The growth of Earth’s inner core: a new technique to constrain seismic properties in its outermost layers
Dr. Lauren Waszek, Department of Physics, NMSU
The inner core displays a hemispherical difference in seismic velocity, attenuation, and anisotropy, which is well-established from seismic studies. Recent observations reveal increasingly complex and regional features. However, geodynamical models generally only attempt to explain the basic east-west asymmetry. Regional seismic features, such as depth-dependence anisotropy or variation in hemisphere boundaries, are difficult to reproduce and relatively poorly constrained by seismic data. Processes to generate these complex features are debated.
The structures of the inner core are suggested to be formed as the inner core grows over time. Thus, the most recently-formed outermost layers likely hold the key to understanding the geodynamical mechanisms generating the inner core properties. Current datasets of the uppermost inner core and inner core boundary are limited by uneven data coverage, however. In the very uppermost inner core, seismic waves arrive with similar travel times and interfere, making measurements difficult.
Despite the uneven coverage of current datasets, we can use them to infer a very slow inner core super-rotation. The first ever global tomographical inversion for the inner core allows us to make regional observations, and map the lateral variation in the hemispherical structures. In the uppermost inner core, we have developed a new waveform modeling technique with synthetic data to separate these seismic phases, allowing us to measure the seismic properties in the very uppermost inner core. This, in combination with geodynamical modeling, will help us determine how the inner core hemispheres and other features are generated.
Observing the Baryon Cycle in Hydrodynamic Cosmological Simulations
Jacob Vander Vliet, NMSU
An understanding of galaxy evolution requires an understanding of the flow of baryons in and out of a galaxy. The accretion of baryons is required for galaxies to form stars, while stars eject baryons out of the galaxy through stellar feedback mechanisms such as supernovae, stellar winds, and radiation pressure. The interplay between outflowing and infalling material form the circumgalactic medium (CGM). Hydrodynamic simulations provide understanding in the connection between stellar feedback and the distribution and kinematics of baryons in the CGM. To compare simulations and observations properly the simulated CGM must be observed in the same manner as the real CGM. I have developed the Mockspec code to generate synthetic quasar absorption line observations of the CGM in cosmological hydrodynamic simulations. Mockspec generates synthetic spectra based on the phase, metallicity, and kinematics of CGM gas and mimics instrumental effects. Mockspec includes automatic analysis of the spectra and identifies the gas responsible for the absorption. Mockspec was applied to simulations of dwarf galaxies at low redshift to examine the observable effect different feedback models have on the CGM. While the different feedback models had strong effects on the galaxy, they all produced a similar CGM that failed match observations. Mockspec was applied to the VELA simulation suite of high redshift, high mass galaxies to examine the variance of the CGM across different galaxies in different environments. The observable CGM showed little variation between the different galaxies and almost no evolution from z=4 to z=1. The VELAs were not able to generate a CGM to match the observations. The properties of cells responsible for the absorption were compared to the derived properties from Voigt Profile decomposition. VP modeling was found to accurately describe the HI and MgII absorbing gas but failed for high ionization species such as CIV and OVI, which do not arise in the assumed coherent structures. The technique of mock QAL is useful for testing the accuracy of the simulated CGM and for verifying observational techniques, but not for differentiating between feedback prescriptions in dwarf galaxies.