KICP Seminars & Colloquia, Winter 2020

Seminar schedule for Winter 2020
January 10, 2020
Friday noon seminar
Nicholas Orlofsky
University of Wisconsin-Madison
New mass windows and detection prospects for primordial black hole dark matter   [Abstract]
January 17, 2020
Friday noon seminar
Dylan J Temples
Northwestern Universtiy / Fermilab
Understanding neutrino background implications in LXe-TPC dark matter searches using 127Xe electron captures   [Abstract]
January 22, 2020
Wednesday colloquium
Eric Dahl
Northwestern University
Scintillating Bubble Chambers   [Abstract]
January 24, 2020
Friday noon seminar
Evan E Schneider
Princeton University
The Origin of Multiphase Galaxy Outflows   [Abstract]
January 30, 2020
Open Group seminar
Ethan O Nadler
KIPAC/Stanford
The Galaxy--Halo Connection Including the Impact of the Large Magellanic Cloud
January 31, 2020
Friday noon seminar
Raymond T Co
University of Michigan
X-ray Search for Axions from Nearby Isolated Neutron Stars   [Abstract]
February 5, 2020
Wednesday colloquium
Abigail Crites
University of Toronto
Measuring the Epoch of Reionization with Line Intensity Mapping using TIME   [Abstract]
February 7, 2020
Friday noon seminar
Jessica M Turner
Fermilab
Heavy neutrinos and their role in the early Universe   [Abstract]
February 14, 2020
Friday noon seminar
Tien-Tien Yu
University of Oregon
A New Look at the Migdal Effect   [Abstract]
February 19, 2020
Wednesday colloquium
James Bock
California Institute of Technology
SPHEREx: An All-sky Infrared Spectral Survey Explorer Satellite
February 21, 2020
Friday noon seminar
Carmen Carmona Benitez
Pennsylvania State University
Near Future of Dark Matter Searches: Go Big, or Go Low   [Abstract]
February 28, 2020
Friday noon seminar
Dhanesh Krishnarao
University of Wisconsin-Madison
The Inner Milky Way: Our New Closest LI(N)ER   [Abstract]
February 28, 2020
Open Group seminar
Allison Strom
Carnegie Observatories
Rethinking metallicity: the quest to measure the chemistry of distant galaxies   [Abstract]
March 4, 2020
Wednesday colloquium
Tobias Marriage
Johns Hopkins University
The Cosmology Large Angular Scale Surveyor   [Abstract]
 
COLLOQUIA

  • January 22, 2020 | 3:30 PM | ERC 161 | Wednesday colloquium
    Scintillating Bubble Chambers
    Eric Dahl, Northwestern University

    Moderately superheated bubble chambers have proven to be an excellent method for WIMP hunting thanks to their world-leading electron-recoil discrimination, easy scalability, and diversity of potential WIMP targets. While the PICO Collaboration continues to increase the size and sensitivity of these devices, the successes of the past decade have also enabled a new bubble chamber variant where the superheated target is also a liquid scintillator. In these Scintillating Bubble Chambers, the nuclear recoil from a WIMP interaction simultaneously nucleates a bubble and creates a flash of scintillation light. On paper, this technique combines the electron recoil discrimination of a bubble chamber with the event-by-event energy reconstruction of a scintillator. In practice, these two signals conspire to allow scintillating bubble chambers to run at much lower thresholds than can be achieved in a standard PICO chamber. Superheated noble liquids, in particular, may be completely insensitive to electron recoils even when running at thresholds as low as 100 eV. I will describe our current understanding of why scintillating bubble chambers can reach these low thresholds, review the unique dark matter and neutrino physics open to a detector capable of electron/nuclear recoil discrimination at sub-keV energies, and update our progress on the first physics-scale scintillating bubble chamber, a 10-kg argon detector now under construction at Fermilab.
  • February 5, 2020 | 3:30 PM | ERC 161 | Wednesday colloquium
    Measuring the Epoch of Reionization with Line Intensity Mapping using TIME
    Abigail Crites, University of Toronto

    TIME is an instrument being developed to use line intensity mapping (LIM) to study emission from the faint objects in our universe. We will use this instrument to study the epoch of reionization, advancing our understanding of the first astronomical objects that ionized the neutral hydrogen in the universe. TIME is a mm-wavelength spectrometer using Transition Edge Sensor (TES) bolometers. The instrument spans the frequency range of 200-300 GHz with 60 spectral pixels and 16 spatial pixels. TIME will measure redshifted ionized carbon ( [CII] ) emission over the redshift range 5 to 9 in order to probe the evolution of our universe during the epoch of reionization. TIME will also detect low-redshift CO fluctuations and determine the cosmic history of molecular gas in the epoch of peak cosmic star formation, redshift 0.5 to 2. This new instrument and emerging technique will allow us to make complementary measurements to galaxy surveys that are probing these epochs. TIME was installed for an engineering test on the 12m ALMA prototype antenna in Spring of 2019 at the Arizona Radio Observatory on Kitt Peak and will return to the telescope for 3 seasons of science observations in ~ winter 2020/2021.
  • February 19, 2020 | 3:30 PM | ERC 161 | Wednesday colloquium
    SPHEREx: An All-sky Infrared Spectral Survey Explorer Satellite
    James Bock, California Institute of Technology

    SPHEREx, a mission in NASA's Medium Explorer (MIDEX) program, is an all-sky survey satellite designed to address all three science goals in NASA's astrophysics division, with a single instrument, a wide-field spectral imager. We will probe the physics of inflation by measuring non-Gaussianity by studying large-scale structure, surveying a large cosmological volume at low redshifts, complementing high-z surveys optimized to constrain dark energy. The origin of water and biogenic molecules will be investigated in all phases of planetary system formation - from molecular clouds to young stellar systems with protoplanetary disks - by measuring ice absorption spectra. We will chart the origin and history of galaxy formation through a deep survey mapping large-scale spatial power in two deep fields located near the ecliptic poles. Following in the tradition of all-sky missions such as IRAS, COBE and WISE, SPHEREx will be the first all-sky near-infrared spectral survey. SPHEREx will create spectra (0.75 '?'€'?' 3.8 um at R ~ 40, and 3.8 '?'€'?' 5 um at R ~ 120) with high sensitivity using a cooled telescope with a wide field-of-view for large mapping speed. During its two-year mission, SPHEREx will produce four complete all-sky maps that will serve as a rich archive for the astronomy community. With over a billion detected galaxies, hundreds of millions of high-quality stellar and galactic spectra, and over a million ice absorption spectra, the archive will enable diverse scientific investigations including studies of young stellar systems, brown dwarfs, high-redshift quasars, galaxy clusters, the interstellar medium, asteroids and comets.
  • March 4, 2020 | 3:30 PM | ERC 161 | Wednesday colloquium
    The Cosmology Large Angular Scale Surveyor
    Tobias Marriage, Johns Hopkins University

    The Cosmology Large Angular Scale Surveyor (CLASS) is a project to probe reionization and inflation by measuring the largest scales in the Cosmic Microwave Background (CMB) polarization. These scales are made accessible due to specialized front-end modulation technology and a survey strategy that covers 75% of the sky from Chile's Atacama Desert. Operating since 2016, CLASS observes at frequencies from 40 to 220 GHz to distinguish between CMB and Galactic emission. We are currently publishing results from the first two years of 40 GHz observations, which demonstrate recovery of large angular scale polarization. In this talk, I will give an overview and an update on CLASS as well as a discussion of the two-year results.

 
FRIDAY NOON SEMINARS

  • January 10, 2020 | 12:00 PM | ERC 401 | Friday noon seminar
    New mass windows and detection prospects for primordial black hole dark matter
    Nicholas Orlofsky, University of Wisconsin-Madison

    Recent developments have opened up new possible windows where primordial black holes (PBHs) can make up all of dark matter (DM). In the first half of the talk, I will describe how microlensing of X-ray pulsars could help to probe the asteroid-mass window. In the second half, I will discuss how stable (nearly) extremal PBHs with masses below traditional evaporation bounds could populate all of DM. These extremal PBHs could give rise to energetic signals when present-day binaries merge.
  • January 17, 2020 | 12:00 PM | ERC 401 | Friday noon seminar
    Understanding neutrino background implications in LXe-TPC dark matter searches using 127Xe electron captures
    Dylan J Temples, Northwestern Universtiy / Fermilab

    Dark matter searches using dual-phase xenon time projection chambers (LXe-TPC) rely on the discrimination between electronic recoils (background) and nuclear recoils (signal) based on the ratio of ionization electrons to scintillation photons produced by the interaction in the liquid xenon. This discrimination is calibrated at low energies using tritium β-decays. However, neutrino and Compton scatters from inner-shell electrons of xenon atoms result in the emission of Auger electrons and x-rays in addition to the primary recoiling electron, and thus have a different event topology than β-decays and valence-shell electron recoils. Due to their low kinetic energy and large numbers, these secondary particles can deposit larger amounts of energy within a small radius, which is uncharacteristic of valence electron recoils and is more akin to nuclear recoils. This affects the profile of the neutrino-electron scattering background in a way that is, so far, uncalibrated and unaccounted for in LXe-TPC dark matter searches, and presents the possibility of a false discovery claim. To investigate the significance of this effect, electrons capture decays of 127Xe are used to simulate the vacancies produced by inner-shell e-ν scatters in the Xenon Electron-recoil L-shell Discrimination Analyzer (XELDA) detector. The 127Xe source produces a high-purity sample of inner-shell vacancies accompanied by an Auger cascade that can easily be isolated from the prompt γ's emitted in the decay. In this talk, I will present preliminary results from a cross-calibration of the XELDA detector using both 127Xe EC-decays and 3H β-decays. The observed discrepancy reduces the efficiency with which neutrino-induced electron recoils can be rejected in large-scale LXe-TPC dark matter searches, such as LUX-ZEPLIN and DARWIN.
  • January 24, 2020 | 12:00 PM | ERC 401 | Friday noon seminar
    The Origin of Multiphase Galaxy Outflows
    Evan E Schneider, Princeton University

    Star-forming galaxies are often observed to host outflows - gas that is flowing away from the galaxy in phases ranging from cold molecular clouds to hot X-ray emitting plasma. While these multiphase outflows are routinely observed, theoretically constraining their origin and evolution has proven difficult. Explaining the prevalence and velocities of the cool ionized phase (T~10^4 K) in particular poses a challenge. In this talk, I will discuss a potential dual origin for this cool gas. Through a series of extremely high-resolution simulations run with the GPU-based Cholla code, I will show that in high star formation surface density systems, dense disk gas can be pushed out by the collective effect of clustered supernovae, explaining the low-velocity material. Subsequent shredding and mixing of these clouds creates gas with intermediate densities and temperatures that is prone to radiative cooling, allowing momentum to transfer between phases and producing high velocity cool gas. In addition to explaining the nature of outflows themselves, these multiphase winds could potentially be a source of the cool photo-ionized gas that is found in abundance in galaxy halos.
  • January 31, 2020 | 12:00 PM | ERC 401 | Friday noon seminar
    X-ray Search for Axions from Nearby Isolated Neutron Stars
    Raymond T Co, University of Michigan

    We performed a search for axion-like particles (ALPs) in the nearby isolated neutron stars and interpreted the recently observed excess in X-ray by an axion model. These ALPs can be produced from the hot cores of the neutron stars at temperatures around 10^8 K and be converted into X-ray photons within the magnetosphere of the neutron stars. The dominant production modes are the nucleon bremsstrahlung and Cooper pair-breaking-formation processes. These ALPs and the produced photons carry energies of order the core temperature or the superfluid gaps and are therefore much hotter than the surface temperature of around 10^6 K. X-ray dim isolated neutron stars are excellent targets due to low background in the signal range of 1-100 keV. We fit the axion model to an X-ray excess in 2-8 keV observed by XMM-Newton and Chandra and discuss prospects of confirming or ruling out the axion interpretation by future measurements of NuSTAR.
  • February 7, 2020 | 12:00 PM | ERC 401 | Friday noon seminar
    Heavy neutrinos and their role in the early Universe
    Jessica M Turner, Fermilab

    I will discuss the role of heavy neutrinos in the early Universe and how they can generate the observed matter anti-matter asymmetry, the electroweak scale and light neutrino masses. In addition, I will discuss a novel mechanism of baryogenesis which proceeds via a time-varying operator.
  • February 14, 2020 | 12:00 PM | ERC 401 | Friday noon seminar
    A New Look at the Migdal Effect
    Tien-Tien Yu, University of Oregon

    Searches for sub-GeV dark matter rely on sensitivity to small ionization signals. These signals can arise from dark matter-electron scattering, in which the scattered electron produces the ionization signal. However, the signal can also arise in dark matter-nucleus scattering through a process known as "Migdal" scattering. In this talk, I will review the theory behind "Migdal" ionization and demonstrate the connection between dark matter-electron scattering and Migdal scattering. As a concrete example, I will compare the two dark matter processes for a dark photon mediator.
  • February 21, 2020 | 12:00 PM | ERC 401 | Friday noon seminar
    Near Future of Dark Matter Searches: Go Big, or Go Low
    Carmen Carmona Benitez, Pennsylvania State University

    The identification of dark matter is presently one of the greatest challenges in science, fundamental to our understanding of the Universe. There are a number of experiments and R&D projects planned in the near future aiming to directly detect dark matter particles, and they largely fall into two categories: larger iterations of previous experiments; and novel techniques that seek to drive sensitivity towards low mass particles. One of the former, the LUX-ZEPLIN (LZ) experiment has grown out of its two precursors with the goal of constructing a next generation dark matter detector at Sanford Underground Research Facility (SURF) in South Dakota, with 7 tonnes of fully active liquid xenon. LZ has been designed to explore much of the parameter space available for WIMP models, with excellent sensitivity for WIMP masses between a few GeV and a few TeV. In this talk I will present an overview of the LZ detector design, current project status and timeline.
    As for the latter, we explore the use of a novel technique, the Snowball chamber, in the search for low-mass dark matter. This chamber uses supercooled water as the target, employing an exotic phase transition of metastable water in a similar fashion to a bubble chamber in reverse, but with enhanced low energy threshold (sub-keV) and background discrimination as a function of thermodynamic conditions. I will discuss the potential of this new technology to drastically expand detector sensitivity in the sub-GeV range, opening up a new parameter space currently out of reach.
  • February 28, 2020 | 12:00 PM | ERC 401 | Friday noon seminar
    The Inner Milky Way: Our New Closest LI(N)ER
    Dhanesh Krishnarao, University of Wisconsin-Madison

    Recently, we discovered diffuse ionized gas associated with the bar of the Milky Way ~1-2 kpc from Galactic Center (The Tilted Disk) that exhibits optical emission line ratios characteristic of Low Ionization (Nuclear) Emission Regions [LI(N)ERs] in other galaxies. This makes the inner Milky Way the closest example of a LI(N)ER in the universe and gives us a unique opportunity to study and constrain many individual sources of ionization with spatially resolved, multi-wavelength observations. Additionally, continued studies of large samples of nearby galaxies can provide a face-on perspective towards understanding the distribution of the ISM near bars and the impact of bars on the ISM. I will share our current understanding of the ionizing radiation field throughout the Milky Way as constrained through optical line observations with the Wisconsin H-Alpha Mapper (WHAM) and compare with findings from extragalactic integral field observations of Milky Way Analogs from SDSS MaNGA. In particular, the unique ionization mechanisms and anomalous optical line ratios surrounding bars will be shown and future steps towards constraining these mechanisms using simulations and new observations in the Milky Way will be discussed. Bridging the Milky Way with extragalactic systems allows for the power of statistics to provide insight on the formation and evolution of The Galaxy through cosmic time while also extrapolating high resolution observations from within to explain extragalactic trends and relations.

 
OPEN GROUP SEMINARS

  • January 30, 2020 | 1:30 PM | ERC 401 | Open Group seminar
    The Galaxy--Halo Connection Including the Impact of the Large Magellanic Cloud
    Ethan O Nadler, KIPAC/Stanford

    The population of Milky Way (MW) satellites contains the faintest known galaxies, and thus provides essential insight into galaxy formation and dark matter microphysics. Here, we present a model of the galaxy -- halo connection combined withnewly derived observational selection functions based on satellite searches in DES and Pan-STARRS to fit the position-dependent MW satellite luminosity function. We report decisive evidence for the statistical impact of the LMC system on the MW satellite population due to an estimated 6.5 ± 1.5 currently observed LMC-associated satellites, consistent with the number of LMC satellites inferred from Gaia proper motion measurements. Moreover, we show based on satellite abundances that the LMC fell into the MW within the last 2 Gyr, and we find that the faintest observed satellites inhabit halos with peak virial masses below 2 × 10^8 M⊙ at 95% confidence. We place robust constraints on the fraction of halos that host galaxies in this low-mass regime, and we predict that the faintest potentially detectable satellites occupy halos with peak virial masses above 10^6 M⊙.
  • February 28, 2020 | 3:30 PM | ERC 419 | Open Group seminar
    Rethinking metallicity: the quest to measure the chemistry of distant galaxies
    Allison Strom, Carnegie Observatories

    Large near-infrared spectroscopic surveys have confirmed that star-forming galaxies at cosmic noon (z~2-3) exhibit emission line spectra that are distinct from their local counterparts. These differences reflect important changes in the physical conditions and chemical enrichment patterns of galaxies at early times, correlated with differences in their star formation histories relative to most present-day galaxies. At z~2, almost all galaxies have nearly constant or rising star formation histories, but by z~0, galaxies overall have more modest star formation rates and many have largely finished forming stars. Using spectra from the Keck Baryonic Structure Survey (KBSS) and photoionization models designed to reconcile the joint rest-UV-optical spectra of high-z star-forming galaxies, I have demonstrated that the majority of z~2-3 galaxies have moderate oxygen enrichment but sub-solar iron enrichment as a result of their rapid assembly histories. I will show that this marked alpha-enhancement means that it is imperative to consider abundance patterns rather than a single "metallicity" when describing galaxies' chemical enrichment. I will also report new measurements of the correlation between galaxy stellar mass and multiple chemical tracers (inluding O, N, and Fe) at z~2-3 using my model method and discuss extant challenges to comparing metallicity scaling relations with predictions from cosmological simulations. These comparisons are critical for understanding the way in which energetic feedback acts to regulate star formation in galaxies throughout cosmic time, which remains an open question in modern astrophysics and will be one of the key science drivers of upcoming facilities such as the James Webb Space Telescope and the ELTs.