Bulletin of the American Physical Society
APS April Meeting 2023
Volume 68, Number 6
Minneapolis, Minnesota (Apr 15-18)
Virtual (Apr 24-26); Time Zone: Central Time
Session B02: Observations Confront Theory: Emerging Cosmological TensionsInvited
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Sponsoring Units: DAP DGRAV Chair: Priyamvada Natarajan, Yale University Room: MG Salon A - 3rd Floor |
Saturday, April 15, 2023 10:45AM - 11:21AM |
B02.00001: Massive galaxies at the beginning of cosmic time with James Webb: do they break our cosmological model? Invited Speaker: Erica Nelson Already in the first six months of observations, the James Webb Space Telescope has made many surprising discoveries. One of these is the existence of six candidate very massive galaxies just 500–800 million years after the Big Bang. These candidate galaxies are so massive at such early cosmic times that according to our lambda-CDM cosmological model, there should not be enough baryons available to form them. I will discuss these remarkable objects and their implications for our understanding of how the universe began. |
Saturday, April 15, 2023 11:21AM - 11:57AM |
B02.00002: The first Gyr of the PBH-LCDM Universe Invited Speaker: Nico Cappelluti e explore the observational implications of a model in which primordial black holes (PBHs) with a broad birth mass function ranging in mass from a fraction of a solar mass to 106 M?, consistent with current observational limits, constitute the dark matter component in the Universe. The formation and evolution of dark matter and baryonic matter in this PBH-LambdaCDM~Universe are presented. In this picture, PBH DM mini-halos collapse earlier than in standard LambdaCDM, baryons cool to form stars at z~15-20, and growing PBHs at these early epochs start to accrete through Bondi capture. The volume emissivity of these sources peaks at z∼20 and rapidly fades at lower redshifts. As a consequence, PBH DM could also provide a channel to make early black hole seeds and naturally account for the origin of an underlying dark matter halo - host galaxy and central black hole connection that manifests as the M-sigma correlation. To estimate the luminosity function and contribution to integrated emission power spectrum from these high-redshift PBH DM halos, we develop a Halo Occupation Distribution (HOD) model. In addition to tracing the star formation and reionizaton history, it permits us to evaluate the Cosmic Infrared and X-ray Backgrounds (CIB and CXB). We find that accretion onto PBHs/AGN successfully accounts for the detected backgrounds and their cross-correlation, with the inclusion of an additional IR stellar emission component. Detection of the deep IR source count distribution by the JWST could reveal the existence of this population of high-redshift star-forming and accreting PBH DM. |
Saturday, April 15, 2023 11:57AM - 12:33PM |
B02.00003: Tensions on small scales: too many galaxy-galaxy strong lenses in galaxy clusters? Invited Speaker: Massimo Meneghetti In the standard cosmological model, the matter content of the Universe is dominated by cold dark matter (CDM), collisionless particles that interact with ordinary matter (baryons) only through gravity. Gravitationally bound dark-matter halos form hierarchically, with the most massive systems growing through mergers of smaller ones. As structure assembles in this fashion, large dark-matter halos contain smaller-scale substructures in the form of embedded subhalos. I will show that observations of gravitational lensing can be used to map the inner mass distribution of cosmic structures such as galaxy clusters to test these predictions of the CDM paradigm. Interestingly, the reconstructed granularity of cluster cores implies an excess of galaxy-galaxy strong lensing (GGSL) probability compared to expectations in the ?CDM cosmological model. The theoretical estimates on the GGSL probability are based on the analysis of hydrodynamical simulations, while the observational measurements are derived from parametric strong lensing reconstructions combining inputs from HST and JWST imaging and MUSE/VLT spectroscopy. In an attempt to understand this issue, cluster-size halos simulated with different mass and force resolutions and implementing several AGN energy feedback schemes have been analyzed. The feedback model has a significant impact on the properties of subhalos and on their ability to produce GGSL effects. However, none of the hydrodynamical simulations studied so far are in agreement with observations. They persistently have difficulty reproducing the stellar mass and the internal structure of cluster galaxies simultaneously. The reported mismatch may indicate an unidentified problem with either prevailing simulation methods or standard cosmology. |
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