arXiv subjects

E. Battaner

Publications and source records attributed to E. Battaner.

167 records · Page 10Linked to original sources

arXiv1997

Geometrical parametrization of warps for edge-on galaxies

We propose new parameters to describe the geometry of a warped disc when viewed edge-on, a global warp parameter $w$, and a family of three parameters $A$, $B$ and $C$ that describe, independently, the shape of the warp. These parameters are useful to detect some key effects in the understanding of warps. We have also developed software (WIG) which is able to calculate these parameters for a given image of a galaxy in any wavelength and which is described here with some examples, namely ESO 235-53 in the optical, NGC 4013 in 21 cm and NGC 4565 in 1.2 mm continuum.

astro-ph↗

arXiv1997

Magnetic fields and large-scale structure in a hot universe. II. Magnetic flux tubes and filamentary structure

In paper I, we obtained an equation for the evolution of density inhomogeneities in a radiation dominated universe when they are affected by magnetic fields. In this second paper we apply this equation to the case in which the subjacent magnetic configuration is a flux tube. For scales of the order of 1 Mpc or less the differential equation is elliptical. To solve it, we have used the numerical method based on "Simultaneous Over Relaxation", SOR, with Chebyshev acceleration and we have treated the problem as a boundary value problem, which restricts the prediction ability of the integration. For large-scale flux tubes, much larger than 1 Mpc, the equation can be analytically integrated and no assumption about the final shape or magnitude of the inhomogeneity is required. In both cases we obtain an evolution which does not differ very much from linear in time. The inhomogeneity in the density becomes filamentary. Large scale structures ($\ge$ 10 Mpc) are probably unaffected by damping, non-linear and amplification mechanisms after Equality, so that this model provides a tool to interpret the present observed large scale structure. Filaments are very frequently found in the large-scale structure in the Universe. It is suggested here that they could arise from primordial magnetic flux tubes, thus providing an alternative hypothesis for its interpretation; in particular we consider the case of the Coma-A1367 supercluster, where the magnetic field is known to be high.

astro-ph↗

arXiv1997

The radial scale length of the Milky Way

The radial scale length of the exponential component of the disc of the Milky Way has been determined in the near infrared. We have used the TMGS (Two Micron Galactic Survey) database which contains positions and K-magnitudes of about 700.000 stars distributed in serveral regions along the galactic plane. From those we have selected areas more than $5^\circ$ off the plane to minimize the effect of extinction and the contributions of the young disc; and with longitudes ranging from $30^\circ$ to $70^\circ$, to avoid contaminations from the central bulge, the bar and the molecular ring, in the inner end, and from the local arm, the warp and the truncation of the disc, in the outer end. We observed stars with magnitude $ 9 \leq m_K \leq 10 $. The use of the NIR K-band also reduces the effect of extinction. In the observation region, m_K=9.5 mag stars are K2-K5 III stars, with an absolute magnitude that is nearly constant, which also greatly simplifies the problem. We have obtained the value $2.1 \pm 0.3 kpc$ for the radial scale length, which is a typical value when compared with external galaxies of similar types.

astro-ph↗

arXiv1997

Magnetic fields and large scale structure in a hot Universe. III. The polyhedric network

We provide a new tool to interpret the large scale structure of the Universe. As suggested in Paper II, energy density filaments could have been produced by subjacent magnetic flux tubes when the Universe was dominated by radiation. In more recent time epochs, small scale filaments have evolved in a complicated way, but large scale filaments have probably survived and should be identified with present observed matter filaments of clusters. A primordial magnetic field lattice made up of magnetic flux tubes would then have originated a matter lattice made up of cluster filaments. Taking into account some restrictions in the magnetic field configuration we speculate what type of matter network this would have generated. The simplest lattice is made up of octohedra connected at their vertexes, reminding us of a structure of superimposed egg cartons. The vertexes would correspond to large superclusters, which would therefore have eight filaments emerging from them. Some observational evidence is found in the Local Supercluster, which is spider-like, with eight legs.

astro-ph↗

arXiv1997

Magnetic Fields and Large Scale Structure in a hot Universe. I. General Equations

We consider that no mean magnetic field exists during this epoch, but that there is a mean magnetic energy associated with large-scale magnetic inhomogeneities. We study the evolution of these inhomogeneities and their influence on the large scale density structure, by introducing linear perturbations in Maxwell equations, the conservation of momentum-energy equation, and in Einstein field equations. The primordial magnetic field structure is time independent in the linear approximation, only being diluted by the general expansion, so that $\vec{B}R^2$ is conserved in comoving coordinates. Magnetic fields have a strong influence on the formation of large-scale structure. Firstly, relatively low fields are able to generate density structures even if they were inexistent at earlier times. Second, magnetic fields act anisotropically more recently, modifying the evolution of individual density clouds. Magnetic flux tubes have a tendency to concentrate photons in filamentary patterns.

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