P. Katgert

The ESO Nearby Abell Cluster Survey.* XII. The Mass and Mass-to-Light Ratio Profiles of Rich Clusters

We determine the mass profile of an ensemble cluster built from 3056 galaxies in 59 nearby clusters observed in the ESO Nearby Abell Cluster Survey. The mass profile is derived from the distribution and kinematics of the early-type (elliptical and S0) galaxies only, with projected distances from the centers of their clusters ?1.5r200. These galaxies are most likely to meet the conditions for the application of the Jeans equation, since they are the oldest cluster population and are thus quite likely to be in dynamical equilibrium with the cluster potential. In addition, the assumption that the early-type galaxies have isotropic orbits is supported by the shape of their velocity distribution. For galaxies of other types (the brightest elliptical galaxies, with MR ? -22 + 5 log h, and the early and late spirals) these assumptions are much less likely to be satisfied. For the determination of the mass profile we also exclude early-type galaxies in subclusters. Application of the Jeans equation yields a nonparametric estimate of the cumulative mass profile M(<r), which has a logarithmic slope of -2.4 ? 0.4 in the density profile at r200 (approximately the virial radius). We compare our result with several analytical models from the literature and estimate their best-fit parameters from a comparison of observed and predicted velocity-dispersion profiles. We obtain acceptable solutions for all models (NFW, Moore et al., softened isothermal sphere [SIS], and Burkert). Our data do not provide compelling evidence for the existence of a core; as a matter of fact, the best-fitting core models have core-radii well below 100 h-1 kpc. The upper limit that we put on the size of the core-radius provides a constraint for the scattering cross section of dark matter particles. The total-mass density appears to be traced remarkably well by the luminosity density of the early-type galaxies. On the contrary, the luminosity density of the brightest elliptical galaxies increases faster toward the center than the mass density, while the luminosity density profiles of the early and late spirals are somewhat flatter than the mass density profile.

The ESO Nearby Abell Cluster Survey. XIII. The orbits of the different types of galaxies in rich clusters

We study the orbits of the various types of galaxies observed in the ESO Nearby Abell Cluster Survey. We combine the observed kinematics and projected distributions of galaxies of various types with an estimate of the mass density profile of the ensemble cluster to derive velocity-anisotropy profiles. Galaxies within and outside substructures are considered separately. Among the galaxies outside substructures we distinguish four classes, on the basis of their projected phase-space distributions. These classes are: the brightest ellipticals (with MR ≤− 22 + 5l ogh), the other ellipticals together with the S0s, the early- type spirals (Sa-Sb), and the late-type spirals and irregulars (Sbc-Irr) together with the emission-line galaxies (except those of early morphology). The mass profile was determined from the distribution and kinematics of the early-type (i.e. elliptical and S0) galaxies outside substructures; the latter were assumed to be on isotropic orbits, which is supported by the shape of their velocity distribution. The projected distribution and kinematics of the galaxies of other types are used to search for equilibrium solutions in the gravitational potential derived from the early-type galaxies. We apply the method described by Binney & Mamon as implemented by Solanes & Salvador-Sole to derive, to our knowledge for the first time, the velocity anisotropy profiles of all galaxy classes individually (except, of course, the early-type class). We check the validity of the solutions for β � (r) ≡ (� v 2 � (r)/� v 2 � (r)) 1/2 ,w herev 2 � (r )a ndv 2 � (r) are the mean squared components of the radial and tangential velocity, respectively, by comparing the observed and predicted velocity-dispersion profiles. For the brightest ellipticals we are not able to construct equilibrium solutions. This is most likely the result of the formation history and the special location of these galaxies at the centres of their clusters. For both the early and the late spirals, as well as for the galaxies in substructures, the data allow equilibrium solutions. The data for the early spirals are consistent with isotropic orbits (β � (r) ≡ 1), although there is an apparent radial anisotropy at � 0.45r200. For the late spirals an equilibrium solution with isotropic orbits is rejected by the data at the >99% confidence level. While β � (r) ≈ 1 within 0.7r200, β � increases linearly with radius to a value � 1.8 at 1.5r200. Taken at face value, the data for the galaxies in substructures indicate that isotropic solutions are not acceptable, and tangential orbits are indicated. Even though the details of the tangential anisotropy remain to be determined, the general conclusion appears robust. We briefly discuss the possible implications of these velocity-anisotropy profiles for current ideas of the evolution and transformation of galaxies in clusters.

Characteristics of the structure in the Galactic polarized radio background at 350 mhz

Angular power spectra and structure functions of the Stokes parameters Q and U and polarized intensity P are derived from three sets of radio polarimetric observations. Two of the observed fields have been studied at multiple frequencies, allowing determination of power spectra and structure functions of rotation measure RM as well. The third field extends over a large part of the northern sky, so that the variation of the power spectra over Galactic latitude and longitude can be studied. The power spectra of Q and U are steeper than those of P, probably because a foreground Faraday screen creates extra structure in Q and U, but not in P. The extra structure in Q and U occurs on large scales, and therefore causes a steeper spectrum. The derived slope of the power spectrum of P is the multipole spectral index alpha(P), and is consistent with earlier estimates. The multipole spectral index alpha(P) decreases with Galactic latitude (i.e. the spectrum becomes flatter), but is consistent with a constant value over Galactic longitude. Power spectra of the rotation measure RM show a spectral index alpha(RM) approximate to 1, while the structure function of RM is approximately flat. The structure function is flatter than earlier estimates from polarized extragalactic sources, which could be due to the fact that extragalactic source RM probes the complete line of sight through the Galaxy, whereas as a result of depolarization diffuse radio polarization only probes the nearby ISM.

The large-scale magnetic field in the fourth Galactic quadrant

Aims. We have re-examined the published rotation measures (RMs) of extragalactic point sources and pulsars with |b| < 3 ◦ to study the magnetic field in the fourth Galactic quadrant. Methods. We reduced the influence of structure in electron density as much as possible by excluding objects for which Hα-data indicate large fluctuations in ne somewhere along the line of sight. We also excluded objects for which the RM may have been significantly “corrupted” by an intervening supernova remnant. We modeled RM(l), the longitude dependence of RMof the unaffected extragalactic sources and pulsars. Weassumed several geometries for thelarge-scalefield.All but one of those arebased on logarithmic spiral arms (with various pitch angles and widths), while one has circular symmetry. We also made different assumptions about the large-scale ne-distribution. Results. The data suggest the following generic behaviour of the large-scale field in the 4th Galactic quadrant. The field is most likely organized along logarithmic spiral arms and shows two significant reversals: from the Norma arm (CCW field) to the Norma-Crux interarm region (CW field), and from the Norma-Crux interarm region to the Crux arm (CCW field). The present data do not constrain the field in and beyond the Crux-Carina interarm region. Although the models give a good description of the global character of RM(l), individual RM-estimates deviate by typically 15 times their measurement errors. We argue that these large deviations are most likely due to the “small-scale” field that dominates on scales of up to several hundred pc. Conclusions. The picture that emerges is thus of a field that has significant structure on smaller scales, but for which the average values in arms and interarm regions are nevertheless well-defined. In addition, this smaller-amplitude large-scale field appears to reverse at each arm-interarm boundary that we can study with the present data. We briefly discuss the link between these results and theoretical predictions.

Rotation measure synthesis at the 2 m wavelength of the FAN region : unveiling screens and bubbles

Context. Rotation measure synthesis of the Westerbork Synthesis Radio Telescope (WSRT) observations at {

Properties of the warm magnetized ISM, as inferred from WSRT polarimetric imaging

λ

WSRT Faraday tomography of the Galactic ISM at

} ~{} 2 m of the FAN region at l = 137{deg}, b = +7{deg} shows the morphology of structures in the ionized interstellar medium. Aims: We interpret the diffuse polarized synchrotron emission in terms of coherent structures in the interstellar medium and the properties of the interstellar magnetic field. Methods: We performed statistical analysis of the polarization data cube obtained through rotation measure synthesis. For the first time, cross-correlation is applied to identify and characterize polarized structures in Faraday depth space. Complementary information about the medium are derived from H{

\lambda

α

~ 0.86 m - I. The GEMINI data set at (l, b) = (181°, 20°)

} emission, properties of nearby pulsars, and optical polarized starlight measurements. Results: We find an overall asymmetric Faraday dispersion function in a Faraday depth range of [-13, +5] rad m

The orbits of cluster galaxy populations as evolutionary constraints

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