Calendar

Aug
31
Mon
Pizza Lunch: Alessondra Springmann
Aug 31 @ 12:30 pm – 1:30 pm
Pizza Lunch: Alessondra Springmann

Radar observations of asteroids

Sep
25
Fri
Colloquium: Miguel Aragon-Calvo
Sep 25 @ 3:15 pm – 4:15 pm
Colloquium: Miguel Aragon-Calvo @ BX102

Galaxy formation in the Cosmic Web

Miguel Angel Aragon-Calvo, University of California Santa Cruz

The Cosmic Web is the stage where galaxy formation and evolution occurs. Despite the many observations relating galaxies and their environment, and our recent ability to replicate galaxy properties in computer simulations, we still do not have a clear understanding of the environmental processes shaping galaxies. In this talk I will present a model of galaxy formation that, based on galaxy-LSS interactions, is able to reproduce and explain several observations including galaxy conformity, the galaxy color-mass/luminosity distribution and the evolution of the cosmic star formation rate. While introducing the model I will present several novel analysis and simulation techniques and discuss the importance of data visualization as a driver of scientific discovery.

Apr
22
Fri
Colloquium: Paul Abell (Host: Nancy Chanover)
Apr 22 @ 3:15 pm – 4:15 pm
Colloquium:  Paul Abell  (Host: Nancy Chanover) @ BX102

Asteroid Exploration

Paul Abell, NASA Johnson Flight Center

I will present the current status of NASA’s Asteroid Redirect Mission (ARM) that is planned for launch in December 2021. Specifically I will discuss how a solar-electric powered robotic spacecraft will visit a large near-Earth asteroid (NEA), collect a multi-ton boulder from its surface, perform a planetary defense technique at the NEA, and return with the boulder into a stable orbit around the Moon. I will also discuss how astronauts aboard an Orion spacecraft will subsequently explore the boulder, conduct investigations during their extravehicular activities, and return samples to Earth. I will demonstrate how the ARM is part of NASA’s plan to advance technologies, capabilities, and spaceflight experience needed for a human mission to the Martian system in the 2030s. Finally I will discuss how the ARM and subsequent availability of the asteroidal material in cis-lunar space, provide significant opportunities to advance our knowledge of small bodies in terms of science, planetary defense, and in-situ resource utilization (ISRU).

Feb
17
Fri
Colloquium: Michael Boylan-Kolchin
Feb 17 @ 3:15 pm – 4:15 pm
Colloquium: Michael Boylan-Kolchin @ BX 102

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.

Mar
2
Thu
Colloquium: Jack Burns (Host: Nancy Chanover)
Mar 2 @ 3:15 pm – 4:15 pm
Colloquium: Jack Burns (Host: Nancy Chanover) @ Domenici Hall Room 106

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.

 

Mar
31
Fri
Colloquium PhD Defense: Sean Markert
Mar 31 @ 3:15 pm – 4:15 pm
Colloquium PhD Defense: Sean Markert

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.

Oct
23
Mon
Pizza Lunch: Kristian Finlator
Oct 23 @ 12:30 pm – 1:30 pm
Pizza Lunch: Kristian Finlator @ AY 119

Vastly Improved Simulations of the Hydrogen Reionization Epoch: Too Much for One Paper?

Oct
19
Fri
Colloquium: Sanchayeeta Borthakur (Host: Kristian Finlator)
Oct 19 @ 3:15 pm – 4:15 pm
Colloquium:  Sanchayeeta Borthakur (Host: Kristian Finlator) @ BX102

Understanding How Galaxies Reionized the Universe

 Sanchayeeta Borthakur, Arizona State University

Identifying the population of galaxies that was responsible for the reionization of the universe is a long-standing quest in astronomy. While young stars can produce large amounts of ionizing photons, the mechanism behind the escape of Lyman continuum photons (wavelength < 912 A) from star-forming regions has eluded us. To identify such galaxies and to understand the process of the escape of Lyman continuum, we present an indirect technique known as the residual flux technique. Using this technique, we identified (and later confirmed) the first low-redshift galaxy that has an escape fraction of ionizing flux of 21%. This leaky galaxy provides us with valuable insights into the physics of starburst-driven feedback. In addition, since direct detection of ionizing flux is impossible at the epoch of reionization, the residual flux technique presents a highly valuable tool for future studies to be conducted with the upcoming large telescopes such as the JWST.