P. Katgert’s research while affiliated with Leiden University and other places

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, which are most likely to meet the conditions for the application of the Jeans equation. We assume that the Early-type galaxies have isotropic orbits, as supported by the shape of their velocity distribution. The brightest ellipticals (with M_R < -22+5 log h), and the Early-type galaxies in subclusters are excluded from the sample. Application of the Jeans equation yields a non-parametric estimate of the cumulative mass profile M(<r), which has a logarithmic slope of -2.4 +/- 0.4 in the density profile at the virial radius. We compare our result with several analytical models from the literature (NFW, Moore et al. 1999, softened isothermal sphere, and Burkert 1995) and find that all are acceptable. However, 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 kpc. The upper limit 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 ellipticals increases faster towards 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. (Abridged) Comment: ApJ, accepted

We discuss the properties of the galaxies in about 60 rich, nearby clusters, using kinematic data from the ESO Nearby Abell Cluster Survey, combined with new imaging data. The images were used to classify the galaxies, and to recalibrate the galaxy types derived from the ENACS spectra; this yields galaxy-type estimates for about4800 galaxies. For about 1200 galaxies, a bulge/disk decomposition could be made, which yields sizes and luminosities of bulges and disks. From the projected radial distances and relative l.o.s.-velocities we derived the galaxy ensembles with significantly different phase-space distributions. We find that galaxies in and outside substructure must be distinguished. The morphological composition of the substructures appears to vary with projected radius. Outside substructures, 4 galaxy ensembles must be defined: viz. the brighest Es, the other early-type galaxies, the early spirals(Sa-Sb), and the late spirals (including the emission-line galaxies). We also study the morphology-density relation, and we find that the segregation of the late spirals is driven mostly by global factors, while the segregation of Es, S0s and early spirals is driven mostly by local density. The properties of early spirals and S0ssupport the picture in which early spirals transform into S0s, while the properties of the late spirals do not support such a relation.

We determine the mass profile of a synthetic cluster built from the combination of 59 nearby clusters observed in the ESO Nearby Abell Cluster Survey (ENACS). We use ellipticals and S0s as tracers of the cluster potential, and solve the Jeans equation assuming isotropic orbits. Such an assumption is justified by the analysis of the shape of the velocity distribution of ellipticals and S0s. We find that the cluster mass profile is consistent with the Navarro, Frenk and White(NFW) model. We use this cluster mass profile to search for equilibrium solutions for the other cluster galaxy populations: very bright ellipticals (M R≤–22+5 log h),early-type spirals (Sa-Sb), and late-type spirals and irregulars (Sbc-Ir), together with emission-line galaxies. We find equilibrium solutions for both the early- and the late-spirals, but not for the very bright ellipticals. The dynamics of very bright ellipticals is probably affected by dissipative processes which invalidate the use of the collisionless Jeans equation. The equilibrium solution found for the early-spirals implies them to move on nearly-isotropic orbits. Late-spirals are instead found to be on mildly radial orbits, with the radial anisotropy increasing outwards. We discuss the implications of these results for the evolutionary histories of the different populations of cluster galaxies.

We study a conspicuous ring-like structure with a radius of about 1.4 degr which was observed with the Westerbork Synthesis Radio Telescope (WSRT) at 5 frequencies around 350 MHz. This ring is very prominent in Stokes Q and U, and less so in polarized intensity P. No corresponding structure is visible in total intensity Stokes I, which indicates that the ring is created by Faraday rotation and depolarization processes. The polarization angle changes from the center of the ring outwards to a radius >&ap; 1.7degr . Thus, the structure in polarization angle is not ring-like but resembles a disk, and it is larger than the ring in P. The rotation measure RM decreases almost continuously over the disk, from RM ~ 0 rad m-2 at the edge, to -8 rad m-2 in the center, while outside the ring the RM is slightly positive. This radial variation of RM yields stringent constraints on the nature of the ring-like structure, because it rules out any spherically symmetrical magnetic field configuration, such as might be expected from supernova remnants or wind-blown bubbles. We discuss several possible connections between the ring and known objects in the ISM, and conclude that the ring is a predominantly magnetic funnel-like structure. This description can explain both the field reversal from outside to inside the ring, and the increase in magnetic field, probably combined with an electron density increase, towards the center of the ring. The ring-structure in P is most likely caused by a lack of depolarization due to a very uniform RM distribution at that radius. Beyond the ring, the RM gradient increases, depolarizing the polarized emission, so that the polarized intensity decreases. In the southwestern corner of the field a pattern of narrow filaments of low polarization, aligned with Galactic longitude, is observed, indicative of beam depolarization due to abrupt changes in RM. This explanation is supported by the observed RM.

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, and is consistent with earlier estimates. The multipole spectral index 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 of about 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.

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, and is consistent with earlier estimates. The multipole spectral index 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 of about 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.

With the Westerbork Synthesis Radio Telescope (WSRT), multi-frequency polarimetric images were taken of the diffuse radio synchrotron background in a region centered on (l,b) = (161,16). The observations were done simultaneously in 5 frequency bands from 341 MHz to 375 MHz, with 5 arcmin resolution. Ubiquitous structure on arcminute and degree scales in the polarized intensity and polarization angle, combined with no observed structure in total intensity, indicates that the structure in the polarized radiation must be due to Faraday rotation and depolarization mostly in the warm nearby Galactic interstellar medium (ISM). Beam depolarization most likely creates "depolarization canals" of one beam wide, while depth depolarization is responsible for creating most of the structure on scales larger than a beam width. Rotation measures RM are in the range -17 < RM < 10 rad/m2 with a non-zero average of about -3.4 rad/m2. The gradient and average RM are consistent with a regular magnetic field of about 1 uG which has a pitch angle of p = -14 degrees. 13 Extragalactic sources in the field have |RM| < 13 rad/m2, with an estimated intrinsic source contribution of 3.6 rad/m2. The RMs of the extragalactic sources show a gradient (with a sign reversal) that is about 3 times larger than the gradient in the RMs of the diffuse emission, and that is approximately in Galactic latitude. This difference is ascribed to a vastly different effective length of the line of sight. The observations are interpreted in terms of a single-cell-size model of the warm ISM which contains gas and magnetic fields, with a polarized background.

We study the evolution of galaxies in clusters by the analysis of a sample of about 3000 galaxies, members of 59 clusters from the ESO Nearby Abell Cluster Survey (ENACS). We distinguish four cluster galaxy populations, based on their radial and velocity distributions within the clusters. Using the class of ellipticals and S0's (excluding the very bright ellipticals), we determine the average cluster mass profile, that we compare with mass models available from numerical simulations. We then use this cluster mass profile to solve for the anisotropy profiles of the three other cluster galaxy populations, viz. the very bright ellipticals, the early spirals, and the late spirals with the emission-line galaxies. We discuss the implications of our findings for the evolution of cluster galaxies.

We determine the mass profile of an ensemble cluster built from combining together 59 galaxy clusters, observed in the ESO Nearby Abell Cluster Survey. The mass profile is derived from the projected phase-space distribution of elliptical and S0 galaxies, for which there is independent evidence that they move on nearly isotropic orbits in the cluster potential. Application of the Jeans equation yields a non-parametric estimate of the cumulative mass profile of the ensemble cluster. We compare our estimate with several analytical models from the literature, and find that a sizeable core in the cluster mass distribution is not required by our data. The total cluster mass density is well traced by the luminosity density of ellipticals and S0s, when the brightest ellipticals (with MR <= -22+5 log h) are excluded from the sample.