MN Institute for Astrophysics Colloquium

semester, 2016

Friday, August 12th 2016
11:00 am:
Untitled in PAN 110
Speaker: Xavier Prochaska, U of California Santa Cruz
Subject: Rise of the Giant Lya Nebulae

I will describe the discovery and analysis of giant (>100kpc)
Lya nebulae in the z~2 universe, found predominantly around luminous AGN. These phenomena reveal massive (~10^11 Msun) reservoirs of cool, enriched gas with kinematics suggestive of gravitationally infalling material and galactic-scale outflows. I’ll review the recent results and describe anticipated advances with the advent of optical IFUs on 10m-class telescopes.

Friday, September 9th 2016
There is no colloquium this week.

Friday, September 16th 2016
Speaker: Daniel Weisz, U.C. Berkeley
Subject: A PHAT New Measurement of the High-Mass Stellar IMF

The initial mass function (IMF) for stars above ~1 Msun is essential to testing and validating theories of star formation, constraining chemical enrichment models, the frequency of core-collapse supernovae, and interpreting the stellar populations of galaxies across cosmic time. Yet, despite more than 60 years of research, observational constraints on the high-mass IMF remain remarkably uncertain. Widely used high-mass IMFs (e.g., Kroupa) have associated uncertainties approaching an order-of-magnitude, making it virtually impossible to determine if the high-mass IMF varies with respect to environment (e.g., metallicity or star formation intensity) or is “Universal". In this talk, I will present the most precise measurement of the high-mass IMF to date. Using ~100 young, resolved star clusters in M31 imaged as part of the Panchromatic Hubble Andromeda Treasury (PHAT) survey, we find the high-mass IMF slope to be Gamma=1.45+/-0.03. Compared to the canonical Kroupa IMF (Gamma=1.3+/-0.7), the high-mass IMF in M31 is 0.15 dex steeper (i.e., fewer massive stars) and represents a factor of ~20 improvement in precision. There are no significant trends between the cluster IMF slopes and their ages, masses, and sizes, indicating that the IMF is remarkably “Universal” in this sample of ~100 clusters. I will illustrate some of the broader implications of a steeper IMF slope (e.g., on star formation rate indicators, core-collapse supernovae rates) and will conclude by discussing the prospects for precision IMF measurements in other environments.

Friday, September 23rd 2016
Speaker: See the listing for the SPA colloquium on Sept. 22nd - Lucy Fortson

Friday, September 30th 2016
Speaker: Caryl Gronwall, Penn State University
Subject: HETDEX and Star-Forming Galaxies of the z ~ 2 Universe

Next spring, the Hobby Eberly Telescope Dark Energy Experiment will begin obtaining redshifts for roughly a million Ly-alpha emitting galaxies (LAEs) between 1.9 < z < 3.5. While the main purpose of the project is to study the evolution of Dark Energy, the project will provide an incredible data base for studies of galaxy evolution. In preparation for this, we have been investigating the physical and chemical properties of emission-line galaxies in the z ~ 2 universe, using LAEs discovered from the ground and samples of [O III]-emitting objects identified from space. We show that LAEs are not “low mass, dust-poor galaxies caught in the act of formation”, but instead span the entire range of stellar masses, from at least 7.5 < log M/Msun < 10.5. We then use our galaxy samples to explore issues such as the (non)-Fundamental Metallicity Relation, the systematics of star-formation rate indicators, the behavior of dust attenuation laws versus stellar mass, and the question of what makes an LAE and LAE.

Friday, October 7th 2016
Speaker: Brad Peterson, Professor Emeritus, Ohio State University and Distinguished Visiting Astronomy, Space Telescope Sci. Institute
Subject: Exploring the Inner Structure of Active Galactic Nuclei by Reverberation
Prof. Petrson was recently awarded an Outstanding Achievement Award from the University

The innermost structure of active galactic nuclei (AGNs) consists of an accretion disk surrounding a supermassive black hole and, on somewhat larger scales, rapidly moving diffuse gas. The ultraviolet through near IR spectrum of AGNs is dominated by thermal continuum emission from the accretion disk and broad emission lines and absorption features from the diffuse gas. The continuum flux from the accretion disk varies with time, and the emission lines also change in brightness, or “reverberate,” in response to these variations, with a delay due to the light-travel time across the line-emitting region. Measurement of the emission-line time delay yields the size of the line-emitting region and by combining this with the emission-line Doppler width, the central black hole mass can be inferred. I will discuss results from recent “reverberation mapping” experiments, including a 179-orbit HST Cycle 21 program, that have been designed to explore the dynamics of the emission-line gas and are yielding a wealth of new and quite surprising information about AGN structure.

Thursday, October 13th 2016
7:00 pm:
Speaker: Dr. Vuk Mandic, School of Physics & Astronomy, MN Institute for Astrophysics

Advanced LIGO gravitational-wave detectors recently recorded the first signals coming from mergers of binary black hole systems, marking the beginning of gravitational-wave astronomy and astrophysics. For the first time we are able to observe and study the universe with gravitational waves, and to learn about objects never observed before. Dr. Mandic will describe the LIGO detectors and the events they recorded, and he will discuss the implications of these observations as well as expectations for future observations.

Friday, October 14th 2016
Speaker: Dr. Andreas Faisst, IPAC, Caltech
Subject: Insights into the high-redshift Universe using Spitzer and Local Galaxies

How do the first galaxies form? What is their connection to reionization? With today’s large samples of galaxies at z > 5, this is one of the burning question in modern astrophysics. Current spectrographs are not able to probe the spectral properties of the very first galaxies until the advent JWST. However, by combining deep Spitzer data with detailed studies of local galaxies we can probe the formation of the first galaxies in depth and provide the optimal samples for follow-up with JWST as well as other upcoming facilities. My talk will focus on what we learn pre-JWST about the properties and formation of
the first galaxies.

Friday, October 21st 2016
Speaker: Nathan Smith, U of Arizona, Steward Observatory
Subject: Blast waves in circumstellar gas, and implications for the pre-supernova evolution of massive stars

The interaction between a supernova blast wave and dense circumstellar material (CSM) provides a unique way to investigate the very latest-phases in the pre-core collapse evolution of massive stars, because mass shed by the star in the preceding decade is illuminated and shock heated. Recent studies of such supernovae have shown that these late phases of stellar evolution must, in some cases, be punctuated by violent instabilities that precede the supernova by a few years to decades. The cause of these and the types of stars which fall subject to the instability remains as an open question, but depending on the explosion energy and the mass distribution of CSM, the conversion of kinetic energy into light can produce some of the most luminous supernovae in the universe. Because of high efficiency, this process can also produce moderately luminous transients even from non-terminal eruptions or low-energy explosions. Because many of these non-terminal eruptions can repeat, because low-energy explosions can come from relatively low-mass stars, and because some of the resulting supernovae are extraordinarily luminous, CSM interaction may figure prominently in the vast array of unusual transients now being discovered by transient searches (and by LSST in the future). The talk will explore the diversity of different transients that may result from CSM interaction, including a discussion of several individual observed examples that illustrate extremes in parameter space. I'll end with a very famous and very peculiar astronomical object, where a simple model of CSM interaction may help resolve some long-standing mysteries and paradoxes that have seen little progress in the last 30 years.

Friday, October 28th 2016
Speaker: Dr. Cornelia Lang, U. Iowa
Subject: The Central Molecular Zone of the Galaxy: Dense Molecular Clouds, Massive Stars and Magnetic Fields

In addition to harboring a supermassive black hole at its very core, the Galactic Center is one of the most physically extreme environments in the Galaxy. Dense and massive molecular clouds are abundant in this region, yet star formation is not as active as one might expect. In addition, radio observations have revealed a population of synchrotron-emitting filaments that provide insight on the magnetic field strength and configuration in this unique region of the Galaxy. Physical interactions may be occurring at the interfaces of dense molecular clouds and the interstellar magnetic filaments. I will review recent observational results of several unusual molecular clouds and the population of magnetized filaments that stand out in radio continuum images of the Galactic center and discuss the implications for better understanding the astrophysics of this region.

Friday, November 4th 2016
Speaker: Attila Kovacs, MIfA, U. Minnesota
Subject: Frontier science in the submillimeter and far-infrared

I will present some recent, on-going, and upcoming efforts that push the boundaries of submillimeter and far-infrared astrophysics. The submillimeter and FIR wavelengths can probe where no other wavelengths can, and sample the distant Universe uniformly, largely unaffected by dimming. They can also provide insights into optically obscured environments of star-formation locally, in the Galaxy. I will discuss recent results from 2-mm deep fields, and resolved SZ cluster morphologies; ongoing efforts at spectroscopic redshift searches using a novel technology; future mm-wave surveys; and probing star-formation locally, in the Galaxy, via FIR polarimetry with SOFIA/HAWC+ and spectroscopy with SOFIA/HIRMES.

Friday, November 11th 2016
Speaker: John Phillips, MIfA, U. Minnesota
Subject: The Evolution of Systems of Satellite Galaxies in Local Group-like Environments.

The Local Group is fertile ground for study of many astrophysical topics, yet still much is unknown about how it came to be as we see it today. This talk will motivate the need to study the Local Group in context of similar sparse groups in the local Universe, and will discuss some recent findings concerning the effects that membership in structures like the Local Group have on galactic evolution.

Friday, November 18th 2016
Speaker: Marc Huertas-Company, University of Diderot, Paris
Subject: Quenching and bulge growth in massive galaxies

The life of a galaxy is a balance between processes that trigger star formation by accelerating gas cooling and others which tend to prevent stars to form by expelling or heating gas. Over the past years, the picture is emerging that, during most of its life, a galaxy seems to live a rather quiet life, gradually growing in stellar mass through the formation of new stars which are formed at a rate remarkably proportional to its stellar mass, This is interpreted as an indirect evidence that fuel in the form of cold gas is somehow continuously being fed into the galaxies to sustain star formation. Two major events, eventually related, can break this apparent equilibrium. An episode of high star formation activity (e.g starburst) can be triggered. Or, suddenly something might happen that prevents the galaxy to continue forming new stars. Quenching is probably the most important event that a galaxy experiences during its life and a fundamental mechanism that helps understanding most of the properties of our surrounding Universe. There are a variety of different mechanisms entertained for the quenching process, e.g. feedback, interactions, halo driven shock heating, morphological quenching etc. Which one is dominantly driving galaxy evolution (if there is) or under which circumstances one or another process is triggered is still a mystery.

In my talk I will focus on the relation between structure and quenching in massive galaxies. By using advanced machine intelligence techniques, I will analyze the relation between quenching and bulge growth in massive galaxies from z~3. I will in fact show evidences of two distinct channels for the growth of bulges in the massive end of the present day Hubble sequence (Huertas-Company+15ab). I will also discuss challenges and solutions to estimate galaxy morphologies in future big-data surveys like EUCLID.

Friday, November 25th 2016
Speaker: No Colloquium - UofM closed for Thanksgiving holiday

Friday, December 2nd 2016
Speaker: Ming Sun, U. Alabama, Huntsville
Subject: Study Baryon Physics with Galaxy Groups and Clusters

Galaxy groups and clusters are the least massive systems where the bulk of baryons are accounted for and also the most massive systems that are gravitationally bound. Baryons locked into stars and baryons remaining diffuse provide orthogonal constraints on cosmic structure formation, which makes groups and clusters ideal systems to study baryon physics. In this talk, I will summarize new results on two projects on baryon physics in galaxy groups and clusters. The first one will focus on X-ray scaling relations of local galaxy groups. I will also discuss our recent results on stacking and its application on cluster cosmology. In the second part, I will focus on ram pressure stripping of cluster galaxies. The last decade has witnessed a burst of new discoveries about ram pressure stripping emerging from multi-wavelength, multi-scale observations. Stripped tails have emerged as another kind of ideal targets in clusters to study multi-phase media, along with cool cores. New results on optical, CO and X-rays will be discussed.

Friday, December 9th 2016
There will be no colloquium this week.

Friday, December 16th 2016
There is no colloquium this week.

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