Hintze Centre for Astrophysical Surveys

Abstract:

Increasing attention has been paid to multi-hazards in environmental disaster studies produced during the last decade. Multi-hazard studies focus on the occurrence, interaction and effect of several natural hazards in the same region. Despite the increasing number of multi-hazard studies, few investigations have focused on global-scale multi-hazard events. With the aim of closing this gap, our study focuses on the identification of periods during the last 1.5 million years of the Pleistocene epoch, with the quasi-parallel appearance of natural hazards (e.g., asteroid impacts and large volcanic eruptions with a Volcanic Explosivity Index (VEI) of 8 and 7) amplifying their individual effects and thus causing long-term, global-scale changes. Of the seven identified potential multi-hazard events, three were considered as possible global-scale events with a longer term environmental (paleoclimatic) impact; dated to c.a., 1.4 Ma (marine isotope stage – MIS45), 1.0 Ma (MIS 27), and 100 ka (MIS 5c), respectively. Two additional periods (around 50 and 20 ka) were identified as being associated with more restricted scale multi-hazard events, which might cause a “Little Ice Age-like” climatic episode in the history of the Pleistocene Period. In addition, we present a hypothesis about the complex climatic response to a global-scale multi-hazard event consisting of a series of asteroid impacts and volcanic eruption linked to a geomagnetic polarity change, namely the Matuyama-Brunhes Boundary, which might be accompanied by global cooling and result in the final step of the Early Middle Pleistocene Transition

Abstract:

We measure the harmonic-space auto-power spectrum of the galaxy overdensity in the LOFAR Two-metre Sky Survey (LoTSS) First Data Release and its cross correlation with the map of the lensing convergence of the cosmic microwave background (CMB) from the Planck collaboration. We report a ∼5σ detection of the cross-correlation. We show that the combination of the clustering power spectrum and CMB lensing cross-correlation allows us to place constraints on the high-redshift tail of the redshift distribution, one of the largest sources of uncertainty in the use of continuum surveys for cosmology. Our analysis shows a preference for a broader redshift tail than that predicted by the photometric redshifts contained in the LoTSS value added catalog, as expected, and more compatible with predictions from simulations and spectroscopic data. Although the ability of CMB lensing to constrain the width and tail of the redshift distribution could also be valuable for the analysis of current and future photometric weak lensing surveys, we show that its performance relies strongly on the redshift evolution of the galaxy bias. Assuming the redshift distribution predicted by the Square Kilometre Array Design simulations, we use our measurements to place constraints on the linear bias of radio galaxies and the amplitude of matter inhomogeneities σ8, finding σ8=0.69+0.14−0.21 assuming the galaxy bias scales with the inverse of the linear growth factor, and σ8=0.79+0.17−0.32 assuming a constant bias.