* Astronomy

Title: Dwarf Galaxies and the Cosmic Web
Authors: Alejandro Benitez-Llambay, Julio F. Navarro, Mario G. Abadi, Stefan Gottloeber, Gustavo Yepes, Yehuda Hoffman, Matthias Steinmetz

We use a cosmological simulation of the formation of the Local Group of Galaxies to identify a mechanism that enables the removal of baryons from low-mass halos without appealing to feedback or reionisation. As the Local Group forms, matter bound to it develops a network of filaments and pancakes. This moving web of gas and dark matter drifts and sweeps a large volume, overtaking many halos in the process. The dark matter content of these halos is unaffected but their gas can be efficiently removed by ram-pressure. The loss of gas is especially pronounced in low-mass halos due to their lower binding energy and has a dramatic effect on the star formation history of affected systems. This "cosmic web stripping" may help to explain the scarcity of dwarf galaxies compared with the numerous low-mass halos expected in \Lambda CDM and the large diversity of star formation histories and morphologies characteristic of faint galaxies. Although our results are based on a single high-resolution simulation, it is likely that the hydrodynamical interaction of dwarf galaxies with the cosmic web is a crucial ingredient so far missing from galaxy formation models.

Read more (764kb, PDF)

Title: A List of Dwarf Galaxies in the Local Supercluster
Authors: D. I. Makarov, R. I. Uklein

We report a list of groups consisting of dwarf galaxies only. The sample contains 126 objects, mainly combined in pairs. The most populated group contains six dwarf galaxies. The majority of systems considered reside in the low-density regions and evolve unaffected by massive galaxies. The characteristic sizes and velocity dispersions of groups are 30 kpc and 11 km/s, respectively. They resemble the associations of dwarf galaxies, but are more compact. On the whole, groups and associations form a continuous sequence. Alike the associations, our groups possess high mass-to-luminosity ratios, what is indicative of a large amount of dark matter present in these systems.

Read more (896kb, PDF)

Hubble Uncovers Tiny Galaxies Bursting with Starbirth in Early Universe

Using its infrared vision to peer nine billion years back in time, the NASA/ESA Hubble Space Telescope has uncovered an extraordinary population of tiny, young galaxies that are brimming with star formation.
The galaxies are churning out stars at such a rate that the number of stars in them would double in just ten million years. For comparison, the Milky Way has taken a thousand times longer to double its stellar population.
These newly discovered dwarf galaxies are around a hundred times smaller than the Milky Way. Their star formation rates are extremely high, even for the young Universe, when most galaxies were forming stars at higher rates than they are today. They have turned up in the Hubble images because the radiation from young, hot stars has caused the oxygen in the gas surrounding them to light up like a fluorescent sign.
Astronomers believe this rapid starbirth represents an important phase in the formation of dwarf galaxies, the most common galaxy type in the cosmos.
Read more 

Puzzling dwarf galaxies finally make sense
Supercomputer model factored in a phenomenon known as stellar wind

It has long been a mystery why small galaxies don't have as many stars and matter in their centers as predicted. Now scientists have found the answer with a new simulation of galaxy and star formation.
All galaxies are thought to form inside large cradles of invisible stuff called dark matter. Scientists can't measure dark matter directly, but they suspect it's there because of its telltale gravitational tug on regular matter. And miniature galaxies called dwarf galaxies seem to have even higher proportions of dark matter than regular galaxies.
Read more