DFs) for stellar haloes. The DFs have five free parameters, controlling the inner and outer density slope, break radius, flattening, and anisotropy, respectively. The DFs generate flattened stellar haloes with a rapidly varying logarithmic slope in density, as well as a spherically aligned velocity ellipsoid with a long axis that points towards the Galactic Centre - all attributes possessed by the stellar halo of the Milky Way. We use our action-based DF to model the blue horizontal branch stars extracted from the Sloan Digital Sky Survey as stellar halo tracers in a spherical Galactic potential. As the selection function is hard to model, we fix the density law from earlier studies and solve for the anisotropy and gravitational potential parameters. Our best-fitting model has a velocity anisotropy that becomes more radially anisotropic on moving outwards. It changes from β ≈ 0.4 at Galactocentric radius of 15 kpc to ≈0.7 at 60 kpc. This is a gentler increase than is typically found in simulations of stellar haloes built from the multiple accretion of smaller systems. We find the potential corresponds to an almost flat rotation curve with amplitude of ≈200 km s-1 at these distances. This implies an enclosed mass of ≈4.5 × 1011 M⊙ within a spherical shell of radius 50 kpc.

  3. Subaru Hyper Suprime Cam Survey of the Andromeda Halo

    NASA Astrophysics Data System (ADS)

    Chiba, Masashi; Tanaka, Mikito; Komiyama, Yutaka

    2016-08-01

    We present a progress report on our deep and wide-field imaging survey of the Andromeda halo with Hyper Suprime Cam (HSC) mounted on Subaru. HSC is the upgraded prime focus camera after Suprime-Cam, having a field of view of 1.77 square degree (1.5 degree in diameter), namely about 10 times larger than that of Suprime-Cam. This camera will thus offer us great opportunities to explore unique and legacy surveys for the Andromeda halo, as well as for other Galactic Archaeology science cases.

  4. Generation and maintenance of bisymmetric spiral magnetic fields in disk galaxies in differential rotation

    NASA Astrophysics Data System (ADS)

    Sawa, Takeyasu; Fujimoto, M.

    1993-05-01

    The approximate dynamo equation, which yields asymptotic solutions for the large scale bisymmetric spiral (BSS) magnetic fields rotating rigidly over a large area of the galactic disk, is derived. The vertical thickness and the dynamo strength of the gaseous disk which are necessary to generate and sustain the BSS magnetic fields is determined. The globally BSS magnetic fields which propagate over the disk as a wave without being twisted more tightly are reproduced. A poloidal field configuration is theoretically predicted in the halo around the disk, and is observed in the edge-on galaxy NGC4631. Mathematical methods for the galactic dynamo are shown to be equivalent. Those methods give different growth rates between the BSS and the axisymmetric spiral (ASS) magnetic fields in the disk. Magnetohydrodynamical excitation is discussed between the BSS magnetic fields and the two armed spiral density waves.

  5. Galactic and extragalactic contributions to the astrophysical muon neutrino signal

    NASA Astrophysics Data System (ADS)

    Neronov, Andrii; Semikoz, Dmitry

    2016-06-01

    In a previous study, we have shown that spectral and anisotropy properties of IceCube astrophysical neutrino signals reveal evidence for a sizeable Galactic contribution to the neutrino flux in the Southern Hemisphere. We check if the Galactic contribution is detectable in the astrophysical muon neutrino flux observed from a low positive declinations region of the Northern sky. Estimating the Galactic neutrino flux in this part of the sky from γ -ray and Southern sky neutrino data, we find that the Northern sky astrophysical muon neutrino signal shows an excess over the Galactic flux. This points to the presence of an additional hard spectrum (extragalactic or large-scale Galactic halo) component of the astrophysical neutrino flux. We show that the Galactic flux component should still be detectable in the muon neutrino data in a decade-long IceCube exposure.

  6. Magnetic fields in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Krause, Marita

    2015-03-01

    The magnetic field structure in edge-on galaxies observed so far shows a plane-parallel magnetic field component in the disk of the galaxy and an X-shaped field in its halo. The plane-parallel field is thought to be the projected axisymmetric (ASS) disk field as observed in face-on galaxies. Some galaxies addionionally exhibit strong vertical magnetic fields in the halo right above and below the central region of the disk. The mean-field dynamo theory in the disk cannot explain these observed fields without the action of a wind, which also probably plays an important role to keep the vertical scale heights constant in galaxies of different Hubble types and star formation activities, as has been observed in the radio continuum: At λ6 cm the vertical scale heights of the thin disk and the thick disk/halo in a sample of five edge-on galaxies are similar with a mean value of 300 +/- 50 pc for the thin disk and 1.8 +/- 0.2 kpc for the thick disk (a table and references are given in Krause 2011) with our sample including the brightest halo observed so far, NGC 253, with strong star formation, as well as one of the weakest halos, NGC 4565, with weak star formation. If synchrotron emission is the dominant loss process of the relativistic electrons the outer shape of the radio emission should be dumbbell-like as has been observed in several edge-on galaxies like e.g. NGC 253 (Heesen et al. 2009) and NGC 4565. As the synchrotron lifetime t syn at a single frequency is proportional to the total magnetic field strength B t -1.5, a cosmic ray bulk speed (velocity of a galactic wind) can be defined as v CR = h CR /t syn = 2 h z /t syn , where h CR and h z are the scale heights of the cosmic rays and the observed radio emission at this freqnency. Similar observed radio scale heights imply a self regulation mechanism between the galactic wind velocity, the total magnetic field strength and the star formation rate SFR in the disk: v CR ~ B t 1.5 ~ SFR ~ 0.5 (Niklas & Beck 1997).

  7. The Galactic center wind

    NASA Technical Reports Server (NTRS)

    Chevalier, Roger A.

    1992-01-01

    The combined effect of winds from a cluster of stars in the central 0.8 pc of the Galaxy is modeled as uniform power and mass input over the central region. The flow becomes supersonic outside the central region, and the expected decrease in pressure is in approximate accord with observations. The pressure variations on a larger scale suggest that the Galactic center wind passes through a shock front at a radius of a few pc, leading to a shocked wind bubble on a scale of 100 pc. The tangential magnetic field can come to dominate the pressure in the shocked wind flow even if the energy density of the magnetic field in the initial wind is only 0.1 percent of the wind kinetic energy density. The magnetic region produced in this way may be related to some of the apparently magnetized structures observed in the central region of the Galaxy.

  8. 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.

  9. Anisotropy and corotation of galactic cosmic rays.

    PubMed

    Amenomori, M; Ayabe, S; Bi, X J; Chen, D; Cui, S W; Danzengluobu; Ding, L K; Ding, X H; Feng, C F; Feng, Zhaoyang; Feng, Z Y; Gao, X Y; Geng, Q X; Guo, H W; He, H H; He, M; Hibino, K; Hotta, N; Hu, Haibing; Hu, H B; Huang, J; Huang, Q; Jia, H Y; Kajino, F; Kasahara, K; Katayose, Y; Kato, C; Kawata, K; Labaciren; Le, G M; Li, A F; Li, J Y; Lou, Y-Q; Lu, H; Lu, S L; Meng, X R; Mizutani, K; Mu, J; Munakata, K; Nagai, A; Nanjo, H; Nishizawa, M; Ohnishi, M; Ohta, I; Onuma, H; Ouchi, T; Ozawa, S; Ren, J R; Saito, T; Saito, T Y; Sakata, M; Sako, T K; Sasaki, T; Shibata, M; Shiomi, A; Shirai, T; Sugimoto, H; Takita, M; Tan, Y H; Tateyama, N; Torii, S; Tsuchiya, H; Udo, S; Wang, B; Wang, H; Wang, X; Wang, Y G; Wu, H R; Xue, L; Yamamoto, Y; Yan, C T; Yang, X C; Yasue, S; Ye, Z H; Yu, G C; Yuan, A F; Yuda, T; Zhang, H M; Zhang, J L; Zhang, N J; Zhang, X Y; Zhang, Y; Zhang, Yi; Zhaxisangzhu; Zhou, X X

    2006-10-20

    The intensity of Galactic cosmic rays is nearly isotropic because of the influence of magnetic fields in the Milky Way. Here, we present two-dimensional high-precision anisotropy measurement for energies from a few to several hundred teraelectronvolts (TeV), using the large data sample of the Tibet Air Shower Arrays. Besides revealing finer details of the known anisotropies, a new component of Galactic cosmic ray anisotropy in sidereal time is uncovered around the Cygnus region direction. For cosmic-ray energies up to a few hundred TeV, all components of anisotropies fade away, showing a corotation of Galactic cosmic rays with the local Galactic magnetic environment. These results have broad implications for a comprehensive understanding of cosmic rays, supernovae, magnetic fields, and heliospheric and Galactic dynamic environments. PMID:17053141

  10. NM counts in relation to CMEs and Magnetic fields

    NASA Astrophysics Data System (ADS)

    Mishra, Rajesh Kumar; Agarwal, Rekha

    2016-07-01

    The global network of neutron monitors (NMs) have provided data to the heliophysics community for over sixty years to study the time variations of the galactic cosmic ray (GCR) intensity. Simpson recommended a standard NM for worldwide use during the International Geophysical Year (IGY, 1957-58). NM data have been used extensively for the time variation studies ranging from minutes to decades. Coronal Mass Ejections are vast structures of plasma and magnetic fields that are expelled from the sun into the heliosphere, which is detected by remote sensing and in-situ spacecraft observations. The present study is related with behaviour of four types of CMEs namely Asymmetric 'Full' Halo CMEs, Partial Halo CMEs, Asymmetric and Complex 'Full' Halo CMEs and 'Full' Halo CMEs on cosmic ray neutron monitor intensity. The data of two different ground based neutron monitors having different cutoff rigidity threshold and CME events observed with instruments onboard and Wind spacecraft have been used in the present work. The superposed epoch (Chree) analysis has been applied to the arrival times of these CMEs. The occurrence frequency of three different types of CMEs used in the present analysis shows complex behavior. Significant fluctuations in cosmic ray intensity is observed few days after the onset of asymmetric full halo and few days after the onset of full halo CMEs. The fluctuations in cosmic ray intensity are more prior to the onset of both types of the CMEs. However, during Partial Halo CMEs the cosmic ray intensity peaks, 8- 9 days prior to the onset of CMEs and depressed 3 days prior to the onset of CMEs, whereas in case of asymmetric and complex full CMEs, the intensity depressed 2 days prior to the onset of CMEs and enhanced 2 days after the onset of CMEs. The deviations in cosmic ray intensity are more pronounced in case for asymmetric and complex full halo CMEs compared to other CMEs. The cosmic ray intensity shows nearly good anti-correlation with interplanetary

  11. The Making of the Milky Way Halo

    NASA Astrophysics Data System (ADS)

    1999-02-01

    The VLT Watches a Dissolving Stellar Cluster A group of ESO astronomers [1] has used new observations, obtained with the first 8.2-m VLT Unit Telescope (UT1) during the "Science Verification" programme, to show that a globular cluster in the Milky Way galaxy is "evaporating" and has already lost its faintest stars. This is the first observational result of its kind and has important implications for future studies. It may be explained by a gradual loss of such stars from the cluster into the Milky Way halo, a roughly spherical region around the much flatter, spiral structure in which most of the stars and nebulae are located. The new result lends strong support to current theories about the evolution of the structure of this halo and also provides insights into the formation of the galaxy in which we live. Globular clusters and the halo of the Milky Way The stars that we observe in the halo of the Milky Way represent only a small fraction of the total mass in this region. Investigations of the motions of stars in our Galaxy have shown that this halo must harbour much more matter, which is hidden from our view. The same phenomenon has been observed in other galaxies, and astronomers refer to it as "dark matter". It is at this moment not known what this matter consists of. The brightest objects in the halo are the globular clusters . They are large groupings of stars that were formed together in the very early evolutionary phases of the Milky Way, some 12,000 - 14,000 million years ago. This happened soon after the moment when the first structures emerged in the large cloud of primordial hydrogen in which our Galaxy was born. A popular scenario describes the first build-up of galactic structure, i.e. of stars and gas, as when normal matter began to collect inside the dark-matter halo, due to its strong gravitational attraction. The globular clusters were most probably the first denizens of this protogalaxy . It is believed that the Milky Way Galaxy subsequently

  12. Characterizing stellar halo populations - I. An extended distribution function for halo K giants

    NASA Astrophysics Data System (ADS)

    Das, Payel; Binney, James

    2016-08-01

    We fit an extended distribution function (EDF) to K giants in the Sloan Extension for Galactic Understanding and Exploration survey. These stars are detected to radii ˜80 kpc and span a wide range in [Fe/H]. Our EDF, which depends on [Fe/H] in addition to actions, encodes the entanglement of metallicity with dynamics within the Galaxy's stellar halo. Our maximum-likelihood fit of the EDF to the data allows us to model the survey's selection function. The density profile of the K giants steepens with radius from a slope ˜-2 to ˜-4 at large radii. The halo's axis ratio increases with radius from 0.7 to almost unity. The metal-rich stars are more tightly confined in action space than the metal-poor stars and form a more flattened structure. A weak metallicity gradient ˜-0.001 dex kpc-1, a small gradient in the dispersion in [Fe/H] of ˜0.001 dex kpc-1, and a higher degree of radial anisotropy in metal-richer stars result. Lognormal components with peaks at ˜-1.5 and ˜-2.3 are required to capture the overall metallicity distribution, suggestive of the existence of two populations of K giants. The spherical anisotropy parameter varies between 0.3 in the inner halo to isotropic in the outer halo. If the Sagittarius stream is included, a very similar model is found but with a stronger degree of radial anisotropy throughout.

  13. Characterising stellar halo populations I: An extended distribution function for halo K giants

    NASA Astrophysics Data System (ADS)

    Das, Payel; Binney, James

    2016-05-01

    We fit an Extended Distribution Function (EDF) to K giants in the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. These stars are detected to radii ˜80 kpc and span a wide range in [Fe/H]. Our EDF, which depends on [Fe/H] in addition to actions, encodes the entanglement of metallicity with dynamics within the Galaxy's stellar halo. Our maximum-likelihood fit of the EDF to the data allows us to model the survey's selection function. The density profile of the K giants steepens with radius from a slope ˜-2 to ˜-4 at large radii. The halo's axis ratio increases with radius from 0.7 to almost unity. The metal-rich stars are more tightly confined in action space than the metal-poor stars and form a more flattened structure. A weak metallicity gradient ˜-0.001 dex/kpc, a small gradient in the dispersion in [Fe/H] of ˜0.001 dex/kpc, and a higher degree of radial anistropy in metal-richer stars result. Lognormal components with peaks at ˜-1.5 and ˜-2.3 are required to capture the overall metallicity distribution, suggestive of the existence of two populations of K giants. The spherical anisotropy parameter varies between 0.3 in the inner halo to isotropic in the outer halo. If the Sagittarius stream is included, a very similar model is found but with a stronger degree of radial anisotropy throughout.

  14. QUANTIFYING KINEMATIC SUBSTRUCTURE IN THE MILKY WAY'S STELLAR HALO

    SciTech Connect

    Xue Xiangxiang; Zhao Gang; Luo Ali; Rix, Hans-Walter; Bell, Eric F.; Koposov, Sergey E.; Kang, Xi; Liu, Chao; Yanny, Brian; Beers, Timothy C.; Lee, Young Sun; Bullock, James S.; Johnston, Kathryn V.; Morrison, Heather; Rockosi, Constance

    2011-09-01

    We present and analyze the positions, distances, and radial velocities for over 4000 blue horizontal-branch (BHB) stars in the Milky Way's halo, drawn from SDSS DR8. We search for position-velocity substructure in these data, a signature of the hierarchical assembly of the stellar halo. Using a cumulative 'close pair distribution' as a statistic in the four-dimensional space of sky position, distance, and velocity, we quantify the presence of position-velocity substructure at high statistical significance among the BHB stars: pairs of BHB stars that are close in position on the sky tend to have more similar distances and radial velocities compared to a random sampling of these overall distributions. We make analogous mock observations of 11 numerical halo formation simulations, in which the stellar halo is entirely composed of disrupted satellite debris, and find a level of substructure comparable to that seen in the actually observed BHB star sample. This result quantitatively confirms the hierarchical build-up of the stellar halo through a signature in phase (position-velocity) space. In detail, the structure present in the BHB stars is somewhat less prominent than that seen in most simulated halos, quite possibly because BHB stars represent an older sub-population. BHB stars located beyond 20 kpc from the Galactic center exhibit stronger substructure than at r{sub gc} < 20 kpc.

  15. Stellar Haloes with the Illustris Simulation: Mock Observations and Assembly

    NASA Astrophysics Data System (ADS)

    Pillepich, Annalisa; Torrey, Paul; Nelson, Dylan; Snyder, Greg; Rodriguez-Gomez, Vicente; Genel, Shy; Vogelsberger, Mark; Hernquist, Lars

    2015-08-01

    Illustris is a state-of-the-art simulation which combines the statistical power of a ˜106 Mpc-side cosmological volume with gasdynamics, prescriptions for star formation, feedback, and kpc resolution. It allows us to analyze about ˜5,000 well-resolved galaxies spanning a variety of morphologies, environments, and halo masses (3×10^11 < Mvir < 10^14 Msun). Illustris therefore provides the most realistic and richest sample of simulated galactic stellar haloes available up to date. Based on the properties of the stellar particles in each simulated galaxy/halo, we have produced synthetic images in different luminosity bands and extracted information about the mass distribution, smoothness, and phase-space structures up to large galactocentric distances at different limits of surface brightness. We can therefore gain insight and provide theoretically-motivated expectations for the build-up and properties of the stellar haloes, and their relation to the underlying DM haloes, their central galaxies, and their halo assembly histories.

  16. Two New Ultra-Faint Star Clusters in the Milky Way Halo

    NASA Astrophysics Data System (ADS)

    Kim, Dongwon

    2016-08-01

    Kim 1 & 2 are two new star clusters discovered in the Stromlo Missing Satellite Survey. Kim 1, located at a heliocentric distance of 19.8 +/- 0.9 kpc, features an extremely low total luminosity (M V = 0.3 +/- 0.5 mag) and low star concentration. Together with the large ellipticity (ɛ = 0.42 +/- 0.10) and irregular isophotes, these properties suggest that Kim 1 is an intermediate mass star cluster being stripped by the Galactic tidal field. Kim 2 is a rare ultra-faint outer halo globular cluster located at a heliocentric distance of 104.7 +/- 4.1 kpc. The cluster exhibits evidence of significant mass loss such as extra-tidal stars and mass-segregation. Kim 2 is likely to follow an orbit confined to the peripheral region of the Galactic halo, and/or to have formed in a dwarf galaxy that was later accreted into the Galactic halo.

  17. Giant magnetized outflows from the centre of the Milky Way.

    PubMed

    Carretti, Ettore; Crocker, Roland M; Staveley-Smith, Lister; Haverkorn, Marijke; Purcell, Cormac; Gaensler, B M; Bernardi, Gianni; Kesteven, Michael J; Poppi, Sergio

    2013-01-01

    The nucleus of the Milky Way is known to harbour regions of intense star formation activity as well as a supermassive black hole. Recent observations have revealed regions of γ-ray emission reaching far above and below the Galactic Centre (relative to the Galactic plane), the so-called 'Fermi bubbles'. It is uncertain whether these were generated by nuclear star formation or by quasar-like outbursts of the central black hole and no information on the structures' magnetic field has been reported. Here we report observations of two giant, linearly polarized radio lobes, containing three ridge-like substructures, emanating from the Galactic Centre. The lobes each extend about 60 degrees in the Galactic bulge, closely corresponding to the Fermi bubbles, and are permeated by strong magnetic fields of up to 15 microgauss. We conclude that the radio lobes originate in a biconical, star-formation-driven (rather than black-hole-driven) outflow from the Galaxy's central 200 parsecs that transports a huge amount of magnetic energy, about 10(55) ergs, into the Galactic halo. The ridges wind around this outflow and, we suggest, constitute a 'phonographic' record of nuclear star formation activity over at least ten million years. PMID:23282363

  18. PARAMETERS FOR QUANTIFYING BEAM HALO

    SciTech Connect

    C.K. ALLEN; T.P. WANGLER

    2001-06-01

    Two different parameters for the quantitative description of beam halo are introduced, both based on moments of the particle distribution. One parameter is a measure of spatial halo formation and has been defined previously by Wangler and Crandall [3], termed the profile parameter. The second parameter relies on kinematic invariants to quantify halo formation in phase space; we call it the halo parameter. The profile parameter can be computed from experimental beam profile data. The halo parameter provides a theoretically more complete description of halo in phase space, but is difficult to obtain experimentally.

  19. HALOE Science Investigation

    NASA Technical Reports Server (NTRS)

    Benner, D. Chris

    1998-01-01

    This cooperative agreement has investigated a number of spectroscopic problems of interest to the Halogen Occultation Experiment (HALOE). The types of studies performed are in two parts, namely, those that involve the testing and characterization of correlation spectrometers and those that provide basic molecular spectroscopic information. In addition, some solar studies were performed with the calibration data returned by HALOE from orbit. In order to accomplish this a software package was written as part of this cooperative agreement. The HALOE spectroscopic instrument package was used in various tests of the HALOE flight instrument. These included the spectral response test, the early stages of the gas response test and various spectral response tests of the detectors and optical elements of the instruments. Considerable effort was also expended upon the proper laboratory setup for many of the prelaunch tests of the HALOE flight instrument, including the spectral response test and the gas response test. These tests provided the calibration and the assurance that the calibration was performed correctly.

  20. Galactic Diffuse Polarized Emission

    NASA Astrophysics Data System (ADS)

    Carretti, Ettore

    2011-12-01

    Diffuse polarized emission by synchrotron is a key tool to investigate magnetic fields in the Milky Way, particularly the ordered component of the large scale structure. Key observables are the synchrotron emission itself and the RM is by Faraday rotation. In this paper the main properties of the radio polarized diffuse emission and its use to investigate magnetic fields will be reviewed along with our current understanding of the galactic magnetic field and the data sets available. We will then focus on the future perspective discussing RM-synthesis - the new powerful instrument devised to unlock the information encoded in such an emission - and the surveys currently in progress like S-PASS and GMIMS.

  1. A stellar feedback origin for neutral hydrogen in high-redshift quasar-mass haloes

    NASA Astrophysics Data System (ADS)

    Faucher-Giguère, Claude-André; Feldmann, Robert; Quataert, Eliot; Kereš, Dušan; Hopkins, Philip F.; Murray, Norman

    2016-09-01

    Observations reveal that quasar host haloes at z ˜ 2 have large covering fractions of cool dense gas (≳60 per cent for Lyman limit systems within a projected virial radius). Most simulations have so far failed to explain these large observed covering fractions. We analyse a new set of 15 simulated massive haloes with explicit stellar feedback from the FIRE project, covering the halo mass range Mh ≈ 2 × 1012 - 1013 M⊙ at z = 2. This extends our previous analysis of the circum-galactic medium of high-redshift galaxies to more massive haloes. Active galactic nuclei (AGN) feedback is not included in these simulations. We find Lyman limit system covering fractions consistent with those observed around quasars. The large H I covering fractions arise from star formation-driven galactic winds, including winds from low-mass satellite galaxies that interact with cosmological filaments. We show that it is necessary to resolve these satellite galaxies and their winds to reproduce the large Lyman limit system covering fractions observed in quasar-mass haloes. Our simulations predict that galaxies occupying dark matter haloes of mass similar to quasars but without a luminous AGN should have Lyman limit system covering fractions comparable to quasars.

  2. Testing the Caustic Ring Dark Matter Halo Model Against Observations in the Milky Way

    NASA Astrophysics Data System (ADS)

    Dumas, Julie; Newberg, Heidi Jo; Niedzielski, Bethany; Susser, Adam; Thompson, Jeffery M.; Weiss, Jake; Lewis, Kim M.

    2016-06-01

    One prediction of axion dark matter models is they can form Bose-Einstein condensates and rigid caustic rings as a halo collapses in the non-linear regime. In this thesis, we undertake the first study of a caustic ring model for the Milky Way halo (Duffy & Sikivie 2008), paying particular attention to observational consequences. We first present the formalism for calculating the gravitational acceleration of a caustic ring halo. The caustic ring dark matter theory reproduces a roughly logarithmic halo, with large perturbations near the rings. We show that this halo can reasonably match the known Galactic rotation curve. We are not able to confirm or rule out an association between the positions of the caustic rings and oscillations in the observed rotation curve, due to insufficient rotation curve data. We explore the effects of dark matter caustic rings on dwarf galaxy tidal disruption with N-body simulations. Simulations of the Sagittarius (Sgr) dwarf galaxy in a caustic ring halo potential, with disk and bulge parameters that are tuned to match the Galactic rotation curve, match observations of the Sgr trailing tidal tails as far as 90 kpc from the Galactic center. Like the Navarro-Frenk-White (NFW) halo, they are, however, unable to match the leading tidal tail. None of the caustic, NFW, or triaxial logarithmic halos are able to simultaneously match observations of the leading and trailing arms of the Sagittarius stream. We further show that simulations of dwarf galaxies that move through caustic rings are qualitatively similar to those moving in a logarithmic halo. This research was funded by NSF grant AST 10-09670, the NASA-NY Space Grant, and the American Fellowship from AAUW.

  3. 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.

  4. SAS-2 galactic gamma ray results, 1

    NASA Technical Reports Server (NTRS)

    Thompson, D. J.; Fichtel, C. E.; Hartman, R. C.; Kniffen, D. A.; Bignami, G. F.; Lamb, R. C.; Oegelman, H.; Oezel, M. E.; Tuemer, T.

    1976-01-01

    Continuing analysis of the data from the SAS-2 high energy gamma-ray experiment has produced an improved picture of the sky at photon energies above 35 MeV. On a large scale, the diffuse emission from the galactic plane is the dominant feature observed by SAS-2. This galactic plane emission is most intense between galactic longitude 310 and 45 deg, corresponding to a region within 7kpc of the galactic center. Within the high-intensity region, SAS-2 observes peaks around galactic longitudes 315 deg, 330 deg, 345 deg, 0 deg, and 35 deg. These peaks appear to be correlated with such galactic features and components as molecular hydrogen, atomic hydrogen, magnetic fields, cosmic ray concentrations, and photon fields.

  5. PIPER and Polarized Galactic Foregrounds

    NASA Technical Reports Server (NTRS)

    Chuss, David

    2009-01-01

    In addition to probing inflationary cosmology, PIPER will measure the polarized dust emission from the Galaxy. PIPER will be capable of full (I,0,U,V) measurement over four frequency bands ' These measurements will provide insight into the physics of dust grains and a probe of the Galactic magnetic field on large and intermediate scales.

  6. 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.

  7. CN ANOMALIES IN THE HALO SYSTEM AND THE ORIGIN OF GLOBULAR CLUSTERS IN THE MILKY WAY

    SciTech Connect

    Carollo, Daniela; Martell, Sarah L.; Beers, Timothy C.; Freeman, Ken C. E-mail: smartell@aao.gov.au E-mail: kcf@mso.anu.edu.au

    2013-06-01

    We explore the kinematics and orbital properties of a sample of red giants in the halo system of the Milky Way that are thought to have formed in globular clusters based on their anomalously strong UV/blue CN bands. The orbital parameters of the CN-strong halo stars are compared to those of the inner- and outer-halo populations as described by Carollo et al., and to the orbital parameters of globular clusters with well-studied Galactic orbits. The CN-strong field stars and the globular clusters both exhibit kinematics and orbital properties similar to the inner-halo population, indicating that stripped or destroyed globular clusters could be a significant source of inner-halo field stars, and suggesting that both the CN-strong stars and the majority of globular clusters are primarily associated with this population.

  8. The age of the galactic disk

    NASA Technical Reports Server (NTRS)

    Sandage, Allan

    1988-01-01

    The galactic disk is a dissipative structure and must, therefore be younger than the halo if galaxy formation generally proceeds by collapse. Just how much younger the oldest stars in the galactic disk are than the oldest halo stars remains an open question. A fast collapse (on a time scale no longer than the rotation period of the extended protogalaxy) permits an age gap of the order of approximately 10 to the 9th power years. A slow collapse, governed by the cooling rate of the partially pressure supported falling gas that formed into what is now the thick stellar disk, permits a longer age gap, claimed by some to be as long as 6 Gyr. Early methods of age dating the oldest components of the disk contain implicit assumptions concerning the details of the age-metallicity relation for stars in the solar neighborhood. The discovery that this relation for open clusters outside the solar circle is different that in the solar neighborhood (Geisler 1987), complicates the earlier arguments. The oldest stars in the galactic disk are at least as old as NGC 188. The new data by Janes on NGC 6791, shown first at this conference, suggest a disk age of at least 12.5 Gyr, as do data near the main sequence termination point of metal rich, high proper motion stars of low orbital eccentricity. Hence, a case can still be made that the oldest part of the galactic thick disk is similar in age to the halo globular clusters, if their ages are the same as 47 Tuc.

  9. Galactic orbital motions of star clusters: static versus semicosmological time-dependent Galactic potentials

    NASA Astrophysics Data System (ADS)

    Haghi, Hosein; Zonoozi, Akram Hasani; Taghavi, Saeed

    2015-07-01

    In order to understand the orbital history of Galactic halo objects, such as globular clusters, authors usually assume a static potential for our Galaxy with parameters that appear at the present day. According to the standard paradigm of galaxy formation, galaxies grow through a continuous accretion of fresh gas and a hierarchical merging with smaller galaxies from high redshift to the present day. This implies that the mass and size of disc, bulge, and halo change with time. We investigate the effect of assuming a live Galactic potential on the orbital history of halo objects and its consequences on their internal evolution. We numerically integrate backwards the equations of motion of different test objects located in different Galactocentric distances in both static and time-dependent Galactic potentials in order to see if it is possible to discriminate between them. We show that in a live potential, the birth of the objects, 13 Gyr ago, would have occurred at significantly larger Galactocentric distances, compared to the objects orbiting in a static potential. Based on the direct N-body calculations of star clusters carried out with collisional N-body code, NBODY6, we also discuss the consequences of the time-dependence of a Galactic potential on the early- and long-term evolution of star clusters in a simple way, by comparing the evolution of two star clusters embedded in galactic models, which represent the galaxy at present and 12 Gyr ago, respectively. We show that assuming a static potential over a Hubble time for our Galaxy as it is often done, leads to an enhancement of mass-loss, an overestimation of the dissolution rates of globular clusters, an underestimation of the final size of star clusters, and a shallower stellar mass function.

  10. Galactic Evolution

    NASA Astrophysics Data System (ADS)

    Brekke, Stewart

    2013-04-01

    All galaxies began as spiral galaxies. The early universe began with sets of two or more pre-galactic arms orbiting each other. As gravitational attraction between the arms took effect, the fore-sections of the arms tangentially collided forming spiral galaxies when they attached with the orbital motion of the arms being converted to the rotational motion of the newly formed spiral galaxies or (Iφ)arm1+ (Iφ)arm2+ ...+ (Iφ)armn= (Iφ)galaxy. If the centripetal force on the arms is more than the gravitational force on the arms, the spiral galaxy remains a spiral galaxy i.e. mv^2/r>=Gmarmmgalaxy/r^2. If the galaxy is slowly rotating, the spiral arms collapse into the body of the galaxy because the gravitational force is greater than the centripetal force on the arms and an elliptical galaxy is formed i.e. mv^2/r < Gmarmsmgalaxy/r^2.

  11. Subaru Hyper Suprime Cam Survey of the Andromeda Halo

    NASA Astrophysics Data System (ADS)

    Chiba, Masashi; Tanaka, Mikito; Komiyama, Yutaka

    2015-08-01

    We present a progress report on our deep and wide-field imaging survey of the Andromeda halo with Hyper Suprime Cam (HSC) mounted on Subaru. HSC is the upgraded prime focus camera after Suprime-Cam, having a field of view of 1.77 square degree (1.5 degree in diameter), namely about 10 times larger than that of Suprime-Cam. This camera will thus offer us great opportunities to explore unique and legacy surveys for the Andromeda halo, as well as for other Galactic Archaeology science cases. We are now carrying out an intensive survey program of the Andromeda halo reaching a depth of 27.4 and 26.4 mag in g and i bands, respectively, which allows us to map out numerous horizontal branch (HB) stars in large halo areas: a wealth of new, faint halo features as expected from LCDM models can be identified through these HB stars. whereas these were not detected by previous surveys based on the analysis of RGB stars. This HSC survey will also provide lower luminosity dwarf satellites and globular clusters through identification of member HBs than hitherto possible, thereby providing important insight into the true luminosity and spatial distributions of these objects. We will report on the progress we have made so far and show our further survey plan.

  12. Probing the Shape and History of the Milky Way Halo with Stellar Orbits

    NASA Astrophysics Data System (ADS)

    Valluri, Monica

    2010-05-01

    One of the key predictions of Lambda-CDM cosmological simulations is that the dark matter halos of galaxies such as the Milky Way are prolate or triaxial. However simulations show that both the shapes and density profiles of dark matter halos can be dramatically altered by the condensation of baryons. I will describe how Laskar's Frequency mapping technique can be used to analyze the phase-space structure of the Milky Way's halo with halo stellar orbits. From Frequency Maps of halo stars it is possible to set constrains, not just on the present shape and phase space distribution of the Milky Way halo, but also on its past shape history. The power of this technique is demonstrated by applying it to a series of controlled simulations in which dynamically realistic disks are grown in isolated triaxial dark matter halos. I will demonstrate that even when the growth of a baryonic disk causes the halo's shape to become oblate or close to spherical, it is possible to determine if it was originally prolate or triaxial as predicted by cosmological N-body simulations. Current and future Galactic surveys (e.g. RAVE, Segue, Gaia and LAMOST) are expected to obtain the full 6 dimensional phase space orbits of hundreds of thousands of halo stars. This technique will be a new and valuable tool that will complement on-going efforts to constrain the shape of the halo with tidal streams. Reliable indicators of the halo's shape can be obtained with as few as 5000-10000 halo stellar orbits.

  13. Dark matter massive fermions and Einasto profiles in galactic haloes

    NASA Astrophysics Data System (ADS)

    Siutsou, I.; Argüelles, C. R.; Ruffini, R.

    2015-07-01

    On the basis of a fermionic dark matter model we fit rotation curves of The HI Nearby Galaxy Survey (THINGS) sample and compare our 3-parametric model to other models widely used in the literature: 2-parametric Navarro-Frenk-White, pseudoisothermal sphere, Burkhert models, and 3-parametric Einasto model, suggested as the new "standard dark matter profile" model in the paper by Chemin et al., Astron. J. 142 (2011) 109. The results from the fitting procedure provides evidence for an underlying fermionic nature of the dark matter candidate, with rest mass above the keV regime.

  14. A mechanism for inducing climatic variations through ozone destruction: Screening of galactic cosmic rays by solar and terrestrial magnetic fields

    NASA Technical Reports Server (NTRS)

    Chamberlain, J. W.

    1976-01-01

    A perturbation analysis, allowing for temperature and opacity feedbacks, is developed to calculate depletions in the O3 abundance and reductions of stratospheric solar heating that result from increases in NOx concentration. A pair of perturbation coefficients give the reduction in O3 and temperature through the stratosphere for a specified NOx increase. This type of analysis illustrates the tendency for various levels to self-heal when a perturbation occurs. Physical arguments indicate that the expected sign of the climatic effect is correct, with colder surface temperatures produced by reduced magnetic shielding. In addition, four qualitative reasons are suggested for thinking that significant ozone reductions by cosmic ray influxes will lead to an increased terrestrial albedo from stratospheric condensation. In this view, long-term (approximately 10,000 years) climatic changes have resulted from secular geomagnetic variations while shorter (approximately 100 years) excursions are related to changes in solar activity.

  15. 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

  16. The MiMeS survey of magnetism in massive stars: CNO surface abundances of Galactic O stars

    NASA Astrophysics Data System (ADS)

    Martins, F.; Hervé, A.; Bouret, J.-C.; Marcolino, W.; Wade, G. A.; Neiner, C.; Alecian, E.; Grunhut, J.; Petit, V.

    2015-03-01

    Context. The evolution of massive stars is still partly unconstrained. Mass, metallicity, mass loss, and rotation are the main drivers of stellar evolution. Binarity and the magnetic field may also significantly affect the fate of massive stars. Aims: Our goal is to investigate the evolution of single O stars in the Galaxy. Methods: For that, we used a sample of 74 objects comprising all luminosity classes and spectral types from O4 to O9.7. We relied on optical spectroscopy obtained in the context of the MiMeS survey of massive stars. We performed spectral modelling with the code CMFGEN. We determined the surface properties of the sample stars, with special emphasis on abundances of carbon, nitrogen, and oxygen. Results: Most of our sample stars have initial masses in the range of 20 to 50 M⊙. We show that nitrogen is more enriched and carbon and oxygen are more depleted in supergiants than in dwarfs, with giants showing intermediate degrees of mixing. CNO abundances are observed in the range of values predicted by nucleosynthesis through the CNO cycle. More massive stars, within a given luminosity class, appear to be more chemically enriched than lower mass stars. We compare our results with predictions of three types of evolutionary models and show that for two sets of models, 80% of our sample can be explained by stellar evolution including rotation. The effect of magnetism on surface abundances is unconstrained. Conclusions: Our study indicates that in the 20-50 M⊙ mass range, the surface chemical abundances of most single O stars in the Galaxy are fairly well accounted for by stellar evolution of rotating stars. Based on observations obtained at 1) the Telescope Bernard Lyot (USR5026) operated by the Observatoire Midi-Pyrénées, Université de Toulouse (Paul Sabatier), Centre National de la Recherche Scientifique of France; 2) at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut

  17. Probable new halo stars toward L = 360 deg, B = +30 deg

    NASA Astrophysics Data System (ADS)

    Osborn, Wayne; MacConnell, D. J.

    1987-12-01

    Eighty-three probable halo giants have been identified in Stock's recently published objective-prism survey of an intermediate galactic latitude field. Approximate radial velocities derived from the objective-prism plates yield a velocity dispersion of 98±8 km sec-1 for these stars.

  18. Small-scale variations in the galactic magnetic field - The rotation measure structure function and birefringence in interstellar scintillations

    NASA Technical Reports Server (NTRS)

    Simonetti, J. H.; Cordes, J. M.; Spangler, S. R.

    1984-01-01

    The structure function of rotation measures of extragalactic sources and birefringence in interstellar scintillations are used to investigate variations in the interstellar magnetic field on length scales of about 0.01-100 pc and 10 to the 11th cm, respectively. Model structure functions are derived for the case of a power-law power spectrum of irregularities in the quantity (n(e)B), and an estimate for the structure function is computed for several regions of the sky using data on extragalactic sources. The results indicate an outer angular scale for rotation measure (RM) variations of not less than about 5 deg (a linear scale of about 9-90 pc at a distance of 0.1-1 kpc). There is also evidence for RM variations on angular scales as small as 1 arcmin, but it cannot be determined whether these are intrinsic to the source or caused by the interstellar medium. The effect of a random, Faraday-active medium on the diffraction of radio waves is derived, and an upper limit to the variations in n(e)B on a length scale of 10 to the 11th cm is obtained from available observations.

  19. MACHO (MAssive Compact Halo Objects) Data

    DOE Data Explorer

    The primary aim of the MACHO Project is to test the hypothesis that a significant fraction of the dark matter in the halo of the Milky Way is made up of objects like brown dwarfs or planets: these objects have come to be known as MACHOs, for MAssive Compact Halo Objects. The signature of these objects is the occasional amplification of the light from extragalactic stars by the gravitational lens effect. The amplification can be large, but events are extremely rare: it is necessary to monitor photometrically several million stars for a period of years in order to obtain a useful detection rate. For this purpose MACHO has a two channel system that employs eight CCDs, mounted on the 50 inch telescope at Mt. Stromlo. The high data rate (several GBytes per night) is accommodated by custom electronics and on-line data reduction. The Project has taken more than 27,000 images with this system since June 1992. Analysis of a subset of these data has yielded databases containing light curves in two colors for 8 million stars in the LMC and 10 million in the bulge of the Milky Way. A search for microlensing has turned up four candidates toward the Large Magellanic Cloud and 45 toward the Galactic Bulge. The web page for data provides links to MACHO Project data portals and various specialized interfaces for viewing or searching the data. (Specialized Interface)

  20. Direct Microlensing-Reverberation Observations of the Intrinsic Magnetic Structure of Active Galactic Nuclei in Different Spectral States: A Tale of Two Quasars

    NASA Astrophysics Data System (ADS)

    Schild, Rudolph E.; Leiter, Darryl J.; Robertson, Stanley L.

    2008-03-01

    We show how direct microlensing-reverberation analysis performed on two well-known quasars (Q2237, the Einstein Cross, and Q0957, the Twin) can be used to observe the inner structure of two quasars which are in significantly different spectral states. These observations allow us to measure the detailed internal structure of Q2237 in a radio-quiet high-soft state, and compare it to Q0957 in a radio-loud low-hard state. When taken together we find that the observed differences in the spectral states of these two quasars can be understood as being due to the location of the inner radii of their accretion disks relative to the co-rotation radii of the magnetospheric eternally collapsing objects (MECO) in the centers of these quasars. The radiating structures observed in these quasars are associated with standard accretion disks and outer outflow structures, where the latter are the major source of UV-optical continuum radiation. While the observed inner accretion disk structure of the radio-quiet quasar Q2237 is consistent with either a MECO or a black hole, the observed inner structure of the radio-loud quasar Q0957 can only be explained by the action of the intrinsic magnetic propeller of a MECO with its accretion disk. Hence a simple and unified answer to the long-standing question: "Why are some quasars radio loud?" is found if the central objects of quasars are MECO, with radio-loud and radio-quiet spectral states similar to the case of galactic black hole candidates.

  1. Anomalous resistivity and the evolution of magnetic field topology

    NASA Technical Reports Server (NTRS)

    Parker, E. N.

    1993-01-01

    This paper explores the topological restructuring of a force-free magnetic field caused by the hypothetical sudden onset of a localized region of strong anomalous resistivity. It is shown that the topological complexity increases, with the primitive planar force-free field with straight field lines developing field lines that wrap half a turn around each other, evidently providing a surface of tangential discontinuity in the wraparound region. It is suggested that the topological restructuring contributes to the complexity of the geomagnetic substorm, the aurora, and perhaps some of the flare activity on the sun, or other star, and the Galactic halo.

  2. Do Not Forget the Forest for the Trees: The Stellar-mass Halo-mass Relation in Different Environments

    NASA Astrophysics Data System (ADS)

    Tonnesen, Stephanie; Cen, Renyue

    2015-10-01

    The connection between dark matter halos and galactic baryons is often not well constrained nor well resolved in cosmological hydrodynamical simulations. Thus, halo occupation distribution models that assign galaxies to halos based on halo mass are frequently used to interpret clustering observations, even though it is well known that the assembly history of dark matter halos is related to their clustering. In this paper we use high-resolution hydrodynamical cosmological simulations to compare the halo and stellar mass growth of galaxies in a large-scale overdensity to those in a large-scale underdensity (on scales of about 20 Mpc). The simulation reproduces assembly bias, in which halos have earlier formation times in overdense environments than in underdense regions. We find that the ratio of stellar mass to halo mass is larger in overdense regions in central galaxies residing in halos with masses between 1011 and 1012.9 M⊙. When we force the local density (within 2 Mpc) at z = 0 to be the same for galaxies in the large-scale over- and underdensities, we find the same results. We posit that this difference can be explained by a combination of earlier formation times, more interactions at early times with neighbors, and more filaments feeding galaxies in overdense regions. This result puts the standard practice of assigning stellar mass to halos based only on their mass, rather than considering their larger environment, into question.

  3. 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

  4. Halo formation in high-power klystrons

    SciTech Connect

    Pakter, R.; Chen, C.

    1999-07-01

    Beam losses and radio-frequency (rf) pulse shortening are important issues in the development of high-power microwave (HPM) sources such as high-power klystrons and relativistic magnetrons. In this paper, the authors explore the formation and characteristics of halos around intense relativistic electron beams in a Periodic Permanent Magnet focusing klystron as well as in a uniform solenoidal focusing klystron. A self-consistent electrostatic model is used to investigate intense relativistic electron beam transport as an rf field induced mismatch between the electron beam and the focusing field develops. To model the effect of such mismatch in the PPM klystron experiment, they initialize the beam with an envelope mismatch. For zero canonical angular momentum and an initial mismatch of 100 percent, for example, the preliminary results show halo particles with a maximum radius extending up to several core radii at the rf output section. Transient effects and the influence of finite canonical angular momentum are being studied.

  5. Special Features of Galactic Dynamics

    NASA Astrophysics Data System (ADS)

    Efthymiopoulos, Christos; Voglis, Nikos; Kalapotharakos, Constantinos

    This is an introductory article to some basic notions and currently open problems of galactic dynamics. The focus is on topics mostly relevant to the so-called `new methods' of celestial mechanics or Hamiltonian dynamics, as applied to the ellipsoidal components of galaxies, i.e., to the elliptical galaxies and to the dark halos and bulges of disk galaxies. Traditional topics such as Jeans theorem, the role of a `third integral' of motion, Nekhoroshev theory, violent relaxation, and the statistical mechanics of collisionless stellar systems are first discussed. The emphasis is on modern extrapolations of these old topics. Recent results from orbital and global dynamical studies of galaxies are then shortly reviewed. The role of various families of orbits in supporting self-consistency, as well as the role of chaos in galaxies, are stressed. A description is then given of the main numerical techniques of integration of the N-body problem in the framework of stellar dynamics and of the results obtained via N-Body experiments. A final topic is the secular evolution and self-organization of galactic systems.

  6. Systematic uncertainties from halo asphericity in dark matter searches

    SciTech Connect

    Bernal, Nicolás; Forero-Romero, Jaime E.; Garani, Raghuveer; Palomares-Ruiz, Sergio E-mail: je.forero@uniandes.edu.co E-mail: sergio.palomares.ruiz@ific.uv.es

    2014-09-01

    Although commonly assumed to be spherical, dark matter halos are predicted to be non-spherical by N-body simulations and their asphericity has a potential impact on the systematic uncertainties in dark matter searches. The evaluation of these uncertainties is the main aim of this work, where we study the impact of aspherical dark matter density distributions in Milky-Way-like halos on direct and indirect searches. Using data from the large N-body cosmological simulation Bolshoi, we perform a statistical analysis and quantify the systematic uncertainties on the determination of local dark matter density and the so-called J factors for dark matter annihilations and decays from the galactic center. We find that, due to our ignorance about the extent of the non-sphericity of the Milky Way dark matter halo, systematic uncertainties can be as large as 35%, within the 95% most probable region, for a spherically averaged value for the local density of 0.3-0.4 GeV/cm {sup 3}. Similarly, systematic uncertainties on the J factors evaluated around the galactic center can be as large as 10% and 15%, within the 95% most probable region, for dark matter annihilations and decays, respectively.

  7. Galactic Archaeology with the Subaru Prime Focus Spectrograph

    NASA Astrophysics Data System (ADS)

    Chiba, Masashi; Cohen, Judith; Wyse, Rosemary

    2015-08-01

    We present our Galactic Archaeology survey plan with the Prime Focus Spectrograph (PFS) for Subaru. PFS is a massively-multiplexed, fiber-fed optical and near-infrared 3-arm spectrograph (N_fiber = 2,400, 380 < lambda < 1260 nm, 1.3 degree diameter hexagonal field, low- and medium-resolution modes of R = 2,000-3,000 and 5,000, respectively), offering us unique opportunities in survey astronomy. Following successful design reviews, the instrument is now under construction with first light anticipated in 2018. In the Galactic Archaeology program, for which we expect to have about 100 nights over 5 years, radial velocities and chemical abundances of stars in the Milky Way and M31 will be used to infer the past assembly histories of these galaxies and the structure of their dark matter halos. Data will be secured for numerous stars in the Galactic thick-disk, halo and tidal streams as faint as V = 22 mag, including stars with V < 20 mag to complement the goals of the Gaia mission. A medium-resolution mode with R = 5,000 to be implemented in the red arm will allow the measurement of multiple alpha-element abundances and more precise velocities for Galactic stars, elucidating the detailed chemo-dynamical structure and evolution of each of the main stellar components of the Milky Way Galaxy and of its dwarf spheroidal galaxies. The M31 campaign will target red giant branch stars with 21.5 < V < 22.5 mag, obtaining radial velocities and metallicities over an unprecedented large area of its stellar halo. In synergy with these planned PFS survey, the coordinated imaging surveys with Hyper Suprime Cam are going on over wide areas of the Galactic satellites and the M31 halo, based on the combination of broad-band and narrow-band filters to separate candidate giants from foreground dwarfs as spectroscopic targets.

  8. SAS-2 gamma-ray results from the galactic plane and their implications for galactic structure and galactic cosmic-ray dynamics

    NASA Technical Reports Server (NTRS)

    Fichtel, C. E.; Kniffen, D. A.; Thompson, D. J.

    1977-01-01

    The final SAS-2 results related to high energy galactic gamma-ray emission show a strong correlation with galactic structural features seen at other wavelenghts, when the known gamma-ray sources are subtracted. Theoretical considerations and analysis of the gamma-ray data suggest that the galactic cosmic rays are dynamically coupled to the interstellar matter through the magnetic fields, and hence the cosmic ray density is enhanced where the matter density is greatest on the scale of the galactic arms. This concept has been explored in a galactic model that assumes: (1) cosmic rays are galactic and not universal; (2)on the scale of the galactic arms, the cosmic ray column (surface) density is proportional to the total interstellar gas column density; (3)the cosmic ray scale height is significantly larger than the scale height to the matter; and (4) ours is a spiral galaxy characterized by an arm to interarm density ratio of over 2:1.

  9. Fading features found in the kinematics of the far-reaching Milky Way stellar halo

    NASA Astrophysics Data System (ADS)

    Bird, Sarah A.; Flynn, Chris

    2015-09-01

    We test the long-term kinematical stability of a Galactic stellar halo model, due to Kafle et al. (2012), who study the kinematics of approximately 5000 blue horizontal branch stars in the Sloan Digital Sky Survey. The velocity dispersion σ and anisotropy parameter β of the stars have been determined as functions of Galactocentric radius, over the range 6 < RGC < 25 kpc, and show a strong dip in the anisotropy profile at RGC ˜ 17 kpc. By directly integrating orbits of particles in a 3D model of the Galactic potential with these characteristics, we show that the σ and β profiles quickly evolve on a time-scale of a few × 10 Myr whereas the density ρ profile remains largely unaffected. We suggest that the feature is therefore transient. The origin of such features in the Galactic halo remains unclear.

  10. Galactic cosmic ray antiprotons and supersymmetry

    NASA Technical Reports Server (NTRS)

    Stecker, F. W.; Walsh, T.; Rudaz, S.

    1985-01-01

    The physics of the annihilation of photinos is considered as a function of mass in detail, in order to obtain the energy spectra of the cosmic ray antiprotons produced under the assumption that photinos make up the missing mass in the galactic halo. The modulated spectrum is at 1 a.w. with the cosmic ray antiprotons data. A very intriguing fit is obtained to all of the present antiprotons up to 13.4 GeV data for similar to 15 GeV. A cutoff is predicted in the antiprotons spectrum at E = photino mass above which only a small flux from secondary production should remain.

  11. OUTFLOW VERSUS INFALL IN SPIRAL GALAXIES: METAL ABSORPTION IN THE HALO OF NGC 891

    SciTech Connect

    Bregman, Joel N.; Seitzer, Patrick; Cowley, C. R.; Miller, Matthew J.; Miller, Eric D.

    2013-03-20

    Gas accreting onto a galaxy will be of low metallicity while halo gas due to a galactic fountain will be of near-solar metallicity. We test these predictions by measuring the metal absorption line properties of halo gas 5 kpc above the plane of the edge-on galaxy NGC 891, using observations taken with HST/STIS toward a bright background quasar. Metal absorption lines of Fe II, Mg II, and Mg I in the halo of NGC 891 are clearly seen, and when combined with recent deep H I observations, we are able to place constraints on the metallicity of the halo gas for the first time. The H I line width defines the line broadening, from which we model opacity effects in these metal lines, assuming that the absorbing gas is continuously distributed in the halo. The gas-phase metallicities are [Fe/H] = -1.18 {+-} 0.07 and [Mg/H] = -0.23 + 0.36/ - 0.27 (statistical errors) and this difference is probably due to differential depletion onto grains. When corrected for such depletion using Galactic gas as a guide, both elements have approximately solar or even supersolar abundances. This suggests that the gas is from the galaxy disk, probably expelled into the halo by a galactic fountain, rather than from accretion of intergalactic gas, which would have a low metallicity. The abundances would be raised by significant amounts if the absorbing gas lies in a few clouds with thermal widths smaller than the rotational velocity of the halo. If this is the case, both the abundances and [Mg/Fe] would be supersolar.

  12. Revisiting the luminosity function of single halo white dwarfs

    NASA Astrophysics Data System (ADS)

    Cojocaru, Ruxandra; Torres, Santiago; Althaus, Leandro G.; Isern, Jordi; García-Berro, Enrique

    2015-09-01

    Context. White dwarfs are the fossils left by the evolution of low- and intermediate-mass stars, and have very long evolutionary timescales. This allows us to use them to explore the properties of old populations, like the Galactic halo. Aims: We present a population synthesis study of the luminosity function of halo white dwarfs, aimed at investigating which information can be derived from the currently available observed data. Methods: We employ an up-to-date population synthesis code based on Monte Carlo techniques, which incorporates the most recent and reliable cooling sequences for metal-poor progenitors as well as an accurate modeling of the observational biases. Results: We find that because the observed sample of halo white dwarfs is restricted to the brightest stars, only the hot branch of the white dwarf luminosity function can be used for these purposes, and that its shape function is almost insensitive to the most relevant inputs, such as the adopted cooling sequences, the initial mass function, the density profile of the stellar spheroid, or the adopted fraction of unresolved binaries. Moreover, since the cutoff of the observed luminosity has not yet been determined only the lower limits to the age of the halo population can be placed. Conclusions: We conclude that the current observed sample of the halo white dwarf population is still too small to obtain definite conclusions about the properties of the stellar halo, and the recently computed white dwarf cooling sequences, which incorporate residual hydrogen burning, should be assessed using metal-poor globular clusters.

  13. The Galactic Nucleus

    NASA Astrophysics Data System (ADS)

    Melia, Fulvio

    Exciting new broadband observations of the galactic nucleus have placed the heart of the Milky Way under intense scrutiny in recent years. This has been due in part to the growing interest from theorists motivated to study the physics of black hole accretion, magnetized gas dynamics, and unusual star formation. The center of our Galaxy is now known to harbor the most compelling supermassive black hole candidate, weighing in at 3-4 million solar masses. Its nearby environment is comprised of a molecular dusty ring, clusters of evolved and young stars, diffuse hot gas, ionized gas streamers, and several supernova remnants. This chapter will focus on the physical makeup of this dynamic region and the feasibility of actually imaging the black hole's shadow in the coming decade with mm interferometry.

  14. 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

  15. Adiabatic Halo Formation

    SciTech Connect

    Bazzani, A.; Turchetti, G.; Benedetti, C.; Rambaldi, S.; Servizi, G.

    2005-06-08

    In a high intensity circular accelerator the synchrotron dynamics introduces a slow modulation in the betatronic tune due to the space-charge tune depression. When the transverse motion is non-linear due to the presence of multipolar effects, resonance islands move in the phase space and change their amplitude. This effect introduces the trapping and detrapping phenomenon and a slow diffusion in the phase space. We apply the neo-adiabatic theory to describe this diffusion mechanism that can contribute to halo formation.

  16. Rotation of halos in open and closed universes - differentiated merging and natural selection of galaxy types

    SciTech Connect

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

    1988-07-01

    Computer simulations are used here to study the properties of galactic halos formed from Gaussian initial density perturbations in both open and closed dark matter universes. It is shown that if galaxies form through gravitational collapse from initial, Gaussian density perturbations, then their luminous parts do not have the original values of either specific angular momentum (ellipticals) or spin parameter lambda (spirals). The rotational properties of a halo depend only weakly on either the halo density or the density of its environment. Variations of the large-scale density of the environment have an expected, dramatic effect on the density of individual halos. Dissipationless merging forces the cores of the merging objects into the core of the merger product. In the process, cores become more bound and lose angular momentum. These findings are extrapolated to propose a model for galaxy formation in which both ellipticals and spirals come into being through mergers. 59 references.

  17. Axial Ratio of Edge-On Spiral Galaxies as a Test for Bright Radio Halos

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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 & 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.

  18. 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)

  19. A strip search for new very wide halo binaries

    NASA Astrophysics Data System (ADS)

    Quinn, D. P.; Smith, M. C.

    2009-12-01

    We report on a search for new wide halo binary stars in Sloan Digital Sky Survey (SDSS) Stripe 82. A list of new halo wide binary candidates which satisfy common proper motion and photometric constraints is provided. The projected separations of the sample lie between 0.007 and 0.25 pc. Although the sample is not large enough to improve constraints on dark matter in the halo, we find the wide binary angular separation function is broadly consistent with past work. We discuss the significance of the new sample for a number of astrophysical applications, including as a testbed for ideas about wide binary formation. For the subset of candidates which have radial velocity information, we make use of integrals of motion to investigate one such scheme in which the origin of Galactic wide binaries is associated with the accretion/disruption of stellar systems in the Galaxy. Additional spectroscopic observations of these candidate binaries will strengthen their usefulness in many of these respects. Based on our search experience in Stripe 82 we estimate that the upcoming Pan-STARRS survey will increase the sample size of wide halo binaries by over an order of magnitude.

  20. The influence of halo evolution on galaxy structure

    NASA Astrophysics Data System (ADS)

    White, Simon

    2015-03-01

    If Einstein-Newton gravity holds on galactic and larger scales, then current observations demonstrate that the stars and interstellar gas of a typical bright galaxy account for only a few percent of its total nonlinear mass. Dark matter makes up the rest and cannot be faint stars or any other baryonic form because it was already present and decoupled from the radiation plasma at z = 1000, long before any nonlinear object formed. The weak gravito-sonic waves so precisely measured by CMB observations are detected again at z = 4 as order unity fluctuations in intergalactic matter. These subsequently collapse to form today's galaxy/halo systems, whose mean mass profiles can be accurately determined through gravitational lensing. High-resolution simulations link the observed dark matter structures seen at all these epochs, demonstrating that they are consistent and providing detailed predictions for all aspects of halo structure and growth. Requiring consistency with the abundance and clustering of real galaxies strongly constrains the galaxy-halo relation, both today and at high redshift. This results in detailed predictions for galaxy assembly histories and for the gravitational arena in which galaxies live. Dark halos are not expected to be passive or symmetric but to have a rich and continually evolving structure which will drive evolution in the central galaxy over its full life, exciting warps, spiral patterns and tidal arms, thickening disks, producing rings, bars and bulges. Their growth is closely related to the provision of new gas for galaxy building.

  1. 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.

  2. The role of galaxy formation in the structure and dynamics of dark matter halos

    NASA Astrophysics Data System (ADS)

    Tonini, Chiara

    2009-02-01

    The structure and dynamics of dark matter halos, as predicted by the hierarchical clustering scenario, are at odds with the properties inferred from the observations at galactic scales. My Thesis addresses this problem by taking an evolutionary approach. I analysed in detail the many and different observational evidences of a discrepancy the predicted halo equilibrium state and the one inferred from the measurable properties of disk galaxies, as well as of the scaling relations existing between the angular momentum, geometry and mass distribution of the luminous and dark components, and realized that they all seem to point towards the same conclusion: the baryons hosted inside the halo, by collapsing and assembling to form the galaxy, perturb the halo equilibrium structure and made it evolve into new configurations. From the theoretical point of view, the behaviour of dark matter halos as collisionless systems of particles makes their equilibrium structure and mass distribution extremely sensitive to perturbations of their inner dynamics. The galaxy formation occurring inside the halos is a tremendous event, and the dynamical coupling between the baryons and the dark matter during the protogalaxy collapse represents a perturbation of the halo dynamical structure large enough to trigger a halo evolution, according to the relative mass and angular momentum of the two components. My conclusion is that the structure and dynamics of dark matter halos, as well as the origin of the connection between the halo and galaxy properties, are to be understood in in terms of a joint evolution of the baryonic and dark components, originating at the epoch of the collapse and formation of the galaxy.

  3. Post-AGB Stars in the Halos of Nearby Galaxies

    NASA Astrophysics Data System (ADS)

    Bond, Howard E.

    1999-02-01

    The visually brightest members of Population II are post-AGB (PAGB) stars evolving through spectral types F and A. The aim of this proposal is to find such PAGB stars in the halos of three galaxies that lie just outside the Local Group: Sextans A, NGC 3109, and NGC 5237. The importance of PAGB stars is: (1) they can probe the structure of galactic halos, in the form of test particles much more numerous than planetary nebulae or globular clusters, with which we can look for features such as clumps or tidal streams; (2) the number counts will tell us the theoretically poorly known transition time from AGB to planetary nebula; and (3) we believe that PAGB stars will prove to be a superb new PRIMARY distance indicator, comparable to or better than Cepheids. PAGB stars of types F and A are easily recognized because of their large Balmer jumps. Our uBVI photometric system is optimal for revealing them in galactic halos, due to their unique u-B colors, and the method is extremely efficient in its telescope time requirements. Sextans A and NGC 3109 have Cepheid and TRGB distances, so they are excellent test beds for a confrontation with our proposed Pop II primary standard candles. NGC 5237 has an uncertain distance, which PAGB stars should considerably improve. The 0.9-m telescope will be used (1) to obtain uBVI calibrations of our fields, thus saving the 4-m BTC mosaic for the deep observations; and (2) to complete our survey of Milky Way globular clusters for PAGB stars to used as Galactic calibrators of their luminosities and metallicity dependence.

  4. ON THE HOT GAS CONTENT OF THE MILKY WAY HALO

    SciTech Connect

    Fang, Taotao; Bullock, James; Boylan-Kolchin, Michael

    2013-01-01

    The Milky Way appears to be missing baryons, as the observed mass in stars and gas is well below the cosmic mean. One possibility is that a substantial fraction of the Galaxy's baryons are embedded within an extended, million-degree hot halo, an idea supported indirectly by observations of warm gas clouds in the halo and gas-free dwarf spheroidal satellites. X-ray observations have established that hot gas does exist in our Galaxy beyond the local hot bubble; however, it may be distributed in a hot disk configuration. Moreover, recent investigations into the X-ray constraints have suggested that any Galactic corona must be insignificant. Here we re-examine the observational data, particularly in the X-ray and radio bands, in order to determine whether it is possible for a substantial fraction of the Galaxy's baryons to exist in {approx}10{sup 6} K gas. In agreement with past studies, we find that a baryonically closed halo is clearly ruled out if one assumes that the hot corona is distributed with a cuspy Navarro-Frenk-White profile. However, if the hot corona of the galaxy is in an extended, low-density distribution with a large central core, as expected for an adiabatic gas in hydrostatic equilibrium, then it may contain up to 10{sup 11} M {sub Sun} of material, possibly accounting for all of the missing Galactic baryons. We briefly discuss some potential avenues for discriminating between a massive, extended hot halo and a local hot disk.

  5. 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.

  6. A Receding Halo Sub-structure Towards Norma

    NASA Astrophysics Data System (ADS)

    Chakrabarti, Sukanya

    2016-01-01

    We present results from follow-up spectroscopic observations of clustered Cepheid candidates identified from K-band light curves towards the Norma constellation (Chakrabarti et al. 2015), as well as others that we have found more recently. The average radial velocity of these stars is ~ 200 km/s, which is large and distinct from that of the Galaxy's stellar disk. These objects at l ~ -27 and b ~ -1 are therefore halo stars; using the period-luminosity relation of Type I Cepheids, they are at ~ 90 kpc. While the spectra do not have sufficient S/N to independently determine the metallicity and spectral type of the stars, there is a clear correspondence between the observed Brackett series lines in these observations and in known Type I Cepheids. Distances determined from the K-band period-luminosity relation (Matsunaga et al. 2013) and the 3.6 μm period-luminosity relation (Scowcroft et al. 2011) agree closely, and I-band observations have confirmed the periods of these sources. The extinction corrected J - Ks colors of these sources are comparable to known Type I Cepheids (Persson et al. 2004). The observed radial velocity of these stars agrees with predictions from dynamical models (Chakrabarti & Blitz 2009). If these stars are indeed members of the predicted dark-matter dominated dwarf galaxy that perturbed the outer HI disk of the Milky Way, this would represent the first application of Galactoseismology. These observations also challenge models of the Galactic halo. Young Cepheid variables are unexpected in models of the Galactic halo, though star formation due to infall of gas-rich dwarf galaxies may well produce a small population of yet undiscovered Cepheids in the outer halo.

  7. The response of dark matter haloes to elliptical galaxy formation: a new test for quenching scenarios

    NASA Astrophysics Data System (ADS)

    Dutton, Aaron A.; Macciò, Andrea V.; Stinson, Gregory S.; Gutcke, Thales A.; Penzo, Camilla; Buck, Tobias

    2015-11-01

    We use cosmological hydrodynamical zoom-in simulations with the smoothed particle hydrodynamics code GASOLINE of four haloes of mass M200 ˜ 1013 M⊙ to study the response of the dark matter to elliptical galaxy formation. Our simulations include metallicity-dependent gas cooling, star formation and feedback from massive stars and supernovae, but not active galactic nuclei (AGN). At z = 2 the progenitor galaxies have stellar-to-halo mass ratios consistent with halo abundance matching, assuming a Salpeter initial mass function. However, by z = 0 the standard runs suffer from the well-known overcooling problem, overpredicting the stellar masses by a factor of ≳ 4. To mimic a suppressive halo quenching scenario, in our forced quenching (FQ) simulations, cooling and star formation are switched off at z = 2. The resulting z = 0 galaxies have stellar masses, sizes and circular velocities close to what is observed. Relative to the control simulations, the dark matter haloes in the FQ simulations have contracted, with central dark matter density slopes d log ρ/d log r ˜ -1.5, showing that dry merging alone is unable to fully reverse the contraction that occurs at z > 2. Simulations in the literature with AGN feedback, however, have found expansion or no net change in the dark matter halo. Thus, the response of the dark matter halo to galaxy formation may provide a new test to distinguish between ejective and suppressive quenching mechanisms.

  8. Applying galactic archeology to massive galaxies using deep imaging surveys

    NASA Astrophysics Data System (ADS)

    Duc, Pierre-Alain

    2015-04-01

    Various programs aimed at exploring the still largely unknown low surface brightness Universe with deep imaging optical surveys have recently started. They open a new window for studies of galaxy evolution, pushing the technique of galactic archeology outside the Local Group (LG). The method, based on the detection and analysis of the diffuse light emitted by collisional debris or extended stellar halos (rather than on stellar counts as done for LG systems), faces however a number of technical difficulties, like the contamination of the images by reflection halos and Galactic cirrus. I review here the on-going efforts to address them and highlight the preliminary promising results obtained with a systematic survey with MegaCam on the CFHT of nearby massive early-type galaxies done as part of the ATLAS3D, NGVS and MATLAS collaborations.

  9. Near Ballistic Halo-to-Halo Transfers between Planetary Moons

    NASA Astrophysics Data System (ADS)

    Lantoine, Gregory; Russell, Ryan P.

    2011-07-01

    Intermoon transfers are important components of planetary tour missions. However, these transfers are challenging to design due in part to the chaotic environment created by the multi-body dynamics. The specific objective of this work is to develop a systematic methodology to find fuel optimal, near ballistic Halo-to-Halo trajectories between planetary moons, and we achieve this goal by combining dynamical systems theory with a variety of nonlinear programming techniques. The spacecraft is constrained to start at a Halo orbit of a moon and end at another Halo orbit of a second moon. Our approach overcomes the obstacles of the chaotic dynamics by combining multiple "resonant-hopping" gravity assists with manifolds that control the low-energy transport near the Halo orbits of the moons. To help construct good initial guesses, contours of semimajor axes that can be reached by falling off a Halo orbit are presented. An empirical relationship is then derived to find quickly the boundary conditions on the Halo orbits that lead to ballistic capture and escape trajectories, and connect to desired resonances. The overall optimization procedure is broken into four parts of increasing fidelity: creation of the initial guess from unstable resonant orbits and manifolds, decomposition and optimization of the trajectory into two independent ideal three-body portions, end-to-end refinement in a patched three-body model, and transition to an ephemeris model using a continuation method. Each step is based on a robust multiple shooting approach to reduce the sensitivities associated with the close approach trajectories. Numerical results of an intermoon transfer in the Jovian system are presented. In an ephemeris model, using only 55 m/s and 205 days, a spacecraft can transfer between a Halo orbit of Ganymede and a Halo orbit of Europa.

  10. REVISITING SCALING RELATIONS FOR GIANT RADIO HALOS IN GALAXY CLUSTERS

    SciTech Connect

    Cassano, R.; Brunetti, G.; Venturi, T.; Kale, R.; Pratt, G. W.; Markevitch, M.

    2013-11-10

    Many galaxy clusters host megaparsec-scale radio halos, generated by ultrarelativistic electrons in the magnetized intracluster medium. Correlations between the synchrotron power of radio halos and the thermal properties of the hosting clusters were established in the last decade, including the connection between the presence of a halo and cluster mergers. The X-ray luminosity and redshift-limited Extended GMRT Radio Halo Survey provides a rich and unique dataset for statistical studies of the halos. We uniformly analyze the radio and X-ray data for the GMRT cluster sample, and use the new Planck Sunyaev-Zel'dovich (SZ) catalog to revisit the correlations between the power of radio halos and the thermal properties of galaxy clusters. We find that the radio power at 1.4 GHz scales with the cluster X-ray (0.1-2.4 keV) luminosity computed within R{sub 500} as P{sub 1.4}∼L{sup 2.1±0.2}{sub 500}. Our bigger and more homogenous sample confirms that the X-ray luminous (L{sub 500} > 5 × 10{sup 44} erg s{sup –1}) clusters branch into two populations—radio halos lie on the correlation, while clusters without radio halos have their radio upper limits well below that correlation. This bimodality remains if we excise cool cores from the X-ray luminosities. We also find that P{sub 1.4} scales with the cluster integrated SZ signal within R{sub 500}, measured by Planck, as P{sub 1.4}∼Y{sup 2.05±0.28}{sub 500}, in line with previous findings. However, contrary to previous studies that were limited by incompleteness and small sample size, we find that 'SZ-luminous' Y{sub 500} > 6 × 10{sup –5} Mpc{sup 2} clusters show a bimodal behavior for the presence of radio halos, similar to that in the radio-X-ray diagram. Bimodality of both correlations can be traced to clusters dynamics, with radio halos found exclusively in merging clusters. These results confirm the key role of mergers for the origin of giant radio halos, suggesting that they trigger the relativistic particle

  11. Revisiting Scaling Relations for Giant Radio Halos in Galaxy Clusters

    NASA Technical Reports Server (NTRS)

    Cassano, R.; Ettori, S.; Brunetti, G.; Giacintucci, S.; Pratt, G. W.; Venturi, T.; Kale, R.; Dolag, K.; Markevitch, Maxim L.

    2013-01-01

    Many galaxy clusters host megaparsec-scale radio halos, generated by ultrarelativistic electrons in the magnetized intracluster medium. Correlations between the synchrotron power of radio halos and the thermal properties of the hosting clusters were established in the last decade, including the connection between the presence of a halo and cluster mergers. The X-ray luminosity and redshift-limited Extended GMRT Radio Halo Survey provides a rich and unique dataset for statistical studies of the halos. We uniformly analyze the radio and X-ray data for the GMRT cluster sample, and use the new Planck Sunyaev-Zel'dovich (SZ) catalog to revisit the correlations between the power of radio halos and the thermal properties of galaxy clusters. We find that the radio power at 1.4 GHz scales with the cluster X-ray (0.1-2.4 keV) luminosity computed within R(sub 500) as P(sub 1.4) approx. L(2.1+/-0.2) - 500). Our bigger and more homogenous sample confirms that the X-ray luminous (L(sub 500) > 5 × 10(exp 44) erg/s)) clusters branch into two populations-radio halos lie on the correlation, while clusters without radio halos have their radio upper limits well below that correlation. This bimodality remains if we excise cool cores from the X-ray luminosities. We also find that P(sub 1.4) scales with the cluster integrated SZ signal within R(sub 500), measured by Planck, as P(sub 1.4) approx. Y(2.05+/-0.28) - 500), in line with previous findings. However, contrary to previous studies that were limited by incompleteness and small sample size, we find that "SZ-luminous" Y(sub 500) > 6×10(exp -5) Mpc(exp 2) clusters show a bimodal behavior for the presence of radio halos, similar to that in the radio-X-ray diagram. Bimodality of both correlations can be traced to clusters dynamics, with radio halos found exclusively in merging clusters. These results confirm the key role of mergers for the origin of giant radio halos, suggesting that they trigger the relativistic particle acceleration.

  12. TURBULENCE AND RADIO MINI-HALOS IN THE SLOSHING CORES OF GALAXY CLUSTERS

    SciTech Connect

    ZuHone, J. A.; Markevitch, M.; Giacintucci, S.

    2013-01-10

    A number of relaxed, cool-core galaxy clusters exhibit diffuse, steep-spectrum radio sources in their central regions, known as radio mini-halos. It has been proposed that the relativistic electrons responsible for the emission have been reaccelerated by turbulence generated by the sloshing of the cool core gas. We present a high-resolution MHD simulation of gas sloshing in a galaxy cluster coupled with subgrid simulations of relativistic electron acceleration to test this hypothesis. Our simulation shows that the sloshing motions generate turbulence on the order of {delta}v {approx} 50-200 km s{sup -1} on spatial scales of {approx}50-100 kpc and below in the cool core region within the envelope of the sloshing cold fronts, whereas outside the cold fronts, there is negligible turbulence. This turbulence is potentially strong enough to reaccelerate relativistic electron seeds (with initial {gamma} {approx} 100-500) to {gamma} {approx} 10{sup 4} via damping of magnetosonic waves and non-resonant compression. The seed electrons could remain in the cluster from, e.g., past active galactic nucleus activity. In combination with the magnetic field amplification in the core, these electrons then produce diffuse radio synchrotron emission that is coincident with the region bounded by the sloshing cold fronts, as indeed observed in X-rays and the radio. The result holds for different initial spatial distributions of pre-existing relativistic electrons. The power and the steep spectral index ({alpha} Almost-Equal-To 1-2) of the resulting radio emission are consistent with observations of mini-halos, though the theoretical uncertainties of the acceleration mechanisms are high. We also produce simulated maps of inverse-Compton hard X-ray emission from the same population of relativistic electrons.

  13. Turbulence and Radio Mini-halos in the Sloshing Cores of Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    ZuHone, J. A.; Markevitch, M.; Brunetti, G.; Giacintucci, S.

    2013-01-01

    A number of relaxed, cool-core galaxy clusters exhibit diffuse, steep-spectrum radio sources in their central regions, known as radio mini-halos. It has been proposed that the relativistic electrons responsible for the emission have been reaccelerated by turbulence generated by the sloshing of the cool core gas. We present a high-resolution MHD simulation of gas sloshing in a galaxy cluster coupled with subgrid simulations of relativistic electron acceleration to test this hypothesis. Our simulation shows that the sloshing motions generate turbulence on the order of δv ~ 50-200 km s-1 on spatial scales of ~50-100 kpc and below in the cool core region within the envelope of the sloshing cold fronts, whereas outside the cold fronts, there is negligible turbulence. This turbulence is potentially strong enough to reaccelerate relativistic electron seeds (with initial γ ~ 100-500) to γ ~ 104 via damping of magnetosonic waves and non-resonant compression. The seed electrons could remain in the cluster from, e.g., past active galactic nucleus activity. In combination with the magnetic field amplification in the core, these electrons then produce diffuse radio synchrotron emission that is coincident with the region bounded by the sloshing cold fronts, as indeed observed in X-rays and the radio. The result holds for different initial spatial distributions of pre-existing relativistic electrons. The power and the steep spectral index (α ≈ 1-2) of the resulting radio emission are consistent with observations of mini-halos, though the theoretical uncertainties of the acceleration mechanisms are high. We also produce simulated maps of inverse-Compton hard X-ray emission from the same population of relativistic electrons.

  14. Generalized halo independent comparison of direct dark matter detection data

    SciTech Connect

    Nobile, Eugenio Del; Gelmini, Graciela; Huh, Ji-Haeng; Gondolo, Paolo E-mail: gelmini@physics.ucla.edu E-mail: jhhuh@physics.ucla.edu

    2013-10-01

    We extend the halo-independent method to compare direct dark matter detection data, so far used only for spin-independent WIMP-nucleon interactions, to any type of interaction. As an example we apply the method to magnetic moment interactions.

  15. Kinematically Detected Halo Streams

    NASA Astrophysics Data System (ADS)

    Smith, Martin C.

    Clues to the origins and evolution of our Galaxy can be found in the kinematics of stars around us. Remnants of accreted satellite galaxies produce over-densities in velocity-space, which can remain coherent for much longer than spatial over-densities. This chapter reviews a number of studies that have hunted for these accretion relics, both in the nearby solar-neighborhood and the more-distant stellar halo. Many observational surveys have driven this field forwards, from early work with the Hipparcos mission, to contemporary surveys like RAVE and SDSS. This active field continues to flourish, providing many new discoveries, and will be revolutionized as the Gaia mission delivers precise proper motions for a billion stars in our Galaxy.

  16. DOES THE SAGITTARIUS STREAM CONSTRAIN THE MILKY WAY HALO TO BE TRIAXIAL?

    SciTech Connect

    Ibata, R.; Martin, N. F.; Lewis, G. F.; Bellazzini, M.; Correnti, M.

    2013-03-01

    Recent analyses of the stellar stream of the Sagittarius dwarf galaxy have suggested that the kinematics and three-dimensional location of the M-giant stars in this structure constrain the dark matter halo of our Galaxy to possess a triaxial shape that is extremely flattened, being essentially an oblate ellipsoid oriented perpendicular to the Galactic disk. Using a new stream-fitting algorithm, based on a Markov Chain Monte Carlo procedure, we investigate whether this claim remains valid if we allow the density profile of the Milky Way halo greater freedom. We find stream solutions that fit the leading and trailing arms of this structure even in a spherical halo, although this would need a rising Galactic rotation curve at large Galactocentric radius. However, the required rotation curve is not ruled out by current constraints. It appears therefore that for the Milky Way, halo triaxiality, despite its strong theoretical motivation, is not required to explain the Sagittarius stream. This degeneracy between triaxiality and the halo density profile suggests that, in future endeavors to model this structure, it will be advantageous to relax the strict analytic density profiles that have been used to date.

  17. Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor.

    PubMed

    Frebel, Anna; Kirby, Evan N; Simon, Joshua D

    2010-03-01

    Current cosmological models indicate that the Milky Way's stellar halo was assembled from many smaller systems. On the basis of the apparent absence of the most metal-poor stars in present-day dwarf galaxies, recent studies claimed that the true Galactic building blocks must have been vastly different from the surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt on this conclusion. Verification of the iron-deficiency, however, and measurements of additional elements, such as the alpha-element Mg, are necessary to demonstrate that the same type of stars produced the metals found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars be conclusively linked to early stellar halo assembly. Here we report high-resolution spectroscopic abundances for 11 elements in S1020549, confirming its iron abundance of less than 1/4,000th that of the Sun, and showing that the overall abundance pattern follows that seen in low-metallicity halo stars, including the alpha-elements. Such chemical similarity indicates that the systems destroyed to form the halo billions of years ago were not fundamentally different from the progenitors of present-day dwarfs, and suggests that the early chemical enrichment of all galaxies may be nearly identical. PMID:20203604

  18. Neutral hydrogen in galaxy haloes at the peak of the cosmic star formation history

    NASA Astrophysics Data System (ADS)

    Faucher-Giguère, Claude-André; Hopkins, Philip F.; Kereš, Dušan; Muratov, Alexander L.; Quataert, Eliot; Murray, Norman

    2015-05-01

    We use high-resolution cosmological zoom-in simulations from the FIRE (Feedback in Realistic Environments) project to make predictions for the covering fractions of neutral hydrogen around galaxies at z = 2-4. These simulations resolve the interstellar medium of galaxies and explicitly implement a comprehensive set of stellar feedback mechanisms. Our simulation sample consists of 16 main haloes covering the mass range Mh ≈ 109-6 × 1012 M⊙ at z = 2, including 12 haloes in the mass range Mh ˜ 1011-1012 M⊙ corresponding to Lyman break galaxies (LBGs). We process our simulations with a ray tracing method to compute the ionization state of the gas. Galactic winds increase the H I covering fractions in galaxy haloes by direct ejection of cool gas from galaxies and through interactions with gas inflowing from the intergalactic medium. Our simulations predict H I covering fractions for Lyman limit systems (LLSs) consistent with measurements around z ˜ 2-2.5 LBGs; these covering fractions are a factor ˜2 higher than our previous calculations without galactic winds. The fractions of H I absorbers arising in inflows and in outflows are on average ˜50 per cent but exhibit significant time variability, ranging from ˜10 to ˜90 per cent. For our most massive haloes, we find a factor ˜3 deficit in the LLS covering fraction relative to what is measured around quasars at z ˜ 2, suggesting that the presence of a quasar may affect the properties of halo gas on ˜100 kpc scales. The predicted covering fractions, which decrease with time, peak at Mh ˜ 1011-1012 M⊙, near the peak of the star formation efficiency in dark matter haloes. In our simulations, star formation and galactic outflows are highly time dependent; H I covering fractions are also time variable but less so because they represent averages over large areas.

  19. Characteristic time for halo current growth and rotation

    NASA Astrophysics Data System (ADS)

    Boozer, Allen

    2015-11-01

    Halo currents, Ih, flow in part through plasma on open magnetic lines and in part through the walls. A halo current has the same function as the wall current of a resistive wall mode and arises when a kink cannot be wall stabilized. When flowing in the plasma, the halo current can produce no forces, so j->h = (j∥ / B) B-> with B-> . ∇ -> j∥ / B = 0 . To avoid too strong a coupling to stable kinks, the wall interception must be of sufficient toroidal extent, which implies the width of the halo current channel Δh aIh /Ip , where aIh /Ip is the amplitude of the kink, a is the minor radius, and Ip is the plasma current. The equation for the growth of the halo current is dIh / dt =Ip /τg , where τg (μ0 /ηh) (a2 / 4) /seff and seff is a dimensionless stability coefficient. The rocket effect of the plasma flowing out of the two ends of the magnetic field lines in the halo can set the magnetic perturbation into toroidal rotation at a Mach number, Mh, comparable to unity. The rotation period is τr = (2 πR0 /Cs) /Mh , where R0 is the major radius and Cs =√{ (Te +Ti) /mi } is the speed of sound. NSTX results appear consistent for seff 0 . 5 , Mh 1 , and Te , i = 10 eV. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences under Award Number De-FG02-03ER54696.

  20. Evidence for core-halo decoupling in halo systems

    SciTech Connect

    Aguilera, E. F.; Kolata, J. J.; Acosta, L.

    2010-01-15

    Evidence is presented showing that for the {sup 6}He+{sup 209}Bi system, the reaction cross sections can be entirely accounted for by interactions of the halo state of {sup 6}He plus reactions that occur with the {sup 4}He core. These and similar conclusions about core-halo decoupling reported earlier for {sup 8}B+{sup 58}Ni are further supported by proving that no such decoupling occurs for reactions with {sup 17}O, whose valence neutron is rather weakly bound but does not form a halo. The preceding conclusions are based on comparisons with purely experimental data, using a quite reasonable scaling. Thus such a decoupling seems to stand out as a characteristic feature of true halo systems.

  1. 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.

  2. The evolution of disk galaxies in cold dark matter halos

    NASA Astrophysics Data System (ADS)

    Font, Andreea S.

    2005-11-01

    We use high resolution N-body simulations to investigate the dynamical effects that substructure in Cold Dark Matter (CDM) halos have on galactic disks, with particular emphasis on their secular evolution, heating, tilting and warping. The simulations analyzed here are some of the largest and most realistic simulations of disk heating/warping available in the appropriate cosmological context. Our detailed treatment of the dark matter distinguishes them from previous numerical simulations that have focused on the interaction with a single satellite. Our study shows that substructure halos with masses, densities and orbits expected in the CDM paradigm typically play only a minor dynamical role in the heating of the disk over several Gyrs, and thus do not typically pose a danger to the stability of thin disks. This is largely because the most massive dark satellites, which dominate the secular heating, seldom approach the disk, where tidal effects are strongest. Occasionally, however, massive subhalos couple effectively with the disk, resulting in noticeable tidal effects on the structure of the stellar disk, including: (i) tilting and (ii) the forcing of short-lived, asymmetric warps as a result of tidal impulses that arise during each pericentric passage. I show that this is a viable mechanism for creating asymmetric disk warps such as those observed in the local Universe. Moreover, the fact that a satellite can have recurrent interactions with the disk suggests a natural explanation for the observed frequency of the warps, which would otherwise be very short lived. I conclude that dark matter halo substructure does not preclude virialized CDM halos from being acceptable hosts of thin stellar disks like that of the Milky Way and that the ubiquity of minor stellar warps may be associated with the recurrent tidal influence on the disk of the most massive substructure halos.

  3. HOT GAS HALOS IN EARLY-TYPE FIELD GALAXIES

    SciTech Connect

    Mulchaey, John S.; Jeltema, Tesla E. E-mail: tesla@ucolick.or

    2010-05-20

    We use Chandra and XMM-Newton to study the hot gas content in a sample of field early-type galaxies. We find that the L {sub X}-L {sub K} relationship is steeper for field galaxies than for comparable galaxies in groups and clusters. The low hot gas content of field galaxies with L {sub K} {approx_lt} L {sub *} suggests that internal processes such as supernovae-driven winds or active galactic nucleus feedback expel hot gas from low-mass galaxies. Such mechanisms may be less effective in groups and clusters where the presence of an intragroup or intracluster medium can confine outflowing material. In addition, galaxies in groups and clusters may be able to accrete gas from the ambient medium. While there is a population of L {sub K} {approx_lt} L {sub *} galaxies in groups and clusters that retain hot gas halos, some galaxies in these rich environments, including brighter galaxies, are largely devoid of hot gas. In these cases, the hot gas halos have likely been removed via ram pressure stripping. This suggests a very complex interplay between the intragroup/intracluster medium and hot gas halos of galaxies in rich environments, with the ambient medium helping to confine or even enhance the halos in some cases and acting to remove gas in others. In contrast, the hot gas content of more isolated galaxies is largely a function of the mass of the galaxy, with more massive galaxies able to maintain their halos, while in lower mass systems the hot gas escapes in outflowing winds.

  4. Hyperfine Structure Constant of the Neutron Halo Nucleus Be+11

    NASA Astrophysics Data System (ADS)

    Takamine, A.; Wada, M.; Okada, K.; Sonoda, T.; Schury, P.; Nakamura, T.; Kanai, Y.; Kubo, T.; Katayama, I.; Ohtani, S.; Wollnik, H.; Schuessler, H. A.

    2014-04-01

    The hyperfine splittings of ground state Be+11 have been measured precisely by laser-microwave double resonance spectroscopy for trapped and laser cooled beryllium ions. The ions were produced at relativistic energies and subsequently slowed down and trapped at mK temperatures. The magnetic hyperfine structure constant of Be+11 was determined to be A11=-2677.302 988(72) MHz from the measurements of the mF-mF'=0-0 field independent transition. This measurement provides essential data for the study of the distribution of the halo neutron in the single neutron halo nucleus Be11 through the Bohr-Weisskopf effect.

  5. 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.

  6. Heliolatitude distribution of galactic cosmic rays

    SciTech Connect

    Antonucci, E.; Attolini, M.R.; Cecchini, S.; Galli, M.

    1985-08-01

    An analysis of the annual and semiannual variation of the galactic cosmic ray intensity has been performed for the period 1953-1979 by using the data from the Climax and Dourbes neutron monitors. This analysis, based on a method developed for searching periodicities and recurrences in the cosmic ray intensity, has confirmed the existence of such variations and their phase changes associated with the reversals of the solar magnetic dipole. Hence the importance in the cosmic ray transport of transverse diffusion arising from drift effects due to the curvature and gradient of the interplanetary magnetic field is confirmed, since this is the mechanism which can explain the dependence on the solar magnetic cycle. Such a mechanism is effective when the polarity configuration of the interplanetary magnetic field is well defined and stable. A phase advance of the semiannual variation is observed, which can be explained through the modulation of the heliolatitude distribution of cosmic rays by the activity of the solar magnetic regions migrating in both hemispheres toward the equator, during the 11-year cycle of solar activity. A residual annual variation, detectable when averaging out the effects of the magnetic cycle or when the polarity configuration of the interplanetary magnetic field is not well defined, probably indicates the existence of a preferential azimuthal direction for the access of low-energy galactic cosmic rays into the heliosphere, along the galactic magnetic field.

  7. The Fractions of Inner- and Outer-halo Stars in the Local Volume

    NASA Astrophysics Data System (ADS)

    An, Deokkeun; Beers, Timothy C.; Santucci, Rafael M.; Carollo, Daniela; Placco, Vinicius M.; Lee, Young Sun; Rossi, Silvia

    2015-11-01

    We obtain a new determination of the metallicity distribution function (MDF) of stars within ˜5-10 kpc of the Sun, based on recently improved co-adds of ugriz photometry for Stripe 82 from the Sloan Digital Sky Survey. Our new estimate uses the methodology developed previously by An et al. to study in situ halo stars, but is based on a factor of two larger sample than available before, with much-improved photometric errors and zero-points. The newly obtained MDF can be divided into multiple populations of halo stars, with peak metallicities at [Fe/H] ≈ -1.4 and -1.9, which we associate with the inner-halo and outer-halo populations of the Milky Way, respectively. We find that the kinematics of these stars (based on proper-motion measurements at high Galactic latitude) supports the proposed dichotomy of the halo, as stars with retrograde motions in the rest frame of the Galaxy are generally more metal-poor than stars with prograde motions, consistent with previous claims. In addition, we generate mock catalogs of stars from a simulated Milk Way halo system, and demonstrate for the first time that the chemically and kinematically distinct properties of the inner- and outer-halo populations are qualitatively in agreement with our observations. The decomposition of the observed MDF and our comparison with the mock catalog results suggest that the outer-halo population contributes on the order of ˜35%-55% of halo stars in the local volume.

  8. Supernumerary ice-crystal halos?

    PubMed

    Berry, M V

    1994-07-20

    Geometric-optics singularities in the intensity profiles of refraction halos formed by randomly oriented ice crystals are softened by diffraction and decorated with fine supernumerary fringes. If the crystals have a fixed symmetry axis (as in parhelia), the geometric singularity is a square-root divergence, as in the rainbow. However, the universal curve that describes diffraction is different from the rainbow's Airy function, with weak maxima (supernumerary fringes) on the geometrically dark region inside the halo (and even fainter fringes outside); these are much smaller than their counterparts on the light side of rainbows. If the crystals have no preferred orientation (as in the 22° halo), the geometric singularity is a step. In this case the universal diffraction function has no maxima, and its supernumeraries are shoulders rather than maxima. The low contrast of the fringes is probably the main reason why supernumerary halos are rarely if ever seen. PMID:20935824

  9. MAPPING THE STELLAR STRUCTURE OF THE MILKY WAY THICK DISK AND HALO USING SEGUE PHOTOMETRY

    SciTech Connect

    De Jong, Jelte T. A.; Rix, Hans-Walter; Martin, Nicolas F.; Yanny, Brian; Dolphin, Andrew E.; Beers, Timothy C.

    2010-05-01

    We map the stellar structure of the Galactic thick disk and halo by applying color-magnitude diagram (CMD) fitting to photometric data from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) survey. The SEGUE imaging scans allow, for the first time, a comprehensive analysis of Milky Way structure at both high and low latitudes using uniform Sloan Digital Sky Survey photometry. Incorporating photometry of all relevant stars simultaneously, CMD fitting bypasses the need to choose single tracer populations. Using old stellar populations of differing metallicities as templates, we obtain a sparse three-dimensional map of the stellar mass distribution at |Z|>1 kpc. Fitting a smooth Milky Way model comprising exponential thin and thick disks and an axisymmetric power-law halo allows us to constrain the structural parameters of the thick disk and halo. The thick-disk scale height and length are well constrained at 0.75 {+-} 0.07 kpc and 4.1 {+-} 0.4 kpc, respectively. We find a stellar halo flattening within {approx}25 kpc of c/a = 0.88 {+-} 0.03 and a power-law index of 2.75 {+-} 0.07 (for 7 kpc {approx_lt}R{sub GC} {approx_lt} 30 kpc). The model fits yield thick-disk and stellar halo densities at the solar location of {rho}{sub thick,sun} = 10{sup -2.3{+-}0.1} M{sub sun} pc{sup -3} and {rho}{sub halo,sun} = 10{sup -4.20{+-}0.05} M{sub sun} pc{sup -3}, averaging over any substructures. Our analysis provides the first clear in situ evidence for a radial metallicity gradient in the Milky Way's stellar halo: within R {approx_lt} 15 kpc the stellar halo has a mean metallicity of [Fe/H] {approx_equal} -1.6, which shifts to [Fe/H] {approx_equal} -2.2 at larger radii, in line with the two-component halo deduced by Carollo et al. from a local kinematic analysis. Subtraction of the best-fit smooth and symmetric model from the overall density maps reveals a wealth of substructures at all latitudes, some attributable to known streams and overdensities, and some

  10. Absolute proper motions to B approximately 22.5: Evidence for kimematical substructure in halo field stars

    NASA Technical Reports Server (NTRS)

    Majewski, Steven R.; Munn, Jeffrey A.; Hawley, Suzanne L.

    1994-01-01

    Radial velocities have been obtained for six of nine stars identified on the basis of similar distances and common, extreme transverse velocities in the proper motion survey of Majewski (1992) as a candidate halo moving group at the north Galactic pole. These radial velocities correspond to velocities perpendicular to the Galactic plane which span the range -48 +/- 21 to -128 +/- 9 km/sec (but a smaller range, -48 +/- 21 to -86 +/- 19 km/sec, when only our own measurements are considered), significantly different than the expected distribution, with mean 0 km/sec, for a random sample of either halo or thick disk stars. The probability of picking such a set of radial velocities at random is less than 1%. Thus the radial velocity data support the hypothesis that these stars constitute part of a halo moving group or star stream at a distance of approximately 4-5 kpc above the Galactic plane. If real, this moving group is evidence for halo phase space substructure which may be the fossil remains of a destroyed globular cluster, Galactic satellite, or Searle & Zinn (1978) 'fragment.'

  11. Analysis of the halo background in femtosecond slicing experiments.

    PubMed

    Schick, Daniel; Le Guyader, Loïc; Pontius, Niko; Radu, Ilie; Kachel, Torsten; Mitzner, Rolf; Zeschke, Thomas; Schüßler-Langeheine, Christian; Föhlisch, Alexander; Holldack, Karsten

    2016-05-01

    The slicing facility FemtoSpeX at BESSY II offers unique opportunities to study photo-induced dynamics on femtosecond time scales by means of X-ray magnetic circular dichroism, resonant and non-resonant X-ray diffraction, and X-ray absorption spectroscopy experiments in the soft X-ray regime. Besides femtosecond X-ray pulses, slicing sources inherently also produce a so-called `halo' background with a different time structure, polarization and pointing. Here a detailed experimental characterization of the halo radiation is presented, and a method is demonstrated for its correct and unambiguous removal from femtosecond time-resolved data using a special laser triggering scheme as well as analytical models. Examples are given for time-resolved measurements with corresponding halo correction, and errors of the relevant physical quantities caused by either neglecting or by applying a simplified model to describe this background are estimated. PMID:27140149

  12. MAGNETIZED GAS IN THE SMITH HIGH VELOCITY CLOUD

    SciTech Connect

    Hill, Alex S.; McClure-Griffiths, Naomi M.; Mao, S. A.; Benjamin, Robert A.; Lockman, Felix J. E-mail: naomi.mcclure-griffiths@csiro.au E-mail: benjamir@uww.edu

    2013-11-01

    We report the first detection of magnetic fields associated with the Smith High Velocity Cloud. We use a catalog of Faraday rotation measures toward extragalactic radio sources behind the Smith Cloud, new H I observations from the Robert C. Byrd Green Bank Telescope, and a spectroscopic map of Hα from the Wisconsin H-Alpha Mapper Northern Sky Survey. There are enhancements in rotation measure (RM) of ≈100 rad m{sup –2} which are generally well correlated with decelerated Hα emission. We estimate a lower limit on the line-of-sight component of the field of ≈8 μG along a decelerated filament; this is a lower limit due to our assumptions about the geometry. No RM excess is evident in sightlines dominated by H I or Hα at the velocity of the Smith Cloud. The smooth Hα morphology of the emission at the Smith Cloud velocity suggests photoionization by the Galactic ionizing radiation field as the dominant ionization mechanism, while the filamentary morphology and high (≈1 Rayleigh) Hα intensity of the lower-velocity magnetized ionized gas suggests an ionization process associated with shocks due to interaction with the Galactic interstellar medium. The presence of the magnetic field may contribute to the survival of high velocity clouds like the Smith Cloud as they move from the Galactic halo to the disk. We expect these data to provide a test for magnetohydrodynamic simulations of infalling gas.

  13. X-ray inverse Compton emission from the radio halo of M87

    NASA Technical Reports Server (NTRS)

    Feigelson, E. D.

    1984-01-01

    A significant fraction of known galaxies contain an active galactic nucleus (AGN) at their cores, the site of violent activity and non-stellar radiation seen across the entire electromagnetic spectrum. This activity is thought to be due to the accretion of gas onto a massive black hole. A fraction of AGNs also eject collimated beams of energetic material, usually seen by virtue of its synchrotron emission in the radio band. Efforts to study these jets from AGNs in the X-ray band with the Einstein Observatory has led to several detections, most notably the jets in the nearby radio galaxies Centaurus A and Virgo A = M87. In their study of M87, Schreier, Gorenstein and Feigelson (1982) noted that, in addition to the synchrotron jet 10"-20" from the nucleus, X-rays appear to be generated in the diffuse radio halo 2'-5' from the nucleus. This finding may be particularly important as it may constitute the first known case of X-ray inverse Compton emission from AGN ejecta, allowing for the first time direct determination of the magnetic field strengths.

  14. The Case for the Dual Halo of the Milky Way

    SciTech Connect

    Beers, Timothy C.; Carollo, Daniela; Ivezic, Zeljko; An, Deokkeun; Chiba, Masashi; Norris, John E.; Freeman, Ken C.; Lee, Young Sun; Munn, Jeffrey A.; Fiorentin, Paola Re; Sivarani, Thirupathi; /Bangalore, Indian Inst. Astrophys. /Kentucky U.

    2011-04-01

    similar to those previously derived. An additional test of the reality of the retrograde signature is provided, based exclusively on the observed proper motions of low-metallicity stars. Further evidence for a complex halo comes from inspection of the metallicity distribution function of the Carollo et al. sample as a function of distance from the Galactic plane. We summarize additional lines of evidence for a dual halo, based on different stellar samples from the SDSS and other surveys. We conclude that the overwhelming body of evidence rejects the single-halo interpretation beyond reasonable doubt.

  15. Star counts as an indicator of galactic structure and quasar evolution

    NASA Technical Reports Server (NTRS)

    Bahcall, J. N.; Soneira, R. M.

    1980-01-01

    A detailed model of the stellar content of the Galaxy is described briefly. Illustrative applications of the model are made, using existing data, to indicate how star counts can be used to determine some parameters of galactic structure, to detect a massive (stellar) halo, and to constrain models of quasar evolution.

  16. Results from the Arecibo Galactic HI Survey (GALFA-HI)

    NASA Astrophysics Data System (ADS)

    Begum, Ayesha; Ballering, N.; Stanimirovic, S.; Douglas, K.; Gibson, S. J.; Grcevich, J.; Heiles, C.; Korpela, E.; Lee, M.; Peek, J. E. G.; Putman, M. E.

    2009-12-01

    The consortium for Galactic studies with the Arecibo L-band Feed Array (ALFA) is conducting a neutral hydrogen survey of the whole Arecibo sky (declination range from -1 to 38 deg), over a velocity range of -700 to +700 km/s, with high angular (3.5 arcmin) and velocity resolution (0.2 km/s). We present highlights from TOGS (Turn On GALFA Survey), the largest portion of GALFA-HI, which is covering thousands of square degrees in commensal drift scan observations with the ALFALFA and AGES extragalactic ALFA surveys. The unprecedented resolution and sensitivity of our survey resulted in the detection of numerous isolated, ultra-compact HI clouds at low Galactic velocities, which are distinctly separated from the HI disk emission. We will discuss properties of this population, and their role in the interplay between the Galactic disk and halo.

  17. The Chemical Composition of Halo Stars on Extreme Orbits

    NASA Astrophysics Data System (ADS)

    Stephens, Alex

    1999-04-01

    Presented within is a fine spectroscopic analysis of 11 metal-poor (-2.15<[Fe/H]<-1.00) dwarf stars on orbits that penetrate the outermost regions of the Galactic halo. Abundances for a select group of light metals (Na, Mg, Si, Ca, and Ti), Fe-peak nuclides (Cr, Fe, and Ni), and neutron-capture elements (Y and Ba) were calculated using line strengths measured from high-resolution (R~48,000), high signal-to-noise ratio (S/N~110pixel^-1) echelle spectra acquired with the Keck I 10 m telescope and HIRES spectrograph. Ten of the stars have apogalactica, a proxy for stellar birthplace, which stretch between 25 and 90 kpc; however, these ``outer halo'' stars exhibit strikingly uniform abundances. The average, Fe-normalized abundances-<[Mg/Fe]>=+0.23+/-0.09, <[Si/Fe]>=+0.24+/-0.10, <[Ca/Fe]>=+0.22+/-0.07, <[Ti/Fe]>=+0.20+/-0.08, <[Cr/Fe]>=0.02+/-0.07, <[Ni/Fe]>=-0.09+/-0.07, and <[Ba/Fe]>=+0.01+/-0.12-exhibit little intrinsic scatter; moreover, the evolution of individual ratios (as a function of [Fe/H]) is generally consistent with the predictions of galactic chemical evolution models dominated by the ejecta of core-collapse supernovae. Only <[Y/Fe]>=-0.13+/-0.21 exhibits a dispersion larger than observational uncertainties, which suggests a different nucleosynthesis site for this element. It has been conjectured that stars on high-energy orbits-either those that penetrate the remote halo or ones with extreme retrograde velocities-were once associated with a cannibalized satellite galaxy. Such stars, as shown here, are indistinguishable from metal-poor dwarfs of the inner Galactic halo. The uniformity of the abundances, regardless of kinematic properties, suggests that physically, spatially, and temporally distinct star-forming regions within (or near) the growing Milky Way experienced grossly similar chemical evolution histories. Implications for galaxy formation scenarios are discussed.

  18. The kinetic Sunyaev-Zel'dovich effect of the milky way halo

    SciTech Connect

    Birnboim, Yuval; Loeb, Abraham E-mail: aloeb@cfa.harvard.edu

    2009-06-01

    We calculate the expected imprint of the ionized gas in the Milky-Way halo on the Cosmic Microwave Background (CMB) through the kinetic Sunyaev-Zel'dovich (kSZ) effect. Unlike other Galactic foregrounds, the halo kSZ signature covers the full sky, generates anisotropies on large angular scales, is not accompanied by spectral distortions, and could therefore be confused with primordial CMB anisotropies. We construct theoretical models for various halo components, including smooth diffuse gas, filaments of cold inflowing gas and high velocity clouds. We find that the kSZ effect for all components is above the sensitivity of the Planck satellite, over a range of angular scales. However, the typical halo contribution is well below the cosmic variance noise in the primordial CMB power spectrum. High velocity clouds could dominate the halo contribution and better observational data is required to mask them out. We derive expected kSZ maps based on existing data from tracers of the halo gas distribution, such as 21cm maps of neutral hydrogen and H{sub α} maps of recombining gas. The cross-correlation of these maps with the WMAP5 data does not yield any statistically significant signal.

  19. A DEEP X-RAY VIEW OF THE HOT HALO IN THE EDGE-ON SPIRAL GALAXY NGC 891

    SciTech Connect

    Hodges-Kluck, Edmund J.; Bregman, Joel N.

    2013-01-01

    NGC 891 is a nearby edge-on galaxy that is similar to the Milky Way and has a hot X-ray-emitting halo that could arise from accretion, a galactic fountain, or a combination of the two. The metallicity of the gas can help distinguish between these models, and here we report on results that use 138 ks of archival Chandra data and 92 ks of new XMM-Newton data to measure the temperature and metallicity of the hot halo of the galaxy. We find good fits for a thermal model with kT {approx} 0.2 keV and Z {approx} 0.1 Z {sub Sun }, and rule out solar metallicity to more than 99% confidence. This result suggests accretion from the intergalactic medium as the origin for the hot halo. However, it is also possible to fit a two-temperature thermal model with solar metallicity where kT {sub 1} {approx} 0.1 keV and kT {sub 2} {approx} 0.25 keV. A consideration of the cooling rate and scale height prefers the single-temperature model. We also find that the cooling rate in the hot gas cannot explain the massive H I halo in the steady state. In addition, a galactic fountain model cannot eject enough mass to account for the H I halo, and we speculate that the neutral halo may be gas from a prior outflow that has since cooled.

  20. Chemical Tagging in the SDSS-III/APOGEE Survey: New Identifications of Halo Stars with Globular Cluster Origins

    NASA Astrophysics Data System (ADS)

    Martell, Sarah L.; Shetrone, Matthew D.; Lucatello, Sara; Schiavon, Ricardo P.; Mészáros, Szabolcs; Allende Prieto, Carlos; García Hernández, D. A.; Beers, Timothy C.; Nidever, David L.

    2016-07-01

    We present new identifications of five red giant stars in the Galactic halo with chemical abundance patterns that indicate they originally formed in globular clusters. Using data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) Survey available through Sloan Digital Sky Survey (SDSS) Data Release 12, we first identify likely halo giants, and then search those for the well-known chemical tags associated with globular clusters, specifically enrichment in nitrogen and aluminum. We find that 2% of the halo giants in our sample have this chemical signature, in agreement with previous results. Following the interpretation in our previous work on this topic, this would imply that at least 13% of halo stars originally formed in globular clusters. Recent developments in the theoretical understanding of globular cluster formation raise questions about that interpretation, and we concede the possibility that these migrants represent a small fraction of the halo field. There are roughly as many stars with the chemical tags of globular clusters in the halo field as there are in globular clusters, whether or not they are accompanied by a much larger chemically untaggable population of former globular cluster stars.

  1. SAS-2 galactic gamma-ray results. 1: Diffuse emission

    NASA Technical Reports Server (NTRS)

    Thompson, D. J.; Fichtel, C. E.; Hartman, R. C.; Kniffen, D. A.; Bignami, G. F.; Lamb, R. C.; Oegelman, H.; Oezel, M. E.; Tuemer, T.

    1977-01-01

    Continuing analysis of the data from the SAS-2 high energy gamma ray experiment has produced an improved picture of the sky at photon energies above 35 MeV. On a large scale, the diffuse emission from the galactic plane is the dominant feature observed by SAS-2. This galactic plane emission is most intense between galactic longitudes 310 deg and 45 deg, corresponding to a region within 7 kpc of the galactic center. Within the high-intensity region, SAS-2 observes peaks around galactic longitudes 315, 330, 345, 0, and 35 deg. These peaks appear to be correlated with galactic features and components such as molecular hydrogen, atomic hydrogen, magnetic fields, cosmic-ray concentrations, and photon fields.

  2. Stellar populations of stellar halos: Results from the Illustris simulation

    NASA Astrophysics Data System (ADS)

    Cook, B. A.; Conroy, C.; Pillepich, A.; Hernquist, L.

    2016-08-01

    The influence of both major and minor mergers is expected to significantly affect gradients of stellar ages and metallicities in the outskirts of galaxies. Measurements of observed gradients are beginning to reach large radii in galaxies, but a theoretical framework for connecting the findings to a picture of galactic build-up is still in its infancy. We analyze stellar populations of a statistically representative sample of quiescent galaxies over a wide mass range from the Illustris simulation. We measure metallicity and age profiles in the stellar halos of quiescent Illustris galaxies ranging in stellar mass from 1010 to 1012 M ⊙, accounting for observational projection and luminosity-weighting effects. We find wide variance in stellar population gradients between galaxies of similar mass, with typical gradients agreeing with observed galaxies. We show that, at fixed mass, the fraction of stars born in-situ within galaxies is correlated with the metallicity gradient in the halo, confirming that stellar halos contain unique information about the build-up and merger histories of galaxies.

  3. 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.