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.
Preparing to Explore the Universe with the James Webb Space Telescope
Dr. Jane Rigby (NASA Goddard, Deputy Project Scientist for JWST)
Abstract: NASA’s James Webb Space Telescope (JWST), scheduled to be launched in 2019, will revolutionize our view of the Universe. As the scientific successor to the Hubble Space Telescope, JWST will rewrite the textbooks and return gorgeous images and spectra of our universe. In my talk, I will show how JWST will revolutionize our understanding of how galaxies and supermassive black holes formed in the first billion years after the Big Bang, and how they evolved over cosmic time. I’ll describe how our international team is preparing for launch, how we decide what targets to observe, and how we are testing the telescope to be sure it will work in space.
More information about the telescope can be found at https://www.jwst.nasa.gov/.
Solving the Puzzles of the Moon
Shun Karato, Yale University
After 50 years from the first landing of men on the Moon, about 380 kg of samples were collected by the Apollo mission. Chemical analyses of these samples together with a theory of planetary formation led to a “giant impact” paradigm (in mid 1970s). In this paradigm, the Moon was formed in the later stage of Earth formation (not the very late stage, though), when the proto-Earth was hit by an impactor with a modest size (~ Mars size) at an oblique angle. Such an impact is a natural consequence of planetary formation from a proto-planetary nebula. This collision may have kicked out mantle materials from the proto-Earth to form the Moon. This model explains mostly rocky composition of the Moon and the large angular momentum of the Earth-Moon system. High temperatures caused by an impact likely removed much of the volatile components such as water.
However, two recent geochemical observations cast doubt about the validity of such a paradigm. They include (i) not-so-dry Moon suggested from the analysis of basaltic inclusions in olivine, and (ii) the high degree of similarities in many isotopes. The first observation is obviously counter-intuitive, but the second one is also hard to reconcile with the standard model of a giant impact, because many models show that a giant impact produces the Moon mostly from the impactor. In this presentation, I will show how one can solve these puzzles by a combination of physics/chemistry of materials with some basic physics of a giant impact.