Calendar

Feb
5
Fri
Colloquium: Steve Finkelstein (Host: Kristian Finlator)
Feb 5 @ 3:15 pm – 4:15 pm
Colloquium:  Steve Finkelstein   (Host: Kristian Finlator) @ BX102

Galaxy Evolution during the Epoch of Reionization

 Steve Finkelstein,  University of Texas at Austin

 

                       Abstract: The advent of the Wide Field Camera 3 on the Hubble Space Telescope has heralded a new era in our ability to study the earliest phases of galaxy formation and evolution.  The number of candidates for galaxies now known at redshifts greater than six has grown to be in the thousands.  This allows us to move beyond mere counting of galaxies, to endeavor to understand the detailed physics regulating the growth of galaxies.  I will review the recent progress our group in Texas has made in this arena using the exquisite datasets from the CANDELS and Frontier Fields programs.  Specifically, our detailed new measurements of both the evolution of the stellar mass function and rest-frame UV luminosity function now allow us to probe the effect of feedback on low-mass galaxies, the star-formation efficiency in high-mass galaxies, and the contribution of galaxies to the reionization of the universe.  Our most recent result comes from the Frontier Fields, where we have used an advanced technique to remove the light from the cluster galaxies to uncover z > 6 galaxies as faint as M_UV=-13.  Our updated luminosity functions show no sign of a turnover down to these extremely faint levels, providing the first empirical test of reionization models which require such faint galaxies, and is in modest tension with simulations which predict a turnover at brighter levels.   I will also discuss our spectroscopic followup efforts, which have yielded two of the four highest redshift confirmed galaxies, and also provide further insight into reionization, by the scattering of Lyman alpha emission by neutral gas in the intergalactic medium.  I will conclude with a look ahead to the problems we can expect to tackle with ALMA, JWST, and even more future facilities.

Oct
17
Mon
Pizza Lunch: Caitlin Doughty
Oct 17 @ 12:30 pm – 1:30 pm
Pizza Lunch: Caitlin Doughty @ AY 119

Title: Probing the z~6 UVB with Aligned Metal Absorbers

Caitlin Doughty

 

Jan
30
Mon
Pizza Lunch: Caitlin Doughty
Jan 30 @ 12:30 pm – 1:30 pm
Pizza Lunch: Caitlin Doughty @ AY 119

Title: Effect of molecular gas on simulated C II, C IV absorber fractions (598 Talk)

Caitlin Doughty

 

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.

 

Apr
7
Fri
Colloquium: Lauren Waszek (Host: Jason Jackiewicz)
Apr 7 @ 3:15 pm – 4:15 pm
Colloquium: Lauren Waszek (Host: Jason Jackiewicz) @ BX102

The growth of Earth’s inner core: a new technique to constrain seismic properties in its outermost layers

Dr. Lauren Waszek, Department of Physics, NMSU

The inner core displays a hemispherical difference in seismic velocity, attenuation, and anisotropy, which is well-established from seismic studies. Recent observations reveal increasingly complex and regional features. However, geodynamical models generally only attempt to explain the basic east-west asymmetry. Regional seismic features, such as depth-dependence anisotropy or variation in hemisphere boundaries, are difficult to reproduce and relatively poorly constrained by seismic data. Processes to generate these complex features are debated.

The structures of the inner core are suggested to be formed as the inner core grows over time. Thus, the most recently-formed outermost layers likely hold the key to understanding the geodynamical mechanisms generating the inner core properties. Current datasets of the uppermost inner core and inner core boundary are limited by uneven data coverage, however. In the very uppermost inner core, seismic waves arrive with similar travel times and interfere, making measurements difficult.

Despite the uneven coverage of current datasets, we can use them to infer a very slow inner core super-rotation. The first ever global tomographical inversion for the inner core allows us to make regional observations, and map the lateral variation in the hemispherical structures. In the uppermost inner core, we have developed a new waveform modeling technique with synthetic data to separate these seismic phases, allowing us to measure the seismic properties in the very uppermost inner core. This, in combination with geodynamical modeling, will help us determine how the inner core hemispheres and other features are generated.

 

 

 

 

 

 

Sep
8
Fri
Colloquium: Travis Metcalfe (Host: Jason Jackiewicz)
Sep 8 @ 3:15 pm – 4:15 pm
Colloquium: Travis Metcalfe (Host: Jason Jackiewicz) @ BX102

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.

Oct
16
Mon
Pizza Lunch: Ken Naiff
Oct 16 @ 12:30 pm – 1:30 pm
Pizza Lunch: Ken Naiff @ AY 119

Dark Sky Images

Ken Naiff

Ken, an retired engineer, is a highly technically skilled and artistic
astrophotographer.  He will be sharing some of his work and elaborating on
the technical methods and processing techniques he applies to obtain his
unique and enhanced images.  You can see Ken’s work at:

https://darkskyimagesbyken.com/products