I went on a little bit of a twitter bender yesterday concerning the early claims about excessive mass galaxies at excessive redshift, which went on lengthy sufficient I assumed I ought to share it right here.
For these watching the astro group freak out about vibrant, excessive redshift galaxies being detected by JWST, some historic context in an amusing anecdote…
The 1998 October convention was titled “After the darkish ages, when galaxies had been younger (the universe at 2 < z < 5).” That proper there tells you what we had been anticipating. Redshift 5 was excessive – when the universe was a mere billion years outdated. Earlier than that, not a lot occurring (darkish ages).
This was when the now well-known SN Ia outcomes corroborating the acceleration of the enlargement price predicted by concordance LCDM had been shiny and new. Many people already strongly suspected we would have liked to place the Lambda again in cosmology; the SN outcomes sealed the deal.
One of many many traces of proof resulting in the rehabilitation of Lambda – beforehand anathema – was that we would have liked a bit extra time to get noticed buildings to kind. One desires the universe to be older than its contents, an on and off downside with globular clusters for ceaselessly.
A pure query that arises is simply how early do galaxies kind? The horizon of z=7 got here up in dialogue at lunch, with these of us who had been observers questioning how we’d entry that (JWST being the reply lengthy within the making).
Famed simulator Carlos Frenk was there, and warranted us to not fear. He had already accomplished LCDM simulations, and knew the timing.
“There may be nothing above redshift 7.”
He additionally added “don’t quote me on that,” which I’ve revered till now, however I believe the statute of limitations has expired.
Everybody current instantly pulled out their pockets and chipped in $5 to endow the “7-up” prize for the primary persuasive detection of an object at or above redshift seven.
A committee was fashioned to guage claims which may seem within the literature, composed of Carlos, Vera Rubin, and Bruce Partridge. They made it clear that they might require a excessive commonplace of proof: not less than two well-identified traces; no dropouts or photo-z’s.
That commonplace wasn’t met for over a decade, with z=6.96 being the file holder for some time. The 7-up prize was solely tongue in cheek, and everybody forgot about it. Marv Leventhal had supplied to carry the cash; I suppose he ended up pocketing it.
I imagine the winner of the 7-up prize ought to have been Nial Tanvir for GRB090423 at z~8.2, however I haven’t checked if there is perhaps different credible claims, and I can’t communicate for the committee.
At any price, I don’t assume anybody would now severely dispute that there are galaxies at z>7. The query is how massive do they get, how early? And the everlasting cell goalpost, what does LCDM actually predict?
Carlos was not mistaken. There is no such thing as a onerous cutoff, so I gained’t quibble about arbitrary boundaries like z=7. It takes time to assemble massive galaxies, & LCDM does make a fairly clear prediction concerning the timeline for that to happen. Mainly, they shouldn’t be all that massive that quickly.
Here’s a determine tailored from the thesis Jay Franck wrote right here 5 years in the past utilizing Spitzer information (spherical factors). It reveals the attribute brightness (Schechter M*) of galaxies as a operate of redshift. The info diverge from the LCDM prediction (squares) as redshift will increase.
Remarkably, the information roughly observe the inexperienced line, which is an L* galaxy magically put in place on the inconceivably excessive redshift of z=10. Galaxies appear to have gotten massive impossibly early. Because of this you see us astronomers flipping our lids on the JWST outcomes. Can’t occur.
Besides that it will probably, and was predicted to take action by Bob Sanders 1 / 4 century in the past: “Objects of galaxy mass are the primary virialized objects to kind (by z=10) and bigger construction develops quickly.”
The reason being MOND. After decoupling, the baryons discover themselves bereft of radiation assist and out of the blue deep within the low acceleration regime. Construction grows quick and turns into nonlinear nearly instantly. It’s as if there’s tons extra darkish matter than we infer these days.
I referreed that paper, and was a bit upset that Bob had beat me to it: I used to be doing one thing comparable on the time, with comparable outcomes. As an alternative of being onerous to kind construction shortly as in LCDM, it’s virtually inconceivable to keep away from in MOND.
He beat me to it, so I deserted writing that paper. No must say the identical factor twice! Didn’t assume we’d have to attend so lengthy to check it.
I’ve reviewed this many instances. Most lately in January, in anticipation of JWST, on my weblog.
See additionally http://astroweb.case.edu/ssm/mond/LSSinMOND.html… and the references therein. For a extra formal evaluate, see A Story of Two Paradigms: the Mutual Incommensurability of LCDM and MOND. Or Modified Newtonian Dynamics (MOND): Observational Phenomenology and Relativistic Extensions. Or Modified Newtonian Dynamics as an Various to Darkish Matter.
However you get the purpose. Each time you see somebody describe the large galaxies JWST is seeing as surprising, what they imply is surprising in LCDM. It doesn’t shock me in any respect. It’s solely anticipated in MOND, and was predicted a priori.
The actually fascinating factor to me, although, stays what LCDM actually predicts. I already see individuals rationalizing excuses. I’ve seen this occur earlier than. Many instances. That’s why the sector is in a rut.
So are we gonna speak our manner out of it this time? I’m not enthusiastic about how; I’m positive somebody will recommend one thing that can acquire traction regardless of how unsatisfactory.
The one fascinating query is that if LCDM makes a prediction right here that may’t be fudged. If it does, then it may be falsified. If it doesn’t, it isn’t science.
However can we? Is LCDM topic to falsification? Or will we but once more gaslight ourselves into believing that we knew all of it alongside?
