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.
The Orbital and Planetary Phase Variations of Jupiter-Sized Planets: Characterizing Present and Future Giants
Laura Mayorga, NMSU
It is commonly said that exoplanet science is 100 years behind planetary science. While we may be able to travel to an exoplanet in the future, inferring the properties of exoplanets currently relies on extracting as much information as possible from a limited dataset. In order to further our ability to characterize, classify, and understand exoplanets as both a population and as individuals, this thesis makes use of multiple types of observations and simulations.
Firstly, direct-imaging is a technique long used in planetary science and is only now becoming feasible for exoplanet characterization. We present our results from analyzing Jupiter’s phase curve with Cassini/ISS to instruct the community in the complexity of exoplanet atmospheres and the need for further model development. The planet yields from future missions may be overestimated by today’s models. We also discuss the need for optimal bandpasses to best differentiate between planet classes.
Secondly, photometric surveys are still the best way of conducting population surveys of exoplanets. In particular, the Kepler dataset remains one of the highest precision photometric datasets and many planetary candidates remain to be characterized. We present techniques by which more information, such as a planet’s mass, can be extracted from a transit light curve without expensive ground- or space-based follow-up observations.
Finally, radial-velocity observations have revealed that many of the larger “planets” may actually be brown dwarfs. To understand the distinction between a brown dwarf and an exoplanet or a star, we have developed a simple, semi-analytic viscous disk model to study brown dwarf evolutionary history. We present the rudimentary framework and discuss its performance compared to more detailed numerical simulations as well as how additional physics and development can determine the potential observational characteristics that will differentiate between various formation scenarios.
Exoplanet science has already uncovered a plethora of previously unconsidered phenomenon. To increase our understanding of our own planet, as well as the other various possible end cases, will require a closer inspection of our own solar system, the nuanced details of exoplanet data, refined simulations, and laboratory astrophysics.
The Vulture Survey of MgII and CIV Absorbers: Feasting on the Bones of Spectra Left to Die
Nigel Mathes, NMSU
We present detailed measurements of the absorption properties and redshift evolution of MgII and CIV absorbers as measured in archival spectra from the UVES spectrograph at the Very Large Telescope (VLT/UVES) and the HIRES spectrograph at the Keck Telescope (Keck/HIRES) to equivalent width detection limits below 0.01 angstroms. This survey examines 860 high resolution spectra from various archival data sets representing 700 unique sightlines, allowing for detections of intervening MgII absorbers spanning redshifts 0.1 < z < 2.6 and intervening CIV absorbers spanning redshifts 1 < z < 5. We employ an accurate, automated approach to line detection which consistently detects redshifted absorption doublets. We observe three distinct epochs of evolution in the circumgalactic medium (CGM) as traced by MgII and CIV absorbers. At high redshifts, from 3 < z < 5, galaxies rapidly build up a metal enriched halo where, despite significant evolution in the ionizing background, the production of metals through star formation driven outflows dominates observed trends increasing the number of observed absorbers per redshift path length towards z = 3. At mid redshifts, from 2 < z < 3, a large cosmic increase in the global star formation rate drives large numbers of high column density outflows into the halos of galaxies. At this time, metal line absorption of all species is increased above all other epochs. At low redshifts, for z < 2, the universe becomes more quiescent in both star formation and ionizing background. Weak, low column density MgII absorbers proliferate, while strong MgII absorbers likely fragment or re-accrete onto their host galaxy. Strong CIV absorbers, at this time, still increase in number per absorption path, while their weaker counterparts begin to disappear. MgII and CIV absorbers appear to originate in star formation driven outflows, but their different evolutionary properties imply they represent two physically distinct phases of gas. These two phases comprise the CGM and contribute separately to the cycle of baryons into and out of galaxies.
A Faint Flux-Limited LAE Sample at z = 0.3
Isak Wold, UT Austin
Observational surveys of Lya emitters (LAEs) have proven to be an efficient method to identify and study large numbers of galaxies over a wide redshift range. To understand what types of galaxies are selected in LAE surveys – and how this evolves with redshift – it is important to establish a low-redshift reference sample that can be directly compared to high-redshift samples. The lowest redshift where a direct Lya survey is currently possible is at a redshift of z~0.3 via the Galaxy Evolution Explorer (GALEX ) FUV grism data. Using the z~0.3 GALEX sample as an anchor point, it has been suggested that at low redshifts high equivalent width (EW) LAEs become less prevalent and that the amount of escaping Lya emission declines rapidly. A number of explanations for these trends have been suggested including increasing dust content, increasing neutral column density, and/or increasing metallicity of star-forming galaxies at lower redshifts. However, the published z~0.3 GALEX sample is pre-selected from bright NUV objects. Thus, objects with strong Lya emission but faint continuum (high-EW LAEs) could be missed. In this talk, I will present my efforts to re-reduce the deepest archival GALEX FUV grism data and obtain a sample that is not biased against high-EW LAEs. I will discuss the implications of this new sample on the evolutionary trends listed above.
The Magnetic Mid-life Crisis of the Sun
Dr. Travis Metcalfe, Space Sciences Institute
After decades of effort, the solar activity cycle is exceptionally well characterized but it remains poorly understood. Pioneering work at the Mount Wilson Observatory demonstrated that other sun-like stars also show regular activity cycles, and suggested two possible relationships between the rotation rate and the length of the cycle. Neither of these relationships correctly describe the properties of the Sun, a peculiarity that demands explanation. Recent discoveries have started to shed light on this issue, suggesting that the Sun’s rotation rate and magnetic field are currently in a transitional phase that occurs in all middle-aged stars. We have recently identified the manifestation of this magnetic transition in the best available data on stellar cycles. The results suggest that the solar cycle may be growing longer on stellar evolutionary timescales, and that the cycle might disappear sometime in the next 0.8-2.4 Gyr. Future tests of this hypothesis will come from ground-based activity monitoring of Kepler targets that span the magnetic transition, and from asteroseismology with the TESS mission to determine precise masses and ages for bright stars with known cycles.
Long duration solar gamma ray flares
Lisa Winter, LANL
Long duration solar gamma ray flares (LDGRFs) present a challenge to models of solar flares. While the gamma ray emission initially was thought to be the high energy extension of emission produced at the footprints of flare loops, LDGRFs are more energetic than expectations and last hours after the X-ray emission subsides. Evidence of gamma ray emission from flares on the backside of the Sun prompted the idea that LDGRFs instead are created from acceleration of particles in the shock waves of coronal mass ejections (CMEs). To determine which of these scenarios is more likely, we conducted a study of the flare and CME properties for LDGRFs detected by the Fermi Gamma-Ray Observatory. We also performed a reverse association analysis to determine which flares and CMEs do not produce gamma-ray emission. In this talk, these results are presented, showing that LDGRFs are most likely associated with CME acceleration.
Asteroseismology of Red Giants: The Detailed Modeling of Red Giants in Eclipsing Binary Systems
Jean McKeever, NMSU
Asteroseismology is an invaluable tool that allows one to peer into the inside of a star and know its fundamental stellar properties with relative ease. There has been much exploration of solar-like oscillations within red giants with recent advances in technology, leading to new innovations in observing. The Kepler mission, with its 4-year observations of a single patch of sky, has opened the floodgates on asteroseismic studies. Binary star systems are also an invaluable tool for their ability to provide independent constraints on fundamental stellar parameters such as mass and radius. The asteroseismic scaling laws link observables in the light curves of stars to the physical parameters in the star, providing a unique tool to study large populations of stars quite easily. In this work we present our 4-year radial velocity observing program to provide accurate dynamical masses for 16 red giants in eclipsing binary systems. From this we find that asteroseismology overestimates the mass and radius of red giants by 15% and 5% respectively. We further attempt to model the pulsations of a few of these stars using stellar evolution and oscillation codes. The goal is to determine which masses are correct and if there is a physical cause for the discrepancy in asteroseismic masses. We find there are many challenges to modeling evolved stars such as red giants and we address a few of the major concerns. These systems are some of the best studied systems to date and further exploration of their asteroseismic mysteries is inevitable.
Breaking the Self-Similarity of Galaxy Formation: A Circumgalactic Medium Perspective
Benjamin Oppenheimer, University of Colorado Boulder
If you could see a dark matter halo directly without knowing the scale, you probably could not distinguish a Milky Way halo from a cluster-sized halo. However, if you look at the galaxies, you would likely see a dominant spiral galaxy in the former and a many quenched and quenching galaxies in the latter. The study of galaxy formation aims to understand how very different galaxies form in dark matter halos of different masses. I will argue for the importance of understanding the gaseous baryons in this context. In contrast to the hot intracluster medium detected in emission in clusters, the circumgalactic medium (CGM) has to be probed by absorption lines toward background quasars and tells a vastly different and complicated story. I will demonstrate, with the aid of hydrodynamic simulations, how the CGM is multi-phase (with cool ~10^4 K clouds embedded in a hot, ambient medium), plus how non-equilibrium ionization processes altering the heavy element ions we probe in spectra. The next frontiers in the CGM require understanding the dynamics encoded not only in absorption line spectra of the UV, but in the X-ray via emission and absorption.
Science with the James Webb Space Telescope
Jane Rigby, NASA/GSFC
NASA’s James Webb Space Telescope (JWST) will have revolutionary capabilities and sensitivity for imaging and spectroscopy from 0.7 to 28 micron. JWST should make major scientific advances across astrophysics, including the physics of reionization, galaxy formation and assembly, planetary science, and extrasolar planets. In anticipation of a scheduled launch in 2019, JWST Cycle 1 Guest Observer proposals will be due in spring of 2018. I will review the scientific capabilities of the telescope, the integration and test program, and how observers will plan observations and analyze JWST data.