Stellar Archeology: A Cosmological View of Dwarf Galaxies
Living metal-poor stars represent the fossil records of the early cosmic star formation.
What Defines a Galaxy?
“A galaxy is a gravitationally bound collection of stars whose properties cannot be explained by a combination of baryons and Newton’s laws of gravity.” (Willman & Strader, http://arxiv.org/abs/1203.2608)
Unplugging the “Christmas tree”: what happened to high-redshift clumps of star formation?
The lack of observed major mergers at high-redshift has prompted discussion of inside-out growth, that is, galaxies building up their stellar populations by cold gas accretion, starting in the inner regions and gradually moving outwards. This picture is far from settled, however, and so the authors of this paper set out to investigate whether or not the observations match the theory.
Where’s the gas around galaxies at z~2?
Researchers at Caltech have used data from the Keck Baryonic Structure Survey to place quantitative constraints on the circumgalactic medium around galaxies at z~2. Measurements like these help us fine-tune our understanding of the interplay between gas and galaxies and, ultimately, galaxy formation and evolution.
A look-alike of z~2 galaxies in our backyard
NGC 5845 is a nearby compact galaxy, more similar to the recently discovered high redshift z~2 compact galaxies than to its low-redshift mates. This makes it rare and interesting, as its structure and kinematics can be studied much better than is possible at high redshift. The analysis reveal a prominent rotating stellar disk, suggesting that similar structures could be present in high-redshift compact galaxies too.
Have the tides turned for the formation of cE galaxies?
A specific class of elliptical galaxies called compact ellipticals, or cEs, are unusually compressed. Some speculate that these galaxies are petite because their outer layers have been stripped away by a neighboring galaxy; however, an alternative theory claims that these are regular elliptical galaxies that simply formed small and never contained stars in their outer regions. In order to differentiate between these two models, Howley et al. 2012 measured the dynamics of individual stars in one of our nearest neighbors, the compact elliptical M32.