Outer Planets Update
Dr. Amy Simon, NASA
The Hubble Outer Planet Atmospheres Legacy (OPAL) program is a yearly program for observing each of the outer planets over two full rotations. Observations began with Uranus in 2014, adding Neptune and Jupiter in 2015 (Saturn will be included in 2018, after the end of the Cassini mission). These observations have provided interesting new discoveries in their own right, but are also now being combined with observations from a number of facilities, including NASA’s IRTF, Keck, the VLA, as well as the Kepler and Spitzer missions to further expand the breadth of science they contain. This talk will cover the latest observations for each of these planets and what we are learning from these data sets.
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.
Galaxy Evolution in High Definition Via Gravitational Lensing
Dr. Jane Rigby
Deputy Project Scientist for JWST, NASA Goddard Space Flight Center
Abstract: In hundreds of known cases, “gravitational lenses” have deflected, distorted, and amplified images of galaxies or quasars behind them. As such, gravitational lensing is a way to “cheat” at studying how galaxies evolve: lensing can magnify galaxies by factors of 10–100 times, transforming them from objects we can barely detect to bright objects we can study in detail. For such rare objects, we are studying how galaxies formed stars at redshifts of 1–4, the epoch when most of the Universe’s stars were formed. For lensed galaxies, we can obtained spectral diagnostics that are currently unavailable for the distant universe, but will become routine with next-generation telescopes.
In particular, I’ll discuss MEGaSaURA, The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas, which comprises high signal-to-noise, medium spectral resolution (R~3300) spectra of 15 extremely bright gravitationally lensed galaxies at redshifts of 1.6<z<3.6. The sample, drawn from the SDSS Giant Arcs Survey, are many of the brightest lensed galaxies known. The MEGaSaURA spectra reveal a wealth of spectral diagnostics: absorption from the outflowing wind; nebular emission lines that will be key diagnostics for JWST, GMT, and TMT; and photospheric absorption lines and P Cygni profiles from the massive stars that power the outflow.
Charting the Outer Reaches of Exoplanetary Systems: Wide-Separation Giant Planet Demographics with Direct Imaging
Eric Nielsen, Kavli Institute for Particle Astrophysics and Cosmology, Stanford University
Over the past decade, the combination of advances in adaptive optics, coronagraphy, and data processing has enabled the direct detection and characterization of giant exoplanets orbiting young, nearby stars. In addition to the wealth of information about exoplanetary atmospheres we obtain from spectroscopy of directly imaged planets, the demographics of these wide-separation planets allow us to directly test theories of planet formation, probing the outer planetary systems compared to transit and radial velocity techniques. In this talk I will present results from the Gemini Planet Imager Exoplanet Survey (GPIES), which surveyed 521 nearby stars for giant planet and brown dwarf companions orbiting beyond 5 AU, and is one of the largest, deepest direct imaging searches for exoplanets every conducted. The overall occurrence rate of substellar companions, and trends with companion mass, semi-major axis, and stellar mass are consistent with giant planets forming via core accretion, and point to different formation mechanisms for giant planets and brown dwarfs between 10 and 100 AU.
Simulating Planetesimal Formation in the Kuiper Belt and Beyond
Rixin Li, University of Arizona
A critical step in planet formation is to build super-km-sized planetesimals in protoplanetary disks. The origin and demographics of planetesimals are crucial to understanding the Solar System, circumstellar disks, and exoplanets. I will overview the current status of planetesimal formation theory. Specifically, I will present our recent simulations of planetesimal formation by the streaming instability, a mechanism to aerodynamically concentrate pebbles in protoplanetary disks. I will then discuss the connections between our numerical models and recent astronomical observations and Solar System explorations. I will explain why all planetesimals likely formed as binaries.