Far away galaxies are very active!

[bojan]

Two interesting articles on star formation in distant galaxies..
Old times were a very busy place, it seems!
http://physicsworld.com/cws/article/news/2013/oct/23/farthest-confirmed-galaxy-is-a-prolific-star-creator
http://physicsworld.com/cws/article/news/2013/oct/18/astronomers-discover-furthest-gravitational-lens

[madbadgalaxyman]

See also this recent Nature paper about a primeval galaxy with a Star Formation Rate of several hundred solar masses per annum.

www.nature.com/nature/journal/v502/n7472/full/nature12657.html (http://www.nature.com/nature/journal/v502/n7472/full/nature12657.html)

You can access the first page, for free, using "ReadCube"

(a related observation is that most of the stars in the bulge component of our own Galaxy formed 10-12 billion years ago )

(the current SFR of the Milky Way is about 2 solar masses per annum, according to a recent weighted average. This is about typical for a large spiral galaxy. )
(NGC 253 has about 3 or 4 solar masses in stars, right near to its centre, forming every year, due to a circum-nuclear starburst. )

[Shiraz]

interesting reading Bojan - thanks for posting.

Robert, looks like the Nature paper is the one referenced in the first article Bojan linked to (Finkelstein et al)

[madbadgalaxyman]

The degree to which there was "early assembly" of galaxies (stars formed early on in the universe) vs. "late assembly" of galaxies (e.g. stars formed at many times, up to and including today) still seems to cause controversy. Large Bulges and Large elliptical galaxies formed early on, but smaller galaxies and the disk components of spiral galaxies seem to still be growing due to considerable ongoing star formation.
Some evidence for later (and ongoing) galaxy formation is:
- gas being funnelled into the centres of spiral galaxies by their bar components, leading to the gradual formation of small bulges
- evidence (not conclusive) for the accretion of cold gas in the outermost parts of spiral galaxies, leading to star formation and the build-up of the disk component in the outer parts of a galaxy. This gas may come from intergalactic space.
- Massive gaseous halos around dwarf galaxies that contain enough gas to keep small galaxies growing and forming stars for a long time into the future.
- merger and accretion of galaxies, e.g. obvious cases of ongoing galaxy merger, plus less obvious cases where the halos of galaxies like M31 and the Milky Way contain stars that originated in dwarf galaxies that were cannibalized.
- some elliptical galaxies are surrounded by "incipient disks" of gas, which may eventually form disks of stars around the elliptical component. The gas is at very low density, so more sensitive HI surveys may conceivably find that this phenomenon is common.

cheers,
Bad galaxy man

Added in edit:
The current Star Formation Rate (e.g. in solar masses per annum) in galaxies is, on average, much lower than it is in distant galaxies seen at large look-back times. Thus, several textbooks give the impression that the universe is today nearing the end of ongoing star formation (with the galaxies gradually dimming due to the death of the existing stars). However, results such as Williams et al., 2009, ApJ, 695, L15 (( http://iopscience.iop.org/1538-4357/695/1/L15)) , which implies that the outer disk of M33 is much younger than its inner disk, suggest that the outer parts of spiral galaxies are able to capture gas from external sources and therefore continue building up their stellar mass by means of star formation that continues for billions of years into the future. So perhaps we are much further from the dreaded "cold dark" era when the universe is completely dead!

Williams et al suggest that the rules of galaxy evolution may well be very distinct for relatively low mass galaxies like the LMC and M33. The type of gradual galaxy growth they infer for M33 is known in the trade as "inside-out disk formation"

[madbadgalaxyman]

The entire Nature paper which is causing all the fuss about a galaxy existing, apparently only 700 million years after the hypothetical big bang, can be found here, in preprint form:
(Nature insists on hiding all but the first page of the paper!!)

http://arxiv.org/abs/1310.6031

Some important results in this paper are:
(1) the extremely high star formation rate of this galaxy
(2) The fact that this is a small galaxy
(3) the idea that the gas in this galaxy , from which its stars are currently forming, is already enriched in heavy elements which (as far as we know) had to be expelled from previous generations of stars
(or is it possible that we are wrong about nucleosynthesis in the Big Bang?)

Hmmmm.....I must have a look at the actual evidence!
___________________________

Avi Loeb has recently written a book about the first galaxies that formed in the universe:

http://press.princeton.edu/titles/9914.html

(He is a theorist, so don't expect a simple exposition!!)

One well-regarded book about galaxy formation, which is suitable for scientifically literate people with a good amount of university maths and physics, is the second edition of Galaxy Formation by Malcolm S. Longair; this was published in 2007/2008 by Springer-Verlag.

http://www.amazon.com/Galaxy-Formation-Astronomy-Astrophysics-Library/dp/3540734775/ref=sr_1_1?ie=UTF8&qid=1382706451&sr=8-1&keywords=galaxy+formation+longair

[[ I have got this book on order, as I found that I could understand at least some of the easier chapters in a library copy of it (I have some tertiary physics and maths)
But even Longair's clear exposition is very theoretical and mathematical, with an awful lot of cosmology, and not a lot of hard evidence. It is not for the faint hearted! ]]