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.
Fresh Perspectives on Star
Formation from LEGUS, the Legacy ExtraGalactic Ultraviolet Survey
David Thilker, Johns Hopkins University
The Legacy ExtraGalactic Ultraviolet Survey (LEGUS) was a Cycle 21 Large Treasury HST program which obtained ~parsec resolution NUV- to I-band WFC3 imaging for 50 nearby, representative star-forming Local Volume galaxies, with a primary goal of linking the scales of star formation from the limit of individual stars, to clusters and associations, eventually up through the hierarchy to giant star forming complexes and galaxy-scale morphological features.
I will review the basics of the survey, public data products and science team results pertaining to clusters and the field star hierarchy. I will then describe work to optimize photometric selection methods for massive main sequence O star candidates and LBV candidates, in the former case establishing a means to statistically constrain the fraction of O stars in very isolated locales. I will introduce new ideas on how to quantify the complex spatio-temporal nature of hierarchical star formation using multi-scale clustering methods. The first steps of this work have yielded a landmark OB association database for 36 LEGUS target fields (in 28 of the nearest available galaxies), with tracer stellar populations selected and interpreted uniformly. I will finish with discussion of a pilot HST program to demonstrate remarkably increased survey efficiency of WFC3 UV imaging enabled by use of extra-wide (X) filter bandpasses. Such efficiency is required as we move beyond LEGUS and begin to rigorously explore low surface brightness star-forming environments where canonical results for the IMF and cluster formation efficiency are increasingly called into question.