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M Urbanik - One of the best experts on this subject based on the ideXlab platform.
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the large scale magnetic field structure of the Spiral Galaxy ngc 5775
Astronomy and Astrophysics, 2011Co-Authors: M Soida, Martin Krause, R J Dettmar, M UrbanikAbstract:Context. The origin of large-scale magnetic fields in Spiral galaxies is still a theoretical riddle and better observational constraints are required to make further progress. Aims. In order to better determine the large-scale 3D-structure of magnetic fields in Spiral galaxies we present a Faraday rotation analysis of the edge-on Spiral Galaxy NGC 5775. Methods. Deep radio-continuum observations in total power and linear polarization were performed at 8.46 GHz with the VLA and the 100-m Effelsberg telescope. They were analyzed together with archival 4.86 and 1.49 GHz VLA-data. We thus can derive rotation measures from a comparison of three frequencies and determine the intrinsic magnetic field structure. Results. A very extended halo is detected in NGC 5775, with magnetic field lines forming an X-shaped structure. Close to the galactic disk the magnetic field is plane-parallel. The scaleheights of the radio emission esimated for NGC 5775 are comaprable with other galaxies. The rotation measure distribution varies smoothly on both sides along the major axis from positive to negative values. Conclusions. From the derived distribution of rotation measures and the plane-parallel intrinsic magnetic field orientation along the galactic midplane we conclude that NGC 5775 has an even axisymmetric large-scale magnetic field configuration in the disk as generated by an αΩ-dynamo which is accompanied by a quadrupolar poloidal field. The magnetic field lines of the plane-parallel component are pointing outwards. The observed X-shaped halo magnetic field, however, cannot be explained by the action of the disk’s mean-field dynamo alone. It is probably due to the influence of the galactic wind together with the dynamo action.
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the large scale magnetic field structure of the Spiral Galaxy ngc 5775
arXiv: Astrophysics of Galaxies, 2011Co-Authors: M Soida, Martin Krause, R J Dettmar, M UrbanikAbstract:In order to better determine the large-scale 3D-structure of magnetic fields in Spiral galaxies we present a Faraday rotation analysis of the edge-on Spiral Galaxy NGC 5775. Deep radio-continuum observations in total power and linear polarization were performed at 8.46 GHz with the VLA and the 100-m Effelsberg telescope. They were analyzed together with archival 4.86 and 1.49 GHz VLA-data. We thus can derive rotation measures from a comparison of three frequencies and determine the intrinsic magnetic field structure. A very extended halo is detected in NGC 5775, with magnetic field lines forming an X-shaped structure. Close to the galactic disk the magnetic field is plane-parallel. The scaleheights of the radio emission esimated for NGC 5775 are comaprable with other galaxies. The rotation measure distribution varies smoothly on both sides along the major axis from positive to negative values. From the derived distribution of rotation measures and the plane-parallel intrinsic magnetic field orientation along the galactic midplane we conclude that NGC 5775 has an 'even axisymmetric' large-scale magnetic field configuration in the disk as generated by an \alpha \Omega -dynamo which is accompanied by a quadrupolar poloidal field. The magnetic field lines of the plane-parallel component are pointing 'outwards'. The observed X-shaped halo magnetic field, however, cannot be explained by the action of the disk's mean-field dynamo alone. It is probably due to the influence of the galactic wind together with the dynamo action.
Paolo Salucci - One of the best experts on this subject based on the ideXlab platform.
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dwarf spheroidal Galaxy kinematics and Spiral Galaxy scaling laws
Monthly Notices of the Royal Astronomical Society, 2012Co-Authors: Paolo Salucci, E K Grebel, M I Wilkinson, Matthew Walker, Gerard Gilmore, Andreas Koch, Christiane Frigerio Martins, Rosemary F G WyseAbstract:Kinematic surveys of the dwarf spheroidal (dSph) satellites of the Milky Way are revealing tantalising hints about the structure of dark matter (DM) haloes at the low-mass end of the Galaxy luminosity function. At the bright end, modelling of Spiral galaxies has shown that their rotation curves are consistent with the hypothesis of a Universal Rotation Curve whose shape is supported by a cored dark matter halo. In this paper, we investigate whether the internal kinematics of the Milky Way dSphs are consistent with the particular cored DM distributions which reproduce the properties of Spiral gal axies. Although the DM densities in dSphs are typically almost two orders of magnitude higher than those found in (larger) disk systems, we find consistency between dSph kinematics an d Burkert DM haloes whose core radii r0 and central densitiesρ0 lie on the extrapolation of the scaling law seen in Spiral galaxies: log ρ0≃α log r0 + const with 0.9< α< 1.1. We similarly find that the dSph data are consistent with the relation betweenρ0 and baryon scale length seen in Spiral galaxies. While the origin of these scaling relations is unclear, the fi nding that a single DM halo profile is consistent with kinematic data in galaxies of widely varying size, luminosity and Hubble Type is important for our understanding of observed galaxies and must be accounted for in models of Galaxy formation.
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dwarf spheroidal Galaxy kinematics and Spiral Galaxy scaling laws
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Paolo Salucci, E K Grebel, M I Wilkinson, Matthew Walker, Gerard Gilmore, Andreas Koch, Christiane Frigerio Martins, Rosemary F G WyseAbstract:Kinematic surveys of the dwarf spheroidal (dSph) satellites of the Milky Way are revealing tantalising hints about the structure of dark matter (DM) haloes at the low-mass end of the Galaxy luminosity function. At the bright end, modelling of Spiral galaxies has shown that their rotation curves are consistent with the hypothesis of a Universal Rotation Curve whose shape is supported by a cored dark matter halo. In this paper, we investigate whether the internal kinematics of the Milky Way dSphs are consistent with the particular cored DM distributions which reproduce the properties of Spiral galaxies. Although the DM densities in dSphs are typically almost two orders of magnitude higher than those found in (larger) disk systems, we find consistency between dSph kinematics and Burkert DM haloes whose core radii r0 and central densities {\rho}0 lie on the extrapolation of the scaling law seen in Spiral galaxies: log {\rho}0 \simeq {\alpha} log r0 + const with 0.9 < {\alpha} < 1.1. We similarly find that the dSph data are consistent with the relation between {\rho}0 and baryon scale length seen in Spiral galaxies. While the origin of these scaling relations is unclear, the finding that a single DM halo profile is consistent with kinematic data in galaxies of widely varying size, luminosity and Hubble Type is important for our understanding of observed galaxies and must be accounted for in models of Galaxy formation.
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The Tully-Fisher relation of Spiral galaxies
Proceedings of the International Astronomical Union, 2005Co-Authors: Irina A. Yegorova, Paolo SalucciAbstract:salucci@sissa.it The Tully-Fisher (TF) relation is an empirically establish correlation between the luminosity of Spiral Galaxy and its rotational velocity (Tully-Fisher, 1977). We used the Tully-Fisher relation in order to probe the dark matter (DM) distribution in the optical regions of Spiral galaxies. We investigated a sample of rotation curves that includes 957 galaxies. The new technique applied takes advantages on the full knowledge of the Galaxy rotation curves.
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The mass function of Spiral Galaxy haloes
Monthly Notices of the Royal Astronomical Society, 1993Co-Authors: Keith M. Ashman, Paolo Salucci, Massimo PersicAbstract:We derive the mass function of Spiral Galaxy haloes using the luminosity function and the inferred variation in mass-to-light ratio with Spiral Galaxy luminosity. We show that the resulting mass function is consistent with hierarchical clustering models of Galaxy formation. This contrasts with previous results based on the assumption of a constant mass-to-light ratio for all Spirals, which predict too many low-luminosity galaxies. By reversing the argument, we show that, if Spirals form through hierarchical clustering, then the observed luminosity function requires an increase in the dark matter fraction with decreasing luminosity
Asantha Cooray - One of the best experts on this subject based on the ideXlab platform.
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high resolution 3d radiative transfer modeling i the grand design Spiral Galaxy m 51
Astronomy and Astrophysics, 2014Co-Authors: Ilse De Looze, J Fritz, A Boselli, M Baes, G J Bendo, L Cortese, M Boquien, Peter Camps, Asantha CoorayAbstract:Context. Dust reprocesses about half of the stellar radiation in galaxies. The thermal re-emission by dust of absorbed energy is considered to be driven merely by young stars so is often applied to tracing the star formation rate in galaxies. Recent studies have argued that the old stellar population might be responsible for a non-negligible fraction of the radiative dust heating. Aims. In this work, we aim to analyze the contribution of young (≲100 Myr) and old (~10 Gyr) stellar populations to radiative dust heating processes in the nearby grand-design Spiral Galaxy M 51 using radiative transfer modeling. High-resolution 3D radiative transfer (RT) models are required to describe the complex morphologies of asymmetric Spiral arms and clumpy star-forming regions and to model the propagation of light through a dusty medium. Methods. In this paper, we present a new technique developed to model the radiative transfer effects in nearby face-on galaxies. We construct a high-resolution 3D radiative transfer model with the Monte-Carlo code SKIRT to account for the absorption, scattering, and non-local thermal equilibrium (NLTE) emission of dust in M 51. The 3D distribution of stars is derived from the 2D morphology observed in the IRAC 3.6 μm, GALEX FUV, Hα, and MIPS 24 μm wavebands, assuming an exponential vertical distribution with an appropriate scale height. The dust geometry is constrained through the far-ultraviolet (FUV) attenuation, which is derived from the observed total-infrared-to-far-ultraviolet luminosity ratio. The stellar luminosity, star formation rate, and dust mass have been scaled to reproduce the observed stellar spectral energy distribution (SED), FUV attenuation, and infrared SED. Results. The dust emission derived from RT calculations is consistent with far-infrared and submillimeter observations of M 51, implying that the absorbed stellar energy is balanced by the thermal re-emission of dust. The young stars provide 63% of the energy for heating the dust responsible for the total infrared emission (8−1000 μm), while 37% of the dust emission is governed through heating by the evolved stellar population. In individual wavebands, the contribution from young stars to the dust heating dominates at all infrared wavebands but gradually decreases towards longer infrared and submillimeter wavebands for which the old stellar population becomes a non-negligible source of heating. Upon extrapolation of the results for M 51, we present prescriptions for estimating the contribution of young stars to the global dust heating based on a tight correlation between the dust heating fraction and specific star formation rate.
M Soida - One of the best experts on this subject based on the ideXlab platform.
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Ram pressure stripping of the multiphase ISM and star formation in the Virgo Spiral Galaxy NGC 4330
Astronomy and Astrophysics - A&A, 2012Co-Authors: B. Vollmer, M Soida, A. Chung, J. Braine, R. Beck, A. Abramson, H. H. Crowl, J. D. P. Kenney, J. H. Van GorkomAbstract:It has been shown that the Virgo Spiral Galaxy NGC 4330 shows signs of ongoing ram pressure stripping in multiple wavelengths: at the leading edge of the interaction, the Halpha and dust extinction curve sharply out of the disk; on the trailing side, a long Halpha/UV tail has been found which is located upwind of a long HI tail. We complete the multiwavelength study with IRAM 30m HERA CO(2-1) and VLA 6 cm radio continuum observations of NGC 4330. The data are interpreted with the help of a dynamical model including ram pressure and, for the first time, star formation. Our best-fit model reproduces qualitatively the observed projected position, radial velocity of the Galaxy, the molecular and atomic gas distribution and velocity field, and the UV distribution in the region where a gas tail is present. However, the observed red UV color on the windward side is currently not reproduced by the model. Based on our model, the Galaxy moves to the north and still approaches the cluster center with the closest approach occurring in ~100 Myr. In contrast to other Virgo Spiral galaxies affected by ram pressure stripping, NGC 4330 does not show an asymmetric ridge of polarized radio continuum emission. We suggest that this is due to the relatively slow compression of the ISM and the particular projection of NGC 4330. The observed offset between the HI and UV tails is well reproduced by our model. Since collapsing and starforming gas clouds decouple from the ram pressure wind, the UV-emitting young stars have the angular momentum of the gas at the time of their creation. On the other hand, the gas is constantly pushed by ram pressure. The reaction (phase change, star formation) of the multiphase ISM (molecular, atomic, ionized) to ram pressure is discussed in the framework of our dynamical model.
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the large scale magnetic field structure of the Spiral Galaxy ngc 5775
Astronomy and Astrophysics, 2011Co-Authors: M Soida, Martin Krause, R J Dettmar, M UrbanikAbstract:Context. The origin of large-scale magnetic fields in Spiral galaxies is still a theoretical riddle and better observational constraints are required to make further progress. Aims. In order to better determine the large-scale 3D-structure of magnetic fields in Spiral galaxies we present a Faraday rotation analysis of the edge-on Spiral Galaxy NGC 5775. Methods. Deep radio-continuum observations in total power and linear polarization were performed at 8.46 GHz with the VLA and the 100-m Effelsberg telescope. They were analyzed together with archival 4.86 and 1.49 GHz VLA-data. We thus can derive rotation measures from a comparison of three frequencies and determine the intrinsic magnetic field structure. Results. A very extended halo is detected in NGC 5775, with magnetic field lines forming an X-shaped structure. Close to the galactic disk the magnetic field is plane-parallel. The scaleheights of the radio emission esimated for NGC 5775 are comaprable with other galaxies. The rotation measure distribution varies smoothly on both sides along the major axis from positive to negative values. Conclusions. From the derived distribution of rotation measures and the plane-parallel intrinsic magnetic field orientation along the galactic midplane we conclude that NGC 5775 has an even axisymmetric large-scale magnetic field configuration in the disk as generated by an αΩ-dynamo which is accompanied by a quadrupolar poloidal field. The magnetic field lines of the plane-parallel component are pointing outwards. The observed X-shaped halo magnetic field, however, cannot be explained by the action of the disk’s mean-field dynamo alone. It is probably due to the influence of the galactic wind together with the dynamo action.
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the large scale magnetic field structure of the Spiral Galaxy ngc 5775
arXiv: Astrophysics of Galaxies, 2011Co-Authors: M Soida, Martin Krause, R J Dettmar, M UrbanikAbstract:In order to better determine the large-scale 3D-structure of magnetic fields in Spiral galaxies we present a Faraday rotation analysis of the edge-on Spiral Galaxy NGC 5775. Deep radio-continuum observations in total power and linear polarization were performed at 8.46 GHz with the VLA and the 100-m Effelsberg telescope. They were analyzed together with archival 4.86 and 1.49 GHz VLA-data. We thus can derive rotation measures from a comparison of three frequencies and determine the intrinsic magnetic field structure. A very extended halo is detected in NGC 5775, with magnetic field lines forming an X-shaped structure. Close to the galactic disk the magnetic field is plane-parallel. The scaleheights of the radio emission esimated for NGC 5775 are comaprable with other galaxies. The rotation measure distribution varies smoothly on both sides along the major axis from positive to negative values. From the derived distribution of rotation measures and the plane-parallel intrinsic magnetic field orientation along the galactic midplane we conclude that NGC 5775 has an 'even axisymmetric' large-scale magnetic field configuration in the disk as generated by an \alpha \Omega -dynamo which is accompanied by a quadrupolar poloidal field. The magnetic field lines of the plane-parallel component are pointing 'outwards'. The observed X-shaped halo magnetic field, however, cannot be explained by the action of the disk's mean-field dynamo alone. It is probably due to the influence of the galactic wind together with the dynamo action.
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Ram pressure stripping of the multiphase ISM in the Virgo cluster Spiral Galaxy NGC 4438
Astronomy and Astrophysics - A&A, 2009Co-Authors: B. Vollmer, M Soida, A Boselli, A. Chung, L. Chemin, J. Braine, R. BeckAbstract:Ram pressure stripping of the multiphase ISM is studied in the perturbed Virgo cluster Spiral Galaxy NGC 4438. This Galaxy underwent a tidal interaction ~100 Myr ago and is now strongly affected by ram pressure stripping. Deep VLA radio continuum observations at 6 and 20 cm are presented. We detect prominent extraplanar emission to the west of the galactic center, which extends twice as far as the other tracers of extraplanar material. The spectral index of the extraplanar emission does not steepen with increasing distance from the Galaxy. This implies in situ re-acceleration of relativistic electrons. The comparison with multiwavelength observations shows that the magnetic field and the warm ionized interstellar medium traced by Halpha emission are closely linked. The kinematics of the northern extraplanar Halpha emission, which is ascribed to star formation, follow those of the extraplanar CO emission. In the western and southern extraplanar regions, the Halpha measured velocities are greater than those of the CO lines. We suggest that the ionized gas of this region is excited by ram pressure. The spatial and velocity offsets are consistent with a scenario where the diffuse ionized gas is more efficiently pushed by ram pressure stripping than the neutral gas. We suggest that the recently found radio-deficient regions compared to 24 mum emission are due to this difference in stripping efficiency.
Cristina Popescu - One of the best experts on this subject based on the ideXlab platform.
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a radiative transfer model for the Spiral Galaxy m33
Monthly Notices of the Royal Astronomical Society, 2020Co-Authors: Jordan J Thirlwall, Cristina Popescu, Richard J Tuffs, Giovanni Natale, Mark A Norris, M T Rushton, M W Grootes, Benjamin Timothy CarrollAbstract:We present the first radiative transfer (RT) model of a non-edge-on disk Galaxy in which the large-scale geometry of stars and dust is self-consistently derived through fitting of multiwavelength imaging observations from the UV to the submm. To this end we used the axi-symmetric RT model of Popescu et al. and a new methodology for deriving geometrical parameters, and applied this to decode the{spectral energy distribution (SED) of M33. We successfully account for both the spatial and spectral energy distribution, with residuals typically within 7% in the profiles of surface brightness and within 8% in the spatially-integrated SED. We predict well the energy balance between absorption and re-emission by dust, with no need to invoke modified grain properties, and we find no submm emission that is in excess of our model predictions. We calculate that 80±8% of the dust heating is powered by the young stellar populations. We identify several morphological components in M33, a nuclear, an inner, a main and an outer disc, showing a monotonic trend in decreasing star-formation surface-density (ΣSFR) from the nuclear to the outer disc. In relation to surface density of stellar mass, the ΣSFR of these components define a steeper relation than the "main sequence" of star-forming galaxies, which we call a "structurally resolved main sequence". Either environmental or stellar feedback mechanisms could explain the slope of the newly defined sequence. We find the star-formation rate to be SFR=0.28+0.02−0.01M⊙yr−1.