Colloquium PhD Thesis Defense: Gordon MacDonald
Mar 2 @ 3:15 pm – 4:15 pm
Colloquium PhD Thesis Defense: Gordon MacDonald @ BX102

Colloquium Title

Gordon MacDonald, NMSU


Colloquium PhD Thesis Defense: Sten Hasselquist
Apr 6 @ 3:15 pm – 4:15 pm
Colloquium PhD Thesis Defense: Sten Hasselquist @ BX102

Colloquium Title

Sten Hasselquist, NMSU


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.

Colloquium: Phil Judge (Host James McAteer)
Nov 15 @ 3:15 pm – 4:15 pm
Colloquium: Phil Judge (Host James McAteer) @ BX102

Using every photon to learn about the physics of solar plasmas

Phil Judge, High Altitude Observatory, Boulder CO.

The Sun has traditionally been the Rosetta Stone that can overcome the gap in regimes between laboratory and astronomical plasmas.   Theories applicable in the laboratory may not readily apply to solar plasmas, and vice-versa. Yet we still face challenges in understanding how the observable plasmas are produced, and why the magnetic field threading and energizing them must globally reverse every 11 years. I will give a general overview of currently pressing problems in solar physics, followed by two specific examples: one concerning the physics of flares through infrared spectroscopy and polarimetry, the other concerning how we might wring every last ounce of information from the emitted photons. Along the way I will introduce the NMSU-operated Dunn Solar Telescope, the new DKIST, Parker Solar Probe and Solar Orbiter, and suggest how we might take advantage of these new facilities to make lasting progress.

Colloquium: Elise Boera (Host: Kristian Finlator)
Dec 6 @ 3:15 pm – 4:15 pm
Colloquium: Elise Boera (Host: Kristian Finlator) @ BX102

Revealing reionization with the thermal history of the intergalactic medium

Elisa Boera, SISSA Trieste

During hydrogen reionization the UV radiation from the first luminous sources injected vast amount of energy into the intergalactic medium, photo-heating the gas to tens of thousands of degree Kelvin. This increase in temperature has left measurable `imprints’ in the thermal history of the cosmic gas: a peak in the temperature evolution at the mean density and a smoothing out of the gas in the physical space by the increased gas pressure following reionization (i.e. Jeans smoothing effect). The structures of the HI Lyman-alpha forest at high redshift are sensitive to both these effects and therefore represent a powerful tool to understand when and how reionization happened. I will present the most recent constraints on the thermal history of the intergalactic medium obtained using the Lyman-alpha forest flux power spectrum at z>5. I will show how these results can be used to obtain information on the timing and the sources of the reionization process and I will discuss their consistency with different possible reionization scenarios.
Colloquium:Mausumi Dikpati (Host: Juie Shetye)
Dec 4 @ 3:00 pm – 4:00 pm
Colloquium:Mausumi Dikpati (Host: Juie Shetye) @ BX102

Role of solar Rossby waves in causing space weather on intermediate time-scales

Mausumi Dikpati, HAO

Forecasting our weather was built on the recognition that global Rossby waves, interacting with mean east-west flow on the Earth’s atmosphere, produce jet streams, which are responsible for causing winter storms, and cold outbreaks that we experience in midlatitudes. Rossby waves arise in thin layers within fluid regions of stars and planets. These global wave‐like patterns occur due to the variation in Coriolis forces with latitude. It has recently been discovered that the Sun has Rossby waves too. Therefore, the Sun’s global magnetic fields and flows are also influenced by these global‐scale waves. But unlike the Earth’s Rossby waves, due to the presence of strong magnetic fields solar Rossby waves are magnetically modified. In this talk, I will demonstrate through model-simulations how solar Rossby waves, nonlinearly interacting with differential rotation and spot-producing magnetic fields, can cause the seasonal/sub-seasonal (6-18 months) variability in solar activity, which is, in turn, the origin of space weather on intermediate time-scales. Space weather occurring on a very short time-scale (hours-to-days) and on much longer time-scale (decadal-to-millennial) have been studied extensively, but there exists a gap, namely the occurrence of space weather on intermediate time-scale of a few weeks to several months. I will also demonstrate that combining observations with our model by data-assimilation procedure it is possible to forecast an upcoming space-weather season several months ahead of time.