What is the significance of the recently discovered nearby newborn galaxies?

[hellfire]

Recently, the NASA's Galaxy Evolution Explorer has found new forming galaxies at very low redshifts (z < 0.5):

http://www.galex.caltech.edu/MEDIA/2004-01/text.html

Quoting from the press release:

Previously, astronomers thought the universe's birth rate had dramatically declined and only small galaxies were forming.

What are the estimations of galaxy formation at present, and how "small" are these galaxies to be expected? Are there (mass) differences between the halos formed at z ~ 30, 20,... and the ones which lead to these new galaxies? Are these galaxies expected to contain stars without any metal content, or do these galaxies form in a qualitatively different ambient than the ones formed at z ~ 30, 20,...?

References would be appreciated.

 

[SpaceTiger]

What are the estimations of galaxy formation at present, and how "small" are these galaxies to be expected?

I'm a little bit confused by that quote from the press release, as I don't think that even small galaxies are expected to be forming at present. Perhaps they're referring to those formed out of the debris of interactions between larger galaxies.

The universe is thought to evolve in what's known as a "bottom-up" scenario, implying that the little things form first and then the big things form as combinations of the little ones. At the present epoch, things on the scale of galaxy clusters (tens of megaparsecs) are the most actively forming. We expect galaxies themselves (for the most part) to have formed long ago.

Here's a sample reference: link

Are these galaxies expected to contain stars without any metal content, or do these galaxies form in a qualitatively different ambient than the ones formed at z ~ 30, 20,...?

It's unlikely that they'd be formed from gas completely uncontaminated by metals, as even the intergalactic medium contains a small fraction that was presumably expelled from star-forming galaxies. They may have low metal content, however.

I would be hesitant to jump to the conclusion that these are "baby galaxies" of the type we see at high redshift, not just because of cosmological models, but also because there are other ways to induce bursts of star formation (such as interactions).

 

[hellfire]

Thank you for your comment.

Just a clarification to my previous post: When talking about „baby galaxies“ it is meant objects which are belived to have been massively formed from protogalaxies at z < 5, and mainly going through some process of bursts of star formation. I was wrong above assuming that yet an earlier phase of galaxy formation was meant.

You are right that smaller objects (starting from clouds of the size of globular clusters, sometime after recombination) merge to form the larger ones. Formation of baby galaxies takes place late, but it seams that early enough to assume that rather no formation is still ongoing. What I would like to know is in which extent the formation (mergers) may have some statistical “tail” which extends up to very low redshifts.

I would be hesitant to jump to the conclusion that these are "baby galaxies" of the type we see at high redshift, not just because of cosmological models, but also because there are other ways to induce bursts of star formation (such as interactions).

Yes, you may be right. But note that it seams that the other possibility is also open… (quoting from http://www.astronomy.com/asy/default.aspx?c=a&id=2674 "Living fossil" galaxies found nearby):

Alice Shapley of the University of California, Berkeley, notes that while the newborn galaxies closely resemble young galaxies soon after the Big Bang, they raise questions of comparison. She asks, "Are these newborn galaxies really identical to the distant galaxies in the early universe? Or are they hiding older stars masked by the glare of the young stars producing such large amounts of ultraviolet light?"

Another unsolved puzzle concerns what is triggering the strong bursts of star-making in the newborn galaxies. Shapley wonders, "Why is this happening only recently instead of 10 billion years ago, when the Milky Way formed?"

It could be that a long-running process is approaching an end, replies Heckman. "We know the rate of galaxy formation declined strongly over the history of the universe, and, right now, we could be seeing the last dregs of galaxy birth, the last few stragglers."

I was unable to find any paper, or something different than press releases about this subject.