Probing the dark matter issue in f(R)-gravity via gravitational lensing

A few days ago in gr-qc  journal club we discussed an interesting paper by a member of our own institute, Probing the dark matter issue in f(R)-gravity via gravitational lensing.1. Background Dark Matter We theoretically expect dark matter to exist based largely on  extensive observations of both dynamics (rotation curves and objects such as the Read More …

Halos gone MAD

I have previously blogged about Structure finding in cosmological simulations and the Haloes Going Mad conference in Madrid this past spring–there you will find the basic background if you are unfamiliar with the subject and I’ll skip that in this post. The result of this conference was a Halo-finder comparison project and its findings were recent posted on the physics arxiv in the paper Haloes gone MAD: The Halo-Finder Comparison Project. I’ll summarize them here.

The paper concentrates on comparing codes on given test data, not comparing the results of various codes to observations, provides a standard test suite and proposes a standard methodology of comparison, both on test, isolated, halos and on a simulation of cosmological volume. Read More …

Kliq Soft Launch

Kliq soft launched this weekend. You can schedule a meetup (dinner, drinks, you name it) in just a few thumb taps with your local facebook friends or be adventurous and be introduced to a friend of a friend. This is just a taste of what’s to come. Get Kliq on the iPhone App Store at http://itunes.apple.com/lt/app/kliq/id412169676 or visit http://kliq.in. Read More …

Locally Cold Flows from Large-Scale Structure

Walls, filaments and voids: it is thought that the large scale distribution of matter is a complex network of galaxies and galaxy clusters connected by elongated filaments and sheetlike walls, outlining vast underdense regions known as voids and meeting at dense and compact regions known as haloes. Aragon-Calvo et. al. in [1] build upon the SpineWeb framework outlined in [2] , which has the capability of identifying these walls, filaments and clusters in cosmological simulations to examine the effect of environment (namely whether a galaxy is “living” in a wall or a void) on the dispersion of the Hubble flow around the Milky, which is significantly lower than theoretical expectations. They show that the measured dispersion could be a result of the fact that Milky Way resides inside a wall of radius around 10Mpc, which is supported by data. Read More …

Green's functions

Some of the most important equations in physics can be solved by constructing a beast with a curious set of properties, called a Green’s function. This post contains some interesting nuggets from a lecture I gave on St. Patrick’s day about Green’s functions to the course I assist, Mathematical Methods in the Physical Sciences II. I’ll Read More …

The Andromeda Galaxy's Globular Cluster System

Globular Clusters (GCs) Globular clusters are groups of roughly spherical, densely packed stars. They are thought to have formed at the same time as most galaxies and the stars which make them up are some of the oldest known–thus GCs are an excellent probe of galaxy formation and evolution. They have a high central stellar Read More …