The observed infall of galaxies towards the Virgo cluster

We examine the velocity field of galaxies around the Virgo cluster induced by its overdensity. A sample of 1792 galaxies with distances from the Tip of the Red Giant Branch, the Cepheid luminosity, the SNIa luminosity, the surface brightness fluctuation method, and the Tully-Fisher relation has been used to study the velocity-distance relation in the Virgocentric coordinates. Attention was paid to some observational biases affected the Hubble flow around Virgo. We estimate the radius of the zero-velocity surface for the Virgo cluster to be within (5.0 - 7.5) Mpc corresponding to (17 - 26)^\circ at the mean cluster distance of 17.0 Mpc. In the case of spherical symmetry with cosmological parameter \Omega_m=0.24 and the age of the Universe T_0= 13.7 Gyr, it yields the total mass of the Virgo cluster to be within M_T=(2.7 - 8.9) * 10^{14} M_\sun in reasonable agreement with the existing virial mass estimates for the cluster.Comment: 22 pages, 11 figures, 2 tables. Accepted for publication in MNRA

Our Peculiar Motion Away from the Local Void

The peculiar velocity of the Local Group of galaxies manifested in the Cosmic Microwave Background dipole is found to decompose into three dominant components. The three components are clearly separated because they arise on distinct spatial scales and are fortuitously almost orthogonal in their influences. The nearest, which is distinguished by a velocity discontinuity at ~7 Mpc, arises from the evacuation of the Local Void. We lie in the Local Sheet that bounds the void. Random motions within the Local Sheet are small. Our Galaxy participates in the bulk motion of the Local Sheet away from the Local Void. The component of our motion on an intermediate scale is attributed to the Virgo Cluster and its surroundings, 17 Mpc away. The third and largest component is an attraction on scales larger than 3000 km/s and centered near the direction of the Centaurus Cluster. The amplitudes of the three components are 259, 185, and 455 km/s, respectively, adding collectively to 631 km/s in the reference frame of the Local Sheet. Taking the nearby influences into account causes the residual attributed to large scales to align with observed concentrations of distant galaxies and reduces somewhat the amplitude of motion attributed to their pull. On small scales, in addition to the motion of our Local Sheet away from the Local Void, the nearest adjacent filament, the Leo Spur, is seen to be moving in a direction that will lead to convergence with our filament. Finally, a good distance to an isolated galaxy within the Local Void reveals that this dwarf system has a motion of at least 230 km/s away from the void center. Given the velocities expected from gravitational instability theory in the standard cosmological paradigm, the distance to the center of the Local Void must be at least 23 Mpc from our position. The Local Void is large!Comment: Tentatively scheduled for Astrophysical Journal, 676 (March 20), 2008. 18 figures, 3 tables including web link for 2 tables, web links to 2 video

Light to Mass Variations with Environment

Large and well defined variations exist between the distribution of mass and the light of stars on extragalactic scales. Mass concentrations in the range 10^12 - 10^13 M_sun manifest the most light per unit mass. Group halos in this range are typically the hosts of spiral and irregular galaxies with ongoing star formation. On average M/L_B ~ 90 M_sun/L_sun in these groups . More massive halos have less light per unit mass. Within a given mass range, halos that are dynamically old as measured by crossing times and galaxy morphologies have distinctly less light per unit mass. At the other end of the mass spectrum, below 10^12 M_sun, there is a cutoff in the manifestation of light. Group halos in the range 10^11 - 10^12 M_sun can host dwarf galaxies but with such low luminosities that M/L_B values can range from several hundred to several thousand. It is suspected that there must be completely dark halos at lower masses. Given the form of the halo mass function, it is the low relative luminosities of the high mass halos that has the greatest cosmological implications. Of order half the clustered mass may reside in halos with greater than 10^14 M_sun. By contrast, only 5-10% of clustered mass would lie in entities with less than 10^12 M_sun.Comment: 15 pages, 9 figures, 2 tables, Accepted Astrophysical Journal 619, 000, 2005 (Jan 1

The influence of galaxy surface brightness on the mass-metallicity relation

We study the effect of surface brightness on the mass-metallicity relation using nearby galaxies whose gas content and metallicity profiles are available. Previous studies using fiber spectra indicated that lower surface brightness galaxies have systematically lower metallicity for their stellar mass, but the results were uncertain because of aperture effect. With stellar masses and surface brightnesses measured at WISE W1 and W2 bands, we re-investigate the surface brightness dependence with spatially-resolved metallicity profiles and find the similar result. We further demonstrate that the systematical difference cannot be explained by the gas content of galaxies. For two galaxies with similar stellar and gas masses, the one with lower surface brightness tends to have lower metallicity. Using chemical evolution models, we investigate the inflow and outflow properties of galaxies of different masses and surface brightnesses. We find that, on average, high mass galaxies have lower inflow and outflow rates relative to star formation rate. On the other hand, lower surface brightness galaxies experience stronger inflow than higher surface brightness galaxies of similar mass. The surface brightness effect is more significant for low mass galaxies. We discuss implications on the different inflow properties between low and high surface brightness galaxies, including star formation efficiency, environment and mass assembly history

A CFD and FEM Approach to a Multicompartmental Poroelastic Model for CSF Production and Circulation with Applicationsin Hydrocephalus Treatment and Cerebral Oedema

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.This study introduces a Multiple-Network Poroelastic Theory (MPET) model, coupled with finite-volume based Computational fluid dynamics (CFD) for the purpose of studying, in detail, the effects of obstructing Cerebrospinal fluid (CSF) transport within an image-derived cerebral environment. The MPET representation allows the investigation of fluid transport between CSF, brain parenchyma and cerebral blood, in an integral and comprehensive manner. Key novelties of this model are the casting of multidimensional MPET in a Finite Element Method (FEM) framework, the amalgamation of anatomically accurate choroid plexuses with their feeding arteries and a simple relationship relaxing the constraint of a unique permeability for the CSF compartment. This model is used to demonstrate the impact of fourth ventricle outlet obstruction (FVOO). The implications of treating such a clinical condition with the aid of endoscopic third (ETV) and endoscopic fourth (EFV) ventriculostomy are considered. Finally, we outline the impact of the FEM based MPET framework in understanding oedema, and its ongoing evolution