CMC2 - Speakers

Invited opening talk: A selection of observations in conflict with ΛCDM 

Abstract: The ever-growing quantity and quality of astronomical data today has underpinned both the ΛCDM model of cosmology and general relativity as effective working theories.  Yet also tensions between theoretical prediction and observation, and even between different observations arose.  In my short presentation will focus on a selection of such discrepancies; in particular those that appear to represent significant challenges to the Cosmological Principle, upon which the ΛCDM model is built.  First and foremost, this concerns the excess amplitude of the cosmic matter dipole in the number density of high-redshift galaxies.  Apart from its history I will highlight more recent developments and future prospects.  This discovery may well share connection with other, lower-redshift observations of deviations from an isotropic ΛCDM universe; for instance those of larger-than-expected bulk flows or possible anisotropies in the Hubble expansion.  I will present a brief critical commentary.

Invited talk: Correlated galaxy formation at the scale of the sound horizon: What can proto superclusters tell us about the distant Cosmic Web?

Abstract: On scales much larger than 100 Mpc the Universe is assumed to be homogeneous and isotropic. Smaller-scale fluctuations grow into sheets, filaments, clusters, and voids over billions of years--resembling a large-scale cosmic web. Cosmological simulations trace the early evolution of these fluctuations in the first few Gys, but still struggle to capture the baryonic complexity (particularly that of cold gas and star-formation) that arises from non-linear structure growth at the galaxy level. Informed by observations of rare hyperluminous submillimeter galaxies (HyLIRG SMGs), with star-formation rates exceeding one thousand solar masses per year, the puzzling phenomenon of spatially correlated star-formation among massive galaxies is found. On comoving distances much larger than what is expected for the formation of individual galaxy clusters, several objects are now known to trace enhanced and correlated structure formation at the scale of the sound horizon in the early Universe. In this talk, I will present the case of HS1549+19 at z=2.85, a potential proto supercluster hosting a surprisingly large number of massive, bright SMGs--of which 15 are rare HyLIRGs--spread over a flattened "pancake"-like sheet of 20 x 30 pMpc (80 x 120 cMpc). The velocity distribution of this enormous collapsing sheet predicts a size that is larger than 99.99% of simulated protoclusters at z=3. Moreover, only a fraction of all galaxies will end up in a central massive cluster, instead, the SMGs will likely be pushed by the Hubble flow and assemble a rich supercluster by z=0. At this point, it is unclear whether HS1549+19 presents a real challenge to concordance cosmology as no adequate benchmark cosmological simulation exists to date that unites a large volume with appropriate star-formation physics to sample such extreme outliers.