High redshift QSO absorption line systems show a wide range of metallicities, from one thousandth solar up to 1/3 solar. Thus, while the average metallicity of the Universe certainly must have increased since the early epochs, the situation is more complex than a simple picture where high redshift means metal-poor, and low redshift metal-rich. Objects with high and low metallicities are found at all redshifts. Surely we expect objects that in the local Universe appear as metal deficient to be even more deficient at high redshift, if we could observe their precursors. Also the ancestors of the local metal rich galaxy population, i.e. the giant spirals and ellipticals, should have started out with very low abundances unless they were gradually built up by merging smaller galaxies. Currently, both the theoretical and observational pictures, tell that the latter is an important mechanism. Dwarf galaxies, the survivors who form the local metal-poor galaxy population, may thus be the principal building blocks of the Universe on large scales.
The morphology density relation is believed to indicate that galaxy evolution is affected by the environment in which the galaxy finds itself. Specifically, there is strong evidence to suggest that star formation is suppressed when galaxies enter high density environments such a clusters. This suppression of star formation is not well understood, and a number of processes (including ram pressure stripping, galaxy strangulation and galaxy harassment) have been proposed to account for it.
I cannot tell, I haven't seen such data. Maybe someone else knows better.seabass101 said:Thus, shouldn't we see a statistically significant difference in metallicity when we compute the mean for old and new galaxies? Is the problem that it's hard to tell the difference based on the data available?
The Hubble Deep Field (HDF) is an image taken by the Hubble Space Telescope (HST) in 1995 that shows a small patch of the sky in the constellation Ursa Major. It is considered one of the most important astronomical images ever taken because it captures thousands of galaxies, some of which are among the oldest and most distant in the universe.
The Hubble Deep Field was created by pointing the HST at a seemingly empty patch of sky and taking multiple long-exposure images over the course of 10 days. These images were then combined to create a single, deep image that revealed thousands of galaxies that were previously unknown.
The ancient galaxies in the Hubble Deep Field are some of the oldest and most distant galaxies ever observed. They give us a glimpse into the early universe and help us understand how galaxies formed and evolved over time.
The Hubble Deep Field allows us to see galaxies that existed as far back as 13 billion years ago, just a few hundred million years after the Big Bang. This is because the light from these galaxies has been traveling towards us for billions of years, giving us a glimpse into the distant past of the universe.
The Hubble Deep Field and ancient galaxies have taught us a great deal about the history of the universe. They have helped confirm the Big Bang theory, provided evidence for the existence of dark matter, and shed light on how galaxies form and evolve. They have also sparked further research and discoveries in the field of astronomy and astrophysics.