Metal Absorption in the Circumgalactic Medium During the Epoch of Reionization
Caitlin Doughty, NMSU
The characteristics of metal absorption arising from the circumgalactic medium of galaxies have been demonstrated to be related to conditions in the galaxy which sourced them, as well as to the ambient ultraviolet background. I propose a three- pronged thesis in order to better understand and utilize these relationships. First, I will explore whether the spectral energy distributions of binary stars, incorporated into a custom version of GADGET-3, can explain the discrepancy between observed and simulated absorber statistics. Second, I will study the relationship between neu- tral oxygen absorbers and the neutral hydrogen fraction in simulated quasar sight- lines and relate the results to observations of neutral oxygen at z ≥ 4.0. Third, I will study the relationships between the emissive properties of galaxies, stemming from their nebular gas, and the metal absorbers which they source. Taken as a whole, this thesis will improve the ability of cosmological simulations to reproduce realistic metal absorption, probe the local progress and topology of reionization, and under- stand what emissive galaxy traits we expect at z > 5 based on observations of metal absorbers.
Impact heating of the early Martian climate
Kathryn Steakley, NMSU Astronomy
The nature of Mars’ ancient climate has been the subject of debate for decades. Abundant geologic evidence suggests that liquid water flowed on the surface of Mars during the late Noachian and early Hesperian eras (~3.5 – 3.8 billion years ago), but climate models struggle to reproduce such warm and wet conditions. Characterizing the climate that supported this aqueous activity and constraining the duration and intensity of warm and wet periods is crucial to understanding whether Mars was habitable in the past. 1-D climate modeling studies suggest that asteroid impacts are capable of inducing greenhouse warming on early Mars due to the substantial amounts of energy and water that are injected into the atmosphere (Segura et al., 2008). We use a 3-D global climate model (GCM) to simulate the post-impact climate conditions presented in Segura et al. (2008) (30-, 50-, and 100-km impactors in 150 mbar, 1 bar, and 2 bar atmospheres) and examine the resulting global distributions of surface temperatures and precipitation to assess whether these post-impact climates can facilitate valley network formation in Mars’ southern highlands. We find that these post-impact scenarios do result in above-freezing temperatures and 10s of cm of rainfall in the southern highlands, but that ultimately these warm and wet periods are short lived (on the order of years) and do not support the sustained warm and wet conditions that facilitate valley network formation. We find that scenarios with high surface pressures and scenarios with radiatively active clouds experience longer periods of above-freezing temperatures and result in higher final mean annual temperatures (up to 272.8K in our warmest scenario). In future work, we will investigate other greenhouse gases delivered by impacts in addition to water, including hydrogen and/or methane, to test whether this prolongs the warm and wet periods following impacts.
NASA, Exoplanets, and Life After NMSU
Dawn Gelino, NASA Exoplanet Science Institute, CalTech
Abstract: Are you interested in learning more about the search for life in the Universe? Or perhaps you may be interested in being awarded time on 10 m telescopes for your science? Or maybe you are ready to learn more about prestigious NASA Postdoctoral Fellowships? This talk will touch on some recent and exciting results in the exoplanet field, as well as the different NASA HQ programs that I currently run for all of astrophysics (many of which may be helpful and applicable to YOU), and the path I took from NMSU to where I am now.
Stellar Winds and Stellar Rotation
Don Terndrup, Ohio State University
For more than 50 years, we have known that stars rotate quickly when they are young and slow down as they age. This process gives us important clues about magnetic field strength and geometry, as well as the nature of stellar winds, in solar-like stars. We have been working to put the analysis of stellar rotation on a modern statistical footing, and in this talk I will give you an update on our efforts. There are a number of critical observational problems that must be considered in calibrating models of angular momentum loss, especially problems of data censorship (older or less active stars are not detected in studies of rotation). I will conclude by evaluating the prospects for using stellar rotation as an age indicator, and demonstrate that such ages are far less precise – though still useful – than our group and others have previously claimed.
The Chemical Composition and Dynamics of Titan’s Atmosphere as Revealed by ALMA
Alexander Thelen, NMSU
Over the last century, remarkable advances in our understanding of Titan’s atmosphere have been accomplished by a campaign of ground- and space-based observations revealing a wealth of complex, organic species in the moon’s upper atmosphere. Many of Titan’s atmospheric constituents produced through the photochemistry and ionospheric interactions of N2 and CH4 exhibit significant variations with latitude and time, particularly towards the poles and within the winter circumpolar vortex. The measurement of spatial and temporal variations in Titan’s atmosphere enables us to elucidate connections between its dynamics, photochemistry, and the influence of seasonal changes. At the end of the Cassini mission in 2017, we can employ the Atacama Large Millimeter/submillimeter Array (ALMA) for future observations of Titan’s atmosphere. Here we detail the analysis of numerous short integration (~3 minute) ALMA observations from 2012 to 2015 to investigate Titan’s stratospheric composition, temporal variations, and search for new molecular species. Using the Non-linear optimal Estimator for MultivariatE spectral analySIS (NEMESIS) radiative transfer code, we retrieved vertical profiles of temperature and abundance in Titan’s lower stratosphere through mesosphere (~50–550 km) from three spatially independent regions. We modeled CO emission lines to obtain temperature measurements, and retrieved abundance profiles for HCN, HC3N, C3H4, and CH3CN. The combination of integrated flux maps and vertical atmospheric profiles from spatially resolved observations allowed us to study the circulation of Titan’s middle atmosphere during northern spring. We observed increased temperatures in Titan’s stratopause at high northern latitudes and a persistent northern enrichment of HCN, C3H4, and CH3CN during this epoch; however, increased abundances of all molecules in the southern mesosphere, particularly HCN, and spatial maps of HC3N also show evidence for subsidence at the south pole. We validated these measurements through direct comparisons with contemporaneous Cassini data, previous ground-based observations, and photochemical model results. While no new trace species were detected, ALMA has proven to be a highly capable asset to enhance the data from the final few years of the Cassini mission, and for the continued study of Titan’s atmospheric dynamics, composition, and chemistry into Titan’s northern summer.