MN Institute for Astrophysics Colloquium

semester, 2017


Friday, January 20th 2017
No Colloquium

Friday, January 27th 2017
Speaker: Sanchayeeta Borthakur, Johns Hopkins, Dept. of Physics & Astronomy
Subject: Role of Baryon Flows in Galaxy Evolution: Hidden Pathways Connecting Galaxies to the Cosmic Web
Candidate for the MIfA Assistant Professor position

Galaxies are not isolated. They constantly exchange matter and energy with their surroundings. In spite of these pathways being obscure, they have had immense consequences. For example, galaxy growth and subsequent star formation is maintained by gradual accretion of gas from the cosmic web. In turn, young stars produce vast amounts of energy that may ionize gas in the cosmic web as well as spew out metals in the intergalactic medium (IGM). I will talk about the advances we have made in understanding the physics behind these pathways via studies of the circumgalactic medium (CGM). It is the vast reservoir of faint tenuous gas that extends from the edge of the disks of galaxies out to their virial radii. Therefore, the CGM holds crucial keys to understanding the various inflow and outflow processes. I will discuss observations of the CGM that suggests of these pathways via which galaxies acquire gas, condense it into their interstellar medium, form stars, and finally, release matter and energy back into their CGM and the IGM.


Friday, February 3rd 2017
Speaker: Brendan Bowler, University of Texas - Austin, Hubble Fellow
Subject: Revealing the Formation and Atmospheres of Exoplanets with Direct Imaging
Candidate for the MIfA Assistant Professor position

Finding and characterizing extrasolar planets has become one of the fastest-paced and most rapidly evolving fields in modern astronomy. Direct imaging— spatially resolving exoplanets from their host stars— is especially challenging but provides unique insight into the architectures, atmospheres, and formation of giant planets. By exploring planetary systems from the outside-in and directly detecting photons originating in their atmospheres, imaging complements other planet-finding techniques sensitive to smaller orbital separations and enables detailed studies of atmospheric structure and composition. In this talk I will review the field of high-contrast adaptive optics imaging with an emphasis on observational programs I am leading to test theories of planet formation, primarily by means of large surveys, planet population statistics, and near-infrared spectroscopy. I will also outline the long-term future of the field; imaging planets has been a consistent motivating factor for the next generation of telescopes like JWST, WFIRST, and the 30 meter-class telescopes. Eventually these facilities will pave the way for the ultimate objective: a dedicated space-based mission to image and characterize Earth analogs.


Friday, February 10th 2017
Speaker: Thayne Currie, National Astronomical Obs. of Japan, Subaru Telescope
Subject: The Bright Future for Directly Imaging Extrasolar Planets with Extreme Adaptive Optics
Candidate for the MIfA Assistant Professor position

Direct imaging is the new frontier in exoplanet detection and the means by which we will eventually discover a true Earth twin. In this talk, I first will review the advanced methods used to image planets and the wealth of information we have gathered from photometry and spectra of the first imaged planets using Subaru, LBT, and other large telescopes that clarifies key atmospheric properties like clouds, chemistry, and surface gravity. Direct imaging is in the midst of a revolution, driven by the development of ``extreme adaptive optics" systems that reveal planets 100 times fainter possible than before. I will detail design, capabilities, and first-light discoveries from the newly-commissioned extreme AO system with which I'm involved, the Subaru Coronagraphic Extreme Adaptive Optics system (SCExAO), which shares a technological heritage with LBTAO. Finally, I will close by describing the future promise for SCExAO on Subaru and as a PI instrument on the Thirty Meter Telescope, transformative planned and potential upgrades for LBTAO, and how both systems could work together to image and characterize younger versions of Jupiter in thermal emission to jovian or even rocky, habitable zone planets in reflected light within the next 10-15 years.


Friday, February 17th 2017
Speaker: Ian Roederer, University of Michigan
Subject: Heavy Metals from the First Stars to Today
Candidate for the MIfA Assistant Professor position

NASA's Cosmic Origins program aims to address the question, "How did we get here?" My work addresses this question through three broad themes: the nature of the first stars, the formation and evolution of the Milky Way and Local Group, and the origin of the elements. I study dwarf galaxies, globular clusters, and stars in the halo using optical and ultraviolet high-resolution spectroscopic data from various telescopes on the ground and the Hubble Space Telescope. I will present observations of heavy elements that change our understanding of when and how they were first produced in the early Universe, including perhaps by the first stars. Observations of heavy elements in a recently-discovered low-luminosity galaxy, Reticulum II, reveal that the r-process---one of the fundamental ways that stars produce heavy elements---may occur in mergers of neutron stars. At Minnesota, access to instruments at the LBT, MMT, Magellan, and Bok Telescopes would enable critical spectroscopic followup of new stellar systems discovered by the Dark Energy Survey, Pan-STARRS Telescope, and Large Synoptic Survey Telescope in the next decade. These data would help guide our interpretation of observations from the Advanced LIGO/Virgo experiment and the James Webb Space Telescope, and these research directions would present new opportunities for collaboration with the nuclear astrophysics community.


Friday, February 24th 2017
Speaker: Patrick Kelly, University of California - Berkeley
Subject: Using Galaxy Cluster Lenses as Extreme Probes
Candidate for the MIfA Assistant Professor position

Galaxy clusters can highly magnify galaxies behind them, making cluster lenses powerful tools for studying the high-redshift universe. The James Webb Space Telescope, when pointed towards foreground cluster fields, will be sensitive to even low-luminosity galaxies at redshift z > 6 (~35th magnitude) thought to drive reionization. In regions of high magnification, however, cluster magnification maps show strong disagreements. I will describe the first-known multiply imaged, strongly lensed supernova (SN), which appeared in late 2014 in an Einstein cross configuration in the MACS1149 galaxy-cluster field. The timing of the reappearance of the SN, at an offset of ~8 arcseconds, in 2015 disagrees with most but not all predictions, and illustrates a promising approach for identifying the most accurate cluster-modeling techniques and magnification maps. I will next discuss observations of an individual star at high redshift, which acts as a new window into the nature of galaxy-cluster dark matter. Detections of hundreds of thousands of SNe and thousands of lensed transients by the Large Synoptic Survey Telescope and the Wide-Field Infrared Survey Telescope will allow new insights into star formation and stellar evolution beginning at z~15-20, as well as the nature of dark matter and dark energy.


Friday, March 3rd 2017
Speaker: Andrew Mann, University of Texas - Austin
Subject: Tracing Planetary Evolution from Formation to Maturity
Candidate for the MIfA Assistant Professor position

Planets are not born in their final state; rather, they change significantly over their lifetimes. Understanding how planets evolve has been a central question since the discovery of the first exoplanets. The first few hundred million years are thought to be the most formative, but planets in this age range are also the most difficult to identify and characterize. Instead, research has focused on inferring the history of planets through patterns in the population of older systems. In this talk I will discuss how this paradigm is shifting, as novel search techniques and new missions have enabled our discovery of Earth- to Neptune-size planets as young as 10 Myr. These discoveries have altered our understanding of how planets migrate and lose atmosphere, but raise further questions about the physical drivers of these changes. The upcoming TESS mission will discover hundreds more young planets, including analogues of a young Earth. Combined with follow-up from NIR spectrographs (e.g., iLocater on LBT), the TESS sample will enable new tests of planet formation and evolution through population statistics. Eventually, JWST, LBT, and 30m-class telescopes can be used to study the atmospheres of young, rocky planets, providing unique insight into the history of potentially habitable planets.


Friday, March 10th 2017
There will be no colloquium this week.

Friday, March 17th 2017
No Colloquium; Spring Break

Friday, March 24th 2017
Speaker: Charles 'Chick' Woodward
Subject: Small Worlds – New Vistas

Our solar system contains a surprising diversity of planetary environments whose import has direct bearing on understanding the condensation of materials out of a cooling solar nebula, planetesimal evolution, and the eventual migration of giant worlds beyond the frost line to new orbital positions. Highlighted during this presentation will be recent observational exploration of solar system small bodies, with new remote sensing techniques from ground-based and space-based facilities motivated by the question: How have the myriad chemical and physical processes that shaped the solar system operated, interacted, and evolved over time? Vistas within our solar system shed light on processes that are likely repeated among the plethora of exo-planetary systems and may help us how comprehend how common life might be.


Friday, March 31st 2017
There is no colloquium this week.

Friday, April 7th 2017
Speaker: Today's MIfA colloquium has been cancelled.

During solar and stellar flares, the majority of the radiated energy from the lower atmosphere escapes as white-light continuum emission in the near- ultraviolet and optical wavelength regimes. The spectral energy distribution of the white-light emission is important for assessing biomarkers in planetary atmospheres around M dwarfs and for constraining models of heating at the highest densities in flares. In this talk, I will discuss the properties of solar flares gleaned from recent IRIS data and review recent observations of M dwarf flares, including the hottest and most energetic that has been observed to date. Spectral observations and radiative-hydrodynamic modeling suggest that the white-light continuum and the chromospheric line flux in solar and stellar flares originate over two flaring layers in the lower-to-mid chromosphere. However, the fluxes of accelerated particles that are necessary to reproduce the observations are so high that the propagation of the particles to the lower atmosphere may be affected by beam instabilities. I will present our new prescription for modeling the electric pressure broadening in flare spectra, which will help resolve the problem of how the highest densities in the stellar atmosphere are heated during flares. Finally, I will speculate on aspects of habitability in the recently discovered planetary systems around the flare stars Proxima Centauri and TRAPPIST-1.


Friday, April 14th 2017
Speaker: Carl Ferkinhoff, Winona State
Subject: Far-infrared fine-structure line studies of early galaxies: Where are we? Where do we need to go?

This year marks the 42nd anniversary of the first far-infrared fine-structure line detection, the [OIII] 88 micron line, by the NASA Learjet in 1975. Additional pioneering work through the early 90’s revealed the astrophysical importance of the full suite of far-IR lines and demonstrated their power as probes of the physics conditions in the interstellar medium (ISM). While inaccessible from ground at their rest wavelengths, they begin falling into the short submillimeter telluric-windows (~200 to 500 μm) from high-z systems at z~1. Over the past one and half decades ISO, Herschel and now SOFIA have provided detailed studies of the lines in the local universe while ground based observations made the first detections of the lines from the early universe. These first detections in the high-z universe demonstrated the lines’ utility for studying high redshift systems. This includes the ability to constrain the size of star-forming regions, quantity of ionized gas, age of the starburst, and gas phase abundances to name a few. Now in the ALMA era, studies using the fine-structure lines have the potential to dramatically increase our understanding of early galaxies, both in their formation and evolution. Much work is required, however, to fully realize this potential. In this talk I will seek to answer two questions in regards to the far-IR fine-structure lines: Where are we and where do we need to go? In answering these questions, I will summarize the current state of fine-structure line studies—both locally and in the distant universe—while highlighting some of my recent work with ALMA and explaning the “[CII] deficit”. In the last part of the talk, I will discuss future multi-wavelength studies, including that ZINGRS Radio Survey, which will help realize the full scientific potential of the FIR fine-structure lines for studying the early universe.


Friday, April 21st 2017
Speaker: Stephanie Juneau, NOAO; CEA-Saclay
Subject: Cosmic Hide-and-Seek with Supermassive Black Holes

Supermassive black holes - with masses of millions to billions of times that of the Sun - reside in the nuclei of galaxies. While black holes are not directly visible, surrounding material becomes extremely luminous before being accreted, creating telltale signatures of black hole activity. In turn, the amount of activity tells us about black hole growth, and energy injection back into the host galaxies. This so-called black hole feedback is thought to play a role in galaxy evolution. Black hole activity is normally detectable at a range of wavebands including high energy X-rays. However, in some extreme cases, the usual signatures are either absorbed or obscured by intervening material along the line-of-sight. I will start by reviewing the state of the art in terms of black hole obscuration, and highlight new findings from a multi-scale analysis of gas ionization and dynamics thanks to 3D spectroscopy with the MUSE instrument. I will conclude with a global view of black hole growth and feedback in galaxies, including major questions that remain open for new capabilities such as the James Webb Space Telescope (JWST), and large galaxy survey experiments such as DESI and Euclid.


Friday, April 28th 2017
Subject: No MIfA speaker this week. See the SPA colloquium April 27th
Adriano Fontana, Nat'l Institute for Astrophysics (Italy)

Friday, May 5th 2017
Speaker: Adam Kowalski, University of Colorado
Subject: The Spectral Signatures of Deep Atmospheric Heating in Solar and Stellar Flares

During solar and stellar flares, the majority of the radiated energy from the lower atmosphere escapes as white-light continuum emission in the near-ultraviolet and optical wavelength regimes. The spectral energy distribution of the white-light emission is important for assessing biomarkers in planetary atmospheres around M dwarfs and for constraining models of heating at the highest densities in flares. In this talk, I will discuss the properties of solar flares gleaned from recent IRIS data and review recent observations of M dwarf flares, including the hottest and most energetic that has been observed to date. Spectral observations and radiative-hydrodynamic modeling suggest that the white-light continuum and the chromospheric line flux in solar and stellar flares originate over two flaring layers in the lower-to-mid chromosphere. However, the fluxes of accelerated particles that are necessary to reproduce the observations are so high that the propagation of the particles to the lower atmosphere may be affected by beam instabilities. I will present our new prescription for modeling the electric pressure broadening in flare spectra, which will help resolve the problem of how the highest densities in the stellar atmosphere are heated during flares. Finally, I will speculate on aspects of habitability in the recently discovered planetary systems around the flare stars Proxima Centauri and TRAPPIST-1.


Friday, September 8th 2017
There is no colloquium this week.

Friday, September 15th 2017
2:30 pm:
MN Institute for Astrophysics Colloquium in Tate Lab of Physics and Astronomy 101
Speaker: Sarah Vigeland, U. Wisconsin, Milwaukee
Subject: Detecting Low-Frequency Gravitational Waves with NANOGrav
Refreshments to be served in the MIfA Interaction Area (Tate 285-11) following the colloquium.

For the past decade pulsar timing arrays (PTAs) have been monitoring
millisecond pulsars looking for the correlated timing residuals
caused by low-frequency gravitational waves (GWs) with frequencies
between 1 - 100 nHz. One type of source in this regime are
supermassive black hole binaries (SMBHBs). PTAs are sensitive to both
GWs from individual SMBHBs as well as a GW stochastic background produced
by the superposition of all SMBHBs. I will discuss the detection techniques
used by PTAs as well as the current status of the North American Nanohertz
Observatory for Gravitational Waves (NANOGrav) PTA.

Faculty Host: Vuk Mandic

Friday, September 22nd 2017
There will be no colloquium this week.

Friday, September 29th 2017
Speaker: No colloquium this week
Subject: See the Misel lecture information for September 27th

Friday, October 6th 2017
Speaker: Anna Nierenberg, Ohio State U
Subject: Dwarf galaxy formation and the nature of dark matter
Refreshments to be served in the MIfA Interaction Area (Tate 285-11) following the colloquium.

The abundance of low mass dark matter halos (M_vir <10^9 M_sun) provides key insight into the nature of dark matter, as this abundance depends on the free-streaming length of dark matter at early times and thus its particle properties. Measuring the abundance of low mass halos is difficult as stars become increasingly poor tracers of structure on these scales owing to the complex and not yet well understood physics of star formation in these systems. I will present two complementary approaches to resolving these issues. First I will present measurements of the properties of faint satellite galaxies at a range of redshifts and around a variety of host types and demonstrate how these place strong new constraints on theoretical models of star formation in low mass halos. Secondly, I will present a novel approach to gravitational lensing which makes it possible directly measure the subhalo mass function to masses well below the mass scale of the missing satellite problem in a much larger sample of systems than previously possible. I will conclude by discussing future prospects for these programs given the next generation of ground and space based facilities.

Faculty Host: Liliya L.R. Williams

Thursday, October 12th 2017
Speaker: Lawrence Rudnick, University of Minnesota
Subject: A Walk on the Dark Side

Our Universe is comprised of far more than meets the eye. For 13.8 billion years, gravity has been creating enormous bound structures, the largest of which are clusters of galaxies. Modern telescopes are uncovering an astonishing variety of structures in these clusters which are invisible to the human eye – from X-ray emitting gas at 100s of millions of degrees, to supermassive black holes at the centers of cluster galaxies, to the popularized but not yet understood dark matter that holds everything together. Even the enigmatic dark energy plays a role in cluster formation. Our tour of clusters will start with the first recognition of curious concentrations of fuzzy objects in the sky to the latest discoveries using telescopes across the Earth and space.

About the Speaker: Professor Rudnick is a Distinguished Teaching Professor of Astrophysics, whose research focuses on clusters of galaxies and other large scale structures in the Universe. He uses ground and space telescopes, primarily in the radio and X-ray part of the spectrum. His teaching includes eclectic freshman seminars such as “The Ultimate Questions,” and “Nothing.” Professor Rudnick has been active for many years with a variety of television, radio, and other public programming, and is now working toward the opening of the Bell Museum and Planetarium in 2018 on the St. Paul campus.


Friday, October 13th 2017
Speaker: Eliza Kempton, Grinnell College
Subject: Revealing the Atmospheres of Extrasolar Super-Earths
Refreshments to be served in the MIfA Interaction Area (Tate 285-11) following the colloquium.

Discoveries of extrasolar planets over the last two decades have reshaped our understanding of how planetary systems form. Super-Earths – planets intermediate in size/mass between Earth and Neptune – do not exist in our Solar System, and the discovery of such planets poses a challenge to theories of planetary formation and composition based on the Solar System paradigm. Through observations of the atmospheres of these planets, we can learn about their formation history, their climate, and in some cases their propensity to support life. This talk will focus on the modeling of super-Earth atmospheres as it relates to current and future observations. I will detail the current state of characterization efforts for super-Earth atmospheres, focusing on the challenges and successes in modeling and interpreting the early observations of these objects. I will conclude with a forward-looking view of super-Earth atmospheric studies over the next 5-10 years, in the era of the James Webb Space Telescope (JWST) and 30-meter class ground-based telescopes.

Faculty Host: Liliya L.R. Williams

Friday, October 20th 2017
Speaker: Nicholas Battaglia, Princeton University
Subject: Large-Scale Structure Information Encoded in the Cosmic Microwave Background
Refreshments to be served in the MIfA Interaction Area (Tate 285-11) following the colloquium.

A new window into the growth and evolution of large-scale structure has opened up with the recent measurements kinetic Sunyaev-Zel’dovich (SZ) effect. I will show how we can constrain the important baryonic process that govern galaxy formation through SZ measurements. Additionally, I will describe the prospects for future cosmic microwave background experiments to constrain fundamental physics from kinetic SZ observations and how to mitigate the modeling uncertainties associated with the baryonic processes that will limit these constraints.

Faculty Host: Shaul Hanany

Friday, October 27th 2017
Speaker: Stuart Bale, Berkeley Space Science Lab.
Refreshments to be served in the MIfA Interaction Area (Tate 285-11) following the colloquium.
Faculty Host: Cynthia Cattell

Friday, November 3rd 2017
Speaker: Ori Fox, Space Telescope Science Institute
Refreshments to be served in the MIfA Interaction Area (Tate 285-11) following the colloquium.

Friday, November 17th 2017
Speaker: Anne Jaskot, Smith College
Refreshments to be served in the MIfA Interaction Area (Tate 285-11) following the colloquium.
Faculty Host: M. Claudia Scarlata

Friday, November 24th 2017
Speaker: No colloquium - Thanksgiving Holiday

Friday, December 1st 2017
Speaker: Shea Brown, U of Iowa
Refreshments to be served in the MIfA Interaction Area (Tate 285-11) following the colloquium.
Faculty Host: Lawrence Rudnick

Friday, December 8th 2017
Speaker: Jeremy Webb, Indiana U
Refreshments to be served in the MIfA Interaction Area (Tate 285-11) following the colloquium.
Faculty Host: Liliya L.R. Williams

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