Merger as Intermittent Accretion

The Self-Similar Secondary Infall Model (SSIM) is modified to simulate a merger event. The model encompass spherical versions of tidal stripping and dynamical friction that agrees with the Syer & White merger paradigm's behaviour. The SSIM shows robustness in absorbing even comparable mass perturbations and returning to its original state. It suggests the approach to be invertible and allows to consider accretion as smooth mass inflow merging and mergers as intermittent mass inflow accretion.Comment: letter accepted by A&A 29/09/08, 4 pages, colour figure

X-ray Constraints on Cluster Magnetic Fields

Lower limits to the intracluster magnetic field are derived from modeling broad band X-ray spectra of 6 galaxy clusters with radio halos (A401, A754, A1367, Coma (A1656), A2256, and A2319). The 0.7 - 10 keV spectra for all clusters were obtained with the Advanced Satellite for Cosmology and Astrophysics (ASCA) Gas Imaging Spectrometer (GIS). For A401, A754, A1367, and A1656, data from the HEAO1-A2 High Energy Detector (HED) (2-60 keV) was included in a joint fit to further constrain the allowed non-thermal component. Upperlimits to the non-thermal X-ray emission are a factor of approximately 10 improvement over previous values. Lower limits to the average magnetic field derived from these upperlimits and the radio spectral parameters range from 0.08 - 0.30 microGauss. A seed intracluster field amplified by turbulence from galaxy motion through the intracluster medium should have an average value in the range of 0.1-0.2 (Goldman & Rephaeli, 1991; De Young, 1992), thus the lack of any detections makes it unlikely that field amplification is due to galaxy wakes. In addition, all of these clusters have an asymmetric surface brightness distribution while several also have X-ray spectroscopic evidence of a merger. We suggest that cluster mergers rather than galaxy wakes are the source of the magnetic field amplification.Comment: 24 pages, 6 figures, to appear in PASJ 5

Isolated and non-isolated dark matter halos and the NFW profile

We compare the conclusions reached using the coarse-graining technique employed by Henriksen (2004) for a one degree of freedom (per particle) collisionless system, to those presented in a paper by Binney (2004) based on an exact one degree of freedom model. We find agreement in detail but in addition we show that the isolated 1D system is self-similar and therefore unrelaxed. Fine graining of this system recovers much less prominent wave-like structure than in a spherically symmetric isotropic 3D system. The rate of central flattening is also reduced in the 1D system. We take this to be evidence that relaxation of collisionless systems proceeds ultimately by way of short wavelength Landau damping. N-body systems, both real and simulated, can be trapped in an incompletely relaxed state because of a break in the cascade of energy to small scales. This may be due to the rapid dissipation of the small scale oscillations in an isolated system, to the existence of conserved quantities such as angular momentum, or to the failure in simulations to resolve sub-Jeans length scales. Such a partially relaxed state appears to be the NFW state, and is to be expected especially in young systems. The NFW core is shown to be isolated. In non-isolated systems continuing coarse-grained relaxation should be towards a density core in solid body rotation.Comment: 14 pages, MNRAS, submitted 21 June 200

Estimated central blood volume in cirrhosis

The estimated central blood volume (i.e., blood volume in the heart cavities, lungs and central arterial tree) was determined by multiplying cardiac output by circulatory mean transit time in 19 patients with cirrhosis and compared with sympathetic nervous activity and circulating level of atrial natriuretic factor. Arterial norepinephrine level, an index of overall sympathetic nervous activity (3.08 nmol/L in patients vs. 1.36 nmol/L in controls; p < 0.01) was negatively correlated (r = -0.54, p < 0.01) with estimated central blood volume (mean = 23 ml/kg in patients vs. 27 ml/kg in controls; p < 0.05). Similarly, renal venous norepinephrine level (an index of renal sympathetic tone; 4.26 nmol/L in patients vs. 1.78 nmol/L in controls; p < 0.01) was inversely correlated with estimated central blood volume (r = -0.53, n = 18, p < 0.02). No significant correlation could be established between arterial atrial natriuretic factor level (8.9 pmol/L in patients vs. 9.6 pmol/L in controls; not significant) and estimated central blood volume. Hemodynamic values were subsequently modified with oral propranolol (80 mg). During -adrenergic blockade, the mean estimated central blood volume was not altered significantly, except in six patients who exhibited decreases in mean arterial blood pressure (85 to 69 mm Hg; n = 6) and decreases in mean estimated central blood volume (23.2 to 20.6 ml/kg; n = 6, p < 0.05). Slight increases were observed in mean right atrial pressure (2.2 to 3.7 mm Hg; n = 14, p < 0.05); this change was positively correlated with the change in estimated central blood volume (r = 0.44, n = 14, p = 0.06). In conclusion, reduced estimated central blood volume probably unloads volume receptors and baroreceptors, thus provoking enhanced overall and renal sympathetic nervous activity and thereby contributing to increased water and salt retention in cirrhosis. During -adrenergic blockade estimated central blood volume changes correlated with alterations in preload and afterload. These findings indicate that central circulatory and arterial underfilling is a key element of the hemodynamic derangement observed in cirrhosis