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  • 1.
    Dieckmann, Mark E
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Folini, Doris
    École Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, Lyon, France .
    Hotz, Ingrid
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Nordman, Aida
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Dell'Acqua, Pierangelo
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Ynnerman, Anders
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Walder, Rolf
    École Normale Supérieure, Lyon, CRAL, UMR CNRS 5574, Université de Lyon, Lyon, France .
    Structure of a collisionless pair jet in a magnetized electron–proton plasma: flow-aligned magnetic field2019In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 621, article id A142Article in journal (Refereed)
    Abstract [en]

    Aims. We study the effect a guiding magnetic field has on the formation and structure of a pair jet that propagates through a collisionless electron–proton plasma at rest.

    Methods. We model with a particle-in-cell (PIC) simulation a pair cloud with a temperature of 400 keV and a mean speed of 0.9c (c - light speed). Pair particles are continuously injected at the boundary. The cloud propagates through a spatially uniform, magnetized, and cool ambient electron–proton plasma at rest. The mean velocity vector of the pair cloud is aligned with the uniform background magnetic field. The pair cloud has a lateral extent of a few ion skin depths.

    Results. A jet forms in time. Its outer cocoon consists of jet-accelerated ambient plasma and is separated from the inner cocoon by an electromagnetic piston with a thickness that is comparable to the local thermal gyroradius of jet particles. The inner cocoon consists of pair plasma, which lost its directed flow energy while it swept out the background magnetic field and compressed it into the electromagnetic piston. A beam of electrons and positrons moves along the jet spine at its initial speed. Its electrons are slowed down and some positrons are accelerated as they cross the head of the jet. The latter escape upstream along the magnetic field, which yields an excess of megaelectronvolt positrons ahead of the jet. A filamentation instability between positrons and protons accelerates some of the protons, which were located behind the electromagnetic piston at the time it formed, to megaelectronvolt energies.

    Conclusions. A microscopic pair jet in collisionless plasma has a structure that is similar to that predicted by a hydrodynamic model of relativistic astrophysical pair jets. It is a source of megaelectronvolt positrons. An electromagnetic piston acts as the contact discontinuity between the inner and outer cocoons. It would form on subsecond timescales in a plasma with a density that is comparable to that of the interstellar medium in the rest frame of the latter. A supercritical fast magnetosonic shock will form between the pristine ambient plasma and the jet-accelerated plasma on a timescale that exceeds our simulation time by an order of magnitude.

  • 2.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    Murphy, Gareth
    Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland .
    Meli, Athina
    Center for Astroparticle Physics, Friedrich-Alexander-University Erlangen-Nuremberg, 91058 Erlangen, Germany .
    Drury, Luke O'C
    Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland .
    Particle-in-cell simulation of a mildly relativistic collision of an electron-ion plasma carrying a quasi-parallel magnetic field: Electron acceleration and magnetic field amplification at supernova shocks2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 509, no 1, p. A89-Article in journal (Refereed)
    Abstract [en]

    Context. Plasma processes close to supernova remnant shocks result in the amplification of magnetic fields and in the acceleration of electrons, injecting them into the diffusive acceleration mechanism.

    Aims. The acceleration of electrons and the magnetic field amplification by the collision of two plasma clouds, each consisting of electrons and ions, at a speed of 0.5c is investigated. A quasi-parallel guiding magnetic field, a cloud density ratio of 10 and a plasma temperature of 25 keV are considered.

    Methods. A relativistic and electromagnetic particle-in-cell simulation models the plasma in two spatial dimensions employing an ion-to-electron mass ratio of 400.

    Results. A quasi-planar shock forms at the front of the dense plasma cloud. It is mediated by a circularly left-hand polarized electromagnetic wave with an electric field component along the guiding magnetic field. Its propagation direction is close to that of the guiding field and orthogonal to the collision boundary. It has a frequency too low to be determined during the simulation time and a wavelength that equals several times the ion inertial length. These properties would be indicative of a dispersive Alfvén wave close to the ion cyclotron resonance frequency of the left-handed mode, known as the ion whistler, provided that the frequency is appropriate. However, it moves with the super-alfvénic plasma collision speed, suggesting that it is an Alfvén precursor or a nonlinear MHD wave such as a Short Large-Amplitude Magnetic Structure (SLAMS). The growth of the magnetic amplitude of this wave to values well in excess of those of the quasi-parallel guiding field and of the filamentation modes results in a quasi-perpendicular shock. We present evidence for the instability of this mode to a four wave interaction. The waves developing upstream of the dense cloud give rise to electron acceleration ahead of the collision boundary. Energy equipartition between the ions and the electrons is established at the shock and the electrons are accelerated to relativistic speeds.

    Conclusions. The magnetic fields in the foreshock of supernova remnant shocks can be amplified substantially and electrons can be injected into the diffusive acceleration, if strongly magnetised plasma subshells are present in the foreshock, with velocities an order of magnitude faster than the main shell.

  • 3.
    Dieckmann, Mark Eric
    et al.
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, Faculty of Science & Engineering.
    Sarri, Gianluca
    Queen's University Belfast. BT7 1NN, Belfast, United Kingdom.
    Markoff, Sera
    University of Amsterdam, 1098 XH Amsterdam, The Netherlands.
    Borghesi, Marco
    Queen's University Belfast, BT7 1NN, Belfast, United Kingdom.
    Zepf, Matt
    Queen's University Belfast, BT7 1NN, Belfast, United Kingdom.
    PIC simulation study of the interaction between a relativisticallymoving leptonic micro-cloud and ambient electrons.2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 577, no A137, p. 1-10Article in journal (Refereed)
    Abstract [en]

    Context. The jets of compact accreting objects are composed of electrons and a mixture of positrons and ions. These outflows impinge on the interstellar or intergalactic medium and both plasmas interact via collisionless processes. Filamentation (beam-Weibel) instabilities give rise to the growth of strong electromagnetic fields. These fields thermalize the interpenetrating plasmas.

    Aims. Hitherto, the effects imposed by a spatial non-uniformity on filamentation instabilities have remained unexplored. We examine the interaction between spatially uniform background electrons and a minuscule cloud of electrons and positrons. The cloud size is comparable to that created in recent laboratory experiments and such clouds may exist close to internal and external shocks of leptonic jets. The purpose of our study is to determine the prevalent instabilities, their ability to generate electromagnetic fields and the mechanism, by which the lepton micro-cloud transfers energy to the background plasma.

    Methods. A square micro-cloud of equally dense electrons and positrons impinges in our particle-in-cell (PIC) simulation on a spatially uniform plasma at rest. The latter consists of electrons with a temperature of 1 keV and immobile ions. The initially charge- and current neutral micro-cloud has a temperature of 100 keV and a side length of 2.5 plasma skin depths of the micro-cloud. The side length is given in the reference frame of the background plasma. The mean speed of the micro-cloud corresponds to a relativistic factor of 15, which is relevant for laboratory experiments and for relativistic astrophysical outflows. The spatial distributions of the leptons and of the electromagnetic fields are examined at several times.

    Results. A filamentation instability develops between the magnetic field carried by the micro-cloud and the background electrons. The electromagnetic fields, which grow from noise levels, redistribute the electrons and positrons within the cloud, which boosts the peak magnetic field amplitude. The current density and the moduli of the electromagnetic fields grow aperiodically in time and steadily along the direction that is anti-parallel to the cloud’s velocity vector. The micro-cloud remains conjoined during the simulation. The instability induces an electrostatic wakefield in the background plasma.

    Conclusions. Relativistic clouds of leptons can generate and amplify magnetic fields even if they have a microscopic size, which implies that the underlying processes can be studied in the laboratory. The interaction of the localized magnetic field and high-energy leptons will give rise to synchrotron jitter radiation. The wakefield in the background plasma dissipates the kinetic energy of the lepton cloud. Even the fastest lepton micro-clouds can be slowed down by this collisionless mechanism. Moderately fast charge- and current neutralized lepton micro–clouds will deposit their energy close to relativistic shocks and hence they do not constitute an energy loss mechanism for the shock.

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  • 4.
    Garcia-Benito, R.
    et al.
    CSIC, Spain.
    Zibetti, S.
    INAF Osservatorio Astrofis Arcetri, Italy.
    Sanchez, S. F.
    University of Nacl Autonoma Mexico, Mexico.
    Husemann, B.
    European So Observ, Germany.
    de Amorim, A. L.
    University of Federal Santa Catarina, Brazil.
    Castillo-Morales, A.
    University of Complutense Madrid, Spain.
    Cid Fernandes, R.
    University of Federal Santa Catarina, Brazil.
    Ellis, S. C.
    Australian Astron Observ, Australia.
    Falcon-Barroso, J.
    Institute Astrofis Canarias, Spain; University of La Laguna, Spain.
    Galbany, L.
    University of Chile, Chile; University of Chile, Chile.
    Gil de Paz, A.
    University of Complutense Madrid, Spain.
    Gonzalez Delgado, R. M.
    CSIC, Spain.
    Lacerda, E. A. D.
    University of Federal Santa Catarina, Brazil.
    Lopez-Fernandez, R.
    CSIC, Spain.
    de Lorenzo-Caceres, A.
    University of St Andrews, Scotland.
    Lyubenova, M.
    University of Groningen, Netherlands; Max Planck Institute Astron, Germany.
    Marino, R. A.
    University of Complutense Madrid, Spain.
    Mast, D.
    Centre Brasileiro Pesquisas Fis, Brazil.
    Mendoza, M. A.
    CSIC, Spain.
    Perez, E.
    CSIC, Spain.
    Vale Asari, N.
    University of Federal Santa Catarina, Brazil.
    Aguerri, J. A. L.
    Institute Astrofis Canarias, Spain; University of La Laguna, Spain.
    Ascasibar, Y.
    Autonomous University of Madrid, Spain.
    Bekeraite, S.
    Leibniz Institute Astrophys Potsdam AIP, Germany.
    Bland-Hawthorn, J.
    University of Sydney, Australia.
    Barrera-Ballesteros, J. K.
    Institute Astrofis Canarias, Spain; University of La Laguna, Spain.
    Bomans, D. J.
    Ruhr University of Bochum, Germany; RUB Research Department Plasmas Complex Interact, Germany.
    Cano-Diaz, M.
    University of Nacl Autonoma Mexico, Mexico.
    Catalan-Torrecilla, C.
    University of Complutense Madrid, Spain.
    Cortijo, C.
    CSIC, Spain.
    Delgado-Inglada, G.
    University of Nacl Autonoma Mexico, Mexico.
    Demleitner, M.
    Heidelberg University, Germany.
    Dettmar, R. -J.
    Ruhr University of Bochum, Germany; RUB Research Department Plasmas Complex Interact, Germany.
    Diaz, A. I.
    Autonomous University of Madrid, Spain.
    Florido, E.
    University of Groningen, Netherlands; University of Granada, Spain.
    Gallazzi, A.
    INAF Osservatorio Astrofis Arcetri, Italy; University of Copenhagen, Denmark.
    Garcia-Lorenzo, B.
    Institute Astrofis Canarias, Spain; University of La Laguna, Spain.
    Gomes, J. M.
    University of Porto, Portugal.
    Holmes, L.
    Royal Mil Coll Canada, Canada.
    Iglesias-Paramo, J.
    CSIC, Spain; CSIC, Spain.
    Jahnke, K.
    Max Planck Institute Astron, Germany.
    Kalinova, V.
    University of Alberta, Canada.
    Kehrig, C.
    CSIC, Spain.
    Kennicutt, R. C. Jr.
    University of Cambridge, England.
    Lopez-Sanchez, A. R.
    Australian Astron Observ, Australia; Macquarie University, Australia.
    Marquez, I.
    CSIC, Spain.
    Masegosa, J.
    CSIC, Spain.
    Meidt, S. E.
    Max Planck Institute Astron, Germany.
    Mendez-Abreu, J.
    University of St Andrews, Scotland.
    Molla, M.
    CIEMAT, Spain.
    Monreal-Ibero, A.
    University of Paris Diderot, France.
    Morisset, C.
    University of Nacl Autonoma Mexico, Mexico.
    del Olmo, A.
    CSIC, Spain.
    Papaderos, P.
    University of Porto, Portugal.
    Perez, I.
    University of Granada, Spain; University of Granada, Spain.
    Quirrenbach, A.
    Heidelberg University, Germany.
    Rosales-Ortega, F. F.
    Institute Nacl Astrofis Opt and Electr, Mexico.
    Roth, M. M.
    Leibniz Institute Astrophys Potsdam AIP, Germany.
    Ruiz-Lara, T.
    University of Granada, Spain; University of Granada, Spain.
    Sanchez-Blazquez, P.
    Autonomous University of Madrid, Spain.
    Sanchez-Menguiano, L.
    CSIC, Spain; University of Granada, Spain.
    Singh, R.
    Max Planck Institute Astron, Germany.
    Spekkens, K.
    Royal Mil Coll Canada, Canada.
    Stanishev, Vallery
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Institute Super Tecn, Portugal.
    Torres-Papaqui, J. P.
    University of Guanajuato, Mexico.
    van de Ven, G.
    Max Planck Institute Astron, Germany.
    Vilchez, J. M.
    CSIC, Spain.
    Walcher, C. J.
    Leibniz Institute Astrophys Potsdam AIP, Germany.
    Wild, V.
    University of St Andrews, Scotland.
    Wisotzki, L.
    Leibniz Institute Astrophys Potsdam AIP, Germany.
    Ziegler, B.
    University of Vienna, Austria.
    Alves, J.
    University of Vienna, Austria.
    Barrado, D.
    CSIC, Spain.
    Quintana, J. M.
    CSIC, Spain.
    Aceituno, J.
    CSIC, Spain.
    CALIFA, the Calar Alto Legacy Integral Field Area survey III. Second public data release2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 576, no A135Article in journal (Refereed)
    Abstract [en]

    This paper describes the Second Public Data Release (DR2) of the Calar Alto Legacy Integral Field Area (CALIFA) survey. The data for 200 objects are made public, including the 100 galaxies of the First Public Data Release (DR1). Data were obtained with the integral-field spectrograph PMAS /PPak mounted on the 3.5 m telescope at the Calar Alto observatory. Two different spectral setups are available for each galaxy, (i) a low-resolution V500 setup covering the wavelength range 3745-7500 angstrom with a spectral resolution of 6.0 angstrom (FWHM); and (ii) a medium-resolution V1200 setup covering the wavelength range 3650-4840 angstrom with a spectral resolution of 2.3 angstrom (FWHM). The sample covers a redshift range between 0.005 and 0.03, with a wide range of properties in the color-magnitude diagram, stellar mass, ionization conditions, and morphological types. All the cubes in the data release were reduced with the latest pipeline, which includes improved spectrophotometric calibration, spatial registration, and spatial resolution. The spectrophotometric calibration is better than 6% and the median spatial resolution is 2 4. In total, the second data release contains over 1.5 million spectra.

  • 5.
    Murphy, GC
    et al.
    Dublin Institute for Advanced Studies (DIAS), Dublin 2, Ireland.
    Dieckmann, Mark Eric
    Linköping University, Department of Science and Technology, Media and Information Technology. Linköping University, The Institute of Technology.
    Bret, Antoine
    ETSI Industriales Universidad de Castilla-La Mancha, 13071 Ciudad Real, Spain.
    Drury, LOC
    Dublin Institute for Advanced Studies (DIAS), Dublin 2, Ireland.
    Magnetic field amplification and electron acceleration to near-energy equipartition with ions by a mildly relativistic quasi-parallel plasma protoshock2010In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 524, p. A84-Article in journal (Refereed)
    Abstract [en]

    Context. The prompt emissions of gamma-ray bursts (GRBs) are seeded by radiating ultrarelativistic electrons. Kinetic energy dominated internal shocks propagating through a jet launched by a stellar implosion, are expected to dually amplify the magnetic field and accelerate electrons.

    Aims. We explore the effects of density asymmetry and of a quasi-parallel magnetic field on the collision of two plasma clouds.

    Methods. A two-dimensional relativistic particle-in-cell (PIC) simulation models the collision with 0.9c of two plasma clouds, in the presence of a quasi-parallel magnetic field. The cloud density ratio is 10. The densities of ions and electrons and the temperature of 131 keV are equal in each cloud, and the mass ratio is 250. The peak Lorentz factor of the electrons is determined, along with the orientation and the strength of the magnetic field at the cloud collision boundary.

    Results. The magnetic field component orthogonal to the initial plasma flow direction is amplified to values that exceed those expected from the shock compression by over an order of magnitude. The forming shock is quasi-perpendicular due to this amplification, caused by a current sheet which develops in response to the differing deflection of the upstream electrons and ions incident on the magnetised shock transition layer. The electron deflection implies a charge separation of the upstream electrons and ions; the resulting electric field drags the electrons through the magnetic field, whereupon they acquire a relativistic mass comparable to that of the ions. We demonstrate how a magnetic field structure resembling the cross section of a flux tube grows self-consistently in the current sheet of the shock transition layer. Plasma filamentation develops behind the shock front, as well as signatures of orthogonal magnetic field striping, indicative of the filamentation instability. These magnetic fields convect away from the shock boundary and their energy density exceeds by far the thermal pressure of the plasma. Localized magnetic bubbles form.

    Conclusions. Energy equipartition between the ion, electron and magnetic energy is obtained at the shock transition layer. The electronic radiation can provide a seed photon population that can be energized by secondary processes (e.g. inverse Compton).

  • 6.
    Petrushevska, T.
    et al.
    Stockholm University, Sweden.
    Amanullah, R.
    Stockholm University, Sweden.
    Goobar, A.
    Stockholm University, Sweden.
    Fabbro, S.
    NRC Herzberg Institute Astrophys, Canada.
    Johansson, J.
    Weizmann Institute Science, Israel.
    Kjellsson, T.
    Stockholm University, Sweden.
    Lidman, C.
    Australian Astron Observ, Australia.
    Paech, K.
    Ludwig Maximilians University of Munchen, Germany; Excellence Cluster University, Germany.
    Richard, J.
    University of Lyon 1, France.
    Dahle, H.
    University of Oslo, Norway.
    Ferretti, R.
    Stockholm University, Sweden.
    Kneib, J. P.
    EPFL, Switzerland.
    Limousin, M.
    University of Provence, France.
    Nordin, J.
    Humboldt University, Germany.
    Stanishev, Vallery
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    High-redshift supernova rates measured with the gravitational telescope A 16892016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 594, article id A54Article in journal (Refereed)
    Abstract [en]

    Aims. We present a ground-based, near-infrared search for lensed supernovae behind the massive cluster Abell 1689 at z = 0.18, which is one of the most powerful gravitational telescopes that nature provides. Methods. Our survey was based on multi-epoch J-band observations with the HAWK-I instrument on VLT, with supporting optical data from the Nordic Optical Telescope. Results. Our search resulted in the discovery of five photometrically classified, core-collapse supernovae with high redshifts of 0.671 amp;lt; z amp;lt; 1.703 and magnifications in the range Delta m = -0.31 to -1.58 mag, as calculated from lensing models in the literature. Owing to the power of the lensing cluster, the survey had the sensitivity to detect supernovae up to very high redshifts, z similar to 3, albeit for a limited region of space. We present a study of the core-collapse supernova rates for 0.4 amp;lt; z amp;lt; 2.9, and find good agreement with previous estimates and predictions from star formation history. During our survey, we also discovered two Type Ia supernovae in A 1689 cluster members, which allowed us to determine the cluster Ia rate to be 0.14(-0.09)(+0.19) SNuB h(2) (SNuB 10(-12) SNe L-circle dot,B(-1) yr(-1)), where the error bars indicate 1 sigma confidence intervals, statistical and systematic, respectively. The cluster rate normalized by the stellar mass is 0.10(-0.06)(+0.13) +/- 0.02 in SNuM h(2) (SNuM = 10(-12) SNe M-1 yr(-1)). Furthermore, we explore the optimal future survey for improving the core-collapse supernova rate measurements at z greater than or similar to 2 using gravitational telescopes, and for detections with multiply lensed images, and we find that the planned WFIRST space mission has excellent prospects. Conclusions. Massive clusters can be used as gravitational telescopes to significantly expand the survey range of supernova searches, with important implications for the study of the high-z transient Universe.

  • 7.
    Sanchez-Menguiano, L.
    et al.
    CSIC, Spain; University of Granada, Spain.
    Sanchez, S. F.
    University of Nacl Autonoma Mexico, Mexico.
    Perez, I.
    University of Granada, Spain.
    Garcia-Benito, R.
    CSIC, Spain.
    Husemann, B.
    European So Observ, Germany.
    Mast, D.
    ICRA, Brazil; University of Nacl Cordoba, Argentina.
    Mendoza, A.
    CSIC, Spain.
    Ruiz-Lara, T.
    University of Granada, Spain.
    Ascasibar, Y.
    University of Autonoma Madrid, Spain; UAM, Spain.
    Bland-Hawthorn, J.
    University of Sydney, Australia.
    Cavichia, O.
    University of Federal Itajuba, Brazil.
    Diaz, A. I.
    University of Autonoma Madrid, Spain; UAM, Spain.
    Florido, E.
    University of Granada, Spain.
    Galbany, L.
    Millennium Institute Astrophys MAS, Chile; University of Chile, Chile.
    Gonzalez Delgado, R. M.
    CSIC, Spain.
    Kehrig, C.
    CSIC, Spain.
    Marino, R. A.
    University of Complutense Madrid, Spain; Swiss Federal Institute Technology, Switzerland.
    Marquez, I.
    CSIC, Spain.
    Masegosa, J.
    CSIC, Spain.
    Mendez-Abreu, J.
    University of St Andrews, Scotland.
    Molla, M.
    CIEMAT, Spain.
    del Olmo, A.
    CSIC, Spain.
    Perez, E.
    CSIC, Spain.
    Sanchez-Blazquez, P.
    University of Autonoma Madrid, Spain; UAM, Spain.
    Stanishev, Vallery
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering.
    Walcher, C. J.
    Leibniz Institute Astrophys Potsdam AIP, Germany.
    Lopez-Sanchez, A. R.
    Australian Astron Observ, Australia; Macquarie University, Australia.
    Shape of the oxygen abundance profiles in CALIFA face-on spiral galaxies2016In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, no A70Article in journal (Refereed)
    Abstract [en]

    We measured the gas abundance profiles in a sample of 122 face-on spiral galaxies observed by the CALIFA survey and included all spaxels whose line emission was consistent with star formation. This type of analysis allowed us to improve the statistics with respect to previous studies, and to properly estimate the oxygen distribution across the entire disc to a distance of up to 3 4 disc effective radii (r(e)). We confirm the results obtained from classical H II region analysis. In addition to the general negative gradient, an outer flattening can be observed in the oxygen abundance radial profile. An inner drop is also found in some cases. There is a common abundance gradient between 0.5 and 2.0 r(e) of alpha(O/H) = -0.075 dex/r(e) with a scatter of sigma = 0.016 dex/r(e) when normalising the distances to the disc effective radius. By performing a set of Kolmogorov-Smirnov tests, we determined that this slope is independent of other galaxy properties, such as morphology, absolute magnitude, and the presence or absence of bars. In particular, barred galaxies do not seem to display shallower gradients, as predicted by numerical simulations. Interestingly, we find that most of the galaxies in the sample with reliable oxygen abundance values beyond similar to 2 effective radii (57 galaxies) present a flattening of the abundance gradient in these outer regions. This flattening is not associated with any morphological feature, which suggests that it is a common property of disc galaxies. Finally, we detect a drop or truncation of the abundance in the inner regions of 27 galaxies in the sample; this is only visible for the most massive galaxies.

  • 8.
    Stanishev, Vallery
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, Faculty of Science & Engineering. Inst Super Tecn, Portugal.
    Goobar, A.
    Stockholm Univ, Sweden.
    Amanullah, R.
    Stockholm Univ, Sweden.
    Bassett, B.
    African Inst Math Sci, South Africa; South African Astron Observ, South Africa; Univ Cape Town, South Africa.
    Fantaye, Y. T.
    Univ Roma Tor Vergata, Italy.
    Garnavich, P.
    Univ Notre Dame, IN 46556 USA.
    Hlozek, R.
    Princeton Univ, NJ 08544 USA.
    Nordin, J.
    Humboldt Univ, Germany.
    Okouma, P. M.
    South African Astron Observ, South Africa; Univ Western Cape, South Africa.
    Ostman, L.
    Stockholm Univ, Sweden.
    Sako, M.
    Australian Natl Univ, Australia.
    Scalzo, R.
    Univ Penn, PA 19104 USA.
    Smith, M.
    Univ Southampton, England.
    Type Ia supernova Hubble diagram with near-infrared and optical observations2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 615, article id A45Article in journal (Refereed)
    Abstract [en]

    Context. Type Ia Supernovae (SNe Ia) have been used as standardizable candles in the optical wavelengths to measure distances with an accuracy of similar to 7% out to redshift z similar to 1 : 5. There is evidence that in the near-infrared (NIR) wavelengths SNe Ia are even better standard candles, however, NIR observations are much more time-consuming. Aims. We aim to test whether the NIR peak magnitudes could be accurately estimated with only a single observation obtained close to maximum light, provided that the time of B band maximum, the B - V color at maximum and the optical stretch parameter are known. Methods. We present multi-epoch UBVRI and single-epoch J and H photometric observations of 16 SNe Ia in the redshift range z = 0 : 037 0 : 183, doubling the leverage of the current SN Ia NIR Hubble diagram and the number of SNe beyond redshift 0.04. This sample was analyzed together with 102 NIR and 458 optical light curves (LCs) of normal SNe Ia from the literature. Results. The analysis of 45 NIR LCs with well-sampled first maximum shows that a single template accurately describes the LCs if its time axis is stretched with the optical stretch parameter. This allows us to estimate the peak NIR magnitudes of SNe with only few observations obtained within ten days from B-band maximum. The NIR Hubble residuals show weak correlation with Delta M-15 and the color excess E(B V), and for the first time we report a potential dependence on the J(max) - H-max color. With these corrections, the intrinsic NIR luminosity scatter of SNe Ia is estimated to be similar to 0.10 mag, which is smaller than what can be derived for a similarly heterogeneous sample at optical wavelengths. Analysis of both NIR and optical data shows that the dust extinction in the host galaxies corresponds to a low R-V similar or equal to 1.8-1.9. Conclusions. We conclude that SNe Ia are at least as good standard candles in the NIR as in the optical and are potentially less affected by systematic uncertainties. We extended the NIR SN Ia Hubble diagram to its nonlinear part at z similar to 0 : 2 and confirmed that it is feasible to accomplish this result with very modest sampling of the NIR LCs, if complemented by well-sampled optical LCs. With future facilities it will be possible to extend the NIR Hubble diagram beyond redshift z similar or equal to 1; and our results suggest that the most efficient way to achieve this would be to obtain a single observation close to the NIR maximum.

  • 9.
    Tengstrand, Olof
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Guainazzi, M.
    ESA.
    Siemiginowska, A.
    Harvard Smithsonian Centre for Astrophysics.
    Fonseca Bonilla, N.
    ESA.
    Labiano, A.
    CSIC.
    M. Worrall, D.
    University of Bristol.
    Grandi, P.
    INAF.
    Piconcelli, E.
    INAF.
    The X-ray view of giga-hertz peaked spectrum radio galaxies2009In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 501, no 1, p. 89-102Article in journal (Refereed)
    Abstract [en]

    Context. This paper presents the X-ray properties of a flux- and volume-limited complete sample of 16 giga-hertz peaked spectrum (GPS) galaxies. Aims. This study addresses three basic questions in our understanding of the nature and evolution of GPS sources: a) What is the physical origin of the X-ray emission in GPS galaxies? b) Which physical system is associated with the X-ray obscuration? c) What is the "endpoint" of the evolution of compact radio sources? Methods. We discuss in this paper the results of the X-ray spectral analysis, and compare the X-ray properties of the sample sources with radio observables. Results. We obtain a 100% (94%) detection fraction in the 0.5-2 keV (0.5-10 keV) energy band. GPS galaxy X-ray spectra are typically highly obscured (less than N-H(GPS)greater than = 3 x 10(22) cm(-2); sigma(NH) similar or equal to 0.5 dex). The X-ray column density is larger than the HI column density measured in the radio by a factor 10 to 100. GPS galaxies lie well on the extrapolation to high radio powers of the correlation between radio and X-ray luminosity known in low-luminosity FR I radio galaxies. On the other hand, GPS galaxies exhibit a comparable X-ray luminosity to FR II radio galaxies, notwithstanding their much larger radio luminosity. Conclusions. The X-ray to radio luminosity ratio distribution in our sample is consistent with the bulk of the high-energy emission being produced by the accretion disk, as well as with dynamical models of GPS evolution where X-rays are produced by Compton upscattering of ambient photons. Further support to the former scenario comes from the location of GPS galaxies in the X-ray to O[III] luminosity ratio versus N-H plane. We propose that GPS galaxies are young radio sources, which would reach their full maturity as classical FR II radio galaxies. However, column densities greater than or similar to 10(22) cm(-2) could lead to a significant underestimate of dynamical age determinations based on the hotspot recession velocity measurements.

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