107 research outputs found
The four leading arms of the Magellanic Cloud system
No full textContext. The Magellanic Cloud system (MCS) interacts via tidal and drag forces with the Milky Way galaxy.
Aims. Using the Parkes Galactic All-Sky Survey (GASS) of atomic hydrogen we explore the role of drag on the evolution of the so-called Leading Arm (LA).
Methods. We present a new image recognition algorithm that allows us to differentiate features within a 3D data cube (longitude, latitude, radial velocity) and to parameterize individual coherent structures. We compiled an Hi
Unveiling Dark Matter with HI and Halpha Data - Observational Problems
No full textWe present combined Halpha+HI rotation curves for a sample of spiral galaxies. Most of the velocity profiles (spectra at single points) in these galaxies are asymmetric, preventing the use of standard methods like the first moment analysis and the single Gaussian fitting. We thus propose a method similar to the Envelope-Tracing method (Sofue & Rubin 2001) to analyse those profiles from which we obtain HI rotation curves in good agreement with the Halpha rotation curves. These final rotation curves provide the required high resolution in the inner parts of the galaxies, but also extend out to typically 2-3 optical radii. They will hence allow us to investigate the distribution of dark matter
X-raying the Galactic interstellar medium: first all-sky correlation of X-ray and HI-data
No full textThe 3-D structure and composition of the Galactic interstellar medium can be deduced from soft X-ray absorption observations. For this purpose, we cross-correlate the ROSAT all-sky survey with the HI 21-cm line all-sky distribution provided by the Leiden/Dwingweloo and Instituto Argentino de Radioastronomía surveys. We analyse the data for the whole ROSAT-PSPC energy window (0.1 keV to 2.1 keV) to derive a consistent model of the diffuse X-ray background radiation. This approach allows to deduce the 3-D structure of X-ray absorbing and emitting gas and to constrain the distance to some high- (HVC) and intermediate-velocity cloud (IVC) complexes.Fil: Pradas, J.. Universitaet Bonn; AlemaniaFil: Kerp, J.. Universitaet Bonn; AlemaniaFil: Kalberla, P. M. W.. Universitaet Bonn; AlemaniaFil: Arnal, Edmundo Marcelo. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Bajaja, Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Morras, Ricardo. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Pöppel, Wolfgang G. L.. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentin
Large Scale characteristics of the galactic HI distribution
No full textsing the new LAB HI survey, a combination of the Leiden/Dwingeloo and the Argentine Surveys processed in Bonn, we study the morphology of the HI distribution in the Milky Way. Assuming circular motions of the gas and hydrodynamical equilibrium we fit a z-density distribution law to extract scale height zh, deviation from the plane ẑ and peak density n̂ . We find that the galactic disk flares from 0.3 kpc at R=9 kpc up to 1 kpc at R=30 kpc without discernable dependence on azimuth. The warp of the galactic disk is also clearly visible, with a symmetric part up to R=17 kpc where the deviation reaches a maximum of 1 kpc, and an asymmetric part where in quadrants 1&2 the deviation reaches a maximum of more than 5kpc at R=28 kpc while in quadrants 3&4 the deviation from the plane drops back to zero. Finally we discuss spiral structure in the peak density plots. Applying the linear density-wave theory we try to model the spiral structure of the Galaxy.Fil: Dedes, L.. Radioastronomisches Institut der Universität Bonn; AlemaniaFil: Kalberla, P. M. W.. Radioastronomisches Institut der Universität Bonn; AlemaniaFil: Arnal, Edmundo Marcelo. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Bajaja, Esteban. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Morras, Ricardo. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; ArgentinaFil: Poeppel, W. G. L.. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Instituto Argentino de Radioastronomía. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto Argentino de Radioastronomía; Argentin
Caustics and velocity caustics in the diffuse interstellar medium at high Galactic latitudes
No full textContext. The far-infrared (FIR) distribution at high Galactic latitudes, observed with Planck, is filamentary with coherent structures in polarization. These structures are also closely related to H
Caustics and velocity caustics in the diffuse interstellar medium at high Galactic latitudes
No full textThe FIR distribution at high Galactic latitudes, observed with Planck, is
filamentary with coherent structures in polarization. These structures are also
closely related to HI filaments with coherent velocity structures. There is a
long-standing debate about the physical nature of these structures. They are
considered either as velocity caustics, fluctuations engraved by the turbulent
velocity field or as cold three-dimensional density structures in the
interstellar medium (ISM). We discuss different approaches to data analysis and
interpretation in order to work out the differences. We considered mathematical
preliminaries for the derivation of caustics that characterize filamentary
structures in the ISM. Using the Hessian operator, we traced individual FIR
filamentary structures in HI from channel maps as observed and alternatively
from data that are provided by the velocity decomposition algorithm (VDA). VDA
is claimed to separate velocity caustics from density effects. Based on the
strict mathematical definition, the so-called velocity caustics are not
actually caustics. These VDA data products may contain caustics in the same way
as the original HI observations. Caustics derived by a Hessian analysis of both
databases are nearly identical with a correlation coefficient of 98%. However,
the VDA algorithm leads to a 30% increase in the alignment uncertainties when
fitting FIR/HI orientation angles. We used HI absorption data to constrain the
physical nature of FIR/HI filaments and determine spin temperatures and volume
densities of FIR/HI filaments. HI filaments exist as CNM structures; outside
the filaments no CNM absorption is detectable. The CNM in the diffuse ISM is
exclusively located in filaments with FIR counterparts. These filaments at high
Galactic latitudes exist as cold density structures; velocity crowding effects
are negligible.Comment: 16 pages, 11 figure
Molecular hydrogen in filaments at high Galactic latitudes
No full textContext. Neutral atomic hydrogen (H
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