Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

© 2020 IOP Publishing Ltd and Sissa Medialab. One of the most important checks for systematic errors in CMB studies is the cross correlation of maps made by independent experiments. In this paper we report on the cross correlation between maps from the Atacama B-mode Search (ABS) and Atacama Cosmology Telescope (ACT) experiments in both temperature and polarization. These completely different measurements have a clear correlation with each other and with the Planck satellite in both the EE and TE spectra at ℓ<400 over the roughly 0110 deg2 common to all three. The TB, EB, and BB cross spectra are consistent with noise. Exploiting such cross-correlations will be important for future experiments operating in Chile that aim to probe the 30<ℓ<8,000 range.

Abstract:

The Heliospheric Imagers on board National Aeronautics and Space Administration (NASA)'s twin STEREO spacecraft show that coronal mass ejections (CMEs) can be visually complex structures. To explore this complexity, we created a citizen science project with the U.K. Science Museum, in which participants were shown pairs of CME images and asked to decide which image in each pair appeared the most “complicated.” A Bradley‐Terry model was then applied to these data to rank the CMEs by their “complicatedness,” or “visual complexity.” This complexity ranking revealed that the annual average visual complexity values follow the solar activity cycle, with a higher level of complexity being observed at the peak of the cycle. The average complexity of CMEs observed by STEREO‐A was also found to be significantly higher than those observed by STEREO‐B. Visual complexity was found to be associated with CME size and brightness, but our results suggest that complexity may be influenced by the scale‐sizes of structure in the CMEs.

Abstract:

Massive black hole (MBH) coalescences are powerful sources of low-frequency gravitational waves. To study these events in the cosmological context, we need to trace the large-scale structure and cosmic evolution of a statistical population of galaxies, from dim dwarfs to bright galaxies. To cover such a large range of galaxy masses, we analyse two complementary simulations: HORIZON-AGN with a large volume and low resolution that tracks the high-mass (> 107 M☉) MBH population, and NEWHORIZON with a smaller volume but higher resolution that traces the low-mass (< 107 M☉) MBH population. While HORIZON-AGN can be used to estimate the rate of inspirals for pulsar timing arrays, NEWHORIZON can investigate MBH mergers in a statistical sample of dwarf galaxies for LISA, which is sensitive to low-mass MBHs. We use the same method to analyse the two simulations, post-processing MBH dynamics to account for time delays mostly determined by dynamical friction and stellar hardening. In both simulations, MBHs typically merge long after galaxies do, so that the galaxy morphology at the time of the MBH merger is no longer determined by the structural disturbances engendered by the galaxy merger from which the MBH coalescence has originated. These time delays cause a loss of high-z MBH coalescences, shifting the peak of the MBH merger rate to z ∼ 1-2. This study shows how tracking MBH mergers in low-mass galaxies is crucial to probing the MBH merger rate for LISA and investigate the properties of the host galaxies.