Birth Pictures Of A Galaxy

August 13, 2015 9:19 AM

The Cosmic Web Imager at Palomar Observatory has been studying a system 10 billion light years away illuminated by two quasars. Now, a Caltech team has published pictures of the giant swirling disk of a protogalaxy being fed cool - 30,000 degree - gas by a filament of the cosmic web. This is the first time we have ever seen a galaxy being built, and it reveals unique new evidence about the early Universe and the still poorly-understood life and evolution of the galactic population. Abstract of letter in Nature (full paper paywalled).
posted by Devonian (11 comments total)

this is interesting because, until a few years (a decade?) ago, people assumed that gas that accreted onto galaxies during initial, early formation was heated by shocks. the problem then was that the hot gas didn't form stars quickly enough (because the gas needs to cool and clump together).

so astronomers were seeing galaxies that existed earlier than their models said was possible.

a solution to the problem was the suggestion that galaxies are fed with cooler gas in some way - the cool gas can form stars more quickly and so galaxies can form earlier. and this is evidence of that.
posted by andrewcooke at 9:34 AM on August 13, 2015 [3 favorites]

Yes, it's one of those marvellous occasions in science where there are some clearly-defined, incompatible, competing theories and one good observation heavily swings the balance.

There should be more soon: one of the rules of astronomy is that there's never just one of anything, and the team says they've got two more candidates already. Once you know what to look for, it's amazing what comes out. Plus, there's an upgraded instrument due to be installed on the Keck soon, so - ahem - watch this space...
posted by Devonian at 9:50 AM on August 13, 2015

So Devonian sorta answered my question with the term "incompatible"... I was going to ask if these were mutually exclusive. Is that true? That the cool model disproves the hot model?
posted by symbioid at 9:56 AM on August 13, 2015

the theory for hot gas accretion (spherical accretion, virialized via shocks) is pretty solid, classical physics. there's no reason it can't happen, and it probably does. it just can't do enough soon enough. and it's hard to prove something never happens. so it's more like "ok, we can see option B working, we don't need to wish for option A plus some weird effect we can't think of to make it early enough".

but i was an astronomer a long time ago, so i may be out of touch.

edit: actually, the spherical model may still be needed to explain damped lyman alpha systems and the like?
posted by andrewcooke at 10:03 AM on August 13, 2015

Non-paywalled paper. Cursory search didn't turn up the arXiv version, but Nature has some Stone Age rules about that, so it might take a while for the arXiv version to appear.

I'm apparently some sort of astronomer these days, but mostly in the dark matter end of things (and by mostly, I mean pretty nearly exclusively). I'll point out that the "cosmic web" that they are talking about looks like this. You can see the dark matter in simulation forming a spider-web like structure with nodes as the strands meet. Those nodes are the locations of proto-galaxies, and the paper is claiming they are seeing gas funneling into the galaxy along the strands themselves.

Here's another video of the same simulation with the visible matter and dark matter shown together. We obviously can't see the dark matter directly, so we need to find ways to infer its existence. But since it completely dominates gravitationally on large scales (i.e. outside of the inner portions of galaxies), the motion of visible matter on galactic and cosmological scales is driven by the location and evolution of dark matter.
posted by physicsmatt at 10:17 AM on August 13, 2015 [9 favorites]

If I'm not mistaken, the full paper is available from the Caltech library:
A giant protogalactic disk linked to the cosmic web (PDF).
(I can't tell for sure if there's a paywall or not from here, sorry.)
posted by RedOrGreen at 10:19 AM on August 13, 2015

Perhaps 'incompatible' was too strong; I've only ever been an amateur astronomer, and not much of one at that. Another of the rules of astronomy is that if something can happen, it probably has. But the next stage will be to start to find out the frequency with which the cold-gas system occurs and what sort of variances it has and thus how much of the galactic population it may apply to.

(on preview, I was going to say mumble-mumble dark matter is also involved so really this is early days mumble-mumble but I see the grown-ups have arrived. And that is a stunningly beautiful simulation of the cosmic web in physicsmatt's link...)
posted by Devonian at 10:23 AM on August 13, 2015 [1 favorite]

I love natural science breakthroughs that come accompanied by a youtube video explaining what's up. It's just nice to be able to see scientists really enthusiastic about what they're doing; that enthusiasm alone makes it that much easier to understand.
posted by lilies.lilies at 11:36 AM on August 13, 2015 [1 favorite]

the funny thing is that this is a really boring explanation for the early formation of galaxies... just more normal physics.
posted by ennui.bz at 7:24 PM on August 13, 2015

i'm not trying to be down on the research, just trying to point out that this is a pebble on the side of "anomalous existence of galaxies at early epoch can be explained by standard physics", which is way less exciting than the opposite. no cosmic string defects here...
posted by ennui.bz at 7:27 PM on August 13, 2015

The idea of a cold-gas accretion mode is not new -- it goes back to several papers in 1977. It was set aside for a while, but started to come back into fashion around 10 years ago when more accurate simulations of gas behavior found that continuous streams of dense, cold gas could funnel into galaxies without being shock-heated. For an example of what recent simulations show, see this paper.

It would thus be absolutely no surprise to find that this galaxy is accreting cold gas streaming along a filament -- that's now thought to be the dominant mode of gas accretion for the first few billion years of cosmic history. I have to admit that I don't find the press release image to be compelling evidence that they are actually seeing such a filament, though (which would be expected to be continuous, not gappy like the thing outlined in that image). Perhaps there is stronger evidence in the paywalled paper, though.
posted by janewman at 8:01 PM on August 13, 2015