# The impossible early galaxy formation

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## Main Question or Discussion Point

Is there general consensus that the universe is to young?

arXiv:1506.01377 [pdf, ps, other]
The Impossibly Early Galaxy Problem
Charles L. Steinhardt, Peter Capak, Dan Masters, Josh S. Speagle
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The current hierarchical merging paradigm and $\Lambda$CDM predict that the $z \sim 4-8$ universe should be a time in which the most massive galaxies are transitioning from their initial halo assembly to the later baryonic evolution seen in star-forming galaxies and quasars. However, no evidence of this transition has been found in many high redshift galaxy surveys including CFHTLS, CANDELS and SPLASH, the first studies to probe the high-mass end at these redshifts. Indeed, if halo mass to stellar mass ratios estimated at lower-redshift continue to $z \sim 6-8$, CANDELS and SPLASH report several orders of magnitude more $M \sim 10^{12-13} M_\odot$ halos than are possible to have formed by those redshifts, implying these massive galaxies formed impossibly early. We consider various systematics in the stellar synthesis models used to estimate physical parameters and possible galaxy formation scenarios in an effort to reconcile observation with theory. Although known uncertainties can greatly reduce the disparity between recent observations and cold dark matter merger simulations, even taking the most conservative view of the observations, there remains considerable tension with current theory.

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marcus
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Dearly Missed
Is there general consensus that the universe is too young?
arXiv:1506.01377 [pdf, ps, other]
The Impossibly Early Galaxy Problem
Charles L. Steinhardt, Peter Capak, Dan Masters, Josh S. Speagle
....
I don't think the age of the universe is at issue here, Wooly.
It is about astronomer's models of star formation, and galaxy formation. The authors, at the end with their conclusions, propose 3 possible explanations for what they see and they all have to do with modeling how structure formation works better--so that it can happen somewhat earlier.