Cosmology Lunchtime Seminar

semester, 2017


Monday, January 16th 2017
12:15 pm:
There will be no seminar this week.

Monday, January 23rd 2017
12:15 pm:
Speaker: Lauren Pearce, University of Minnesota
Subject: Phenomenology of Trapped Inflation

While there is good support for the inflationary paradigm, evidence does not clearly point to any particular inflationary model. Therefore, it is imperative that careful calculations are done to allow cosmological observations to constrain models. In this talk, we will look at cosmological constraints on trapped inflation, amodel in which the inflaton undergoes slow roll because it is losing energy to particle production, not because of the flatness of its potential.


Monday, January 30th 2017
12:15 pm:
Speaker: Burcin Mutlu-Pakdil, UMN
Subject: Discovery of an extremely rare galaxy: PGC 1000714

Non-barred ringed galaxies are among the ideal galaxies to study the role of both the internal dynamics of galaxies and the physics of accretion/interaction mechanisms. An especially interesting ring case is Hoag's Object with its peculiar morphology: an elliptical-like core with a nearly perfect outer ring, and no signs of bar and stellar disc. Hoag-type galaxies, which bear strong resemblance to Hoag's Object, are extremely rare and their origin is still debated. Our recent work has revealed a unique case for Hoag-type galaxies: PGC 1000714 presents strong resemblance to Hoag's Object in the optical and near-ultraviolet bands,with an additional structure — a second inner ring, which is more diffuse, and redder than the outer ring. Such peculiar systems help our understanding of galaxy formation in general, since they represent extreme cases, providing clues on formation mechanisms.

In the first part of my talk, I will simply overview the concept of ringed galaxies and introduce Hoag-type galaxies. Then, I will present my work on PGC 1000714 and finally conclude with a discussion about the implications of our findings.


Monday, February 6th 2017
12:15 pm:
Speaker: Brian D. Nord, Fermi National Accelerator Laboratory
Subject: The Power of Galaxy Surveys and Strong Gravitational Lensing for Probing the Cosmos

Current and future galaxy surveys will provide data sets unprecedented in size and precision with which to probe dark energy, dark matter and the early universe through probes like strong gravitational lensing. I will discuss modern experiments, like the Dark Energy Survey (DES) and the Dark Energy Spectroscopic Instrument (DESI) and the opportunities they offer for studying dark energy. In particular, I will discuss the burgeoning role of strong lensing in these surveys, as well as new techniques in deep machine learning that we are deploying in this era of big astronomical data.

Faculty Host: Marco Peloso

Monday, February 13th 2017
12:15 pm:
Speaker: Zhen Yuan, Shanghai Jiao Tong University
Subject: A possible formation mechanism of Fornax-like dSph: major merger after infall to Milky Way

The extended star formation history of some MW satellites (Fornax, Carina) is always a puzzle in galaxy formation theory on small scales. Similar cases can be also found in M31 satellites. Both Fornax and Carina are estimated to become MW satellites pretty early (~8, ~10 Gyr ago) from proper motion information. The extreme long SFH until recently contradicts the classic galaxy formation models. Some hints from zoom-in MW simulations suggest a possible mechanism of new gas supply is from a companion through major merger after satellite infall. Inspired by the empirical chemical evolution model, I found that Fornax-like dSph needs to be much more diffused in order to explain the elemental abundance pattern ([alpha/Fe] vs. [Fe/H]). It is consistent with the major merger scenario which makes the system expand and consequently a much more inhomogeneous chemical enrichment environment. My collaborators and I made artificial major merger cases of satellites when they infall to MW. Assuming the satellites have some initial stellar configuration, we tracked the evolution of both the dark matter and star particles under growing MW potential. I will discuss our current results and interesting implications.

Faculty Host: Yong-Zhong Qian

Monday, February 20th 2017
12:15 pm:
Speaker: Lilya Williams, UMN
Subject:  Interplay between dark and baryonic matter in galaxy centers: new constraints from dynamics and lensing

The central 5-10 kpc of elliptical galaxies, while in long term steady state, are not truly relaxed. The primary reason is that baryons and dark matter are not fully mixed. We demonstrate this by comparing observed and simulated galaxies to theoretically derived prediction for dynamically relaxed collisionless systems, and by examining the observed population of quadruply imaged lensed systems hosted by galaxies. The unrelaxed state can be used to our advantage, to extract information about the formation and evolution of the central regions of galaxies and hence all that they depend on: baryonic processes, central supermassive black hole, and especially dark matter properties. I will describe some ongoing work on this, and sketch future directions.


Monday, February 27th 2017
12:15 pm:
Speaker: Patrick Meyers, UMN
Subject: Searching for the stochastic gravitational-wave background in Advanced LIGO's first observing run

One of the most exciting prospects of gravitational-wave astrophysics and cosmology is the measurement of the stochastic gravitational-wave background. In this talk, we discuss the most recent searches for a stochastic background with Advanced LIGO—the first performed with advanced interferometric detectors. We search for an isotropic as well as an anisotropic background, and perform a directed search for persistent gravitational waves in three promising directions. Additionally, with the accumulation of more advanced LIGO data and the anticipated addition of Advanced Virgo to the network in 2017, we can also start to consider what the recent gravitational-wave detections—GW150914 and GW151226—tell us about when we can expect a detection of the stochastic background from binary black hole coalescences.


Monday, March 6th 2017
12:15 pm:
Speaker: Darryl Wright, UMN
Subject: Supernova Hunters: combining human and machine classifications

Efficient identification and follow-up of astronomical transients is hindered by the need to manually select promising candidates from data streams that contain many false positives. With data from Pan-STARRS1 we present the citizen science project, Supernova Hunters created with the Zooniverse project builder. The project allows us to crowdsource classifications of supernova candidates, and test methods to combine human and machine classifications. We show this combination produces a purer and more complete sample of supernovae than either individually.


Monday, March 20th 2017
12:15 pm:
Speaker: Hugh Dickinson, UMN
Subject:  Visual Classification of Illustris Galaxy Morphologies: Evaluating Cosmological Simulations using Galaxy Zoo

Illustris is one of the first large-scale simulation projects with sufficient resolution and physical realism to model the evolution of galaxy-sized structures within a wider cosmological context. If synthetic observational data for the Illustris galaxies accurately emulate observations of galaxies in the real Universe, then arguments for corresponding parity between physics and history of galaxy formation in simulation and reality and become more credible. Conversely, discrepancies between the simulated and observed populations can be used to infer shortcomings of the Illustris simulation and identify avenues for its potential enhancement.

I will briefly review two traditional approaches that have already been used to quantify the degree of correspondence between simulated and observed galaxy properties. I will then introduce an ongoing initiative to obtain visual morphological classifications for the Illustris galaxies using the Galaxy Zoo citizen science platform. Comparing the initial results of this study with identically obtained data for galaxies observed by the Sloan Digital Sky Survey indicates substantial mismatches between the visual appearance of the real and simulated datasets. I will explore the contexts in which these disparities are apparent before discussing plausible explanations for their origin and promising avenues for further investigation.


Monday, March 27th 2017
12:15 pm:
Speaker: Qi Wen, UMN
Subject:  Falling Rotation Curves of The Star-forming Galaxies Ten Billion Years Ago

In the standard model of cosmology, the mass ratio of baryons to dark matter is about 1 : 5. The mass of the outer disks in nearby (z ~0) massive galaxies are usually dominated by dark matter, which explains the observations of the common flat or slightly rising shapes of galaxies' rotation curves in the local universe. However, a recent study reported that the rotation curves of star-forming galaxies at z ~ 0.6-2.6 may commonly be falling with radius. In this talk, I will discuss this study in detail about their observations, sample selection and methodology. Finally we will look at some implications from the results obtained.


Monday, April 3rd 2017
12:15 pm:
Speaker: Yong-Zhong Qian, UMN
Subject: Effects of eV-Scale Sterile Neutrinos on Supernova Explosion and Nucleosynthesis

We show that for the active-sterile flavor mixing parameters suggested by the reactor neutrino anomaly, substantial conversion between neutrinos (antineutrinos) of the electron and sterile flavors occurs in regions with electron fraction close to 1/3 near the core of an 8.8 solar mass supernova. Compared to the case without such conversion, the neutron-richness of the ejected material is enhanced to allow production of elements from Sr, Y, and Zr up to Cd in broad agreement with observations of the metal-poor star HD 122563. Active-sterile flavor conversion also strongly suppresses neutrino heating at times when it is important for the revival of the supernova shock. Our results suggest that simulations of supernova explosion and nucleosynthesis may be used to constrain active-sterile mixing parameters in combination with neutrino experiments and cosmological considerations.


Monday, April 10th 2017
12:15 pm:
Speaker: D'Ann Barker, UMN
Subject: Low Energy Background Model for CDMSlite

One trend in dark matter direct detection is the development of techniques which will lower experimental thresholds and achieve sensitivity to low-mass dark matter particles. In doing so, it is necessary to have an understanding of the low energy spectrum and the major background components. To understand this region for the Super Cryogenic Dark Matter Search (SuperCDMS), a variety of specialized low energy models have been simulated and compared against theoretical calculations and SuperCDMS data. An important application of this model is to the CDMS low ionization threshold experiment (CDMSlite). CDMSlite has reached world-leading sensitivities in the search for low-mass weakly interacting massive particle dark matter. The sensitivity of the current data can be improved by understanding and modeling the experimental backgrounds down to threshold. Development of the machinery for creating a low energy background model will also be useful in the future SuperCDMS SNOLAB experiment which will operate multiple high voltage detectors in a manner similar to CDMSlite.


Monday, April 17th 2017
12:15 pm:
Speaker: Terry J. Jones, UMN
Subject: Things That Go Bump In the Night

Gamma Ray, X-Ray, and fast radio bursts - Oh My! A potpourri of recent observations of transient events at cosmological distances.


Monday, April 24th 2017
12:15 pm:
Speaker: Evan Skillman, UMN
Subject: Carbon

I will report on recent measurements of carbon abundances from optical recombination lines of star forming regions in the spiral galaxy M101 obtained with the Modular Double Spectrograph on the Large Binocular Telescope. These observations allow us to study the evolution of the relative abundance of carbon as a function of absolute abundance.


Monday, May 1st 2017
12:15 pm:
Speaker: Micaela Bagley, UMN
Subject: A High Space Density of Luminous Lyman-alpha Emitters at z~6.5

I will present the results of a systematic search for Lyman-alpha emitters (LAEs) at 6 < z < 7.6 using the HST WFC3 Infrared Spectroscopic Parallel (WISP) Survey. Our survey covers a volume ~ 8x10^5 Mpc^3, comparable to many of the narrowband surveys despite their larger area coverage. We identify two LAEs at z ~ 6.4, which are among the brightest LAEs discovered at these redshifts. Taking advantage of the broad spectral coverage of WISP, we are able to rule out almost all lower-redshift contaminants. These LAEs reside in Mpc-scale ionized bubbles that allow the Ly-alpha photons to redshift out of resonance before encountering the neutral IGM. Based on the observed constraints, we conclude that the observed LAEs alone are not sufficient to ionize their surrounding bubbles.


Friday, August 4th 2017
12:15 pm:
No Seminar, Labor Day

Monday, September 4th 2017
12:15 pm:
No Seminar, Labor Day

Monday, September 11th 2017
12:15 pm:
Speaker: Kelley Hess, Department of Astronomy, University of Cape Town
Subject: Galaxy groups and the assembly of large scale structure

Galaxy groups are the most common environment, and the site where the majority of galaxy evolution occurs. Gas processing--through tidal interactions, ram pressure stripping, viscous stripping, etc--depletes the cold gas, shuts down star formation, and contributes to the build-up of the warm-hot intragroup medium that is sometimes detected in X-rays. As groups accrete more galaxies, the groups themselves become increasingly poor in neutral atomic hydrogen (HI), and more cluster-like. I will present the results of stacking ROSAT All-Sky Survey images for a large sample of groups for which we have complementary HI data from the ALFALFA HI survey in an attempt to detect the build-up of the WHIM in intermediate mass groups M>10^13 M_Sun, where we begin to see the impact of the group environment on the HI content of their member galaxies.

Understanding pre-processing in galaxy groups is in-turn critical to understanding the galaxy cluster population, and in the second half I will present two nearby clusters where we have used wide-field observations in radio, infrared, optical, and X-ray to identify substructure and used the galaxies' kinematics, HI gas, stellar, and hot gas properties to deconstruct the cluster assembly history.

Faculty Host: Liliya L.R. Williams

Monday, September 18th 2017
12:15 pm:

Monday, September 25th 2017
12:15 pm:
There will be no seminar this week.

Monday, October 2nd 2017
12:15 pm:
Speaker: Samir Banik, NISER, Bhubaneswar, India
Subject: LIPs analysis in SuperCDMS

Standard model for particle physics does not demand quantization of particle charges. This opens the possibility of finding particles with fractional charges. These particles lose energy at a rate which is proportional to square of charges, much more slowly than any known minimum ionizing particles. These particles are commonly termed as Lightly Ionizing Particles or LIPs. SuperCDMS low threshold detectors offer an opportunity to search for LIPs with very small fractional charges. I will discuss about some previous LIPs search experiments and will present LIPs analysis in SuperCDMS.

Faculty Host: Priscilla Cushman

Monday, October 9th 2017
12:15 pm:
Speaker: Anthony Villano, UMN
Subject: The Sensitivity Frontier for Cryogenic Semiconductor Detectors

Cryogenic semiconductor particle detectors are undergoing revolutionary advancements that can greatly improve the reach of dark matter direct detection experiments. In order to fully realize the potential of these detector advancements, major challenges in ultra-low-energy calibration and device physics must be overcome. I will discuss techniques to use sub-keV energy deposits to bring the physics of detector response into sharper focus. Using the framework developed to study detector response at this level we will then muse about future devices with even more extraordinary capabilities.

Faculty Host: Priscilla Cushman

Monday, October 16th 2017
12:15 pm:
Speaker: Tom Jones, UMN
Subject: Particle Acceleration in Galaxy Clusters

Monday, October 23rd 2017
12:15 pm:
Speaker: Colin Hill, Department of Physics, Columbia University
Subject: New Information in Ancient Photons: Novel Approaches to CMB Foregrounds and Secondary Anisotropies

Studies of the cosmic microwave background (CMB) radiation have driven the current era of precision cosmology. The tightest cosmological constraints to date have been derived from the primary CMB anisotropies, which predominantly probe the universe in its infancy. However, CMB experiments have recently entered a new regime in which constraints derived from the secondary anisotropies -- sourced by effects between our vantage point and the surface of last scattering -- substantially improve upon those derived from the primary anisotropies alone. Moreover, the secondary anisotropies contain valuable astrophysical information about the distribution and thermodynamic properties of baryons and dark matter at late times. I will describe new approaches to extract information from these signals, highlighting recent results related to the thermal (tSZ) and kinematic Sunyaev-Zel'dovich (kSZ) effects, which refer to the Compton-scattering of CMB photons off ionized gas with high temperature or non-zero bulk momentum, respectively. In particular, I will show how the kSZ effect probes the abundance of ionized gas in and around modern-day galaxies, which I have used to resolve the long-standing "missing baryon problem". I will then discuss new methods for combining multi-frequency CMB data to extract these signals in the presence of large (and correlated) foregrounds, with additional applications to CMB polarization analyses. I will conclude with a look ahead to such measurements with the Simons Observatory (SO), focusing on methods to determine the optimal frequency coverage of the large-aperture SO telescope for secondary anisotropy science, including CMB lensing.

Faculty Host: Shaul Hanany

Monday, October 30th 2017
12:15 pm:
Speaker: Andrew Matas, UMN
Faculty Host: Vuk Mandic

Monday, November 6th 2017
12:15 pm:
Speaker: Vihang Mehta, UMN
Subject: Galaxy formation
Faculty Host: M. Claudia Scarlata

Monday, November 13th 2017
12:15 pm:
Speaker: Karl Young, UMN
Faculty Host: Shaul Hanany

Monday, November 20th 2017
12:15 pm:
Speaker: Allison Noble, MIT, Kavli Institute
Subject: Dissecting z~1 Galaxy Clusters
Faculty Host: Lawrence Rudnick

Monday, November 27th 2017
12:15 pm:
Speaker: Nader Mirabolfathi, Texas A&M University
Subject: Directional dark matter detector
Faculty Host: Priscilla Cushman

Monday, December 4th 2017
12:15 pm:
Speaker: Larry Rudnick, UMN

Monday, December 11th 2017
12:15 pm:
Speaker: Patrick Kelly, UMN

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