On the Edge: Exoplanets with Orbital Periods Shorter Than a Peter Jackson Movie
Brian Jackson, Boise State Univeristy
From wispy gas giants to tiny rocky bodies, exoplanets with orbital periods of several days and less challenge theories of planet formation and evolution. Recent searches have found small rocky planets with orbits reaching almost down to their host stars’ surfaces, including an iron-rich Mars-sized body with an orbital period of only four hours. So close to their host stars that some of them are actively disintegrating, these objects’ origins remain unclear, and even formation models that allow significant migration have trouble accounting for their very short periods. Some are members of multi-planet system and may have been driven inward via secular excitation and tidal damping by their sibling planets. Others may be the fossil cores of former gas giants whose atmospheres were stripped by tides.
In this presentation, I’ll discuss the work of our Short-Period Planets Group (SuPerPiG), focused on finding and understanding this surprising new class of exoplanets. We are sifting data from the reincarnated Kepler Mission, K2, to search for additional short-period planets and have found several new candidates. We are also modeling the tidal decay and disruption of close-in gaseous planets to determine how we could identify their remnants, and preliminary results suggest the cores have a distinctive mass-period relationship that may be apparent in the observed population. Whatever their origins, short-period planets are particularly amenable to discovery and detailed follow-up by ongoing and future surveys, including the TESS mission.
Simulations of the interstellar medium at high redshift: What does [CII] trace?
Dr. Karen Olsen, Arizona State University
We are in an exciting era were simulations on large, cosmological scales meet modeling of the interstellar medium (ISM) on sub-parsec scales. This gives us a way to predict and interpret observations of the ISM, and in particular the star-forming gas, in high-redshift galaxies, useful for ongoing and future ALMA/VLA projects.
In this talk, I will walk you though the current state of simulations targeting the the fine structure line of [CII] at 158 microns, which has now been observed in several z>6 galaxies. [CII] can arise throughout the interstellar medium (ISM), but the brightness of the [CII] line depends strongly on local environment within a galaxy, meaning that the ISM phase dominating the [CII] emission can depend on galaxy type. This complicates the use of [CII] as a tracer of either SFR or ISM mass and calls for detailed modeling following the different ways in which [CII] can be excited.
I will present SÍGAME (Simulator of GAlaxy Millimeter/submillimeter emission) – a novel method for predicting the origin and strength of line emission from galaxies. Our method combines data from cosmological simulations with sub-grid physics that carefully calculates local radiation field strength, pressure, and ionizational/thermal balance. Preliminary results will be shown from recent modeling of [CII] emission from z~6 star-forming galaxies with SÍGAME. We find strong potential for using the total [CII] luminosity to derive the ISM and molecular gas mass of galaxies during the Epoch of Reionization (EoR).
Near-field Cosmology: Big Science from Small Galaxies
Dr. M. Boylan-Kolchin, UT Austin
The local Universe provides a unique and powerful way to explore galaxy formation and cosmological physics. Through measurements of the abundances, kinematics, and chemical composition of nearby systems that can be studied in exquisite detail, we can learn about the initial spectrum of cosmological density fluctuations, galaxy formation, dark matter physics, and processes at cosmic dawn that might otherwise remain unobservable. I will summarize some of the new and surprising results in this rapidly-changing subject of “near-field cosmology” and discuss how these results are driving advances in both astronomy and particle physics.
Cosmology from the Moon: The Dark Ages Radio Explorer (DARE)
Dr. Jack Burns, University of Colorado Boulder
In the New Worlds, New Horizons in Astronomy & Astrophysics Decadal Survey, Cosmic Dawn was singled out as one of the top astrophysics priorities for this decade. Specifically, the Decadal report asked “when and how did the first galaxies form out of cold clumps of hydrogen gas and start to shine—when was our cosmic dawn?” It proposed “astronomers must now search the sky for these infant galaxies and find out how they behaved and interacted with their surroundings.” This is the science objective of DARE – to search for the first stars, galaxies, and black holes via their impact on the intergalactic medium (IGM) as measured by the highly redshifted 21-cm hyperfine transition of neutral hydrogen (HI). DARE will probe redshifts of 11-35 (Dark Ages to Cosmic Dawn) with observed HI frequencies of 40-120 MHz. DARE will observe expected spectral features in the global signal of HI that correspond to stellar ignition (Lyman-α from the first stars coupling with the HI hyperfine transition), X-ray heating/ionization of the IGM from the first accreting black holes, and the beginning of reionization (signal dominated by IGM ionization fraction). These observations will complement those expected from JWST, ALMA, and HERA. We propose to observe these spectral features with a broad-beam dipole antenna along with a wide-band receiver and digital spectrometer. We will place DARE in lunar orbit and take data only above the farside, a location known to be free of human-generated RFI and with a negligible ionosphere. In this talk, I will present the mission concept including initial results from an engineering prototypes which are designed to perform end-to-end validation of the instrument and our calibration techniques. I will also describe our signal extraction tool, using a Markov Chain Monte Carlo technique, which measures the parameterized spectral features in the presence of substantial Galactic and solar system foregrounds.
THE SIGNAL OF WEAK GRAVITATIONAL LENSING FROM GALAXY
GROUPS AND CLUSTERS,
Dr. S. Markert, NMSU
The weak gravitational lensing of galaxy clusters is a valuable tool. The deflection of light around a lens is solely dependent on the underlying distribution of foreground mass, and independent of tracers of mass such as the mass to light ratio and kinematics. As a direct probe of mass, weak lensing serves as an independent calibration of mass-observable relationships. These massive clusters are objects of great interest to astronomers, as their abundance is dependent on the conditions of the early universe, and accurate counts of clusters serve as a test of cosmological model. Upcoming surveys, such as LSST and DES, promise to push the limit of observable weak lensing, detecting clusters and sources at higher redshift than has ever been detected before. This makes accurate counts of clusters of a given mass and redshift, and proper calibration of mass-observable relationships, vital to cosmological studies.
We used M> 10 13.5 h −1 M ⊙ halos from the MultiDark Planck simulation at z∼0.5 to study the behavior of the reduced shear in clusters. We generated 2D maps of convergence and shear the halos using the GLAMER lensing library. Using these maps, we simulated observations of randomly placed background sources, and generate azimuthal averages of the shear. This reduced shear profile, and the true reduced shear profile of the halo, is fit using analytical solutions for shear of the NFW, Einasto, and truncated NFW density profile. The masses of these density profiles are then compared to the total halo masses from the halo catalogs.
We find that fits to the reduced shear for halos extending past ≈ 2 h −1 Mpc are fits to the noise of large scale structure along the line of sight. This noise is largely in the 45 ◦ rotated component to the reduced tangential shear, and is a breakdown in the approximation of g tan ≈g tot required for density profile fitting of clusters. If fits are constrained to a projected radii of < 2 h −1 Mpc, we see massively improved fits insensitive to the amount of structure present along the line of sight.