Accelerated Structure Formation: the Early Emergence of Massive Galaxies and Clusters of Galaxies (2406.17930v2)

Abstract: Galaxies in the early universe appear to have grown too big too fast, assembling into massive, monolithic objects more rapidly than anticipated in the hierarchical $\Lambda$CDM structure formation paradigm. The available photometric data are consistent with there being a population of massive galaxies that form early ($z \gtrsim 10$) and quench rapidly over a short ($\lesssim 1$ Gyr) timescale, consistent with the traditional picture for the evolution of giant elliptical galaxies. Similarly, kinematic observations as a function of redshift show that massive spirals and their scaling relations were in place at early times. Explaining the early emergence of massive galaxies requires either an extremely efficient conversion of baryons into stars at $z>10$ or a more rapid assembly of baryons than anticipated in $\Lambda$CDM. The latter possibility was explicitly predicted in advance by MOND. We discuss some further predictions of MOND, such as the early emergence of clusters of galaxies and early reionization.

• The paper highlights the tension between observations of massive galaxies at high redshifts ( z ≳ 10) and the slow hierarchical assembly predicted by the standard Cold Dark Matter (CDM) model.
• It discusses alternative frameworks like Modified Newtonian Dynamics (MOND), suggesting its non-linear dynamics could explain the unexpectedly rapid, potentially monolithic, formation of massive early galaxies.
• The implications suggest existing models may need significant revision or alternative gravitational theories should be considered, emphasizing the importance of future observational data for verification.

Accelerated Structure Formation: The Early Emergence of Massive Galaxies and Clusters of Galaxies

The formation and evolution of galaxies remain central to cosmological research. The hierarchical paradigm of cold dark matter (CDM) posits a gradual assembly of galaxies through mergers of smaller subunits. However, discrepancies have emerged, leading researchers to question the adequate understanding of this process, particularly regarding the development of massive galaxies in the early universe. In the document "Accelerated Structure Formation: the Early Emergence of Massive Galaxies and Clusters of Galaxies," the authors scrutinize unexplained observations, propose alternative models, and identify predictions inconsistent with the conventional CDM paradigm.

Key Observations and Challenges

The data considered indicate an abundance of massive galaxies at redshifts $z \gtrsim 10$, a discovery at odds with the hierarchical model's expectations for gradual assembly and star formation in stages. The observation of substantial masses within less than 1 billion years post-Big Bang challenges models that typically expect hierarchical assembly to predominate on timescales of several gigayears. Furthermore, the presence of well-established scaling relations such as the Tully-Fisher relation early in the timeline suggests rapid formation of organized, dynamically mature galaxy structures.

MOND and Alternative Scenarios

The Modified Newtonian Dynamics (MOND) framework has been posited as an alternative, offering a compelling explanation for the unexpectedly early galaxy formation. MOND's nonlinear dynamics enable more efficient and accelerated baryonic collapse compared to traditional CDM models. Specifically, in MOND, galaxies may form rapidly as monolithic entities, without requiring extensive restructuring from smaller components. This alleviates the time constraint difficulties imposed by hierarchical assembly.

The authors further discuss MOND's predictions for early universe phenomena, such as the early reionization corresponding to rapid first-light sources, and the early formation of large-scale structures. These predictions align with current empirical findings—such as rapid star formation bursts and their subsequent quenching over brief timelines. Such observations support reconsidering galaxy formation theories beyond the CDM-dominated models.

Implications and Speculations

The implications of these observations are profound, affecting both theoretical astrophysics and observational cosmology. From a theoretical standpoint, accommodating these data within existing frameworks may demand significant revisions to star formation efficiency estimates, adjustments in baryonic feedback processes, and potentially re-evaluating foundational cosmological assumptions. Empirically, future high-confidence spectroscopic datasets provided by next-generation observatories, such as the James Webb Space Telescope, will be instrumental in further elucidating these formation epochs and providing robust verifications or falsifications of theory.

Conclusion

The document sparks critical discussion on standard cosmological models, urging reevaluation in light of emerging contradictions. By highlighting the tensions between the early emergence of massive galaxies and the predicted hierarchical assembly timeline, the authors promote exploration into modified gravitational theories like MOND and call for integrated cosmological frameworks capable of reconciling these observations with theoretical predictions. Continued endeavors in this domain may not only refine our cosmological paradigm but also enhance our comprehension of galaxy formation mechanics on cosmic scales.